JP2012035600A - Black inkjet recording sheet and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for economically manufacturing a black inkjet recording sheet with such an advantage that suitability for inkjet print is imparted, the whiteness degree of the surface is low and no color shading is found.SOLUTION: The method for manufacturing the black inkjet recording sheet, among other procedures, prepares a coating material for ink receptive layer which contains a synthetic silica as a pigment, a polyvinyl alcohol and an ethylene-vinyl acetate resin as binder, a cationic resin as an ink adhesion promoter, and a nonionic black coloring pigment as a coloring agent. In this preparation, the binder content accounts for 40 to 60 parts to 100 parts of synthetic silica and the black coloring pigment content accounts for 3.5 to 5.5 mass% to the total solids of the coating material. Further, the polyvinyl alcohol is added to and mixed with silica slurry at least ahead of the ethylene-vinyl acetate resin and the cationic resin. In this case, the addition rate of the cationic resin is less than 40 L/minute to 1,000 L of silica slurry.

Description

  The present invention relates to an ink jet recording sheet excellent in ink jet printability, and more particularly to a method for producing a black ink jet recording sheet specialized for white ink and a black ink jet recording sheet. That is, a black ink jet having a black hue, a surface of the recording sheet having a matte tone and less light reflection, a large brightness difference between the surface of the recording sheet and the white printed portion, and the printed portion being reflected The present invention relates to a method for economically producing a recording sheet and a black inkjet recording sheet.

  In recent years, full-color and high-definition images can be easily obtained with the progress of inkjet printers and plotters.

  The ink jet recording method is a method in which fine droplets of ink are ejected by various operating principles and adhered to a recording paper such as paper to record images and characters. Inkjet printers and plotters are rapidly spreading in various applications in recent years as hard copy creation apparatuses for image information such as characters and various graphics created by a computer. In particular, a color image formed by a multicolor ink jet method can obtain an inferior recording even when compared with a multicolor printing by a plate making method or a printing by a color photographic method, and in an application with a small number of production copies. Are being widely applied because color images can be obtained at a lower cost than other printing techniques or photographic techniques.

  An ink jet recording sheet is required to have ink absorbability, color reproducibility, and the like, and an ink receiving layer containing a pigment, a binder, and various additives is formed. The pigment, binder and various additives used in the ink receiving layer have been devised to satisfy various requirements. As the pigment, a porous synthetic pigment is often used in order to obtain ink absorbability. Furthermore, in order to make the color of the inkjet image clear, it is usual to increase the whiteness or finely adjust the chromaticity. As the pigment, for example, porous synthetic amorphous silica can be used because it has excellent ink-jet ink absorbability. In addition, the binder is used for the purpose of fastening the pigment. As the binder, various water-based binders are used, and in particular, binders that are excellent in ink jet ink absorbency have been used.

  In the plotter field, special color inks and pigment inks with high opacity have been developed, and the color of the recording medium need not necessarily conform to white. On the contrary, in many cases, a printed matter that aims at artisticity such as a commercial advertisement is printed with ink with high opacity such as special color ink or white pigment ink, and in that case, a recording medium with a deep color tone is required. Examples of the white ink having high opacity include white ink for JV-33 manufactured by Mimaki Corporation. In particular, there are cases where an ink jet recording medium based on black in which ink with high brightness appears is useful. An inkjet recording medium based on black can economically obtain a unique image tone in which a negative tone is reversed. For example, it can be a medium that can easily be developed into a new style in which black and white is reversed in an ink-jet painting that is representative of monotone. Furthermore, inkjet recording media based on black have cases where printed one-point logos, various illustrations, characters, etc. have a better attractiveness than media based on white. The utility value is extremely high. It is also rare. In the past, when printing a monotone image with white ink based on black, a large amount of black ink was ejected onto an inkjet recording medium based on uncolored white. It is consumed as described above, and it is uneconomical for the printing personnel or personal users.

  Psychologically influential information emitted from the entire printed material includes the background color of the printed material, the glossiness of the surface of the printed material, etc. in addition to the image area of the printed material. The information transmission is limited to only the line portion, and transmission information other than characters and images is not effective.

  Despite the above background, tinted inkjet recording sheets are not very commercially available. As an attempt to adjust the color tone of the ink receiving layer, a technique of adding a color pigment to the ink receiving layer has been disclosed (see, for example, Patent Document 1).

JP 2001-277702 A

  When printing with white ink, if the whiteness of the surface of the medium to be printed is not below a certain threshold, not only the performance of the white ink with high opacity as described above can be brought out, but also the attractiveness of various other inks is conspicuous. The effect of making it lowers. Attempts to adjust the color tone of the ink receiving layer including Patent Document 1, the amount of the colorant added is small, the whiteness cannot be reduced below a certain threshold, and is not suitable for printing with white ink. .

  In order to reduce the whiteness of the surface of the printed medium to a certain threshold value or less, in an ink jet recording medium, it is possible to color the ink receiving layer. However, as described above, the ink receiving layer contains a pigment, a binder, and various additives. In particular, the type, total amount, and blending ratio in the case of using a plurality of binders must be appropriately selected appropriately, and vary depending on the purpose. Furthermore, when chemicals that cause agglomeration or chemicals that lower the coating layer strength are used in the paint, the proper viscosity can be maintained and the coating layer strength can be sufficiently maintained. It is necessary to appropriately select the total amount of binder added. Moreover, when using multiple types of binders which buffer an impact, it is necessary to select the blending ratio and the total amount of binder added appropriately. When the total amount of the binder added is too large, the ink absorbability is inferior. On the other hand, if the amount is too small, the ink absorbency is good, but the coating layer strength becomes low, and the coating layer falls off or wears out, and there is concern about the quality after printing and the durability of the printed product. Comes out. As a prior art, there is no specification of selection of binder type, blending ratio and total amount added when a large amount of color pigment is contained in the ink receiving layer, and even if it is attempted to manufacture such a colored ink jet recording paper, At present, trial and error is unavoidable.

  When trying to tint the ink receiving layer, color unevenness due to agglomeration of the paint tends to occur unless the paint preparation conditions are properly controlled depending on the type and amount of the color pigment. Further, since the color pigment inhibits the binding force of the binder, the coating layer strength becomes extremely low, and it is difficult to impart commercial value. In particular, since a large amount of black pigment is used for coloring the coating layer with a black pigment, it is difficult to produce an ink jet recording paper having a uniform coated surface quality and having no uneven color. Conventionally, there has not been established a production method that appropriately controls the aggregation of the paint and does not cause a decrease in the coating layer strength. Patent Document 1 does not describe such a problem, and such technical difficulty is estimated.

  The object of the present invention is that there is no blurring of printing with an ink jet printer on the ink jet recording surface, the strength of the ink receiving layer provided on the recording surface is also practical, the surface whiteness is low, especially the white ink It is an object of the present invention to provide a black ink jet recording sheet which is an achromatic system without color unevenness that can print. Another object of the present invention is to provide a method for producing a black ink jet recording sheet economically without aggregation and thickening in the preparation of paint.

  As a result of earnest investigation, examination and research, the present inventors have provided an ink jet recording surface in which an ink receiving layer mainly composed of a pigment and a binder is provided on at least one surface of a white support mainly composed of wood fibers. Although the color tone may be adjusted using a plurality of pigments, a black ink jet recording sheet characterized by mainly adjusting the color tone with a black pigment has been completed. By setting the whiteness, lightness, and chromaticity ranges to predetermined conditions regarding the degree of color tone, a recording sheet capable of printing white ink was completed. In simple terms, the degree of whiteness visually felt is a condition where the density of blackness is high below a certain threshold and the whiteness of the white ink is noticeable. In addition, the range of brightness and chromaticity is a condition in which chromatic colors are not felt. As a result of being able to visually feel the blackness of achromatic colors, white printing is enhanced and the printing quality and attractiveness become significant. The following effects occur. If the density of blackness is insufficient or the influence of chromatic colors on the color tone becomes large, white printing will not stand out. The coating material for the ink receiving layer is made of porous synthetic silica as an ink absorbent, which is a pigment, a predetermined amount of polyvinyl alcohol and ethylene vinyl acetate resin as a binder, and the black color of a recording sheet mainly intended for white ink. It is essential to include a black color pigment for color tone adjustment. By setting the addition amount of the binder within an appropriate range, the strength and ink absorbability of the ink receiving layer can be maintained.

  In addition, in preparing the ink-receiving layer coating, by prescribing the prescribed conditions for the addition of each chemical, the order of mixing, and the timing of adding the chemical, the agglomeration of the coating is suppressed, the coating layer strength is ensured, and the print quality is improved. The maintained black ink jet recording sheet without uneven color can be efficiently produced, and the above-mentioned problems have been achieved.

  The method for producing a black inkjet recording sheet according to the present invention comprises synthetic silica as a pigment, polyvinyl alcohol and ethylene vinyl acetate resin as a binder, a cationic resin as an ink fixing agent, and a nonionic black coloring as a colorant. A method for producing a black ink jet recording sheet comprising a pigment and an essential component as a main component, coated on at least one side of a support mainly composed of wood fibers and provided with one or more ink-receiving layers, The paint for forming the ink-receiving layer contains 40 to 60 parts by mass of the binder with respect to 100 parts by mass of the synthetic silica, and the black color pigment in the total solid content of the paint. 5 to 5.5% by mass, and the synthetic silica is a silica slurry dispersed in water, and the silica slurry contains the essential components. The polyvinyl alcohol is added and mixed at least before the ethylene vinyl acetate resin and the cationic resin, and the addition rate of the cationic resin is less than 40 L / min with respect to 1000 L of the silica slurry. It is characterized by.

In the method for producing a black ink jet recording sheet according to the present invention, the coating material has a B-type viscosity at 60 rpm under a condition of 20 ° C. of a primary mixture obtained by adding the polyvinyl alcohol to the silica slurry and thoroughly mixing it. Measured actual viscosity η _{obs. 1} is a theoretical values calculated from the number 1 volume average viscosity eta _{average calc. 1} difference amount .DELTA..eta ₁ with, | .DELTA..eta _{1 |} <a 700 mPa · s, and completely by the addition of either one of the primary mixture into liquid wherein the ethylene vinyl acetate resin or the cationic resin Measured viscosity η _obs. Measured B-type viscosity at 60 rpm under the condition of 20 ° C. of the mixed secondary mixture _{. 2} is a theoretical values calculated from the number 2 volume average viscosity eta _{average calc.} Difference amount .DELTA..eta ₂ with _2, | .DELTA..eta _{2 |} <a 700 mPa · s, and, to complete addition of the other of said second mixture into liquid wherein the ethylene vinyl acetate resin or the cationic resin Measured viscosity η _obs. Measured for B-type viscosity at 60 rpm under the condition of 20 ° C. of the mixed tertiary mixture _{. The} volume average viscosity η _{average calc. 3} and the difference amount .DELTA..eta ₃ of, | is preferably <is 700mPa · s | Δη _3.
( _Equation 1) η _{average calc. 1} = (η ₁ × V ₁ ) / V ₁
( _Equation 2) η _{average calc. 2} = {(η ₁ × V ₁ ) + (η ₂ × V ₂ )} / (V ₁ + V ₂ )
( _Equation 3) η _{average calc. 3} = {(η ₁ × V ₁ ) + (η ₂ × V ₂ ) + (η ₃ × V ₃ )} / (V ₁ + V ₂ + V ₃ )
In Equations 1, 2, and 3, η ₁ [mPa · s] is the viscosity of a 10% aqueous solution of polyvinyl alcohol obtained by measuring B-type viscosity at 60 rpm under 20 ° C., and V ₁ [L] is It is the addition amount of the polyvinyl alcohol aqueous solution. η ₂ [mPa · s] is an aqueous dispersion of an ethylene vinyl acetate resin having a solid content concentration of 50% by mass or a cationic resin water having a solid content concentration of 30% by mass, as measured for B-type viscosity at 60 rpm under 20 ° C. V ₂ [L] is the added amount of either an aqueous dispersion of ethylene vinyl acetate resin or an aqueous dispersion of cationic resin. η ₃ [mPa · s] is an aqueous dispersion of an ethylene vinyl acetate resin having a solid content concentration of 50% by mass or a cationic resin having a solid content concentration of 30% by mass, which was measured for B-type viscosity at 60 rpm under 20 ° C. V ₃ [L] is the added amount of either the aqueous dispersion of ethylene vinyl acetate resin or the aqueous dispersion of cationic resin. The state of the paint can be in a good state without aggregation and thickening, and as a result, the coating layer strength can be ensured and the coated surface can have no uneven color.

  In the method for producing a black ink jet recording sheet according to the present invention, the coating material is preferably prepared in a batch system. In each step, since the mixing is completely achieved, the contact between the chemicals that tend to aggregate can be minimized.

  In the method for producing a black ink jet recording sheet according to the present invention, the addition rate of the cationic resin is preferably more than 5 L / min with respect to 1000 L of the silica slurry. Aggregation can be dispersed and the state of the paint can be made good. Moreover, since consumption of unnecessary energy can be suppressed without reducing the production speed, it can be manufactured more economically.

  In the method for producing a black inkjet recording sheet according to the present invention, the addition rate of the polyvinyl alcohol exceeds 20 L / min with respect to 1000 L of the silica slurry, and the addition rate of the ethylene vinyl acetate resin is the silica slurry. It is preferable to exceed 20 L / min with respect to 1000 L. Since consumption of unnecessary energy can be suppressed without reducing the production speed, it can be manufactured more economically.

The black ink jet recording sheet according to the present invention is a black ink jet recording sheet in which one or more ink receiving layers containing a pigment, a binder and a colorant are provided on at least one side of a support mainly composed of wood fibers. The ink receiving layer contains synthetic silica as the pigment, contains polyvinyl alcohol and an ethylene vinyl acetate resin as the binder, and contains only a nonionic coloring pigment as the colorant. The colored pigment contains a black colored pigment, and the ink receiving layer contains the black colored pigment in an amount of 3.5 to 5.5% by mass based on the total solid content of the ink receiving layer. And 40-60 parts by mass of the binder with respect to 100 parts by mass of the synthetic silica, and the surface of the ink receiving layer is (I) (1) JIS P 815 : 2004 "Paper and board - Determination method of color (C / 2 °) - diffuse illumination method" lightness index defined in ^{(L *)} is 20 ≦ ^{L *} ≦ 28, chromaticity index ^(a *, ^{b *)} is It is in the range of −0.4 ≦ a ^* ≦ 0.2 and −0.7 ≦ b ^* ≦ 0.3. (2) The Chamber of Commerce Color Coordination Chart “The Chamber Color Coordination Chart: The Chamber” satisfying at least one of (1) or (2) having a luminosity equivalent to Bk (20) Black or Bk (10) Black in "Of Commerce and Industry Color Coordination Chart (CCIC)", and (II) ISO whiteness as defined in JIS P 8148: 2001 “Paper, paperboard and pulp—Method of measuring ISO whiteness (diffuse blue light reflectance)” Is not more than 10%, and (III) the maximum color difference ΔE ^* obtained by a method of calculating from the lightness index (L ^* ) and the perceptual chromaticity index (a ^* , b ^* ) at 10 cm × 10 cm square It has the area | region which is 0.5 or less.

  In the black ink jet recording sheet according to the present invention, the ink receiving layer contains the black color pigment and the chromatic color pigment as the color pigment, and the ratio of the chromatic color pigment among the color pigments is 0.17% by mass or less is preferable. Since the color tone can be finely adjusted, the color variations can be made abundant, and the color tone can be adjusted so as not to feel a chromatic color, a sheet on which white ink printing can be obtained can be obtained.

  In the black ink jet recording sheet according to the invention, the ink receiving layer preferably further contains a cationic resin as an ink fixing agent. Fixability and color developability of the ink-jet ink can be improved.

  In the present invention, there is no blurring of printing by an ink jet printer on the ink jet recording surface, the strength of the ink receiving layer provided on the recording surface is also practical, the surface whiteness is low, and white ink printing can be displayed. It is possible to provide a black ink jet recording sheet which is an achromatic system having no color unevenness. Another object of the present invention is to provide a method for producing a black ink jet recording sheet economically without aggregation and thickening in the preparation of paint.

The model of the preparation flow of the coating material for ink receiving layers is shown.

  Next, the present invention will be described in detail with reference to embodiments, but the present invention is not construed as being limited to these descriptions. As long as the effect of the present invention is exhibited, the embodiment may be variously modified.

The black inkjet recording sheet according to the present embodiment is a black inkjet recording sheet in which one or more ink receiving layers containing a pigment, a binder, and a colorant are provided on at least one side of a support mainly composed of wood fibers. The ink receiving layer contains synthetic silica as the pigment, contains polyvinyl alcohol and ethylene vinyl acetate resin as the binder, and contains only a nonionic coloring pigment as the colorant. And the color pigment contains a black color pigment, and the ink receiving layer contains the black color pigment in an amount of 3.5 to 5.5% by mass based on the total solid content of the ink receiving layer. And 40-60 parts by mass of the binder with respect to 100 parts by mass of the synthetic silica, and the surface of the ink receiving layer is (I) (1) JIS P 8 50: 2004 "Paper and board - color (C / 2 °) measuring method - diffuse illumination method" lightness index defined in ^{(L *)} is 20 ≦ ^{L *} ≦ 28, chromaticity index ^{(a *, b} *) Is within the range of −0.4 ≦ a ^* ≦ 0.2 and −0.7 ≦ b ^* ≦ 0.3, (2) “Combination Chamber Color Coordination Chart: The It has a visual chromaticity equivalent to Bk (20) Black or Bk (10) Black in “Chamber of Commerce and Industry Color Coordination Chart (CCIC)”, and satisfies at least one of (1) and (2) , (II) JIS P 8148: 2001 "paper, paperboard and pulp-ISO white as defined by ISO whiteness (diffuse blue light reflectance) measurement method" Maximum color difference obtained using a method of calculating chromaticity from 10% or less and (III) the lightness index (L ^* ) and the perceptual chromaticity index (a ^* , b ^* ) at 10 cm × 10 cm square It has a region where ΔE ^* is 0.5 or less. Hereinafter, the surface on which the ink receiving layer is provided may be referred to as an inkjet recording surface, and the surface opposite to the surface on which the ink receiving layer is provided may be referred to as a back surface.

  The ink receiving layer contains only a nonionic color pigment as a colorant. Since the color pigment contains a black color pigment, the inkjet recording surface is colored black. The paint for forming the ink receiving layer (hereinafter referred to as the ink receiving layer paint) uses a strong ionic assistant such as an ink fixing agent, so that the ionic coloring pigment is likely to aggregate. , Causing uneven color.

  The color tone of the ink jet recording surface can be adjusted by the content of the black color pigment. The black inkjet recording sheet according to this embodiment contains 3.5 to 5.5% by mass of a black color pigment in the ink receiving layer with respect to the total solid content of the ink receiving layer. More preferably, it is 4.5-5.5 mass%. By setting this range, it is possible to increase the density of blackness that can be visually observed. Therefore, it is possible to obtain the printability of white ink, which has been limited in use. If the amount is less than 3.5% by mass, the density of blackness is insufficient, the difference in brightness from the printed portion due to the high brightness ink such as white is reduced, and the printed portion does not stand out. When it exceeds 5.5% by mass, the binding force of the binder is inhibited, and the strength of the coating layer is lowered. Further, the black coloring pigment becomes excessive, which is uneconomical.

  As the black color pigment, only a black color pigment exhibiting black alone may be used, but a chromatic color pigment can be appropriately added for the purpose of fine-tuning the color tone mainly using the black color pigment. . When the chromatic color pigment is added, the ratio of the chromatic color pigment in the color pigment in the ink receiving layer is preferably 0.17% by mass or less. More preferably, it is 0.10 mass% or less. Since the color tone can be finely adjusted, the color variations can be made abundant, and the color tone can be adjusted so as not to feel a chromatic color, a sheet on which white ink printing can be obtained can be obtained.

  Examples of the black coloring pigment include titanium black, carbon black, and iron black. As the chromatic coloring pigment, commercially available ones can be used as long as they are nonionic. The color of the chromatic color pigment is not particularly limited, and is, for example, blue or purple. Examples of the blue coloring pigment include cobalt blue, alkali blue, and phthalocyanine blue. Examples of the purple coloring pigment include cobalt violet and mineral violet.

The surface of the ink receiving layer has a lightness index (L ^* ) defined by JIS P 8150: 2004 “Paper and paperboard—Measurement method of color (C / 2 °) —Diffusion illumination method” of 20 ≦ L ^* ≦ 28, color The degree index (a ^* , b ^* ) is in the range of −0.4 ≦ a ^* ≦ 0.2 and −0.7 ≦ b ^* ≦ 0.3. The lightness index (L ^* ) is more preferably 22 ≦ L ^* ≦ 26, and the chromaticity index (a ^* , b ^* ) is more preferably −0.3 ≦ a ^* ≦ 0.1, − 0.6 ≦ b ^* ≦ 0.2. By setting it within this range, it is possible to increase the density of blackness with an achromatic color that allows the ink jet recording surface to be visually observed, and it is possible to make the printed portion of ink with high brightness such as white stand out. When 20> L ^* , white printing cannot be performed with white ink with a too dark background and poor concealment. When L ^* > 28, the density of blackness felt visually is low, and white printing cannot be performed. When −0.4> a ^* and a ^* > 0.2, a chromatic color is felt and white printing cannot be seen. When −0.7> b ^* and b ^* > 0.3, a chromatic color is perceived and white printing cannot be displayed.

  The surface of the ink receiving layer is equivalent to Bk (20) Black or Bk (10) Black in the Chamber of Commerce Color Coordination Chart: The Chamber of Commerce and Industry Color Coordination Chart (CCIC). Visual chromaticity. CCIC expresses color by a combination of tone and lightness, and is suitable for intuitive understanding of color. By setting the surface of the ink receiving layer to the above-described visual chromaticity, the degree of whiteness perceived by the eye is low, the density of blackness can be increased, and the printed portion by ink having high brightness such as white is conspicuous. Can be made.

In the present embodiment, (1) Lightness index (L ^* ) and chromaticity index (a ^* , stipulated in JIS P 8150: 2004 “Paper and paperboard—color (C / 2 °) measurement method—diffuse illumination method”) b ^* ) within the above range, or (2) the Chamber Color Coordination Chart: The Chamber of Commerce and Industry Color Coordination Chart (CCIC). Any one of (1) and (2) may be satisfied. (1) and (2) are almost equivalent visually.

  The surface of the ink receiving layer has an ISO whiteness of 10% or less as defined in JIS P 8148: 2001 “Paper, Paperboard and Pulp—Method of Measuring ISO Whiteness (Diffusion Blue Light Reflectance)”. More preferably, it is 8% or less. If it exceeds 10%, the density of blackness is insufficient, the difference in brightness from the printed portion due to the high brightness ink such as white becomes small, and the printed portion cannot stand out.

The surface of the ink receiving layer has a maximum color difference ΔE in a 10 cm × 10 cm square determined by a method of calculating from the lightness index (L ^* ) defined by JIS P 8150: 2004 and the perceptual chromaticity index (a ^* , b ^* ). ^It has a region where ^* is 0.5 or less. More preferably, it is 0.4 or less. When the maximum color difference ΔE ^* exceeds 0.5, the color unevenness increases and the commercial value decreases. In the sheet to be evaluated, no matter which area of the ink jet recording surface is set to a 10 cm × 10 cm square, the maximum color difference ΔE ^* is 0.5 or less. It is more preferable at the point which can do. ΔE ^* is the maximum value and the minimum value of each of the lightness index (L ^* ) and perceptual chromaticity index (a ^* , b ^* ) measured at an arbitrary n location in an arbitrarily set 10 cm × 10 cm square. It can obtain | require from Formula 4 using a difference. Specifically, for example, a 10 cm × 10 cm square is divided into a grid pattern with an interval of 2 cm, and 36 locations on the vertical and horizontal contacts are measured, and the lightness index (L ^* ) and perceptual chromaticity index (a ^* , b ^* ) are measured ^. ) Using the difference between the maximum value and the minimum value of each).

なお、数４において、インクジェット記録面の１０ｃｍ×１０ｃｍ角中における明度指数（Ｌ^＊）及び色度指数（ａ^＊、ｂ^＊）の各々の最大値をＬ^＊ｘ、ａ^＊ｘ、ｂ^＊ｘと表記し、各々の最小値をＬ^＊、ａ^＊、ｂ^＊と表記する。また、本実施形態において、測定機器は、分光式白色度計・色差計（商品名：ＳＰＥＣＴＲＯ ＣＯＬＯＲ ＭＥＴＥＲ、型式：ＭＯＤＥＬ ＰＦ−１０、日本電色工業社製）を用いて測定した。

In Equation 4, the maximum value of each of the lightness index (L ^* ) and chromaticity index (a ^* , b ^* ) in the 10 cm × 10 cm square of the inkjet recording surface is expressed as L ^* x, a ^* x, b ^* x. And the minimum value of each is expressed as L ^* , a ^* , b ^* . Moreover, in this embodiment, the measurement apparatus measured using the spectroscopic whiteness meter and the color difference meter (Brand name: SPECTRO COLOR METER, model: MODEL PF-10, Nippon Denshoku Industries Co., Ltd. make).

  Wood fibers used for coated support base paper (hereinafter referred to as base paper) include chemical pulp such as hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP), ground pulp, pressurized groundwood pulp, refiner groundwood pulp Wood pulp such as mechanical pulp such as thermomechanical pulp (TMP), chemimechanical pulp, chemiground pulp, and waste paper pulp such as deinked pulp. In the case of fresh bleached pulp, ECF pulp or TCF pulp is desirable in consideration of the environment. Considering quality aspects such as whiteness, ECF pulp is optimal.

  The pulp is a pulp slurry having an appropriate beating degree. The pulp beating degree of each layer is not limited in this embodiment, but is 350 to 600 ml CSF at Canadian standard freeness (freeness) (JIS P 8121: 1995 “Pulp Freeness Test Method”). It is preferable that More preferably, it is 400-570 ml CSF. If it is less than 350 ml CSF, since the fiber-to-fiber bond of the pulp becomes strong, the porosity decreases, and there is a tendency that the air resistance increases and the ink absorbability decreases. When it exceeds 600 ml CSF, the strength of the support is lowered, and paper dust is likely to be generated during guillotine cutting. In addition, there is a possibility that printing troubles such as generation of a pile due to fiber dropping and peeling of paper at the time of ink transfer may occur.

  In addition, one or more kinds of various papermaking chemicals such as conventionally known fillers, binders, sizing agents, fixing agents, yield improvers, and paper strength enhancers can be appropriately used in the pulp slurry as necessary. The method for preparing the pulp slurry, blending, and adding each papermaking chemical are not particularly limited as long as the effects of the present invention are not impaired. The prepared pulp slurry can be formed into a web using various paper machines such as a long net paper machine, a circular net paper machine, and a twin wire paper machine, and then dried to obtain a base paper. In particular, it is desirable to use a base paper excellent in ink absorbability.

  The base paper structure may be either a single layer or a multilayer. The design can be changed as appropriate according to the purpose. In the case of multiple layers, it is possible to have an asymmetric structure on both sides. In particular, in the case of three or more layers, by using waste paper pulp for the middle layer, environmental measures and cost reduction by recycling waste paper can be made possible. In addition, it is possible to manufacture the intermediate layer with various pigments / dyes to improve opacity. In addition, there is an advantage that post-processing suitability can be freely controlled by adjusting the addition ratio of the paper strength agent and filler in each layer.

  For the purpose of imparting strength, etc. on both sides of the base paper, use one or more of starch, polyacrylamide, polyvinyl alcohol, carboxymethylcellulose, etc. as a sizing agent using equipment such as a size press, gate roll, sizer, etc. It is good also as a support body by apply | coating the size liquid containing this.

  The fiber of the support is mainly made of wood fiber. It is preferable that the ratio of the wood fibers in the fibers in the dry mass of the support is 50% by mass or more. More preferably, it is 70 mass% or more. More preferably, it is 90 mass% or more. Most preferably, it is only wood fiber (100 mass%) as a fiber.

  The ink receiving layer contains synthetic silica as a pigment because of its high ink absorptivity. Synthetic silica may be contained alone, or two or more kinds may be blended and used in combination with other pigments. Other pigments that can be used in combination include calcined clay, colloidal silica, colloidal alumina, pseudoboehmite, aluminum hydroxide, alumina, magnesium carbonate, magnesium hydroxide, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, natural zeolite, and synthetic zeolite. , Light calcium carbonate, heavy calcium carbonate, hydroxyapatite, various intercalation compounds, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white and other white inorganic pigments, styrenic plastics Examples thereof include organic pigments such as pigments, acrylic plastic pigments, and various microcapsules. In addition, for the purpose of possessing multiple functions, a material in which pigment particles are used as seed particles and composite particles of different materials are formed by an aqueous precipitation method or a hydrothermal synthesis method, CVD (Chemical Vapor Deposition), PVD (Physical Vapor) Build different metal oxide composites by composite materials of different metal oxides obtained by surface treatment such as Deposition, MOCVD (Metal Organic CVD), MBE method (Molecular Beam Epitaxy), various ion exchange methods, sol-gel method, etc. Hybrid type pigment particles such as a material that is made up, a material in which an organic substance is chemically bonded to the surface of the inorganic pigment by various polymerization reactions, or a material that is physically mixed may be used as appropriate. You may use suitably the material which has as a main component the bioceramics formed by the manufacturing programming which DNA (deoxyribonucleic acid) has, or the inorganic substance accumulated by scaling. In addition, synthetic silica that is preferably used is a material whose surface structure has been altered using a physical technique such as plasma etching, or a material that has been surface modified using a mechanochemical reaction (substances other than water in water systems). If not, the number of hydroxyl groups on the surface of the synthetic silica increases.), Coupling agents, materials modified by various heat treatments (in this case, the number of hydroxyl groups on the surface of the synthetic silica decreases), etc. May be used according to the purpose. In addition, the various minerals described above may be any mineral as long as the desired performance is satisfied even if there is no description of natural or synthetic, and in the case of synthesis, the synthesis method is not particularly limited.

  In the present embodiment, the ink receiving layer contains polyvinyl alcohol and ethylene vinyl acetate resin as binders from the viewpoints of the absorbability and affinity of the inkjet ink. Polyvinyl alcohol includes modified polyvinyl alcohol. Here, when only polyvinyl alcohol is used, the print density is increased and the print quality is improved. However, depending on the humidity condition, the ink-receiving layer may be altered, and the water resistance is deteriorated accordingly. On the other hand, when only the ethylene vinyl acetate resin is used, although the water resistance is sufficient, the printing density does not increase and the printing quality cannot be ensured. Therefore, as a kind of binder, combined use of polyvinyl alcohol and ethylene vinyl acetate resin is desirable. Furthermore, it is possible to add a crosslinkable functional group to these molecular chains.

  The blending ratio of polyvinyl alcohol and ethylene vinyl acetate resin is 15:35 to 10:30 when the mass ratio of polyvinyl alcohol and ethylene vinyl acetate resin is 100 parts by mass of inorganic white pigment such as synthetic silica. It is preferable that More preferably, it is 14: 34-12: 32. When the ratio of polyvinyl alcohol is higher than this range, the water resistance may be inferior depending on the humidity conditions. On the other hand, if it is low, the print density does not increase and the desired print quality may not be ensured.

  Other binders can be used in combination with the ink receiving layer. Examples of binders that can be used in combination include cellulose derivatives such as hydroxyethyl cellulose and carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl pyridine, polyacrylamide, polyethylene oxide, polypropylene oxide, starch, and modified starch (including physical latex modified biolatex). Water-soluble binder such as polyacrylic acid, sodium polyacrylate, ethyl polyacrylate, sodium alginate, polystyrene sulfonate soda, casein, gelatin, terpene, polyethylene, polypropylene, polyisobutylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, Polyvinyl acetate, polyvinyl acetal, polymethyl methacrylate, polyacrylonitrile, polytetrafluoroethylene, polyvinyl fluoride Den, polybutadiene, polyisoprene, polychloroprene, nylon, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyacetal, polybischloromethyloxacyclobutane, polyphenylene oxide, polysulfone, poly-P-xylylene, polyimide, polybenzimidazole, phenol resin , Urea resin, melamine resin, epoxy resin, alkyd resin, unsaturated polyester resin, diallyl phthalate resin, styrene-butadiene copolymer, modified styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, methyl methacrylate-butadiene copolymer Polymer, acrylic acid ester-methacrylic acid ester copolymer, vinyl acetate-maleic acid ester copolymer, vinyl acetate-acrylic acid Alcohol copolymer, ethylene - vinyl acetate - can be exemplified a urethane resin binder is an emulsion-type binder, or emulsion-type acrylic copolymer. The degree of polymerization, the degree of saponification, Tg (glass transition temperature), MFT (minimum film-forming temperature), etc. of these binders are not limited. In addition, two or more of the above-mentioned binders may be blended and used, or various polymers and monomers may be used in combination in addition to being physically mixed. In addition to the modification of the functional group, modification by electromagnetic waves (including radiation and light), electrical energy, thermal energy, mechanical energy (including sound waves), magnetism, and organisms may be performed. Furthermore, an engineering polymer, a biopolymer, an ion exchange resin, or the like that responds to various energies may be appropriately applied depending on the purpose. And the synthesis method of the binder shown above is not particularly limited.

  When other binders are used in combination with polyvinyl alcohol and ethylene vinyl acetate resin, the total content of polyvinyl alcohol and ethylene vinyl acetate resin is 90% of the total content of all binders contained in the ink receiving layer. It is preferable to set it as mass% or more. More preferably, it is 100 mass%.

  The ink receiving layer contains 40 to 60 parts by mass of the binder with respect to 100 parts by mass of the synthetic silica. More preferably, it is 45-55 mass parts. If it is less than 40 parts by mass, the strength of the coating layer becomes weak, the coating layer falls off or wears out, and there is concern about the quality after printing and the durability of the printed product. When it exceeds 60 parts by mass, the ink absorbability is inferior.

  In the black ink jet recording sheet according to the present embodiment, the ink receiving layer preferably further contains a cationic resin as an ink fixing agent in order to improve the fixability and color developability of the ink jet ink. Examples of cationic resins include polyethyleneimine, epichlorohydrin-modified polyalkylamine, polyamine polyamide epichlorohydrin, dimethylamine ammonia epichlorohydrin, polyvinylbenzyltrimethylammonium halide, polydiacryldimethylammonium halide, polydimethylaminoethyl methacrylate hydrochloride, polyvinylpyridium halide, cation Polystyrene copolymer, diallyldimethylammonium chloride polymer, diallyldimethylammonium chloride sulfur dioxide copolymer, diallyldimethylammonium chloride amide copolymer, dicyandiamide formalin polycondensate, dicyandiamide diethylenetriamine polycondensate, polyallylamine, polyallylamine hydrochloride Salt, polyacrylic Bromide resins, polyamide epoxy resins, melamine resins acid colloids, urea-based resins, cation-modified polyvinyl alcohol, amino acid type amphoteric surfactants, betaine type compounds, other quaternary ammonium salts, polyamines and the like can be exemplified. Two or more kinds of ink fixing agents may be blended in order to obtain desired performance. Then, those having the same chemical composition or different molecular weights may be blended. Further, not only physically mixing, but also chemical combination may be used while changing the combination of the constituents of copolymerization. Furthermore, for the purpose of enhancing the water resistance of the ink-jet ink, those having a higher degree of cationization and those having a reduced degree of cationization for the purpose of enhancing light resistance may be used as appropriate.

  In addition to pigments, binders, and colorants, the ink receiving layer may further include a dispersant, an antifoaming agent, a pH adjusting agent, a wetting agent, a water retention agent, a viscosity adjusting agent, a crosslinking agent, a release agent, Preservatives, softeners, waxes, antistatic agents, antistatic agents, sizing agents, waterproofing agents, plasticizers, fluorescent whitening agents, reducing agents, UV absorbers, antioxidants, fragrances, deodorants, flameproofing agents Auxiliaries such as repellents and rust preventives can be contained as long as the effects of the present invention are not impaired. Furthermore, various medicinal components, essential oil components, antibacterial agents, various enzymes, and the like can be used within the range that does not impair ink jet printing suitability for non-medical use. In addition to a simple physical mixture, those forms may be appropriately selected from encapsulated or chemically bonded types by reactive functional group introduction, or encapsulated composite materials inside the resin by polyion complexes. Appropriately chosen. Moreover, it is not specifically limited about the process and method of adding these, for example making it contain in a silica slurry or making it contain in a binder.

  The ink receiving layer may be provided only on one side of the support or on both sides. When the ink receiving layer is provided only on one side, the support may be exposed on the surface opposite to the surface on which the ink receiving layer is provided, pencil writing property, water / oil-based ballpoint pen suitability, crayon writing property Furthermore, water- and oil-based paint absorption suitability, print print suitability, and stamping suitability may be imparted. Further, as listed below, various types of coatings for various purposes may be appropriately applied according to the purpose. For example, a non-pigment paint may be applied for the purpose of curling. In order to give the ink-jet suitability of the water-based ink, for example, a paint having high absorbability combining synthetic silica, polyvinyl alcohol, and an ethylene vinyl acetate polymer may be applied. Among ink jet aptitudes, in particular, a paint containing a resin such as acrylic resin, ester resin, styrene butadiene latex, acrylonitrile latex, chloroprene latex may be applied so as to be suitable for solvent ink or UV ink. I do not care. In order to give thermal transfer recording suitability or gravure printing suitability, for example, a paint having a heat insulating property, a high surface smoothness and a high cushioning property combining calcium carbonate, clay, organic pigment, and synthetic silica is applied. It doesn't matter. In order to impart toner fixing properties, paints that combine various binders with high affinity with toner and appropriate dielectric constant, various pigments with high thermal insulation, and various electrolytes are applied. You can work. In order to impart general offset sheet-fed printing suitability, for example, a paint combining calcium carbonate, clay, and styrene butadiene latex may be applied. Moreover, in order to give the offset rotary printing aptitude which heat set is in process, you may apply the coating material containing the latex which has heat resistance, a printing aptitude improving agent, etc. In order to impart pressure-sensitive adhesiveness, a paint containing natural rubber or the like may be applied. Further, as a special application, a heat sensitive color developing layer, a pressure sensitive color developing layer, a photosensitive color developing layer, or the like may be provided. Furthermore, for the purpose of dealing with squeezing out, etc., various phosphorus having self-extinguishing properties and flame retardancy, and a compound containing an inert substance may be impregnated. In addition, in order to impart functions other than the recording suitability, various functional chemicals and materials can be appropriately applied.

  In the preparation of paints and various treatment solutions, the use and handling of chemicals that are harmful or dangerous to the human body should be avoided as much as possible. However, as much as possible, selection of chemicals that are less harmful is a prerequisite. Therefore, it is the best choice if it is a chemical that decomposes easily in the natural environment and does not release harmful substances after decomposition. It is not wise to select chemicals to be used, such as those that are extremely chemically modified that do not exist in nature, or substances that have a considerably advanced degree of polymerization. In addition, selection of chemicals that have good handling and good workability such as easy dissolution, dispersion, or mixing can be a very important item in the manufacturing process. In addition to work efficiency and harmfulness, it is also important to use trouble-free and safe chemicals.

  At the time of preparing the ink receiving layer coating material, there is a step of mixing various chemicals, but the production efficiency varies depending on the stirring method. It also affects not only the efficiency but also the physical properties of the paint. In general, paint preparation in the paper industry is batch and not continuous. In the method for producing a black ink jet recording sheet according to the present embodiment, the coating preparation method is preferably a batch method. In batch mode, the next chemical is added after mixing is completely achieved in each process, so the order of addition of various chemicals is set to the prescribed conditions to minimize contact between chemicals that tend to aggregate. Can do. As a result, production efficiency can be improved, and further, physical properties of the paint can be prevented from being lowered. Further, it is desirable that the required time per batch is a minimum necessary short time. Furthermore, various efficiencies change depending on the stirring conditions including the shape and size of the stirring tank, the stirrer in the shape of a bar / plate / propeller, and the difference in peripheral machines such as baffles. In order to achieve complete mixing at the time of preparing the paint, it is preferable that the stirring tank has a shape ratio shown below. That is, the diameter of the stirring tank interior is D (m), the liquid level is H (m), the diameter of the stirring bar is d (m), and the height from the bottom of the stirring tank to the center of the stirring bar is h (m ), D / D (−) is set to 3.0 / 7.5 to 5.0 / 5.5, and h / H (−) is set to 1.0 / 9.0 to 3.0 / 7. 0.0 and H / D (−) is preferably 7.0 / 7.5 to 9.0 / 5.5. The stirring condition is preferably within a range of 2.8 to 9.4 (km / hr), which is a value obtained by multiplying the peripheral speed of the stirrer by the radius and angular velocity of the stirrer. Examples of the shape of the stirring bar include a propeller type, a turbine type, an anchor type, a saddle type, a planet type, a screw type, a ribbon type, an intensive type, and a helical ribbon type. The diameter and shape of the stirrer of the stirrer are not particularly limited as long as the entire paint can be uniformly stirred.

  In general, in the production of an ink jet recording sheet, an expensive paint is applied to the surface of the sheet, so that the production cost is higher than that of a general printing sheet. In addition, the components of the paint may include those having high reactivity and poor dispersibility. When such components are included, it takes time to prepare the paint. Since the manufacturing cost also depends on the manufacturing time, the extension of the preparation process time may promote the cost increase. When preparing a coating for the ink receiving layer, depending on the rate at which the chemicals are added, the order of addition, etc. Occurs and preparation becomes difficult. Moreover, since the coating material which caused such a trouble has impaired the applicability of application, when it is applied, the control of the appropriate application amount becomes poor and uneven coating occurs. On the obtained coated surface, defects such as poor smoothness occur, and post-processing suitability such as ink jet printing, printing, various cuttings, blister pack processing, etc. becomes inferior, and the commercial value may be lost. Therefore, when preparing the paint, the order of addition and the rate of addition of various chemicals must be taken into consideration. In particular, in the present embodiment, since the ink receiving layer is colored black, color unevenness is easy to understand. Moreover, since most of the black pigments reduce the strength of the coating layer, utmost care must be taken not to cause agglomeration of the paint. Furthermore, in the state in which complete mixing is achieved, the subsequent stirring becomes a snake foot, which not only wastes time-dependent manufacturing costs, but also accounts for the required power cost of an extra rotating body, which is economical. Is not a preferred state.

  In the preparation of paints, chemicals whose pH changes greatly when injected, chemicals that significantly change the imbalance between hydrophilicity and hydrophobicity that have a hydrophobic field effect, and steric hindrance such as molecular chains When using chemicals or chemicals that cause a viscosity increase caused by a relatively weak moment force due to dielectric action, the order of charging, the charging speed, and the timing of charging become important management items. As the number of charges, pH, etc. change greatly, a phenomenon in which the viscosity of the paint changes greatly is observed (in most cases, the viscosity tends to increase), especially when the degree of increase in viscosity exceeds the limit. And subsequent preparation becomes difficult. Even if the coating can be performed, the coating surface becomes rough or the strength of the coating layer becomes weak, and the influence cannot be ignored. In particular, the coating layer strength tends to decrease as the amount of the color pigment added increases. When the paint is in an aggregated state, it adversely affects the formed coating layer. Further, when the color pigments are aggregated, the color unevenness becomes remarkable. Compared to other colors, black is more likely to have uneven color and has a higher probability of being a defective product. However, if the porous structure of the formed coating layer is not properly maintained, ink absorptivity of ink jet is not sufficient, but soft aggregation (light aggregation) is necessary. Here, there is a case where such a phenomenon can be improved by delaying the charging time of the chemical to some extent, but if the charging time is too long, unnecessary energy is consumed, and the production speed is reduced. Since it drops, it is not preferable in terms of economy.

  FIG. 1 shows a model of the flow of preparing the ink receiving layer coating material. The method for producing a black inkjet recording sheet according to the present embodiment includes synthetic silica as a pigment, polyvinyl alcohol and ethylene vinyl acetate resin as a binder, a cationic resin as an ink fixing agent, and a nonionic black system as a colorant. A method for producing a black ink jet recording sheet, wherein a paint containing a coloring pigment as an essential component is applied to at least one surface of a support mainly composed of wood fibers to provide one or more ink-receiving layers. The coating material for forming the ink receiving layer contains 40 to 60 parts by mass of the binder with respect to 100 parts by mass of the synthetic silica, and 3% of the total solid content of the coating material of the black color pigment. The synthetic silica is contained in a silica slurry dispersed in water, as shown in FIG. In addition, among the essential components, the polyvinyl alcohol is added and mixed at least before the ethylene vinyl acetate resin and the cationic resin, and the addition rate of the cationic resin is based on 1000 L of the silica slurry. Less than 40 L / min.

  In the method for producing a black ink jet recording sheet according to this embodiment, in preparing the ink receiving layer coating material, first, the synthetic silica to be contained as a pigment in the ink receiving layer is a silica slurry dispersed in water. The silica slurry can be obtained by blending synthetic silica and water and using a known disperser. At the time of dispersion, it is preferable to add a pH adjuster in addition to the synthetic silica and water. Examples of the pH adjuster include acetic acid, formic acid oxalic acid, and tartaric acid. A known disperser is, for example, a cowless disperser.

  Next, at least polyvinyl alcohol is added to the silica slurry prior to the ethylene vinyl acetate resin and the cationic resin and mixed. Since the surface of the synthetic silica in the silica slurry is anionic, contact between the synthetic silica and the cationic resin causes aggregation and thickening, and this adversely affects the coating preparation and the coating layer obtained. By adding polyvinyl alcohol first, the polyvinyl alcohol protects the surface of the synthetic silica, and even if a cationic resin is added next, aggregation and thickening hardly occur. On the other hand, when ethylene vinyl acetate resin comes into contact with synthetic silica, it tends to cause aggregation and thickening. Although the mechanism is unknown, by adding polyvinyl alcohol first, polyvinyl alcohol protects the surface of the synthetic silica, and even when ethylene vinyl acetate resin is added next, aggregation and thickening hardly occur.

  Various chemicals such as polyvinyl alcohol, ethylene vinyl acetate resin, cationic resin, and black color pigment to be added to the silica slurry in the preparation of the ink-receiving layer coating are used in the form of an aqueous solution or It is preferable to add as a dispersion. In this embodiment, a 10% polyvinyl alcohol aqueous solution, an aqueous dispersion of an ethylene vinyl acetate resin having a solid concentration of 50% by mass, and an aqueous dispersion of a cationic resin having a solid concentration of 30% by mass are used. Is not limited to the concentration of the aqueous solution or aqueous dispersion.

  At the time of preparing the ink-receiving layer paint, the time from the beginning to the end of the addition of each chemical, that is, the charging time is t (minutes), and the chemical loading is V (L). Was defined by Equation 5.

(Equation 5) V _n / t _n
In Equation 5, n is a positive integer of 1 to 3, and corresponds to the addition steps 1 to 3 in FIG.

  It can be said that the smaller the value of the chemical addition rate obtained in Equation 5, the shorter the manufacturing time and the better the economy. On the contrary, the larger the value of the addition rate, the longer the production time, and the lower the cost. Therefore, in manufacturing the recording sheet, the recording sheet can be manufactured economically by managing the value of the addition rate as an economic index. However, as described above, in the case of chemicals that have a large effect on the liquid properties of the paint, such as chemicals that greatly change the pH, if the rate of addition is too high, the physical properties of the subsequent paint will be adversely affected. There is a need.

  When the cationic resin is added, the pH of the paint greatly changes. Therefore, if the addition speed is too fast, the physical properties of the paint may be adversely affected, for example, the viscosity of the paint may be greatly increased. Therefore, in the method for producing a black inkjet recording sheet according to this embodiment, the addition rate of the cationic resin is set to less than 40 L / min with respect to 1000 L of silica slurry. More preferably, it is less than 39 L / min. Moreover, it is preferable that the addition rate of a cationic resin exceeds 5 L / min with respect to 1000 L of silica slurries. More preferably, it is over 20 L / min, and particularly preferably over 30 L / min. At 5 L / min or less, the reaction with the silica slurry and the previously added chemical is slow, but the generated agglomeration cannot be dispersed, and the above-mentioned adverse effects may be exerted on the paint and the coating layer. In addition, it is possible to suppress a significant increase in the viscosity of the paint, and it is possible to improve the paint liquid property and the physical properties of the coated surface. It is an economy. On the other hand, if it is 40 L / min or more, the viscosity of the coating material is greatly increased, the time required for complete mixing is extended, and the amount of electric power consumed is uneconomical. In addition, when the viscosity increases so that it cannot be completely mixed, the above-mentioned adverse effects are exerted on the paint and the coating layer.

  In the method for producing a black inkjet recording sheet according to the present embodiment, it is preferable that the addition rate of polyvinyl alcohol exceeds 20 L / min with respect to 1000 L of silica slurry. More preferably, it is over 30 L / min. Since consumption of unnecessary energy can be suppressed without reducing the production speed, it can be manufactured more economically. However, since there is a possibility of aggregation, it is preferable that the upper limit value of the addition rate should not exceed 40 L / min.

  In the method for producing a black inkjet recording sheet according to the present embodiment, the addition rate of the ethylene vinyl acetate resin preferably exceeds 20 L / min with respect to 1000 L of silica slurry. More preferably, it is over 30 L / min. Since consumption of unnecessary energy can be suppressed without reducing the production speed, it can be manufactured more economically. However, since there is a possibility of aggregation, it is preferable that the upper limit value of the addition rate should not exceed 40 L / min.

As described above, in preparing the paint, it is necessary to set the degree of change in the viscosity of the paint (increase or decrease in viscosity, particularly increase in viscosity) to an appropriate range. This is important in that the physical properties of the layer can be improved. Therefore, in the method for producing a black ink jet recording sheet according to the present embodiment, each chemical obtained by using the B-type viscosity at 60 rpm and the respective volume under 20 ° C. condition of each chemical alone constituting the paint is added. When the theoretical volume average viscosity η _{average calc. n} and measured value η _obs. of viscosity when each chemical is added _{. The} amount of difference Δη _n from _n was managed as an index of the degree of interaction such as chemical reaction between chemicals. In the preparation of the ink-receiving layer coating material, when the order of addition of the chemicals to the silica slurry is n, the single viscosity of the chemicals measured for B-type viscosity at 60 rpm under 20 ° C. is η _n and the volume is V _n is the theoretical volume average viscosity η _{average calc. n} is generalized by Equation 6. It should be noted that complete mixing is assumed when measuring physical properties.

( _Equation 6) η _{average calc. n} = [(η ₁ × V ₁ ) + (η ₂ × V ₂ ) +... + (η _n / V _n )] / (V ₁ + V ₂ +... + V _n ) = Σ (η _n × V _n ) / ΣV _n

The measured B-type viscosity at 60 rpm under the condition of 20 ° C. when the nth chemical was added was η _{obs. n,} and η _{obs. n} and η _{average calc. The} amount of difference Δη _n from _n was used as an index positioned as the degree of interaction such as chemical reaction between chemicals, and was defined by Equation 7.

(Equation 7) Δη _n = η _{obs. n-} η _{average calc. n}
In Equation 7, n is a positive integer and indicates the order in which the chemical is added.

Explaining using the flow model of FIG. 1, the paint is measured viscosity η _obs measured by measuring B-type viscosity at 60 rpm under the condition of 20 ° C. of a primary mixture obtained by adding polyvinyl alcohol to silica slurry and mixing them thoroughly. _{. 1} is a theoretical values calculated from the number 1 volume average viscosity eta _{average calc. 1} difference amount .DELTA..eta ₁ with, | .DELTA..eta _{1 |} <a 700 mPa · s, and was mixed thoroughly by adding one of the primary mixing ethylene vinyl acetate-based to liquid resin or a cationic resin No. Measured viscosity η _obs. Measured for B-type viscosity at 60 rpm under the condition of 20 ° C. of the secondary mixture _{. 2} is a theoretical values calculated from the number 2 volume average viscosity eta _{average calc.} Difference amount .DELTA..eta ₂ with _2, | .DELTA..eta _{2 |} <a 700 mPa · s, and was mixed thoroughly by adding the other of the second mixing ethylene vinyl acetate-based to liquid resin or a cationic resin No. Measured viscosity η _obs. Measured for type B viscosity at 60 rpm under 20 ° C. condition of the tertiary mixture _{. The} volume average viscosity η _{average calc. 3} and the difference amount .DELTA..eta ₃ of, | is preferably <is 700mPa · s | Δη _3.

( _Equation 1) η _{average calc. 1} = (η ₁ × V ₁ ) / V ₁
( _Equation 2) η _{average calc. 2} = {(η ₁ × V ₁ ) + (η ₂ × V ₂ )} / (V ₁ + V ₂ )
( _Equation 3) η _{average calc. 3} = {(η ₁ × V ₁ ) + (η ₂ × V ₂ ) + (η ₃ × V ₃ )} / (V ₁ + V ₂ + V ₃ )
In Equations 1, 2, and 3, η ₁ [mPa · s] is the viscosity of a 10% aqueous solution of polyvinyl alcohol obtained by measuring B-type viscosity at 60 rpm under 20 ° C., and V ₁ [L] is It is the addition amount of the polyvinyl alcohol aqueous solution. η ₂ [mPa · s] is an aqueous dispersion of an ethylene vinyl acetate resin having a solid content concentration of 50% by mass or a cationic resin water having a solid content concentration of 30% by mass, as measured for B-type viscosity at 60 rpm under 20 ° C. V ₂ [L] is the added amount of either an aqueous dispersion of ethylene vinyl acetate resin or an aqueous dispersion of cationic resin. η ₃ [mPa · s] is an aqueous dispersion of an ethylene vinyl acetate resin having a solid content concentration of 50% by mass or a cationic resin having a solid content concentration of 30% by mass, which was measured for B-type viscosity at 60 rpm under 20 ° C. V ₃ [L] is the added amount of either the aqueous dispersion of ethylene vinyl acetate resin or the aqueous dispersion of cationic resin. Hereinafter, Δη ₁ , Δη _2, and Δη ₃ may be collectively referred to as Δη _n .

When polyvinyl alcohol is added to the silica slurry and then a cationic resin is added, η ₂ [mPa · s] is the viscosity of the aqueous dispersion of the cationic resin having a solid content concentration of 30% by mass alone. Yes, V ₂ [L] is the amount of cationic resin aqueous dispersion added. η ₃ [mPa · s] is the viscosity of an aqueous dispersion of ethylene vinyl acetate resin having a solid content concentration of 50% by mass, and V ₃ [L] is the amount of addition of the aqueous dispersion of ethylene vinyl acetate resin. It is. In addition, when ethylene vinyl acetate resin is added next to polyvinyl alcohol, η ₂ [mPa · s] is the viscosity of an aqueous dispersion of ethylene vinyl acetate resin having a solid concentration of 50% by mass. , V ₂ [L] is the amount of ethylene vinyl acetate resin aqueous dispersion added. η ₃ [mPa · s] is the viscosity of the aqueous dispersion of the cationic resin having a solid content concentration of 30% by mass, and V ₃ [L] is the addition amount of the aqueous dispersion of the cationic resin.

The viscosity of the chemical alone measured for B-type viscosity at 60 rpm under 20 ° C. is η _n and the theoretical volume average viscosity η _{average calc.} The difference amount Δη _n and _n is, more preferably, | a <650mPa · s | Δη _n. When | Δη _n | ≧ 700 mPa · s, since the viscosity change of the paint is large, it may be difficult to maintain the state of the paint in a state suitable for coating.

  In the preparation of the ink receiving layer coating material, the timing of adding the colorant is not limited as long as the effects of the present invention are exhibited. For example, it may be added and dispersed together with synthetic silica when preparing the silica slurry, or may be added to the prepared silica slurry. When added to the prepared silica slurry, it may be added before polyvinyl alcohol, ethylene vinyl acetate resin or cationic resin, which are other essential components, or after polyvinyl alcohol. Moreover, you may add, after adding another essential component.

  In the case where the coating layer is adjusted to a color tone that feels black with visual sensation, the paint needs to be colored with a certain threshold or more. In general, coating methods include a flattening coating method such as a rod coater and a blade coater, and a contour coating method such as an air knife coater. If the coloration is below a certain threshold, the flattening coating method may cause a difference in color density due to the amount of coating caused by irregularities on the surface of the base paper to be coated, impairing the product color uniformity. There is. In the contour coating method, a wind pattern may occur. On the other hand, although the coating amount is constant with respect to the base paper, there is a case in which a difference in tightness is caused by a calendar process or the like, and the unevenness of the unevenness of the base is felt visually. As described above, coloring the paint at a certain threshold value or more is an effective means for ensuring the uniformity of the product surface. The black inkjet recording sheet according to the present embodiment contains 3.5 to 5.5% by mass of the black color pigment in the ink receiving layer with respect to the total solid content of the ink receiving layer. Coloring can be realized.

  The coating method of the ink receiving layer coating is not particularly limited in the present embodiment, and a known general coating machine can be used. Known general coating machines include, for example, blade coaters, roll coaters, air knife coaters, rod coaters, lip coaters, curtain coaters, spray coaters, die coaters, chipless coaters, chip blade-coaters, and spin coaters on a lab scale. It is. Further, at the time of coating, any of normal pressure, reduced pressure, and pressurized may be selected for the purpose of controlling the coating layer structure.

The dry coating amount per side of the ink receiving layer is preferably 5 to ²⁰ g / m ² . More preferably 10 to 15 g / ^{m 2.} If it is less than 5 g / m ² , it is difficult to completely cover the surface of the support with a paint, ink absorption by the coating layer becomes insufficient, and uneven absorption may occur. On the other hand, if the dry coating amount exceeds 20 g / m ² , the adhesive strength between the ink receiving layer and the support may be at a level that cannot be practically used. The construction layer may fall off or peel off, which may be a serious problem. Even if the ink absorbency is excellent, troubles in the subsequent post-processing may cause a great economic loss in addition to losing the trust of the customer. Alternatively, the ink receiving layer coating may be applied two or more times to form two or more ink receiving layers.

  As the coating method, there are an off-machine coating machine in a separate process from the paper machine and an on-machine coating machine attached to the paper machine. In this embodiment, it is desirable to be on-machine. For example, when used as a postcard paper, a clear solution prepared with a water-soluble polymer or the like may be applied to the back surface in order to impart suitability as an address surface. At this time, a base paper with a low degree of coloration is made on-machine as a support, and then a size liquid is applied to both sides with a size press, and a coating for the ink receiving layer is applied to the surface to be a communication surface of the obtained support. And it can be produced efficiently by continuously applying the clear liquid on the opposite surface. When changing colors, it can be done by simply replacing each paint. Off-coating where coating is performed with an off-machine coating machine causes a loss of time such as downtime at the time of frame change. To do. Therefore, the pursuit of profit, which is the main purpose of production, becomes insufficient. Furthermore, the probability of product defects such as contamination of foreign matters such as insects and contamination in the process increases, and a reduction in the finishing rate of the product is inevitable. In addition, when performing in-process quality assurance, there are disadvantages in that the number of items to be controlled increases, which places a burden on the tester and further increases the number of personnel.

  Examples of the drying method after coating include hot air drying, infrared drying, and drum drying, but are not particularly limited in the present embodiment. For the purpose of binder migration and / or control of the coating layer structure, drying conditions such as drying temperature, drying temperature gradient, and drying time may be appropriately changed and applied.

  In addition, for the purpose of controlling the smoothness of the surface of the ink receiving layer, a calendar process may be performed as necessary. Examples of the calendar process include a super calendar, a machine calendar, and a soft calendar. It is also possible to arrange a humidifier or the like in the process before and after the calendar. The calendar arrangement may be either a vertical type or a horizontal type, and as long as desired physical properties are obtained, the number of stacks in the vertical type or the number in the horizontal type is not limited at all. In addition, processing conditions such as processing speed, processing temperature, processing pressure, and hardness / roughness of the roll surface are also appropriately selected. As with coating, it is desirable to perform on-machine because of its many economic advantages. Performing the calendering process off-machine, as with off-coating, causes time loss such as downtime at the time of frame change, and in the actual work, the total process time becomes longer and the energy consumption is reduced. A loss will also be recorded. Therefore, the pursuit of profit, which is the main purpose of production, becomes insufficient. Furthermore, the probability of product defects such as contamination of foreign matters such as insects and contamination in the process increases, and a reduction in the finishing rate of the product is inevitable. In addition, when performing in-process quality assurance, there are disadvantages in that the number of items to be controlled increases, which places a burden on the tester and further increases the number of personnel.

  Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. Further, “parts” and “%” in the examples represent “parts by mass” and “% by mass”, respectively, unless otherwise specified. The number of added parts is a value in terms of solid content.

Example 1
<Preparation of base paper>
To a pulp slurry of 100 parts of LBKP (Canadian standard freeness of 500 ml CSF), 1.00 parts of cationic starch (trade name: Neotac 40T, manufactured by Nippon Food Processing Co., Ltd.) and talc (trade name: trade name: NTL, manufactured by Nippon Talc Co., Ltd.) 5.00 parts, acidic rosin sizing agent (trade name: AL1203, manufactured by Seiko PMC Co., Ltd.) 0.200 parts, and liquid sulfuric acid band 1.00 parts are provided to obtain a paper material. It was. The obtained paper stock was paper-made with a long net paper machine to obtain a base paper having a basis weight of 180 g / m ² .

<Preparation of support by size press application>
Subsequently, a 6% solid concentration aqueous solution of oxidized starch (trade name: Oji Ace A, manufactured by Oji Constarch Co., Ltd.) as a sizing solution on the base paper is dried by a size press so that the dry coating amount is 1.5 g / m ² per side. It was coated on both sides with an on-machine and dried with a cylinder dryer to obtain a support.

<Preparation of paint for ink receiving layer>
50.0 parts of synthetic amorphous silica (trade name: Silojet P407, manufactured by Grace Devison) as an pigment and synthetic amorphous silica (trade name: Cyloid 74X6500, Grace Devison) having an average particle diameter of 6 μm as pigments 50.0 parts of water) and 0.500 parts of acetic acid as a pH adjuster were blended, and a silica slurry having a solid content concentration of 28% was prepared with a Cowles disperser. 15.0 parts of polyvinyl alcohol (trade name: PVA-117, manufactured by Kuraray Co., Ltd.) as a binder in this silica slurry, and cationic resin (trade name: Sumirez Resin SR1001, manufactured by Sumitomo Chemical Co., Ltd.) 15.0 as an ink fixing agent Parts, 35.0 parts of ethylene vinyl acetate resin (trade name: Sumikaflex 401, manufactured by Sumitomo Chemical) as a binder, and black color pigment (trade name: TB510 BlackTR, manufactured by Dainichi Seika Co., Ltd.) 9.00 as a colorant. The ink receiving layer coating material having a solid content concentration of 25% was obtained by sequentially adding and stirring the parts. In the preparation of the ink-receiving layer coating material, it is basic to add one chemical and mix thoroughly, and then add the next chemical. Stirring was interrupted and the following chemicals were added.

In the preparation of the ink-receiving layer coating material, the stirring tank and the stirring conditions are as shown in the shape ratio shown below. As described above, the stirring tank has a diameter D (m) inside the stirring tank, a liquid level height H (m), a diameter of the stirring bar d (m), and from the bottom of the stirring tank to the center of the stirring bar. When the height is h (m),
d / D (-): 3.0 / 7.5 to 5 / 5.5
h / H (-): 1.0 / 9.0 to 3.0 / 7.0
H / D (-): 7.0 / 7.5 to 9.0 / 5.5
However, in this embodiment,
d / D = 4.0 / 6.5
h / H = 2.0 / 8.0
H / D = 8.0 / 6.5
It was. In addition, it is the conditions which do not consider the fluctuation | variation of the value by the liquid holdup at the time of stirring. In addition, as described above, the stirring condition is performed within the range of 2.8 to 9.4 (km / hour), which is a value obtained by calculating the peripheral speed of the stirrer by the radius and the angular velocity of the stirrer. Although it is preferable, in this example, it was set to 4.7 (km / hour).

  In the preparation of the ink-receiving layer coating material, a method for visualizing the flow under a scale-down condition in which the shape ratio was maintained in advance was used as a method for determining complete mixing during stirring. That is, when adding polyvinyl alcohol, ethylene vinyl acetate resin or cationic resin under scale-down conditions, nonionic dye is added at the same time, and the state in which the color of the dye is uniformly dispersed is visually judged as a completely mixed state The time from the start of addition to the time when the color of the dye was uniformly dispersed was defined as the time required for complete mixing, and this time was applied to the stirring time when preparing with an actual machine. As a nonionic dye, Black CN Liquid manufactured by Nippon Kayaku Co., Ltd. was used.

  Moreover, the addition rate (V / t) calculated | required from the number 5 of the cationic resin was 39 L / min with respect to 1000 L of silica slurries. The addition rate of other chemicals was 22 L / min with respect to 1000 L of silica slurry.

<Formation of ink receiving layer>
The obtained ink-receiving layer coating composition was then applied on-machine using an air knife coater so that the dry coating amount was 10 g / m ^{2 on the} surface to be the inkjet recording surface of the support. The ink receiving layer was formed by drying with hot air using a dryer.

<Smoothing process>
Subsequently, using a soft calender on-machine, surface treatment was performed under the conditions of a linear pressure of 30 kg / cm, 25 ° C., and 2 nips and 1 pass to prepare a black ink jet recording sheet. Here, the brightness (hereinafter referred to as L ^* ), chromaticity (hereinafter referred to as a ^* , b ^* ), ISO whiteness, and chamber color coordination chart (hereinafter referred to as CCIC) of the ink jet recording surface. .) Was as follows. In addition, L ^* , a ^* , b ^* and ISO whiteness of the ink jet recording surface are spectroscopic whiteness meter / color difference meter (trade name: SPECTRO COLOR METER, model: MODEL PF-10, manufactured by Nippon Denshoku Industries Co., Ltd.) It measured using. CCIC used the Chamber of Commerce Color Coordination Chart (CCIC) to judge and evaluate the color sense values.
L ^* : 22.0, a ^* : 0.14, b ^* : -0.20, ISO whiteness: 4.91, CCIC: Bk (10) Black equivalent

(Example 2)
In Example 1, a black inkjet recording sheet was prepared in the same manner as in Example 1 except that the black color pigment was reduced 2/3 times to 6.00 parts in the preparation of the ink-receiving layer coating material. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were as follows.
L ^* : 26.76, a ^* : 0.16, b ^* : -0.03, ISO whiteness: 7.17, CCIC: equivalent to Bk (20) Black

(Example 3)
In Example 1, except that 0.015 part of a violet pigment (trade name: TB1500 Violet 3R, manufactured by Dainichi Seika Co., Ltd.) was added in the preparation of the ink-receiving layer coating material. A recording sheet was prepared. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were as follows.
L ^* : 21.7, a ^* : -0.21, b ^* : 0.21, ISO whiteness: 5.24, CCIC: equivalent to Bk (10) Black

(Example 4)
In Example 1, except that 0.0008 part of a blue pigment (trade name: TB520 Blue 2B, manufactured by Dainichi Seika Co., Ltd.) was added in preparation of the ink-receiving layer coating material, black ink jet ink was applied. A recording sheet was prepared. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were as follows.
L ^* : 21.8, a ^* : 0.12, b ^* : -0.57, ISO whiteness: 5.29 CCIC: Bk (10) Black equivalent

(Example 5)
In Example 1, a black ink jet recording sheet was prepared in the same manner as in Example 1 except that the addition rate of the cationic resin was changed to 6 L / min in the preparation of the ink-receiving layer coating material. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Example 6)
In Example 1, a black ink jet recording sheet was prepared according to Example 1 except that the order of addition of chemicals was polyvinyl alcohol, ethylene vinyl acetate resin, and cationic resin in the preparation of the ink-receiving layer coating material. did. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Example 7)
In Example 1, according to Example 1, except that the amount of polyvinyl alcohol added was 10.0 parts and the amount of ethylene vinyl acetate resin was 30.0 parts in the preparation of the ink-receiving layer coating material. A black inkjet recording sheet was prepared. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Example 8)
In Example 1, according to Example 1, except that the amount of polyvinyl alcohol added was 20.0 parts and the amount of ethylene vinyl acetate resin added was 40.0 parts in the preparation of the ink-receiving layer coating material. A black inkjet recording sheet was prepared. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

Example 9
In Example 1, a black inkjet recording sheet was prepared according to Example 1, except that the addition rate of polyvinyl alcohol was set to 20 L / min in the preparation of the ink-receiving layer coating material. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Example 10)
In Example 1, a black inkjet recording sheet was prepared in the same manner as in Example 1 except that the addition rate of the ethylene-vinyl acetate resin was set to 20 L / min in the preparation of the ink-receiving layer coating material. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Example 11)
In Example 1, a black inkjet recording sheet was prepared according to Example 1, except that the addition rate of the cationic resin was changed to 5 L / min in the preparation of the ink-receiving layer coating material. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Comparative Example 1)
An ink jet recording sheet was prepared in the same manner as in Example 1 except that the ink receiving layer was not provided. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were as follows.
L ^* : 93.80, a ^* : -0.90, b ^* : 3.78, ISO whiteness: 80.12, CCIC: Wt (95) White equivalent

(Comparative Example 2)
In Example 1, an ink jet recording sheet was prepared in the same manner as in Example 1 except that no black color pigment was added in the preparation of the ink-receiving layer coating material. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were as follows.
L ^* : 92.63, a ^* : -0.82, b ^* : 2.01, ISO whiteness: 83.42, CCIC: Wt (95) White equivalent

(Comparative Example 3)
An ink jet recording sheet was prepared in the same manner as in Example 1 except that the black color pigment was reduced to 1/10 times to 0.90 parts in the preparation of the ink receiving layer coating material. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were as follows.
L ^* : 52.17, a ^* : 0.56, b ^* : 2.95, ISO whiteness: 25.07, CCIC: mG (60) Medium grayish equivalent

(Comparative Example 4)
In Example 1, a black inkjet recording sheet was prepared according to Example 1 except that the addition rate of the cationic resin was 40 L / min in the preparation of the ink-receiving layer coating material. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Comparative Example 5)
In Example 1, a black ink jet recording sheet was prepared in the same manner as in Example 1 except that the order of addition of the chemicals was ethylene vinyl acetate resin, polyvinyl alcohol, and cationic resin. Produced. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Comparative Example 6)
In Example 1, a black ink jet recording sheet was prepared in the same manner as in Example 1 except that the order of addition of the chemicals was ethylene vinyl acetate resin, cationic resin, and polyvinyl alcohol. Produced. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Comparative Example 7)
In Example 1, a black ink jet recording sheet was prepared according to Example 1 except that the order of addition of chemicals was the order of cationic resin, polyvinyl alcohol, and ethylene vinyl acetate resin in the preparation of the ink receiving layer coating. Produced. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Comparative Example 8)
In Example 1, a black ink jet recording sheet was prepared according to Example 1 except that the order of addition of chemicals was the order of cationic resin, ethylene vinyl acetate resin, and polyvinyl alcohol in the preparation of the ink receiving layer coating. Produced. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Comparative Example 9)
In Example 1, the preparation of the ink receiving layer coating material was performed in accordance with Example 1 except that the addition amount of polyvinyl alcohol was 5.00 parts and the addition amount of ethylene vinyl acetate resin was 25.0 parts. A black inkjet recording sheet was prepared. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Comparative Example 10)
In Example 1, the preparation of the ink receiving layer coating material was carried out in the same manner as in Example 1 except that the addition amount of polyvinyl alcohol was 25.0 parts and the addition amount of ethylene vinyl acetate resin was 45.0 parts. A black inkjet recording sheet was prepared. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were the same as those in Example 1.

(Comparative Example 11)
In Example 1, except that an anionic black color pigment (trade name: TB786 Black, manufactured by Dainichi Seika Kogyo Co., Ltd.) was added in place of the nonionic black color pigment in the preparation of the ink receiving layer coating material. A black inkjet recording sheet was prepared according to 1. Here, L ^* , a ^* , b ^* , ISO whiteness, and CCIC of the inkjet recording surface were as follows.
L ^* : 21.0, a ^* : 0.16, b ^* : -0.15, ISO whiteness: 4.70, CCIC: equivalent to Bk (10) Black

The black ink jet recording sheet and the ink jet recording sheet thus obtained were evaluated by the following method, and the volume average viscosity η _{average calc.} When polyvinyl alcohol, ethylene vinyl acetate resin and cationic resin were added, respectively _{. n} and measured value η _obs. of viscosity when each chemical is added _. a difference amount .DELTA..eta _n and _n shown in Table 1. Table 2 shows the evaluation results of surface uniformity, color unevenness, IJ printing quality, Gakushin type friction fastness and economic efficiency.

<B-type viscosity difference amount of paint (B-type viscosity difference amount)>
The B-type viscosity at 60 rpm under the conditions of 20 ° C. of the paint at the time of chemical addition or each chemical alone was measured using a B viscometer (model: B-8L, manufactured by Tokyo Keiki Co., Ltd.). The mold viscosity difference amount Δη _n (n = 1, 2, 3) was calculated. The measurement of the actual viscosity was based on complete mixing. However, when complete mixing was difficult due to aggregation or thickening, stirring was interrupted halfway and the viscosity was measured. A measured viscosity η _{obs. Of} a primary mixture obtained by adding a 10% aqueous solution of polyvinyl alcohol to a silica slurry and thoroughly mixing the mixture at 20 rpm under a condition of 20 ° C. ₁ is a theoretical values calculated from the number 1 volume average viscosity eta _{average calc.} The difference amount between ₁ and Δη _1. A secondary mixture in which either an aqueous dispersion of an ethylene vinyl acetate resin having a solid content concentration of 50% or an aqueous dispersion of a cationic resin having a solid content concentration of 30% was added to the primary mixed solution and thoroughly mixed. Measured viscosity η _obs. Measured B-type viscosity at 60 rpm under 20 ° C. condition of the mixture _{. 2} is a theoretical values calculated from the number 2 volume average viscosity eta _{average calc. The} amount of difference from ₂ was Δη2. A third mixture in which either the aqueous dispersion of an ethylene vinyl acetate resin having a solid content of 50% or the aqueous dispersion of a cationic resin having a solid content of 30% was added to the second mixed liquid and mixed thoroughly. Measured viscosity η _obs. Measured B-type viscosity at 60 rpm under 20 ° C. condition of the mixture _{. The} volume average viscosity η _{average calc.} The difference between the amount of the ₃ was Δη _3.

( _Equation 1) η _{average calc. 1} = (η ₁ × V ₁ ) / V ₁
( _Equation 2) η _{average calc. 2} = {(η ₁ × V ₁ ) + (η ₂ × V ₂ )} / (V ₁ + V ₂ )
( _Equation 3) η _{average calc. 3} = {(η ₁ × V ₁ ) + (η ₂ × V ₂ ) + (η ₃ × V ₃ )} / (V ₁ + V ₂ + V ₃ )
In Equations 1, 2, and 3, η ₁ [mPa · s] is the viscosity of a 10% aqueous solution of polyvinyl alcohol obtained by measuring B-type viscosity at 60 rpm under 20 ° C., and V ₁ [L] is It is the addition amount of the polyvinyl alcohol aqueous solution. η ₂ [mPa · s] is an aqueous dispersion of an ethylene vinyl acetate resin having a solid content concentration of 50% or a cationic resin having a solid content concentration of 30%, which was measured for B-type viscosity at 60 rpm under 20 ° C. V ₂ [L] is the addition amount of either an aqueous dispersion of an ethylene vinyl acetate resin or an aqueous dispersion of a cationic resin. η ₃ [mPa · s] is an aqueous dispersion of an ethylene vinyl acetate resin having a solid content concentration of 50% or an aqueous dispersion of a cationic resin having a solid content concentration of 30%. V ₃ [L] is the added amount of either the aqueous dispersion of ethylene vinyl acetate resin or the aqueous dispersion of cationic resin.

The B type viscosity difference amount of the paint is described in Table 1 according to the following procedure.
Δη _n (n = 1, 2, 3) is | Δη _n | <700 mPa · s... (Practical level),
Δη _n (n = 1, 2, 3) is | Δη _n | ≧ 700 cps... × (not suitable for practical use).

<Uniformity of ink jet recording surface (uniformity of surface feeling)>
The surface uniformity of the inkjet recording surface, that is, the smoothness of the surface was comprehensively evaluated visually and described in Table 2 according to the following procedure.
○: surface smoothness is high and good (practical level), Δ: surface smoothness is slightly inferior and slightly poor (practical lower limit level), ×: surface smoothness is low and poor ( Not suitable for practical use.)

<Maximum color difference (color unevenness) on the inkjet recording surface>
The color unevenness of the inkjet recording surface was evaluated by the maximum color difference ΔE ^* at 10 cm × 10 cm square. ΔE ^* is in a range of 10 cm × 10 cm square arbitrarily set on the ink jet recording surface using a method of calculating from the lightness index L ^* and the perceptual chromaticity index a ^* and b ^* defined in JIS P 8150: 2004. The difference between the maximum value and the minimum value of each of the lightness index (L ^* ) and the perceptual chromaticity index (a ^* , b ^* ) measured at any 10 locations was evaluated as ΔE ^* . ΔE ^* was determined from Equation 4.

なお、数４において、明度指数（Ｌ^＊）及び知覚色度指数（ａ^＊、ｂ^＊）の最大値をＬ^＊ｘ、ａ^＊ｘ、ｂ^＊ｘと表記し、明度指数（Ｌ^＊）及び知覚色度指数（ａ^＊、ｂ^＊）の最小値をＬ^＊、ａ^＊、ｂ^＊と表記する。また、測定機器は、分光式白色度計・色差計（商品名：ＳＰＥＣＴＲＯ ＣＯＬＯＲ ＭＥＴＥＲ、型式：ＭＯＤＥＬ ＰＦ−１０、日本電色工業社製）を用いて測定した。

In Equation 4, the maximum values of the lightness index (L ^* ) and the perceptual chromaticity index (a ^* , b ^* ) are expressed as L ^* x, a ^* x, b ^* x, and the lightness index (L ^* ) and The minimum value of the perceptual chromaticity index (a ^* , b ^* ) is expressed as L ^* , a ^* , b ^* . Moreover, the measuring apparatus measured using the spectroscopic whiteness meter and the color difference meter (Brand name: SPECTRO COLOR METER, Model: MODEL PF-10, Nippon Denshoku Industries Co., Ltd. make).

The color unevenness is described in Table 2 according to the following procedure.
○ ... ΔE ^* is 0.5 or less (practical level), x ... ΔE ^* exceeds 0.5 (not suitable for practical use).

<Ink printing quality (IJ printing quality (IJ printing suitability / clearness of white printing))>
Using an ink jet printer (model: JV-33, manufactured by Mimaki), a test print pattern (characters, lines and solids) was printed on the ink jet recording surface with white ink for JV-33, and the visual evaluation was performed.

The IJ printing quality was evaluated in terms of IJ printing suitability such as printing bleeding and the sharpness of white printing, and is described in Table 2 according to the following procedure.
IJ printability:
○: No blurring of printing is good (practical level), Δ: Slight blurring of printing is slightly poor (practical lower limit level), x: Bleeding of printing is poor (practical) Absent.).
White print sharpness:
○: White ink printing is good and good (practical level), △: White ink printing is hard to see and is slightly bad (practical lower limit level), ×: White ink printing is not good and bad (Not suitable for practical use.)

<Gakushin friction fastness test on inkjet recording surface (Gakushin friction)>
The surface strength of the inkjet recording surface was measured using a Gakushin friction fastness tester (AB-301 COLOR FASTNESS RUBBING TESTER, manufactured by Tester Sangyo Co., Ltd.). The test conditions were such that the ink-receiving layer of the obtained recording sheet and copy paper (trade name: Maricopy R70, manufactured by Hokuetsu Kishu Paper Co., Ltd.) were reciprocated 20 times under the condition of a load of 300 g, and the coating layer The degree of shaving and the degree of the coating layer dropped on the copy paper were visually evaluated, and are described in Table 2 according to the following procedure.
○: The coating layer is good without being rubbed (practical level), Δ: The coating layer is slightly scraped and weak (practical lower limit level), ×: The coating layer is scraped and clearly weak (not suitable for practical use) .

<Economic index (economy)>
The time from the beginning to the end of addition of polyvinyl alcohol, cationic resin or ethylene vinyl acetate resin to the silica slurry during preparation of the ink-receiving layer coating is defined as the input time: t (minutes), and the amount of chemical input : As V (L), the rate of chemical addition was defined by Equation 5, and the value was used as an economic index. In other words, the smaller the calculated value obtained in Equation 5, the better the economy, and vice versa. However, if the rate of addition of a chemical that greatly changes the pH (cationic resin in this example) is too high, the subsequent physical properties of the paint are adversely affected.

(Equation 5) V _n / t _n
In Formula 5, n is a positive integer of 1 to 3, and is a number corresponding to the order of adding polyvinyl alcohol, cationic resin, or ethylene vinyl acetate resin to the silica slurry.

The economy is described in Table 2 according to the following procedure.
1) Addition of cationic resin 5 L / min <V / t <40 L / min... ○ (practical level),
When V / t ≦ 5 L / min or 40 L / min ≦ V / t... × (not suitable for practical use).
2) Addition other than cationic resin 20 L / min <V / t ・ ・ ・ ○ (practical level),
In the case of 20 L / min ≧ V / t... × (not suitable for practical use).

  Examples 1 to 11 are superior in surface uniformity of the inkjet recording surface as compared with Comparative Examples 1 to 11, have good surface strength of the inkjet recording surface in the Gakushin type friction fastness test, and inkjet Printing with white ink because of excellent print quality with a printer, low whiteness on the ink jet recording surface, lightness index and chromaticity index within a predetermined range, and CCIC of Bk (10) or Bk (20) Was shining. Furthermore, it could be produced economically.

  In Example 9, since the addition rate of polyvinyl alcohol was slow, it was inferior in economic efficiency compared with other examples, but it was excellent in surface uniformity of the ink jet recording surface, and in the Gakushin friction fastness test. The surface strength of the ink jet recording surface is good, the printing quality of the ink jet printer is excellent, the whiteness of the ink jet recording surface is low, the lightness index and the chromaticity index are within a predetermined range, and CCIC is Bk (10) Or, since it was Bk (20), printing of white ink was shining. In Example 10, since the addition rate of the ethylene vinyl acetate resin was slow, it was inferior in economic efficiency as compared with the other examples, but was excellent in surface uniformity of the ink jet recording surface, and Gakushin type friction fastness. The surface strength of the ink jet recording surface in the test is good, the printing quality with the ink jet printer is excellent, the whiteness of the ink jet recording surface is low, the lightness index and the chromaticity index are within a predetermined range, and CCIC is Bk. Since it was (10) or Bk (20), printing of white ink was shining. In Example 11, since the addition rate of the cationic resin was slow, the thickening of the paint could be suppressed, but the aggregation could not be dispersed, and the surface feel uniformity, inkjet printing quality, and Gakushin friction fastness were low. Somewhat inferior. Moreover, it was inferior to economical efficiency compared with the other Example.

  In Comparative Example 1, since no ink receiving layer was provided, the whiteness was high and printing of white ink was not possible. In Comparative Example 2, since no black coloring pigment was added to the ink receiving layer, the whiteness was high and printing of white ink was not possible. Since the comparative example 3 made the black coloring pigment too small, whiteness became high and the printing of white ink was not reflected. In Comparative Example 4, since the addition rate of the cationic resin was fast, the paint thickened when the cationic resin was added, and the surface uniformity, color unevenness, and Gakushin friction fastness were inferior. Moreover, the printing of the white ink of the uneven color part did not shine. In Comparative Example 5, since the ethylene vinyl acetate resin was added to the silica slurry prior to the polyvinyl alcohol, aggregation occurred, resulting in poor surface uniformity, color unevenness, and Gakushin friction fastness. Moreover, the printing of the white ink of the uneven color part did not shine. In Comparative Example 6, since the ethylene vinyl acetate resin and the cationic resin were added to the silica slurry prior to the polyvinyl alcohol, aggregation occurred, and surface uniformity, color unevenness, and Gakushin friction fastness were inferior. Moreover, the printing of the white ink of the uneven color part did not shine. In Comparative Example 7, since the cationic resin was added to the silica slurry prior to the polyvinyl alcohol, aggregation occurred, resulting in inferior surface feeling uniformity, color unevenness, and Gakushin friction fastness. Moreover, the printing of the white ink of the uneven color part did not shine. In Comparative Example 8, since the cationic resin and the ethylene vinyl acetate resin were added to the silica slurry prior to the polyvinyl alcohol, aggregation occurred, and surface uniformity, color unevenness, and Gakushin friction fastness were inferior. Moreover, the printing of the white ink of the uneven color part did not shine. Since the comparative example 9 made the addition amount of the binder too small, Gakushin friction fastness was inferior. In Comparative Example 10, since the added amount of the binder was excessive, the ink absorptivity was poor and printing bleeding was observed. In Comparative Example 11, since the black color pigment was anionic, aggregation occurred and surface uniformity, color unevenness, and Gakushin friction fastness were inferior. Moreover, the printing of the white ink of the uneven color part did not shine.

  As is clear from the above results, the black ink jet recording sheets obtained in the examples according to the present invention are excellent in ink jet printing in the printing of pigment inks with high lightness having concealability on the ink jet recording surface, particularly white ink. Had the aptitude. Further, the black inkjet recording sheet could be produced economically.

Claims (8)

Wood fiber is a paint containing, as essential components, synthetic silica as a pigment, polyvinyl alcohol and ethylene vinyl acetate resin as a binder, a cationic resin as an ink fixing agent, and a nonionic black color pigment as a colorant. A method for producing a black ink jet recording sheet comprising at least one ink-receiving layer coated on at least one side of a support mainly comprising:
The paint for forming the ink-receiving layer contains 40 to 60 parts by mass of the binder with respect to 100 parts by mass of the synthetic silica, and the black color pigment in the total solid content of the paint. 5 to 5.5% by mass,
The synthetic silica is a silica slurry dispersed in water,
Among the essential components, the polyvinyl alcohol is added to and mixed with the silica slurry prior to at least the ethylene vinyl acetate resin and the cationic resin.
The method for producing a black inkjet recording sheet, wherein the addition rate of the cationic resin is less than 40 L / min with respect to 1000 L of the silica slurry. The paint was measured by measuring the B-type viscosity at 60 rpm under the condition of 20 ° C. of a primary mixture obtained by adding the polyvinyl alcohol to the silica slurry and thoroughly mixing it _{. 1} is a theoretical values calculated from the number 1 volume average viscosity eta _{average calc. 1} difference amount .DELTA..eta ₁ with, | .DELTA..eta _{1 |} <a 700 mPa · s, and completely by the addition of either one of the primary mixture into liquid wherein the ethylene vinyl acetate resin or the cationic resin Measured viscosity η _obs. Measured B-type viscosity at 60 rpm under the condition of 20 ° C. of the mixed secondary mixture _{. 2} is a theoretical values calculated from the number 2 volume average viscosity eta _{average calc.} Difference amount .DELTA..eta ₂ with _2, | .DELTA..eta _{2 |} <a 700 mPa · s, and, to complete addition of the other of said second mixture into liquid wherein the ethylene vinyl acetate resin or the cationic resin Measured viscosity η _obs. Measured for B-type viscosity at 60 rpm under the condition of 20 ° C. of the mixed tertiary mixture _{. The} volume average viscosity η _{average calc. 2. The} method for producing a black ink jet recording sheet according to claim 1, wherein a difference amount Δη _{3 from 3} is | Δη ₃ | <700 mPa · s.
( _Equation 1) η _{average calc. 1} = (η ₁ × V ₁ ) / V ₁
( _Equation 2) η _{average calc. 2} = {(η ₁ × V ₁ ) + (η ₂ × V ₂ )} / (V ₁ + V ₂ )
( _Equation 3) η _{average calc. 3} = {(η ₁ × V ₁ ) + (η ₂ × V ₂ ) + (η ₃ × V ₃ )} / (V ₁ + V ₂ + V ₃ )
In Equations 1, 2, and 3, η ₁ [mPa · s] is the viscosity of a 10% aqueous solution of polyvinyl alcohol obtained by measuring B-type viscosity at 60 rpm under 20 ° C., and V ₁ [L] is It is the addition amount of the polyvinyl alcohol aqueous solution. η ₂ [mPa · s] is an aqueous dispersion of an ethylene vinyl acetate resin having a solid content concentration of 50% by mass or a cationic resin water having a solid content concentration of 30% by mass, as measured for B-type viscosity at 60 rpm under 20 ° C. V ₂ [L] is the added amount of either an aqueous dispersion of ethylene vinyl acetate resin or an aqueous dispersion of cationic resin. η ₃ [mPa · s] is an aqueous dispersion of an ethylene vinyl acetate resin having a solid content concentration of 50% by mass or a cationic resin having a solid content concentration of 30% by mass, which was measured for B-type viscosity at 60 rpm under 20 ° C. V ₃ [L] is the added amount of either the aqueous dispersion of ethylene vinyl acetate resin or the aqueous dispersion of cationic resin.   The method for producing a black ink jet recording sheet according to claim 1 or 2, wherein a method of preparing the paint is a batch type.   The method for producing a black inkjet recording sheet according to any one of claims 1 to 3, wherein an addition rate of the cationic resin exceeds 5 L / min with respect to 1000 L of the silica slurry. The addition rate of the polyvinyl alcohol exceeds 20 L / min with respect to 1000 L of the silica slurry,
The method for producing a black inkjet recording sheet according to any one of claims 1 to 4, wherein an addition rate of the ethylene vinyl acetate resin exceeds 20 L / min with respect to 1000 L of the silica slurry. . A black inkjet recording sheet provided with at least one ink receiving layer containing a pigment, a binder and a colorant on at least one side of a support mainly composed of wood fibers,
The ink receiving layer contains synthetic silica as the pigment, contains polyvinyl alcohol and ethylene vinyl acetate resin as the binder, and contains only a nonionic coloring pigment as the colorant,
The color pigment contains a black color pigment,
The ink receiving layer contains 3.5 to 5.5% by mass of the black color pigment with respect to the total solid content of the ink receiving layer, and the binder is added to 100 parts by mass of the synthetic silica. 40-60 parts by mass,
The surface of the ink receiving layer is
(I) (1) JIS P 8150: 2004 “Paper and paperboard—Method of measuring color (C / 2 °) —diffuse illumination method” The lightness index (L ^* ) is 20 ≦ L ^* ≦ 28, chromaticity Index (a ^* , b ^* ) is in the range of −0.4 ≦ a ^* ≦ 0.2, −0.7 ≦ b ^* ≦ 0.3, (2) “Commerce and Industry” which is a chamber system color system (1) or (2) which has a luminous chromaticity corresponding to Bk (20) Black or Bk (10) Black in The Chamber Color Coordination Chart: The Chamber of Commerce and Industry Color Coordination Chart (CCIC) Meet at least one of
And (II) JIS P 8148: 2001 "paper, paperboard and pulp-ISO whiteness (diffuse blue light reflectance) measurement method" ISO whiteness specified in 10% or less,
(III) The maximum color difference ΔE ^* obtained using a method of calculating from the lightness index (L ^* ) and the perceptual chromaticity index (a ^* , b ^* ) at 10 cm × 10 cm square is 0.5 or less. A black ink jet recording sheet having a region.   The ink receiving layer contains the black color pigment and the chromatic color pigment as the color pigment, and the ratio of the chromatic color pigment in the color pigment is 0.17% by mass or less. The black ink jet recording sheet according to claim 6, wherein the recording sheet is a black ink jet recording sheet. The black ink jet recording sheet according to claim 6, wherein the ink receiving layer further contains a cationic resin as an ink fixing agent.

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