JPH11140791A - Newsprint for offset printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a newsprint for offset printing, providing an excellent quality of color printing and hardly causing a powder piling of a blanket paper by coating a specific surface treating agent on a base paper to enlarge a contact angle with water. SOLUTION: This newsprint for offset printing having >=90 deg. contact angle with water (the value at 1 sec after dropping a water drop on the paper) is obtained by coating a surface treating agent comprising an aqueous composition containing a water-soluble adhesive such as oxidation-modified starch, and a water-soluble polymer containing 40-80 wt.% styrene monomer, e.g. a styrene/ acrylic ester copolymer, on the surface of a base paper so that the coating amount (a solid component) may be 0.02-0.2 g/m<2> , preferably 0.03-0.1 g/m<2> .

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 having excellent printing workability and excellent color printing quality.

[0002]

2. Description of the Related Art In recent years, newspaper printing has rapidly changed from a conventional letterpress printing method to an offset printing method, and at present, it is said that 80% or more of newspaper printing is based on the offset printing method. Offset printing is a method in which a printing plate, usually called a PS plate, is prepared, and printing is performed by supplying dampening water and ink to the printing plate. The printing plate is a lithographic plate, on which the image areas have been treated to have a lipophilic surface, while the non-image areas have been treated to have a hydrophilic surface. When fountain solution and ink are supplied to the plate, ink is applied to the image area and water is attached to the non-image area. From this plate, ink is transferred to paper via a blanket and printed. do.

In this offset printing, the surface strength of the paper is required to be high in order to use ink having a relatively high tack. Also, if the paper surface is treated with dampening water to use a paper with a weak surface strength or a surface with weak water resistance, paper dust may accumulate on the blanket,
When mixed with the ink, a trouble such as generation of so-called blur occurs on the printing surface. In addition, the demand for high opacity after printing is increasing along with the weight reduction of newsprint paper, and inorganic pigments such as white carbon, titanium oxide, and talc are often used as fillers in papermaking to increase the opacity of paper. Became used. These inorganic pigments are easily leached out of the paper layer by fountain solution during offset printing, and are one of the main components of the paper powder to be piled on the blanket.

[0004] In order to cope with such a problem at the time of offset printing, conventionally, starch or starch is applied to the surface of newsprint paper.
It has been common practice to apply a polymer material such as polyvinyl alcohol or polyacrylamide. These surface treatment agents can improve the strength of the paper surface and strongly adhere the fine fibers and fillers on the paper surface to the paper.However, when the coating amount increases, the adhesiveness of the paper surface called Nepali increases, Attach to the blanket at the time of printing, induce paper breakage, and furthermore, using a lot of these surface treatment agents suppresses the penetration of ink to the paper surface,
In color printing, ink absorption unevenness (color unevenness on the printed surface) due to coating unevenness is apt to occur.

Various methods have heretofore been proposed for suppressing surface tackiness and increasing surface strength. For example, a method of increasing the strength of the paper surface by applying a specific polyacrylamide-based compound to the surface, and further increasing the surface water resistance by using a polyhydric aldehyde in combination (JP-A-8-13384), A method for improving the surface sizing property, surface strength, and surface tackiness by applying a composition obtained by adding a block copolymer of ethylene oxide and propylene oxide to polyvinyl alcohol (JP-A-5-59689) has been proposed. However, it is not always sufficient to achieve both a reduction in surface tackiness and a surface strength, and the fact is that ink absorption unevenness on a color printing surface has not yet been improved.

In addition, by using an internal sizing agent such as a rosin emulsion sizing agent to increase the sizing degree of the paper surface and to suppress the penetration of dampening water into the paper layer during offset printing, paper dust is generated. Has been traditionally done,
These internal sizing agents easily cause troubles due to foaming in a white water system in a high-speed paper machine such as a newspaper paper machine. In addition, newsprint frequently uses ground pulp, which hardly exhibits a size effect, as a raw material. Therefore, when a yield improver is used together with an internal sizing agent, the pitch and the like in the papermaking system are incorporated into the paper. It has the drawback of lowering the whiteness of paper.

[0007]

SUMMARY OF THE INVENTION The present inventors have intensively studied an offset printing newsprint having excellent offset printing workability and printing (finished) quality. As a result, the present invention provides a paper surface treatment with a surface treatment agent, thereby significantly increasing the initial contact angle of the paper surface as compared with the related art, so that blanket paper powder piling does not occur and excellent color printability. The present invention provides a newsprint for offset printing, comprising:

[0008]

According to the present invention, in a newsprint for offset printing obtained by applying a surface treating agent onto a base paper and drying, a contact angle between the newsprint and water (water droplets dropped on the paper surface). (A value after one second after) is 90 degrees or more. In particular, in the surface treatment agent, styrene monomer as a surface sizing agent contains 40%.
８０80% by weight of a water-soluble polymer, and the amount of the surface sizing agent applied to base paper is 0.03-0.1 g /
When it is m ² , an extremely excellent effect can be obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, starch, polyvinyl alcohol, polyacrylamide and the like are generally applied to newsprint for offset printing on the paper surface. All of these surface treatment agents are effective in suppressing the generation of paper dust, but when the coating amount is increased, it can be applied to the blanket during printing based on ink absorption unevenness and adhesiveness (hereinafter referred to as Nepari) in color printing. This causes a problem such as sticking.

A feature of the present invention resides in that the contact angle between the paper surface and water (a value one second after dropping on the paper surface) is specified to be 90 degrees or more. The reason why such identification of the contact angle contributes to the suppression of paper dust and the improvement of the suitability for color printing at the same time is not necessarily clear, but is presumed as follows. That is, the dampening water applied to the paper surface during the offset printing easily penetrates the paper layer, and when the wetness with the pulp fiber is too good, the fine fiber in the paper layer and the external filler with the internal filler are discharged to the outside. It is anticipated that there will be bleeding and, as a result, the fine raw material bleeding will be the basis of the paper dust. Conventionally, newsprint has a high water absorbency due to its pulp (paper layer) structure, and paper powder and the like are easily induced. Therefore, by making the paper layer as hard as possible to be wet with water, it is possible to suppress water absorption and consequently to suppress the emergence of the fine raw material by water, and to reduce or eliminate the generation of paper dust and the like. Is done.

Accordingly, the present inventors have conducted various studies on the suppression of water absorption of the paper layer. As a result, by using water that is relatively hard to get wet, the contact angle at one second after water falls on the paper of newsprint is adjusted to be 90 degrees or more, preferably 95 degrees or more. In addition, the bleeding action of the fine fibers and the internal filler inside the paper layer is reduced, and the generation of paper powder is greatly suppressed, while at the same time, the familiarity with the ink is improved, and the ink adhesion is improved, As a result, it was found that ink absorption unevenness or the like was reduced or eliminated, and the present invention was completed. Although the upper limit of the contact angle is not particularly limited, about 110 degrees is practically sufficient. It is not preferable to increase the contact angle more than that because it is necessary to use a large amount of the polymer surface sizing agent, and as a result, a change in the appearance of the paper and an adverse effect on offset printing suitability are expected.

Here, the larger the contact angle of the sheet, the harder it is to get wet with water. Generally, the contact angle of paper to water is measured according to TAPPI T-458-84. In this method, the measurement is performed 5 seconds or 1 minute after the water droplet is dropped on the paper surface. However, in the actual offset printing, since the dampening solution is almost instantaneously attached to the plate surface and comes into contact with the blanket and the paper surface, the wettability in such a short time is determined by the TAPPI T-458-84. The contact angle measured according to the method cannot be reproduced well. Thus, the present inventors have further studied the suitability for water wetting. As a result, a contact angle meter [Dynamic absorption tester DAT1100 (FIBRO)] capable of measuring in a short time.
The contact angle was measured one second after water was dropped onto the paper using
By employing this value, it has been found that there is an extremely high correlation between the contact angle and the generation of paper dust in the actual offset printing. In addition, the measurement for less than 1 second showed an unstable shape due to the impact when water was dropped on the paper, and a satisfactory measurement could not be performed.

The method of adjusting the paper so that the contact angle measured by the above-mentioned contact angle measuring device is 90 ° or more is not particularly limited, but conventionally used internal sizing agents such as rosin size are used. Can be used to make it difficult to wet the inside of the paper layer, but the strong water repellency of the surface desired by the present invention cannot be obtained. On the other hand, by using a relatively large amount of the externally added surface sizing agent, the contact angle of the surface can be effectively increased. In particular, a desirable effect can be obtained by using a surface sizing agent containing a large amount of styrene as a monomer component.

The surface treating agent used in the present invention comprises a surface sizing agent and an adhesive. Examples of the surface sizing agent include an olefin / maleic acid copolymer and a styrene / acrylic acid / acrylate ester. Examples of known adhesives include polymers and styrene / maleic acid ester copolymers. Examples of the adhesive include starches such as corn starch, oxidized starch, dialdehyde starch, phosphoric acid-modified starch, and cationized starch, and polyvinyl alcohol. And polyacrylamide. In order to obtain a high contact angle as specified in the present invention, a styrene / acrylate copolymer is particularly preferably used.

The amount of the surface sizing agent to be added is not particularly limited as long as the contact angle specified in the present invention can be obtained, but is usually 0.02 to 0.2 g / m ² , preferably 0 to 0.2 g / m ² . 0.03 to 0.1 g / m ² .
Incidentally, when the addition amount is less than 0.02 g / m ² , it is difficult to obtain the desired high contact angle of the present invention, and when it exceeds 0.2 g / m ² , the surface strength becomes weak, and At times, there is a possibility that troubles such as picking may occur.

In a more preferred embodiment, a styrene monomer is used as a component of the surface sizing agent (water-soluble copolymer) in a solid content ratio of 40 to 80% by weight, preferably 40 to 60% by weight, based on all components. The use of the water-soluble polymer which has been blended is preferable because a higher contact angle desired by the present invention can be obtained. The reason is not necessarily clear, but is presumed as follows.

That is, by increasing the ratio of the styrene monomer which is hydrophobic, water (fountain solution)
It is considered that the wettability of the paper surface is deteriorated, and as a result, a high contact angle is obtained. When the ratio is less than 40% by weight, it is difficult to obtain a high contact angle. On the other hand, when it exceeds 80% by weight, the contact angle becomes extremely high. There is a concern that the quality of the newsprint may decrease, and furthermore, the appearance and the quality of the newsprint may change.

The surface treating agent thus obtained is applied to a newsprint base paper after adjusting the solid content to 1 to 10% by weight. In such a case, the coating amount is usually 0.05 to 1 g / m ² , preferably 0.1 to 0.5 g / m ^{2 on} a dry weight basis.
It is applied on both sides in the range of m ² . By the way, the application amount is 0.
When it is less than 05 g / m ² , it is difficult to obtain a sufficient surface strength. On the other hand, when it exceeds 1 g / m ² , the Neppari strength increases, which may cause troubles such as sticking to a blanket. Examples of the coating device for applying the surface treatment agent to the base paper include a size press, a blade metaling size press, a rod metaling size press, a gate roll coater, a blade coater, a bar coater, a rod blade coater, and an air knife coater. In general, publicly known and publicly used devices are appropriately used. In general, the surface is smoothed by calendering after coating. In that case, machine calendering with a double-sided metal roll or soft calendering with a metal roll and an elastic roll is performed.

As the base paper for newsprint according to the present invention, chemical pulp (NBKP, LBKP, etc.) as raw material pulp,
Mechanical pulp (GP, CGP, RGP, PGW, TMP
Etc.), and used paper pulp (DIP etc.) alone or in a mixture at an arbitrary ratio. In addition, white carbon,
Papermaking fillers such as clay, amorphous silica, talc, titanium oxide and calcium carbonate are added during papermaking. In addition, other well-known and commonly used papermaking chemicals such as a paper strength enhancer, a retention aid, a sizing agent such as a strengthened rosin sizing agent and an emulsion sizing agent, a water-proofing agent, and an ultraviolet ray inhibitor are appropriately added. Then, the paper is generally made on a publicly known public paper machine. The basis weight of the base paper is not particularly limited, but is generally about 35 to 50 g / m ² .

[0020]

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

Example 1 (Making of base paper) A mixture of 10 parts of softwood kraft pulp, 40 parts of thermomechanical pulp, 20 parts of ground pulp, and 30 parts of deinked waste paper pulp was mixed and defibrated with a refiner to obtain a freeness of 120 ml (csf / csf). After adding 1% of white carbon as a filler to the pulp slurry (paper material) prepared in Canadian Standard Freeness, based on the absolutely dried pulp, papermaking was carried out by a fourdrinier paper machine to obtain a base paper for newspaper of 42 g / m ^{2 in} rice tsubo. Was.

(Production of surface sizing agent) Stirrer, cooling pipe,
In a flask equipped with a dropping funnel, a nitrogen inlet tube and a thermometer, 45 parts of styrene, 10 parts of n-butyl acrylate, 45 parts of methacrylic acid, 35 parts of isopropyl alcohol,
35 parts of water and 5 parts of 2,2′-azobisisobutyronitrile were charged as a polymerization initiator, and the mixture was maintained at 80 to 85 ° C. for 5 hours while stirring under a nitrogen stream. Then, it was neutralized with a predetermined amount of water and 28% ammonia water to obtain a surface sizing agent. The appearance was a slightly cloudy liquid, the apparent viscosity at 25 ° C. was about 1000 cps, the nonvolatile content was 20.5%, and the pH was 9.0.

(Application of Surface Treatment Agent) As a water-soluble polymer adhesive, 100 parts of oxidized modified starch (trade name: Ace A / Oji Cornstarch) and 40 parts of the surface sizing agent obtained above were mixed and diluted. A surface treatment agent having a solid content of 4% was obtained. The surface treating agent thus obtained was applied to the above-described base paper for newspaper (Yonetsubo 4).
2 g / m ² ), using a gate roll coater on both sides, 0.3 g / m ² (oxidized modified starch = 0.21 g / m ² , surface sizing agent = 0.09 g / m ² ) on a dry weight basis
² ) After coating and drying on both sides so as to be as described above, apply a linear pressure of 150 k to a machine calendar consisting of metal rolls / metal rolls.
One nip was passed under the condition of g / cm to obtain newsprint paper for offset printing.

Example 2 In Example 1, offset printing was performed in the same manner as in Example 1 except that the number of parts of the styrene monomer was changed to 65 parts and the amount of methacrylic acid was changed to 25 parts in the preparation of the surface sizing agent. Newspaper was obtained. The appearance of this surface sizing agent is a slightly cloudy liquid, has an apparent viscosity at 25 ° C. of about 1500 cps, a nonvolatile content of 20.5%, and a pH of 9.0.
Met.

Example 3 In the preparation of the surface sizing agent of Example 1, 85 parts of styrene monomer and 5 parts of n-butyl acrylate were added.
Parts and methacrylic acid were changed to 10 parts, respectively, to obtain newsprint for offset printing in the same manner as in Example 1. The appearance of this surface sizing agent is a slightly cloudy liquid,
The apparent viscosity at 25 ° C. was about 1400 cps, the nonvolatile content was 20.5%, and the pH was 9.0.

Example 4 In the preparation of the surface treating agent of Example 1, an oxidized modified starch (trade name: Ace A / Oji Cornstarch) 100
Parts, and the surface sizing agent was changed to 100 parts,
Newsprint paper for offset printing was obtained in the same manner as in Example 1. The amount of the surface treating agent applied at this time was 0.2 g / m ² per dry surface (oxidized modified starch = 0.1 g /
m ² , surface sizing agent = 0.1 g / m ² ).

Example 5 In the preparation of the surface treating agent of Example 1, a water-soluble polymer
Oxidized modified starch (trade name: Ace C / Ojiko)
100 parts, surface support used in Example 1.
Mix 40 parts of an oiling agent, dilute with water and apply a surface treatment of 4% solids.
A physical agent was obtained. Newspaper using this surface treatment agent in Example 1
Use a gate roll coater on the base paper to
0.2g / m in dry weight^Two(Oxidized modified starch = 0.1
4g / m ^Two, Surface sizing agent = 0.06 g / m^Two) Becomes
Roll on the metal roll after coating and drying on both sides
130kg / linear pressure on machine calender consisting of rolls
cm for one-nip, and a new offset printing
I got a question paper.

Example 6 In the preparation of the surface treating agent of Example 1, a water-soluble polymer
Polyacrylamide is used instead of oxidized modified starch
(Product name: Santax NP14 / Mitsui Toatsu Chemicals)
Using 100 parts, surface treatment agent is dry weight per one side
0.15g / m ^Two(Polyacrylamide = 0.11 g /
m^Two, Surface sizing agent = 0.04 g / m^Two)
Coated and dried in the same manner as in Example 1, and then similar to Example 1.
Thus, newsprint paper for offset printing was obtained.

EXAMPLE 7 15 parts of softwood kraft pulp, 35 parts of thermomechanical pulp, 10 parts of ground pulp, deinked waste paper pulp 40
Talc was added as a filler to a pulp slurry prepared to a freeness of 150 ml (csf / Canadian standard freeness) at a ratio of 1% based on the absolutely dry pulp. 43 tsubo
/ M ² of newsprint base paper. Except for using this base paper, newsprint paper for offset printing was obtained in the same manner as in Example 1.

Comparative Example 1 Newsprint paper for offset printing was obtained in the same manner as in Example 1 except that no surface sizing agent was added in the preparation of the surface treating agent of Example 1.

Comparative Example 2 A surface sizing agent contained in the surface treating agent of Example 1 was prepared in the same manner as in Example 1, except that the number of styrene monomers was 20 parts, n-butyl acrylate was 15 parts, and methacrylic acid was 65 parts. Newsprint paper for offset printing was obtained in the same manner as in Example 1. The appearance of this surface sizing agent was a slightly cloudy liquid, the apparent viscosity at 25 ° C. was about 800 cps, the nonvolatile content was 20.0%, and the pH was 9.0.

Comparative Example 3 A newspaper for offset printing was prepared in the same manner as in Example 1 except that the amount of the surface sizing agent was changed to 5 parts per 100 parts of the oxidized modified starch in the preparation of the surface treating agent of Example 1. I got the paper. At this time, the applied amount of the surface treatment agent was 0.3 g / m ² (oxidized modified starch = 0.286 g) on one side by dry weight.
/ M ² , surface sizing agent = 0.014 g / m ² ).

Comparative Example 4 Newspaper for offset printing was obtained in the same manner as in Example 5, except that the amount of the surface sizing agent was changed to 10 parts per 100 parts of the oxidized modified starch. At this time, the amount of the surface treatment agent applied was 0.2 g per side on a dry weight basis.
/ M ² (oxidized modified starch = 0.182 g / m ² , surface sizing agent = 0.018 g / m ² ).

Comparative Example 5 In Example 6, the amount of the surface sizing agent added was
Except for changing to 10 parts for 100 parts of luamide
Newsprint paper for offset printing was obtained in the same manner as in Example 6. This
The amount of the surface treatment agent applied is the dry weight per side
0.15g / m^Two(Polyacrylamide = 0.136 g
/ M^Two, Surface sizing agent = 0.014 g / m ^Two)
Was.

The quality of the newsprint for offset printing obtained in the examples and comparative examples thus obtained was evaluated as shown below, and the obtained results are shown in Table 1.

[Ink Absorption Unevenness] Using an offset printing machine (Komori SYSTEM C-20), four-color printing was performed, and the ink density unevenness in the indigo / red overlapping portions was visually judged. A: A uniform and clear image without any ink density unevenness. ：: A uniform image with almost no ink density unevenness. Δ: An uneven density image was observed, and the image was slightly uneven. ×: Inconsistent image of ink density, non-uniform image.

[Pilging of Blanket Paper Powder] Using an offset printing machine (Komori SYSTEM C-20), four-color printing was performed, and after printing 5000 copies, the degree of deposition of paper powder on the blanket non-image area was visually observed. Was determined. ◎: No generation of paper dust was observed. : Generation of paper dust is slightly observed, but there is no practical problem. Δ: Generation of paper dust is clearly observed. ×: A lot of paper powder is deposited on the blanket, and the blanket is white.

[Contact Angle] A newsprint sample was cut into an appropriate size, 5 μl of water (20 ° C.) was dropped, and the contact angle after one second was measured by a contact angle meter (Dynamic Absorption Tester DAT1100 / FIBRO). It measured using.

[0039]

[Table 1]

[0040]

As is clear from the results shown in Table 1, the newsprint obtained in Examples of the present invention has excellent color printing quality and excellent blanking paper powder without piling or blanket sticking. It was newsprint paper for offset printing.

Claims (3)

[Claims] In a newsprint paper for offset printing obtained by applying a surface treating agent on a base paper and drying, the contact angle between the newsprint paper and water (a value one second after a water drop falls on the paper) is obtained. 9
Newspaper for offset printing characterized by being at least 0 degrees. 2. The aqueous composition according to claim 1, wherein the surface treating agent comprises a water-soluble polymer adhesive and a water-soluble polymer containing 40 to 80% by weight of a styrene monomer as a surface sizing agent. Newsprint paper for offset printing. 3. The newsprint paper for offset printing according to claim ² , wherein the amount of the surface sizing agent applied to the base paper is 0.03 to 0.1 g / m ² in solid content.