GB2210071A

GB2210071A - An ink jet recording paper

Info

Publication number: GB2210071A
Application number: GB8822136A
Authority: GB
Inventors: Yutaka Kojima; Takashi Omori
Original assignee: Jujo Paper Co Ltd
Current assignee: Jujo Paper Co Ltd
Priority date: 1987-09-21
Filing date: 1988-09-21
Publication date: 1989-06-01
Anticipated expiration: 2008-09-21
Also published as: FR2620655A1; FR2620655B1; DE3832112A1; JPS6478877A; GB8822136D0; JPH082686B2; GB2210071B; DE3832112C2

Description

U U/ 11 AN INK JET RECORDING PAPER,p

This invention relates to a recording paper for ink jet printers (hereinafter referred to as ink jet recording paper). Description of the Prior Art

Recently, the demand for color printers is on the increase. Particularly, an ink jet printert one of the nonimpact recording systems, is held in high estimation because of its capabilities in comparatively rapid color recording for its simple system. However, there are many problems for obtaining multi-color image exactly in high speed recording.

Considering this from the standpoint of using ink jet recording papers, these papers must have sufficient inkabsorbency and dryability. In order to solve the problems of superposing the plural ink droplets and of increasing the number of ink droplets per unit area, it is required that the ink-absorptive capacity is.enough excellent and owing to the high speed recording the rapid drying of the ink after the fixing is necessary. Meanwhile, ink jet recording papers are mainly divided into two groups; one is the plain type ink jet recording paper, which consists of only cellulosic fibers or of cellulosic fibers and a filler in order that inks may be absorbed in the space between fibers or spaces which are formed fiber and filler, and the other is the coated type ink jet recording paper, which consists of paper, a - 2 substrate, and coating materials, which consists of pigment and binder, in order that inks may Se absorbed in a fine void of the coating layer. Although the coated type recording paper provides a small spread and a circular form of ink dot, as well as a high resolution power, it has poor ink absorptivity capacity and slow ink absorption rate. Hence the paper ha. the drawback that it is unsuitable for the multi-color printing of a large amount of iffl- and too expensive.

Recently, the demand of plain type papers excellent in the economics, paper-like figures and feeling is increased with high speed printing.

Incidentally, there are two trends in the plain type technology; one trend is disclosed, for example, in Japanese patent application laid-open publications sho 53-49113 and sho 58-8685. The former disclosed that water-soluble polymer is coated or impregnated into the sheet filled with ureaformalin resin, whitle the latter disclosed that a watersoluble polymers is coated on or impregnate into a sheet filled with synthetic silicate and/or glass fiber.

The feature of these ink jet recording sheets is that the high speed printing is possible owing to the ink absorbency improved by non-sizing paper filled with fine powder.

When the sheet of this type, which consists of only so-called "inkreceptive layer", is multi-color-printed with a large amount of ink, ink spreads to lateral direction, and ink dots are feathered and become large so that the resolution power is lowered. As ink also penetrates in the 1 i paper deeply, the optical density is reduced With the increase of"the light scattering on the upper layer of the recording sheet. Besides these sheets have the drawback that ink causes the print through, that is, show through and strike through in the recorded parts.

The other trend is disclosed in Japanese patent application laid-open publications sho 60-27588 and sho 6150795, for example. This trend is directed to control the spreading of inks on the paper by reducing inkabsorbency to some extent by weak sizing. According to sho 60-27588, a wet strength agent is added to the sheet and then a small amount of coating color is applied to the sheet, wherein stbckigt sizing degree of the obtained sheet is controlled to below 3 seconds. According to sho 6150795, a recording paper is produced by sizing with a petrochemically produced, emulsified resin-type size. In these ink jet recording papers, drawbacks of the afore-mentioned recording papers - the undesirable print through and spreading of inks - can be certainly reduced owing to the above sizing effect, but inkabsorbency becomes so poor that the obtained papers are fundamentally unsuitable for multi-color recording.

Further, Japanese patent application laid-open publication sho 55-150370 di scloses an ink jet recording process by the use of the recording sheet having a stuff of synthetic pulp and wood pulp, or by the use of the recording sheet having the above stuff on a wood paper. In either case, however, synthetic pulp needs to melt in the paper surface by heat treatment after ink jet recording, so that this - 4 method needs a special machine only for the heat treatment. Without the heat treatment, the affinity of inks for synthetic pulp is so weak that the coloring in dots are uneven, wherein the uniform image is not obtained. Moreover, the problem is that the optical density is insufficient because of the light scattering occuring on the surface, and the sheet is inferior in paper-like figuries and hand-feeling. Summary of the Invention

Under the circumstances, the present inventors made intensive studies to eliminate drawbacks of conventional ink jet recording papers and finally accomplished this invention by finding a novel ink jet recording paper, characterized by comprising a base layer that contains an internal size, and an ink-receptive layer that is made out of a material having good affinity for inks, wherein said ink-receptive layer is superposed on either one or both sides of said base layer by a multiply papermanufacturing process. According to this invention, drawbacks of conventional ink jet recording papers can be all removed by layers, wherein the confronting properties are harmonized with each other. Accordingly, it is an object of this invention to provide an ink jet recording paper which gives uniform images and excellent optical density, provides a good ink-absorbency well fitted to multi-color recording, and lessens the print through. The above and other objects and features of this invention will appear more fully hereinafter from a consideration of the following description taken in connection with the accompanying drawing. In the

1 drawing: - Figs 1 through 3 are a cross-sectional view of an ink jet recording paper of this invention, wherein the numeral 1 denotes the base layer and the numeral 2 denotes the inkreceptive layer. Detailed Description of the Preferred Embodiment

As seen from the drawing, an ink jet recording paper of this invention comprises a plurality of layers; that is, it is produced by superposing a plurality of ink-receptive layers either one or both sides of at least one base layer, or combining a base layer and an ink-receptive layer. A recording sheet having the desired property may be obtained by giving confronting properties to each of the layers, if necessary.

The function required for the base layer is mainly to prevent inks coming into the ink-receptive layer from further penetrating deeply and rapidly. Concretely, in order to achieve the function, the opacity and the sizing degree are important factors. To be exact, the opacity is desirable to be 75 % and over, when measured according to JIS P8138; and the sizing degree measured in terms of the Stbckigt sizing degree is preferable to be 3 seconds and over, on condition that a base layer of 60 g/m 2 is measured according to JIS P8122. When the recording inks have passed through the ink-receptive layer"and reached the base layer of which the opacity is 75 % and over, show through which is observed from the back side of the ink jet recording paper, is reduced and hence the print through becomes lessened too.

- 6 Also, in the case that the St6ckigt sizing degree is 3 seconds and over, inks having passed through the inkreceptive layer and reached the base layer are prevented from further penetrating into the base layer near its surface (strike through), with the result that the print through is improved. However, when the sizing degree is extremely high, and a large amount of ink is applied, the ink-receptive layer cannot afford to hold the ink any more; thus, it flows out, which is undesirable. Contrary to this, when the sizing degree is too low, ink penetrates into the base layer so deeply that the print through becomes noticeable. Also, with the decrease of ink staying in the ink-receptive layer, the density declines, and the clearness of recorded images is reduced, which is undesirable. For these reasons, the sizing degree is desirable to be in a so-called weak sizing degree, although it has to be 3 seconds and over.

The ink-receptive layer has to be provided with good ink-absorbency enough to hold plentiful ink from multicolored recording; additionally, it must be good in colorreproducibility, and can give uniform images and increased optical density. Therefore, the ink-receptive layer should consist of a material having good affinity for inks, and it should be a porous layer having a uniform thickness and higher transparency as described hereinafter. If the ink-receptive layer lacks in affinity with ink's solvents, not only will ink be not absorbed but also its drying is retarded, whereby the ink flows out or recorded images are so easily injured by abrasion that this kind of layer becomes unsuitable for multi-colored recording using plentiful ink. Likewise, if any material in the ink-receptive layer has little affinity for ink-dyes, the inks are not fixing in the material, whereby some portions in ink dots are not dying, with the result that uniform images cannot be produced. For these reasons, when a aqueous ink is used for the ink jet recording, the addition of more than a certain amount of a sizing agent to the ink-receptive layer deteriorates the penetration and the drying of water as solvent, whereby the object of this invention cannot be fully accomplished. Likewise, if such material as synthetic pulp having little affinity for water and dyes is contained in the ink-receptive layer exceeding a certain quantitative limit, uniform images cannot be produced because the material leaves some portions in ink dots unfixed, which performs the object of this invention impossible.

Since the color inks are produced in accordance with the principle of the color subtraction, it is expected that the less light scattering is in the ink-receptive layer, i.e., the more transparent the ink-receptive layer is, the better the ink's color reproducibility becomes and the clearer the images look.

when the surfaces of the recorded ink-receptive layer is exposed to a certain amount of light energy, the light energy is sufficiently absorbed. Thereby, the less the light is scattered, the better the color reproduction and the higher the color density become.

The base layer of this invention comprises pulp, filler, internal size, retention aid, and other auxiliary agents. The pulp mainly includes plant pulps, such as wood pulp and linter pulp, and recycled pulp from waste paper; however, it may include an inorganic fiber such as glass fiber, or synthetic pulp, for example, if necessary.

Among the fillers used in this invention are calcium carbonate, clay, activated clay, talc, silica, aluminium hydroxide, diatomaceous earth, barium sulfate, tianium dioxide, organic resinous pigment, and the like, all of which are commonly used in the paper-manufacturing or paperconverting factories. These are produced in many different grades, but this invention does not limit the use.of any of them. Moreover, if necessary, a mixture of plurality of different fillers or a mixture of same filler of different grades can be used. In order to increase the opacity of the base layer, such fillers as titanium oxide and calcium carbonate that have high refractive index and can be atomized easily are preferable, and, in view of the availability and the economy,. finely powdered precipitated calcium darbonate is the most preferable of all.

Used as the internal sizing agent are acid sizing agents such as fortified rosin size, petrolum resin size, and emulsion-type rosin size, and neutral sizing agents used in the paper manufacturing, such as alkylketene dimer and cationic size. In the selection of these sizing agents, there should be chosen the agents that hardly diffuse into the ink-receptive layer 1 9 - from the base layer. In this respect, if a diffusible one is employed, the ink-receptive layer becomes so water-repellent that its ink-absorbency deteriorates which is undesirable. Considering this, such sizing agents having a strong affinity with pulp and a high molecular weight is suitable for this aim; in this sense, styrene-acrylic cationic resin is desirable for this invention.

The ink-receptive layer of this invention comprises pulp, filler, retention aid, and auxiliary agent, such as water-soluble resin etc., which control the paper qualities or productivity. The pulp in the inkreceptive layer includes wood pulp, linter pulp, and recycled pulp from waste paper. Unlike the base layer, such pulp or fiber that has not affinity with ink's solvents or dyes cannot be used for the ink-receptive layer. Therefore, glass fiber or synthetic pulp, which may be mixed inthe base layer, should not be mixed in the ink-receptive layer. A similar kind of fillers to those used in the base layer may be used for the inkreceptive layer as well. In selecting from those fillers, care must be taken in such a way as to increase the inkabsorbency and lessen the light scattering of the ink receptive layer.

As for the transparency of the ink-receptive layer, fillers should not necessarily be used. However, it is rather desirable to use filler so as to further increase the ink-absorbency, and control the spread and form of inkdots in order to give clear images, high color density and - 10 high resolution. In this connection, experiments revealed that ground calcium carbonate pulverized to medium size is more desirable than precipitated calcium carbonate or synthetic silica.

The reason for this is unclear yet, but it seems to the present inventors that very fine filler such as precipitated calcium carbonate and silica adheres to fiber and thereby increase the light scattering and reduce the transparency of the ink-receptive layer, whereas medium-sized ground calcium carbonate does not deteriorates the transparency of the inkreceptive layer so much as the fine filler because it adheres to fiber less than they do, and most of them lie in a space between fibers.

The term "transparency", as far as it is used in this invention, means an extent to which incident light in the ink-receptive layer is scattered thereby; in this sense, the more incident light is scattered in the inkreceptive layer, the lower the transparency thereof becomes, whereby recorded images look whitish as much.

Thus, this transparency can be represented in terms of the specific light scattering coefficient (S) of the KubelkaMunk equation, which indicates the degree of light scattering. In connection with the specific light scattering coefficient, wood pulp is 200 - 700 cm 2 /g, synthetic pulp is 900 - 1300 cm 2 /g, and fillers are 600 - 1000 cm 2/g on the average. These values (S) differs with the kind of the materials by the treatment processes and or the particle S 11 - size of material; therefore, some of the above-mentioned material sometimes indicate greatercoefficient than their average.

The value (S) decreases with the increase of pulp beating degree; thus, in order to produce more vivid images by reducing light scattering in the ink-receptive layer, it is desirable to use high beating pulp. However, when the beating is too high, the vacant spaces for absorbing inks are decreased; in consequence, they reduce the ink-absorbency of the inkreceptive layer. From this point of view, excessively high beating is undesirable.

Among the water-soluble resins to be used in this invention are starch, cationic starch, polyvinylalcohol, gelatin, sodium alginate, hydroxyethylcellulose, carboxymethylcellulose, polyacrylamide, polystyrene sulfonate, polyacrylate, polydimethyldiallylammonium chloride, polyvinylbenzyltrimethylammonium chloride, polyvinylpyridine, polyvinylpyrrolidone, polyethyleneoxide, hydrolysis product of starchacrylonitrile graftpolymer, polyethyleneimine, polyalkylenepolyaminedicyandiamideammonium condensate, polyvinylpyridinium halide, poly-(meth)acrylalkyl quaternary salts, poly-(meth)acrylamide-alkyl quaternary salts and the like. Among these, cationic starch, whose aqueous solution shows low viscosity, polyacrylamide, polydimethyldiallylammonium chloride, and polyvinylpyrrolidone are particularly desirable for this invention.

It is desirable to coat or saturate into the ink-recep- tive layer with fine filler in order to produce clearer images and higher density. Alumina, aluminium hydroxider silicate, and silica are desirable for this purpose, and among these, synthetic silica is the best of all. Thereforer synthetic silica, obtained by the precipitation process, the gel process, and the vapor phase process, can be used as fine silica. In any case, when the specific surface area of silica, determined by the B.E.T. method, is equal to or greater than 150 m 2 /g, and the particle size distribution thereof is of the narrowest possible, images of high color density are produced.

In the case that such kind of fillers are used for coating or impregnating method, a water-soluble resin or latex as a binder can be added to them. Additionally, such additives as a viscosity control agent, an agent for giving recorded images of a water-resistance, or an agent for controlling the spread of dots can also be mixed in their coating color.

Among the water-soluble resin mentioned above are starchr cationic starch, polyvinylalcohol, gelatin, alginate, hydroxyethylcellulose, carboxymethylcellulose, polyacrylamide, polystyrene sulfonate, polyacrylate, polyvinylpyridine, polyvinylpyrrolidone, polyethyleneoxide, hydrolysis product of starch-acrylonitrile graftpolymer and the like. Among these substances, a high water-absorptive water-soluble resin can effectively be used to improve not only the surface binding strength but also the ink-absorbency of the ink- - 13 absorbency of the ink-receptive layer. Employing a large amount of latex provides the poor ink-absorbency, but the coating of the ink-receptive layer with so much latex as not to deteriorate the ink-absorbency is effective in order to improve the surface binding strength and the water- resistance of the ink-receptive layer.

As the water resistance agent, there are polyethyleneimine, polydimethyldiallylammonium salt, polyalkylenepolyaminedicyandiamideammonium condensate, polyvinylpyridinium halide, poly(meth)acrylalkyl quaternary salts, poly- (meth)acrylamidealkyl quaternary salts, polyvinylbenzyltrimethylammonium, w-chloropoly(oxyethylene-polymethylene-trialkylammonium salt), and the like, which produce a complex in association with dyes in inks. Because the specific light scattering coefficient of the inkreceptive layer having greater than 500 cm 2/g provides the lower color density and whitish recorded images, it is, therefore, desirable to take good care so that the specific light scattering coefficient of the ink-receptive layer stays not greater than 500 cm 2 /g by adjusting the mixing ratio of a filler and a binder or the amount thereof.

Particularly, in the case that fine silica is used as a filler, an image having a sufficient ink-absorbency and high optical density and clear color is obtained by coating or impregnating the ink-receptive layer with 0.5 - 10 9/M 2 or preferably 1 - 5 g/m 2 of the silica. If, however, their amount to coat or impregnate with exceeds 5 g/m 2, the surface strength declines so that the fillers come off or the depth of ink's penetration into the ink-receptive layer increases# whereby the optical density tends to decrease.

When an ink jet recording paper with more than one layer is produced according to this invention, materials for both the ink-receptive and the base layers are prepared respectively in advance, from which a multi-ply sheet is manufactured, for example, a two, three, or four ply sheet as shown in Fig. 1 through 3, by the use of cylinder vat-type papermanufacturing. machines, such as Suction Former and Ultra Former, or OnTopTwin-Former type paper manufacturing machines, such as Arcu-Former (produced by Tampella AB, OY), Ultra-Twin-Former (produced by Kabushiki Kaisha Kobayashi Seisakusho), and Alladin-Former (produced by Sanki Tekko Kabushiki Kaisha).

As stated so far,..according to this invention, there is produced a multiply ink jet recording paper by superposing an ink-receptive layer, composed only of a material having good affinity for inks, on either one or both sides of a comparatively ink-unabsorbable base layer. The structure of the ink jet recording paper being such that, when ink ejected from a printer has reached the surface of the ink-receptive layer, the ink is rapidly absorbed and penetrated into the layer because of its good affinity for inks solvents and dyes, and high porosity. The ink, having passed through the ink-receptive layer, reaches to the surface of the base layer; however, because it is sized, the further penetration of the ink is hindered by the surface of the base layer. For these reasons, the optical density of the ink jet recording paper is improved, and the print throughp and wrinkles by the absorption of inks are prevented.

Because the degree of print through depends upon the physical ink penetration depth and the visually ink penetration depth (show through), the show through can be improved by increasing the opacity of the base layer to more than a certain level, and thereby the print through can be improved more widely.

Contrary to this, by reducing the specific light scattering coefficient of the ink-receptive layer, recorded images become vivid and superior in the reproducibility of original colors.

In order to be provided with better ink-absorbency and higher optical density, the ink-receptive layer had better be coated or impregnated with a filler having a comparatively large specific surface area. Being supported with a comparatively ink-unpenetratable base layer, sufficient ink-absorbency and good optical density can be imparted to the inkreceptive layer by coating or impregnating it with lesser amount of a coating color.

If a single-sheet of recording paper would be conventionally treated with size from the view of improving the print-through, inks would hardly penetrate in the recording paper whatever weak sizing may be applied, and this would give inferior inkabsorbency and ink-dryability thereby would not fit to a high speed color printing machine. Also, if the higher porosity of sheet would be used from the view of improving ink-absorbency, too much ink would penetrate up to the back side of the recording paper, and thereby the print through would be terrible. If a sheet of recording paper would be coated with a filler to improving ink-absorbency, the recording paper would lose a desirable paper-like figures and become economically uncompetitive with its production cost. According to this invention, however, the layers of confronting properties are effectively selected, and thereby the harmonized multi-ply recording paper is obtained.

In order that thisInvention may be more clearly understood, reference will now be made to the following examples; however, the examples are only to illustrate this invention and not to be construed to limit this invention.

In the examples, part means part by weight calculated in terms of the solid content of respective agents unless otherwise described. Example 1 parts of LBKP (hardwood bleached kraft pulp), whose freeness (C.S.F.) were 300 ml, was used as a material for the base layer. 20 parts of a filler (calcite-group precipitated calcium carbonate, spindle shape, 50 % mean particle size: 4.1 Pm, BET specific surface area: 5 m 2 /g), 0.2 parts of size A (polystyrene-acrylate quaternary ammonium salts), and 0. 02 parts of retention aid agent m (cationic polyacrylamide, viscosity: 590 c.p.s. at 0.5 % consistency) were added thereto. A base layer of the weight 60 g/m 2 was manufactured 17 by the use of a square, hand-made paper manufacturing test machine (produced by Tozai Seiki Kgbushiki Kaisha), and kept standing in the condition before pressing.

Subsequently, 0.02 parts of the same retention aid M as used for the base layer were added to 100 parts of LMP of 300 ml freeness, and an inkreceptive layer of the weight 30 gIm 2 was produc'ed by the use of the same paper manufacturing test machine as used for the base layer. The inkreceptive layer was laid on the base layer; According to the hand-made paper manufacturing test procedure JIS P8209, they were dehydrated and pressed and then dried. As a result, a two-ply ink jet recording paper of the weight 90 g/m 2 was obtained. Examples 2, 3, and 4, and Comparative Example 1 In Examples 2, 3, and 4, only the amount of size A was changed to 1.0, 0. 5, and 0.05 parts respectively. In Comparative Example 1, only size A was omitted.

As apparent from Table 1, the higher the sizing degree is, the higher the color density is. At the same time, the print-through is improved considerably because their penetration is prevented. In the sheet of Comparative Example 1 having its base layer containing no such sizing agent, even if it is a two-ply sheet, inks having passed through the inkreceptive layer penetrate in the base layer deeply. For this reason, the image density becomes weak, and the penetration of inks increased so greatly that the sheet of Comparative Example 1 cannot be put to practical use.

18 - Notwithstanding, the ink-absorbency, the image resolutionr color uniformity, and hand-feelinglare all good. Comparative Examples 2 and 3 Used for the ink-receptive layer were 100 parts of LMP of 300 mI freeness, to which 10 parts of calcite group ground calcium carbonate (amorphous type, 50 % mean particle size: 4.6 pm, BET bpecific surface area: 3.4 m 2 /g), and 0.02 parts of retention aid M. the same one as used in Example 1, 2 were added. An ink-receptive layer of the weight 90 g/m was produced as Comparative Example 2 by the use of the square, hand-made paper manufacturing test machine used in Example 1.

Separately, a two-ply ink jet recording paper was produced as Comparative Example 3 in the same way as in Example 1, except that 0.2 parts of cationic polymer size A were mixed in the ink-receptive layer of Example 1.

As obvious from Table 1, Comparative Example 2 shows such terrible strike through and as a result it cannot be put to practical use, because of worse print through. Even if it is a two-ply, Comparative Example 3 contains the sizing agents in both the ink-receptive and the base layers, so that inks are not allowed to spread properly, the apparent density is too low. and the ink-absorbency is so poor that there appears in part the flowing-out of inks. Examples 5 and 6 An ink jet recording paper of Example 5 was produced in the same way as in Example 1, except that its base layer n - 19 was prepared from 80 parts of WKP of 350 rnl freeness, 20 parts of NBRP (softwood bleached kraft pulp) of 250 ml freeness, and 0.2 parts of size B (alkylketene dimer, consistency: 15.5 %, viscosity: 80 c.p.s.).

Separately, another ink jet recording paper of Example 6 was produced in the same way as in Example 5, except that 100 parts of LUP of 280 ml freeness were used for the base layer, in place of LMP in EXample 5.

As clearly seen from Table 2, the print-through becomes slightly noticeable with the increase of the base layer's transparency. Nevertheless, there is recognized almost no change in the ink-absorbency, hand-feeling and density. Examples 7, 8, 9, and 10 Ink jet recording papers of Examples 7 and 8 were produced in the same way as in Example 1, except that 100 parts of WKP of 250 ml freeness, and 100 parts of NMP of 200 M1 freeness were used respectively for the ink- receptive layer, in place of WKP in Example 1.

Another ink jet recording paper of Example 9 was produced in the same way as in Example 1, except that 20 parts of calcite group precipitated calcium carbonate (spindle shape, 50 % mean particle size: 4.1 pm, BET specific surface area: 5 J /g) were added to 100 parts of the pulp to produce an ink-receptive layer, and 0.15 parts of size C (alkenylsuccinicanhydride, a reactive neutral size, viscosity: 420 c.p.s., specific gravity: 0.95), 1 part of aluminum sulfate, and 0.5 parts of retention aid N (cationic starch CATO F, produced by Ohji National Co.) were added to 100 parts of the pulp to produce a base' layer.

still another ink jet recording paper of Example 10 was produced in the same way as in Example 1, except that 10 parts of calcite group ground calcium carbonate (amor- phous type, 50 % mean particle size: 4.4 pm, BET specific 2 surface area: 3.5 m /g) were added to the pulp to produce an ink- receptive layer, and 20 parts of kaolin (kaolinite group, spherical aggregate, mean primary particle size: 0.1 pm, specific gravity: 2.2), 0. 15 parts of fortified rosin size D (Coropal CS, produced by Seiko Kagaku Kogyo Co.), and 1.0 part of aluminum sulfate were added to 100 parts of the pulp to produce a base layer.

As apparent from Table 3, the light scattering coefficient of the inkreceptive layer declines, the transparency thereof increases, and the density of images increases. As the light scattering coefficient exceeds 500 cm 2 /g, recorded images begin to look whitish, and the density begins to decrease. Comparative Example 4 An ink jet recording paper was produced in the same way as in Example 1, except that 43 parts of synthetic pulp (polyethylene, mean fiber length: 1.6 mm, freeness: 300 rnl) were added to 100 parts of the pulp to produce an ink-receptive layer.

As shown in Table 3, the use of synthetic pulp provides the increased light scattering coefficient of the ink- receptive layer and the extremly decreased density. Also, in an observation at recorded image's, there are unfixed area in ink dots, whereby images lack in image uniformity. Examples 11, 12, and 13 Added to 1430 parts of water were 100 parts of fine silica produced by the precipitated process (50 % mean particle size: 2.7pm, BET specific surface area: 270 m 2 /g), 67 parts of 28 % cationic resin aqueous solution (polydimethyldiallylammonium chloride, mean molecular weight: 120,000), as an agent for giving images water-resistance, and 50 parts of 10 % PVA aqueous solution (saponification degree: ca. 99 %, mean polymerization degree: 1700), as a binder. In this case a impregnating solution of 8 % total solid content was produced. The ink-receptive layer prepared in Example 1 was coated with this impregnating solution in 2 order to produce the solid-content of 2 g/m An ink jet recording paper thus produced was numbered with Example 11.

Another ink jet recording paper of Example 12 and 13 were produced in the same way as in Example 1, except that the silica produced by the precipitated process was replaced with silica produced by the gel process (50 % mean particle size: 12 pm, BET specific surface area: 320 m 2 /g) and silica produced by the vapor process (mean primary particle size: ca. 12 nm, BET specific surface area: 200 m 2 /g), respectively.

As apparent from Table 4, the thin coating (impregnating) of the inkreceptive layer with silica provides the widely i increased density. It also improves the color reproduce whereby there appear brilliant images. Example 14 Similarly in Example 1, a first ink-receptive layer of the weight 30 g/m 2, a first base layer of the weight 30 9/m 2 a second base layer of the weight 30 g/m 2, and a second inkreceptive layer ofthe weight 30 g/m 2 were layed one on another in this order, and a multi-ply ink jet recording paper of the weight 120 g/m 2 was obtained, as shown in Fig. 3. Meanwhile, the freeness of LBKP used for each of the layers is 300 ml.

Both sides of the ink jet recording sheet are superior in ink-absorbency, resolution, and optical density. At the same time, the recording paper shows no print through, and had a good hand-feeling.

Items of the result in Table 1 to 4 are assessed as follows. (1) Opacity and specific light scattering coefficient:

The normalization of the Hunter reflectometer Lproduced by Kabushiki Kaisha Toya, Seiki Seisakusho) is made according to the Hunter's Brightness test method JIS P8123 by the use of a green filter. The reflection of the respective sample recording papers backed with the standard white plate (R0.89) and the reflection of the same sample recording sheet backed with the standard black plate (R0) are measured, and they are put in the following equation in order to obtain the opacity thereof.

1 i Opacity = - Ro RD. 8 9 X 100 The specific light scattering coefficient can also be obtained from.RO and RO.99 by the use of the following Kubelka-Munk equations (1) and (2).

S ln (1 - Re R W (l/R. Z7:_) (1 - P.O/R.

weight of a sheet of recording paper per one square meter (g/M2) Ro: reflection index of a sheet of recording paper backed with a black plate R.: reflection index of a sheet of recording paper having a sufficient thickness R. can be calculated by using the following equation.

R. b + /b2 - 4a2 2a where a = - 0.89 C0.69RD b = 0.89Co.99 + Co.egRO 0.89Ro, and C0.89 RO RO. 9 9 The opacity and the specific light scattering coefficient of each of the base and the ink-receptive layers are measured. For the measurement of the opacity, the weight of each of the sample 'Layerb is made 60 g/m 2, and for the measurement of the specific light scattering coefficient, 2 it is rnade 90 g/m (2) Recorded optical density:

A solid colored area, 1.5 cm wide x 2.0 cm size, is marked on the respective sample recording sheet with black, cyan, magenta, and yellow by the use of Sharp Color-image Printer 10-700.

(1) (2) 24 - The density on the area is measured by the use of Macbeth RD 915, produced by Kollmongen Corporation. The respective color densities of the four colors are summed upr and given in Table 1. The recording paper giving a total color density of 3.3 and above are assessed as "good". (3) Print through:

The print through of the respective sample recording papers is assessed according to the following assessment criterion by the inspecting the reverge side of recorded images.

Assessment A: No strike through, almost no show through observed Assessment B: No strike through, slight show through observed Assessment C: Almost no strike through, but terrible show through observed Assessment D: Strike through, and terrible show through observed As is apparent from the above detailed description, this invention comprises superposing an ink-receptive layer of good ink affinity on either or both sides of a base layer containing a sizing agent, so that a multi-ply sheet, i.e. a novel superior ink jet recording paper, of desirable hand feeling and good ink-absorbency is produced.

Further, the ink jet recording paper of this invention provides excellent resolution power, uniform dot size and - high color density# with no print through, which have so far been obtained by a conventional coa-ted type ink jet recording paper.

Furthermore, the recording paper of this invention can be produced by using an ordinary paper manufacturing machine and, if necessary, a simplestructured on-machine treatment.

In addition, the recording paper of this invention has lots of such advantages that great improvement can be expected in both production operation and economy.

1 Co!position Table 1

Comp. Comp. Comp.

Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 1 Ex. 2 Ex. 3 Ink-receptive layer LMP 100 100 100 100 100 100 100 Ground CaCO 3' 10 Size A 0.2 Retention aid M 0.02 M 0.02 M 0.02 M 0.02 M 0.02 M 0.02 M 0.02 Base layer WKP 100 100 100 100 100 100 Precipitated CaCO 3 20 20 20 20 20 20 Size A 0.2 A 1.0 A 0.5 A 0.05 A 0.2 Retention aid M 0.02 M 0.02 M 0.02 M 0.02 M 0.02 M 0.02 Assessment Ink-receptive layer Spec. light 462 462 462 462 462 491 462 scattering coef.

Base layer opacity 84.9 84.9 84.9 84.9 94.9 84.9 Size (Sec.) 5 28 16 2 0 5 Assessment optical density 3.63 3.85.3.74 3.56 3.51 3.46 2.35 Print through A A A B c D A > 1.

1 1 Table 2

Ex. 1 Ex. 5 Ex. 6 Ink-receptive layer LMP 100 100 100 Retention aid M 0.02 M 0.02 M 0.02 Base layer LBKP NBKP Precipitated CaCO 20 Size 3 Retention aid As'se'ssffient A 0.2 M 0. 02 100 20 B 0.2 B 0.2 M 0. 02 M 0.02 Ink-receptive layer Spec. light 462 462 462 scattering coef.

Base layer Opacity (%) 84.9 71.0 78.2 Size (sec.) 5 8 7 Optical density 3.63 3.68 3.65 Print through A B P.

1 N) _j 1 Table 3

Ex. 1 Ex. 7 Composition Comp Ex. 8 Ex. 9 Ex. 10 Ex. 4 Ink-receptive layer LMP 100 100 100 100 100 NMP 100 Synthetic pulp 43 Ground CaCO 3 10 Precipitated CaCO 3 20 Retention aid M 0.02 M 0.02 M 0.02 M 0.02 M 0.02 M 0.02 Base layer LMP 100 100 100 100 100 100 Precipitated CaCO 20 20 20 20 20 3 CO Kaolin 20 Size A 0.2 A 0.2 A 0.2 C 0.15 D 0.15 A 0.2 Retention aid M 0.02 M 0.02 M 0.02 N 0.5 M 0.02 Aluminum sulfate 1 1 Assessment Ink-receptive layer Spec. light 462 376 219 548 491 706 scattering coef.

Base layer opacity 84.9 84.9 84.9 84.9 83.9 84.9 Size (sec.) 5 5 5 5 7 5 Ass'esswent optical density 3.63 3.68 4.29 3.32 3.44 2.79 Print through A A A A A A A 1 A 'I 11 Table 4

Ex. 1 Ex. 11 Composition Ink-receptive layer LMP Ground CaCO Retention aid Base layer LMP Ground CaCO 3 Precipitated CaCO Size Retention aid Assessnent Ink-recepti;- ve layer Spec. light scattering coef.

Base layer opacity Size (sec.) Assessment Optical density Print through Ex. 12 Ex. 13 EX. 14 lst 2nd M 0. 02 M 0. 02 3 20 A 0.2 M 0. 02 462 A 0.2 M 0. 02 462 84.9 84.9 5 M 0. 02 M 0. 02 A 0.2 M 0.02 462 M 0. 02 M 0.02 0.2 A 0.2 0. 02 M 0.02 462 476 A 0.2 M 0.02 462 84.9 84.9 83.8 83.0 5 3.63 4.12 3.80 4.45 3.50 A A A A A 3.65 A 1 M W 1

Claims

- 30 CLAIMS

An ink jet recording paper which comprises a base layer that contains an internal sizing agent, and an ink-receptive layer superposed on one or both sides of said base layer by a multi-ply paper-manufacturing process.
2. An ink jet recording paper according to claim 1, wherein the specific light scattering coefficient of said ink-receptive layer is not greater than 500 CM2 /g, and the opacity of said base layer is not snibller than 75 percent.
3. An ink jet recording paper according to claim 1 or 2, wherein said ink-receptive layer is coated or impregnated with fine silica at a rate of 0.5 to 10 g/m2 to form a thin coated layer.
4. An ink jet recording paper according to claim 3, wherein said thin coated layer comprises at least one agent selected from polyethylene imine, polydimethyldialkylammonium chloride, polyalkylene-polyaminedicyandiamideammonium condensate, polyvinylpyridinium halide, poly-(meth)acrylalkyl quaternary salts, poly-(meth)acrylamidealkyl quaternary salts, poly-vinylbenzyltrimethylammonium and w-chloro-poly(oxy ethylenepolymethylene-trialkylammonium salt).
5. An ink jet recording paper according to any one of the preceding claims wherein said ink-receptive layer comprises pulp, filler, retention aid, and optional auxiliary agent.

7
6. An ink jet recording paper according to any one of claims 1 to 5 wherein said base-layer contains as filler at least one of calcium carbonate, clay, activated clay, talc, silica, aluminium hydroxide, diatomaceous earth, barium sulfate, titanium dioxide and organic resinous pigment.
7. An ink jet recording paper according to any one of claims 1 to 5 wherein said base-layer contains finely powdered precipitated calcium carbonate as filler.
8. An ink jet recording paper according to any one of the preceding claims wherein said ink-receptive layer contains as filler at least one of calcium carbonate, clay, activated clay, talc, silica, aluminium hydroxide, diatomaceous earth, barium sulfate, titanium dioxide and organic resinous pigment.
9. An ink jet recording paper according to any one of claims 1 to 7 wherein said ink-receptive layer contains ground calcium carbonate as filler.
10. An ink jet recording paper according to claim 1 substantially as described in any one of the Examples.

Publuhed 198a a, ne pa.en. M-.-_ StZtA ROUSE 6671 Hie'. Ho'-:r y be obtained frc.-n M e Patent 0Elce - C n. London WC1R 4TF 11ir-hez. ccpies.ia_ r Wes Branch, St Mary Cray, Orpington. Kent BR5 3RD. Printed by Multiplex techruques ltd. St Mary Crky. Xent. Con. 1.87.