JP4276488B2 - Polyethylene resin extruded foam sheet, molded body of foam sheet, assembly box, lining sheet for concrete formwork, and method for producing foam sheet - Google Patents

Description

  The present invention relates to a polyethylene resin extruded foam sheet, a molded body obtained by thermoforming the foamed sheet, an assembly box obtained from the foamed sheet, and a liner sheet for a concrete mold formed by forming a large number of communication holes in the extruded foam sheet. And a method for producing a foam sheet.

  Conventionally, a polyethylene-based resin extruded foam has been used in various fields as a cushioning material or a packaging material. 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 the second DSC curve obtained by differential scanning calorimetry having a specific temperature relationship. ing. Patent Document 2 discloses a foam using high-density polyethylene modified with a peroxide, and Patent Document 3 is a mixture of low-density polyethylene and high-density polyethylene. A foam using 70% by weight is disclosed.

JP-A-6-184346 Special table 2001-505605 gazette JP 56-28837 A

  However, the foamed sheet described in Patent Document 1 has a problem that it has low rigidity and hangs down when having an end on one side of the sheet. Further, the foam described in Patent Document 2 has a problem that it is expensive because the manufacturing process becomes complicated with the addition and use of peroxide. Furthermore, since the foam described in Patent Document 3 has a high open cell ratio, it has a problem of lack of rigidity and poor moldability.

  The present invention has been made in view of such conventional problems, and provides a polyethylene resin extruded foam sheet having high rigidity, a smooth surface and good appearance, excellent impact resistance at low temperatures, and inexpensive. Objective. The present invention also provides a molded body formed by thermoforming the extruded foam sheet, an assembly box obtained from the extruded foam sheet, and a concrete form liner sheet formed by forming a large number of communication holes in the extruded foam sheet. Objective. 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 the flexural modulus of the polyethylene resin composition constituting the foam sheet is 300 MPa or more. The melt tension (A) at 190 ° C. of the resin 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. A polyethylene resin extruded foam sheet characterized by having a value of 100 or more,
(2) The above (1) description, wherein the polyethylene-based resin composition constituting the polyethylene-based resin extruded 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 not more than 970 g / L. Polyethylene resin extruded foam sheet,
(3) The polyethylene resin composition constituting the polyethylene resin extruded foam sheet has (i) a density of not less than 930 g / L and not less than 10% by weight and less than 50% by weight of polyethylene, and (ii) a density exceeding 930 g / L. The polyethylene-based resin extruded foam sheet according to the above (1) or (2), comprising more than 50% by weight of polyethylene of 970 g / L or less and 90% by weight or less,
(4) The polyethylene resin extruded foam 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 polyethylene-based resin extruded foam sheet according to any one of (1) to (4), wherein the total thickness is 1 mm or more and 10 mm or less,
(6) The polyethylene resin extruded foam according to (4) above, wherein the polyethylene resin constituting the polyethylene resin layer contains an antistatic agent, and the resin layer has a semi-permanent antistatic performance. Sheet,
(7) The polyethylene-based resin extruded foam sheet according to any one of (1) to (6), wherein the warpage is 5% or less,
(8) A molded body obtained by thermoforming the polyethylene resin extruded foam sheet according to any one of (1) to (7) above,
(9) An assembly box comprising the polyethylene resin extruded foam sheet according to any one of (1) to (7) above,
(10) A concrete form liner sheet formed by forming a large number of communication holes in the polyethylene resin extruded 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 resin composition 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 not more than 970 g / L, and a flexural modulus of 300 MPa or more, The melt tension (A) at 190 ° C. is 15 to 400 mN, and the product (A × B) of the melt tension (A) and MFR (B: g / 10 minutes) is 100 or more. Production method of polyethylene resin extruded foam sheet,
Is a summary.

The polyethylene resin extruded foam sheet of the present invention is a polyethylene resin extruded foam 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 it exhibits specific physical property values, it has high rigidity such as low sag when having one end of the foam sheet, smooth surface, good appearance, and excellent impact resistance at low temperatures.
The foam 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 not more than 970 g / L, so that the surface of the foam sheet is smooth and has 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 not more than 970 g / L. In addition, it is excellent in mold reproducibility, and further excellent in mold reproducibility, which is the same shape as the mold in thermoforming.
Moreover, 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.
Moreover, the foamed sheet of this invention is suitably used for an assembly box or a partition material, when a thickness is 1 mm or more and 10 mm or less, such as thermoforming containers and trays.
The foamed 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 is free from dust, and is used for food and machinery. The foam sheet is suitable for parts, and when the foam sheet comes into contact with the package, the surface of the package is not whitened or sticky, and the antistatic performance of the foam sheet is maintained. In addition, the molded product of the present invention obtained by thermoforming a foam sheet and the assembly box of the present invention obtained from the foam sheet are excellent in rigidity, surface smoothness, and impact resistance at low temperatures, and are suitable as packaging containers. .
In addition, a concrete formwork lining sheet formed with a number of communicating holes in a foam sheet does not hang down when its end is held with one hand, so workability when installing to a formwork, specifically Is excellent. Moreover, when used as a lining sheet, a beautiful concrete surface is formed.
According to the method of the present invention, it is possible to efficiently produce a polyethylene resin extruded foam sheet having a low open cell ratio and excellent rigidity.

  The polyethylene resin extruded foam sheet of the present invention (hereinafter sometimes simply referred to as “foam sheet”) has a flexural modulus of 300 MPa or more of the polyethylene resin composition constituting the foam sheet, and the resin composition The melt tension (A) at 190 ° C. 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 (mN).・ G / 10 minutes) or more.

If the flexural modulus of the polyethylene-based resin composition constituting the foamed sheet is less than 300 MPa, the foamed sheet may have a low bending 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 value is that if the bending elastic modulus is too high, the buffering property is lowered, and the content may be damaged when used as a packaging container or the like. Therefore, the bending elastic modulus is preferably 1500 MPa or less, and 1200 MPa. The following is more preferable, and 1000 MPa or less is particularly preferable.
The flexural modulus of the polyethylene resin composition is JIS K7171 (1994), using a test piece having a size of thickness 2 mm × width 25 mm × length 40 mm, a span distance of 30 mm, and an indenter radius R ₁ of The value measured and calculated under the conditions of 5.0 mm, the radius of support R ₂ is 2.0 mm, and the test speed is 2 mm / min is adopted. When the resin layer is provided, the test piece is defoamed with a heating press or a cooling press using a foam sheet from which the resin layer has been removed (hereinafter also simply referred to as “foam layer”). A non-foamed resin sheet is used, and a resin sheet laminated by a heat press and a cooling press so as to have the thickness of the test piece described above is used.

  Moreover, the melt tension (A) at 190 ° C. of the resin composition is 15 mN to 400 mN. Such a foam sheet can be formed by putting a polyethylene resin composition having a melt tension of 15 mN to 400 mN into an extruder, and extruding the foamed resin composition as a melt foamable resin composition. If the melt tension is less than 15 mN, the foamability may be reduced, so that it may not be a lightweight foam sheet, or when thermoformed, the foam sheet may have a low thermoformability such as poor expansion 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 exceeds 400 mN, since it is easy to form open cells by foaming due to an increase in the die pressure when extrusion foaming, the melt tension is 400 mN or less because there is a possibility that rigidity and thermoformability may be lowered. It is preferable that it is 300 mN or less.

The melt tension at 190 ° C. of the polyethylene resin composition can be measured by, for example, a melt tension tester type II manufactured by Toyo Seiki Seisakusho Co., 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 into a string from the nozzle at a resin temperature of 190 ° C. and an extrusion piston speed of 10 mm / min. Then, after the string-like object is hung on a tension detection pulley having a diameter of 45 mm, the stringing speed is about 5 rpm / second (string-like object stringing acceleration: 1.3 × 10 ⁻² m / second ² ). While gradually increasing the diameter, scrape with a scraping roller having a diameter of 50 mm.

  A specific method for obtaining the melt tension of the resin composition is to measure the melt tension of the string-like material detected by a detector that performs scooping at a scooping speed of 100 (rpm) and is connected to a tension detecting pulley over time. When measured and shown in a chart with melt tension (mN) on the vertical axis and time (seconds) on the horizontal axis, a graph with amplitude is obtained. Next, the median value of the amplitude of the stable portion is taken. In this specification, this value is adopted as the melt tension of the resin composition. Note that the specific amplitude that occurs infrequently is ignored.

  However, when the string-like material hung on the tension detection pulley is cut up to 100 (rpm), the stringing speed when the string-like material is cut is determined as R (rpm). Next, at a constant scraping speed of R × 0.7 (rpm), the median is adopted as the melt tension from the graph obtained in the same manner as described above.

  The product of the melt tension (mN) and MFR (g / 10 min) of the polyethylene resin composition is 100 (mN · g / 1 min) or more. 110 or more are preferable, 120 or more are more preferable, and 150 or more are more preferable from a viewpoint of being excellent in foamability, such as a low-density foam sheet being easily obtained. On the other hand, the upper limit is preferably 1000 or less, more preferably 700 or less, and even more preferably 500 or less, from the viewpoint of excellent appearance such as the surface of the foam sheet having no irregularities.

  Further, the MFR is preferably 0.3 g / 10 min or more. If it is less than 0.3 g / 10 minutes, the foamed sheet is likely to be open-celled due to an increase in the die pressure during extrusion foaming, which may reduce the bending rigidity. There is a possibility that thermoformability such as poor elongation is lowered. 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 more preferable. On the other hand, the upper limit of MFR is preferably 20.0 g / 10 min or less. If this value is exceeded, it becomes extremely difficult to make the melt tension (MT) at 190 ° C. 15 mN or more, and a low-density foam sheet is obtained. There is a possibility that it will not become a lightweight foamed sheet, and there is a possibility that thermoformability will be lowered. From such a viewpoint, 15.0 g / 10 min or less is more preferable, and 10.0 g / 10 min or less is more preferable. Such a foamed sheet can be formed by putting a polyethylene resin composition having an MFR within the above range into an extruder and extrusion-foaming it as a melt-foamable resin composition.

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

In addition, when the polyethylene-type resin composition used by the measurement of the said melt tension and MFR has a resin layer, it defoams with a heating press and a cooling press using a foaming layer which removed the resin layer, and is non-foaming. Resin will be used.
The foamed sheet of the present invention comprises 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”). -A polyethylene-based resin composition that may be abbreviated as "polyethylene" is preferable 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. Among them, 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 0.3 g / 10 min to 20.0 g / 10 min from the viewpoint of improving the appearance such that the surface of the foamed sheet has no irregularities, and 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 more preferable. In addition, the melt tension of L-polyethylene is preferably 20 mN to 400 mN from the viewpoint of a low-density foam sheet.

Moreover, as said H-polyethylene, what is called a linear polyethylene is mentioned, Specifically, a high density polyethylene etc. are mentioned. The MFR of the above-mentioned H-polyethylene is preferably 1.0 g / 10 minutes or more, more preferably 2.0 g / 10 minutes or more, and more preferably 3.0 g / 10 minutes or more from the viewpoint of improving the appearance such as no irregularities on the surface. Is more preferable. On the other hand, the upper limit of MFR is preferably 20.0 g / 10 min or less, more preferably 15.0 g / 10 min or less, from the viewpoint of improving impact resistance at low temperatures without reducing rigidity. 0 g / 10 min or less is more preferable.
In addition, it is preferable that the melt tension of H-polyethylene is 2 mN or more and less than 20 mN from the viewpoint of forming a foamed sheet that does not have a decrease in rigidity due to open cell formation. 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 MFR (B: g / 10 minutes), a foamed sheet having a low density and excellent rigidity is obtained.
Furthermore, the density of the H-polyethylene described above is preferably 940 g / L or more, more preferably 950 g / L or more, and further 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 proportion of H-polyethylene exceeds 90% by weight with respect to 100% of the total amount of the polyethylene resin composition. % To be less than%, the rigidity of the foam sheet is low when holding one end, impact resistance at low temperatures, and the same mold as the mold when thermoforming It is preferable for improving mold reproducibility. When the ratio of H-polyethylene with respect to the total amount of the polyethylene resin composition exceeds 90% by weight, the open cell ratio of the foamed sheet and the apparent density are likely to increase, and the thermoformability decreases when thermoforming. There is a fear. Moreover, when the ratio of H-polyethylene is 50 weight% or less, there exists a possibility that the rigidity of a foamed sheet may fall. A more preferable ratio of H-polyethylene to the total amount of the polyethylene-based resin composition is more than 50% by weight and 85% by weight or less, and more preferably more than 50% by weight and 80% by weight or less.

  The polyethylene resin composition constituting the foamed sheet may contain a polyethylene resin other than the L-polyethylene and H-polyethylene. Examples of the polyethylene resin that can be blended with L-polyethylene and H-polyethylene in the polyethylene resin composition include 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. % Of ethylene-based copolymers and the like, and two or more of them can be used in combination.

  The polyethylene-based resin composition constituting the foamed sheet may contain the above-described polyethylene-based resin in addition to L-polyethylene and H-polyethylene, but L-polyethylene and H-polyethylene are used. It is preferable that both of them are contained in a total 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 in the polyethylene-based 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, there is an advantage of excellent recyclability because it is a mixture of polyethylene only.

  The foamed sheet of the present invention may contain various additives in the polyethylene resin composition. Examples of additives include nucleating agents, antioxidants, heat stabilizers, antistatic agents, conductivity-imparting agents, weathering agents, UV 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 is 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 purpose and effect of the foamed sheet of the present invention are not impaired. A vinyl chloride resin such as a vinyl resin or polyvinyl chloride can be added. In this 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 with respect to 100% by weight of the polyethylene resin composition.

  The overall thickness of the foamed sheet of the present invention is preferably 1 mm to 50 mm, more preferably 1 mm to 40 mm, and even more preferably 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 for 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 foam sheet may have insufficient rigidity and cushioning properties. From this 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 thick, the foamed sheet preferably has a thickness of 8 mm or less, and may be 6 mm or less because there is a risk of poor handling when processing or molding a partition material or an assembly box. More preferred. In particular, when thermoforming, 3 mm or less is preferable from the viewpoint of achieving the same shape as the mold.

  When the foamed sheet has a thickness exceeding 50 mm, a laminated foamed sheet obtained by adhering the foamed sheet to two or more layers can be obtained. Further, when the foamed sheet has a thickness of less than 50 mm, it may be a laminated foamed sheet bonded to two or more layers. In the case of a laminated foam sheet having two or more layers, if the same foam sheet can be laminated, foam sheets having different thicknesses, bubble diameters, and apparent densities, and further colors, base resins, functional additives, etc. Different types of foam sheets can be laminated.

In addition, although the whole thickness of the foam sheet said by this specification may have a polyethylene-type resin layer on at least one side so that it may mention later, in that case, the said thickness means the whole thickness containing a resin layer. The thickness of the foam sheet is measured as follows.
First, the foam sheet is cut perpendicular to the direction perpendicular to the extrusion direction, 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 at each photographed point is measured, The arithmetic average value of the obtained values is taken as the thickness of the foamed sheet. Also, when having a polyethylene-based resin layer on at least one side of the foam sheet, at each point taken as described above, the thickness of the entire foam sheet and the thickness of the resin layer are measured, and the arithmetic average of the obtained measured values The value is the thickness of the entire foamed sheet and each 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 taken as the thickness of the foam layer.

  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 foamed sheet is preferably 10 μm or more in order to further increase the rigidity such as less drooping when holding the end of one side of the sheet, and more preferably 15 μm or more in terms of further improving the rigidity. preferable. The thicker the resin layer is, the higher the rigidity is. However, if the thickness is too thick, the weight may increase and the lightness may be deteriorated. Therefore, the thickness of the resin layer is preferably 500 μm or less, and more preferably 400 μm or less. In particular, when a polyethylene resin layer is provided on both surfaces, 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.

  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, although there is no restriction | limiting in particular in the upper limit of MFR, Usually, it is 30.0 g / 10min or less.

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

  Examples of the polyethylene resin constituting the resin layer include, for example, ethylene homopolymers such as high-density polyethylene, low-density polyethylene, and linear low-density polyethylene, ethylene-vinyl acetate copolymers, ethylene-propylene copolymers, Ethylene-propylene-butene-1 copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer, ethylene-octene-1 copolymer, etc. And an ethylene copolymer, and a mixture of two or more of these.

  The 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, and the like within a range that does not impair the purpose and effect of the foam sheet of the present invention. A vinyl chloride resin such as 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 polyethylene-based resin layer described above includes, for example, functional additives such as nucleating agents, antioxidants, heat stabilizers, antistatic agents, conductivity imparting agents, weathering agents, ultraviolet absorbers, flame retardants, and inorganic fillers. Various additives such as these may be contained.

  When the foamed sheet of the present invention has a resin layer on at least one side, 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 this specification, the antistatic agent is a resin having a molecular weight of at least 300 daltons, preferably 300 to 300000 daltons, more preferably 600 to 15000 daltons, and a surface resistivity of less than 1 × 10 ¹² Ω. Indicates. In addition, the antistatic agent in the present specification 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 molecular weight of the antistatic agent is about 500,000 daltons.

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

  In the foam sheet of the present invention, when the antistatic agent described above is used, when the foam sheet comes into contact with the package body, the surface of the package body is not whitened or sticky, and the antistatic performance of the foam sheet. Is something that lasts.

In the present specification, the antistatic agent is specifically an ionomer such as polyethylene oxide, polypropylene oxide, polyethylene glycol, polyether, polyester amide, polyether ester amide, ethylene-methacrylic acid copolymer, or polyethylene glycol methacrylate. Among one or a mixture of two or more selected from quaternary ammonium salts such as polymers, or two or more copolymers, and copolymers thereof with other resins such as polypropylene, etc. Examples include resins that have polar groups in the molecular chain and are capable of complexing or solvating inorganic salts or low molecular weight organic protonic acid salts. There may be.
The upper limit of the melting point of the antistatic agent is about 270 ° C., and the lower limit is about 70 ° C.

Among the antistatic agents used in the present invention, in particular, polyether ester amide, polyether, and a copolymer or mixture of one or more kinds of antistatic agents and other resins such as polypropylene and polyamide as a main component. It is preferable to use what to do. In this specification, the main component means that it is contained in a proportion of 50% by weight or more, preferably 75% by weight or more, and more preferably 85% by weight or more. By forming a network structure using these antistatic agents, a resin layer having a surface resistivity of 1 × 10 ¹³ (Ω) or less can be easily formed.

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

  The melting point of the polyetheresteramide is preferably 230 ° C. or less, and more preferably 200 ° C. or less. When the melting point 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 may be deteriorated. . Moreover, when laminating | stacking by a coextrusion method, although depending on the lamination amount of a resin layer, there exists a possibility that a foam layer may become an open-cell structure and rigidity may fall.

The antistatic performance as used herein refers to a surface resistivity of 1 × 10 ⁸ (Ω) to 1 × 10 ¹³ (Ω).

The semi-permanent antistatic performance in this specification means having antistatic performance even after washing, and specifically, a test piece (length 100 mm × width 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 foam sheet, and the test piece was immersed in ethanol and washed with an ultrasonic cleaner for 24 hours, and then 30 ° C. The sample was dried for 36 hours in an atmosphere of 30% humidity, and then left for 1 hour in an atmosphere of 23 ° C. and 50% humidity. Then, the surface resistance was measured, and the surface resistivity was calculated from the average value 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 warpage within 5%, whether it has a polyethylene-based resin layer on at least one side or not. Foamed sheets with a warpage of 5% or less are excellent in handleability, such as being able to reduce the stacking height when they are stacked and not having to bother to open and process warped foamed sheets. From such a viewpoint, 4% or less is more preferable, 3% or less is more preferable, and 0% is particularly preferable. For this reason, it can be widely used in the field of plate materials such as panels, partition materials and box materials.

The warp described above is obtained by the following measuring 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 foam sheet cannot be cut into the above-mentioned size, cut it into a square with 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 convex upward. At this time, a total of four points from the lower surface of the sample to the upper surface of the table on which the sample is placed are measured at the four central portions of the four sides of the square sample. Furthermore, the sample is turned over and the sample is placed on a horizontal table so that the warpage is convex downward. Similarly, at the corners of the square (four points), a total of four points are measured from the lower surface of the sample to the upper surface of the table on which the sample is placed. The largest numerical value L (mm) is adopted among the total of eight measurement results obtained as described above, and the ratio of warpage is obtained from the following equation.

  Warpage (%) = L (mm) / (Length of one side of square (mm)) × 100 (1)

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

The foamed sheet of the present invention has an apparent density of 70 to 350 g / L regardless of whether the thickness exceeds 10 mm or a foamed sheet of 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 that when the end of one side of the sheet is held, the drooping is small. In order for the foam sheet to have excellent rigidity and better heat insulation, the lower limit of the apparent density of the foam sheet is preferably 95 g / L or more, and more preferably 100 g / L or more. Moreover, it is preferable that the upper limit of the apparent density of a foam sheet is 320 g / L or less, and it is more preferable that it is 300 g / L or less.
In addition, the apparent density of a foam sheet as used in this specification means the apparent density of a foam layer.

In this specification, the apparent density of the foam sheet is measured as follows.
The thickness of the foam sheet is measured by the method described above. In the case of having a polyethylene resin layer on at least one surface, the thickness of the resin layer is also measured in advance. Further, the basis weight of the foam sheet and the basis weight of the resin layer are measured.

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

In the case of having a resin layer, the basis weight (g / m ² ) of the resin layer is obtained by multiplying the thickness of the resin layer measured in advance by the total weight constituting the resin layer and the density obtained from the volume, and in unit conversion To find out.

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, in units (g / cm ³ ). . When having a resin layer on at least one side, a value obtained by dividing the basis weight of the foam layer by subtracting the basis weight of all the resin layers from the basis weight of the foam sheet by the thickness of the foam layer obtained by subtracting the thickness of all the resin layers. Is calculated in units (g / cm ³ ).

  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 decreases even when the polyethylene resin layer is provided on at least one side. Moreover, when obtaining the molded object formed by heat-softening a foam sheet and shape | molding with a metal mold | die, it is preferable that the open cell ratio of a foam sheet is 20% or less.

The open cell ratio of foamed sheet in the present specification: S (%) is measured using an air comparison type hydrometer 930 type manufactured by Toshiba Beckman Co., Ltd. in accordance with Procedure C described in ASTM D2856-70. The actual volume of the foamed sheet (the sum of the volume of the closed cells and the volume of the resin portion): a value calculated from the following equation (2) from Vx (L).
The sample can be used as it is even in a foam 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 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 foam sheet and the weight W (g) of the foam
Can be obtained from a sample obtained by performing an operation of defoaming the foamed sheet with a hot press and then cooling.

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

The foamed sheet of the present invention has a flexural modulus of 50 MPa or more, and is excellent in rigidity, such as not hanging down by its own weight when it has one end of the foamed sheet. In order to have more excellent rigidity, those having a flexural modulus of 60 MPa or more are preferable, and those having a bending modulus of 75 MPa or more are more preferable. On the other hand, if the flexural modulus is too large, the buffering properties may be reduced depending on the application, and the contents may be damaged when used as a packaging container or the like. Therefore, the flexural modulus is preferably 1000 MPa or less, preferably 750 MPa or less. More preferably, 500 MPa or less is particularly preferable.
In addition, the bending elastic modulus of a foam sheet employ | adopts the value which measured the extrusion direction (MD) and the width direction (TD) based on JISK7203 (1982), and arithmetically averaged the obtained value. The test piece is 100 mm long × 25 mm wide × the total thickness of the foam sheet, the fulcrum tip R = 5 (mm), the pressure tip R = 5 (mm), the distance between the fulcrums is 50 mm, and the bending speed is 10 mm / min. To do. When the resin layer is laminated only on one side of the foamed sheet, the measurement is performed with the resin layer side facing down. The value measured in this way is defined as the flexural modulus.

The foamed sheet of the present invention preferably has an impact punching strength at a low temperature of 2.5 J or more. If it is less than 2.5 J, there are problems such as brittleness and cracking when used in a low temperature atmosphere. In order to have more excellent cold impact resistance, 4.0 J or more is preferable, and 5.0 J or more is more preferable. The upper limit is preferably that the opening does not open due to the impact opening strength, and more preferably 39.2 J or less, which is the limit value of the measurement method described later.
The impact punching strength at low temperature is JIS P8134 (1976), and the test size is a foamed sheet with a thickness of mm × 150 mm × 150 mm, kept in a thermostatic bath at −15 ° C. for 6 hours, and then at room temperature. Take out below, perform the test within 3 seconds, and adopt the value obtained.

  The average cell diameter of the foam sheet is preferably 100 to 700 μm. When the average cell diameter is less than 100 μm, a fold in the width direction called a corrugate is generated on the surface of the foam sheet, which may cause the foam sheet thickness to be non-uniform, and the open cell ratio is also high. 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 buffering property may be lowered.

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

  The molded body of the present invention is obtained by heating and softening a foam sheet having a thickness of 1 mm or more and 10 mm or less, or having a polyethylene resin layer on at least one side of the foam sheet, and then from a male mold and / or a female mold. It can obtain by the thermoforming method which shape | molds using the metal mold | die which becomes. The thermoforming methods include vacuum forming, pressure forming, and free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, and air slip forming. , Plug assist molding, plug assist reverse draw molding and the like, and molding methods combining these. Such a thermoforming method is a preferable method because a molded body can be obtained continuously in a short time.

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

The concrete form liner sheet of the present invention (hereinafter also simply referred to as “liner sheet”) is formed by forming a large number of communication holes in the foam sheet. Since the lining sheet of the present invention does not hang down when the end is held with one hand, it is excellent in workability when it is installed, 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 large number of communication holes, preventing the occurrence of water and air blows on the concrete surface, and water As the cement particles and fine aggregates gather on the surface layer of the concrete along the flow and the concrete structure of the surface layer is densified, a beautiful concrete surface is formed. As a specific construction method, a laminate, a nonwoven fabric, and a lining sheet are laminated in order of a tucker or a double-sided tape. The nonwoven fabric may or may not be provided as necessary.
The shape of the communication hole described above may be one type or a combination of two or more types of + shape, − shape, circular shape, elliptical shape, triangular shape, quadrangular shape, and polygonal shape. Among them, a circular shape is preferable from the viewpoint that the shape is simple and easy to form, and the diameter is such that the uncured concrete can drain only excess water without leaking, and when the concrete hardens, the surface is uneven due to the holes From the viewpoint of avoiding this, the diameter is preferably 0.1 to 2 mm, and more preferably 0.1 to 1.5 mm. Moreover, when it is + shape and-shape, width 0.1-0.7mm and length 1-10mm are preferable. The interval between these communication holes is preferably 0.5 to 5 mm, more preferably 0.5 to 3 mm, although it depends on the shape and size of the communication holes. In addition, the space | interval of a communicating hole means the shortest distance with an adjacent communicating hole. The shape and number of the above-described communication holes are appropriately determined according to the properties of the concrete used, for example, the amount of cement, the amount of moisture, and the size and amount of aggregate.
As a method of forming a large number of the above-described communication holes, for example, it is formed using a press die or a roll in which needle-like objects having the shape of a communication hole whose tip is desired are attached at a desired interval. Specifically, in the case of a press die, it is formed by pressing, and in the case of a roll, one roll is a roll to which many needles are attached, and the other is a receiving roll. Formed through. In that case, you may heat the press die or roll of the side which forms many communicating holes as needed.
Further, it is preferable that a textured process such as a convex pattern is formed on the surface of the lining sheet from the viewpoint that the finished concrete surface can be finished cleanly.
As the convex shape, for example, one or more of a cylindrical 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 may be combined. Good. Among the above, a quadrangular pyramid shape is preferable from the viewpoint of excellent drainage. The convex height is preferably 0.3 to 1 mm, more preferably 0.3 to 0.8 mm, from the viewpoint that the strength of the lining sheet and the surface of the obtained concrete can be finished finely. In the case of the above-mentioned conical shape, elliptical cone shape, triangular pyramid shape, quadrangular pyramid shape and polygonal pyramid shape, the distance between adjacent convex shapes is a recess even if the adjacent convex shapes are arranged without gaps with an interval of 0 mm. Since water is formed, water can be drained. From such a viewpoint, the lower limit of the gap between the convex shapes is preferably 0 mm or more, and more preferably 0.5 mm or more. On the other hand, the upper limit in the case where adjacent convex shapes are arranged at intervals 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. Further, in the case of a columnar shape, a triangular prism shape, a quadrangular prism shape, or a polygonal prism shape, it is possible to arrange adjacent convex shapes with an interval of 0.5 to 5 mm from the viewpoint of clean finish of the concrete surface and drainage. Preferably, it is more preferable to arrange with an interval of 0.5 to 3 mm. Note that the convex spacing means the shortest distance between valleys formed by adjacent convex shapes. The above-mentioned convex shape and number are appropriately determined according to the properties of the concrete used, for example, the amount of cement, the amount of moisture, and the size and amount of aggregate.
The above-mentioned embossing is formed by pressing with a press die or between rolls, and may be heated as necessary, but forms a convex pattern from the viewpoint that it can be reliably formed even if the convex pattern is shallow. It is preferable to heat the pressing die or roll on the side to be used.
The embossing may be performed simultaneously with the formation of the communication hole, or after or before the formation of the communication hole, but before the formation of the communication hole, it is preferable because there is less possibility of blocking the communication hole.

  The foamed sheet of the present invention is excellent in low-temperature impact resistance and is used for various applications, but is an assembly box formed by streaking a foamed sheet in which a resin layer is provided on at least one side of the foamed sheet Has less side deflection in the box. Further, it is an assembly box excellent in low-temperature impact resistance such that a stored item is stored in an assembled box and the box container itself does not crack even when dropped at a low temperature. A foam sheet in which resin layers are provided on both surfaces of the foam sheet is preferable from the viewpoint of reducing the side deflection of the box and making the assembly box excellent in low-temperature impact resistance. In addition, the assembly box made of foamed sheets with resin layers on both sides of the foamed sheet has a resin layer on the inside, so that scratches such as scratches are difficult to put in and out of stored items, and the durability of the assembly box is improved. To do. On the other hand, since the resin layer is also formed on the outside, the surface smoothness is excellent, and the printability is also good.

  The assembly box is formed from the foam sheet of the present invention by creating a development view of the box with a punching blade, forming a hinge line, bonding the joint portion, and bending the hinge part. The Examples of the above-described formation of the scribe line include cutting groove processing using a cutter, a needle, and the like, and streaking processing using an iron pressing blade. Of these, streaking is preferred because it has a good balance of folding resistance and productivity, such as being difficult to tear from the hinge portion even if folding is repeated. Examples of the streaking process include a method of forming a hinge by pressing a leading end portion against a foam sheet by heating with a steel streak pushing blade as necessary. At that time, from the viewpoint of productivity, it is possible to attach the cutting blade for punching and the pressing blade for streaking to the press machine and cut out the assembly box developed from the flat foam sheet and push the streak at the same time. Is desirable. The shape of the assembly box of the present invention includes, but is not limited to, a rectangular parallelepiped and a cube.

  The foam sheet of the present invention, which is excellent in rigidity, shock-absorbing property, and impact resistance at low temperatures, is used for the above-mentioned molded products, assembly boxes, etc., and for applications such as corrugated cardboard substitutes, partition materials, and concrete formwork curing plates. Is preferred.

Hereinafter, the manufacturing method of the foam sheet of this invention is demonstrated.
In the method of the present invention, using a specific polyethylene-based resin composition containing L-polyethylene and H-polyethylene, a melt-foamable resin composition containing a foaming agent in the resin composition is extruded and foamed to obtain an apparent density. A foamed sheet having a continuous cell ratio of 40% or less is obtained from 70 g / L to 500 g / L.
The foamed sheet of the present invention is prepared by, for example, supplying a polyethylene resin composition and an additive such as a bubble regulator to an extruder and heating, melting and kneading, and then supplying a foaming agent and kneading with the molten resin composition. The melt-foamable resin composition obtained in this manner can be obtained by a known extrusion foaming method in which foaming is performed by extrusion from an extruder.

  In such an extrusion foaming method, the method of the present invention includes L-polyethylene and H-polyethylene as a polyethylene resin composition, 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 melt tension and MFR of 100 or more is used.

If 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 a low bending rigidity. 400 MPa or more is more preferable, and 500 MPa or more is particularly preferable from the viewpoint of efficiently obtaining a foam sheet having high bending rigidity.
On the other hand, the upper limit value is preferably 1500 MPa or less, more preferably 1200 MPa or less, and particularly preferably 1000 MPa or less because a foamed sheet having a high open cell ratio may be obtained.
In addition, the bending elastic modulus of a polystyrene-type resin composition is measured by the method mentioned above.

  The flexural modulus of the polyethylene resin composition is measured by the measurement method described above. In addition, the test piece is prepared by direct compression molding.

Moreover, when melt tension is less than 15 mN, since foamability falls, there exists a possibility that a lightweight foamed sheet cannot be obtained. The melt tension of the polyethylene resin composition is more preferably 17 mN or more, and further preferably 20 mN or more. On the other hand, when the melt tension exceeds 400 mN, the open cell ratio is increased due to heat generation due to an increase in the die pressure during extrusion foaming, and the rigidity and thermoformability may be lowered. Therefore, the melt tension is 400 mN or less. It is preferable that it is 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 MFR (g / 10 minutes) of the polyethylene resin composition is 100 (mN · g / 10 minutes) or more, but the appearance is excellent with a low apparent density. 120 (mN · g / 10 minutes) or more is preferable, and 150 (mN · g / 10 minutes) or more is more preferable from the viewpoint that a foamed sheet can be efficiently obtained. On the other hand, the upper limit is preferably 1000 (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 ratio. 500 (mN · g / 10 minutes) or less. The MFR is preferably 0.3 g / 10 min or more. If it is less than 0.3 g / 10 minutes, the foamed sheet obtained has an increased open cell ratio, and there is a possibility that the rigidity is lowered and the moldability during thermoforming is lowered. The MFR of the polyethylene resin composition is more preferably 1.0 g / 10 min or more. Further, the MFR is preferably 20.0 g / 10 min or less. If this value is exceeded, it may be extremely difficult to make the melt tension (MT) at 190 ° C. 15 mN or more.

  In the method of the present invention, the MFR measurement method 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 described above 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 a polyethylene resin composition that has already been melt-kneaded using a twin screw extruder or kneader is charged as the polyethylene resin composition when being charged into the extruder, the polyethylene resin composition to be charged Is directly measured. In addition, when charged into the extruder, when two or more resins are separately charged as a polyethylene resin composition, or when a polyethylene resin composition that has already been 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 melt-kneading conditions assumed after the introduction of these extruders is used.

  In the method of the present invention, examples of L-polyethylene and H-polyethylene include the aforementioned polyethylene.

In the method of the present invention, the polyethylene resin composition containing L-polyethylene and H-polyethylene has the above-mentioned specific melt tension, and the melt tension (A) and MFR (B: g / 10 min). It is preferable that the melt tension of L-polyethylene is 20 mN to 400 mN so that the product (A × B) value of
Further, the MFR of L-polyethylene is preferably 0.3 g / 10 min to 20.0 g / 10 min, and preferably 1.0 g / 10 min to 15.0 g / 10 from the viewpoint of efficiently obtaining a foam sheet having a low open cell ratio. Min is more preferable, and 2.0 g / 10 min to 10.0 g / 10 min is more preferable.
Further, H-polyethylene has a MFR of 1.0 g / 10 min or more from the viewpoint that it is not necessary to reduce the discharge amount because a load is applied to the extruder due to heat generation when the polyethylene composition is melt-kneaded. Preferably, 2.0 g / 10 min or more is more preferable, and 3.0 g / 10 min or more is more preferable. On the other hand, the upper limit of MFR is preferably 20.0 g / 10 min or less, and preferably 15.0 g / 10 min or less from the viewpoint that the foamed sheet hangs down during extrusion and wrinkles are not formed on the surface of the foamed sheet. More preferred is 10.0 g / 10 min or less.
In addition, it is preferable that L-polyethylene has the above-described melt tension and that the melt tension of H-polyethylene is 2 mN to less than 20 mN from the viewpoint of forming a foamed sheet that does not have a decrease in rigidity due to open cell formation. 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 MFR ( B: A foamed sheet having a low density and excellent rigidity can be obtained by using a resin composition having a product (A × B) of (g / 10 minutes).
Furthermore, the density of the H-polyethylene described above is preferably 940 g / L or more, more preferably 950 g / L or more, and further 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 L-polyethylene and H-polyethylene have a proportion of H-polyethylene of more than 50% by weight with respect to the total amount (100% by weight) of the polyethylene-based resin composition. Is preferably 90% by weight or less from the viewpoint of obtaining a foam sheet having excellent bending reproducibility, cold shock resistance, and mold reproducibility which is the same shape as the mold during thermoforming. If the ratio of H-polyethylene with respect 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 decrease. . Moreover, when the ratio of H-polyethylene is 50 weight% or less, there exists a possibility that the bending rigidity of a foamed sheet may fall. A more preferable ratio of H-polyethylene to the total amount of L-polyethylene and H-polyethylene is more than 50% by weight and 85% by weight or less, and more preferably more than 50% by weight and 80% by weight or less.

  In the method of the present invention, the polyethylene resin composition constituting the foamed sheet may contain a polyethylene resin other than the L-polyethylene and the H-polyethylene. Examples of the polyethylene resin that can be blended with L-polyethylene and H-polyethylene in the polyethylene resin composition include ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene-butene- Ethylene component unit 50 such as 1 copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer, ethylene-octene-1 copolymer, etc. Examples thereof include ethylene copolymers exceeding mol%, and these can be used in combination of two or more.

  The polyethylene-based resin composition constituting the foamed sheet may contain the above-described polyethylene-based resin in addition to L-polyethylene and H-polyethylene, but L-polyethylene and H-polyethylene are used. It is preferable that both of them are contained in a total 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 in the polyethylene-based 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, there is an advantage of excellent recyclability because it is a mixture of polyethylene only.

  The foamed sheet of the method of the present invention may contain various additives in the polyethylene resin composition. Examples of additives include nucleating agents, antioxidants, heat stabilizers, antistatic agents, conductivity-imparting agents, weathering agents, UV 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 ionomer or ethylene-propylene rubber, polybutene, etc., as long as the purpose and effect of the foamed sheet of the present invention are not impaired. Vinyl chloride resins such as butene resins and polyvinyl chloride can be added. In this case, the amount added is preferably 30% by weight or less, more preferably 20% by weight or less, and particularly preferably 10% by weight or less.

  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 less drooping when having one end of the sheet. An apparent density of 70 g / L to 350 g / L is preferable in order to have high buffering properties and high rigidity such as less sag when the sheet has one end. An apparent density of 200 g / L to 500 g / L is preferable in order to obtain a foam sheet that is excellent in thermoformability such as mold reproducibility and has the same shape as the mold and has high rigidity.

  The foam 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, the foam sheet has low rigidity. In order to obtain a foam sheet suitable for thermoforming, the open cell ratio is preferably 20% or less.

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

  As the foaming agent in the method of the present invention, the same inorganic foaming agent and organic physical foaming agent as those conventionally used for the production of polyethylene resin foams can be used. Examples of the inorganic foaming agent include oxygen, nitrogen, carbon dioxide, and air. Examples of the organic physical foaming agent include fats such as propane, normal butane, isobutane, normal pentane, isopentane, normal hexane, isohexane, and cyclohexane. Group hydrocarbons, chlorohydrocarbons such as methyl chloride and ethyl chloride, and fluorinated hydrocarbons such as 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane. Decomposable foaming agents such as azodicarbonamide can also be used. The above foaming agents can be used in combination of two or more. Of these, particularly preferred are those containing, as a main component, normal butane, isobutane, or a mixture thereof having good compatibility with polyethylene resins and good foamability.

  Moreover, it is preferable to add a bubble regulator to the polyethylene resin composition. 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 phosphate-2,2-methylenebis (4,6-tert-butylphenyl), 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 amount of the foaming agent added 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 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. .

  In addition to the air conditioner, the polyethylene resin composition further has functionalities 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 and foamed from a die. When a foamed sheet is obtained, a flat resin, a circular die or the like is used to form a polyethylene resin composition from the die. It is obtained by adding a foaming agent to the product and extrusion 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. The case where an annular die is used will be described in detail. Extrusion and foaming from the annular die is made into a cylindrical foam. Next, the foamed sheet can be obtained by cutting the inner surface of the cylindrical foam after passing through the columnar cooling device and cooling it.

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

  Among these methods, the multilayer coextrusion method has a simpler process than other methods and is a preferable method from the viewpoint of cost. And a favorable foam sheet with high adhesive strength of a foam layer and a resin layer is obtained. The method of obtaining the foam sheet by the multilayer coextrusion method will be described in more detail. (1) A method of co-extrusion into a sheet shape using a flat die and (2) a method of co-extrusion using a circular die to form a cylindrical foam. There is a method of manufacturing and then cutting a cylindrical foam into a foam sheet. Of the above, a multilayer coextrusion method using an annular die is suitable for obtaining a wide foam sheet having a width of 1000 mm or more.

  In addition, when obtaining the foam sheet which has a resin layer on the foam sheet surface by coextrusion, you may laminate | stack on the exit of a die | dye, or the exit of a die | dye. As an extruder, an annular die, a cylindrical cooling device, and a device for opening a cylindrical foam in the case of extrusion foaming using an annular die, a known one that has 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 1-5, Comparative Examples 1-4
L-polyethylene (manufactured by Nippon Unicar Co., Ltd., low density polyethylene “NUC8008”, MFR: 4.5 g / 10 min, 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”), and a foaming agent per 100 parts by weight of the polyethylene resin composition As a foam control agent, “Fine Cell Master SSC-PO208K” manufactured by Dainichi Seika Kogyo Co., Ltd., which is a mixture of monosodium citrate and sodium bicarbonate as a foam regulator, is supplied to the extruder at the ratio shown in Table 1 and heated and melt-kneaded. The foamed molten resin composition was adjusted to the extrusion temperature shown in Table 1 and introduced into the annular die, and the air was discharged from the die lip to the atmosphere. A discharge rate 120 kg / time was foamed extruded into a tubular shape. After taking up the cylindrical foam and cooling the inner surface through a cylindrical cooling device (diameter 350 mm, length 1500 mm), the cylindrical foam is cut along the extrusion direction, and uncrosslinked foam The sheet was wound into a roll.

  In Example 4, a die is used for co-extrusion, a 50 mm diameter extruder is connected to the die part, a polyethylene resin is co-extruded, and a foamed sheet having a polyethylene resin layer having a thickness of 25 μm on both sides of the foamed sheet. It was. Moreover, in Example 5, it was set as the foam sheet which has a 200-micrometer polyethylene-type resin layer on both surfaces of a foam sheet by the co-extrusion method, respectively. In Examples 4 and 5, the polyethylene resin composition for forming the polyethylene resin layer is a mixture of resin A: 70% by weight and resin B: 30% by weight.

The average cell diameters of Examples 1 to 5 and Comparative Examples 1 to 4 were the results shown below. The average bubble size of Example 1 is 240 μm, the average bubble size of Example 2 is 260 μm, the average bubble size of Example 3 is 550 μm, the average bubble size of Example 4 is 240 μm, and the average bubble size of Example 5 The diameter was 210 μm, the average bubble diameter in Comparative Example 1 was 370 μm, the average bubble diameter in Comparative Example 2 was 290 μm, the average bubble diameter in Comparative Example 3 was 250 μm, and the average bubble diameter in Comparative Example 4 was 360 μm. It 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 Nippon Polyolefin Co., Ltd. as H-polyethylene was mixed in the proportions shown in Table 1. In the same manner as above, an uncrosslinked foam sheet having a polyethylene resin layer having a thickness of 25 μm on both surfaces of the foam sheet was obtained. When the obtained foam sheet and the foam sheet of Example 4 were compared, the flexural modulus was improved. The average bubble diameter was 210 μm.

Example 7
Polyethylene resin constituting the resin layer is 70% by weight of resin A and 30% by weight of resin B, and per 100 parts by weight of the polyethylene resin, an antistatic agent (trade name Pelestat 300 (manufactured by Sanyo Chemical Industries, Ltd., polyether-polypropylene block) A non-crosslinked foam having a polyethylene resin layer having a thickness of 7 μm on both sides of the foamed sheet 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 average cell diameter was 220 μm, and the surface resistivity of the obtained foamed sheet was 3.0 × 10 ¹⁰ Ω. The measurement was performed as described above.

Example 8
Similarly to Example 1, an uncrosslinked 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 concrete form lining sheet was formed by forming a large number of communication holes by the following method.
Using a heated roll and a rubber roll whose surfaces are processed so that a quadrangular pyramid shape having a height of 0.5 mm and a square of 1.2 mm as a convex pattern is formed at intervals of 0 mm. 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 needle-like objects and a rubber roll, the foam sheet is formed into a roll of the communication holes formed in a circular shape with a diameter of 0.2 mm and an interval of 2 mm. The communication hole was formed by passing between them.
The obtained lining sheet was cut into a size of 910 mm wide × 1820 mm long and laminated by a tucker in the order of the formwork and the lining sheet. At that time, the lining sheet was arranged so that the convex pattern became the concrete placing surface, and used as a concrete formwork. The finished concrete surface was beautiful due to the lining sheet.

Measurement of surface resistivity is based on JIS-K6911 (1979), Takeda Riken Kogyo Co., Ltd., “TR8601” applied with applied voltage 500V, surface resistance value after 1 minute adopted Then, the surface resistivity was determined from the average value of the measured values obtained.
Specifically, from the obtained foamed sheet, a test piece (length 100 mm × width 100 mm × thickness: thickness of the test piece) was cut out into three pieces at equal 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 specific resistivity. Further, after adjusting the state of the test piece as shown below, the specimen was left for 1 hour in an atmosphere of 23 ° C. and 50% humidity, and then the surface resistivity was measured. As a result, the surface resistivity did not change to 3.0 × 10 ¹⁰ Ω.
[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 cleaning device 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.

Comparative Example 5
A non-crosslinked foamed sheet was obtained in the same manner as in Example 1 except that L-polyethylene was made 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.

  The foamed sheets obtained in Examples 1 to 7 had less sagging when having one end of the foamed sheet.

The foamed sheets obtained in Comparative Example 1, Comparative Example 4 and Comparative Example 5 are less drooping when having one end of the foamed sheet, but when extruded, a crystallized product appears 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 the foam sheet had an end on one side.

Using the foamed sheets wound up in rolls obtained in Examples 1, 2, 4, 7 and Comparative Examples 1, 3, 4, and 5, the surface of the foamed sheet is as shown in Table 2 in a heating furnace. A component tray having the highest value, heat-softening the foam sheet, housing six component size thickness 20 mm × width 55 mm × length 80 mm, rectangular shape of the opening, and partition with a height of 5 mm, Thermoforming was performed using a mold having an outer size of depth 25 mm × width 200 mm × length 300 mm, inner diameter size depth 20 mm × width 170 mm × length 270 mm.
The molded bodies obtained using the foamed sheets of Examples 1, 2, 4 and 7 had the same shape as the mold, and were good without thickness and thickness.
The molded bodies obtained using the foamed sheets of Comparative Examples 1, 4 and 5 were those in which the same shape as the mold was not obtained. Moreover, although the molded object obtained using the foamed sheet of the comparative example 3 had the same shape as a metal mold | die, when a component was inserted, the shape of the molded object deform | transformed.

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

The foamed sheets obtained in Examples 5 and 6 were used to form a JIS Z 1507 (1989) grooved shape and a box shape of code number 0201 (length 430 mm, width 250 mm, height 230 mm). The above-mentioned box wire is composed of three pressing blades, and the height of the central pressing blade is 0.1 mm higher than the height of the pressing blades at both ends. The length of each pressing blade was 1 mm, and the length direction was set to be the extrusion direction (MD direction) of the foamed sheet, and the wire was formed on the outer side.
The assembly box using the foamed sheets of Examples 5 and 6 was excellent in surface smoothness. In particular, in Example 5, there was little deflection when the contents were put in the assembly box and stacked.

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

The flexural modulus, melt tension (A) at 190 ° C., and MFR (B) values in Table 1 indicate that when the resin layer is present, the foam layer is removed by removing the resin layer, and the foam layer is heated and cooled. This is a value obtained by defoaming with a non-foamed resin. When there is no resin layer, it is a value obtained by using a non-foamed resin by defoaming the foamed sheet as it is with a heat press and a cooling press.
Although not shown in the table, as a result of measuring the flexural modulus, melt tension at 190 ° C. and MFR for the polyethylene resin composition to be introduced into the extruder, the foamed sheet was defoamed and a non-foamed resin was used. It was the same value as the obtained value.
In addition, the test piece was created using the resin obtained by melt-kneading H-polyethylene and L-polyethylene at 190 degreeC previously using the twin-screw extruder.

Evaluation of rigidity, evaluation of low temperature impact resistance and evaluation of appearance in Table 2 were performed as follows.
<Rigidity evaluation>
Evaluation was made based on the value of the flexural modulus.
◎ ・ ・ ・ 150 MPa or more ○ ・ ・ ・ 50 MPa or more and less than 150 MPa × ・ ・ ・ less than 50 MPa <Evaluation of low temperature impact resistance>
Evaluation was made based on the value of punching strength at low temperatures.
◎ ... 10.0J or more ○ ... 2.5J or more and less than 10.0J × ... less than 2.5J <Evaluation of appearance>
The surface of the foam sheet was visually evaluated.
○ ・ ・ ・ No irregularities on the surface and good appearance × ・ ・ ・ Unevenness on the surface and poor appearance

Claims (11)

A polyethylene-based 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 the flexural modulus of the polyethylene resin composition constituting the foam sheet is 300 MPa or more, and the resin 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. It is the above, The polyethylene-type resin extrusion foam sheet characterized by the above-mentioned. 2. The polyethylene resin according to claim 1, wherein the polyethylene resin composition constituting the polyethylene resin extruded foam sheet comprises 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. The polyethylene-based resin composition constituting the polyethylene-based resin extruded foam sheet has (i) a density of 10% by weight or more and less than 50% by weight of polyethylene having a density of 930 g / L or less, and (ii) a density exceeding 930 g / L and 970 g / L. The polyethylene-based resin extruded foam sheet according to claim 1 or 2, comprising more than 50% by weight of polyethylene and 90% by weight or less. The polyethylene-based resin extruded foam sheet according to any one of claims 1 to 3, which has a polyethylene-based resin layer of 5 µm or more on at least one side. The polyethylene resin extruded foam sheet according to any one of claims 1 to 4, wherein the entire thickness is from 1 mm to 10 mm. The polyethylene-based resin extruded foam sheet according to claim 4, wherein the polyethylene-based resin constituting the polyethylene-based resin layer contains an antistatic agent, and the resin layer has a semi-permanent antistatic performance. The polyethylene resin extruded foam sheet according to any one of claims 1 to 6, wherein the warpage is 5% or less. The molded object formed by thermoforming the polyethylene-type resin extrusion foam sheet in any one of Claims 1-7. The assembly box which consists of a polyethylene-type resin extrusion foam sheet in any one of Claims 1-7. A lining sheet for a concrete mold formed by forming a large number of communication holes in the polyethylene resin extruded foam sheet according to any one of claims 1 to 7. A 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 resin composition The resin composition comprises polyethylene having a density of 930 g / L or less and polyethylene having a density of more than 930 g / L and not more than 970 g / L, and has a flexural modulus of 300 MPa or more and 190 ° C. The melt tension (A) is 15 mN to 400 mN, and the product (A × B) of the melt tension (A) and MFR (B: g / 10 min) is 100 or more. A method for producing an extruded foam sheet.