WO2019187889A1

WO2019187889A1 - Recording sheet

Info

Publication number: WO2019187889A1
Application number: PCT/JP2019/007213
Authority: WO
Inventors: 昌也登坂; 吉田　義雄; 望美豊田; 明子松村
Original assignee: 日本製紙株式会社
Priority date: 2018-03-29
Filing date: 2019-02-26
Publication date: 2019-10-03
Also published as: JPWO2019187889A1; JP6657492B1

Abstract

[Problem] To provide a recording sheet that is suited for inkjet printing, and in particular, industrial inkjet printing, in addition to general printing suitability for offset printing, letterpress printing, or the like. [Solution] Provided is a recording sheet that has, on at least one surface of a base sheet, a recording layer that contains an inorganic pigment and a binder, wherein: the recording layer is a cast coating layer; the inorganic pigment contains, in relation to 100 wt% of the inorganic pigment, 40 to 65 wt% of kaolin and 35 to 60 wt% of heavy calcium carbonate; the kaolin and the heavy calcium carbonate total 90 wt% or greater; the binder contains at least styrene-butadiene latex; the styrene-butadiene latex constitutes 15 to 25 parts by weight in relation to 100 parts by weight of the inorganic pigment; and a mixed solution with 57.5 wt% of ethylene glycol monoethyl ether and 42.5 wt% of formaldehyde has a contact angle of 20 to 40 degrees, 5 seconds after being dripped onto the recording layer.

Description

Recording sheet

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

In general, coated paper with high surface gloss is coated with a pigment on the surface, and calendered as needed, or a heated drum with a mirror finish on a wet coating layer ( Known is cast coated paper that is gloss-finished by press-bonding to the surface of the cast drum) and drying. Among them, cast coated paper has higher surface gloss and superior surface smoothness compared to calendered coated paper, and therefore, such as offset printing and letter press (a type of letterpress printing method). Widely used as coated paper for general printing.
Furthermore, a technique using cast coated paper for ink jet recording paper has 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 a recording sheet and adhered to form dots to perform recording. However, in recent years, ink jet printers, inks, recording media, etc. Due to technological progress, it has become easy to increase the recording speed, reduce the noise, and form an image with high print quality, and it is used in various fields.
In particular, in the field of commercial printing, digital information can be printed at high speed without making a plate, and it is possible to handle a variety of small lots and variable information printing, so it can replace offset printing and letter press in on-demand printing. It is being introduced as a printing and recording method.

For this reason, cast coated paper is required to be suitable for inkjet recording, especially industrial inkjet recording, in addition to conventional offset printing, letter press, and other general printing aptitudes.
Here, industrial inkjet printers used in fields such as commercial printing are required to be able to print in large quantities in a short time, so the resolution is lower than that of household inkjet printers, and the amount of ink to be ejected is low. Significantly less. Some also have a drying device.
Therefore, the recording paper used for industrial inkjet printers requires less ink absorbency than the recording paper used for household inkjet printers. It is important that the obtained ink spreads moderately (has a certain dot diameter).

Japanese Patent Laid-Open No. 08-132730 JP 2010-234789 A JP 2012-213924 A

However, since the conventional cast coated paper described in Patent Document 1 uses light calcium carbonate as a main component and increases the amount of voids in the coated layer, an industrial inkjet printer with a small amount of ink injection In this case, the ink density enters the gap in the coating layer and the amount remaining on the surface layer is particularly small, so that the print density is inferior. Further, since the ink spread is insufficient, there is a problem that white lines (banding) are generated in the printing portion.

In addition, the cast inkjet paper described in Patent Document 2 that is assumed to be used in an inkjet printer for home use is mainly composed of silica, which is a bulky pigment, and increases the amount of voids in the coating layer. For this reason, there is a problem that banding occurs due to insufficient ink spreading 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 ink jet paper described in Patent Document 3, which is supposed to be used in an industrial (aqueous ink) ink jet printer, is excellent in ink jet recording aptitude, particularly industrial ink jet recording aptitude. Since silica is used, general printability is poor.

Accordingly, an object of the present invention is to provide a recording paper having ink jet recording suitability, particularly industrial ink jet recording suitability, in addition to general print suitability such as offset printing and letter press.

The inventors of the present invention have made extensive studies in order 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 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 side of the base paper, wherein the recording layer is a cast coating layer, and the inorganic pigment is 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 with respect to 100 wt% of the inorganic pigment, and the total of the kaolin and the heavy calcium carbonate is 90 wt%. And the binder contains at least a 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, and 57.5% by weight of ethylene glycol mono 5 seconds after the mixed solution of ethyl ether and 42.5 wt% formaldehyde was dropped 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 ° specular glossiness of 80 to 100%.
In the recording paper of the present invention, the recording layer preferably has a smoothness (Oken method) defined by JIS P8155: 2010 of 4000 seconds or more.
In the recording paper of the present invention, it is preferable that the air permeability resistance (Oken tester method) defined in JIS P8117: 2009 of the recording layer is 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 release agent.

According to the present invention, it is possible to obtain a recording paper having not only general printing aptitude such as offset printing or letter press but also ink jet recording aptitude, particularly industrial ink jet recording aptitude.

The recording paper of the present invention contains a predetermined proportion of kaolin and heavy calcium carbonate as inorganic pigments in the recording layer, and further contains a predetermined proportion of styrene butadiene latex (hereinafter also referred to as “SBL”) as a binder, and will be described later. Define the corners.
Heavy calcium carbonate in inorganic pigments, compared with light calcium carbonate, has a recording layer consisting of a cast coating layer to ensure a sufficient gap for recording with an (industrial) ink jet printer, and (industrial) ink jet recording. This has the effect of retaining ink on the surface layer.
SBL also has the effect of suppressing ink from penetrating into the recording layer in (industrial) ink jet recording and retaining the ink on the surface layer. Further, SBL ensures general printability such as offset printing and letter press. In general printing, ink is brought into contact with a printing object to be transferred, so that the printing object needs a certain surface strength. SBL also has the effect of increasing the glossiness of the printed portion. Moreover, when the surface of the cast drum is pressure-bonded and dried to give a gloss finish, the releasability (peelability) from the cast drum is excellent.
Further, since SBL has an effect of suppressing ink permeation in the internal direction of the recording layer, when SBL is increased, the ink tends to spread in the plane direction (direction along the surface) of the recording layer.

However, in general, cast coated paper has a high surface water repellency, so that it prevents the ink from penetrating into the recording layer too much. If excessive ink is retained on the surface layer, the dried and solidified ink is granular on the surface layer. As a result, the definition of the recorded image decreases. In addition, it may cause poor drying of the ink. In addition, if the ink is retained on the surface layer but spreads too much in the plane direction, unintended ink mixing occurs, and the dried and solidified ink becomes grainy on the surface layer, which may reduce the fineness of the recorded image. is there.
Therefore, by defining the contact angle, color developability is improved in (industrial) ink jet recording, and banding (stretching) and beading (graininess) can be suppressed.

Banding is a print defect in which a white portion that is not originally printed on a portion of the print portion is formed due to reasons such as ink not spreading in the recording layer, resulting in white stripes.
Beading (graininess) refers to both (i) defective 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 when the ink does not penetrate into the recording layer and does not spread in the plane direction. Hard to be granular.
On the other hand, if the ink spreads too much in the plane direction, the ink overlaps particularly in the mixed color portion, and it becomes easy to cause unevenness in the image or poor drying, and this becomes 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)
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 with respect to 100 wt% of the inorganic pigment in the recording layer, and the total of kaolin and heavy calcium carbonate is 90 wt% That's it.
Kaolin has the effect of improving the smoothness of the recording layer and improving the glossiness of the blank paper. However, the amount of kaolin is large because the internal voids are small and it is flat and easy to form a dense recording layer. The voids in the recording layer are reduced, and the above-described beading (graininess) is likely to occur in (industrial) ink jet recording.

On the other hand, heavy calcium carbonate has an effect of suppressing the occurrence of beading in (industrial) ink jet recording because the internal voids are larger than kaolin. However, if the amount of heavy calcium carbonate is large, the voids in the recording layer As a result, the ink becomes difficult to spread and easily penetrates into the paper, and the above-mentioned banding (leakage) is likely to occur. Also, the print density is lowered. Furthermore, there is a tendency that the smoothness of the recording layer is lowered and the glossiness of the white paper is lowered.
In the present invention, it is possible to obtain good quality by blending kaolin and heavy calcium carbonate in the above ratio.

When the proportion of heavy calcium carbonate is less than 35% by weight or when the proportion of kaolin exceeds 65% by weight, the recording layer has insufficient voids and beading occurs in (industrial) ink jet recording.

On the other hand, when the proportion of heavy calcium carbonate exceeds 60% by weight or when the proportion of kaolin is less than 40% by weight, 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 decreases.

As the inorganic pigment for the recording layer, silica, talc, alumina or the like may be used in combination with other pigments. However, when the total of kaolin and heavy calcium carbonate is less than 90% by weight, that is, other pigments are used. When used in an amount of 10% by weight or more, problems such as (industrial) ink jet recording that the ink is difficult to spread and banding occurs, the recording layer is insufficient in strength for general printing, and the ink inking property is inferior. Will occur. In addition, since the smoothness of the recording layer is lowered, there is a tendency that the glossiness of the blank paper is lowered.

(binder)
The recording layer contains at least styrene butadiene latex as a binder, and 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.
When the ratio of SBL is less than 15 weights, banding occurs when recording with an (industrial) ink jet printer. Moreover, the strength of the recording layer is insufficient for general printing applications, and the general printing suitability is poor. When the SBL ratio exceeds 25 parts by weight, beading occurs when recording with an (industrial) ink jet printer. In general printing applications, the ink is inferior in dryness, causing set-off, resulting in poor general printing suitability.

(Contact angle)
The contact angle after 5 seconds after dropping a mixed solution of 57.5 wt% ethylene glycol monoethyl ether and 42.5 wt% formaldehyde on 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 ink becomes excessive, unintentional ink mixing occurs in the mixed color solid part, etc., and the dried and solidified ink becomes grainy on the surface layer, resulting in a fine image. I can't get it. For this reason, beading (graininess) in (industrial) ink jet recording is inferior.
When the contact angle exceeds 40 degrees, the spread of the ink becomes excessively small, and a gap is formed between the dots, so that banding (stripe loss) in (industrial) ink jet recording is inferior. In addition, 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 defined in JIS-K6768: 1999. This is the composition of the wetting reagent indicating / m. (Industrial) The behavior of ink during recording is confirmed by using a wetting reagent having the same surface tension as that of ink used in an ink jet printer.

(Release agent)
In the present invention, after the recording layer coating liquid is applied and the recording layer is provided, while the recording layer surface is in a wet state, it is pressed and dried on the surface of a heated mirror (cast drum) having a mirror finish. And cast. At that time, it is preferable to contain a release agent in the recording layer before casting so that the recording layer after drying is smoothly peeled off from the casting 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 repellency (water repellency) is generally used, The contact angle of the recording layer tends to be higher than other coated papers. Therefore, by using a polyethylene release agent that can suppress water repellency while maintaining the release effect, it becomes easy to manage 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, paraffinic, zinc stearate, special surfactant, carnauba wax, ethylenebisstearic acid amide is used, the contact angle tends to exceed 40 degrees. Note that 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 release agent belongs to a synthetic wax having 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 (San Nopco), Polylon L-618 (Chukyo Yushi).

The contact angle was measured by using a mixed solution of 57.5% by weight of ethylene glycol monoethyl ether and 42.5% by weight of formaldehyde, and dropping the mixed solution onto the recording layer, after 5 seconds. Is measured with a contact angle measuring device (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 adhere the inorganic pigment and the base paper and do not cause blocking between the papers.
Such binders include fully 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. Olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, terminal alkyl-modified polyvinyl alcohol, and the like; hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, acetyl cellulose Cellulose ethers and derivatives thereof; starches such as starch, enzyme-modified starch, thermochemically modified starch, oxidized starch, esterified starch, etherified starch (for example, hydroxyethylated starch), cationized starch; polyacrylamide, cation Polyacrylamides such as water-soluble polyacrylamide, anionic polyacrylamide, and amphoteric polyacrylamide; urethane resins such as polyester polyurethane resins, polyether polyurethane resins, polyurethane ionomer resins; (meth) acrylic acid and (meth) acrylic Acrylic resin consisting of monomer components (excluding olefins) copolymerizable with acid; 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 admixture 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 securing a necessary degree of 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 is good and the glossiness of the white paper is also good.

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

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

The recording layer coating method may be any coating method used in the production of general pigment coated paper, such as blade coater, air knife coater, roll coater, curtain coater, bar coater, gravure coater, comma coater, etc. It can select suitably from well-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 per side, and the dry film thickness of the coating layer is 5 to 30 μm. preferable.

Further, if necessary, an undercoat layer mainly composed of the above-described inorganic pigment and binder 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 the production of the general pigment-coated paper described above.
The coating amount of the undercoat layer (dry coating amount) is preferably 5 to 30 g / m 2, more preferably 10 to 20 g / m 2 per side.

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

Examples of the coagulant used for the coagulation liquid in the coagulation method include 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 is a cylindrical drum that is usually heated to 100 ° C. and mirror-finished. By using this, a 75-degree specular gloss on the surface of the recording layer, which is a cast coating layer, is used. The degree can be easily and stably set to 80 to 100%.

The smoothness (Oken method) defined in JIS P8155: 2010 of the recording layer is preferably 4000 seconds or more.
The smoothness (Oken method) is a factor that affects how the ink spreads. If the smoothness (Oken method) is less than 4000 seconds (surface is uneven), the ink is difficult to spread, banding occurs, 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, for example, 8000 seconds.

It is preferable that the air permeability resistance (Oken type tester method) defined in JIS P8117: 2009 of the recording layer is 3000 seconds or more and 12000 seconds or less.
The air permeation resistance (Oken type tester method) is a factor affecting ink penetration. If the air permeation resistance (Oken tester method) is less than 3000 seconds, the ink penetrates into the recording layer and the print density is lowered, and banding may occur. On the other hand, if the air resistance exceeds 12000 seconds, the penetration of the ink into the paper is reduced, and the ink may overflow and become 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 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) Blank paper glossiness Measured by a method according to JIS P8142: 2005.
(2) Smoothness It was measured by a method (Oken method) according to JIS P8155: 2010.
(3) Air permeability resistance It measured by the method (Oken type testing machine method) according to JIS P8117: 2009.
(4) Contact angle It measured by the above-mentioned method.

(5) Surface strength (dry pick)
After printing ink on the recording layer using an RI printer under the following conditions and drying, the state of paper picking and paper dust adhering to the roll (confirmed by backing) is visually evaluated according to the following criteria. did. If evaluation is (circle) and (triangle | delta), there is no problem practically.
Ink type: SMX tack grade black (tack: 20)
Ink quantity: 0.4ml
Roll used: Rubber roll ○: Neither paper picking nor paper dust adhesion to the roll.
(Triangle | delta): There exists some paper dust adhesion to paper picking or a roll.
X: There is much paper dust adhesion to paper picking or a roll.

(6) Ink fillability The ink is printed on the recording layer using an RI printer under the following conditions, dried, and allowed to stand in an environment of 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: 0.3 ml
Roll used: Rubber roll The ink inking property was evaluated according to the following criteria. If evaluation is (circle) and (triangle | delta), there is no problem practically.
○: Printed portion density (black) is 2.3 or more Δ: Printed portion density (black) is 2.1 or more and less than 2.3 ×: Printed portion density (black) is less than 2.1

(7) Set off Ink is printed on the recording layer under the following conditions using an RI printer, and bonded to general coated paper (A2 coated paper) 1 minute or 5 minutes after printing, and then RI printed. After being nipped with a machine and allowed to stand for one 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 set-off was evaluated according to the following criteria. If evaluation is (circle) and (triangle | delta), there is no problem practically.
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 of 0.3 or more, or concentration after 5 minutes is 0.1 or more

(8) Inkjet recording suitability for industrial use Inkjet printing was performed on the recording layer with a color ink jet printer PX-045A (printing condition: plain paper, fast) manufactured by Seiko Epson Corporation, and the following was evaluated. In addition, by setting the printing condition to plain paper and fast mode with a home inkjet printer, the resolution and the ink ejection amount of the industrial inkjet printer are comparable.
<Print density>
Each solid image was printed for 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 area 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 evaluation is (circle) and (triangle | delta), there is no problem practically.
○: The total print density of the four colors is 7.0 or more. Δ: The total print density of the four colors is 6.0 or more and less than 7.0. X: The total print density 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 for 24 hours in an environment of 23 ° C. and 50% RH, and then evaluated according to the following criteria. If evaluation is (circle) and (triangle | delta), there is no problem practically.
○: There is no white missing portion, and it is a beautiful black solid image.
Δ: Some lines are white.
X: The white stripe | line | muscle is conspicuous.

<Beading>
A solid green image (5 cm long × 5 cm wide) 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 evaluation is (circle) and (triangle | delta), there is no problem practically.
○: There is no graininess or bleeding of the ink, and it is a beautiful green solid image.
Δ: Some ink particles are visible.
X: The granular feeling of ink is conspicuous.

<Example 1>
100 parts of hardwood bleached kraft pulp (LBKP) with 420 ml of CSF as the raw material for pulp, paper containing 10 parts of heavy calcium carbonate, 0.2 part of alkyl ketene dimer and 0.5 part of aluminum sulfate with respect to 100 parts of pulp After the paper was made with a long net paper machine, a calendar process was performed to obtain a base paper having a basis weight of 80 g / m 2.

Each of the following blends was stirred and dispersed to obtain a recording layer coating solution and a coagulation solution.
<Coating liquid for recording layer>
Kaolin (manufactured by Engelhard, product name: Ultra White 90) 50.0 parts Heavy calcium carbonate (manufactured by Sankyo Flour Mills, product name: Escalon 2000) 50.0 parts Binder (styrene butadiene latex, manufactured by JSR,
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 (produced by San Nopco, product name: SN wet 964) 1 copy

<Coagulation liquid>
Calcium formate 10.0 parts Water 90.0 parts

Next, the recording liquid for the recording layer is applied on one side of the base paper using a roll coater so that the coating amount is 20 g / m 2 in terms of solid content, and then the coagulation liquid is applied and the coagulation treatment is performed. did.

Next, 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, whereby a recording paper was obtained.

In Example 2, a recording paper was obtained in the same manner as in Example 1 except that the blending 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 paper was obtained in the same manner as in Example 1 except that the blending 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 blending ratio of kaolin and heavy calcium carbonate as the inorganic pigment was changed as shown in Tables 1 and 2.
In Example 6, polyethylene (same as in Example 1) and higher fatty acid calcium (San Nopco, trade name: SN Coat 246) were used as release agents for the recording layer in the ratios shown in Tables 1 and 2. A recording sheet was obtained in the same manner as 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 recording layer coating liquid was applied using a roll coater so that the coating amount was 12 g / m 2 in terms of solid content.
In Example 8, a recording paper was obtained in the same manner as in Example 1 except that the recording layer coating liquid was applied using a roll coater so that the coating amount was 35 g / m 2 in terms of solid content.

Comparative Example 1 uses light calcium carbonate (manufactured by Shiraishi Kogyo Co., Ltd., product name: Univers 70) instead of heavy calcium carbonate as an inorganic pigment, and changes the blending ratio of kaolin and light calcium carbonate as shown in Table 1 and Table 2. A recording sheet was obtained in the same manner as in Example 1 except that.

In Comparative Examples 2 and 3, a recording paper was obtained in the same manner as in Example 1 except that the blending ratio of kaolin and heavy calcium carbonate as the inorganic pigment was changed as shown in Tables 1 and 2.
In Comparative Examples 4 and 5, a recording paper was obtained in the same manner as in Example 1 except that the blending 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 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 was used as the release agent for the recording layer in the ratios shown in Tables 1 and 2.

Comparative Example 8 was the same as 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. A record sheet was obtained.

The blank sheet glossiness, contact angle, smoothness, and air resistance of the obtained recording paper are as shown in Tables 1 and 2, and printability obtained when used as general printing paper, and industrial use. 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 embodiment in which a predetermined ratio of kaolin and heavy calcium carbonate are included as the inorganic pigment of the recording layer, and a predetermined ratio of SBL is further included as a binder, and the contact angle is defined. In addition to ensuring general printing suitability such as offset printing and letter press, color development (printing density) is improved in industrial inkjet recording, and banding (stretching) and beading (graininess) can be suppressed. did it.

In the case of Example 3 in which the smoothness (Oken method) is less than 4000 seconds and the air permeability resistance (Oken tester method) is less than 3000 seconds, compared with other examples, industrial inkjet aptitude (print density) , Banding, beading) is slightly inferior, but there is no practical problem.

In the case of Comparative Example 1 in which the recording layer did not contain heavy calcium carbonate, the printing density in industrial inkjet recording was inferior, and the banding (leakage) was also reduced.
This is presumably because the effect of retaining ink on the surface layer was reduced because the voids in the recording layer increased.
In the case of Comparative Example 2 in which the ratio of heavy calcium carbonate in the recording layer was less than 35% by weight and the ratio of kaolin exceeded 65% by weight, beading (graininess) occurred in industrial inkjet recording.
This is presumably because the gap in the recording layer was reduced, so that the ink did not penetrate into the recording layer and did not spread in the plane direction.

In the case of Comparative Example 3 in which the ratio of heavy calcium carbonate in the recording layer exceeded 60% by weight and the ratio of kaolin was less than 40% by weight, banding occurred. This is presumably 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 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 with an industrial inkjet printer. Further, the strength of the recording layer was insufficient for general printability.

In 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 with an industrial inkjet printer. Moreover, as a general printability, set-off occurred due to poor ink drying.

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 is 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 is insufficient as general printability, and the ink setting property Also inferior.

Claims

A recording paper having a recording layer containing an inorganic pigment and a binder on at least one side 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 with respect to 100 wt% of the inorganic pigment. The total is 90% by weight or more,
The binder contains at least a styrene butadiene latex;
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 contact angle after 5 seconds after dropping a mixed solution of 57.5% by weight of ethylene glycol monoethyl ether and 42.5% by weight of formaldehyde on the recording layer is 20 degrees or more and 40 degrees or less,
Recording paper characterized by being.
The recording paper according to claim 1, wherein the recording layer has a 75 ° specular glossiness of 80 to 100%.
The recording paper according to claim 1 or 2, wherein the recording layer has a smoothness (Oken method) defined by JIS P8155: 2010 of 4000 seconds or more.
The recording paper according to claim 1 or 2, wherein the air permeability resistance (Oken tester method) defined in JIS P8117: 2009 of the recording layer is 3000 seconds or more and 12000 seconds or less.
The recording paper according to any one of claims 1 to 4, wherein the recording layer further contains a polyethylene release agent.