TWI782042B - Coated paper for printing and envelope paper - Google Patents

Abstract

The present invention relates to a coated paper for printing, which is provided with a pigment coating layer on at least one side of a base paper, and the pigment coating layer contains calcium carbonate with an average particle diameter (D50) of 0.80 μm or less. In 100 parts by weight of the pigment in the pigment coating layer, it is preferable to contain 40 parts by weight or more of the calcium carbonate. This coated printing paper has excellent peel resistance and ink drying properties.

Description

Coated paper for printing and envelope paper

The invention relates to a coated printing paper and envelope paper.

In recent years, in the field of printing, there is an increasing trend towards small batches and short delivery times, and ink dryness has become an important indicator. If the drying property of the ink is not good, it is easy to cause the problem of "offset" where the ink is transferred to other places when stacking the printed matter. Therefore, in order to prevent the printed matter from sticking to the paper, measures such as using powder such as starch or placing the printed matter at rest so that friction does not occur after stacking are taken. Especially in the case of double-sided printing, if the above-mentioned "smudge" occurs, the printed image will be stained and the value of the printed matter will be significantly damaged. Therefore, it is necessary to lengthen the standing time after single-sided printing. Allow ink to dry until no "smearing" occurs. If the drying property of the ink is not good, the standing time will be longer, so the work efficiency will be lowered. Furthermore, when printing is applied to the opposite side in double-sided printing, since the printed image on the printed side is rubbed by a roller, etc., if the drying property of the ink is not good, the printed image may be stained risk. This tendency is more conspicuous in matte-tone coated paper with lower gloss. Compared with glossy coated paper, matte-like coated paper has larger unevenness on the surface, so in order to make the ink adhering to the paper surface easy to penetrate and increase the printing density, it needs to transfer a large amount of ink, so the dryness is reduced. Accordingly, in order to cope with an increase in printing speed or double-sided printing, the performance of ink drying quickly is required. In order to meet this demand, a technique of providing a pigment coating layer containing flat pigments such as kaolin is proposed (Patent Document 1).

However, one of the uses of printing paper is envelopes. The envelope is cut in the processing step, pasted with an adhesive, and then shaped into an envelope. Since envelopes are often used for sending documents that do not want to be seen by others or documents that want to prevent forgery, high confidentiality preservation (secrecy) performance is required for envelopes. As the confidentiality maintaining performance of the envelope, the content cannot be seen through, and it is not easy to open the seal from the adhesive part. Hitherto, for envelope paper that has opacity such that the contents cannot be seen through, it is known to use a pigment with high light-scattering properties such as titanium oxide in the base paper, and to further improve the opacity by coloring the surface of the paper. technology (Patent Document 2), or a technology in which it is difficult to distinguish the characters of the contents by printing on the inner surface of the envelope. However, a detailed study on the opening properties of the joints of the envelopes has hardly been carried out. Generally speaking, peeling in the adhesive layer where peeling traces are difficult to remain, or peeling between the paper surface and the adhesive, is considered unfavorable because there is a risk that the envelope will be opened and the document in it may be forged; The peeling in the base paper layer accompanied by the peeling between the paper layers is considered to be better. The above-mentioned coated printing paper with excellent ink drying properties exhibits excellent absorbency even for adhesives. As a result, the amount of adhesive held on the surface of the paper is reduced, and sufficient adhesive strength cannot be obtained. Peeling in the adhesive layer occurred. Therefore, it is considered difficult to achieve both ink drying properties and envelope peelability. [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 2017-48493 [Patent Document 2] Japanese Patent Laid-Open No. 2009-114573 [Patent Document 3] Japanese Patent Laid-Open No. 2013-256730

[Non-Patent Document] [Non-Patent Document 1] Journal of the Association of Pulp Technology (Japan TAPPI journal), Vol.62(2008) No.6, p.694-699

[Problem to be Solved by the Invention]

When the present inventors applied the coated printing paper with excellent ink drying properties described in Patent Document 1 to envelopes and studied the detachability of the pasted parts, they found that the detachment was not between the paper layers or within the adhesive layer, but Debonding occurs within the coating. Peeling inside the coating layer is not preferable from the viewpoint of counterfeiting prevention. Flat pigments such as kaolin have an acidic main surface and an alkaline side surface (Non-Patent Document 1), and general adhesives for envelopes usually contain acidic groups. Therefore, the peeling system inside the coating layer can be attributed to the fact that the main surface of the flat pigment has a low affinity with the adhesive, and although the side surface of the flat pigment is alkaline and has a high affinity with the adhesive, The area is small and a sufficient bonding area cannot be achieved. Accordingly, an object of the present invention is to provide a coated printing paper having excellent envelope peelability and ink quick-drying properties. [Means to solve the problem]

The inventors of the present invention have found that coated printing paper provided with a pigment coating layer containing specific calcium carbonate particles can solve the above-mentioned problems. That is, the aforementioned problems can be solved by the following present invention. (1). A coated paper for printing, which is equipped with a pigment coating layer on at least one side of the base paper, and the pigment coating layer contains calcium carbonate having an average particle diameter (D50) of 0.80 μm or less. (2). The coated printing paper according to (1), wherein 40 parts by weight or more of the calcium carbonate is contained in 100 parts by weight of the pigment in the pigment coating layer. (3). The coated paper for printing as described in (1) or (2), wherein the average particle diameter (D50) of the aforementioned calcium carbonate is 0.50 to 0.75 μm. (4). The coated printing paper according to any one of (1) to (3), wherein 90 parts by weight or more of chemical pulp is contained in 100 parts by weight of the pulp of the aforementioned base paper. (5). The coated paper for printing according to any one of (1) to (4), wherein the whiteness measured under the condition not including ultraviolet rays is 85% or more. (6). The coated printing paper described in any one of (1) to (5), wherein the glossiness of the white paper is 40% or less. (7). An envelope paper using the coated printing paper described in (1) to (6) above. (8). An envelope made of the envelope paper described in (7) above. [Effect of the invention]

According to the present invention, it is possible to provide a coated printing paper having excellent envelope peelability and ink quick-drying properties.

[Best Mode for Carrying Out the Invention]

Hereinafter, the present invention will be described in detail. "~" in the present invention includes its endpoints. That is, "X~Y" includes the values of X and Y. Also, "X or Y" means any one of X and Y, or both. 1. Coated printing paper The so-called coated printing paper refers to printing paper with a pigment coating layer provided on the base paper. The so-called pigment-coated layer refers to a layer containing white pigment as a main component. In the coated printing paper of the present invention, the pigment coating layer contains calcium carbonate having an average particle diameter (D50) of 0.80 μm or less. The coated printing paper of the present invention can be used for commercial printing such as offset printing, gravure printing, and on-demand printing (laser method, inkjet method, electrophotographic method) on the surface of the paper. , can include envelopes, books, magazines, posters, calendars, etc., but envelopes are preferred.

(1) Pigment coating layer 1) Pigment The pigment coating layer contains calcium carbonate (hereinafter also referred to as "first calcium carbonate") having an average particle diameter (D50) of 0.80 μm or less. D50 is the average particle size of 50% of the volume. The particle size distribution and D50 of the pigment by the sedimentation method can be measured with MASTERSIZER 3000 manufactured by Malvern Co., Ltd. or the like. In the present invention, by using such superfine calcium carbonate, it can have both excellent envelope peelability and ink quick-drying performance. From this point of view, the upper limit of D50 of the first calcium carbonate is preferably 0.75 μm or less, more preferably 0.70 μm or less, and the lower limit is preferably 0.50 μm or more, and more preferably 0.55 μm or more .

If the pigment coating layer exists on both sides of the base paper, although it is only necessary to include the first calcium carbonate on one side of the pigment coating layer, it is better to include the first calcium carbonate on both sides of the pigment coating layer. . Also, although the pigment coating layer may exist in multiple layers on one surface, in this case, it is preferable that at least the outermost pigment coating layer contains the first calcium carbonate.

In the case of having one pigment coating layer, the lower limit of the blending amount of the first calcium carbonate is preferably 40 parts by weight or more and 45 parts by weight in 100 parts by weight of the pigment in the pigment coating layer. More than one serving is better. Also, the upper limit of the blending amount of the first calcium carbonate is preferably not more than 70 parts by weight, more preferably not more than 60 parts by weight, and not more than 55 parts by weight in 100 parts by weight of the pigment in the pigment coating layer. for better. If there are two or more pigment coating layers on one side, it is preferable to include the first calcium carbonate in the aforementioned amount in at least one pigment coating layer, and to include the aforementioned amount in the outermost pigment coating layer. The first amount of calcium carbonate is also preferred. The first calcium carbonate is preferably heavy calcium carbonate or light calcium carbonate produced in the causticizing step of the pulp manufacturing step (causticizing light calcium carbonate, refer to Japanese Patent No. 5274077).

As white pigments other than the first calcium carbonate in the pigment coating layer, pigments generally used in this field can be used. Examples thereof include kaolin, clay, engineered kaolin, layered clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicon Inorganic pigments such as acid salt, colloidal silica, satin white, etc., and organic pigments such as dense type, hollow type, or core-shell type. These pigments can be used in combination of multiple types.

As white pigments other than the first calcium carbonate, it is preferable to use heavy calcium carbonate or light calcium carbonate (hereinafter also referred to as "second calcium carbonate") whose D50 exceeds 0.80 μm. Calcium carbonate has excellent adhesion to the adhesive (adhesive) and improves whiteness, so it has both ink drying and envelope peelability, and can achieve high whiteness and printability. If there is one layer of pigment coating layer, in 100 parts by weight of the pigment in the pigment coating layer, the total amount of the first and second calcium carbonate is preferably 90 parts by weight or more, and 100 parts by weight. The weight part is more preferably. If there are two or more pigment coating layers on one surface, the total amount of the first and second calcium carbonate in at least one pigment coating layer is preferably within the aforementioned range, The total amount in the outermost pigment coating layer is also preferably within the aforementioned range. The second calcium carbonate is preferably heavy calcium carbonate or causticized light calcium carbonate.

2) Adhesive The pigment coating layer contains an adhesive (adhesive) as a matrix. The adhesive is not limited, and known adhesives can be used. Examples thereof include styrene-butadiene copolymers, styrene-acrylic copolymers, ethylene-vinyl acetate copolymers, butadiene-methyl methacrylate copolymers, ethyl acetate・Emulsions of butyl acrylate copolymers, maleic anhydride-based polymers, acrylic acid-methyl methacrylate-based copolymers, etc.; fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, acetylene Polyvinyl alcohols such as acyl-modified polyvinyl alcohol; proteins such as casein, soybean protein, and synthetic protein; etherification of oxidized starch, positive starch, urea-esterified starch, and hydroxyethyl-etherified starch Starches such as starch and dextrin; cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, and hydroxymethylcellulose; and the like. These types can be used in combination.

The amount of the adhesive is preferably 5-30 parts by weight, more preferably 8-25 parts by weight, relative to 100 parts by weight of the pigment in the full-pigment coating layer in terms of printability and coating suitability. good. If the total amount of the adhesive is more than 25 parts by weight, the viscosity of the pigment coating liquid will become high, which will easily cause operational problems during coating. Furthermore, it was found that the drying property of the ink tended to decrease. On the other hand, when the total amount of the adhesive agent is less than 5 parts by weight, it becomes difficult to obtain sufficient surface strength.

The coated printing paper of the present invention preferably contains 10 to 80% by weight of styrene-butadiene copolymer latex in the form of emulsion in the full adhesive, and more preferably contains 15 to 70% by weight of latex. good. If the pigment coating layer is more than 2 layers, it is better that the layer closest to the base paper contains 10-80% by weight of latex in the full adhesive, and the layer farther away from the base paper contains 30-60% by weight of latex More preferably, as the latex system, styrene-butadiene-based latex is more preferable. As other adhesives, starch is particularly preferred, and its amount is preferably 30-90% by weight in the full adhesive for the layer closest to the base paper, and 40-70% by weight for the layer far away from the base paper. Compared with latex, since starches can improve the water retention of the pigment coating solution, the coating solution is less likely to penetrate the base paper, and can effectively cover the base paper with the pigment coating layer. In other words, if starches are used, the covering property of the base paper by the pigment coating layer will become good. As a result, improvement of printing quality (particularly printing glossiness) and improvement of ink drying properties can be expected. In the present invention, the ratio of latex to starch is preferably 3:5~5:7.

3) Other additives The pigment coating layer can contain dispersants, thickeners, water retention agents, defoamers, water repellents, dyes, pigments for coloring, etc., as required, which are usually formulated in pigments for coated paper Various additives. In the present invention, it is preferable to use organic particles having a larger particle size than the aforementioned pigments. In the case where the pigment coating layer exists in multiple layers, by making the organic particles contained in the outermost coating layer farthest from the base paper, the paper surface stain caused by the friction between the printed papers is reduced, And can improve printability. Uncooked starch granules are preferred as the organic particle system, and the above-mentioned effect can be obtained by adding 0.5 to 10% by weight to the above-mentioned pigment. The particle size of the organic particles is preferably 8-25 μm with an average particle size (D50) measured by a laser diffraction particle size distribution analyzer.

4) Coating amount The coating amount of the pigment coating layer is preferably 2 g/m ² or more, more preferably 5 g/m ² or more, and more preferably 10 g/m ² or more. good. If the coating amount is less than 5 g/m ² , since the unevenness on the surface of the paper substrate cannot be sufficiently covered, the receptivity of the printing ink may be significantly lowered. On the other hand, the coating amount of the pigment coating layer is preferably not more than 50 g/m ² , more preferably not more than 40 g/m ² , and more preferably not more than 35 g/m ² . If the pigment coating layer is multi-layered, as long as the total coating amount is within the aforementioned range, the coating amount of the innermost pigment coating layer is preferably 2 to 15 g/m ² , and Preferably it is 4~14g/m ² , more preferably 5~12g/m ² . In addition, the coating amount of the outermost pigment coating layer is preferably 6~20g/m ² , more preferably 8~15g/m ² . Since the influence of the outermost coating layer on the ink drying property is greater, it is preferable to apply a large amount of the outermost coating layer.

(2) Base paper 1) Pulp Well-known pulp can be used as base paper. Examples of known pulps include chemical pulp, groundwood pulp (GP), chip groundwood pulp (RGP), thermally refined pulp (TMP), chemically thermally ground pulp (CTMP), chemically groundwood pulp (CGP), semi Chemical pulp (SCP), old paper pulp, etc. It is preferred to use chemical pulp in the present invention. There are chemical pulp produced by the kraft pulp method and those produced by the sulfite pulp method, and both of them can be used in the present invention, but the chemical pulp produced by the kraft pulp method is different in terms of production cost. Words are suitable. The content of the chemical pulp in the raw material pulp is preferably at least 60% by weight, more preferably at least 80% by weight, and more preferably at least 90% by weight, from the viewpoint of whiteness and the like. Preferably, more than 95% by weight is especially preferred.

2) Filler Well-known fillers can be used in base paper. Examples of well-known fillers include heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica composite, kaolin, fired kaolin, layered kaolin, white carbon black, and talc. , Magnesium carbonate, Barium carbonate, Barium sulfate, Aluminum hydroxide, Calcium hydroxide, Magnesium hydroxide, Zinc hydroxide, Zinc oxide, Titanium oxide, Amorphous carbon dioxide produced by neutralizing the mineral acid of sodium silicate Inorganic fillers such as silicon, or organic fillers such as urea-formaldehyde resins, melamine-based resins, polystyrene resins, and phenol resins. Among them, heavy calcium carbonate or light calcium carbonate, which are typical fillers for neutral papermaking or alkaline papermaking, can also be preferably used in order to increase opacity. The calcium carbonate system that uses as filler can be aforesaid the 1st calcium carbonate, also can be the 2nd calcium carbonate, but be again preferably with light calcium carbonate. The filler rate in paper is not particularly limited, but it is preferably 1-40% by weight, more preferably 10-35% by weight. In consideration of the strength of the base paper, etc., it is more preferably 10 to 20% by weight.

3) Others Well-known additives for papermaking can also be used. Internal additives for papermaking such as aluminum sulfate or various anionic, cationic, nonionic, or amphoteric yield enhancers, water drainage enhancers, various paper strength enhancers or internal sizing agents can be used as required. Auxiliary. Polyacrylamide, cationized starch, etc. are mentioned as a dry paper strength improvement agent, Polyamide polyamine epichlorohydrin etc. are mentioned as a wet paper strength improvement agent. These medicines can be added within a range that does not affect texture or operability. Examples of the internal sizing agent include alkyl ketene dimer, alkenyl succinic anhydride, rosin sizing agents, and the like. Furthermore, dyes, pigments, fluorescent whitening agents, pH adjusters, defoamers, resin control agents, and sludge control agents can also be added as needed.

⁴ ) ^Basis weight of base ^paper for better.

5) Clear coating The coated printing paper system of the present invention may have a clear (clear) coating layer on one side or both sides of the above-mentioned base paper. By applying a transparent coating to the base paper, the surface strength and smoothness of the base paper can be improved, and the coating suitability for pigment coating can also be improved. The amount of transparent coating is preferably 0.1~3.0g/m ² in terms of solid content per side, more preferably 0.2~2.0g/m ² , more preferably 0.5~2.0g/m ² .

The so-called clear coating in the present invention refers to the coating using, for example, two-roll groove size filter press, gate roll coater, pre-measured size filter press, curtain coater, spray coater, etc. Machines (coating machines) that use water-soluble polymers such as starch, oxidized starch, and various modified starches (self-modified, cationic-modified, etc.) and water-soluble polymers such as polyacrylamide and polyvinyl alcohol as the main components Coating coating liquid (surface treatment liquid), coating coating (size press filter/size press) on the base paper. The clear coating liquid may also be coated with a sizing agent contained therein. In the present invention, coating starch is preferred.

2. Production method The coated printing paper of the present invention can be produced by known methods, but it is preferably produced by coating the base paper with a pigment coating liquid containing a pigment and an adhesive. (1) Preparation of base paper The raw material used for the base paper used in the present invention is as described above. The base paper can be manufactured according to a well-known papermaking method. For example, a fourdrinier paper machine including a top wire, an on top former, a gap former, a cylinder paper machine, a board paper machine using a combination of a fourdrinier paper machine and a cylinder paper machine, and a Yankee paper machine can be used. It is carried out by drying a paper machine (Yankee drye) or the like. The pH system during papermaking can be any of acidic, neutral, and alkaline, but neutral or alkaline is preferred. The papermaking speed is also not particularly limited. The base paper used in the present invention may be single-layer or multi-layer, but single-layer base paper is most suitable for use.

(2) Smoothing treatment of base paper Before coating the pigment coating solution on the obtained base paper, it is better to apply smoothing treatment to the base paper by various calender devices. Generally used calender apparatuses, such as a super calender and a soft calender, can be suitably used as said calender apparatus. As the processing conditions of the calender, the temperature of the rigid roll, the pressure of the calender, the number of nips, the speed of the roll, and the moisture content of the paper before calendering are properly selected according to the required quality. In the present invention, it is preferable to subject the base paper to a calender treatment in order to impart smoothness while maintaining a matte-like appearance. By applying calender treatment to the base paper, the smoothness of the base paper is improved, and the paint coating suitability is also improved.

(3) Preparation of pigment coating liquid The pigment coating liquid system can be prepared by dispersing or dissolving pigments, adhesives, and additives as required in water. The formulation of each component is adjusted in such a way that the aforementioned pigment coating layer can be formed. In the case of blade coating, the solid content concentration of the pigment coating solution is preferably 40-70% by weight, and more preferably 60-70% by weight. The viscosity of the pigment coating liquid is preferably in the range of 500~5000mPa･s by B-type viscosity measured at 60rpm at room temperature. Also, when the coating is performed using a roll coater, the solid content of the pigment coating solution is preferably 50 to 70% by weight, and more preferably 60 to 70% by weight. If the weight of the solid content is too low, backflow or the like will occur, and if it is too high, the load on the blade will increase, resulting in abrasion of the blade, etc., which will affect the operability.

(4) Coating method The coating method is not limited, and known coating machines such as a roll coater and a knife coater can be used. The coating speed is not particularly limited, but it is preferably 400-1800 m/min in the case of a knife coater, and 400-2000 m/min in the case of a roll coater. In the present invention, the pigment coating layer of one layer may be coated by using a knife coater, or it may be coated by a roll coater and then coated by a knife coater, or it may be used After coating with a knife coater, use a knife coater to coat, but in order to improve the smoothness of the surface, it is better to use a knife coater for the coating of the outermost coating layer.

Although one or more pigment coating layers can be provided, it is preferable to provide two or more pigment coating layers in order to improve printing gloss in the coated printing paper of the present invention. By making two or more pigment-coated layers, fiber coverage is improved and smoothness is also enhanced. As mentioned above, a clear coat layer is provided on the base paper, and a pigment coat layer may also be provided thereon.

(5) Other steps There is no limitation on the method of drying the coating layer in the wet state. For example, steam heating cylinders, heated hot air dryers, gas heating dryers, electric heating dryers, or infrared heating dryers can be used.

The coated paper for printing of the present invention can be surface treated according to the needs of the coated paper produced in the above-mentioned manner, but if it is desired to obtain a style that imitates the matte feeling, it is advisable not to carry out the calender treatment . In the case of calender processing, generally used calender devices such as super calenders and soft calenders can be suitably used. As the processing conditions of the calender, the temperature of the rigid roll, the pressure of the calender, the number of nips, the speed of the roll, and the moisture content of the paper before calendering are properly selected according to the required quality.

3. Paper quality (1) Peeling index The coated printing paper of the present invention preferably has a peeling index of 35-55. The so-called peeling index refers to the standard of the adhesiveness of the smeared part in the envelope, so the higher the value, the easier it is to cause peeling on the base paper layer, that is, it means that the adhesiveness is excellent. The coated printing paper of the present invention having a peel index within this range is suitable as envelope paper. The peel index can be obtained by the following method. A PET film having a thickness of 40 μm and having an opening of 5 mm in width and 70 mm in length in the central portion was prepared. Prepare a set of paper samples for evaluation. The dimensions of each sample were 50 mm in width and 100 mm in length. The aforementioned PET film was stacked on one paper sample (A), and the paste was uniformly applied to the opening so that the thickness became about 40 μm. Another paper sample (B) was quickly stacked thereon, left under a load of 4.17 g/cm ² for 1 minute, after which the load was released and 4 minutes later, peeling was performed by hand. By visually observing the part of the coated paste in the peeled paper sample (A), it can be confirmed that the peeling of the other than the paste layer is observed at an interval of 4 mm in the longitudinal direction of the opening using SEM-EDS 12 point (field of view: length 1.9mm×width 2.6mm), and measure the ratio of C (carbon), O (oxygen), Al (aluminum), Si (silicon dioxide), and Ca (calcium) at each point, and deduct The average value of the C ratios of the total 8 points of the upper 2 points and the lower 2 points of each numerical value was used as the peeling index. On the other hand, when peeling of the paste layer was confirmed, the peeling index was set to zero. The larger the peeling index is, the easier it is to peel off the base paper layer, that is, it shows that the suitability for envelopes is good. On the other hand, the lower the peeling index is, the more easily the peeling of the coating layer occurs, that is, it indicates that the suitability for envelopes is poor.

(2) Whiteness The coated printing paper of the present invention preferably has a whiteness of 85% or more. In the present invention, the whiteness is measured under the conditions not including ultraviolet rays according to JIS P8148.

(3) Glossiness of white paper The glossiness of white paper is an index indicating the degree of gloss when using white paper, so it is measured in accordance with JIS-P8142 in the present invention. In order to present an excellent imitation matte feeling, the glossiness of the white paper is preferably less than 40%, more preferably less than 35%, and more preferably less than 30%. The lower limit of the glossiness of white paper is not limited, but it is preferably 15% or more. If the glossiness of the white paper is within this range, it has the advantages of no glare, easy identification of printing, and less slippage when made into an envelope.

(4) Basis weight The basis weight of the coated printing paper of the present invention is preferably 60-250 g/m ² , and more preferably 70-210 g/m ² .

(5) Ink drying property The ink drying property of the coated paper for printing of the present invention is excellent. Generally speaking, the quality of ink drying of coated printing paper can be identified by checking the ink transfer to other places or friction stains on the printed surface when checking the printed matter after stacking.

(5-1) Evaluation by nitrogen adsorption method (total pore volume of paper) In the present invention, the pore structure of the pigment coating layer is generally evaluated by using the nitrogen adsorption method that can be measured under low pressure conditions, Thus, the ink drying property of the coated printing paper of the present invention can be evaluated. Regarding the relationship between the pigment coating layer and the solvent absorbability, the Lucas-Washburn formula represented by the formula (1) in which many fine pores existing in the pigment coating layer are regarded as capillary aggregates is widely used. Here, L is the penetration depth of the solvent, r is the average radius of the capillary, t is the time, γ is the surface tension of the solvent, θ is the contact angle between the capillary wall and the solvent, and η is the viscosity of the solvent. Also, if the pore structure of the pigment coating layer is assumed to be arranged as n cylindrical tubes with an average radius r, since the ink solvent penetration amount ν of the pigment coating layer can be expressed by formula (2), the formula (1) is deformable as formula (3). D is the thickness of the pigment coating layer, V is the pore volume of the pigment coating layer, and k is the viscosity of the ink. That is, the larger the pore diameter and pore volume in the pigment coating layer, and the smaller the thickness of the pigment coating layer, the greater the amount of solvent permeation per certain period of time. Therefore, it is considered that the drying property of the ink is improved. In the present invention, the pore volume obtained by Tristar 3000 is regarded as the pore volume of the pigment coating layer, and the average pore diameter is regarded as the average pore diameter of the pigment coating layer.

The pore volume V of the coated printing paper of the present invention is preferably greater than 0.04 cm ³ /g, and more preferably greater than 0.045 cm ³ /g. The upper limit is preferably not more than 0.09 cm ³ /g, more preferably not more than 0.085 cm ³ /g, more preferably not more than 0.08 cm ³ /g. Coated printing paper having a pore volume V higher than 0.04 cm ³ /g is excellent in ink drying properties.

The total pore volume (cm ³ /m ² ) of the coated printing paper of the present invention is defined based on the pore volume V (cm ³ /g) × coating amount c (g/m ² ), which is It is preferably at least 0.55 cm ³ /m ² , more preferably at least 0.60 cm ³ /m ² , and more preferably at least 0.80 cm ³ /m ² . The upper limit of the total pore volume is preferably not more than 1.00 cm ³ /m ² , more preferably not more than 0.95 cm ³ /m ² , and more preferably not more than 0.90 cm ³ /m ² .

The average pore diameter m of the coated printing paper of the present invention is preferably 30 nm or more. The upper limit of the average pore diameter m is preferably 60 nm or less. Specifically, in the present invention, the average pore diameter is obtained from the adsorption-desorption isotherm obtained by the nitrogen adsorption method. In this application, the average pore diameter obtained by Tristar 3000 is regarded as the average pore diameter of the pigment coating layer.

4. Applications The coated printing paper of the present invention is advantageous as envelope paper because it has both excellent peel resistance and ink quick-drying properties. The so-called envelope paper refers to the paper used to form an envelope by bending and laminating. FIG. 1 shows an envelope produced using the coated printing paper of the present invention as envelope paper. In the figure, 1 is the envelope, 10 is the envelope paper, and 20 is the bonding part. In the coated printing paper (envelope paper) of the present invention, peeling does not occur in the adhesive layer but mainly occurs in the base paper layer at the bonding portion 20, so the confidentiality is high. Furthermore, since the coated printing paper (envelope paper) of the present invention has excellent ink quick-drying properties, it is also suitable for mass printing. [Example]

<Evaluation method> (1) Basis weight: measured in accordance with JIS P 8124. (2) Paper thickness: measured in accordance with JIS P 8118. (3) Density: Calculated from basis weight and paper thickness according to JIS P 8118. (4) PPS roughness: PPS surface roughness measured in accordance with ISO8791. The measurement was performed using a hard backing. (5) ISO whiteness: According to JIS P8148, it was measured with a color difference meter CMS-35SPX manufactured by Murakami Color Co., Ltd., under conditions including ultraviolet light. (6) Whiteness: According to JIS P8148, it was measured with a color difference meter CMS-35SPX manufactured by Murakami Color Co., Ltd., under the condition that ultraviolet light was not included. (7) Glossiness of white paper: measured in accordance with JIS-P8142.

(8) Envelope suitability: evaluate according to the peel index. The peel index was measured by the following procedure. 1) A PET film having a thickness of 40 μm and having an opening portion having a width of 5 mm and a length of 70 mm in the central portion was prepared. 2) Prepare a set of paper samples for evaluation. The dimensions of the paper sample were 50 mm in width and 100 mm in length. 3) The PET film of 1) was overlaid on one paper sample (A), and the paste (DBA163 manufactured by Saiden Chemical Co., Ltd.) was uniformly applied to the opening so that the thickness became 40 μm. 4) After the paste was applied, another paper sample (B) was quickly superimposed on it, and it was left under a load of 4.17 g/cm ² for 1 minute, after which the load was released and 4 minutes later, it was peeled off by hand. For this sample (A), the peeling index was determined according to the above-mentioned method.

(9) Ink dryness Using a lithographic cut-sheet printing machine (4 colors) manufactured by Roland Co., using ink for lithographic cut-sheets (NEX-M manufactured by Toyo Ink) at a printing speed of 8,000 sheets/hr, with full-coated parts After printing so that the ink concentration becomes ink 2.00, immediately after printing, use fingertips to touch the ink-filled printing part every 10 minutes, and perform sensory evaluation on the rapidity of ink drying. A: good B: bad

(10) Pore Volume (i) Sample Preparation and Measurement The pore volume, total pore volume, and average pore diameter of the coated paper were determined by the nitrogen adsorption method. (Preparation of sample) The paper sample of length 40cm x width 15cm was divided into two layers so that the thickness direction may become uniform, and the laminated body containing a pigment coating layer and a base paper layer was obtained. In the case of double-sided coated paper, two laminates and one layer mainly composed of the base paper layer can be obtained; in the case of single-sided coated paper, one laminate can be obtained One layer and one layer mainly composed of base paper layers. A laminate including a pigment coating layer and a base paper layer was used as a sample sheet and used for measurement. In the case of double-sided coated paper, either one was used for the measurement as a sample sheet. The basis weight t (g/m ² ) of the sample sheet was measured. Select any 4 points in one sample sheet, cut it into long strips, and put it into the measuring tank in such a way that the measured sample becomes about 1~2g in absolute dry weight. Let the absolute dry weight at this time be w (g). The pretreatment was carried out overnight at a treatment temperature of 120°C in a vacuum state.

(Measurement) Using the aforementioned apparatus, the pore volume and the average pore diameter were measured from the pigment coating layer side of the aforementioned measurement sample. Specifically, the BJH method is used to obtain the pore volume and average pore diameter of the measurement sample based on the adsorption-desorption isotherm, and the average value of the four samples is obtained, which is used as the pore volume V' and the average pore diameter of the measurement sample. Hole diameter m'. The pore volume V' is a value converted per unit coating amount, and this is defined as the pore volume V of the pigment coating layer of the present invention. The obtained average pore diameter m' is directly set as the average pore diameter m of the pigment coating layer of the present invention. The weight of the pigment coating layer of the measurement sample is calculated by the following formula: weight of the pigment coating layer (g) = absolute dry weight w (g) of the measurement sample × coating amount c (g/m ² ) ÷ weight of the sample sheet Basis weight t (g/m ² ). The coating amount c (g/m ² ) can be obtained by the measurement method described later. For measurement and analysis, Tristar 3000 manufactured by Shimadzu Corporation was used.

(Amount of Coating) The amount of coating was measured according to the method described in Japanese Patent No. 5827187. Specifically, it was measured by the following procedure. 1) Cut the measurement sample (paper) into a size of 5cm×5cm, and measure the weight x after humidity control at a temperature of 23°C and a relative humidity of 50%. 2) Place the sample in such a way that the pigment coating is in contact with the styrene polymer plate, and fix it on the watch glass with clamps. 3) Put it into a dryer at 120~150°C, melt the styrene polymer and make it adhere to the pigment coating layer, let it cool, and then perform humidity control at a temperature of 23°C and a relative humidity of 50% for about half a day And measure the weight y. 4) After immersing the measurement sample obtained in the previous step in the ethylenediamine copper solution for about 3 to 4 hours, use a brush to carefully peel off the base paper layer and the pigment coating layer. This step is repeated until the pulp fibers attached to the pigment coating layer are gone. 5) The pigment coating layer was washed with water and dried, and after conditioning for about half a day at a temperature of 23° C. and a relative humidity of 50%, the weight z was measured. 6) Calculate the coating amount according to the following formula. Coating amount c(g/m ² )=(xA)×400 A=yz

[Example 1] Using 100% by weight of chemical pulp and adding light calcium carbonate so that the ash content in the paper was 13.5% by weight, base paper with a basis weight of 97.9 g/m ² was prepared. As a pigment, 55 parts by weight of ground calcium carbonate (manufactured by Fimatec Co., Ltd., product name: FMT97, D50=0.88 μm) of the second calcium carbonate and particulate ground calcium carbonate of the first calcium carbonate (manufactured by Fimatec Co., Ltd., Trade name: FMT100YF, D50=0.60μm) 45 parts by weight, for this deployment as an adhesive 4 parts by weight of styrene-butadiene copolymer latex, 6 parts by weight of oxidized starch, fluorescent dye (manufactured by Canasia Japan Co., Ltd., Trade name: Canwhite TS 120 liq) 0.5 parts by weight, further adding water to obtain a pigment coating solution with a solid content concentration of 66% by weight. The pigment coating liquid was coated on both sides with a knife coater so that the dry coating amount per one side was 15.0 g/m ² on the base paper, and then dried to obtain a coated printing paper. The coated paper for printing was evaluated by the above-mentioned method.

[Example 2] In addition to using other 1st calcium carbonate, particulate ground calcium carbonate (manufactured by Fimatec Co., Ltd., trade name: FMT100, 50=0.66 μm) instead of particulate ground calcium carbonate (manufactured by Fimatec Co., Ltd., Trade name: FMT100YF), except that no fluorescent dye was used, a pigment coating liquid was prepared in the same manner as in Example 1, and this was used as a coating liquid for top coating. Further, 100 parts by weight of heavy calcium carbonate (manufactured by Fimatec Co., Ltd., trade name: FMT97, D50=0.88 μm) and 7 parts by weight of styrene-butadiene copolymer latex as an adhesive were prepared as the second calcium carbonate. , 3 parts by weight of oxidized starch, and then adding water to obtain a primer coating solution with a solid content concentration of 66% by weight. On the aforementioned base paper, the undercoat pigment coating solution was coated on both sides with a knife coater so that the dry coating amount per one side would be 6.5 g/m ² , and dried. Next, on the base paper, the topcoat pigment coating solution was coated on both sides with a knife coater so that the dry coating amount per one side was 10.5 ^g /m2, and dried to obtain a printing coating. covered paper. The coated paper for printing was evaluated by the above-mentioned method.

[Example 3] In addition to using other 1st calcium carbonate in the top coating liquid, granular ground calcium carbonate (manufactured by Imerys, trade name: Carbilux, D50=0.65 μm) instead of particulate ground calcium carbonate (Fimatec Co., Ltd. Co., Ltd., brand name: FMT100, 50 = 0.66 μm), and the dry coating amount of the primer pigment coating liquid was set to 7.5 g/m ² , and the dry coating amount of the top coat pigment coating liquid was set to 9.5 g. /m ² , in the same manner as in Example 2, a coated printing paper was produced and evaluated.

[Example 4] 100 parts by weight of self-made causticized light calcium carbonate (D50=1.38 μm) was used as a pigment, and 2.5 parts by weight of styrene-butadiene copolymer latex and 21 parts by weight of oxidized starch were prepared as an adhesive part, and water was further added to obtain an undercoat pigment coating solution with a solid content concentration of 50% by weight.

45 parts by weight of self-made causticized light calcium carbonate (D50=0.64 μm) of the first calcium carbonate and 55 parts by weight of self-made causticized light calcium carbonate (D50=1.02 μm) of the second calcium carbonate were used as pigments. As an adhesive, 4 parts by weight of styrene-butadiene-based copolymer latex and 6 parts by weight of oxidized starch were prepared, and water was added to obtain a top-coating pigment coating solution with a solid content concentration of 66% by weight. On the aforementioned base paper, the undercoat pigment coating liquid was coated on both sides by a gate roll coater so that the dry coating amount per one side became 4.5 g/m ² , and dried. Next, on this base paper, the top coat pigment coating solution was coated on both sides with a knife coater so that the dry coating amount on one side became 10.5 ^g /m2, and dried to obtain a coating for printing. Paper. The coated paper for printing was evaluated by the above-mentioned method.

[Comparative Example 1] As the base paper, prepare 90% by weight of chemical pulp, 10% by weight of deinked pulp, add light calcium carbonate so that the ash content in the paper is 13.5% by weight, and have a basis weight of 97.9g/ ^m2 base paper. 100 parts by weight of ground calcium carbonate (manufactured by Fimatec Co., Ltd., trade name: FMT97, D50=0.88 μm) as the second calcium carbonate as a pigment, and 7.6 parts by weight of styrene-butadiene copolymer latex as an adhesive parts, 6 parts by weight of oxidized starch, and then add water to obtain a pigment coating solution with a solid content concentration of 66% by weight. The pigment coating liquid was coated on both sides with a knife coater so that the dry coating amount per one side was 15.0 g/m ² on the base paper, and then dried to obtain a coated printing paper. The coated paper for printing was evaluated by the above-mentioned method.

[Comparative Example 2] In addition to using grade 2 clay (manufactured by Imerys, trade name: KCS, D50=4.05 μm) instead of particulate ground calcium carbonate, and changing the amount of the adhesive as shown in Table 1, and In Example 1, a pigment coating solution was prepared in the same manner to manufacture and evaluate coated printing paper.

[Comparative Example 3] In addition to using grade 2 clay (manufactured by Imerys, trade name: KCS, D50=4.05 μm) instead of particulate ground calcium carbonate, the pigment coating liquid was prepared in the same manner as in Example 1, thereby Manufacture and evaluation of coated paper for printing. The results are shown in Table 1.

As shown in Table 1, it can be clearly seen that the coated printing paper of the present invention is excellent in ink quick-drying property and envelope suitability.

1‧‧‧envelope 10‧‧‧envelope paper 20‧‧‧attached parts

[Fig. 1] is a diagram showing one aspect of the envelope of the present invention.

Claims (10)

A coated paper for printing, which is equipped with a pigment coating layer on at least one side of a base paper, the pigment coating layer comprising a first calcium carbonate having an average particle diameter (D50) of 0.80 μm or less, and a calcium carbonate having an average particle diameter (D50) of more than 0.80 μm. For the second calcium carbonate having an average particle diameter (D50) of μm, the total amount of the first and second calcium carbonates is 90 parts by weight or more relative to 100 parts by weight of the pigment in the pigment coating layer. The coated printing paper according to claim 1, wherein 40 parts by weight or more of the first calcium carbonate is contained in 100 parts by weight of the pigment in the pigment coating layer. The coated printing paper according to claim 1 or 2, wherein the average particle diameter (D50) of the first calcium carbonate is 0.50 to 0.75 μm. The coated printing paper according to claim 1 or 2, wherein 90 parts by weight or more of chemical pulp is contained in 100 parts by weight of the pulp of the base paper. The coated printing paper according to claim 3, wherein 90 parts by weight or more of chemical pulp is contained in 100 parts by weight of the pulp of the base paper. The coated paper for printing according to claim 1 or 2, wherein the whiteness measured under the condition not including ultraviolet rays is 85% or more. The coated printing paper according to Claim 1 or 2, wherein the glossiness of the white paper is 40% or less. The coated paper for printing according to claim 3, wherein the glossiness of the white paper is 40% or less. A kind of envelope paper, it is to use the coated paper for printing as claimed item 1-8. An envelope, which is made of the envelope paper according to claim 9.

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