JPS6410197B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an aqueous overcoating composition and a printing method using the same, and more specifically to overcoating a wet oil-based ink printing surface with the composition in the form of a thin film. Therefore, the present invention provides an aqueous overcoating composition and a printing method using the same, which prevents set-off, blocking, etc., while promoting the setting of oil-based ink and improving the workability of printing and post-processing of printed matter. This is what I am trying to do. Prior Art Currently, oil-based inks used in planographic printing, letterpress printing, etc. mainly contain resins, drying oils, and mineral oils as binders, and are mainly dried by oxidative polymerization drying. Looking at the drying process of oil-based ink in more detail, when oil-based ink is printed on paper, some of the mineral oil and drying oil in the ink penetrate into the paper and form a semi-dry film on the paper. is formed (this state is generally called set), and then the drying oil reacts with oxygen to undergo oxidative polymerization and harden, resulting in complete drying. It usually takes 15 to 30 minutes for setting and 3 to 10 hours for complete drying. In the set state, if a small amount of printed matter is piled up in a bar, no set-off or blocking will occur, but under more extreme conditions, such as stacking a large quantity of printed matter or post-processing such as cutting or folding. They do not have sufficient resistance, and their suitability cannot be achieved unless they are almost completely dry. As mentioned above, it takes an extremely long time to set and dry these oil-based inks, and the drying of the printing ink becomes a major problem as it impedes the printing speed and the required work efficiency. Ta. Therefore, in sheet-fed planographic printing, for example, fine powder such as starch (spray powder) is sprinkled on the printed surface immediately after printing to prevent set-off and also to remove slats. The reality is that it is happening. However, with this method, fine powder scatters and floats, which poses environmental hygiene problems.Fine powder also adheres to the printing surface, which deteriorates gloss and makes the surface rough, reducing print quality. It is the cause. Further, even if such spray powder is applied, it is not possible to stack the desired amount of printed matter sufficiently, resulting in a significant decrease in work efficiency.
Furthermore, it is not suitable for post-processing such as cutting or bending, and it is necessary to leave it for several hours to wait for the ink to dry. In addition, in rotary printing, undried ink adheres to mechanical parts such as the paper roll feed roller, tension roller, folding machine, etc. built into the printing press, and this ink transfers back onto the printed material, staining the printed material. When folded, rolled, or folded printed materials are bundled, they tend to set off or block each other, making high-speed rotary printing impossible. To prevent this, we use evaporative drying ink, which mainly evaporates the solvent in the ink, and use a large dryer such as a burner, infrared heater, or hot air to heat the paper surface to around 130℃ and dry it. Inks such as UV inks that harden quickly with active energy rays are used. However, in the case of the former type of ink (generally called heat-set ink), the solvent in the ink is rapidly evaporated, so energy consumption such as gas and electricity is large, and the steam containing the solvent is large. There are problems such as air pollution and odor due to the exhaust, and furthermore, it is difficult to obtain printed matter with various aptitudes such as gloss. In addition, in the latter case, special equipment is required due to the use of special reactive ink, and special printing plates, blankets, and ink cleaning agents are required, and the ink is not only expensive but also has a long shelf life. , have problems such as lack of stability and workability,
It has not become very popular. In contrast, recently, a film of water-based coating agent is formed on the wet printing surface immediately after lithographic printing, which improves the above-mentioned problems caused by the drying of printing ink, and at the same time gives the printed surface various resistances such as gloss. Coating methods have been developed. Purpose of the Invention However, by applying the water-based coating agent used in this method onto the oil-based ink in a wet state, the surface of the oil-based ink is covered.
Although it can prevent phenomena such as set-off or blocking caused by stacking printed matter to some extent, it only has the ability to cover the oil-based ink and may accelerate the setting or drying of the oil-based ink. There was no significant effect at all, and post-printing work could only be done several hours after printing, as in the past. In addition, when a water-based coating agent is applied on wet oil-based ink, sufficient adhesion may not be obtained.
They had problems such as not being able to achieve the level of gloss or abrasion resistance required for high-grade printed matter. In order to solve the above-mentioned drying problems of oil-based inks, the present inventors have conducted extensive research on water-based overcoating compositions to be applied over wet oil-based inks. It has adhesive properties and not only improves the coating performance of oil-based inks, such as gloss and abrasion resistance, but also prevents set-off and blocking phenomena on the stacking side after printing, while also improving the setting of oil-based inks. Alternatively, they have discovered an aqueous overcoating composition that has the effect of significantly improving drying properties, and have completed the present invention. Structure of the Invention The present invention provides an aqueous overcoating composition for coating onto oil-based ink in a wet state after printing, the composition comprising an aqueous resin dispersion mainly composed of an acrylic copolymer;
For aqueous overcoating, which contains 1% by weight or more of ethylene glycol dialkyl ether represented by the following general formula based on the total amount of the composition, and has the ability to form a film at ambient temperature during printing or heating operations. It is intended to provide a composition. General formula R ₁ -O-C ₂ H ₂ -O-R ₂ (wherein R ₁ ,
( _R2 represents an alkyl group having 1 to 4 carbon atoms) Furthermore, the present invention provides a printing method using the above aqueous overcoating composition. Hereinafter, the aqueous overcoating composition according to the present invention will be explained in more detail. The aqueous overcoating composition according to the present invention is mainly composed of an aqueous resin dispersion obtained by emulsion polymerization of a polymerizable acrylic monomer, and the atmospheric temperature during printing or heating drying operation is preferably 80°C. More preferably, it is necessary to have the ability to form a film at room temperature. 80℃
If this is the case, a large amount of energy is required for film formation, and a device similar to a conventional drying device is required. If the temperature is 80° C. or lower, relatively little energy is required for film formation, and therefore a simple drying device can be used, which is preferable from the viewpoint of the purpose of the present invention. For those that form a film at room temperature,
This is more preferable because it does not particularly require energy for film formation. Such aqueous resin dispersions are produced by emulsion polymerization of acrylic monomers, taking into account the glass transition temperature Tg of the polymer of the acrylic monomers used, By setting the polymerization ratio, etc.
The desired film-forming temperature of the dispersion can be adjusted, and a dispersion that forms a continuous film at a desired temperature can be produced. In setting Tg,
By setting the polymerization ratio according to Wood's approximate formula, the desired Tg dispersion can be obtained. In this case, the film forming temperature should be 80°C, taking into consideration the atmospheric temperature during application of the dispersion and the heating energy given for continuous film formation as necessary.
Hereinafter, it is more preferable to use the film forming method at room temperature. Examples of acrylic monomers that can be used to synthesize the above dispersion include the following. First, examples of acrylic monomers capable of obtaining polymers with relatively high Tg include methyl methacrylate and ethyl methacrylate, and further examples of other monomers include styrene and α-methylstyrene. Acrylic monomers that can obtain polymers with relatively low Tg include alkyl esters of acrylic acid or methacrylic acid other than the above-mentioned methyl methacrylate and ethyl methacrylate, such as methyl,
ethyl, propyl, isopropyl, n-butyl,
Examples include esters having a linear or side chain alkyl group such as s-butyl, t-butyl, hexyl, and lauryl. In addition, it is also possible to copolymerize other acrylic monomers in addition to the above-mentioned monomers, such as acrylic monomers having functional groups such as unsaturated carboxylic acids such as acrylic acid and methacrylic acid. However, when using a monomer having a functional group among the above-mentioned monomers, a stable dispersion may not be obtained.
In addition, even if obtained, it may have a negative effect on the water resistance, chemical resistance, etc. of the film after film formation, so it is important that the acid value is 50 or less. , there is an adverse effect on film-forming properties,
It is necessary to adjust the amount used depending on the purpose of use. To obtain these dispersions, the monomers mentioned above may be stably dispersed by emulsion polymerization using a hydrophilic catalyst such as ammonium persulfate, potassium persulfate, or hydrogen peroxide or a redox catalyst by a generally known method. Emulsifiers can also be added if desired. It is sufficient to copolymerize a mixture of acrylic monomers in an emulsified state in the presence of an anionic or nonionic surfactant as an emulsifier, but in general, the use of a low-molecular surfactant will improve the water resistance of the resulting film.
This may have a negative effect on chemical resistance, etc.
When water resistance is particularly required, polymeric anionic activators are suitable as emulsifiers. The aqueous dispersion resin according to the present invention also has excellent performance by using such an emulsifier. Examples of such polymeric emulsifiers include silica, acrylic acid copolymers having carboxyl groups, or maleic acid copolymers, and aqueous alkaline solutions thereof can be used. As mentioned above, it is also possible to set the desired film-forming temperature for the emulsion polymerized dispersion itself and use a dispersion made of a single copolymer resin, but it is also possible to use a dispersion made of a polymer with a relatively high Tg. It is also possible to obtain the desired dispersion by preparing a dispersion of a polymer with a relatively low Tg and applying it to Wood's equation described above to blend these dispersions (polymer blend). I can do it. The solvent added to the aqueous resin dispersion is one represented by the following general formula, and is 1% by weight based on the total amount of the aqueous overcoating composition.
As mentioned above, it is necessary to contain preferably 1 to 8% by weight, more preferably 3 to 5% by weight. If the amount added is less than 1% by weight, the desired effect of the present invention cannot be obtained, and if it is more than 8% by weight, it may have an adverse effect on the storage stability of the dispersion, which is not preferable. The solvent to be added has the general formula R ₁ -O-C ₂ H ₂
-O-R ₂ (wherein R ₁ and R ₂ represent an alkyl group having 1 to 4 carbon atoms), specifically, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene Examples include glycol methyl ethyl ether, ethylene glycol methyl butyl ether, and ethylene glycol ethyl butyl ether. Conventional aqueous coating agents include alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, and glycerin, and ethylene glycol monomethyl ether and ethylene glycol monoethyl ether. Water-miscible solvents such as cellosolves were added as appropriate to control the drying properties of the coating agent.
These solvents were only effective in controlling the drying properties of the coating agent, and did not contribute in any way to improving the setting properties and drying properties of the underlying oil-based ink. However, the aqueous overcoating composition comprising the aqueous resin dispersion and the above-mentioned specific solvent according to the present invention exhibits a remarkable effect on improving the setting or drying properties of the oil-based ink in the lower layer, and the oil-based ink can be used immediately after printing. When applied in layers, it is possible to perform processing such as cutting or bending immediately after application, and it has extremely excellent performance, allowing post-processing to be performed immediately, which previously could only be done several hours after printing. It is something. The composition for aqueous overcoating according to the present invention is mainly composed of the above-mentioned aqueous resin dispersion and the above-mentioned solvent. From the viewpoint of improving coating film performance such as abrasion resistance after drying, 0 to 15% by weight of a water-soluble varnish can be added to the aqueous overcoating composition as necessary. In this case, the water-soluble varnish used can be an aqueous solution of an alkali-soluble resin that has been conventionally used as a varnish for water-based printing inks. Alkaline aqueous solutions of various resins such as casein and casein can be used. Adding a large amount of this water-soluble varnish will reduce drying performance, but will also greatly affect film-forming performance, which may impede the improvement of setting performance, which is the objective of the present invention. Requires attention. Other optional components may be included in the aqueous overcoating composition as needed, and various additives, such as alcohol, may be added in consideration of various coating properties such as viscosity adjustment, dryness adjustment, gloss, and abrasion resistance, or leveling. It is also possible to add antifoaming agents, waxes, and various mold release agents. The following methods can be used to coat the oil-based ink in a wet state immediately after printing using the aqueous overcoating composition as described above. One method is
A coating device can be installed after the final printing unit of the printing press to coat the printed products immediately after printing. FIG. 1 shows a case where a coating device is installed after the final printing unit, where 1 is the final printing unit, 2 is the coating device, and 3 is a drying device provided as necessary. Although FIG. 1 illustrates a typical roller coating unit, it goes without saying that other coating methods such as spray coating, air knife coating, engraved roll coating, etc. can be applied. As another coating method, for example, in the case of lithographic printing, a surplus printing unit of a lithographic printing machine can be used to coat the printed matter immediately after printing using a conventional dampening water supply device. FIG. 2 shows a specific example of coating with an aqueous overcoating composition using a conventional general final printing unit. Using the aqueous overcoating composition according to the present invention instead of dampening water, the dampening water supply device 5
From there, coating is applied via a blanket 7 through a printing plate 6 (after performing operations such as converting the printing plate into a coating pattern as necessary). Alternatively, as shown in FIG. 3, in the final printing unit, the plate cylinder 6 and the blanket 7 are separated and a device 11 is provided for supplying the aqueous overcoating composition directly to the blanket. can be coated. By using the various coating methods explained above, it is possible to apply a desired coating on the oil-based ink in a wet state immediately after printing on the printing machine (online or inline), which is different from conventional methods. The object of the present invention can be achieved without any special modifications to the existing printing press or by incorporating a simple coating device. In this way, by coating the aqueous overcoating composition on the wet oil-based ink immediately after printing, and heating the composition to form a film as necessary, it not only improves suitability for high-speed printing, but also improves suitability for high-speed printing.
It also has immediate suitability for post-processing, making it extremely advantageous for increasing the efficiency of printing and post-processing operations. The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples. Synthesis Example 1 Aqueous resin dispersions shown as Dispersions 1 to 10 were obtained using the acrylic monomers shown in Table 1 in the respective proportions and according to a conventional emulsion polymerization method. As an emulsifier, an ammonia aqueous solution of an acrylic copolymer (johncryl67, manufactured by Johnson & Son) was used. Further, the nonvolatile content in the aqueous resin dispersion was adjusted to about 45%, and the nonvolatile content of the acrylic copolymer as a dispersant was adjusted to about 3% in the aqueous resin dispersion.

[Table] Synthesis Example 2 Using Dispersion 3 and Dispersion 5 obtained in Synthesis Example 1, polymer blend each dispersion at a ratio of 20:80 and 40:60, and make each dispersion into a dispersion.
11 and 12. Examples 1 to 12 and Comparative Examples 1 to 8 Using the dispersions 1 to 12 obtained in Synthesis Examples 1 and 2, according to Table 2, for 95% by weight of each dispersion, the solvent specified in the present invention and the conventional aqueous Aqueous overcoating compositions were prepared by adding and mixing 5% by weight of each of the solvents commonly added to dispersions and the like. Note that Comparative Example 1 shows the case where the dispersant was 100%.

[Table] Printing test 1 In order to evaluate the drying properties of the aqueous overcoating composition according to the present invention and the effect of promoting the setting of oil-based inks, paper laminated with aluminum foil was used instead of ordinary paper, and oil-based ink was The following tests were conducted with the penetration of mineral oil, etc., into the paper being inhibited. Using an R1 tester, print a regular offset ink as an oil-based ink on the aluminum surface of paper laminated with aluminum foil. Each aqueous overcoating composition obtained in Examples 1 to 2, 4 to 12 and Comparative Examples 1 to 8 was used on the ink in a wet state immediately after printing, and coated with a bar coater at an ambient temperature of 25°C. The drying properties of the overcoating composition and the setting state of the offset ink were examined. The results are shown in Table-3.

[Table] Evaluation method 1 Drying property: After applying the water-based coating agent, rub the surface with a rubber spatula and check the drying time of the coating agent. Those that took more than 1 minute were evaluated as △, and those that took more than 1 minute as ×. 2 Setting state of offset ink After applying the aqueous coating agent, it was left to stand for 90 seconds, cellophane tape was pasted on the coating agent, and the difference in the peeling state of the cellophane tape was evaluated as follows. In other words, when the offset ink is set, a type of cohesive rupture does not occur in the ink layer, so in the situation of peeling off the cellophane tape, the tape/overlay can be removed while maintaining sufficient peeling strength. coating agent interface,
Alternatively, those that break off at the offset ink/aluminum foil interface are marked with an ○, those that complete setting after 5 minutes even if cohesive cracking occurs between the offset ink layers are marked with a △, and those that are set even after 5 minutes are marked with a △. Those that were not completed were evaluated as ×. As is clear from the above results, it can be seen that the aqueous overcoating composition containing the solvent specified in the present invention has excellent drying properties of the coating agent itself, and has a large effect on improving the setting of oil-based ink. . However, although the water-miscible solvents commonly used in the past can dry the coating agent itself to some extent due to the evaporation properties of the solvent, it has been found that they have no effect on setting. Examples 13 to 18 and Comparative Example 9 In order to investigate the difference in effects depending on the amount of the solvent specified in the present invention, 8% by weight of the mixed solvent shown in Table 4 was added to 92% by weight of Dispersion 1 at different ratios. % added,
An aqueous overcoating composition is prepared.
Furthermore, each of the prepared coating compositions was evaluated in the same manner as in Printing Test 1, and the results are listed in Table 4.

[Table] From the above results, it can be seen that the aqueous coating agent containing 1% by weight or more of the solvent specified in the present invention can significantly improve the setting of offset ink. It should be noted that if it is added in an amount of 8% by weight or more, a sufficient effect can be obtained in terms of improving set, etc., but it is not sufficient in terms of storage stability. Examples 19 to 21 Comparative Example 10 An aqueous solution type varnish (acrylic copolymer, A similar aqueous overcoating composition was prepared as shown in Table 5 by mixing an aqueous ammonia solution of Johncryl 67 (resin content: 30%), and the difference in effect due to the addition of an aqueous varnish was evaluated. The same evaluation as in Printing Test-1 was performed, and the results are listed in Table-5.

[Table] From the above results, the addition of aqueous varnish by weight tends to impede the drying properties and setting properties of offset ink, and the amount of varnish needs to be 15% or less. Printing test-2 As a case of coating continuously with the printing process,
Carton printing was carried out using ordinary lithographic printing ink on a 4-color lithography machine, and 20 sheets of printed matter were coated with an aqueous overcoating composition, piled up with a load of 5 kg/cm ² , and 1 After a period of time, the presence or absence of set-off and blocking was evaluated. Immediately after coating, the printed matter was cut out using a slicing machine, and the presence or absence of wrinkles was evaluated. The results are shown in Table-6. The aqueous overcoating composition was supplied from the dampening water device of the last printing unit (fourth color) and applied onto the three-color printed surface. Printing conditions: 25℃, printing speed 6000
It is set as 1 sheet per hour. In addition, as the aqueous overcoating composition, examples 1, 2, 8, 11
and Comparative Examples 1, 2, 4, and 7, and if not applied, use a normal anti-set-off agent (spray powder)
A standard amount of was used.

[Table] As is clear from the above results, those using the aqueous coating composition according to the present invention had excellent drying properties and setting properties, and did not cause set-off or blocking. In addition, even if the product coated with the aqueous overcoating composition of the present invention is cut immediately after coating, there is no fading phenomenon due to insufficient drying of the oil-based ink, which not only improves printing workability but also improves post-processing. This significantly improved workability. On the other hand, in the case of the comparative example, the fading phenomenon was not improved until several hours had passed after application. Printing test-3 As a case where the printing process, coating process, and heating process are performed continuously, a low-temperature drying type heat set ink is used in a planographic rotary printing machine, a gravure heater is installed between the printing machine and the dryer, and printing is performed. Examples 1, 2, 3, 8, 11, 14, 19 and Comparative Examples 1, 2,
Aqueous overcoating compositions Nos. 4 and 7 were applied. The printing conditions are 25℃ and printing speed.
Using a dryer consisting of a burner and hot air at a speed of 300 m/min, the heating conditions of the dryer were measured to prevent staining of various guide rollers during the printing paper ejection process. Furthermore, we investigated the occurrence of stains on the folding machine that folds the printed matter, and the occurrence of blocking after cutting and bundling. The results are shown in Table-7.

[Table] From the above results, by using the aqueous overcoating composition of the present invention, it is possible to significantly lower the dryer temperature of a rotary lithographic printing press.
Furthermore, heating can be eliminated. Further, there was no staining caused by belts or the like in the folding machine, nor did set-off or blocking occur after bundling. (Note 1) and (Note 2) in Table 7 have the same meanings as in Table 6 above.

[Brief explanation of drawings]

FIG. 1 shows an embodiment in which a coating device is installed after the final printing unit. FIG. 2 shows an embodiment in which a conventional final printing unit is used to coat the printing plate with the aqueous overcoating composition of the present invention in place of the conventional fountain solution, with the oil-based ink supply means separated from the printing plate. FIG. 3 shows an embodiment in which the aqueous overcoating composition is applied directly to the blanket while the plate and blanket are separated in the final printing unit. 1: Final printing unit, 2: Coating device, 3: Drying device, 4: Oil-based ink supply means,
5: dampening water supply device, 6: printing plate, 7: blanket, 8: printing paper.

Claims (1)

[Scope of Claims] 1. An aqueous overcoating composition for coating onto a wet oil-based ink printed surface immediately after printing, wherein the composition is an aqueous resin dispersion mainly composed of an acrylic copolymer. and,
General formula R ₁ -O-C ₂ H ₂ -O-R ₂ (However, R ₁ , R ₂
represents an alkyl group having 1 to 4 carbon atoms) at least 1% by weight based on the total amount of the composition, and has the ability to form a film at ambient temperature during printing or heating drying operations. An aqueous overcoating composition comprising: 2 The aqueous overcoating composition is heated to 80°C.
Claim 1: The film is formed at the following atmospheric temperature:
The aqueous overcoating composition described in 1. 3. The aqueous overcoating composition according to claim 1, which forms a film at room temperature. 4. The aqueous overcoating composition according to any one of claims 1 to 4, wherein the aqueous resin dispersion has an acid value of 50 or less. 5 1 ethylene glycol dialkyl ether
The aqueous overcoating composition according to any one of claims 1 to 5, characterized in that it contains 8% by weight. 6 An aqueous resin dispersion mainly composed of an acrylic copolymer and a general formula R ₁ -O-C ₂ H ₂ -O
- Contains 1% by weight or more of ethylene glycol dialkyl ether represented by R ₂ (R ₁ and R ₂ represent an alkyl group having 1 to 4 carbon atoms), and forms a film at ambient temperature during printing or heating drying operation. Printing characterized by applying a thin film of an aqueous overcoating composition having the property of Method. 7. A printing method according to claim 6, characterized in that a coating device is installed after the final printing unit of the printing press, and the aqueous overcoating composition is applied by the coating device. 8. Claim 6, characterized in that the aqueous overcoating composition is applied using a dampening water supply device of the final printing unit of a lithographic printing press.
Printing method described in section. 9. A printing method according to claim 6, characterized in that a device is provided for supplying the aqueous overcoating composition to the blanket of the final printing unit of the lithographic printing press.