JP2000290420A - Method for producing pre-foamed granule of polyolefin- based resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the pre-foamed granules which have excellent flexibility and excellent shock absorbability, scarcely contract and have a high expansion ratio without using a conventional evaporable foaming agent and without deteriorating the mechanical strengths, heat resistance and water resistance of the obtained molded article foamed in the mold. SOLUTION: This method for producing the pre-foamed granules of a polyolefin-based resin comprises dispersing the granules of a polyolefin-based resin composition comprising 100 pts.wt. of the polyolefin-based resin and 0.01 to 20 pts.wt. of a hydrophilic polymer in an aqueous dispersing medium in a closed vessel, heating the dispersed resin granules at a higher temperature than the softening point of the resin granules of the polyolefin-based resin composition to obtain the water-containing resin granules having a water content of 1 to 50 wt.%, and then releasing the dispersion into a low pressure vessel having a lower pressure than the inner pressure of the closed vessel. Therein, the released pre-foamed granules are brought into contact with saturated steam and then cooled to a drying temperature over 5 min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing pre-expanded particles of a polyolefin resin composition. More specifically, the present invention relates to a method for producing pre-expanded particles of a polyolefin-based resin composition which can be suitably used as a raw material of an in-mold foam molded article.

[0002]

2. Description of the Related Art Conventionally, polyolefin resin particles are dispersed in an aqueous dispersion medium in a closed container, heated and pressurized, and then discharged into a low pressure region to obtain polyolefin resin pre-expanded particles. Is well known (for example, JP-A-59-176336).

As one of the pre-expansion methods for polyolefin resin particles, for example, as disclosed in Japanese Patent Publication No. 7-5784, thermoplastic resin particles containing a volatile blowing agent are placed in a pressure vessel. After dispersing in water and bringing the resulting mixture to a high-temperature and high-pressure state, a low-pressure atmosphere or a low-pressure atmosphere in which steam is introduced, wherein the pressure is lower than that in the pressure-resistant container and the temperature is 40 ° C. or higher. There is a method of releasing it inside and foaming it. By such a method, polyolefin-based resin pre-expanded particles which have a small shrinkage and can be suitably used for in-mold foam molding are manufactured.

[0004] Further, as a pre-expansion device for polyolefin resin pre-expanded particles, since there is no driving part and the structure is simple, it can be manufactured at a lower cost than conventional ones, and there is no failure and handling is very difficult. A pre-foaming apparatus has been developed which is simple and excellent in maintenance.
146856 publication). This prefoaming device is an excellent device capable of producing pre-expanded polyolefin resin particles having low shrinkage and suitable for use in in-mold foam molding.

On the other hand, the present inventors disperse particles of a composition comprising a polyolefin-based resin and a hydrophilic polymer in an aqueous dispersion medium and heat the mixture to a temperature equal to or higher than the softening temperature of the polyolefin-based resin composition so that the water content is 1%. ５０50% by weight of hydrated particles and then released into a low-pressure atmosphere to foam the hydrated particles, thereby providing a volatile blowing agent and / or
Without using an inorganic gas-based foaming agent, water-dispersing medium was used as a foaming agent, and a revolutionary method for producing polyolefin-based resin composition pre-expanded particles having desired physical properties was developed. (Japanese Patent Application No. 8-84124).

[0006] This technology uses water as a foaming agent, so it is inexpensive, safe without flammability, is environmentally friendly, and is more versatile than when an inorganic gas foaming agent such as air or nitrogen is used. It is an excellent technology that makes it easy to increase the expansion ratio, but since water is used as the blowing agent, the boiling point is higher and the latent heat of evaporation is higher than conventional volatile blowing agents.
If the expansion ratio of the pre-expanded particles is increased, probably because the gas permeability to the polyolefin resin is high, the expanded particles have a disadvantage that they are greatly shrunk depending on the ambient temperature released from the closed container. .

Therefore, the present inventors have disclosed in Japanese Patent Laid-Open No. 10-14 / 1998.
Using a prefoaming device disclosed in Japanese Patent Publication No. 6856, an attempt was made to use water as a blowing agent of the technology disclosed in Japanese Patent Publication No. 7-5784, but the obtained prefoamed particles were: The shrinkage was not large enough for practical use.

[0008]

Means for Solving the Problems Normally, when the polyolefin-based resin pre-expanded particles are molded in a mold, if moisture remains on the surface and / or inside of the pre-expanded particles, the polyolefin resin is charged into the mold. In some cases, poor filling may occur, lowering productivity and lowering the quality of molded products such as dimensional accuracy and mechanical strength. It is. In particular, in the case of the technique using water as the blowing agent, the importance of the drying step is higher than ever because a large amount of water exists inside the pre-expanded particles.

[0009] The drying step is usually performed by blowing hot air on the wet pre-expanded particles using a stationary drier. At this time, at the beginning of the drying step,
Temporarily the temperature around the pre-expanded particles will drop to near the dew point ("Chemical Engineering-Commentary and Exercise-", Maki Shoten, 1
First edition, March 20, 984, 157).

The present inventors have thought that this may be the cause of the shrinkage of the pre-expanded particles.

[0011] By carefully managing the temperature around the pre-expanded particles from the foaming step to the drying step, it is thought that the problem of the shrinkage can be solved. After contacting the pre-expanded particles discharged from the closed container with the saturated steam, the pre-expanded particles are cooled to the drying temperature over 5 minutes or more, and when the process proceeds to the drying step, the shrinkage of the pre-expanded particles is reduced. Is prevented,
It has been found that pre-expanded particles having a practically sufficient appearance can be obtained. Furthermore, when the expansion ratio of the obtained pre-expanded particles in which the shrinkage was reduced / prevented was measured, surprisingly, the shrinkage was larger than the expansion ratio measured after recovering the shrinkage of the pre-expanded particles larger. It was also found that the expansion ratio was improved by 2 to 6 times, and the present invention was completed.

That is, the present invention provides an aqueous dispersion of resin particles comprising a polyolefin resin composition containing 100 parts by weight (hereinafter referred to as "parts") of a polyolefin resin and 0.05 to 20 parts of a hydrophilic polymer in a closed container. The resin particles are dispersed in a solvent, and the resin particles are heated to a temperature equal to or higher than the softening temperature of the particles made of the polyolefin resin composition to obtain water-containing resin particles having a water content of 1 to 50% by weight. When pre-foaming by discharging into a low-pressure container (hereinafter, also referred to as a low-pressure container), the released particles are allowed to contact with saturated steam and then cooled to a drying temperature over 5 minutes or more. The method for producing pre-expanded polyolefin resin composition particles (claim 1), wherein the temperature in the low-pressure container is equal to or higher than the softening temperature of the polyolefin resin composition; The method for producing pre-expanded polyolefin resin composition particles according to claim 1 (claim 2), wherein saturated steam is used as a transport medium for transporting the released particles out of a low-pressure container. The method for producing pre-expanded polyolefin resin composition particles according to claim 1 or 2, wherein the internal pressure in the closed container is nitrogen,
4. The polyolefin resin composition pre-expanded particles according to claim 1, 2 or 3, wherein the pressure is increased by introducing air or an inorganic gas mainly composed of air and then pre-expanded by discharging the air into a container having a pressure lower than the internal pressure. And a method for producing pre-expanded particles of a polyolefin-based resin composition according to claims 1, 2, 3 or 4, wherein the polyolefin-based resin is a polypropylene-based resin.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, 100 parts of a polyolefin resin and 0.05 to 20 hydrophilic polymers are used.
Resin particles comprising a polyolefin-based resin composition containing a part are used for producing pre-expanded particles.

The above-mentioned polyolefin resin is a component used to obtain pre-expanded particles having a high expansion ratio and excellent balance of foaming property, moldability, mechanical strength, heat resistance and flexibility of the obtained molded article. is there.

The polyolefin resin contains olefin monomer units in an amount of 50 to 100% by weight, more preferably 70 to 10% by weight.
It is a resin containing 0% by weight and containing 0 to 50% by weight, and more preferably 0 to 30% by weight of a unit of a monomer copolymerizable with an olefin monomer. Since the polyolefin-based resin contains the olefin monomer unit in an amount of 50% by weight or more, a molded article that is lightweight and excellent in mechanical strength, workability, electrical insulation, water resistance, and chemical resistance can be obtained. The unit of the monomer copolymerizable with the olefin monomer is a component used for modifying adhesiveness, transparency, impact resistance, gas barrier properties, etc. 2% by weight to get
As described above, it is preferable to use 5% by weight or more.

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 olefin monomers such as norbornene-based monomers. Of these, ethylene,
Propylene is preferred because it is inexpensive and the properties of the resulting polymer are improved. These may be used alone,
Two or more kinds may be used in combination.

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

The melt index (MI) of the polyolefin resin is, for example, 0.5 to 30 g / 10 min for a polypropylene resin described below, and more preferably 3 to 30 g.
10 g / 10 min is preferred. The MI is 0.5 g
If it is less than / 10 minutes, the melt viscosity is too high to obtain pre-expanded particles having a high expansion ratio, and if it exceeds 30 g / 10 minutes, the melt viscosity with respect to the elongation of the resin at the time of foaming becomes low and the foam easily breaks, There is a tendency that it is difficult to obtain pre-expanded particles having a high expansion ratio.

The flexural modulus (JIS K 7203) of the polyolefin resin is, for example, 5,000 to 20,000 kg / cm for a polypropylene resin.
² G, more preferably from 8000~16000kg / cm ² G. The bending strength is 5000 kg / cm ² G
If it is less than 2,000, mechanical strength and heat resistance tend to be insufficient. If it exceeds 20,000 kg / cm ² G, the flexibility and cushioning properties of the obtained foamed molded article tend to be insufficient.

The melting point of the polyolefin resin is, for example, 125 to
A temperature of 165 ° C, more preferably 135 to 150 ° C, is preferable. When the melting point is less than 125 ° C., the heat resistance tends to be insufficient, and when it exceeds 165 ° C., the fusion property at the time of molding and the secondary foaming power tend to be insufficient.

Specific examples of the polyolefin resin include, for example, an ethylene-propylene random copolymer,
Ethylene-propylene-butene random terpolymer,
Ethylene-propylene block copolymer, polypropylene resin such as homopolypropylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer,
Examples include polyethylene resins such as ethylene-methyl methacrylate copolymer, as well as polybutene and polypentene. 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 high expansion ratio are easily obtained as compared with other polyolefin-based resins, and a molded article produced from the obtained pre-expanded particles has good mechanical strength and heat resistance. Therefore, a polypropylene-based resin is preferable.

[0022] The hydrophilic polymer is a component used to bring the polyolefin resin composition to a predetermined water content.

The hydrophilic polymer is ASTM D57
0 means a polymer having a water absorption of 0.5% by weight or more, which is a concept containing so-called hygroscopic polymer, water-absorbing polymer and water-soluble polymer.
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, and a cellulose derivative.

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,
Two or more kinds may be used in combination. 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. It is particularly excellent 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), copolymerization Nylon (EMS Hemy (EMS-CHEM)
IE AG), trade name: Grilltex, etc., with a water absorption of 1.5 to 3% by weight). These may be used alone or in combination of two or more.

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% by weight).
These may be used alone or in combination of two or more.

Specific examples of the cellulose derivative include:
For example, cellulose acetate, cellulose propionate and the like can be mentioned. These may be used alone or in combination of two or more.

Among the hygroscopic polymers, an ionomer resin, particularly the ethylene ionomer, is excellent in dispersibility in a polyolefin resin, and a polyolefin resin composition having a high water content can be obtained in a relatively small amount. Therefore, it is preferable.

The water-absorbing polymer is a polymer that absorbs water several times to several hundred times its own weight without being dissolved in water, and is hardly dehydrated even when pressure is applied.

Examples of the water-absorbing polymer are basically a cross-linked polyacrylate polymer, a starch-acrylic acid graft copolymer, a cross-linked polyvinyl alcohol polymer,
Crosslinked polyethylene oxide polymer, isobutylene-
Maleic acid copolymers and the like can be mentioned. These may be used alone or in combination of two or more.

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. These may be used alone or in combination of two or more.

Specific examples of the crosslinked polyvinyl alcohol polymer include various crosslinked polyvinyl alcohol polymers represented by Aqua Reserve GP (trade name) manufactured by Nippon Synthetic Chemical Industry Co., Ltd. These may be used alone or in combination of two or more.

Specific examples of the above-mentioned crosslinked polyethylene oxide polymer include various crosslinked polyethylene oxide polymers represented by, for example, Aqua Coke (trade name) manufactured by Sumitomo Seika Co., Ltd. These may be used alone or in combination of two or more.

Specific examples of the isobutylene-maleic acid copolymer include various isobutylene-maleic acid copolymers represented by, for example, KI gel (trade name) manufactured by Kuraray Co., Ltd. These may be used alone or in combination of two or more.

Among the above-mentioned water-absorbing polymers, crosslinked polyethylene oxide is preferred because it has excellent dispersibility in a polyolefin-based resin, and a relatively small amount of water-containing resin particles having a high water content can be obtained.

The above-mentioned water-soluble polymer is a polymer that is soluble in water at normal or high temperature.

Examples of the water-soluble polymer include poly (meth) acrylic acid-based polymers, poly (meth) acrylate-based polymers, polyvinyl alcohol-based polymers, polyethylene oxide-based polymers, and water-soluble polymers. Cellulose derivatives and the like can be mentioned. These may be used alone,
More than one species may be used in combination.

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. These may be used alone or in combination of two or more.

Specific examples of the poly (meth) acrylate polymer include, for example, sodium polyacrylate,
Examples thereof include sodium polymethacrylate, potassium polyacrylate, and potassium polymethacrylate. These may be used alone or in combination of two or more.

Specific examples of the polyvinyl alcohol-based polymer include, for example, polyvinyl alcohol and vinyl alcohol-vinyl acetate copolymer. These may be used alone or in combination of two or more.

Specific examples of the polyethylene oxide-based polymer include polyethylene oxide having a molecular weight of tens of thousands to several millions. These may be used alone or in combination of two or more.

Specific examples of the water-soluble cellulose derivative include carboxymethyl cellulose, hydroxyethyl cellulose and the like. These may be used alone or in combination of two or more.

The above-mentioned hygroscopic polymer, water-absorbing polymer and water-soluble polymer may be used alone or in combination of two or more.

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, and are used at a temperature not lower than the softening temperature of the polyolefin resin. In order to obtain a polyolefin-based resin composition which preferably becomes a water-containing resin particle having a water content of 1 to 50% by weight when heated to a temperature equal to or lower than the softening temperature + 20 ° C., usually 100 parts of the polyolefin-based resin is used. , 0.05 part or more, preferably 0.5 part or more. 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 20 parts or less, preferably 10 parts or less.

When the polyolefin resin composition used in the present invention contains a filler, that is, an inorganic filler and / or an organic filler, pre-expanded particles having uniform cells and high expansion ratio can be obtained. Preferred from the point.

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 uniform cells and a high expansion ratio can be easily obtained.

The organic filler is not particularly limited as long as it is solid at a heating temperature 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.

The fillers may be used alone or in combination of two or more.

With respect to the average particle size of the filler, pre-expanded particles having uniform cells and high expansion ratio can be obtained, and a molded article excellent in mechanical strength, flexibility and the like can be obtained from the pre-expanded particles. From the point, 50 μm or less, further 10 μm
It is preferably at most 0.1 μm, more preferably at least 0.5 μm, from the viewpoint of secondary aggregation and handling workability.

The amount of the filler to be used is preferably 0.01 part or more, more preferably 0.1 part, per 100 parts of the polyolefin resin in order to obtain pre-expanded particles having a high expansion ratio.
1 part or more is preferable, and when forming the pre-expanded particles, from the viewpoint of exhibiting excellent fusibility and obtaining a molded article excellent in mechanical strength and flexibility from the pre-expanded particles, It is preferably at most 3 parts, more preferably at most 2 parts.

The polyolefin resin composition used in the present invention, which contains the polyolefin resin, hydrophilic polymer, and if necessary, a filler, is usually melt-kneaded using an extruder, kneader, Banbury mixer, roll, or the like. Then, it is preferable to obtain particles formed into particles of a desired shape that can be easily used for preliminary foaming, such as columnar, elliptical, spherical, cubic, and rectangular parallelepiped.

The conditions for producing the particles and the size of the resin particles are not particularly limited. For example, the resin particles obtained by melt-kneading in an extruder are usually 0.5 to 5 m
g / grain.

In the present invention, the resin particles made of the polyolefin resin composition are dispersed in an aqueous dispersion medium in a closed container, and the resin particles are heated to a temperature higher than the softening temperature of the resin particles made of the polyolefin resin composition. , And preferably, an inorganic gas is introduced into the closed vessel to adjust the pressure in the close vessel to 6 to 75 kgf / cm ² and the water content to 1
５０50% by weight of the water-containing resin particles, and then, while pre-foaming by discharging into a container having a pressure lower than the internal pressure of the closed container while maintaining the pressure, contacting the discharged particles with saturated steam. Thereafter, the polyolefin-based resin composition pre-expanded particles are produced by cooling to a drying temperature over 5 minutes or more.

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

When dispersing the particles in the aqueous dispersion medium in the closed container, as a dispersant, for example, tribasic calcium phosphate, basic magnesium carbonate, basic zinc carbonate, calcium carbonate or the like, or as a small amount of a surfactant, For example, sodium dodecylbenzene sulfonate, sodium n-paraffin sulfonate, sodium α-olefin sulfonate and the like can be used. The amounts of the dispersing agent and the surfactant are not particularly limited, and may be amounts generally used.

The amount of the resin particles comprising the polyolefin resin composition dispersed in the aqueous dispersion medium is 3 to 100 parts, preferably 10 to 5 parts, per 100 parts of the aqueous dispersion medium.
0 parts is preferred. When the amount of the resin particles is less than 3 parts, the productivity is reduced and the method is not economical.
During heating, the resin particles tend to fuse together in the container.

The temperature at which the resin particles are dispersed and heated is a temperature not lower than the softening temperature of the polyolefin resin composition to be used, preferably a temperature not higher than the melting point + 20 ° C., and further a temperature not lower than the melting point + 5 ° C. to the melting point + 15 ° C. Is preferred. Specifically, for example, in the case of an ethylene-propylene copolymer having a softening temperature of 63 ° C and a melting point of 145 ° C, the temperature is preferably 63 ° C or more, more preferably 63 to 165 ° C, particularly preferably 150 to 160 ° C. When the temperature exceeds 165 ° C., the mechanical strength and heat resistance of the obtained foam are not sufficient, and the resin particles tend to fuse with each other in the container.

As described above, the specific resin particles are dispersed in the aqueous dispersion medium, heated to a temperature higher than the softening temperature of the polyolefin resin composition, and usually stirred for 10 minutes to 12 hours to form the polyolefin resin composition. The water content of the resin particles can be adjusted to 1 to 50% by weight, preferably 3 to 30% by weight. In addition, the resin particles can be made into uniform pre-expanded particles without forming a lump in the closed container during the production of the pre-expanded particles. When the water content is less than 1% by weight, it is difficult to obtain a sufficient expansion ratio, and the expansion ratio tends to be less than 3 times. When the water content is more than 50% by weight, the dispersibility of the resin particles in the aqueous dispersion medium is reduced, and the pre-expansion is performed. During the production of the particles, the resin particles comprising the polyolefin-based resin composition become a lump in a closed container, and it is difficult to uniformly prefoam the resin particles. The moisture content can be adjusted by adjusting the heating temperature, the heating time, and the like.

The water absorption of the hydrophilic polymer is a value measured at room temperature, and the water content is a value measured at a high temperature (above the softening temperature of the resin composition). Is 0.5% by weight or more, a water content of 1% by weight or more is obtained.

The softening temperature of the polyolefin resin composition indicates a heat distortion temperature of the polyolefin resin composition and is determined in accordance with ASTM D648.

The melting point of the polyolefin resin composition is from 40 ° C. to 220 ° C. by DSC.
The temperature was raised at a rate of 10 ° C./min, cooled to 40 ° C. at a rate of 10 ° C./min, and then raised again to a temperature of 220 ° C. at a rate of 10 ° C./min. is there. .

The water content is the water content under a water vapor pressure at a temperature equal to or higher than the softening temperature of the polyolefin resin composition, and is determined as follows.

That is, in a 300 cc pressure-resistant ampoule, resin particles 50 made of the polyolefin resin composition were used.
g, water 150 g, powdery basic tribasic calcium phosphate 0.5 g as a dispersant, and sodium n-paraffin sulfonate 0.03 g, and after sealing, an oil bath set at a temperature equal to or higher than the softening temperature of the polyolefin resin composition. 3 in
Heat treatment for hours. After further cooling to room temperature, take out,
After thoroughly washing with water to remove the dispersant, the weight (X) of the water-containing particles of the obtained polyolefin-based resin composition from which moisture adhering to the surface has been removed is determined, and then a temperature 20 ° C. higher than the softening temperature of the resin particles. 3 in the oven set to
The weight (Y) after drying for a period of time and cooling to room temperature in a desiccator is determined, and is determined according to the formula: water content (% by weight) = {(XY) / Y} × 100. The water content in the case where a filler or the like is contained in the resin particles made of the polyolefin resin composition is a water content based on the total amount of the polyolefin resin and the hydrophilic polymer.

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.

[0066] The pressure in the closed vessel after the introduction of the inorganic gas is preferably 6~75kg / cm ² G as described above, 10 to 70 kg / cm ² G are preferred. When the pressure is less than 6 kg / cm ² G, the effect of introducing an inorganic gas, that is, the effect of obtaining pre-expanded particles having a higher expansion ratio than when no inorganic gas is used tends to be insufficient, If it exceeds 75 kg / cm ² G, the cell diameter tends to be too fine, the closed cell ratio decreases, and the shrinkage, shape stability, mechanical strength and heat resistance of the molded article tend to be impaired.

It is preferable that the pressure inside the container during the discharge is maintained at the above-mentioned ultimate pressure.

There is no particular limitation on the time from when the inorganic gas is pressurized to reach a predetermined pressure until the water-containing resin particles are discharged together with the aqueous dispersion medium into the low-pressure container, but from the viewpoint of improving productivity. If possible, it is preferable that the length be as short as possible.

The pressure lower than the internal pressure of the closed container may be a pressure lower than the internal pressure of the closed container, and a pressure near the atmospheric pressure is usually obtained.

Further, the low-pressure container is a space including a scattering locus of a mixture of the discharged particles and water,
A container that allows the released particles to come into contact with saturated steam. One example will be described with reference to the low-pressure container 6 shown in the schematic explanatory view shown in FIG. 1. The shape is a duct having a width of 400 mm × a height of 400 mm × a length of 2000 mm, and the steam inlet 8 at the front end of the closed container 3.
And a filtration section 12 is provided at the rear end to separate the discharged particles 7 and the dispersion medium 10 from each other.
0 is discharged from the outlet 9, and the discharged particles 7 are transported by the transport medium 14 supplied from the transport medium supply unit 11 at the rear end.
A container that is transported to the dryer 15 through the low-pressure container outlet 13 at the same time is exemplified, but the container is not limited to such a container. XX of the low-pressure container 6
A cross-sectional view is schematically shown in FIG.

The saturated steam is used to reduce or prevent the shrinkage of the particles by bringing them into contact with the released particles, and to give a practically sufficient appearance. It is determined by the pressure of the container. For example, when the pressure of the low-pressure container is near atmospheric pressure, it is usually water vapor within a temperature range of 90 to 110 ° C.

The temperature in the low-pressure container is preferably not lower than the softening temperature and not higher than the melting point of the polyolefin resin composition. If the temperature in the low-pressure container is lower than the softening temperature, water in the particles will rapidly aggregate,
Particle shrinkage is large, making it difficult to produce particles that can withstand practical use.If the melting point is exceeded, the bubbles of pre-expanded particles due to release tend to break, and particles tend to fuse together Occurs.

The time for which the released particles are brought into contact with the saturated steam is 0.1 seconds or more, preferably 1 second or more. If the contact time is less than 0.1 seconds, the particles are rapidly cooled. As a result, the internal water vapor aggregates, resulting in particles having large shrinkage. The upper limit of the contact time is usually about 3 seconds, and the effect is hardly changed even if the contact is made longer.

The particles that have been brought into contact with the saturated steam are transported to the dryer by the transport medium and cooled to the drying temperature in 5 minutes or more.

Examples of the transport medium include saturated steam, nitrogen, air, and inorganic gas mainly composed of these. Among them, it is preferable to use saturated steam and to carry out the contact with the released particles and the transport of the particles at one time.

The temperature of the water vapor used as the transport medium is preferably adjusted within a temperature range from the softening temperature to the melting point of the raw resin composition used for the pre-expanded particles.

The reason why it takes 5 minutes or more to cool the particles to the drying temperature is to allow the particles to gradually cool.
Preferably, it takes 0 minutes. If the cooling time is less than 5 minutes,
Before the resin becomes sufficiently hard, the water vapor inside the pre-expanded particles condenses and the pre-expanded particles shrink. Even after shrinking once and drying, shrinkage does not completely recover.

In drying, it is preferable that the inorganic gas is continuously or intermittently introduced into the drier to lower the drying temperature, since pre-expanded particles that do not shrink can be obtained in a short time.

The drying temperature is not higher than the melting point of the raw resin composition of the pre-expanded particles and is not lower than 40 ° C.
The temperature of 0 ° C. or higher, particularly 60 ° C. or higher, is because the surface and / or internal moisture of the wet pre-expanded particles evaporates quickly, and the time required for drying can be shortened. It is preferable because it leads to improvement in performance. If the drying temperature is too low, the drying time is prolonged, poor drying is likely to occur, and the particles are likely to contract. On the other hand, if the drying temperature is too high, the air bubbles of the particles will break, and the particles will easily fuse together.

After the particles have been transported to the dryer, the transport line is closed, and then the inorganic gas is fed in while controlling the flow rate to lower the temperature to the drying temperature.

The polyolefin resin composition pre-expanded particles thus obtained have an expansion ratio of 3 to 50 times, more preferably 4 to 40 times, a closed cell ratio of 80 to 100%, further 90 to 100%, and an average Bubble diameter of 50 to 500 μm,
Further, it preferably has a thickness of 50 to 300 μm. When the expansion ratio is less than 3 times, the flexibility of the obtained molded article,
If the buffering properties and the like tend to be insufficient, and if it exceeds 50 times, the mechanical strength, heat resistance and the like of the obtained molded article tend to be insufficient. Further, when the closed cell ratio is less than 80%, the secondary foaming power is insufficient, so that poor fusion occurs at the time of molding, and the mechanical strength and the like of the obtained molded body are likely to be reduced. When the average bubble diameter is less than 50 μm,
Problems such as distortion of the shape of the obtained molded body are likely to occur, and when it exceeds 500 μm, the mechanical strength of the obtained molded body tends to decrease.

The pre-expanded particles of the polyolefin resin composition produced by the method of the present invention have a closed cell ratio of 80% or more. The molded article may be filled with a molding die after being air-impregnated by time treatment, and then subjected to foam heating in the die by steam heating to produce a molded product as the die. The foam molded article thus obtained is excellent in flexibility and cushioning property, and has a small dimensional shrinkage and small shape deformation, so that it has extremely high commercial value.

[0083]

The production method of 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.

The methods for evaluating the expansion ratio of the obtained pre-expanded particles are summarized below.

(Expansion Ratio (Dry Ratio)) Pre-expanded Particle 3
After taking about 10 g and drying at 60 ° C. for 6 hours or more, the weight w is measured, the volume v is measured by a submerged method, and the true specific gravity ρ _b = w / v of the pre-expanded particles is determined. Density ρ _r
The ratio of to determine the expansion ratio K = ρ _r / ρ _b.

(Containing Ratio) The pre-expanded particles immediately after foaming
The foaming was measured by using the pre-expanded particles in a state in which the pressure inside the pre-expanded particles was raised above the atmospheric pressure and the shrinkage of the pre-expanded particles was completely recovered by allowing to stand for 2 hours under an air pressure of 0 kgf / cm ^2. Magnification, which is considered to be the maximum possible magnification of the pre-expanded particles.

(Shrinkage recovery rate) This is a value obtained by dividing the drying magnification by the composition ratio, and is an index of how much the magnification has recovered by drying.

Example 1 Polyolefin resin (ethylene-propylene random copolymer, density 0.91 g / cm ³ , ethylene unit content 3% by weight, MI = 5.5 g / 10 min, flexural modulus 10
An ionomer (85% by weight of ethylene units and 15 units of methacrylic acid units) in which the carboxyl group of a hydrophilic polymer (ethylene-methacrylic acid copolymer was converted to a salt with sodium ions and crosslinked between molecules was added to 100 parts of 000 kg / cm ² G). % Of methacrylic acid unit.
Form a salt), MI = 0.9 g / 10 min,
2 parts of melting point 89 ° C., water absorption 1%) and 1 part of talc (average particle diameter 7 μm) were added, and the mixture was fed to a 50 mmφ single screw extruder, melt-kneaded, extruded from a 1.5 mmφ cylindrical die, and cooled with water. After cutting with a cutter, resin particles (pellets) composed of a columnar polyolefin resin composition
(1.8 mg / particle) was obtained. The obtained resin particles had a softening temperature of 63 ° C., a melting point of 145 ° C. and a density measured by JIS K 7112 of 0.90 g / cm ³ .

100 parts of the obtained resin particles, 1.4 parts of tribasic calcium phosphate as a dispersant and 0.03 parts of sodium dodecylbenzenesulfonate as a surfactant were added to water 2 parts.
Pressure-resistant sealed container 3 of the apparatus as shown in FIG.
And heated to 155.0 ° C. while stirring the contents of the container. The pressure at this time was about 5 kg / cm ² G.

After that, the pressure in the container was increased to 27 kg / cm ² G by air pressurization. Immediately, the valve 4 at the lower part of the closed container was opened, and the aqueous dispersion (hydrous particles and aqueous dispersion medium) was passed through the orifice 5 having a diameter of 4 mmφ. Internal pressure 1.0kgf
/ Cm ² to obtain a pre-expanded particle having a closed cell structure. At this time, the pressure was maintained using air so that the pressure in the container did not decrease during the discharge.

In the low-pressure vessel 6, 1.0 kgf / cm ² of saturated steam at about 100 ° C. was introduced from the steam inlet 8 and brought into contact with the particles 7 discharged.

The supply of the saturated steam was carried out from the transport medium supply unit 11 shown in FIG. 1, and the discharged particles 7 were transferred from the low-pressure container 6 to the dryer 15. The time required for transferring the particles 7 discharged into the low-pressure vessel 6 through the orifice 5 to the dryer 15 through the low-pressure vessel outlet 13 was about 3 seconds.

After transporting the particles to the dryer 15, the transport line is closed, and while adjusting the temperature in the dryer 15 with the temperature recorder 17, the flow rate of nitrogen gas is adjusted from the N ₂ inlet 16 and introduced. The temperature in the dryer 15 was reduced from 100 ° C. to 90 ° C. over 20 minutes. After lowering the temperature in the dryer 15 to 90 ° C., which is the drying temperature, hot air at 90 ° C. was introduced into the dryer 15 through the drying air blower 18 and the air heater 19 and dried for 3 hours.

In FIG. 1, 1 is a polyolefin resin particle, 2 is an aqueous dispersion medium, and 20 is a dry air abandonment line.

The expansion ratio and the content ratio of the obtained pre-expanded particles were measured to determine the shrinkage recovery rate. Table 1 shows the results.

COMPARATIVE EXAMPLE 1 The saturated water vapor was not transported, and all the particles were transported to the dryer.
The same operation as in Example 1 was carried out except that no steam was blown into the transport medium supply section) to obtain pre-expanded particles. Table 1 shows the results.

[0097]

[Table 1]

[0098]

According to the production method of the present invention, pre-expanded particles which prevent shrinkage and have a practically sufficient appearance can be obtained. Further, pre-expanded particles having a high expansion ratio can be obtained.
Further, since the pre-expanded particles have a large shrinkage recovery effect by drying, there is no need to provide a step for shrinkage recovery,
Economically advantageous.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of an apparatus for producing pre-expanded particles used in Examples and Comparative Examples of the present invention.

FIG. 2 is a schematic explanatory view schematically showing a XX cross-sectional view of the low-pressure container 6.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 resin particles composed of polyolefin resin composition 2 aqueous dispersion medium 3 pressure-tight closed vessel 4 valve 5 orifice 6 low-pressure vessel 7 discharged particles 8 vapor inlet 9 discharge port 10 dispersion medium 11 transport medium supply section 12 filtration section 13 low pressure container outlet 14 of transport 15 dryer 16 N ₂ blow port 17 temperature recorder 18 dry air blower 19 air heater 20 dry air abandoned line

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeshi Obayashi 5-1-1 Torikai Nishi, Settsu-shi, Osaka Inside Kanebuchi Chemical Industry Co., Ltd. (72) Inventor Shigehiko Akamatsu 5-1-1 Torikai Nishi, Settsu-shi, Osaka 1 Kanebuchi Chemical Industry Co., Ltd. F term (reference) 4F074 AA16 AA17 AA23 AA24 BA34 CA34 CA35 CA38 CA39 CC04X CC05Z CC28Z CC32X CC34X CC34Y CC36Z 4J002 AB022 AB032 BB031 BB051 BB061 BB071 BB121 BB171 BB232

Claims (5)

[Claims] 1. A resin particle comprising a polyolefin resin composition containing 100 parts by weight of a polyolefin resin and 0.05 to 20 parts by weight of a hydrophilic polymer is dispersed in an aqueous dispersion medium in a closed vessel. After heating to a temperature equal to or higher than the softening temperature of the particles made of the polyolefin-based resin composition to obtain water-containing resin particles having a water content of 1 to 50% by weight, the particles are discharged into a container having a pressure lower than the internal pressure in the closed container. A method for producing polyolefin resin composition pre-expanded particles, wherein the pre-expanded particles are cooled to a drying temperature over 5 minutes or more after contacting the discharged particles with saturated steam when pre-expanded. 2. The low-pressure container has a temperature within a range from the softening temperature to the melting point of the polyolefin resin composition.
A method for producing the pre-expanded particles of the polyolefin resin composition according to the above. 3. The method according to claim 1, wherein saturated water vapor is used as a transport medium for transporting the released particles out of the low-pressure container.
Or the method for producing pre-expanded particles of the polyolefin resin composition according to 2 above. 4. The method according to claim 1, wherein the internal pressure in the closed container is increased by introducing nitrogen, air or an inorganic gas mainly composed of nitrogen and air, and then pre-foamed by discharging the gas into the container at a lower pressure than the internal pressure. 4. The method for producing pre-expanded polyolefin resin composition particles according to 1, 2, or 3. 5. The method for producing pre-expanded polyolefin resin composition particles according to claim 1, wherein the polyolefin resin is a polypropylene resin.