JP7029028B2 - Paper with light calcium carbonate inside - Google Patents

Description

The present invention relates to a paper containing light calcium carbonate.

In general, a filler, which is an inorganic substance, may be added to paper composed of cellulosic fibers, and the filler is used to improve optical properties, mainly whiteness and opacity, which tend to be insufficient with cellulosic fibers alone. Is added to. In recent years, in order to raise environmental awareness and reduce production costs, efforts have been made to reduce the amount of cellulosic fibers used as raw materials for wood and instead increase the filling rate in paper to increase the filling rate in paper. There is. However, when the filler is added, the optical characteristics are improved, but the tensile strength, the tear strength, the degree of stakehito size, and the like are lowered. Generally, chemicals such as paper strength enhancers and internal sizing agents are added to compensate for the reduced strength characteristics and sizing properties, but as the amount of chemicals used increases, not only does the burden on production costs increase. , The problem of internal dirt also arises.

In recent years, neutral papermaking has progressed, and light calcium carbonate is widely used as a filler. The reason is that the whiteness is higher than that of fillers such as talc and clay, and the particle shape, particle size, agglomeration state, etc. can be adjusted depending on the synthesis method, and it is easy to control the physical properties given to the paper. Therefore, many studies have been conducted on the particle shape and particle size of light calcium carbonate for fillers.

For example, Patent Document 1 describes primary particles having an average particle size of 4.0 to 15.0 μm and a BET specific surface area of 5.0 to 10 m ² / g as a filler and having needle-like and columnar shapes, and / or those thereof. It has been proposed to use light calcium carbonate consisting of aggregates.

Further, Patent Document 2 describes a paper in which a filler is added, and the filler is light calcium carbonate having a secondary particle diameter of 1 to 10 μm, in which primary particles of spindle-shaped calcium carbonate are floc-aggregated. Therefore, light calcium carbonate having a BET specific surface area of 8 to 20 m ² / g and a pore volume of 1.5 to 3.5 cm ³ / g has been proposed.

Further, Patent Document 3 proposes to reduce the drying load at the time of paper production by using rosetta-type calcium carbonate in which primary particles of spindle-shaped calcium carbonate are aggregated in a squid shape and talc as a filler. There is.

Furthermore, Patent Document 4 describes a rosette-type light calcium carbonate in which primary particles are radially aggregated, having a BET specific surface area of 1.0 to 8.0 m ² / g and an average particle diameter (D50) of 3.0. It is described that light calcium carbonate having a size of about 15.0 μm is added to the paper.

Japanese Unexamined Patent Publication No. 2013-60692 International release WO2004 / 108597 Japanese Unexamined Patent Publication No. 2012-172287 International release WO2015 / 146964

Since the shape of the primary particles of calcium carbonate described in Patent Document 1 is needle-like or columnar, the tip of the primary particles of light calcium carbonate is very thin when added to paper due to the characteristics of the shape, and the fiber. Since it easily enters the gap, it has a drawback that it hinders the formation of interfiber bonds of the paper and weakens the interlayer strength of the paper.

Further, the light calcium carbonate of Patent Document 2 has the same problem as that of Patent Document 1 because the aspect of the primary particles is high. Further, calcium carbonate according to Patent Document 2 has a high specific surface area of secondary particles formed by floc aggregation, and generally, when a filler having a high specific surface area is used, the amount of paper-making chemicals adsorbed on the filler surface also increases. Therefore, in order to obtain a certain chemical addition effect, it is necessary to add more chemicals than when a filler having a low specific surface area is used.

Further, Patent Document 3 describes that the dry load is reduced when talc is used in combination with rosetta-type light calcium carbonate, but nothing is examined about the relationship between the shape of rosetta-type light calcium carbonate and the strength of paper. Not.

Furthermore, although Patent Document 4 describes that rosette-type light calcium carbonate is internally added to paper, there are cases where the prevention of strike-through during printing is not sufficient.
In view of the above circumstances, an object of the present invention is to provide a paper in which strike-through during printing is effectively suppressed and the decrease in strength is suppressed.

As a result of diligent research, the present inventors have found that the above-mentioned problems can be solved by using light calcium carbonate having a specific particle morphology.
The present invention includes, but is not limited to, the invention of the following aspects.
(1) Paper filled with light calcium carbonate in which primary particles aggregate to form secondary particles. The primary particles of light calcium carbonate are spherical with an aspect ratio of 2.5 or less, and are light carbonic acid. The above paper, wherein the BET specific surface area of the secondary calcium particles is 15 to 40 m ² / g, and the average particle size of the secondary particles of light calcium carbonate is 3.0 to 15.0 μm.
(2) The paper according to (1), wherein the light calcium carbonate is obtained by aggregating 100 or more primary particles to form secondary particles.
(3) The paper according to (1) or (2), wherein the secondary particles of the light calcium carbonate have an average particle size of 3.5 to 10.0 μm.
(4) The paper according to any one of (1) to (3), wherein the average particle size of the secondary particles of the light calcium carbonate is 4.0 to 8.0 μm.
(5) The paper according to any one of (1) to (4), wherein the light calcium carbonate has an aspect ratio of 1.0 to 2.3.
(6) The paper according to any one of (1) to (5), wherein the light calcium carbonate has an aspect ratio of 1.1 to 2.1.
(7) The paper according to any one of (1) to (6), wherein the light calcium carbonate has an aspect ratio of 1.2 to 1.9.
(8) The paper according to any one of (1) to (7), wherein the secondary particles of the light calcium carbonate have a BET specific surface area of 15.5 to 30 m ² / g.
(9) The paper according to any one of (1) to (8), wherein the secondary particles of the light calcium carbonate have a BET specific surface area of 16 to 20 m ² / g.
(10) The paper according to any one of (1) to (9), which is a non-coated paper having no pigment coating layer.
(11) The paper according to any one of (1) to (10), wherein the ash content in the paper is 3 to 30% by weight.

According to the present invention, by using light calcium carbonate having a specific BET specific surface area and average particle size as a filler, strike-through during printing is effectively suppressed, and a paper in which a decrease in strength is suppressed is obtained. Can be manufactured.

FIG. 1 is an electron micrograph of light calcium carbonate (Sample 1). FIG. 2 is an electron micrograph of light calcium carbonate (Sample 2). FIG. 3 is an electron micrograph of light calcium carbonate (Sample 3). FIG. 4 is an electron micrograph of light calcium carbonate (Sample 4).

The present invention relates to a paper filled with light calcium carbonate, in which a large number of primary particles aggregate to form secondary particles.
Light calcium carbonate in which primary particles aggregate to form secondary particles
In the present invention, light calcium carbonate having a specific average particle size and BET specific surface area is used. When light calcium carbonate, in which a large number of primary particles aggregate to form secondary particles, is used as an internal filler, the present inventors surprisingly effectively suppress strike-through during printing. We have found that paper with excellent strength characteristics such as tensile strength and tear strength can be obtained. Generally, light calcium carbonate has a crystal system such as calcite type and aragonite type, and has various shapes such as columnar, needle-like, spindle-shaped, and cubic-shaped. However, the light calcium carbonate according to the present invention has spherical primary particles. Aggregate to form secondary particles, and the shape of the secondary particles is special, so that the BET specific surface area is large.

In general, light calcium carbonate is advantageous in terms of production cost and operability, and is also excellent in that paper having high opacity can be obtained with a low addition amount. In addition, the light calcium carbonate of the present invention has a special shape, and when it is highly blended (internally added) to the base paper, the opacity of the base paper is greatly improved and strike-through is effectively prevented.

Although the reason why the excellent effect is obtained in the present invention is not clear, the light calcium carbonate of the present invention is characterized by having a relatively large average particle size of secondary particles and a large BET specific surface area. Generally, when comparing light calcium carbonates having the same particle shape and average particle size, the smaller the BET specific surface area, the larger the primary particles. In the light calcium carbonate according to the present invention, spherical primary particles having a small aspect ratio are gathered to form secondary particles, so that the secondary particles have a porous structure. Therefore, it is considered that calcium carbonate adsorbs the ink component during printing and suppresses the excessive penetration of the ink into the paper, and as a result, the strike-through is suppressed.

The light calcium carbonate used in the present invention is obtained by aggregating primary particles such as calcite-based calcium carbonate or aragonite-based calcium carbonate to form secondary particles, and is higher than other forms of calcium carbonate. It has the characteristics of showing specific surface area and oil absorption.

The BET specific surface area of the light calcium carbonate of the present invention needs to be 15 to 40 m ² / g. If it is less than 15 m ² / g, the absorption of ink and water at the time of printing is poor, and the effect of preventing strike-through may not be sufficient. Further, when the BET specific surface area exceeds 40 m ² / g, the formation of interfiber bonds of the paper is inhibited, and the tensile strength and the tear strength are lowered. The BET specific surface area is preferably 15.5 to 30 m ² / g, more preferably 16 to 20 m ² / g.

The light calcium carbonate of the present invention has an average particle size (D50) of secondary particles measured by a laser diffraction method of 3.0 μm or more and 15.0 μm or less. When D50 exceeds 15.0 μm, the filler yield improves, but since the filler in the paper is localized, the tensile strength and tear strength tend to decrease and the strike-through prevention effect tends to decrease. Be done. Further, when D50 is less than 3.0 μm, the filler distribution in the paper becomes uniform, but the filler inhibits the interfiber bond in the paper, so that the paper strength tends to decrease, and the filler yield tends to decrease. As it worsens, the effect of preventing strike-through tends to decrease. Furthermore, if D50 is small, it is necessary to add chemicals such as yield improvers, which may increase the load on production costs, and also increase the amount of ash and chemicals in white water, resulting in scale deposition. The problem of internal dirt such as is also generated. Therefore, in order to obtain a paper having a high yield as a filler and excellent paper strength characteristics and size, the D50 is preferably 3.5 μm or more, and more preferably 4.0 μm or more. The upper limit of D50 is preferably 10.0 μm or less, and more preferably 8.0 μm or less.

Further, the light calcium carbonate of the present invention has further excellent paper strength and physical characteristics when the particle size (d50) of 50% by volume of the particle size distribution curve measured by the X-ray transmission method is 2.0 to 5.0 μm. It is preferable, and 2.2 to 3.4 μm is particularly preferable.

In a preferred embodiment, the calcium carbonate according to the present invention has an extremely large number of primary particles aggregated to form secondary particles having a broccoli-like shape. In the calcium carbonate according to the present invention, for example, 100 or more primary particles are aggregated to form secondary particles, but the number of primary particles may be 500 or more or 1000 or more. The upper limit of the number of primary particles is not particularly limited, but may be, for example, 100,000 or less, and may be 10,000 or less.

The calcium carbonate according to the present invention has a spherical primary particle shape. The aspect ratio of the primary particles is 2.5 or less, preferably 1.0 to 2.3, more preferably 1.1 to 2.1, and even more preferably 1.2 to 1.9. The particle size of the primary particles is preferably 0.1 to 1.0 μm, more preferably 0.2 to 0.75 μm, and even more preferably 0.3 to 0.5 μm. The particle size and aspect ratio of the primary particles can be calculated by observing the shape using an electron microscope.

Generally, the method for producing light calcium carbonate is a "liquid-gas" method (carbonic acid gas method) in which carbonic acid gas is blown into a slaked lime slurry to react, and a "liquid-liquid" method (solubilized salt method) using sodium carbonate or the like. Is known, and in the present invention, light calcium carbonate obtained by any of the production methods can be used. The present invention does not particularly limit the method for producing light calcium carbonate, but a step of obtaining slaked lime by adding and mixing sedative water in a range where the molar ratio to fresh lime is 2.5 or less by the above-mentioned "liquid-gas" method. (A), a step (B) of obtaining a slaked lime slurry by mixing the slaked lime and water, and a step of blowing carbon dioxide-containing gas into the slaked lime slurry to carbonize it by appropriately adjusting the temperature and stirring conditions (B). The light calcium carbonate produced through C) is the best because the desired particle shape, particle size, and BET specific surface area can be easily obtained.

Paper with light calcium carbonate internally The paper of the present invention using specific light calcium carbonate as a filler has good surface smoothness and excellent strength characteristics such as tensile strength without impairing the optical characteristics of the paper. Since it can effectively suppress strike-through during printing, it can be used for various purposes without any particular limitation. The types of paper include various types of coating base paper, newspaper paper, high-quality and medium-quality paper, electrophotographic transfer paper, inkjet paper, heat-sensitive paper, pressure-sensitive paper, kraft paper, crimp recording paper, wrapping paper, and paper containers. Examples thereof include base paper, paperboard, wallpaper base paper, fiberboard base paper, photographic base paper, impregnation base paper, and flame-retardant paper. Among them, in one aspect, the paper of the present invention is suitable as a printing paper used for various printing methods such as offset printing and gravure printing.

Hereinafter, as specific examples of the paper impregnated with the light calcium carbonate of the present invention, the use as uncoated paper, coated base paper and coated paper, and transfer paper for electrophotographic photography will be described in detail. The paper of the present invention is not limited to these uses.

(Uncoated paper)
The basis weight of the non-coated paper having no pigment coating layer, which is internally added with the light calcium carbonate of the present invention as a filler, is not particularly limited, but the desired effect is exhibited at 30 to 650 g / g. The range is about m ² . In one embodiment, the basis weight of the uncoated paper according to the present invention is about 35 to 200 g / m ² , and may be about 40 to 120 g / m ² . The light calcium carbonate of the present invention can be added to multi-layered paperboard, cardboard, and other thick papers that exceed this range.

Examples of the pulp used as a raw material for papermaking include bleached chemical pulps such as LBKP and NBKP, unbleached pulps such as LUKP and NUKP, crushed wood pulp (GP), pressurized crushed wood pulp (PGW), and refiner crushed wood pulp (PGW). RGP), mechanical pulp such as thermomechanical pulp (TMP), deinked pulp (DIP), used paper pulp, waste paper and the like are appropriately mixed and used. Further, one or more kinds of pulp fiber, synthetic pulp, inorganic fiber and the like obtained from non-wood fiber raw materials such as kenaf can be blended in the base paper. Mechanical pulp, deinked pulp (DIP), and used paper pulp can be bleached and used as needed, and the degree of bleaching can be arbitrary.

The light calcium carbonate of the present invention is a commonly used filler, for example, heavy calcium carbonate, light calcium carbonate other than the present application, calcium sulfite, gypsum, talc, kaolin, engineered kaolin, calcined kaolin, white carbon, etc. Inorganic fillers such as amorphous silica, delaminated kaolin, caustic soil, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, paper sludge, and recycled inorganic particles from deinked floss. It can also be mixed with organic fillers such as urea formalin resin, vinyl chloride resin, polystyrene resin, urea / formalin resin, melamine resin, styrene / butadiene copolymer resin, phenol resin, and plastic hollow particles. can. The mixing ratio can be adjusted according to the quality of the paper, and is not particularly limited, but when 10 parts by weight or more of the light calcium carbonate of the present invention is used, the effect of the present invention becomes large. In order to obtain a paper having good yield as a filler, good size and surface smoothness, and greatly improved paper strength characteristics, the light calcium carbonate of the present invention should be added to 100 parts by weight of the internal filler of the paper. It is preferably contained in an amount of 50 parts by weight or more, more preferably 60 parts by weight or more, and particularly preferably 70 parts by weight or more.

If the ash content in the paper is less than 3% by weight, the optical characteristics, mainly whiteness, and opacity of the paper tend to be insufficient. Therefore, the ash content of the paper of the present invention is preferably 5% by weight or more, and 10% by weight. The above is more preferable. On the other hand, if the ash content exceeds 30% by weight, problems such as wire wear and stains in the paper machine system are likely to occur. Therefore, in general, it is preferable to add the filler in the range of 3 to 30% by weight, and it is particularly preferable to add the filler in the range of 5 to 20% by weight.

In addition to pulp and fillers, paper agents include internal sizing agents, anionic, nonionic, cationic or amphoteric yield improvers, drainage improvers, paper strength enhancers, dyes, fluorescent dyes, bulky agents, etc. Various internal aids for papermaking exemplified in 1 can be used as needed. Specific examples of the internal sizing agent include alkyl ketene dimer-based, alkenyl succinic anhydride-based, styrene-acrylic, higher fatty acid-based, petroleum resin-based sizing agent, rosin-based sizing agent, and the like. Specific examples of the yield improver, drainage improver, and paper strength enhancer include polyvalent metal compounds such as aluminum (specifically, sulfate band, aluminum chloride, sodium aluminate, basic aluminum compound, etc.). , Various starches, cellulose nanofibers, carboxymethyl cellulose, hydroxyethyl cellulose, cellulose derivatives such as methyl cellulose, polyacrylamide, urea resin, polyamide / polyamine resin, polyethyleneimine, polyamine, polyvinyl alcohol, polyethylene oxide and the like. The paper containing the light calcium carbonate of the present invention has high chemical addition efficiency and excellent size expression.

When adding the filler containing the light calcium carbonate of the present invention to the pulp raw material, it is preferable to add the filler while sufficiently stirring the pulp raw material, and examples of the place of addition include a machine chest inlet and a fan pump suction port. Be done.

The papermaking conditions are not particularly limited, and the paper machine includes, for example, a long net paper machine, a twin wire paper machine, an on-top paper machine, a circular net paper machine, a short net paper machine, and the like on a commercial scale. The machine can be mentioned, and it can be appropriately selected and used according to the purpose.

As the papermaking method, any method such as acidic papermaking, neutral papermaking, and weakly alkaline papermaking can be used, but since calcium carbonate dissolves in the acidic region, papermaking is performed in the range of neutral to weakly alkaline. Is desirable.

A surface treatment agent may be applied to the paper in order to improve the surface strength, impart water resistance, improve ink inking property, and the like. The type of surface treatment agent is not particularly limited, but self-modification produced by thermochemical modification or enzymatic modification in a papermaking factory using raw starch, oxidized starch, esterified starch, cationized starch, and acetylated tapioca starch as raw materials. It preferably contains starch such as starch, modified starch such as aldehyded starch and hydroxyethylated starch. Cellulous derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose and cellulose nanofibers, modified alcohols such as polyacrylamide, polyvinyl alcohol, carboxyl-modified polyvinyl alcohol and acetacetylated polyvinyl alcohol, styrene-butadiene copolymers, polyvinyl acetate and chloride. It is also possible to use a vinyl-vinyl acetate-based copolymer, polyvinyl chloride, polyvinylidene chloride, polyacrylic acid ester and the like in combination. Further, for the purpose of enhancing the sizing property, it is also possible to use a surface sizing agent such as a styrene-based sizing agent, an olefin-based sizing agent, an acrylate-based sizing agent, a styrene-acrylic sizing agent, and a cationic sizing agent in combination. Further, in the present invention, various auxiliary agents such as dispersants, thickeners, water retention materials, defoamers, water resistant agents, colorants, conductive agents, etc., which are blended in ordinary clear coating, are appropriately used, if necessary. used.

As an apparatus for applying the surface treatment coating liquid, a known size press apparatus, for example, a 2-roll type, a 3-roll type, a gate roll type, a film transfer type, or the like can be used. The film transfer type is a method in which a wet coating film is formed on an applicator roll and the coating film is transferred to the surface of the base paper. Examples thereof include a transfer roll coater and a rod metering size press coater. Further, the coating may be applied using a coater (coating machine) such as a curtain coater, a spray coater, or a blade coater.

It is also possible to apply the surface treatment coating liquid to the base paper by 0.1 to 5.0 g / m ² per side with these coating devices, and then dry it with a dryer to finish it. However, in order to improve printability, machine calendar and soft calendar can be used. , It is preferable to process with a calendar device such as a shoe calendar. Further, the surface treatment liquid may be applied to both surfaces.

(Coated base paper and coated paper)
The paper containing the light calcium carbonate of the present invention may be used as the coated base paper, and the coated paper having at least one coating layer containing a pigment and an adhesive as main components may be used. By adding the light calcium carbonate of the present invention internally, the interlayer strength is improved, so that the blister suitability is excellent and the sizing property is exhibited, so that a coated paper having excellent surface smoothness can be obtained.

Usually, the above-mentioned paper on which light calcium carbonate is added and coated with a coating liquid containing a surface treatment agent may be used as a coating base paper. By applying this surface treatment, there is an effect of improving the surface strength of the coated base paper or cleaning foreign substances on the surface of the coated base paper, and it is possible to suppress the occurrence of streaks and the like. However, in the case of an on-machine coater that makes a base paper for coating and coats and dries a coating layer containing pigments and adhesives as the main components, surface treatment is performed to avoid restrictions on drying capacity and the risk of paper breakage. May be omitted.

The coated base paper can also be smoothed and finished by a machine calendar, a soft calendar, or the like.
The pigment used for the coating layer is not particularly limited, and pigments used in the field of ordinary coated paper, such as heavy calcium carbonate, light calcium carbonate of the present invention or other, calcium sulfite, and gypsum. , Tarku, Kaolin, Engineered Kaolin, Calcined Kaolin, White Carbon, Amorphous Silica, Delaminated Kaolin, Kaiso Soil, Magnesium Carbonate, Titanium Dioxide, Aluminum Hydroxide, Calcium Hydroxide, Magnesium Hydroxide, Zinc Hydroxide, Papermaking Inorganic pigments such as sludge and recycled inorganic particles from deinked floss, urea formalin resin, vinyl chloride resin, polystyrene resin, urea / formalin resin, melamine resin, styrene / butadiene copolymer resin, phenol resin, plastic hollow One type or two or more types of organic pigments such as particles can be appropriately selected and used in combination as needed. The mixing ratio can be adjusted according to the quality of the paper and is not particularly limited.

In the pigment coating liquid, as an adhesive, an adhesive used in the field of ordinary coated paper and various surface treatment agents used as a surface treatment agent in the non-coated paper are used as an adhesive. You may. Further, these adhesives can be used alone or in combination of two or more.

The blending amount of the adhesive is not particularly limited, but 1 to 50 parts by weight, preferably 5 to 30 parts by weight, is blended per 100 parts by weight of the pigment.
Also, if necessary, colored dyes, colored pigments, fluorescent whitening dyes, thickeners, water retention agents, antioxidants, antioxidants, conduction inducers, defoamers, UV absorbers, dispersants, pH adjustments. Various auxiliaries such as agents, mold release agents, water resistant agents, and water repellent agents can be appropriately blended.

The solid content concentration of the pigment coating liquid can be selected in the range of 25 to 80% by mass. Considering the adjustment of the coating amount and the operability, the range of 50 to 70% by mass is desirable.
The coating layer provided on the coating base paper is not particularly limited as to one layer or two or more layers. In the case of multiple layers, not all of them need to be the same and can be appropriately adjusted according to the required quality level. Further, the coating amount of the coated layer is not particularly limited, and can be adjusted according to the blank paper quality, print quality, etc. of the coated paper, but generally, 0. It is about 5 to 40.0 g / m ² .

Regarding the coating method for providing the coating layer in the present invention, various coating devices used in the ordinary field of coated paper manufacturing, such as an air knife coater, various blade coaters, gate roll coaters, and roll coaters. , Die coater, curtain coater, spray coater and the like can be used as appropriate.

After applying the pigment coating liquid to the base paper, the coating layer is dried to obtain a coated paper. As the drying method, for example, a usual method such as a steam heater, a gas heater, an infrared heater, an electric heater, a hot air heater, a microwave, or a cylinder dryer can be arbitrarily selected and used.

The coated paper thus obtained may be passed through various publicly known and public finishing devices such as a super calendar, a gloss calendar, a soft calendar, a mat calendar, and the like to finish the product.

(Transfer paper for electrophotographic)
Transfer paper for electrophotographic can be produced using the paper containing the specific light calcium carbonate of the present invention. By adding the light calcium carbonate of the present invention internally, the interlayer strength is improved, so that it is possible to obtain an electrophotographic transfer paper that is less likely to cause curl or paper dust during printing. Further, since the light calcium carbonate of the present invention does not easily wear the wire of the paper machine, it can be used for paper making using a general paper machine. In particular, the paper making machine used for making transfer paper for electrophotographic photography is preferably, but is not limited to, a hybrid former or an on-top former having a double-sided dehydration mechanism.

The pulp raw material for the electrophotographic transfer paper produced in the present invention is not particularly limited, as long as it is generally used as a papermaking raw material, such as various pulps exemplified for uncoated paper. good. Above all, it is desirable to use more deinked pulp and used paper pulp from the environmental point of view.

The light calcium carbonate of the present invention can be used alone or in combination with other papermaking fillers. When used in combination with other papermaking fillers, the known fillers exemplified for uncoated paper can be used alone or in combination of two or more as appropriate. The mixing ratio can be adjusted according to the quality of the paper, and in order to reduce curl and paper dust during printing and suppress wire wear during papermaking, the specific light calcium carbonate of the present invention is applied to the paper. It is preferable to contain 50 parts by weight or more, more preferably 60 parts by weight or more, and particularly preferably 70 parts by weight or more in 100 parts by weight of the internal filler.

If the ash content in the paper is less than 3% by weight, the optical characteristics, mainly whiteness, and opacity of the paper tend to be insufficient. Therefore, the ash content is preferably 5% by weight or more, and more preferably 10% by weight or more. On the other hand, if the ash content exceeds 30% by weight, the wire is worn, the inside of the paper machine is dirty, and the bending stiffness is reduced. Problems such as are likely to occur. Therefore, in general, it is preferable to add it in the range of 3 to 30% by weight, and it is particularly preferable to add it in the range of 5 to 20% by weight.

When producing a transfer paper for electrophotographic using the light calcium carbonate of the present invention, various papermaking chemicals as exemplified in the above uncoated paper and one or more auxiliary agents are used in combination. can do. These auxiliaries may be added to the slurry of light calcium carbonate of the present invention in advance and then applied to the paper machine, or may be applied to the paper machine separately from the slurry of light calcium carbonate of the present invention. .. Similarly to the above, high chemical addition efficiency can be obtained in the transfer paper for electrophotographic, so that the size development is excellent.

For the purpose of increasing the surface strength, the surface treatment agent may be applied on the transfer paper for an electrophotographic train in which the specific light calcium carbonate of the present invention is added. As the surface treatment agent, the surface treatment agent exemplified in the above-mentioned non-coated paper may be used. In addition, in order to control the electrical resistance and improve the toner fixability, an inorganic conductive agent such as sodium chloride, sodium sulfate, or potassium chloride or an organic conductive agent such as dimethylaminoethyl methacrylate is added as a conductive agent to the outside. It is preferable to apply it together. The coating amount of the surface treatment agent containing the conductive agent is appropriately adjusted, but the usual coating amount is about 0.5 to 4.0 g / m ² on both sides. The amount of the conductive agent applied is about 0.02 to 0.5 g / m ² on both sides.

The basis weight of the electrophotographic transfer paper of the present invention can be, for example, 40 to 80 g / m ² , and the physical properties may be adjusted to a level having a friction coefficient or the like of a normal electrophotographic transfer paper.

Hereinafter, the details of the present invention will be specifically described with reference to experimental examples, but the present invention is not limited to the following examples. In the present specification, unless otherwise specified, "%" is all "% by weight", and the numerical range includes the end points thereof.

Experiment 1: Production and evaluation of light calcium carbonate Light calcium carbonate was synthesized by the carbon dioxide gas method. Specifically, calcined quicklime is mixed and reacted with water to obtain a slaked lime solution (lime), the lime is cooled to an appropriate temperature with a heat exchanger, and then an organic acid (auxiliary agent) is added. Then, carbonic acid gas was blown into the tank, which is a reaction vessel, while stirring to obtain light calcium carbonate of Samples 1 to 12. The table below shows the lime concentration, organic acid (auxiliary) addition rate, carbonation start temperature, and carbonation time.

In addition, the obtained calcium carbonate was evaluated by the following evaluation method.
(1) Average particle size Using a laser diffraction / scattering type particle size distribution measuring instrument (Malburn, Mastersizer 2000), the 50% point (D50) of the volume cumulative distribution was taken as the average particle size.
(2) BET specific surface area Measurement was performed according to JIS Z 8830-2001.
(3) Boiled flaxseed oil was used as the oil for measuring the amount of oil absorption, and the measurement was carried out according to JIS K 6217-4.
(4) Aspect ratio of primary particles The sample is magnified and observed with an electron microscope, and the lengths of the long and short sides of 10 to 20 primary particles randomly selected are measured, and the average value of this ratio is calculated. Adopted.
(5) Abrasion (plate wear)
The plate wear characteristics were evaluated by measuring the softness of light calcium carbonate using an Einlaner AT-1000 wear tester. Specifically, the long net brass wire screen standard attached to the wear tester is exposed to a 10% light calcium carbonate suspension for 174,000 revolutions. The weight of the long net wire screen before and after the treatment was measured, and the wear weight (milligram) of the long net wire screen was calculated from the difference. The evaluation criteria are as follows.
◎ (Excellent): Wire wear is less than 1.2 mg ○ (Good): Wire wear is 1.2 mg or more and less than 2.0 mg △ (Medium): Wire wear is 2.0 mg or more and less than 4.0 mg × (Bad): Wire Abrasion of 4.0 mg or more (6) Particle size of primary particles The sample was magnified and observed with an electron microscope, and the length of the long side was measured for 10 to 20 randomly selected primary particles, and the average value was measured. It was adopted.

The results are shown in Table 1 and FIGS. 1 to 4. By lowering the lime concentration, increasing the addition rate of auxiliaries, and lowering the carbonation start temperature, it was possible to synthesize light calcium carbonate with a small primary particle size (large specific surface area) and a large secondary particle size (Sample 1). ). In particular, in the calcium carbonates of Samples 1, 5 to 9 according to the present invention, 1000 or more primary particles aggregated to form secondary particles.

Furthermore, the aspect ratio of the primary particles is set to the conditions that inhibit the growth of the primary particles (low lime concentration, high organic acid addition rate, low carbonation start temperature, short carbonation time). Could be a low light calcium carbonate.

Experiment 2: Manufacture and evaluation of calcium carbonate inner paper A pulp slurry made of 100% broad-leaved bleached kraft pulp (LBKP, CSF: 360 ml) contains 0.5% aluminum sulfate and ash content in paper with respect to the total solid content of the pulp slurry. Light calcium carbonate (samples 1 to 12 of Experiment 1) was added so that the value was 10%, and the paper material was prepared.

Using this paper material as a raw material, a circular hand-made paper machine was used to prepare a hand-made paper having a basis weight of about 60 g / m ² according to JIS P 8222. In the drying of the wet paper after press dehydration, the paper was obtained by drying with a lab-scale cylinder dryer instead of the method of bringing the wet paper into close contact with the metal plate specified in JIS P 8222.

The physical characteristics of the paper thus produced were evaluated by the following procedure.
(Ash content) Measured according to JIS P8251 (ashing temperature: 525 ° C.).
(Basis weight) Measured according to JIS P 8124.
(Paper thickness) Measured according to JIS P 8118.
(ISO whiteness) Measured according to JIS P 8148.
(Opacity) Measured according to JIS P 8149.
(Tensile strength) Measured according to JIS P 8113.
(Breakthrough)
For the felt surface of uncoated paper, the printing surface density measured with a Macbeth reflection densitometer is the two colors of newspaper ink (Vantean Echo, manufactured by Toyo Ink Co., Ltd.) indigo and crimson using an RI printing machine. After printing in layers so as to be 1.30 and adjusting the humidity in an environment of 23 ° C. and 50 RH% for 24 hours, the Y value before and after printing was measured for the back side when the printed side was the front side (after printing). Y value / Y value before printing) × 100 was defined as a strike-through value.

In addition, "strike-through quality", "paper strength", and "plate wear" were evaluated on a four-point scale based on the following criteria (◎: excellent, ○: good, △: medium, ×: inferior).
(Evaluation of strike-through quality)
⊚: strike-through value is 76.8 or more ○: strike-through value is 76.0 or more and less than 76.8 Δ: strike-through value is 73.0 or more and less than 76.0 ×: strike-through value is less than 73.0 (paper) Evaluation of power)
⊚: Tensile strength is 2.63 or more ○: Tensile strength is 2.57 or more and less than 2.63 Δ: Tensile strength is 2.50 or more and less than 2.57 ×: Tensile strength is less than 2.50 (evaluation of plate wear)
⊚: Wire wear resistance is less than 1.2 mg ○: Wire wear resistance is 1.2 mg or more and less than 2.0 mg Δ: Wire wear resistance is 2.0 mg or more and less than 4.0 mg ×: Wire wear resistance is 4.0 mg or more

The results are shown in Table 2. In Sample 1, which is an example of the present invention, the BET specific surface area of light calcium carbonate is higher and the oil absorption of the printing ink is higher than that of Samples 2 to 3 (Comparative Example), so that the strike-through quality is improved.

Further, in Sample 1 (Example), the particle size (secondary particle size) of light calcium carbonate is larger than that of Sample 2 and Sample 4 (Comparative Example), so that the filler inhibits the interfiber bond in the paper. It was difficult to reduce the paper strength (tensile strength).

Further, comparing Samples 1 to 3, when the BET specific surface area of the used light calcium carbonate is large, that is, the primary particle size is small, wire wear during fabrication and plate wear during printing can be suppressed. In general, it is considered that the particle size and particle morphology of particles have a great influence on the wear resistance, and if the primary particle diameter is large, the morphology is irregular and has sharp edges, the wear resistance (plate wear) tends to deteriorate. be.

Claims (10)

Paper filled with light calcium carbonate, in which 1000 or more primary particles aggregate to form secondary particles.
The primary particles of light calcium carbonate are spherical with an aspect ratio of 1.9 or less , the BET specific surface area of the secondary particles of light calcium carbonate is 15 to 40 m ² / g, and the average particle size of the secondary particles of light calcium carbonate is. The above paper, which is 3.0 to 15.0 μm. The paper according to claim 1, wherein the secondary particles of the light calcium carbonate have an average particle size of 3.5 to 10.0 μm. The paper according to claim 1 or 2, wherein the secondary particles of the light calcium carbonate have an average particle size of 4.0 to 8.0 μm. The paper according to any one of claims 1 to 3, wherein the light calcium carbonate has an aspect ratio of 1.0 or more . The paper according to any one of claims 1 to 4, wherein the light calcium carbonate has an aspect ratio of 1.1 or more . The paper according to any one of claims 1 to 5, wherein the primary particles of the light calcium carbonate have an average particle size of 0.1 to 1.0 μm. The paper according to any one of claims 1 to 6, wherein the secondary particles of the light calcium carbonate have a BET specific surface area of 15.5 to 30 m ² / g. The paper according to any one of claims 1 to 7, wherein the secondary particles of the light calcium carbonate have a BET specific surface area of 16 to 20 m ² / g. The paper according to any one of claims 1 to 8, which is a non-coated paper having no pigment coating layer. The paper according to any one of claims 1 to 9, wherein the ash content in the paper is 5 to 30% by weight.

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