JP2001019789A - Pre-expanded beads of polyolefin resin and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject pre-expanded beads of polyolefin resin composition having excellent properties only in one step in no need of volatile foaming agent by dispersing polyolefin resin composition in an aqueous medium, introducing an inorganic gas into the dispersion and heating them. SOLUTION: The objective pre-expanded beads comprises a composition including 100 pts.wt. of polyolefin resin and 0.01-20 pts.wt. of a hydrophilic polymer, shows the expansion ratio of 2-15 and the dispersion of the expansion ratio of <=10% according to the formula (Kav is the average expansion ratio calculated from the weight fractions of individual expanded beads remaining on the sieve and the expansion ratio, when the beads are sieved with the standard sieve according to JIS 28801; σ is the standard deviation calculated from above-stated values). The pre-expanded beads can be obtained by dispersing the resin composition, a slightly soluble inorganic compound and a surfactant in an aqueous medium, pressurizing them with an inorganic gas at a pressure of >=0.1 MPa, then or simultaneously heating them higher than the softening point and extruding out through a squeezing plate into the low-pressure atmosphere at a flow rate of 15-50 m/sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pre-expanded polyolefin resin composition particle and a method for producing the same.
More specifically, it belongs to the technical field of, for example, polyolefin-based resin composition pre-expanded particles that can be suitably used as a raw material of an in-mold foam molded article, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, polyolefin resin particles are dispersed in an aqueous dispersion medium in a closed container and a volatile foaming agent is contained therein. A method for obtaining pre-expanded particles of a polyolefin-based resin composition by heating to a softening temperature or higher and then releasing the mixture into a low-pressure atmosphere is well known (for example, JP-A-58-199125). However, when the pre-expanded particles are produced by the method, the use of the volatile foaming agent not only increases the cost but also makes it difficult to control the expansion ratio due to the large impregnation unevenness of the volatile foaming agent. , Number 1:

[0003] The variation in magnification represented by the formula (1) is as high as 20% or more, and pre-expanded particles having good characteristics cannot be obtained. When the volatile foaming agent is a flammable gas such as propane or butane, there is a problem in safety such as combustion and explosion.

Japanese Patent Application Laid-Open No. 60-229936 discloses that pre-expanded particles are produced by discharging polyolefin-based resin particles containing a nitrogen-containing inorganic gas as a blowing agent into a low-pressure atmosphere. ing. In this method, the cost and safety problems due to the use of the volatile foaming agent are eliminated, but the impregnation of the nitrogen-containing inorganic gas into the polyolefin resin is poor, and the rate of escape from the polyolefin resin particles is low. The bubbles of the foam obtained due to the use of the nitrogen-containing inorganic gas are too small,
It leads to a decrease in moldability and physical properties of molded products.

Japanese Patent Application Laid-Open No. 60-221440 discloses that ethylene-propylene random copolymer resin particles having an ethylene content of 1 to 12% by weight are dispersed in water, and then an inorganic gas is introduced, followed by heating and outflow. Speed 200-5
It describes the production of pre-expanded particles by discharging into a low pressure atmosphere at 00 m / sec. However, in this method, since the outflow speed at the time of discharging into a low-pressure atmosphere is too large, it is difficult to maintain the pressure inside the can at a constant and maintain the outflow speed at the time of release, and to obtain the obtained pre-expanded particles. Magnification variation becomes worse.

On the other hand, the present inventors have disclosed in Japanese Patent Application Laid-Open No. 10-176.
No. 077, 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. 1:

[0007] A method for producing pre-expanded particles having a magnification variation of 15% or less is reported. However, in this method, it is difficult to obtain pre-expanded particles having a desired expansion ratio by single-stage foaming and not having a desired expansion ratio of 10% or less in single-stage expansion.

[0008]

Means for Solving the Problems Accordingly, the present inventors have:
Obtained without using a volatile foaming agent and by one-stage foaming,
Expansion ratio 2 to 15 times, number 1:

As a result of intensive studies on pre-expanded particles of the polyolefin resin composition having a magnification variation of 10% or less and a method for producing the same, the polyolefin resin composition was dispersed in an aqueous dispersion medium, After the introduction, or simultaneously, it was found that the above problem could be solved by discharging to a low-pressure atmosphere while maintaining a certain outflow speed through the diaphragm, and completed the present invention. .

That is, the present invention comprises a polyolefin resin composition containing 100 parts by weight of a polyolefin resin and 0.01 to 20 parts by weight of a hydrophilic polymer,
Foaming ratio of 2 to 15 times and number 1

The polyolefin resin composition pre-expanded particles wherein the variation in magnification represented by the formula is 10% or less (Claim 1), wherein the polyolefin resin is a polypropylene resin. Pre-expanded particles of a resin composition (Claim 2), wherein the hydrophilic polymer is an ethylene ionomer. Pre-expanded particles of a polyolefin resin composition (Claim 3), (A) a polyolefin resin. A sealed container containing resin particles comprising a polyolefin resin composition containing 100 parts by weight and 0.01 to 20 parts by weight of a hydrophilic polymer, (B) a poorly water-soluble inorganic compound as a dispersant, and (C) a surfactant. After dispersing in an aqueous dispersion medium within, and introducing an inorganic gas into a closed container and applying a pressure of 0.1 MPa or more, or simultaneously, Heating the fat particles to a temperature above the softening temperature of the said polyolefin-based resin composition, moisture content 2.5
Pre-expanded polyolefin-based resin composition, wherein the pre-expanded particles of the polyolefin resin composition are discharged at a flow rate of 15 to 50 m / sec through a diaphragm plate into an atmosphere at a pressure lower than the internal pressure in a closed vessel The method for producing pre-expanded polyolefin resin composition particles according to claim 4, wherein the inorganic gas is nitrogen, air or an inorganic gas mainly containing these. Item 5).

[0012]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, 100 parts of a polyolefin resin and 0.01 to 20 hydrophilic polymers are used.
Resin particles (A) comprising a polyolefin-based resin composition containing a part are used for the production of pre-expanded particles.

The above-mentioned polyolefin resin is a component used to obtain pre-expanded particles having a high expansion ratio, which are excellent in balance between expandability, moldability, mechanical strength, heat resistance and flexibility of the obtained molded article. In addition, the hydrophilic polymer is a component used to increase the water content of the polyolefin resin composition.

The polyolefin resin contains 50 to 100% by weight of an olefin monomer unit, and more preferably 70 to 10% by weight.
The resin contains 0% by weight, and 0 to 50% by weight, and more preferably 0 to 30% by weight of a monomer unit copolymerizable with the olefin monomer. Since the olefin monomer unit is contained in an amount of 50% by weight or more, a molded article that is lightweight and has excellent mechanical strength, workability, electrical insulation, water resistance, and chemical resistance can be obtained. The monomer unit copolymerizable with the olefin monomer has adhesiveness,
It is a component used for modifying transparency, impact resistance, gas barrier properties, and the like. In order to obtain the effect of use, it is preferably used in an amount of 2% by weight or more, more preferably 5% by weight or more. .

Specific examples of the olefin monomer include:
Ethylene, propylene, butene, pentene, hexene,
C2-C8 alpha-olefin monomers, such as heptene and octene, and cyclic olefins, such as a norbornene monomer, are mentioned. These may be used alone,
More than one species may be used in combination. Of these, ethylene,
Propylene is preferred because it is inexpensive and the properties of the resulting polymer are improved. Specific examples of the monomer copolymerizable with the olefin monomer include a vinyl alcohol ester such as vinyl acetate, an alkyl group such as methyl methacrylate, ethyl acrylate, and hexyl acrylate having 1 to 6 carbon atoms (meth). Examples include alkyl acrylate, vinyl alcohol, methacrylic acid, and vinyl chloride. These may be used alone or in combination of two or more. 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.

Specific examples of the polyolefin resin include, for example, an ethylene-propylene random copolymer,
Ethylene-propylene-butene random terpolymer,
Polypropylene resins such as polyethylene-polypropylene block copolymer and homopolypropylene; low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer And polyethylene-based resins; polybutene, polypentene and the like.

The polyolefin-based resin may be used in a non-crosslinked state, or may be used after being crosslinked by peroxide or radiation. These polymers may be used alone or in combination of two or more. Among these, pre-expanded particles having a relatively small expansion ratio and relatively high expansion ratio are obtained as compared with other polyolefin-based resins, and the mechanical strength of a molded article manufactured from the obtained pre-expanded particles. Polypropylene resins are preferred because of their good heat resistance.

The melt index (MI) of the polyolefin resin is, for example, 0.2 to 50 g / 10 min for a polypropylene resin, and more preferably 1 to 30 g / min.
10 minutes is preferable, and the flexural modulus (JIS K
7203) is, for example, 5,000 to 20,000 kg / cm ² G for a polypropylene resin,
000~16000kg / cm ² G, as the melting point, for example, one hundred twenty-five to one hundred sixty-five ° C. in polypropylene resin, more preferably from 130 to 160 ° C.. When the MI is less than 0.2 g / 10 min, the melt viscosity is too high to obtain pre-expanded particles having a high expansion ratio, and when it exceeds 50 g / 10 min, the melt viscosity with respect to the elongation of the resin during foaming is low. The foam tends to be broken, and pre-expanded particles having a high expansion ratio tend to be hardly obtained. Further, the bending strength is 50
When it is less than 00 kg / cm ² G, mechanical strength and heat resistance tend to be insufficient, and when it exceeds 20,000 kg / cm ² G, the flexibility and cushioning properties of the obtained foamed molded article tend to be insufficient. Further, when the melting point is less than 125 ° C.,
If the heat resistance is insufficient and the temperature exceeds 165 ° C., the adhesiveness during molding and the secondary foaming power tend to be insufficient.

The hydrophilic polymer is ASTM D5
A polymer having a water absorption of 0.5% by weight or more as measured according to No. 70, and is a so-called hygroscopic polymer, a water-absorbing polymer (water that is several to several hundred times its own weight without being dissolved in water. And a water-soluble polymer (a polymer that dissolves in water at room temperature or high temperature). In the molecule of the hydrophilic polymer, a hydrophilic group such as a carboxyl group, a hydroxyl group, an amino group, an amide group, an ester group, and a polyoxyethylene group may be contained.

Examples of the hygroscopic polymer include a carboxyl group-containing polymer, a polyamide, a thermoplastic polyester elastomer, a cellulose derivative and the like.

Specific examples of the carboxyl group-containing polymer include, for example, ethylene-acrylic acid-maleic anhydride terpolymer (water absorption: 0.5 to 0.7% by weight), ethylene- (meth) acrylic acid copolymer. An ionomer resin (water absorption: 0.7 to 1.4% by weight) in which a carboxylic acid group of a polymer is converted into a salt with an alkali metal ion such as sodium ion or potassium ion and cross-linked between molecules, ethylene- (meth) acrylic Acid copolymers (water absorption: 0.5 to 0.7% by weight). These may be used alone or in combination of two or more. Among these carboxyl group-containing polymers, an ethylene ionomer obtained by crosslinking the molecules of an ethylene- (meth) acrylic acid copolymer with an alkali metal ion such as sodium ion or potassium ion has a dispersibility in a polyolefin resin. In particular, they are particularly preferably used in the present invention.

Specific examples of the polyamide include, for example, nylon-6 (water absorption: 1.3 to 1.9% by weight), nylon-6,6 (water absorption: 1.1 to 1.5% by weight), copolymer Nylon (EMS Hemy (EMS-CHEM)
IE AG), trade name: Grilltex, etc. (water absorption: 1.5 to 3% by weight).

Specific examples of the thermoplastic polyester elastomer include, for example, a block copolymer of polybutylene terephthalate and polytetramethylene glycol (water absorption: 0.5 to 0.7%).

Specific examples of the cellulose derivative include:
For example, cellulose acetate, cellulose propionate and the like can be mentioned.

Among the above-mentioned hygroscopic polymers, the ionomer resin has excellent dispersibility in the polyolefin resin, so that the obtained pre-expanded particles have a small variation in magnification. In addition, a water-containing polyolefin resin composition having a high water content can be obtained in a relatively small amount, and thus pre-expanded particles having a desired expansion ratio can be obtained in one step, which is preferable.

Examples of the water-absorbing polymer include a crosslinked polyacrylate polymer, a starch-acrylic acid graft copolymer, a crosslinked polyvinyl alcohol polymer,
Crosslinked polyethylene oxide polymer, isobutylene-
Maleic acid copolymers and the like can be mentioned.

Specific examples of the crosslinked polyacrylate polymer include, for example, Aqualic (trade name) manufactured by Nippon Shokubai Co., Ltd. and Diawet (trade name) manufactured by Mitsubishi Chemical Corporation. And a cross-linked sodium polyacrylate polymer.

Specific examples of the crosslinked polyvinyl alcohol-based polymer include various crosslinked polyvinyl alcohol-based polymers represented by Aqua Reserve GP manufactured by Nippon Synthetic Chemical Industry Co., Ltd., for example.

Specific examples of the crosslinked polyethylene oxide-based polymer include various crosslinked polyethylene oxide-based polymers represented by, for example, Aqua Coke manufactured by Sumitomo Seika Co., Ltd.

Specific examples of the isobutylene-maleic acid copolymer include various isobutylene-maleic acid copolymers represented by, for example, KI gel manufactured by Kuraray Co., Ltd. Among the water-absorbing polymers, a crosslinked polyethylene oxide is preferable because of its dispersibility in a polyolefin-based resin and a relatively small amount of a high water content.

Examples of the water-soluble polymer include poly (meth) acrylic acid-based polymer, poly (meth) acrylate-based polymer, polyvinyl alcohol-based polymer, polyethylene oxide-based polymer, and water-soluble cellulose derivative. And so on.

Specific examples of the poly (meth) acrylic acid-based polymer include, for example, polyacrylic acid, acrylic acid-
Ethyl acrylate copolymer, polyhydroxyethyl methacrylate and the like can be mentioned.

Specific examples of the poly (meth) acrylate polymer include, for example, sodium polyacrylate,
Examples thereof include sodium polymethacrylate, potassium polyacrylate, and potassium polymethacrylate.

Specific examples of the polyvinyl alcohol-based polymer include, for example, polyvinyl alcohol and vinyl alcohol-vinyl acetate copolymer.

Specific examples of the polyethylene oxide-based polymer include polyethylene oxide having a molecular weight of tens of thousands to several millions.

Specific examples of the water-soluble cellulose derivative include carboxymethyl cellulose, hydroxyethyl cellulose and the like.

The above-mentioned hygroscopic polymer, water-absorbing polymer and water-soluble polymer may be used alone or in combination of two or more. Further, the present invention is not limited to those described here.

The amount of the hydrophilic polymer used depends on the type of the hydrophilic polymer, but the resin particles composed of the polyolefin resin composition are dispersed in an aqueous dispersion medium in a closed vessel to soften the polyolefin resin composition. In order to obtain a polyolefin resin composition having a water content of 2.5 to 50% by weight when heated to a temperature equal to or higher than the softening temperature + 20 ° C., the polyolefin resin 10 is usually used.
The amount is 0.01 part by weight or more, preferably 0.1 part by weight or more based on 0 part by weight. In addition, the production stability and foaming characteristics during the production of the pre-expanded particles are improved, and the molded article obtained from the pre-expanded particles is given excellent mechanical strength and heat resistance, and the dimensional change upon water absorption is reduced. From
It is at most 20 parts by weight, preferably at most 10 parts by weight.

The polyolefin resin composition used in the present invention contains a filler, that is, an inorganic filler and / or an organic filler, because the dispersion in magnification is small, the cells are uniform and the foaming is relatively high. This is preferable in that pre-expanded particles having a higher magnification can be obtained.

Specific examples of the inorganic filler include talc, calcium carbonate, calcium hydroxide and the like. Among these inorganic fillers, talc is
This is preferable because pre-expanded particles having a small variation in magnification, uniform cells, and a relatively high expansion ratio are provided.

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 resin. Specific examples of the organic filler include a fluororesin powder, a silicone resin powder, and a thermoplastic polyester resin powder.
These fillers may be used alone or in combination of two or more.

The average particle diameter of the filler is such that pre-expanded particles having uniform cells and a relatively high expansion ratio can be obtained, and the pre-expanded particles have excellent mechanical strength and flexibility. 50 μm from the point where the body can be obtained
Hereinafter, the thickness is more preferably 10 μm or less, and is preferably 0.1 μm or more, and more preferably 0.5 μm or more from the viewpoint of secondary aggregation and handling workability.

The amount of the filler used is 0.001 part by weight or more, more preferably 0.005 part by weight, based on 100 parts by weight of the polyolefin resin, in order to obtain pre-expanded particles having a relatively high expansion ratio. It is preferred to be not less than part by weight, and when molding the pre-expanded particles, from the viewpoint of expressing excellent fusion properties and obtaining a molded article excellent in mechanical strength and flexibility from the pre-expanded particles, It is at most 3 parts by weight, preferably at most 2 parts by weight.

The polyolefin-based resin composition containing the polyolefin-based resin, the hydrophilic polymer, and, if necessary, a filler is usually melt-kneaded using an extruder, a kneader, a Banbury mixer, a roll, and the like, and then formed into a cylindrical shape. It is preferable to form the particles into a desired particle shape which can be easily used for preliminary foaming, such as an elliptic column, a sphere, a cube, and a cuboid. The conditions for producing the particles, the size of the resin particles, and the like are not particularly limited. For example, particles obtained by melt-kneading in an extruder are usually 0.5 to 5 mg / particle.

In the present invention, the resin particles (A), the poorly water-soluble inorganic compound (inorganic dispersant) (B), and the surfactant (dispersion aid) (C) comprising the polyolefin resin composition are used. After dispersing in an aqueous dispersion medium in a closed container, introducing inorganic gas into the closed container and applying pressure, or simultaneously, heating the resin particles to a temperature equal to or higher than the softening temperature of the polyolefin resin composition, and Is 2.5 to 50
% Hydrated particles and then through a squeezing machine at an outflow velocity of 15%.
Pre-expanded particles of the polyolefin-based resin composition are produced by discharging into an atmosphere at a pressure lower than the internal pressure of the closed vessel while maintaining the flow rate at a certain specific rate within a range of 50 m / sec.

Poorly water-soluble inorganic compound (inorganic dispersant) (B)
Examples include inorganic salts such as tribasic calcium phosphate, basic magnesium carbonate, basic zinc carbonate, and calcium carbonate, and clays such as bentonite and kaolin. Of these, tribasic calcium phosphate is preferred because of its strong dispersing power.

As the surfactant (dispersing aid) (C),
For example, anionic surfactants such as sodium dodecylbenzene sulfonate, sodium n-paraffin sulfonate, sodium α-olefin sulfonate, sodium alkylnaphthalene sulfonate, benzalkonium chloride, alkyltrimethylammonium chloride, dialkyldimethylammonium chloride and the like And cationic surfactants.
Among these, sodium n-paraffin sulfonate is preferred because it gives good dispersing power and is easily biodegradable.

The aqueous dispersion medium for dispersing the resin particles (A) may be any solvent that does not dissolve the polyolefin resin composition, and is usually water or water and ethylene glycol, glycerin, methanol, ethanol, isopropyl alcohol and the like. A mixture with at least one of the above is exemplified, but water is preferable in terms of environment, economy and the like.

Usually, such water is deaerated, but in the present invention, it is preferable to use the water without deaeration. The reason is that a gas dissolved in water also acts as a blowing agent.

The amount of the resin particles (A) dispersed in the aqueous dispersion medium is 3 to 100 parts by weight, preferably 10 to 50 parts by weight, based on 100 parts by weight of the aqueous dispersion medium.
Parts by weight are preferred. When the amount of the resin particles (A) is less than 3 parts by weight, the productivity is reduced and the method is not economical. When the amount exceeds 100 parts by weight, particles tend to fuse in the container during heating.

Further, poorly water-soluble inorganic compounds (inorganic dispersants)
The amounts of (B) and the surfactant (dispersing aid) (C) are not particularly limited, and generally used amounts may be used, but the poorly water-soluble inorganic compound (inorganic dispersant)
(B) is 0.0% based on 100 parts by weight of the resin particles (A).
5 to 10 parts by weight are preferred, and a surfactant (dispersing aid)
(C) is 0.0% based on 100 parts by weight of the resin particles (A).
005 to 1 part by weight is preferred.

Resin particles (A), poorly water-soluble inorganic compound (inorganic dispersant) (B), and surfactant (dispersion aid)
(C) is dispersed in an aqueous dispersant in a closed container, and before heating,
Alternatively, an inorganic gas is introduced at the same time as heating, and the pressure in the closed container is set to 0.10 to 4.0 MPa, preferably 0.10 to 4.0 MPa.
3.0 MPa. If the pressure is less than 0.1 MPa, the resin particles (A) hardly foam, and pre-expanded particles having a desired expansion ratio cannot be obtained. In addition, the bubbles of the pre-expanded particles obtained when the pressure exceeds 4.0 MPa are too small,
The closed cell ratio tends to decrease, and the shrinkage, shape stability, mechanical strength, and heat resistance of the molded article tend to be impaired.

Here, the step of introducing the inorganic gas to pressurize the closed container may be performed simultaneously with the heating, but is more preferably performed before the heating is started. Although the reason is not known, the inorganic gas is dissolved in the resin particles (A) in advance, and then heated, so that water easily and uniformly enters the resin particles (A) in a short time. It is thought that this makes the expansion ratio of the pre-expanded particles uniform, and also contributes to the improvement of the expansion ratio in addition to the amount of water absorbed as the blowing agent.

As the inorganic gas, nitrogen, air or these are mainly used (usually 50% by volume or more, more preferably 70% by volume or more).
Volume%), an inert gas such as argon, helium, xenon, or an inorganic gas containing a small amount of water vapor, oxygen, hydrogen, ozone (50% by volume or less, further 30% by volume or less) can be used. Nitrogen and air are preferred from the viewpoints of performance, productivity, safety, and environmental compatibility.

The temperature at which the resin particles (A) are dispersed and the inorganic gas is added or simultaneously heated is at a temperature higher than the softening temperature of the polyolefin resin composition to be used, specifically, higher than the melting point, preferably higher than the melting point. The temperature is not lower than + 5 ° C, preferably not higher than the melting point + 20 ° C, more preferably not higher than the melting point + 15 ° C. For example, in the case of an ethylene-propylene copolymer having a melting point of 145 ° C, the temperature is 145 to 165 ° C, more preferably 150 to 160 ° C. If it is less than 145 ° C., it is difficult to foam, and if it exceeds 165 ° C., the mechanical strength and heat resistance of the pre-expanded particles obtained are not sufficient, and the particles tend to be easily fused in the container.

As described above, the resin particles (A) are dispersed in an aqueous dispersion medium, heated to a temperature higher than the softening temperature of the polyolefin resin composition, and stirred for 30 minutes to 12 hours. It can be adjusted to 0.5 to 50% by weight. The adjustment of the water content can be performed by adjusting the heating temperature, the heating time and the like. 1. Moisture content
When the amount is less than 5% by weight, the expansion ratio tends to be less than twice. The preferred moisture content is 3% or more. On the other hand, if the content exceeds 50% by weight, the dispersibility of the resin particles in the aqueous dispersion medium decreases, and the resin particles tend to be clumped in a closed container during the production of the pre-expanded particles, making it difficult to uniformly pre-expand. The preferred water content is 30% by weight or less. The water absorption of the hydrophilic polymer is a value measured at room temperature, and the water content is high (above the softening temperature (melting point) of the resin).
For example, if the water absorption of the hydrophilic polymer used is 0.5% by weight or more, it is 2.5% by weight.
The above moisture content is obtained.

The resin particles (A) are heated to a temperature equal to or higher than the softening temperature of the polyolefin resin composition so that the water content becomes 2.5 to
Since the expansion ratio is 50% by weight, the expansion ratio can be 2 to 15 times, and the resin particles can be made into uniform pre-expanded particles without forming a lump in a closed container during production of the pre-expanded particles.

The softening temperature of the polyolefin resin composition was 10 ° C. by DSC (differential scanning calorimetry).
/ Min is the temperature at the top of the melting peak as measured at the rate of temperature rise. The water content is the water content under the steam pressure at the foaming temperature. The water content can be replaced with a value determined as follows.

That is, resin particles (A) comprising the polyolefin resin composition in a 300 cc pressure resistant ampoule
50 g, water 150 g, a poorly water-soluble inorganic compound (inorganic dispersant) (B), 0.5 g of powdery basic calcium triphosphate, and 0.03 g of sodium n-paraffin sulfonate as a surfactant (C) are sealed. Thereafter, heat treatment is performed for 3 hours in an oil bath set at a temperature (foaming temperature) equal to or higher than the softening temperature of the polyolefin-based resin composition. Further, after cooling to room temperature, it is taken out and washed sufficiently with water to remove the poorly water-soluble inorganic compound (inorganic dispersant) (B), and then the weight of the obtained polyolefin-based resin composition obtained by removing the surface adhering water of the water-containing particles. (X) is determined, and then dried in an oven set at a temperature 20 ° C. higher than the melting point of the resin particles for 3 hours, and cooled in a desiccator to room temperature, and the weight (Y) is determined. 2:

[0060]

(Equation 2) Is required in accordance with

The water content when the fillers and the like are contained in the resin particles made of the polyolefin resin composition is the water content based on the total amount of the polyolefin resin composition and the hydrophilic polymer.

The pressure in the closed vessel rises due to the heating, and is then released to the low pressure region through the throttle plate. At that time, if necessary, an inorganic gas may be further introduced into the closed vessel. The pressure in the closed vessel when it is released to the low pressure area is 0.5
Preferably, the pressure is up to 5.0 MPa. 0.5MPa pressure
If it is less than a, the resin particles (A) hardly foam, and pre-expanded particles having a desired expansion ratio cannot be obtained. On the other hand, if it exceeds 5.0 MPa, the cells of the pre-expanded particles obtained are too small, the closed cell ratio is lowered, and the shrinkage, shape stability, mechanical strength and heat resistance of the molded article tend to be impaired.

The orifice type, the nozzle type, the venturi type, etc. can be used as the above-mentioned diaphragm, and a combination thereof can also be used. However, the orifice type can keep the outflow speed constant, and the prefoaming with little variation in magnification. This is preferable because particles can be obtained and the structure is simple. Although one or two or more openings are provided in the diaphragm, the use of a plurality of openings is advantageous because the production speed increases.

When an orifice plate is used, its diameter is preferably 2.0 to 5.0 mm, and more preferably 2.5 to 4.0 mm. When the diameter is less than 2.0 mm, the opening is easily closed by the resin, and when the diameter exceeds 5.0 mm, it becomes difficult to keep the outflow speed at the time of release constant, and the variation in the magnification of the obtained pre-expanded particles is reduced. Getting worse.

The thickness of the orifice plate is 0.2 to 10 m.
m, more preferably 0.5 to 5 mm. 0.2 thickness
If it is less than 10 mm, the pressure at the time of release may cause breakage of the orifice plate, and if it exceeds 10 mm, the expansion ratio of the obtained pre-expanded particles may be reduced to obtain pre-expanded particles having a desired expansion ratio. Becomes difficult,
The opening may be closed by the resin.

In the present invention, the outflow rate at the time of release is 1
5 to 50 m / sec. Preferably, it is 20 to 40 m / sec. If the outflow speed is less than 15 m / sec, the resin particles (A) hardly foam, and pre-expanded particles having a desired expansion ratio cannot be obtained. If it exceeds 50 m / sec, the cells of the pre-expanded particles obtained will be too small, the closed cell ratio will decrease, and the shrinkage, shape stability, mechanical strength and heat resistance of the molded article will tend to be impaired.

From the viewpoint of obtaining pre-expanded particles having little variation in magnification, it is preferable to maintain the outflow speed at the time of release.

[0068]

The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

Examples 1 to 3 Ethylene-propylene random copolymer as a polyolefin resin (density 0.91 g / cm ³ , ethylene content 3% by weight, melting point 145 ° C., MI = 5.5 g / 10 min,
An ionomer (85% by weight of ethylene unit and 15% by weight of methacrylic acid unit) obtained by neutralizing a carboxyl group of a hydrophilic polymer (ethylene-methacrylic acid copolymer) with sodium ions with respect to 100 parts by weight of a flexural modulus of 10,000 kg / cm ² G. %, In which 60% by weight of the methacrylic acid unit forms a salt, MI = 0.9 g / 10 min,
Melting point 89 ° C., water absorption 1% by weight)) 2 parts by weight and talc (average particle diameter 7 μm) 0.3 part by weight were added, and 50 mm
After supplying to a single screw extruder and melting and kneading, the diameter is 1.5m
Extruded from a cylindrical die of mφ, cut with a cutter after water cooling,
Particles (pellets) (1.8 mg / particle) were obtained from the columnar polyolefin-based resin composition. The melting point of the obtained particles was 145 ° C., and the density was 0.90 g / cm ^{3 as} measured according to JIS K7112.

Obtained particles (water content was determined to be 5.0 by setting the oil bath temperature to 154.5 ° C. by the above-described method for measuring water content).
% By weight) 100 parts by weight (1.5 kg), as a poorly water-soluble inorganic compound (inorganic dispersant)
1 part by weight and 0.005 parts by weight of sodium n-paraffin sulfonate as a surfactant (dispersing aid) were charged together with 300 parts by weight of water in the pressure-tight container 3 of the apparatus shown in FIG. After introducing air into the pressure-resistant closed container 3 and pressurizing it to the pressure shown in Table 1, 154.5 while stirring the contents of the container.
Heated to ° C. The pressure in the pressure vessel when the temperature reached 154.5 ° C. was as shown in Table 1. After that, the valve 4 at the lower part of the closed vessel is opened, and the aqueous dispersion (water-containing particles and aqueous dispersion medium) is discharged into the low-pressure vessel 6 through the orifice 5 having one opening having a diameter of 3.2 mm and a thickness of 5 mm. Pre-expanded particles 7 having a desired expansion ratio were obtained. During discharge of the aqueous dispersion, the outflow rate was kept constant by pressurizing air.
In addition, 1 in FIG. 1 is the resin particle which consists of a polyolefin resin composition, 2 is an aqueous dispersion medium.

COMPARATIVE EXAMPLES 1 AND 2 Examples 1 to 2 were repeated except that the water dispersion was discharged into a low-pressure container after heating to a pressure shown in Table 1 after heating without applying air pressure before heating. In the same manner as in Example 2, pre-expanded particles were obtained.

Comparative Example 3 Except that the diaphragm was changed to increase the outflow speed at the time of discharge,
Pre-expanded particles were obtained in the same manner as in Example 3. The expansion ratio of the obtained pre-expanded particles was measured according to the following method.

Comparative Example 4 Pre-expanded particles were obtained in the same manner as in Example 1 except that the hydrophilic polymer was not blended with the polyolefin resin. (Expansion ratio (drying ratio)) After weighing about 3 to 10 g of the pre-expanded particles and drying at 60 ° C. for 6 hours or more, the weight w
Was measured, the volume v was measured by the submersion method, the true specific gravity ρb = w / v of the pre-expanded particles was determined, and the expansion ratio K = ρr / ρb was determined from the ratio to the density ρr of the raw material composition.

[0074]

[Table 1]

[0075]

According to the present invention, pre-expanded particles comprising a specific composition of a polyolefin resin and a hydrophilic polymer are pressurized to 0.1 MPa or more with an inorganic gas without using a volatile foaming agent, or simultaneously with the softening point temperature or more. By heating to
Water and / or inorganic gas are uniformly absorbed and dispersed in the pre-expanded particles.

According to the method for producing pre-expanded particles of the present invention, water and / or an inorganic gas are used as a blowing agent to obtain a foaming ratio of 2 to 2.
Pre-expanded particles having a very small variation in magnification of 10% or less at 15 times can be obtained. As a result, an in-mold foam molded article that is economically advantageous and has good characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for producing pre-expanded particles of a polyolefin resin composition used in Examples of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 resin particles composed of polyolefin resin composition 2 aqueous dispersion medium 3 pressure tight container 4 valve 5 orifice 6 low pressure container 7 pre-expanded particles

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) C08L 77:10 67:02) F term (reference) 4F074 AA16 AA24 AA25 AA31 AC31 AD15 BA33 BA84 BC01 BC02 CA35 CA39 CC04X CC34Y CC45 DA02 4J002 AB022 AB032 BB031 BB042 BB061 BB071 BB081 BB082 BB101 BB121 BB141 BB151 BB161 BB182 BB232 BF022 BG012 BH022 BN232 BP021 CF102 CH022 CH052 CL012 CL032 CL052 DE236 DE276 DH DH

Claims (5)

[Claims] 1. A polyolefin resin composition comprising 100 parts by weight of a polyolefin resin and 0.01 to 20 parts by weight of a hydrophilic polymer, having an expansion ratio of 2 to 15
Times and number 1: Pre-expanded particles of a polyolefin-based resin composition, characterized in that the variation in magnification represented by (1) is 10% or less. 2. The pre-expanded polyolefin resin composition particles according to claim 1, wherein the polyolefin resin is a polypropylene resin. 3. The pre-expanded polyolefin resin composition particles according to claim 1, wherein the hydrophilic polymer is an ethylene ionomer. 4. A resin particle comprising a polyolefin resin composition containing (A) 100 parts by weight of a polyolefin resin and 0.01 to 20 parts by weight of a hydrophilic polymer,
(B) a poorly water-soluble inorganic compound which is a dispersant, and (C)
After the surfactant is dispersed in the aqueous dispersion medium in the closed container, and the inorganic gas is introduced into the closed container and the pressure is applied to 0.1 MPa or more, or at the same time, the resin particles are used for the softening temperature of the polyolefin resin composition or more. After heating to a temperature of 2.5 to 50% by weight, the resin particles having a water content of 2.5 to 50% by weight are discharged through a diaphragm plate at an outflow speed of 15 to 50 m / sec into an atmosphere having a pressure lower than the internal pressure in the closed vessel. A method for producing pre-expanded particles of a polyolefin-based resin composition, characterized in that: 5. The method for producing pre-expanded polyolefin resin composition particles according to claim 4, wherein the inorganic gas is nitrogen, air or an inorganic gas mainly containing these.