JP7178941B2 - Polyethylene resin multilayer foam sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyethylene resin multilayer foam sheet, and more particularly, to a polyethylene resin multilayer foam sheet that is thick and has excellent cushioning properties, as well as excellent surface antistatic properties and cross-sectional antistatic properties.

Electronic parts, semiconductor products, and the like are sometimes wrapped in cushioning materials for transportation in order to prevent damage during transportation.
As a cushioning material used for such applications, there is a polyethylene-based resin foam sheet. The foam sheet is required to have excellent antistatic properties in addition to excellent cushioning properties in order to suppress adhesion of dust and the like to parts and products.

As such a polyethylene resin foam sheet, for example, Patent Document 1 describes a sheet having a thickness of 0.05 to 5 mm, an apparent density of 18 to 500 kg/m ³ , and a polymeric antistatic agent content of 1.5 to 1.5. A polyethylene-based resin foam sheet with a content of 8% by weight is disclosed.

JP 2015-199893 A

The polyethylene-based resin foam sheet as described above may be required to have a greater thickness in addition to the cushioning properties and antistatic properties depending on the application. However, when the thickness of the foam sheet increases, the exposure of the cross-sectional portion of the foam sheet increases, and the exposed portion tends to be easily electrified. In order to suppress electrification of the cross section of the foam sheet, it is preferable to add a large amount of antistatic agent to the foam sheet. However, when a foam sheet containing a large amount of an antistatic agent and having a large thickness and a low apparent density is produced by extrusion foaming, the foam sheet after production shrinks significantly, and even after curing, the shrinked foam sheet cannot be produced. Since the desired thickness cannot be restored, it has been difficult to obtain a foamed sheet with excellent cushioning properties.

An object of the present invention is to solve the above-mentioned problems and to provide a polyethylene-based resin foam sheet that is thick, has excellent cushioning properties, and is excellent in both surface antistatic properties and cross-sectional antistatic properties. is.

According to the present invention, the following polyethylene-based resin foam sheet is provided.
[1] A polyethylene-based resin foam core layer and a polyethylene-based resin intermediate layer laminated and adhered to both sides of the foamed core layer and positioned between the polyethylene-based resin foam core layer and the polyethylene-based resin antistatic layer. and a polyethylene resin antistatic layer laminated and adhered to each of the intermediate layers, wherein
The foam core layer contains one or more polymeric antistatic agents ( A) selected from polyethers, polyetheresteramides, block copolymers of polyethers and polyolefins, and ionomer resins. ,
The antistatic layer contains one or more polymeric antistatic agents ( B) selected from polyethers, polyetheresteramides, block copolymers of polyethers and polyolefins, and ionomer resins. ,
the intermediate layer contains one or more anti-shrinkage agents selected from fatty acid esters, fatty amines and fatty acid amides and is substantially free of polymeric antistatic agents;
The multilayer foam sheet has an overall thickness of more than 2 mm and 30 mm or less, and an overall apparent density of the multilayer foam sheet of 0.01 to 0.1 g/cm ³ ,
A ratio of 50% compressive stress in the thickness direction of the multilayer foam sheet to the total apparent density of the multilayer foam sheet is 2.0 MPa/(g/cm ³ ) or more,
A polyethylene-based resin multilayer foam sheet, wherein the surface resistivity of the multilayer foam sheet is less than 1×10 ¹² Ω, and the surface resistivity of the foam core layer in the cross section of the multilayer foam sheet is less than 1×10 ¹² Ω.
[2] The content of the polymeric antistatic agent (A) in the foam core layer is 100% by weight in total of the polyethylene resin and the polymeric antistatic agent (A) constituting the foam core layer 2. The polyethylene-based resin multilayer foam sheet according to 1 above, wherein the content is 5 to 30% by weight.
[3] The content of the polymeric antistatic agent (B) in the antistatic layer is based on the total 100% by weight of the polyethylene resin and the polymeric antistatic agent (B) that constitute the antistatic layer 3. The polyethylene-based resin multilayer foam sheet according to 1 or 2 above, wherein the content is 5 to 30% by weight.
[4] The polyethylene-based resin multilayer foam sheet according to any one of [1] to [3] above, wherein the polymeric antistatic agent (A) and the polymeric antistatic agent (B) are ionomer resins.
[5] Any one of the above 1 to 4, wherein the amount of the shrinkage inhibitor in the intermediate layer is 0.7 to 3 parts by weight with respect to 100 parts by weight of the polyethylene resin constituting the intermediate layer. The polyethylene-based resin multilayer foam sheet described above.
[6] The polyethylene system according to any one of the above 1 to 5, wherein the foam core layer contains one or more shrinkage inhibitors selected from fatty acid esters, fatty amines and fatty acid amides. Resin multilayer foam sheet.
[7] The antistatic layer according to any one of the above 1 to 6, wherein the antistatic layer does not substantially contain one or more anti-shrinkage agents selected from fatty acid esters, fatty amines and fatty acid amides. Polyethylene-based resin multilayer foam sheet.
[8] The polyethylene-based resin multilayer foam sheet according to any one of the above 1 to 7, wherein the closed cell rate of the multilayer foam sheet is 30% or more.
[9] The polyethylene-based resin multilayer foam sheet according to any one of the above 1 to 8, wherein the multilayer foam sheet has an overall apparent density of 0.015 to 0.060 g/m ³ .
[10] 1 to 1 above, wherein the ratio of the basis weight [g/m ² ] per side of the intermediate layer to the total basis weight [g/m ² ] of the multilayer foam sheet is 0.02 to 0.25. 10. The polyethylene-based resin multilayer foam sheet according to any one of 9.
[11] The foam core layer of the multilayer foam sheet has an average cell diameter in the thickness direction of 0.5 to 1.5 mm and an average cell diameter in the horizontal direction of 0.5 to 1.5 mm. 11. The polyethylene-based resin multilayer foam sheet according to any one of 10 .

The multilayer foam sheet of the present invention comprises a foam core layer, two intermediate layers laminated and adhered to both sides of the foam core layer, and two antistatic layers laminated and adhered to each intermediate layer. It has a multi-layered structure of at least five layers, the intermediate layer containing an anti-shrinkage agent, and the antistatic layer and the foamed core layer containing a polymeric antistatic agent. With such a configuration, the multilayer foam sheet is prevented from shrinking after production, and therefore has a large thickness, excellent cushioning properties, and excellent antistatic property on the surface and antistatic property on the cross section.

Hereinafter, the multilayer foam sheet of the present invention will be described in detail.
The multilayer foam sheet of the present invention comprises a polyethylene resin foam core layer (hereinafter also simply referred to as foam core layer), a polyethylene resin intermediate layer (hereinafter also simply referred to as intermediate layer), and a polyethylene resin antistatic layer. (hereinafter also simply referred to as an antistatic layer). The intermediate layer is laminated and adhered to both sides of the foam core layer, and the antistatic layer is laminated and adhered to each of the intermediate layers, for a total of at least five layers.
The antistatic layer may have a multilayer structure as long as the desired object of the present invention can be achieved. For example, a layer containing a polymer antistatic agent and a polymer antistatic agent substantially It may be an antistatic layer having a multi-layer structure having a layer that does not contain
Further, the intermediate layer may or may not be foamed, but from the viewpoint of enhancing the cushioning properties, it is preferable that the intermediate layer is foamed. In this case, the intermediate layer is preferably foamed to have the same apparent density as the foam core layer.

In the present invention, the polyethylene-based resin used for the foam core layer includes high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and copolymers of ethylene and comonomers such as ethylene-vinyl acetate copolymers. Examples include those containing more than 50 mol % of components and mixtures of two or more of these.
Among the polyethylene-based resins, it is preferable to use a polyethylene-based resin containing low-density polyethylene as a main component, because it is easy to obtain a foamed sheet having excellent extrusion foamability and excellent cushioning properties. Low-density polyethylene refers to a polyethylene-based resin having a density of 0.91 g/cm ³ or more and 0.93 g/cm ³ or less. Moreover, the phrase "mainly composed of low-density polyethylene" means that the low-density polyethylene is contained in the polyethylene-based resin in an amount of 50% by weight or more.

The polyethylene resin constituting the foamed core layer has a melt flow rate (MFR) at 190° C. of 0.05 to 10 g/10 min, more preferably 0.1 to 8.0 g/10 min. , is preferable for obtaining a foamed core layer having a desired apparent density. The melt flow rate (MFR) is a value measured at a test temperature of 190°C and a load of 2.16 kg according to JIS K7210 (1999) A method.

As the polyethylene-based resin forming the intermediate layer, the polyethylene-based resin exemplified as the base resin of the foam core layer can be used. In order to improve the adhesiveness between the intermediate layer and the foamed core layer, it is preferable to use the same polyethylene-based resin as the polyethylene-based resin of the foamed core layer.

As the polyethylene-based resin constituting the antistatic layer, the polyethylene-based resin exemplified as the base resin of the foam core layer can be used. In order to improve the adhesion between the antistatic layer and the intermediate layer, it is preferable to use the same polyethylene-based resin as that of the intermediate layer.

In the present invention, the foamed core layer, the intermediate layer and the antistatic layer contain synthetic resins other than polyethylene resins such as styrene resins, elastomer components, etc., within a range that does not impede the object and effect of the present invention. good too.

In the present invention, the foam core layer contains the polymeric antistatic agent (A). As a result, the cross section of the multilayer foam sheet of the present invention has antistatic properties.
The antistatic layer also contains a polymeric antistatic agent (B). As a result, the surface of the multilayer foam sheet of the present invention has antistatic properties.

Examples of the polymeric antistatic agent include polyethers, polyetheresteramides, block copolymers of polyethers and polyolefins, and ionomer resins.
The block copolymer has 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 and imide bonds.
The ionomer resin is a resin obtained by intermolecular cross-linking between molecules of a copolymer of ethylene and unsaturated carboxylic acid with metal ions. Examples of unsaturated carboxylic acids include acrylic acid and methacrylic acid. Moreover, lithium, sodium, potassium, calcium etc. are mentioned as a metal ion.
Among these, it is preferable to use an ionomer resin. The ionomer has a low surface resistivity and can impart good antistatic performance to the multilayer foam sheet. Contamination of the items to be packaged can be suppressed.
Among the above ionomer resins, potassium ionomers, which are copolymers of ethylene and unsaturated carboxylic acid using potassium as metal ions, are preferable because they can impart good antistatic performance to the multilayer foam sheet.
Examples of ionomer resins include "Entira SD100" and "Entira MK400" manufactured by Mitsui-DuPont Polychemicals.

The surface resistivity of these polymeric antistatic agents is preferably less than 1×10 ¹² Ω, more preferably 1×10 ¹¹ Ω or less, even more preferably 1×10 ¹⁰ Ω or less, and particularly preferably 1×10 10 Ω or less. 10 ⁹ Ω or less.
The surface resistivity of the polymeric antistatic agent is measured according to JIS K6271 (2001).

The content of the polymeric antistatic agent (A) in the foam core layer is 5 to 5 to 100% by weight in total of the polyethylene resin and the polymeric antistatic agent (A) constituting the foam core layer. 30% by weight is preferred. If the content is within this range, while suppressing the migration of low-molecular-weight components derived from the high-molecular-weight antistatic agent, excellent buffering properties are obtained, and the antistatic performance of the cross section of the foamed core layer is stably exhibited. It becomes easy to obtain a foamed sheet that does.
From this point of view, the lower limit of the content is more preferably 6% by weight, still more preferably 8% by weight, and particularly preferably 10% by weight. On the other hand, the upper limit of the content is more preferably 25% by weight, more preferably 20% by weight.

The content of the polymeric antistatic agent (B) in the antistatic layer is 5 to 100% by weight in total of the polyethylene resin and the polymeric antistatic agent (B) constituting the antistatic layer. 30% by weight is preferred. When the content is within this range, the antistatic performance of the surface of the antistatic layer can be stably exhibited while suppressing the migration of low-molecular-weight components derived from the high-molecular-type antistatic agent.
From this point of view, the lower limit of the content is more preferably 6% by weight, still more preferably 8% by weight, and particularly preferably 10% by weight. On the other hand, the upper limit of the content is more preferably 25% by weight, more preferably 20% by weight.

In the present invention, the foam core layer and the antistatic layer contain a polymeric antistatic agent, whereas the intermediate layer does not substantially contain a polymeric antistatic agent.
When the intermediate layer contains a polymer type antistatic agent, the shrinkage prevention effect of the multilayer foam sheet by the shrinkage preventing agent described later does not appear during the production of the multilayer foam sheet, and the multilayer foam sheet has excellent cushioning properties. may not be able to obtain
Here, "substantially does not contain a polymeric antistatic agent" means that the content of the polymeric antistatic agent in the intermediate layer is generally 5% by weight or less with respect to 100% by weight of the intermediate layer. means The content is more preferably 3% by weight or less, still more preferably 2% by weight or less. Most preferably, the intermediate layer does not contain a polymeric antistatic agent.

The intermediate layer in the present invention contains one or more shrinkage inhibitors selected from fatty acid esters, fatty amines and fatty acid amides. By including the shrinkage inhibitor in the intermediate layer, it is possible to prevent the influence of the shrinkage of the foam core layer that occurs during the production of the multilayer foam sheet, and it is possible to obtain a multilayer foam sheet having a large thickness and excellent cushioning properties.

The fatty acid ester is preferably an ester of a fatty acid having 8 to 30 carbon atoms and a polyhydric alcohol having 3 to 7 hydroxyl groups. Examples of fatty acids having 8 or more carbon atoms include lauric acid, oleic acid, stearic acid, behenic acid, lignoceric acid, cerotic acid, heptakoic acid, montanic acid, melissic acid and laxeric acid. Examples of polyhydric alcohols having 3 to 7 hydroxyl groups include glycerin, diglycerin, triglycerin, erythritol arabit, xylimaat, mannitol, sorbitol and sorbitan.
Among these ester compounds, partially esterified compounds, particularly monoesterified compounds, are preferred because they provide a more remarkable anti-shrinkage effect, and stearic acid monoglyceride, behenic acid monoglyceride, or a mixture of stearic acid monoglyceride and behenic acid monoglyceride are more preferred.

Examples of the aliphatic amine include dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, eicosylamine, docosylamine, N-methyloctadecylamine, N-ethyloctadecylamine, hexadecylpropylenediamine, octadecylpropylenediamine, and the like. are mentioned.

The fatty acid amides include lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, N-methylstearic acid amide, N-ethylstearic acid amide, N,N-dimethylstearic acid amide, N,N - diethylstearic acid amide, dilauric acid amide, distearic acid amide, trilauric acid amide, tristearic acid amide and the like.

The content of the shrinkage inhibitor in the intermediate layer is preferably 0.7 to 3 parts by weight with respect to 100 parts by weight of the polyethylene resin constituting the intermediate layer. When the content is within this range, it is possible to stably obtain a multi-layered foam sheet having excellent cushioning properties while suppressing the migration of the shrinkage inhibitor to the package.
From this point of view, the blending amount is more preferably 0.8 to 2 parts by weight.
In addition, when the intermediate layer contains stearic acid monoglyceride as a shrinkage preventing agent, the amount of stearic acid monoglyceride compounded is 0.7 to 3 parts by weight with respect to 100 parts by weight of the polyethylene resin constituting the intermediate layer. is preferred, 0.8 to 2 parts by weight is more preferred, and 0.9 to 1.5 parts by weight is even more preferred.

In the present invention, the anti-shrinkage agent can be blended into the foamed core layer. That is, the foam core layer can contain one or more shrinkage inhibitors selected from the fatty acid esters, fatty amines and fatty acid amides described above.
When the foam core layer contains an anti-shrinkage agent, it becomes easier to prevent the foaming agent from escaping from the cross-section of the foam core layer during the production of the multilayer foam sheet, making it easier to obtain a multilayer foam sheet with excellent cushioning properties. . When the foam core layer contains a shrinkage preventing agent, the content of the shrinkage preventing agent in the foam core layer is 0.5 to 3 parts by weight with respect to 100 parts by weight of the polyethylene resin constituting the foam core layer. It is preferably 0.7 to 2 parts by weight, more preferably 0.7 to 2 parts by weight.

In addition, in the present invention, the antistatic layer preferably does not substantially contain the anti-shrinkage agent. Since the antistatic layer does not substantially contain the anti-shrinkage agent, migration of the anti-shrinkage agent to the object to be packaged can be suppressed when the multilayer foam sheet and the object to be packaged come into contact with each other.
Here, "substantially free of anti-shrinkage agent" means that the content of the anti-shrink layer in the antistatic layer is approximately 5 parts by weight or less per 100 parts by weight of the antistatic layer. The content of the anti-shrinkage agent in the antistatic layer is more preferably 3 parts by weight or less, still more preferably 2 parts by weight or less. Most preferably, the antistatic layer does not contain an anti-shrinking agent.

Next, the physical properties of the multilayer foam sheet of the present invention will be described.
The overall thickness of the multilayer foam sheet is more than 2 mm and 30 mm or less. If the overall thickness is too small, electronic parts and the like, which require thickness and cushioning (appropriate compression characteristics), such as cushioning materials that can fill the space in the container, etc., for packing the items to be packaged. It may become difficult to use as a cushioning material for semiconductor products. If the overall thickness is too large, it may be difficult to obtain a multilayer foam sheet with excellent cushioning properties by extrusion foaming. From this point of view, the lower limit of the thickness is preferably 3 mm, more preferably 4 mm, and even more preferably 5 mm. The upper limit of the thickness is preferably 25 mm, more preferably 20 mm, still more preferably 16 mm.

The total thickness of the multilayer foam sheet is the arithmetic mean value of the thicknesses (mm) measured at intervals of 1 cm in the width direction over the entire width of the multilayer foam sheet.

In the present invention, the total basis weight of the multilayer foam sheet is preferably from 50 to 500 g/m ² because the multilayer foam sheet has an excellent balance between cushioning properties and lightness.
From this point of view, the total basis weight is more preferably 60-450 g/m ² , still more preferably 80-400 g/m ² .

The multilayer foam sheet has an overall apparent density of 0.01-0.1 g/cm ³ . When the overall apparent density is within the above range, the balance between physical properties such as rigidity and compressive strength and cushioning properties is excellent. If the overall apparent density is too low, the strength and cushioning properties will be too low, and there is a risk that it will not be usable as a cushioning material for electronic parts, semiconductor products, and the like. If the overall apparent density is too high, the cushioning properties may be reduced, resulting in increased cost. From this point of view, the lower limit of the total apparent density is preferably 0.015 g/cm ³ , more preferably 0.020 g/cm ³ , still more preferably 0.025 g/cm ³ . The upper limit of the apparent density is preferably 0.080 g/cm ³ , more preferably 0.060 g/cm ³ , still more preferably 0.050 g/cm ³ , and particularly preferably 0.040 g/cm 3 . ^cm3 .

The basis weight and overall apparent density of the multilayer foam sheet can be calculated as follows. First, the thickness of the multilayer foam sheet is calculated as described above. Next, the basis weight is measured. The basis weight [g/m ² ] of the multilayer foam sheet is obtained by cutting a test piece of a predetermined size (for example, 10 cm × width of the multilayer foam sheet × thickness of the multilayer foam sheet) from the multilayer foam sheet, and measuring the weight of the test piece [g ], and then divide this weight value by the area of the test piece. The basis weight [g/m ² ] thus obtained is divided by the thickness [mm] of the multilayer foam sheet, and the unit is converted to calculate the overall apparent density [g/cm ³ ] of the multilayer foam sheet. be able to.

In the present invention, the ratio of the basis weight (g/m ² ) per side of the intermediate layer to the total basis weight (g/m ² ) of the multilayer foam sheet is 0.02 to 0.25. preferable. By setting the ratio within the above range, shrinkage of the multilayer foam sheet can be suppressed, and a multilayer foam sheet having excellent cushioning properties and low cross-sectional resistivity can be stably obtained.
From this point of view, the lower limit of the ratio is more preferably 0.04, more preferably 0.06. Moreover, the upper limit thereof is preferably 0.20%, more preferably 0.15% by weight, and still more preferably 0.12% by weight.
From the same viewpoint, the basis weight per side of the intermediate layer is preferably 5 to 50 g/m ² , more preferably 10 to 30 g/m ² .

The basis weight of the intermediate layer can be calculated from the relationship between the weight and the area by cutting out the intermediate layer from the multilayer foam sheet, measuring the weight of the cut intermediate layer of a predetermined size. In addition, when the multilayer foam sheet is produced by co-extrusion, the following formula (1) is used to calculate the intermediate layer discharge amount per one side during extrusion X [g / hour], the foam sheet width W [m ] and the take-up speed L [m/h] of the foamed sheet during extrusion.

Basis weight of intermediate layer per side [g/m ² ]=[X/(L×W)] (1)

The basis weight of the antistatic layer may be calculated from the relationship between the weight and area of the antistatic layer by measuring the weight of the antistatic layer, and the thickness of the antistatic layer is multiplied by the density of the antistatic layer to convert the unit can be found by doing
The basis weight of the antistatic layer per side of the multilayer foam sheet is preferably approximately 1 to 50 g/m ² , more preferably 2 to 40 g/m ² , still more preferably 3 to 30 g/m 2 . ^m2 .

The 50% compressive strength of the multilayer foam sheet is preferably 0.050 to 0.15 MPa in order to enhance the cushioning properties. From this point of view, the lower limit of the compressive strength is preferably 0.060 MPa, more preferably 0.070 MPa. The upper limit of the compressive strength is preferably 0.12 MPa, more preferably 0.10 MPa.
From the same point of view, the 10% compression strength of the multilayer foam sheet is preferably 0.004 to 0.01 MPa, more preferably 0.005 to 0.008 MPa. Moreover, the 25% compressive strength of the multilayer foam sheet is preferably 0.020 to 0.030 MPa.

In the present invention, the ratio of the 50% compressive stress in the thickness direction of the multilayer foam sheet to the total apparent density of the multilayer foam sheet is required to be 2.0 MPa/(g/cm ³ ) or more.
When the ratio satisfies the above range, it means that the multilayer foam sheet has a low apparent density and moderate compression properties. Therefore, a multilayer foam sheet that satisfies the above ratio has excellent cushioning properties. It can be suitably used as a cushioning material for electronic parts, semiconductor products, etc., which require good elasticity (appropriate compressive properties).
In addition, when a large amount of shrinkage occurs in the foam sheet during the production of the multilayer foam sheet, the apparent density of the multilayer foam sheet tends to decrease and the compression characteristics tend to deteriorate. It becomes difficult to obtain a sheet.
In addition, from the viewpoint of allowing the multilayer foam sheet to exhibit appropriate cushioning properties, the upper limit of the ratio of the 50% compressive stress in the thickness direction of the multilayer foam sheet to the overall apparent density of the multilayer foam sheet is approximately 6.0 MPa / (g / cm ³ ), more preferably 5.0 MPa/(g/cm ³ ), even more preferably 4.0 MPa/(g/cm ³ ).

The 50% compressive stress in the thickness direction of the multilayer foam sheet is obtained as follows based on JIS K6767 (1999).
First, a test piece having a total thickness (mm) of the multilayer foam sheet, a length of 50 (mm), and a width of 50 (mm) is cut out from the multilayer foam sheet. Next, the test piece is compressed by 10%, 25%, and 50% with respect to the thickness of the test piece at a compression speed of 10 mm/min, and the compressive stress at each time point is measured. This measurement was performed three times or more, and the arithmetic average value of the compressive stress under each measured compression condition was calculated as 10% compressive stress (MPa), 25% compressive stress (MPa) and 50% compressive stress (MPa) of the multilayer foam sheet. and
If the thickness of the test piece (total thickness of the multilayer foam sheet) is less than 20 mm, multiple test pieces of a predetermined size cut from the multilayer foam sheet are stacked, and the total thickness of the test piece is 20 to 40 mm. The test piece is adjusted so that the total range and thickness of the test piece approaches 30 mm as much as possible. Using this thickness-adjusted test piece, the compressive stress is measured.

In the present invention, the average bubble diameter in the thickness direction is preferably 0.5 to 1.5 mm. By setting it as the said range, it can be set as the multilayer foam sheet which is excellent in cushioning property and surface smoothness, suppressing corrugation. From this point of view, the average cell diameter is more preferably 0.6 to 1.2 mm.
For the same reason, the average cell diameter in the horizontal direction of the multilayer foam sheet is preferably 0.5 to 1.5 mm, more preferably 0.6 to 1.2 mm.
In addition, the average cell diameter in the horizontal direction is the average cell diameter in one direction perpendicular to the thickness direction of the multilayer foam sheet (for example, the average cell diameter in the extrusion direction of the foam sheet), and the average cell diameter in the extrusion direction of the multilayer foam sheet. It is the geometric mean of the average cell diameter in the direction orthogonal to the one direction (for example, the average cell diameter in the width direction of the foam sheet).

The average bubble diameters in the thickness direction and horizontal direction can be obtained as follows.
First, a cut surface along the extrusion direction of the foam sheet (extrusion direction vertical cross section) and a cut surface along the thickness direction of the foam sheet and perpendicular to the extrusion direction (width direction vertical cross section) are cut out and examined with a microscope or the like at a magnification of 50. magnify to obtain magnified images of each section. Next, the bubble diameters in the thickness direction, extrusion direction, and width direction of each bubble are measured for all bubbles observed on the enlarged image. Five positions for cutting the extruded foam sheet are selected at random, the cut surface is specified at each position, and the diameter of each cell in each vertical section is measured by the method for measuring the diameter of cells described above. The measured cell diameters are arithmetically averaged, and the obtained values are defined as the average cell diameters in the thickness direction, extrusion direction and width direction. Further, the average cell diameter in the horizontal direction is calculated by taking the geometric mean of the average cell diameter in the extrusion direction and the average cell diameter in the width direction.

Since peeling of the antistatic layer can be suppressed, the peel strength when the antistatic layer is peeled off from the multilayer foam sheet is preferably 1 N/25 mm or more, more preferably 2 N/25 mm or more, and still more preferably 3 N. /25 mm or more, particularly preferably 5 N/25 mm or more.
The upper limit is preferably approximately 20 N/25 mm, more preferably 15 N/25 mm.

Peel strength is measured as follows.
First, from a multilayer foam sheet, a belt-shaped test piece with a width of 25 mm and a length of 1000 mm is cut out parallel to the direction of extrusion. Then, in accordance with JIS Z0237, each antistatic layer is subjected to a 90° peeling test at a peeling speed of 100 mm / min, and the arithmetic average value of the obtained measured values (N / 25 mm) is taken as the peel strength. .

In the present invention, the multilayer foam sheet should have a surface resistivity of less than 1×10 ¹² Ω.
Since the antistatic layer is laminated and adhered to the intermediate layer, the multilayer foam sheet of the present invention has excellent antistatic properties on the surface, and can be used as a packaging material or cushioning material for electronic parts or semiconductor products. It can be preferably used.
The surface resistivity is preferably 1×10 ¹¹ Ω or less, more preferably 1×10 ¹⁰ Ω or less, in order to further prevent charging of the multilayer foam sheet.
Although the lower limit of the surface resistivity is not particularly limited, it is preferably approximately 1×10 ⁷ Ω.

The surface resistivity in this specification is measured according to JIS K6271 (2008). Specifically, first, a test piece of 100 mm length x 100 mm width x thickness: the thickness of the multilayer foam sheet is cut out from the multilayer foam sheet, and the test piece is left in an atmosphere at a temperature of 23°C and a relative humidity of 50% for 24 hours. condition adjustment. Next, a voltage of 500 V is applied to each surface of the test piece in an atmosphere of 23° C. and a relative humidity of 50%, and the surface resistivity [Ω] of the test piece is measured 1 minute after application.

Furthermore, the cross-sectional surface resistivity (also simply referred to as cross-sectional resistivity) of the foamed core layer of the multi-layer foamed sheet is required to be less than 1×10 ¹² Ω. Even if the surface resistivity is less than 1×10 ¹² Ω, if the surface resistivity of the foam core layer in the cross section of the multilayer foam sheet is high, the multilayer foam sheet will be charged, and the electronic components, etc., which are the packaged items, will be damaged. There is a risk of damage due to impact. From this point of view, the cross-sectional resistivity is preferably 1×10 ¹¹ Ω or less, more preferably 5×10 ¹⁰ Ω or less.
Although the lower limit of the cross-sectional resistivity is not particularly limited, it is preferably approximately 1×10 ⁷ Ω.

The measurement of cross-sectional resistivity in this specification is performed as follows in accordance with JIS C2170 (2004). First, a test piece of length 100 mm x width 100 mm x thickness: the thickness of the multilayer foam sheet is cut out from the multilayer foam sheet, and left in an atmosphere of 23°C and 50% relative humidity for 24 hours to condition the test piece. . Next, a voltage was applied at an applied voltage of 100 V to the four cross-sectional foam core layers of each test piece, and after 15 seconds from the start of voltage application, the surfaces of the four cross-sectional foam core layers Each resistivity is measured and the arithmetic mean value of these is determined. This measurement is performed on five test pieces, and the arithmetic mean value of these is taken as the cross-sectional resistivity of the multilayer foam sheet.
As a measuring device, for example, PROSTAT PRS-801 (microprobe: PRF-912B) can be used. In this case, the center of the probe shall be positioned at the center of the multilayer foam sheet in the thickness direction.

The cushioning properties of the multilayer foam sheet can be increased, and when the antistatic layer is laminated by heat lamination or the like, the peel strength between the antistatic layer and the intermediate layer can be increased. The closed cell ratio is preferably 30% or more, more preferably 40% or more, and still more preferably 60% or more. The upper limit of the closed cell content is preferably approximately 90%.

The closed cell ratio of the multilayer foam sheet: S (%) was measured using an air comparison type hydrometer (manufactured by Toshiba Beckman Co., Ltd., Model 930) in accordance with Procedure C described in ASTM D2856-70. Actual volume of multilayer foam sheet (sum of volume of closed cells and volume of resin portion): can be calculated from Vx(L) by the following formula (2). For example, the foam sheet having a three-layer structure during production of the multilayer foam sheet of the present invention can also be similarly measured for closed cell content.
S (%) = (Vx-W/ρ) x 100/(Va-W/ρ) (2)
However, Va, W, and ρ in the above formula (2) are as follows.
Va: Apparent volume of multilayer foam sheet used for measurement (cm ³ )
W: Weight of multilayer foam sheet in test piece (g)
ρ: Density of resin constituting multilayer foam sheet (g/cm ³ )
In the measurement, a test piece having a length of 25 mm, a width of 40 mm, and the total thickness of the multilayer foam sheet is cut out from the multilayer foam sheet and used for the measurement. When the thickness of the test piece (total thickness of the multilayer foam sheet) is less than 20 mm, multiple test pieces of a predetermined size cut from the multilayer foam sheet are stacked, and the total thickness of the test piece is within a range of 20 to 40 mm. In addition, the test piece is adjusted so that the total thickness of the test piece approaches 25 mm as much as possible, and the closed cell ratio is measured using this thickness-adjusted test piece.
Further, the density ρ of the resin constituting the multilayer foam sheet can be determined from a non-foamed sample obtained by defoaming the multilayer foam sheet by, for example, heat pressing.

Next, the method for producing the multilayer foam sheet of the present invention will be described.
The multilayer foam sheet of the present invention has a foam core layer and an intermediate layer laminated and adhered to the foam core layer, and the intermediate layer is preferably laminated and adhered to the foam core layer by a co-extrusion foaming method. . Three embodiments are exemplified as the production method using the co-extrusion foaming method.
A first aspect of manufacturing a multilayer foam sheet is a method of manufacturing a multilayer foam sheet in one step by a co-extrusion method. Specifically, an extruder for forming a foam core layer is used to form a molten resin for forming a foam core layer, an extruder for forming an intermediate layer is used to form a molten resin for forming an intermediate layer, and an extruder for forming an antistatic layer is formed. An extruder is used to form a molten resin for forming an antistatic layer, these are introduced into a co-extrusion die, and the molten resin for forming an intermediate layer is laminated on both sides of the molten resin for forming a foamed core layer. The antistatic layer-forming molten resin is laminated on both sides of the forming molten resin, and these are extruded from a co-extrusion die into a low-pressure atmosphere (usually atmospheric pressure) to foam the foaming core layer-forming molten resin. At the same time as forming a foam core layer, a multilayer foam sheet having a five-layer structure can be obtained in which an intermediate layer is laminated on both sides of the foam core layer and an antistatic layer is laminated on both sides of the intermediate layer.

The molten resin for forming the foamed core layer comprises the polyethylene resin, the polymeric antistatic agent (A), the shrinkage inhibitor blended as necessary, and a cell control agent to form the foamed core layer. It is supplied to an extruder for industrial use, heat-melted and kneaded to obtain a molten resin, and a physical foaming agent is injected into the molten resin to form the resin.

The molten resin for forming the intermediate layer is obtained by supplying the polyethylene-based resin and the shrinkage preventing agent to the extruder for forming the intermediate layer, heat-melting and kneading to obtain a molten resin, and optionally adding a volatile It can be formed by injecting a plasticizer or a physical blowing agent.

The antistatic layer-forming molten resin is obtained by supplying the polyethylene-based resin and the polymeric antistatic agent (B) to the antistatic layer-forming extruder, heating, melting and kneading to form a molten resin. , can be formed by pressing a volatile plasticizer into it as needed.

A second mode of manufacturing a multilayer foam sheet is to form a foam sheet having a three-layer structure in which an intermediate layer is laminated and adhered to both sides of a foam core layer in one step by the coextrusion method described above, and the intermediate layer is subjected to heat treatment. This is a method of obtaining a multilayer foam sheet by laminating or adhering an antistatic layer containing a polymeric antistatic agent (B) by lamination or extrusion lamination.
When a heat lamination method is employed, a multilayer foam sheet can be obtained by laminating and adhering polyethylene-based resin antistatic films containing the polymeric antistatic agent (B) by heat lamination. In the case of extrusion lamination, a polyethylene resin and a polymeric antistatic agent (B) are supplied to an extruder for extrusion lamination to form a molten resin, and the resulting molten resin is formed into a film using a T-die. A multilayer foam sheet can be obtained by extrusion and lamination bonding.
In adopting the co-extrusion method in the second aspect, the molten resin for forming the foam core layer and the molten resin for forming the intermediate layer are the same as the molten resin for forming the foam core layer and the molten resin for forming the intermediate layer in the first aspect. can be formed in the same manner as

A third aspect of manufacturing a multilayer foam sheet is to first form a three-layer structure foam sheet in which intermediate layers are laminated and adhered to both sides of a foam core layer in one step by the co-extrusion method described above. An antistatic layer containing a polymeric antistatic agent (B) is laminated and adhered to one side of the foamed sheet by heat lamination or extrusion lamination to produce a laminated foamed sheet having an antistatic layer laminated only on one side. do. Next, of the two laminated foamed sheets thus produced, the intermediate layers on which the antistatic layer is not laminated are respectively heated with hot air or the like, and then the intermediate layers are overlapped and heat-sealed to obtain a multilayered foamed sheet. The method.
In this case, the two heat-sealed intermediate layers become part of the foam core layer in the multilayer foam sheet. Further, in adopting the co-extrusion method in the third aspect, the molten resin for forming the foam core layer and the molten resin for forming the intermediate layer are the same as the molten resin for forming the foam core layer and the molten resin for forming the intermediate layer in the first aspect. can be formed in the same manner as

From the viewpoint that it is easy to obtain a wide foam sheet having a width of 1000 mm or more, the co-extrusion method involves co-extrusion of molten resin into a tubular shape using an annular die to produce a tubular multilayer foam, and then a mandrel or the like. It is preferable to adopt a method of manufacturing a multilayer foam sheet by cutting open the tubular multilayer foam along the extrusion direction while pulling the tubular multilayer foam along the widening device.

Examples of physical foaming agents added to the molten resin for forming the foam core layer and the molten resin for forming the intermediate layer include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, normal hexane, and isohexane. , cyclopentane, cyclohexane, and other alicyclic hydrocarbons; methyl chloride, ethyl chloride, and other chlorinated hydrocarbons; 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, and other fluorocarbons; Inorganic physical foaming agents such as system physical foaming agents, nitrogen, carbon dioxide, air and water can be used. In some cases, decomposable blowing agents such as azodicarbonamide can also be used. Two or more of the physical foaming agents described above can be used in combination. Among these, it is preferable to use an organic physical foaming agent from the viewpoint of excellent extrusion foamability of the polyethylene resin, and among them, those containing normal butane, isobutane, or a mixture thereof as a main component can be preferably used.

The amount of physical foaming agent added is adjusted according to the type of foaming agent and the desired apparent density. For example, in order to obtain a multilayer foam sheet having the above apparent density range using a mixed butane containing 30% by weight of isobutane and 70% by weight of normal butane as a foaming agent, the added amount of the mixed butane is It is preferably 3 to 30 parts by weight, more preferably 4 to 20 parts by weight, still more preferably 6 to 18 parts by weight.

The volatile plasticizer is selected from aliphatic hydrocarbons and alicyclic hydrocarbons having 3 to 7 carbon atoms, aliphatic alcohols having 1 to 4 carbon atoms, and aliphatic ethers having 2 to 8 carbon atoms. A species or two or more species can be preferably used.

A cell regulator is usually added to the molten resin for forming the foamed core layer. Both organic and inorganic foam control agents can be used. Examples of inorganic cell control agents include metal borate salts such as zinc borate, magnesium borate, and borax, sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate, sodium bicarbonate, and the like. Examples of organic foam control agents include 2,2-methylenebis(4,6-tert-butylphenyl)sodium phosphate, sodium benzoate, calcium benzoate, aluminum benzoate, and sodium stearate. A combination of citric acid and sodium bicarbonate, an alkali salt of citric acid and sodium bicarbonate, or the like can also be used as the cell control agent. These cell control agents can also use 2 or more types together. These additives can also be added to the molten resin for forming the intermediate layer, if necessary.
The addition amount of the cell control agent is preferably 0.01 to 3 parts by weight, more preferably 0.1 to 1 part by weight, per 100 parts by weight of the base resin constituting each layer.

INDUSTRIAL APPLICABILITY The multi-layer foam sheet of the present invention can be suitably used as a cushioning material for electronic parts, semiconductor products, and the like, in applications where an object to be packaged is inserted into a container or the like and packed. The multilayer foam sheet of the present invention has appropriate thickness, flexibility, strength, and cushioning properties. By filling the space inside the container or the like containing the object to be packaged without gaps, it is possible to suppress the movement of the object to be packaged inside the container. Furthermore, the multi-layered foam sheet absorbs external shocks and the like in the sealed container, thereby protecting the packaged items against shocks.

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the examples.

In Examples and Comparative Examples, the following polyethylene resins, polymeric antistatic agents, shrinkage inhibitors, and cell control agents were used.
(1) Polyethylene resin Abbreviated name “LDPE1”: “8321” manufactured by NUC Co., Ltd. (density 920 kg/m ³ , MFR 2.4 g/10 minutes)
Abbreviated name “LDPE2”: “NS-1s” manufactured by NUC Co., Ltd. (density 920 kg/m ³ , MFR 0.3 g/10 minutes)
(2) Polymeric antistatic agent (A), polymeric antistatic agent (B)
Abbreviated name “SD100”: “Potassium ionomer polymer type antistatic agent: Entira SD100” manufactured by DuPont Mitsui Polychemical Co., Ltd. (density 970 kg/m ³ , MFR 1.5 g/10 minutes, melting point 93° C., surface resistivity 1.0%) 0×10 ⁷ Ω)
(3) Anti-shrinkage agent abbreviation "GMS": stearic acid monoglyceride (4) Cellular regulator talc (manufactured by Matsumura Sangyo Co., Ltd., high filler #12)
(5) Physical blowing agent abbreviation "SB": mixed butane (normal butane / isobutane = 70 wt% / 30 wt%)

The following apparatus was used in Examples and Comparative Examples.
(1) Apparatus for manufacturing a laminated foam sheet with a three-layer structure A tandem extruder in which a first single-screw extruder with an inner diameter of 115 mm and a second single-screw extruder with an inner diameter of 180 mm are connected in series as an extruder for forming a foam core layer. Using. A single-screw third extruder with an inner diameter of 115 mm was used as an intermediate layer forming extruder. An annular co-extrusion die was attached to the outlet of the second extruder, and the outlet of the third extruder was connected to the co-extrusion die to form a co-extrusion apparatus.

Example 1
A polyethylene resin (low density polyethylene) of the type shown in Table 1, a polymeric antistatic agent (A), an anti-shrinking agent, and a cell control agent are supplied to the first extruder, heated and melted and kneaded, and then introduced into the same extruder. After injecting and kneading the physical foaming agent of the type and amount shown in Table 1, the extruded resin temperature was adjusted to that shown in Table 3 by a second extruder to obtain a molten resin for forming a foam core layer. The polyethylene resin was supplied in a total of 100 parts by weight so that the mass ratio of LDPE1 and LDPE2 was 1:1. Moreover, the amounts (parts by weight) of the shrinkage inhibitor, the cell control agent, and the physical foaming agent are the values (parts by weight) per 100 parts by weight of the polyethylene resin. The blending amount (% by weight) of the polymeric antistatic agent (A) is the value (% by weight) relative to the total 100% by weight of the polyethylene resin and the polymeric antistatic agent (A).
Similarly, the type of polyethylene resin (low-density polyethylene) shown in Table 2, the shrinkage inhibitor, the physical foaming agent, and the cell adjustment agent are supplied to the third extruder according to the formulation shown in Table 2, and after heating, melting and kneading, After injecting and kneading physical foaming agents of the type and amount shown in Table 2, the extruded resin temperature was adjusted to that shown in Table 3 to obtain a molten resin for forming an intermediate layer. The amounts (parts by weight) of the anti-shrinkage agent, physical foaming agent, and cell regulator are values (parts by weight) per 100 parts by weight of the polyethylene resin. The blending amount (% by weight) of the polymeric antistatic agent (B) is a value (% by weight) relative to the total 100% by weight of the polyethylene resin and the polymeric antistatic agent (B).

The molten resin for forming the foam core layer and the molten resin for forming the intermediate layer are introduced into the coextrusion annular die at the total discharge amount and the discharge amount ratio shown in Table 3, respectively, and the molten resin for forming the intermediate layer is introduced into the die. is laminated on both sides (outer surface and inner surface) of the molten resin for forming the foam core layer flowing in an annular shape, and coextruded from an annular die lip (diameter 96 mm) attached to the downstream side of the annular co-extrusion die to form a foam core The layer forming molten resin and the intermediate layer forming molten resin were foamed into a cylindrical shape. The obtained cylindrical foam was cut open while being drawn along a cylindrical cooling pipe (345 mm in diameter) to obtain a three-layer foam sheet. In addition, the molten resin for forming the intermediate layer is distributed at a discharge ratio of 1:1 by a distributor attached to the downstream side of the second extruder, and then introduced into the co-extrusion die to obtain a foam core. It laminated|stacked on both surfaces of the molten resin for layer formation.
Table 4 shows the physical properties of the obtained three-layer foamed sheet.
The intermediate layer was foamed to have the same apparent density as the foam core layer.

In Table 4, the thickness, apparent density, and closed cell ratio were measured by the methods described above.

In Table 4, the presence or absence of shrinkage was visually determined. Specifically, when no significant shrinkage is observed in the foam sheet immediately after production, and the thickness of the foam sheet cured for 24 hours at a temperature of 40°C is equal to or greater than the thickness of the foam sheet immediately after production. "Shrinkage: none" indicates that the foam sheet immediately after production has a large shrinkage, or the foam sheet cured for 24 hours at a temperature of 40 ° C has not recovered to the thickness of the foam sheet immediately after production. "Shrinkage: Yes" was determined.

On one side of the three-layer foamed sheet obtained above, a polyethylene resin film containing the following polymeric antistatic agent for forming an antistatic layer is laminated and adhered by heat lamination, and an antistatic layer is formed on one side. A laminated foam sheet having
Polyethylene resin film: base resin "low density polyethylene", polymeric antistatic agent (B) "SD100 (content 15% by weight)", basis weight 20 g/m ²
The content (% by weight) of the polymeric antistatic agent (B) is the value (% by weight) relative to the total 100% by weight of the polyethylene resin and the polymeric antistatic agent (B).

Next, using a hot air lamination device, after heating the intermediate layers on which the antistatic layer is not laminated of the two laminated foam sheets produced by heating with hot air, the intermediate layers are overlapped and heat-sealed. to obtain a multilayer foamed sheet having a 5-layer structure having antistatic layer/intermediate layer/foam core layer/intermediate layer/antistatic layer.
Tables 5 and 6 show the physical properties of the resulting multilayer foam sheet. The resulting multilayer foam sheet was excellent in surface antistatic properties, cross-sectional antistatic properties, peel strength, and compression properties.

Example 2
A laminated foam sheet was produced in the same manner as in Example 1, except that the die lip clearance was made larger than in Example 1 and the die pressure was made lower. The resulting foamed sheet had a lower closed cell content than the foamed sheet obtained in Example 1. A multilayer foam sheet was produced in the same manner as in Example 1 using the obtained laminated foam sheet. The resulting multilayer foam sheet was excellent in surface antistatic properties and cross-sectional antistatic properties. However, the 90° peel strength and compression properties were lower than those of Example 1.

Example 3
A laminated foam sheet was produced in the same manner as in Example 1, except that the die lip clearance was made larger than in Example 2 and the die pressure was lowered. The resulting foamed sheet had a lower closed cell content than the foamed sheet obtained in Example 2. A multilayer foam sheet was produced in the same manner as in Example 1 using the obtained laminated foam sheet. The resulting multilayer foam sheet was excellent in surface antistatic properties and cross-sectional antistatic properties. However, the 90° peel strength and compression properties were lower than those of Example 2.

Example 4
A foam sheet was produced in the same manner as in Example 1, except that the take-up speed was made lower than in Example 1 and the thickness and basis weight were increased. A multilayer foam sheet was produced in the same manner as in Example 1 using the obtained foam sheet. The resulting multilayer foam sheet was excellent in surface antistatic properties, cross-sectional antistatic properties, peel strength, and compression properties.

Example 5
A foam sheet similar to that of Example 1 was produced, and the same polyethylene-based resin films as in Example 1 were laminated and adhered to both sides of this foam sheet to obtain a multi-layer foam sheet having a five-layer structure. The resulting multilayer foam sheet was excellent in surface antistatic properties, cross-sectional antistatic properties, peel strength, and compression properties.

Comparative example 1
As an extruder for forming a foam core layer, an extruder in which a first single-screw extruder with an inner diameter of 115 mm and a second single-screw extruder with an inner diameter of 180 mm are connected in series is used alone, and the manufacturing conditions shown in Tables 1 and 3 are used. This is an example in which a foamed sheet consisting only of a foamed core layer was obtained in the same manner as in Example 1 except that the foamed core layer was formed.
The obtained foam sheet shrinks significantly after production because the intermediate layer containing the shrinkage preventing agent is not laminated and adhered, and the foam core layer contains the polymer type antistatic agent (A) together with the shrinkage preventing agent. However, the thickness was not fully restored by curing. A multilayer foam sheet (antistatic layer/foamed core layer/antistatic layer) was produced in the same manner as in Example 1 using the resulting foamed sheet. The resulting multilayer foam sheet had a low compression stress ratio (50% compression stress/total apparent density).

Comparative example 2
This is an example of producing a foamed sheet in the same manner as in Example 1, except that the type and amount of polymeric antistatic agent (B) shown in Table 2 was added to the intermediate layer together with the shrinkage preventing agent. By blending the polymer type antistatic agent (B) in the intermediate layer, the anti-shrinkage effect of the anti-shrinkage agent is not exhibited, and the resulting foam sheet shrinks significantly after production, and the thickness is sufficiently recovered by curing. It was not. A multi-layer foamed sheet was produced in the same manner as in Example 1 using the obtained foamed sheet. The resulting multilayer foam sheet had a low compression stress ratio (50% compression stress/total apparent density).

Comparative example 3
This is an example in which a foamed sheet consisting of only a foamed core layer was obtained in the same manner as in Comparative Example 1, except that the polymeric antistatic agent (A) was not added to the molten resin for forming the foamed core layer.
A multilayer foam sheet (antistatic layer/foamed core layer/antistatic layer) was produced in the same manner as in Example 1 using the resulting foamed sheet. The multi-layered foam sheet thus obtained was inferior in antistatic properties of the cross section of the foam sheet.

In Table 5, the overall thickness, overall apparent density, overall basis weight, closed cell ratio, and average cell diameter were measured by the methods described above.
The total basis weight is measured by the method described above, and the basis weight of the foam core layer and the basis weight of the intermediate layer (one side) are determined by measuring the total basis weight of the molten resin for forming the foam core layer and the molten resin for forming the foam intermediate layer. It was obtained by dividing proportionally by the ratio of the amounts.
The basis weight of the antistatic layer (one side) is the basis weight of the laminated polyethylene resin film.
In the basis weight configuration (intermediate layer/foam core layer/intermediate layer), the basis weights of the intermediate layer and the foam core layer are the basis weight of the foam core layer and the basis weight of the intermediate layer in Table 4, and the layer configuration of the multilayer foam sheet. It is a value calculated from The two intermediate layers of the foam sheet heat-sealed during the production of the multilayer foam sheet were regarded as the foam core layer, and the basis weight of the foam core layer was calculated.

In Table 6, antistatic properties (surface resistivity, cross-sectional resistivity), 90° peel strength, and compressive stress were determined by the methods described above.

Claims (11)

a polyethylene-based resin foam core layer, a polyethylene-based resin intermediate layer laminated and bonded to both sides of the foam core layer and positioned between the polyethylene-based resin foam core layer and the polyethylene-based resin antistatic layer; In a multilayer foam sheet having a polyethylene-based resin antistatic layer laminated and adhered to each of the intermediate layers,
The foam core layer contains one or more polymeric antistatic agents (A) selected from polyethers, polyetheresteramides, block copolymers of polyethers and polyolefins, and ionomer resins. ,
The antistatic layer contains one or more polymeric antistatic agents (B) selected from polyethers, polyetheresteramides, block copolymers of polyethers and polyolefins, and ionomer resins. ,
the intermediate layer contains one or more anti-shrinkage agents selected from fatty acid esters, fatty amines and fatty acid amides and is substantially free of polymeric antistatic agents;
The multilayer foam sheet has an overall thickness of more than 2 mm and 30 mm or less, and an overall apparent density of the multilayer foam sheet of 0.01 to 0.1 g/cm ³ ,
A ratio of 50% compressive stress in the thickness direction of the multilayer foam sheet to the total apparent density of the multilayer foam sheet is 2.0 MPa/(g/cm ³ ) or more,
A polyethylene-based resin multilayer foam sheet, wherein the surface resistivity of the multilayer foam sheet is less than 1×10 ¹² Ω, and the surface resistivity of the foam core layer in the cross section of the multilayer foam sheet is less than 1×10 ¹² Ω.
The content of the polymeric antistatic agent (A) in the foam core layer is 5 to 5% with respect to the total 100% by weight of the polyethylene resin and the polymeric antistatic agent (A) constituting the foam core layer. The polyethylene-based resin multilayer foam sheet according to claim 1, which is 30% by weight.
The content of the polymeric antistatic agent (B) in the antistatic layer is 5 to 100% by weight in total of the polyethylene resin and the polymeric antistatic agent (B) constituting the antistatic layer. The polyethylene-based resin multilayer foam sheet according to claim 1 or 2, which is 30% by weight.
The polyethylene-based resin multilayer foam sheet according to any one of claims 1 to 3, wherein the polymeric antistatic agent (A) and the polymeric antistatic agent (B) are ionomer resins.
5. The method according to any one of claims 1 to 4, wherein the amount of the shrinkage inhibitor in the intermediate layer is 0.7 to 3 parts by weight with respect to 100 parts by weight of the polyethylene resin constituting the intermediate layer. Polyethylene resin multilayer foam sheet.
The polyethylene-based resin multilayer according to any one of claims 1 to 5, wherein the foam core layer contains one or more shrinkage inhibitors selected from fatty acid esters, fatty amines and fatty acid amides. foam sheet.
The polyethylene according to any one of claims 1 to 6, wherein the antistatic layer does not substantially contain one or more anti-shrinkage agents selected from fatty acid esters, fatty amines and fatty acid amides. A multi-layer foamed sheet made of resin.
The polyethylene-based resin multilayer foam sheet according to any one of claims 1 to 7, wherein the closed cell rate of the multilayer foam sheet is 30% or more.
The polyethylene-based resin multilayer foam sheet according to any one of claims 1 to 8, wherein the multilayer foam sheet has an overall apparent density of 0.015 to 0.060 g/cm ³ .
The ratio of the basis weight [g/m ² ] per side of the intermediate layer to the total basis weight [g/m ² ] of the multilayer foam sheet is 0.02 to 0.25. The polyethylene-based resin multilayer foam sheet according to any one of items.
The foam core layer of the multilayer foam sheet has an average cell diameter in the thickness direction of 0.5 to 1.5 mm and an average cell diameter in the horizontal direction of 0.5 to 1.5 mm. The polyethylene-based resin multilayer foam sheet according to any one of items .