JP7596882B2 - Print surface protection film and multi-layer body, as well as packaging body and packaging article - Google Patents

Description

The present invention relates to a print surface protection film and a multilayer body, as well as a package and a packaged article.

Liquid toner is attracting attention as a technology for printing on container packaging for beverages, food, daily necessities, etc. Liquid toner is capable of producing color in a thinner film than conventional toners, and is known to be able to increase the resolution of printed images.

In order to impart chargeability to the liquid toner, a polymer having ionic groups is used as a material.
For example, Patent Document 1 proposes a liquid toner in which a pigment is added to a polymer having a maleic anhydride functional group and an ethylene methacrylic acid copolymer, and the resulting mixture is dispersed in a paraffin hydrocarbon fraction. This liquid toner exhibits excellent binding properties due to the interaction between the carboxyl group contained in the maleic anhydride and the hydroxyl group of the base paper.

Special Publication No. 2003-520997

However, printed matter obtained using liquid toner may deteriorate or deform in a humid and hot environment such as a retort, etc. Although water resistance can be improved by thermally laminating a protective film on the printed matter, the resistance to a high humidity and heat environment is insufficient.
Therefore, an object of the present invention is to provide a print surface protection film that is excellent in thermal lamination suitability and moist heat resistance.

The inventors conducted extensive research to achieve the above-mentioned objectives, and as a result, focused on solving the above-mentioned objectives and completed the present invention. That is, the gist of the present invention is as follows.

[1] Having at least a base layer and a sealant layer,
The base layer contains a thermoplastic resin (A) as a main component,
The print surface protection film, wherein the sealant layer is made of a cured product of a resin composition containing a cyclic ether group-containing conjugated diene polymer (B), and the crosslink density of the cured product is 1 mol/m3 or ^more and 3000 mol/m3 ^or less.
[2] The printing surface protection film described in [1] above, wherein the thickness of the substrate layer is 5 μm or more and 50 μm or less.
[3] The printing surface protection film according to [1] or [2] above, wherein the thickness of the sealant layer is 1 μm or more and 30 μm or less.
[4] The printing surface protection film according to any one of the above [1] to [3], wherein the thermoplastic resin (A) is at least one selected from the group consisting of polyester resins and polyolefin resins.
[5] The printing surface protection film according to any one of the above [1] to [4], wherein the cyclic ether group-containing conjugated diene polymer (B) contains an epoxy group and has an epoxy equivalent of 100 g/eq or more and 1500 g/eq or less.
[6] The printing surface protection film according to any one of the above [1] to [5], wherein the cyclic ether group-containing conjugated diene polymer (B) is a cyclic ether-modified conjugated diene polymer.
[7] The printing surface protection film according to the above [6], wherein the conjugated diene polymer is a polymer containing a structural unit derived from at least one of butadiene, isoprene, and chloroprene.
[8] The printing surface protection film according to any one of the above [1] to [7], wherein the resin composition contains a crosslinking agent.
[9] The printing surface protection film according to the above [8], wherein the crosslinking agent is a radical initiator.
[10] The printing surface protection film according to the above [9], wherein the radical initiator is an organic peroxide.
[11] The printing surface protection film according to any one of the above [1] to [10], which has a release layer on the opposite side of the sealant layer to the surface facing the substrate layer.
[12] A multilayer body comprising the printing surface protection film according to any one of [1] to [11] above and a printing layer, wherein the printing surface protection film is thermally laminated onto the printing layer.
[13] The multilayer body according to [12] above, wherein the printed layer is formed using a liquid toner.
[14] The multilayer body according to the above [13], wherein the liquid toner contains a carboxyl group-containing polymer.
[15] A packaging body comprising the multilayer body according to any one of [12] to [14] above.
[16] A packaged article packaged using the packaging body described in [15] above.

The print surface protection film proposed by this invention has excellent suitability for thermal lamination and resistance to moist heat.

The following describes in detail an embodiment of the present invention. However, the present invention is not limited to the embodiment described below.

<Printing surface protection film>
The print surface protection film of the present invention (hereinafter, sometimes referred to as "the film") has at least a base layer and a sealant layer. The sealant layer only needs to be provided on at least one surface of the base layer, and the sealant layer may be directly laminated on the surface of the base layer, or another layer may be appropriately provided between the sealant layer and the base layer.
The present film may have a release layer on the side of the sealant layer opposite to the surface facing the substrate layer.
The sealant layer may constitute the outermost surface of the film if no release layer is present, or may be in direct contact with the release layer if one is provided.
For the purpose of imparting further functionality, the film may have a multi-layer structure including at least one layer selected from a protective layer, an anti-reflection layer, an antibacterial layer, a smooth layer, a hard coat layer, etc. However, when the film has a multi-layer structure, it is preferable that the number of layers other than the substrate layer, the sealant layer, and the release layer is 5 or less from the viewpoint of transparency.

[Suitability for heat lamination]
The film has good thermal lamination suitability for printed matter.
The thermal lamination suitability in the present invention can be evaluated by laminating the present film and a printed material by passing them through heated nip rolls, and then measuring the peel strength.

[Moisture and heat resistance]
By thermally laminating this film onto printed matter, it is possible to improve the resistance to moist heat.
In the present invention, the moist heat resistance means that the film does not peel off from the printed matter even in a moist heat environment, and indicates retort resistance. More specifically, the sample obtained after thermally laminating the film and the printed matter is left in pressurized hot steam at 120° C. for 0.5 hours, and then the appearance is observed to evaluate the resistance.

[Thickness]
The thickness of the present film is preferably 6 μm to 80 μm, more preferably 8 μm to 60 μm, and even more preferably 10 μm to 40 μm. Note that the thickness of the present film does not include the release layer, if any.
When the thickness of the present film is 6 μm or more, the transportability and handling properties during thermal lamination are improved, whereas when the thickness is 80 μm or less, the transparency of the present film is good.

Each layer is explained below.

1. Substrate Layer The substrate layer in the present invention is mainly composed of a thermoplastic resin (A). The substrate layer in the present film is suitable for thermal lamination because it is mainly composed of a thermoplastic resin (A).
In the present invention, a "main component" refers to a component that accounts for 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and still more preferably 90% by mass or more (including 100% by mass) of all components constituting the layer.

[Thermoplastic resin (A)]
The thermoplastic resin (A) of the present invention is preferably a polyester resin or a polyolefin resin. When the base layer contains a polyester resin or a polyolefin resin, the moist heat resistance of the present film is improved.

Specific examples of polyester resins include thermoplastic polyester resins such as poly(ethylene glycol) terephthalate, poly(ethylene glycol) isophthalate, poly(ethylene glycol) succinate, poly(ethylene glycol) oxalate, poly(ethylene glycol) adipate, poly(butanediol) terephthalate, poly(hexanediol) terephthalate, poly(1,4-cyclohexanedimethanol) terephthalate, and copolymers thereof. These polyester resins can be used alone or in combination of two or more. The copolymers referred to here mean those in which a component other than the constituent components of each polymer is copolymerized in each polymer, and the same applies below. The copolymerization may be graft polymerization or the like.
Among the above, poly(ethylene glycol) terephthalate is preferred because it can reduce the stickiness and tackiness of the film and has excellent interlayer adhesion with the sealant layer and heat resistance.

Specific examples of polyolefin resins include polyethylene, polypropylene, polymethylpentene, and copolymers thereof such as poly(ethylene-vinyl acetate) copolymers and maleic acid-modified polypropylene. These polyolefin resins can be used alone or in combination of two or more.
Among the above, polypropylene is preferred because it can reduce the stickiness and tackiness of the film and has excellent interlayer adhesion with the sealant layer and heat resistance.

The base layer may be a single layer or may be a multi-layer. Even if it is a multi-layer, each layer may be mainly composed of a thermoplastic resin, and it is preferable to use a polyolefin resin or a polyester resin as the thermoplastic resin in each layer.
In the substrate layer, a polyolefin resin and a polyester resin may be used in combination. For example, a multi-layer substrate layer may have both a layer containing a polyolefin resin as a main component and a layer containing a polyester resin as a main component.

The base layer of the present invention may contain various additives such as a plasticizer, a curing agent, etc. in addition to the thermoplastic resin (A).
The substrate layer may be a non-stretched film, or a uniaxially or biaxially stretched film.

[Thickness]
The thickness of the substrate layer is preferably from 5 μm to 50 μm, more preferably from 7 μm to 40 μm, and further preferably from 8 μm to 30 μm.
When the thickness of the substrate layer is 5 μm or more, the transportability and handling properties during thermal lamination are good, whereas when the thickness is 50 μm or less, the transparency of the present film is good.

2. Sealant Layer The sealant layer in the present invention comprises a cured product of a resin composition containing the cyclic ether group-containing conjugated diene polymer (B).

[Resin composition]
The content of the cyclic ether group-containing conjugated diene polymer (B) in the resin composition constituting the sealant layer is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 99% by mass or less, and even more preferably 70% by mass or more and 98% by mass or less.
When the content of the cyclic ether group-containing conjugated diene polymer (B) is 50% by mass or more, the wet heat resistance is good, whereas when the content is 100% by mass or less, the winding property of the present film is good.

It is important that the cured product of the resin composition of the present invention is crosslinked. Therefore, the sealant layer contains a crosslinked product of the cyclic ether group-containing conjugated diene polymer (B).
When the sealant layer contains a crosslinked product of the cyclic ether group-containing conjugated diene polymer (B), when the sealant layer comes into contact with a printed surface formed by a liquid toner, the ionic groups of the liquid toner components react with the cyclic ether groups, improving the adhesion between the sealant layer and the printed matter and improving the moist heat resistance.
In addition, while typical thermoplastic resins become suddenly soft when they exceed their flow-start temperature, the crosslinked product of the cyclic ether group-containing conjugated diene polymer exhibits viscoelastic behavior with a wide rubber-like plateau after softening, and therefore has a wide temperature range in which it can be thermally laminated but does not flow. Therefore, when the sealant layer contains the crosslinked product of the cyclic ether group-containing conjugated diene polymer (B), it also has good thermal lamination suitability and heat resistance.
The degree of crosslinking can be measured by the crosslink density. The crosslink density of the cured product is 1 mol/m ³ or more and 3000 mol/m ³ or less, preferably 2 mol/m ³ or more and 2500 mol/m ^{3 or} less, more preferably 5 mol/m ³ or more and 2000 mol/m ³ or less, even more preferably 10 mol/m ³ or more and 1500 mol/m ³ or less, and particularly preferably 50 mol/m ³ or more and 1000 mol/m ³ or less. When the crosslink density is 1 mol/m ³ or more, the elastic modulus of the cured product is improved, so that it is difficult to flow, and the heat lamination property and moist heat resistance of the sealant layer are also good. When the crosslink density is 3000 mol/m ³ or less, the rubber-like plateau, which is the temperature range in which the cured product has moderate flexibility, is moderately wide, so that good heat lamination property of the sealant layer can be ensured.
The crosslink density of the cured product can be adjusted by appropriately selecting the type of cyclic ether group-containing conjugated diene polymer (B), the crosslinking agent, and the crosslinking conditions.

The crosslink density of the present invention can be determined by measuring the tensile storage modulus E' or shear storage modulus G' of the cured product constituting the sealant layer at 100° C. The tensile storage modulus E' or shear storage modulus G' may be measured from a measurement sample taken from the sealant layer of the print surface protection film.
However, when it is difficult to obtain a measurement sample, it is preferable to prepare a measurement sample of a cured product made of a resin composition equivalent to the resin composition constituting the sealant layer, and measure the tensile storage modulus E' or shear storage modulus G' of the measurement sample at 100°C as described below.
That is, when the resin composition before curing is solid or nearly solid and can be formed into a film to measure the tensile storage modulus, a film having a thickness of 80 μm is produced from the resin composition, which is then cured by heat treatment, and the tensile storage modulus E' is measured at 100° C. On the other hand, when the resin composition is nearly liquid and it is difficult to form into a film to measure the tensile storage modulus, a resin composition layer is formed on a release film, which is then cured by heat treatment, and the shear storage modulus G' is measured at 100° C.
The heat treatment for preparing the sample should be carried out under the same conditions as those for the heat treatment for actually curing the resin composition.
The tensile storage modulus E' can be measured using a dynamic viscoelasticity measuring device under conditions described in the Examples, for example. The shear storage modulus G' can be measured using a rheometer under conditions described in the Examples, for example.
The crosslink density can be calculated from the tensile storage modulus E' or the shear storage modulus G' at 100° C. using the following formula.
n = E'/3RT
E' = 3G'
n: Crosslinking density [mol/m ³ ]
E': tensile storage modulus [Pa], G': shear storage modulus [Pa]
R: gas constant [8.31 x J/mol K] T: absolute temperature [K]
When the thickness of the sealant layer in the print surface protection film is less than 80 μm, multiple sheets may be stacked to adjust the overall thickness to 80 μm or more, and then the tensile storage modulus E' or storage modulus G' at 100° C. may be measured.

[Cyclic Ether Group-Containing Conjugated Diene Polymer (B)]
The cyclic ether group-containing conjugated diene polymer (B) of the present invention preferably has at least one of an epoxy group and an oxetane group as the cyclic ether group, and more preferably has an epoxy group.
By having a highly reactive cyclic ether group such as an epoxy group or an oxetane group, the reactivity with the ionic groups of the liquid toner components is improved, and the moisture and heat resistance can be improved.

When the cyclic ether group-containing conjugated diene polymer (B) has an epoxy group, the epoxy equivalent is preferably from 100 g/eq to 1,500 g/eq, more preferably from 120 g/eq to 1,000 g/eq, even more preferably from 150 g/eq to 500 g/eq, and still more preferably from 180 g/eq to 300 g/eq.
When the epoxy equivalent is 100 g/eq or more, the thermal lamination suitability is good, whereas when the epoxy equivalent is 1500 g/eq or less, the moist heat resistance is good.
The epoxy equivalent in the present invention is measured in accordance with the potentiometric titration method of JIS K7236:2009.

The cyclic ether group-containing conjugated diene polymer (B) is preferably a cyclic ether modified conjugated diene polymer.
The conjugated diene polymer is preferably a polymer containing a structural unit derived from at least one of butadiene, isoprene, and chloroprene. Since the structural units derived from butadiene, isoprene, and chloroprene have double bonds in the molecular skeleton, crosslinking is possible when the polymer is a polymer of a monomer containing at least one of these.
The conjugated diene polymer may be a homopolymer of butadiene, isoprene or chloroprene, or may be a copolymer. When the conjugated diene polymer is a copolymer, it may be a copolymer of at least one of butadiene, isoprene and chloroprene, or a copolymer of acrylonitrile, butadiene and at least one of styrene and olefin. These may be used alone or in combination of two or more.
Among the above-mentioned conjugated diene polymers, polybutadiene is preferred from the viewpoints of availability, heat resistance, and film-forming properties. That is, the cyclic ether group-containing conjugated diene polymer (B) is preferably a cyclic ether-modified polybutadiene, and among them, epoxidized polybutadiene is more preferred.

It is known that the cyclic ether group-containing conjugated diene polymer (B) can be obtained by treating the carbon-carbon double bonds in the precursor conjugated diene polymer with a peroxide such as an organic peracid or hydrogen peroxide. It is also available commercially as "NISSO PB (Nippon Soda Co., Ltd.)" and "Epolead (Daicel Corporation)."

The resin composition constituting the sealant layer of the present invention may contain a crosslinking agent as a component other than the cyclic ether group-containing conjugated diene polymer (B).
The crosslinking agent is preferably one that is reactive with the carbon-carbon double bond of the cyclic ether group-containing conjugated diene polymer (B), and sulfur or a radical initiator is preferably selected, more preferably a radical initiator. As the radical initiator, an azo compound, an organic peroxide, a redox initiator, or the like can be selected. Among them, an organic peroxide is preferred in terms of compatibility and the tendency to generate bubbles.
The organic peroxide is not particularly limited and can be appropriately selected depending on the purpose. Examples of the organic peroxide include diacyl peroxides such as benzoyl peroxide and lauroyl peroxide, dialkyl peroxides such as dicumyl peroxide and di-t-butyl peroxide, peroxydicarbonates, peroxyketals, hydroperoxides, peroxyesters, ketone peroxides, and other peroxides.
The amount of the crosslinking agent added is preferably 0.1% by mass or more and 10% by mass or less in the resin composition, more preferably 0.5% by mass or more and 8% by mass or less, and even more preferably 1% by mass or more and 6% by mass or less. When the amount is 0.1% by mass or more, the cyclic ether group-containing conjugated diene polymer (B) is sufficiently crosslinked, heat lamination properties are obtained, and the wet heat resistance is also improved. On the other hand, when the amount is 10% by mass or less, the cyclic ether group-containing conjugated diene polymer (B) is prevented from being excessively crosslinked and losing flexibility, so that the heat lamination properties are good.

The resin composition constituting the sealant layer of the present invention may contain, as components other than the cyclic ether group-containing conjugated diene polymer (B) and the crosslinking agent, reaction aids, other resins, fillers, antioxidants, etc., for the purpose of improving the reactivity, transparency, antiblocking properties, and gelation of the sealant layer.

[Thickness]
The thickness of the sealant layer is preferably from 1 μm to 30 μm, more preferably from 2 μm to 25 μm, and even more preferably from 3 μm to 20 μm.
When the thickness of the sealant layer is 1 μm or more, the film has good thermal lamination suitability, whereas when the thickness is 30 μm or less, the film has good transparency.

3. Release layer The present film may have a release layer on the side of the sealant layer opposite to the surface facing the substrate layer. By having the release layer, it is possible to prevent process troubles during winding and the inclusion of foreign matter. It is preferable that the release layer is peeled off when the present film is thermally laminated with a printed material.

The release layer is not particularly limited as long as it has releasability from the sealant layer, but examples include various release films such as fluororesin films, polyester films coated with a release agent, and polyolefin films coated with a release agent. When using a release film coated with a release agent, it is recommended that the surface coated with the release agent be in contact with the sealant layer.

The thickness of the release layer is preferably from 10 μm to 100 μm, more preferably from 15 μm to 80 μm, and even more preferably from 20 μm to 60 μm.
When the thickness of the release layer is 10 μm or more and 100 μm or less, the release layer can be easily removed during thermal lamination with a printed material.

4. Manufacturing Method of the Present Film An example of a manufacturing method of the print surface protection film of the present invention will be described below, but the present invention is not limited to only the print surface protection film manufactured by this manufacturing method.

This film can be obtained, for example, by feeding the resin composition material constituting the sealant layer into an extruder, extrusion laminating the resin composition from a T-die extrusion nozzle onto a film that serves as a base layer to form a resin composition layer, and then heat treating the film.
The gap of the T-die used is determined based on the final required film thickness, stretching conditions, draft rate, various conditions, etc., and is generally about 0.1 to 3.0 mm, preferably 0.5 to 1.0 mm. A gap of 0.1 mm or more is preferable from the viewpoint of production speed, and a gap of 3.0 mm or less is preferable from the viewpoint of production stability because the draft rate does not become too large. In addition, from the viewpoint of interlayer adhesion, it is preferable that the film to be the base layer has been subjected to a corona treatment in advance at least on the side on which the sealant layer is laminated.

In extrusion lamination, the extrusion processing temperature is adjusted as appropriate depending on the flow characteristics and moldability of the resin, but is generally preferably 30 to 150°C, more preferably 35 to 120°C, and even more preferably 40 to 100°C. A temperature of 30°C or higher is preferable because it provides a sufficiently low viscosity of the molten resin, excellent moldability, and improved productivity. On the other hand, by setting the temperature at 150°C or lower, it is possible to suppress the generation of gel due to deterioration of the resin and crosslinking during extrusion lamination.

In extrusion lamination, a release film can be introduced to prevent the sealant layer from sticking or blocking. More specifically, during extrusion lamination, a resin composition layer is extruded from a T-die extrusion die onto a film that will be a substrate layer, and a release film is placed on top of the extrusion film and integrated with a press roll. This method can reduce troubles during winding and prevent adhesion of foreign matter. The release film may serve as a release layer in this film.
The press roll temperature and pressure can be appropriately selected depending on the thickness of the sealant layer in the print surface protection film. Specifically, by increasing the temperature or pressure, a thinner sealant layer can be obtained and the production speed can be improved.

After the resin composition layer is formed by extrusion lamination, a heat treatment is performed to harden the resin composition layer. The heat treatment temperature is not particularly limited, but is preferably 80 to 170° C., and more preferably 100 to 160° C. The heat treatment time is not particularly limited, but is preferably 1 to 120 minutes, and more preferably 3 to 60 minutes.
The resin composition layer may be cured by ultraviolet irradiation or electron beam irradiation, or may be cured in combination with a heat treatment.

<Multilayer body>
In the present invention, the above-mentioned printing surface protection film is preferably laminated on the printing layer and used. The printing surface protection film is laminated on the printing layer by thermal lamination. In this case, the sealant layer of the printing surface protection film is preferably opposed to the printing layer.
The print surface protection film of the present invention has excellent suitability for thermal lamination, and can be easily formed into a multilayer body by thermally laminating it onto a printed matter having a printed layer. The multilayer body includes the print surface protection film and the printed layer. That is, the multilayer body includes a base layer, a laminate layer, and a printed layer in this order. The printed layer is usually formed on the surface of the printed matter, and therefore, the multilayer body is preferably formed on the surface of the printed matter.

The present film can be suitably used when the printed layer is formed by liquid toner, since the crosslinked product of the cyclic ether group-containing conjugated diene polymer (B) contained in the sealant layer can have good moist heat resistance by reacting with liquid toner components. The printed layer may be formed, for example, by printing the liquid toner with a known printer and appropriately drying it.
The liquid toner preferably contains a polymer having an ionic group capable of reacting with a cyclic ether group, and more preferably contains a carboxyl group-containing polymer.
In the case where the liquid toner contains a carboxyl group-containing polymer, the present film can be used more preferably since the reactivity with the crosslinked product of the cyclic ether group-containing conjugated diene polymer (B) is high.

The printed matter in the present invention is not particularly limited and may be any of paper, film, cloth, etc., and it is preferable that a printed layer is formed on the surface of these. The printed layer may be formed on a primer layer provided on the surface of the printed matter. The film-like matter may be composed of a resin film alone, or a laminated film having two or more layers including a resin film.

The multilayer body of the present invention may be used as a package for packaging various items. For example, as described above, a printed material formed on the surface of the multilayer body may be used as a package. The multilayer body of the present invention has good moist heat resistance, and therefore has excellent retort suitability, and can be suitably used as a packaging film. Note that a packaging film is a printed material made from the film-like material described above. It is more preferable that a package such as a packaging film is used for retort.

The packaged article of the present invention is a package in which various items such as beverages, food, and daily necessities, or containers for storing various items, are packaged with the above-mentioned package. The packaging form is not particularly limited, and various items may be stored inside a package in the shape of a bag or container, or the package may encase part or all of the item or the container for storing the item.

In the present invention, when expressed as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as the meaning of "preferably larger than X" and "preferably smaller than Y".
In the present invention, when it is expressed as "X or more" (X is any number), it includes the meaning of "preferably larger than X" unless otherwise specified, and when it is expressed as "Y or less" (Y is any number), it includes the meaning of "preferably smaller than Y" unless otherwise specified.

The present invention will be described in more detail below with reference to examples and manufacturing examples. However, the present invention is not limited to the examples and manufacturing examples described below, and various modifications are possible without departing from the gist of the present invention.

<Measurement and evaluation methods>
(1) Thickness The thickness of the base layer, the release layer and the print surface protection film was measured at five random locations with a 1/1000 mm dial gauge and the average value was calculated.
The thickness of the sealant layer was calculated by subtracting the thicknesses of the substrate layer and release layer from the thickness of the print surface protection film.

(2) Crosslink Density The crosslink density of the cured product of the resin composition constituting the sealant layer was determined by the following method.
In the case where the resin composition is in a solid state or is nearly solid and can be formed into a film to measure the tensile storage modulus, the laminate is extruded from a T-die to obtain a laminate of release layer C-1 (38 μm)/resin composition layer (80 μm)/release layer C-1 (38 μm), and then heat-treated in an oven at 150 ° C. for 30 minutes to cure the resin composition layer, and then the release layers C-1 on both sides are peeled off, and the remaining cured layer is used as a measurement sample. Using a dynamic viscoelasticity measuring device (manufactured by IT Measurement & Control Co., Ltd., "DVA-200") and a tension jig, the tensile storage modulus of the measurement sample was measured at a measurement temperature of -100 to 250 ° C., a frequency of 1 Hz, and a heating rate of 3 ° C./min, and the tensile storage modulus E' at 100 ° C. was read.
On the other hand, when the resin composition is close to a liquid state and cannot be made into a film to measure the tensile storage modulus, the laminate is extruded from a T-die to obtain a laminate of release layer C-1 (38 μm)/resin composition layer (80 μm)/release layer C-1 (38 μm), and then heat-treated in an oven at 150 ° C. for 30 minutes to harden the resin composition layer, and then punched out into a circle having a diameter of 20 mm. Thereafter, the release layers C-1 on both sides are peeled off, and the cured layer is attached to the parallel plates of a rheometer ("MARS" manufactured by Eiko Seiki Co., Ltd.), and the shear storage modulus is measured with an adhesive jig: Φ25 mm parallel plate, distortion: 0.5%, frequency: 1 Hz, measurement temperature: 20 to 250 ° C., and heating rate: 3 ° C./min, and the shear storage modulus G' at 100 ° C. is read.
The crosslink density was calculated from the tensile storage modulus E' or shear storage modulus G' at 100° C. obtained as above, using the following formula.
n = E'/3RT
E' = 3G'
n: crosslinking density [mol/m ³ ]
E': tensile storage modulus [Pa], G': shear storage modulus [Pa]
R: gas constant [8.31 x J/mol K] T: absolute temperature [K]

(3) Suitability for Thermal Lamination For the multilayer film after thermal lamination, the peel strength between the sealant layer of this film and the printed matter sample was measured by the method described below, and the suitability for thermal lamination was evaluated according to the following evaluation criteria.
○ (good): peel strength is 2N/15mm or more × (poor): peel strength is less than 2N/15mm

[Measurement of Peel Strength]
The peel strength between the film and the printed matter sample was measured for the multilayer film after thermal lamination in accordance with JIS Z0237. First, the printed matter sample on which the film was thermally laminated was cut to 50 mm wide x 150 mm long as a sample, and cellophane tape (manufactured by Nichiban Co., Ltd., JIS Z1522) was attached in the vertical direction to the surface of the film of the sample, folded back at 90° so that the back surface of the tape overlapped, and peeled off 25 mm from the sample. Next, one end of the sample at the peeled part was fixed to the lower chuck of a tensile tester (manufactured by Intesco Co., Ltd., Intesco IM-20ST), the tape was fixed to the upper chuck, and the peel strength was measured at a test speed of 300 mm/min. After the measurement, the measured value of the first 25 mm length was ignored, and the peel strength measured value of the 50 mm length peeled off from the test piece was averaged to obtain the peel strength. If the film does not peel off and only the tape peels off, the peel strength of the film is deemed to be equal to or greater than the peel strength of the tape alone.

(4) Moisture and heat resistance (retort resistance)
The printed matter samples thermally laminated with this film were treated in high-pressure steam at 120°C for 0.5 hours using a pressure cooker tester (EHS-411M, manufactured by Espec Corp.), and the appearance after treatment was evaluated according to the following criteria.
◯ (good): No peeling occurred over the entire film surface.
× (poor): Peeling occurred in some areas.

<Ingredients>
[Base layer]
A-1: Corona-treated biaxially stretched polyester film (thickness 12 μm, product name "Diafoil H600C", manufactured by Mitsubishi Chemical Corporation)
[Sealant layer]
B-1: 97 parts by mass of epoxidized polybutadiene (product name "NISSO PB JP200", manufactured by Nippon Soda Co., Ltd., epoxy equivalent: 227 g/eq) and 3 parts by mass of dicumyl peroxide as an organic peroxide were kneaded at 100° C. to obtain a uniform viscous liquid.
B-2: 97 parts by mass of epoxidized polybutadiene (product name "NISSO PB JP100", manufactured by Nippon Soda Co., Ltd., epoxy equivalent: 200 g/eq) and 3 parts by mass of dicumyl peroxide as an organic peroxide were kneaded at 100° C. to obtain a uniform viscous liquid.
B-3: 97 parts by mass of epoxidized polybutadiene (product name "NISSO PB JP200", manufactured by Nippon Soda Co., Ltd., epoxy equivalent: 227 g/eq) and 3 parts by mass of benzoyl peroxide as an organic peroxide were kneaded at 60°C to obtain a uniform viscous liquid.
B-4: 97 parts by mass of epoxidized polybutadiene (product name "NISSO PB JP200", manufactured by Nippon Soda Co., Ltd., epoxy equivalent: 227 g/eq) and 3 parts by mass of di-t-butyl peroxide as an organic peroxide were kneaded at 100°C to obtain a uniform viscous liquid.
B-5: 97 parts by mass of polybutadiene (product name "NISSO PB B-3000", manufactured by Nippon Soda Co., Ltd., not epoxy-modified) and 3 parts by mass of dicumyl peroxide as an organic peroxide were kneaded at 100° C. to obtain a uniform viscous liquid.
B-6: 97 parts by mass of an ethylene-glycidyl methacrylate resin (product name "LOTADER AX8840", manufactured by Tokyo Materials Co., Ltd., epoxy equivalent: 1800 g/eq) and 3 parts by mass of dicumyl peroxide as an organic peroxide were mixed by dry blending.
B-7: Epoxidized polybutadiene (product name "NISSO PB JP200", manufactured by Nippon Soda Co., Ltd., epoxy equivalent: 227 g/eq) was used as it was.
B-8: 85 parts by mass of epoxidized polybutadiene (product name "NISSO PB JP200", manufactured by Nippon Soda Co., Ltd., epoxy equivalent: 227 g/eq) and 15 parts by mass of dicumyl peroxide as an organic peroxide were kneaded at 100°C to obtain a uniform viscous liquid.
[Release layer]
C-1: Release polyester film (thickness 38 μm, product name "Diafoil MRF-38", manufactured by Mitsubishi Chemical Corporation)

Example 1
The sealant layer material B-1 was heat-melted at 70°C, extruded from a T-die and cast between the base layer A-1 and the release layer C-1, roll-pressed at a linear speed of 0.03 m/min between a metal roll and a rubber roll set at 70°C, and then heat-treated in an oven at 150°C for 30 minutes to obtain a printing surface protection film with a total thickness of 70 μm.
The release layer C-1 of the obtained printed surface protection film was peeled off, and the sealant layer was placed so that the printed surface of the printed matter sample faced each other. The sample was then passed between a heating roll and a rubber roll set at 110°C at a speed of 0.1 m/min and a linear pressure of 0.5 MPa cm to perform thermal lamination, thereby obtaining the multilayer film (multilayer body) of Example 1.

[Preparation of printed matter samples]
A nylon film (product name: "Harden N1200", manufactured by Toyobo Co., Ltd., thickness 15 μm) and an unstretched polypropylene film (product name: "FRTK-G", manufactured by Futamura Chemical Co., Ltd., thickness 50 μm) were laminated in this order by dry lamination to obtain a laminated film.
For lamination by dry lamination, a urethane adhesive (product name: "Takelac A-515V/Takenate A-5", manufactured by Mitsui Chemicals, Inc.) was used, and the adhesive was applied with a gravure plate so that the coating amount when dried was 3.5 g/ ^m2 . After lamination, aging was performed at 40°C for 48 hours. Thereafter, the nylon film side was corona-treated, and polyethyleneimine (product name: "Epomin P1000", manufactured by Nippon Shokubai Co., Ltd.) was used as a primer, and a gravure roller was used to apply a weight of 0.15 g/ ^m2 to cover the entire surface of the nylon film side. Next, a printing layer was solid-printed on one side of the primer-coated surface of the laminated film using HP Indigo WS6600 digital printing machine with magenta HP Indigo Electroink. This resulted in a printed sample.

Example 2
A multilayer film of Example 2 was obtained in the same manner as in Example 1, except that the material of the sealant layer was changed to B-2.

Example 3
A multilayer film of Example 2 was obtained in the same manner as in Example 1, except that the material of the sealant layer was changed to B-3 and the heat treatment temperature in the oven after roll pressing was changed from 150°C to 110°C.

Example 4
A multilayer film of Example 2 was obtained in the same manner as in Example 1, except that the material of the sealant layer was changed to B-4 and the heat treatment time in an oven at 150°C after roll pressing was changed from 30 minutes to 3 hours.

<Comparative Example 1>
A multilayer film of Comparative Example 1 was obtained in the same manner as in Example 1, except that the material of the sealant layer was changed to B-5.

<Comparative Example 2>
A multilayer film of Comparative Example 2 was obtained in the same manner as in Example 1, except that the material of the sealant layer was changed to B-6 and the T-die temperature and the heating roll temperature were changed to 180°C.

<Comparative Example 3>
A multilayer film of Comparative Example 3 was obtained in the same manner as in Example 1, except that the material of the sealant layer was changed to B-7.

<Comparative Example 4>
A multilayer film of Comparative Example 4 was obtained in the same manner as in Example 1, except that the material of the sealant layer was changed to B-8.

In Examples 1 to 4, the sealant layer was made of a cured product of the resin composition containing the cyclic ether group-containing conjugated diene polymer (B), and the crosslink density of the cured product was 1 mol/m3 or ^more and 3000 mol/ ^m3 or less, so that a print surface protection film excellent in thermal lamination suitability and moist heat resistance was obtained.
On the other hand, in Comparative Example 1, the main component resin constituting the sealant layer did not contain an epoxy group, so no reaction occurred with the liquid toner components, resulting in a film with poor moist heat resistance. In Comparative Example 2, the main component resin constituting the sealant layer was not a conjugated diene polymer, so the rubber-like plateau in the viscoelastic behavior was narrow, resulting in a film with poor moist heat resistance. In Comparative Example 3, the crosslinking of the resin composition constituting the sealant layer was insufficient, so the sealant layer flowed, resulting in insufficient thermal lamination properties. In Comparative Example 4, the crosslinking of the resin composition constituting the sealant layer was excessive, resulting in insufficient thermal lamination properties.

Claims (16)

The adhesive sheet has at least a base layer and a sealant layer,
The base layer contains a thermoplastic resin (A) as a main component,
The print surface protection film, wherein the sealant layer is made of a cured product of a resin composition containing a cyclic ether group-containing conjugated diene polymer (B), and the crosslink density of the cured product is 1 mol/m3 or ^more and 3000 mol/m3 ^or less. The print surface protection film according to claim 1, wherein the thickness of the substrate layer is 5 μm or more and 50 μm or less. The print surface protection film according to claim 1 or 2, wherein the thickness of the sealant layer is 1 μm or more and 30 μm or less. The print surface protection film according to any one of claims 1 to 3, wherein the thermoplastic resin (A) is at least one selected from the group consisting of polyester resins and polyolefin resins. The print surface protection film according to any one of claims 1 to 4, wherein the cyclic ether group-containing conjugated diene polymer (B) contains an epoxy group and has an epoxy equivalent of 100 g/eq or more and 1500 g/eq or less. The print surface protection film according to any one of claims 1 to 5, wherein the cyclic ether group-containing conjugated diene polymer (B) is a cyclic ether modified conjugated diene polymer. The print surface protection film according to claim 6, wherein the conjugated diene polymer is a polymer containing structural units derived from at least one of butadiene, isoprene, and chloroprene. The print surface protection film according to any one of claims 1 to 7, wherein the resin composition contains a crosslinking agent. The print surface protection film according to claim 8, wherein the crosslinking agent is a radical initiator. The print surface protection film according to claim 9, wherein the radical initiator is an organic peroxide. The print surface protection film according to any one of claims 1 to 10, which has a release layer on the side of the sealant layer opposite the surface facing the substrate layer. A multilayer body comprising the print surface protection film according to any one of claims 1 to 11 and a print layer, in which the print surface protection film is thermally laminated onto the print layer. The multilayer body according to claim 12, wherein the printing layer is formed by liquid toner. The multilayer body according to claim 13, wherein the liquid toner comprises a carboxyl group-containing polymer. A packaging body comprising the multilayer body according to any one of claims 12 to 14. A packaged article packaged with the packaging body according to claim 15.