JP2004043813A - Polyethylene-based resin extruded and foamed sheet, shaped product of the foamed sheet, assembled box, lining sheet for concrete formwork, and manufacturing method of the formed sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyethylene-based resin extruded and foamed sheet which has stiffness and cushioning property, does not cause warpage, is excellent in impact resistance at a low temperature and in stability, and is useful for a heat-shaped product, a lining sheet for concrete formwork, an assembled box, a panel member, a partition member or the like, and to provide a manufacturing method of the polyethylene-based resin extruded and foamed sheet. <P>SOLUTION: The polyethylene-based resin extruded and foamed sheet is characterized in that it has an apparent density of 70-350 g/l and an open cell ratio of 40 % or less, in that the flexural modulus of the polyethylene-based resin composition for constituting the foamed sheet is not less than 300 MPa, in that the melt-tension (A) of the resin composition at 190 °C is 15-400 mN, and in that the product of the melt-tension (A) and the MFR (B)(g/10 min)(wherein MFR means Melt Flow Rate), i.e. (A×B) is not less than 100. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an extruded polyethylene resin foam sheet, a molded article obtained by thermoforming the foam sheet, an assembly box obtained from the foam sheet, and a lining sheet for a concrete form having a large number of communicating holes formed in the extruded foam sheet. And a method for producing a foamed sheet.

ポ リ エ チ レ ン Extruded polyethylene resin foams have been used in various fields as cushioning materials and packaging materials. For example, Patent Document 1 discloses a foam sheet having an apparent density of 2 to 150 g / L, a thickness of 1 to 10 mm, and an endothermic peak appearing on a second DSC curve obtained by differential scanning calorimetry having a specific temperature relationship. ing. Patent Literature 2 discloses a foam using a high-density polyethylene modified using a peroxide, and Patent Literature 3 discloses a mixture of a low-density polyethylene and a high-density polyethylene, and a high-density polyethylene having a density of 30 to 50%. A foam using 70% by weight is disclosed.

JP-A-6-184346 JP 2001-505605 A JP-A-56-28837

However, the foamed sheet described in Patent Literature 1 has a low rigidity and has a problem that the sheet hangs down when one end of the sheet is held. Further, the foam described in Patent Literature 2 has a problem in that the production process becomes complicated with the addition and use of the peroxide, so that the foam becomes expensive. Furthermore, the foam described in Patent Literature 3 has a problem that it has poor rigidity and poor moldability due to a high open cell ratio.

The present invention has been made in view of such conventional problems, and it is an object of the present invention to provide an inexpensive polyethylene resin extruded foam sheet having high rigidity, a smooth surface, good appearance, excellent impact resistance at low temperatures, and low cost. Aim. The present invention also provides a molded body obtained by thermoforming the extruded foam sheet, an assembly box obtained from the extruded foam sheet, and a lining sheet for a concrete form having a large number of communication holes formed in the extruded foam sheet. Aim. Still another object of the present invention is to provide a method for producing a polyethylene resin extruded foam sheet having excellent rigidity.

That is, the present invention
(1) A polyethylene resin extruded foam sheet having an apparent density of 70 g / L to 350 g / L and an open cell ratio of 40% or less, and a flexural modulus of the polyethylene resin composition constituting the foam sheet is 300 MPa or more. And a melt tension (A) at 190 ° C. of the resin composition of 15 mN to 400 mN, and a product (A × B) of the melt tension (A) and the MFR (B: g / 10 minutes) of the resin composition. Extruded polyethylene resin foam sheet, characterized in that the value is 100 or more,
(2) The above-mentioned (1), wherein the polyethylene resin composition constituting the extruded polyethylene resin foam sheet contains polyethylene having a density of 930 g / L or less and polyethylene having a density of more than 930 g / L and 970 g / L or less. Extruded polyethylene resin foam sheet,
(3) When the polyethylene resin composition constituting the extruded polyethylene resin foam sheet is (i) 10% by weight or more and less than 50% by weight of polyethylene having a density of 930 g / L or less, (ii) the density exceeds 930 g / L. The extruded polyethylene resin foam sheet according to the above (1) or (2), comprising more than 50% by weight and not more than 90% by weight of polyethylene of 970 g / L or less,
(4) The extruded polyethylene resin sheet according to any one of the above (1) to (3), which has a polyethylene resin layer of 5 μm or more on at least one surface.
(5) The extruded polyethylene resin foam sheet according to any one of the above (1) to (4), wherein the overall thickness is 1 mm or more and 10 mm or less,
(6) The polyethylene resin extruded foam according to (4), wherein the polyethylene resin constituting the polyethylene resin layer contains an antistatic agent, and the resin layer has semipermanent antistatic performance. Sheet,
(7) The extruded polyethylene resin foam sheet according to any one of the above (1) to (6), wherein the warpage is 5% or less,
(8) a molded article obtained by thermoforming the extruded polyethylene resin sheet according to any one of (1) to (7);
(9) An assembly box made of the extruded polyethylene resin foam sheet according to any one of the above (1) to (7),
(10) A lining sheet for a concrete form obtained by forming a large number of communicating holes in the extruded polyethylene resin foam sheet according to any one of (1) to (7) above,
(11) A foamed sheet having an apparent density of 70 g / L to 500 g / L and an open cell ratio of 40% or less obtained by extrusion foaming a melt-foamable resin composition obtained by adding a foaming agent to a polyethylene-based resin composition. Wherein the resin composition comprises a polyethylene having a density of 930 g / L or less and a polyethylene having a density of more than 930 g / L and 970 g / L, and a flexural modulus of 300 MPa or more, The melt tension (A) at 190 ° C. is 15 mN to 400 mN, and the value of the product (A × B) of the melt tension (A) and the MFR (B: g / 10 minutes) is 100 or more. A method for producing an extruded polyethylene resin foam sheet,
It is the gist.

The extruded polyethylene resin sheet of the present invention is an extruded polyethylene resin sheet having an apparent density of 70 g / L to 500 g / L and an open cell ratio of 40% or less, and the polyethylene resin composition constituting the foam sheet is Since the foamed sheet exhibits specific physical property values, the foamed sheet has high rigidity such as little droop when held at one end, has a smooth surface, has a good appearance, and has excellent impact resistance at low temperatures.
In addition, since the foamed sheet of the present invention contains polyethylene having a density of 930 g / L or less and polyethylene having a density of more than 930 g / L and 970 g / L or less, the foamed sheet has a smooth surface, good appearance, and excellent rigidity. It will be.
In addition, the foamed sheet of the present invention has a specific weight ratio between polyethylene having a density of 930 g / L or less and polyethylene having a density of more than 930 g / L and 970 g / L or less. It is excellent in reproducibility, and also excellent in mold reproducibility, which is the same shape as the mold at the time of thermoforming.
When the foamed sheet of the present invention has a polyethylene resin layer having a thickness of 5 μm or more on at least one side, a sufficient effect can be obtained by adding a small amount of a functional additive to the resin layer.
Further, when the foamed sheet of the present invention has a thickness of 1 mm or more and 10 mm or less, it is suitably used for thermoforming containers and trays, as well as for assembling boxes and partitioning materials.
Further, the foam sheet of the present invention contains an antistatic agent in the polyethylene resin constituting the polyethylene resin layer, and since the resin layer has a semi-permanent antistatic performance, it does not adhere to dust, and is used for food and machinery. The foamed sheet is suitable for parts, and when the foamed sheet comes into contact with the packaged body, the surface of the packaged body does not whiten or stick, and the antistatic performance of the foamed sheet is maintained. In addition, the molded article of the present invention obtained by thermoforming a foamed sheet, and the assembled box of the present invention obtained from a foamed sheet are both excellent in rigidity, surface smoothness, and low-temperature impact resistance, and are suitable as packaging containers. .
In addition, the lining sheet for concrete formwork, which has a large number of communication holes formed in the foam sheet, does not hang down when the end is held with one hand. Is excellent. Also, when used as a lining sheet, a beautiful concrete surface is formed.
According to the method of the present invention, an extruded polyethylene resin foam sheet having a low open cell ratio and excellent rigidity can be efficiently produced.

The extruded polyethylene resin foam sheet of the present invention (hereinafter may be simply referred to as “foam sheet”) has a flexural modulus of 300 MPa or more of a polyethylene resin composition constituting the foam sheet. Has a melt tension (A) at 190 ° C. of 15 mN to 400 mN, and a product (A × B) of the melt tension (A) and the MFR (B: g / 10 minutes) of the resin composition has a value of 100 (mN). G / 10 min) or more.

If the flexural modulus of the polyethylene resin composition constituting the foam sheet is less than 300 MPa, the foam sheet may have low flexural rigidity. From the viewpoint of increasing the bending rigidity of the foamed sheet, 400 MPa or more is more preferable, and 500 MPa or more is particularly preferable.
On the other hand, the upper limit is such that if the flexural modulus is too high, the buffering property is reduced and the contents may be damaged when used as a packaging container or the like. Therefore, the flexural modulus is preferably 1500 MPa or less, and 1200 MPa or less. The following is more preferable, and 1000 MPa or less is particularly preferable.
In addition, the flexural modulus of the polyethylene-based resin composition was determined according to JIS K7171 (1994) by using a test piece having a size of thickness 2 mm × width 25 mm × length 40 mm and a span-to-span distance of 30 mm and a radius R _{1 of} an indenter. 5.0 mm, the radius _{R 2} of the support base is 2.0 mm, the test speed is measured under the condition of 2 mm / min, to adopt the calculated value. When the test piece is provided with a resin layer, the foam layer is defoamed with a hot press and a cooling press using a foam sheet from which the resin layer has been removed (hereinafter, also simply referred to as a “foam layer”). A non-foamed resin sheet is used in which the resin sheet is laminated by a heating press and a cooling press so as to have the thickness of the test piece described above.

溶 融 The resin composition has a melt tension (A) at 190 ° C of 15 mN to 400 mN. Such a foamed sheet can be formed by charging a polyethylene-based resin composition having a melt tension of 15 mN to 400 mN into an extruder, extruding as a melt-foamable resin composition, and foaming. When the melt tension is less than 15 mN, the foamability is reduced, so that a lightweight foam sheet may not be obtained. In the case of thermoforming, the foam sheet may have poor thermoformability such as poor elongation of the foam sheet. There is. From the above viewpoint, it is more preferably 17 mN or more, and further preferably 20 mN or more. On the other hand, when the melt tension is more than 400 mN, the rigidity and thermoformability are likely to be reduced since the foam is easily formed by the rise of the die pressure during extrusion foaming, so that the melt tension is 400 mN or less. And more preferably 300 mN or less.

The melt tension at 190 ° C. of the polyethylene-based resin composition can be measured by, for example, a melt tension tester type II manufactured by Toyo Seiki Seisaku-sho, Ltd. Specifically, using a melt tension tester having a nozzle having a nozzle diameter of 2.095 mm and a length of 8 mm, the resin composition is extruded from the nozzle into a string at a resin temperature of 190 ° C. and an extrusion piston speed of 10 mm / min. After hanging the string on a tension detecting pulley having a diameter of 45 mm, the winding speed is about 5 rpm / sec (acceleration of winding the string: 1.3 × 10 ⁻² m / sec ² ). Is gradually wound up with a winding roller having a diameter of 50 mm.

A specific method for determining the melt tension of the resin composition is to take up the melt tension of the string-like object detected by a detector connected to a pulley for tension detection at a winding speed of 100 (rpm) over time. When the measured values are shown in a chart in which the vertical axis indicates the melt tension (mN) and the horizontal axis indicates the time (second), a graph having an amplitude is obtained. Next, the median value of the amplitude of the portion where the amplitude is stable is taken. In this specification, this value is adopted as the melt tension of the resin composition. It should be noted that the specific amplitude that rarely occurs is ignored.

However, if the string hanged on the pulley for tension detection breaks up to the winding speed of 100 (rpm), the winding speed when the string breaks is calculated as R (rpm). Next, at a constant winding speed of R × 0.7 (rpm), the median value is adopted as the melt tension from the graph obtained in the same manner as described above.

積 The product of the above-mentioned melt tension (mN) and MFR (g / 10 min) of the polyethylene resin composition is 100 (mN · g / 1 min) or more. It is preferably 110 or more, more preferably 120 or more, and still more preferably 150 or more, from the viewpoint of excellent foamability such as easily obtaining a low-density foam sheet. On the other hand, the upper limit is preferably 1,000 or less, more preferably 700 or less, and still more preferably 500 or less, from the viewpoint of excellent appearance such as no irregularities on the surface of the foam sheet.

Ｍ Further, the MFR is preferably 0.3 g / 10 minutes or more. When it is less than 0.3 g / 10 minutes, the foamed sheet tends to become open cells due to an increase in die pressure during extrusion foaming, and there is a concern that bending rigidity may be reduced. There is a possibility that thermoformability such as poor elongation may be reduced. From such a viewpoint, 1.0 g / 10 min or more is preferable, 2.0 g / 10 min or more is more preferable, and 3.0 g / 10 min or more is further preferable. On the other hand, the upper limit of the MFR is preferably 20.0 g / 10 minutes or less, and if it exceeds this value, it becomes extremely difficult to make the melt tension (MT) at 190 ° C. to 15 mN or more, and a low-density foamed sheet is obtained. Therefore, there is a possibility that a lightweight foam sheet may not be obtained, and that thermoformability may decrease. From such a viewpoint, 15.0 g / 10 minutes or less is more preferable, and 10.0 g / 10 minutes or less is further preferable. Such a foamed sheet can be formed by charging a polyethylene-based resin composition having an MFR within the above range into an extruder and extruding and foaming as a melt-foamable resin composition.

The melt flow rate (MFR) is measured at 190 ° C. and a load of 21.17 N in accordance with JIS K7210 (1976).

The polyethylene-based resin composition used in the measurement of the melt tension and the MFR, when having a resin layer, uses a foamed layer from which the resin layer has been removed, and is defoamed by a heating press and a cooling press to obtain a non-foamed material. Resin is used.
The foamed sheet of the present invention includes a polyethylene having a density of 930 g / L or less (hereinafter sometimes abbreviated as “L-polyethylene”) and a polyethylene having a density of more than 930 g / L and 970 g / L or less (hereinafter, “H-polyethylene”). -May be abbreviated as "polyethylene") in that the foamed sheet has a smooth surface, good appearance, and excellent rigidity. Examples of the L-polyethylene include so-called low-density polyethylene, linear low-density polyethylene, and linear ultra-low-density polyethylene. Above all, low-density polyethylene having good foamability such as a foam sheet having a low apparent density is preferable. The lower limit of the density of L-polyethylene is usually about 910 g / L.

The MFR of the above-mentioned L-polyethylene is preferably from 0.3 g / 10 min to 20.0 g / 10 min, and more preferably from 1.0 g / 10 min to 15. 0 g / 10 min is more preferable, and 2.0 g / 10 min to 10.0 g / 10 min or less is further preferable. Further, it is preferable that the melt tension of L-polyethylene is from 20 mN to 400 mN from the viewpoint of obtaining a low-density foamed sheet.

The H-polyethylene includes a so-called linear polyethylene, and specifically, a high-density polyethylene and the like. The MFR of the above-described H-polyethylene is preferably 1.0 g / 10 min or more, more preferably 2.0 g / 10 min or more, and more preferably 3.0 g / 10 min or more, from the viewpoint of improving the appearance such as no irregularities on the surface. Is more preferred. On the other hand, the upper limit of the MFR is preferably 20.0 g / 10 minutes or less, more preferably 15.0 g / 10 minutes or less, and more preferably 15.0 g / 10 minutes or less, from the viewpoint of increasing impact resistance at low temperatures without reducing rigidity. 0 g / 10 minutes or less is more preferable.
Further, it is preferable that the melt tension of H-polyethylene is 2 mN or more and less than 20 mN from the viewpoint of obtaining a foamed sheet having no decrease in rigidity due to open cells. As described above, the foamed sheet of the present invention uses L-polyethylene and H-polyethylene having a specific melt tension, a specific flexural modulus, a specific melt tension, a specific melt tension (A) and an MFR (B: g). / 10 minutes), the foamed sheet has a low density and excellent rigidity.
Further, the density of the H-polyethylene is preferably 940 g / L or more, more preferably 950 g / L or more, and even more preferably 955 g / L or more from the viewpoint of further increasing the rigidity of the foamed sheet.

The polyethylene resin composition constituting the foamed sheet contains L-polyethylene and H-polyethylene, and the ratio of H-polyethylene exceeds 50% by weight and 90% by weight based on 100% of the total amount of the polyethylene resin composition. % Of the foamed sheet, the rigidity of the foamed sheet having one side with little sagging when held, impact resistance at low temperatures, and the same shape as the mold used for thermoforming. It is preferable for improving the mold reproducibility. When the ratio of H-polyethylene to the total amount of the polyethylene resin composition exceeds 90% by weight, the open cell ratio and apparent density of the foamed sheet tend to increase and the thermoformability decreases when thermoforming. There is a fear. When the proportion of H-polyethylene is 50% by weight or less, the rigidity of the foam sheet may be reduced. The more preferable ratio of H-polyethylene to the total amount of the polyethylene resin composition is more than 50% by weight and 85% by weight or less, and further preferably more than 50% by weight and 80% by weight or less.

ポ リ エ チ レ ン The polyethylene resin composition constituting the foamed sheet may contain a polyethylene resin other than the above-mentioned L-polyethylene and H-polyethylene. Examples of the polyethylene resin that can be blended with the L-polyethylene and the H-polyethylene in the polyethylene resin composition include, for example, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene-butene- 50 moles of ethylene component units such as 1 copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer, ethylene-octene-1 copolymer % Or more, and these can be used as a mixture of two or more.

The polyethylene-based resin composition constituting the foamed sheet may contain the above-mentioned polyethylene-based resin in addition to L-polyethylene and H-polyethylene. It is preferable that both are contained in a total amount of 70% by weight or more so that the advantage is sufficiently exhibited. The total weight of L-polyethylene and H-polyethylene in the total weight of the polyethylene resin composition is more preferably 80% by weight or more, and the total of both is 90% by weight. When the total weight of L-polyethylene and H-polyethylene in the polyethylene-based resin composition is 90% by weight, the mixture is a mixture of only polyethylene, and thus has an advantage of excellent recyclability.

発 泡 The foamed sheet of the present invention may contain various additives in the polyethylene resin composition. Examples of the additives include nucleating agents, antioxidants, heat stabilizers, antistatic agents, conductivity-imparting agents, weathering agents, ultraviolet absorbers, functional additives such as flame retardants, inorganic fillers, and the like. .

The polyethylene-based resin composition constituting the foamed sheet of the present invention may be a styrene-based resin such as polystyrene, an elastomer such as ionomer or ethylene propylene rubber, or a butene such as polybutene, as long as the object and effects of the foamed sheet of the present invention are not impaired. And a vinyl chloride resin such as polyvinyl chloride. In that case, the addition amount is preferably 30% by weight or less, more preferably 20% by weight or less, and particularly preferably 10% by weight or less, based on 100% by weight of the polyethylene resin composition.

か ら The overall thickness of the foamed sheet of the present invention is preferably from 1 mm to 50 mm, more preferably from 1 mm to 40 mm, even more preferably from 1 mm to 30 mm, from the viewpoint of excellent buffering properties. In particular, when a container, a tray, or the like is thermoformed, or when the foamed sheet of the present invention is used as a raw material such as an assembly box or a partition material, the thickness is preferably 1 mm or more and 10 mm or less. If the thickness is less than 1 mm, the rigidity and cushioning of the foam sheet may be insufficient. From such a viewpoint, the thickness of the foam sheet is preferably 1.2 mm or more, and more preferably 1.5 mm or more. On the other hand, when the thickness of the foamed sheet is too large, there is a possibility that handling may be poor when processing or forming the partition material or the assembly box. Therefore, the thickness of the foamed sheet is preferably 8 mm or less, and 6 mm or less. More preferred. In particular, at the time of thermoforming, it is preferably 3 mm or less from the viewpoint that the same shape as the mold can be obtained.

場合 When the foamed sheet has a thickness of more than 50 mm, a laminated foamed sheet obtained by bonding the foamed sheet to two or more layers can be obtained. Further, when a foamed sheet having a thickness of less than 50 mm is used, a laminated foamed sheet formed by bonding two or more layers may be used. In the case of a laminated foamed sheet of two or more layers, if the same foamed sheet can be laminated, foamed sheets having different thicknesses, cell diameters, and apparent densities, as well as formulations of colors, base resins, functional additives, etc. Different types of foam sheets can be laminated.

The overall thickness of the foamed sheet referred to in the present specification may have a polyethylene resin layer on at least one side as described later. In such a case, the thickness refers to the entire thickness including the resin layer. The thickness of the foamed sheet is measured as follows.
First, the foam sheet is cut perpendicularly to the direction perpendicular to the extrusion direction, the thickness of the cut surface is photographed at equal intervals by a microscope in the width direction at 10 points, and the thickness of the foam sheet at each photographed point is measured. The arithmetic average of the obtained values is defined as the thickness of the foam sheet. In addition, when the foamed sheet has a polyethylene resin layer on at least one side, at each point photographed as described above, the thickness of the entire foamed sheet and the thickness of the resin layer are measured, and the arithmetic average of the obtained measurement values The value is defined as the thickness of each of the entire foamed sheet and the resin layer. Next, the thickness of the resin layer is subtracted from the obtained thickness of the entire foam sheet, and the thickness obtained by the subtraction is defined as the thickness of the foam layer.

(4) It is preferable that the foamed sheet has a polyethylene resin layer of 5 μm or more on at least one side, because the effect is enhanced by adding a small amount of a functional additive to the resin layer. The thickness of the resin layer provided on at least one side of the foam sheet is preferably 10 μm or more in order to further increase rigidity such as less droop when holding the edge of one side of the sheet, and more preferably 15 μm or more in terms of improving rigidity. preferable. Although the rigidity increases as the thickness of the resin layer increases, the thickness of the resin layer is preferably 500 μm or less, more preferably 400 μm or less, because if the thickness is too large, the weight may increase and the lightness may deteriorate. In particular, when a polyethylene resin layer is provided on both sides, the thickness is preferably 300 μm or less. The polyethylene resin layer can be formed by a known method such as laminating a polyethylene resin film on a foam sheet.

ポ リ エ チ レ ン The polyethylene resin constituting the polyethylene resin layer preferably has a melt flow rate (MFR) of 3.0 g / 10 min or more from the viewpoint of improving the appearance. On the other hand, the upper limit of the MFR is not particularly limited, but is usually 30.0 g / 10 minutes or less.

The above-mentioned melt flow rate (MFR) shall be measured in the same manner as the MFR of the polyethylene resin composition constituting the foamed sheet described above.
In addition, the test piece shall use what cut the resin layer from the foamed sheet.

As the polyethylene resin constituting the resin layer, for example, high-density polyethylene, low-density polyethylene, ethylene homopolymer such as linear low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, Ethylene-propylene-butene-1 copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer, ethylene-octene-1 copolymer, etc. And a mixture of two or more thereof.

Polyethylene resin constituting the polyethylene resin layer is a styrene resin such as polystyrene, an elastomer such as ionomer or ethylene propylene rubber, a butene resin such as polybutene, as long as the purpose and effects of the foamed sheet of the present invention are not impaired. A vinyl chloride resin such as polyvinyl chloride can be added. In this case, the amount of addition is preferably 40% by weight or less, more preferably 25% by weight or less, and particularly preferably 10% by weight or less.

The polyethylene-based resin layer includes, for example, nucleating agents, antioxidants, heat stabilizers, antistatic agents, conductivity-imparting agents, weathering agents, ultraviolet absorbers, functional additives such as flame retardants, inorganic fillers, and the like. And other various additives.

In the foamed sheet of the present invention, when at least one side has a resin layer, the polyethylene resin constituting the resin layer contains an antistatic agent, and the resin layer has a semi-permanent antistatic performance, so that dust is not attached. It becomes a foam sheet suitable for food and machine parts.

In the present specification, the antistatic agent is a resin having a molecular weight of at least 300 daltons or more, preferably 300 to 300,000 daltons, more preferably 600 to 15,000 daltons, and a surface resistivity of less than 1 × 10 ¹² Ω. Is shown. Further, the antistatic agent in the present specification is an inorganic salt or a low molecular weight organic protonic acid salt, for example, 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 and the} like may be contained. The upper limit of the molecular weight of the antistatic agent is about 500,000 daltons.

The above molecular weight is a weight average molecular weight obtained by using a column calibrated by gel permeation chromatography using polystyrene having a known molecular weight.

In the foamed sheet of the present invention, when the antistatic agent is used, when the foamed sheet comes into contact with the packaged object, the surface of the packaged object is not whitened or tacky, and the antistatic performance of the foamed sheet is prevented. Is what lasts.

In the present specification, the antistatic agent is, specifically, polyethylene oxide, polypropylene oxide, polyethylene glycol, polyether, polyester amide, polyether ester amide, ionomers such as ethylene-methacrylic acid copolymer, polyethylene glycol methacrylate-based Among one or more mixtures selected from quaternary ammonium salts such as polymers, or two or more copolymers, and furthermore, copolymers thereof with other resins such as polypropylene, and the like, A resin having a polar group in the molecular chain and capable of forming a complex or solvating an inorganic salt or a low molecular weight organic protonic acid salt. There may be.
The upper limit of the melting point of the antistatic agent is approximately 270 ° C., and the lower limit is approximately 70 ° C.

Among the antistatic agents used in the present invention, in particular, polyetheresteramide, polyether, and a copolymer or a mixture of one or more of the above-described one or more antistatic agents and other resins such as polypropylene and polyamide as a main component It is preferable to use one that does. In the present specification, the term "main component" means that the content is 50% by weight or more, preferably 75% by weight or more, more preferably 85% by weight or more. By forming a network structure using these antistatic agents, a resin layer having a surface specific resistivity of 1 × 10 ¹³ (Ω) or less can be easily formed.

It is more preferable that the polyetheresteramide and the polyether are mixed or copolymerized with a polyamide or a polyolefin of the same type as the matrix in which the esteramide and the polyether are mixed. When a polyamide mixed or copolymerized is used, a network structure or the like can be formed more reliably. Further, since the polyolefin is mixed or copolymerized, the compatibility of the polyetheresteramide or the polyether in the matrix is improved, so that the antistatic performance is improved and the deterioration in physical properties can be suppressed.

融 点 The melting point of the polyetheresteramide is preferably 230 ° C or lower, more preferably 200 ° C or lower. When the melting point exceeds 230 ° C., when the polyethylene resin and the polyetheresteramide are melted and mixed, the temperatures of the two resins must be increased more than necessary, so that the polyethylene resin may be deteriorated. . In the case of laminating by the co-extrusion method, the foamed layer may have an open-cell structure and the rigidity may be reduced, depending on the amount of the resin layer laminated.

As used herein, the term “antistatic performance” refers to a surface specific resistivity of 1 × 10 ⁸ (Ω) to 1 × 10 ¹³ (Ω).

The term “permanent antistatic performance” as used herein means having antistatic performance even after washing, and specifically, a test piece (100 mm × 100 mm ×) in accordance with JIS K6911 (1979). (Thickness: test piece thickness) was cut out at equal intervals in the width direction perpendicular to the extrusion direction of the foamed sheet, and the test piece was immersed in ethanol, washed with an ultrasonic cleaner for 24 hours, and then cooled to 30 ° C. After drying in an atmosphere at a humidity of 30% for 36 hours, and then left for 1 hour in an atmosphere at a temperature of 23 ° C. and a humidity of 50%, the surface resistance was measured, and the surface resistivity was calculated from the average of the measured values. In this case, it means that the surface resistivity is in the range of 1 × 10 ⁸ (Ω) to 1 × 10 ¹³ (Ω).

The foamed sheet preferably has a polyethylene-based resin layer on at least one side or not, and preferably has a warpage of 5% or less. A foamed sheet having a warpage of 5% or less is excellent in handleability, for example, the stacking height when stacked can be reduced, and there is no troublesome work of opening and processing the warped foamed sheet. From such a viewpoint, 4% or less is more preferable, 3% or less is further preferable, and 0% is particularly preferable. Therefore, it can be widely used in the field of plate materials such as panels, partition materials, and box materials.

The warpage is determined by the following measurement method.
A sample of 500 mm × 500 mm (thickness is the thickness of the foam sheet) is cut out from the foam sheet. However, if the above size cannot be cut out due to the size of the foam sheet, cut out into a square having the maximum length that can be cut out as one side. The cut sample is placed on a horizontal table so that the warped portion is upwardly convex. At this time, a total of four distances from the lower surface of the sample to the upper surface of the table on which the sample is placed are measured at four points at the center of the four sides of the square sample. Further, the sample is turned over and the sample is placed on a horizontal table so that the warp is convex downward. Similarly, the distance from the lower surface of the sample to the upper surface of the table on which the sample is placed is measured at a total of four points at the corners (4 points) of the square. The largest numerical value L (mm) of the eight measurement results obtained as described above is adopted, and the warpage ratio is calculated from the following equation.

{Warp (%) = L (mm) / (length of one side of square (mm)) × 100} (1)

In order to obtain a foamed sheet having a warpage of 5% or less, a method of introducing a foamed sheet into a heating furnace and subjecting the sheet to heating and stretching is adopted. As a method of heating and stretching the foamed sheet in a heating furnace, for example, a method of heating and stretching by immediately introducing into a heating furnace after extrusion foaming, or a foamed sheet obtained by extrusion foaming is once wound into a roll, and then, A method in which the film is introduced into a heating furnace in another step and is heated and stretched may be used.

Regarding the foamed sheet of the present invention, the apparent density of the foamed sheet is 70 to 350 g / L both when the thickness exceeds 10 mm and when the foamed sheet is 1 mm to 10 mm. When the apparent density is in the above-described range, the cushioning property is good, and the rigidity is high, such as little droop when the sheet has one end. In order for the foamed sheet to have excellent rigidity and excellent heat insulation properties, the lower limit of the apparent density of the foamed sheet is preferably 95 g / L or more, and more preferably 100 g / L or more. The upper limit of the apparent density of the foam sheet is preferably 320 g / L or less, and more preferably 300 g / L or less.
In addition, the apparent density of the foam sheet referred to in the present specification refers to the apparent density of the foam layer.

The measurement of the apparent density of the foam sheet in the present specification is performed as follows.
The thickness of the foamed sheet is measured by the method described above. When a polyethylene resin layer is provided on at least one side, the thickness of the resin layer is also measured in advance. Further, the basis weight of the foamed sheet and the basis weight of the resin layer are measured.

The basis weight of the foamed sheet is a value obtained by cutting out a test piece having a length of 25 mm × width 25 mm × thickness of the foamed sheet, measuring the weight (g) of the test piece, multiplying the value by 1600 times, and converting it to the weight per 1 m ^2. (G / m ² ).

When a resin layer is provided, the basis weight (g / m ² ) of the resin layer is calculated by multiplying the previously measured thickness of the resin layer by the density obtained from the total weight and the volume of the resin layer, and converted into a unit. And ask for it.

The apparent density of the foamed sheet is obtained by converting the basis weight (g / m ² ) of the foamed sheet obtained as described above by the thickness (mm) of the foamed sheet into a unit conversion (g / cm ³ ). . When at least one side has a resin layer, the value obtained by dividing the basis weight of the foamed layer obtained by subtracting the basis weight of all the resin layers from the basis weight of the foamed sheet by the thickness of the foamed layer obtained by subtracting the thickness of all the resin layers. Is converted to a unit (g / cm ³ ).

発 泡 The foam sheet of the present invention has an open cell ratio of 40% or less. When the open cell ratio exceeds 40%, the rigidity is reduced even when a polyethylene resin layer is provided on at least one side. Further, in the case of obtaining a molded product obtained by so-called thermoforming in which a foamed sheet is heated and softened and molded with a mold, it is preferable that the open cell ratio of the foamed sheet is 20% or less.

The open cell ratio: S (%) of the foamed sheet in the present specification is measured using an air comparison type hydrometer 930 manufactured by Toshiba Beckman Co., Ltd. in accordance with Procedure C described in ASTM D2856-70. Actual volume of foamed sheet (sum of volume of closed cell and volume of resin portion): value calculated from Vx (L) by the following equation (2).
The sample can be used as it is even in the case of a foamed sheet having a resin layer.

{S (%) = (Va−Vx) × 100 / (Va−W / ρ)} (2)

However, Va, W, and ρ in the above equation (2) are as follows.
Va: Apparent volume (L) of the foam sheet calculated from the outer dimensions of the foam sheet used for the measurement
W: Weight of foam sheet in test piece (g)
ρ: Density of resin constituting foam sheet (g / L)
The density ρ (g / L) of the resin constituting the foamed sheet and the weight W (g) of the foamed body
Can be determined from the obtained sample by performing an operation of defoaming the foamed sheet by a hot press and then cooling the foamed sheet.

In addition, since a test piece must be stored in the sample cup attached to the air comparison type hydrometer in an uncompressed state, the length and width are each 25 mm, and the apparent volume of the test piece is 15 to 16 cm ^3. Use a minimum number.

The foamed sheet of the present invention has a flexural modulus of 50 MPa or more, and is excellent in rigidity such that the foamed sheet does not sag under its own weight when it has one end. In order to have more excellent rigidity, those having a flexural modulus of 60 MPa or more are preferable, and those having a flexural modulus of 75 MPa or more are more preferable. On the other hand, if the flexural modulus is too large, the buffering property is reduced depending on the application, and the content may be damaged when used as a packaging container or the like. Therefore, the flexural modulus is preferably 1000 MPa or less, and 750 MPa or less. It is more preferable, and particularly preferably 500 MPa or less.
The flexural modulus of the foamed sheet is determined by measuring the extrusion direction (MD) and the width direction (TD) in accordance with JIS K 7203 (1982), and adopting a value obtained by arithmetically averaging the obtained values. The test piece is 100 mm long × 25 mm wide × the total thickness of the foam sheet, the tip R of the fulcrum R = 5 (mm), the tip R of the pressurization R = 5 (mm), the distance between the fulcrums is 50 mm, and the bending speed is 10 mm / min. I do. When the resin layer is laminated only on one surface of the foam sheet, the measurement is performed with the resin layer surface facing downward. The value measured in this way is defined as the flexural modulus.

The foam sheet of the present invention preferably has an impact opening strength at a low temperature of 2.5 J or more. If it is less than 2.5 J, there is a problem that it is brittle and cracks when used in a low-temperature atmosphere. In order to have more excellent cold shock resistance, it is preferably 4.0 J or more, more preferably 5.0 J or more. It is preferable that the upper limit is not opened by the impact opening strength, and it is more preferable that the upper limit is 39.2 J or less, which is a limit value of a measurement method described later.
The impact opening strength at low temperature is JIS P8134 (1976), and the test size is a foam sheet having a thickness of mm x 150 mm x 150 mm. Take out below, conduct the test within 3 seconds, and adopt the obtained value.

平均 The average cell diameter of the foam sheet is preferably 100 to 700 µm. When the average cell diameter is less than 100 μm, pleated in the width direction called corrugation occurs on the surface of the foamed sheet, and the thickness of the foamed sheet may become non-uniform. There is a possibility that the thickness cannot be obtained. On the other hand, when the average cell diameter exceeds 700 μm, the surface of the foamed sheet becomes uneven, so that the surface smoothness and appearance may be deteriorated, and the cushioning property may be reduced.

The average bubble diameter is determined as follows.
First, a cross section of the foamed sheet perpendicular to the extrusion direction, that is, a plane defined by a width direction and a thickness direction orthogonal to the extrusion direction is photographed with a microscope, and the thickness t of the foamed layer is measured on the photograph of the cross section. Next, a straight line is drawn in the thickness direction of each cross-sectional photograph, and the number n of all the bubbles in the foam layer that intersects the straight line is counted.
From the thus obtained t and n, the cell diameter (t / n) of the foam layer is calculated for each cross-sectional photograph. Thus, the cell diameter of the foamed layer is measured, and the average value is defined as the average cell diameter of the foamed layer.

The molded article of the present invention is obtained by heating and softening a foamed sheet having a thickness of 1 mm or more and 10 mm or less, or a foamed sheet having a polyethylene-based resin layer on at least one side, and then removing the molded article from a male mold and / or a female mold. Can be obtained by a thermoforming method of molding using a mold. Examples of the thermoforming method include vacuum forming and pressure forming, and furthermore, free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, air slip forming. , Plug-assist molding, plug-assist reverse draw molding, and a molding method combining these. Such a thermoforming method is a preferable method because a molded article can be continuously obtained in a short time.

The molded article of the present invention is excellent in rigidity, cushioning property and impact resistance at low temperatures, and can be suitably used for packaging materials such as trays and containers.

Further, the lining sheet for concrete formwork of the present invention (hereinafter, also simply referred to as "lining sheet") is formed by forming a large number of communication holes in the above-mentioned foam sheet. The lining sheet of the present invention does not hang down when the end is held with one hand, so that it is excellent in workability when it is constructed, specifically, when it is attached to a formwork. In addition, when used as a lining sheet, excess water and air bubbles in the concrete can be discharged to the outside through a number of communication holes, so that water pudging on the concrete surface and air pudging are prevented, and The cement particles and fine aggregate are gathered in the surface layer of the concrete along with the flow, and the concrete structure of the surface layer is densified, so that a beautiful concrete surface is formed. As a concrete construction method, a formwork, a nonwoven fabric, and a lining sheet are laminated in this order by a tucker or a double-sided tape. The nonwoven fabric may or may not be provided as needed.
The shape of the communication hole may be one or more of a + shape, a − shape, a circular shape, an elliptical shape, a triangular shape, a square shape, and a polygonal shape. Above all, a circular shape is preferable from the viewpoint of simple shape and easy formation, and the diameter thereof is such that the unhardened concrete can drain only the excess water without leaking, and when the concrete hardens, the surface becomes uneven due to the holes. The diameter is preferably from 0.1 to 2 mm, more preferably from 0.1 to 1.5 mm, from the viewpoint of preventing the occurrence of the diameter. Further, in the case of the + shape and the − shape, the width is preferably 0.1 to 0.7 mm and the length is 1 to 10 mm. The interval between these communication holes depends on the shape and size of the communication holes, but is preferably 0.5 to 5 mm, more preferably 0.5 to 3 mm. The interval between the communication holes means the shortest distance between adjacent communication holes. The shape and number of the communication holes are appropriately determined according to the properties of the concrete used, for example, the amount of cement, the amount of water, and the size and amount of the aggregate.
As a method of forming the plurality of communication holes, for example, the communication holes are formed by using a press die or a roll in which needle-like objects each having a desired communication hole at the tip are attached at desired intervals. Specifically, in the case of a press die, they are formed by pressing, and in the case of a roll, one of them is a roll to which a large number of needle-like objects are attached, and Formed through the gap. At that time, the press die or roll on the side where a large number of communication holes are formed may be heated as necessary.
In addition, it is preferable that the surface of the lining sheet is formed with a graining process such as a convex pattern from the viewpoint of further finishing the surface of the finished concrete.
The convex shape may be, for example, one or more of a columnar shape, a conical shape, an elliptical cone shape, a triangular prism shape, a triangular pyramid shape, a quadrangular prism shape, a quadrangular pyramid shape, a polygonal prism shape, and a polygonal pyramid shape. Good. Among them, the square pyramid shape is preferable from the viewpoint of excellent drainage. In addition, the convex height is preferably from 0.3 to 1 mm, more preferably from 0.3 to 0.8 mm, from the viewpoint of the strength of the lining sheet and the finish of the obtained concrete surface. In the case of the conical shape, the elliptical cone shape, the triangular pyramid shape, the quadrangular pyramid shape, and the polygonal pyramid shape as the above-mentioned adjacent convex intervals, even if the interval is 0 mm and the adjacent convex shapes are arranged without gaps, the concave portions are formed. Water can be drained from the formation of water. From such a viewpoint, the lower limit of the gap between the convexes is preferably 0 mm or more, more preferably 0.5 mm or more. On the other hand, when the adjacent convex shapes are arranged at intervals, the upper limit is preferably 5 mm or less, and more preferably 3 mm or less, from the viewpoint that the surface of the concrete is finished finely. In addition, in the case of a columnar shape, a triangular prism shape, a quadratic prism shape, and a polygonal column shape, adjacent convex shapes may be arranged at intervals of 0.5 to 5 mm from the viewpoint of the concrete surface being finished cleanly and the viewpoint of drainage. More preferably, they are arranged at intervals of 0.5 to 3 mm. Note that the term “convex interval” refers to the shortest distance between adjacent convex troughs. The shape and number of the above-mentioned convex shapes are appropriately determined according to the properties of the concrete to be used, for example, the amount of cement, the amount of water, and the size and amount of the aggregate.
The above-mentioned graining is formed by pressing with a press mold or passing between rolls, and may be heated as necessary, but a convex pattern is formed from the viewpoint that the convex pattern can be surely formed even if it is shallow. It is preferable to heat the press die or roll on the side to be pressed.
The graining may be performed simultaneously with the formation of the communication hole or before or after the formation of the communication hole, but is preferably performed before the formation of the communication hole because there is less possibility of blocking the communication hole.

The foamed sheet of the present invention has excellent low-temperature impact resistance and is used for various applications, but is an assembly box formed by forming a foamed sheet having a resin layer provided on at least one surface of the foamed sheet by streak extrusion. Has less side deflection in the box. Further, the assembled box is excellent in low-temperature impact resistance such that the box container itself is not cracked even when stored items are stored in the assembled box and dropped at a low temperature. A foamed sheet having resin layers provided on both sides of a foamed sheet is preferable from the viewpoint of reducing the deflection of the side surface of the box and assembling the box with excellent low-temperature impact resistance. In addition, the assembly box made of a foam sheet in which resin layers are provided on both sides of the foam sheet has a resin layer on the inside, making it difficult for scratches or the like to be scratched when putting things in and out, and improving the durability of the assembly box I do. On the other hand, since the resin layer is also formed on the outside, the surface is excellent in smoothness and the printability is also good.

The assembly box is formed from the foam sheet of the present invention by forming an exploded view of the box with a cutting blade for punching, forming a scribe line at a hinge portion, bonding a joint portion, and bending the hinge portion. You. The formation of the above-mentioned ruled line includes, for example, cutting groove processing with a cutter, a needle, or the like, and streak pressing with an iron pressing blade. Among the above, the streak-pressing process is preferable because the balance between the folding resistance and the productivity is excellent, for example, even when the folding is repeated and the hinge is not easily torn. As the streaking process, for example, there is a method in which a hinge is formed by pressing the front end portion against a foamed sheet by heating as necessary with an iron pressing blade for streaking. At that time, it is necessary to attach a cutting blade for punching and a pushing blade for pushing the streak to the press machine, and simultaneously cut out the assembly box developed from the flat foam sheet and push the streak from the viewpoint of productivity. Is desirable. The shape of the assembly box of the present invention includes a rectangular parallelepiped, a cube, and the like, but is not limited thereto.

The foamed sheet of the present invention, which is excellent in rigidity, cushioning property, and impact resistance at low temperature, is used for molded articles, assembly boxes, etc., as well as for corrugated cardboard substitutes, partitioning materials, curing boards for concrete forms, and the like. It is suitable.

Hereinafter, the method for producing the foamed sheet of the present invention will be described.
In the method of the present invention, a specific polyethylene-based resin composition containing L-polyethylene and H-polyethylene is used to extrusion-foam a melt-foamable resin composition obtained by adding a foaming agent to the resin composition, and to obtain an apparent density. A foamed sheet having 70 g / L to 500 g / L and an open cell ratio of 40% or less is obtained.
The foamed sheet of the present invention is, for example, a polyethylene-based resin composition and an additive such as a cell regulator are supplied to an extruder, heated, melted and kneaded, and then a foaming agent is supplied and kneaded with the molten resin composition. The obtained melt-foamable resin composition can be obtained by a known extrusion foaming method in which the composition is extruded from an extruder and foamed.

In such an extrusion foaming method, in the method of the present invention, the polyethylene resin composition contains L-polyethylene and H-polyethylene, has a flexural modulus of 300 MPa or more, a melt tension at 190 ° C. of 15 mN to 400 mN, and A product having a product of the melt tension and the MFR of 100 or more is used.

When the flexural modulus of the polyethylene resin composition constituting the foamed sheet in the method of the present invention is less than 300 MPa, the foamed sheet may have low flexural rigidity. From the viewpoint of efficiently obtaining a foamed sheet having high flexural rigidity, 400 MPa or more is more preferable, and 500 MPa or more is particularly preferable.
On the other hand, the upper limit is preferably 1500 MPa or less, more preferably 1200 MPa or less, and particularly preferably 1000 MPa or less, since a foamed sheet having a high open cell rate may be obtained.
The flexural modulus of the polystyrene resin composition is measured by the method described above.

曲 げ The flexural modulus of the polyethylene resin composition is measured by the above-mentioned measuring method. In addition, a test piece manufactured by direct compression molding is used.

If the melt tension is less than 15 mN, the foamability is reduced, so that a lightweight foam sheet may not be obtained. The polyethylene resin composition has a melt tension of preferably 17 mN or more, more preferably 20 mN or more. On the other hand, when the melt tension exceeds 400 mN, the open cell ratio increases due to the heat generated by the increase in the die pressure during extrusion foaming, and the rigidity and thermoformability may decrease. Therefore, the melt tension is 400 mN or less. And more preferably 300 mN or less.
The melt tension at 190 ° C. of the polyethylene resin composition is measured by the method described above.

In the method of the present invention, the product of the melt tension (mN) and the MFR (g / 10 minutes) of the polyethylene resin composition is 100 (mN · g / 10 minutes) or more, but the appearance is low and the appearance is excellent. 120 (mN · g / 10 min) or more is preferable, and 150 (mN · g / 10 min) or more is more preferable from the viewpoint that the foamed sea is efficiently obtained. On the other hand, the upper limit is preferably 1,000 (mN · g / 10 minutes) or less, more preferably 700 (mN · g / 10 minutes) or less, and still more preferably from the viewpoint of obtaining a low open cell rate. 500 (mN · g / 10 minutes) or less. Further, the MFR is preferably 0.3 g / 10 minutes or more. If it is less than 0.3 g / 10 minutes, the obtained foamed sheet may have an increased open cell ratio, decrease rigidity, and decrease moldability during thermoforming. The MFR of the polyethylene resin composition is more preferably at least 1.0 g / 10 minutes. Further, the MFR is preferably 20.0 g / 10 minutes or less, and if it exceeds this value, it may be extremely difficult to set the melt tension (MT) at 190 ° C. to 15 mN or more.

Ｍ In the method of the present invention, the MFR is measured by the method described above.

In the method of the present invention, the sample to be measured for the flexural modulus, melt tension, and MFR of the polyethylene resin composition is a polyethylene resin composition that forms a foam layer when a foam sheet is extruded from an extruder. Use the one corresponding to the object. Specifically, when the polyethylene resin composition is melt-kneaded using a twin-screw extruder or a kneader as the polyethylene resin composition, the polyethylene resin composition to be charged is added. Is used as a measurement target. In addition, when charged into an extruder, when two or more resins are separately charged as a polyethylene-based resin composition, or when a polyethylene-based resin composition already melt-kneaded and a cell regulator are separately charged, A sample obtained by melt-kneading using a twin-screw extruder or a kneader in advance under the assumed melt-kneading conditions after the introduction of the extruder is used.

に お い て In the method of the present invention, the L-polyethylene and the H-polyethylene include, for example, the aforementioned polyethylene.

In the method of the present invention, the polyethylene resin composition containing L-polyethylene and H-polyethylene has the specific melt tension described above, and the melt tension (A) and MFR (B: g / 10 minutes) In order for the value of the product (A × B) to be a specific value, the melt tension of L-polyethylene is preferably from 20 mN to 400 mN.
Further, the MFR of L-polyethylene is preferably from 0.3 g / 10 min to 20.0 g / 10 min, more preferably from 1.0 g / 10 min to 15.0 g / 10, from the viewpoint of efficiently obtaining a foamed sheet having a low open cell ratio. Minutes is more preferable, and 2.0 g / 10 minutes to 10.0 g / 10 minutes is even more preferable.
In addition, H-polyethylene has an MFR of 1.0 g / 10 min or more, which causes a load on the extruder due to heat generation when the polyethylene composition is melt-kneaded, so that it is not necessary to reduce the discharge amount. Preferably, 2.0 g / 10 min or more is more preferable, and 3.0 g / 10 min or more is further preferable. On the other hand, the upper limit of the MFR is preferably 20.0 g / 10 min or less, more preferably 15.0 g / 10 min or less, from the viewpoint that the foamed sheet does not sag during extrusion and wrinkles do not form on the surface of the foamed sheet. It is more preferably 10.0 g / 10 minutes or less.
In addition, it is preferable that L-polyethylene has the above-described melt tension and H-polyethylene has a melt tension of 2 mN to less than 20 mN from the viewpoint of providing a foamed sheet having no decrease in rigidity due to open cells. As described above, the foamed sheet obtained by the method of the present invention uses L-polyethylene and H-polyethylene having a specific melt tension, a specific flexural modulus, a specific melt tension, a specific melt tension (A), and an MFR ( B: g / 10 minutes), a foamed sheet having low density and excellent rigidity can be obtained.
Further, the density of the H-polyethylene is preferably 940 g / L or more, more preferably 950 g / L or more, and even more preferably 955 g / L or more from the viewpoint of further increasing the rigidity of the foamed sheet.

In the method of the present invention, the polyethylene resin composition is such that the ratio of L-polyethylene and H-polyethylene exceeds 50% by weight based on the total amount of the polyethylene resin composition (100% by weight). It is preferable that the foamed sheet is excellent in flexural rigidity, cold shock resistance, and mold reproducibility, which is the same shape as a mold at the time of thermoforming. If the ratio of H-polyethylene to the total amount of L-polyethylene and H-polyethylene exceeds 90% by weight, the open cell ratio of the foamed sheet tends to increase and the rigidity tends to decrease, and the thermoformability may be reduced. . If the proportion of H-polyethylene is 50% by weight or less, the bending rigidity of the foamed sheet may be reduced. The more preferable ratio of H-polyethylene to the total amount of L-polyethylene and H-polyethylene is more than 50% by weight and not more than 85% by weight, more preferably more than 50% by weight and not more than 80% by weight.

に お い て In the method of the present invention, the polyethylene-based resin composition constituting the foamed sheet may include a polyethylene-based resin other than the above-described L-polyethylene and H-polyethylene. Examples of the polyethylene resin that can be blended with the L-polyethylene and the H-polyethylene in the polyethylene resin composition include, for example, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene-butene- Ethylene component units such as 1 copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer, ethylene-octene-1 copolymer, etc. Ethylene-based copolymers and the like in excess of mol% are mentioned, and these can be used as a mixture of two or more.

The polyethylene-based resin composition constituting the foamed sheet may contain the above-mentioned polyethylene-based resin in addition to L-polyethylene and H-polyethylene. It is preferable that both are contained in a total amount of 70% by weight or more so that the advantage is sufficiently exhibited. The total weight of L-polyethylene and H-polyethylene in the total weight of the polyethylene resin composition is more preferably 80% by weight or more, and the total of both is 90% by weight or more. When the total weight of L-polyethylene and H-polyethylene in the polyethylene-based resin composition is 90% by weight or more, since the mixture is a mixture of polyethylene only, there is an advantage that the recyclability is excellent.

発 泡 The foam sheet of the method of the present invention may contain various additives in the polyethylene resin composition. Examples of the additives include nucleating agents, antioxidants, heat stabilizers, antistatic agents, conductivity-imparting agents, weathering agents, ultraviolet absorbers, functional additives such as flame retardants, inorganic fillers, and the like. .

The polyethylene-based resin composition constituting the foamed sheet of the method of the present invention is a styrene-based resin such as polystyrene, an elastomer such as an ionomer or ethylene propylene rubber, or a polybutene or the like, as long as the purpose and effect of the foamed sheet of the present invention are not impaired. A vinyl chloride resin such as a butene resin or polyvinyl chloride can be added. In that case, the addition amount is preferably 30% by weight or less, more preferably 20% by weight or less, and particularly preferably 10% by weight or less.

発 泡 The foamed sheet obtained by the method of the present invention has an apparent density of 70 g / L to 500 g / L. When the apparent density is within the above range, the sheet has high rigidity such as little droop when the sheet has one end. The apparent density is preferably 70 g / L to 350 g / L in order to have a cushioning property and a high rigidity such as a small sag when the sheet has one end. The apparent density is preferably 200 g / L to 500 g / L in order to obtain a highly rigid foamed sheet having excellent moldability such as mold reproducibility and the same shape as the mold.

発 泡 The foamed sheet obtained by the method of the present invention has an open cell ratio of 40% or less. When the open cell ratio is exceeded, a foamed sheet having low rigidity is obtained. In order to obtain a foam sheet suitable for thermoforming, the open cell ratio is preferably 20% or less.

と In order to keep the open cell ratio of the foamed sheet obtained by the method of the present invention in the above range, for example, a method of adjusting the amount of the cell adjuster, a method of adjusting the extrusion temperature, and the like can be mentioned.

発 泡 As the foaming agent in the method of the present invention, the same inorganic foaming agent, organic physical foaming agent and the like as those conventionally used in the production of polyethylene resin foams can be used. Examples of the inorganic foaming agent include oxygen, nitrogen, carbon dioxide, and air, and examples of the organic physical foaming agent include propane, normal butane, isobutane, normal pentane, isopentane, normal hexane, isohexane, and fats such as cyclohexane. Group hydrocarbons, chlorinated hydrocarbons such as methyl chloride and ethyl chloride, and fluorinated hydrocarbons such as 1,1,1,2, -tetrafluoroethane and 1,1-difluoroethane. Decomposition type foaming agents such as azodicarbonamide can also be used. The above-mentioned foaming agents can be used by mixing two or more kinds. Among these, those containing as a main component normal butane, isobutane, or a mixture thereof, which have good compatibility with the polyethylene-based resin and good foaming properties are particularly preferable.

Further, it is preferable to add a cell regulator to the polyethylene resin composition. Both organic and inorganic foam control agents can be used. Examples of the inorganic air conditioner include metal borates such as zinc borate, magnesium borate, and borax, sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate, and sodium bicarbonate. Examples of the organic foam adjuster include sodium 2,2-methylenebis (4,6-tert-butylphenyl) phosphate, sodium benzoate, calcium benzoate, aluminum benzoate, and sodium stearate. Also, a combination of citric acid and sodium bicarbonate, or a combination of an alkali salt of citric acid and sodium bicarbonate, and the like can be used as the cell regulator. These foam control agents can be used as a mixture of two or more kinds.

添加 The amount of the foaming agent is adjusted according to the type of the foaming agent and the desired density. Further, the amount of the cell regulator added is adjusted according to the target cell diameter. That is, when isobutane is used as the foaming agent and talc is used as the cell regulator, the amount of isobutane added is 1.0 to 5.0 parts by weight, preferably 1.5 to 4.5 parts per 100 parts by weight of the base resin. Parts by weight, more preferably 2.0 to 3.0 parts by weight, and the amount of talc added is 0.1 to 2 parts by weight, preferably 0.2 to 1.5 parts by weight, per 100 parts by weight of the resin. .

The polyethylene-based resin composition further includes, in addition to a cell regulator, functional properties such as a nucleating agent, an antioxidant, a heat stabilizer, an antistatic agent, a conductivity-imparting agent, a weathering agent, an ultraviolet absorber, and a flame retardant. Additives, inorganic fillers and the like can be added.

Next, the foamable molten resin composition is adjusted to an appropriate temperature and then extruded from a die to foam. When a foamed sheet is obtained, a polyethylene resin composition is obtained from the die using a flat die or an annular die. It is obtained by incorporating a foaming agent into the product and extruding and foaming the melt-foamable resin composition. Among the above, it is preferable to use an annular die in that a wide foam sheet can be easily obtained. Specifically, a case where an annular die is used is extruded and foamed from the annular die to temporarily form a tubular foam. Next, the inner surface of the tubular foam is passed through a columnar cooling device, cooled, and then cut open to obtain a foam sheet.

In the method of the present invention, in order to obtain a foamed sheet having a polyethylene resin layer on at least one side, (1) a foamed layer is once produced as described above, and then the resin layer is formed on a production process line or another line. A resin melt to be supplied from another extruder and laminating the resin layer on the foam layer, (2) producing the foam layer once, and forming the resin layer on this production process line or on another line A resin-based resin film for supplying a melt of the same resin as the resin constituting the resin layer from another extruder, and laminating the resin film on the foamed layer. (3) (4) and a method in which a single-layer or multilayer film is introduced on this manufacturing process line or another line and laminated by a hot roll, and a resin layer (single-layer or single-layer And a method for producing a foam sheet having a resin layer) of the layer and the like.

多層 Among these methods, the multi-layer coextrusion method is a preferable method from the viewpoint of cost because the steps are simpler than other methods. Then, a good foam sheet having a high adhesive strength between the foam layer and the resin layer can be obtained. The method of obtaining a foamed sheet by the multi-layer coextrusion method will be described in further detail. (1) A method of coextruding and laminating into a sheet shape using a flat die, and (2) a method of coextruding using a circular die to form a tubular foam. There is a method of manufacturing and then cutting out the tubular foam to form a foam sheet. Among them, a multilayer coextrusion method using an annular die is suitable for obtaining a wide foamed sheet having a width of 1000 mm or more.

When a foamed sheet having a resin layer on the foamed sheet surface is obtained by co-extrusion, the foamed sheet may be laminated at the exit of the die or outside the exit of the die. As the extruder, the annular die, the columnar cooling device, and the device for cutting the cylindrical foam when extruding and foaming using the annular die, known devices that have been conventionally used in the field of extrusion foaming may be used. it can.

Hereinafter, the present invention will be described in more detail with reference to examples.
Examples 1 to 5, Comparative Examples 1 to 4
L-polyethylene (manufactured by Nippon Unicar Co., Ltd., low density polyethylene "NUC8008", MFR: 4.5 g / 10 minutes, density: 917 g / L, hereinafter referred to as "resin A"), H-polyethylene (Idemitsu Petrochemical Co., Ltd.) , A high-density polyethylene “130J”, MFR: 11 g / 10 min, density 955 g / L, hereinafter referred to as “resin B”) mixed at a ratio shown in Table 1 per 100 parts by weight of a polyethylene-based resin composition, and a blowing agent As a mixture of monosodium citrate and sodium bicarbonate as a cell regulator, "Fine Cell Master SSC-PO208K" manufactured by Dainichi Seika Kogyo Co., Ltd. in the ratio shown in Table 1 and supplied to an extruder to be heated and melt-kneaded. Then, the foamed molten resin composition was adjusted to the extrusion temperature shown in Table 1 and introduced into an annular die. A discharge rate 120 kg / time was foamed extruded into a tubular shape. After taking the tubular foam and passing the inner surface of the tubular foam through a cylindrical cooling device (350 mm in diameter, 1500 mm in length) to cool it, the tubular foam is cut open along the extrusion direction to obtain a non-crosslinked foam. The sheet was wound into a roll.

In Example 4, the die was changed to a co-extrusion die, a 50 mm diameter extruder was connected to the die portion, and a polyethylene resin was co-extruded to form a foam sheet having a polyethylene resin layer having a thickness of 25 μm on both sides of the foam sheet. And In Example 5, a foamed sheet having a polyethylene resin layer of 200 μm on each side of the foamed sheet was formed by a co-extrusion method. In Examples 4 and 5, the polyethylene-based resin composition for forming the polyethylene-based resin layer was prepared by blending 70% by weight of resin A and 30% by weight of resin B.

The average cell diameters of Examples 1 to 5 and Comparative Examples 1 to 4 were the results shown below. The average cell diameter of Example 1 is 240 μm, the average cell diameter of Example 2 is 260 μm, the average cell diameter of Example 3 is 550 μm, the average cell diameter of Example 4 is 240 μm, and the average cell diameter of Example 5 is The diameter was 210 μm, the average cell diameter of Comparative Example 1 was 370 μm, the average cell diameter of Comparative Example 2 was 290 μm, the average cell diameter of Comparative Example 3 was 250 μm, and the average cell diameter of Comparative Example 4 was 360 μm. Was.

Example 6
Example 4 except that resin A was used as L-polyethylene and high-density polyethylene “KM690L” (MFR: 8 g / 10 min, density 964 g / L) manufactured by Japan Polyolefin Co., Ltd. at the ratios shown in Table 1 as H-polyethylene. Similarly to the above, a non-crosslinked foamed sheet having a polyethylene resin layer having a thickness of 25 μm on both sides of the foamed sheet was obtained. When the obtained foam sheet and the foam sheet of Example 4 were compared, it was found that the flexural modulus was improved. The average bubble diameter was 210 μm.

Example 7
The polyethylene resin constituting the resin layer was 70% by weight of resin A and 30% by weight of resin B. An antistatic agent (Pelestat 300 (polyether-polypropylene block, manufactured by Sanyo Chemical Industries, Ltd.) was used per 100 parts by weight of the polyethylene resin. Non-crosslinked foam having a 7 μm-thick polyethylene-based resin layer on both sides of a foam sheet in the same manner as in Example 6 except that 15 parts by weight of a copolymer, MFR: 100 g / 10 min or more, melting point: 136 ° C.) was added. The foamed sheet had an average cell diameter of 220 μm, and the foamed sheet had a surface resistivity of 3.0 × 10 ¹⁰ Ω. Was measured as described above.

Example 8
In the same manner as in Example 1, a non-crosslinked foamed sheet was obtained under the conditions shown in Table 1. Table 2 shows the properties of the obtained foamed sheet.
Using the obtained foamed sheet, a lining sheet for a concrete form having a number of communicating holes was formed by the method described below.
Heating rolls and rubber rolls whose surfaces have been processed so that quadrangular pyramids having a height of 0.5 mm and a square of 1.2 mm on each side are formed at intervals of 0 mm as convex patterns. While rotating the roll, the foamed sheet was passed between the rolls to form a convex pattern.
Further, while rotating a roll having a large number of needles and a rubber roll formed as a communication hole having a circular shape having a diameter of 0.2 mm and an interval of 2 mm, the foamed sheet is rolled over the roll. A communication hole was formed by passing through the gap.
The obtained lining sheet was cut into a size of 910 mm in width × 1820 mm in length, and laminated by a tucker in the order of a formwork and a lining sheet. At this time, the lining sheet was arranged so that the convex pattern became the concrete casting surface, and used as a concrete formwork. The surface of the finished concrete was beautiful with the lining sheet.

The measurement of the surface resistivity is based on JIS-K6911 (1979), and employs the surface resistance value 1 minute after applying the voltage of 500 V with “TR8601” manufactured by Takeda Riken Kogyo Co., Ltd. Then, the surface resistivity was determined from the average value of the obtained measured values.
Specifically, three test pieces (100 mm long × 100 mm wide × thickness: test piece thickness) were cut out from the obtained foamed sheet at regular intervals in the width direction perpendicular to the extrusion direction of the foamed sheet. After leaving the piece in an atmosphere of 23 ° C. and 50% humidity for 24 hours, the surface resistivity was measured, and the average value of the measured values was defined as the surface resistivity. Furthermore, after performing the following condition adjustment of the test piece, it was left for 1 hour in an atmosphere of 23 ° C. and a humidity of 50%, and then the surface resistivity was measured. As a result, the surface resistivity was not changed to 3.0 × 10 ¹⁰ Ω.
[Adjustment of test piece condition]
"BRANSONIC 220" manufactured by Branson was used as an ultrasonic cleaning device. First, 500 ml of ethanol was weighed into a 500 ml beaker, and the temperature of the ethanol was maintained at 23 ° C. Next, the test piece was immersed in ethanol having a purity of 99.5 vol% or more by submerging the test piece in a beaker using a wire mesh. Thereafter, the beaker in which the test piece was submerged was covered with a foil, and the beaker was put into a concave storage portion of the ultrasonic cleaning device containing 1.7 liters of water at 23 ° C., and allowed to stand. The cleaning device was turned on and cleaning was started. After an elapse of 8 hours from the start of the washing and further after an elapse of 16 hours from the start of the washing, an operation of adding ethanol at 23 ° C. was performed so that the ethanol in the beaker became 500 ml. In addition, this ethanol addition operation is an operation of replenishing ethanol because the amount of ethanol is reduced by volatilization due to the ultrasonic cleaning and the amount of ethanol is initially present in the beaker. After 24 hours from the start of the cleaning, the ultrasonic cleaning device was stopped, the test piece was taken out of the beaker, and this test piece was immediately left standing in an atmosphere of a relative humidity of 30% and a temperature of 30 ° C. for 36 hours to be dried. Conditioning of the test piece was completed.

Comparative Example 5
A non-crosslinked foamed sheet was obtained in the same manner as in Example 1 except that L-polyethylene was manufactured by Nippon Unicar Co., Ltd., and low-density polyethylene "NUC8350" (MFR: 20 g / 10 min, density 916 g / L). The average bubble diameter was 340 μm.

(4) The foamed sheets obtained in Examples 1 to 7 had little droop when holding one end of the foamed sheet.

The foamed sheets obtained in Comparative Example 1, Comparative Example 4 and Comparative Example 5 have less sagging when holding one end of the foamed sheet, but when extruded, crystallized products are formed due to the influence of high-density polyethylene. The surface of the foam sheet was uneven and the appearance was poor, and even if the amount of the foaming agent was increased, a foam sheet having a low density and a smooth surface could not be obtained.
The foamed sheets obtained in Comparative Examples 2 and 3 had a large sag when holding one end of the foamed sheet.

Using the foamed sheet wound in a roll shape obtained in Examples 1, 2, 4, 7 and Comparative Examples 1, 3, 4, and 5, the surface of the foamed sheet was heated in a heating furnace as shown in Table 2. The highest value, the foam sheet is heated and softened, the component size is 20 mm × 55 mm × 80 mm in length, and the shape of the opening is rectangular and the component tray has a partition of 5 mm in height, Thermoforming was performed using a mold having an outer size of 25 mm × width 200 mm × length 300 mm and an inner size of depth 20 mm × width 170 mm × length 270 mm.
The molded articles obtained by using the foamed sheets of Examples 1, 2, 4 and 7 had the same shape as the metal mold, and were good without thickness and thickness.
The molded articles obtained using the foamed sheets of Comparative Examples 1, 4 and 5 did not have the same shape as the mold. The molded article obtained by using the foamed sheet of Comparative Example 3 had the same shape as the metal mold, but the shape of the molded article was changed when parts were inserted.

Using the foamed sheet wound in a roll shape obtained in Examples 5 and 6, a stretching ratio of 1.04 (width after heating / width before heating) was measured by a heating stretching apparatus capable of sandwiching the end of the foamed sheet. ) To obtain a foamed sheet having a length of 2000 mm.
When the warpage was measured by the method described above, the warp of the foam sheet of Example 5 was 2%, and the warp of the foam sheet of Example 6 was 3%.
Since the warpage of the obtained foamed sheet was 5% or less, the stacking height could be reduced when stacked.

The foamed sheets obtained in Examples 5 and 6 were cut into a JIS Z 1507 (1989) grooving shape and a box shape of code 0201 (length 430 mm, width 250 mm, height 230 mm). In the above-mentioned box scribe line, the height of the push blade at the center is 0.1 mm higher than the height of the push blades at both ends using three push blades, and the push blade at the center and the push blade at both ends are used. Were formed so that the length direction was the extrusion direction (MD direction) of the foam sheet and the scribe line was on the outside.
The assembly boxes using the foam sheets of Examples 5 and 6 were excellent in surface smoothness. In particular, in Example 5, when the contents were put in an assembly box and stacked, the deflection was small.

The flexural modulus of the polyethylene resin composition (mixture of L-polyethylene and H-polyethylene) used for extrusion foaming, the melt tension at 190 ° C. (A), the value of MFR (B), and the melt tension (A) The value of the product ((A) × (B)) of MFR (B) is also shown in Table 1. Evaluation of basis weight, apparent density (the apparent density in Table 2 is the apparent density of the foamed layer when at least one side has a resin layer), thickness, open cell ratio, flexural modulus, and rigidity of the obtained foamed sheet. Table 2 shows the results of the evaluation of the opening strength at low temperature, the impact resistance at low temperature, the evaluation of the appearance, and the temperature of the foamed sheet surface.

In Table 1, the values of the flexural modulus, the melt tension at 190 ° C. (A), and the MFR (B) are as follows. Is a value obtained by using a non-foamed resin after defoaming. When there is no resin layer, the value is obtained by using a non-foamed resin by defoaming the foamed sheet as it is with a hot press and a cooling press.
In addition, although not shown in the table, the bending elastic modulus, the melt tension at 190 ° C., and the MFR of the polyethylene resin composition to be charged into the extruder were measured. As a result, the foamed sheet was defoamed and a non-foamed resin was used. The value was the same as the obtained value.
In addition, the test piece was prepared using a resin obtained by melt-kneading H-polyethylene and L-polyethylene at 190 ° C. in advance using a twin-screw extruder.

Evaluation of rigidity, evaluation of low-temperature impact resistance and evaluation of appearance in Table 2 were performed as follows.
<Evaluation of rigidity>
The evaluation was based on the value of the flexural modulus.
・ ・ ・: 150 MPa or more ○: 50 MPa to less than 150 MPa ×: less than 50 MPa <Evaluation of low-temperature impact resistance>
The evaluation was based on the value of the drilling strength at a low temperature.
◎: 10.0 J or more ○: 2.5 J or more and less than 10.0 J ×: less than 2.5 J <Evaluation of appearance>
The surface of the foam sheet was visually evaluated.
・ ・ ・: Good appearance with no irregularities on the surface x: bad appearance with irregularities on the surface

Claims (11)

An extruded polyethylene resin foam sheet having an apparent density of 70 g / L to 350 g / L and an open cell rate of 40% or less, wherein the polyethylene resin composition constituting the foam sheet has a flexural modulus of 300 MPa or more, The melt tension (A) at 190 ° C. of the composition is 15 mN to 400 mN, and the product (A × B) of the melt tension (A) and the MFR (B: g / 10 minutes) of the resin composition is 100. An extruded polyethylene resin foam sheet characterized by the above. The polyethylene resin according to claim 1, wherein the polyethylene resin composition constituting the extruded polyethylene resin foam sheet includes polyethylene having a density of 930 g / L or less and polyethylene having a density of more than 930 g / L and 970 g / L or less. Extruded foam sheet. When the polyethylene resin composition constituting the extruded polyethylene resin foam sheet is (i) 10% by weight or more and less than 50% by weight of polyethylene having a density of 930 g / L or less, (ii) the density exceeds 930 g / L and 970 g / L. The extruded polyethylene resin foam sheet according to claim 1 or 2, comprising more than 50% by weight and not more than 90% by weight of the following polyethylene. The polyethylene resin extruded foam sheet according to any one of claims 1 to 3, having a polyethylene resin layer of 5 µm or more on at least one surface. The extruded polyethylene resin foam sheet according to any one of claims 1 to 4, wherein the overall thickness is 1 mm or more and 10 mm or less. 5. The extruded polyethylene resin sheet according to claim 4, wherein the polyethylene resin constituting the polyethylene resin layer contains an antistatic agent, and the resin layer has semipermanent antistatic performance. The extruded polyethylene resin foam sheet according to any one of claims 1 to 6, wherein the warpage is 5% or less. A molded product obtained by thermoforming the extruded polyethylene resin foam sheet according to any one of claims 1 to 7. An assembly box comprising the extruded polyethylene resin foam sheet according to any one of claims 1 to 7. A lining sheet for a concrete form, comprising a plurality of communicating holes formed in the extruded polyethylene resin foam sheet according to any one of claims 1 to 7. Method for producing a foamed sheet having an apparent density of 70 g / L to 500 g / L and an open cell ratio of 40% or less obtained by extrusion foaming a melt-foamable resin composition obtained by adding a foaming agent to a polyethylene-based resin composition. Wherein the resin composition comprises a polyethylene having a density of 930 g / L or less and a polyethylene having a density of more than 930 g / L and 970 g / L, and a flexural modulus of 300 MPa or more and 190 ° C. A polyethylene-based resin having a melt tension (A) of 15 mN to 400 mN and a product (A × B) of the melt tension (A) and the MFR (B: g / 10 minutes) of 100 or more. A method for producing an extruded foam sheet.