JP5103289B2 - Polyethylene resin composition for injection molded container lid - Google Patents

Description

  The present invention relates to a polyethylene resin composition for lids of containers that contain liquids such as soft drinks, particularly carbonated drinks, and more specifically, high-speed moldability, high fluidity, rigidity, impact resistance, particularly in injection molding. It is related with the polyethylene resin composition for container lids which was excellent in the property, stress crack resistance, slipperiness, low odor property, food safety, openability, and closure performance.

Plastic containers are excellent in various physical properties, moldability, light weight, economy, etc., and are suitable for reusability in response to environmental issues. Recently, conventional containers made of metal or glass have been used. Overwhelming, it is widely used for daily necessities and industrial use.
Among plastic containers, so-called PET bottles (polyethylene terephthalate containers) have been approved as containers for food and drink due to their excellent mechanical strength, transparency, high gas shielding properties, and non-polluting properties. As containers for beverages, the demand is very high. In particular, recently, small PET bottles have been heavily used by consumers as small containers for portable beverages, and the heat resistance and pressure resistance of PET bottles have improved, so that portable hot drinks for winter and long-term storage can be used. It is also widely used as a container for high-temperature sterilized beverages.
Along with polyester resins typified by PET bottles, polyethylene resins are also regarded as important as container materials for beverages such as soft drinks, and demand is increasing.

In addition, in PET bottles as containers for soft drinks such as carbonated drinks, conventionally, metal containers made of aluminum have been used as the container lids. From the viewpoint of properties, polyolefin products are often used. These container lids are molded by continuous compression molding (CCM) for the purpose of high-speed molding.
The lid of containers such as soft drinks is an important product along with the container itself, in terms of the container's sealing and opening properties, food safety and durability, and other essential performances. From the viewpoints of various physical properties such as moldability and rigidity and heat resistance, the technical improvement of the lid member made of polyolefin, particularly polyethylene resin, has been continuously studied. Many improvement proposals are disclosed (for example, refer to patent documents 1 to 6).

Among these improvement proposals, when a representative improvement proposal is viewed, Patent Document 1 discloses a MFR (melt flow rate) of a polyethylene component in order to improve pressure resistance and gas tightness with respect to a cap for a carbonated beverage container. A polyethylene resin composition having a specified density is disclosed, and Patent Document 2 discloses an ethylene / α-olefin copolymer having an MFR, a density and a maximum melting peak temperature in order to improve flexibility and heat resistance. An ethylene resin composition for injection molding comprising a combination and a specific additive such as glycerin fatty acid ester is disclosed.
However, the composition disclosed in Patent Document 1 has insufficient low-molecular weight components, so that high-speed moldability is insufficient, and the composition disclosed in Patent Document 2 improves mold releasability. Since a specific additive component is included for the purpose, it is not satisfactory in terms of food safety due to component elution.

In recent years, the polyethylene resin compositions disclosed in Patent Documents 3 and 4 have improved various performances such as sealability and rigidity in compression molding, and in order to shorten the container lid molding cycle and increase production efficiency, Practical use has been made using fluid polyolefin resin.
Furthermore, in recent years, for the reason of improving economy, the container lid has been made thinner along with the higher molding cycle to increase the molding speed. However, when the container lid is made thinner, the container lid is deformed by the internal pressure of the container. In order to prevent the contents from leaking from the seal portion, higher rigidity is required. In recent years, a form in which containers containing green tea or other beverages are heated and sold with a heater has appeared, and in this warming sale, the shape is maintained even at high temperatures, and cracking occurs due to tightening of the container lid. In order to avoid this, higher rigidity is required.
From such a viewpoint, Patent Document 5 describes the density of the resin material and the improvement in the resealability as well as various performance improvements such as moldability and stress crack resistance, as well as low resin elongation at high temperatures. A material in which the flow rate ratio (FRR) of MFR and HLMFR is defined is disclosed and put into practical use by compression molding.

  By the way, in Patent Document 4 and Patent Document 6 that presents a material in which the density of the resin material, the flow rate ratio (FRR) of MFR and HLMFR, and the number of short chain branches are specified, the disclosed polyethylene-based resin material A material having various performances such as heat resistance, rigidity, moldability, and stress crack resistance can be realized, and a polyethylene resin material that can withstand the internal pressure of carbonated beverages has begun to be used as a carbonated beverage container lid.

In recent years, with further technical progress of injection molding, it has become possible to form a container lid at high speed. In the above-described conventional polyethylene for container lids, attempts have been made to mold by injection molding. In the polyethylene, the molecular weight distribution has been widened for the purpose of improvement.
However, by widening the molecular weight distribution, defects that did not become a problem in continuous compression molding (CCM) occur, making high-speed injection molding difficult. Specifically, the container lid tears in the vertical direction, anisotropy of shrinkage occurs, and the dimensions are not stable. In addition, there is a problem that the bridge portion for opening the lid cannot be cut.
In view of such circumstances, there is a demand for a polyethylene material having an appropriate molecular weight distribution that can be injection-molded while having the stress crack resistance, rigidity, and impact resistance required for conventional lids.
JP 58-103542 A Japanese Patent Laid-Open No. 08-302084 JP 2000-159250 A JP 2000-248125 A Japanese Patent Laid-Open No. 2004-123955 JP 2002-060559 A

  The object of the present invention is excellent in high-speed moldability, high fluidity, balance between rigidity and impact resistance, stress crack resistance, slipperiness, low odor, food safety, and particularly contains a carbonated beverage liquid. To provide a resin composition for a container lid, which is a material suitable for a container lid for the container lid, and has an appropriate molecular weight distribution, and in particular, a container lid having excellent performance even in injection molding. It is in.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have satisfied these characteristics by making a resin composition in which two kinds of ethylene polymers having specific properties are combined at a specific ratio. The present inventors have found a polyethylene resin material for a container lid to complete the present invention.

That is, according to the first invention of the present invention, a polyethylene resin comprising 20% by mass or more and less than 40% by mass of an ethylene polymer (A) and more than 60% by mass of 80% by mass or less of an ethylene polymer (B). A composition comprising:
The ethylene polymer (A) has a melt flow rate (HLMFR) of 1 g / 10 min to 10 g / 10 min at a temperature of 190 ° C. and a load of 21.6 kg, and a density of 0.910 g / cm ^{3 to} 0.935 g. / cm ³ or less, ethylene polymer (B), the temperature 190 ° C., a melt flow rate (MFR) 30 g / 10 minutes or more 150 g / less than 10 minutes at a load 2.16 Kg, and density 0.960 g / cmi ³ or more, and the polyethylene resin composition has (i) MFR 1 g / 10 min or more and less than 10 g / 10 min, HLMFR 70 g / 10 min or more and less than 400 g / 10 min, HLMFR / MFR 40 or more and less than 80 , and the and (ii) a density polyethylene for injection molding the container closure, characterized in that it is less than 0.953 g / cm ³ or more 0.965 g / cm ³ Styrene resin composition is provided.

According to the second invention of the present invention, in the first invention, (iii) the flexural modulus is 800 MPa or more, (iv) the tensile yield strength is 25 MPa or more, and (v) the hydrocarbon volatile content is 80 ppm or less. (Vi) The shrinkage ratio anisotropy (MD / TD) of the injection molded plate of 120 × 120 × 2 mm is 1.0 or more and less than 2.0, and (vii) the constant strain ESCR is 10 Hr or more and 1000 Hr or less. A polyethylene resin composition for injection molded container lids is provided.
Furthermore, according to the third invention of the present invention, in the second invention, (viii) FNCT at 1.9 MPa has a FNCT of 60 hours or more, and is a polyethylene-based resin composition for injection-molded container lids Is provided.

According to a fourth invention of the present invention, in any one of the first to third inventions, the injection molded container lid is a carbonated beverage container lid, and the polyethylene resin composition for an injection molded container lid Is provided.

  The polyethylene resin composition for an injection-molded container lid of the present invention is suitable for a container lid for containing a PET bottled beverage liquid, and the injection moldability is improved while maintaining stress crack resistance and rigidity. There is an effect that the shrinkage rate anisotropy is small and the bridge break of the container lid is appropriate.

The present invention is described in detail below.
The polyethylene resin composition of the present invention is composed of a plurality of types of ethylene polymers, and specifically comprises the following components (A) and (B), and has the following characteristics (i ) And (ii).
Component (A): Temperature 190 ° C., a melt flow rate (HLMFR) is 1 g / 10 min or more 10 g / 10 minutes or less at a load 21.6 Kg, density 0.910 g / cm ³ or more 0.950 g / cm ³ or less of ethylene Polymer: 20% by mass or more and less than 40% by mass Component (B): Melt flow rate (MFR) at a temperature of 190 ° C. and a load of 2.16 kg is 30 g / 10 min or more and less than 150 g / 10 min, and the density is 0.960 g / cm ³ or more ethylene polymer: more than 60 mass% and 80 mass% or less

Characteristic (i): MFR is 1 g / 10 min or more and less than 10 g / 10 min, HLMFR is 70 g / 10 min or more and less than 400 g / 10 min, and HLMFR / MFR is 40 or more and less than 80. Characteristic (ii): Density is 0.953 g / Cm ³ or more and less than 0.965 g / cm ³

Component (A) ethylene polymer, that is, HLMFR of ethylene polymer (A) is 1 g / 10 min or more and 10 g / 10 min or less, preferably 3 g / 10 min or more and 10 g / 10 min or less, More preferably, it is 5 g / 10 min or more and 9 g / 10 min or less. Further, the density of the component (A), or less 0.910 g / cm ³ or more 0.950 g / cm ^3, preferably 0.910 g / cm ³ or more 0.945 g / cm ³ or less, more preferably 0.910 g / cm ³ or more 0.935 g / cm ^3, more preferably not more than 0.920 g / cm ³ or more 0.935 g / cm ^3.
When the HLMFR of the component (A) is less than 1 g / 10 minutes, the fluidity is lowered, the moldability is poor, the shrinkage ratio anisotropy tends to increase, and it is difficult to satisfy the characteristic (i). is there. On the other hand, when HLMFR exceeds 10 g / 10 min, the stress crack resistance tends to decrease. The density of the component (A) is less than 0.910 g / cm ^3, the rigidity becomes insufficient, while when it exceeds 0.950 g / cm ^3, the stress crack resistance tends to decrease. Further, when the density is out of this range, it is difficult to satisfy the characteristic (ii). Here, HLMFR and density are values measured by the measurement methods described later.

Further, the MFR of the ethylene polymer of the component (B), that is, the ethylene polymer (B) is 30 g / 10 min or more and less than 150 g / 10 min, preferably 40 g / 10 min or more and 130 g / 10 min or less, more preferably Is 50 g / 10 min or more and 100 g / 10 min or less. The density of component (B), 0.960 g / cm ³ or more, preferably at 0.960 g / cm ³ or more 0.970 g / cm ³ or less.
If the MFR of the component (B) is less than 30 g / 10 minutes, the fluidity tends to be lowered and the moldability tends to be poor. On the other hand, if it is 150 g / 10 minutes or more, the stress crack resistance is lowered, and this range Outside, it is difficult to satisfy the characteristic (i). Moreover, when the density of a component (B) is less than 0.960 g / cm < ³ >, there exists a possibility that rigidity may fall. The upper limit of the density of the component (B) is not particularly limited, but is usually 0.980 g / cm ³ or less. Here, the MFR and the density are values measured by a measuring method described later.

  The ratio of component (A) to component (B) is 20% by mass or more and less than 40% by mass, preferably 22% by mass or more and 38% by mass or less, and component (B) exceeds 60% by mass. 80% by mass or less, preferably 62% by mass or more and 78% by mass or less (here, the sum of component (A) and component (B) is 100% by mass). When the component (A) is less than 20% by mass, the stress crack resistance is lowered. On the other hand, when it is 40% by mass or more, the moldability is lowered and the characteristic (i) is not satisfied. Moreover, if a component (B) is 60 mass% or less, a moldability will fall, and when it exceeds 80 mass%, stress crack resistance will fall. Further, the ratio of the components (A) and (B) is important. If the ratio is outside this range, the HLMFR / MFR of the characteristic (i) does not satisfy 40 or more and less than 80, and the shrinkage rate anisotropy increases. .

  The composition comprising the component (A) and the component (B) can be obtained by mixing the ethylene polymer of the component (A) and the ethylene polymer of the component (B). In the composition, component (A) is produced in one reactor, and then component (B) is newly produced in the same reactor, or component (B) is produced in one reactor. Then, it can be produced by newly producing the component (A) in the same reactor and mixing the component (A) and the component (B). The composition can also be produced using two or more reactors in series and / or in parallel. In this case, the component (A) is produced by dividing it into a plurality of reactors, and the polymers produced in the respective reactors may be combined into a single polymer (component (A)) as a whole. It is good also as dividing into several reactors and combining the polymer manufactured by each, and it is good also as one polymer (component (B)) as a whole. Preferably, those obtained by successively polymerizing the ethylene polymer of component (A) and the ethylene polymer of component (B) are desirable for reasons such as resin uniformity.

As the polymerization catalyst for the ethylene polymer, various catalysts such as a Ziegler catalyst, a Phillips catalyst, and a metallocene catalyst are used. Any polymerization catalyst can be used as long as hydrogen exhibits a chain transfer action of olefin polymerization.
Specifically, any catalyst that is composed of a solid catalyst component and an organometallic compound and that is suitable for slurry-based olefin polymerization such that hydrogen exhibits a chain transfer action of olefin polymerization can be used.
The solid catalyst component is not particularly limited as long as it is used as a solid catalyst for olefin polymerization containing a transition metal compound. As the transition metal compound, compounds of elements of Group 4 to Group 10 of the periodic table, preferably Group 4 to Group 6, can be used, and specific examples include Ti, Zr, Hf, V, Cr. And compounds such as Mo.

  Examples of preferred catalysts include solid Ziegler catalysts comprising Ti and / or V compounds and organometallic compounds of Group 1 to Group 3 elements of the periodic table. Furthermore, a combination of a complex called a metallocene catalyst, which is a ligand having a cyclopentadiene skeleton coordinated to a transition metal, and a promoter is exemplified. As a specific metallocene catalyst, a complex catalyst in which a ligand having a cyclopentadiene skeleton such as methylcyclopentadiene, dimethylcyclopentadiene or indene is coordinated to a transition metal containing Ti, Zr, Hf, lanthanide series, etc. And an organometallic compound of Group 1 to Group 3 elements of the periodic table such as aluminoxane as a co-catalyst, and a supported type in which these complex catalysts are supported on a carrier such as silica. . Particularly preferred solid catalyst components for olefin polymerization include those containing at least titanium and / or vanadium and magnesium.

  As the organometallic compound that can be used together with the solid catalyst component containing at least titanium and / or vanadium and magnesium, an organoaluminum compound, particularly, a trialkylaluminum is preferable. The amount of the organoaluminum compound used in the polymerization reaction is not particularly limited, but when used, it is usually preferably in the range of 0.05 mol to 1000 mol with respect to 1 mol of the titanium compound.

  The ethylene polymer according to the present invention is a homopolymer of ethylene, or ethylene and an α-olefin having 3 to 12 carbon atoms, such as propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1- It can be obtained by copolymerization with pentene, 1-octene or the like. Also, copolymerization with a diene for the purpose of modification is possible. Examples of the diene compound used at this time include butadiene, 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene, and the like. The comonomer content during the polymerization can be arbitrarily selected. For example, in the case of copolymerization of ethylene and an α-olefin having 3 to 12 carbon atoms, an ethylene / α-olefin copolymer is used. The α-olefin content is 40 mol% or less, preferably 30 mol% or less.

The ethylene polymer according to the present invention can be produced by a production process such as a gas phase polymerization method, a solution polymerization method, or a slurry polymerization method, and preferably a slurry polymerization method. Among the polymerization conditions for the ethylene-based polymer, the polymerization temperature can be selected from the range of 0 ° C. or more and 300 ° C. or less. In slurry polymerization, polymerization is performed at a temperature lower than the melting point of the produced polymer. The polymerization pressure can be selected from the range of atmospheric pressure to about 100 kg / cm ² . It is selected from aliphatic hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as benzene, toluene and xylene, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, etc. in a state where oxygen and water are substantially cut off. It can be produced by slurry polymerization of ethylene and α-olefin in the presence of an inert hydrocarbon solvent.

In slurry polymerization, hydrogen supplied to the polymerization vessel is consumed as a chain transfer agent, determines the average molecular weight of the produced ethylene-based polymer, and partly dissolves in a solvent and is discharged from the polymerization vessel. The solubility of hydrogen in the solvent is small, and the hydrogen concentration near the polymerization active point of the catalyst is low unless a large amount of gas phase is present in the polymerization vessel. Therefore, if the hydrogen supply amount is changed, the hydrogen concentration at the polymerization active point of the catalyst changes rapidly, and the molecular weight of the produced ethylene polymer changes following the hydrogen supply amount in a short time. Therefore, a more homogeneous product can be produced by changing the hydrogen supply rate in a short cycle. For these reasons, it is preferable to employ a slurry polymerization method as the polymerization method. Moreover, the aspect of changing the hydrogen supply amount is preferably changed discontinuously rather than continuously because the effect of broadening the molecular weight distribution can be obtained.
In the ethylene polymer according to the present invention, it is important to change the hydrogen supply amount, but other polymerization conditions such as polymerization temperature, catalyst supply amount, supply amount of olefin such as ethylene, 1-butene It is also important to change the supply amount of the comonomer and the like, the supply amount of the solvent, etc., simultaneously with the change of hydrogen or separately.

  As described above, the composition comprising the component (A) and the component (B) of the present invention may be a mixture obtained by polymerizing the component (A) and the component (B) separately. Furthermore, the ethylene-based polymer of component (A) can be constituted by polymerizing the same component in a plurality of reactors connected in series and / or in parallel. The ethylene polymer may be a polymer successively polymerized in a multistage polymerization reactor using one kind of catalyst, or in a single stage or multistage polymerization reactor using a plurality of kinds of catalysts, The produced polymer may be sufficient and what mixed the polymer polymerized using the 1 type or multiple types of catalyst may be used. The ethylene polymer of component (B) can also be composed of a plurality of components as in the case of producing the polymer of component (A). The ethylene polymer may be a polymer successively polymerized in a multistage polymerization reactor using one kind of catalyst, or in a single stage or multistage polymerization reactor using a plurality of kinds of catalysts, The produced polymer may be sufficient and what mixed the polymer polymerized using the 1 type or multiple types of catalyst may be used.

The so-called multi-stage polymerization method in which polymerization is performed in a plurality of reactors connected in series and / or in parallel is a production condition for producing a high molecular weight component in the first polymerization zone (first-stage reactor) as long as the claims are satisfied. In the order of transferring the resulting polymer to the next reaction zone (second stage reactor) and producing low molecular weight components in the second stage reactor, the first polymerization In the zone (first stage reactor), polymerization is carried out using the production conditions for producing low molecular weight components, and the resulting polymer is transferred to the next reaction zone (second stage reactor). Either the order of producing the high molecular weight components in the second-stage reactor may be used, or the high molecular weight components and the low molecular weight components may be produced separately in a plurality of parallel reactors, and then mixed.
A specific preferable polymerization method is the following method. That is, using a Ziegler catalyst containing a titanium-based transition metal compound and an organoaluminum compound and at least two reactors, introducing ethylene and α-olefin into the first-stage reactor, A polymer is produced, and the polymer extracted from the first-stage reactor is transferred to the second-stage reactor, and ethylene and hydrogen are introduced into the second-stage reactor to reduce the density. This is a method for producing a polymer having a molecular weight component. In this case, a polymer having a low density and a high molecular weight component may be produced in a plurality of reactors (a plurality of first-stage reactors may be used), or a polymer having a high density and a low molecular weight component may be prepared. You may manufacture with a some reactor (it is good also considering the reactor of a 2nd step | stage as a plurality).
In the case of multistage polymerization, the amount of ethylene polymer produced in the polymerization zone from the second stage onwards and its properties are determined by determining the amount of polymer produced in each stage (can be determined by analysis of unreacted gas, etc.) The physical properties of the polymer extracted after each stage can be measured, and the physical properties of the polymer produced at each stage can be determined based on the additivity.

  The ethylene polymer produced by the above method can be pelletized by mechanical melt mixing with a pelletizer or homogenizer according to a conventional method, and then molded by various molding machines to obtain a desired molded product. . In addition to the other olefin polymers and rubbers, etc., the ethylene polymer obtained by the above-mentioned method is not limited to antioxidants, ultraviolet absorbers, light stabilizers, lubricants, antistatic agents, Known additives such as a clouding agent, an antiblocking agent, a processing aid, a color pigment, a crosslinking agent, a foaming agent, an inorganic or organic filler, and a flame retardant can be blended.

  As additives, for example, antioxidants (phenolic, phosphorus-based, sulfur-based), lubricants, antistatic agents, light stabilizers, ultraviolet absorbers, and the like can be appropriately used in combination of one or more. As filler, calcium carbonate, talc, metal powder (aluminum, copper, iron, lead, etc.), silica, diatomaceous earth, alumina, gypsum, mica, clay, asbestos, graphite, carbon black, titanium oxide, etc. can be used. Of these, calcium carbonate, talc and mica are preferably used. In any case, various additives may be blended with the ethylene polymer as necessary, and the mixture may be kneaded with a kneading extruder, a Banbury mixer, or the like to obtain a molding material.

As described above, the polyethylene resin composition of the present invention has the following characteristics.
Characteristic (i): MFR is 1 g / 10 min or more and less than 10 g / 10 min, HLMFR is 70 g / 10 min or more and less than 400 g / 10 min, and HLMFR / MFR is 40 or more and less than 80. Characteristic (ii): Density is 0.953 g / Cm ³ or more and less than 0.965 g / cm ³

The melt flow rate (MFR) at a temperature of 190 ° C. and a load of 2.16 kg of the polyethylene resin composition is 1 g / 10 min or more and less than 10 g / 10 min, preferably 2 g / 10 min or more and 9 g / 10 min or less, more preferably Is 3 g / 10 min or more and 7 g / 10 min or less. When the MFR is less than 1 g / 10 minutes, the high-speed moldability at the time of injection molding is inferior, whereas when it is 10 g / 10 minutes or more, the stress crack resistance of the container lid is inferior. Here, MFR is a value measured according to JIS K6922-2: 1997 “Plastics—Polyethylene (PE) molding and extrusion materials—Part 2: How to make test pieces and properties”. .
MFR can be adjusted by ethylene polymerization temperature, use of a chain transfer agent, etc., and a desired thing can be obtained. That is, by increasing the polymerization temperature of ethylene and α-olefin, the molecular weight can be decreased, and as a result, the MFR can be increased. By decreasing the polymerization temperature, the molecular weight can be increased, and as a result, the MFR can be decreased. . In addition, the molecular weight can be lowered by increasing the amount of hydrogen coexisting in the copolymerization reaction of ethylene and α-olefin (chain transfer agent amount), resulting in an increase in MFR, and the amount of hydrogen coexisting (chain transfer). The molecular weight can be increased by decreasing the (drug amount), and as a result, the MFR can be reduced.

The melt flow rate (HLMFR) of the polyethylene resin composition at a temperature of 190 ° C. and a load of 21.6 kg is 70 g / 10 min or more and less than 400 g / 10 min, preferably 80 g / 10 min or more and 300 g / 10 min or less. is there. When the HLMFR is less than 70 g / 10 minutes, the high-speed moldability is inferior. On the other hand, when the HLMFR is 400 g / 10 minutes or more, the stress crack resistance of the container lid is inferior. Here, HLMFR is a value measured according to JIS K6922-2: 1997 “Plastics—Polyethylene (PE) molding and extrusion materials—Part 2: How to make test pieces and properties”. .
HLMFR can also be adjusted by the ethylene polymerization temperature, the use of a chain transfer agent, and the like, and a desired product can be obtained while balancing with other physical properties. That is, the molecular weight can be decreased by increasing the polymerization temperature of ethylene and α-olefin, and as a result, the HLMFR can be increased, and the molecular weight can be increased by decreasing the polymerization temperature, and as a result, the HLMFR can be decreased. Can do. In addition, by increasing the amount of hydrogen coexisting in the copolymerization reaction of ethylene and α-olefin (amount of chain transfer agent), the molecular weight can be lowered, resulting in an increase in HLMFR, and the amount of coexisting hydrogen (chain transfer). The molecular weight can be increased by reducing the amount of the agent, and as a result, the HLMFR can be reduced.

The HLMFR / MFR, that is, the flow rate ratio (FRR) of the polyethylene resin composition is 40 or more and less than 80, preferably 45 or more and less than 80, and more preferably 50 or more and less than 75. When HLMFR / MFR is less than 40, high-speed moldability is poor, while when it is 80 or more, shrinkage ratio anisotropy is increased.
HLMFR / MFR can be increased or decreased by adjusting the molecular weight distribution. This HLMFR / MFR, that is, the flow rate ratio (FRR) has a correlation with the molecular weight monodispersity (weight average molecular weight Mw / number average molecular weight Mn) by gel permeation chromatography. HMWFR / MFR = 40 corresponds to about 6 of monodisperse Mw / Mn. HLMFR / MFR and Mw / Mn can be adjusted by the type of catalyst, the type of cocatalyst, the polymerization temperature, the residence time in the polymerization reactor, the number of polymerization reactors, etc. It can be adjusted by the speed, etc., preferably by adjusting the mixing ratio of the high molecular weight component and the low molecular weight component, and can be increased by increasing the difference in the average molecular weight of each component.

The density of the polyethylene resin composition is less than 0.953 g / cm ³ or more 0.965 g / cm ^3, preferably 0.953 g / cm ³ or more 0.963 g / cm ³ or less, more preferably 0.953 g / Cm ³ or more and 0.961 g / cm ³ or less. When the density is less than 0.953 g / cm ³ , the rigidity of the container lid is inferior, and the container lid is easily deformed at a high temperature, and the container lid is deformed by the influence of the internal pressure of the container and causes leakage. On the other hand, when the density is 0.965 g / cm ³ or more, the stress crack resistance of the container lid is inferior. Here, the density is a value measured according to JIS K6922-1, 2: 1997.
A desired density can be obtained by changing the density depending on the kind and amount of the comonomer copolymerized with ethylene.

Furthermore, in the polyethylene resin composition of the present invention, the cap (container lid) is not easily deformed even at high temperatures, and in order to enable thinning, (iii) the flexural modulus is 800 MPa or more, preferably 850 MPa or more, More preferably, it is 900 MPa or more. When the flexural modulus is less than 800 MPa, the rigidity is lowered, and the container lid is easily deformed by the internal pressure of the container, and particularly easily deformed at a high temperature. Although the upper limit of a bending elastic modulus is not specifically limited, Usually, it is 2000 MPa or less. Here, the flexural modulus is a value measured according to JIS K6922-2 using a 4 × 10 × 80 mm plate injection-molded at 210 ° C. as a test piece.
The flexural modulus can be adjusted by increasing or decreasing the molecular weight and density of polyethylene, and increasing the molecular weight or density can increase the flexural modulus.

In the polyethylene resin composition of the present invention, (iv) the tensile yield strength is 25 MPa or more, preferably 26 MPa or more, more preferably 27 MPa or more. When the tensile yield strength is less than 25 MPa, the rigidity is lowered, and the feel when the cap is opened becomes soft. The upper limit of the tensile yield strength is not particularly limited, but is usually 50 MPa or less. Here, the tensile yield strength is a value measured according to JIS K6922-2: 1997, using a JIS No. 1 tensile test piece injection molded at 210 ° C. as a test piece.
The tensile yield strength can be adjusted by increasing or decreasing the molecular weight and density of polyethylene, and increasing the molecular weight or density can increase the tensile yield strength.

Further, in the polyethylene resin composition of the present invention, (v) hydrocarbon volatile matter is 80 ppm or less, preferably 50 ppm or less, so as not to impair the taste or to give the contents a strange odor or alteration. More preferably, it is 30 ppm or less. The hydrocarbon referred to in the present invention refers to a compound containing at least carbon and hydrogen, and is usually measured by gas chromatography. By satisfying the requirements of the present invention, the odor and taste of the contents of the container The effect can be prevented.
Here, the hydrocarbon volatile content is measured by gas chromatography of the air in the head space when 1 g of the polyethylene resin composition is placed in a 25 ml glass sealed container and heated at 130 ° C. for 60 minutes.
In the present invention, in order to reduce the hydrocarbon volatile content to a predetermined value or less, the polymerized polyethylene polymer is subjected to a volatile content removal operation, for example, steam stripping treatment, hot air deodorization treatment, vacuum treatment, nitrogen purge treatment, etc. By carrying out the above, it can be achieved, and in particular, by performing the steam deodorization treatment, the effect of the present invention can be remarkably exhibited. The conditions for the steam treatment are not particularly limited, but the ethylene polymer may be brought into contact with 100 ° C. steam for about 8 hours.

  In the polyethylene resin composition of the present invention, (vi) the shrinkage ratio anisotropy at the time of injection molding is such that MD / TD is 1.0 or more and less than 2.0. It is desirably 1.0 or more and less than 1.9, and more desirably 1.1 or more and less than 1.8. This value is obtained by molding a flat plate of 120 × 120 × 2 mm by injection molding at 190 ° C., adjusting the state at 23 ° C. for 48 hours, and measuring the dimensions in the flow direction (MD) and the right-angle direction (TD), It is a numerical value obtained by obtaining the shrinkage rate and dividing the MD value by the TD value. When this value is 2.0 or more, the injection product is easily broken, and when it is less than 1.0, the product is easily deformed. The shrinkage rate anisotropy can be adjusted by molecular weight distribution.

  In addition, in the polyethylene resin composition of the present invention, (vii) constant strain ESCR, that is, stress resistance under a constant strain, so that the cap breaks due to stress cracks at the point of sale at the point of sale, and the content does not leak. The cracking property is 10 hours or more and 1000 hours or less. Desirably, it is 15 hours or more and 1000 hours or less, and more desirably 60 hours or more and 1000 hours or less. If this value is less than 10 hours, it will not withstand the internal pressure of the container during product storage and will be destroyed. Moreover, since the thing exceeding 1000 hours cannot satisfy | fill other requirements, it is not realistic. Increasing the constant strain ESCR can be achieved by adding a low density and high molecular weight component.

In the polyethylene resin composition of the present invention, because of the full notch creep (stress crack resistance or crack propagation resistance) characteristic that is an indicator of fracture due to weak stress over a long period of time, (viii) the breaking time at 1.9 MPa by the full notch creep test ( FNCT) is 60 hours or longer, preferably 80 hours or longer, more preferably 130 hours or longer. If the FNCT is less than 60 hours, the probability that breakage due to stress cracks will occur in the container lid during high temperature storage in summer is increased. Here, FNCT is measured in accordance with JIS K6774: 1998 “Polyethylene pipe for gas” at a temperature of 80 ° C. and using a 1% Emar aqueous solution manufactured by Kao Corporation.
Increasing the FNCT can be achieved by adding low density and high molecular weight components.

  In the present invention, it is also effective to use a nucleating agent in order to accelerate the crystallization rate. The nucleating agent is not particularly limited, and a general organic or inorganic nucleating agent can be used.

Using the polyethylene resin composition of the present invention as a raw material, various molded products are obtained mainly by injection molding, compression molding or the like. Since the polyethylene resin composition of the present invention satisfies the above characteristics, it is excellent in moldability, high fluidity, odor, impact resistance, food safety, particularly injection moldability, rigidity, and heat resistance. . Therefore, it can be used for applications such as containers and container lids that require such characteristics, and in particular, food oils such as edible oil and wasabi, seasonings, alcoholic beverages, carbonated beverages and beverage containers and container lids, It can be used for applications such as cosmetics and hair cream containers and container lids, and can be suitably used for food containers molded by injection molding and the like and their container lids.
In particular, the polyethylene resin composition of the present invention exhibits an excellent effect on a container lid for a carbonated beverage. The container lid for carbonated beverages using the material of the present invention can be molded at high speed, can be cycled, and can be formed into a one-piece shape, and is suitably used for containers such as PET bottles.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist. In addition, the measuring method used in the Example is as follows.
(1) Melt flow rate (MFR) at a temperature of 190 ° C. and a load of 2.16 kg: measured in accordance with JIS K6922-2: 1997.
(2) Melt flow rate (HLMFR) at a temperature of 190 ° C. and a load of 21.6 kg: measured in accordance with JIS K6922-2: 1997.
(3) Density: Measured according to JIS K6922-1,2: 1997.
(4) Fracture time at 1.9 MPa (FNCT) by full notch creep test: JIS K6774: In accordance with 1998, the temperature was 80 ° C., and the liquid used was measured using an Emar 1% aqueous solution manufactured by Kao Corporation.

(5) Flexural modulus: measured using a 4 × 10 × 80 mm plate injection-molded at 210 ° C. as a test piece in accordance with JIS K6922-2.
(6) Tensile yield strength: measured in accordance with JIS K6922-2: 1997.
(7) Constant strain ESCR: Measured according to JIS K6922-2: 1997.
(8) Hydrocarbon volatiles: 1 g of resin was placed in a 25 ml glass sealed container, and the components in the sealed container after heating at 130 ° C. for 60 minutes were analyzed and measured by gas chromatography.

(9) Shrinkage ratio anisotropy (MD / TD): One side film gate (gate thickness 0.2 mm) at a molding temperature of 190 ° C. and a mold temperature of 40 ° C. using an IS-80 injection molding machine manufactured by Toshiba Machine A 120 × 120 × 2 mm flat plate is formed, and after the forming, the shrinkage in the flow direction (MD) and the flow perpendicular direction (TD) after being left at 23 ° C. for 48 hours is measured. MD / TD is calculated from the measured value.
(10) Odor sensory test: A test piece having a size of about 20 × 20 mm was cut from the flat plate obtained by the molding of (9) above, put into a 300 ml glass wide-mouth bottle, stoppered, and 80 ° C. For 2 hours in a heated oven. After the heating, the jar was taken out and sensory evaluation was performed within 10 minutes according to the following odor standards.
0: Odorless 1: Feeling finally 2: Feeling 3: Smelling considerably 4: Smelling strongly 5: Smelling intensely

[Example 1]
<Manufacture of catalyst>
As the solid catalyst component, a Ti-based catalyst obtained by a dissolution precipitation method was used. The manufacturing method is as follows.
The inside of a 1 liter three-necked flask equipped with a stirrer and a condenser was sufficiently purged with nitrogen, and then dried hexane 250 ml, anhydrous magnesium chloride 11.4 g previously pulverized in a 3 liter vibration mill for 1 hour and n -110 ml of butanol was added and heated at 68 ° C for 2 hours to obtain a uniform solution (1a). After cooling this solution (1a) to room temperature, 8 g of methylpolysiloxane having a kinematic viscosity at 25 ° C. of 25 cSt was added and stirred for 1 hour to obtain a uniform solution (1b). After the solution (1b) was cooled with water, 50 ml of titanium tetrachloride and 50 ml of dry hexane were dropped into the solution using an addition funnel over 1 hour to obtain a solution (1c). The solution (1c) was uniform, and the complex of the reaction product was not precipitated. The solution (1c) was heated at 68 ° C. for 2 hours while refluxing. About 30 minutes after the start of heating, precipitation of the reaction product complex (1d) was observed. This was collected, washed 6 times with 250 ml of dry hexane, and further dried with nitrogen gas to recover 19 g of the reaction product complex (1d).
When the reaction product complex (1d) was analyzed, it contained Mg 14.5% by mass, n-butanol 44.9% by mass and Ti 0.3% by mass, and the specific surface area was 17 m ² / g. .
4.5 g of the reaction product complex (1d) was collected in a 1-liter three-necked flask equipped with a stirrer and a condenser under a nitrogen atmosphere, and 250 ml of dry hexane and 25 ml of titanium tetrachloride were added to this and refluxed. After heat treatment at 68 ° C. for 2 hours and cooling to room temperature, it was washed 6 times with 250 ml of dry hexane and dried with nitrogen gas to recover 4.6 g of the solid catalyst component (1e).
When this solid catalyst component (1e) was analyzed, it contained 12.5% by mass of Mg, 17.0% by mass of n-butanol and 9.0% by mass of Ti, and the specific surface area was 29 m ² / g. . When this solid catalyst component (1e) was observed with an SEM, the particle size was uniform and a shape close to a sphere.

<Manufacture of polymer>
As the first stage reactor, the solid catalyst component (1e) obtained in the above <Production of catalyst> (14.3 g / hr) from the catalyst supply line was added to the first stage polymerizer having an internal volume of 200 liters, and triethylaluminum (TEA ) At a rate of 56 mmol / hr continuously from the organometallic compound supply line, and while discharging the polymerization content at the required rate, at 70 ° C., the polymerization solvent (n-hexane) 70 (l / hr) ), Hydrogen 1.46 (mg / hr), ethylene 18.0 (kg / hr), 1-butene 1.50 (kg / hr), total pressure 1.4 MPa, average residence time 1. The first stage copolymerization was carried out continuously under the condition of 7Hr.
A part of the polymerization product in the first-stage reactor was collected, the polymer was recovered, and the physical properties were measured. The results are shown in Table 2 as “Component (A)”.
The slurry-like polymerization product produced in the first stage reactor is introduced as it is into the second stage reactor having an internal volume of 400 liters through a continuous tube having an inner diameter of 50 mm, and the contents of the polymerizer are discharged at the required speed. At 82 ° C., at a rate of polymerization solvent (n-hexane) 100 (l / hr), hydrogen 14.7 (g / hr), ethylene 33.4 (kg / hr), total pressure 1.3 MPa The second stage polymerization was carried out continuously under the condition of an average residence time of 1.2 Hr.
The polymerization product discharged from the second stage reactor was introduced into a flushing tank, the polymerization product was continuously withdrawn, and unreacted gas was removed from the degassing line.
The obtained polymer was subjected to a steam stripping treatment, granulated with a pelletizer, and then evaluated for physical properties. The results are shown in Table 2. In Table 2, the physical properties of the “component (B)” produced in the second stage reactor are the physical properties of the polyethylene composition as the final product and the physical properties of the component (A) obtained in the first stage reactor. From the above, it was obtained by calculation based on the additivity rule. As is apparent from Table 2, the obtained polymer was excellent in mechanical properties such as tensile yield strength, flexural modulus, FNCT, and shrinkage anisotropy (MD / TD) was 1.3. It was.

[Examples 2 to 6]
The procedure was the same as in Example 1 except for the conditions shown in Table 1. The evaluation results of the obtained polymer are shown in Table 2. The obtained polymer was excellent in mechanical properties such as tensile yield strength, flexural modulus, FNCT, and shrinkage anisotropy (MD / TD) was an appropriate value.

[Comparative Examples 1-8]
The procedure was the same as in Example 1 except for the conditions shown in Table 1. The evaluation results of the obtained polymer are shown in Table 3. From Table 3, although Comparative Example 1 has no problem in mechanical properties, the shrinkage ratio anisotropy is large, and a problem occurs in the injection molded product. In Comparative Examples 2 and 3, there is no problem in mechanical properties, but the shrinkage ratio anisotropy is large, and a problem occurs in the injection molded product.
Further, in Comparative Examples 4 and 5, although the shrinkage ratio anisotropy is an appropriate value, the FNCT and the constant strain ESCR are small, suggesting that cracks are generated in the product. In Comparative Example 6, the HLMFR was large, the density was small, the flexural modulus and the tensile yield strength were small, and therefore the container lid suitability was not sufficient.
Further, although Comparative Example 7 has a relatively good physical property balance, it has a large shrinkage ratio anisotropy. In Comparative Example 8, the shrinkage ratio anisotropy is an appropriate value, bending elastic modulus, tensile yield. Since the strength and FNCT were small, the container lid suitability was not sufficient.

  According to the present invention, it is suitable for a lid of a container for containing a liquid of a PET bottled beverage, and the injection moldability is improved and the shrinkage ratio anisotropy is small while maintaining stress crack resistance and rigidity. In addition, it is possible to provide a container lid in which a bridge break of the container lid is appropriate.

Claims (4)

A polyethylene resin composition comprising 20% by mass or more and less than 40% by mass of an ethylene polymer (A) and more than 60% by mass of 80% by mass or less of an ethylene polymer (B),
The ethylene polymer (A) has a melt flow rate (HLMFR) of 1 g / 10 min to 10 g / 10 min at a temperature of 190 ° C. and a load of 21.6 kg, and a density of 0.910 g / cm ^{3 to} 0.935 g. / cm ³ or less, ethylene polymer (B), the temperature 190 ° C., a melt flow rate (MFR) 30 g / 10 minutes or more 150 g / less than 10 minutes at a load 2.16 Kg, and density 0.960 g / cmi ³ or more, and the polyethylene resin composition has (i) MFR 1 g / 10 min or more and less than 10 g / 10 min, HLMFR 70 g / 10 min or more and less than 400 g / 10 min, HLMFR / MFR 40 or more and less than 80 , and the and (ii) a density polyethylene for injection molding the container closure, characterized in that it is less than 0.953 g / cm ³ or more 0.965 g / cm ³ Styrene resin composition.   Furthermore, (iii) the flexural modulus is 800 MPa or more, (iv) the tensile yield strength is 25 MPa or more, (v) the hydrocarbon volatile content is 80 ppm or less, and (vi) the shrinkage ratio of the injection molded plate of 120 × 120 × 2 mm is different. The polyethylene resin composition for an injection-molded container lid according to claim 1, wherein the isotropic (MD / TD) is 1.0 or more and less than 2.0, and (vii) the constant strain ESCR is 10Hr or more and 1000Hr or less. object. Furthermore, (viii) FNCT in 1.9 MPa is 60 hours or more, The polyethylene-type resin composition for injection-molded container lids of Claim 2 characterized by the above-mentioned. The polyethylene resin composition for an injection-molded container lid according to any one of claims 1 to 3 , wherein the injection-molded container lid is a carbonated beverage container lid.