JP2003147110A - Foam of polyolefin composition and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foam having a cell structure which is uniform and fine and has a high closed cell ratio and a small anisotropy within a wide density range, using a polyolefin composition excellent in recyclability. SOLUTION: The foam is composed of a polyolefinic polymer composition featured by a melt tension of 3-7 gf and a draw-down property of 60-100 m/min. Preferably, the polyolefinic polymer composition has a strain hardening index of at least 0.20.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a foam made of a polyolefin-based polymer composition, and more specifically, it uses a polyolefin-based polymer composition having excellent recyclability and has a uniform density in a wide density range. The present invention relates to a foam having a high closed cell rate and a cell structure having small anisotropy and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION In recent years, molded containers made of resin sheet foam have been widely used as food packaging materials. In particular, in recent years, in addition to conventional foam containers for selling fish and meat, in accordance with changes in lifestyle, they are being sold in large numbers for bento and retort foods at convenience stores and supermarkets. The containers used for these are also
It is obtained by secondary molding of a resin sheet foam.

In recent years, there have been regulations such as the Container Recycling Law, and the resins used in these containers are typified by materials that are easier to recycle, such as polyolefin polymer compositions. There are also applications where conversion to new materials has begun.

An extrusion foaming method has been widely adopted as a method for producing such a sheet-like foam. This means a method in which a thermoplastic resin and a foaming agent are melt-kneaded in an extruder and then extruded under low pressure to foam. For example, in the extrusion foaming method of a polyolefin-based polymer composition, when the resin and the foaming agent are melt-kneaded in the extruder, and the foaming agent in the melt-kneaded product expands when extruded under low pressure from the extruder. Foaming is carried out.

At this time, when the temperature of the resin is raised, the viscosity is drastically lowered, and the resin cannot hold the foaming agent and deviates from the resin. As a result, the cells coalesce and break, resulting in a non-uniform foam having a cell structure with a low closed cell rate.
Therefore, if the temperature is lowered for the purpose of increasing the viscosity of the resin, the resin will crystallize, so that a low-density foam cannot be obtained, and uniform foaming will not be performed.As a result, the surface will be uneven and the appearance will be poor. I can't get it.

For the above reasons, in order to obtain a foam having a uniform and fine cell structure with a high closed cell ratio in a wide range of density from high density to low density, the resin viscosity It is necessary to pay attention to the elastic behavior and adjust the operating conditions such as the blending amount of additives such as a foaming agent and the temperature setting. In addition, since the temperature range in which viscoelasticity suitable for foaming is obtained (hereinafter referred to as the optimum molding temperature range) differs depending on the type of resin, it is necessary to select a compounding recipe with a wide optimum molding temperature range through material design and material selection. The point is whether to do it.

However, the crystalline polyolefin-based polymer composition such as polyethylene or polypropylene has an optimum molding temperature range because the viscoelasticity of the resin largely changes with temperature as compared with the amorphous polymer composition such as polystyrene. Is extremely narrow. For this reason, it is very difficult to control the molding temperature because the properties of the foam obtained by a slight temperature fluctuation during foam molding, such as the expansion ratio, the appearance properties such as irregularities on the foam surface, and the cell structure are greatly different.

Further, since the crystalline polyolefin polymer composition has a high degree of crystallinity, it generates a large amount of heat during crystallization. The heat generated by this crystallization hinders the solidification of the bubble wall, and coalesces and destroys the bubbles. For this reason, in extrusion foaming of a polyolefin-based polymer composition, a technique such as performing a cooling operation from the outside to solidify the cell walls to obtain a good foam is taken.

However, the heat generation due to crystallization cannot be sufficiently removed by the cooling means only outside. Therefore, a technique has been adopted in which a large amount of a foaming agent is blended and the heat of vaporization when the foaming agent expands is used to drastically lower the temperature of the resin to accelerate the solidification of the cell walls.

However, conventionally, for example, in the case of non-crosslinked polypropylene, a good foam can be obtained only when the density is less than 0.7 g / cm ³ and the expansion ratio is low, or when the density is 0.01 g / cm 3. It is said to have a high expansion ratio of less than ³ . It is considered that such a problem is due to the high crystallinity of polypropylene as described above.

In order to solve this problem, by introducing long chain branching, the strain hardening index and melt tension are high,
In addition, non-crosslinked polypropylene having a low drawdown property is used.

However, in such an uncrosslinked polypropylene, since the melt tension is too high, the expansion of the foaming agent is suppressed at the initial stage of foaming when extruded from the extruder under a low pressure, so that a sufficient expansion ratio can be obtained. There are problems such as not being able to do it and having to add a large amount of foaming agent.
In addition, since the drawdown property is too low, the stretchability of the base resin is poor at the time of foaming, and when passing through the take-up step in actual production, the horizontal direction (take-away direction) and the vertical direction (take-away direction) of the sheet are There is a problem that anisotropy of the bubble structure occurs in the vertical direction). Such anisotropy is
Not only will it adversely affect the secondary formability, but it will also exhibit unfavorable physical properties as a product.

[0013]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and in particular, it uses a polyolefin-based polymer composition having excellent recyclability and has a uniform density in a wide density range. It is an object of the present invention to provide a foam having a high closed cell ratio and a cell structure having small anisotropy.

[0014]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a polyolefin-based polymer composition having a specific melt tension and drawdown property is used. The inventors have found that a cell structure having a uniform fineness, a high closed cell rate, and a small anisotropy can be obtained in a wide range of density regions, and the present invention has been completed.

That is, the present invention is specified by the items described below. (1) A foam comprising a polyolefin-based polymer composition having a melt tension of 3 to 7 gf and a drawdown property of 60 to 100 m / min.

(2) The foam according to (1) above, wherein the polyolefin-based polymer composition has a strain hardening index of 0.20 or more.

(3) Density of 0.70 to 0.01 g / cm
^3. The foam according to (1) or (2) above, which is ³ .

(4) The foam according to any one of (1) to (3) above, wherein the foaming agent is carbon dioxide.

(5) Anisotropy of cell structure is 0.5 to 1.0
The foam according to any one of (1) to (4) above.

According to the present invention, the melt tension is 3 to 7 gf and the drawdown property is 60 to 100 m / m.
In property, or in addition, strain hardening index is 0.20
The steps of adding a polyolefin-based polymer composition having the above properties to the inside of the extruder, plasticizing it, and heating and melting, a step of supplying a foaming agent into the molten polyolefin-based polymer composition, and a step of melting inside the extruder After kneading the polyolefin-based polymer composition and the foaming agent, a step of cooling to a temperature suitable for foaming, and transferring the molten polyolefin-based polymer composition to a die connected to the exit side of the extruder, and extruding. Provided is a method for producing a foam, which comprises a step of foaming by extruding from a machine under a low pressure.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the polyolefin-based polymer used in the present invention include high-density polyethylene, low-density polyethylene, linear ultra-low-density polyethylene, polypropylene (homo polypropylene, block copolymer polypropylene, random copolymer polypropylene). Etc.), polybutene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer Examples thereof include polymer, ethylene-based resin such as ethylene-maleic anhydride copolymer, and ionomer resin (for example, ethylene-methacrylic acid copolymer ionomer resin). These may be used alone or in combination of two or more. If necessary, the above polymer may be mixed with other resins as long as the object of the present invention is not impaired. Of the above polymers, polypropylene is more preferred.

Examples of the resin that can be used as a mixture include, for example, styrene resins other than those mentioned above (for example, polystyrene, butadiene-styrene copolymer (HIPS), acrylonitrile-styrene copolymer (AS resin), acrylonitrile-butadiene-). Styrene copolymer (ABS
Resin)), saturated polyester resin (for example, polyethylene terephthalate, polybutylene terephthalate, etc.), thermoplastic polyurethane, thermoplastic elastomer,
Biodegradable resin (eg, condensation product of hydroxycarboxylic acid such as polylactic acid, condensation product of diol and carboxylic acid such as polybutylene succinate), polyvinyl chloride,
Polyvinylidene chloride, polycarbonate, polyacetal, polyphenylene oxide, polyvinyl alcohol,
Examples thereof include polymethyl methacrylate, polyamide resin, polyimide resin, fluororesin, polysulfone, polyether sulfone, polyarylate, polyether ether ketone, and liquid crystal polymer.

A characteristic feature of the polyolefin polymer composition of the present invention comprising a combination of the above polymers is that the melt tension is preferably 3 to 7 gf, more preferably 5 to less than 7 gf, and especially 5 to 6.9
It is preferably gf.

When the melt tension exceeds 7 gf, the expansion of the foaming agent is suppressed at the initial stage of foaming when extruded from the extruder under a low pressure, and a sufficient expansion ratio may not be obtained, which is not preferable. Further, when a composition having a melt tension of more than 7 gf is used and a large amount of a foaming agent is blended in order to obtain a sufficient expansion ratio, the heat of vaporization when the foaming agent expands is too large, and the temperature of the resin rapidly decreases. And tends to be difficult to obtain the desired foam.

When the melt tension is less than 3 gf,
In some cases, it becomes difficult for the base material to follow the strain generated when the foaming agent expands, and bubbles may be destroyed, resulting in instability. Therefore, it tends to be difficult to obtain a foam having a sufficient expansion ratio.

Drawdown property is also an important factor. When the drawdown property is too low, when the bubbles grow, the stretchability of the base material is poor, and during the actual production process such as the take-up process, anisotropy of the bubble structure occurs in the horizontal and vertical directions of the sheet. There is a problem such as shutting down. The anisotropy of bubbles not only adversely affects the secondary moldability, but also develops physical properties unfavorable as a product.

Therefore, the drawdown property is 60 m / mi.
It is preferably n or more. However, even if the drawdown property is too large, it becomes difficult to maintain the foam shape, so the upper limit is preferably 100 m / min, and more preferably 90 m / min.

Further, in the process of maintaining and solidifying the bubble from the process of growing the bubble, a large strain is applied to the substrate as the bubble grows. Therefore, in order to grow and maintain the bubbles and further solidify them stably, the substrate is required to have a viscosity corresponding to the strain. If the substrate cannot follow the strain during cell growth, the cells will coalesce and the cells will be destroyed, and a sufficient expansion ratio cannot be obtained, and the appearance of the foam may be good. I can't get it. However, when the polyolefin-based polymer composition of the present invention is used as a base material, the strain effect index is 0.20 or more, so that the base material viscosity increases in accordance with the strain accompanying the bubble growth of the base material. It is possible to obtain a cell structure having a sufficient expansion ratio, a uniform and fine cell structure, and a high closed cell rate.

The density of the foam of the present invention is 0.70-0.
It is preferably 01 g / cm ³ , more preferably 0.60 to 0.05 g / cm ³ , and still more preferably 0.50 to 0.10 g / cm ³ .

In addition, the cell structure in the foam of the present invention has an anisotropic cell structure as a ratio of the minimum cell diameter to the maximum cell diameter (minimum cell diameter / maximum cell diameter) observed in the cross section of the foam. Those having a property of 0.5 to 1.0 are preferable.

As the foaming agent used in the present invention, an inorganic foaming agent, a volatile foaming agent, a decomposable foaming agent or the like can be used without particular limitation.

Air, nitrogen, water, carbon dioxide, argon or the like can be used as the inorganic foaming agent.

Volatile blowing agents include aliphatic hydrocarbons such as propane, n-butane, i-butane, pentane, n-hexane, i-hexane, heptane and i-heptane, and cyclic compounds such as cyclobutane and cyclopentane. Aliphatic hydrocarbons, trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride,
Halogenated hydrocarbons such as ethyl chloride and methylene chloride, alcohols such as ethanol, diethyl ether, dimethyl ether, petroleum ether, acetone and the like can be used.

As the decomposition type foaming agent, azodicarbonamide (ADCA), N, N'-dinitrosopentamethylenetetramine (DPT), azobisisobutyronitrile (AIBN), diazoaminobenzene, N, N '. -Dimethyl-N, N'-dinitrosoterephthalamide, benzenesulfonium hydrazide, p-toluenesulfonium hydrazide (TSH), p, p'-oxybisbenzenesulfonium hydrazide (OBSH), p-toluenesulfonium hydrazide, trihydrazinotriazine Barium azodicarboxylate, ammonium carbonate, sodium bicarbonate, ammonium bicarbonate, ammonium nitrite, citric acid and the like.

Although these foaming agents can be used alone,
There is no limitation in using them in combination. Of these, carbon dioxide is more preferable. Further, when carbon dioxide and a thermal decomposition type foaming agent are used, it becomes easier to make the cell diameter of the obtained foam uniform.

In the present invention, a cell regulator may be further added to the melt-kneaded product of the polyolefin polymer composition and the foaming agent. Examples of the air bubble modifier include inorganic powder such as talc and silica, an acid salt of polyvalent carboxylic acid, and a reaction mixture of polyvalent carboxylic acid and sodium carbonate or sodium bicarbonate. Of these, a mixture of sodium bicarbonate and citric acid is more preferable, and these masterbatches may be used in consideration of dispersibility in the base polymer.

The bubble control agent may be added in an amount of 0.0001 to 10 parts by weight, more preferably 0.001 to 5 parts by weight, still more preferably 0.01 to 1 part by weight, based on 100 parts by weight of the polyolefin-based polymer composition. preferable.

If necessary, the polyolefin-based polymer composition may further contain a foaming aid, a pigment, a dye, a lubricant, a heat stabilizer, an ultraviolet absorber, an antioxidant, a filler, a plasticizer, a flame retardant, and a charge. Additives such as inhibitors, cross-linking agents and antibacterial agents can also be added.

The method for producing the polyolefin-based polymer composition, which is the raw material for the polyolefin-based polymer composition foam of the present invention, is not particularly limited, and a commonly known method can be adopted. For example, the polyolefin polymer and the additives to be added as necessary are uniformly mixed with a high-speed stirrer or the like, and then a uniaxial or multiaxial extruder having sufficient kneading ability, a mixing roll, a kneader, a Brabender, etc. It can be produced by a method such as melt kneading. In addition, the polyolefin polymer and the above-mentioned additives, which are optionally added, may be used as they are in a state of being uniformly mixed.

For example, when carbon dioxide is used as a foaming agent, a polyolefin-based polymer, a thermally decomposable foaming agent optionally added, an aliphatic carboxylic acid and its derivative, a molten polyolefin-based material such as an inorganic fine powder. The polymer composition is required to prevent carbon dioxide from being separated until the gas dissolving step and the cooling step are completed, but for that purpose, it should be maintained at a pressure equal to or higher than the critical pressure of carbon dioxide. Is preferred.

The method for producing the polyolefin polymer composition foam in the present invention is not particularly limited with respect to the matters other than those specified in the present invention. An example of an embodiment of the present invention will be described below with reference to the drawings. Here, T
-The example using a die is illustrated, but the use of a circular die is also included in the present invention.

FIG. 1 is a schematic diagram showing an example of a method for continuously producing a foamed sheet by the method for producing a polyolefin-based polymer composition foam of the present invention.

In FIG. 1, (1) is a liquefied carbon dioxide cylinder, (2) is a metering pump, (3) is a pressure-holding valve, (4) is a refrigerant circulator, (5) is a heater, and (6) is a flow meter. , (1
2) hopper, (13) screw, (16) T
A die, (17) a foamed sheet, (18) a chill roll, and (19) an extruder.

In FIG. 1, 100 parts by weight of the polyolefin-based polymer composition was added to the hopper (1
From 2), it is added into the extruder (19) constituting the inlet side of the continuous plasticizer and heated and melted. Further, carbon dioxide is temperature-controlled from a liquefied carbon dioxide cylinder (1) and injected into a metering pump (2), where the pressure is increased and 0.1 to 1.0 parts by weight of the pressure-controlled carbon dioxide is discharged into the extruder (1).
It is added to the molten polyolefin polymer composition in 9) to dissolve gas.

At this time, the carbon dioxide present in the extruder (19) significantly enhances the dissolution and diffusion with respect to the melted polyolefin-based polymer composition, and permeates the polyolefin-based polymer composition in a short time. In order to make it possible, it is preferable that the inside of the system is maintained above the critical pressure and the critical temperature of the carbon dioxide. In the case of carbon dioxide, the critical pressure is 7.4 MPa, the critical temperature is 31 ° C., and the pressure in the extruder (19) is 7.4 to 40 MPa, preferably 10 to 30 MPa, and the temperature is 150 to 300 ° C. ,
It is preferably in the range of 160 to 280 ° C.

Further, carbon dioxide added to the polyolefin-based polymer composition melted in the extruder (19) may be added after it is heated and pressurized to become a supercritical state before being added. .

The polyolefin-based polymer composition and carbon dioxide melted in the extruder (19) are screw (13).
To form a compatible state of the polyolefin-based polymer composition and carbon dioxide.

In the cooling step after compatibility, the temperature is lowered to a temperature suitable for foaming in order to increase the solubility of carbon dioxide in the polyolefin polymer composition. The temperature at this time is 100 to 250 ° C., preferably 130 to 220 ° C., and is maintained at a temperature equal to or higher than the plasticizing temperature of the molten polyolefin-based polymer composition to cool it so that the viscosity becomes suitable for the subsequent foaming. Adjust the temperature to.

This cooling step is a step for reasonably approaching the temperature conditions suitable for foaming. Sufficient cooling in this step facilitates continuous and stable production of a polyolefin-based polymer composition foam.

Next, the molten polyolefin-based polymer composition is transferred to the T-die (16) connected to the outlet side of the continuous plasticizing apparatus set to the optimum foaming temperature, and foaming is started.
At the outlet of the T-die (16), the pressure is reduced under controlled conditions to bring the carbon dioxide into a supersaturated state. The molten polyolefin-based polymer composition in the supersaturated state becomes thermally unstable and generates a large number of bubbles.

The molten polyolefin polymer composition which has started foaming is extruded from the outlet of the T-die (16) and starts foaming at the same time. However, the cooling roll (18) installed in front of the T-die (16) is used. ) To cool while adjusting the thickness,
A polyolefin polymer composition foamed sheet (17) is obtained by shaping into a sheet.

In the present invention, it is necessary to prevent the molten polyolefin-based polymer composition from being separated into the polyolefin-based polymer composition and carbon dioxide until the gas dissolving step and the cooling step are completed. However, for that purpose, it is preferable to maintain a pressure equal to or higher than the critical pressure of carbon dioxide.

In the method for producing a polyolefin-based polymer composition foam by extrusion molding of the present invention, carbon dioxide is added to the molten polyolefin-based polymer composition in the extruder (19), and the mixture is sufficiently kneaded. Form a compatible state of the polyolefin-based polymer composition and carbon dioxide, at the outlet side of the continuous plasticizer, lower the temperature of the molten polyolefin-based polymer composition, start the foaming by the pressure drop, and foam by the cooling device. By controlling the ratio, it becomes possible to continuously produce a polyolefin-based polymer composition foam with a constant quality.

[0054]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The evaluation test methods in Examples and Comparative Examples are as follows. [1] Melt Fluorate In the present invention, for measuring the melt fluorate of the composition, an auto melt indexer of TP406 of Tester Sangyo Co., Ltd. is used, and a nozzle of the melt indexer (caliber 2.09)
5 mm, length 8 mm), the measurement temperature was 230 ° C., and the load was 2.16 kgf.

[2] Melt Tension and Drawdown Property In the present invention, the melt tension and drawdown property of the composition were measured by using a melt indexer and a CAPIROGRAPH 1C manufactured by Toyo Seiki Seisaku-sho, Ltd. in combination. The melt tension and drawdown properties were measured as follows. CAPIROGRAPH1
23 from C nozzle (caliber 2.95 mm, length 8 mm)
The molten composition heated to 0 ° C. is loaded from above to 10
It is extruded into a string at a constant speed of mm / min. The extrudate,
Pass it through the tension detection pulley and guide it to the feed roll for winding. On the other hand, the winding speed is gradually increased to cut the string-like object, and the tension immediately before the cutting is read, and this is taken as the melt tension (gf). Further, the winding speed of the string-like material at the time of cutting is defined as drawdown property.

[3] Strain hardening index In the present invention, the extensional viscosity of the composition was measured by using an extensional flow measuring device (trade name: RME) manufactured by Rheometric Co. as follows. A measurement sample was prepared from the composition, and the relationship between the elongation viscosity η _E ⁺ (Pa · s) at the strain rate (sec ⁻¹ ) of this sample and the time t (sec) (elongation viscosity curve) was graphed. The measurement temperature is 180 ℃
And An example of the measurement results for resin C is shown in FIG.

On the other hand, the viscosity when this composition was assumed to have no strain hardening property was calculated according to the linear viscoelasticity law. In the calculation, the shear viscosity was determined from the frequency dispersion of the melt viscoelasticity measured at a measurement temperature of 180 ° C. similar to the elongational viscosity measurement.

From the above measurement results, the strain ε is plotted on the abscissa and the ratio λ _n between the actually measured extensional viscosity curve and the viscosity value obtained by the linear viscoelastic law is plotted on the ordinate and plotted.
The slope of the straight line obtained from this relationship was defined as the strain hardening index.
An example of the measurement results for resin C is shown in FIG.

[4] Foam observation (foam density, sheet surface condition) The density of the obtained foam sheet was measured. A foam sheet cut into 0.5 to 5 g was used as a sample, and the measurement method was carried out by an underwater substitution method under an atmosphere of a temperature of 23 ° C. and a humidity of 50%. The surface condition of the obtained foam sheet was observed by the following evaluation method. ◎ ・ ・ ・ Smooth state with no unevenness on the surface, ○ ・ ・ ・ Almost smooth state with some unevenness on the surface, × ・ ・ ・ Remarkably uneven surface or severe corrugation

[5] Observation of Foam (Anisotropy of Cell Structure) Bubbles were observed within a rectangular area of 100 mm × 80 mm in a photograph (magnification: 50) of a cross section of the obtained foam sheet taken with an optical microscope. . At this time, the maximum bubble diameter and the minimum bubble diameter in each bubble were calculated, and the anisotropy of the bubble structure was determined from the average value of this ratio (minimum bubble diameter / maximum bubble diameter).

(Example 1) A polyolefin polymer composition (polypropylene brand: J101 [manufactured by Grand Polymer Co., Ltd.] and polypropylene brand: PF-814 [manufactured by Sun Allomer Co., Ltd.] was mixed at a weight ratio of 9: 1. 100 parts by weight), 0.10 parts by weight (0.9% by weight) of Hydrocerol CF [manufactured by Boehringer] as a bubble nucleating agent.
5 wt%), and uniformly mixed with a high speed stirrer. In addition,
The type and physical properties of the polymer composition used are as described in Table 1. After that, the above mixture was added from the hopper (12) into the extruder (19) constituting the inlet side of the continuous plasticizer and was heated and melted at 210 ° C.
The extruder used was a uniaxial extruder having a screw diameter of 50 mm and an L / D of 32.

The carbon dioxide used as the foaming agent is
From the liquefied carbon dioxide cylinder (1), the temperature was controlled to -30 ° C., and it was injected into the metering pump (2) where it was pressurized and 1.0 part by weight of pressure-controlled carbon dioxide was melted in the extruder (19). It was added to the coalescing composition. After kneading the molten polyolefin-based polymer composition in the extruder (19) and carbon dioxide with the screw (13),
In the cooling step, the temperature was lowered to 165 ° C. to a temperature suitable for foaming.

Next, the molten polyolefin-based polymer composition was transferred to a T-die (16) connected to the outlet side of the continuous plasticizer set at 160 ° C. to start foaming. The molten polyolefin-based polymer composition that has begun to foam is T
-Although it is extruded from the die (16) outlet and starts foaming at the same time, it is cooled while being adjusted to a thickness of 2 mm by a cooling roll (18) installed in front of the T-die (16) and shaped into a sheet. A foamed sheet (17) of a polyolefin-based polymer composition was obtained. At this time, the roll temperature was 50 ° C. and the roll take-up speed was 1.0 m / min. The density, sheet appearance and bubble anisotropy of the polyolefin polymer composition foamed sheet obtained under the above conditions were observed. Table 2 shows the density, appearance, and bubble anisotropy at this time.

(Example 2, Comparative Examples 3 to 7) Example 1 was the same as Example 1 except that the types of polymers used, the physical properties, and the amounts of foaming agents added were as shown in Tables 1 and 2. It evaluated similarly. Table 2 shows the density, appearance, and bubble anisotropy at this time.

[0065]

[Table 1]

[0066]

[Table 2]

[0067]

EFFECT OF THE INVENTION The present invention provides a foam using a polyolefin polymer composition having excellent recyclability. Further compared to the extruded foam based on the conventional non-crosslinked polypropylene-based polymer composition according to the present invention,
A wide foaming temperature range makes it easy to control the extrusion foaming temperature, and it is possible to obtain a foam having a uniform fine structure, a high closed cell ratio and a small anisotropic cell structure in a wide density range. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an apparatus for producing a polyolefin-based polymer composition foam of the present invention.

FIG. 2 is an example of a graph showing an extensional viscosity curve of a polymer composition used in Examples of the present invention.

FIG. 3 is an example of a graph for determining the strain hardening index of the polymer composition used in the examples of the present invention.

[Explanation of symbols]

(1) Liquefied carbon dioxide cylinder (2) Metering pump (3) Pressure holding valve (4) Refrigerant circulator (5) Heater (6) Flow meter (12) Hopper (13) Screw (16) T-die (17) Foamed sheet (18) Cooling roll (19) Extruder

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4F074 AA17A AA18 AA20 AA21                       AA22 AA23 AA24 AA24A                       AA24B AA25 AA26 AA26A                       AA47A AA51A BA03 BA04                       BA05 BA06 BA08 BA13 BA14                       BA16 BA17 BA18 BA19 BA20                       BA31 BA32 BA33 BA34 BA35                       BA36 BA38 BA39 BA40 BA44                       BA45 BA47 BA53 BA54 BA55                       BA73 BA74 CA22 CC04X                       CC05Y CC05Z CC22X CC22Y                       CC34Y DA02 DA33 DA34

Claims (6)

[Claims] 1. A foam comprising a polyolefin-based polymer composition having a melt tension of 3 to 7 gf and a drawdown property of 60 to 100 m / min. 2. 180 of a polyolefin-based polymer composition
The rise of extensional viscosity at 0 ° C. (hereinafter referred to as strain hardening index) is 0.20 or more.
The foam according to. 3. The foam according to claim 1, which has a density of 0.70 to 0.01 g / cm ³ . 4. The foam according to claim 1, wherein the foaming agent is carbon dioxide. 5. The foam according to claim 1, wherein the anisotropy of the cell structure is 0.5 to 1.0. 6. A polyolefin-based polymer composition having a melt tension of 3 to 7 gf and a drawdown property of 60 to 100 m / min, or a strain hardening index of 0.20 or more is extruded. After the plasticizing by adding to the machine, the step of heating and melting, the step of supplying a foaming agent into the molten polyolefin-based polymer composition, and after kneading the polyolefin-based polymer composition and the foaming agent melted in the extruder , A step of cooling to a temperature suitable for foaming, and a step of transferring the molten polyolefin-based polymer composition to a die connected to the exit side of the extruder and extruding under low pressure from within the extruder to foam Body manufacturing method.