JP7815965B2 - Hydrophilizing agents for printing plates - Google Patents

Description

The present invention relates to a hydrophilizing agent for printing plates.

Gravure printing, offset printing, letterpress printing, and other printing methods that use printing plates such as intaglio, lithographic, and relief printing are widely used because they allow the quality of the print to be controlled by changing the shape of the plate and enable high-resolution printing.

Lithographic printing is a printing method that essentially takes advantage of the property that water and oil do not mix, with one side of the printing surface consisting of a non-image area, which is an area that accepts water and repels oil-based ink, and an image area, which is an area that repels water and accepts oil-based ink. Dampening water is used to moisten the non-image area, increasing the interfacial chemical differences between the image and non-image areas, thereby increasing the ink repellency of the non-image area and the ink receptivity of the image area. To achieve this, various chemical substances have been added to dampening water, and extensive research has been conducted to maximize its performance.

In addition, oil-based inks are often used in gravure printing and other intaglio printing processes, but this poses problems in terms of working conditions, the global environment, disaster prevention, and even residual solvents when used on food-related products. Therefore, plate printing using water-based inks has attracted attention. However, with water-based inks, surface tension causes poor ink wetting of the plate surface, which can lead to problems with ink transfer and other issues, making it difficult to obtain high-quality printed materials. Therefore, various proposals have been made to address this issue.

Patent Document 1 discloses a dampening water composition containing a glycerin triester represented by a specific formula. This dampening water composition is said to suppress blanket piling, thereby enabling long periods of continuous printing (long-run printing), to have good cleanability for the resulting deposits, to suppress water supply roller staining (excellent stain resistance), to be emulsification-resistant, and to have resistance to the printing plate surface, resulting in good printability. Meanwhile, because dampening water is generally diluted with water before use, it is required to have low foaming properties so as not to foam when diluted. However, the low foaming properties of the dampening water composition described in Patent Document 1 were insufficient.

Patent Document 2 describes a dampening water composition for lithographic printing plates that contains a propylene glycol monoalkyl ether represented by a specific formula, propylene glycol represented by a specific formula, and 2-ethyl-1,3-hexanediol. This dampening water composition is said to offer a comfortable and safe working environment and can replace the isopropyl alcohol-based agents that have traditionally been used as wettability enhancers, and to exhibit good and stable printing suitability even under conditions involving components rotating at high speeds. However, the dampening water composition described in Patent Document 2 had insufficient rust prevention properties for printing plates and equipment.

Patent Document 3 discloses a dampening water for a lithographic printing plate having at least a hydrophilic swelling layer on a substrate, containing an anionic surfactant whose hydrophilic group is a sulfate ester salt and/or a phosphate ester salt, and having a pH of 6 to 11. This dampening water is said to improve the storage stability and printing characteristics of dampening water for lithographic printing plates, particularly its excellent ink drying properties, and to be less susceptible to rust by avoiding the acidic conditions that make printing presses prone to rust. However, the dampening water described in Patent Document 3 requires a pH of 6 to 11 to ensure storage stability and print smear prevention, especially when using an anionic surfactant of the sulfate ester salt type. Furthermore, the dampening water may foam when diluted or when used with a surfactant at a high concentration of 1.0% by weight or more, depending on the printing plate material and the composition of the water-soluble ink.

Japanese Patent Application Laid-Open No. 2017-205873 Japanese Patent Application Laid-Open No. 2001-138655 Japanese Patent Application Publication No. 11-48633

In light of the problems with the prior art discussed above, the present invention aims to provide a hydrophilizing agent for printing plates that has good wettability to printing plates, does not foam even at high concentrations of active ingredients such as 1.0% by weight or higher, and does not corrode metal plates or equipment regardless of pH.

The inventors conducted extensive research to solve the above problems. As a result, they discovered that the above problems can be solved by using the specific compounds shown below.

That is, the present invention relates to a hydrophilizing agent for printing plates that contains, as an active ingredient, a compound represented by the following formula (1):

(EO is an oxyethylene group, and a is the average number of moles of oxyethylene groups added represented by EO. AO is an oxyalkylene group having 3 to 4 carbon atoms, and b is the average number of moles of oxyalkylene groups added represented by AO. a is 1 to 60, b is 0 to 15, and a and b satisfy the relationship 0.8≦a/(a+b)≦1. R represents a linear or branched alkyl group, and the alkyl group has 1 to 10 carbon atoms. m is 1 or 2. M is a hydrogen atom, alkali metal, alkaline earth metal, ammonium ion, or organic ammonium ion.)

The present invention provides a hydrophilizing agent for printing plates that has good wettability to printing plates, does not foam even at high concentrations of active ingredient such as 1.0% by weight or more, and does not corrode metal plates or equipment regardless of pH.

Embodiments of the present invention will be described below. Note that in this specification, numerical ranges defined using the symbol "to" include the numerical values at both ends of the symbol (upper and lower limits). For example, "2 to 10" represents a range from 2 to 10.

The hydrophilizing agent for printing plates according to an embodiment of the present invention contains a compound represented by the following formula (1) as an active ingredient.

(EO is an oxyethylene group, and a is the average number of moles of oxyethylene groups added represented by EO. AO is an oxyalkylene group having 3 to 4 carbon atoms, and b is the average number of moles of oxyalkylene groups added represented by AO. a is 1 to 60, b is 0 to 15, and a and b satisfy the relationship 0.8≦a/(a+b)≦1. R represents a linear or branched alkyl group, and the alkyl group has 1 to 10 carbon atoms. m is 1 or 2. M is a hydrogen atom, alkali metal, alkaline earth metal, ammonium ion, or organic ammonium ion.)

In formula (1), R is a linear or branched alkyl group having 1 to 10 carbon atoms. If the alkyl group has 4 or more carbon atoms, a branched structure is preferred. The carbon number of R is preferably 1 to 4. If the carbon number is more than 10, low-foaming properties and rust prevention properties may be inferior.

In formula (1), AO is an oxyalkylene group having 3 to 4 carbon atoms, and examples include an oxypropylene group, an oxytrimethylene group, an oxyisobutylene group, an oxy1-ethylethylene group, an oxy2-butylene group, and an oxytetramethylene group. When the average number of moles of AO added, b, is 2 or more, the two or more AOs may be the same or different groups. When AO is two or more different groups, it may be either a random addition (random copolymer) or a block addition (block copolymer). AO is preferably an oxypropylene group having 3 carbon atoms.

In formula (1), if the average number of moles of oxyethylene groups added, represented by EO, is a, and the number of moles of oxyalkylene groups having 3 to 4 carbon atoms, represented by AO, is b, then a is 1 to 60 and b is 0 to 15. Preferably, a is 2 to 55 and b is 0 to 13, and more preferably, a is 5 to 45 and b is 0 to 10. If a is greater than 60, water solubility may decrease, and if b is greater than 15, wettability may decrease.

When EO and AO are present, there are no particular restrictions on the order of addition, and the addition may be random or block, provided that the sum of the average number of moles of each added, a + b (a > 0, b > 0), is 2 or greater. From the perspective of low foaming properties, an addition form in which the EO chain is bonded to R is preferred.

The upper limit of a+b, which is the sum of the average number of moles added, is not particularly limited, but from the viewpoints of solubility and handleability when diluted, it is preferably 75 or less, more preferably 70 or less, and even more preferably 55 or less. The lower limit of a+b may be 1 or more, but from the viewpoint of wettability, it is preferably 4 or more.

a/(a+b) represents the balance between the highly hydrophilic polyoxyethylene group and the highly lipophilic polyoxyalkylene group having 3 to 4 carbon atoms, and satisfies the relationship 0.8≦a/(a+b)≦1. If a/(a+b) is less than 0.8, low foaming properties and wettability may decrease.

In formula (1), m may be 1 or 2, but tends to vary depending on the material of the printing plate being used. For example, m = 2 is preferred for copper plates, and m = 1 is preferred for aluminum plates and SUS plates.

When m=2, the ester groups represented by RO-[(EO) _a /(OA) _b ]- in formula (1) may be the same or different, but are preferably the same.

In formula (1), M is a hydrogen atom, an alkali metal, an alkaline earth metal, an ammonium ion, or an organic ammonium ion. Examples of alkali metals include lithium, sodium, and potassium. Examples of alkaline earth metals include calcium, magnesium, strontium, and barium. Examples of organic ammonium ions include monoethanolamine, diethanolamine, and triethanolamine. M is preferably a hydrogen atom, sodium, or potassium. Furthermore, when m = 1, the M's may be the same or different, but are preferably the same.

The weight-average molecular weight of the compound represented by the aforementioned formula (1) is not particularly limited and can be, for example, 150 to 7,000.

The compound represented by the aforementioned formula (1) can be synthesized according to standard methods, but commercially available products can also be used.

The hydrophilizing agent for printing plates may contain only one compound represented by the aforementioned formula (1), or two or more compounds may be used in combination.

The hydrophilizing agent for printing plates may consist solely of the compound represented by formula (1) above, but may also contain auxiliary agents such as preservatives, chelating agents, and colorants in addition to the compound.

The printing plate hydrophilizing agent can be diluted with water such as ion-exchanged water, tap water, or well water, or with an organic solvent, as needed. The organic solvent can be selected appropriately depending on the printing plate and printing method to be used, and examples include water-soluble organic solvents such as acetone. The dilution ratio is determined appropriately depending on the intended use and purpose, and is, for example, 1.5 to 10,000 times. This diluted product is also included in the category of the printing plate hydrophilizing agent according to the present invention.

The hydrophilizing agent for printing plates contains a compound represented by formula (1), making it suitable as a hydrophilizing agent for a variety of printing plates and printing methods. For example, as described below, it exhibits favorable low-foaming properties at high concentrations, anti-rust effects, and wettability independent of pH. There are no particular restrictions on the material of the printing plate to which it can be applied, but application to metal plates is effective, and application to plates made of copper, stainless steel (SUS), or aluminum is even more effective.

The following provides a detailed explanation of embodiments of the present invention using examples, but the present invention is not limited to these examples in any way.

(Test example)
(1) Low Foaming Properties Using various compounds shown in Tables 1 and 3 below, Examples 1 to 8 were prepared using compounds or compositions in the blending ratios shown in Table 2 as hydrophilizing agents for printing plates, and Comparative Examples 1 to 5 were prepared using compounds or compositions in the blending ratios shown in Table 3 as hydrophilizing agents for printing plates. These were then diluted with ion-exchanged water to prepare 100 g of each 2% aqueous solution. 30 mL of this was placed in a 50 mL measuring cylinder with a lid, shaken manually for 10 seconds, and then allowed to stand for 10 seconds, after which the foam height was measured. The evaluation criteria were as follows:
◎: Foam height 0 mm or more, less than 1 mm ○: Foam height 1 mm or more, less than 2 mm △: Foam height more than 2 mm

(2) Rust Prevention Effect As in (1), hydrophilizing agents for printing plates of Examples 1 to 8 and Comparative Examples 1 to 5 were prepared. These were then diluted with ion-exchanged water to prepare 100 g of 1% aqueous solutions (pH 2, 7, 13), respectively. The pH of these aqueous solutions was adjusted with hydrochloric acid or sodium hydroxide. Furthermore, oxygen-free copper plates manufactured by TP Giken Co., Ltd., from which the oxide film had been removed, were prepared as copper plates. The oxide film was removed using sandpaper.
0.3 mL of each of the aqueous solutions was applied to the copper plate from which the oxide film had been removed, and after 10 minutes, the copper plate was wiped off. The condition of the copper plate was then visually observed. The observation results were classified into the following five levels.
1 point: No change at all pH levels 2 points: The copper plate was slightly discolored at some pH levels 3 points: The copper plate was slightly discolored at some pH levels 4 points: The copper plate was discolored at some pH levels

The evaluation criteria were as follows: A score of 3 or less was considered to be acceptable.
◎: 1 point ○: 2 points or 3 points △: 4 points

(3) Wettability As in (1), hydrophilizing agents for printing plates of Examples 1 to 8 and Comparative Examples 1 to 5 were prepared. These were then diluted with acetone to prepare 100 g of each 0.1% acetone solution. 0.5 g of the acetone solution was applied to a copper, aluminum, or SUS plate (50 × 15 × 1.5 mm), which was then air-dried for 30 minutes to remove the acetone. 1.0 μL of ion-exchanged water was dropped onto the treated plate, and the contact angle was measured after 1,100 ms.
The evaluation was performed as follows. Blanks were prepared in the same manner, except that ion-exchanged water was used instead of the 0.1% acetone solution. The contact angles of the blanks were 70.9° for the copper plate, 93.4° for the aluminum plate, and 103.0° for the SUS plate. The copper plate was oxygen-free copper manufactured by TP Giken Co., Ltd., the aluminum plate was aluminum plate (A5052P) manufactured by TP Giken Co., Ltd., and the SUS plate was stainless steel plate SUS304 manufactured by TP Giken Co., Ltd., and the contact angle meter was DropMaster DM-701 manufactured by Kyowa Interface Science Co., Ltd., and the analysis software was FAMAS. The evaluation criteria were as follows.
⊚: The rate of change from the blank was 50% or more. ○: The rate of change from the blank was 30% or more but less than 50%. △: The rate of change from the blank was less than 30%. The rate of change (%) from the blank was calculated using the following formula.

Table 1 shows the correspondence between compounds A1 to A6 and A'1 used in the examples and comparative examples and formula (1). The names of compounds A1 to A6 and A'1 are as follows. In Table 1, MEA stands for monoethanolamine. The synthesis methods of compounds A1 to A6 and A'1 will be described later.
A1: Polyoxyethylene methyl ether phosphate monoester A2: Polyoxyethylene methyl ether phosphate diester A3: Polyoxyethylene polyoxypropylene propyl ether phosphate monoester A4: Polyoxyethylene polyoxypropylene methyl ether phosphate diester monoethanolamine A5: Polyoxyethylene methyl ether phosphate diester sodium A6: Polyoxyethylene polyoxybutylene isononyl ether phosphate monoester A'1: Polyoxyethylene lauryl ether phosphate monoester

(Synthesis Example 1: Synthesis of Compound A1)
To phosphorus oxychloride, 0.8 to 1.3 times the molar amount of polyoxyethylene methyl ether (UNIOX M-400, manufactured by NOF Corporation) and 1.0 to 3.0 times the molar amount of triethylamine were added dropwise, and the mixture was reacted in toluene at 30°C or less for 1 to 5 hours. After the reaction, 2.0 to 10.0 times the molar amount of ion-exchanged water was added, and hydrolysis was carried out at 40 to 70°C for 1 to 5 hours. Then, the solvent was removed and the mixture was filtered to obtain Compound A1.

(Synthesis Example 2: Synthesis of Compound A2)
Polyoxyethylene methyl ether (UNIOX M-1000, manufactured by NOF Corporation) in an amount of 2.0 to 2.3 times by molar amount relative to phosphorus oxychloride and triethylamine in an amount of 2.0 to 3.0 times by molar amount were added dropwise, and the mixture was reacted in toluene at 30°C or less for 2 to 6 hours. After the reaction, ion-exchanged water in an amount of 1.0 to 10.0 times by molar amount was added, and hydrolysis was carried out at 40 to 70°C for 1 to 5 hours. Compound A2 was then obtained by removing the solvent and filtering.

(Synthesis Example 3: Synthesis of Compound A3)
Compound A3 was obtained in the same manner as in Synthesis Example 1, except that polyoxyethylene polyoxypropylene propyl ether was used instead of polyoxyethylene methyl ether (UNIOX M-400, manufactured by NOF Corporation).

(Synthesis Example 4: Synthesis of Compound A4)
Except for using polyoxyethylene polyoxypropylene methyl ether instead of polyoxyethylene methyl ether (UNIOX M-1000, manufactured by NOF Corporation), the components were reacted and hydrolyzed in the same manner as in Synthesis Example 2, followed by removal of the solvent and filtration. The resulting mixture was then neutralized with monoethanolamine (MEA) to obtain Compound A4.

(Synthesis Example 5: Synthesis of Compound A5)
Except for using polyoxyethylene methyl ether (UNIOX M-2000, manufactured by NOF Corporation) instead of polyoxyethylene methyl ether (UNIOX M-1000, manufactured by NOF Corporation), the components were reacted and hydrolyzed in the same manner as in Synthesis Example 2, followed by removal of the solvent and filtration. The resultant was then neutralized with sodium hydroxide to obtain Compound A5.

(Synthesis Example 6: Synthesis of Compound A6)
Polyoxyethylene polyoxybutylene isononyl ether in an amount of 0.8 to 1.3 times by molar relative to phosphorus oxychloride and triethylamine in an amount of 1.0 to 3.0 times by molar were added dropwise, and the mixture was reacted in toluene at 30° C. or less for 1 to 5 hours. After the reaction, ion-exchanged water in an amount of 2.0 to 10.0 times by molar was added, and hydrolysis was carried out at 40 to 70° C. for 1 to 5 hours. The mixture was then washed with ion-exchanged water at 50 to 70° C., and the solvent was removed to obtain Compound A6.

(Synthesis Example 7: Synthesis of Compound A'1)
Compound A'1 was obtained in the same manner as in Synthesis Example 6, except that polyoxyethylene lauryl ether (Nonion K-204, manufactured by NOF Corporation) was used instead of polyoxyethylene polyoxybutylene isononyl ether.

The compounds used in Comparative Examples 2 to 5 in Table 3 were the following commercially available products.
Polyoxyethylene methyl ether: NOF Corporation "Uniox M-1000"
Tris(2-ethylhexyl) phosphate: manufactured by Tokyo Chemical Industry Co., Ltd. Triacetin: manufactured by Tokyo Chemical Industry Co., Ltd. Propylene glycol mono-n-butyl ether: manufactured by Tokyo Chemical Industry Co., Ltd. Propylene glycol: manufactured by ADEKA Corporation 2-ethyl-1,3-hexanediol: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

(result)
Examples 1 to 8 have good wettability to the plate, and even in a highly diluted solution containing the compound represented by formula (1) at a concentration of 2%, foaming does not occur or foaming is significantly suppressed, and it can be seen that corrosion of the copper plate is significantly suppressed regardless of the pH.

In contrast, it can be seen that Comparative Examples 1 to 5 do not provide sufficient performance compared to Examples 1 to 8. In Comparative Example 1, the number of carbon atoms in R is 12, so the low-foaming properties and rust-preventing effect are not good. In Comparative Example 2, the compound does not contain a phosphate group, so the low-foaming properties, wettability, and rust-preventing effect are not good. In Comparative Example 3, the compound is a triester and does not contain a specified polyether chain, so the wettability is not good. In Comparative Example 4, the low-foaming properties and wettability are not good. In Comparative Example 5, the low-foaming properties and rust-preventing effect are not good. Note that the low-foaming properties and rust-preventing effect of Comparative Example 3 could not be measured because the water solubility of tris(2-ethylhexyl) phosphate was low and an appropriate dilution could not be prepared.

Claims (1)

A hydrophilizing agent for a printing plate, comprising a compound represented by the following formula (1) as an active ingredient:
(EO is an oxyethylene group, a is the average number of moles of oxyethylene groups added represented by EO, AO is an oxyalkylene group having 3 to 4 carbon atoms, and b is the average number of moles of oxyalkylene groups added represented by AO. a is 5 to 22.7 , b is 0 to 2 , and a and b satisfy the relationship 0.8≦a/(a+b)≦1. R represents a linear or branched alkyl group, and the alkyl group has 1 to 4 carbon atoms. m is 1 or 2. M is a hydrogen atom .)