JP2008031603A - One-side gross craft paper and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide one-side gloss craft paper suitable for highly delicate offset printing at a high speed, and to provide a method for easily producing one-side gloss craft paper at a low cost without staining at production facility. <P>SOLUTION: This one-side gloss craft paper based on JIS P 3401 is characterized by disposing a coating layer on one side of one side-glaced paper containing craft pulp as a main material, wherein the coating layer is formed by coating a coating liquid consisting mainly of starch and an inorganic pigment in a solid content of 2 to 7 g/m<SP>2</SP>; the paper surface pH of a coating layer-disposed glaced surface is 6.0 to 9.0; and the paper surface pH of the non-gloss surface is 4.3 to 5.9. The method for producing the one-side gloss craft paper is characterized by comprising at least a wet paper-forming process, a pressing process, and a drying process using a yankee dryer, coating one side making contact with the yankee dryer in the drying process of one-side gloss paper containing craft pulp as a main raw material with a coating liquid at a solid content of 2 to 7 g/m<SP>2</SP>to form a coating layer, and then contacting and drying the coating layer with the yankee dryer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to glossy kraft paper and a method for producing the same. More specifically, it is excellent in printability such as ink drying property and bag-making suitability, and does not cause yellowing, settling, bleeding, etc. on the printed matter, and has high glossiness and high surface strength while having gloss, The present invention relates to a single gloss kraft paper suitable for high-speed and high-definition offset printing, and a method for easily manufacturing the single gloss kraft paper at a low cost without causing stains in a manufacturing facility.

  Conventionally, for example, to produce coated paper such as glossy coated paper, it has been common to apply a coating solution offline to base paper such as glossy paper, and perform flattening, Since the coating of the coating liquid is complicated and a separate coating facility is required, there is a problem that the productivity is low and the cost is high.

  Therefore, various techniques have been developed to solve the problems in the manufacturing process as described above.

  For example, in Patent Document 1, a surface treatment agent made of starch and containing an inorganic pigment or an organic pigment as necessary is spray-coated on a substrate at a penetration depth of 10 μm from the outermost surface, and then calendered. A technique for manufacturing printing paper and improving printing workability is disclosed.

  However, although the above technique can be applied to the production of general coated paper for printing, it is usually applied on-machine by adding to a Yankee machine so that the coated surface is dried with a Yankee dryer. When applied to the production of single glossy kraft paper, there are problems that the surface treatment agent sinks into the base material and it becomes difficult to form a surface treatment layer, and contamination in the production facility occurs.

  Further, for example, in Patent Document 2, a strong alkaline aqueous solution having a pH of 8.5 to 12 is applied to a wet paper made of kraft pulp at a wet paper stage before a drying process with a Yankee dryer, and the pH of the glossy surface is 4. A technique for providing a glossy paper with less ink set-off by adjusting to a strong acidity of 3 to 5.0 is disclosed.

  However, when a strong alkaline aqueous solution is applied as in the above technique, the surface fibers of the glossy paper swell, the glossy surface formed by the drying process with the Yankee dryer is damaged, and the gloss is lowered. There is a problem.

In this way, single glossy kraft paper with excellent printability, high gloss, high gloss and high surface strength, and low cost without producing stains in the production facility. Therefore, development of a method that can be easily manufactured is awaited.
JP 2005-82906 A JP-A-5-339899

  The present invention has been made in view of the above-mentioned background art, is excellent in printability such as ink drying properties and bag-making suitability, does not cause yellowing, setback, bleeding, etc., and has high glossiness. The purpose is to provide a single glossy kraft paper suitable for offset printing, for example, at high speed and with high surface strength while having a gloss, and the single glossy kraft paper does not cause stains in manufacturing facilities. Another object of the present invention is to provide a method that can be easily manufactured at low cost.

That is, the present invention
Kraft paper according to JIS P 3401,
A coating layer is provided on one side of single glossy paper made mainly of kraft pulp,
The coating layer is formed by applying a coating liquid mainly composed of starch and an inorganic pigment in a solid content of ² to 7 g / m ² ,
The glossy surface provided with the coating layer has a paper surface pH of 6.0 to 9.0, and the non-glossy surface of the glossy surface is 4.3 to 5.9. , Related to single gloss kraft paper.

The present invention also provides
At least a wet paper forming process, a pressing process and a drying process with a Yankee dryer,
Between the wet paper forming process and the drying process, the coating liquid is 2 to 7 g / in solid content on one side of the glossy paper made from kraft pulp as the main raw material on the side contacting the Yankee dryer in the drying process. m ² coating to form a coating layer,
The coated layer is dried by bringing it into contact with a Yankee dryer.

  The single gloss kraft paper of the present invention is excellent in printability such as ink drying property and bag making suitability, and does not cause yellowing, settling, bleeding, etc. on the printed matter, and has a high glossiness and gloss. The strength is high, and it can be suitably used for high-speed, high-definition offset printing, for example. Further, according to the production method of the present invention, such excellent single-sided kraft paper can be easily produced at low cost without causing dirt in the production facility.

(Embodiment)
The single glossy kraft paper of the present invention is a standard kraft paper according to JIS P 3401 “kraft paper”, and a coating layer is provided on one side of a single glossy paper (wet paper) made mainly of kraft pulp. Is.

  First, the kraft pulp (hereinafter referred to as KP) used in the present invention will be described. KP has the advantage that, compared with mechanical pulp, the fiber length is usually long and high strength can be secured. There is no particular limitation on the type of KP. For example, unbleached softwood pulp (hereinafter referred to as NUKP), unbleached hardwood pulp (hereinafter referred to as LUKP), bleached softwood pulp (hereinafter referred to as NBKP), bleached hardwood pulp (hereinafter referred to as LBKP) and the like can be used, and one or more of these can be appropriately selected and used. Among these, NBKP and LBKP are preferable, and considering that the obtained glossy kraft paper is applied to a product that particularly requires strength, 50-80% by mass of NBKP and 20-50% by mass of LBKP Are preferably used in combination.

  In the present invention, pulp containing 50% by mass or more of KP as a main raw material is used. In addition to KP, for example, used newspaper, magazine used paper, cardboard used paper, office used paper, liquid container used paper, ticket used paper One or more kinds of waste paper pulp such as craft waste paper can be appropriately selected and used.

  In the present invention, the above-mentioned KP is used as a main raw material, and other pulps are mixed as necessary to prepare a papermaking raw material (paper slurry). Examples of the papermaking raw material include an internally added sizing agent, paper strength, and the like. Various additives such as an enhancer and a yield improver that are usually blended in paper can be used by appropriately adjusting the type and blending amount.

  Papermaking raw materials such as those described above can be made with an ordinary wet papermaking machine equipped with, for example, a wire part, a press part, a coating facility, a Yankee dryer, and the like to obtain single glossy paper (wet paper).

The basis weight of single glossy paper is not particularly limited. However, if it is too small, the coating liquid described later may be excessively impregnated in the paper, and the manufacturing equipment may be easily contaminated. Therefore, JIS P 8124 It is preferably 30 g / m ² or more, more preferably 40 g / m ² or more as measured according to the method described in “Paper and paperboard—basis weight measurement method”. The drying capability of the Yankee dryer is lost, and the drying capability after applying the coating liquid to single glossy paper is reduced, which may cause a decrease in gloss (gloss) and uneven surface strength. ² or less, and further preferably not 180 g / m ² or less.

  Next, a coating layer is formed on one side of such single glossy paper. The production method of the present invention includes at least a wet paper web forming step, a pressing step, and a drying step using a Yankee dryer, and the side that contacts the Yankee dryer in the drying step between the wet paper web forming step and the drying step. Apply the coating solution to one side of the glossy paper.

  The coating solution used in the present invention is mainly composed of starch and an inorganic pigment. Thus, by using the coating liquid which has starch and an inorganic pigment as a main component, the influence on the white water in a papermaking system can be eliminated.

  Examples of starch include conventionally used modified starch such as etherified starch and esterified starch, oxidized starch, positive starch, etc., but has high film-forming ability (coverability) and elution rate into water. Is preferably used. Furthermore, thixotropic starch, for example, exhibits high fluidity during application of a coating liquid by spray coating, but the fluidity is suppressed after coating, and the coating liquid into single glossy paper is suppressed. This is preferable in that permeation is suppressed.

  As a suitable starch as described above, for example, when applying the coating liquid by spray coating, in order to make the particle size of the spray particles a desired small size, it is easy to adjust to a relatively low viscosity, for example, Examples include modified starches such as etherified starches such as hydroxyethylated starches and modified esterified starches such as carboxylic acid esterified starches and phosphate esterified starches, which are modified tapioca starches. These etherified starch and esterified starch have high coating properties and also exhibit the effect of improving the bag-making suitability when making single-glazed kraft paper.

  Etherified starch has an effect of improving surface strength, and is suitable for the production of single-glazed kraft paper that tends to have a relatively low surface strength. The etherified starch is also effective in releasability from a Yankee dryer and securing a glossy surface.

  Among the etherified starches, hydroxyethylated starch is particularly preferable. Hydroxyethylated starch is firmly fixed on the fiber by the interaction of hydrogen bonds of hydroxyethyl groups even when the paper surface is dampened with fountain solution during offset printing. It is thought that the adhesiveness can be lowered. In particular, the hydroxyethylated starch (wet) treated in a slurry (wet) state has a high affinity with the inorganic pigment simultaneously contained in the coating liquid, significantly improves the surface strength, and improves the surface strength. Both covering effects are considered to be high.

  In particular, in the production method of the present invention, since the coating liquid is applied at the wet paper stage, the covering property on the glossy paper is high, and the surface strength is easy to improve in the first place. Therefore, the coating liquid containing starch having a high film-forming ability is more markedly spread in the MD direction and CD direction than the penetration of the paper in the Z direction. It is considered that the fine fibers existing on the paper surface and the inorganic pigment in the coating liquid can be prevented from coming into direct contact with the Yankee dryer. On the other hand, the coating liquid containing starch with low film-forming ability is difficult to form a coating (coating layer) of the coating liquid on the wet paper surface. For example, dampening water added to the paper surface during offset printing is easily There is a risk that the ink penetrates into the paper layer, causing bleeding of offset ink, loss of halftone dots, and damage of the coating layer.

  As the esterified starch used in the present invention, carboxylic acid esterified starch is suitable. Particularly preferred as carboxylic acid esterified starch is 1-octenyl succinate esterified starch. When such a specific carboxylated esterified starch is used, it is particularly effective for improving the surface strength and improving the peelability from the Yankee dryer. Esterified starch has high film-forming ability like the above-mentioned etherified starch, and carboxylic esterified starch has high hydrophobicity and lowers the paper surface free energy. As a result, for example, the penetration of the dye (pigment) component in the offset ink into the coating layer is suppressed, the printing density is improved, and a fine printed surface can be obtained. Among these, esterified starch derived from tapioca starch is particularly preferable from the viewpoint of excellent viscosity and film forming property.

  Examples of the inorganic pigment contained in the coating liquid include calcium carbonate, kaolin, clay, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate, colloidal silica, and satin white. One or more of them can be appropriately selected and used, and among these, calcium carbonate is preferable from the viewpoint of excellent print quality such as glossy surface (print glossiness) and ink setting properties.

  The calcium carbonate is preferably used because it is low in price and high in whiteness compared to other inorganic pigments, and both the particle shape and particle diameter can be arbitrarily changed. Particularly, in the present invention, for example, light calcium carbonate having a cumulative deposition rate of 70% or more is preferable.

  Light calcium carbonate is a carbon dioxide compound method in which quick lime and carbon dioxide obtained by baking limestone are purified, and quick lime is dissolved in water to form lime milk, and carbon dioxide is blown into the carbon dioxide compound, or Precipitated raw calcium carbonate synthesized by a carbonate solution produced by reacting lime milk or calcium chloride solution with sodium carbonate is shown. The light calcium carbonate can adjust the crystal shape, size, shape, etc. of calcite-type, argonite-type, etc., depending on conditions such as the synthesis reaction, etc. In this case, it is preferably used because an optimum shape and particle system can be arbitrarily selected.

  In the case of the calcite-based light calcium carbonate, there are usually a spindle shape and a squid shape in which they are aggregated and a cubic shape (cubic shape and dumpling shape). In the case of aragonite-based light calcium carbonate, it usually has a shape called a rod shape or a needle shape.

  In the present invention, calcite-type light calcium carbonate having an aspect ratio of 3 or more, further 4 or more, and 5 or less can be preferably used. Among them, a shape having relatively rounded corners is preferable. Such calcite-based light calcium carbonate, for example, compared with aragonite-based light calcium carbonate, particularly when a coating layer is provided, has a high affinity with pulp fibers constituting the glossy paper surface, Therefore, the strength reduction of the coating layer is less. In addition, calcite-based light calcium carbonate has a slightly lower surface coverage due to less strength reduction.For example, by combining it with esterified starch or etherified starch with high coating properties, the coating liquid can be applied to glossy paper. Glossy surface and surface strength can be sufficiently secured by drying with a Yankee dryer after coating.

  If the aspect ratio of the calcite light calcium carbonate is too small, inorganic particles may enter between the pulp fibers on the surface of the glossy paper, and the flatness of the surface of the glossy paper may be deteriorated. On the other hand, if the aspect ratio is too large, for example, when the coating liquid is applied by spray coating, nozzle clogging or dripping tends to occur, and the surface strength of the coating layer may be reduced.

  The light calcium carbonate most suitable for the present invention is calcite-type spindle-shaped light calcium carbonate, and the drying with a Yankee dryer and the copy of the Yankee dryer mirror surface are higher than when using other forms of light calcium carbonate. The glossy surface, surface strength, and printability of the desired glossy kraft paper become extremely high. The reason is not clear, but it is considered that, for example, spindle-shaped light calcium carbonate forms a coating layer without particular directionality, so that the coating layer is dried at a low density. .

  In the present specification, the aspect ratio refers to the ratio of the major axis to the minor axis of the pigment.

  Moreover, when using a light calcium carbonate, the compounding quantity does not have limitation in particular, A light calcium carbonate may be sufficient as the total amount of inorganic pigments, for example, about 30-90 mass% of the total amount may be sufficient.

  In the present invention, it is possible to use a combination of hydroxyethylated starch or carboxylic acid esterified starch as the starch and light calcium carbonate as the inorganic pigment, the surface strength of the glossy kraft paper, the drying speed of the coating layer, and color printing. It is preferable from the viewpoint that the effect of improving the sensitivity is particularly large.

  The ratio of the starch and the inorganic pigment in the coating liquid is not particularly limited, and for example, it is preferable to adjust the starch to be about 6 parts by mass or more with respect to 100 parts by mass of the inorganic pigment.

  In the present invention, as described later, it is preferable to spray the coating liquid, but it is desirable to reduce the particle size of the spray particles during the spray coating. In order to reduce the particle size of the spray particles in this manner, for example, the modified starch that is easily adjusted to a relatively low viscosity may be used, or the solid content concentration of starch in the coating solution may be adjusted.

  When the solid content concentration of the starch is too low, the coating amount of the coating liquid increases, and the drying load in the Yankee dryer may increase. Therefore, it is 3% or more, and further 4% or more. On the other hand, if it is too high, dripping, fouling, and tool fouling are likely to occur at or near the spray coating equipment, so it is preferably 10% or less, more preferably 9% or less.

  The coating solution used in the present invention contains 50% by mass or more of the starch and the inorganic pigment as the main components. Examples of the coating solution include styrene-butadiene copolymer, styrene- Acrylic copolymer, ethylene-vinyl acetate copolymer, butadiene-methyl methacrylate copolymer, vinyl acetate-butyl acrylate copolymer, polyvinyl alcohol, maleic anhydride copolymer, acrylic acid-methyl methacrylate system Synthetic adhesives such as copolymers: Proteins such as casein, soy protein, synthetic proteins: ordinary adhesives for coated paper such as cellulose derivatives such as carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, etc. Can be appropriately blended within a range that does not inhibit the above.

  Furthermore, for example, various commonly used auxiliaries such as a dispersant, a thickener, a water retention agent, an antifoaming agent, and a water resistance-imparting agent can be appropriately blended in the coating liquid.

  In the method for producing single glossy kraft paper of the present invention, the coating liquid is applied to one side of single glossy paper between a wet paper forming step and a drying step with a Yankee dryer.

  In general, coated paper coated with a composition composed mainly of a white pigment such as kaolin and calcium carbonate and an aqueous binder is mainly a coater such as a blade coater, a gate roll coater, and a metering size press. It is manufactured by applying the composition. When manufacturing coated paper, the major issue is how to coat the base paper satisfactorily with a small amount of coating, particularly in terms of cost. In order to obtain good covering properties, it is important to make the coating layer bulky with little pushing into the base paper. However, when these coaters are used, due to the mechanism, the coating solution is pushed into the base paper in a considerable amount, and the coating layer is unlikely to be bulky.

  On the other hand, in the case of a so-called non-contact type coating method such as curtain coating with a curtain coater or spray coating with a spray coater, the coating liquid is not pushed into the base paper, and the coating layer Is known to be bulky. However, curtain coating is a method in which a free-falling coating liquid film is provided on the base paper, so that on one side of the glossy paper on the side in contact with the Yankee dryer (the surface corresponding to the glossy surface) as in the present invention. In addition, it is difficult to perform curtain coating between the wet paper web forming process and the drying process with a Yankee dryer, and it involves major modifications of the equipment. Furthermore, in the case of curtain coating, it is necessary to make fine adjustments to the coating liquid such as viscosity and surface tension, and it is not easy to perform such curtain coating. From the above points, in the present invention, spray coating is exemplified as an optimum coating method.

  There is no limitation in particular in the spray apparatus at the time of spray coating, The well-known spray apparatus used for general coating etc. can be used. As the spray device, for example, a device including a coating liquid storage unit, a gas supply unit such as an air compressor or a gas cylinder, and an injection nozzle that mixes and sprays these coating liquid and gas is used. it can. Moreover, the spray apparatus which sprays only a coating liquid only with a hydraulic pressure without mixing gas may be sufficient. The arrangement and the number of spray nozzles are appropriately adjusted so that spray coating is performed as uniformly as possible on the surface corresponding to the glossy surface of the single glossy paper. For example, it is possible to adjust the distance from the paper surface to the ejection nozzle, or employ a means for arranging a plurality of ejection nozzles side by side in the paper width direction or the paper longitudinal direction.

  The particle size of the coating liquid spray particles sprayed from the spray device is preferably 150 μm or less, more preferably 30 to 100 μm. Thus, in order to set the particle size of the spray particles to, for example, 150 μm or less, an appropriate injection nozzle is selected, the viscosity of the coating liquid mainly composed of starch and inorganic pigment, the pressure of the spray, What is necessary is just to adjust flow volume etc. appropriately. For example, when the spray pressure is increased or the viscosity of the coating liquid is decreased, the particle size can be decreased. Further, in order to reduce the particle size of the coating liquid spray particles as described above, it is desirable to relatively reduce the viscosity of the starch slurry as described above. For example, modified starch is used as the starch, or the starch is heated. It is preferable to dissolve with water and adjust the solid content concentration to 3 to 10%.

  The particle size of the coating liquid spray particles can be measured by a measuring device using a laser diffraction principle. In addition, the particle size of the spray particles of the coating liquid varies within a predetermined range. Here, the particle size is the average value of the Sauta ("surface area to volume ratio", which is the same as the total volume of all particles relative to the total surface area of all particles). Particle size).

  For example, rotor dampening (trade name, manufactured by Nikka Co., Ltd.) is suitable as a liquid application device for spray coating a coating liquid having a spray particle size of about 30 to 100 μm. The liquid applicator includes a plurality of rotatable hollow disk-shaped rotors arranged in a line at predetermined intervals, and a pulley connected to and fixed to each rotor in a concentric manner and driven to rotate by a drive motor. Thus, each pulley is driven to rotate at high speed via a belt and a coating liquid is supplied into each rotor. As a result, a liquid in the rotor rotating at a high speed of about 5000 rpm is ejected from the outer periphery of the rotor by centrifugal force to form a thin film-like spray flow composed of fine mist, and the width of the spray flow from each rotor is reduced to the shutter. By controlling in step S1, a continuous spray coating flow is formed in which spray coating is uniformly performed with a predetermined spray coating width. In such a high-speed rotating rotor, the spray particles can be spray-coated with a spray droplet having a spray particle size of about 30 to 100 μm, for example, about 75 μm by centrifugal force, and the coating amount can be accurately set. It can also be controlled. The particle size of the spray particles is 30 μm or more in order to eliminate the possibility that the spray particle scattering area becomes wide and the equipment in the vicinity of the coating equipment is soiled and the formation of the coating layer is insufficient. It is more preferable that the thickness is 100 μm or less in order to eliminate the possibility of liquid dripping in the coating equipment and the difficulty in adjusting the coating amount.

  In the production method of the present invention, in addition to the spray coating, for example, a roll transfer coating using a roll coater can be used in combination as a method of coating the coating liquid on one side of the glossy paper. is there. The roll transfer coating is excellent in that it can be applied to a small amount of coating liquid, can be applied to the surface of the paper, and can improve flatness, similar to spray coating. ing. When roll transfer coating is used in combination, it is preferable to perform roll transfer coating in advance before spray coating. As the roll coater, for example, a Massey coater, a KCM coater, a gate roll coater, or the like can be used.

  The process for producing glossy kraft paper consists of at least a wet paper forming process, a pressing process, and a drying process using a Yankee dryer. The coating solution is applied to one side of the glossy paper that contacts the Yankee dryer. The working layer may be formed between the wet paper forming process and the drying process, or between the wet paper forming process and the pressing process, or between the pressing process and the drying process. .

  When applying the coating liquid between the wet paper forming process and the pressing process, since the glossy paper after the wet paper forming process is in a wet state, the coating liquid is difficult to penetrate into the paper layer, Sinking of the coating liquid into the paper layer can be prevented, and there is an advantage that an excellent coating layer is easily formed due to the covering property.

  On the other hand, when applying the coating liquid between the press process and the drying process, it is used for drying with a Yankee dryer immediately after applying the coating liquid to single glossy paper. The coating layer is formed before the liquid penetrates, and there is an advantage that no contamination occurs in tools and equipment such as a blanket.

The coating amount of the coating liquid is determined so that the Yankee dryer is essentially low in drying capacity so that the desired single glossy kraft paper can be manufactured without sacrificing its production capacity. In order to ensure sufficient coverage of the glossy paper, the solid content is 2 g / m ² or more, preferably 3 g / m ² or more, so as not to cause poor drying with a Yankee dryer. The solid content is 7 g / m ² or less, preferably 6.5 g / m ² or less.

  The moisture content of the glossy paper coated with the coating liquid (moisture content at the entrance of the Yankee dryer) is 20 in consideration of sufficient drying with the Yankee dryer and the surface strength of the target glossy kraft paper. It is preferable to adjust to -50 mass%.

  One side of the glossy paper coated with the coating liquid in this way and formed with a coating layer is strongly pressed against the surface of the Yankee dryer heated by the touch roll, and the coating layer is heated. After drying, the smoothness of the surface of the Yankee dryer is transferred as it is to the coating layer. As a result, single gloss kraft paper having gloss characteristics can be obtained.

  The glossy kraft paper of the present invention thus obtained has a glossy surface provided with a coating layer having a surface pH of 6.0 or more, preferably 6.5 or more, and 9.0 or less, preferably 8.5. It is as follows. By maintaining the pH of the glossy surface to be printed in the neutral region in this way, an inexpensive sizing agent for the acidic region is used, and the pH of the single glossy paper is 4.3 to 5.5. Even when papermaking is performed, for example, in offset printing, it is possible to improve the printability such as ink drying property of the glossy surface itself.

  When the paper surface pH of the glossy surface is less than 6.0, for example, the drying property of the offset ink is deteriorated, and during high-speed offset printing, the print is offset and the inorganic pigment such as light calcium carbonate is oxidized. Conversely, if the glossy paper surface pH exceeds 9.0, yellowing of the glossy kraft paper due to alkali burning occurs, starch deterioration occurs, and the coating layer strength decreases.

  The glossy kraft paper of the present invention has a non-glossy paper surface pH of 4.3 or more, preferably 4.4 or more, and 5.9 or less, preferably 5.5 or less. is there. By keeping the non-glossy paper surface pH in the acidic to neutral region in this way, an inexpensive acidic sizing agent can be used without using an expensive neutral size, and a size effect can be easily obtained. It can be made on the extension line of the acidic papermaking technology.

  If the paper surface pH of the non-glossy surface is less than 4.3, the paper is rapidly deteriorated and the paper quality is lowered. Moreover, the effect of a chemical | medical agent falls and cost effectiveness worsens. In addition, there is a risk that the frequency of repairs of equipment will increase. On the other hand, if the paper surface of the non-glossy surface exceeds 5.9, an expensive neutral sizing agent must be used, and the production cost increases, and depending on the type of papermaking, the balance in the papermaking machine system is lost. , Equipment troubles such as pitch troubles and flocks occur.

  The glossy and non-glossy paper surface pH is determined by the JAPAN TAPPI Paper Pulp Test Method No. 49-2: 2000 “Paper and paperboard—Surface pH test method—Part 2: Indicator method”.

  Thus, the single gloss kraft paper of the present invention has a coating layer formed on one side of a single gloss paper made of kraft pulp by a specific coating amount of coating liquid containing starch and an inorganic pigment. Since the paper surface pH of the surface is maintained in the neutral region and the paper surface pH of the non-glossy surface is maintained in the acidic to neutral region, it is excellent in printability such as ink drying property and bag-making property, and the printed matter is yellowed and offset. In addition, it does not cause bleeding, and has high glossiness, high gloss and high surface strength. For example, it can be suitably used for high-speed, high-definition offset printing. Further, in the production method of the present invention, the coating liquid is applied between the wet paper forming step and the drying step with a Yankee dryer, and thus such excellent single-sided kraft paper is caused to generate stains in the production facility. And can be easily manufactured at low cost.

  Next, the glossy kraft paper of the present invention and the method for producing the same will be described in more detail based on examples, but the present invention is not limited only to these examples.

Examples 1-10 and Comparative Examples 1-7 (Manufacture of single gloss kraft paper)
First, kraft cooking is performed using softwood chips or hardwood chips as raw materials, N-material KP or L-material KP is produced, and conforms to the method described in JIS P 8123 “Testing Method for Hunter Whiteness of Paper and Pulp” after raw material adjustment A bleached pulp having a Hunter whiteness of 85% was produced.

  Next, NBKP freeness (Canadian Standard Freeness (C.S.F.)) 580 mL and LBKP freeness (C.S.F.) 530 mL were beaten with a double risk refiner and blended in the proportions shown in Table 1. With respect to 100 parts by mass of this pulp (absolutely dry pulp mass), 1.8 parts by mass of a sulfuric acid band, 0.2 parts by mass of an internal sizing agent (trade name: Hersize, manufactured by Harima Chemical Co., Ltd.) and paper strength enhancement 0.2 parts by mass of an agent (product surface: Hermide, manufactured by Harima Chemicals Co., Ltd.) was added to obtain a pulp slurry.

The obtained pulp slurry was subjected to a Yankee dryer paper machine (design speed: 280 m / min, basis weight: 70 g / m ² , moisture: 5.5) consisting of a wire part process, a press part process, a coating facility, and a Yankee dryer process. 5% during manufacture) and made a glossy paper (wet paper) of basis weight shown in Table 1 (measured in accordance with the method described in JIS P 8124 “Paper and paperboard—basis weight measurement method”). .

  Next, the coating liquid having the composition shown in Table 2 supplied to the coating equipment (two-fluid spray provided at equal intervals in the paper machine width direction) is applied to Table 2 on one side of the glossy paper. Coating was carried out with the coating amount shown to form a coating layer having a thickness of about 2 to 5 μm. In addition, the particle size of the coating liquid spray particle | grains at this time was about 40-100 micrometers.

  Next, the surface on which the coating layer was formed was brought into contact with a Yankee dryer, the coating layer was dried, and wound with a reel to obtain single gloss craft paper. The water content of the glossy paper after application of the coating liquid (water content at the entrance of the Yankee dryer) was adjusted to the values shown in Table 2.

  In Comparative Examples 2 and 5, the coating liquid was not applied. Therefore, one surface was brought into contact with the Yankee dryer, and the contacted surface was treated as a glossy surface. Furthermore, in Examples 1-10, generation | occurrence | production of the stain | pollution | contamination in a manufacturing facility was not recognized in the manufacture process of single gloss kraft paper.

  The obtained glossy kraft paper was examined for physical properties and characteristics by the following methods. The results are shown in Table 3.

(A) Paper surface pH
For the glossy surface and the non-glossy surface, which is the back side of the glossy surface, the JAPAN TAPPI paper pulp test method no. 49-2: 2000 “Paper and paperboard—Surface pH test method—Part 2: Indicator method”.

(B) White paper glossiness It was measured according to the method described in JIS P 8142 “Testing method for 75 ° specular glossiness of paper and paperboard”.

(C) Whiteness The whiteness was measured according to the method described in JIS P 8123 “Testing Method for Hunter Whiteness of Paper and Pulp”.

(D) Yellowing The glossy surface of a single glossy kraft paper sample in accordance with the method described in JIS Z 8729 “Color Display Method-L * a * b * Color System and L * u * v * Color System” The b value was measured with a color analyzer (spectrophotometer, manufactured by Gretag Macbeth). This sample was heat-treated in an oven heated to 110 ° C. for 48 hours, and the b value was measured in the same manner. From these values, the color difference (ΔE) before and after the heat treatment was determined and evaluated based on the following evaluation criteria. In addition, it shows that there are few yellowing and it is excellent, so that a color difference is small.
(Evaluation criteria)
A: Color difference is less than 5.
○: Color difference is 5 or more and less than 7.
Δ: Color difference is 7 or more and less than 10.
X: The color difference is 10 or more.

(E) Surface strength Single glossy kraft paper using 0.4 mL of special ink (SMX Tack Grade 15, Toyo Ink Manufacturing Co., Ltd.) and RI type printing tester (Ishikawajima Industrial Machinery Co., Ltd., RII type) The glossy surface was printed and backed. The glossy surface was peeled off visually and evaluated based on the following evaluation criteria.
(Evaluation criteria)
(Double-circle): The fiber of glossy surface is not taken out at all, and favorable printability is shown.
○: Slightly recognized glossy fibers are observed, but there is no practical problem.
(Triangle | delta): The fiber taken out of a glossy surface is scattered and has a problem practically.
X: The coating layer is peeled off and cannot be used.

(F) Set-off Using a two-color ink of red and indigo (Tack No. 9, manufactured by Dainippon Ink & Chemicals, Inc.) on a Roland Fabrit RZF01 type printer (Deckman Roland Co., Ltd.) 5000 offset printing was performed on the glossy surface of single glossy kraft paper. Powder for preventing set-off (NIKKA-OXY POWDER No. 3500, manufactured by Nikka Co., Ltd.) was used in an amount of 0.01 g / m ² , and the ink was red, indigo, red 3 g / m ² , indigo 2.1 g / m. Printed ² overlaid. After standing for 24 hours with the printed materials superposed, the state of the set-off was visually observed, the number of the set-up printed items was examined, and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: The setback is less than 5 sheets.
○: The setback is 5 or more and less than 8.
Δ: The setback is 8 or more and less than 15.
X: Set-off is 15 or more.

(G) Ink drying property Using an RI printing machine (Ishikawajima Industrial Machinery Co., Ltd.), print on the glossy surface of glazed kraft paper, and after 2 hours, apply cast paper to the printed surface. Air pressure was crimped without kneading. After crimping, the ink set-off state on the cast paper was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
(Double-circle): There is no back-off of an ink and dryness is especially excellent.
○: There is almost no ink set-off, and the drying property is excellent.
Δ: Some ink set-off was observed, and the drying property was slightly inferior.
X: Ink set-up is remarkable and the drying property is inferior.

(H) Halftone dot reproducibility Using an offset color printing machine (model number: LITHRONE44, manufactured by Komori Corporation), a test pattern document was printed on the glossy surface of single glossy kraft paper at a printing speed of 800 rpm. About the halftone dot printed part of the obtained test pattern, the size, shape and double state of the halftone dot were observed using an enlargement magnifier of about 200 times, and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: The size and shape of the halftone dots are the same as the original, and no double is recognized.
○: The size and shape of the halftone dots are almost the same as the original, and almost no double is observed.
(Triangle | delta): A halftone dot is partly generated and a double is recognized.
X: Notch and halftone dot are remarkable.

(I) Bag-making suitability Using an automatic bag-making machine (model number: 185T, manufactured by Neurong Co., Ltd.), investigation of processing workability (presence of conveyance failure and folding failure) when processing 500 handbags from single glossy kraft paper. And evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: Neither conveyance failure nor folding failure occurred even once.
○: A conveyance failure or a folding failure occurred only once.
Δ: Conveyance failure or folding failure occurred twice or more and less than 10 times.
X: Conveyance failure or folding failure occurred 10 times or more.

(J) Coating layer cracking About the handbag obtained in the bag-making aptitude test, the folded surface was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
(Double-circle): A coating layer crack is not recognized at all.
○: Slight cracking of coating layer is observed, but there is no practical problem.
(Triangle | delta): The coating layer crack is recognized and there exists a problem practically.
X: Coating layer cracking is remarkable and impractical.

  As shown in Table 3, the glossy kraft papers of Examples 1 to 10 were coated with a specific amount of a coating liquid containing starch and an inorganic pigment on one side of the glossy paper to form a coating layer. The glossy paper surface pH is maintained in a neutral range of a specific range, while the non-glossy paper surface pH is maintained in a specific range of acidic to neutral region. Therefore, the glossy kraft papers of Examples 1 to 10 are excellent in printability such as ink drying property and bag making suitability, yellowing and set-off hardly occur in the printed matter, and there is no blur and halftone dot reproducibility. It is excellent and has high gloss and high surface strength while having gloss.

  On the other hand, the glossy kraft papers of Comparative Examples 1 to 7 are not provided with a coating layer (Comparative Examples 2 and 5), or are provided with a coating layer. Is too much or too little (Comparative Examples 6 and 7), and the paper surface of glossy and non-glossy surfaces is inappropriate (Comparative Examples 1, 3, 4, and 5). Contrary to the glossy kraft paper of Examples 1 to 10, it is inferior to most of the properties in terms of suitability, yellowing of printed matter, transfer and bleeding, glossiness, surface strength and the like.

  By the production method of the present invention, for example, glossy kraft paper suitable for high-speed, high-definition offset printing can be easily produced at low cost without causing stains in production equipment.

Claims (8)

Kraft paper according to JIS P 3401,
A coating layer is provided on one side of single glossy paper made mainly of kraft pulp,
The coating layer is formed by applying a coating liquid mainly composed of starch and an inorganic pigment in a solid content of ² to 7 g / m ² ,
The glossy surface provided with the coating layer has a paper surface pH of 6.0 to 9.0, and the non-glossy surface of the glossy surface is 4.3 to 5.9. , Single gloss craft paper.   The glossy kraft paper according to claim 1, wherein the inorganic pigment is light calcium carbonate.   The glossy kraft paper according to claim 2, wherein the light calcium carbonate is a calcite spindle-shaped light calcium carbonate.   The glossy kraft paper according to claim 1 or 2, wherein the starch is hydroxyethylated starch or carboxylic acid esterified starch. At least a wet paper forming process, a pressing process and a drying process with a Yankee dryer,
Between the wet paper forming process and the drying process, the coating liquid is 2 to 7 g / in solid content on one side of the glossy paper made from kraft pulp as the main raw material on the side contacting the Yankee dryer in the drying process. m ² coating to form a coating layer,
The method for producing single gloss kraft paper according to claim 1, wherein the coating layer is dried by contacting with a Yankee dryer.   The manufacturing method according to claim 5, wherein the coating liquid is applied to one side of the glossy paper between the wet paper forming step and the pressing step.   The manufacturing method of Claim 5 which coats a coating liquid on the single side | surface of a glossy paper between a press process and a drying process.   The manufacturing method of Claim 5 which coats a coating liquid on the single side | surface of glossy paper by spray coating.