JPH10130421A - Preparation of foamed resin particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for preparing an antistatic, foamed resin particle which is stable in the state of suspension in the step of impregnation of a foaming agent, is free from flat, blocked and other irregular shape particles, and, in molding, has excellent fillability into a narrow portion and can provide a molding having good appearance. SOLUTION: This process for preparing a foamed resin particle comprises the steps of: placing a polyolefin resin particle contg. 0.1 to 5 pts.wt. antistatic agent, water, an inorg. dispersant, a dispersing assistant, and a volatile foaming agent into an autoclave; heating the mixture to a temp. of the softening point of the resin particle or above while stirring to impregnate the resin particle with the volatile foaming agent; and foaming the resin particle impregnated with the foaming agent. The dispersing assistant used is a nonionic surfactant having an HLB value of 5 to 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing foamed resin particles, and more particularly, to a method for producing foamed resin particles having excellent anti-static properties and excellent workability without abnormally shaped particles.

[0002]

2. Description of the Related Art Conventionally, foamed polyolefin resin foams are excellent in heat resistance, chemical resistance, impact resistance, etc., and therefore, shock absorbing materials such as bumper cores, helmets, and cushioning packaging materials for various devices. It is used for such purposes. However, since the polyolefin-based resin foam molded article has a high surface specific resistance and is easily charged, dust is easily adsorbed on the surface of the molded article, and its use in electrical equipment, cushioning packaging materials, component trays, and the like is limited.

[0003] In order to solve the above problems, there is known a method for producing expanded resin particles impregnated with an antistatic agent (Japanese Patent Application Laid-Open Nos. 3-28239 and 7-30489).
No. 5, JP-A-7-330942, JP-A-8-330942
No. 12798, etc.). By the way, in these methods, in the step of impregnating the resin particles with a foaming agent, an anionic surfactant is used as a dispersing aid in order to use an inorganic dispersant as a dispersant and further stabilize a suspension state. Used together.

However, in the above method, when the amount of the antistatic agent added is large or when the amount of the resin particles is large in order to enhance the productivity, the suspension state is not stabilized during the impregnation with the foaming agent. The obtained foaming agent-impregnated resin particles and the subsequent foaming resin particles contain a large amount of flat shaped particles or agglomerates formed by fusing two or more particles (hereinafter referred to as blocking). The foamed resin particles having such a blocking have a drawback in that the compactability of the compact is poor during molding and a compact having excellent surface appearance cannot be obtained.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a stable suspension state in a foaming agent impregnating step, and therefore, an abnormal shape such as a flat shape or a blocking shape. An object of the present invention is to provide a method for producing foamed resin particles having antistatic properties, which can provide a molded article having no particles and excellent in detail filling property and surface appearance during molding.

[0006]

That is, the gist of the present invention is to provide a polyolefin resin particle containing 0.1 to 5 parts by weight of an antistatic agent, water, an inorganic dispersant, a dispersing aid and a volatile foaming agent. After being contained in a pressure vessel, the temperature is raised to a temperature equal to or higher than the softening point of the resin particles under stirring conditions to impregnate the resin particles with a volatile blowing agent, and then expand the obtained blowing agent-impregnated resin particles. A method for producing expanded resin particles, comprising using a nonionic surfactant having an HLB value of 5 to 15 as the dispersing agent.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
First, in the present invention, polyolefin-based resin particles containing an antistatic agent, water, an inorganic dispersant, a dispersing aid and a volatile foaming agent are accommodated in a pressure vessel, and then the resin particles are stirred under stirring conditions. The temperature is raised to the softening point temperature or higher to impregnate the resin particles with the volatile foaming agent.

The above-mentioned polyolefin resin is usually a propylene homopolymer, an ethylene / propylene random copolymer, a 11 / butene / propylene random copolymer, an ethylene / 1 / butene / propylene random copolymer, a propylene / propylene random copolymer. Random copolymer of α-olefin and propylene such as 11-hexene random copolymer, block copolymer of ethylene / propylene, block copolymer of α-olefin and propylene such as 11-butene / propylene block copolymer And polyethylene resins such as high-pressure low-density polyethylene, high-density polyethylene, and linear low-density polyethylene. Two or more of these resins may be used in combination.

As the above-mentioned polyolefin resin, a polypropylene resin having high compressive stress, high rigidity, excellent buffering properties and heat resistance even if the density is low is preferable. Temperature dependence, dimensional stability,
A 1-butene / propylene random copolymer containing 5 to 20% by weight of 1-butene excellent in moldability and the like is particularly preferred.

The above-mentioned polyolefin resin may be used in combination with another resin or elastomer for the purpose of reforming, as long as the properties of the polyolefin resin are not impaired. As such an elastomer, for example, ethylene-
Elastomers such as propylene-based elastomers and polybutadiene are exemplified. These resins and elastomers can be mixed in a proportion of usually less than 100 parts by weight, preferably less than 50 parts by weight, based on 100 parts by weight of the polyolefin-based resin.

As the above-mentioned antistatic agent, one having an excellent antistatic property suitable for polyolefin resins can be selected from cationic, anionic, amphoteric and nonionic types. Among these, nonionic antistatic agents such as fatty acid glycerin esters and polyoxyethylene alkylamines are preferred because they have good compatibility with polyolefin resins, do not easily discolor, and have heat resistance. Further, an ethanolamine-based antistatic agent such as alkyldiethanolamine monoalkylate is particularly preferable because it has excellent immediate action and durability.

The molecular weight of the above antistatic agent is usually 200
１０００1000, preferably 300３００900. The addition amount of the antistatic agent is 0.1 to 5 parts by weight, preferably 1 to 4 parts by weight, based on 100 parts by weight of the resin particles.

The polyolefin-based resin particles containing an antistatic agent are phosphorus-based, phenol-based,
An antioxidant such as a sulfur-based compound, and a hindered amine-based light stabilizer for improving weather resistance may be added. In addition, an ultraviolet absorber, a metal deactivator, a pigment, a dye, an inorganic filler, and the like may be added. These may be used in combination of two or more. In addition, the polyolefin-based resin particles may contain a rosin acid ester-based antistatic auxiliary agent such as rosin-modified pentaerythritol in order to cause a molded article obtained from the foamed resin particles to exhibit an antistatic property in a short time. Good.

The polyolefin resin particles containing the antistatic agent are prepared by dispersing the antistatic agent and the above-mentioned various additives in the polyolefin resin particles, and extruding the resulting mixture in a molten state to form pellets.

As a method for dispersing an antistatic agent or the like in the polyolefin resin particles, a melt kneading method, a heat impregnation method, a melt coprecipitation method and the like are usually mentioned, and the melt kneading method is preferably used. In the melt-kneading method, a polyolefin-based resin is heated by a kneader such as an extruder, a Banbury mixer, and a mixing roll, and various additives are added and kneaded to uniformly disperse the resin in the resin.

Then, in order to make the dispersibility of the additives uniform, a masterbatch containing various additives at a high concentration is prepared, and the masterbatch and the resin are melt-kneaded with an extruder to mix the various additives. A method of uniformly dispersing is preferred. Generally, the above-mentioned melt-kneaded material is extruded from an orifice provided at the tip of an extruder, and is appropriately cut into resin particles.

The water used in the present invention acts as a dispersion medium, and the amount of the water is usually 200 to 500 parts by weight based on 100 parts by weight of the resin particles. Examples of the inorganic dispersant include aluminum oxide, titanium oxide, calcium carbonate, basic magnesium carbonate, and tribasic calcium phosphate. The amount of the resin particles 100
Usually 0.5 to 8 parts by weight, preferably 1 to 1 part by weight
5 parts by weight.

In the present invention, HL is used as a dispersing aid.
It is necessary to use a nonionic surfactant having a B value of 5 to 15, preferably 6 to 13. When the HLB value is less than 5 or when the HLB value exceeds 15, the anti-blocking effect is not exhibited.

According to the present invention, the use of the nonionic surfactant having the above HLB value makes it possible to stabilize the suspension state of the resin particles containing the antistatic agent during the impregnation of the blowing agent, A molded article that does not contain abnormally shaped particles such as flat and blocking particles and has excellent detail filling properties and surface appearance during molding can be obtained.

The above nonionic surfactants include H
Any nonionic surfactant may be used as long as the LB value is within the above range, but a polyoxyethylene condensation type is usually used. As the polyoxyethylene condensation type nonionic surfactant, an alkylphenol represented by the following general formula, which has excellent heat stability, acid resistance, alkali resistance, and hard water resistance, and has a high interfacial tension lowering effect. Are preferred. As the condensate, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether and the like are preferable.

[0021]

## STR2 ## _{R-Ph-O- (CH 2} CH 2 O) n -H ( where, R represents an alkyl group having 8 to 12 carbon atoms, Ph represents a phenyl group, n is an integer of 5-30.)

The amount of the nonionic surfactant added is as follows:
Depending on the ratio of the resin particles, water, inorganic dispersant, volatile foaming agent and the like, it is usually in the range of 0.01 to 1 part by weight based on 100 parts by weight of the resin particles. When the amount of the nonionic surfactant is less than 0.01 part by weight, sufficient blocking tends not to be obtained. When the amount exceeds 1 part by weight, foaming becomes severe and foamed resin particles and / or foamed Handling in post-treatment steps such as washing and drying of the resin particles becomes difficult.

The HLB value is calculated according to the following J.V. T. Dav
It can be obtained from the equation of is.

[0024]

HLB = Σ (number of hydrophilic groups) −Σ (number of hydrophobic groups) +7

Examples of the volatile foaming agent include volatile hydrocarbons such as butane, pentane and propane; halogenated hydrocarbons such as monochloromethane, dichloromethane and dichlorodifluoroethane; and inorganic gases such as carbon dioxide and nitrogen. Can be These may be used in combination of two or more.

The amount of the volatile foaming agent varies depending on the expansion ratio of the foamed particles, the type of the foaming agent, the ratio of the resin particles, water and the like, the impregnation or foaming temperature, etc. It is in the range of ４０40 parts by weight.

In the present invention, in order to impregnate the resin particles with a volatile foaming agent, polyolefin resin particles containing an antistatic agent, water, an inorganic dispersant, a dispersing aid and a volatile foaming agent are placed in a pressure vessel. Then, the temperature is raised to a temperature equal to or higher than the softening point of the resin particles under stirring conditions. In this case, the stirring conditions are not particularly limited, but the stirring is performed so as to obtain a sufficient suspension state, and the heating temperature is usually lower than the melting point of the resin particles.

Next, in the present invention, the foaming agent impregnated resin particles are foamed. As the foaming, a method of discharging the foaming agent-impregnated resin from a content discharge port provided at one end in the pressure-resistant container to an atmosphere having a pressure lower than the internal pressure of the pressure-resistant container is preferable. However, a method may be used in which the pressure-resistant container is cooled to a temperature equal to or lower than the softening point of the resin particles, and then the blowing agent-impregnated resin particles are taken out, transferred to another container, and then brought into contact with a heating medium such as steam to cause foaming.

The foamed resin particles having antistatic properties obtained in the present invention do not contain abnormally shaped particles, and the molded product is excellent in fineness filling property and surface appearance. A molded article obtained from such foamed resin particles is excellent in antistatic properties, and thus is suitably used for electrical equipment, cushioning packaging materials, component trays, and the like.

[0030]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. In addition, in each of the following examples, each physical property was obtained as follows.

<Abnormal Shape Particle Amount> Expanded Resin Particle 1000
g was spread on white paper to select abnormally shaped particles, the weight (g) thereof was measured, and the ratio (%) of the abnormally shaped particle weight (g) to the foamed resin particles 1000 (g) was shown.

<Appearance of the molded body> The rising portion, the flat bottom portion, etc. of the molded body were visually judged and evaluated according to the criteria shown in Table 1 below.

[0033]

[Table 1] <Detailed filling property> ：: The foamed resin particles are filled into the rising details. X: Wrinkles were generated due to poor filling properties at the rising portion. <Surface Appearance> ：: Surface is smooth with no gap between foamed resin particles. X: The surface is not smooth because there are gaps in the expanded resin particles.

<Surface specific resistance> Humidity 55%, temperature 25
After leaving the sample at 48 ° C for 48 hours, a surface resistivity meter
("Hirester, detection terminal HR-100 round type" manufactured by Dia Instruments) was measured at an applied voltage of 500 V for 10 seconds. The surface specific resistance was represented by the average of the measured values.

Example 1 Butene-1 / propylene random copolymer (butene content: 10% by weight, melting point: 151 ° C., MFR: 10 g / 10 mi)
n) 100 parts by weight, 3 parts by weight of stearyl diethanolamine monostearate (antistatic agent) and 0.1 part by weight of tris (2,4-di-t-butylphenyl) phosphate (thermal deterioration inhibitor) in a ribbon blender 20
Mix for minutes.

This mixture was melt-mixed at 220 ° C. in a single screw extruder having a diameter of 60 mm and extruded from 50 orifices having a diameter of 1.5 mm. The obtained 50 strands were cooled and solidified by passing through a cooling water tank, and then dried by passing through a dryer that blows out hot air at 70 ° C. to obtain strands having a diameter of 1 mm. The obtained strand was cut into a length of about 2 mm by a rotary blade type cutter.

In a pressure vessel, 100 parts by weight of the above resin particles, 300 parts by weight of water, 5 parts by weight of tribasic calcium phosphate (inorganic dispersant), and polyoxyethylene nonyl phenyl ether (HLB value) having 11 moles of oxyethylene added were used. 6.7) 0.1 part by weight of (dispersion aid) and 25 parts by weight of butane (volatile foaming agent) are accommodated, and the temperature in the pressure vessel is raised to 140 ° C. in 60 minutes under stirring conditions for 15 minutes. Held. The pressure in the pressure vessel at this time is 20 kg / cm ²
Met. Then, the diameter 2 provided at the lower part of the pressure vessel
The contents were discharged from an outlet of 0 mm into a container at atmospheric pressure to obtain foamed resin particles.

Next, an aqueous solution of nitric acid having a pH of 2 was applied to the foamed resin particles from a spray nozzle provided at the top of the container under atmospheric pressure.
By spraying for 0 minutes, the tribasic calcium phosphate on the surface of the foamed resin particles was removed while dissolving. Thereafter, the liquid in the container at atmospheric pressure was discharged, and water was sprayed from the spray nozzle for 20 minutes to wash the nitric acid aqueous solution on the surface of the foamed resin particles. The obtained foamed resin particles were dehydrated by a centrifugal separator and dried in a drying chamber at 60 ° C. for 24 hours. The expanded resin particles have a density of 18
g / L, and had no abnormally shaped particles such as blocking at all, and was uniform in shape.

After the above foamed resin particles are compression-filled into a mold capable of obtaining a box-shaped molded body having a rising portion with a thickness of 10 mm and a height of 50 mm, 3.0 kg / cm ² is introduced into the mold.
G steam was introduced to thermally fuse the foamed resin particles to each other. Then, after cooling water was introduced into the mold to cool the molded body, the foamed molded body was taken out of the mold and dried in a drying chamber at 60 ° C. for 24 hours. This molded product was sufficiently filled with the foamed resin particles even in the rising portion, and was excellent in detail filling properties, surface appearance, and the like. In addition, this molded body has a density of 30.
g / L, and the surface specific resistance was in the range of 10 ¹⁰ to 10 ¹¹ Ω. Table 2 summarizes the manufacturing conditions and the characteristics of the molded product.

Examples 2 to 9 and Comparative Examples 1 to 4 The procedure of Example 1 was repeated except that the particles shown in Tables 2, 4 and 6 were used as the foamed resin particles and the conditions shown in the same table were employed. Foaming and molding were performed as in Example 1. Tables 2, 4, and 6 summarize the manufacturing conditions and the characteristics of the molded product.
The foamed resin particles of the present invention having antistatic properties did not have particles having an abnormal shape, and the molded article was excellent in detail filling properties and surface appearance.

[0041]

[Table 2] {Example 1 2 3 4 5} ───────────────────────────────── Resin BT-CO-PR BT-CO-PR BT-CO-PR BT -CO-PR BT-CO-PR Antistatic agent SDEMS SDEMS SDEMS SDEMS SDEMS Addition amount (parts) 3.0 3.0 3.0 3.0 3.0 Dispersing aid POENFE POENFE POENFE POEOFE POEOFE EO addition amount (mol) 11 11 30 10 25 HLB value 6.7 6.7 13.0 6.9 11.8 Amount (parts) 0.1 0.05 0.1 0.1 0.1 Foaming temperature (° C) 140 140 140 140 140 Amount of volatile foaming agent (parts) 25 13 25 25 25 Bulk density of foamed particles (g / L) 18 40 18 18 18 Abnormal particle size (%) 0 0 0 0 0 Molding density (g / L) 30 70 30 30 30 Compact filling of compacts ○ ○ ○ ○ ○ Surface appearance ○ ○ ○ ○ ○ ──────── ────────────────────────────

[0042]

[Table 3] BT-CO-PR: Butene-propylene random copolymer (same below) SDEMS: Stearyl diethanolamine monostearate (same below) EO: ethylene oxide (same below) POENFE: polyoxyethylene nonyl phenyl ether (same below) POEOFE: Polyoxyethylene octyl phenyl ether (the same applies hereinafter)

[0043]

[Table 4] {Example 6 7 8 9}樹脂 Resin BT-CO-PR BT-CO-PR ET-CO-PR LLDPE electrification Inhibitor SDEMS SMG NHENHS NHENHS Addition amount (parts) 3.0 3.0 3.0 3.0 Dispersing aid POESE POEOFE POEOFE POEOFE EO addition amount (mol) 12 10 10 10 HLB value 6.6 6.9 6.9 6.9 Addition amount (parts) 0.1 0.1 0.1 0.1 Foaming temperature ( ° C) 140 140 132 119 Volatile foaming agent (parts) 25 25 20 23 Expanded particle bulk density (g / L) 18 16 18 21 Abnormal shape particle amount (%) 0 00 0 Molded object density (g / L) 30 27 31 33 Detail filling ○ ○ ○ ○ Surface appearance ○ ○ ○ ○ ────────────────────────────────── ──

[0044]

[Table 5] NHENHS: N-hydroxyethyl N-2-hydroxystearylamine (same below) POESE: polyoxyethylene stearyl ether (same below) SMG: monoglyceride stearate (same below) LLDPE: linear low density polyethylene (same as below) same as below)

[0045]

[Table 6] {Comparative Example 1 2 3 4}樹脂 Resin BT-CO-PR BT-CO-PR ET-CO-PR ET- CO-PR Antistatic agent SDEMS SDEMS SDEMS SDEMS Addition amount (parts) 3.0 3.0 3.0 3.0 Dispersing aid POENFE POENFE DBSN LDMAP EO addition amount (mol) 3.0 84 − − HLB value 4.1 31.0 − − Addition amount (parts) 0.1 0.1 0.1 0.1 Foaming temperature (° C) 140 140 140 140 Volatile foaming agent (parts) 25 25 25 25 Bulk density of foamed particles (g / L) 24 Unmeasurable Unmeasurable Unmeasurable Unusual shape particle amount (%) 23 50 75 80 Molded product Density (g / L) 36 Not moldable Not moldable Not moldable Compacted body compactability × − − − Surface appearance × − − − ────────────────────── ──────────────

[0046]

[Table 7] DBSN: Sodium dodecylbenzenesulfonate LDMAP: Pentyl lauryl dimethylaminoacetate

[0047]

According to the method for producing expanded resin particles of the present invention described above, there are no irregularly shaped particles such as flat and blocking,
It is possible to provide foamed resin particles having an antistatic property capable of obtaining a molded article excellent in detail filling property and surface appearance during molding.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 71:00)

Claims (5)

[Claims] 1. A polyolefin-based resin particle containing 0.1 to 5 parts by weight of an antistatic agent, water, an inorganic dispersant, a dispersing aid, and a volatile foaming agent are accommodated in a pressure-resistant container, and then stirred. A method for producing foamed resin particles, in which the resin particles are impregnated with a volatile foaming agent by raising the temperature to a temperature equal to or higher than the softening point temperature of the resin particles, and then the obtained foaming agent-impregnated resin particles are foamed. A method for producing expanded resin particles, characterized by using a nonionic surfactant having an HLB value of 5 to 15 as an auxiliary agent. 2. The method according to claim 1, wherein the polyolefin resin is a polypropylene resin. 3. The method according to claim 1, wherein the antistatic agent has a tertiary nitrogen atom. 4. The production method according to claim 1, wherein the dispersion aid is represented by the following general formula. ## STR1 ## _{R-Ph-O- (CH 2} CH 2 O) n -H ( where, R represents an alkyl group having 8 to 12 carbon atoms, Ph represents a phenyl group, n is an integer of 5-30.) 5. The foaming of the foaming agent-impregnated resin particles is performed by discharging the foaming agent-impregnated resin particles from a content discharge port provided at one end of the pressure-resistant container into an atmosphere having a pressure lower than the internal pressure of the pressure-resistant container. The method according to claim 1.