JP7363588B2 - cap - Google Patents

Description

The present invention relates to a molded article made of a thermoplastic elastomer layer and a polyethylene layer, and a cap made of the same.

Conventionally, crown-shaped caps, pull-top caps, and screw caps have been used to seal the contents of containers. Screw caps have better sealing and resealing properties than non-screw caps such as crown-shaped caps and pull-top caps, and are therefore particularly suitable for use in applications where they are opened and tightened repeatedly.

The ease with which a screw cap can be opened is affected by the diameter, shape, type of knurling, material, etc. of the cap. Commonly available screw caps are constructed from relatively slippery materials such as metal, polypropylene, polyethylene, and the like. If the content is a milk drink such as milk, polyethylene is used based on the "Ministerial Ordinance Concerning Ingredient Standards for Milk and Dairy Products (Containers and Packaging Related)" (hereinafter referred to as the "Milk Ministerial Ordinance"). ing.

BACKGROUND ART Conventionally, as a device for improving the grip of a screw cap and making it easier to open the cap, it is known that the outer peripheral surface of the screw cap is subjected to an uneven surface treatment called knurling. However, in the case of a cap with a small diameter, knurling alone does not provide a sufficient effect, and it may be difficult to open the cap.

From the viewpoint of improving grip properties, Patent Document 1 discloses that a styrene-based thermoplastic elastomer, an olefin-based thermoplastic elastomer, a blend of a styrene-based thermoplastic elastomer and a polyolefin, or a blend of an olefin-based thermoplastic elastomer and a polyolefin are used. It is stated that in plastic products, by increasing the proportion of styrene-based thermoplastic elastomer or olefin-based thermoplastic elastomer, the plastic surface can be made less slippery and can be used as various grips.

Japanese Patent Application Publication No. 11-5848

As mentioned above, by using the olefin-based thermoplastic elastomer composition or the styrene-based thermoplastic elastomer composition described in Patent Document 1, it is thought that a screw cap with a non-slip surface and excellent grip properties can be obtained. . On the other hand, as mentioned above, polyethylene is suitable for bottle caps for milk drinks such as milk, based on the Milk Ministerial Ordinance.
Therefore, the screw cap has a laminated structure of a thermoplastic elastomer layer made of an olefin-based thermoplastic elastomer composition or a styrene-based thermoplastic elastomer composition described in Patent Document 1, and a polyethylene layer, with the outside being the thermoplastic elastomer layer and the inside being the thermoplastic elastomer layer. It is thought that by using a polyethylene layer, both grip performance and standard compliance can be achieved.

However, when the present inventor tried to fuse the olefin-based thermoplastic elastomer composition or styrene-based thermoplastic elastomer composition described in Patent Document 1 with polyethylene, it was found that these were difficult to fuse, making it difficult to use a practical screw. It turned out that the cap could not be molded.

Additionally, Patent Document 1 states, ``In order to reduce costs, only the surface portion is made of an olefin-based thermoplastic elastomer composition or a styrene-based thermoplastic elastomer composition, and the other parts are made of general-purpose plastic. For example, the inner layer of the container may be made of a general-purpose plastic such as low-density polyethylene, high-density polyethylene, polypropylene, etc., and the outer layer may be made of an olefin-based thermoplastic elastomer composition or a styrene-based thermoplastic elastomer composition. However, regarding the polyolefin to be blended with the styrenic thermoplastic elastomer, it is stated that the polyolefin used in the present invention is Examples include polyethylene, polypropylene, or polyethylene-propylene, and a specific example of a commercially available product thereof includes "Tisso Polypro, Grade: XK6004" available from Chisso Corporation. '', there is no study on the density of the polyethylene to be blended, and there is no specific example of blending polyethylene. Further, in Patent Document 1, no study is made on the fusion property with the polyethylene layer.

An object of the present invention is to provide a molded article formed by fusing a thermoplastic elastomer layer and a polyethylene layer, in which the thermoplastic elastomer layer and the polyethylene layer have sufficient fusion strength. . Another object of the present invention is to provide a cap such as a screw cap that has both grip properties and conformity to standards using this molded product.

As a result of extensive studies to solve the above problems, the present inventors have discovered that by using a styrene-based thermoplastic elastomer composition containing polyethylene having a specific density, the thermoplastic elastomer layer and the polyethylene layer can be sufficiently fused. It has been found that the screw cap has good adhesion strength and can be used as a screw cap to achieve both grip performance and standard compliance, leading to the present invention.
That is, the present invention has the following features.

[1] A molded article in which a thermoplastic elastomer layer made of a styrene-based thermoplastic elastomer composition containing polyethylene having a density of 0.910 to 0.960 g/cm ³ and a polyethylene layer are fused together.

[2] The molded article according to [1], wherein the styrenic thermoplastic elastomer composition has a Duro hardness A of 30 to 90.

[3] The molded article according to [1] or [2], wherein the styrenic thermoplastic elastomer composition contains the following components (A) to (C).
Component (A): Linear low-density polyethylene having a density of 0.910 to 0.960 g/ ^cm Component (B): Hydrogenated styrene/conjugated diene block copolymer component (C) : Softener for hydrocarbon rubber

[4] The molded article according to [3], wherein the styrenic thermoplastic elastomer composition contains 100 to 300 parts by mass of the component (B) based on 100 parts by mass of the component (A).

[5] The molded article according to [3] or [4], wherein the styrenic thermoplastic elastomer composition contains 200 to 400 parts by mass of the component (C) based on 100 parts by mass of the component (A). .

[6] The content of the component (B) in the styrenic thermoplastic elastomer composition is 35 to 65% by mass based on the total of the component (B) and the component (C), [3] to [ 5].

[7] The molded article according to any one of [1] to [6], wherein the polyethylene layer is made of high-density polyethylene.

[8] A cap made of the molded article according to any one of [1] to [7].

[9] The cap according to [8], which is a screw cap.

[10] The cap according to [8] or [9], which is a cap for a beverage container.

According to the present invention, a molded article in which a thermoplastic elastomer layer and a polyethylene layer are laminated and integrated with sufficient fusion strength is provided.
According to the present invention, by using this molded product, the inner surface of the cap that may come into contact with the contents of the bottle is made of a polyethylene layer, and the outer surface, where slip resistance is required for grip, is made of a thermoplastic elastomer layer. Therefore, it is possible to provide a cap such as a screw cap that has both grip properties and conformity to standards.

FIG. 1 is a partially sectional front view showing an example of a screw cap.

Embodiments of the present invention will be described in detail below.

A screw cap, which is a preferred use of the molded article of the present invention, has a shape as shown in FIG. 1, for example. As shown in FIG. 1, the screw cap 1 has a thread 1A carved on its inner circumferential surface for opening and tightening by screwing into the thread on the container opening. The outer peripheral surface 1B of the screw cap 1 is usually knurled.
In the present invention, the outer circumferential surface of a cap such as a screw cap that is held by hand when opening and tightening the cap is referred to as a "grip portion." Furthermore, the ability to open or close the cap when gripping the grip portion to open and close the cap is referred to as "grip ability."
When the molded article of the present invention is applied to a screw cap as shown in FIG. 1, the outer circumferential surface 1B in FIG. It is preferable that the inner side is a base material made of a polyethylene layer.

[Molded object]
The molded article of the present invention is a styrenic thermoplastic elastomer composition containing polyethylene having a density of 0.910 to 0.960 g/cm ³ (hereinafter sometimes referred to as "the styrenic thermoplastic elastomer composition of the present invention"). A thermoplastic elastomer layer (hereinafter sometimes referred to as "thermoplastic elastomer layer of the present invention") consisting of a polyethylene layer and a polyethylene layer are fused together.

[Styrenic thermoplastic elastomer composition]
<Polyethylene with a density of 0.910 to 0.960 g/cm ³ >
The polyethylene contained in the styrenic thermoplastic elastomer composition of the present invention is characterized by having a density of 0.910 to 0.960 g/cm ³ as measured according to JIS K7112. By setting the density of the polyethylene contained in the styrenic thermoplastic elastomer composition of the present invention within the above range, it is hard to slip, has excellent grip when used as a cap, and promotes recrystallization with polyethylene in a molten state. This makes it possible to increase the strength of the fusion bond with the polyethylene layer.
The lower limit of the density of the polyethylene contained in the styrenic thermoplastic elastomer composition of the present invention is preferably 0.915 g/cm ³ or more, more preferably 0.920 g/cm ³ or more. On the other hand, the upper limit thereof is preferably 0.950 g/cm ³ or less, more preferably 0.940 g/cm ³ or less.

As the polyethylene having a density of 0.910 to 0.960 g/ ^cm3 , known polyethylene can be used, and it may be a homopolymer of ethylene or a copolymer of ethylene with α-olefin or other vinyl compounds. It may also be a polymer.

Specific examples of polyethylene having a density of 0.910 to 0.960 g/ ^cm3 include low density polyethylene (LDPE), high density polyethylene (HDPE), medium density polyethylene (MDPE), and linear low density polyethylene (LLDPE). ), very low density polyethylene (VLDPE), low crystalline ethylene/1-butene random copolymer (EBM), ethylene/propylene copolymer, ethylene/vinyl acetate copolymer, ethylene/acrylic acid copolymer, ethylene - Examples include acrylic ester copolymers.

Among these, linear low density polyethylene is preferred. Linear low-density polyethylene is effective in improving the stability of molding processability and stability of peel strength, as well as improving the fusion strength with the polyethylene layer.

The melt flow rate (MFR) of polyethylene having a density of 0.910 to 0.960 g/cm ³ is preferably 0.1 g/10 minutes or more, more preferably 0.5 g/10 minutes or more. , preferably 100 g/10 minutes or less, more preferably 80 g/10 minutes or less. When the MFR of this polyethylene is within the above range, the thermoplastic elastomer layer of the present invention made of the styrenic thermoplastic elastomer composition of the present invention tends to have excellent molded appearance and tensile stress at cutting. Here, the MFR of polyethylene is a value measured according to JIS K6922 at a temperature of 190° C., a load of 21.2 N, and 10 minutes.

Polyethylene having a density of 0.910 to 0.960 g/cm ³ is available commercially. As commercially available products, appropriate ones can be selected and used from the "Novatec (registered trademark)" series manufactured by Nippon Polyethylene Co., Ltd., the "Umerit series" manufactured by Ube Maruzen Polyethylene Co., Ltd., and the like.

Only one type of polyethylene having a density of 0.910 to 0.960 g/cm ³ may be used, or two or more types having different physical properties, copolymer compositions, structures, etc. may be used as a mixture.

<Styrenic thermoplastic elastomer>
The styrenic thermoplastic elastomer contained in the styrenic thermoplastic elastomer composition of the present invention has at least one polymer block P derived from a vinyl aromatic compound and at least one polymer block Q derived from a conjugated diene. and a block copolymer obtained by hydrogenating the block copolymer (hydrogenated block copolymer).

The polymer block P is a monomeric polymer block mainly composed of a vinyl aromatic compound, while the polymer block Q is a monomeric polymer block mainly composed of a conjugated diene. Here, "consisting mainly" means that the content in the block is 50 mol% or more.

The monomeric vinyl aromatic compound constituting the polymer block P is not limited, but styrene derivatives such as styrene, α-methylstyrene, and chloromethylstyrene are preferred. Among these, it is preferable to mainly use styrene. These may be used alone or in combination of two or more. Note that the polymer block P may contain a monomer other than the vinyl aromatic compound as a raw material.

The monomer constituting the polymer block Q is not limited, but preferable examples include butadiene alone, isoprene alone, and a mixture of butadiene and isoprene. These may be used alone or in combination of two or more. Note that the polymer block Q may contain monomers other than butadiene and isoprene as raw materials.

Moreover, the polymer block Q may be a hydrogenated derivative obtained by hydrogenating the double bond it has after polymerization, that is, a hydrogenated block copolymer. The hydrogenation rate of the polymer block Q is not limited, but is preferably 50 to 100% by mass, more preferably 80 to 100% by mass. By hydrogenating the polymer block Q within the above range, thermal stability and weathering stability tend to improve. The same applies to the case where the polymer block P uses a diene component as a raw material. The hydrogenation rate can be measured by ¹³ C-NMR.

The styrene thermoplastic elastomer preferably has a styrene unit content of 8 to 45% by mass. When the styrene unit content of the styrenic thermoplastic elastomer is at least the above-mentioned lower limit, bleed-out of the hydrocarbon rubber softener from the styrenic thermoplastic elastomer composition can be suppressed. On the other hand, when it is below the above upper limit, it is possible to suppress the hardness of the styrenic thermoplastic elastomer from becoming too high. The styrene unit content of the styrenic thermoplastic elastomer is more preferably 10 to 40% by mass.
The term "styrene unit content" is used to include not only the content of styrene units but also the content of constituent units in which the aromatic ring of the styrene unit is substituted with an atom or atomic group other than a hydrogen atom. The styrene unit content can be measured by ¹³ C-NMR.

The chemical structure of the copolymer having the above-mentioned polymer block P and polymer block Q in the styrene thermoplastic elastomer may be linear, branched, radial, etc., but may be expressed by the following formula (1) Or, it is preferable that it is a block copolymer represented by (2).

Furthermore, the block copolymer represented by the following formula (1) or (2) is preferably a hydrogenated derivative (hydrogenated block copolymer). When the copolymer represented by the following formula (1) or (2) is a hydrogenated block copolymer, heat resistance stability and weather resistance stability tend to be good.
P-(Q-P) _m (1)
(P-Q) _n (2)
(In the formula, P represents the polymer block P, Q represents the polymer block Q, m represents an integer from 1 to 5, and n represents an integer from 1 to 5.)

In formula (1) or (2), m and n are preferably larger in terms of lowering the order-disorder transition temperature as a rubber-like polymer, but smaller in terms of ease of production and cost. .

In addition, the block copolymer and/or hydrogenated block copolymer (hereinafter collectively referred to as "(hydrogenated) block copolymer") of a styrenic thermoplastic elastomer has excellent rubber elasticity, so the formula The (hydrogenated) block copolymer represented by formula (1) is more preferable than the (hydrogenated) block copolymer represented by (2).

The upper limit of the weight average molecular weight of the styrenic thermoplastic elastomer is not limited, but is usually 700,000 or less, preferably 500,000 or less, and more preferably 300,000 or less. Further, the lower limit of the weight average molecular weight of the styrenic thermoplastic elastomer is not limited, but is usually 40,000 or more, preferably 60,000 or more, and more preferably 90,000 or more. By controlling the weight average molecular weight of the styrenic thermoplastic elastomer to be equal to or less than the above upper limit, moldability and appearance of the molded product can be maintained favorably. Further, by setting the weight average molecular weight to the above lower limit or more, it is possible to suppress the softener for hydrocarbon rubber from bleeding out from the styrenic thermoplastic elastomer composition, and it is possible to maintain good grip properties.

The weight average molecular weight of the styrene thermoplastic elastomer is a polystyrene equivalent value measured by gel permeation chromatography (hereinafter sometimes abbreviated as GPC) under the following conditions.
<Measurement conditions for gel permeation chromatography (GPC)>
Equipment: HLC-8120 manufactured by Tosoh Corporation
Column: TSKgel Super H1000+H2000+H3000 manufactured by Tosoh Corporation
Detector: Differential refractive index detector (RI/built-in)
Solvent: Tetrahydrofuran Temperature: 40℃
Flow rate: 0.5mL/min Injection volume: 10μL
Concentration: 0.2% by mass
Calibration sample: Monodisperse polystyrene Calibration method: Polystyrene conversion

The method for producing the styrenic thermoplastic elastomer is not particularly limited and may be any method as long as the above structure and physical properties can be obtained. For example, it can be obtained by block polymerization in an inert solvent using a lithium catalyst or the like. Further, for the hydrogenation of the block copolymer, a known method such as hydrogenation in an inert solvent in the presence of a hydrogenation catalyst can be employed.

Styrene-based thermoplastic elastomers include styrene/conjugated diene block copolymers and/or hydrogenated products thereof, in which the conjugated diene of the styrene/conjugated diene block copolymers is composed of one or more selected from isoprene and butadiene. Preferred are hydrogenated compounds that are The styrene/conjugated diene block copolymer and/or its hydrogenated product may have a polar group if necessary.
Examples of the styrene/conjugated diene block copolymer and/or its hydrogenated product include styrene/butadiene block copolymer and/or its hydrogenated product, styrene/butadiene/styrene block copolymer and its hydrogenated product, and styrene/isoprene. Examples include block copolymers and/or hydrogenated products thereof, styrene-butadiene-isoprene block copolymers and/or hydrogenated products thereof, styrene-isoprene-butadiene-styrene block copolymers and hydrogenated products thereof.

Hydrogenated products of styrene/butadiene block copolymer include styrene/butadiene/butylene copolymer (SBB), styrene/ethylene/butylene copolymer (SEB), styrene/ethylene/butylene copolymer (SEB), etc. can be mentioned.
Examples of hydrogenated products of styrene/butadiene/styrene block copolymers include styrene/ethylene/butylene/styrene copolymers (SEBS).
Examples of hydrogenated products of styrene/isoprene block copolymers include styrene/ethylene/propylene/styrene copolymers (SEPS).
Examples of hydrogenated products of styrene/isoprene/butadiene/styrene block copolymers include styrene/ethylene/ethylene/propylene/styrene copolymers (SEEPS).

Among these, from the viewpoint of tensile strength and compression set, styrene-ethylene-butylene-styrene copolymer (SEBS), which is a hydrogenated product of styrene-butadiene-styrene block copolymer, and styrene-isoprene-butadiene-styrene block copolymer are recommended. Styrene-ethylene-ethylene-propylene-styrene copolymer (SEEPS), which is a hydrogenated polymer, is preferred. These may be completely hydrogenated or partially hydrogenated.

It is also possible to use a commercially available styrene thermoplastic elastomer. Commercially available products include "Krayton (registered trademark)" G series manufactured by Kraton Polymer Japan Co., Ltd., "TAIPOL (registered trademark)" manufactured by TSRC, "VECTOR (registered trademark)" SEBS series, and "Septon (registered trademark)" manufactured by Kuraray Co., Ltd. )” series, etc., as appropriate.

The styrenic thermoplastic elastomer may be used alone or in combination of two or more different in physical properties, block structure, presence or absence of hydrogenation, etc.

<Preferred embodiment of styrenic thermoplastic elastomer composition>
From the viewpoint of grip properties, the styrenic thermoplastic elastomer composition of the present invention preferably has a Duro hardness A of 30 to 90 as measured by ISO 7619-1. By setting the Duro hardness A to 30 or more, a grip portion that is soft enough to be gripped without being deformed when the cap is opened can be obtained. By setting the Duro hardness A to 90 or less, the grip portion can have an appropriate hardness, and it is possible to prevent fingers from slipping when opening the cap.

The styrenic thermoplastic elastomer composition of the preferred embodiment of the present invention preferably contains the following components (A) to (C).
Component (A): Linear low-density polyethylene having a density of 0.910 to 0.960 g/cm ³ Component (B): Hydrogenated product of styrene/conjugated diene block copolymer Component (C): Hydrocarbon type Softener for rubber

(Component (A))
The linear low density polyethylene having a density of 0.910 to 0.960 g/cm ³ as component (A) is the linear low density polyethylene described above in the section <Polyethylene having a density of 0.910 to 0.960 g/cm ³ >. Chain-shaped low density polyethylene can be used.

(Component (B))
As the hydrogenated product of the styrene/conjugated diene block copolymer of component (B), the hydrogenated product of the styrene/conjugated diene block copolymer described above in the section of <Styrenic thermoplastic elastomer> can be used.

(Component (C))
Component (C), a hydrocarbon rubber softener, softens the styrene thermoplastic elastomer composition and improves grip properties.

As component (C), process oil such as hydrocarbon oil is used. As the hydrocarbon oil, paraffinic, naphthenic, and other process oils are used. Among these, paraffinic process oil is preferred because it effectively softens the styrenic thermoplastic elastomer composition of the present invention.

As the component (C), a softener for hydrocarbon rubber, a commercially available product may be used. Commercial products include "Nisseki Polybutene (registered trademark)" HV series manufactured by JX Nippon Oil & Energy, "Diana (registered trademark) process oil" PW series manufactured by Idemitsu Kosan, and "Lucant (registered trademark)" manufactured by Mitsui Chemicals. series, and can be appropriately selected and used from these.

Component (C), a softener for hydrocarbon rubber, may be used alone or in combination of two or more.

(Ingredient content ratio)
In the styrenic thermoplastic elastomer composition of the preferred embodiment of the present invention, the content of component (B) relative to 100 parts by mass of component (A) is preferably 100 to 300 parts by mass, particularly 120 to 280 parts by mass. By setting the content of component (B) within the above range, good grip properties can be obtained.
Further, the content of component (B) is preferably 35 to 65% by mass, particularly 40 to 60% by mass, based on the total of component (B) and component (C). By setting the content of component (B) to the above lower limit or more, it is possible to suppress the bleeding of the component (C), the softener for hydrocarbon rubber, from the thermoplastic elastomer layer and the surface of the molded product becoming slippery, which is good. Provides excellent grip. By setting the content of component (B) below the above upper limit, it is possible to prevent the hardness of the thermoplastic elastomer composition from becoming too high, and sufficient grip properties can be obtained.

In the styrenic thermoplastic elastomer composition of the preferred embodiment of the present invention, the content of component (C) is preferably 200 to 400 parts by mass, particularly 220 to 380 parts by mass, based on 100 parts by mass of component (A). preferable. By setting the content of component (C) within the above range, good grip properties can be obtained.

(Other ingredients)
The styrenic thermoplastic elastomer composition of the preferred embodiment of the present invention may contain other components other than the above-mentioned components (A) to (C) as necessary, as long as the object of the present invention is not impaired. good.

Other components that may be contained in the styrenic thermoplastic elastomer composition of the preferred embodiment of the present invention include various anti-blocking agents, sealing property improvers, heat stabilizers, antioxidants, light stabilizers, and ultraviolet rays. Examples include absorbents, lubricants, crystal nucleating agents, colorants, resins other than components (A) and (B), and the like.

Here, as the antioxidant, for example, 2,6-di-tert-butyl-p-cresol, 2,6-di-tert-butylphenol, 2,4-dimethyl-6-tert-butylphenol, 4,4 Examples include phenolic antioxidants such as -dihydroxydiphenyl and tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, phosphite antioxidants, and thioether antioxidants. Among these, phenolic antioxidants and phosphite antioxidants are preferred. When an antioxidant is used, the amount thereof is preferably 0.01 to 3.0 parts by weight, more preferably 0.05 to 2.0 parts by weight, based on 100 parts by weight of component (A).

Resins other than components (A) and (B) that may be contained in the thermoplastic styrene elastomer composition of the preferred embodiment of the present invention include thermoplastic styrene elastomers (excluding those falling under component (B)); Polyolefin resins other than component (A), polyester resins, polyamide resins, styrene resins, acrylic resins, polycarbonate resins, polyvinyl chloride resins, polyphenylene ether resins, polystyrene resins, liquid crystal resins, various elastomers other than the above (component (B)) (excluding applicable items). The other resins mentioned above may contain only one type or two or more types.
When the styrenic thermoplastic elastomer composition of the preferred embodiment of the present invention contains resins other than components (A) and (B), the effects of containing components (A) to (C) can be sufficiently obtained. In the above, the content of the other resin is preferably 40 parts by mass or less, particularly 30 parts by mass or less, based on the total of 100 parts by mass of components (A) to (C).

(Method for producing thermoplastic elastomer composition)
The styrenic thermoplastic elastomer composition of the preferred embodiment of the present invention can be prepared by mixing the above-mentioned components (A) to (C) and other components as necessary by a known method such as a Henschel mixer, a V blender, a tumbler, etc. After mechanically mixing in a blender, the mixture is mechanically melt-kneaded by a known method and extruded through a die to obtain a solid material such as a pellet. For the mechanical melt-kneading, general melt-kneaders such as a Banbury mixer, various kneaders, and a single-screw or twin-screw extruder can be used.

[Polyethylene layer]
The polyethylene layer of the molded article of the present invention is made of polyethylene. Although any known polyethylene can be used for the polyethylene layer, high-density polyethylene obtained by a known method such as a low-pressure polymerization method is preferred from the viewpoint of compliance with the Ministerial Ordinance on Milk, etc.

The lower limit of the density of the polyethylene of the polyethylene layer measured according to JIS K7112 is preferably 0.940 g/cm ³ or more, more preferably 0.942 g/cm ³ or more from the viewpoint of making the polyethylene layer difficult to break. . On the other hand, the upper limit of the density is preferably 0.970 g/cm ³ or less from the viewpoint of fusion strength with the styrene-based thermoplastic elastomer composition constituting the thermoplastic elastomer layer, and 0.968 g/cm ³ or less. It is even more preferable that there be.

Further, the melt flow rate (MFR) of the polyethylene in the polyethylene layer is preferably 0.1 g/10 minutes or more, more preferably 0.5 g/10 minutes or more, and 100 g/10 minutes or less. is preferable, and more preferably 50 g/10 minutes or less. When the MFR of the polyethylene of the polyethylene layer is within the above range, the molded appearance and tensile yield stress of the polyethylene layer tend to be excellent. Here, the MFR of polyethylene is a value measured according to JIS K6922 at a temperature of 190° C., a load of 21.2 N, and 10 minutes.

It is also possible to use a commercially available product as the polyethylene for the polyethylene layer. Commercially available products include the "Novatec (registered trademark)" series manufactured by Nippon Polyethylene Co., Ltd. and the "Creolex (registered trademark)" series manufactured by Asahi Kasei Chemicals, etc., and the appropriate product should be selected from these and used. I can do it.

Only one type of polyethylene may be used in the polyethylene layer, or a mixture of two or more types may be used.

Note that the polyethylene layer of the present invention may contain resins other than polyethylene and the additives listed as additives that may be included in the styrenic thermoplastic elastomer composition of the preferred embodiment of the present invention described above. However, in general, it is preferable to use only polyethylene in compliance with the Ministerial Ordinance on Milk, etc.

<Method for manufacturing molded body>
Although there are no particular limitations on the method for producing the molded article of the present invention, preferably, pellets of the styrenic thermoplastic elastomer composition of the present invention and polyethylene constituting the polyethylene layer are injection molded using an injection molding machine or the like. This can be obtained by

For example, when manufacturing a cap-shaped molded body, first, a base material portion is molded using polyethylene using an injection molding machine or the like. Thereafter, this base material part is inserted into another mold, and the styrenic thermoplastic elastomer composition of the present invention is injection molded around the outer periphery of the base material at a temperature of usually 160 to 250°C, preferably 180 to 240°C. A cap-shaped molded product is obtained by heat-sealing the outer peripheral surface of the material part and the inner peripheral surface of the grip part made of the styrene-based thermoplastic elastomer composition of the present invention (insert molding). A grip portion made of the styrene thermoplastic elastomer composition of the present invention may be molded first, the grip portion may be inserted into a mold, and then polyethylene may be injection molded.

A similar molded product can also be obtained by injection molding using rotary two-color molding, core-back two-color molding, or the like.

[Application]
The styrenic thermoplastic elastomer composition of the present invention can form a grip part with excellent grip properties, and has excellent fusion properties with the polyethylene of the base material, so the molded article of the present invention is suitable for caps. used for.

As the cap, a screw cap that requires grip properties is preferable. The shape, diameter, and type of rolling process of the screw cap do not matter. In a cap in which a grip part and a base part are fused together, the grip part made of the styrene thermoplastic elastomer composition of the present invention covers the outer periphery of the base part, such as the side surface, or a part or all of the outer surface of the base part. It is preferable from the viewpoint of grip properties that the shape covers the surface. The thickness of the grip portion is preferably 0.1 to 5 mm from the viewpoint of grip properties.

The cap made of the molded product of the present invention is suitable as a screw cap for bottles of various beverages, foods, pharmaceuticals, cosmetics, toiletries, daily necessities, etc., a screw cap for standing pouches, a twist cap, a pull-top cap, a female-shaped cap, etc. It can be used for.
The contents in the container to be sealed with the cap made of the molded product of the present invention may be liquid, powder, solid, gel-like substance, etc., but the cap of the present invention is particularly suitable for containing milk or dairy products. Suitable as a cap for containers.

Hereinafter, the content of the present invention will be explained in more detail using Examples, but the present invention is not limited by the following Examples unless it exceeds the gist thereof. The values of various manufacturing conditions and evaluation results in the following examples have the meaning of preferable upper or lower limits in the embodiments of the present invention, and the preferable ranges are the above-mentioned upper or lower limits and the following. It may be a range defined by a value of an example or a combination of values of examples.

[raw materials]
The raw materials used in the following Examples and Comparative Examples are shown below.

<Polyethylene of polyethylene layer>
Manufactured by Japan Polyethylene Co., Ltd. Product name Novatec HD (registered trademark) HJ451
MFR: 2.3g/10min (Measurement conditions: 190°C, load 21.2N (JIS K6922))
Density: 0.955g/ ^cm3

<Styrenic thermoplastic elastomer composition>
Component (A): Linear low-density polyethylene having a density of 0.910 to 0.960 g/cm ³ A-1: Manufactured by Nippon Polyethylene Co., Ltd. Product name Novatec LL (registered trademark) UJ990
MFR: 35g/10min (Measurement conditions: 190℃, load 21.2N (JIS K6922))
Density: 0.937g/ ^cm3
A-2: Manufactured by Japan Polyethylene Co., Ltd. Product name Novatec LL (registered trademark) UJ480
MFR: 30g/10min (Measurement conditions: 190℃, load 21.2N (JIS K6922))
Density: 0.923g/ ^cm3
A-3: Manufactured by Japan Polyethylene Co., Ltd. Product name Novatec LL (registered trademark) UJ580
MFR: 20g/10min (Measurement conditions: 190℃, load 21.2N (JIS K6922))
Density: 0.925g/ ^cm3
A-4: Manufactured by Japan Polyethylene Co., Ltd. Product name Novatec HD (registered trademark) HJ451
MFR: 2.3g/10min (Measurement conditions: 190°C, load 21.2N (JIS K6922))
Density: 0.955g/ ^cm3
A-5: Manufactured by Japan Polyethylene Co., Ltd. Product name Novatec LD (registered trademark) LJ802
MFR: 22g/10min (Measurement conditions: 190℃, load 21.2N (JIS K6922))
Density: 0.918g/ ^cm3

Component (a): Polypropylene (for comparison)
a-1: Manufactured by Nippon Polypro Co., Ltd. Product name Novatec PP (registered trademark) MA1B
MFR: 21g/10min (Measurement conditions: 230℃, load 21.2N (JIS K7210))
Density: 0.900g/ ^cm3

Component (B): Styrene/ethylene/butylene/styrene block copolymer B-1: Manufactured by TSRC, trade name TAIPOL (registered trademark) 6151
Styrene unit content: 32% by mass
Weight average molecular weight (Mw): 246,000

Component (C): Softener for hydrocarbon rubber (hydrocarbon oil)
C-1: Manufactured by Idemitsu Kosan Co., Ltd. Product name Diana Process Oil (registered trademark) PW90

[Examples 1 to 6 and Comparative Example 1]
<Preparation of pellets made of styrenic thermoplastic elastomer composition>
It was mixed with each raw material listed in Table 1 in the amount (parts by mass).
100 parts by mass of the obtained mixture and tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane (Irganox (registered trademark) 1010 manufactured by BASF Japan Co., Ltd.) )0.1 part by mass was fed into a twin-screw extruder with a compression ratio L/D of 33 and a cylinder diameter of 45 mm, melted and kneaded at 200°C, extruded from a die into a strand shape, and then cut to obtain a styrene thermoplastic elastomer. A pellet consisting of the composition was obtained.

<Creation of single layer sheet>
The obtained pellets were fed to an in-line screw type injection molding machine (IS130GN manufactured by Toshiba Machine Co., Ltd.), and injection molded under the conditions of injection pressure 50 MPa, cylinder temperature 220°C, and mold temperature 40°C to form styrene-based pellets with a wall thickness of 2 mm. A monolayer sheet of thermoplastic elastomer composition was obtained. The Duro hardness A of this single layer sheet was measured by the method (1) below.

<Creation of two-layer sheet>
Novatec HD (registered trademark) HJ451, which is polyethylene for the polyethylene layer, was supplied to an inline screw type injection molding machine (IS130GN manufactured by Toshiba Machine Co., Ltd.), and injection was performed under conditions of an injection pressure of 50 MPa, a cylinder temperature of 220 °C, and a mold temperature of 40 °C. By molding, a base sheet made of polyethylene with a wall thickness of 2 mm, a length of 100 mm, and a width of 100 mm was obtained. A lacquer spray containing silver powder (adhesion inhibiting substance) was applied to an area of 1/3 of the edge of one side of the obtained sheet and dried.
This sheet was inserted into a mold with a thickness of 3 mm so that the part to which the fusion inhibiting substance was applied was on the flow end side of the resin, and the side to which the fusion inhibitor was applied was the fusion surface. A styrene thermoplastic elastomer composition was injection molded into this mold at 220°C to create a two-layer sheet in which a polyethylene base sheet and a thermoplastic elastomer layer made of the styrene thermoplastic elastomer composition were fused together. .
This two-layer sheet is a two-layer sheet with a total thickness of 3 mm, which is made by laminating and integrating a base sheet made of polyethylene with a thickness of 2 mm and a thermoplastic elastomer layer made of a styrene-based thermoplastic elastomer composition with a thickness of 1 mm. be.

Using the obtained two-layer sheet, the fusion strength was evaluated by the method (2) below.

(1) Duro hardness A
The hardness (type A durometer) of the obtained monolayer sheet of the styrenic thermoplastic elastomer composition was measured based on ISO 7619-1. In order to use it as a grip part of a screw cap, it is preferable that the Duro hardness is A30 or more and 90 or less.

(2) Fusion strength A two-layer sheet obtained by injection molding was conditioned for 48 hours or more in an environment of 23° C. and 50%. Thereafter, three cuts with a width of 25 mm were made in the thermoplastic elastomer layer made of the styrene-based thermoplastic elastomer composition of the two-layer sheet in parallel to the flow direction of the resin during injection molding, and the thermoplastic elastomer layer was tested using a tensile tester at 23°C. Both sheets were peeled off from the area coated with the fusion inhibiting substance under a 50% environment, and a 90 degree peel test (test speed 200 mm/min) was conducted to measure the fusion strength. It is practical if the fusion strength is 10 N/25 mm or more, and preferably 20 N/25 mm or more.

[Reference example 1]
Similar to the method for creating a single-layer sheet of a styrene-based thermoplastic elastomer composition described above, a single-layer sheet of polyethylene was created using Novatec HD (registered trademark) HJ451, which is polyethylene for the polyethylene layer, and this single-layer sheet Duro hardness A was measured using the method (1) above.

[Evaluation results]
The above evaluation results are shown in Table-1.

[Consideration]
It can be seen that the molded bodies of Examples 1 to 6 had good evaluation results for both Duro hardness A and fusion strength, and were suitable as molded bodies for caps.
On the other hand, in Comparative Example 1, polyethylene having a density of 0.910 to 0.960 g/cm ³ was not used as component (A) of the styrene-based thermoplastic elastomer composition, so the fusion strength was low.
The polyethylene single-layer sheet of Reference Example 1 had a Duro hardness A of 100 or more, and was evaluated to be slippery and have poor grip properties.

1 Screw cap

Claims (9)

A cap made of a molded body in which a thermoplastic elastomer layer made of a styrene-based thermoplastic elastomer composition containing polyethylene and a polyethylene layer are fused together and have a density of 0.910 to 0.960 g/cm ³ . The cap according to claim 1, wherein the styrenic thermoplastic elastomer composition has a Duro hardness A of 30 to 90. The cap according to claim 1 or 2, wherein the styrenic thermoplastic elastomer composition contains the following components (A) to (C).
Component (A): Linear low-density polyethylene having a density of 0.910 to 0.960 g/ ^cm Component (B): Hydrogenated styrene/conjugated diene block copolymer component (C) : Softener for hydrocarbon rubber The cap according to claim 3, wherein the styrenic thermoplastic elastomer composition contains 100 to 300 parts by mass of the component (B) based on 100 parts by mass of the component (A). The cap according to claim 3 or 4, wherein the styrenic thermoplastic elastomer composition contains 200 to 400 parts by mass of the component (C) based on 100 parts by mass of the component (A). Any one of claims 3 to 5, wherein the content of the component (B) in the styrenic thermoplastic elastomer composition is 35 to 65% by mass based on the total of the component (B) and the component (C). The cap described in paragraph 1. Cap according to any one of claims 1 to 6, wherein the polyethylene layer is made of high density polyethylene. Cap according to any one of claims 1 to 7 , which is a screw cap. The cap according to any one of claims 1 to 8 , which is a cap for a beverage container.

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