JP2000054287A - Newsprint paper for offset printing and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a newsprint paper for offset printing excellent in opacity and whiteness degree with an especially small amount of titanium dioxide used in relation to a lightweight newsprint paper. SOLUTION: This newsprint paper has a distribution state of titanium dioxide in which the total area occupied by the titanium dioxide is 2-30% (area ratio) based on the paper surface area used for measurement and <=5 μm2 number- average area of the titanium dioxide when evaluating the paper surface of the newsprint paper according to a mapping analytical method by using an electron probe microanalyzer (EPMA) in the newsprint paper containing the titanium dioxide therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to newsprint, and more particularly to newsprint for offset printing which is excellent in opacity and whiteness with a small amount of titanium dioxide used, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, as a part of measures to reduce environmental problems due to an increase in garbage and to reduce transportation costs, the weight of paper has been greatly reduced. On the other hand, the negative effect on the paper quality due to the weight reduction of the paper is great, and the reduction of the opacity, which is one of the important quality requirements, is a serious problem. The problem of the opacity is that the opacity of the white paper of the paper is reduced due to the decrease in the bulk due to the weight reduction of the paper, so that the printed image of the lower paper can be seen through. The vehicle (resin and solvent) in the ink penetrates into the printing paper and deteriorates the optical characteristics of the printing paper, so that the printed image on the front surface can be seen transparently on the back side of the printed material. ), A decrease in opacity after printing, which can cause a big problem such as difficulty in reading and difficulty in reading as an end user as a strike-through trouble.

[0003] As a method for solving the problem of the decrease in opacity, pigments such as titanium dioxide, white carbon, calcined kaolin, structured kaolin, hollow plastic pigment and calcium carbonate are added to a pulp-based paper stock. An internal addition method for papermaking, an external addition coating method in which a pigment such as the above-mentioned titanium dioxide is coated on a base paper together with an adhesive, and a method in which the above internal addition method and the external addition coating method are used in combination are adopted. Can be

Fillers (pigments) used for internal or external application
Among them, titanium dioxide has a greater effect of improving opacity than other pigments, and has been widely used as a pigment most effective in improving opacity. For example, JP-A-3-59194 discloses a method of using rutile-type titanium dioxide having a specific particle size distribution as a pigment of a coating layer for the purpose of preventing fading of a high-yield pulp used for base paper. JP-A-4-146297 proposes a method of blending a specific amount of titanium dioxide in the undercoat layer and the overcoat layer of a relatively light-weight (for example, 80 g / m ² or less) rice coated paper. ing.

Incidentally, titanium dioxide is, for example, JIS
As described in K5116, there are various types depending on the crystal type and the surface treatment, and when used for the purpose of improving the opacity of paper, the effect differs depending on the type of titanium dioxide. In addition, generally, titanium dioxide is contained as an internal filler in a stock containing a sulfuric acid band, such as newsprint paper, and an acid paper-made paper or an acid paper-made paper is coated with a surface treatment agent containing titanium dioxide. The dried paper undergoes agglomeration during the papermaking process or during the application of a surface treatment agent containing titanium dioxide. As a result, a desired effect of improving the desired opacity cannot be obtained. In short, the titanium dioxide particles easily agglomerate under the conditions of the aqueous liquid, for example, the presence of the sulfate band, the pH of the liquid and the type and amount of the adhesive used together, or the effect of the auxiliary agent, etc. Can not be expected to have a sufficient opacity expression effect originally possessed. Here, when using expensive titanium dioxide to improve the opacity of paper, it is extremely important that the amount used is as small as possible while maximizing the effect of improving the opacity. It is.

[0006] In particular, in papers such as newsprints, the weight of which is intended to be much lighter, applying a pigment such as titanium dioxide internally and / or externally can keep the weight of the product constant. In this case, it means that the weight of the pulp fiber is relatively reduced by the increase in weight due to the addition of the pigment. As a result, although opacity can be improved,
Another problem may occur, such as a decrease in paper thickness or rigidity (paper stiffness). Therefore, while minimizing the amount of titanium dioxide used, the development of high-quality, lightweight newsprint that maximizes the effect of improving its opacity and hardly reduces the thickness or rigidity of the paper. It is strongly desired.

[0007]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a light-weight paper which efficiently improves the opacity of paper, uses a small amount of titanium dioxide, has high whiteness, and has excellent suitability for offset printing. And a method of manufacturing the same for offset printing.

[0008]

SUMMARY OF THE INVENTION According to the present invention, in a newsprint for offset printing containing titanium dioxide, the distribution of titanium dioxide is determined by using an electron beam microanalyzer (EPMA). When evaluated by mapping analysis, the total area occupied by titanium dioxide is 2 to 30% (area ratio) of the paper surface area used for measurement, and the number average area of titanium dioxide is 5 μm ² or less. Newspaper for offset printing characterized by the following.
Further, in a method for producing newsprint paper for offset printing by applying an aqueous pigment composition containing titanium dioxide and an adhesive to the base paper surface, in preparing the aqueous pigment composition,
For 100 parts of titanium dioxide in advance, a water-soluble polymer having a carboxyl group relative to the solid content is 0.5 to
Add 2 parts and use slurried titanium dioxide,
The aqueous pigment composition is prepared so as to satisfy the following condition (1), and the coating amount of titanium dioxide is 0.1 to 1.5 g / m ² per one side by dry weight. A method of producing newsprint for offset printing as described above. [Condition (1): 100 ppm of aluminum sulfate (as Al ₂ (SO ₄ ) ₃ ) was added to and mixed with the aqueous pigment composition (coating solution), and then the aqueous pigment composition was treated with titanium dioxide. The aqueous pigment composition obtained by diluting with water so as to have a weight concentration of 20 ppm has a light transmittance of 55%.
Below)

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, titanium dioxide which is the main point of the present invention will be described. Titanium dioxide is known in three types, anatase type, rutile type, and brookite type, depending on its crystal type. Practically, anatase type and rutile type are used, and titanium dioxide used in the present invention can preferably use these two types of crystal types. Normally, titanium dioxide used for the purpose of improving opacity and whiteness has the highest effect when the particle diameter is about half of the wavelength of light. It is adjusted by pulverization or the like to have a thickness of about 0.3 μm. The surface of the titanium dioxide particles is coated with a metal oxide such as aluminum, silicon, zirconium, zinc, tin, and titanium from the viewpoint of dispersibility and weather resistance. Further, it is known that rutile-type titanium dioxide has a higher refractive index than the anatase type, and the former gives higher opacity than the latter, due to the above-mentioned difference in crystal type.

The present inventors have conducted intensive studies on the effect of improving the opacity of paper containing titanium dioxide. As a result, the effect of improving the opacity greatly differs depending on the type of titanium dioxide and the method of use, and depending on the method of use. Experiments have confirmed that sufficient effects cannot be obtained. That is,
Conventionally, titanium dioxide has an action not only depending on its particle size and crystal form, but also on the type and amount of the surface treatment agent, particularly the conditions when prepared as an aqueous liquid, the dispersion (distribution) state in paper, and the like. We have found that the effect is greatly affected.
For example, titanium dioxide particles tend to aggregate depending on the pH of the solution, the presence of a sulfuric acid band, or the type of adhesive used, and once aggregated and the particle size increases, the high opacity inherent to titanium dioxide and The degree of whiteness is reduced, and a sufficient effect cannot be exhibited.

Therefore, the present inventors have made intensive studies on the physical properties of such titanium dioxide. As a result, even if titanium dioxide is simply mechanically dispersed and added to paper stock to make paper, or mixed with an adhesive or the like to prepare an aqueous liquid, it is applied to base paper and dried to finish the product. It has been found that the original high opacity and high whiteness of titanium are not sufficiently exhibited. This is because titanium dioxide particles are not sufficiently dispersed in each system, or even once dispersed, by finishing as an aqueous pigment composition, various metal ions present in the system and It is presumed that, depending on the type of the adhesive, the dispersion becomes unstable and the particles aggregate and enlarge, resulting in insufficient optical characteristics. From the above,
Titanium dioxide particles are maintained in a state of fine particle dispersion as much as possible.
It has been found that the excellent opacity and whiteness inherent in titanium dioxide particles are exhibited extremely efficiently by distributing them on the surface, and the present invention has been completed.

According to a first aspect of the present invention, in a newsprint for offset printing containing titanium dioxide, the distribution state of the titanium dioxide is determined by examining the paper surface of the newsprint using an electron beam micro analyzer (EPMA). ), The total area occupied by the titanium dioxide is 2 to 30% (area ratio) of the paper surface area used for the measurement, and the number average area of the titanium dioxide is 5 μm ^2.
Newspaper for offset printing characterized by the following.

According to the present invention, whether titanium dioxide is internally added to base paper or a method by surface treatment (external addition coating), the surface of newsprint as a product is analyzed by mapping using an electron beam microscopic analyzer. This has a feature in that the distribution state of the titanium dioxide particles is specified.
It is important that the titanium dioxide particles are distributed as small as possible in the base paper surface or in the base paper layer. By the way, it is possible to distribute titanium dioxide particles near the base paper layer and the surface layer by internal addition.However, actually adding fine particles such as titanium dioxide particles to the base paper and making paper are performed during the paper making process. The yield is extremely poor and cannot be economically preferable. On the other hand, in the present invention, an excellent aspect is an external addition coating method capable of extremely efficiently adding titanium dioxide to the base paper surface. As described above, the present invention will be described in detail in the case of newsprint for offset printing obtained by applying an external additive, which has a good yield of titanium dioxide on base paper and an excellent effect of improving opacity.

First, a mapping analysis method performed by using the electron beam microscopic analyzer according to the present invention will be described. Here, an energy dispersive X
Electron beam analyzer equipped with an electron beam spectrometer (EPMA,
JXA-8621MX / JEOL). The above device (JXA-8621MX) includes all automatic analysis functions and analysis programs, further expands micro analysis to the macro area, displays the two-dimensional distribution state of component elements and compounds as color images in real time, and performs data analysis. This is a wide-area and condition analyzer with a function to perform Display the concentration distribution of a specific element, further display the existence state and element ratio of multiple elements, or digitized backscattered electrons,
The secondary electron video signal can also be displayed as a color map.
With this method, it is an apparatus capable of observing the distribution of constituent elements / compounds over the entire sample, which could not be known only by analyzing a minute area.

Hereinafter, a specific measuring method will be described.
First, carbon vapor deposition is performed on the surface of a sample (paper product) to which titanium dioxide particles have been previously applied. Then, using the sample on which the carbon deposition was performed, using the above-mentioned electron beam micro analyzer (JXA-8621MX), acceleration voltage 15 kv, current 6 × 10 ⁻⁹ A, magnification 2500 times, and The measurement is performed under the condition of a measurement area of 33.25 μm × 28.5 μm to obtain a map of the original intensity of the titanium element. Based on this original intensity map, binarization is performed using the median intensity level as a threshold to obtain a map of titanium elements by mapping analysis.

Next, the intensity map obtained above was scanned with a scanner (GT-9000 / Epson) at a resolution of 150 dpi and an image size of 530 pixels × 500.
The image is input to a computer as a pixel, and the image processing / resolution system (dot analyzer DA-500)
(0 / Oji Scientific Instruments) to obtain a distribution diagram of the titanium dioxide element. Based on this distribution diagram, the same system was used to determine the total area (area ratio) and the number average area of the titanium dioxide particles in the measurement area as described below. ● Titanium dioxide area ratio (%): (total area of titanium dioxide particles / measured area) × 10
0 ● Number average area (μm ² ): total area of titanium dioxide particles / total number of titanium dioxide particles present in the measurement area In the measurement, a map of titanium elements is randomly obtained at five places on the sample surface. Then, for each map, a distribution diagram of titanium dioxide elements at four locations is obtained at random.
Based on this distribution state diagram, the area ratio and number average area of each titanium dioxide are calculated using an image processing / resolution system, and the average value of a total of 20 measurement points is calculated, and the area ratio and number average area are calculated. And In addition, among the titanium dioxide particles, those having a particle size of less than 0.2 μm are:
It was excluded from the calculation as a contaminant.

In the present invention, the area ratio of the titanium dioxide particles obtained by the above-described measurement method to the measurement area is 2 to 2.
It is specified to be 30%. By the way, if it is less than 2%, the effect of improving the opacity desired by the present invention cannot be obtained, while if it exceeds 30%, the amount of titanium dioxide particles is too large and paper dust is generated. However, blanket piling or the like is easily induced during offset printing, which is not preferable.

Further, an important requirement is not only the area ratio occupied by the titanium dioxide particles, but also the size of the titanium dioxide particles distributed on the base paper. Ideally, each titanium dioxide particle is a single fine particle (particle size;
3 μm) is desirable because the highest opacity can be obtained. Unfortunately, there is little distribution of substantially complete single particles, and usually
A plurality of particles are distributed in an aggregated state. This is because the aqueous composition containing the titanium dioxide particles is constituted together with other substances, for example, an adhesive or an auxiliary agent, so that the influence of the pH of the aqueous liquid and the influence of other polymer adhesives and the like are obtained. Or, when an aqueous composition containing titanium dioxide is applied to paper or the like obtained by acidic papermaking using a paper material usually containing a sulfuric acid band, such as newsprint, the sulfuric acid band or the like in the paper may elapse over time. It is eluted in the aqueous composition (coating solution), and a certain degree of aggregation cannot be avoided due to the influence of aluminum ions and the like therein. The effect of improving the obtained opacity depends on the state of formation of the aggregates. Therefore, how to minimize this agglomeration is key to achieving maximum opacity effect with a small amount of titanium dioxide particles.

As described above, in the present invention, various sizes of titanium dioxide particles are distributed on the base paper as the size of the titanium dioxide particles, but the titanium dioxide particles having a particle diameter as small as possible (preferably 0.2 to 0. (A single particle such as 3 μm) must be distributed on the base paper.
Therefore, in the present invention, the size of the titanium dioxide particles added to the base paper is specified by the number average area. That is, it is a value (number average area) obtained by dividing the area value occupied by all of the titanium dioxide particles by the number of titanium dioxide particles of various sizes existing in the measurement area (specific). 5 [mu] m ² or less as the number average area, preferably not 5 [mu] m ² or less, to identify the 0.04 .mu.m ² or more. By the way, when this number average area exceeds 5 μm ² , it means that the amount of the aggregated titanium dioxide particles increases by that amount. As the value increases, the titanium dioxide having a small particle diameter decreases and the enlarged particles become conspicuous. As a result, the effect of improving opacity is reduced by that amount, which is not preferable. In addition, under the influence of various ions and polymers present in the paint, it is impossible that titanium dioxide particles exist in a completely single dispersed state, and usually, a plurality of particles are aggregated, For example, in most cases, the particle form is larger than 0.2 μm, and it is not necessary to specify the lower limit. However, for particles smaller than 0.04 μm ^{2 in} the size of titanium dioxide particles appearing in the mapping analysis. Was regarded as particles in which the effect of improving opacity could not be expected because the particles were substantially too small, and particles having a number average area smaller than this were excluded from the measured values.

As described above, according to the first invention of the present invention, the distribution state of titanium dioxide particles in newsprint when evaluated by a mapping analysis method using an electron beam microscopic analyzer is as follows.
Area occupied by titanium dioxide particles (area ratio) and average area occupied by particles (size)
It has a feature in the point specified by. In short, these two specifications are based on the amount of titanium dioxide particles required (indicated by area) and the dispersion of a large number of these particles on the base paper (or in the base paper) in the state of small particles as much as possible without being in a lump state (number average). (Indicated by area).

The amount of titanium dioxide actually coated on the base paper is 0.1% by dry weight per one side.
To 1.5 g / m ² , more preferably 0.2 to 1.0 g / m ²
m ² . By the way, when it is less than 0.1 g / m ² ,
If the amount is too small, the effect of improving the opacity desired by the present invention may not be expected. On the other hand, when the amount exceeds 1.5 g / m ² , although the effect of improving the opacity can be expected, there is concern about the generation of paper powder and the like, and there is a risk of blanket piling. Furthermore, the more the amount, the more the final product rice tsubo is decided,
This means that the amount of pulp fiber is reduced by that amount, and this is not preferable because the stiffness of the product is reduced.

As for the type of titanium dioxide used in the present invention, the anatase type and the rutile type are used rather than the crystalline type as described above. Among them, titanium dioxide particles (JIS K5116-rutile type I), which are rutile type having relatively excellent opacity and whose surface is coated with aluminum, are preferably used.

Further, the newsprint for offset printing of the present invention has a distribution state of titanium dioxide particles that is specified by a mapping analysis method using the electron beam microscopic analyzer described above. Further, the distribution state of the titanium dioxide particles in the thickness direction (paper layer) is further characterized by a first layer (surface layer) and a fourth layer (surface layer) when the paper layer of the newsprint is divided into four parts. The total weight of titanium dioxide present in the back layer) is 2% of the total weight of titanium dioxide present in the second and third layers (each an intermediate layer).
Those which are twice or more are particularly preferred. The presence of titanium dioxide particles closer to the surface layer (outer layer) than to the inner layer makes it easier to obtain better whiteness and higher opacity.

Incidentally, the analysis of the amount of titanium dioxide by dividing the paper layer was carried out as follows. First, a coating solution in which the ratio of titanium dioxide to oxidized starch is 5/5 (weight ratio of solid content) is prepared, and the weight of the titanium dioxide is adjusted to one side using a Meyer bar on base paper mainly composed of pulp fibers. 0.
50 to 1 g / m ^2, and coated on both sides at 80 ° C.
After drying with a cylinder dryer, the paper was subjected to a 1-nip paper passing process with a soft calender to prepare papers having different titanium dioxide contents. Using these titanium dioxide-containing papers, a fluorescent X-ray measuring device (device name: XRF-1700 /
Calibration curves of titanium strength and titanium dioxide content are obtained by Shimadzu Corporation. Then, the paper report of "Paper Layer Peeling with Adhesive Tape" described in a research report (Distribution of vessel elements and fillers in a paper layer and vessel picking) in the February 1987 issue of Paper and Paper Technical Association, page 159 (Appendix). Paper layer Z applying the method
Method of Measuring Filler Distribution and Vessel Distribution in Direction ", the newsprint according to the present invention is divided into four parts, and the above-mentioned fluorescent X-ray measuring apparatus is used so that X-rays are irradiated on the paper layer surface side. Then, the strength of each titanium was measured, and the amount of titanium dioxide contained in each paper layer was determined from the above calibration curve.

As described above, the titanium dioxide in the base paper is preferably present as close as possible to the surface layer. In particular, the amount of titanium dioxide present in the surface layer portion and the back layer portion is determined by the amount of the second and third layers contained therein. It is preferable that the amount of titanium dioxide is at least twice the amount of titanium dioxide present in the layer. To achieve such a state, treatment by an external coating method is preferable, and a film transfer coating method (for example, a coating apparatus such as a gate roll coater or a rod metering size press) is particularly preferable.

According to a second aspect of the present invention, an external additive
The present invention relates to a method for producing newsprint paper for offset printing obtained by applying titanium dioxide to a base paper surface, and in particular, newsprint paper for offset printing obtained by applying an aqueous pigment composition containing titanium dioxide and an adhesive to a base paper surface. In the production method of, in preparing the aqueous pigment composition, 0.5 to 2 parts of a water-soluble polymer having a carboxyl group as a dispersant is added to 100 parts of titanium dioxide in advance with respect to solid content,
A slurry containing titanium dioxide is used, and the aqueous pigment composition is prepared so as to satisfy the following condition (1);
The method for producing newsprint paper for offset printing as described above, wherein the applied amount of titanium dioxide is 0.1 to 1.5 g / m ² per one side in dry weight. [Condition (1): 100 ppm of aluminum sulfate (as Al ₂ (SO ₄ ) ₃ ) was added to and mixed with the aqueous pigment composition (coating solution), and then the aqueous pigment composition was treated with titanium dioxide. The aqueous pigment composition obtained by diluting with water so as to have a weight concentration of 20 ppm has a light transmittance of 55%.
Below)

The production method according to the present invention shows a preferred embodiment for specifically obtaining the newsprint paper for offset printing specified above. In summary, the present invention proposes a production method intended to suppress the aggregation of titanium dioxide as much as possible with a small amount of titanium dioxide and to distribute a large number of small particles in the base paper layer. Thus, in the present invention, in preparing an aqueous pigment composition containing an adhesive and titanium dioxide (hereinafter simply referred to as a paint), an aqueous pigment composition having a carboxyl group as a solid content relative to 100 parts of titanium dioxide in advance is used. 0.5 to 2 using a conductive polymer as a dispersant
It is important that titanium dioxide is dispersed in fine particles by adding a part of the mixture, and then appropriately mixed and dispersed with an adhesive or other material to finish a paint, and that the paint satisfies the following condition (1). It is what becomes. [Condition (1): 100 ppm of aluminum sulfate (as Al ₂ (SO ₄ ) ₃ ) was added to and mixed with the aqueous pigment composition (coating solution), and then the aqueous pigment composition was treated with titanium dioxide. The aqueous pigment composition obtained by diluting with water so as to have a weight concentration of 20 ppm has a light transmittance of 55%.
Below)

Titanium dioxide particles have the property of being easily agglomerated as compared with other pigments and the like, and the agglomerated and enlarged particles impair the effect of expressing opacity. (0.2-0.3 [mu] m). In addition, as in the present invention, in order to use the smallest possible amount of titanium dioxide to maximize the opacity, which is a characteristic of the titanium dioxide, it is necessary to distribute the particles as finely as possible in the base paper layer (surface). Is an essential condition. However, the entity is
Depending on the dispersion conditions (type and amount of dispersant, etc.) of titanium dioxide, pH conditions in the paint system, compatibility with adhesives used in combination, various auxiliaries, etc., it is possible to prepare the paint even if it is once sufficiently dispersed. It is a pigment that is easily aggregated in the process of forming into large particles, and is difficult to take a stable dispersion state. For example, if aluminum sulfate (sulfuric acid band), which is widely used as a fixing agent such as a dye in acidic papermaking, is present in the dispersion system, titanium dioxide easily aggregates, and a stable dispersion state cannot be maintained. Causes enlarged particles. Most of base paper for newsprint is made by acidic papermaking, and is made using a sulfuric acid band. Therefore, for example, when a coating containing titanium dioxide is applied to the base paper by a gate roll coater or the like, with the passage of time, the sulfuric acid band in the base paper is mixed into the coating system, and the titanium dioxide in the coating gradually aggregates, There is a problem because it becomes enlarged titanium dioxide particles.

According to the present inventors, the titanium dioxide particles dispersed in the paint as described above agglomerate and enlarge according to circumstances, and the effect of the titanium dioxide particles to exhibit the high opacity inherent therein is reduced. In view of the inability to obtain the desired effect, the morphology of the titanium dioxide particles does not easily change due to the presence of a sulfate band, a pH change in the coating system, or other changes in conditions, and the coating can maintain a stable dispersed state. The preparation was intensively studied. As a result, the titanium dioxide particles were added in advance with a dispersant consisting of a water-soluble polymer having a carboxyl group to 100 parts of titanium dioxide, in a solid content of 0.5 to
After adding 2 parts, forming a dispersion slurry, mixing the titanium dioxide slurry with an adhesive and other necessary materials,
By mixing and preparing the paint by stirring, even if the sulfuric acid band is mixed into the paint or the pH of the paint changes,
The titanium dioxide particles in the paint do not easily aggregate,
The present inventors have found that the fine particle dispersion state is maintained for a long period of time, and have completed the present invention.

That is, when dispersing the titanium dioxide particles, a water-soluble polymer having a carboxyl group is used as a dispersant, and 0.5 to 2 parts by weight relative to the solid content is added to 100 parts of titanium dioxide to disperse the pigment. And to obtain a stable dispersion slurry of titanium dioxide. The reason why the water-soluble polymer having a carboxyl group in the dispersion of titanium dioxide shows a remarkable action and effect is not always clear, but a large amount of carboxyl groups (− ions) are formed around the titanium dioxide particles dispersed in fine particles. It is presumed that the presence of the dispersing agent has a higher priority on the mutually repelling forces and suppresses the association of the titanium dioxide particles. In such a situation, even if aluminum ions and the like enter from the outside, the result is the same, and the chelating action by the carboxyl group effectively captures the aluminum ions and the like, and facilitates aggregation. It is presumed that this is creating a situation that cannot occur. By the way, if the addition amount is less than 0.5 part, the amount is too small, and the titanium dioxide particles are likely to aggregate due to a change in the pH of the coating system or the presence of a small amount of sulfuric acid band, which is not preferable. On the other hand, if the amount exceeds 2 parts, the viscosity of the whole coating system and the re-agglomeration of the titanium dioxide particles occur, which is unfavorable because the quality is adversely affected.

In the present invention, as described above, in a paint containing titanium dioxide, the finely dispersed state of titanium dioxide is maintained in a stable state even after the paint is finished. It is extremely important that In the present invention, by defining the light transmittance for titanium dioxide as an index indicating the dispersion state, the dispersion state of titanium dioxide (in other words, the aggregation state) can be grasped, and the titanium dioxide in the paint can be grasped. By setting a limit on the state of aggregation, they have found that high opacity can be obtained with a small amount of titanium dioxide. That is, after adding and mixing aluminum sulfate to a paint (aqueous liquid) containing titanium dioxide and an adhesive so as to have a concentration of 100 ppm [as Al ₂ (SO ₄ ) ₃ ], the aqueous pigment composition is mixed with the weight of titanium dioxide. The aqueous pigment composition obtained by diluting with water so as to have a concentration of 20 ppm has a light transmittance of 55%.
The following shows that the dispersibility of titanium dioxide in the paint is maintained by preparing the paint so as to be 50% or less, more preferably. Incidentally, the higher the light transmittance exceeds 55%, the more the titanium dioxide in the paint is agglomerated and the larger the number of particles. The lower limit is not particularly limited, but according to the experiments of the present inventors, as described above, only titanium dioxide particles were sufficiently dispersed in water using a dispersant alone, as described above. The titanium dioxide was diluted with water so as to have a weight concentration of 20 ppm, and the light transmittance was measured. As a result, a value of about 30% was obtained. In addition,
The light transmittance can be adjusted mainly by the type and amount of the water-soluble polymer (dispersant) having a carboxyl group to be used.

Here, paint containing titanium dioxide (aqueous liquid)
On the other hand, the meaning of adding aluminum sulfate equivalent to 100 ppm is determined by the present inventors based on the following experience. That is, newsprint paper made by actual acidic papermaking is usually coated on its surface with a paper strength enhancer such as starch or polyacrylamide as a surface treatment agent (external coating). Then, in the process of applying the surface treatment agent to the base paper, a part of the aluminum sulfate in the base paper elutes into the surface treatment agent as time elapses. Therefore, the present inventors sampled the surface treatment agent in the service tank after continuous 12 hours of operation during newspaper making on an actual machine, and measured the concentration of aluminum sulfate contained therein. 50 ppm [Al ₂ (SO ₄ )
₃ ). In view of the effect on aluminum sulfate, the dispersibility (dispersion stability) of titanium dioxide with respect to a somewhat higher amount of aluminum sulfate (100 ppm) was determined by light transmittance (55% or less). Therefore, it was determined that if this condition was satisfied, there would be no problem as far as the aggregation of titanium dioxide particles by aluminum sulfate was concerned in the production of newsprint in ordinary acidic papermaking.

Next, as the water-soluble polymer having a carboxyl group used as a dispersant for titanium dioxide particles, for example, styrene / maleic acid copolymer, styrene /
Acrylic acid copolymer, alkyl methacrylate /
Acrylic acid such as methacrylic acid copolymer, acrylic acid / maleic acid copolymer, acrylic acid / sulfonic acid copolymer,
Examples thereof include a polymer compound containing maleic acid and the like, a polymer compound such as carboxy-modified polyvinyl alcohol, and cellulose ethers such as carboxymethyl cellulose.
Among them, particularly, acrylic acid / maleic acid copolymer and / or styrene / maleic acid copolymer are preferably used because of excellent dispersion effect of titanium dioxide.

The light transmittance in the present invention is measured by using an ultraviolet-visible spectrophotometer (UV3300 / Hitachi).
It was measured under the conditions of a wavelength of 572 nm and a cell optical path length of 1 cm. Incidentally, as the value of the light transmittance increases, the number of aggregates increases as described above, and as a result, the effect of improving the opacity by the titanium dioxide particles cannot be expected.

Hereinafter, the paint according to the present invention will be described. As the coating material, titanium dioxide previously subjected to pigment dispersion using a specific dispersant (average particle diameter of 0.2 to
0.3 μm) and an aqueous composition mainly composed of an adhesive. Since the pigments are easily aggregated, they are appropriately stirred and dispersed together with a dispersant or the like to finish the paint. In the present invention, it is desirable that at least 50% by weight of titanium dioxide be contained in all the pigments. By the way, the amount of titanium dioxide to be applied is 0.1 to
An extremely small amount, such as 1.5 g / m ² , is added. If the amount of titanium dioxide in the coating material is small, it is necessary to apply a large amount of the entire solid content. As a result, it is not preferable for a thin product having a fixed final rice tsubo (measurement scale) because the pulp fiber must be reduced accordingly.

As a method for preparing the titanium dioxide slurry, a dispersing machine (apparatus) for dispersing a pigment generally used in the production of coated paper, for example, a high-speed high-shear mixer such as a Cores dissolver, a K-mill, or a sand mill A titanium dioxide slurry is obtained by using a wet crusher or the like using fine balls as a medium. In dispersing, a general pigment dispersant can be appropriately used, but in the present invention, a water-soluble polymer having a carboxyl group is particularly used as the dispersant. This water-soluble polymer having a carboxyl group has an excellent effect of dispersing titanium dioxide particles. In particular, even after the dispersed titanium dioxide particles are mixed with an adhesive or various materials and finished into a paint, the water-soluble polymer has an excellent dispersing effect. Titanium particles are preferably used because they tend to suppress aggregation of the titanium particles with other pigment particles.

In this case, the amount of the water-soluble polymer having a carboxyl group is 100 parts by weight of titanium dioxide.
It is adjusted at 0.5 to 2 parts relative to the solid content. Incidentally, 0.
In the case of less than 5 parts, when the amount is insufficient, when the paint is finished, a stable dispersibility cannot be maintained and the particles are aggregated,
On the other hand, if the addition amount exceeds 2 parts, the dispersing effect is maintained, but the viscosity of the coating material increases, and in some cases, the dispersed titanium dioxide particles may re-agglomerate. It is not preferable because adverse effects on other quality are also concerned. Incidentally, the concentration of the dispersed solid content of the titanium dioxide particles is usually adjusted to 10 to 75% by weight,
Used for paint preparation. In preparing the coating, the slurry of titanium dioxide and the adhesive prepared as described above and an adhesive, and an auxiliary agent are appropriately added or prepared, or the slurry of titanium dioxide and another pigment slurry, an adhesive, and an auxiliary agent are prepared. A method of preparing by appropriately adding is used. When combined with other pigments, at least titanium dioxide as the pigment is 50% by weight or more, preferably 80% by weight or more of the total pigment. By the way, if it is less than 50% by weight, the effect of improving opacity may not be expected.

Incidentally, pigments used in combination with titanium dioxide include, for example, kaolin, calcined kaolin, structured kaolin, heavy calcium carbonate, light calcium carbonate, calcium sulfate, magnesium carbonate, aluminum hydroxide, barium sulfate, zinc oxide, Examples thereof include amorphous silica such as satin white and white carbon, and organic pigments such as plastic pigment and urea resin.

Examples of the adhesive include modified starches such as oxidized starch, etherified starch, esterified starch and cationized starch, water-soluble cellulose compounds such as carboxymethylcellulose, methylcellulose and hydroxyalkylcellulose, and styrene-butadiene copolymer. Coalesced latex,
Copolymer latex such as styrene-methacrylic acid ester copolymer latex, or polyvinyl alcohol or polyacrylamide can be exemplified. Incidentally, the amount of the adhesive was 5 parts by weight based on the solid content with respect to 100 parts of titanium dioxide.
Adjusted from 0 to 150 parts.

Various additives such as a dispersant, an antifoaming agent, a water-proofing agent, a surface sizing agent, and a preservative are appropriately added to a paint prepared by mixing the pigment and the adhesive as described above. . In addition, the solid content concentration of the paint is appropriately adjusted according to a coating device and a target coating amount, but is usually in a range of 2 to 60% by weight.

The coating material obtained by the above method is applied to a coating device generally used in the papermaking field, for example, a size press, a blade metering size press, a rod metering size press, a gate roll coater, a blade coater, a bar coater. The material is applied to the surface of the base paper by appropriately using a known and publicly used device such as a rod blade coater or an air knife coater. Above all, when using a film transfer type coating device such as a gate roll coater, blade metering size press, or rod metering size press, the film-like coating film is transferred to the base paper, and the coating material is placed inside the base paper. Rather than penetrating, the titanium dioxide tends to stay on the surface layer of the base paper, and as a result, the possibility that titanium dioxide is scattered in a portion near the base paper surface layer is increased, which is a preferable embodiment.

Using such an apparatus, titanium dioxide
Is applied to the base paper. In addition, application amount
Is the solid content of titanium dioxide 0.1 to 1.5 g per side
/ M ^TwoIs applied and dried. By the way, 0.1
g / m^TwoIf less than, sufficient opacity cannot be obtained,
1.5g / m on the other hand^TwoIf applied over
If the amount is constant, the weight of the base paper,
The weight of lup fiber is reduced, reducing the paper thickness and rigidity, and furthermore
Reduces paper strength, leading to troubles such as paper breakage in the printing process
It is easy to emit and it is not preferable. In addition, with titanium dioxide
After the paint has been applied to the base paper and dried,
And then pressurized and smoothed to finish the product
Can be In that case, the normal calender
Machine roll to be a combination of metal roll / metal roll
Metal / resin roll configuration rather than render
Using a soft calender applies more pressure to the base paper layer.
This is a more preferable embodiment because smoothing can be performed without using the same.

Next, as the pulp constituting the base paper,
Chemical pulp (bleached or unbleached NKP or LKP
), High yield pulp (GP, CGP, RGP, PG
W, TMP, etc.), used paper pulp (DIP, etc.) and the like are used alone or in a mixture at an arbitrary ratio. In addition, when making paper, an appropriate amount of an amorphous silica-based inorganic pigment such as white carbon, calcined kaolin, structured kaolin, calcium carbonate, and titanium dioxide, and further a papermaking filler such as urea-formaldehyde resin are required in the paper stock. It can be added according to. Further, in the paper stock, together with the above-mentioned fillers, sizing agents such as a sulfuric acid band, a paper strength enhancer, a retention enhancer, a reinforced rosin sizing agent, and an emulsion sizing agent, a water-proofing agent, and a UV absorber and other generally known papermaking. The chemical is added and the paper is made on a normal paper machine. In the case of the present invention,
The basis weight of the base paper is not particularly limited.
The desired effect is remarkably exhibited in the case of a relatively low basis weight of about 0 to 45 g / m ² .

[0044]

EXAMPLES The present invention will be specifically described below with reference to examples. Of course, the present invention is not limited to these examples. Parts and% in Examples are parts by weight and% by weight, respectively, unless otherwise specified.

Example 1 (Preparation of base paper) Softwood kraft pulp (NKP) 14
Parts, thermomechanical pulp (TMP) 40 parts, ground pulp (GP) 7 parts, newspaper deinked waste paper pulp (DI
P) A pulp slurry having a ratio of 39 parts was beaten with a refiner to a freeness (csf) of 110 ml to prepare a pulp slurry. A rosin emulsion size (trade name: SPN-7) is added to the pulp slurry thus obtained.
73 / Arakawa Chemical Industries, Ltd.) 0.3%, sulfuric acid band 1%
A paper stock was prepared by adding (all compared to the pulp solid content), and using the stock, a pilot paper machine equipped with a twin wire was used to obtain a base paper of 41 g / m ^{2 in} rice tsubo.

(Preparation of Newspaper) One part of a styrene / maleic acid copolymer (trade name: Polymalon 1318 / Arakawa Chemical Industries, Ltd.) was added as a dispersant in water, and then rutile coated with aluminum was added. While adding 100 parts of titanium dioxide (trade name: CR-50 / Ishihara Sangyo Co., Ltd.) and stirring with a Cores dissolver (dispersion machine).
A titanium dioxide slurry having a solid content of 70% was obtained. This titanium dioxide slurry was mixed with 100 parts of an oxidized starch paste solution (trade name: Ace A / Oji Cornstarch Co., Ltd.) having a solid content concentration of 20%, which was heated and dissolved with hot water, and stirred to prepare a coating material. All are based on weight solids).

Next, the paint was eluted from the newsprint base paper.
Assuming aluminum sulfate, the paint
Nium [Al_Two(SO_Four)_ThreeAs 100 ppm
And then add 0.1 part of defoamer and water to solidify.
It was finished to a coating composition having a form concentration of 12%. In addition, this coating
Light transmittance [measured in accordance with condition (1) of claim 6]
Was 43%. Using this paint,
41 g / m2 of rice tsubo obtained by making paper with an Ilot paper machine ^TwoBase paper
After drying using a gate roll coater on both sides
Weight is 0.6g / m per side^Two(As titanium dioxide
0.3g / m^Two), Apply it and dry it.
Finish the paper through one nip with a tocalender, 7% moisture
Newspaper was obtained. In addition, about the obtained newsprint,
Transparent plastic adhesive tape (width 38mm, tesa)
A piece of paper (sample) with a size of 30 mm x 200 mm using
Was described in the research report of the February 1987 issue of the Japan Paper Association
Divide into 4 parts according to the prescription listed and included in each layer
The amount of titanium dioxide is measured by a fluorescent X-ray measuring device,
Compared to the calibration curve prepared in advance,
As a result of determining the amount of titanium oxide, the first layer (surface layer) and the fourth layer
The total amount of titanium dioxide contained in the (back layer) is
4.3 times the total amount of titanium dioxide contained in the third and third layers
Met.

Example 2 In preparing the newsprint of Example 1, polymalon 1318 (1 part) was used as a dispersant with an acrylic acid / maleic acid copolymer (trade name: Aron A-6330 / Toa Gosei Co., Ltd.).
1.5 parts), and JR-600A (Taica) was used instead of CR-50 as rutile-type titanium dioxide coated with aluminum, and a coating material having a light transmittance of 41% was used. Except for the above, newsprint was obtained in the same manner as in Example 1.

Example 3 In preparing the newsprint of Example 1, polymalon 1318 (1 part) was used as a dispersant, and acrylic acid / maleic acid copolymer (Aron A-6330 / the above-mentioned... 0.4 part) was used. And carboxy-modified polyvinyl alcohol (trade name: Gohsenal T-330H / Nippon Synthetic Chemical Company ... 0.4 part)
To titanium dioxide CR-50 (described above)
R-600A (described above), using a paint having a light transmittance of 50%, and a coating amount after drying of 0.4 g / m per side.
^A newsprint was obtained in the same manner as in Example 1 except that the amount was ² (0.2 g / m ² as titanium dioxide).

Example 4 In preparing the newsprint of Example 1, polymalon 1318 (1 part) was used as a dispersant, and acrylic acid / maleic acid copolymer (Aron A-6330 / the above-mentioned... 0.5 part) and Carboxymethyl cellulose (trade name: FINFIX)
Ace A (oxidized starch) as an adhesive was replaced with a polyacrylamide copolymer (trade name: Santax NP-10 / Mitsui Chemicals).
Except that a coating material having a light transmittance of 52% was used and the coating amount after drying was 1.0 g / m ² (0.5 g / m ² as titanium dioxide) per one side. In the same manner as in Example 1, newsprint was obtained.

Comparative Example 1 In preparing the newsprint of Example 1, as a dispersant, polymalon 1318 (1 part) was replaced with a polyphosphate (trade name:
Hydroparat 884 / San Nopco Ltd .... 1 part) was used in the same manner as in Example 1 except that a paint having a light transmittance of 59% was used.

Comparative Example 2 In preparing the newsprint of Example 2, the dispersant was added in an amount of 0.3 part, and ace A (oxidized starch) was further used as an adhesive with a polyacrylamide copolymer (Santax N).
P-10 / the above), and a newsprint was obtained in the same manner as in Example 2 except that a paint having a light transmittance of 85% was used.

Comparative Example 3 In preparing the newsprint of Example 3, the dispersant was added in the following amounts: Aron A-6330 / 1.5 parts, and Gohsenal T-330H / 1.5 parts. A newsprint was obtained in the same manner as in Example 3, except that the paint was changed and a light transmittance of 70% was used.

Comparative Example 4 The procedure of Example 1 was repeated except that the amount of the aqueous pigment composition applied was 0.08 g / m ^{2 on} one side in the preparation of the newsprint of Example 1. Newsprint was obtained.

With respect to the newsprint thus obtained, the area ratio of titanium dioxide and the number average area by the mapping analysis and the following items were measured and evaluated, and the obtained results are shown in Table 1.

(Opacity of white paper) Measured using a spectral whiteness colorimeter (Suga Test Instruments Co., Ltd.) in accordance with JIS-8138.

(Opacity after printing) Printing was performed using an RI printing machine while changing the ink amount of the ink for rotary offset printing (black ink). When the reflectance of the printing surface was 9%, the reflectance of the back surface before printing (printing) was changed. The ratio of the back surface reflectance after printing to the surface opposite to the surface) was determined. The reflectance was measured using a spectral whiteness colorimeter (described above).

[0058]

[Table 1]

[0059]

As is clear from Table 1, the newsprint according to the embodiment of the present invention has excellent white paper opacity and post-print opacity, and a small amount of titanium dioxide is efficiently dispersed on the base paper layer surface. The transparency effect was sufficiently exhibited.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kazuhiro Nojima 4-3-1 Jokoji, Amagasaki-shi, Hyogo Oji Paper Co., Ltd. Amagasaki Research Center F-term (reference) 4L055 AG03 AG08 AG19 AG46 AG48 AG63 AG64 AG70 AG71 AG72 AG89 AG94 AG98 AH02 AH33 AH37 AJ04 BE02 BE07 BE08 CH11 EA14 EA17 EA25 EA32 EA34 FA12 GA16 GA19

Claims (8)

[Claims] 1. In an offset printing newsprint containing titanium dioxide, the distribution state of the titanium dioxide changes the surface of the newsprint to an electron beam microanalyzer (EPMA).
Using, when evaluated by the mapping analysis method, the total area occupied by titanium dioxide is 2 to 2 of the paper surface area used for measurement
30% (area ratio) and a number average area of titanium dioxide of 5 μm ² or less, newsprint paper for offset printing. 2. The newsprint paper for offset printing according to claim 1, wherein the titanium dioxide is contained by coating the base paper surface. 3. The newsprint paper for offset printing according to claim ² , wherein the amount of titanium dioxide applied to the base paper surface is 0.1 to 1.5 g / m ^{2 on} one side in terms of dry weight. 4. The titanium dioxide has a rutile type crystal form,
The newsprint for offset printing according to any one of claims 1 to 3, wherein the newsprint is titanium dioxide having a surface coated with aluminum. 5. The distribution of titanium dioxide in the Z direction (paper layer) in newsprint paper for offset printing is as follows.
When divided, the total weight of titanium dioxide present in the first layer (surface layer) and the fourth layer (back layer) is twice the total weight of titanium dioxide present in the second layer and the third layer (intermediate layer). The newsprint for offset printing according to any one of claims 1 to 4, which is the above. 6. A method for producing newsprint paper for offset printing comprising applying an aqueous pigment composition containing titanium dioxide and an adhesive to a base paper surface, wherein 100 parts of titanium dioxide is previously prepared for preparing the aqueous pigment composition. On the other hand, a water-soluble polymer having a carboxyl group relative to the solid content is used as a dispersing agent in an amount of 0.1.
5 to 2 parts were added and titanium dioxide slurried was used, and the aqueous pigment composition was prepared so as to satisfy the following condition (1). method for manufacturing offset printing newsprint according to claim 2, characterized in that a 0.1 to 1.5 g / m ^2. [Condition (1): 100 ppm of aluminum sulfate (as Al ₂ (SO ₄ ) ₃ ) was added to and mixed with the aqueous pigment composition (coating solution), and then the aqueous pigment composition was treated with titanium dioxide. The aqueous pigment composition obtained by diluting with water so as to have a weight concentration of 20 ppm has a light transmittance of 55%.
Below) 7. The method for producing newsprint paper for offset printing according to claim 6, wherein the apparatus for applying the aqueous pigment composition to the base paper is a coating apparatus of a film transfer system. 8. An aqueous pigment composition is applied, dried, and then smoothed by a soft calender to finish the composition.
Or the method for producing newsprint paper for offset printing according to 7.