JPH10176077A - Polyolefin-based resin preexpanded particle and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce the subject particle capable of manifesting a high expansion ratio, a small dispersion of the ratio, a high closed-cell ratio and a large cell diameter without using a foaming agent causing problems in safety, environmental aspects, a high cost, etc., by using a specific polyolefin-based resin composition as a substrate resin. SOLUTION: This polyolefin-based preexpanded particle has 7-50 times expansion ratio, <=15% dispersion of the ratio defined by formula I Kav is a value of the average expansion ratio defined by the formula Kav =Σ(Ki ×Wi ) [Wi is the weight fraction of the oversize expanded particle of each sieve when sieved through the JIS standard sieves (eight kinds of 3.5, 4, 5, 6, 7, 8, 9 and 10 meshes); Ki is the expansion ratio]; σm is a value of the standard deviation defined by formula II}, >=80% closed-cell ratio and 200-500μm average cell diameter. A polyolefin-based resin composition comprising 100 pts.wt. polyolefin- based resin and 0.05-5 pts.wt. filler (e.g. talc having the surface treated with a coupling agent) is used as a substrate resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of producing and using low-expanded polyolefin-based resin particles and then pre-expanded polyolefin-based resin particles. More specifically, for example, polyolefin-based resin low-expanded particles used for production of polyolefin-based resin pre-expanded particles that can be suitably used as a raw material of an in-mold foam molded article are produced, and then polyolefin-based resin pre-expanded particles are produced. Belongs to the technical field used.

[0002]

2. Description of the Related Art Conventionally, a pre-expanded particle produced from polyolefin-based resin particles by a one-step method or a multi-step method and then formed into an in-mold body is used as a cushioning material, a heat insulating material, a packaging material, a vehicle shock absorbing material. It is used as such.

For example, Japanese Patent Application Laid-Open No. 57-25336 discloses that polyolefin resin particles containing an inorganic filler are
It is described that under high pressure, a volatile foaming agent-impregnated material is discharged under low pressure to produce pre-expanded particles.

JP-A-58-199125 discloses a resin obtained by impregnating a resin particle obtained by adding an inorganic nucleating agent such as talc to a thermoplastic resin such as a polyolefin resin and impregnating a volatile foaming agent. Release under low pressure to produce pre-expanded particles is described.

Further, Japanese Unexamined Patent Publication (Kokai) No. 60-229936 discloses a method of producing pre-expanded particles by releasing particles containing a nitrogen-containing inorganic gas as a blowing agent into particles of a polyolefin resin or the like under a low pressure. Is described.

[0006] Apart from the production of the pre-expanded polyolefin resin particles by the one-stage method, the production by the multi-stage method is also disclosed in, for example, JP-A-58-65734. After the first stage of foaming, a low-boiling organic compound or an inorganic gas is added to impart foaming power, and by heating, foaming of the second and subsequent stages is performed to perform preliminary foaming. It describes that particles are produced and used as in-mold molded articles.

Japanese Patent Application Laid-Open No. 59-62120 discloses that polypropylene particles containing, for example, a volatile foaming agent as a foaming agent are produced by discharging under low pressure.
A description is given of producing a pre-expanded particle by imparting an expanding ability to expanded particles having a specific relationship between an expansion ratio and the number of cells (cell diameter), and heating the expanded particles to 1.5 times the expanded particles by heating. Have been.

Further, Japanese Patent Application Laid-Open No. Hei 4-372630 discloses that polyolefin-based resin particles are impregnated with carbon dioxide under high pressure to form expandable resin particles, which are then heated and foamed. It is described that a pre-expanded particle having a high expansion ratio is produced by forming expanded particles of 0.8 cm ³ / g and further performing multi-stage expansion.

[0009]

However, when pre-expanded particles are produced by the method described in JP-A-57-25336 and JP-A-58-199125, the cost is increased due to the use of a volatile foaming agent. In addition to the high foaming ratio, it is difficult to control the expansion ratio, and when the volatile blowing agent is propane, butane, etc., there are safety problems such as toxicity and flammability. In such cases, there is an environmental problem such as destruction of the ozone layer. In addition, since foaming is performed in one stage, the formula (I) of the pre-expanded particles: Variation in magnification = (σ _m / Kav) × 100 (%) (I) (where Kav is a JIS Z8801 standard sieve (3.5,
7, 8, 9, 10 the weight fraction W _i of each sieve residual foamed particles upon sieved with a mesh eight), wherein the expansion ratio _{K i: Kav = Σ (K} i × the average expansion ratio sought W _i), σ _m is JIS Z8801 standard sieve (3.
5, 4, 5, 6, 7, 8, 9, 10 mesh (8 types), the weight fraction W _i of each of the particles remaining after sieving when sieved,
From the expansion ratio _Ki , the formula is:

[0010]

(Equation 3)

The variation in magnification expressed by the standard deviation obtained in (1) is as high as 20% or more, and pre-expanded particles having good characteristics cannot be obtained.

When pre-expanded particles are produced by the method described in Japanese Patent Application Laid-Open No. 60-229936 using a nitrogen-containing inorganic gas as a foaming agent, the use of a volatile foaming agent increases the cost and safety. , Environmental problems are eliminated, but impregnation into polyolefin resin particles is poor,
Moreover, the use of a nitrogen-containing inorganic gas, which has a high rate of escape from the polyolefin-based resin, causes the foam of the obtained foam to be too small, resulting in a problem of lowering moldability and physical properties. Because of foaming, the variation in magnification of the pre-expanded particles becomes as high as 20% or more, and pre-expanded particles having good characteristics cannot be obtained.

On the other hand, when the pre-expanded particles are produced by the method described in JP-A-59-62120, in which the pre-expanded particles are produced by the multi-stage method, the variation in magnification becomes as high as 20% or more. Pre-expanded particles cannot be obtained.

[0014] Further, when the expanded particles and then the pre-expanded particles are produced by the method described in JP-A-4-372630, the variation in the magnification is as high as 20% or more, and the expanded particles having good characteristics are obtained. In addition, since pre-expanded particles cannot be obtained, and CO ₂ is used as a blowing agent, it causes global warming, which is environmentally problematic.

[0015]

SUMMARY OF THE INVENTION The present invention provides a high expansion ratio without using a conventional volatile blowing agent such as butane and chlorofluorocarbon and an inorganic gas blowing agent such as CO _{2 which} causes global warming. The purpose of the present invention is to provide uniform pre-expanded particles having a small variation in magnification, a high closed cell ratio, a relatively large cell diameter, and a small cell variation. ) And a polyolefin-based resin composition comprising 0.05 to 5 parts of a filler as a base resin, foaming ratio: 7 to 50 times, Formula (I): Variation in magnification = (σ _m / Kav) × 100 (%) ( I) (where Kav is JIS Z8801 standard sieve (3.5,
7, 8, 9, 10 the weight fraction W _i of each sieve residual foamed particles upon sieved with a mesh eight), wherein the expansion ratio _{K i: Kav = Σ (K} i × the average expansion ratio sought W _i), σ _m is JIS Z8801 standard sieve (3.
5, 4, 5, 6, 7, 8, 9, 10 mesh (8 types), the weight fraction W _i of each of the particles remaining after sieving when sieved,
From the expansion ratio _Ki , the formula is:

[0016]

(Equation 4)

The polyolefin-based resin pre-expanded particles having a variation in magnification of 15% or less, a closed cell ratio of 80% or more, and an average cell diameter of 200 to 500 μm (claim 1), wherein the polyolefin resin is ethylene. The polyolefin-based resin pre-expanded particles according to claim 1, which is a propylene random copolymer or a linear low-density polyethylene (claim 2), the polyolefin-based resin 10
A polyolefin resin composition comprising 0 part and a filler of 0.05 to 5 parts was used as a base resin, and the expansion ratio was 1.5 to 5 parts.
Times, Formula (I): Variation in magnification = (σ _m / Kav) × 100 (%) (I) (where Kav is a JIS Z8801 standard sieve (3.5,
7, 8, 9, 10 the weight fraction W _i of each sieve residual foamed particles upon sieved with a mesh eight), wherein the expansion ratio _{K i: Kav = Σ (K} i × the average expansion ratio sought W _i), σ _m is JIS Z8801 standard sieve (3.
5, 4, 5, 6, 7, 8, 9, 10 mesh (8 types), the weight fraction W _i of each of the particles remaining after sieving when sieved,
From the expansion ratio _Ki , the formula is:

[0018]

(Equation 5)

The low-expanded polyolefin resin particles (I) having a variation in magnification of 15% or less, a closed cell ratio of 90% or more, and an average cell diameter of 50 to 200 μm expressed by the following formula (standard deviation): The polyolefin-based resin low-expanded particles according to claim 3, wherein the resin is an ethylene-propylene random copolymer or a linear low-density polyethylene (claim 4), and the polyolefin-based resin low-expanded particles (I) according to claim 3. , Nitrogen in a closed container,
0.5 or less using air or an inorganic gas mainly
After applying foaming ability by pressurizing to 25 kg / cm ² G, heating to a temperature not lower than the softening temperature of the base resin to expand the polyolefin resin low-expanded particles (I) to 1.5 to 30 times. The method for producing pre-expanded polyolefin resin particles according to claim 1, wherein the polyolefin resin is an ethylene-propylene random copolymer or a linear low-density polyethylene (claim 5). Claim 6) dispersing resin particles having a polyolefin resin composition comprising 100 parts of a polyolefin resin and 0.05 to 5 parts of a filler as a base resin in an aqueous dispersion medium in a closed container; After heating to a temperature equal to or higher than the softening temperature, nitrogen, air or an inorganic gas mainly composed of nitrogen and air is introduced into the closed vessel to reduce the pressure in the closed vessel to 1
4. The polyolefin-based resin low-expanded particles according to claim 3, wherein the dispersion is discharged under an atmosphere at a pressure lower than the internal pressure of the closed container while maintaining the pressure at 0 to 45 kg / cm ² g. The method of claim I), wherein the polyolefin resin is an ethylene-propylene random copolymer or a linear low-density polyethylene.
The present invention relates to the manufacturing method described in claim 8.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The pre-expanded polyolefin resin particles (II) of the present invention comprise a polyolefin resin (A) 10
Pre-expanded particles using a polyolefin-based resin composition (C) comprising 0 part and a filler (B) of 0.05 to 5 parts as a base resin.

The polyolefin-based resin (A) contains 50 to 100% (% by weight, the same applies hereinafter) of an olefin monomer unit, and more preferably 70 to 100%, and is a monomer which can be copolymerized with the olefin monomer. 0-50% body unit, even 0
It is a resin containing up to 30%. Since it contains 50% or more of olefin monomer units, it is lightweight and has mechanical strength, processability,
Excellent electrical insulation, water resistance and chemical resistance. The monomer unit copolymerizable with the olefin monomer has adhesiveness, transparency,
It is a component used for modifying impact resistance, gas barrier properties, and the like, and is preferably used in an amount of 2% or more, and more preferably 5% or more, in order to obtain the effect of use.

Specific examples of the olefin monomer include:
Ethylene, propylene, butene, pentene, hexene,
Examples thereof include α-olefin monomers having 2 to 8 carbon atoms such as heptene and octene, and cyclic olefins such as norbornene-based monomers. Among them, ethylene and propylene are preferable because they are inexpensive and the physical properties of the obtained polymer are improved. These may be used alone or in combination of two or more.

Specific examples of the monomer copolymerizable with the olefin monomer include vinyl alcohol esters such as vinyl acetate, and alkyl groups having 1 to 6 carbon atoms such as methyl methacrylate, ethyl acrylate and hexyl acrylate. Examples thereof include (meth) acrylic acid alkyl esters, vinyl alcohol, methacrylic acid, and vinyl chloride. Among them, vinyl acetate is preferred from the viewpoint of adhesiveness, flexibility and low-temperature characteristics, and methyl methacrylate is preferred from the viewpoint of adhesiveness, flexibility, low-temperature characteristics and thermal stability. These may be used alone or in combination of two or more.

The MI of the polyolefin resin (A) is, for example, 230 ° C. in the case of a polypropylene resin.
0.5 to 30 g / 10 min, and further 3 to 10 g / 10
And the flexural modulus (JIS K
7203) as 5000 to 20000 kgf / cm
² , 8000-16000 kgf / cm ² , melting point 125-165 ° C, further 135-150 ° C
Are preferred. When the MI is less than 0.5 g / 10 min, the melt viscosity is too high to obtain pre-expanded particles having a high expansion ratio, and when the MI exceeds 30 g / 10 min,
The melt viscosity with respect to the elongation of the resin at the time of foaming is low, so that the foam tends to break, and pre-expanded particles having a high expansion ratio tend to be hardly obtained. The flexural modulus is 5000 kgf / cm.
^{If it is} less than ² , the mechanical strength of the obtained molded article will be insufficient, and if it exceeds 20,000 kgf / cm ² , the flexibility and cushioning property of the obtained molded article will tend to be insufficient. When the melting point is less than 125 ° C., the heat resistance of the obtained molded body is insufficient, and when it exceeds 165 ° C., the molding pressure tends to be high, which is not preferable.

For example, in the case of polyethylene resin, MI is 190 ° C. at 0.5 to 30 g / 10 min.
Further, those having a flexural rigidity (ASTM D747) of 1000 to 80 are preferred.
00 kgf / cm ² , and even 2000-5000 kg
f / cm ² and a melting point of 100 to 140 ° C., preferably 115 to 130 ° C. are preferable. The MI is 0.5
When the viscosity is less than g / 10 min, the melt viscosity is too high to obtain pre-expanded particles having a high expansion ratio, and when it exceeds 30 g / 10 min, the melt viscosity with respect to the elongation of the resin during foaming is low and the foam is broken. This tends to make it difficult to obtain pre-expanded particles having a high expansion ratio. The flexural rigidity is 10
If it is less than 00 kgf / cm ² , the resulting molded article tends to have insufficient mechanical strength, and if it exceeds 8000 kgf / cm ² , the resulting molded article tends to have insufficient flexibility and cushioning properties. When the melting point is less than 100 ° C., the heat resistance of the obtained molded body becomes insufficient, and when it exceeds 140 ° C., the molding pressure tends to be high, which is not preferable.

Specific examples of the polyolefin resin as described above include, for example, polypropylene-based copolymers such as ethylene-propylene random copolymer, ethylene-propylene-butene random terpolymer, ethylene-propylene block copolymer, and homopolypropylene. Resins, polyethylene resins such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, polybutene, and polypentene. These polyolefin-based resins may be used in a non-crosslinked state, or may be used after being crosslinked by peroxide or radiation. Among them, ethylene-propylene random copolymer (ethylene content of about 1 to 10%) is easy to obtain pre-expanded particles having a high expansion ratio, and the mechanical strength of the obtained molded article;
It is preferable because the heat resistance is good. In addition, linear low-density polyethylene is easy to obtain pre-expanded particles having a high expansion ratio without cross-linking, and is preferable in terms of mechanical strength and buffering properties. These may be used alone or in combination of two or more.

The filler (B) used in the present invention is a component used to obtain pre-expanded particles having uniform cells and a high expansion ratio.

The average particle diameter of the filler (B) is such that pre-expanded particles having uniform cells and high expansion ratio can be obtained.
Further, from the viewpoint that a molded article having excellent mechanical strength, flexibility, and the like can be obtained from the pre-expanded particles, the thickness is preferably 50 μm or less, and more preferably 10 μm or less. 0.1μ from the point of workability
m or more, more preferably 0.5 μm or more.

The filler (B) includes an inorganic filler and an organic filler. Specific examples of the inorganic filler include, for example, talc, calcium carbonate, calcium hydroxide and the like. Among them, talc is preferable because pre-expanded particles having a small expansion ratio, uniform cells, and a high expansion ratio are easily obtained. Especially as inorganic fillers,
For example, those surface-treated with a fatty acid, a titanate coupling agent, a silane coupling agent, a resin acid or the like are preferable. The organic filler is not particularly limited as long as it is solid at a temperature equal to or higher than the softening temperature of the polyolefin-based resin (A), and specific examples thereof include fluororesin powder, silicone resin powder, and thermoplastic polyester resin. And the like. The filler may be used alone or in combination of two or more.

In order to obtain pre-expanded particles having a high expansion ratio, the amount of the filler (B) used is not less than 0.05 part with respect to 100 parts of the polyolefin resin (A).
8 parts or more is preferable, and in order to exhibit excellent fusibility when molding the pre-expanded particles and obtain a molded article having excellent mechanical strength and flexibility from the pre-expanded particles, 5 parts or more are required. Or less, preferably 2 parts or less.

In the present invention, the polyolefin resin (A)
The polyolefin resin composition (C) containing the filler and the filler (B) is usually melt-kneaded using an extruder, a kneader, a Banbury mixer, a roll, or the like, and then has a columnar shape, an elliptic columnar shape, a spherical shape, a cubic shape, Resin particles are produced by molding into a desired particle shape that can be easily used for preliminary foaming, such as a rectangular parallelepiped.

The conditions for producing the resin particles, the size of the resin particles, and the like are not particularly limited, but may be, for example, melt-kneaded in an extruder, extruded, cut, and cut into 0.5 to 5 mg.
/ Grain particles are generally produced.

The resin particles thus produced are dispersed in an aqueous dispersion medium in a closed container, and the temperature of the resin particles (normally, the temperature of the aqueous dispersion medium is measured because it is not equal to the temperature of the aqueous dispersion medium) Is heated to a temperature equal to or higher than the softening temperature of the base resin (softening temperature of the polyolefin-based resin (A)) to form water-containing resin particles. Pressure is 10-45kg / cm
^The polyolefin-based resin low-expanded particles (I) are produced by discharging the hydrated resin particles into an atmosphere at a pressure lower than the internal pressure of the closed container while maintaining the pressure at ² G to expand the hydrated resin particles.

The aqueous dispersion medium in which the resin particles are dispersed is as follows:
Any solvent that does not dissolve the polyolefin resin (A) may be used. Usually, water or a mixture of water and one or more of ethylene glycol, glycerin, methanol, ethanol, and the like is used. Water is preferred from the viewpoint of economy and the like.

The aqueous dispersion medium usually contains 0.1 to 1 part and 0.001 to 0.01 part of a surfactant, which is a dispersant and a dispersing aid, per 100 parts of the aqueous dispersion medium.
About 10 parts by weight. As a specific example of the dispersant,
Specific examples of the surfactant such as tribasic calcium phosphate, basic magnesium carbonate, basic zinc carbonate and calcium carbonate include, for example, sodium dodecylbenzenesulfonate, sodium n-paraffinsulfonate, α-
Sodium olefin sulfonate and the like can be mentioned.

The amount of the resin particles to be dispersed in the aqueous dispersion medium is such that the resin particles 3 to 1 are added to 100 parts of the aqueous dispersion medium.
00 parts, more preferably 10 to 50 parts. When the amount of the resin particles is less than 3 parts, the productivity is reduced, the production cost is increased, and it is not economical. On the other hand, when the amount is more than 100 parts, the resin particles are easily fused to each other in the container during heating. Become.

The temperature at which the resin particles are dispersed and heated is a temperature equal to or higher than the softening temperature of the polyolefin resin to be used.
50 ° C., preferably from melting point to melting point + 20 ° C., for example, in the case of an ethylene-propylene copolymer having a melting point of 145 ° C., at 145 ° C. or more, preferably at 145 to 165 ° C.
If the temperature is lower than 145 ° C., foaming becomes difficult. If the temperature exceeds 165 ° C., the obtained foam has insufficient mechanical strength and heat resistance, and resin particles are easily fused in the container.
The softening temperature referred to in the present invention is ASTM D648,
The value based on a load of 4.6 kg / cm ² , and the melting point is the temperature at the top of the melting peak as measured by DSC at 10 ° C./min.

After the temperature in the closed container reaches the predetermined temperature in this way, preferably after reaching the predetermined temperature, 5
After holding for 5 to 5 hours, and further for 15 minutes to 1 hour, the pressure in the closed container is set to a predetermined holding pressure, and the water in the closed container is dispersed in an atmosphere having a pressure lower than the internal pressure of the closed container, usually at atmospheric pressure. The material is released and foamed to produce low-expanded polyolefin resin particles.

The predetermined pressure is adjusted to 10 to 45 kg / c by introducing an inorganic gas into the closed container as necessary.
It can be adjusted to m ² G, preferably 15 to 35 kg / cm ² G. When the pressure in the closed container is set to the above-mentioned pressure, the expansion ratio can be increased without reducing the cell diameter and lowering the closed cell ratio.

The time from when the predetermined pressure is reached to when the water-containing resin particles are discharged together with the aqueous dispersion medium into a low-pressure atmosphere is not particularly limited, but is preferably as fast as possible from the viewpoint of improving productivity.

The pressure in the container during the discharge is preferably maintained at the predetermined pressure in order to facilitate the release of the water-containing resin particles from the closed container into the low-pressure atmosphere.
Specifically, it is preferable to supply the inorganic gas into the closed container and discharge the inorganic gas while maintaining the pressure in the closed container at the predetermined pressure.

Examples of the inorganic gas include nitrogen, air, or an inorganic gas containing these (at least 50% by volume, more preferably at least 70% by volume, and the remaining gas is an inert gas such as argon, helium, xenon, etc.). Inorganic gas comprising water vapor, oxygen, hydrogen, ozone, etc.) can be used, but nitrogen and air are preferred from the viewpoint of economy, productivity, safety, environmental compatibility and the like.

The polyolefin-based resin low-expanded particles (I) obtained in this manner have an expansion ratio of 1.5 to 5 times, more preferably 2 to 4 times, and a ratio variation of 15% or less, and more preferably 10 times or less.
% Or less, closed cell rate of 90% or more, further 95% or more, and average cell diameter of 50 to 200 μm, and more preferably 100 to 2
It has a thickness of 00 μm.

When the expansion ratio is less than 1.5 times, it is difficult to increase the foaming of the obtained pre-expanded particles, and when it exceeds 5 times, is the cell diameter of the obtained pre-expanded particles too small? Or, the variation of the bubble diameter becomes large. When the closed cell ratio is less than 90%, the second-stage foaming power of the low-expanded particles (I) is insufficient, making high-expansion difficult. Also, the physical properties such as the mechanical strength of the obtained molded article are reduced.
Further, when the average cell diameter is less than 50 μm, problems such as a decrease in the closed cell rate of the pre-expanded particles after two-stage expansion occur. When the average cell diameter exceeds 200 μm, the cells of the pre-expanded particles become coarse. Too much, and the mechanical strength of the resulting molded article is reduced.

The obtained low-expanded particles (I) are mixed with nitrogen, air or an inorganic gas mainly containing these in a closed container at 0.5 to 25 kg / cm ² G, and further at 5 to 15 k.
g / cm ² G, for example, for 1 to 72 hours, and even 3 to
After applying foaming ability by applying pressure at room temperature to 100 ° C. for 24 hours, heating is performed at a temperature equal to or higher than the softening temperature of the base resin (for example, the low foaming particles are heated in a closed vessel with steam set to a predetermined steam pressure). Then, the polyolefin-based resin pre-expanded particles (II) of the present invention are produced by expanding the polyolefin-based resin low-expanded particles (I) 1.5 to 30 times, and more preferably 3 to 15 times.

Examples of the inorganic gas include nitrogen, air or an inorganic gas containing these (these include 50% by volume or more, more preferably 70% by volume or more, and the remaining gas is an inert gas such as argon, helium, or xenon). Inorganic gas comprising water vapor, oxygen, hydrogen, ozone, etc.) can be used, but nitrogen and air are preferred from the viewpoint of economy, productivity, safety, environmental compatibility and the like.

The polyolefin resin pre-expanded particles (II) thus obtained have an expansion ratio of 7 to 50 times, more preferably 7 to 40 times, and a ratio variation of 15% or less, and more preferably 1 to
0% or less, closed cell rate of 80% or more, further 90% or more, especially 92% or more, and average cell diameter of 200 to 50
0 μm, and more preferably 220 to 400 μm.

When the expansion ratio is less than 5 times, the flexibility and cushioning properties of the obtained molded article become insufficient.
If it exceeds 0 times, the mechanical strength, heat resistance and the like of the obtained molded product become insufficient. Further, the closed cell ratio is 80
%, The secondary foaming power of the pre-expanded particles is insufficient,
Poor fusion occurs at the time of molding, and the mechanical strength and the like of the obtained molded body decrease. Further, the average bubble diameter is 200 μm.
If it is less than m, problems such as distortion of the shape of the obtained molded article occur, and if it exceeds 500 μm, the mechanical strength of the obtained molded article decreases.

Since the polyolefin resin pre-expanded particles of the present invention have a closed cell rate of 80% or more, the pre-expanded particles can be treated as they are or, if necessary, under a pressure for 30 minutes under heat and pressure in a pressure vessel. After performing air impregnation, it may be filled in a molding die, and may be subjected to foam heating in the mold by steam heating to produce a molded product according to the die.

The foam molded article thus obtained is excellent in flexibility, cushioning property, etc., and has a small dimensional shrinkage and a small change in shape.
It can be suitably used for applications such as cushioning materials.

[0051]

EXAMPLES Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to only these examples.

The main materials used in the examples and comparative examples are summarized below.

Polyolefin resin Ethylene-propylene random copolymer A: ethylene content 3.1%, melting point 145 ° C., MI 6.0 g / 10
Min, flexural modulus 10500 kgf / cm ² ethylene-propylene random copolymer B: ethylene content 4.5%, melting point 137 ° C, MI 9.0 g / 10
Min, flexural modulus 8100 kgf / cm ² linear low density polyethylene A: density 0.93 g / cm ³ ,
Melting point 122 ° C, MI 2.1g / 10min, Flexural rigidity 40
00 kgf / cm ² linear low density polyethylene B: density 0.92 g / cm ³ ,
Melting point: 120 ° C., MI: 2.1 g / 10 min, flexural rigidity: 30
00kgf / cm ²

Filler Talc: average particle size 9.5 μm Calcium carbonate: average particle size 1.8 μm, fatty acid surface treatment

The evaluation in Examples and Comparative Examples was performed by the following method.

(Average Expansion Ratio and Variation in Expansion Ratio) 1 kg of the expanded particles was subjected to a JIS Z8801 standard sieve (3.5,
4, 5, 6, 7, 8, 9, 10 mesh). The weight fraction W _i and the expansion ratio K _i of each of the expanded particles after sieving were measured, and the average expansion ratio Kav was calculated from the equation: Kav = Σ (K _i × W _i ).

[0057]

(Equation 6)

The standard deviation σ _m of the expansion ratio was calculated from the above formula, and the variation (%) of the magnification was obtained from the following equation (I): variation of magnification = (σ _m / Kav) × 100 (%) (I)

(Closed cell rate) Air comparison type hydrometer (BEC)
True expanded particle volume v (cm ³ ) and apparent expanded particle volume V (c) measured using a KMAN type 930)
m ³ ), the weight W of the foamed particles, and the density ρ (g / cm ³ ) of the base resin of the foamed particles, the formula: closed cell rate = (v−W / ρ) / (V−W / ρ) × 100
(%).

(Average cell diameter) Arbitrarily 3 out of foamed particles
0 foamed particles were taken out, the cell diameter was measured in accordance with JIS K6402, and the average cell diameter (d) was calculated.

(Variation of Bubble) Variation U is obtained from the equation: U (%) = (σ / d) × 100 using the average bubble diameter (d) and the standard deviation (σ) representing the variation of the bubble diameter. Evaluation was made according to the following criteria. The smaller U is, the more uniform the bubbles are. ：: The value of U is less than 35% Δ: The value of U is 35 to 45% ×: The value of U exceeds 45%

Examples 1 to 5 and Comparative Examples 1 to 3 100 parts of the polyolefin resin described in Tables 1 and 2
Pellets (resin particles, 1.8 mg / particle) of the polyolefin-based resin composition obtained by adding and mixing the fillers described in No. 2 in the amounts described in Tables 1 and 2 were produced.

100 parts of the obtained pellets, 0.5 part of powdery basic calcium triphosphate and 0.0 part of sodium n-paraffin sulfonate as a dispersant and a dispersing aid.
06 parts together with 300 parts of water in a closed container,
The mixture was heated to the temperature shown in Tables 1 and 2 over 0 minutes, and further kept at the same temperature for 15 minutes.

Thereafter, nitrogen gas was introduced into the closed vessel to raise the pressure in the closed vessel to the holding pressure shown in Table 1,
While maintaining this pressure, the valve at the bottom of the closed vessel was immediately opened to release the aqueous dispersion under atmospheric pressure to foam.

The average expansion ratio, variation in magnification, closed cell ratio and average cell diameter of the obtained low-expanded particles were measured. The results are shown in Tables 1 and 2.

The obtained low-expanded particles were treated under the air pressurization conditions shown in Tables 1 and 2, and air was impregnated in the low-expanded particles.
Next, pre-expanded particles were obtained by heating under steam heating conditions shown in Tables 1 and 2 to effect two-stage foaming. The average expansion ratio, magnification variation, closed cell ratio, average cell diameter, and cell variation of the obtained pre-expanded particles were measured. The results are shown in Tables 1 and 2.

[0067]

[Table 1]

[0068]

[Table 2]

[0069]

According to the method for producing low-expanded particles of the present invention, a conventional volatile foaming agent comprising a hydrocarbon compound such as butane or a halogen-based compound such as chlorofluorocarbon, or an inorganic gas foaming agent such as CO ₂ can be used. In addition, low-expanded particles suitable for two-stage foaming can be produced with a high closed-cell rate and little variation in magnification.

According to the method for producing pre-expanded particles of the present invention, pre-expanded particles of good quality can be produced by expanding the low-expanded particles in two stages.

Further, in the method for producing low-expanded particles and the method for producing pre-expanded particles of the present invention, hydrocarbon compounds such as butane which may cause a fire or an explosion, and halogen compounds such as chlorofluorocarbon which may cause ozone layer destruction or toxicity. Polyolefin resins can be highly foamed only with nitrogen, air and water without using compounds and inorganic gases such as CO _{2 that} cause global warming. It can be greatly reduced, which is economically advantageous.

Claims (8)

[Claims] 1. A polyolefin-based resin composition comprising 100 parts by weight of a polyolefin-based resin and 0.05 to 5 parts by weight of a filler is used as a base resin, and has an expansion ratio of 7 to 50 times. σ _m / Kav) × 100 (%) (I) (where Kav is a JIS Z8801 standard sieve (3.5,
7, 8, 9, 10 the weight fraction W _i of each sieve residual foamed particles upon sieved with a mesh eight), wherein the expansion ratio _{K i: Kav = Σ (K} i × the average expansion ratio sought W _i), σ _m is JIS Z8801 standard sieve (3.
5, 4, 5, 6, 7, 8, 9, 10 mesh (8 types), the weight fraction W _i of each of the particles remaining after sieving when sieved,
Formula from expansion ratio K _i : Variation 15 expressed by the standard deviation obtained by
%, Closed cell rate 80% or more, average cell diameter 200 to 5
Pre-expanded polyolefin resin particles having a size of 00 μm. 2. The pre-expanded polyolefin resin particles according to claim 1, wherein the polyolefin resin is an ethylene-propylene random copolymer or a linear low-density polyethylene. 3. A polyolefin resin composition comprising 100 parts by weight of a polyolefin resin and 0.05 to 5 parts by weight of a filler is used as a base resin, and has an expansion ratio of 1.5 to 5 times.
Formula (I): Variation in magnification = (σ _m / Kav) × 100 (%) (I) (where Kav is a JIS Z8801 standard sieve (3.5,
7, 8, 9, 10 the weight fraction W _i of each sieve residual foamed particles upon sieved with a mesh eight), wherein the expansion ratio _{K i: Kav = Σ (K} i × the average expansion ratio sought W _i), σ _m is JIS Z8801 standard sieve (3.
5, 4, 5, 6, 7, 8, 9, 10 mesh (8 types), the weight fraction W _i of each of the particles remaining after sieving when sieved,
Formula from expansion ratio K _i : Variation 15 expressed by the standard deviation obtained by
% Or less, closed cell rate of 90% or more, average cell diameter of 50 to 20
Polyolefin-based resin low-expanded particles (I) having a size of 0 μm. 4. The low-expanded polyolefin resin particles according to claim 3, wherein the polyolefin resin is an ethylene-propylene random copolymer or a linear low-density polyethylene. 5. The polyolefin-based resin low-expanded particles (I) according to claim 3 are mixed in a closed container with nitrogen, air or an inorganic gas mainly containing 0.5 to 25 kg / kg.
After imparting foaming ability by pressurizing to cm ² G, the foam is heated to a softening temperature of the base resin or higher and foamed to 1.5 to 30 times the polyolefin-based resin low foamed particles (I). The method for producing pre-expanded polyolefin resin particles according to claim 1. 6. The method according to claim 5, wherein the polyolefin resin is an ethylene-propylene random copolymer or a linear low-density polyethylene. 7. A resin particle having a polyolefin-based resin composition comprising 100 parts by weight of a polyolefin-based resin and 0.05 to 5 parts by weight of a filler as a base resin, dispersed in an aqueous dispersion medium in a closed vessel, and After heating to a temperature equal to or higher than the softening temperature of the material resin, nitrogen, air or an inorganic gas mainly composed of nitrogen and air is introduced into the closed container to adjust the pressure in the closed container to 10 to 45 kg / cm ² G. The method for producing low-expanded polyolefin-based resin particles (I) according to claim 3, wherein the dispersion is released under an atmosphere at a pressure lower than the internal pressure of the closed container while maintaining the pressure. 8. The method according to claim 7, wherein the polyolefin resin is an ethylene-propylene random copolymer or a linear low-density polyethylene.