JP2022001411A - Polyethylene-based resin multilayer extrusion expanded sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer extruded foam sheet having excellent antistatic performance, excellent slipperiness and good appearance, while extremely suppressing the transfer of low molecular weight components and the like to an object to be packaged or the like. Make it an issue.
SOLUTION: The polyethylene-based resin multilayer extruded foam sheet of the present invention is used.
It has a polyethylene-based resin foam layer and a resin layer laminated by coextrusion.
The resin layer has an antistatic layer and a non-antistatic layer,
The antistatic layer contains a polyethylene-based resin (B) and an ionomer resin, and in a specific vertical cross section (a), a dispersed phase in which the ionomer resin is layered in a continuous phase of the polyethylene-based resin (B). The average number of layers of the formed and dispersed phase is 3 or more per 1 μm in the thickness direction.
The non-antistatic layer contains the polyethylene-based resin (C) and substantially no antistatic agent.
The average thickness of the non-antistatic layer is within a specific range,
The surface resistivity of the multilayer extruded foam sheet is 1 × 10 ¹² Ω or less.

[Selection diagram] None

Description

The present invention relates to a polyethylene-based resin multi-layer extruded foam sheet. Specifically, the present invention is a polyethylene-based resin multi-layer extruded foam sheet that can be used as a paper or packaging material for electronic devices, etc., and has a good appearance and excellent antistatic performance. At the same time, the present invention relates to a multi-layer extruded foam sheet in which the amount of low molecular weight components and the like transferred to an object to be packaged is extremely small.

A multi-layer extruded foam sheet in which a resin layer made of polyethylene resin is laminated on a foam sheet made of polyethylene resin is lightweight and has excellent cushioning properties, so that it is packed between glass plates used for liquid crystal panels. It is widely used in the packaging field of electronic devices such as interleaving paper and its materials.

In such applications, usually, in order to suppress the adhesion of dust, dust, etc. to the polyethylene-based resin multi-layer extruded foam sheet (hereinafter, also simply referred to as multi-layer extruded foam sheet or foam sheet), the multi-layer extruded foam sheet is used. Antistatic performance is added. As a method of imparting antistatic performance to a multi-layer extruded foam sheet, for example, when a multi-layer extruded foam sheet is manufactured by a coextrusion method, a polymer-type antistatic agent is added to a resin melt for forming a resin layer. Then, coextrusion is performed to form a resin layer containing a polymer-type antistatic agent (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2016-20427

When the multi-layer extruded foam sheet is used as the interstitial paper or the like, it is required not only to have excellent antistatic properties but also to not contaminate an object to be packaged such as a glass plate. In addition, in recent years, in multi-layer extruded foam sheets used for interstitial paper for glass plates for electronic devices, in order to further suppress contamination of the packaged material, a low molecular weight derived from a polymer-type antistatic agent is used. There is a demand for a multi-layer extruded foam sheet in which the transfer of contaminants such as components to the packaged material is further suppressed.

In order to reduce the transfer amount of the low molecular weight component or the like, it is conceivable to use a high molecular weight antistatic agent having a low content of the low molecular weight component. Examples of the high molecular weight antistatic agent having a low content of low molecular weight components include ionomer resins.

However, conventionally, when a polyethylene-based resin layer containing an ionomer resin (hereinafter, also simply referred to as a resin layer) is laminated on a polyethylene-based resin foamed layer by coextrusion to produce a multi-layer extruded foamed sheet, desired charging is desired. It was difficult to stably develop the preventive property, and it was difficult to stably produce a multilayer extruded foam sheet having good antistatic performance.

Further, the multi-layer extruded foam sheet containing an ionomer resin tends to be inferior in slipperiness, and depending on the application, the workability when packaging the object to be packaged with the multi-layer extruded foam sheet may be lowered. Further, when the multi-layer extruded foam sheet is manufactured by the co-extrusion method, if the amount of the ionomer resin blended in the resin layer is increased, the slipperiness of the multi-layer extruded foam sheet is lowered, and the multi-layer extruded foam sheet is wavy when it is picked up. In some cases, it may be difficult to pick up the foam, or the traces may remain and the appearance of the foamed sheet may be impaired.

Further, even when the ionomer resin is used as the antistatic agent, the low molecular weight component slightly contained in the ionomer resin may be transferred to the packaged material, and depending on the application, the low molecular weight component may be transferred to the packaged material. There is a demand for a multi-layer extruded foam sheet with extremely suppressed migration.

The present invention solves the above-mentioned problems and provides a multilayer extruded foam sheet having excellent antistatic performance, excellent slipperiness, and a good appearance, while extremely suppressing the transfer of low molecular weight components and the like to an object to be packaged or the like. The task is to do.

According to the present invention, the multi-layer extruded foam sheet shown below is provided.
[1] A multi-layer extruded foam sheet having a foam layer made of a polyethylene-based resin (A) and a resin layer laminated by coextrusion on at least one side of the foam layer.
The resin layer has an antistatic layer and a non-antistatic layer located on the surface of the multilayer extruded foam sheet.
The antistatic layer contains a polyethylene-based resin (B) and an ionomer resin-based antistatic agent, and the ionomer resin-based antistatic agent is formed in a vertical cross section (a) orthogonal to the width direction of the multilayer extruded foam sheet. Formed a dispersed phase dispersed in layers in the continuous phase of the polyethylene resin (B), and the average number of layers of the dispersed phase was 3 or more per 1 μm in the thickness direction of the multilayer extruded foam sheet.
The non-antistatic layer contains a polyethylene-based resin (C) and substantially no antistatic agent.
The average thickness of the antistatic layer is 0.5 to 15 μm, and the antistatic layer has an average thickness of 0.5 to 15 μm.
A polyethylene-based resin multi-layer extruded foam sheet having a surface resistivity of the surface of the multi-layer extruded foam sheet on the resin layer side of 1 × 10 ^{12 Ω or less.}
[2] The multilayer extruded foam sheet according to 1 above, wherein the dispersed phase has an average aspect ratio of 2 or more in the vertical cross section (a).
[3] The polyethylene according to 1 or 2 above, wherein in the vertical cross section (a), the median value of the dispersed area based on the number of dispersed phases is 1 × 10 ^{2 to} 5 × 10 ⁵ nm ^2. Based resin multi-layer extruded foam sheet.
[4] The polyethylene according to any one of 1 to 3 above, wherein the median horizontal dispersion diameter based on the number of dispersed phases is 200 to 3000 nm in the vertical cross section (a). Based resin multi-layer extruded foam sheet.
[5] In the vertical cross section (a), the average value of the area occupied by the dispersed phase is 30 in the rectangular range of the central portion of the antistatic layer having a length of 500 nm in the thickness direction and a length of 1500 nm in the width direction. The polyethylene-based resin multilayer extruded foam sheet according to any one of 1 to 4 above, which is characterized by having an area of about 80%.
[6] The antistatic layer contains polyalkylene glycol, and the content of the polyalkylene glycol is 0.3 with respect to a total of 100 parts by weight of the polyethylene-based resin (B) and the ionomer resin-based antistatic agent. The polyethylene-based resin multilayer extruded foam sheet according to any one of 1 to 5 above, which is characterized by having an amount of about 6 parts by weight.
[7] The polyethylene-based resin multilayer extruded foam sheet according to any one of 1 to 6, wherein the surface resistivity is ^{less than 1 × 10 10 Ω.}

The polyethylene-based resin multilayer extruded foam sheet of the present invention has a foam layer and a resin layer, and the resin layer has an antistatic layer and a non-antistatic layer that does not substantially contain an antistatic agent. .. Further, in the antistatic layer, the ionomer resin-based antistatic agent is present in a specific morphology, and the thickness of the non-antistatic layer is in a specific range, so that the foamed sheet has excellent antistatic properties. There is. Further, even though the antistatic layer contains an ionomer resin-based antistatic agent, the thickness of the non-antistatic layer is within a specific range, so that it can be applied to an object to be packaged such as a low molecular weight component in the ionomer resin. Transition is extremely suppressed. Further, by providing the non-antistatic layer, the foamed sheet is a multi-layer extruded foamed sheet having excellent slipperiness and a good appearance.

FIG. 1 is a drawing showing an example of a cross-sectional view of the multilayer extruded foam sheet of the present invention. FIG. 2 is an electron micrograph (magnification: 17500 times) of the multilayer extruded foam sheet obtained in Example 1 in which a vertical cross section (a) was taken. FIG. 2 is an electron micrograph (magnification: 70,000 times) of the multilayer extruded foam sheet obtained in Example 1 in which a vertical cross section (a) was taken. FIG. 2 is an electron micrograph (magnification: 17500 times) of the multilayer extruded foam sheet obtained in Comparative Example 1 in which a vertical cross section (a) was taken.

Hereinafter, the polyethylene-based resin multi-layer extruded foam sheet of the present invention (hereinafter, also simply referred to as a multi-layer extruded foam sheet or a foam sheet) will be described in detail.
The multi-layer extruded foam sheet of the present invention is a multi-layer extruded foam sheet having a foam layer made of a polyethylene-based resin (A) and a resin layer laminated by coextrusion on at least one side of the foam layer. Further, the resin layer has an antistatic layer and a non-antistatic layer. Therefore, the multilayer extruded foam sheet has at least a three-layer structure (non-antistatic layer / antistatic layer / foam layer), and as shown in FIG. 1, if resin layers are laminated on both sides of the foam layer, 5 It has a layer structure (non-antistatic layer / antistatic layer / foam layer / antistatic layer / non-antistatic layer). The antistatic layer and the non-antistatic layer are laminated and bonded by coextrusion. In FIG. 1, 1 is a multilayer extruded foam sheet, 2 is a foam layer, 3 is a resin layer, 3a is an antistatic layer, and 3b is a non-antistatic layer.
By providing another layer between the resin layer and the foam layer of one or both, a 6-layer structure and a 7-layer structure can be obtained (not shown).

First, the components constituting the foam layer will be described.
In the multilayer extruded foamed sheet of the present invention, the foamed layer is made of a polyethylene-based resin (A). That is, the foam layer contains a polyethylene resin (A) as a main component. In the present specification, the "main component" means that the content ratio of the component is 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, still more preferably 80% by weight or more. Particularly preferably, it is 90% by weight or more.

In the present specification, the polyethylene-based resin means a resin having an ethylene component unit of 50 mol% or more. Examples of the polyethylene-based resin (A) include low-density polyethylene (LDPE), ethylene-vinyl acetate copolymer (EVA), linear low-density polyethylene (LLDPE), ultra-low-density polyethylene (VLDPE), and mixtures thereof. And so on. The low-density polyethylene, density having a long chain branching structure is preferably 910 kg / ^{m 3} or more 930 kg / ^{m 3} than polyethylene resin, a linear low density polyethylene, ethylene and 4 to 8 carbon atoms α- substantially molecular chain comprising a copolymer of an olefin is a linear, preferably density is 910 kg / m ³ or more 930 kg / m ³ than polyethylene resin, high-density polyethylene, ethylene homopolymer or A polyethylene-based resin which is a copolymer of ethylene and an α-olefin having 4 to 8 carbon atoms and has a density of 930 kg / m ^{3 or more is preferable.}

As the polyethylene-based resin (A) constituting the foamed layer, low-density polyethylene is preferable because it has excellent foamability and the multilayer extruded foamed sheet has more excellent cushioning property.

The melting point of the polyethylene resin (A) is preferably 100 to 135 ° C. The polyethylene-based resin (A) having a melting point in the above range is excellent in extrusion foamability and can stably form a foam layer having excellent cushioning property. For this reason, the melting point of the polyethylene resin (A) is preferably 100 to 130 ° C, more preferably 100 to 120 ° C, and even more preferably 100 to 115 ° C.

The melting point of the polyethylene-based resin (A) in the present specification is a value obtained by heat flux differential scanning calorimetry according to JIS K7121-1987. Specifically, in the measurement, JIS K7121-1987, 3. Condition adjustment of the test piece Using the test piece whose condition was adjusted according to the condition (2) (however, the cooling rate was 10 ° C./min), the melting peak was obtained by raising the temperature at 10 ° C./min. The temperature at the apex of the obtained melting peak is taken as the melting point. However, when two or more melting peaks appear, the temperature at the apex of the melting peak having the largest area is used as the melting point.

The melt flow rate (MFR) of the polyethylene resin (A) is preferably 0.1 to 20 g / 10 min, more preferably 0.1 to 10 g / min, and 0. .1 to 5 g / 10 min is more preferable. Further, since the closed cell ratio of the foamed sheet can be further increased, it is more preferable to use the polyethylene resin (A) having a melt flow rate (MFR) of 0.1 to 1.5 g / 10 min.
The melt flow rate (MFR) in the present specification is a value measured at a test temperature of 190 ° C. and a load of 2.16 kg in accordance with JIS K7210-1 (2004) A method.

If necessary, the polyethylene-based resin (A) constituting the foam layer may be blended with a resin other than the polyethylene-based resin (A) or another polymer such as an elastomer. When other polymers are blended, the blending amount is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, still more preferably 10 parts by weight, based on 100 parts by weight of the polyethylene resin constituting the foam layer. Is 5 parts by weight or less, and is particularly preferably 3 parts by weight or less.

The foam layer has a bubble regulator, a nucleating agent, an antioxidant, a heat stabilizer, a weather resistant agent, an ultraviolet absorber, a flame retardant, an antibacterial agent, and a shrinkage prevention agent as long as the object and effect of the present invention are not impaired. Additives such as agents and inorganic fillers can be added.

Next, the components constituting the resin layer will be described.
The resin layer has an antistatic layer (1) and a non-antistatic layer (2), and the antistatic layer (1) contains a polyethylene-based resin (B) and an ionomer resin-based antistatic agent. The non-antistatic layer (2) contains a polyethylene-based resin (C) and does not substantially contain an antistatic agent.

The antistatic layer (1) contains a polyethylene-based resin (B). As the polyethylene-based resin (B), the polyethylene-based resin exemplified as the polyethylene-based resin (A) can be used. Above all, it is preferable to use the same type of polyethylene resin (A) as it is excellent in adhesiveness to the foam layer. Specifically, low density polyethylene is preferable. However, different types of polyethylene-based resins can also be used.

The polyethylene-based resin (B) constituting the antistatic layer may be blended with a resin other than the polyethylene-based resin (B) or another polymer such as an elastomer, if necessary. When other polymers are blended, the blending amount thereof is preferably 20 parts by weight or less with respect to 100 parts by weight of the polyethylene-based resin (C) constituting the antistatic layer.

The melting point of the polyethylene resin (B) is preferably 100 to 120 ° C. By setting the melting point within the above range, the adhesion between the resin layer and the foamed layer is improved, a homogeneous antistatic layer is formed, and good antistatic performance is exhibited over the entire multilayer extruded foamed sheet. For this reason, the melting point is more preferably 102 to 115 ° C. The melting point of the polyethylene-based resin (B) can be determined by the same method as that of the polyethylene-based resin (A).

The antistatic layer (1) contains the ionomer resin-based antistatic agent (hereinafter, also simply referred to as ionomer resin). Since the ionomer resin is a polymer-type antistatic agent and has a low surface resistivity, it is possible to impart good antistatic performance to a multilayer extruded foamed sheet.
Further, since the ionomer resin contains a small amount of low molecular weight components, it is excellent in antifouling property, and it is possible to suppress contamination of the packaged material due to the transfer of the low molecular weight component to the packaged material.

The ionomer resin is a resin in which the molecules of a copolymer of an olefin such as ethylene or propylene and a carboxylic acid such as acrylic acid, methacrylic acid, and maleic acid are cross-linked with metal ions. , Lithium ion, sodium ion, alkali metal ion such as potassium ion, alkaline earth metal ion such as calcium ion and the like. Of these, an ethylene-based potassium ionomer resin, which is a copolymer of ethylene and an unsaturated carboxylic acid, using potassium ions as metal ions is preferable because it can impart good antistatic performance to the multilayer extruded foamed sheet.

The melting point of the ionomer resin-based antistatic agent is preferably about 80 to 110 ° C, more preferably 85 to 100 ° C. The melting point of the ionomer resin can be obtained by the same method as the melting point of the polyethylene-based resin (A).

The surface resistivity of the ionomer resin is preferably less than ^{1 × 10 12 Ω.} By forming the antistatic layer using an ionomer resin having a surface resistivity of ^{less than 1 × 10 12} Ω, a multilayer extruded foam sheet having excellent antistatic performance can be stably obtained. For this reason, the surface resistivity ^{is more preferably 1 × 10 11} Ω or less, further preferably 1 × 10 ¹⁰ Ω or less, and particularly preferably 1 × 10 ⁹ Ω or less.
The surface resistivity of the ionomer resin can be measured according to the method of JIS K6271 (2001).

Specific examples of the ionomer resin include those commercially available under trade names such as "Entila SD100" and "Entila MK400" manufactured by Mitsui-DuPont Polychemical Co., Ltd.

The antistatic layer of the present invention preferably contains polyalkylene glycol. When the multi-layer extruded foam sheet is produced by coextrusion, if the antistatic layer contains polyalkylene glycol, the ionomer resin is satisfactorily dispersed in the continuous phase of the polyethylene resin (B) in a layered manner. A specific dispersed state (morphology) described later can be formed more reliably, and a multilayer extruded foam sheet having excellent antistatic performance can be stably obtained.
Further, when the resin layer contains polyalkylene glycol, the humidity dependence of the antistatic performance is reduced, and a multi-layer extruded foam sheet exhibiting good antistatic performance even under low humidity conditions can be obtained. can.

As the polyalkylene glycol, a polyalkylene glycol having an HLB value of 8 or more can be preferably used. Examples of such polyalkylene glycols include polyethylene glycol, polyoxyethylene polyoxypropylene glycol and the like. Further, two or more kinds of polyalkylene glycols may be used in combination.
Among these, polyethylene glycol should be used because the ionomer resin can be stably dispersed in the polyethylene resin (B), and the humidity dependence of the antistatic performance can be further reduced while improving the antistatic performance. Is preferable.

In the present invention, the HLB value is a value obtained by the Griffin method (Equation (1)).
HLB = 20 × molecular weight of the hydrophilic group part / molecular weight of the entire hydrophilic compound ・ ・ ・ (1)

In the present specification, when the HLB value of polyalkylene glycol is determined by the Griffin method, specifically, it is carried out as follows.
For example, when polyalkylene glycol is composed of a copolymer of polyethylene glycol and other polyalkylene glycol, polyethylene glycol is regarded as a hydrophilic group moiety, and other polyalkylene glycols are lipophilic and hydrophilic. In consideration of the above, it is determined whether it is a hydrophilic group portion or a hydrophobic group portion, and the HLB value is obtained by the Griffin method. In the case of polyethylene glycol, since all of them are hydrophilic group portions, the upper limit of the HLB value of polyalkylene glycol is 20.
In order to satisfactorily disperse the ionomer resin in the polyethylene-based resin, the HLB value is preferably 10 or more, and more preferably 15 or more.

When polyethylene glycol is used as the polyalkylene glycol, its number average molecular weight is preferably 100 to 10000, more preferably 150 to 1000, and even more preferably 200 to 600. By setting the molecular weight of polyethylene glycol in the above range, a multilayer extruded foamed sheet exhibiting excellent antistatic performance can be stably obtained.
The number average molecular weight of polyethylene glycol is determined by a well-known method calculated from the hydroxyl value.

The content of the polyalkylene glycol in the antistatic layer is preferably 0.3 to 8 parts by weight, preferably 0.3 to 6 parts by weight, based on 100 parts by weight of the total of the polyethylene resin (B) and the ionomer resin. It is more preferably a part by weight. Within the above range, a multilayer extruded foam sheet having excellent antistatic performance can be stably obtained.
When polyethylene glycol is used as the polyalkylene glycol, the content thereof is preferably 0.3 to 6 parts by weight based on 100 parts by weight of the total of the polyethylene resin (B) and the ionomer resin. It is more preferably 5 to 5 parts by weight, further preferably 0.8 to 4 parts by weight, and particularly preferably 1 to 4 parts by weight.

In the antistatic layer, the weight ratio of the polyalkylene glycol to the ionomer resin is preferably 0.03 to 0.5. Within the above range, the ionomer resin can be better dispersed in the polyethylene-based resin.
From this point of view, the weight ratio is more preferably 0.04 to 0.4, further preferably 0.05 to 0.3, and particularly preferably 0.05 to 0.1. ..

As described above, the antistatic layer (1) of the present invention contains the polyethylene-based resin (B) and the ionomer resin, and the ionomer resin-based antistatic agent is contained in the continuous phase of the polyethylene-based resin (B). It forms a dispersed phase dispersed in layers, and forms a morphology in which the average number of layers of the dispersed phase is 3 or more per 1 μm in the thickness direction. In the present specification, the specific morphology is also referred to as an antistatic morphology structure. It is considered that the multilayer extruded foam sheet of the present invention forms an antistatic network by forming the antistatic morphology structure, and exhibits excellent antistatic properties having ^{a surface resistivity of 1 × 10 12 Ω or less.} ..

Next, the antistatic morphology structure (hereinafter, also simply referred to as a morphology structure) will be described.
The morphology structure can be confirmed in the vertical cross section (a) orthogonal to the width direction of the multilayer extruded foam sheet. That is, in the morphology structure, in the vertical cross section (a), the ionomer resin forms a dispersed phase in which the ionomer resin is layered in the continuous phase of the polyethylene resin (B), and the average number of layers of the dispersed phase is , It is a morphology confirmed to have three or more layers per 1 μm in the thickness direction. Here, the “dispersed phase dispersed in layers” means a dispersed phase having an aspect ratio of 2 or more.

An example of the antistatic morphology structure is shown in FIGS. 2 and 3. 2 and 3 are electron micrographs of the multilayer extruded foam sheet obtained in Example 1 taken in a vertical cross section (a) orthogonal to the width direction thereof. The magnification of the electron micrograph in FIG. 2 is 17,500 times, and the magnification of the electron micrograph in FIG. 3 is 70,000 times.

From FIGS. 2 and 3, the polyethylene-based resin (B) forms the continuous phase 4, and the antistatic morphology structure in which the ionomer resin forms the dispersed phase 5 layered in the continuous phase is formed. It is confirmed that it has been done.
In FIGS. 2 and 3, the portion having a stronger black color is the dispersed phase 5, and the portion having a weaker black color and a whitish color is the continuous phase 4.

In the antistatic morphology structure, the average number of layers of the dispersed phase is required to be 3 or more per 1 μm in the thickness direction. When the average number of layers is 3 or more, ^{excellent antistatic properties having a surface resistivity of 1 × 10 12} Ω or less can be exhibited. If the average number of layers is less than 3 ^{, antistatic properties having a surface resistivity of 1 × 10 12} Ω or less may not be exhibited. Therefore, the average number of layers is preferably 4 or more, more preferably 5 or more, 6 or more, 7 or more, and even more preferably 8 or more. The upper limit is approximately 20 layers.

In the antistatic layer, the polyethylene-based resin (B) forms a continuous phase in the antistatic layer, so that the flexibility of the multilayer extruded foam sheet of the present invention is improved. On the other hand, as described above, the ionomer resin is dispersed in layers in the continuous phase of the polyethylene-based resin (B), and the average number of layers of each layered dispersed phase is 3 or more per 1 μm in the thickness direction. It overlaps with each other. Therefore, unlike the conventional multi-layer extruded foam sheet, the multi-layer extruded foam sheet of the present invention exhibits excellent antistatic properties even though it uses an ionomer resin as a polymer type antistatic agent. The reason is considered to be that the ionomer resin forms a dispersed phase, and the dispersed phase is stretched in a layered manner to form a network of polymer-type antistatic agents. Specifically, when the dispersed phase is stretched in layers so that its aspect ratio is 2 or more, an excellent network is formed. The aspect ratio will be described later.

In the present invention, the ionomer resin is dispersed so that the median distribution area based on the number of dispersed phases is 1 × 10 ^{2 to} 5 × 10 ⁵ nm ^{2 in the vertical cross section (a).} preferable.
For the median value of the dispersed area, the number of dispersed phases and the cross-sectional area (dispersion area) of each dispersed phase are measured for the morphology appearing in the vertical cross section (a), and the measured cross-sectional area of each dispersed phase is large. It is a value located at the center of the total number of dispersed phases (50% of the total number of dispersed phases) when arranged in order. By adopting the median value, the dispersed state of the ionomer resin that contributes to the antistatic performance can be appropriately evaluated.

The fact that the median value of the dispersion area is within the above range means that the dispersion diameter of the dispersed phase made of the ionomer resin is small, and many small dispersed phases are dispersed in the continuous phase made of the polyethylene resin (B). It means that it exists. When such a dispersed phase is formed, the antistatic property of the multilayer extruded foam sheet becomes better. This is because a large number of dispersed phases having a small dispersion diameter made of an ionomer resin are dispersed in the continuous phase (the median value of the dispersed area is small), so that the conductive network structure of the ionomer resin is further enhanced in the polyethylene resin. It is considered that this is because it is surely formed.
In order to further enhance the antistatic performance of the multilayer extruded foam sheet, the lower limit of the median value ^{is preferably 5 × 10 2} nm ² , more preferably 1 × 10 ³ nm ² , and particularly preferably 1 × 10. ^{It is 4} nm ² . The upper limit of the median value ^{is preferably 1 × 10 5} nm ² , more preferably 7 × 10 ⁴ nm ² .

Further, in the vertical cross section (a), the median value B of the horizontal dispersion diameter of the dispersed phase of the ionomer resin is preferably 200 to 3000 nm. When the median B is within this range, it means that the dispersed phase of the ionomer resin is elongated in the horizontal direction, and an excellent antistatic network is easily formed. From this point of view, the median value B of the dispersion diameter in the horizontal direction is more preferably 300 to 2000 nm, and further preferably 500 to 1500 nm.

Further, in the vertical cross section (a), it is preferable that the average aspect ratio of the dispersed phase of the ionomer resin is 2 or more.
The average aspect ratio is a value obtained by dividing the median value B of the dispersion diameter in the horizontal direction by the median value A of the dispersion diameter in the thickness direction. The large average aspect ratio means that the dispersed phase composed of the ionomer resin exists in a layered and stretched state. Therefore, when the above range is satisfied, the conductive network structure of the ionomer resin is likely to be formed, and a multi-layer extruded foam sheet exhibiting excellent antistatic performance can be obtained more stably.
From this point of view, the aspect ratio is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more. The upper limit of the aspect ratio is approximately 20, preferably 15.
The dispersed phase is preferably stretched at least in the extrusion direction, and more preferably stretched in the width direction as well. The width direction is orthogonal to the extrusion direction of the multilayer extruded foam sheet and is orthogonal to the thickness direction of the multilayer extruded foam sheet.

Further, in the vertical cross section (a), the area occupied by the dispersed phase of the ionomer resin-based antistatic agent in the rectangular range of the central portion of the antistatic layer having a length of 500 nm in the thickness direction and a length of 1500 nm in the width direction. The average value of the ratio is preferably 30 to 80 area%. That is, in the vertical cross section (a), when a rectangular range having a thickness direction length of 500 nm and a width direction length of 1500 nm is set in the central portion of the antistatic layer, the area occupied by the dispersed phase of the ionomer resin-based antistatic agent. The average value of the ratio is preferably 30 to 80 area%.

The average value of the ratio is the dispersed phase of the ionomer resin occupied in the range along the extrusion direction including the portion having a length of 500 nm in the thickness direction centered on the center in the thickness direction of the antistatic layer in the vertical cross section (a). It is a numerical value indicating the ratio of the total area of. The average value is considered to be a value reflecting the weight ratio of the ionomer resin to the antistatic layer. That is, it is considered that the larger the average value, the larger the weight ratio of the ionomer resin in the antistatic layer. In the conventional technique, particularly when the ionomer resin is blended in a high concentration, the slipperiness is remarkably lowered, and for example, the workability when the ionomer resin is interposed between the glass plates and packed may be lowered. Further, at the time of manufacturing, it becomes difficult to take back the multi-layer extruded foam sheet, which may cause appearance defects such as waviness. When the average value is within the above range, a high concentration of ionomer resin is present in the antistatic layer, so that particularly excellent antistatic properties are exhibited. Further, the multi-layer extruded foam sheet of the present invention has a non-antistatic layer containing no antistatic agent, and the non-antistatic layer is located on the surface of the resin layer of the multi-layer extruded foam sheet so as to cover the antistatic layer. Since it is present in the above and the thickness is within a specific range, the slipperiness is good even though the ionomer resin is blended in a high concentration. In addition, the transfer of low molecular weight components to the packaged material is effectively prevented. The non-antistatic layer will be described later.

In order to develop the antistatic property of the multilayer extruded foam sheet to a higher degree, the average value of the ratio is more preferably 35 area% or more. Further, in consideration of improving the slipperiness of the multilayer extruded foam sheet and more reliably suppressing the migration of low molecular weight components, the average value of the ratio is more preferably 70 area% or less. It is more preferably 60 area% or less.

The median distribution area based on the number of dispersed phases, the median dispersion diameter A in the thickness direction based on the number of dispersed phases, the median horizontal dispersion diameter B of the dispersed phases, and the dispersed phases within the predetermined range. The average value of the ratio of the occupied area is obtained by cutting out a vertical cross section orthogonal to the width direction of the multi-layer extruded foam sheet to prepare an ultrathin section containing a resin layer portion, staining this, and then using a transmission electron microscope. , Can be calculated based on the photographs obtained by imaging the stained ultrathin sections. A specific measurement method will be described in detail in Examples.

As shown in FIG. 1, the resin layer constituting the multilayer extruded foam sheet of the present invention has a non-static layer 3b located on the surface of the multilayer extruded foam sheet. That is, the resin layer 3 has an antistatic layer 3a and a non-antistatic layer 3b, the antistatic layer 3a is located in contact with the foam layer 2, and the non-antistatic layer 3b is on the surface of the multilayer extruded foam sheet. It is located and is positioned so as to cover the antistatic layer 3a. The non-antistatic layer contains a polyethylene-based resin (C) and substantially no antistatic agent. Therefore, the non-antistatic layer does not contaminate the packaged object with the low molecular weight component derived from the antistatic agent. Further, since the non-antistatic layer does not contain an ionomer resin, the slipperiness of the multi-layer extruded foam sheet is prevented from being lowered, and the handleability when using the multi-layer extruded foam sheet is ensured. Further, since the occurrence of waviness during the production of the multi-layer extruded foam sheet is prevented, a multi-layer extruded foam sheet having an excellent appearance can be obtained.

The multi-layer extruded foam sheet shown in FIGS. 2 and 3 shows an antistatic layer. In FIGS. 2 and 3, the portion indicated by reference numeral 3a is the antistatic layer on which the antistatic morphology structure peculiar to the present invention is formed, and the portion indicated by reference numeral 3b is the non-antistatic layer.

In the present specification, the term "without antistatic agent" means that the content ratio of the antistatic agent is 3% by weight or less in the non-antistatic layer, preferably 2% by weight or less, and more preferably 1% by weight. % Or less, more preferably 0.5% by weight or less, and particularly preferably 0.

The antistatic agent is not limited to the ionomer resin, but is an antistatic agent such as a polymer type antistatic agent such as a polyether, a polyether ester amide, a block copolymer of a polyether and a polyolefin, and an antistatic agent such as a surfactant. It is a concept that includes all components having sex.

The non-antistatic layer is located on the surface of the resin layer of the multilayer extruded foam sheet, exists in the thickness direction from the surface of the resin layer, and is laminated so as to cover the antistatic layer. The average thickness of the non-static layer in the vertical cross section (a) is 0.5 to 15 μm. When the average thickness of the non-antistatic layer is within this range, the desired antistatic property can be exhibited and the migration of low molecular weight components derived from the ionomer resin contained in the antistatic agent layer can be suppressed. can. In order to more reliably suppress the migration of low molecular weight components and more reliably secure the slipperiness of the multilayer extruded foam sheet, the lower limit of the average thickness is preferably 0.8 μm, more preferably 1 μm. , More preferably 1.5 μm. If the average thickness is too large, the desired antistatic property may not be exhibited. In order to more reliably develop the desired antistatic property, the upper limit of the average thickness is preferably 13 μm, more preferably 8 μm, still more preferably 5 μm. A method for measuring the average thickness of the non-static layer in the vertical cross section (a) will be described later.

The non-antistatic layer is formed of a polyethylene-based resin (C) as a main component. As the polyethylene-based resin (C), the polyethylene-based resin exemplified as the polyethylene-based resin (B) can be used. When the same type as the polyethylene-based resin (B) is used, the adhesiveness with the antistatic layer can be further enhanced. Specifically, low density polyethylene is preferable. Further, when linear low-density polyethylene is used as the polyethylene-based resin (C), the amount of migration of low molecular weight components can be further suppressed. However, different types of polyethylene-based resins can also be used.

The melting point of the polyethylene resin (C) is preferably 100 to 120 ° C. By setting the melting point within the above range, the laminated state with the antistatic layer becomes good, and it becomes easy to obtain a multi-layer extruded foam sheet exhibiting good antistatic performance over the entire multi-layer extruded foam sheet. For this reason, the melting point is more preferably 102 to 115 ° C. The melting point of the polyethylene-based resin (C) can be determined by the same method as that of the polyethylene-based resin (A).

The polyethylene-based resin (C) constituting the non-antistatic layer may be blended with a resin other than the polyethylene-based resin (C) or another polymer such as an elastomer, if necessary. When other polymers are blended, the blending amount thereof is preferably 20 parts by weight or less with respect to 100 parts by weight of the polyethylene-based resin (C) constituting the antistatic layer.
By including the polystyrene-based resin in the non-antistatic layer, the slipperiness can be further enhanced.

The non-antistatic layer and the antistatic layer include bubble regulators, nucleating agents, antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, as long as they do not impair the object and effect of the present invention. Additives such as antibacterial agents, antistatic agents, and inorganic fillers can be added.

Next, the physical characteristics of the multilayer extruded foam sheet of the present invention will be described.
The multilayer extruded foam sheet of the present invention has excellent antistatic properties due to having the above-mentioned structure. Specifically, the surface resistivity of the multilayer extruded foam sheet is 1 × 10 ¹² Ω or less. When the surface resistivity is within the above range, the multi-layer extruded foam sheet having sufficient antistatic performance can be obtained, and the adhesion of dust and the like can be suppressed.
For this reason, the surface resistivity ^{is preferably 1 × 10 11} Ω or less, more preferably less than ^{1 × 10 10 Ω.}
The lower limit of the surface resistivity is not particularly limited, it is generally 1 × 10 ⁷ Ω.

The surface resistivity in the present specification is measured according to JIS K6271-2001. Specifically, a test piece having a length of 100 mm, a width of 100 mm, and a thickness (the thickness of the multi-layer extruded foam sheet) cut out from the multi-layer extruded foam sheet is allowed to stand for 24 hours in an atmosphere having a temperature of 23 ° C and a relative humidity of 50%. By doing so, the state of the test piece was adjusted, a voltage of 500 V was applied under the same conditions (temperature 23 ° C, relative humidity 50%), and the surface resistivity [Ω] 1 minute after the application was measured and obtained. Let the value be the surface resistivity.

The apparent density of the multilayer extruded foam sheet of the present invention is preferably ^{15 to 300 kg / m 3.}
When the apparent density of the multi-layer extruded foam sheet is within the above range, the multi-layer extruded foam sheet has an excellent balance between mechanical properties such as strength, light weight and cushioning property. From this point of view, the lower limit of the apparent density is more preferably 18 kg / m ³ and even more preferably 20 kg / m ³ . On the other hand, the upper limit of the apparent density is more preferably 200 kg / m ³ , still more preferably 150 kg / m ³ , and particularly preferably 100 kg / m ³ .

The total thickness of the multilayer extruded foam sheet is preferably 0.05 to 2 mm, more preferably 0.1 to 1.8 mm, and even more preferably 0.2 to 1.5 mm. When the thickness of the multilayer extruded foam sheet is within this range, the balance between cushioning property and flexibility is good.

Preferably the total basis weight of the multilayer extruded foam sheet is 5 to 100 g / ^{m 2,} more preferably 10~90g / ^{m 2,} more preferably from 20 to 80 g / ^{m 2.} When the total basis weight is within this range, the balance between lightness and mechanical properties is good.

In the present invention, the thickness, basis weight, and apparent density of the multilayer extruded foam sheet are measured as follows.
First, a rectangular test piece having a total width [mm] × 100 mm of the sheet is cut out from the multilayer extruded foam sheet along the width direction, and the thickness of the test piece is set from one end to the other end in the width direction, etc. The measurement is performed every 1 cm at intervals, and the arithmetic mean value of the obtained values is taken as the thickness of the entire multilayer extruded foam sheet. Next, the weight [g] of the test piece is measured, the weight is divided by the area of the test piece (specifically, the total width of the sheet [mm] × 100 mm), and the unit is converted into the tsubo of the multilayer extruded foam sheet. Obtain the amount [g / m ^2]. Further, the basis weight is divided by the thickness of the entire multi-layer extruded foam sheet obtained earlier, and the apparent density [kg / m ³ ] of the multi-layer extruded foam sheet is obtained in terms of units.

The basis weight of the antistatic layer and the nonstatic layer is obtained by multiplying the thickness of each layer by the density of the resin composition constituting each layer and performing unit conversion. Specifically, the multilayer extruded foam sheet is cut along the width direction to form a vertical cross section. Next, in the vertical cross section, 10 or more enlarged photographs of the surface side of the multilayer extruded foam sheet are taken at equal intervals in the width direction (20 or more in total on both sides). In the enlarged photograph of each point, the thicknesses of the antistatic layer and the non-antistatic layer are measured at intervals of 1 cm (actual length) in the width direction. Then, the arithmetic mean value of each of the obtained values is used as the thickness of the antistatic layer and the non-antistatic layer for each surface. By multiplying the thickness by the density of the resin composition and converting it into a unit, the basis weight per one side of each of the antistatic layer and the non-static layer can be obtained.
When the antistatic layer and the non-antistatic layer contain an additive such as an inorganic filler, the density of the resin composition is the density containing the additive.

Further, the discharge amount X [kg / hour] of the antistatic layer per one side, the discharge amount Y [kg / hour] of the non-antistatic layer per one side, the width W [m] of the multi-layer extruded foam sheet, and the multi-layer extruded foam sheet. When the take-up speed L [m / hour] is known, it can also be obtained by the following equations (2) and (3) using these values.
Basis weight per one side of antistatic layer [g / m ² ] = [X / (1000 × L × W)] ... (2)
Basis weight per one side of the non-static layer [g / m ² ] = [Y / (1000 × L × W)] ... (3)

The closed cell ratio of the multilayer extruded foam sheet of the present invention is preferably 30% or more, more preferably 40% or more, particularly more preferably 40% or more in consideration of the surface protection of the packaged object, appropriate slipperiness, stiffness and the like. It is preferably 50% or more.

The closed cell ratio was measured using the true volume Vx of the multilayer extruded foam sheet (cut sample) measured using the air comparative hydrometer 930 type of Toshiba Beckman Co., Ltd. according to the procedure C of ASTM-D2856-70. , The closed cell ratio S (%) is calculated by the following equation (4). A plurality of samples having a thickness of 25 mm × 25 mm × multi-layer extruded foam sheet are cut out and stacked to obtain a cut sample for measurement of 25 mm × 25 mm × about 20 mm.

S (%) = (Vx-W / ρ) x 100 / (Va-W / ρ) (4)
^{Vx: The true volume (cm 3} ) of the cut sample measured by the above method, which corresponds to the sum of the volume of the resin constituting the cut sample and the total volume of the closed cell portion in the cut sample.
Va: The apparent volume of the cut sample calculated from the outer dimensions of the cut sample used for the measurement (cm ³ ).
W: Total weight (g) of the cut sample used for the measurement.
ρ: Resin density (g / cm ³ ) obtained by defoaming a multilayer extruded foam sheet

Next, a method for manufacturing the multilayer extruded foam sheet of the present invention will be described.
The multilayer extruded foam sheet of the present invention can be obtained by the following method. That is,
[1] An antistatic layer formed by kneading a foam layer forming resin melt obtained by kneading a polyethylene resin (A) and a physical foaming agent, and a polyethylene resin (B) and an ionomer resin antistatic agent. By co-extruding the forming resin melt and the non-antistatic layer forming resin melt formed by kneading the polyethylene resin (C),
Multi-layer extrusion foaming having a foam layer made of a polyethylene resin (A), an antistatic layer laminated and adhered to at least one side of the foam layer, and a non-antistatic layer laminated and adhered to the antistatic layer. It ’s a method of manufacturing sheets.
In the antistatic layer, the ionomer resin-based antistatic agent is dispersed in a layer in the continuous phase of the polyethylene-based resin (B) in a vertical cross section (a) orthogonal to the width direction of the multilayer extruded foam sheet. A phase is formed, and the average number of layers of the dispersed phase is 3 or more per 1 μm in the thickness direction.
The non-antistatic layer does not substantially contain an antistatic agent, exists in the thickness direction from the surface of the multilayer extruded foam sheet on the resin layer side, and has an average thickness of 0.5. ~ 15 μm,
The multi-layer extruded foam sheet can be obtained by a method for producing a polyethylene-based resin multi-layer extruded foam sheet having a surface resistivity of the surface of the resin layer of the multi-layer extruded foam sheet of 1 × 10 ^{12 Ω or less.}
As a further preferred embodiment, [2] the production of the polyethylene-based resin multilayer extruded foam sheet according to the above [1], in which a polyalkylene glycol and / or a volatile plasticizer is added to the resin melt for forming an antistatic layer at the time of coextrusion. The multi-layer extruded foam sheet can be obtained by the method.

Next, a specific manufacturing method of the multilayer extruded foam sheet of the present invention will be described.
As a method for producing the multilayer extruded foam sheet, a conventionally known method can be used. As a typical method thereof, for example, in a coextrusion die, a molten resin for forming a resin layer is laminated on one side or both sides of a molten resin for forming a foam layer, and these are coextruded and a foam layer is formed. A multi-layer coextrusion method for producing a multi-layer extruded foam sheet by foaming a molten resin for use is preferably mentioned.
Further, in the present invention, it is necessary to coextrude the resin layer as a laminated body of the antistatic layer 3a and the non-antistatic layer 3b. Specifically, the molten resin for forming the resin layer is separately formed into the molten resin for forming the antistatic layer and the molten resin for forming the non-antistatic layer by using separate extruders. The molten resin for forming the antistatic layer forms a specific antistatic morphology structure by using a polyethylene resin (B), an ionomer resin, and if necessary, a polyalkylene glycol and / or a volatile plasticizer. Form as possible. At the same time, the molten resin for forming the non-antistatic layer is formed by using the polyethylene-based resin (C) or the like. Next, the molten resin for forming the antistatic layer and the molten resin for forming the non-antistatic layer are introduced into the coextrusion die, and the molten resin for forming the antistatic layer is formed on one side or both sides of the molten resin for forming the foam layer. And the molten resin for forming a non-antistatic layer are laminated in this order, and these are co-extruded, and the molten resin for forming a foam layer is foamed and taken up to obtain the multilayer extruded foam sheet of the present invention. Can be done.

The multi-layer co-extrusion method includes (1) co-extruding into a sheet using a flat die to obtain a multi-layer extruded foam sheet, and (2) co-extruding into a cylinder using an annular die to form a tubular multi-layer foam. There is a method of manufacturing and then cutting out a tubular multilayer foam along the extrusion direction to obtain a multilayer extrusion foam sheet. Among the above, since it is easy to obtain a wide multilayer extruded foam sheet having a width of 1000 mm or more, a multilayer coextrusion method using an annular die can be preferably used.

The method of co-extruding using the annular die will be described in detail below.
First, the polyethylene-based resin (A) and an additive such as a bubble adjusting agent added as needed are supplied to an extruder for forming a foam layer, heat-kneaded, and then a physical foaming agent is placed in the extruder. It is press-fitted and further kneaded to obtain a resin melt for forming a foam layer. At the same time, the polyethylene-based resin (B), the ionomer resin-based antistatic agent, and the polyalkylene glycol and / or the volatile plasticizer added as needed are supplied to the antistatic layer forming extruder and heated. Knead to obtain a resin melt for forming an antistatic layer. At the same time, the polyethylene-based resin (C) or the like is supplied to an extruder for forming a non-antistatic layer and kneaded by heating to obtain a resin melt for forming a non-antistatic layer.
The obtained resin melt for forming a foam layer, the resin melt for forming an antistatic layer, and the resin melt for forming a non-antistatic layer were introduced into a coextrusion annular die, laminated, and coextruded. Extruded and foamed in the air to obtain a tubular foam. A multilayer extruded foam sheet can be obtained by cutting open the tubular foam while taking it along a widening device such as a mandrel.

The difference between the melting point Tm (B) of the polyethylene-based resin (B) used in the resin melt for forming the antistatic layer and the melting point Tm (i) of the ionomer resin [Tm (B) -Tm (i)]. Is preferably 5 to 30 ° C, preferably 8 to 28 ° C, and more preferably 10 to 25 ° C.

The multilayer extruded foam sheet of the present invention exhibits excellent antistatic performance by forming the antistatic morphology structure between the polyethylene resin and the ionomer resin.
However, conventionally, when an ionomer resin is used as a polymer-type antistatic agent constituting an antistatic layer and a polyethylene-based resin extruded foam sheet is manufactured by a coextrusion method, it is difficult to form the morphology structure. there were. That is, in the case of producing a multilayer extruded foam sheet by coextrusion, in order to disperse the ionomer resin in the resin constituting the continuous phase, usually, the temperature conditions for extruding the resin melt for forming the antistatic layer are sufficient. It was necessary to set it to a high temperature. However, in order to maintain the bubble structure of the foam layer in a good state, the temperature of the resin melt for forming the antistatic layer cannot be set to a sufficiently high temperature, and in addition, low temperature conditions that can form a good foam layer can be obtained. Then, since the melt viscosity of the ionomer resin tends to increase, conventionally, when a polyethylene resin and an ionomer resin are used as the resin constituting the antistatic layer, they have a certain melting point difference. , It was difficult to disperse the ionomer resin in the polyethylene resin.
On the other hand, by adding the polyalkylene glycol and / or the volatile plasticizer to the resin melt for forming the antistatic layer at the time of coextrusion, even if there is a difference in melting point as in the above range, the ionomer The resin can be dispersed in the polyethylene-based resin, and a multi-layer extruded foam sheet exhibiting excellent antistatic performance over the entire surface of the multi-layer extruded foam sheet can be stably obtained.

As the polyalkylene glycol, the above-mentioned polyalkylene glycol can be used. When polyethylene glycol is used as the polyalkylene glycol, the amount added thereof is preferably 0.3 to 6 parts by weight, preferably 0.5 to 6 parts by weight, based on 100 parts by weight of the total of the polyethylene resin (B) and the ionomer resin. It is more preferably 5 parts by weight, further preferably 0.8 to 4 parts by weight, and particularly preferably 1 to 4 parts by weight.

As the volatile plasticizer, one having a function of lowering the melt viscosity of the resin melt and one that volatilizes from the resin layer and does not exist in the resin layer after the resin layer is formed is used. Specifically, one or 2 selected from an aliphatic hydrocarbon having 3 to 7 carbon atoms, an alicyclic hydrocarbon, an aliphatic alcohol having 1 to 4 carbon atoms, and an aliphatic ether having 2 to 8 carbon atoms. More than a seed is preferably used. When a so-called lubricant having low volatility is used instead of the volatile plasticizer, the lubricant may remain in the resin layer and contaminate the surface of the packaged object. On the other hand, the volatile plasticizer is preferable because it efficiently plasticizes the resin of the resin layer and the volatile plasticizer itself does not easily remain in the obtained resin layer (antistatic layer and non-antistatic layer). .. From the viewpoint of improving the dispersed state of the ionomer resin, it is preferable to use these volatile plasticizers in combination with the polyalkylene glycol.

The boiling point of the volatile plasticizer is preferably 120 ° C. or lower, more preferably 80 ° C. or lower, because it easily volatilizes from the resin layer. If the boiling point of the volatile plasticizer is within the above range, if the obtained multi-layer extruded foam sheet is left after co-extrusion, it will be exposed to the heat immediately after co-extrusion and at room temperature when the foam sheet is stored later. The volatile plasticizer is naturally volatilized and removed from the resin layer by the permeation of the gas. The lower limit of the boiling point of the volatile plasticizer is approximately −50 ° C.

Among the volatile plasticizers, one selected from alcohols having a boiling point of 120 ° C. or lower, saturated hydrocarbons having 3 to 5 carbon atoms and / or dialkyl ethers having an alkyl chain having 1 to 3 carbon atoms. It is preferable to use two or more kinds because the dispersed state of the ionomer resin can be improved. In particular, when an alcohol having a boiling point of 120 ° C. or lower and a saturated hydrocarbon having 3 to 5 carbon atoms and / or a dialkyl ether having an alkyl chain having 1 to 3 carbon atoms are used in combination as a volatile plasticizer, the above-mentioned Even when polyalkylene glycol is not used, a good antistatic morphology structure can be stably formed.

It is preferable that the volatile plasticizer is added to both the antistatic layer forming resin melt and the non-antistatic layer forming resin melt. By adding a volatile thermoplastic to the resin melt, when a multi-layer extruded foam sheet is manufactured by co-extrusion, the resin melt for forming an antistatic layer layer and the resin melt for forming a non-static layer are extruded. The temperature can be brought close to the extrusion temperature of the resin melt for forming the foam layer, and the melt elongation of the softened antistatic layer and the non-antistatic layer can be remarkably improved. Then, the bubbles in the foamed layer are less likely to be destroyed by the heat of the resin layer (antistatic layer and non-antistatic layer) during foaming, and the elongation of the resin layer easily follows the elongation during foaming of the foamed layer. In this case, the antistatic morphology structure is more likely to be formed more stably.

The amount of the volatile plasticizer is 5 for a total of 100 parts by weight of the polyethylene-based resin and the polymer-type antistatic agent added as needed in each of the antistatic layer and the resin melt for forming the non-antistatic layer. It is preferably added in an amount of 10 to 50 parts by weight, more preferably 8 to 30 parts by weight, and particularly preferably 10 to 25 parts by weight.

The amount of the ionomer resin added to the antistatic layer is preferably 30 to 80% by weight (however, the total of the polyethylene-based resin (B) and the ionomer resin is 100% by weight). When the addition amount is within the above range, the antistatic morphology structure becomes stronger, and particularly excellent antistatic property is exhibited. Since the multilayer extruded foam sheet of the present invention has the non-static layer, it is excellent in slipperiness and prevents migration of low molecular weight components even when an ionomer resin is added at a high concentration. In order to further improve the antistatic property of the multilayer extruded foam sheet, the addition amount is more preferably 35% by weight or more. Further, in order to obtain effects such as better slipperiness of the multilayer extruded foam sheet and more reliable suppression of migration of low molecular weight components, the addition amount should be 70% by weight or less. It is more preferably 60% by weight or less.

Further, in the antistatic layer forming resin melt and the non-antistatic layer forming resin melt, various additives may be added to the resin forming the melt as long as the object of the present invention is not impaired. .. Examples of various additives include antioxidants, heat stabilizers, weather resistant agents, ultraviolet absorbers, flame retardants, fillers, antibacterial agents and the like. In that case, the amount to be added is appropriately determined according to the purpose and effect of the additive, but 10 parts by weight each for a total of 100 parts by weight of the polyethylene-based resin and the polymer-type antistatic agent added as needed. The following is preferable, 5 parts by weight or less is more preferable, and 3 parts by weight or less is particularly preferable.

Examples of the physical foaming agent added to the foamed layer forming resin melt include aliphatic hydrocarbons such as propane, normal butane, isopentane, normal pentane, isopentane, normal hexane and isohexane, and fats such as cyclopentane and cyclohexane. Hydrocarbons such as cyclic hydrocarbons, methyl chloride and ethyl chloride, organic physical foaming agents such as fluorocarbons such as 1,1,1,2-tetrafluoroetan and 1,1-difluoroetan, nitrogen and dioxide. Examples thereof include inorganic physical foaming agents such as carbon, air, and water. In some cases, a degradable foaming agent such as azodicarbonamide can also be used. Two or more of the above-mentioned physical foaming agents can be used in combination. Of these, organic physical foaming agents are particularly preferable because they are excellent in compatibility with polyethylene resin and foamability, and among them, those containing normal butane, isobutane, or a mixture thereof as a main component are preferable.

The amount of the 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 extruded foam sheet in the apparent density range using isobutane as a foaming agent, the amount of isobutane added is preferably 3 to 30 per 100 parts by weight of the polyethylene resin (A) constituting the foam layer. It is by weight, more preferably 5 to 25 parts by weight, still more preferably 8 to 20 parts by weight.

A bubble adjusting agent is usually added as a main additive added to the foamed layer forming resin melt. As the bubble adjusting agent, either an organic type or an inorganic type can be used. Examples of the inorganic bubble adjusting agent include boric acid metal salts such as zinc borate, magnesium borate, and borax, sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate, and sodium bicarbonate. Examples of the organic bubble adjusting agent include sodium 2,2-methylenebis (4,6-tert-butylphenyl) phosphate, sodium benzoate, calcium benzoate, aluminum benzoate, sodium stearate and the like. Further, a combination of citric acid and sodium bicarbonate, an alkali salt of citric acid and sodium bicarbonate and the like can also be used as the bubble adjusting agent. Two or more of these bubble adjusting agents can be used in combination.
The amount of the bubble adjusting agent added is preferably 0.01 to 3 parts by weight, more preferably 0.03 to 1 part by weight, per 100 parts by weight of the base resin.

As the manufacturing apparatus such as the annular die and the extruder, known ones conventionally used in the field of extrusion foaming can be used.

The multi-layer extruded foamed sheet of the present invention is a foamed sheet having excellent cushioning properties and appearance, excellent antistatic properties, and an extremely small amount of low molecular weight components transferred to the object to be packaged. It can be suitably used as a packaging material for electronic devices.

Hereinafter, the present invention will be described in more detail based on Examples. However, the present invention is not limited to the examples.

Next, the raw materials used in Examples and Comparative Examples will be described.
Table 1 shows the polyethylene-based resins used in Examples and Comparative Examples.

In Table 1, the melting point, melt flow rate (MFR), melt viscosity (η), and melt tension (MT) were measured as follows.
The melting point of the polyethylene resin was determined by heat flux differential scanning calorimetry according to JIS K7121-1987. Specifically, in the measurement, JIS K7121-1987, 3. Condition adjustment of the test piece The peak of the melting peak obtained by raising the temperature at 10 ° C./min using the test piece whose condition was adjusted according to the condition (2) (however, the cooling rate was 10 ° C./min). The temperature of was taken as the melting point.

The melt flow rate of the polyethylene-based resin was measured based on JIS K7210-1 (2014) under the conditions of 190 ° C. and a load of 2.16 kg.

The melt viscosity was measured using a measuring machine of Capillograph 1D manufactured by Toyo Seiki Seisakusho Co., Ltd. A cylinder having a cylinder diameter of 9.55 mm and a length of 350 mm and an orifice having a nozzle diameter of 1.0 mm and a length of 10 mm were used, and the set temperature of the cylinder and the orifice was set to 190 ° C. Put 15 g of the sample for measurement in the cylinder, leave it for 4 minutes to make it into a molten resin ^{, extrude the molten resin from the orifice in a string shape at a shear rate of 100 sec -1} , and measure the viscosity of the molten resin at the time of extrusion. This value was taken as the melt viscosity.

The melt tension (MT) was measured by Capillograph 1D manufactured by Toyo Seiki Seisakusho Co., Ltd. Specifically, a cylinder having a cylinder diameter of 9.55 mm and a length of 350 mm and an orifice having a nozzle diameter of 2.095 mm and a length of 8.0 mm are used, the set temperature of the cylinder and the orifice is set to 190 ° C., and the required amount of the sample is set. After putting it in the cylinder and leaving it for 4 minutes, the molten resin is extruded from the orifice in a string shape at a piston speed of 10 mm / min, and this string-like material is hung on a tension detection pulley having a diameter of 45 mm and picked up in 4 minutes. While increasing the pick-up speed at a constant speed so that the speed reaches from 0 m / min to 200 m / min, the string-like object is picked up by the take-up roller, and the maximum value of the tension immediately before the string-like object breaks is set. obtain. Here, the reason why the time required for the pick-up speed to reach 200 m / min from 0 m / min is set to 4 minutes is to suppress thermal deterioration of the resin and improve the reproducibility of the obtained value. The above operation was performed using different samples, and a total of 10 measurements were performed, and 3 values were removed in order from the largest value of the maximum value obtained in 10 times, and 3 values were removed in order from the smallest value of the maximum value. The value obtained by arithmetically averaging the remaining four intermediate maximum values was taken as the melt tension (mN).

Ionomer resin (polymer type antistatic agent)
Abbreviation "SD100": Ethylene potassium ionomer resin "Entila SD100" manufactured by Mitsui DuPont Polychemical Co., Ltd. (density 990 kg / m ³ , MFR 5 g / 10 minutes, melt viscosity 823 Pa · s, melting point 92 ° C, surface resistance 1.0 × 10 ⁷ Ω)
The MFR, melt viscosity, and melting point of the ionomer resin were determined by the same method as for the polyethylene resin.

Polyalkylene glycol Abbreviation "PEG": Polyethylene glycol "PEG300" manufactured by Sanyo Chemical Industries, Ltd. (number average molecular weight 300)

Physical foaming agent Isobutane

Volatile plasticizer mixed butane (mixture of 35% by weight of normal butane and 65% by weight of isobutane)

Bubble conditioner As a bubble adjuster, 20% by weight of talc (manufactured by Matsumura Sangyo Co., Ltd., trade name High Filler # 12) is blended with 80% by weight of low density polyethylene (manufactured by Japan Polyethylene Corporation, "LA500M"). A bubble conditioner masterbatch was used.

Equipment A multi-layer extrusion foam sheet manufacturing equipment equipped with the following extruders and dies was used.
Foam layer forming extruder: First extruder with a barrel inner diameter of 115 mm Antistatic layer forming extruder: Barrel inner diameter 65 mm second extruder Non-static layer forming extruder: Third extruder with an inner diameter of 50 mm Die: Outlet Circular die for coextrusion with a diameter of 96 mm

Examples 1 to 4, Comparative Examples 1 to 4
First, the polyethylene-based resin (A) of the types shown in Table 2 (Example) and Table 3 (Comparative Example) and 2 parts by weight of the bubble adjusting agent masterbatch with respect to 100 parts by weight of the polyethylene-based resin (A). After supplying to an extruder and kneading them at about 200 ° C., isobutane in the amounts shown in Tables 2 and 3 was press-fitted as a physical foaming agent and further kneaded. This kneaded product was adjusted to the extruded resin temperature shown in Table 4 (Example) and Table 5 (Comparative Example) to form a resin melt for forming a foam layer.
At the same time, the types shown in Tables 2 and 3, the amount of polyethylene resin (B), the types shown in Tables 2 and 3, the amount of ionomer resin, the types shown in Tables 2 and 3, and the amount of polyalkylene glycol were added. (2) After supplying to an extruder and kneading them at about 200 ° C., the amount of mixed butane (normal butane / isobutane = 65% by weight / 35% by weight) shown in Tables 2 and 3 is press-fitted as a volatile plasticizer. Then, the mixture was further kneaded and adjusted to the extruded resin temperatures shown in Tables 4 and 5 to form a resin melt for forming an antistatic layer.
At the same time, the types shown in Tables 2 and 3, the amount of polyethylene resin (C), the types shown in Tables 2 and 3, the amount of ionomer resin, the types shown in Tables 2 and 3, and the amount of polyalkylene glycol. The amount of talc masterbatch shown in Tables 2 and 3 is supplied to the third extruder, and after kneading this at about 200 ° C., the amount of mixed butane (normal butane / isobutane) shown in Table 2 is used as a volatile plasticizer. (= 35% by weight / 65% by weight) was press-fitted and further kneaded to obtain an extruded resin temperature shown in Tables 4 and 5 to obtain a resin melt for forming a non-static layer.

For coextrusion of the resin melt for forming the foam layer, the resin melt for forming the antistatic layer, and the resin melt for forming the non-static layer, respectively, at the discharge amounts shown in Table 4 (Example) and Table 5 (Comparative Example). It is introduced into the annular die, and the resin melt for forming the antistatic layer is merged and laminated on both the inner and outer surfaces of the resin melt for forming the foam layer, and further, the non-static layer is formed on both the inner and outer surfaces of the resin melt for forming the antistatic layer. The forming resin melts were merged and laminated. This laminate is co-extruded from an annular die, an antistatic layer layer is laminated and adhered to both the inner and outer surfaces of the foam layer, and a non-antistatic layer is laminated and adhered to each antistatic layer (in Comparative Examples 1 to 3). Formed a tubular multilayer foam (three-layer structure). Table 4; While picking up at the pick-up speed shown in Table 5, the tubular laminated foam was cut open along the extrusion direction to obtain a multilayer extruded foam sheet.

In Tables 2 and 3, the blending amounts of the polyethylene-based resin, ionomer resin, polyalkylene glycol, etc. are described, and these blending amounts are the polyethylene-based resin, ionomer resin, poly, which constitute the obtained multilayer extruded foam sheet. It is the content of alkylene glycol and the like.

The physical characteristics of the multilayer extruded foam sheets obtained in Examples and Comparative Examples are shown in Table 6 for Examples and Table 7 for Comparative Examples.

Comparative Example 1 is an example of a multilayer extruded foam sheet manufactured in Example 1 without providing an antistatic layer. The multilayer extruded foam sheet obtained in Comparative Example 1 is excellent in antistatic property because it has an antistatic morphology structure, but is inferior in glass contamination prevention property because it does not have a non-antistatic layer. Met. In addition, the value of static friction force is large and slipperiness is insufficient depending on the application. Further, the multilayer extruded foam sheet of Comparative Example 1 had a large friction with the mandrel when the sheet was taken up, and wavy in the extrusion direction, resulting in poor appearance.

Comparative Example 2 is an example of Comparative Example 1 produced by blending talc with an antistatic layer. The multi-layer extruded foam sheet obtained in Comparative Example 2 had improved slipperiness by blending talc, but cracked and deteriorated in appearance. In addition, the glass contamination prevention property was significantly reduced.

Comparative Example 3 is an example of a multilayer extruded foam sheet produced in Example 1 without providing a non-static layer, changing the blending amount of ionomer resin in the antistatic layer, and not blending polyethylene glycol. .. In the multilayer extruded foam sheet obtained in Comparative Example 3, the ionomer resin was not dispersed in layers in the continuous layer of the polyethylene resin in the antistatic layer, and the average number of dispersed layers was remarkably small. That is, it did not have an antistatic morphology structure. Therefore, the desired antistatic property could not be obtained.

Comparative Example 4 is an example of Example 1 in which the discharge amount and the take-up speed of the resin melt for forming the antistatic layer are changed. In the multilayer extruded foam sheet obtained in Comparative Example 4, the desired antistatic property could not be obtained because the thickness of the non-antistatic layer was too large.

The measurement and evaluation of each physical property in Tables 6 and 7 were performed as follows.
(1) Apparent density, basis weight, and overall thickness of the multi-layer extruded foam sheet Five rectangular test pieces having a total width [mm] × 100 mm of the sheet were cut out from the multi-layer extruded foam sheet along the width direction thereof. The thickness of each test piece was measured every 1 cm in the width direction of the multilayer extruded foam sheet and arithmetically averaged to obtain the thickness [mm] of each test piece. The arithmetic mean value of the thickness of each test piece was taken as the thickness [mm] of the entire multilayer extruded foam sheet. Further, the weight of each test piece is measured, the weight is divided by the area of the test piece (specifically, the sheet width [mm] × 100 mm), and the unit is converted into the basis weight [g / m) of each test piece. ² ] was requested. The arithmetic mean value of the basis weight of each test piece was defined as the basis weight [g / m ² ] of the multilayer extruded foam sheet. Furthermore, the basis weight was divided by the average thickness and converted into units to obtain the apparent density [kg / m ³ ] of the multilayer extruded foam sheet.

(2) Basis weight of antistatic layer and non-antistatic layer From the discharge amount of each of the antistatic layer and the non-antistatic layer, the antistatic layer and the non-antistatic layer are used according to the above methods using the formulas (2) and (3). The basis weight of the antistatic layer was calculated. Since the multi-layer extruded foam sheet was manufactured under the condition that the basis weights of the antistatic layer and the non-antistatic layer on one surface side and the other surface side of the multi-layer extruded foam sheet are the same, the multi-layer extruded foam sheet is shown in Tables 6 and 7. Shows the basis weight on only one side.

(3) Evaluation of antistatic property (measurement of surface resistivity)
From the central portion in the width direction and the vicinity of both ends of the multilayer extruded foam sheet, three test pieces having the same thickness as the length 100 mm × width 100 mm × thickness: multilayer extruded foam sheet were cut out. A voltage of 500 V was applied to the test piece in an atmosphere of 23 ° C. and a relative humidity of 50% according to JIS K6271-2001, and the surface resistivity of the test piece was measured 1 minute after the application. The surface resistivity was measured on both sides of the test piece (3 test pieces x both sides: 6 times in total), and the surface resistivity was obtained from the arithmetic mean value of the obtained measured values. As a measuring device, "SM-8220" manufactured by Hioki Electric Co., Ltd. was used.
Based on the measured value of surface resistivity, the antistatic property was evaluated according to the following criteria.
⊚: Surface resistivity is 1.0 × 10 ¹⁰ Ω or less ○: Surface resistivity ^{exceeds 1.0 × 10 10} Ω and 1.0 × 10 ¹² Ω or less ×: Surface resistivity is 1.0 × 10 Over ¹²

(4) The closed cell ratio of the multilayer extruded foam sheet was measured by the above method.

(5) Antistatic morphology structure (5-1) Observation method of antistatic morphology structure First, in the vicinity of the center portion in the width direction and both ends in the width direction of the multilayer extruded foam sheet, the thickness direction and the extrusion direction of the multilayer extruded foam sheet. A multi-layer extruded foam sheet was cut along the same line, and three samples having a cross section along the extrusion direction (vertical cross section (a) orthogonal to the width direction) were cut out.
Next, from each cross section of the three cut-out samples, an ultrathin section containing the entire resin layer (resin layer on the surface side of the multilayer extruded foam sheet taken out without facing the mandrel) was prepared. Next, the ultrathin sections were stained with ruthenium tetroxide so that the polyethylene-based resin and the ionomer resin could be distinguished by the shade. Next, using a transmission electron microscope (JEM-1400Plus manufactured by JEOL), the sections stained at an acceleration voltage of 100 kV were observed, and cross-sectional photographs of the resin layer were taken under the conditions of magnifications of 17500 times and 70,000 times.

In the cross-sectional photograph taken, the portion having a higher degree of blackness is the dispersed phase (dispersed phase of ionomer resin). 2 and 3 show a cross-sectional photograph of the multilayer extruded foam sheet obtained in Example 1 (magnification: 17500 times, 70,000 times), and FIG. 4 shows a cross-sectional photograph of the multilayer extruded foam sheet obtained in Comparative Example 1. (Magnification: 17,500 times) is shown.

The obtained cross-sectional photograph was subjected to pretreatment for color-coding the dispersed phase and the portion other than the dispersed phase into black and white. Here, the dispersed phase and the non-dispersed phase (continuous phase) were determined based on the shading of the cross-sectional photograph, the presence or absence of the lamellar structure, and the like, and the photographs were color-coded. Since the ionomer resin usually has more amorphous portions than the polyethylene-based resin, it can be judged as a portion having a smaller lamellar structure than the continuous phase in the cross-sectional photograph. In addition, the interface between the dispersed phase and the continuous phase was clarified by color-coding them.
Then, using the image processing software "NS2K-pro" manufactured by Nanosystem Co., Ltd., image processing and measurement were performed on the prepared cross-sectional photograph under the following conditions.
(1) Monochrome conversion (2) Smoothing filter (processing count 1 to 10 times)
(3) NS method binarization (sharpness 41, sensitivity 10, noise removal, density range 45 to 255)
(4) Ferret diameter and area measurement

(5-2) Average number of layers in the thickness direction of the dispersed phase A morphology in which a layered ionomer resin dispersed phase is present appears in the cross section obtained by the measurement of the image processing under the conditions (1) to (4) above. If so, the average number of layers of the dispersed phase per 1 μm in the thickness direction was measured. Specifically, in the cross-sectional photograph, a line segment perpendicular to the extrusion direction in the thickness direction at a portion where the ionomer resin antistatic agent is dispersed in a layered phase in the continuous phase of the polyethylene resin (B). Ten minutes were subtracted at regular intervals. Here, the length of each line segment corresponds to the thickness of the antistatic layer at the position where each line segment is drawn. For each of the 10 line segments, the number of dispersed phases intersecting the line segment is counted, the number of dispersed layers per 1 μm in the thickness direction is measured and arithmetically averaged, and the number of layers per 1 μm in the thickness direction of the dispersed phase is calculated. Was calculated. Here, the dispersed phase having a cross-sectional area of 1 nm ² or less was not measured. Further, the dispersed phase having an aspect ratio of less than 2 was not measured. Furthermore, in the cross-sectional photograph, the black part that is distinguished from the dispersed phase, such as the wrinkled part of the section generated during the preparation of the ultrathin section and the outermost part of the morphology structure, was not included in the measurement range. This measurement was performed on the three test pieces, and the arithmetic mean value of the three test pieces was taken as the average number of layers per 1 μm in the thickness direction of the dispersed phase.

(5-3) Method for measuring the median value of the dispersed area based on the number of dispersed phases
In the measurement of image processing under the conditions (1) to (4) above, if a morphology in which a dispersed phase is present appears in the obtained cross section, a measurement range is randomly selected and the total area of the measurement range is The measurement was performed so as to be 100 μm ² or more, and the number of all dispersed phases included in the measurement range and the cross-sectional area (dispersion area) were measured. The dispersed phase intersecting the boundary of the measurement range was measured, and the cross-sectional area of the dispersed phase was measured. In addition, the dispersed phase having a cross-sectional area of 1 nm ² or less was not measured. Furthermore, in the cross-sectional photograph, the black part that is distinguished from the dispersed phase, such as the wrinkled part of the section generated during the preparation of the ultrathin section and the outermost surface part of morphology, was not included in the measurement range. This measurement was performed on the three test pieces, and the median value based on the number of cross-sectional areas of the dispersed phases was calculated from the number of all dispersed phases measured by the three test pieces and the cross-sectional area of each dispersed phase. .. The median value is a value located at the center of the total number of dispersed phases (50% of the total number of dispersed phases) when the cross-sectional areas of the dispersed phases are arranged in order of size.

(5-4) Method for determining the presence or absence of an antistatic morphology structure In the vertical cross section (a) of the multilayer extruded foam sheet, an ionomer resin antistatic agent is present in a layered phase in the continuous phase of the polyethylene resin. Moreover, it was judged that the antistatic morphology structure was formed when the dispersed phase was present in 3 layers / μm or more in the thickness direction.

(5-5) Method for Measuring Average Thickness of Non-Antistatic Layer In the cross-sectional photograph of the multi-layer extruded foam sheet in which the morphology appears, the image processing was performed under the conditions of (1) to (4). The region from the outermost surface of the sheet to the portion where the morphology was formed was determined to be a non-antistatic layer, and the thickness of the non-antistatic layer was measured. Specifically, at any point in the cross-sectional photograph, a straight line perpendicular to the extrusion direction is drawn from the outermost surface of the multilayer extruded foam sheet in the thickness direction, and the ionomer resin is dispersed on the outermost surface of the multilayer extruded foam sheet. The distance to the phase was measured. This measurement was performed at 10 points at equal intervals, and the thickness of the antistatic layer was calculated by arithmetic mean. This measurement was performed on the three test pieces, and the arithmetic average value of the thickness of the non-antistatic layer calculated by the three test pieces was taken as the average thickness of the non-antistatic layer containing no antistatic agent.

In the micrographs taken of the multilayer extruded foam sheet obtained in Example 1, FIGS. 2 and 3, a black dispersed phase dispersed in a white continuous phase was confirmed, and an ionomer resin dispersed phase was not present. The non-static layer is confirmed. On the other hand, in the micrograph taken of the multilayer extruded foam sheet obtained in Comparative Example 1 and FIG. 4, a black dispersed phase dispersed in a white continuous phase is confirmed, but a dispersed phase does not exist. No non-static layer is observed.

(5-6) Method for Measuring Average Aspect Ratio of Dispersed Phases In the cross section obtained by the measurement of image processing under the conditions of (1) to (4) above, the vertical and horizontal ferret diameters of all the dispersed phases are used. Was measured. Here, the vertical ferret diameter corresponds to the length of the dispersed phase in the thickness direction of the morphology structure (the direction perpendicular to the surface of the foam sheet), and the horizontal ferret diameter is the length of the dispersed phase in the horizontal direction orthogonal to the thickness direction. Corresponds to the length. The dispersed phase intersecting the boundary of the measurement range was measured, and the vertical and horizontal ferret diameters of the dispersed phase were measured.
This measurement was performed on the three test pieces, and the median value based on the number of each ferret diameter was obtained from the vertical and horizontal ferret diameters of all the dispersed phases measured by the three test pieces. The median of the obtained vertical ferret diameter is the median value of the dispersion diameter in the thickness direction based on the number of dispersed phases. The median value B of the dispersion diameter was used.
The median value means a value located at the center of the total number of dispersed phases (50% of the total number of dispersed phases) when the diameters of the dispersed phases are arranged in order of size.
By dividing the median value B of the dispersion diameter in the horizontal direction orthogonal to the thickness direction based on the number of dispersed phases by the median value A of the dispersion diameter in the thickness direction based on the number of dispersed phases, the cross section of the antistatic layer can be used. The average aspect ratio of the dispersed phase was calculated.

(5-7) Method for measuring the average value of the ratio of the area occupied by the dispersed phase In the cross-sectional photograph obtained by the measurement of the image processing under the conditions (1) to (4), the antistatic layer having the morphology. In addition to setting the substantially center in the thickness direction as the center in the thickness direction, a rectangular range of 1500 nm in the extrusion direction × 500 nm in the thickness direction was defined at an arbitrarily selected location in the width direction, and an enlarged photograph of the rectangular range was taken. .. Next, the sum of the dispersed areas of all the dispersed phases existing in the rectangular range was measured, and the ratio of the total dispersed area of the dispersed phases to the area of the rectangular range was calculated. This measurement was performed on the three test pieces, and the arithmetic mean value of the ratio calculated by the three test pieces was taken as the average value of the ratio of the area occupied by the dispersed phase in a predetermined range.

(6) Glass contamination prevention test Glass for liquid crystal panels was used as the object to be packaged. 10 sheets of this glass and 11 multi-layer extruded foam sheets are laminated to form a glass laminate, and "NDH2000" manufactured by Nippon Denshoku Kogyo Co., Ltd. is used to haze the glass laminate in the thickness direction (glass laminate direction). (1) was measured. A sample (multilayer extruded foam sheet obtained in Examples / Comparative Examples) was placed on each glass ^{under a load of 50 g / cm 2} in surface pressure to bring them into close contact with each other, and allowed to stand still for 168 hours under the conditions of a temperature of 60 ° C. and a relative humidity of 90%. Placed. Then, the sample was removed from the glass, 10 sheets of glass were stacked, and the haze (2) of the glass laminate was measured in the same manner as the haze (1). The amount of change in haze was calculated by subtracting the value of haze (1) from the value of haze (2) (glass haze after test (%) -glass haze before test (%)), and the transferability was evaluated according to the following criteria. .. The smaller the amount of change in haze, the smaller the transfer of low molecular weight components contained in the polymer antistatic agent of the multilayer extruded foam sheet to the glass.
⊚: Haze change amount is less than 0.5 〇: Haze change amount is 0.5 or more and less than 1 Δ: Haze change amount is 1 or more and less than 2 ×: Haze change amount is 2 or more

(7) Evaluation of slipperiness: static friction force The static friction force was measured by a method based on JISK7125: 1999. First, six 50 mm × 50 mm square test pieces were cut out from randomly selected parts of the multi-layer extruded foam sheet so that one side of the test piece coincided with the extrusion direction of the multi-layer extruded foam sheet. Next, the test piece was placed in an atmosphere of 23 ° C. and 50% humidity for 24 hours to adjust the state of the test piece, and then the test piece had a bottom surface size of 50 mm × 50 mm and a weight of 125 g (5 g / cm ² ). It was fixed to the bottom surface of the measuring jig and placed on a slide glass (manufactured by Matsunami Glass Industry Co., Ltd., product name "Standard large white edge polishing No. 2", product number S9112). Then, the test piece was slid on the slide glass by aligning the extrusion direction of the multilayer extruded foam sheet with the tensile direction of the measuring jig and pulling the measuring jig horizontally at a speed of 100 mm / min. .. The first maximum point load at this time was defined as the static friction force (N) in the test piece. Of the 6 test pieces, the static friction force on the mandrel contact surface side was obtained for 3 test pieces, and the static friction force on the opposite surface side to the mandrel contact surface was obtained for the remaining 3 pieces. The arithmetic mean value (n = 6) of the static friction force in each test piece was defined as the static friction force (N) under a low load of the multilayer extruded foam sheet.
Based on the measured value of static friction force, slipperiness was evaluated according to the following criteria.
〇: Static friction force is 2.5N or more and less than 4N ×: Static friction force is 4N or more

(8) Appearance (8-1) Cracks The obtained multi-layer extruded foam sheet was observed, and the occurrence of cracks was evaluated according to the following criteria.
〇: The multi-layer extruded foam sheet is visually inspected, and the surface is clearly not torn.
X: The multi-layer extruded foam sheet is visually inspected and the surface is torn.
(8-2) Waves in the extrusion direction The obtained multi-layer extruded foam sheet was observed, and the waves in the extrusion direction were evaluated according to the following criteria.
〇: Visually observing the multi-layer extruded foam sheet, there is no obvious waviness (poor appearance) in the extrusion direction.
X: The multi-layer extruded foam sheet is visually inspected, and waviness (poor appearance) occurs in the extrusion direction.

1 Multi-layer extruded foam sheet 2 Foam layer 3 Resin layer 3a Antistatic layer 3b Non-static layer 4 Continuous phase of polyethylene resin (B) 5 Dispersed phase of ionomer resin

Claims (7)

A multi-layer extruded foam sheet having a foam layer made of a polyethylene-based resin (A) and a resin layer laminated by coextrusion on at least one side of the foam layer.
The resin layer has an antistatic layer and a non-antistatic layer located on the surface of the multilayer extruded foam sheet.
The antistatic layer contains a polyethylene-based resin (B) and an ionomer resin-based antistatic agent, and the ionomer resin-based antistatic agent is formed in a vertical cross section (a) orthogonal to the width direction of the multilayer extruded foam sheet. Formed a dispersed phase dispersed in layers in the continuous phase of the polyethylene resin (B), and the average number of layers of the dispersed phase was 3 or more per 1 μm in the thickness direction of the multilayer extruded foam sheet.
The non-antistatic layer contains a polyethylene-based resin (C) and substantially no antistatic agent.
The average thickness of the antistatic layer is 0.5 to 15 μm, and the antistatic layer has an average thickness of 0.5 to 15 μm.
A polyethylene-based resin multi-layer extruded foam sheet having a surface resistivity of the surface of the multi-layer extruded foam sheet on the resin layer side of 1 × 10 ^{12 Ω or less.}
The multilayer extruded foam sheet according to claim 1, wherein the dispersed phase has an average aspect ratio of 2 or more in the vertical cross section (a).
The polyethylene-based resin according to claim 1 or 2, wherein in the vertical cross section (a), the median value of the dispersed area based on the number of dispersed phases is 1 × 10 ^{2 to} 5 × 10 ⁵ nm ^2. Multi-layer extruded foam sheet.
The polyethylene-based resin according to any one of claims 1 to 3, wherein the median horizontal dispersion diameter based on the number of dispersed phases is 200 to 3000 nm in the vertical cross section (a). Multi-layer extruded foam sheet.
In the vertical cross section (a), the average value of the ratio of the area occupied by the dispersed phase is 30 to 80 areas in the rectangular range of the central portion of the antistatic layer having a length of 500 nm in the thickness direction and a length of 1500 nm in the width direction. The polyethylene-based resin multilayer extruded foam sheet according to any one of claims 1 to 4, wherein the content is%.
The antistatic layer contains polyalkylene glycol, and the content of the polyalkylene glycol is 0.3 to 6 weights based on 100 parts by weight of the total of the polyethylene-based resin (B) and the ionomer resin-based antistatic agent. The polyethylene-based resin multilayer extruded foam sheet according to any one of claims 1 to 5, characterized in that it is a part.
The polyethylene-based resin multilayer extruded foam sheet according to any one of claims 1 to 6, wherein the surface resistivity is ^{less than 1 × 10 10 Ω.}

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