JP2009263855A - Coated paper for offset printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated paper for offset printing having good white paper face feeling and printing quality and excellent in printability though the paper is lightweight. <P>SOLUTION: The coated paper for offset printing is obtained by providing a coated layer composed of a pigment and an adhesive on at least one side of a base paper. In the coated paper for printing, basis weight of the coated paper is ≤50 g/m<SP>2</SP>and the base paper contains a broad-leaved tree mechanical pulp and the coating pigment contains titanium dioxide and the content of the titanium dioxide is 0.5-25 pts.wt. based on 100 pts.wt. pigment. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a coated paper for offset printing having a particularly excellent blank paper feeling despite being lightweight.

  In recent years, the demand for offset printing paper has been increasing year by year in the commercial printing field for the purpose of advertising and advertising such as flyers, catalogs, pamphlets, and direct mail, and its production volume has been steadily increasing. Among them, in recent years, the production rate of lightweight coated paper and fine coated paper is characterized by a large growth rate. There is a strong demand for coated paper for high-quality printing that can visually convey the content visually by using a lot of photographs and designs on the printed matter and making it more colored. On the other hand, there is a strong demand for weight reduction of users who want to reduce costs in terms of resource saving, transportation and mailing costs. These two requirements are contradictory, and high-quality printing coated paper has a large amount of base paper and coating amount, is expensive, and does not meet the demand for light weight and low price. Therefore, there is a demand for a technique for realizing a higher grade quality with a so-called lower grade coated paper having a low basis weight and a low coating weight.

  Of the coated paper qualities, the important ones are whiteness, opacity, white paper gloss, printing gloss, stiffness, surface strength and white paper feel. It is important that whiteness is related to contrast, opacity is back-through, glossiness is related to high-quality prints, stiffness is mainly related to printing workability, and these are all satisfied with a good balance. In particular, the white paper texture is a very important factor that greatly affects the final appearance of the printed material and is greatly related to the finished product and the high quality.

  If the stiffness of the coated paper for printing is low, there will be a problem that the paper corner will be bent at the paper discharge section after offset printing, and it will be necessary to reduce the printing speed, resulting in remarkable work efficiency. Since it falls, it is not preferable. Also in this respect, stiffness is a very important quality.

  In addition to the stiffness, the surface strength of the printing paper is required as a quality item related to printing workability. Especially in offset printing, this tendency is remarkable because ink with relatively strong tack is used. Since dampening water is added to the surface of the paper during printing, using paper with a surface with weak surface strength causes paper dust to accumulate on the blanket or mix with the ink, resulting in so-called blurring on the printed surface. Trouble of piling occurs.

  In the case of reducing the weight of the coated paper, there is a method of reducing the basis weight of the base paper or (and) reducing the coating weight. When the base paper has a low basis weight, the paper thickness is reduced in proportion to the weight reduction, the rigidity is lowered, and further, a problem of an ear fold is likely to occur in offset rotary printing. If the coating amount is low, it is considered that the coverage of the base paper of the coating layer is deteriorated, but a piling trouble is likely to occur, and further, the blank paper feeling is likely to be deteriorated.

From the viewpoint of machine operability, when manufacturing thin coated paper with a high speed paper machine with a paper making speed of 1000 m / min or more, there is a concern that paper breakage may occur. Therefore, it is difficult to reduce the basis weight of the base paper, 30 g / m It is difficult to produce a base paper of ² or less. For this reason, in thin coated paper having a basis weight of 50 g / m ² or less, it is necessary to reduce the coating amount, and a thin coating layer of 1 to 8 g / m ² is often provided on one side of the base paper. In this way, when manufacturing thin coated paper with a high-speed machine, it is difficult to reduce the basis weight of the base paper, so it is necessary to reduce the coating amount, resulting in increased coating unevenness and white paper texture. In addition, there is a problem that the printing surface is liable to deteriorate.

  In order to solve the above problems, a method of blending a hollow plastic pigment and titanium dioxide by using a material having a sharp particle size of pigment particles for a coating layer is disclosed (Patent Document 1). However, this method is very likely to deteriorate the white paper surface feeling, and it is difficult to obtain a product having a good white paper surface feeling and high whiteness.

In general, the coated paper is often provided with a coating layer of 3.0 g / m ² or more per one side of the base paper, and then the surface is smoothed by a calendar process. At that time, as a result of the paper being compressed by the calendar process, the stiffness of the paper is lowered. Furthermore, so-called calendar burn may occur depending on the calendar processing, and the blank paper surface may be impaired.

  As a method for improving the white paper surface feeling, a method is disclosed in which a black dye is blended in the coating layer so that the difference between the whiteness of the base paper and the whiteness of the coating layer is within 6% (Patent Document 2). . However, by simply adding a black dye to bring the whiteness of the coating layer close to the whiteness of the base paper, the white paper feel is improved, but the whiteness of the product is reduced.

  As described above, in the prior art, it is difficult to obtain a coated paper for offset printing that is light in weight, has a good white paper feel and printing quality, and has excellent printing workability.

JP 2004-3083 A Japanese Patent Laid-Open No. 01-97295

  In view of the circumstances as described above, an object of the present invention is to provide a coated paper for offset printing that is light in weight, has a good white paper feel and printing quality, and is excellent in printing workability.

As a result of intensive studies to achieve the above-mentioned objects, the inventors of the present invention have developed a mechanical pulp produced from hardwood wood chips in a printing paper provided with a coating layer containing a pigment and an adhesive on the base paper. Was found to be extremely effective when the base paper is contained in the base paper and titanium dioxide is contained in the coating layer.
That is, in order to solve the above problem, the coated paper for offset printing of the invention according to claim 1 is a printing coated paper in which a coating layer comprising a pigment and an adhesive is provided on at least one side of a base paper. The basis weight of the coated paper is 50 g / m ² or less, the base paper contains hardwood mechanical pulp, the coated pigment contains titanium dioxide, and the content is 0.5 parts by weight per 100 parts by weight of the pigment. The content is 25 parts by weight or less.
Similarly, the coated paper for offset printing of the invention according to claim 2 is characterized in that the hardwood mechanical pulp has a freeness of 100 to 200 ml.
The coated paper for offset printing of the invention according to claim 3 has a coating layer weight of 1 g / m ² or more and 8 g / m ² or less, preferably 2 g / m ² or more and 7 g / m ² or less. More preferably 3 g / m ² or more and 6 g / m ² or less.

Even if the basis weight of the coated paper is 50 g / m ² or less, the base paper contains hardwood mechanical pulp and the coating pigment contains titanium dioxide, so it has excellent whiteness and suppresses blank paper texture and blanket piling. A coated paper for offset printing having excellent effects can be obtained.
Further, the coated paper for offset printing of the present invention has good rigidity, white glossiness, and opacity, and therefore is suitable for offset printing and further excellent in printing workability.

  The hardwood mechanical pulp used in the coated base paper of the present invention is a mechanical pulp made from hardwood, and refiner grandwood pulp (RGP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), alkaline excess. Examples thereof include hydrogen oxide mechanical pulp (APMP) and alkali hydrogen peroxide thermomechanical pulp (APTMP). From the viewpoint of obtaining bulkiness, high opacity, and high whiteness, it is preferable to use CTMP, APMP, and APTMP.

The above hardwood mechanical pulp should be manufactured by impregnating wood chips with alkaline hydrogen peroxide solution, performing normal pressure or pressure refining treatment, and holding with chemicals at room temperature or under heating for a certain period of time. Is preferred. Further, in order to obtain higher bulkiness and higher whiteness, it is preferable to use mechanical pulp produced from hardwood wood chips having a bulk weight of 450 kg / m ³ or more. Further, the mechanical pulp produced from the hardwood used in the present invention preferably has a sheet density of 0.45 g / cm ³ or less at a freeness of 100 ml, and preferably has a pulp sedimentation volume of 200 ml / g or less. The sedimentation volume refers to the pulp slurry adjusted to a predetermined concentration in a graduated cylinder or test tube, and the volume of the sedimented pulp slurry measured after a certain time is divided by the absolute dry weight of the sample at the time of measurement. Value. This technique is often used to evaluate the degree of pulp beating. The sedimentation volume usually depends on the specific surface area of the pulp fiber and tends to increase as the specific surface area increases. In the present invention, the pulp slurry adjusted to a concentration of 0.25% by weight was placed in a 100 ml graduated cylinder, and the volume of the pulp slurry settled after standing at room temperature for 30 minutes was measured and calculated.

CTMP can be obtained, for example, by the following production method. It is pulped through a manufacturing process including a pretreatment process of hardwood wood chips, a defibrating process by primary refining, and a beating process by secondary refining.
The impregnation treatment with the sodium sulfite aqueous solution can be achieved by compressing the chip and compressing the chip or immersing it in the sodium sulfite aqueous solution after being compressed, and then impregnating the sodium sulfite while releasing the pressure and expanding the chip. In this sodium sulfite aqueous solution impregnation step, it is important that the chemical solution is sufficiently impregnated in the chip. It is important that the compression ratio is 4: 1 to 16: 1. If the compression ratio is lower than 4: 1, the restoring force of the chip is weak, and the penetration of the sodium sulfite aqueous solution into the chip becomes insufficient. Therefore, it is not preferable. Compression ratios exceeding 16: 1 are impractical in terms of equipment. The compression ratio is defined as volume before compression: volume after compression. In order to complete the impregnation of the aqueous sodium sulfite solution, a surge bin can also be provided after the plex screw or the impeller.

The addition rate of sodium sulfite is 0.5 to 2.0% by weight with respect to the absolutely dry chip. Depending on the pH of the aqueous sodium sulfite solution, the average fiber length after primary refining is slightly different.
The initial pH of the sodium sulfite aqueous solution to be impregnated is 4.5 to 9.5, preferably 7.0 to 9.5. For this pH adjustment, sulfuric acid or sodium hydroxide is used. In this range, the higher the pH, the greater the long fiber content and the longer the average fiber length. If the pH exceeds 9.5, the level is turned off, resulting in poor chemical efficiency. A pH of less than 4.5 is not preferable because there is a risk of metal corrosion of the equipment.

  The chip impregnated with the aqueous sodium sulfite solution is preferably preheated prior to the primary refining for the purpose of improving the defibration. The temperature in this case is preferably 100 to 135 ° C. The preheated chip is defibrated with a primary pressure refiner. The apparatus used is a pressure refining apparatus. Except for the refiner plate (refiner segment), other conditions are defibrated to pulp fibers by a known method. As the refining device, a single disc refiner, a conical disc refiner, a double disc refiner, a twin disc refiner, or the like can be used. However, the higher the concentration during defibration, the more fibrillation of the pulp fibers proceeds and a high quality pulp can be obtained. Therefore, a single disc refiner is preferably used. The concentration of chips during the refining process is preferably about 20 to 60% by solid weight, and the processing temperature is preferably 100 to 180 ° C. More preferably, it is 120-135 degreeC.

The defibrated pulp is then sent to the secondary refiner under normal pressure and beaten to the target freeness. As a device, a known refining device is used, and it is pulverized under known conditions and reduced to a desired pulp freeness. This step is performed under normal pressure, and it is preferable to use a general normal pressure type apparatus as the refining apparatus, and the concentration can be carried out at about 4 to 60%. The secondary refiner may be a single stage or a plurality of stages.
APMP is manufactured by impregnating an alkali hydrogen peroxide solution containing sodium hydroxide, hydrogen peroxide, and sodium silicate, and refining at atmospheric pressure, and APTMP is refined at high temperature and pressure. After the refining treatment to obtain higher whiteness, the alkaline hydrogen peroxide aqueous solution is further kept at room temperature or under heating for 5 minutes or more.

More preferably, APMP and APTMP can be produced through the following steps a) to i).
a) A step of compressing hardwood wood chips at a compression ratio of at least 4: 1 and impregnating with a chelating agent when releasing the pressure.
b) A step of holding the impregnated chip at a temperature of 10 ° C. to 80 ° C. for 5 minutes or more.
c) a step of further compressing the impregnated tip at a compression ratio of at least 4: 1 and impregnating with an alkaline chemical at the time of release.
d) A step of holding the impregnated chip at a temperature of 10 ° C. to 80 ° C. for about 10 minutes to 1 hour.
e) A step of making wood pulp by impregnating the treated chips with an alkali peroxide and passing the chips through a pressure or atmospheric refining device to defibrate the chips.
f) The process of hold | maintaining the said manufactured pulp at the temperature of 50 degreeC or more for 5 minutes or more.
g) A step of diluting the manufactured pulp to a concentration of 5% or less, washing it and then concentrating it again to 15% or more.
h) A step of refining the produced pulp under pressure or atmospheric pressure to obtain a pulp having a desired freeness.
i) The pulp obtained as necessary is produced through a step of bleaching in one or more stages using an oxidizing agent or a reducing agent.

  In the step a), it is preferable to use about 0.05 to 0.4% of a chelating agent, and the alkaline agent used in the step c) is about 0.2 to about 0.2 to the weight of the absolutely dry chip. 2.0% sodium hydroxide, about 0.2-2.0% sodium silicate, about 0.01-0.2% magnesium sulfate, about 0.05-0.4% chelating agent and about 0 An aqueous solution containing 2 to 5.0% hydrogen peroxide is preferable.

In the step e), an alkali peroxide containing a chelating agent is added to the wood chip that has been bleached and softened immediately before the primary refining, and the pulp fiber is dissolved in a pressure or atmospheric refining device. Be fine. For refining, a general defibrating apparatus is sufficient, and defibration is preferably performed with a single disc refiner, a conical disc refiner, a double disc refiner, a twin disc refiner, or the like. The freeness of pulp
It is preferable that it is 100-200 mL by CSF, More preferably, it is 100-150 mL, More preferably, it is 110-150 mL. If it is 200 mL or more, the surface of the base paper becomes rough and the desired surface smoothness cannot be obtained, and if it is 100 mL or less, it is preferable for the surface smoothness of the base paper, but the density of the base paper becomes high and the flexibility of the base paper becomes poor.

  If the resulting bulky mechanical pulp requires high whiteness, the pulp can be further bleached by one or more known bleaching steps. In this case, an oxidizing agent such as hydrogen peroxide, ozone or peracetic acid or a reducing agent such as hydrosulfite (sodium dithionite), sodium hydrogen sulfate, sodium borohydride, formamidine sulfinic acid (FAS), etc. Can be used.

The mechanical pulp manufactured through the above manufacturing process has high whiteness, high opacity, and high strength. In particular, the mechanical pulp produced from a high-volume heavy material having a bulk weight of 450 kg / m ³ or more is rigid because the fiber lumen (lumen) is hard to be crushed. Therefore, the sheet containing this pulp fiber maintains a bulky structure, The density can be lowered. As the tree species to be used, Eucalyptus is preferable, and Eucalyptus globules, Eucalyptus grandis and the like are more preferable. Also, hardwood mechanical pulp used, the sheet density is preferably 0.45 g / cm ³ or less when the freeness is 100 ml, more preferably 0.35 g / cm ³ or less. In the present invention, in order to further exhibit the effect of mechanical pulp, the bulky mechanical pulp is preferably 5 to 95% by weight, more preferably 5 to 50% by weight in the total pulp.

  In addition to the bulky mechanical pulp described above, the raw paper for the coated paper for printing of the present invention is a chemical pulp (a bleached kraft pulp of softwood (NBKP) or an unbleached kraft pulp (NUKP), a bleached kraft pulp of hardwood (LBKP). Or unbleached kraft pulp (LUKP), etc.), mechanical pulp (groundwood pulp (GP), refiner mechanical pulp (RGP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), etc.), deinked pulp (DIP) ) Are used alone or mixed in any proportion. The base paper can be made by a known paper machine such as a long paper machine, a gap former, and a hybrid former (on-top former). The papermaking conditions are not particularly defined, and the pH during papermaking may be acidic, neutral, or alkaline.

  In the present invention, it is preferable that the content of mechanical pulp in the total pulp is 10% by weight or more in order not to cause a problem of broken ears. Since mechanical pulp has more rigid fibers than chemical pulp, the base paper blended with mechanical pulp is less likely to be crushed by various pressures applied in the paper making process. Accordingly, the use of mechanical pulp increases the overall bulkiness, so that the amount of voids inside the base paper increases, opacity increases, and at the same time rigidity increases. Among mechanical pulps, ground pulp can be preferably used in the present invention because it contributes greatly to reducing the density.

  In the present invention, the filler used for the production of the base paper includes heavy calcium carbonate, light calcium carbonate, calcium carbonate such as chalk, kaolin, clay, calcined clay, amorphous silicate, light calcium carbonate-silica composite, and pyrolo. Silicates such as phyllite, sericite, and talc and inorganic fillers such as titanium dioxide can be used alone or in combination. For these fillers, it is preferable to use a light calcium carbonate-silica composite in which the surface of the amorphous silicate or the light calcium carbonate is covered with silica in order to improve the printing surface quality and the printing workability. The amorphous silicate may be any insoluble silicate, and examples thereof include hydrous aluminum silicate, hydrous aluminum silicate soda, hydrous calcium silicate, hydrous magnesium silicate and the like. Furthermore, dyes, fluorescent brighteners, pH adjusters, antifoaming agents, pitch control agents, slime control agents and the like can be added as necessary.

  In the present invention, a surface treatment agent containing a water-soluble polymer as a main component may be applied for the purpose of improving the surface strength and size in the production of the base paper. As the water-soluble polymer, those usually used as a surface treating agent such as starch, oxidized starch, processed starch, carboxymethyl cellulose, polyacrylamide, polyvinyl alcohol, etc. can be used alone or a mixture thereof. In addition to the water-soluble polymer, a paper strength enhancer for the purpose of water resistance and surface strength improvement and an external sizing agent for the purpose of imparting sizing can be added to the surface treatment agent. The surface treatment agent can be applied by a coating machine such as a two-roll size press coater, a gate roll coater, a blade metalling coater, or a rod metalling coater.

  In the present invention, a coating layer containing a pigment and an adhesive is provided on the coated base paper obtained as described above.

  Examples of the pigment used in the coating layer in the present invention include kaolin, clay, delaminated clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, and silicate. Conventional pigments such as inorganic pigments such as colloidal silica and satin white, and organic pigments such as plastic pigments can be used alone or in combination of two or more. In the present invention, it is necessary that 0.5 to 25 parts by weight of titanium dioxide is blended out of 100 parts by weight of pigment. The amount is preferably 1 part by weight or more and 20 parts by weight or less, more preferably 3 parts by weight or more and 15 parts by weight or less. When the amount is less than 0.5 parts by weight, there is a problem that the opacity of the coated paper is lowered and the back-through is worsened. When it exceeds 25 parts by weight, the blank paper glossiness and surface strength of the coated paper are lowered, and blanket piling during printing is deteriorated, so that the printability is poor.

  The adhesive used in the present invention is not particularly limited, and styrene / butadiene series, styrene / acrylic series, ethylene / vinyl acetate series, butadiene / methacrylate series, vinyl acetate / butyl series conventionally used for coated papers. Synthetic adhesives such as acrylate-based copolymers and polyvinyl alcohol, maleic anhydride copolymers, acrylic acid / methyl methacrylate copolymers; proteins such as casein, soy protein, synthetic proteins; oxidized starch, positive Starch, urea phosphated starch, etherified starch such as hydroxyethyl etherified starch, starches such as dextrin; one or more ordinary adhesives for coated paper of cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, hydroxymethylcellulose It can be appropriately selected and used. These adhesives are used in the range of 5 to 50 parts by weight, more preferably about 5 to 30 parts by weight per 100 parts by weight of the pigment. When the amount exceeds 50 parts by weight, the viscosity of the coating material becomes high, which causes an operability problem that makes it difficult to pass through piping and a screen. If the amount is less than 5 parts by weight, a sufficient surface strength cannot be obtained, which is not preferable.

  In the present invention, various auxiliary agents blended in ordinary coating pigments such as a dispersant, a thickener, a water retention agent, an antifoaming agent, a water resistance agent, a colorant, and a printability improver as necessary. It can be used as appropriate.

  In the present invention, the paper surface strength required at the time of printing in offset printing, the ink inking property indicating the ink inking state, the water resistance to dampening water (pyling), and the ink drying in offset rotary printing are required. In order to impart blister resistance, a printability improver can be used as an auxiliary agent in the coating layer.

The prepared coating solutions are: Fladed nip blade coater, jet fountain blade coater, short dwell time application type coater, bar coater, roll coater, air knife coater, reverse roll coater, curtain coater, 2 roll size press coater, One or two or more layers on the base paper using a known roll coater such as a gate roll coater, blade metering size press coater, rod metering size press coater, shim sizer, or other film transfer type roll coater or die coater. Apply to. The coating amount of the coating layer of the present invention is preferably 1 g / m ² or more and 8 g / m ² or less, more preferably 2 g / m ² or more and 7 g / m ² or less, more preferably 3 g / m ² or more per side. 6 g / m ² or less.

  As a method of drying the wet coating layer, various methods such as a steam heating cylinder, a heated hot air air dryer, a gas heater dryer, an electric heater dryer, and an infrared heater dryer are used alone or in combination. Since the dry state affects the curl of the paper, it is preferable to use an apparatus capable of controlling the dry balance between the front and back sides in the present invention.

  In the present invention, the coated paper thus obtained can be subjected to a calendar process in order to increase the smoothness. The calendar process may be performed using a super calendar, a gloss calendar, a soft calendar, or the like that is usually used for smoothing the coated paper, or these may be used in combination. From the viewpoint of improving the balance between the printing surface quality and the printing workability, it is particularly preferable to perform a soft calendar process. Moreover, it is preferable that the processing temperature of the metal roll at the time of a calendar process shall be 100 degreeC or more, and it is preferable to set it as 150-250 degreeC especially. By doing so, it becomes difficult to damage the Clark stiffness of the coated paper for offset printing, so that not only the printing workability is improved, but also the printing surface quality is excellent. The linear pressure during the calendar treatment is preferably 10 to 200 kg / cm, and more preferably 10 to 100 kg / cm.

The blank surface feeling of the coated paper for offset printing of the present invention is evaluated by the DAV2 value of the appearance analyzer of DuPont, and the lower this value, the less the feeling of visual discoloration and the better the blank surface feeling. is there. Further, as having excellent printability in offset printing machine or a low basis weight (sheet passing property and ears I aptitude), ISO bending stiffness in the MD direction is preferably at 37cm ^3/100 or more.
The coated paper for offset printing of the present invention has a basis weight of 50 g / m ² or less, preferably 35 g / m ^{2 to} 48 g / m ² , more preferably 35 to 45 g / m ² , and particularly preferably The effect of the present invention can be exhibited more at 38 to 42 g / m ² .

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples. In addition, parts by weight and% by weight indicate parts by weight of solid content and% by weight of solid content. Moreover, about the physical property of the material for coating materials, and the performance of the obtained coated paper, the test was implemented based on the evaluation method as shown below.
(1) Basis weight Measured according to JIS P 8124.
(2) Blank Paper Glossiness The 75 ° glossiness of the blank paper portion was measured using a gloss meter GM26D manufactured by Murakami Color Co., Ltd.
(3) Blanket piling evaluation Using an offset rotary press (Toshiba offset rotary press: 0A-4B2T-600), four-color printing (color order of black, indigo, red, yellow) was performed 10,000 copies at a printing speed of 700 rpm. Thereafter, the degree of accumulation of the paper dust of the black blanket was visually evaluated.
A: No occurrence of paper dust was observed. ○: Little generation of paper dust was observed.
Δ: Some generation of paper dust was observed. ×: A lot of paper dust was deposited. (4) Feeling of blank paper Using a DuPont Appearance Analyzer, the haze on the coated paper surface was evaluated as a DAV2 value. . The larger the value, the more uneven the surface and the poor white surface feeling.
100 or less: very good (◎)
100-110: Good (◯)
110-120: Slightly inferior (△)
120 or more: Inferior (×)

<Preparation of bulky mechanical pulp>
CTMP (Chemothermomechanical method)
As a chemical solution, sodium sulfite was added to wood chips of Eucalyptus globulus (volume weight 557 kg / m ³ ), which is a broad-leaved tree, at 2.0% per dry weight and impregnated at room temperature under reduced pressure for 30 minutes. After infiltration with the chemical solution, the chip was taken out and adjusted to a raw material concentration of 40%. Next, primary refining was carried out using a pressure refiner for laboratories (BRP45-300SS manufactured by Kumagai Riki Kogyo Co., Ltd.). Then, secondary refining was performed with a normal pressure refiner for laboratories (BRP45-300CB, manufactured by Kumagai Riki Kogyo Co., Ltd.) at a pulp concentration of 20%. In addition, the freeness after secondary refining was adjusted to 120 ml by Canadian Standard Freeness (CSF) to obtain manufactured pulp A. The sheet density of this manufactured pulp A when the freeness was 100 ml was 0.32 g / cm ³ .

APTMP (Alkaline Hydrogen Peroxide Thermomechanical Pulp) Method Hardwood Eucalyptus Globulus (volume weight 557kg / m ³ ) wood chips with chemicals (1.5% sodium hydroxide per wood chip dry weight, diethylenetriaminepentaacetic acid) : DTPA 0.3%, sodium silicate 2.0%, magnesium sulfate 0.05%) was added for 30 minutes at room temperature under reduced pressure (-760 mmHg). Once the pressure was returned to normal pressure, 2.5% of a hydrogen peroxide solution was added to the chemical solution and impregnated again at room temperature under reduced pressure for 1 hour. After holding the chip at a temperature of 60 ° C. for 30 minutes, primary refining was performed using a pressure refiner for laboratories (BRP45-300SS manufactured by Kumagai Riki Kogyo Co., Ltd.). Then, secondary refining was performed with a normal pressure refiner for laboratories (BRP45-300CB, manufactured by Kumagai Riki Kogyo Co., Ltd.) at a pulp concentration of 20%. Moreover, the freeness after secondary refining was adjusted to 120 ml with Canadian Standard Freeness (CSF) to obtain manufactured pulp B. The sheet density when the freeness of this manufactured pulp B was 100 ml was 0.35 g / cm ³ .

[Example 1]
<Preparation of base paper>
Production pulp A obtained above (CTMP method) has a pulp composition comprising 20% per pulp weight, kraft pulp 60%, deinked pulp 20%, and 11 wt% of light calcium carbonate added internally, 0.03% by weight of a sizing agent and 0.8% by weight of a sulfuric acid band as a fixing agent were added, and papermaking was performed at a high speed of 1200 m / min with a twin wire paper machine to obtain a base paper having a basis weight of 32.4 g / m ^2. It was.

<Preparation of coating solution>
Engineered kaolin (Imeris: Contour 1500, average particle size 1.95 μm) 60.0 parts by weight, secondary clay (manufactured by Huber: KCS: average particle size 1.18 μm) 21.5 parts by weight, and rutile type dioxide To a pigment composed of 10.0 parts by weight of titanium (manufactured by DuPont: RPS-V), 0.2 part by weight of sodium polyacrylate as a dispersant is added as a dispersant and dispersed with a serie mixer. % Pigment slurry was prepared. To the pigment slurry thus obtained, 8.5 parts by weight of a hollow plastic pigment having a diameter of 1.0 μm (manufactured by ZEON Corporation: MH8101), non-thickening type styrene-butadiene copolymer latex (glass transition temperature) 15 ° C., gel content 75%) 13.5 parts by weight, hydroxyethyl etherified starch (Penford: PG295) 7.5 parts, printability improver (PA 6650: Seiko PMC) 0.5 parts by weight And water was further added to obtain a coating solution having a concentration of 60%.

<Preparation of coated paper>
The above coating liquid is applied to both sides of the base paper using a blade coater at a coating speed of 1200 m / min so that the coating amount per side is 4.5 g / m ^2. After passing through a dryer, it was dried with a cylinder dryer so that the moisture in the paper was 5.5%.
<Calendar processing>
Next, soft nip calendering was performed under the conditions of a metal roll temperature of 160 ° C., an elastic roll with a Shore hardness of 85, a paper feed speed of 1200 m / min, a linear pressure of 100 kg / cm, and a calender nip number of 4 nips. A coated paper for offset printing was obtained.
[Example 2]
A coated paper for offset printing was obtained in the same manner as in Example 1 except that the manufactured pulp A (CTMP method) used in Example 1 was changed to the manufactured pulp B (APTMP method).

[Comparative Example 1]
A coated paper for offset printing was obtained in the same manner as in Example 1 except that the manufactured pulp A (CTMP method) used in Example 1 was changed to softwood groundwood pulp (GP).
[Comparative Example 2]
A coated paper for offset printing was obtained in the same manner as in Example 1 except that the manufactured pulp A (CTMP method) used in Example 1 was changed to conifer thermal mechanical pulp (TMP).
[Comparative Example 3]
Except that the titanium dioxide used in Example 1 was not used at all and 31.5 parts by weight of secondary clay (manufactured by Huber: KCS: average particle size 1.18 μm) was used instead. Thus, a coated paper for offset printing was obtained.
[Comparative Example 4]
Except for using 40 parts by weight of 60.0 parts by weight of engineered kaolin (Imeris: Contour 1500, average particle size 1.95 μm) used in Example 1, and using 30 parts by weight of titanium dioxide instead. In the same manner as in Example 1, a coated paper for offset printing was obtained.

  Table 1 shows the test results of the offset printing coated paper obtained in each Example and Comparative Example.

As is apparent from the results shown in Table 1, the coated papers of Examples 1 and 2 are superior in rigidity and whiteness compared to Comparative Examples 1 and 2 in spite of being light in weight. It turns out that the blanket piling suppression effect is also excellent. In addition, since the rigidity, white glossiness, and opacity were good, it was confirmed that it was suitable for offset printing.
Further, when Example 1 is compared with Comparative Example 3 not containing titanium dioxide, the other conditions are the same in both cases. However, Example 1 is effective in whiteness, opacity, blanket piling suppression effect and blank paper feeling. It was excellent and it was confirmed that Comparative Example 3 was inferior to all of them.
On the other hand, it was confirmed that Comparative Example 1 and Comparative Example 2 were inferior in blank paper feeling. It was confirmed that Comparative Example 3 was inferior in opacity.
When Example 1 was compared with Comparative Example 4, it was confirmed that the glossiness of blank paper was inferior and blanket piling was also deteriorated.
From the above, the coated paper for offset printing of the present invention has a white paper by containing hardwood mechanical pulp in the base paper and titanium dioxide in the coating pigment even if the basis weight is 50 g / m 2 or less. It was found to be excellent in whiteness and blanket piling suppression effect.
Further, the coated paper for offset printing of the present invention has good rigidity, white glossiness, and opacity, so that it is suitable for offset printing and further has excellent printing workability.

Claims (3)

In the printing coated paper provided with a coating layer comprising a pigment and an adhesive on at least one side of the base paper, the basis weight of the coated paper is 50 g / m ² or less, and the base paper contains hardwood mechanical pulp, A coated paper for offset printing, wherein the coated pigment contains titanium dioxide, and the content thereof is 0.5 to 25 parts by weight per 100 parts by weight of the pigment.   The coated paper for offset printing according to claim 1, wherein a freeness of the hardwood mechanical pulp is 100 ml or more and 200 ml or less. The coating layer weight of the coated paper is 1 g / m ² or more and 8 g / m ² or less, preferably 2 g / m ² or more and 7 g / m ² or less, more preferably 3 g / m ² or more and 6 g / m ² or less. The coated paper for offset printing according to claim 1 or 2, wherein: