JPWO2019187889A1 - Recording paper manufacturing method - 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 wt% or more and 65 wt% or less of kaolin and 35 wt% or more and 60 wt% or less of heavy calcium carbonate, the total of kaolin and heavy calcium carbonate is 90 wt% or more, and the binder is at least styrene. A mixture of styrene-butadiene latex in an amount of 15 parts by weight or more and 25 parts by weight or less, and 57.5% by weight of ethylene glycol monoethyl ether and 42.5% by weight of formaldehyde, containing butadiene latex and 100 parts by weight of an 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 an inkjet recording paper, particularly a recording paper which can be suitably used as an industrial inkjet recording paper.

Generally, as a coated paper with a high surface gloss, a coated paper that is coated with a pigment on the surface and, if necessary, calendered, or a heated drum (mirrored surface of the coating layer in a wet state) There is known a cast coated paper or the like, which is pressed onto the surface of a cast drum) and dried to give a gloss finish. Among them, cast coated paper has higher surface gloss and superior surface smoothness as compared with calendered coated paper, so that it can be used for offset printing, letter press (a type of letterpress printing method), etc. Widely used as a coated paper for general printing.
Furthermore, a technique using a cast coated paper as an inkjet recording paper has also been developed (Patent Documents 1 to 3).

The inkjet recording method is a method in which droplets of ink are ejected from fine nozzles onto recording paper to form dots by adhering them to perform recording, but in recent years, inkjet printers, inks, recording media, etc. Due to technological advances, it has become easier to speed up recording, reduce noise, and easily form images with high print quality, and it is used in various fields.
Especially in fields such as commercial printing, it is possible to print digital information at high speed without making a plate, and handle small lots of various types and variable information printing. It is being introduced as a printing and recording method.

Therefore, cast coated paper is required to have inkjet recording suitability, particularly industrial inkjet recording suitability, in addition to conventional general printing suitability such as offset printing and letter press.
Here, industrial inkjet printers used in the fields of commercial printing and the like are required to be capable of printing a large amount in a short period of time, and therefore have a lower resolution than household inkjet printers, and the amount of ejected ink is small. Significantly less. Some also have a drying device.
Therefore, recording paper used in industrial inkjet printers requires less ink absorption than recording paper used in household inkjet printers, but in order to obtain good image quality, it is necessary to type It is important that the deposited ink spreads appropriately (having a constant dot diameter).

Japanese Patent Laid-Open No. 08-132730 JP, 2010-234789, A JP2012-213924A

  However, the conventional cast coated paper described in Patent Document 1 is mainly composed of light calcium carbonate and is configured to increase the amount of voids in the coating layer. Therefore, an industrial inkjet printer with a small amount of ejected ink. When the recording is carried out, the amount of the ink entering the voids of the coating layer and remaining on the surface layer is particularly small, so that the print density is poor. In addition, there is also a problem that white stripes (banding) are generated in the printing portion because the spread of ink is insufficient.

  Further, the cast inkjet paper described in Patent Document 2 which is intended for use in a household inkjet printer is also configured to use silica, which is a bulky pigment, as a main component to increase the amount of voids in the coating layer. Therefore, when recording with an industrial inkjet printer, there is a problem that banding occurs because the spread of ink is insufficient. Further, since silica is used as a pigment, the strength of the coating layer is insufficient and the general printability is poor as to the general printability such as offset printing and letter press.

  The cast inkjet paper described in Patent Document 3, which is supposed to be used in an industrial (water-based ink) inkjet printer, is excellent in inkjet recording suitability, particularly industrial inkjet recording suitability, but as a pigment as in Reference Document 2. Since silica is used, general printability is poor.

  Therefore, it is an object of the present invention to provide a recording sheet having inkjet printing suitability, particularly industrial inkjet recording suitability, in addition to general printing suitability such as offset printing and letter press.

The inventors of the present invention have made earnest studies to solve the above problems, and as a result, have made it possible to achieve the object of the present invention by using the following configurations.
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 Containing 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 parts by weight or more and 25 parts by weight or less with respect to 100 parts by weight of the inorganic pigment. A mixed solution of ethyl ether and 42.5% by weight of formaldehyde was dropped onto the recording layer and contacted 5 seconds later. Angle is equal to or more than 20 degrees 40 degrees, a.

In the recording paper of the present invention, it is preferable that the recording layer has a 75-degree specular gloss of 80 to 100%.
In the recording paper of the present invention, it is preferable that the recording layer has a smoothness (Oken method) defined in JIS P8155: 2010 of 4000 seconds or more.
In the recording paper of the present invention, it is preferable that the recording layer has an air permeability resistance (Oken type tester method) defined in JIS P8117: 2009 of 3000 seconds or more and 12000 seconds or less.
In the recording paper of the present invention, it is preferable that the recording layer further contains a polyethylene-based release agent.

  According to the present invention, it is possible to obtain 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.

The recording paper of the present invention contains a predetermined proportion of kaolin and ground calcium carbonate as the inorganic pigment of the recording layer, and further contains a predetermined proportion of styrene-butadiene latex (hereinafter also referred to as “SBL”) as a binder, and the contact described later. Define the corner.
Compared with light calcium carbonate, heavy calcium carbonate in the inorganic pigment secures the voids necessary for recording with an (industrial) inkjet printer in the recording layer consisting of a cast coating layer, and (industrial) inkjet recording. In, there is an effect of retaining ink on the surface layer.
Further, SBL also has an effect of suppressing ink from penetrating into the inside of the recording layer in (industrial) ink jet recording, and retaining the ink on the surface layer. Furthermore, SBL ensures general printability such as offset printing and letter press. In general printing, since ink is transferred by contacting it with a printing object, the printing object requires a certain surface strength. SBL also has the effect of increasing the glossiness of the printed portion. In addition, when the surface of the cast drum is pressure-bonded, dried, and gloss-finished, the mold releasability (peelability) from the cast drum is excellent.
Further, since SBL has an effect of suppressing the permeation of ink into the inside of the recording layer, increasing SBL tends to spread the ink in the plane direction of the recording layer (the direction along the surface).

However, since cast coated paper generally has high water repellency on the surface, it suppresses the ink from penetrating into the inside of the recording layer too much, and if excess ink is retained on the surface layer, the ink after drying and solidification is granular on the surface layer. And the fineness of the recorded image is reduced. In addition, it may cause ink drying failure. Further, even if the ink is retained on the surface layer, if it spreads too much in the plane direction, undesired mixing of the ink may occur, and the dried and solidified ink may become granular on the surface layer, resulting in deterioration of the definition of the recorded image. is there.
Therefore, by defining the contact angle, it is possible to improve the color developability in (industrial) inkjet recording, and to suppress the occurrence of banding (stripping) and beading (graininess).

Banding is a printing defect in which a white portion that is not originally printed is formed in the printing portion due to the reason that the ink does not spread in the recording layer, resulting in white streaks.
The beading (granularity) refers to both (i) a printing defect in which the ink is dried and solidified in a granular state, and (ii) image unevenness or drying defect. (i) is likely to occur when the ink does not permeate in the inner direction of the recording layer and does not spread in the plane direction, and even if the ink is difficult to permeate in the inner direction of the recording layer, if it spreads in the plane direction Hard to be granular.
On the other hand, when the ink spreads too much in the plane direction, the inks overlap each other particularly in the mixed color portion, which causes unevenness in the image and poor drying, which is the printing defect (ii).
Since (i) occurs when the ink contact angle is too high and (ii) occurs when the ink contact angle is too low, it is necessary to define the upper and lower limits of the contact angle.

(Inorganic pigment)
Containing 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 in 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 the white paper, but since the internal voids are small and it is easy to form a dense recording layer that is flat, the kaolin content is high. Thus, the voids in the recording layer are reduced, and the above beading (graininess) is likely to occur in (industrial) inkjet recording.

On the other hand, since ground calcium carbonate has a larger internal void than kaolin, it has the effect of suppressing the occurrence of beading in (industrial) ink jet recording, but if the blending amount of heavy calcium carbonate is large, it will become void in the recording layer. Is excessive, the ink is hard to spread, and the ink easily penetrates into the paper, so that the above-mentioned banding (strike-out) easily occurs. Also, the print density is reduced. Furthermore, there is a tendency that the smoothness of the recording layer decreases and the glossiness of the white paper decreases.
In the present invention, by mixing kaolin and ground calcium carbonate in the above ratio, good quality can be obtained.

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

  On the other hand, if the proportion of ground calcium carbonate exceeds 60% by weight or if the proportion of kaolin is less than 40% by weight, the voids in the recording layer become excessive, making it difficult for the ink to spread and penetrating into the paper. As a result, banding occurs and the print density also decreases.

  As the inorganic pigment for the recording layer, other pigments such as silica, talc, and alumina may be used in combination, but when the total of kaolin and ground calcium carbonate is less than 90% by weight, that is, another pigment is used. When it is used in an amount of 10% by weight or more, the ink hardly spreads in (industrial) ink jet recording to cause banding, the strength of the recording layer becomes insufficient for general printing applications, and the ink inking property becomes poor. Occurs. Further, since the smoothness of the recording layer is lowered, the white paper gloss tends to be lowered.

(binder)
The recording layer contains at least styrene-butadiene latex as a binder, and the SBL is 15 parts by weight or more and 25 parts by weight or less with respect to 100 parts by weight of the inorganic pigment.
If the proportion of SBL is less than 15% by weight, banding will occur when recording with an (industrial) inkjet printer. In addition, the strength of the recording layer is insufficient for general printing applications, and general printability is poor. If the SBL ratio exceeds 25 parts by weight, beading will occur when recording with an (industrial) inkjet printer. In addition, for general printing applications, the drying property of the ink is poor, set-off occurs, and the general printing suitability is poor.

(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 into 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 the solid portion of the color mixture, and the dried and solidified ink becomes granular on the surface layer, resulting in a fine image. I can't get it. Therefore, the beading (graininess) in (industrial) inkjet recording is inferior.
If the contact angle exceeds 40 degrees, the spread of the ink becomes too small and a gap is formed between the dots, so that banding (blanking) in (industrial) inkjet recording is poor. Further, problems such as a decrease in print density also occur.

  The "mixed solution of 57.5 wt% ethylene glycol monoethyl ether and 42.5 wt% formaldehyde" means a surface tension of 36.0 mN according to the wetting test method specified in JIS-K6768: 1999. The composition of the wetting reagent showing / m. The behavior of the ink at the time of recording is confirmed by using a wetting reagent having a surface tension similar to that of the ink used in an (industrial) inkjet printer.

(Release agent)
In the present invention, after the recording layer coating liquid is applied to form the recording layer, while the surface of the recording layer is in a wet state, the surface of the mirror-finished heating drum (cast drum) is pressed and dried. And cast it. At this time, it is preferable to add a release agent to the recording layer before the casting process so that the recording layer after drying can be smoothly peeled off from the cast drum.

The release agent can be appropriately selected and used from various known release agents that are generally used. However, since a release agent having high water-repellent property (water repellency) is generally used, The contact angle of the recording layer tends to be higher than that of other coated papers. Therefore, by using a polyethylene-based releasing agent that can relatively suppress water repellency while maintaining the releasing 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 easily exceeds 40 degrees. The contact angle is the lowest when the release agent is not 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 the synthetic wax having polyethylene as a homopolymer.

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

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

(Other binders)
The recording layer may contain a binder other than SBL. Other binders are not particularly limited as long as they sufficiently bond the inorganic pigment and the base paper and do not cause blocking between the 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, 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, acetyl cellulose, etc. And its derivatives; starches, enzyme-modified starches, thermochemically-modified starches, oxidized starches, esterified starches, etherified starches (eg, hydroxyethylated starches), cationized starches and other starches; polyacrylamides, cations Polyacrylamides such as hydrophilic polyacrylamide, anionic polyacrylamide, amphoteric polyacrylamide; urethane resins such as polyester polyurethane resin, polyether polyurethane resin, polyurethane ionomer resin; (meth) acrylic acid and (meth) acrylic Acrylic resins composed of monomer components (excluding olefins) that can be copolymerized with acids; polyolefin resins such as polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, 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 by a coagulation method, as described later, from the viewpoint of improving the glossiness of the recording layer and ensuring a sufficient amount of voids for recording with an (industrial) inkjet printer. Is preferred. Therefore, it is preferable to use proteins suitable for the coagulation method as the other binder, 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, since the workability is good and the glossiness of the white paper is also good.

  In the recording layer, in addition to the above-mentioned inorganic pigment, binder, release agent, if necessary, a dye for adjusting the hue, a pigment dispersant, an antiseptic agent, an antifoaming agent, a pH adjusting agent, etc. Various auxiliaries can be appropriately selected and used.

  The base paper can be appropriately selected and used from known base papers. 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, for example, blade coater, air knife coater, roll coater, curtain coater, bar coater, gravure coater, comma coater, etc. 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 / m @ 2, more preferably 15 to 30 g / m @ 2, and the dry film thickness of the coating layer is 5 to 30 .mu.m. preferable.

In addition, if necessary, an undercoat layer containing the above-mentioned inorganic pigment and binder as a main component 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 for producing the above-described general pigment-coated paper.
The coating amount (dry coating amount) of the undercoat layer is preferably 5 to 30 g / m <2>, more preferably 10 to 20 g / m <2> per side.

  As a method for forming the cast coating layer by drying the recording layer before the cast treatment, a mirror surface heated while the recording layer is in a wet state is used because the void amount is adjusted to a predetermined range with high glossiness. Of the casting methods of pressing on the finished surface and drying, it is preferable to use the casting method by the solidification method.

  The coagulant used in the coagulation liquid in the coagulation method includes, for example, formic acid, acetic acid, citric acid, tartaric acid, lactic acid, hydrochloric acid, sulfuric acid and the like 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, it is preferable to use formate, and more preferable to use calcium formate.

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

The smoothness (Oken method) of JIS P8155: 2010 of the recording layer is preferably 4000 seconds or more.
The smoothness (Ohken method) is a factor that influences how the ink spreads. When the smoothness (Oken method) is less than 4000 seconds (the surface is uneven), the ink is difficult to spread, banding occurs, and a uniform dot diameter cannot be obtained, and the fineness of the image may deteriorate.
The upper limit of the smoothness (Oken method) is not limited, but is 8000 seconds, for example.

It is preferable that the recording layer has an air permeability resistance (Oken type tester method) defined by JIS P8117: 2009 of 3000 seconds or more and 12000 seconds or less.
Permeability (Oken type tester method) is a factor that affects ink penetration. If the air resistance (Oken type tester method) is less than 3000 seconds, the ink may penetrate into the inside of the recording layer to lower the printing density, and banding may occur. On the other hand, when the air permeation resistance exceeds 12000 seconds, the ink is less permeated into the paper, and the ink may overflow into particles to cause beading.

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

(1) White paper glossiness It was measured by a method according to JIS P8142: 2005.
(2) Smoothness The smoothness was measured by a method (Oken method) according to JIS P8155: 2010.
(3) Air Permeability The resistance was measured by a method (Oken type tester method) according to JIS P8117: 2009.
(4) Contact angle Measured by the method described above.

(5) Surface strength (dry pick)
After the ink was printed on the recording layer using the RI printer under the following conditions and dried, the picking of the paper and the state of paper dust adhesion to the roll (confirmed by the liner) were 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: 0.4 ml
Rolls used: Rubber rolls ○: No picking of paper or adhesion of paper dust to the rolls.
Δ: There is some picking of paper or adhesion of paper powder to the roll.
X: Paper picking or paper dust adhered to the roll is large.

(6) Ink inking property The ink was printed on the recording layer using an RI printer under the following conditions, dried, and allowed to stand for 24 hours in an environment of 23 ° C / 50% RH, and then the density of the printed portion (black ) 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 The ink receptivity was evaluated according to the following criteria. If the evaluation is ◯ or Δ, there is no problem in practical use.
◯: 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 the RI printer under the following conditions, and 1 or 5 minutes after the printing, the ink is attached to the general coated paper (A2 coated paper), and the RI printing is performed. After nipping with a machine and standing for 1 day in an environment of 23 ° C. and 50% RH, the density (black) of the transferred ink was measured with a reflection densitometer (GretagMacbeth RD-19I). The setoff was evaluated according to the following criteria. If the evaluation is ◯ or Δ, there is no problem in practical use.
Ink type: TOYO ink TK NEX MZ black ink amount: 0.4ml
Roll used: Rubber roll ○: The density after 1 minute is less than 0.1 Δ: The density after 1 minute is 0.1 or more and less than 0.3, and the density after 5 minutes is less than 0.1 ×: After 1 minute Concentration of 0.3 or more or concentration after 5 minutes is 0.1 or more

(8) Industrial inkjet recording suitability The recording layer was inkjet-printed with a color ink jet printer PX-045A (printing conditions: plain paper, fast) manufactured by Seiko Epson Corporation, and the following was evaluated. In addition, by setting the printing condition to the plain paper and the quick mode in the household inkjet printer, the resolution and the ink ejection amount of the industrial inkjet printer are approximately the same.
<Print density>
Solid images were printed on cyan, magenta, yellow, and black, and allowed to stand for 24 hours in an environment of 23 ° C. and 50% RH, and 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 problem in practical use.
◯: Total print density of four colors is 7.0 or more Δ: Total print density of four colors is 6.0 or more and less than 7.0 ×: Total print density of four colors is less than 6.0

<Banding>
A black solid image (length 5 cm × width 5 cm) was printed, left standing 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 problem in practical use.
◯: A solid black image with no white spots.
Δ: There are some white streaks.
X: White streaks are conspicuous.

<Beading>
A green solid image (length 5 cm × width 5 cm) was printed, and allowed to stand for 24 hours in an environment of 23 ° C. and 50% RH, and then evaluated according to the following criteria. If the evaluation is ◯ or Δ, there is no problem in practical use.
◯: A clean green solid image with no granularity or bleeding of ink.
B: Some ink particles are visible.
X: The graininess of the ink is noticeable.

<Example 1>
Paper using 100 parts of hardwood bleached kraft pulp (LBKP) of 420 ml of CSF 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 to 100 parts of pulp. After the material was made with a Fourdrinier machine, it was calendered to obtain a base paper having a basis weight of 80 g / m 2.

The following formulations were stirred and dispersed to obtain a recording layer coating liquid and a coagulating liquid.
<Coating liquid for recording layer>
Kaolin (manufactured by Engelhard, product name: Ultra White 90) 50.0 parts Heavy calcium carbonate (manufactured by Sankyo Milling Co., product name: Escalon 2000) 50.0 parts Binder (styrene butadiene latex, manufactured by JSR Co.,
Product name: JSR0617) 20.0 parts Binder (casein, made in New Zealand,
Product name: Lactic casein 6.0 parts Release agent (polyethylene type, manufactured by San Nopco, product name: SN coat 287) 4.0 parts Surfactant (manufactured by San Nopco, product name: SN Wet 964) 1 copy

<Coagulation liquid>
Calcium formate 10.0 parts Water 90.0 parts

  Then, one side of the base paper was coated with the recording layer coating solution using a roll coater so that the coating amount was 20 g / m 2 in terms of solid content, and then the coagulation solution was coated to perform coagulation treatment. did.

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

In Example 2, a recording paper was obtained in the same manner as in Example 1 except that the compounding 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., Ltd., 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 compounding ratio of SBL as a binder was changed as shown in Tables 1 and 2.
In Example 5, a recording paper was obtained in the same manner as in Example 1 except that the mixing ratios of kaolin and ground calcium carbonate as inorganic pigments were changed as shown in Tables 1 and 2.
In Example 6, a polyethylene type (same as Example 1) and a higher fatty acid calcium type (manufactured by San Nopco, trade name: SN coat 246) were used as a release agent for the recording layer in the ratios shown in Tables 1 and 2. A recording sheet was obtained in the same manner as in Example 1 except for the above.

In Example 7, a recording paper was obtained in the same manner as in Example 1 except that the coating liquid for recording layer was applied in a solid content of 12 g / m 2 using a roll coater.
In Example 8, a recording paper was obtained in the same manner as in Example 1 except that the coating liquid for the recording layer was applied in a solid content of 35 g / m 2 using a roll coater.

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

In Comparative Examples 2 and 3, recording papers were obtained in the same manner as in Example 1 except that the compounding ratios of kaolin and ground calcium carbonate as inorganic pigments were changed as shown in Tables 1 and 2.
In Comparative Examples 4 and 5, recording sheets were obtained in the same manner as in Example 1 except that the compounding 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 higher fatty acid calcium type was used as the release agent for the recording layer in 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-based release agents were used in the proportions shown in Tables 1 and 2.

  Comparative Example 8 was carried out 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 the inorganic pigments in the ratios shown in Tables 1 and 2. I got a recording sheet.

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

  As is clear from Tables 1 and 2, in the case of each example in which the recording layer contains a predetermined proportion of kaolin and ground calcium carbonate as an inorganic pigment, and further a predetermined proportion of SBL as a binder, the contact angle is specified. In addition to ensuring general printability such as offset printing and letter press, it is possible to improve the color developability (printing density) in industrial inkjet recording, and suppress the occurrence of banding (strikeout) and beading (graininess). did it.

  In addition, in the case of Example 3 in which the smoothness (Oken method) is less than 4000 seconds and the air resistance (Oken type tester method) is less than 3000 seconds, industrial inkjet suitability (printing density) is higher than that of other Examples. , Banding, beading) was slightly inferior, but there is no problem in practical use.

In the case of Comparative Example 1 in which the recording layer does not contain heavy calcium carbonate, the print density in industrial inkjet recording was poor, and banding (strike-through) was also reduced.
It is considered that this is because the effect of retaining the ink on the surface layer was reduced because the voids in the recording layer increased.
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.
It is considered that this is because the voids in the recording layer were reduced, so that the ink did not penetrate into the inside of the recording layer and did not spread in the planar direction.

  In the case of Comparative Example 3 in which the proportion of heavy calcium carbonate in the recording layer was more than 60% by weight and the proportion of kaolin was less than 40% by weight, banding occurred. It is considered that this is because the voids in the recording layer increased and the ink easily penetrated into the paper, and the smoothness was low and the ink was difficult to spread.

  In the case of Comparative Example 4 in which 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 with an industrial inkjet printer. Moreover, the strength of the recording layer was insufficient for general printability.

  In the case of Comparative Example 5 in which SBL was more than 25 parts by weight with respect to 100 parts by weight of the inorganic pigment in the recording layer, beading occurred during recording with an industrial inkjet printer. As for general printability, the drying property of the ink was poor, and set-off occurred.

In the case of Comparative Example 6 in which the contact angle of the recording layer exceeded 40 degrees, banding occurred.
In 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 amount of kaolin and ground 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 as general printability, and ink receptivity was high. Was also inferior.

Claims (5)

A recording paper having a recording layer containing an inorganic pigment and a binder on at least one surface of a base paper,
The recording layer is a cast coating layer,
The inorganic pigment contains 40 wt% or more and 65 wt% or less of kaolin and 35 wt% or more and 60 wt% or less of heavy calcium carbonate based on 100 wt% of the inorganic pigment. The total is 90% by weight or more,
The binder contains at least styrene butadiene latex,
15 parts by weight or more and 25 parts by weight or less of the styrene-butadiene latex based on 100 parts by weight of the inorganic pigment,
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 into the recording layer is 20 degrees or more and 40 degrees or less,
A recording sheet characterized by being.   The recording paper according to claim 1, wherein the recording layer has a 75-degree specular gloss of 80 to 100%.   The recording sheet according to claim 1 or 2, wherein the recording layer has a smoothness (Oken method) defined in JIS P8155: 2010 of 4000 seconds or more.   The recording sheet according to claim 1 or 2, wherein the recording layer has an air permeability resistance (Oken type tester method) defined in JIS P8117: 2009 of 3000 seconds or more and 12000 seconds or less.   The recording paper according to claim 1, wherein the recording layer further contains a polyethylene-based release agent.