Formulation for ink receptive coating and coated substrate produced with same

Abstract

A coating formulation includes fumed silica, boric acid, a binder, water, and, optionally, ethanol and / or pseudo-boehmite. A pH of the formulation is from 2.0 to 3.0, a ratio of fumed silica to binder by weight is from 3.0:1 to 4.5:1, a ratio of boric acid to binder by weight is from 9.5% to 28%, and a ratio of boric acid to the total amount of both fumed silica and pseudo-boehmite is at least 3.0%.

Description

Docket No. - 2024205P2- 1 of 13-TITLEFORMULATION FOR INK RECEPTIVE COATING AND COATED SUBSTRATE PRODUCED WITH SAMEBACKGROUND1. Field.

[0001] This invention relates to ink receptive coating formulations for paper and other substrates.2. Description of the Related Art,

[0002] Ink receptive coatings (IRC) are designed to enhance the printing surface of a substrate such as paper or fdm. The key function of ink receptive coatings is to control droplet spread, or drop gain, while absorbing the ink carrier fluid and leaving the colorant on the substrate surface. Pseudo-boehmite is often used as an ink receptive agent but has poor scratch resistance. Fumed silica has high porosity and can provide anti-scratch resistance in coatings but sometimes results in cracking at the surface of the coated substrate. Thus, it is desirable to have a fumed silica-based IRC that provides good crack resistance.SUMMARY

[0003] In one embodiment, a coating formulation includes fumed silica, boric acid, a binder, water, and, optionally, ethanol and / or pseudo-boehmite. A pH of the formulation is from 2.0 to 3.0, a ratio of fumed silica to binder by weight is from 3.0: 1 to 4.5: 1, a ratio of boric acid to binder by weight is from 9.5% to 28%, and a ratio of boric acid to the total amount of both fumed silica and pseudo-boehmite is at least 3.0%.

[0004] The coating formulation may further include a glyoxal-based cross-linker, and a ratio of the total amount of glyoxal-based cross-linker and boric acid to binder by weight may be up to 50%. The fumed silica may have a surface area of 200 to 350 m2 / g as measured by ASTM D6556. Ethanol may be present in an amount of up to 20 wt%, for example, up to 17 wt%. Pseudo-boehmite may be present in an amount of up to 0.7 wt%, for example, up to 0.65 wt%.Docket No. - 2024205P2- 2 of 13-

[0005] The fumed silica may be present in an amount of 70-80% by mass (dry basis). The fumed silica may have a particle size distribution, as measured by laser scattering, with D50 of 80 - 140 nm, D90 of 110-250 nm, or both. The binder may be polyvinyl alcohol, a cationic polyurethane, or a cationic acrylic polymer. The coating formulation may further include hydrochloric acid or nitric acid.

[0006] A method of preparing an ink receptive coating may include coating a substrate, e.g., paper, fabric, or a plastic substrate, with any of the coating formulations described above and allowing the paper to dry.

[0007] Coating may include roll coating or air knife coating. The coating may be 15-30 gsm. The method may be used to coat a substrate, e.g., paper, fabric, or a plastic substrate, and the coated substrate may exhibit no cracks in an area of 600-625 cm2observed under 50x magnification.

[0008] ft is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present invention, as claimed.DETAILED DESCRIPTION

[0009] Without being bound by any particular theory, it is believed that reducing the pH of the formulation reduces the crosslinking kinetics of boric acid with the binder. This increases the work time of the coating formulation and reduces the formation of air bubbles that may be detrimental to coating quality. It is also believed that the reduced pH and the increased boric acid concentration increase the crosslink density of the binder, further improving crack resistance.

[0010] Thus, in one embodiment, a coating formulation includes fumed silica, boric acid, a binder, and water. The coating formulation optionally includes one or both of ethanol or pseudo-boehmite. The pH of the formulation is from 2.0 to 3.0. The ratio of fumed silica to binder by weight is from 3.0: 1 to 4.5: 1. The ratio of boric acid to binder by weight is from 9.5% to 28%. The ratio of boric acid to the total amount of both fumed silica and pseudo-boehmite is at least 3.0%.[OOH] As noted above, the pH of the formulation is from 2.0 to 3.0. For example, the pH may be from 2.2 to 2.9 or 2.3 to 2.85 or from 2.4 to 2.6. The pH may be adjusted with the use of any conventional acid in the methods described below. For example, aside from theDocket No. - 2024205P2- 3 of 13- use of boric acid, acids such as hydrochloric acid, nitric acid, and acetic acid may be employed.

[0012] The fumed silica may be any fumed silica having a surface area of 200 to 350 m2 / g as measured by ASTM D6556. For example, the fumed silica may have a surface area of 240 to 310 m2 / g or 230 to 275 m2 / g. Suitable fumed silicas are available commercially from a variety of sources, including but not limited to Cabot Corporation, Evonik Industries, Tokuyama Corporation, and Wacker Chemie AG. The fumed silica dispersion in deionized water may have a particle size D50 of 80 - 140 rnn and / or a D90 of 110-250 nm. For example, fumed silica dispersions having the D90 property may have a D50 as high as 150 nm or 160 nm. Particle size may be measured by laser scattering, e.g., in a Horiba LA950V2 instrument, with 1-2 drops of the fumed silica dispersion added to 180- 200 mL water in the sampling cell. As noted above, the ratio of fumed silica to binder by weight is from 3.0: 1 to 4.5: 1. For example, the ratio of fumed silica to binder by weight may be from 3.3: 1 to 4.4: 1, e.g., from 3.7: 1 to 4.3: 1 or 4.0: 1 to 4.3: 1. The total amount of fumed silica in the formulation may be from 70 wt% to 80 wt% on a dry basis, for example from 71% to 76%.

[0013] Boric acid assists with cross-linking of the binder in the formulation. The ratio of boric acid to binder is from 9.5% to 28% (boric acid* 100% / binder) by weight. For example, the ratio of boric acid to binder may be from 15% to 25% or from 17% to 23%. Pseudo-boehmite may be used in the formulation to improve colorfastness and color density of the printed ink. Pseudo-boehmite may be sued in an amount of up to 0.7 wt% on a dry basis, for example, up to 0.65% or up to 0.5 wt%. The ratio of boric acid to the total amount of both fumed silica and pseudo-boehmite (when present) is at least 3% (boric acid*100% / (silica + pseudoboehmite)) by weight. For example, the ratio may be from 3% to 13%, e.g., from 3.5% to 10% or from 4% to 7%.

[0014] The binder may be any binder known to those of skill in the art for preparing ink receptive coatings. For example, the binder may be a polyvinyl alcohol, a cationic polyurethane, or a cationic acrylic polymer. Exemplary polymers are available from Kururay, Seiko PMC, and other suppliers known to those of skill in the art. The ratio of particulates (fumed silica and optional pseudo-boehmite) to binder by mass may be from 3.3: 1 to 4.7 to 1, for example, from 3.4: 1 to 4.6: 1, from 3.7: 1 to 4.7: 1, or from 4.3: 1 to 4.6:1.Docket No. - 2024205P2- 4 of 13-

[0015] The formulation is preferably aqueous to reduce volatiles and hazardous waste. Ethanol may be used in amounts up to 20 wt% (total formulation) or up to 17%, for example, up to 10 wt%, to manipulate the viscosity of the formulation.

[0016] Glyoxal and / or glyoxal-based materials may be added to the formulation as an additional cross-linking agent. Suitable glyoxal-based cross-linkers include but are not limited to TSI, FCI, TSI-NG, EPI, and GH products available from Archroma under the CARTABOND® brand and glyoxal itself. The total amount of glyoxal-based cross-linker and boric acid by weight with respect to binder may be up to 50%, for example, from 15% to 25%.

[0017] The formulation may be prepared by preparing dispersions of the various components. The dispersions, except for the cross-linker, are combined in the desired proportions and then the pH adjusted with acid, following which the boric acid and optional glyoxal-based cross-linker are added. For example, aqueous dispersions may be prepared with the fumed silica, pseudo-boehmite, binder, and boric acid. If necessary, a dispersant such as poly(diallyldimethylammonium chloride) may be employed to promote dispersion of the fumed silica.

[0018] In one embodiment, the formulation is coated onto a substrate, e.g., paper, fabric, or a plastic substrate, for example, by roll coating or using an air knife, and allowed to dry. In some embodiments, drying is performed over a series of gradually increasing temperatures, which may reduce cracking. The final coating may be present in an amount of 15-30 gsm, for example 18-25 gsm. Deposition of the formulation in multiple layers may better allow the escape of air bubbles from the coating and reduce cracking. Preferably, no cracks are observed on the coated substrate, for example, an A4 or 8.5 x 11 inch sheet (600-625 cm2) under 50x magnification. Typically, the paper is a nonwoven web prepared, e.g., by air laying or wet laying relatively short fibers to form a web or sheet or by melt-extrusion processes as melt blowing and spin bonding. The paper may include only cellulose fibers, a mixture of cellulose fibers and synthetic fibers, or only synthetic fibers. In addition, the paper also may contain additives and other materials, such as fillers, e.g., clay and titanium dioxide, as is well known in the papermaking art. Fabric may be woven or non-woven from natural or synthetic fibers, for example, cotton, polypropylene, rayon, polyester, elastane, polyamides, polyvinyl chloride, acrylic, other natural and synthetic fibers known to those of skill in the art, and blends of two or more of any of these.Docket No. - 2024205P2- 5 of 13-Plastic substrates may include films or other surfaces, such as packaging materials, including boxes, bags, bottles, or other containers, and may be fabricated from any polymer used for such purposes, such as polyethylene, polyethylene terephthalate, polystyrene, polypropylene, and polyvinyl chloride.

[0019] The claimed invention will be further clarified by the following examples which are intended to be only exemplary in nature.EXAMPLESExample 1 - Preparation of fumed silica dispersion

[0020] Deionized water and poly(diallyldimethylammonium chloride) (PDADMAC) (50L, 50% solids, Zhangjiagang Kaibaolai Environmental Protection Technology Co., Ltd.) were charged into a 500 mL double walled cup (max sample 333 mL) in the proportions listed in Table 1 below with circulating cooling water and mixed with a Dispermat CV mixer for five minutes at 500 rpm. The mixing speed was increased to 2000 rpm and the fumed silica (CAB-O-SIL MS-55LV silica, Cabot Corporation) was added, and stirring was continued until all the silica was incorporated. The dispersion was stirred at 8000 rpm for two hours and then at 35000 rpm for 15-20 minutes until the particle size reached D50 < 110 nm and D90 < 200 run as measured in a Horiba LA950V2 instrument, with 1-2 drops of dispersion added to 180-200 mL water in the sampling cell. The dispersion was then passed through a 10 micron filter.Table 1Preparation of Coating Formulation

[0021] A pseudo-boehmite dispersion was prepared by adding nitric acid (Aladdin Scientific) to deionized water to achieve a pH of 4 and then adding pseudo-boehmite (Disperal HP14, Sasol Chemicals) to achieve a concentration of 27.66 wt%. A poly(vinyl alcohol) (PVA) dispersion was made by dissolving 15 g PVA 95-88 (Kururay) in 85gDocket No. - 2024205P2- 6 of 13- deionized water and stirring at 500-800 rpm in a 90-95 °C water bath until dissolved. A boric acid solution was prepared by dissolving 5 g boric acid (Aladdin Scientific) in 95 g deionized water and stirring at 500 rpm for 10 min. All components were used in the amount listed in Table 2 below.

[0022] The 20% silica dispersion described in connection with Table 1 was charged into a 200 mL plastic can. The pseudo-boehmite dispersion was added while stirring at 500-800 rpm using the Dispermat CV mixer, and stirring was continued for five minutes. The binder solution was added to the silica / pseudo-boehmite dispersion while stirring was continued, followed by additional stirring for about five minutes at 800 rpm until the dispersion appeared homogenous, following which ethanol (99.8%, Aladdin Scientific) was added. After an additional five minutes of stirring at 500 rpm, the pH was adjusted with 37% HC1 (Aladdin Scientific) to the pH indicated in Table 2. The boric acid solution was added to the silica dispersion and the mixture stirred an additional five minutes at 800 rpm. The mixture was passed through a 5 micron filter to produce a coating formulation. As Table 2 notes, formulations having a pH greater than 4 tended to gel, rendering them unfit for use in coating. It was observed that formulations having a pH greater than 3 tended to be too viscous (e.g., greater than 700 cps at room temperature when tested in a Brookfield DV II T viscometer with an SI 4# spindle at 50 rpm) to coat onto a substrate.Dockct No. - 2024205P2-7 of 13-Table 2Docket No. - 2024205P2- 8 of 13-Coating of paper with ink receptive coating

[0023] The coating formulation was incubated in a 50 °C water bath for at least 30 min. A 150 micron drawdown bar was used to apply the coating formulation on the glossy photo base paper substrate, which was then dried in a 70 °C oven for 20 min. As can be seen from Table 2, only samples with a ratio of filler to PVA of at least 3% and a ratio of boric acid to filler of at least 3% provided crack free coatings. However, samples with too little or too much boric acid (boric acid / PVA of 9%, 30%, or 40%) also exhibited cracking, as did samples with a ratio of boric acid to filler of less than 3%. A test pattern was printed on the coated papers using an Epson L805 inkjet printer operated in high precision mode. Samples with a higher fumed silica / binder ratio (at least 4: 1), exhibited faster drying times during inkjet printing.Example 2

[0024] Coating formulations were prepared as described in Example 1 using the formulations in Table 3 below. CARTABOND TSI liquid (42% solids) was purchased from Archroma. The resulting formulations had 16% solids and a viscosity, measured as described above, of 500-700 cps. The formulations were coated onto high gloss photo printing paper (Lucky Film Company) and a test pattern printed and evaluated as described in Example 1. Waterfastness of the coating was evaluated on test patterns printed as described above after leaving the printed sample for the time specified in Table 3 at room temperature. The printed substrate was dipped in water and rubbed with a finger immediately thereafter. The use of a glyoxal-based cross-linker in the final coating led to increased waterfastness of colored patterns printed on the coated substrate.Docket No. - 2024205P2- 9 of 13-Table 3Example 3

[0025] A coating was prepared using the methods and formulation for Example 2-2 above, except that 3L of the coating formulation was proceesed in a 5L soybean milk maker (Qiyuan) used in place of the Dispermat mixer. Incorporation of the PDADMAC and fumed silica were performed at the third or fourth speed setting. Incorporation of the fumed silica required 2-3 hours, following which the mixing speed was increased to the 11thspeed setting (of 26 total) and the particle size distribution tested at five minute intervals until the desired distribution was achieved, 5-10 minutes. The final silica dispersion had a D50 of 141 nm and D90 of 242 nm. Coating performance was similar to that of Example 2-2 above.Example 4

[0026] A coating was prepared using the methods and formulation for Example 2-2 above, except that incorporation of the PDADMAC and fumed silica were performed using a high speed agitator supplied by Delixi Electric. The mixing speed was maintained at 2000 rpm until all the silica was incorporated. 20 kg of the full coating formulation was processed in a 20L three-stage rotor-stator homogenizer pump (Model HEX3-140, Ningbo Elengshi)Docket No. - 2024205P2- 10 of 13- used in place of the Dispermat maker. The pump was operated at 4500 rpm with a 14 cm rotor; 2-3 passes was sufficient to achieve the desired particle size distribution. The final silica dispersion had a D50 of 148 nm and D90 of 233 nm. Coating performance was similar to that of Example 2-2 above.

[0027] The foregoing description of various embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the claimed invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings, or may be acquired from practice of the claimed invention. The embodiments were chosen and described in order to explain the principles of the claimed invention and its practical application to enable one skilled in the art to utilize the claimed invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.

[0028] What is claimed is:

Claims

Docket No. - 2024205P2- 11 of 13-CLAIMS1. A coating formulation, comprising: fumed silica; boric acid; a binder; water; and optionally, ethanol and / or pseudo-boehmite, wherein a pH of the formulation is from 2.0 to 3.0, a ratio of fumed silica to binder by weight is from 3.0: 1 to 4.5: 1, a ratio of boric acid to binder by weight is from 9.5% to 28%. and a ratio of boric acid to the total amount of both fumed silica and pseudo-boehmite is at least 3.0%.

2. The coating formulation of claim 1, further comprising a glyoxal-based crosslinker, wherein a ratio of the total amount of the glyoxal-based cross-linker and boric acid to binder by weight is up to 50%.

3. The coating formulation of claim 1 or 2, wherein the fumed silica has a surface area of 200 to 350 m2 / g as measured by ASTM D6556.

4. The coating formulation of any preceding claim, wherein ethanol is present in an amount of up to 20 wt%, for example, up to 17 wt%.

5. The coating formulation of any preceding claim, wherein pseudo-boehmite is present in an amount of up to 0.7 wt%, for example, up to 0.65 wt%.

6. The coating formulation of any preceding claim, wherein the fumed silica is present in an amount of 70-80% by mass (dry basis).

7. The coating formulation of any preceding claim, wherein the fumed silica has a particle size distribution, as measured by laser scattering, with D50 of 80 - 140 nm, D90 of 110-250 nm, or both.

8. The coating formulation of any preceding claim, wherein the binder is polyvinyl alcohol, a cationic polyurethane, or a cationic acrylic polymer.

9. The coating formulation of any preceding claim, further comprising hydrochloric acid or nitric acid.Docket No. - 2024205P2- 12 of 13-10. A method of preparing an ink receptive coating, comprising coating a substrate with the coating formulation of claim 1 and allowing the coating formulation to dry.

11. The method of claim 10, wherein coating comprises roll coating or air knife coating.

12. The method of claim 10 or 11, wherein the coating is 15-30 gsm.

13. The method of any of claims 10-12, wherein the substrate is paper, fabric, or plastic.

14. A coated substrate prepared by the method of any of claims 10-12.

15. The coated substrate of claim 14, wherein no cracks are observed under 50x magnification of an area of 600-625 cm2.

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