JPH08295077A - Recording medium, image forming method using the medium and dispersing liquid and manufacture of recording medium using the dispersing liquid - Google Patents

Abstract

PURPOSE: To provide a recording medium excellent in ink absorptivity and improved surface hardness, an image forming method using the medium, a dispersing liquid suitable for manufacturing the recording medium, and a method for manufacturing the recording medium using the dispersing liquid. CONSTITUTION: A recording medium is formed of an ink receiving layer using a dispersing liquid which contains a pigment and a water-soluble collagen and whose TI value is within the range of 1.1-5.0, on a base material, and an image is formed by giving ink droplets to the medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium used for recording with an aqueous ink and an image forming method using the medium.

[0002]

2. Description of the Related Art In recent years, the ink jet recording system is one in which minute ink droplets are ejected according to various operating principles and adhered to a recording medium such as paper to record images, characters, etc., but at high speed. It has characteristics such as low noise, easy multicoloring, great flexibility in recording patterns, and no need for development and fixing, and is rapidly spreading in various applications such as information equipment as various image recording devices. Furthermore, images formed by the multicolor ink jet system can be recorded in comparison with multicolor printing by the plate making system and printing by the color photographic system. Since it is cheaper than multicolor printing and printing, it is being widely applied to the field of full-color image recording. The recording apparatus and recording method have been improved with the improvement of recording characteristics such as high-speed recording, high-definition, full-color recording, etc. It's coming.

In order to meet such requirements, various types of recording media have been proposed in the past. For example, JP-A-55-5830 discloses an ink jet recording paper having an ink-absorptive coating layer provided on the surface of a support, and JP-A-55-51583 discloses a non-ink-jet recording paper. An example using amorphous silica is also disclosed in JP-A-55-55.
JP-A-146786 discloses an example using a water-soluble polymer coating layer.

In recent years, recording media having a coating layer using alumina hydrate having a boehmite structure have been proposed, for example, US Pat. Nos. 4,879,166 and 5;
No. 104730, JP-A-2-276670 and JP-A-3
No. 275378, No. 3-281384, and No. 5-32037.

Further US Pat. No. 4,374,804
No. 5,104,730, JP-A-58-110287, JP-A-1-97678, and JP-A-2-27667.
As disclosed in Japanese Patent Laid-Open No. 1-37456 and Japanese Patent Laid-Open No. 4-37576, it has been practiced to form an ink receiving layer having a multilayer structure by using a silica or alumina material.

In a recording medium using these alumina hydrates, the alumina hydrate has a positive charge, so that the dye in the ink can be fixed well and an image with good color development can be obtained. The advantages of using a silica compound are that it does not cause browning of the black ink that has occurred, problems with light resistance, etc., and that it is preferable to conventional recording media in terms of image quality, especially in full-color images. is there.

[0007]

However, in order to fully exert the advantages of the alumina hydrate on the recording medium, it is necessary to improve the following problems.

1) The viscosity of the coating liquid containing the alumina hydrate is high, and the viscosity increases with time, so that the coating is difficult or the solid content concentration cannot be increased, and the productivity is poor. There's a problem. On the other hand, a method of using a low-polymerization degree polymer binder or adding a monocarboxylic acid has been disclosed (JP-A-4-67985 and 4-67).
No. 986), cracks are generated, water resistance is reduced, an irritating odor is generated, and the tint of the ink is changed.

2) In order to improve ink absorbency and resolution, methods such as increasing the thickness of the ink receiving layer and forming a multilayer structure have been disclosed (US Pat. No. 5,104,510).
No. 730, Japanese Patent Publication No. 3-72460, Japanese Patent Laid-Open No. 4-3
No. 7576), there is a problem that the number of coating / drying steps of the ink receiving layer increases and a problem that cracks occur.

3) A method of adding various acids in order to maintain a good dispersion state of the alumina dispersion liquid is disclosed (JP-A-4-67985), but the tint of the ink is changed. .

In order to solve the above problems, the present inventors have proposed a recording medium having an ink receiving layer containing hydrated alumina and specific gelatin (Japanese Patent Application No. 5-2672).
33 and Japanese Patent Application No. 5-189638).

According to this recording medium, by using a specific gelatin, its sol-gel conversion is utilized,
An ink receiving layer having a good thickness can be formed stably with good productivity, and a sufficient resolution and a good image quality can be obtained.

However, in the above-mentioned recording medium, when a writing tool such as a ballpoint pen or a mechanical pencil, or a pointing stick or the like is touched on the ink receiving layer to indicate the printing portion or the non-printing portion, the surface of the ink receiving layer is damaged. There was an occasion. That is, the surface hardness of the ink receiving layer was not yet practically sufficient.

Therefore, the present invention has been made for the purpose of solving the above problems. That is, it is an object of the present invention to provide a recording medium having excellent ink absorbency and improved surface hardness, and an image forming method using the recording medium. The present invention also provides a dispersion liquid suitable for producing the recording medium and a method for producing the recording medium using the dispersion liquid.

[0015]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that, by using water-soluble collagen as a pigment and its binder, as compared with the case of using gelatin as a binder, The present inventors have found that a recording medium having a scratch-resistant ink receiving layer with improved surface hardness can be obtained while maintaining good ink absorbability, and the present invention has been completed.

That is, the present invention provides a recording medium having at least an ink receiving layer formed on a substrate, wherein the ink receiving layer contains a pigment and water-soluble collagen. To do.

Further, the present invention provides an image forming method for ejecting ink droplets from fine holes and applying the ink droplets to a recording medium for printing, using the recording medium as the recording medium. provide.

Further, the present invention provides a dispersion containing alumina hydrate and water-soluble collagen and having a TI value in the range of 1.1 to 5.0.

Furthermore, the present invention provides a method for producing a recording medium, characterized in that the dispersion is applied onto a substrate by a method such as a kiss coating method, an extrusion method, a slide hopper method and a curtain coating method. provide.

[0020]

The present invention will be described in detail below with reference to the drawings.

In the recording medium of the present invention, as shown in FIG. 1, an ink receiving layer 2 composed of a pigment and water-soluble collagen is formed on a substrate 1. The ink receiving layer of the recording medium of the present invention has a total pore volume of 0.1 to 1.0 m.
It is preferable to form it in the range of 1 / g.

When the pore volume of the ink receiving layer is larger than the above range, cracks and powder fall occur in the ink receiving layer,
If it is less than the above range, the ink absorption becomes poor,
In particular, when multicolor printing is performed, the ink easily overflows from the ink receiving layer, and bleeding easily occurs in the image.

The BET specific surface area of the ink receiving layer is preferably ^{20 to} 450 m ² / g. When it is less than this range, the glossiness of the ink receiving layer is lost, and haze is increased, so that white smear appears on the image. On the other hand, if it exceeds the above range, cracks are likely to occur in the ink receiving layer. The BET specific surface area and the pore volume can be determined by a nitrogen adsorption / desorption method after degassing at 120 ° C. for 24 hours.

Examples of pigments used in the ink receiving layer of the present invention include calcium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titania, zinc oxide, zinc carbonate, aluminum silicate, alumina hydrate, silicic acid, It is possible to use inorganic pigments such as sodium silicate, magnesium silicate, calcium silicate, and silica, organic pigments such as plastic pigments and urea resin pigments, and a combination thereof. Particularly preferred pigments from the viewpoint of image suitability such as ink absorbency and resolution are silica and alumina hydrate.

As silica, natural silica, synthetic silica, amorphous silica and the like and chemically modified silica compounds can be used, but silica having a positive charge is particularly preferable. For example, trade name "Adelite CT- 100 "
(Made by Asahi Denka Co., Ltd.), "Snowtex AK"
(Manufactured by Nissan Chemical Industries, Ltd.) and the like are commercially available and are preferably used.

Alumina hydrate has a positive charge, so that the dye in the ink can be fixed well, and an image with high gloss and good color development can be obtained as compared with other pigments. Is more preferable.

The alumina hydrate used in the present invention is represented by the following general formula.

[0028]

Embedded image In the formula, Al ₂ O _3-n (OH) _2n · mH ₂ O, n represents an integer of 0, 1, 2 or 3, and m represents 0 to 10, preferably 0 to Represents a value of 5.
Since “mH ₂ O” represents a detachable aqueous phase that is not often involved in the formation of a crystal lattice, “mH ₂ O” can take a value other than an integer. Also, when this type of alumina hydrate is calcined, m can reach zero.

As the alumina hydrate used in the present invention, amorphous alumina hydrate is suitable according to the analysis by the X-ray diffraction method, and in particular, Japanese Patent Application Nos. 5-125437 and 5-125438. No. 5-125439, 6-1
It is preferable to use the alumina hydrate described in 14571.

Although the physical properties of the pores of the alumina hydrate are adjusted in the manufacturing process, the BE of the ink receiving layer is adjusted.
In order to satisfy the requirements regarding the T specific surface area and the pore volume, it is preferable to use an alumina hydrate having a pore volume of 0.1 to 1.0 ml / g. If the pore volume of the alumina hydrate is outside the above range, it becomes difficult to set the pore volume of the ink receiving layer within the above specified range.

The BET specific surface area is 40 to
It is preferable to use an alumina hydrate that is 500 m ² / g. If the BET specific surface area of the alumina hydrate is out of the above range, it becomes difficult to set the specific surface area of the ink receiving layer within the specified range.

The water-soluble collagen used in the ink receiving layer of the present invention is collagen obtained by molecularly separating and purifying it.

Collagen is an important fibrous protein existing in all animal bodies, and is contained in most tissues and trachea such as skin and bones, cornea of the eye, endothelium of blood vessels, and connects the cells to keep the body shape of the animal body constant. Its main function is to maintain the protein in the animal body, which is indispensable for maintaining the animal body. Structurally, three polypeptide chains with a molecular weight of about 100,000 are helically wound into a fibrous form. It is a thing.

This collagen is essentially insoluble,
In recent years, solubilization technology has made remarkable progress, and technology for obtaining water-soluble collagen by separating and purifying collagen into a molecular form has been developed.
The range in which the original performance of collagen can be industrially used has expanded.

The water-soluble collagen used in the ink receiving layer of the recording medium of the present invention includes acid-soluble, neutral salt-soluble, alkali-soluble, enzyme-solubilized collagen and the like, and any of them can be used. It is preferable to use acid-soluble collagen, because soluble collagen and alkali-soluble collagen are partially modified (gelatinized) and not uniform.

The water-soluble collagen may be of type I, type II, type III or type I depending on the composition of its polypeptide chain.
There are V-type and the like, and any of them can be used, but I-type is particularly preferable, and since the enzyme-solubilized collagens of II-IV types have low gelling ability, it is preferable to use it in combination with I-type.

Furthermore, water-soluble collagen modified by various chemical modifications such as succinylation and esterification on the functional groups of the side chains of various amino acid residues, or enzymatically modified water-soluble collagen can also be used.

One of the characteristics of the water-soluble collagen of the present invention is that the molecular weight distribution is extremely narrow. That is a factor that can achieve the object of the present invention. The index (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) is used as an index showing the spread of the molecular weight distribution. In the present invention, the value is 1.0 to 2.0. Are preferable, and those of 1.0 to 1.5 are more preferable. If it is out of the range, the molecular weight distribution is widened, and if the amount on the high molecular weight side is larger than the set molecular weight range, the viscosity increases or the coating suitability decreases when mixed with the pigment, and conversely, the low molecular weight. When the number of the inks is large, the surface hardness of the ink receiving layer is lowered and cracks are generated. In the present invention, water-soluble collagen having a weight average molecular weight of 250,000 to 400,000 and a number average molecular weight of 200,000 to 400,000 is preferably used. Outside of these molecular weight ranges, the same inconveniences as those outside the Mw / Mn ratio range occur.

In the present invention, the reason why the surface hardness is improved by using the water-soluble collagen as compared with the case of using the gelatin is presumed as follows.

That is, gelatin is prepared by pre-treating collagen with acid or alkali and then hydrolyzing it to solubilize it, and most of the helix chains become one by one, and further decomposed to lower the molecular weight. . In addition, the type and number of bonds between tropocollagen contained in collagen are not constant for each part in the raw material, and these bonds are cleaved to different extents during pretreatment with acid or alkali, and are eluted during extraction. Various types of gelatin are produced in terms of molecular weight and branching degree. Furthermore, irregular hydrolysis of the main chain occurs in the concentration / drying process after extraction. For these reasons, the molecular weight distribution becomes wider than that of collagen and water-soluble collagen. Usually, the molecular weight of gelatin (not hydrolyzed or enzymatically decomposed) is about 100,000 to 200,000, and Mw / Mn is about 2 to 5.

As described above, since water-soluble collagen has a very narrow molecular weight distribution, few low molecular weight ones, and a large molecular weight, compared to gelatin containing a wide molecular weight distribution and a low molecular weight one. The layer has improved surface hardness and is less likely to be scratched.

Collagen is generally more excellent in water absorption than gelatin, and it is considered that water absorbs capillaries in the slits in the fibrils of collagen. The water-soluble collagen used in the present invention can also swell by sufficiently absorbing a large amount of water contained in the inkjet ink. Further, like gelatin, it exhibits good absorbability and swelling ability even in high boiling point solvents such as polyhydric alcohols added to the ink solvent. In the present invention, the water-soluble collagen simultaneously with the pores of the pigment such as alumina hydrate has the effect of contributing to the ink absorbability.

The water-soluble collagen used in the present invention is
You may use it, mixing with another binder. Other binders are preferably water-soluble polymers and water-dispersible polymers. For example, polyvinyl alcohol or a modified product thereof (cation modified, anion modified, silanol modified), starch or a modified product thereof (oxidized or etherified), gelatin or a modified product thereof, casein or a modified product thereof, carboxymethyl cellulose, gum arabic, hydroxy. Cellulose derivatives such as ethyl cellulose and hydroxypropyl methyl cellulose, SBR latex, NBR latex, conjugated diene-based copolymer latex such as methyl methacrylate-butadiene copolymer, functional group-modified polymer latex, vinyl-based ethylene vinyl acetate copolymer and the like. Copolymer latex, polyvinylpyrrolidone, maleic anhydride or its copolymer, acrylic acid ester copolymer and the like are preferable. Further, it is also possible to add hydrolyzed collagen whose molecular weight has been lowered by hydrolysis. These binders may be used alone or in combination of two or more.

The binder is water-soluble collagen 10
The amount is preferably 40 parts by weight or less with respect to 0 parts by weight. If used in a larger amount, the original performance of water-soluble collagen is lost and the surface hardness of the ink receiving layer is reduced.

As long as the BET specific surface area and the pore volume of the ink receiving layer are satisfied, the mixing ratio of the pigment and the binder is 1: 1 to 30: 1 by weight, preferably 5: 1 to 20 :. 1 can be arbitrarily selected. If the amount of the binder is less than the above range, the mechanical strength of the ink receiving layer is insufficient, cracks and powder fall occur,
The surface hardness also decreases. When the amount is larger than the above range, the pore volume becomes small and the ink absorption becomes poor.

The specific recording medium of the present invention is obtained by forming a ink receiving layer by coating and drying a dispersion containing a pigment and water-soluble collagen on a substrate using a coating device. As a coating method, a blade coating method, an air knife method, a roll coating method, a brush coating method,
A gravure coating method, a kiss coating method, a die coating method, an extrusion method, a slide hopper (slide bead) method, a curtain coating method, a spray method and the like can be used. If necessary, a calendar roll or the like may be used to improve the surface smoothness of the ink receiving layer.

The coating amount of the dispersion liquid is 0.5 in terms of dry solid content.
-60 g / m < ² >, more preferably 5-45 g / m < ² >, but in order to obtain good ink absorption and resolution, 15
It is necessary that the thickness of the ink receiving layer be at least μm, preferably at least 20 μm, more preferably at least 25 μm.

The water-proofing agent can be freely selected from known materials such as halogenated quaternary ammonium salts and quaternary ammonium salt polymers.

The support may be appropriately sized paper, non-sized paper, resin-coated paper or the like, a sheet-like material such as a thermoplastic film, or a cloth, and is not particularly limited.

Polyester in the case of a thermoplastic film,
It is also possible to use a transparent film such as polystyrene, polyvinyl chloride, polymethylmethacrylate, cellulose acetate, polyethylene or polycarbonate, or a sheet opaque by filling with alumina hydrate or fine foaming.

Further, in order to improve the adhesiveness between the substrate and the ink receiving layer, surface treatment such as corona treatment may be carried out, or an easily adhesive layer may be provided as an undercoat layer. Further, in order to prevent curling, a curl preventing layer such as a resin layer or a pigment layer may be provided on the back surface of the support or at a predetermined portion.

The dispersion liquid for performing the above-mentioned coating exhibits thixotropy, although the reason is not clear. Particularly, when alumina hydrate is used as a pigment, remarkable thixotropy is recognized. In the present invention, the TI value is used as an indicator of the degree of thixotropy. The TI value is a Thixotropic Index, which is a value obtained by dividing the value at high speed rotation by the value at low speed rotation by measuring the viscosity by using a rotational viscometer such as B type viscometer at different rotational speeds. Is. In this case, 6 rpm / 6
It was calculated as a numerical value of 0 rpm. When this value is greater than 1, the liquid forms a structure and exhibits thixotropic properties. The TI value in the dispersion liquid of the present invention varies depending on the solid content concentration, dispersion conditions, etc., but is preferably 1.1 to 5.0,
More preferably 1.3 to 4.5, particularly preferably 1.
It is 6 to 4.1. It is preferable to adjust the dispersion liquid in such a range.

Since the dispersion of the present invention exhibits thixotropy, its viscosity will decrease when a large force is applied. For example, when coating with a slide hopper (slide bead) system, it flows out in layers from the slide hopper. While it is in a low state, it has a low viscosity and easily flows, but when it is placed on the support, it is in a stopped state (a state in which no force is applied), so that the viscosity increases and it becomes difficult to level and becomes dull. Therefore, this thixotropy suppresses the dripping of the dispersion liquid and facilitates the formation of a thick ink receiving layer. Above T
In the range of I value or less, the thixotropic property is low or there is no thixotropic property, so that the dripping of the dispersion liquid coated on the support occurs. Above this range, a disperser to which a large force is applied is required to reduce the viscosity, and when the device becomes large or the force is insufficient, the viscosity does not decrease and coating becomes difficult.

A dispersion containing pigments and water-soluble collagen as a main component, if necessary, contains a dispersant, a thickener, a pH adjuster, a lubricant, a fluidity modifier, a surfactant, an antifoaming agent, and water resistance. Agent, foam suppressor, release agent, foaming agent, penetrant, coloring dye,
It is also possible to add a fluorescent whitening agent, an ultraviolet absorber, an antioxidant, a preservative, and an antifungal agent, if necessary.

The ink used in the image forming method of the present invention mainly contains a coloring material (dye or pigment), a water-soluble organic solvent and water. As the dye, for example, a water-soluble dye represented by a direct dye, an acid dye, a basic dye, a reactive dye, an edible pigment, etc. is preferable, and fixing property, color developability, vividness, stability in combination with a recording medium are preferable. Any material can be used as long as it gives an image satisfying the required performance such as light resistance.

The water-soluble dye is generally used by dissolving it in water or a solvent consisting of water and an organic solvent, and the solvent component thereof is preferably a mixture of water and various water-soluble organic solvents. Used, the water content in the ink is 20 to 90% by weight, preferably 60 to 90% by weight
It is preferable to adjust so as to fall within the range.

A solubilizing agent may be added to the ink in order to dramatically improve the solubility of the water-soluble dye in the solvent. To further improve the properties, a viscosity modifier,
Additives such as a surfactant, a surface tension adjusting agent, a pH adjusting agent, a specific resistance adjusting agent, and a storage stabilizer can also be added and used.

An ink jet recording method is preferable as an image forming method for recording by applying the above ink to the recording medium, and the recording method effectively separates the ink from the nozzles to form the ink on the recording medium. Any method may be used as long as it can be applied. In particular, JP-A-54-59
In the method described in Japanese Patent Publication No. 936, the ink that has been subjected to the action of thermal energy causes a rapid volume change, and the ink jet method in which the ink is ejected from the nozzle by the action force due to this state change can be effectively used. it can.

[0059]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Preparation of Alumina Hydrate Aluminum dodoxide was prepared by the method described in US Pat. No. 4,242,271. Next, the aluminum alkoxide was hydrolyzed by the method described in U.S. Pat. No. 4,202,870 to produce an alumina slurry. Water was added to this alumina slurry until the alumina hydrate solid content became 7.9%. The pH of the alumina slurry was 9.5. The pH was adjusted by adding a 3.9% nitric acid solution. Then, it was aged at an aging temperature of 100 ° C. in an oven for 10 hours (before aging, pH 6.
6) and further spray-dried at 75 ° C. to obtain an alumina hydrate. The BET specific surface area of this alumina hydrate is 15
It was 0.3 m ² / g and the pore volume was 0.68 ml / g. The pore volume was measured by using nitrogen adsorption / desorption after degassing at 120 ° C. for 24 hours (measuring device: AutoSorb I manufactured by Cantachrome), and the BET specific surface area was determined by the method of Brunauer et al. It was calculated by using.

Example 1 White polyester film (manufactured by Toray Industries, Inc., Lumirror X-21, thickness 100 μm)
After corona treatment, a liquid having the following composition was applied on the treated surface by a slide hopper method to form an ink receiving layer having a thickness of 30 μm, and a recording medium of the present invention was obtained.

Alumina hydrate 13.6 parts by weight Water-soluble collagen 1.4 parts by weight (Collmatrix Type IA, manufactured by Nitta Gelatin Industry Co., Ltd.) Ion-exchanged water 85 parts by weight Surface of ink receiving layer of this recording medium The hardness was 2H to 3H as evaluated by pencil hardness (according to JIS K5400; however, the load was changed from 1 kg to 500 g). Further, when touched with a mechanical pencil to the extent shown in the drawing, no particular scratches were found and good results were obtained.

Further, with respect to the obtained recording medium, 1 m
Inkjet recording is performed with an ink having the following composition by using an inkjet printer having four nozzles Y, M, C, and Bk, each of which has 128 nozzles at a nozzle interval of 16 in m. The absorbency, beading and water resistance were evaluated. Ink composition Ink dye 5 parts Ethylene glycol 10 parts Polyethylene glycol 10 parts Water 75 parts The ink dyes used are as follows.

Y: C.I. I. Direct Yellow 86 M: C.I. I. Acid Red 35 C: C.I. I. Direct Blue 199 Bk: C.I. I. Food Black 2 The ink absorbency was examined by touching the recording portion with a finger to check the ink absorption state on the surface of the recording medium immediately after solid printing of the Y, M, CC, and Bk inks of the above composition in a single color or multiple colors. As a result, the ink amount is 300% (the ink amount in single color printing is 10%
Even when it was set to 0%), the ink did not adhere to the finger and good results were obtained.

Example 2 Colloidal silica (produced by Asahi Denka Co., Ltd., Adelite CT-) was used as the alumina hydrate of Example 1.
The recording medium was manufactured and evaluated in the same manner as in Example 1 except that the recording medium was changed to 100).

As a result, the surface hardness of the ink receiving layer was 2H to 3H in terms of pencil hardness, and scratches did not occur even when touched with a mechanical pencil, and good results were obtained. Also, regarding the ink absorbency, even when the ink amount was 300%, good results were obtained without the ink adhering to the finger. (Comparative Example 1) Japanese Patent Application No. 5-
The recording medium was manufactured and evaluated in the same manner as in Example 1 except that gelatin a described in Example 189638 was used.

As a result, regarding the ink absorbability, even if the ink amount was 300%, the ink did not adhere to the finger, and a good result was obtained, but the surface hardness of the ink receiving layer was F to H, and the ink receiving layer was touched with a mechanical pencil. I found it scratched.

[0068]

As described above, according to the present invention,
By forming the ink receiving layer using a pigment such as alumina hydrate and water-soluble collagen as a binder thereof, it is possible to improve the surface hardness of the ink receiving layer of the recording medium and prevent scratches.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the basic structure of a recording medium of the present invention.

[Explanation of symbols]

 1 substrate 2 ink receiving layer

Claims (9)

[Claims] 1. A recording medium having an ink receiving layer formed on at least a substrate, wherein the ink receiving layer contains a pigment and water-soluble collagen. 2. The recording medium according to claim 1, wherein the pigment is an alumina hydrate. 3. The ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the water-soluble collagen.
Is in the range of 1.0 to 2.0. 4. An image forming method in which a small ink droplet is ejected from a fine hole and is applied to a recording medium to perform printing.
An image forming method using the recording medium according to any one of claims 1 to 3. 5. The image forming method according to claim 4, wherein the ink droplets are ejected by an inkjet method. 6. The image forming method according to claim 5, wherein the inkjet method is a method in which thermal energy is applied to the ink to eject ink droplets. 7. A dispersion liquid containing alumina hydrate and water-soluble collagen, and having a TI value in the range of 1.1 to 5.0. 8. A method for producing a recording medium, which comprises applying the dispersion according to claim 7 onto a substrate. 9. The manufacturing method according to claim 8, wherein the coating is performed using a method selected from the group consisting of a kiss coating method, an extrusion method, a slide hopper method, and a curtain coating method.