INK-JET RECEPTOR SHEET, AND METHOD OF MANUFACTURING THE SHEET

Abstract: An ink-jet recording sheet and method of manufacture and use wherein a recording composition of a binder, pigment particles, electrolyte and optionally a cationic organosilane coupling agent is coated onto a substrate.

Description: INK- JET RECEPTOR SHEET, AND METHOD OF MANUFACTURING THE SHEET FIELD OF THE INVENTION 5 The invention broadly relates to image receiving elements and methods of manufacturing and using such elements. More specifically, the invention relates to ink jet receptors, also known as ink jet recording sheets, and methods of manufacturing and using such elements. 0 BACKGROUND OF THE INVENTION Inkjet printing is a printing technique in which images (e.g., graphs, pictures, symbols, text, etc.) are produced by the ejection of uniformly shaped droplets of ink 5 onto the receptor surface of a recording sheet. This printing technique is widely used in the personal and small office markets. Other applications include low end proofing, and medical referral markets. The maximum image resolution and throughput of an ink jet printer are 0 primarily determined by the size of the jetted drop and the rate of drop ejection. Several factors limit ink jet printers from attaining the maximum image resolution capable of being achieved by the printer. One of these limiting factors is the nature of the recording sheet receiving the jetted drops. 5 Investigators have found image quality to be directly related to the ink absorption and dye adsorption rate of the receptor surface, with image quality increasing with an increase in absorption and adsorption rates. As a general matter, investigators have found that when the ink droplets are not absorbed quickly enough, the ink tends to spread and interact with neighboring droplets of ink, resulting in such 0 defects as feathering, pooling, or bleeding. Investigators have also found that when the ink is not adsorbed quickly enough, the ink tends to bleed through the receptor and possess reduced resolution, reduced water fastness, and reduced smudge resistance. Such problems are exacerbated as the droplet ejection frequency is increased for purposes of increasing throughput. Ink receptor surfaces can be divided into two basic types: continuous phase systems and discontinuous phase systems. Continuous phase systems generally function by swelling to absorb water or ink deposited onto the receptor surface, with the rate of absorption determined by the chemical nature of the polymer used in the system. Typical polymers used in continuous phase systems include gelatins, polyvinyl alcohol and cellulose. Exemplary continuous phase systems are discussed in United States Patents Nos. 3,889,270, 4,503,111, and 5,141,599. While generally effective as an ink jet receptor surface, most polymeric continuous phase systems are water soluble, thereby reducing the waterfastness of the receptor. Some polymeric continuous phase systems have overcome the waterfastness issue by mixing an insoluble cross-linked polymer into the system (e.g., forming a semi-interpenetrating network as described in United States Patents Nos. 5,342,688 and 5,389,723). However, the introduction of an insoluble cross-linked polymer into the system intrinsically reduces the absorption rate of the system. Discontinuous phase systems function by providing pores within the receptor surface capable of absorbing ink by capillary forces. Discontinuous phase systems are generally preferred over continuous phase systems as they absorb ink considerably faster than continuous phase systems. Discontinuous phase systems are divided into two basic types. A first type of a discontinuous phase system, known as a "porous discontinuous phase system", utilizes micron sized porous pigment particles in the recording layer for purposes of absorbing ink jetted onto the recording layer into the particles through a multitude of tiny interconnected pores in each particle. Ink recording sheets having a porous, discontinuous phase system recording layer are disclosed in United States Patent Nos. 5,165,973; 5,270,103; 5,397,619; and 5,478,631, and International Published Application WO 97 01448. A second alternative type of discontinuous phase system, known as a "nonporous discontinuous phase system" utilizes nonporous pigment particles held together by a polymeric binder in such a manner that interstitial voids are created between the pigment particles capable of absorbing ink jetted onto the receptor surface. Inkjet recording sheets with a recording layer of the porous discontinuous phase system type generally provide good ink absorptivity and superior ink capacity, in exchange for some loss in the glossy appearance of the recording sheet. Alternatively, ink jet recording sheets with a recording layer of the nonporous discontinuous phase system type provide superior ink absorptivity and a glossy appearance in exchange for a limited ink capacity due to practical limitations upon the thickness of the coating. Discontinuous phase system receptor surfaces often incorporate a mordant or dye fixing agent for purposes of binding the dye molecules adsorbed within the pores of the receptor surface. A number of different types of mordants have been used, including neutral silane coupling agents, such as disclosed in JP 8164667 (polyalkylene oxide silane), JP 3218887 (silicon compounds), JP 62178384 (silane coupling agents) and JP 60224580 (silane coupling agents with chloro, amino, aminoethyl or vinyl functionality); and monomers, oligomers and polymers of primary, secondary and tertiary amines and quaternary ammonium salts, such as disclosed in United States Patents Nos. 5,302,437 and 5,750,200. While neutral silane coupling agents, cationic monomeric, oligomeric and polymeric amines, and quaternary ammonium salts are generally effective for providing an acceptable rate of adsorption of dye to a receptor surface, a substantial need continues to exist for an ink receptor surface capable of providing a superior J dye adsorption rate while maintaining dye adsorption capacity, bonding strength of the dye to the surface of the receptor layer, ink absorption rate and ink absorption capacity. SUMMARY OF THE INVENTION A first aspect of the invention is an ink jet recording sheet providing a superior adsorption rate of dye by the receptor layer while maintaining dye adsorption capacity, bonding strength of the dye to the surface of the receptor layer, ink absorption rate and ink absorption capacity, comprising a receptor layer of a binder, pigment particles, and an electrolyte. A second aspect of the invention is a method of making an ink jet recording sheet comprising (1) coating a layer of a recording composition on a major surfaces of a substrate wherein the recording composition is a dispersion containing at least (i) a binder, (ϋ) pigment particles, and (iii) an electrolyte, and (2) drying the recording layer. A third aspect of the invention is a method of using an ink jet recording sheet comprising (1) obtaining a substrate having a layer of a recording composition on at least one of the major surfaces of the substrate , wherein the recording composition is a dispersion comprising at least (i) a binder, (ii) pigment particles, and (iii) an electrolyte, and (2) jetting inkjet printing ink upon the major surface of the substrate coated with the recording composition so as to produce an image upon the sheet. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an enlarged side view of one embodiment of the invention. H DETAILED DESCRIPTION OF THE INVENTION 10 Ink Jet Recording Sheet 20 Substrate 30 Subbing Layer 40 Recording Layer 50 Anti-curling Layer Definitions As utilized herein, including the claims, the term "thickness", when used in connection with the recording layer, means the thickness of the recording layer on a dry basis. As utilized herein, including the claims, "wt%" is based upon the solids content of the composition (i.e., calculated on a dry basis). Construction The discontinuous ink jet recording sheet 10 includes a coating of a discontinuous recording layer 40 on a suitable substrate 20, wherein the recording layer 40 is capable of quickly adsorbing dye while maintaining dye adsorption capacity, bonding strength of the dye to the surface of the receptor layer, ink absorption rate and ink absorption capacity. SUBSTRATE The substrate 20 may be any of the typical materials used in the construction of ink jet recording sheets capable of providing the necessary visual appearance and structural support for the recording layer(s) 40. Examples of suitable substrates include paper, cloth, polymers, metals, and glass. Thin flexible sheets are generally preferred, with paper the substrate of choice when an opaque support is desired, and polymeric films used when a translucent or transparent appearance is desired. The thickness of the substrate 20 is preferably in the range of about 0.05 to 1.0 mm. SUBBING LAYER The major surface of the substrate 20 to be coated with the recording layer 40 may optionally be treated with a subbing layer 30, such as a primer or an antistatic layer, before the recording layer 40 is coated onto the substrate 20. RECORDING LAYER The recording layer 40 is comprised of pigment particles treated with an electrolyte and held together by a binder. The recording layer 40 should have a thickness of greater than about 30 μm in order to provide sufficient capacity. Recording layers 40 possessing an acceptable appearance can be formed up to a thickness of about 100 μm, with a thickness of between about 35 to 85 μm preferred. Pigment Particles The recording layer 40 contains pigment particles of the type conventionally used in ink jet recording layers. The pigment particles may be porous or nonporous. Exemplary pigment particles include specifically, but not exclusively, (i) inorganic pigments such as alumina, aluminum hydroxide, aluminum oxide, aluminum silicate, barium sulfate, calcium carbonate, calcium silicate, calcium sulfate, kaolin, magnesium silicate, amorphous silica, colloidal silica, silicic acid, sodium silicate, talc, titania, titanium dioxide, zinc carbonate, and zinc oxide, and (ii) organic pigments such as styrene and acrylic plastic pigments, urea resin pigments, and melamine resin. Pigment particles having an average particle size of less than about 500 nm are capable of producing a recording layer 40 having the desired appearance and performance. Pigment particles having an average particle size of between about 10 - 500 nm are generally preferred, with particles having an average particle size of between about 50 - 300 nm desired and particles having an average particle size of between about 50 - 100 nm favored. The pigment particles can be of substantially any desired shape, with symmetrical particles, particularly spherical particles, generally preferred as they enhance the performance characteristics of the recording layer 40. Binder The pigment particles are held together by a binder. The binder is provided in an amount sufficient to hold the pigment particles together and provide an acceptable appearance. It is generally desired to limit the amount of binder so as to provide pores (i.e., interconnected interstitial voids) within the recording layer 40 for purposes of enhancing performance. Ink jetted onto the recording layer 40 will be absorbed into and stored within the pores (i.e., pores within the pigment particle or pores between the pigment particles) in the layer 40 through capillary action. Substantially any of the conventional binders may be employed, including specifically, but not exclusively: starch derivatives such as oxidized starch, etherified starch and phosphate starch; cellulose derivatives such as carboxymethyl cellulose and hydroxymethyl cellulose; conjugated diene-type copolymer latexes such as styrene-butadiene and methyl methacrylate-butadiene copolymers; acrylic polymer resins and latexes such as polymers and copolymers of acrylic and methacrylic acid esters; vinyl-type polymer latexes such as ethylene-vinyl acetate copolymer; the aforementioned latexes modified to include a functional group such as a carboxyl group; aqueous adhesives such as melamine or urea resins; synthetic resins such as polyurethanes, unsaturated polyesters, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral and alkyd resins; casein, gelatin, soybean protein, polyvinyl alcohol and derivatives thereof, polyvinyl pyrolidone, and maleic anhydride resins. Relative Concentrations of Pigment Particles andBinder The amount of binder used in the recording layer 40 relative to the amount of pigment particles should be selected to balance the competing interests of integrity and wear resistance (enhanced by increased amounts of binder) with ink absoφtion rate and ink absorption capacity (enhanced by decreased amounts of binder). Hence, a careful consideration of binder concentration is important to create a suitable ink jet recording layer 40 having a proper balance of performance characteristics. As a general matter, a weight ratio of pigment to binder of about 1:2 to 20:1, preferably about 2:1 to 10:1, provides acceptable balancing of the competing performance characteristics. Electrolyte The recording layer 40 includes an electrolyte. As utilized herein, electrolyte means a substance effective as an ionic conductor when dissolved in a suitable solvent. In other words, the substance dissociates into anions (negatively charged particles) and cations (positively charges particles) when dissolved. Suitable electrolytes includes specifically, but not exclusively, acids such as acetic, butyric, chloroacetic, lactic, and tartaric; inorganic salts such as sodium chloride, calcium chloride, ammonium sulfate, sodium sulfate, aluminum chloride, calcium sulfate, iron chloride, potassium chloride, potassium carbonate, lithium bromide and zinc sulfide. The recording layer should include about 0.5 to 25 wt%, preferably about 1 to 15 wt%, electrolyte. Insufficient electrolyte does not produce a meaningful increase in the rate of dye adsorption while an excess of electrolyte tends to interfere with the other desired properties of the recording layer. Cationic Silane Coupling Agent The recording layer may optionally include a cationic organosilane coupling agent. Suitable cationic organosilane coupling agents include a first moiety (R 1 ) capable of dissociating in water to produce a positively charged group on the organosilane coupling agent, and a second moiety (R") effective for bonding to the pigment particles. When dissociated, the first moiety is effective for electrostatically attracting and forming an insoluble salt with dyes having an electron donating group (e.g., an -SO3 " ) such as is present on many of the Azo, direct and acid dyes typical of ink jet inks. Preferred cationic silane coupling agents possess the basic structure: R' L Si R" 3 wherein: (i) R' is a quaternary ammonium group, (ii) L is a single bond or divalent linking group, and (iii) each R" is independently an alkoxy group. A more preferred cationic organosilane coupling agent has the basic structure: wherein: (i) R' is -R^N ^ L- where L is a single bond or divalent linking group, and each R 3 is independently hydrogen, alkyl, aryl or alkaryl with at least two R 3 being alkyl, aryl or alkaryl, (ii) each R" is independently an alkoxy group; and (iii) n is l or 2. Exemplary suitable cationic organosilane coupling agents include specifically, but not exclusively: N,N-didecyl-N-methyl-N-(3-trimethoxysilylpropyl) ammonium chloride, octadecyldimethyl (3-trimethoxysilylpropyl) ammonium chloride, N- trimethoxysilylpropyl-N,N,N-trimethylammonium chloride, tetradecyldimethyl (3- trimethoxysilylpropyl) ammonium chloride, N-trimethoxysilylethyl benzyl-N,N,N- trimethyl ammonium chloride, N-(trimethoxysilylpropyl) isothiouronium chloride, N- trimethoxysilylpropyl-N,N,N-tri-n-butyl ammonium chloride, N- trimethoxysilylpropyl-N,N,N-tri-n-butyl ammonium bromide, 3-[2-N- benzylaminoethylaminopropyl] trimethoxysilane hydrochloride, N-(3- trimethoxysilylpropyl)-N-methyl-N,N-diallyl ammonium chloride, and 3-N- styryljnethyl-2-aminoethylamino-propyltrimethoxysilane hydrochloride. Additives Other typical additives such as dispersants, lubricants, surfactants, plasticizers, antistatic agents, pH adjusters, buffers, coating aids, matting agents, particulates for managing mechanical processing of the ink jet recording sheet, antifoaming agents, foam suppressants, water-proofing agent, hardeners, colorants, viscosity modifiers, preservatives, ultraviolet absorbent, antioxidants, antiseptics, mildewproofing agents, and the like may optionally be incoφorated into the ink jet recording layer as desired. ANΉ-CURLING LAYER An anti-curl layer 50 may optionally be coated on the back side of the substrate 20. l b Method of Manufacture BLENDING OF CONSTITUENTS The constituents of the recording layer may be blended together by substantially any convenient method. Exemplary procedures include, (i) sequentially charging pigment, electrolyte and binder into a sufficient quantity of solvent (preferably water) under constant agitation, (ii) simultaneously charging the pigment, electrolyte and binder with sufficient solvent into a suitable mixer, and (iii) dispersing the pigment in water, adding the electrolyte to the aqueous dispersion of pigment, and then adding the electrolyte-containing aqueous dispersion of pigment into an aqueous dispersion of the binder. COATING AND DRYING OF RECORDING LAYER The recording layer 40 may be coated by any of the conventional techniques for coating such materials, including specifically, but not exclusively, extrusion coating, direct and indirect gravure coating, knife coating, Mayer rod coating, roll coating, etc. Similarly, the coated recording layer 40 may be dried by any of the conventional techniques for drying such coated recording layers. OPTIONAL PROCESSING The recording layer 40 can be calendered to improve gloss, with the calendar rolls heated or unheated and rotating concurrent or countercurrent with respect to movement of the ink jet recording sheet 10. K EXPERIMENTAL Glossary Airflex 500 A nonionic latex of ethylene vinyl acetate copolymer having an average particle size of 170 nm and a Tg of 5 °C (41 °F) available from Air Products of Allentown, Pennsylvania. Epson Stylus® Color 800 Inkjet printer available from Epson Printer America, Inc. of Torrence, CA. Epson Stylus® 800 Color Color ink jet cartridge containing cyan, Ink magenta and yellow available from Epson America, Inc. of Torrence, CA under model number S020089. Epson Stylus® 800 Black Black ink jet cartridge available from Ink Epson America, Inc. of Torrence, CA under model number S020108. MP1040 Paniculate silica having a diameter of 100±30 nm available from Nissan Chemical Industries, Ltd. of Tokyo, Japan. Imation Photograde Inkjet Paper sheets S l Λ by 11) available from Paper Imation Coφ. of St. Paul, Minnesota. PET Polyethylene Terephthalate PVDC Polyvinylidenechloride 3MSP3BAC1 The cationic silane N- trimethoxysilylpropyl-N,N,N-tri-n-butyl ammonium chloride available from Gelest, Inc. of Tullytown, PA under catalog number SIT 8414.0. 3MSEB3MAC1 The cationic silane N- trimethoxysilylethyl benzyl-N,N,N- trimethyl ammonium chloride available from Gelest, Inc. of Tullytown, PA under catalog number SIS 6994.0. \ Y Testing Procedures COLOR S ATURAΉON TESTING PROTOCOL Epson Stylus® Color 800™ ink is jetted from an Epson Stylus® Color 800™ printer onto the recording layer of the sample sheet in step patches ranging from 0 (no color) to 16 (full color saturation). Printed samples from midtone to full color patches (i.e., patches between 6 and 16) were selected for testing unless otherwise noted. Color saturation is measured with a Gretag™ spectrophotometer as the log of the ratio of the intensity of visible light given out by the bulb in the spectrophotometer over the intensity of visible light reflected by the printed sample. The color saturation is recorded. DROP SIZE TESTING PROTOCOL Epson Stylus® Color 800™ ink is jetted from an Epson Stylus® Color 800™ printer onto the recording layer of an Imation™ Photograde Inkjet sample sheet for a midtone patch. Drop size of the jetted ink is viewed through a microscope, aimed peφendicular to the surface of the recording layer, giving a top view of the ink drop absorbed into the layer. The microscope is attached to a video camera and frame- grabber capable of permitting computer analysis and storage of the image. Computer analysis of the image yields drop size, with the average of approximately twenty five drops reported as the drop size for the sample. Standard Sample Construction Into a beaker equipped with a magnetic stirrer was placed deionized water and MP 1040™, in the amount set forth in Table One, to form a silica dispersion. The silica dispersion was stirred for 30 minutes. A silane coupling agent, of the type and in the amount set forth in Table One, was then optionally added to the silica 0 dispersion and stirred overnight at approximately 25 °C (77 °F). Into the stirred silica dispersion was then added sodium sulfate, in the amount set forth in Table One, followed after 30 minutes of stirring by the addition of Airflex™ 500, in the amount set forth in Table One, to form a final dispersion. The final dispersion was stirred for one to four hours prior to coating. The stirred final dispersion was coated onto a PVDC primed PET sheet using a knife coater with a seven millimeter gap. The coated PET sheet was oven dried at 120°F (48.9°C) for seven minutes to form an ink jet recording sheet with a recording layer. Examples COMPARATIVE EXAMPLE C 1 EXAMPLE 1 (Color Saturation and Drop Size) (Without Silane Coupling Agent) Sample ink jet recording sheets having a recording layer were constructed in accordance with the Standard Sample Construction Procedure. The color saturation of the sample recording sheets was tested in accordance with the Color Saturation Testing Protocol. Drop size was tested in accordance with the Drop Size Testing Protocol. The results of the testing were recorded, and are set forth in Tables Two and Three respectively. As shown in Table Two, color saturation (density) and dot size (resolution) is generally improved for recording sheets having a recording layer containing the electrolyte sodium sulfate when compared to sheets with a recording layer containing no electrolyte, with the greatest improvement observed when conducting high saturation ink jet printing. COMPARATIVE EXAMPLES C2ι ow , C2 med , C2hi„ AND C3 EXAMPLES 2Aι 0W , 2A me d, 2A h i gh , 2Bι 0W , 2B med , 26^ AND 3 (Color Saturation and Drop Size) (Different Concentrations of Cationic Silane Coupling Agents) Inkjet recording sheets having a recording layer containing different concentrations of a silane coupling agent were constructed in accordance with the Standard Sample Construction Procedure. The color saturation of the recording sheets were tested in accordance with the Color Saturation Testing Protocol. Drop size was also tested in accordance with the Drop Size Determination Protocol. The results of the testing were recorded, and are set forth in Tables Two and Three respectively. As shown in Table Two, color saturation (density) and dot size (resolution) is generally improved for recording sheets having a recording layer containing the electrolyte sodium sulfate when compared to sheets with a recording layer containing no electrolyte, with the greatest improvement observed when conducting high saturation ink jet printing. \ζ TABLE ONE (Composition of Ink jet Receptor Layer) TABLE TWO (Color Saturation) . ' ■ ■';■ i yfs ' i CO 00 o O VO 00 »- VO Os CN VO Os cs O © ill TABLE THREE (Drop Size) *>-

Claims: We claim: 1. An ink jet recording sheet comprising: (a) a substrate having first and second major surfaces, and (b) a recording layer on at least one of the major surfaces of the substrate comprising at least: (1) a binder, (2) a pigment particle, and (3) an electrolyte. 2. The ink jet recording sheet of claim 1 wherein the recording layer further comprises a cationic organosilane coupling agent. 3. The ink jet recording sheet of any of claims 1 -2 wherein the binder is a latex binder. 4. The ink jet recording sheet of any of claims 1-3 wherein the pigment particle is a silica pigment particle. 5. The ink jet recording sheet of any of claims 1-4 wherein the electrolyte is an acid or an inorganic salt. 6. The ink jet recording sheet of any of claims 1-5 wherein the cationic organosilane coupling agent has the structure: R' L Si R" 3 wherein: (i) R 1 is a quaternary ammonium group, (ii) L is a single bond or divalent linking group, and (iii) each R" is independently an alkoxy group. n 7. The ink jet recording sheet of any of claims 1-6 wherein the cationic organosilane coupling agent has the structure: wherein: (i) R 1 is R 3 3 N * L- where L is a single bond or divalent linking group, and each R 3 is independently hydrogen, alkyl, aryl or alkaryl with at least two R 3 being alkyl, aryl or alkaryl, (ii) each R" is independently an alkoxy group; and (iii) n is 1 or 2. 8. The ink jet recording sheet of any of claims 1-7 wherein (i) each R" is independently an alkoxy group containing 1 to 3 carbon atoms, and (ii) n is 1. 9. A method of making an ink jet recording sheet comprising: (a) obtaining a substrate having first and second major surfaces, (b) coating a layer of a recording composition on at least one of the major surfaces of the substrate wherein the recording composition is a dispersion containing at least (i) a binder, (ii) pigment particles, and (iii) an electrolyte, and (c) drying the recording layer. 10. A method of using an ink jet recording sheet comprising: (a) obtaining a substrate having a layer of a recording composition on at least one of the major surfaces of the substrate , wherein the recording composition is a dispersion comprising at least (i) a binder, (ii) pigment particles, and (iii) an electrolyte, and (b) jetting inkjet printing ink upon the major surface of the substrate coated with the recording composition so as to produce an image upon the sheet. *H

Inventors: STEINER MICHAEL L, YARMEY SUSAN K, STEINER, MICHAEL, L., YARMEY, SUSAN, K.
Applicants: IMATION CORP, IMATION CORP.
Application year: 2000
Main classification: B41M5
IPC codes: B41J2, B41M5