JP5423934B1 - Composite white pigment for gravure ink and gravure ink - Google Patents

Abstract

The present invention provides a composite white pigment for gravure ink that achieves both high coating gloss, high adhesion between the coating film and the substrate, and high concealment ratio, and improvement of plate-resistant fog. Objective. The present invention is a composite particle comprising titanium oxide particles, barium sulfate particles and / or calcium carbonate particles disposed around the titanium oxide particles, a coating layer covering the composite particles and containing an aluminum compound, The present invention relates to a composite white pigment for gravure inks.

Description

The present invention relates to a composite white pigment for gravure ink and gravure ink.

In gravure printing, printing ink is supplied to a gravure plate cylinder having cells formed on the surface, excess ink on the surface of the plate cylinder is scraped off by a doctor blade, and then printed on paper, plastic, etc. It is actively used as a printing method for packaging materials and building material sheets.

Titanium oxide is used as a white pigment in a wide range of fields such as paints, inks, plastics, paper, and the like, and those currently on the market are roughly classified into anatase type and rutile type depending on the crystal form. The rutile type has a narrow band gap and a high refractive index of visible light compared to the anatase type, so rutile type titanium oxide is mainly used as a white pigment for paints and inks. It has been adopted. When the band gap is narrow, the photocatalytic action hardly occurs, and the decoloring action of the ink and the decomposition action of the resin hardly occur. Moreover, when the refractive index of visible light is high, a pigment with a high concealment rate can be obtained.

Patent Document 1 discloses a printing ink composition in which silicon oxide and / or aluminum oxide is coated on the surface of anatase-type titanium oxide porous particles having an average particle diameter in the range of 0.2 to 1.0 μm. Titanium oxide pigments are described.
Patent Document 2 describes an inorganic pigment characterized by containing rosette-like crystals.

JP 2010-180402 A JP 05-051549 A

One of the features that gravure printing does not have in other printing systems is a printing process in which excess ink is scraped off by a doctor blade. As a printing problem not found in other plate-type printing, there is a problem of plate fog due to ink scraping of the doctor blade. Plate fogging refers to a phenomenon in which a portion that is not scratched by a doctor blade is generated in a non-image area of a plate, and ink is adhered to a blank portion that should not be transferred to a printing medium, resulting in smearing.

The gravure ink is required to have a high coating film gloss, a high adhesion between the coating film and the substrate, and a high hiding ratio. In order to satisfy these requirements, mechanical dispersion has been carried out to near the primary particles of the pigment particles, or the pigment particles themselves have been made smaller. However, on the other hand, if the dispersion is too strong or the pigment particles are too small, for example, the pigment particles leak from the gap between the doctor blade and the plate, causing plate fogging, resulting in high coating gloss, coating film and substrate. In the past, it has been difficult to eliminate the problem of plate covering while achieving high adhesion and high concealment.

In the porous titanium oxide pigment described in Patent Document 1, wear of the doctor blade is suppressed by using anatase-type titanium dioxide having a smaller Mohs hardness as compared with the rutile type. However, the anatase type has a lower hiding power than the rutile type, and if the pigment concentration is increased to improve the hiding ratio, problems such as uneven density due to re-aggregation and poor adhesion may occur. is there.

In the gravure printing ink characterized by containing an inorganic pigment having rosette-like crystals described in Patent Document 2, as a result of controlling the particle size distribution, adhesion and suitability for a doctor blade have been improved. Depending on the resin, the dispersibility of the rosette-like crystal itself is poor, and there is a problem that the concealment rate and glossiness do not reach the required levels.

Therefore, the present inventors have intensively studied and completed a composite white pigment for gravure ink based on a technical idea completely different from Patent Documents 1 and 2 as a pigment for gravure ink that satisfies the requirements for the above gravure ink. did.

That is, the present invention
Composite particles comprising titanium oxide particles and barium sulfate particles and / or calcium carbonate particles disposed around the titanium oxide particles;
A coating layer that coats the composite particles and contains an aluminum compound;
The present invention relates to a composite white pigment for gravure inks.

The composite white pigment for gravure ink of the present invention forms composite particles in which barium sulfate particles and / or calcium carbonate particles are arranged around titanium oxide particles, and the composite particles are covered with a coating layer. Barium sulfate particles and / or calcium carbonate particles arranged around the titanium oxide particles prevent aggregation of the titanium oxide particles. Here, when the titanium oxide particles are aggregated to increase the particle size, the particles do not have a particle size that exhibits a high concealment rate. On the other hand, since the composite white pigment for gravure ink of the present invention can prevent aggregation of titanium oxide particles, the number of particles having a particle diameter exhibiting a high concealment rate is maintained. Therefore, the concealment rate of the ink coating film can be increased. Furthermore, the occurrence of density unevenness and printing unevenness can be suppressed. On the other hand, since the size of one composite particle is larger than the size of one titanium oxide particle by the amount of barium sulfate particles and / or calcium carbonate particles, it is easily scraped off by a doctor blade, and plate fog is less likely to occur.
In addition, by coating the composite particles with a coating layer, the composite white pigment for gravure ink has high dispersion stability and is well adapted to the resin used for the gravure ink.

FIG. 1 is a perspective view schematically showing an example of composite particles including titanium oxide particles and barium sulfate particles and / or calcium carbonate particles arranged around the titanium oxide particles. FIG. 2A is a perspective view schematically showing an example of a composite white pigment for gravure ink of the present invention in which the composite particles shown in FIG. 1 are coated with a coating layer, and FIG. It is AA sectional view taken on the line of 2 (a). FIG. 3 is an example of a transmission electron microscope image of the composite white pigment for gravure ink of the present invention. FIG. 4 is an enlarged cross-sectional view schematically showing the vicinity of the coating layer shown in FIG. FIG. 5 is an enlarged cross-sectional view schematically showing a multilayer coating layer.

Hereinafter, the composite white pigment for gravure ink of the present invention will be described.
The composite white pigment for gravure ink of the present invention is
Composite particles comprising titanium oxide particles and barium sulfate particles and / or calcium carbonate particles disposed around the titanium oxide particles;
A coating layer that coats the composite particles and contains an aluminum compound;
It is characterized by providing.

The composite white pigment for gravure ink of the present invention can be produced through a step of obtaining composite particles by dispersing raw material powder in water adjusted to pH 4-10.
Titanium oxide particles, barium sulfate particles and / or calcium carbonate particles are used as the raw material powder. When the raw material powder is dispersed in water adjusted to pH 4 to 10, particles are formed in each particle. The electrostatic interaction works due to the potential difference based on the electric double layer.
Then, barium sulfate particles and / or calcium carbonate particles are electrostatically adsorbed on the surface of the titanium oxide particles to form composite particles in which the barium sulfate particles and / or calcium carbonate particles are arranged around the titanium oxide particles. .

FIG. 1 is a perspective view schematically showing an example of composite particles including titanium oxide particles and barium sulfate particles and / or calcium carbonate particles arranged around the titanium oxide particles.
In FIG. 1, in water adjusted to pH 4 to 10, titanium oxide particles 10 and barium sulfate particles and / or calcium carbonate particles 20 arranged around the titanium oxide particles 10 form composite particles 2. Is shown.
As described above, the barium sulfate particles and / or the calcium carbonate particles 20 are arranged around the titanium oxide particles 10 by being electrostatically adsorbed on the surfaces of the titanium oxide particles 10.

FIG. 2A is a perspective view schematically showing an example of a composite white pigment for gravure ink of the present invention in which the composite particles shown in FIG. 1 are coated with a coating layer, and FIG. It is AA sectional view taken on the line of 2 (a).
The composite white pigment 1 for gravure ink shown in FIGS. 2 (a) and 2 (b) is formed by coating the composite particles 2 shown in FIG. 1 with a coating layer 30 containing an aluminum compound.
FIG. 2B schematically shows a state where the surface of the composite particle 2 is covered with the coating layer 30.
In FIG. 2B, the coating layer 30 covers the surface of the titanium oxide particles 10 and also covers the surface of the barium sulfate particles and / or the calcium carbonate particles 20. Further, the coating layer 30 may be formed between the surface of the titanium oxide particles 10 and the surface of the barium sulfate particles and / or the calcium carbonate particles 20.
The coating layer in the present invention is a layer that covers the surface of the composite particles substantially uniformly, and in a transmission image (for example, an image as shown in FIG. 3) of the composite white pigment for gravure ink by a transmission electron microscope (TEM). The layer has an average thickness of 1 nm or more.
When the composite particles are coated with a coating layer, the positional relationship between the titanium oxide particles, the barium sulfate particles and / or the calcium carbonate particles is easily maintained, and the powder is in a composite white pigment for gravure ink and an organic solvent. In the dispersed composite white pigment for gravure ink, it is easy to maintain the state of composite particles, and easy dispersibility and dispersion stability are improved.

In the composite white pigment for gravure ink of the present invention, the shortest distance between the surface of the titanium oxide particles and the surface of the barium sulfate particles or the surface of the calcium carbonate particles is preferably in the range of 0 to 100 nm. More preferably, it is 0-10 nm, More preferably, 0-1.0 nm is good. When the shortest distance between the surface of the titanium oxide particles and the surface of the barium sulfate particles or the surface of the calcium carbonate particles exceeds 100 nm, it is difficult to obtain a high concealment rate and a plate fog improving effect.
When the shortest distance between the surface of the titanium oxide particles and the surface of the barium sulfate particles or the surface of the calcium carbonate particles is in the range of 0 to 100 nm, the barium sulfate particles and / or the calcium carbonate particles are arranged around the titanium oxide particles. Thus, it can be considered that the titanium oxide particles, the barium sulfate particles and / or the calcium carbonate particles form composite particles.
When the barium sulfate particles and / or calcium carbonate particles are in contact with the titanium oxide particles, the shortest distance between the surface of the titanium oxide particles and the surface of the barium sulfate particles or the surface of the calcium carbonate particles is 0 nm. Composite particles are formed by contacting barium sulfate particles and / or calcium carbonate particles around the particles.
Further, even if the barium sulfate particles and / or calcium carbonate particles are separated from the titanium oxide particles, if the shortest distance is shorter than 100 nm, the barium sulfate particles and / or calcium carbonate particles are arranged around the titanium oxide particles. Thus, composite particles are formed.
The shortest distance between the surface of the titanium oxide particles and the surface of the barium sulfate particles or the surface of the calcium carbonate particles can be determined by observing with a TEM or the like.

FIG. 3 is an example of a transmission electron microscope image of the composite white pigment for gravure ink of the present invention. The titanium oxide particles 10 have the coating layer 30 formed on the surface with the barium sulfate particles 20 arranged around them, so that the composite white pigment 1 for gravure ink of the present invention is obtained. The covering layer 30 shown in FIG. 3 has an average thickness of 1 nm or more.

FIG. 4 is an enlarged cross-sectional view schematically showing the vicinity of the coating layer shown in FIG.
The coating layer 31 shown in FIG. 4 is a coating layer containing an aluminum hydroxide (aluminum hydroxide), and is a single-layer coating layer.
When a coating layer containing aluminum hydroxide is formed on the composite particles, it becomes a composite white pigment for gravure inks that has a high affinity for resins and organic solvents that are components of gravure inks. Smoothness and the like can be expressed.

The titanium oxide particles constituting the composite white pigment for gravure ink of the present invention are not particularly limited in the production method, shape, crystal form and particle diameter. For example, the titanium oxide particles may be produced by a chlorine method or a sulfuric acid method. From the viewpoint of suppressing wear of the doctor blade, those manufactured by the sulfuric acid method are preferable.
The crystal form of the titanium oxide particles may be rutile, anatase, or brookite. The rutile type is preferable in that a higher concealment rate can be obtained. The average particle diameter of the titanium oxide particles is preferably from 0.1 to 1.0 μm, more preferably from 0.1 to 0.5 μm, and even more preferably from 0.2 to 0, from the viewpoint of expressing high glossiness and hiding ratio. .3 μm. When the average particle diameter of the titanium oxide particles is less than 0.1 μm, the concealment rate is lowered, and scraping with a doctor blade is likely to occur, which easily causes plate fogging. Moreover, when the average particle diameter of the titanium oxide particles exceeds 1.0 μm, the concealment rate and the glossiness may be lowered.

Moreover, as a titanium oxide particle, what was manufactured by the sulfuric acid method can be used preferably. An example of the manufacturing process in this case is as follows.
1. Dissolution process: The dried and pulverized ilmenite ore is dissolved with sulfuric acid to obtain a solution of mainly titanium sulfate (TiOSO ₄ ) and ferrous sulfate (FeSO ₄ ).
2. Cooling and separation step: Ferrous sulfate (FeSO ₄ · 7H ₂ O) crystallized by cooling the dissolved stock solution is separated by a centrifuge to obtain a stock solution.
3. Hydrolysis step: The stock solution from which ferrous sulfate is separated is heated and separated into titanium hydroxide (TiO (OH) ₂ ) and sulfuric acid.
4). Firing step: The white precipitate of titanium hydroxide obtained by the hydrolysis reaction is sufficiently washed with water and filtered, and then calcined at 900 ° C. or higher to obtain rutile-type titanium oxide (TiO ₂ ) having a predetermined particle size.

As the barium sulfate particles constituting the composite white pigment for gravure ink of the present invention, precipitated barium sulfate obtained by a method called mirabilite method or sulfuric acid method may be used. It is also possible to use fertile barium sulfate as obtained. For example, a commercially available product may be precipitated barium sulfate BF-1 (0.05 μm, manufactured by Sakai Chemical Industry Co., Ltd.).

As the calcium carbonate particles constituting the composite white pigment for gravure ink of the present invention, calcium carbonate may be so-called heavy calcium carbonate made by pulverizing limestone, or synthetic calcium carbonate made by chemical reaction. Also good. For example, as a commercially available product, synthetic calcium carbonate white gloss flower O (0.03 μm, manufactured by Shiroishi Kogyo Co., Ltd.) can be mentioned.

The average particle diameter of the barium sulfate particles and the calcium carbonate particles is preferably 1/1000 to 3 times the average particle diameter of the titanium oxide particles. It is more preferably 1/100 to 1 time, and further preferably 1/10 to 1/2 times.
When the average particle diameter of the barium sulfate particles and the calcium carbonate particles is less than 1/1000 times the average particle diameter of the titanium oxide particles, the effect of preventing aggregation of the titanium oxide particles may not be exhibited. Further, when the average particle diameter of the barium sulfate particles and the calcium carbonate particles exceeds three times the average particle diameter of the titanium oxide particles used at the same time, it is difficult to obtain a high concealment ratio and gloss when used as a gravure ink.

The coating layer constituting the composite white pigment for gravure ink of the present invention contains an aluminum compound.
Examples of the aluminum compound include aluminum hydroxide, aluminum oxide, and aluminum phosphate. The coating layer may include any of aluminum hydroxide, aluminum oxide, and aluminum phosphate, and among aluminum hydroxide, aluminum oxide, and aluminum phosphate, Two or all of them may be included.
The coating layer may contain a compound containing other elements in addition to the aluminum compound, and is made of titanium, silicon, zirconium, zinc, phosphorus, antimony, tin, calcium, magnesium, cerium, barium, and strontium. A compound containing at least one element selected from the group may be included.
Examples of the compound containing the other element include a hydroxide and / or an oxide.

The coating layer may be a mixture of the above compounds. Examples of the mixture include a coating layer made of a mixture of aluminum oxide (alumina) and titanium oxide (titania).
When the coating layer is a mixture, it is possible to control the dispersibility and smoothness of the ink composition and ink coating by changing the mixing ratio and composition of the mixture, making it a gravure ink suitable for various applications. Can be used.

Further, the coating layer may be a composite that is a compound including two or more metal elements or metalloid elements. Examples of the composite include intermetallic compounds and solid solutions, such as aluminum titanate (Al ₂ TiO ₅ ) and aluminum silicate (Al ₂ SiO ₅ ).
When a mixture or a composite is used for the coating layer, affinity for various resins can be ensured.

The coating layer may be a multilayer. By making the coating layer into multiple layers, it is possible to design so as to increase the affinity with a specific resin, and the degree of freedom in design is improved.
FIG. 5 is an enlarged cross-sectional view schematically showing a multilayer coating layer.
The covering layer 34 shown in FIG. 5 includes a lower covering layer 32 and an upper covering layer 33.
In the case of a multilayer coating layer, the lower coating layer and the upper coating layer are coating layers having different compositions, and one of the coating layers contains an aluminum compound.
Examples of the multi-layer coating layer include a coating layer composed of a lower coating layer containing silica (SiO ₂ ), which is an oxide of silicon, and an upper coating layer containing aluminum oxide (alumina).
Other examples include a lower coating layer containing titanium hydroxide, an upper coating layer containing aluminum hydroxide, a lower coating layer containing silicon hydroxide, and aluminum. The coating layer which consists of a coating layer of the upper layer containing these hydroxides is mentioned.
In addition, the number of layers when the coating layer is a multilayer is not limited to two layers, and may be composed of three or more layers.
Moreover, it is desirable that the coating layer containing aluminum is the outermost layer, and in this case, the coating layer is more easily adapted to the resin used in the gravure ink.

The weight of the coating layer containing the aluminum compound is preferably 0.3 to 15% with respect to the weight of the titanium oxide particles. More preferably, it is 0.3-10%, More preferably, it is 0.3-5%. If the weight of the coating layer containing the aluminum compound is less than 0.3% with respect to the weight of the titanium oxide particles, the affinity for the resin or organic solvent is lowered, and high dispersibility and high smoothness are exhibited. It becomes difficult. On the other hand, when the weight of the coating layer containing the aluminum compound exceeds 15% with respect to the weight of the titanium oxide particles, the titanium oxide content becomes low and it is difficult to obtain a high concealment rate when used as a gravure ink.

Next, the gravure ink of the present invention will be described.
The gravure ink of the present invention contains the composite white pigment for gravure ink of the present invention.
Since the gravure ink of the present invention contains the composite white pigment for gravure ink of the present invention, plate gravure is difficult to cause in gravure printing such as back printing and surface printing and has excellent printability. Moreover, the hiding ratio, smoothness, and glossiness are high. The substrate to be printed can be selected without limitation, such as plastics, paper, and metal foil.

The gravure ink of the present invention preferably contains other raw materials such as an ink resin in addition to the composite white pigment for gravure ink of the present invention.
Examples of the ink resin include urethane resin, vinyl chloride resin, chlorinated propylene resin, polyamide resin, acrylic resin, maleic acid resin, cyclized rubber resin, nitrified cotton, and rosin resin. It can be appropriately selected depending on the situation.
These ink resins may be any of a solvent type, an emulsion type, a colloidal dispersion type, and a curing method such as a room temperature curing type, a thermosetting type, an ultraviolet curing type, and an electron beam curing type can be used without limitation.
Furthermore, the gravure ink may contain an organic compound such as an alcohol compound, an ester compound, an ether compound, a ketone compound, an aromatic hydrocarbon compound, an aliphatic hydrocarbon compound, water or a mixed solvent thereof as a solvent. good.
In addition, colorants such as organic pigments, inorganic pigments, dyes, extenders, surfactants, antistatic agents, plasticizers, curing aids, antifoaming agents, lubricants, antioxidants, UV absorbers, chelating agents Various additives such as these may be included.
The compounding amount of the composite white pigment for gravure ink of the present invention is preferably in the range of 0.5 to 10 parts by weight with respect to 1 part by weight of the solid content of the ink resin. The range is more preferable, and if it is for surface printing, the range of 0.5 to 2 parts by weight is more preferable.

The gravure ink of the present invention is added to the composite white pigment for the gravure ink of the present invention, if necessary, by adding an ink resin and a solvent. It is obtained by mixing and dispersing using a disperser. Various additives may be added at the time of dispersion or after dispersion.

Below, an example of the method of manufacturing the composite white pigment for gravure ink of this invention is demonstrated.
The method for producing the composite white pigment for gravure ink of the present invention,
(Step 1) Step of dispersing titanium oxide particles and barium sulfate particles and / or calcium carbonate particles in water adjusted to pH 4 to 10 to obtain composite particle-containing slurry containing composite particles,
(Step 2) A step of forming a coating layer on the composite particles in the composite particle-containing slurry to obtain a pigment-containing slurry containing the composite white pigment for gravure ink of the present invention,
(Step 3) A step of solid-liquid separating the pigment-containing slurry to obtain a pigment,
(Step 4) drying the separated pigment to obtain a dry pigment; and
(Step 5) A step of pulverizing the dry pigment using a fluid mill,
Including.

In (Step 1), a predetermined amount of titanium oxide particles are dispersed in water adjusted to pH 4 to 10 and stirred to prepare a titanium oxide slurry, and barium sulfate particles and / or calcium carbonate particles are added to the titanium oxide slurry. By stirring, composite particles are formed to obtain a composite particle-containing slurry.
The ratio of titanium oxide particles to barium sulfate particles and / or calcium carbonate particles is desirably 100: 1 to 100: 30 in terms of mass.
In addition, the temperature of the slurry during the above process is desirably 20 to 80 ° C.
Barium sulfate particles and / or calcium carbonate particles may be dispersed in water to form a barium sulfate or calcium carbonate slurry, and composite particles may be formed by adding titanium oxide particles.

In (Step 2), a composite layer is formed on the composite particles by adding a compound containing aluminum and other compounds as required to the composite particle-containing slurry.
When forming a single-layer coating layer containing an aluminum hydroxide, a sodium aluminate aqueous solution is added while maintaining the pH of the slurry at 4 to 10 while maintaining the temperature of the composite particle-containing slurry at 10 to 90 ° C. Add with acid over 1-300 minutes. Then, the pigment containing slurry containing the composite white pigment for gravure ink in which the coating layer was formed by aging for 15 to 240 minutes is obtained.
The procedure for forming other types of coating layers will be described later.

In (Step 3), the pigment-containing slurry is subjected to solid-liquid separation to obtain a pigment.
In (Step 4), the pigment is dried to obtain a dry pigment. As drying conditions, it is desirable to dry at a temperature of 30 to 150 ° C. for 1 to 24 hours.
In (Step 5), a composite white pigment for gravure ink is obtained by pulverizing the dry pigment using a fluid mill.

Hereinafter, a process different from the above process will be described as an example of a procedure for forming a coating layer of a type other than a single coating layer containing an aluminum hydroxide.

(An example of a method for forming a coating layer containing an oxide)
The case where the coating layer containing an oxide is formed will be described.
When the dried pigment obtained by the steps of (Step 1) to (Step 4), on which a coating layer containing a hydroxide is formed, is calcined at 200 to 1200 ° C. for 1 to 24 hours, the hydroxide changes to an oxide. Therefore, a fired pigment having a coating layer containing an oxide can be obtained.
By pulverizing the calcined pigment using a fluid mill according to the procedure of (Step 5), a composite white pigment for gravure ink in which the coating layer contains an oxide can be obtained.

(An example of a method of forming a multilayer coating layer containing hydroxide)
A case will be described in which a lower coating layer is a silicon hydroxide and an upper coating layer is an aluminum hydroxide.
In (Step 2), after adding an aqueous sodium silicate solution to the composite particle-containing slurry obtained in (Step 1) and stirring for 5 to 80 minutes, an acid is added over 30 to 480 minutes to adjust the pH of the slurry. The lower coating layer is formed by adjusting to 3 to 9 and further stirring for 5 to 80 minutes.
Subsequently, while maintaining the pH of the slurry at 4 to 10, an aqueous sodium aluminate solution is added simultaneously with the acid over 1 to 300 minutes. Thereafter, by aging the slurry for 15 to 240 minutes, a pigment-containing slurry in which a lower coating layer made of silicon hydroxide and an upper coating layer made of aluminum hydroxide were formed in order from the surface of the composite particles. can get.
Thereafter, by following the procedures of (Step 3), (Step 4), and (Step 5), a composite white pigment for gravure ink in which the coating layer is a multilayer coating layer containing a hydroxide can be obtained.

(An example of a method for forming a coating layer containing a mixture of hydroxides)
Although the coating layer is a single layer containing aluminum, the case where there are a plurality of compounds constituting the coating layer and they form a mixture will be described.
In (Step 2), the titanyl sulfate aqueous solution and the sodium aluminate aqueous solution are simultaneously added to the composite particle-containing slurry obtained in (Step 1) while maintaining the pH at 4 to 10 over 1 to 300 minutes, and then the temperature is set to 10. A coating layer containing a mixture of titanium hydroxide and aluminum hydroxide is formed on the composite particle surface by coprecipitation of titanium hydroxide and aluminum hydroxide by aging for 0 to 60 minutes while maintaining at ~ 90 ° C. A pigmented slurry is obtained.
Then, the composite white pigment for gravure ink whose coating layer is a coating layer containing the mixture of the hydroxide of titanium and aluminum can be obtained by following the procedure of (Process 3) (Process 4) (Process 5).

(An example of a method of forming a multilayer coating layer containing oxide)
A case will be described in which a lower coating layer is formed of silica, which is an oxide of silicon, and an upper coating layer is formed of alumina, which is an oxide of aluminum.
After the above-described multilayer coating layer containing aluminum hydroxide is formed, the dried pigment on which the multilayer coating layer containing hydroxide is formed is baked at 200 to 1200 ° C. for 1 to 24 hours. Since the hydroxide changes to an oxide, a fired pigment in which a multilayer coating layer containing an oxide is formed can be obtained. The lower coating layer formed is silica, and the upper coating layer is alumina.
By pulverizing the fired pigment using a fluid mill according to the procedure of (Step 5), a composite white pigment for gravure ink, in which the coating layer is a multilayer coating layer containing an oxide, can be obtained.

(An example of a method for forming a coating layer containing a mixture of oxides)
A case where a coating layer made of a mixture of aluminum oxide (alumina) and titanium oxide (titania) is formed will be described.
In (Step 2), the titanyl sulfate aqueous solution and the sodium aluminate aqueous solution are simultaneously added to the composite particle-containing slurry obtained in (Step 1) while maintaining the pH at 4 to 10 over 1 to 300 minutes, and then the temperature is set to 10. A coating layer containing a mixture of titanium hydroxide and aluminum hydroxide is formed on the composite particle surface by coprecipitation of titanium hydroxide and aluminum hydroxide by aging for 0 to 60 minutes while maintaining at ~ 90 ° C. A pigmented slurry is obtained.
Then, a dry pigment is obtained according to the procedures of (Step 3) and (Step 4).
Further, when the dried pigment is baked at 200 ° C. to 1200 ° C. for 1 to 24 hours, titanium hydroxide and aluminum hydroxide are changed to titanium oxide and aluminum oxide, respectively. Therefore, a mixture of aluminum oxide (alumina) and titanium oxide (titania). A fired pigment having a coating layer made of is obtained.
By pulverizing the calcined pigment using a fluid mill according to the procedure of (Step 5), a composite white pigment for gravure ink in which the coating layer contains a mixture of oxides can be obtained.

(An example of a method for forming a coating layer containing an oxide composite)
The case where a coating layer made of aluminum titanate, which is a composite of aluminum oxide (alumina) and titanium oxide (titania), is described.
In the step of firing a dry pigment as an example of a method for forming a coating layer containing a mixture of oxides, depending on the firing conditions and the thickness of the coating layer, aluminum oxide and titanium oxide further react to form aluminum titanate. Therefore, a composite white pigment for gravure ink in which the coating layer contains an oxide composite can be obtained.

Examples of the present invention will be described below, but the present invention is not limited to these examples.
Example 1
Rutile-type titanium oxide particles having an average primary particle size of 0.20 μm obtained by the sulfuric acid method were added to water, and the titanium oxide concentration was adjusted to 400 g / L to obtain a titanium oxide slurry. While stirring 0.5 L of this titanium oxide slurry, the temperature of the slurry was adjusted to 70 ° C. and the pH to 7 and while maintaining this temperature, 3 parts by mass in terms of barium sulfate per 100 parts by mass of titanium oxide. Of barium sulfate particles (average particle size: 0.05 μm BF-1 Sakai Chemical Industry Co., Ltd.) was added. Next, an aqueous solution of sodium aluminate and dilute sulfuric acid in an amount corresponding to 3 parts by mass in terms of alumina are added simultaneously over 90 minutes per 100 parts by mass of titanium oxide so as to keep the pH of the slurry at 7 and then aged for 60 minutes. Then, a coating layer containing aluminum hydroxide was formed on the surface of each of the titanium oxide particles and barium sulfate particles to obtain a pigment-containing slurry. The pigment-containing slurry was washed, solid-liquid separated, and dried at a temperature of 120 ° C. for 8 hours to obtain a dry pigment. Next, the dry pigment is pulverized using a fluid mill to form a single-layer coating layer containing aluminum hydroxide on composite particles in which barium sulfate particles are arranged around titanium oxide particles. A composite white pigment for ink was obtained.

(Example 2)
A composite white pigment for gravure ink was obtained by the same procedure as in Example 1 except that rutile-type titanium oxide particles having an average primary particle size of 0.29 μm were used.

(Example 3)
Rutile-type titanium oxide particles having an average primary particle size of 0.20 μm obtained by the sulfuric acid method were added to water, and the titanium oxide concentration was adjusted to 400 g / L to obtain a titanium oxide slurry. While stirring 0.5 L of this titanium oxide slurry, the temperature of the slurry was adjusted to 70 ° C. and the pH to 7 and while maintaining this temperature, 3 parts by mass in terms of calcium carbonate per 100 parts by mass of titanium oxide. The amount of calcium carbonate particles (average particle size: 0.03 μm Hakujyo Hana Shiraishi Kogyo Co., Ltd.) was added. Next, an aqueous solution of sodium aluminate and dilute sulfuric acid in an amount corresponding to 3 parts by mass in terms of alumina are added simultaneously over 90 minutes per 100 parts by mass of titanium oxide so as to keep the pH of the slurry at 7 and then aged for 60 minutes. Then, a coating layer containing aluminum hydroxide was formed on the surface of each of the titanium oxide particles and calcium carbonate particles to obtain a pigment-containing slurry. The pigment-containing slurry was washed, solid-liquid separated, and dried at a temperature of 120 ° C. for 8 hours to obtain a dry pigment. Next, the dry pigment is pulverized using a fluid mill, and a gravure in which a single-layer coating layer containing aluminum hydroxide is formed on composite particles in which calcium carbonate particles are arranged around titanium oxide particles. A composite white pigment for ink was obtained.

Example 4
Rutile-type titanium oxide particles having an average primary particle size of 0.29 μm obtained by the sulfuric acid method were added to water, and the titanium oxide concentration was adjusted to 400 g / L to obtain a titanium oxide slurry. While stirring 0.5 L of this titanium oxide slurry, the temperature of the slurry was adjusted to 70 ° C. and the pH to 7 and while maintaining this temperature, 3 parts by mass in terms of barium sulfate per 100 parts by mass of titanium oxide. The amount of barium sulfate particles (average particle size: 0.05 μm BF-1 Sakai Chemical Industry Co., Ltd.) was added to obtain a composite particle-containing slurry. Next, the temperature of the composite particle-containing slurry is kept at 80 ° C., an amount of sodium silicate aqueous solution corresponding to 4 parts by mass in terms of silica is added per 100 parts by mass of titanium oxide, and the mixture is stirred for 20 minutes. The pH was adjusted to 7 over 120 minutes and then stirred for 20 minutes. Further, an aqueous solution of sodium aluminate equivalent to 3 parts by mass in terms of alumina and dilute sulfuric acid were added simultaneously over 60 minutes so that the pH could be maintained, and then aged over 60 minutes to obtain titanium oxide particles and barium sulfate. A lower coating layer made of silicon hydroxide and an upper coating layer made of aluminum hydroxide were formed in order from the surface of each particle of the particles to obtain a pigment-containing slurry.
The pigment-containing slurry was washed, solid-liquid separated, and dried at a temperature of 120 ° C. for 8 hours to obtain a dry pigment. Next, the dry pigment is pulverized using a fluid mill, and the composite particles in which the barium sulfate particles are arranged around the titanium oxide particles are converted into the lower coating layer made of silicon hydroxide, the aluminum hydroxide. A composite white pigment for gravure ink was obtained in which an upper coating layer (multiple coating layer) was formed.

(Comparative Example 1)
Titanium oxide pigment A was obtained in the same procedure as in Example 1 except that barium sulfate particles were not added. The titanium oxide pigment A is a pigment in which a single coating layer containing aluminum hydroxide is formed on titanium oxide particles.

(Comparative Example 2)
Titanium oxide pigment B was obtained in the same procedure as in Example 2 except that barium sulfate particles were not added.

(Comparative Example 3)
An amount of barium sulfate equivalent to 3 parts by mass in terms of barium sulfate per 100 parts by mass of titanium oxide pigment A obtained in Comparative Example 1 (average particle diameter: 0.05 μm BF-1 manufactured by Sakai Chemical Industry Co., Ltd. ) To obtain titanium oxide pigment C which is a mixed powder of titanium oxide pigment A and barium sulfate particles.

(Create dispersion paste)
The following raw materials were stirred for 40 minutes using a disperser Paint Conditioner to obtain a dispersion paste.
Composite white pigment for gravure ink or titanium oxide pigment A to C produced in any of Examples 1 to 4 and Comparative Examples 1 to 3: 30 g
40% polyamide: 21.2 g
25% nitrified cotton: 6g
Solvent: 6g
1.5 mm glass beads (V / V = 2/3): 70 g
Here, 40% polyamide is obtained by dissolving S-2310 (Rheamide Kao Co., Ltd.) using toluene / isopropyl alcohol (hereinafter IPA) = 2/1 so that the weight of the polyamide is 40%. Pointing,
25% nitrified cotton is made of nitrified cotton (made by Bergerac NC (formerly Asahi Kasei Co., Ltd., Celnova)) using toluene / IPA / ethyl acetate (hereinafter referred to as EA) = 2/1/1. Refers to those dissolved to 25%,
Solvent refers to a mixture of toluene / IPA / EA = 6/3/1.

(Creation of gravure ink)
Next, a gravure ink was prepared using the dispersion paste.
Above dispersion paste: 63.2 g
40% polyamide: 42.4 g
25% nitrified cotton: 12.0g
Solvent: 2.3 g

(Glossiness evaluation)
The glossiness of the gravure ink was measured. The above gravure ink is developed with a bar coater (# 7) to a film thickness of about 2 μm, dried, and then measured for 60 ° specular gloss with a gloss meter (GM-26, manufactured by Murakami Color Research Laboratory Co., Ltd.) Table 1 summarizes the results.
The glossiness was measured according to JIS K5600-4-7: 1999.

(Evaluation of concealment rate)
The concealment rate of the gravure ink was measured. The Y value of the film developed with a bar coater (# 4) on an OPP film with a black background on the back surface was measured with a spectroscopic colorimeter (SE-2000 manufactured by Nippon Denshoku Industries Co., Ltd.), and the contrast ratio (Contrast Ratio, hereinafter referred to as CR) from the Y value of the black background portion and the Y value of the white background portion,
C. R. (%) = Y value (black background) / Y value (white background) × 100
Are summarized in Table 1.
The concealment rate was measured according to JIS K5600-4-1: 1999.

(Evaluation of plate fog)
The gravure inks obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were placed on a gravure rotary printing machine, printing was performed, the printing state of the printing film was judged visually, and the results are shown in Table 1. Evaluation was performed in the following three stages.
○: There is no transition (fogging) to the plain part of the printed film. Δ: Very slight transition (fogging) to the plain part of the printing film is observed. ×: The transition (fogging) to the plain part of the printing film is remarkably recognized. Be

* 1 Weight% of silicon in the coating layer converted to silica
* 2 Weight% of aluminum contained in the coating layer converted to alumina

The gravure ink using the composite white pigment for gravure ink created in Examples 1 to 4 had high glossiness and hiding ratio, and no plate fogging occurred.

In the gravure ink using the titanium oxide pigments A and B prepared in Comparative Examples 1 and 2, the doctor blade did not scrape the pigment particles well due to the absence of composite particles, and plate fogging was observed. It was.

In the gravure ink using the titanium oxide pigment C prepared in Comparative Example 3, since the titanium oxide particles and barium sulfate particles do not form composite particles, the doctor blade does not scrape the pigment particles well, and plate fog is observed. It was.

DESCRIPTION OF SYMBOLS 1 Composite white pigment for gravure ink 2 Composite particle 10 Titanium oxide particle 20 Barium sulfate particle and / or calcium carbonate particle 30 Coating layer 31 Coating layer (single layer coating layer containing aluminum hydroxide)
32 Lower coating layer 33 Upper coating layer 34 Coating layer (multi-layer coating layer)

Claims (10)

Composite particles comprising titanium oxide particles and barium sulfate particles and / or calcium carbonate particles disposed around the titanium oxide particles;
A coating layer that coats the composite particles and contains an aluminum compound;
A composite white pigment for gravure ink, comprising: The composite white pigment for gravure ink according to claim 1, wherein the titanium oxide particles have an average particle diameter of 0.1 to 1.0 μm. 3. The composite white pigment for gravure ink according to claim 1, wherein an average particle diameter of the barium sulfate particles and the calcium carbonate particles is 1/1000 to 3 times an average particle diameter of the titanium oxide particles. The composite white pigment for gravure ink according to any one of claims 1 to 3, wherein a crystal form of the titanium oxide particles is a rutile type. The composite white pigment for gravure ink according to any one of claims 1 to 4, wherein the titanium oxide particles are obtained by a sulfuric acid method. The said coating layer further includes at least one compound selected from the group consisting of titanium, silicon, zirconium, zinc, phosphorus, antimony, tin, calcium, magnesium, cerium, barium and strontium. A composite white pigment for gravure ink as described in 1. The composite white pigment for gravure ink according to any one of claims 1 to 6, wherein the coating layer contains an oxide and / or a hydroxide. The said coating layer is a mixture or a composite, The composite white pigment for gravure inks in any one of Claims 1-7. The said coating layer is a multilayer, The composite white pigment for gravure inks in any one of Claims 1-8. A gravure ink comprising the composite white pigment for a gravure ink according to claim 1.