Polyethylene-based resin foam sheet

Abstract

To provide a polyethylene-based resin foam sheet which can improve stiffness and cushioning property even in a high expansion ratio and a small thickness.SOLUTION: A polyethylene-based resin foam sheet has a foam layer containing low density polyethylene (A1) as a base material resin, wherein thickness of the polyethylene-based resin foam sheet is 0.05 mm or more and 3 mm or less, a ratio of density (kg / m3) of the low density polyethylene (A1) to apparent density (kg / m3) of the polyethylene-based resin foam sheet is 20 or more and 80 or less, the foam layer further contains linear low density polyethylene (A2), density of the linear low density polyethylene (A2) is 915 kg / m3 or more and MFR of the linear low density polyethylene (A2) measured under the condition of a temperature of 190°C and a load of 2.16 kg, on the basis of JIS K 7210-1:2014 is 10 g / 10 min or less, the linear low density polyethylene (A2) is a copolymer of ethylene and α-olefin having 8 carbon atoms, and the content of the linear low density polyethylene (A2) in the foam layer is 5 mass% or more and 45 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyethylene resin foam sheet. [Background technology]

[0002] Polyethylene-based resin foam sheets have cushioning properties and are used as cushioning materials for logistics. In particular, polyethylene-based resin foam sheets using low-density polyethylene as the base resin have high cushioning properties and are therefore suitable for use as glass sheet interleaving sheets, which are placed between glass sheets to prevent surface scratches during transportation of multiple glass sheets. To improve suitability for such applications, polyethylene-based resin foam sheets are sometimes required to have high stiffness. For example, Patent Document 1 discloses a technique for improving the stiffness of a polyethylene-based resin foam sheet by blending a polystyrene resin into resin layers laminated and bonded to both sides of a foam layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-180534 Summary of the Invention [Problem to be solved by the invention]

[0004] There has been a growing demand for cushioning materials for logistics and slip sheets for glass plates that are thin but have excellent stiffness and cushioning properties. In response to this demand, efforts have been made to improve the stiffness and cushioning properties of polyethylene-based resin foam sheets, even in thin products. Furthermore, in recent years, from the perspective of resource conservation, there has been a demand for products with a high expansion ratio in the field of polyethylene-based resin foam sheets. Such polyethylene-based resin foam sheets with a high expansion ratio are particularly prone to a decrease in stiffness, and in conventional technologies, there has been room for improvement in stiffness depending on the expansion ratio of the polyethylene-based resin foam sheet.

[0005] An object of the present invention is to provide a polyethylene resin foam sheet which has a high expansion ratio and is excellent in stiffness and cushioning properties even when it is thin. [Means for solving the problem]

[0006] The present invention is summarized as follows: (1) to (7).

[0007] (1) A polyethylene-based resin foam sheet having a foam layer containing low-density polyethylene (A1) as a base resin, The thickness of the polyethylene resin foam sheet is 0.05 mm or more and 3 mm or less, The apparent density (kg / m 3 ) to the density (kg / m 3 ) is 20 or more and 80 or less, the foam layer further contains a linear low-density polyethylene (A2), The density of the linear low-density polyethylene (A2) is 915 kg / m 3 or more, and the MFR of the linear low-density polyethylene (A2) measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 190°C and a load of 2.16 kg is 10 g / 10 min or less, the linear low-density polyethylene (A2) is a copolymer of ethylene and an α-olefin having 8 carbon atoms, A polyethylene resin foam sheet, wherein the content of the linear low-density polyethylene (A2) in the foam layer is 5% by mass or more and 45% by mass or less. (2) The polyethylene-based resin foam sheet has the foam layer and a resin layer laminated on at least one side of the foam layer, the resin layer contains a low-density polyethylene (B1) and a linear low-density polyethylene (B2), The density of the linear low-density polyethylene (B2) is 915 kg / m 3 or more, and the MFR of the linear low-density polyethylene (B2) measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 190°C and a load of 2.16 kg is 10 g / 10 min or less, the linear low-density polyethylene (B2) is a copolymer of ethylene and an α-olefin having 8 carbon atoms, The polyethylene resin foam sheet according to (1) above, wherein the content of the linear low-density polyethylene (B2) in the resin layer is 5% by mass or more and 45% by mass or less. (3) The polyethylene resin foam sheet according to (1) or (2), wherein the linear low-density polyethylene (A2) has an MFR of 3.0 g / 10 min or less, as measured in accordance with JIS K7210-1:2014 at a temperature of 190°C and a load of 2.16 kg. (4) The MFR of the linear low-density polyethylene (A2) measured under conditions of a temperature of 190°C and a load of 2.16 kg based on JIS K7210-1:2014 is LL The MFR of the low-density polyethylene (A1) measured under conditions of a temperature of 190°C and a load of 2.16 kg based on JIS K7210-1:2014 is defined as MFR LD In this case, the MFR LL and the MFR LD The absolute value of the difference between [│(MFR LD )-(MFR LL )│] is 3.0 g / 10 min or less. (5) The polyethylene resin foam sheet according to any one of (2) to (4) above (provided that (3) and (4) above are dependent on (2) above), wherein the linear low-density polyethylene (B2) has an MFR of 3.0 g / 10 min or less, as measured in accordance with JIS K7210-1:2014 at a temperature of 190°C under a load of 2.16 kg. (6) The polyethylene resin foam sheet according to any one of (2) to (5) above (provided that (3) to (5) above are limited to cases where they are subordinate to (2) above), wherein the resin layer contains a polymeric antistatic agent. (7) The polyethylene resin foam sheet according to any one of (2) to (5) above (provided that (3) to (5) above are limited to cases where they are subordinate to (2) above), wherein the resin layer contains an ionomer resin.

[0008] The present invention also provides (8) a method for determining the MFR of the linear low-density polyethylene (A2) measured under conditions of a temperature of 190°C and a load of 2.16 kg in accordance with JIS K7210-1:2014. LL(A2) The MFR of the low-density polyethylene (A1) measured under conditions of a temperature of 190°C and a load of 2.16 kg based on JIS K7210-1:2014 is defined as MFR LD(A1) The MFR of the linear low-density polyethylene (B2) measured under conditions of a temperature of 190°C and a load of 2.16 kg based on JIS K7210-1:2014 is defined as MFR LL(B2) The MFR of the low-density polyethylene (B1) measured under conditions of a temperature of 190°C and a load of 2.16 kg based on JIS K7210-1:2014 is defined as MFR LD(B1) In this case, The MFR LL(A2) and the MFR LD(A1) The absolute value of the difference between [│(MFR LD(A1) )-(MFR LL(A2) )│] is 3.0 g / 10 min or less, and the MFR LL(B2) and the MFR LD(B1) The absolute value of the difference between [│(MFR LD(B1) )-(MFR LL(B2))│] is 3.0g / 10min or less, The polyethylene-based resin foam sheet may be the polyethylene-based resin foam sheet described in (2) above, the polyethylene-based resin foam sheet described in (3) above which is dependent on (2) above, or the polyethylene-based resin foam sheet described in any one of (5), (6), and (7) above which is dependent on other than (4) above. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a polyethylene resin foam sheet that has a high expansion ratio and is excellent in stiffness and cushioning properties even when it is thin. [Brief explanation of the drawings]

[0010] [Figure 1] 1A, 1B and 1C are cross-sectional views illustrating an embodiment of a foamed sheet according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] An example of an embodiment of the present invention will be described below. Note that the present invention is not limited to the embodiments described below. In this specification, an example of an embodiment of the present invention will be described in the order of a first embodiment, a second embodiment, and an application example. When stating that something applies to the entire specification, including the first embodiment, the second embodiment, the application example, and the examples, the term "in this specification" may be used.

[0012] Unless otherwise specified, in this specification, when a numerical range for a variable (e.g., melt flow rate) and a numerical range further narrowing that numerical range (referred to as a limited numerical range) are described, the numerical range defined by the upper limit of the numerical range and the lower limit of the limited numerical range, or the numerical range defined by the lower limit of the numerical range and the upper limit of the limited numerical range, may be adopted for that variable. For example, when a variable is a first variable (e.g., melt flow rate or the content of a specific resin), if it is described that the first variable is preferably from MA1 to MB1 and from MA2 to MB2, the first variable may be from MA1 to MB2 or from MA2 to MB1, as long as it can mathematically exist as a numerical range. The same applies when upper and lower limits of the numerical range for a variable are specified in this specification. For example, if a variable is a first variable, and it is stated that the lower limit of the first variable is MA1, preferably MA2, and the upper limit of the first variable is MB1, preferably MB2, then as long as it can mathematically exist as a numerical range, the first variable may be not only MA1 or more and MB1 or less, or MA2 or more and MB2 or less, but also MA1 or more and MB2 or less, or MA2 or more and MB1 or less. Note that MA1, MB1, MA2, and MB2 each represent a numerical value. MA11, MA12, MB11, MB12, MA21, MA22, MB21, and MB22, described below, each represent a numerical value.

[0013] The same applies to combinations of multiple variables that can be determined independently of each other. When there are first and second variables that can be determined independently of each other, and it is stated that the first variable is preferably between MA11 and MB11 and preferably between MA12 and MB12, and the second variable is preferably between MA21 and MB21 and preferably between MA22 and MB22, the first variable may be between MA11 and MB12 or between MA12 and MB11, and the second variable may be between MA21 and MB22 or between MA22 and MB21, as long as these ranges can mathematically exist as numerical ranges. The same applies when upper and lower limit values ​​for the variables are specified in this specification.

[0014] In addition, in this specification, the expression "MA1 to MB1", which expresses a numerical range using the symbol "to", is synonymous with "not less than MA1 and not more than MB1", and represents a numerical range that includes MA1 and MB1, which are the endpoints of the numerical range.

[0015] In this specification, a polyethylene resin foam sheet may be abbreviated as a foam sheet. In this specification, low-density polyethylene may be abbreviated as LDPE or PE-LD, as needed. Furthermore, in this specification, linear low-density polyethylene may be abbreviated as LLDPE or PE-LLD.

[0016] [1 First embodiment] [1-1 Composition of polyethylene resin foam sheet] A polyethylene-based resin foam sheet according to a first embodiment of the present invention has a foam layer containing low-density polyethylene as a base resin. In this specification, the low-density polyethylene constituting the base resin of the foam layer is referred to as low-density polyethylene (A1). In the first embodiment, for example, as shown in FIG. 1A, the polyethylene-based resin foam sheet (foam sheet 10) comprises a foam layer 11. FIG. 1A is a cross-sectional view showing an example of the foam sheet 10 according to the first embodiment.

[0017] (Thickness of foam sheet) The foam sheet according to the first embodiment has a relatively thin thickness (total thickness) (mm), specifically, 0.05 mm or more and 3 mm or less. Considering the applicability of the foam sheet to applications requiring thinness, the thickness (mm) of the foam sheet is preferably 0.05 mm or more and 2.5 mm or less. Furthermore, from the same viewpoint as above, the upper limit of the foam sheet thickness is more preferably 2.0 mm, and even more preferably 1.5 mm. From the viewpoint of further enhancing the cushioning properties of the foam sheet, the lower limit of the foam sheet thickness is more preferably 0.08 mm, even more preferably 0.10 mm, and particularly preferably 0.15 mm.

[0018] (Method for measuring the thickness of foam sheets) The thickness of a foam sheet is measured as follows. First, a rectangular piece is cut out from a foam sheet, and this piece is used as a test piece. The rectangular piece has a widthwise dimension equal to the overall width (mm) of the sheet and a longitudinal dimension of 100 mm. The thickness (mm) of the test piece is measured by dividing the length from one end to the other end in the widthwise direction (sheet width direction) into 10 equal parts at equal intervals. The thickness at each measurement position is measured, and the arithmetic mean value of the thickness values ​​obtained at each measurement position is used as the thickness of the foam sheet. A vernier caliper or the like is used to measure the thickness at each measurement position.

[0019] (Low density polyethylene (A1)) The low-density polyethylene (A1) is a polyethylene resin having a long-chain branched structure, and preferably has a density of 910 kg / m 3 More than 930kg / m 3 Less than or equal to 915 kg / m 3 More than 925kg / m 3 Show that:

[0020] As used herein, the term "base resin" for a target layer (e.g., a foam layer) refers to a resin that accounts for more than 50% by mass of the total amount (TM) of polymers constituting the target layer, where TM is taken as 100% by mass. Therefore, as used herein, the term "base resin of low-density polyethylene (A1)" for a foam layer means that the proportion of low-density polyethylene (A1) exceeds 50% by mass in 100% by mass of polymers constituting the foam layer. By using low-density polyethylene as the base resin, the foam sheet exhibits excellent cushioning properties. As used herein, "excellent cushioning" refers to a level of protection of packaged items that can be achieved by a foam sheet having a foam layer containing low-density polyethylene as the base resin. To obtain a foam sheet with good foamability and improved cushioning properties, the proportion of low-density polyethylene (A1) in 100% by mass of polymers constituting the foam layer is preferably 55% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more.

[0021] (Apparent density ratio) The foamed sheet according to the first embodiment has an apparent density (kg / m 3 ) to the density of low density polyethylene (A1) (kg / m 3 ) is 20 or more and 80 or less. In the above formula of DPA / DT, DT represents the apparent density of the foamed sheet, and DPA represents the density of the low-density polyethylene (A1). The ratio (DPA / DT) can be said to be a value indicating the expansion ratio (times) of the foamed sheet. From the viewpoints of resource conservation and improving cushioning properties, the ratio (DPA / DT) is preferably 25 or more, more preferably 30 or more, even more preferably 35 or more, particularly preferably 40 or more, and most preferably 45 or more. Furthermore, from the viewpoint of easily maintaining stiffness of the foamed sheet, the ratio (DPA / DT) is preferably 75 or less.

[0022] (Method for measuring apparent density of foam sheet) Apparent density of foam sheet (kg / m3 ) can be determined, for example, by the following method: First, the overall basis weight (g / m 2 ) and the thickness (mm) of the foam sheet are measured, and the overall basis weight of the foam sheet is divided by the thickness of the foam sheet to calculate the value. The calculated value is converted into units to determine the apparent density (kg / m 3 ) can be obtained.

[0023] The thickness of the foam sheet can be determined by the above-mentioned measurement. The overall basis weight of the foam sheet can be measured, for example, as follows: A sample is cut out from the foam sheet, the weight of the sample is measured, and the measured value is used as the basis weight for 1 m 2 This is converted into the weight (g) of the foam sheet per unit area, and the resulting weight is calculated as the basis weight (g / m 2 Specifically, a sheet-like test piece was cut out from the foam sheet with dimensions of 250 mm length x 250 mm width x thickness of the foam sheet, and the weight (g) of the test piece was measured and multiplied by 16 to obtain a test piece of 1 m 2 Value converted to weight per unit (g / m 2 ) is calculated and this value is the total basis weight of the foam sheet.

[0024] (Method for measuring density of low-density polyethylene (A1)) Density of low-density polyethylene (A1) (kg / m 3 ) is measured based on JIS K 7112 (1999) Method B (pycnometer method).

[0025] (Tensile strength of low density polyethylene (A1)) The tensile strength (MPa) of the low-density polyethylene (A1) is preferably 10 MPa or more from the viewpoints of maintaining stiffness and stable production of a foamed sheet.

[0026] (Method for measuring tensile strength of low-density polyethylene (A1)) The tensile strength (MPa) of the low-density polyethylene (A1) is a value measured by the following method. First, the low-density polyethylene (A1) is heat-pressed under conditions of 190°C and 10 MPa to produce a film with a thickness of 1.5 mm, and an unstretched film-like test piece is produced using a dumbbell-shaped punching blade (gauge length 40 mm). A tensile test is performed using the above test piece at a test speed of 500 mm / min in accordance with JIS K7161-2:2014, and the maximum point stress (MPa) is measured. This maximum point stress is the tensile strength of the low-density polyethylene (A1). The tensile strength of the low-density polyethylene (B1), which will be described later in the second embodiment, can also be measured by the same method.

[0027] (Melting point of low density polyethylene (A1)) The melting point (°C) of the low-density polyethylene (A1) is preferably 100°C or higher and 120°C or lower, from the viewpoint of easily increasing the closed cell ratio and cushioning properties of the foamed sheet. Furthermore, from the viewpoint of further increasing the cushioning properties of the foamed sheet, the melting point (°C) of the low-density polyethylene (A1) is more preferably 105°C or higher and 118°C or lower, and even more preferably 108°C or higher and 115°C or lower.

[0028] (Measuring method for melting point of low-density polyethylene (A1)) The melting point (°C) of low-density polyethylene (A1) is determined in accordance with JIS K7121-1987. Specifically, first, the low-density polyethylene test specimen is conditioned based on "(2) Measuring the melting temperature after a certain heat treatment" in "3. Conditioning of test specimens" in JIS K7121-1987. Conditioning is performed at a heating rate and cooling rate of 10°C / min. A DSC curve is obtained by heating the conditioned test specimen from 23°C to 230°C at a heating rate of 10°C / min. The flow rate of nitrogen gas in the measurement environment is 30 mL / min. The melting point is determined as the apex temperature of the melting peak that appears on the DSC curve. A heat flux differential scanning calorimeter (DSC7020, manufactured by SII Nanotechnology, Inc.) is used as the measurement device. If multiple melting peaks appear on the DSC curve, the apex temperature of the melting peak with the greatest heat of fusion is determined as the melting point. The melting point of the low-density polyethylene (B1) described later in the second embodiment can also be measured by the same method.

[0029] (Melt flow rate of low density polyethylene (A1)) The melt flow rate (MFR) (g / 10 min) of the low-density polyethylene (A1) is preferably 0.03 g / 10 min to 8 g / 10 min, more preferably 0.05 g / 10 min to 5 g / 10 min, even more preferably 0.1 g / 10 min to 3 g / 10 min, and particularly preferably 0.2 g / 10 min to 1.5 g / 10 min. When the melt flow rate (MFR) of the low-density polyethylene (A1) is within the above range, even when the foam layer contains a linear low-density polyethylene (A2) described below, the foamability is easily maintained, and a foamed sheet with a high closed cell content can be more stably produced.

[0030] The MFR of the low-density polyethylene (A1) is a melt mass-flow rate value measured at a temperature of 190°C and a load of 2.16 kg according to JIS K7210-1: 2014. In this specification, the term melt flow rate is synonymous with melt mass-flow rate.

[0031] (Linear low-density polyethylene (A2)) The foam sheet further contains a linear low-density polyethylene (A2) as a polymer in addition to the low-density polyethylene (A1) that is the base resin described above. In a first embodiment, the foam layer contains the linear low-density polyethylene (A2). The linear low-density polyethylene (A2) is a copolymer of ethylene and an α-olefin having 8 carbon atoms. The linear low-density polyethylene (A2) has a substantially linear polyethylene main chain and short-chain branches derived from the α-olefin having 8 carbon atoms. When the linear low-density polyethylene (A2) is a copolymer of ethylene and an α-olefin having 8 carbon atoms, the stiffness of the foam sheet is improved. An example of the α-olefin having 8 carbon atoms is 1-octene.

[0032] (Density of linear low-density polyethylene (A2)) Density of linear low-density polyethylene (A2) (kg / m 3 ) is 915 kg / m 3 From the viewpoint of obtaining the effect of improving stiffness of the foamed sheet, it is preferable that the density of the linear low-density polyethylene (A2) is high. From this viewpoint, it is preferable that the density (kg / m 3 ) is 917 kg / m 3 It is preferable that the saturation is 920 kg / m or more. 3 More preferably, it is 922 kg / m or more. 3 More preferably, it is 925 kg / m or more. 3 From the viewpoint of production stability when producing a foamed sheet by extrusion foaming, the density of the linear low-density polyethylene (A2) is preferably 935 kg / m or more. 3More preferably, it is 930 kg / m or less. 3 The following is the result.

[0033] (Method for measuring density of linear low-density polyethylene (A2)) The density of the linear low-density polyethylene (A2) can be measured by the same method as the above-mentioned method for measuring the density of the low-density polyethylene (A1).

[0034] (Melt flow rate of linear low-density polyethylene (A2)) The melt flow rate (MFR) (g / 10 min) of the linear low-density polyethylene (A2) is 10 g / 10 min or less. In this specification, the melt flow rate is abbreviated as MFR, and in the description of the first embodiment, the MFR of the linear low-density polyethylene (A2) is referred to as MFR LL In the description of the second embodiment below, the MFR of the linear low-density polyethylene (A2) is sometimes expressed as MFR LL(A2) The MFR (g / 10 min) of linear low-density polyethylene (A2) is sometimes expressed as MFR LL (MFR LL(A2) (which may be expressed as "melt mass-flow rate") is the melt mass-flow rate measured at a temperature of 190°C and a load of 2.16 kg in accordance with JIS K7210-1:2014.

[0035] From the viewpoint of improving the stiffness of the foamed sheet, the MFR of the linear low-density polyethylene (A2) LL It is preferable that MFR is small. LL When the MFR of the linear low-density polyethylene (A2) is low, the linear low-density polyethylene (A2) is less likely to inhibit foaming even when the foaming ratio of the foamed layer is increased. LLThe MFR of the linear low-density polyethylene (A2) is preferably 8.0 g / 10 min or less, more preferably 5.0 g / 10 min or less, even more preferably 3.0 g / 10 min or less, particularly preferably 2.0 g / 10 min or less, and most preferably 1.5 g / 10 min or less. From the viewpoint of production stability when producing a foamed sheet by extrusion foaming, the MFR of the linear low-density polyethylene (A2) is LL is preferably 0.2 g / 10 min or more.

[0036] (Absolute value of difference in melt flow rate) The MFR of the linear low-density polyethylene (A2) measured under conditions of a temperature of 190°C and a load of 2.16 kg based on JIS K7210-1:2014 is LL The MFR of the low-density polyethylene (A1) measured under conditions of a temperature of 190°C and a load of 2.16 kg based on JIS K7210-1:2014 is defined as MFR LD In this case, MFR LL and MFR LD is defined as the absolute value of the difference between LD )-(MFR LL It is preferable that the value of [MFR] is 3.0 g / 10 min or less. The melt flow rate (MFR) (g / 10 min) of the low-density polyethylene (A1) is LL In the first embodiment, [|(MFR LD )-(MFR LL When the value of [|(MFR LD )-(MFR LL The value of [|(MFR LD )-(MFR LLWhen the value of [MFR] is 1.5 g / 10 min or less, the stiffness improvement effect is more reliably exhibited, and it is easier to maintain a high closed cell content even when the expansion ratio of the foamed layer of the foamed sheet is increased. In the description of the first embodiment, the MFR of the low-density polyethylene (A1) is expressed as MFR LD However, in the description of the second embodiment described later, the MFR of the low-density polyethylene (A1) is expressed as MFR LD(A1) It is sometimes written as:

[0037] (Tensile strength of linear low-density polyethylene (A2)) From the viewpoint of improving stiffness, the tensile strength (MPa) of the linear low-density polyethylene (A2) is preferably 10 MPa or more. From the viewpoint of further enhancing the effect of improving stiffness, the tensile strength (MPa) of the linear low-density polyethylene is more preferably 11 MPa or more, further preferably 12 MPa or more, and particularly preferably 13 MPa or more.

[0038] (Method for measuring tensile strength of linear low-density polyethylene (A2)) The tensile strength (MPa) of the linear low-density polyethylene (A2) can be measured using the same method as described for measuring the tensile strength of the low-density polyethylene (A1). Note that the tensile strength of the linear low-density polyethylene (B2) described later in the second embodiment can also be measured using the same method as for measuring the tensile strength (MPa) of the linear low-density polyethylene (A2).

[0039] (Melting point of linear low-density polyethylene (A2)) The melting point (°C) of the linear low-density polyethylene (A2) is preferably 110°C or higher and 130°C or lower, from the viewpoints of improving the extrusion stability of the foamed sheet and facilitating an increase in the closed cell ratio and cushioning properties. Furthermore, from the viewpoints of improving the extrusion stability of the foamed sheet and further increasing the closed cell ratio and cushioning properties, the melting point (°C) of the low-density polyethylene (A1) is more preferably 115°C or higher and 128°C or lower, and even more preferably 118°C or higher and 125°C or lower.

[0040] (Measuring method for melting point of linear low-density polyethylene (A2)) The melting point (°C) of the linear low-density polyethylene (A2) can be measured using a method similar to that described for measuring the melting point of the low-density polyethylene (A1) based on JIS K7121-1987. The melting point of the linear low-density polyethylene (B2) described later in the second embodiment can also be measured using a method similar to that for measuring the melting point of the linear low-density polyethylene (A2).

[0041] (Linear low-density polyethylene (A2) content) In the foam sheet according to the first embodiment, the content of the linear low-density polyethylene (A2) in the foam layer is 5% by mass or more and 45% by mass or less. The content (% by mass) of the linear low-density polyethylene (A2) refers to the ratio (% by mass) of the linear low-density polyethylene (A2) in the foam layer, where the total amount of polymers contained in the foam layer is taken as 100% by mass. In the first embodiment, when the content of the linear low-density polyethylene (A2) satisfies this range, the stiffness of the foam sheet can be improved. If the content of the linear low-density polyethylene (A2) is less than 5% by mass, the stiffness of the foam sheet may be insufficient. If the content of the linear low-density polyethylene (A2) exceeds 45% by mass, the extrusion temperature of the foam layer-forming melt becomes too high during production of the foam sheet, making it difficult to sufficiently cool the foam sheet. This may result in a decrease in the closed cell content of the resulting foam sheet and a deterioration in appearance. From the viewpoint of further enhancing the effect of improving stiffness, reducing the difficulty of cooling, and reducing the decrease in the closed cell content, the content (mass %) of linear low-density polyethylene is preferably 8 mass % or more and 40 mass % or less, more preferably 10 mass % or more and 35 mass % or less, and even more preferably 12 mass % or more and 30 mass % or less.

[0042] (Materials and content of other polymers) The foam layer of the foam sheet according to the first embodiment may contain "other polymers" other than the low-density polyethylene (A1) and the linear low-density polyethylene (A2), provided that the effects of the present invention are not impaired. Examples of the "other polymers" include thermoplastic resins such as high-density polyethylene (PE-HD), ethylene-vinyl acetate copolymer (EVA), and polystyrene-based resins, and elastomers such as ethylene-propylene rubber and styrene-butadiene-styrene block copolymers. From the viewpoints of ensuring sufficient cushioning properties of the foam sheet and enhancing recyclability, the content of the other polymer in the foam layer is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, particularly preferably 1 part by mass or less, and most preferably 0 part by mass, i.e., the polymer components constituting the foam layer consist solely of "low-density polyethylene (A1) and linear low-density polyethylene (A2)."

[0043] The foamed sheet according to the first embodiment has excellent stiffness (strength of stiffness) even when it has a high expansion ratio and a thin thickness, and is easy to work with when used for applications such as interleaving sheets for glass plates. The foamed sheet also has cushioning properties.

[0044] (Body strength) In this specification, the stiffness of a foamed sheet is evaluated based on a test for measuring the amount of sagging (mm).

[0045] (Sagging bending measurement test) The measurement of the sagging amount (mm) of a foam sheet can be performed as follows. Ten locations are randomly selected from the foam sheet, with the extrusion direction (MD) of the foam sheet aligned with the length direction of the test specimen. Test specimens are cut from each location with dimensions of 200 mm wide x 200 mm long x the same thickness as the foam sheet. Each of the resulting 10 test specimens is placed on a horizontal base so that it extends 100 mm from the edge of the base in the length direction of the test specimen. A weight is then placed on top of the test specimen to secure it in place. The length direction (MD) of the test specimen is aligned with the direction of extension of the test specimen. The top surface of the base is used as a reference position, and the vertical distance from the reference position to the bottom of the hanging test specimen is measured. This measurement is performed on each of the 10 test specimens to obtain a measurement value. The arithmetic mean of the obtained measurements is then calculated. The arithmetic mean value is then determined as the amount of sagging.

[0046] (25% compressive strength (kPa) measurement test) A foam sheet with high compressive strength can be said to have higher cushioning properties. Compressive strength can be measured by testing the 25% compressive strength (kPa) of a foam sheet. The 25% compressive strength (kPa) of a foam sheet is the compressive stress at 25% strain measured in accordance with JIS K 6767:1999. Several pieces of foam sheet measuring 50 mm long x 50 mm wide x the thickness of the foam sheet were cut out and stacked to create a laminate approximately 25 mm thick. Three laminates were prepared. Each of these laminates served as a test specimen. One of the specimens was compressed in the thickness direction using a compression tester at a compression rate of 10 mm / min, and the compressive stress (kPa) of the specimen at 25% compressive strain was measured. The compressive stress (kPa) was measured for each of the three specimens, and the arithmetic mean value of the measured compressive stresses was taken as the compressive stress at 25% compressive strain.

[0047] The foam sheet according to the first embodiment is also excellent in terms of the closed cell ratio of the foam sheet.

[0048] (closed cell ratio) The closed cell content of the foam sheet is preferably 45% or more. The higher the closed cell content of the foam sheet, the better the stiffness and cushioning performance of the foam sheet. From the viewpoint of obtaining a foam sheet with better cushioning performance, the closed cell content of the foam sheet is preferably 48% or more, more preferably 50% or more, and even more preferably 52% or more. The upper limit of the closed cell content of the foam sheet may be 90%, 85%, or even 80%.

[0049] (Method for measuring closed cell ratio) The closed cell percentage (%) of a foam sheet can be measured as follows. A foam sheet is cut from the center of its width to prepare multiple test pieces measuring 25 mm long x 25 mm wide x the thickness of the foam sheet. A test specimen is prepared by stacking multiple test pieces so that the total thickness (total thickness of the test pieces) is as close to 20 mm as possible. The actual volume (Vx(L)) of the test piece (the sum of the volume of the closed cells and the volume of the resin portion) is measured using an air-comparison hydrometer (e.g., Model 930 manufactured by Toshiba Beckman Corporation) according to Procedure C described in ASTM D2856-70. The closed cell percentage (%) of the test piece is calculated using the obtained value according to the following formula (1). The above measurement is performed on five test pieces, and the arithmetic average value is taken as the closed cell percentage (%) of the foam sheet.

[0050]

number

[0051] In the above formula (1), Va, W, and ρ are as follows: Va: Apparent volume (cm) of the specimen used for measurement 3 ) W: Mass of the specimen used in the measurement (g) ρ: Density of the entire resin constituting the foam layer (g / cm 3 )

[0052] (non-crosslinked) The foam sheet is preferably a non-crosslinked sheet. "Non-crosslinked" refers to a gel fraction of less than 5% (including 0). Non-crosslinked sheets can be obtained by avoiding the application of a process of forming a crosslinked structure in the base resin by reacting the base resin with a crosslinking agent such as a polyfunctional compound, or a process of forming a crosslinked structure in the foam sheet by electron beam irradiation, etc. Non-crosslinked sheets have an excellent balance between compressive strength and cushioning performance and can be produced inexpensively, so they can be widely used in applications such as cushioning materials used in packaging. They also have excellent recyclability.

[0053] (Method for measuring gel fraction) The gel fraction of a foam sheet can be determined as follows. Approximately 50 mg of foam sheet is precisely weighed and immersed in 25 ml of xylene at 130°C for 3 hours. The sheet is then filtered through a 200-mesh stainless steel wire mesh and washed with acetone. The insoluble matter remaining on the wire mesh is then vacuum-dried, and the mass (mg) of this insoluble matter is then precisely weighed, and the gel fraction (%) is calculated as a percentage according to the following formula (2). Note that the mass (mg) of the foam weighed in formula (2) is the mass of the foam sheet precisely weighed before immersion in xylene.

[0054]

number

[0055] [1-2 Manufacturing method of polyethylene resin foam sheet] The polyethylene-based resin foam sheet according to the first embodiment can be produced by, for example, the so-called extrusion foaming method. The polyethylene-based resin foam sheet according to the first embodiment obtained by the extrusion foaming method can be called, for example, an extruded polyethylene-based resin foam sheet. Next, an example of the extrusion foaming method will be described.

[0056] (Extruder) The extruder used to produce a polyethylene resin foam sheet can be a typical manufacturing apparatus for producing extruded foam sheets. An example will be described using an extruder as the manufacturing apparatus. The extruder is equipped with a die on the downstream side and is configured to extrude a foam layer-forming melt (described later) from the upstream side to the downstream side. The manufacturing apparatus preferably includes a mandrel, which is a cooling cylinder for cooling the cylindrical foam, downstream of the annular die, and a cutter for slicing the extruded and cooled cylindrical foam into a sheet foam. The manufacturing apparatus also preferably includes a winder for taking up the slicing sheet foam into a roll. Note that the upstream and downstream sides are defined based on the direction of transport of the raw resin. The manufacturing apparatus shown here is merely an example and is not limited thereto. The raw resin refers to the resin used to form the foam layer-forming melt. When forming a resin layer (described later in the second embodiment), the raw resin is defined for both the foam layer-forming melt and the resin layer-forming melt, and refers to the resin used to form each of the foam layer-forming melt and the resin layer-forming melt.

[0057] (Extrusion foaming) Low-density polyethylene (A1) and linear low-density polyethylene (A2) are fed into an extruder as raw resins, with additives added as needed. A physical foaming agent is also fed, and these are melt-kneaded to obtain a molten material for forming a foam layer. The resulting molten material for forming a foam layer is adjusted to a predetermined temperature, and the foamable resin molten material is extruded from the annular die under a pressure atmosphere (usually atmospheric pressure) lower than the pressure inside the extruder, and foams while being extruded, resulting in a tubular foam. This tubular foam is drawn along the mandrel and cut into sheets using a cutter or the like installed downstream of the mandrel to form a sheet foam, which is a polyethylene resin foam sheet. The sheet foam is then wound into a roll using a winder.

[0058] In the above description, an example was given in which the production apparatus was equipped with an annular die, but the die may be a T-die, and a foam sheet can also be produced by extrusion foaming through a T-die. Furthermore, although the case in which a tubular foam placed along a mandrel is cut to produce a sheet-like foam has been described, a sheet-like foam may also be produced by crushing a tubular foam formed using an annular die in the radial direction of the tubular foam and fusing the inner surfaces of the tubular foam together to form a sheet.

[0059] (Foamable resin melt) The foamable resin melt contains a low-density polyethylene (A1), a linear low-density polyethylene (A2), and a physical foaming agent. The low-density polyethylene (A1) and the linear low-density polyethylene (A2) are as described above, and therefore detailed description thereof will be omitted.

[0060] (physical foaming agent) The physical foaming agent is not particularly limited, but examples thereof include organic physical foaming agents and inorganic physical foaming agents. Examples of organic physical foaming agents include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, normal hexane, and isohexane; alicyclic hydrocarbons such as cyclopentane and cyclohexane; chlorinated hydrocarbons such as methyl chloride and ethyl chloride; and fluorohydrocarbons such as 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, 1-chloro-3,3,3-trifluoropropene (HCFO-1233zd), and 1,3,3,3-tetrafluoropropene (HFO-1234ze). Examples of inorganic physical foaming agents include inorganic molecules such as nitrogen, carbon dioxide, air, and water. The foam layer-forming melt may contain one or more physical foaming agents (e.g., a combination of normal butane and isobutane). From the viewpoints of compatibility with the low-density polyethylene (A1) and foamability, the foam layer-forming melt preferably contains an organic physical foaming agent as the physical foaming agent, and more preferably contains an organic physical foaming agent containing normal butane, isobutane, or a mixture thereof as the main component.

[0061] The amount of the physical foaming agent in the foam layer-forming melt may be determined depending on various conditions such as the type of physical foaming agent, the apparent density of the foam layer to be produced, etc. Taking a mixed butane consisting of 30 mass % isobutane and 70 mass % normal butane as an example, the amount of the physical foaming agent may be set to a value within the range of approximately 5 to 40 parts by mass, preferably 8 to 35 parts by mass, and more preferably 10 to 30 parts by mass, per 100 parts by mass of the total of the low-density polyethylene (A1) and the linear low-density polyethylene (A2).

[0062] A cell control agent is preferably added to the foam layer-forming melt. Inorganic or organic cell control agents can be used as the cell control agent. Examples of inorganic cell control agents 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 cell control agents 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 cell control agents. The cell control agent added to the foam layer-forming melt may be one type or a combination of two or more types. The amount of cell control agent added to the foam layer-forming melt can be appropriately determined depending on the type of physical foaming agent and the various conditions of the foam layer.

[0063] (additives) The foamable resin melt may contain, in addition to the above-mentioned low-density polyethylene (A1), linear low-density polyethylene (A2), physical foaming agent, and cell regulator, other additives as necessary. Examples of the other additives include shrinkage inhibitors, antioxidants, heat stabilizers, antistatic agents, conductivity-imparting agents, weather resistance agents, ultraviolet absorbers, flame retardants, antibacterial agents, inorganic fillers, etc.

[0064] [1-3 Actions and Effects] In the industrial fields where polyethylene-based resin foam sheets are used, such as cushioning materials for logistics and sheet materials functioning as interleaving sheets for glass plates, there is a demand for thin, highly shock-absorbing sheets. Furthermore, particularly when foam sheets are used as interleaving sheets for glass plates, there is a demand for high stiffness in order to improve the workability when inserting the foam sheet between glass plates and the work efficiency when removing the foam sheet from the glass plates after use. Therefore, there is a demand for polyethylene-based resin foam sheets that are thin but have high stiffness and high shock-absorbing properties.

[0065] In general, polyethylene-based resin foam sheets tend to have reduced stiffness and cushioning properties as their thickness decreases. Increasing the expansion ratio of a polyethylene-based resin foam sheet is considered to improve the cushioning properties of the polyethylene-based resin foam sheet. Increasing the expansion ratio is also desirable from the viewpoint of reducing the amount of resin used as a raw material for the polyethylene-based resin foam sheet (i.e., from the viewpoint of resource conservation). However, in general, polyethylene-based resin foam sheets tend to have reduced stiffness as their expansion ratio increases. In light of these points, and in order to meet the demands of the above-mentioned industrial fields, polyethylene-based resin foam sheets are required that have excellent cushioning properties and excellent stiffness even when they are thin and have a high expansion ratio.

[0066] The polyethylene-based resin foam sheet according to the first embodiment has a thin thickness because the total thickness is within a predetermined range. In the first embodiment, the base resin of the foam layer is low-density polyethylene (A1), and the sheet has excellent shock-absorbing properties. In addition, the apparent density (kg / m) of the polyethylene-based resin foam sheet is 3 ) is within a predetermined range. Therefore, the polyethylene resin foam sheet according to the first embodiment has a high expansion ratio.

[0067] The polyethylene-based resin foam sheet according to the first embodiment has specific physical properties and contains a linear low-density polyethylene (A2) having a specific structure within a predetermined range. That is, in the first embodiment, the linear low-density polyethylene (A2) is a copolymer of ethylene and an α-olefin having 8 carbon atoms, and the density and melt flow rate of the linear low-density polyethylene (A2) satisfy the predetermined ranges. Therefore, the polyethylene-based resin foam sheet according to the first embodiment has excellent cushioning properties and excellent stiffness even when it is thin and has a high expansion ratio. Although the reason why the stiffness of a foam sheet can be improved when the linear low-density polyethylene (A2) is a copolymer of ethylene and an α-olefin having 8 carbon atoms is not clear, it is believed that the linear low-density polyethylene (A2) has longer side chains (short-chain branches) than copolymers of ethylene and an α-olefin having 4 carbon atoms or copolymers of ethylene and an α-olefin having 6 carbon atoms, which are commonly used as linear low-density polyethylenes. This improves molecular entanglement with the low-density polyethylene (A1) having a long-chain branched structure in the foam layer-forming molten material, thereby enabling a good foaming state to be maintained when producing a foam sheet with a high expansion ratio. As a result, it is believed that the resulting foam sheet is more likely to suppress a decrease in the closed cell content even when the expansion ratio is high.

[0068] [2 Second embodiment] [2-1 Composition of polyethylene resin foam sheet] The polyethylene-based resin foam sheet according to the second embodiment of the present invention comprises a foam layer containing low-density polyethylene (A1) as a base resin and a resin layer laminated on at least one side of the foam layer. For example, as shown in FIGS. 1B and 1C, a polyethylene-based resin foam sheet (foam sheet 10) comprises a foam layer 11 and a resin layer 12. FIGS. 1B and 1C are cross-sectional views showing an example of the foam sheet 10 according to the second embodiment. FIG. 1C shows an example of the second embodiment. When the resin layer 12 is formed on both sides of the foam layer 11 as shown in FIG. 1C, the resin layer 12 formed on one side of the foam layer 11 and the resin layer 12 formed on the other side of the foam layer 11 may have the same or different configurations. The polyethylene-based resin foam sheet according to the second embodiment of the present invention is similar to the polyethylene-based resin foam sheet according to the first embodiment of the present invention, except for the inclusion of the resin layer. Unless otherwise specified, all descriptions relating to the polyethylene-based resin foam sheet according to the second embodiment of the present invention can be applied to all descriptions relating to the polyethylene-based resin foam sheet according to the first embodiment of the present invention.

[0069] (Foam layer) In the second embodiment, the foam layer has the same configuration as the foam layer described in the first embodiment, except that a resin layer is laminated thereon, and therefore, detailed description of the foam layer will be omitted in the second embodiment.

[0070] (Thickness of foam sheet) The thickness of the foam sheet according to the second embodiment is 0.05 mm or more and 3 mm or less. The thickness of the foam sheet according to the second embodiment is the total thickness of the foam layer and the resin layer. Considering the applicability of the foam sheet to applications requiring thinness, the thickness (mm) of the foam sheet is preferably 0.05 mm or more and 2.5 mm or less. Furthermore, from the same viewpoint as above, the upper limit of the thickness of the foam sheet is more preferably 2.0 mm, and even more preferably 1.5 mm. From the viewpoint of further improving the cushioning properties of the foam sheet, the lower limit of the thickness of the foam sheet is more preferably 0.08 mm, even more preferably 0.10 mm, and particularly preferably 0.15 mm.

[0071] (Apparent density ratio) The foamed sheet according to the second embodiment has an apparent density (kg / m 3 ) to the density of low density polyethylene (A1) (kg / m 3 ) is 20 or more and 80 or less. In the above formula of DPA / DT, DT represents the overall apparent density of the foam sheet, and DPA represents the density of the low-density polyethylene (A1), as explained in the first embodiment. The ratio (DPA / DT) can be said to be a value indicating the expansion ratio of the foam sheet. As in the first embodiment, the ratio (DPA / DT) of the foam sheet according to the second embodiment is preferably 25 or more, more preferably 30 or more, even more preferably 35 or more, particularly preferably 40 or more, and most preferably 45 or more, from the viewpoint of resource conservation and improving cushioning properties. Furthermore, from the viewpoint of easily maintaining stiffness of the foam sheet, the ratio (DPA / DT) is preferably 75 or less.

[0072] (Method for measuring apparent density of foam sheet) The apparent density of the foamed sheet according to the second embodiment can be measured by the same method as that for measuring the apparent density of the foamed sheet described in the first embodiment.

[0073] (resin layer) The resin layer preferably uses low-density polyethylene (B1) as the base resin. Regarding the resin layer, "using low-density polyethylene (B1) as the base resin" means that the proportion of low-density polyethylene (B1) exceeds 50% by mass in 100% by mass of the polymer constituting the base resin of the resin layer. From the viewpoint of improving the lamination state with the foamed layer, the proportion of low-density polyethylene (B1) in 100% by mass of the polymer constituting the resin layer is preferably 55% by mass or more, more preferably 60% by mass or more. Furthermore, from the viewpoint of improving the appearance and slip properties of the foamed sheet, the resin layer is preferably a non-foamed layer. However, the resin layer may contain a small amount of very small bubbles.

[0074] The low-density polyethylene (B1) may be of the same type (material, density, tensile strength, melting point, MFR, etc.) as the low-density polyethylene (A1) contained in the foamed layer, or may be of a different type (material, density, tensile strength, melting point, MFR, etc.) from the low-density polyethylene (A1).

[0075] (Low density polyethylene (B1)) The low-density polyethylene (B1) is a polyethylene resin having a long-chain branched structure, similar to the low-density polyethylene (A1) described in the first embodiment, and preferably has a density of 910 kg / m 3 More than 930kg / m 3 Less than or equal to 915 kg / m 3 More than 925kg / m 3 The density, tensile strength, melting point and MFR of the low-density polyethylene (B1) can be specified in the same manner as for the low-density polyethylene (A1), and it is preferable that each of the numerical ranges satisfies the same numerical ranges as for the low-density polyethylene (A1).

[0076] (Linear low-density polyethylene (B2)) The resin layer preferably contains a linear low-density polyethylene (B2) as a polymer in addition to the low-density polyethylene (B1) as the base resin. The linear low-density polyethylene (B2) is a copolymer of ethylene and an α-olefin having 8 carbon atoms, similar to the linear low-density polyethylene (A2) described in the first embodiment. The linear low-density polyethylene (B2) has a substantially linear polyethylene main chain and short-chain branches derived from the α-olefin having 8 carbon atoms. In the second embodiment, the foam layer contains the linear low-density polyethylene (A2) described in the first embodiment in addition to the low-density polyethylene (A1) as the base resin. The linear low-density polyethylene (A2) is a copolymer of ethylene and an α-olefin having 8 carbon atoms. In this way, by including the linear low-density polyethylene (B2), which is a copolymer of ethylene and an α-olefin having 8 carbon atoms, in the resin layer in addition to the foam layer, the stiffness strength of the foam sheet is further improved.

[0077] The ranges that the density and melt flow rate of the linear low-density polyethylene (B2) can take are the same as those of the linear low-density polyethylene (A2) described in the first embodiment. However, the linear low-density polyethylene (A2) and the linear low-density polyethylene (B2) do not necessarily have to be the same type. When the density and melt flow rate of the linear low-density polyethylene (B2) contained in the resin layer satisfy the above-mentioned ranges, the stiffness strength of the foamed sheet can be further improved.

[0078] In this specification, the melt flow rate of the linear low-density polyethylene (A2) and the melt flow rate of the linear low-density polyethylene (B2) are abbreviated as the MFR of the linear low-density polyethylene (A2) and the MFR of the linear low-density polyethylene (B2), respectively. In addition, in the description of the second embodiment, since the MFR of the linear low-density polyethylene (A2) and the MFR of the linear low-density polyethylene (B2) are common to both, unless a distinction is made between the MFR of the linear low-density polyethylene (A2) and the MFR of the linear low-density polyethylene (B2), both the MFR of the linear low-density polyethylene (A2) and the MFR of the linear low-density polyethylene (B2) will be referred to as the MFR. LL In the description of the second embodiment, when distinguishing between the MFR of the linear low-density polyethylene (A2) and the MFR of the linear low-density polyethylene (B2), the MFR of the linear low-density polyethylene (A2) and the MFR of the linear low-density polyethylene (B2) are respectively referred to as MFR LL(A2) , M.F.R. LL(B2) This also applies to low-density polyethylene (A1) and low-density polyethylene (B1). In other words, since the content is common to the MFR of low-density polyethylene (A1) and the MFR of low-density polyethylene (B1), when there is no particular distinction between the MFR of low-density polyethylene (A1) and the MFR of low-density polyethylene (B1), both the MFR of low-density polyethylene (A1) and the MFR of low-density polyethylene (B1) are referred to as MFR LD In the description of the second embodiment, when distinguishing between the MFR of the low-density polyethylene (A1) and the MFR of the low-density polyethylene (B1), the MFR of the low-density polyethylene (A1) and the MFR of the low-density polyethylene (B1) are respectively referred to as MFR LD(A1) , M.F.R. LD(B1) It is written as follows.

[0079] In the second embodiment, the MFR of the linear low-density polyethylene (B2) LL(B2) When the MFR satisfies the above range, the stiffness of the foamed sheet can be improved. LL(B2)More preferably, the viscosity is 8.0 g / 10 min or less, even more preferably 5.0 g / 10 min or less, even more preferably 3.0 g / 10 min or less, particularly preferably 2.0 g / 10 min or less, and most preferably 1.5 g / 10 min or less.

[0080] Therefore, in the second embodiment, the MFR LL(A2) and MFR LL(B2) From the viewpoint of improving the stiffness of the foamed sheet, the MFR LL(A2) and MFR LL(B2) are preferably all 3.0 g / 10 min or less, more preferably all 2.0 g / 10 min or less, and even more preferably all 1.5 g / 10 min or less.

[0081] In the foamed sheet according to the second embodiment, from the viewpoint of improving stiffness of the foamed sheet, the density (kg / m 3 ) is 915 kg / m 3 It is preferable that the saturation is 917 kg / m or more. 3 More preferably, it is 920 kg / m or more. 3 More preferably, it is 922 kg / m or more. 3 It is particularly preferable that the value is 925 kg / m or more. 3 From the viewpoint of production stability when producing a foamed sheet by extrusion foaming, the density (kg / m ) of the linear low-density polyethylene (B2) is preferably 1.0 or more. 3 ) is preferably 935 kg / m 3 More preferably, it is 930 kg / m or less. 3 The density (kg / m) of the linear low-density polyethylene (B2) is as follows: 3 ) was measured by measuring the density (kg / m) of the linear low-density polyethylene (A2) shown in the first embodiment. 3 ) can be measured by a method similar to that of

[0082] (Tensile strength of linear low-density polyethylene (B2)) From the viewpoint of improving stiffness, the tensile strength (MPa) of the linear low-density polyethylene (B2) is preferably 10 MPa or more, more preferably 11 MPa or more, even more preferably 12 MPa or more, and particularly preferably 13 MPa or more, similar to that of the linear low-density polyethylene (A2). The tensile strength of the linear low-density polyethylene (B2) can be measured by the same method as that for the linear low-density polyethylene (A2) described in the first embodiment above.

[0083] The melting point of the linear low-density polyethylene (B2) can be specified in the same manner as that of the linear low-density polyethylene (A2), and it is preferable that the numerical range thereof satisfies the same numerical range as that of the linear low-density polyethylene (A2).

[0084] (Absolute value of difference in melt flow rate) In the second embodiment, for both the foam layer and the resin layer, the melt flow rate (MFR) (g / 10 min) of the low-density polyethylene is LD In this case, the difference in melt flow rate is the MFR LL and MFR LD is defined as the absolute value of the difference between LD )-(MFR LL The melt flow rate (MFR) (g / 10 min) of the low-density polyethylene is preferably 3.0 g / 10 min or less. LL In the second embodiment, [|(MFR LD )-(MFR LL )│] is 3.0 g / 10 min or less, the stiffness of the foamed sheet can be improved. LD )-(MFR LL)│] is more preferably 1.5 g / 10 min or less, and even more preferably 1.0 g / 10 min or less. LD )-(MFR LL )│] is more preferably 2.5 g / 10 min or less.

[0085] Therefore, in the second embodiment, from the viewpoint of more effectively improving the stiffness of the foamed sheet, [|(MFR LD(A1) )-(MFR LL(A2) )│] and [│(MFR LD(B1) )-(MFR LL(B2) )│] is preferably 3.0 g / 10 min or less. As for the foam layer, the melt flow rate (MFR) (g / 10 min) of the low-density polyethylene (A1) is preferably 3.0 g / 10 min or less. LD(A1) The melt flow rate (MFR) (g / 10 min) of the linear low-density polyethylene (A2) was calculated as MFR LL(A2) In this case, [│(MFR LD(A1) )-(MFR LL(A2) )│] is preferably 3.0 g / 10 min or less, and from the viewpoint of more effectively improving stiffness of the foamed sheet, it is preferably 1.5 g / 10 min or less, and more preferably 1.0 g / 10 min or less. Regarding the resin layer, the melt flow rate (MFR) (g / 10 min) of the low-density polyethylene (B1) is LD(B1) The melt flow rate (MFR) (g / 10 min) of the linear low-density polyethylene (B2) was calculated as MFR LL(B2) In this case, [│(MFR LD(B1) )-(MFR LL(B2) )│] is preferably 3.0 g / 10 min or less, and more preferably 2.5 g / 10 min or less.

[0086] In the second embodiment, [|(MFR LD )-(MFR LL )│], [│(MFR LD(A1) )-(MFR LL(A2) )│] and [│(MFRLD(B1) )-(MFR LL(B2) The values ​​of |)|] may be the same or different as long as they each satisfy the above-mentioned numerical range.

[0087] (Linear low-density polyethylene (B2) content) In the foamed sheet according to the second embodiment, the content of the linear low-density polyethylene (B2) in the resin layer is preferably 5% by mass or more and 45% by mass or less. However, the content (% by mass) of the linear low-density polyethylene (B2) indicates the ratio (% by mass) of the content of the linear low-density polyethylene (B2) in the resin layer when the total amount of the polymer contained in the resin layer is taken as 100 (% by mass). In this specification, the content of the linear low-density polyethylene (B2) is referred to as MW LL(B2) In the second embodiment, the MW LL(B2) When the value of MW satisfies such a range, the surface condition of the foamed sheet can be improved and the stiffness of the foamed sheet can be improved. From the viewpoint of further enhancing this effect, the content of the linear low-density polyethylene (B2), MW LL(B2) (% by mass) is more preferably 8% by mass or more and 40% by mass or less, even more preferably 10% by mass or more and 35% by mass or less, and particularly preferably 12% by mass or more and 30% by mass or less. From the viewpoint of further improving the adhesion between the foam layer and the resin layer, the mass ratio of the low-density polyethylene (B1) to the linear low-density polyethylene (B2) in the resin layer, when the total of both is taken as 100% by mass, is preferably low-density polyethylene (B1):linear low-density polyethylene (B2)=95:5 to 50:50, more preferably 90:10 to 60:40.

[0088] In the second embodiment, the content of the linear low-density polyethylene (B2) and the content of the linear low-density polyethylene (A2) may be the same or different as long as they satisfy the above-mentioned numerical ranges. In this specification, the content of the linear low-density polyethylene (A2) is defined as the MW LL(A2)It is sometimes written as:

[0089] (Difference in linear low-density polyethylene content between resin layer and foam layer) MW, which is the content of linear low-density polyethylene (B2) in the resin layer LL(B2) (mass%) and the MW of the linear low-density polyethylene (A2) in the foam layer LL(A2) The absolute value of the difference (mass%) ([|(MW LL(B2) )-(MW LL(A2) )|]) is preferably 15% by mass or less (including 0), more preferably 10% by mass or less (including 0), and even more preferably 5% by mass or less (including 0). LL(B2) )-(MW LL(A2) When the value of [Ratio] satisfies the above-mentioned range, the resin compositions constituting the resin layer and the foam layer are similar to each other, and the laminated state of the resin layer and the foam layer can be improved.

[0090] (Other resin materials and content) The resin layer of the foam sheet according to the second embodiment may contain "other polymers" other than the low-density polyethylene (B1) and the linear low-density polyethylene (B2), provided that the effects of the present invention are not impaired. Examples of the "other polymers" include thermoplastic resins such as high impact polystyrene (HIPS) and polystyrene-based resins (GPPS), and elastomers such as ethylene-propylene rubber and styrene-butadiene-styrene block copolymers (SEBS). The content of the other polymers in the resin layer is preferably 30 parts by mass or less, and more preferably 25 parts by mass or less, per 100 parts by mass of the total of the low-density polyethylene (B1) and the linear low-density polyethylene (B2).

[0091] (polymer antistatic agent) In the second embodiment, the resin layer may contain a polymeric antistatic agent, such as polyether, polyether ester amide, a block copolymer of polyether and polyolefin, or an ionomer resin.

[0092] According to the foam sheet of the second embodiment, the resin layer contains a polymeric antistatic agent, which makes the foam sheet more likely to exhibit antistatic properties. In this case, adhesion of dust and dirt to the surface of the foam sheet is suppressed, making the foam sheet suitable for use as, for example, packaging materials for precision instruments such as electronic devices, interleaving sheets for glass plates, and the like.

[0093] From the viewpoint of imparting antistatic properties to the foam sheet, the surface resistivity of the polymeric antistatic agent is preferably 1×10 8 Ω or less, and more preferably 5×10 7 Ω or less. Specific examples of such polymeric antistatic agents include block copolymers of polyether and polyolefin, such as "Pelestat 300," "Pelestat 230," "Pelestat HC250," "Pelestat PVH," "Pelestat PVL," "Pelestat HS," and "Pelestat LMP," manufactured by Sanyo Chemical Industries, Ltd. Examples of ionomer resins that can be used as polymeric antistatic agents include those commercially available under the trade names "Entira SD100" and "Entira MK400," manufactured by DuPont-Mitsui Polychemicals Co., Ltd.

[0094] The block copolymers cited as examples of polymeric antistatic agents include those having a structure in which polyolefin blocks and polyether blocks are repeatedly and alternately bonded via bonds such as ester bonds, amide bonds, ether bonds, urethane bonds, imide bonds, etc. Ionomer resins are metal salt crosslinked copolymers of copolymers of ethylene and carboxylic acids such as acrylic acid, methacrylic acid, and maleic acid, and examples of metal salts used to form the metal salt crosslinked copolymers include alkali metal salts, alkaline earth metal salts, typical metal salts, and transition metal salts, among which potassium ionomers containing potassium salts are preferred.

[0095] In the foam sheet according to the second embodiment, the resin layer contains a polymeric antistatic agent, which not only provides antistatic properties but also facilitates an increase in the foaming ratio of the foam layer. Although the reason for this is unclear, it is believed that when the resin layer contains a polymeric antistatic agent, the resin layer functions as a gas barrier layer during the production of the foam sheet, making it difficult for the physical foaming agent contained in the foam layer to diffuse out of the foam sheet.

[0096] In the foamed sheet according to the second embodiment, it is preferable that the resin layer contains an ionomer resin from the viewpoint of further improving the gas barrier properties of the resin layer and increasing the expansion ratio of the foamed layer. From the viewpoint of increasing the expansion ratio of the foamed layer, the ionomer resin may not exhibit antistatic properties. However, from the viewpoint of being more suitable for applications such as glass interleaf paper, it is preferable that the ionomer resin exhibits antistatic properties. In this case, the resin layer contains the ionomer resin as a polymeric antistatic agent.

[0097] Furthermore, from the viewpoint of exhibiting antistatic properties and suitably using the foam sheet according to the second embodiment for applications such as slip sheets between glass plates, and from the viewpoint of the effect of increasing the expansion ratio of the foam layer, it is preferable that the resin layer is formed on both sides of the foam layer. By forming the resin layer on both sides of the foam layer, the resin layer functions as a gas barrier layer, and it is possible to more effectively realize a state in which the physical foaming agent contained in the foam layer is less likely to diffuse to the outside of the foam sheet.

[0098] From the viewpoint of exhibiting antistatic properties, the content of the polymer antistatic agent in the resin layer is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 25% by mass or less, when the total of the low-density polyethylene (B1) and the linear low-density polyethylene (B2) is taken as 100% by mass.

[0099] Furthermore, when the resin layer contains an ionomer resin, from the viewpoint of making the resin layer function easily as a gas barrier layer, the content thereof is preferably from 5% to 35% by mass, and more preferably from 10% to 20% by mass, where the total of the low-density polyethylene (B1) and the linear low-density polyethylene (B2) is taken as 100% by mass.

[0100] (Other additives) The resin layer of the foam sheet according to the second embodiment may optionally contain the aforementioned "other polymers," low-density polyethylene (B1), linear low-density polyethylene (B2), and "other additives" excluding polymeric antistatic agents. Examples of other additives that may be added to the resin layer include talc. Other additives that may be added to the resin layer include antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, antibacterial agents, and inorganic fillers. Adding talc to the resin layer can improve the slipperiness of the foam sheet, resulting in a foam sheet with superior handleability. From the viewpoint of efficient expression of the effects, the amount of talc added to the resin layer is preferably 3% by mass or more and 25% by mass or less, and more preferably 5% by mass or more and 20% by mass or less, based on 100% by mass of the total of the low-density polyethylene (B1) and the linear low-density polyethylene (B2).

[0101] [2-2 Manufacturing method of polyethylene resin foam sheet] The polyethylene-based resin foam sheet according to the second embodiment can be produced, for example, by a co-extrusion foaming method. In the co-extrusion foaming method, a foam layer-forming melt and a resin layer-forming melt are co-extruded to obtain a sheet having a polyethylene-based resin foam layer and a resin layer provided on at least one side of the polyethylene-based resin foam layer. The co-extrusion foaming method is included in the concept of the extrusion foaming method. The polyethylene-based resin foam sheet according to the second embodiment obtained by the extrusion foaming method can be referred to as a multi-layer extruded polyethylene-based resin foam sheet. Next, the description will be continued with an example of the method for producing a foam sheet.

[0102] (Co-extrusion equipment) An example of an extrusion device that can be used to produce a foam sheet is a co-extrusion device applicable in the technical field of extrusion foaming. A specific example of a co-extrusion device is a co-extrusion device equipped with an extruder for forming a foam layer configured to extrude a melt for forming a foam layer, an extruder for forming a resin layer configured to extrude a melt for forming a resin layer, and a co-extrusion die to which the outlets of the extruder for forming the foam layer and the extruder for forming the resin layer are connected. In such a co-extrusion device, a multi-layer extruded foam sheet can be produced by co-extruding the melt for forming the foam layer and the melt for forming the resin layer through the co-extrusion die. An example of the co-extrusion die is an annular die, such as a circular die.

[0103] In the co-extrusion device, it is preferable that the co-extrusion die connected to the extruder for forming the resin layer is configured so as to be able to extrude the molten material for forming the resin layer so as to form a resin layer that is provided on the desired surface of the foam layer.

[0104] (Melted material for forming foam layer) As described in the first embodiment, the melt for forming a foam layer contains low-density polyethylene (A1), linear low-density polyethylene (A2), and a physical foaming agent. The melt for forming a foam layer can be obtained, for example, by the following method. The low-density polyethylene (A1) and linear low-density polyethylene (A2) are fed into an extruder for forming a foam layer, and the mixture is melt-kneaded. The physical foaming agent is fed under pressure to the melt containing the branched low-density polyethylene molten in the extruder for forming a foam layer, and the melt to which the physical foaming agent has been fed is further kneaded. This allows the melt for forming a foam layer to be obtained.

[0105] (physical foaming agent) The physical foaming agent may be any of the various compounds described in the first embodiment.

[0106] (Foam regulators and other additives) The foam layer-forming melt may contain the cell control agent described in the first embodiment. As described in the first embodiment, additives may be added to the foam layer-forming melt as needed in addition to the low-density polyethylene (A1), the linear low-density polyethylene (A2), the physical foaming agent, and the cell control agent.

[0107] (Melted material for forming resin layer) The melt for forming the resin layer contains a low-density polyethylene (B1) and preferably a linear low-density polyethylene (B2). The low-density polyethylene (B1) and the linear low-density polyethylene (B2) are as explained above, so detailed explanations will be omitted. The melt for forming the resin layer can be obtained, for example, by the following method. The low-density polyethylene (B1) and the linear low-density polyethylene (B2) are fed into an extruder for forming a resin layer and melt-kneaded.

[0108] Other additives may be supplied to the extruder for forming the resin layer as needed. This allows a melt for forming the resin layer to be obtained. Specifically, for example, a polymeric antistatic agent may be added as an additive to the melt for forming the resin layer. The polymeric antistatic agent has been described above, so a detailed description will be omitted. Examples of other additives that can be added to the melt for forming the resin layer include various additives that can also be added to the melt for forming the foam layer.

[0109] (volatile plasticizer) The resin layer-forming melt may contain a volatile plasticizer, which has the effect of reducing the melt viscosity of the resin layer-forming melt and is configured to be unlikely to remain in the foamed sheet, i.e., to volatilize from the resin layer after coextrusion.

[0110] The volatile plasticizer contained in the resin layer-forming melt is preferably one or more selected from the group consisting of hydrocarbons having 3 to 5 carbon atoms, alcohols, and dialkyl ethers. These volatile plasticizers can appropriately plasticize the resin layer-forming melt and improve the melt elongation of the resin layer-forming melt. Furthermore, the layer of the resin layer-forming melt is more likely to elongate in response to the expansion of the layer of the foam layer-forming melt accompanying the foaming of the foam layer-forming melt. Therefore, even if the extrusion temperature of the resin layer-forming melt is brought close to the extrusion temperature of the foam layer-forming melt, the risk of cracks or the like occurring in the resin layer can be suppressed. As a result, the resin layer can be formed satisfactorily.

[0111] Examples of hydrocarbons having 3 to 5 carbon atoms that can be used as volatile plasticizers include propane, isobutane, normal butane, pentane, and hexane. Examples of alcohols include aliphatic alcohols having 1 to 4 carbon atoms. Specific examples of alcohols include methyl alcohol, ethyl alcohol (ethanol), n-propyl alcohol, i-propyl alcohol, and butyl alcohol. Among these, ethanol is preferred from the viewpoints of ease of handling and safety. Examples of dialkyl ethers include aliphatic dialkyl ethers having 2 to 8 carbon atoms. Specific examples of dialkyl ethers include dimethyl ether, diethyl ether, diisopropyl ether, and dibutyl ether. Among these, dimethyl ether is preferred from the viewpoints of ease of handling and safety. The volatile plasticizer added to the resin layer-forming melt may be one of the above-mentioned compounds, or a combination of two or more of them.

[0112] The boiling point of the volatile plasticizer is preferably 120°C or lower, and more preferably 80°C or lower. Volatile plasticizers with boiling points in this range tend to spontaneously volatilize from the resin layer after coextrusion and are easily removed from the resin layer. The lower limit of the boiling point of the volatile plasticizer is preferably approximately -50°C.

[0113] The amount of volatile plasticizer contained in the resin layer-forming melt (if the volatile plasticizer is composed of a combination of multiple types of compounds, the total amount of each compound) is preferably 1 part by mass or more and 30 parts by mass or less, and more preferably 10 parts by mass or more and 25 parts by mass or less, when the total amount of the resin layer-forming melt excluding the volatile plasticizer is 100 parts by mass, from the viewpoint of achieving both the effect of reducing the melt viscosity of the resin layer-forming melt and rapid evaporation from the resin layer.

[0114] (coextrusion) The co-extrusion of the foam layer-forming melt and the resin layer-forming melt described above can be carried out, for example, as follows. In a co-extrusion device, the foam layer-forming melt is introduced from the foam layer-forming extruder to a co-extrusion die. The resin layer-forming melt is introduced from the resin layer-forming extruder to a co-extrusion die and extruded to the outside through an extrusion opening of the co-extrusion die. When the co-extrusion die is a circular die, for example, in the case of forming resin layers on both sides of a foam layer, a three-layer laminated melt consisting of a resin layer-forming melt, a foam layer-forming melt, and a resin layer-forming melt is formed, and the laminated melt is extruded in a cylindrical shape from the co-extrusion die. When the laminated melt is extruded into the atmosphere from the extrusion opening, the foam layer-forming melt expands while foaming, forming a foam layer. Accordingly, a cylindrical laminated foam is formed in which resin layers are laminated on both sides of the foam layer. The cylindrical laminated foam is expanded from the inside with compressed air or the like, and the inside of the cylindrical laminated foam is drawn along an expanding device such as a mandrel and cooled with a roller or the like, thereby solidifying the foam layer and the resin layer. This largely fixes the cell structure formed in the foam layer. The cylindrical laminated foam is then cut open on the expanding device. This results in a foam sheet having a foam layer and a resin layer provided thereon.

[0115] In the above description of the method for producing a multilayer extruded foam sheet, the co-extrusion die was an annular die, but the co-extrusion die may also be a flat die. In this case, a laminated melt is extruded into a sheet form from the extrusion port of the flat die. When the laminated melt is extruded into the atmosphere from the extrusion port, the melt for forming the foam layer expands while foaming. This forms a sheet-like laminated foam comprising a foam layer and a resin layer laminated together. The sheet-like laminated foam extruded from the extrusion port is then drawn along a width-expanding device and cooled, solidifying the foam layer and the resin layer. This fixes the cell structure of the foam layer and stabilizes its dimensions. This allows a foam sheet to be obtained.

[0116] [2-3 Actions and Effects] The foam sheet according to the second embodiment has excellent cushioning properties and excellent stiffness even when the foam layer has a high expansion ratio and a small thickness, and can achieve the same effects as those of the first embodiment.

[0117] Furthermore, in the foamed sheet according to the second embodiment, when the resin layer contains a polymeric antistatic agent, preferably when the polymeric antistatic agent is an ionomer resin, the expansion ratio of the foamed layer can be increased more efficiently. Specifically, a foamed sheet with a desired expansion ratio can be produced with a smaller amount of foaming agent.

[0118] [3. Application Examples] The foamed sheet according to the present invention has excellent stiffness and cushioning properties even when the foam layer has a high expansion ratio and a thin thickness, and therefore can be suitably used as a sheet material that functions as a cushioning material for packaging or an interleaf sheet for glass plates. Examples of the cushioning material for packaging include cushioning materials for packaging electronic devices, fruits, etc.

[0119] Next, a more detailed explanation will be given using examples. [Example]

[0120] As foam sheet manufacturing apparatuses, an extrusion apparatus and a co-extrusion apparatus were prepared.

[0121] (Extrusion equipment) The extrusion device was equipped with an extruder for forming a foam layer and a circular extrusion die (diameter 96 mm) connected downstream of the extruder for forming a foam layer.

[0122] (Co-extrusion equipment) The co-extrusion device is equipped with an extruder for forming a foam layer, an extruder for forming a resin layer, and an annular die for co-extrusion (diameter 96 mm) connected to the extruder for forming the foam layer and the extruder for forming the resin layer. The annular die for co-extrusion is configured to be able to form a laminate having a two-kind, three-layer laminate structure in which a melt for forming a resin layer, a melt for forming a foam layer, and a melt for forming a resin layer are laminated in this order.

[0123] (low density polyethylene) Two types of low-density polyethylene were prepared as shown in Table 1. The two types of low-density polyethylene are designated LDPE1 and LDPE2 as shown in the resin type column in Table 1. LDPE1 is used as the low-density polyethylene (B1) contained in the resin layer. LDPE2 is used as the low-density polyethylene (A1) contained in the foam layer.

[0124] In Table 1, in addition to the resin type, the manufacturer name, product name, density (g / cm 3 ), MFR (g / 10 min), melting point (°C) and tensile strength (MPa). 3 ), MFR (g / 10 min), melting point (°C) and tensile strength (MPa) can be measured by the methods explained in the above-mentioned methods for measuring the density of low-density polyethylene (A1), method for measuring the MFR (g / 10 min) of low-density polyethylene (A1), method for measuring the melting point of low-density polyethylene (A1), and method for measuring the tensile strength of low-density polyethylene (A1), respectively.

[0125] (linear low-density polyethylene) Four types of linear low-density polyethylene were prepared, as shown in Table 1. The four types of linear low-density polyethylene are designated LLDPE1, LLDPE2, LLDPE3, and LLDPE4, as listed in the resin type column of Table 1. The C8 entry in the comonomer column of Table 1 indicates that the copolymerized copolymer with ethylene is an α-olefin with eight carbon atoms. The C4 entry in the comonomer column of Table 1 indicates that the copolymerized copolymer with ethylene is an α-olefin with four carbon atoms. The C6 entry in the comonomer column of Table 2 indicates that the copolymerized copolymer with ethylene is an α-olefin with six carbon atoms. Therefore, both LLDPE1 and LLDPE2 are copolymers of ethylene and an α-olefin with eight carbon atoms. LLDPE3 is a copolymer of ethylene and an α-olefin with four carbon atoms. LLDPE4 is a copolymer of ethylene and an α-olefin with six carbon atoms. Both LLDPE1 and LLDPE2 may be used as the linear low-density polyethylene (A2), and both may be used as the linear low-density polyethylene (B2).

[0126] In Table 1, in addition to the resin type and comonomer, the manufacturer name, grade (product name), density (g / cm ) and other information are listed for LLDPE1, LLDPE2, LLDPE3 and LLDPE4. 3 ), MFR (g / 10 min), melting point (°C) and tensile strength (MPa). 3 ), MFR (g / 10 min), melting point (°C) and tensile strength (MPa) can be measured by the methods shown in the above-mentioned methods for measuring the density of linear low-density polyethylene (A2), method for measuring MFR (g / 10 min) of linear low-density polyethylene (A2), method for measuring the melting point of linear low-density polyethylene (A2), and method for measuring tensile strength of linear low-density polyethylene (A2), respectively.

[0127] (foaming agent) The blowing agents used were i-Bu (isobutane) and s-Bu (silver butane). i-Bu (isobutane) and s-Bu (silver butane) are physical blowing agents. s-Bu refers to a mixed butane consisting of 70% by weight of normal butane and 30% by weight of isobutane.

[0128] (additives) As additives, talc and polymeric antistatic agents were prepared as shown in Tables 2 to 4.

[0129] (talc) The talc used was a talc masterbatch (talc concentration 20% by mass) prepared by blending 80% by mass of low-density polyethylene ("LA500M" manufactured by Japan Polyethylene Corporation, MFR measured at 190°C under a load of 2.16 kg is 4 g / 10 min) with 20% by mass of talc (manufactured by Matsumura Sangyo Co., Ltd., trade name "Hi Filler #12"). In Tables 2 to 4, the talc masterbatch is referred to as "Talc MB." Talc can function as a cell regulator and a slippage improver. The low-density polyethylene used as the base resin of the talc masterbatch corresponds to low-density polyethylene (A1) and low-density polyethylene (B1).

[0130] (polymer antistatic agent) As the polymer-type antistatic agent (in Tables 2 to 4, the polymer-type antistatic agent is abbreviated as ASP), an ethylene-based potassium ionomer resin manufactured by DuPont-Mitsui Polychemicals Co., Ltd., trade name "Entira SD100" (MFR 5 g / min, melting point 92°C, surface resistivity 1.0 × 10 7 Ω), a polyether-polyolefin block copolymer manufactured by Sanyo Chemical Industries, Ltd., trade name "Pelectron LMP" (MFR 42 g / min, melting point 116°C, surface resistivity 8.0 x 10 6 In Tables 2 to 4, the product Entira SD100 manufactured by DuPont-Mitsui Polychemicals Co., Ltd. is listed as SD100 in the grade column, and the product Pelektron LMP manufactured by Sanyo Chemical Industries, Ltd. is listed as LMP in the grade column.

[0131] (volatile plasticizer) As the volatile plasticizer, s-Bu (silver butane) and EtOH were prepared as shown in Tables 2 to 4. EtOH represents ethanol.

[0132] (other resins) In addition to low-density polyethylene and linear low-density polyethylene, SEBS and HIPS were also prepared as shown in Tables 2 to 4. SEBS refers to a styrene-ethylene-butylene-styrene block copolymer (manufactured by Asahi Kasei Corporation, product name Tuftec H1041). HIPS refers to high-impact polystyrene (manufactured by PS Japan Co., Ltd., product name 408).

[0133] [Table 1]

[0134] Examples 1 to 6 (Melted material for forming foam layer) Using a co-extrusion device, low-density polyethylene, linear low-density polyethylene, and a physical foaming agent (simply referred to as "foaming agent" in Tables 2 to 4) were fed into the extruder for forming the foam layer under the conditions of the resin types and blending amounts shown in the "Foam Layer" column in Table 2, and these were melt-kneaded. Furthermore, talc (manufactured by Matsumura Sangyo Co., Ltd., product name "Hi-Filler #12") was fed in an amount of 0.4 parts by mass per 100 parts by mass of the low-density polyethylene and linear low-density polyethylene combined, and further melt-kneaded. This produced a molten material for forming the foam layer. The physical foaming agent was i-Bu.

[0135] In Table 2, low density polyethylene and linear low density polyethylene are shown in the LDPE and LLDPE columns, respectively. The blending amount (parts by mass) of the physical foaming agent is shown when the total of the low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) that make up the molten material for forming the foam layer is taken as 100 parts by mass. The LDPE column in Table 2 also shows the MFR (g / 10 min). Furthermore, the LLDPE column in Table 2 shows the MFR (g / 10 min) value and the MFR of LLDPE (MFR LL (g / 10min) and MFR of LDPE (MFR LD The absolute value of the difference between the (g / 10min) and the (MFR LD )-(MFR LL ) |] and tensile strength (MPa) are also shown. The same applies to Tables 3 and 4. LD )-(MFR LL The value (g / 10 min) of [MFR difference from LDPE] is shown in the "Absolute value of the difference in MFR from LDPE" column in Tables 2 to 4.

[0136] (Melted material for forming resin layer) Low-density polyethylene and linear low-density polyethylene were supplied to the extruder for forming the resin layer, and melt-kneaded, under the conditions of the resin type and blending amount shown in the resin layer column in Table 2. Depending on the example, additives such as polymeric antistatic agent (ASP) and talc (talc MB), resins such as SEBS and HIPS, and a volatile plasticizer were supplied to the extruder for forming the resin layer under the conditions of the resin type and blending amount shown in Table 2. This formed a melt for forming the resin layer.

[0137] In Table 2, the resin type and blending amount of each low-density polyethylene and linear low-density polyethylene are shown in the LDPE and LLDPE columns of the resin layer column, respectively. The LDPE and LLDPE columns of the resin layer column in Table 2 also show the MFR (g / 10 min). The blending amounts (mass%) of ASP, talc MB, and SEBS, HIPS, and other resins added to the resin layer-forming melt shown in Table 2 are calculated based on the total amount of the resin layer-forming melt being 100 mass%. The blending amount (parts by mass) of volatile plasticizer shown in Table 2 is calculated based on the total amount of each component constituting the resin layer-forming melt, excluding the volatile plasticizer, being 100 mass parts. The same information regarding blending amounts shown in Table 2 applies to Tables 3 and 4.

[0138] (Extrusion process) The melt for forming the foam layer is adjusted to the resin temperature shown in Table 2 (the temperature listed in the resin temperature column for the foam layer) and then transferred to the annular die for co-extrusion connected downstream of the extruder for forming the foam layer. The melt for forming the resin layer is adjusted to the resin temperature shown in Table 2 (the temperature listed in the resin temperature column for the resin layer) and then transferred to the annular die connected downstream of the extruder for forming the resin layer. The melt for forming the resin layer and the melt for forming the foam layer are extruded from the annular die for co-extrusion. The output rates (kg / h) of the melt for forming the resin layer and the melt for forming the foam layer are as shown in Table 2. At this time, a cylindrical laminate is formed having a layered structure in which the melt for forming the resin layer, the melt for forming the foam layer, and the melt for forming the resin layer are layered in this order from the inside. Within the laminate, the layer of the melt for forming the foam layer is foamed, and a cylindrical foam is obtained. The cylindrical foam was cut open with a cutter while being cooled on a 350 mm diameter mandrel, and then taken up into a roll by a winder (roller) at the take-up speed (m / min) shown in Table 2, to obtain a foam sheet. The resin layers of these foam sheets were all in a non-foamed state. The foam sheets of Examples 1 to 6 correspond to the polyethylene-based resin foam sheet of the second embodiment described above, and are examples of multi-layer extruded polyethylene-based resin foam sheets.

[0139] The thickness (mm), basis weight (g / m2) of the obtained foamed sheet 2 ), apparent density (kg / m 3 ), and the closed cell ratio (%) of the foamed sheet were measured. The results of each measurement are shown in Table 2. Table 2 also shows the LLDPE content (mass%) and expansion ratio (times). The LLDPE content (mass%) indicates the content of LLDPE constituting the foamed layer when the total amount (mass) of polymers constituting the foamed layer is taken as 100 (100 mass%). The expansion ratio is the apparent density (kg / m) of the entire foamed sheet. 3 ) to the density of low density polyethylene (A1) (kg / m 3 ) (values ​​corresponding to the above-mentioned ratio (DPA / DT)). In Table 2, the closed cell percentage (%) of the foamed sheet is simply described as the closed cell percentage (%). The thickness (mm), basis weight (g / m2) of the foamed sheet shown here are 2 ), apparent density (kg / m 3 The same applies to Tables 3 and 4 with respect to the closed cell ratio (%), LLDPE content (mass %), and expansion ratio (times).

[0140] For the foam sheet, the thickness (mm) is the total thickness and can be measured according to the method described above. The basis weight (g / m 2 ), apparent density (kg / m 3 The thickness (mm), basis weight (g / m 2 ) and closed cell content (%) of the foamed sheet can also be measured by the method described above. 2 ), apparent density (kg / m 3 The same applies to Tables 3 and 4 with respect to the measurement methods for the closed cell ratio (%) and the closed cell content (%).

[0141] (amount of sagging) Furthermore, the amount of sagging in the MD direction (extrusion direction of the foam sheet) of the obtained foam sheet was measured. The method for measuring the amount of sagging was as described above. The measurement results are shown in Table 2. If the amount of sagging (mm) is 6 mm or less, it can be determined that the foam sheet has sufficient stiffness, and is preferably 5 mm or less, more preferably 4 mm or less, and even more preferably 3 mm or less.

[0142] Examples 7 and 8 The foamed sheets obtained in Examples 7 and 8 have a foamed layer, and unlike Examples 1 to 6, do not have a resin layer formed thereon.

[0143] Using an extrusion device, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and a physical foaming agent were fed into the extruder under the resin types and blending amounts shown in the "Foam Layer" column in Table 3, and then kneaded. This produced a melt for forming a foam layer. As in Example 1, the melt for forming a foam layer was adjusted to the resin temperature shown in Table 3, and then extruded from an annular die connected downstream of the extruder for forming a foam layer at the throughput rate (kg / h) shown in Table 3 to obtain a tubular foam. As in Example 1, the tubular foam was cut open with a cutter while being cooled on a mandrel, and taken up into a roll by a winder (roller) at the take-up speed (m / min) shown in Table 3 to obtain a foam sheet. The foam sheets of Examples 7 and 8 correspond to the polyethylene-based resin foam sheet of the first embodiment described above and are examples of extruded polyethylene-based resin foam sheets.

[0144] The thickness (mm) and basis weight (g / m) of the obtained foamed sheet were measured in the same manner as in Examples 1 to 6. 2 ), apparent density (kg / m 3 The foamed sheet was measured for the closed cell ratio (%) and the closed cell content (%) of the foamed sheet. The measurement results are shown in Table 3. In Examples 7 and 8 of Table 3, the LLDPE content (% by mass) and the expansion ratio (times) are shown, similarly to Examples 1 to 6.

[0145] Furthermore, the amount of sagging (mm) in the MD direction of the obtained foamed sheet was measured. The amount of sagging (MD direction) was measured in the same manner as in Example 1. The measurement results are shown in Table 3.

[0146] (25% compressive strength) The foamed sheet was also measured for 25% compressive strength (kPa). The 25% compressive strength (kPa) is the compressive stress (kPa) at 25% strain, and was measured according to JIS K 6767:1999 as described above. The measurement results are shown in Table 3.

[0147] Examples 9 and 10 For Examples 9 and 10, the same method as in Examples 1 to 6 was applied, except that the resin types and other details (raw material blend details) constituting the resin layer and the foam layer were configured as shown in Table 3. The resin layers of these foam sheets were all in a non-foamed state. The foam sheets of Examples 9 and 10 correspond to the polyethylene resin foam sheet according to the second embodiment described above. The thickness (mm), basis weight (g / m2), and other parameters of the obtained foam sheets were measured in the same manner as in Examples 1 to 6. 2 ), apparent density (kg / m 3 The foam sheet was measured for its closed cell content (%) and sagging (mm). The results of each measurement are shown in Table 3. In Examples 9 and 10 of Table 3, the LLDPE content (% by mass) and expansion ratio (times) are shown, similarly to Examples 1 to 6.

[0148] Comparative Example 1 Comparative Example 1 was carried out in the same manner as in Examples 1 to 6, except that the resins (raw material blends) constituting the foam layer and the resin layer were as shown in Table 4. The thickness (mm), basis weight (g / m ) and other properties of the obtained foam sheet were measured in the same manner as in Examples 1 to 6. 2 ), apparent density (kg / m 3The foam sheet was measured for its closed cell content (%), sagging (mm), and sagging ratio (mm). The results of each measurement are shown in Table 4. In Comparative Example 1 of Table 4, the LLDPE content and expansion ratio are shown, similarly to Examples 1 to 6.

[0149] Comparative Examples 2, 3 and 4 Comparative Examples 2, 3, and 4 were prepared in the same manner as in Examples 7 and 8, except that the resin composition (raw material composition) constituting the foam layer was as shown in Table 4. The thickness (mm), basis weight (g / m2), and other properties of the obtained foam sheets were measured in the same manner as in Examples 7 and 8. 2 ), apparent density (kg / m 3 The foam sheet was measured for its closed cell content (%), sagging (mm), and compressive stress (kPa). The results of each measurement are shown in Table 4. In Comparative Examples 2, 3, and 4 in Table 4, the LLDPE content (% by mass) and expansion ratio (times) are shown, similarly to Examples 7 and 8.

[0150] [Table 2]

[0151] [Table 3]

[0152] [Table 4]

[0153] According to Examples 1 to 6, Example 9, and Comparative Example 1, it was confirmed that by incorporating linear low-density polyethylene (linear low-density polyethylene (A2) and linear low-density polyethylene (B2)) in both the foam layer and the resin layer, the resulting foam sheet could significantly reduce the amount of sagging (mm) despite a high expansion ratio, and a foam sheet with excellent stiffness could be obtained. According to Example 10 and Comparative Example 1, it was confirmed that by incorporating linear low-density polyethylene in at least the foam layer, the resulting foam sheet could reduce the amount of sagging (mm) despite a high expansion ratio. Furthermore, according to Examples 7 and 8, and Comparative Example 2, it was confirmed that by incorporating linear low-density polyethylene (A2) in the foam layer, the resulting foam sheet could significantly reduce the amount of sagging (mm) despite a high expansion ratio. Furthermore, it was confirmed that Examples 7 and 8 could achieve a higher compressive stress (kPa) than Comparative Example 2, and thus had sufficiently excellent cushioning properties. Furthermore, according to Examples 7 and 8 and Comparative Examples 3 and 4, it was confirmed that the use of a copolymer of ethylene and an α-olefin having 8 carbon atoms as the linear low-density polyethylene in the foam layer made it possible to obtain a foamed sheet having a high expansion ratio and excellent stiffness strength and cushioning properties. [Explanation of symbols]

[0154] 10: Foam sheet 11: Foam layer 12: Resin layer

Claims

1. A polyethylene resin foam sheet having a foam layer containing a low-density polyethylene (A1) as a base resin, The polyethylene resin foam sheet has a thickness of 0.05 mm or more and 3 mm or less, The apparent density (kg / m) of the polyethylene resin foam sheet ３ ) relative to the density (kg / m ３ ) is 20 or more and 80 or less, the foam layer further comprises a linear low-density polyethylene (A2), The density of the linear low-density polyethylene (A2) is 915 kg / m ３ or more, and the MFR of the linear low-density polyethylene (A2) measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 190°C and a load of 2.16 kg is 10 g / 10 min or less, the linear low-density polyethylene (A2) is a copolymer of ethylene and an α-olefin having 8 carbon atoms, A polyethylene-based resin foam sheet, wherein the content of the linear low-density polyethylene (A2) in the foam layer is 5% by mass or more and 45% by mass or less.

2. The polyethylene-based resin foam sheet has the foam layer and a resin layer laminated on at least one side of the foam layer, the resin layer contains a low-density polyethylene (B1) and a linear low-density polyethylene (B2), The density of the linear low-density polyethylene (B2) is 915 kg / m ３ or more, and the MFR of the linear low-density polyethylene (B2) measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 190°C and a load of 2.16 kg is 10 g / 10 min or less, the linear low-density polyethylene (B2) is a copolymer of ethylene and an α-olefin having 8 carbon atoms, The polyethylene resin foam sheet according to claim 1, wherein the content of the linear low-density polyethylene (B2) in the resin layer is 5% by mass or more and 45% by mass or less.

3. 3. The polyethylene-based resin foam sheet according to claim 1 or 2, wherein the linear low-density polyethylene (A2) has an MFR of 3.0 g / 10 min or less, as measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 190°C and a load of 2.16 kg.

4. The MFR of the linear low-density polyethylene (A2) measured under conditions of a temperature of 190°C and a load of 2.16 kg in accordance with JIS K7210-1:2014 is ＬＬ The MFR of the low-density polyethylene (A1) measured under conditions of a temperature of 190°C and a load of 2.16 kg in accordance with JIS K7210-1:2014 is ＬＤ When the MFR ＬＬ and the MFR ＬＤ The absolute value of the difference between [|(MFR ＬＤ )-(MFR ＬＬ 3. The polyethylene resin foam sheet according to claim 1, wherein the elongation constant (E) is 3.0 g / 10 min or less.

5. The polyethylene-based resin foam sheet according to claim 2, wherein the linear low-density polyethylene (B2) has an MFR of 3.0 g / 10 min or less, as measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 190°C and a load of 2.16 kg.

6. The polyethylene-based resin foam sheet according to claim 2 , wherein the resin layer contains a polymer-type antistatic agent.

7. The polyethylene-based resin foam sheet according to claim 2 , wherein the resin layer contains an ionomer resin.

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