JP7425532B2 - metal printing ink - Google Patents

Description

The present invention relates to a metal printing ink suitable for printing on metal substrates, particularly on the outer surface of metal cans.

Metal cans and metal containers are widely used as packaging containers for foods, drinks, and the like. Various types of printing are applied to the outside of these metal cans in order to display the content, its image, or its source in a design, and to increase the product value.

Metal cans can be roughly divided into three-piece cans with a side seam in the can body and two-piece cans without a seam in the can body. With 3-piece cans, it is possible to print on the material (blank) before forming, whereas with 2-piece cans, deformation occurs due to plastic flow of the material during drawing or drawing/ironing, so the can body after forming can be printed. The mainstream method is to print on the body. As a method for printing on the can body after molding, a method is adopted in which ink is transferred from a printing plate such as a waterless lithographic plate or a resin letterpress to a blanket onto the can body through ink (Patent Document 1) , 2).

Japanese Patent Application Publication No. 2001-129966 Japanese Patent Application Publication No. 2002-103775

Among these, in the so-called letterpress dry offset method in which a letterpress is used as a printing plate, lines and halftone dots tend to become thicker when ink is transferred from the printing plate to the blanket. If the drawing lines or halftone dots become thick, there is a risk that characters or images may become distorted or color mixing may occur when ink of each color is transferred to the blanket.
The present invention was developed in view of the above circumstances, and can be suitably used for printing on metal substrates, especially the outer surface of metal cans, and even when printing using the letterpress dry offset method, lines and meshes can be printed. An object of the present invention is to provide a metal printing ink in which dot thickening is suppressed.

The present invention includes a pigment, a resin including an alkyd resin having a weight average molecular weight of 10,000 or more and 150,000 or less, a number average molecular weight of 2,000 or more and 7,000, and a molecular weight distribution of 2 or more and 100 or less, and a solvent. The present invention relates to a metal printing ink characterized by the following.

According to the metal printing ink of the present invention, it is possible to suppress thickening of lines and halftone dots even when printing by letterpress dry offset method.

The metal printing ink of the present invention comprises a pigment, a resin containing an alkyd resin having a weight average molecular weight of 10,000 or more and 150,000 or less, a number average molecular weight of 2,000 or more and 7,000, and a molecular weight distribution of 2 or more and 100 or less, and a solvent. including. Each component of the metal printing ink of the present invention will be explained in detail below.

The resin used in the metal printing ink of the present invention has a weight average molecular weight (Mw) of 10,000 to 150,000, a number average molecular weight (Mn) of 2,000 to 7,000, and a molecular weight distribution (Mw/Mn) of 2. This includes alkyd resins having a molecular weight of 100 or higher. In this specification, alkyd resin has a skeleton of a condensate of polybasic acid and polyhydric alcohol, and is composed of fatty acids or their hydrogenated products, oils or their hydrogenated products, monovalent acids, monovalent alcohols, etc. It is a modified resin. It may be modified with an epoxy resin or an acrylic resin, and the components used for modification are not particularly limited, and raw materials that can be used for the synthesis of alkyd resins can be used.

Examples of polybasic acids used in the synthesis of alkyd resins include phthalic anhydride, isophthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, tetrachlorophthalic anhydride, and tetrabromophthalic anhydride. Aromatic dibasic acids, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 1,4-cyclohexanedicarboxylic acid, alicyclic dibasic acids such as het acid anhydride, malonic acid, ethylmalonic acid, dimethylmalonic acid, succinic acid, Aliphatic dibases such as dimethylsuccinic acid, succinic anhydride, alkenylsuccinic anhydride, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic anhydride, itaconic acid, himic anhydride, etc. Acids, polybasic acids such as trimellitic anhydride, pyromellitic anhydride, methylcyclohexylhexentricarboxylic anhydride, benzophenone tetracarboxylic acid, etc. can be used, and one type or a combination of two or more types can be used.

Examples of polyhydric alcohols include ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, butylene glycol, hexanediol, neopentyl glycol, octanediol, butylethylpropanediol, bisphenol A, hydrogenated bisphenol A, bisphenol F, glycerin, and diol. Examples include glycerin, trimethylolethane, trimethylolpropane, ditrimethylolpropane, trishydroxymethylaminomethane, pentaerythritol, dipentaerythritol, and the like, and one type or a combination of two or more types can be used.

There are no particular restrictions on the oil or fatty acid, and oils and fatty acids that are normally used in the synthesis of alkyd resins can be used. Linseed oil, tung oil, safflower oil, soybean oil, tall oil, bran oil, palm oil, castor oil, dehydrated castor oil, sunflower oil, coconut oil, fatty acids of these oils, caprylic acid, pelargonic acid, Capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, isostearic acid, oleic acid, linoleic acid, linoleic acid, ricinoleic acid, eleostearic acid, etc. One type or a combination of two or more types can be used.

Examples of the monovalent acid include, but are not limited to, benzoic acid, p-tert-butylbenzoic acid, rosin acid, hydrogenated rosin acid, etc., and one type or a combination of two or more types can be used.
Examples of the monohydric alcohol include octyl alcohol, decanol, lauryl alcohol, cetyl alcohol, stearyl alcohol, isostearyl alcohol, glycol esters, glycol ethers such as phenyl glycol, rosin alcohol, and hydrogenated rosin alcohol. Two or more types can be used in combination.

The alkyd resin can also be modified by forming an epoxy ester with a compound having a monovalent or divalent or more epoxy group. A vinyl compound such as an acrylic ester or styrene may be graft-polymerized to the unsaturated double bond of the alkyd resin using a radical polymerization initiator.

The alkyd resin used in the metal printing ink of the present invention has a weight average molecular weight (Mw) of 10,000 to 150,000, a number average molecular weight (Mn) of 2,000 to 7,000, and a molecular weight distribution (Mw/Mn) of 2. 100 or less. In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are values measured by gel permulation chromatography (GPC) under the following conditions. By using such an alkyd resin, thickening of lines and halftone dots can be suppressed.

Measuring device: HLC-8320GPC manufactured by Tosoh Corporation
Column: Tosoh Corporation TSKgel 4000HXL, TSKgel 3000HXL, TSKgel 2000HXL, TSKgel 1000HXL
Detector: RI (differential refractometer)
Data processing: Multi-station GPC-8020model II manufactured by Tosoh Corporation
Measurement conditions: Column temperature 40℃
Developing solvent Tetrahydrofuran
Flow rate 0.35ml/min standard; monodisperse polystyrene
Sample: A 0.2% by mass tetrahydrofuran solution (calculated as resin solid content) filtered through a microfilter (100μl)

The weight average molecular weight (Mw) of the alkyd resin used in the metal printing ink of the present invention is more preferably 20,000 or more, and more preferably 100,000 or less. The number average molecular weight (Mn) is more preferably 3000 or more, and more preferably 5000 or less. The molecular weight distribution (Mw/Mn) is more preferably 5 or more, and more preferably 50 or less. Thereby, thickening of drawing lines and halftone dots can be suppressed more reliably.

In addition, if you want to make a metal printing ink with excellent misting suppression and high-speed printing suitability, the weight average molecular weight (Mw) is 40,000 to 150,000, the number average molecular weight (Mn) is 4,000 to 7,000, and the molecular weight distribution (Mw) is 40,000 to 150,000. /Mn) is preferably 9 or more and 100 or less. When a metal printing ink with better on-press stability is desired, the weight average molecular weight (Mw) is 10,000 or more and 90,000 or less, more preferably 100,000 or more and 53,000 or less, the number average molecular weight (Mn) is 2,000 or more and 5,000 or less, and the molecular weight distribution is It is preferable to use an alkyd resin having (Mw/Mn) of 2 or more and 12 or less. It may be adjusted as appropriate depending on the required aptitude.

The weight average molecular weight (Mw) and number average molecular weight (Mn) can be adjusted by, for example, the molar ratio of polybasic acid and polyhydric alcohol used in the reaction, reaction time, catalyst, reaction temperature, etc.
The molecular weight distribution (Mw/Mn) can be adjusted to a desired range, for example, by using a trifunctional or higher functional polybasic acid or polyhydric alcohol as the polybasic acid or polyhydric alcohol used in the synthesis of the alkyd resin skeleton. can. Alternatively, the molecular weight distribution (Mw/Mn) can also be adjusted by the reaction method of polybasic acid and polyhydric alcohol when synthesizing the alkyd resin skeleton. When the condensate used as a raw material is used as the skeleton of an alkyd resin, the molecular weight distribution is different depending on whether a bifunctional monomer and a trifunctional monomer are reacted at the same time or when a trifunctional monomer is reacted after the bifunctional monomer is reacted. Molecular weight distribution can also be adjusted using such a technique. A modifier may be added to a condensate of a polybasic acid and a polyhydric alcohol and then heated and melted.

One embodiment of the alkyd resin preferably used in the present invention has a backbone of a condensate of a polybasic acid and a polyhydric alcohol, fatty acids or hydrogenated products thereof, oils or hydrogenated products thereof, monovalent acids, monovalent Examples of alkyd resins include resins modified with alcohol, etc., in which the average number of functional groups of hydroxyl groups included in the polyhydric alcohol is 3.5 or more and 4.5 or less. By using the reaction product of a polybasic acid and such a polyhydric alcohol as the skeleton, the weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw/Mn) can be kept within the desired range. Certain alkyd resins can be obtained efficiently. Such polyhydric alcohols include, for example, bifunctional alcohols such as neopentyl glycol and 1,6-hexanediol, and hexafunctional alcohols such as dipentaerythritol, which have an average functional number of hydroxyl groups of 3. You may use a composition adjusted to have a hydroxyl group of 5 or more and 4.5 or less, or a trifunctional alcohol such as trimethylolethane or trimethylolpropane and a hexafunctional alcohol such as dipentaerythritol. You may use the composition adjusted so that the average number of functional groups may be 3.5 or more and 4.5 or less. Only a tetrafunctional alcohol such as pentaerythritol may be used.

One embodiment of the alkyd resin preferably used in the present invention is a resin having a backbone composed of a condensate of a polybasic acid and a polyhydric alcohol and modified with a fatty acid, wherein the fatty acid used for modification has a carbon atom number of 8 or more and 18 It is preferable that the following fatty acids are included. Furthermore, it is preferable that the fatty acid used for modification does not contain unsaturated bonds. Furthermore, it is preferable that 95 mol% or more of the fatty acids used for modification be saturated fatty acids having 8 or more and 18 or less carbon atoms. By using such an alkyd resin, misting can be suppressed and a metal printing ink with excellent on-press stability can be obtained.

One embodiment of the alkyd resin preferably used in the present invention is a resin whose skeleton is a condensate of a polybasic acid and a polyhydric alcohol, and which is modified with a fatty acid, in which the proportion of capric acid among the fatty acids used for modification is 40%. It is preferably at least 50% by mass, more preferably at least 50% by mass. Further, the proportion of capric acid may be 100% by mass of the fatty acids used for modification. It is preferably 80% by mass or less, more preferably 70% by mass or less. By using such an alkyd resin, misting can be suppressed, and a metal printing ink can be obtained that has excellent on-press stability and high-speed printing suitability.

One embodiment of the alkyd resin preferably used in the present invention is a resin whose skeleton is a condensate of a polybasic acid and a polyhydric alcohol, and which is modified with a fatty acid, in which the proportion of lauric acid among the fatty acids used for modification is 8. It is preferably at least 13% by mass, more preferably at least 13% by mass. Further, the proportion of lauric acid is preferably 30% by mass or less, more preferably 25% by mass or less of the fatty acids used for modification. By using such an alkyd resin, misting can be suppressed, and a metal printing ink can be obtained that has excellent on-press stability and high-speed printing suitability.

One embodiment of the alkyd resin preferably used in the present invention is a resin whose skeleton is a condensate of a polybasic acid and a polyhydric alcohol, modified with a fatty acid, and whose oil length is preferably 30 or more and 70 or less. In this specification, the oil length of an alkyd resin refers to the mass percentage of triglyceride contained in the alkyd resin when fatty acids react with glycerin to form triglyceride.

The acid value of the alkyd resin used in the present invention is preferably 0.1 mgKOH/g or more and 25 mgKOH/g or less. The hydroxyl value is preferably adjusted to 70 mgKOH/g or more and 200 mgKOH/g or less.

In addition to such alkyd resins, it is also possible to use other resins normally used in metal printing inks, such as alkyd resins other than the above-mentioned alkyd resins, petroleum resins, epoxy resins, ketone resins, rosin-modified maleic acid, etc. Examples include resins, amino resins, benzoguanamine resins, oil-free polyester resins, rosin phenol resins, and the like. These resins can be used alone or in combination of two or more.

The resin content in the metal printing ink of the present invention is not particularly limited as long as it can be adjusted to an ink tack value suitable for metal printing, but it is preferably 5% by mass or more and 70% by mass or less of the total amount of the metal printing ink, and 30% by mass or less. % or more and 70% by mass or less is more preferable.
Moreover, when using other resins in addition to the above-mentioned alkyd resin, it is preferable that the content of the above-mentioned alkyd resin in the resin added to the metal printing ink is 50% by mass or more.

As the solvent used in the present invention, known solvents commonly used in metal printing inks can be used. For example, aliphatic hydrocarbons with a boiling point range of about 230° C. to 400° C., aromatic hydrocarbons such as alicyclic hydrocarbons and alkylbenzenes, and higher alcohols can be used, and one type or a combination of two or more types can be used.
The content of the solvent in the metal printing ink of the present invention is not particularly limited as long as it can be adjusted to an ink tack value suitable for metal printing, but as an example, it is 5% by mass or more and 60% by mass or less of the total amount of the metal printing ink. be.

The inorganic pigments and organic pigments used in the metal printing ink of the present invention may vary depending on the contents, but as long as they have heat resistance, light resistance, and retort resistance, they may be the same as those conventionally used in metal printing inks. Inorganic pigments include titanium oxide, silica, carbon black, and the like. Examples of organic pigments include phthalocyanine pigments, azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, and quinophthalone pigments.
Although the content of these pigments is appropriately adjusted depending on the type and purpose, it is preferably 10% by mass or more and 60% by mass or less of the total amount of the metal printing ink.

The metal printing ink of the present invention may contain a pigment dispersant, an acid catalyst, a wax, an auxiliary solvent, and the like, if necessary. As the auxiliary solvent, one or a combination of two or more arbitrary solvents can be used depending on the printing suitability and the coatability of the overprint varnish, including glycol-based, glycol ether-based, glycol ester-based, and higher alcohol-based solvents. Examples include solvents.

The metal printing ink of the present invention can be prepared by a conventional method using a roll mill.

The method of forming a printing layer using the metal printing ink of the present invention is not particularly limited. By using the metal printing ink of the present invention, it is possible to suppress the thickening of lines and halftone dots even when printing using a dry offset method using a resin letterpress plate, but is not limited thereto. It is also possible to print by the dry offset method used, the lithographic offset method using ordinary water, etc. The film thickness of the ink is arbitrary, and may be adjusted within a range of, for example, 0.3 μm or more and 3 μm or less.

The printing layer formed using the metal printing ink of the present invention may be formed on the entire surface of the underlying metal base material, or may be formed only on a part of the underlying metal base material. In the area where the metal printing ink of the present invention is not printed, a printing layer may be formed with a metal printing ink other than the metal printing ink of the present invention, or between the base metal base material or between the base metal base material and the print layer. A layer formed by another paint applied to the surface may be exposed.

The base metal base material used for printing on the metal base material is not particularly limited, and may be a two-piece can made of metal molded into a cylindrical can shape, or an unpainted or painted metal plate before molding. Examples of the base metal include aluminum and iron, and the base metal may be subjected to chemical conversion treatment, plating treatment, size paint, white coating, etc., or laminated with PET film or the like.

In the metal printing ink of the present invention, an overprint varnish is coated on the printing layer of the metal printing ink using a wet-on-wet method, and then baked at 180° C. to 280° C. for about 5 seconds to 90 seconds to heat cure. The overprint varnish is not particularly limited, and any water-based or solvent-based overprint varnish that is cured by heating, such as those normally used for metal printing, can be used. The overprint varnish can be applied, for example, by a coater method.

The present invention will be explained below with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Blend compositions and other numerical values are based on mass unless otherwise specified.

(Synthesis of alkyd resin)
Alkyd resins 1 to 11 were synthesized by a conventional method using a composition of a saturated fatty acid having 8 or more and 18 or less carbon atoms, isophthalic acid, and a polyhydric alcohol composition whose average number of functional groups was adjusted to 4. The oil length, acid value, hydroxyl value, weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw/Mn) of the synthesized resin are summarized in Tables 1 and 2.

Note that the oil lengths in Tables 1 and 2 are calculated values.
As for the acid value, 5.0 g (in terms of solid content) of the sample was accurately weighed, 30 mL of a neutral solvent was added to dissolve it, and titration was performed using a 0.1 mol potassium hydroxide solution (methanolic). Phenolphthalein was used as an indicator. The measurement results were converted into the amount of potassium hydroxide required to neutralize 1 g of the sample, and the unit was mgKOH/g.

For the hydroxyl value, 4.0 g (solid content equivalent) of the sample was accurately weighed, 25 mL of an acetylating agent consisting of acetic anhydride/pyridine (volume ratio 1/19) was added, the mixture was sealed, and the mixture was heated at 100° C. for 1 hour. After the acetylation, 10 mL of ion-exchanged water and 100 mL of tetrahydrofuran were added, and titration was performed using a 0.5 mol potassium hydroxide solution (alcoholic). Phenolphthalein was used as an indicator. The measurement results were converted into the amount of potassium hydroxide required to neutralize the acetic acid produced when 1 g of the sample was acetylated, and the unit was mgKOH/g.

(Adjustment of metal printing ink)
Using a pigment, an alkyd resin, a solvent, and an auxiliary agent, the formulations shown in Tables 3 and 4 were adjusted to have a tack value of 5.5, and metal printing inks of Examples and Comparative Examples were obtained. The pigment used to prepare the metal printing ink was a phthalocyanine pigment ("FASTGEN Blue FA5375" manufactured by DIC Corporation), and the solvent was alkylbenzene ("Alkene L" manufactured by Nippon Oil Corporation).

(evaluation)
The metal printing inks of Examples 1 to 9, Comparative Example 1, and Comparative Example 2 were evaluated as follows, and the results are summarized in Tables 3 and 4.

(Print suitability)
In a room controlled at 25°C ± 2°C, the D value (mm), which corresponds to the spread diameter, was measured after 60 seconds using a spread meter method described in 4.1 of JIS K5701-1. As the D value increases, the thickness of the drawing lines and halftone dots increases, and if the D value is too small, the ink receptivity decreases, so a value of 31 or more and 40 or less was considered to be a pass.

(Misting)
2.64 cc of the adjusted metal printing ink was placed in an RI tester (manufactured by Mei Seisakusho Co., Ltd.) and rotated at a rotation speed of 1600 rpm for 5 minutes in an environment of 55° C.±2° C. The amount (mg) of metallic printing ink that adhered in 5 minutes was measured on a 10 cm square plate that had been placed in advance at a position 5 cm from the RI tester so as to be parallel to the rotation axis of the RI tester. Since the measurements were made under harsher environments than actual printing conditions, both the inks of the Examples and Comparative Examples can withstand practical use, but the amount is preferably 100 mg or less, more preferably 70 mg or less.

(onboard stability)
After spreading 0.1 cc of metal printing ink on a quarter roll using an RI tester, the ink was transferred to the blanket. After that, without replenishing the ink, printing was carried out on an aluminum plate (opened two-piece can with a wall thickness of 50 to 100 μm) at 25 ± 2 °C by rotating the blanket at a constant angle at regular intervals, and the ink was The time taken until metastasis stopped was investigated and evaluated on a four-point scale.
◎: Ink does not transfer even after 20 minutes 〇: Ink stops transferring after 15 minutes or more and less than 20 minutes △: Ink stops transferring after 10 minutes or more and less than 15 minutes ×: Ink stops transferring after less than 10 minutes

(Suitable for high speed printing)
The metal printing ink composition was uniformly transferred onto a rubber roll for testing using a high-speed printing suitability tester (PM901PT manufactured by SMT Co., Ltd.) so that the wet ink film thickness was 2 μm. The image was transferred onto an open two-piece can with a thickness of 50 to 100 μm at a printing speed of 9 m/s. Regarding printed two-piece cans, those with good ink transferability and surface smoothness of the ink film are ◎, and those with a small amount of ink transfer and extremely poor surface smoothness of the ink film, which are not suitable for practical use. Relative evaluation was performed on a four-level scale.

As is clear from Tables 3 and 4, the metal printing ink of the present invention showed excellent suitability as a metal printing ink.

Claims (6)

Contains a pigment, a resin including an alkyd resin, and a solvent,
The alkyd resin is a resin whose skeleton is a condensate of a polybasic acid and a polyhydric alcohol and is modified with a fatty acid, and the average number of functional groups of hydroxyl groups included in the polyhydric alcohol is 3.5 or more and 4.5 or less. Among the fatty acids, the proportion of capric acid is 40% by mass or more, the weight average molecular weight is 10,000 or more and 150,000 or less, the number average molecular weight is 2,000 or more and 7,000 or less, and the molecular weight distribution is 2 or more and 50 or less. the law of nature,
The content of the pigment is 10% by mass or more and 60% by mass or less, the content of the resin is 5% by mass or more and 70% by mass or less, and the content of the alkyd resin in the resin is 50% by mass or more. A metal printing ink , wherein the content of the solvent is 5% by mass or more and 60% by mass or less . The metal printing ink according to claim 1, wherein the alkyd resin has a weight average molecular weight of 10,000 or more and 90,000 or less, a number average molecular weight of 2,000 or more and 5,000 or less, and a molecular weight distribution of 2 or more and 12 or less. The metal printing ink according to claim 1 or 2, wherein 95 mol% or more of the fatty acid is a saturated fatty acid having 8 or more and 18 or less carbon atoms. The metal printing ink according to any one of claims 1 to 3 , wherein the proportion of lauric acid in the fatty acid is 8% by mass or more and 25% by mass or less. The metal printing ink according to any one of claims 1 to 4, wherein the alkyd resin has an oil length of 30 or more and 70 or less. It has a metal base material and a printing layer formed on the metal base material, and the printing layer is formed using the metal printing ink according to any one of claims 1 to 5. laminate.