JP2009242634A - Antistatic styrenic resin foamed molding and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molding method which, relating to a method of manufacturing a styrenic foamed molding by impregnating styrenic resin particles with an easily-volatile foaming agent and a surfactant, filling the pre-expanded particles obtained by heating into a mold and subjecting to heating and cooling processes, can give a foamed molding having higher antistatic properties and free of portion-to-portion fluctuations of the antistatic properties of the obtained foamed molding. <P>SOLUTION: In carrying out in-mold foam molding by impregnating styrenic resin particles with an easily-volatile foaming agent and a surfactant, filling the pre-expanded particles obtained by heating into a mold and subjecting to heating and cooling processes, after the cooling process following the in-mold foaming is conducted, an additional water treatment process is conducted. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an antistatic styrene resin foam molded article and a method for producing the same.

Styrenic resin foam moldings are widely used as cushioning packaging materials for mechanical parts such as automobile parts and electrical products because of their excellent impact resistance, wear resistance and oil resistance.
However, since the styrene resin has high electrical insulation, it is easily charged by friction, and not only the appearance of the foamed molded product is damaged by the adhesion of dust, but also the contents are contaminated by dust collection and electrostatic breakdown. There was a problem in using it as a packaging material for electronic parts such as liquid crystals.

  In International Publication No. WO2004 / 090029 (Patent Document 1), styrene-modified olefin resin particles are impregnated with a volatile foaming agent to obtain expandable resin particles, and then 100 parts by weight of the expandable resin particles are added. On the other hand, a method for obtaining an antistatic styrene resin foam molded article from expandable styrene modified olefin resin particles having excellent antistatic properties by impregnating with 0.1 to 2.0 parts by weight of a surfactant is described. Has been.

  On the other hand, in JP-A-56-64842 (Patent Document 2), in the in-mold molding process, the mold is once opened during the cooling process, exposed to air, and then clamped again. Thus, a method for shortening the cooling time and increasing the molding cycle is described.

International Publication Number WO2004 / 090029 JP 56-64842 A

  However, the styrenic resin foam molded article obtained by the method described in Patent Document 1 has good antistatic performance when viewed as the whole foam molded article, but the performance varies depending on the part of the foam molded article. In addition, it cannot be applied to a site where higher antistatic performance is required.

  On the other hand, Patent Document 2 does not describe antistatic performance, and this method further performs mold opening during cooling in order to increase cooling efficiency. Patent Document 2 describes that when the mold is opened, the mold may be opened together with water cooling. However, since voids are generated, the foam does not flow in a state where water drops, and further, high foaming is performed. Since the mold is opened with pressure, the foam expands in the opened instantaneous mold, and a molded body with the target dimensions cannot be obtained.

  Therefore, styrene resin foam molding is performed by impregnating styrene resin particles with a readily volatile foaming agent and a surfactant, heating the pre-expanded particles obtained in the mold, and subjecting them to heating and cooling processes. There is a demand for an in-mold foam molding method that can provide a foamed molded product having higher antistatic performance and a non-fluctuating antistatic performance depending on the portion of the resulting molded product.

  As a result of intensive studies, the inventors of the present invention have impregnated styrene resin particles with a readily volatile foaming agent and a nonionic surfactant, and filled the pre-expanded particles obtained by heating into the mold. When performing in-mold foam molding by subjecting it to heating and cooling steps, after performing the cooling step after in-mold foaming, further water treatment step has higher antistatic performance, Surprisingly, it was found that a foamed molded product having no variation in antistatic performance depending on the portion of the molded product obtained was obtained, and the present invention was achieved.

  Thus, according to the present invention, the styrene resin particles are impregnated with 0.5 to 3.5 parts by weight of a non-volatile surfactant with respect to 100 parts by weight of the volatile foaming agent and the styrene resin particles, and heated. When pre-foamed particles are used and the pre-foamed particles are subjected to in-mold foam molding in the mold, the cooling step after in-mold foaming is performed until the foaming pressure of the foam molded body in the mold is reduced to 0.01 MPa or less. Thereafter, there is provided a method for producing an antistatic styrene resin foam molded article in which a water treatment step of bringing water into a mold and contacting the surface of the foam molded article is performed.

Further, according to the present invention, there is provided an antistatic styrene resin foam molded article obtained by the above method, wherein the foam molded article has an average surface resistivity of 1 × 10 ¹¹ Ω or less. .

  According to the present invention, it is possible to obtain a styrenic resin foam molded article having higher antistatic performance and having excellent antistatic properties with no variation in antistatic performance depending on the portion of the obtained foam molded article.

Hereinafter, the present invention will be described in more detail.
As the styrene resin particles in the present invention, polystyrene, polymethylstyrene, styrene-acrylonitrile copolymer, styrene-acrylonitrile butadiene copolymer, styrene-acrylic acid ester copolymer, styrene-methyl methacrylate copolymer, polystyrene And particles made of polyethylene or polypropylene cross-linked resin. These resins may be mixed, or other resins other than polystyrene resins may be mixed. Examples of other resins include polyolefin resins such as polyethylene and polypropylene. In the present invention, a polyolefin-modified styrene resin is particularly preferable, and a polyethylene-modified styrene resin is more preferable.

  Polyethylene-modified styrene-based resin has polyolefin resin particles dispersed and held as described in, for example, Japanese Patent Publication No. 51-46138, Japanese Patent Publication No. 59-3487, and Japanese Patent Publication No. 63-28443. It can be obtained by adding a styrenic monomer to an aqueous medium for polymerization. Here, there is no restriction | limiting in the ratio of a polyethylene-type resin and a styrene-type monomer.

  On the other hand, expandable styrene resin particles can be obtained by impregnating the styrene resin particles with a readily volatile foaming agent. As the readily volatile foaming agent, for example, hydrocarbons such as propane, butane, isobutane, pentane, isopentane, cyclopentane, hexane and the like can be used alone or in admixture of two or more. Although the usage-amount of a foaming agent is determined by the foaming multiple of the target molded object, it is preferable that it is 10-30 weight part with respect to 100 weight part of styrene resin particles.

  Furthermore, a foaming aid such as cyclohexane, ethylbenzene, or toluene may be used to facilitate foaming and molding of the expandable styrene resin particles. The foaming assistant is preferably 2 parts by weight or less with respect to 100 parts by weight of the polyethylene-modified styrene resin particles.

  Furthermore, the addition amount of the nonionic surfactant added at this stage is 0.5 to 3.5 parts by weight, preferably 1.0 to 3.0 parts by weight with respect to 100 parts by weight of the styrene resin particles. It is. If the amount is less than 0.5 parts by weight, the antistatic property may not be sufficient. If the amount is more than 3.5 parts by weight, the foamed molded product may become sticky, and the dust tends to adhere to it.

  Examples of the nonionic surfactant impregnated in the styrene resin particles of the present invention include polyoxyethylene alkylamine (for example, polyoxyethylene laurylamine), polyethylene glycol fatty acid ester, alkyldiethanolamide, alkyldiethanolamine, alkylmonoethanol. Surfactants having an HLB value of 7 or less, such as amines and polyalkylene glycol derivatives, can be used. Among them, preferably, polyoxyethylene alkylamine (more preferably, polyoxyethylene laurylamine), alkyldiethanolamine, and alkylmonoethanolamine are used. The alkyl is preferably an alkyl having 8 to 18 carbon atoms, and more preferably an alkyl having 11 to 13 carbon atoms.

When the obtained expandable styrenic resin particles are used as pre-expanded particles, water vapor is brought into contact therewith to expand to a predetermined density. The expanded particles are usually stored and aged for about 24 hours.
Thereafter, the pre-expanded particles are filled in the mold, heated again, the pre-expanded particles are expanded in-mold, the particles are heat-fused, and cooled to obtain a foam-molded article. As the heating medium, water vapor with a gauge pressure of 0.05 to 0.15 MPa is preferably used.

Generally, the heating process in the in-mold molding using the styrene-based pre-expanded particles is performed in the order of the mold heating process, the one heating process, the reverse one heating process, and the double-side heating process.
A cooling process is performed after completion | finish of a series of heating processes. In the styrenic resin molding method, the cooling process is divided into a water cooling process, a drainage process, and a cooling process. In the present invention, after the water cooling process, the water treatment process is performed without performing the draining process and the cooling process. You may do it.

Water at room temperature (about 25 ° C.) is used for the water treatment process.
The cooling step is usually expressed in time, and the cooling time is the time from when the water is started to be poured into the mold until the foaming pressure (surface pressure) of the foamed molded product is reduced to 0.01 MPa or less. ~ 400 seconds. Moreover, the time of the water cooling process in a cooling process is 5 to 30 seconds normally.

The time of the water treatment step is to maintain the pressure in the mold at 0 to 0.02 MPa after the foaming pressure (surface pressure) of the foamed molded body in the mold is reduced to 0.01 MPa or less. It is the time from the start of injecting water to the stop of water, and preferably 20 to 200 seconds. If it is less than 20 seconds, higher antistatic performance cannot be obtained, and if it exceeds 200 seconds, the mold is extremely cooled. Therefore, in order to newly manufacture using this mold, it must be heated for a long time. Productivity may decrease due to the absence of changes in antistatic performance.
After the water treatment step, the foamed molded product is taken out through a drainage step.

In the present invention, the presence or absence of antistatic properties is determined by measuring the surface resistivity of the foamed molded product.
Furthermore, regarding the variation in the antistatic performance in the partial portion of the foamed molded article of the present invention, the standard deviation is determined for the degree of variation in the surface resistivity.

EXAMPLES The present invention will be described in detail below by examples, but the present invention is not limited to these examples.
In addition, the measuring method of the surface resistivity of the foaming molding obtained by the Example and the comparative example and the evaluation method of the variation degree of surface resistivity are described below.

(Surface resistivity measurement method)
Measured by the method described in JIS K6911: 1995 “General Test Method for Thermosetting Plastics”. In other words, using a test device (digital super high resistance / microammeter R8340 manufactured by Advantest Co., Ltd. and resiliency chamber R12702A), an electrode is crimped to a sample sample with a load of about 30 N, and the resistance after charging for 500 V for 1 minute. The value was measured and calculated by the following formula. The sample sample was 100 × 100 × original thickness (10 or less) mm, and 10 samples were cut out from the same foamed molded article and measured for each. If the surface resistivity was 1 × 10 ¹¹ Ω or less, the foamed molded article was judged to have higher antistatic properties.

ρs = π (D + d) / (D−d) × Rs
ρs: Surface resistivity (MΩ)
D: Inner diameter (cm) of surface annular electrode
d: outer diameter of inner circle of surface electrode (cm)
Rs: Surface resistance (MΩ)

(Evaluation method for variation in surface resistivity)
The degree of variation in surface resistivity was determined as follows. The surface resistivity measured at n = 10 was returned in logarithm (log ₁₀ ), and the standard deviation was determined for the logarithm. If the standard deviation was 1.0 or less, it was judged that there was very little variation.

(Measuring method of melt flow rate)
The melt flow rate was measured by the method described in JIS K 7210: 1999 “Testing method for melt mass flow rate (MFR) and melt volume flow rate (MVR) of plastic-thermoplastic plastic” B method.

Production Example 1 (Preparation of polyethylene resin pellets)
With respect to 100 parts by weight of an ethylene-vinyl acetate copolymer having a melt flow rate of 0.3 g / 10 minutes and a vinyl acetate content of 5.5% by weight, 0.3 part by weight of calcium silicate as a foam regulator and steer After adding 0.1 parts by weight of calcium phosphate and uniformly kneading with an extruder, the mixture was granulated to obtain polyethylene resin pellets.

Production Example 2 (Preparation of polyethylene-modified styrene resin particles)
In a pressure-resistant container with a stirrer having an internal volume of 100 liters, 40 parts by weight of the polyethylene resin pellets, 120 parts by weight of water, 0.45 parts by weight of magnesium pyrophosphate and 0.02 parts by weight of sodium dodecylbenzenesulfonate are added and stirred. The temperature was raised to 85 ° C. Separately, 0.3 parts by weight of benzoyl peroxide as a radical polymerization initiator and 0.02 parts by weight of t-butylperoxybenzoate and 0.8 parts by weight of dicumyl peroxide as a crosslinking agent were added to 60 parts by weight of styrene monomer. The solution was dissolved to form a solution, and this was added to the water and absorbed in polyethylene resin pellet particles, and maintained for 4 hours for polymerization. Thereafter, the temperature was raised to 140 ° C. and held for 3 hours, and then cooled to take out polyethylene-modified styrene resin particles.

Example 1 (Impregnation of foaming agent and foam molding)
100 parts by weight of polyethylene-modified styrene resin particles and 2 polyoxyethylene laurylamine (Elegant S-100 manufactured by NOF Corporation) as a nonionic surfactant in a V-type blender with an internal volume of 50 liters that can be sealed with pressure resistance. 0.0 part by weight was added, and 14 parts by weight of butane was press-fitted while sealing and stirring. And after maintaining the inside of a container at 50 degreeC for 4 hours, it cooled and took out the foamable resin particle. The taken-out foamable resin particles were immediately pre-foamed to a bulk multiple of 30 times (bulk density 0.033 g / cm ³ ) with a batch type foaming machine, and then stored at room temperature for 24 hours.

The pre-expanded particles were filled in a mold of a 400 × 300 × 30 mm molding machine, and heated and foamed with water vapor having a gauge pressure of 0.08 MPa. The details of the heating process were a mold heating process, a one-side heating process, a reverse one-side heating process, and a double-sided heating process, which were injected for 5 seconds, 5 seconds, 5 seconds, and 20 seconds, respectively, and heated and foamed. Next, as a cooling process, the water cooling process was taken for 15 seconds, drained, and the vacuum cooling process was performed until the foaming pressure showed 0.005 MPa. After showing 0.005 MPa, the water treatment step was performed for 50 seconds, and after draining was completed, the mold was released, and a foamed molded product having a multiple of 30 times (density 0.033 g / cm ³ ) was taken out from the mold.
The obtained foamed molded article was dried in a drying room at 40 ° C. for 8 hours or more.
A schematic diagram of this step is shown in FIG.

Example 2
A foamed molded product was obtained in the same manner as in Example 1 except that the water treatment step was set to 150 seconds.
Example 3
A foamed molded article was obtained in the same manner as in Example 1 except that the vacuum cooling step in the cooling step was performed until the foaming pressure showed -0.02 MPa.
A schematic diagram of this step is shown in FIG.

Example 4
A foamed molded article was obtained in the same manner as in Example 1 except that the water cooling step in the cooling step was performed until a foaming pressure of 0.01 MPa was exhibited.
Example 5
A water-cooled process in the cooling process was performed until a foaming pressure of 0.01 MPa was exhibited, and a foamed molded article was obtained in the same manner as in Example 1 except that the water treatment process was performed for 150 seconds.

Examples 6-10
Foam-molded articles in the same manner as in Examples 1 to 5 except that the amount of polyoxyethylene laurylamine (ELEGAN S-100 manufactured by NOF Corporation), which is a nonionic surfactant, was 1.0 part by weight. Got.
Example 11
A foamed molded product was obtained in the same manner as in Example 1 except that the water treatment step was performed for 20 seconds.

Example 12
A foamed molded article was obtained in the same manner as in Example 1 except that the amount of polyoxyethylene laurylamine (Elegant S-100 manufactured by NOF Corporation), which is a nonionic surfactant, was 3.0 parts by weight. .
Example 13
Example 1 except that polyoxyethylene laurylamine (Elegant S-100, manufactured by NOF Corporation), which is a nonionic surfactant, was changed to alkyl monoethanolamine (Nymeen L-201, manufactured by NOF Corporation). A foamed molded product was obtained.

Example 14
In a polymerization vessel equipped with a stirrer having an internal volume of 100 liters, 40 liters of water, 100 g of tribasic calcium phosphate and 2.0 g of calcium dodecylbenzenesulfonate were placed, followed by stirring with 40.0 kg of styrene, 96.0 g of benzoyl peroxide, t- 28.0 g of butyl peroxide was added, the temperature was raised at 90 ° C. and held for 6 hours. Further, the temperature was raised to 125 ° C. and then cooled for 2 hours to obtain styrene resin particles.

1. 100 parts by weight of the styrene resin particles prepared above in a V-type blender having an internal volume of 50 liters that can be sealed with pressure resistance, and 2. polyoxyethylene laurylamine (ELEGAN S-100 manufactured by NOF Corporation) as a nonionic surfactant. 0 part by weight was added, and 14 parts by weight of butane was press-fitted while sealing and stirring. And after maintaining the inside of a container at 50 degreeC for 4 hours, it cooled and took out the foamable resin particle. After taking out the expandable styrene resin particles for 5 days in an atmosphere of 13 ° C., the foamed styrene resin particles are pre-foamed to a bulk multiple of 30 times (bulk density 0.033 g / cm ³ ) with a batch type foaming machine, and then stored at room temperature for 24 hours. did. The pre-expanded particles are filled in a mold of a 400 × 300 × 30 mm molding machine, and the mold heating step, one heating step, the opposite one heating step, and the double-side heating step are performed using water vapor with a gauge pressure of 0.08 MPa, Injection was carried out for 5 seconds, 5 seconds, 5 seconds and 20 seconds, respectively, and foamed by heating. The water cooling step was taken for 15 seconds, drained, and the vacuum cooling step was performed until the foaming pressure was 0.005 MPa. After showing 0.005 MPa, the water treatment step was performed for 50 seconds, and after draining was completed, the mold was released, and a foamed molded product having a multiple of 30 times (density 0.033 g / cm ³ ) was taken out from the mold. The obtained foamed molded article was dried in a drying room at 40 ° C. for 8 hours or more.

Comparative Example 1
The same as in Example 1 except that the amount of polyoxyethylene laurylamine (Elegan S-100 manufactured by NOF Corporation), which is a nonionic surfactant, was 2.0 parts by weight and the water treatment step was not performed. A foamed molded product was obtained.
A schematic diagram of this step is shown in FIG.

Comparative Examples 2-6
Foam-molded products in the same manner as in Examples 1 to 5, except that the amount of polyoxyethylene laurylamine (Elegance S-100 manufactured by NOF Corporation), which is a nonionic surfactant, was 0.1 parts by weight. Got.
Comparative Example 7
Rather than adding a nonionic surfactant, an aliphatic quaternary ammonium salt that is an ionic surfactant (Cathogen ES-L manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) is added to the polyethylene-modified styrene resin. A foamed molded article was obtained in the same manner as in Example 1 except that 0.5 part by weight was added.

Comparative Example 8
The same procedure as in Example 1 was performed except that the amount of polyoxyethylene laurylamine (Elegan S-100 manufactured by NOF Corporation) was 5.0 parts by weight. The obtained pre-expanded particles and the foamed molded article had stickiness on the surface, and dust was easily changed and adhered. Since it was not a good foamed molded article, the surface resistivity was not measured.

  About the foaming molding obtained above, the measurement of antistatic performance was performed according to the measuring method of the above-mentioned surface resistivity measurement. A measurement sample was cut out from the obtained foamed molded article and measured after being stored for 24 hours or more in an environment of a temperature of 20 ° C. and a humidity of 65%. Further, the degree of variation was evaluated from the obtained surface resistivity by the above method. The results are described below together with the amount of surfactant used, the pressure and time in each step.

  As described above, according to the present invention, a pre-expanded particle obtained by impregnating a styrene resin with a readily volatile foaming agent and a nonionic surfactant and heating it is filled in a mold and heated. In the method of producing a foamed molded article by subjecting it to a cooling step, after the cooling step is performed until the foaming pressure of the molded body is reduced to 0.01 MPa or less, if a water treatment step is further performed, higher antistatic performance can be obtained. In addition, a foamed molded product of a styrenic resin having excellent antistatic properties with no variation in antistatic performance depending on the portion of the foamed molded product obtained is obtained.

2 is a schematic diagram of a process of Example 1. FIG. FIG. 6 is a schematic diagram of a process of Example 3. 5 is a schematic view of a process of Comparative Example 1. FIG.

Claims (5)

The styrene-based resin particles are impregnated with 0.5 to 3.5 parts by weight of a non-ionic surfactant with respect to 100 parts by weight of the readily volatile foaming agent and the styrene-based resin particles, and heated to obtain pre-expanded particles. When the foamed particles are subjected to in-mold foam molding in the mold, the cooling step after foaming in the mold is performed until the foaming pressure of the foam molded body in the mold decreases to 0.01 MPa or less, and then the mold is placed in the mold. A method for producing an antistatic styrene-based resin foam molded article, comprising performing a water treatment step of bringing water into contact with the surface of the foam molded article. The method for producing an antistatic styrene resin foam molded article according to claim 1, wherein the styrene resin particles are polyolefin-modified styrene resin particles. The manufacturing method according to claim 1 or 2, wherein the water treatment step is performed for 20 to 200 seconds while maintaining the pressure in the mold at 0 to 0.02 MPa. It is a foaming molding obtained by the manufacturing method as described in any one of Claims 1-3, The said foaming molding has an average surface resistivity of 1 * 10 < ¹¹ > (ohm) or less, Antistatic property characterized by the above-mentioned. Styrenic resin foam molding. The antistatic styrene resin foam molded article according to claim 4, wherein the foam molded article has a standard deviation of a surface resistivity of 1.0 or less.

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