JP7220523B2 - metal printing ink - Google Patents

Description

TECHNICAL FIELD 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 food, beverages, and the like. Various types of printing are applied to the outer surface of the metal can for the purpose of indicating the content, its image, or its source in a design and increasing the commercial value.

Metal cans are roughly classified into three-piece cans with side seams on the can body and two-piece cans without seams on the can body. For three-piece cans, printing can be done on the material (blank) before forming, but for two-piece cans, deformation occurs due to plastic flow of the material during drawing or drawing and ironing. The mainstream method is to print on the body. As a method for printing on the can body after molding, a method of transferring ink from a printing plate such as a waterless planographic plate or a resin letterpress onto a blanket via the ink to the can body is adopted (Patent Document 1. , 2).

Japanese Patent Application Laid-Open No. 2001-129966 JP-A-2002-103775

Among them, in the so-called letterpress dry offset method using a letterpress as a printing plate, lines and halftone dots tend to become thick when transferring ink from the printing plate to a blanket. If the lines and halftone dots become thicker, characters and images may be distorted, and color mixing may occur when the inks of different colors are transferred to the blanket.
The present invention has been made in view of such circumstances, and can be suitably used for printing on metal substrates, particularly on the outer surface of metal cans. An object of the present invention is to provide a metal printing ink that suppresses thickening of dots.

The present invention includes a pigment, a resin containing an alkyd resin having a weight average molecular weight of 10000 or more and 150000 or less, a number average molecular weight of 2000 or more and 7000 or less, and a molecular weight distribution of 2 or more and 100 or less, and a solvent. It relates to a metal printing ink characterized by:

According to the metal printing ink of the present invention, it is possible to suppress the thickening of lines and halftone dots even in the case of printing by the 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 or less, 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 described in detail below.

The resin used in the metal printing ink of the present invention has a weight average molecular weight (Mw) of 10000 or more and 150000 or less, a number average molecular weight (Mn) of 2000 or more and 7000 or less, and a molecular weight distribution (Mw/Mn) of 2. including alkyd resins that are greater than or equal to 100 or less. In the present specification, the alkyd resin has a condensate of a polybasic acid and a polyhydric alcohol as a skeleton, and 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 in the synthesis of ordinary alkyd resins can be used.

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, tetrabromophthalic anhydride, and the like. Aromatic dibasic acids, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 1,4-cyclohexanedicarboxylic acid, alicyclic dibasic acids such as hetic anhydride, malonic acid, ethylmalonic acid, dimethylmalonic acid, succinic acid, Dimethylsuccinic acid, succinic anhydride, alkenylsuccinic anhydride, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic anhydride, itaconic acid, hymic acid anhydride, etc. polybasic acids such as acids, trimellitic anhydride, pyromellitic anhydride, methylcyclohexylhexentricarboxylic anhydride, and benzophenonetetracarboxylic acid, and the like, and may be used alone or in combination of two or more.

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, di Glycerin, trimethylolethane, trimethylolpropane, ditrimethylolpropane, trishydroxymethylaminomethane, pentaerythritol, dipentaerythritol, etc., can be used alone or in combination of two or more.

Oils and fatty acids are also not particularly limited, and oils and fatty acids that are commonly used for synthesizing alkyd resins can be used. Flaxseed oil, paulownia oil, safflower oil, soybean oil, tall oil, bran oil, palm oil, castor oil, dehydrated castor oil, sunflower oil, coconut 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. It can be used alone or in combination of two or more.

Examples of the monovalent acid include, but are not limited to, benzoic acid, p-tertiarybutylbenzoic acid, rosin acid, hydrogenated rosin acid, and the like, and may be used alone or in combination of two or more.
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, hydrogenated rosin alcohol, and the like. Two or more kinds 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 higher epoxy group. A vinyl compound such as an acrylic acid 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 10000 or more and 150000 or less, a number average molecular weight (Mn) of 2000 or more and 7000 or less, and a molecular weight distribution (Mw/Mn) of 2. 100 or less. As used herein, the weight average molecular weight (Mw) and number average molecular weight (Mn) are values measured by gel permeation 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; TSKgel 4000HXL, TSKgel 3000HXL, TSKgel 2000HXL, TSKgel 1000HXL manufactured by Tosoh Corporation
Detector; RI (differential refractometer)
Data processing; Multi-station GPC-8020modelII manufactured by Tosoh Corporation
Measurement conditions; Column temperature 40°C
Developing solvent Tetrahydrofuran
Flow rate 0.35 ml/min standard; monodisperse polystyrene
Sample; 0.2% by mass of tetrahydrofuran solution in terms of resin solid content filtered through a microfilter (100 μl)

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 3,000 or more, and more preferably 5,000 or less. More preferably, the molecular weight distribution (Mw/Mn) is 5 or more, and 50 or less. As a result, it is possible to more reliably suppress thickening of the drawing lines and halftone dots.

In addition, when it is desired to suppress misting and make a metal printing ink excellent in high-speed printability, the weight average molecular weight (Mw) is 40000 or more and 150000 or less, the number average molecular weight (Mn) is 4000 or more and 7000 or less, and the molecular weight distribution (Mw /Mn) is preferably 9 or more and 100 or less. When a metal printing ink with excellent on-press stability is desired, the weight average molecular weight (Mw) is 10000 or more and 90000 or less, more preferably 100000 or more and 53000 or less, the number average molecular weight (Mn) is 2000 or more and 5000 or less, and the molecular weight distribution It is preferable to use an alkyd resin with (Mw/Mn) of 2 or more and 12 or less. It may be appropriately adjusted according to the necessary 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, and the like.
The molecular weight distribution (Mw/Mn) can be adjusted to a desired range by using, for example, a trifunctional or higher polybasic acid or polyhydric alcohol as the polybasic acid or polyhydric alcohol used for synthesizing the skeleton of the alkyd resin. can. Alternatively, the molecular weight distribution (Mw/Mn) can also be adjusted by the reaction method of the polybasic acid and the polyhydric alcohol when synthesizing the skeleton of the alkyd resin. When the condensate used as a raw material is used as the skeleton of the alkyd resin, the molecular weight distribution differs depending on whether the bifunctional monomer and the trifunctional monomer are reacted at the same time or when the trifunctional monomer is reacted after the bifunctional monomer is reacted. Such techniques can also be used to adjust the molecular weight distribution. A modifier may be added to a condensate of a polybasic acid and a polyhydric alcohol and heated and melted.

As one aspect of the alkyd resin preferably used in the present invention, a condensate of a polybasic acid and a polyhydric alcohol is used as a skeleton, and fatty acids or hydrogenated products thereof, oils or hydrides thereof, monovalent acids, monovalent Alkyd resins, which are resins modified with alcohols, etc., in which the average number of functional groups of hydroxyl groups contained in the polyhydric alcohol is 3.5 or more and 4.5 or less. By using a reaction product of a polybasic acid and such a polyhydric alcohol as a skeleton, the weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw/Mn) are within desired ranges. Certain alkyd resins can be obtained efficiently. Examples of such polyhydric alcohols include bifunctional alcohols such as neopentyl glycol and 1,6-hexanediol, and hexafunctional alcohols such as dipentaerythritol. A composition adjusted to be 5 or more and 4.5 or less may be used, or a trifunctional alcohol such as trimethylolethane or trimethylolpropane and a hexafunctional alcohol such as dipentaerythritol are added to the hydroxyl group. A composition adjusted to have an average functional group number of 3.5 or more and 4.5 or less may be used. Only tetrafunctional alcohols such as pentaerythritol may be used.

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

As one aspect of the alkyd resin preferably used in the present invention, a resin modified with fatty acids having a condensate of a polybasic acid and a polyhydric alcohol as a skeleton, wherein the proportion of capric acid is 40% of the fatty acids used for modification. It is preferably at least 50% by mass, more preferably at least 50% by mass. Also, the ratio of capric acid may be 100% by mass of the fatty acid 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 excellent in on-press stability and high-speed printability can be obtained.

One aspect of the alkyd resin preferably used in the present invention is a resin modified with a fatty acid having a condensate of a polybasic acid and a polyhydric alcohol as a skeleton, wherein 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. Also, the proportion of lauric acid in the fatty acid used for modification is preferably 30% by mass or less, more preferably 25% by mass or less. By using such an alkyd resin, misting can be suppressed, and a metal printing ink excellent in on-press stability and high-speed printability can be obtained.

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

The alkyd resin used in the present invention preferably has an acid value of 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 that are commonly used in metal printing inks. resins, amino resins, benzoguanamine resins, oil-free polyester resins, rosin phenol resins and the like. These resins can be used singly or in combination of two or more.

The content of the resin 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. % or more and 70 mass % or less is more preferable.
Moreover, when other resins are used in addition to the above alkyd resins, the content of the above alkyd resins in the resins added to the metal printing ink is preferably 50% by mass or more.

As the solvent used in the present invention, known solvents that are commonly used in metal printing inks can be used. For example, aliphatic hydrocarbons having a boiling point range of about 230° C. to 400° C., aromatic hydrocarbons such as alicyclic hydrocarbons and alkylbenzenes, and higher alcohols can be mentioned, and one or more of them can be used in combination.
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. be.

As the inorganic pigment or organic pigment used in the metal printing ink of the present invention, depending on the content, if it has heat resistance, light resistance, and retort resistance, it may be used in conventional metal printing inks. Inorganic pigments include titanium oxide, silica, and carbon black. Examples of organic pigments include phthalocyanine-based pigments, azo-based pigments, quinacridone-based pigments, diketopyrrolopyrrole-based pigments, and quinophthalone-based pigments.
The content of these pigments is appropriately adjusted depending on the type and purpose, but is preferably 10% by mass or more and 60% by mass or less of the total amount of the metal printing ink.

Pigment dispersants, acid catalysts, waxes, co-solvents and the like can be used in the metal printing ink of the present invention, if necessary. As the auxiliary solvent, any solvent can be used alone or in combination of two or more depending on the printability and the coatability of the overprint varnish. A solvent etc. are mentioned.

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

The method for forming a printed layer with 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 in the case of printing by a dry offset method using a resin relief printing plate. Printing can also be performed by the dry offset method used, the lithographic offset method using ordinary water, or the like. Although the film thickness of the ink is arbitrary, it may be adjusted within a range of 0.3 μm or more and 3 μm or less, for example.

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

The base metal base used for printing on the metal base is not particularly limited and may be a two-piece can formed by molding a metal into a cylindrical can shape, or an uncoated or coated metal plate before molding. Examples of the base metal include aluminum and iron, and it may be chemically treated, plated, coated with a size paint or white coating, or laminated with a PET film or the like.

The metal printing ink of the present invention is obtained by applying an overprinting varnish on a printed layer of the metal printing ink by a wet-on-wet method, followed by baking at 180° C. to 280° C. for about 5 to 90 seconds for heat curing. The overprinting varnish can be any water-based or solvent-based overprinting varnish that is cured by heating, such as those commonly used for metal printing, and is not particularly limited. The overprint varnish can be applied, for example, by a coater method.

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples, but the present invention is not limited thereto. 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 saturated fatty acid having 8 to 18 carbon atoms, isophthalic acid, and a polyhydric alcohol composition having an average number of functional groups adjusted to tetrafunctional. Tables 1 and 2 summarize 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.

The oil lengths in Tables 1 and 2 are calculated values.
As for the acid value, 5.0 g of a sample (converted to solid content) was accurately weighed, dissolved in 30 mL of a neutral solvent, and titrated with 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 of sample (in terms of solid content) was accurately weighed, 25 mL of an acetylating agent consisting of acetic anhydride/pyridine (1/19 by volume) was added, and the mixture was sealed and heated at 100° C. for 1 hour. After 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 so that the tack value was 5.5, and metallic printing inks of Examples and Comparative Examples were obtained. The pigment used for preparing 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 Co., Ltd.).

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

(Printability)
In a room controlled at 25° C.±2° C., the D value (mm) corresponding to the spread diameter after 60 seconds was measured by the spread meter method described in 4.1 of JIS K5701-1. As the D value increases, the lines and halftone dots become thicker, and if the D value is too small, the inking property decreases.

(Misting)
2.64 cc of the prepared metal printing ink was placed in an RI tester (manufactured by Akira Seisakusho Co., Ltd.) and rotated at a rotational speed of 1600 rpm for 5 minutes in an environment of 55°C ± 2°C. The amount (mg) of metal printing ink adhered in 5 minutes was measured on a 10 cm square plate that had been placed in advance so as to be parallel to the rotation axis of the RI tester at a position 5 cm from the RI tester. Both the inks of Examples and Comparative Examples are sufficiently durable for practical use because they are measured under an environment that is more severe than the actual printing conditions.

(In-flight stability)
After drawing 0.1 cc of metal printing ink onto a 4-part roll using the RI tester, the ink was transferred to the blanket. After that, without replenishing the ink, the blanket was rotated at a constant angle at 25 ± 2 ° C at regular intervals to print on an aluminum plate (a two-piece can with a thickness of 50 to 100 μm was opened), and the ink was removed. The time until metastasis ceased was examined and evaluated on a 4-point scale.
◎: Ink transfer occurs even after 20 minutes. ○: Ink transfer does not occur after 15 minutes or more and less than 20 minutes. △: Ink transfer does not occur after 10 minutes or more and less than 15 minutes.

(suitability for high-speed printing)
Using a high-speed printability tester (PM901PT, manufactured by SMTE Co., Ltd.), the metal printing ink composition was uniformly transferred to a test rubber roll so that the thickness of the wet ink film was 2 μm, and then transferred to an aluminum plate (thickness). 50-100 μm thick open two-piece can) 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 ⊚. It was set to x and relative evaluation was carried out in 4 steps.

As is clear from Tables 3 and 4, the metal printing inks of the present invention exhibited excellent suitability as metal printing inks.

Claims (6)

A pigment, a resin containing an alkyd resin having a weight average molecular weight of 40000 or more and 150000 or less, a number average molecular weight of 4000 or more and 7000 or less, and a molecular weight distribution of 9 or more and 32 or less, and a solvent, The content 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, the content of the alkyd resin in the resin is 50% by mass or more, and the A metal printing ink having a solvent content of 5% by mass or more and 60% by mass or less . 2. The alkyd resin has a skeleton of a condensate of a polybasic acid and a polyhydric alcohol, and the polyhydric alcohol has an average functionality of hydroxyl groups of 3.5 or more and 4.5 or less. A metal printing ink as described in . The alkyd resin has a condensate of a polybasic acid and a polyhydric alcohol as a skeleton, and is a resin modified with a fatty acid, and 95 mol% or more of the fatty acid is a saturated fatty acid having 8 to 18 carbon atoms. 3. A metal printing ink according to claim 1 or 2, characterized in that: The alkyd resin has a condensate of a polybasic acid and a polyhydric alcohol as a skeleton, and is a resin modified with a fatty acid, wherein the proportion of capric acid in the fatty acid is 40% by mass or more. A metal printing ink according to any one of claims 1 to 3. The alkyd resin is a resin modified with a fatty acid having a condensate of a polybasic acid and a polyhydric alcohol as a skeleton, and the proportion of lauric acid in the fatty acid is 8% by mass or more and 25% by mass or less. 5. A metal printing ink as claimed in any one of claims 1 to 4. The metal printing ink according to any one of claims 1 to 5, wherein the alkyd resin has an oil length of 30 or more and 70 or less.