JP4332198B2 - Returnable box material made of propylene-based resin foam laminated flat plate - Google Patents

Description

The present invention relates to a returnable box material made of a polypropylene resin foam laminated flat plate which can be used as various core materials, partition materials, folded materials, boxing materials, and the like.

  2. Description of the Related Art Conventionally, a simple packaging box called a returnable box is used in a company or factory to transfer products and intermediate products from one department to another department or store them temporarily. Conventionally, corrugated cardboard boxes have been widely used as this kind of returnable box. However, the corrugated cardboard return box has a problem that paper dust comes out of the material and contaminates the product. Also, in confectionery factories, foods such as candy may be stored in boxes, but paper cardboard boxes are not water-resistant and cannot be washed, are unsanitary, and are used for a long time. There was a problem that it could not be used repeatedly.

If a synthetic resin is used as the material of the returnable box, the above-mentioned problem of the returnable box made of cardboard can be solved. As a synthetic resin material that has lightness and shape retention like paper cardboard and can be used in place of paper cardboard, for example, plastic cardboard or T-die is extruded and foamed. Examples thereof include a low-foamed propylene-based resin foam plate having a density of about 0.5 to 0.3 g / cm ³ (foaming ratio of about 2 to 3 times).

  Plastic cardboard is water resistant and can be washed. However, plastic corrugated cardboard, like paper corrugated cardboard, has a hollow structure in which a corrugated sheet material is interposed between a front surface material and a back surface material, so that water penetrates into the hollow portion of the corrugated cardboard when washed. It is not preferable because it remains. Also, plastic corrugated cardboard is made by interposing a non-foamed corrugated sheet material between the non-foamed surface material and the back material, so it is heavier than paper cardboard and has an edge that is more than paper cardboard. Furthermore, there is also a problem that the operator can easily cut his / her hand because it is hard and sharp.

  On the other hand, low-foamed propylene resin foam boards are also heavier than paper corrugated cardboard, and have a thick skin in the manufacturing process, so the rigidity, especially the 10% compressive strength, is too high, and the workability is poor. Inferior toughness, for example, when adopting a normal corrugated cardboard box form, when sealing the upper and / or lower surface of the cardboard box without using a gum tape, it is not possible to assemble the tongue pieces alternately was there. Further, a propylene-based resin foam sheet obtained by extrusion foaming from an annular die described in JP-A-4-363227 has a higher expansion ratio than the propylene-based resin foam plate obtained by extrusion foaming from a T die. However, there is a problem that the rigidity is insufficient and warping occurs, and the surface flatness is also insufficient.

On the other hand, the propylene-based resin plate-like foam described in JP-A-8-231745 has a density of 0.06 to 0.3 g / cm by making the bubbles in the inner layer portion of the foam into a specific shape. ³ is lightweight and excellent in cushioning and punching properties, but has poor surface smoothness, resulting in poor appearance and printability and insufficient rigidity. On the other hand, a synthetic resin film having a tensile strength of 10 kg / mm ² or more is laminated on at least one surface of a plate-like propylene-based resin foam having a density of 0.07 to 0.25 g / cm ³ previously proposed by the present applicant. The resulting propylene-based resin foam laminate (Japanese Patent Application No. 8-175588) has excellent physical properties such as excellent buffering and punching properties and relatively high rigidity. However, it is necessary to use a stretched film as a synthetic resin film having a tensile strength of 10 kg / mm ² or more laminated on the foam, which increases the cost and increases the production efficiency for laminating the stretched film or the like on the foam. As a result, the manufacturing cost is high.

As a result of intensive studies to solve the above problems, the present inventors have found that a core layer made of a propylene resin foam and a surface layer made of a propylene resin film or a low propylene resin foam are laminated and integrated. When manufacturing a returnable box material consisting of a resin-based resin foam laminated flat plate, a cylindrical foam is obtained by extruding into a cylindrical shape by a coextrusion method, and a core layer and a surface layer are laminated and integrated, and then the cylindrical foam is cut open. After adopting a method of heat-treating to a specific temperature and taking up with a roll etc. after adopting a plate shape, it is lightweight but rigid and surface smoothness without laminating a film with high tensile strength such as stretched film In addition, the present inventors have found that a returnable box material made of a propylene-based resin foam laminated flat plate having excellent printability, appearance, buffering property, and excellent punching property has been obtained, and the present invention has been completed.

The returnable box material made of the propylene-based resin foam laminated flat plate of the present invention has a surface layer made of an unstretched propylene-based resin film on at least one side of a core layer made of a propylene-based resin extruded foam and the following (A) or (I) ) Is a returnable box material made of a propylene-based resin foam laminated flat plate that is laminated and integrated by the lamination method, wherein the returnable box material made of the foamed laminated flat plate has a density of the propylene-based resin extruded foam constituting the core layer. 0.07 to 0.30 g / cm ³ , the basis weight of the unstretched propylene-based resin film constituting the surface layer is 20 g / m ² or more and less than 60 g / m ² , and the density of the entire foamed laminated flat plate is 0.10 to 0.35 g / cm ³ , the overall thickness is 2 to 10 mm, and the surface glossiness of the surface on which the surface layer is laminated is less than 50%, and the centerline average roughness on the surface Is 5 μm or less.
(A): The propylene-based resin foamable melt constituting the core layer and the propylene-based resin non-foamable melt constituting the surface layer are coextruded and foamed, and the core layer and the surface layer are laminated and integrated.
(A): A core layer and a surface layer are laminated and integrated by extruding and laminating a propylene-based resin non-foamable melt on at least one surface of a propylene-based resin extruded foam.

The returnable box material composed of the propylene-based resin foam laminated flat plate of the present invention has a tensile strength of an unstretched propylene-based resin film constituting the surface layer: E (kgf / cm) and a basis weight of the film: X (g / m It is preferable that the following expression ( 1 ) holds between ² ) and ² ).
E <0.07X ( 1 )

Moreover, it is preferable that the returnable box material made of the propylene-based resin foam laminated flat plate of the present invention contains 5 to 30% by weight of an inorganic filler in the propylene-based resin constituting the surface layer.

As described propylene-based resin foam composed of a laminated plate-returnable container material of the present invention, the density of the propylene-based resin foam is 0.07 ~0.30g / cm 3 constituting a core ^layer, made of foamed laminate flat or The overall density of the returnable box material 1 is 0.10 to 0.35 g / cm ³ , the overall thickness is 2 to 10 mm, and the basis weight of the unstretched propylene-based resin film is 20 g / m ² or more and 60 g / m ^2. If the surface layer is less than 50%, the surface glossiness of the surface on which the surface layer is laminated is less than 50%, and the center line average roughness on the surface is 5 μm or less. It is preferably used for molding applications, the surface state of the core layer is improved, there is no color unevenness during printing, ink lamination with a uniform thickness is good, and not only mere printing, but, for example, uniform conductive paint Stackability By improving the effect and the like of uniform performance is expressed, appearance, there is an effect that excellent washing properties.

The unstretched propylene resin film layer constituting the surface layer has no warpage even when unstretched propylene resin film is provided only on one side of the core layer, one side of the core layer unstretched propylene resin film Regardless of whether they are laminated to each other or both sides.

Figure 1 shows an example of a returnable container blank 1 made of a propylene-based resin foamed laminate flat of the present invention, returnable container blank 1 consisting of the foam laminate flat plate, on both sides of the core layer 2 made of propylene-based resin foam, no It has a structure in which a surface layer 3 made of a stretched propylene resin film is laminated and integrated. The surface layer 3 may be laminated only on one side of the core layer 2, but is preferably laminated on both sides in order to obtain higher rigidity.

In the present invention, the returnable box material 1 composed of the above foamed laminated flat plate supplies the propylene-based resin foamable melt and the propylene-based resin non-foamable melt to the annular coextrusion die at the tip of the extruder, After joining, a cylindrical foam obtained by extruding from an annular coextrusion die can be produced by a coextrusion method such as cutting it in the extrusion direction to form a plate. In order to obtain a foamed laminated flat plate (not shown) having the surface layer 3 only on one side of the core layer 2, only the inner surface side of the foamed layer of the cylindrical foam extruded from the above-mentioned annular coextrusion die, or The propylene-based resin foamable melt and the propylene-based resin non-foamable melt may be merged by the annular coextrusion die so that the non-foamed layer is formed only on the outer surface side. In order to obtain a returnable box material 1 composed of a foamed laminated flat plate having surface layers 3 on both sides of the core layer 2 as shown in FIG . 1, a non-foamed layer is formed on both sides of the foamed layer of the cylindrical foam. What is necessary is just to make a propylene-type resin foamable melt and a propylene-type resin non-foamable melt merge by the die | dye for cyclic | annular coextrusion.

When producing the returnable box material 1 composed of the propylene-based resin foam laminated flat plate of the present invention, the tubular foam is cut along the extrusion direction to form a foam laminated plate, and then both the front and back surfaces of the foam laminated plate are formed. Further, it is possible to employ a method in which the surface layer 3 is heated to a temperature higher than that of the propylene-based resin constituting the surface layer 3 (heat distortion temperature -20 ° C.) and taken up with a roll or the like. The above-mentioned “after” means that the foamed laminated board may be heated online, or the foamed laminated board may be wound up into a roll once, and then the roll may be unwound and heated later. . In addition, when both the surface layers 3 of the core layer 2 and / or the multilayer surface layer 3 have different thermal deformation temperatures of the base resin of each surface layer 3, the higher thermal deformation temperature is used as a reference (thermal deformation temperature − 20 ° C) or higher. The temperature at which the front and back surfaces of the foam laminate are heated is preferably 120 to 165 ° C, more preferably 123 to 155 ° C. Examples of the method for heating the foam laminate include a method using radiant heating with a far infrared ray, near infrared ray or the like using a heating furnace, and a method using contact heating with a hot roll. Note that heating above the (heat deformation temperature -20 ° C.) of the propylene-based resin constituting the surface layer 3 means that the foamed laminate immediately after coming out of the heating means is heated by heating means such as a heating furnace. It means that the surface temperature of the surface layer 3 is obtained by temperature measurement with infrared rays without delay, and the temperature is (heat distortion temperature−20 ° C.) or higher. The heat distortion temperature is a temperature measured according to JIS K7207 (bending stress 4.6 kgf / cm ² ). In addition, when the propylene-type resin containing an inorganic filler is used for the surface layer 3, let the heat deformation temperature of the propylene-type resin containing the inorganic filler be a heat deformation temperature.
Moreover, since the upper limit of the heating temperature on both the front and back surfaces of the foam laminate is a value that varies depending on the heat resistance of the propylene-based resin constituting the foam laminate, the range in which the surface state of the foam laminate does not deteriorate, It is adjusted below the melting point of the propylene-based resin constituting both the front and back surfaces of the foam laminate.

  As described above, both surfaces of the foamed laminate formed by cutting and opening the cylindrical foam obtained by the coextrusion method are heated to a temperature higher than that of the propylene-based resin forming the surface layer (thermal deformation temperature −20 ° C.). By adopting the take-up method, it is possible to eliminate the wave generated at both ends in the width direction of the foamed laminate and the winding of the laminate, and the mechanical strength and surface smoothness of the laminate are further improved. It becomes good. In addition, as a method of heating and taking out the foamed laminated board, after heating the laminated board with a heating furnace, a method of taking up with a roll or a conveyor, a method of simultaneously heating and taking up with a hot roll, etc. A wide variety of combinations are possible. In particular, it is preferable in terms of surface smoothness and the like to adopt a roll that can be heated or can press the surface of the heated foamed laminate as a take-up means.

A foamed laminated board obtained by cutting a cylindrical foamed body along the extrusion direction when obtaining a returnable box material 1 composed of a foamed laminated flat plate having the structure shown in FIG. In the step of heating both surfaces, the side where the heating temperature is not less than (thermal deformation temperature−20 ° C.) of the propylene-based resin forming the surface layer 3 and located on the outer side (outer peripheral surface side) of the cylindrical foam It is preferable that the heating temperature of the surface is higher by 5 ° C. or more than the heating temperature of the surface located on the inner side (inner peripheral surface side) of the cylindrical foam. In particular, both surfaces of the foamed laminate having the surface layer 3 laminated on both surfaces of the core layer 2 are set to a temperature equal to or higher than the (thermal deformation temperature−20 ° C.) of the resin constituting the surface layer 3 and as described above, By providing a heating temperature difference of 5 ° C. or more and heating, the residual strain on the front and back surfaces of the foamed plate can be relaxed in a well-balanced manner, so that a flat plate with good appearance can be obtained.

Examples of the base resin of the core layer 2 in the return box material 1 made of a propylene-based resin foam laminated flat plate include a non-crosslinked propylene homopolymer, a propylene-based block copolymer that is a copolymer of propylene and other olefins, Examples include propylene random copolymers. Examples of the olefin constituting the propylene-based copolymer include ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, 4-methyl-1-pentene, 3-methyl-1-hexene and the like can be mentioned. Two or more of these may be copolymerized with propylene. The olefin content in the propylene-based copolymer is preferably 0.5 to 30% by weight, particularly 1 to 10% by weight. Furthermore, 3 to 20% by weight of a rubber component such as ethylene-propylene rubber can be mixed with the base resin.

  In addition, inorganic pigments such as chromate, ferrocyanide, sulfide, phosphate, carbon and silicate, organic pigments such as azo, phthalocyanine, quinacridone and dioxazine and other dyes are used as the base resin. 0.01 to 5% by weight of a colorant comprising 0.1 to 2 of an antistatic agent such as glycerin fatty acid ester, sorbitan fatty acid ester, N, N-bis (hydroxyethyl) -N-alkylamine, and alkylsulfonic acid. % By weight, 0.01-2% by weight of hindered amine light stabilizer, benzotriazole ultraviolet absorber, phenolic antioxidant, phosphorus antioxidant, etc., carbon black, silver powder, nickel powder, graphite, 1-20% by weight of conductivity imparting agents such as aluminum flakes, flame retardants, bubble regulators, fluidity improvers, thermal stabilizers, inorganic fillers, etc. It is preferable to appropriately blended according to necessity.

The propylene-based resin preferably has a drawdown property of 60 m / min or less, particularly 30 m / min or less. Those drawdown exceeds 60 m / min, tend to cause the corrugated When you obtain a foam by the extrusion foaming, tends as many of the surface irregularities. The drawdown property of the propylene-based resin can be adjusted by the number and length of long chain branches. In general, as the number of long chain branches increases and the branch length increases, the drawdown property tends to decrease.

  A propylene resin having a drawdown property of 60 m / min or less is a low-temperature decomposition type (decomposition temperature is lower than a normal crystalline linear propylene resin containing an atactic component and / or an isotactic component that is not crystallized. Add a peroxide from room temperature to about 120 ° C. and heat to 120 ° C. or less to bond atactic or / and non-crystallized isotactic components as branched chains to the main chain of the propylene resin. It is obtained by the method.

  Examples of the low-temperature decomposition type peroxide include di (s-butyl) peroxydicarbonate, bis (2-ethoxy) peroxydicarbonate, dicyclohexylperoxydicarbonate, di-n-propylperoxydicarbonate, di- Examples thereof include n-butyl peroxydicarbonate, diisopropyl peroxydicarbonate, t-butyl peroxyneodecanoate, t-amyl peroxyneodecanoate, t-butyl peroxypivalate and the like.

  The drawdown property of the propylene-based resin is such that a melted 230 ° C. resin is injected from a melt indexer nozzle (bore 2.095 mm, length 8 mm) with a piston pressing speed of 10 mm / min. It is the winding speed when the string-like resin is cut when it is extruded into a string shape and the winding speed of the winding roll is gradually increased to wind up. The propylene resin constituting the foam is preferably one having a melt tension of 10 g or more. Melt tension was determined by applying a 230 ° C. resin from a melt indexer nozzle (2.095 mm in diameter, 8 mm in length) to a piston pressing speed of 10 mm / min. The value is detected by the load cell connected to the movable pulley that is first applied to the extruded string-like resin, and the load cell is detected by gradually increasing the winding speed of the string-like resin. The value when the value is stable.

  In the present invention, the propylene-based resin foam is preferably a non-crosslinked one based on a propylene-based resin that mainly satisfies the conditions of the drawdown property and the melt tension. Non-crosslinked foams are preferred because they are excellent in recyclability and productivity. In the present invention, the term “non-crosslinked” includes those that have been finely crosslinked to improve melting characteristics. Specifically, even a gel fraction of less than 5% by weight is included in the non-crosslinking range referred to in the present invention. The gel fraction was extracted in boiling xylene for 15 hours, filtered through a 75 μm mesh screen of JIS Z8801 (1995), and the insoluble matter was dried under reduced pressure for 24 hours to obtain the remaining amount of extraction (g). The percentage of the remaining resin extraction (g) with respect to the weight (g) before extraction is obtained.

  The above-mentioned propylene-based resin can be used as a base material resin of a foam by mixing other resins as necessary, but it is preferable that the drawdown property of the mixture does not exceed 60 m / min. Examples of resins that can be mixed and used include propylene resins having a drawdown property exceeding 60 m / min, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene- Examples include polyethylene resins such as butene copolymers and ethylene-maleic anhydride copolymers, polybutene resins, polyvinyl chloride, polyvinyl chloride resins such as vinyl chloride-vinyl acetate copolymers, and polystyrene resins. .

As the propylene-based resin constituting the surface layer 3 laminated on the core layer 2 made of the propylene-based resin foam, the above-described propylene-based resin having drawdown property and melt tension may be used. From the aspect, it is preferable to use other propylene-based resins. Further, in order to further improve the rigidity and surface smoothness of the returnable box material made of the foamed laminated flat plate of the present invention, 5-30 wt% of the inorganic filler is contained in the propylene-based resin constituting the surface layer 3. It is preferable to make it. When the surface layer is a multilayer, it is preferable in terms of surface smoothness that the base resin constituting the outermost layer contains an inorganic filler. Examples of the inorganic filler include talc, magnesium carbonate, calcium carbonate, magnesium sulfate, silica, clay, zeolite, alumina, and magnesium hydroxide.

Further, the base resin constituting the surface layer 3 is made of inorganic pigments such as chromate, ferrocyanide, sulfide, phosphate, carbon, silicate, azo, phthalocyanine, quinacridone, dioxazine, etc. 0.01 to 5% by weight of a colorant comprising an organic pigment or other dye, an antistatic agent such as glycerin fatty acid ester, sorbitan fatty acid ester, N, N-bis (hydroxyethyl) -N-alkylamine, alkylsulfonic acid 0.1-2% by weight, hindered amine light stabilizers, benzotriazole ultraviolet absorbers, phenolic antioxidants, phosphoric antioxidants, etc. 0.01-2% by weight, carbon black, silver powder 1-20% by weight of conductivity imparting agents such as nickel powder, graphite, aluminum flakes, etc., flame retardants, bubble regulators, fluidity improvers, thermal stability It is preferable to appropriately blended as required and the like.
Alternatively, a film in which indium oxide is formed as the conductive surface layer can be used.
The surface layer 3 is not limited to a single layer, and may be made of a multilayer polypropylene resin in which a polypropylene resin or the like containing an inorganic filler such as talc is laminated.

As the most preferred specific example of the present invention, the case where the surface layer made of the non-foamed propylene resin film is laminated on the core layer made of the propylene resin foam has been described as above. The surface layer has a density of 0.3 g / propylene resin low foam exceeds cm ^3, preferably is even 0.45 g / cm ³ or more propylene-based resin low foam can achieve the intended object of the present invention. In the present invention, the surface layer is composed of a propylene-based resin film or a low-foamed propylene resin film. Therefore, unless a special additive is added, the density of the propylene-based resin itself as the base material is the density of the surface layer. The upper limit of.
A surface layer made of a low foam can be obtained by coextrusion with a resin constituting the core layer by appropriately adding a heat decomposable foaming agent such as azodicarbonamide, a volatile foaming agent or the like to the base resin. it can.

The return box material 1 made of the propylene-based resin foam laminated flat plate of the present invention has a density of the propylene-based resin foam constituting the core layer 2 of 0.07 to 0.30 g / cm ³ , and the non-stretched material constituting the surface layer 3. the basis weight of the propylene-based resin film is 20 g / ^{m 2} or more and less than 60 g / ^{m 2,} the density of the entire foam laminated flat plates 0.10~0.35g / cm ^3, the overall thickness in the range of 2~10mm those, but still is less than 50% surface gloss of the surface on the side where the surface layer 3 are laminated, and the center line average roughness of the surface of Ru needs der that is 5μm or less.

In returnable box blank 1 consisting of the foam laminate flat plate of the present invention, to be insufficient in rigidity when the density of the core layer 2 is too small, light weight if the density exceeds 0.30 g / cm ^3, Secondary processability and buffering properties are insufficient. The density of the core layer 2 is particularly preferably 0.07 to 0.18 g / cm ^{3 in} terms of moldability, light weight, and workability. In the case the density of the entire foam laminated flat plate is less than 0.10 g / cm ^3, to be insufficient in rigidity, if it exceeds 0.35 g / cm ^3, the light weight, the secondary processability and buffering It will be insufficient. Further, when the thickness of the foam laminate 1 is less than 2 mm, the rigidity is insufficient, and when it exceeds 10 mm, the secondary workability is insufficient.

Further returnable box blank 1 consisting of the foam laminate flat plate of the present invention also has a basis weight of unoriented propylene resin film constituting the surface layer 3 as described above is 20 g / m ² or more, of less than 60 g / m ² The surface glossiness of the surface on which the surface layer 3 is laminated is less than 50%, and the center line average roughness on the surface is 5 μm or less, preferably 3 μm or less. When a film is laminated, the effect of improving rigidity is somewhat exhibited, but it is preferably used for thermoforming by a mold, the surface state of the core layer 2 is improved, and there is no color unevenness during printing. In addition, the ink lamination with a uniform thickness becomes good, and not only mere printing, but also, for example, by improving the uniform laminating property of the conductive paint, the effects such as the appearance of uniform performance, appearance, and cleaning properties There is an effect that it is excellent. When the basis weight of the film is 60 g / m ² or more, it may be difficult to set the thermoforming conditions and it may be difficult to obtain a molded product having a complicated shape, and when the surface glossiness is 50% or more. , The appearance is insufficient. On the other hand, when the center line average roughness exceeds 5 μm, the printability and cleaning properties are insufficient.

In the present invention, the value of the surface gloss is a value measured by the 60-degree specular gloss method of JIS Z8741. Moreover, the value of centerline average roughness is calculated | required by the centerline average roughness measurement of JISB0601. In addition, the surface glossiness and centerline average roughness of the returnable box material 1 made of the foamed laminated flat plate of the present invention shall be measured with respect to the surface layer 3 laminated on the core layer 2, and have the surface layer 3 on both sides. The measured value of each surface must satisfy the value specified by the present invention.

In addition, the density of the propylene-type resin extrusion foam which comprises the core layer 2 of the return box raw material 1 which consists of a foaming laminated flat plate, and the basic weight of the unstretched propylene-type resin film which comprises the surface layer 3 are measured as follows. be able to.

First from the sample a returnable container blank 1 made of foamed laminated plates were cut into square vertical 10cm × horizontal 10cm at any position, determine the total basis weight of the foam laminate flat plate. Then, the foamed laminate flat plate core layer 2 a cut surface in the thickness direction is enlarged by a microscope, each arbitrary thickness of 10 places of the surface layer 3 was measured, the core layer 2 the average of the measured values, the surface layer The basis weight of the surface layer 3 is determined from the raw material density of the propylene-based resin constituting the surface layer 3 and the thickness of the surface layer 3. Also it can be determined from the basis weight of the whole of the foamed laminate flat plate, a value obtained by subtracting the basis weight of the surface layer 3 as the basis weight of the core layer 2.

Above, the propylene-based density of the resin foam is 0.07 ~0.30g / cm ^3, the density of the entire foam laminated flat plates 0.10~0.35g / cm ³ constituting the core layer 2, the total thickness 2 to 10 mm, and the basis weight of the unstretched propylene-based resin film constituting the surface layer 3 is 20 g / m ² or more and less than 60 g / m ² , and the surface on which the surface layer 3 is laminated The returnable box material 1 made of a foamed laminated flat plate having a surface glossiness of less than 50% and a center line average roughness of 5 μm or less on the surface can be obtained by the above-described coextrusion method, or the propylene-based material constituting the core layer 3 It can also be obtained by a method of extruding and laminating a propylene-based resin non-foamable melt on the surface of a resin extruded foam. When manufactured by the coextrusion method, it is possible to laminate the surface layer 3 on both surfaces of a flat plate simultaneously in one step, and it is easy to laminate a surface layer having a basis weight of less than 60 g / m ^2. There are advantages.

In the returnable box material 1 made of the foamed laminated flat plate of the present invention, the propylene-based resin foam constituting the core layer 2 preferably has a closed cell ratio of 50% or more, particularly preferably 65% or more. When the closed cell ratio of the propylene-based resin foam constituting the core layer 2 is 50% or more, the rigidity and toughness of the core layer 2 are improved, and thus the physical properties such as the rigidity of the obtained foamed laminated flat plate are improved. A propylene-based resin foam having a closed cell ratio of 50% or more can be easily obtained by the above-described coextrusion method. The closed cell ratio of the foamed sheet was determined by the following formula ( 2 ) using an air comparison type hydrometer based on ASTM D2856.

Closed cell ratio (%) =
{[Vx−Va (ρf / ρs)] / [Va−Va (ρf / ρs)]} × 100 ( 2 )
However, in the above formula ( 2 ), Vx is the actual volume of the foam sheet sample (the sum of the volume of the resin constituting the foam sheet sample and the total volume of bubbles in the closed cell portion in the foam sheet sample) (cm ³ ), Va is the apparent volume (cm ³ ) of the foamed sheet sample, ρf is the apparent density (g / cm ³ ) of the foamed sheet sample, and ρs is the density of the resin (g / cm ³ ).

In addition, it is particularly preferable that the returnable box material 1 made of the foamed laminated flat plate of the present invention has a 10% compressive strength of less than 10 kg / cm ² in terms of buffering properties. The 10% compressive strength is 50 mm in length, 50 mm in width, and a test piece prepared by laminating so as to have a thickness of about 25 mm is measured with a universal testing machine (Orientec Co., Ltd .: Tensilon, etc.) 10 mm / min. And 10% compression, and the stress value at that time is adopted.

In the present invention, the term “non-stretched” of the unstretched propylene-based resin film constituting the surface layer 3 is used for differentiating the film constituting the surface layer 3 and the stretched film in the present invention. is there. As one indication of the "non-oriented" in the present invention, the basis weight of the film and X (g / ^{m 2),} tensile strength of the film: between E (kgf / cm), the following (1) A film that satisfies the formula is preferred.
E <0.07X ( 1 )

In order to satisfy the relationship of the above formula ( 1 ) between the basis weight and the tensile strength of the unstretched propylene-based resin film constituting the surface layer 3, for example, a core layer is formed by extruding a coextrusion method or a molten resin. The surface layer 3 may be formed by the method of laminating the two. The tensile strength of the film was determined by measuring a test piece of 50 mm long × 10 mm wide × film thickness using a tensile tester between chucks of 30 mm and a tensile speed of 200 mm / min. The breaking strength was determined in the extrusion direction and the width direction, and the arithmetic average value of the breaking strength in the extrusion direction and the width direction of the film was taken as the tensile strength of the film.

The returnable box material 1 made of the foamed laminated flat plate of the present invention has excellent surface rigidity, appearance, lightness, workability, washability, toughness, and sufficient rigidity depending on the basis weight of the surface layer. it is suitable as a material, but not only use remains plate, Ru can be used in thermoformed into a desired shape. Further, a resin layer other than polypropylene resin, an aluminum foil layer, or the like can be further laminated and bonded to the returnable box material 1 made of a foamed laminated flat plate.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.
Examples 1 to 3
As a propylene resin for constituting the core layer, a propylene homopolymer (PF814) manufactured by Montel is used, and as a propylene resin for constituting the surface layer, a propylene resin having a heat distortion temperature shown in Table 1 is used. It was. In the extruder, a mixture of isobutane and normal butane (weight ratio 1: 2) in the amount shown in Table 2 was added to the propylene resin constituting the core layer to form a foamable melt, while the others A non-foamable melt composed of a propylene-based resin containing talc shown in Table 1 is formed in the propylene-based resin constituting the surface layer in the extruder, and the non-foamable melt is formed on both sides or one side of the foamable melt. The two layers are joined together inside the annular die for coextrusion so as to be laminated, then extruded from the annular die into a cylindrical foam, and then the cylindrical foam is cut along the extrusion direction. Both surfaces of the foam were heated in a heating furnace and taken up with a roll. The surface temperature of the laminated foamed flat plate immediately after coming out of the heating furnace was measured with a far-infrared thermometer attached to the outlet of the heating furnace, and this temperature is shown in Table 2 as the heating temperature of the laminated foam surface. . In this way, a laminated foamed flat plate having surface layers on both sides or one side of the core layer was obtained. Table 2 shows the properties of the obtained laminated foamed flat plate.

Comparative Example 1
A propylene homopolymer (PF814) manufactured by Montel Co., Ltd. was used as the propylene-based resin for constituting the core layer, and the amount shown in Table 2 in the propylene-based resin constituting the core layer in the extruder was the same as in Example 1. A foaming melt was obtained by adding a foaming agent, extruded from a circular die into a cylindrical shape, and then cut into a sheet-like polypropylene resin foam, which was wound into a roll. Next, the roll-shaped foam was heated and stretched to obtain a foamed flat plate. A biaxially oriented polypropylene film was thermally bonded to the obtained flat plate to obtain a laminated foamed flat plate having a surface layer on one side of the core layer. The obtained laminated foamed flat plate was somewhat warped. Other properties are shown in Table 2.

※１：筒状発泡体の外側に位置していた側の面
※２：筒状発泡体の内側に位置していた側の面

* 1: Surface on the outer side of the cylindrical foam * 2: Surface on the inner side of the cylindrical foam

※１：筒状発泡体の外側に位置していた側の面
※２：筒状発泡体の内側に位置していた側の面
※３：発泡平板表面の中心線平均粗さ（μｍ）

* 1: Surface on the outside of the cylindrical foam * 2: Surface on the inside of the cylindrical foam * 3: Center line average roughness (μm) on the surface of the foam plate

Comparative Example 2
A foamed flat plate was obtained in the same manner as in Comparative Example 1. In Comparative Example 2, no film was laminated on the foamed flat plate. Table 3 shows properties of the obtained foamed flat plate.

Comparative Example 3
As a propylene-based resin for constituting the core layer, a propylene homopolymer (PF814) manufactured by Montel Co., Ltd. was used, and the amount shown in Table 3 in the propylene-based resin constituting the core layer in the extruder was the same as in Example 1. The foaming material was added to obtain a foamable melt, extruded from a circular die into a cylindrical shape, and then cut open to obtain a foamed sheet. Table 3 shows properties of the obtained foamed sheet.

In addition, the measurement of surface glossiness uses a gloss meter made by Nippon Denshoku Industries Co., Ltd .: PG-3D type, and in each surface layer of the laminated foamed flat plate, the extrusion direction and the width direction are measured. The arithmetic average value of the surface glossiness in the width direction was defined as the surface glossiness of the surface layer. The centerline average roughness is measured in the extrusion direction and the width direction on each measurement surface of the laminated foamed flat plate or foamed flat plate, and the arithmetic average value of the centerline average roughness in the extrusion direction and the width direction is measured on the measurement surface. The center line average roughness.
Moreover, the measurement of the heating temperature of the foam surface was measured using THRMO-HUNTER MODEL PT-3LF made from OPTEX.

It is a conceptual diagram which shows the structure of the returnable box raw material which consists of a propylene-type resin foaming laminated flat plate of this invention.

Explanation of symbols

1 Returnable box material made of propylene resin foam laminated flat plate 2 Core layer 3 Surface layer

Claims (3)

A propylene-based resin foam laminate in which a surface layer made of an unstretched propylene-based resin film is laminated and integrated by at least one side of a core layer made of a propylene-based resin extruded foam by the following lamination method (a) or (b) It is a returnable box material made of a flat plate, and the foamed laminated flat plate has a density of 0.07 to 0.30 g / cm ^{3 of} a propylene-based resin extruded foam constituting a core layer, and an unstretched propylene-type constituting a surface layer The basis weight of the resin film is 20 g / m ² or more and less than 60 g / m ² , the density of the entire foamed laminated flat plate is 0.10 to 0.35 g / cm ³ , the total thickness is 2 to 10 mm, and the surface layer is together with the surface glossiness of the surface of the laminated side it is less than 50%, returnable center line average roughness of the surface is made of a propylene-based resin foamed laminate flat, characterized in that it is 5μm or less Material.
(A): The propylene-based resin foamable melt constituting the core layer and the propylene-based resin non-foamable melt constituting the surface layer are coextruded and foamed, and the core layer and the surface layer are laminated and integrated.
(A): A core layer and a surface layer are laminated and integrated by extruding and laminating a propylene-based resin non-foamable melt on at least one surface of a propylene-based resin extruded foam. The following formula ( 1 ) is established between the tensile strength of the unstretched propylene-based resin film constituting the surface layer: E (kgf / cm) and the basis weight of the film: X (g / m ² ). A return box material comprising the propylene-based resin foam laminated flat plate according to claim 1 .
E <0.07X ( 1 ) The returnable box material comprising the propylene-based resin foam laminated flat plate according to claim 1 or 2 , wherein the propylene-based resin constituting the surface layer contains 5 to 30% by weight of an inorganic filler.

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