A PAPER SUBSTRATE HAVING ENHANCED PRINT DENSITY

Description

Field of the Invention

[0001] The present invention relates to a size press applied sizing composition as defined in claim 1 that, when applied to paper substrate, creates a substrate, preferably suitable for inkjet printing, having increased print density, print sharpness, low HST, and/or image dry time, the substrate preferably having high brightness and reduced color-to-color bleed as well.

Background of the Invention

[0002] Ink jet recording systems using aqueous inks are now well known. These systems usually generate almost no noise and can easily perform multicolor recordings for business, home and commercial printing applications. Recording sheets for ink jet recordings are known. See for example U.S. Pat. Nos. 5,270,103; 5,657,064; 5,760,809; 5,729,266; 4,792,487; 5,405,678; 4,636,409; 4,481,244; 4,496,629; 4,517,244; 5,190,805; 5,320,902; 4,425,405; 4,503,118; 5,163,973; 4,425,405; 5,013,603; 5,397,619; 4,478,910; 5,429,860; 5,457,486; 5,537,137; 5,314,747; 5,474,843; 4,908,240; 5,320,902; 4,740,420; 4,576,867; 4,446,174; 4,830,911; 4,554,181; 6,764,726 and 4,877,680.

[0003] GB 2 205 967 A discloses a light-sensitive photopolymerizable material with paper support.

[0004] US 2,322,888 A relates to a process for producing high wet strength paper.

[0005] GB 551,950 A deals with improvements in or relating to the treatment of paper.

[0006] DE 195 34 327 discloses a coating paint for ink-jet paper.

[0007] However, conventional paper substrates, such as those above remain poor in balancing good print density, HST, color-to-color bleed, print sharpness, and/or image dry time. Accordingly, there is a need to provide such higli-perforrnance functionality to paper substrates useful in inkjet printing, especially those substrates preferably having high brightness.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] 

Figure 1: A first schematic cross section of just one exemplified embodiment of the paper substrate that is included in the paper substrate of the present invention.

Figure 2: A second schematic cross section of just one exemplified embodiment of the paper substrate that is included in the paper substrate of the present invention.

Figure 3: A third schematic cross section of just one exemplified embodiment of the paper substrate that is included in the paper substrate of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0009] The present inventors have discovered a sizing composition that, when applied to paper or paperboard substrates, improves the substrate's print density, color-to-color bleed, print sharpness, and/or image dry time. Further, the paper substrate preferably has a high brightness.

[0010] The sizing composition contains at least one pigment. Examples of pigments are clay, calcium carbonate, calcium sulfate hemihydrate, and calcium sulfate dehydrate, calcium carbonate, preferably precipitated calcium carbonate, in any form including ground calcium carbonate and silica-treated calcium carbonate. When the pigment is a calcium carbonate, it may be in any form. Examples include ground calcium carbonate and/or precipitated calcium carbonate. Commercially available products that are preferred are those offered as Jetcoat 30 from Specialty Minerals Inc., Jetcoat MD1093 from Specialty Minerals Inc., XC3310-1 from Omya Inc, and OmyaJet B5260, C4440 and 6606 from Omya Inc.

[0011] The pigment may have any surface area. Those pigments having a high surface area are included, including those having a surface area of greater than 20 square meters/gram, preferably greater than 30 square meters/gram, more preferably greater than 50 square meters/gram, most preferably greater than 100 square meters/gram. This range includes greater than or equal to 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100 square meters/gram, including any and all ranges and subranges contained therein.

[0012] The composition includes at least 30wt%, most preferably at least 45wt% pigment based upon the total weight of the solids in the composition. This range may include 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100wt% of pigment based upon the total weight of the solids in the composition, including any and all ranges and subranges contained therein. The most preferred amount being about 52 wt% pigment based upon the total weight of the solids in the composition.

[0013] The sizing composition contains at least two binder. The at least two binders are starch combined with polyvinyl alcohol.

[0014] The sizing composition contains a ratio of starch/PVOH wt%. solids based on the total weight of the solids in the composition of 8/1 to 1/11. 8/1, 7/1, 6/1, 5/1, 4/1, 3/1, 2/1, 1/1, including any and all ranges and subranges therein. The most preferred starch/PVOH ratio being 6/1.

[0015] The polyvinyl alcohol (PVOH) is produced by hydrolyzing polyvinyl acetate (PVA). The acetate groups are replaced with alcohol groups and the higher the hydrolysis indicates that more acetate groups have been replaced. Lower hydrolysis/molecular weight PVOH are less viscous and more water soluble. The PVOH may have a %hydrolysis ranging from 100% to 75%. The % hydrolysis may be 75, 76, 78, 80, 82, 84, 85, 86, 88, 90, 92, 94, 95, 96, 98, and 100%hdrolysis, %, including any and all ranges and subranges therein. Preferably, the % hydrolysis of the PVOH is greater than 90%.

[0016] The at least two binders amount to at least 20wt%, most preferably at least 30 wt% based on the total weight of the solids in the composition. This range may include 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100wt% based on the total weight of the solids in the composition, including any and all ranges and subranges contained therein. The most preferred being about 37wt% binder based on the total weight of the solids in the composition.

[0017] In one embodiment, when the sizing composition contains a binder and a pigment, the weight ratio of the binder/pigment may be any ratio. The binder pigment weight ratio may be from 99/1 to 1/99, preferably from 50/1 to 1/10, more preferably from 25/1 to 1/5, most preferably from 10/1 to 1/3. This range includes 99/1, 50/1, 25/1, 10/1, 5/1, 2/1, 1/1, 1/2, 2/3, 1/3, 1/4, 1/5, 10/1, 25/1, 50/1, and 99/1, including any and all ranges and subranges therein. The most preferred binder/pigment weight ratio is 7/10.

[0018] The sizing composition contains at least one nitrogen containing organic species. Nitrogen containing organic species are oligomers containing at least one ammonium functional group or polymers containing one or more quaternary ammonium functional groups. Such functional groups may vary widely and include substituted and unsubstituted amines, imines, amides, urethanes, quaternary ammonium groups, dicyandiamides and the like. Illustrative of such materials are polyamines, polyethyleneimines, polymers and 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. Examples of nitrogen containing species include those mentioned in US Patent Number 6,764,726. The most preferred nitrogen containing species are polymers and copolymers of diallyldimethyl ammonium chloride (DADMAC).

[0019] The sizing composition contains the nitrogen containing species at an amount ranging from to 1 to 20 wt %, most preferably from 2 to 10 wt% based on the total weight of the solids in the composition. This range may include 1, 2, 3, 4, S, 6, 7, 8, 9, 10, 15, 20 wt% based on the total weight of the solids in the composition, including any and all ranges and subranges contained therein. In a preferred embodiment, the composition contains about 8wt% of the nitrogen containing species based on the total weight of the solids in the composition.

[0020] The sizing composition contains at least one inorganic salt. Suitable inorganic salts may be monovalent and/or divalent and/or trivalent and may contain any level of hydration complexes thereof. The inorganic salts comprise at least one cationic metal selected from Groups 1, 2 and 13 from the Periodic Table of Elements. The cationic metal may be sodium, calcium, magnesium, and aluminum preferably. The anionic counterion to the cationic metal of the inorganic salt may be any halogen such as chloride, boride, fluoride. The most preferred inorganic salt being sodium chloride.

[0021] The sizing composition contains from 0.5 to 5, most preferably from 1 to 3 wt% of the inorganic salt based on the total weight of the solids in the composition. This range may include 0.5, 1, 2, 3, 4, 5 wt% based on the total weight of the solids in the composition, including any and all ranges and subranges contained therein. In a preferred embodiment, the sizing composition contains about 2.5wt% of the inorganic salt based on the total weight of the solids in the composition.

[0022] The sizing composition may contain at least one optical brightening agent (OBA). Suitable OBAs may be those mentioned in USSN 60/654,712 filed February 19, 2005, and USP 6,890,454. The OBAs may be commercially available from Clariant. Further, the OBA may be either cationic and/or anionic. Example OBA is that commercially available Leucophore BCW and Leucophore FTS from Clariant. In one embodiment, the OBA contained in the sizing composition is cationic.

[0023] The sizing composition contains anionic OBA at an amount from 20 to 40wt% based on the total weight of the solids in the composition. This range may include 20, 25, 30, 35, 40 wt% anionic OBA based on the total weight of the solids in the composition, including any and all ranges and subranges contained therein. In a preferred embodiment, the sizing composition contains about 35wt% of anionic OBA based on the total weight of the solids in the composition.

[0024] The sizing composition contains cationic OBA at an amount from 20 to 40 wt% based on the total weight of the solids in the composition. This range may include 20, 25, 30, 35, 40 wt% anionic OBA based on the total weight of the solids in the composition, including any and all ranges and subranges contained therein.

[0025] The present invention also relates to a paper substrate containing any of the sizing compositions described above.

[0026] The paper substrate contains a web of cellulose fibers. The source of the fibers may be from any fibrous plant. The paper substrate of the present invention may contain recycled fibers and/or virgin fibers. Recycled fibers differ from virgin fibers in that the fibers have gone through the drying process at least once.

[0027] The paper substrate of the present invention may contain from 1 to 99 wt%, preferably from 5 to 95 wt%, most preferably from 60 to 80 wt% of cellulose fibers based upon the total weight of the substrate, including 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 99 wt%, and including any and all ranges and subranges therein.

[0028] While the fiber source may be any, the preferable sources of the cellulose fibers are from softwood and/or hardwood. The paper substrate of the present invention may contain from 1 to 100 wt%, preferably from 5 to 95 wt%, cellulose fibers originating from softwood species based upon the total amount of cellulose fibers in the paper substrate. This range includes 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100wt%, including any and all ranges and subranges therein, based upon the total amount of cellulose fibers in the paper substrate.

[0029] The paper substrate of the present invention may contain from 1 to 100 wt%, preferably from 5 to 95 wt%, cellulose fibers originating from hardwood species based upon the total amount of cellulose fibers in the paper substrate. This range includes 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100wt%, including any and all ranges and subranges therein, based upon the total amount of cellulose fibers in the paper substrate.

[0030] When the paper substrate contains both hardwood and softwood fibers, it is preferable that the hardwood/softwood ratio be from 0.001 to 1000. This range may include 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 including any and all ranges and subranges therein and well as any ranges and subranges therein the inverse of such ratios.

[0031] Further, the softwood and/or hardwood fibers contained by the paper substrate of the present invention may be modified by physical and/or chemical means. Examples of physical means include, but is not limited to, electromagnetic and mechanical means. Means for electrical modification include, but are not limited to, means involving contacting the fibers with an electromagnetic energy source such as light and/or electrical current. Means for mechanical modification include, but are not limited to, means involving contacting an inanimate object with the fibers. Examples of such inanimate objects include those with sharp and/or dull edges. Such means also involve, for example, cutting, kneading, pounding, impaling, etc means.

[0032] Examples of chemical means include, but is not limited to, conventional chemical fiber modification means including crosslinking and precipitation of complexes thereon. Examples of such modification of fibers may be, but is not limited to, those found in the following patents 6,592,717, 6,592,712, 6,582,557, 6,579,415, 6,579,414, 6,506,282, 6,471,824, 6,361,651, 6,146,494, H1,704, 5,731,080, 5,698,688, 5,698,074, 5,667,637, 5,662,773, 5,531,728, 5,443,899, 5,360,420, 5,266,250, 5,209,953, 5,160,789, 5,049,235, 4,986,882, 4,496,427, 4,431,481, 4,174,417, 4,166,894, 4,075,136, and 4,022,965. Further modification of fibers is found in United States Patent Applications having Application Number 60/654,712 filed February 19, 2005; 11/358,543 filed February 21, 2006; 11/445,809 filed June 2, 2006; and 11/446,421 filed June 2, 2006, which may include the addition of optical brighteners (i.e. OBAs) as discussed therein.

[0033] One example of a recycled fiber is a "fine". Sources of "fines" may be found in SaveAll fibers, recirculated streams, reject streams, waste fiber streams. The amount of "fines" present in the paper substrate can be modified by tailoring the rate at which such streams are added to the paper making process.

[0034] The paper substate preferably contains a combination of hardwood fibers, softwood fibers and "fines" fibers. "Fines" fibers are, as discussed above, recirculated and are any length. Fines may typically be not more that 100 µm in length on average, preferably not more than 90 µm, more preferably not more than 80 µm in length, and most preferably not more than 75 µm in length. The length of the fines are preferably not more than 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100 µm in length, including any and all ranges and subranges therein.

[0035] The paper substrate may contain fines at any amount. The paper substrate may contain from 0.01 to 100 wt% fines, preferably from 0.01 to 50wt%, most preferably from 0.01 to 15wt% based upon the total weight of the fibers contained by the paper substrate. The paper substrate contains not more than 0.01, 0.05, 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 100wt% fines based upon the total weight of the fibers contained by the paper substrate, including any and all ranges and subranges therein.

[0036] The paper substrate may also contain an internal sizing and/or external sizing composition. The internal sizing composition may be applied to the fibers during papermaking at the wet end, while the external sizing composition may be applied to the fibers via a size press and/or coater. The above mentioned sizing compositions of the present invention may be the internal and/or external sizing composition contained by the paper substrate of the present invention.

[0037] Figures 1-3 demonstrate different embodiments of the paper substrate 1 in the paper substrate of the present invention. Figure 1 demonstrates a paper substrate 1 that has a web of cellulose fibers 3 and a sizing composition 2 where the sizing composition 2 has minimal interpenetration of the web of cellulose fibers 3. Such an embodiment may be made, for example, when a sizing composition is coated onto a web of cellulose fibers.

[0038] Figure 2 demonstrates a paper substrate 1 that has a web of cellulose fibers 3 and a sizing composition 2 where the sizing composition 2 interpenetrates the web of cellulose fibers 3. The interpenetration layer 4 of the paper substrate 1 defines a region in which at least the sizing solution penetrates into and is among the cellulose fibers. The interpenetration layer may be from 1 to 99% of the entire cross section of at least a portion of the paper substrate, including 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 99% of the paper substrate, including any and all ranges and subranges therein. Such an embodiment may be made, for example, when a sizing composition 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.

[0039] Figure 3 demonstrates a paper substrate 1 that has a web of cellulose fibers 3 and a sizing solution 2 where the sizing composition 2 is approximately evenly distributed throughout the web of cellulose fibers 3. Such an embodiment may be made, for example, when a sizing composition is added to the cellulose fibers prior to a coating method and may be combined with a subsequent coating method if required. Exemplified addition points may be at the wet end of the paper making process, the thin stock, and the thick stock.

[0040] The paper substrate may be made by contacting any component of the sizing solution with the cellulose fibers consecutively and/or simultaneously. Still further, the contacting may occur at acceptable concentration levels that provide the paper substrate of the present invention to contain any of the above-mentioned amounts of cellulose and components of the sizing solution. The contacting may occur anytime in the papermaking process including, but not limited to the thick stock, thin stock, head box, and coater with the preferred addition point being at the thin stock. Further addition points include machine chest, stuff box, and suction of the fan pump. Preferably, the components of the sizing solution are preformulated either together and/or in combination within a single and/or separate coating layer(s) and coated onto the fibrous web via a size press and/or coater.

[0041] The paper or paperboard of this invention can be prepared using known conventional techniques. Methods and apparatuses for forming and making and applying a coating formulation to a paper substrate are well known in the paper and paperboard art. See for example, G.A. Smook referenced above and references cited therein. All such known methods can be used in the practice of this invention and will not be described in detail.

[0042] The paper substrate may contain the sizing composition at any amount. The paper substrate may contain the sizing composition at an amount ranging from 31.8 to 136.2kg/ton (70 to 300 lbs/ton) of paper, preferably from 36.3 to 113.5 kg/ton (80 to 250lbs/ton) of paper, more preferably from 45.4 to 90.8 kg/ton (100 to 200 lbs/ton) of paper, most preferably from 56.8 to 79.5 kg/ton (125 to 175 lbs/ton) of paper. This range includes 318, 36.3, 40.9, 45.4, 49.9, 54.5, 59, 63.6, 68.1, 72.6, 77.2, 81.7, 86.3, 90.8, 95.3, 99.9, 104.4, 108.9, 113.5, 118, 122.6, 127.1, 131.7, and 136.2 kg/ton (70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270 280, 290, and 300 lbs/ton) of paper, including any and all ranges and subranges therein. In a preferred embodiment the paper substrate contains a size press applied sizing composition at an amount of 68.1 kg/ton (150 lbs/ton) of paper substrate.

[0043] Given the above mentioned preferred amounts of sizing composition contained in the substrate of the present invention, combined with the above-mentioned amounts of pigment, binder, nitrogen containing compound, and inorganic salt; the amounts of each of the pigment, binder, nitrogen containing compound, inorganic salt that are contained in the paper may be easily calculated. For example, if 50wt% of pigment is present in the sizing solution based upon the total weight of solids in the composition, and the paper substrate contains 38.1 kg (150lbs) of the sizing composition/ton, then the paper substrate contains 50% x 68.1 kg/ton (150lbs/ton) of paper=34.1 kg (75 lbs) pigment/ton of paper, which is 34.1 kg/408 kg (75 lbs/2000lbs)x 100= 3.75wt% pigment based upon the total weight of the paper substrate.

[0044] The OBA may be cationic and/or anionic. The OBA may be supplied by the sizing composition as mentioned above and/or within the substrate itself. For example, the OBA may be premixed with the fibers at the wet end of the papermaking and even before the headbox. Preferred examples of using OBA:fiber mixes is found in United States Patent Applications having Application Number 60/654,712 filed February 19, 2005; 11/358,543 filed February 21, 2006; 11/445,809 filed June 2; 2006; and 11/446,421 filed June 2, 2006.

[0045] In one embodiment of the present invention, the paper substrate contains internal OBA and externally applied OBA. The internal OBA may be cationic or anionic, but is preferably anionic. The externally applied OBA may be cationic or anionic, but is preferably cationic. The externally applied OBA is preferably applied as a member of the sizing composition at the size press as mentioned above in the above preferred amounts of OBA. However, external OBA may also be applied at the coating section.

[0046] In one embodiment, the OBA is present in as sufficient amount so that the paper has at least 80% GE brightness. The GE brightness is preferably at least 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, and 100%, including any and all ranges and subranges contained therein.

[0047] Further, the paper may have a suitable amount of OBA and other additives (such as dyes) so that the paper preferably has a CIE whiteness of at least 130. The CIE whiteness may be at least 130, 135, 140, 145, 150, 155, 160, 65, 170, 175, 180, 185, 190, 195, and 200 CIE whiteness points, including any and all ranges and subranges therein.

[0048] In one embodiment, the substrate contains an effective amount of OBA. An effective amount of OBA is such that the GE brightness is at least 90, preferably at least 92, more preferably at least 94 and most preferably at least 95% brightness. The OBA may be a mixture of the above-mentioned internal and externally applied OBA, whether cationic and/or anionic so long as it is an effective amount.

[0049] The density, basis weight and caliper of the web of this invention may vary widely and conventional basis weights, densities and calipers may be employed depending on the paper-based product formed from the web. Paper or paperboard of invention preferably have a final caliper, after calendering of the paper, and any nipping or pressing such as may be associated with subsequent coating of from 25.4 µm(1mils) to 889 µm (35 mils) although the caliper can be outside of this range if desired. More preferably the caliper is from 101.6 µm(4 mils) to 508 µm(20 mils) and most preferably from 177.8 µm (7mils) to 431.8 µm (17 mils). The caliper of the paper substrate preferably from 177.8µm (7 mils) to 431.8 µm (17 mils). The caliper of the paper substrate with or without any coating may be 25,4, 50.8, 76.2, 101.6, 127, 152.4, 177.8, 203.2, 228.6, 254, 279.4, 304.8, 330.2, 355.6, 381, 431.8, 508, 558.8, 635, 685.8, 762, 812.8, and 889 (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 20, 22, 25, 27, 30, 32, and 35), including any and all ranges and subranges therein.

[0050] Paper substrates of the invention preferably exhibit basis weights of from 16.3 g/m² (10 lb/3000ft²) to 815 g/m² (600 lb/3000ft²), although web basis weight can be outside of this range if desired. More preferably the basis weight is from 48.9 g/m² (30lb/3000ft²) to 3126 g/m² (200lb/3000ft²), and most preferably from 244.5g/m² (150lb/3000ft²). The basis weight may be 16.3, 19.5, 24.5, 27.7, 32.6, 35.9, 40.8, 48.9, 52.2, 57.1, 60.3, 65.2, 73.4, 81.5, 89.7, 97.8, 105.9, 114.1, 122.3, 130.4, 138.6, 146.7, 154.9, 163, 179.3, 195.6, 211.9, 228.2, 244.5, 260.8, 277.1, 293.4, 309.7, 326, 366.8, 407.5, 448.3, 489, 529.8, 570.5, 611.3, 652, 692.8, 733.5, 815 g/m² (10, 12, 15, 17, 20, 22, 25, 30, 32, 35, 37, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 500 lb/3000ft²), including any and all ranges and subranges therein.

[0051] The final density of the papers may be calculated by any of the above-mentioned basis weights divided by any of the above-mentioned calipers, including any and all ranges and subranges therein. Preferably, the final density of the papers that is, the basis weight divided by the caliper, is preferably from 0.38 g/cm³( 6lb/3000ft ²/mil) to 0.897 g/cm³ (141lb/3000ft²/mil) although web densities can be outside of this range if desired. More preferably the web density is from 0.45 g/cm³(7lb/3000ft²/mil) to 0.77 g/cm³ 0.83 g/cm³ (13lb/3000ft²/mil) and most preferably from 0.58 g/cm³(9lb/3000ft²/ mil) to 0.77 g/cm³ (12 lb/3000ft²/mil).

[0052] The web may also include other conventional additives such as, for example, starch, expandable microspheres, mineral fillers, bulking agents, sizing agents, retention aids, and strengthening polymers. Among the fillers that may be used are organic and inorganic pigments such as, by way of example, polymeric particles such as polystyrene latexes and polymethylmethacrylate, and minerals such as calcium carbonate, kaolin, and talc. Other conventional additives include, but are not restricted to, wet strength resins, internal sizes, dry strength resins, alum, fillers, pigments and dyes. Internal sizing helps prevent the surface size from soaking into the sheet, thus allowing it to remain on the surface where it has maximum effectiveness. The internal sizing agents encompass any of those commonly used at the wet end of a paper machine. These include rosin sizes, ketene dimers and multimers, and alkenylsuccinic anhydrides. The internal sizes are generally used at levels of from 0.00 wt. % to 0.25 wt. % based on the weight of the dry paper sheet. Methods and materials utilized for internal sizing with rosin are discussed by E. Strazdins in The Sizing of Paper, Second Edition, edited by W. F. Reynolds, Tappi Press, 1989, pages 1-33. Suitable ketene dimers for internal sizing are disclosed in U.S. Pat. No. 4,279,794, and in United Kingdom Patent Nos. 786,543; 903,416; 1,373,788 and 1,533, 434, and in European Patent Application Publication No. 0666368 A3. Ketene dimers are commercially available, as Aquapel.RTM. and Precis.RTM. sizing agents from Hercules Incorporated, Wilmington, Del. Ketene multimers for use in internal sizes are described in: European Patent Application Publication No. 0629741A1, corresponding to U.S. patent application Ser. No. 08/254,813, filed Jun. 6, 1994; European Patent Application Publication No. 0666368A3, corresponding to U.S. patent application Ser. No. 08/192,570, filed Feb. 7, 1994; and U.S. patent application Ser. No. 08/601,113, filed Feb. 16, 1996. Alkenylsuccinic anhydrides for internal sizing are disclosed in U. S. Pat. No. 4,040,900, and by C. E. Farley and R. B. Wasser in The Sizing of Paper, Second Edition, edited by W. F. Reynolds, Tappi Press, 1989, pages 51-62. A variety of alkenylsuccinic anhydrides are commercially available from Albemarle Corporation, Baton Rouge, La.

[0053] The paper substrate may be made by contacting further optional substances with the cellulose fibers as well. The contacting of the optional substances and the cellulose fibers may occur anytime in the papermaking process including, but not limited to the thick stock, thin stock, head box, size press, water box, and coater. Further addition points include machine chest, stuff box, and suction of the fan pump. The cellulose fibers, components of the sizing composition, and/or optional components may be contacted serially, consecutively, and/or simultaneously in any combination with each other. The cellulose fibers components of the sizing composition may be pre-mixed in any combination before addition to or during the paper-making process.

[0054] The paper substrate may be pressed in a press section containing one or more nips. However, any pressing means commonly known in the art of papermaking may be utilized. The nips may be, but is not limited to, single felted, double felted, roll, and extended nip in the presses. However, any nip commonly known in the art of papermaking may be utilized.

[0055] 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 10% water.

[0056] 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). At the size press, sizing agents such as binders may be contacted with the substrate. Optionally these same sizing agents may be added at the wet end of the papermaking process as needed. After sizing, the paper substrate may or may not be dried again according to the above-mentioned exemplified means and other commonly known drying means in the art of papermaking. 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 10% water. Preferably, the sizing apparatus is a puddle size press.

[0057] 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. While not wishing to be bound by theory, it is thought that the presence of the expandable microspheres and/or composition and/or particle of the present invention may reduce and alleviate requirements for harsh calendaring means and environments for certain paper substrates, dependent on the intended use thereof.

[0058] The paper substrate may be microfinished according to any microfinishing means commonly known in the art of papermaking. Microfinishing is a means involving frictional processes to finish surfaces of the paper substrate. The paper substrate may be microfinished with or without a calendering means applied thereto consecutively and/or simultaneously. Examples of microfinishing means can be found in United States Published Patent Application 20040123966 and references cited therein, as well as USSN 60/810181 filed on June 2, 2006.

[0059] The Hercules Sizing Test Value ("HST") of the substrate is selected to provide the desired waterfastness characteristics. The HST is measured using the procedure of TAPPI 530 pm-89.

[0060] The HST may be is as low as 0.1, 1, 5 and 10 seconds. In a preferred embodiment of this invention, the HST is less than 10 seconds, preferably, less than 5 seconds, more preferably less than 3 seconds HST, most preferably less than about 1 second. The HST may be 0.001, 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 and 10 seconds, including any and all ranges and subranges therein. As it is well known to those of ordinary skill in the art, the HST will vary directly with the basic weight of the substrate and other factors known to those of ordinary skill in the art. Based upon the foregoing information, one of ordinary skill in the art can use conventional techniques and procedures to calculate, determine and/or estimate a particular HST for the substrate used to provide the desired image waterfastness characteristics.

[0061] The paper substrate of the present invention may have any black optical density as measured by TAPPI METHOD T 1213 sp-03. The black optical density is at least 1.0, more preferably from 1.0 to 1.5. The black optical density may be 1.0, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.2, 1.3, 1.4, and 1.5, including any and all ranges and subranges therein.

[0062] From density, one can naturally calculate waterfastness using the following equation:


The paper substrate of the present invention may have any waterfastness. The paper substrate may have a waterfastness of at least 90%, preferably at least 95%, more preferably greater than 98%, most preferably greater than 100%, including any and all ranges and subranges therein.

[0063] In one embodiment of the present invention, the paper substrate may contain an effective amount of pigment and binder. An effective amount of pigment and binder is that which bestows on the paper a black optical density that is at least 1.0, preferably from 1 to 2, more preferably from 1 to 1.5 and most preferably from 1.1 to 1.3, including any and all ranges and subranges therein.

[0064] The present invention relates to a method of decreasing the HST of a paper substrate. Preferably, the above-mentioned sizing composition is contacted with a substrate having a first HST and containing a web of cellulose fibers and optional substances mentioned above at a size press or coating section so as to prepare a paper substrate having a second HST that is less than the first HST and containing the sizing composition, the web of cellulose fibers, and optional substance. While the second HST is less than the first HST, the present invention preferably reduces the first HST by at least 10%, more preferably by at least 25%, most preferably by at least 50%. This reduction range may be at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 75, 80, 95 and 99% of the first HST, including any and all ranges and subranges therein.

[0065] The present invention is explained in more detail with the aid of the following embodiment example which is not intended to limit the scope of the present invention in any manner.

EXAMPLES

Example 1.

[0066] The following size press formulations were prepared for treating the un-surface sized base paper.

Table 1

Chemicals	1	2	3	4	5	6	7
Jetcoat MD1093 Precipitated calcium carbonate	100	100	100
XC3310-1 ground calcium carbonate				100			100
TX-75NX, silica treated calcium carbonate					100
TX-75ZX silica treated calcium carbonate						100
Polyvinyl alcohol	20	10	10	10			10
Oxidized starch		30	60	60	100
Cationic starch						l00	60
Polydadmac	10	10	10	l0			10
Calcium chloride	5	5	5	5			5
%solids	13	13	13	13	13	13	13
PH	6.7	7.0	7.3	7	6.9	6.8	6.9
Brookfiled viscosity	27	46	80	55	118	38	27
Temperature, (F)°C	(117) 47	(120) 49	(117) 47	(130) 54	(130) 54	(130) 54	(130) 54

[0067] The pigmented size press formulations were applied to an unsurface sized 90 gsm base paper using a rod metering size press. The target coat weight or pick up is 6 gsm. Calendering was done on a steel-to-steel lab calender at room temperature with a nip pressure of 620.5kPa (90 psi). The smoothness target is 125 Sheffield smoothness.

Table 2 The paper samples from example 1 were evaluated for print performance on an Kodak Versamark 5000 digital press. ExceJJent print quality were obtained. The print density test results on the trial samples provided in example 1 are listed in the following table.

Condition	Print density on Kodak Versamark 5000
1	1.15
2	1.12
3	1.13
4	1.09
5	1.11
6	1.18
7	1.14

Example 2:

[0068] Paper substrates having a basis weight of 90 g/m² (24 lb/1300 square feet) were made and a sizing composition was applied thereto both surfaces of the paper substrate at size press. The sizing compositions applied to the paper substrate are those according to the following Table 3.

Table 3

functionality	Chem \ Prop'ties \ Cond'ns	1	2	3	4	5
	SP configuration	puddle	puddle	Puddle	puddle	puddle
pigment (2)	SMI JetCoat® 30	100
	SMI MD 1093		100	100	100	100
Binder (2)	Clinton 442 starch	60	60	60	60	60
	Mowiol 28-99	10	10	10	10	10
fixative (2)	Gen Floc F71100	10
	Cartafix VXZ		10	10	15	15
salt (2)	NaCl	8	8	8	8	8
	CaCl2					5
brightener (2)	Leucophore BCW (wet pts)	100
	Leucophore FTS (wet pts)		20	20	20	20
Wet-xer (1)	Amres 24HP		5			5
properties	target %solids	15	15	15	15	15
	actual %solids	15.2	15.1	15.1	15.1	15.3
	Brookfield #2 @ 50 rpm	122	160	89	76	61
	Brookfield #2 @ 100 rpm	100	125	84	70	69
	pH	8.0	7.3	7.8	7.8	7.0
	temperature	(109) 48	(112) 44	(147) 64	(140)	(143) 60
	Pickup g/m2 (lbs/3,300 ft2)	(4.8) 7.8	(4.6) 7.5	(4.6) 7.5	(5.0) 8.2	(4.9) 8
	pickup (gsm)	7.1	6.8	6.8	7.4	7.25
	pickup kg/ton (lbs/ton) of paper	(157) 71.3	(151) 68.6	(151) 68.6	(164) 74.5	(161) 73.1
	ODori[a]	1.15/1.14	1.13/1.14	1.23/1.19	1.22/1.17	1.20/1.17
	ODsaak&dry[a]	1.13/1.19	1.14/1.19	1.22/1.19	1.22/1.17	1.19/1.17
	ODbleed[a]	0.26/0.33	0.44/0.48	0.13/0.11	0.04/0.12	0.08/0.18
	%Bleed[a]	22.83/29.13	39.26/42.00	10.35/8.85	2.76/10.41	6.42/15.47
	%H2Ofastness[a]	97.78/104.08	100.98/105.05	99.60/100.42	100.14/100.15	99.31/100.15

Gen Floc F71100 (General Chemicals) and Cartafix VXZ (Clariant) are both of the chemical nature of poly(dadmac) and are nitrogen-containing species. Amres, a kymene wet-strength resin from Kamira is also nitrogen-containing species. Mowiol 28-99 (Clariant) is a version of PVOH, which is 99% hydrolyzed and is of high molecular weight. Starch and PVOH were cooked separately and diluted to a solids level of about 15%. Each of the formulation was prepared in accordance with the recipe as tabulated above and was thoroughly mixed together. An overall %solids was first arrived at greater than the targeted 15%, because the rest of the ingredients all have a solids level above 15%. For each of the formulations, the actual initial %solids was measured and then diluted, as close as possible, to 15%. Each of the formulations was sent to the 14" pilot size press, which was pre-configured to C2S puddle operation. The paper after size press was dried to 4.2 to 5.0% moisture. The subscript [a] denotes average, which means each of the numbers was averaged from 4 or even more readings. The two numbers before and after the slash sign represent readings from the two sides of the paper, respectively.

[0069] Ink jet print densities are measured by means of optical densities with an X-rite densitometer. The density according to TAPPI METHOD T 1213 sp-03 is the optical -negative logarithm to base 10 of transmittance for transparent material or the reflectance for an opaque material and has the equation Optical Density = long10 1/R, where R = Reflectance. The following densitometer was used: X-Rite Densitometer, manufactured byX-Rite Inc. Density is a function of the percentage of light reflected. From this density procedure, one can easily measure Waterfastness and % bleed as well using the following equations:

Calculation for % Waterfastness:

[0070] 

Calculation for % Bleed:

[0071] 

Claims

1. A size press applied sizing composition for application to a paper substrate comprising
at least one pigment at an amount of at least 30wt% based upon the total weight of the solids of the composition;
at least two binders at an amount of at least 20wt% based upon the total weight of the solids of the composition;
at least one nitrogen containing organic species at an amount ranging from 1 to 20wt% based upon the total weight of the solids of the composition;
and at least one inorganic salt at an amount ranging from 0.5 to 5wt% based upon the total weight of the solids of the composition,
and wherein
the at least two binders are polyvinyl alcohol and starch and are present at a starch/polyvinyl alcohol weight ratio of from 8/1 to 1/1;
the at least one nitrogen containing organic species is at least one member selected from the group consisting of an oligomer containing at least one ammonium functional group or a polymer containing at least one quaternary ammonium functional group; and
the inorganic salt comprises at least one cationic metal selected from Groups 1, 2 or 13 of the periodic table of elements and at least one halogen.

2. The sizing composition according to Claim 1, further comprising from 20 to 40wt% based on the total weight of the solids in the composition of an optical brightening agent.

3. The composition according to Claim 2, wherein the optical brightening agent is cationic.

4. A paper substrate, comprising the composition according to Claim 1.

5. The paper substrate according to Claim 4, wherein the substrate has a print density of at least 1.0 and HST of not more than 10 seconds.

Ansprüche

1. Eine mittels einer Leimpresse aufgebrachte Leimzusammensetzung zur Aufbringung auf ein Papiersubstrat, umfassend
mindestens ein Pigment mit einer Menge von mindestens 30 Gew.-%, bezogen auf das Gesamtgewicht der Feststoffe der Zusammensetzung;
mindestens zwei Bindemittel mit einer Menge von mindestens 20 Gew.-%, bezogen auf das Gesamtgewicht der Feststoffe der Zusammensetzung;
mindestens eine stickstoffhaltige organische Spezies mit einer Menge im Bereich von 1 bis 20 Gew.-%, bezogen auf das Gesamtgewicht der Feststoffe der Zusammensetzung; und
mindestens ein anorganisches Salz mit einer Menge im Bereich von 0,5 bis 5 Gew.-%, bezogen auf das Gesamtgewicht der Feststoffe der Zusammensetzung,
und wobei
die mindestens zwei Bindemittel Polyvinylalkohol und Stärke sind und mit einem Stärke/Polyvinylalkohol-Gewichtsverhältnis von 8/1 bis 1/1 vorliegen;
die mindestens eine stickstoffhaltige organische Spezies mindestens ein Vertreter ist, ausgewählt aus der Gruppe, bestehend aus einem Oligomer, das mindestens eine funktionelle Ammoniumgruppe enthält, oder einem Polymer, das mindestens eine quaternäre funktionelle Ammoniumgruppe enthält; und
das anorganische Salz mindestens ein kationisches Metall, ausgewählt aus den Gruppen 1, 2 oder 13 des Periodensystems der Elemente, und mindestens ein Halogen umfasst.

2. Die Leimzusammensetzung nach Anspruch 1, ferner umfassend 20 bis 40 Gew.-% eines optischen Aufhellers, bezogen auf das Gesamtgewicht der Feststoffe in der Zusammensetzung.

3. Die Zusammensetzung nach Anspruch 2, wobei der optische Aufheller kationisch ist.

4. Ein Papiersubstrat, umfassend die Zusammensetzung nach Anspruch 1.

5. Das Papiersubstrat nach Anspruch 4, wobei das Substrat eine Druckdichte von mindestens 1,0 und ein HST von nicht mehr als 10 Sekunden aufweist.

Revendications

1. Composition de collage appliquée à une presse encolleuse pour une application sur un substrat de papier, comprenant :

- au moins un pigment dans une quantité d'au moins 30 % en poids sur la base du poids total des matières solides de la composition ;

- au moins deux liants dans une quantité d'au moins 20 % en poids sur la base du poids total des matières solides de la composition ;

- au moins une espèce organique contenant de l'azote dans une quantité se situant dans la plage de 1 à 20 % en poids sur la base du poids total des matières solides de la composition ; et

- au moins un sel inorganique dans une quantité se situant dans la plage de 0,5 à 5 % en poids sur la base du poids total des matières solides de la composition,

et dans laquelle
les au moins deux liants sont l'alcool polyvinylique et l'amidon et sont présents à un rapport en poids amidon/alcool polyvinylique de 8/1 à 1/1 ;
la au moins une espèce organique contenant de l'azote est au moins un élément choisi dans le groupe consistant en un oligomère contenant au moins un groupe fonctionnel ammonium ou un polymère contenant au moins un groupe fonctionnel ammonium quaternaire ; et
le sel inorganique comprend au moins un métal cationique choisi dans les Groupes 1, 2 ou 13 de la classification périodique des éléments et au moins un halogène.

2. Composition de collage selon la revendication 1, comprenant en outre de 20 à 40 % en poids sur la base du poids total des matières solides dans la composition d'un agent d'azurage optique.

3. Composition selon la revendication 2, dans laquelle l'agent d'azurage optique est cationique.

4. Substrat de papier, comprenant la composition selon la revendication 1.

5. Substrat de papier selon la revendication 4, dans lequel le substrat a une densité d'impression d'au moins 1,0 et un HST de pas plus de 10 secondes.

Drawing