HK1248194B - Lid - Google Patents

Abstract

This lid has at least a substrate layer, an anchor coat layer, a stress relaxation layer, and a hot-melt adhesive layer, and has a structure obtained by layering said layers in this order. The hot-melt adhesive that constitutes the hot-melt adhesive layer contains 20-50 mass% of an ethylene-vinyl acetate copolymer as a component (A), and relative to 100 parts by mass of the ethylene-vinyl acetate copolymer constituting the component (A), also contains 8-80 parts by mass of an adhesiveness-imparting agent as a component (B), 85-230 parts by mass of a wax as a component (C), and 15-200 parts by mass of talc as a component (D).

Description

Cover material

Technical Field

The present invention relates to a cover material which uses hot plate heating or high-frequency induction heating to bond and seal the opening of a plastic container containing liquid or fluid foods such as yogurt, lactic acid bacteria beverages, and fruit beverages, powdered foods such as wheat flour, solid foods such as ham and cheese, and various pharmaceuticals.

Background Art

Usually, the opening of the container body containing food or the like is sealed with a cover material having thermal adhesiveness. In recent years, from the viewpoint of ensuring the safety of food or the like, such a cover material is required to have a small amount of substances eluted into the organic solvent (the amount eluted into the organic solvent) when the cover material is immersed in the organic solvent. As a cover material to meet such a requirement, a cover material having a laminated structure of a base material layer such as aluminum foil/an adhesive coating layer such as a polyurethane resin/a stress relaxation layer such as a polyethylene film/an ethylene-vinyl acetate resin-based hot melt adhesive layer has been proposed (Patent Document 1).

Regarding the constituent material of the hot melt adhesive layer in the cover material that is in direct contact with the contents contained in the container body, it is proposed to select a material that has less elution in an organic solvent. Specifically, the hot melt adhesive layer is formed by a hot melt adhesive containing 25 to 55 weight % of ethylene-vinyl acetate copolymer having a vinyl acetate content of 24 to 35 weight % and a melt index of 30 to 400 g/10 minutes, 30 to 65 weight % of polyethylene wax having a molecular weight of 700 to 3,500 and a melting point of 95 to 125° C., and 10 to 30 weight % of a polymer-based adhesive imparting agent having a molecular weight of 700 to 1,400 and a softening point of 100 to 125° C.

Prior art literature

Patent Literature

Patent document 1: Japanese Patent Application Laid-Open No. 10-156995.

Summary of the invention

Problems to be solved by the invention

However, although the amount of substances eluted from the cover material proposed in Patent Document 1 in edible oils and ethanol is very small and there is no problem in normal use, the amount of substances eluted in hexane (the amount eluted in hexane) is greater than the amount of substances eluted in edible oils and ethanol. Therefore, it is considered to reduce the amount of elution in hexane by relatively reducing the content of low molecular weight impurities by changing the constituent materials of the hot melt adhesive to materials with higher molecular weight.

However, if a material with a higher molecular weight is used as the material constituting the hot melt adhesive, the sealing property of the hot melt adhesive layer of the cover material is reduced, so the sealing strength may be reduced under the same sealing conditions as before. In order to avoid this, strict sealing conditions may be considered, but it is very difficult to find the most suitable sealing conditions under strict conditions.

The purpose of the present invention is to solve the problems of the above-mentioned prior art, and the purpose is to achieve good sealing under the same sealing conditions as before for a cover material formed by stacking a substrate layer/adhesive coating layer/stress relief layer/hot-melt adhesive layer in sequence, even when the material constituting the hot-melt adhesive layer is changed to a material with a higher molecular weight to suppress the dissolution amount in an organic solvent.

Means for solving problems

The present inventors have discovered that if a hot-melt adhesive layer of a cover material including a base layer/adhesive coating layer/stress relief layer/hot-melt adhesive layer laminated in this order is formed by a hot-melt adhesive obtained by mixing a specific amount of talc into a mixture of ethylene-vinyl acetate copolymer, an adhesion-imparting agent and wax in amounts within a specific range, the sealing performance will not be reduced even when a material with a higher molecular weight is selected as the material constituting the hot-melt adhesive in order to reduce the dissolution amount of the cover material in an organic solvent, thereby completing the present invention.

That is, the present invention provides a cover material, which has at least a base material layer, an anchor coating layer, a stress relaxation layer and a hot-melt adhesive layer, wherein the above-mentioned layers are stacked in the order described, and the hot-melt adhesive constituting the hot-melt adhesive layer contains 20 to 50% by mass of ethylene-vinyl acetate copolymer as component (A), and further contains the following components (B) to (D) in the following mass parts relative to 100 parts by mass of component (A).

(A) 100 parts by mass of ethylene-vinyl acetate copolymer;

(B) 8 to 80 parts by weight of an adhesive agent;

(C) 85 to 230 parts by mass of wax; and

(D) Talc: 15 to 200 parts by mass.

In addition, the present invention provides a container-packed food, characterized in that it is composed of a food container having an opening with a flange, liquid or solid food contained therein, and a cover material bonded to the flange formed at the opening of the food container, the cover material being the above-mentioned cover material, and the cover material is bonded to the flange of the opening from the hot-melt adhesive layer side.

Effects of the Invention

In the cover material of the present invention, which is formed by sequentially stacking a base material layer, an adhesive coating layer, a stress relaxation layer, and a hot-melt adhesive layer, a hot-melt adhesive is used as a hot-melt adhesive for forming the hot-melt adhesive layer, in consideration of the sealing performance and the amount of dissolution in an organic solvent. A hot-melt adhesive is used in which a specific amount of talc is blended into a mixture of ethylene-vinyl acetate copolymer, an adhesiveness imparting agent, and wax in a specific range of amounts. Therefore, even when a material with a higher molecular weight is selected as a material constituting the hot-melt adhesive in order to reduce the amount of dissolution of the cover material in an organic solvent, the sealing performance can be kept unchanged.

BRIEF DESCRIPTION OF THE DRAWINGS

[Fig. 1] Fig. 1 is a schematic cross-sectional view of a cover material according to the present invention.

[Fig. 2] Fig. 2 is a diagram showing seal strength characteristics by hot plate heating, focusing on the type of filler.

[Fig. 3] Fig. 3 is a diagram showing seal strength characteristics by high-frequency induction heating, focusing on the type of filler.

[ Fig. 4] Fig. 4 is a diagram showing seal strength characteristics by hot plate heating, focusing on the amount of talc blended.

[ Fig. 5] Fig. 5 is a diagram showing seal strength characteristics by high-frequency induction heating, focusing on the amount of talc added.

[ Fig. 6] Fig. 6 is a diagram showing seal strength characteristics by hot plate heating, focusing on the average particle size of talc.

[ Fig. 7] Fig. 7 is a diagram showing seal strength characteristics by high-frequency induction heating, focusing on the average particle size of talc.

DETAILED DESCRIPTION

Hereinafter, the cover material of the present invention will be described with reference to the accompanying drawings.

＜Cover material＞

As shown in Fig. 1, the cover material 10 of the present invention has a structure in which a base material layer 1, an anchor coating layer 2, a stress relaxation layer 3, and a hot melt adhesive layer 4 are sequentially laminated. The cover material 10 is a material for sealing the opening of the container body. As the constituent material of such a container body, plastics such as polystyrene, polypropylene, polyethylene, polyvinyl chloride, polycarbonate, and polyacrylonitrile, composite laminates lined with these plastics, metals, polyethylene laminated paper, glass, etc. can be cited.

"Substrate layer 1"

The substrate layer 1 is the main layer that imparts initial mechanical strength to the cover material, and can be formed into the same structure as the substrate layer of the previous cover material. For example, it can be selected from thin films of metals or alloys such as iron, stainless steel, copper, aluminum, gold, etc., thin films of ceramics such as silicon nitride, films of resins such as polyethylene terephthalate, polyurethane, polystyrene, polyamide, polyimide, papermaking paper, and composite materials formed by stacking them, etc., according to the purpose of use. In particular, in order to impart high-frequency induction heating characteristics to the cover material 10, as the substrate layer 1, it is preferred to use a metal film that induces eddy currents in itself and generates heat when a high-frequency wave is applied. Among them, aluminum foil can be preferably cited from the aspects of formability, suitability for high-frequency heating, and economy.

The thickness of the substrate layer 1 is usually 5 to 300 μm in consideration of mechanical strength and the material used. For example, when a metal film such as aluminum foil is used, the thickness is preferably 5 to 50 μm, more preferably 20 to 40 μm in consideration of high-frequency induction heating characteristics.

The substrate layer 1 can be formed by a known method according to the type and thickness of the raw material. In the case of a metal or alloy thin film, it can be formed by cold rolling, vacuum evaporation, electroless plating, electrolytic plating, etc. In the case of a resin thin film, it can be formed by melt extrusion molding, solution casting, calendering, etc. In addition, the resin thin film can be stretched.

In addition, as conditions of high-frequency induction heating, conditions such as 140 W and 1.4 seconds can be mentioned, and it can be changed appropriately according to the layer structure and the raw materials used.

"Stick Coat 2"

The anchor coating layer 2 is a layer for making the base layer 1 and the stress relaxation layer 3 adhere to each other, and can be selected according to their materials.

As the anchor coating layer 2, a layer formed of a modified polyolefin-based anchor coating agent modified with chlorine or acid, a polyester-based anchor coating agent, or a polyurethane-based anchor coating agent can be applied. It should be noted that the anchor coating layer 2 may contain various additives such as fillers within a range that does not hinder the adhesion between the base layer 1 and the stress relaxation layer 3.

If the thickness of the anchor coating 2 is too thin, the sealing strength will decrease, and if it is too thick, the sealing strength will tend to decrease due to cohesive failure () inside the anchor coating 2. Therefore, the thickness is preferably 0.1 to 6.0 μm, and more preferably 0.2 to 4.5 μm.

The anchor coating layer 2 can be formed by a solution coating method.

"Stress relaxation layer 3"

The stress relief layer 3 enhances the mechanical strength of the cover material, relieves the stress during high-frequency heating, and also functions as a layer that suppresses excessive heat from being applied to the hot-melt adhesive layer 4 and firmly bonds the hot-melt adhesive layer 4 to the back of the cover material. As such a stress relief layer 3, a resin layer formed of a polyolefin-based thermoplastic resin such as polyethylene and polypropylene, or a resin layer formed of a polyester-based thermoplastic resin such as polyethylene terephthalate can be used. Considering the stability of the high-frequency sealing strength, etc., a polyethylene layer, especially a non-stretched polyethylene layer, can be preferably used.

The thickness of the stress relaxation layer 3 is preferably 6 to 60 μm, more preferably 9 to 50 μm. Within the above range, sufficient stress relaxation and thermal relaxation can be achieved, and sufficient heat can be conducted from the base material layer 1 to the hot-melt adhesive layer 4 .

It should be noted that when the stress relaxation layer 3 is a polyethylene layer, the layer thickness is preferably 10 to 50 μm, more preferably 15 to 40 μm, in consideration of high-frequency sealing properties and moldability.

As a method for providing the stress relaxation layer 3 on the anchor coating layer 2, a known method can be adopted. For example, the material constituting the stress relaxation layer 3 may be directly melt-extruded and laminated on the anchor coating layer 2, or a film formed of the material constituting the stress relaxation layer 3 may be dry-laminated on the anchor coating layer 2.

"Hot-melt adhesive layer 4"

The hot-melt adhesive layer 4 is not only a layer that is bonded to the opening of the container body by heat conducted from the base material layer 1 , but is also a layer that comes into contact with the content contained in the container body.

The adhesion amount of the hot melt adhesive layer 4 is preferably 3 to 40 g/m ² , more preferably 5 to 30 g/m ² . Within the above range, sufficient high-frequency sealing properties (especially sealing strength) can be obtained by high-frequency heating, the cover material can be peeled off stably, and the amount of elution in organic solvents can be reduced.

The hot-melt adhesive layer 4 can be formed by a known method such as a gravure roll coating method.

The hot melt adhesive layer 4 is a layer in contact with the contents contained in the container body, and therefore is required to be composed of an adhesive material that can be bonded to the container body and is not easily dissolved in the contents. In the present invention, it is formed of a hot melt adhesive containing the following components (A) to (D).

(A) Ethylene-vinyl acetate copolymer

(B) Adhesion-imparting agent

(C) Wax

(D) Talc.

＜Ingredients (A)＞

The ethylene-vinyl acetate copolymer of the component (A) functions as a main component of the hot melt adhesive and is used because it is easily bonded to metals, resins, glass and the like and is also compatible with wax and the like.

The content of the ethylene-vinyl acetate copolymer as component (A) in the hot melt adhesive is 20 to 50% by mass, preferably 25 to 45% by mass. Within the above range, the heat seal strength is not reduced and the amount of elution into organic solvents can be suppressed.

In the present invention, it is preferable to use an ethylene-vinyl acetate copolymer having the following properties (a1) to (a3).

(Characteristic (a1): Vinyl acetate content)

The vinyl acetate content of the ethylene-vinyl acetate copolymer is preferably 14 to 41% by mass, and more preferably 19 to 33% by mass. Within the above range, the sealing strength may not be reduced, and the amount of dissolution in an organic solvent may be suppressed. The vinyl acetate content may be measured in accordance with JIS K6924-2.

(Characteristic (a2): MFR value)

The MFR value (JIS K7210) of the ethylene-vinyl acetate copolymer is preferably 5 to 400 g/10 minutes, more preferably 5 to 150 g/10 minutes. Within the above range, the coating properties of the hot melt adhesive are not impaired, and the amount of dissolution in the organic solvent can be suppressed. The MFR value can be measured in accordance with JIS K7210.

(Characteristic (a3): Vicat softening point)

The Vicat softening point of the ethylene-vinyl acetate copolymer is preferably 25 to 75° C., more preferably 30 to 65° C. Within the above range, the amount of dissolution in organic solvents can be suppressed, and a decrease in seal strength can be suppressed. The Vicat softening point can be measured in accordance with JIS K7206.

As specific examples of ethylene-vinyl acetate copolymers having the above-described properties (a1) to (a3), preferably, there are "Evaflex (registered trademark) EV420, EV220" manufactured by Mitsui Dupon Polychemica, Inc., "Ultrasen (registered trademark) 750" manufactured by Tosoh Corporation, etc. For example, properties (a1) to (a3) of "Evaflex EV420" are as follows.

Characteristics (a1): Vinyl acetate content 19 mass%

Characteristics (a2): MFR value 150g/10min

Characteristics (a3): Vicat softening point 42°C.

＜Ingredient (B)＞

The tackifier as the component (B) is a component that imparts tackiness to the hot melt adhesive.

The content of the tackifier as component (B) in the hot melt adhesive is 8 to 80 parts by mass, preferably 14 to 60 parts by mass, relative to 100 parts by mass of the ethylene-vinyl acetate copolymer as component (A). Within the above range, a decrease in seal strength can be suppressed, and the amount of elution into an organic solvent can be suppressed.

As the tackifier, a known tackifier may be used, and examples thereof include alicyclic saturated hydrocarbon resins, aliphatic aromatic copolymer resins, terpene resins, and rosin-based resins. Among them, rosin-based resins are preferably used from the viewpoint of improving the adhesive force.

In the present invention, the tackifier represented by such a rosin-based resin has the following property (b1).

(Characteristic (b1): Softening point)

The softening point of the adhesive agent represented by the rosin resin is preferably 80 to 150° C., more preferably 85 to 130° C. Within the above range, the amount of dissolution in the organic solvent can be suppressed from increasing, and the reduction in the sealing strength can be suppressed. The softening point can be measured by the ring and ball method.

Specific examples of the tackifier having the characteristic (b1) described above include “Alcon (registered trademark) P-125” (softening point 125° C.) manufactured by Arakawa Chemical Industries, Ltd., “Kinton (registered trademark) D100” (softening point 99° C.) manufactured by Nippon Zeon Co., Ltd., “Super Ester A-115” (softening point 108° C.) manufactured by Arakawa Chemical Industries, Ltd., “Penser (registered trademark) AZ” (softening point 95° C.) manufactured by Arakawa Chemical Industries, Ltd., and “Haritake ER95” (softening point 85° C.) manufactured by Harima Chemicals Co., Ltd.

＜Ingredient (C) Wax＞

The wax as the component (C) is a component that reduces the viscosity of the hot melt adhesive and imparts wettability.

The content of the wax as component (C) in the hot melt adhesive is 85 to 230 parts by mass, preferably 110 to 200 parts by mass, relative to 100 parts by mass of the ethylene-vinyl acetate copolymer as component (A). Within the above range, the reduction in coating processability due to the high viscosity of the adhesive material can be suppressed, the reduction in coating processability due to the low viscosity can be suppressed, and the reduction in sealing strength can be suppressed.

As the wax, known waxes can be used. Examples include natural waxes such as refined beeswax, refined carnauba wax, refined montan wax, paraffin wax, and microcrystalline wax; and synthetic waxes such as polyethylene wax, polypropylene wax, and Fischer-Tropsch wax. Among them, synthetic waxes are preferred, and Fischer-Tropsch wax is more preferred, from the perspectives of melting point, stability of molecular weight distribution, and the like.

Such a wax preferably has the following property (c1).

(Characteristic (c1): Melting point)

The melting point of waxes such as polyethylene wax is preferably 80 to 130° C., more preferably 85 to 120° C. Within the above range, the amount of dissolution in organic solvents can be suppressed, and the reduction in sealing properties at low temperatures can be suppressed. The melting point can be measured by DSC.

Specific examples of the wax having the above-described property (c1) include “Neowax L” manufactured by Yashara Chemical Co., Ltd. (melting point 110±10° C.), “Hiworks NL900” manufactured by Mitsui Chemicals, Inc. (melting point 103° C.), and “FT105” manufactured by Nippon Seiro Co., Ltd. (melting point 102° C.).

＜Ingredient (D) Talc＞

The hot melt adhesive used in the present invention contains talc as a component (D). Talc has excellent dispersibility in other resin components, can improve the cohesive force of the hot melt adhesive, and is a component for transferring heat from the base material layer 1 to the hot melt adhesive layer 4 without excessive heat diffusion.

The content of talc as component (D) in the hot melt adhesive is 15 to 200 parts by mass, preferably 60 to 170 parts by mass, relative to 100 parts by mass of the ethylene-vinyl acetate copolymer as component (A). Within the above range, it is possible to suppress not only the reduction in sealing properties at low temperatures but also the amount of elution into organic solvents, and not only the reduction in compatibility with other compounding materials such as resins but also the reduction in coating properties due to the reduction in fluidity.

In the present invention, it is preferable to use talc having the following properties (d1) to (d3).

(Characteristic (d1): Particle size (D50))

The particle size (D50) (median particle size) of talc is preferably 0.1 to 50 μm, and more preferably 0.5 to 25 μm. Within the above range, the increase in the volume of the particles can be suppressed, and the coating preparation can be facilitated. In addition, the decrease in thermal conductivity and the decrease in heat sealing properties can be suppressed. The particle size (D50) can be measured by laser diffraction.

(Characteristic (d2): Apparent density)

The apparent density of talc is preferably 0.05 to 0.7 g/mL, more preferably 0.08 to 0.6 g/mL. If it is within the above range, the increase in the volume of the particles can be suppressed, and the coating preparation can be easily performed. In addition, the reduction in thermal conductivity can be suppressed, and the reduction in heat sealing properties can be suppressed. The measurement of the apparent density can be carried out according to JIS K5101.

(Characteristic (d3): Specific surface area)

The specific surface area of talc is preferably 1.5 to 100 ^{m 2} /g, more preferably 2.5 to 40 m ² /g. Within the above range, a decrease in thermal conductivity and sealing strength can be suppressed, and coating preparation can be easily performed. The specific surface area can be measured by the BET method.

Specific examples of talc having the above-described characteristics (d1) to (d3) include preferably “Microace (registered trademark) K-1” manufactured by Japan Taluk Co., Ltd. (particle size (D50) 8.0 μm, apparent density 0.25 g/mL, specific surface area 7.0 m ² /g), “MS-K” manufactured by Japan Taluk Co., Ltd. (particle size (D50) 16 μm, apparent density 0.40 g/mL, specific surface area 4.0 m ² /g), and “MS-KY” manufactured by Japan Taluk Co., Ltd. (particle size (D50) 25 μm, apparent density 0.55 g/mL, specific surface area 2.5 m ² /g).

The hot melt adhesive layer 4 described above can be formed by applying the hot melt adhesive to the stress relaxation layer 3 using a known coating method such as a gravure coater, a comma coater, or a die coater and cooling the stress relaxation layer 3. In this case, the hot melt adhesive layer 4 may be in a flat film shape, an embossed film shape, a dot shape, or a line shape.

“Printing layer, protective layer”

A printed layer may be provided on the cover material of the present invention, and the printed layer may be formed on the outer surface of the substrate layer 1 by a known method. Furthermore, a transparent protective layer may be provided. In addition, as required, an embossing process may be performed on the outer surface of the substrate layer 1 side of the cover material. As required, a printed layer may be provided on the surface where the hot-melt adhesive layer is processed, or a printed layer may be provided on the substrate layer.

"Sealing properties"

The cover material of the present invention has the structure described above, and therefore, when a sealing process is performed by hot plate heating, high-frequency induction heating, ultrasonic heating, etc., it shows good sealing characteristics (strength). For example, when hot plate heating is used, the sealing conditions include a sealing temperature of 80 to 240°C, a sealing time of 0.5 to 3 seconds, and a sealing pressure of 0.1 to 0.5 MPa. When high-frequency induction heating is used, the sealing conditions include a power of 110 to 170 W, a sealing time of 0.5 to 1.5 seconds, and a sealing pressure of 0.1 to 0.3 MPa.

(Dissolution amount in organic solvents)

For the cover material of the present invention, a hot melt adhesive layer 4 in contact with the contents of the container is formed by a hot melt adhesive obtained by mixing a specific amount of talc in a mixture of ethylene-vinyl acetate copolymer, an adhesive imparting agent and wax in a specific range of amounts. Therefore, the sealing property can be kept intact, and therefore, even when a substance with a higher molecular weight is selected as a material constituting the hot melt adhesive, the amount of dissolution of the cover material in an organic solvent can be reduced. In particular, for the cover material of the present invention, the oily food dissolution test based on the evaporation residue test method (dissolution liquid n-heptane) specified in the standard test for utensils and container packaging based on the standard standard of the Japanese Food Sanitation Law (Notice No. 370 of the Ministry of Health, Labor and Welfare in 1977) can make the residue (dissolution amount in heptane) less than 30μg/mL.

Furthermore, the cover material of the present invention can have a residue (amount eluted into hexane) of 30 mg/L or less when tested by the test method described below.

(Based on evaporation residue of dissolution test in n-hexane)

According to the National Standard of the People's Republic of China "Analysis Method for Hygienic Standards of Polyethylene, Polystyrene and Polypropylene Molded Products for Food Packaging" (GB/T5009.60-2003), a sample cut into a size of 10 cm square is immersed in 200 mL of n-hexane for 2 hours at 25°C to prepare a test solution. The test solution is transferred to an eggplant-shaped flask and concentrated under reduced pressure until the residual amount becomes several mL. To the obtained concentrated solution, the washing liquid obtained by washing the inner wall of the flask used in the reduced pressure concentration twice with 5 mL of n-hexane is added, and the washing liquid is transferred to an evaporating dish of known weight that has been dried at 105°C in advance, and evaporated to dryness. Next, dry at 105°C for 2 hours, and then cool naturally in a desiccator. After natural cooling, weigh, find the mass difference before and after the test of the evaporating dish, and calculate the amount of evaporation residue (mg) per 1L of test solution.

"Method for manufacturing lid material"

As described above, the cover material of the present invention can be produced by forming the anchor coating layer 2 on the base material layer 1 by a known method, further providing the stress relaxation layer 3, and further providing the hot-melt adhesive layer 4.

＜Application of cover material＞

The cover material of the present invention can be preferably used as a cover material for container-packed food, which is composed of a food container having an opening with a flange, a liquid or solid food contained therein, and a cover material bonded to the flange formed at the opening of the food container. In this case, the cover material is applied to the flange of the opening from the adhesive layer side and is thermally bonded by high-frequency induction heating. The "container-packed food" obtained in the above manner is also one embodiment of the present invention. As food containers, well-known food containers made of polystyrene and the like can be cited.

The "liquid or solid" in liquid or solid food refers to a state in which the shape of the food as the content is deformed (flowing out, flowing, etc.) when the container is tilted, or a state in which the shape of the food as the content is not deformed (solid). Examples of such liquid or solid food include, but are not limited to, dairy products such as yogurt and lactic acid beverages, jam products, soups, curry sauces, stews, and food seasonings for rice.

Example

The present invention will be described in more detail below with reference to Examples and Comparative Examples.

Example 1

(AL foil/adhesive coating/LDPE/hot melt adhesive layer)

A two-component curable adhesive coating agent for extrusion and lamination (isocyanate-based) was applied to one side of an aluminum foil (alloy number: 1N30 specified in JIS H4160) having a thickness of 30 μm using a gravure roll coater and dried to form a 0.35 μm thick adhesive coating layer. A 30 μm thick low-density polyethylene (MFR = 7) was extruded and laminated on the adhesive coating layer. Furthermore, a hot-melt adhesive having the following formulation was applied in a dotted pattern using a gravure roll coater in a coating amount of 12.7 g/ ^m2 to obtain a cover material.

[Table 1]

Element Compounding amount (parts by mass) Ethylene-vinyl acetate copolymer (vinyl acetate content 28%, MFR value 18g/10min, Vicat softening point 40℃) 35 Adhesive agent (rosin ester resin with a softening point of 85°C) 5 Wax (Fischer-Tropsch wax with a melting point of 102°C) 60 30

Comparative Example 1

A hot-melt adhesive was prepared in the same manner as in Example 1 except that talc was not added to the hot-melt adhesive and the coating amount of the hot-melt adhesive was 12.1 g/m ² , and a cover material was produced.

Comparative Example 2

A hot melt adhesive was prepared in the same manner as in Example 1, except that calcium carbonate (light calcium carbonate, average particle size 2.0×0.4 μm) was used instead of talc and the coating amount of the hot melt adhesive was changed to 14.4 g/m ² , and a cover material was produced.

Comparative Example 3

A hot melt adhesive was prepared in the same manner as in Example 1, except that rutile titanium oxide (average particle size 0.25 μm, specific gravity 4.1, oil absorption 19 g/100 g) was used instead of talc and the coating amount of the hot melt adhesive was changed to 14.6 g/m ² , and a cover material was produced.

Comparative Example 4

A hot melt adhesive was prepared in the same manner as in Example 1, except that anatase titanium oxide (average particle size 0.25 μm, oil absorption 25 g/100 g) was used instead of talc and the coating amount of the hot melt adhesive was changed to 14.0 g/m ² , and a cover material was produced.

Comparative Example 5

A hot melt adhesive was prepared in the same manner as in Example 1, except that kaolin (average particle size 0.4 μm, oil absorption 43 g/100 g) was used instead of talc and the coating amount of the hot melt adhesive was changed to 12.2 g/m ² , and a cover material was produced.

Comparative Example 6

A hot melt adhesive was prepared in the same manner as in Example 1, except that 10 parts by mass of silica (average particle size 3.5-4.3 μm, oil absorption 300-350 mL/100 g (linseed oil)) was used instead of talc and the coating amount of the hot melt adhesive was changed to 11.8 g/m ² , and a lid material was produced.

(Evaluation test)

"Seal strength based on hot plate heating"

The cover materials obtained in Example 1 and Comparative Examples 1 to 6 were cut into strips of 10 cm in length and 15 mm in width to make test pieces. The end 20 mm of the test piece was sealed to a polystyrene plate at the sealing temperature in Table 2, the sealing time of 1 second, and the sealing pressure of 0.2 MPa. The other end of the test piece whose end was sealed to the polystyrene plate was placed in a tensile testing machine (Autograph (registered trademark) AGS-500NJ, Shimadzu Corporation), and a 180° peel test was performed at a peeling speed of 300 mm/min, 5 times each. The average values of the 5 sealing strengths obtained are shown in Table 2 and Figure 2. Under the sealing conditions this time, from a practical point of view, it is preferred that the sealing strength is 10N/15mm width or more at a sealing temperature of 140°C. In addition, it is more preferred that the sealing temperature is 5N/15mm width or more at a sealing temperature of 100°C.

[Table 2]

"Seal strength based on high frequency induction heating"

The cover material obtained in Example 1 and Comparative Examples 1 to 6 was cut into a circle with an outer diameter of 38 mm, installed in a polystyrene container with a volume of 65 mL in the shape of a bottle with an outer diameter of 24 mm at the opening and an inner diameter of 20 mm at the opening, and sealed with a power of 110 to 170 W, a sealing pressure of 0.05 MPa, and a sealing time of 1.4 seconds. After sealing, the end of the cover material was peeled off at a speed of 300 mm/min in a direction of 45 degrees relative to the surface of the container sealed with the cover material, and the maximum value during peeling was taken as the sealing strength. The peeling test was performed 5 times, and the average value was used. From a practical point of view, it is preferred to maintain a sealing strength of more than 7N at a power of 125 W. The results obtained are shown in Table 3 and Figure 3.

[Table 3]

Embodiments 2 to 6

Hot melt adhesives were prepared in the same manner as in Example 1, and lid materials were produced, except that the amount of talc added was changed from 30 parts by mass to 5 parts by mass (Example 2), 10 parts by mass (Example 3), 20 parts by mass (Example 4), 50 parts ^by mass (Example 5), or 70 parts by mass (Example 6), and the amount of hot melt adhesive applied was changed from 12.7 g/m ² to 12.5 g/m ² , 14.5 g/m ² , 14.0 g/m ² , 14.2 g/m ² , or 14.8 g/m 2, respectively.

(Evaluation test)

Regarding the lid materials of Examples 2 to 6, the tests of "seal strength by hot plate heating" and "seal strength by high-frequency induction heating" were carried out in the same manner as in Example 1. The results obtained in the former are shown in Table 4 and FIG. 4 together with the results of Example 1 and Comparative Example 1, and the results obtained in the latter are shown in Table 5 and FIG. 5 together with the results of Example 1 and Comparative Example 1.

[Table 4]

[Table 5]

Embodiment 7, 8

A hot melt adhesive was prepared in the same manner as in Example 1, and a lid material was produced, except that the talc having an average particle size (D50) of 16 μm (Example 1) was changed to talc having an average particle size (D50) of 8 μm (apparent density 0.25 g/mL, specific surface area 7.0 m ² /g) (Example 7) or talc having an average particle size (D50) of 25 μm (apparent density 0.55 g/mL, specific surface area 2.5 ^{m 2} /g) (Example 8), and the coating amount of the hot melt adhesive was changed from 12.7 g/m ² to 12.4 g/m ² or 12.8 g/m ² , respectively.

(Evaluation test)

Regarding the lid materials of Examples 7 and 8, the tests of "seal strength by hot plate heating" and "seal strength by high-frequency induction heating" were carried out in the same manner as in Example 1. The results obtained by the former are shown in Table 6 and FIG. 6 together with the results of Example 1, and the results obtained by the latter are shown in Table 7 and FIG. 7 together with the results of Example 1.

[Table 6]

[Table 7]

"Dissolution in n-hexane"

The lid materials of Comparative Example 1 (no talc), Example 1 (30 parts by mass of talc), Example 5 (50 parts by mass of talc) and Example 6 (70 parts by mass of talc) were cut into 10 cm square pieces to prepare test pieces. The test pieces were immersed in 200 mL of n-hexane for 2 hours at 25°C according to the National Standard of the People's Republic of China "Analysis Method for Hygienic Standards of Polyethylene, Polystyrene and Polypropylene Molded Products for Food Packaging" (GB/T5009.60-2003), thereby preparing the test solution. The obtained test solutions were transferred to eggplant flasks and concentrated under reduced pressure until the residual amount became several mL. The washing liquid obtained by washing the inner wall of the flask used in the reduced pressure concentration twice with 5 mL of n-hexane was added to the obtained concentrated solution, and the washing liquid was transferred to an evaporating dish of known weight that had been dried at 105°C in advance, and evaporated to dryness. Then, it was dried at 105°C for 2 hours, and then naturally cooled in a dryer. After natural cooling, the evaporating dish was weighed to determine the mass difference before and after the test, and the amount (mg) of the evaporation residue per 1 L of the test solution was calculated. The obtained results are shown in Table 8.

[Table 8]

n-Hexane dissolution Comparative Example 1 No Talc 36 mg/L Example 1 Talc 30 parts by mass 28 mg/L Example 5 Talc 50 parts by mass 24 mg/L Example 6 Talc 70 parts by mass 21 mg/L

(Inspection)

From the results of Table 2 (Figure 2) and Table 3 (Figure 3), it can be seen that among various fillers, talc can improve the sealing strength based on hot plate heating and high-frequency induction heating. In particular, in the case of Example 1 using talc, a sealing strength of 15.2N/15mm width was obtained by hot plate heating at 140°C, which maintained excellent sealing strength compared with Comparative Examples 2 to 6 using other fillers. In high-frequency induction heating, it also maintained excellent sealing strength compared with other fillers.

From the results of Table 4 (Figure 4) and Table 5 (Figure 5), it can be seen that there is a tendency that if the talc content is increased from 5 parts by mass, the sealing strength is improved (Examples 1 to 6). In the case of hot plate heating, it is known that if 5 parts by mass or more of talc is added, the sealing strength at 140°C is 10N/15mm width or more, which is the preferred sealing strength. Even at 100°C, if the talc addition amount is 20 parts by mass or more, it is maintained at 5N/15mm width or more, so it is more preferred. In high-frequency induction heating, it is known that by adding 5 parts by mass or more of talc, a sealing strength of 7.1N is maintained even at a low power of 125W, and processing can be performed even in low-power areas.

From the results of Table 6 (Figure 6) and Table 7 (Figure 7), it can be seen that there is a tendency that as the particle size of talc decreases, the sealing strength increases under higher sealing conditions (Examples 1, 7, and 8). Within the range of the experimental results of this time, excellent sealing strength can be obtained even under low sealing conditions.

It should be noted that, as can be seen from the results of Table 8, as the talc content increases, the n-hexane dissolution amount decreases. In addition, in accordance with the standard criteria of the Food Sanitation Act, an evaporation residue test was performed using n-heptane as the dissolution liquid. As a result, in all of Examples 1, 5, and 6, the residue relative to n-heptane was 20 μg/mL or less, and excellent quality was maintained with respect to n-heptane dissolution based on the standard criteria of the Food Sanitation Act.

Industrial Applicability

In the cover material of the present invention in which a substrate layer, an adhesive coating layer, a stress relief layer and a hot-melt adhesive layer are sequentially laminated, a hot-melt adhesive is used to form the hot-melt adhesive layer, and a hot-melt adhesive is used in which a specific amount of talc is mixed in a mixture of ethylene-vinyl acetate copolymer, an adhesive imparting agent and wax in a specific range of amounts. Therefore, even in the case where a material with a higher molecular weight is selected as a material constituting the hot-melt adhesive in order to reduce the dissolution amount of the cover material in the organic solvent, the sealing property can be kept unchanged. Therefore, it is useful as a cover material for food containers and pharmaceutical containers.

BRIEF DESCRIPTION OF THE DRAWINGS

1. Substrate layer

2 Adhesive coating

3 Stress relief layer

4 Hot melt adhesive layer

10 Cover material.

Claims (7)

1. A cover material comprising at least a substrate layer, an anchor coating layer, a stress relaxation layer and a hot-melt adhesive layer, wherein the layers are laminated in the above order, and the hot-melt adhesive constituting the hot-melt adhesive layer contains 20 to 50% by mass of ethylene-vinyl acetate copolymer as component A, and further contains the following components B to D in the following mass parts relative to 100 parts by mass of component A: A: 100 parts by mass of ethylene-vinyl acetate copolymer; B: 8 to 80 parts by weight of an adhesive agent; C: 85 to 230 parts by mass of wax; and D: talc 60 to 170 parts by mass, The talc of component D has the following characteristics d1 to d3: d1: particle size D50 0.1～50μm; d2: apparent density 0.05-0.7 g/mL; and d3: Specific surface area 1.5～100m ² /g, The ethylene-vinyl acetate copolymer of component A has the following properties a1 to a3: a1: Vinyl acetate content 14-41% by mass; a2: MFR value 5 to 400 g/10 minutes; and a3: Vicat softening point 25～75℃, The adhesiveness imparting agent of component B has the following property b1: b1: Softening point 80～150℃, The wax of component C has the following properties c1: c1: melting point 80～130℃, The thickness of the substrate layer is 5 to 300 μm, the thickness of the anchor coating layer is 0.1 to 6.0 μm, the thickness of the stress relaxation layer is 6 to 60 μm, and the adhesion amount of the hot melt adhesive layer is 3 to 40 g/m ² . According to the National Standard of the People's Republic of China GB/T5009.60-2003 "Analysis Method for Hygienic Standards of Polyethylene, Polystyrene and Polypropylene Molded Products for Food Packaging", the evaporation residue in the n-hexane dissolution test is less than 30 mg. The residue amount in the evaporation residue test of oily food using n-heptane as the dissolution liquid is stipulated in the standard test for utensils and containers and packaging of the Ministry of Health, Labor and Welfare Notice No. 370 of 1974, the standard standard of the Food Sanitation Law of Japan, that is, the dissolution amount in heptane is less than 30μg/mL. 2. The lid material according to claim 1, wherein, in the following sealing strength evaluation test based on hot plate heating and sealing strength evaluation test based on high-frequency induction heating, the sealing strength based on hot plate heating is 10N/15mm width or more at a sealing temperature of 140°C, and is 5N/15mm width or more at a sealing temperature of 100°C, and the sealing strength based on high-frequency induction heating is 7N or more at a power of 125W, "Seal strength evaluation test based on hot plate heating" The end 20 mm of the test piece cut into a strip with a length of 10 cm and a width of 15 mm was sealed to a polystyrene plate at a sealing temperature of 100°C and 140°C, a sealing time of 1 second, and a sealing pressure of 0.2 MPa. The other end of the test piece whose end was sealed to the polystyrene plate was placed in a tensile testing machine, and a 180° peeling test was performed at a peeling speed of 300 mm/min. "Seal strength evaluation test based on high-frequency induction heating" The test piece was cut into a circle with an outer diameter of 38 mm and installed in a polystyrene container with a capacity of 65 mL in the shape of a bottle with an outer diameter of 24 mm at the opening and an inner diameter of 20 mm at the opening. After sealing with a power of 125 W, a sealing pressure of 0.05 MPa, and a sealing time of 1.4 seconds, the end of the cover material was peeled off at a speed of 300 mm/min in a direction of 45 degrees to the surface of the container sealed with the cover material, and the maximum value at the time of peeling was measured. 3 . The lid material according to claim 1 , wherein the adhesiveness imparting agent of component B is a rosin-based resin, and the wax of component C is a Fischer-Tropsch wax. 4. The cover material according to claim 1 or 2, wherein: The substrate layer is a metal or alloy film or a resin film. The adhesive coating is a modified polyolefin adhesive coating layer, a polyester adhesive coating layer or a polyurethane adhesive coating layer. The stress relaxation layer is a polyolefin-based or polyester-based thermoplastic resin layer. 5 . The lid material according to claim 4 , wherein the base material layer is an aluminum foil having a thickness of 5 to 50 μm. The cover material according to claim 5 , wherein a printed layer is formed on an outer surface of the base material layer. 7. A food container, characterized in that it comprises a food container having an opening with a flange, liquid or solid food contained therein, and a cover material bonded to the flange formed at the opening of the food container, wherein the cover material is the cover material according to any one of claims 1 to 6, and the cover material is bonded to the flange of the opening from the hot-melt adhesive layer side.