Patent Description:
The demand in the marketplace is increasing for recording sheets, printing papers, writing papers, and the like which have superior printing and optical properties. To improve brightness and whiteness, for example, optical brighteners (OBAs) are being used in larger amounts. The OBAs are expensive, however, and their increased use contributes substantially to higher product costs.

To improve printing properties such as ink density and dry time, cationic metals have been used. Calcium chloride is currently used in ink jet recording media to enhance inkjet print density and dry time. See, for example, <CIT>, which discloses a recording sheet with improved image dry time which contains water soluble divalent metal salts. Other metal salts have been used in ink jet recording media. <CIT> discloses paper stock which contains polyvalent metal cations. <CIT> discloses an ink jet recording sheet having a recording surface which includes a water soluble polyvalent metal salt. <CIT> discloses a paper sizing for inkjet printing substrate that includes various cationic metal salts. <CIT> discloses a surface treatment composition for an inkjet printing substrate which contains a divalent metal salt. <CIT> discloses an ink jet recording base paper having a coating which includes a polyvalent metal salt. It has been found, however, that many of these cationic additives decrease the brightness and whiteness. Calcium chloride, for example, undesirably quenches stilbene-based optical brighteners such as often used at the size press. Overcoming this decrease in brightness and whiteness imposes additional costs on the papermaking process.

Another disadvantage is that the use of certain cationic additives, such as calcium chloride can create runnability issues in paper machines; and calcium chloride affects the pH of size press formulations. Starches used at the size press require a narrow pH range to be effective: too high of a pH may result in the yellowing of the starch; too low of a pH may cause the starch to precipitate and/or gel. Calcium chloride can also interact with other chemicals such as those used in the wet end when the paper is broked or recycled.

Synergistic mixtures of complexing agents, such as the known chelant, diethylenetriaminepentakis(methyl)phosphonic acid (DTPA), and polyacrylic acid have been used to enhance brightness in chemical and mechanical pulps. See, for example, <CIT>. Chelating agents have also been used to produce acid-stabilized calcium carbonate slurries. See, e.g., <CIT>. <CIT> discloses that the use of reducing agents in combination with certain chelants enhance the brightness of a paper product via increased thermal stability of the pulp and reduction of chromophoric structures in pulp. There, it is disclosed that chelants include compounds that are capable of chelating transitional metals that form colored products with pulp constituents and catalyze color-forming reactions in the bleached pulp or paper products.

There is thus a need for a recording sheet with improved optical properties yet which reduces the costs associated with OBAs. <CIT> describes a simplified method for the optical brightening of paper either in the pulp mass, the size or metering press or by coating by the use of a formulation of an optical brightening agent together with a swellable layered silicate. <CIT> describes oxidative compositions processes that preserve and enhance the brightness and improve color of pulp or paper when applied during different stages of the papermaking process.

The invention is defined in the claims. The above problems, and others, are solved by the present invention. Quite surprisingly, the present inventors have found that a composition, comprising a water-soluble salt of a divalent calcium, a complexing agent having an affinity for the divalent calcium, and an optical brightening agent inheres several advantages. When used in a papermaking process, one embodiment of the present invention improves the optical properties such as whiteness and brightness of the paper product. In a recording sheet, another embodiment of the present invention exhibits improved optical properties while desirably maintaining the beneficial printing properties. It has also been found that another embodiment of the present invention desirably avoids precipitation and other runnability issues in the papermaking process.

Various embodiments of the present invention are described in conjunction with the accompanying drawings, in which:.

One example of the present invention desirably achieves improved optical properties with lower amounts of optical brighteners. Another example of the present invention desirably achieves improved ink and printing properties. Another example of the present invention desirably achieves improved optical properties and improved ink and printing properties. Another example of the present invention desirably achieves improved paper machine runnability. Another example of the present invention desirably achieves improved optical properties and improved machine runnability. Another example of the present invention desirably achieves improved ink and printing properties and improved machine runnability. Another example of the present invention desirably achieves improved optical properties, ink and printing properties, and improved runnability. Another example of the present invention desirably achieves ink fastness.

One comparative example relates to a composition, which comprises:.

Another example relates to a method for making a recording sheet, comprising serially, consecutively, and/or simultaneously contacting:.

an optical brightening agent, wherein the paper substrate has a basis weight of at least <NUM>/m<NUM> (101bs/3000ft<NUM>)to produce a recording sheet having a basis weight of at least <NUM>/m<NUM> (10lbs/3000ft<NUM>).

Another comparative example relates to a method, comprising:
forming an image with a printing apparatus on a surface of a recording sheet, said recording sheet comprising:.

Another example relates to a recording sheet, comprising:.

The composition according to the present disclosure includes at least one divalent metal salt. When used in a recording sheet, the recording sheet may suitably contain an effective amount of the divalent water soluble metal salt in contact with at least one surface of the substrate. As used herein, an "effective amount" is an amount which is sufficient to obtain a good dry time or printing property. This total amount of divalent water soluble metal salt in the substrate can vary widely, provided that the desired result is maintained or achieved. Usually, this amount is at least <NUM>/m<NUM>, although lower or higher amounts can be used. The amount of divalent water soluble metal salt is preferably from about <NUM>/m<NUM> to about <NUM>/m<NUM>, which ranges includes all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>/m<NUM> or any combination thereof, and most preferably from about <NUM>/m<NUM> to about <NUM>/m<NUM>. In one comparative example, the amount of divalent water soluble metal salt is preferably from about <NUM>/m<NUM> to about <NUM>/m<NUM>.

Any water soluble divalent metal salt can be used in the practice of this disclosure. Suitable divalent water soluble metal salts include but are not limited to compounds containing divalent calcium, magnesium, barium, zinc, or any combination of these. The counter ions (anions) may be simple or complex and may vary widely. Illustrative of such materials are calcium chloride, magnesium chloride, calcium acetate, calcium lactate, calcium EDTA, Mg EDTA, and the like, and combinations thereof. Preferred divalent water soluble metal salts for use in the practice of this invention are water soluble salts of divalent calcium, especially calcium chloride.

According to the present disclosure, the divalent metal salt may be a mineral or organic acid salt of a divalent cationic metal ion, or a combination thereof. According to the present disclosure, the water soluble metal salt may include a halide, nitrate, chlorate, perchlorate, sulfate, acetate, carboxylate, hydroxide, nitrite, or the like, or combinations thereof, of calcium, magnesium, barium, zinc(II), or the like, or combinations thereof. Some examples of divalent metal salts include, according to the present disclosure, without limitation, calcium chloride, magnesium chloride, magnesium bromide, calcium bromide, barium chloride, calcium nitrate, magnesium nitrate, barium nitrate, calcium acetate, magnesium acetate, barium acetate, calcium magnesium acetate, calcium propionate, magnesium propionate, barium propionate, calcium formate, calcium <NUM>-ethylbutanoate, calcium nitrite, calcium hydroxide, zinc chloride, zinc acetate, and combinations thereof. Mixtures or combinations of salts of different divalent metals, different anions, or both are possible according to the present disclosure. The relative weight of the divalent cationic metal ion in the divalent metal salt may be maximized, if desired, with respect to the anion in the salt to provide enhanced efficiencies based on the total weight of applied salt. Consequently, for this reason, for example, calcium chloride may be preferred over calcium bromide. Equivalent performance in ink and print properties is expected when equivalent dosages of divalent metal cations in the divalent metal salts are present in the paper, expressed on a molar basis.

According to the present disclosure, one or more divalent metal salts are used.

According to the present disclosure, the divalent metal salt is soluble in the amount used in an aqueous sizing formulation. In one example, it is soluble at about pH <NUM> to about pH <NUM>. The aqueous sizing medium may be in the form of an aqueous solution, emulsion, dispersion, or a latex or colloidal composition, and the term "emulsion" is used herein, as is customary in the art, to mean either a dispersion of the liquid-in-liquid type or of the solid-in-liquid type, as well as latex or colloidal composition.

According to the present disclosure, the water solubility of the divalent metal salt may suitably range from slightly or moderately soluble to soluble, measured as a saturated aqueous solution of the divalent metal salt at room temperature. The water solubility may range from <NUM> mol/L and upwards. This range includes all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> mol/L and higher. In one example, the water solubility of the divalent metal salt is <NUM> mol/L or greater.

The composition contains one or more complexing agents. So long as it has an affinity for the divalent metal (ion), the complexing agent is not particularly limited. In this regard, the complexing agent may be any compound, molecule, or the like that has a chemical, physical, or physicochemical affinity for the divalent metal. Examples of such affinities include, but should not be considered to be limited to chelation, electron donation, Van der Waals attraction, physisorption, chemisorption, ion-pairing, ionic, electrostatic, metal-ligand, steric, and the like. The affinity may be reversible or irreversible. In one example, the affinity results in an association between the complexing agent and the divalent metal, to form an associated complex.

The associated complex may be neutrally charged, or it may have a positive or slightly positive charge. The associated complex may arise from any number of divalent metal ions associated with any number of complexing agents. The ratio of metal to complexing agent may suitably range from <NUM>:<NUM> to <NUM>:<NUM>, or any value or subrange therebetween, including any one of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> to any one of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

In one embodiment, the water solubility of the associated complex that results from the association may suitably range from slightly or moderately soluble to soluble, measured as a saturated aqueous solution of the associated complex at room temperature. The water solubility may range from <NUM> mol/L and upwards. This range includes all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> mol/L and higher. In one embodiment, the water solubility of the associated complex is <NUM> mol/L or greater.

The associated complex may be colorless or it may have color. It may be advantageous in some applications that the associated complex is both water-soluble and colorless.

In one embodiment the associated complex is compatible with the optical brightening agent either in the solution phase or in the solid phase, or both. So long as there is some association and/or interaction between the complexing agent and the divalent metal, the nature of the affinity is not particularly limited.

Without wishing to be bound by theory, it is hypothesized that the complexing agent may "encage" the divalent metal ion while still leaving some excess positive charge on the metal ion which will contribute to good ink fixation. It is also possible that complex cage-type associations, which contain sufficient organic molecular surfaces, would be more compatible with the optical brightening agent (for example preventing the optical brightening agent from precipitating from solution) than the metal ion alone would be with the optical brightening agent.

In one example, the complexing agent may include one or more electron donating atoms such as nitrogen, oxygen, phosphorus, sulfur, and the like.

Some examples of complexing agents include organic phosphonate, phosphate, carboxylic acid, dithiocarbamate, EDTA salt, EGTA salt, DTPA salt, crown ether, EDTA (CAS <NUM>-<NUM>-<NUM>), EDTA disodium salt [<NUM>-<NUM>-<NUM>], EDTA tetrasodium salt [<NUM>-<NUM>-<NUM>], EDTA trisodium salt, EDTA disodium magnesium salt [<NUM>-<NUM>-<NUM>], EDTA disodium calcium salt, EDTA diammonium salt [<NUM>-<NUM>-<NUM>], EDTA dipotassium salt [<NUM>-<NUM>-<NUM>], EDTA tripotassium salt [<NUM>-<NUM>-<NUM>], EDTA dilithium salt [<NUM>-<NUM>-<NUM>], EDTA tetramethylammonium salt, EDTA calcium salt, EDTA magnesium salt, EDTA aluminum salt, polyacrylic acid, polyacrylic acid salt, polysorbate, poly-<NUM>-styrene sulfonic acid salt, glycerol formal, formamidinesulinic acid, sodium hypophosphite, potassium hypophosphite, calcium hypophosphite, organic phosphonate, organic phosphate, carboxylic acid, dithiocarbamate, sorbitol, sorbic acid, cellulose ether, CMC cellulose, hydroxyethyl cellulose, PEG, PEG derivatives, PPG, PPG derivatives, ionic liquids, <NUM>-butyl-<NUM>-methyl-imidazolium-thiocyanate, and salts thereof. Combinations are possible.

Examples of ionic liquids include those based on alkyl imidazolium, i.e. methyl imidazolium (such as from BASF) and phosphonium salts (such as from Cytec). The anions could be halides, sulfates or alkyl sulfates, tetrachloroaluminate, acetate, thiocyanates, salicylates, hexafluorophosphates, hexafluoroborates, dioctylsulfosuccinate, decanoate, dodecylbenzenesulfonate. Further common examples of alkyl imidazoliums may include, but are not limited to, <NUM>-ethyl-<NUM>-methylimidazolium thiocyanate, <NUM>-ethyl-<NUM>-methylimidazolium acetate, <NUM>-ethyl-<NUM>-methylimidazolium methyl sulfate, <NUM>-butyl-<NUM>-methylimidazolium thiocyanate (or acetate, or methyl sulfate, or ethyl sulfate).

In some examples, it may be advantageous to use EDTA (CAS <NUM>-<NUM>-<NUM>), EDTA disodium salt [<NUM>-<NUM>-<NUM>], EDTA tetrasodium salt [<NUM>-<NUM>-<NUM>], EDTA trisodium salt, EDTA disodium magnesium salt [<NUM>-<NUM>-<NUM>], EDTA disodium calcium salt, either alone, or in combination, as the complexing agent.

In one example, the term, "organic phosphonate" may refer to organic derivatives of phosphonic acid, HP(O)(OH)<NUM>, containing a single C--P bond, such as HEDP (CH<NUM>C(OH)(P(O)(OH)<NUM>), <NUM>-hydroxy-<NUM>,<NUM>-propanediylbis-phosphonic acid ((HO)<NUM>P(O)CH(OH)CH<NUM>CH<NUM>P(O)(OH)<NUM>)); preferably containing a single C--N bond adjacent (vicinal) to the C--P bond, such as DTMPA
((HO)<NUM>P(O)CH<NUM>N[CH<NUM>CH<NUM>N(CH<NUM>P(O)(OH)<NUM>)<NUM>]<NUM>), AMP (N(CH<NUM>P(O)(OH)<NUM>)<NUM>), PAPEMP ((HO)<NUM>P(O)CH<NUM>)<NUM>NCH(CH<NUM>)CH<NUM>(OCH<NUM>CH(CH<NUM>))<NUM>N(CH<NUM>)<NUM>N(CH<NUM>P(O)(OH)<NUM>)<NUM>), HMDTMP ((HO)<NUM>P(O)CH<NUM>)<NUM>N(CH<NUM>)<NUM>N(CH<NUM>P(O)(OH)<NUM>)<NUM>), HEBMP (N(CH<NUM>P(O)(OH)<NUM>)<NUM>CH<NUM>CH<NUM>OH), salts thereof, and the like. Combinations are possible.

In one example, the term, "organic phosphates" may refer to organic derivatives of phosphorous acid, P(O)(OH)<NUM>, containing a single C--P bond, including triethanolamine tri(phosphate ester) (N(CH<NUM>CH<NUM>OP(O)(OH)<NUM>)<NUM>), salts thereof, and the like. Combinations are possible.

In one example, the term, "carboxylic acids" may refer to organic compounds containing one or more carboxylic group(s), --C(O)OH, preferably aminocarboxylic acids containing a single C--N bond adjacent (vicinal) to the C--CO<NUM>H bond, such as EDTA ((HO<NUM>CCH<NUM>)<NUM>NCH<NUM>CH<NUM>N(CH<NUM>CO<NUM>H)<NUM>), DTPA ((HO<NUM>CCH<NUM>)<NUM>NCH<NUM>CH<NUM>N(CH<NUM>CO<NUM>H)CH<NUM>CH<NUM>N(CH<NUM>CO<NUM>H)<NUM>), and the like and alkaline and alkaline earth metal salts thereof. Combinations are possible.

In one example, the term, "dithiocarbamates" may refer to monomeric dithiocarbamates, polymeric dithiocarbamates, polydiallylamine dithiocarbamates, <NUM>,<NUM>,<NUM>-trimercapto-<NUM>,<NUM>,<NUM>-triazine, disodium ethylenebisdithiocarbamate, disodium dimethyldithiocarbamate, salts thereof, and the like. Combinations are possible.

In one example, the complexing agent is a phosphonate. In one example, the phosphonate is diethylene-triamine-pentamethylene phosphonic acid (DTMPA) and salts thereof.

In one example, the complexing agent is a carboxylic acid. In one example, the carboxylate is selected from diethylenetriaminepentaacetic acid (DTPA) and salts thereof and ethylenediaminetetraacetic acid (EDTA) and salts thereof.

In one example, the complexing agent is one or more ionic liquids. An example of an ionic liquid is <NUM>-butyl-<NUM>-methyl-imidazolium-thiocyanate. In another example, the complexing agent is a combination of an ionic liquid and another (non ionic liquid) complexing agent.

According to the present disclosure, the amount of complexing agent is not particularly limiting. When starch is used in a sizing formulation, the complexing agent is present at an amount ranging from <NUM> to <NUM>/t (<NUM> to <NUM> lbs/ton) of paper substrate, according to the present invention. According to the present disclosure, when starch is used in a sizing formulation, the complexing agent may be present in an amount ranging from about <NUM> Lb / <NUM> Lb starch to about <NUM> Lb / <NUM> Lb starch. This range includes all values and subranges therebetween, including about <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> Lb complexing agent / <NUM> Lb starch. If no starch is used, then the complexing agent may be present in an amount ranging from about <NUM> Lb / ton of paper to about <NUM> Lb / ton of paper. This range includes all values and subranges therebetween, including about <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> Lb complexing agent / ton of paper. In one example, the amount of complexing agent ranges from about <NUM> to about <NUM> Lbs / ton of paper. Further one lb/ton is equal to approximately <NUM>/ton.

The composition contains one or more optical brightening agents, sometimes referred to herein as optical brighteners or OBAs. Typically, the optical brightening agents are fluorescent dyes or pigments that absorb ultraviolet radiation and reemit it at a higher wavelengths in the visible spectrum (blue), thereby effecting a white, bright appearance to the paper sheet when added to the stock furnish. Representative optical brighteners include, but are not limited to azoles, biphenyls, coumarins, furans, stilbenes, ionic brighteners, including anionic, cationic, and anionic (neutral) compounds, such as the Eccobrite™ and Eccowhite™ compounds available from Eastern Color & Chemical Co. (Providence, R. ); naphthalimides; pyrazenes; substituted (e.g., sulfonated) stilbenes, such as the Leucophor™ range of optical brighteners available from the Clariant Corporation (Muttenz, Switzerland), and Tinopal™ from Ciba Specialty Chemicals (Basel, Switzerland); salts of such compounds including but not limited to alkali metal salts, alkaline earth metal salts, transition metal salts, organic salts and ammonium salts of such brightening agents; and combinations of one or more of the foregoing agents.

In one example, the optical brighteners are selected from the group including disulfonated, tetrasulfonated, and hexasulfonated stilbene-based OBAs, and combinations thereof.

In one example, an effective dosage of divalent metal salt, complexing agent, and optical brightener is the amount necessary to achieve the desired brightness and whiteness yet maintain good ink and printing properties.

The amount of optical brightening agent is not particularly limited according to the present disclosure so long as the desirable whiteness and/or brightness is obtained, which is easily determined by one of ordinary skill in the papermaking art. When used in a sizing composition, the optical brighteners may be added in any amount ranging from <NUM> to <NUM> pounds per <NUM> pounds of sizing agent (e.g., ethylated starch). This range includes all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> pounds. One pound is equal to approximately <NUM>. In another example, the optical brightening agent may be added in amounts ranging from about <NUM> to about <NUM> weight percent based on the weight of the paper product, such as a recording sheet. This range includes all values and subranges therebetween, including about <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> weight percent based on the weight of the paper product.

For example, the composition can be added to bleached pulp or paper product at any point in the paper manufacturing process. Some examples of addition points include, but are not limited to (a) to the pulp slurry in the latency chest; (b) to the pulp during or after the bleaching stage in a storage, blending or transfer chest; (c) adding EDTA or DTPA before the final debleaching stage where the pH is alkaline (and upon bleaching by the final D stage, the pH will drop which will immobilize the complexing agent inside or upon the pulp fiber); (d) to pulp after bleaching, washing and dewatering followed by cylinder or flash drying; (e) before or after the cleaners; (<NUM>) before or after the fan pump to the paper machine headbox; (g) to the paper machine white water; (h) sprayed or showered onto the moving wet web after head box forming but before wet press; (i) to the silo or save all; (j) in the press section using, for example, a size press, coater or spray bar; (k) in the drying section using, for example, a size press, coater or spray bar; (l) on the calender using a wafer box; (m) on paper in an off-machine coater or size press; and/or (n) in the curl control unit. Combinations are possible.

The precise location where the composition is added will depend on the specific equipment involved, the exact process conditions being used and the like. In some cases, one or more of the divalent metal salt, complexing agent, and optical brightening agent may be added at one or more locations for optimal effectiveness.

Application can be by any means conventionally used in papermaking processes, including by "split-feeding" whereby one or more of the divalent metal salt, complexing agent, and optical brightening agent is/are applied at one point in the papermaking process, for example on pulp or a wet sheet (before the dryers) and the remaining portion of one or more of the divalent metal salt, complexing agent, and optical brightening agent is added at a subsequent point, for example in the size press.

In one example, the complexing agent and/or optical brightener can be added to a bleached pulp or paper product before, after or simultaneously with the divalent metal salt. The optical brightener and/or complexing agent may also be formulated with the divalent metal salt.

In another embodiment, the composition may be mixed with a surface sizing solution and applied in the size press.

In one embodiment, the composition is applied to a paper substrate to produce a recording sheet. The paper substrate suitably comprises a plurality of cellulosic fibers. The type of cellulosic fiber is not critical, and any such fiber known or suitable for use in paper making can be used. For example, the substrate can made from pulp fibers derived from hardwood trees, softwood trees, or a combination of hardwood and softwood trees. The fibers may be prepared for use in a papermaking furnish by one or more known or suitable digestion, refining, and/or bleaching operations such as, for example, known mechanical, thermomechanical, chemical and/or semichemical pulping and/or other well known pulping processes. The term, "hardwood pulps" as may be used herein include fibrous pulp derived from the woody substance of deciduous trees (angiosperms) such as birch, oak, beech, maple, and eucalyptus. The term, "softwood pulps" as may be used herein include fibrous pulps derived from the woody substance of coniferous trees (gymnosperms) such as varieties of fir, spruce, and pine, as for example loblolly pine, slash pine, Colorado spruce, balsam fir and Douglas fir. In some embodiments, at least a portion of the pulp fibers may be provided from non-woody herbaceous plants including, but not limited to, kenaf, hemp, jute, flax, sisal, or abaca, although legal restrictions and other considerations may make the utilization of hemp and other fiber sources impractical or impossible. Either bleached or unbleached pulp fiber may be utilized. Recycled pulp fibers are also suitable for use.

The paper substrate may suitably contain from <NUM> to <NUM> wt% of cellulosic fibers based upon the total weight of the substrate. In one embodiment, the paper substrate may contain from <NUM> to <NUM> wt% of cellulosic fibers based upon the total weight of the substrate. These ranges include any and all values and subranges therebetween, for example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> wt%.

The paper substrate may optionally contain from <NUM> to <NUM> wt% cellulosic fibers originating from softwood species based upon the total amount of cellulosic fibers in the paper substrate. In one embodiment, the paper substrate may contain <NUM> to <NUM> wt% cellulosic fibers originating from softwood species based upon the total amount of cellulosic fibers in the paper substrate. These ranges include <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and 100wt% and any and all ranges and subranges therein, based upon the total amount of cellulosic fibers in the paper substrate.

In one embodiment, the paper substrate may alternatively or overlappingly contain from <NUM> to <NUM> wt% fibers from softwood species, based on the total weight of the paper substrate. In another embodiment, the paper substrate may contain from <NUM> to 60wt% fibers from softwood species based upon the total weight of the paper substrate. These ranges include any and all values and subranges therein. For example, the paper substrate may contain not more than <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and 99wt% softwood based upon the total weight of the paper substrate.

All or part of the softwood fibers may optionally originate from softwood species having a Canadian Standard Freeness (CSF) of from <NUM> to <NUM>. In one embodiment, the paper substrate contains fibers from a softwood species having a CSF from <NUM> to <NUM>. These ranges include any and all values and subranges therebetwen, for example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> CSF. Canadian Standard Freeness is as measured by TAPPI T-<NUM> standard test.

The paper substrate may optionally contain from <NUM> to <NUM> wt% cellulosic fibers originating from hardwood species based upon the total amount of cellulosic fibers in the paper substrate. In one embodiment, the paper substrate may contain from <NUM> to <NUM> wt% cellulosic fibers originating from hardwood species, based upon the total amount of cellulosic fibers in the paper substrate. These ranges include <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and 100wt%, and any and all values and subranges therein, based upon the total amount of cellulosic fibers in the paper substrate.

In one embodiment, the paper substrate may alternatively or overlappingly contain from <NUM> to <NUM> wt% fibers from hardwood species, based upon the total weight of the paper substrate. In another embodiment, the paper substrate may alternatively or overlappingly contain from <NUM> to 90wt% fibers from hardwood species, based upon the total weight of the paper substrate. These ranges include any and all values and subranges therebetween, including not more than <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and 99wt%, based upon the total weight of the paper substrate.

All or part of the hardwood fibers may optionally originate from hardwood species having a Canadian Standard Freeness of from <NUM> to <NUM>. In one embodiment, the paper substrate may contain fibers from hardwood species having CSF values of from <NUM> to <NUM>. These ranges include <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> CSF, and any and all ranges and subranges therein.

The paper substrate may optionally contain less refined fibers, for example, less refined softwood fibers, less refined hardwood, or both. Combinations of less refined and more refined fibers are possible. In one embodiment, the paper substrate contains fibers that are at least <NUM>% less refined than that of fibers used in conventional paper substrates. This range includes all values and subranges therebetween, including at least <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>%. For example, if a conventional paper contains fibers, softwood and/or hardwood, having a Canadian Standard Freeness of <NUM>, then, in one embodiment, the paper substrate may contain fibers having a CSF of <NUM> (i.e. refined <NUM>% less than conventional) and still perform similar, if not better, than the conventional paper. Nonlimiting examples of some performance qualities of the paper substrate are discussed below. Examples of some reductions in refining of hardwood and/or softwood fibers include, but are not limited to: <NUM>) from <NUM> to at least <NUM> CSF; <NUM>) from <NUM> to at least <NUM> CSF; <NUM>) from <NUM> to at least <NUM> CSF; and <NUM>) from <NUM> to at least <NUM> CSF. In some embodiments, the reduction in fiber refinement may be at least <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>% reduction in refining compared to those fibers in conventional paper substrates.

When the paper substrate contains both hardwood fibers and softwood fibers, the hardwood/softwood fiber weight ratio may optionally range from <NUM> to <NUM>. In one embodiment, the hardwood/softwood ratio may range from <NUM>/<NUM> to <NUM>/<NUM>. These ranges include all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

The softwood fibers, hardwood fibers, or both may be optionally modified by physical and/or chemical processes. Examples of physical processes include, but are not limited to, electromagnetic and mechanical processes. Examples of electrical modifications include, but are not limited to, processes involving contacting the fibers with an electromagnetic energy source such as light and/or electrical current. Examples of mechanical modifications include, but are not limited to, processes involving contacting an inanimate object with the fibers. Examples of such inanimate objects include those with sharp and/or dull edges. Such processes also involve, for example, cutting, kneading, pounding, impaling, and the like, and combinations thereof.

Nonlimiting examples of chemical modifications include conventional chemical fiber processes such as crosslinking and/or precipitation of complexes thereon. Other examples of suitable modifications of fibers include those found in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> H, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>. Still other examples of suitable modifications of fibers may be found in <CIT>, and <CIT>, which may include the further addition of optical brighteners (i.e. OBAs) as discussed therein.

The paper substrate may optionally include "fines. " "Fines" fibers are typically those fibers with average lengths of not more than about <NUM>. Sources of "fines" may be found in SaveAll fibers, recirculated streams, reject streams, waste fiber streams, and combinations thereof. The amount of "fines" present in the paper substrate can be modified, for example, by tailoring the rate at which streams are added to the paper making process. In one embodiment, the average lengths of the fines are not more than about <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, including any and all ranges and subranges therein.

If used, the "fines" fibers may be present in the paper substrate together with hardwood fibers, softwood fibers, or both hardwood and softwood fibers.

The paper substrate may optionally contain from <NUM> to <NUM> wt% fines, based on the total weight of the paper substrate. In one embodiment, the paper substrate may contain from <NUM> to 50wt% fines, based upon the total weight of the substrate. These ranges include all values and subranges therebetween, including not more than <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and 100wt% fines, based upon the total weight of the paper substrate.

In one embodiment, the paper substrate may alternatively or overlappingly contain from <NUM> to <NUM> wt% fines, based upon the total weight of the fibers in the paper substrate. This range includes all values and subranges therebetween, including not more than <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> wt% fines, based upon the total weight of the fibers in by the paper substrate.

If desired, according to the present disclosure, the recording sheet may contain at least one sizing agent in addition to the composition. The sizing agent is not particularly limited, and any conventional papermaking sizing agent may be used. The sizing agent may be nonreactive, reactive, or a combination of nonreactive and reactive. The sizing agent may, optionally and if desired, impart a moisture or water-resistance in varying degrees to the paper substrate. Non-limiting examples of sizing agents can be found in the "Handbook for Pulp and Paper Technologists" by G. Smook (<NUM>), Angus Wilde Publications. Preferably, the sizing agent is a surface sizing agent. According to the present invention, the sizing agent is starch. Preferable examples of further sizing agents are alkyl ketene dimer (AKD), alkenyl ketene dimer (ALKD), alkenyl succinic anhydride (ASA), ASA/ALKD, styrene acrylic emulsion (SAE) polyvinyl alcohol (PVOH), polyvinylamine, alginate, carboxymethyl cellulose, etc. However, any further sizing agent may be used. See, for example, the sizing agents disclosed in Us <NUM><NUM><NUM> B1.

Many nonreactive sizing agents are known in the art. Examples include, without limitation, BASOPLAST® 335D nonreactive polymeric surface size emulsion from BASF Corporation (Mt. ), FLEXBOND® <NUM> emulsion of a copolymer of vinyl acetate and butyl acrylate from Air Products and Chemicals, Inc. (Trexlertown, Pa. ), and PENTAPRINT® nonreactive sizing agents (disclosed for example in <CIT>) from Hercules Incorporated (Wilmington, Del. ), to name a few.

For papermaking carried out under alkaline pH manufacturing conditions, sizing agents based on alkyl ketene dimers (AKDs) or alkenyl ketene dimers (ALKDs) or multimers and alkenyl succinic anhydride (ASA) sizing agents may be suitably used. Combinations of these and other sizing agents may also be employed. Ketene dimers used as sizing agents for papermaking are well known. AKDs, containing one β-lactone ring, are typically prepared by the dimerization of alkyl ketenes made from two fatty acid chlorides. Commercial alkyl ketene dimer sizing agents are often prepared from palmitic and/or stearic fatty acids, e.g. Hereon® and Aquapel® sizing agents (both from Hercules Incorporated).

Alkenyl ketene dimer sizing agents are also commercially available, e.g. Precis® sizing agents (Hercules Incorporated).

<CIT>, provides a nonlimiting exemplary disclosure of AKD sizing agents with wax blends and water soluble cationic resins.

Ketene multimers containing more than one β-lactone ring may also be employed as sizing agents.

Sizing agents prepared from a mixture of mono- and dicarboxylic acids, have been disclosed as sizing agents for paper in <CIT>and <CIT>.

<CIT> discloses alkyl ketene dimer and multimer mixtures as sizing agents in paper used in high speed converting and reprographic machines. The alkyl ketene multimers are made from the reaction of a molar excess of monocarboxylic acid, typically a fatty acid, with a dicarboxylic acid. These multimer compounds are solids at <NUM>° C.

<CIT> and Bottorff et al. in <CIT> disclose paper for high speed or reprographic operations that is internally sized with an alkyl or alkenyl ketene dimer and/or multimer sizing agent. The preferred <NUM>-oxetanone multimers are prepared with fatty acid to diacid ratios ranging from <NUM>:<NUM> to <NUM>:<NUM>.

Commercial ASA-based sizing agents are dispersions or emulsions of materials that may be prepared by the reaction of maleic anhydride with an olefin (C<NUM> -C<NUM>).

Examples of hydrophobic acid anhydrides useful as sizing agents for paper include:.

Some examples of anhydrides of formula (I) include myristoyl anhydride; palmitoyl anhydride; olcoyl anhydride; and stearoyl anhydride.

Examples of substituted cyclic dicarboxylic acid anhydrides falling within the above formula (II) include substituted succinic, glutaric anhydrides, i- and n-octadecenyl succinic acid anhydride; i- and n-hexadecenyl succinic acid anhydride; i- and n-tetradecenyl succinic acid anhydride, dodecyl succinic acid anhydride; decenyl succinic acid anhydride; ectenyl succinic acid anhydride; and heptyl glutaric acid anhydride.

Other examples of nonreactive sizing agents include a polymer emulsion, a cationic polymer emulsion, an amphoteric polymer emulsion, polymer emulsion wherein at least one monomer is selected from the group including styrene, α-methylstyrene, acrylate with an ester substituent with <NUM> to <NUM> carbon atoms, methacrylate having an ester substituent with <NUM> to <NUM> carbon atoms, acrylonitrile, methacrylonitrile, vinyl acetate, ethylene and butadiene; and optionally including acrylic acid, methacrylic acid, maleic anhydride, esters of maleic anhydride or mixtures thereof, with an acid number less than about <NUM>, and mixtures thereof.

If desired, the polymer emulsion may stabilized by a stabilizer predominantly including degraded starch, such as that disclosed, for example, in <CIT>, <CIT>, and <CIT>. If desired, a polymer emulsion may be used in which the polymer has a glass transition temperature of about -<NUM>° C to about <NUM>° C.

For traditional acid pH papermaking conditions, nonreactive sizing agents in the form of dispersed rosin sizing agents may be suitably used. Dispersed rosin sizing agents are well known. Nonlimiting examples of rosin sizing agents are disclosed in, for example, <CIT> and <CIT>.

The rosin may be any modified or unmodified, dispersible or emulsifiable rosin suitable for sizing paper, including unfortified rosin, fortified rosin and extended rosin, as well as rosin esters, and mixtures and blends thereof. As used herein, the term "rosin" means any of these forms of dispersed rosin useful in a sizing agent.

The rosin in dispersed form is not particularly limited, and any of the commercially available types of rosin, such as wood rosin, gum rosin, tall oil rosin, and mixtures of any two or more, in their crude or refined state, may be used. In one embodiment, tall oil rosin and gum rosin are used. Partially hydrogenated rosins and polymerized rosins, as well as rosins that have been treated to inhibit crystallization, such as by heat treatment or reaction with formaldehyde, may also be employed.

The fortified rosin is not particularly limited. One example of such a rosin includes the adduct reaction product of rosin and an acidic compound containing the
<CHM>
group and is derived by reacting rosin and the acidic compound at elevated temperatures of from about <NUM>° C to about <NUM>° C.

The amount of acidic compound employed will be that amount which will provide fortified rosin containing from about <NUM>% to about <NUM>% by weight of adducted acidic compound based on the weight of the fortified rosin. Methods of preparing fortified rosin are well known to those skilled in the art. See, for example, the methods disclosed and described in <CIT> and <CIT>.

Examples of acidic compounds containing the
<CHM>
group that can be used to prepare the fortified rosin include the α-β-unsaturated organic acids and their available anhydrides, specific examples of which include fumaric acid, maleic acid, acrylic acid, maleic anhydride, itaconic acid, itaconic anhydride, citraconic acid and citraconic anhydride. Mixtures of acids can be used to prepare the fortified rosin if desired.

Thus, for example, a mixture of the acrylic acid adduct of rosin and the fumaric acid adduct can be used to prepare a dispersed rosin sizing agent. Also, fortified rosin that has been substantially completely hydrogenated after adduct formation can be used.

Rosin esters may also be used in the dispersed rosin sizing agents. Suitable exemplary rosin esters may be rosin esterified as disclosed in <CIT>) or <CIT>).

The unfortified or fortified rosin or rosin esters can be extended if desired by known extenders such as waxes (particularly paraffin wax and microcrystalline wax); hydrocarbon resins including those derived from petroleum hydrocarbons and terpenes; and the like. This may be suitably accomplished by melt blending or solution blending with the rosin or fortified rosin from about <NUM>% to about <NUM>% by weight, based on the weight of rosin or fortified rosin, of the extender.

Blends of fortified rosin and unfortified rosin; blends of fortified rosin, unfortified rosin, rosin esters and rosin extender can be used. Blends of fortified and unfortified rosin may include, for example, about <NUM>% to <NUM>% fortified rosin and about <NUM>% to <NUM>% unfortified rosin. Blends of fortified rosin, unfortified rosin, and rosin extender may include, for example, about <NUM>% to <NUM>% fortified rosin, <NUM> to <NUM>% rosin, and about <NUM>% to <NUM>% rosin extender.

Hydrophobic organic isocyanates, e.g., alkylated isocyanates, may also be used as sizing agents.

Other conventional paper sizing agents include alkyl carbamoyl chlorides, alkylated melamines such as stearylated melamines, and styrene acrylates.

An external sizing agent or both internal and surface sizing agents may be used. Either or both may contain the divalent metal salt, the optical brightening agent, and the complexing agent. When both internal and external sizing agents are present, they may be present in any weight ratio and may be the same and/or different. In one embodiment, the weight ratio of surface sizing agent to internal sizing agent is from <NUM>/<NUM> to <NUM>/<NUM>, more preferably from <NUM>/<NUM> to <NUM>/<NUM> surface/intemal sizing agent. This range includes <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM> and <NUM>/<NUM>, including any and all ranges and subranges therein. A preferred example of an internal sizing agent is alkenyl succinic anhydride (ASA).

When starch is used as a sizing agent, which is the case according to the present invention, starch may be modified or unmodified. Examples of starch may be found in the "Handbook for Pulp and Paper Technologists" by G. Smook (<NUM>), Angus Wilde Publications, mentioned above. Preferable examples of modified starches include, for example, oxidized, cationic, ethylated, hydroethoxylated, etc. In addition, the starch may come from any source, preferably potato and/or corn. Most preferably, the starch source is corn.

In one embodiment, a mixture comprising calcium chloride, complexing agent, optical brightening agent, and one or more starches is in contact with at least one surface of the substrate. Illustrative of useful starches include naturally occurring carbohydrates synthesized in corn, tapioca, potato and other plants by polymerization of dextrose units. All such starches and modified forms thereof such as starch acetates, starch esters, starch ethers, starch phosphates, starch xanthates, anionic starches, cationic starches, oxidized starches, and the like which can be derived by reacting the starch with a suitable chemical or enzymatic reagent can be used. If desired, starches may be prepared by known techniques or obtained from commercial sources. For example, one example of a commercial starches include Ethylex <NUM> from A. Staley, PG-<NUM> from Penford Products, oxidized corn starches from ADM, Cargill, and Raisio, and enzyme converted starches such as Amyzet <NUM> from Amylum.

Modified starches may be used. Non-limiting examples of a type of modified starches include cationic modified chemically modified starches such as ethylated starches, oxidized starches, and AP and enzyme converted Pearl starches. Most preferred are chemically modified starches such as ethylated starches, oxidized starches, and AP and enzyme converted Pearl starches.

In one embodiment, a water soluble metal salt, for example, calcium chloride, and Ethylex <NUM> starch together with a complexing agent and an optical brightening agent are used in a sizing formulation applied to both sides of a sheet of paper, and an improved dry time of the sheet is obtained when the weight ratio of the calcium chloride to the starch is equal to or greater than about <NUM> to about <NUM>%. This range includes all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>%, and any combination thereof. In one embodiment, the weight ratio of the calcium chloride to the starch may range from about <NUM> to about <NUM>%. In another embodiment, the weight ratio may range from about <NUM> to about <NUM>%. In another embodiment, the weight ratio may range from about <NUM>% to about <NUM>%. The weight ratios of the calcium chloride to the starch may be one-half of those stated if the starch/salt mixture is only applied to one side of the paper, and starch without salt is applied to the other side. In this case, the improved print properties would only be expected on the side of the paper containing the salt.

The amount of divalent water soluble metal salt and one or more starches in and/or on the substrate may vary widely, and any conventional amount can be used.

When polyvinyl alcohol is used as a sizing agent, it may have any % hydrolysis. Preferable polyvinyl alcohols are those having a % hydrolysis ranging from <NUM>% to <NUM>%. The % hydrolysis of the polyvinyl alcohol may be <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>% hydrolysis, including any and all ranges and subranges therein.

The paper substrate may contain PVOH at any wt%. Preferably, when PVOH is present, it is present at an amount from <NUM>. 001wt% to 100wt% based on the total weight of sizing agent contained in and/or on the substrate. This range includes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and 100wt% based on the total weight of sizing agent in the substrate, including any and all ranges and subranges therein.

The sizing agent may also include one or more optional additives such as binders, pigments, thickeners, defoamers, surfactants, slip agents, dispersants, optical brighteners, dyes, and preservatives, which are well-known. Examples of pigments include, but are not limited to, clay, calcium carbonate, calcium sulfate hemihydrate, and calcium sulfate dehydrate, chalk, GCC, PCC, and the like. A preferable pigment is calcium carbonate with the preferred form being precipitated calcium carbonate. Examples of binders include, but are not limited to, polyvinyl alcohol, Amres (a Kymene type), Bayer Parez, polychloride emulsion, modified starch such as hydroxyethyl starch, starch, polyacrylamide, modified polyacrylamide, polyol, polyol carbonyl adduct, ethanedial/polyol condensate, polyamide, epichlorohydrin, glyoxal, glyoxal urea, ethanedial, aliphatic polyisocyanate, isocyanate, <NUM>,<NUM> hexamethylene diisocyanate, diisocyanate, polyisocyanate, polyester, polyester resin, polyacrylate, polyacrylate resin, acrylate, and methacrylate. Other optional additives include, but are not limited to silicas such as colloids and/or sols. Examples of silicas include, but are not limited to, sodium silicate and/or borosilicates. Other additives which may be used include one or more solvents such as, for example, water. Combinations of additives are possible.

It may be advantageous that a majority of the total amount of sizing agent is located at or near the outside surface or surfaces (in the case of the sizing applied to both surfaces) of the paper substrate. In one embodiment, the paper substrate contains the sizing agent such that they (the substrate and the sizing agent) cooperate to form an I-beam structure. I-beam structures are discussed, for example, in <CIT>, and <CIT>, as well as in the <CIT>. In this regard, it is not required that the sizing agent interpenetrate with the cellulosic fibers of the substrate. However, if the sizing or coating layer and the cellulose fibers interpenetrate, it will create a paper substrate having an interpenetration layer, which is within the ambit of the present invention.

In one embodiment, the interpenetration layer of the paper substrate may define a region in which at least the sizing solution penetrates into and is among the cellulose fibers. The interpenetration layer may be from <NUM> to <NUM>% of the entire cross section of at least a portion of the paper substrate, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>% of the paper substrate, including any and all ranges and subranges therein. Such an embodiment may be made, for example, when a sizing solution is added to the cellulose fibers prior to a coating method and may be combined with a subsequent coating method if required. Addition points may be at the size press, for example.

In one embodiment, the cross-sectional thickness of the interpenetration layer may be minimized. Alternatively, or additionally, the concentration of the sizing agent preferably increases as one moves (in the z-direction normal to the plane of the substrate) from the interior portion towards the surface of the paper substrate. Therefore, the amount of sizing agent present towards the top and/or bottom outer surfaces of the substrate may be greater than the amount of sizing agent present towards the inner middle of paper substrate. Alternatively, a majority percentage of the sizing agent may preferably be located at a distance from the outside surface of the substrate that is equal to or less than <NUM>%, more preferably <NUM>%, of the total thickness of the substrate. This aspect may also be known as the Qtotal, which is measured by known methodologies outlined, for example, in <CIT>. If Qtotal is equal to <NUM>, then the sizing agent is approximately evenly distributed throughout the paper substrate. If Qtotal is greater than <NUM>, then there is more sizing agent towards the central portion (measured by the z-direction normal to the plane of the substrate) of the paper substrate than towards the paper substrate's surface or surfaces. If Qtotal is less than <NUM>, then there is less sizing agent towards the central portion of the paper substrate than towards the paper substrate's surface or surfaces. In light of the above, the paper substrate preferably has a Qtotal that is less than <NUM>, preferably less than <NUM>, more preferably less than <NUM>, most preferably less than <NUM>. Accordingly the Qtotal of the paper substrate may be from <NUM> to less than <NUM>. This range includes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, including any and all ranges and subranges therein.

As noted above, the determination of Q may be suitably carried out according to the procedures in <CIT>.

In essence, Q is a measurement of the amount of the starch as one progresses from the outside edges towards the middle of the sheet from a cross section view. It is understood herein that the Q may be any Q such that it represents an enhanced capacity to have starch towards the outside surfaces of the cross section of the sheet and Q may be selected (using any test) such that any one or more of the above and below-mentioned characteristics of the paper substrate are provided (e.g. Internal Bond, Hygroexpansivity, IGT Pick, and/or IGT VPP delamination, etc).

Other methods are available for measuring the equivalent of Q. In one embodiment, any Q measurement, or a similar method of measuring the ratio of the amount of sizing agent containing the composition towards the core of the substrate compared to the amount of sizing agent towards the outside surface or surfaces of the substrate is acceptable. In one embodiment, this ratio is such that as much sizing agent as possible is located towards the outside surfaces of the substrate, thereby minimizing the interpenetration zone and/or minimizing the amount of starch located in the interpenetration layer, is achieved. It is also possible that the distribution of sizing agent occurs even at very high level of sizing agent loadings, preferably external sizing agent loadings, within and/or onto the substrate. Thus, in the case that an I-beam structure is formed, it is desirable to control the amount of sizing agent located within the interpenetration layer as more and more external sizing agent is loaded thereon its surface by either minimizing the concentration of the sizing agent in this interpenetration layer or by reducing the thickness of the interpenetration layer itself. In one embodiment, the characteristics of the recording sheet and/or paper substrate are those that can be achieved by such control of the sizing agent. While this controlled loading of the sizing agent can occur in any manner, it is preferable that the sizing agent is loaded or applied via a size press.

The recording sheet may be made by contacting the composition, containing a sizing agent with the cellulose fibers of the paper substrate. The contacting may occur at acceptable concentration levels of the sizing agent and/or other additives.

The recording sheet may be made by contacting the substrate with an internal and/or surface sizing solution or formulation containing the composition according to the present invention and additionally at least one sizing agent. The contacting may occur anytime in the papermaking process including, but not limited to the wet end, head box, size press, water box, and/or coater. Further addition points include machine chest, stuff box, and suction of the fan pump. The cellulose fibers, sizing agent, and/or optional components may be contacted serially, consecutively, and/or simultaneously in any combination with each other. Most preferably, the paper substrate is contacted with the size press formulation at the size press.

The paper substrate may be passed through a size press, where any sizing means commonly known in the art of papermaking is acceptable. The size press, for example, may be a puddle mode size press (e.g. inclined, vertical, horizontal) or metered size press (e.g. blade metered, rod metered). Preferably, the size press is a metered size press.

To prepare the size press formulation, according to the present disclosure, one or more divalent water soluble metal salts may be admixed with one or more sizing agents for example, starches, and one or more optional additives can be dissolved or dispersed in an appropriate liquid medium, preferably water, and can be applied to the substrate.

For example, the size press formulation can be applied with conventional size press equipment having vertical, horizontal or inclined size press configurations conventional used in paper preparation as for example the Symsizer (Valmet) type equipment, a KRK size press (Kumagai Riki Kogyo Co. , Nerima, Tokyo, Japan) by dip coating. The KRK size press is a lab size press that simulates a commercial size press. This size press is normally sheet fed, whereas a commercial size press typically employs a continuous web.

In one embodiment, the sizing agent is applied in an amount such such that a dry pickup of <NUM> to <NUM> lbs of starch/ton of paper at <NUM>-<NUM>% solids for the size press formulation. Here, lbs/ton is calculated on a paper having a basis weight equal to <NUM> gsm. Further one lb/ton is equal to approximately <NUM>/ton.

The aforementioned range of starch includes all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> lbs/ton. Here, lbs/ton is calculated on a paper having a basis weight equal to <NUM> gsm. One lb/ton is equal to approximately <NUM>/ton.

It should be readily apparent that the amounts in lbs/ton and moles/ton may vary in a known manner according to the basis weight of the paper, and the invention is not limited to only paper having a basis weight of <NUM> gsm.

In one embodiment, wherein an I-beam structure is formed, in which calcium chloride is used as the water soluble metal salt, and in which a sizing agent is present on both sides of a sheet of paper, the amount ranges from about <NUM> to about <NUM> lbs of CaCl<NUM>/ton of paper on a paper having a basis weight equal to <NUM> gsm. This range includes all values and subranges therebetween, including about <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> lbs of CaCl<NUM>/ton of paper. This range is equal to a range from about <NUM> to <NUM> lbs of CaCl<NUM>/ton of paper on a paper having a basis weight equal to <NUM> gsm. This range includes all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> lbs of CaCl<NUM>/ton of paper. One lb/ton is equal to approximately <NUM>/ton.

In one embodiment, the % solids in the size press formulation may suitably range from at least <NUM>-<NUM>%. This range includes all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>%.

In one embodiment, the dry pickup of the sizing agent may suitably range from <NUM> to <NUM> gsm, which range includes all values and subranges therebetween, for example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> gsm, and any combination thereof.

In one embodiment, the wet film thickness is adjusted to give proper pickup. For example, in one embodiment, the wet film thickness may suitably range from greater than zero to <NUM>. This range includes all values and subranges therebetween, including greater than zero, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> micrometre (microns). In one embodiment, the wet film thickness ranges from <NUM> to <NUM> micrometre (microns). In one embodiment, the wet film thickness ranges from <NUM> to <NUM> micrometre (microns).

In one embodiment, the amount of pigment at the size press (in the sizing formulation) may suitably range from <NUM> to <NUM> lbs/ton. This range includes all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> lbs/ton. Here, lbs/ton is calculated using a basis weight of <NUM># bond paper (<NUM> gsm). One lb/ton is equal to approximately <NUM>/ton.

In one embodiment, the temperature at the size press may suitably range from <NUM> to <NUM> (<NUM>-<NUM>° F). This range includes all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>° F).

In one embodiment, a rod-metered size press is used. In such an embodiment, a suitable rod volume may range from <NUM> in<NUM>/in to <NUM> in<NUM>/in. This range includes all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> in<NUM>/in.

When the cellulosic fibers are contacted with the size press formulation at the size press, it is preferred that the viscosity of the sizing solution is from <NUM> to <NUM> centipoise using a Brookfield Viscometer, number <NUM> spindle, at <NUM> rpm and <NUM>,<NUM> (<NUM>°F). These ranges include all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> centipoise as measured using a Brookfield Viscometer, number <NUM> spindle, at <NUM> rpm and <NUM>,<NUM> (<NUM>°F), including any and all ranges and subranges therein. In one embodiment, the viscosity ranges from <NUM> to <NUM> centipoise. In another embodiment, the viscosity ranges from <NUM> to <NUM> centipoise.

The paper substrate may be pressed in a press section containing one or more nips. Any pressing means commonly known in the art of papermaking may be utilized. The nips may be, but are not limited to, single felted, double felted, roll, and extended nip in the presses. When the sizing solution containing the sizing agent is contacted with the fibers at the size press to make the paper substrate, the effective nip pressure is not particularly limited so long as integrity of the I-beam structure is maintained. For example, the nip pressure may suitably range from greater than zero to <NUM> kN/m. This range includes all values and subranges therebetween, including greater than zero, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> kN/m, including any and all ranges and subranges therein. In one embodiment, the nip pressure ranges from <NUM> to <NUM> kN/m.

The nip width is not particularly limited, and may suitably range from greater than zero to <NUM>. This range includes all values and subranges therebetween, including greater than zero, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In one embodiment, the nip width ranges from <NUM> to <NUM>.

The rolls of the size press may have a P&J hardness, preferably any P&J hardness. Since there are two rolls, a first roll may have a first hardness, while a second roll may have a second hardness. The roll hardness may suitably range from <NUM> to <NUM> P&J hardness. This range includes all values and subranges therebetween, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> P&J hardness. If two rolls are used, they may have the same or different hardnesses. The first hardness and the second hardness may be equal and/or different from one another. As an example, the P&J of a first roll at the size press may have a first hardness that independently ranges from <NUM> to <NUM> P&J hardness, while the second roll may have a second hardness that independently ranges from <NUM> to <NUM> P&J hardness.

The paper substrate may be dried in a drying section. Any drying means commonly known in the art of papermaking may be utilized. The drying section may include and contain a drying can, cylinder drying, Condebelt drying, IR, or other drying means and mechanisms known in the art. The paper substrate may be dried so as to contain any selected amount of water. Preferably, the substrate is dried to contain less than or equal to <NUM>% water.

The paper substrate may be calendered by any commonly known calendaring means in the art of papermaking. More specifically, one could utilize, for example, wet stack calendering, dry stack calendering, steel nip calendaring, hot soft calendaring or extended nip calendering, etc..

The paper substrate may be microfinished according to any process commonly known in the art of papermaking. Microfinishing typically involves frictional processes to finish surfaces of the paper substrate. The paper substrate may be microfinished with or without a calendering applied thereto consecutively and/or simultaneously. Examples of microfinishing processes can be found in <CIT> and references cited therein, as well as <CIT>.

In one embodiment, the paper substrate comprising the composition and a sizing agent may be further coated by any conventional coating layer application means, including impregnation means. A preferred method of applying the coating layer is with an in-line coating process with one or more stations. The coating stations may be any of known coating means commonly known in the art of papermaking including, for example, brush, rod, air knife, spray, curtain, blade, transfer roll, reverse roll, and/or cast coating means, as well as any combination of the same.

The further coated paper substrate may be dried in a drying section. Any drying means commonly known in the art of papermaking and/or coatings may be utilized. The drying section may include and contain IR, air impingement dryers and/or steam heated drying cans, or other drying means and mechanisms known in the coating art.

The further coated substrate may be finished according to any finishing means commonly known in the art of papermaking. Examples of such finishing means, including one or more finishing stations, include gloss calendar, soft nip calendar, and/or extended nip calendar.

These paper substrate and/or recording sheet may be added to any conventional papermaking processes, as well as converting processes, including abrading, sanding, slitting, scoring, perforating, sparking, calendaring, sheet finishing, converting, coating, laminating, printing, etc. In one embodiment, the conventional processes include those tailored to produce paper substrates capable to be utilized as coated and/or uncoated paper products, board, and/or substrates. These and other suitable processes may be found in textbooks such as the "<NPL>.

The recording sheet and/or paper substrate may also include one or more optional substances such as retention aids, binders, fillers, thickeners, and preservatives. Examples of fillers include, but are not limited to, clay, calcium carbonate, calcium sulfate hemihydrate, and calcium sulfate dehydrate, chalk, GCC, PCC, and the like. A preferable filler is calcium carbonate with the preferred form being precipitated calcium carbonate. Examples of binders include, but are not limited to, polyvinyl alcohol, Amres (a Kymene type), Bayer Parez, polychloride emulsion, modified starch such as hydroxyethyl starch, starch, polyacrylamide, modified polyacrylamide, polyol, polyol carbonyl adduct, ethanedial/polyol condensate, polyamide, epichlorohydrin, glyoxal, glyoxal urea, ethanedial, aliphatic polyisocyanate, isocyanate, <NUM>,<NUM> hexamethylene diisocyanate, diisocyanate, polyisocyanate, polyester, polyester resin, polyacrylate, polyacrylate resin, acrylate, and methacrylate. Other optional substances include, but are not limited to silicas such as colloids and/or sols. Examples of silicas include, but are not limited to, sodium silicate and/or borosilicates. Another example of optional substances are solvents including but not limited to solvents such as water. Combinations of optional substances are possible.

The recording sheet of the present invention may contain from <NUM> to <NUM> wt% of the optional substances based on the total weight of the substrate, preferably from <NUM> to <NUM> wt %, most preferably <NUM> to <NUM>. 0wt%, of each of at least one of the optional substances. This range includes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and 20wt% based on the total weight of the substrate, including any and all ranges and subranges therein.

Other conventional additives that may be present include, but are not limited to, wet strength resins, internal sizes, dry strength resins, alum, fillers, pigments and dyes. The substrate may include bulking agents such as expandable microspheres, pulp fibers, and/or diamide salts.

The paper substrate or sizing agent may optionally contain a bulking agent in any amount, if present, ranging from <NUM> to <NUM> dry lbs per ton of finished substrate, preferably from <NUM> to <NUM>, dry lb per ton of finished product when such bulking means is an additive. This range includes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> dry lb per ton of finished product, including any and all ranges and subranges therein. One pound is equal to approximately <NUM>. Further one lb/ton is equal to approximately <NUM>/ton.

The bulking agent may be an expandable microsphere, composition, and/or particle for bulking paper articles and substrates. However, any bulking agent can be utilized, while the expandable microsphere, composition, particle and/or paper substrate of that follows is the preferred bulking means. Other alternative bulking agents include, but are not limited to, surfactants, Reactopaque, pre-expanded spheres, BCTMP (bleached chemi-thermomechanical pulp), microfinishing, and multiply construction for creating an I-beam effect in a paper or paper board substrate. Such bulking agents may, when incorporated or applied to a paper substrate, provide adequate print quality, caliper, basis weight, etc in the absence of harsh calendaring conditions (i.e. pressure at a single nip and/or less nips per calendaring means), yet produce a paper substrate having the a single, a portion of, or combination of the physical specifications and performance characteristics mentioned herein.

In one embodiment, the paper substrate may contain from <NUM> to <NUM> wt%, preferably from <NUM> to <NUM> wt%, more preferably from <NUM> to <NUM> wt%, most preferably from <NUM> to <NUM> wt% of expandable microspheres based on the total weight of the substrate.

Examples of expandable microspheres having bulking capacity are those described in <CIT>, and <CIT>. Further examples include those found in <CIT>, and <CIT>, filed June <NUM>, <NUM>.

Some examples of bulking fibers include, but are not limited to, mechanical fibers such as ground wood pulp, BCTMP, and other mechanical and/or semi-mechanical pulps. When such pulps are added, from <NUM> to <NUM> wt%, preferably less than 60wt% of total weight of the fibers used may be from such bulking fibers.

Examples of diamide salts include those described in <CIT>. Non-limiting examples of such salts include mono- and distearamides of animoethylethalonalamine, which may be commercially known as Reactopaque <NUM>, (Omnova Solutions Inc. , Performance Chemicals, <NUM> J. Cochran By-Pass, Chester, S. <NUM>, USA and marketed and sold by Ondeo Nalco Co. , with headquarters at Ondeo Nalco Center, Naperville, Ill. <NUM>, USA) or chemical equivalents thereof. When such salts are used, about <NUM> to about <NUM> wt % by weight dry basis of the diamide salt may be used.

Other optional components include nitrogen containing compounds. Non-limiting examples of these include nitrogen containing organic species, for example oligomers and polymers which contain one or more quaternary ammonium functional groups. Such functional groups may vary widely and include, for example, substituted and unsubstituted amines, imines, amides, urethanes, quaternary ammonium groups, dicyandiamides, guanides, and the like. Illustrative of such materials are polyamines, polyethyleneimines, copolymers of diallyldimethyl ammonium chloride (DADMAC), copolymers of vinyl pyrrolidone (VP) with quaternized diethylaminoethylmethacrylate (DEAMEMA), polyamides, cationic polyurethane latex, cationic polyvinyl alcohol, polyalkylamines dicyandiamid copolymers, amine glycigyl addition polymers, poly[oxyethylene (dimethyliminio) ethylene (dimethyliminio) ethylene] dichlorides, guanidine polymers, and polymeric biguanides. Combinations of these nitrogen containing compounds are possible. Some examples of these compounds are described in, for example, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

The expandable microspheres may contain an expandable shell forming a void inside thereof. The expandable shell may comprise a carbon and/or heteroatom containing compound. An example of a carbon and/or heteroatom containing compound may be an organic polymer and/or copolymer. The polymer and/or copolymer may be branched and/or crosslinked.

Expandable microspheres preferably are heat expandable thermoplastic polymeric hollow spheres containing a thermally activatable expanding agent. Examples of expandable microsphere compositions, their contents, methods of manufacture, and uses can be found, in <CIT>; <CIT>; <CIT>; <CIT>; and <CIT>. Further reference can be made to <CIT>; <CIT>; <CIT>; and <CIT>. Microspheres may be prepared from polyvinylidene chloride, polyacrylonitrile, poly-alkyl methacrylates, polystyrene or vinyl chloride.

Microspheres may contain a polymer and/or copolymer that has a Tg ranging from - <NUM> to +<NUM>, preferably from <NUM> to <NUM>, most preferably from <NUM> to <NUM>.

Microspheres may also contain at least one blowing agent which, upon application of an amount of heat energy, functions to provide internal pressure on the inside wall of the microsphere in a manner that such pressure causes the sphere to expand. Blowing agents may be liquids and/or gases. Further, examples of blowing agents may be selected from low boiling point molecules and compositions thereof. Such blowing agents may be selected from the lower alkanes such as neopentane, neohexane, hexane, propane, butane, pentane, and mixtures and isomers thereof. Isobutane is the preferred blowing agent for polyvinylidene chloride microspheres. Examples of coated unexpanded and expanded microspheres are disclosed in <CIT> and <CIT>.

The expandable microspheres may have a mean diameter ranging from about <NUM> to <NUM> micrometre (microns), preferably from <NUM> to <NUM> micrometre (microns), most preferably from <NUM> to <NUM> micrometre (microns) in the unexpanded state and having a maximum expansion of from about <NUM> and <NUM> times, preferably from <NUM> to <NUM> times, most preferably from <NUM> to <NUM> times the mean diameters.

In one embodiment, the expandable microspheres may be neutral, negatively or positively charged, preferably negatively charged.

If desired, one or more reducing agents may be optionally added to enhance the effect of the optical brighteners. Some examples of reducing agents are discussed in <CIT>. If utilized, one measure of an effective amount of reducing agent added to bleached pulp or paper product is that which enhances the brightness and resistance to thermal yellowing of the pulp or paper compared to pulp or paper which is not treated with the reducing agents. Methods for determining brightness and resistance to thermal yellowing are known.

In one embodiment, a reducing agent is not used.

In one example, a recording sheet prepared with the composition which contains a divalent metal salt, a complexing agent, and an optical brightening agent desirably exhibits an enhanced image dry time as determined by the amount of ink transferred from a printed to an unprinted portion of the recording sheet after rolling with a roller of fixed weight. The "ink transfer", that is defined as the amount of optical density transferred after rolling with a roller; it is expressed as a percentage of the optical density transferred to the unprinted portion of the recording sheet after rolling with a roller. The method involves printing solid colored blocks on paper, waiting for a fixed amount of time, <NUM> seconds after printing, and then folding in half so that the printed portion contacts an unprinted portion of the recording sheet, and rolling with a <NUM> lb hand roller as for example roller item number HR-<NUM> from Chem Instruments, Inc. , Mentor, OH, USA. The optical density is read on the transferred (ODT), the non-transferred (ODa) portions of the block, and an un-imaged area (ODB) by a reflectance densitometer (X-Rite, Macbeth. The percent transferred ("IT%") is defined as IT% = [(ODT - ODB)/(ODO - ODB)]X <NUM>.

Given the teachings herein, the Hercules Sizing Test Value ("HST") of the substrate prepared with the composition may be suitably selected such that the recording sheet has a percent ink transferred ("IT%") equal to or less than about <NUM>. Preferably, the IT% is from <NUM>% to about <NUM>%. More preferably, the IT% is from <NUM>% to about <NUM>%. Most preferably, the IT% is from <NUM>% to about <NUM>%.

In addition to improved image dry time, the recording sheets exhibit good print quality. As used herein, print quality (PQ) is measured by two important parameters: print density and edge acuity. Print density is measured using a reflectance densitometer (X-Rite, Macbeth. ) in units of optical density ("OD"). The method involves printing a solid block of color on the sheet, and measuring the optical density. There is some variation in OD depending on the particular printer used and the print mode chosen, as well as the densitometer mode and color setting. The printer is not particularly limited and may be, for example, an HP Deskjet <NUM>, manufactured by Hewlett-Packard, which uses a #<NUM> (HP product number 51645A) black inkjet cartridge. The print mode is determined by the type of paper and the print quality selected. The default setting of Plain Paper type and Fast Normal print quality print mode may be suitably selected. A suitable densitometer may be an X-Rite model <NUM> spectrodensitometer with a <NUM> aperture. The density measurement settings may suitably be Visual color, status T, and absolute density mode. An increase in print density may typically be seen when sufficient amounts of divalent water soluble metal salts are on the paper surface. In general, the target optical density for pigment black ("ODo ") is equal to or greater than <NUM> in the standard (plain paper, normal) print mode for the HP desktop ink jet printers that use the most common black pigment ink (equivalent to the #<NUM> ink jet cartridge). Preferably, the ODO is equal to or greater than about <NUM>. More preferably, the ODa is equal to or greater than about <NUM>. Most preferably, the OD is equal to or greater than about <NUM>.

Recording sheets exhibit good edge acuity ("EA"). Edge acuity is measured by an instrument such as the QEA Personal Image Analysis System (Quality Engineering Associates, Burlington, MA), the QEA ScannerIAS, or the ImageXpert KDY camera-based system. All of these instruments collect a magnified digital image of the sample and calculate an edge acuity value by image analysis. This value is also called edge raggedness, and is defined in ISO method <NUM>. The method involves printing a solid line <NUM> millimeters or more in length, sampling at a resolution of at least <NUM> dpi. The instrument calculates the location of the edge based on the darkness of each pixel near the line edges. The edge threshold is defined as the point of <NUM>% transition from the substrate reflectance factor (light area, Rmax) to the image reflectance factor (dark area, Rmax) using the equation R<NUM> = Rmax - <NUM>% (Rmax - Rmin). The edge raggedness is then defined as the standard deviation of the residuals from a line fitted to the edge threshold of the line, calculated perpendicular to the fitted line. The value of edge acuity is preferably less than about <NUM>. Preferably, the EA is less than about <NUM>. More preferably, the EA is less than about <NUM>. Most preferably, the EA is less than about <NUM>.

A recording sheet prepared using the composition may have any CIE whiteness, but preferably has a CIE whiteness of greater than <NUM>, more preferably greater than <NUM>, most preferably greater than <NUM> or even greater than <NUM>. The CIE whiteness may be in the range of from <NUM> to <NUM>, preferably from <NUM> to <NUM>, most preferably from <NUM> to <NUM>. The CIE whiteness range may be greater than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> CIE whiteness points, including any and all ranges and subranges therein. Examples of measuring CIE whiteness and obtaining such whiteness in a papermaking fiber and paper made therefrom can be found, for example, in <CIT>. Further, examples of measuring CIE whiteness and obtaining such whiteness in a papermaking fiber and paper made therefrom can be found, for example, in <CIT>, and <CIT>; <CIT>; and <CIT>.

The recording sheet of the present invention may have any ISO brightness, but preferably greater than <NUM>, more preferably greater than <NUM>, most preferably greater than <NUM> ISO brightness points. The ISO brightness may be preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, most preferably from <NUM> to <NUM> ISO brightness points. This range include greater than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> ISO brightness points, including any and all ranges and subranges therein. Examples of measuring ISO brightness and obtaining such brightness in a papermaking fiber and paper made therefrom can be found, for example, in <CIT>. Further, examples of measuring ISO brightness and obtaining such brightness in a papermaking fiber and paper made therefrom can be found, for example, in <CIT>, and <CIT>.

A recording sheet prepared in accordance with the present invention has an improved print performance and improved runnability (e.g. print press performance). Print performance may be measured by determining improved ink density, dot gain, trapping, print contrast, and/or print hue, to name a few. Colors traditionally used in such performance tests include black, cyan, magenta and yellow, but are by no means limited thereto. Press performance may be determined by print contamination determinations through visual inspection of press systems, blankets, plates, ink system, etc. Contamination usually includes fiber contamination, coating or sizing contamination, filler or binder contamination, piling, etc. The recording sheet has an improved print performance and/or runnability as determined by each or any one or combination of the above attributes.

A recording sheet prepared using the composition may have any surface strength. Examples of physical tests of a substrate's surface strength that also seem to correlate well with a substrate's print performance are the IGT pick tests and wax pick tests. Further, both tests are known in the art to correlate well with strong surface strength of recording sheets. While either of these tests may be utilized, IGT pick tests are preferred. IGT pick test is a standard test in which performance is measured by Tappi Test Method <NUM>, which corresponds to the standard test ISO <NUM>.

Paper substrates suitable for use herein may have any basis weight. It may have either a high or low basis weight, including basis weights of at least <NUM> lbs/<NUM> square foot, preferably from at least <NUM> to <NUM> lbs/<NUM> square foot, more preferably from at least <NUM> to <NUM> lbs/<NUM> square foot. The basis weight may be at least <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> lbs/<NUM> square feet, including any and all ranges and subranges therein. One lb/sq ft is equal to approximately <NUM>/m<NUM>.

The recording sheet may be suitably printed by generating images on a surface of the recording sheet using conventional printing processes and apparatus as for example laser, ink jet, offset and flexo printing processes and apparatus. In this method, the recording sheet is incorporated into a printing apparatus; and an image is formed on a surface of the sheet. The recording sheet may be printed with ink jet printing processes and apparatus such as, for example, desk top ink jet printing and high speed commercial ink jet printing. In one example, an ink jet printing process is contemplated wherein an aqueous recording liquid is applied to the recording sheet in an image wise pattern. In another example, an inkjet printing process is contemplated which includes (<NUM>) incorporating into an ink jet printing apparatus containing an aqueous ink the recording sheet, and (<NUM>) causing droplets of the ink to be ejected in an image wise pattern onto the recording sheet, thereby generating one or more images on the recording sheet. Inkjet printing processes are well known, and are described in, for example, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>. In one example, the ink jet printing apparatus employs a thermal ink jet process wherein the ink in the nozzles is selectively heated in an imagewise pattern, thereby causing droplets of the ink to be ejected onto the recording sheet in imagewise pattern. The recording sheet can also be used in any other printing or imaging process, such as printing with pen plotters, imaging with color laser printers or copiers, handwriting with ink pens, offset printing processes, or the like, provided that the toner or ink employed to form the image is compatible with the recording sheet. The determination of such compatibility is easily carried out given the teachings herein combined with the ordinary skill of one knowledgeable in the printing art.

The relevant contents of each of <CIT>; <CIT>; <CIT>; <CIT>; <CIT> are references.

The entire contents of "Handbook for Pulp and Paper Technologists" by G. Smook (<NUM>) Angus Wilde Publications.

All of the references, as well as their cited references, cited herein with respect to relative portions related to the subject matter of the present invention and all of its embodiments.

The present invention may be described in further detail with reference to the following examples. The examples are intended to be illustrative, but the invention is not considered as being limited to the materials, conditions, or process parameters set forth in the examples. All parts and percentages are by unit weight unless otherwise indicated.

A lab-scale puddle size press was used for the treatment on a Mill A produced base paper. The size press formulation was conventionally represented on the basis of each <NUM> (<NUM> lb) of starch. In this experiment, <NUM> (<NUM> Lb) of OBA (Clariant Leucophor BCW) was used per <NUM> (<NUM> Lb) of cooked ethylated starch (Penford Gum <NUM>, cooked at <NUM>% solids). In one case, <NUM> (<NUM> Lb) of CaCl<NUM> was added. In another case, no Ca(II) was used.

<FIG> and the tables below show the effect of Ca(II) on CIE whiteness. It is quite clear, with these two runs (repeated a few days apart), that the presence of Ca(II) significantly decreased the paper optical properties.

Bench-top size-press, <NUM> Lb OBA per <NUM> Lb of ethylated starch.

Another run, at <NUM> # of OBA per <NUM> lb of ethylated starch.

A lab-scale size press treatment was conducted, similar to Example <NUM>. In the formulation, <NUM> (<NUM> Lb) of OBA (Leucophore BCW) and <NUM> Lb of complexing agents were used per <NUM> (<NUM> Lb) of ethylated starch. In one case, <NUM> Lb of CaCl<NUM> was added in the formulation. In another case, no CaCl<NUM> was added.

The results (as shown in the following tables and graphically in <FIG>) indicate that complexing agents may improve whiteness of paper. Especially in the presence of Ca(II), EDTA complexes with Ca(II) improves whiteness, while EDTA with no Ca(II) does not show a beneficial effect.

Soluble Ca(II) is known to improve ink-jet printing properties, such as ink density. In this experiment, treated paper samples as in Example <NUM> were tested for printing properties. It is shown clearly that adding complex agents with Ca(II) did not negatively impact the printing properties. The results are illustrated in the following table and graphically in <FIG> and <FIG>.

In a size-press experiment as by Example <NUM> with <NUM> (<NUM> Lb) of OBA (Leucophore BCW), two doses of EDTA were added for comparison. The dose response of EDTA is illustrated in the following table and graphically in <FIG>.

A pilot scale size press experiment was conducted to evaluate the effectiveness of EDTA (Dow's Versene-<NUM>). Another objective was to obtain a side-by-side comparison with a commercial additive (Nalco's Extra White™ NW-<NUM>).

Mill B base paper was used, with size-press running at ~ <NUM>,<NUM>/min, <NUM> (<NUM> ft/min, <NUM>°F), pH~<NUM>, pick-up of about <NUM> (<NUM> Lb starch/ton) of paper:.

The results are shown in <FIG> and <FIG>. It is shown that EDTA (Versene) may improve optical properties - or it may significantly lower the amounts of OBA necessary to achieve the same target whiteness or brightness. It was found that Nalco's Extra White encountered incompatibility and size press runnability issues with the Ca(II) chemistry, and no benefit in optical properties were observed.

Base paper sheets were dipped into the aqueous solution containing OBA, CaCl<NUM> and complexing agents. The concentration was adjusted so that the pick-up will correspond to similar size press formulation ratios (but without starch).

From the results, which are shown in the following tables and graphically in <FIG>, <FIG>, and <FIG>, it is obvious that the whiteness gain can be confirmed for the complexing agents. It was also observed that FAS resulted in substantial brightness gain.

Lab scale size press treatments were carried out as in Example <NUM>. The treated paper sheets were then subjected to aging conditions:.

EDTA-Ca(II), DTPA-Ca(II), FAS-Ca(II), (But no by PEG-Ca(II) itself); PEG synergy : PEG/FAS-Ca(II), PEG/EDTA-Ca(II), PEG/DTPA-Ca(II). <FIG> shows felt side sheet brightness and whiteness data before and after UV and daylight exposure. <FIG> shows a synergy effect of addition of PEG to Ca(II) on UV and photo stability before and after <NUM> hour exposure to UV and daylight.

Lab scale size press treatment was carried out as by Example <NUM>. In the size press formulation, <NUM> (<NUM> Lb) of CaCl<NUM> and <NUM> (<NUM> Lb) of OBA (Leucophor BCW) were used on the basis of <NUM> (<NUM> Lb of starch per ton) of paper.

An Ionic Liquid, BMIM (<NUM>-butyl-<NUM>-methyl-imidazolium-thiocyanate), was used as an additive of interest and was compared with sodium EDTA (Versene-<NUM>) and tetramethyl ammonium EDTA. All these chemicals were applied at <NUM> Lb per <NUM> Lb starch.

It was surprisingly found that an ionic liquid may act as a complexing agent and improve the paper optical properties. The results are shown in the table below.

Ink-Jet printing properties were also tested in some of the paper samples, and were compared with the CaCl<NUM> control as well as a commercial HP Ca(II) paper control. The results are shown in the table below. All the printing properties are within the specification targets.

As used throughout, ranges are used as a short hand for describing each and every value that is within the range, including all subranges therein.

Numerous modifications and variations on the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the accompanying claims, the invention may be practiced otherwise than as specifically described herein.

Claim 1:
A recording sheet, comprising
a paper substrate comprising a plurality of cellulosic fibers;
a water-soluble salt of divalent calcium;
a complexing agent for the divalent calcium, the complexing agent being present at an amount ranging from <NUM> to <NUM>/t (<NUM> to <NUM> lbs/ton) of paper substrate;
a sizing agent being starch; and
an optical brightening agent, wherein the paper substrate has a basis weight of at least <NUM>/m<NUM> (10lbs/3000ft<NUM>).