JP6713333B2 - Penetration drying type black ink composition for offset printing, and method for reducing drydown when printing by penetration drying method using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a penetration-drying type black ink composition for offset printing, and a method of using the same for reducing drydown in printing on waste paper.

Offset printing is a printing method that utilizes the property that an oil-based ink composition for offset printing (hereinafter, appropriately abbreviated as "ink composition" or "ink") repels water, and printing with unevenness. Unlike the letterpress printing method using a plate, it is characterized by using a printing plate having no unevenness. This printing plate is provided with a lipophilic image portion and a hydrophilic non-image portion instead of the unevenness. When printing, first, the non-image area of the printing plate is wetted with dampening water to form a water film on the surface, and then the ink composition is supplied to the printing plate. At this time, the supplied ink composition repels and does not adhere to the non-image area where the water film is formed, and adheres only to the lipophilic image area. Thus, an image is formed by the ink composition on the surface of the printing plate, and then the image is transferred to the blanket and the paper one after another to perform printing.

Among such offset printing, an offset rotary press is used for newspaper printing that requires high-speed and large-scale printing. In the offset rotary press, the printing paper is mounted on the paper supply unit in a wound state, and by unwinding the winding, the printing paper is supplied to the printing unit to perform printing. The printed printing paper is cut by a cutting unit and then subjected to necessary processing such as folding to form a booklet-shaped newspaper. According to such a printing method, tens of thousands to hundreds of thousands of copies can be printed at one time, which is efficient. The printing speed may reach a high speed of 100,000 copies or more per hour. Under such circumstances, a large number of products having high-speed printing suitability have been proposed as an ink composition for offset printing (see, for example, Patent Document 1).

By the way, newsprint printed by offset printing, if the ink composition adhering to the surface is not in a sufficiently dry state, when it is folded into a booklet, set-off occurs, or with fingers. Since the ink adheres when touched, it cannot be sent to a subsequent step or distributed as a product. Therefore, a step of drying the ink composition adhering to the surface of the paper is required after performing offset printing. Here, as a method of drying the ink composition in newspaper printing, a penetration drying method is adopted. In this drying method, after printing, the oil component contained in the ink composition present on the surface of the paper permeates into the interior of the paper, so that the ink composition loses its adhesiveness on the surface of the paper ( (Set state) and drying is completed. In this state, even if it is touched with a finger, the ink composition existing on the surface of the paper does not adhere, so that it becomes possible to perform post-processes such as cutting and folding into a booklet.

JP 2012-102217 A

The drying by the permeation drying method is a special feature for drying because the ink composition can be quickly dried on a printing paper having high oil absorption (fast oil permeation speed) such as a waste paper used in newspaper printing. It is excellent in that it requires no equipment or energy, and can suppress the release of VOC (volatile organic compound) into the atmosphere unlike the evaporation drying method. However, when the ink composition is dried by the permeation drying method, a phenomenon called dry down tends to occur in which the coloring density of the ink on the paper surface decreases with time. Although the reason why this phenomenon occurs is not always clear, the ink composition contains a component (coloring component such as a coloring pigment) that imparts a coloring power to the ink composition, which should normally be fixed on the surface of the printing paper. It is presumed that the transfer of the oil component to the inside of the printing paper together with the oil component is a factor. A printed matter that is strongly dried down has a problem in that the color density of the image formed by the ink composition is reduced, resulting in a loss of sharpness on the paper surface. Then, such a phenomenon tends to be noticeable in a black-colored image as a contrast to white which is the background color of the printing paper.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a black ink composition capable of suppressing dry down in printing by a penetration drying method that tends to cause dry down. ..

As a result of intensive studies to solve the above problems, the present inventors reduced or did not use the amount of the Gilsonite resin, which is a general dispersant for carbon black, and instead used a specific carbon black. That is, neutral carbon black having a specific coloring power of 71 to 120%, an average primary particle diameter of 20 to 40 nm, a nitrogen adsorption specific surface area of 41 to 90 m ² /g, and a DBP oil absorption of 70 to 109 cm ³ /100 g is used as a coloring pigment. It has been found that a black ink composition that can be used and suppresses drydown in printing by a permeation drying method can be obtained by using an alkyd resin to help disperse this. The present invention has been made based on the above findings, and provides the following.

（上記一般式（１）において、左端の酸素原子はノボラック樹脂の芳香族性水酸基に含まれる酸素原子に由来するものであり、Ｗ ^１ 及びＸ ^１ はそれぞれ独立に炭素数１〜１９の二価の炭化水素基であり、ｉは１〜３０の整数であり、ｊは０〜３０の整数であり、Ｒ ^１ は水素原子又はメチル基である。）
（Ｂ）下記一般式（２）で表す構成単位を鎖中に少なくとも１０モル％含み、質量平均分子量３０００〜１０００００である共重合体。

（上記一般式（２）において、Ｗ ^２ 及びＸ ^２ はそれぞれ独立に炭素数１〜１９の二価の炭化水素基であり、ｐは１〜３０の整数であり、ｑは０〜３０の整数であり、Ｒ ^２ は水素原子又はメチル基であり、Ｒ ^３ は水素原子又はメチル基である。） The present invention provides a neutral carbon black having a specific coloring power of 71 to 120%, an average primary particle diameter of 20 to 40 nm, a nitrogen adsorption specific surface area of 41 to 90 m ² /g, and a DBP oil absorption of 70 to 109 cm ³ /100 g, and rosin. A modified phenol resin and an alkyd resin, wherein the Gilsonite resin content is less than 2% by mass , the alkyd resin content is 2 to 4% by mass, and further as a pigment dispersant for the carbon black. Permeation-drying type comprising the following modified novolac resin (A) and/or the following graft copolymer (B) having a ring-opening structure of an epoxy group with a carboxyl group derived from an aromatic ring and a hydroxycarboxylic acid. It is a black ink composition for offset printing.
(A) A modified novolac resin having at least one group represented by the following general formula (1) in the molecule.

(In the general formula (1), the oxygen atom at the left end is derived from the oxygen atom contained in the aromatic hydroxyl group of the novolak resin, and W ¹ and X ¹ are each independently a divalent group having 1 to 19 carbon atoms. Is a hydrocarbon group, i is an integer of 1 to 30, j is an integer of 0 to 30, and R ¹ is a hydrogen atom or a methyl group.)
(B) A copolymer containing a structural unit represented by the following general formula (2) in the chain of at least 10 mol% and having a mass average molecular weight of 3,000 to 100,000.

(In the general formula (2), W ² and X ² are each independently a divalent hydrocarbon group having 1 to 19 carbon atoms, p is an integer of 1 to 30, and q is an integer of 0 to 30. And R ² is a hydrogen atom or a methyl group, and R ³ is a hydrogen atom or a methyl group.)

The content of the Gilsonite resin is preferably less than 1% by mass.

The present invention is also a method of suppressing dry-down of a printing paper surface with time when printing is carried out by a penetration drying method, which is characterized by using the above-mentioned penetration-drying type black ink composition for offset printing.

ADVANTAGE OF THE INVENTION According to this invention, the black ink composition which can suppress drydown is provided in the printing by the penetration drying system which is apt to produce drydown.

Hereinafter, one embodiment of the ink ink composition for permeation drying type offset printing of the present invention (hereinafter, also simply referred to as “ink composition”) and the drydown when printing is carried out by the permeation drying method of the present invention will be described. One embodiment of the suppression method (hereinafter, also simply referred to as “drydown suppression method”) will be described, but the present invention is not limited to the following embodiments and embodiments. Hereinafter, the ink composition of the present invention and the method for suppressing drydown of the present invention will be described in this order.

<Permeation dry type black ink composition for offset printing>
The ink composition of the present invention is not particularly limited because it can suppress drydown when printing by a permeation drying method on printing paper such as highly-absorptive paper, which is not particularly limited. It is preferably used as an application. The ink composition of the present invention is a neutral carbon black having a specific coloring power of 71 to 120%, an average primary particle diameter of 20 to 40 nm, a nitrogen adsorption specific surface area of 41 to 90 m ² /g, and a DBP oil absorption of 70 to 109 cm ^3. , A rosin-modified phenol resin, and an alkyd resin, and the content of the Gilsonite resin is less than 2% by mass. In addition to these, an oil component is appropriately used to dissolve the resin and impart fluidity to the ink composition. Hereinafter, each component will be described.

[Neutral carbon black]
The ink composition of the present invention is a black ink and contains carbon black as a coloring pigment. In the ink composition of the present invention, a neutral carbon black is used, and in particular, a specific coloring power of 71 to 120%, an average primary particle diameter of 20 to 40 nm, a nitrogen adsorption specific surface area of 41 to 90 m ² /g, and DBP. One of the features is that an oil absorption amount of 70 to 109 cm ³ /100 g is used.

Some carbon blacks have acidic groups such as phenolic hydroxyl groups and carboxyl groups on the surface due to the difference in the manufacturing method and the chemical treatment after formation.Roughly speaking, the large amount is acidic carbon. It is black, and the less one is called neutral carbon black. Since these acidic groups show a high affinity for the resin and oil components contained in the ink composition, an acidic carbon black containing a large amount of acidic groups generally has a higher dispersibility than a neutral carbon black lacking an acidic group. As a result, an ink composition having high color development and excellent fluidity is provided. However, according to the study of the present inventors, when printing on a highly oil-absorptive printing paper such as newsprint, when an ink composition containing acidic carbon black as a coloring component is used for printing, However, after printing, there is a tendency for dry down, which is a phenomenon in which the density of printed matter decreases with the passage of time. It is not preferable that the printed matter that has undergone dry-down tends to give a reader the impression that it is a printed matter that has a punchy print surface, especially in solid areas, and has no punch.

On the other hand, in the case of using a neutral carbon black, according to the study of the present inventors, although the dry down when printed on a highly oil-absorptive printing paper is improved, such as the coloring property and fluidity of the ink composition. In this respect, the performance tends to be insufficient as compared with the case where the acidic carbon black is used. In general, neutral carbon black has poor dispersibility, and this tendency is particularly remarkable in carbon black having a small particle size and high color development. Therefore, if it is desired to obtain high color developability, the dispersibility will be insufficient and the fluidity of the ink composition will be deteriorated. When neutral carbon black is used, both the color developability and fluidity are compatible. The reality is that it was difficult to get them to do it.

From the above, the inventors of the present invention have made earnest studies to find a neutral carbon black capable of achieving both coloring and fluidity, and have a specific coloring power of 71 to 120% and an average primary particle diameter of 20. -40 nm, nitrogen adsorption specific surface area 41-90 m ² /g, and DBP oil absorption amount 70-109 cm ³ /100 g are used in combination with an alkyd resin to be described later to achieve both coloring and fluidity. It has been found that an ink composition that can be obtained is obtained. The present invention has been made on the basis of such knowledge, and is characterized by using a specific neutral carbon black, which will be described below.

The carbon black used in the present invention is neutral, the specific coloring power is 71 to 120%, the average primary particle size is 20 to 40 nm, the nitrogen adsorption specific surface area is 41 to 90 m ² /g, and the DBP oil absorption is 70 to. It is 109 cm ³ /100 g. In the carbon black, primary particles are aggregated to form an aggregate (structure) like a bunch of grapes, and as described above, the average primary particle diameter is 20 to 40 nm, the DBP oil absorption is 70 to 109 cm ³ /100 g. The carbon black is classified into small particle size and medium to large structure. As the DBP oil absorption of carbon black is preferably ^{70~108cm 3 / 100g, 70~102cm 3 /} 100g and more preferably. These specific coloring power, nitrogen adsorption specific surface area, and DBP oil absorption are all defined in accordance with JIS K6217. The average primary particle diameter is an arithmetic average value of particle diameters obtained by observing particles with an electron microscope. Since these numerical values are also described in the catalog provided by the manufacturer of carbon black, it suffices to search for a product within the above range and purchase and use it.

The content of the carbon black in the ink composition is preferably in the range of 10 to 30% by mass. When the content is 10% by mass or more, good blackness can be obtained, and when the content is 30% by mass or less, good printability is obtained, which is preferable. The content of the carbon black in the ink composition is more preferably 15 to 25% by mass.

[Rosin modified phenolic resin]
The rosin-modified phenolic resin is a component for dispersing the carbon black in the ink composition, and also functions as a binder for fixing the carbon black on the surface of the printing paper. The mass average molecular weight of the rosin-modified phenol resin is preferably about 10,000 to 200,000.

The rosin-modified phenolic resin is used in the state of being dissolved or dispersed into a varnish by being heated together with an oil component described later. When preparing a varnish, a gel varnish may be prepared by adding a divalent or higher valent metal alkoxy compound as a gelling agent to a dissolved varnish obtained by dissolving a resin. It is preferable to prepare a gelled varnish from a binder resin and use this for the preparation of an ink composition, because it is possible to impart appropriate viscoelasticity to the ink composition.

The content of the rosin-modified phenolic resin in the ink composition is preferably about 10 to 45% by mass. If necessary, a resin other than the rosin-modified phenol resin may be added to the ink composition. Examples of such resin include rosin-modified maleic acid resin and petroleum resin. When such a resin is used in combination with a rosin-modified phenolic resin, the total content in the ink composition is preferably within the above range.

[Alkyd resin]
One of the features of the ink composition of the present invention is that the neutral carbon black is used in combination with an alkyd resin. The alkyd resin is a kind of polyester, and the one obtained by reacting a fat and oil, a polybasic acid, and a polyalcohol can be exemplified as an ink composition application. As such an alkyd resin, a commercially available one can be obtained and used.

The content of the alkyd resin in the ink composition is preferably about 2 to 10% by mass, more preferably about 2 to 7% by mass, and even more preferably about 2.5 to 5% by mass. When the content is 2% by mass or more, the above neutral carbon black is satisfactorily dispersed and the printability is improved, which is preferable. When the content is 10% by mass or less, good emulsification suitability is obtained. Therefore, it is preferable.

[Oil component]
The oil component is used to dissolve the above resin to form a varnish and to adjust the viscosity of the ink composition. Examples of the oil component include vegetable oils and/or mineral oils, and those which have been used in the preparation of ink compositions so far can be used without particular limitation.

In the present invention, the vegetable oil may include a vegetable oil-derived fatty acid ester compound in addition to the vegetable oil. Examples of the vegetable oil include soybean oil, cottonseed oil, linseed oil, safflower oil, tung oil, tall oil, dehydrated castor oil, canola oil, and other drying oils and semi-drying oils. Examples of the vegetable oil-derived fatty acid ester compound include the above-mentioned vegetable oil-derived fatty acid monoalkyl ester compounds. As the fatty acid constituting the fatty acid monoalkyl ester compound, a saturated or unsaturated fatty acid having 16 to 20 carbon atoms is preferably exemplified. As such a saturated or unsaturated fatty acid, stearic acid, isostearic acid, hydroxystearic acid, Preferable examples are oleic acid, linoleic acid, linolenic acid, eleostearic acid and the like. The alkyl group constituting the fatty acid monoalkyl ester compound is preferably exemplified by an alkyl group having 1 to 10 carbon atoms, and more specifically, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, Preferable examples are a tert-butyl group and a 2-ethylhexyl group.

These vegetable oils can be used alone or in combination of two or more. Preferable examples of the vegetable oil include soybean oil and soybean oil fatty acid ester. The content of the vegetable oil in the ink composition can be, for example, about 20 to 60 mass% with respect to the entire ink composition.

In the present invention, examples of the mineral oil include light mineral oil also called a solvent, heavy mineral oil that is a lubricating oil, and the like.

Examples of the light mineral oil include non-aromatic petroleum solvents having a boiling point of 160° C. or higher, preferably 200° C. or higher. Examples of such non-aromatic petroleum solvents include No. 0 solvent, AF solvent 5, AF solvent 6, AF solvent 7 and the like manufactured by JX Nikko Nisseki Energy Co., Ltd.

Examples of heavy mineral oils include various lubricating oils that have been classified as spindle oils, machine oils, dynamo oils, cylinder oils, and the like. Among these, from the viewpoint of conforming to the OSHA standard and EU standard in the United States, it is preferable that the content of the condensed polycyclic aromatic component is suppressed. Examples of such mineral oils include ink oil H8 and ink oil H35 manufactured by JX Nikko Nisseki Energy Co., Ltd. (all trade names), SNH8, SNH46, SNH220, and SNH540 manufactured by Sankyo Yuka Kogyo Co., Ltd. (All are trade names) and the like.

These mineral oils can be used alone or in combination of two or more. The content of the mineral oil in the ink composition can be, for example, about 0 to 50% by mass based on the entire ink composition.

[Dispersant]
It is one of the points that the content of the Gilsonite resin in the ink composition of the present invention is less than 2% by mass. Gilsonite resin has excellent properties as a dispersant for carbon black, and is often used as a component of black ink containing carbon black. However, in the study conducted by the present inventors to improve the drydown, the black ink composition prepared using the Gilsonite resin tends to have a large drydown when printed on a highly oil-absorbent printing paper. It turned out to be. The present invention has been made based on the above findings, and is characterized in that the content of the Gilsonite resin in the ink composition is reduced as much as possible. And, as described above, the decrease in the dispersibility due to the reduction of the Gilsonite resin can be solved by combining the specific neutral carbon black and the alkyd resin, and if necessary, the dispersant described later may be used in combination. Good. The content of Gilsonite resin in the ink composition of the present invention is less than 2% by mass, preferably less than 1% by mass, more preferably less than 0.5% by mass, and 0.2% by mass. It is more preferable that the content is not more than 0.1% by mass, more preferably not more than 0.1% by mass, and most preferably no (ie 0% by mass).

The Gilsonite resin referred to in the present invention refers to Gilsonite and an aliphatic hydrocarbon-based resin which is an extract from Gilsonite and has a softening point of 120 to 125°C. Gilsonite, as defined in JIS K 5500, refers to asphaltite from Utah and is a type of hard bitumen. The extract from Gilsonite is Gilsonite, that is, an aliphatic hydrocarbon resin having a softening point of 120 to 125° C. extracted from natural asphaltite.

When a dispersant is used to supplement the dispersibility as described above, a pigment dispersant for carbon black can be used. In the present invention, the Gilsonite resin is not included in the dispersant for carbon black. Various types of such pigment dispersants for carbon black are commercially available, and they can also be used.

As the dispersant for carbon black, more preferably, the following modified novolac resin (A) and/or the following graft copolymer (B) having an aromatic ring and a ring-opening structure of an epoxy group by a carboxyl group derived from a hydroxycarboxylic acid are used. ) Can be mentioned. The content of such a dispersant in the ink composition may be 0.2% by mass to 5% by mass. Next, the modified novolac resin (A) and the graft copolymer (B) will be described.

The modified novolac resin (A) is a novolac resin having an aromatic ring and an epoxy group ring-opening structure with a carboxyl group derived from a hydroxycarboxylic acid and having at least one group represented by the following general formula (1) in the molecule. is there.

In the above general formula (1), the oxygen atom at the left end is derived from the oxygen atom contained in the aromatic hydroxyl group of the novolak resin, and W ¹ and X ¹ are each independently a divalent group having 1 to 19 carbon atoms. It is a hydrocarbon group, i is an integer of 1 to 30, j is an integer of 0 to 30, and R ¹ is a hydrogen atom or a methyl group.

Such a modified novolak resin (A) is obtained by reacting a novolak resin having an epoxy group with a monohydroxy fatty acid having 2 to 20 carbon atoms or a condensation polymer thereof.

The novolak resin having an epoxy group is synthesized by reacting a novolak resin having a phenolic hydroxyl group with an epichlorohydrin derivative such as epichlorohydrin or β-methylepichlorohydrin by a conventional method. In addition, since such a novolac resin introduced with an epoxy group is commercially available, it may be used.

As the novolak resin having a phenolic hydroxyl group, a novolak resin derived from a monohydric or polyhydric phenol and an aldehyde by a conventional method can be used.

Among these, examples of monohydric phenols include unsubstituted phenols such as phenol, cresol, xylenol, trimethylphenol, propylphenol, butylphenol, amylphenol, hexylphenol, octylphenol, nonylphenol and dodecylphenol, and substituted phenols such as alkylphenols. You can Examples of the polyhydric phenols include catechol, resorcinol, hydroquinone, trihydroxybenzene, or substitution products thereof, dihydroxydiphenylmethanes such as bisphenol A and bisphenol F, and dihydroxybiphenyls. These phenols can be used alone or in combination of two or more.

As the aldehydes, those generally used for producing a novolak resin can be mentioned without particular limitation. Specific examples thereof include lower aliphatic aldehydes such as formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde and glyoxal, and aromatic aldehydes such as furfural and phenylaldehyde. .. These aldehydes can be used alone or in combination of two or more.

To synthesize a novolac resin, the above-mentioned phenols and aldehydes can be synthesized by a conventional method in the presence of an acid catalyst such as paratoluenesulfonic acid, perchloric acid, hydrochloric acid, nitric acid, sulfuric acid, chloroacetic acid, oxalic acid and phosphoric acid. May be reacted at 80 to 130°C. The progress of this reaction can be monitored by gel permeation chromatography (GPC) or the like.

The monohydroxy fatty acid having 2 to 20 carbon atoms may have an unsaturated bond or a branched structure in the molecule. Such monohydroxy fatty acids include glycolic acid, lactic acid, oxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, hydroxycaprylic acid, hydroxycapric acid, hydroxylauric acid, hydroxymyristic acid, hydroxypalmitic acid, ricinoleic acid and castor oil fatty acid. , And hydrogenated products thereof, 12-hydroxystearic acid and the like. These monohydroxy fatty acids have in their molecule a possible carboxyl group capable of reacting with an epoxy group, and react with the epoxy group contained in the molecule of the above-mentioned novolak resin having an epoxy group to form a reactant. ..

Further, the polycondensation product of monohydroxy fatty acid having 2 to 20 carbon atoms is obtained by polycondensing the above monohydroxy fatty acid in the presence of an esterification catalyst or the like. Since the above monohydroxy fatty acid has both a hydroxyl group and a carboxyl group in the molecule, it is possible to produce a polyester compound by dehydration condensation (esterification reaction) between the monohydroxy fatty acids. Such a polyester compound contains a carboxyl group capable of reacting with an epoxy group in its molecule and reacts with the epoxy group contained in the molecule of the above-mentioned novolak resin having an epoxy group to form a reaction product.

Among these monohydroxy fatty acids or polycondensates thereof, polyesters obtained by polycondensing 12-hydroxystearic acid are preferably exemplified in the present invention.

To obtain a modified novolak resin (A) by reacting a novolak resin having an epoxy group with a monohydroxy fatty acid having 2 to 20 carbon atoms or a condensation polymer thereof (hereinafter, also simply referred to as “monohydroxy fatty acid etc.”). For these, these may be mixed and then heated. At that time, if necessary, a suitable solvent such as dimethylformamide (DMF), toluene, xylene, etc. may be added. The reaction temperature during the reaction may be, for example, about 100 to 175°C, but is not particularly limited. As the novolak resin having an epoxy group reacts with monohydroxy fatty acid and the like, the carboxyl group contained in the monohydroxy fatty acid and the like is consumed and the acid value of the reaction mixture decreases, so by monitoring the acid value during the reaction, It is possible to judge the progress and end of the reaction. The acid value at the end of the reaction can be, for example, about 0.1 to 1.0 mgKOH/g, but is not particularly limited.

The mixing ratio of the epoxy group-containing novolak resin and the monohydroxy fatty acid is determined by the number of epoxy groups contained in one molecule of the epoxy group-containing novolac resin and the number of carboxyl groups contained in one molecule of the hydroxy fatty acid. It may be appropriately determined in consideration of the above. The mixing ratio of the epoxy group-containing novolac resin to the monohydroxy fatty acid or the like is such that the carboxyl group contained in the monohydroxy fatty acid or the like is 0.5 to 0. A preferable ratio is 9 mol, and a ratio of 0.6 to 0.85 mol of a carboxyl group contained in monohydroxy fatty acid or the like to 1 mol of an epoxy group contained in a novolac resin having an epoxy group is preferable. Although it can be more preferably exemplified, it is not particularly limited.

The modified novolac resin (A) thus obtained may be used as it is, or if necessary, a compound having two or more carboxyl groups in the molecule is further added and reacted to obtain a modified product. You may use thing as a modified novolak resin (A). In this case, if a novolac resin having two or more epoxy groups in the molecule is used as a raw material of the modified novolac resin (A), the novolac resins modified with monohydroxy fatty acid or the like are mixed with each other by a compound having two or more carboxyl groups. It is possible to obtain a modified novolak resin (A) that is crosslinked and has a higher molecular weight. By using the modified novolak resin (A) having a high molecular weight in this manner, problems such as misting often observed when a low molecular weight resin compound is added to an ink composition can be suppressed, which is preferable.

The compound having two or more carboxyl groups is not particularly limited as long as it is a compound having two or more carboxyl groups in the molecule, and examples of such compounds include isophthalic acid, terephthalic acid, adipic acid, pimelic acid, Examples thereof include suberic acid and sebacic acid.

The reaction temperature at the time of crosslinking with a compound having two or more carboxyl groups can be, for example, about 125 to 175°C, but is not particularly limited. As the unreacted epoxy group reacts with the compound having two or more carboxyl groups, the carboxyl groups contained in the compound having two or more carboxyl groups decrease and the acid value of the reaction mixture decreases. By monitoring the acid value, it is possible to judge the degree of progress and completion of the reaction. For example, if the acid value does not decrease even if the reaction is continued, it means that the epoxy groups are exhausted, and it can be determined that the reaction is completed.

The addition amount of the compound having two or more carboxyl groups may be appropriately determined according to the amounts of the epoxy groups contained in the epoxy group-containing novolac resin used in the reaction and the carboxyl groups contained in the monohydroxy fatty acid and the like. As an example of such an addition amount, the difference between the number of moles of epoxy groups contained in the novolak resin having an epoxy group and the number of moles of carboxyl groups contained in monohydroxy fatty acid etc. is 1 mole, and 2 or more carboxyl groups are included. The number of moles of the carboxyl group contained in the compound having 1 to 0.5 can be preferably exemplified, and the number of moles of the carboxyl group contained in the compound having 2 or more carboxyl groups is 0.6. The ratio of up to 0.85 mol can be more preferably exemplified, but is not particularly limited.

The graft copolymer (B) has an aromatic ring and an epoxy group ring-opening structure with a carboxyl group derived from a hydroxycarboxylic acid, and contains at least 10 mol% of the structural unit represented by the general formula (2) in the molecule, It is a copolymer of ethylenically unsaturated monomers having a mass average molecular weight of 3,000 to 100,000. In addition, containing 10 mol% of the constitutional unit represented by the following general formula (2) in the molecule means that the graft copolymer (B) which is a polymer of an ethylenically unsaturated monomer is an ethylenically unsaturated monomer. This means that the structural unit derived from the monomer is divided and at least 10 mol% of the structural unit represented by the general formula (2) is contained in all structural units.

In the general formula (2), W ² and X ² are each independently a divalent hydrocarbon group having 1 to 19 carbon atoms, p is an integer of 1 to 30, and q is an integer of 0 to 30. R ² is a hydrogen atom or a methyl group, and R ³ is a hydrogen atom or a methyl group.

The graft copolymer (B) is composed of 10 to 90 mol% of glycidyl ester of (meth)acrylic acid represented by the following general formula (3), and other functional groups having high reactivity with an epoxy group. After obtaining a copolymer containing an epoxy group by an ordinary method using 10 to 90 mol% of an ethylenically unsaturated monomer and a radical polymerization initiator such as a peroxide or an azo compound, the copolymer is obtained. The epoxy group may be reacted with the monohydroxy fatty acid described in the modified novolak resin (A). The reaction product thus obtained may be crosslinked by allowing the compound having two or more carboxyl groups described in the modified novolak resin (A) to act. In carrying out these reactions, the reaction conditions and the amounts of the monohydroxy fatty acid and the compound having two or more carboxyl groups may be the same as in the case of the modified novolac resin (A).

（上記一般式（３）において、Ｒ^２及びＲ^３は上記一般式（２）におけるものと同じである。）

(In the general formula (3), R ² and R ³ are the same as those in the general formula (2).)

Other ethylenically unsaturated monomers which do not have a functional group having high reactivity with an epoxy group include vinyltoluene, α-methylstyrene, dimethylstyrene, ethylstyrene, isopropylstyrene, t-butylstyrene and the like. Alkyl-substituted styrene, halogen-substituted styrene such as chlorostyrene, dichlorostyrene, bromostyrene and fluorostyrene, alkoxy-substituted styrene such as methoxystyrene and butoxystyrene, aryloxy-substituted styrene such as phenoxystyrene, methyl (meth)acrylate, ethyl ( (Meth)acrylate, propyl(meth)acrylate, butyl(meth)acrylate, cyclohexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, lauryl(meth)acrylate, dodecyl(meth)acrylate, cetyl( (Meth) acrylate, stearyl (meth) acrylate, behenyl (meth) acrylate, norbornyl (meth) acrylate, etc. alkyl esters of (meth) acrylic acid, tetrahydrofurfuryl (meth) acrylate, etc. having a cyclic ether group (meth) (Meth)acrylates having an aliphatic hydroxyl group such as acrylate and 2-hydroxyethyl (meth)acrylate, and (meth)acrylates having a tertiary amino group such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate. Examples thereof include vinyl ethers such as methyl vinyl ether, dodecyl vinyl ether, propenyl ether propylene carboate, vinyl ethers having an aliphatic hydroxyl group such as hydroxybutyl vinyl ether, and allyl esters of various acids such as allyl acetate. In addition, in this specification, (meth)acryl means acryl or methacryl, and (meth)acrylate means acrylate or methacrylate.

[Other ingredients]
Various components can be added to the ink composition of the present invention, if necessary, in addition to the components described above, from the viewpoint of improving printing performance. Examples of such various components include colorless pigments, salts such as phosphates, waxes such as polyethylene wax/olefin wax/Fischer-Tropsch wax, alcohols, and antioxidants.

The colorless pigment is also called an extender pigment and is preferably used for controlling properties such as viscosity in the ink composition. Examples of colorless pigments include clay, talc, kaolinite (kaolin), barium sulfate, calcium carbonate, silicon oxide, bentonite, and titanium oxide. The addition amount of the colorless pigment is, for example, about 0 to 33% by mass with respect to the entire ink composition, but is not particularly limited.

[Method for preparing ink composition]
In producing the ink composition of the present invention using each of the above components, a conventionally known method can be used. As such a method, after mixing the above components and dispersing the color pigment by kneading with a bead mill or a three-roll mill, mineral oil and additives (antioxidant, alcohol , Waxes, etc.) and well stirred to further adjust the viscosity. The viscosity of the ink composition may be appropriately set in consideration of the configuration of a printing machine to which the ink composition is applied, the paper quality of printing paper, and the like. As an example, the value at 25° C. measured by a Raleigh viscometer is 2.0 to The pressure may be 20 Pa·s, but is not particularly limited.

<Method of suppressing the dry down of the printing paper surface with time when printing is performed by the permeation drying method>
Next, a method of suppressing drydown according to the present invention will be described. The method for suppressing dry down of the present invention is to suppress dry down of a printing paper surface with time when printing is performed by a permeation drying method, and it is possible to perform printing using the ink composition of the present invention. It is a feature.

As described above, the ink composition of the present invention is used because it is excellent in the effect of suppressing the drydown when printing is performed on the printing paper having a high oil absorption property such as a waste paper by the permeation drying method. By performing the printing by the permeation drying method, it is possible to suppress the drydown with time after printing. Examples of such printed matter include those produced by printing by a permeation drying method on printing paper having a high oil absorption property such as newspapers, telephone directories, etc. As a printing method, an offset rotary printing method can be preferably exemplified, but is not particularly limited.

Hereinafter, the printing ink composition of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. In the following description, "%" means "mass%" and "part" means "part by mass" unless otherwise specified.

[Synthesis of modified novolac resin]
A separable flask equipped with a cooling tube, a water separation tube, a thermometer, and a nitrogen introduction tube was charged with a mixture of 300 parts of 12-hydroxystearic acid, 30 parts of xylene, and 0.3 parts of tetra-n-butyl titanate, under a nitrogen stream. The water generated in 1. was heated and stirred at 180 to 200° C. for 3 hours while being separated by a water separation tube. Then, xylene was distilled off under reduced pressure to obtain a polyester A which is a light brown polymer having a weight average molecular weight of 800 and an acid value of 80.

A reaction vessel was charged with a mixed solution of 30 parts of a novolak resin having an epoxy group (Nippon Steel & Sumikin Chemical Co., Ltd., YDPN-638), 64 parts of the polyester A and 50 parts of DMF, and 2 hours at 130 to 150° C. under a nitrogen stream. Heated and stirred. Next, 6 parts of terephthalic acid was added and reacted for 2 hours, 6 parts of succinic anhydride was added, and the mixture was heated and stirred for another 3 hours. Then, DMF was distilled off under reduced pressure to obtain a modified novolak resin having a weight average molecular weight of 9000 and an acid value of 32.

[Preparation of varnish for ink composition]
In a four-necked flask equipped with a cooling tube, a thermometer and a stirrer, 35 parts of a rosin-modified phenolic resin having a mass average molecular weight of 100,000 (manufactured by Arakawa Chemical Industry Co., Ltd.), 20 parts of soybean oil and AF Solvent No. 6 (JX Nippon Mining After charging 44.5 parts of Nisseki Energy Co., Ltd., the temperature was raised to 200° C., and the temperature was maintained for 1 hour to dissolve the resin, and then ethyl acetoacetate aluminum diisopropylate (Kawaken Fine Chemical Co., Ltd.) 0.5 parts of ALCH) manufactured by the company was charged and then heated and maintained at 170° C. for 60 minutes to obtain a varnish.

[Preparation of ink composition]
An ink composition was prepared by mixing various materials according to the formulation shown in Table 2 and kneading with a three-roll mill. The blending amounts shown in Table 2 are parts by mass. In Table 2, "varnish" is the varnish for ink composition prepared by the above procedure, "modified novolac resin" is the modified novolac resin prepared by the above procedure, and "Gilsonite varnish" is Gilsonite (American 20 parts of Gilsonite Company, product name: Gilsonite S325L) was dissolved in 80 parts of AF Solvent No. 6 (manufactured by JX Nippon Oil & Energy Corporation), and alkyd resin was product name SYNOLAC 7412 (soybean oil and flaxseed). Oil-modified alkyd resin, manufactured by Cray Valley), "base oil" is naphthenic base oil (Sankyo Yuka Kogyo Co., Ltd., product name SNH540), and "naphthenic mixture" is naphthenic base oil and naphthenic vacuum distillation. It is a mixture with the residue (manufactured by Sankyo Yuka Co., Ltd., product name A/OMIX).

The physicochemical properties of carbon blacks A to C in Table 2 are as shown in A to C of Table 1 below. Further, in Table 2, the content (unit is mass%) of the Gilsonite resin in each ink composition is shown in the "Gillsonite resin amount" column.

[Drydown evaluation]
The dry-down evaluation of the ink compositions of Examples and Comparative Examples was performed as follows. First, 0.1 cc of the ink composition sample was color-developed on a new paper (SL+ manufactured by Oji Paper Co., Ltd.) using an RI color-developing machine (two-division roll, manufactured by Akira Seisakusho Co., Ltd.). After measuring the concentration with a Spectroeye densitometer (manufactured by Gretagmacbeth), the concentration was measured again after standing for 24 hours in the room. Then, the value obtained by subtracting the density value after 24 hours from the density value immediately after the color development was taken as the dry-down amount, and evaluation was performed according to the following criteria according to the dry-down amount. The results are shown in the "dry down" column of Table 2.
○ Dry down amount is 0.13 or less, which is good. △ Dry down amount is 0.14 to 0.15, which is somewhat defective. × Dry down amount is 0.16 or more, which is defective.

[Liquidity evaluation]
The fluidity, which is one of the physical properties of the ink composition, is an element that affects the piping pumping of the ink composition to the printing machine. Becomes a factor that causes uneven density in the printed matter. Therefore, in order to realize good printing, the ink composition is required to have a certain degree of fluidity. Therefore, the fluidity of each of the ink compositions of Examples and Comparative Examples was evaluated. To evaluate the fluidity of the ink compositions of the respective Examples and Comparative Examples, the distance at which 0.5 cc of the printing ink composition flowed by gravity for 10 minutes was measured at 25° C. using a vertical glass plate rheometer. I went by. The larger this distance is, the better the fluidity is, and each ink composition was evaluated according to the following criteria according to the size of this distance. The results are shown in the "Liquidity" column of Table 2.
○ The flow distance of the ink composition is 40 mm or more, which is good. △ The flow distance of the ink composition is 30 mm or more and less than 40 mm, which is somewhat poor. × The flow distance of the ink composition is less than 30 mm. Is bad

As shown in Table 2, according to the ink composition of the present invention, the dry down after printing is small and the fluidity of the ink composition is sufficiently secured. On the other hand, in Comparative Example 1 in which the amount of Gilsonite resin was 2% by mass, the fluidity of the ink composition was good, but the drydown after printing was extremely poor. Further, Comparative Example 2 using carbon black B which is not the carbon black prescribed by the present invention results in insufficient fluidity of the ink composition, and Comparative Example 3 which uses carbon black C which is not the carbon black prescribed by the present invention is also used. Since the dry-down gives a remarkably poor result, when a carbon black that does not satisfy the requirements of the present invention is used, the result is a lack of balance between fluidity and dry-down suppression. From the above, it can be seen that the present invention provides an ink composition having a small drydown after printing and good fluidity.

Claims (3)

Neutral carbon black having a specific coloring power of 71 to 120%, an average primary particle diameter of 20 to 40 nm, a nitrogen adsorption specific surface area of 41 to 90 m ² /g, and a DBP oil absorption of 70 to 109 cm ³ /100 g, and a rosin-modified phenol resin. , Alkyd resin, and
The content of the Gilsonite resin is less than 2% by mass, the content of the alkyd resin is 2 to 4% by mass, and further, as a pigment dispersant for the carbon black, an aromatic ring and a carboxyl group derived from a hydroxycarboxylic acid. A permeation-drying type black ink composition for offset printing , comprising the following modified novolak resin (A) and/or the following graft copolymer (B) having an epoxy group ring-opening structure according to the above.
(A) A modified novolac resin having at least one group represented by the following general formula (1) in the molecule.

(In the general formula (1), the oxygen atom at the left end is derived from the oxygen atom contained in the aromatic hydroxyl group of the novolak resin, and W ¹ and X ¹ are each independently a divalent group having 1 to 19 carbon atoms. Is a hydrocarbon group, i is an integer of 1 to 30, j is an integer of 0 to 30, and R ¹ is a hydrogen atom or a methyl group.)
(B) A copolymer containing a structural unit represented by the following general formula (2) in the chain of at least 10 mol% and having a mass average molecular weight of 3,000 to 100,000.

(In the general formula (2), W ² and X ² are each independently a divalent hydrocarbon group having 1 to 19 carbon atoms, p is an integer of 1 to 30, and q is an integer of 0 to 30. And R ² is a hydrogen atom or a methyl group, and R ³ is a hydrogen atom or a methyl group.) The ink ink composition for permeation dry type offset printing according to claim 1, wherein the content of the Gilsonite resin is less than 1% by mass. 3. Use of the ink ink composition for permeation drying type offset printing according to claim 1 or 2 to suppress dry down of a printing paper surface with time when printing is carried out by a permeation drying method. Method.