AU2018344119B2

AU2018344119B2 - Electron beam-curable water-based flexo ink for surface printing and boilable/retort pouch using same

Info

Publication number: AU2018344119B2
Application number: AU2018344119A
Authority: AU
Inventors: Tsutomu Haruyama; Toshinori Ishibashi; Shigeki Itou; Nobuo SAWATARI
Original assignee: DIC Graphics Corp
Current assignee: DIC Graphics Corp
Priority date: 2017-10-02
Filing date: 2018-09-25
Publication date: 2020-10-01
Anticipated expiration: 2038-09-25
Also published as: CN111108159B; AU2018344119A1; JP6557799B1; CN111108159A; AU2018344119B9; WO2019069736A1; JPWO2019069736A1

Abstract

The present invention addresses the problem of providing a boilable retort pouch that is surface printed using an electron beam-curable water-based flexo ink for surface printing on the outside of the pouch container, wherein the amount of VOC in the ink is almost 0% and the ink has an excellent abrasion resistance and an excellent boilability and retortability. The electron beam-curable water-based flexo ink for surface printing contains a water-based resin (X), an ethylenic double bond-bearing electron beam-curable compound (Y), a pigment, and water, and is characterized in that the mass ratio between the solids fraction of the water-based resin (X) and the solids fraction of the ethylenic double bond-bearing electron beam-curable compound (Y) is within the range of (X)/(Y) = 5/100 to 400/100.

Description

DESCRIPTION

Title of Invention: ELECTRON BEAM-CURABLE WATER-BASED FLEXO

INK FOR SURFACE PRINTING AND BOILABLE/RETORT POUCH USING SAME

Technical Field

[0001]

The present invention relates to an exclusively

surface-printing water-based flexo ink that can be used for

water-based flexography equipped with electron beam-curable

equipment, and to a boilable/retort pouch made therewith.

Background Art

[0002]

Water-based flexography has been widely used to give

esthetics and functionality to printed articles.

In recent years, changes in lifestyle in recent years,

such as increases in the number of double-income families

and the number of one-person households, have caused the

consumption of food pouches, including gas-filled pouches

for snacks packaging, heat-resistant boilable pouches, and

heat- and pressure-resistant retort pouches, in particular

the consumption of boilable/retort food pouches, to increase

year by year.

Examples of boilable/retort pouches include packaging

for solid and liquid foods such as curries, hamburgers,

pasta sauces, soups, and toppings for rice bowls. Boilable pouches are subjected to heating, for example at temperatures of about 90°C to 98°C for about 30 to 60 minutes. Retort pouches are subjected to heating and pressurization, for example heating at temperatures of about

110°C to 130°C for about 20 to 60 minutes under pressure.

Inks for boilable/retort pouches therefore are required

to withstand the above heat and pressure tests and also to

have durability, such as abrasion resistance to prevent the

print from being damaged during transportation/storage.

Currently available boilable/retort pouches are generally

made using laminate packaging, i.e., a laminate of materials

back-printed with solvent inks and joined together using a

solvent adhesive, but as people are becoming more conscious

about safety to food and about the environment, expectations

are emerging for a turn to packaging materials with a safer

and less eco-harmful configuration.

[0003]

To address such demands, packaging materials made with

a water-based ink and a solventless adhesive have been

proposed. The fact, however, is that a water-based ink,

made using hydrophilic raw materials, and a solventless

adhesive fail to achieve sufficient adhesive strength and

cannot supersede the known configuration of a solvent ink/a

solvent adhesive.

Moreover, whatever the combination is, i.e., whether the ink is water-based or solvent-based and whether the adhesive is solvent-based or solventless, lamination is required after back printing to ensure the durability, such as abrasion resistance, of the ink. This means an aging step after lamination is essential, and the printed material cannot proceed to processing and filling steps immediately.

The known, back-printed boilable/retort packaging has their

limitations in terms of expediting delivery to customers.

[0004]

Inventions have been made that indicate high energy

beam-curable water-based compositions made up of water and a

water-soluble compound containing an a,3-ethylenic

unsaturated radiation-polymerizable double bond, but these

are by no means sufficient in terms of abrasion resistance

and boilability/retortability, which is deemed essential for

retort pouches (e.g., PTL 1 to 3).

Citation List

Patent Literature

[00051

PTL 1: Japanese Unexamined Patent Application

Publication No. 2003-147001

PTL 2: Japanese Unexamined Patent Application

Publication No. 2003-147230

PTL 3: Japanese Unexamined Patent Application

Publication No. 2008-150610

[0005A]

Any discussion of documents, acts, materials, devices,

articles or the like which has been included in the present

specification is not to be taken as an admission that any or

all of these matters form part of the prior art base or were

common general knowledge in the field relevant to the

present disclosure as it existed before the priority date of

each of the appended claims.

Summary of Invention

[0005B]

Throughout this specification the word "comprise", or

variations such as "comprises" or "comprising", will be

understood to imply the inclusion of a stated element,

integer or step, or group of elements, integers or steps,

but not the exclusion of any other element, integer or step,

or group of elements, integers or steps.

- 4A

Technical Problem

[00061

The problem to be solved by the present invention is to

provide a boilable/retort pouch for which the ink contains

substantially 0% VOCs (Volatile Organic Compounds) and that

has been surface-printed on its outer container surface with

an electron beam-curable surface-printing water-based flexo

ink, which is superior in abrasion resistance and

boiling/retort suitability.

Solution to Problem

[0007]

After extensive research to solve the above problem,

the inventors have found that the problem can be solved by

adding a pigment and water to a resin and an electron beam

polymerizable compound especially preferred for the

formulation of exclusively surface-printing water-based

flexo inks that can be used for water-based flexography

equipped with electron beam-curable equipment. The present

invention was completed on the basis of these findings.

[00081

The present invention is a discovery of the fact that

even in water-based flexography, the use of an electron beam

(EB)-curable water-based ink, which is superior in

waterproofness, heat resistance, abrasion resistance, etc., for surface printing of boilable/retort pouches provides a solution to the above problem. That is, laminated printing paper is prepared in advance, and printing is done on the surface of the paper immediately after an order is placed.

Since an electron beam (EB)-curable water-based ink forms a

strong coating upon EB irradiation, the printed material can

proceed to filling and processing steps immediately after

the end of the printing step. This enables expedited

delivery of boilable/retort packaging to customers.

[0009]

That is, the present invention relates to an electron

beam-curable surface-printing water-based flexo ink that

contains a water-based resin (X), at least one electron

beam-polymerizable compound having an ethylenic double bond

(Y), at least one pigment, and water. The ratio by mass

between the solids content of the water-based resin (X) and

that of the electron beam-polymerizable compound having an

ethylenic double bond (Y) is in the range of (X)/(Y) = 5/100

to 400/100.

[0010]

The present invention also relates to an electron beam

curable surface-printing water-based flexo ink in which the

electron beam-polymerizable compound having an ethylenic

double bond (Y) is a water-soluble (meth)acrylic monomer

and/or a water-soluble (meth)acrylic oligomer.

[0011]

The present invention also relates to an electron beam

curable surface-printing water-based flexo ink in which the

electron beam-polymerizable compound having an ethylenic

double bond (Y) is polyethylene glycol di(meth)acrylate.

[0012]

The present invention also relates to an electron beam

curable surface-printing water-based flexo ink in which the

water-based resin (X) is a nonreactive water-based urethane

resin.

[00131

The present invention also relates to an electron beam

curable surface-printing water-based flexo ink in which the

energy intensity of the electron beam is between 30,000 and

300,000 eV, and the irradiation dose of the electron beam is

between 5 and 100 kGy.m/min. (kilogray)

[0014]

The present invention also relates to a printed article

that includes a plastic film and an electron beam-curable

surface-printing water-based flexo ink as described above

applied thereto using a flexographic printer.

[0015]

The present invention, moreover, relates to a

multilayer material that includes the resulting printed

article and a substrate laminated together using a lamination adhesive and is suitable particularly for use in, for example, boilable pouches and retort pouches, which need to have heat resistance and waterproofness.

Advantageous Effects of Invention

[0016]

The electron beam-curable surface-printing water-based

flexo ink according to the present invention contains 0%

VOCs and, when used for printing on the outer container

surface of a retort pouch, gives a boilable/retort pouch

superior in boiling/retort suitability, such as abrasion

resistance, waterproofness, and heat resistance.

Description of Embodiments

[00171

An electron beam-curable surface-printing water-based

flexo ink according to the present invention is an electron

beam-curable surface-printing water-based flexo ink that

contains a water-based resin (X), at least one electron

beam-polymerizable compound having an ethylenic double bond

(Y), at least one pigment, and water. The ratio by mass

between the solids content of the water-based resin (X) and

that of the electron beam-polymerizable compound having an

ethylenic double bond (Y) is in the range of (X)/(Y) = 5/100

to 400/100.

[0018]

Here is described the simplest layer structure of retort-pouch packaging.

The best-known layer structure in the related art is a

composite film, for example obtained by joining aluminum

foil to substrate polypropylene film using an adhesive and

then joining the aluminum foil to polyethylene terephthalate

(hereinafter also referred to as PET) film.

If the composite film has a print layer, the order is

usually PET film/a solvent-based back-printing ink layer/an

adhesive layer (aging required)/an aluminum foil or

deposited aluminum film layer/adhesive layer/polypropylene

substrate film, from the top layer (Hereinafter the layers

down to "PET film/a solvent-based back-printing ink layer"

may be referred to as the upper layers, and the layers down

to "an aluminum foil or deposited aluminum film layer/an

adhesive layer/polypropylene substrate film" may be referred

to as the lower layers.), and the composite film is produced

typically by back-printing on PET film using a solvent-based

back-printing ink, then applying an adhesive, and joining

the workpiece and aluminum foil or deposited aluminum film

together. A highly functional film available as an

integrated form of the lower layers, i.e., "an aluminum foil

or deposited aluminum film layer/an adhesive

layer/polypropylene substrate film," may occasionally be

used. The polypropylene substrate film in the lower layers

is not essential and may be replaced with another olefin film.

A typical processing procedure is: After back printing

with a solvent-based back-printing ink, an adhesive is

applied, the workpiece is laminated with the other necessary

film(s), the laminate is optionally aged to give a composite

film, and the composite film is shaped into a bag to give a

retort-pouch package. Filling step it with its content will

make it retort-pouch packaging.

[0019]

The electron beam-curable surface-printing water-based

flexo ink according to the present invention is an

exclusively surface-printing water-based flexo ink that can

be used in the layer structure formed by an electron beam

curable water-based ink layer/a PET film layer/an adhesive

layer/an aluminum foil or deposited aluminum film layer/an

adhesive layer/polypropylene substrate film, in order from

the top layer. This enables printing with an electron beam

curable water-based ink on the PET surface of a multilayer

film prepared beforehand as a laminate of the layers down to

"a PET film layer/an adhesive layer/an aluminum foil or

deposited aluminum film layer/an adhesive

layer/polypropylene substrate film."

[00201

If a solvent-based back-printing ink and an adhesive

are used as in the related art, the printing and lamination steps involve the emission of VOCs in drying steps. The combination of a water-based flexo ink and a solventless adhesive helps reduce VOC emissions but fails to achieve sufficient adhesive strength because the binder in the ink used is a water-based resin. Furthermore, whatever the types of the ink and adhesive, a packaging material made by back printing/lamination requires an aging step and therefore is time-consuming and is inferior in productivity.

In the present application, by contrast, printing can

be done on the surface of a multilayer film prepared

beforehand as a laminate of all layers excluding the print

layer and using an electron beam (EB)-curable surface

printing water-based ink, which is superior in

waterproofness, heat resistance, and abrasion resistance.

The process from printing to bag making and filling is

therefore significantly expedited compared with the known

production process for a packaging material, which has a

lamination step after back printing.

Besides the expedited delivery to customers and reduced

inventory owing to such a reduction in process time, the

present application can lead to a considerable amount of

cost-cutting by the use of fewer layers and volume

reduction. Furthermore, flexography helps achieve higher

productivity with its high-speed printing capability.

In addition, further coating the surface-print layer, to which the electron beam-curable surface-printing water based flexo ink has been placed, with an electron beam (EB) curable overprint varnish layer, for example using a roll coater, and then curing the varnish layer with an electron beam (EB) would help further improve characteristics such as abrasion resistance/surface glossiness.

[00211

The electron beam-curable surface-printing water-based

flexo ink according to the present invention is intended for

the application of surface printing on the outer container

surface of retort pouches. To combine abrasion resistance,

waterproofness, heat resistance, and other qualities

required as boiling/retort suitability, the ink contains a

water-based resin (X) as an essential ingredient.

Preferred examples of water-based resins (X) include

aqueous solutions of or dispersed (emulsions or dispersions

of) resins made from binder resins that are copolymers of

acrylic or methacrylic acid and its alkylate, styrene, etc.,

as primary monomer components, such as water-based acrylic

resins, water-based styrene-acrylic resins, water-based

styrene-maleic acid resins, water-based styrene-acrylic

maleic acid resins, water-based polyurethane resins, and

water-based polyester resins. The resin (X) can be

urethane-resin beads, such beads dispersed in an aqueous

solvent (Also referred to as a dispersion. Materials such as urethane-resin dispersions and aliphatic polyurethane dispersions are included), or a water-based aliphatic polyurethane dispersion. Of these resins, aqueous polyurethane resins are particularly preferred for the reasons of, for example, adhesion to substrates and suitability for long-run printing.

Moreover, for the reasons of the odor of the ink made

with it and migration as a packaging material, it is

preferred that the water-based resin (X) be a nonreactive

water-based urethane resin. It may be used in mixture with

a reactive water-based urethane resin having a

(meth)acryloyl group. The water-based resin (X) may be a

commercially available one. In that case, it is available

as a dispersion or emulsion of a water-based resin.

[00221

The electron beam-curable surface-printing water-based

flexo ink according to the present invention contains an

electron beam-polymerizable compound having an ethylenic

double bond (Y) as an essential ingredient. The electron

beam-polymerizable compound having an ethylenic double bond

can be a known electron beam-curable monomer or oligomer,

but preferably it is a water-soluble (meth)acrylic monomer

or water-soluble (meth)acrylic oligomer to ensure solubility

in water.

Specific examples of water-soluble (meth)acrylates include hydroxyethyl (meth)acrylate, hydroxypropyl

(meth)acrylate, hydroxybutyl (meth)acrylate, polyethylene

glycol (meth)acrylate, methoxypolyethylene glycol

(meth)acrylate, N-(2-hydroxyethyl)acrylamide (abbreviation:

HEAA), N-(2-hydroxyethyl)methacrylamide, N-(2

hydroxymethyl)acrylamide, N-(2-hydroxymethyl)methacrylamide,

acryloylmorpholine, methylolacrylamide, dimethylacrylamide,

methoxymethylacrylamide, diethylacrylamide,

isopropylacrylamide, and polyethylene glycol

di(meth)acrylate, but are not limited to these.

[00231

Examples of water-soluble (meth)acrylic oligomers

include CN549, CN131, CN131B, CN2285, CN 3100, CN3105,

CN132, CN133, and CN 132 (Sartomer), Ebecryll40, Ebecryl

1140, Ebecryl 40, Ebecryl 3200, Ebecryl 3201, and Ebecryl

3212 (Cytec Industries), PHOTOMER 3660, PHOTOMER 5006F,

PHOTOMER 5429, and PHOTOMER 5429F (Cognis), and LAROMER PO

33F, LAROMER PO 43F, LAROMER PO 94F, LAROMER UO 35D, LAROMER

PA 9039V, LAROMER PO 9026V, LAROMER 8996, LAROMER 8765, and

LAROMER 8986 (BASF).

Water-soluble (meth)acrylic monomers and water-soluble

(meth)acrylic oligomers may be used alone or in mixture. In

particular, polyethylene glycol di(meth)acrylate is

preferred.

[0024]

In the electron beam-curable surface-printing water

based flexo ink according to the present invention, the

ratio by mass between the solids content of the water-based

resin (X) and that of the electron beam-polymerizable

compound having an ethylenic double bond (Y) needs to be in

the range of (X)/(Y) = 5/100 to 400/100.

More desirably, (X)/ (Y) = 7/100 to 250/100. Even more

desirably, the ratio is in the range of (X)/(Y) = 7/100 to

/100. The most desirably, the ratio is in the range of

(X)/(Y) = 7/100 to 25/100.

Regarding this ratio by mass, water-based resins are

effective in imparting flexibility to the ink coat

irradiated with an electron beam and improving the coat's

adhesion to the substrate, but if the proportion of the

water-based resin component is high, concern tends to be

high about incomplete curing, poor abrasion resistance, poor

heat resistance, poor waterproofness, etc., as a result of a

low concentration of double bonds in the ink paint.

If the water-based resin (X) is a commercially

available one, it is a dispersion or emulsion of a water

based resin in most cases. In this case, the dry solids

content of the dispersion or emulsion of a water-based resin

is used.

[00251

Examples of pigments used in the electron beam-curable surface-printing water-based flexo ink according to the present invention include organic or inorganic pigments and dyes used in ordinary inks, paints, recording agents, and the like.

[0026]

The organic pigments include azo, phthalocyanine,

anthraquinone, perylene, perinone, quinacridone, thioindigo,

dioxazine, isoindolinone, quinophthalone, azomethine-azo,

diketopyrrolopyrrole, isoindoline, and other pigments.

[0027]

The inorganic pigments include carbon black, titanium

oxide, zinc oxide, zinc sulfide, barium sulfate, calcium

carbonate, chromium oxide, silica, red iron oxide, aluminum,

mica, and others. Besides these, shiny pigments that are

glass flakes or lump flakes as the base material with a

coating of metal or metal oxide thereon (Metashine; Nippon

Sheet Glass Co., Ltd.) can be used. It is preferred,

because of cost and tinctorial strength, to use titanium

oxide for white ink, carbon black for black ink, aluminum

for gold or silver ink, and mica for pearl ink. Aluminum is

in powder or paste form, but preferably it is used in paste

form for ease of handling and safety reasons. Whether to

use leafing or non-leafing aluminum is selected as

appropriate in light of brightness felt and density.

As for the total of the pigment(s), it is preferred that the pigment(s) be contained in an amount sufficient to ensure the density and tinctorial strength of the ink, i.e., at a percentage of 1% to 50% by mass of the total weight of the ink. Colorants may be used alone or as a combination of two or more.

[0028]

The electron beam-curable surface-printing water-based

flexo ink according to the present invention can further

contain a solvent and other appropriate auxiliaries.

The solvent can be water alone or a water-miscible

organic solvent. Examples of organic solvents include

alcohols, such as methyl alcohol, ethyl alcohol, isopropyl

alcohol, and n-propyl alcohol, polyhydric alcohols, such as

propylene glycol and glycerol, and ethers, such as propylene

glycol monomethyl ether, propylene glycol monoethyl ether,

propylene glycol mono-n-propyl ether, and ethyl carbitol.

[0029]

As for auxiliary ingredients other than solvents, it is

possible to optionally use, for example, waxes and aliphatic

amides for imparting abrasion resistance, sliding

smoothness, and other qualities, such as paraffin waxes,

polyethylene waxes, PTFE waxes, and carnauba wax and oleic

acid amide, stearic acid amide, and erucic acid amide,

silicone or non-silicone antifoams for controlling foaming

during printing, dispersants that improve the wetting of the pigment, and wetting agents that improve wettability on the substrate.

[0030]

The electron beam-curable surface-printing water-based

flexo ink relating to the present invention is produced

using, for example, equipment that is common in the

production of gravure and flexographic inks, such as an

Eiger mill, a sand mill, a gamma mill, or an attritor.

For the electron beam-curable surface-printing water

based flexo ink according to the present invention, its

viscosity only needs to be between 5 and 35 seconds, more

preferably between 8 and 20 seconds, at 250C when a Rigo

Zahn cup #5 is used. In millipascal-seconds, the viscosity

only needs to be in the range of 100 to 1000 (mPa-s), more

preferably in the range of 180 to 600 (mPa-s), at 25°C.

The surface tension at 250C of the electron beam-curable

surface-printing water-based flexo ink according to the

present invention is preferably between 25 and 50 mN/m, and

it would be more preferred that it be between 33 and 43

mN/m. The wettability of the ink on the substrate, such as

film, improves with decreasing surface tension of the ink,

but a surface tension lower than 25 mN/m tends to cause a

type of dirt on the print surface called dot bridging as a

result of the ink spreading to an extent that adjacent dots

in halftone-dot areas join together. With a surface tension higher than 50 mN/m, however, the wettability of the ink on the substrate, such as film, is likely to be low; such a surface tension therefore tends to cause repellence.

[0031]

The electron beam-curable surface-printing water-based

flexo ink according to the present invention is superior in

adhesion to different film substrates and can be used for

printing on thermoplastic resin films and plastic products.

Examples of substrate films include films of

thermoplastic resins, such as polyamide resins, e.g., nylon

(Ny) 6, nylon 66, and nylon 46, polyester resins, e.g., PET,

polyethylene naphthalate, polytrimethylene terephthalate,

polytrimethylene naphthalate, polybutylene terephthalate,

and polybutylene naphthalate, polyhydroxycarboxylic acids,

e.g., polylactic acid, biodegradable resins, typified by

aliphatic polyester resins, e.g., poly(ethylene succinate)

and poly(butylene succinate), polyolefin resins, e.g., PP

and polyethylene, polyimide resins, polyarylate resins, and

mixtures thereof as well as a stack of such films, but in

particular, polyester, polyamide, polyethylene, and

polypropylene films are suitable for use. These substrate

films may be non-oriented films or oriented films and are

not limited to a particular production process. The

thickness of the substrate film is not critical either, but

usually it only needs to be in the range of 1 to 500 pm.

The print surface of the substrate film has preferably

been treated with a corona discharge. Silica or alumina,

for example, may have been deposited.

[0032]

The electron beam-curable surface-printing water-based

flexo ink according to the present invention is an

exclusively surface-printing water-based flexo ink that can

be used in layer structures formed at least by an electron

beam-curable water-based ink layer/a film layer/an adhesive

layer/aluminum foil/an adhesive layer/substrate film, in

order from the top layer, and the two upper layers, "an

electron beam-curable water-based ink layer/a film layer,"

correspond to a surface-printed material produced by film

printing. Placing an additional "electron beam-curable

water-based OP varnish layer" on top of the "electron beam

curable water-based ink layer" helps improve the abrasion

resistance and glossiness of the surface of the printed

material. The lower layers, aluminum/an adhesive

layer/substrate film, may be, for example, a substrate film

that has been coated with deposited aluminum in advance or a

highly functional film that has a multilayer structure.

[0033]

For the electron beam-curable surface-printing water

based flexo ink according to the present invention, an

electron bearm (also referred to as EB) beam, or electrons artificially propelled in an accelerator, is used to cure a coating of the ink on the surface of a printed material produced by printing on a plastic film using a flexographic printer.

In EB curing, the applied layer of ink is formed

directly as an ink coat. With an EB-curable composition,

which contains no photoinitiator unlike ultraviolet curable,

the characteristics of the composition are reflected in

those of the ink coat as designed. Once completely

polymerized by EB curing, the ink coat is characteristically

odorless or of low odor, containing little or no low

molecular-weight component, such as a photoinitiator.

Additionally, the EB curing treatment seldom causes

thermal warping, creasing, deformation, etc., to thin film

because the impact of heat on the target of irradiation is

small. The EB curing treatment, moreover, provides high

speed processing at a line speed of several 10s to 400

meters per minute or faster, whereas the ultraviolet curing

treatment is not as effective if with limited generation of

heat. With an UV lamp, furthermore, the light source

inevitably ages and loses its luminous intensity with the

passage of service time. EB equipment, by contrast, always

maintains a constant output power through beam current

control.

Preferably, the energy intensity of the electron beam used is between 30,000 and 300,000 eV, and the irradiation dose of the electron beam is between 5 to 100 kGy-m/min.

(kilogray).

If the printed film is varnished, for example using a

roll coater, to place an additional "electron beam-curable

water-based OP varnish layer" on top of the "electron beam

curable water-based ink layer," the ink and OP varnish

layers

can be simultaneously electron beam-cured with the

electron beam.

EXAMPLES

[0034]

The following describes the present invention in detail

by examples and comparative examples. In the following, all

"parts" and "%" are by mass.

[0035]

(Electron Beam-Curable Surface-Printing Water-Based Flexo

Inks; Production Method)

Flexo inks according to the formulae in Table 1 were

adjusted as electron beam-curable surface-printing water

based flexo inks containing a water-based resin (X),

electron beam-polymerizable compound(s) having an ethylenic

double bond (Y), a pigment, and water.

To take ink 1 as an example, a DIC indigo pigment

concentrate (WFJ R507 color indigo concentrate, containing

% by mass phthalocyanine pigment in a dispersion medium),

a nonreactive urethane dispersion, an aliphatic epoxy

acrylate, (Laromar LR8765, BASF) polyethylene glycol

diacrylate, and an antifoam (BYK-019, BYK) were thoroughly

mixed by stirring in accordance with the numbers of parts

specified in Table 1. Then the viscosity was adjusted with

water to be 12 seconds (25°C) with a Zahn cup #5 (Rigo),

completing printing ink (ink 1). The amount of water is

"Balance" in the table.

[0036]

[Table 1]

Adjustment Examples Ink 1 Ink2 Ink 3 Ink 4 Ink 5 Pigment Indigo concentrate (DIC WFJ 35.0 35.0 35.0 35.0 R507 color indigo concentrate) Black concentrate (DIC WFJ 35.0 R805 black concentrate) Water-based resin Nonreactive urethane (X) dispersion 24.8 10.0 24.8 54.8 59.8 (Polyester urethane dispersion, amine-neutralized) Electron beam- Urethane acrylate polymerizable (Daicel water-based UV- 14.8 compound(s) having curable resin, 35% solids) an ethylenic double bond (Y) Aliphatic epoxy acrylate (Laromar LR8765, BASF) 20.0 20.0 10.0

Polyethylene glycol diacrylate 20.0 20.0 30.0 10.0 5.0 Additive Antifoam (BYK-019, BYK) 0.2 0.2 0.2 0.2 0.2 Water Balance Balance Balance Balance Balance Total (parts) 100.0 100.0 100.0 100.0 100.0

[0037]

In the table, abbreviations and similar forms of words

represent the following.

Water-based resin (X)

A nonreactive urethane dispersion (nonvolatile content,

39% by mass)

Electron beam-polymerizable compounds having an ethylenic

double bond (Y)

Urethane acrylate (a Daicel water-based UV-curable

resin, 35% solids)

An aliphatic epoxy acrylate (Laromar LR8765, BASF)

Polyethylene glycol diacrylate

Pigments

An indigo concentrate (DIC WFJ R507 color indigo

concentrate, containing 40% by mass phthalocyanine pigment

in a dispersion medium)

A black concentrate (DIC WFJ R805 black concentrate,

containing 40% by mass black-concentrate carbon black

[00381

(Printing Method)

A multilayer film for boilable/retort packaging had

been prepared beforehand as a laminate formed by "corona

treated polyethylene terephthalate (PET) film/an adhesive

layer/aluminum foil/an adhesive layer/polypropylene

substrate film," in order from the top layer, and surface printing was done with each of inks 1 to 5, obtained by the production method described above, using a CI 6-color flexographic printer (SOLOFLEX, Windmoeller & Hoelscher).

If an EB-curable OP varnish was applied by printing

after the surface printing, each ink of inks 1 to 5 as

described above was applied first, then a DIC EB-curable OP

varnish (WFJ M1000 varnish) was applied by printing, and the

ink and varnish were irradiated with an electron beam.

After printing, the film was immediately irradiated

with an electron beam with an energy intensity of 80,000 eV

at an irradiation dose of 60 kGy-m/min. (kilogray) using EB

equipment.

It should be noted that since the irradiation dose

varied with the pigment used in the ink, inks 1, 2, 4, and

, which were made with an indigo concentrate (DIC WFJ R507

color indigo concentrate), were cured with the anilox line

count (lines/cm) set to 315 and the cell volume (cm3 ) to

4.5. Table 2 also summarizes the anilox line count

(lines/cm) and cell volume (cm 3 ) used for the black

concentrate (DIC WFJ R805 black concentrate) and those for

the OP varnish, which contained no pigment.

A printed multilayer film for boilable/retort packaging

is hereinafter referred to as "a printed multilayer film."

[00391

[Table 2] (Table 2) Ink used Indigo concentrate Black concentrate OP varnish Anilox line count 315 315 197 (lines/cm) Cell volume (cm 3 ) 4.5 4.5 8.0

[0040]

[Test Item 1: Adhesion to a Substrate]

Nichiban 18-mm adhesive tape was stuck firmly to the

printed surface of the printed multilayer film, and then the

adhesive tape was quickly peeled off perpendicular to the

surface. The degree of detachment of the ink was graded

visually.

O: No detachment is observed

0: Very minor detachment is observed

A: Detachment is observed in part

x: The ink detaches in a considerable area

[0041]

[Test Item 2: Abrasion Resistance]

The printed surface of the printed multilayer film was

subjected to an abrasion test using a color fastness rubbing

tester (Daiei Kagaku Seiki Mfg.) under the conditions of a

load of 200 g and 100 cycles of rubbing. Abrasion

resistance was graded by the magnitude of damage to the

surface of the ink paint.

The test was conducted as a friction test between

portions of the printed surface.

0: There is no damage

0: There is very minor damage

A: Damage is observed in a considerable area

x: Damage is throughout the test portions

[0042]

[Test Item 3: Boiling Suitability]

The printed multilayer film was shaped into a pouch

with a size of 12 cm x 12 cm, and the pouch was filled with

g of simulated food, a mixture of vinegar, salad oil, and

meat sauce in a 1:1:1 ratio by weight, tightly sealed, and

boiled by immersing it in hot water at 98°C for 60 minutes.

Immediately after that, the printed multilayer film was

observed for any change in the condition of the print

thereon.

0: There is no change

0: The print has changed slightly

A: The print has changed in a considerable area

x: The entire print has changed

[0043]

[Test Item 4: Retort Suitability]

The printed multilayer film was shaped into a pouch

with a size of 120 mm x 120 mm, and the pouch was filled

with 40 g of simulated food, a mixture of vinegar, salad

oil, and meat sauce in a 1:1:1 ratio by weight, and tightly

sealed. The prepared pouch was subjected to steam retort sterilization at 120°C for 30 minutes, and then, immediately after that, the printed multilayer film was observed for any change in the condition of the print thereon.

O: There is no change

0: The print has changed slightly

A: The print has changed in a considerable area

x: The entire print has changed

[0044]

Table 3 summarizes the ink used, whether or not an EB

curable OP varnish layer was placed, the water content of

the ink, the amount of the nonreactive (non-electron-beam

curable) resin, the amount of the electron beam

polymerizable compound(s), the proportion of the nonreactive

resin to the amount of the electron beam-polymerizable

compound(s) as 100, the VOC content of the ink, and the

results of testing on a printed multilayer film for Examples

1 to 5 and Comparative Example 1. The numerical values in

Table 3 represent numbers of "parts" by mass.

[00451

[Table 3]

(Table 3) Examples Comparative 1 2 3 4 5 Example 1 Ink used Ink1 Ink2 Ink3 Ink3 Ink4 Ink 5 EB-curable OP varnish No No No Yes No No (DIC WFJM1000 varnish) Water content of the ink (wt%) 33.0 33.0 33.0 33.0 51.0 54.0 Water-based resin (X) 9.7 3.9 9.7 9.7 21.4 23.3 (amount of nonreactive resin) (wt%) Electron beam-polymerizable compound(s) (Y) Amount of the electron beam-polymerizable 40.0 49.3 40.0 40.0 10.0 5.0 compound(s) (wt%) Proportion of the nonreactive resin to the electron 24.25 7.91 24.25 24.25 214.0 466.0 beam-polymerizable compound(s) as 100 (XY) VOC content of the ink (wt%) 0 0 0 0 0 0 Adhesion to a substrate 0 A 0 0 G G Test Boiling suitability ( G G G A x results Retort suitability 0 0 G 0 A x

Abrasion resistance 0 0 0 ® A x

[00461

The electron beam-curable surface-printing water-based

flexo ink according to the present invention can be used

without considering its VOC content (%) and does not need

aging time after printing. An outer container surface of a

boilable/retort pouch printed with this ink is superior in

abrasion resistance and boiling/retort suitability.

Claims

[Claim 1]

An electron beam-curable surface-printing water-based

flexo ink comprising a water-based resin (X), at least one

electron beam-polymerizable compound having an ethylenic

double bond (Y), at least one pigment, and water, wherein

a ratio by mass between a solids content of the water

based resin (X) and a solids content of the electron beam

polymerizable compound having an ethylenic double bond (Y)

is in a range of (X)/(Y) = 5/100 to 400/100.
[Claim 2]

The electron beam-curable surface-printing water-based

flexo ink according to Claim 1, wherein the electron beam

polymerizable compound having an ethylenic double bond (Y)

is a water-soluble (meth)acrylic monomer and/or a water

soluble (meth)acrylic oligomer.
[Claim 3]

The electron beam-curable surface-printing water-based

flexo ink according to Claim 1 or 2, wherein the electron

beam-polymerizable compound having an ethylenic double bond

(Y) is polyethylene glycol di(meth)acrylate.
[Claim 4]

The electron beam-curable surface-printing water-based

flexo ink according to any one of Claims 1 to 3, wherein the

water-based resin (X) is a nonreactive water-based urethane

resin.
[Claim 5]

The electron beam-curable surface-printing water-based

flexo ink according to any one of Claims 1 to 4, wherein

energy intensity of the electron beam is between 30,000 and

300,000 eV, and an irradiation dose of the electron beam is

between 5 and 100 kGy.m/min. (kilogray)
[Claim 6]

A printed article comprising a plastic film and an

electron beam-curable surface-printing water-based flexo ink

according to any one of Claims 1 to 5 applied thereto using

a flexographic printer.
[Claim 7]

A multilayer material comprising a printed article

according to Claim 6 and a substrate laminated together

using a lamination adhesive.
[Claim 8]

A boilable pouch comprising a printed article according to Claim 6 and a substrate laminated together using a lamination adhesive.
[Claim 9]

A retort pouch comprising a printed article according

to Claim 6 and a substrate laminated together using a

lamination adhesive.