JP3418075B2 - Method for producing expanded resin particles - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing expanded resin particles, and more particularly to a method for producing expanded resin particles having an antistatic property which is free from abnormally shaped particles and has excellent processability.

[0002]

2. Description of the Related Art Conventionally, foamed polyolefin resin molded articles are excellent in heat resistance, chemical resistance, impact resistance, etc., and are therefore shock absorbing materials for bumper core materials, helmets, etc., and cushioning packaging materials for various equipment. It is used for. However, since the polyolefin resin foamed molded product has a high surface specific resistance value and is easily charged, dust is easily adsorbed on the surface of the molded product, and its use in electric devices, cushioning packaging materials, trays for parts, etc. is restricted.

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

However, in the above method, when the amount of antistatic agent added is large or the amount of resin particles is large in order to improve productivity, the suspension state is not stabilized during impregnation of the foaming agent, The resulting foaming agent-impregnated resin particles and the subsequent foamed resin particles contain a large amount of flat particles and agglomerates of two or more particles fused together (hereinafter referred to as blocking). The foamed resin particles having such blocking have a drawback that the molded product has a poor detail filling property at the time of molding and a molded product having excellent surface appearance cannot be obtained.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a stable suspension state in a foaming agent impregnation step, and therefore, an abnormal shape such as a flat shape or a blocking shape. It is an object of the present invention to provide a method for producing expanded resin particles having antistatic properties, which is free from particles and can provide a molded product 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 dispersion aid and a volatile foaming agent. After being stored in a pressure-resistant container, the resin particles are heated to a softening point temperature or higher under stirring conditions to impregnate the resin particles with a volatile foaming agent, and then the resulting foaming agent-impregnated resin particles are foamed. A method for producing expanded resin particles, which is characterized in that a nonionic surfactant having an HLB value of 5 to 15 is used as the dispersion aid.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
First, in the present invention, after the polyolefin resin particles containing an antistatic agent, water, an inorganic dispersant, a dispersion aid and a volatile foaming agent are housed in a pressure vessel, the resin particles of the resin particles are stirred under stirring conditions. The temperature is raised above the softening point temperature to impregnate the resin particles with the volatile foaming agent.

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

As the above-mentioned polyolefin-based resin, a polypropylene-based resin having a high compression stress, a high rigidity and an excellent buffering property, and a heat-resistant property is preferable even if it has a low density. Temperature dependence, dimensional stability,
A 1-butene / propylene random copolymer containing 5 to 20% by weight of 1-butene excellent in moldability is particularly preferable.

Other resins and elastomers may be used in combination with the above polyolefin-based resin for the purpose of modification, as long as the characteristics of the polyolefin-based resin are not impaired. Examples of such an elastomer include ethylene-
Examples include elastomers such as propylene-based elastomers and polybutadiene. These resins and elastomers can be mixed in an amount 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, usually, a cationic type, anionic type, amphoteric type, nonionic type, or the like, which has excellent antistatic properties and is compatible with polyolefin resins, can be selected. Among these, nonionic antistatic agents such as fatty acid glycerin esters and polyoxyethylene alkylamines are preferable because they have good compatibility with polyolefin resins, are resistant to discoloration, and have heat resistance. Further, an ethanolamine-based antistatic agent such as alkyldiethanolamine monoalkylate is particularly preferable because it has excellent immediate effect and sustainability.

The molecular weight of the above antistatic agent is usually 200.
The range is from 1000 to 1000, preferably from 300 to 900. 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.

Polyolefin resin particles containing an antistatic agent are phosphorus-based, phenol-based, and
Sulfur-based antioxidants and hindered amine-based light stabilizers may be added to improve weather resistance. In addition, an ultraviolet absorber, a metal deactivator, a pigment, a dye, an inorganic filler, etc. may be added. These may be used in combination of two or more kinds. Further, the above polyolefin-based resin particles may contain a rosin acid ester-based antistatic aid such as rosin-modified pentaerythritol in order to allow the molded article obtained from the expanded resin particles to exhibit antistatic properties 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 obtained mixture in a molten state into pellets.

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

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

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

In the present invention, as the dispersion aid, HL is used.
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 antiblocking effect is not exhibited.

According to the present invention, by using the nonionic surfactant having the above HLB value, the suspension state of the resin particles containing the antistatic agent becomes stable during the impregnation of the foaming agent, It is possible to obtain a molded product which does not contain particles having an abnormal shape such as a flat shape and blocking and which is excellent in detail filling property and surface appearance property at the time of molding.

As the above-mentioned nonionic surfactant, H
Any nonionic surfactant may be used as long as it has an LB value within the above range, but a polyoxyethylene condensed type is usually used. And, as the polyoxyethylene condensation type nonionic surfactant, an alkylphenol represented by the following general formula, which is excellent in thermal stability, acid resistance, alkali resistance, and hard water resistance, and has a high interfacial tension lowering effect. The condensate of is preferred. And as said condensate, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, etc. are preferable.

[0021]

Embedded image R—Ph—O— (CH ₂ CH ₂ O) _n —H (wherein R represents an alkyl group having 8 to 12 carbon atoms, Ph represents a phenyl group, and n represents an integer of 5 to 30).

The amount of the above-mentioned nonionic surfactant added is
Although it varies depending on the ratio of the resin particles, water, the inorganic dispersant, the volatile foaming agent, etc., it is usually in the range of 0.01 to 1 part by weight with respect to 100 parts by weight of the resin particles. When the amount of the nonionic surfactant added is less than 0.01 part by weight, sufficient blocking tends not to be obtained, and when it exceeds 1 part by weight, foaming becomes severe and the foamed resin particles and / or foaming is caused. It becomes difficult to handle the resin particles in a post-treatment process such as washing and drying.

The HLB value is as described in J. T. Dav
It can be obtained from the expression of is.

[0024]

[Formula 1] 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. To be These may be used in combination of two or more kinds.

The amount of the volatile foaming agent added varies depending on the foaming ratio of the foamed particles, the type of the foaming agent, the ratio of resin particles, water, etc., the impregnation temperature or the foaming temperature, and is usually 5 parts by weight per 100 parts by weight of the resin particles. -40 parts by weight.

In the present invention, since resin particles are impregnated with a volatile foaming agent, polyolefin resin particles containing an antistatic agent, water, an inorganic dispersant, a dispersion aid and a volatile foaming agent are placed in a pressure resistant container. Then, the temperature is raised to above the softening point temperature of the resin particles under stirring conditions. In this case, the stirring conditions are not particularly limited, but the stirring is performed so that a sufficient suspended state is obtained, and the heating temperature is usually set to a temperature 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 is preferred in which the foaming agent-impregnated resin is discharged from a content discharge port provided at one end of the pressure resistant container to an atmosphere having a pressure lower than the internal pressure of the pressure resistant container. However, a method may also be used in which the pressure-resistant container is cooled below the softening point temperature of the resin particles, the foaming agent-impregnated resin particles are taken out, transferred to another container, and then contacted with a heating medium such as steam to foam.

The foamed resin particles having an antistatic property obtained in the present invention do not contain abnormally shaped particles, and the molded product is excellent in detail filling property and surface appearance property. A molded product obtained from such expanded resin particles has excellent antistatic properties, and thus is suitably used for electric devices, 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 as long as the gist thereof is not exceeded. In addition, in each of the following examples, each physical property was determined as follows.

<Abnormal Shape Particle Amount> Expanded resin particles 1000
The abnormal shape particles were selected by spreading g on a white paper, the weight (g) was measured, and the ratio (%) of the abnormal shape particle weight (g) to the foamed resin particles 1000 (g) was shown.

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

[0033]

<Table 1><Detail filling property> ◯: The foamed resin particles are filled up to the rising details. X: Wrinkles are generated because the filling property of the rising portion is poor. <Surface appearance> Good: The surface of the foamed resin particles is smooth with no gaps. X: Foamed granule resin particles are present in some places and the surface is not smooth.

<Surface resistivity> Humidity 55%, temperature 25
After leaving the sample at ℃ for 48 hours, measure the surface resistivity
(Dia Instruments Co., Ltd. "High Rester, detection terminal HR-100 round type") was used, and the applied voltage was 500 V, and measurement was performed for 10 seconds. Then, the surface specific resistance value was represented by the average value 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, stearyldiethanolamine monostearate (antistatic agent) 3 parts by weight and tris (2,4-di-t-butylphenyl) phosphate (heat deterioration inhibitor) 0.1 parts by weight with a ribbon blender. 20
Mix for minutes.

This mixture was melt-mixed at 220 ° C. by a single screw extruder having a diameter of 60 mm and extruded through 50 orifices having a diameter of 1.5 mm. The 50 strands thus obtained were passed through a cooling water tank to be cooled and solidified, and then passed through a drier for blowing hot air of 70 ° C. to be dried to obtain a strand having a diameter of 1 mm. The obtained strand was cut into a length of about 2 mm with a rotary blade type cutter.

100 parts by weight of the above resin particles, 300 parts by weight of water, 5 parts by weight of tricalcium phosphate (inorganic dispersant), and polyoxyethylene nonyl phenyl ether (HLB value) having an oxyethylene addition mole number of 11 moles were placed in a pressure vessel. 6.7) 0.1 part by weight of (dispersion aid) and 25 parts by weight of butane (volatile foaming agent) are contained, and the temperature inside the pressure vessel is raised to 140 ° C. for 60 minutes under stirring conditions for 15 minutes. Held At this time, the pressure inside the pressure vessel is 20 kg / cm ²
Met. After that, the diameter of 2
The contents were discharged into a container at atmospheric pressure from a 0 mm discharge port to obtain expanded resin particles.

Next, an aqueous nitric acid solution having a pH of 2 was applied to the foamed resin particles from a spray nozzle provided above the atmospheric pressure container.
By spraying for 0 minutes, the tricalcium phosphate on the surface of the expanded resin particles was removed while being dissolved. Then, 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 foamed resin particles obtained were dehydrated by a centrifuge and dried in a drying room at 60 ° C. for 24 hours. The foamed resin particles have a density of 18
It was g / L, and there were no abnormally shaped particles such as blocking, and the shape was uniform and uniform.

The above-mentioned foamed resin particles were compressed and filled in a mold capable of obtaining a box-shaped molded body having a rising portion of 10 mm in thickness and 50 mm in height, and then 3.0 kg / cm ² in the mold.
The water vapor of G was introduced to heat-bond the expanded resin particles to each other. Then, cooling water was introduced into the mold to cool the molded product, and then the foamed molded product was taken out from the mold and dried in a drying chamber at 60 ° C. for 24 hours. The molded body was also fully filled with the expanded resin particles even in the rising portion, and was excellent in detail filling property, surface appearance property and the like. In addition, this molded body has a density of 30.
The surface resistivity was in the range of 10 ¹⁰ to 10 ¹¹ Ω. Table 2 summarizes the production conditions and the characteristics of the molded body.

Examples 2 to 9 and Comparative Examples 1 to 4 In Example 1, except that the particles shown in Tables 2, 4 and 6 were used as the expanded resin particles and the conditions shown in the same table were adopted. Foaming and molding were carried out in the same manner as in Example 1. The manufacturing conditions and the characteristics of the molded product are summarized in Tables 2, 4, and 6.
The foamed resin particles of the present invention having an antistatic property did not have particles having an abnormal shape, and the molded product was excellent in detail filling property and surface appearance property.

[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 (part) 3.0 3.0 3.0 3.0 3.0   Dispersion 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   Addition amount (part) 0.1 0.05 0.1 0.1 0.1   Foaming temperature (℃) 140 140 140 140 140   Volatile foaming agent amount (part) 25 13 25 25 25   Expanded particle bulk density (g / L) 18 40 18 18 18   Abnormal shape particle amount (%) 0 0 0 0 0   Compact density (g / L) 30 70 30 30 30   Detail filling of molded products ○ ○ ○ ○ ○   Surface appearance ○ ○ ○ ○ ○ ────────────────────────────────────

[0042]

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

[0043]

[Table 4] ────────────────────────────────────   Example 6 7 8 9 ────────────────────────────────────   Resin BT-CO-PR BT-CO-PR ET-CO-PR LLDPE   Antistatic agent SDEMS SMG NHENHS NHENHS   Addition amount (part) 3.0 3.0 3.0 3.0   Dispersion 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 (part) 0.1 0.1 0.1 0.1   Foaming temperature (℃) 140 140 132 119   Volatile foaming agent (part) 25 25 20 23   Expanded particle bulk density (g / L) 18 16 18 21   Abnormal shape particle amount (%) 0 0 0 0   Compact density (g / L) 30 27 31 33   Detail fillability ○ ○ ○ ○   Surface appearance ○ ○ ○ ○ ────────────────────────────────────

[0044]

[Table 5]   NHENHS: N-hydroxyethyl N-2-hydroxystearylamine (hereinafter             the same)   POESE: Polyoxyethylene stearyl ether (hereinafter the same)   SMG: Monoglyceride stearate (same below)   LLDPE: Linear low-density polyethylene (same below)

[0045]

[Table 6] ────────────────────────────────────   Comparative Example 1 2 3 4 ────────────────────────────────────   Resin BT-CO-PR BT-CO-PR ET-CO-PR ET-CO-PR   Antistatic agent SDEMS SDEMS SDEMS SDEMS   Addition amount (part) 3.0 3.0 3.0 3.0   Dispersion aid POENFE POENFE DBSN LDMAP   EO addition amount (mol) 3.0 84 − −   HLB value 4.1 31.0 − −   Addition amount (part) 0.1 0.1 0.1 0.1   Foaming temperature (℃) 140 140 140 140   Volatile foaming agent (part) 25 25 25 25   Expanded particle bulk density (g / L) 24 Not measurable Not measurable Not measurable   Abnormal shape particle amount (%) 23 50 75 80   Molded product density (g / L) 36 Not moldable Not moldable Not moldable   Detail filling of molded products × − − −   Surface appearance × − − − ────────────────────────────────────

[0046]

[Table 7] DBSN: Sodium dodecylbenzene sulfonate LDMAP: Lauryl dimethylaminoacetic acid pentaine

[0047]

[Effect] The above-described method for producing expanded resin particles of the present invention is free from particles having an abnormal shape such as flat shape and blocking,
It is possible to provide foamed resin particles having an antistatic property, which can provide a molded product excellent in detail filling property and surface appearance property during molding.

Claims (5)

(57) [Claims] 1. A polyolefin resin particle containing 0.1 to 5 parts by weight of an antistatic agent, water, an inorganic dispersant, a dispersion aid and a volatile foaming agent are placed in a pressure resistant container and then stirred. A method for producing expanded resin particles, in which the resin particles are impregnated with a volatile foaming agent by elevating the temperature above the softening point temperature of the resin particles, and then the resulting foaming agent-impregnated resin particles are foamed. A method for producing expanded resin particles, which comprises 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. Embedded image R—Ph—O— (CH ₂ CH ₂ O) _n —H (wherein R represents an alkyl group having 8 to 12 carbon atoms, Ph represents a phenyl group, and n represents an integer of 5 to 30). 5. The foaming agent-impregnated resin particles are foamed by discharging the foaming agent-impregnated resin particles into an atmosphere having a pressure lower than the internal pressure of the pressure resistant container from a content outlet provided at one end of the pressure resistant container. The manufacturing method according to claim 1.