Polyethylene-based resin foam sheet

Abstract

To provide a polyethylene-based resin foam sheet that possesses cushioning properties and also exhibits relatively good thermal insulation performance.SOLUTION: A polyethylene-based resin foam sheet comprises a polyethylene-based resin composition containing a polyethylene-based resin and contains a plurality of cells, where the sheet has a thickness from 2 mm to 12 mm inclusive, a total light transmittance of 50% or less, and a haze of 95% or more.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] A polyethylene-based resin foam sheet is a foam sheet mainly made of a polyethylene-based resin. Polyethylene-based resin foam sheets can be produced at low cost and have excellent cushioning and heat insulating properties, so they are used as heat insulating materials and cushioning materials for keeping fresh foods cold (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6724509 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in recent years, with the decline in the supply of dry ice, there has been a demand for improved insulation to maintain cold storage performance while reducing the amount of dry ice used. Furthermore, there is a strong demand for improved cold and heat retention from the perspective of energy conservation. Among resin foams, polyurethane-based resin foams are known to have relatively excellent insulating properties. However, these types of resin foams lack flexibility and are difficult to use in situations where cushioning is required.

[0005] Therefore, an object of the present invention is to provide a polyethylene resin foam sheet having cushioning properties and relatively excellent heat insulation properties. [Means for solving the problem]

[0006] The polyethylene resin foam sheet according to the present invention comprises: A polyethylene-based resin foam sheet comprising a polyethylene-based resin composition and containing a plurality of bubbles, The thickness is 2 mm or more and 12 mm or less, The total light transmittance is 50% or less, and the haze is 95% or more. [Effects of the Invention]

[0007] According to the present invention, a polyethylene resin foam sheet having cushioning properties and relatively excellent heat insulation properties is provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an example of a sheet manufacturing apparatus for manufacturing a polyethylene resin foam sheet. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will be described below. The polyethylene-based resin foam sheet of this embodiment is composed of a polyethylene-based resin composition containing a polyethylene-based resin. In the following, the embodiment of the present invention will be described taking as an example a case where the polyethylene-based resin foam sheet is an extruded foam sheet obtained by an apparatus such as that shown in FIG. 1. The polyethylene-based resin foam sheet 10 has an extrusion direction (MD), a width direction (TD) perpendicular to the MD direction, and a thickness direction (VD) perpendicular to the MD and TD directions.

[0010] The polyethylene-based resin foam sheet 10 of the present embodiment may be, for example, an extruded foam sheet produced by a sheet manufacturing apparatus 13 illustrated in Fig. 1. The sheet manufacturing apparatus 13 illustrated in Fig. 1 includes a tandem extruder 31.

[0011] The extruder 32 (hereinafter also referred to as the "first extruder") located upstream of the tandem extruder 31 includes a hopper 21 for feeding a polyethylene resin composition that is a raw material for the polyethylene resin foam sheet, and a gas supply device 35 and a gas supply section 37 for supplying a foaming agent such as a hydrocarbon into the cylinder.

[0012] The sheet manufacturing apparatus 13 of the present embodiment also includes an extruder 33 (hereinafter also referred to as a "second extruder") downstream of the first extruder 32. In the second extruder 33, a resin composition containing a foaming agent is melt-kneaded.

[0013] The sheet manufacturing apparatus 13 of the present embodiment further includes a circular die 41 that cylindrically discharges the polyethylene resin composition melt-kneaded in the tandem extruder 31. The sheet manufacturing apparatus 13 further includes a cooling device 62 that air-cools the polyethylene resin foam sheet cylindrically extruded from the circular die 41, and a mandrel 51 that expands the diameter of the cylindrical polyethylene resin foam sheet to form a cylindrical shape of a predetermined size.

[0014] The sheet manufacturing apparatus 13 further includes a cutting blade 61, a plurality of rollers 71, and a take-up roller 72. The cylindrical polyethylene-based resin foam sheet having a predetermined diameter that has passed through the mandrel 51 is cut open by the cutting blade 61 to obtain a strip-shaped polyethylene-based resin foam sheet. Thereafter, the strip-shaped polyethylene-based resin foam sheet passes through the plurality of rollers 71 and is then taken up by the take-up roller 72.

[0015] The polyethylene-based resin foam sheet of this embodiment is made of a polyethylene-based resin composition containing a polyethylene-based resin and contains a plurality of bubbles. The polyethylene-based resin is a resin having a chemical structure formed by polymerizing ethylene. Examples of the polyethylene-based resin include one type of polyethylene selected from the group consisting of very low-density polyethylene (PE-VLD), low-density polyethylene (PE-LD), linear low-density polyethylene (PE-LLD), medium-density polyethylene (PE-MD), and high-density polyethylene (PE-HD), or a mixture of two or more types of polyethylene.

[0016] The polyethylene resin used in the polyethylene resin foam sheet of this embodiment is preferably low-density polyethylene (PE-LD) in order to provide the polyethylene resin foam sheet with excellent cushioning properties. The polyethylene resin foam sheet preferably contains multiple low-density polyethylenes (PE-LD) in order to facilitate imparting melting properties suitable for foaming to the resin composition constituting the polyethylene resin foam sheet. The polyethylene resin foam sheet preferably contains two types of low-density polyethylenes (PE-LD) whose melting points (peak temperatures) determined by DSC (under a nitrogen atmosphere, at a heating rate of 10°C / min) differ by 1°C or more and 5°C or less.

[0017] From the viewpoint of enabling the production of a polyethylene-based resin foam sheet having excellent cushioning properties at low cost, the content of the polyethylene-based resin in the polyethylene-based resin composition may be, for example, 90% by mass or more, 95% by mass or more, or 99% by mass or more.

[0018] In one embodiment, the polyethylene resin composition may further contain a cell control agent. Examples of the cell control agent include a cell nucleating agent that forms cells in the melt-kneaded product together with a blowing agent (described later), or compound particles that generate gas upon thermal decomposition. Examples of the cell nucleating agent include those commonly used in extrusion foaming. Examples include particles of inorganic compounds such as talc, mica, silica, diatomaceous earth, aluminum oxide, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate, potassium sulfate, barium sulfate, or glass beads, or particles of organic compounds such as polytetrafluoroethylene. The cell nucleating agent may be one of the compounds exemplified herein, or a mixture of two or more of them. Examples of compound particles that generate gas upon thermal decomposition include azodicarbonamide, sodium bicarbonate, or a mixture of sodium bicarbonate and citric acid. The polyethylene resin composition preferably contains a cell nucleating agent as the cell control agent.

[0019] The amount of the cell regulator added is preferably 0.05 parts by mass or more and 0.20 parts by mass or less, and more preferably 0.06 parts by mass or more and 0.15 parts by mass or less, relative to 100 parts by mass of the polyethylene resin.

[0020] When the amount of the cell regulator added is within the above range, fine cells are easily formed in the polyethylene resin foam sheet, and better heat insulation properties are obtained.

[0021] In addition to the polyethylene resin, the polyethylene resin composition may contain, as necessary, one or more additives selected from a thickener, a lubricant, an antishrinkage agent, an antistatic agent, a weather resistance stabilizer, a light stabilizer, an antioxidant, an antibacterial agent, a deodorizer, a pigment, and an inorganic filler.

[0022] The content of one or more additives in the polyethylene resin composition may be, for example, 5.0 parts by mass or less, or 2.0 parts by mass or less, relative to 100 parts by mass of the polyethylene resin.

[0023] In one embodiment of the polyethylene resin foam sheet of the present embodiment, the average cell diameter of each of the cells (hereinafter simply referred to as "cells") in the plurality of cells is 0.75 mm or less, preferably 0.70 mm or less, and more preferably 0.65 mm or less. The lower limit of the average cell diameter of the cells is not particularly limited, but is usually 0.05 mm or more.

[0024] The average cell diameter can be determined as follows. The polyethylene resin foam sheet is cut perpendicularly to the surface from the widthwise center along the MD direction (extrusion direction) and TD direction (width direction perpendicular to the extrusion direction) of the polyethylene resin foam sheet. The cross section was photographed at 40x magnification using a scanning electron microscope (TM3030plus, Hitachi High-Technologies Corporation). Two microscope images were taken for each cross section cut along the MD direction (MD cross section) and the TD cross section (TD cross section), for a total of four fields of view, and printed on A4 paper. Three arbitrary lines (60 mm long) parallel to the MD direction were drawn on each of the two MD cross section images, and three arbitrary lines (60 mm long) parallel to the TD direction were drawn on each of the two TD cross section images. In addition, three lines (60 mm long) parallel to the VD direction were drawn on one MD cross section image and one TD cross section image, and six 60 mm arbitrary lines parallel to the MD, TD, and VD directions were drawn in each direction. Note that the arbitrary lines were drawn with the utmost care to avoid contact with air bubbles at their contact points. If contact occurs, these air bubbles were also counted. The number of bubbles counted for six arbitrary straight lines in each of the MD, TD, and VD directions is calculated as the arithmetic mean, which is the number of bubbles in each direction.The average chord length t of the bubbles is calculated using equation (s1) from the image magnification at which the number of bubbles was counted and the number of bubbles. Average chord length t (mm) = 60 / (number of bubbles × image magnification) (s1) The image magnification is calculated by measuring the scale bar on the image to 1 / 100 mm using a Digimatic caliper (Mitutoyo Corporation) and using the following formula: Image magnification = Scale bar actual measurement value (mm) / Scale bar display value (mm) Calculate the bubble diameter in each direction using equation (s2). Bubble diameter D (mm) = t / 0.616 (s2) Furthermore, the cube root of the product of these is defined as the average bubble diameter (equation (s3)). Average bubble diameter (mm) = (D MD ×D TD ×D VD ) 1 / 3 (s3) D MD : MD bubble diameter (mm) D TD : bubble diameter in the TD direction (mm) D VD : Bubble diameter in VD direction (mm)

[0025] In order to set the average cell diameter within the above range, in the production of a polyethylene-based resin foamed sheet, the amount of foaming agent added during melt-kneading of the polyethylene-based resin composition can be set to 7.5 parts by mass or more and 10.0 parts by mass or less per 100 parts by mass of the polyethylene-based resin.

[0026] The foaming agent may be any foaming agent used in conventional extrusion foaming methods, such as water, hydrocarbons, dimethyl ether, nitrogen, carbon dioxide, or gases such as argon. Examples of the hydrocarbon include normal butane, isobutane, and propane.

[0027] Bubble diameter in MD (D MD ), bubble diameter in the TD direction (D TD ) and VD direction bubble diameter (D VD) may be approximately the same. From the viewpoint of improving the thermal insulation property of the polyethylene-based resin foam sheet in the VD direction, the cells preferably have a larger diameter in at least one of the MD and TD directions than the VD direction, and more preferably have a larger diameter in both the MD and TD directions than the VD direction.

[0028] In one aspect, the polyethylene resin foam sheet of the present embodiment has a cell diameter (D VD The diameter (D) of the bubbles in the VD direction is 0.70 mm or less, preferably 0.65 mm or less, and more preferably 0.60 mm or less. VD ) is within the above range, the heat insulating property of the polyethylene resin foam sheet in the VD direction is further improved.

[0029] In one aspect, the polyethylene-based resin foam sheet of the present embodiment has a ratio of the cell diameter in the VD direction of the cells to the cell diameter in the TD direction (D VD / D TD ) is 0.30 or more and 0.90 or less, preferably 0.30 or more and 0.80 or less, and more preferably 0.30 or more and 0.70 or less.

[0030] In one aspect, the polyethylene-based resin foam sheet of the present embodiment has a ratio of the cell diameter in the VD direction of the cells to the cell diameter in the MD direction (D VD / D MD ) is 0.30 or more and 0.99 or less, preferably 0.30 or more and 0.95 or less, and more preferably 0.30 or more and 0.90 or less.

[0031] The bubble diameter ratio (D VD / D TD ) and the bubble diameter ratio (D VD / D MD When both of the cell diameter ratio (D VD / D TD ) and the bubble diameter ratio (DVD / D MD ) is preferably smaller within the above range.

[0032] Regarding the shape of the bubbles, the bubble diameter ratio (D VD / D TD ) and the bubble diameter ratio (D VD / D MD In order to make the above numerical range, in the step of extrusion foaming a polyethylene-based resin foam sheet, the ratio of the outer diameter φM of the mandrel 51 to the diameter φC of the annular slit formed in the circular die 41 (outer diameter φM of the mandrel / diameter φC of the annular slit), i.e., the blow-up ratio, can be set to 3.0 or more and 4.0 or less. Note that the "diameter φC of the annular slit" refers to the diameter of the inner edge of the slit between the outer edge and the inner edge.

[0033] The polyethylene resin foam sheet of the present embodiment has a thickness of 2 mm or more and 12 mm or less, or may be 2 mm or more and 9 mm or less, or may be 2 mm or more and 6 mm or less.

[0034] The polyethylene-based resin foam sheet of the present embodiment exhibits haze and total light transmittance as described below due to the presence of many fine bubbles overlapping in the thickness direction, each of which has a dimension in the thickness direction (VD direction) shorter than the dimensions in the extrusion direction (MD direction) and the width direction (TD direction).

[0035] The thickness of the polyethylene resin foam sheet can be determined as follows. Using a constant pressure thickness measuring instrument (Teclock, model SCM-627), a cylindrical weight was used to measure the thickness of a circular surface with a diameter of 4.4 cm (area: 60.8 cm). 2 ) and measure the thickness of the polyethylene resin foam sheet when a load of 100 g (including its own weight) is applied to the polyethylene resin foam sheet. Measurements are taken at 50 points every 5 cm in the width direction, and the arithmetic mean of the measurements is taken as the sheet thickness. If it is not possible to obtain 50 measurement points, measure as many as possible, and take the arithmetic mean of the measurements as the thickness.

[0036] The basis weight of the polyethylene-based resin foam sheet of the present embodiment is, in one embodiment, 80 g / m 2 More than 140g / m 2 and preferably 90 g / m 2 More than 130g / m 2 The following is the result.

[0037] The basis weight of a polyethylene resin foam sheet can be calculated as follows: The polyethylene resin foam sheet is cut into a piece 20 cm wide in the extrusion direction and in the direction perpendicular to the extrusion direction, and the basis weight is calculated by multiplying the mass W (g) and the area S (cm 2 ) and the following formula (1). If the polyethylene resin foam sheet cannot be cut into a width of 20 cm in the direction perpendicular to the extrusion direction, cut it into a rectangular piece of a size that can be cut, and calculate the mass W (g) and area S (cm 2 ) is calculated using the following formula (1). Basis weight (g / m 2 )=W(g) / S(cm 2 )×10000···(1)

[0038] The apparent density of the polyethylene resin foam sheet of the present embodiment is, in one embodiment, 25 kg / m 3 More than 45kg / m 3 or less, preferably 30 kg / m 3 More than 40kg / m 3 The following is the result.

[0039] The apparent density of the polyethylene resin foam sheet can be determined as follows. The apparent density is determined by the sheet thickness (T: mm) of the polyethylene resin foam sheet determined as above and the basis weight (Y: g / m 2 ) and is calculated using the following formula (2). Apparent density (kg / m 3 )=Y / T (2)

[0040] The polyethylene-based resin foam sheet of this embodiment has a total light transmittance of 50% or less and a haze of 95% or more. The total light transmittance of the polyethylene-based resin foam sheet is preferably 47% or less, more preferably 45% or less. The total light transmittance of the polyethylene-based resin foam sheet may be 5% or more, or may be 10% or more. The haze of the polyethylene-based resin foam sheet is preferably 97% or more, more preferably 98% or more. The upper limit of the haze of the polyethylene-based resin foam sheet is not particularly limited, and a higher haze is preferable.

[0041] The total light transmittance can be measured in accordance with JIS K7361-1, and the haze can be measured in accordance with JIS K7136. Specifically, the total light transmittance and haze of the polyethylene resin foam sheet can be measured using a haze meter (NDH5000) commercially available from Nippon Denshoku Industries Co., Ltd.

[0042] The polyethylene resin foam sheet of the present embodiment, when prepared as described above, exhibits excellent heat insulation and cushioning properties.

[0043] For example, the thermal conductivity of a polyethylene resin foam sheet in the thickness direction is 50 × 10 -3 The thermal conductivity of the polyethylene resin foam sheet in the thickness direction is adjusted to 40×10 -3 It is preferable that the thermal conductivity of a polyethylene-based resin foam sheet in the thickness direction is low. However, it is difficult to produce a polyethylene-based resin foam sheet with an excessively low thermal conductivity. Therefore, the thermal conductivity of a polyethylene-based resin foam sheet in the thickness direction is, for example, 10 × 10 -3 The thermal conductivity of the polyethylene resin foam sheet can be measured by the method described in the examples.

[0044] The polyethylene-based resin foam sheet is prepared so that its compression hardness, measured as the reaction force when compressed 25% in the thickness direction, is 50 kPa or less. The compression hardness of the polyethylene-based resin foam sheet is preferably 40 kPa or less, and more preferably 30 kPa or less. If the compression hardness of the polyethylene-based resin foam sheet is too low, it is difficult for the sheet to exhibit impact absorption properties, so the polyethylene-based resin foam sheet preferably has a compression hardness of 10 kPa or more. The compression hardness of the polyethylene-based resin foam sheet can be measured by the method described in the Examples.

[0045] The polyethylene-based resin foam sheet of this embodiment is preferably used as a wall material for thermally insulated containers, such as thermally insulated cases used in food delivery businesses and refrigerated carts used in food factories and supermarkets, by laminating an aluminum vapor-deposited film on the surface thereof. The polyethylene-based resin foam sheet of this embodiment is suitable for use as a wall constituent material for thermally insulated containers, but is not limited to such use and can also be used for various other uses.

[0046] The matters disclosed in this specification include the following. (1) A polyethylene-based resin foam sheet comprising a polyethylene-based resin composition and containing a plurality of bubbles, The thickness is 2 mm or more and 12 mm or less, The total light transmittance is 50% or less and the haze is 95% or more. Polyethylene resin foam sheet. (2) The average bubble diameter of the bubbles is 0.75 mm or less. The polyethylene resin foam sheet according to (1). (3) The bubble diameter in the VD direction of the bubbles is 0.70 mm or less. The polyethylene resin foam sheet according to (1) or (2). (4) The ratio of the bubble diameter in the VD direction of the bubbles to the bubble diameter in the TD direction of the bubbles is 0.30 or more and 0.90 or less. The polyethylene resin foam sheet according to any one of (1) to (3).

[0047] The present invention is not limited to the above-described embodiments, and various improvements, modifications, or variations can be made based on the knowledge of those skilled in the art without departing from the spirit of the present invention. The present invention may be embodied in a form in which any specific feature is replaced with another technology within the scope of producing the same function or effect. [Example]

[0048] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0049] Five types of polyethylene resins, abbreviated as "PE1" to "PE5," and a cell control agent, abbreviated as "NA1," were prepared. PE1: Low-density polyethylene resin produced by high-pressure polymerization, density: 921 kg / m 3 , MFR=0.3g / 10min. PE2: Low-density polyethylene resin produced by high-pressure polymerization, density: 926 kg / m 3 , MFR=0.4g / 10min. PE3: Low-density polyethylene resin produced by high-pressure polymerization, density: 919 kg / m 3 , MFR=2.0g / 10min. PE4: Low-density polyethylene resin derived from plants produced by high-pressure polymerization, density: 923 kg / m 3 , MFR=2.7g / 10min. PE5: Low-density polyethylene resin produced by melt-kneading again a molded product made from low-density polyethylene resin produced by high-pressure polymerization. Density: 921 kg / m 3 , MFR=0.8g / 10min. NA1: Azodicarbonamide

[0050] Example 1 Polyethylene resins "PE1" and "PE2" were blended in the proportions shown in Table 1, and 0.06 parts by weight of the cell control agent "NA1" was added to 100 parts by weight of the polyethylene resins "PE1" and "PE2" to prepare a mixture. The mixture was placed in a single-screw extruder with a 90mm diameter and a 180mm diameter extruder, and heated to a maximum temperature of 210°C. The mixture was then melt-kneaded in the extruder. 1.4 parts by weight of a shrinkage inhibitor (glycerin monostearate) and 8.8 parts by weight of a volatile blowing agent (normal butane / isobutane = 60 / 40) were added by pressure during the extrusion process. The resin temperature was then cooled to 113°C, and extrusion foaming was performed through a circular die with a mold diameter of 125mm and a die slit clearance of 0.36mm. The extruded cylindrical sheet was then cooled on a 440mm diameter cooling mandrel, and cut open to obtain a flat foam sheet.

[0051] (Examples 2, 3, and 4) Polyethylene resin foam sheets were produced in the same manner as in Example 1, except that the blending ratio of the polyethylene resin, the amount of the blowing agent injected, and the amount of the cell adjusting agent added were changed as shown in Table 1.

[0052] Example 5 A polyethylene resin foamed sheet was produced in the same manner as in Example 1, except that the die slit was set to 0.3 mm, and the amount of foaming agent injected and the amount of cell control agent added were changed as shown in Table 1.

[0053] (Comparative Examples 1 and 2) Polyethylene resin foam sheets were produced in the same manner as in Example 1, except that the amount of foaming agent injected and the amount of cell-regulating agent added were changed as shown in Table 1.

[0054] (Comparative Example 3) Instead of the polyethylene resin foam sheet of Example 1, a product name "Minafoam (model number #230)" manufactured by Sakai Chemical Industry Co., Ltd. was used.

[0055] Comparative Example 4 A polyethylene resin foamed sheet was produced in the same manner as in Example 1, except that the die slit was set to 0.3 mm, and the amount of foaming agent injected and the amount of cell control agent added were changed as shown in Table 1.

[0056] (sheet thickness) The thickness of the polyethylene-based resin foam sheet produced in each Example and Comparative Example was measured. The thickness of the polyethylene-based resin foam sheet was measured using a constant pressure thickness measuring instrument (manufactured by Teclock, model "SCM-627") and a cylindrical weight on a circular surface with a diameter of 4.4 cm (area: 60.8 cm). 2 ) and a load of 100 g (including its own weight) was applied to the polyethylene resin foam sheet, and the thickness of the polyethylene resin foam sheet was measured. Measurements were taken at 50 points every 5 cm in the width direction, and the arithmetic mean value of the measured values ​​was used as the sheet thickness. When it was not possible to obtain 50 measurement points, measurements were taken as many times as possible, and the arithmetic mean value of the measured values ​​was used as the thickness.

[0057] (Basic weight) The basis weight of the polyethylene-based resin foam sheet produced in each Example and Comparative Example was determined. The polyethylene-based resin foam sheet was cut in a width of 20 cm in the extrusion direction and in a direction perpendicular to the extrusion direction, and the basis weight was calculated by dividing the mass W (g) and area S (cm 2 ) was calculated using the following formula (1). If the polyethylene resin foam sheet cannot be cut into a width of 20 cm in the direction perpendicular to the extrusion direction, it was cut into a rectangular piece of a size that can be cut, and the mass W (g) and area S (cm 2 ) was calculated using the following formula (1). Basis weight (g / m 2 )=W(g) / S(cm 2 )×10000···(1)

[0058] (Apparent density) The apparent density of the polyethylene-based resin foamed sheets produced in each Example and Comparative Example was determined. The apparent density was calculated by multiplying the thickness (T: mm) of the polyethylene-based resin foamed sheet determined as described above by the basis weight (Y: g / m 2 ) was used to calculate the value using the following formula (2). Apparent density (kg / m 3 )=Y / T (2)

[0059] (average bubble diameter) The average cell diameter of the polyethylene resin foam sheet was determined as follows. The polyethylene resin foam sheet was cut perpendicular to the surface from the center in the width direction along the MD direction (extrusion direction) and TD direction (width direction perpendicular to the extrusion direction) of the polyethylene resin foam sheet. The cross sections were photographed at 40x magnification using a scanning electron microscope (TM3030plus, Hitachi High-Technologies Corporation). Two microscopic images were taken of each cross section cut along the MD direction (MD cross section) and the TD cross section (TD cross section), for a total of four fields of view. These images were printed on A4 paper. Three arbitrary lines (60 mm long) parallel to the MD direction were drawn on each of the two MD cross section images, and three arbitrary lines (60 mm long) parallel to the TD direction were drawn on each of the two TD cross section images. Three lines (60 mm long) parallel to the VD direction were drawn on one MD cross section image and one TD cross section image, and six 60 mm arbitrary lines parallel to the MD, TD, and VD directions were drawn in each direction. The arbitrary lines were carefully designed to avoid contact with air bubbles at their contact points. If contact did occur, these air bubbles were also counted. The number of bubbles counted along six random lines in each of the MD, TD, and VD directions was calculated as the arithmetic mean, and the number of bubbles in each direction was calculated.The average chord length t of the bubbles was calculated using equation (s1) from the image magnification at which the number of bubbles was counted and the number of bubbles. Average chord length t (mm) = 60 / (number of bubbles × image magnification) (s1) The image magnification was calculated by measuring the scale bar on the image to 1 / 100 mm using a Digimatic caliper (Mitutoyo Corporation) and using the following formula: Image magnification = Scale bar actual measurement value (mm) / Scale bar display value (mm) The bubble diameter in each direction was calculated using equation (s2). Bubble diameter D (mm) = t / 0.616 (s2) Furthermore, the cube root of the product of these values ​​was defined as the average bubble diameter (equation (s3)). Average bubble diameter (mm) = (D MD ×D TD ×D VD )1 / 3 (s3) D MD : MD bubble diameter (mm) D TD : bubble diameter in the TD direction (mm) D VD : Bubble diameter in VD direction (mm)

[0060] (Total light transmittance and haze) The total light transmittance was measured in accordance with JIS K7361-1, and the haze was measured in accordance with JIS K7136. Specifically, the total light transmittance and haze of the polyethylene-based resin foam sheets produced in each of the Examples and Comparative Examples were measured using a haze meter (NDH5000) commercially available from Nippon Denshoku Industries Co., Ltd.

[0061] (thermal conductivity) The thermal conductivity of the polyethylene-based resin foam sheets produced in each example and comparative example was measured using a thermal conductivity measuring device HC-074 / 200 (AutoΛ) manufactured by Eiko Seiki Co., Ltd., according to the method described in JIS A1412-2 "Method for measuring thermal resistance and thermal conductivity of thermal insulating materials - Part 2: Heat flow meter method (HFM method)." Test pieces measuring 200 mm long x 200 mm wide were cut from the polyethylene resin foam sheet and placed in a 40°C thermostatic chamber for 96 hours to remove the foaming agent. These test pieces were then left for 24 hours under standard conditions of 23°C ± 2°C and 50% ± 5% humidity, after which five were stacked. The thermal conductivity of these test pieces was measured using the thermal conductivity measuring device described above at an average temperature of 23°C (hot plate temperature 38°C, cold plate temperature 8°C) with a plate temperature difference of 30°C. The calibration standard used for the thermal conductivity measuring device was NIST (National Institute of Standards and Technology) SRM1450B.

[0062] (tensile strength) Tensile strength was measured in accordance with JIS K6767:1999. Specifically, tensile strength was measured using a Tensilon universal testing machine (Model RTG-1310) manufactured by A&D Co., Ltd. Test specimens were cut in the extrusion direction (MD) and the direction perpendicular to the extrusion direction (TD) using a dumbbell-shaped type 1 (specified in ISO 1798). Five test specimens were cut in each direction. Test specimens were conditioned for 16 hours in a standard atmosphere (JIS K7100:1999, "23 / 50" grade 2) before use. Measurements were performed under the same conditions, with a test speed of 500 mm / min and a grip spacing of 80 mm. The average tensile strength was calculated.

[0063] (25% compression hardness) The 25% compression hardness was measured in accordance with JIS K6767:1999. That is, the 25% compression hardness was measured using a Tensilon universal testing machine (model RTG-1310) manufactured by A&D Co., Ltd. The foam was cut into 50 mm x 50 mm pieces and stacked to a thickness of approximately 25 mm, and the initial thickness was measured. Three test pieces were used. The sample was placed on a flat plate and compressed to 25% of the initial thickness at a rate of 10 mm / min, then stopped. After 20 seconds, the load P (N) and the area Q (mm) of the test piece were measured. 2 ) and calculated the 25% compression hardness (kPa) using the following formula (3), and the average value was obtained. 25% compression hardness (kPa) = P (N) / Q (mm 2 )×1000···(3)

[0064] The evaluation results of each example and each comparative example are shown in Table 1.

[0065] [Table 1]

[0066] As can be seen from the results in Table 1, the examples that satisfied all of the constituent requirements of the present invention exhibited better results in terms of thermal conductivity than the comparative examples.

[0067] From the above, it can be seen that the present invention can provide a polyethylene resin foam sheet having cushioning properties and relatively excellent heat insulation properties. [Explanation of symbols]

[0068] 10...Polyethylene resin foam sheet, 13...Sheet manufacturing apparatus, 21...Hopper, 31...Tandem extruder, 32...First extruder, 33...Second extruder, 35...Gas supply device, 37...Gas supply section, 41...Circular die, 45...Expanded cylindrical foam, 51...Mandrel, 61...Cutting blade, 62...Cooling device, 71...Roller, 72...Winding roller.

Claims

1. A polyethylene-based resin foam sheet comprising a polyethylene-based resin composition and containing a plurality of bubbles, The thickness is 2 mm or more and 12 mm or less, The total light transmittance is 50% or less and the haze is 95% or more. Polyethylene resin foam sheet.

2. The average bubble diameter of the bubbles is 0.75 mm or less. The polyethylene resin foam sheet according to claim 1.

3. The bubble diameter in the VD direction of the bubbles is 0.70 mm or less. The polyethylene resin foam sheet according to claim 1.

4. a ratio of the bubble diameter in the VD direction of the bubbles to the bubble diameter in the TD direction of the bubbles is 0.30 or more and 0.90 or less; The polyethylene resin foam sheet according to any one of claims 1 to 3.

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