CN112895644A

CN112895644A - Multilayer resin sheet and molded container

Info

Publication number: CN112895644A
Application number: CN201911219109.3A
Authority: CN
Inventors: 杉本和也; 德永久次; 大岛和宏; 周腾飞
Original assignee: Denka Co Ltd
Current assignee: Denka Co Ltd
Priority date: 2019-12-03
Filing date: 2019-12-03
Publication date: 2021-06-04
Also published as: TW202122261A; WO2021111815A1; JPWO2021111815A1

Abstract

The present invention provides a multilayer resin sheet, which is formed by laminating a surface layer, an oxygen barrier layer, an intermediate layer, a base material layer and an outermost layer through an adhesive layer, wherein the surface layer is formed by a polyolefin resin layer containing a mixture of a polyethylene resin and a polypropylene resin; the outermost layer is formed of a polystyrene resin layer, and the layer structure ratio of the thickness of the outermost layer to the total thickness of the sheet is 1% to 8%. The multilayer resin sheet and thermoformed container thereof according to the present invention have oxygen barrier properties and good heat sealability, can be brought into sufficient contact with a lid material when used as a food packaging container, can be stably peeled off, can suppress the rupture or stringing of the lid material, and have good notch cracking properties, so that individual containers can be easily separated when a plurality of containers are assembled into a single container group.

Description

Multilayer resin sheet and molded container

Technical Field

The present invention relates to a thermoplastic multilayer resin sheet and a molded container obtained by thermoforming the same.

Background

In recent years, multilayer resin sheets as disclosed in patent documents 1 to 5, which are thermoplastic resin sheets for forming food packaging containers required to have oxygen barrier properties, such as containers for packaging dairy products such as foods containing a large amount of moisture and yogurts containing anaerobic components, and containers made of the same have become widespread. The container formed of the multilayer resin sheet is capable of suppressing permeation of oxygen from the inside of the container and preventing deterioration of the quality of the packaged contents due to permeation of moisture inside and outside the container caused by moisture absorption or volatilization of the contents.

Further, the multilayered resin sheets of patent documents 1 to 4 are mainly characterized in that a thermoplastic resin layer, a polyolefin resin layer having excellent properties, and an ethylene-vinyl alcohol copolymer resin layer having excellent oxygen barrier properties are laminated together to impart thermoformability. The focus of patent document 5 is to provide the multilayer resin sheet with the above-described properties such as oxygen barrier properties and heat sealability.

Patent document 1: japanese patent laid-open No. H11-58619

Patent document 2: japanese patent laid-open No. H11-138705

Patent document 3: japanese patent No. 3967899

Patent document 4: japanese patent laid-open No. 2000-108287

Patent document 5: japanese patent laid-open No. 2018-12263

However, in the techniques disclosed in the above patent documents 1 to 5, when the lid material is peeled off after heat sealing, a phenomenon (hereinafter referred to as "wire drawing phenomenon") occurs in which the lid material is broken or in which a resin constituting a skin layer or a lid material sealing layer of a multilayer resin sheet is coagulated and broken when the lid material is used as a food packaging container. There is a risk that residues resulting from the breakage of the lid material or the resin after the wire drawing may be mixed into the contents in the packaging container. Further, the molded containers formed of a multilayer resin sheet disclosed in patent documents 1 to 5 have a problem that the cut crack property is poor when the individual container body is separated from the container group in which a plurality of containers are integrally formed.

Disclosure of Invention

In view of the above-described problems of the prior art, an object of the present invention is to provide a multilayer resin sheet which has an oxygen barrier property and, at the same time, has good heat sealability so as to be sufficiently joined to a lid material and stably peelable when used as a food packaging container, which can suppress the above-described lid material cracking and wire drawing phenomenon, and which has good notch cuttability so as to easily separate individual containers when a plurality of containers are combined into a single container group. The present invention also provides a molded container obtained by thermoforming the multilayer resin sheet.

A multilayer resin sheet according to an embodiment of the present invention is a multilayer resin sheet in which a skin layer, an oxygen barrier layer, an intermediate layer, a base material layer, and an outermost layer are laminated via an adhesive layer, and is characterized in that: the skin layer is composed of a polyolefin resin layer, and the polyolefin resin layer contains a mixture of polyethylene resin and polypropylene resin; the outermost layer is composed of a polystyrene resin layer, and the thickness of the outermost layer is 1% to 8% of the total thickness of the sheet.

In addition, in the multilayer resin sheet provided by the invention, the polyolefin resin layer has dynamic viscoelasticity, and both the storage elastic modulus and the loss elastic modulus are more than 1E +04Pa and less than 1E +07Pa in the temperature range of 110-130 ℃.

In the multilayer resin sheet of the present invention, the base layer is composed of a polystyrene resin layer, and the content of rubber contained in the polystyrene resin of the base layer is 6% or less.

In the multilayer resin sheet of the present invention, the base layer contains 1% or more of a polyolefin resin component incompatible with the polystyrene resin.

In the multilayer resin sheet of the present invention, the content of rubber contained in the polystyrene resin of the base layer is 3% to 6%.

In the multilayer resin sheet of the present invention, the polypropylene resin in the polyolefin resin layer constituting the skin layer is mixed in a proportion of 5% to 50%.

In the multilayer resin sheet of the present invention, the polyethylene resin is low-density polyethylene; the polypropylene resin is composed of a random copolymer or a block copolymer.

The present invention also provides a molded container obtained by thermoforming the multilayer resin sheet.

According to the multilayer resin sheet of the present invention, when used as a molded container, the skin layer forming a heat seal surface with the lid material is a polyolefin resin layer using a mixed resin obtained by dispersing and mixing a polyethylene resin and a polypropylene resin at a different mixing ratio. Therefore, the peeling strength when peeling the lid material can be adjusted, the lid material can be prevented from being broken, and the occurrence of the wire drawing phenomenon can be sufficiently suppressed. Further, since the laminate sheet has a thin outermost layer made of a polystyrene resin in a layer structure ratio of 1% to 8% with respect to the entire thickness of the sheet, crack propagation is improved when the individual container bodies are separated by the cuts at the time of container molding, and good cut cracking properties are obtained.

Drawings

FIG. 1 is a longitudinal sectional view showing one example of the layer structure of a multilayer resin sheet of the present invention;

fig. 2 is a schematic perspective view showing one example of a food packing container as a molded container of the present invention;

fig. 3 is a schematic view showing the method of the present invention for evaluating bending resistance.

Detailed Description

As shown in fig. 1, the multilayer resin sheet according to one embodiment of the present invention is such that an oxygen barrier layer 12 is laminated between a skin layer 10a and an intermediate layer 10b, which are composed of a polyolefin resin layer, via an adhesive layer 11a and an adhesive layer 11b, the intermediate layer 10b is laminated on a base layer 13, which is composed of a polystyrene resin layer, via an adhesive layer 11c, and the base layer 13 is laminated on an outermost layer 14, which is composed of a polystyrene resin layer. That is, the multilayer resin sheet according to the present embodiment has a structure of a skin layer 10a, an adhesive layer 11a, an oxygen barrier layer 12, an adhesive layer 11b, an intermediate layer 10b, an adhesive layer 11c, a base layer 13, and an outermost layer 14 from the top as shown in fig. 1.

The following description sequentially describes the skin layer 10a, the intermediate layer 10b, the adhesive layers 11a, 11b, and 11c, the oxygen barrier layer 12, the base layer 13, and the outermost layer 14 in this order, and further describes the multilayer resin sheet of the present invention itself and a food packaging container as a molded container formed from the same.

Skin layer 10a and intermediate layer 10b

The skin layer 10a and the intermediate layer 10b are layers necessary for imparting a water vapor barrier property to the multilayer resin sheet, and the skin layer 10a is an important layer to be a heat-sealing surface with a lid material when the multilayer resin sheet is used as a food packaging container, and is formed of a resin mixture of a polyethylene resin and a polypropylene resin, which are polyolefin resins. In the present embodiment, the intermediate layer 10b is made of the same material as the skin layer 10a in order to facilitate the production of the multilayer resin sheet.

As the polyethylene resin constituting the main component of the resin mixture, for example, low density polyethylene, medium density polyethylene, high density polyethylene, linear (linear) polyethylene, ethylene- α -olefin copolymer polymerized using a metallocene catalyst, ethylene-vinyl acetate copolymer, ethylene ionomer resin, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl methacrylate copolymer, ethylene-propylene copolymer, and the like can be generally used. The polypropylene resin constituting the resin mixture may be generally, for example, a homopolymer, a random copolymer, or a block copolymer, and the resin mixture is a dispersed mixed resin obtained by mixing a polyethylene resin with any one of a homopolymer, a random copolymer, and a block copolymer.

Among these, low-density polyethylene is preferably used as the polyethylene resin from the viewpoint of tearability at the time of forming a cut. In addition, from the viewpoint of film formability and thermoformability of the multilayer resin sheet, a random copolymer and a block copolymer are preferably used as the polypropylene-based resin.

The mixing method of the polyolefin-based resin mixture of the present embodiment is not particularly limited, and a usual mixing method can be employed. For example, a dry mixing method in which individual small particles are simply mixed using a mixing stirrer such as a drum, or a compounding method in which resin pellets are heated using an extruder and then melt-mixed may be used.

The mixing ratio of the resin mixture is preferably 5% to 50% of the polypropylene resin. When the mixing ratio of the polypropylene-based resin is 5% or more, the peel strength at the time of peeling the lid material can be appropriately suppressed, and the breakage of the lid material can be suppressed. When the mixing ratio is 50% or less, a sufficient peel strength can be obtained in practical use. Further, the mixing ratio of the polypropylene-based resin in the resin mixture is preferably 10% or more and 40% or less.

The skin layer (10 a) comprising a polyolefin resin layer containing the resin mixture has a dynamic viscoelasticity such that both the storage elastic modulus and the loss elastic modulus are 1E +04Pa or more and less than 1E +07Pa in a temperature range of 110 ℃ to 130 ℃. When both the storage elastic modulus and the loss elastic modulus are 1E +04Pa or more, thermal deformation of the skin layer 10a can be appropriately suppressed, so that the problem that the skin layer 10a is greatly thermally deformed by heat at the time of heat sealing to cause entanglement of the sealing layer of the lid material can be solved, and the problem that the wire drawing phenomenon occurs at the time of peeling off the lid material can be sufficiently solved. On the other hand, when both the storage elastic modulus and the loss elastic modulus are less than 1E +07Pa, the thermal deformation of the skin layer 10a is moderate, so that the bonding area with the lid material is moderate, and sufficient bonding strength required for peeling the lid material in practical use can be easily obtained. The dynamic viscoelasticity of the skin-like layer 10a formed of the polyolefin resin layer containing the resin mixture can be adjusted by adjusting the blending ratio of the polypropylene resin.

As described above, the constituent resins of the skin layer 10a and the intermediate layer 10b generally only need to contain a polyethylene resin and a polypropylene resin, but other resins such as a methylpentene polymer and a polybutene polymer, which do not contain a polyethylene resin or a polypropylene resin, may be blended, and various additional components other than the resin component may be added, within the range not to impair the effects of the present invention. Examples of the additive component include colorants such as pigments and dyes, particulate lubricants such as talc, clay, and silica, antistatic agents such as chlorine compounds of sulfonic acid and alkali metals, and antistatic agents such as polypropylene glycol, ultraviolet absorbers, and antibacterial agents.

Examples of the resin constituting the sealing layer of the lid material to be heat sealed include, but are not limited to, low density polyethylene, block low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl methacrylate copolymer, ethylene ionomer resin, and ethylene-propylene copolymer.

The total thickness of the skin layer 10a and the intermediate layer 10b is preferably 1 to 30% of the total thickness of the multilayer resin sheet. More preferably, the layer structure ratio is 2% or more and 10% or less. The layer structure ratio referred to herein is a value obtained by dividing the total thickness of the skin layer 10a and the intermediate layer 10b by the thickness of the entire sheet, in terms of percentage. When the layer structure ratio is 1% or more, a sufficient thickness of the polyolefin-based resin layer can be secured and the polyolefin-based resin layer can be sufficiently exhibited, particularly even when the entire thickness of the multilayer resin sheet is small. On the other hand, when the layer structure ratio is 30% or less, the depth of insertion of the cutting blade can be made shallow when forming the notch in the container, and the appearance defect called whisker burr generated by the expansion of the resin can be suppressed.

The skin layer 10a and the intermediate layer 10b formed by the above method can control the peel strength with the lid material to 4 to 30N when the multilayer resin sheet is thermoformed and used as a packaging container. When the peel strength is 4N or more, sufficient sealing properties can be secured, and leakage of the contents can be suppressed. When the peel strength is 30N or less, the occurrence of breakage or wire drawing of the lid material during peeling of the lid material can be suppressed.

In the present embodiment, the intermediate layer 10b is formed of the same material as the skin layer 10a, but the intermediate layer 10b may be formed of a different material from the skin layer 10 a.

Adhesive layers 11a, 11b, 11c

The adhesive layers 11a, 11b, and 11c of the present embodiment play an important role as an adhesive material for laminating different kinds of constituent resins, and a modified polyolefin polymer is preferable as a constituent material thereof. Examples of the modified polyolefin-based polymer constituting the adhesive layer include homopolymers of olefins having about 2 to 8 carbon atoms such as ethylene, propylene, and 1-butene; olefin resins such as copolymers of these olefins with other olefins having 2 to 20 carbon atoms such as ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, and 1-decene, vinyl compounds such as vinyl acetate, vinyl chloride, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, and polystyrene, copolymer rubbers such as ethylene-propylene copolymers, ethylene-propylene-diene copolymers, ethylene-1-butene copolymers, and propylene-1-butene copolymers, and copolymers such as acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, and tetrahydrophthalic acid, and unsaturated carboxylic acids or acid halides thereof, Derivatives such as amides, imides, acid anhydrides, and esters, specifically, maleyl chloride (malenyl chloride), maleimide, maleic anhydride, citraconic anhydride, monomethyl maleate, dimethyl maleate, and glycidyl maleate, are modified under the grafting reaction conditions.

Among the above materials as the modified polyolefin-based polymer, preferred are unsaturated dicarboxylic acids or anhydrides thereof, particularly maleic acid or anhydrides thereof modified ethylene-based resins, propylene-based resins, or ethylene-propylene or 1-butene copolymer rubbers.

The thickness of each of the adhesive layers 11a, 11b, and 11c is preferably 2 to 50 μm, and more preferably 10 to 30 μm, and when the thickness is 2 μm or more, sufficient adhesive strength can be obtained, and when the thickness is 50 μm or less, appearance defects called whisker burrs, which are generated by press working after hot forming, can be suppressed.

Oxygen barrier layer 12

The oxygen barrier layer 12 of the present embodiment is a layer necessary for imparting oxygen barrier properties to a multilayer resin sheet, and representative examples of the oxygen barrier resin constituting the oxygen barrier layer 12 include, but are not limited to, ethylene-vinyl alcohol copolymer resins, polyamide resins, polyvinyl alcohol, polyvinyl chloride, and the like. Among them, an ethylene-vinyl alcohol copolymer resin is preferable from the viewpoint of processability and moldability.

The ethylene-vinyl alcohol copolymer resin is usually obtained by saponifying an ethylene-vinyl acetate copolymer, and in order to achieve both oxygen barrier properties and extrusion moldability, the ethylene content is preferably 10 to 65 mol% (more preferably 20 to 50 mol%) and the saponification degree is preferably 90% or more (more preferably 95% or more).

Further, the polyamide resin may be exemplified by the following: namely, lactam polymers such as caprolactam and azacyclotridecane-2-one; aminocarboxylic acid polymers such as 6-aminocaproic acid, 11-aminocaproic acid, 12-aminododecanoic acid, etc.; a polycondensate of an aliphatic diamine such as 1, 6-hexanediamine, 1, 10-diaminodecane, dodecanediamine, 2, 4-or 2,4, 4-trimethylhexamethylenediamine, an alicyclic diamine such as 1, 3-or 1, 4-bis (aminomethyl) cyclohexane, 4,4' -diaminodicyclohexylmethane, a diamine unit such as an aromatic diamine such as m-xylylenediamine or p-xylylenediamine, and a dicarboxylic acid unit such as an aliphatic dicarboxylic acid such as adipic acid, suberic acid or sebacic acid, an alicyclic carboxylic acid such as cyclohexanedicarboxylic acid, or an aromatic dicarboxylic acid such as terephthalic acid or isophthalic acid; and copolymers of the above.

Specific examples of the polyamide resin include nylon 6, nylon 9, nylon 11, nylon 12, nylon 66, nylon 610, nylon 611, nylon 612, nylon 6T, nylon 6I, nylon MXD6, nylon 6/66, nylon 6/610, nylon 6/6T, and nylon 6I/6T, and among them, nylon 6 and nylon MXD6 are preferable.

The thickness of the oxygen barrier layer 12 is preferably 5 to 50 μm (more preferably 10 to 40 μm). When the thickness is 5 μm or more, the oxygen barrier layer does not break in the container after the multilayer resin sheet is thermoformed, and sufficient oxygen barrier property can be obtained, so that the quality of the content sealed in the container can be sufficiently maintained. When the thickness is 50 μm or less, since the oxygen barrier layer can be sufficiently thermally stretched at the time of container molding, a sufficient thickness of the container can be secured, and a molded container having a good appearance can be obtained.

Substrate layer 13

The base layer 13 of the present embodiment is a polystyrene resin layer, and examples of the polystyrene resin constituting the polystyrene resin layer 13 include homopolymers or copolymers of polystyrene monomers such as styrene, 2-phenyl-1-propylene, 4-methylstyrene, polydimethylstyrene, p-tert-butylstyrene, and polychlorostyrene; copolymers of these polystyrenic monomers with other monomers such AS styrene-acrylonitrile copolymers (AS resins), or graft polymers of the foregoing polystyrenic monomers with other polymers, for example, graft polymers obtained by graft polymerization in the presence of diene rubber polymers such AS polybutadiene, polystyrene-butadiene copolymers, polyisoprene, polychloroprene, etc., such AS high impact polystyrene (HIPS resins), styrene-acrylonitrile graft polymers (ABS resins), etc.

As the polystyrene-based resin, a mixture of polystyrene (GPPS resin) and high impact polystyrene (HIPS resin) is preferable from the viewpoint of rigidity and moldability, and it is preferable that the polystyrene-based resin contains a rubber component of 6% or less. More preferably, the amount of the rubber contained in the polystyrene resin is 3% to 6%. When the amount of the rubber contained in the polystyrene-based resin is 3% or more, sufficient impact resistance can be obtained, and the container is less likely to be broken when the molded container is dropped. When the rubber content is 6% or less, cracks are easily propagated, and therefore, when the respective containers are separated by the cuts formed at the time of container formation, the cut portions can be easily broken.

Further, it is preferable that the polystyrene-based resin layer contains 1% or more of a polyolefin-based resin as a component incompatible with the polystyrene-based resin. The multilayer resin sheet is brittle due to the polyolefin-based resin as an immiscible component, and can be easily broken when the cuts are broken. Further, it is more preferable that the polyolefin resin contained in the polystyrene resin layer as a component incompatible with the polystyrene resin is 1% or more and 5% or less.

As with the other layers, the base layer 13 may be mixed with other resins within a range not hindering the effect of the present invention, and various additives other than the constituent resins are not excluded, and the additives may be compatible materials that are compatible with each other, colorants such as pigments and dyes, release agents such as silicone oil and ethyl esters, fibrous reinforcing agents such as glass fibers, particulate lubricants such as talc, clay, and silica, chlorine compounds such as sulfonic acid and alkali metals, antistatic agents such as polypropylene glycol, ultraviolet absorbers, and antibacterial agents. Further, the waste resin generated in the production process of the multilayer resin sheet or food packaging container of the present invention may be used in combination.

The thickness of the substrate layer 13 is preferably 180-. When the thickness is 180 μm or more, the container obtained by thermoforming can have sufficient rigidity, and when the thickness is 1300 μm or less, heat transfer in the sheet thickness direction at the time of thermoforming can be made more sufficient, and therefore, good thermoformability is provided, and a shaped container having good appearance can be obtained.

Outermost layer 14

The outermost layer 14 is formed of a polystyrene-based resin, and is preferably formed of the same or similar resin as the polystyrene-based resin mixed in the base layer 13. Therefore, as the polystyrene resin used, for example, a homopolymer or a copolymer of polystyrene monomers such as polystyrene, α -methyl polystyrene, p-methyl polystyrene, polydimethylstyrene, p-t-polybutylstyrene, polychlorostyrene and the like; copolymers of these polystyrenic monomers with other monomers such AS polystyrene-acrylonitrile copolymers (AS resins), or graft polymers of the foregoing polystyrenic monomers with other polymers, for example, graft polymers obtained by graft polymerization in the presence of diene rubber polymers such AS polybutadiene, polystyrene-butadiene copolymers, polyisoprene, polychloroprene, etc., such AS high impact polystyrene (HIPS resins), polystyrene-acrylonitrile graft polymers (ABS resins), etc. From the viewpoint of rigidity and thermoformability, polystyrene (GPPS resin) and high impact polystyrene (HIPS resin) are generally used.

The thickness of the outermost layer 14 is preferably 1% to 8% in the layer structure ratio with respect to the thickness of the entire sheet. When the layer structure ratio thereof is 8% or less, sufficient crack propagation can be obtained when the individual container bodies are separated by the cut formed at the time of container molding, so that the fracture can be easily performed at the cut. More preferably, the outermost layer 14 has a layer structure ratio of 1% to 6% in thickness of the entire sheet. When the layer structure ratio is 1% or more, the appearance defects of the multilayer resin sheet due to the waste resin returned to the base material layer and the like are not exposed on the sheet surface, and a multilayer resin sheet having a good appearance can be obtained.

The base layer 13 and the outermost layer 14 having the above-described configuration. The multi-layered resin sheet has a folding endurance of less than 5 cycles as an index of bending endurance, and is easily broken even when the sheet is bent at an angle of less than 60 degrees, and is easily separated into individual container bodies by cuts formed during container molding.

Multilayer resin sheet

The multilayer resin sheet according to one embodiment of the present invention basically has a layer structure of a skin layer 10a, an adhesive layer 11a, an oxygen barrier layer 12, an adhesive layer 11b, an intermediate layer 10b, an adhesive layer 11c, a base layer 13, and an outermost layer 14, as shown in fig. 1, but the layer structure is not limited thereto. For example, each layer may be composed of two or more layers. Further, the portion called scrap generated in the manufacturing process of the multilayer resin sheet or the molding container of the present invention is not discarded, and may be recycled after being finely pulverized, or re-pelletized after being thermally melted as a recycling material to be returned to the structure of the multilayer resin sheet to form a new layer.

The thickness of the multilayer resin sheet is preferably 200-1300 μm. When the thickness is 200 μm or more, the side surface and the bottom of the container obtained by thermoforming can be sufficiently thick, and sufficient container strength can be obtained. On the other hand, when the thickness is 1300 μm or less, heat conduction in the thickness direction of the sheet material during thermoforming is easily sufficiently performed, so that the thermoformability is good, and a molded container having a good appearance can be obtained.

The method for producing the multilayer resin sheet is not particularly limited, and a general method can be employed. For example, a method of melt-extruding each raw material resin using 4 or more single-screw extruders or twin-screw extruders and obtaining a multilayer resin sheet by a distributor with a guide column and a T-die, a method of obtaining a multilayer resin sheet by a multi-channel die, or the like.

Food packing container

The molded container of the present invention is obtained by thermoforming the multilayer resin sheet of the present invention. Examples of the thermoforming method include a general vacuum forming method, a pressure forming method, a plunger press method in which a plunger is brought into contact with one surface of a sheet to form the sheet, a forming method in which a pair of male and female molds are brought into contact with both surfaces of a sheet to form the sheet, and so on, which is called a matched mold forming method. But the method is not limited thereto. Meanwhile, as a method for heating and softening the sheet before molding, a known sheet heating method such as non-contact heating in which radiation heating is performed by an infrared heater can be used.

When the molded container of the present invention is used as a food packaging container, notches are formed on both the surface and the outer surface of the molded container. For example, the food packaging container is formed by connecting a plurality of separable containers, and the plurality of connected containers separated by folding at the connecting position of each container are formed with a slit at the folding position for facilitating folding. The cross-sectional shape of the notch is generally formed in a V-shape, and it can be formed by heating by a hot plate method or the like and then inserting a V-shaped blade. Fig. 2 shows an example of a yogurt container having a cut-out.

Examples

The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the contents of the following examples and the like.

The resin raw materials used in examples and the like are as follows

(1) Polyolefin resin layer

LDPE resin: q400

(MI, manufactured by China petrochemical Shanghai petrochemical company, Ltd., MI: 4.0g/10min, (190 ℃, 2.16kgf))

HDPE resin: j2200

(Mi manufactured by Letian chemical Co., Ltd.; MI: 5.0g/10min, (190 ℃, 2.16kgf))

PP resin: PPB-M09

(MI, manufactured by Zhenhai refining chemical Co., Ltd., China, 9.0g/10min, (190 ℃, 2.16kgf))

(2) Oxygen barrier layer

Ethylene-vinyl alcohol copolymer (EVOH): EVAL J171B

(produced by Kuraray, MI: 1.7g/10min, (190 ℃, 2.16kgf), ethylene content: 32 mol%)

(3) Adhesive layer

Modified olefin-based polymer (modified PO): MODIC F502C

(Mitsubishi chemical Co., Ltd., MI: 1.3g/10min, (190 ℃, 2.16kgf))

(4) Polystyrene resin layer

HIPS resin: 4241

(MI: 4.0g/10min, (200 ℃, 5.0kgf))

GPPS resin: 1050

(MI, manufactured by Total Petrochemicals, 2.8g/10min, (200 ℃, 5.0kgf))

Each evaluation of the multilayer resin sheet was carried out by the following method

(A) Thickness of each layer

Test pieces were cut out at five points at evenly spaced positions from the width direction perpendicular to the flow direction of the multilayer resin sheet, the test pieces were cut into thin pieces using a single-edged knife, and the thickness of each layer was measured using an electron microscope

The thickness of each layer was calculated as an average value of the thickness of each layer at five points in the width direction of the multilayer resin sheet

Measurement machine: electron microscope KH7700 (manufactured by Hirox corporation)

(B) Peel strength from cover material

The surface of the skin-like layer 10a of the multilayer resin sheet and the lid material were heat-sealed under the following conditions, left to stand at a temperature of 23. + -. 2 ℃ and a relative humidity of 50. + -. 10% for 1 hour, then the unsealed end portion was fixed by sandwiching, and the peel strength was measured by a universal tester under a temperature of 23. + -. 2 ℃ and a relative humidity of 50. + -. 10%

(Heat sealing Condition)

Heat sealing temperature: 185 deg.C

Heat sealing pressure: 0.1MPa

Heat sealing time: 1.6 seconds

(stripping Condition)

A stripping machine: precision universal tester AGS-X (produced by Shimadzu corporation)

The measurement conditions were as follows: the average value of the stable peel strength region was calculated by performing vertical peeling at a drawing speed of 250 mm/min.

(C) Phenomenon of wire drawing

The peel appearance was visually observed using a test specimen of peel strength with a lid material, and evaluated according to the following criteria

1: no wire drawing phenomenon

2: there is a wire drawing phenomenon of less than 10mm

3: the phenomenon of wire drawing of more than 10mm exists

(D) Dynamic viscoelasticity test

A test piece (5 mm in width) was cut from an arbitrary position of the multilayer resin sheet, the test piece was cut with a single-blade knife, the skin layer was separated by peeling with a hand at the cut point, both ends of the peeled skin layer were fixed, and evaluation was performed under the following conditions using a dynamic viscoelasticity measuring apparatus

Fixed distance: 10mm

Measuring temperature: 50-150 deg.C

Temperature rise rate: 5 ℃/min

Frequency: 1Hz

Strain: 0.1 percent of

Measurement mode: stretching

(E) Rubber content of polystyrene resin in resin component of base layer

The measurement was performed by thermal decomposition gas chromatography. Cutting a test piece from an arbitrary position of the multilayer resin sheet, cutting a corresponding multilayer resin sheet layer constituting part from the test piece, thermally decomposing the scraped test piece under an environment heated to a certain high temperature by a thermal decomposition gas chromatograph, measuring gas peak areas of generated butadiene monomer and styrene monomer, and calculating a rubber component content contained in the test piece based on a calibration curve of other resin for determining a rubber component

The corresponding multilayer resin sheet layer constituting part is a base material layer. Specifically, first, a layer other than the analysis object is cut by a blade to be a base material layer only, and then the layer is sampled to be the analysis object

(F) Bending resistance/number of folding times

A test piece (15 mm. times.100 mm) was cut from an arbitrary position of the multilayer resin sheet, both ends of the test piece were clipped, and a folding endurance test was performed using a folding endurance tester

Folding endurance test machine: FPC folding resistance tester

The measurement conditions were as follows: the test piece was bent at a bending angle of 80 ℃ and a bending speed of 135rpm in a state where a load of 1100g was applied until the number of times of bending when the multilayer resin sheet was broken

(G) Bending resistance/bending angle

A test piece (15 mm. times.100 mm) was cut from an arbitrary position of the multilayer resin sheet, and the bending angle at which the multilayer resin sheet was broken when the test piece was bent was measured

The notch rupture characteristic of the formed container body is an important property that a consumer can easily separate the individual container bodies, and among the (F) bending resistance/rupture number, the smaller the number of times of rupture until the multilayer resin sheet is ruptured when the multilayer resin sheet is bent indicates the easier rupture, and the (G) bending resistance/rupture angle, as shown in fig. 3, the smaller the angle until rupture when the multilayer resin sheet is bent indicates the easier rupture. The (F) bending resistance/folding endurance and the G) bending resistance/folding angle are indices of ease of breaking.

EXAMPLE 1

A multilayer resin sheet having a layer structure of a 40 μm skin layer 10 a/10 μm adhesive layer 11 a/30 μm oxygen barrier layer 12/10 μm adhesive layer 11 b/40 μm intermediate layer 10 b/10 μm adhesive layer 11b/1035 μm base layer 13/25 μm outermost layer 14 and a total thickness of 1200 μm was obtained by a dispenser method using 2 φ 45mm single-screw extruders, 1 φ 65mm single-screw extruder, 1 φ 75mm single-screw extruder, and 1 φ 120mm single-screw extruder.

As a resin mixture of polyethylene resin and polypropylene resin, the skin layer 10a and the intermediate layer 10b are formed by mixing LDPE resin "Q400" and PP resin "M09" at a mass ratio of 80/20, the adhesive layers 11a, 11b and 11c are formed by mixing modified olefin polymer "MODIC F502C", the oxygen barrier layer 12 is formed by mixing ethylene-vinyl alcohol copolymer "EVAL J171B", the base layer 13 is formed by mixing HIPS resin "4241", GPPS resin "1050" and LDPE "Q400" at a mass ratio of 50/50/1, and the outermost layer is formed by mixing HIPS resin "4241".

The obtained multilayer resin sheet and container were subjected to various evaluations by the above-described various evaluation methods for multilayer resin sheets. The results are shown in Table 1.

As shown in Table 1, the peel strength of the container formed of the multilayer resin sheet of example 1 from the lid material was 18N (in the range of 4 to 30N), and the index of the drawing phenomenon was 1. The number of folding endurance times as bending characteristics was 2 times and reached the standard of less than 5 times, and the bending angle as bending characteristics was 40 degrees and reached the standard of less than 60 degrees. In example 1, the dynamic viscoelasticity of the skin layer 10a has a storage elastic modulus of 1.3E + 05Pa (in the range of 1E +04Pa to less than 1E +07 Pa) and a loss elastic modulus of 5.2E +04Pa (in the range of 1E +04Pa to less than 1E +07 Pa), so that the amount of thermal deformation of the skin layer 10a at the time of heat sealing is controlled within an appropriate range, and the entanglement of the sealing layer of the lid material is reduced, whereby a sufficient peel strength required for practical use can be obtained while suppressing the wire drawing phenomenon. Therefore, the container formed of the multilayer resin sheet of example 1 had good heat sealability, was able to be sufficiently joined to the lid material, was able to be stably peeled, was able to suppress the lid material from cracking and wire drawing, and had good notch crack properties, which were able to easily separate a plurality of container bodies formed as an integral container.

EXAMPLES 2 to 12, COMPARATIVE EXAMPLES 1 to 6

The multilayer resin sheet thus formed was the same as in example 1, except that the mixing ratio of the skin layer 10a, the intermediate layer 10b and the substrate layer 13 and the thickness of each layer were changed as shown in tables 1 and 2.

EXAMPLES 2 to 3

Specifically, as shown in table 1, in examples 2 and 3, only the skin layer component was changed from that of example 1, and the molded containers obtained therefrom all met the standards for peel strength with the lid material, the index of the drawing phenomenon, the fold endurance as the bending characteristics, and the bending angle. In the dynamic viscoelasticity of the skin layer 10a in examples 2 and 3, both the storage elastic modulus and the loss elastic modulus are in the range of 1E +04Pa or more and less than 1E +07Pa, and therefore the thermal deformation amount of the skin layer 10a at the time of heat sealing is controlled in an appropriate range, and the entanglement of the sealing layer of the lid material is reduced, whereby the wire drawing phenomenon is suppressed, and a sufficient peel strength required for practical use can be obtained. Therefore, the containers formed of the multilayer resin sheets of examples 2 and 3 have good heat sealability, can be sufficiently joined to the lid material, can be stably peeled, can suppress the lid material from cracking and wire drawing, and have good notch cracking properties, which can easily separate a plurality of container bodies formed as an integral container.

Examples 4 and 7

In examples 4 and 7, the composition of the HIPS resin and the GPPS resin in the base layer was changed from that of example 1, and the molded container formed therefrom met the standards for peel strength from the lid material, index of the drawing phenomenon, the number of times of folding resistance as bending characteristics, and the bending angle. In the dynamic viscoelasticity of the skin layer 10a in examples 4 and 7, both the storage elastic modulus and the loss elastic modulus are in the range of 1E +04Pa or more and less than 1E +07Pa, and therefore the thermal deformation amount of the skin layer 10a at the time of heat sealing is controlled in an appropriate range, and the entanglement of the sealing layer of the lid material is reduced, whereby the wire drawing phenomenon is suppressed, and a practical and sufficient peel strength can be obtained. Therefore, the containers formed of the multilayer resin sheets of examples 4 and 7 have good heat sealability, can be sufficiently joined to the lid material, can be stably peeled, can suppress the lid material from cracking and wire drawing, and have good notch cracking properties, and can easily separate a plurality of container bodies formed as an integral container.

EXAMPLE 5

In example 5, the composition of the polyolefin resin in the base layer was changed from that of example 1, and the molded container formed therefrom achieved the same standards as those for the peel strength from the lid material, the index of the drawing phenomenon, the number of folding times as bending characteristics, and the bending angle. In the dynamic viscoelasticity of the skin layer 10a in example 5, both the storage elastic modulus and the loss elastic modulus are in the range of 1E +04Pa or more and less than 1E +07Pa, and therefore the thermal deformation amount of the skin layer 10a at the time of heat sealing is controlled in an appropriate range, and the entanglement of the sealing layer of the lid material is reduced, whereby the wire drawing phenomenon is suppressed and a sufficient peel strength required for practical use can be obtained. Therefore, the container formed of the multilayer resin sheet of example 5 has good heat sealability, can be sufficiently joined to the lid material, can be stably peeled, can suppress the lid material from cracking and stringing, and has good notch cuttability, which enables easy separation of a plurality of container bodies formed as an integral container.

Examples 6 and 8

In examples 6 and 8, the thicknesses of the base material layer and the outermost layer and the composition ratio of the outermost layer were changed from those of example 1, and the molded container formed therefrom achieved the respective standards for peel strength from the lid material, index of the drawing phenomenon, the number of folding endurance and the bending angle as bending characteristics. In the dynamic viscoelasticity of the skin layer 10a in examples 6 and 8, both the storage elastic modulus and the loss elastic modulus are in the range of 1E +04Pa or more and less than 1E +07Pa, and therefore the thermal deformation amount of the skin layer 10a at the time of heat sealing is controlled in an appropriate range, and the entanglement of the sealing layer of the lid material is reduced, whereby the wire drawing phenomenon is suppressed, and a sufficient peel strength required for practical use can be obtained. Therefore, the containers formed of the multilayer resin sheets of examples 6 and 8 have good heat sealability, can be sufficiently joined to the lid material, can be stably peeled, can suppress the lid material from cracking and wire drawing, and have good notch cracking properties, and can easily separate a plurality of container bodies formed as an integral container.

EXAMPLE 9

In example 9, the polyolefin resin was not added to the base layer in comparison with example 1, only the resin component of the base layer was changed, and the molded container formed therefrom achieved standards for peel strength from the lid material, index of the drawing phenomenon, and the number of times of folding resistance and the bending angle as bending characteristics. In the dynamic viscoelasticity of the skin layer 10a in example 9, since both the storage elastic modulus and the loss elastic modulus are in the range of 1E +04Pa or more and less than 1E +07Pa, the thermal deformation amount of the skin layer 10a at the time of heat sealing is controlled in an appropriate range, and the entanglement of the sealing layer of the lid material is reduced, whereby the wire drawing phenomenon is suppressed and a sufficient peel strength required for practical use can be obtained. Therefore, the container formed of the multilayer resin sheet of example 9 had good heat sealability, was able to be sufficiently joined to the lid material, was able to be stably peeled, was able to suppress the lid material from cracking and wire drawing, and had good notch cuttability, which enabled easy separation of a plurality of container bodies formed as an integral container.

EXAMPLE 10

In example 10, the rubber content of the polystyrene-based resin in the resin component in the base layer was changed from that in example 1, and the polyolefin-based resin was not added to the base layer. The formed container has peel strength to the lid material, a drawing ratio index, and a folding endurance and a folding angle as bending characteristics all satisfying corresponding standards. In the dynamic viscoelasticity of the skin layer 10a in example 10, since both the storage elastic modulus and the loss elastic modulus are in the range of 1E +04Pa or more and less than 1E +07Pa, the thermal deformation amount of the skin layer 10a at the time of heat sealing is controlled in an appropriate range, and the entanglement of the sealing layer of the lid material is reduced, whereby the wire drawing phenomenon is suppressed and a sufficient peel strength required for practical use can be obtained. Therefore, the container formed of the multilayer resin sheet of example 10 had good heat sealability, was able to be sufficiently joined to the lid material, was able to be stably peeled, was able to suppress the lid material from cracking and wire drawing, and had good notch cuttability, which enabled easy separation of a plurality of container bodies formed as an integral container.

EXAMPLE 11

In example 11, the rubber content of the polystyrene resin in the resin component in the base layer was changed from that in example 1. The formed container has peel strength to the lid material, a drawing ratio index, and a folding endurance and a folding angle as bending characteristics all satisfying corresponding standards. In the dynamic viscoelasticity of the skin layer 10a in example 11, both the storage elastic modulus and the loss elastic modulus are in the range of 1E +04Pa or more and less than 1E +07Pa, and therefore the thermal deformation amount of the skin layer 10a at the time of heat sealing is controlled in an appropriate range, and the entanglement of the sealing layer of the lid material is reduced, whereby the wire drawing phenomenon is suppressed and a sufficient peel strength required for practical use can be obtained. Therefore, the container formed of the multilayer resin sheet of example 11 had good heat sealability, was able to be sufficiently joined to the lid material, was able to be stably peeled, was able to suppress the lid material from cracking and wire drawing, and had good notch cuttability, which enabled easy separation of a plurality of container bodies formed as an integral container.

EXAMPLE 12

In example 12, the rubber content of the polystyrene-based resin in the resin component in the base layer was changed to 7% relative to example 1. By changing the rubber content to 7%, the impact resistance of the multilayer resin sheet is improved, and although the fold resistance is increased and the folding angle is increased as compared with other examples, the formed container still has a fold resistance of less than 5 and a folding angle of less than 60 degrees, so that a plurality of container bodies formed into an integral container can be easily separated. In addition, in the dynamic viscoelasticity of the skin layer 10a in example 12, since both the storage elastic modulus and the loss elastic modulus are in the range of 1E +04Pa or more and less than 1E +07Pa, the thermal deformation amount of the skin layer 10a at the time of heat sealing is controlled in an appropriate range, the entanglement of the sealing layer of the lid material is reduced, the wire drawing phenomenon is suppressed, and a sufficient peel strength required for practical use can be obtained.

Comparative example 1

On the other hand, as shown in table 2, in comparative example 1, the skin layer was formed of only the LDPE resin as compared to example 1. The molded container thus obtained had a peel strength from the lid material of more than 30N and an index of the drawing phenomenon of 3. In the dynamic viscoelasticity of the skin layer, the storage elastic modulus and the loss elastic modulus were both higher than those of example 1, and since the fluidity of the skin layer resin as the heat seal surface layer was high, the bonding area with the lid material was large, the lid material was not easily peeled off from the container, and the wire drawing phenomenon was also generated.

Comparative example 2

In comparative example 2, the skin-like layer was formed only of the PP resin, compared to example 1. The peel strength from the lid member of the molded container thus formed was zero, the storage elastic modulus and the loss elastic modulus of the dynamic viscoelasticity of the skin layer were both lower than those of example 1, the fluidity of the skin layer resin as the heat seal surface layer was small, the bonding area with the lid member was small, the lid member could not be sufficiently bonded to the container, and the folding endurance number was 186 times, and the container bodies formed as an integral container could not be easily separated.

Comparative example 3

In comparative example 3, the skin layer was formed only from the HDPE resin, as compared to example 1. The molded container thus formed had a folding endurance of 127 times, and it was not easy to separate the plurality of container bodies formed as an integral container.

Comparative examples 4, 5 and 6

In comparative examples 4, 5 and 6, the thicknesses of the base material layer and the outermost layer and the composition ratio of the outermost layer were changed from those of example 1. The molded container thus formed has a folding endurance of 5 or more and a folding angle of 60 degrees or more, and therefore, it is not easy to separate a plurality of container bodies formed as an integral container.

TABLE 1

。

TABLE 2

Claims

1. A multilayer resin sheet comprising a skin layer, an oxygen barrier layer, an intermediate layer, a substrate layer, and an outermost layer laminated via an adhesive layer, characterized in that:

the skin layer is composed of a polyolefin resin layer, and the polyolefin resin layer contains a mixture of polyethylene resin and polypropylene resin;

the outermost layer is composed of a polystyrene resin layer

The outermost layer has a layer structure ratio of 1% to 8% with respect to the total thickness of the sheet.

2. The multilayer resin sheet according to claim 1,

the dynamic viscoelasticity of the polyolefin resin layer is that the storage elastic modulus and the loss elastic modulus are both more than 1E +04Pa and less than 1E +07Pa in the temperature range of 110-130 ℃.

3. The multilayer resin sheet according to claim 1 or 2,

the base material layer is composed of a polystyrene resin layer, and the content of rubber contained in the polystyrene resin of the base material layer is 6% or less.

4. The multilayer resin sheet according to claim 3,

the base material layer contains more than 1% of polyolefin resin component which is not compatible with polystyrene resin.

5. The multilayer resin sheet according to claim 3,

the rubber content in the polystyrene resin of the base layer is 3% to 6%.

6. The multilayer resin sheet according to claim 1 or 2,

the blending ratio of the polypropylene resin in the polyolefin resin layer constituting the skin layer is 5% or more and 50% or less.

7. The multilayer resin sheet according to claim 1 or 2,

the polyethylene resin is composed of low-density polyethylene; the polypropylene resin is composed of a random copolymer or a block copolymer.

8. A molded container thermoformed from the multilayer resin sheet claimed in any one of claims 1 to 7.