JP4377425B2 - Manufacturing method of fine coated paper - Google Patents

Description

The present invention relates to a method for producing finely coated paper. In particular, it has a high rigidity with a weight of 60 g / m ² or less, and a coating amount of 10 g / m ² or less per side and a low coating amount, while maintaining whiteness, blank paper gloss, and printing gloss. The present invention relates to a method for producing an excellent finely coated paper.

Currently, on-machine coaters in which a paper machine and a coating machine are integrated are widely used in order to efficiently produce coated paper at a low cost. As the coating method using an on-machine coater, there are mainly a film transfer method and a blade coating method. Of these, film transfer coaters such as gate roll coaters and rod metering coaters are compact, have good operability, and are easily adaptable to various product quality requirements. It is widely used as a construction facility and pigment coating facility.
The film transfer method is a method of transferring the measured coating solution on the applicator roll to the base paper (base paper), and the load on the base paper during coating is relatively small compared to the blade coating method, There is an advantage that there are few paper break troubles at the time of operation, and extremely high production efficiency can be obtained. Moreover, since the film transfer coater can perform coating along the contour of the base paper surface, so-called contour coating, it can be said that the surface of the base paper has high coverage and is suitable for producing coated paper.
Printing paper is becoming lighter, that is, a shift from coated paper to finely coated paper from the viewpoints of resource saving and transportation cost reduction. As a means of weight reduction, reduction of the base paper weight of the paper and reduction of the coating amount are reduced, but the reduction of the base paper weight of the paper basis causes a decrease in rigidity due to a decrease in the paper thickness. There is a problem of decrease in glossiness and printing glossiness. The decrease in stiffness is likely to cause problems in high-speed printing, automatic control, and paper conveyance. Also, the reduction in thickness of the base paper contradicts the current full colorization in terms of printing opacity. It also has a surface. When the coating amount is reduced, the surface coverage is lowered, and not only the white paper glossiness and printing glossiness are lowered, but also gloss unevenness occurs and the cosmetic properties are lowered. There is a demand for the development of finely coated paper that solves these problems, maintains rigidity while reducing weight, and enables high-speed printing.
In order to improve the rigidity, there is a method of blending a tougher softwood pulp (Patent Document 1). However, the increase in the distribution of softwood pulp having a long fiber length causes a decrease in surface properties and a decrease in printability, resulting in printability. However, it is not preferable because it reduces the linear pressure in the flattening process, and a method of minimizing the decrease in stiffness can be considered, but the flatness and glossiness cannot be imparted to the paper, and printing is performed after printing. This is not preferable because the gloss of the portion is lowered.
As a method of obtaining sufficient blank paper glossiness and printing glossiness even at a low linear pressure, there is a method of adding an organic pigment that is easily crushed, but the fluidity of the coating liquid is deteriorated, resulting in coating unevenness and gloss unevenness. It is not preferable in terms of both quality and work.
JP 2006-097149 A

The main problem to be solved by the present invention is that while the weight per square meter is 60 g / m ² or less and light weight, it has high rigidity and the coating amount is 10 g / m ² or less per side while it is white and white. The present invention relates to a method for producing a finely coated paper having an excellent strength, white paper glossiness and printing glossiness. The “fine coated paper” refers to a coated paper having a pigment coating layer coating amount of 12 g / m ² or less on one side, but the fine coated paper of the present invention has a coating amount on one side. For coated paper of 10 g / m ² or less.

The present invention that has solved this problem is as follows.
[Invention of Claim 1]
On at least one side of the base paper,
A coating mainly composed of oxidized starch is applied at a rate of 0.1 g / m ² to 1.0 g / m ² per side ,
After application of the oxidized starch , calendar treatment is performed at a linear pressure of 10 to 50 KN / m,
At least one pigment coating layer mainly composed of a pigment and a binder is applied with a film transfer type roll coater to 6.0 g / m ² to 9.5 g / m ² per side ,
Furthermore, it is calendered at a metal roll temperature of 100 ° C. or higher and a linear pressure of 100 to 600 KN / m,
These oxidized starch coating, calendering, pigment coating, and calendering in this order are on-machine manufacturing methods for finely coated paper,
The weight ratio of waste paper pulp to the raw material pulp of the base paper is 70% or more,
Add a cationic coagulant and a cationic flocculant to the pulp slurry before the screen and an anionic flocculant after the screen.
The anionic flocculant is bentonite or colloidal silica;
The pigment contains 10 to 50 parts by mass of delaminated clay having an average particle diameter of 0.4 to 0.8 μm and an aspect ratio of 5 or more with respect to 100 parts by mass of the pigment,
10 to 50 parts by mass of clay other than the delaminated clay is contained with respect to 100 parts by mass of the pigment,
Total oxidized starch and pigment coating layer and per side ^{5.1g / m 2 ~10g / m 2} ,
Bulk density is 1.0g / cm ³ ~1.2g / cm ³ and a ratio stiffness to lead the following expression is 0.25m ² /g~0.4m ² / g, the white paper gloss according to JIS P 8142 30 A method for producing finely coated paper, comprising obtaining finely coated paper having -60% and a basis weight of 60 g / m ² or less.
Specific stiffness (m ² / g) = (Stiffness (length) × Stiffness (width)) ^1/2 ÷ US tsubo

[Invention of Claim 2]
The method for producing a finely coated paper according to claim 1, wherein the bentonite is added in a pure content of 0.1 wt% to 5.0 wt% with respect to the pulp.

[Invention of Claim 3]
The method for producing finely coated paper according to claim 1 or 2, wherein the cationic coagulant is polyethyleneimine and the cationic flocculant is polyacrylamide.

[Invention of Claim 4]
The method for producing a finely coated paper according to any one of claims 1 to 3, wherein the cationic flocculant has an average molecular weight of 6 million to 16 million.

It has a high rigidity with a weight of less than 60 g / m ² , and excellent in whiteness, white paper gloss, and printing gloss while having a low coating weight of 10 g / m ² or less per side. A finely coated paper is obtained.

Next, an embodiment of the present invention will be described.
[Fine coated paper]
The finely coated paper according to the present invention can be produced by roll-coating a coating liquid made of starch on a base paper, then roll-coating a coating liquid made of a pigment and an adhesive, and performing surface finishing.
The finely coated paper according to the present invention is preferably applied to the surface of the base paper by applying a water-soluble polymer by a film transfer method using a roll coater, and after the application of the water-soluble polymer, by the same film transfer method. A pigment coating layer mainly composed of a pigment and an adhesive is provided. Examples of water-soluble polymers include starch and derivatives thereof, synthetic polymers such as polyvinyl alcohol and polyacrylate, paper strength enhancers, and sizing agents.
A particularly preferred water-soluble polymer in the present invention is starch, and by applying this starch to a base paper by film transfer, the rigidity of the paper can be improved even at a low coating amount. By coating, it is possible to improve white paper gloss and printing gloss even at a low coating amount, and by reducing these coating amounts and increasing the proportion of pulp in the entire paper, low rice basis weight, particularly 60 g / Sufficient rigidity that can withstand high-speed printing can be obtained with fine coated paper of m ² or less.

Lightly coated paper obtained is bulk density is 1.0g / cm ³ ~1.2g / cm ³ and a ratio stiffness to lead the following expression is at 0.25m ² /g~0.45m ² / g preferably there, more preferably 0.30m ² /g~0.40m ² / g, and most preferably 0.32m ² /g~0.40m ² / g.
Specific stiffness (m ² / g) = (rigidity (longitudinal) × rigidity (horizontal)) ^1/2 ÷ tsubo We refer to the measurement methods of stiffness and tsubo here. When the specific stiffness is less than 0.25 m ² / g, it becomes a coated paper that is not stiff, the processing and printing workability is lowered, and it becomes a cheesy paper that does not have a flickering hand feeling. On the other hand, if the specific stiffness exceeds 0.40 m ² / g, it becomes so rigid that it is difficult to handle in printing applications, and printing workability is reduced.

To obtain such a coated paper, coating weight per coated paper one side, it is preferred that the total of the water-soluble polymer and the pigment coating layer is ^{3g / m 2 ~10g / m 2} . The coating amount of the water-soluble polymer is preferably 0.1 to 1.5 g / m ² , and the coating amount of the pigment coating layer is preferably 2.9 to 9.9 g / m ² . When the coating amount is less than 3 g / m ² , not only the rigidity but also the white paper glossiness is inferior. When the coating amount exceeds 10 g / m ² , not only the rigidity but also the bulkiness is inferior.
In addition, by applying a water-soluble polymer and then performing a flattening treatment with a pre-calender, the smoothness and gloss after pigment coating can be improved, and the weight of the coating layer can be reduced.

  In the pigment coating layer, a delaminated clay having an average particle size of 0.2 μm to 1.0 μm, preferably 0.4 μm to 0.8 μm, and an aspect ratio of 5 or more, preferably 10 or more, is 10 parts by mass to It is preferable to include 60 parts by mass, more preferably 10 parts by mass to 50 parts by mass. A delaminated clay having an average particle diameter of 0.2 μm or more and an aspect ratio of 5 or more has high coverage on the surface of the coating layer, and therefore can impart high gloss and smoothness even at a low coating amount. The printing ink is preferable because it tends to stay on the surface of the coating layer and can improve printing gloss. A clay having an average particle diameter of less than 0.2 μm and an aspect ratio of less than 5 is not only inferior in covering property, but also the clay is likely to sink into the base paper, and thus the above effect cannot be obtained. The upper limit of the aspect ratio is not particularly limited. However, if it exceeds approximately 50, the viscosity of the paint increases, coating properties such as coating unevenness are likely to occur, and voids due to overlapping of clays increase, The ink cannot form a uniform film at the time of printing, and the printing gloss is lowered.

  On the other hand, the fine coated paper according to the present invention preferably has a white paper glossiness of 30 to 60% based on JIS P 8142: 2005, and more preferably 40 to 45%. If the glossiness of the blank paper is less than 30%, the clearness of the clear print information and the print information with good contrast cannot be expressed, and the fineness is lacking. On the other hand, the glossiness of blank paper may exceed 60%, but by setting it to 60% or less, it becomes a coated paper that does not seem to be so-called glaring and is easy on the eyes. As described above, when using a delaminated clay with good surface coverage and a film transfer coating of a pigment coating layer, a coating layer surface with high coverage can be obtained while having a low coating amount. Coated paper with excellent gloss and printing gloss. In addition, in the super calendar process for giving gloss after coating, the linear pressure (nip pressure) required to obtain a predetermined gloss level is low, so that the crushing of the paper can be minimized, A finely coated paper excellent in rigidity, which is an object of the present invention, is obtained.

[Pulp blend]
As for the base paper of this form, the kind of raw material pulp is not specifically limited. Examples of the raw material pulp include wood pulp, non-wood pulp, synthetic pulp, and waste paper pulp. More specifically, ground pulp (GP), stone ground pulp (SGP), refiner ground pulp (RGP), additive pulp, and the like. Pressed ground pulp (PGW), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), bleached chemithermomechanical pulp (BCTMP) and other mechanical pulp (MP), chemical mechanical pulp (CGP), semi-chemical pulp (SCP), hardwood bleached kraft pulp (LBKP), kraft pulp (KP) such as softwood bleached kraft pulp (NBKP), chemical pulp such as soda pulp (AP), sulfite pulp (SP), dissolved pulp (DP) (CP), nylon, rayon, polyester, polyvinyl alcohol Raw paper pulp such as synthetic pulp, deinked pulp (DIP), and waist pulp (WP), waste pulp (TP), cotton, flax, hemp, jute, manila hemp, ramie, etc. One or several kinds can be appropriately selected and used from slag pulp, straw pulp, esparto pulp, bagasse pulp, bamboo pulp, kenaf pulp, and other auxiliary pulps such as bast pulp.
However, in the base paper of this embodiment, the raw material pulp type is preferably such that the mass ratio of NBKP: LBKP: waste paper pulp is 0 to 10: 0 to 30:70 to 100. 20: 70-100 is more preferable. If the mass ratio of NBKP exceeds 10%, the base paper tends to have uneven thickness because it is difficult to obtain a uniform base paper formation due to the long fibers peculiar to the N material. When the mass ratio of LBKP exceeds 30%, the density of the base paper tends to be high, and cushioning properties and bulkiness in the thickness direction (Z-axis direction) are lowered. When the weight ratio of the used paper pulp is less than 70%, the number of flat and flexible fibers peculiar to the used paper pulp decreases, and the flatness and glossiness of the paper surface decrease.

[Wet end]
In order to obtain the finely coated paper of the present invention, it is preferable to add a filler, a coagulant, and a flocculant to the pulp slurry made of the pulp.
<Coagulant>
Examples of the coagulant include organic polymer coagulants such as polyacrylamide (PAM), polyvinylamine (PVAm), polydiallyldimethylammonium chloride (polydadomac, PDADMAC), polyamine (PAm), polyethyleneimine (PEI), and sulfuric acid. Examples thereof include inorganic coagulants such as bands and polyaluminum chloride. Among these, it is preferable to use at least one of PAM, PDADMAC, PAm, and PEI. In particular, PEI is preferable because it has a high cation density and a high action to efficiently collect anionic fine components, and thus the surface properties of the obtained base paper can be improved. The average molecular weight of PEI is preferably 100,000 to 4,000,000, and more preferably 1,000,000 to 2,000,000. If the average molecular weight is less than 100,000, the anionic fine fibers cannot be sufficiently adsorbed, and if the average molecular weight exceeds 4 million, the anionic fine fibers are collected too much and the texture of the base paper is destroyed. This is not preferable because it causes unevenness and a decrease in cosmetics. The addition amount of the coagulant is preferably adjusted so that the cation requirement reduction rate and the cation requirement of the paper filtrate after addition of the cationic coagulant are satisfied. Therefore, although the addition amount of the cationic coagulant depends on the addition amount of the flocculant described later, it is 0.1% to 0.5%, more preferably 0.15% to 0% in solid content with respect to the pulp. .4% is preferable. If the addition amount of the coagulant is less than 0.1%, the effect may be insufficient. On the other hand, if it exceeds 0.5%, the texture of the base paper is destroyed, resulting in coating unevenness and a decrease in cosmetic properties. There is a fear.
In the present invention, as described above, it is preferable to add a coagulant in the pulp preparation stage. For example, the pulp and filler, and if necessary, an internal sizing agent, a fixing agent, a yield improver, a cation Various paper-making aids such as an agent, a paper strength enhancer, and an antifoaming agent are mixed in a compounding chest to become a finished raw material. Accordingly, it is preferable that a coagulant is added between the compound chest and the machine chest, and in order to sufficiently mix the cationic coagulant with the finished raw material, it is more preferable to add the coagulant to the compound chest.

<Cationic flocculant>
In the present invention, it is preferable that a cationic coagulant is added in the first stage of the paper making process following the pulp preparation stage after the cationic coagulant is added in the pulp preparation stage.
Since the paper stock is composed of pulp and filler exhibiting anionic property, the aggregation action can be obtained by adding a cationic flocculant. Examples of the cationic flocculant include a cationic water-soluble polymer or copolymer having an average molecular weight of 6 million to 16 million, more preferably 10 million to 14 million, and a cationization degree of 0 to 10 meq / g. Can be used. In the present invention, it is preferable to use PAM capable of forming a large floc because the yield of fine fibers can be improved and the surface properties of the base paper can be improved. If the average molecular weight of the cationic flocculant is less than 6 million, the effect of using the cationic flocculant may not be sufficiently exhibited. On the other hand, if the average molecular weight is larger than 16 million, the floc becomes large and the texture is lost. Unevenness due to unevenness of work and unevenness of gloss occurs. On the other hand, if the degree of cationization is less than 0 meq / g, the effect of using the cationic flocculant may not be sufficiently exhibited. Unevenness due to unevenness of work and unevenness of gloss occurs.
Moreover, it is preferable that the addition amount of a cationic flocculant is 0.01%-0.1% in a pure part with respect to a pulp, Furthermore, it is preferable that it is 0.02%-0.05%. If the addition amount of the cationic flocculant is less than 0.01%, the predetermined agglomeration effect may not be sufficiently exhibited. On the other hand, if it exceeds 0.1%, the flocs become large and the texture is lost. Unevenness due to gloss unevenness occurs.

<Anionic flocculant>
In the present invention, it is preferable to add the anionic flocculant after adding the cationic coagulant and the cationic flocculant. By adding an anionic flocculant, flocs generated by the cationic flocculant can be effectively agglomerated, and surface properties can be improved as the yield of fine fibers is improved. As the anionic flocculant, those conventionally used as a yield improver can be used. Specific examples include anionic polyacrylamide-based materials, colloidal silica, and bentonite, and one or two or more types selected from these groups may be used in combination. In the present invention, bentonite that has higher dispersibility with respect to the pulp slurry and easily binds the pulps is preferable.
The addition amount of bentonite is preferably 0.1% to 5.0%, and more preferably 0.5% to 3.0%, pure with respect to the pulp. If the added amount of bentonite is less than 0.1%, the predetermined agglomeration effect may not be sufficiently exhibited. On the other hand, if it exceeds 5.0%, the agglomeration effect is biased and the texture tends to collapse, resulting in uneven coating. Or uneven glossiness is undesirable.
As a location for adding the cationic flocculant and the anionic flocculant, it is preferable to add the cationic flocculant before the screen and the anionic flocculant after the screen. In order to improve the surface properties of the base paper by maximizing the yield of fine fibers while suppressing the formation of flocs to such an extent that the texture does not deteriorate, after obtaining a large floc with a cationic flocculant, This is because it is preferable that the floc is once decomposed by the share of the screen and then the floc is formed again with the anionic flocculant.
As in the present invention, in the coated paper in which the waste paper pulp is highly blended to 70% or more, the high rigidity, which is the object of the present invention, can be achieved particularly by improving the yield of fine fibers. In other words, due to the presence of fine fibers, the surface of the base paper is uniform and coating unevenness is unlikely to occur, the blank paper glossiness and printing glossiness are easily improved, and the nip pressure in the calendar process can be reduced, so that the rigidity is increased. Excellent fine coated paper is obtained. In order to sufficiently improve the surface property and glossiness of the coated paper, it is preferable to combine a predetermined cationic coagulant, a cationic flocculant, and an anionic flocculant in a predetermined ratio as described above.

[Paper making equipment]
The papermaking equipment that can be used in the present invention is not particularly limited, but in order to obtain high rigidity and bulkiness, which is the object of the present invention, a wire part made of a gap former, a press part made of a straight-through type without an open draw. It is preferable to combine a dryer part consisting of a single deck dryer. The reason is as follows.
<Wire part (head box)>
The prepared pulp slurry is sent to the wire part via the head box. The wire part is not particularly limited, such as a long-form former, a combination of a long-form former and an on-top former, or a twin wire former, but the paper jet ejected from the head box is immediately sandwiched between two wires. A gap-type gap former is preferable because there is little difference between the front and back because it dehydrates from both sides, and it is difficult to cause a difference in front and back in uneven coating and printing.
<Press part>
The paper layer in the wire part is transferred to the press part and further dewatered. The press machine can be either a straight-through type, an invar type, or a reverse type, and a combination of these can also be used, but the straight-through type with no open draw is easy to hold the paper, This is preferable because there are few operational troubles such as paper breaks. As the dehydration method, a commonly used method such as a suction roll method or a grooved press method can be used, but a shoe press is more preferable because it can improve dewaterability and smoothness.
<Pre-dryer part>
The wet paper that has passed through the press part is transferred to a single-deck pre-dryer part and dried. The pre-dryer part is preferably a no-open draw type single-deck dryer that has few paper breaks and can be dried efficiently without reducing the bulk. A drying method using a double deck method is also possible, but it is not preferable because it is inferior to a single deck method in terms of operability such as canvas marks, paper breaks, wrinkles, and paper splicing.

[Undercoating]
For the purpose of improving the rigidity, the above base paper is undercoated with a water-soluble polymer using a roll coater.
Examples of water-soluble polymers include starches such as oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch and raw starch or derivatives thereof, synthetic polymers such as polyacrylamide and polyvinyl alcohol, and water resistance and surface strength improvement. The paper strength enhancing agent described above, the externally added sizing agent for the purpose of imparting sizing properties, or those commonly used as surface treatment agents can be used alone or in combination. Among these, oxidized starch is particularly preferable because it can improve the workability while minimizing the decrease in whiteness while improving the rigidity.
Coating amount in the case of using the oxidized starch as a water-soluble polymer is not particularly limited, preferably 0.1~1.5g per side / m ^2, more preferably 0.2~1.3g / m ^2, most preferably from 0.3 to 1.0 g / m ^2. If it is less than 0.1 g / m ² , the coverage is poor and the effect of improving the stiffness of the base paper is small. If it exceeds 1.5 g / m ² , the stiffness will improve, but the original color of starch will tend to appear on the coated paper, and not only will the whiteness decrease, but the coating liquid will increase and the coating will start from the roll surface. Since the liquid is scattered, coating mist is generated, and defects and foreign matters are easily generated, and workability is deteriorated.
Such a water-soluble polymer is applied to, for example, a two-roll size press coater, a gate roll coater, a blade metering size press coater, a rod metering size press coater, or a film transfer type roll coater such as a shim sizer or a JF sizer. Can be applied by machine tool. The film transfer type roll coater is preferable because it has a high surface coverage even when the coating amount is small, and a coated paper having high rigidity can be obtained even at a low coating amount. Coating machines other than those described above, such as blade coaters and air knife coaters, are unfavorable because the coatability is poor at low coating amounts and non-coated parts are likely to occur, and uniform coating is required for spray coaters and curtain coaters. Cannot be obtained, and gloss unevenness is likely to occur.

[Flatening treatment (pre-calendar)]
The base paper after the undercoating is preferably subjected to a flattening process using a precalender before the topcoating (pigment coating). As the pre-calender, a soft calender having a metal roll on the upper side and an elastic roll on the lower side is preferable because of its high surface improvement. The pre-calendar can be performed in one stage or a combination of two or more stages as required. By pre-calendar treatment, the surface of the base paper after the application of water-soluble polymer can be flattened, and it is not necessary to excessively flatten the post-calendar to increase the paper tension. Therefore, the flatness of the surface of the base paper can be improved, and a coated paper having high rigidity and high bulk can be obtained. Further, the surface of the base paper is flattened to improve the coating property of the top coating, to suppress the generation of mist, and to suppress the coating unevenness of the coating liquid. The linear pressure of the pre-calender is preferably 10 to 80 KN / m, more preferably 10 to 50 KN / m. If it is less than 10 KN / m, flattening of the base paper after application of the water-soluble polymer will not proceed. If it exceeds 80 KN / m, the base paper will be compressed more than necessary, so that the stiffness will decrease and the tightness will decrease. It is not preferable because it rises and is inferior in bulk.

[Top coating (pigment coating)]
Next, a coating layer containing a pigment and an adhesive is applied to one or both sides of the base paper to provide a coating layer. The pigment is preferably blended with a delaminated clay having an average particle size of 0.2 μm or more and an aspect ratio of 5 or more. The blending amount of the delaminated clay is 10 to 60 parts by mass, more preferably 10 to 50 parts by mass with respect to 100 parts by mass of the pigment. In order to obtain high white paper glossiness and high printing glossiness with a lower coating amount, which is the object of the present application, it is preferable to use a delaminated clay having high coverage. However, delaminated clay has poor fluidity in the coating solution, and if it exceeds 60 parts by mass, coating unevenness occurs, which is not preferable. On the other hand, when the blending amount is less than 10 parts by mass, the desired coverage cannot be obtained, and the blank paper glossiness and printing glossiness are lowered.
In addition to the above-mentioned surface property improvement effect by improving the yield of fine fibers, by applying a coating liquid consisting of delaminated clay as a pigment coating, the coating amount can be reduced while maintaining the gloss of white paper. The proportion of pulp in the whole increases, and a further improvement in stiffness is obtained.
Conventionally, if the surface property of the base paper is poor, there is a problem that the paint becomes a mist and scatters during film transfer coating, especially when blended with a delaminated clay with poor paint fluidity. It was. However, by applying a water-soluble polymer before pigment coating, the smoothness of the base paper can be improved and uniform film transfer coating is possible, so delaminated clay is blended while suppressing mist scattering. It became possible to do. In addition, by applying a water-soluble polymer, it becomes easier to improve the smoothness after top coating, and it becomes easier to obtain gloss, so the amount of coating can be reduced and the rigidity derived from pulp can be further improved. . On the other hand, as the glossiness of the white paper is improved, the printing glossiness is also improved by a synergistic effect.

As pigments other than delaminated clay, for example, kaolin, fine kaolin, calcium carbonate, talc, satin white, calcium sulfite, gypsum, barium sulfate, white carbon, calcined kaolin, structured kaolin, diatomaceous earth, magnesium carbonate, titanium dioxide, Inorganic pigments such as aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, magnesium oxide, bentonite, sericite, polystyrene resin fine particles, urea formalin resin fine particles, fine hollow particles, porous fine particles, etc. One or two or more organic pigments may be appropriately selected and blended. In addition to the delaminated clay, calcium carbonate having a large whiteness improving effect, more preferably inexpensive heavy calcium carbonate can be used.
An organic pigment that exhibits high white paper glossiness at a low nip can be blended to reduce the nip pressure of the calendar, but coating unevenness tends to occur. Since the present invention is a method for obtaining the desired high rigidity, bulkiness, high white paper glossiness, and high printing glossiness without using an organic pigment, it does not need to be blended.

  There are no particular limitations on the type of adhesive blended in the coating solution together with the above pigments, for example, proteins such as casein and soybean protein; styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, Conjugated diene latex such as styrene-methyl methacrylate-butadiene copolymer latex, acrylic latex such as polymer latex or copolymer latex of acrylate ester and / or methacrylate ester, ethylene-vinyl acetate polymer latex, etc. Latex compounds such as alkali partially soluble or non-soluble latex obtained by modifying vinyl-based latex or various copolymer latexes thereof with a functional group-containing monomer such as carboxyl group; polyvinyl alcohol, olefin-maleic anhydride resin , Me Synthetic resin adhesives such as min resin, urea resin, urethane resin; starches such as oxidized starch, positive starch, esterified starch, dextrin; cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, etc. Adhesives used for paper can be mentioned, and one or two or more of these can be appropriately selected and used.

Although there is no limitation in particular in the ratio of the pigment in a coating agent, and an adhesive agent, Preferably an adhesive agent is 3-17 mass parts by solid content ratio with respect to 100 mass parts of pigments, More preferably, it is 5-15. Part by mass. When the amount of the adhesive is less than 3 parts by mass, the formability of the coating layer is lowered and the surface strength is lowered. On the other hand, when the amount exceeds 17 parts by mass, the amount of the adhesive is too large, and the gloss derived from the pigment is hardly exhibited, and the glossiness of the white paper is lowered.
Furthermore, for example, various commonly used auxiliaries such as a fluorescent brightening agent, a fluorescent brightening agent fixing agent, an antifoaming agent, a release agent, a coloring agent, and a water retention agent are appropriately blended in the coating liquid. You can also
The coating of the top coat layer (pigment coating layer) on the base paper is preferably performed, for example, in a coater part between dryer parts which is performed in a plurality of stages, usually two stages of a pre-dryer part and an after-dryer part. . In this coater part, as in the case of undercoat coating, for example, a film transfer type roll such as a 2-roll size press coater, a gate roll coater, a blade metering size press coater, a rod metering size press coater, or a shim sizer or JF sizer. It can apply | coat with coating machines, such as a coater. A film transfer type roll coater is preferable because a coated paper having high surface coverage and high rigidity can be obtained even with a low coating amount. Coating machines other than the above, such as blade coaters and air knife coaters, are not preferred because they cannot be applied at low coating amounts, and spray coaters and curtain coaters can be applied at low coating amounts but are uniform. Since a coated surface cannot be obtained, gloss unevenness tends to occur, which is not preferable.

In addition to the above-mentioned improvement in the yield of fine fibers and the improvement in surface properties due to the delaminated clay, combining the improvement in surface properties due to the uniform pigment coating layer obtained by film transfer coating results in a synergistic effect. In addition to improving the glossiness of blank paper, the ink absorbability during printing can be made uniform and a uniform ink film is formed, so the printed matter obtained has a glossiness of 70% or higher, and further improved to 75% or higher. Can be made. By producing a finely coated paper by the above combination, while the weight per square meter is 60 g / m ² or less and lightweight, it is highly rigid, while the coating amount is 10 g / m ² or less per side and the coating amount is low. A finely coated paper having excellent whiteness, white paper gloss and printing gloss can be obtained.
In addition, it is preferable to use an on-machine coater integrated with a paper machine because the coating apparatus can be applied to a higher temperature base paper and can further improve the white paper glossiness and printing glossiness as compared to the off-machine coater. In addition, as a drying method in the dryer part, for example, various heating drying methods such as hot air heating, gas heater heating, and infrared heater heating can be appropriately employed.
The coating amount of the coating liquid on the base paper is preferably 2.9 g / m ^{2 to} 9.9 g / m ² , more preferably 5.0 g / m ^{2 to} 9.5 g / m ² , most preferably per one side. is ^{6.0g / m 2 ~9.0g / m 2} . If the amount of the coating liquid is less than 2.9 g / m ² per side, an uncoated part is likely to occur on the paper surface, and there is a risk that the glossiness of the white paper will be lowered or the printing gloss will be uneven. When 9.9 g / m ² or more is applied per side, since the density of the pigment coating layer is higher than that of the base paper, the weight and tightness of the resulting coated paper increase, and a bulky coated paper cannot be obtained.

[Calendar part]
For the purpose of imparting glossiness, flatness, and printability to the coating layer, a pair of rolls, at least one of which is a hot roll, preferably a paper is passed between an elastic roll and a metal roll to perform a flattening treatment. preferable. In general, in the flattening treatment, a coated paper is passed between an elastic roll and a metal roll, a high nip pressure is applied to the coated paper, the coated paper surface is polished by frictional force, and gloss is imparted. Since the paper is crushed by the nip pressure, the stiffness and bulkiness of the paper are impaired, and the nip pressure and frictional force are concentrated on the fine convex portions of the coated paper, causing fiber scorching, and heat and pressure. There was a problem of fading, such as the paper itself turning yellow. In order to avoid this problem, the linear pressure of the calendar is preferably 100 to 600 KN / m, and more preferably 100 to 400 KN / m. If it is less than 100 KN / m, the pigment coating layer will not be flattened. If it exceeds 600 KN / m, the base paper will be compressed more than necessary, so that the rigidity will decrease and the tightness will increase. . 100-300 degreeC is preferable and the temperature of a metal roll has more preferable 100-200 degreeC. When the temperature is less than 100 ° C, the pigment coating layer does not flatten, and when the temperature exceeds 300 ° C, fiber burns occur, or the coated paper itself turns yellow due to heat and pressure. Is not preferable.
As the calendar facility, a flattening facility such as a super calendar or a soft calendar can be used. Among them, a multi-nip calender, more preferably a 6-, 8-, or 10-stage multi-nip calender is optimal because it is easy to adjust the nip pressure and the rigidity and white paper gloss. Moreover, as an installation place of a calendar, an on-machine type integrated with a paper machine and a coating machine is preferable. In the on-machine type, flattening can be performed immediately after coating at a high paper surface temperature, so that the glossiness of blank paper is easily improved and the desired coated paper is easily obtained.

Next, although the fine coated paper of this invention is demonstrated still in detail based on an Example, this invention is not limited only to these Examples.
[Examples 1 to 29, Comparative Examples 1 to 20]
First, as raw material pulp, MDIP produced from LBKP, NBKP and magazine waste paper is mixed at a ratio (mass ratio) of 5:25:70, and each 100 parts by mass (absolute dry amount) of this pulp is solid content. , Light calcium carbonate (product number: TP-121-6S, manufactured by Okutama Kogyo Co., Ltd.) 10%, cationized starch (product number: Amilofax T-2600, manufactured by Abebe Japan Co., Ltd.) 3%, cationic coagulant ( Product number: Cassiofast SF, manufactured by BASF Co., Ltd.) 0.2%, Cationic flocculant (Product number: Percoll E24X, manufactured by Ciba Specialty Chemicals Co., Ltd.) 0.03%, Anionic flocculant (Product number: Bentonite) Ciba Specialty Chemicals Co., Ltd.) 2.0% was added to obtain a pulp slurry. However, Comparative Example 18 did not contain a cationic coagulant, Comparative Example 19 did not contain a cationic flocculant, and Comparative Example 20 did not contain an anionic flocculant.
Next, after a paper sheet was manufactured through a wire part, a press part, and a pre-dryer part, a starch coating solution was applied to the both surfaces with a coating amount described in Tables 1 and 2 under the coating conditions. After this undercoating, the film was dried by an after dryer part, and a pre-calender part was subjected to a flattening treatment at a nip pressure described in Tables 1 and 2. Next, in the coater part, coating solutions containing pigments and adhesives (10 parts by mass with respect to 100 parts by mass of pigment) prepared under the conditions described in Tables 1 and 2 are listed in Tables 1 and 2. Coating was performed on both sides of the base paper with the installation locations and equipment described in Tables 1 and 2 so that the coating amount was reached.

Details of the pigment and the adhesive are as follows.
(Pigment)
・ Fine granulated kaolin clay (Product number: AMAZON, manufactured by Kadam)
・ Delaminated kaolin clay (Product number: Capim DG, manufactured by Imerizu Minerals Japan, aspect ratio 11)
・ Wet heavy calcium carbonate (Part No .: Escalon # 90, Sankyo Flour Milling Co., Ltd.)
(adhesive)
・ Styrene-butadiene latex (Part No .: PA5036, manufactured by Nippon A & L Co., Ltd.)

Next, the base paper with the coating layer formed on both sides was applied to an after dryer part to dry the coating layer, and the calendar part was subjected to flattening treatment under the calendar conditions shown in Table 1. Then, it was used for the reel part and the winder part to obtain coated paper.
Paper was made using a gap former for the wire part, a straight-through type without an open draw for the press part, and a single deck dryer for the dryer part. In the coater part, after undercoating with a film transfer type roll coater, it was flattened with a pre-calender and overcoated with a film transfer type roll coater. In the calendar part, a flattening process was performed using a multi-nip calendar.

About the obtained coated paper, each physical property was investigated with the following method. The results are shown in Tables 1 and 2.
(A) US tsubo Measured according to the method described in JIS P 8124: 1998 “Paper and paperboard—Method for measuring basis weight”.
(B) Paper thickness and density (strength)
Measured according to the method described in JIS P 8118: 1998 “Paper and paperboard—Test methods for thickness and density”.
(C) Stiffness The longitudinal and lateral directions of the paper were measured in accordance with the method described in JIS P 8143: 2000 “A stiffness test method using a paper Clark stiffness tester”.
(D) Specific stiffness Calculated using the following equation.
Specific stiffness (m ² / g) = (rigidity (longitudinal) × rigidity (horizontal)) ^1/2 ÷ tsubo (e) whiteness Measured with a color analyzer (model number: MS-2020PLUS, manufactured by Macbeth Gretag). Measurement conditions are UVIN (including ultraviolet rays), SCI (including reflected light), C light source, viewing angle 2 °.
(F) White paper glossiness Measured according to the method described in JIS P 8142: 2005 “Paper and paperboard—Measurement method of 75 ° specular gloss”.
(G) Print Glossiness A print test specimen was prepared under the following conditions, and the glossiness was measured by the same method as the blank paper glossiness to obtain the print glossiness.
Printing machine: RI-3 type, manufactured by Meiko Seisakusho Co., Ltd. Ink: WebRex Nouver HIMARK process indigo, manufactured by Dainichi Seika Co., Ltd. Ink amount: 0.3 ml for the upper roll and 0.2 ml for the lower roll
Test method: The ink was kneaded for 3 minutes each with the upper and lower rolls (kneaded for 2 minutes, then the roll was inverted and further kneaded for 1 minute), and two-color simultaneous printing was performed at a rotation speed of 30 rpm.
(H) Operability The coating unevenness was evaluated based on the following evaluation criteria.
A: Coating unevenness did not occur and coating could be performed stably. ○: Coating unevenness occurred slightly, but coating could be performed relatively stably.
Δ: Some coating unevenness occurred, and a stable coating could not be obtained.
X: Coating unevenness occurred and coating was not stable.
Of the evaluation criteria, ◎, ○, and Δ are judged to be actually usable.

Both coated papers of Examples 1-29, high specific stiffness is a 0.25m ² /g~0.45m ² / g, bulk density is the 1.0g / cm ³ ~1.2g / cm ³ bulky However, it is an excellent coated paper having predetermined whiteness, white paper gloss (30 to 60%), and print gloss, and good operability.
On the other hand, the coated papers of Comparative Examples 1 to 20 are not specified with respect to the coating method and the coating amount as in the examples, so the specific stiffness, tightness, whiteness, white paper gloss, printing gloss The coated paper is bad in either degree or workability.

  Since the finely coated paper of the present invention is bulky, it has resource saving, cost reduction, volume feeling, high-class feeling and high rigidity, so that there are no problems in high-speed printing, automatic control, and paper conveyance. In addition, since it is excellent in whiteness, white paper glossiness, and printing glossiness, it has high cosmetics and can be suitably used for commercial printing such as flyers, magazines, and brochures.

Claims (4)

On at least one side of the base paper,
A coating mainly composed of oxidized starch is applied at a rate of 0.1 g / m ² to 1.0 g / m ² per side ,
After application of the oxidized starch , calendar treatment is performed at a linear pressure of 10 to 50 KN / m,
At least one pigment coating layer mainly composed of a pigment and a binder is applied with a film transfer type roll coater to 6.0 g / m ² to 9.5 g / m ² per side ,
Furthermore, it is calendered at a metal roll temperature of 100 ° C. or higher and a linear pressure of 100 to 600 kN / m,
These oxidized starch coating, calendering, pigment coating, and calendering in this order are on-machine manufacturing methods for finely coated paper,
The weight ratio of waste paper pulp to the raw material pulp of the base paper is 70% or more,
Add a cationic coagulant and a cationic flocculant to the pulp slurry before the screen and an anionic flocculant after the screen.
The anionic flocculant is bentonite or colloidal silica;
The pigment contains 10 to 50 parts by mass of delaminated clay having an average particle diameter of 0.4 to 0.8 μm and an aspect ratio of 5 or more with respect to 100 parts by mass of the pigment,
10 to 50 parts by mass of clay other than the delaminated clay is contained with respect to 100 parts by mass of the pigment,
Total oxidized starch and pigment coating layer and per side ^{5.1g / m 2 ~10g / m 2} ,
Bulk density is 1.0g / cm ³ ~1.2g / cm ³ and a ratio stiffness to lead the following expression is 0.25m ² /g~0.4m ² / g, the white paper gloss according to JIS P 8142 30 A method for producing finely coated paper, comprising obtaining finely coated paper having -60% and a basis weight of 60 g / m ² or less.
Specific stiffness (m ² / g) = (Stiffness (length) × Stiffness (width)) ^1/2 ÷ US tsubo The method for producing a finely coated paper according to claim 1, wherein the bentonite is added in a pure content of 0.1 wt% to 5.0 wt% with respect to the pulp.   The method for producing finely coated paper according to claim 1 or 2, wherein the cationic coagulant is polyethyleneimine and the cationic flocculant is polyacrylamide. The method for producing a finely coated paper according to any one of claims 1 to 3, wherein the cationic flocculant has an average molecular weight of 6 million to 16 million.