JPH1177867A - Air bubble cushioning sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the balance between mechanical characteristics such as tear strength, impact strength or the like and folding endurance by laminating a plastic film having specific density and formed of a large number of embosses composed of a specific polyethylene compsn. and a planar plastic film. SOLUTION: A plastic film 22 having a large number of embosses 21 formed on its entire surface and a planar plastic film 24 are laminated to form air bubbles 3 in the embosses 21. The density of the films 22, 24 is set to a 0.915-0.960 (g/cm<3> ). Further, the compounding ratio of respective components of an ethylene/α-olefin copolymer (x) (wt.%) and high pressure low density polyethylene (z) (wt.%) contained in a polyethylene compsn. constituting the films 22, 24 is set to a range shown by x+y+z=100, 45<=x+z<=95, 5<=x<=90 and 5<=z<=90 (wt.%). By this constitution, the balance between mechanical characteristics and folding endurance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition of a plastic foam cushioning sheet having convex closed cells.

[0002]

2. Description of the Related Art Among various thermoplastic resins, among various thermoplastic resins, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE) and the like can be used as materials for plastic foam cushioning sheets. Are generally used.

[0003] Plastic foam cushioning sheets are disclosed, for example, in Japanese Patent Publication No. 37-13772 and Japanese Patent Publication No. 38-3.
It is manufactured by a known method described in No. 30, for example, a method of laminating a plastic embossed film on which a large number of embosses are formed, and a plastic base film bonded to the embossed film. I have. JP-A-9-123320 discloses a cellular buffer sheet made of polyethylene having a specific density, melt flow rate, melt flow rate ratio, and molecular weight distribution.

[0004] As a characteristic of the foamed cushioning sheet, a composition obtained by blending a material mainly composed of low-density polyethylene, which is preferably applied, with tens of weight% of high-density polyethylene, has a higher bending strength than a single composition of low-density polyethylene. Strong, for example, the texture of a foamed cushioning sheet, that is, a strong stiffness can be obtained, but on the other hand, the tear strength or the impact resistance of the convex portion forming a convex closed cell decreases, the molding temperature increases, etc. There is a problem. Therefore, it has good mechanical properties such as good balance between folding strength and tear strength and impact strength of the convex part forming a convex closed cell, no winding around the embossing roll, and no deformation of the cell shape. In addition, a foamable cushioning sheet having good moldability and stable continuous production for a long period of time without deterioration or discoloration of the polymer has not been obtained. Furthermore, when manufacturing a foamed cushioning sheet, there is a case where the molten resin is molded while being stretched, and the tear strength in the longitudinal direction and the transverse direction due to the stretching becomes unbalanced, and there is a limit in increasing the amount of high-density polyethylene. .

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems relating to the production of a foamed cushioning sheet, and provides good moldability, mechanical properties such as tear strength and impact strength, and folding strength (texture). The present invention relates to a resin composition of a plastic foamed cushioning sheet having convex closed cells having an excellent balance with the waist).

[0006]

SUMMARY OF THE INVENTION A foamed buffer sheet having convex closed cells formed by laminating a plastic film (1) having a large number of embosses and a planar plastic film (2) is provided. The film (1) and / or (2) has a density of 0.915-0.
960 (g / cm ³ ), comprising a polyethylene composition containing (A) an ethylene-α-olefin copolymer, (B) a high-density polyethylene, and (C) a high-pressure low-density polyethylene having the following properties: The components of (A) ethylene-α-olefin copolymer, (B) high-density polyethylene and (C) high-pressure low-density polyethylene in the polyethylene composition are represented by the following general formulas (1) to (4). The present invention relates to a cellular buffer sheet characterized by the following.

X + y + z = 100 (1) 45 ≦ x + z ≦ 95 (2) 5 ≦ x ≦ 90 (3) 5 ≦ z ≦ 90 (4) In the formulas (1) to (4), x: (A) Ethylene-α-olefin copolymer (% by weight) y: (B) High density polyethylene (% by weight) z: (C) High pressure method low density polyethylene (% by weight)

(A) Ethylene-α-olefin copolymer
Body: (A-1) Density (d) = 0.880 to 0.960 (g /
cm^Three(A-2) Melt at 190 ° C. and 2.16 Kg load
Flow rate (MFR _2.16) = 0.01 to 200 (g /
(A-3) Melt at 190 ° C. and 21.6 kg load
Flow rate (MFR _21.6) And 190 ° C, 2.16 Kg
Melt flow rate under load (MFR_2.16) And ratio
 (MFR_21.6) / (MFR_2.16) = 1-20 (A-4) Molecular weight distribution (Mw / Mn) = 2.0-4.0

(B) high-density polyethylene (provided that
(A) Excluding ethylene-α-olefin copolymer): (B-1) Density (d) = 0.935 exceeding 0.970
Below (g / cm^Three(B-2) Melt at 190 ° C. and 2.16 Kg load
Flow rate (MFR _2.16) = 0.01-20 (g / 1
0 minutes) (C) High-pressure low-density polyethylene (provided that (A)
(Excluding the Tylene-α-olefin copolymer): (C-1) Density (d) = 0.915 to 0.935 (g /
cm^Three(C-2) Melt at 190 ° C. and 2.16 Kg load
Flow rate (MFR _2.16) = 0.01 to 50 (g / 1)
0 minutes)

More preferably, the (A) ethylene-
The present invention relates to a cellular buffer sheet characterized in that an α-olefin copolymer is produced from a single-site catalyst.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The cellular cushioning sheet of the present invention is:
Plastic film with many embosses (1)
And a planar plastic film (2) are laminated on each other to form a foamed buffer sheet having a large number of convex closed cells. A plastic film (2) is bonded to the plastic film (1) to form air bubbles inside the convex projections, or a second planar film ( A three-layer structure obtained by bonding 3) may be used. Instead of the plastic film (2) and / or the planar film (3), a material other than the plastic film such as kraft paper may be used. It is characterized in that the polyethylene composition is used for at least one of the foamed buffer sheets [plastic film (1) and / or plastic film (2)], and the structure of the foamed buffer sheet is particularly limited. In addition, the plastic film (1) or (2) and the plastic film (3) are made of other polyethylene, polyester, including the polyethylene composition, excluding the polyethylene composition.
Thermoplastic resins such as polyamide and polysulfone can be used.

The plastic film (1) and / or the plastic film (2) has a density of 0.9.
It is in the range of 15 to 0.960 g / cm ³ , preferably in the range of 0.925 to 0.950 g / cm ³ , more preferably in the range of 0.925 to 0.945 g / cm ³ , and particularly preferably. Is 0.922 to 0.942 g / c
m ³ .

When the density of the plastic film (1) and / or the plastic film (2) is less than the above range, the folding resistance of the foamed cushioning sheet becomes small, and the texture, that is, the strength of the waist cannot be secured. . On the other hand, if it is larger than the above range, the bending resistance of the foamed cushioning sheet is increased, so that the stiffness is increased and the cushioning function is impaired.

The tear strength of the plastic film (1) and / or the plastic film (2) is M
D direction is 0.38 kgf or more, further 0.40 kgf
Above, especially 0.45 kgf or more is preferable. Also, TD
The direction is preferably 1.76 Kgf or more, more preferably 1.80 Kgf or more, and particularly preferably 1.85 Kgf or more. When the tear strength in the MD or TD direction is smaller than the above value,
The sheet is apt to tear, which is not preferable for a cellular buffer sheet. In particular, when the MD direction is 0.38 kgf or more and the TD direction is 1.76 kgf or more, the tear strength in the vertical and horizontal directions is excellent, so that it can be preferably used for a cellular buffer sheet.

The cap impact strength of the plastic film (1) and / or the plastic film (2) is 12 gf / 26 inches or more, and further 15 gf / 2.
It is preferably 6 inches or more, particularly preferably 20 gf / 26 inches or more. If the cap impact strength is smaller than the above range, the cap is broken, which is not preferable for the cellular cushioning sheet.

The plastic film (1) and / or the plastic film (2) have an 80% deformation strength of 16 to 22 Kg / cm ³ , and more preferably 16.5 to 22 K.
g / cm ³ , particularly preferably 17 to 22 Kg / cm ³ . 8
When the 0% deformation strength is out of the above range, the cushioning property is low, which is not preferable for the cellular cushioning sheet.

The plastic film (1) and / or the plastic film (2) has a bending strength of 9
0-160 cm, further 95-150, especially 95-14
5 is preferred. If the bending strength is smaller than the above range,
If the foamed cushioning sheet has a weak stiffness, which is not preferable, and if it is larger than the above range, the foamed cushioning sheet has a strong stiffness, which is not preferred.

The embossed shape of the plastic film (1) is mainly a cylinder, but may be a polygonal prism such as a triangular prism, a prism, a pentagonal prism or a hexagonal prism, a cone, a triangular pyramid, a pyramid, a pentagonal pyramid or a hexagonal pyramid. It can be a pyramid, a truncated cone, a truncated pyramid, a truncated pyramid, a truncated pyramid, a truncated pyramid such as a truncated pyramid, a hemisphere, an egg, a spheroid, or the like. Further, a plurality of these shapes may be combined.

The height of the emboss of the plastic film (1) is preferably in a range of 1 to ²⁰ mm and a bottom area of 0.1 to 15 cm ² . Also, the emboss is 0.5 ~
Preferably, they are arranged on the entire surface of the plastic film (1) at intervals of 20 mm.

Plastic films (1) and (2)
The film thickness of the flat film (3) can be appropriately selected depending on the material to be used.
μm, more preferably 40 to 80 μm, particularly preferably 50 to 70 μm.

The ethylene-α-olefin copolymer which is the component (A) of the polyethylene composition of the plastic film (1) and / or (2) has physical properties in the following specific ranges.

(A) Ethylene-α-olefin copolymer
Body: (A-1) Density (d) = 0.880 to 0.960 (g /
cm^Three), Preferably 0.895 to 0.960 (g / c
m^Three), More preferably 0.915 to 0.960 (g
/ Cm^Three), Particularly preferably 0.910 to 0.930
(G / cm^Three(A-2) Melt at 190 ° C. and 2.16 Kg load
Flow rate (MFR _2.16) = 0.01 to 200 (g /
10 minutes), preferably 1 to 50 (g / 10 minutes), and
Preferably 1 to 20 (g / 10 min), particularly preferably 1
(A-3) Melt at 190 ° C. under a load of 21.6 Kg
Flow rate (MFR _21.6) And 190 ° C, 2.16 Kg
Melt flow rate under load (MFR_2.16) And ratio
 (MFR_21.6) / (MFR_2.16) = 1-20, preferred
(A-4) molecular weight distribution (Mw / Mn) = 2.0 to 4.0,
Preferably 2.3 to 3.7, more preferably 2.5 to 3.7.
3.5, particularly preferably 2.6-3.4

Among the above properties, (1) If the density is smaller than the above range, the bending strength is low, and the texture required for the foamed cushioning sheet, that is, the stiffness, cannot be secured. If it is larger than the above range, the bending strength is large, and the stiffness of the foamed cushioning sheet is too strong,
The cushioning function is impaired, the impact strength of the convex projections is reduced, and the molding temperature for melting the thermoplastic resin needs to be set high. In some cases, it is difficult to peel off the bubble-absorbing sheet from a roll such as a roll, and it may be difficult to perform stable production such as winding around the roll or deforming the bubble shape.

(2) If the MFR _2.16 is less than the above range, the fluidity during molding is poor and melt fracture occurs, so that the surface of the foamed cushioning sheet is not smooth. If it is larger than the above range, the melt tension is reduced, the drawdown is increased, and molding becomes difficult.

(3) If (MFR _21.6 ) / (MFR _2.16 ) is larger than the above range, the stretchability is reduced, the molding speed needs to be reduced, and the thickness of the foamed cushioning sheet varies. Or the smoothness of the sheet surface is reduced.
If it is smaller than the above range, a method of manufacturing a plastic film directly from a T-die and then immediately manufacturing a bubble-absorbing sheet results in large neck-in, large trimming loss, and uneconomical.

(4) If the molecular weight distribution (Mw / Mn) is larger than the above range, the stretchability is reduced, and it is necessary to greatly reduce the molding speed, and the thickness of the foamed cushioning sheet varies, The smoothness of the sheet surface decreases. If it is smaller than the above range, a method of manufacturing a plastic film directly from a T-die and then immediately manufacturing a bubble-absorbing sheet results in large neck-in, large trimming loss, and uneconomical.

Examples of the (A) ethylene-α-olefin copolymer include a catalyst such as chromium oxide supported on alumina or silica-alumina (Philips method), a catalyst such as molybdenum oxide supported on alumina (standard method),
Ziegler catalysts comprising a transition metal compound and an organometallic compound, such as a copolymer obtained by copolymerization of ethylene and an α-olefin having 3 to 10 carbon atoms in the presence of a so-called single-site catalyst such as a metallocene catalyst system. Can be used.

As the ethylene-α-olefin copolymer (A), in particular, ethylene and C 3 -C 10 are used in the presence of a so-called single-site catalyst such as a metallocene catalyst.
A copolymer obtained by copolymerization of the above with an α-olefin is preferred because it has excellent mechanical properties such as tear strength and impact strength.

The α-olefin having 3 to 10 carbon atoms includes propylene, butene-1, pentene-1, hexene-
1,4-methylpentene-1, octene-1 and the like.

The repeating unit derived from α-olefin in the copolymer of ethylene and α-olefin is as follows:
Usually, it is contained in a range of 30 mol% or less, preferably in a range of 10 mol% or less, more preferably in a range of 0.1 to 5 mol%, and particularly preferably in a range of 0.1 to 4 mol%.
The α-olefin may be used alone or in combination of two or more in the ethylene-α-olefin copolymer.

As the single-site catalyst, a combination of a metallocene compound of a transition metal of Group IV or V of the periodic table with an organoaluminum compound and / or an ionic compound is used.

The transition metals of Groups IV or V of the Periodic Table include:
Titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V) and the like are preferable.

The metallocene compound is a compound which is cross-linked by at least one cyclopentadienyl group, substituted cyclopentadienyl group, hydrocarbyl silicon, or the like. Further, the cyclopentadienyl group is cross-linked by oxygen, nitrogen and phosphorus atoms. Any known metallocene compound having a compound as a ligand can be used.

Specific examples of these metallocene compounds include dimethylsilyl (2,4-dimethylcyclopentadienyl) (3 ', 5'-dimethylcyclopentadienyl) zirconium dichloride, dimethylsilyl (2,4-dimethyl Silicon-bridged metallocene compounds such as cyclopentadienyl) (3 ', 5'-dimethylcyclopentadienyl) hafnium dichloride, ethylenebisindenylzirconium dichloride, ethylenebisindenylhafnium dichloride, ethylenebis (methylindenyl)
Examples include indenyl-based cross-linked metallocene compounds such as zirconium dichloride and ethylenebis (methylindenyl) hafnium dichloride.

The organoaluminum compound used in combination with the metallocene compound in the present invention is represented by the following general formula:
A linear or cyclic polymer represented by (-Al (R) O-) n (R is a hydrocarbon group having 1 to 10 carbon atoms and partially substituted with a halogen atom and / or an RO group) N is the degree of polymerization and is 5 or more, preferably 10 or more), and specific examples are methylalumoxane, ethylalumoxane, and isobutylethylalumoxane, wherein R is a methyl, ethyl, or isobutyl group, respectively. And the like.

Further, other organic aluminum compounds include trialkylaluminum, dialkylhalogenoaluminum, sesquialkylhalogenoaluminum, alkenylaluminum, dialkylhydroaluminum, sesquialkylhydroaluminum and the like.

The ionic compound is represented by the general formula: C ⁺ .A
^- , C ⁺ is an oxidizing cation of an organic compound, an organometallic compound, or an inorganic compound, or a Bronsted acid comprising a Lewis base and a proton, and reacts with an anion of a metallocene ligand to form a metallocene cation. Can be generated. Specific examples thereof are disclosed in
JP-A-5-253711, JP-A-4-305585, JP-A-5-507756 and JP-A-5-502906 can be used.

In particular, an ionic compound of a tetrakis (pentafluorophenyl) borate anion and a triphenylcarbonium cation or a dialkylanilinium cation is preferred. These ionic compounds can be used in combination with the aforementioned organic aluminum compounds.

As a method for copolymerizing ethylene with a single-site catalyst, various well-known methods can be employed, such as fluidized-bed gas-phase polymerization or inert gas-phase polymerization in an inert gas, or an inert solvent. And bulk polymerization using a monomer as a solvent.

The high-density polyethylene (B) of the present invention comprises:
It has the physical properties in the specific range described above (however,
((A) Excluding ethylene-α-olefin copolymer)). (B-1) Density (d) = 0.935 exceeding 0.970
Below (g / cm^Three), Preferably 0.940 to 0.97
0 (g / cm^Three), More preferably 0.950-0.
970 (g / cm^Three), Particularly preferably 0.960 to
0.970 (g / cm^Three(B-2) Melt at 190 ° C. and 2.16 Kg load
Flow rate (MFR _2.16) = 0.01-20 (g / 1
0 min), preferably 0.1 to 10 (g / 10 min),
Preferably 1 to 10 (g / 10 minutes), particularly preferably
3-8 (g / 10 minutes)

Among the above properties, (1) if the density is smaller than the above range, the bending resistance required for the foamed cushioning sheet becomes low, and the texture, that is, the strength of the waist cannot be secured. If it is larger than the above range, the bending strength of the foamed cushioning sheet increases, the stiffness becomes too strong, the cushioning function is impaired, the impact strength of the convex projections is reduced, and the thermoplastic resin is used. It is necessary to set the molding temperature at the time of melting high, and as a result, it becomes difficult to peel the foamable cushioning sheet from a roll such as an embossing roll of the foaming cushioning sheet manufacturing apparatus, and it is difficult to wind around the roll and to form the foam. In some cases, stable production may be difficult, for example, deformation may occur. In addition, when a plastic film is manufactured using an extruder or a T-die, it is necessary to set a high molding temperature, deterioration of the polyethylene composition in the extruder or the T-die is promoted, and cleaning in the extruder or the T-die is required. It is necessary to perform the production frequently, and it is difficult to perform stable production for a long time.

(2) If MFR _2.16 is smaller than the above range, the fluidity during molding is poor and melt fracture occurs, so that the surface of the foamed cushioning sheet is not smooth. If it is larger than the above range, the melt tension is reduced, the drawdown is increased, and molding becomes difficult.

Examples of the high-density polyethylene include a homopolymer of polyethylene or a copolymer of ethylene and a small amount of α-olefin. For example, a Philips method obtained by polymerizing using a catalyst such as chromium oxide supported on ethylene and alumina or silica-alumina, a standard method obtained by polymerizing using a catalyst such as molybdenum oxide supported on alumina, etc. Examples include polyethylene, polyethylene obtained by polymerization using a Ziegler-based catalyst composed of a transition metal compound and an organometallic compound, and the like.

(C) High-pressure low-density polyethylene of the present invention
Has physical properties in the following specific ranges (however,
However, the (A) ethylene-α-olefin copolymer is excluded.
H). (C-1) Density (d) = 0.915 to 0.935 (g /
cm^Three), Preferably 0.915 to 0.930 (g / c
m^Three), Particularly preferably 0.915 to 0.925 (g / g).
cm^Three(C-2) Melt at 190 ° C. and 2.16 Kg load
Flow rate (MFR _2.16) = 0.01 to 50 (g / 1)
0 minutes), preferably 0.05 to 10 (g / 10 minutes).
More preferably 0.05 to 5 (g / 10 minutes), particularly preferred
Or 0.5 to 5 (g / 10 minutes)

Among the above-mentioned properties, (1) if the density is smaller than the above range, the bending resistance required for the cellular cushioning sheet is low, and the texture, that is, the strength of the waist cannot be secured.

(2) If MFR _2.16 is smaller than the above range, the fluidity during molding is poor and melt fracture occurs, so that the surface of the foamed cushioning sheet is not smooth. If it is larger than the above range, the melt tension is reduced, the drawdown is increased, and molding becomes difficult.

The high-pressure low-density polyethylene as the component (C) can be produced by high-pressure radical polymerization.

As the high-pressure low-density polyethylene,
In addition to the ethylene homopolymer, a copolymer with another monomer such as an ethylene-vinyl acetate copolymer can be used. When using an ethylene-vinyl acetate copolymer, the repeating unit derived from vinyl acetate in the copolymer,
Usually, it is preferred that it is 20 wt% or less.

The mixing ratio of each component in the polyethylene composition of the present invention is as follows: (A) an ethylene-α-olefin copolymer, (B) a high-density polyethylene, and (C) a high-pressure low-density polyethylene. 1), general formula (2), preferably general formula (5), general formula (3), preferably general formula (6), particularly preferably general formula (7) and general formula (4), preferably Is a range surrounded by the general formula (8), particularly preferably the general formula (9).

X + y + z = 100 (1) 45 ≦ x + z ≦ 95 (2) 5 ≦ x ≦ 90 (3) 5 ≦ z ≦ 90 (4), 50 ≦ x + z ≦ 90 (5), 10 ≦ x ≦ 90 (6) ), 10 ≦ x ≦ 80 (7), 10 ≦ z ≦ 90 (8), 10 ≦ z ≦ 80 (9) However, in the general formulas (1) to (9), x: (A) ethylene-α -Olefin copolymer (wt%) y: (B) high-density polyethylene (wt%) z: (C) high-pressure low-density polyethylene (wt%)

When the mixing ratio of each component in the polyethylene composition of the present invention is out of the above range, the balance between mechanical properties such as tear strength and cap impact strength and bending strength is not sufficient, and the plastic film (1) And / or the moldability such as neck-in during the production of (2) is undesirably reduced.

Further, in the above general formulas (1) to (4), when the proportion of (A) the ethylene-α-olefin copolymer is smaller than the above range, the effect of lowering the molding temperature is poor, and The effect of improving mechanical properties such as strength and impact strength is small, and if it is larger than the above range, the melt tension is reduced, and the thickness of the convex portion of the foamed buffer sheet varies, or the plastic film (1) And / or when the plastic film (2) is supplied by the T-die method, the neck-in increases and the trimming loss increases. When the plastic film (2) is supplied as a film, the film is cut in a heating step of the film. Trouble occurs.

(B) When the proportion of the high-density polyethylene is smaller than the above range, the bending strength is low, and the texture required for the cellular cushioning sheet, that is, the strength of the waist cannot be secured. If it is large, the bending strength will be high, the stiffness of the foamed cushioning sheet will be too strong, the flexibility will be reduced and the cushioning function will be impaired, the commercial value will be reduced due to reduced transparency, and the molding temperature will be reduced. The degradation of the polymer in the extruder or T-die die for producing the plastic film (1) and / or the plastic film (2) is promoted, and stable continuous operation for a long time becomes difficult. There are cases.

(C) When the proportion of the high-pressure method low-density polyethylene is smaller than the above range, the melt tension is small, the molding stability is lacking, and the transparency of the cellular buffer sheet is reduced. When it is larger than the above range, the mechanical properties such as tear strength and cap impact strength are not sufficient, and it is difficult to obtain a cellular cushioning sheet having an excellent texture.

The above polyethylene composition is obtained by mixing and kneading the components using various kneaders such as a Banbury mixer, a roll mixer, a kneader, a high-speed mixer, an extruder, preferably a single-screw or twin-screw extruder. be able to. Also, kneading can be performed during film inflation or T-die molding. Alternatively, they can be mixed by a solution blend using an appropriate good solvent.

The above polyethylene composition may be selected from lubricants such as higher fatty acids, higher aliphatic amides, metal soaps and glycerin esters, natural silica, synthetic silica,
Talc, diatomaceous earth and other anti-blocking agents, phenol-based, phosphorus-based, antioxidants such as BHT, benzophenone,
UV absorbers such as benzotriazole and HALS; aluminum and magnesium hydroxides; flame retardants such as phosphorus and halogen; inorganic and organic fillers such as silica, calcium carbonate, mica, and carbon black; azo and phthalocyanine , Quinacridone, iron oxide, ultramarine blue and other pigments,
An antistatic agent, a surfactant and the like can be added.

The above plastic film (1) and / or
Or (2), the polyethylene composition can be suitably produced by an inflation molding method or a T-die molding method.

The foamed cushioning sheet of the present invention is prepared by contacting the molten thin film extruded from the T-die or the thin film formed in advance through a heating roll or the like with the embossing roll and immediately contacting the embossing roll cavity. Suctioned into a tee (plastic film (1)), and a molten thin film extruded from a T-die or a preformed thin film melted through a heating roll or the like onto the state (plastic thin film (plastic)) The film (2)) is pressure-bonded to obtain a molten cellular laminate, which is then rapidly cooled and solidified, and then forcibly peeled off from the embossing roll.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited only to these embodiments.

As a preferred embodiment of the method for producing the foamed cushioning sheet shown in FIGS. 1 and 2, (1) a step of producing a plastic film (1) 22 having a large number of embosses 21 formed on a plastic film; 2) Immediately after the emboss 21 is formed, the plastic film (1) 22
The flat plastic film (2) 24 is manufactured by a process of forming a closed cell 3 having a convex shape by press-bonding and heat-sealing the plastic film (2) 24 thereon.

In the embossing roll 109, a large number of embosses 21 are formed on the film 23 by sucking the plastic film 23 heated and melted before forming the emboss with a vacuum pump at a degree of vacuum of 40 to 100 hPa. (1) Assume 22. A flat plastic film (2) 24 heated and melted on the plastic film (1) 22 is applied to the pressure roll 12
While being press-bonded by 1, heat-sealing is performed on the embossing roll 109 to form convex closed cells 3. Next, while being pressed against the embossing roll 109 by the cooling roll 112, the cooling is performed to form the foamed buffer sheet 1.

[0062]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to only these examples. The characteristic values were measured as follows.

The characteristics of various polyethylenes constituting the plastic film used in the present invention were determined by the following measuring methods. The results are shown in Tables 1 to 3. [1] Density (g / cm ³ ): MFR under a load of 2.16 kg at 190 ° C. according to JIS K7112.
The strand obtained at the time of the measurement was heat-treated at 100 ° C. for 1 hour, and the sample which was gradually cooled to room temperature over 1 hour was measured using a density gradient tube. [2] Melt flow rate (MFR _2.16 ): JIS
In accordance with K7210, 19
It was determined by measuring the weight of the resin extruded in a strand shape for 10 minutes at a load of 2.16 kg at 0 ° C. [3] Melt flow rate ratio (MFR _21.6 ) / (MFR
_2.16 ): A value obtained by dividing MFR _21.6 obtained by a load of _21.6 kg in the same manner as in the above method (2) by MFR _2.16 .

[4] Molecular weight distribution: The molecular weight distribution (Mw / Mn) of the polyethylene composition was measured by gel permeation chromatography (GPC). The measurement method is shown below. (1) Measuring device: WATERS 150CV was used. (2) Measurement sample: polyethylene composition at a temperature of 14
It was dissolved in a solvent (o-dichlorobenzene) at 5 ° C at a concentration of 1 mg / ml. (3) Measurement of molecular weight distribution: Measurement sample of (2) above.
4 ml was injected into two GPC columns AT-806MS, and the solvent was o-dichlorobenzene, the temperature was 145 ° C., and 1.
Performed at a flow rate of 0 ml / min. 35 measured by GPC
Minutes. The polymer concentration in the solution separated by the GPC column was measured with a differential refractometer (RI). The molecular weight was converted using a polystyrene standard. (4) Data processing: Data processing is performed in VAX-STATI
ON3100 was used. G obtained by the above measurement (3)
When a baseline is drawn on the PC chromatogram, the area is integrated using data processing software attached to the apparatus, and the number average molecular weight (Mn), weight average molecular weight (Mw), Mw / Mn
Is automatically calculated. The GPC chromatogram is defined on the screen of the apparatus as the size of the figure, with the horizontal axis standardizing 125 mm per 20 minutes of measurement time and the vertical axis the total integrated elution amount as 100,
The measurement was performed at 13 mm per 20 mm.

Examples 1 to 8 and Comparative Examples 1 to 6 For the plastic film (1) and the plastic film (2), a polyethylene composition in which the components shown in Table 4 were uniformly mixed in advance by dry blending was used. Using the two T-die molding machines, the polyethylene composition is discharged from one die into a plastic film 23 before embossing in the form of a molten thin film, and the plastic film (2) 24 in the same state is discharged from the other die. The foamable buffer sheet was manufactured by the manufacturing method shown in FIG. The clearance of the molded T-die of the molten thin film of the plastic film 23 and the plastic film (2) 24 is 0.75 mm, respectively.
And, assuming 0.5 mm, the T-die discharge resin temperature is plastic film 23 and plastic film (2) 2.
In all cases, the temperature was 215 ° C. At this time, the ratio of the discharge amounts of the plastic film 22 and the plastic film 23 is 2:
It was set to 1. After the plastic film 23 came into contact with the embossing roll 109, the embossing 21 was formed, and the plastic film (1) 22 was produced on the embossing roll. The distance from the tip of the T die to the contact of the plastic film (1) 22 with the plastic film (2) 24 was 110 mm. The two molten thin-film plastic films (1) 22 and the plastic film (2) 24 are pressed with an embossing roll 109 at 30 ° C. and a pressing roll 121 at 30 ° C. while forming a bubble of 85 g / m ² at a forming speed of 10 m / min. Thus, a water-resistant buffer sheet 1 was obtained.

The properties and moldability of the obtained foamed cushioning sheet were evaluated according to the following methods, and the results are shown in Table 5.

Evaluation Method of Characteristics of Cellular Buffer Sheet (1) Density (g / cm ³ ): This was performed using a polyethylene composition obtained by cutting a film extruded from an extruder into small pieces. 1. At 190 ° C. according to JIS K7112.
The strand obtained at the time of MFR measurement under a load of 16 kg was heat-treated at 100 ° C. for 1 hour, and the sample which was gradually cooled to room temperature over 1 hour was measured using a density gradient tube. (2) Tensile strength (Kgf / 15mm): JIS K7127
It went according to. (3) Tear strength (Kgf): Performed according to ASTM D1922.

(4) Cap impact strength (gf / 26 inch): ASTM D882 is applied to the convex part (bubble part) of the cellular cushioning sheet.
According to Method A, the dart was dropped from a height of 26 inches, and the drop load when the convex portion (bubble portion) was broken was defined as the cap impact strength. (5) 80% deformation strength (Kgf / cm ² ): JIS Z-02
34A. 12cm × foam cushioning sheet
It was cut to 12 cm. A stack of six of these sheets was pressed at a compression speed of 10 mm / min, and the stress when deformed by 85% was measured.

(6) Folding strength (cm): The test was performed using a foamed cushion sheet cut into a size of 30 cm in the embossing roll axial direction × 10 cm in the embossing roll circumferential direction. One end in the circumferential direction of the cut foamed cushioning sheet was fixed with a horizontal chuck. The chuck has a grip width of 2 cm and a central portion of the chuck width is fixed to a rotatable shaft having a height of 5 cm. This chuck fixed shaft is rotated 3/4 in 4 seconds,
The foamed cushioning sheet was wound around the chuck from below the rotatable shaft. At this time, the other end not fixed by the chuck was moved in the chuck direction by rotation of the chuck.
This moving distance was measured. The measurement was performed by fixing the plastic film (2) to the chuck in two directions of the lower surface and the upper surface. The bending strength was defined as the average value of the moving distances selected for fixing in these two directions.

(7) Formability: Cell shape and fusing property during production of foamed buffer sheet, releasability from embossing roll, deterioration of polymer in extruder and die during production of foamed buffer sheet The moldability was determined by taking into account the properties and the resin pressure of the extruder during the production of the cellular buffer sheet. Peelability and deterioration were evaluated visually. ○: No problem, ×: Problem

[0071]

[Table 1]

[0072]

[Table 2]

[0073]

[Table 3]

[0074]

[Table 4]

[0075]

[Table 5]

[0076]

The foamed cushioning sheet of the present invention has excellent mechanical properties such as tear strength and cap impact strength,
That is, it is possible to obtain a foamed cushioning sheet which is excellent in balance with waist and has good moldability and which is suitably used as a packaging material for articles.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing an example of a method for producing a cellular buffer sheet of the present invention.

FIG. 2 is a flowchart schematically showing an example of a method for producing the cellular buffer sheet of the present invention.

[Explanation of Signs] 1 foam buffer sheet, 3 convex closed cells, 21 emboss, 22 plastic film (1), 23 plastic film before emboss formation, 24 plastic film (2), 109 emboss roll, 111 roll, 112 cooling roll, 113 roll, 121 pressure roll

Claims (2)

[Claims] 1. A plastic having a large number of embossments
Film (1) and flat plastic film (2)
Cushioning with convex closed cells formed by stacking
In the sheet, the plastic film (1) and
And / or (2) has a density of 0.915 to 0.960 (g / c
m^ThreeAnd (A) ethylene-α having the following properties:
-An olefin copolymer, (B) a high density polyethylene and
(C) Polyethylene containing high-pressure low-density polyethylene
(A) in a polyethylene composition
Ethylene-α-olefin copolymer, (B) high density poly
Each component of ethylene and (C) high-pressure low-density polyethylene
Is represented by the following general formulas (1) to (4).
Foamed cushioning sheet. x + y + z = 100 (1) 45 ≦ x + z ≦ 95 (2) 5 ≦ x ≦ 90 (3) 5 ≦ z ≦ 90 (4) In the formulas (1) to (4), x: (A) ethylene-α -Olefin copolymer (weight
%) Y: (B) high-density polyethylene (% by weight) z: (C) high-pressure method low-density polyethylene (% by weight) (A) ethylene-α-olefin copolymer: (A-1) density (d) = 0.880 to 0.960 (g /
cm^Three(A-2) Melt at 190 ° C. and 2.16 Kg load
Flow rate (MFR _2.16) = 0.01 to 200 (g /
(A-3) Melt at 190 ° C. and 21.6 kg load
Flow rate (MFR _21.6) And 190 ° C, 2.16 Kg
Melt flow rate under load (MFR_2.16) And ratio
 (MFR_21.6) / (MFR_2.16) = 1 to 20 (A-4) Molecular weight distribution (Mw / Mn) = 2.0 to 4.0 (B) High-density polyethylene (provided that the (A) ethylene
(Excluding -α-olefin copolymer): (B-1) Density (d) = 0.935 exceeding 0.935
Below (g / cm^Three(B-2) Melt at 190 ° C. and 2.16 Kg load
Flow rate (MFR _2.16) = 0.01-20 (g / 1
0 minutes) (C) High-pressure low-density polyethylene (provided that (A)
(Excluding the Tylene-α-olefin copolymer): (C-1) Density (d) = 0.915 to 0.935 (g /
cm^Three(C-2) Melt at 190 ° C. and 2.16 Kg load
Flow rate (MFR _2.16) = 0.01 to 50 (g / 1)
0 minutes) 2. The foamable buffer sheet according to claim 1, wherein said (A) ethylene-α-olefin copolymer is produced from a single-site catalyst.