JP2017213731A - Inkjet recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet recording medium excellent in waterproofness and ink absorption.SOLUTION: An inkjet recording medium comprises: a first porous layer which is an outermost surface layer and contains inorganic particles and a water-insoluble resin; a second porous layer which is next to the first porous layer and contains inorganic particles and a water-soluble resin; and a substrate. The contact angle (°) of water 60 seconds after contact of the water with the surface of the first porous layer is 50° or greater.SELECTED DRAWING: None

Description

  The present invention relates to an inkjet recording medium.

  In recent years, the ink jet recording apparatus has been increasingly used for printing advertisements such as posters. In particular, an inkjet recording medium used in printing advertisements for outdoor posting is required to have excellent water resistance. Usually, an ink jet recording medium is provided with a porous layer on a base material to improve ink absorbability. In order to improve not only ink absorbability but also water resistance in an ink jet recording medium, various studies have been made on the porous layer of the recording medium. It has been proposed to form a water-repellent layer containing inorganic particles of hydrophobic silica on a porous layer (see Patent Document 1). A porous layer containing amorphous synthetic silica of inorganic particles, a water-insoluble resin, and a water-soluble resin has been proposed (see Patent Documents 2 and 3).

JP 2012-196922 A JP 2002-137537 A JP 2002-283714 A

  The present inventors examined using the inkjet recording medium described in patent documents 1-3. As a result of evaluating the ink jet recording medium described in Patent Document 1, it was found that sufficient ink absorbability was not obtained although water resistance was obtained. Thus, water resistance and ink absorbency are in a trade-off relationship, and the ink jet recording medium described in Patent Document 1 can achieve both water resistance and ink absorbency at a sufficiently high level. There wasn't. Furthermore, as a result of evaluating the inkjet recording media described in Patent Documents 2 and 3, it was not possible to achieve both water resistance and ink absorption at a sufficiently high level.

  Accordingly, an object of the present invention is to provide an ink jet recording medium excellent in water resistance and ink absorbability.

  The present invention is an outermost surface layer, a first porous layer containing inorganic particles and a water-insoluble resin, a second porous layer adjacent to the first porous layer and containing inorganic particles and a water-soluble resin. An ink jet recording medium having a porous layer and a substrate, wherein a contact angle (°) of water after 60 seconds from the contact of water with the surface of the first porous layer is 50 °. The present invention relates to a recording medium characterized by the above.

  According to the present invention, an ink jet recording medium excellent in water resistance and ink absorbability can be provided.

It is a graph which shows transition of the contact angle of water with progress of time.

  Hereinafter, embodiments of the present invention will be described in detail. In the present invention, hereinafter, an inkjet recording medium may be referred to as a “recording medium”. In addition, the inorganic particles are secondary particles formed by collecting a plurality of primary particles. Various physical property values are values at a temperature of 25 ° C. unless otherwise specified.

  First, the present inventors have studied the reason why it is difficult to achieve both water resistance and ink absorbency in the recording media described in Patent Documents 1 to 3. In the recording medium described in Patent Document 1, the particles of hydrophobic silica contained in the water-repellent layer are bonded by -Si-O- bonds. Since this -Si-O- bond forms a three-dimensional network structure and fills voids formed between the particles of hydrophobic silica, the recording medium described in Patent Document 1 has excellent water resistance. However, the inventors speculate that the ink absorbability is insufficient. The recording media described in Patent Documents 2 and 3 contain a water-insoluble resin and a water-soluble resin in the outermost surface layer of the porous layer. Therefore, both the recording media described in Patent Documents 2 and 3 have a water contact angle (°) 60 seconds after water contacts the surface of the outermost porous layer of the recording medium. It becomes less than 50 °. As a result, the water resistance becomes insufficient, and it has been found that both water resistance and ink absorbability cannot be achieved at a sufficiently high level.

  The inventors of the present invention have reached the present invention based on the studies in Patent Documents 1 to 3.

  The recording medium according to the present invention has a first porous layer as the outermost surface, a second porous layer adjacent to the first porous layer, and a substrate. The first porous layer contains inorganic particles and a water-insoluble resin, and the contact angle (°) of water 60 seconds after water contacts the surface of the first porous layer is 50 More than °. Thereby, the water resistance of the recording medium is obtained. The mechanism will be described.

  Since the first porous layer contains a water-insoluble resin having no hydrophilic group such as a hydroxy group, the first porous layer has high hydrophobicity. Therefore, the water that has contacted the surface of the first porous layer is difficult to be absorbed up to the inside of the layer. Further, compared with the water repellent layer of the recording medium described in Patent Document 1, the ink absorbability is also excellent. The inorganic particles contained in the first porous layer are secondary particles made up of a plurality of primary particles. Since the plurality of primary particles are bonded through the water-insoluble resin, pores are formed between the plurality of primary particles, and ink absorbability is obtained.

  The contact angle decreases with time, but after a certain time, the value does not change. According to the study by the present inventors, it was found that the contact angle (°) of water was substantially constant 60 seconds after water contacted the surface of the first porous layer. (FIG. 1). Therefore, in the present invention, in specifying the water resistance of the recording medium, the provision of “the contact angle of water 60 seconds after the water contacts the surface of the first porous layer” is adopted. And the water contact angle (°) 60 seconds after the water contacts the surface of the first porous layer is 50 ° or more, so that the water contacts the surface of the first porous layer. Then, water is easily repelled on the surface, so that water resistance is obtained.

  On the other hand, when ink is ejected from an ink jet recording head and an image is recorded on a recording medium, the surface tension of the ink is lower than the surface tension of water. Specifically, the surface tension of water is 70 mN / m, whereas the surface tension of ink is usually 40 mN / m or less. Ink having a lower surface tension than water has the first porous layer even if the contact angle of water is 50 ° or more 60 seconds after the water contacts the surface of the first porous layer. Can penetrate. Since the inorganic particles contained in the first porous layer are secondary particles formed by collecting a plurality of primary particles, pores are formed between the plurality of primary particles. The ink enters the pores between the primary particles and reaches the boundary between the first porous layer and the second porous layer.

  The second porous layer contains inorganic particles and a water-soluble resin. Thereby, ink absorbability is obtained. The mechanism will be described. Since the second porous layer contains a water-soluble resin having a hydrophilic group such as a hydroxy group, the second porous layer has high hydrophilicity. Since the ink is easily compatible with the second porous layer having high hydrophilicity, the second porous layer has a power to draw the ink that has entered the first porous layer. As a result, the absorption of the ink reaching the boundary between the first porous layer and the second porous layer is promoted. As a result, it is estimated that ink absorbability can be obtained.

<Recording medium>
The recording medium of the present invention has a first porous layer that is the outermost surface layer, a second porous layer adjacent to the first porous layer, and a substrate. Hereinafter, components that can be used in the recording medium will be described. References to “(meth) acrylic acid” and “(meth) acrylate” represent “acrylic acid, methacrylic acid” and “acrylate, methacrylate”, respectively. In the present invention, the thickness of the first porous layer, the second porous layer, and the substrate is determined by cutting a section of the recording medium with a microtome and observing the section with a scanning electron microscope. Let it be the average value of the values obtained by measuring the thickness of any 100 or more points of the material.

(First porous layer and second porous layer)
The first porous layer and the second porous layer may be provided only on one side of the substrate, or may be provided on both sides. The total coating amount (g / m ² ) of the first porous layer and the second porous layer varies depending on the required ink absorption amount, but is 15 g in dry coating amount (g / m ² ). / M ² or more and 40 g / m ² or less is preferable. If the dry coating amount (g / m ² ) is less than 15 g / m ² , the area where ink can be absorbed becomes narrow, and ink absorbability may not be sufficiently obtained. Furthermore, if the dry coating amount (g / m ² ) exceeds 40 g / m ² , the coating amount is too large and cracks are likely to occur.

  The ratio of the thickness (μm) of the first porous layer to the total thickness (μm) of the first porous layer and the second porous layer is 8% or more and 30% or less. It is preferable. If the proportion is less than 8%, the proportion of the first porous layer in all the porous layers is small, so that sufficient water resistance may not be obtained. When the ratio exceeds 30%, the ratio of the second porous layer in all the porous layers is small, and ink absorbability may not be sufficiently obtained.

[First porous layer]
The first porous layer contains inorganic particles and a water-insoluble resin, and the contact angle (°) of water after 60 seconds from the contact of water with the surface of the first porous layer is 50 ° or more. It is preferable that it is 50 degree or more and 85 degrees or less. Here, the contact angle is measured using an automatic absorption characteristic tester. The value of the contact angle (°) of water after 60 seconds from the contact of water with the surface of the first porous layer can be adjusted by the type and amount of the water-insoluble resin contained in the first porous layer. .

  The thickness (μm) of the first porous layer is preferably 3 μm or more and 10 μm or less, and more preferably 4 μm or more and 6 μm or less. When the thickness is less than 3 μm, the distance between the surface of the recording medium and the boundary surface between the first porous layer and the second porous layer is reduced. The surface of the second porous layer is hydrophilic and easily blends with water. As a result, sufficient water resistance may not be obtained. When the thickness exceeds 10 μm, the distance between the surface of the recording medium and the boundary surface between the first porous layer and the second porous layer becomes long. Since it takes time for the ink adhering to the surface of the recording medium to enter the boundary surface between the first porous layer and the second porous layer, the ink absorbability may not be sufficiently obtained.

[Inorganic particles]
The oil absorption amount (mL / 100 g) of the inorganic particles contained in the first porous layer is preferably 150 mL / 100 g or more and 240 mL / 100 g or less, and more preferably 160 mL / 100 g or more and 180 mL / 100 g or less. When the present inventors examined, the amount of the water-insoluble resin entering the pores between the plurality of primary particles of the inorganic particles contained in the first porous layer depends on the oil absorption amount of the inorganic particles. found. This oil absorption is measured according to the “refined linseed oil method” defined in JIS K 5101-13-1. When the oil absorption amount of the inorganic particles is less than 150 mL / 100 g, the water-insoluble resin is less likely to enter the pores, but the amount of ink absorbed is also small, and the ink absorbability may not be sufficiently obtained. When the oil absorption of the inorganic particles exceeds 240 mL / 100 g, the water-insoluble resin easily enters the pores, and the water-insoluble resin that enters the pores between the inorganic particles (secondary particles) in the first porous layer. Since the amount decreases, water resistance may not be sufficiently obtained.

Further, the BET specific surface area (m ² / g) of the inorganic particles is preferably 45 m ² / g or more. Here, the BET specific surface area (m ² / g) is a specific surface area determined by the BET method. The BET method is a method in which a specific surface area of a sample is measured from an adsorbed amount by adsorbing a molecule or ion of a known size on the sample surface. In the present invention, nitrogen gas is used as the gas adsorbed on the sample. When the BET specific surface area (m ² / g) of the inorganic particles is less than 45 m ² / g, the particle size of the inorganic particles is too large, so that the area in contact with the resin is reduced, and the inorganic particles and the resin are closely bonded. It becomes difficult to do.

  The oil absorption amount and the BET specific surface area of the inorganic particles can be measured as follows. First, the first porous layer is scraped off and heated at a temperature of 600 ° C. for 2 hours. Here, when scraping off the first porous layer, care must be taken not to scrape off the second porous layer. The residue obtained by heating the first porous layer can be regarded as inorganic particles contained in the first porous layer.

  Examples of inorganic particles include alumina hydrate, alumina, silica, colloidal silica, titanium dioxide, zeolite, kaolin, talc, hydrotalcite, zinc oxide, zinc hydroxide, aluminum silicate, calcium silicate, magnesium silicate, and calcium carbonate. , Zirconium oxide, zirconium hydroxide and the like. These inorganic particles can be used alone or in combination of two or more as required. Among these, it is preferable to use silica having relatively large pores between the primary particles as the inorganic particles. Even if the resin enters the pores between the primary particles, the pores are not easily filled with the resin, and the ink can be absorbed.

Silica is roughly classified into a wet method and a dry method (gas phase method) depending on its production method. Among these, silica obtained by a wet method (hereinafter referred to as “wet method silica”) is preferably used. Wet process silica has more silanol groups in which hydroxy groups are directly bonded to silicon on the silica surface than silica obtained by a dry process. The hydroxy group has an oxygen atom polarized to δ ⁻ and a hydrogen atom polarized to δ ⁺ . Therefore, a hydrogen bond is formed between the δ ⁻ polarized oxygen atom of one silica and the δ ⁺ polarized hydrogen atom of the other silica, and a plurality of silicas are closely bonded in the layer. Is possible. Preferable examples of the wet process silica include precipitation process silica and gel process silica. Precipitated silica can be produced, for example, by reacting sodium silicate and sulfuric acid under alkaline conditions. Silica particles on which the particles have grown during the production process are aggregated and settled, and then processed through filtration, washing, drying, pulverization and classification. The silica secondary particles produced by this method are agglomerated particles that are relatively easily pulverized. The gel method silica can be produced, for example, by reacting sodium silicate and sulfuric acid under acidic conditions. In the case of gel method silica, small silica particles are dissolved in the production process and re-precipitated so that primary particles of relatively large particles are bonded to each other, so that relatively hard aggregated particles having an internal void structure are formed.

  The average secondary particle diameter (μm) of the inorganic particles is preferably 0.2 μm or more and 10.5 μm or less, and more preferably 3.0 μm or more and 9.0 μm or less. Here, the average secondary particle diameter (μm) of the inorganic particles is measured by a laser diffraction method. The content (mass%) of the inorganic particles in the first porous layer is preferably 45.00 mass% or more and 70.00 mass% or less, and is 55.00 mass% or more and 65.00 mass% or less. More preferably it is.

(Water-insoluble resin)
A water-insoluble resin is a resin having no hydrophilic group such as a hydroxy group. Compared to resins having ester groups that are easily hydrolyzed, such as water-insoluble polyester-modified urethane resins, acrylic resins, polycarbonate-modified urethane resins, and polyether-modified urethane resins are hardly hydrolyzed and have high hydrophobicity. From the viewpoint of water resistance, the water-insoluble resin is preferably at least one selected from the group consisting of a water-insoluble acrylic resin, a water-insoluble polycarbonate-modified urethane resin, and a water-insoluble polyether-modified urethane resin.

  The acrylic resin preferably has a unit derived from alkyl (meth) acrylate. Examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, and lauryl (meth). Alkyl (meth) acrylates having no hydroxy group such as acrylate and stearyl (meth) acrylate; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate and the like Examples include alkyl (meth) acrylates having a hydroxy group. A homopolymer of these monomers may be used, or a copolymer of these monomers and other monomers may be used. Other monomers include styrenes such as styrene, vinyl toluene, vinyl benzoic acid, α-methyl styrene, p-hydroxymethyl styrene, styrene sulfonic acid, and derivatives thereof; methyl vinyl ether, butyl vinyl ether, methoxyethyl vinyl ether, N -Vinyl ethers such as vinyl pyrrolidone, 2-vinyl oxazone, vinyl sulfonic acid and derivatives thereof.

  Hereinafter, the polycarbonate-modified urethane resin and the polyether-modified urethane resin are collectively referred to as “urethane resin”. The urethane resin preferably has units derived from polyisocyanate and polyol. Polyisocyanate is a compound having two or more isocyanate groups. Examples of polyisocyanates include aromatic polyisocyanates, aliphatic isocyanates, and alicyclic polyisocyanates. Examples of the aromatic polyisocyanate include tolylene diisocyanate, diphenylmethane diisocyanate, polymeric diphenylmethane diisocyanate, tolidine diisocyanate, naphthalene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, and the like. Examples of the aliphatic isocyanate include hexamethylene diisocyanate and trimethylhexamethylene diisocyanate. Examples of the alicyclic polyisocyanate include isophorone diisocyanate, cyclohexane-1,3-diisocyanate, and cyclohexane-1,4-diisocyanate. These may be used individually by 1 type and may be used in combination of 2 or more type. The proportion of units derived from polyisocyanate in the urethane resin is preferably 10.00 mass% or more and 80.00 mass% or less.

  Examples of the polyol include polycarbonate polyol and polyether polyol. Examples of the polycarbonate polyol include polyhexamethylene carbonate. Examples of the polyether polyol include polypropylene glycol, polyethylene glycol, and polytetramethylene glycol. These may be used individually by 1 type and may be used in combination of 2 or more type. The proportion of units derived from polyol in the urethane resin is preferably 5.00% by mass or more and 40.00% by mass or less.

  The content (% by mass) of the water-insoluble resin (solid content) contained in the first porous layer is preferably 30.00% by mass or more and 50.00% by mass or less, and preferably 35.00% by mass or more and 45% by mass. More preferably, it is 0.000 mass% or less. Further, the content (% by mass) of the water-insoluble resin is 0.50 times or more and 1.00 times or less in terms of the mass ratio with respect to the content (% by mass) of the inorganic particles in the first porous layer. Preferably, it is 0.60 times or more and 0.80 times or less. When the ratio is less than 0.50, the amount of water-insoluble resin with respect to the inorganic particles is reduced, the surface of the first porous layer is not easily hydrophobic, and sufficient water resistance cannot be obtained. There is a case. When the ratio exceeds 1.00 times, the amount of water-insoluble resin increases with respect to the inorganic particles, and thus ink absorbability may not be sufficiently obtained.

(Water-soluble resin)
The first porous layer does not contain a water-soluble resin or contains a water-soluble resin, and the content (% by mass) of the water-soluble resin in the first porous layer is the content of a water-insoluble resin. The mass ratio with respect to (mass%) is preferably 0.11 times or less. When the ratio exceeds 0.11 times, the ratio of the water-soluble resin having a hydroxyl group that easily forms a hydrogen bond with water increases, so that the hydrophilicity of the surface of the first porous layer is easily increased. As a result, sufficient water resistance may not be obtained.

  Examples of water-soluble resins include starch, gelatin, casein, or modified products thereof; cellulose derivatives such as methyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose; polyvinyl alcohol (fully saponified, partially saponified, low saponified, etc.) or modified Products (cation modified products, anion modified products, silanol modified products, etc.); urea resins, melamine resins, epoxy resins, epichlorohydrin resins, urethane resins, polyethyleneimine resins, polyamide resins, polyvinylpyrrolidone resins, Examples thereof include polyvinyl butyral resins, poly (meth) acrylic acid or copolymer resins thereof, acrylamide resins, maleic anhydride copolymer resins, and polyester resins. Of these, polyvinyl alcohol or a modified product thereof is preferably used as the water-soluble resin.

[Second porous layer]
The second porous layer is adjacent to the first porous layer and contains inorganic particles and a water-soluble resin. A plurality of other layers may be provided between the substrate and the second porous layer.

[Inorganic particles]
The content (mass%) of the inorganic particles in the second porous layer is preferably 60.00 mass% or more and 80.00 mass% or less, and is 65.00 mass% or more and 75.00 mass% or less. More preferably it is. As the inorganic particles contained in the second porous layer, the same inorganic particles as those contained in the first porous layer can be used.

(Water-soluble resin)
The content (% by mass) of the water-soluble resin in the second porous layer is preferably a mass ratio with respect to the content (% by mass) of the inorganic particles in the second porous layer and is 0.50 times or less. More preferably, it is 0.20 times or more and 0.40 times or less. When the ratio is larger than 0.50 times, the water-soluble resin tends to enter the pores between the primary particles, and the ink absorbability may not be sufficiently obtained. The content (% by mass) of the water-soluble resin in the second porous layer is preferably 5.00% by mass or more and 50.00% by mass or less, and 8.00% by mass or more and 30.00% by mass or less. It is more preferable that The water-soluble resin contained in the second porous layer can be the same as the water-soluble resin contained in the first porous layer.

[Other ingredients]
The first porous layer and the second porous layer may contain other additives other than those described so far. Specifically, cross-linking agents, pH adjusters, thickeners, fluidity improvers, antifoaming agents, antifoaming agents, surfactants, mold release agents, penetrating agents, coloring pigments, coloring dyes, fluorescent whitening agents UV absorbers, antioxidants, antiseptics, antifungal agents, water resistance agents, ink fixing agents, curing agents, weathering materials, and the like. Examples of the crosslinking agent include aldehyde compounds, melamine compounds, isocyanate compounds, zirconium compounds, titanium compounds, amide compounds, aluminum compounds, boric acid, borates, carbodiimide compounds, oxazoline compounds, and the like. It is done. The ink fixing agent preferably contains a cationic resin other than the acrylic resin or urethane resin, or a polyvalent metal salt.

  Examples of the cationic resin include polyethyleneimine resins, polyamine resins, polyamide resins, polyamide epichlorohydrin resins, polyamine epichlorohydrin resins, polyamide polyamine epichlorohydrin resins, polydiallylamine resins, and dicyandiamide condensates.

  Examples of the polyvalent metal salt include calcium compounds, magnesium compounds, zirconium compounds, titanium compounds, and aluminum compounds. As the polyvalent metal salt, a calcium compound is preferable, and calcium nitrate tetrahydrate is more preferable.

(Base material)
The substrate is preferably paper having a resin layer, plastic film, and cloth. A substrate provided with a plurality of layers may be used. Examples of the paper having a resin layer include paper having a resin layer containing a thermoplastic resin. Examples of the thermoplastic resin include an acrylic resin, an acrylic silicone resin, a polyolefin resin, and a styrene-butadiene copolymer. Examples of the paper include paper made from wood pulp as a main raw material, and if necessary, synthetic pulp such as polypropylene and synthetic fibers such as nylon and polyester. Examples of the plastic film include polyethylene, polyethylene terephthalate (PET), polypropylene, polyvinyl chloride, and polyester. Examples of the cloth include cotton, hemp, rayon, nylon, and acrylic. The thickness (μm) of the substrate is preferably 50 μm or more and 400 μm or less, and more preferably 70 μm.

<Method for manufacturing recording medium>
As a method for producing a recording medium, there are a step of preparing a coating liquid for the first porous layer and the second porous layer, and a step for applying the first porous layer and the second porous layer. There is a method for manufacturing a recording medium including a step of applying a working liquid to a substrate. Hereinafter, a method for manufacturing the recording medium will be described.

  Examples of the method for applying the first porous layer and the second porous layer to the substrate include the following methods. First, a coating solution for the first porous layer and the second porous layer is prepared. And the recording medium of this invention can be obtained by apply | coating and drying the said coating liquid on a base material. Coating methods for the coating liquid include roll coaters, blade coaters, bar coaters, air knife coaters, gravure coaters, reverse coaters, transfer coaters, die coaters, kiss coaters, rod coaters, curtain coaters, and extrusion coaters. For example, a coater using a slide hopper system can be used. Furthermore, you may heat a coating liquid at the time of coating.

  Further, prior to the application of the first porous layer and the second porous layer, a surface treatment liquid containing a surface treatment agent is applied to the surface of the base material on which the coating liquid is applied. May be. By doing so, the wettability to the base material of a coating liquid increases, and the adhesiveness of an ink receiving layer and a base material can be improved. In this case, examples of the surface treating agent include thermoplastic resins such as acrylic resins, urethane resins, polyester resins, polyethylene resins, polyvinyl chloride resins, polypropylene resins, polyamide resins, and styrene butadiene copolymers, and silane coupling agents. It is done. These can be used individually by 1 type or in combination of 2 or more types. In addition, the surface treatment liquid may contain inorganic particles as long as the effects of the present invention are not impaired. As the inorganic particles, those listed above can be used. In addition, as a drying method after coating, use hot air dryers such as straight tunnel dryers, arch dryers, air loop dryers, sine curve air float dryers, and dryers using infrared rays, heated dryers, microwaves, etc. The method of doing is mentioned.

<Image recording method>
It is preferable to record an image by applying aqueous ink to the recording medium of the present invention. The method for applying ink to the recording medium is not particularly limited, but it is preferable to use an ink jet recording method. This method is a method of recording an image on a recording medium by ejecting ink with an ink jet recording head. Examples of the method for ejecting ink include a method for applying mechanical energy to the ink and a method for applying thermal energy to the ink.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited at all by the following Example, unless the summary is exceeded. In addition, what is described as “parts” and “%” with respect to the component amounts is based on mass unless otherwise specified.

<Preparation of recording medium>
(Base material)
Polypropylene synthetic paper (New YUPO FGS110, manufactured by YUPO Corporation) was prepared as a base material.

(Preparation of dispersions 1 to 3, 6, and 7 of inorganic particles)
After adding the inorganic particles shown in Table 1 to pure water, the mixture is stirred for 30 minutes with a mixer, and the dispersions 1 to 3 of inorganic particles whose solid content (mass%) is 20.00%, 6 and 7 were obtained.

(Preparation of inorganic particle dispersion 4)
Into pure water, 1.50 parts of methanesulfonic acid and inorganic particles listed in Table 1 were added in this order, and then treated with a high-pressure homogenizer. The solid content (mass%) was 27.00%. A dispersion 4 of inorganic particles was obtained.

(Preparation of inorganic particle dispersion 5)
To pure water, 5.00 parts of polydiallyldimethylamine hydrochloride (Charol DC902P, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and inorganic particles listed in Table 1 were added in order. Then, it processed twice with the high voltage | pressure homogenizer, and obtained the dispersion liquid 5 of the inorganic particle whose content (mass%) of solid content is 20.00%.

The average secondary particle diameter (μm) of the inorganic particles 1 to 7 in the dispersion was measured using a laser diffraction device (SALD2300, manufactured by Shimadzu Corp.). Further, the oil absorption (mL / 100 g) of the inorganic particles 1 to 7 in the dispersion was measured by an oil method using purified sesame. Furthermore, the BET specific surface area (m ² / g) of the inorganic particles 1 to 7 in the dispersion was measured using an automatic specific surface area / pore distribution measuring device (Tristar 3000, manufactured by Shimadzu Corporation). The average secondary particle diameter (μm), oil absorption, and BET specific surface area (m ² / g) of inorganic particles 1 to 7 in the dispersion are shown in Table 1, respectively.

(Preparation of coating solutions 1 to 24)
Each component (part) described in Tables 2 and 3 was placed in a beaker and mixed with a stirrer to obtain coating liquids 1 to 24. Mobile 7820 (resin content: 45.00%) is a liquid containing a water-insoluble acrylic resin made by Nippon Gosei. Hydran WLS210 (resin content is 35.00%) is a liquid containing a water-insoluble polycarbonate-modified urethane resin made by DIC. Hydran WLS201 (resin content is 35.00%) is a liquid containing a water-insoluble polyether-modified urethane resin made by DIC. NS310X (resin content is 14.00%) is a liquid containing a water-insoluble polyester-modified urethane resin made of Takamatsu Yushi.

(Recording media 1 to 24)
On the base material, the coating solution for the second porous layer described in Table 4 was coated with a bar coder, and dried with hot air at a temperature of 115 ° C. for 3 minutes. On the second porous layer, the coating solution for the first porous layer shown in Table 4 was applied with a bar coder, and dried with hot air at a temperature of 115 ° C. for 3 minutes to obtain recording media 1 to 24. It was. Table 4 shows combinations of the respective coating liquids used in the first porous layer and the second porous layer. Further, the thickness (μm) of each of the first porous layer and the second porous layer, and the contact angle of water (°) after 60 seconds from the contact of water with the surface of the first porous layer. ).

(Recording medium 25-28)
The recording medium described in Example 1 of Patent Document 1 was used as the recording medium 25. The recording medium described in Example 7 of Patent Document 2 was used as the recording medium 26. The recording medium described in Example 10 of Patent Document 2 was used as the recording medium 27. The recording medium described in Example 1 of Patent Document 3 was used as the recording medium 28. Table 4 shows the layer thicknesses of the recording media 25 to 28 and the contact angle (°) of water 60 seconds after water contacts the surface of the first porous layer. The recording medium 25 has a water repellent layer on the first porous layer. The thickness of the water repellent layer was 5 μm, and the contact angle (°) of water 60 seconds after water contacted the surface of the water repellent layer was greater than 50 °.

  The thickness (μm) of the first porous layer and the second porous layer is determined by cutting a section of the recording medium with a microtome and observing the section with a scanning electron microscope. The average value of the values obtained by measuring the thickness of 100 or more points was used. The contact angle (°) of water was measured using an automatic absorption characteristic tester (1100 DAT machine, manufactured by FIBRO).

<Evaluation>
In the present invention, in the evaluation criteria for the following items, 3 to 5 are acceptable levels, and 1 or 2 are unacceptable levels.

(water resistant)
Flowing water at a temperature of 80 ° C. was allowed to flow for 48 hours on the surface of the obtained recording medium, and then dried overnight. Black paper New Color R (manufactured by Lintec) was pressed against the surface of the recording medium while applying a load of 75 g / cm ² , using a Gakushin type friction fastness tester (AB-301 COLOR FASTNESS RUBBING TESTER, manufactured by Tester Sangyo). It was reciprocated 20 times. The optical density of the black paper portion not in contact with the ink receiving layer surface and the black paper portion in contact with the ink receiving layer surface was measured using a spectral densitometer (500 spectral densitometer, manufactured by X-Rite). From the measured value, film strength (optical density of black paper in contact with the ink receiving layer surface / optical density of black paper not in contact with the ink receiving layer surface × 100 (%)) was determined and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 5.
5: The film strength was 90% or more.
4: The film strength was 80% or more and less than 90%.
3: The film strength was 70% or more and less than 80%.
2: The film strength was 60% or more and less than 70%.
1: The film strength was less than 70%.

  Here, similarly, the recording medium before the running water test was reciprocated 20 times using the above-mentioned Gakushin type friction fastness tester, and then the black paper portion not in contact with the ink receiving layer surface and the ink receiving layer surface The film density was evaluated by measuring the optical density of the black paper portion in contact with the spectral densitometer. As a result, the film strength was 90% or more in all cases.

(Ink absorption)
A solid image of cyan ink is recorded on the recording media 1 to 28 in a standard mode of synthetic paper (no glue) using an ink jet recording apparatus, and the degree of ink absorption in the obtained image is visually observed and evaluated as follows. Evaluated by criteria. As an ink jet recording apparatus, imagePROGRAF iPF6400 (manufactured by Canon) was used, and ink cartridge PFI-106 (manufactured by Canon) was mounted for recording. The recording conditions were temperature: 23 ° C. and relative humidity: 50%. The evaluation results are shown in Table 5.
5: Ink was absorbed within 3 seconds after recording.
4: Over 3 seconds after recording, ink was absorbed within 5 seconds.
3: Over 5 seconds after recording, ink was absorbed within 8 seconds.
2: Over 8 seconds after recording, ink was absorbed within 10 seconds.
1: Ink was not absorbed even after 10 seconds after recording.

Claims (9)

A first porous layer which is an outermost surface layer and contains inorganic particles and a water-insoluble resin;
An inkjet recording medium having an inorganic particle, a second porous layer containing a water-soluble resin, and a substrate adjacent to the first porous layer,
A recording medium, wherein the contact angle (°) of water 60 seconds after contact of water with the surface of the first porous layer is 50 ° or more.   The ratio of the thickness (μm) of the first porous layer to the total thickness (μm) of the first porous layer and the second porous layer is 8% or more and 30% or less. The recording medium according to claim 1.   The recording medium according to claim 1, wherein a thickness (μm) of the first porous layer is 3 μm or more and 10 μm or less.   The content (mass%) of the water-soluble resin in the first porous layer is 0.11 times or less as a mass ratio with respect to the content (mass%) of the water-insoluble resin. The recording medium according to claim 1.   The water-insoluble resin is at least one selected from the group consisting of a water-insoluble acrylic resin, a water-insoluble polycarbonate-modified urethane resin, and a water-insoluble polyether-modified urethane resin. The recording medium according to item.   The recording medium according to any one of claims 1 to 5, wherein an oil absorption amount (mL / 100 g) of the inorganic particles contained in the first porous layer is 150 mL / 100 g or more and 240 mL / 100 g or less.   2. The content (mass%) of the water-insoluble resin is 0.50 times or more and 1.00 times or less as a mass ratio with respect to the content (mass%) of the inorganic particles of the first porous layer. The recording medium according to any one of items 1 to 6.   The water-soluble resin content (% by mass) of the second porous layer is 0.50 times or less in terms of a mass ratio with respect to the inorganic particle content (% by mass) of the second porous layer. Item 8. The recording medium according to any one of Items 1 to 7. The recording medium according to claim 1, wherein a contact angle (°) of water is 50 ° or more and 85 ° or less.