JPH08176334A - Polyolefin resin composition for foam-molding and foam product using the same - Google Patents

Abstract

PURPOSE: To provide a polyolefin resin composition which gives foam products having fine and uniform cells without large voids, thus is useful as a packaging material such as a tray by formulating a specific amount of a specific higher fatty acid amide to a polyolefin resin. CONSTITUTION: When (A) a polyolefin resin is melt-kneaded with an inert gas in an extruder to effect extrusion foam molding, (B) 0.1-5wt.% of an amide of a higher fatty acid of 20 or more carbon atoms, preferably behenic acid amide is formulated to (A) the polyolefin resin to give this resin composition. In a preferable embodiment, the component A comprises 95-85wt.% of a polypropylene resin and 5-15wt.% of polyethylene and further (C) 5-40wt.% of an inorganic filler.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin resin composition for foam molding and a foam using the composition. More specifically, it is a lightweight, heat-insulating material having a good foaming state with few voids. A polyolefin resin composition for foam molding capable of producing a foam exhibiting excellent and high specific strength and used for packaging materials such as trays and boxes, panel materials for heat insulation, core materials, etc., using the composition. It relates to a foam.

[0002]

2. Description of the Related Art Conventionally, there is known a technique in which an inert gas is injected into a resin in an extruder and kneaded, followed by extrusion foam molding.
For example, after injecting an inert gas into the decompression section of the extruder and kneading and sorbing the inert gas to the molten resin by the high resin pressure inside the extruder, the inert gas is extruded from the die outlet under atmospheric pressure to A method of foaming by the pressure of the active gas, cooling at the time when the foaming ratio reaches a predetermined level to produce a foam, and passing between rolls or belts to obtain surface smoothness as necessary ( Japanese Patent Publication No. 54-18707) has been proposed.

In the above method, when sorbing an inert gas such as nitrogen gas, carbon dioxide gas or chlorofluorocarbon to the molten resin, a pressure capable of sorbing an amount of the inert gas sufficient to obtain the desired expansion ratio. Has been proposed (Japanese Patent Publication No. 54-23386).

As still another method, a method of forming an unfoamed molded product in which gas is sorbed in a supersaturated state and reheating the molded product to foam it by the internal gas pressure (Japanese Patent Publication No. 1-50).
No. 0583) is also proposed. In this method, an inert gas is injected into the depressurization section of the extruder and kneaded, and the inert gas is sorbed on the molten resin by the high resin pressure inside the extruder, and then the sorbed molten resin of the gas is cooled by the refrigerant. While not cooling under high pressure, the foaming is suppressed and extruded from the die outlet to obtain an unfoamed molded product.

As a variation of this method, instead of cooling in an extruder or a die to suppress foaming, the temperature is lowered as much as possible to perform melt extrusion, followed by rapid cooling immediately after extrusion to suppress foaming or to a minimum. A method has been proposed in which foaming is suppressed and a molded product is obtained, and then the molded product is reheated.

However, in the above conventional method, amorphous polystyrene is used. When a crystalline resin is used, the viscosity of the crystalline resin changes in the vicinity of the melting point and the melt tension rapidly changes. Therefore, problems such as bursting of bubbles occur during reheating and foaming. Among them, polyolefin resins such as polypropylene resin have insufficient melt tension, and therefore have low affinity with inert gas such as nitrogen gas, and have a low dissolution rate in the melted polyolefin resin, and thus in the extruder. Since it is difficult to sorb the gas into the molten resin uniformly in a high concentration in a short time, there is a problem that the gas that could not be completely dispersed becomes large voids and is extruded as it is. No foam was obtained. In order to solve such a problem, a special extrusion device has been proposed (Actual Development Sho 55-1).
No. 34225) has the drawback of being complicated and costly.

[0007]

Inert gas such as nitrogen gas is inherently poor in compatibility with molten resin, and it is difficult to sorb a high concentration and to disperse it uniformly. Therefore, the non-uniformly adsorbed inert gas becomes a huge void and is extruded as it is, and in the worst case, it becomes a through hole,
It not only impairs the appearance of the foam, but also adversely affects the mechanical strength.

An object of the present invention is to solve the above-mentioned problems, to use a special extruder or the like device, to have a good foaming state with few voids, to be lightweight, excellent in heat insulation,
To provide a polyolefin resin composition for foam molding capable of producing a foam exhibiting high specific strength, and to use it for packaging materials such as trays and boxes, panel materials for heat insulation, core materials, etc. It is to provide a foam to be used.

[0009]

Means for Solving the Problems As a result of repeated studies by the present inventors with various additives, fillers, blends of resins and the like in order to solve the above-mentioned problems, as a result, a specific higher fatty acid amide was added to a polyolefin resin. It was found that an inert gas can be uniformly sorbed at a high concentration by blending a specific amount, and the present invention has been completed.

According to the first aspect of the present invention, when an inert gas is melt-kneaded with a polyolefin resin in an extruder and extrusion-foamed, the polyolefin resin contains 0 or more higher fatty acid amide having 20 or more carbon atoms. The polyolefin resin composition for foam molding is characterized by containing 1 to 5% by weight.

The invention of claim 2 of the present invention provides the polyolefin resin composition for foam molding according to claim 1, wherein
The polyolefin-based resin is characterized in that a polypropylene-based resin is a main component.

The invention of claim 3 of the present invention is the polyolefin resin composition for foam molding according to claim 2, wherein
The polyolefin resin is polypropylene resin 9
It is characterized by being 5 to 85% by weight and 5 to 15% by weight of polyethylene.

The invention of claim 4 of the present invention is the invention of claims 1 to 3.
In the polyolefin resin composition for foam molding according to any one of items 1 to 3, the higher fatty acid amide is behenic acid amide.

The invention of claim 5 of the present invention is the invention of claims 1 to 4.
In the polyolefin resin composition for foam molding according to any one of 1 to 5, 5 to 40% by weight of an inorganic filler in the composition.
It is characterized by blending.

The invention of claim 6 of the present invention is the same as that of claim 1.
5 to 5 are melt-kneaded with an inert gas in an extruder and then extrusion-foam molded to obtain a foaming ratio of 1.2 to 5.0.
It is a foam that is double.

The present invention will be described in detail below. The inert gas as referred to in the present invention is a gas that does not cause a chemical reaction with the polyolefin resin during extrusion molding, and does not pose a risk of flammable explosion during extrusion foam molding or secondary processing. Specific examples thereof include nitrogen gas, air containing nitrogen gas as a major component, carbon dioxide gas, argon, helium, and steam.

The polyolefin resin in the present invention is a homopolymer of α / olefin such as ethylene, propylene, butene-1,4-methylpentene-1, hexene-1, octene-1, or a mutual copolymer thereof. Specifically, high / medium / low density polyethylene, ultra-low density polyethylene, polypropylene, homopolymers of polybutene-1, etc., copolymers of ethylene and propylene, butene-1, etc., propylene and ethylene, butene-1, etc. Crystalline polyolefins such as copolymers with other α-olefins, ethylene-vinyl ester copolymers, ethylene-α, β-unsaturated carboxylic acids and / or their alkyl ester copolymers, thermoplastic ethylene-propylene elastomers, Examples thereof include olefin-based ionomer resins.

More specifically, low density polyethylene (L
DPE), ultra low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), polypropylene (PP), poly-1-butene, poly-4-methyl-1-pentene, high pressure Radical polymerization ethylene vinyl acetate copolymer (EVA), ethylene / (meth)
Acrylic acid copolymers, ethylene copolymers such as ethylene / (meth) acrylate acrylate copolymers, random copolymers containing ethylene and propylene as main components (EPM),
Examples of the third component include a random copolymer (EPDM) containing a diene monomer (dicyclopentadiene, ethylidene norbornene, etc.) as a main component, and these are used alone or in combination of two or more. You may. Olefin-based ionomer resin is based on olefin / α, β-unsaturated carboxylic acid copolymer as a base resin, and all or part of its carboxyl group, usually 5 to
It is an ionomer resin in which 100% is neutralized with metal ions. Among the olefin-based ionomer resins, the ethylene-based ionomer resin is particularly preferable.

The density, melt flow rate (MFR) and the like of these polyolefin resins are not particularly limited, but the melt flow rate (MFR) is 0.1 to 15 g / 10 minutes, especially high in the case of general resins. In the case of high crystalline polyolefin such as density polyethylene or polypropylene, it is preferably selected in the range of 0.2 to 10 g / 10 minutes.

Among these polyolefin resins,
A polyolefin-based resin containing a polypropylene-based resin as a main component or a polyolefin-based resin obtained by mixing 95 to 85% by weight of a polypropylene-based resin with 5 to 15% by weight of polyethylene can be preferably used. As the polypropylene resin, a known polypropylene (co) polymer such as a propylene homopolymer, a block copolymer with other α-olefin containing propylene as a main component, or a random copolymer can be used. .

The higher fatty acid amide having 20 or more carbon atoms used in the present invention may be a natural product or a synthetic product and is not particularly limited. Specific examples of the higher fatty acid amide having 20 or more carbon atoms include behenic acid amide, lignoceric acid amide, serotinic acid amide, heptacoic acid amide, montanic acid amide, melicinic acid amide, and laxeric acid amide. Among these, behenic acid amide can be preferably used. The content of these higher fatty acids is 0.1 to 5% by weight, preferably 0.5, based on the total composition of the present invention.
-4% by weight, more preferably 1-3% by weight.
If it is less than 0.1% by weight, voids are generated and a uniform foaming state cannot be obtained. If it exceeds 5% by weight, stable extrusion molding becomes difficult and molding of the foam becomes impossible.

An inorganic filler may be added to the polyolefin resin composition for foam molding of the present invention in order to impart other properties such as control of the foaming state and improvement of the mechanical properties of the foam. As the inorganic filler, calcium sulfate, calcium silicate, clay, diatomaceous earth, talc, alumina, silica sand, glass powder, iron oxide, metal powder, graphite,
Silicon carbide, silicon nitride, silica, boron nitride, aluminum nitride, carbon black, mica, glass plate, sericite, pyrophyllite, aluminum flakes, graphite, silas paloon, metal paloon, glass paloon, pumice stone, glass fiber, carbon fiber , Whiskers, metal fibers, graphite fibers, silicon carbide fibers, asbestos, wollastonite and the like.

When an inorganic filler or the like is used, the surface of the filler may be a fatty acid such as stearic acid, oleic acid or palmitic acid or a metal salt thereof, paraffin,
A surface treatment such as coating with wax, polyethylene wax or a modified product thereof, organic silane, organic borane, organic titanate, etc. may be performed. These inorganic fillers are added to the composition in an amount of about 5 to 40% by weight. If the amount is less than 5% by weight, the improvement effect is small, and if it exceeds 40% by weight, the surface of the foam is roughened and mechanical properties such as impact strength are deteriorated, which is not preferable.

Further, with respect to the polyolefin resin composition for foam molding of the present invention, organic fillers, antioxidants, lubricants, organic or inorganic pigments, ultraviolet absorbers, dispersants, etc. are included within the scope of the present invention. You may add a plasticizer, a nucleating agent, etc.

The method for producing the polyolefin resin composition for foam molding of the present invention is not particularly limited,
It can be manufactured by a known method. For example, 0.1 to 5% by weight of a higher fatty acid amide having 20 or more carbon atoms in a polyolefin resin, optionally an inorganic filler, an antioxidant, a lubricant, an organic or inorganic pigment, an ultraviolet absorber, a dispersant, etc. May be used as it is after dry blending with an ordinary tumbler or the like, or it may be further subjected to ordinary kneading with a Banbury mixer, a pressure kneader, a kneading extruder, a twin-screw extruder, a roll or the like. It may be melt-kneaded by a machine and uniformly dispersed before use.

The foam produced using the polyolefin resin composition for foam molding of the present invention has a good foaming state due to fine cells. The above-mentioned fine bubbles are bubbles having a diameter of 0.5 mm or less at the maximum. The foaming state is the type and blending ratio of the polyolefin resin composition,
The amount of inert gas to be injected, extrusion foaming conditions such as temperature and pressure, reheating foaming conditions, and the resulting expansion ratio, etc., so that in order to produce a foam having a good foaming state, It is essential to adequately control these conditions.

The expansion ratio of the foam of the present invention can be changed according to the above-mentioned conditions such as the kind and blending ratio of the polyolefin resin composition, the amount of inert gas to be injected, and the like.
It is about 1.2 to 5.0 times. If the expansion ratio is less than 1.2, the effect of improving heat insulation, specific strength, cushioning, etc. is small,
If it exceeds 5.0, huge voids may be formed, or in the worst case, through holes may be formed, impairing the appearance of the foam and lowering the mechanical strength.

[0028]

By adding 0.1 to 5% by weight of higher fatty acid amide having 20 or more carbon atoms such as behenic acid amide to the polyolefin resin, the inert gas is melted in the molten polyolefin resin. Can be uniformly sorbed at a high concentration. By blending behenic acid amide or the like, the inert gas is uniformly dispersed and sufficiently sorbed in the melted polyolefin resin, and a huge void is not extruded as it is, and a good product is obtained.

The term "voids" as used in the present invention refers to the bubbles of an inert gas originally present in the molten polyolefin resin which should not be foamed at the exit of the die during extrusion foam molding. It is considered that these are excess gases that could not be sorbed to the resin in the extruder. These become coarser bubbles during foaming, resulting in a marked loss of appearance of the resulting foam. The size of these voids is several times as large as that of ordinary foamed cells, and the diameter thereof is 0.5 mm or more at the smallest, and can be easily distinguished from ordinary cells by the naked eye.

When a resin containing a polypropylene resin as a main component is used as the polyolefin resin, it is possible to produce a foam having excellent heat resistance and high specific strength.

By using a composition comprising 95 to 85% by weight of polypropylene resin and 5 to 15% by weight of polyethylene, a foam having further flexibility and impact resistance can be obtained.

If behenic acid amide is used as the higher fatty acid amide, the inert gas can be uniformly sorbed in the molten polyolefin resin at a high concentration, and is easily available and economical.

When the polyolefin resin composition for foam molding of the present invention is blended with an inorganic filler in an amount of 5 to 40% by weight based on the whole composition, the foaming state can be controlled and the mechanical properties of the foam are improved. Other properties can be added.

[0034]

The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention.

Example 1 Propylene-ethylene block copolymer [abbreviated as BPP hereinafter. Ethylene concentration 10% by weight, MFR 0.5 g / 10 min] to behenic acid amide 1
Extrusion foam molding was carried out using an extruder using the compound to which the weight% was added. The resin temperature during extrusion molding is 220
℃, resin pressure is 150-200kg at the top of the cylinder
It was about / cm ² . The amount of resin discharged at this time is 240
g / min, pressure 100 k from the reduced pressure part of the extruder
Nitrogen gas was supplied at g / cm ² at 400 normal ml / min for sorption. For extrusion of molten resin, 1
Using a hanger coat type T die having a width of 50 mm, it was immersed in water immediately after extrusion and rapidly cooled to obtain a substantially unfoamed molded body, which was then reheated by an infrared heater to foam. The obtained foam had 2 to 3 voids of 0.5 mm or less / 100 cm ² , and a foam having a good foaming ratio of 2.5 times the expansion ratio was obtained. The results are shown in Table 1.

(Example 2) Pressure 1 from the depressurized portion of the extruder
Nitrogen gas is 100 normal ml / m at 00 kg / cm ^2.
A foam was produced in the same manner as in Example 1 except that in was injected. As a result, a beautiful foam having a void expansion ratio of 2.2 was obtained. The results are shown in Table 1.

(Example 3) Homopolypropylene [hereinafter,
Abbreviated as HPP. MFR 0.5 g / 10 min], and a compound in which 1% by weight of behenic acid amide was added was used to perform extrusion foam molding using an extruder. The resin temperature during extrusion molding is 240 ° C, and the resin pressure is 150-
It was about 200 kg / cm ² . The amount of resin discharged at this time was 220 g / min, and 400 normal ml of nitrogen gas was supplied from the depressurized portion of the extruder at a pressure of 100 kg / cm ^2.
It was supplied at a rate of / min for sorption. When extruding the molten resin, a hanger coat type T die with a width of 150 mm was used. Immediately after extrusion, the product was immersed in water and rapidly cooled to obtain a substantially unfoamed molded product, which was then reheated with an infrared heater. And foamed. The obtained foam had 5 to 8 voids of 0.5 mm or less / 100 cm ² , and a foam having a good expansion state with an expansion ratio of 1.9 was obtained.
The results are shown in Table 1.

Example 4 Low density polyethylene [hereinafter abbreviated as LDPE] was used for the BPP used in Example 1. Density 0.9
22 g / cm ³ , MFR 0.3 g / 10 min] was blended with 10% by weight of the resin composition, and a compound in which 1% by weight of behenic acid amide was further added was extrusion foamed using an extruder. The resin temperature during extrusion molding is 220 ° C,
Resin pressure is 150 to 200 kg / c at the top of the cylinder
It was about m ² . The amount of resin discharged at this time is 250 g /
min, pressure from the depressurized part of the extruder is 100 kg /
Nitrogen gas was supplied at 400 normal ml / min in cm ² , and sorption was performed. When extruding the molten resin, 150
Using a mm-width hanger coat type T-die, it was immersed in water immediately after extrusion and rapidly cooled to obtain a substantially unfoamed molded body, which was then reheated by an infrared heater to foam. The resulting foam has 6-0.5 mm or less voids.
It was 8/100 cm ² , and a foam having a good expansion state with an expansion ratio of 2.6 was obtained. The results are shown in Table 1.

(Example 5) Talc (trade name: Micron White 5000SM) was added to the BPP used in Example 1 in an amount of 20.
A compound obtained by further adding 1% by weight of behenic acid amide to the resin composition blended by% by weight was extrusion foamed using an extruder. The resin temperature during extrusion molding is 220
℃, resin pressure is 150-200kg at the top of the cylinder
It was about / cm ² . The amount of resin discharged at this time is 200
g / min, pressure 100 k from the reduced pressure part of the extruder
Nitrogen gas was supplied at a rate of 300 g / cm ² at a normal volume of 300 ml / min for sorption. For extrusion of molten resin, 1
Using a hanger coat type T die having a width of 50 mm, it was immersed in water immediately after extrusion and rapidly cooled to obtain a substantially unfoamed molded body, which was then reheated by an infrared heater to foam. The obtained foam had 6 to 8 voids of 0.5 mm or less / 100 cm ² , and a foam having a good expansion state with an expansion ratio of 1.9 was obtained. The results are shown in Table 1.

Comparative Example 1 A foam was produced in the same manner as in Example 1 except that behenic acid amide was not added to the BPP used in Example 1. As a result, the foam obtained had a void of 0.5 mm or more of several hundreds / 100 cm ² and had a poor appearance. The expansion ratio was 1.6 times. The results are shown in Table 1.
Shown in

(Comparative Example 2) Without adding behenic acid amide to the BPP used in Example 1, nitrogen gas was supplied from the reduced pressure portion of the extruder at a pressure of 100 kg / cm ² to 100 normal ml / n.
A foam was produced in the same manner as in Example 1 except that min was supplied. As a result, the obtained foam had 20 to 30 voids / 100 cm ² of 0.5 mm or more, and the appearance was poor. The expansion ratio was 1.4 times. The results are shown in Table 1.

Comparative Example 3 A foam was produced in the same manner as in Example 1 except that behenic acid amide was not added to the BPP used in Example 1 but 1% by weight of stearic acid amide was added instead. 0.5 mm for the resulting foam
There were several hundred voids / 100 cm ^{2 of the} above voids and the appearance was poor. The expansion ratio was 1.4 times. The results are shown in Table 1.

Comparative Example 4 A foam was produced in the same manner as in Example 3 except that behenic acid amide was not added to the HPP used in Example 3. As a result, the foam obtained had a void of 0.5 mm or more of several hundreds / 100 cm ² and had a poor appearance. The expansion ratio was 1.4 times. The results are shown in Table 1.
Shown in

(Comparative Example 5) Extrusion foam molding was carried out in the same manner as in Example 1 except that the compound obtained by adding 0.05% by weight of behenic acid amide to the BPP used in Example 1 was used. As a result, the foam obtained had a void of 0.5 mm or more of several hundreds / 100 cm ² and had a poor appearance. The expansion ratio was 1.6 times. The results are shown in Table 1.

(Comparative Example 6) Extrusion foam molding was attempted by the same means as in Example 1 except that the compound obtained by adding 8% by weight of behenic acid amide to the BPP used in Example 1 was used. However, if behenic acid having a lubricating effect is mixed up to 8% by weight, slipping occurs inside the extruder, and the extrusion discharge amount becomes extremely unstable, so that a satisfactory molded product cannot be obtained. The results are shown in Table 1.

[0046]

[Table 1]

[0047]

EFFECTS OF THE INVENTION By blending 0.1 to 5% by weight of a higher fatty acid amide having 20 or more carbon atoms such as behenic acid amide with a polyolefin-based resin with respect to the entire composition, an inert gas such as nitrogen gas is added. Since it can be uniformly sorbed in the molten polyolefin resin at a high concentration, a foam having uniform and fine cells in a good foaming state without huge voids can be obtained. The foam of the present invention has a high-grade appearance, is expected to have higher mechanical properties, is lightweight, and is excellent in heat insulating property, etc., as compared with a conventional foam having coarser cells. Used for packaging materials such as trays and boxes, panel materials for heat insulation, and core materials.

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Claims (6)

[Claims] 1. In the melt-kneading of an inert gas with a polyolefin resin in an extruder and extrusion foam molding, 0.1 to 5% by weight of a higher fatty acid amide having 20 or more carbon atoms is added to the polyolefin resin. A polyolefin resin composition for foam molding, characterized in that 2. The polyolefin-based resin contains a polypropylene-based resin as a main component.
The polyolefin resin composition for foam molding according to item 4. 3. The polyolefin resin is 95 to 85% by weight of polypropylene resin and 5 to 15 of polyethylene.
% Of the polyolefin resin composition for foam molding according to claim 2. 4. The polyolefin resin composition for foam molding according to claim 1, wherein the higher fatty acid amide is behenic acid amide. 5. The composition contains 5 to 40% by weight of an inorganic filler.
The polyolefin resin composition for foam molding according to any one of claims 1 to 4, wherein 6. The composition according to any one of claims 1 to 5 is melt-kneaded with an inert gas in an extruder and then extrusion-foam molded to have a foaming ratio of 1.2 to 5.0. And foam.