JP7584338B2 - Inkjet recording medium - Google Patents

Description

The present invention relates to an inkjet recording medium.

As a recording medium for use in inkjet printers, an inkjet recording medium has been proposed in which an ink-receiving layer is provided on a substrate such as paper, cloth, or plastic film.

Such inkjet recording media are manufactured by a method such as that disclosed in Patent Document 1.

Specifically, Patent Document 1 discloses a method for producing a recording medium, which includes applying and drying a primer layer coating liquid containing a resin and a crosslinking agent to form a primer layer, performing an aging treatment for 10 days or more in an environment of 25°C to 45°C after the primer layer is formed, and then applying and drying a coating liquid for an ink receiving layer on the primer layer to form an ink receiving layer.

Specific examples of the ink receiving layer include those containing inorganic particles and a hydrophilic binder, as disclosed in Patent Documents 2 and 3.

JP 2003-164798 A JP 2018-171747 A JP 2004-338100 A

The inventors have investigated the use of polyvinyl alcohol resin as a hydrophilic binder in an ink receiving layer that contains inorganic particles and a hydrophilic binder.

The greater the porosity of the ink receiving layer, the faster the ink dries in the ink receiving layer. One way to increase the porosity of the ink receiving layer is to increase the amount of inorganic particles packed into the ink receiving layer. However, in configurations that use polyvinyl alcohol resin as the hydrophilic binder, if the content of inorganic particles is high, the ink receiving layer that is formed is prone to cracking.

In addition, high water resistance is also required when inkjet recording media are exposed for long periods of time to environments where they are likely to come into contact with water, such as outdoors.

Therefore, there is a demand for inkjet recording media that suppress cracking, improve ink drying speed, and improve water resistance.

In addition, polyvinyl alcohol resin, which has traditionally been used as a hydrophilic binder, has low adhesion to substrates, such as plastic substrates. For this reason, the manufacturing method disclosed in Patent Document 1, for example, requires pretreatment such as the formation of a primer layer and a long aging process of 10 days or more, as well as complex steps and special manufacturing equipment for these steps.

Therefore, there is a demand for inkjet recording media that can be manufactured using simpler methods.

The present invention aims to provide an inkjet recording medium that can be produced in a simple manner while suppressing cracking, improving ink drying speed, and water resistance.

The inventors have discovered that the above object can be achieved by the following means:

Aspect 1
The ink-receiving layer includes a base layer and an ink-receiving layer laminated on the base layer.
The ink receiving layer contains a polyvinyl alcohol resin having a monomer unit represented by the following formula (1) and inorganic particles:
Inkjet recording media:

Aspect 2
2. The inkjet recording medium according to aspect 1, wherein the content of the monomer unit represented by formula (1) in the polyvinyl alcohol resin is 6.0 mol % to 11.0 mol %.

Aspect 3
The inkjet recording medium according to aspect 1 or 2, wherein the polyvinyl alcohol resin further has a monomer unit represented by the following formula (2):

Aspect 4
Aspect 4. The inkjet recording medium according to any one of Aspects 1 to 3, wherein a ratio of the mass of the polyvinyl alcohol resin to a total mass of the polyvinyl alcohol resin and the inorganic particles is 10% by mass to 30% by mass.

Aspect 5
5. The inkjet recording medium according to any one of Aspects 1 to 4, wherein the inorganic particles are fumed silica particles.

Aspect 6
The inorganic particles have an average primary particle size of 7 nm to 20 nm, and a specific surface area of 100 m ² /g to 400 m ² /g.
6. The inkjet recording medium according to any one of aspects 1 to 5.

Aspect 7
7. The inkjet recording medium according to any one of Aspects 1 to 6, wherein the ink receiving layer further comprises a dispersant and a hardener.

Aspect 8
8. The inkjet recording medium according to embodiment 7, wherein the dispersant is a quaternary ammonium salt compound having a molecular weight of 5,000 to 50,000.

Aspect 9
9. The inkjet recording medium according to embodiment 8, wherein the curing agent is a water-dispersible hexamethylene diisocyanate or a water-based chelating agent.

Aspect 10
10. The inkjet recording medium according to any one of aspects 1 to 9, wherein the ink receiving layer has a thickness of 10 μm to 30 μm.

The present invention provides an inkjet recording medium that can be produced in a simple manner while simultaneously suppressing cracking and providing quick-drying ink.

FIG. 1 is a schematic diagram showing an inkjet recording medium according to a first embodiment of the present invention. FIG. 2 is a schematic diagram showing an inkjet recording medium according to a second embodiment of the present invention.

The following describes in detail the embodiments of the present invention. Note that the present invention is not limited to the following embodiments, and can be modified in various ways within the scope of the invention.

The inkjet recording medium of the present invention has a base layer and an ink receiving layer laminated on the base layer, and the ink receiving layer contains a polyvinyl alcohol resin having a monomer unit represented by the following formula (1) and inorganic particles:

Figure 1 is a schematic diagram showing an inkjet recording medium 1 according to a first embodiment of the present invention.

As shown in FIG. 1, an inkjet recording medium 1 according to a first embodiment of the present invention has a base layer 10 and an ink receiving layer 20 laminated on the base layer 10. Here, the ink receiving layer contains a polyvinyl alcohol resin having a monomer unit represented by the above formula (1), and inorganic particles.

Although not limited by the principle, the principle by which the inkjet recording medium of the present invention can be produced in a simple manner while suppressing cracking, improving ink quick-drying properties, and water resistance is as follows.

As described above, by increasing the loading amount of inorganic particles in the ink receiving layer, the ink quick-drying property of the ink receiving layer can be improved. However, increasing the loading amount of inorganic particles in the ink receiving layer tends to increase cracking of the ink receiving layer.

When a polyvinyl alcohol resin having a monomer unit represented by the above formula (1) is used as the binder resin for the ink receiving layer, cracks are less likely to occur in the ink receiving layer, even when the loading amount of inorganic particles is high, and the water resistance of the ink receiving layer can be improved.

In addition, the polyvinyl alcohol resin having the monomer unit represented by the above formula (1) has high adhesion to the substrate. Therefore, the inkjet recording medium of the present invention can significantly reduce the pretreatment required to ensure adhesion between the ink receiving layer and the substrate. In other words, it can be manufactured more easily.

Therefore, the inkjet recording medium of the present invention can be produced in a simple manner while suppressing cracking, improving ink quick-drying properties, and water resistance.

The inkjet recording medium of the present invention can be applied to any object on which inkjet printing is performed. The inkjet recording medium of the present invention may be, for example, printing paper, packaging, signs, stickers, etc. In particular, since the inkjet recording medium of the present invention has high water resistance, it may be used for signs, such as stickers, applied to walls and bulletin boards of buildings, and vehicles such as automobiles and motorcycles.

<Ink Receiving Layer>
The ink receiving layer is a layer in the ink recording medium that absorbs and retains ink. The ink receiving layer is laminated on the base layer.

The ink receiving layer contains a polyvinyl alcohol resin having a monomer unit represented by the above formula (1) and inorganic particles.

The ratio of the mass of the polyvinyl alcohol resin to the total mass of the polyvinyl alcohol resin and inorganic particles in the ink receiving layer is preferably 10% by mass to 30% by mass.

When the mass ratio of the polyvinyl alcohol resin is 10% by mass or more, the content of the polyvinyl alcohol resin is significantly larger than the content of the inorganic particles, so that cracking of the ink receiving layer is further suppressed. On the other hand, when the mass ratio of the polyvinyl alcohol resin is 30% by mass or less, the content of the inorganic particles can be significantly increased, so that the porosity of the ink receiving layer can be improved, thereby further increasing the quick-drying property of the ink.

The mass percentage of the polyvinyl alcohol resin may be 10% by mass or more, 15% by mass or more, 20% by mass or more, or 25% by mass or more, and may be 30% by mass or less, 25% by mass or less, 20% by mass or less, or 15% by mass or less.

The thickness of the ink receiving layer is preferably 10 μm to 30 μm.

When the thickness of the ink receiving layer is 10 μm or more, the amount of voids in the ink receiving layer can be increased, making it easier to absorb ink. This can improve the quick-drying properties of the ink. On the other hand, when the thickness of the ink receiving layer is 30 μm or less, the ink recording medium as a whole can be made thinner. Furthermore, for example, when the substrate layer is a transparent substrate layer, the transparency of the ink recording medium can be increased when the thickness of the ink receiving layer is 30 μm or less.

The thickness of the ink receiving layer may be 10 μm or more, 15 μm or more, 20 μm or more, or 25 μm or more, and may be 30 μm or less, 25 μm or less, 20 μm or less, or 15 μm or less. Note that the "thickness" of the ink receiving layer refers to the average thickness.

The ink receiving layer preferably further contains a dispersant and a hardener.

<Polyvinyl alcohol resin>
The polyvinyl alcohol resin contained in the ink receiving layer of the present invention has a monomer unit represented by the above formula (1). Hereinafter, the polyvinyl alcohol resin having a monomer unit represented by the above formula (1) may be referred to as a "partially benzacetalized polyvinyl alcohol".

The content of the monomer unit represented by formula (1) in the partially benzacetalized polyvinyl alcohol may be 6.0 mol% to 11.0 mol%.

The content of the above monomer units in the partially benzacetalized polyvinyl alcohol may be 6.0 mol% or more, 7.0 mol% or more, 8.0 mol% or more, or 9.0 mol% or more, and may be 11.0 mol% or less, 10.0 mol% or less, 9.0 mol% or less, or 8.0 mol% or less.

The degree of polymerization of the partially benzacetalized polyvinyl alcohol may be 1000 to 5000. The degree of polymerization may be 1000 or more, 1500 or more, 2000 or more, or 2500 or more, and may be 5000 or less, 4500 or less, 4000 or less, or 3500 or less.

Partially benzacetalized polyvinyl alcohol can be produced, for example, by reacting polyvinyl alcohol with benzaldehyde.

Note that polyvinyl alcohol resin may be saponified during production and may have acetyl groups in the side chains. Therefore, partially benzacetalized polyvinyl alcohol may further have a monomer unit represented by the following formula (2):

<Inorganic particles>
In the present invention, the ink receiving layer contains inorganic particles.

The inorganic particles can be any inorganic particles that can form voids in the ink receiving layer and allow the voids to receive, e.g., absorb and/or retain, ink.

Examples of inorganic particles that can be used include silica, talc, kaolin, clay, alumina white, calcium carbonate, magnesium carbonate, aluminum sulfate, barium sulfate, and mixtures thereof. The silica may be fumed silica particles.

The average primary particle diameter of the inorganic fine particles used in the present invention is preferably 7 nm to 20 nm.

When the average primary particle diameter of the inorganic fine particles is 7 nm or more, the size of the voids formed in the ink receiving layer can be kept more appropriate, and the ink drying speed can be further improved. On the other hand, when the average primary particle diameter of the inorganic fine particles is 20 nm or less, the transparency of the ink receiving layer can be further improved.

The average primary particle size is the arithmetic mean value of the measurements taken using a transmission electron microscope (TEM), such as a Titan Cube G2 60-300 (manufactured by Thermo Fisher Scientific), to measure the maximum diagonal of 100 or more randomly selected particles, or the major axis (longitudinal tangent) if the particles are rounded.

The inorganic fine particles used in the present invention preferably have a specific surface area of 100 m ² /g to 400 m ² /g. The specific surface area can be measured by the BET flow method using HM model-1208 (manufactured by Mountec Co., Ltd.) in accordance with JIS Z8830.

When the specific surface area of the inorganic fine particles is 100 ^m2 /g or more, the size of the voids formed in the ink receiving layer can be more appropriately maintained, and the ink drying speed can be further improved. On the other hand, when the specific surface area of the inorganic fine particles is 400 ^m2 /g or less, cracking of the ink receiving layer can be further suppressed.

The specific surface area of the inorganic fine particles may be 100 m ² /g or more, 150 m ² /g or more, 200 m ² /g or more, or 250 m ² /g or more, and may be 400 m ² /g or less, 350 m ² /g or less, 300 m ² /g or less, or 250 m ² /g or less.

<Dispersant>
In the present invention, the ink receiving layer may contain a dispersant.

When the ink receiving layer contains a dispersant, the viscosity of the coating liquid used to form the ink receiving layer can be improved during production. This makes it easier to form the ink receiving layer.

From the viewpoint of dispersibility and sedimentation stability, the dispersant is preferably a cationic polymer. Among them, a quaternary ammonium salt compound having a molecular weight of 5,000 to 50,000 is particularly preferred. Other cationic compounds may also be used in combination.

When a quaternary ammonium salt compound is used as a dispersant, a molecular weight of 5,000 or more can improve dispersion stability. On the other hand, a molecular weight of 50,000 or less can maintain a suitable viscosity of the coating liquid, making it easy to apply.

When a quaternary ammonium salt compound is used as a dispersant, the molecular weight may be 5,000 or more, 5,000 or more, 15,000 or more, or 20,000 or more, and may be 50,000 or less, 45,000 or less, 30,000 or less, or 25,000 or less.

The content of the dispersant is preferably 1 to 10% by mass relative to the content of the inorganic filler in the ink receiving layer.

The content of the dispersant may be 1% by mass or more, 2% by mass or more, 3% by mass or more, or 4% by mass or more, and may be 10% by mass or less, 9% by mass or less, 8% by mass or less, or 7% by mass or less, relative to the content of the inorganic filler in the ink receiving layer.

<Hardening agent>
In the present invention, the ink receiving layer may contain a curing agent.

If the ink receiving layer contains a curing agent, the water resistance of the ink receiving layer can be improved.

The curing agent may be a boron compound, a glyoxylate, an aqueous chelating agent such as an organic titanium or organic zirconium compound, or a water-dispersible hexamethylene diisocyanate.

From the viewpoint of ensuring the transparency of the ink receiving layer, it is preferable that the curing agent is a water-based chelating agent or a water-dispersible hexamethylene diisocyanate.

<<Base layer>>
The substrate layer is a layer that serves as a substrate on which the ink receiving layer is laminated.

The substrate layer may be a layer of any material onto which the ink-receiving layer can be laminated. The substrate layer may be paper, cloth, plastic, or the like. When the substrate layer is plastic, polycarbonate, nylon, polyethylene, polypropylene, polystyrene, polyethylene terephthalate, or the like may be used.

The substrate layer may be a transparent substrate layer.

In the present invention, the amount of inorganic particles packed in the ink receiving layer can be increased while suppressing cracking, so the ink quick-drying property of the ink receiving layer can be improved while reducing the thickness of the ink receiving layer. Furthermore, reducing the thickness of the ink receiving layer improves the transparency of the ink receiving layer.

Therefore, when the substrate layer is a transparent substrate layer, the present invention can also improve the transparency of the inkjet recording medium itself.

Here, "transparent" means that the layer, such as a substrate layer, is transparent enough that one side of the layer can be seen clearly from the other side.

Transparent means, for example, that the total light transmittance is 80% or more, 85% or more, 90% or more, 95% or more, or 100%. The haze value may be 30% or less, 25% or less, 20% or less, or 15% or less.

Here, the total light transmittance can be measured in accordance with JIS K 7361. The haze value can be measured in accordance with JIS K7136.

Adhesive layer
In the ink jet recording medium of the present invention, an adhesive layer can be laminated on the side of the base layer opposite to the side on which the ink receiving layer is laminated.

The adhesive layer is a layer for attaching the inkjet recording medium of the present invention to another object.

The adhesive layer may be, for example, an acrylic adhesive resin.

The adhesive layer may contain, for example, an ultraviolet absorber to prevent deterioration of adhesiveness over time.

When a transparent substrate layer is used as the substrate layer, it is preferable that the adhesive layer is also a transparent layer.

Figure 2 is a schematic diagram showing an inkjet recording medium 2 according to a second embodiment of the present invention.

As shown in FIG. 2, the inkjet recording medium 2 according to the second embodiment of the present invention is similar to that shown in FIG. 1, except that an adhesive layer 30 is laminated on the side of the base layer 10 opposite to the side on which the ink receiving layer 20 is laminated.

Examples 1 to 3 and Comparative Examples 1 to 4
Example 1
The ink jet recording medium of Example 1 was prepared as follows.

(Preparation of vapor-phase silica dispersion)
To 50 parts by weight of ion-exchanged water, 1.7 parts by weight of an aqueous cationic polymer solution (solid content: 52.3 wt%) was added as a dispersant, followed by the addition of 35 parts by weight of 2-propanol to prepare a dispersion medium.

The dispersion medium was stirred at 3000 rpm with a homogenizer (product name: Biomixer BM-2, manufactured by Nippon Seiki Seisakusho Co., Ltd.) while 15 parts by weight of vapor-phase silica was added in small amounts to obtain a dispersion with a solid content of 15.6 wt%.

(Preparation of Coating Fluid)
31 parts by weight of a water/2-propanol solution (solid content 8.4 wt%) of partially benzacetalized polyvinyl alcohol (polyvinyl alcohol resin having a monomer unit represented by the above formula (1), degree of polymerization: 3500, degree of benzacetalization: 8 mol%) was mixed with 70 parts by weight of a silica dispersion to give a resin/silica solid content ratio of 20/80. Next, 0.1 parts by weight of a hexamethylene diisocyanate-based curing agent (solid content 100 wt%) was added and stirred to obtain a coating liquid.

(Formation of ink-receiving layer)
A transparent biaxially oriented polyethylene terephthalate film having a thickness of 75 μm was used as the substrate.

The coating liquid was applied to the substrate using a desktop coater (product name: Control Coater 7000, manufactured by Imoto Manufacturing Co., Ltd.), then dried in an oven at 80°C for 3 minutes, and then aged at 60°C for 1 day to form an ink-receiving layer.

The composition of the inkjet recording medium of Example 1 is shown in Table 1 below.

Example 2
An ink jet recording medium of Example 2 was prepared in the same manner as in Example 1, except that the solids ratio of resin/silica was 30/70.

The composition of the inkjet recording medium of Example 2 is shown in Table 1 below.

Example 3
An inkjet recording medium of Example 2 was prepared in the same manner as in Example 2, except that a partially benzacetalized polyvinyl alcohol having a benzacetalization degree of 9 mol % and a polymerization degree of 2000 was used.

The composition of the inkjet recording medium of Example 3 is shown in Table 1 below.

Comparative Example 1
An inkjet recording medium of Comparative Example 1 was prepared in the same manner as in Example 1, except that the coating liquid was prepared as follows.

59 parts by weight of the above silica dispersion was mixed with 42 parts by weight of a water/2-propanol solution (solid content 9.0 wt%) of partially saponified polyvinyl alcohol (polymerization degree: 3000, saponification degree: 88 mol%) to give a resin/silica solid content ratio of 30/70. Next, 0.1 parts by weight of a hexamethylene diisocyanate-based hardener (solid content 100 wt%) was added and stirred to obtain a coating liquid.

The composition of the inkjet recording medium for Comparative Example 1 is shown in Table 1 below.

Comparative Example 2
An ink jet recording medium of Comparative Example 2 was prepared in the same manner as Comparative Example 1, except that the solids ratio of resin/silica was 40/60.

The composition of the inkjet recording medium for Comparative Example 2 is shown in Table 1 below.

Comparative Example 3
An inkjet recording medium of Comparative Example 3 was prepared in the same manner as in Example 1, except that the coating liquid was prepared as follows.

59 parts by weight of the above silica dispersion was mixed with 42 parts by weight of a water/2-propanol solution (solid content 9.0 wt%) of acetoacetyl-modified polyvinyl alcohol (polymerization degree: 1200, saponification degree: 91 mol%) to give a resin/silica solid content ratio of 30/70. Next, 0.1 parts by weight of a hexamethylene diisocyanate-based hardener (solid content 100 wt%) was added and stirred to obtain a coating liquid.

The composition of the inkjet recording medium for Comparative Example 3 is shown in Table 1 below.

Comparative Example 4
An ink jet recording medium of Comparative Example 4 was prepared in the same manner as in Comparative Example 3, except that the resin/silica solids ratio was 40/60.

The composition of the inkjet recording medium for Comparative Example 4 is shown in Table 1 below.

<evaluation>
The performance of the ink jet recording medium of each example was evaluated as follows.

(Cracks)
The ink receiving layer of each example of the ink jet recording medium was visually inspected for the presence or absence of cracks. The evaluation results are shown in Table 1 below.

In Table 1 below, the ink receiving layer is rated as "good" if no cracks were observed, as "fair" if there were slight cracks, and as "poor" if cracks were observed over the entire surface of the ink receiving layer or if the ink receiving layer could not be formed.

(Transparency)
The ink jet recording medium of each example was measured in accordance with JIS K 7361 using a haze meter (product name: haze transmittance/reflectance measuring meter HR-100, manufactured by Murakami Color Research Laboratory Co., Ltd.).

In Table 1 below, a total light transmittance of 85% or more is rated "good", a total light transmittance of 80% or more but less than 85% is rated "fair", and a total light transmittance of less than 80% is rated "poor".

(Quick-drying ink)
Using an inkjet printer (Canon PIXUS iP4830), 100-point characters were printed in aqueous pigment ink, and the time it took for the ink to dry was measured. Specifically, the time when the ink was ejected from the printer was set as 0 seconds, and after 5 seconds had passed, the printed surface was pressed against gauze to check whether the ink was transferred to the gauze.

In Table 1 below, items with absolutely no ink transfer to the gauze and no blurring or crumbling of the printed characters are rated "good," items with some ink transfer but no blurring or crumbling of the characters are rated "fair," and items with significant ink transfer and blurring or crumbling of the characters are rated "poor."

(Adhesion to substrate)
A Cellophane (registered trademark) tape was applied to the ink receiving layer and then peeled off, and it was confirmed whether the ink receiving layer was also peeled off at that time.

In Table 1 below, the product in which the ink receiving layer did not peel off is rated "good," the product in which the ink receiving layer partially peeled off but did not pose a problem in use is rated "fair," and the product in which most of the ink receiving layer peeled off is rated "poor."

(water resistance)
The ink receiving layer was wiped 200 times with gauze soaked in water, and it was confirmed whether the ink receiving layer disappeared or not.

In Table 1 below, the following criteria are used: "Good" indicates that the ink receiving layer was not lost at all, "Average" indicates that the ink receiving layer was slightly burned off but did not cause any problems in use, and "Poor" indicates that most of the ink receiving layer was lost.

<result>
The configuration and evaluation results of each example are shown in Table 1 below.

As shown in Table 1, the inkjet recording media of Examples 1 to 3, which used partially benzacetalized polyvinyl alcohol as the binder resin in the ink receiving layer, achieved good results in terms of cracking, transparency, ink quick-drying property, substrate adhesion, and water resistance. In other words, all evaluations were "good."

In contrast, the inkjet recording media of Comparative Examples 1 to 4, which used partially saponified polyvinyl alcohol or acetoacetyl-modified polyvinyl alcohol as the binder resin in the ink receiving layer, were rated "good" or "fair" in some evaluations, but "poor" in others.

1 and 2 Inkjet recording medium 10 Base layer 20 Ink receiving layer 30 Adhesive layer

Claims (9)

The ink-receiving layer includes a base layer and an ink-receiving layer laminated on the base layer.
The ink receiving layer contains a polyvinyl alcohol resin having a monomer unit represented by the following formula (1) and inorganic particles ,
The ratio of the mass of the polyvinyl alcohol resin to the total mass of the polyvinyl alcohol resin and the inorganic particles is 10% by mass to 30% by mass.
Inkjet recording media:
The inkjet recording medium according to claim 1, wherein the content of the monomer unit represented by formula (1) in the polyvinyl alcohol resin is 6.0 mol % to 11.0 mol %. 3. The inkjet recording medium according to claim 1, wherein the polyvinyl alcohol resin further comprises a monomer unit represented by the following formula (2):
4. The ink jet recording medium according to claim 1, wherein the inorganic particles are fumed silica particles. The inorganic particles have an average primary particle size of 7 nm to 20 nm, and a specific surface area of 100 m ² /g to 400 m ² /g.
The inkjet recording medium according to any one of claims 1 to 4 . The ink-jet recording medium according to any one of claims 1 to 5 , wherein the ink-receiving layer further comprises a dispersant and a hardener. 7. The inkjet recording medium according to claim 6 , wherein the dispersant is a quaternary ammonium salt compound having a molecular weight of 5,000 to 50,000. The inkjet recording medium according to claim 7 , wherein the curing agent is a water-dispersible hexamethylene diisocyanate or a water-based chelating agent. The inkjet recording medium according to any one of claims 1 to 8 , wherein the ink receiving layer has a thickness of 10 µm to 30 µm.

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