JP2670694B2 - Method for producing coated lightweight printed paper and coated lightweight printed paper - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to opacity in the production of coated lightweight printing paper,
The present invention relates to a method for producing a coated lightweight printing paper capable of significantly improving printability such as smoothness and gloss after printing without substantially reducing bulk and rigidity.

[Prior Art] Printed paper has become more and more lightweight in recent years in view of the spread and increase of direct mail, catalogs, page increase of publications, low cost and resource saving.

As the lightweight printing paper having a basis weight of about 25 to 60 g / m ² , plain paper, surface-treated paper, lightly coated paper, or lightweight coated paper is used.

On the other hand, there is an increasing demand for visualization and high quality printing, and even light-weight printing paper is required to have printability similar to general printing paper. Lightweight printing paper is required to have improved opacity and bulkiness as well as improved printability.

That is, the thinner the paper, the easier it becomes to be transparent.
Opacity is required so that the back side print cannot be seen from the front side.

Therefore, when a large amount of highly opaque filler such as titanium oxide is used, the paper loses its rigidity, and when printing in plain format,
When feeding paper and biting it one by one, it is easy to get broken and misaligned, causing trouble.

The bulkier the paper, the better the rigidity, so the thinner it is, the higher the bulk is required. However, the higher the bulk, the poorer the smoothness and the poor print gloss. After pigment treatment, it is usually calendered in order to obtain surface smoothness and other printability, but this calendering usually increases the density of paper, lowers opacity, and reduces bulk. .

Since the weight of light-weight printing paper is particularly light, it is difficult to simultaneously satisfy characteristics such as opacity, bulk and rigidity, surface properties such as smoothness and gloss, and printability.

In order to improve the above properties of lightweight printing paper, up to now the filler having a large refractive index on the base paper surface, the use of a filler having a particle size that enlarges the voids in the paper layer, etc., to improve opacity and a filler having a large oil absorption amount have been used. Is used to improve the ink receptivity of printing ink. Also, in the case of coated paper, from the viewpoint of improving opacity, printing ink inking, and printing gloss,
Various inorganic pigments and organic pigments are selected, and binders such as latex and starch are variously selected.

Generally, printing paper is calendered by machine calender or super calender in order to maintain the surface smoothness, but as a method to suppress the increase in density due to calendering and improve smoothness and gloss, heat with a high temperature roll is used. Known methods include calendering or applying water to the paper surface immediately before calendering.

Thermal calendering is used for the production of high-gloss paperboard, etc., but it is necessary to replenish the amount of heat consumed by the base paper to the rolls, and to transfer heat to the paper in a short time when it passes through the nip between the rolls to heat the paper. Is extremely difficult. Further, it cannot be applied to lightweight printing paper which requires double-sided processing and is thin.

The water application just before the calender treatment has recently been disclosed in JP-A-62-
As can be seen in Japanese Patent No. 177299, the present invention is characterized in that it is a bulky lightweight printing paper using a pulp with a thick fiber wall, and in the point that water is applied immediately before calendering surface-sized paper, Different from the invention. In the case of water coating, the amount of water applied or sprayed is 0.5 to 5 g / m ^{2 on} one side of the paper, which is high (increasing the average water content of the entire paper by 2 to 10%). In addition to being unsuitable for processing, stains on the calendar roll and gloss on the paper easily occur. When the water coating is used for the pigment coated paper which is the object of the present invention, water hardly penetrates through the coating layer to the paper layer, and there is a possibility that the problem of adhesion of the coating material to the calender roll may occur.

[Problems to be Solved by the Invention] The present invention has been made to solve the above problems of lightweight printed paper, particularly coated lightweight printed paper, and the object of the present invention is to provide opacity of the coated lightweight printed paper. The present invention provides a method for producing a coated lightweight printing paper, which can improve printability such as smoothness and gloss after printing, with almost no reduction in bulk and rigidity, and a coated lightweight printing paper obtained by the production method. .

[Means for Solving the Problems] In the method for producing a coated lightweight printing paper according to the present invention, a mild superheated steam at a low pressure is added immediately before the calendering treatment (1) to
Under the condition of (2), the method for producing a coated lightweight printing paper is characterized in that the paper is jetted in parallel with the paper, the surface of the paper is humidified and heated, and then calendering is performed.

(1) Immediately before calendering, 0.01 to 0.3 seconds before, a low pressure and mild superheated steam is ejected.

(2) The amount of vapor deposited on the surface of the paper is 0.05 per side of the paper.
Eject at a rate of ~ 0.3g / m ² .

In addition, the present invention has a whiteness of 85% or more, an opacity of 80% or more, and a smoothness of a vapor-treated surface of 400 seconds or more (JAPAN TAPPI N
O5 type smoothness tester), which is a coated lightweight printing paper having a coating amount of 3 to 10 g / m ² (coating solid content) of the pigment coating obtained by the above production method.

A feature of the present invention is that, just before the calendar treatment of coated lightweight printed paper, a low pressure and mildly superheated steam is adhered to the surface of the paper under specific conditions. Conventionally, steam is used to prevent curling of the paper. However, there have been no proposals to be made so far in the calendering process, because there was no suitable form, characteristics, and use conditions of the steam used.

Recently, in JP-A-62-223388, parallel to a paper sheet,
Moreover, a device (steam shower) for supplying a steam flow to the surface of the sheet in a direction opposite to the moving direction of the sheet has been proposed. The present inventors have paid attention to the fact that this device has a feature that the sheet is uniformly humidified and heated while the vapor flow is jetted to the sheet and flows in the direction opposite to the traveling direction of the sheet. We thought that it might be one of the preferable vapors for applying it to the coated light-weight printing paper, and examined its application conditions.

In general, calendering improves the smoothness and glossiness by increasing the nip pressure of calender rolls, the number of nips, the water content of the paper, the temperature of the paper, the nip time, etc., but the bulkiness and the opacity decrease greatly. . To improve the smoothness and gloss of printed paper, it is necessary to make the paper dense.

In order to achieve this goal in calendering without reducing bulk, reducing stiffness, and reducing opacity, the densification of the paper is stopped only on the fine surface of the paper and how the entire paper layer is stored without crushing. Attributed to that.

The present inventors have found that by applying a vapor flow generated from the proposed device to the calendering process for densifying only the fine surface of the paper, the above problems of the coated lightweight printed paper can be solved. After that, he proceeded with earnest research.

That is, as described above, in order to increase the smoothness of the paper and improve the printing gloss, as shown in JP-A-62-177299, water application (water damping) is performed, and then calendar processing is performed. Is well known.

However, water coating has a limit in reducing the amount to be coated, and even if it is uncoated paper or the coated surface of about the surface size even if it is coated, it can be uniformly coated on the paper surface. Since the coating film surface using a synthetic resin latex as a binder, such as a pigment coating, is hydrophobic, it is difficult to apply water uniformly, and the temperature is usually room temperature.

However, the steam used in the present invention is easy to control the steam amount unlike water and the temperature is high. Therefore, the pigment coating surface is also momentarily softened by the heat amount of the steam being given, and even a small amount of steam is used for pigment coating. It is possible to pass through the layer and reach only the paper surface below the coating layer, and neither heat nor steam reaches the center of the layer. Therefore, when calendered immediately after steam treatment, of the paper layer, only the layer close to the pigment coating layer increases in density, but the central layer does not increase in density, the central layer of the paper layer itself has low density, and only the surface layer. The castella structure has a high density, and the pigment coating layer is smooth, so that the average density as a whole does not increase so much, and although it is bulky, a lightweight printing paper with printing gloss can be obtained. .

The coated lightweight printing paper of the present invention has a basis weight of 25 to 60 g / m ² of inorganic,
It is a coated lightweight printing paper in which a coating material comprising an organic pigment and a binder is coated on one side or both sides of a base paper in an amount of 3 to 10 g / m ² per side.

The present invention can be applied to pigment-coated paper to obtain remarkable effects,
It is preferable that the sizing degree of the paper is high, that the Steckigt sizing degree is 3 seconds or more, and that the coating amount containing the pigment or the surface sizing agent is large.

The calendar treatment of the present invention can be applied to all general calendars such as super calendars, on-machine calendars, and gloss calendars.

The low pressure and mildly superheated steam flow device of the present invention is a device that sprays steam in parallel with the paper from a device nozzle that sprays the steam at an angle onto the surface of the paper. Any material can be used as long as it can be adjusted to appropriately raise the temperature and moisture of the sheet.

The steam used in the present invention is a low pressure and mildly superheated steam with a vapor pressure of 1.0 to 2.0 Kg / cm ² , preferably 1.2 to 1.5 Kg / cm ^2.
It is. If the vapor pressure is too high, the moisture and heat applied to the paper will cause burnout in the roll nip or destruction of the coated surface of the coated paper. If the vapor pressure is too low, it is difficult to improve smoothness and printing gloss.

The amount of vapor deposited on the surface of paper is 0.05 to 0 per side of paper.
3 g / m ^2, preferably 0.1~0.25g / m ^2. If the vapor deposition amount is too small, the deposited vapor film may not cover the entire paper surface, which may cause uneven smoothness and gloss, and if it is too large, excess water that covers the paper surface may penetrate into the paper. As a result, the opacity decreases.

The time required to enter the calender roll nip after vapor coating should be 0.01 to 0.3 seconds. If the time is longer than this, the vapor drain particles adhering to the paper penetrate into the inside of the paper, resulting in a decrease in opacity.

The nip pressure during calendering differs depending on the calender used, but it has a low nip pressure and high smoothness compared to conventional calendering that does not use steam. Since printing gloss is obtained, bulk can be obtained without increasing the density.

The limitations of the above various conditions include the opacity, the bulk, and the like when the present inventors carry out the calendar treatment of the coated light-weight printing paper having a low basis weight.
As a method of improving printability such as smoothness and printing gloss without lowering rigidity, it was determined by repeating a test in which a mild superheated steam flow was applied to the paper surface at low pressure to deposit a vapor film on the paper surface. is there.

The above-mentioned known method of applying water requires a considerable amount of water in order to wet the entire paper surface. 0.5 to 5 per side
If you apply g / m ² of water or atomize it, the water content of the paper will increase by 4 to 20% by double-sided treatment. Under such a high water content condition, the calendering treatment (which requires a certain amount of nip pressurization and pressurizing times) to obtain the high smoothness and printability aimed at by the present invention largely loses the bulk and opacity.

It is difficult to evenly wet the entire surface of the paper with a larger amount of coating or atomized coating.

In that respect, the method of wetting the paper surface with the low pressure and slight superheated steam of the present invention is the method of wetting the paper with the thinnest film among various methods. That is, the surface of the paper can be wet with an amount equivalent to a monomolecular film of water.

Furthermore, another purpose of using this vapor is to raise the temperature of the paper surface by releasing latent heat after the vapor adheres to the paper surface.

As a result, it is possible to obtain the same effect as calendering with a high temperature roll.

It is preferable that the amount of water is small in order to impart the moisture to the surface of the paper immediately before the calendering treatment and bring about the above-mentioned effect.
As described above, the larger the amount of adhering water, the larger the decrease in bulk and the decrease in opacity.

From this, in the present invention, the amount of adhering water can be limited by using a low pressure and mildly superheated steam. In the case of water application, one side of the paper is 0.5 to 5 g / m ² (which increases the average water content of the paper by 2 to 10%), while the low pressure and mild superheated steam of the present invention is 0.1 to 0.3 g / m on one side. ^{A value of 2} is sufficient, which means that the increase in the water content of the paper is 1% or less even when double-side coating is performed. In the present invention, steam may be adhered to both sides of the double-sided coated paper, or steam may be adhered to both sides of the single-sided coated paper.

[Examples] Examples of the present invention will be described.

A 10-step normal super calender consisting of a combination of chilled rolls and cotton rolls is used for calendar processing, and steam is jetted to the back side of the paper to be passed before the nip between the top chilled rolls of the calender and the 2nd cotton roll. As described above, a test machine for a steam shower device (steam foil of Thermo Electron Web Systems, Inc.) was installed and the following experiment was conducted.

(1) Examination of the time before entering the calendar nip Lightly coated light-weight printing paper with a basis weight of 45 g / m ² is passed through a super calender, and the position of the steam shower tester is moved to determine opacity and printing gloss. Table 1 shows the results of the measurement.

Paper passing conditions are speed 250m / min, 9 nip, nip pressure 230Kg / c
m, the roll is not heated and is at room temperature.

The steam pressure of the steam shower was 1.2 Kg / cm ² , and the amount of steam deposited on the paper surface was 0.17 g / m ² .

From the results shown in Table 1, the time was set to 0.01 seconds, which is the closest position to the calender nip, to 0.3 seconds, considering the range in which the decrease in opacity is allowable.

Paper test method Basis weight: JIS P 8124 Thickness: JIS P 8118 Density: Same as above Opacity: JIS P 8138 Smoothness: Measured by JAPAN TAPPI No5 Oken type smoothness tester Printing gloss: Ink amount by RI test printing machine Measured according to JIS P 8142 after printing 0.5 g / m ² Stiffness: JIS P 8143 Clark stiffness test Steckigt method Size degree: JIS P 8122 (2) Examination of the amount of vapor deposited on the paper surface Same as (1) above Using a small amount of light-weight coated paper with a basis weight of 40 g / m ² for the super calender, the paper passing speed is 50
Same as (1) except that 0 m / min, 3 nip, and nip pressure of 120 Kg / cm, steam was spouted on the back side of the paper with a steam shower, and the steam spouting amount was adjusted to adjust the amount of steam adhering to the paper surface. Table 2 shows the results obtained by changing

From the results shown in Table 2, it is considered that the vapor deposition amount is about 0.3 g / m ² due to the decrease in opacity and the decrease in bulk due to the increase in density.

(3) Examination of the sizing degree of the paper and the effect of using steam Regarding the lightweight printing paper having the Steckigt sizing degree shown in Table 3 by internally sizing and surface sizing,
Table 3 shows the results of a comparative test conducted on the presence or absence of steam in the same manner as the experimental condition (1).

According to the results of Table 3, when the sizing degree of the paper is 1 second or less, the density increase and the opacity decrease are large, and the sizing degree is 4
In the case of seconds and 7 seconds, it can be seen that the smoothness can be improved with almost no increase in density and decrease in opacity.

Examples 1 to 4 and Comparative Examples 1 to ² A slightly coated light weight printing machine having a basis weight of 45 g / m ² was subjected to a steam flow on the back surface of the paper just before the calendering treatment under the same experimental conditions as above to generate steam. Supercalendering treatment was performed while adhering, and the results shown in Table 4 were obtained. The amount of vapor adhering to the paper surface and the conditions under which the calender is fed are as shown in the table.

The results shown in Table 3 show that the examples of the present invention do not increase the density of the paper so much and decrease the opacity so much as compared with the normal calendering process (Comparative Examples 1 and 2) using no steam. The smoothness and the printing glossiness could be significantly improved without this.

From the results in the table, the method of the present invention can increase the printing glossiness by 60 to 80% without increasing the density under the same calendering condition, as compared with the case where steam is not used. In addition, even if the density is reduced by 10% compared to the conventional method, it is possible to obtain paper with the same print gloss, that is, it is possible to obtain paper with the same print gloss and a thickness of 10%. Become. Therefore, according to the method of the present invention, in the calendar treatment of the conventional coated lightweight printing paper, it is possible to improve the printability such as smoothness and printing gloss without sacrificing properties such as opacity, bulk, and rigidity of the paper. What was not found was to solve the above problems by finding out the application conditions of low pressure and mild superheated steam flow in calendering. As is clear from the results in Table 4, the density is hardly increased and the white It has become possible to manufacture coated lightweight printing paper with smoothness of 400 seconds or more and printing gloss of 45% or more while maintaining opacity of 80% or more at 85% or more.

[Advantages of the Invention] The production method of the present invention conventionally improves the printability such as smoothness and printing gloss when the coated lightweight printing paper is subjected to calendar treatment without lowering the opacity, bulk and rigidity of the paper. It was not possible to reduce the opacity, bulk, and rigidity by calendering by applying a mild superheated steam flow at low pressure to the coated paper surface under the specific conditions of the present invention. The printability was able to be improved significantly without causing the above.

As a result, the same level of printing glossiness as in the past can be obtained with a paper having a thickness of about 10% thick, and good results can be given to bulk and rigidity.

In addition, according to the method of the present invention, a whiteness of 85 is obtained with almost no increase in density (while maintaining the bulk without decreasing the thickness).
% Or more, opacity is 80% or more, and smoothness is 40
It is possible to stably obtain a coated lightweight printing paper having a printing gloss of 45% or more for 0 seconds or more.

Claims (2)

(57) [Claims] 1. A method for producing coated light-weight printing paper, wherein a superheated steam of a low pressure and a slight degree of superheat is added immediately before calendering.
Under the conditions of (2) to (2), the paper is jetted in parallel, the surface of the paper is humidified and heated, and then calendering is performed. The basis weight is 25 to 60 g / m ² , and the coating amount of the single side is Hit 3
A method for producing a coated lightweight printing paper having a coating solid content of ~ 10 g / m ² . (1) Immediately before calendering, 0.01 to 0.3 seconds before jetting a mildly superheated steam at low pressure. (2) The amount of steam adhering to the paper surface is 0.05 to 0.
3g / m ² 2. The whiteness of 85% or more, the opacity of 80% or more, and the smoothness of the steam-treated surface of 400 seconds or more (according to Japan TAPPI No. 5 Oken smoothness tester). A coated lightweight printing paper having a basis weight of 25 to 60 g / m ² and a coating amount of 3 to 10 g / m ² (solid coating content) per side obtained by the production method.