Ink jet recording sheet having an ink-receptive layer containing polyethylene oxide

Abstract

 An ink jet recording sheet comprising a support and an ink-receptive layer containing polyethylene oxide and a white filler; in accordance with more preferred embodiments, the layer additionally includes a resin to enhance binding strength and a cationic resin or salt.

Description

Background of the Invention

[0001] The present invention relates to a recording sheet suitaole for use in ink jet recording.

[0002] InK jet recording processes nave emerged as one of the most important tecnnologies for hign speed electronic printing. With tneir emergence there has arisen a need for recording papers having designed recording properties.

[0003] The basic imaging technique in inK jet recording involves the use of one or more inK jet assemblies connected to a source of ink. Each ink jet includes a small orifice whicn is electromagnetically energized by magneto- restrictive, piezoelectric, thermal, or similar means to emit uniform droplets of inK as a continuous stream or as individual droplets on demand. Tne droplets are directed onto tne surface of a moving we_D and controlled to form printed characters.

[0004] - - The quality of tne record obtained in an ink jet recording process is hignly dependent on jet operation and the properties of the ink and the recording paper. Tne ink must be capable of forming stable ink droplets under pressure and must readily emerge from the ink jet orifice. Aqueous inks containing a water soluble dye and a numectant to prevent the ink from drying out in the jet assemply .have been found to be particularly desirable. However, the absorption of these inks by the recording sheet has been somewhat problematic, particularly in the area of multicolor printing where two or more inK drops may overlap on the surface of the recording sheet.

[0005] To oDtain good image quality, tne recording sneet must absorb tne ink rapidly and at the same time insoluoil- ize the ink dye on the sneet surface. Tne former property reduces tne tendency for set-off (i.e., transfer of tne inK from tne paper to sneet hanaling rollers and tne like) whereas tne latter property insures tnat images having high optical density are obtained. Unfortunately, these two properties are in conflict with one another. Papers having high absorbency draw the ink deeply into the paper, and as a result, the optical density of the image formed at tne paper surface is reduced. Tney also suffer from feathering, poor edge acuity, and show-through. Papers with low absorbency, such as hignly sized papers, provide good optical density by retaining tne ink at the paper surface but nave a nigh tendency to set-off because tne ink venicle is not absorbed rapidly.

[0006] Tne perfect ink jet recording sheet nas been described as a blotter witn a magic film. The blotter rapidly absorbs the ink venicle while tne magic film insures that the colorant is retained at tne surface of tne sheet where its lignt absorbing and reflecting properties are greatest. If tne colorant is carried deeply into the paper web, its absorbing strength is reduced, web fibers conduct the ink laterally and poor image sharpness and show-through occurs. See P.A. McManus et al, *Paper Requirements for Color Imaging with InK Jets", TAPPI, Vol. 66, No. 7, July, 1983, pp. 81-5.

[0007] Several types of papers nave been proposed for use in ink jet recording. In some cases the basis weignt, apparent density and filler content of a paper are adjusted to obtain modified absorption properties (see Japan KoKai 74340/1977 to Jujo Paper Mfg. Co.). In other cases certain cationic sizing agents, such as cationized petroleum resins, have been added to tne paper in the size press to achieve more desirable ink absorption cnaracteristics (see Japan Kokai 109783/1981 to Mitsubisni Paper Mills, Ltd.). Dye absorbing layers containing certain dye mordants have been provided on the surface of the recording sheet in some cases.

[0008] Where high quality copies are desired, it has been known to use a paper having an ink receptive layer on the surface thereof. The ink receptive layer is formed of white pigments and an aqueous binder. Tne pigments ennance the quality of tne image by imparting a high level of whiteness to tne copy and reflecting incident lignt and also serve as a substrate whicn binds the inK jet recording ink. Aqueous binders are used to enhance tne absorption of the ink vehicle.

[0009] Crooks et al, IBM Technical Disclosure Bulletin, Vol. 21, No. 6, Novem_Der 1978 discloses a recording paper coated with a layer of a water soluble polymer such as starch, gelatin, polyvinyl pyrrolidone and polyvinyl alcohol.

[0010] Maekawa et al, U.S. Patent 4,446,174 describes a recording paper having an ink-receptive layer including a dye-absorbing pigment such as zeolite, clay, attapulgite, and diatomaceous earth and a binder. A number of binders are disclosed in the patent including binders having dissociable dye-absorbing groups such as polyacrylates, styrene-maleic annydride copolymer, sodium alginate, ethylene-maleic anhydride copolymer and cationic search; and binders not having dissociable groups such as starch, polyvinyl alcohol, polyvinyl pyrrolidone and styrene-butadiene latex.

[0011] Murakami et al, U.S. Patent 4,425,405 discloses an inK-jet recording sheet in which the ink receptive layer contains polyvinylpyrrolidone and/or vinylpyrrolidone-vinyl acetate copolymer and a white filler. Optionally tne layer may also include a water insoluble binder to impart moisture resistance.

[0012] Ink jet recording papers are also Known in wnich the dye-absoroing characteristics of tne paper itself are beneficially modified by incorporating certain polymers or sizing agents into the paper itself. Maekawa et al, U.S. Patent 4,308,542, and Minagawa, U.S. Patent 4,269,891 describe inK jet recording papers prepared from syntnetic paper. Tne papers are designed to enable viewing tne images by reflection or by transmission of lignt through tne recording sheet. Certain water soluble adhesives having a highly nydrophilic cnaracters, including among tnem polyetnylene oxide, are added to tne pulp to improve surface strengtn and improve tne inK aosorption properties. While tnere are numerous examples of inK jet recording papers in the art, tnere is a need for alternative papers and there is particularly a need for coated papers suitable in hign quality printing.

Summary of the Invention

[0013] It is one object of tne present invention to provide an ink jet recording paper useful in hign quality printing applications.

[0014] It is another object of the present invention to provide an inK jet recording paper naving an inK-receptive layer containing a white pigment and a binder wnich exhibits excellent ink receptivity and is able to control ink dot spreading (i.e., size and uniformity).

[0015] It is a further object of tne present invention to provide an inK jet recording paper naving an inK-receptive layer containing a pigment and a binder wnicn exhioits less tacK at nign moisture/numidity levels and provides waterfastness.

[0016] Still another object of the present invention is to provide a pigmented ink jet recording layer that is useful with botn aqueous and solvent based inks.

[0017] Tnese and otner objects are acnieved in accordance with the present invention which provides an ink jet recording paper comprising a paper support and an inK-receptive coating on at least one surface of said support, said inK-receptive coating including a wnite pigment dispersed in polyethylene oxide.

Detailed Description of the Invention

[0018] The ink-absorptive qualities of tne paper of the present invention will vary with tne amount and the molecular weight of the polyetnylene oxide incorporated into the ink-receptive layer as well as otner factors such as the nature of the pigment,,the presence of other additives, and the manner of coating. Tne inK-receptive layer used in the present invention in its simplest form includes a white pigment and polyethylene oxide. However, polyethylene oxide does not provide sufficient binding strength to satisfy all the requirements of the recording process. Ink receptive layers consisting of polyethylene oxide and pigment tend to dust, i.e., lose pigment more readily and sometimes crack. For this reason it is preferred to include an additional resin in the composition to ennance binding strength and thereby reduce dusting and improve the integrity of the layer.

[0019] The molecular weight of the polyethylene oxide used in the present invention may range from about 100,000 to 900,000 and preferably from about 100,000 to 300,000.

[0020] Suitable resins useful in ennancing tne binding strength of polyetnylene oxide can be selected from among a number of hign molecular materials conventionally used in papers or paper coatings. A binder snoula be selected whicn is compatible with the polyethylene oxide. Representative examples of useful polymers include polyvinyl acetate, ethylene-vinyl acetate copolymer, polymetn- acrylates, polyacrylates, polyvinyl alcohol, oxidized starch, carboxymethyl cellulose, hydroxyethyl cellulose, styrene-maleic acid copolymer, styrene-_Dutadiene copolymer and the like. Polyvinyl alcohol and starch are usually used because they are relatively inexpensive and tney provide good binding strength.

[0021] Tne polyethylene oxide is usually used in the inK-receptive layer in an amount of about 5 to 70% by weight and preferably 10 to 40% by weight based on the dry weight of tne ink-receptive layer. Tne amount of otner resin included- in the ink-receptive layer to enhance binding strength will vary with its nature, the amount and nature of the filler used and other factors. Typically, these other resins may be incorporated into the coating in an amount of about 0 to 60% by weight (dry) or in weight ratio to the polyethylene oxide of about 1:10 to 10:1.

[0022] Examples of fillers which can be used in the practice of the invention in combination with polyetnylene oxide include clay, talc, calcium caroonate, alumina and alumina hydrate, zeolite, synthetic silica, calcium sulfate, diatomaceous earth, magnesium silicate, barium carbonate, barium sulfate, aluminum silicate, magnesium oxide, magnesium carbonate, calcium silicate, satin wnite, etc. Tne preferred filler is synthetic silica (e.g., Syloid 244 from W. R. Grace Co.). It may be desiraole to dilute the silica with another white filler in some cases. Tne filler is generally used in an amount of about 5 to 90% and preferably 40 to 90% by weight based on the dry weight of tne recording layer.

[0023] Tne recording cnaracteristics of tne ink jet recording paper of the present invention are generally improved by the addition of a cationic resin and/or polyvalent metal salt. In most applications, aqueous ink compositions containing acid or direct dyes are used in ink jet recording. These dyes advantageously react with the cations provided by the resin or tne metal salt and become more rapidly set in the inK receptive layer. Tnis tends to prevent off-set and further reduce featnering and dot spread.

[0024] Useful cationic polymers are cnaraccerized by a hign cationic cnaracter. Such polymers are typically made up of at least 3 mol % cationic monomer units and preferably at least 10 mol % and up to 100%. Polymeric amines such as polymers of quaternary amines or amines converted to quaternary amines under acid conditions can be used. The cationic character of these polymers can oe expressed as a nitrogen concentration since the nitrogen present in the polymers generally is in the form of cationic quaternary ammonium groups. Thus, tne polymeric cationic amines used in the present invention can be characterized as having a nitrogen content in excess of about 0.1%, preferably in excess of 1.5_% and still more preferably in excess of 3.0% by weight.

[0025] A useful class of cationic polymers are so-called electroconductive polymers which are conventionally used in electrophotographic, electrographic or electrostato- graphic processes. Examples of such polymers are described in U.S. Patents 3,011,918; 3,544,318; 4,148,639; 4,171,417; 4,316,943; and 3,813,264. Tnese polymers are characterized by the presence of a high percentage of cationic groups such as tertiary amino and quaternary ammonium cationic groups. Representative polymers are nomopolymers or copolymers of cationic monomers such as quaternary diallyl- diakylammonium chlorides such as diallyldimethylammonium chloride, N-alkylammonium chlorides, methacrylamidopropyl- trimethylammonium chloride, methacryloxyethyl trimetnylammonium chloride, 2-hydroxy-3-methacryloxypropyl trimethylammonium chloride, methacryloxyethyl trimethylammonium me_Lhosulfate, vinylbenzyl trimetnylammonium chloride and quaternized 4-vinylpyridine.

[0026] Representative examples of commercially available cationic polymers that are useful in the present invention are Warcofix 808 (a guanidine-formaldehyde polymer available from Sun Chemical Corp.), Calgon 261 LV and Calgon Conductive Polymer 7091 RV (polydimethydiallylammonium chlorides available from Calgon Corp.), Nalco 8674 (a cationic polyamine available from Nalco Corp.), and CAT Floc C (available from Calgon Corp.).

[0027] The polyvalent metal salts used in the present invention are polyvalent water soluble salts of polyvalent cations from Group II, Group III or the Transition Metals of the Periodic Table of Elements. Typically, these salts can be dissolved in water in an amount greater than 5 g/ 100ml at 23°C. Tne most readily available and cost effective salts are Zn²⁺, Al³⁺, Mg , Ca and Ba²⁺ salts.

[0028] Salts which tend to color the paper such as Fe , Fe , and Cu2+, while functional, must be used in limited amounts or not at all. Preferably, tne salts are salts of one of the aforesaid polyvalent cations and an anion of a weak acid such as an anion of an acid naving a pKa value greater than 2.0 and, more preferably, greater than 3.0. Salts of strong acid anions such as alum are capable of insolubilizing an ink jet dye but are generally undesirable because they impart high acidity to the paper wnicn accelerates degradation. Thus, while chlorides, sulfates, chlorates, and nitrates are useful, tne preferred salts are acetates, formates, chlorohydrates, malonates, succinates, and salts of other weak organic acids.

[0029] Specific examples of salts useful in the present invention are alum, calcium formate, and aluminum cnloro- hydrate. Certain zirconium Zr³⁺, Zr⁴⁺, and Zr⁵⁺ salts are also believed to be useful such as zirconium oxychloride and zirconium hydroxychloride.

[0030] The ink-receptive layer of the present invention may contain about 5 to 50% by weight of the aforementioned cationic resins and/or about 1 to 25% by weight of the polyvalent metal salt.

[0031] The ink-receptive layer is typically formed by preparing an aqueous dispersion of polyetnylene oxide, filler and any other additive(s) and coating it onto a support in a conventional manner. Conventional paper coating machines such as blade coaters, air knife coaters, roll coaters, brush coaters, gravure coaters, size presses, rod coaters, and curtain coaters may be used for this purpose. The coating composition may be applied to the support in an amount of about 1 to 40 g/m² on a dry basis and preferably 5 to 20 g/m², The upper limit on the thickness is not as critical. After the coating is dried it may be smoothed by calendering if desired.

[0032] In general, there are no restrictions on the type of paper that may support an inK-receptive layer in accordance with the present invention. Any restrictions on tne paper support typically are a product of the recording application or the recording apparatus rather than the coating composition. For most applications, papers having a basis weight of about 12 to 30 pounds per 1300 sq. ft., an apparent density in the- range of 0.3 to 1.2 and filler content of 0 to 40% are useful. In general, conventional _Dleached Kraft and bleached sulfite pulps can be used in tne present invention. Waterleaf, low size, hign size and bond paper can be used. The coating can also be used with certain synthetic papers or applied to polymeric films.

[0033] The preferred support tnickness is about 30 to 150 microns.

[0034] Representative examples of thermoplastic films whicn can be used in the present invention include polyester films sucn as polyethylene terephthalate, polystyrene, polyvinyl chloride, polymetnylmethacrylate and cellulose acetate.

[0035] The ink jet recording paper of the present invention is preferably used in conjunction witn aqueous inK jet recording inks but it can also be used with certain solvent-based inks. Representative examples of useful dyes include acid dyes such as Tartrazine (CI 19140), Quinoline Yellow (CI 47005), Eosin (CI 45380), Erytnrosine (CI 45430), Brilliant Cyanine 6B (CI 42660), Acid Black 1 (CI 20470), Acid Black 36 (CI 27275) and Acid Blue Black 10B (CI 20470), Acid Blue 193 (CI 15707), Acid Blue 194 (CI 17941), Acid Blue 249 (CI 74220); and direct dyes sucn as Direct Black 19, Direct BlacK 49, Direct Black 56, Direct Black 74, Direct Black 103, Direct Black GW, Cap- amine Black ESA, Deep BlacK XA (CI Direct BlacK 154), Black G (CI 35255), Pnthalocyanine Blue (CI 74180), Direct Blue 78, Direct Blue 239, Direct Blue 120, Direct Blue 110, Direct Blue 19, Direct Scarlet 4BS (CI 29160). The CI number in the description above indicates the identification number in the Color Index, 3rd Edition, the Society of Dyers and Colorists, Bradford, Yorkshire (1971).

[0036] The present invention will be illustrated in more detail by the following non-limiting examples:

Example 1

[0037] A coating composition was prepared by comDining the following:

[0038] The coating was drawn down on a hard size raw stock using a .0.5 ml bird bar. As dried, the ink-receptive layer contained 12.5% polyvinyl alcohol, 12.5% polyethylene oxide, 25% aluminum silicate and 50% barium sulfate. When a commercially available acid magenta recording ink was applied to the layer with a fountain pen, the ink displayed no tendency to feather.

Example 2

[0039] Three ink jet recording papers were prepared as in Example 1 except the molecular weight of the polyethylene oxide was varied. Sample A was prepared using a 100,000 molecular weight polyetnylene oxide. Sample B was prepared using a 200,000 molecular weight polyethylene oxide and Sample C was prepared using a 300,000 molecular weight polyethylene oxide. A solvent based magenta recording ink was applied to the.ink-receptive layer of each of tne sneers with an Advanced Color Technology ACT-1 Printer. Tne dot area, parameter and shape were measured. Tne results are shown in Table I. For comparison, dot size is shown for the same ink as applied to a commercial oond paper.

Example 3

[0040] Ink jet recording papers were prepared by coating the compositions shown in Table 2 below on a commercial rawstock using a rod coater. Samples 1-3 correspond to samples prepared according to the teachings in U.S. Patent 4,425,405 containing polyvinyl pyrrolidone in tne inK-receptive layer. Samples 4-6 are papers prepared in accordance with the present invention.

[0041] Images were formed on each of the sheets using commercially available aqueous based cyan, magenta, yellow and black ink jet recording inks and a solvent-cased magenta ink and the optical density was measured. Tne results are shown in Table 3 from which it can be seen tnat the polyethylene oxide based recording layer in accordance witn tne present invention performs at least as well as recording layers containing polyvinyl pyrrolidone.

[0042] Having described the invention in detail and by reference to specific embodiments thereof it will be apparent that modifications and variations are possible without departing from the scope of the following claims:

Claims

1. An ink jet recording paper comprising a support and an ink-receptive coating provided on at least one surface thereof, said coating including a white pigment and polyethylene oxide.

2. Tne ink jet recording paper of claim 1 wnere, in addition to said polyethylene oxide, said coating includes a resin which is compatible with polyetnylene oxide and wnich enhances binding strength.

3. The ink jet recording paper of claim 2 wherein said resin is selected from the group consisting of polyvinyl acetate, ethylene-vinyl acetate copolymer, polymethacrylates, polyacrylates, polyvinyl alconol, oxidized starch, carboxymethyl cellulose, hydroxyethyl cellulose, styrene-butadiene copolymer and styrene-maleic acid copolymer.

4. Tne ink jet recording paper of claim 3 wherein said wnite filler is selected from the group consisting of clay, talc, calcium carbonate, calcium sulfate, diatomaceous earth, magnesium silicate, barium carbonate, aluminum silicate, magnesium oxide, magnesium carbonate, calcium silicate, satin white, synthetic silica and alumina.

5. The ink jet recording paper of claim 4 wherein said filler is present in said coating in an amount of about 5 to 90% by weight.

6. The ink jet recording paper of claim 5 wherein the weight ratio of said resin to said polyethylene oxide is about 1:10 to 10:1.

7. The ink jet recording paper of claim 1 wnerein said polyethylene oxide has a molecular weight in the range of about 100,000 to 300,000.

8. The ink jet recording paper of claim 7 wnerein said white filler is a synthetic silica.

9. Tne ink jet recording paper of claim 2 wherein said resin is polyvinyl alcohol.

10. Tne ink jet recording paper of claim 1 wnerein said support is selected from the group consisting of waterleaf, low size, high size or bond paper.

11. Tne ink jet recording paper of claim 1 wnerein said support is paper.

12. The ink jet recording paper of claim 1 wherein said ink-receptive coating is calendered.

13. The ink jet recording paper of claim 1 wherein said ink-receptive coating comprises polyethylene oxide, polyvinyl alcohol, and synthetic silica.

14. The ink jet recording paper of claim 2 wherein said ink-receptive coating additionally includes a cationic resin.

15. The ink jet recording paper of claim 2 wherein said ink-receptive coating additionally includes a polyvalent metal salt.

16. The ink jet recording paper of claim 14 wherein said cationic resin is a polymeric amine.

17. The ink jet recording paper of claim 15 wherein said salt is a salt of Zn²⁺, Al³⁺, Mg²⁺, Ca²⁺ or Ba²⁺.