JP4062627B2 - Method for manufacturing ink jet recording medium - Google Patents

Description

  The present invention relates to a method for manufacturing an ink jet recording medium in which an ink receiving layer is formed by a transfer roll coater.

  The ink jet recording method is a recording method in which fine droplets of ink ejected by various methods are attached to a recording paper such as paper to form an image or characters. This recording method is remarkably widespread for home users because it is easy to achieve high speed and full color, has low noise during recording, and is inexpensive. In the field of commercial use, non-impact (NIP) printing has traditionally been used for printing variable information (such as utility bills and credit bills and receipts, delivery slips, and advertisements). It is beginning to replace printing with high-speed ink jet printers with a head.

Recording media used in inkjet recording systems are broadly divided into non-coated paper types that do not have an ink-receiving layer containing pigments and coated paper types that have an ink-receiving layer that contains pigments. An inexpensive non-coated paper type is used for the report, and a coated paper type capable of reproducing a high-definition image is used for the output of a digital camera or the like.
In particular, with the expansion of the application of the ink jet recording method, a coated paper type ink jet recording medium that can print on both sides and can reproduce a high-definition image at low cost is required. For this reason, in order to improve the productivity of the inkjet recording medium and reduce the cost, a technique that can be manufactured by an on-machine coater is required.
In addition, a background (ruled lines, logo marks, etc.) may be printed in advance on the recording medium by offset printing before printing by inkjet, and offset printing suitability is also required for the inkjet recording medium.

  As a technique for producing an inkjet recording medium with an on-machine coater, a technique for producing an offset-printable inkjet recording paper with an on-machine coater (see, for example, Patent Document 1), or a technique for producing an inkjet recording paper having the feel of plain paper (See, for example, Patent Document 2). In addition, as a technique for producing general printing paper at a high speed, a technique for producing a printing pigment and paper with a gate roll coater (see, for example, Patent Document 3) is disclosed.

JP 2002-127487 A JP-A-4-219267 JP-A-6-25997

  However, in the case of the technique described in Patent Document 1, the on-machine coater cannot be manufactured with a transfer roll coater (gate roll coater, rod metering size press, blade metering size press, etc.). It is only applicable. In order to apply with a transfer roll coater, it is necessary to lower the high shear viscosity of the paint. However, in the case of the technique described in Patent Document 1, the transfer roll is reduced as a result of lowering the solid content of the paint in order to lower the high shear viscosity of the paint. The coater cannot give a predetermined coating amount. On the other hand, if the solid content of the coating is increased in order to obtain a predetermined coating amount, poor coating with a transfer roll coater occurs. On the other hand, in an air knife coater, it is difficult to produce an inkjet recording medium having ink receiving layers on both sides at low cost, and thus an inkjet recording medium capable of duplex printing cannot be realized.

  In the case of the technique described in Patent Document 2, the coating layer coating applied to the base paper has a very low B-type viscosity of 1 to 100 Pa · s at a low strain rate. When the work is performed, problems such as conspicuous coating defects due to a peeling pattern when the paper is peeled from the roll occur, and it is difficult to perform the coating process at a high speed. In addition, since this technique is aimed at the feel of plain paper, there are disadvantages that the ratio of the pigment in the coating layer is low, the ink absorption capacity is insufficient, and sufficient ink jet suitability cannot be obtained.

On the other hand, the technique described in Patent Document 3 merely discloses a general technique for producing a pigment-coated paper, and has not been studied at all about ink jet printing suitability.
Accordingly, an object of the present invention is to provide a method for producing an ink jet recording medium that can be produced by a transfer roll coater that is capable of offset printing, is excellent in ink jet recording suitability, and is suitable for high-speed coating.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have incorporated a predetermined light calcium carbonate-silica composite in a pigment and used a coating liquid having a predetermined viscosity, thereby forming a transfer roll coater. It has been found that an ink-receiving layer having excellent performance can be formed.
That is, the above object of the present invention is to apply at least one surface of the support at a high speed of 300 m / min or more and 500 m / min or less by a transfer roll coater with a coating liquid mainly composed of a pigment and a binder, A method for producing an ink jet recording medium, wherein an ink receiving layer is provided by drying, wherein the coating solution has a Hercules viscosity of 20 to 30 mPa · s, the pigment has an oil absorption of 140 to 180 ml / 100 g, a BET specific surface area of 21 It was achieved by a method for producing an inkjet recording medium for offset printing , comprising a light calcium carbonate-silica composite having a mean particle size of 3.1 to 7.3 μm and ˜30 m ² / g.

The light calcium carbonate-silica composite is adjusted to a pH of 7-9 by adding mineral acid at a temperature not higher than the boiling temperature of the liquid to a mixture of light calcium carbonate and an aqueous alkali metal silicate solution. The light calcium carbonate / silica composite preferably has a light calcium carbonate / silica solid content ratio of 30/70 to 70/30. Moreover, it is preferable that the coating amount of the ink receiving layer is ² to 7 g / m ² per side, or that the coating liquid contains a cationic resin.

  According to the method for producing an inkjet recording medium of the present invention, an inkjet recording medium having high inkjet suitability (print density, water resistance, etc.) and having offset print suitability can be produced with high productivity. It is also easy to provide an ink receiving layer on both sides.

  Embodiments of the present invention will be described below. The method for producing an ink jet recording medium of the present invention is carried out by coating the following coating liquid on at least one surface of a support with a transfer roll coater to provide an ink receiving layer. An ink receiving layer can be applied to both sides as required.

  The support used in the present invention may be any sheet as long as it is in the form of a sheet, but it is particularly preferable to use uncoated paper made from wood fibers. This paper is mainly composed of papermaking pulp. Examples of the papermaking pulp include chemical pulps such as LBKP and NBKP, mechanical pulps such as GP and TMP, and used paper pulp. However, the present invention is not particularly limited to these, and these are used as necessary. It can be used alone or in combination. Furthermore, there are no particular limitations on the various internal chemicals such as fillers, sizing agents, and paper strength enhancers that are internally added to the base paper, and they are appropriately selected from known fillers and various internal chemicals. be able to. If necessary, an antifoaming agent, a pH adjusting agent, a dye, an organic pigment, a fluorescent dye, and the like can be internally added to the base paper.

  The ink receiving layer is formed by applying a coating liquid having a predetermined viscosity mainly composed of a pigment and a binder. The viscosity of the coating solution will be described later.

<Pigment of coating liquid>
The pigment of the coating liquid has an oil absorption of 100 to 250 ml / 100 g, preferably 110 to 240 ml / 100 g, a BET specific surface area of 5 to 150 m ² / g, preferably 10 to 130 m ² / g, and an average particle size of 1.0 to 10 μm. Light calcium carbonate-silica composite.

<Light calcium carbonate-silica composite>
The light calcium carbonate-silica composite is considered to have both the characteristics of silica and the characteristics of light calcium carbonate. By adjusting the composite ratio and the like, the viscosity of the coating liquid, the obtained ink receiving layer There is an advantage that the ink absorptivity, print density, and the like can be adjusted appropriately. The reason why the oil absorption, the BET specific surface area, and the average particle diameter of the light calcium carbonate-silica composite are defined in the above ranges is that when the oil absorption is less than 100 ml / 100 g, the ink absorbability of the obtained ink receiving layer is lowered. On the other hand, if it exceeds 250 ml / 100 g, the surface strength of the ink receiving layer is lowered (for example, the offset printability is lowered). In addition, if the BET specific surface area of the light calcium carbonate-silica composite is less than 5 m ² / g, the ink absorbability decreases, and if it exceeds 150 m ² / g, the viscosity of the coating liquid increases and the operability (for example, On-machine coating suitability) deteriorates. When the average particle size of the light calcium carbonate-silica composite is less than 1.0 μm, the amount of voids in the light calcium carbonate-silica composite decreases, making it difficult to hold the ink. The print density is reduced by penetrating the inside of the support. On the other hand, when the average particle diameter exceeds 10 μm, the light calcium carbonate-silica composite itself has high opacity and the printing density is lowered. In addition, the average particle diameter of a light calcium carbonate-silica composite can be measured using a laser method particle size measuring machine (for example, trade name: Mastersizer S type manufactured by Malvern).
Further, the light calcium carbonate / silica solid content mass ratio (CaCO ₃ / SiO ₂ ) in the light calcium carbonate-silica composite is preferably 30/70 to 70/30. When the ratio is less than 30/70, the surface properties of the ink receiving layer are likely to be lowered because the characteristics of silica are manifested throughout. On the other hand, when the ratio exceeds 70/30, the characteristics of light calcium carbonate are greatly developed, and the ink absorbability and the print density of the ink receiving layer are liable to be lowered.

The crystal form (homogeneous image) of light calcium carbonate (CaCO ₃ ) used for the production of the light calcium carbonate-silica composite may be either calcite or aragonite. The light calcium carbonate may have any of a needle shape, a column shape, a spindle shape, a spherical shape, a cubic shape, and a rosette type. The rosetta type refers to a shape in which spindle-shaped light calcium carbonate primary particles are aggregated in a chestnut shape.
In particular, it is preferable to use rosetta-type calcite light calcium carbonate, since the absorption characteristics of the pigment are improved and the ink-jet suitability (particularly ink absorbability) of the obtained ink-receiving layer is improved.

<Production of light calcium carbonate-silica composite>
The light calcium carbonate-silica composite is obtained, for example, by adding mineral acid to a liquid obtained by mixing light calcium carbonate and an aqueous alkali metal silicate solution at a temperature equal to or lower than the boiling temperature, and adjusting the pH of the liquid to 7-9. The coating liquid containing the light calcium carbonate-silica composite obtained as described above in the pigment is preferable because the Hercules viscosity is low even when the solid content concentration is high. In addition, according to such a manufacturing method, it is thought that the surface of the light calcium carbonate becomes a composite coated with silica.

Specifically, in the production method described above, first, the light calcium carbonate is dispersed in water, and an alkali solution of silicic acid (alkali is, for example, sodium or potassium) is added thereto. Although the molar ratio of silicic acid and alkali is not limited, No. 3 silicic acid (SiO ₂ : Na ₂ O = about 3: 1 to 3.4: 1) is generally easily available and can be suitably used. The solid content mass ratio (CaCO ₃ / SiO ₂ ) can be adjusted by adjusting the charge mass ratio between the light calcium carbonate and the alkali solution of silicic acid.
Next, a light calcium carbonate-silica composite can be produced by stirring and dispersing the mixture and then neutralizing with a mineral acid. The mineral acid may be anything, and the mineral acid may contain an acidic metal salt such as sulfate band or magnesium sulfate. Addition of mineral acid (or acid containing the above acidic metal salt aqueous solution in mineral acid) is performed at a temperature not higher than the boiling point of the above mixture, and silicic acid is deposited on the surface of the light calcium carbonate particles to form amorphous silicic acid. Form and coat to obtain a light calcium carbonate-silica composite. It is important to complete this neutralization reaction at pH = 7-9. If the pH is less than 7, decomposition of light calcium carbonate occurs. If the pH exceeds 9, precipitation of silicic acid is not performed sufficiently, and unreacted silicic acid remains. This is not preferable because it causes loss.

  Adjustment of the average particle size of the light calcium carbonate-silica composite is carried out by wet stirring or pulverization during aging during the neutralization reaction, or by solid-liquid separation after completion of the neutralization reaction or after completion of the reaction. Can be carried out by pulverization. The aging means that the addition of the acid to be added at the time of neutralization is temporarily interrupted and left only after stirring.

<Other pigments>
The pigment of the coating liquid may be composed only of the light calcium carbonate-silica composite, but in addition to the light calcium carbonate-silica composite, heavy calcium carbonate, light calcium carbonate, kaolin, baking Any of the commonly used pigments for coated paper, such as clay, organic pigments, and titanium oxide, can be used in combination.

<Combination of light calcium carbonate-silica composite into coating solution>
The light calcium carbonate-silica composite produced by the neutralization reaction can be mixed into the coating liquid preferably without going through a drying step, thereby reducing the coating liquid production cost and producing inkjet recording paper at a lower cost. can do.

<Binder>
The binder of the coating solution is not particularly limited and can be appropriately selected from, for example, known resins. However, a water-soluble polymer adhesive, a synthetic emulsion adhesive, or the like that can be dissolved or dispersed in water is desirable. Examples of the water-soluble polymer adhesive include starch or a modified product thereof, polyvinyl alcohol and a modified product thereof, and casein. Examples of synthetic emulsion adhesives include acrylic resin emulsions, vinyl acetate resin adhesives, styrene butadiene latex, urethane resin emulsions, etc. It is desirable to use it. Specifically, fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, cation-modified polyvinyl alcohol, anion-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, oxidized starch, hydroxyethyl etherified starch, phosphate esterified starch, etc. Can be mentioned.
In particular, when the binder has a high Hercules viscosity, the coating liquid tends to have a high Hercules viscosity. Therefore, a binder having a low Hercules viscosity even in a high concentration state (for example, PVA or hydroxyethyl ether having a polymerization degree of 1,000 or less). (Modified starch) is preferably used.

<Cationic resin>
In the present invention, in order to impart water resistance to the anionic inkjet ink, it is preferable that a cationic resin serving as a dye fixing agent is contained in the ink receiving layer (that is, the coating liquid).

  The cationic resin is a cationic water-soluble polymer, and it is more desirable to use a resin having an anion requirement of 5 meq / g or more and a molecular weight of 5,000 to 200,000 from the viewpoint of improving the ink water resistance. The reason is presumed as follows. In other words, it is considered that the ink for ink jet is adsorbed to the minute voids inside the pigment in the ink receiving layer or the pigment surface. Therefore, in order to make this ink water resistant, it is necessary to distribute the cationic resin that binds to the ink in the minute voids inside the pigment in the ink receiving layer and the pigment surface. The molecular weight of the cationic resin is 200, If it exceeds 000, it cannot be distributed in the voids inside the pigment, and water resistance cannot be imparted to ink that has entered the voids inside the pigment. On the other hand, if the molecular weight of the cationic resin is less than 5,000, it can be distributed in minute voids inside the pigment and can impart water resistance to the ink that has entered the pigment, but the ink is fixed inside the pigment. This is not preferable because the print density decreases. In addition, the molecular weight of the cationic resin also affects the Hercules viscosity of the coating liquid to be finally adjusted. When a cationic resin having a molecular weight exceeding 200,000 is used, the Hercules viscosity of the coating liquid increases. Therefore, it is not preferable in the present invention. If the anion requirement of the cationic resin is 5 meq / g or less, the fixing ability of the ink is not sufficient.

  Examples of cationic resins include polyethylenimine quaternary ammonium salt derivatives; polyamine polyamide epihalohydrin polycondensates; polycondensates obtained by reacting ammonia with amines such as monoamines and polyamines and epihalohydrins (dialkylamines, Ammonia / epichlorohydrin condensation polymer, etc.); dicyandiamide / formaldehyde resin; diethylenetriamine / dicyandiamide / ammonium chloride polymer; dimethyldiallylammonium chloride polymer, etc. Among these, polycondensation products obtained by reacting ammonia, amines and epihalohydrins, which improve the fixability of inkjet ink, are particularly preferable.

<Condensation polymer used for cationic resin>
Examples of amines in the polycondensation product include primary amines, secondary amines, tertiary amines, polyalkylene polyamines, alkanolamine monoamines, and the like. Examples of the amine include dimethylamine, diethylamine, dipropylamine, methylethylamine, methylpropylamine, methylbutylamine, methyloctylamine, methyllaurylamine, and dibenzylamine. . Specific examples of the tertiary amine include trimethylamine, triethylamine, tripropylamine, triisopropylamine, tri-n-butylamine, tri-sec-butylamine, tri-tert-butylamine, tripentylamine, trihexylamine, and trioctyl. Examples include amines and tribenzylamine. Of these, secondary amines dimethylamine and diethylamine are particularly preferred.
As the epihalohydrins in the above polycondensation product, for example, one or more selected from epichlorohydrin, epibromohydrin, epiiodohydrin, methyl epichlorohydrin, etc. can be used, and among these, epichlorohydrin is the most preferable.
As a method for synthesizing the above condensation polymer, for example, known methods described in JP-A-10-152544 and JP-A-10-147057 can be used. As the obtained condensation polymer, one kind alone may be blended in the coating liquid, or those having different polymerization degrees may be mixed and blended in the coating liquid. Good. Moreover, the said polycondensation product may synthesize | combine suitably, and may use a commercial item.

<Coating of coating liquid>
In the present invention, the ink receiving layer is formed by coating at a high speed (300 m / min or more, 1000 m / min or more is possible) by a transfer roll coater. As a result, productivity is greatly improved, and an ink receiving layer can be easily provided on both sides of the support, and an inkjet recording medium capable of double-sided printing can be manufactured at low cost. A transfer roll coater is a pre-weighing method (print coating method) that applies a coating solution to a support (a coating solution that is weighed with multiple rolls, bars, blades, etc.) using an application roll. Compared with a coater that is applied by a post-weighing method such as a blade coater or bar coater (a method that scrapes off the coating liquid adhering to the support) such as a blade coater or bar coater, the load applied to the paper during coating Since it is small, it is difficult to cut the paper, and there are advantages such as coating at higher speed.

Examples of transfer roll coaters include gate roll coaters, rod metering size presses, and blade metering size presses. These can be coated on both sides simultaneously on a support and can be easily installed on a machine (paper machine). It is a method.
The transfer roll coater may be an on-machine coater or an off-machine coater. Here, the on-machine coater is installed on a support manufacturing machine (such as a paper machine) and is applied on the same line as the manufacture of the support. The off-machine coater is a support manufacturing machine. The support that has been installed separately is wound up once and coated with a coater on a separate line. In terms of improving production efficiency and reducing costs, it is preferable to use an on-machine coater transfer roll coater.

  In addition, blade coaters, air knife coaters, bar coaters, curtain coaters, etc. are used as coating methods in the production of conventional inkjet recording media, but it is difficult to apply both sides to the support simultaneously using these methods. However, double-sided coating causes problems such as an increase in the number of manufacturing steps and an increase in drying load, which is not practical.

<Hercules viscosity of coating liquid>
Here, in order to enable coating with a transfer roll coater, it is necessary to adjust the viscosity of the coating liquid to be the ink receiving layer so that the Hercules viscosity at 8800 rpm and 30 ° C. is 5 to 30 mPa · s. It is. By controlling the Hercules viscosity within the above range, high-speed coating with a transfer roll coater can be stably performed. When the Hercules viscosity of the coating liquid is less than 5 mPa · s, no operational problem occurs, but the necessary coating amount described later cannot be obtained. On the other hand, when the Hercules viscosity exceeds 30 mPa · s, the coating surface deteriorates during coating with a transfer roll coater, and in the case of a gate roll coater, the coating liquid scatters (usually referred to as “jumping”). This is not preferable because it causes poor coating.

  The Hercules viscosity of the coating solution is adjusted by using the light calcium carbonate-silica composite as a pigment. In addition, the use of PVA or hydroxyethyl etherified starch having a low polymerization degree as a binder, or the incorporation of a cationic resin having a molecular weight of 200,000 or less in the coating solution makes it easier to adjust the Hercules viscosity. . Here, the Hercules viscosity means a viscosity (high shear viscosity) when a high shear rate is given.

Thus, by adjusting the Hercules viscosity of the coating liquid within the above range, the amount of the coating liquid can be preferably controlled to be ² to 7 g / m ² in terms of solid content per one side of the support. Here, when the coating amount of the coating liquid is less than 2 g / m ² , coating unevenness occurs and the support surface cannot be uniformly covered with the ink receiving layer, and thus ink absorption unevenness occurs. Solid printing may become non-uniform, that is, ink jet aptitude may be reduced. On the other hand, if the coating amount exceeds 7 g / m ² , the operability is lowered, and powder recording during cutting of the recording medium tends to occur, which may be undesirable.

In order to manage the coating amount within the above range using a transfer roll coater, it is preferable to define the B-type viscosity of the coating liquid and the solid content concentration of the coating liquid within a predetermined range.
The B-type viscosity of the coating liquid is preferably 10 to 1,000 mPa · s. If it exceeds 1,000 mPa · s, it tends to be difficult to feed the coating liquid to the transfer roll coater and the Hercules viscosity tends to be high. On the other hand, if it is less than 10 mPa · s, it may be difficult to obtain a coating amount sufficient for ink jet recording suitability.
The solid content concentration of the coating solution is preferably 10 (mass)% or more, particularly preferably 20% or more, and most preferably 30% or more. That is, when the concentration is less than 10%, coating can be performed with a transfer roll coater, but the solid content of the coating solution is too low and the coating amount of the ink receiving layer is set to 2 g / m ² or more. May not be possible. The above concentration is preferably as high as possible. However, if the concentration is too high, it becomes difficult to control the coating amount and the viscosity is excessively increased, so that there is a practical problem. Therefore, the upper limit is usually about 55%, preferably 45%. To do.

  In addition, the sizing agent, the dye, the fluorescent dye, the water retention agent, the water resistance agent, the pH adjusting agent, the antifoaming agent, the lubricant, and the preservative in the coating liquid to be the ink receiving layer as long as the effect of the present invention is not impaired. It is possible to use additives such as a surfactant, a conductive agent, an ultraviolet absorber, and an antioxidant, and in particular, the addition of a sizing agent improves the sharpness of the printed portion, so it is desirable to add it. In addition, when using various additives, it is desirable that it is cationic or nonionic from the viewpoint of compatibility with the cationic resin.

<Example>
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples. In addition, the following “parts” and “%” are parts by mass and mass% unless otherwise specified, and in the case of an aqueous solution or the like, values converted into solid contents are shown.

<Measurement of coating liquid properties>
1. Average particle size of pigment in coating solution: Sample (pigment) slurry is dropped and mixed in pure water to which sodium hexametaphosphate 0.2% is added as a dispersing agent to form a uniform dispersing agent. Laser particle size measuring machine (Malvern) Measured using a master sizer S type).
2. The BET specific surface area of the pigment of the coating solution was calculated from the nitrogen adsorption amount using a Gemini 2360 type manufactured by Micromeritics.
3. Oil absorption amount of pigment in coating solution: Measured according to JIS K5101.
4). Measurement of Hercules Viscosity of Coating Solution: Using a high shear viscometer (Model HR-801C, manufactured by Kumagai Riki Kogyo Co., Ltd.), measurement was performed under conditions of a liquid temperature of 30 ° C. and 8,800 rpm.
5. Measurement of the B-type viscosity of the coating liquid: Using a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.), the measurement was performed at a liquid temperature of 30 ° C. and a rotational speed of 60 rpm.

<Production of light calcium carbonate-silica composite A>
In a reaction vessel (12 L), 262 g of commercially available Rosetta-type light calcium carbonate (trade name: Albuquer 5970, Speciaty Minerals Inc., average particle size: 3.0 μm) was dispersed in water, and this was mixed with a sodium silicate solution (SiO 2 ₍₂ concentration 18.0 wt / wt%, Na ₂ O concentration 6.1 wt / wt%) 3,400 g was added, then water was added to make the total volume 12L. This mixed slurry was heated to 85 ° C. with sufficient stirring with a laboratory agitator. A 10% sulfuric acid solution was added to the slurry by a rotary pump, and at this time, the sulfuric acid-added portion was added immediately below the stirring blade of the laboratory agitator. Under the above conditions in which the added sulfuric acid was sufficiently dispersed, sulfuric acid was added at a constant temperature and at a constant rate so that the final pH of the slurry after completion of sulfuric acid addition was 8.0 and the total sulfuric acid addition time was 240 minutes. After the obtained slurry was passed through a 100 mesh sieve to separate coarse particles, No. Using a filter paper No. 2, suction filtration was performed to obtain a light calcium carbonate-silica composite A having a light calcium carbonate / silica mass ratio of 30/70. The composite had an oil absorption of 180 ml / 100 g, a BET specific surface area of 30 m ² / g, and an average particle size of 7.3 μm.

<Production of light calcium carbonate-silica composite B>
Except that the amount of dispersion of the Rosetta-type light calcium carbonate was 612 g, the light calcium carbonate / silica mass ratio was 50/50, and the oil absorption was exactly the same as the production of the light calcium carbonate-silica composite A. A light calcium carbonate-silica composite B having 160 ml / 100 g, a BET specific surface area of 28 m ² / g, and an average particle size of 4.4 μm was obtained.

<Production of light calcium carbonate-silica composite C>
Except that the amount of dispersion of the rosetta-type light calcium carbonate was 1,436 g, the light calcium carbonate / silica mass ratio was 70/30, and the oil absorption was exactly the same as the production of the light calcium carbonate-silica composite A. A light calcium carbonate-silica composite C having an amount of 140 ml / 100 g, a BET specific surface area of 26 m ² / g, and an average particle size of 3.6 μm was obtained.

<Production of light calcium carbonate-silica composite D>
In the production of the light calcium carbonate-silica composite 1, the weight ratio of light calcium carbonate / silica was 80/20 in the same manner except that the amount of dispersion of the commercially available rosetta type light calcium carbonate used in the reaction was 2,450 g. A light calcium carbonate-silica composite having an oil absorption of 140 ml / 100 g, a BET specific surface area of 21 m ² / g, and an average particle size of 3.1 μm was obtained.

<Production of pigment (synthetic silica)>
(Production of synthetic silica 1)
First step: Commercially available No. 3 sodium silicate (SiO ₂ : 20.0%, Na ₂ O: 9.5%) was diluted with water in a reaction vessel (200 L) to obtain a 6.7% by weight diluted sodium silicate solution as SiO ₂ 200 L was prepared. After heating this sodium silicate solution to 85 ° C., a dropping rate of 200 g / min of aluminum sulfate corresponding to 20% of the neutralization equivalent (concentration of Al ₂ O ₃ min. Then, an amount of sulfuric acid (concentration 98% by mass) corresponding to 30% of the neutralization equivalent was added under sufficient strong stirring in the same manner as described above. After completion of the addition, the partially neutralized liquid obtained was aged while being stirred, and at the same time, the target particle size was 7 μm using a vertical sand grinder (capacity 7.57 L, filling rate of glass beads with a diameter of 1 mm of 70%). Was circulated and ground. This aging and pulverization treatment was performed for 3 hours.
Second step: Next, the slurry temperature is raised to 90 ° C., and sulfuric acid having the same concentration as in the first step is added up to 80% of the neutralization equivalent under the same conditions as in the first step. Aged.
Third step: Subsequently, sulfuric acid having the same concentration as above was similarly added to the slurry after aging at an addition rate of 76 g / min, and the slurry pH was adjusted to 6.
Grinding by wet grinding; the slurry after completion of the third step was filtered, washed with water, repulped into pure water, and the hydrated silica slurry was recovered. The obtained slurry is diluted to a concentration indicating a liquid state, and this diluted slurry is put into a horizontal sand grinder having a filling rate of 80% of glass beads having a bead diameter of 0.6 to 0.8 mm (manufactured by Toyo Ballotini), Wet grinding was performed.

(Production of synthetic silica 2)
A slurry was obtained and wet pulverized in the same manner as in Production 1 of synthetic silica, except that no band was used in the first step and sulfuric acid was used for 100% of the neutralization equivalent.

(Production of synthetic silica A, D, E, G)
In the production 1 of synthetic silica, the processing time of wet grinding was adjusted to obtain the following types of synthetic silica. Silica having an oil absorption of 147 ml / 100 g, a BET specific surface area of 80 m ² / g, and an average particle diameter of 2.1 μm is referred to as synthetic silica A, and an oil absorption of 214 ml / 100 g, a BET specific surface area of 78 m ² / g and an average particle diameter of 3.4 μm. Was synthetic silica D, and silica having an oil absorption of 82 ml / 100 g, a BET specific surface area of 95 m ² / g, and an average particle size of 0.5 μm was used as synthetic silica E.
Further, in the production 2 of synthetic silica, the silica having an oil absorption of 135 ml / 100 g, a BET specific surface area of 102 m ² / g, and an average particle diameter of 0.6 μm obtained by adjusting the wet pulverization time was defined as synthetic silica G.

10 parts of kaolin and 1.0 part of band are added as fillers to 100 parts of pulp slurry made of hardwood bleached kraft pulp (freezing degree 450 ml csf), and the basis weight is 80 g / m with a twin wire type paper machine. to obtain a support Y and papermaking to be ^2.
On both sides of the support Y, 100 parts of light calcium carbonate-silica composite A, 20 parts of polyvinyl alcohol (PVA117: manufactured by Kuraray), 5 parts of polyvinyl alcohol (PVA103: manufactured by Kuraray), hydroxyethyl etherified starch (Penford) Gum 295: manufactured by Nissei Kyoben Co., Ltd.) 25 parts, cationic resin (polyamine ammonia epichlorohydrin, anion requirement: 6 meq / g, molecular weight 100,000), 20 parts, cationic sizing agent (SS335: manufactured by PMC Japan) ) 10 parts of coating liquid (solid content: 23%, Hercules viscosity: 28.3 mPa · s, B-type viscosity: 650 mPa · s) with a blade metering size press installed on-machine at 500 m / Coating is performed at a rate of min, and after drying, further calendering (linear pressure 1960 N / m performed (200kgf / cm) · 1NIP), to obtain a recording medium sample. The coating amount of the coating solution was 3.6 g / m ² on one side.

Except that the light calcium carbonate-silica composite B was used in place of the light calcium carbonate-silica composite A, the coating liquid (solid content: 25%, Hercules viscosity: 25.6 mPa) was the same as in Example 1. S, B type viscosity: 630 mPa · s), and this coating solution was applied to the support Y in the same manner as in Example 1 to obtain a recording medium sample. The coating amount of the coating solution was 3.4 g / m ² on one side.

Except that the light calcium carbonate-silica composite C was used instead of the light calcium carbonate-silica composite A, the coating solution (solid content: 25%, Hercules viscosity: 24.3 mPa) was the same as in Example 1. S, B type viscosity: 590 mPa · s), and this coating solution was applied to the support Y in the same manner as in Example 1 to obtain a recording medium sample. The coating amount of the coating solution was 3.3 g / m ² on one side.

Except that the light calcium carbonate-silica composite D was used instead of the light calcium carbonate-silica composite A, the coating solution (solid content: 23%, Hercules viscosity: 23.5 mPa) was the same as in Example 1. S, B-type viscosity: 550 mPa · s), and this coating solution was applied to the support Y in the same manner as in Example 1 to obtain a recording medium sample. The coating amount of the coating solution was 3.0 g / m ² on one side.

<Comparative Example 1>
15 parts of calcium carbonate as filler and 100 parts of internal sizing agent (size pine NT-87: manufactured by Arakawa Chemical Co., Ltd.) to 100 parts of pulp slurry consisting of hardwood bleached kraft pulp (freezing degree 350 ml csf) A support X was obtained by adding 0.8 parts of% cationized starch and making paper with a twin wire type paper machine to a basis weight of 80 g / m ² .
Synthetic silica E100 parts, polyvinyl alcohol (PVA103: manufactured by Kuraray Co., Ltd.) 50 parts, cationic resin (polyamine ammonia epichlorohydrin, anion requirement: 6 meq / g, molecular weight 100,000) on both sides of the support X Part, cationic sizing agent (SS335: manufactured by Japan PMC) 10 parts coating liquid (solid content: 28%, Hercules viscosity: 18.5 mPa · s, B-type viscosity: 360 mPa · s) on machine The sample was coated at a speed of 1,000 m / min with a gate roll coater installed in the substrate, dried and then calendered (linear pressure 1960 N / cm (200 kgf / cm) · 2 NIP) to obtain an ink jet recording medium sample. It was. The coating amount of the coating solution was 5.0 g / m ² on one side.

<Comparative Example 2>
Polyvinyl alcohol (PVA103: manufactured by Kuraray Co., Ltd.) with respect to 100 parts of silica (Fine Seal X37 (manufactured by Tokuyama Corporation), oil absorption: 260 ml / 100 g, BET specific surface area: 275 m ² / g, average particle size: 2.7 μm) 40 parts, hydroxyethyl etherified starch (Penford gum 295: manufactured by Nissei Kyoben Co., Ltd.), 40 parts, cationic resin (polyamine ammonia epichlorohydrin, anion requirement: 6 meq / g, molecular weight: 100,000) 20 parts Except for using a coating liquid (solid content: 25%, Hercules viscosity: 17.0 mPa · s, B-type viscosity: 540 mPa · s) consisting of 10 parts of a cationic sizing agent (SS335: manufactured by Japan PMC) A recording medium sample was obtained in exactly the same manner as in Comparative Example 1. The coating amount of the coating solution was 4.9 g / m ² on one side. Since this sample had low surface strength, the coating layer dropped off during drying.

<Comparative Example 3>
For 100 parts of synthetic silica A, 50 parts of polyvinyl alcohol (PVA117: manufactured by Kuraray), 20 parts of cationic resin (polyamine ammonia epichlorohydrin, anion requirement: 6 meq / g, molecular weight: 100,000), cationic A coating liquid (solid content: 20%, Hercules viscosity: 39.5 mPa · s, B-type viscosity: 700 mPa · s) consisting of 10 parts of a sizing agent (SS335: manufactured by Japan PMC) was exactly the same as Comparative Example 1. Coating on the support X was attempted, but the coating liquid was so scattered (jumping) that a recording medium sample could not be obtained.

<Comparative Example 4>
Polyvinyl alcohol (PVA103: manufactured by Kuraray Co., Ltd.) with respect to 100 parts of dry pulverized silica (NIPSIL E743 (manufactured by Nippon Silica Kogyo Co., Ltd.), oil absorption 160 ml / 100 g, BET specific surface area 40 m ² / g, average particle size 1.5 μm) 50 parts, 20 parts of cationic resin (polyamine ammonia epichlorohydrin, anion requirement: 6 meq / g, molecular weight: 100,000), 10 parts of cationic sizing agent (SS335: manufactured by Nippon PMC) A recording medium sample was obtained in exactly the same manner as in Comparative Example 1 except that (solid content: 28%, Hercules viscosity: 19.7 mPa · s, B-type viscosity: 650 mPa · s) was used. The coating amount of the coating solution was 4.9 g / m ² on one side. When this sample was dried, the coating layer was slightly removed.

<Comparative Example 5>
Synthetic silica G100 parts, polyvinyl alcohol (PVA103: manufactured by Kuraray Co., Ltd.) 50 parts, cationic resin (polyamine ammonia epichlorohydrin, anion requirement: 6 meq / g, molecular weight 100,000), cationic sizing agent (SS335) : Nippon PMC Co., Ltd.) 10 parts coating solution (solid content: 23%, Hercules viscosity: 12.5 mPa · s, B-type viscosity: 280 mPa · s) was prepared. This coating solution was applied to the support Y in exactly the same manner as in Example 1 to obtain a recording medium sample. The coating amount of the coating solution was 2.5 g / m ² on one side.

<Comparative Example 6>
Coating was carried out in the same manner as in Example 1 except that 50 parts of synthetic silica D and 50 parts of light calcium carbonate (Tama Pearl 123CS: manufactured by Okutama Kogyo Co., Ltd.) were used instead of 100 parts of light calcium carbonate-silica composite A. A liquid (solid content: 30%, Hercules viscosity: 14.3 mPa · s, B-type viscosity: 290 mPa · s) was prepared, and this coating solution was applied to the support Y in the same manner as in Example 1, A recording medium sample was obtained. The coating amount of the coating solution was 4.8 g / m ² on one side.

<Evaluation>
Each example and comparative example were evaluated by the following methods.

1) Printing density The sample was inkjet printed (black) with a SCITEX 6240 system printer (manufactured by SCITEX), and the printing density after 24 hours was measured with a Macbeth densitometer (RD918). If the print density is less than 1.2, the decrease in the print density is not preferable.
2) Ink absorbability The ink absorbability when the sample was inkjet printed (solid black) with the SCITEX 6240 system printer was visually evaluated.
A: Absorption is very fast.
○: Absorption is fast.
(Triangle | delta): Although absorption is a little slow, the level which does not have a problem in practical use.
X: Absorption is slow, leading to contamination of the device and printing, and cannot be used.

3) Water resistance The above-mentioned SCITEX 6240 system printer was subjected to ink jet printing (black) with “Electrical” characters on the sample, and after 3 hours, 20 μl of water was dropped onto the printing portion to evaluate the water resistance.
○: Bleeding of the printed part is hardly seen.
Δ: Although blurring of the printed part is seen, the characters can be distinguished.
X: The printed part bleeds out and characters can hardly be distinguished.
4) Applicability for offset printing Printing was performed with an offset printing machine (printing speed: 70 m / min) and evaluated.
A: Level at which there is no problem at all.
○: Slightly falling off of the coating layer occurs, but it is possible to operate without problems.
Δ: Slight blanket stains, faint prints, etc., but at a level where operation is possible.
×: Level at which the blanket is smudged and the printed portion is faint, causing operational problems.

5) Coating suitability with an on-machine coater ○: Scattering of the coating liquid (jumping) and falling off of the coating layer hardly occur.
Δ: A level at which the coating liquid is scattered (jumping) and the coating layer is slightly dropped, resulting in a decrease in operation efficiency.
X: A level that causes a large problem in operation due to scattering of the coating liquid (jumping) and dropping of the coating layer.

The obtained results are shown in Tables 1 and 2. Synthetic silica and light calcium carbonate-silica composites were indicated as “silica pigment”.

  As is clear from Tables 1 and 2, in each case, the printing density, water resistance, offset printing suitability, and on-machine coating suitability are all excellent, and offset printing and double-sided printing are possible. On-machine transfer roll coater It was found that this is an inkjet recording medium that can be manufactured by

On the other hand, in the case of Comparative Example 1 in which the oil absorption amount of the silica pigment in the coating liquid is less than 100 ml / 100 g and the average particle diameter is less than 1.0 μm, the print density and the ink absorbability are greatly reduced. . In the case of Comparative Example 2 in which the oil absorption of the silica pigment in the coating solution exceeds 250 ml / 100 g and the BET specific surface area exceeds 150 m ² / g, both the offset printing suitability and the on-machine coating suitability are greatly reduced. did. In the case of Comparative Example 3 in which the Hercules viscosity of the coating solution exceeded 30 mPa · s, coating with an on-machine gate roll coater could not be performed.
Furthermore, in the case of Comparative Example 4 in which dry silica was used as the silica pigment, the oil absorption amount, BET specific surface area, and average particle diameter of the silica pigment in the coating liquid were within the specified ranges of the present invention. Decreased significantly. Similarly, the oil absorption, BET specific surface area, and average particle diameter of the silica pigment in the coating liquid are within the specified range of the present invention, but a comparison using a mixture of synthetic silica and light calcium carbonate as the silica pigment. In the case of Example 6 as well, the ink absorptivity decreased significantly and the printing density also decreased. From these facts, the superiority of the present invention using a light calcium carbonate-silica composite as a pigment in the coating solution is clear.
In the case of Comparative Example 5 in which the average particle size of the silica pigment in the coating solution was less than 1.0 μm, the printing density was greatly reduced.

Claims (6)

Ink jet which is provided with an ink-receiving layer on at least one surface of a support by applying a coating liquid mainly composed of a pigment and a binder at a high speed of 300 m / min to 500 m / min with a transfer roll coater and then drying. A method for producing a recording medium, wherein the coating solution has a Hercules viscosity of 20 to 30 mPa · s, the pigment has an oil absorption of 140 to 180 ml / 100 g, a BET specific surface area of 21 to 30 m ² / g, an average A method for producing an inkjet recording medium for offset printing , comprising a light calcium carbonate-silica composite having a particle diameter of 3.1 to 7.3 μm. The light calcium carbonate-silica composite is adjusted to a pH of 7-9 by adding mineral acid at a temperature not higher than the boiling temperature of the liquid to a mixture of light calcium carbonate and an aqueous alkali metal silicate solution. The method for producing an inkjet recording medium for offset printing according to claim 1 , wherein the inkjet recording medium is obtained as described above. 3. The inkjet recording medium for offset printing according to claim 1, wherein the light calcium carbonate-silica composite has a light calcium carbonate / silica solid content mass ratio of 30/70 to 70/30. Production method. The inkjet recording medium for offset printing according to claim 2 or 3, wherein the light calcium carbonate-silica composite obtained by adjusting to the pH is blended in a coating solution without undergoing a drying step. Manufacturing method. The method for producing an inkjet recording medium for offset printing according to any one of claims 1 to 4, wherein the coating amount of the ink receiving layer is ² to 7 g / m ² per side. The manufacturing method of the inkjet recording medium for offset printing in any one of Claims 1-5 which contain cationic resin in the said coating liquid.