JP2991276B2 - Stencil printing paper - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to paper having performance suitable for stencil printing.

[0002]

2. Description of the Related Art Stencil printing is a method in which ink is placed on a plate consisting of a portion that transmits ink and a portion that does not transmit ink, and the ink that has passed through the plate is applied to paper or the like to print a line drawing. Is known as a printing method based on a completely different principle from printing by a general printing method such as that described above, and printing by an electrophotographic method employed in a copying machine or the like.

[0003] As the stencil printing system,
There are transcript printing, type stencil printing, screen printing, etc.In recent years, with the development of electronic technology, a line drawing to be printed is read by a CCD camera, digitally processed, and reduced by a thermal head or the like according to the signal obtained therefrom. A digital plate making method for making a plate by making a hole has also been developed. already,
A stencil printing machine employing this plate making method (hereinafter referred to as a digital stencil printing machine) is also on the market. Compared with a copying machine adopting an electrophotographic method, operability and printing speed are equal or higher. , And its advantages are that the cost of printing a large number of sheets is low. More recently, devices have been developed that have the ability to send document data created by a word processor or personal computer directly to this printing press for printing. As an element of a desktop publishing system, the importance of such digital stencil printing machines has been developed. Sex is increasing.

Generally, in stencil printing, the plate is not damaged,
In order to obtain good plate reproducibility at the time of the transfer, a liquid ink having a low viscosity and a good fluidity is used so that the ink is lightly and evenly extended by a roller. Therefore, in the fixing of ink after printing (ink set), there are many parts that contribute to the absorbing action of paper in addition to the evaporation and curing of the ink itself, and the characteristics of paper greatly affect the printing quality. , Traditionally,
The performance required for the stencil printing paper has not been deeply studied due to the limited demand. However, the appearance of digital stencil printing machines
With the spread of the paper, its supply has been required in earnest, and it has become urgent to consider the performance that such paper should have.

[0005] In particular, recent digital stencil printing machines have a double-sided printing function. In stencil printing, there are many opportunities to print on both sides of paper. Often there. This is because the ink component oozes out from one side to the other side, or the vehicle in the ink component penetrates the paper, reducing the opacity of the paper, and the image on the other side from one side is reduced. It refers to the phenomenon of seeing through, but due to this strikethrough, printed matter printed on both sides by stencil printing tends to be very unsightly.

The printing speed of a digital stencil printing machine is as follows:
Compared to conventional stencil printing, there is a tendency for each stage to be faster and even faster. On the other hand, since this printing machine usually does not have a special ink drying mechanism inside,
The ink set after printing takes about the same time as other stencil printing. Therefore, when paper immediately after printing is stacked on a stacker or the like, the unfixed printed ink is transferred to the back side of the paper stacked on it, so-called set-off becomes a major problem here. Come.

[0007] Therefore, the performance of the stencil printing paper that must be considered first is the performance to be given to the paper in order to solve these problems. But in that case, the other necessary properties must not be sacrificed. In particular, in consideration of use in a digital stencil printing machine, the resolution and paper passing performance required when the printing speed is increased must not be sacrificed.

Until now, in digital stencil printing machines, high quality paper, medium quality paper, and the like used in electrophotographic copying machines and the like have been diverted as printing paper. However, as described above, stencil printing is completely different from electrophotographic printing, in which toner, which is a powder, is fused and fixed to the paper surface for printing. Therefore, the above-mentioned problems are unlikely to occur in a copying machine or the like, and even if they do occur, the means required to solve them, that is, the performance to be given to paper is naturally different.

Further, stencil printing cannot be considered equivalent to letterpress printing or offset printing. These methods, in which ink is placed on a plate or printing blanket and transferred directly to paper for printing, and stencil printing, in which ink passing through holes or the like in the plate is transferred to paper for printing, are used. This is because not only the printing principle, but also the properties of the inks used for the printing and the properties of the paper to be used for them differ.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a stencil sheet in which strike-through and set-off hardly occur and which have the required resolution and paper-passing properties.

[0011]

Means for Solving the Problems As a result of various studies to solve the above problems, the present inventors have found that in stencil printing, strikethrough, set-off, resolution, and paper passing property are reduced. It has a correlation with oil absorption, specific scattering coefficient and stiffness.
To provide a well-balanced stencil sheet with the required resolution and paper-passing properties, where set-off hardly occurs, the oil absorption and specific scattering coefficient of the paper must be higher with the lowest possible filler usage. Further, the inventors have found that by applying a film-forming polymer substance to the surface of the paper thus obtained, the oil absorption can be controlled relatively freely, thereby completing the present invention.

Hereinafter, the present invention will be described in detail. The countermeasure against set-off and the improvement in resolution can be achieved by greatly increasing the absorbability of ink to paper. In stencil printing, the ink
In order to prevent clogging of the pores of the plate, a low viscosity is required when passing through the plate, and after passing through the pores and transferring to paper, it is necessary to reduce the viscosity to obtain a clear image. It is required to have viscosity. Water / oil type emulsion inks are used as inks suitable for this purpose, but the present inventors have found that the absorption of the oil component among these two components, especially the oil component, is offset, and the resolution is high. It has been found that the better the paper has a higher oil-absorbing property, the less the set-off is likely to occur and the better the resolution is.

However, if the oil absorbency is blindly increased greatly, then, when this paper is printed by a digital stencil printing machine, a large number of white spots where no ink is applied in a solid printing portion are generated. A so-called phenomenon occurs and the image quality deteriorates. In other words, in digital stencil printing, a number of small holes are made in accordance with a document to be printed on a master paper (stencil sheet), and all characters and images are expressed by a set of ink dots passing through the small holes. However, if the oil absorbency of the paper is too good, the spread of the ink transferred to the paper in the lateral direction on the paper surface, that is, the leveling becomes small (though the resolution becomes high), and the shape of the small holes is faithful. Because of this leveling, the part between the holes, which are usually filled with ink by this leveling, and the ink does not pass through, remains as it is,
This is particularly noticeable as a white spot in the solid printing portion. After all, in this case, the resolution as the stencil printing paper is not of the type that the higher the resolution, the better it is required to be within a certain required range. In digital plate making using a thermal head that is currently being carried out, a method is used in which a plastic film is attached to a porous support such as Japanese paper as a master paper, and this is melted to form small holes. Since the fibers of Japanese paper that do not melt due to the heat of the thermal head remain in the small holes, if the oil absorbency of the paper is too good, the fibers will partially block the small holes, making it difficult for ink to pass through. The lost portion is reproduced as it is as a portion on which no ink is applied, which also causes white spots.

Therefore, in the stencil printing paper, it is necessary to improve the oil absorbency in order to prevent set-off and to improve the resolution, and at the same time, it is necessary to control the stencil printing paper so that it is not so good that white voids occur. Of particular importance at
There are two factors: the oil absorption indicating the degree of oil absorption, and the oil absorption coefficient indicating the speed. That is, in order to satisfy the oil absorbency required for stencil printing paper, the oil absorption amount is 18 to 30 ml / m ² , and the oil absorption coefficient is 60 to 105 ml.
/ M ² · s ^1/2 must be satisfied. If the oil absorption is less than 18 ml / m ² or the oil absorption coefficient is less than 60 ml / m ² · s ^1/2 , set-off occurs,
On the other hand, the resolution is deteriorated, while the oil absorption exceeds 30 ml / m ² or the oil absorption coefficient is 105 ml / m ² · s ^1/2.
Exceeding the range causes white spots in the solid printing portion to increase, causing a deterioration in image quality. Here, the oil absorption is a value measured by the Bristow method at a contact time of 0.05 seconds, and the oil absorption coefficient is determined by the same method as the contact time of 0.0 seconds.
The amount of oil absorption at 1, 0.02, and 0.04 seconds was determined, and was calculated as the slope of a regression line representing the correlation between this and the contact time. The oil used for both measurements is a mineral oil showing 10.5 cp (B-type viscometer) at 24 ° C.

The following two approaches can be roughly divided into measures for making it difficult for strikethrough of paper to occur.
In other words, in stencil printing, the measure is to suppress the penetration of the ink component printed on the paper surface and / or to suppress the decrease in the opacity of the paper due to the penetration of the vehicle into the paper (penetration; (Improvement of strike-through property)
Thus, it can be considered that the image printed in this way is provided with such performance that it is difficult to see through the back surface of the image in the first place (see-through; improvement in show-through property). Of these, the strike-through property is improved by increasing the oil absorption of the paper, so in the present invention, the above measures automatically lead to the improvement,
This is not enough as a countermeasure against strikethrough. However, as described above, it is impossible to increase the oil absorption unnecessarily. The present inventors have further studied and found that show-through properties can be improved by improving the specific scattering coefficient of paper calculated from the following equation.

[0016]

(Equation 1) (Equation 1) S = W ^-1 · ln [(R ₀ · R _p -1) / (R ₀ / R _p -1)] · (1 / R
_p- R _p ) ^-1 where S is the specific scattering coefficient, W is the basis weight of the paper, R ₀ is the reflectance of the paper when measured against a black standard plate, and R _P is the paper itself. Represents reflectivity.

That is, in this case, the specific scattering coefficient of the paper is 43
If it is 0 or more, the show-through property can be improved to a level effective as a measure against strikethrough of stencil printing paper within the above oil absorption range. Incidentally, this value is basically effective for improving show-through property as the value is higher, but it is technically difficult to make this larger than 800.
It can be said that finding a value exceeding this is not practical.

Further, when high-speed printing of the stencil sheet on a digital stencil printing machine or the like is considered, its rigidity is also an important factor. This is because paper with low stiffness easily causes a paper passing trouble such as a paper jam in a printing machine at the time of high-speed printing, and has a problem in paper passing property. According to the study of the present inventors, in consideration of the paper passing property at the time of such high-speed printing, the paper has a Clark stiffness of MD65L ³ /
A stiffness of 100 or more is required. However also, albeit than higher is good when considering sheet passing property, it is preferable from a practical as a printing paper is MD300L ^3/100 or less.

Among the above performances, one of the effective methods for improving the oil absorption and the oil absorption coefficient is to add a filler into paper. However, an increase in the filler content in the paper leads to a decrease in the stiffness of the paper. In order to ensure the above-mentioned Clark stiffness, in the present invention, the amount of filler in the paper must be 10% by weight or less based on the total weight of the paper. Accordingly, the quality of the filler used here is also an important factor in order to achieve the required oil absorption and oil absorption coefficient at this content. Therefore, the present inventors also studied the quality of this filler, and such a problem was solved when the oil absorption was 110 ml.
It has been found that the problem can be solved by using a high oil-absorbing filler of at least / 100 g. That is, such a highly oil-absorbing filler is based on the total weight of the paper (hereinafter, unless otherwise specified,
All filler amounts are expressed as values relative to the total weight of the paper. ) 1
If it is contained in an amount of not less than 10% by weight, the total amount of the filler in the paper is 10% by weight or less, in other words, even with the amount of filler capable of securing the Clarke stiffness, the oil absorption and oil absorption coefficient required for the stencil sheet are achieved. You can do it.

However, it is difficult to control the oil absorbency of paper when a highly oil-absorbent filler is used, and the paper made by adding such a filler tends to have excessively high oil absorbency. In other words, when using such a high oil-absorbing filler, it is possible to relatively easily cope with a certain range of required oil absorption and clearing the lower limit of the oil absorption coefficient by increasing the amount of addition, In order for these values not to exceed the upper limit, it is difficult to respond only by adjusting the amount of addition. For this reason, in the present invention, it is preferable to use one having an oil absorption of 300 ml / 100 g or less as the highly oil-absorbing filler, but this alone is not sufficient.
The present inventors further studied a simpler method of controlling the oil absorbency of paper in such a case, and as a result, applied a water-soluble polymer substance having a film forming property such as oxidized starch and PVA to the paper surface. Has been found to be extremely effective as a technique for suppressing its oil absorbency. That is, the oil absorbency of the stencil printing paper of the present invention is enhanced by adding a highly oil-absorbing filler at the time of papermaking, and furthermore, by coating such a water-soluble polymer substance after papermaking to suppress this. By taking the processing, it is possible to control easily and freely. The amount of the water-soluble polymer material required for coating on the paper surface is relatively small, about 0.2 to 1.2 g. It is advantageous to use a gate roll coater (GRC) suitable for small amount coating.

In addition, the highly oil-absorbing filler used here preferably has a specific scattering coefficient of 2000 cm ² / g or more. When such a highly oil-absorbing filler is used as described above, it alone achieves not only the oil absorption amount and the oil absorption coefficient, but also the specific scattering coefficient required for the stencil printing paper of the present invention. Because it can be. However, in the case of fillers used for papermaking, obtaining a material having a high specific scattering coefficient is naturally limited, and otherwise, there is a trade-off with the production cost. It is appropriate to use one having a scattering coefficient of up to 7500 cm ² / g.

The stencil printing paper of the present invention is a paper particularly suitable as a digital stencil printing paper, but is an excellent paper which is unlikely to cause strikethrough and set-off even when used for other stencil printing. This can be used for other printing paper, electrophotographic transfer paper, general office paper, and the like.

As the pulp as the main raw material of the stencil printing paper of the present invention, chemical pulp, mechanical pulp, recycled pulp (DIP) and the like can be appropriately used, and if necessary, a mixture thereof is used. You can also. Further, at the time of papermaking, commonly used dyes, fillers, sizing agents, fixing agents, dry paper strength enhancers, etc. can be added as necessary, and the pH at that time can be adjusted to neutral or acidic as required. Can be adjusted.

[0024]

[Function] In stencil printing, among the ink components used, the absorbability of the oil component to paper is particularly set off.
Affects resolution. In other words, if the oil absorbency of the paper is good, set-off is unlikely to occur, and the resolution is also improved.However, if it is too good, the resolution will be too good, the ink leveling will be small, and the master used for stencil printing will be Because it is faithfully reproduced, characters and letters are collected by a set of ink dots.
In digital stencil printing for displaying an image, it causes white spots in a solid printing portion.

Therefore, in the present invention, as a countermeasure, the amount of oil absorption indicating the degree of oil absorbency of paper and the oil absorption coefficient indicating the speed are 18 to 30 ml / m ² and 60 to 60 ml / m ² , respectively.
Control is performed in the range of 105 ml / m ² · s ^1/2 . If both are not above the lower limit, set-off occurs due to poor oil absorbency of the paper and the resolution is poor, and if neither is below the upper limit, then the oil absorbency of the paper Is too good, the resolution becomes too good, and white spots occur.

Further, in the present invention, by setting the specific scattering coefficient of the paper to 430 or more, a countermeasure against strike-through of the stencil printing paper is taken. As a countermeasure for strike-through, two approaches, improvement of strike-through property and improvement of show-through property, can be considered. However, this specific scattering coefficient has a great effect particularly on show-through property, and is set to be equal to or more than this value. As a result, strikethrough can be improved.

When high-speed printing with a digital stencil printing machine or the like is considered, the stiffness of the stencil printing paper is also important as a factor that affects the paper passing property. Therefore,
All the stencil printing papers of the present invention have a stiffness of MD65.
It is assumed that L is ^3/100 or more. Paper with lower stiffness may cause paper jams in the printing press during high-speed printing.
This is because it easily causes paper passing trouble.

In order to obtain a stencil sheet having the above performance, it is advantageous to use a highly oil-absorbing filler having an oil absorption of 110 ml / 100 g or more. Among the fillers in paper, if such a highly oil-absorbing filler is contained in an amount of 1% by weight or more based on the total weight of the paper, the amount of oil absorption and oil absorption coefficient required for stencil printing paper should be a filler amount that can secure Clarke stiffness. Is achieved. However, it is difficult to control the oil absorbency of the paper only by using such a high oil-absorbing filler, and the oil-absorbing property of the paper made by adding such a filler is likely to be excessive, so that in this case, the paper after the paper-making is further added. At least one side, that is, oxidized starch, PVA, etc. on the side printed as stencil printing paper,
This is suppressed and controlled by applying a water-soluble polymer substance having a film forming property. It is considered that such an effect of the coating is because these water-soluble polymers form a hydrophilic film on the paper surface and hinder penetration of oil components. Therefore,
For example, such an effect cannot be obtained only by imparting sizing properties to paper with a surface sizing agent, that is, merely by suppressing the water absorbency. It is important to control the oil absorption.

In addition, the highly oil-absorbing filler used here is desired to have a specific scattering coefficient of 2000 cm ² / g or more. When such a highly oil-absorbing filler is used as described above, it alone achieves not only the oil absorption amount and the oil absorption coefficient, but also the specific scattering coefficient required for the stencil printing paper of the present invention. Because it can be.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

Example 1 Oil absorption 202 ml / 100
g, zeolite having a specific scattering coefficient of 2118 cm ² / g, an oil absorption of 45 ml / 100 g, and a specific scattering coefficient of 690 cm ² / g
g of talc in a ratio of 4: 3 was mixed with 85% by weight of LBKP and NBKP so that the amount of filler in paper was 7% by weight.
It was added to the pulp slurry, which was a mixture of 15% by weight. In this slurry, a sulfuric acid band was added at 0.8% by weight based on pulp (hereinafter, all added amounts of additives were assumed to be based on pulp), and cationized starch was added at 0.5% as pulp.
Wt%, internal sizing agent 0.2 wt%, retention agent 100
ppm, and then mixed. The resulting material was used to make paper using an on-top type twin-wire paper machine.
6.3 g / m ² of paper was obtained, and oxidized starch (Nippon Starch SK-20) was applied on both sides of the paper using GRC at a rate of 0.33 g / m ² per one side. The amount of filler in the obtained paper was analyzed and calculated as the amount of ash contained in the paper, and this was confirmed (the same applies hereinafter).

Example 2 As a filler, an oil absorption of 116 m
1/100 g, calcined clay with specific scattering coefficient of 2596 cm ² / g, oil absorption of 35 ml / 100 g, specific scattering coefficient of 18
A mixture of 00 cm ² / g light calcium carbonate at a ratio of 3: 7 was used, and was added to the pulp slurry so that the amount of filler in the paper was 7% by weight. The raw material was prepared and paper-made to obtain a paper having a basis weight of 66.0 g / m ² . And also about this, the oxidized starch was apply | coated to both sides by 0.70 g / m < ² > per one side by GRC, and it was set as the co-test sample.

Comparative Example 1 A mixture obtained by mixing the talc of Example 1 and the light calcium carbonate of Example 2 at a ratio of 3: 7 was used as a filler so that the amount of filler in paper was 3% by weight. The raw material was prepared and paper-made in the same manner as in Example 1 except that the raw material was added to the pulp slurry, but this was used as a co-test sample without coating the paper after paper-making.

[Comparative Example 2] As the filler, the light calcium carbonate of Example 2 was used alone, and the amount of filler in paper was 10%.
Except that it was added to the pulp slurry to give
The raw material was prepared and paper-made in the same manner as in Example 1, but this was used as a co-test sample without coating the paper after the paper-making.

[Comparative Example 3] As the filler, the light calcium carbonate of Example 2 was used alone, and the amount of filler in paper was 15%.
A paper obtained by performing raw material preparation, papermaking, and coating in the same manner as in Example 1 except that it was added so as to be a weight percent was used as a co-test sample.

Comparative Example 4 Raw materials were prepared and paper-made in the same manner as in Example 1, but were used as co-test samples without coating the paper after the paper-making.

[Comparative Example 5] Raw materials were prepared and paper-made in the same manner as in Example 2, but the coated paper was used as a co-test sample without coating.

Comparative Example 6 A raw material was prepared and paper-made in the same manner as in Example 2, and oxidized starch was applied to both sides of the paper after the paper-making at 1.57 g / m ² per side using GRC. Was used as a co-test sample.

With respect to the samples obtained in the above Examples and Comparative Examples, respective physical property values for calculating oil absorption, specific scattering coefficient, and stiffness were measured, and set-off, white spots, strike-through, and paper passing property were measured. Was visually evaluated.

Table 1 shows the results.

[Table 1]

As is clear from the table, in Examples 1 and 2, a high oil-absorbing filler having an oil absorption of 110 ml / 100 g or more and a specific scattering coefficient of 2000 cm ² / g or more was added in an amount of 4 wt. % Or 3% by weight, and paper is coated with oxidized starch, so that the oil absorption, oil absorption coefficient, specific scattering coefficient, and rigidity are all within the scope of the present invention. Was obtained.
These papers had good evaluations in all of set-off, white spots, strike-through, and paper passing properties.

In Comparative Examples 1 and 2, papermaking was carried out using a filler having both an oil absorption and a specific scattering coefficient lower than the above values. However, in the obtained paper, the oil absorption and / or the oil absorption coefficient and the specific scattering coefficient were measured. Was lower than the range of the present invention. As a result, in these papers, although good evaluation was obtained for white spots, both set-off and strike-through were not practically satisfactory. On the other hand, in order to solve these problems, in Comparative Example 3, the same filler as that of Comparative Example 2 was used, and the amount of the filler was increased to prepare a paper having a filler content of 15% by weight. After oxidized starch coating on the surface,
All of these values fall within the range of the present invention. In this paper, set-off and strike-through, which were problems in Comparative Examples 1 and 2, were evaluated as good, and white spots due to excessive oil absorbency were also caused. was not, this time stiffness of the paper for the addition amount of the filler is too large, smaller than MD65L ^3/100, it has become a problem in the sheet passing property occurs.

Even if the paper was made under exactly the same conditions as in Example 1 or 2, unless the coated paper was coated (Comparative Examples 4 and 5), the oil absorption and / or oil absorption of the paper was Since the coefficient exceeds the range of the present invention, the evaluation of white spots becomes worse. Conversely, if the coating amount is too large (Comparative Example 6), the oil absorption coefficient becomes lower than the range of the present invention. Although good evaluation was obtained for white spots, there was a problem in set-off.

[0044]

The present invention focuses on the oil absorption, oil absorption coefficient, specific scattering coefficient, and stiffness of the paper, and by defining these, provides a paper suitable for use in stencil printing. . That is, paper whose performance is within the scope of the present invention is hard to cause set-off, strike-through, and white spots, and has the necessary resolution and paper-passing properties. Even in high-speed printing used, excellent image quality can be obtained, and no paper passing trouble occurs.

The present invention also provides a paper having the above-mentioned properties, which is obtained by using a filler having an oil absorption and a specific scattering coefficient of a certain value or more. By using such a filler, the amount of the entire filler used can be suppressed, so that it is possible to easily obtain paper having the required rigidity, that is, the paper passing property, and also having other properties necessary for use in stencil printing. Can be.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tsutomu Naito 5-2-1-1, Oji, Kita-ku, Tokyo Nippon Paper Industries Co., Ltd. Central Research Laboratory (56) References JP-A-5-331796 (JP, A) Kaihei 2-99696 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) D21H 17/00-21/56

Claims (3)

(57) [Claims] 1. A high oil-absorbing filler having an oil absorption of 110 ml / 100 g or more and a specific scattering coefficient of 2000 cm ² / g or more, containing 1% by weight or more and 10% by weight or less based on the total weight thereof. A layer of a water-soluble polymer substance having a film property is provided on at least one surface, and the Clarke stiffness is in the papermaking direction (M
A is 65L ^3/100 or more D), an oil absorption of 18
30 ml / m ² and oil absorption coefficient is 60 to 105 ml / m ²
A stencil sheet having a s ^1/2 and a specific scattering coefficient of 430 cm ² / g or more. 2. The specific scattering coefficient of the highly oil-absorbing filler is 2000 c.
^2. The stencil printing paper according to claim 1, which has an m ² / g or more. 3. The stencil printing paper according to claim 1, wherein the water-soluble polymer having a film-forming property is oxidized starch.