JP7238472B2 - Gravure or flexographic white ink and its use - Google Patents

Description

The present invention relates to gravure or flexographic white inks. More particularly, it relates to a gravure or flexographic white ink that exhibits excellent printability, whiteness and opacity when printed on a substrate such as a resin film.

BACKGROUND ART Packaging materials using various resin films are used for food, confectionery, household goods, pet food, and the like from the viewpoint of design, economy, content protection, transportability, and the like. In addition, gravure printing and flexographic printing are applied to many packaging materials with the intention of imparting designs and messages appealing to consumers.
In the printing configuration used in such a printing method, front printing is performed on the surface of the packaging material, or reverse printing is performed by applying an adhesive or an anchor agent to the printed surface as necessary and laminating the film. done. In addition, surface printing refers to printing from the front side of a transparent film substrate, and is used when there is a risk that the ink ingredients may affect the contents, and the pattern is printed in a form that can be visually recognized directly. say. Reverse printing, on the other hand, refers to a form of printing in which the orientation and order of printing are reversed on a transparent film base material, and printing is performed from the back side. This printing form enhances the printing effect and prevents wear and contamination of the printed surface. The pattern refers to a printed form that can be recognized through a transparent film.

In recent years, there has been a demand for gravure inks having high whiteness and opacity and excellent printability. In the prior art, titanium oxide pigments are used as pigments in gravure white inks in order to improve the whiteness and opacity of printed matter for both reverse printing and surface printing. (Patent Literature 1, Patent Literature 2, Patent Literature 3) However, while a printed matter of gravure white ink using a titanium oxide pigment has high whiteness and opacity, titanium oxide has a high Mohs hardness. Printability such as plate fogging and doctor streaks during gravure printing was not sufficient.

Further, when titanium oxide is used as a pigment, there is a demand for stability over time in gravure or flexographic white ink. Titanium oxide has a high specific gravity, and even if it is dispersed and stabilized with a bead mill or other dispersing machine, the pigment content tends to settle over time. had to be more than As a result, sedimentation over time becomes more pronounced, and a technique that can solve this problem has been desired.

JP-A-05-097959 JP 2012-012597 A JP 2013-256551 A

An object of the present invention is to obtain a gravure or flexographic white ink which has excellent stability over time, can form a printing layer having excellent whiteness and opacity, can reduce plate fogging and doctor streaks, and has excellent printability. .

As a result of earnest studies, the present inventors have found that the above problems can be solved by using the gravure or flexographic white ink described below, and have completed the present invention.

That is, the present invention relates to a gravure or flexographic white ink containing a pigment containing a zinc sulfide pigment and a binder resin, wherein the gravure or flexographic white ink satisfies the following (1) and (2).
(1) The zinc sulfide pigment has an average particle size of 100-500 nm and a Mohs hardness of 1-6.
(2) The binder resin contains polyurethane resin or polyamide resin.

The present invention also relates to the gravure or flexographic white ink, wherein the zinc sulfide pigment has a bulk density of 1 to 3 L/kg.

The present invention also relates to the above gravure or flexographic white ink, which further contains a vinyl chloride-vinyl acetate copolymer resin and/or a cellulose resin.

The present invention also relates to the above gravure or flexographic white ink containing 10 to 50% by mass of zinc sulfide pigment in the total mass of the ink.

The present invention also relates to the gravure or flexographic white ink, further comprising a titanium oxide pigment, wherein the weight ratio of the zinc sulfide pigment and the titanium oxide pigment is 90:10-10-90.

The present invention also relates to the above gravure or flexographic white ink, wherein the zinc sulfide pigment is surface-treated with an amine compound.

The present invention also relates to a printed matter having a printing layer made of the gravure or flexographic white ink on the substrate 1 .

The present invention was able to form a printing layer with high whiteness and excellent opacity, reduce plate fogging and doctor streaks, and obtain a gravure white ink with excellent printability.

Further, when the gravure or flexographic white ink of the present invention is used, it provides a printing layer with excellent aging stability and excellent wear resistance when used not only for reverse printing but also for front printing. can do.

The present invention is a gravure or flexographic white ink containing a zinc sulfide pigment and a binder resin, wherein the gravure or flexographic white ink satisfies the following (1) and (2). One mode of gravure printing will be described below.
(1) The zinc sulfide pigment has an average particle size of 100-500 nm and a Mohs hardness of 1-6.
(2) The binder resin contains polyurethane resin or polyamide resin.
By using the above zinc sulfide as a pigment, whiteness, opacity, and plate fogging resistance are improved, and by using a polyurethane resin or polyamide resin as a binder resin, the printed layer becomes tough, and lamination strength and abrasion resistance are improved. do.

(zinc sulfide pigment)
In the present invention, from the viewpoint of printability, the zinc sulfide pigment has an average particle size of 100 to 500 nm, preferably 100 to 400 nm, and more preferably 200 to 400 nm. The average particle size refers to a value measured by a laser diffraction method, and can be measured, for example, using a particle size distribution analyzer, for example, using a particle size distribution analyzer such as Microtrac MT3000II manufactured by Microtrack Bell. .
The Mohs hardness of the zinc sulfide pigment should be from 1 to 6, preferably from 3 to 6, in order to improve printability. In a more preferred form, the zinc sulfide pigment has a bulk density of 1 to 3 L/kg, preferably 1.2 to 2.8 L/kg, and more preferably 1.5 to 2.5 L/kg. is still preferred. Furthermore, the zinc sulfide pigment preferably has an oil absorption of 7 to 20 g/100 g, more preferably 10 to 18 g/100 g. Bulk density refers to the mass of the powder sample in an untapped state and the volume ratio of the powder including the factor of the space volume between particles. For example, there is a method using a graduated cylinder. Bulk density and oil absorption can be measured by the method described in DIN53199 or the method described in JISK5101.
The Mohs hardness of the zinc sulfide pigment is within the above range, preferably the bulk density, etc. sedimentation property) is exhibited. This is thought to be due to the fact that resin adsorption on the surface of zinc sulfide is promoted more than ordinary titanium oxide, and the effect is more pronounced when vinyl chloride-vinyl acetate copolymer and/or cellulose resin are used in combination. is demonstrated in In addition, this invention is not restrict|limited at all by this.

It is also preferable that the surface of the zinc sulfide pigment is surface-treated. Here, "surface treatment" refers to a state in which a part or all of the surface of the zinc sulfide pigment is coated. The surface treatment may be performed by a known treatment method, but the surface treatment with an amine compound is particularly preferred. The amine compound is not particularly limited as long as it has an amino group, and examples thereof include organic silane coupling agents and surfactants.

It is also preferable to blend other white pigments within a range that does not impair the effects of the present invention. Other white pigments include, for example, zinc oxide (zinc oxide), white lead, lead sulfate, titanium oxide, antimony oxide, and the like.
In particular, it is preferable to use a titanium oxide pigment together, and the mass ratio of the zinc sulfide pigment and the titanium oxide pigment is preferably 90:10 to 10:90, more preferably 30:70 to 70:30. The total oil absorption of the white pigment containing zinc sulfide is preferably 15 to 30 g/100 g. This is because, in addition to having excellent printability, the printed layer of the printed matter can have sufficient opacity and whiteness. Furthermore, it is preferable that the content of the zinc sulfide pigment is 10 to 50% by mass based on the total mass of the white gravure ink.

(binder resin)
A binder resin is a binder resin in a printing layer made of gravure white ink. The binder resin includes polyurethane resin or polyamide resin. Preferably, the binder resin further contains a vinyl chloride-vinyl acetate copolymer and/or a cellulose resin. These are preferably contained as a main component (50% by mass or more) in the total mass of the binder resin. It is more preferable to contain 70% by mass or more.
Among them, a combined form of a polyurethane resin and a cellulose resin or a combination of a polyurethane resin and a vinyl chloride-vinyl acetate copolymer resin is preferred. The former is preferably used together in an amount that provides a weight ratio of polyurethane resin: cellulose resin = 95:5 to 5:95, more preferably 95:5 to 30:70, more preferably 50:50 to 70:30. It is more preferable to use them together in a mass ratio. In the latter case, the weight ratio of polyurethane resin: vinyl chloride-vinyl acetate copolymer is preferably 95:5 to 5:95, more preferably 95:5 to 30:70. :10 to 50:50 is more preferable.
As another form, it is preferable to use a polyamide resin and a cellulose resin together, and the mass ratio of the polyamide resin: the cellulose resin is preferably 95:5 to 30:70, preferably 90:10 to 50:50. is still more preferred.

The content of the binder resin in the total mass of the gravure white ink in the present invention is suitably 2 to 20% by mass, more preferably 3 to 15% by mass.

[Polyurethane resin]
The polyurethane resin described above preferably has an amine value and/or a hydroxyl value, and the amine value is preferably 0.5 to 20 mgKOH/g, more preferably 0.5 to 15 mgKOH/g. The hydroxyl value is preferably 0.5-20 mgKOH/g, more preferably 0.5-15 mgKOH/g.
As the polyurethane resin, a polyurethane resin obtained by reacting a polyisocyanate compound, a polyol compound, and, if necessary, a chain extender, a reaction terminator, etc., can be preferably used.

(Polyisocyanate compound)
Examples of polyisocyanate compounds include aliphatic diisocyanate compounds such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate, and alicyclic diisocyanate compounds such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, and 4,4-cyclohexylmethane diisocyanate. , xylylene diisocyanate, α,α,α',α'-tetramethylxylylene diisocyanate and other araliphatic diisocyanate compounds;

(Polyol compound)
The polyol compound is preferably a diol compound, more preferably a polymer diol compound, having a number average molecular weight of 500 to 3000, more preferably 500 to 2000, and consisting of one kind of diol compound. or a combination of a plurality of diol compounds. Within the above range, white ink has good adhesiveness and oil resistance.
Preferred specific examples of diol compounds include low-molecular-weight diols having a molecular weight of 300 or more, polyester diols composed of condensates of dibasic acids and low-molecular-weight diols, polyether diols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. The polyether diol may be a polyether diol obtained by polyaddition of an oxyalkylene such as ethylene oxide or propylene oxide, or tetrahydrofuran to a compound such as a low molecular weight diol or bisphenol. Diol compounds such as polylactone diols, polycarbonate diols and polyolefin diols are also included.
Examples of polyester diols include linear glycols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-propanediol, neopentyl glycol, 3-methyl branched glycols such as 1,5-pentanediol, 2,4-diethyl-1,5-pentanediol and ethylbutylpropanediol; low-molecular-weight diols such as ether diols such as diethylene glycol and triethylene glycol; and succinic acid , adipic acid, azelaic acid, sebacic acid, saturated and unsaturated aliphatic dicarboxylic acids such as maleic acid, dicarboxylic acid compounds such as aromatic dicarboxylic acids such as phthalic acid, polyester diols obtained by polycondensation, lactones, etc. A polyester diol compound obtained by subjecting a cyclic ester compound to a ring-opening reaction can be suitably exemplified.
Further, as described above, linear or side chain polycarbonate diols, polybutadiene glycol, and the like can also be used in combination.
In order to obtain good printability in a system that does not contain aromatic hydrocarbon organic solvents (toluene, etc.) in consideration of the environment and contains a large amount of highly polar organic solvents such as alcohols and esters, It is preferable to use a polyester diol compound and/or a polyether diol compound as the diol compound.

(Chain extender and reaction terminator)
Furthermore, it is also possible to use a polyurethane resin obtained using a chain extender or a reaction terminator. alicyclic diamines such as isophoronediamine and 4,4'-dicyclohexylmethanediamine; polyamines such as diethylenetriamine and triethylenetetratriamine; aromatic diamines such as toluylenediamine; araliphatic diamines such as xylenediamine. diamines having a hydroxyl group such as N-(2-hydroxyethyl)ethylenediamine, N-(2-hydroxyethyl)propylenediamine, N,N'-di(2-hydroxyethyl)ethylenediamine, ethylene glycol, propylene glycol, Diol compounds such as 1,4-butanediol, neopentyl glycol, diethylene glycol and triethylene glycol can be exemplified.
Examples of the reaction terminator include monoalcohols such as methanol and ethanol, alkylamines such as n-propylamine, n-butylamine and di-n-butylamine, and alkanolamines such as monoethanolamine and diethanolamine. be able to.

In order to obtain the polyurethane resin used in the present invention using the above synthetic components, first, the molar equivalent ratio of the NCO of the polyisocyanate compound to the OH of the diol compound (the molar equivalent of NCO of the diisocyanate compound/the molar equivalent of the diol compound OH molar equivalent) = 0.5 or more and 3.0 or less, preferably 1.2 or more and 1.5 or less, and then reacting with a chain extender and reaction terminator as necessary Obtainable. The polyurethane resin can be produced, for example, by the methods described in JP-A-2016-150944, JP-A-2015-108057, and the like.

(polyamide resin)
Although the polyamide resin is not limited to the following, it is preferably an organic solvent-soluble thermoplastic polyamide obtained by polycondensation of a polybasic acid and a polyvalent amine. In particular, a polyamide resin containing a reaction product of an acid component containing a polymerized fatty acid and/or a dimer acid and an aliphatic and/or aromatic polyamine is preferred, and further contains a portion of primary and secondary monoamines. is preferred.

Polybasic acids used as raw materials for polyamide resins include, but are not limited to, succinic acid, adipic acid, sebacic acid, azelaic acid, phthalic anhydride, isophthalic acid, suberic acid, glutaric acid, and fumaric acid. acid, pimelic acid, oxalic acid, malonic acid, succinic acid, maleic acid, terephthalic acid, 1,4-cyclohexyldicarboxylic acid, trimellitic acid, dimer acid, hydrogenated dimer acid, polymerized fatty acid, etc. Among them, dimer A polyamide resin containing a structure derived from an acid or a polymerized fatty acid as a main component (50% by mass or more in the polyamide resin) is preferred. Here, the polymerized fatty acid is obtained by a cyclization reaction of an unsaturated fatty acid or the like, and includes a monobasic fatty acid, a dimerized polymerized fatty acid (dimer acid), a trimerized polymerized fatty acid, and the like. Fatty acids constituting the dimer acid or polymerized fatty acid are preferably derived from natural oils such as soybean oil, palm oil and rice bran oil, and are preferably obtained from oleic acid and linoleic acid.
A monocarboxylic acid can also be used together with a polybasic acid. Monocarboxylic acids used in combination include acetic acid, propionic acid, lauric acid, palmitic acid, benzoic acid, and cyclohexanecarboxylic acid.

Polyamines include polyamines, primary or secondary monoamines, and the like. Examples of polyamines used in polyamide resins include aliphatic diamines such as ethylenediamine, propylenediamine, hexamethylenediamine and methylaminopropylamine, and aliphatic polyamines such as diethylenetriamine and triethylenetetramine. , cyclohexylene diamine, isophorone diamine, and the like. Examples of araliphatic polyamines include xylylenediamine, and examples of aromatic polyamines include phenylenediamine and diaminodiphenylmethane. Further, primary and secondary monoamines include n-butylamine, octylamine, diethylamine, monoethanolamine, monopropanolamine, diethanolamine, dipropanolamine, and the like.

Further, the polyamide resin preferably has a softening point of 80 to 140° C. In this range, the ink film becomes strong. Also, from the viewpoint of the solubility of the polyamide resin, the weight average molecular weight is preferably in the range of 2,000 to 50,000. More preferably, it is between 2,000 and 10,000. When the softening point is 80° C. or higher, the surface tack removal of the ink film on the printed matter is good, and blocking is prevented. When the softening point is 140° C. or lower, the ink film becomes flexible and the adhesiveness to the substrate is improved. When the weight-average molecular weight is in the range of 2,000 or more, the ink film strength is improved, and the scratch resistance, heat resistance, and high-speed printability are improved. When the molecular weight is 50,000 or less, the viscosity of the ink can be lowered and the storage stability is improved. In addition, a softening point represents the value measured by JISK2207 (ring and ball method).

(vinyl chloride-vinyl acetate copolymer resin)
A vinyl chloride-vinyl acetate copolymer resin is a resin obtained by copolymerizing vinyl chloride and vinyl acetate. Preferred embodiments are shown below.
As for the molecular weight, a weight average molecular weight of 5,000 to 70,000 is preferable, and 5,000 to 50,000 is more preferable. The structure derived from the vinyl acetate monomer in 100% by mass of the solid content of the vinyl chloride-vinyl acetate copolymer resin is preferably 1 to 30% by mass, and the structure derived from the vinyl chloride monomer is preferably 70 to 95% by mass. . In order to obtain pigment dispersion stability integrated with the polyurethane resin, the vinyl chloride-vinyl acetate copolymer resin preferably has a hydroxyl value of 20 to 200 mgKOH/g. Also, the glass transition temperature is preferably 60°C to 80°C.

(cellulose resin)
Cellulose resin refers to a fibrous carbon-based resin that is soluble in organic solvents. Preferred embodiments are shown below.
The cellulose resin preferably has a weight average molecular weight of 5,000 to 100,000, more preferably 10,000 to 70,000. Further, those having a glass transition temperature of 100° C. to 160° C. are preferable. Examples of the cellulose resin include nitrocellulose, cellulose acetate alkylates such as cellulose acetate propionate and cellulose acetate butyrate, and alkyl celluloses such as hydroxyalkyl cellulose and carboxyalkyl cellulose. Examples include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, pentyl group, hexyl group and the like, and the alkyl group may further have a substituent. Among them, cellulose acetate propionate, cellulose acetate butyrate, and nitrocellulose are preferred.
The nitrogen content of nitrocellulose is preferably 10 to 13% by mass. This is because the ink has good stability over time and good printability even under low temperature conditions, and also has good adhesion to the substrate, physical properties of the film, laminate strength, and the like.

(Organic solvent)
The organic solvent used in the present invention is preferably an organic solvent that does not contain toluene, xylene and other aromatic organic solvents in consideration of the environment. Organic solvents that do not contain aromatic hydrocarbon organic solvents mainly include alcohol organic solvents such as methanol, ethanol, n-propanol, isopropanol and butanol; ketone organic solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; Ester-based organic solvents such as methyl acetate, ethyl acetate, propyl acetate, and butyl acetate; aliphatic hydrocarbon-based organic solvents such as n-hexane, n-heptane, and n-octane; and cyclohexane, methylcyclohexane, ethylcyclohexane, and cyclohexane. Alicyclic hydrocarbon-based organic solvents such as heptane and cyclooctane can be mentioned, and they can be mixed and used in consideration of the solubility and drying properties of the binder resin. However, among the above organic solvents, it is preferable to suppress ketone-based organic solvents as much as possible. It is preferable to contain a mixed solvent of an ester-based organic solvent and an alcohol-based organic solvent, and the ratio of ester-based organic solvent:alcohol-based organic solvent is preferably 95:5 to 50:50. The amount of these organic solvents used is 15.0% by mass or more in the white gravure ink of the present invention in consideration of printability. From the viewpoint of printability, it is preferable that the white laminating gravure ink contains 5.0% by mass or more, more preferably 10.0% by mass or more of propyl acetate.

<Other additives>
In addition, if necessary, pigment dispersant, chelate cross-linking agent, leveling agent, defoaming agent, hydrocarbon wax, fatty acid amide wax, plasticizer, light stabilizer, infrared absorber, ultraviolet absorber, fragrance, flame retardant It is preferable to include additives such as
When the gravure white ink of the present invention is used for surface printing, it preferably contains a pigment dispersant, a chelate crosslinking agent, a leveling agent, an antifoaming agent, a hydrocarbon wax and a fatty acid amide wax. When used for reverse printing, it preferably contains a pigment dispersant, a leveling agent, an antifoaming agent, a hydrocarbon wax and a fatty acid amide wax.

[Combined resin]
The white gravure ink of the present invention preferably contains a combined resin in addition to the binder resin. The combined resin preferably has a melting point or glass transition temperature of 50 to 250° C. and is soluble in an organic solvent. Examples thereof include dimer acid-based resins, rosin-based resins, rosin-modified maleic acid resins, rosin ester resins, maleic acid-based resins, petroleum resins, terpene resins, ketone resins, dimmer resins, and copal resins. Among them, at least one resin selected from rosin-based resins, rosin-modified maleic acid resins, rosin ester resins and ketone resins is preferable. This is because the same effect can be obtained with each of them. It is preferably contained in an amount of 0.1 to 20% by mass based on the total amount of the binder resin of the present invention.

<Method for producing gravure white ink>
The white gravure ink of the present invention can be obtained by mixing a zinc sulfide pigment with a binder resin and an organic solvent and then dispersing the mixture with a dispersing machine such as a bead mill.
For example, zinc sulfide is dispersed in an organic solvent using a polyurethane resin and vinyl chloride-vinyl acetate copolymer resin using a disperser, and the obtained pigment dispersion is mixed with other resins, various additives, organic solvents, etc. can be manufactured by Commonly used dispersing machines, such as roller mills, ball mills, pebble mills, attritors and sand mills, can be used. The particle size distribution of the pigment in the pigment dispersion is adjusted by appropriately adjusting the size of the grinding media of the disperser, the filling rate of the grinding media, the dispersion processing time, the ejection speed of the pigment dispersion, the viscosity of the pigment dispersion, and the like. be able to. A sand mill is preferably used as the disperser. Further, the gravure white ink of the present invention preferably has a viscosity of 40 to 600 mPa·s.

<Printing with gravure white ink>
(gravure version)
The gravure white ink in the present invention is printed using a gravure plate. In the present invention, the gravure plate is made of metal and has a cylindrical shape. There are no restrictions on the use of engraving and laser, and settings can be made arbitrarily according to the pattern. A line number of 100 to 300 lines/inch is appropriately used, and the higher the number of lines, the higher the precision of printing.
(Printer)
A printing machine equipped with the above-mentioned gravure plate can be suitably used as the printing machine. Normally, a printing unit is installed for each color, and each unit is equipped with a doctor blade that scrapes off the ink while the gravure plate rotates. be taken. A furnisher roll can optionally be used for gravure printing. Each unit also has a drying oven through which the printed substrate is dried. The drying temperature is usually about 40-60°C.

<Base material 1>
The gravure white ink of the present invention is printed on the base material 1 or on the surface or the back surface of the base material 1 of the laminate including the base material 1 and the base material 2 to form a printed matter.
Substrates to which the white gravure ink of the present invention can be applied include polyethylene, polypropylene and other polyolefin substrates, polycarbonate substrates, polyester substrates (polyethylene terephthalate, polylactic acid, etc.), polystyrene substrates, AS resins, ABS resins, and the like. Polystyrene-based resin, polyamide base material, polyvinyl chloride base material, polyvinylidene chloride base material, cellophane base material, paper base material, aluminum foil base material, etc., or film-like or sheet-like materials made of these composite materials there is something Among them, a polyester base material and a polyamide base material having a high glass transition temperature are preferably used.

The base material may be subjected to vapor deposition coating treatment such as metal oxide on the surface and/or coating treatment such as polyvinyl alcohol. For example, GL- Examples include AE and IB-PET-PXB manufactured by Dai Nippon Printing Co., Ltd. Further, if necessary, those treated with additives such as antistatic agents and ultraviolet inhibitors, and those treated with corona treatment or low-temperature plasma treatment on the surface of the base material can also be used.

<Base material 2>
Substrate 2 may be the same as substrate 1 and may be the same or different. A thermoplastic substrate (sometimes referred to as a sealant) is preferable, and an unstretched polyethylene substrate, an unstretched polypropylene substrate, an unstretched polyester substrate, or the like is preferable.

<Laminate>
It is also possible to produce a laminate using the printed material. Such a laminate is a laminate having at least the base material 1, the printed layer, and the base material 2 in this order. It is preferable to use a laminate having at least a base material 1, a printed layer, an adhesive layer, and a base material 2 in this order.
The laminate of the present invention is obtained by providing an adhesive layer on a printed layer of a printed material printed with gravure white ink, and bonding (laminating) the base material 2 together. A typical example of lamination processing is a dry lamination method or the like. The dry lamination method is a method in which an adhesive is applied onto a printed layer of a printed material, dried, and laminated by thermocompression bonding with a sealant.

<Adhesive layer>
The adhesive layer is obtained by applying an adhesive and drying it. As the adhesive, a two-liquid type adhesive comprising a mixture of a polyol and an isocyanate curing agent is suitable, and examples of the polyol include polyester-based and polyether-based adhesives. Specific examples include TM-250HV/CAT-RT86L-60, TM-550/CAT-RT37, TM-314/CAT-14B manufactured by Toyo-Morton Co., Ltd.

EXAMPLES The present invention will be described in detail below with reference to Examples, but the present invention is not limited to these Examples. Parts and % in the present invention represent parts by mass and % by mass unless otherwise specified. Examples 1 and 2 are Reference Examples 1 and 2.

(hydroxyl value)
It was obtained according to JIS K0070.
(acid value)
It was obtained according to JIS K0070.
(amine value)
The amine value was obtained in mg of potassium hydroxide equivalent to the equivalent of hydrochloric acid required to neutralize the amino groups contained in 1 g of the resin according to JIS K0070 according to the following method.
0.5 to 2 g of the sample was accurately weighed (sample solid content: Sg). 50 mL of a mixed solution of methanol/methyl ethyl ketone=60/40 (mass ratio) was added to the accurately weighed sample to dissolve the sample. Bromophenol blue was added to the resulting solution as an indicator, and the resulting solution was titrated with a 0.2 mol/L ethanolic hydrochloric acid solution (potency: f). The point at which the color of the solution changed from green to yellow was defined as the end point, and the titration amount (AmL) at this time was used to determine the amine value by the following (formula 2).
(Formula 2) Amine value = (A x f x 0.2 x 56.108) / S [mgKOH/g]

(Weight average molecular weight)
The weight-average molecular weight was obtained by measuring the molecular weight distribution using a GPC (gel permeation chromatography) device (HLC-8220 manufactured by Tosoh Corporation) and obtaining the converted molecular weight using polystyrene as a standard substance. Measurement conditions are shown below.
Column: The following columns were connected in series and used.
TSKgel SuperAW2500 manufactured by Tosoh Corporation
TSKgel SuperAW3000 manufactured by Tosoh Corporation
TSKgel SuperAW4000 manufactured by Tosoh Corporation
TSKgel guard column SuperAWH manufactured by Tosoh Corporation
Detector: RI (differential refractometer)
Measurement conditions: Column temperature 40°C
Eluent: Tetrahydrofuran Flow rate: 1.0 mL/min (softening point)
The softening point of the resin was obtained according to the method described in JISK5902.

(Average particle size)
The average particle size of the pigments used below was determined according to the laser diffraction method. As a measuring instrument, Microtrac MT3000II was used.

[Synthesis Example 1] (Polyurethane resin A solution)
257.86 parts of poly(1,2-propylene glycol) having a number average molecular weight of 2000 (hydroxyl value of 56.1 mgKOH/g) was added to a four-necked flask equipped with a stirrer, thermometer, reflux condenser and nitrogen gas inlet tube. 18.01 parts of isophorone diisocyanate, 20.27 parts of diphenylmethane diisocyanate, 0.03 parts of tin (II) 2-ethylhexanoate, and 200 parts of ethyl acetate were charged and reacted at 90° C. for 3 hours under a stream of nitrogen to give a terminal isocyanate pre-precipitate. 496.14 parts of a polymer solution were obtained. Then, a mixture of 3.86 parts of isophoronediamine, 280 parts of isopropyl alcohol and 220 parts of ethyl acetate is gradually added to the resulting isocyanate-terminated prepolymer solution at room temperature, followed by reaction at 50° C. for 1 hour, A polyurethane resin A solution having a solid content of 30.0%, a weight average molecular weight of 78000 and an amine value of 3.0 mgKOH/g was obtained.

(Example 1) [Preparation of white gravure ink S1]
40 parts of zinc sulfide 1 (zinc sulfide treated with an amine compound, average particle size: 0.3 μm, Mohs hardness: 4, bulk density: 1.6 L/kg, oil absorption: 14 g/100 g), polyurethane resin A solution (solid content: 30% ) and 26 parts of n-propyl acetate (NPAC)/isopropanol (IPA) = 70/30 as an organic solvent were mixed with a disper for 10 minutes, then dispersed with a bead mill (γ mill) for 20 minutes, and gravure A white ink S1 was obtained.

(Gravure printing with gravure white ink S1)
For gravure printing, 100 parts of the white gravure ink S1 and 50 parts of a mixed solvent (methyl ethyl ketone:n-propyl acetate:isopropyl alcohol=30:40:30) were mixed and diluted. Next, using a Helio 175-line solid plate (plate type compressed, 100% solid pattern), the corona-treated surface of a corona-treated OPP film (FOR #20, manufactured by Futamura Chemical Co., Ltd., film thickness 20 μm) was printed at a speed of 100 m/min at an oven drying temperature. Gravure printing was performed at 60° C. to obtain a printed material.

(Examples 2 to 12) [Preparation of white gravure inks S2 to S12]
Gravure white inks S2 to S12 were obtained in the same manner as in Example 1 except that the pigments and resin solutions shown in Table 1 were used. After that, gravure printing was performed in the same manner as in Example 1 to obtain prints of white gravure inks S2 to S12. The pigments and resin solutions in Table 1 are shown below.
<Pigment>
・Zinc sulfide 2: Average particle size: 0.35 μm, Mohs hardness: 3, bulk density: 2.4 L/kg, oil absorption: 14 g/100 g No surface treatment ・Titanium oxide: Average particle size: 0.25 μm, Mohs hardness: 7.5 With surface treatment (manufactured by Tayca, product name Titanix JR806 surface treatment: aluminum hydroxide, silica)

<Polyamide resin solution>
30 parts of a polyamide resin having a softening point of 116 ° C. and a weight average molecular weight of 4000 containing 50% by mass or more of structural units derived from dimer acid is mixed and dissolved in 50 parts of methylcyclohexane and 20 parts of isopropyl alcohol to obtain a solid content of 30%. A polyamide resin solution was obtained.
<Cellulose resin solution>
30 parts of nitrocellulose having a weight-average molecular weight of 40,000 and a nitrogen content of 12% by mass was mixed and dissolved in 20 parts of ethyl acetate, 20 parts of isopropyl alcohol, and 30 parts of methylcyclohexane to obtain a nitrocellulose resin solution with a solid content of 30%. .
<Vinyl chloride-vinyl acetate copolymer resin solution>
30 parts of vinyl chloride-vinyl acetate copolymer resin (manufactured by Nissin Chemical Co., Ltd., product name Solbin TA5R) was mixed and dissolved in 70 parts of ethyl acetate to obtain a vinyl chloride-vinyl acetate copolymer resin solution with a solid content of 30%. . Solbin TA5R has a hydroxyl value of 140 mgKOH/g and a weight average molecular weight of 50,000.

(Comparative Example 1) [Preparation of ink T1]
40 parts of zinc sulfide 3 (zinc sulfide average particle size 10 μm manufactured by Osaki Kogyo Co., Ltd.), 24 parts of polyurethane resin A solution (solid content 30%), and 10 parts of vinyl chloride-vinyl acetate copolymer resin solution (solid content 30%) 26 parts of n-propyl acetate (NPAC)/isopropanol (IPA) = 70/30 as an organic solvent were added and mixed for 10 minutes in a bead mill to obtain white gravure ink T1. Furthermore, a printed matter was obtained by the method described in Example 1.

(Comparative Examples 2 and 3) [Preparation of Inks T2 and T3]
Gravure white inks T2 and T3 were obtained in the same manner as in Comparative Example 1 except that the pigments and resin solutions shown in Table 2 were used. Furthermore, a printed matter was obtained by the method described in Example 1.

[Characteristic evaluation]
Using the white gravure inks S1 to S12 obtained in Examples 1 to 12, the inks T1 to T3 obtained in Comparative Examples, and their prints, the following characteristics were evaluated.

(whiteness)
Using a spectrophotometer (X-Rite eXact) for the printed layer of each printed matter obtained above, measure the L value of the printed surface under the conditions of a light source of D50, a 2-degree field of view, and density status E. bottom. Due to the black backing (measured on a black backing paper), a high L value means high hiding power and whiteness.
(Evaluation criteria)
A: L value is 75 or more (good)
B: L value is 65 or more and less than 75 (acceptable)
C: L value is less than 65 (defective)

(Plate fogging evaluation and doctor streak evaluation)
An impression cylinder made of NBR (nitrile butadiene rubber) with a rubber hardness of 80 Hs, a ceramic plated doctor blade with a cutting edge thickness of 60 μm (base material thickness of 40 μm, one side ceramic layer thickness of 10 μm), Toyo FPP Co., Ltd. chromium hardness of 1050 Hv. A white diluted printing ink was set on a gravure printing machine manufactured by Fuji Machine Industry Co., Ltd. with an electronic engraving plate (stylus angle of 120 degrees, 200 lines/inch), and idling was performed 60 times at a doctor pressure of 2 kg/cm ² and a rotation speed of 200 m/min. The area of the fogging portion due to the ink on the plate was used to evaluate the plate fogging property, and the streak-like defect on the plate was evaluated.
(Plate fogging: evaluation criteria)
A: No plate fogging was observed on the plate, or it was observed in less than 5% (good)
B: Plate fogging was observed in an area of 5% or more and less than 10% on the plate (acceptable)
C: Plate fogging was observed in an area of 10% or more on the plate (defective)
(Doctor Suzy: Evaluation Criteria)
A: Doctor streaks were not seen on the plate (good)
B: One or two thin doctor streaks were observed on the plate (acceptable)
C: Many doctor streaks were observed on the plate (defective)

(Ink stability (stability over time))
The gravure white inks prepared in the above Examples and Comparative Examples were placed in a closed container and allowed to stand in an oven at 40° C. for 14 days to confirm stability over time. After standing, the sedimentation property was evaluated under the conditions of 25° C. according to the criteria described below.
(Evaluation criteria)
A: No sedimentation of the pigment is observed at the bottom of the container when probed with a spoon.
B: A slight sedimentation of the pigment is observed at the bottom of the container when probed with a spoon, but it returns to its original state upon stirring.
C: A large amount of pigment sedimentation/or hard sedimentation of pigment at the bottom of the container when probed with a spoon.

As a result of the above examination, it was possible to provide a gravure ink which is excellent in ink stability, whiteness, and printability. Furthermore, the effect of improving the stability of the ink over time was exhibited.

The gravure ink of the present invention can be applied not only to the fields of flexible packaging lamination and surface printing, but also to flexographic ink printing.

Claims (5)

A gravure or flexographic white ink containing a pigment containing a zinc sulfide pigment and a binder resin, wherein the gravure or flexographic white ink satisfies the following (1) to (3) .
(1) The zinc sulfide pigment has an average particle size of 100-500 nm and a Mohs hardness of 1-6.
(2) 10 to 50% by mass of zinc sulfide pigment is contained in the total mass of the ink;
(3) The binder resin contains polyurethane resin and vinyl chloride-vinyl acetate copolymer resin, or polyamide resin and cellulose resin . A gravure or flexographic white ink according to claim 1, wherein the zinc sulfide pigment has a bulk density of 1-3 L/kg. 3. The gravure or flexographic white ink according to claim 1 , further comprising a titanium oxide pigment, wherein the weight ratio of the zinc sulfide pigment and the titanium oxide pigment is 90:10-10-90. 4. The gravure or flexographic white ink according to claim 1 , wherein the zinc sulfide pigment is surface-treated with an amine compound. A printed matter having a print layer formed of the gravure or flexographic white ink according to any one of claims 1 to 4 on a substrate 1.