JP5075046B2 - Foam sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a layered foamed sheet having antistatic function with flexibility and shock-absorbing property, whereby the surface of a body such as an object to be wrapped thereby and contacted with the sheet is not contaminated, and an excellent appearance and uniform antistatic effect on the surface can be provided. <P>SOLUTION: A foamed sheet comprises a polyolefin resin foam layer in which a polyolefin resin layer having a polymer antistatic agent is layered on at least one surface of the polyolefin resin foam layer such that the polyolefin resin layer is the top layer. The foamed sheet has an apparent density from 15g/L to less than 100 g/L and a surface resistivity from 1.0&times;10<SP>8</SP>to 1.0&times;10<SP>13</SP>(&Omega;) after applying ultrasonic washing with ethanol. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

The present invention relates to a foam sheet having a semi-permanent antistatic property, wherein a resin layer is laminated on at least one surface of a foam layer so as to be an outermost layer.

Conventionally, foams made of polyethylene resin have been used as materials for cushioning materials, packaging materials and the like. In particular, polyethylene-based resin foams containing an antistatic agent in the resin have been used as a suitable material as a cushioning material because it is difficult to damage dust and is flexible because it is difficult to damage.

As the antistatic agent, a so-called surfactant type is used, and for example, glycerin fatty acid ester, polyoxyethylene alkylamine, alkyldiethanolamide and the like are used (for example, see Patent Document 1).

Further, there is a thermoplastic resin foam sheet obtained by laminating a conductive non-foam layer made of a polyolefin resin on a foam layer made of a polyolefin resin material. As the conductive non-foamed layer, a thermoplastic resin mainly composed of a thermoplastic additive and a conductive additive (antistatic agent) blended therein, or a thermoplastic resin having conductivity per se is used. Carbon black is used as the conductive additive (see, for example, Patent Document 2).

JP-A-9-169072 (pages 3 to 4, paragraph number 0016) JP 2001-347589 A (page 3, paragraph number 0018)

When a bleed-out type antistatic agent such as glycerin aliphatic ester is contained in the resin and imparted with an antistatic function, the antistatic agent adsorbs moisture in the air and exhibits an antistatic effect. For this reason, the antistatic effect is hardly exhibited in a relatively low humidity environment, particularly in winter, while the antistatic effect is exhibited in a relatively high humidity environment, particularly in summer, but the antistatic agent and the adsorbed moisture As a result, there is a problem that the surface of the packaged body is caused to become sticky or whitened to cause surface contamination of the packaged body.

In the case of a foam sheet having a conductive non-foamed layer containing a conductive additive (antistatic agent) such as carbon black described in [Patent Document 2], if the thickness of the resin layer is reduced, carbon There was a problem that the resin layer was torn due to the influence of black particles. Furthermore, since the conductive additive such as carbon black colors the resin layer black, there is a problem that the color of the laminated sheet is limited to black.

The present inventors tried to obtain a foamed sheet by adding a polymer type antistatic agent to a polyolefin resin to be a foam. However, when an antistatic agent in an amount sufficient to exhibit the antistatic function was added, a good polyolefin resin foam sheet could not be obtained.

Accordingly, an attempt has been made to obtain a foamed sheet obtained by coextruding a polyolefin resin obtained by adding a polymer type antistatic agent as a resin layer to a foam layer. However, the obtained foam sheet has a high density and does not have sufficient buffering properties. As a result of analyzing the cause, the polyolefin resin to which the polymer type antistatic agent constituting the resin layer is added generates heat by kneading, and the heat raises the resin temperature of the resin melt forming the foam layer. , And it was found that the bubbles were broken.

The present invention has been made in view of the above problems, and does not contaminate the surface of the other party to be contacted, such as a packaged body, is excellent in appearance, has a uniform antistatic effect on the surface, and has flexibility and buffering. It aims at providing the foam sheet which has the antistatic function provided with property.

That is, the present invention
(1) A foam sheet that is laminated by coextrusion so that a polyethylene resin layer containing a polymer-type antistatic agent becomes a surface layer on at least one surface of a polyethylene resin foam layer, The addition amount of the molecular antistatic agent is 5 to 100 parts by weight with respect to 100 parts by weight of the polyethylene resin constituting the surface layer, and the apparent density of the foamed sheet is 15 g / L or more, less than 100 g / L, and ethanol. A foam sheet having a surface resistivity after ultrasonic cleaning of 1.0 × 10 ^{8 to} 1.0 × 10 ¹³ (Ω),
(2) The foamed sheet according to the above (1), wherein the thickness of the polyethylene resin layer containing the polymer-type antistatic agent is 50 μm or less,
Is a summary.

The foamed sheet of the present invention has flexibility and buffering properties, and can exhibit an antistatic effect even if the surface of the foamed sheet is wiped off. Moreover, the antistatic effect can be exhibited immediately after manufacture or even in a wet state. Moreover, the surface of the other party which contacts, such as a packaged body, is not contaminated.
Moreover, when the thickness of the polyethylene resin layer containing the polymer type antistatic agent is 50 μm or less, a foamed sheet having particularly excellent flexibility and buffering properties can be obtained.
Furthermore, the, a polymer-type antistatic agent resin layer is polyethylene-based resin containing the so foam layer is made of polyethylene resin, the flexibility of such surface hardness excellent surface protection of the package lower It can be set as the excellent foam sheet.

In the foam sheet of the present invention, for example, as shown in FIG. 1, a polyethylene resin (A), a polymer antistatic agent (B), and a volatile plasticizer (C) are used in the first extruder 11. kneading the polyethylene resin layer forming resin melt comprising the (D), polyethylene resin foam layer formed by kneading the polyethylene resin (E) and physical blowing agent (F) in the second extruder 12 A cylindrical laminate is obtained by co-extrusion with the forming resin melt (G), and one end thereof is cut open to produce a foamed sheet (J).

Foam sheet by co-extrusion (J), in the embodiment shown in FIGS. 1 and 2, a polyethylene resin layer containing a polymeric antistatic agent as a front and back surfaces of the surface layer of a polyethylene resin foam layer (H) ( I) is laminated. Although not specifically shown, the polyethylene resin layer (I) containing the polymer type antistatic agent is laminated only on the surface on one side of the polyethylene resin foam layer (H) other than the above-described embodiment. Also good. Alternatively, a polyethylene resin layer (I) containing a polymer antistatic agent is laminated on one surface of the polyethylene resin foam layer (H), and the polymer antistatic agent is contained on the other surface. A non-polyolefin resin layer may be laminated. In addition, a polymer type antistatic agent is contained on the surface of the polyethylene resin layer (I) containing the polymer type antistatic agent on one side of the foam sheet (J) of the embodiment shown in FIGS. A non-polyolefin resin layer may be laminated. Further, a polyethylene resin layer (I) containing a polymer type antistatic agent is laminated on one surface of the polyethylene resin foam layer (H), and a polymer type antistatic agent is contained on the other surface. not polyolefin resin layer is laminated on the surface of the polyolefin-based resin layer containing no antistatic agent, a polyethylene-based resin layer containing a polymeric antistatic agent (I) may be stacked .

A volatile plasticizer (C) is added to the resin melt (D) for forming a polyethylene resin layer of the first extruder 11, and the addition timing of the volatile plasticizer (C) is determined based on polyethylene. It is preferable to add the polymer antistatic agent (B) after sufficiently dispersing it in the resin (A). This is because when the polyethylene resin (A) and the polymer antistatic agent (B) are kneaded, the polymer antistatic agent (B) is dispersed by maintaining the viscosity at a certain level. When it is reliably performed to form the conductive network structure and coextruded with the polyethylene resin foam layer, the melting temperature of the resin melt for forming the resin layer (resin temperature) is added by adding a volatile plasticizer. It is also possible to lower the temperature to a temperature at which foaming of the foam layer is not hindered, and to impart extensibility to follow the foam layer. In particular, the polyethylene resin foam layer is effective when the foaming ratio is high, and a reliable foam sheet can be produced.

In the foam sheet (J) obtained by coextruding and laminating a polyethylene resin layer (I) containing a polymer antistatic agent as a surface layer of the polyethylene resin foam layer (H), the polyethylene resin layer The volatile plasticizer in (I) is almost volatilized by the heat at the time of extrusion at the time of extrusion. Depending on the volatile plasticizer, a part of the volatile plasticizer may remain, but after the extrusion, it volatilizes and hardly remains in the polyethylene resin layer (I).

Polyethylene resin layer forming resin melt (sometimes referred to as resin layer forming melt) (D) and polyethylene resin foam layer forming resin melt (also referred to as foam layer forming melt) (G) means that the temperature is adjusted to an appropriate temperature in each of the extruders 11 and 12 and then co-extruded from the die 13 to foam the polyethylene resin foam layer. A flat die, a circular die or the like is used as the die 13 at the tip of the extruder, and the polyethylene resin foam layer (H) is a polyethylene resin foam layer forming resin melt (G) containing a foaming agent from the die 13 (G). ) Obtained by extrusion foaming.

The appropriate temperature in the extruders 11 and 12 of the melts (D) and (G) is a temperature at which a low-density foam layer can be easily obtained. Specifically, the temperature of the resin layer-forming melt (D) is not less than [crystallization temperature + 5 ° C.] and not more than [crystallization temperature + 30 ° C.] of the polyethylene resin of each layer, and [melting for foam layer formation] The temperature of the product (G) is −30 ° C.] and is [the temperature of the foam layer forming melt (G) + 30 ° C.] or less, so that the open cell ratio of the foam layer is improved and the foam sheet is contracted. It is preferable from a viewpoint of restraining, and more preferably [temperature of foam layer forming melt (G) −15 ° C.] or more and [temperature of foam layer forming melt (G) + 15 ° C.] or less.

The multilayer coextrusion method can also be used to obtain a foamed sheet in which the polyethylene- based resin layer (I) containing the polymer type antistatic agent is laminated only on the surface layer on one side.

The method for obtaining the foamed sheet by the multilayer coextrusion method will be described in more detail. (1) A method in which a flat die is used and the sheet is coextruded and laminated from the beginning, and (2) a cylindrical shape is first coextruded using an annular die. There is a method in which a foam is manufactured, and then a cylindrical foam is cut open to form a foam sheet.

Among the methods described above, the method using the annular die (2) as the die 13 at the tip of the extruder can suppress the generation of a corrugated pattern called a corrugate and can easily produce a wide foam sheet having a width of 1000 mm or more. There are advantages.

When co-extrusion using the annular die of (2) above, first, the polyethylene resin (A), the polymer antistatic agent (B) and the like are supplied to the first extruder 11, heated and melted and kneaded. Thereafter, a volatile plasticizer (C) is added and melt kneaded to obtain a polyethylene resin layer forming resin melt (D). At the same time, the polyethylene resin (E) and the air conditioner are supplied to the second extruder 12, heated and melted and kneaded, and then the physical foaming agent (F) is press-fitted, and further kneaded and polyethylene resin foam. Let it be the resin melt for layer formation (G).

Next, the polyethylene resin foam layer forming resin melt (G) and the polyethylene resin layer forming resin melt (D) are adjusted to appropriate temperatures, and then introduced into one annular die 13. Then, it is co-extruded from the annular die 13 as a cylindrical laminated foam. Next, after the inner surface of the cylindrical laminated foam is cooled by passing through a cylindrical cooling device, the foamed sheet can be formed by cutting the cylindrical laminated foam.

In the coextrusion method, the resin layer and the foam layer may be laminated outside the annular die outlet or outside the die outlet. In addition, as the annular die, the extruder, the columnar cooling device, the device for opening the cylindrical laminated foam, etc., known ones conventionally used in the field of extrusion foaming can be used.

In order for the polyethylene- based resin layer (I) containing the polymer antistatic agent to exhibit sufficient antistatic performance, the dispersion state of the polymer antistatic agent in the resin is important. That is, it is considered that the polymer antistatic agent can form a conductive network in the resin by dispersing the antistatic agent into a network or a layer by kneading. On the other hand, if the kneading of the polymer antistatic agent is insufficient, the polymer antistatic agent will not be uniformly dispersed in the polyethylene resin, but will be scattered and form a sufficient conductive network. I can't.

In the resin melt (D) for forming a polyethylene resin layer, the crystallization temperature of the polymer antistatic agent and the polyethylene resin can be used to disperse the polymer antistatic agent (B) and form a conductive network. The balance of viscosity during the kneading of the layer forming resin melt (D) is important. Specifically, when selecting a polyethylene resin layer forming resin melt polyethylene resin (A) and the polymeric antistatic agent (D) to (B), the relationship between the crystallization temperature and the melt viscosity of below Need to be satisfied.

[About crystallization temperature]
Tb <[Ta + 30 ° C.] (1)
However, (1) wherein Tb is the polymeric antistatic agent is a crystallization temperature of (B) (° C.), Ta is the crystallization temperature of the polyethylene resin used in the polyethylene-based resin layer (A) (° C.) It is. This is because when the relationship between the crystallization temperatures of the polymer antistatic agent (B) and the polyethylene resin (A) does not satisfy the above formula, that is, when Tb is higher than [Ta + 30 ° C.], a foam sheet is produced. When doing so, the polymer antistatic agent (B) may crystallize and become a lump, and the surface of the foam sheet may be uneven. Therefore, sufficiently high molecular type antistatic agent at a melt temperature of polyethylene resins (A) (B) it is important that the melted.

In this specification, the value measured with the following method is employ | adopted for the crystallization temperature of polyethylene- type resin (A), (E) and a polymer type antistatic agent (B).

[Measurement method of crystallization temperature]
It is measured by a method according to JIS K7122 (1987). Details are as follows. 2 to 4 mg of a sample was taken and measured using a differential scanning calorimeter at a heating rate of 10 ° C./min from room temperature 23 ° C. to 200 ° C. and then down to 40 ° C. at a cooling rate of 10 ° C./min. To do. Using the curve obtained when the temperature is lowered to 40 ° C. at a cooling rate of 10 ° C./min, the temperature at the peak apex is set as the crystallization temperature. When two or more exothermic peaks appear, the temperature at the apex of the largest exothermic peak is defined as the crystallization temperature. However, when there are a plurality of exothermic peaks having the largest area, the peak of the highest exothermic peak among them is defined as the crystallization temperature.

[About melt viscosity]
Ma> Mb (2)
However, the melt viscosity of (2) Ma in formula is the melt viscosity of the polyethylene resin used in the polyethylene resin layer (I) (A) (Pa · s), Mb is the polymeric antistatic agent (B) (Pa · s).

Wherein (2) is higher than the melt viscosity of the melt viscosity (Ma) is a polymer type antistatic agent of the polyethylene resin used in the polyethylene resin layer (I) (A) (Mb) as, given The antistatic performance can be exhibited. When the melt viscosity of the polyethylene resin (A) is the same as or lower than the melt viscosity of the polymer antistatic agent (B), it becomes difficult to adopt a conductive network structure of the polymer antistatic agent.

The relationship between Ma and Mb in the formula (2) is preferably such that Mb is less than 0.90 Ma from the viewpoint that the antistatic performance can be exhibited with a small amount of the polymeric antistatic agent added. More preferably less than 70 Ma. On the other hand, the lower limit is preferably Mb exceeding 0.10 Ma, more preferably Mb exceeding 0.15 Ma, from the viewpoint of exhibiting predetermined antistatic performance.

[Relationship between melt viscosity and volume fraction]
In the polyethylene resin layer (I), the melt viscosity (Pa · s) of the polyethylene resin (A) is Ma, the melt viscosity (Pa · s) of the polymer antistatic agent (B) is Mb, and the polyethylene resin ( When the volume fraction (%) of A) is φa and the volume fraction (%) of the polymer antistatic agent (B) is φb, (Ma · φb) / (Mb · φa) is expressed as “phase structure index It says PI value "shows the mixed state of the polyethylene-based resin and the polymeric antistatic agent of the polyethylene resin layer (I). This phase structure index PI value preferably satisfies the following formula (3). In addition, although φa and φb are originally volume fractions at the time of melting, their volumes can be simply calculated from the density of each raw material at room temperature.

0.27 ≦ (Ma · φb) / (Mb · φa) ≦ 5.00 (3)

When the phase structure index PI value in the polyethylene- based resin layer (I) of the foamed sheet is less than 0.27, the surface resistivity after ultrasonic cleaning using ethanol (details will be described later) is 1 × 10 ¹³ ( Ω) The following antistatic performance may not be obtained. From the above viewpoint, the phase structure index PI value is preferably 0.30 or more, and more preferably 0.40 or more. On the other hand, if the upper limit of the phase structure index PI value exceeds 5.00, the adhesion to the foam layer may be reduced. From the above viewpoint, 3.00 or less is preferable, and 2.00 or less is more preferable.

The melt viscosity of the polyethylene resin used in the polyethylene resin layer (I) (A) (Ma ) is, 250~1800Pa · s is preferred. If the melt viscosity (Ma) exceeds 1800 Pa · s, the load on the extruder becomes too high and control during extrusion is difficult, and there is a possibility that a foam sheet with good appearance cannot be obtained due to insufficient elongation of the resin. is there. From the above viewpoint, 1600 Pa · s or less is more preferable. On the other hand, if the melt viscosity is less than 250 Pa · s, the kneadability with the polymer antistatic agent is deteriorated, the uniform dispersibility of the polymer antistatic agent is adversely affected, and the antistatic effect may be reduced. . From the above viewpoint, 300 Pa · s or more is more preferable.

The melt viscosity (Mb) of the polymer antistatic agent (B) used for the polyethylene resin layer (I) is preferably 400 Pa · s or less, more preferably 300 Pa · s or less. The lower limit of the melt viscosity (Mb) of the polymer antistatic agent (B) is preferably 80 Pa · s or more, and more preferably 100 Pa · s or more. Thereby, the foam sheet which is excellent in kneadability with a polyethylene resin and more easily exhibits an antistatic effect is obtained.

In this specification, the value measured as follows is used for the melt viscosity. A Leobis 2100 manufactured by Thiast Co., Ltd. is used as a measuring device, and measurement is performed under conditions of an orifice diameter of 1 mm, an orifice length of 10 mm, a measurement temperature of 190 ° C., and a shear rate of 100 sec ⁻¹ .

Po Li olefin resin is a resin olefin component is 50 mol% or more, examples of the polyolefin resins, polypropylene resins, although a polyethylene resin and the like, polyethylene-based resin layer forming resin melt in the present invention ( As the resin used in D), among the polyolefin resins, polyethylene resins are used from the viewpoint of flexibility such as low surface hardness and excellent surface protection of the package.
Examples of such polyethylene resins include ethylene homopolymers such as high-density polyethylene, low-density polyethylene, and linear low-density polyethylene, ethylene-vinyl acetate copolymers, ethylene-vinyl acetate copolymers, and high density. A mixture of polyethylene resins, an ethylene-propylene copolymer having an ethylene component exceeding 50 mol%, an ethylene-propylene-butene-1 copolymer, an ethylene-butene-1 copolymer, an ethylene-hexene-1 copolymer, an ethylene- Examples thereof include ethylene copolymers such as 4-methylpentene-1 copolymer and ethylene-octene-1 copolymer, and a mixture of two or more thereof.

The polymer type antistatic agent (B) has a number average molecular weight of at least 300, preferably 300 to 300,000, more preferably 600 to 15000, and a density exceeding 935 g / L and preferably 1500 g / L or less. It is preferably 950 g / L or more and 1200 g / L or less, and further comprises a resin having a surface resistivity of less than 1 × 10 ¹² Ω. The polymeric antistatic agent (B) is an inorganic salt or a low molecular weight organic protonic acid salt such as LiCLO ₄ , LiCF ₃ SO ₃ , NaCLO ₄ , LiBF ₄ , NaBF ₄ , KBF ₄ , KCLO ₄ , KPF ₃ SO ₃ , Ca (CLO ₄ ) ₂ , Mg (CLO ₄ ) ₂ , Zn (CLO ₄ ) ₂ or the like may be contained. The upper limit of the number average molecular weight of the polymer antistatic agent (B) is about 500,000.

In addition, the said number average molecular weight is the number average molecular weight (polystyrene conversion value) converted using the calibration curve obtained from polystyrene with known molecular weight using gel permeation chromatography.

Specific examples of the polymer type antistatic agent (B) include polyethylene oxide, polypropylene oxide, polyethylene glycol, polyether, polyester amide, polyether ester amide, ethylene-methacrylic acid copolymer ionomer, and polyethylene glycol methacrylate. Among one or a mixture of two or more kinds selected from quaternary ammonium salts such as polymers, or two or more kinds of copolymers, and copolymers of these with other resins such as polypropylene, etc. And a resin having a polar group in the molecular chain and capable of complexing or solvating an inorganic salt or a low molecular weight organic protonic acid salt. May be.

The melting point of the polymer antistatic agent (B) is 70 to 270 ° C, preferably 80 to 230 ° C, more preferably 80 to 200 ° C. By selecting a polymer-type antistatic agent (B) having a melting point within the above range, the polymer-type antistatic agent (B) is substantially the same as the melting temperature of the polyethylene resin (A) during extrusion Therefore, it is preferable from the viewpoint of lack of melting and generation of crystallized products.

In the present specification, the melting point of the polymer antistatic agent (B) is a value measured by the following method.

[Measuring method of melting point]
It is measured by a method according to JIS K7121 (1987). A melting peak is obtained by raising the temperature at 10 ° C./min under the condition (2) for adjusting the state of the test piece (however, the cooling rate is 10 ° C./min). The temperature at the top of the obtained melting peak is taken as the melting point. When two or more melting peaks appear, the temperature at the top of the melting peak having the largest area is defined as the melting point. However, when there are a plurality of melting peaks having the largest area, the melting peak on the highest temperature side of the peak temperature of those melting peaks is taken as the melting point.

The polymer antistatic agent (B) has a crystallization temperature (Tb) of less than [Ta + 30 ° C.] based on the crystallization temperature (Ta) of the polyethylene resin (A). When the crystallization temperature of the polymer antistatic agent (B) is selected as described above, an excellent appearance can be obtained when a foam sheet is obtained by a coextrusion method.

The polymer antistatic agent (B) preferably has a crystallization temperature of 120 ° C. or lower. When a polymer type antistatic agent having a crystallization temperature of 120 ° C. or lower is used, there is no generation of a crystallized product in the polyethylene resin layer (I), and a foam sheet with a smoother surface can be obtained. Further, the lower limit of the crystallization temperature of the polymer antistatic agent (B) is not particularly limited, but it is easy to handle when kneading the polyethylene resin layer forming resin melt (D). It is preferable that the temperature is not lower than ° C.

The polymer type antistatic agent (B) is preferably composed mainly of polyetheresteramide or polyether. In order to improve the compatibility with the polyethylene resin (A) in these polymer type antistatic agents, and to provide an excellent antistatic effect, and to suppress the deterioration of physical properties due to the addition of the antistatic agent. In addition, a mixture or copolymer of the same type of polyolefin resin or polyamide can be used. In this case, the content of the polymer antistatic agent is 50% by weight or more, preferably 75% by weight or more, and more preferably 85% by weight or more. The polyether ester amide is obtained by a polymerization reaction of the polyamide (1) exemplified below and an alkylene oxide adduct (2) of bisphenols.

The polyamide (1) is (a) a lactam ring-opening polymer, (b) a polycondensate of aminocarboxylic acid, or (c) a polycondensate of dicarboxylic acid and diamine. Examples of the lactam used in the (a) lactam ring-opening polymer include caprolactam, enantolactam, laurolactam, and undecaractam. (B) As aminocarboxylic acid of the polycondensate of aminocarboxylic acid, ω-aminocaproic acid, ω-aminoenanthic acid, ω-aminocaprylic acid, ω-aminopergonic acid, ω-aminocapric acid, 11-aminoundecanoic acid , 12-aminododecanoic acid and the like. (C) Examples of the dicarboxylic acid of the polycondensate of dicarboxylic acid and diamine include adipic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, isophthalic acid, etc., and diamines include hexamethylenediamine and heptamethylenediamine. , Octamethylenediamine, decamethylenediamine and the like. Two or more amide-forming monomers may be used. Among these, caprolactam, 12-aminododecanoic acid, and adipic acid-hexamethylenediamine are preferable, and caprolactam is particularly preferable.

Examples of bisphenols of the alkylene oxide adduct (2) of bisphenols include bisphenol A (4,4′-dihydroxydiphenyl-2,2-propane), bisphenol F (4,4′-dihydroxydiphenylmethane), bisphenol S ( 4,4′-dihydroxydiphenylsulfone), 4,4′-dihydroxydiphenyl-2,2-butane, etc., among which bisphenol A is particularly preferable. Examples of the alkylene oxide of the bisphenol alkylene oxide adduct (2) include ethylene oxide, propylene oxide, 1,2- or 1,4-butylene oxide, and a mixture of two or more of these. Of these, ethylene oxide is preferred.

The melting point of the polyether ester amide used as the polymer type antistatic agent (B) is preferably 230 ° C. or lower, and more preferably 200 ° C. or lower. When the melting point of the polyether ester amide exceeds 230 ° C., when the polyethylene resin and the polyether ester amide are melted and mixed, the temperature of both resins must be increased more than necessary, so that the polyethylene resin deteriorates. There is a fear. Moreover, when laminating | stacking by a coextrusion method, there exists a possibility that sufficient antistatic performance may not be obtained because the polymer type antistatic agent (B) is insufficiently melted.

When the melting point of the polyether ester amide is 200 ° C. or less, there is almost no possibility that the polyethylene resin constituting the outermost resin layer is deteriorated, and even when laminated by a coextrusion method, a polymer type antistatic agent There is almost no possibility that the antistatic performance due to insufficient melting of (B) is lowered.

The polyether used as the polymer type antistatic agent (B) includes: a) an oxyalkylene ether obtained by addition reaction of an alkylene oxide with a phenol / divinylbenzene addition polymer, b) polyoxyethylene glycol, poly Diglycidyl ethers such as oxypropylene glycol, polyoxybutylene glycol, bisphenol alkylene oxide adducts and the like, and hexyl, n-octyl, 2-ethylhexyl, nonyl, decyl, dodecyl, tetradecyl, octadecyl, oleyl, etc. An amine compound having an aliphatic hydrocarbon group having 22 (preferably 6 to 22 carbon atoms) and an alkyl sulfate such as dimethyl sulfate and diethyl sulfate; an alkyl carbonate such as dimethyl carbonate and diethyl carbonate; It is a reaction product with quaternizing agents such as various phosphates or halides such as fate, alkyl benzyl chloride, benzyl chloride, alkyl chloride, and alkyl bromide, and is composed of a compound having two or more quaternary ammonium bases in the molecule. Examples thereof include cationic antistatic agents.

Examples of the alkylene oxide used in the production of the oxyalkylene ether include ethylene oxide, propylene oxide, and butylene oxide. Among these, ethylene oxide and a copolymer of ethylene oxide and propylene oxide are preferable. The added mole number of alkylene oxide is usually 1 to 500, preferably 20 to 300, and the oxyalkylene content in the oxyalkylene ether is 10 to 95% by weight, preferably 20 to 90% by weight, more preferably 30 to 30%. 80% by weight.

Bisphenols used for the production of the above-mentioned cationic antistatic agent diglycidyl ether include bisphenol A (4,4′-dihydroxydiphenyl-2,2-propane), bisphenol F (4,4′-dihydroxydiphenylmethane), Bisphenol S (4.4′-dihydroxydiphenyl sulfone), 4,4′-dihydroxydiphenyl-2,2-butane and the like can be mentioned. Particularly preferred among the diglycidyl ethers are polyoxyethylene glycol glycidyl ether, bisphenols ethylene oxide adduct diglycidyl ether, and mixtures thereof.

Of the amine compounds used in the cationic antistatic agent, N-alkyl (C1-18) diethanolamine is particularly preferable. Of the quaternizing agents used in the production of the cationic antistatic agent, dimethyl sulfate and diethyl sulfate are particularly preferable.

In order to impart an excellent antistatic effect to the polyethylene resin layer containing the polymer type antistatic agent (B), and to suppress deterioration of physical properties due to the addition of the antistatic agent in the resin, The same type of polyolefin resin as the polyethylene resin constituting the polyethylene resin layer (particularly, a modified polyolefin resin having a number average molecular weight of 800 to 25000) is added to the resin melt (D) for forming the polyethylene resin layer. More preferably, it is mixed or copolymerized with the polymer type antistatic agent (B).

Polyamide mixed with polyethylene resin layer forming resin melt (D) or copolymerized with polymer antistatic agent (B) is derived from diamine and dicarboxylic acid and / or aminocarboxylic acid or corresponding lactam. And polyamides and copolyamides. Specifically, polyamide 4, polyamide 6, polyamide 6/6, 6/10, 6/9, 6/12, 4/6, 12/12, polyamide 11, polyamide 12, m-xylenediamine and adipic acid Aromatic polyamides, polyamides obtained by adding an elastomer from hexamethylenediamine and isophthalic acid and / or terephthalic acid, if necessary, a copolymer of the above polyamide and polyolefin, olefin copolymer, ionomer or elastomer, polyamide And a block copolymer of polyethylene glycol, polypropylene glycol or polytetramethylene glycol, polyamide or copolyamide modified with EPDM or ABS, and the like. The content of these polyamides is 50% by weight or less, preferably 25% by weight or less.

The polyethylene resin layer (I) containing the polymer antistatic agent does not lose its antistatic effect even before and after ultrasonic cleaning with ethanol. On the other hand, when a surfactant-based antistatic agent such as monoglycerin ester is added to the resin layer, the antistatic agent bleeds out to the surface of the molded product under normal conditions, taking in moisture in the air and providing an antistatic effect. Even if it is exhibited, after the ultrasonic cleaning with ethanol, the antistatic agent is washed away from the resin surface and the antistatic effect is lost. Therefore, measuring the surface resistance after ultrasonic cleaning with ethanol is effective as a means for determining the durability of the antistatic performance of the resin layer.

The polyethylene- based resin layer (I) containing the polymer antistatic agent (B) has a surface resistivity of 1.0 × 10 ⁸ (Ω) to 1.0 × by forming a conductive network structure therein. It is formed to be 10 ¹³ (Ω). The polymer antistatic agent (B) does not exhibit antistatic performance if it is simply blended with the polyethylene resin (A). The polymer antistatic agent (B) is a polyethylene resin layer ( I) A conductive network structure must be formed on the surface. The conductive network structure is a structure in which a continuous layer is formed when the polymer antistatic agent (B) is dispersed in the resin constituting the polyethylene resin layer (I).

Conductive network structure is easily formed by the time of forming the polyethylene-based resin layer polyethylene resin layer forming resin melt (D) extruding the (I), applying a moderate orientation. In addition, the polymer antistatic agent is extremely expensive, and it is preferable to use the minimum necessary amount in consideration of the cost of the product. Therefore, the polymer type antistatic agent is blended only in the polyethylene resin layer that becomes the surface layer of the foamed sheet. The resin layer on the surface is preferably formed as thin as possible. The specific thickness of the polyethylene- based resin layer (I) is preferably 50 μm or less from the viewpoint of obtaining a flexible foam sheet that can be easily packed in a packaged body, and more preferably 25 μm or less. The lower limit is approximately 0.3 μm. The co-extrusion method can easily form a thin resin layer.

When the surface resistivity of the foamed sheet (J) exceeds 1.0 × 10 ¹³ (Ω), the antistatic performance is insufficient, and static charges accumulate on the surface of the foamed sheet (J), and dust adheres. It's easy to do. Further, when the surface resistivity of the foamed sheet (J) is less than 1.0 × 10 ⁸ (Ω), there is a risk that the quality becomes excessive as the required physical property of the antistatic performance and the cost is increased. From the viewpoint of preventing the adhesion of dust, the surface resistivity of the foamed sheet (J) is preferably 5.0 × 10 ¹² (Ω) or less, and more preferably 1.0 × 10 ¹² (Ω) or less.

The surface resistivity in the present invention (however, the surface resistivity after ultrasonic cleaning using ethanol follows the description described later) is measured in accordance with JIS K6911 (1979). Specifically, three test pieces (length 100 mm × width 100 mm × thickness: thickness of test piece) were cut out from the foamed sheet, and the test piece was left in an atmosphere at a temperature of 23 ° C. and a humidity of 50% for 24 hours, and then the surface resistance. The surface resistivity is determined from the average value of the measured values. Since the foamed sheet of the present invention is provided with a polyethylene- based resin layer containing a polymer type antistatic agent as a surface layer, it does not depend on standing time, humidity conditions, etc., and 1.0 × 10 ¹³ (Ω) immediately after production. The following surface resistivity is shown.

The addition amount of the polymer type antistatic agent (B) is 5 to 100 parts by weight with respect to 100 parts by weight of the polyethylene resin (A). The addition amount of the polymeric antistatic agent (B), the polyethylene resin (A) in the case of less than 5 parts by weight per 100 parts by weight of the antistatic performance is insufficient, when it exceeds 100 parts by weight polyethylene It becomes difficult to lower the physical properties of the resin layer (I), to form the resin layer itself, and to produce an inexpensive foam sheet. From the above viewpoint, the lower limit is preferably 7 parts by weight or more, and more preferably 13 parts by weight or more. On the other hand, the upper limit is preferably 70 parts by weight or less, and more preferably 50 parts by weight or less.

In the present invention, the polyethylene resin layer (I) containing the polymer type antistatic agent may be formed as a non-foamed layer or a foamed layer. When the polyethylene resin layer (I) is a foam layer, the lower limit of the apparent density is 100 g / L.

The volatile plasticizer (C) contained in the resin melt for forming a polyethylene resin layer (D) has a function of lowering the melt viscosity in the state of being present in the resin melt for forming a polyethylene resin layer. At the same time, after the formation of the polyethylene resin layer (I), those which are volatilized from the polyethylene resin layer and can be removed from the resin layer are used. By volatile plasticizer (C) is added to the polyethylene resin layer forming resin melt (D), when prepared by co-extruding foamed sheets, significantly melt elongation of the polyethylene resin layer (I) can be improved, elongation of the polyethylene resin layer (I) in association with elongation of the polyethylene-based resin foam layer (H), can prevent cracking caused by elongation shortage of the polyethylene resin layer (I).

The volatile plasticizer (C) is one or two selected from an aliphatic hydrocarbon having 2 to 7 carbon atoms, an aliphatic alcohol having 1 to 4 carbon atoms, or an aliphatic ether having 2 to 8 carbon atoms. The above are preferably used. When a plasticizer with a low volatility such as a lubricant is used, it may remain in the polyethylene resin layer (I) and contaminate the surface of the packaged body. On the other hand, the volatile plasticizer is preferable in that the resin of the polyethylene resin layer (I) is efficiently plasticized, and the volatile plasticizer itself does not easily remain in the obtained polyethylene resin layer (I). It is.

Examples of the aliphatic hydrocarbon having 2 to 7 carbon atoms include ethane, propane, normal butane, isobutane, normal pentane, isopentane, isohexane, cyclohexane, and heptane.
Examples of the aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, propanol, butanol, isopropyl alcohol, isobutyl alcohol, normal butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol.
Examples of the aliphatic ether having 2 to 8 carbon atoms include methyl ether, ethyl ether, propyl ether, isopropyl ether, methyl ethyl ether, methyl propyl ether, methyl isopropyl ether, methyl butyl ether, methyl isobutyl ether, methyl amyl ether, Examples include methyl isoamyl ether, ethyl propyl ether, ethyl isopropyl ether, ethyl butyl ether, ethyl isobutyl ether, ethyl amyl ether, ethyl isoamyl ether, vinyl ether, allyl ether, methyl vinyl ether, methyl allyl ether, ethyl vinyl ether, and ethyl allyl ether.

The volatile plasticizer (C) preferably has a boiling point of 120 ° C. or less from the viewpoint that it easily volatilizes from the polyethylene resin layer (I), and more preferably has a boiling point of 80 ° C. or less. If the volatile plasticizer (C) has the above boiling point, the polyethylene- based resin layer of the foam sheet is formed by coextruding and leaving it to stand by heat immediately after the coextrusion or subsequent gas permeation of the volatile plasticizer. Can be volatilized spontaneously and removed from the polyethylene resin layer (I). The lower limit of the boiling point is approximately -50 ° C.

The amount of the volatile plasticizer (C) added is 5 to 50 parts by weight with respect to 100 parts by weight of the kneaded product of the polyethylene resin (A) and the polymer antistatic agent (B). When the addition amount of the volatile plasticizer (C) is less than 5 parts by weight, the polyethylene- based resin to which the polymer type antistatic agent constituting the resin layer is added generates heat by kneading, and the foam layer is formed by the heat. There is a possibility that the resin temperature of the resin melt to be formed rises, whereby bubbles are broken and a low-density foam layer cannot be obtained. Further, the polyethylene resin layer (I) is excellent in extensibility following the foam layer, and the polyethylene resin layer (I) is preferably 7 parts by weight or more from the viewpoint that the thickness of the polyethylene resin layer (I) is thin and easy to laminate. Is more preferable. On the other hand, volatile When the amount of the plasticizer (C) is more than 50 parts by weight per 100 parts by weight of polyethylene resin, polyethylene resin layer (I) resin property decrease or volatile plasticizer itself resin layer As a result, the volatile plasticizer is ejected from the die lip. As a result, a hole is opened in the resin layer of the foam sheet, and the surface becomes uneven, and the surface smoothness may be lowered. From the above viewpoint, the amount is preferably 45 parts by weight or less, and more preferably 40 parts by weight or less. By making the addition amount of a volatile plasticizer (C) into the said range, the temperature fall effect of the resin melt for polyethylene- type resin layer formation at the time of co-extrusion and the extendability improvement effect are securable.

In the production of foamed sheets of the present invention, the polyethylene resin to form a polyethylene resin layer forming resin melt (D), from the viewpoint of uniformly diffusing volatile plasticizer (C), a polyethylene resin foamed to be described later It is preferable to add the materials exemplified as the cell regulator of the layered resin melt (G). In that case, the addition amount is preferably from 0.01 to 5 parts by weight with respect to 100 parts by weight of the polyethylene resin forming the resin melt for forming a polyethylene resin layer (D).

Further, the polyethylene-based resin layer forming resin melt is (D), cell regulators that the polyethylene-based resin forming the polyethylene resin layer forming resin melt (D) in a range that does not impair the object of the present invention Various additives other than those may be added. Examples of the various additives include antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, fillers, antibacterial agents, and the like. In this case, the addition amount is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and particularly preferably 3 parts by weight or less with respect to 100 parts by weight of the resin. The lower limit is approximately 0.01 parts by weight.

Polyethylene resin foam layer forming resin melt (G) polyethylene resin (E) used in the density among described above is what is preferable that the main component of the following polyethylene resin 935 g / L. For example, examples of the polyethylene resin having a density of 935 g / L or less include low density polyethylene and linear low density polyethylene. Among them, low density polyethylene having good foamability is preferable. The “main component” of the above-mentioned polyethylene resin having a density of 935 g / L or less means that the content of the polyethylene resin is 50% by weight or more of the total weight constituting the foam layer. The lower limit of the density of the polyethylene resin polyethylene resin preferably used as (E) is 910 g / L.

Further, among the above-described polyethylene resins, polyethylene resins having a melt tension at 190 ° C. of 20 mN to 400 mN are preferable. When the melt tension at 190 ° C. of the polyethylene resin is less than 20 mN, there is a risk of reduction in magnification or open cell formation. On the other hand, when the melt tension at 190 ° C. of the polyethylene resin exceeds 400 mN, the viscosity of the resin increases, and there is a concern that the load is high during extrusion. The melt tension at 190 ° C. of the polyethylene resin is more preferably 30 mN or more, and further preferably 40 mN or more, from the viewpoint that it is easy to obtain a low-density foam layer. Moreover, the melt tension at 190 ° C. of the polyethylene resin is more preferably 300 mN or less, and even more preferably 250 mN or less, from the viewpoint that it is easy to obtain a foam layer having a low open cell ratio.

The melt tension (may be described as melt tension or MT) at 190 ° C. of the polyethylene resin (E) used for the resin melt for forming a polyethylene resin foam layer (G) is, for example, Toyo Seiki Seisakusho Co., Ltd. It can be measured by a manufactured melt tension tester type II or the like. Specifically, using a melt tension tester having a nozzle with a nozzle diameter of 2.095 mm and a length of 8 mm, the resin is extruded from the nozzle at a resin temperature of 190 ° C. and an extrusion piston speed of 10 mm / min. After this string-like object is hung on a tension detection pulley having a diameter of 45 mm, the stringing speed is gradually increased at a rate of about 5 rpm / sec (string-like string take-up acceleration: 1.3 × 10 ⁻² m / sec ² ). While increasing it, scrape off with a scraping roller having a diameter of 50 mm.

A specific method for obtaining the melt tension of the polyethylene resin is to measure the melt tension of the string-like material detected with a detector connected to a tension detecting pulley by scooping at a scooping speed of 500 (rpm) over time. When the measurement is made and shown in a chart with MT (mN) on the vertical axis and time (seconds) on the horizontal axis, a graph with amplitude is obtained. Next, the median value (X) of the amplitude of the portion where the amplitude is stable is taken. In this specification, this value (X) is the melt tension. In the measurement, a specific amplitude that occurs infrequently is ignored.

However, when the string-like object hung on the pulley for tension detection is cut up to a stringing speed of 500 (rpm), the stringing speed R (rpm) when the string-like object is cut is obtained. Next, the median value (X) of the amplitude is adopted as the melt tension from the graph obtained in the same manner as described above at a constant scraping speed of R × 0.7 (rpm).

Examples of the physical foaming agent (F) added to the resin melt for forming a polyethylene resin foam layer (G) include propane, normal butane, isobutane, normal pentane, isopentane, normal hexane, isohexane, and cyclohexane. Organic physical foaming agents such as aliphatic hydrocarbons, chlorinated hydrocarbons such as methyl chloride and ethyl chloride, fluorinated hydrocarbons such as 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane, oxygen, nitrogen Inorganic foaming agents such as carbon dioxide and air, and decomposable foaming agents such as azodicarbonamide. The above-mentioned physical foaming agents can be used in combination of two or more. Among these, an organic foaming agent is particularly preferable from the viewpoint of compatibility with a polyethylene resin and foamability, and among them, those having normal butane, isobutane, or a mixture thereof as a main component are preferable.

A bubble regulator is usually added to the resin melt (G) for forming a polyethylene resin foam layer. As the bubble adjusting agent, either an organic type or an inorganic type can be used. Examples of the inorganic foam regulator include borate metal salts such as zinc borate, magnesium borate, borax, sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate, sodium bicarbonate, and the like. Examples of the organic bubble regulator include sodium 2,2-methylenebis (4,6-tert-butylphenyl) phosphate, sodium benzoate, calcium benzoate, aluminum benzoate, and sodium stearate. A combination of citric acid and sodium bicarbonate, an alkali salt of citric acid and sodium bicarbonate, or the like can also be used as the bubble regulator. These bubble regulators can be used in combination of two or more.

The addition amount of the foaming agent in the resin melt (G) for forming a polyethylene resin foam layer is adjusted according to the type of foaming agent and the target density. Moreover, the addition amount of a bubble regulator is adjusted according to the target bubble diameter. That is, when a butane mixture of 30% by weight of isobutane and 70% by weight of normal butane is used as the blowing agent, the amount of butane mixture added is 3 to 30 parts by weight, preferably 4 to 20 parts by weight per 100 parts by weight of the polyethylene resin. More preferably, it is 10 to 20 parts by weight. Moreover, as a bubble regulator, for example, when a masterbatch prepared by blending 10 parts by weight of talc and 5 parts by weight of sodium citrate with respect to 100 parts by weight of low density polyethylene is used, the amount of bubble regulator added is polyethylene. It is 0.5-10 weight part per 100 weight part of resin, Preferably it is 1-8 weight part.

In the resin melt (G) for forming the polyethylene resin foam layer, a styrene resin such as polystyrene, an elastomer such as ionomer and ethylene propylene rubber, and a butene system such as polybutene may be used as long as the objects and effects of the present invention are not impaired. A vinyl chloride resin such as a resin or polyvinyl chloride can be added. In this case, the amount added is preferably 40% by weight or less, more preferably 25% by weight or less, and particularly preferably 10% by weight or less. The lower limit is approximately 0.01% by weight.

Various additives may be added to the resin described above in the resin melt (G) for forming a polyethylene resin foam layer. Examples of the various additives include a nucleating agent, an antioxidant, a heat stabilizer, a weathering agent, an ultraviolet absorber, a flame retardant, an inorganic filler, an antibacterial agent, and an anti-shrink agent. In this case, the amount added is preferably 10% by weight or less, more preferably 5% by weight or less, and particularly preferably 3% by weight or less. The lower limit is approximately 0.01% by weight.

Hereinafter, the foam sheet of the present invention will be described. The foamed sheet of the present invention is a polyethylene resin foamed sheet containing 0.3 to 10% by weight of a polymeric antistatic agent, and the apparent density of the foamed sheet is 15 g / L or more and less than 100 g / L. The surface resistivity after ultrasonic cleaning using ethanol is 1.0 × 10 ^{8 to} 1.0 × 10 ¹³ (Ω).

If the foamed sheet only contains a polymer-type antistatic agent within the above-described range uniformly, predetermined antistatic performance may not be exhibited, or a low-density foamed sheet may not be obtained. In order to obtain a predetermined surface resistivity with the content of the polymeric antistatic agent within the above-mentioned range, it is necessary to make the polymeric antistatic agent present at a high concentration on the surface of the foamed sheet.

As a method for causing the polymer antistatic agent to be present at a high concentration on the surface of the foam sheet, for example, at least comprising a resin layer preliminarily containing a polymer antistatic agent and a resin layer that can be adhered to the foam layer There is a thermal laminating method in which two or more multilayer resin layers are produced and the multilayer resin layers are laminated on the foam layer by heat. In this case, the multilayer resin layer may be laminated by a co-extrusion method, or each resin layer may be prepared in advance and laminated by heat. Further, as a method for causing the polymer antistatic agent to be present at a high concentration on the surface of the foam sheet, there is a method of laminating a resin layer containing a polymer antistatic agent on the foam layer by the coextrusion method described above. It is done. Above all, by laminating a resin layer containing a polymer-type antistatic agent on the foam layer by the coextrusion method described above, a foam sheet having a low apparent density can be obtained without inhibiting foaming of the foam. preferable. The “polymer antistatic agent content” in the foam sheet or resin layer is calculated from the weight of the polymer antistatic agent used relative to the total weight of the resin used in the foam sheet or resin layer. The value of 100% will be adopted.

The polyethylene resin used in the foam sheet of the present invention, for example, polyethylene resin described above.

The foamed sheet of the present invention contains 0.3 to 10% by weight of a polymer type antistatic agent. If the content of the polymer type antistatic agent is less than 0.3% by weight, it may be difficult to obtain the above-described surface resistivity. From the above viewpoint, 0.5% by weight or more is preferable, and 1.0% by weight or more is more preferable. On the other hand, if the content of the polymer type antistatic agent exceeds 10% by weight, the foamed sheet is poor in appearance and physical properties and may not be an inexpensive foamed sheet. From the above viewpoint, the content of the polymeric antistatic agent is preferably 8% by weight or less, and more preferably 6% by weight or less.

Further, as shown in FIG. 2, the foamed sheet of the present invention has a foamed polyethylene resin layer (I) containing a polymer antistatic agent on at least one surface of the polyethylene resin foam layer (H). It is laminated so as to be a surface layer which is the outermost layer of the sheet. The foamed sheet (J) has an apparent density of 15 g / L or more and less than 100 g / L, and a surface resistivity after ultrasonic cleaning with ethanol of 1.0 × 10 ^{8 to} 1.0 × 10 ¹³ (Ω). ) And has a semi-permanent antistatic performance. As an example of the manufacturing method of the foam sheet shown in FIG. 2, there is the method shown in FIG.

Wherein the foam sheet, polyethylene resin layer containing a polymeric antistatic agent on at least one surface of a polyethylene resin foam layer (H) (I) becomes the surface layer is the outermost layer of the foam sheet Are stacked.

The thickness of the foamed sheet (J) of the present invention is 0.3 to 50 mm from the viewpoint that when the foamed sheet is used as a packaging sheet, it has excellent buffering properties and is easy to handle when packaging a packaged body. It is preferable to be formed. From the above viewpoint, the thickness of the foamed sheet (J) is more preferably 30 mm or less, further preferably 10 mm or less, and particularly preferably 8 mm or less. On the other hand, from the viewpoint that the foamed sheet (J) obtains sufficient buffering properties, the thickness is preferably 0.5 mm or more, and more preferably 0.8 mm or more. Moreover, when thermoforming into a desired shape using a metal mold | die, 6 mm or less is preferable and 4 mm or less is more preferable. The thickness of the foam sheet (J) is the total thickness of the resin layer (I) and the foam layer (H).

When the foamed sheet has a thickness exceeding 50 mm, it can be configured as a laminated foamed sheet obtained by laminating and adhering a plurality of foamed sheets. Moreover, even when the thickness of the foam sheet is less than 50 mm, it may be formed as a laminated foam sheet formed by laminating and adhering a plurality of foam sheets. In the case of laminated foam sheets, if the same foam sheet can be laminated, foam sheets with different thicknesses, bubble diameters and apparent densities, and different types of foam sheets with different formulations such as color, base resin, and functional additives are laminated. You can also Note that it is preferable to provide the resin layer (I) on the outermost layer without providing the resin layer (I) on the laminated surface side, because a laminated foamed sheet can be obtained efficiently.

The foamed sheet (J) shown in FIG. 2 has a thickness of the polyethylene- based resin layer (I) containing a polymer type antistatic agent of 50 μm or less from the viewpoint that a foamed sheet that does not impair flexibility and buffering properties can be obtained. It is preferable that it is 40 μm or less. The lower limit of the thickness of the resin layer (I) is preferably 0.3 μm or more from the viewpoint of uniform antistatic effect, more preferably 0.5 μm or more, and the viewpoint of further improving flexibility. Is more preferably 25 μm or less from the balance between the cost and the cost.

In this specification, the method for measuring the thickness of the foam sheet is as follows.
First, the foam sheet is cut perpendicularly to the direction perpendicular to the extrusion direction, and the thickness of the cut surface is photographed at 10 points in the width direction at equal intervals with a microscope, and the thickness of the foam sheet (J) at each photographed point is The thickness of the polyethylene resin layer (I) is measured, and the arithmetic average value of the obtained values is taken as the thickness of the foamed sheet (J) and the thickness of the polyethylene resin layer (I), respectively. Next, the thickness of the polyethylene resin layer (I) is subtracted from the obtained thickness of the foam sheet (J), and the thickness obtained by the subtraction is taken as the thickness of the polyethylene resin foam layer (H).
Note that either one of the layers can be colored so that the thickness of the polyethylene resin foam layer (H) or the thickness of the polyethylene resin layer (I) can be easily measured.

The adjustment of the thickness of the foam sheet (J) and the thickness of the polyethylene resin layer (I) is adjusted to the above-described range by adjusting the discharge amount and the take-up speed.

The apparent density of the foamed sheet (J) of the present invention is 15 g / L or more and less than 100 g / L. If the apparent density of the foamed sheet (J) is less than 15 g / L, the packaging material may have insufficient strength. From the above viewpoint, the apparent density of the foamed sheet (J) is preferably 18 g / L or more, and more preferably 20 g / L or more. On the other hand, if the apparent density of the foamed sheet (J) is 100 g / L or more, the cushioning property of the obtained sheet may be lowered. From the above viewpoint, the apparent density of the foamed sheet (J) is preferably less than 70 g / L, more preferably 50 g / L or less, and even more preferably 37 g / L or less.

In the present invention, the method for measuring the apparent density of the foam sheet is as follows. First, the thickness of the foamed sheet (J) and the thickness of the polyethylene resin layer (I) are measured in advance by the method described above. Next, the basis weight of the foamed sheet (J) and the basis weight of the polyethylene- based resin layer (I) are measured. The basis weight of the foam sheet (J) is obtained by cutting out a test piece having a length of 25 mm × width 25 mm × foamed sheet, measuring the weight (g) of the test piece, multiplying the weight by 1600, and converting the unit. Is obtained (g / m ² ). The basis weight (g / m ² ) of the polyethylene resin layer (I) is obtained by multiplying the thickness of the resin layer (I) obtained by the thickness measurement method by the density of the base resin constituting the resin layer. Calculate by unit conversion. However, when the inorganic material is contained in a large amount, the resin layer is removed from the foam sheet and the basis weight of the foam layer is obtained in the same manner as the basis weight of the foam sheet, and the basis weight of the foam layer is determined from the basis weight of the foam sheet. The value obtained by subtracting the amount is adopted as the basis weight of the resin layer.

The density of the polyethylene resin foam layer (H) is a unit conversion of the value obtained by dividing the basis weight (g / m ² ) of the foam layer by the thickness (mm) of the foam layer, and the polyethylene resin foam layer Density (g / L).

In this specification, “ultrasonic cleaning using ethanol” means that ethanol at 23 ° C. is placed in a beaker and three pieces are cut out from the foamed sheet (100 mm long × 100 mm wide × thickness: test piece) The thickness of the test piece is submerged for 24 hours by ultrasonic cleaning, and then the test piece is allowed to dry for 36 hours in an atmosphere of 30 ° C. and 30% relative humidity. As the surface resistivity after ultrasonic cleaning with ethanol, a value measured in accordance with JIS K6911 (1979) is adopted except that the test piece immediately after the ultrasonic cleaning operation is used as a conditioned test piece.

The antistatic agent contained in the foamed sheet of the present invention is a polymer type antistatic agent, which does not depend on the standing time or humidity conditions, and is 1.0 × 10 ¹³ (Ω) or less immediately after production. It is preferable from the viewpoint that the surface resistivity can be shown. Examples of the polymer antistatic agent include the polymer antistatic agents described above.

The surface resistivity of the foamed sheet of the present invention is 1.0 × 10 ¹³ (Ω) or less, but is preferably 8.0 × 10 ¹² (Ω) or less from the viewpoint of being difficult to get dust, and 5.0 × 10 ^12. (Ω) or less is more preferable. Moreover, the surface resistivity of a foam sheet shall be 1.0 * 10 < ⁸ > ((ohm)) or more from a viewpoint which does not become quality excess.

In the foam sheet shown in FIG. 2, the open cell ratio of the polyethylene- based resin foam layer (H) is preferably 60% or less, more preferably 50% or less, most preferably, in order to provide buffering properties. Is 0%. Open cell ratio of polyethylene- based resin foam layer (H): S (%) is based on the procedure C described in ASTM D2856-70, and uses an air comparison type hydrometer 930 type manufactured by Toshiba Beckman Co., Ltd. The actual volume of the foamed sheet measured in this way (the sum of the volume of closed cells and the volume of the resin portion): a value calculated from the following equation (4) from Vx (L).

S (%) = (Va−Vx) × 100 / (Va−W / ρ) (4)
However, Va, W, and ρ in the above equation (4) are as follows.
Va: Apparent volume of foam sheet used for measurement (L)
W: Weight of the foam sheet in the test piece (g)
ρ: Density of resin constituting the foam sheet (g / L)

The density ρ (g / L) of the resin constituting the foamed sheet and the weight W (g) of the foamed sheet were obtained by performing the operation of cooling the foamed sheet after defoaming the foamed sheet with a heating press. Can be obtained from Since the test piece must be stored in a non-compressed state in the sample cup attached to the air comparison hydrometer, the minimum number of sheets is 25 mm in length and 40 mm in width so that the apparent volume of the test piece is approximately 25 cm ^3. And

The flexural modulus of the polyethylene resin constituting the foam layer in the foam sheet is preferably less than 300 MPa from the viewpoint of flexibility and buffering properties such as excellent surface protection of the packaged body because it is soft. More preferably, it is 200 MPa or less. The lower limit is approximately 80 MPa.

The flexural modulus is in accordance with JIS K7171 (1944), using a test piece of size 2 mm x width 25 mm x length 40 mm, span distance 30 mm, indenter radius R ₁ is 5.0 mm, support base radius _{R 2} of 2.0 mm, the test speed is measured under the condition of 2 mm / min, to adopt the calculated value. Further, the test piece is a foam layer from which the resin layer is removed, and the foam layer is defoamed with a heating press and a cooling press to form a non-foamed resin sheet. It is assumed that a laminate formed by a heating press and a cooling press is used.

The foamed sheet of the present invention has a low surface hardness and the surface of the packaged body that the resin constituting the polyethylene resin foam layer and the polyethylene resin layer containing the polymeric antistatic agent are both made of polyethylene resin. It is preferable from the viewpoint of flexibility such as excellent protection.

The resin constituting the polyethylene resin layer containing a polyethylene-based resin foam layer and the polymeric antistatic agent described above, the polyethylene resin described above In view of the above can be used.

Applications of the foam sheet of the present invention include buffer materials such as electronic parts, packaging materials, and the like.

The Example of this invention is shown.
In addition, the bubble regulator used in Examples 1-7 and Comparative Examples 4-6 is 11.8 weight of talc (Matsumura Sangyo Co., Ltd. brand name "High filler # 12") with respect to 100 weight part of low density polyethylene. Part, a foam control agent master batch comprising 5.9 parts by weight of sodium citrate was used.

Example 1
Using a tandem extruder consisting of two extruders having a diameter of 90 mm and a diameter of 120 mm as an extruder for a polyethylene resin foam layer, a diameter of 65 mm as an extruder for a polyethylene resin layer containing a polymer type antistatic agent, An extruder with L / D = 46 was used. An annular die having a diameter of 95 mm was used for coextrusion of the foam sheet.

For forming a polyethylene resin foam layer, low-density polyethylene [a] (density 922 g / L, melt viscosity 850 Pa · s, crystallization temperature 95.8 ° C., trade name “NUC8321” manufactured by Nihon Unicar Co., Ltd.) 100 weight 3 parts by weight of an air conditioner master batch was blended with respect to the part, supplied to the raw material charging port of an extruder with a diameter of 90 mm, heated and kneaded to obtain a molten resin mixture adjusted to about 200 ° C. Using a butane mixed foaming agent of 70% by weight of normal butane and 30% by weight of isobutane (simply referred to as “butane” in the table) as a physical foaming agent in the molten resin mixture, 16 weights per 100 parts by weight of low density polyethylene And then fed into an extruder with a diameter of 120 mm connected to the downstream side of the extruder with a diameter of 90 mm to obtain a resin melt for forming a polyethylene- based resin foam layer at 108 ° C.

On the other hand, in order to form a polyethylene- based resin layer containing a polymer type antistatic agent, the polymer type antistatic agent is used for 100 parts by weight of low density polyethylene [a] (trade name “NUC8321” manufactured by Nihon Unicar Co., Ltd.). As a polyether-polypropylene block copolymer (melt viscosity 270 Pa · s, melting point 136 ° C., crystallization temperature 90 ° C., density 990 g / L, trade name “Pelestat 300” manufactured by Sanyo Chemical Industries, Ltd.) The molten resin mixture is supplied to the raw material inlet of the extruder and heated to melt and adjusted to about 200 ° C., and the molten resin mixture is composed of 70% by weight normal butane and 30% by weight isobutane as a volatile plasticizer. (In the table, simply “butane”) was added to 100 parts by weight of a molten resin mixture of low-density polyethylene and a polymeric antistatic agent. And press-fitted at 16 parts by weight, followed by adjusting the resin temperature to 108 ° C. to obtain a polyethylene resin layer forming resin melt containing a polymeric antistatic agent.

The obtained resin melt for forming a polyethylene- based resin layer and the resin melt for forming a polyethylene- based resin foam layer are fed into a merging die, and the resin melt for forming a polyethylene- based resin layer containing a polymer type antistatic agent polyethylene but containing polyethylene resin layer / polyethylene resin foam layer / polymeric antistatic agent containing a polymeric antistatic agent from laminated merging is allowed annular die coextrusion, from the outside so that the surface layer A cylindrical laminated foam laminated in a three-layer configuration in the order of the resin layer was formed. The tubular laminated foam was cut out while taking the extruded cylindrical laminated foam along the cooled cylinder to obtain the desired foamed sheet.

Example 2
The physical foaming agent of the resin melt for forming a polyethylene resin foam layer is 13 parts by weight, and the resin of the resin melt for forming a polyethylene resin layer is low density polyethylene [b] (density 917 g / L, crystallization temperature 93. 5 ° C., melt viscosity 640 Pa · s, trade name “NUC8008” manufactured by Nihon Unicar Co., Ltd.) 100 parts by weight, and using 3 parts by weight of a bubble regulator masterbatch, the amount of volatile plasticizer A foam sheet was produced using the same raw materials and production method as in Example 1 except that the amount was 7.5 parts by weight. The temperature of the foam layer forming melt was 108 ° C., and the temperature of the resin layer forming melt was 115 ° C.

Example 3
Low density polyethylene [c] (density 916 g / L, crystallization temperature 91.3 ° C., melt viscosity 460 Pa · s, trade name “NUC8009” manufactured by Nippon Unicar Co., Ltd.) 100 as a resin of the resin melt for forming a polyethylene resin layer A foamed sheet was produced with the same raw materials and production method as in Example 1 except that 5 parts by weight of a foam regulator master batch was used with respect to parts by weight. The temperature of the resin melt for forming a foam layer was 107 ° C., and the temperature of the resin melt for forming a resin layer was 109 ° C.

Example 4
1% by weight of stearic acid monoglyceride (melting point: 65 ° C., trade name “S-100” manufactured by Riken Vitamin Co., Ltd.) was added to the melt-kneaded product for forming a polyethylene resin foam layer as shown in Table 2. A foam sheet is produced with the same raw materials and production method as in Example 1, except that the temperature of the resin melt for forming the foam layer, the blending amount of the antistatic agent relative to the total weight of the foam sheet, the overall thickness and the resin layer thickness are set. did. In addition, the stearic acid monoglyceride was added by the above-mentioned mixing | blending using the masterbatch of 10% which made low density polyethylene the base resin.

Example 5
Low density polyethylene [d] (density 916 g / L, crystallization temperature 91.1 ° C., melt viscosity 330 Pa · s, trade name “NUC 8350” manufactured by Nihon Unicar Co., Ltd.) 100 as a resin of the resin melt for forming a polyethylene resin layer The same raw materials and production as in Example 1 except that 3 parts by weight of a foam regulator master batch was blended with respect to parts by weight, and the temperature of the resin melt for forming a foam layer shown in Table 2 was used. A foam sheet was produced by this method. The temperature of the resin melt for forming a foam layer was 107 ° C., and the temperature of the resin melt for forming a resin layer was 108 ° C.

Example 6
Low density polyethylene [a] (density 922 g / L, crystallization temperature 95.8 ° C., melt viscosity 850 Pa · s, trade name “NUC8321” manufactured by Nippon Unicar Co., Ltd.) 100 as a resin of the resin melt for forming a polyethylene resin layer Except for using 3 parts by weight of a foam control agent masterbatch with respect to parts by weight, using dimethyl ether (referred to as DME in the table) as a volatile plasticizer, and using 13 parts by weight as the blending amount. A foam sheet was produced using the same raw materials and production method as in Example 1. The temperature of the resin melt for forming a foam layer was 108 ° C., and the temperature of the resin melt for forming a resin layer was 108 ° C.

Example 7
Low density polyethylene [a] (density 922 g / L, crystallization temperature 95.8 ° C., melt viscosity 850 Pa · s, trade name “NUC8321” manufactured by Nippon Unicar Co., Ltd.) 100 as a resin of the resin melt for forming a polyethylene resin layer 18 parts by weight of a polymer type antistatic agent (trade name “Pelestat 300” manufactured by Sanyo Chemical Industries, Ltd.) is blended with respect to parts by weight, and the blending amount of the antistatic agent with respect to the total weight of the foamed sheet shown in Table 2 A foamed sheet was produced with the same raw materials and production method as in Example 1 except that. The temperature of the resin melt for forming a foam layer was 108 ° C., and the temperature of the resin melt for forming a resin layer was 108 ° C.

Comparative Example 1
The polymer type antistatic agent (trade name “Pelestat 300” manufactured by Sanyo Chemical Industries, Ltd.) used in Example 1 is directly added to the melt-kneaded material for forming the polyethylene resin foam layer. 17 parts by weight with respect to parts by weight was added, and extrusion foaming was performed only with the melt-kneaded product for forming the foam layer without using a confluence die. However, the bubbles in the foam layer were broken, whereby the surface of the foam sheet became uneven and the appearance was poor, and a foam sheet having buffering properties could not be obtained.

Comparative Example 2
3% by weight of bleed-type antistatic agent (trade name “PEX94AS-026” polyoxyethylene alkylamine fatty acid ester 10% contained by Tokyo Ink Co., Ltd.) is directly added to the melt-kneaded material for forming the polyethylene resin foam layer. In addition, without using a merging die, extrusion foaming was performed only with the melt-kneaded product for forming the foam layer to obtain a sheet consisting only of the foam layer to which the antistatic agent was added. The obtained foamed sheet had extremely low surface resistivity after washing with ethanol.

Comparative Example 3
The amount of the volatile plasticizer added to the melt-kneaded product for forming a polyethylene resin layer was 3 parts by weight, and the temperature of the resin melt for forming a foam layer and the temperature of the resin melt for forming a resin layer shown in Table 2 were used. Except for the above, coextrusion was carried out in the same manner as in Example 2. However, a good resin layer could not be formed, and a foam sheet on which the resin layer was laminated was not obtained.

Comparative Example 4
Polyethylene resin [g] (density 915 g / L, crystallization temperature 91.1 ° C., melt viscosity 170 Pa · s, trade name “NUC8360” manufactured by Nihon Unicar Co., Ltd.) used for the melt-kneaded product for forming a polyethylene resin layer, With the same raw materials and production method as in Example 2, except that the volatile plasticizer was not used and the temperature of the foam layer forming resin melt and the temperature of the resin layer forming resin melt shown in Table 2 were used. A foam sheet was produced. Although the resin layer can be formed without heat generation of the resin layer because the melt viscosity of the polyethylene resin used for the melt-kneaded material for forming the polyethylene resin layer is extremely low, the surface resistivity of the obtained foam sheet is extremely poor. there were.

Comparative Example 5
Polyethylene resin [g] (density 915 g / L, crystallization temperature 91.1 ° C., melt viscosity 170 Pa · s, trade name “NUC8360” manufactured by Nihon Unicar Co., Ltd.) used for the melt-kneaded product for forming a polyethylene resin layer, Implementation was performed except that the amount of the volatile plasticizer added was 13 parts by weight with respect to 100 parts by weight of the resin, and the temperature of the resin melt for forming a foam layer and the temperature of the resin melt for forming a resin layer shown in Table 2 were used. A foam sheet was produced using the same raw materials and production method as in Example 2. The obtained foamed sheet had a poor surface resistivity.

Comparative Example 6
Using an antistatic agent (trade name “IRGASTAT P18” manufactured by Ciba Specialty Chemicals) having a high crystallization temperature (148.1 ° C.), the temperature of the resin melt for forming a foam layer shown in Table 2, A foamed sheet was obtained in the same manner as in Example 2 except that the temperature of the resin melt for forming the resin layer was used. “IRGASTAT P18” is a mixture of polyether ester amide and polyamide, and has a melt viscosity of 1110 Pa · s, a melting point of 180 ° C., and a density of 1043 g / L. The obtained foamed sheet was cracked in the resin layer and had poor film forming properties.

The crystallization temperature is room temperature at a temperature rising rate of 10 ° C./min using a differential thermal scanning calorimeter “DSC50” manufactured by Shimadzu Corporation in accordance with the method according to JIS K7122 (1987). The sample heated to 200 ° C. and melted was measured by lowering the temperature to 40 ° C. at a temperature drop rate of 10 ° C./min, and the peak of the crystallization calorific value peak was defined as the crystallization temperature (° C.).

About the foam sheet of Examples 1-7 and Comparative Examples 1-6, the kind of resin in a polyethylene- type resin foam layer, the crystallization temperature, the kind of physical foaming agent, compounding quantity, the kind of resin in a polyethylene- type resin layer, a crystal | crystallization Crystallization temperature [Ta], melt viscosity [Ma], blending amount of polymer antistatic agent, melt viscosity [Mb], crystallization temperature [Tb], volatile plasticizer type, blending amount, melt viscosity and volume fraction Table 1 shows the relationship between rates (simply described as “PI value” in the table). In the table, unnecessary items and places where measurement could not be performed were indicated by “-”, and low density polyethylene was abbreviated as LDPE.

In addition, the temperature of the resin melt for forming the polyethylene resin foam layer, the temperature of the resin melt for forming the polyethylene resin layer, the film formability of the resin layer, the blending amount of the antistatic agent with respect to the total weight of the foam sheet, the apparent density, The total thickness, resin layer thickness (front and back resin layer thickness laminated on both sides of the foam layer), surface resistivity and open cell ratio were measured. The results are shown in Table 2. Items that are not necessary in the table and places that could not be measured are marked with “-”.

In addition, the evaluation method of the film formability of a resin layer, the measuring method of a surface resistivity, and an open cell rate were shown below.
<Evaluation of film formability of resin layer>
And the elongation of the polyethylene-based resin layer in correspondence to the elongation of the polyethylene-based resin foam layer, whether cracks due elongation shortage of the polyethylene resin layer occurs and rated from the appearance of the foamed sheet.
○ ···········································································.

<Measurement of surface resistivity>
In the table, the untreated sample was a test piece (length 100 mm × width 100 mm × thickness: test piece thickness) cut out from a foam sheet. In accordance with the method of JIS K6911 (1979) described above, the surface resistivity after 1 minute was applied after application at an applied voltage of 500 V, and the surface resistivity was determined from the average value of the measured values. As a measuring apparatus, “TR8601” manufactured by Takeda Riken Kogyo Co., Ltd. was used.
The surface resistivity after the ethanol washing in the table was measured after measuring the untreated surface resistivity, adjusting the state of the test piece as shown below, and immediately measuring the surface resistance under an environment of 23 ° C. and 50% RH. At that time, in accordance with the method of JIS K6911 (1979) described above, the surface resistance value after 1 minute was applied after application at an applied voltage of 500 V, and the surface resistivity was obtained from the average value of the obtained measured values. . As a measuring apparatus, “TR8601” manufactured by Takeda Riken Kogyo Co., Ltd. was used.

[Test specimen condition adjustment]
Branson's “BRANSONIC 220” was used as an ultrasonic cleaning device.
First, 500 ml of ethanol was weighed in a 500 ml beaker, and the ethanol temperature was maintained at 23 ° C. Next, the test piece was immersed in ethanol having a purity of 99.5 Vol% or more by submerging it in a beaker using a wire mesh. Thereafter, the beaker with the test piece submerged is covered with a foil, and the beaker is placed in the concave storage portion of the ultrasonic cleaning apparatus containing 1.7 liters of water at 23 ° C. The apparatus was turned on and cleaning was started. After 8 hours from the start of washing, and further after 16 hours from the start of washing, an operation of adding ethanol at 23 ° C. was performed so that ethanol in the beaker became 500 ml. This additional operation of ethanol is an operation of replenishing ethanol because it is volatilized by ultrasonic cleaning and is reduced from the amount originally present in the beaker. After 24 hours from the start of cleaning, the ultrasonic cleaning apparatus was stopped, the test piece was taken out from the beaker, and immediately the test piece was left to stand for 36 hours in an atmosphere with a relative humidity of 30% and a temperature of 30 ° C. The condition adjustment of the test piece was completed.

<Measurement of open cell ratio>
Open cell ratio: S (%) is the actual volume of the foam sheet measured in accordance with Procedure C described in ASTM D2856-70 and using an air comparison type hydrometer 930 type manufactured by Toshiba Beckman Co., Ltd. (Sum of the volume of closed cells and the volume of the resin part): Calculated from Vx (L) by the following equation (4).

S (%) = (Va−Vx) × 100 / (Va−W / ρ) (4)

However, Va, W, and ρ in the above equation (4) are as follows.
Va: Apparent volume of foam sheet used for measurement (L)
W: Weight of the foam sheet in the test piece (g)
ρ: Density of resin constituting the foam sheet (g / L)
The density ρ (g / L) of the resin constituting the foamed sheet and the weight W (g) of the foamed sheet were obtained by performing the operation of cooling the foamed sheet after defoaming the foamed sheet with a heating press. Was used. Since the test piece must be stored in a non-compressed state in the sample cup attached to the air comparison hydrometer, the minimum number of sheets is 25 mm in length and 40 mm in width so that the apparent volume of the test piece is approximately 25 cm ^3. It was. Moreover, the apparent volume [Va] (L) of the foamed sheet used for the measurement was a value obtained by increasing the volume when the foamed sheet used for the measurement was immersed in water in a 200 ml graduated cylinder.

It is explanatory drawing which shows an example of the manufacturing method of the foam sheet of this invention. It is sectional drawing which shows one example of the foam sheet of this invention.

DESCRIPTION OF SYMBOLS 11 1st extruder 12 2nd extruder A Polyethylene resin B Polymer type antistatic agent C Volatile plasticizer D Polyethylene resin layer forming resin melt E Polyethylene resin F Physical foaming agent G Polyethylene resin Foam layer forming resin melt H polyethylene resin foam layer I polyethylene resin layer J Foam sheet

Claims (2)

A foamed sheet that is laminated by coextrusion so that a polyethylene- based resin layer containing a polymer-type antistatic agent is a surface layer on at least one surface of a polyethylene- based resin foam layer,
The addition amount of the polymer antistatic agent is 5 to 100 parts by weight with respect to 100 parts by weight of the polyethylene resin constituting the surface layer,
The apparent density of the foamed sheet is 15 g / L or more and less than 100 g / L, and the surface resistivity after ultrasonic cleaning with ethanol is 1.0 × 10 ^{8 to} 1.0 × 10 ¹³ (Ω). Characteristic foam sheet. The foamed sheet according to claim 1, wherein the thickness of the polyethylene- based resin layer containing the polymer-type antistatic agent is 50 μm or less.

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