JP2020192735A - Polyethylene-based resin laminate extrusion foam sheet - Google Patents

Abstract

To provide a laminate foam sheet which suppresses shift of a low-molecular-weight component and the like to an object to be packed and is excellent in antistatic performance.SOLUTION: A polyethylene-based resin laminate foam sheet has a foam layer and a polyethylene-based resin layer laminated and bonded to the foam layer, in which the resin layer is formed of a resin composition containing a polyethylene-based resin (B) and an ionomer resin, a continuous phase composed of the polyethylene-based resin and a dispersion phase composed of an ionomer resin dispersed in the continuous phase are formed in the resin composition, a central value of a dispersion area on a number base of the dispersion phase in a vertical cross section orthogonal to the width direction of the laminate foam sheet is within a specific value, a ratio (B/A) of a central value B of a dispersion value in a direction orthogonal to a thickness direction on the number base of the dispersion phase to a central value A of a dispersion diameter in a thickness direction on the number base of the dispersion phase is 2 or more, and surface reflectivity on the side of the resin layer of the laminate foam sheet is equal to or smaller than a specific value.SELECTED DRAWING: None

Description

The present invention relates to a polyethylene-based resin extruded laminated foam sheet, and more particularly to a polyethylene-based resin extruded laminated foam sheet having excellent antistatic performance and a small amount of transfer of low molecular weight components and the like to an object to be packaged or the like.

A laminated extruded foam sheet (hereinafter, also simply referred to as a laminated foam sheet) in which a resin layer made of a polyethylene resin is laminated on a foam sheet made of a polyethylene resin is lightweight and has excellent cushioning properties, so that it can be used as a liquid crystal panel. It is widely used in the field of packaging electronic devices and their materials, such as interstitial paper between glass plates used for packaging.

In such applications, antistatic performance is usually imparted to the laminated foam sheet in order to suppress adhesion of dust, dust, etc. to the laminated foam sheet. As a method of imparting antistatic performance to a laminated foam sheet, for example, when a laminated foam sheet is manufactured by a coextrusion method, a polymer-type antistatic agent is blended with a resin melt for forming a resin layer. A method of coextruding to form a resin layer containing a polymer-type antistatic agent can be mentioned (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2016-20427

In addition to being excellent in antistatic properties, the interleaving paper is required not to contaminate an object to be packaged such as a glass plate. In addition, in recent years, in laminated foam sheets used for glass plate interleaving paper for electronic devices, etc., in order to prevent contamination of the packaged object, a low molecular weight derived from a high molecular weight antistatic agent on the packaged object is used. There is a demand for a laminated foam sheet in which the transfer of components and the like is further suppressed.

In order to reduce the amount of migration of low molecular weight components and the like, it is preferable to use a high molecular weight antistatic agent having a low content of low molecular weight components. Examples of high molecular weight antistatic agents having a low content of low molecular weight components include ionomer resins.

However, conventionally, when a polyethylene-based resin layer containing an ionomer resin is laminated on a polyethylene-based resin foamed layer by coextrusion to produce a laminated foamed sheet, the desired antistatic property is stably exhibited. It was difficult to stably produce a laminated foam sheet having good antistatic performance.

An object of the present invention is to solve the above-mentioned problems and to provide a laminated foam sheet having excellent antistatic performance while suppressing the transfer of low molecular weight components and the like to an object to be packaged or the like.

According to the present invention, the polyethylene-based resin laminated extrusion foam sheet shown below is provided.
[1] In a polyethylene resin laminated extrusion foam sheet having a polyethylene resin foam layer and a polyethylene resin layer laminated and adhered to at least one surface of the foam layer, the resin layer is higher than the polyethylene resin (B). It is formed from a resin composition containing a molecular antistatic agent and
The polymer-type antistatic agent is an ionomer resin, and the resin composition is composed of a continuous phase composed of the polyethylene-based resin and the polymer-type antistatic agent dispersed in the continuous phase. The dispersed phase is formed, and the median value of the dispersed area based on the number of the dispersed phases is 1 × 10 ² to 1 × 10 ⁶ nm ² in the vertical cross section orthogonal to the width direction of the laminated extruded foam sheet. At the same time, the ratio (B / A) of the median value B of the dispersion diameter in the direction orthogonal to the thickness direction based on the number of dispersed phases is 2 or more with respect to the median value A of the dispersion diameter in the thickness direction based on the number of dispersed phases. The polyethylene-based resin laminated extrusion foam sheet is characterized in that the surface resistance of the laminated extrusion foam sheet on the resin layer side is 1 × 10 ¹² Ω or less.
[2] The polyethylene-based resin laminated extrusion foam sheet according to 1 above, wherein the content ratio of the polymer-type antistatic agent in the resin layer is 5 to 30% by weight.
[3] The polyethylene-based resin laminated extrusion foam sheet according to 1 or 2 above, wherein the ionomer resin is a potassium ionomer, which is a copolymer of ethylene and an unsaturated carboxylic acid.
[4] The polyethylene-based resin laminated extrusion foam sheet according to any one of 1 to 4, wherein the melt flow rate of the ionomer resin is 3 g / 10 minutes or less.
[5] The polyethylene resin (B) has a melting point Tmp of 100 to 120 ° C.
The polyethylene-based resin laminated extrusion foam sheet according to any one of 1 to 3 above, wherein the difference (Tmp-Tmi) between the melting point Tmp of the polyethylene resin and the melting point Tmi of the ionomer resin is 5 to 30 ° C.
[6] The polyethylene-based resin laminated extrusion foam sheet according to any one of 1 to 5, wherein the laminated extrusion foam sheet has an apparent density of 20 to 200 kg / m ³ .
[7] The polyethylene-based resin laminated extrusion foam sheet according to any one of 1 to 6 above, wherein the basis weight per one side of the resin layer is 1 to ²⁰ g / m ² .
[8] The polyethylene-based resin laminated extrusion foam sheet according to any one of 1 to 7, wherein an average of one or more dispersed phases are present on a straight line along the thickness direction in the vertical cross section.

In the laminated extruded foam sheet of the present invention, by using an ionomer resin as a polymer antistatic agent, the transfer of low molecular weight components and the like to an object to be packaged and the like is suppressed, and further, the ionomer resin is contained in the resin layer. By dispersing in a specific state, excellent antistatic performance can be stably exhibited.

FIG. 1 is a cross-sectional photograph taken of the laminated extruded foam sheet obtained in Example 1 (magnification: 7000 times). FIG. 2 is a cross-sectional photograph taken of the laminated extruded foam sheet obtained in Example 1 (magnification: 70,000 times). FIG. 3 is a cross-sectional photograph taken of the laminated extruded foam sheet obtained in Comparative Example 1 (magnification: 7000 times).

Hereinafter, the polyethylene-based resin laminated extrusion foam sheet of the present invention (hereinafter, also simply referred to as a laminated foam sheet) will be described in detail.
The laminated extrusion foam sheet of the present invention is manufactured by an extrusion foaming method. The laminated foam sheet has a polyethylene-based resin foam layer (hereinafter, also simply referred to as a foam layer) and a polyethylene-based resin layer (hereinafter, also simply referred to as a resin layer), and the resin layer is at least the foam layer. It is laminated and bonded to one side. In order to further prevent the adhesion of dust and dirt, it is preferable that the resin layer is laminated and adhered to both sides of the foam layer.
The laminated foam sheet can be efficiently manufactured by a coextrusion foaming method as described later.

Next, the polyethylene-based resin constituting the foam layer and the resin composition constituting the resin layer will be described in this order.
In the present invention, the foamed layer is made of a polyethylene resin (A). The polyethylene-based resin (A) is a copolymer of ethylene and comonomer such as high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and ethylene-vinyl acetate copolymer, and has an ethylene component of 50 mol%. These include those that exceed and mixtures of two or more of these.
Among these polyethylene-based resins (A), a polyethylene-based resin containing low-density polyethylene as a main component is preferable because it is a laminated foamed sheet having excellent extrusion foamability and excellent cushioning properties.

In the present specification, "mainly composed of low-density polyethylene" means that the low-density polyethylene is contained in the polyethylene-based resin in an amount of 50% by weight or more. The low density polyethylene is preferably a polyethylene resin density of less than 0.91 g / cm ³ or more 0.93 g / cm ^3.

The polyethylene-based resin (A) may contain other components such as synthetic resins and elastomers other than the polyethylene-based resin as long as the object and effect of the present invention are not impaired. In this case, the content of the other components is preferably 20% by weight or less, more preferably 10% or less, based on 100% by weight of the polyethylene resin (A).

The content of the low-density polyethylene in the polyethylene-based resin (A) is preferably 60% by weight or more, more preferably 70% by weight or more, still more preferably 80% by weight or more, and particularly preferably 90% by weight or more. It is most preferable that the polyethylene-based resin (A) is composed of only low-density polyethylene.

The polyethylene-based resin (A) forming the foam layer contains a bubble modifier, a nucleating agent, an antioxidant, a heat stabilizer, a weather resistant agent, an ultraviolet absorber, and difficulty as long as the object and effect of the present invention are not impaired. Additives such as flame retardants, antibacterial agents, shrinkage inhibitors, and inorganic fillers can be added.

Next, the resin composition constituting the resin layer will be described.
The resin layer in the present invention is composed of a resin composition containing a polyethylene-based resin (B) and a polymer-type antistatic agent.

As the polyethylene-based resin (B), the resin exemplified as the polyethylene-based resin (A) can be used. Among these polyethylene-based resins, it is preferable to use a polyethylene-based resin containing low-density polyethylene as a main component as the polyethylene-based resin (B) because a laminated foamed sheet having excellent antistatic performance can be stably produced. It is more preferable to use density polyethylene.
When low-density polyethylene is used as the polyethylene-based resin (B), it is preferable to use low-density polyethylene as the polyethylene-based resin (A) because the adhesiveness between the resin layer and the foamed layer is excellent.

The content of the polyethylene-based resin (B) in the resin layer is preferably 50% by weight or more, more preferably 60% by weight or more, and further preferably 70% or more.

The resin composition may contain polyalkylene glycol such as polyethylene glycol as long as the object and effect of the present invention are not impaired.

The resin layer may contain other components such as a synthetic resin and an elastomer other than the polyethylene-based resin as long as the object and effect of the present invention are not impaired.
It is preferable that the resin layer does not substantially contain a polystyrene-based resin. Specifically, the content of the polystyrene resin in the resin layer is preferably less than 5% by weight, more preferably 3% by weight or less, and most preferably 0. By reducing the content of the polystyrene-based resin in the resin layer, the cushioning property and recyclability of the laminated foam sheet can be improved.

As the polystyrene-based resin, polystyrene (general-purpose polystyrene), rubber-modified polystyrene (impact-resistant polystyrene), and styrene containing 50% or more of components derived from styrene and a vinyl-based monomer copolymerizable with styrene are used. Examples include copolymers.

The polymer-type antistatic agent contained in the resin composition constituting the resin layer is an ionomer resin.
The ionomer resin has a low surface resistivity, can impart good antistatic performance to the laminated foam sheet, and has a low content of low molecular weight components. Therefore, due to the transfer of low molecular weight components to the packaged material. , Contamination of the packaged object can be suppressed.

The ionomer resin is a resin in which the molecules of a copolymer of ethylene and an unsaturated carboxylic acid are intermolecularly crosslinked with metal ions. Examples of unsaturated carboxylic acids include acrylic acid and methacrylic acid. Moreover, as a metal ion, lithium, sodium, potassium, calcium and the like can be mentioned.
Among the ionomer resins, potassium ionomer, which is a copolymer of ethylene and unsaturated carboxylic acid, using potassium as a metal ion is preferable because it can impart good antistatic performance to the laminated foamed sheet.
Examples of commercially available ionomer resins include "Entila SD100" and "Entila MK400" manufactured by Mitsui-DuPont Polychemical Co., Ltd.

The surface resistivity of the ionomer resin is preferably less than 1 × 10 ¹² Ω. By forming the resin layer using an ionomer resin having a surface resistivity of less than 1 × 10 ¹² Ω, a laminated 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), as will be described later.

In the resin layer, the content ratio of the polymer type antistatic agent is preferably 5 to 30% by weight. When the content ratio is within this range, the antistatic performance of the surface of the resin layer can be stably exhibited while suppressing the migration of low molecular weight components derived from the polymer type antistatic agent.
Therefore, the lower limit of the content ratio is more preferably 6% by weight, further preferably 8% by weight, and particularly preferably 10% by weight. On the other hand, the upper limit of the content ratio is more preferably 25% by weight, still more preferably 20% by weight.
The content ratio of the polymer-type antistatic agent is a ratio to a total of 100% by weight of the content of the polyethylene-based resin (B) and the content of the polymer-type antistatic agent.

In the present invention, a continuous phase and a dispersed phase dispersed in the continuous phase are present in the resin composition constituting the resin layer, and the continuous phase is composed of the polyethylene-based resin (B) and is dispersed. The phase is composed of the polymer type antistatic agent. By forming a continuous phase of the polyethylene-based resin (B), the resin layer has excellent flexibility and cushioning properties. Furthermore, despite the fact that an ionomer resin is used as the polymer-type antistatic agent, excellent antistatic properties are exhibited. The reason is that, as described below, the polymer-type antistatic agent forms a dispersed phase, and the dispersed phase is stretched in a streak pattern to form a network of polymer-type antistatic agents. It is possible that it has been done.

The dispersed phase of the ionomer resin in the present invention is characterized in that it is stretched as well as small, the degree to which the dispersed phase is small is represented by the median value of a specific dispersion area, and the degree to which it is stretched is a specific ratio ( It is represented by B / A). Next, the range and meaning of the median of the dispersed area and the range and meaning of the ratio (B / A) will be described in this order.

In the present invention, the median value of the dispersed area based on the number of dispersed phases in the vertical cross section orthogonal to the width direction of the laminated foam sheet is 1 × 10 ² to 1 × 10 ⁶ nm ² .
For the median value, the number of dispersed phases in a vertical cross section orthogonal to the width direction of the laminated foam sheet and the cross-sectional area (dispersion area) of each dispersed phase were measured, and the measured cross-sectional areas of the dispersed phases were arranged in order of size. It is a value located at the center of the total number of dispersed phases (50% of the total number of dispersed phases). By adopting the median value, it is possible to appropriately evaluate the dispersed state of the dispersed phase, which has a high abundance rate in the continuous phase and contributes to the antistatic performance.
The fact that the median value of the dispersion area is within the above range means that a large amount of dispersed phase made of ionomer resin (polymer type antistatic agent) having a small dispersion diameter is dispersed in the continuous phase made of polyethylene resin (B). It means that it exists. The median value is smaller than the median value in the conventional resin layer, and is a value that could not be realized in the past.
If the median is too small, good antistatic performance may not be exhibited. On the other hand, if the median value is too large, the polymer-type antistatic agent may not be well dispersed in the resin composition, and good antistatic performance may not be exhibited.
In order to further enhance the antistatic performance of the laminated foam sheet, the lower limit of the median value is preferably 5 × 10 ² , and more preferably 1 × 10 ³ . The upper limit of the median value is preferably 1 × 10 ⁵ nm ² , more preferably 5 × 10 ⁴ nm ² .
The width direction of the laminated foam sheet is a direction orthogonal to the extrusion direction and the thickness direction of the laminated foam sheet.

The laminated foam sheet of the present invention has excellent antistatic properties even though the resin layer contains an ionomer resin as a polymer-type antistatic agent.
The reason why the resin layer in the present invention exhibits antistatic properties is that a large number of dispersed phases having a small dispersion diameter made of ionomer resin are dispersed in the continuous phase (the median value of the dispersion area is small). It is considered that the conductive network structure of the ionomer resin is formed in the polyethylene-based resin because the dispersed phase is stretched and exists in a streak shape. Specifically, in a vertical cross section orthogonal to the width direction of the laminated foam sheet, the dispersion diameter in the direction orthogonal to the thickness direction based on the number of dispersed phases with respect to the median value A of the dispersion diameter in the thickness direction based on the number of dispersed phases. It is required that the ratio (B / A) of the median value B of is 2 or more.
Here, the median value of each dispersion diameter is obtained by measuring the number of dispersed phases in a vertical cross section orthogonal to the width direction of the laminated foam sheet, each vertical ferret diameter, and each horizontal ferret diameter, and measuring each of the measured ferret diameters. It means 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. The vertical ferret diameter corresponds to the length of the dispersed phase in the thickness direction of the resin layer, and the horizontal ferret diameter corresponds to the length of the dispersed phase in the direction orthogonal to the thickness direction.
When the ratio (B / A) is large, it means that the dispersed phase is stretched in one direction, and the dispersed phase of the ionomer resin exists in a stretched state. It is considered that this facilitates the formation of a conductive network structure of the ionomer resin (polymer type antistatic agent) and exhibits better antistatic properties.
If the ratio (B / A) is too small, the polymer-type antistatic agent does not exist in a well-stretched state in the resin composition, so that good antistatic performance may not be exhibited.
From this point of view, in the vertical cross section, the ratio of the median value B of the dispersion diameter in the thickness direction based on the number of dispersed phases to the median value B of the dispersion diameter in the direction orthogonal to the thickness direction based on the number of dispersed phases (B / A). ) Is preferably 3 or more. The upper limit of the ratio (B / A) is preferably about 20, more preferably 10, and even more preferably 6.
The thickness direction of the dispersed phase coincides with the thickness direction of the laminated foam sheet (thickness direction of the resin layer).

In the resin layer of the present invention, as described above, since the median dispersion area is within a specific range, the ionomer resin is finely dispersed in the polyethylene resin (B), and the ratio of the median dispersion diameters (B). When / A) is within a specific range, the ionomer resin is stretched, and as will be described later, it is possible to exhibit good antistatic properties such that the surface resistivity is 1 × 10 ¹² Ω or less. Further, since the ionomer resin contains a small amount of low molecular weight components, the laminated foamed sheet on which the resin layer is laminated is less likely to contaminate the packaged object.

In the vertical cross section, the median value A of the dispersion diameter in the thickness direction based on the number of dispersed phases is preferably 10 to 1000 nm, more preferably 15 to 600 nm, and further preferably 20 to 500 nm. , 30-300 nm is particularly preferable. When the median value A is within this range, a laminated foam sheet having excellent antistatic performance can be obtained more stably.

In the present invention, it is preferable that one or more dispersed phases are present on an average in a straight line along the thickness direction in the vertical cross section. If the dispersed phase is present in this range, it becomes easy to obtain a laminated foamed sheet in which the desired antistatic performance is stably exhibited.
From this point of view, it is more preferable that two or more of the dispersed phases are present on average, and it is further preferable that five or more of the dispersed phases are present. Further, the dispersed phases preferably exist in an average of 100 or less, more preferably in an average of 30 or less, and further preferably in an average of 20 or less.
The average number of dispersed phases is such that straight lines along the thickness direction of the resin layer are formed at intervals of 2 μm over the entire resin layer in a vertical cross section orthogonal to the width direction of six or more randomly selected laminated foam sheets. It is a value obtained by subtracting 5 lines in 1 and measuring the number of dispersed phases intersecting with this straight line, and then dividing the total number of measured dispersed phases by the total number of straight lines.

The median value of the dispersed area based on the number of dispersed phases, 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 in the direction orthogonal to the thickness direction based on the number of dispersed phases, and the thickness direction. Regarding the average value of the number of dispersed phases existing on a straight line along the line, a vertical cross section orthogonal to the width direction of the laminated foam sheet was cut out to prepare an ultrathin section including a resin layer portion, and after dyeing this. , Can be measured based on a photograph obtained by imaging a stained ultrathin section using a transmission electron microscope. A specific measurement method will be described in detail in Examples.

Next, the physical properties of the laminated foam sheet of the present invention will be described.
The surface resistivity of the laminated foam sheet of the present invention on the resin layer side is 1 × 10 ¹² Ω or less. When the surface resistivity is within the above range, the laminated foam sheet is sufficiently exhibited in antistatic performance, and the adhesion of dust and the like can be suppressed.
For this reason, the surface resistivity is more preferably 5 × 10 ¹¹ Ω or less, and further preferably 1 × 10 ¹¹ Ω or less.
When the resin layers are laminated on both sides of the laminated foamed sheet, the surface resistivity of each of both sides of the laminated foamed sheet is 1 × 10 ¹² Ω or less.
If the surface resistivity is within the above range, a surface resin layer that does not substantially contain a polymer-type antistatic agent may be further laminated on the surface of the resin layer.

In the present specification, the surface resistivity is measured as follows.
A plurality of test pieces having predetermined dimensions (for example, length 100 mm × width 100 mm × thickness: sheet thickness) are cut out from the laminated foam sheet and applied to the resin layer of the test pieces according to the method of JIS K6271 (2001). The surface resistivity value 1 minute after application at a voltage of 500 V can be measured, and the surface resistivity can be obtained from the average value of the obtained measured values. The surface resistivity of the polymer-type antistatic agent (ionomer resin) was also applied to a sample in which the ionomer resin was formed into a flat plate at an applied voltage of 500 V based on the method of JIS K6271 (2001). The surface resistivity value 1 minute after that is measured, and it can be obtained from the average value of the obtained measured values.
As the surface resistivity measuring device, for example, Takeda Riken Kogyo Co., Ltd., model: TR8601 or the like can be used.

Overall apparent density of the laminated foam sheet of the present invention is preferably 20 to 200 kg / ^{m 3,} more preferably 30~150kg / ^{m 3,} more preferably from 50~120kg / ^{m 3.} A laminated foam sheet having an apparent density within the above range is excellent in a balance of light weight, handleability, and cushioning property. For the same reason, the entire basis weight of the laminated foam sheet is preferably 10 to 200 g / ^{m 2,} more preferably 15 to 100 / ^{m 2,} more preferably from 20 to 80 g / ^{m 2.}

In the present specification, the basis weight of the laminated foam sheet is measured as follows. First, a test piece having a predetermined size (for example, a length of 10 cm) is cut out over the entire width of the laminated foam sheet, the weight (g) of the test piece is measured, and then the weight is divided by the area of the test piece to divide the laminated foam sheet. Basis weight is calculated.
Further, the overall apparent density of the laminated foamed sheet is obtained by dividing the basis weight (g / m ² ) of the laminated foamed sheet by the total thickness (mm) of the laminated foamed sheet and converting it into a unit.

The total thickness of the laminated foam sheet is preferably 0.05 to 2 mm. When the overall thickness is within the above range, the cushioning property can be enhanced, and when used as a paper sheet for plate-like objects such as glass plates, the loading efficiency when stacking and transporting glass plates can be enhanced. ..
From this point of view, the upper limit is preferably 1.5 mm, more preferably 1.2 mm, and even more preferably 1.0 mm. On the other hand, the lower limit thereof is preferably 0.1 mm, more preferably 0.2 mm, still more preferably 0.3 mm in order to secure higher cushioning properties.

The upper limit of the basis weight per one side of the resin layer is preferably 20 g / m ² , more preferably 15 g / m ² , still more preferably 10 g / m ² , and particularly preferably 5 g / m ² . is there. When the upper limit of the thickness is within the above range, it is possible to improve the cost and lightness while exhibiting the desired antistatic performance. On the other hand, the lower limit is approximately 1 g / m ² . When the lower limit is within the above range, the film forming property required for forming the resin layer can be ensured.

The basis weight [g / m ² ] of the resin layer is the discharge amount X [kg / hour] of the resin layer at the time of manufacturing the laminated foam sheet, the width W [m] of the obtained laminated foam sheet, and per unit time. It can be obtained by substituting the length L [m / hour] of the laminated foam sheet extruded into the following equation (1). When the resin layers are laminated on both sides of the foam layer, the basis weight of the resin layer on each surface can be obtained from the discharge amount of each resin layer.
Basis weight of the entire resin layer [g / m ² ] = [1000X / (L × W)] ... (1)

Next, the method for producing the laminated foam sheet of the present invention will be described in detail.
The laminated foam sheet of the present invention is obtained by kneading a resin melt for forming a foam layer formed by kneading a polyethylene resin and a physical foam agent, and a polyethylene resin, a polymer antistatic agent, and a volatile plasticizer. It can be produced by co-extruding with a resin melt for forming a resin layer.
Specifically, a polyethylene-based resin (A) is supplied to an extruder for forming a foam layer, heated and melted to obtain a molten resin, a physical foaming agent is press-fitted, and the resin melt for forming a foam layer is further kneaded. And.
On the other hand, a polyethylene resin (B) and a polymer-type antistatic agent (ionomer resin) are supplied to a resin layer forming extruder, heated and melted to form a molten resin, and then a volatile plasticizer is press-fitted. Further kneading is used to obtain a resin melt for forming a resin layer. The obtained resin melt for forming a foam layer and the resin melt for forming a resin layer are introduced into a coextrusion die, laminated, and coextruded under low pressure (usually atmospheric pressure). In this way, the resin melt for forming the resin layer and the resin melt for forming the foam layer are laminated, and the resin melt for forming the foam layer is foamed, whereby the resin layer is laminated and adhered to the foam layer. Is obtained.

In the above-mentioned coextrusion foaming method, since the formation of the foam layer and the lamination of the resin layer on the foam layer are performed by using the coextrusion die, the productivity is excellent and the space between the resin layer and the foam layer is high. This is a method capable of obtaining a laminated foam sheet having high adhesive strength.

As a method for producing a laminated foam sheet by a coextrusion foaming method, a method of extruding a foamable resin melt into a sheet using a flat die for coextrusion to obtain a laminated foam sheet, or an annular die for coextrusion is used. Then, there is a method of extruding the foamable resin melt into a tubular shape to obtain a tubular laminated foam, and then cutting open the tubular laminated foam to obtain a laminated foam sheet. Among these, the method using an annular die for coextrusion is preferable because a wide laminated foam sheet having a width of 1000 mm or more can be easily produced.

When a laminated foam sheet is produced by a coextrusion method using the annular die, first, the polyethylene-based resin (A) and an additive such as a bubble adjusting agent added as needed are extruded for forming a foam layer. It is supplied to a machine, heat-melted and kneaded, then a physical foaming agent is press-fitted, and further kneaded to obtain a resin melt for forming a foam layer. On the other hand, the polyethylene-based resin (B) and the polymer-type antistatic agent (ionomer resin) are supplied to a resin layer forming extruder, heat-melted and kneaded, and then a volatile plasticizer is press-fitted and further kneaded. To obtain a resin melt for forming a resin layer. Next, the resin melt for forming the foam layer and the resin melt for forming the resin layer are introduced into the annular die for coextrusion.

The target apparent density of the polyethylene-based resin (A) is a polyethylene-based resin having a melt flow rate (MFR) of 0.5 to 15 g / 10 minutes and further 1 to 12 g / 10 minutes at 190 ° C. It is preferable to obtain the foam layer of. 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.

The melting point Tmp of the polyethylene resin (A) is preferably 100 to 135 ° C. Since the polyethylene-based resin (A) having the melting point Tmp in the above range is excellent in extrusion foamability, a foamed layer having excellent cushioning property can be stably formed. For this reason, the melting point Tmp 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 in accordance with JIS K7121-1987. 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 of the apex of the melting peak having the largest area is taken as the melting point.

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. Cyclic hydrocarbons, chloride hydrocarbons such as methyl chloride and ethyl chloride, organic physical foaming agents such as fluorocarbons such as 1,1,1,2-tetrafluoroethane and 1,1-difluoroetan, nitrogen and dioxide. Examples thereof include inorganic physical foaming agents such as carbon, air, and water. In some cases, a decomposing foaming agent such as azodicarbonamide can also be used. The above-mentioned physical foaming agents can be used in combination by mixing two or more kinds. Of these, organic physical foaming agents are particularly preferable from the viewpoint of compatibility with polyethylene resins and foamability, and among these, 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. The amount of the bubble adjusting agent added is adjusted according to the target bubble diameter. For example, in order to obtain a laminated foam sheet in the overall apparent density range using a butane mixture of 35% by weight of isobutane and 65% by weight of normal butane as a foaming agent, the amount of the butane mixture added is the polyethylene resin (A). It is preferably about 3 to 30 parts by weight, more preferably 4 to 20 parts by weight, and even more preferably 6 to 18 parts by weight per 100 parts by weight.

A bubble modifier is usually 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 modifier include metal borate 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 regulator include sodium 2,2-methylenebis (4,6-tert-butylphenyl) phosphate, sodium benzoate, calcium benzoate, aluminum benzoate, sodium stearate and the like. Further, a sodium bicarbonate-citric acid-based chemical foaming agent or the like, which is a combination of citric acid and sodium bicarbonate, an alkaline salt of citric acid and sodium bicarbonate, or the like can also be used as the bubble adjusting agent. Two or more of these bubble modifiers can be mixed and used.

The melt flow rate (MFR) of the polyethylene resin (B) is preferably 1 to 20 g / 10 minutes (temperature 190 ° C., load 2.16 kg), and more preferably 5 to 15 g / 10 minutes. .. When the MFR is within this range, a good resin layer can be stably and efficiently formed by the coextrusion foaming method.
The MFR of the polyethylene-based resin (B) is preferably the same as the MFR of the polyethylene-based resin (A) or higher than the MFR of the polyethylene-based resin (A).

The melt flow rate (MFR) of the ionomer resin is preferably 10 g / 10 minutes or less (temperature 190 ° C., load 2.16 kg), more preferably 7 g / 10 minutes or less, and further preferably 3 g / 10 minutes. Less than a minute. On the other hand, the lower limit is approximately 1 g / 10 minutes (temperature 190 ° C., load 2.16 kg).
In particular, an ionomer resin having a melt flow rate (MFR) of 3 g / 10 minutes or less is more preferable because the amount of low molecular weight components contained in the polymer antistatic agent tends to be small.

And MFR (MFR _E) of the polyethylene resin, the difference between the MFR (MFR _I) of said ionomer resin _(MFR E -MFR _I) is preferably from 5 to 20 g / 10 min, 6 to 15 g / 10 min Is more preferable, and 6 to 12 g / 10 minutes is even more preferable.
When a laminated foam sheet is obtained by coextrusion, if the difference between the MFR of the polyethylene-based resin constituting the continuous phase and the MFR of the ionomer resin constituting the dispersed phase becomes large, when the resin melt for forming the resin layer is extruded. When the temperature condition of is set to a relatively low temperature, it becomes difficult to disperse the ionomer resin in the polyethylene-based resin. On the other hand, in the present invention, as will be described later, by using a volatile plasticizer at the time of extrusion, the ionomer resin can be dispersed in the polyethylene-based resin even when the difference is within the above range. A laminated foam sheet having excellent antistatic performance can be stably obtained over the entire layer.

The melting point Tmp of the polyethylene resin (B) is preferably 100 to 120 ° C. By setting the melting point Tmp within the above range, the laminated state of the resin layer and the foamed layer is improved, a homogeneous resin layer is formed, and the laminated foamed sheet exhibits good antistatic performance over the entire laminated foamed sheet. It becomes easier to obtain a sheet. For this reason, the melting point Tmp is more preferably 102 to 115 ° C.

The difference (Tmp-Tmi) between the melting point Tmp of the polyethylene resin (B) and the melting point Tmi of the ionomer resin is preferably 5 to 30 ° C, preferably 8 to 28 ° C, and 10 to 25 ° C. More preferably, it is ° C.
When a laminated foam sheet is obtained by coextrusion, the temperature condition for extruding the resin melt for forming a resin layer is usually set to a sufficiently high temperature so that a polymer type can be contained in the resin constituting the continuous phase. It becomes easier to disperse the antistatic agent. 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 resin layer cannot be made excessively high, and under relatively low temperature conditions, the melt viscosity of the ionomer resin becomes high. Since it tends to increase, conventionally, when a polyethylene-based resin and an ionomer resin having a certain melting point difference are used as the resin composition constituting the resin layer, the ionomer resin is dispersed in the polyethylene-based resin. It was difficult to get it done.
On the other hand, in the present invention, as will be described later, by using a volatile plasticizer at the time of extrusion, the ionomer resin is dispersed in the polyethylene-based resin even when there is a difference in melting point as in the above range. It is possible to stably obtain a laminated foam sheet having excellent antistatic performance over the entire resin layer.
The melting point Tmi of the ionomer resin is preferably about 80 to 110 ° C, more preferably 85 to 100 ° C.

The melting points of the polyethylene-based resin (B) and the ionomer resin in the present specification are values measured in the same manner as the melting points of the polyethylene-based resin (A), and are measured by heat flux differential scanning calorimetry in accordance with JIS K7121-1987. It is a value obtained by.

In order to form the resin melt for forming the resin layer, it is preferable to add a volatile plasticizer to the melted mixed resin. As the volatile plasticizer kneaded together with the polyethylene resin and the polymer antistatic agent, an alcohol (A) having a boiling point of 120 ° C. or lower, a saturated hydrocarbon having a carbon number of 3 to 5 and / or a carbon number of an alkyl chain One or more selected from 1 to 3 dialkyl ethers (B) can be used. The volatile plastic agent preferably contains an alcohol (A) having a boiling point of 120 ° C. or lower, an alcohol (A) having a boiling point of 120 ° C. or lower, a saturated hydrocarbon having 3 to 5 carbon atoms, and / or carbon having an alkyl chain. It is more preferable to contain dialkyl ethers (B) having a number of 1 to 3.

The ionomer resin is a resin in which a pseudo crosslinked structure is formed in the resin by repeatedly binding and dissociating metal ions and carboxylic acid. In such an ionomer resin, when the molten resin temperature is high, the bond / dissociation occurs and the melt viscosity decreases, but when the molten resin temperature becomes low to about the foaming temperature condition of the polyethylene resin, the bond / dissociation occurs. Is less likely to occur, and the melt viscosity increases. Therefore, when an attempt is made to produce a laminated foam sheet in which a resin layer containing an ionomer resin is laminated on a foam layer by coextrusion, the extrusion temperature at the time of coextrusion is adjusted to a temperature suitable for foaming the resin melt for forming a foam layer. Therefore, the molten resin temperature of the resin layer containing the ionomer resin becomes low, and the melt viscosity of the ionomer resin tends to increase. As a result, it becomes difficult for the ionomer resin to disperse well in the polyethylene-based resin, and it becomes difficult to stably produce a laminated foam sheet having good antistatic performance. In particular, this tendency becomes remarkable when an ionomer resin having a low MFR is used.

However, by using a volatile plasticizer containing alcohol (A), which has a large plasticizing effect on ionomer resin, the extrusion temperature of the resin melt for forming the resin layer is adjusted to the extrusion temperature of the resin melt for forming the foam layer. Even when it is lowered, the melt viscosity of the ionomer resin can be kept low. This effect is effectively exhibited even when an ionomer resin having a small MFR is used.
It is considered that due to this effect, a resin layer in which the ionomer resin is well dispersed in the polyethylene-based resin is formed, and a laminated foamed sheet having excellent antistatic performance can be obtained.

In addition, when a volatile plasticizer containing saturated hydrocarbons having 3 to 5 carbon atoms and / or dialkyl ether, which has a large plasticizing effect on the polyethylene resin, is used, the melt viscosity of the polyethylene resin (A) is stabilized. Can be kept low. Therefore, even under the extrusion temperature condition of the resin melt for forming the resin layer, which is set to a relatively low temperature corresponding to the extrusion foaming temperature (100 to 140 ° C.) of the resin melt for forming the foam layer, the resin for forming the resin layer It becomes easy to keep the melt viscosity of the entire melt low. Due to this effect, the ionomer resin has a uniform thickness, the ionomer resin is well dispersed in the resin composition, the stretched resin layer is easily formed, and a laminated foamed sheet having excellent antistatic performance can be obtained more stably. It is thought that

Examples of the alcohol (A) having a boiling point of 120 ° C. or lower include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl2-propanol and the like. Can be mentioned.
Among these, ethanol is preferably used, and at least an alcohol containing ethanol is preferably used because the melt viscosity of the ionomer resin can be sufficiently lowered and it is easy to handle during the production of the laminated foamed sheet.

When the alcohol (A) contains ethanol, the proportion of ethanol in the alcohol (A) is preferably 50% by weight or more, more preferably 60% by weight, still more preferably 70% by weight, and particularly preferably 80% by weight. % Or more.

When the boiling point of the alcohol (A) is 120 ° C. or lower, the added alcohol can be rapidly dissipated from the resin layer after the production of the laminated foam sheet, and the alcohol can be effectively prevented from remaining in the resin layer. In order to make this effect effective, the boiling point of the alcohol is preferably 100 ° C. or lower, more preferably 90 ° C. or lower, and even more preferably 85 ° C. or lower. On the other hand, the lower limit of the boiling point of alcohol is preferably about 40 ° C, more preferably 50 ° C. If the boiling point of the alcohol is within the above range, it will be easy to handle during the production of the laminated foam sheet.

Examples of the saturated hydrocarbon having 3 to 5 carbon atoms include propane, normal butane, isobutane, normal pentane, and isopentane. Among these, butane (normal butane, isobutane) is preferably used because it has a large plasticizing effect on the polyethylene resin and can efficiently reduce the melt viscosity of the polyethylene resin at the time of extrusion.

Examples of the dialkyl ether having 1 to 3 carbon atoms in the alkyl chain include dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether and the like. Among these, dimethyl ether is preferably used because it has a large plasticizing effect on the polyethylene-based resin and can efficiently reduce the melt viscosity of the resin during extrusion.

The blending amount of the volatile plasticizer is preferably 0.1 to 10 mol per 1 kg of the total of the polyethylene resin (B) and the ionomer resin. Within the above range, a homogeneous resin layer can be easily formed, and the laminated state of the resin layer and the foamed layer can be improved.
For this reason, the blending amount is preferably 0.5 to 9 mol, more preferably 1 to 8 mol, and more preferably 2 to 7 mol, per 1 kg of the total of the polyethylene resin (B) and the ionomer resin. Is more preferable.

When the volatile plastic agent contains the alcohol (A) and the saturated hydrocarbon and / or dialkyl ether (B), the alcohol (A) and the saturated hydrocarbon and / or dialkyl ether (B) The molar ratio of is preferably 5:95 to 95: 5, more preferably 6:94 to 80:20, further preferably 10:90 to 70:30, and 20:80 to 20:80. It is more preferably 60:40.
When the molar ratio is within this range, both the polyethylene resin and the ionomer resin can be plasticized, and a homogeneous resin layer can be formed.

The blending amount of the alcohol (A) is preferably 1 to 25 mol per 1 kg of ionomer resin. By adding an amount of alcohol (A) in this range to the ionomer resin, the ionomer resin is appropriately plasticized, and the melt viscosity of the ionomer resin is adjusted to a range suitable for extrusion molding even under the temperature conditions during coextrusion. It will be quick. Further, in the obtained resin layer, the ionomer resin is well dispersed in the polyethylene-based resin and is appropriately stretched, so that the desired antistatic performance can be easily exhibited.
From this point of view, the lower limit of the blending amount is preferably 2 mol, more preferably 3 mol, further preferably 4 mol, and particularly preferably 6 mol. On the other hand, the upper limit of the blending amount is more preferably 24 mol, further preferably 20 mol, and particularly preferably 16 mol.

The laminated foam sheet of the present invention can be preferably used as a paper between plate-shaped objects, and in particular, between glass substrates used for glass panels for various image display devices such as liquid crystal displays, plasma displays, and electroluminescence displays. It can be suitably used as a glass plate interleaving paper for protecting a glass substrate to be inserted and used.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples. However, the present invention is not limited to the examples.
The polyethylene resin, ionomer resin (polymer type antistatic agent), bubble modifier, and evaluation method used in Examples and Comparative Examples are described below.

Polyethylene resin (low density polyethylene)
(1) Abbreviation "LDPE1": "Low density polyethylene: trade name NUC8009" manufactured by NUC Co., Ltd. (density 0.917 g / cm ³ , MFR 9.0 g / 10 minutes, melting point 107 ° C)

Ionomer resin (polymer type antistatic agent)
(1) Abbreviation "MK400": Ethylene-based potassium ionomer resin "Entila MK400" manufactured by Mitsui DuPont Polychemical Co., Ltd. (density 970 kg / m ³ , MFR 1.5 g / 10 minutes, melting point 93 ° C., surface resistivity 1.0 × 10 ⁷ Ω)

Physical foaming agent mixed butane (mixture of 35% by weight of normal butane and 65% by weight of isobutane)

Volatile plasticizer (1) Ethanol: "Ethanol" manufactured by Kanto Chemical Co., Inc .: Product name Ethanol (99.5) Deer 1st grade (2) Mixed ethanol: "Mixed alcohol" manufactured by Yamaichi Chemical Co., Ltd .: Product name Mix Ethanol NP
(Ethanol: 85.5 wt%, Isopropyl alcohol 4.9 wt%, Normal propyl alcohol 9.6 wt%)
(3) Mixed butane (mixture of 35% by weight of normal butane and 65% by weight of isobutane)
(4) Dimethyl ether

Bubble regulator Dainichiseika Kogyo: PO-217K (citric acid-sodium hydrogen carbonate chemical foaming agent)

Equipment As an extruder for forming a foam layer, a tandem extruder in which two extruders, a first extruder having a diameter of 90 mm and a second extruder having a diameter of 120 mm, are connected in series is used, and as an extruder for forming a resin layer. A third extruder having a diameter of 50 mm was used, and an apparatus was used in which the outlet of the second extruder and the outlet of the third extruder were connected to an annular die for coextrusion. The co-extrusion annular die has a structure in which the resin melt for forming a resin layer is merged and laminated on the inside and outside of the resin melt for forming a foam layer flowing in a tubular shape at the middle portion of the die, and the lip of the die outlet. The diameter is 94 mm.

Example 1
About 200 parts by weight of the polyethylene resin (LDPE1) and 100 parts by weight of the polyethylene resin are supplied with 2 parts by weight of the bubble adjusting agent to the raw material inlet of the first extruder and heated, melted and kneaded. The temperature was adjusted to a molten resin. 12 parts by weight of mixed butane was press-fitted into the molten resin as a physical foaming agent, further kneaded, and then transferred to a second extruder connected to the downstream side of the first extruder to raise the resin temperature to about 112 ° C. Was adjusted to obtain a resin melt for forming a foam layer.

On the other hand, the polyethylene-based resin shown in Table 1 and the ionomer resin (polymer-type antistatic agent) shown in Table 1 are supplied to the raw material inlet of the third extruder and adjusted by heating, melting and kneading to about 200 ° C. The mixture was prepared as a molten resin mixture. Next, a volatile plasticizer of the type and amount shown in Table 1 was press-fitted into the molten resin mixture, further kneaded, and then the resin temperature was adjusted to about 120 ° C. to form a resin layer resin melt. Got

Each of the antistatic forming resin melt and the foam layer forming resin melt is introduced into the coextrusion annular die at the discharge amounts shown in Table 1, and the resin layer forming resin melt flows in a tubular shape. The resin melt for forming a foam layer was merged and laminated on the inside and outside and co-extruded from an annular die in a tubular shape to form a tubular laminated foam in which a resin layer was laminated on the inner and outer surfaces of the tubular foam layer. The extruded tubular laminated foam is widened by a tubular widening device (mandrel) with a diameter of 350 mm, and the foam layer is cut open while adjusting the take-up speed so that the total basis weight is as shown in Table 2. A polyethylene-based resin laminated foam sheet in which resin layers were laminated on both sides was obtained.

Examples 2 and 3, Comparative Examples 1 and 2
A polyethylene-based resin laminated foam sheet was obtained in the same manner as in Example 1 except that the volatile plasticizer was changed to the type and blending amount shown in Table 1.

Table 2 shows the physical properties, antistatic properties, and migration properties of the laminated foam sheets obtained in Examples and Comparative Examples.

The total thickness, total basis weight, total apparent density, basis weight per one side of the resin layer, and surface resistivity of the laminated foam sheet in Table 2 were measured as described above.

(Measurement method of median dispersion area based on the number of dispersed phases)
First, the laminated foam sheet is cut along the thickness direction and the extrusion direction of the laminated foam sheet in the vicinity of the central portion in the width direction and both ends in the width direction of the laminated foam sheet, and the cross section along the extrusion direction (vertical cross section in the extrusion direction). Three samples having the above were cut out.
Next, from the cross section of each of the three cut-out samples, an ultrathin section containing a resin layer portion (the surface side of the laminated 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 polymer-type antistatic agent could be distinguished by their shades. Next, using a transmission electron microscope (JEM-1400Plus manufactured by JEOL), the sections stained at an accelerating voltage of 100 kV were observed, and cross-sectional photographs of the resin layer were taken under the conditions of magnifications of 7,000 and 70,000. In the cross-sectional photograph taken, the portion having a higher blackness becomes the dispersed phase (polymer type antistatic agent). 1 and 2 show a cross-sectional photograph of the laminated foam sheet obtained in Example 1 (magnification: 7000 times, 70,000 times), and FIG. 3 shows a cross-sectional photograph of the laminated foam sheet obtained in Comparative Example 1 (magnification:: 7000 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 shade 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 parts than the polyethylene-based resin, it can be judged as a part having less lamellar structure than the continuous phase in the cross-sectional photograph. The interface between the dispersed phase and the continuous phase was color-coded as the dispersed phase.
Then, using the image processing software "NS2K-pro" manufactured by Nanosystem Co., Ltd., the prepared cross-sectional photograph was subjected to image processing and measurement 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

In the measurement under the conditions (1) to (4), a measurement range is randomly selected for the cross-sectional portion of the resin layer in which the dispersed phase is present, and the total area of the measurement range is 100 μm ² or more. The measurement was carried out in this manner, 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 when the ultrathin section was prepared and the outermost surface part of the resin layer, was not included in the measurement range. This measurement was performed on the above 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.

(Measuring method of median dispersion diameter A in the thickness direction based on the number of dispersed phases and median dispersion diameter B in the direction orthogonal to the thickness direction based on the number of dispersed phases)
By the measurement under the conditions (1) to (4) above, the vertical ferret diameter and the horizontal ferret diameter of all the dispersed phases were measured. Here, the vertical ferret diameter corresponds to the length of the dispersed phase in the thickness direction of the resin layer, and the horizontal ferret diameter corresponds to the length of the dispersed phase in the direction orthogonal to the thickness direction.
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 above three test pieces, and the median value based on the number of each ferret diameter was obtained from the vertical ferret diameter or the horizontal ferret diameter of all the dispersed phases measured by the three test pieces. The median of the obtained vertical ferret diameter is the median of the dispersion diameter in the thickness direction based on the number of dispersed phases A, and the median of the obtained horizontal ferret diameter is the dispersion in the direction orthogonal to the thickness direction based on the number of dispersed phases. The median diameter B 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 magnitude.

(Measuring method of the average value of the number of dispersed phases existing on a straight line along the thickness direction)
In a cross-sectional photograph of a cross section of a resin layer in which a dispersed phase exists (a vertical cross section orthogonal to the width direction of a laminated foam sheet), five straight lines along the thickness direction of the resin layer are drawn at intervals of 2 μm over the entire resin layer. The number of dispersed phases intersecting the straight line was counted. By performing this measurement on six different cross-sectional photographs and dividing the total number of measured dispersed phases by the total number of straight lines, the dispersion in the thickness direction existing on the straight line along the thickness direction The average value of the number of phases was calculated.

(Measurement method of surface resistivity of laminated foam sheet)
Specifically, the surface resistivity of each surface of the laminated foam sheet was measured as follows. Three test pieces (length 100 mm × width 100 mm × thickness: test piece thickness) were randomly cut out from the obtained laminated foam sheet. After adjusting the condition of the test pieces, use "TR8601" manufactured by Takeda Riken Kogyo Co., Ltd. as a measuring device, and apply the surface resistivity to the test pieces 1 minute after starting the application at an applied voltage of 500 V to the three test pieces. It was measured. The surface resistivity was measured on both sides of the test piece, and the arithmetic mean of the obtained measured values was taken as the surface resistivity of each surface of the laminated foam sheet. In Table 2, the M surface is the surface of the laminated foam sheet taken up facing the mandrel, and the S surface is the surface of the laminated foam sheet taken up without facing the mandrel.

(Antistatic property)
The antistatic property in Table 2 was evaluated according to the following criteria.
⊚: The surface resistivity of each surface of the laminated foam sheet is 1 × 10 ¹¹ Ω or less.
◯: The surface resistivity of each surface of the laminated foam sheet is 1 × 10 ¹² Ω or less, and the surface resistivity of at least one surface of the laminated foam sheet exceeds 1 × 10 ¹¹ Ω.
X: The surface resistivity of at least one surface of the laminated foam sheet exceeds 1 × 10 ¹² Ω.

(Transition test method)
As a transferability test, the following haze measurements were performed on the laminated foam sheets obtained in Examples 1 to 3.
First, as a packaged object, 10 preclinic slide glasses manufactured by Matsunami Glass Industry Co., Ltd. were laminated to form a glass laminate. Next, the haze (1) with respect to the thickness direction (glass lamination direction) of the glass laminate was measured using "NDH2000" manufactured by Nippon Denshoku Kogyo Co., Ltd. Next, 11 samples (laminated foam sheets obtained in the examples) and 10 glasses were alternately laminated to form a laminate, and the laminate was formed under a pressure of 3.8 g / cm ² and a temperature of 60 ° C. The mixture was allowed to stand for 24 hours under a condition of 90% relative humidity. Then, the sample was removed from the laminate, and 10 pieces of glass were laminated to form a glass laminate, and the haze (2) in the thickness direction of the glass laminate was measured in the same manner as in (1). The amount of change in haze (%) was obtained by subtracting the value (%) of haze (1) from the value (%) of haze (2), and the transitionability 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 to the glass, which means that the laminated foam sheet has less transfer.
〇: Haze change amount (%) is 1.5 or less ×: Haze change amount (%) exceeds 1.5

Claims (8)

In a polyethylene-based resin laminated extrusion foam sheet having a polyethylene-based resin foam layer and a polyethylene-based resin layer laminated and adhered to at least one surface of the foamed layer.
The resin layer is formed of a resin composition containing a polyethylene-based resin (B) and a polymer-type antistatic agent.
The polymer-type antistatic agent is an ionomer resin,
In the resin composition, a continuous phase composed of the polyethylene-based resin (B) and a dispersed phase composed of the polymer-type antistatic agent dispersed in the continuous phase are formed.
In the vertical cross section orthogonal to the width direction of the laminated extruded foam sheet, the median value of the dispersed area based on the number of the dispersed phases is 1 × 10 ² to 1 × 10 ⁶ nm ² .
The ratio (B / A) of the median value B of the dispersion diameter in the direction orthogonal to the thickness direction based on the number of dispersed phases is 2 or more with respect to the median value A of the dispersion diameter in the thickness direction based on the number of dispersed phases. ,
A polyethylene-based resin laminated extrusion foam sheet having a surface resistivity on the resin layer side of the laminated extrusion foam sheet of 1 × 10 ¹² Ω or less.
The polyethylene-based resin laminated extrusion foam sheet according to claim 1, wherein the content ratio of the polymer-type antistatic agent in the resin layer is 5 to 30% by weight.
The polyethylene-based resin laminated extrusion foam sheet according to claim 1 or 2, wherein the ionomer resin is a potassium ionomer, which is a copolymer of ethylene and an unsaturated carboxylic acid.
The polyethylene-based resin laminated extrusion foam sheet according to any one of claims 1 to 3, wherein the melt flow rate of the ionomer resin is 3 g / 10 minutes or less.
The polyethylene resin (B) has a melting point Tmp of 100 to 120 ° C.
The polyethylene-based resin laminate according to any one of claims 1 to 4, wherein the difference (Tmp-Tmi) between the melting point Tmp of the polyethylene-based resin (B) and the melting point Tmi of the ionomer resin is 5 to 30 ° C. Extruded foam sheet.
The polyethylene-based resin laminated extrusion foam sheet according to any one of claims 1 to 5, wherein the overall apparent density of the laminated extrusion foam sheet is 20 to 200 kg / m ³ .
The polyethylene-based resin laminated extrusion foam sheet according to any one of claims 1 to 6, wherein the basis weight per one side of the resin layer is 1 to 20 g / m ² .
The polyethylene-based resin laminated extrusion foam sheet according to any one of claims 1 to 7, wherein an average of one or more dispersed phases are present on a straight line along the thickness direction in the vertical cross section.