US20050139338A1

US20050139338A1 - Recording paper

Info

Publication number: US20050139338A1
Application number: US10/969,784
Authority: US
Inventors: Masaya Shibatani; Hiroyuki Onishi
Original assignee: Seiko Epson Corp
Current assignee: Seiko Epson Corp
Priority date: 2003-10-22
Filing date: 2004-10-20
Publication date: 2005-06-30
Also published as: JP2005126840A

Abstract

The invention relates to a recording paper comprising a sheet core layer mainly comprising a recycled pulp, and having multiplied on both sides of said sheet core layer, at least one sheet surface layer mainly comprising a bleached chemical pulp.

Description

FIELD OF THE INVENTION

The present invention relates to a recording paper suitable for various recording processes such as an ink-jet process. More specifically, the invention relates to a global environment-friendly recording paper using a recycled pulp.

BACKGROUND OF THE INVENTION

The methods for recording letters and images include various printing processes such as an ink-jet process, an electrophotographic process, and a melt-transfer process. As recording papers, paper is mainly used from the viewpoints of usability and cost.
Hitherto, paper for use as the recording papers is desirably one obtained using as a raw material a virgin pulp which is produced from cut-down trees from tree plantation and natural forest. However, in recent years, based on social demands for environmental protection and garbage reduction, it is strongly desired to promote use of recycled pulps using recycled waste paper as the raw material, and thus recycled pulps have been utilized for the recording papers.
As a recording paper using a recycled pulp, there is an ink-jet recording paper comprising a white pigment layer on the surface of a base paper, wherein a recycled pulp using recycled waste paper as the raw material and/or a grind pulp is used in the base paper in an amount of 10% by weight or more based on the weight of the whole pulp of the base paper (see Patent Document 1). Further, there is an ink-jet recording paper comprising a base paper having provided thereon an ink-receiving coated layer containing a porous pigment and a binder, wherein the base paper contains a recycled pulp obtained from recycled waste paper and contains at least one filler selected from zeolite, silica, and calcined kaolin in an amount of 1 to 30% by weight based on the weight of the whole pulp, and Stöckigt sizing degree (JIS-P8122) of the recording paper is 40 seconds or less (see Patent Document 2).

- Patent Document 1: JP 10-278416 A
- Patent Document 2: JP 2001-171223 A

As recycled waste paper for use as the raw material of recycled pulps, old newspaper, old magazine, office waste paper, and the like are used. Of these, since a mechanical pulp having a large lignin content is blended in old newspaper and old magazine in a high ratio, there is a problem that a recycled pulp using these as raw materials is apt to induce so-called yellowing with time, i.e., color change into yellow with the passage of time. Therefore, as a recycled pulp to be used for a recording paper, one would like to use recycled waste paper having a small lignin content, such as office waste paper, and avoid a mechanical pulp as far as possible. However, at present, it is difficult to completely prevent contamination of a mechanical pulp under the present situation of waste paper recycling. In the case that a recycled pulp is used as the raw material for a recording paper, it is important how to overcome the problem of yellowing with time. Further, since a recycled pulp is subjected to extra processes such as a deinking step and a bleaching step and hence keratinization of the fibers tends to proceed, so that there are also problems of weak mechanical strength and deterioration of texture when the pulp is converted into sheets.
As above, a recycled pulp has defects such as easy yellowing with time and insufficient mechanical strength when it is converted into sheets. Therefore; paper produced by simply blending the recycled pulp has a problem especially in storability, and hence is unsuitable for important documents and as silver salt photograph substitutes where a long-term storage is desired. In addition, even when a coated layer such as a white-pigment layer or an ink-receiving coated layer is provided on a base paper containing the recycled pulp as in the above-mentioned ink-jet recording paper, the storability of the base paper itself is not improved, so that a satisfactory recording quality cannot be maintained for a long period of time even though such a quality is maintained for a while after image recording.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a recording paper which satisfies social demands such as environmental protection and garbage reduction by using a recycled pulp and is capable of a long-term storage with hardly inducing yellowing with time and degradation with time.
Other objects and effects of the invention will become apparent from the following description.
The above-described objects of the invention have been achieved by providing a recording paper comprising a sheet core layer mainly comprising a recycled pulp, and having multiplied on both sides of said sheet core layer, at least one sheet surface layer mainly comprising a bleached chemical pulp.
Since the recording paper of the invention has a constitution that the sheet core layer mainly comprising a recycled pulp is sandwiched between the sheet surface layers mainly comprising a bleached chemical pulp, the problems of yellowing with time and degradation with time, which are concerns for a sheet core layer, are solved in the recording paper as a whole, and thus the recording paper can be used with security even in a recording application where a long-term storage is desired. Namely, the recording paper of the invention is a global environment-friendly recording paper which achieves both of global environment protection and storability, which had been difficult with conventional recording papers using a recycled pulp.

DETAILED DESCRIPTION OF THE INVENTION

The recording paper of the invention is described in detail below.
The recording paper of the invention is a sheet-shape product obtained by multiplying one or more sheet surface layers on each of both sides of a sheet core layer.
The sheet core layer is a paper layer mainly comprising a recycled pulp. In the invention, the recycled pulp means a paper-making material obtained by subjecting recycled waste paper to maceration. As the recycled waste paper, office waste paper, old newspaper, old magazine, advertising leaflet, and the like can be used. The recycled waste paper are not particularly limited but preferred are waste paper mainly comprising a chemical pulp. The larger content of a chemical pulp in the waste paper is more preferable. Such waste paper is suitable as a material for the recycled pulp according to the invention since it is resistant to yellowing with time and degradation with time owing to high cellulose purity, i.e., low lignin content. In general, most of office paper mainly comprises a chemical pulp and hence office waste paper, i.e., waste paper thereof can be suitably used in the invention.
Further, a recycled pulp is generally obtained though a maceration step where waste paper is macerated with water to obtain a pulp suspension, a rough selection/fine selection step where foreign matter in the pulp suspension is separated, a deinking step wherein printing ink is separated, and a bleaching step using ozone or the like. In the invention, however, not only the recycled pulp obtainable by these respective steps but also a recycled pulp obtained without subjecting to the deinking treatment or bleaching treatment or a recycled pulp obtained without subjecting to the deinking treatment and bleaching treatment may be used.
The blending amount of the recycled pulp is preferably 50% by weight or more based on the weight of the whole pulp in the sheet core layer.
As other pulps capable of blending with the recycled pulp in the sheet core layer, a mechanical pulp may be used, but preferred is a bleached chemical pulp. As the bleached chemical pulp, those for use in the sheet surface layer described below can be employed.
As components other than pulps, if necessary, various additives such as dispersion aid for a pulp slurry, a dry paper-strength enhancer, a wet paper-strength enhancer, a filler, a sizing agent, a fixing agent, a pH regulator, a dye, a colored pigment, and a fluorescent whitening agent may be added to the sheet core layer.
Examples of the dispersion aid include polyethylene oxide, polyacrylamide, and Hibiscus manihot L. Examples of the paper-strength enhancer include anionic paper-strength enhancers such as vegetable gum, starch, and carboxy-modified polyvinyl alcohol and cationic paper-strength enhancers such as cationized starch, cationized polyacrylamide, and polyamidepolyamine epichlorohydrin resins. Examples of the filler include clay, kaolin, talc, heavy calcium carbonate, precipitated calcium carbonate, barium sulfate, titanium oxide, aluminum hydroxide, and magnesium hydroxide. Examples of the sizing agent include higher fatty acid salts, rosin, rosin derivatives such as maleylated rosin, dialkyl ketene dimers, alkenyl- or alkyl-succinic acid salts, epoxydized fatty acid amides, and polysaccharide esters. Examples of the fixing agent include polyvalent metal salts such as aluminum sulfate and aluminum chloride, cationic polymers such as cationized starch and polyamidepolyamine epichlorohydrin resins. Examples of the pH regulator include hydrochloric acid, caustic soda, and sodium carbonate.
On the other hand, the sheet surface layer to be multiplied on each of both sides of the above sheet core layer is a paper layer mainly comprising a bleached chemical pulp. In the invention, the bleached chemical pulp means one obtained by bleaching, using any of various bleaching agents such as chlorine-based chemicals, hydrogen peroxide, enzymes and ozone, an unbleached virgin pulp obtained by a digester process such as a kraft digester process, a polysulfide digester process, or a sulfite digester process each starting with broad-leaved wood or coniferous wood. Various methods are known for the digesting treatment and bleaching treatment, respectively but the treating methods are not particularly limited in the invention.
As the raw material for the bleached chemical pulp, wood fibers from coniferous tree and broad-leaved tree are generally used but grass fibers from straw, esparto, bagasse and kenaf, bast fibers from hemp, paper mulberry, clove-like bush and mitumata (Edgeworthia papyrifera), and cotton can be also employed. A mixture of two or more thereof may be also used. The pulp which receives forest standard council from FSC (Forest Stewardship Council) or PEFC (Pan European Forest Certification) meets global environment protection that is a purpose of the invention and hence is preferably used.
Preferred as the bleached chemical pulp is a bleached chemical pulp obtained by a kraft digester process (kraft pulp). The kraft pulp is excellent in not only productivity and mechanical strength of sheets but also efficient utilization of resources due to a high pulp yield from starting wood as compared with pulps obtained by other digester processes, so that the kraft pulp satisfies the purpose of the invention, i.e., global environment protection. Examples of the kraft pulp include a coniferous tree bleached kraft pulp (NBKP) and a broad-leaved tree bleached kraft pulp (LBKP). More preferred is a kraft pulp subjected to a bleaching method (so-called ECF bleaching) in which the bleaching treatment after kraft digesting does not use elemental chlorine as used in chlorine bleaching or hypochlorite bleaching, which discharges organic chlorinated substances.
As the recording papers, those having a high degree of whiteness are preferred. From such a point of view, the bleached chemical pulp preferably has an ISO whiteness defined by JIS-P8148 of 85% or more, more preferably 90% or more. There is a correlation between whiteness and degree of delignification of a pulp. In general, the higher the degree of delignification is, the higher the degree of whiteness is and the more excellent the stability of whiteness is, so that the pulp is resistant to yellowing with time. The degree of delignification of a pulp can be evaluated using chlorine consumption defined by IS03260-1982 or a hypo value defined by TAPPI T253. The larger these values are, the larger the lignin content remaining in the pulp is. The degree of delignification can be adjusted by suitably controlling the treating conditions of digesting and bleaching in the pulp production process.
The bleached chemical pulp is blended in the sheet surface layer preferably in a large amount as far as possible from the viewpoint of enhancing suitability for recording papers. It is desired that the whole pulp in the sheet surface layer comprises the bleached chemical pulp.
To the sheet surface layer, as components other than pulps, various additives such as dispersion aid for a pulp slurry, a dry paper-strength enhancer, a wet paper-strength enhancer, a filler, a sizing agent, a fixing agent, a pH regulator, a dye, a colored pigment, and a fluorescent whitening agent may be added, if necessary. As these additives, those which can be used in the sheet core layer can be employed.
The recording paper of the invention comprising the sheet core layer and the sheet surface layer can be produced by carrying out paper-making of the respective layers together using a cylinder paper-making machine. The above-mentioned individual pulps are usually beaten by a beating machine such as double disc refiner in order to improve paper-making suitability and various properties of paper, such as strength, smoothness and uniformity of texture. The degree of beating is not particularly limited and may be selected from the range of about 100 to 600 ml in terms of Canadian Standard Freeness (CSF) according to the intended purposes.
With regard to the ratio in thickness of the sheet surface layer (multiplied to either one surface of the sheet core layer) to the sheet core layer, it is preferably in the range of 0.4 to 4.0. When the thickness of the sheet surface layer is less than 0.5 relative to the thickness of the sheet core layer, the disadvantage of the sheet core layer, i.e., storability (aptness to induce yellowing with time and degradation with time) can be not sufficiently compensated. When the relative thickness exceeds 4.0, the blending rate of the recycled pulp decreases in the recording paper as a whole and thus it is impossible to sufficiently contribute environmental protection.
In this connection, the thickness of the sheet surface layer on one side of the sheet core layer is usually made the same as the thickness of the sheet surface layer on the other said of the sheet core layer, but they may be different from each other. Further, it is sufficient that at least one sheet surface layer is multiplied on each of both sides of the sheet core layer. One side or both sides of the sheet core layer may be covered with a sheet surface layer having a multilayer structure containing two or more layers. Further, the number of the sheet surface layer may be different between one side and the other side of the sheet core layer.
The surface pH of the recording surface of the recording paper of the invention is preferably 6.5 or higher. When the surface pH of the recording paper is less than 6.5, there is a possibility that an acid hydrolysis reaction proceeds with time to invite decrease of mechanical strength and yellowing. The surface pH herein is measured in accordance with Method A (a coating method) of the surface pH test method of paper and paper board defined by Japan Technical Association of the Pulp and Paper Industry [J. TAPPI No. 6], and means surface pH (paper face-pH) determined by adding dropwise an indicator for pH measurement to an objective surface to be measured, spreading the indicator with defatted cotton thinly and rapidly, and subsequently comparing the hue of the objective surface to be measured with the hues described in pH Standard Color-change Table at the time point when 10 seconds have passed from the dropwise addition of the indicator for pH measurement. Examples of methods for adjusting the surface pH of the recording paper to be 6.5 or higher include a method of making the sheet core layer and sheet surface layer (especially sheet surface layer) by a so-called neutral paper-making process, a method of applying an appropriate alkali agent onto the recording paper, and the like.
Further, the recording paper of the invention preferably has a good surface smoothness. Beck's smoothness measured in accordance with JIS-P8119 is preferably 50 seconds or more, more preferably 100 seconds or more. The smoothness can be adjusted by compressing the recording paper through applying pressure using a calendar or the like during or after making the recording paper.
The recording paper of the invention can be suitably used for various recording processes, such as an ink-jet recording process, an offset printing process, a gravure printing process, a sublimation-transfer process, melt-transfer process, and an electrostatic toner-recording process, as well as handwriting. In particular, the recording paper can be suitably used in recording applications where a long-term storage is desired, e.g., printing of important documents and as ink-jet photo papers which are expected to give an output of photo-grade quality.
In general, the recording paper for ink-jet recording is required to have a high ink absorbability with respect to an aqueous ink is required. Therefore, as the recording paper for ink-jet recording, an ink-receiving layer is preferably multiplied on at least one side of the above recording paper. The ink-receiving layer is described in detail below.
As one example of the ink-receiving layer applicable to the invention, a porous ink-receiving layer containing a pigment as an essential component may be mentioned. The ink-receiving layer has numerous pores on the surface and thus is also called void-type one or the like.
Examples of the pigment suitable as an ink-receiving layer component include inorganic pigments such as precipitated calcium carbonate, heavy calcium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, synthetic amorphous silica, colloidal silica, colloidal alumina, pseudo boehmite, aluminum hydroxide, alumina, lithopone, zeolite, hydrated halocite, magnesium carbonate and magnesium hydroxide, and organic pigments such as styrene-based plastic pigments, acrylic plastic pigments, polyethylene, urea resins, and melamine resins. In the invention, one of them may be used singly, or two or more thereof may be used in combination.
Particularly, vapor-phase-process silica, alumina compounds (alumina hydrate, aluminum oxide ultrafine particles) are preferably used in the invention.
The vapor-phase-process silica for use in the invention is preferably in the form of ultrafine particles having an average primary particle diameter of 3 to 50 nm. Particularly preferred average primary particle diameter is from 5 to 30 nm. The secondary particle diameter formed by conjunction thereof is preferably from 10 to 200 nm, but the form thereof in the coated layer is not certain and the size of secondary particles are not so important. With regard to the amorphous silica fine particles synthesized by a vapor phase process, examples of commercially available products include Aerosil (Degussa AG).
The alumina hydrate for use in the invention can be represented by the general formula Al₂O₃.nH₂O. Alumina hydrate is classified into gypsite, bialite, norstrandite, boehmite, boehmite gel (pseudo boehmite), diaspore, amorphous one, and the like according to difference in composition and crystal form. Of these, the case that the value of n in the above formula is 1 represents alumina hydrate having a boehmite structure, the case that n is larger than 1 and less than 3 represents alumina hydrate having a pseudo boehmite structure, and the case that n is 3 or more represents alumina hydrate having an amorphous structure. In particular, preferable alumina hydrate in the invention is alumina hydrate having a pseudo boehmite structure where n is larger than 1 and less than 3. Further, the shape of alumina hydrate may be any of tabular shape, fiber shape, needle shape, spherical shape, rod shape, etc., and preferable shape in view of ink absorbability is tabular shape. The tabular-shape alumina hydrate has an average aspect ratio of 3 to 8, preferably an average aspect ratio of 3 to 6. The aspect ratio is represented by the ratio of “diameter” to “thickness” of a particle. The diameter of the particle herein means a diameter of a circle having an area equal to the projected area of the particle when the alumina hydrate is observed under an electron microscope. When the aspect ratio is smaller than the above range, the pore distribution in the ink-receiving layer becomes narrow and ink absorbability decreases. On the other hand, when the aspect ratio exceeds the above range, it becomes difficult to produce an alumina hydrate of uniform particles.
As the alumina hydrate, commercially available products can also be suitably employed. Examples thereof include Cataloid AS-1, Cataloid AS-2, Cataloid AS-3 (they are manufactured by Catalysts & Chemicals Ind. Co., Ltd.), Alumina Sol 100, Alumina Sol 200, Alumina Sol 520 (they are manufactured by Nissan Chemical Industries, Ltd.), M-200 (it is manufactured by Mizusawa Industrial Chemicals, Ltd.), and Alumi Sol 10, Alumi Sol 20, Alumi Sol 132, Alumi Sol 132S, Alumi Sol SH5, Alumi Sol CSA55, Alumi Sol SV102, Alumi Sol SB52 (they are manufactured by Kawaken Fine Chemicals Co., Ltd.).
As the aluminum oxide ultrafine particles for use in the invention, γ-form aluminum oxide fine particles that are γ-form crystals are preferably employed. Crystallographically, the γ-form crystals are further classified into γ-group and δ-group. Fine particles having a crystal form of δ-group are preferred. Further, the γ-form aluminum oxide fine particles preferably have an average particle diameter of primary particles of less than 80 nm. When secondary particles composed of primary particles having an average particle diameter of 80 nm or more are used, brittleness increases and defects on the coated film markedly tend to occur. Examples of commercially available γ-type aluminum oxide fine particles include aluminum oxide C (manufactured by Japan Aerosil) belonging to the 6-group, AKP-G015 (manufactured by Sumitomo Chemical Co., Ltd.) belonging to the γ-group, and the like.
The content of the foregoing pigment is preferably in the range of 40 to 90% by weight based on the total weight of solid matter in the ink-receiving layer. When the content is less than 40% by weight, there is a possibility of decrease in ink absorbability. When the content exceeds 90% by weight, there is a possibility of decrease in coated film strength of the ink-receiving layer.
Into the ink-receiving layer, as a binder for the pigment, a polymer compound having an affinity to an ink can be incorporated. Examples of such a polymer compound include polyvinyl alcohol, silanol-modified polyvinyl alcohol, polyvinyl acetate, starch, cellulose derivatives such as carboxymethyl cellulose, casein, gelatin, latexes of conjugated diene copolymers such as styrene-butadiene copolymers, latexes of vinyl copolymers such as ethylene-vinyl acetate copolymers, latexes of acrylic copolymers such as polymers of acrylic acid and methacrylic acid, vinylpyrolidone/vinyl acetate copolymers, and acetal resins such as polyvinylbutyral and polyvinylformal. One of them may be used singly, or two or more thereof may be used in combination. Particularly, use of polyvinyl alcohol is preferred. The content of the polymer compound (binder) is preferably from 2 to 50% by weight relative to the weight of the pigment. The content of the polymer compound less than 2% by weight relative to the pigment weight may invite insufficient strength of the coated film. To the contrary, when the content exceeds 50% by weight, there is a possibility of decrease in ink absorbability.
Into the ink-receiving layer, in addition to the pigment and polymer compound (binder), a pigment dispersant, a thickening agent, a flow improver, a viscosity stabilizer, a pH regulator, a surfactant, a deforming agent, a form inhibitor, a releasing agent, a foaming agent, a penetrant, a fluorescent whitening agent, a UV absorber, an antioxidant, a leveling agent, an antiseptic, an antifungal agent, a water-resisting agent, a wet paper-strength enhancer, a dry paper strength enhancer, and the like can be suitably incorporated.
Further, into the ink-receiving layer, for the purpose of further enhancing color-developing property and water resistance of recorded images, a cationic substance can be incorporated. Examples of the cationic substance include low-molecular-weight compounds such as primary to secondary amine compounds, primary to tertiary amine salts, and quaternary ammonium salts, oligomers having a primary to secondary amino group, a primary to tertiary amine salt group, and a quaternary ammonium salt group, and polymers having one of these groups, and specifically include cationic organic substances such as diallyldimethylammonium chloride polymers, epihalohydrin-secondary amine copolymers, diallyldimethylammonium chloride-sulfur dioxide copolymers, diallyldimethylammonium chloride-acrylamide copolymers, diallylmethylammonium salt polymers, diallylamine hydrochloride salt-sulfur dioxide copolymers, dimethylmethylamine hydrochloride salt copolymers, polyallylamine, polyethyleneimine, polyethyleneimine quaternary ammonium salt compounds, (meth)acrylamide alkylammonium salt polymers, and ionenes containing a quaternary ammonium salt group. In addition, multivalent metal ions such as Al³⁺, Ca²⁺, and Mg²⁺ and cationic surfactants such as benzalkonium chloride can be also used as the above cationic substances. Preferred are polymers having a quaternary ammonium salt group.
The content of the cationic substance is preferably in the range of 0.5 to 15% by weight based on the total weight of solid matter in the ink-receiving layer. When the content of the cationic substance is less than 0.5% by weight, an improving effect of color-developing property and water resistance is poor. When the content exceeds 15% by weight, there is a possibility that deterioration in ink absorbability and too high glossiness (so-called bronzing) induced by precipitation of an ink color material occurs, which may contrarily deteriorate image quality.
The ink-receiving layer can be multiplied on the sheet surface layer using a known coating method. For example, the ink-receiving layer can be formed by applying a coating liquid for the ink-receiving layer containing the above respective components on the sheet surface layer using one of various coating instruments such as an air-knife coater, a curtain coater, a slid lip coater, a die coater, a blade coater, a gate roll coater, a bar coater, a rod coater, a roll coater, a bill blade coater, a short dowel blade coater, and a size press, followed by drying. The constitution of the ink-receiving layer may be a monolayer structure or may be a multilayer structure having two or more layers.
The coating amount of the ink-receiving layer is not particularly limited but is preferably from 10 to 40 g/m², more preferably from 20 to 30 g/m²in terms of solid matter. When the coating amount is less than 10 g/m², the improving effect of the ink-jet suitability is poor. When the amount exceeds 40 g/m², there is a possibility of generation of powder dropping and also the effect is saturated, so that the case is inferior in economical efficiency. Incidentally, the thickness is preferably from 10 to 40 μm, more preferably from 20 to 30 μm.
The so-called void-type ink-receiving layer as described above can be adjusted to have any surface texture, e.g., delustered tone (mat tone) where glossiness is subtly adjusted, semi-glossy tone (luster tone), and highly glossy tone where glossiness is excellent. As a method for enhancing gloss, a method for smoothing the coated ink-receiving layer by calendering treatment may be mentioned. Equipments for the calendering treatment at that time include a gloss calender, a super calender, a soft calender, and the like. In particular, heat calendering treatment where smoothing is carried out under heating is preferably employed. Also, the gloss of the coated ink-receiving layer can be enhanced by a so-called casting method where the surface of the coated ink-receiving layer is transcribed to a mirror plane of a metal, a film, or the like.
Further, as another example of the ink-receiving layer applicable to the invention, a so-called swelling ink-receiving layer containing a water-soluble resin as a main component may be mentioned. The water-soluble resins include polyvinyl alcohol, polyvinyl pyrrolidone, acrylic resins, cellulose modified resins, gelatin, and the like. One of these water-soluble resins may be used singly, or two or more thereof may be used in combination. Into the swelling ink-receiving layer, as components other than the water-soluble resin, various agents usable for the aforementioned void-type ink-receiving layer may be incorporated.

EXAMPLES

The present invention will be illustrated in greater detail with reference to the following Examples, but the invention should not be construed as being limited thereto.

Example 1

Preparation of Slurry for Sheet Core Layer
Used office paper made of a bleached chemical pulp was subjected to deinking treatment to obtain a recycled pulp having ISO whiteness of 80%. Then, a 1:1 mixture of the recycled pulp and a bleached chemical pulp (LBKP, ISO whiteness of 90%) was beaten until it reached a value of 300 ml as Canadian Standard Freeness, whereby a pulp slurry was prepared. To the pulp slurry were added, as a sizing agent, 0.5% by weight of an alkylketene dimer based on the pulp weight and, as a paper strength-enhancer, 1.0% by weight of polyacrylamide based on the pulp weight, 2.0% by weight of cationized starch based on the pulp weight and 0.5% by weight of a polyamide epichlorohydrin resin based on the pulp weight, followed by dilution with water to form a 1% slurry.
Preparation of Slurry for Sheet Surface Layer
A 1:1 mixture of LBKP and NBKP (both having ISO whiteness of 90%) was beaten until it reached a value of 300 ml as Canadian Standard Freeness, whereby a pulp slurry was prepared. To the pulp slurry were added, as a sizing agent, 0.5% by weight of an alkylketene dimer based on the pulp weight and, as a paper strength-enhancer, 1.0% by weight of polyacrylamide based on the pulp weight, 2.0% by weight of cationized starch based on the pulp weight and 0.5% by weight of a polyamide epichlorohydrin resin based on the pulp weight, followed by dilution with water to form a 1% slurry.
Using the slurry for a sheet core layer and the slurry for a sheet surface layer, a recording paper (basis weight of 84 g/m², waste paper blending rate of 20%) having a three-layer structure, in which a sheet surface layer having a basis weight of 20 g/m²is multiplied on each of both sides of a sheet core layer having a basis weight of 44 g/m², was made by a cylinder paper-making machine. This paper was used as the sample of Example 1. The recording surface of the recording paper had a surface pH of 6.7.

Example 2

Composition of Coating Liquid 1 for Ink-Receiving Layer

An aqueous solution containing vapor-phase-process silica and SHALLOL DC902P was dispersed by a high-pressure homogenizer, and polyvinyl alcohol etc. were added thereto to prepare a coating liquid 1 for an ink-receiving layer having the following composition.



	Vapor-phase-process silica	100 parts by
	(average primary particle diameter of 7 nm,	weight
	specific surface area by BET method
	of 300 m²/g)
	Polyvinyl alcohol	25 parts by
	(trade name: PVA 235, manufactured by	weight
	Kuraray Co., Ltd.)
	Methyldiallylammonium chloride	3 parts by
	polycondensate	weight
	(trade name: SHALLOL DC902P,
	manufactured by Daiichi Kogyo Seiyaku
	Co., Ltd.)
	Amphoteric surfactant	0.3 parts by
	(trade name: SWAM AM-2150, Nihon	weight
	Surfactant Kogyo K. K.)

The above coating liquid 1 for an ink-receiving layer was uniformly applied to one side of a recording paper having the same constitution as the sample of Example 1 using a wire bar, and then dried by a drier to form an ink-receiving layer having a thickness of 40 μm (coated amount of 25 g/cm²). A recording paper for ink-jet recording thus manufactured is used as the sample of Example 2. The recording surface of the recording paper had a surface pH of 6.6.

Example 3

A recording paper for ink-jet recording was manufactured in the same manner as in Example 2, except that a coating liquid 2 for an ink-receiving layer having the below-shown composition was used instead of the coating liquid 1 for an ink-receiving layer in Example 2. The recording paper was used as the sample of Example 3. The recording surface of the recording paper had a surface pH of 6.7.



Composition of coating liquid 2 for ink-receiving layer

	Silica gel	100 parts by
	(trade name: Finesil X37B, manufactured	weight
	by Tokuyama Corp.)
	Polyvinyl alcohol	16 parts by
	(trade name: PVA 117, manufactured by	weight
	Kuraray Co., Ltd.)
	Cationic substance (ink fixing agent)	5 parts by
	(trade name: Sumirase Resin 1001,	weight
	manufactured by Sumitomo Chemical Co.,
	Ltd.)
	Ammonia water	0.1 parts by
		weight

Comparative Example 1

A recording paper having a waste paper-blending rate of 20% (trade name: Hyperpirenu Tough, manufactured by Nippon Paper Industries Co., Ltd., basis weight of 84.3 g/m²) is used as it is as the sample of Comparative Example 1. The recording surface of the recording paper had a surface pH of 6.5.

Comparative Example 2

A recording paper for ink-jet recording was manufactured in the same manner as in Example 2, except that in the constitution of Example 2 the above-mentioned Hyperpirenu Tough was used instead of the recording paper having the same constitution as the sample of Example 1. The recording paper thus prepared was used as the sample of Comparative Example 2. The recording surface of the recording paper had a surface pH of 4.2.

Comparative Example 3

A recording paper for ink-jet recording was manufactured in the same manner as in Example 3, except that in the constitution of Example 3 the above-mentioned Hyperpirenu Tough was used instead of the recording paper having the same constitution as the sample of Example 1. The recording paper thus prepared was used as the sample of Comparative Example 3. The recording surface of the recording paper had a surface pH of 5.5.

Test Example

On the above respective examples, bleeding, whiteness, yellowing resistance, and heat degradation resistance were evaluated according to the following methods. The evaluation results thereof were shown in the following Table 1.
Method for Evaluation of Bleeding
Using an ink-jet printer (PM-4000PX, manufactured by Seiko Epson Corp.), color patches of respective colors having OD (optical density) of 1 were printed on the recording surface of each of the above samples using aqueous pigment inks of four colors of cyan (C), magenta (M), yellow (Y), and black (K). Then, the area where the color patches of Y and C are adjoining (i.e., a portion where decrease of image quality can be most easily recognized) was visually observed immediately after printing. Cases where no color mixing was observed were ranked as A, cases where color mixing was slightly observed but was not problematic from a practical standpoint were ranked as B, and cases where color mixing was observed to such an extent that color boundary was unclear were ranked as C.
Method for Evaluation of Whiteness
On the recording surface of each of the above samples, ISO whiteness was measured in accordance with JIS-P8148. Samples having a measured value of 90% or more were ranked as A (good for recording papers), samples having a measured value of 85% or more to less than 90% were ranked B (no problem from a practical standpoint), and samples having a measured value of less than 85% were ranked as C (impossible to use practically)
Method for Evaluation of Yellowing Resistance
Each of the above samples was left on standing in a constant-temperature and constant-humidity chamber set at the temperature of 80° C. and the relative humidity of 50% RH for 1 week. Then, ΔE on the recording surface of each sample between before and after standing was measured in accordance with L*a*b* (CIE 1976) using a color-difference meter (Spectrolino, manufactured by Gretag Macbeth). Samples having ΔE of 4 or less were ranked as A (good yellowing resistance), samples having ΔE in the range of more than 4 to less than 8 were ranked as B (no problem from a practical standpoint), and samples having AE of 8 or more were ranked as C (impossible to use practically).
Method for Evaluation of Heat Degradation Resistance
Each of the above samples was left on standing in a constant-temperature and constant-humidity chamber set at the temperature of 80° C. and the relative humidity of 65% RH for 2 weeks. Then, on each sample after standing, tear strength was measured in accordance with Elmendorff JIS-P8116 and the ratio (%) thereof to the tear strength of each sample before standing which had been measured beforehand [(tear strength of sample after standing/tear strength of sample before standing)×100] was determined. Samples having a value of 80% or more were ranked as A (good heat degradation resistance), samples having a value in the range of more than 50% to less than 80% were ranked as B (no problem from a practical standpoint), and samples having a value of 50% or less were ranked as C (impossible to use practically).

TABLE 1

Ratio of

thickness

Core Heat

layer:Surface Bleed- White- Yellowing degradation

layer ing ness resistance resistance

Example 1 1:1 B A A A

Example 2 1:1 A A A B

Example 3 1:1 A A A A

Comparative — B B C C

Example 1

Comparative — A A C C

Example 2

Comparative — A A C C

Example 3
While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
The present application is based on Japanese patent application 2003-362009 filed Oct. 22, 2003, the contents thereof being herein incorporated by reference.

Claims

1. A recording paper comprising a sheet core layer mainly comprising a recycled pulp, and having multiplied on both sides of said sheet core layer, at least one sheet surface layer mainly comprising a bleached chemical pulp.

2. The recording paper according to claim 1, wherein said at least one sheet surface layer on either one of the both sides has a thickness that gives a ratio of 0.4 to 4.0 relative to the thickness of the sheet core layer.

3. The recording paper according to claim 1, wherein said bleached chemical pulp in said sheet surface layer is one obtained by a kraft digester process.

4. The recording paper according to claim 1, wherein said bleached chemical pulp in said sheet surface layer has a whiteness of 85% or higher.

5. The recording paper according to claim 4, wherein the whiteness of said bleached chemical pulp is 90% or higher.

6. The recording paper according to claim 1, wherein at least one of said sheet surface layers further comprises at least one of a sizing agent and a paper strength-enhancer.

7. The recording paper according to claim 1, further having, on at least one side thereof, a porous ink-receiving layer containing a pigment.

8. The recording paper according to claim 7, wherein the pigment contained in said porous ink-receiving layer comprises at least one of gas-phase-process silica and an alumina compound.

9. The recording paper according to claim 8, wherein said gas-phase-process silica has an average primary particle diameter of 3 to 50 nm.

10. The recording paper according to claim 8, wherein said alumina compound is alumina hydrate of a tabular shape having an average aspect ratio of 3 to 8.

11. The recording paper according to claim 8, wherein said alumina compound is γ-form aluminum oxide ultrafine particles having an average primary particle diameter of less than 80 nm.

12. The recording paper according to claim 7, wherein said porous ink-receiving layer contains the pigment in an amount of 40 to 90% by weight based on the total weight of solid matter therein.

13. The recording paper according to claim 7, wherein said porous ink-receiving layer further comprises a binder in an amount of 2 to 50% by weight based on the weight of said pigment.

14. The recording paper according to claim 7, wherein said porous ink-receiving layer further comprises a cationic substance.

15. The recording paper according to claim 14, wherein said cationic substance is a polymer having a quaternary ammonium salt group.

16. The recording paper according to claim 14, wherein said porous ink-receiving layer contains said cationic substance in an amount of 0.5 to 15% by weight based on the total weight of solid matter therein.

17. The recording paper according to claim 7, wherein said porous ink-receiving layer has a coating amount of 10 to 40 g/m²in terms of solid matter.

18. The recording paper according to claim 1, further having, on at least one side thereof, an ink-receiving layer containing a water-soluble resin as a main component.