JPH0232995B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved printing surface coating method,
More specifically, by using an aqueous dispersion resin composition that does not form a continuous film when applied to the printed surface as a coating agent, but can form a continuous film by heating after application, the printed surface can be improved. When coated, it can prevent printing ink drying problems such as various roller stains and set-off.
This is an improved product that can be heated to form a continuous film, giving the printed surface various resistances such as gloss, blocking resistance, abrasion resistance, and scratch resistance. The present invention aims to provide a method for coating a printed surface. Currently, large quantities of printed matter are produced using various printing methods such as lithographic printing, letterpress printing, gravure printing, and screen printing, but as work efficiency improves and printing machines become faster, drying of printing ink has become a major problem. I'm getting used to it. On the other hand, there is a strong preference for high-quality printed materials,
Therefore, it is required to apply various coating agents on the printed surface to impart gloss (glossy) and various types of resistance to the printed surface. The present invention aims to provide an improved printing surface coating method that meets these demands. The prior art will be explained below using lithographic printing as an example. The printing ink used in lithographic printing is an oil-based ink that takes an extremely long time to dry, making it impossible to stack or roll up printed materials due to problems such as back-printing. . Therefore, in the sheet-fed format, a fine powder such as starch (spray powder) is sprinkled on the printed surface immediately after printing to prevent back-printing and to remove slats. This is the reality. However, with this method, fine powder is scattered and
They become airborne, causing problems in terms of environmental hygiene, and also cause fine powder to adhere to the printing surface, deteriorating gloss and making the surface rough, thereby degrading printing quality. In addition, the printed matter cannot be stacked in a sufficient manner, resulting in a significant decrease in work efficiency. Additionally, in rotary printing machines, partially dried ink adheres to the mechanical parts of the printing press, such as the paper roll feed roller, tension roller, and folder, and this ink transfers back onto the printed material, causing it to become smeared. High-speed rotary printing is not possible because the printed matter that has been wound up or folded over each other is turned upside down or blocked. To prevent this, we use evaporative drying ink, which mainly evaporates the solvent in the ink, and dry it by heating using a large dryer such as a burner, infrared heater, or hot air, or use active energy such as UV ink. They also use ink that hardens quickly when exposed to light. 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. is exhausted, causing air pollution and odor problems,
Furthermore, there is a problem that it is difficult to obtain printed matter having various properties such as gloss. In addition, in the latter case, special equipment is required due to the use of special reactive ink, special printing plates, blankets, and ink cleaning agents are required, and the ink is not only expensive but also has a long shelf life. It has problems such as lack of stability and workability, and has not become very popular. In contrast, recently, aqueous resin dispersion or UV
Research has been carried out on coating methods for printing surfaces that form a film of a coating agent to improve problems caused by drying of printing ink while also imparting gloss and the like. However, since the aqueous resin dispersions used in these methods have the ability to form a continuous film when applied to the printed surface, the aqueous resin dispersion itself on the printed surface may Not only is the drying speed still insufficient and a powerful dryer is required for drying, but the Tg of the dispersion resin is low,
For example, there have been problems such as secondary blocking occurring during stacking in single wafer format. Furthermore, since these aqueous dispersion resins are coated on undried oil-based ink, sufficient adhesion cannot be obtained, and gloss, durability, etc. required for high-quality printed materials cannot be obtained. In addition, while UV coating agents have the same problems as the UV inks mentioned above, they have poor adhesion with oil-based inks and are particularly prone to film distortion due to differences in drying speed, and are not suitable for printed materials with sufficient durability. is something that cannot be obtained. As described above, there are several methods for improving the problem of ink drying in lithographic printing, but each method has various problems and is not satisfactory. On the other hand, with the trend toward higher quality printed materials, post-processing of printed materials is being carried out, and various coating agents are used on the printed surface after it has been dried or set to provide durability, especially gloss. The coating agents used in these processes are generally vinyl chloride-vinyl acetate copolymer resin, nitrified cotton, and acrylic ester. Synthetic resins such as copolymer resins were dissolved in organic solvents such as aromatic hydrocarbons, esters, and ketones, and additives such as mold release agents were added as necessary. But these are
Since organic solvents are used, there are problems in terms of work hygiene and fire hazards such as ignition, and on the other hand, the process cannot be carried out continuously with the printing process and is performed in a separate process, resulting in poor work efficiency. Although aqueous dispersion resins are sometimes used in this field, their use is quite limited due to their lack of gloss, lack of various resistances, and poor suitability for hot press processing. In view of the above-mentioned drying problem of printing ink and the trend toward higher quality printed materials, the inventors of the present invention have conducted intensive research on coating methods for printing surfaces, and have solved the drying problem of printing ink while using conventional polishing methods. An improved method for coating a printed surface has been discovered which allows processing, particularly imparting resistance comparable to hot pressing, to be carried out continuously with the printing process. That is, the present invention uses an aqueous dispersion resin composition that does not form a continuous film when applied to a printing surface as a coating agent, but can form a continuous film by heating after application. When coated on the printing surface, it can prevent printing ink drying problems, such as various roller stains and set-off, and by heating to form a continuous film, it can add gloss to the printing surface. ), blocking resistance,
It is an object of the present invention to provide an improved coating method for a printed surface that can impart various resistances such as abrasion resistance and scratch resistance. Regarding the terms used in the present invention,
Let me clarify its meaning. "Coating" used in the present invention refers to known coating equipment such as gravure coater, roll coater, spray, air knife coater, and
This includes not only applying the coating agent using printing means, but also applying the coating agent from the dampening water supply equipment that is part of the lithographic printing machine or from the coating agent supply equipment attached to the blanket. . Regarding "coating continuous with the printing process", continuous means coating on the printing machine or directly connected to the printing process (online), and generally applied on wet ink or completely dry. This corresponds to the case of coating on ink that has not been used yet, and the coating is done separately from the printing process, that is, off-line, which is called discontinuous, and corresponds to the case of coating on dry or set ink, and corresponds to post-processing. Furthermore, regarding ``heating continuously or discontinuously with coating'', when heating is performed online after coating to form a continuous film, it is called continuous, and after coating, the coating agent does not form a continuous film. Discontinuous storage refers to the case where a relatively long period of time elapses without storage.
This refers to preservation by winding up a roll, and means that an off-line heating process is performed. Furthermore, the term "printed surface" is not limited to printed matter printed by lithographic printing, but includes printed matter printed by various printing methods such as a letterpress method, a gravure method, and a screen method. However, since an aqueous dispersion resin composition is used as a coating agent, the printing material is limited to those printed on various types of paper due to adhesive problems. In particular, in the method of the present invention, after printing ink on printing paper, a coating agent is applied onto the wet ink without any special drying acceleration means, and then the coating agent is applied. 80-150
The purpose is to form a film by heating to a temperature range of .degree. Therefore, it cannot be applied to inks that require special curing means for drying the ink itself, such as thermosetting inks and ultraviolet curable inks that are printed on non-absorbing surfaces such as metals other than paper. In addition, "continuous film" refers to a state in which a uniform film of a coating agent made of an aqueous dispersion resin is formed and the external epithelial film appears transparent, and the dispersion resin in the coating agent is in solid form. A state in which the film exists non-uniformly and appears opaque or translucent in appearance indicates that a continuous film is not formed. After clearly explaining the terms used in the present invention, the present invention will be described in more detail below. The coating agent used in the present invention does not have the ability to form a continuous film when applied to the printing surface, but when water permeates or evaporates, the coating agent forms a form in which the dispersed resin adheres to the printing surface in the form of fine particles. By taking the particles and subjecting them to heat treatment, these particles fuse together to form a continuous film. Such coating agents are prepared by emulsion polymerization of vinyl monomers and other vinyl monomers, taking into account the glass transition temperature (Tg) of the vinyl monomer homopolymer used to produce aqueous dispersion resin. By setting the polymerization ratio, the minimum film forming temperature (MFT) of the desired aqueous dispersion resin can be adjusted, and an aqueous dispersion resin that forms a continuous film at the desired temperature can be produced. . In setting the Tg, the polymerization ratio is set according to Wood's approximate formula, and an aqueous dispersion resin with the desired Tg can be obtained. In this case, considering the ambient air temperature during application of the coating agent and the heating energy for continuous film formation, the MFT should be in the range of 80 to 150°C, and the Tg of the aqueous dispersion resin should be 50°C or higher. This setting is preferable in terms of obtaining gloss and anti-blocking properties. On the other hand, the desired MFT coating agent can also be prepared by blending an aqueous dispersion resin made of a relatively high Tg polymer and an aqueous dispersion resin made of a relatively low Tg polymer. I can do it. Examples of vinyl monomers that can be used to synthesize the aqueous dispersion resin according to the present invention include the following. First, vinyl monomers from which homopolymers with relatively high Tg can be obtained include methyl methacrylate, ethyl methacrylate, styrene, α-
An example is methylstyrene. Vinyl monomers from which homopolymers with relatively low Tg can be obtained 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, S-butyl, t-butyl, hexyl,
Examples include esters having a linear or side chain alkyl group such as 2-ethylhexyl, decyl, and lauryl. In addition to the monomers mentioned above, it is also possible to copolymerize other vinyl monomers, such as unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and α- and β-unsaturated dicarboxylic acids such as itaconic acid, fumaric acid, and maleic acid. acids, acrylamide derivatives containing at least one N-substituted methylol group, such as N-methylol-acrylamide, N-butoxymethylacrylamide;
Mono- or diacrylic esters or methacrylic esters of glycols such as ethyl glycol, diethylene glycol, propylene glycol, and dipropylene glycol, monomers such as glycidyl ether of acrylic acid and methacrylic acid, acrylonitrile, vinyl chloride, and vinyl acetate. , vinyl propionate, vinylidene chloride, and the like. When using monomers with functional groups among these monomers, it may not be possible to obtain a stable dispersion, and even if a stable dispersion is obtained, it may have an adverse effect on the water resistance and other resistance of the film after film formation. Therefore, it is necessary to adjust the amount used depending on the purpose of use. In order to obtain these aqueous dispersion resins, the monomers described above may be stably dispersed by emulsion polymerization using a hydrophilic catalyst such as ammonium persulfate, potassium persulfate, hydrogen peroxide, or a redox catalyst by a generally known method. An emulsifier can also be added depending on the situation. As an emulsifier, it is sufficient to copolymerize a mixture of vinyl monomers in an emulsified state in the presence of an anionic or nonionic surfactant, but in general, the use of low-molecular surfactants is not recommended due to the water resistance of the resulting film. If water resistance is particularly required, polymeric anionic activators are suitable as emulsifiers because they may have a negative effect. The aqueous dispersion resin according to the present invention also has the best 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 MFT in the emulsion polymerized aqueous dispersion resin itself and use an aqueous dispersion resin made of one copolymer resin, but it is also possible to use a dispersion made of a polymer with a relatively high Tg. This can also be done by preparing a resin dispersion of a polymer with a relatively low Tg and blending it with a dispersion obtained by applying Wood's formula described above. The coating agent according to the present invention can be made using the above-mentioned aqueous dispersion resin, but after coating,
In order to prevent fine particles of dispersed resin adhering to the printing surface from detaching when drying non-continuously, etc.,
If necessary, 0 to 30% water-soluble varnish may be added to the coating agent. In this case, the water-soluble varnish used can be an aqueous solution of alkali-soluble resin, which has been conventionally used as a varnish for water-based printing inks. , casein, etc. can be used. As the alkali used for water solubilization, any known alkali can be used, including ammonia, organic amines such as triethylamine, monoethylamine, etc., but highly volatile alkalis are preferred from the viewpoint of drying the water-soluble resin. Adding a large amount of this water-soluble varnish will reduce the drying properties of the coating agent and will greatly affect the film-forming performance, so sufficient caution is required. Note that when a polymer emulsifier is used as the emulsifier, the addition of a water-soluble varnish can be omitted. Other optional ingredients may be included in the coating agent as necessary, and various additives such as alcohols, waxes, Various mold release agents can be added. When using an aqueous dispersion resin containing a high proportion of styrene-based vinylmonomer in the coating agent of the present invention and applying it to hot press processing, the peelability from the press plate may not be sufficient. , it is desirable to add a conventional mold release agent. 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 Using the vinyl monomers shown in Table 1 in the respective proportions, Dispersion 1 was prepared according to the usual emulsion polymerization method.
An aqueous resin dispersion designated as ~10 was obtained. As an emulsifier, an ammonia aqueous solution of an acrylic copolymer (Joncryl 67, manufactured by Jonson & Son) was used. Further, the nonvolatile content in the aqueous resin dispersion was adjusted to about 40%, and the nonvolatile content of the acrylic copolymer as a dispersant was adjusted to about 4% in the aqueous resin dispersion. Table 1 also lists the glass transition temperature (Tg) of the aqueous dispersion resin, and for Dispersions 2 to 5 and Dispersions 7 to 10, those calculated by the approximate formula are added.

[Table] Synthesis Example 2 Using Dispersion 1 and Dispersion 6 obtained in Synthesis Example 1, polymer blend each dispersion at a ratio of 80:20 and 60:40, and make each dispersion into a dispersion.
11 and 12. Example 1 Each of the dispersions obtained in Synthesis Examples 1 and 2 was used and coated on a lithographic print (art paper) using a bar coater at an ambient temperature of 25°C, and the drying properties of the dispersion were evaluated. The state of the film, the continuous film formation temperature, and the gloss after continuous film formation were investigated. The results are shown in Table-2.

【table】

[Table] Example 2 As a case of coating continuously with the printing process,
Carton printing was performed using a four-color lithographic sheet-fed press using ordinary lithographic printing ink, and the suitability for bar stacking was examined.
The results are shown in Table-3. The coating agent is the last printing unit (4th color).
A method was adopted in which the dampening water was supplied from a dampening water device and applied onto the printed surface that had been printed in three colors. The printing conditions are 25℃, printing speed 6000 sheets/hour, and maximum number of sheets stacked in a bar of 2000 sheets. In addition, as coating agents, use dispersion 3, dispersion 5, dispersion 9, and dispersion 10 obtained in Synthesis Example 1. If no coating agent is applied, use an ordinary anti-set-off agent (spray powder). ) was used in standard amounts.

[Table]
(Note 2)... Ink offset occurred. As is clear from the above results, the coatings using the coating agents (dispersions 3 and 9) according to the present invention have sufficient stick stacking suitability and offset. No blocking occurs, and there is no need to use conventional spray powder, which causes environmental pollution and reduction in gloss. Furthermore, when the coated product according to the present invention was piled up in a bar and then heated to form a continuous film, printed matter with excellent gloss was obtained. The gloss was evaluated in the same manner as in Example 1, and Table Shown in 3. Example 3 In 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 lithographic rotary printing machine, a gravure coater is installed between the printing machine and the dryer, and printing Example 2 on the surface
Coating was carried out using the same coating agent. 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. Note that the gloss was measured in the same manner as in Example 1. The results are shown in Table-4.

[Table] From the above results, by using the coating agent of the present invention, it is possible to significantly lower the dryer temperature of a rotary lithographic printing press, and it is also possible to obtain printed matter with excellent gloss. I understood. Example 4 The following experiment was conducted in order to compare with the vinyl processing method. In Experimental Example 2, Dispersion 3 was used as a coating agent.
and a printed matter coated with Dispersion 5 is used. On the other hand, as a coating agent for vinyl coating, the solvent-based coating agent used for conventional vinyl coating is based on salt/vinyl acetate copolymer resin (solid content).
40%) was used for polishing. A general vinyl processing machine is used as the equipment, and it is used as a dryer.
A 25Kw/hr infrared heater and hot air type were used. The results are shown in Table 5.

[Table] From the above results, the coating agent according to the present invention has sufficient suitability for vinyl processing and is capable of polishing with superior gloss compared to conventional solvent-based coating agents for vinyl finishing. . Furthermore, unlike conventional coating agents, there were no hygienic or fire hazards due to the generation of solvent vapor. Example 5 In the same manner as in Example 2, a coated material obtained by applying a coating agent to a printed matter was used and hot-pressed. Dispersion 2 and Dispersion 5 were used as coating agents, and as coating agents for conventional press processing,
Using a commercially available solvent-based mixture of salt/vinyl acetate copolymer resin and acrylic copolymer resin (solids content approximately 40%), coat the printed surface with a solids content of 10g/ ^m2 . After drying with a hot air dryer, use an endless press at a temperature of 130°C and a press pressure of 250 kg/cm ² at a press speed.
Pressing was performed at a speed of 20 m/min. The peelability and gloss were compared with that of a press plate, and the results are shown in Table 6.

[Table] From the above results, Dispersion 2 used as a coating agent according to the present invention can obtain a gloss comparable to that of a conventional coating agent for solvent-based press processing, and has less peeling from the press plate. There were no problems, sanitary or fire hazards due to solvent evaporation. Example 6 The following durability comparisons were made between the vinyl-processed and press-processed printed matter obtained in Example 4 and Example 5. The results are shown in Table-7.

[Table] As is clear from the above results, coatings using the coating agent of the present invention have excellent resistance. In addition, each test and evaluation was performed as follows. Anti-blocking property: The coated surfaces of the printed materials that have been processed are brought into close contact with each other using a pressure of 0.5 kg/ ^cm2.
After leaving it at an ambient temperature of 50°C for 24 hours, it was peeled off and the state of blocking was examined. Items that can be peeled off without any resistance are ○, items that do not reach blocking but have considerable resistance to peeling are △, and items that cause blocking are ×.
And so. Adhesion: The condition of the coating agent was examined by quickly peeling off cellophane tape after adhesion. Those that do not peel off at all are marked as 0. Bending resistance: Printed matter subjected to each process was folded and changes in the coating agent surface were observed. Those with no change at all were rated as 0, those that remained after being bent were rated as △, and those with cracks at the bent portion were rated as ×. Heat resistance...Using a heat-sealing machine, prints that have undergone each processing are overlapped and subjected to pressure 6.
Kg/cm ² and heated at 140°C for 10 seconds to observe changes in the coating agent. Those that do not change at all are marked as ○, those that change mutually and have resistance to peeling are marked as △, and those that cannot be peeled off are marked as ×. Friction resistance…Using a Gakushin type friction resistance tester,
The printed surface was rubbed 50 times under a load of 500 g/cm ² to check for stains. Something that doesn't get dirty at all 〇
Those with slight stains were rated △, and those with ink stains were rated ×. Light resistance: The coating agent was exposed for 40 hours using a fedometer, and changes in the coating agent were examined. Those that did not change at all were rated ○, and those that changed were rated ×.

Claims (1)

[Scope of Claims] 1. A method of applying a coating agent to the printed surface immediately after printing in a state continuous with the printing process, wherein the coating agent is mainly made of an aqueous dispersion resin having a glass transition temperature of 50°C or higher. A water-based coating that does not form a continuous film when applied to the printed surface, but can form a continuous film by heating the coating agent to a temperature range of 80 to 150°C. Using the dispersion resin composition, the coating agent is applied onto the wet ink of the printed matter immediately after printing the printing ink on the printing paper, and the coating agent is applied continuously or continuously with the above coating process of the coating agent. 1. A method for coating a printed surface, comprising heating the coating agent after coating to a temperature in the range of 80 to 150° C. in a discontinuous state to form a continuous film of the coating agent. 2. The method for coating a printed surface according to claim 1, wherein the coating agent after coating is heated using a heating means selected from infrared rays, a burner, and hot air. 3. The method for coating a printed surface according to claim 1, wherein the coating agent after coating is heated using a hot press machine.