JP2010229325A - Method for producing styrene-modified polyethylene resin pre-foamed particle and styrene-modified polyethylene resin foamed body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing styrene-modified polyethylene resin pre-foamed particles for easily providing the styrene-modified polyethylene resin pre-foamed particles having a high foaming rate and providing a styrene-modified polyethylene resin foamed body having excellent surface properties even when in-mold foaming molding is performed after a foaming agent of the styrene-modified polyethylene resin pre-foamed particles is scattered. <P>SOLUTION: In the method for producing the styrene-modified polyethylene resin pre-foamed particles, styrene-modified polyethylene resin particles are dispersed in an aqueous dispersion medium in the presence of a plasticizer in a pressure vessel, a foaming agent is put in the pressure vessel and heated to impregnate the styrene-modified polyethylene resin particles with the foaming agent and then one end of the pressure vessel is opened to discharge a mixture including the styrene-modified polyethylene resin particles and the aqueous dispersion medium to a region having lower pressure than the pressure inside the pressure vessel. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing styrene-modified polyethylene resin pre-expanded particles. Furthermore, the present invention relates to a styrene-modified polyethylene resin foam molded article having excellent surface properties.

  Polyolefin resin foam moldings are generally used as packaging materials because they are generally highly elastic and have a high strain recovery capability against repeated stresses, as well as being excellent in oil resistance and split resistance. ing. However, it has the disadvantages of low rigidity, easy shrinkage of the foamed molded product after in-mold foam molding, and low compressive strength.

  As a method for improving such a defect, a foam molded article made of a styrene-modified polyethylene resin obtained by polymerizing a polyethylene resin impregnated with a styrene monomer is known.

  For example, in Patent Document 1, in a modified thermoplastic resin particle obtained by polymerizing a polyethylene resin by impregnating a styrene monomer, the polyethylene particle is added to the styrene monomer for the purpose of improving the weather resistance. An initiator having a 10-hour half-life temperature of 60 ° C. to 105 ° C. of an organic peroxide having no benzene ring as a polymerization catalyst when adding, polymerizing and crosslinking is used, and having no benzene ring as a polyethylene crosslinking agent Polymerization / crosslinking reaction is performed using an initiator having an organic oxide 10-hour half-life temperature of 100 ° C. to 125 ° C. Furthermore, a method is disclosed in which pre-expanded particles are obtained by impregnating the resin particles obtained above after the polymerization / crosslinking reaction with a foaming agent.

  However, in the styrene-modified polyethylene resin pre-expanded particles obtained by the above method, good moldability of the pre-expanded particles is obtained, and the molded body formed by molding the pre-expanded particles has high crack resistance. It is difficult to achieve both, and various attempts have been made.

  For example, Patent Document 2 describes a gel amount and a molecular weight range for achieving both crack resistance and moldability, and pre-expanded particles having excellent moldability are obtained. However, the evaluation of the pre-expanded particles in Patent Document 2 is merely evaluating the molding and surface properties of the pre-expanded particles cured at room temperature for one day after the pre-expansion.

  As described above, many studies have been made on improving the surface properties of a styrene-modified polyethylene resin foamed molded article composed of styrene-modified polyethylene resin pre-expanded particles.

  On the other hand, the bead-method in-mold foam molded article is manufactured by filling pre-expanded particles into a mold and heating and foaming. As a method for producing the pre-expanded particles, the resin particles and the foaming agent are dispersed in a dispersion medium such as water in a pressure-tight airtight container, heated and impregnated in the resin particles with the foaming agent. A so-called pressure-reducing foaming method is known.

  When producing pre-expanded particles from a styrene-modified polyethylene resin, a decompression foaming method can be applied. However, the decompression foaming method requires a higher foaming pressure in order to obtain high-expansion pre-foamed particles.

  Therefore, development of a production method capable of easily obtaining styrene-modified polyethylene resin pre-expanded particles having a high expansion ratio has been desired.

JP-A-4-126726 JP 2006-29895 A

  In view of the above situation, the present invention can easily obtain a styrene-modified polyethylene resin pre-foamed particle having a high expansion ratio, and the mold after the foaming agent escapes from the styrene-modified polyethylene resin pre-foamed particle. An object of the present invention is to provide a method for producing styrene-modified polyethylene resin pre-expanded particles, which can obtain a styrene-modified polyethylene resin foam molded article having excellent surface properties even when inner foam molding is performed.

  As a result of intensive studies to solve the above problems, styrene-modified polyethylene resin particles are dispersed in a water-based dispersion medium together with a dispersant in a pressure vessel, and a foaming agent is placed in the pressure vessel and heated. After impregnating the foamed resin particles with the foaming agent, one end of the pressure vessel is opened, and the mixture containing the styrene-modified polyethylene resin particles and the aqueous dispersion medium is released to a lower pressure region than in the pressure vessel. In the so-called depressurization foaming method, it has been found that when styrene-modified polyethylene resin particles are dispersed in an aqueous dispersion medium in the presence of a plasticizer, styrene-modified polyethylene resin pre-expanded particles having a high expansion ratio can be obtained. Furthermore, the styrene-modified polyethylene resin pre-foamed particles obtained in this way are styrene modified with good surface properties even after the foaming agent has passed through the sun. It found that it is possible to produce a polyethylene resin expansion molding.

That is, the present invention has the following configuration.
[1] In a pressure vessel, styrene-modified polyethylene resin particles are dispersed in an aqueous dispersion medium in the presence of a plasticizer, and a foaming agent is placed in the pressure vessel and heated. After impregnating with a foaming agent, one end of the pressure vessel is opened, and a mixture comprising styrene-modified polyethylene resin particles and an aqueous dispersion medium is released to a lower pressure region than in the pressure vessel. Manufacturing method of resin pre-expanded particles.
[2] The method for producing styrene-modified polyethylene resin pre-expanded particles according to [1], wherein the plasticizer is a non-volatile plasticizer.
[3] The styrene-modified polyethylene according to [1] or [2], wherein the plasticizer is used in an amount of 0.1 to 5 parts by weight with respect to 100 parts by weight of the styrene-modified polyethylene resin particles. For producing resin-based pre-expanded particles.
[4] The method for producing styrene-modified polyethylene resin pre-expanded particles according to any one of [1] to [3], wherein the plasticizer is dibutyl sebacate.
[5] Styrene-modified polyethylene resin pre-expanded particles obtained by the production method according to any one of [1] to [4].
[6] A styrene-modified polyethylene resin foam molded product obtained by in-mold foam molding of the styrene-modified polyethylene resin pre-expanded particles according to [5].

  According to the production method of the present invention, it is possible to obtain styrene-modified polyethylene resin pre-expanded particles having a high expansion ratio without increasing the foaming pressure in the pressure-resistant container in the pressure-reducing foaming method. In addition, the obtained styrene-modified polyethylene resin pre-expanded particles are obtained from the styrene-modified polyethylene resin pre-expanded styrene-modified polyethylene resin pre-expanded particles, even after the foaming agent escapes from the styrene-modified polyethylene resin pre-expanded particles. can get.

  The method for producing styrene-modified polyethylene resin pre-foamed particles of the present invention comprises impregnating a polyethylene resin particle with a styrene monomer and polymerizing it to form styrene-modified polyethylene resin particles. After dispersing styrene-modified polyethylene resin particles in an aqueous dispersion medium in the presence of a plasticizer, placing the foaming agent in the pressure vessel and heating, and impregnating the styrene-modified polyethylene resin particles with the foaming agent One end of the pressure vessel is opened, and a mixture containing styrene-modified polyethylene resin particles and an aqueous dispersion medium is discharged into a lower pressure region than the inside of the pressure vessel and foamed.

  In the present invention, dispersion in the presence of a plasticizer means that styrene-modified polyethylene resin particles are released at the time when a mixture comprising styrene-modified polyethylene resin particles and an aqueous dispersion medium is released from the pressure vessel. Therefore, the plasticizer may be added when the styrene-modified polyethylene resin particles or other raw materials are put in the pressure vessel, or the plasticizer is impregnated in advance. The resin particles may be introduced into the pressure vessel.

  When adding a plasticizer when adding styrene-modified polyethylene resin particles or other raw materials into the pressure vessel, for example, a method of dispersing in a water-based dispersion medium in advance or dropping the mixture into the mixture after sealing the pressure vessel It can be added by the method.

  For example, in a pressure vessel, styrene-modified polyethylene resin particles, plasticizer, foaming agent, aqueous dispersion medium, and if necessary, a dispersant and a dispersion aid are charged and stirred at a predetermined temperature (hereinafter referred to as “foaming temperature”). The styrene-modified polyethylene resin particles are impregnated with a foaming agent, and an additional foaming agent is added as necessary, and the inside of the pressure vessel is kept at a constant pressure (hereinafter referred to as “foaming pressure”). It is preferable that the mixture containing the styrene-modified polyethylene resin particles and the aqueous dispersion medium is discharged from the lower part of the pressure vessel to a lower pressure region than the pressure inside the pressure vessel.

  There is no particular limitation on the pressure vessel to be used, and any vessel that can withstand the vessel pressure and the temperature in the vessel at the time of producing the pre-foamed particles may be used. For example, an autoclave type pressure vessel may be mentioned.

  The plasticizer used in the present invention is not particularly limited, and examples thereof include aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; alicyclic hydrocarbons such as cyclohexane; diisodecyl phthalate (DIDP), and bis (phthalate) ( Phthalic acid esters such as 2-ethylhexyl) (DOP) and dibutyl phthalate (DBP); Aliphatic dibasic acid esters such as dioctyl adipate (DOA), dibutyl adipate (DBA) and dibutyl sebacate (DBS) Acetylated products such as ricinoleic acid and glycerin; glycerin fatty acid esters such as epoxidized soybean oil, coconut oil and palm oil.

  Nonvolatile plasticizers are particularly preferred because they remain in the pre-expanded particles over time and good in-mold foam moldability can be obtained. The non-volatile plasticizer is one that hardly evaporates at the time of preliminary foaming, in-mold foam molding and under long-term storage. Specifically, in consideration of normal pre-foaming temperature and in-mold foam molding temperature, specifically 200 ° C. Those having the above boiling points are preferred. Specifically, phthalate esters such as diisodecyl phthalate (DIDP), bis (2-ethylhexyl) phthalate (DOP), dibutyl phthalate (DBP); dioctyl adipate (DOA), dibutyl adipate (DBA) And aliphatic dibasic acid esters such as dibutyl sebacate (DBS); acetylated products such as ricinoleic acid and glycerin; and glycerin fatty acid esters such as epoxidized soybean oil and coconut oil. Among these, dibutyl sebacate is particularly preferable.

  The amount of the plasticizer used is preferably from 0.1 to 5 parts by weight, more preferably from 0.3 to 2 parts by weight, based on 100 parts by weight of the styrene-modified polyethylene resin particles. It is. If the amount is less than 0.1 part by weight, significant improvement of the expansion ratio and in-mold foam moldability may not be obtained. On the other hand, if the amount is more than 5 parts by weight, the heat resistance of the resulting styrene-modified polyethylene resin pre-expanded particles is lowered, and the styrene-modified polyethylene resin foam molded product obtained by in-mold foam molding tends to shrink greatly. is there.

  The aqueous dispersion medium in the present invention is not particularly limited as long as it does not dissolve the resin particles. Examples thereof include water, methanol, ethanol, glycerin, and ethylene glycol, and these may be used in combination. In particular, it is preferable to use water. The amount of the aqueous dispersion medium used is preferably 50 parts by weight or more and 1000 parts by weight or less with respect to 100 parts by weight of the styrene-modified polyethylene resin particles.

  The dispersant that can be used in the present invention may be a known one, and examples thereof include poorly water-soluble inorganic salts such as tricalcium phosphate, magnesium carbonate, calcium carbonate, aluminum oxide, hydroxyapatite, magnesium pyrophosphate, and kaolin. These can be preferably used.

  In the present invention, a dispersion aid may be used to efficiently disperse the styrene-modified polyethylene resin particles with a small amount of dispersant.

  Examples of the dispersion aid include surfactants, and specific examples include anionic surfactants such as sodium dodecylbenzene sulfonate, higher alcohol sodium sulfate, n-paraffin sulfonate sodium, alkyl naphthalene sulfonate sodium. , Cationic surfactants such as benzalkonium chloride, alkyltrimethylammonium chloride, and dialkyldimethylammonium chloride. In particular, an anionic surfactant is suitable.

  The amount of these dispersants and dispersion aids used varies depending on the type thereof, the type and amount of styrene-modified polyethylene resin, the type of foaming agent, etc., but is usually based on 100 parts by weight of the aqueous dispersion medium. The dispersant is preferably 0.05 part by weight or more and 3 parts by weight or less, and the dispersion aid is 0.0001 part by weight or more and 0.2 part by weight or less.

  Further, for the purpose of reducing the amount of dispersant adhering to the styrene-modified polyethylene resin pre-expanded particles, an acid may be mixed with the aqueous dispersion medium to make the aqueous dispersion medium acidic.

  The mixture comprising the styrene-modified polyethylene resin particles and the aqueous dispersion medium prepared in the pressure vessel as described above is preferably 120 ° C. to 170 ° C., more preferably 130 ° C. to 150 ° C. with stirring. The temperature is raised to the following predetermined foaming temperature, and is maintained at that temperature for a certain period of time, usually 5 minutes to 180 minutes, preferably 10 minutes to 60 minutes, and the pressure in the pressure vessel rises. A foaming agent is impregnated into the styrene-modified polyethylene resin particles. Thereafter, if necessary, a foaming agent is additionally supplied until a predetermined foaming pressure is reached, and the foaming agent may be maintained for a certain period of time, usually 5 minutes to 180 minutes, preferably 10 minutes to 60 minutes. is there. In this way, the styrene-modified polyethylene resin particles held at the foaming temperature and the foaming pressure are opened at one end of the pressure vessel, generally a valve provided at the lower portion of the pressure vessel. Styrene modified polyethylene resin pre-expanded particles can be obtained by discharging to atmospheric pressure.

  When the styrene-modified polyethylene resin particles are discharged to a low pressure region, they can be discharged through an opening orifice of 1 to 10 mmφ for the purpose of adjusting the flow rate and reducing the variation in magnification. In some cases, the low pressure region is filled with saturated steam for the purpose of increasing the expansion ratio.

  The styrene-modified polyethylene resin particles of the present invention are preferably impregnated with 150 parts by weight or more and 400 parts by weight or less, more preferably 180 parts by weight or more and 300 parts by weight or less of the styrene monomer with respect to the polyethylene resin particles. It was obtained by polymerization. Within this range, in-mold foam moldability is good, and the resulting styrene-modified polyethylene resin foam molded article tends to be pre-foamed styrene-modified polyethylene resin particles with good crack resistance. .

  Polyethylene resins constituting the polyethylene resin particles used in the present invention are ethylene homopolymers such as high-density polyethylene and low-density polyethylene, polyethylene, and propylene, 1-butene, 1-pentene, 1-hexene, for example. And a copolymer with α-olefin such as vinyl acetate, acrylic acid ester, vinyl chloride and the like. Among these, a copolymer of ethylene and vinyl acetate is preferable. Furthermore, an ethylene / vinyl acetate copolymer having a melt flow rate (hereinafter sometimes referred to as MFR) of 1.5 g / 10 min or less and a vinyl acetate content of 10 wt% or less is preferable. If the MFR exceeds 1.5 g / 10 min, the development of crack resistance tends to be difficult. If the vinyl acetate exceeds 10% by weight, the melting point is low, so that resin deformation tends to occur during polymerization. The MFR is a value measured according to JIS K 6924.

  The polyethylene resin is previously made into polyethylene resin particles by melting using, for example, an extruder, a kneader, a Banbury mixer, a roll, or the like. The shape is preferably a particle state such as powder or pellet. The average particle weight of the polyethylene resin particles is preferably in the range of 0.1 mg / particle to 3 mg / particle. If it is less than 0.1 mg / grain, the foaming agent may dissipate rapidly, making it difficult to increase the magnification. If it is greater than 3 mg / grain, the moldability during in-mold foam molding may deteriorate. is there. At this time, a plasticizer may be added, or various additives such as a bubble regulator may be added as necessary.

  As the styrene monomer used in the present invention, styrene and styrene derivatives such as α-methyl styrene, paramethyl styrene, t-butyl styrene and chlorostyrene can be used as main components. In addition, components capable of copolymerization with styrene derivatives such as esters of acrylic acid and methacrylic acid such as methyl acrylate, butyl acrylate, methyl methacrylate, and ethyl methacrylate, acrylonitrile, dimethyl fumarate, ethyl fumarate, etc. These various monomers may be used alone or in combination of two or more. Furthermore, polyfunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate can also be used.

  It is preferable to use a polymerization initiator when the styrene monomer is polymerized on the polyethylene resin particles. As the polymerization initiator that can be used, radical generating polymerization initiators generally used for the production of thermoplastic polymers can be used. Typical examples include benzoyl peroxide, lauroyl peroxide, t- Butyl perpivalate, t-butyl peroxyisopropyl carbonate, di-t-butyl peroxyhexahydroterephthalate, 1,1-di (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-di Examples thereof include organic peroxides such as (t-butylperoxy) cyclohexane, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators can be used alone or in admixture of two or more. The weight average molecular weight can be adjusted by the amount of the polymerization initiator and the reaction temperature.

  The amount of the polymerization initiator used is preferably 0.05 parts by weight or more and 1.0 parts by weight or less, more preferably 0.1 parts by weight or more and 0.5 parts by weight or less with respect to 100 parts by weight of the styrene monomer. Part or less.

  In the present invention, as a method of polymerizing styrene-modified polyethylene resin particles, a styrene monomer is continuously or intermittently added to an aqueous suspension containing polyethylene resin particles charged in a container equipped with a stirrer. By adding to the polyethylene resin particles, the polyethylene resin particles are impregnated with a styrene monomer and polymerized. In the polymerization, the weight average molecular weight of the styrene-modified polyethylene resin pre-expanded particles can be adjusted by arbitrarily selecting the addition rate of the styrene monomer to be added. A polymerization temperature of 70 ° C. or higher and 90 ° C. or lower is preferred because styrene-modified polyethylene resin pre-expanded particles having a desired weight average molecular weight can be obtained.

  In the present invention, the styrene-modified polyethylene resin pre-expanded particles preferably contain a gel insoluble in xylene, and a cross-linking agent is preferably used to form a gel insoluble in xylene. Specifically, it is preferable to use a radical species-generating crosslinking agent having a 10-hour half-life temperature of 100 ° C. or more and 125 ° C. or less. Examples of such radical species-generating crosslinking agents include di-t-butyl peroxide (10-hour half-life temperature: 123 ° C.), dicumyl peroxide (10-hour half-life temperature: 116 ° C.), and t-butyl peroxy. Benzoate (10-hour half-life temperature: 104 ° C.), t-butyl peroxyacetate (10-hour half-life temperature: 102 ° C.), 2,2-bis-t-butyl peroxybutane (10-hour half-life temperature: 103 ° C.) Etc. These crosslinking agents can be added to the polymerization system before addition of the styrene monomer or together with the styrene monomer. The crosslinking reaction may be performed at the time of polymerization or at the time of decompression foaming. In the present invention, it is preferable that 50% by weight or more of the total amount of gel components insoluble in xylene is generated during decompression foaming. Thus, the adjustment of the gel formation timing is to adjust the polymerization temperature of the styrene-modified polyethylene resin, the temperature in the pressure-resistant container at the time of preliminary foaming, the 10-hour half-life temperature of the crosslinking agent, the method of adding the crosslinking agent, and the like. Can be done.

  Examples of the blowing agent that can be used in the present invention include known ones, for example, aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, normal pentane, and neopentane, difluoroethane, tetrafluoroethane, and the like. Examples thereof include volatile foaming agents such as hydrofluorocarbons having an ozone depletion coefficient of zero, and inorganic gases such as nitrogen and carbon dioxide. These foaming agents can be used in combination.

  The amount of the foaming agent varies depending on the type of styrene-modified polyethylene resin to be used, the composition of the base resin, the type of foaming agent, the target foaming ratio, etc. The amount is preferably 10 parts by weight or more and 60 parts by weight or less, more preferably 15 parts by weight or more and 30 parts by weight or less, based on 100 parts by weight of the modified polyethylene resin particles. If it is less than 10 parts by weight, a sufficient expansion ratio cannot be obtained, and it may be difficult to obtain styrene-modified polyethylene resin pre-expanded particles having good in-mold foam moldability. If it exceeds 60 parts by weight, the dispersion state of the resin particles when impregnated with the foaming agent becomes unstable, and the resins tend to aggregate. In some cases, a method of using water contained in the aqueous dispersion medium as a foaming agent is used.

  The styrene-modified polyethylene resin pre-expanded particles obtained as described above preferably contain a gel insoluble in xylene. The amount of gel insoluble in xylene is preferably 10% by weight or more and 50% by weight or less, and more preferably 15% by weight or more and 40% by weight or less in the pre-expanded particles of styrene-modified polyethylene resin. Within this range, when performing in-mold foam molding, high-pressure or long-time steam heating is not required, and a styrene-modified polyethylene resin foam-molded article that is easy to increase in magnification and has good crack resistance can be obtained. There is a tendency.

  The amount of gel insoluble in xylene is measured as follows. Place 0.4 g of pre-expanded resin particles in a 200-mesh wire mesh bag, immerse in 450 ml of xylene boiled under atmospheric pressure for 2 hours, take it out after cooling, and then remove the resin in new boiled xylene. For 1 hour and after cooling, it is taken out from xylene. Thereafter, the immersion and elution were repeated for 2 hours and 1 hour in the same manner. After that, the liquid was drained overnight at room temperature, dried in an oven at 150 ° C. for 1 hour, allowed to cool naturally to room temperature, and the residue after cooling was removed. The gel component is used, and the weight ratio of the amount of the gel component to the initial amount of pre-expanded particles is used as the gel amount.

  The styrene-modified polyethylene resin pre-expanded particles obtained by the production method of the present invention preferably have a weight average molecular weight of 150,000 or more and 350,000 or less of components soluble in tetrahydrofuran. Within this range, when performing in-mold foam molding, high-pressure or long-time steam heating is not required, and a styrene-modified polyethylene resin foam-molded article that is easy to increase in magnification and has good crack resistance can be obtained. There is a tendency.

  Here, the weight-average molecular weight of the component soluble in tetrahydrofuran refers to a component extracted by immersing 0.02 g of styrene-modified polyethylene resin pre-expanded particles in 20 ml of normal temperature tetrahydrofuran for 24 hours through a 0.2 μm filter. This is a value obtained by gel permeation chromatography GPC (Tosoh HLC-8220 GPC, detector: RI8020, column: TSKgel-GMHHR × 2) based on a standard polystyrene sample.

  The styrene-modified polyethylene resin pre-expanded particles thus obtained can be subjected to in-mold foam molding by a general in-mold foam molding method to obtain a styrene-modified polyethylene resin foam molded article. Specifically, it is filled in a mold that can be closed but cannot be sealed, and is heat-sealed to obtain a styrene-modified polyethylene resin foam molded article. The obtained styrene-modified polyethylene resin foam molded article exhibits excellent fusing properties.

  In addition, the styrene-modified polyethylene resin pre-expanded particles of the present invention can be used when the foaming agent escapes after the production, and the foaming agent in the styrene-modified polyethylene resin pre-expanded particles becomes 1% by weight or less. Even in such a case, good in-mold foam moldability is exhibited, and the obtained styrene-modified polyethylene resin foam molded article exhibits good surface properties.

  Examples and comparative examples will be described below, but the present invention is not limited thereby. In addition, about measurement evaluation, it implemented as follows.

<Foaming power>
The bulk magnification when foaming at a foaming pressure of 2.3 MPa was defined as foaming force, and 30 times or more was regarded as acceptable. The obtained styrene-modified polyethylene resin pre-expanded particles were worn and collected in a 3000 mL volume container, the resin weight was measured, and the bulk magnification was determined based on the following equation.
Bulk magnification (times) = 3000 (mL) ÷ resin weight (g) x resin specific gravity (g / mL)

<Surface condition of foam molded article>
After the obtained styrene-modified polyethylene resin pre-foamed particles are dehydrated and dried, the pre-foamed particles (immediately after) are cured at room temperature for 2 days, and the amount of the remaining foaming agent is changed to pre-foamed particles in a drying chamber at about 35 ° C. In contrast, the pre-foamed particles (aged) dried to 1% by weight or less were subjected to in-mold foam molding, and the foam molded article stored in a drying room at about 35 ° C. for one day after in-mold foam molding was visually observed. Evaluation was made by observation. The surface with the larger numerical value is the surface state with fewer gaps between the particles, and 3 or more expressed with a perfect score of 5 was regarded as acceptable.
5: Gaps are not found 4: There are some gaps but almost unknown 3: There are gaps in some places, but the tolerance level as a whole 2: The gaps are conspicuous 1: There are many gaps

<Measurement of gel amount>
Place 0.4 g of pre-expanded particles in a 200-mesh wire mesh bag, immerse in 450 ml of xylene boiled under atmospheric pressure for 2 hours, take it out after cooling, and then add 1 resin into the newly boiled xylene. Immerse for a time and remove from xylene after cooling. Thereafter, the immersion and elution were repeated for 2 hours and 1 hour in the same manner. After that, the liquid was drained overnight at room temperature, dried in an oven at 150 ° C. for 1 hour, naturally cooled to room temperature, and the remaining content after cooling. Was the gel component, and the weight ratio of the amount of the gel component to the initial pre-expanded particles was the gel component.

<Weight average molecular weight of tetrahydrofuran soluble component>
The components extracted by immersing 0.02 g of styrene-modified polyethylene resin pre-expanded particles in 20 ml of normal temperature tetrahydrofuran for 24 hours were filtered through a 0.2 μm filter and subjected to gel permeation chromatography (GPC). : Tosoh HCL-8220GPC, detector: RI8020, column: TSKgel-GMHHR × 2), and standard polystyrene sample.

(Manufacture of styrene-modified polyethylene resin particles)
Using "Evaate F1103-1" manufactured by Sumitomo Chemical Co., Ltd. as the polyethylene resin, 0.2 part by weight of talc is mixed with 100 parts by weight of the polyethylene resin, melt-mixed in the extruder, granulated, and submerged in water. By cutting immediately after extrusion, spherical polyethylene resin particles having a particle weight of about 1 mg / particle were produced.

  Subsequently, 150 parts by weight of water, 1 part by weight of tribasic calcium phosphate, 0.024 part by weight of sodium α-olefin sulfonate, and 30 parts by weight of polyethylene resin particles are suspended in a 6 L autoclave, and a polymerization initiator is added to 15 parts by weight of styrene. 0.26 parts by weight of benzoyl peroxide (10-hour half-life temperature: 74 ° C.) and 0.60 part by weight of t-butyl peroxybenzoate (10-hour half-life temperature: 104 ° C.) as a radical species-generating crosslinking agent The dissolved solution was added. Thereafter, this aqueous suspension was heated to 70 ° C. and maintained for 30 minutes to impregnate the polyethylene resin particles with the styrene monomer solution. Furthermore, the temperature was raised to 85 ° C., 55 parts by weight of a styrene monomer was dropped into the reaction system over 3 hours and 40 minutes to perform polymerization, and the temperature was further raised to 125 ° C. and held for 30 minutes. Styrene-modified polyethylene resin particles were obtained by dehydration and drying.

Example 1
A 10 L autoclave is charged with 300 parts by weight of water, 0.5 parts by weight of dibutyl sebacate, 2.0 parts by weight of tricalcium phosphate, 0.02 parts by weight of sodium n-paraffin sulfonate, and 100 parts by weight of styrene-modified polyethylene resin particles. It is. After adding 22 parts by weight of normal rich butane (normal butane / isobutane = 70/30) as a foaming agent to the autoclave, the temperature was raised to 140 ° C. and held for 50 minutes to advance the impregnation of the foaming agent and the crosslinking reaction. Thereafter, the styrene-modified polyethylene resin pre-foamed particles are discharged under atmospheric pressure with a water-based dispersion medium through an orifice having an opening diameter of 5 mm from the autoclave at a foaming pressure of 2.30 MPa (gauge pressure). Got. During the discharge under atmospheric pressure, the pressure in the autoclave was adjusted to be kept constant by introducing high-pressure nitrogen (hereinafter sometimes referred to as a foaming step).

  The obtained styrene-modified polyethylene resin pre-foamed particles were dehydrated and dried, and then pre-foamed particles cured at room temperature for 2 days, and the amount of residual foaming agent in the drying chamber at about 35 ° C. was 1 with respect to the pre-foamed particles. Two types of pre-expanded particles dried to a weight percent or less are prepared, heated with steam at a pressure of 0.10 MPa (gauge pressure), and molded with a 300 × 450 × 25 (t) mm size mold. Inner foam molding was performed to obtain and evaluate a styrene-modified polyethylene resin foam molding. The evaluation results are shown in Table 1. The amount of the remaining foaming agent in the pre-expanded particles is determined by accurately weighing about 2 g of the pre-expanded particles, heat-treating in an oven at 150 ° C. for 30 minutes, cooling to room temperature, and measuring again. It calculated by calculating | requiring the weight% of.

(Example 2)
Styrene-modified polyethylene resin pre-expanded particles were obtained in the same manner as in Example 1 except that 1.0 part by weight of dibutyl sebacate was used in the foaming step in a 10 L autoclave. The obtained styrene-modified polyethylene resin pre-expanded particles were evaluated by in-mold foam molding in the same manner as in Example 1.

Example 3
Styrene-modified polyethylene resin pre-foamed particles were obtained in the same manner as in Example 1 except that dibutyl sebacate was changed to 5.0 parts by weight in the foaming step in a 10 L autoclave. The obtained styrene-modified polyethylene resin pre-expanded particles were evaluated by in-mold foam molding in the same manner as in Example 1.

Example 4
Styrene-modified polyethylene resin pre-expanded particles were obtained in the same manner as in Example 1 except that 5 parts by weight of toluene was used instead of dibutyl sebacate in the foaming process in a 10 L autoclave. The obtained styrene-modified polyethylene resin pre-expanded particles were evaluated by in-mold foam molding in the same manner as in Example 1.

(Example 5)
Styrene-modified polyethylene resin pre-expanded particles were obtained in the same manner as in Example 1 except that 5 parts by weight of cyclohexane was used instead of dibutyl sebacate in the foaming process in a 10 L autoclave. The obtained styrene-modified polyethylene resin pre-expanded particles were evaluated by in-mold foam molding in the same manner as in Example 1.

(Comparative Example 1)
Styrene-modified polyethylene resin pre-expanded particles were obtained in the same manner as in Example 1 except that 0 part by weight of dibutyl sebacate was used in the foaming process in a 10 L autoclave. The obtained styrene-modified polyethylene resin pre-expanded particles were evaluated by in-mold foam molding in the same manner as in Example 1.

  The styrene-modified polyethylene resin pre-expanded particles obtained by the production method of the present invention are excellent in in-mold foam moldability even if not immediately after the pre-expansion. In addition, since the styrene-modified polyethylene resin foam molded article obtained from the styrene-modified polyethylene resin pre-expanded particles is excellent in crack resistance, it can be suitably used especially for automobile members and cushioning materials.

Claims (6)

  In a pressure vessel, styrene-modified polyethylene resin particles are dispersed in an aqueous dispersion medium in the presence of a plasticizer, a foaming agent is placed in the pressure vessel and heated, and the styrene-modified polyethylene resin particles are expanded into a foaming agent. Then, one end of the pressure vessel is opened and a mixture of styrene-modified polyethylene resin particles and an aqueous dispersion medium is released to a lower pressure region than the pressure vessel to pre-expand the styrene-modified polyethylene resin. Particle manufacturing method.   The method for producing pre-expanded particles of styrene-modified polyethylene resin according to claim 1, wherein the plasticizer is a non-volatile plasticizer.   The styrene-modified polyethylene resin pre-expanded particles according to claim 1 or 2, wherein the plasticizer is used in an amount of 0.1 to 5 parts by weight with respect to 100 parts by weight of the styrene-modified polyethylene resin particles. Manufacturing method.   The method for producing pre-expanded particles of styrene-modified polyethylene resin according to any one of claims 1 to 3, wherein the plasticizer is dibutyl sebacate.   A styrene-modified polyethylene resin pre-expanded particle obtained by the production method according to any one of claims 1 to 4.   A styrene-modified polyethylene resin foam molded article obtained by in-mold foam molding of the styrene-modified polyethylene resin pre-expanded particles according to claim 5.