JP2003165859A - Hollow foam of polyppopylene resin composition and method for producing the foam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a lightweight and moderately expanded polypropylene resin foam made from a monolayer parison using a monolayer molding machine, having a skin layer consisting of an unfoamed resin layer ≥0.3 mm thick on the outer surface, having a specific gravity of 0.2-0.7, good at mold transferability, design and an appearance, and having high mechanical strength, rigidity and heat resistance. <P>SOLUTION: The method for producing the hollow foam comprises the steps of melt-extruding a polypropylene resin composition containing a foaming agent to foam a parison, nipping and fixing the parison with a pair of molds, injecting air at 0.3-1 MPa into the hollow part of the parison to expand it, pressing it against the molds for 2-30 s, and reducing the air pressure to 0.001-0.1 MPa to foam the parison; wherein the mold temperature is controlled so as to meet the relationship: Tme-50≤Tmo≤Tme-5 (Tmo is the surface temperature of the molds on the cavity side; and Tme is the crystallization temperature of the raw material polypropylene resin composition). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene resin composition-made hollow foam (hereinafter sometimes simply referred to as a hollow foam) made of a polypropylene resin composition, and a method for producing the same.

[0002]

2. Description of the Related Art As a method for producing a hollow container from a thermoplastic resin, (1) a thermoplastic resin is melt-extruded to form a parison, and the parison is sandwiched and fixed by a pair of molds, and then the hollow container is hollowed. A method of manufacturing a hollow container after injecting a pressurized fluid into the part to expand the parison and pressing it against the mold to shape it,
A so-called direct blow molding method, (2) a preform is once molded by injection molding or extrusion molding of a thermoplastic resin, and the preform is heated in another mold, or mechanically and / or without heating. Two methods, a stretch blow molding method of stretching with a pressurized gas, are known.

Of these, the raw material resin used in direct blow molding must have the characteristics that the parison is difficult to draw down and is easily melt-stretched uniformly. Therefore, the direct blow molding method uses polyethylene resin or polystyrene having a relatively high molecular weight. A hollow container made of polypropylene resin or polyester resin having a low melt tension, which is used for forming a polyvinyl chloride hollow container, is mainly formed by a stretch blow molding method.

Weight reduction in a thermoplastic resin hollow container,
Alternatively, a hollow container made of a resin foam obtained by foaming the above resin for the purpose of decorativeness, and a method for manufacturing the hollow container are also known. As the resin used in this hollow foam, the resin used in the above-mentioned direct blow molding container has only been put into practical use, and polypropylene resin has hardly been studied.

A hollow foam made of a thermoplastic resin composition is usually prepared by melting a thermoplastic resin containing a foaming agent to form a parison, and then sandwiching the parison with a pair of molds to perform blow molding. However, since the hollow foam produced by ordinary blow molding has foam cells on the surface as well, only a poor appearance can be obtained.

Several methods have been proposed for improving the surface appearance of such a hollow foam made of a thermoplastic resin composition. For example, JP-A-56-44632 proposes a method of forming a skin layer on the surface of a foam by lowering the mold temperature. However, the resin described as an example in the same publication is only polystyrene, and when a manufacturing method using this low-temperature mold is adopted for polypropylene resin, only a foam having a low expansion ratio is obtained, and the surface appearance is It turned out to be inferior.

As a method for producing a hollow foam having a good appearance with a polypropylene resin, for example, JP-A-11-
No. 181136 discloses a method using a propylene / ethylene copolymer, but the effect is hardly recognized by this method.

Further, JP-A-11-188823 discloses a multilayer structure in which a propylene / ethylene random copolymer layer containing no foaming agent as a surface layer and a foam layer formed from a propylene resin containing a foaming agent as an inner layer are laminated. The polypropylene foam hollow molded article is described, and it is described that the surface gloss is high and the appearance is excellent. However, since this hollow foam is a molded product having a multi-layer structure, it cannot be easily manufactured, and a special device called a multi-layer molding container molding device is required.

[0009]

SUMMARY OF THE INVENTION The present invention is intended to solve the above conventional problems. A first object of the present invention is to provide a hollow foam made of a polypropylene resin composition, which can be molded by a single-layer molding apparatus, has an unfoamed layer on the surface of the hollow foam, and is appropriately foamed, and a method for producing the same. That is. A second object of the present invention is to provide a polypropylene resin composition hollow foam which is excellent in mold transferability and design and has a good appearance, and a method for producing the hollow foam. A third object of the present invention is to appropriately foam.
A hollow foam made of a polypropylene resin composition which is lightweight, has high strength and rigidity, and is excellent in heat resistance, and a method for producing the hollow foam.

[0010]

The present invention is the following hollow foam made of a polypropylene resin composition and a method for producing the same. (1) A hollow foam made of a polypropylene resin composition containing polypropylene resin as a main component and molded from a single-layer parison, and having a skin layer made of an unfoamed resin layer of 0.3 mm or more on the outer surface. And has a specific gravity of 0.2-
A polypropylene resin composition-made hollow foam, which is 0.7. (2) The polypropylene resin composition comprises (A) a propylene homopolymer or a propylene / α-olefin copolymer in an amount of 20 to 80 parts by weight, (B) a strain-curable polypropylene resin in an amount of 5 to 50 parts by weight, and (C). ) A resin composition containing 0 to 30 parts by weight of a high-pressure method low-density polyethylene resin (provided that (A) + (B) + (C) = 100 parts by weight), which is 23 according to ASTM D-1238.
Melt flow rate measured under 0.degree. C. and a load of 2.16 kg is 0.1 to 20 g / 10 min, The hollow foam made of the polypropylene resin composition according to (1) above. (3) A polypropylene resin composition containing a foaming agent is melt-extruded to form a parison, and the parison is sandwiched and fixed by a pair of molds.
Primary air having a pressure (primary pressure) of 3 to 1 MPa is injected to expand the parison, and the parison is pressed for 2 to 30 seconds to form a skin layer, and then the air pressure is set to 0.0.
Method for producing a hollow foam body in which the parison interior is foamed by reducing the pressure to a pressure of 0.1 to 0.1 MPa (secondary pressure), and the molded product is cooled and solidified by holding for a certain period of time and then the mold is opened to take out the molded product In equation (1), the surface temperature (Tmo) of the mold on the cavity side is represented by the following formula (1) Tme-50 ≤ Tmo ≤ Tme-5 (1) (where Tmo is the surface temperature of the mold on the cavity side (° C) ), And Tme is the crystallization temperature (° C.) of the polypropylene resin composition forming the parison.) The above-mentioned (1) or (2), wherein a hollow foam having a good appearance is obtained. 1. A method for producing a hollow foam made from the polypropylene resin composition of.

In the present invention, a polypropylene resin composition containing polypropylene resin as a main component is used as a material for the hollow foam. As this polypropylene resin composition,
(A) 20 to 80 parts by weight of a propylene homopolymer or propylene / α-olefin copolymer, (B) 5 to 50 parts by weight of a polypropylene resin having a strain hardening property, and (C) a high-pressure low-density polyethylene resin 0 to A resin composition containing 30 parts by weight (provided that (A) + (B) + (C) = 100 parts by weight) according to ASTM D-12.
A polypropylene resin composition having a melt flow rate of 0.1 to 20 g / 10 min as measured by No. 38 at 230 ° C. under a load of 2.16 kg is preferable.

The propylene homopolymer or propylene / α-olefin copolymer (A) is a propylene homopolymer or propylene / α-olefin copolymer having no strain hardening property. Component (A) Propylene / α-
The olefin copolymer (A) is a copolymer of propylene and a small amount of other α-olefin, and as a comonomer, ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene. Α-olefins having up to 10 carbon atoms, such as 1, 1-heptene, 1-octene and 1-decene can be preferably used. The copolymer may be a random copolymer or a block copolymer. It is desirable that the content of the other comonomer is 20% by weight or less, preferably 10% by weight or less.

Propylene homopolymer or propylene
The α-olefin copolymer (A) has a density of 0.890 to
0.920 g / cm ³ , preferably 0.900 to 0.9
10 g / cm ³ and ASTM D-1238
The melt flow rate (MFR) measured at 230 ° C. under a load of 2.16 kg is 0.1 to 20 g / 10 mi.
n, preferably 0.5 to 10 g / 10 min.

Propylene homopolymer or propylene
The blending amount of the α-olefin copolymer (A) is (A),
2 for 100 parts by weight of the total of the components (B) and (C)
It is desirable that the amount is 0 to 80 parts by weight, preferably 30 to 60 parts by weight. When the amount of the component (A) is less than 20 parts by weight, the smoothness of the product surface or the inner surface is deteriorated due to the generation of corrugates or the like. Further, if it exceeds 80 parts by weight, it is difficult to obtain a uniform cell shape and open cells are generated.

The strain-hardening polypropylene resin (B) used in the present invention generally corresponds to a resin having a very small amount of long-term relaxation component in its molecular chain, and the following resins are known. Therefore, in the present invention, any of the following resins 1) to 3) may be used, or they may be used in combination. 1) Polypropylene resin containing ultra-high molecular weight component 2) Polypropylene resin having crosslinked structure 3) Polypropylene resin having long chain branching

Here, strain hardening
The term "means that when plastic deformation is applied to the resin, its elastic limit increases, and the resistance to plastic deformation increases. Ordinary polypropylene resin does not have strain hardening property. The polypropylene resin (B) having strain hardening property is
The ratio (BT / YT) of the yield point tension (YT: g) and the breaking point tension (BT: g) obtained from the load-time plot in the measurement of uniaxial elongational viscosity at a strain rate of 0.1 sec ^-1 is 1.0. It is a polypropylene resin showing the above, and this ratio (BT / Y
It is preferable to use a polypropylene resin having T) of 1.5 or more.

The strain-curable polypropylene resin (B) preferably has the following physical properties. As polypropylene resin containing ultra high molecular weight component, 135 ℃
Intrinsic viscosity [η] measured in decalin of 6 to 12 dl
/ G, preferably 7 to 10 dl / g of high molecular weight component 5
-20% by weight, preferably 7-15% by weight and according to ASTM D-1238 230 ° C, 2.16 kg
MFR measured under load is 1 to 50 g / 10 min,
It is preferably 3 to 20 g / 10 min.

The amount of the polypropylene resin (B) having strain hardening property is 5 to 50 parts by weight, preferably 1 to 100 parts by weight of the total of the components (A), (B) and (C).
It is preferably 0 to 45 parts by weight. When the blending amount of the polypropylene resin (B) having strain hardening property is less than 5 parts by weight, it is difficult to obtain a uniform cell shape, and when it exceeds 50 parts by weight, the smoothness of the product surface or the inner surface is deteriorated.

As the high-pressure low-density polyethylene (C) used in the present invention, known high-pressure low-density polyethylene (HPLD) containing long-chain branch can be used, and the density is 0.90 to 0.9.
4 g / cm ³ , preferably 0.91 to 0.93 g / c
m ^3, ASTM D-1238 by 190 ° C., 2.1
MFR measured under 6kg load is 0.1-10g / 1
It is preferably 0 min, preferably 0.3 to 5 g / 10 min.

The amount of the high-pressure low-density polyethylene (C) to be blended is 0 to 30 parts by weight, preferably 5 to 25 parts by weight, based on 100 parts by weight of the total of the components (A), (B) and (C). Is desirable. When the high-pressure low-density polyethylene (C) is blended, not only the smoothness of the product surface or inner surface is improved, but also the drawdown property is improved. On the other hand, if it exceeds 30 parts by weight, the rigidity and heat resistance of the hollow foam are impaired.

A blowing agent is added to the polypropylene resin composition used as a raw material in the present invention in order to impart foamability. As the foaming agent used in the present invention, various known foaming agents can be used. The foaming agent may be a solvent-type foaming agent, a decomposition-type foaming agent, or a gaseous foaming agent.

The solvent-type foaming agent or the gaseous foaming agent is
It is a substance that is injected from the cylinder part of an extruder and absorbed or dissolved in a molten polypropylene resin composition, and evaporated in the cylinder to function as a foaming agent, carbon dioxide gas,
Alternatively, a low-boiling point aliphatic hydrocarbon such as propane, butane, neopentane, heptane, isohexane, hexane, isoheptane, heptane, or a low-boiling point fluorine-containing hydrocarbon represented by CFC gas is used.

The decomposing type foaming agent is a compound which is pre-blended with the polypropylene resin composition and supplied to the extruder, and the foaming agent decomposes under the cylinder temperature condition of the extruder to generate a gas such as carbon dioxide gas or nitrogen gas. However, an inorganic foaming agent or an organic foaming agent may be used, and an organic acid or the like that promotes gas generation may be added together.

The following compounds may be mentioned as specific examples of the decomposable foaming agent. (A) Inorganic foaming agent: sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium carbonate, ammonium nitrite, citric acid, sodium citrate and the like.

(B) Organic blowing agents: N-nitroso compounds such as N, N'-dinitrosoterephthalamide, N, N'-dinitrosopentylenetetramine; azodicarbonamide, azobisisobutyronitrile, azo Azo compounds such as cyclohexyl nitrile, azodiaminobenzene, barium azodicarboxylate; benzenesulfonyl hydrazide, toluenesulfonyl hydrazide, p,
Sulfonyl hydrazide compounds such as p′-oxybis (benzenesulfenyl hydrazide) and diphenyl sulfone-3,3′-disulfonyl hydrazide; azide compounds such as calcium azide, 4,4′-diphenyl disulfonyl azide and p-toluene sulfonyl azide Such.

Of these, carbonates or hydrogen carbonates such as sodium hydrogencarbonate are preferable, and it is preferable to use an organic carboxylic acid together as a foaming auxiliary. The mixing ratio of the carbonate or hydrogen carbonate and the organic carboxylic acid is preferably in the range of 65 to 30 parts by weight of the carbonate or hydrogen carbonate and 35 to 70 parts by weight of the organic carboxylic acid.

The amount of the foaming agent added is 0.1 to 6 parts by weight, preferably 0.5 to 2 parts by weight, based on 100 parts by weight of the polypropylene resin composition. Within this range, a hollow foam having a more uniform cell diameter can be obtained. The amount of the foaming agent added is selected according to the physical properties of the hollow foam, taking into consideration the amount of gas generated from the foaming agent, the desired expansion ratio, and the like.

The polypropylene resin composition used in the present invention may optionally contain various resins, elastomers, inorganic fillers, additives and the like within a range not impairing the object of the present invention.

The elastomer (D) used in the present invention in the polypropylene resin composition as required includes
Linear ethylene / α-olefin random copolymer (D
-1), ethylene / α-olefin / non-conjugated polyene random copolymer (D-2), hydrogenated block copolymer, other elastic polymers, and mixtures thereof.

The linear ethylene / α-olefin random copolymer (D-1) comprises ethylene and 3 to 20 carbon atoms.
Is a linear random copolymer with α-olefin.
Specific examples of the α-olefin having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-hexene.
Examples include octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-eicosene. These α-olefins can be used alone or in combination of two or more. Among these, propylene, 1-butene, 1-hexene and 1-octene are particularly preferably used.

The linear ethylene / α-olefin random copolymer (D-1) has a molar ratio of ethylene and α-olefin (ethylene / α-olefin) of 95/5 to 60.
It is desirable that it is / 40, preferably 90/10 to 70/30. The linear ethylene / α-olefin random copolymer (D-1) is 1 according to ASTM D-1238.
MFR measured at 90 ° C. under a load of 2.16 kg is 0.
1 g / 10 min or more, preferably 0.3 to 20 g / 1
It is preferably 0 min.

The ethylene / α-olefin / non-conjugated polyene random copolymer (D-2) is a random copolymer rubber of ethylene, an α-olefin having 3 to 20 carbon atoms and a non-conjugated polyene. Examples of the α-olefin having 3 to 20 carbon atoms include the same ones as described above. Examples of the non-conjugated polyethylene include 5-ethylidene-2-norbornene, 5-propylidene-5-norbornene, dicyclopentadiene, 5-vinyl-2-norbornene,
Acyclic dienes such as 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, norbornadiene; 1,4-hexadiene, 4-methyl-1,4-
Hexadiene, 5-methyl-1,4-hexadiene, 5
-Methyl-1,5-heptadiene, 6-methyl-1,5
-Heptadiene, 6-methyl-1,7-octadiene,
Examples thereof include chain-like non-conjugated dienes such as 7-methyl-1,6-octadiene; and trienes such as 2,3-diisopropylidene-5-norbornene. Among these,
1,4-hexadiene, dicyclopentadiene and 5-ethylidene-2-norbornene are preferably used.

The ethylene / α-olefin / non-conjugated polyene random copolymer (D-2) has a molar ratio of ethylene / α-olefin / non-conjugated polyene (ethylene / α-olefin / non-conjugated polyene) of 90 /. 5 / 5-30 / 4
5/25, preferably 80/10 / 10-40 / 40 /
20 is desirable.

The ethylene / α-olefin / non-conjugated polyene random copolymer (D-2) is ASTM D-12.
38, the MFR measured at 230 ° C. under a load of 2.16 kg is 0.05 g / 10 min or more, preferably 0.1.
It is preferably 1 to 10 g / 10 min. Specific examples of the ethylene / α-olefin / non-conjugated polyene random copolymer (D-2) include ethylene / propylene / diene terpolymer (EPDM).

Inorganic fillers that may be added to the polypropylene resin composition in the present invention include talc, silica, mica, calcium carbonate, glass fibers, glass beads, barium sulfate, magnesium hydroxide, wallacenite, calcium silicate. Fiber, carbon fiber, magnesium oxysulfate fiber, potassium titanate fiber, titanium oxide, calcium sulfite, white carbon, clay,
Examples include calcium sulfate. These inorganic fillers may be used alone or in combination of two or more.

Additives to be added as necessary are
Nucleating agent, antioxidant, hydrochloric acid absorber, heat stabilizer, weather stabilizer, light stabilizer, ultraviolet absorber, slip agent, antiblocking agent, antifogging agent, lubricant, antistatic agent, flame retardant, pigment, dye Well-known additives such as dispersants, copper damage inhibitors, neutralizing agents, plasticizers, antifoaming agents, crosslinking agents, flow improvers such as peroxides, weld strength improvers, natural oils, synthetic oils, waxes, etc. Agent.

A hollow foam made of the polypropylene resin composition of the present invention comprises the polypropylene resin composition as a raw material,
A hollow foam molded from a single-layer parison, the outer surface of which is 0.3 mm or more, preferably 0.4 to 1.5 m.
m, more preferably 0.4 to 1.2 mm, which is a skin layer made of an unfoamed resin layer, and the specific gravity of the entire hollow foam is 0.2 to 0.7, preferably 0.3 to 0. 6 is a polypropylene resin composition-made hollow foam. Here, the unfoamed resin layer means a resin layer having a foaming ratio of 1.03 or less.

The polypropylene resin composition hollow foam of the present invention can be produced by the following method using the polypropylene resin composition as a raw material. As a molding machine used in the manufacturing method of the present invention, a general blow molding machine can be used. That is, an extruder capable of melting a polypropylene resin composition, a die for extruding a molten resin as a cylindrical parison provided at the tip of the extruder, and a structure in which the parison is sandwiched between upper and lower parts and fixed. A pair of left and right dies that operate, a device for adjusting the temperature of the dies,
A device for injecting a pressure fluid into the parison is provided, and the temperature of the mold and the pressure in the parison are adjustable. The extruder may be provided with an accumulator so that the parison can be extruded at high speed.

In the manufacturing method of the present invention, first, a polypropylene resin composition containing a foaming agent is melted. The resin temperature needs to be a resin temperature at which the generated foaming gas can be dissolved in the resin composition after the foaming agent is once decomposed,
Specifically, when an inorganic foaming agent is used as the foaming agent, it is preferable to carry out kneading at about 160 to 210 ° C, preferably 165 to 200 ° C. Next, the molten resin composition is extruded from a die as a single-layer parison. The molten resin foams due to the pressure drop from the moment it exits the die. It is preferable to use an accumulator because the foam cells can be generated and their growth can be promoted. The extrusion rate with an accumulator is preferably in the range of 600 to 15000 sec ⁻¹ in terms of shear rate. If the extrusion speed in the accumulator is too slow, the expansion ratio decreases and the advantage of using the accumulator is lost. On the other hand, if it is too fast, the parison surface is roughened or the parison is distorted and extruded.

The molten parison extruded from the die is clamped to fix the upper and lower parts with a mold, and then 0.3 to 1 MPa, preferably 0.4 to 0.
Primary air having a pressure of 8 MPa (referred to as primary pressure) is press-fitted to expand the parison, and the primary pressure is maintained for a certain period of time (referred to as primary pressurizing step). As a result, the foamed cells on the surface of the parison are crushed and cooled by the mold to form a skin layer made of an unfoamed resin layer. After that, the pressure is reduced to a pressure of 0.001 to 0.1 MPa, preferably 0.01 to 0.05 MPa (referred to as a secondary pressure), and the pressure is maintained for a certain period of time (referred to as a secondary pressure step). As a result, the uncooled resin inside the parison, that is, the inside of the skin layer, is foamed, and the entire hollow foam body is cooled over time. The depressurization can be performed by switching the valve to switch the air to be injected from the primary air to the secondary air having the secondary pressure.
Gases such as air and nitrogen are generally used as the primary air and the secondary air.

If the pressure of the primary air is too low, the parison does not adhere to the mold, resulting in a surface with poor transferability, and it is difficult to form an unfoamed layer (skin layer) on the surface. On the other hand, if the pressure of the primary air is too high, the parison locally expands and it becomes difficult to obtain a molded product having a good wall thickness distribution. Further, if the pressure of the secondary air is too high, the expansion ratio of the entire hollow foam becomes low. The time for maintaining the primary pressure (referred to as primary pressurization time) is in the range of 2 seconds to 30 seconds, preferably 5 seconds to 20 seconds. If the primary pressing time becomes long, the skin layer becomes too thick, and the overall expansion ratio decreases.

The time for holding the secondary pressure (referred to as secondary pressurization time) is 20 to 600 seconds, preferably 30 to 48 seconds.
It is in the range of 0 seconds. If it is shorter than this range, deformation due to insufficient cooling occurs. On the other hand, when the length is longer than the above range, cooling progresses, the expansion ratio does not increase, and the molding cycle becomes too long, so that the molding efficiency decreases. The more rapidly the pressure reduction transitions from the primary pressure to the secondary pressure, the higher the expansion ratio.

In the manufacturing method of the present invention, the surface temperature of the mold on the cavity side (hereinafter,
(Temperature may be referred to as a mold temperature) (Tmo) is represented by Formula (1), preferably Formula (2) Tme-50 ≤ Tmo ≤ Tme-5 (1) Tme-45 ≤ Tmo ≤ Tme-15 (2) (2) ( In formulas (1) and (2), Tmo is controlled within the range of the surface temperature (° C.) of the mold on the cavity side, and Tme is within the range of the crystallization temperature (° C.) of the polypropylene resin composition forming the parison. . The method of controlling the mold temperature (Tmo) within the above range is not limited, but methods such as flowing heating fluid, steam, etc. into the mold cooling pipe, performing electromagnetic wave heating, adopting an adiabatic mold, etc. are available. Can be adopted.

When the mold temperature (Tmo) is lower than the lower limit of the above formula (1), the expansion ratio of the obtained hollow foam becomes low, and the hollow foam having the specific gravity cannot be obtained. On the other hand, the upper limit is exceeded. And the skin layer is hard to be formed. The crystallization temperature (Tme) of the polypropylene resin composition can be determined by a differential scanning calorimeter (DSC).

In the present invention, as described above, the mold temperature (Tm
o) and the holding time are strictly adjusted, and the polypropylene resin hollow foam has a skin layer of the above-mentioned thickness, has a high expansion ratio, is excellent in mold transferability and design and has a good appearance. Can be easily manufactured. According to the method for producing a hollow foam of the present invention, the hollow foam can be easily produced at low cost without using a multi-layer blow molding machine.

Since the hollow foam of the present invention has an unfoamed resin layer (skin layer) of an appropriate thickness as described above and also has an appropriately expanded foam cell, it is lightweight and has a smooth surface and an appearance. Excellent, high rigidity and strength, and excellent heat insulation.

Since the hollow foam of the present invention has the above-mentioned characteristics, it can be suitably used for various applications such as industrial materials such as sawdust and resin concrete panels, and automobile materials such as automobile interior materials.

[0048]

The polypropylene resin composition hollow foam of the present invention is molded from a single layer of parison, has a skin layer consisting of an unfoamed resin layer of 0.3 mm or more on the outer surface, and has a specific gravity of 0. Since it is from 0.2 to 0.7, it is excellent in mold transferability and designability, has a good appearance, and appropriately foams,
Light weight, high strength and rigidity, and excellent heat resistance. The method for producing a polypropylene resin composition-made hollow foam of the present invention is a hollow foam by forming a skin layer under specific conditions in a primary pressure step and then foaming a parison in the secondary pressure step under specific conditions. In the method for producing (1), since the mold temperature (Tmo) is controlled within a specific temperature range, the hollow foam can be easily produced at a low cost by a single-layer molding device.

[0049]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below with reference to Examples, but the present invention is not limited to these Examples. The following resins were used as raw materials.

(A) Propylene / α-olefin copolymer / propylene / ethylene block copolymer (A-1) MFR (ASTM D-1238, 230 ° C., load 2.
16 kg) = 0.5 g / 10 min Density: 0.90 g / cm ³ Ethylene content: 5.8 wt% (B) Strain-hardening polypropylene resin / propylene homopolymer (B-1) Intrinsic viscosity [η] Content of high molecular weight component of 9 dl / g =
10 wt% MFR (ASTM D-1238, 230 ° C, load 2.
16 kg) = 7 g / 10 min Ratio of yield point tension (YT: g) and breaking point tension (BT: g) (BT / g) obtained from load-time plot in measurement of uniaxial elongational viscosity at strain rate of 0.1 sec ⁻¹ YT) = 1.8 (C) High-pressure method low-density polyethylene / high-pressure method low-density polyethylene (C-1) MFR (ASTM D-1238, 190 ° C., load 2.
16 kg) = 0.5 g / 10 min Density: 0.92 g / cm ³

Example 1 A box-shaped hollow foam container having a length of 30 cm, a width of 21 cm, and a height of 6 cm was blow-molded by the following method using a hollow molding machine equipped with a 65 mmφ extruder with an accumulator. The propylene / ethylene block copolymer (A-1) 5
0 parts by weight, propylene homopolymer (B-1) 35 parts by weight, high pressure method low density polyethylene (C-1) 15 parts by weight,
Further, 3 parts by weight of a masterbatch containing 40% by weight of citric acid / sodium bicarbonate = 1/1 as a foaming agent was mixed with a tumbler for 2 minutes to prepare a polypropylene resin composition containing a foaming agent. The crystallization temperature (Tme) of this polypropylene resin composition was 115 ° C.

The resin composition was heated to 190 ° C. with an extruder.
Melt at ℃, 140 from the die tip with an accumulator
A single layer parison was fired at a rate of 0s ^-1 . Immediately, the mold temperature (Tmo) was adjusted to 70 ° C, the mold was closed, compressed air with a pressure (gauge pressure) of 0.6 MPa was blown into the parison fixed in the mold, and the condition was maintained for 10 seconds. A skin layer of the unfoamed resin layer was formed. After that, 0.
Switch the valve to 02 MPa compressed air, and then 18
After holding for 0 seconds to cause foaming and cooling, the hollow foam was taken out. This hollow foam was evaluated. The results are shown in Table 1. The molded product was evaluated by the following method.

<Expansion Ratio> The density of the foam was measured by the underwater substitution method, and the value obtained by dividing the solid density by the foam density was taken as the expansion ratio. <Thickness of Skin Layer> The bottom of the box was cut out, a cross section thereof was photographed with a micrograph, and the thickness of the unfoamed portion was measured with a ruler. <Appearance of Foam> The appearance is related to the quality of transferability on a flat surface or a textured surface. Therefore, the appearance was evaluated according to the following criteria depending on the presence or absence of bubbles in the skin layer. ◯: The expansion ratio of the skin layer is 1.03 or less, and the specific gravity of the entire foam is 0.2 to 0.7 Δ: The expansion ratio of the skin layer is more than 1.03 and 1.10 or less, and the foam Overall specific gravity is 0.2 to 0.7 ×: The expansion ratio of the skin layer exceeds 1.10, or the specific gravity of the entire foam is outside the range of 0.2 to 0.7.

Example 2, Comparative Examples 1 to 3 Example 1 was repeated except that the mold temperature (Tmo) was changed to Table 1. The results are shown in Table 1.

Example 3, Comparative Examples 4 to 5 The same procedure as in Example 2 was carried out except that the primary and secondary injection pressures were changed. The results are shown in Table 2.

[0056]

[Table 1]

[0057]

[Table 2]

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08L 23/10 C08L 23/10 // B29K 23:00 B29K 23:00 105: 04 105: 04 B29L 22: 00 B29L 22:00 F term (reference) 4F074 AA17 AA17A AA24 AA24A AC22 AC23 AC24 AC26 AC29 AC32 AC34 AG01 BA02 BA03 BA04 BA05 BA08 BA13 BA14 BA16 BA17 BA18 BA19 BA32 BA35 BA36 BA37 BA39 BA40 BA53 DA02 DA23 4F07 A20 AA11 AB02 AG02 AR06 AR11 AR15 LA01 LB01 LG22 LJ09 LN04 LN13 4J002 BB02Y BB03Y BB12W BB12X BB14W BB15W FD010 FD320

Claims (3)

[Claims] 1. A hollow foam formed of a polypropylene resin composition containing polypropylene resin as a main component and molded from a single-layer parison, the skin layer comprising an unfoamed resin layer of 0.3 mm or more on the outer surface. And a specific gravity of 0.2 to 0.7, which is a hollow foam made of a polypropylene resin composition. 2. A polypropylene resin composition comprising (A) 20 to 80 parts by weight of a propylene homopolymer or propylene / α-olefin copolymer, and (B) a polypropylene resin having a strain hardening property of 5 to 50.
A resin composition containing 0 to 30 parts by weight of (C) a high-pressure low-density polyethylene resin (where (A) + (B) + (C) = 100 parts by weight), and comprising: D-12
The polypropylene resin composition hollow foam according to claim 1, which has a melt flow rate of 0.1 to 20 g / 10 min as measured by No. 38 at 230 ° C. under a load of 2.16 kg. 3. A polypropylene resin composition containing a foaming agent is melt-extruded to form a parison, and the parison is sandwiched and fixed by a pair of molds. A primary air having a pressure (primary pressure) is injected to expand the parison, and the parison is pressed for 2 to 30 seconds to form a skin layer, and then the air pressure is 0.001 to 0.1 MPa (secondary pressure). The surface temperature of the mold on the cavity side in the manufacturing method of the hollow foam body in which the inside of the parison is foamed by depressurizing to (pressure) and the molded product is cooled and solidified by holding it for a certain period and then the mold is opened to take out the molded product. (Tmo) is a numerical formula (1) Tme-50 <= Tmo <= Tme-5 ... (1) (In a numerical formula (1), Tmo is the surface temperature (° C) of the mold on the cavity side, and Tme is a polypropylene resin forming a parison. set A crystallization temperature of the object (° C.).) Range to the control and method of manufacturing the good appearance hollow foam; and obtaining claim 1 or 2 Polypropylene resin composition hollow foam according to.