EP0174859A2

EP0174859A2 - Ink-jet recording medium and method

Info

Publication number: EP0174859A2
Application number: EP85306499A
Authority: EP
Inventors: Takashi Akiya; Shigeo Toganoh; Ryuichi Arai
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1984-09-13
Filing date: 1985-09-12
Publication date: 1986-03-19
Also published as: EP0174859A3

Abstract

An ink-jet recording method of the present invention, in which a recording is made by jetting ink onto a recording medium, is characterized in that the recording medium is formed by applying an ink acceptor on a base paper having a basis weight of 50 to 90 g/m² and a sizing degree of 5 to 100 seconds, and that the water content and/or liquid physical properties of the ink is set in suitable ranges.

Description

The present invention relates to an ink-jet recording medium and to an ink-jet recording method employing an improved recording medium and inks suited for this recording medium to provide good quality records.
Along with recent progress of recording systems such as printers, plotters and facsimile devices, ink-jet recording methods are greatly noticed because of advantages thereof such that high-speed and low- noise recording is possible and color recording is easy. However, as recording speed is increased and multicolor recording is advanced, the use of common paper as a recording medium can not afford good recording characteristics and therefore particular types of paper, i.e. so-called ink-jet recording papers become to be used. Such ink-jet recording papers include so-called non-sized paper, which is a common paper untreated with size, and a coated paper having a porous ink-absorbing layer on the surface thereof.
Of the above-mentioned ink-jet recording papers, a non-coated paper has drawbacks in that inks on adhering thereto diffuse along fibers thereof and shapes of ink dots are hence disordered, and that recording agents (dyes) penetrate inside the paper, thus the optical density of recorded images being lowered. On the other hand, a coated paper has drawbacks in that it is deficient in the feel of common paper since it is a special processed paper, and that, when ink droplets are applied thereon, microscopically ink dots are good in shape and high in optical density, but macroscopically the ink dot diameter varies from part to part of the paper, unevenness of optical density is observed, and the recorded image looks roughened.
In the manufacture of a conventional ink-jet recording paper, these drawbacks of existing ink-jet recording papers are partly attributable to unevenness of the coating thickness or to unevenness of the coating surface. In recording performances, the recording paper, if having such unevenness, will cause irregular spread of the applied ink droplets, forming no image faithful to input information, and the surface unevenness will cause disordered dot shapes, thus giving images which have not only unevenness of optical density but also coarse feel (the state resulting from the contamination of input information with noises) and lowered sharpness of images.
These various drawbacks of the existing ink-jet recording paper can be offset to some extents by various treatments of the paper. However, only with the correction of these drawbacks of the existing ink-jet recording papers., it is not always possible to obtain satisfactory recording images.
An object of the invention is to correct the above- noted drawbacks of existing ink-jet recording papers and additionally provide an ink-jet recording method which gives good quality image records.
According to a first aspect of the invention there is provided use in ink-jet recording of recording medium comprising a base paper and an ink acceptor coated on the base paper, characterised in that the base paper has a basis weight of 50 to 90 g/m² and a sizing degree of 5 to 100 seconds.
According to another aspect of the invention, there is provided an ink-jet recording method in which a recording is made by jetting ink onto a recording medium, characterised in that the recording medium comprises a base paper and an ink acceptor coated on the base paper, the base paper having a basis weight of 50 to 90 g/m² and a sizing degree of 5 to 100 seconds, and that the water content of the ink is in the range of 10 to 90 % by weight.
According to another aspect of the invention, there is provided an ink-jet recording method in which a recording is made by jetting ink onto a recording medium, characterised in that the recording medium comprises a base paper and an ink acceptor coated on the base paper, the base paper having a basis weight of 50 to 90 g/m² and a sizing degree of 5 to 100 seconds, and that the surface tension of the ink is in the range of-20 to 60 dyn/cm at 20°C.
According to a further aspect of the invention, there is provided an ink-jet recording method in which a recording is made by jetting ink onto a recording medium, characterised in that the recording medium comprises a base paper and an ink acceptor coated on the base paper, the base paper having a basis weight of 50 to 90 g/m² and a sizing degree of 5 to 100 seconds, and that the viscosity of the ink is 25 cp or less at 25°C.
The main feature of the present invention consists in the recording medium having specific structure. Important preferred features lie in the use of inks appropriate to said recording medium.
The preferred recording medium featuring first the present invention is described below in detail. The recording medium can be obtained by providing an ink acceptor on a base paper, in the other words, applying an aqueous coating composition comprising a known filler such as an extender pigment or inorganic pigment, a water-soluble binder such as polyvinyl alcohol, cellulose derivative, polyacrylamide, or starch, and/or an aqueous emulsion (if necessary, a fluorescent whitening agent, dispersant, defoaming agent, surfactant and the like are added) on the base paper of specific properties. For the purpose of securing a good feeling of the resulting recording medium, it is generally desirable to use a common paper as the base paper. In particular, a neutral paper sized in a neutral state is favorably used. That is, according to detailed studies made by the present inventors, ink-jet recording on recording media produced by using prior art papers as base materials of the media raises occasionally various problems such as defective coloration of inks or discoloration or fading of images after recording; further studies made by the present inventors, for the purpose of solving these problems have revealed that almost all the papers hitherto widely used as the base materials have been sheeted under acidic conditions, these acidic papers contain large amounts of acidic components, particularly aluminum sulfate, this aluminum sulfate and other components migrate into ink-receiving layers formed on the papers or adversely affect the ink-receiving layers, changing the layers in quality, and the aluminum sulfate causes defective coloration of dyes contained in inks and discoloration or fading of the dyes after recording.
Accordingly, in the case of the recording medium produced by using the prior art paper as the base material, a considerable amount of a cationic substance is incorporated into the ink-receiving layer to improve the water resistance and thereby reduce the adverse effect of the aluminum sulfate. However, it has been found that the light resistance of dyes is markedly lowered by such an excess cationic substance.
We have found that the above drawbacks of the prior art can be removed by using a neutral paper as the base material of the recording medium.
The neutral paper preferably used in the present invention is a paper produced by sheeting in a neutral state using not aluminum sulfate, which is used in the prior art, but such an paper-making auxiliary as an alky- lketene dimer, and is noticed in that, even after preservation over a long period (several decades to several hundred years), strength of the papers does not vary differing from the acidic paper hitherto generally used.
When such a neutral paper is used as the base material of the recording medium, an ink-receiving layer, when formed thereon, is under no detrimental influence thereof, and such drawbacks of the prior art as noted above in ink-jet recording can be overcome.
In the production of ink-jet recording media according to the prior art, such undesirable matters have been often experienced that drying of an aqueous coating material applied on base paper results in unevenness on the recording surface and curling of the recording medium, and moreover that the aqueous coating material is not uniformly applied on the base paper, forming coatings having minute thickness irregularity. From a great number of investigation data, the present inventors found that the above undesirable matters can be solved almost completely by proper control of characteristics of the base paper. That is, it was revealed that the basis weight and sizing degree of the base paper are specially important factors, and a useful recording medium has been obtained by limiting each of these factors within a specific range.
The base paper used for the recording medium in the invention has a basis weight of 50 to 90 g/m². When the basis weight of the paper is less than 50 g/m², a large portion of the aqueous coating material applied will penetrate the paper and this will tend to develop uneven coating thickness after drying. When the basis weight is heavier than 90 g/m², the paper may be too thick, inferior in feel and undesirable with respect to the recording workability of the resulting recording medium. Measurement of the basis weight of paper is possible in accordance with JIS P 8110 and P 8111, and also in the present invention, was made in accordance therewith.
In addition, the base paper used in the invention needs to have a sizing degree of 5 to 100 seconds. The sizing degree is a value indicating the resistance of paper to wetting with a liquid. Based on this value, it is possible to know the degree of the permeation of an aqueous coating material to the paper . When the sizing degree is less than 5 seconds even the binder contained in the applied coating material will diffuse into the paper and the paper will swell, resulting in waviness, i.e. minute projections and depressions, on the recording surface. On the contrary, when the sizing degree exceeds 100 seconds, the applied coating material will scarcely permeate the paper and be repelled by the paper surface, failing in perfect covering of the paper or causing curling of the recording medium on drying. The above sizing degree was measured in accordance with JIS P 8122.
As described above, the present inventors have found that papers of basis weights ranging from 50 to 90 g/m² and of sizing degrees ranging from 5 to 100 seconds are appropriate as supports for the recording media used in the present invention. In addition to the above requirements, the thickness of the base paper is desired to be in the range of 60 to 100 µm. When the paper thickness is less than 60 pm, the paper will result in inconvenient handling because of limpness of itself. When the thickness exceeds 100 µm, the recording medium will.be felt to be bulky, that is, the preferable feel thereof as a recording medium will be impaired.
The recording medium favourably used in the present invention is obtained by using such a specific base paper as described above and coating the base paper with a known aqueous coating material by a known method.
The ink preferably used in the method of the present invention is composed basically of a recording agent, i.e. a colourant such as a dye, and a liquid medium. Suitable liquid media for the ink include mixtures of water with various organic solvents. The water content of the ink used is preferably adjusted to be from 10 to 90 %, more preferably 30 to 70 %, by weight. When the water content of the ink exceeds 90 % by weight, the affinity of the ink to the surface of the recording medium may prove insufficient even for the recording surface of the above described recording medium, in which case the absorbability of the ink will be low, the ink fixing time will be prolonged, the recording speed will be restricted, and additionally with ink droplets overlap at the recording surface, inks dissimilar in colour will mix together and unnecessary spread of ink dots or disorder thereof will occur. Moreover such an ink tends to involve problems in discharge stability and solution stability of the recording agent. When the water content of the ink is less than 10 % by weight, the coloration, spread, and shape of ink dots may prove insufficient even on the recording surface of the above described recording medium.
When an ink is used for recording, it is generally important to match liquid physical properties (viscosity, surface tension, etc.) of the ink to the recording meidum. For instance, the rate of ink absorption decreases nearly in inverse proportion to the ink viscosity and thereby the ink dot diameter tends to become smaller. Such degrees of changes in recording characteristics vary with the structure and quality of the recording medium. Hence liquid physical properties of the ink need to be matched to the recording medium.
Liquid medium components of the inks used in the method of the present invention may include not only water alone but preferably mixtures of water with various water-miscible organic solvents. The viscosity of the resulting ink preferably exceeds 25 cp, more preferably 15 cp, particularly preferably 12 cp. When the ink viscosity at 25 °C exceeds 25 cp, the ink absorbability of even the above described specific recording medium will be low and therefore the ink fixing time will be prolonged and the recording speed will be restricted, and additionally when ink droplets overlap each other at the recording surface, inks dissimilar in colour will tend to mix together and unnecessary spread of ink dots or disorder thereof may occur, which is undesirable.
Further it is very desirable in the present invention to choose inks high in ability to wet the recording medium. In other words, since the surface tension of the preferred recording medium is from 40 to 50 dyn/cm, it is desirable to use inks having surface tensions near to the range. Consequently, the ink used in the method of the present invention preferably has a surface tension from 20 to 60 dyn/cm, more preferably 35 to 55 dyn/cm, particularly preferably 40 to 50 dyn/cm, at 20°C. When an ink having a surface tension lower than 20 dyn/cm is used for recording even on the above decribed desirable recording medium, the spread of ink dots may be too large though the wettability of the recording medium will be high. On the contrary, when an ink having a surface tension higher than 60 dyn/cm, the wettability of the recording medium will be reduced and as a result the absorbability of the ink and the optical density of ink dots will be reduced.
Liquid medium components of the ink used in the method of the present invention may include not only water alone but preferably mixtures of water with various water-miscible orgnaic solvents.
Water-miscible organic solvents suitable for use in the preparation of such inks as stated above include; C₁- c₄ alkyl alcohols, e.g. methanol, ethanol, n-propanol, isopropanol, n-butanol, see-butanol, tert-butanol and isobutanol; amindes, e.g. dimethylformamide and dimethu- lacetamide; ketones or ketone alcohols, e.g. acetone and diacetone alcohol; ethers, e.g. tetrahydrofurane and dioxane; nitrogent-containing heterocyclic ktones, e.g. N-methyl-2-pyrrolidone and 1,3-dimethyl-2-imidazolidinone; polyalkylene glycols, e.g. polyethylene glycol and polypropylene glycol; alkylene glycols, e.g. having 2 to 6 carbon atoms in the alkylene group, e.g. ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, and diethylene glycol; glycerol; lower alkyl ethers of polyhydric alcohols, e.g. ethylene glycol methyl ether, diethylene glycol methyl (or ethyl) ether, and triethylene glycol monomethyl (or monoethyl) ether.
Of these many water-miscible organic solvents, particularly preferred are diethylene glycol, which is a polyhydric alcohol, and triethylene glycol monomethyl (or monoethyl) ether, which is a lower alkyl ether of polyhydric alcohol. Polyhydric alcohols are particularly favorable because of the great effect thereof as wetting agents for preventing the clogging of the nozzle with the recording agent precipitated on evaporation of water from the ink.
A solubilization agent may be added to the ink. Typical examples of the solubilization agents are nitrogen-containing heterocyclic ketones and the expected action thereof it to improve markedly the solubility of the recording agent in the solvent. For example, N-methyl-2-pyrrolidone and 1,3-dimethyl-2-imidazolidinone are favorably used.
Inks per se prepared from such components as described above are superior in recording characteristics (signal responsiveness, stability for producing droplets, discharge stability, continuous recording workability for many hours, and discharge stability after a long rest), storage stability, and also in such characteristics on the above specified recording medium as dot density, dot shape, degree of spread, clearness of color, ink absorbability, and ink fixability. Additionally, various additives may be incorporated into the inks for the purpose of further improving these characteristics. These additives include; viscosity modifiers, e.g. polyvinyl alcohol, cellulosic resins, and other water-soluble resins; various surfactants of cationic, anionic, and nonionic types; surface tension modifiers, e.g. diethanolamine and triethanolamine; and pH conditioners such as buffers.
For the preparation of the ink to be used in the recording system based on the electrification of the ink, an inorganic salt such as lithium chloride, ammonium chloride, or sodium chloride is used as a resistivity modifier. Urea or thiourea is favorably used for improving the water-holding ability of the ink at a head of a discharge orifice. In the case of the recording system wherein the ink is discharged by the action of thermal energy, thermal properties (e.g. specific heat, coefficient of thermal expansion, and heat conductivity) of the ink may be conditioned.
The ink-jet recording method of the present invention employing the above specified ink and recording medium may be applied on the basis of any technique that is capable of discharging the ink effectively through nozzles and making it adhere to the above specified recording medium that is the target. Representatives of such techniques are detailed, for example, in IEEE Transactions on Industry Applications, Vol, IA-13, No. 1 (Feb. and Mar. 1977), "Nikkei Electronics" issued April 19, 1976, January 29, 1973 and May 6, 1974.
Some of these techniques are briefly described below. The first is the electrostatic attraction technique, which comprises (1) applying a strong electric field between a nozzle and an accelerating electrode placed apart from several milli meters in front of the nozzle to withdraw ink particles successively through the nozzle and applying information signals to deflecting electrodes when the ink particles fly between these electrodes or (2) jetting ink particles in response to information signals without deflecting the path of each particle, thereby recording information.
The second is the supersonic vibration technique, which comprises applying high pressure with a small pump to the ink vibrating the nozzle mechanically by means of e.g. a quartz oscillator to jet fine ink particles forcibly, giving electric charge at the same time to jetted ink particles in response to information signals, and deflecting the path of each ink particles passing between deflecting electrode plates, in response to amount of the charge given to the particles.
Another type of the supersonic vibration technique is the micro-dot ink-jet technique, which comprises discharging two groups of ink droplets different in size through a nozzle by keeping the ink pressure and vibration conditions within respective proper ranges, and utilizing the smaller ink droplets alone for recording. This technique is characterized in that fine ink droplets can be produced even by using a usual large diameter nozzle.
The third is the piezoelectric device technique, which, unlike the other techniques, utilises not any mechanical means such as a pump but a piezoelectric device. This technique comprises jetting ink droplets through a nozzle by applying electric signal to the piezoelectric device to cause mechanical displacement to pressurize the ink. Any of the above various ink-jet recording techniques can be used in the present invention.
It is possible by using the recording medium above described preferably in conjunction with inks as described to obtain good recording results, as will be shown in the following examples, such that the optical density of ink dots is uniform throughout the recording surface, shapes of almost all the ink dots are circles of similar sizes without distortion, and the spread of ink dots is appropriate. Accordingly, the invention permits very distinct, high quality images to be obtained, free of unevenness throughout the recording surface. In addition, the recording medium shows no curling after recording as well and has a good feel.
The invention is illustrated in more detail with reference to the following examples. In the examples parts are all by weight.

Example la

A coating composition was prepared by using precipitated calcium carbonate (average particle size 1 µm) as a filler and poly (vinyl alcohol) and an SBR latex as binders according to the following recipe:
This coating composition was applied on a wood-free paper, as a base paper of 52 g/m² in basis weight, 12 seconds in sizing degree, and 65 µm in thickenss by means of a blade coater to give a coating thickenss of 2 pm, and was dried in the ordinary way. The thus obtained recording medium was free of the unevenness of coating thickness and the curling.
Ink-jet recording on this recording medium was performed by using the following six kinds of inks and a recorder provided with an on-demand type of ink-jet recording head (discharge orifice diameter 65 pm, piezoelectric oscillator driving voltage 70 V, its frequency 3 KHz) for discharging ink droplets therefrom by means of the piezoelectric oscillator, and recording characteristics of the recording medium were evaluated. Thus, extremely distinct images free of recording irregularity were obtained. The recording medium did not curl after recording and was good in feel as a paper.
Ink No. Aa (composition)
Ink No. Ba (composition)
Ink No. Da (composition)
Ink No. Ea (composition)
Ink No. Fa (composition)
Results of the above evaluation of recording characteristics are shown in Table la. Measurements of the evaluation items shown in Table la were made according to the following methods:

(1) Optical density of ink dot: This was measured by using a Sakura Micro densito meter PDM-5 (supplied by Konishiroku Photo Industry Co., Ltd.).
(2) Shape of ink dot: Ink dots were observed with a stereomicroscope, and rated as follows:
- ○ ... nearly complete circles
- Δ ... slightly distorted circles
- X ... irregular shapes
(3) Degree of ink dot spread: The diameter of ink dot was measured with a stereomicroscope and the above degree was expressed by the ratio of the found diameter to the diameter of ink droplets.
(4) Clearness of color: Colors of images ink-jet recorded were compared with one another by visual observation and ranked into groups ○, Δ and X in the order of reducing clearness.
(5) Ink absorbability: Three ink droplets were shot to superpose their dots one upon another and the state of the dots after one second was rated as follows: ₅
- O... No effusion of the ink on the recording surface was observed and the image was distinct
- X ... The state other than the above
(6) Irregularity in dot diameter: Diameters of ink dots were measured with a stereomicroscope, and the irregularity was expressed by ((Standard deviation of dot diameters)/(Average value of dot diameters ))x 100

Example 2a

Various grades of base papers, as shown in Table 2a, different in sizing degree and difinite in basis weight (55 g/m²) and in thickness (70 µm) were coated similarly to Example la with the same coating composition as used therein, thus preparing recording media.
In this case, waviness was observed throughout the recording surface of sample No. 2a-l and many coat-lacking sites were observed on the recording surfaces of samples No. 2a-8 and^-No. 2a-9.
Using each sample medium shown in Table 2a, the recording procedure of Example la was followed (ink No. Ba was used). After recording, the irregularity in dot diameters was determined on each sample. Results thereof are shown in Table 2a.

Example 3a .

A coating composition was prepared by using a silica powder (tradename: Nipsil E 220 A, supplied by Nippon Silica Kogyo Co., Ltd., average particle size 1.0 pm) as a filler according to the following recipe:
A portion of this coating composition was applied on a wood-free paper of 60 g/m² in basis weight, 20 seconds in sizing degree, and 73 pm in thickness by means of a blade coater to give a coating thickness of 2 µm, and was dried in the ordinary way, giving a recording medium. On this recording medium, the unevenness of coating thickness or the coat-lacking site was not observed at all and the curling did not result. Recording on this recording medium was conducted in the same manner as in Exanple la, giving extremely distinct images free of recording irregularity. This recording medium did not curl on recording and was good in feel as paper. Results of evaluating recording characteristics are shown in Table 3a.

Example 4a

Various grades of base papers, as shown in Table 4a, different in basis weight and definite in sizing degree (12 seconds) and in thickenss (70 µm and 85 µm) were coated similarly to Example 3a with a portion of the coating composition prepared therein, thus preparing recording media.
Many coating irregularities were observed on samples No. 4a-1 and No. 4a-2 of these recording media, and sample No. 4a-9 was not good in feel, too.
Ink-jet recording on these recording media (all the samples of this example) was made in the same manner as in Example la (using ink No. Ca). Then the irregularity in dot diameters was measured on each sample. Results thereof are shown in Table 4a.

Example lb

A coating composition was prepared by using precipitated calcium carbonate (average particle size 1 pm) as a filler and polyvinyl alcohol and an SBR latex as binders according to the following recipe:
This coating composition was applied on a wood-free base paper of 52 g/m² in basis weight, 12 seconds in sizing degree and 65 µm in thickness by means of a blade coater to give a coating thickness of 2 pm, and was dried in the ordinary way. The thus obtained recording medium was free of the unevenness of coating thickness and the curling.
Ink-jet recording on this recording medium was performed by using the following 6 kinds of inks and a recorder provided with an on-demand type of ink-jet recording head (discharge orifice diameter 65 pm, piezoelectric oscillator driving voltage 70 V, its frequency 3 KHz) for discharging ink droplets therefrom by means of the piezoelectric oscillator, and recording characteristics of this recording medium were evaluated. Thus, extremely distinct images free of recording unevenness were obtained. The recording medium did not curl on recording and was good in feel as paper.
Ink No. Ab (composition)(viscosity of about 25 cp)
Ink No. Bb (composition)(viscosity of about 20 cp)
Ink No. Cb (composition)(viscosity of about 15 cp)
Ink No. Db (composition)(viscosity of about 10 cp)
Ink No. Eb (composition)(viscosity of about 5 cp) Triethylene glycol monomethyl
Ink No. Fb (composition)(viscosity about 3 cp)
Ink No. Gb (composition)(viscosity of about 1.5 cp)
Results of the above evaluation of recording characteristics are shown in Table lb. Measurements of the evaluation items shown in Table lb were made according to the methods described in Example la.

Example 2b.

Various grades of base papers, a₁ shown in Table 2b, different in sizing degree and definite in basis weight (55 g/m²) and in thickness (70 µm) were coated similarly to Example lb with the same coating composition as used therein, thus preparing recording media.
In this case, waviness developed throughout the recording surface of sample No. 2b-1 and many coat-lacking sites were observed on samples No. 2b-8 and No. 2b-9.
Using each sample medium shown in Table 2b, the recording procedure of Example lb was repeated (ink No. Cb was used). After recording, the irregularity in dot diameters was determined on each sample. Results thereof are shown in Table 2b.

Example 3b

A coating composition was prepared by using a silica powder (tradename: Nipsil E 220 A, supplied by Nippon Silica Kogyo Co., Ltd., average particle size 1.0 µm) as a filler according to the following recipe:
A portion of this coating composition was applied on a wood-free base paper of 60 g/m² in basis weight, 20 seconds in sizing degree, and 73 µm in thickness by means of a blade coater to give a coating thickness of 2 pm, and was dried in the ordinary way, giving a recording medium. On this recording medium, the unevenness of coating thickness or the coat-lacking site was not observed at all and the curling did not result. Recording on this recording medium in a similar way as in Example lb gave extremely distinct images free of record irregularity. This recording medium did not curl on recording and was good in feel as paper. Results of evaluating recording characteristics are shown in Table 3b.

Example 4b

Various grodes of base papers, as shown in Table 4, different in basis weight and definite in sizing degree (12 seconds) and in thickness (70 pm and 85 pm) were coated similarly to Example 3b with a portion of the coating composition prepared in Example 3b, thus preparing recording media.
Many coating irregularities were observed on samples No. 4b-1 and No. 4b-2 of these recording media, and sample No. 4b-9 was not good in feel, too.
Ink-jet recording on these recording media (all the samples of this example) was made in the same manner as in Example lb (using ink No. Cb). Then the irregularity in dot diameters was measured on each sample. Results thereof are shown in Table 4b.

Example lc

A coating composition was prepared by using precipitated calcium carbonate (average particle size 1 µm) as a filler and poly (vinyl alcohol) and an SBR latex as binders according to the following recipe:
This coating composition was applied on a wood-free base paper of 52 g/m² in basis weight, 12 seconds in sizing degree, and 65 pm in thickness by means of a blade coater to give a coating thickness of 2 pm, and was dried in the ordinary way. The thus obtained recording medium was free of the unevenness of coating thickness and the curling.
Ink-jet recording on this recording medium was performed by using the following 6 kinds of inks and a recorder provided with an on-demand type of ink-jet recording head (discharge orifice diameter 65 µm, piezoelectric oscillator driving voltage voltage 70 V, its frequency 3 KHz) for discharging ink droplets therefrom by means of the piezoelectric oscillator, and recording characteristics of this recording medium were evaluated. Thus, extremely distinct images free of recording unevenness were obtained. The recording medium did not curl after recording and was good in feel as paper.
Ink No. Ac (composition)(surface tension of about 60 dyn/cm)
Ink No. Bc (composition)(surface tension of about 55 dyn/cm)
Ink No. Cc (composition)(surface tension of about 50 dyn/cm)
Ink No. Dc (composition)(surface tension of about 45 dyn/cm)
Ink No. Ec (composition)(surface tension of about 40 dyn/cm)
Ink No. Fc (composition)(surface tension of about 35 dyn/cm)
Ink No. Gc (composition)(surface tension of about 30 dyn/cm)
Results of the above evaluation of recording characteristics are shown in Table lc. Measurements of the evaluation items shown in Table lc were made according to the methods described in Example la.

Example 2c

Various grades of base papers, as shown in Table 2, different.in sizing degree and definite in basis weight (55g/m²) and in thickness (70pm) were coated similarly to Example lc with the same coating composition as used therein, thus preparing recording media.
In this case, waviness developed throughout the recording surface of sample No.2c-l and many coat- laking sites were observed on samples No.2c-8 and No. 2c-9.
Using each sample medium shown in Table 2c, the recording procedure of Example lc was followed (ink No.Cc was used). After recording, the irregularity in dot diameters was determined on each sample. Results thereof are shown in Table 2c.

Example 3c

A coating composition was prepared by using a silica powder (tradename: Nipsil E220A, supplied by Nippon Silica Kogyo Co., Ltd., average particle size 1.0 pm) as a filler according to the following recipe:
A portion of this coating composition was applied on a wood-free base paper of 60g/m² in basis weight, 20 seocnds in sizing degree, and 73 µm in thickness by means of a blade coater to give a coating thickness of 2 µm, and was dried in the ordinary way, giving recording medium. On this recording medium, the un--evenness of coating thickness or the coat-lacking site was not observed at all and the curling did not result. Recording on this recording medium in a similar way as in Example 1c gave extremely distinct images free of recording irregularity. This recording medium did not curl on recording and was good in feel as paper. Results of evaluating recording characteristics are shown in Table 3c.

Example 4c

Various grades of base paper, as shown in Table 4c, different in basis weight and definite in sizing degree (12 seconds) and in thickness (70 pm and 85 pm) were coated similarly to Example 3c with a portion of the coating composition prepared in Example 3c, thus preparing recording media.
Many coating irregularities were observed on samples No.4c-l and No.4c-2 of these recording media, and sample No.4c-9 was not good in feel, too.
Then, ink-jet recording on these recording media (all the samples of this examples) was performed in the same manner as in Example lc (using ink No.Dc). Thereafter, the irregularity in dot diameters was measured on each sample. Results thereof are shown in Table 4c.

Example ld

The ink-jet recording and the evaluation of the ink recording characteristics of the recording medium were repeated similarly to Examples la to 4a except for using a neutral paper of 90 g/m in basis weight and 0 seconds in sizing degree being prepared as base paper by mixing a hard wood bleached kraft pulp and a soft wood bleached kraft pulp, as raw material pulps, in a weight ratio of 1 : 1, and beating the mixture in a refiner to a freeness of 100 ml, followed by sheeting, in place of the papers used in Examples la to 4a. Similar results to Examples la to 4a were obtained.

Example 2d

The ink-jet recording and the evaluation of the ink recording characteristics of the recording medium were repeated similarly to Examples lb to 4b except for using a neutral paper of 50g/m² in basis weight and 30 seconds in sizing degree being prepared as base paper in the same manner as in Example ld but using an alkyl- ketene dimer (Size Pine K-902, supplied by Arakawa Chemical Co., Ltd.) in the sheeting process as an auxiliary for preparing neutral paper. Similar results to Examples lb to 4b were obtained.

Example 3d

The ink-jet recording and the evaluation of the ink recording characteristics of the recording medium were repeated similarly to Examples lc to 4c except for using the same neutral paper as in Example 3d. Similar results to Examples lc to 4c were obtained.

Claims

1. Use in ink-jet recording of recording medium comprising a base paper and an ink acceptor coated on the base paper, characterised in that the base paper has a basis weight of 50 to 90 g/m2 and a sizing degree of 5 to 100 seconds.

2. Use according to claim 1, wherein the thickness of the base paper is from 60 to 100 pm.

3. Use according to claim 1 or claim 2 wherein the base paper is a neutral paper that is made in a neutral state.

4. Use according to any preceding claim wherein the ink acceptor comprises a filler and binder resin.

5. An ink-jet recording method utilising a recording medium in accordance with any preceding claim characterised in that the water content of the ink is in the range of 10 to 90 % by weight.

6. An ink-jet recording method utilising a recording medium in accordance with any of claims 1 to 4 characterised in that the viscosity of the ink is 25 cp or less at 25°C.

7. An ink-jet recording method utilising a recording medium in accordance with any of claims 1 to 4 characterised in that the surface tension of the ink is from 20 to 60 dyn/cm at 20°C.

8. A method according to any of claims 5 to 7 wherein the ink comprises a dye, water-miscible organic solvent, and water.

9. A method according to any of claims 5 to 8 wherein the water content of the ink is from 30 to 70 % by weight.

10. A method according to any of claims 5 to 9 wherein the viscosity of the ink is 15 cp or less at 25°C.

11. A method according to claim 10 wherein the viscosity of the ink is 12 cp or less at 25°C.

12. A method according to any of claims 5 to 11 wherein the surface tension of the ink is from 35 to 55 dyn/cm at 20°C.

13. A method according to claim 12 wherein the surface tension of the ink is from 40 to 50 dyn/cm at 20°C.