JPH11189995A - Finely coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a finely coated paper suitable as e.g. a newsprint paper for offset printing use with high opaqueness after printed and excellent in travelability on a printing machine and offset printability. SOLUTION: This finely coated paper is obtained by providing the surface of a base paper with a coating layer consisting mainly of a pigment and an adhesive, wherein, in particular, synthetic noncrystalline silica is included at 10-100 wt.% in the whole pigment and a silicon-contg. water-soluble polymer as the adhesive is included at 10-300 wt.%, on a solid basis, based on the whole pigment, and the density of the coating layer is 0.2-5 g/m<2> , on a dry basis, per one side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finely coated paper, and more particularly to a finely coated paper having high opacity after printing and excellent in running properties on a printing press and suitability for offset printing. About paper.

[0002]

2. Description of the Related Art In recent years, the printing of newsprint has rapidly changed from a letterpress rotary printing method to an offset rotary printing method. Offset printing is a method in which dampening water and ink are supplied to a printing plate, and then the ink is transferred to a rubber plate called a blanket and then transferred to paper to perform printing. Further, since ink having a higher tackiness than that of letterpress printing is used, the paper is required to have high surface strength and high water resistance. By the way, if the surface strength is low or the water resistance is low, the fibers released from the paper due to paper peeling or the pigment contained in the paper will accumulate on the blanket of the printing press or mix into the ink, and the printing surface will be mixed. And cause troubles.

Further, there is a tendency to reduce the weight of newsprint paper in relation to the increase in the number of pages in a newspaper, and a paper having high opacity after printing is demanded along with the weight reduction. In order to increase the opacity of such lightweight paper, pigments such as white carbon, titanium dioxide, calcined kaolin, structured kaolin, calcium carbonate, and urea formaldehyde resin are used as internal fillers in the production of base paper. However, the paper strength is reduced by adding the inorganic or organic pigments as described above, and fine fibers or fine fibers may be formed due to a paper breakage problem in a paper making process or a printing process, or a dampening solution or an ink tack in offset printing. It is easy to cause paper dust troubles such as so-called blanket piling, in which the internal pigment is released from the inside of the paper layer and deposited on the blanket. In order to cope with the problems of paper breakage and paper dust as described above, a paper layer is strengthened by applying a water-soluble polymer such as starch, polyvinyl alcohol, or polyacrylamide to the surface of the paper. Such surface application of a water-soluble polymer can improve surface strength and water resistance by bonding fibers on the paper surface with an internal pigment. However, when the coating amount increases, the surface coating agent partially dissolves in the fountain solution at the time of offset printing, and the paper surface becomes tacky called nappar. As a result, there is a problem that the paper surface sticks to the blanket at the time of printing and induces a paper break.

Further, Japanese Patent Application Laid-Open Nos. 1-174697 and 5-33294 propose a method of providing a coating layer containing a pigment having a high oil absorption in order to improve opacity and ink setting. ing. When such a pigment having a high oil absorption, particularly a synthetic amorphous silica pigment used in the present invention is used as a pigment for a coating layer in a certain amount or more, the water-soluble polymer as described above is used as an adhesive. However, sufficient adhesive strength cannot be provided. Further, a synthetic resin emulsion adhesive widely used as an adhesive for coated paper cannot provide sufficient adhesive strength when the amount of coating as intended in the present invention is small. For this reason, there is a problem that the paper surface trouble and the water resistance of the paper are lowered, and the paper dust trouble is further deteriorated. At present, a method for achieving both opacity and suitability for offset printing has not been established yet. In addition, when the above-mentioned water-soluble polymer is coated on the base paper or when a coating layer containing a pigment is provided, the coefficient of friction of the coated paper tends to decrease. When such coated paper is used as newsprint, especially after printing, when running in a state in which a plurality of webs (paper webs) are overlapped and entering a folding process continuously from the printing process, a printed pattern or printing is performed. As a result of the difference in the number of colors, the elongation of each paper web is different. As a result, if the coefficient of friction of the paper is low, the running property of the paper web located inside becomes unstable, and so-called paper running problems such as wrinkles occur.

On the other hand, for example, Japanese Patent Application Laid-Open No. 9-277695 discloses a method in which synthetic amorphous silica and silanol-modified polyvinyl alcohol are contained as a coating layer of an ink jet recording sheet. However, the ink jet recording paper as proposed in the above-mentioned publication is a non-contact printing of the aqueous ink on the coated paper,
In order to use it for offset printing as intended by the present invention, the adhesive strength of the coating layer is weak and the coating layer is removed from the ink. .

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned drawbacks of newsprint and to obtain a finely coated paper suitable for offset printing. By providing a coating layer containing a pigment and a specific adhesive, it is possible to provide a finely coated paper for offset printing which is excellent in opacity and offset printing suitability without causing paper dust trouble and paper flow. It is.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a finely coated paper comprising a base paper provided with a coating layer mainly composed of a pigment and an adhesive, wherein the pigment is a synthetic amorphous silica as the pigment. 10 to 100% by weight, and a water-soluble polymer containing a silicon element as an adhesive is contained in an amount of 10 to 300% by weight based on the total solid content of the total pigment. It is a finely coated paper characterized by being coated at a rate of 0.2 to 5 g / m ² .

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The water-soluble polymer containing a silicon element in the present invention is described in, for example, JP-A-58-59920.
No. 3, as described in Japanese Patent Publication No. 3 (1994), a vinyl compound containing a silicon element and vinyl acetate are copolymerized and then saponified to convert a vinyl acetate unit into a vinyl alcohol and a silicon element-containing unit into a silanol group. And a starch containing an organic siloxane group as disclosed in Japanese Patent No. 25508089 or an organic siloxane group as disclosed in Japanese Patent Application Laid-Open No. 9-169817. )
An acrylamide polymer is exemplified.

The above-mentioned silicon-containing polyvinyl alcohol preferably has an average degree of polymerization of 500 to 4000. By the way, if it is less than 500, the adhesive strength of the coating layer may be weak and the paper powder trouble may not be improved. If it exceeds 4000, the viscosity of the coating liquid becomes too high and the coating liquid becomes too high. There is a possibility that the control of the applied amount may not be possible. The degree of saponification was 90 mol%.
The above is preferable because it has low so-called napparity and hardly causes a paper cutting trouble or a paper dust trouble.

The water-soluble polymer containing silicon element can be used as an adhesive for a coating layer containing synthetic amorphous silica in an amount of 10 to 300% by weight based on all pigments in the coating layer. Since it was possible to obtain adhesive strength and water resistance, it was difficult to cause the above-mentioned paper dust trouble and paper breakage trouble due to neppari property, and it was found that high opacity was obtained, and the present invention was completed. is there. Incidentally, when the amount of the water-soluble polymer containing a silicon element is less than 10% by weight, sufficient adhesive strength and water resistance cannot be obtained. On the other hand, when the amount exceeds 300% by weight, the opacity decreases, which is preferable. Absent.

Further, when the amount of the water-soluble polymer containing silicon element to be used is 100 to 300% by weight relative to the solid content of the synthetic amorphous silica pigment, the adhesive strength of the coating layer can be further improved. This is a more preferred embodiment because water resistance can be obtained. Incidentally, by using the water-soluble polymer containing a silicon element as described above, the reason for maintaining the surface strength and reducing the nappari property, and making it difficult to cause paper-cutting troubles, etc., are not clear, but are as follows. It is estimated as follows.

That is, when a water-soluble polymer containing a silicon element is used as an adhesive for a synthetic amorphous silica pigment, the adhesive and the pigment are firmly bonded in the form of Si--O--Si, and a good coating is obtained. The adhesive strength of the layer is obtained, and the adhesive itself is improved in water resistance due to the reaction and adhesion of the silicon element, so that the adhesive is less likely to be dissolved by the dampening solution during offset printing. As a result, it is considered that the paper dust trouble and the paper break trouble due to the nepari property are reduced.

In the present invention, in addition to the water-soluble polymer containing a silicon element, an adhesive generally used in the coated paper manufacturing field can be used in combination as long as the effects of the present invention are not impaired. For example, oxidized starch, esterified starch, etherified starch, ordinary modified starches containing no silicon element such as cationized starch, water-soluble cellulose compounds such as carboxymethylcellulose, methylcellulose and hydroxyalkylcellulose, styrene-butadiene copolymer latex And latexes such as styrene-methacrylic acid ester copolymer latex and ordinary polyvinyl alcohol and polyacrylamide containing no silicon element.

Next, the synthetic amorphous silica pigment which is an essential component of the present invention will be described. The synthetic amorphous silica pigment referred to herein includes silicic anhydride obtained by a dry production method and hydrated silicic acid obtained by a wet production method.
In the case of the present invention, hydrous silicic acid, which is a porous, amorphous fine particle having a three-dimensional structure of SiO ₂ formed by gelling of silicic acid, is preferably used because it has a large effect of improving opacity. Further, as the synthetic amorphous silica pigment, so-called white carbon containing silicic acid as described above or, in some cases, calcium silicate as a main component can be used. Such a synthetic amorphous silica pigment is used in an amount of 10 to 100% by weight, preferably 30% by weight, based on the total solid content of the coating layer.
Desirably, it is contained in an amount of about 100% by weight. If the content is less than 10% by weight, the opacity and the coefficient of friction are likely to decrease, which is not preferable.

In the present invention, the reason why the opacity and the degree of friction (coefficient) are improved by using the synthetic amorphous silica pigment as the pigment of the coating layer is presumed as follows. That is, the above-mentioned synthetic amorphous silica pigments are characterized by having a large specific surface area, being bulky and having a high oil absorption, and thereby providing a bulky coating layer. As a result, the chance of scattering light passing through the coated layer is increased, and the opacity of the coated paper is improved. Furthermore, the solvent component and the resin component of the printed ink are efficiently absorbed into the voids of the pigment and the coating layer, and the ink is suppressed from penetrating into the paper layer (deeply). Will be improved. Further, regarding the coefficient of friction, since the specific surface area of the synthetic amorphous silica pigment is large, when the coated paper is finished, when the coated paper comes into contact with each other or between the coated paper and another substance, its friction (coefficient It is considered that the resistance is increased.

In the present invention, as the pigment of the coating layer, other than the above-mentioned synthetic amorphous silica pigment, for example, kaolin, calcined kaolin, structured kaolin, calcium carbonate, calcium sulfate, carbonate Pigments known and used in the coated paper manufacturing field such as magnesium, aluminum hydroxide, titanium dioxide, barium sulfate, zinc oxide, satin white, mica, plastic pigment, and urea resin can be used in combination as appropriate.

[0017] The coating liquid for a coating layer (hereinafter referred to as a paint) in which the specific pigment and the specific adhesive are arranged as described above includes a dye, a surface sizing agent, a defoaming agent, Agent,
It is prepared by adding various auxiliaries such as preservatives as needed and mixing and stirring. Further, the solid content concentration of the paint can be appropriately adjusted according to the coating device and the target coating amount,
Usually, it is adjusted in the range of 3 to 40% by weight. The amount of coating is adjusted in the range of 0.2 to 5 g / m ^{2 on} a dry weight basis. By the way, if it is less than 0.2 g / m ^2, it is difficult to obtain sufficient opacity, while if it exceeds 5 g / m ² , if the weight of the final product is constant, the weight of the base paper will decrease accordingly. As a result, the paper strength is reduced, and the paper is likely to break in a printing process, which is not preferable.

The pulp which is the main component of the base paper used in the present invention includes chemical pulp (bleached or unbleached NKP and LKP) and high yield pulp (GP, CGP, RGP,
PGW, TMP, etc.), deinked waste paper pulp (DIP, etc.) and the like are used alone or in a mixture at an arbitrary ratio. In addition, a papermaking filler such as the synthetic amorphous silica pigment, titanium dioxide, calcined kaolin, structured kaolin, calcium carbonate, urea-formaldehyde resin, etc. referred to in the present invention is added to the stock before papermaking as needed. Can be. Further, in the paper stock, together with the above-mentioned fillers, sizing agents such as a sulfuric acid band, a paper strength enhancer, a retention enhancer, a reinforced rosin sizing agent, and an emulsion sizing agent, a water-proofing agent, and a UV absorber and other generally known papermaking materials. The chemical is added and the paper is made on a normal paper machine. In the case of the present invention, the basis weight of the base paper is not particularly limited, but the desired effect is remarkably exhibited in the case of a relatively low basis weight of 30 to 70 g / m ² .

The method for forming the coating layer on the base paper is not particularly limited, and includes a size press, a blade metering size press, a rod metering size press, a gate roll coater, a blade coater, a bar coater,
A commonly known and used coating apparatus such as a rod blade coater and an air knife coater can be appropriately used. For drying the coating layer, a known and known drying method such as ordinary hot air, infrared rays, or a heat cylinder is appropriately used.
After the coating layer is dried, it can be subjected to a pressure treatment using a machine calender, a soft nip calender, a super calender or the like, if necessary.

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples. Of course, the present invention is not limited to these examples. Parts and% in Examples are parts by weight and% by weight, respectively, unless otherwise specified.

Example 1 [Preparation of hydrous amorphous silica] Commercially available aqueous sodium silicate solution
(SiO_Two/ Na_TwoO 2 molar ratio: 3.05, SiO _TwoDark
Degree 187 g / liter) 53.5 liters, sodium sulfate (N
a_TwoSO_Four) 170 liter of aqueous solution (concentration = 3.9%)
Is supplied to a heating reaction tank with a stirrer having an internal volume of 300 liters.
did. Then, after blowing steam to 45 ° C., stirring
20% sulfuric acid (H_TwoSO_Four8.7 liters
The addition took about 10 minutes. At this time,
The addition ratio of sulfuric acid in the first stage was 38%. First stage
After the addition of sulfuric acid, steam is blown while continuing stirring.
The temperature was raised to 95 ° C. in 20 minutes. In addition, add 1 solution
After holding at 95 ° C for 0 minutes, the remaining sulfuric acid was
Add 14 liters over 90 minutes and stop at pH 5
Then, a hydrous amorphous silica slurry was obtained. Like this
The hydrated amorphous silica slurry obtained in
After dewatering to about 10%, sand grinder (50
Crushed by Arashi Kikai) and then with a 200 mesh screen
The coarse particles are removed to obtain a pigment for internal addition and paint described below.
Used. Incidentally, the average particle diameter of the hydrated amorphous silica is
It was 15 μm.

[Preparation of base paper] Softwood kraft pulp (N
KP) 14 parts, thermomechanical pulp (TMP) 40
Pulp slurry consisting of 7 parts by weight, ground pulp (GP) 7 parts and newspaper deinked waste paper pulp (DIP) 39 parts
The pulp slurry was prepared by beating with a refiner to a freeness (CSF) of 110 ml. Next, 1% of the above-mentioned hydrated amorphous silicic acid, 0.3% of rosin emulsion size (trade name: SPN-773 / Arakawa Chemical Industry Co., Ltd.), and 1% of sulfuric acid band were added to the obtained pulp slurry (all). Then, papermaking was performed using a pilot paper machine equipped with a twin wire to obtain a base paper having a rice area of 41 g / m ² .

[Preparation of paint and coated paper]
Using the above-mentioned hydrated amorphous silica, polyvinyl alcohol containing a silicon element dissolved in hot water at 90 ° C. as an adhesive (trade name: 100 parts (solid content) of the silica)
R-1130, saponification degree 98-99 mol%, polymerization degree 30
(00 / Kuraray Co., Ltd.) to 200 parts (solid content) of the polyvinyl alcohol and 0.1 part (active ingredient) of an antifoaming agent, and further added water to obtain a paint having a solid content of 8%. . Then, using a gate roll coater on both sides of the base paper of 41 g / m ² , the dry weight was 1.0% per one side.
g / m ^2, and after coating and drying, 1 nip paper-finishing was performed with a soft calender to obtain a finely coated paper having a water content of 7%.

Example 2 In the preparation of the paint of Example 1, R was used instead of R-1130 as polyvinyl alcohol containing a silicon element.
-2105 (degree of saponification 98 to 99 mol%, degree of polymerization 500
/ Kuraray Co., Ltd.) was used to obtain a slightly coated paper in the same manner as in Example 1.

Example 3 In the preparation of the coating composition of Example 1, the hydrous amorphous silica 100
100 parts by weight of a polyvinyl alcohol containing a silicon element as an adhesive (R-1130 / the above) and a polyvinyl alcohol not containing a silicon element (trade name: PVA-117, saponification degree: 98 to 99 mol%, Polymerization degree 1700 / Kuraray Co., Ltd.) 100 parts (each in solid content conversion)
Was obtained in the same manner as in Example 1 except that was added.

Example 4 In the preparation of the hydrous amorphous silica of Example 1, except that the sand grinder treatment was strengthened and the hydrous amorphous silica whose average particle diameter was adjusted to 5 μm was used. A slightly coated paper was obtained in the same manner as described above.

Example 5 In the preparation of the coating material of Example 3, 100 parts of the hydrated amorphous silica used as the pigment was replaced with 100 parts of the hydrated amorphous silica.
Parts and titanium dioxide (trade name: FA-55W / Furukawa Kikai Metals Co., Ltd.) 60 parts (each in terms of solid content), except that they were mixed and used to obtain a slightly coated paper in the same manner as in Example 3. .

Example 6 In the preparation of the coating material of Example 5, the hydrated amorphous silica (40
Parts) and 100 parts of a mixed pigment of titanium dioxide (60 parts), 35 parts of a polyvinyl alcohol containing a silicon element (R-1130 / the above) as an adhesive and polyvinyl alcohol without a silicon element (PVA-117 / Except that 165 parts (each described above) (in terms of solid content) were used.
A slightly coated paper was obtained in the same manner as in Example 5.

Example 7 In the production of the finely coated paper of Example 1, the coating amount was changed to the dry weight.
3g / m per side ^TwoExcept that
A slightly coated paper was obtained in the same manner.

Example 8 In the preparation of the coating material of Example 1, instead of polyvinyl alcohol containing silicon element, starch containing silicon element (trade name: CO-BOND 2500 / National Starch Co., Ltd.) was used, A slightly coated paper was obtained in the same manner as in Example 1, except that the concentration was adjusted to 4% and the pH of the paint was adjusted to 8.

COMPARATIVE EXAMPLE 1 In the preparation of the coating material of Example 1, an oxidized starch (trade name: Ace A / Oji Cornstarch) was used in place of the silicon-containing polyvinyl alcohol used for the adhesive. A lightly coated paper was obtained in the same manner as in Example 1.

Comparative Example 2 In the preparation of the coating material of Example 1, instead of the polyvinyl alcohol containing a silicon element used for the adhesive, polyvinyl alcohol containing no silicon element (PVA-1) was used.
17 / described above), except that the above was used, to give a slightly coated paper in the same manner as in Example 1.

Comparative Example 3 In the preparation of the paint of Example 1, a polyacrylamide polymer (trade name: Santax NP-1) was used instead of the silicon-containing polyvinyl alcohol used for the adhesive.
0 / Mitsui Chemicals Co., Ltd.), except that finely coated paper was obtained in the same manner as in Example 1.

Comparative Example 4 Fine coating was carried out in the same manner as in Example 1 except that a pigment was not used and a coating consisting only of polyvinyl alcohol containing silicon element was prepared and used. I got the paper.

With respect to the finely coated papers obtained in the examples and comparative examples thus obtained, the following items were evaluated, and the obtained results are shown in Table 1.

(Average particle diameter of pigment) The pigment was added to a 0.2% aqueous solution of sodium hexametaphosphate, and the mixture was treated with ultrasonic waves at 30%.
After dispersion for 2 seconds, the laser diffraction method (SALD-2000
/ Shimadzu Corporation) to determine the weight average particle diameter.

(Blanket Paper Powder Piling) Using an offset printing press (Komori SYSTEM C-20), 5000 copies were printed using an ink for rotary offset printing (trade name: TERAS N Boku / Dainippon Ink and Chemicals, Inc.). After performing, the degree of paper dust accumulation on the blanket non-image area was visually determined. ◎: No paper dust was observed. ：: Paper dust was slightly observed, but no fuzz was observed in the image area due to the accumulation of paper dust. ×: A large amount of paper dust has accumulated on the blanket, and blurring is observed in the image area due to the accumulation of paper dust.

(Nappari Strength: Blanket Adhesiveness) Two newspaper printing paper samples were cut to an appropriate size and placed in water.
After immersion for 0 seconds, the two sheets were quickly brought into close contact with each other and passed through a calender under the condition of a linear pressure of 50 kg / cm.
% RH in a room for 24 hours. After that, width 15mm
Was adjusted, and the peel strength of the two sheets of paper was measured using a tensile tester. The larger the value, the stronger the adhesiveness,
Paper breaks easily occur on printing presses.

(Print opacity) Printing was performed using an ink for rotary offset printing (ink) with an ink amount changed by an RI printing machine, and the reflectance of the back surface before printing when the printing surface reflectance was 9% was compared with that of the back surface reflectance before printing. After printing, the ratio of the back side (opposite side of the printing side) was determined. The reflectance is measured by a spectral whiteness colorimeter (Suga Test Instruments Co., Ltd.)
Measured using

(Coefficient of friction) ASTM D 1894 was measured using a surface property measuring device (Tribogear-14D / Shinto Kagaku).
The dynamic friction coefficient was measured according to the test method. The larger the value is, the higher the friction coefficient is, and the more difficult it is to cause paper running trouble.

[0041]

[Table 1]

[0042]

As is clear from Table 1, the finely coated paper obtained in the examples according to the present invention has low Neppari strength, does not generate blanket paper powder piling, and has high print opacity. It was excellent in offset printing suitability.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI D21H 19/60 D21H 1/32

Claims (3)

[Claims] 1. A finely coated paper comprising a base paper provided with a coating layer mainly composed of a pigment and an adhesive, wherein the synthetic amorphous silica is used as the pigment in an amount of 10 to 100% by weight based on all pigments. And a water-soluble polymer containing a silicon element as an adhesive is contained in an amount of 10 to 300% by weight based on the total solid content with respect to the total pigment, and the coating layer is 0.2 to 0.2% by dry weight per one side.
Finely coated paper characterized by being coated at 5 g / m ² . 2. The amount of the water-soluble polymer containing silicon element is 100 to 300 based on the solid content of the synthetic amorphous silica.
The lightly coated paper according to claim 1, which is in weight%. 3. The finely coated paper according to claim 1, wherein the main component of the water-soluble polymer containing a silicon element is at least one of polyvinyl alcohol, starch, and a (meth) acrylamide polymer. .