Polyethylene resin and film

Abstract

To provide a polyethylene resin and a film which are excellent in self adhesive force, rigidity, unwinding property, and tear strength.SOLUTION: A polyethylene resin satisfies the followings (A) to (C): (A) density of 915 kg / m3 or more and 935 kg / m3 or less; (B) Mw / Mn in measure of gel permeation chromatography of 3.0 or more and 12.0 or less; and (C) S2 / S1 determined by measurement of ultrahigh speed differential scanning calorimeter of 0.20 or more and 0.90 or less, and Tc1-Tc2 of 3.0°C or higher and 9.0°C or lower (here, S1 is a high temperature crystallization component ratio [%], S2 is a low temperature crystallization component ratio [%], Tc1 is a high temperature crystallization component peak top [°C], and Tc2 is a low temperature crystallization component peak top [°C]).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to polyethylene resins and films. [Background technology]

[0002] Polyethylene resins are molded by various molding methods and used in a wide range of applications. The properties required of polyolefin resins and polyethylene resins vary depending on the molding method and application. For example, a typical application of films is as protective films to prevent the surfaces of products such as metal plates, resin plates, and optical components from being soiled or scratched by dust or dirt during transportation, storage, or processing. Furthermore, in order to prevent contamination of the adherend, protective films are also used as self-adhesive protective films that can be attached to the adherend by their own adhesiveness without using adhesives or other means.

[0003] For example, Patent Document 1 proposes a biaxially oriented self-adhesive protective film that is flexible yet has low elongation and is difficult to stretch, has excellent blocking resistance and adhesiveness during secondary processing, is easy to peel off when necessary, and has sufficient adhesive strength for rough-surfaced adherends to be protected.It is also suitable for the productivity of wide products, and uses a metallocene catalyst and does not require the application of an adhesive, so it is clean, does not leave adhesive residue, and can be produced inexpensively.

[0004] Furthermore, for example, Patent Document 2 proposes a surface protection film that is excellent in adhesive properties, adhesive strength stability over time, transparency, heat resistance, contamination resistance, and payout ability from a roll. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6158689 [Patent Document 2] Patent No. 4855302 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, not only have quality requirements increased year by year, but there has also been growing social interest in environmental issues. To address environmental issues, there is a need for the development of easily recyclable mono-material products, materials with a low environmental impact, biomass-derived resins, and resin recycling technologies.

[0007] However, as shown in Patent Documents 1 and 2, in order to meet the increasing demands for quality, Although a self-adhesive protective film has been developed that uses a composite material made by laminating multiple resins to improve adhesive properties and work efficiency, there are still challenges in developing mono-material products that are easily recyclable, which is required to address environmental issues.

[0008] A specific example of a requirement for the development of a mono-material protective film with self-adhesive properties is a film made solely of polyethylene resin. However, because the adhesive strength of polyethylene film is relatively low, resins such as propylene-ethylene-1-butene copolymers and hydrogenated styrene-based elastomers are used in the adhesive layer to enhance adhesive strength, as disclosed in Patent Documents 1 and 2. Therefore, the market is demanding polyethylene films with even improved self-adhesive properties. One method for improving self-adhesive properties is to increase the amount of comonomer introduced during polyethylene polymerization to lower the density. However, lowering the density reduces the film's rigidity, which can lead to wrinkles and other problems when the protective film is applied to the substrate, potentially reducing handleability. Furthermore, improving the film's self-adhesive properties makes it difficult to peel from a rolled product, making the film prone to wrinkles and streaks. In the worst case scenario, the film may even tear.

[0009] The present invention has been made in view of the above problems, and an object of the present invention is to provide a polyethylene resin and film that are excellent in self-adhesive strength, rigidity, payout ability, and tear strength in order to meet market demands for high quality and environmental concerns. [Means for solving the problem]

[0010] Therefore, the present inventors have conducted extensive research to solve the above problems, and as a result have found that the above problems can be solved by using a polyethylene resin with a specific composition, which has led to the completion of the present invention.

[0011] That is, the present invention is as follows. [1] A polyethylene resin that satisfies the following (A) to (C): (A) Density is 915 kg / m 3 More than 935kg / m 3 That is: (B) Mw / Mn (Mn is number average molecular weight, Mw is weight average molecular weight, and Mw / Mn is molecular weight distribution) measured by gel permeation chromatography (hereinafter referred to as GPC) is 3.0 or more and 12.0 or less, (C) S2 / S1 is 0.20 or more and 0.90 or less, and Tc1-Tc2 is 3.0°C or more and 9.0°C or less, as determined by measurement with an ultrafast differential scanning calorimeter (where S1 is the proportion of high-temperature crystallization component [%], S2 is the proportion of low-temperature crystallization component [%], Tc1 is the peak top of the high-temperature crystallization component [°C], and Tc2 is the peak top of the low-temperature crystallization component [°C]). [2] The polyethylene resin according to [1], having a melt flow rate measured in accordance with JIS K7210 (190°C, 2.16 kg load) of 0.5 g / 10 min or more and 20.0 g / 10 min or less. [3] The polyethylene resin according to [1] or [2], wherein, in an elution temperature-elution amount curve obtained by temperature rising elution fractionation (TREF) of cross fractionation chromatography (CFC), the temperature (Te1) at which the elution amount is greatest is above 70°C, and the elution amount of the component eluted at Te1 is 13.0 mass% or more and 23.0 mass% or less. [4] The polyethylene resin according to any one of [1] to [3], wherein the cumulative elution amount at 70°C or less is 10.0% by mass or more and 50.0% by mass or less in an elution temperature-elution amount curve obtained by temperature rising elution fractionation (TREF) in cross fractionation chromatography (CFC). [5] The polyethylene resin according to any one of [1] to [4], wherein the polyethylene resin comprises high-pressure low-density polyethylene. [6] A film comprising the polyethylene resin according to any one of [1] to [5]. [7] The film according to [6], which has a thickness of 3 to 240 μm and a self-adhesive strength of 0.9 N / 15 mm or more. [8] The film according to [7], having a tear strength of 1.5 N or more and a payout force of less than 2.0 N / 15 mm. [9] The film according to [7] or [8], which consists solely of the polyethylene resin.

[10] A sheet comprising the polyethylene resin according to any one of [1] to [5].

[11] The sheet according to

[10] , having a thickness of 250 μm or more and 10 mm or less and a payout force of less than 2.0 N / 15 mm.

[12] The sheet according to

[12] , which consists solely of the polyethylene resin.

[13] A foam-molded product comprising the polyethylene resin according to any one of [1] to [5]. [Effects of the Invention]

[0012] According to the present invention, a polyethylene resin and a film having excellent self-adhesive strength, rigidity, payout property, and tear strength can be provided. [Brief explanation of the drawings]

[0013] [Figure 1] This is an example of a method for producing a polyethylene resin using a stirred autoclave reactor. [Figure 2] This is an example of a method for analyzing Tc1, Tc2, and Tdiv. [Figure 3] This is an example of an analysis method for S1 and S2. [Figure 4] FIG. 1 is a schematic diagram of the temperature program for ultrafast differential scanning calorimetry. [Figure 5] 1 is an example of the measurement results of ultrafast differential scanning calorimetry. DETAILED DESCRIPTION OF THE INVENTION

[0014] Below, we will explain in detail the embodiment of the present invention (hereinafter referred to as the ``present embodiment''), but the present invention is not limited to this and various modifications are possible within the scope of the gist of the present invention.

[0015] [Polyethylene resin] The polyethylene resin of this embodiment satisfies the following requirements (A) to (C). (A) Density is 915 kg / m 3 More than 935kg / m 3 It must be less than or equal to: (B) The Mw / Mn (Mn is the number average molecular weight, Mw is the weight average molecular weight, and Mw / Mn is the molecular weight distribution) measured by gel permeation chromatography (hereinafter also referred to as "GPC") is 3.0 or more and 12.0 or less. (C) S2 / S1 is 0.20 or more and 0.90 or less, and Tc1-Tc2 is 3.0°C or more and 9.0°C or less, as determined by measurement with an ultrafast differential scanning calorimeter (where S1 is the proportion of high-temperature crystallization component [%], S2 is the proportion of low-temperature crystallization component [%], Tc1 is the peak top of the high-temperature crystallization component [°C], and Tc2 is the peak top of the low-temperature crystallization component [°C]).

[0016] By satisfying these conditions, the polyethylene resin of this embodiment has excellent self-adhesive strength, rigidity, payout properties, and tear strength.

[0017] The polyethylene resin of the present embodiment may be a dry blend or melt blend of two or more kinds in any ratio, as long as the object of the present invention is not impaired.

[0018] [Requirement (A): Density] The polyethylene resin of the present embodiment satisfies the following requirement (A). (A) Density is 915 kg / m 3 More than 935kg / m 3 It must be less than or equal to:

[0019] The density of the polyethylene resin of this embodiment is preferably 922 kg / m 3 More than 934kg / m 3 More preferably, 925 kg / m or less. 3 More than 933kg / m 3 The following is the result.

[0020] The polyethylene resin of this embodiment has a density of 915 kg / m 3 When the density is 935 kg / m or more, the degree of crystallinity tends to be high, and the rigidity and tear strength are improved. 3 By ensuring that the thickness is equal to or less than 100 μm, the degree of crystallinity can be reduced and the self-adhesive strength can be improved.

[0021] The method for adjusting the density of the polyethylene resin is not particularly limited, and examples thereof include a method of adjusting the reaction temperature and / or reaction pressure, the type or amount of chain transfer agent, etc. when polymerizing the polyethylene resin. More specifically, when polymerizing the polyethylene resin, increasing the reaction temperature tends to decrease the density of the polyethylene resin, increasing the reaction pressure tends to increase the density of the polyethylene resin, and increasing the amount of chain transfer agent tends to increase the density of the polyethylene resin.

[0022] In this embodiment, the density can be measured in accordance with JIS K7112:1999, density gradient tube method (23° C.). Specifically, it is measured by the method described in the examples below.

[0023] [Requirement (B): Molecular weight distribution (Mw / Mn)] The polyethylene resin of the present embodiment satisfies the following requirement (B). (B) The Mw / Mn (Mn is the number average molecular weight, Mw is the weight average molecular weight, and Mw / Mn is the molecular weight distribution) measured by gel permeation chromatography (hereinafter also referred to as "GPC") is 3.0 or more and 12.0 or less.

[0024] The Mw / Mn of the polyethylene resin of this embodiment is preferably 3.5 or more and 8.0 or less, more preferably 4.0 or more and 6.0 or less. Because the polyethylene resin of this embodiment has an Mw / Mn of 3.0 or more, it tends to have high melt tension, which results in excellent neck-in and drawdown properties in T-die molding and excellent valve stability in inflation molding. Furthermore, because the polyethylene resin of this embodiment has an Mw / Mn of 12.0 or less, it is easy to suppress the occurrence of unevenness on the film surface due to the die swell phenomenon, and the surface area for adhesion between the film and the adherend tends to increase, thereby improving self-adhesive strength.

[0025] The method for adjusting the molecular weight distribution (Mw / Mn) of the polyethylene resin is not particularly limited, and examples thereof include a method of adjusting the reaction temperature and / or reaction pressure when polymerizing the polyethylene resin. More specifically, when polymerizing the polyethylene resin, increasing the reaction temperature tends to increase the Mw / Mn of the polyethylene resin, and increasing the reaction pressure tends to decrease the Mw / Mn of the polyethylene resin.

[0026] In this embodiment, the molecular weight distribution (Mw / Mn) can be measured by gel permeation chromatography (hereinafter also referred to as "GPC") and determined based on a calibration curve prepared using commercially available monodisperse polystyrene. Specifically, it is measured by the method described in the examples below.

[0027] [Requirement (C): Measurement using a fast scanning calorimetry] The polyethylene resin of the present embodiment satisfies the following requirement (C). (C) S2 / S1 is 0.20 or more and 0.90 or less, and Tc1-Tc2 is 3.0°C or more and 9.0°C or less, as determined by measurement with an ultrafast differential scanning calorimeter.

[0028] Here, S1 is the high-temperature crystallization component ratio [%], S2 is the low-temperature crystallization component ratio [%], Tc1 is the high-temperature crystallization component peak top [°C], and Tc2 is the low-temperature crystallization component peak top [°C].

[0029] An ultrafast differential scanning calorimeter is an instrument that can observe the melting and crystallization behavior of polymer chains under ultrafast heating and cooling, compared to conventional differential scanning calorimeters, and can perform measurements that mimic actual molding processes. Polyethylene film with improved self-adhesive strength is produced by rapidly cooling polyethylene resin in a high-temperature molten state, as it is preferable to sufficiently reduce the crystallinity. Therefore, analysis of polyethylene resin using an ultrafast differential scanning calorimeter is more appropriate than using a conventional differential scanning calorimeter.

[0030] As a result of extensive research, the inventors have found that, in measurements using an ultrafast differential scanning calorimeter, by rapidly cooling a polyethylene resin exposed to high temperatures, the exothermic peak due to crystallization is separated into two, and when the temperature difference (Tc1-Tc2) and ratio (S2 / S1) of the separated crystallization peaks satisfy specific ranges, the polyethylene resin of this embodiment has an excellent balance of self-adhesive strength, rigidity, and payout properties.

[0031] Here, "Tc1" and "Tc2" are the negative peak temperatures obtained from the second derivative of the cooling heat flow obtained after exposing polyethylene to a high temperature of 400°C, with "Tc1" being the crystallization peak temperature on the higher side and "Tc2" being the crystallization peak temperature on the lower side (see Figure 2). Furthermore, "S1" and "S2" are the area ratios of the crystallization peaks observed in the cooling heat flow obtained after exposing polyethylene to a high temperature of 400°C, which are higher than Tdiv. ("S1") and lower than Tdiv. ("S2") (see Figure 3). "Tdiv." is the positive peak temperature obtained from the second derivative of the cooling heat flow obtained after exposing polyethylene to a high temperature of 400°C (see Figure 2). S2, S1, Tc1, and Tc2 are specifically measured by the methods described in the Examples below.

[0032] The reason for this is not particularly limited, but the inventors speculate as follows. First, it is believed that the polyethylene resin, which has molecular chains with both localized areas of high long-chain branching and low short-chain branching, can improve the balance between self-adhesion, rigidity, and payout ability. The molecular chains with localized high long-chain branching and low short-chain branching, i.e., the low-density component (S2) that crystallizes at low temperatures, can sufficiently reduce the crystallinity, improving self-adhesion. On the other hand, high self-adhesion makes it difficult to peel the film when payout from a rolled product, and generally tends to worsen payout ability. However, the difference in crystal size between the component that crystallizes at low temperatures and the component that crystallizes at high temperatures, i.e., the difference in crystallization peak temperature (Tc1 - Tc2), creates fine irregularities on the film surface. When Tc1 - Tc2 falls within a specific range, payout ability is improved without hindering the reduction in self-adhesion. Furthermore, it is believed that the molecular chains with low branching, i.e., the high-density component (S1) that crystallizes at high temperatures, can improve rigidity.

[0033] [Requirement (C): S2 / S1] The S2 / S1 ratio of the polyethylene resin of this embodiment is 0.20 or more and 0.90 or less, preferably 0.30 or more and 0.85 or less, and more preferably 0.40 or more and 0.80 or less. By having an S2 / S1 ratio of 0.20 or more and 0.90 or less, the polyethylene resin of this embodiment has an excellent balance between self-adhesive strength and rigidity.

[0034] The method for adjusting the S2 / S1 ratio of a polyethylene resin is not particularly limited, but examples thereof include a method of polymerizing a polymer of a high molecular weight component with few branches. More specifically, Uniform polymerization can be achieved by increasing the rotation speed of the stirring blades of the stirred autoclave reactor or by decreasing the concentration of the diluted polymerization initiator in the top zone 1 and middle zone 2. In particular, S1 tends to increase.

[0035] Other methods for adjusting the S2 / S1 ratio of polyethylene resins include, but are not limited to, introducing branches such as short-chain branches or long-chain branches into the molecular chain, or introducing vinyl groups by promoting decomposition. More specifically, possible methods include increasing the concentration of the diluted polymerization initiator supplied to Bottom Zone 3 relatively high to locally introduce branches, or adjusting the average polymerization pressure, maximum polymerization temperature, the temperature difference between the reactor outlet and the high-pressure separator inlet, and the pressure inside the high-pressure separator. In particular, S2 tends to increase.

[0036] Other methods for adjusting the S2 / S1 ratio of polyethylene resins include, but are not limited to, adjusting the length of the molecular chain. More specifically, one possible method is to adjust the temperature difference between the top zone 1 and the bottom zone 3. One possible method for adjusting the S2 / S1 ratio within the above range is to combine this with the above-described method of polymerizing a polymer of a high molecular weight component with few branches, or the method of introducing short chain branches or the like into the molecular chain or the method of introducing vinyl groups by promoting decomposition.

[0037] [Requirement (C): Tc1-Tc2] The Tc1-Tc2 of the polyethylene resin of this embodiment is 3.0° C. or more and 9.0° C. or less, preferably 3.5° C. or more and 8.5° C. or less, and more preferably 4.0° C. or more and 8.0° C. or less. By having Tc1-Tc2 of 3.0° C. or more and 9.0° C. or less, the polyethylene resin of this embodiment has an excellent balance between self-adhesive strength and payout properties.

[0038] The method for adjusting the Tc1-Tc2 of the polyethylene resin is not particularly limited, but one possible method is to adjust the difference between a component that crystallizes at low temperatures and a component that crystallizes at high temperatures, which have different crystal sizes, within a specific range. More specifically, one possible method is to adjust the rotation speed of the stirring blades of the stirred autoclave reactor, the concentrations of the diluted polymerization initiator supplied to Top Zone 1 and Middle Zone 2 and Bottom Zone 3, the average polymerization pressure, the maximum polymerization temperature, the temperature difference between the reactor outlet and the high-pressure separator inlet, and the pressure inside the high-pressure separator.

[0039] [Melt flow rate (MFR)] The polyethylene resin of this embodiment has a melt flow rate of preferably 0.5 g / 10 min or more and 20.0 g / 10 min or less, more preferably 1.0 g / 10 min or more and 10.0 g / 10 min or less, and even more preferably 2.0 g / 10 min or more and 6.0 g / 10 min or less. When the polyethylene resin of this embodiment has a melt flow rate of 0.5 g / 10 min or more, the flowability during molding tends to be improved, and the payout ability and transparency tend to be excellent. Furthermore, when the polyethylene resin has a melt flow rate of 20.0 g / 10 min or less, the molecular weight tends to be increased, and the tear strength tends to be excellent.

[0040] The method for adjusting the melt flow rate (MFR) of a polyethylene resin is not particularly limited, and examples thereof include a method of adjusting the reaction temperature and / or reaction pressure, the type or amount of chain transfer agent, etc. when polymerizing the polyethylene resin. More specifically, when polymerizing the polyethylene resin, increasing the reaction temperature tends to increase the melt flow rate of the polyethylene resin, increasing the reaction pressure tends to decrease the melt flow rate of the polyethylene resin, and increasing the amount of chain transfer agent tends to increase the melt flow rate of the polyethylene resin.

[0041] In the present embodiment, the melt flow rate (MFR) of the polyethylene resin can be measured in accordance with JIS K7210:1999 Code D (temperature = 190°C, load = 2.16 kg). Specifically, it is measured by the method described in the examples below.

[0042] [Elution temperature-elution amount curve obtained by CFC measurement] Here, "cross-fractionation chromatography (CFC)" refers to an apparatus that combines a temperature-rising elution fractionation section (hereinafter also referred to as "TREF section") for crystallinity fractionation and a gel permeation chromatography section (hereinafter also referred to as "GPC section") for molecular weight fractionation. By directly connecting the TREF section and the GPC section, the correlation between composition distribution and molecular weight distribution can be analyzed. The elution volume and elution integral of polyethylene at each temperature can be determined by measuring the elution temperature-elution volume curve using the TREF section as follows. Specifically, a column containing a packing material is first heated to 140°C, and a sample solution (e.g., concentration: 20 mg / 20 mL) prepared by dissolving polyethylene resin in orthodichlorobenzene is introduced and maintained for 120 minutes. Next, the temperature is lowered to 40°C at a rate of 0.5°C / min, allowing the sample to be gradually precipitated on the packing surface. After maintaining the temperature at 40°C for 20 minutes, the column temperature is gradually increased at a rate of 20°C / min. The column was first heated from 40°C to 60°C in 10°C intervals, then heated from 60°C to 69°C in 3°C intervals, then heated from 69°C to 100°C in 1°C intervals, and then heated from 100°C to 110°C in 10°C intervals, and then held at 110°C. After holding at each temperature for 21 minutes, the column was heated again, and the concentration of the sample (polyethylene resin) eluted at each temperature was measured. The elution temperature-elution volume curve was then measured based on the elution volume (mass%) of the sample (polyethylene) and the temperature (°C) inside the column at that time, and the elution volume at each temperature was determined. From the elution temperature-elution volume curves obtained by temperature-rising elution fractionation (TREF), the temperature (Te1) (°C) with the highest elution volume, the percentage (mass%) of the eluted component at Te1, and the percentage (mass%) of the cumulative elution volume of components eluting at 70°C or below were determined.

[0043] [The temperature at which the amount of elution is greatest (Te1) and the amount of eluted components at Te1] In the polyethylene resin of this embodiment, the temperature at which the largest elution amount is obtained in an elution temperature-elution amount curve obtained by temperature rising elution fractionation (TREF) of cross fractionation chromatography (CFC) (hereinafter also referred to as the "temperature at which the largest elution amount is obtained (Te1)" or simply "Te1") is preferably 70°C or higher and 88°C or lower, more preferably 76°C or higher and 87°C or lower, and even more preferably 80°C or higher and 85°C or lower. Since the temperature at which the largest elution amount is obtained (Te1) is 70°C or higher, the polyethylene resin of this embodiment tends to contain a large amount of high-molecular-weight components with fewer branches, and tends to have excellent rigidity and tear strength. Furthermore, since the temperature at which the largest elution amount is obtained (Te1) within the above range, the balance between rigidity and tear strength tends to be excellent.

[0044] Furthermore, in the polyethylene resin of this embodiment, the elution amount of components eluted at Te1 (hereinafter also referred to as "elution amount of components eluted at Te1") in an elution temperature-elution amount curve obtained by temperature rising elution fractionation (TREF) in cross fractionation chromatography (CFC) is preferably 13.0% by mass or more and 23.0% by mass or less, more preferably 15.0% by mass or more and 22.0% by mass or less, and even more preferably 17.0% by mass or more and 21.0% by mass or less. Since the elution amount of components eluted at Te1 is 13.0% by mass or more and 23.0% by mass or less, the polyethylene resin of this embodiment tends to have an excellent balance between rigidity and tear strength. Furthermore, the transparency also tends to be excellent.

[0045] The method for adjusting the temperature (Te1) at which the amount of elution of the polyethylene resin is greatest and the amount of eluted components at Te1 is not particularly limited, but includes, for example, a method of polymerizing a polymer of a high-molecular-weight component with few branches. More specifically, a method can be considered in which the polymerization proceeds relatively uniformly by increasing the rotation speed of the stirring blades of a stirred autoclave reactor, thereby adjusting the temperature (Te1) at which the amount of elution of the polyethylene resin is greatest and the amount of eluted components at Te1 to fall within the above-mentioned ranges.

[0046] Furthermore, other methods for adjusting the temperature (Te1) at which the amount of elution of polyethylene resin is greatest and the amount of eluted components at Te1 include, but are not limited to, methods such as introducing short chain branches into the molecular chain and introducing vinyl groups by promoting decomposition. More specifically, methods of adjusting the average polymerization pressure, maximum polymerization temperature, the temperature difference between the reactor outlet and the high-pressure separator inlet, and the pressure inside the high-pressure separator can be considered.

[0047] [Cumulative elution amount at 70°C or below] The polyethylene resin of this embodiment preferably has an integrated elution amount at 70°C or below (hereinafter also simply referred to as "integrated elution amount at 70°C or below") of 10.0% by mass or more and 50.0% by mass or less, more preferably 15.0% by mass or more and 40.0% by mass or less, and even more preferably 20.0% by mass or more and 30.0% by mass or less, in an elution temperature-elution amount curve obtained by temperature rising elution fractionation (TREF) in cross fractionation chromatography (CFC). Since the polyethylene resin of this embodiment has an integrated elution amount at 70°C or below of 10.0% by mass or more, it tends to have a high level of branching and low-molecular-weight components, which tends to reduce crystallinity, and it tends to have excellent self-adhesive strength and transparency. Furthermore, since the polyethylene resin of this embodiment has an integrated elution amount at 70°C or below of 50.0% by mass or less, it tends to have an excellent balance of rigidity, tear strength, and transparency.

[0048] The method for adjusting the cumulative elution amount of polyethylene resin at 70°C or less is not particularly limited, but examples thereof include introducing short chain branches into the molecular chain or introducing vinyl groups by promoting decomposition. More specifically, possible methods include adjusting the average polymerization pressure, the maximum polymerization temperature, the temperature difference between the reactor outlet and the high-pressure separator inlet, and the pressure inside the high-pressure separator.

[0049] 〔film〕 The film of the present embodiment contains the polyethylene resin described above. The method for producing the film can be appropriately selected depending on the application and is not particularly limited, but examples thereof include T-die molding, inflation molding, calendar molding, and skive molding. T-die extrusion molding is particularly preferred.

[0050] The film of this embodiment is not limited to protective film applications, but is also suitable for packaging food wrap film, commercial wrap film, stretch film, sealant film, overwrap film, melt bags, various beverages such as water, juice, milk, sake, shochu, and other alcoholic beverages, cooked rice, as well as various foods such as cooked foods, intermediate cooked foods, sweets, bread, agricultural products, livestock products, seafood, paste products, water-based foods, oily foods, chilled foods, retort foods, frozen foods, seasonings, pharmaceuticals and medical supplies, pesticides, etc. Here, "stretch film" refers to a film that is wrapped around an item or the like when packing or wrapping the item or the like.

[0051] In this embodiment, the term "film" refers to a plastic film having a thickness of less than 250 μm. The thickness of the film in this embodiment is preferably 3 to 240 μm, and more preferably 10 to 200 μm.

[0052] The film of this embodiment preferably has a thickness of 3 to 240 μm and a self-adhesive strength of 0.9 N / 15 mm or more. The self-adhesive strength of the film of this embodiment is more preferably 1.2 N / 15 mm or more and 2.2 N / 15 mm or less, and even more preferably 1.5 N / 15 mm or more and 2.2 N / 15 mm or less. The film of this embodiment has a self-adhesive strength of 0.9 N / 15 mm or more, and therefore, when used, for example, as a protective film, its excellent adhesive strength tends to make it resistant to peeling even in the face of physical stress or environmental changes. This characteristic contributes to protecting the adherend for a long period of time. Furthermore, the film of this embodiment has a self-adhesive strength of 2.2 N / 15 mm or less, which makes it easy to unwind from a rolled product and tends to prevent the occurrence of wrinkles and streaks in the film. This improves the appearance of the film and tends to make it suitable for re-application or removal and reuse as needed. Methods for controlling the self-adhesion of the film within the above range are not particularly limited, but include, for example, adjusting the density, Mw / Mn, low-temperature crystallization component ratio (S2), and cumulative elution amount at 70°C or below of the polyethylene resin, as well as the film production conditions. One possible method for adjusting the film production conditions is to utilize the effects of adding a low-molecular-weight polyethylene polymer. This addition allows the low-molecular-weight polyethylene to function as a plasticizer, increasing the flexibility of the film and increasing the contact area with the adherend surface, thereby increasing the self-adhesion. Another possible method is to slowly cool a resin extruded at low temperature with a high-temperature cooling roll to promote crystal formation, thereby increasing the crystallinity and reducing the self-adhesion of the film. One possible method is to adjust the conditions appropriately while taking these factors into consideration. In this embodiment, the self-adhesive strength of the film can be measured by the method described in the examples below.

[0053] The film of this embodiment preferably has a tear strength of 1.5 N or more and a payout force of less than 2.0 N / 15 mm. The tear strength of the film of this embodiment is more preferably 2.0 N or more and 5.0 N or less, and even more preferably 2.5 N or more and 5.0 N or less. The film of this embodiment has a tear strength of 1.5 N or more, so that when used, for example, as a protective film, its excellent tear strength makes it resistant to physical stress, reducing the risk of breakage during application or handling and tending to improve work efficiency. Furthermore, the film of this embodiment has a tear strength of 5.0 N or less, so that when, for example, a metal plate or resin plate to which a protective film is attached is cut into a specific shape, the film can be prevented from being forcibly stretched, and tends to be suitable for reducing the risk of the protective film peeling off from the product after cutting. Methods for controlling the tear strength of a film within the above range are not particularly limited, but include, for example, adjusting the density, MFR, and amount of components eluted at Te1 of the polyethylene resin, or adjusting the film production conditions. Adjusting the film production conditions includes, for example, controlling molecular orientation by adjusting the take-up speed, and controlling the crystal structure by adjusting the cooling rate. Increasing the take-up speed to tensilely align the film molecules tends to improve tear strength. On the other hand, rapid cooling of the molten resin tends to result in insufficient crystallization, resulting in a decrease in tear strength. A method for adjusting the conditions appropriately while taking these factors into account is one example. In this embodiment, the tear strength of the film can be measured by the method described in the examples below.

[0054] The unwinding force of the film of this embodiment is more preferably 0.01 N / 15 mm or more and less than 1.8 N / 15 mm, and even more preferably 0.03 N / 15 mm or more and less than 1.6 N / 15 mm. The film of this embodiment has a payout force of less than 2.0 N / 15 mm, allowing the film to be pulled out with a low payout force, which tends to effectively prevent wrinkles and streaks that can occur when excessive force is applied. It also tends to effectively reduce the burden on the operator and the machine, as well as energy loss. Furthermore, the film of this embodiment has a payout force of 0.01 N / 15 mm or more, which applies an appropriate tension to the film due to the high payout force, and as a result, tends to effectively prevent sagging and wrinkles. Furthermore, when the film is used as a protective film, for example, if defects such as wrinkles or air bubbles are found after application to an object such as a metal plate or a resin plate, the film may be rewound. In this case, maintaining an appropriate tension prevents the film from slipping on the roll and allows for uniform rewinding, which tends to make the film suitable for reapplication. Methods for controlling the film unwinding force within the above range include, but are not limited to, adjusting the density, Mw / Mn, and crystallization peak temperature difference (Tc1-Tc2) of the polyethylene resin used as the raw material, as well as the film production conditions. Specifically, for example, when the Mw / Mn of the polyethylene resin is high, unevenness on the film surface due to the die swell phenomenon is likely to occur, resulting in a decrease in the adhesion area between the film surfaces and a decrease in the unwinding force. Furthermore, since low density tends to decrease the degree of crystallinity, a method can be considered that improves adhesion and increases the unwinding force. Adjusting the film production conditions, for example, involves rapidly cooling the resin extruded at high temperature with a low-temperature cooling roll to suppress crystal growth and increase the adhesion of the film, thereby increasing the unwinding force. Another possible method is to create physical unevenness on the film surface by adding an antiblocking agent or embossing, thereby reducing the adhesion area between the film surfaces and thereby decreasing the unwinding force. In this embodiment, the film unwinding force can be measured by the method described in the examples below.

[0055] The film of the present embodiment may have two or more layers, and may have a laminate structure having other layers in addition to the layer made of the polyethylene resin. The method for producing such a laminate film is not particularly limited, but examples thereof include a method of producing the film by laminating layers together using a lamination process, and a method of producing the film by a lamination extrusion process.

[0056] [Seat] The sheet of this embodiment contains the polyethylene resin described above. The method for producing the sheet is not particularly limited, but examples thereof include T-die molding, inflation molding, calendar molding, and skiff molding. T-die molding or extrusion inflation molding is particularly preferred.

[0057] The sheet of this embodiment can be suitably used for various purposes, including, but not limited to, a desk mat guard, a mudguard cover, and the like.

[0058] In this embodiment, the term "sheet" refers to a thin plastic plate having a thickness of 250 μm or more. The thickness of the sheet in this embodiment is preferably 250 μm or more, more preferably 300 μm to 10 mm, and even more preferably 0.5 to 10 mm.

[0059] The sheet of this embodiment preferably has a thickness of 250 μm or more and 10 mm or less, and a payout force of less than 2.0 N / 15 mm. In this embodiment, the sheet feeding force is more preferably 0.01 N / 15 mm or more and less than 1.8 N / 15 mm, and even more preferably 0.03 N / 15 mm or more and less than 1.6 N / 15 mm. The sheet of this embodiment has a payout force of less than 2.0 N / 15 mm, allowing the sheet to be pulled out with a low payout force, which tends to effectively prevent streaks and scratches that can occur when excessive force is applied. It also tends to effectively reduce the burden on the operator and the machine, as well as energy loss. Furthermore, the sheet of this embodiment has a payout force of 0.01 N / 15 mm or more, which applies an appropriate tension to the sheet due to the high payout force, and as a result, tends to effectively prevent the sheet from warping or wrinkling. Furthermore, when used as a protective sheet, for example, if defects such as wrinkles or air bubbles are found after application to an object such as a metal plate or a resin plate, the sheet may be rewound. In this case, maintaining an appropriate tension prevents the sheet from slipping on the roll and allows for uniform rewinding, which tends to make the sheet suitable for reapplication. The method for controlling the sheet feeding force within the above range is not particularly limited, but for example, These include adjusting the density, Mw / Mn, and crystallization peak temperature difference (Tc1-Tc2) of the polyethylene resin used as the raw material, as well as the sheet production conditions. For example, when the Mw / Mn of the polyethylene resin is high, unevenness on the sheet surface due to die swelling tends to occur, resulting in a reduced adhesive area between the sheet surfaces and a decreased payout force. Furthermore, because low density tends to lower the degree of crystallinity, a conceivable method is to improve adhesive strength and increase payout force. For example, adjusting the sheet production conditions involves rapidly cooling the resin extruded at high temperature with a low-temperature cooling roll, which suppresses crystal growth and increases the adhesive strength of the sheet, thereby increasing payout force. Another conceivable method is to create physical unevenness on the film surface by adding an antiblocking agent or embossing, thereby reducing the adhesive area between the sheet surfaces and thereby decreasing payout force. In this embodiment, the sheet feeding force can be measured by the method described in the examples below.

[0060] [Foam-molded products] The foam-molded article of this embodiment contains the polyethylene resin described above. The foam-molded article of this embodiment can be obtained using foamed microparticles or the like, and is suitable for various uses, including, but not limited to, cushioning materials for electronic devices and in-vehicle parts. From the viewpoint of ease of recycling, which is required in response to environmental issues, the film, sheet, and foam molded product of this embodiment is preferably made of only polyethylene resin. Note that, in this embodiment, "only polyethylene resin" means that the resin is a single material, and does not preclude the inclusion of additives described below.

[0061] [Method for producing polyethylene resin] The polyethylene resin of the present embodiment is not particularly limited, but can be obtained, for example, by polymerizing ethylene under pressure and heat in the presence of a peroxide as a polymerization initiator. A chain transfer agent may be added to the polymerization system as necessary.

[0062] The peroxide used in the polymerization is not limited to the following, but examples thereof include methyl ethyl ketone peroxide, peroxyketals (specifically, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, 2,2-bis(t-butylperoxy)octane, n-butyl 4,4-bis(t-butylperoxy)valerate, 2,2-bis(t-butylperoxy)butane, etc.), hydroperoxides (specifically, t-butyl hydroperoxide, cumene hydroperoxide, etc.), -oxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, etc.), dialkyl peroxides (specifically, di-t-butyl peroxide, dicumyl peroxide, bis(t-butylperoxyisopropyl)benzene, t-butylcumyl peroxide, 2,5-dimethyl, 2,5-di(t-butylperoxy)hexane, 2,5-dimethyldi(t-butylperoxy)hexane-3, etc.), diacyl peroxides (specifically, , acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, benzoyl peroxide, etc.), peroxydicarbonates (specifically, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxycarbonate, di-n-propyl peroxydicarbonate, di-2-ethoxyethyl peroxycarbonate, dimethoxyisopropyl peroxydicarbonate, dimethoxyisopropyl peroxydicarbonate, di(3-methyl-3 -methoxybutyl peroxydicarbonate, diallyl peroxydicarbonate, etc.), peroxyesters (specifically, t-butyl peroxyacetate, t-butylperoxy-2-ethylhexyl monocarbonate, t-butylperoxyisobutyrate, t-butylperoxypivalate, t-butylperoxyoctate, t-butylperoxyneodecanoate, t-butylperoxyneodecanoate, cumylperoxyneodecanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxy-3,5,6-trimethylhexanoate, t-butyl peroxylaurate, t-butyl peroxybenzoate, t-butyl peroxyisopropyl carbonate, cumyl peroxyoctoate, t-hexyl peroxyneodecanoate, t-hexyl peroxypivalate, t-butyl peroxyneohexanoate, t-hexyl peroxyneohexanoate, cumyl peroxyneohexanoate, etc.), acetylcyclohexylsulfonyl peroxide, t-butyl peroxyallyl carbonate, etc.

[0063] The chain transfer agent is not particularly limited, but examples thereof include alcohols such as methanol, ethanol, normal propyl alcohol, isopropyl alcohol, normal butyl alcohol, and isobutyl alcohol; alkanes or alkenes such as ethane, propane, propylene, butane, 1-butene, and 2-butene; and ketones or aldehydes such as acetone, methyl ethyl ketone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, diisobutyl ketone, methyl isopropyl ketone, formaldehyde, acetaldehyde, normal butyraldehyde, isobutyraldehyde, normal valeraldehyde, and isovaleraldehyde.

[0064] The polyethylene resin of the present embodiment is preferably a high-pressure low-density polyethylene, specifically, for example, a product of high-pressure free radical polymerization under a supercritical condition. High-pressure free radical polymerization is a polymerization method that is opposed to medium- or low-pressure catalytic polymerization.

[0065] The polymerization reactor for the polyethylene resin is not particularly limited, and examples thereof include an autoclave and a tubular reactor. Among these, it is preferable to use an agitation-type autoclave reactor. By using an agitation-type autoclave reactor, the polymer phase having grown polyethylene chains is agitated, thereby increasing the frequency of contact with the monomer phase having a larger number of radicals, broadening the residence time distribution, and promoting the formation of long chain branches.

[0066] In the stirred autoclave reactor, the rotation speed of the stirring blade is preferably 1,000 rpm or more, more preferably 1,200 rpm or more, and even more preferably 1,400 rpm. By setting the rotation speed of the stirring blade to 1,000 rpm or more, the uniformity of the polymerization can be improved, and it becomes easier to adjust S2 / S1, Tc1-Tc2, the temperature (Te1) at which the elution amount is largest, and the elution amount of the component eluted at Te1 within the above ranges.

[0067] FIG. 1 shows a schematic diagram of an example of a polyethylene resin production apparatus according to this embodiment.

[0068] In FIG. 1, ethylene 1 is supplied from T1 and polymerization initiator 1 is supplied from T2 to Top zone 1. Ethylene 2 is supplied from T3 and polymerization initiator 2 is supplied from T4 to Middle zone 2. Polymerization initiator 3 is supplied from T5 to Bottom zone 3.

[0069] The ethylene and polymerization initiator fed to the reactor may be in the form of a gas or a liquid.

[0070] The polymerization initiator to be supplied to the reactor is not particularly limited, but may be diluted with a solvent such as Shellsol.

[0071] The concentration of the diluted polymerization initiator supplied to Top zone 1 and Middle zone 2 is preferably 3% by mass or more and 20% by mass or less, more preferably 4% by mass or more and 15% by mass or less, and even more preferably 5% by mass or more and 10% by mass or less. By setting the concentration of the diluted polymerization initiator supplied to Top zone 1 and Middle zone 2 within the above range, it becomes easier to suppress the introduction of local branches due to local polymerization reactions, and it becomes easier to adjust S2 / S1 and Tc1-Tc2 within the above ranges.

[0072] The concentration of the diluted polymerization initiator supplied to the bottom zone 3 is preferably 5% by mass or more and 25% by mass or less, more preferably 7% by mass or more and 20% by mass or less, and even more preferably 10% by mass or more and 15% by mass or less. By setting the concentration of the diluted polymerization initiator supplied to the bottom zone 3 within the above range, local branching can be easily introduced by a local polymerization reaction in the bottom zone 3, which is the final stage of the reactor, and S2 / S1 and Tc1-Tc2 can be easily adjusted within the above ranges.

[0073] The average polymerization pressure is preferably 170 MPa or more and 230 MPa or less, more preferably 180 MPa or more and 220 MPa or less, and even more preferably 190 MPa or more and 210 MPa or less. When the average polymerization pressure is 230 MPa or less, short-chain branches are easily formed in the molecular chain, and the amount of tertiary carbon is easily adjusted. By setting the average polymerization pressure within the above range, it is easy to adjust Mw / Mn, S2 / S1, Tc1-Tc2, the temperature (Te1) at which the elution amount is large, the elution amount of the component eluted at Te1, and the cumulative elution amount at 70°C or less within the above ranges.

[0074] The maximum polymerization temperature is preferably 200°C or higher and 270°C or lower, more preferably 210°C or higher and 260°C or lower, and even more preferably 220°C or higher and 250°C or lower. A maximum polymerization temperature of 200°C or higher promotes decomposition of molecular chains and actively converts them into radicals. By setting the maximum polymerization temperature within the above range, it becomes easier to adjust Mw / Mn, S2 / S1, Tc1-Tc2, the temperature (Te1) at which the elution amount is greatest, the elution amount of the component eluted at Te1, and the cumulative elution amount at 70°C or lower within the above ranges.

[0075] Furthermore, in the polymerization step, the temperature difference between Top zone 1 and Bottom zone 3 is preferably 15° C. or more and 55° C. or less, more preferably 20° C. or more and 47° C. or less, and even more preferably 25° C. or more and 35° C. or less. By keeping the temperature difference between Top zone 1 and Bottom zone 3 within the above range, it becomes easier to adjust the molecular chain length, and it becomes easier to adjust Mw / Mn, S2 / S1, and Tc1-Tc2 within the above ranges.

[0076] The polyethylene resin polymerized as described above may be cooled in a double-pipe heat exchanger when being sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet is preferably 25°C or more and 55°C or less, more preferably 30°C or more and 50°C or less, and even more preferably 35°C or more and 45°C or less. When the temperature difference between the reactor outlet and the high-pressure separator inlet is within the above range, it becomes easy to adjust the amount of vinyl groups produced by molecular chain decomposition, and it becomes easy to adjust S2 / S1, Tc1-Tc2, the temperature (Te1) at which the elution amount is greatest, the elution amount of the component eluted at Te1, and the cumulative elution amount at 70°C or less within the above ranges.

[0077] The polyethylene resin polymerized as described above is decomposed into polyethylene resin and gas in a high-pressure separator.

[0078] The pressure inside the high-pressure separator is preferably 28 MPa or less, more preferably 26 MPa or less, and even more preferably 24 MPa or less. Generally, the pressure is adjusted to a high pressure in order to efficiently separate the polyethylene resin and the gas, but by setting the pressure inside the high-pressure separator to 28 MPa or less, post-polymerization can be carried out at a low pressure inside the high-pressure separator, making it easier to introduce short-chain branches and double bonds, and it also makes it easier to adjust S2 / S1, Tc1-Tc2, the temperature (Te1) at which the elution amount is greatest, the elution amount of the component eluted at Te1, and the cumulative elution amount at 70°C or less within the above-mentioned ranges.

[0079] Subsequently, the polyethylene resin separated in the high-pressure separator is introduced into a low-pressure separator, where it is further separated into polyethylene resin and gas.

[0080] The polyethylene resin obtained by the polymerization as described above and separation from the raw materials may be granulated into pellets in an extruder, or may be in the form of powder.

[0081] [Additives] If necessary, additives such as slip agents, antioxidants, light stabilizers, antiblocking agents, and antistatic agents may be added to the polyethylene resin of this embodiment to form a resin composition.

[0082] The slip agent is not particularly limited, but examples thereof include aliphatic hydrocarbons, fatty acid esters of alcohols, waxes, higher fatty acid amides, silicone oils, rosins, etc. The content of the slip agent in the resin composition is not particularly limited, but is 2000 ppm or less, preferably 1000 ppm or less, and more preferably 500 ppm or less, and from the viewpoint of reducing self-adhesive strength and contaminating the adherend due to bleed-out of additives, it is preferably substantially 0 mass % (no additives).

[0083] The antioxidant is not particularly limited, but examples thereof include phenolic antioxidants such as 2,6-di-t-butyl-4-methylphenol (dibutylhydroxytoluene), n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate, and tetrakis(methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate))methane; tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylene- Examples of antioxidants include phosphorus-based antioxidants such as diphosphonite, tris(2,4-di-t-butylphenyl)phosphite, and cyclic neopentanetetraylbis(2,4-t-butylphenylphosphite), and phenol-phosphorus-based antioxidants such as 6-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosphepine. The content of antioxidant in the resin composition is not particularly limited, but is 2000 ppm or less, preferably 1000 ppm or less, and more preferably 500 ppm or less. From the viewpoint of reducing self-adhesive strength and contaminating the adherend due to bleed-out of additives, it is preferable that the content be substantially 0% by mass (no additives).

[0084] The light resistance stabilizer is not particularly limited, but specific examples include benzotriazole-based light resistance stabilizers such as 2-(5-methyl-2-hydroxyphenyl)benzotriazole and 2-(3-t-butyl-5-methyl-2-hydroxyphenyl)-5-chlorobenzotriazole; and hindered amine-based light resistance stabilizers such as bis(2,2,6,6-tetramethyl-4-piperidine) sebacate and poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}]. The content of the light resistance stabilizer in the resin composition is not particularly limited, but is 2000 ppm or less, preferably 1000 ppm or less, and more preferably 500 ppm or less, and from the viewpoint of reducing self-adhesive strength and contaminating the adherend due to bleed-out of the additive, it is preferable that the content be substantially 0 mass % (no additives).

[0085] The antiblocking agent is not particularly limited, but examples thereof include aluminosilicate, kaolin, natural silica, synthetic silica, talc, diatomaceous earth, etc. The content of the antiblocking agent in the resin composition is not particularly limited, but is 2000 ppm or less, preferably 1000 ppm or less, and more preferably 500 ppm or less, and from the viewpoint of self-adhesive strength, it is preferably substantially 0 mass % (no addition).

[0086] The antistatic agent is not particularly limited, but examples thereof include nonionic surfactants, ionic surfactants, amphoteric surfactants, mixtures thereof, etc. The content of the antistatic agent in the resin composition is not particularly limited, but is 2000 ppm or less, preferably 1000 ppm or less, and more preferably 500 ppm or less, and from the viewpoint of reducing self-adhesive strength and contaminating the adherend due to bleed-out of the additive, it is preferably substantially 0 mass % (no additives).

[0087] The content of additives in the resin composition is not particularly limited as long as it does not impair the effects of the present invention, but from the viewpoint of self-adhesion and contamination of adherends, it is preferably substantially 0% by mass (no additives). Note that the term "substantially" here means that additives may be contained in cases where trace amounts of additives are unavoidably mixed in during the production of polyethylene resin, or where trace amounts of catalysts, reaction initiators, etc. remain.

[0088] The polyethylene resin of the present embodiment may be dry-blended or melt-blended with one or more thermoplastic resins such as other high-pressure low-density polyethylenes, linear low-density polyethylenes obtained by polymerization using a Ziegler catalyst or a metallocene catalyst, high-density polyethylenes obtained by polymerization using a Ziegler catalyst or a metallocene catalyst, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, ethylene-methyl acrylate copolymers, ethylene-methyl acrylate copolymers, ethylene-ethyl acrylate copolymers, polypropylene, polybutene-1, polyethylene terephthalate, and polyamide.

[0089] The polyethylene resin of this embodiment may be made from ethylene produced from, for example, biomass-derived naphtha or biomass-derived ethanol. For example, the biomass-derived ultra-high molecular weight polyethylene powder can be produced by a cracking method using biomass-derived naphtha as a raw material. Use of such a polyethylene resin further reduces the burden on the environment. [Example]

[0090] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0091] First, the measurement methods used in each example and comparative example will be described in detail below.

[0092] <Measurement method> [Melt flow rate (MFR) measurement at 190°C and a load of 2.16 kg] The melt flow rate of each polyethylene resin obtained in the examples and comparative examples was measured according to JIS K7210 code D:1999 (temperature = 190°C, load = 2.16 kg).

[0093] [Density measurement] The density of each polyethylene resin obtained in the examples and comparative examples was measured by the density gradient tube method (23°C) according to JIS K7112:1999.

[0094] [Measurement of molecular weight distribution (Mw / Mn)] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of each polyethylene resin obtained in the Examples and Comparative Examples were determined by gel permeation chromatography (hereinafter also referred to as "GPC"). The ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) determined from the GPC measurement was defined as the molecular weight distribution. Molecular weight calibration was performed using 12 standard polystyrene MWs (molecular weights) manufactured by Tosoh Corporation ranging from 1,050 to 20,600,000. The MW of each standard polystyrene was multiplied by a coefficient of 0.43 to obtain the polyethylene-equivalent molecular weight. A primary calibration line was created by plotting the elution time against the polyethylene-equivalent molecular weight, and the weight-average molecular weight (Mw) and number-average molecular weight (Mn) were determined. GPC measurement was performed under the measurement conditions shown below. (Measurement conditions) Equipment: Polymer Char GPC-IR Detector: Polymer Char IR5 Column: TSKgel GMH manufactured by Tosoh Corporation HR -H(30)HT2 (1 tube) and TSKgel GMH (Tosoh Corporation) HR -H(S)HT2 (2 pieces) used in series Mobile phase: orthodichlorobenzene Column temperature: 140℃ Flow rate: 1.0mL / min Sample concentration: 16mg / 8mL Sample dissolution temperature: 140℃ Sample dissolution time: 60 minutes

[0095] [Fast scanning calorimetry measurements] Each of the polyethylene resins obtained in the examples and comparative examples was measured using an ultra-high speed differential scanning calorimeter under the measurement conditions shown below. (Measurement conditions) Equipment: Mettler-Toledo Flash DSC1 Chip sensor: MultiSTAR UFS1 sensor Sample area: approximately 150 μm x 150 μm Sample thickness: 25 to 50 μm Atmosphere: Nitrogen 20mL / min Temperature Program: Figure 4 shows the temperature program for the measurements. The sample was heated from -30°C (Tmin) to 150°C (Tmelt) at 100°C / s, then heated from 150°C (Tmelt) to 175°C (Te1) at 10,000°C / s, and held for 0.5 s (Δt) for high-temperature exposure. The sample was then cooled to 150°C (Tmelt) at a rate of 4,000°C / s, then cooled from 150°C (Tmelt) to -30°C (Tmin) at 100°C / s. After a 0.5 s hold, the sample was again heated to 150°C (Tmelt) at 100°C / s, then heated to 177.5°C (Te2) at a rate of 10,000°C / s, and held for 0.5 s (Δt) for high-temperature exposure. The temperature increase step width (ΔT) was 2.5°C. The temperature was then lowered again to 150°C (Tmelt) at 4000°C / s, and then from 150°C (Tmelt) to -30°C (Tmin) at 100°C / s. This procedure was repeated until the exposure temperature reached 400°C (Ten). Figure 5 shows the crystallization peaks observed in the cooling heat flow when the temperature was lowered from 150°C (Tmelt) to -30°C (Tmin) at 100°C / s after high-temperature exposure. Tc1 (peak top of the high-temperature crystallization component [°C]) and Tc2 (peak top of the low-temperature crystallization component [°C]) were determined from the crystallization peaks after exposure to 400°C using the following method. The negative peak top temperatures obtained by second-order differentiation of the cooling heat flow were designated Tc1 (the higher peak top temperature) and Tc2 (the lower peak top temperature) (see Figure 2). Tc1 - Tc2 was calculated from the obtained values. S1 (ratio of high-temperature crystallization components [%]) and S2 (ratio of low-temperature crystallization components [%]) were determined from the crystallization peak after exposure to 400°C using the following method. The baseline was defined as a sigmoid curve between the start and end points of the peak, and the division temperature was defined as the positive peak top temperature of the second derivative of the cooling heat flow (see Figure 2). Of the peak areas obtained, the peak area ratio of the components crystallized at high temperatures was defined as S1, and the peak area ratio of the components crystallized at low temperatures was defined as S2 (see Figure 3). S2 / S1 was also calculated from the obtained values.

[0096] [Cross-fractionation chromatography (CFC) measurement] CFC measurements were carried out for each polyethylene resin obtained in the Examples and Comparative Examples using an Automated 3D analyzer CFC-2 manufactured by Polymer ChAR. A stainless steel microball column (outer diameter 3 / 8 inch x length 150 mm) was used as the TREF column, and a GPC column manufactured by Shodex was used. A total of three columns were used, one UT-807 and two Toso GMHHRH(S)HT, and o-dichlorobenzene (for high performance liquid chromatography) was used as the eluent at a flow rate of 1.0 mL / min. The column containing the packing material was heated to 140°C, and 20 mL of a sample solution (sample concentration: 1.0 g / mL) prepared by dissolving each polyethylene resin obtained in Examples and Comparative Examples in o-dichlorobenzene was introduced and maintained for 120 minutes. Next, the column temperature was lowered to 40°C at a rate of 0.5°C / min and maintained for 20 minutes. During this process, the sample precipitated on the surface of the packing material. The column temperature was then adjusted as follows: first, the column was heated to 40°C and maintained at 40°C. Then, the column was heated to 50°C and maintained at 50°C. The sample was heated to 60°C and held at 60°C. The temperature was then increased from 60°C to 69°C in 3°C intervals. The temperature was then increased from 69°C to 100°C in 1°C intervals. The temperature was then increased from 100°C to 110°C and held at 110°C. The temperature was increased at a rate of 20°C / min and held at each temperature for 21 minutes. The concentration (mass%) of the sample eluted during the 21-minute hold at each temperature was measured, and an elution temperature-elution volume curve was obtained from the hold temperature and elution sample concentration. From the elution temperature-elution volume curve obtained by temperature-rising elution fractionation (TREF) as described above, the temperature (Te1) (°C) with the highest elution volume, the percentage (mass%) of the eluted component at Te1, and the percentage (mass%) of the cumulative eluted component eluting at 70°C or below were calculated.

[0097] Next, the evaluation methods for each of the examples and comparative examples will be described in detail below. <Evaluation method> [Film Preparation] Each polyethylene resin obtained in the examples and comparative examples was molded into a film using a T-die film-forming machine (HM40N manufactured by Hokushin Sangyo Co., Ltd., screw diameter 40 mm, die width 300 mm, plain woven wire mesh of 80 mesh) according to the film-forming conditions shown below. (Film forming conditions) Cylinder temperature: 260℃ Die temperature: 260℃ Extrusion rate: 5 kg / hour Film thickness: 30 μm T-die cooling roll: 215mmφ×350mm 2 rolls T-die cooling roll temperature controller: Yamato Scientific CFW610 T-die cooling roll cooling water temperature: 10℃

[0098] 〔rigidity〕 The thickness of the film was measured using a constant pressure thickness gauge (manufactured by TECLOK CORPORATION, model PG-02, minimum display 0.001 mm), and a portion with a thickness of 30 μm or less ±5% was selected and cut into a strip 100 mm long and 13 mm wide in the resin flow direction to prepare a test piece. Young's modulus was measured under the following conditions. (Measurement conditions) Device: Orientec TENSIRON (RTC-1310A) Pulling speed: 10 mm / min Measurement temperature: 25℃ Chuck distance: 50mm The Young's modulus was calculated using the following formula 1. In formula 1, F is the stress (N) applied when the chuck distance is increased from 50 mm to 51 mm and the specimen is pulled by 1 mm. Young's modulus (MPa) = F (N) / (((51 mm - 50 mm) / 50 mm) × thickness of specimen (mm) × width of specimen (mm)) Equation 1 The rigidity was evaluated according to the following criteria: Excellent, Good, and Fair were considered acceptable, and Bad was considered unacceptable. (Evaluation criteria) ◎ (Excellent): Young's modulus 200 MPa or more Good: Young's modulus is 170 MPa or more and less than 200 MPa △ (Acceptable): Young's modulus is 130 MPa or more and less than 170 MPa × (Not acceptable): Young's modulus less than 130 MPa

[0099] [Self-adhesive strength] The thickness of the film was measured using a constant-pressure thickness gauge (TECLOK CORPORATION, Model PG-02, minimum display 0.001 mm). A section with a thickness of 30 μm or less ±5% was selected and cut into a 150 mm long, 15 mm wide strip in the resin flow direction to serve as a test specimen. This test specimen was attached to a stainless steel (SUS430) plate (1 mm thick, 50 mm wide, 150 mm long) using a TP-701-C heat seal tester manufactured by Tester Sangyo Co., Ltd., at a sealing surface pressure of 0.3 MPa and a sealing temperature of 40°C. The 180° peel strength was then measured under the following conditions, and the 180° peel strength per 15 mm width was taken as the self-adhesive strength (N / 15 mm). (Measurement conditions) Device: Orientec TENSIRON (RTC-1310A) Tensile speed: 300 mm / min Measurement temperature: 25℃ Chuck distance: 50mm The self-adhesive strength was evaluated according to the following criteria: Excellent, Good, Fair: Pass, and Bad: Fail. (Evaluation criteria) ◎(Excellent): Self-adhesive strength 1.5N / 15mm or more Good: Self-adhesive strength 1.2N / 15mm or more and less than 1.5N / 15mm △(Acceptable): Self-adhesive strength 0.9N / 15mm or more but less than 1.2N / 15mm × (Not possible): Self-adhesive strength less than 0.9N / 15mm When measuring a commercially available product (film or sheet), the measurement is carried out as described above, except that the test piece is cut into a strip of 150 mm in length and 15 mm in width.

[0100] [Payout ability] The thickness of the film was measured using a constant-pressure thickness gauge (TECLOK CORPORATION, Model PG-02, minimum display 0.001 mm). A portion with a thickness of 30 μm or less ±5% was selected and cut into two strips 150 mm long and 15 mm wide in the resin flow direction to serve as test specimens. These test specimens were then bonded together using a TP-701-C heat seal tester manufactured by Tester Sangyo Co., Ltd., at a sealing surface pressure of 0.3 MPa and a sealing temperature of 40°C. The 180° peel strength was then measured under the following conditions, and the 180° peel strength per 15 mm width was recorded as the payout force (N / 15 mm). (Measurement conditions) Device: Orientec TENSIRON (RTC-1310A) Tensile speed: 300 mm / min Measurement temperature: 25℃ Chuck distance: 50mm The payout property was evaluated according to the following criteria: Excellent, Good, Fair, was considered acceptable, and Bad was considered unacceptable. (Evaluation criteria) ◎ (Excellent): Feed force less than 1.6N / 15mm Good: Payout force 1.6N / 15mm or more and less than 1.8N / 15mm △ (Acceptable): Payout force 1.8N / 15mm or more and less than 2.0N / 15mm × (Not possible): Payout force 2.0N / 15mm or more When measuring a commercially available product (film or sheet), the measurement is carried out as described above, except that the test piece is cut into a strip of 150 mm in length and 15 mm in width.

[0101] [Tear strength] The thickness of the film was measured using a constant pressure thickness gauge (TECLOK CORPORATION, Model PG-02, minimum display 0.001 mm), and a portion with a thickness of 30 μm or less ±5% was selected and cut using a sharp knife into a test piece with a constant radius as shown in Figure 2 of JIS K7128-2:1998. The test piece was cut so that the minor axis was in the direction of resin flow. The tear test was performed under the following conditions, and the average value of N=5 (number of measurements: 5) was taken as the tear strength (N). (Measurement conditions) Equipment: JamesHeal ElmaTear digital tear tester Standard setting: JIS K7128‐2:1998 Additional weight: Use a pendulum weight that keeps the TearForce range between 20% and 80% Test piece stacking: None (1 piece) The tear strength was evaluated according to the following criteria: Excellent, Good, and Fair were considered acceptable, and Bad was considered unacceptable. (Evaluation criteria) ◎(Excellent): Tear strength 2.5N or more ○ (Good): Tear strength 2.0N or more and less than 2.5N △ (Acceptable): Tear strength 1.5N or more and less than 2.0N × (Not acceptable): Tear strength less than 1.5N When measuring a commercially available product (film or sheet), a portion of the commercially available product with a thickness of 30 μm ±5% or less is selected and cut out with a sharp knife into a shape with a constant radius as shown in Figure 2 of JIS K7128-2:1998 to form a test piece, but the measurement is carried out as described above. When measuring a commercially available product (film or sheet) with a thickness of 30 μm +5% or more, a portion with a thickness of 30 μm to 50 μm is selected, or cut to that thickness, and measured as described above, except that a test piece is cut using a sharp knife into a shape with a constant radius as shown in Figure 2 of JIS K7128-2:1998. When measuring a commercially available product (film or sheet) with a thickness of less than -5% of 30 μm, the commercially available product is stacked to a thickness of 30 μm ± 20 μm, and measured as described above, except that a test piece is cut using a sharp knife into a shape with a constant radius as shown in Figure 2 of JIS K7128-2:1998. For measurements of commercially available products, two test pieces are prepared, each is measured, and the larger value is used as the measurement result. The test piece is cut from the commercially available product while rotated 90 degrees from the first test piece, and this is used as the second test piece.

[0102] [Transparency] The thickness of the film was measured using a constant pressure thickness gauge (TECLOK CORPORATION, Model PG-02, minimum display 0.001 mm). A portion of the film with a thickness of 30 μm or less ±5% was selected and cut into a strip 70 mm long and 500 mm wide in the resin flow direction to serve as a test piece. The haze (%) was measured in accordance with ASTM D1003 using a Haze Meter HM-150 manufactured by Murakami Color Research Laboratory Co., Ltd. The lower the haze, the better the transparency. The transparency was evaluated according to the following criteria: ⊚, ◯, △ were considered acceptable, and × was considered unacceptable. (Evaluation criteria) ◎ (Excellent): Haze less than 2.0% Good: Haze 2.0% or more and less than 3.5% △ (Acceptable): Haze 3.5% or more and less than 5.0% × (unacceptable): Haze 5.0% or more

[0103] Next, the preparation methods of each example and comparative example will be explained in detail below. [Example 1] A polymerization initiator diluted to 9% by mass was supplied to a stirred autoclave reactor fed with ethylene. The polymerization initiator was supplied to Top Zone 1 and Middle Zone 2, and to Bottom Zone 3, where it was diluted to 12% by mass. The polymerization temperature was 205°C in Top Zone 1 and 233°C in Bottom Zone 3. The temperature difference between Top Zone 1 and Bottom Zone 3 was 28°C, the maximum polymerization temperature was 233°C, the average polymerization pressure was 201 MPa, and the stirring blade rotation speed was 1,400 rpm. The polymerized polyethylene resin was cooled in a double-pipe heat exchanger before being sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 40°C. The polyethylene resin separated in the 26 MPa high-pressure separator was introduced into the low-pressure separator, where it was further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 1.

[0104] [Example 2] A polymerization initiator diluted to 6% by mass was supplied to a stirred autoclave reactor fed with ethylene. The polymerization initiator was supplied to Top Zone 1 and Middle Zone 2, and to Bottom Zone 3, where it was diluted to 16% by mass. The polymerization temperature was 239°C in Top Zone 1 and 262°C in Bottom Zone 3. The temperature difference between Top Zone 1 and Bottom Zone 3 was 23°C, the maximum polymerization temperature was 262°C, the average polymerization pressure was 201 MPa, and the stirring blade rotation speed was 1,400 rpm. The polymerized polyethylene resin was cooled in a double-pipe heat exchanger before being sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 42°C. The polyethylene resin separated in the 26 MPa high-pressure separator was introduced into the low-pressure separator, where it was further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 1.

[0105] [Example 3] A polymerization initiator diluted to 6% by mass was supplied to a stirred autoclave reactor fed with ethylene. The polymerization initiator was supplied to Top Zone 1 and Middle Zone 2, and to Bottom Zone 3, where it was diluted to 24% by mass. The polymerization temperature was 250°C in Top Zone 1 and 262°C in Bottom Zone 3. The temperature difference between Top Zone 1 and Bottom Zone 3 was 12°C, the maximum polymerization temperature was 262°C, the average polymerization pressure was 201 MPa, and the stirring blade rotation speed was 1,400 rpm. The polymerized polyethylene resin was cooled in a double-pipe heat exchanger before being sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 56°C. The polyethylene resin separated in the 24 MPa high-pressure separator was introduced into the low-pressure separator, where it was further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 1.

[0106] [Example 4] A polymerization initiator diluted to 19% by mass was supplied to a stirred autoclave reactor fed with ethylene. The polymerization initiator was supplied to Top Zone 1 and Middle Zone 2, and to Bottom Zone 3, where it was diluted to 30% by mass. The polymerization temperature was 210°C in Top Zone 1 and 265°C in Bottom Zone 3. The temperature difference between Top Zone 1 and Bottom Zone 3 was 55°C, the maximum polymerization temperature was 265°C, the average polymerization pressure was 175 MPa, and the stirring blade rotation speed was 1,000 rpm. The polymerized polyethylene resin was cooled in a double-pipe heat exchanger before being sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 37°C. The polyethylene resin separated in the 24 MPa high-pressure separator was introduced into the low-pressure separator, where it was further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 1.

[0107] [Example 5] A polymerization initiator diluted to 7% by mass was fed into a stirred autoclave reactor supplied with ethylene. The polymerization initiator was fed into Top Zone 1 and Middle Zone 2. No polymerization initiator was fed into Bottom Zone 3. The polymerization temperature in Top Zone 1 was 227°C, and the polymerization temperature in Bottom Zone 3 was 256°C. The temperature difference between Top Zone 1 and Bottom Zone 3 was 29°C, the maximum polymerization temperature was 256°C, the average polymerization pressure was 182 MPa, and the stirring blade rotation speed was 1,200 rpm. The polymerized polyethylene resin was cooled in a double-pipe heat exchanger before being sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 25°C. The polyethylene resin separated in the 28 MPa high-pressure separator was introduced into the low-pressure separator and further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 1.

[0108] [Example 6] A polymerization initiator diluted to 14% by mass was supplied to a stirred autoclave reactor fed with ethylene. The polymerization initiator was supplied to Top Zone 1 and Middle Zone 2, and to Bottom Zone 3, where it was diluted to 20% by mass. The polymerization temperature was 190°C in Top Zone 1 and 215°C in Bottom Zone 3. The temperature difference between Top Zone 1 and Bottom Zone 3 was 25°C, the maximum polymerization temperature was 215°C, the average polymerization pressure was 190 MPa, and the stirring blade rotation speed was 1,400 rpm. The polymerized polyethylene resin was cooled in a double-pipe heat exchanger before being sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 39°C. The polyethylene resin separated in the 24 MPa high-pressure separator was introduced into the low-pressure separator, where it was further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 1.

[0109] [Example 7] A polymerization initiator diluted to 14% by mass was supplied to a stirred autoclave reactor fed with ethylene. The polymerization initiator was supplied to Top Zone 1 and Middle Zone 2, and to Bottom Zone 3, where it was diluted to 11% by mass. The polymerization temperature was 184°C in Top Zone 1 and 230°C in Bottom Zone 3. The temperature difference between Top Zone 1 and Bottom Zone 3 was 46°C, the maximum polymerization temperature was 230°C, the average polymerization pressure was 190 MPa, and the stirring blade rotation speed was 1,400 rpm. The polymerized polyethylene resin was cooled in a double-pipe heat exchanger before being sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 42°C. The polyethylene resin separated in the 28 MPa high-pressure separator was introduced into the low-pressure separator, where it was further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 1.

[0110] [Example 8] A polymerization initiator diluted to 13% by mass was supplied to a stirred autoclave reactor fed with ethylene. The polymerization initiator was supplied to Top Zone 1 and Middle Zone 2, and to Bottom Zone 3, where it was diluted to 18% by mass. The polymerization temperature was 183°C in Top Zone 1 and 231°C in Bottom Zone 3. The temperature difference between Top Zone 1 and Bottom Zone 3 was 48°C, the maximum polymerization temperature was 231°C, the average polymerization pressure was 191 MPa, and the stirring blade rotation speed was 1,200 rpm. The polymerized polyethylene resin was cooled in a double-pipe heat exchanger before being sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 41°C. The polyethylene resin separated in the 22 MPa high-pressure separator was introduced into the low-pressure separator, where it was further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 1.

[0111] [Comparative Example 1] A polymerization initiator diluted to 25% by mass was fed to a stirred autoclave reactor supplied with ethylene. The polymerization initiator was supplied to Top Zone 1 and Middle Zone 2, and to Bottom Zone 3, where it was diluted to 30% by mass. The polymerization temperature in Top Zone 1 was 205°C, and the polymerization temperature in Bottom Zone 3 was 210°C. The temperature difference between Top Zone 1 and Bottom Zone 3 was 5°C, the maximum polymerization temperature was 210°C, the average polymerization pressure was 201 MPa, and the stirring blade rotation speed was 800 rpm. The polymerized polyethylene resin was not cooled in a double-pipe heat exchanger when transferred from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 2°C. The polyethylene resin separated in the 30 MPa high-pressure separator was introduced into the low-pressure separator, where it was further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 2.

[0112] Comparative Example 2 A polymerization initiator diluted to 25% by mass was supplied to a stirred autoclave reactor fed with ethylene. The polymerization initiator was supplied to Top Zone 1 and Middle Zone 2, and to Bottom Zone 3, where it was diluted to 20% by mass. The polymerization temperature was 205°C in Top Zone 1 and 210°C in Bottom Zone 3. The temperature difference between Top Zone 1 and Bottom Zone 3 was 5°C, the maximum polymerization temperature was 210°C, the average polymerization pressure was 201 MPa, and the stirring blade rotation speed was 1,200 rpm. The polymerized polyethylene resin was not cooled in a double-pipe heat exchanger when sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 2°C. The polyethylene resin separated in the 30 MPa high-pressure separator was introduced into the low-pressure separator, where it was further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 2.

[0113] Comparative Example 3 A polymerization initiator diluted to 9% by mass was supplied to a stirred autoclave reactor fed with ethylene. The polymerization initiator was supplied to Top Zone 1 and Middle Zone 2, and to Bottom Zone 3, where it was diluted to 30% by mass. The polymerization temperature was 205°C in Top Zone 1 and 210°C in Bottom Zone 3. The temperature difference between Top Zone 1 and Bottom Zone 3 was 5°C, the maximum polymerization temperature was 210°C, the average polymerization pressure was 201 MPa, and the stirring blade rotation speed was 800 rpm. The polymerized polyethylene resin was cooled in a double-pipe heat exchanger before being sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 37°C. The polyethylene resin separated in the 24 MPa high-pressure separator was introduced into the low-pressure separator and further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 2.

[0114] Comparative Example 4 A polymerization initiator diluted to 8% by mass was fed into a stirred autoclave reactor supplied with ethylene in Top Zone 1 and Middle Zone 2. No polymerization initiator was fed into Bottom Zone 3. The polymerization temperature in Top Zone 1 was 254°C, and that in Bottom Zone 3 was 262°C. The temperature difference between Top Zone 1 and Bottom Zone 3 was 8°C, the maximum polymerization temperature was 262°C, the average polymerization pressure was 152 MPa, and the stirring blade rotation speed was 800 rpm. The polymerized polyethylene resin was not cooled in a double-pipe heat exchanger when sent from the reactor outlet to the high-pressure separator, and the temperature difference between the reactor outlet and the high-pressure separator inlet was 2°C. The polyethylene resin separated in the 30 MPa high-pressure separator was introduced into the low-pressure separator and further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 2.

[0115] Comparative Example 5 A polymerization initiator diluted to 25% by mass was fed into a stirred autoclave reactor supplied with ethylene in Top Zone 1 and Middle Zone 2. No polymerization initiator was fed into Bottom Zone 3. The polymerization temperature in Top Zone 1 was 227°C, and the polymerization temperature in Bottom Zone 3 was 256°C. The temperature difference between Top Zone 1 and Bottom Zone 3 was 29°C, the maximum polymerization temperature was 256°C, the average polymerization pressure was 182 MPa, and the stirring blade rotation speed was 800 rpm. The polymerized polyethylene resin was not cooled in a double-pipe heat exchanger when sent from the reactor outlet to the high-pressure separator, and the temperature difference between the reactor outlet and the high-pressure separator inlet was 2°C. The polyethylene resin separated in the 30 MPa high-pressure separator was introduced into the low-pressure separator and further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 2.

[0116] Comparative Example 6 A polymerization initiator diluted to 19% by mass was supplied to a stirred autoclave reactor fed with ethylene. The polymerization initiator was supplied to Top Zone 1 and Middle Zone 2, and to Bottom Zone 3, where it was diluted to 40% by mass. The polymerization temperature was 200°C in Top Zone 1 and 265°C in Bottom Zone 3. The temperature difference between Top Zone 1 and Bottom Zone 3 was 40°C, the maximum polymerization temperature was 265°C, the average polymerization pressure was 175 MPa, and the stirring blade rotation speed was 1,000 rpm. The polymerized polyethylene resin was cooled in a double-pipe heat exchanger before being sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 60°C. The polyethylene resin separated in the 22 MPa high-pressure separator was introduced into the low-pressure separator, where it was further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 2.

[0117] Comparative Example 7 A polymerization initiator diluted to 3% by mass was supplied to a stirred autoclave reactor fed with ethylene. The polymerization temperature in Top Zone 1 was 250°C, the polymerization temperature in Bottom Zone 3 was 262°C, the temperature difference between Top Zone 1 and Bottom Zone 3 was 12°C, the maximum polymerization temperature was 262°C, the average polymerization pressure was 201 MPa, and the stirring blade rotation speed was 1,400 rpm. The polymerized polyethylene resin was cooled in a double-pipe heat exchanger before being sent from the reactor outlet to the high-pressure separator. The temperature difference between the reactor outlet and the high-pressure separator inlet was 60°C. The polyethylene resin separated in the 24 MPa high-pressure separator was introduced into the low-pressure separator and further separated into polyethylene resin and gas. The separated polyethylene resin was pelletized in an extruder. The physical properties and characteristics of the resulting polyethylene resin were measured using the methods described above. The measurement results are shown in Table 2.

[0118] [Table 1]

[0119] [Table 2] [Industrial Applicability]

[0120] The polyethylene resin according to the present invention has industrial applicability as a resin raw material used in a wide range of industrial fields.

Claims

1. A polyethylene resin satisfying the following (A) to (C): (A) Density is 915 kg / m 3 935kg / m or more 3 That is: (B) Mw / Mn (Mn is number average molecular weight, Mw is weight average molecular weight, and Mw / Mn is molecular weight distribution) measured by gel permeation chromatography (hereinafter referred to as GPC) is 3.0 or more and 12.0 or less, (C) S2 / S1 is 0.20 or more and 0.90 or less, and Tc1-Tc2 is 3.0°C or more and 9.0°C or less, as determined by measurement with an ultrafast differential scanning calorimeter (where S1 is the proportion [%] of the high-temperature crystallization component, S2 is the proportion [%] of the low-temperature crystallization component, Tc1 is the peak top [°C] of the high-temperature crystallization component, and Tc2 is the peak top [°C] of the low-temperature crystallization component).

2. 2. The polyethylene resin according to claim 1, which has a melt flow rate measured in accordance with JIS K7210 (190°C, 2.16 kg load) of 0.5 g / 10 min or more and 20.0 g / 10 min or less.

3. 2. The polyethylene resin according to claim 1, wherein, in an elution temperature-elution amount curve obtained by temperature rising elution fractionation (TREF) of cross fractionation chromatography (CFC), the temperature (Te1) at which the elution amount is the largest is above 70°C, and the elution amount of the component eluted at Te1 is 13.0% by mass or more and 23.0% by mass or less.

4. 2. The polyethylene resin according to claim 1, wherein the cumulative elution amount at 70°C or less is 10.0% by mass or more and 50.0% by mass or less in an elution temperature-elution amount curve obtained by temperature rising elution fractionation (TREF) of cross fractionation chromatography (CFC).

5. 2. The polyethylene resin according to claim 1, wherein the polyethylene resin comprises high-pressure low-density polyethylene.

6. A film comprising the polyethylene resin according to any one of claims 1 to 5.

7. The film according to claim 6, having a thickness of 3 to 240 μm and a self-adhesive strength of 0.9 N / 15 mm or more.

8. 8. The film of claim 7, having a tear strength of 1.5 N or greater and an unwinding force of less than 2.0 N / 15 mm.

9. 8. The film according to claim 7, which consists solely of the polyethylene resin.

10. A sheet comprising the polyethylene resin according to any one of claims 1 to 5.

11. The sheet according to claim 10, having a thickness of 250 μm or more and 10 mm or less and a payout force of less than 2.0 N / 15 mm.

12. The sheet according to claim 11, which consists solely of the polyethylene resin.

13. A foam-molded article comprising the polyethylene resin according to any one of claims 1 to 5.

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