JP6657492B1 - Manufacturing method of recording paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recording paper which has inkjet printing suitability, particularly industrial inkjet recording suitability, in addition to general printing suitability such as offset printing and letter press. A recording paper having a recording layer containing an inorganic pigment and a binder on at least one surface of a base paper, wherein the recording layer is a cast coating layer, and the inorganic pigment is 100% by weight of the inorganic pigment. On the other hand, it contains 40% by weight or more and 65% by weight or less of kaolin and 35% by weight or more and 60% by weight or less of heavy calcium carbonate, the total of kaolin and heavy calcium carbonate is 90% by weight or more, and the binder is at least styrene. Mixture of 57.5% by weight of ethylene glycol monoethyl ether and 42.5% by weight of formaldehyde, containing butadiene latex, and 15 to 25 parts by weight of styrene butadiene latex per 100 parts by weight of inorganic pigment. The contact angle 5 seconds after the solution is dropped on the recording layer is 20 degrees or more and 40 degrees or less. [Selection diagram] None

Description

  The present invention relates to a recording paper having a cast coating layer, and more particularly to a recording paper that can be suitably used as an inkjet recording paper, particularly an industrial inkjet recording paper.

Generally, as a coated paper having a high surface gloss, a coated paper having a surface coated with a pigment and further subjected to a calender treatment as necessary, or a heated drum having a wet coated layer mirror-finished ( Cast coated paper and the like, which are pressed against the surface of a cast drum), dried, and gloss-finished, are known. Among them, cast coated paper has higher surface gloss and more excellent surface smoothness than calendered coated paper, so it can be used for offset printing and letter press (a type of letterpress printing method). Widely used as coated paper for general printing.
Further, a technique using cast coated paper for ink jet recording paper has also been developed (Patent Documents 1 to 3).

The ink jet recording method is a method in which ink droplets are ejected from fine nozzles onto recording paper to form dots by attaching the ink droplets, and recording is performed.In recent years, ink jet printers, inks, recording media, and the like have been used. Technological progress has made it easier to increase the speed of recording, reduce noise, and form images with high print quality, and it is widely used.
In particular, in the field of commercial printing, etc., digital information can be printed at high speed without plate making, and it is possible to handle small lot multi-type, variable information printing. It is being introduced as a printing and recording method.

For this reason, cast coated papers are required to have suitability for ink jet recording, particularly industrial ink jet recording, in addition to general print suitability such as conventional offset printing and letter press.
Here, industrial inkjet printers used in the field of commercial printing and the like are required to be able to perform large-scale printing in a short time, and therefore have a lower resolution and a lower ink ejection amount than home inkjet printers. Significantly less. Some have a drying device.
For this reason, recording paper used for industrial inkjet printers requires less ink absorption than recording paper used for home inkjet printers. It is important that the used ink spreads appropriately (has a constant dot diameter).

JP 08-132730 A JP 2010-234789 A JP 2012-213924 A

  However, the conventional cast coated paper described in Patent Document 1 mainly uses light calcium carbonate and has a configuration in which the amount of voids in the coating layer is increased. When recording is performed, the ink enters the gaps of the coating layer and the amount remaining on the surface layer becomes particularly small, so that the print density is poor. In addition, since the spread of the ink is insufficient, white stripes (banding) are generated in the printing portion.

  Further, the cast inkjet paper described in Patent Document 2 which is assumed to be used in a home inkjet printer also has a configuration in which silica, which is a bulky pigment, is mainly used to increase the amount of voids in the coating layer. For this reason, there is a problem that banding occurs due to insufficient ink spread when recording with an industrial inkjet printer. Furthermore, since silica is used as the pigment, the strength of the coating layer is insufficient for general printing suitability such as offset printing and letter press, and the general printing suitability is poor.

  The cast inkjet paper described in Patent Literature 3 which is assumed to be used in an industrial (aqueous ink) inkjet printer is excellent in inkjet recording suitability, particularly in industrial inkjet recording suitability. Since silica is used, general printability is poor.

  Therefore, an object of the present invention is to provide a recording sheet having not only general printing suitability such as offset printing and letter press but also ink jet printing suitability, particularly industrial ink jet printing suitability.

The inventors of the present invention have made intensive studies to solve the above problems, and as a result, have achieved the object of the present invention by using the following configuration.
That is, the recording paper of the present invention is a recording paper having a recording layer containing an inorganic pigment and a binder on at least one surface of the base paper, wherein the recording layer is a cast coating layer, and the inorganic pigment is Contains 40% by weight or more and 65% by weight or less of kaolin and 35% by weight or more and 60% by weight or less of heavy calcium carbonate with respect to 100% by weight of the inorganic pigment, and the total of the kaolin and the heavy calcium carbonate is 90% by weight. % Or more, the binder contains at least styrene-butadiene latex, and the styrene-butadiene latex is 15 to 25 parts by weight with respect to 100 parts by weight of the inorganic pigment. 5 seconds after dropping a mixed solution of ethyl ether and 42.5% by weight of formaldehyde on the recording layer, Angle is equal to or more than 20 degrees 40 degrees, a.

In the recording paper of the present invention, the recording layer preferably has a 75-degree specular gloss of 80 to 100%.
In the recording paper of the present invention, the recording layer preferably has a smoothness (Oken method) specified in JIS P8155: 2010 of 4000 seconds or more.
In the recording sheet of the present invention, the recording layer preferably has an air resistance (Oken test method) specified in JIS P8117: 2009 of not less than 3000 seconds and not more than 12000 seconds.
In the recording paper of the present invention, it is preferable that the recording layer further contains a polyethylene release agent.

  ADVANTAGE OF THE INVENTION According to this invention, in addition to general printing suitability, such as offset printing and letter press, it can obtain the recording paper which also has inkjet recording suitability, especially industrial inkjet recording suitability.

The recording paper of the present invention contains a predetermined ratio of kaolin and heavy calcium carbonate as the inorganic pigment of the recording layer, and further contains a predetermined ratio of styrene-butadiene latex (hereinafter also referred to as “SBL”) as a binder. Specify the corner.
The heavy calcium carbonate in the inorganic pigment makes the recording layer composed of the cast coating layer secure a necessary space when recording with an (industrial) inkjet printer, compared with the light calcium carbonate, and the (industrial) inkjet recording Has the effect of retaining ink on the surface layer.
SBL also has the effect of preventing ink from penetrating into the recording layer in (industrial) ink jet recording and retaining the ink on the surface layer. Furthermore, SBL ensures general printing suitability such as offset printing and letter press. In general printing, a certain surface strength is required for an object to be printed because the ink is transferred by being brought into contact with the object to be printed. SBL also has the effect of increasing the gloss of the printed portion. In addition, when the surface of the cast drum is pressed and dried to obtain a glossy finish, releasability (peelability) from the cast drum is excellent.
Also, since SBL has an effect of suppressing ink penetration into the inside of the recording layer, increasing the SBL tends to spread the ink in the plane direction of the recording layer (direction along the surface).

However, in general, cast coated paper has a high water repellency on the surface, so that too much ink is suppressed from penetrating into the recording layer.If excessive ink is retained on the surface layer, the dried and solidified ink becomes granular on the surface layer. And the definition of the recorded image is reduced. Further, it may cause poor drying of the ink. Also, if the ink is retained on the surface layer and spreads too much in the planar direction, unintentional mixing of the ink will occur, and the dried and solidified ink will also become granular on the surface layer, which may reduce the definition of the recorded image. is there.
Therefore, by defining the contact angle, the color developability in (industrial) ink jet recording is improved, and the occurrence of banding (striation loss) and beading (granularity) can be suppressed.

Banding (striation) is a printing defect in which a white portion that is not originally printed is formed in a printing portion due to, for example, that the ink does not spread in the recording layer, resulting in a white streak-like shape.
The beading (granular feeling) refers to both (i) poor printing in which the ink is dried and solidified in a granular state, and (ii) image unevenness or poor drying. (i) is likely to occur if the ink does not penetrate in the recording layer and does not spread in the plane direction, and if the ink does not easily penetrate in the recording layer, the ink easily spreads in the recording layer. Hard to be granular.
On the other hand, if the ink spreads too much in the plane direction, the ink will overlap, particularly in the mixed color portion, causing unevenness in the image or poor drying, which results in the printing failure (ii).
(I) occurs when the contact angle of the ink is too high, and (ii) occurs when the contact angle of the ink is too low. Therefore, it is necessary to define the upper and lower limits of the contact angle.

(Inorganic pigment)
40% by weight to 65% by weight of kaolin and 35% by weight to 60% by weight of heavy calcium carbonate with respect to 100% by weight of the inorganic pigment of the recording layer, and the total of kaolin and heavy calcium carbonate is 90% by weight. That is all.
Kaolin has the effect of improving the smoothness of the recording layer and improving the glossiness of white paper, but has a large amount of kaolin because the internal voids are small, and it is easy to form a flat and dense recording layer. In addition, the gaps in the recording layer are reduced, and the above-described beading (granularity) easily occurs in (industrial) ink jet recording.

On the other hand, heavy calcium carbonate has an inner space larger than kaolin, and thus has an effect of suppressing the occurrence of beading in (industrial) ink jet recording. Becomes excessive, and the ink becomes difficult to spread and easily penetrates into the paper, so that the above-mentioned banding (striation) tends to occur. Further, the print density also decreases. Further, there is a tendency that the smoothness of the recording layer is reduced and the glossiness of the white paper is reduced.
In the present invention, good quality can be obtained by blending kaolin and heavy calcium carbonate in the above ratio.

  If the proportion of heavy calcium carbonate is less than 35% by weight, or if the proportion of kaolin exceeds 65% by weight, the voids in the recording layer become too small and beading occurs in (industrial) inkjet recording.

  On the other hand, when the proportion of heavy calcium carbonate exceeds 60% by weight or the proportion of kaolin is less than 40% by weight, the voids in the recording layer become excessive, making it difficult for ink to spread and penetrating into paper. This tends to cause banding and reduce the print density.

  In addition, as the inorganic pigment of the recording layer, silica, talc, alumina, or the like may be used in combination as another pigment, but when the total of kaolin and heavy calcium carbonate is less than 90% by weight, that is, the other pigment is used. When used in an amount of 10% by weight or more, problems such as difficulty in spreading ink in (industrial) ink jet recording and banding, insufficient recording layer strength for general printing use, and poor ink adhesion. Occurs. In addition, since the smoothness of the recording layer is reduced, the glossiness of white paper tends to be reduced.

(binder)
The recording layer contains at least styrene butadiene latex as a binder, and has an SBL of 15 to 25 parts by weight based on 100 parts by weight of the inorganic pigment.
If the ratio of SBL is less than 15% by weight, banding occurs when recording with an (industrial) inkjet printer. In addition, the strength of the recording layer is insufficient for general printing use, and the general printing suitability is poor. If the ratio of SBL exceeds 25 parts by weight, beading occurs when recording with an (industrial) ink jet printer. In addition, for general printing applications, set-off occurs due to poor drying properties of the ink, resulting in poor general printing suitability.

(Contact angle)
The contact angle 5 seconds after dropping a mixed solution of 57.5% by weight of ethylene glycol monoethyl ether and 42.5% by weight of formaldehyde to the recording layer is 20 degrees or more and 40 degrees or less.
If the contact angle is less than 20 degrees, the spread of the ink becomes excessive, undesired mixing of the ink occurs in a mixed color solid portion, etc., and the dried and solidified ink becomes granular on the surface layer, and a fine image is formed. I can't get it. For this reason, beading (granularity) in (industrial) ink jet recording is inferior.
If the contact angle exceeds 40 degrees, the spread of the ink becomes too small, and a gap is formed between dots, so that banding (striation loss) in (industrial) inkjet recording is inferior. Further, problems such as a decrease in print density also occur.

  The “mixed solution of 57.5% by weight of ethylene glycol monoethyl ether and 42.5% by weight of formaldehyde” refers to a surface tension of 36.0 mN according to a wetting test method specified in JIS-K6768: 1999. / M is the composition of the wetting reagent. (Industrial) The behavior of the ink at the time of recording is confirmed by using a wetting reagent having the same surface tension as the ink used in the ink jet printer.

(Release agent)
In the present invention, after the recording layer is formed by applying the recording layer coating liquid, the recording layer is pressed and dried on the mirror-finished surface of the heating drum (cast drum) while the surface of the recording layer is in a wet state. And cast. At that time, it is preferable that the recording layer before the casting treatment contains a release agent so that the recording layer after drying is smoothly separated from the cast drum.

The release agent can be appropriately selected and used from various known release agents that are generally used. However, since the release agent (water repellency) having a high water repelling property is generally used, the release of the cast coated paper can be performed. The contact angle of the recording layer tends to be higher than other coated papers. Therefore, by using a polyethylene-based release agent that can relatively suppress water repellency while maintaining the release effect, it becomes easy to control the contact angle of the recording layer to 20 degrees or more and 40 degrees or less. On the other hand, when a release agent such as higher fatty acid calcium, paraffin, zinc stearate, special surfactant, carnauba wax, and ethylenebisstearic acid amide is used, the contact angle tends to exceed 40 degrees. The contact angle is lowest when no release agent is used.
The release agent is classified into natural wax, semi-synthetic wax and synthetic wax according to the composition, and the polyethylene-based release agent belongs to a synthetic wax containing polyethylene as a homopolymer.

  Specific examples of the polyethylene release agent include Maycatex HP series (Meisei Chemical Co., Ltd.), Nopcoat PEM-17, SN coat 287 (Sannopco), Polylon L-618 (Chukyo Yushi) and the like.

  The contact angle was measured using a mixed solution of 57.5% by weight of ethylene glycol monoethyl ether and 42.5% by weight of formaldehyde, and the contact angle 5 seconds after the mixed solution was dropped on the recording layer. Is measured by a contact angle measuring device (manufactured by DAT1100 FIBRO System AB).

(Other binders)
The recording layer may include a binder other than SBL. Other binders are not particularly limited as long as they sufficiently adhere the inorganic pigment to the base paper and do not cause blocking between papers.
Examples of such a binder include completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, and butyral-modified polyvinyl alcohol. Polyvinyl alcohols such as olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, and terminal alkyl-modified polyvinyl alcohol; hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, and acetyl cellulose. Starches such as starch, enzyme-modified starch, thermochemically-modified starch, oxidized starch, esterified starch, etherified starch (eg, hydroxyethylated starch), and cationized starch; polyacrylamide, cation Polyacrylamides, such as polyacrylamide, anionic polyacrylamide, and amphoteric polyacrylamide; urethane resins such as polyester polyurethane resin, polyether polyurethane resin, and polyurethane ionomer resin; (meth) acrylic acid and (meth) acrylic Acrylic resin composed of monomer components (excluding olefin) copolymerizable with acid; polyolefin resins such as polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, and polyvinyl chloride , Polychlorinated Vinylidene, polyacrylic acid ester, gum arabic, polyvinyl butyral, Porisuchirosu and their copolymers, silicone resins, petroleum resins, terpene resins, ketone resins, and the like can be exemplified coumarone resin.
These binders may be used alone or in combination of two or more as long as the effects of the present invention are not impaired.

In the present invention, the recording layer is provided by a casting method using a coagulation method, as described later, in order to secure a sufficient gap when recording with an (industrial) ink jet printer while improving the glossiness of the recording layer. Is preferred. Therefore, it is preferable to use proteins suitable for the coagulation method as other binders, and it is more preferable to use casein.
In the present invention, it is preferable that the casein is 3 parts by weight or more and 12 parts by weight or less with respect to 100 parts by weight of the inorganic pigment, because the operability becomes good and the glossiness of white paper is also good.

  In the recording layer, in addition to the above-mentioned inorganic pigments, binders and release agents, if necessary, dyes for adjusting hue, dispersants for pigments, preservatives, defoamers, pH adjusters and the like Various auxiliaries can be appropriately selected and used.

  The base paper can be appropriately selected from known base papers and used. Specific examples of the base paper include acid paper, neutral paper, waste paper blended paper, and the like.

The coating method of the recording layer may be any coating method used in the production of general pigment coated paper, such as a blade coater, an air knife coater, a roll coater, a curtain coater, a bar coater, a gravure coater, and a comma coater. It can be appropriately selected from known coating methods.
The coating amount (dry coating amount) of the recording layer is preferably 10 to 40 g / m2, more preferably 15 to 30 g / m2 per side, and the dry film thickness of the coating layer is 5 to 30 m. preferable.

If necessary, an undercoat layer containing the above-mentioned inorganic pigment and binder as main components may be provided between the base paper and the recording layer.
The coating method of the undercoat layer can be appropriately selected from the coating methods used in the production of the general pigment-coated paper described above.
The coating amount (dry coating amount) of the undercoat layer is preferably 5 to 30 g / m2, more preferably 10 to 20 g / m2 per one side.

  As a method of drying the recording layer before the cast treatment to form a cast coating layer, since the amount of voids is adjusted to a predetermined range with high gloss, the mirror surface heated while the recording layer is in a wet state is used. It is preferable to use a casting method based on a solidification method among the casting methods of pressing and drying the finished surface.

  Examples of the coagulant used in the coagulation liquid in the coagulation method include, for example, formic acid, acetic acid, citric acid, tartaric acid, lactic acid, hydrochloric acid, sulfuric acid, and various metals such as potassium, calcium, zinc, barium, lead, magnesium, cadmium, and aluminum. Salts, that is, potassium sulfate, potassium citrate, borax, boric acid, and the like are used. In the present invention, formate is preferably used, and calcium formate is more preferably used.

  The heated mirror-finished surface refers to a cylindrical drum that is usually heated to 100 ° C. and mirror-finished, and by using this, the 75-degree specular gloss of the recording layer surface, which is a cast coating layer, is obtained. The degree can be easily and stably set to 80 to 100%.

The recording layer preferably has a smoothness (Oken method) specified in JIS P8155: 2010 of 4000 seconds or more.
Smoothness (Oken method) is a factor that affects how ink spreads. If the smoothness (Oken method) is less than 4000 seconds (the surface is uneven), it becomes difficult to spread the ink, banding occurs, a uniform dot diameter cannot be obtained, and the definition of an image may be reduced.
The upper limit of the smoothness (Oken method) is not limited, but is, for example, 8000 seconds.

It is preferable that the recording layer has an air resistance (Oken type testing machine method) specified in JIS P8117: 2009 of 3000 seconds or more and 12000 seconds or less.
Air permeability resistance (Oken tester method) is a factor that affects ink penetration. If the air permeability resistance (Oken test machine method) is less than 3000 seconds, the ink may penetrate into the recording layer to lower the print density, and banding may occur. On the other hand, if the air resistance exceeds 12,000 seconds, the penetration of the ink into the paper decreases, and the ink overflows in a granular manner, which may cause beading.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto. “Parts” and “%” indicate parts by weight and% by weight, respectively, unless otherwise specified.
The test / measurement methods and evaluation criteria performed on the recording sheets obtained in the examples and comparative examples are as follows.

(1) Glossiness of blank paper It was measured by a method according to JIS P8142: 2005.
(2) Smoothness Measured by a method according to JIS P8155: 2010 (Oken method).
(3) Air permeability resistance Measured by a method according to JIS P8117: 2009 (Oken type testing machine method).
(4) Contact angle It was measured by the method described above.

(5) Surface strength (dry pick)
After printing and drying the ink on the recording layer using the RI printer under the following conditions, the picking of the paper and the adhesion of the paper powder to the roll (confirmed by backing) are visually evaluated according to the following criteria. did. If the evaluation is ○ or Δ, there is no practical problem.
Ink type: SMX tack grade black (tack: 20)
Ink volume: 0.4ml
Roll used: rubber roll ：: Neither paper picking nor paper powder adhesion to the roll.
Δ: There is some paper powder picking or paper powder adhesion to the roll.
X: There is much paper powder picking or paper powder adhesion to the roll.

(6) Ink Adhesion The ink was printed on the recording layer using an RI printer under the following conditions, dried, and allowed to stand at 23 ° C./50% RH for 24 hours. ) Was measured with a reflection densitometer (GretagMacbeth RD-19I).
Ink type: TOYO ink TK NEX MZ black Ink amount: 0.3ml
Roll used: rubber roll Ink adhesion was evaluated according to the following criteria. If the evaluation is ○ or Δ, there is no practical problem.
：: Density (black) of the printed part is 2.3 or more Δ: Density (black) of the printed part is 2.1 or more and less than 2.3 ×: Density (black) of the printed part is less than 2.1

(7) Set-off The ink is printed on the recording layer using a RI printer under the following conditions, and after 1 minute or 5 minutes from the printing, the recording layer is adhered to a general coated paper (A2 coated paper) to perform RI printing. After nipping with a press and leaving it to stand at 23 ° C. and 50% RH for one day, the density (black) of the transferred ink was measured with a reflection densitometer (GretagMacbeth RD-19I). Set-off was evaluated according to the following criteria. If the evaluation is ○ or Δ, there is no practical problem.
Ink type: TOYO ink TK NEX MZ black Ink amount: 0.4 ml
Roll used: rubber roll ○: The concentration after 1 minute is less than 0.1 Δ: The concentration after 1 minute is 0.1 or more and less than 0.3, and the concentration after 5 minutes is less than 0.1 ×: After 1 minute Concentration is 0.3 or more or concentration after 5 minutes is 0.1 or more

(8) Industrial inkjet recording suitability Ink jet printing was performed on the recording layer using a color ink jet printer PX-045A (printing conditions: plain paper, fast) manufactured by Seiko Epson Corporation, and the following was evaluated. Note that by setting the printing conditions to plain paper and fast mode with a home-use inkjet printer, the resolution and ink ejection amount of the industrial inkjet printer are almost the same.
<Print density>
Each solid image was printed for cyan, magenta, yellow, and black, and allowed to stand at 23 ° C. and 50% RH for 24 hours. Then, the print density of each image portion was measured with a reflection densitometer (GretagMacbeth RD-19I). .
The total value of the print densities of the four colors was evaluated according to the following criteria. If the evaluation is ○ or Δ, there is no practical problem.
：: The total value of the print densities of the four colors is 7.0 or more Δ: The total value of the print densities of the four colors is 6.0 or more and less than 7.0 ×: The total value of the print densities of the four colors is less than 6.0

<Banding>
A black solid image (5 cm long × 5 cm wide) was printed and allowed to stand at 23 ° C. and 50% RH for 24 hours, and then evaluated according to the following criteria. If the evaluation is ○ or Δ, there is no practical problem.
：: A beautiful black solid image with no white spots.
Δ: There are some white streaks.
×: White streaks are noticeable.

<Beading>
A green solid image (5 cm long × 5 cm wide) was printed and allowed to stand at 23 ° C. and 50% RH for 24 hours, and then evaluated according to the following criteria. If the evaluation is ○ or Δ, there is no practical problem.
：: A clean green solid image without ink graininess or bleeding.
Δ: Ink particles are slightly visible.
×: The granularity of the ink is conspicuous.

<Example 1>
Paper containing 420 parts of CSF 420 ml of hardwood bleached kraft pulp (LBKP) as a pulp raw material and 10 parts of heavy calcium carbonate, 0.2 part of alkyl ketene dimer and 0.5 part of aluminum sulfate mixed with 100 parts of pulp The paper was machined with a fourdrinier machine and then calendered to obtain a base paper having a basis weight of 80 g / m2.

The compositions having the following composition were respectively dispersed by stirring to obtain a coating liquid for a recording layer and a coagulation liquid.
<Coating liquid for recording layer>
Kaolin (manufactured by Engelhard Co., product name: Ultra White 90) 50.0 parts Heavy calcium carbonate (manufactured by Sankyo Flour Milling Co., Ltd., product name: Escalon 2000) 50.0 parts Binder (styrene butadiene latex, manufactured by JSR Corporation)
Product name: JSR0617) 20.0 parts Binder (casein, New Zealand,
Product name: Lactic casein) 6.0 parts Release agent (polyethylene, manufactured by San Nopco, product name: SN coat 287) 4.0 parts Surfactant (manufactured by San Nopco, product name: SN wet 964) One copy

<Coagulation liquid>
Calcium formate 10.0 parts Water 90.0 parts

  Next, the coating liquid for the recording layer is coated on one side of the base paper using a roll coater so as to have a coating amount of 20 g / m2 as a solid content, and then a coagulation liquid is applied to perform coagulation treatment. did.

  Next, while the obtained recording layer was in a wet state, the recording layer was pressed against the mirror surface of a cast drum heated to 110 ° C. and dried to form a cast coating layer, thereby obtaining recording paper.

In Example 2, a recording sheet was obtained in the same manner as in Example 1 except that the mixing ratio of SBL as a binder was changed as shown in Tables 1 and 2.
In Example 3, a recording paper was obtained in the same manner as in Example 1 except that SBL, polyvinyl alcohol (manufactured by Kuraray Co., product name: PVA117) and casein were used as binders in the ratios shown in Tables 1 and 2. .
In Example 4, a recording sheet was obtained in the same manner as in Example 1 except that the mixing ratio of SBL as a binder was changed as shown in Tables 1 and 2.
In Example 5, a recording sheet was obtained in the same manner as in Example 1, except that the mixing ratio of kaolin and heavy calcium carbonate as inorganic pigments was changed as shown in Tables 1 and 2.
In Example 6, a polyethylene-based (same as in Example 1) and a higher fatty acid calcium-based (manufactured by San Nopco, trade name: SN coat 246) were used as release agents for the recording layer at the ratios shown in Tables 1 and 2. Except for the above, a recording sheet was obtained in the same manner as in Example 1.

In Example 7, a recording paper was obtained in the same manner as in Example 1, except that the coating liquid for the recording layer was applied using a roll coater so that the coating amount was 12 g / m2 in solid content.
In Example 8, a recording paper was obtained in the same manner as in Example 1, except that the coating liquid for a recording layer was applied using a roll coater so that the coating amount was 35 g / m2 in solid content.

  In Comparative Example 1, the mixing ratio of kaolin and light calcium carbonate was changed as shown in Tables 1 and 2 by using light calcium carbonate (manufactured by Shiraishi Kogyo, product name: Univer 70) instead of heavy calcium carbonate as the inorganic pigment. A recording sheet was obtained in the same manner as in Example 1 except for the above.

In Comparative Examples 2 and 3, recording paper was obtained in the same manner as in Example 1 except that the mixing ratio of kaolin and heavy calcium carbonate as inorganic pigments was changed as shown in Tables 1 and 2.
In Comparative Examples 4 and 5, recording paper was obtained in the same manner as in Example 1 except that the mixing ratio of SBL as a binder was changed as shown in Tables 1 and 2.

In Comparative Example 6, a recording paper was obtained in the same manner as in Example 1, except that the higher fatty acid calcium system was used as a release agent for the recording layer at the ratios shown in Tables 1 and 2.
In Comparative Example 7, a recording paper was obtained in the same manner as in Example 1, except that polyethylene was used as the release agent for the recording layer in the proportions shown in Tables 1 and 2.

  Comparative Example 8 was performed in the same manner as in Example 1 except that kaolin, heavy calcium carbonate, and silica (manufactured by Nippon Aerosil Co., Ltd., trade name: Aerosil 300) were used as inorganic pigments in the ratios shown in Tables 1 and 2. Recording paper was obtained.

  The glossiness, contact angle, smoothness, and air resistance of the obtained recording paper are as shown in Tables 1 and 2, and the printability and industrial suitability obtained when used as general printing paper were obtained. The recording suitability obtained when used as an inkjet recording paper is as shown in Tables 1 and 2.

  As is clear from Tables 1 and 2, in the case of each of the examples in which the recording layer contained a predetermined ratio of kaolin and heavy calcium carbonate as the inorganic pigment, further contained a predetermined ratio of SBL as the binder, and defined the contact angle. In addition to ensuring general printing suitability such as offset printing and letter press, the color developability (print density) is improved in industrial ink jet recording, and the occurrence of banding (striation loss) and beading (granularity) can be suppressed. did it.

  In the case of Example 3 in which the smoothness (Oken method) was less than 4000 seconds and the air permeability (Oken test machine method) was less than 3000 seconds, the suitability for industrial inkjet (print density) was lower than in the other examples. , Banding and beading) were slightly inferior, but there was no practical problem.

In the case of Comparative Example 1 in which the recording layer did not contain heavy calcium carbonate, the print density in industrial inkjet recording was poor, and banding (striations) was also reduced.
This is presumably because the effect of retaining the ink on the surface layer was reduced due to the increase in the gaps in the recording layer.
In Comparative Example 2 in which the proportion of heavy calcium carbonate in the recording layer was less than 35% by weight and the proportion of kaolin exceeded 65% by weight, beading (granularity) occurred in industrial inkjet recording.
This is presumably because the voids in the recording layer were reduced, so that the ink did not penetrate into the recording layer and did not spread in the plane direction.

  In Comparative Example 3 in which the proportion of heavy calcium carbonate in the recording layer exceeded 60% by weight and the proportion of kaolin was less than 40% by weight, banding occurred. This is presumably because the gaps in the recording layer increased and the ink easily penetrated into the paper, and the smoothness was low, making it difficult for the ink to spread.

  In the case of Comparative Example 4 in which the SBL was less than 15 parts by weight with respect to 100 parts by weight of the inorganic pigment in the recording layer, banding occurred when recording was performed with an industrial inkjet printer. In addition, the strength of the recording layer was insufficient for general printability.

  In the case of Comparative Example 5 in which the SBL exceeded 25 parts by weight with respect to 100 parts by weight of the inorganic pigment in the recording layer, beading occurred when recording was performed with an industrial inkjet printer. In addition, as for general printing suitability, set-off occurred due to poor drying property of the ink.

In the case of Comparative Example 6 in which the contact angle of the recording layer exceeded 40 degrees, banding occurred.
In the case of Comparative Example 7 in which the contact angle of the recording layer was less than 20 degrees, beading occurred.

  In the case of Comparative Example 8 in which the total of kaolin and heavy calcium carbonate was less than 90% by weight with respect to 100% by weight of the inorganic pigment in the recording layer, the strength of the recording layer was insufficient for general printability, Was also inferior.

Claims (4)

A method for producing a recording paper having a recording layer containing an inorganic pigment and a binder on at least one surface of a base paper,
Forming the recording layer into a cast coating layer by a solidification method,
The inorganic pigment includes 40% by weight or more and 65% by weight or less of kaolin and 35% by weight or more and 60% by weight or less of heavy calcium carbonate with respect to 100% by weight of the inorganic pigment. The total is 90% by weight or more,
The binder contains at least styrene butadiene latex and casein,
For 100 parts by weight of the inorganic pigment, the styrene-butadiene latex is 15 parts by weight or more and 25 parts by weight or less, and the casein is 3 parts by weight or more and 12 parts by weight or less,
5 seconds after dropping a mixed solution of 57.5% by weight of ethylene glycol monoethyl ether and 42.5% by weight of formaldehyde to the recording layer, the contact angle is 20 degrees or more and 40 degrees or less;
A method for manufacturing a recording sheet, wherein the 75-degree specular glossiness of the recording layer is 80 to 100%.   The method for producing a recording sheet according to claim 1, wherein the recording layer has a smoothness (Oken method) specified in JIS P8155: 2010 of 4000 seconds or more.   4. The method for producing a recording sheet according to claim 1, wherein the recording layer has an air resistance (Oken type testing machine method) specified in JIS P8117: 2009 of 3,000 seconds or more and 12000 seconds or less.   The method according to claim 1, wherein the recording layer further contains a polyethylene-based release agent.