Polyethylene resin extruded foam sheet and method for manufacturing the same

Abstract

The present invention provides a method for producing a polyethylene-based resin extruded foam sheet, which has a low apparent density even when linear low-density polyethylene is included, and a polyethylene-based resin extruded foam sheet obtained by this method, which allows for easy production of a good quality extruded foam sheet. [Solution] The method for manufacturing the polyethylene resin extruded foam sheet 1 includes an extrusion foaming step in which a foamable resin molten product, obtained by melt-kneading a polyethylene resin as a base resin and a physical foaming agent, is extruded and foamed. The polyethylene resin includes linear low-density polyethylene. The difference Tcs-Tc between the crystallization start temperature Tcs (unit: °C) and the crystallization temperature Tc (unit: °C) of the linear low-density polyethylene is 8 °C or less. Measurement temperature 150 °C, shear rate 375 s -1 The extensional viscosity λ of linear low-density polyethylene, measured by the Cogswell method under these conditions, is 50,000 Pa·s or higher.

Description

Technical Field

[0001] The present invention relates to a polyethylene-based resin extrusion foamed sheet and a method for producing the same.

Background Art

[0002] Polyethylene-based resin extrusion foamed sheets are highly flexible and excellent in shock absorption, so they are used for applications such as cushioning materials and packaging materials. Conventionally, low-density polyethylene (PE-LD) having a long-chain branched structure has been used for the production of polyethylene-based resin extrusion foamed sheets in consideration of foamability. However, low-density polyethylene is produced by a high-pressure method and is polymerized under high-temperature and high-pressure conditions during production, so there is a problem that the environmental load during production tends to increase. In addition, extrusion foamed sheets made of low-density polyethylene tend to be weak in firmness and there is room for improvement depending on the application.

[0003] Therefore, a method for producing an extrusion foamed sheet using linear low-density polyethylene (PE-LLD), which can be produced under milder conditions, has been studied. For example, Patent Document 1 describes an ethylene-α-olefin copolymer for extrusion foaming molding having a molecular weight distribution of 5 or more and a swell ratio of 1.15 to 1.45.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the physical properties of conventional linear low-density polyethylenes, including the copolymer described in Patent Document 1, are not suitable for the manufacture of extruded foam sheets, making it difficult to produce good extruded foam sheets with a high closed-cell ratio. In particular, when attempting to produce extruded foam sheets with low apparent density, there is a problem that the closed-cell ratio of the extruded foam sheet tends to be low.

[0006] The present invention has been made in view of the above background, and aims to provide a method for producing an extruded foam sheet of polyethylene resin that can easily be obtained, which has a low apparent density and a high closed-cell ratio even when linear low-density polyethylene is included, and a polyethylene resin extruded foam sheet obtained by this method. [Means for solving the problem]

[0007] One aspect of the present invention relates to a method for producing polyethylene resin extruded foam sheets according to the following [1] to [6].

[0008] [1] A foamed resin molten material, obtained by melt-kneading polyethylene resin and a physical foaming agent, is extruded and foamed to produce 10 kg / m³ 3 More than 250kg / m 3 A method for producing a polyethylene resin extruded foam sheet having the following apparent density, comprising an extrusion foaming step for producing a polyethylene resin extruded foam sheet, The polyethylene resin contains linear low-density polyethylene. The difference between the crystallization start temperature Tcs (unit: °C) and the crystallization temperature Tc (unit: °C) of the linear low-density polyethylene, Tcs-Tc, is 8°C or less. Measurement temperature 150°C, shear rate 375s -1 A method for producing a polyethylene resin extruded foam sheet, wherein the extensional viscosity λ of the linear low-density polyethylene measured by the Cogswell method under the specified conditions is 50,000 Pa·s or more.

[0009] [2] Measurement temperature 150°C, shear rate 375 s -1The ratio λ / η of the elongational viscosity λ (unit: Pa·s) of the linear low-density polyethylene to the shear viscosity η (unit: Pa·s) of the linear low-density polyethylene after Bagley correction, measured under the conditions of , being 100 or more, and the method for producing a polyethylene resin extrusion foamed sheet according to [1].

[0010] 〔3〕Measurement temperature 150 °C, shear rate 375 s -1 The ratio λ / η of the elongational viscosity λ (unit: Pa·s) of the linear low-density polyethylene to the shear viscosity η (unit: Pa·s) of the linear low-density polyethylene after Bagley correction, measured under the conditions of , and measurement temperature 150 °C, shear rate 6 s -1 The ratio (λ / η) / (λ' / η') of the ratio λ / η of the elongational viscosity λ (unit: Pa·s) of the linear low-density polyethylene to the shear viscosity η' (unit: Pa·s) of the linear low-density polyethylene after Bagley correction, measured under the conditions of , to the ratio λ' / η' of the elongational viscosity λ' (unit: Pa·s) of the linear low-density polyethylene to the shear viscosity η' (unit: Pa·s) of the linear low-density polyethylene after Bagley correction, measured under the conditions of , being 1.3 or more, and the method for producing a polyethylene resin extrusion foamed sheet according to [1] or [2].

[0011] 〔4〕The crystallization temperature Tc of the linear low-density polyethylene being 105 °C or more, and the method for producing a polyethylene resin extrusion foamed sheet according to any one of [1] to [3]. 〔5〕The density of the linear low-density polyethylene being 920 kg / m 3 or more and 935 kg / m 3 or less, and the method for producing a polyethylene resin extrusion foamed sheet according to any one of [1] to [4]. 〔6〕The average thickness of the extrusion foamed sheet being 0.05 mm or more and 5 mm or less, and the method for producing a polyethylene resin extrusion foamed sheet according to any one of [1] to [5].

[0012] Another aspect of the present invention relates to polyethylene resin extrusion foamed sheets according to the following [7] to

[12] . 〔7〕10 kg / m 3 or more and 250 kg / m 3A polyethylene resin extruded foam sheet having the following apparent density: The closed-cell ratio of the extruded foam sheet is 50% or more. The polyethylene resin constituting the extruded foam sheet contains linear low-density polyethylene. The difference between the crystallization start temperature Tcs (unit: °C) and the crystallization temperature Tc (unit: °C) of the linear low-density polyethylene, Tcs-Tc, is 8°C or less. Measurement temperature 150°C, shear rate 375s -1 A polyethylene resin extruded foam sheet having an extensional viscosity λ of 50,000 Pa·s or more, measured by the Cogswell method under the specified conditions.

[0013] [8] Measurement temperature 150°C, shear rate 375 s -1 The polyethylene resin extruded foam sheet according to [7], wherein the ratio λ / η of the extensional viscosity λ (unit: Pa·s) of the linear low-density polyethylene by the Cogswell method to the Burgray-corrected shear viscosity η (unit: Pa·s) of the linear low-density polyethylene, measured under the following conditions, is 100 or more.

[0014] [9] Measurement temperature 150°C, shear rate 375s -1 The ratio λ / η of the extensional viscosity λ (unit: Pa·s) of the linear low-density polyethylene by the Cogswell method to the Burgray-corrected shear viscosity η (unit: Pa·s) of the linear low-density polyethylene, measured under the following conditions: measurement temperature 150°C, shear rate 6s. -1 A polyethylene resin extruded foam sheet according to [7] or [8], wherein the ratio (λ / η) / (λ' / η') of the extensional viscosity λ' (unit: Pa·s) of the linear low-density polyethylene measured by the Cogswell method to the shear viscosity η' (unit: Pa·s) of the linear low-density polyethylene after Burgray correction, measured under the following conditions, is 1.3 or greater.

[0015]

[10] The polyethylene resin extruded foam sheet according to any one of [7] to [9], wherein the crystallization temperature Tc of the linear low-density polyethylene is 105°C or higher.

[11] The density of the linear low-density polyethylene is 920 kg / m³ 3 More than 935kg / m 3 A polyethylene resin extruded foam sheet as described in any one of the following [7] to

[10] .

[12] The polyethylene resin extruded foam sheet according to any one of [7] to

[11] , wherein the average thickness of the extruded foam sheet is 0.05 mm or more and 5 mm or less. [Effects of the Invention]

[0016] According to the above embodiment, it is possible to easily obtain a good extruded foam sheet made of polyethylene resin, which has a low apparent density and a high closed-cell ratio, even when linear low-density polyethylene is included, and to provide a polyethylene resin extruded foam sheet obtained by this manufacturing method. Furthermore, according to the above embodiment, the stiffness of the extruded foam sheet can be increased. Such an extruded foam sheet can be suitably used for various applications. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 is an explanatory diagram showing the method for measuring the amount of sagging when an extruded foam sheet is fixed in a cantilevered beam configuration in an embodiment. [Modes for carrying out the invention]

[0018] (Method for manufacturing polyethylene resin extruded foam sheets) In the method for manufacturing the polyethylene resin extruded foam sheet (hereinafter referred to as "extruded foam sheet"), the extruded foam sheet having a foam layer is produced by an extrusion foaming method. The extruded foam sheet obtained by the above manufacturing method may have a single-layer structure consisting only of a foam layer. Alternatively, the extruded foam sheet may have a multilayer structure consisting of multiple layers including a foam layer. The method for manufacturing the extruded foam sheet will be described in more detail below.

[0019] [Polyethylene resin] The foamed layer is composed of a polyethylene-based resin as the base resin. That is, the foamed layer contains 50% by mass or more of polyethylene-based resin. The polyethylene-based resin constituting the foamed layer contains linear low-density polyethylene (PE-LLD). The proportion of linear low-density polyethylene in the polyethylene-based resin may be, for example, 30% by mass or more.

[0020] From the viewpoint of further improving the mechanical properties of the extruded foam sheet, it is preferable that the polyethylene resin constituting the foam layer contains linear low-density polyethylene as its main component. More specifically, the proportion of linear low-density polyethylene contained in the polyethylene resin is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more. Furthermore, by increasing the blending ratio of linear low-density polyethylene in the polyethylene resin, the environmental burden associated with the manufacture of the extruded foam sheet can be more easily reduced.

[0021] The linear low-density polyethylene contained in the polyethylene resin is a copolymer of ethylene and an α-olefin having 4 to 8 carbon atoms, and has substantially linear molecular chains. The linear low-density polyethylene is preferably a copolymer of ethylene and one or more comonomers selected from the group consisting of butene, hexene, octene, and 4-methyl-1-pentene, and more specifically, a copolymer of ethylene and one or more comonomers selected from the group consisting of 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene. In this case, a good extruded foam sheet can be obtained more easily.

[0022] The difference between the crystallization onset temperature Tcs (unit: °C) and the crystallization temperature Tc (unit: °C) of linear low-density polyethylene (Tcs-Tc) is 8°C or less. Furthermore, the measurement temperature was 150°C and the shear rate was 375 s. -1The extensional viscosity λ of the linear low-density polyethylene measured by the Cogswell method under these conditions is 50,000 Pa·s or more. Linear low-density polyethylene in which the difference Tcs-Tc and extensional viscosity λ are within the specified range is suitable for extrusion foaming. Therefore, according to the above manufacturing method, even when linear low-density polyethylene is included, a good extruded foam sheet with low apparent density and a high closed-cell ratio can be easily obtained. Furthermore, by using linear low-density polyethylene having the above-mentioned specific physical properties, the mechanical properties of the extruded foam sheet, such as stiffness, can be improved.

[0023] From the viewpoint of more reliably obtaining such effects, the difference Tcs-Tc between the crystallization start temperature Tcs and the crystallization temperature Tc of linear low-density polyethylene is preferably 1°C or more and 8°C or less, and more preferably 2°C or more and 6°C or less. From a similar viewpoint, at a measurement temperature of 150°C and a shear rate of 375 s, -1 The extensional viscosity λ of the linear low-density polyethylene measured by the Cogswell method under these conditions is preferably 50,000 Pa·s or more and 250,000 Pa·s or less, more preferably 60,000 Pa·s or more and 200,000 Pa·s or less, even more preferably 70,000 Pa·s or more and 180,000 Pa·s or less, and particularly preferably 80,000 Pa·s or more and 150,000 Pa·s or less.

[0024] The reason why linear low-density polyethylene with the aforementioned difference Tcs-Tc and extensional viscosity λ within the specified range is suitable for extrusion foaming is not entirely clear, but the following reasons are possible, for example: In extrusion foaming, the foamed resin molten material flows at a relatively high shear rate just before being discharged from the die lip of the extruder, so the extensional flow of the polyethylene resin immediately after being discharged from the die lip is large. In addition, when the foamed resin molten material is discharged from the die lip of the extruder, bubbles are formed in the foamed resin molten material, and the extensional flow of the polyethylene resin is also increased by the formation of these bubbles.

[0025] In contrast, the linear low-density polyethylene has a shear rate of 375 s.-1 Because it has a high extensional viscosity of 50,000 Pa·s or more at a relatively high shear rate, it is considered that the linear low-density polyethylene is less likely to break when stretched by the expansion of bubbles during foaming. Therefore, by using linear low-density polyethylene with an extensional viscosity within the specified range, it is considered that the bursting of bubbles formed in the foamed resin molten material after it is discharged from the die lip of the extruder can be suppressed.

[0026] Furthermore, the linear low-density polyethylene has a relatively small difference between its crystallization temperature Tc and its crystallization onset temperature Tcs (Tcs-Tc). Therefore, it is believed that the foamed resin molten material solidifies quickly after being discharged from the die lip of the extruder, and that the bubbles formed in the foamed resin molten material stabilize quickly.

[0027] Furthermore, it is believed that the linear low-density polyethylene synergistically works to suppress the bursting of bubbles formed in the foamed resin molten material and to stabilize the formed bubbles at an early stage, thereby easily obtaining a good extruded foam sheet with low apparent density and a high percentage of closed cells.

[0028] The crystallization temperature Tc and crystallization onset temperature Tcs of linear low-density polyethylene, as described above, are measured using a differential scanning calorimeter (DSC) based on JIS K7121:2012. More specifically, 1 to 3 mg of linear low-density polyethylene is used as the sample, and the sample is heated from 30°C to 200°C at a heating rate of 10°C / min, and then cooled from 200°C to 30°C at a cooling rate of 10°C / min to obtain a DSC curve during cooling. The peak temperature of the exothermic peak in this DSC curve is defined as the crystallization temperature Tc of linear low-density polyethylene.

[0029] Furthermore, in the portion of the DSC curve that is hotter than the peak of the exothermic peak, the point where the slope of the tangent is greatest is identified, and a tangent is drawn from this point. The temperature corresponding to the intersection of this tangent and the straight line extending the baseline on the hotter side of the DSC curve toward the colder side is defined as the crystallization onset temperature Tcs of linear low-density polyethylene. In other words, the crystallization onset temperature Tcs of linear low-density polyethylene is the extrapolation crystallization onset temperature in JIS K7121:2012. If multiple exothermic peaks appear in the DSC curve, the peak temperature of the exothermic peak with the largest area is defined as the crystallization onset temperature Tc, with the high-temperature baseline as the reference point, and the extrapolation crystallization onset temperature of that exothermic peak is defined as the crystallization onset temperature Tcs.

[0030] The extensional viscosity λ of linear low-density polyethylene by the Cogswell method is measured using a capillary rheometer (for example, "Capillograph® 1D" manufactured by Toyo Seiki Seisakusho Co., Ltd.) in accordance with JIS K7199:1999. Preferably, the measuring device is equipped with a cylindrical furnace body with an inner diameter of 9.55 mm. Specifically, first, either a long die with a capillary of 1 mm inner diameter and 20 mm length, or a short die with a capillary of 1 mm inner diameter and 0.4 mm length, is attached to the outlet of the furnace body of the measuring device. Then, the temperature of the furnace body is raised to 150°C. After the furnace body temperature reaches 150°C, approximately 15 g of linear low-density polyethylene is placed inside the furnace.

[0031] Next, the piston of the measuring device is lowered until molten linear low-density polyethylene is discharged from the capillary. Then, the piston is lowered at a speed of 0.75 mm / min for 4 minutes to remove air from the molten material. After that, the piston is lowered while the lowering speed is continuously increasing, and the load applied to the piston at each lowering speed is measured. The load applied to the piston is then converted into a pressure loss P by dividing the load applied to the piston by the cross-sectional area of ​​the capillary.

[0032] Next, the pressure loss P0 caused by the extensional flow at the capillary outlet is calculated using the following method. The pressure loss P when extruding molten linear low-density polyethylene from a capillary die is expressed as the sum of the pressure loss caused by the shear flow of the molten linear low-density polyethylene inside the capillary and the pressure loss P0 caused by the extensional flow at the capillary outlet. Furthermore, the pressure loss caused by the shear flow of the molten linear low-density polyethylene is proportional to the length L of the capillary. Therefore, the pressure loss P when extruding molten linear low-density polyethylene from a capillary die can be expressed as a linear function of the length L of the capillary. The intercept of this linear function is equal to the pressure loss P0 caused by the extensional flow at the capillary outlet.

[0033] Therefore, the length L of the capillary of the long die obtained by the aforementioned measurement is L , Pressure loss P when linear low-density polyethylene is extruded from a long die at a descent rate corresponding to a desired shear rate L Short-die capillary length L S And the pressure loss P when linear low-density polyethylene is extruded from a short die at a descent rate corresponding to a desired shear rate. S By determining the linear function based on this, the pressure loss P0 caused by the extensional flow at the capillary outlet can be calculated based on the intercept of the linear function. That is, the pressure loss P0 caused by the extensional flow at the capillary outlet is calculated based on the following equation (1). P0=(P S ·L L -P L ·L S ) / (L L -L S ) ···(1)

[0034] Next, the pressure loss P obtained in this way L (Unit: Pa), pressure loss P0 (Unit: Pa), length L of the long die capillary LUsing the dimensions (in mm) and the inner diameter D of the long die capillary (in mm), the shear stress σ is calculated based on the following formula (2). S Calculate the shear stress σ (in Pa) obtained by equation (2). S This represents the true shear stress, corrected to eliminate the effects of extensional flow occurring at the capillary outlet. This correction method, which eliminates the effects of extensional flow at the capillary outlet to determine the true shear stress, is called the Burgley correction. σ S =(P L -P0)×(D / 4L) ···(2)

[0035] Next, the non-Newtonian exponent n of the linear low-density polyethylene fluid is calculated using the following method. First, the true shear stress σ at various shear rates γ is calculated based on equation (2) using the same method as described above. S The value of is calculated. The shear rate γ and the shear stress σ corresponding to the shear rate γ obtained in this way are then calculated. S The pairs are plotted on a log-log graph, with the vertical axis representing the logarithm of shear stress and the horizontal axis representing the logarithm of shear rate.

[0036] Shear stress σ S (Unit: Pa) is the shear rate γ (unit: s -1 ), non-Newtonian exponents n and constant K (unit: Pa·s) -n Using ), it is expressed by the following equation (3). Furthermore, the non-Newtonian exponent n in the following equation (3) is equal to the slope of the line in the log-log graph described above. Therefore, by determining the approximate line of multiple plotted points in the log-log graph described above, the non-Newtonian exponent n can be obtained based on the slope of that approximate line. σ S =K·γ n ...(3)

[0037] Next, the shear rate γ (unit: s) -1 ) and the true shear stress σ at the shear rate γ. SUsing (in Pa), the true shear viscosity η (in Pa·s) at the desired shear rate γ is calculated based on the following equation (4). In the following, the shear viscosity η obtained in this way may be referred to as the "Burgeley-corrected shear viscosity η". η = σ S / γ ···(4)

[0038] The extensional viscosity λ (in Pa·s) of linear low-density polyethylene obtained by the Cogswell method is given by the non-Newtonian exponent n and the shear rate γ (in s) obtained above. -1 ), the true shear viscosity η (unit: Pa·s) and pressure loss P0 (unit: Pa) when extruded at shear rate γ are used to calculate the following based on equation (5). λ=[9(n+1) 2 / 32η]×(P0 / γ) 2 ...(5)

[0039] Therefore, at a temperature of 150°C and a shear rate of 375 s, -1 When attempting to calculate the extensional viscosity λ when linear low-density polyethylene is extruded under the conditions described above, the analysis described above uses a shear rate of 375 s. -1 The true shear viscosity η and pressure loss P0 corresponding to the given values ​​can be calculated, and these values ​​can then be used to determine the extensional viscosity λ. (Note: Temperature 150°C, shear rate 375 s) -1 This condition is set considering the flow field near the die exit (die lip) during extrusion foaming.

[0040] Furthermore, the above formula (5), used to calculate the extensional viscosity λ (unit: Pa·s) of resin by the Cogswell method, is explained in detail, for example, in "High-speed flow behavior of plastic melt in molding processes (4), Seikei-Kakou, Vol.7, No.11, 1995, 717-722" and "High-speed flow behavior of plastic melt in molding processes (5), Seikei-Kakou, Vol.7, No.12, 1995, 763-768".

[0041] Measurement temperature 150°C, shear rate 375s -1It is preferable that the ratio λ / η of the extensional viscosity λ (unit: Pa·s) of the linear low-density polyethylene by the Cogswell method to the Burgray-corrected shear viscosity η (unit: Pa·s) of the linear low-density polyethylene, measured under the specified conditions, is 100 or more. In this case, the range of extrusion foaming temperatures in which a good extruded foamed sheet with a high closed-cell ratio can be produced can be broadened, possibly because the bubbles formed in the foamed resin molten material are less likely to burst.

[0042] Furthermore, the measurement temperature was 150°C and the shear rate was 375s. -1 The ratio λ / η of the extensional viscosity λ (unit: Pa·s) of the linear low-density polyethylene by the Cogswell method to the Burgray-corrected shear viscosity η (unit: Pa·s) of the linear low-density polyethylene, measured under the following conditions: measurement temperature 150°C, shear rate 6s. -1 It is preferable that the ratio (λ / η) / (λ' / η') of the elongation viscosity λ' (unit: Pa·s) of the linear low-density polyethylene measured under the following conditions to the Burgray-corrected shear viscosity η' (unit: Pa·s) of the linear low-density polyethylene by the Cogswell method, λ' / η', is 1.3 or higher. By using linear low-density polyethylene having such physical properties, the range of extrusion foaming temperatures in which good extruded foam sheets with a high closed-cell ratio can be produced can be broadened. Furthermore, it becomes easier to produce extruded foam sheets that are more difficult to manufacture, such as extruded foam sheets with lower apparent density or thinner extruded foam sheets.

[0043] Furthermore, the measurement temperature was 150°C and the shear rate was 375s. -1It is preferable that the ratio λ / η of the extensional viscosity λ (unit: Pa·s) of the linear low-density polyethylene by the Cogswell method to the shear viscosity η (unit: Pa·s) of the linear low-density polyethylene after Burgray correction, measured under these conditions, is 100 or more, and that the ratio (λ / η) / (λ´ / η´) of the ratio λ´ / η´ of the extensional viscosity λ´ (unit: Pa·s) of the linear low-density polyethylene by the Cogswell method to the shear viscosity η´ (unit: Pa·s) of the linear low-density polyethylene after Burgray correction, measured under the conditions of a measurement temperature of 150°C and a shear rate of 6s-1, is 1.3 or more. In this case, it is preferable that extruded foam sheets, which are more difficult to manufacture, such as extruded foam sheets with lower apparent density or thinner extruded foam sheets, can be easily produced over a wider range of extrusion foam temperatures.

[0044] The crystallization temperature Tc of the linear low-density polyethylene is preferably 105°C or higher, more preferably 105°C to 118°C, and even more preferably 108°C to 115°C. In this case, a good extruded foam sheet can be obtained more easily.

[0045] The density of the aforementioned linear low-density polyethylene is set to 920 kg / m³ from the viewpoint of more reliably enhancing the foaming properties of the foamed resin molten material. 3 More than 935kg / m 3 Preferably, it is 925 kg / m 3 More than 934kg / m 3 It is more preferable that the following conditions are met: 928 kg / m 3 More than 933kg / m 3 The following is even more preferable:

[0046] The polyethylene-based resin may contain low-density polyethylene (PE-LD) in addition to linear low-density polyethylene. Since the low-density polyethylene has a long-chain branched structure, a good extruded foam sheet can be obtained more easily. From a similar viewpoint, the density of the low-density polyethylene contained in the polyethylene-based resin is 910 kg / m³. 3 More than 930kg / m3 It is preferable that the density is less than [a certain value]. In this case, a good extruded foam sheet can be obtained more easily. Note that low-density polyethylene having a long-chain branched structure is sometimes called branched low-density polyethylene.

[0047] When the polyethylene resin contains low-density polyethylene in addition to linear low-density polyethylene, the content of low-density polyethylene may be, for example, 3% to 70% by mass, 5% to 60% by mass, 8% to 50% by mass, 10% to 45% by mass, or 15% to 35% by mass in the polyethylene resin. From the viewpoint of environmental considerations and improvement of the mechanical properties of the extruded foam sheet, the content of low-density polyethylene in the polyethylene resin is preferably less than 3% by mass, more preferably 2% or less by mass, even more preferably 1% or less by mass, and particularly preferably 0% by mass, i.e., the polyethylene resin does not contain any low-density polyethylene.

[0048] Conventionally, in the manufacture of polyethylene resin extruded foam sheets, low-density polyethylene having a long-chain branched structure was almost always used as the main component, taking foaming properties into consideration. In contrast, according to the above manufacturing method, by using linear low-density polyethylene in which the difference Tcs-Tc and extensional viscosity λ are within the specified range, a good extruded foam sheet with a high closed-cell ratio can be obtained even when the blending ratio of low-density polyethylene is low or when low-density polyethylene is not blended.

[0049] [Extrusion foaming process] The above manufacturing method includes an extrusion foaming step in which a foamed resin molten material containing the polyethylene resin and a physical foaming agent is foamed while being extruded to form a foamed layer. In the extrusion foaming step, known extrusion apparatus used in the field of extrusion foaming can be used. For example, when it is to produce an extruded foamed sheet with a single-layer structure consisting only of a foamed layer, the extrusion foaming step can be carried out using an extrusion apparatus equipped with an extruder configured to extrude a foamed resin molten material and an extrusion die connected to the discharge port of the extruder.

[0050] The foamed resin molten product is obtained by melting and kneading the linear low-density polyethylene and the physical blowing agent in an extruder. More specifically, first, the linear low-density polyethylene is supplied to the extruder and melted and kneaded to produce a polyethylene-based resin molten product. Next, the physical blowing agent is supplied to the extruder and the polyethylene-based resin molten product and the physical blowing agent are further kneaded to obtain a foamed resin molten product containing polyethylene-based resin and physical blowing agent.

[0051] Organic and inorganic physicoblasting agents can be used as physicoblasting agents. Examples of organic physicoblasting agents include aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, and isohexane; alicyclic hydrocarbons such as cyclopentane and cyclohexane; chlorinated hydrocarbons such as methyl chloride and ethyl chloride; and fluorinated hydrocarbons such as 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, and 1-chloro-3,3,3-trifluoropropene. Examples of inorganic physicoblasting agents include nitrogen, carbon dioxide, air, and water. The foaming resin molten material may contain one type of physicoblasting agent or two or more types of physicoblasting agents.

[0052] From the viewpoint of compatibility with polyethylene resins and foaming properties, it is preferable that the foamed resin molten material contains an organic physicoblasting agent as a physicoblasting agent, and more preferably that it contains an organic physicoblasting agent mainly composed of n-butane, isobutane, or a mixture thereof.

[0053] The amount of physical blowing agent can be appropriately set according to the type of blowing agent and the desired apparent density. For example, when using a mixed butane consisting of 30% by mass of isobutane and 70% by mass of n-butane as a physical blowing agent, 3 to 30 parts by mass, preferably 5 to 25 parts by mass, and more preferably 8 to 20 parts by mass of the mixed butane should be added per 100 parts by mass of polyethylene resin.

[0054] The foamed resin molten material may contain the aforementioned low-density polyethylene as needed. Furthermore, the foamed resin molten material may contain linear low-density polyethylene and other polymers other than low-density polyethylene, to the extent that they do not impair the aforementioned effects.

[0055] Other polymers added to the foamed resin molten product include, for example, polyethylene resins other than low-density polyethylene and linear low-density polyethylene, such as ultra-low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ethylene copolymers; thermoplastic resins other than polyethylene resins, such as polypropylene resins and polystyrene resins; and elastomers such as ethylene propylene rubber and styrene-butadiene-styrene block copolymers. The content of linear low-density polyethylene and other polymers added to the foamed resin molten product is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, particularly preferably 3 parts by mass or less, and most preferably 0 parts by mass, based on 100 parts by mass of the total of linear low-density polyethylene and low-density polyethylene.

[0056] Furthermore, the foamed resin molten material may contain additives such as foam regulators, antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, fillers, and antibacterial agents. The amount of additives in the foamed resin molten material is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of polyethylene resin.

[0057] It is preferable that the foamed resin molten material contains a foam regulator. Inorganic or organic foam regulators can be used. Examples of inorganic foam regulators include metal borate salts such as zinc borate, magnesium borate, and borax, as well as sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate, and sodium bicarbonate. Examples of organic foam regulators include sodium 2,2-methylenebis(4,6-tert-butylphenyl) phosphate, sodium benzoate, aluminum benzoate, and sodium stearate. Furthermore, mixtures of citric acid and sodium bicarbonate, or mixtures of alkali citrate and sodium bicarbonate, can also be used as foam regulators. The foamed resin molten material may contain one type of foam regulator, or two or more types. The amount of foam regulator in the foamed resin molten material should be appropriately set according to the type of physical foaming agent, the desired apparent density, and the desired bubble diameter.

[0058] When producing an extruded foam sheet with a single-layer structure consisting of a foamed layer, in the extrusion foaming process, the foamed resin molten formed in the extruder is guided to an extrusion die, and the foamed resin molten is extruded from the extrusion port of the extrusion die. The extrusion die may be, for example, a flat die with a linear extrusion port. The foamed resin molten, extruded into the atmosphere, expands while foaming, forming a foamed layer. By cooling the foamed layer formed in this way while pulling it along a widening device, the cellular structure of the foamed layer is fixed and the dimensions of the foamed layer are stabilized. As a result, an extruded foam sheet with a single-layer structure can be obtained.

[0059] Furthermore, the extrusion die may be, for example, an annular die equipped with an annular extrusion port. In this case, the foamed resin molten material is extruded in a cylindrical shape from the extrusion port of the annular die. The foamed resin molten material extruded into the atmosphere expands while foaming, forming a cylindrical foam layer. The cylindrical foam layer thus formed is widened from the inside with compressed air or the like, and while the inside is pulled along a widening device such as a mandrel and cooled, the bubble structure of the foam layer is fixed and the dimensions of the foam layer are stabilized. After that, the cylindrical foam layer is cut open on the widening device to obtain an extruded foam sheet. When an annular die is used as the extrusion die, it is easy to manufacture wide extruded foam sheets, for example, with a width of 500 mm or more. It is also easy to manufacture thin sheet-like extruded foam sheets, for example, with an overall thickness of 5 mm or less.

[0060] Furthermore, when attempting to produce a multilayer extruded foam sheet containing a foam layer, the foamable resin molten material and a resin molten material for forming a layer different from the foam layer can be co-extruded in the extrusion foaming process. A co-extrusion apparatus can be used to produce a multilayer extruded foam sheet, which includes a plurality of extruders, including an extruder for forming the foam layer, and a co-extrusion die connected to the extrusion ports of these extruders. The method for producing a multilayer extruded foam sheet is the same as the method for producing a single-layer extruded foam sheet described above, except that a laminate of the foamable resin molten material and a resin molten material for forming a layer different from the foam layer is co-extruded from the co-extrusion die. A multilayer extruded foam sheet may have, for example, a two-layer structure comprising a foam layer and a resin layer formed on one side of the foam layer, or a three-layer structure comprising a foam layer and resin layers formed on both sides of the foam layer. In addition, two or more resin layers can be formed on one or both sides of the foam layer in the extruded foam sheet.

[0061] The extruded foam sheet obtained by the above manufacturing method has a density of 10 kg / m². 3 More than 250kg / m 3It has the following apparent density. The polyethylene-based resin constituting the foamed resin molten product in the above manufacturing method contains linear low-density polyethylene having the above specific physical properties. Therefore, even when linear low-density polyethylene is included in the polyethylene-based resin, the foaming properties of the foamed resin molten product are enhanced to 10 kg / m³. 3 More than 250kg / m 3 Extruded foam sheets having the following apparent densities can be easily formed.

[0062] From the viewpoint of further improving the cushioning properties and mechanical strength of the extruded foam sheet, the apparent density of the extruded foam sheet should be 20 kg / m². 3 Preferably, it should be 25 kg / m 3 It is more preferable that the amount be greater than or equal to 30 kg / m 3 It is even more preferable that the above conditions are met. Furthermore, from the viewpoint of further improving the lightweight properties of the extruded foam sheet, the apparent density of the extruded foam sheet should be 200 kg / m³. 3 Preferably, it is 150 kg / m 3 It is more preferable that the following conditions apply: 100 kg / m 3 The following is even more preferable:

[0063] The method for measuring the apparent density of the extruded foam sheet is as follows. First, the extruded foam sheet is cut in the width direction (i.e., in a direction perpendicular to both the extrusion direction and the thickness direction), and a test specimen is taken. The shape of the test specimen can be, for example, a rectangle in which the vertical dimension is the same as the total width of the extruded foam sheet and the horizontal dimension is 10 cm. The mass (in units: g) of this test specimen is divided by the area of ​​the test specimen, and then the basis weight of the extruded foam sheet is obtained by unit conversion, i.e., 1 m of extruded foam sheet. 2 Mass per unit (unit: g / m³) 2 The basis weight of the extruded foam sheet is then divided by the average thickness of the extruded foam sheet obtained by the method described later, and then converted to units to obtain the apparent density of the extruded foam sheet (unit: kg / m). 3 It is possible to calculate ).

[0064] The average thickness of the extruded foam sheet obtained by the above manufacturing method is preferably 0.05 mm to 25 mm, more preferably 0.1 mm to 10 mm, even more preferably 0.05 mm to 5 mm, and particularly preferably 0.1 mm to 3 mm. As mentioned above, the foamed resin molten material in the above manufacturing method is composed of a polyethylene-based resin containing the specific linear low-density polyethylene. Therefore, according to the above manufacturing method, a good extruded foam sheet can be easily obtained even when producing an extruded foam sheet with a relatively thin thickness of 0.05 mm to 5 mm.

[0065] The method for measuring the average thickness of an extruded foam sheet is as follows: First, at least 10 measurement positions are randomly set on the extruded foam sheet, each differing in position in the extrusion direction. At each of these measurement positions, the thickness is measured at at least 3 positions, where the spacing in the width direction of the extruded foam sheet is equal. The average thickness of the extruded foam sheet can be determined by taking the arithmetic mean of the thickness values ​​at at least 30 positions obtained in this way.

[0066] [Polyethylene resin extruded foam sheet] The extruded foam sheet obtained by the above manufacturing method has a foam layer composed of a polyethylene-based resin as the base resin. The apparent density of the extruded foam sheet is 10 kg / m³. 3 More than 250kg / m 3 The following applies: The polyethylene resin constituting the foam layer contains linear low-density polyethylene. The difference between the crystallization start temperature Tcs (unit: °C) and the crystallization temperature Tc (unit: °C) of the linear low-density polyethylene contained in the foam layer, Tcs-Tc, is 8°C or less, measured at a temperature of 150°C and a shear rate of 375 s. -1The extensional viscosity λ of linear low-density polyethylene measured by the Cogswell method under these conditions is 50,000 Pa·s or more, and the closed-cell ratio of the extruded foam sheet is 50% or more. Despite containing linear low-density polyethylene, the extruded foam sheet has a low apparent density, a good cellular structure is formed, and a high closed-cell ratio. From the viewpoint of further improving the cushioning properties of the extruded foam sheet, the closed-cell ratio of the extruded foam sheet is preferably 55% or more, more preferably 60% or more, even more preferably 65% ​​or more, and particularly preferably 70% or more.

[0067] The closed-cell ratio of extruded foam sheets is measured using an air-comparative hydrometer according to procedure C of ASTM-D2856-70. Specifically, the method for measuring the closed-cell ratio of extruded foam sheets is as follows: First, a measurement sample measuring 25 mm in length, 25 mm in width, and 20 mm in thickness is prepared from the extruded foam sheet. If the thickness of the extruded foam sheet is less than 20 mm, several small pieces measuring 25 mm in length and 25 mm in width can be cut from the extruded foam sheet, and these pieces can be stacked to create a measurement sample with a thickness of approximately 20 mm. Then, in accordance with procedure C of ASTM-D2856-70, the true volume value Vx of the measurement sample is measured using an air-comparative hydrometer (for example, the "930" air-comparative hydrometer manufactured by Toshiba Beckmann Corporation). Then, using the true volume Vx of the measurement sample, the closed-cell ratio (unit: %) of the measurement sample is calculated based on the following formula (6). Closed cell ratio=(Vx-W / ρ)×100 / (Va-W / ρ) ···(6)

[0068] However, the meaning of the symbols in formula (6) above is as follows: Vx: The true volume of the sample measured by the above method, i.e., the sum of the volume of the resin constituting the extruded foam sheet and the total volume of the closed-cell portions within the extruded foam sheet (unit: cm²). 3 ) Va: Apparent volume calculated from the external dimensions of the sample being measured (unit: cm) 3 ) W: Mass of the sample used for measurement (unit: g) ρ: Density of the resin constituting the extruded foam sheet (unit: g / cm³) 3 )

[0069] The composition of the linear low-density polyethylene contained in the foam layer of the extruded foam sheet is the same as that of the linear low-density polyethylene contained in the foaming resin molten material. Therefore, the description of the linear low-density polyethylene contained in the foam layer of the extruded foam sheet can be appropriately referred to in the above-mentioned description of the linear low-density polyethylene contained in the foaming resin molten material.

[0070] From the viewpoint of further improving the mechanical properties of the extruded foam sheet and from the viewpoint of more easily reducing the environmental burden associated with the manufacture of the extruded foam sheet, the blending ratio of linear low-density polyethylene in the polyethylene resin is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more.

[0071] Furthermore, the polyethylene-based resin constituting the foam layer may contain low-density polyethylene in addition to linear low-density polyethylene. Since the low-density polyethylene has a long-chain branched structure, a good extruded foam sheet can be obtained more easily. From a similar viewpoint, the density of the low-density polyethylene contained in the polyethylene-based resin is 910 kg / m³. 3 More than 930kg / m 3 It is preferable that the value is less than this. In this case, a good extruded foam sheet can be obtained more easily.

[0072] The aforementioned extruded foam sheet is preferably a non-crosslinked extruded foam sheet comprising a foam layer composed of a non-crosslinked polyethylene resin. Here, "non-crosslinked" means that the gel fraction of the extruded foam sheet is less than 5% (including 0). A non-crosslinked extruded foam sheet can be obtained by avoiding the application of a process that forms a crosslinked structure in the base resin by reacting the base resin of the foam layer with a crosslinking agent such as a polyfunctional compound, or a process that forms a crosslinked structure in the foam layer by electron beam irradiation or the like. Non-crosslinked extruded foam sheets have excellent recyclability and can contribute to reducing environmental impact.

[0073] The gel fraction of an extruded foam sheet can be determined as follows. First, prepare approximately 50 mg of an extruded foam sheet as a sample and accurately weigh the sample. After weighing, immerse the sample in 25 ml of xylene at 130°C for 3 hours, then filter it through a 200-mesh stainless steel mesh and wash with acetone. Subsequently, vacuum dry the insoluble matter remaining on the mesh. Then, accurately weigh the mass of the dried insoluble matter. The gel fraction (in %) of the extruded foam sheet is calculated using the mass of the sample obtained in this way (in mg) and the mass of the dried insoluble matter (in mg), based on the following formula (7). Gel fraction = [Mass of insoluble matter / Mass of sample] × 100 ... (7)

[0074] The extruded foam sheet can be suitably used for applications such as cushioning material and packaging material. In particular, the extruded foam sheet contains linear low-density polyethylene and has high rigidity, so it can be suitably used as interleaving paper for glass plates to prevent scratches on the glass plates, for example. In this case, the workability when inserting the interleaving paper between glass plates and when removing the interleaving paper from the glass plates after use can be improved. The extruded foam sheet can also be used as an extruded foam sheet for thermoforming, but this is excluded from the preferred applications. [Examples]

[0075] Examples of the extruded foam sheet and its manufacturing method are described below. The physical properties of the linear low-density polyethylene used in this example are shown in Table 1. The physical properties of the low-density polyethylene used in this example are shown in Table 2. All of the low-density polyethylenes used in this example have a long-chain branched structure. In Tables 1 to 4, linear low-density polyethylene is abbreviated as "PE-LLD" and low-density polyethylene as "PE-LD".

[0076] [Table 1]

[0077] [Table 2]

[0078] The methods for measuring the physical properties of polyethylene resins shown in Tables 1-2 are as follows.

[0079] [Meltmass Flow Rate (MFR)] The melt mass flow rate of each resin was measured under conditions of 190°C and 2.16 kg load, in accordance with JIS K7210-1:2014.

[0080] [Melting viscosity] The melt viscosity of each resin was measured using a capillary rheometer (Capillograph 1D, manufactured by Toyo Seiki Seisakusho Co., Ltd.). The inner diameter of the furnace body of the capillary rheometer used in this example was 9.55 mm. The orifice inner diameter of the capillary rheometer was 1 mm, the orifice length was 10 mm, and the measurement temperature was 190°C and the shear rate was 100 s. -1 Measurements were taken under the following conditions.

[0081] [Melting tension] The melt tension of each resin was measured using a capillary rheometer (Capillograph 1D, manufactured by Toyo Seiki Seisakusho Co., Ltd.). The inner diameter of the furnace body of the capillary rheometer used in this example was 9.55 mm. The inner diameter of the orifice of the capillary rheometer was 2.095 mm, and the orifice length was 8 mm. Measurements were performed at a measurement temperature of 190°C and a take-up speed of 15.7 mm / min.

[0082] [Melting point] The melting points of each resin were measured based on DSC curves obtained by differential scanning calorimetry (i.e., DSC) in accordance with JIS K7121-1987. Specifically, first, the samples were conditioned according to "(2) When measuring the melting temperature after performing a certain heat treatment." The heating and cooling rates during conditioning were set to 10°C / min. The conditioned samples were heated from 30°C to 200°C at a heating rate of 10°C / min to obtain DSC curves, and the peak temperature of the melting peak that appeared in the DSC curve was taken as the melting point of each resin. If multiple melting peaks appeared in the DSC curve, the peak temperature of the melting peak with the largest area was taken as the melting point of each resin.

[0083] [Crystallization temperature Tc and crystallization start temperature Tcs] In accordance with JIS K7121:2012, the crystallization temperature Tc and crystallization onset temperature Tcs of each resin were measured using a thermal flux differential scanning calorimeter. The specific measurement methods for the crystallization temperature Tc and crystallization onset temperature Tcs are as described above.

[0084] [Extensional viscosity and shear viscosity after Burgray correction] The extensional viscosity and Burgundy-corrected shear viscosity of the linear low-density polyethylene were measured using a capillary rheometer (Capillograph 1D, manufactured by Toyo Seiki Seisakusho Co., Ltd.) by the Cogswell method. The measurement temperature for extensional viscosity and shear viscosity was 150°C, and the shear rate was 375 s⁻¹. -1 or 6s -1 The specific methods for measuring extensional viscosity and shear viscosity are as described above.

[0085] (Example 1) The extruded foam sheet in this example has a single-layer structure consisting only of a foam layer. The extruded foam sheet in this example was manufactured using an extrusion apparatus equipped with an extruder and an extrusion die connected to the discharge port of the extruder. The extrusion die used in this example is an annular die having an annular extrusion port.

[0086] The manufacturing method for the extruded foam sheet in this example is as follows. First, LLD1 as linear low-density polyethylene and a foam regulator were supplied to the extruder, and a polyethylene resin molten material was formed inside the extruder by melting and kneading these together. A mixture of citric acid and sodium bicarbonate (FineCellMaster® PO217K, manufactured by Dainichi Seika Kogyo Co., Ltd.) was used as the foam regulator.

[0087] Furthermore, a foamed resin molten product was obtained by supplying a physical blowing agent equivalent to 2 moles per 1 kg of polyethylene resin to the polyethylene resin molten product in the extruder under pressure, and further kneading the mixture in the extruder. As the physical blowing agent, a mixed butane consisting of 65% by mass of n-butane and 35% by mass of isobutane was used.

[0088] The foamed resin molten material produced in the extruder was supplied to the extrusion die and extruded from the extrusion port of the extrusion die to create a cylindrical foamed layer. A mandrel with a diameter of 210 mm was then inserted inside this foamed layer, and the foamed layer was pulled along the mandrel while being cut open to obtain the extruded foamed sheet of Example 1. The discharge rate of the foamed resin molten material, the extrusion foaming temperature during extrusion, and the pull-out speed of the foamed layer are as shown in Table 3. The width of the extruded foamed sheet of Example 1 was approximately 650 mm.

[0089] (Example 2) The extruded foam sheets in these examples have the same structure as the extruded foam sheet in Example 1, except that they have the average thickness shown in Table 3. Furthermore, the manufacturing method for the extruded foam sheet in Example 2 is the same as that for the extruded foam sheet in Example 1, except that the take-up speed is changed as shown in Table 3.

[0090] (Examples 3-4) The extruded foam sheets in these examples have the same structure as the extruded foam sheet in Example 1, except that linear low-density polyethylene shown in Table 3 is used instead of LLD1. Furthermore, the manufacturing method for the extruded foam sheets in Examples 3 and 4 is the same as the manufacturing method for the extruded foam sheet in Example 1, except that linear low-density polyethylene shown in Table 3 is used instead of LLD1, and the manufacturing conditions are changed as shown in Table 3.

[0091] (Examples 5-6) The extruded foam sheets of these examples have a configuration that is generally similar to that of the extruded foam sheet of Example 1, except that the polyethylene resin contains LD1 or LD2 as low-density polyethylene in the proportions shown in Table 3. The manufacturing method of the extruded foam sheets of Examples 5 and 6 is the same as that of the extruded foam sheet of Example 1, except that linear low-density polyethylene and low-density polyethylene are used in the proportions shown in Table 3, and the manufacturing conditions are changed as shown in Table 3.

[0092] (Comparative Examples 1-3) The extruded foam sheets of these comparative examples have the same structure as the extruded foam sheet of Example 1, except that linear low-density polyethylene shown in Table 4 is used instead of LLD1. Furthermore, the manufacturing method of the extruded foam sheets of Comparative Examples 1 to 3 is the same as the manufacturing method of the extruded foam sheet of Example 1, except that linear low-density polyethylene shown in Table 4 is used instead of LLD1, and the manufacturing conditions are changed as shown in Table 4.

[0093] (Reference examples 1~3) The extruded foamed sheets of these reference examples have the same configuration as the extruded foamed sheet of Example 1, except that the foamed layer does not contain linear low density polyethylene and is composed of the low density polyethylene shown in Table 4. The manufacturing methods of the extruded foamed sheets of Reference Examples 1 to 3 are the same as the manufacturing method of the extruded foamed sheet of Example 1, except that the foamed resin melt was produced using the low density polyethylene shown in Table 4 instead of linear low density polyethylene, and the manufacturing conditions were changed as shown in Table 4.

[0094] (Physical properties of the extruded foamed sheet) Tables 3 to 4 show various physical properties of the extruded foamed sheets of Examples 1 to 6, Comparative Examples 1 to 3, and Reference Examples 1 to 3. Note that all the extruded foamed sheets used for evaluation were uncrosslinked extruded foamed sheets, and their gel fraction was 0.

[0095] [Average thickness] First, 10 measurement positions with different positions in the extrusion direction were randomly set on the extruded foamed sheet. At each of these measurement positions, the thicknesses of three positions were measured so that the intervals in the width direction of the extruded foamed sheet were equal. The arithmetic mean value of the thicknesses at 30 positions of the extruded foamed sheet thus obtained was taken as the average thickness of the extruded foamed sheet.

[0096] [Apparent density] The extruded foamed sheet was cut in the width direction (i.e., the direction perpendicular to both the extrusion direction and the thickness direction), and a rectangular test piece with a longitudinal dimension equal to the full width of the extruded foamed sheet and a transverse dimension of 10 cm was produced. After dividing the mass (unit: g) of this test piece by the area of the test piece and then performing unit conversion, the basis weight of the extruded foamed sheet, that is, the mass per 1 m 2 of the extruded foamed sheet (unit: g / m 2 ) was calculated. Then, the basis weight of the extruded foamed sheet was divided by the average thickness of the extruded foamed sheet, and then unit conversion was performed to calculate the apparent density (unit: kg / m 3 ) of the extruded foamed sheet.

[0097] [Closed cell ratio] The closed-cell ratio of the extruded foam sheet was measured using an air-comparison hydrometer, based on ASTM-D2856-70 Procedure C. The specific method for measuring the closed-cell ratio is as described above.

[0098] [Mechanical properties] The mechanical properties of the extruded foam sheet were evaluated based on the amount of sagging when the extruded foam sheet was fixed in a cantilevered position. Specifically, a rectangular test piece 10 measuring 400 mm in the direction parallel to the extrusion direction and 200 mm in the width direction was cut from the extruded foam sheet 1. Next, the base end 12 of the test piece 10 was placed on the horizontal surface 211 of the sample stage 21 in the evaluation apparatus 2 shown in Figure 1, such that the length of the portion 11 protruding from the sample stage 21 of the test piece 10 was 300 mm. In this state, a fixing jig 22 was attached to the sample stage 21, and the base end 12 of the test piece 10 was clamped between the sample stage 21 and the fixing jig 22. Then, the amount of sagging H of the portion 11 protruding from the sample stage 21 of the test piece 10, that is, the difference in height between the base end 12 of the test piece 10 and the tip 111 of the portion 11 protruding from the sample stage 21, was measured.

[0099] The amount of sagging obtained by the method described above is an indicator of the stiffness of the extruded foam sheet; a smaller amount of sagging indicates a stiffer extruded foam sheet and better mechanical properties.

[0100] [Table 3]

[0101] [Table 4]

[0102] As shown in Table 3, in the manufacturing methods of Examples 1 to 6, extruded foamed sheets were produced by extruding a foamed resin molten material containing linear low-density polyethylene. Furthermore, the linear low-density polyethylene used in these manufacturing methods has the difference Tcs-Tc between the crystallization onset temperature Tcs and the crystallization temperature Tc within the specified range, and the extensional viscosity λ according to the Cogswell method. Therefore, in these examples, it was possible to easily obtain good extruded foamed sheets with low apparent density and a high closed-cell ratio.

[0103] Furthermore, a comparison between Example 1, which has a similar average thickness of extruded foam sheets, and Reference Example 1 shown in Table 4, and a comparison between Example 2 and Reference Example 2 shown in Table 4, reveals that by incorporating the specific linear low-density polyethylene into the polyethylene resin constituting the foam layer, the amount of sagging when the extruded foam sheet is fixed in a cantilevered state is reduced, and the mechanical properties are improved.

[0104] In contrast, in the manufacturing method of Comparative Example 1, linear low-density polyethylene was used in which the difference between the crystallization onset temperature Tcs and the crystallization temperature Tc (Tcs-Tc) fell outside the specified range, making it impossible to produce a good extruded foam sheet.

[0105] Furthermore, in the manufacturing method of Comparative Example 2, linear low-density polyethylene was used in which the extensional viscosity λ was outside the specified range, making it impossible to produce a good extruded foam sheet.

[0106] Furthermore, in the manufacturing method of Comparative Example 3, linear low-density polyethylene was used in which both the difference between the crystallization onset temperature Tcs and the crystallization temperature Tc (Tcs-Tc) and the extensional viscosity λ were outside the specified range. As a result, the foaming properties were extremely low, and it was not possible to produce a good extruded foam sheet.

[0107] Although embodiments of the polyethylene resin extruded foam sheet and its manufacturing method have been described above based on the examples, the specific embodiments of the polyethylene resin extruded foam sheet and its manufacturing method according to the present invention are not limited to those of the examples, and the configuration can be appropriately modified without impairing the spirit of the present invention. [Explanation of Symbols]

[0108] 1. Polyethylene resin extruded foam sheet

Claims

1. A foamed resin molten material, obtained by melt-kneading polyethylene resin and a physical foaming agent, is extruded and foamed to produce 10 kg / m³ of foam. 3 More than 250kg / m 3 A method for producing a polyethylene resin extruded foam sheet having the following apparent density, comprising an extrusion foaming step for producing a polyethylene resin extruded foam sheet, The polyethylene resin contains linear low-density polyethylene. The difference between the crystallization start temperature Tcs (unit: °C) and the crystallization temperature Tc (unit: °C) of the linear low-density polyethylene, Tcs-Tc, is 8°C or less. Measurement temperature 150°C, shear rate 375 s -1 A method for producing a polyethylene resin extruded foam sheet, wherein the extensional viscosity λ of the linear low-density polyethylene measured by the Cogswell method under the specified conditions is 50,000 Pa·s or more.

2. Measurement temperature 150°C, shear rate 375 s -1 A method for producing a polyethylene resin extruded foam sheet according to claim 1, wherein the ratio λ / η of the extensional viscosity λ (unit: Pa·s) of the linear low-density polyethylene by the Cogswell method to the Burgray-corrected shear viscosity η (unit: Pa·s) of the linear low-density polyethylene, measured under the conditions, is 100 or more.

3. Measurement temperature 150°C, shear rate 375 s -1 The ratio λ / η of the extensional viscosity λ (unit: Pa·s) of the linear low-density polyethylene measured by the Cogswell method to the Burgray-corrected shear viscosity η (unit: Pa·s) of the linear low-density polyethylene, measured under the following conditions: measurement temperature 150°C, shear rate 6s. -1 A method for producing a polyethylene resin extruded foam sheet according to claim 1 or 2, wherein the ratio (λ / η) / (λ' / η') of the extensional viscosity λ' (unit: Pa·s) of the linear low-density polyethylene measured under the conditions λ' / η' to λ' / η' of the shear viscosity η' (unit: Pa·s) of the linear low-density polyethylene after Burgray correction is 1.3 or more.

4. A method for producing a polyethylene resin extruded foam sheet according to claim 1 or 2, wherein the crystallization temperature Tc of the linear low-density polyethylene is 105°C or higher.

5. The density of the aforementioned linear low-density polyethylene is 920 kg / m³. 3 More than 935kg / m 3 The method for producing a polyethylene resin extruded foam sheet according to claim 1 or 2 is as follows:

6. A method for producing a polyethylene resin extruded foam sheet according to claim 1 or 2, wherein the average thickness of the extruded foam sheet is 0.05 mm or more and 5 mm or less.

7. 10 kg / m 3 250 kg / m or more 3 A polyethylene-based resin extrusion foamed sheet having an apparent density of less than or equal to the following: The closed-cell ratio of the extruded foam sheet is 50% or more. The polyethylene resin constituting the extruded foam sheet contains linear low-density polyethylene. The difference between the crystallization start temperature Tcs (unit: °C) and the crystallization temperature Tc (unit: °C) of the linear low-density polyethylene, Tcs-Tc, is 8°C or less. Measurement temperature 150°C, shear rate 375 s -1 A polyethylene resin extruded foam sheet having an extensional viscosity λ of 50,000 Pa·s or more, measured by the Cogswell method under the specified conditions.

8. Measurement temperature 150°C, shear rate 375 s -1 The polyethylene resin extruded foam sheet according to claim 7, wherein the ratio λ / η of the extensional viscosity λ (unit: Pa·s) of the linear low-density polyethylene measured by the Cogswell method to the Burgray-corrected shear viscosity η (unit: Pa·s) of the linear low-density polyethylene, measured under the conditions, is 100 or more.

9. Measurement temperature 150°C, shear rate 375 s -1 The ratio λ / η of the extensional viscosity λ (unit: Pa·s) of the linear low-density polyethylene measured by the Cogswell method to the Burgray-corrected shear viscosity η (unit: Pa·s) of the linear low-density polyethylene, measured under the following conditions: measurement temperature 150°C, shear rate 6s. -1 The polyethylene resin extruded foam sheet according to claim 7 or 8, wherein the ratio (λ / η) / (λ' / η') of the extensional viscosity λ' (unit: Pa·s) of the linear low-density polyethylene measured by the Cogswell method to the Burgray-corrected shear viscosity η' (unit: Pa·s) of the linear low-density polyethylene, λ' / η', is 1.3 or greater.

10. The polyethylene resin extruded foam sheet according to claim 7 or 8, wherein the crystallization temperature Tc of the linear low-density polyethylene is 105°C or higher.

11. The density of the aforementioned linear low-density polyethylene is 920 kg / m³. 3 More than 935kg / m 3 The polyethylene resin extruded foam sheet according to claim 7 or 8, which is as follows:

12. The polyethylene resin extruded foam sheet according to claim 7 or 8, wherein the average thickness of the extruded foam sheet is 0.05 mm or more and 5 mm or less.

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