JP5048024B2 - Newspaper for offset printing - Google Patents

Description

  The present invention relates to newsprint paper for offset printing, and more particularly to newsprint paper for offset printing with high surface strength, improved blanket paper dusting at the time of offset printing, and improved Nepari trouble that paper is removed from the blanket during printing. Is.

  In recent years, newspaper printing is rapidly changing from the conventional letterpress printing method to the offset printing method, and at least 80% of newspaper printing is said to be based on the offset printing method. Offset printing is a method in which a printing plate, usually called a PS plate, is prepared and dampening water and ink are supplied to the printing plate for printing. The printing plate is a lithographic plate, and the image area on the printing plate is treated to have an oleophilic surface, while the non-image area is treated to have a hydrophilic surface. When dampening water and ink are supplied to the printing plate, ink is applied to the image area and water is applied to the non-image area, and the ink is transferred from the printing plate to the paper via the blanket for printing. Is done.

  In offset printing, ink having a relatively strong tack is used, so a printing paper having a high surface strength is required. Also, since dampening water is added to the paper surface during printing, if paper with a surface with low surface strength or poor water resistance is used, paper dust may accumulate on the blanket or mix with ink, Troubles such as so-called blurring occur on the printing surface. In addition, the demand for improvement in printing opacity has increased along with the weight reduction of newsprint, and inorganic pigments such as white carbon, titanium oxide, and talc are often used as fillers for papermaking in order to increase the opacity of paper. became. By the way, these inorganic pigments are one of the paper powder components that are easily leached out of the paper layer by dampening water at the time of offset printing and cause blanket piling. Moreover, since the increase in the amount of deinked pulp is accompanied by an increase in ash content in the paper, blanket piling tends to deteriorate.

  In order to cope with such troubles during offset printing, conventionally, a surface treatment agent containing a water-soluble polymer material such as starch, polyvinyl alcohol, or polyacrylamide is generally applied to the surface of newspaper paper. Yes. These surface treatment agents can improve the strength of the paper surface and strongly adhere fine fibers and fillers on the paper surface to the paper. However, as the coating amount increases, the surface tackiness of the paper surface increases in a wet state. This causes troubles such as sticking to the blanket during printing or causing paper breaks. Furthermore, the use of a large amount of surface treatment agent suppresses the penetration of ink into the paper surface, and as a result, ink absorption unevenness (color unevenness on the printing surface) due to coating unevenness is likely to occur during color printing. Has difficulties.

  Conventionally, various methods for suppressing surface tackiness and increasing surface strength have been proposed. For example, JP-A-8-13384 discloses a method for enhancing the surface water resistance by increasing the strength of the paper surface by applying a specific polyacrylamide compound on the surface and further using a polyvalent aldehyde, or JP-A-5-59689 discloses a method for improving surface size, surface strength, and surface tackiness by applying an aqueous composition obtained by adding a block copolymer of ethylene oxide and propylene oxide to polyvinyl alcohol. Has been proposed. However, in any case, it is not always sufficient to achieve both surface tackiness relaxation and surface strength, and the ink absorption unevenness on the color printing surface is still not improved.

  Also, by using an internally added sizing agent such as rosin emulsion sizing agent, the generation of paper dust is suppressed by increasing the size of the paper surface and suppressing the penetration of dampening water into the paper layer during offset printing. Has been done in the past. However, the internal additive sizing agent as described above tends to cause trouble due to foaming in a white water system in a high speed paper machine such as a newspaper paper machine. Newspaper paper uses a lot of mechanical pulp, whose size effect is less likely to be manifested, and when a yield improver is used in combination with an internal sizing agent, the pitch in the papermaking system is also incorporated into the paper. It has the disadvantage of reducing the whiteness of the paper.

JP-A-8-13384 JP-A-5-59689

  An object of the present invention is to provide newsprint paper for offset printing in which blanket paper dust piling does not occur, surface tackiness is low, and Nepari trouble is reduced.

As a result of intensive studies to obtain an offset printing newsprint having excellent offset printing workability, the present inventors applied a surface treatment agent containing a specific processed starch on a newsprint base paper and dried it. Solved the problem. That is, a specific etherified starch was used as a surface treatment agent, and the B-type viscosity and surface treatment agent measured at 60 rpm using a No. 1 rotor under conditions of a surface treatment agent concentration of 10% and 50 ° C. The problem was solved by making the product of the coating amount of ² to 15 cps · g / m ² .

  In the present invention, it has been possible to provide newsprint paper for offset printing in which blanket paper dust piling does not occur, surface tackiness is low, and Nepari trouble is reduced.

  As described above, a surface treatment agent mainly composed of starch, polyvinyl alcohol, polyacrylamide or the like is conventionally applied to newsprint for offset printing. However, all of the above surface treatment agents increase the coating amount in order to reduce the amount of paper dust generated, and when applied to a blanket during printing based on uneven ink absorption in color printing or surface adhesion in a wet state. Problems such as sticking occur. In other words, the amount of paper dust generated can be reduced by increasing the coating amount of the surface treatment agent, but it is difficult to improve both at the same time due to the conflicting property that the surface tackiness deteriorates when the coating amount is increased. It is.

The present inventors used a specific processed starch as a surface treatment agent, and further measured the B-type viscosity and surface treatment measured at 60 rpm using a No. 1 rotor under the conditions of a concentration of 10% of the surface treatment agent and 50 ° C. It has been found that when the product of the coating amount of the agent is in the range of ² to 15 cps · g / m ² , both paper dust suppression and surface tackiness can be reduced. When the product value is less than ² cps · g / m ² , the paper dust suppression effect is not sufficient, and when it exceeds 15 cps · g / m ² , the paper dust suppression effect is sufficient, but the surface adhesiveness Becomes higher. Even if the value of this product is within the range of the present invention, the unmodified starch and oxidized starch could not simultaneously improve paper dust suppression and surface tackiness. That is, the product of the B-type viscosity and the coating amount defined in the present invention improves the paper dust suppression and surface adhesiveness of newsprint for offset printing at the same time. Processed starch having a specific structure or functional group It is considered that it is established only when using as a surface treatment agent.

The B type viscosity of the surface treating agent used in the present invention is preferably in the range of 5 to 30 cps when measured at 60 rpm using a No. 1 rotor under conditions of a concentration of 10% and 50 ° C. If it is less than 5 cps, the permeability of the surface treatment agent is high and the surface treatment agent does not remain on the paper surface, so the paper dust suppressing effect is not sufficient. On the other hand, if it exceeds 30 cps, the variation in coating amount becomes large, and it is difficult to obtain a uniform product.
As the coating amount of the surface treatment agent of the present invention, 0.05 to 2.0 g / m 2 by solid content weight per ^duplex, and preferably from 0.1 to 1.0 g / m ^2. If the coating amount is less than 0.05 g / m ² , sufficient surface strength cannot be obtained, and the effect of suppressing paper dust may not be sufficient. On the other hand, if it exceeds 2.0 g / m ² , the surface strength is not a problem, but the surface adhesiveness becomes high, and there is a concern about sticking to a blanket or a Nepari trouble such as paper breakage. The solid content concentration when applying the surface treatment agent to the base paper is suitably 3 to 20% by weight.

The specific modified starch used in the present invention is preferably at least one selected from the following a) to c), having high film-forming ability (coverability) and low elution rate in water. .
a) Hydroxyethylated starch or hydroxypropylated starch
b) Carboxylic acid esterified starch esterified with monocarboxylic acid or dicarboxylic acid having a linear, branched or cyclic alkyl group or alkenyl group having 4 to 18 carbon atoms
c) Aldehydated starch Preferred as the etherified starch used in the present invention is hydroxyethylated starch. The reason why such a specific etherified starch is effective in suppressing paper dust and reducing surface tackiness is not necessarily clear, but is presumed as follows. The dampening water added to the paper surface during offset printing easily penetrates into the paper layer, and if the wetness with the pulp fiber is too good, fine fibers and internal fillers in the paper layer are easily released to the outside. To come. As a result, it is presumed that the fine raw material that has exuded becomes the basis of the paper powder. Furthermore, newsprint paper has a high water absorption due to its pulp (paper layer) structure, and is originally configured to easily generate paper dust and the like. Therefore, starch with high film-forming ability spreads more significantly in the MD and CD directions than the penetration of the paint in the Z direction of the paper, resulting in less uneven coating on the paper surface. It is thought that the fine fibers and internal fillers present on the surface can be prevented from coming into direct contact with the blanket. On the other hand, starch with low film-forming ability has poor coverage to fine fibers and fillers, and dampening water added to the paper surface during offset printing easily penetrates into the paper layer, and the fine fibers in the paper layer Internal fillers can be easily released to the outside. As a result, it is presumed that the fine raw material that has exuded becomes the basis of the paper powder. In particular, even when the paper surface is dampened with fountain solution during offset printing, the hydroxyethylated starch is firmly fixed to the fiber by the interaction of the hydrogen bonds of the hydroxyethyl group, so the amount of starch to be eluted is small, It is thought that surface tackiness can be reduced.

  The most preferable hydroxyethylated starch used in the present invention is dry low molecular weight hydroxyethylated starch. This dry viscosity-reduced hydroxyethylated starch is, for example, hydroxyethylated starch as described in US Pat. No. 5,766,366 and US Pat. No. 5,817,180 in a solid state with a water content of 5 to 17%, hydrogen chloride gas, hydrochloric acid. The molecular weight is reduced by acid treatment with sulfuric acid or the like, or oxidation treatment with ammonium persulfate, hydrogen peroxide, chlorine gas or the like. Dry low molecular weight hydroxyethylated starch has more aldehyde groups to form hemiacetal bonds with cellulose fibers than hydroxyethylated starch treated in a slurry (wet) state as before, and covalently bonds to cellulose fibers. Therefore, it is considered that the surface strength is remarkably improved and the effect of suppressing paper dust is high.

  As the carboxylic acid esterified starch used in the present invention, particularly preferred is 1-octenyl succinic acid esterified starch. The reason why such a specific carboxylated esterified starch is effective in suppressing paper dust and lowering the surface tackiness is not necessarily clear, but film formation is high as in the case of the above-mentioned etherified starch. Acid esterified starch is highly hydrophobic and reduces the surface free energy of the paper, so that the paper layer is difficult to wet with water, water absorption is suppressed, and as a result, the embossing (free) of the fine raw material is reduced and the paper is reduced. It is considered that the generation of powder and the like is reduced or eliminated.

  The reason why the aldehyde-modified starch used in the present invention is effective in suppressing paper dust and reducing surface tackiness is not necessarily clear, but it forms a hemiacetal bond with cellulose fibers, and dampening water adheres during offset printing. It is considered that the generation of paper dust is suppressed because the wet surface strength is improved. Moreover, since the cellulose fiber and the hemiacetal bond are formed, since the starch elution rate by the dampening water at the time of offset printing becomes low, it is thought that surface tackiness will fall and Nepari trouble will decrease.

  As described above, as a surface treatment agent that is excellent in the paper dust suppressing effect, it is ideal to have a high film-forming ability, impart water absorption resistance, and form a covalent bond with cellulose fibers. A surface treatment agent in which a sizing agent is mixed with ethylated starch is most desirable.

  The content of the specific processed starch used in the present invention in the solid content of the surface treatment agent is preferably in the range of 20 to 100% by weight. If it is less than 20% by weight, either surface tackiness or surface strength may be insufficient.

The newspaper for offset printing according to the present invention preferably has a Nepari strength of 300 mN / 3 cm (about 30 gf / 3 cm) or less, and if it is less than this value, troubles due to surface tackiness do not occur. The Nepari intensity in the present invention is measured as follows. Cut two newspapers for offset printing into 4 x 6 cm, soak the coated surfaces in water at a temperature of 20 ° C for 5 seconds, and then adhere the coated surfaces together. Subsequently, newsprint base papers are stacked on both sides of the outer side, passed through a roll at a pressure of 50 kg / m ² , and conditioned at 25 ° C. and 60% RH for 24 hours. After preparing a 3 × 6 cm sample piece, the peel strength is measured with a tensile tester under the condition of a tensile speed of 30 mm / min. The larger the measured value, the harder it is to peel off (in other words, the stronger the adhesiveness).

  In the surface treatment agent used in the present invention, as a component other than starch, a sizing agent, a water-soluble polymer, an anti-Nepari agent, an antiseptic, an antifoaming agent, an ultraviolet ray preventing agent, an anti-fading agent, a fluorescent whitening agent, Viscosity stabilizers, lubricants, anti-slip agents and the like may be contained.

  The sizing agent preferably contains at least two of a styrene sizing agent and an olefin sizing agent. As the styrene-based sizing agent, styrene / acrylic acid copolymer, styrene / (meth) acrylic acid copolymer (note that (meth) acrylic acid means “acrylic acid and / or methacrylic acid”). Styrene / (meth) acrylic acid / (meth) acrylic acid ester copolymer, styrene / maleic acid copolymer, styrene / maleic acid half ester copolymer, styrene / maleic acid ester copolymer, etc. . Olefin-based sizing agents include ethylene / acrylic acid copolymer, isobutylene / acrylic acid copolymer, n-butylene / (meth) acrylic acid / (meth) acrylic acid ester copolymer, propylene / maleic acid copolymer And ethylene / maleic acid copolymer. In addition, alkyl ketene dimer, alkenyl succinic anhydride, rosin and the like can be used as the sizing agent.

  Next, the water-soluble polymer will be described. Examples of the water-soluble polymer include starches such as oxidized starch, phosphate-modified starch, cationized starch and enzyme-modified starch other than the specific processed starch of the present invention, polyvinyl alcohol, polyacrylamide and the like.

  The coating apparatus for applying the surface treatment agent to the newsprint base paper is not particularly limited. Generally known and publicly used devices such as bar coaters, rod blade coaters, air knife coaters and the like are appropriately used. In general, the surface is smoothed by calendering after application. In this case, machine calender finishing using a double-sided metal roll or soft calender finishing comprising a metal roll and an elastic roll is applied.

Newspaper base paper used in the present invention is represented by mechanical pulp (MP) such as ground pulp (GP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), semi-chemical pulp, and kraft pulp (KP). Chemical pulp (CP), deinked pulp (DIP) obtained by deinking waste paper containing these pulps, and recovered pulp obtained by disaggregating damaged paper from the papermaking process, alone or in any They are mixed at a ratio and generally made by a publicly known paper machine. The DIP blending ratio is more preferably in the range of 50 to 100% in view of the recent trend toward high DIP blending. The basis weight of the base paper is not particularly limited, but is about 34 to 50 g / m ² .

  The newsprint base paper used in the present invention can be appropriately added with publicly known papermaking fillers and papermaking chemicals as needed. As filler, white carbon, clay, silica, talc, titanium oxide, calcium carbonate, synthetic resin filler (vinyl chloride resin, polystyrene resin, urea formalin resin, melamine resin, styrene / butadiene copolymer resin, etc.) etc. Can be added. Particularly in neutral papermaking, calcium carbonate is effective. Papermaking chemicals include polyacrylamide polymers, polyvinyl alcohol polymers, cationized starch, urea / formalin resin, melamine / formalin resin and other paper strength enhancers; acrylamide / aminomethylacrylamide copolymer Salt / cationized starch, polyethyleneimine, polyethylene oxide, acrylamide / sodium acrylate copolymer drainage / yield improver, rosin sizing agent, emulsion sizing agent, alkyl ketene dimer (AKD), alkenyl succinic anhydride ( Auxiliary agents such as sizing agents such as ASA), aluminum sulfate (sulfuric acid band), UV inhibitors, fading inhibitors and antifoaming agents may be contained. The physical properties of the newsprint base paper need to be printable by an offset printing machine, and may have any physical properties such as tensile strength, tear strength, and elongation equivalent to those of ordinary newsprint.

  The present invention will be specifically described below with reference to examples. Of course, the present invention is not limited to them. Moreover, unless otherwise indicated, the part and% in an example show a weight part and weight%, respectively.

[Example 1]
<Making paper>
Mixed in a ratio of 12 parts softwood kraft pulp, 22 parts thermomechanical pulp, and 66 parts deinked waste paper pulp, disaggregated with a refiner and adjusted to a freeness of 110 ml (Canadian Standard Freeness), white as a filler After adding 2% of carbon per absolute dry pulp, paper was made with a twin wire type paper machine to obtain a newsprint base paper having a basis weight of 42 g / m ² .
<Application of surface treatment agent>
As a surface treatment agent, a paste treatment of dry low molecular weight hydroxyethylated starch (trade name: ETHYLE-2015, manufactured by STALEY, weight average molecular weight 330,000) was diluted to obtain a surface treatment agent having a solid content concentration of 6.8%. . The surface treatment agent thus obtained was applied and dried at a coating speed of 1300 m / min using a gate roll coater on both sides of the above-mentioned newsprint base paper (basis weight 42 g / m ² ), and then a resin roll Using a soft calender consisting of a metal roll, 1 nip treatment was performed under the condition of a linear pressure of 150 kg / cm to obtain a newsprint for offset printing.

[Example 2]
Example 1 except that dry-type low molecular weight hydroxyethylated starch (trade name: ETHYLE-2020, manufactured by STALEY, weight average molecular weight 510,000) was used as the surface treatment agent and applied at a solid content concentration of 6.2%. Thus, newsprint for offset printing was obtained.

[Example 3]
Example 1 except that dry-type low molecular weight hydroxyethylated starch (trade name: ETHYLE-2025, manufactured by STALEY, weight average molecular weight 540,000) was used as the surface treatment agent, and the solid content concentration was 5.8%. Thus, newsprint for offset printing was obtained.

[Example 4]
Example 1 except that dry-type low molecular weight hydroxyethylated starch (trade name: ETHYLE-2035, manufactured by STALEY, weight average molecular weight 840,000) was used as the surface treatment agent, and the solid content concentration was 5.2%. Thus, newsprint for offset printing was obtained.

[Example 5]
50 parts dry low molecular weight hydroxyethylated starch (trade name: ETHYLE-2025, manufactured by STALEY, weight average molecular weight 540,000) and oxidized starch (trade name: SK-20, manufactured by Nippon Corn Starch Co., Ltd.) A newsprint paper for offset printing was obtained in the same manner as in Example 1 except that a mixed paste containing 50 parts (weight average molecular weight 570,000) was used and applied at a solid content concentration of 6.0%.

[Example 6]
50 parts dry low molecular weight hydroxyethylated starch (trade name: ETHYLE-2035, manufactured by STALEY, weight average molecular weight 840,000) and oxidized starch (trade name: SK-20, manufactured by Nippon Corn Starch Co., Ltd.) A newsprint for offset printing was obtained in the same manner as in Example 1 except that a mixed paste containing 50 parts (weight average molecular weight 570,000) was used and applied at a solid content concentration of 5.5%.

[Example 7]
100 parts dry low molecular weight hydroxyethylated starch (trade name: ETHYLE-2025, manufactured by STALEY, weight average molecular weight 540,000), styrene sizing agent (trade name: KN-520, Harima Kasei Co., Ltd.) Example 1 except that a mixed paste consisting of 10 parts and an olefinic sizing agent (trade name: AK-505, manufactured by Seiko Chemical Industry Co., Ltd.) was used and applied at a solid content concentration of 5.8%. Thus, newsprint for offset printing was obtained.

[Example 8]
<Making newspaper paper>
100% of deinked waste paper pulp was disaggregated with a refiner and adjusted to a free slurry of 110ml (Canadian Standard Freeness), with 1% white carbon as filler and 2% talc as dry filler. After the addition, paper making was performed with a twin wire type paper machine to obtain a newsprint base paper having a basis weight of 42 g / m ² .
<Application of surface treatment agent>
As a surface treatment agent, a paste treatment of dry-type low molecular weight hydroxyethylated starch (trade name: ETHYLE-2025, manufactured by STALEY, weight average molecular weight 540,000) was diluted to obtain a surface treatment agent having a solid content concentration of 4.5%. The surface treatment agent thus obtained was applied on both sides of the above-mentioned newsprint base paper (basis weight 42 g / m ² ) using a gate roll coater at a coating speed of 1000 m / min, dried, and then a resin roll Using a soft calender consisting of a metal roll, 1 nip treatment was performed under the condition of a linear pressure of 150 kg / cm to obtain a newsprint for offset printing.

[Example 9]
Newsprint paper for offset printing was obtained in the same manner as in Example 7 except that the surface treatment agent was applied at a solid content concentration of 6.0%.

[Example 10]
Offset printing is performed in the same manner as in Example 1 except that hydroxyethylated starch (trade name: PG-270, manufactured by PENFORD, weight average molecular weight 1 million) is used as the surface treatment agent, and the coating is applied at a solid content concentration of 6.0%. I got newsprint paper.

[Example 11]
50 parts hydroxyethylated starch (trade name: PG-270, manufactured by PENFORD, weight average molecular weight 1 million) and oxidized starch (trade name: SK-20, manufactured by Nippon Corn Starch Co., Ltd., weight average molecular weight 57 as surface treatment agents) A newspaper for offset printing was obtained in the same manner as in Example 1 except that 50 parts of the mixed paste was used and applied at a solid concentration of 6.1%.

[Example 12]
Similar to Example 1 except that aldehyde-modified starch (trade name: OC-0087, manufactured by Oji Cornstarch Co., Ltd., weight average molecular weight 80,000) was used as the surface treatment agent and applied at a solid content concentration of 6.5%. Thus, newsprint for offset printing was obtained.

[Example 13]
Example 1 except that 1-octenyl succinic esterified starch (trade name: Filmkote-370, manufactured by National Starch and Chemicals, weight average molecular weight 1,120,000) was used as a surface treatment agent, and the solid content concentration was 5.5%. In the same manner, newsprint for offset printing was obtained.

[Comparative Example 1]
Offset was applied in the same manner as in Example 1 except that dry low molecular weight hydroxyethylated starch (trade name: ETHYLE-2025, manufactured by STALEY, weight average molecular weight 540,000) was applied as a surface treatment agent at a solid content concentration of 3.0%. I got newsprint for printing.

[Comparative Example 2]
Offset as in Example 1 except that dry low molecular weight hydroxyethylated starch (trade name: ETHYLE-2025, manufactured by STALEY, weight average molecular weight 540,000) was applied as a surface treatment agent at a solid content concentration of 10.0%. I got newsprint for printing.

[Comparative Example 3]
Offset was performed in the same manner as in Example 1 except that oxidized starch (trade name: SK-20, manufactured by Nippon Corn Starch Co., Ltd., weight average molecular weight 570,000) was used as the surface treatment agent, and the coating was applied at a solid content concentration of 3.0%. I got newsprint for printing.

[Comparative Example 4]
Offset was performed in the same manner as in Example 1 except that oxidized starch (trade name: SK-20, manufactured by Nippon Corn Starch Co., Ltd., weight average molecular weight 570,000) was used as the surface treatment agent, and it was applied at a solid content concentration of 10.0%. I got newsprint for printing.

[Comparative Example 5]
Offset was performed in the same manner as in Example 1 except that oxidized starch (trade name: SK-20, manufactured by Nippon Corn Starch Co., Ltd., weight average molecular weight 570,000) was used as the surface treatment agent, and the coating was applied at a solid content concentration of 6.2%. I got newsprint for printing.

[Comparative Example 6]
Newsprint paper for offset printing was obtained in the same manner as in Example 7 except that oxidized starch (trade name: SK-20, manufactured by Nippon Corn Starch Co., Ltd., weight average molecular weight 570,000) was used as the surface treating agent.

[Comparative Example 7]
Offset was performed in the same manner as in Example 7 except that oxidized starch (trade name: SK-20, manufactured by Nippon Corn Starch Co., Ltd., weight average molecular weight 570,000) was used as the surface treatment agent, and the coating was applied at a solid content concentration of 4.5%. I got newsprint for printing.

The offset printing newsprints obtained in the examples and comparative examples were measured for the following items, and the results are shown in Table 1.
-Measurement of B-type viscosity of surface treatment agent The solid content concentration of the surface treatment agent was adjusted to 10%, and the B-type viscosity was measured at 60 rpm using a No. 1 rotor at a temperature of 50 ° C.
-Evaluation of Blanket Paper Powder Piling Amount For the newspapers for offset printing in Examples 1-8, 11-12, and Comparative Examples 1-5, the blanket paper powder pile amount was evaluated as follows. Using an offset printer (Toshiba SYSTEM C-20), the dampening film pressure was 0.9 μm, the printing surface density was 1.15, the printing speed was 600 rpm, and the ink was black ink (trade name: Newsking, Toyo Ink). After printing 20,000 copies, the paper powder adhering to the non-image area (area 200 cm ² ) of the blanket is scraped with ethanol, filtered through a membrane filter with a pore size of 0.45 μm, dried and weighed, and the paper per 100 cm ² Converted to the amount of powder. For the newspapers for offset printing of Examples 9 to 10 and Comparative Examples 6 to 7, the measurement of blanket paper dust pile amount was changed to 1.1 μm dampening water film pressure, and the paper dust amount was measured after printing 60,000 copies. did. There is no practical problem if the amount of the piled paper powder is 50 mg / less. The amount of paper dust was measured on both the F and W sides of the newsprint for offset printing.
-Measurement of Nepari strength Two newspapers for offset printing were cut into 4 x 6 cm pieces, the coated surfaces were immersed in water at a temperature of 20 ° C for 5 seconds, and the coated surfaces were brought into close contact with each other. Newsprint paper was placed on both sides of the outside, passed through a roll at a pressure of 50 kg / m ² , and conditioned at 25 ° C. and 60% RH for 24 hours. After making a 3 × 6 cm sample piece, measurement was performed with a tensile tester under the condition of a tensile speed of 30 mm / min. The larger the measured value, the harder it is to peel off (in other words, the stronger the adhesiveness). In the newsprint paper for offset printing of the present invention, a paper having a Nepari strength of 250 mN / 3 cm or less was defined as “good peelability”.

As shown in Table 1, B when specific modified starches such as hydroxyethylated starch, 1-octenyl succinate esterified starch and aldehyde starch of Examples 1 to 13 were measured at a concentration of 10% and 50 ° C. Newsprint paper for offset printing coated so that the product of the mold viscosity (No. 1 rotor, 60 rpm) and the coating amount is ² to 15 cps · g / m ² has a marked reduction in the amount of blanket paper dust piling during offset printing. Nepari strength was at a level that was not a problem. In particular, in Example 7 in which the surface treatment agent contained a styrene sizing agent and an olefin sizing agent, the amount of paper dust generated was small. On the other hand, as in Comparative Examples 1 and 2, when the aforementioned product was outside the scope of the present invention, the amount of paper dust increased or the Nepari strength increased. Moreover, the offset printing newsprint paper which apply | coated the oxidized starch of Comparative Examples 3-7 is the amount of blanket paper powder piling, Nepari strength, even if the value of the above-mentioned product is in the range of the present invention (Comparative Examples 5-7). None of these were inadequate.

Claims (6)

Newspaper for offset printing, which is obtained by applying a surface treatment agent containing hydroxyethylated starch (excluding those with a weight average molecular weight of 510,000 and 540,000) to a newsprint base paper containing 66 to 100 parts by weight of deinked pulp and drying. It is a paper, and the content of the processed starch in the solid content of the surface treatment agent is 20 to 100% by weight, and further contains a viscosity reducing agent comprising a polyester amide compound having a hydroxyl group and having a branched molecular structure And the B type viscosity (No. 1 rotor, 60 rpm) of the surface treatment agent when measured at a concentration of 10% and 50 ° C. is 5 to 30 cps, and the coating amount of the surface treatment agent (per both sides) ) Is 0.05 to 2.0 g / cm ² , and the product of the B-type viscosity and the coating amount of the surface treatment agent (per both sides) is in the range of ^{2 to} 15 cps · g / m ² . For newspaper .   The processed starch in the surface treatment agent is a dry low molecular weight hydroxyethylated starch which has been reduced in molecular weight by acid treatment or oxidation treatment of hydroxyethylated starch in a solid state having a water content of 5 to 17%. Item 2. Newsprint paper for offset printing according to Item 1.   The newsprint for offset printing according to claim 1 or 2, wherein the surface treatment agent contains a sizing agent.   4. Newsprint paper for offset printing according to claim 1, comprising at least two of a styrene sizing agent and an olefin sizing agent as sizing agents.   The newsprint for offset printing according to any one of claims 1 to 4, wherein the Nepari strength is 300 mN / 3 cm or less. The offset printing according to any one of claims 1 to 5, wherein the B-type viscosity (No. 1 rotor, 60 rpm) of the surface treatment agent when measured at a concentration of 10% and 50 ° C is 20.0 to 25.1 cps. Newspaper.