JP2007168318A - Polyethylene-based resin laminated foam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyethylene-based resin laminated foam which has excellent resistance to cracking and tearing while sufficiently retaining mechanical physical properties such as rigidity, a cushioning property, etc. <P>SOLUTION: The polyethylene resin laminated foam with 2 to 8 mm thickness and 150 to 350 MPa bending modulus, which has polyethylene-based resin layers formed on both surfaces of a polyethylene-based resin foamed layer with 150 to 350 g/L apparent density and lower than the 40% proportion of interconnected cells. In this polyethylene resin laminated foam, the ratio "a/b" of the tensile elongation "a" (mm) of the polyethylene-based resin layer to the 25% compression strength "b" (MPa) of the polyethylene-based resin laminated foam, is not less than 2.4 mm/MPa, and the 25% compression strength "b" (MPa) of the polyethylene-based resin laminated foam is 0.5 to 1.5 MPa. Thus the resultant polyethylene-based resin laminated foam shows excellent resistance to cracking and tearing while sufficiently retaining the mechanical properties such as rigidity, the cushioning property, etc. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polyethylene resin laminated foam.

Polyethylene resin foams are widely used in various applications such as cushioning materials and packaging materials.
As the base resin constituting such a polyethylene resin foam, high-pressure low-density polyethylene is preferably used because of its excellent foamability. However, since this polyethylene has a low density, there is a drawback that the obtained polyethylene-based resin foam is inferior in rigidity, and it has been used only for soft packaging applications.

  Therefore, Patent Document 1 discloses 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 constituting the foam sheet is 300 MPa. The melt tension (A) at 190 ° C. of the resin is 15 mN to 400 mN, and the product (A × B) of the melt tension (A) and the MFR (B: g / 10 min) of the resin is A polyethylene resin extruded foam sheet of 100 or more has been proposed. According to the invention described in Patent Document 1, a polyethylene resin extruded foamed resin sheet having a certain degree of rigidity and buffering properties is provided.

JP 2004-43813 A

  In Patent Document 1, although the rigidity and shock-absorbing property of the polyethylene-based resin extruded foamed resin sheet are improved sufficiently, the polyethylene-based resin when a processed product such as an assembly box is manufactured by performing a process such as bending. The resistance to cracking and tearing of the extruded foamed resin sheet left room for further improvement. That is, in patent document 1, it is requested | required to improve the tolerance with respect to the crack and a tear about a polyethylene-type resin extrusion foaming resin sheet.

  An object of this invention is to provide the polyethylene-type resin laminated foam excellent in the tolerance with respect to a crack and a tear, fully maintaining mechanical physical properties, such as rigidity and a shock absorbing property.

  The present invention includes (1) a thickness of 2 to 8 mm having a polyethylene resin layer on both sides of a polyethylene resin foam layer having an apparent density of 150 g / L to 350 g / L and an open cell ratio of 40% or less, and a flexural modulus of 150 to 350MPa polyethylene resin laminate foam, ratio of tensile elongation (a (mm)) of polyethylene resin layer to 25% compressive strength (b (MPa)) of polyethylene resin laminate foam (a / b) is 2.4 mm / MPa or more, and 25% compressive strength (b (MPa)) of the polyethylene resin laminated foam is 0.5 to 1.5 MPa, (2 ) Polyethylene resin constituting the polyethylene resin foam layer is composed of 40 to 80% by weight of polyethylene (Xa) with a density of 930 g / L or less, and polyethylene (Ya) 20 to 60 with a density of more than 930 g / L and 970 g / L or less. Description in (1) above, comprising: wt% (however, the sum of Xa and Ya is 100 wt%) Polyethylene resin laminated foam, (3) The polyethylene resin that composes the polyethylene resin layer is 10 to 40% by weight of linear polyethylene (Xb) with a density of 930 g / L or less, and the density is over 930 g / L and over 970 g / L or less of polyethylene (Yb) 50 to 90% by weight, and high pressure polyethylene (Xc) having a density of 930 g / L or less 0 to 30% by weight (however, the total of Xb, Yb and Xc is 100% by weight) The gist of the polyethylene-based resin laminate foam according to the above (1) or (2), characterized in that

  According to the present invention, it is possible to obtain a polyethylene-based resin laminated foam which is excellent in mechanical properties such as rigidity and hardly breaks or breaks even when bent.

  The polyethylene-based resin laminated foam of the present invention (hereinafter sometimes simply referred to as a laminated foam) is formed on both surfaces of a polyethylene-based resin foam layer having an apparent density of 150 g / L to 350 g / L and an open cell ratio of 40% or less. A plate-like laminated foam having a polyethylene resin layer with a thickness of 2 to 8 mm and a flexural modulus of 150 to 350 MPa and excellent mechanical properties such as light weight and bending rigidity, the polyethylene constituting the core layer of the laminated foam A polyethylene resin layer (hereinafter sometimes simply referred to as a resin layer) is formed on both sides of a resin-based resin foam layer (hereinafter sometimes simply referred to as a foam layer), and the tensile elongation ( a (mm)) and 25% compressive strength (b (MPa)) of polyethylene-based resin laminated foam, a / b (mm / MPa) is 2.4 or more (however, 25% of polyethylene-based resin laminated foam) Compressive strength (b (MPa)) is 0.5 to 1.5 MPa.) Accordingly, those with improved folding endurance. If the laminated foam of this invention is demonstrated using the graph which shows the relationship between the compressive strength b and the tensile elongation a, this laminated foam applies to the area | region shown by the area | region D in FIG. FIG. 1 is a graph with the compressive strength b on the horizontal axis and the tensile elongation a on the vertical axis. Regions A, B, C, and D are (b <0.5), (b> 1.5), ( An area specified by 0.5 ≦ b ≦ 0.5 and a / b <2.4) and (0.5 ≦ b ≦ 0.5 and a / b ≧ 2.4) is shown.

  The effect obtained by satisfying the configuration of the ratio a / b and the compression strength b of the laminated foam in the present invention can be described with reference to FIG. That is, in FIG. 1, the laminated foam in the region A in which the compression strength b of the laminated foam is less than 0.5 MPa is inferior in the bending rigidity required as a plate-like foam, and the compression strength b of the laminated foam is low. The laminated foam of region B exceeding 1.5 MPa has a problem in terms of workability, buffering property, etc. because its bending rigidity is too high. Further, even if the compressive strength b is 0.5 to 1.5 MPa, the laminated foam in the region C in which the ratio a / b between the tensile elongation a of the polyethylene resin layer and the compressive strength b is less than 2.4 is polyethylene-based. The balance between the tensile breaking strength of the resin layer and the compressive strength of the polyethylene resin foam layer constituting the core layer is poor, and the laminated foam is bent because the compressive strength b is too high or the tensile elongation a is too small. In such a case, the resin layer may break or the foamed layer may crack or tear.

  Therefore, in the laminated foam of the present invention, the ratio a / b between the tensile elongation (a (mm)) of the resin layer and the 25% compressive strength (b (MPa)) of the laminated foam is 2.4 mm / MPa or more. Yes, preferably 3.5 to 5.0 mm / MPa. Further, the upper limit of the ratio a / b is approximately 7.0 mm / MPa.

  In the laminated foam of the present invention, from the above viewpoint, the 25% compressive strength (b) is 0.5 to 1.5 MPa, preferably 0.6 to 1.2 MPa, and more preferably 0.6 to 1.0 MPa.

  In addition, the laminated foam of the present invention has, as preconditions, an apparent density of 150 g / L to 350 g / L, an open cell ratio of 40% or less, a thickness of 2 to 8 mm, and a flexural modulus of 150 MPa to 350 MPa.

  If the flexural modulus of the laminated foam is less than 150 MPa, its rigidity and strength may be insufficient. For example, when processing a laminated foam to obtain a processed product such as an assembly box, There is a risk that the product is insufficient in rigidity and strength, easily bulging, and easily broken. On the other hand, if the flexural modulus of the laminated foam exceeds 350 MPa, the laminated foam may be too rigid and have poor processability. That is, for example, when trying to manufacture a processed product such as an assembly box using a laminated foam, even if the laminated foam is subjected to processing such as folding or giving a crease, Rigidity makes it difficult to perform such processing, which may reduce workability. In addition, when the processed product is an assembly box or the like that is repeatedly bent during its use, if the rigidity of the laminated foam is excessive, the user cannot easily bend, and eventually The processed product is unusable for the user. From the above viewpoint, the flexural modulus of the laminated foam of the present invention is preferably 170 to 300 MPa.

  Also, if the thickness of the laminated foam is less than 2 mm, its rigidity and buffering properties may be insufficient, and if the thickness of the laminated foam exceeds 8 mm, it will be used to partition plates and assembly boxes. In the case of manufacturing a processed product such as, there is a risk that workability may be reduced. From the above viewpoint, the thickness of the laminated foam of the present invention is preferably 2.5 to 6 mm.

  In addition, if the apparent density of the foamed layer of the laminated foam is less than 150 g / L, the rigidity becomes insufficient, and when a processed product such as an assembly box is manufactured using such a laminated foam, the processed product There is a possibility that the strength of the steel becomes insufficient. In addition, when the apparent density of the foamed layer of the laminated foam is higher than 350 g / L, there is a risk that the buffering property and the like may be insufficient, and when a processed product is manufactured using such a laminated foam. In addition, the processed product tends to be excessive and consumes more raw materials than necessary, which may increase the manufacturing cost. From the above viewpoint, the apparent density of the foam layer of the laminated foam of the present invention is preferably 170 to 300 g / L.

  Further, if the open cell ratio of the foamed layer of the laminated foam is larger than 40%, the rigidity and buffering property of the obtained laminated foam may be insufficient. From the above viewpoint, the open cell ratio of the foamed layer of the laminated foam of the present invention is preferably 25% or less.

  The base resin constituting the foam layer of the laminated foam of the present invention (hereinafter referred to as the foam layer base resin) is an ethylene homopolymer such as a high-pressure method low-density polyethylene, high-density polyethylene, or 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-methyl Examples thereof include an ethylene copolymer such as a pentene-1 copolymer and an ethylene-octene-1 copolymer, and a polyethylene resin such as a mixture of two or more of these, and a polyethylene having a density of 930 g / L or less ( (Polyester) containing 40 to 80% by weight (referred to as L-polyethylene) and 20 to 60% by weight of polyethylene (referred to as H-polyethylene) having a density greater than 930 g / L and 970 g / L or less By using an ethylene-based resin (the total of L-polyethylene and H-polyethylene is 100% by weight), it is easy to balance excellent rigidity and excellent elasticity to prevent cracking and tearing. It is preferable because it can be obtained at low cost, and contains 40 to 65% by weight of L-polyethylene and 35 to 60% by weight of H-polyethylene (the total of L-polyethylene and H-polyethylene is 100% by weight). More preferably.

  Examples of the L-polyethylene include so-called linear low density polyethylene, linear ultra-low density polyethylene (in the present invention, the density is 930 g / L or less in combination with the linear low-density polyethylene and linear ultra-low density polyethylene). And high pressure method low density polyethylene (also referred to as high pressure method polyethylene in the present invention). Moreover, as H-polyethylene, so-called high density polyethylene can be mentioned.

  The base resin constituting the foam layer may include a polyethylene resin other than the L-polyethylene and the H-polyethylene. Examples of the foam layer base resin that can be blended with L-polyethylene and H-polyethylene include, for example, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene-butene-1 copolymer More than 50 mol% of ethylene component units such as a polymer, an ethylene-butene-1 copolymer, an ethylene-hexene-1 copolymer, an ethylene-4-methylpentene-1 copolymer, and an ethylene-octene-1 copolymer Examples thereof include an ethylene copolymer.

  In addition to L-polyethylene and H-polyethylene, the foam layer resin may contain the above-mentioned polyethylene resins, but the advantages of using L-polyethylene and H-polyethylene are fully demonstrated. Thus, it is preferable that both are contained in a total of 70% by weight or more. The total weight of L-polyethylene and H-polyethylene in the total weight of the foam layer base resin 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 foam layer base resin is 90% by weight or more, the foam layer is composed of a mixture containing almost only polyethylene. There are excellent advantages.

  Examples of the base resin (resin layer base resin) constituting the resin layer of the laminated foam of the present invention include the same polyethylene-based resins as the above foam layer base resin. Among them, in particular, 10 to 40% by weight of linear polyethylene having a density of 930 g / L or less, 50 to 90% by weight of polyethylene having a density of more than 930 g / L and 970 g / L or less, and a high pressure having a density of 930 g / L or less. Method polyethylene 0-30% by weight (however, the total of linear polyethylene having a density of 930 g / L or less, polyethylene having a density of more than 930 g / L and not more than 970 g / L, and high-pressure method polyethylene having a density of 930 g / L or less) 100% by weight), it is possible to efficiently form a resin layer that can improve the tensile elongation while maintaining the excellent rigidity of the resin layer, and the obtained laminated foam is the foam Combined with the layer structure, it is excellent in rigidity and is preferable for the reason that cracking and tearing can be surely prevented.

  In addition, the resin layer base resin preferably has a tensile elongation of 100% or more from the viewpoint of preventing breakage during bending of the laminated foam.

  In addition, the resin layer base resin preferably has a tensile elastic modulus of 150 to 300 MPa from the viewpoint of preventing strength reduction such as rigidity and preventing breakage during bending.

  The resin layer may be composed of a single layer or a plurality of layers. When the resin layer is composed of a plurality of layers, the composition of the above preferred resin layer base resin, the tensile elongation of the resin layer base resin, and the tensile elastic modulus of the resin layer base resin are the respective configurations. It is preferable that the total basis weight of each layer of the resin layer satisfying the above is 80% or more of the basis weight of the entire resin layer, and it is particularly preferable that all the layers constituting the resin layer are satisfied.

  In addition, various additives may be contained in the base resin of the foam layer or the resin layer. 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. . In particular, in the resin layer, when the resin layer is composed of a plurality of layers, it is preferable to add a material that exhibits a lubricant action such as polyethylene wax to the inner layer laminated in contact with the surface of the foam layer. This makes it possible to lower the melt viscosity of the inner layer within the range satisfying the physical properties such as tensile elongation and tensile elastic modulus of the resin layer in the present invention in the coextrusion foaming method to be described later. A good laminated foam having a low open cell ratio and excellent appearance can be easily obtained.

  The base resin of the foam layer or resin layer is a styrene resin such as polystyrene, an elastomer such as ionomer or ethylene propylene rubber, or a butene system such as polybutene, as long as the purpose and effect of the laminated foam of the present invention are not impaired. A vinyl chloride resin such as a resin or polyvinyl chloride can be added. In this case, the addition amount is preferably 40% 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.

When the resin layer is composed of a plurality of layers, the resin layer (sometimes referred to as the outermost layer) laminated on the outermost side in the laminated foam of the present invention in which the resin layers are laminated so as to sandwich the foam layer. It is particularly preferable that at least one contains a polymer type antistatic agent so that the surface resistivity is 1 × 10 ¹³ Ω or less. Hereinafter, the resin layer is composed of a plurality of layers, and the resin layer laminated between the outermost layer of the resin layer and the foamed layer may be referred to as an inner layer.

  In the laminated foam, since the polymer type antistatic agent is contained in the outermost layer of the polyethylene resin layer, a sufficient antistatic effect can be expected by suppressing the amount of the expensive antistatic agent used. That is, in order to obtain the antistatic effect by adding the antistatic agent, it is necessary to add more than the minimum necessary concentration, and the antistatic agent is added to the required concentration for the thinnest outermost layer. As a result, the amount of expensive polymer antistatic agent used can be saved. Of course, this is not limited to the antistatic agent, and for example, the addition amount of the antibacterial agent and the antifungal agent also exhibits the effect of reducing the addition amount.

The polymer type antistatic agent contained in the polyethylene resin layer is an antistatic agent having a number average molecular weight of 2000 or more, preferably 2000 to 100,000, more preferably 5000 to 60000, and particularly preferably 8000 to 40000. It is distinguished from an antistatic agent comprising a surfactant. The upper limit of the number average molecular weight of the polymer type antistatic agent is approximately 10000000. The polymer antistatic agent is preferably a resin having a surface resistivity of less than 1 × 10 ¹⁰ (Ω). By setting the number average molecular weight of the polymer type antistatic agent within the above range, the antistatic performance is more stably expressed without being influenced by the environment, and the antistatic agent migrates to the packaged body surface. Can be prevented from being contaminated.

  In addition, the said number average molecular weight is calculated | required using high temperature gel permeation chromatography. For example, when the polymer type antistatic agent is a hydrophilic resin mainly composed of polyetheresteramide or polyether, the sample concentration is 3 mg / ml using orthodichlorobenzene as a solvent, and the column temperature is 135 ° C. using polystyrene as a reference substance. It is a value measured under the conditions. In addition, the kind of said solvent and column temperature are suitably changed according to the kind of polymeric antistatic agent.

  The melting point of the polymer antistatic agent is preferably 70 to 270 ° C., more preferably 80 to 230 ° C., and particularly preferably 80 to 200 ° C. Is desirable from the viewpoint of forming a small polyolefin resin layer and exhibiting good antistatic function.

  The melting point of the polymer antistatic agent can be measured by a method based on the following JIS K 7121 (1987). That is, pretreatment is performed according to the condition (2) for condition adjustment of the test piece in JIS K 7121 (1987) (however, the cooling rate is 10 ° C./min), and the melting peak is obtained by raising the temperature at 10 ° C./min. . The temperature at the top of the obtained melting peak is taken as the melting point. When two or more melting peaks appear, the temperature at the top of the melting peak having the largest area is defined as the melting point. However, when there are a plurality of melting peaks having the largest area, the melting point is the temperature at the apex of the melting peak on the highest temperature side among the melting peaks.

  As the polymer type antistatic agent used in the present invention, an ionomer resin containing an alkali metal selected from the group consisting of potassium, rubidium and cesium as metal ions, a polyether ester amide, and a hydrophilic mainly composed of a polyether. Is preferred. In addition, the polymer antistatic agent improves the compatibility of the polyethylene-based resin layer with the base resin and gives an excellent antistatic effect, and also has the effect of suppressing deterioration in physical properties due to the addition of the antistatic agent. For this purpose, it is more preferable to use a block copolymer of the same kind or highly compatible resin as the base resin of the polyethylene resin layer.

  Particularly preferred polymer antistatic agents include ionomers in which part or all of the ethylene-unsaturated carboxylic acid copolymer is neutralized with an alkali metal selected from the group consisting of potassium, rubidium and cesium, and The composition described in -278985 is mentioned.

In the composition described in JP-A-2001-278985, a block of polyolefin (a) and a block of hydrophilic polymer (b) having a volume resistivity of 10 ⁵ to 10 ¹¹ Ω · cm are bonded alternately and repeatedly. It is a block polymer having a number average molecular weight (Mn) of 2000 to 60000 having the above structure. The block (a) and the block (b) have a structure in which they are alternately and repeatedly bonded via at least one bond selected from an ester bond, an amide bond, an ether bond, a urethane bond, and an imide bond. is there. The polymer antistatic agents can be used alone or in combination.
Examples of the polymer type antistatic agent as described above include “Pelestat 300” and “Pelestat NC7530” manufactured by Sanyo Chemical Industries, Ltd.

  The laminated foam of the present invention can be produced as follows.

  First, a foam layer base resin and additives such as a bubble regulator are supplied to an extruder and heated, melted and kneaded, and then a foaming agent is supplied to the extruder and kneaded with a molten resin to be melt foamed. A functional resin composition is obtained. Then, the foamed resin composition is foamed by a known extrusion foaming method that is extruded from an extruder and foamed to form a foamed layer having an apparent density of 150 g / L to 350 g / L and an open cell rate of 40% or less. A foam (hereinafter simply referred to as “foam”) is obtained.

  On the other hand, a polyethylene resin film (hereinafter sometimes simply referred to as a film) is obtained by a known extrusion molding method using a resin layer base resin.

  The foam and the film obtained as described above are passed through a heating roll so that both surfaces of the foam are sandwiched between the films, and the foam and the film are thermally welded together to form a laminated structure. Obtain a foam.

The laminated foam of the present invention is not limited to the case of producing by the above method, and may be produced as follows.
That is, the laminated foam is produced as described above, and then the resin melt obtained by melting the resin layer base resin is separated on the foam production process line or on a separate production line. It may be manufactured by supplying a resin layer on one surface of the foam from the extruder and laminating the resin layer on the other surface of the foam in the same manner.

  In addition, the laminated foam is manufactured once and then the film is supplied on the production line of the foam or a separate production line and heat-sealed to one surface of the foam to form a laminated structure. Further, the other surface of the foam may be formed by supplying a resin melt obtained by melting the resin layer base resin from another extruder and laminating the film on the foam.

  Furthermore, the laminated foam of the present invention is produced by laminating films on both sides of the foam by a coextrusion method, and forming resin layers (single layer or multilayer resin layers) on both sides of the foam layer. Also good.

  In producing the laminated foam of the present invention, among the production methods as described above, the co-extrusion method is simpler than the other methods, such as being able to simultaneously form a resin layer on both sides of the foam layer. Therefore, it is preferable from the viewpoint of manufacturing cost. And since the adhesive strength of a foam layer and a resin layer is high, generation | occurrence | production of delamination is suppressed and a favorable laminated foam is obtained.

  Therefore, the method for obtaining a laminated foam in the form of a sheet by coextrusion will be described in more detail. (1) Method of coextrusion and lamination in a sheet form using a flat die, (2) Coextrusion by using an annular die and cylinder There is a method of producing a sheet-like laminated foam, and then cutting the tubular laminated foam into a sheet form. In the method using an annular die, more specifically, a laminated foam is once produced into a cylindrical shape by extruding and foaming a melt-foamable resin melt from the annular die and then extruding the resin melt, and then the cylindrical shape. The laminated foam is cooled from the inner surface of the cylindrical laminated foam by passing over the columnar cooling device, and a laminated foam having a thickness of 2 to 8 mm can be obtained by cutting this. Of the methods (1) and (2), a coextrusion method using an annular die is suitable for obtaining a wide laminated foam having a width of 1000 mm or more.

  In addition, when a laminated foam is obtained by the above-described coextrusion method, a coextrusion method in which a laminated structure of a resin layer and a foamed layer is formed outside the die outlet or the die outlet may be adopted. . In addition, as an extruder, an annular die, a columnar cooling device, and a device for opening a cylindrical laminated foam in the case of extrusion foaming using an annular die, known ones conventionally used in the field of extrusion foaming are used. be able to.

  The laminated foam of the present invention has an open cell ratio of 40% or less, and as a method for setting the open cell ratio in such a range in producing the laminated foam, for example, the amount of the bubble regulator and the extrusion temperature It can be adjusted by setting the extrusion conditions.

  As the foaming agent used for forming the foam of the laminated foam of the present invention, the same inorganic physical 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 physical foaming agent include oxygen, nitrogen, carbon dioxide, and air. Examples of the organic physical foaming agent include propane, normal butane, isobutane, normal pentane, isopentane, normal hexane, isohexane, and cyclohexane. And aliphatic hydrocarbons, chlorohydrocarbons such as methyl chloride and ethyl chloride. The above foaming agents can be used in combination of two or more. Of these, those having, as a main component, normal butane, isobutane, or a mixture thereof having good compatibility with polyethylene-based resins and good foaming properties are preferable. On the other hand, it is also preferable to use carbon dioxide or a mixture thereof as a foaming agent from the viewpoint of environmental friendliness and safety. A decomposable foaming agent such as azodicarbonamide can also be used in combination.

  The amount of foaming agent added is adjusted according to the type of foaming agent and the apparent density of the desired foam. For example, when isobutane is used as a foaming agent in order to obtain the laminated foam of the present invention, the amount of isobutane added is 0.3 to 5.0 parts by weight, preferably 0.4 to 4.5 parts by weight per 100 parts by weight of the foam layer resin. More preferably 0.5 to 3.0 parts by weight, and when carbon dioxide is used, the amount of carbon dioxide added is 0.1 to 3 parts by weight, preferably 0.12 to 2.5 parts by weight, more preferably 100 parts by weight of the foam layer base resin. 0.15 to 2 parts by weight.

  Moreover, it is preferable that a bubble regulator is added to the foam layer base resin constituting the foam layer. As such a 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 foam regulator include sodium 2,2-methylenebis (4,6-tert-butylphenyl) phosphate, sodium benzoate, calcium benzoate, aluminum benzoate, and sodium stearate. A combination of citric acid and sodium bicarbonate, an alkali salt of citric acid and sodium bicarbonate, or the like can also be used as the bubble regulator. These bubble regulators can be used in combination of two or more.

  The amount of bubble regulator added is adjusted according to the target bubble diameter. When talc is used as the cell regulator, 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 foam layer base resin.

  Since the laminated foam of the present invention is excellent in rigidity, shock-absorbing property and impact resistance, it is used to produce various processed products such as assembly boxes and plate materials and molded products by being processed or molded into appropriate shapes. Can be done. In addition to the processed product as described above, the laminated foam is also preferably used for applications such as a corrugated cardboard substitute, a partition material, an assembly box, and a curing plate for a concrete formwork.

  In the case where simple thermoforming such as a satchel core material is required, the laminated foam of the present invention is, for example, a mold comprising a male mold and / or a female mold after heat-softening a polyethylene resin laminated foam. Can be thermoformed. In addition to vacuum forming and pressure forming, thermoforming methods include free drawing, plug and ridge, ridge, matched mold, straight, drape, reverse draw, air slip, and plug. Examples include assist molding, plug assist reverse draw molding, and a molding method in which these are appropriately combined.

  In the present invention, methods for measuring physical properties of the laminated foam are as follows.

The thickness of the laminated foam is calculated as follows.
First, the laminated foam is cut perpendicularly in a direction perpendicular to the extrusion direction of the laminated foam. Then, the thickness of the cut surface of the laminated foam was photographed at 10 points at equal intervals in the width direction with a microscope, the total thickness at each photographed point was measured, and the arithmetic average value of the obtained values was calculated for the laminated foam The thickness was taken. In the same manner, the thickness of the resin layer can be measured. Furthermore, the thickness of the foamed layer is calculated by subtracting the numerical value indicating the thickness of the resin layer from the numerical value indicating the thickness of the obtained laminated foam.

  The apparent density of the foam layer can be calculated by converting the basis weight of the foam layer excluding the basis weight of the resin layer from the basis weight of the laminated foam by the value corresponding to the thickness of the foam layer. Calculated.

The basis weight of each of the laminated foam and the resin layer is measured as follows.
The basis weight of the laminated foam is calculated by cutting out a test piece of 25 mm long x 25 mm wide x laminated foam thickness calculated as above, measuring the weight (g) of the test piece, and multiplying the measured value by 1600 times. is calculated as a value in terms of weight per 1 m ² Te (g / m ^2).

  The basis weight of the resin layer is obtained by multiplying the thickness of the resin layer calculated as described above by the density of the resin layer and converting the unit.

  The open cell ratio of the foam layer is measured using an air-comparing hydrometer 930 model manufactured by Toshiba Beckman Co., Ltd. in accordance with Procedure C described in ASTM D 2856-70 using a laminate foam as a test piece. It is a value calculated by the following equation (1) from the actual volume (sum of the volume of closed cells and the volume of the resin portion) Vx (L).

(Equation 1)
S (%) = (Va-Vx) × 100 / (Va-W / ρ) (1)

However, in said formula (1), Va, W, and (rho) are as follows.
Va: Its apparent volume (L) measured from the outer dimensions of the specimen used for measurement
W: Weight of test specimen (g)
ρ: Density of resin constituting the test piece (g / L)

  Note that the density ρ (g / L) and weight W (g) of the resin constituting the test piece are cooled by defoaming bubbles from the foamed layer of the laminated foam by hot pressing the test piece. It can be determined from the weight and volume of the sample obtained.

Since the test piece needs to be stored in a non-compressed state in the sample cup attached to the above-mentioned air comparison type hydrometer, this test piece is made from a laminated foam with a thickness of 25 mm and a thickness of 25 mm each. A foam having the thickness of the foam is cut out and used, and a minimum number of sheets having an apparent volume of 15 to 16 cm ³ are stacked and used.

  The flexural modulus of the laminated foam is calculated from the value obtained by measuring the extrusion direction (MD) and the width direction (TD) in accordance with JIS K 7203 (1982) and averaging the obtained values. Measurement in accordance with JIS K 7203 (1982) uses a specimen with a length of 100 mm × width 25 mm × laminated foam thickness as a test piece, with a fulcrum tip R = 5 (mm) and a pressure tip R = 5 ( mm), the distance between fulcrums is 50 mm, and the bending speed is 10 mm / min. For the measurement, five test pieces are used, and measured values in the extrusion direction (MD) and the width direction (TD) are obtained for each test piece, and an arithmetic average value is obtained for each test piece. And the average value of the arithmetic mean value obtained for every test piece was computed, and this computed average value was employ | adopted as a bending elastic modulus.

  The tensile elongation (a (mm)) of the resin layer was determined by cutting a strip-shaped test piece (width 10 mm) with a length of 30 mm or more and a width 10 mm with the extrusion direction of the layered foam from the layered foam. Measured using a part with a cut across the entire width. The cut shape is a V-shaped cut having an inner angle of 45 degrees with the interface between the foam layer and the resin layer as the apex so that the resin layer on one side of the laminated foam is not cut. Next, with the longitudinal direction of the test piece up and down, the upper and lower ends of the test piece are held by a fixture equipped with a gripping tool so that the distance between the gripping tools is kept at 10 mm so as not to wobble in the left-right direction. Secure to. Then, the test piece is pulled up and down at a pulling speed of 500 mm / min, and the distance between the grips stretched until the test piece breaks is measured. From this value, the distance between grips 10 mm before stretching is calculated. The value obtained by subtraction is taken as the tensile elongation (a (mm)).

  The 25% compressive strength (b (MPa)) of the laminated foam is calculated as follows based on the value measured according to JIS K 7220 (1990). First, from the laminated foam, a test piece having a length of 50 mm × width 50 mm × laminate foam was cut out to give a test piece, and the test piece was compressed 25% in the thickness direction at a compression rate of 0.5 mm / min. Compressive stress is measured. In measuring the compressive stress, after adjusting five test pieces, the compressive stress is measured for each test piece. The average value is calculated by arithmetically averaging the values of the five compressive stresses thus measured, and the average value is defined as a 25% compressive strength.

  The tensile elongation and tensile elastic modulus of the resin layer base resin are measured according to JIS K 7127 (1989). In addition, the test piece used for a measurement is adjusted by heat-pressing and then cooling the resin layer cut out from the laminated foam. In addition, five type 2 test pieces with a thickness of 0.9 mm were used for the measurement, and the measured values were obtained under the conditions of a distance between grips of 80 mm and a tensile speed of 500 mm / min for each test piece. The average value was calculated by averaging the measurement data, and the calculated average value was adopted as the tensile elongation. For the measurement, a Tensilon universal testing machine manufactured by Orientec Co., Ltd. is used.

  Next, the laminated foam of this invention is demonstrated concretely using an Example.

Examples 1-5, Comparative Examples 1-3, 5, 6
As an extruder for forming a foamed layer of a laminated foam, a tandem extruder consisting of two extruders with a diameter of 90 mm and a diameter of 120 mm is used, and an extruder with a diameter of 50 mm is used as an extruder for forming an inner resin layer, Further, as an extruder for forming the outermost resin layer, a diameter of 40 mm was used, and an annular die having an annular slit having a diameter of 165 mm for joining and co-extruding the molten resins kneaded by the respective extruders was used.

  First, in order to form a foam layer, 100 parts by weight of the resin shown in Table 1 was mixed with a mixture of a foam regulator monosodium citrate and sodium bicarbonate (“Finecell Master SSC-PO208K, manufactured by Dainichi Seika Kogyo Co., Ltd.). Is blended in 0.7 parts by weight, fed to the raw material inlet of an extruder with a diameter of 90 mm, heated and kneaded to obtain a molten resin mixture prepared at about 200 ° C., and isobutane as a blowing agent in the molten resin mixture The mixture was press-fitted to 1.2 parts by weight with respect to 100 parts by weight, and then supplied to an extruder with a diameter of 120 mm connected to the downstream side of the extruder with a diameter of 90 mm to obtain a foamable molten resin mixture.

  On the other hand, in order to form an inner layer, the resins shown in Table 1 were supplied to an extruder having a diameter of 50 mm and melt kneaded to obtain a molten resin. In order to form the outermost layer, the resins shown in Table 1 were melt-kneaded from an extruder having a diameter of 40 mm to obtain a molten resin. The ratio between the inner layer and the outermost layer was formed as shown in Table 1.

  Each molten resin is fed into the annular die, and the molten resin constituting the outermost layer, the molten resin constituting the inner layer, and the foamable molten resin mixture are laminated and co-extruded from the annular die, and cylindrical immediately after extrusion. Cooling air was blown from the outside of the laminated foam to form a cylindrical laminated foam that was laminated from the outside in the order of outermost layer / inner layer / foamed layer / inner layer / outermost layer.

  The tubular laminated foam formed is cut along a cylindrical cooling device (mandrel) having a diameter of 350 mm, and the tubular product is cut open. Then, both sides of the laminated foam are heated in a heating furnace, and a cooling roll The target plate-like laminated foam was obtained through a flat plate. The laminated foams obtained in Examples 1 to 5 were excellent in appearance such as smoothness.

Example 6, Comparative Example 4
Laminate as in Example 1 except that a 50 mm diameter was used as an extruder for forming the outermost resin layer, and a laminated foam was laminated in a three-layer configuration of outermost layer / foamed layer / outermost layer with no inner layer. A foam was obtained. The laminated foam obtained in Example 6 was excellent in appearance such as smoothness.

Example 7
A plate-like laminated foam was obtained in the same manner as in Example 1 except that carbon dioxide was used as the foaming agent and 0.6 parts by weight of carbon dioxide was injected into 100 parts by weight of the resin for forming the foamed layer. The laminated foam obtained in Example 7 was excellent in appearance such as smoothness.

Comparative Example 7
Plate-like laminated foam as in Example 1, except that 1.4 parts by weight of isobutane is pressed into 100 parts by weight of the resin for forming the foamed layer, and the basis weight of each layer is as shown in Table 2. Got.

In Table 1, the resins used are as shown below.
LD1: Branched low density polyethylene (Density = 922g / L, MFR = 2.4g / 10min, manufactured by Nihon Unicar Co., Ltd., trade name “NUC-8321”)
LD2: Branched low-density polyethylene (Density = 922g / L, MFR = 0.3g / 10min, manufactured by Sumitomo Chemical Co., Ltd., trade name “F-102”)
LL1: Linear low-density polyethylene (density = 924g / L, MFR = 8.0g / 10min, manufactured by Nippon Polyethylene Co., Ltd., trade name “UJ460”)
LL2: Linear low-density polyethylene (Density = 920g / L, MFR = 2.1g / 10min, manufactured by Nippon Polyethylene Co., Ltd., trade name “UF240”)
HD1: High density polyethylene (Density = 964g / L, MFR = 8.0g / 10min, manufactured by Nippon Polyethylene Co., Ltd., trade name “HJ560WUF240”)
HD2: High density polyethylene (Density = 961g / L, MFR = 0.9g / 10min, manufactured by Tosoh Corporation, trade name "5110")
P300: Polymer type antistatic agent based on polyether-polypropylene block copolymer (Density = 990g / L, MFR = 20g / 10min, Sanyo Chemical Industries, Ltd., trade name “Pelestat 300”)

  About the obtained laminated foam, the apparent density of the foam layer, the open cell ratio of the foam layer, the thickness of the laminate foam, the flexural modulus, the tensile elongation of the polyethylene resin layer (a (mm)), 25 of the laminate foam % Compressive strength (b (MPa)) was measured and the value of a / b was calculated. The results are as shown in Table 2.

  Further, the obtained laminated foam was evaluated for folding resistance, crack resistance, rigidity, impact piercing strength, and surface resistivity as shown below, and the results are shown in Table 3.

[Folding resistance]
Folding resistance was evaluated by measuring the number of foldings. The number of folding times was measured based on JIS P 8115 (1994). The number of folding times was measured using a folding tester manufactured by Toyo Seiki Seisakusho Co., Ltd. as follows.
By pressing the laminated foam, a test piece with a width of 15 mm in which a bent part is formed by providing three ruled lines in the width direction is fixed, and both ends of the test piece are fixed with a load of 9.8 N. Using a jig of 0.38 mm as a fulcrum, a reciprocating operation was performed at a bending angle of 135 degrees, and bending was performed at the bent portion. The above bending was repeated at a rate of 175 reciprocations per minute until the test piece was cracked, and the number of times of bending when the crack occurred was measured. This measurement was performed three times, and the average value of the measured values was defined as the folding endurance number. The results are as shown in Table 3.

[Crack resistance]
Ten test pieces each cut to a size of 150 x 20 mm in the extrusion direction and the width direction were adjusted, 20 in total, and each test piece was bent by hand, and the presence or absence of cracks was confirmed visually. . Of the 20 test pieces, the number of test pieces that did not crack was measured, and the crack resistance was evaluated as follows according to the ratio of the test pieces that did not crack.
Cracks do not occur in 80% or more test pieces.・ ・ ・ ・ ・ ・ ・ ・ ◎
Cracks do not occur in specimens of 50% or more and less than 80%.・ ・ ・ ○
Cracks do not occur in test pieces of 20% or more and less than 50%. ... △
Cracks do not occur in test pieces less than 20%.・ ・ ・ ・ ・ ・ ・ ・ ×

[rigidity]
An assembly box of approximately 420 x 240 x 230 (height) mm is made from the laminated foam, and the contents of 15 kg are put into this assembly box, stacked in five stages, and assembled at the bottom stage after 48 hours in an environment of 23 ° C. The degree of blistering (trunk) of the box was measured. Evaluation was carried out as follows by using this blister.
Body blister is 15mm or less ... ○
Bumper is 15mm or more, or can not withstand the weight and collapses ... ×

[Shock drilling strength]
The impact piercing strength was measured according to JIS P 8134 (1976). For the measurement, a test piece with a length of 150 mm x 150 mm x laminated foam is used as a test piece. The test piece is kept in a thermostatic bath at -25 ° C for 15 hours or more. The measurement was carried out under the condition of measuring within 3 seconds after taking out below. This test was performed at least 5 times, and the average value obtained by averaging the measured values in each test was taken as the value indicating the impact drilling strength (F (kgf · cm)), and depending on the value The impact drilling strength was evaluated as follows.
F> 120 (kgf ・ cm) ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ◎
120 （kgf ・ cm） ≧ F> 100 （kgf ・ cm） ・ ○
100 (kgf · cm) ≧ F> 60 (kgf · cm) ・ ・ ・ △
F ≦ 60 (kgf ・ cm) ・ ・ ・ ・ ・ ・ ・ ・ ×

[Surface resistivity]
The surface resistivity of the surface of the laminated foam was measured in accordance with JIS K 6911 (1995) except that the condition of the test piece was adjusted as follows. Specifically, a test piece cut into a size of 100 mm in length and 100 mm in width (thickness is the thickness of the laminated foam) from the laminated foam as a measurement object was used. And then ultrasonically cleaned for 24 hours, and then the specimen is left to dry for 36 hours in an atmosphere of 30 ° C. and 30% relative humidity. As a result, the condition adjustment of the test piece was completed, and voltage application was started under the condition of an applied voltage of 500 V, and the surface resistivity after one minute was obtained.

For explaining the relationship between the tensile elongation (a (mm)) of the polyethylene resin layer and the 25% compressive strength (b (MPa)) of the polyethylene resin laminate foam in the polyethylene resin laminate foam of the present invention It is explanatory drawing.

Claims (3)

  Polyethylene resin laminated foam with an apparent density of 150g / L to 350g / L, a polyethylene resin foam layer with an open cell ratio of 40% or less, a thickness of 2 to 8mm with a polyethylene resin layer on both sides, and a flexural modulus of 150 to 350MPa The ratio (a / b) of the tensile elongation (a (mm)) of the polyethylene resin layer to the 25% compressive strength (b (MPa)) of the polyethylene resin laminated foam is 2.4 mm / MPa. A polyethylene resin laminated foam, wherein the 25% compressive strength (b (MPa)) of the polyethylene resin laminated foam is 0.5 to 1.5 MPa.   The polyethylene resin constituting the polyethylene resin foam layer is composed of polyethylene (Xa) 40 to 80% by weight having a density of 930 g / L or less, and polyethylene (Ya) 20 to 60% by weight having a density of more than 930 g / L and 970 g / L or less. 2. The polyethylene-based resin laminated foam according to claim 1, comprising:% (provided that the total of Xa and Ya is 100% by weight).   The polyethylene resin constituting the polyethylene resin layer is composed of 10 to 40% by weight of linear polyethylene (Xb) having a density of 930 g / L or less, and polyethylene (Yb) 50 to a density of more than 930 g / L to 970 g / L or less. The high-pressure polyethylene (Xc) having a density of 930 g / L or less and 0 to 30% by weight (provided that the total of Xb, Yb and Xc is 100% by weight). 2. Polyethylene resin laminate foam according to 2.

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