JP2009114432A - Styrene modified polyethylene based resin particle, and prefoamed particle obtained from resin particle thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide styrene modified polyethylene based resin particles which excel in molding workability even after scattering of a foaming agent of prefoamed particles, and a foam molded body obtained from which has high crack resistance. <P>SOLUTION: These styrene modified polyethylene based resin particles are obtained by saturating and polymerizing 150-300 pts.wt. of a styrenic monomer to 100 pts.wt. of a polyethylene-based resin. The central part of the styrene modified polyethylene-based resin particles forms a continuous gradient structure of the polyethylene-based resin and a polystylene-based resin with 0.3-1.0 μm of average layer thickness. The ratio of the polyethylene-based resin with the continuous gradient structure at the central part is 30% or higher. The xylene insoluble gel content of the styrene modified polyethylene based resin prefoamed particles obtained form the styrene modified polyethylene-based resin particles is 10-35 wt.%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a styrene-modified polyethylene resin particle having excellent crack resistance and molding processability, pre-foamed particles obtained from the resin particles, and a foam-molded article.

  Polyolefin resin foams are generally widely used as packaging materials because of their high elasticity and excellent strain resistance against repeated stresses, as well as excellent oil resistance and crack resistance. . However, it has disadvantages of low rigidity, easy shrinkage of the foamed molded product after in-mold molding, and low compressive strength.

  As a method for improving such a defect, a styrene-modified polyethylene resin is known in which a polyethylene resin is impregnated with a styrene monomer and polymerized.

  For example, in Patent Document 1, for the purpose of providing a foamed molded article excellent in heat resistance that can withstand repeated compression and maintains impact resistance strength that does not break even by impact, and has improved rigidity, a specific gel component is provided. Modified polyethylene-based resin particles obtained by using crosslinked high-density polyethylene-based resin particles having a rate are disclosed.

  Patent Document 2 describes a method for adding a monomer during polymerization and a method for increasing the impact resistance and chemical resistance of a styrene-modified polyethylene resin by controlling the power required for stirring to make the resin surface rich in olefin. ing.

  Patent Document 3 shows that a styrene-modified polyethylene resin having excellent chemical resistance can be obtained by dispersing styrene-based resin particles of at least 5 μm and 0.8 μm or less from the resin surface. Yes.

  As described above, in the styrene-modified polyethylene foam, many reports on improving crack resistance and chemical resistance have been made, and the importance of the form of the resin particle surface layer has been reported. Further, Patent Document 4 describes a gel amount and a molecular weight range for achieving both crack resistance and molding processability, and pre-expanded particles having excellent molding processability are obtained.

On the other hand, the raw material of the styrene-modified polyethylene foam molded article is transported to the molder in the form of pre-expanded particles and used for molding. Normally, the foaming agent in the pre-expanded particles dissipates every day. Go. Therefore, pre-expanded particles with little dissipation of the foaming agent in the pre-expanded particles, or styrene-modified polyethylene resin pre-expanded particles having excellent moldability even if the foaming agent of the pre-expanded particles is diffused Was desired.
JP 62-59642 A JP-A-2005-97555 JP 2006-70202 A JP 2006-29895 A

  In view of the above situation, the present invention is a styrene-modified polyethylene having excellent surface elongation at the time of molding processing even after the foaming agent escapes from the pre-foamed particles, and the obtained foamed molded article has high crack resistance. It is to provide a resin particle.

  In a modified polyethylene resin obtained by impregnating 100 parts by weight of a polyethylene resin with 150 parts by weight or more and 300 parts by weight or less of a styrene monomer and performing polymerization, the central part of the styrene modified polyethylene resin particles is a layer. Forming a co-continuous structure of polyethylene resin and polystyrene resin having an average thickness of 0.3 μm or more and 1.0 μm or less, and the ratio of the polyethylene resin of the co-continuous structure is 30% or more, By using styrene-modified polyethylene resin particles in which the xylene-insoluble gel component of the styrene-modified polyethylene resin pre-expanded particles obtained from the styrene-modified polyethylene resin particles is 10 wt% or more and 35 wt% or less, After foaming, molding processing is continued even after the foaming agent in the pre-expanded particles of styrene-modified polyethylene resin escapes over time. It was found that styrene-modified polyethylene resin pre-expanded particles capable of obtaining a foam excellent in workability and crack resistance were obtained, and the present invention was completed.

  That is, the first of the present invention is the styrene-modified polyethylene resin particles obtained by polymerizing 100 parts by weight of a polyethylene resin by impregnating 150 parts by weight or more and 300 parts by weight or less of a styrene monomer. The central part of the styrene-modified polyethylene resin particles forms a co-continuous structure of a polyethylene resin and a polystyrene resin having an average layer thickness of 0.3 μm or more and 1.0 μm or less, and the central part co-continuous structure The ratio of the polyethylene resin is 30% or more, and the xylene-insoluble gel component of the styrene-modified polyethylene resin pre-expanded particles obtained from the styrene-modified polyethylene resin particles is 10% by weight to 35% by weight. Relates to a styrene-modified polyethylene resin particle.

As a preferred embodiment,
(1) In the surface layer portion having a depth of 5 μm or less from the surface of the styrene-modified polyethylene resin particles, a spherical polystyrene resin having a diameter of 1.0 μm or less is dispersed in the polyethylene resin.
(2) By adding a crosslinking agent having a 10-hour half-life temperature of 100 ° C. or more and 125 ° C. or less during or after polymerization, and 50% or more of the crosslinking agent is decomposed at 130 ° C. or more and 150 ° C. or less. can get,
The present invention relates to the styrene-modified polyethylene resin particles described above.

  The second aspect of the present invention relates to styrene-modified polyethylene resin pre-foamed particles obtained by pre-foaming the styrene-modified polyethylene resin particles described above, and the third aspect of the present invention is the styrene-modified polyethylene resin described above. The present invention relates to a foamed molded article obtained by molding pre-expanded particles.

  When the styrene-modified polyethylene resin particles of the present invention are pre-foamed into styrene-modified polyethylene resin pre-foamed particles, the molding process is performed even after the blowing agent escapes from the styrene-modified polyethylene resin pre-foamed particles. Excellent in properties. Therefore, the bead life is extended, which is industrially advantageous.

  Moreover, the foaming molding obtained from the styrene modified polyethylene resin pre-expanded particles of the present invention exhibits high crack resistance.

  The styrene-modified polyethylene resin particles of the present invention are styrene-modified polyethylene resin particles in which a styrene monomer is used in an amount of 150 to 300 parts by weight based on 100 parts by weight of a polyethylene resin. The central part of the modified polyethylene resin particles forms a co-continuous structure of a polyethylene resin and a polystyrene resin having an average layer thickness of 0.3 μm or more and 1.0 μm or less, and the polyethylene part of the center part co-continuous structure The resin ratio is 30% or more, and the xylene-insoluble gel component of the styrene-modified polyethylene resin pre-expanded particles obtained from the styrene-modified polyethylene resin particles is 10% by weight or more and 35% by weight or less.

  In the present invention, 150 parts by weight or more and 300 parts by weight or less, preferably 180 parts by weight or more and 250 parts by weight or less of the styrene monomer is polymerized with respect to 100 parts by weight of the polyethylene resin. Within this range, styrene-modified polyethylene resin particles having good moldability and good crack resistance of the resulting foamed molded article when obtained as styrene-modified polyethylene pre-expanded particles can be obtained.

  In the present invention, as a method of polymerizing a polyethylene resin by impregnating a styrene monomer, an aqueous suspension containing polyethylene resin particles processed into a particle shape is charged into a container equipped with a stirrer, and styrene is used. By continuously or intermittently adding the system monomer, the polyethylene resin particles are impregnated with the styrene monomer and polymerized. In the polymerization, it is possible to adjust the weight average molecular weight of the styrene-modified polyethylene resin particles by arbitrarily selecting the addition rate of the styrene monomer to be added.

  In the polymerization in the present invention, as a preferred embodiment, 25 parts by weight or more and 100 parts by weight or less of a styrene monomer are added and impregnated with 100 parts by weight of polyethylene resin particles at a temperature at which the polymerization does not proceed substantially. The remaining styrenic monomer is added under heating. “Under the temperature at which the polymerization does not proceed essentially” means a temperature not higher than the 10-hour half-life temperature of the polymerization initiator used. In the polymerization, by adding and impregnating a part of the styrene monomer to be added at a temperature at which the polymerization does not proceed essentially, the viscosity of the polyethylene resin particles as the polymerization site can be changed. It is easy to adjust the gel component amount and the weight average molecular weight of the modified polyethylene resin pre-expanded particles.

  The polyethylene resin used in the present invention is a homopolymer of ethylene such as high density polyethylene and low density polyethylene, ethylene, and α-olefin such as propylene, 1-butene, 1-pentene, 1-hexene, and acetic acid. Examples thereof include copolymers with vinyl, acrylic acid ester, vinyl chloride and the like. Among these, a copolymer of ethylene and vinyl acetate is preferable. More preferred is 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. If the MFR exceeds 1.5 g / 10 min, the development of crack resistance tends to be difficult. If the vinyl acetate content exceeds 10% by weight, the melting point is low, so that the resin tends to be deformed during polymerization. The melt flow rate is a value measured according to JIS K 6924.

  The polyethylene resin is made into polyethylene resin particles by melting in advance using, for example, an extruder, a kneader, a Banbury mixer, a roll or the like. The shape is preferably a particle shape such as powder or pellet. The average particle weight of these 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 filling property during molding may be deteriorated.

  Various additives can be used in the styrene-modified polyethylene resin particles of the present invention as needed. Examples of the various additives include a plasticizer and a bubble regulator according to the purpose. Examples of the plasticizer include stearic acid triglyceride, palmitic acid triglyceride, lauric acid triglyceride, stearic acid diglyceride, stearic acid monoglyceride and other fatty acid glycerides, palm oil, palm oil, palm kernel oil and other vegetable oils, dioctyl adipate, dibutyl sebacate And the like, organic hydrocarbons such as liquid paraffin and cyclohexane, and organic aromatic hydrocarbons such as toluene and ethylbenzene. These may be used in combination.

  Examples of the foam regulator include organic foam regulators such as aliphatic bisamides and stearamide such as methylene bis stearic acid amide and ethylene bis stearic acid amide, inorganic foams such as talc, silica, calcium silicate, and calcium carbonate. Examples thereof include regulators. These various additives can be used not only at the time of polymerization and at the time of impregnation with a foaming agent, but also by previously mixing with the polyethylene resin particles.

  In particular, in the case of performing the decompression foaming described later, it is preferable to use an inorganic cell regulator, and the preferable usage amount is 0.01 parts by weight or more and 0.5 parts by weight or less with respect to 100 parts by weight of the polyethylene resin. is there. When the amount of the inorganic air-conditioning agent is less than 0.01 parts by weight, it is difficult to stably generate bubbles, and when the amount is more than 0.5 parts by weight, the fusion during molding tends to deteriorate.

  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 monomers, for example, acrylic acid and methacrylic acid esters such as methyl acrylate, butyl acrylate, methyl methacrylate, and ethyl methacrylate, or 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.

  As the polymerization initiator used in the present invention, radical generating polymerization initiators generally used for the production of thermoplastic polymers can be used. Typical examples thereof include benzoyl peroxide and t-butyl peroxide. Oxy-2-ethylhexanoate, lauroyl peroxide, t-butyl perpivalate, t-butyl peroxyisopropyl carbonate, di-t-butyl peroxyhexahydroterephthalate, 1,1-di (t-butylperoxy ) Organic peroxides such as 3,3,5-trimethylcyclohexane and 1,1-di (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.

  A polymerization temperature of 70 ° C. or higher and 90 ° C. or lower is preferable because styrene-modified polyethylene resin pre-expanded particles having a desired weight average molecular weight can be obtained.

  In the polymerization according to the present invention, α-methylstyrene dimer generally used for polymerization of mercaptan chain transfer agents such as n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan and acrylonitrile-styrene resin. Etc. may be used in combination.

  In the present invention, the polymerization is carried out in an aqueous suspension containing polyethylene resin particles. In this case, it is preferable to use a dispersant in order to prevent fusion between the resin particles. Examples of the dispersant that can be used include dispersants generally used for suspension polymerization, for example, polymer dispersants such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyacrylamide, such as calcium phosphate, hydroxyapatite, magnesium pyrophosphate, and kaolin. Examples include poorly water-soluble inorganic salts.

  In addition, when a poorly water-soluble inorganic salt is used, it is preferable to use an anionic surfactant such as α-olefin sodium sulfonate or sodium dodecylbenzene sulfonate because the dispersion stability is increased, which is effective. These dispersants may be added during the polymerization. The amount of the dispersant used is preferably 0.2 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of water, although it depends on the type.

  The “aqueous suspension” of the present invention refers to a state in which resin and monomer droplets are dispersed in water or an aqueous solution by stirring or the like, and a water-soluble surfactant or monomer is dissolved in water. In addition, a water-insoluble dispersant, an initiator, a crosslinking agent, a bubble regulator, a flame retardant, a plasticizer, and the like may be dispersed together. The weight ratio of the obtained styrene-modified polyethylene resin and water is preferably 1.0 / 0.6 to 1.0 / 4.0 in terms of resin / water.

  In the present invention, it is necessary to have a gel component in the styrene-modified polyethylene resin pre-expanded particles, and therefore it is preferable to use a radical species-generating crosslinking agent. In the crosslinking reaction, it is preferable to use a crosslinking agent having a 10-hour half-life temperature of 100 ° C. or more and 125 ° C. or less. When a radical species-generating crosslinking agent having a 10-hour half-life temperature lower than 100 ° C. is used, the crosslinking reaction proceeds excessively during polymerization, and the crosslinking reaction time tends to be shortened at 130 ° C. or higher. If the 10-hour half-life temperature exceeds 125 ° C, it may take too much time for the crosslinking reaction to proceed at a temperature of 130 ° C or higher and 150 ° C or lower. Examples of the radical species-generating crosslinking agent having a 10-hour half-life temperature of 100 ° C. or more and 125 ° C. or less include di-t-butyl peroxide (10-hour half-life temperature: 123 ° C.), dicumyl peroxide (10-hour half-life). Temperature: 116 ° C.), t-butyl peroxybenzoate (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 degreeC) etc. are mentioned. These may be added to the polymerization system before the addition of the styrenic monomer or together with the styrenic monomer, or may be added at the time of preparation for decompression foaming.

  As a crosslinking reaction using a crosslinking agent having a 10-hour half-life temperature of 100 ° C. or more and 125 ° C. or less, 50% or more of the crosslinking agent is preferably decomposed at 130 ° C. or more and 150 ° C. or less. Since the main factor for the decomposition of the crosslinking agent is due to the progress of the crosslinking reaction, the decomposition of 50% or more of the crosslinking agent generally means that 50% or more of the crosslinking reaction has progressed. It is synonymous. When the cross-linking reaction is less than 130 ° C., it is difficult to obtain a co-continuous structure having an average layer thickness of 0.3 μm or more and 1.0 μm or less at the center of the styrene-modified polyethylene resin particles, and the moldability deteriorates Tend. When the crosslinking reaction exceeds 150 ° C., the resin is too soft and the styrene-modified polyethylene resin particles tend to aggregate.

  The cross-linking reaction may be performed during the polymerization or after completion of the polymerization by raising the temperature of the aqueous suspension to the cross-linking reaction temperature, or may be performed at the time of preliminary foaming described later.

  The structure of the central part of the styrene-modified polyethylene resin particles in the present invention forms a co-continuous structure of a polyethylene resin and a polystyrene resin having an average layer thickness of 0.3 μm or more and 1.0 μm or less. The average thickness of the layer is preferably 0.35 μm or more and 0.9 μm or less. If the average thickness of the layer is less than 0.3 μm, the elongation of the resin at the time of molding deteriorates and the moldability is inferior. When the average thickness of the layer exceeds 1.0 μm, it becomes difficult to obtain crack resistance.

  The ratio of the polyethylene resin at the center of the styrene-modified polyethylene resin particles of the present invention is 30% or more, and preferably 40% or more. If the ratio of the polyethylene resin at the center of the styrene-modified polyethylene resin particles is less than 30%, the crack resistance deteriorates.

  The central portion of the styrene-modified polyethylene resin particles referred to here is a region that is 1/3 of the radius of the styrene-modified polyethylene resin particles from the center of the styrene-modified polyethylene resin particles.

  Specifically, the structure of the central part of the styrene-modified polyethylene resin particles is evaluated by slicing the vicinity of the maximum diameter of the styrene-modified polyethylene resin particles into a thin film and using a transmission electron microscope (TEM). . The average thickness of the layers constituting the co-continuous structure is 1 μm in a photograph (hereinafter sometimes referred to as a TEM photograph) taken with a transmission electron microscope of an arbitrary portion of the central part of the styrene-modified polyethylene resin particles. Five straight lines having a length of 5 μm were drawn at intervals, and the thickness of each of the polystyrene-based resin layer and the polyethylene-based resin layer existing on each 5 μm straight line was read and calculated as an average value of the five lines. The average of the thickness of the obtained polystyrene-type resin layer and the thickness of a polyethylene-type resin layer was made into the average thickness of a layer.

  The ratio of the polyethylene resin at the center of the styrene-modified polyethylene resin particles is the length of the polyethylene resin on the straight line with respect to the length of the straight line (5 μm × 5) in the above photograph. It was a ratio.

  In the present invention, the styrene-modified polyethylene resin particles have a spherical polystyrene resin having a diameter of 1.0 μm or less dispersed in the polyethylene resin in the surface layer within a depth of 5 μm from the surface of the styrene-modified polyethylene resin particles. It is preferable. When the diameter of the polystyrene resin exceeds 1.0 μm, the crack resistance tends to deteriorate. In addition, the diameter of the polystyrene resin particles in the surface layer can be determined by observing a photograph of a transmission electron microscope.

  For styrene-modified polyethylene resin particles that undergo a crosslinking reaction when impregnated with a prefoaming foaming agent, the pressure-resistant container was cooled to normal pressure immediately before the prefoaming, and the resin was taken out without foaming. Measure things. The pre-foaming mode will be described later.

  Examples of the blowing agent that can be used in the present invention include known ones such as 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, inorganic gases such as air, nitrogen and carbon dioxide, and water. These foaming agents can be used in combination.

  The foaming agent is generally added after the crosslinking reaction with the radical species generating crosslinking agent, but may be added before the crosslinking reaction is completed.

  The amount of the foaming agent is preferably 10 parts by weight or more and 30 parts by weight or less, and more preferably 15 parts by weight or more and 25 parts by weight or less with respect to 100 parts by weight of the styrene-modified polyethylene resin particles. If it is less than 10 parts by weight, a sufficient expansion ratio may not be obtained, and it may be difficult to obtain pre-expanded particles having good moldability. If it exceeds 30 parts by weight, the dispersion state of the resin when impregnated with the foaming agent becomes unstable and the resins tend to aggregate.

  As a method of impregnating and pre-foaming styrene-modified polyethylene resin particles impregnated and polymerized with polyethylene-based resin particles with a foaming agent, (1) styrene-modified polyethylene resin in a pressure-resistant container Disperse the particles in an aqueous dispersion medium, place the foaming agent in a pressure-resistant container, heat it to a temperature above the softening point of the styrene-modified polyethylene resin particles, and pressurize it above the vapor pressure of the foaming agent. After impregnating the resin particles with a foaming agent, the so-called "" releases a mixture of styrene-modified polyethylene resin particles and an aqueous dispersion medium to a lower pressure region than in the pressure vessel while keeping the temperature and pressure in the pressure vessel constant. A method called “depressurization foaming”, (2) a polyethylene-based resin particle impregnated with a styrene monomer and polymerized, and then impregnated with a foaming agent to produce a foamable styrene-modified polyethylene. A method in which foamable styrene-modified polyethylene resin particles are placed in a container equipped with a stirrer and heated with a heat source such as water vapor. (3) Polyethylene resin particles are impregnated with styrene monomers. A method of polymerizing into styrene-modified polyethylene resin particles, impregnating a foaming agent in a container equipped with a stirrer, and heating with a heat source such as water vapor. It is preferable that an excessive amount of foaming agent is not required to perform impregnation of the foaming agent and prefoaming in a series of operations.

  In the method of (1), specifically, the styrene-modified polyethylene resin particles obtained by the polymerization reaction are taken out from the container once polymerized, washed and dried, and then pressure-resistant for decompression foaming. After charging the container and adding a foaming agent, the temperature is raised by heating, and one end of the container is opened while keeping the temperature and pressure in the pressure container constant, for example, through an orifice having a hole diameter of 1 mm to 10 mm. The styrene-modified polyethylene resin pre-expanded particles having a uniform and fine cell structure can be produced by releasing and foaming the contents in a lower pressure atmosphere, for example, in an atmosphere such as the air.

  The aqueous dispersion medium referred to as decompression foaming indicates a solution in which a dispersant is dissolved or dispersed in water, and the same type of dispersant as in the polymerization can be used as the dispersant. At this time, the weight ratio of styrene-modified polyethylene resin to water is preferably 1.0 / 0.6 to 1.0 / 4.0 in terms of resin / water. You may impregnate various additives, such as a plasticizer and a bubble regulator, at the time of this decompression foaming. This method is efficient because the foaming agent can be impregnated and pre-foamed at the same time, and the foaming agent can be recovered by a suction facility.

  In the method (2), specifically, the foaming agent is added and impregnated following the polymerization reaction by the above-described method. The blowing agent may be added at any timing before and after the crosslinking reaction. At this time, in order to prevent a sudden rise in the internal pressure due to the introduction of the foaming agent, the foaming agent is added after cooling to a temperature at which it is easy to add the foaming agent, if necessary, and then the temperature is raised to increase the foaming agent. Impregnation and crosslinking reaction can also be performed. Thereafter, the styrene-modified polyethylene resin particles impregnated with the foaming agent are discharged from the pressure vessel, washed and dried, and then heated with steam or the like to obtain styrene-modified polyethylene resin pre-expanded particles.

  In (3), specifically, the styrene-modified polyethylene resin particles obtained by carrying out the polymerization reaction are once taken out from the pressure vessel and washed and dried. Transfer to a pressure-resistant vessel equipped with a stirring period for impregnating foaming agent, add a small amount of water, a dispersant and a foaming agent, impregnate the foaming agent, and then discharge and heat with steam, etc. It can be a pre-expanded particle. In this method, since the drying step after impregnating the foaming agent can be omitted by reducing the amount of water charged at the time of impregnation with the foaming agent, the dissipation of the foaming agent until the preliminary foaming can be suppressed.

  The styrene-modified polyethylene resin pre-expanded particles obtained as described above have an amount of gel component insoluble in xylene of 10% by weight to 35% by weight, preferably 15% by weight to 30% by weight. is there. Within the range, when performing in-mold molding, high pressure or long-time steam heating is not required, and a foamed molded article that is easy to increase in magnification and has good crack resistance can be obtained.

  The amount of gel component insoluble in xylene in the present invention is measured as follows. Put 0.4g of styrene-modified polyethylene resin pre-expanded resin particles in a 200 mesh wire mesh bag, immerse in 450ml of xylene boiled under atmospheric pressure for 2 hours, take out once after cooling, and then boil again The resin is soaked in xylene for 1 hour, cooled, and 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. As the gel component, the weight ratio of the amount of the gel component to the amount of the pre-expanded styrene-modified polyethylene resin pre-expanded particles is used as the gel component amount.

  In the styrene-modified polyethylene resin pre-expanded particles of the present invention, a component soluble in tetrahydrofuran has a weight average molecular weight of 150,000 to 400,000. Within the range, when performing in-mold molding, high pressure or long-time steam heating is not required, and a foamed molded article that is easy to increase in magnification and has good crack resistance can be obtained.

  In the present invention, the weight-average molecular weight soluble in tetrahydrofuran is determined by immersing 0.02 g of styrene-modified polyethylene resin pre-foamed particles in 20 ml of normal temperature tetrahydrofuran for 24 hours using a 0.2 μm filter. It is a value obtained on the basis of a standard polystyrene sample by filtration or gel permeation chromatography.

  The styrene-modified polyethylene resin pre-expanded particles of the present invention obtained as described above have good moldability even when the foaming agent escapes. The term “when the foaming agent escapes” as used in the present invention refers to a state in which the amount of the foaming agent in the styrene-modified polyethylene resin pre-expanded particles is 0.9% by weight or less. Specifically, good moldability when the foaming agent escapes means that the moldability is good when the amount of the foaming agent in the styrene-modified polyethylene resin pre-expanded particles becomes 0.9% by weight. That means. It is more preferable that the moldability is good with a smaller amount of foaming agent.

  The amount of foaming agent in the styrene-modified polyethylene resin pre-expanded particles was measured by weighing about 2 g of styrene-modified polyethylene resin pre-expanded particles, drying in an oven at 150 ° C. for 30 minutes, and then cooling to room temperature. Then, the measurement was performed again, and the measurement was performed by determining the weight percent of the weight reduction with respect to the weight of the styrene-modified polyethylene resin pre-expanded particles after drying.

  The styrene-modified polyethylene resin pre-expanded particles thus obtained are molded by a general in-mold molding method. Specifically, it is filled in a mold that can be closed but cannot be sealed, and is heat-sealed to obtain a foam molded article. The obtained foamed molded article has high rigidity and excellent crack resistance. Therefore, it can be suitably used for automobile members, cushioning materials and the like.

  Examples and Comparative Examples are given below, but the present invention is not limited thereby. In addition, about measurement evaluation, it implemented as follows.

<Surface condition of foam molded article>
The surface state of the foamed molded product was evaluated by visual observation. The larger the numerical value, the smaller the surface state between the particles, and a score of 3 or more expressed as a perfect score of 5 was accepted.
5: The gap does not meet 4: There is a gap partially but is almost unknown 3: There are gaps in some places, but the tolerance level as a whole 2: The gap is conspicuous 1: There are many gaps

<Crack resistance (measurement of half fracture height)>
Based on JIS K 7211, a 321 g steel ball was dropped with a sample piece obtained by cutting the foam molded body into 200 × 20 × 20 (t) mm, and the half fracture height was measured.

<Surface condition of the foamed molded product when the foaming agent escapes>
The surface state of the foamed molded product was evaluated by visual observation after storage for 1 day in a drying room at about 35 ° C. The higher the numerical value, the smaller the surface state between the particles, and 3 or more were acceptable.

<Measurement of gel component amount>
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 was used, and the weight ratio of the amount of the gel component to the initial amount of pre-expanded particles was used as the gel component amount.

<Average thickness of the central layer of styrene-modified polyethylene resin particles>
The average thickness at the center of the resin particles was obtained by thinning a RuO ₄ dyed resin by a room temperature ultrathin section method and taking a TEM photograph of the center of the resin. Further, five straight lines having a length of 5 μm were drawn on the TEM photograph at intervals of 1 μm, the average value of the thickness of each layer existing on each 5 μm straight line was read, and the average value of five lines was calculated. In this case, strictly speaking, each layer of polyethylene resin and polystyrene resin includes a graft polymer in which each component reacts in addition to pure polyethylene resin and polystyrene resin, but this measurement does not take into account the non-stained portion of polyethylene resin. The system resin and the dyed part were judged as polystyrene. Moreover, although the polyethylene-type resin component contains the particulate fine polystyrene particle which does not form the continuous layer, we decided to consider this also as a part of polyethylene layer.

<Polyethylene resin ratio at the center of styrene-modified polyethylene resin particles>
The average thickness at the center of the resin particles was obtained by thinning a RuO ₄ dyed resin by a room temperature ultrathin section method and taking a TEM photograph of the center of the resin. Further, five straight lines having a length of 5 μm were drawn on the TEM photograph at intervals of 1 μm, and the length of the polyethylene component in each 5 μm straight line was obtained as a ratio and calculated as an average of the five lines.

<The diameter of the polystyrene resin in the surface layer portion of the styrene-modified polyethylene resin particles>
The resin stained with RuO ₄ was thinned by a room temperature ultrathin section method, and the diameter of the polystyrene resin in the visual field within 5 μm depth from the surface was observed from a TEM photograph of the resin surface.

Example 1
“Evaate F1103-1” manufactured by Sumitomo Chemical Co., Ltd. is used as the polyethylene resin, 0.2 parts by weight of talc is mixed with 100 parts by weight of the polyethylene resin, melt-mixed in the extruder, granulated, and extruded into water. By cutting immediately after the formation, 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 parts by weight of sodium α-olefin sulfonate, and 30 parts by weight of polyethylene resin particles are suspended in a 6 L autoclave, and polymerization is started on 15 parts by weight of styrene. 0.18 parts by weight of benzoyl peroxide (10-hour half-life temperature: 74 ° C.) as an agent and 0.29 parts by weight of dicumyl peroxide (10-hour half-life temperature: 116 ° C.) as a radical species-generating crosslinking agent 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. The temperature was further raised to 85 ° C., 55 parts by weight of a styrene monomer was dropped into the reaction system over 3 hours and 40 minutes, and the mixture was held at 85 ° C. for 1 hour after the completion of dropping. Thereafter, the temperature was raised to 140 ° C. and held for 3 hours to carry out a crosslinking reaction, and after cooling, washing, dehydration and drying were performed to obtain styrene-modified polyethylene resin particles.

  When TEM observation of the obtained styrene modified polyethylene resin particles was performed, the central part of the styrene modified polyethylene resin particles formed a co-continuous structure of polyethylene resin and polystyrene resin, and the average thickness of the layer was It was 0.46 μm. The ratio of the polyethylene resin at the center of the styrene-modified polyethylene resin particles was 49%. The diameter of the polystyrene resin in the surface layer portion of the styrene-modified polyethylene resin particles was 1 μm or less.

  A 4.5 L autoclave was charged with 330 parts by weight of water, 2 parts by weight of tricalcium phosphate, 0.01 parts by weight of sodium n-paraffin sulfonate, and 100 parts by weight of styrene-modified polyethylene resin particles. After adding 22 parts by weight of normal rich butane (normal butane / isobutane = 75/25) as a foaming agent, the temperature was raised to 140 ° C. and held for 30 minutes to impregnate the foaming agent. Thereafter, the styrene-modified polyethylene resin particles together with the aqueous dispersion medium were discharged under atmospheric pressure through an orifice having an opening diameter of 4 mm from the autoclave to obtain styrene-modified polyethylene resin pre-expanded particles having an expansion bulk ratio of 30 times. During the discharge under atmospheric pressure, the pressure in the autoclave was adjusted to be kept constant by introducing high-pressure nitrogen.

  Pre-expanded particles obtained by washing, dehydrating, and drying the obtained styrene-modified polyethylene resin pre-expanded particles for 2 days at room temperature (hereinafter sometimes referred to as “pre-expanded particles immediately after expansion”), and Pre-foamed particles dried in a drying chamber at about 35 ° C. until the residual foaming agent amount is 0.9% of the foamed particles (hereinafter, sometimes referred to as “pre-foamed particles when the foaming agent escapes”), These were produced using a Daisen KR-57 molding machine and molded with a 300 × 450 × 25 (t) mm size mold to obtain a foamed molded product. The crack resistance of the foamed molded product was evaluated and found to be 34 cm. The amount of the foaming agent in the pre-expanded particles is determined by weighing about 2 g of pre-expanded particles, drying in an oven at 150 ° C. for 30 minutes, cooling to room temperature, measuring again, %. The surface state of the foamed molded article formed by using the pre-expanded particles when the foaming agent escaped was 3.

(Example 2)
Polyethylene resin particles were prepared in the same manner as in Example 1.

  Subsequently, 150 parts by weight of water, 1 part by weight of tricalcium phosphate, 0.024 part by weight of sodium α-olefin sulfonate, and 35 parts by weight of polyethylene resin particles were suspended in a 6 L autoclave, and 17.5 parts by weight of styrene was suspended. 0.24 parts by weight of benzoyl peroxide (10-hour half-life temperature: 74 ° C.) as a polymerization initiator and 0.56 weight of t-butyl peroxybenzoate (10-hour half-life temperature: 104 ° C.) as a radical species-generating crosslinking agent The solution in which the part was dissolved 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. The temperature was further raised to 85 ° C., and 47.5 parts by weight of styrene monomer was dropped into the reaction system over 2 hours and 40 minutes. After completion of the dropping, the mixture was further maintained at 85 ° C. for 1 hour. Thereafter, the temperature was raised to 120 ° C. and held for 1 hour to complete the polymerization of the styrene monomer. At this time, the amount of decomposition of the crosslinking agent is about 40% calculated from the 10-hour half-life temperature, and the crosslinking reaction is not completed. After cooling, styrene-modified polyethylene resin particles were obtained by washing, dehydration and drying.

  A 4.5 L autoclave was charged with 330 parts by weight of water, 2 parts by weight of tricalcium phosphate, 0.01 parts by weight of sodium n-paraffin sulfonate, and 100 parts by weight of styrene-modified polyethylene resin particles. After adding 22.5 parts by weight of normal rich butane (normal butane / isobutane = 75/25) as a foaming agent to the autoclave, the temperature was raised to 140 ° C. and held for 50 minutes to impregnate the foaming agent and the remaining about 6 The cross-linking reaction was allowed to proceed. Thereafter, the styrene-modified polyethylene resin particles together with the aqueous dispersion medium were discharged under atmospheric pressure through an orifice having an opening diameter of 4 mm from the autoclave to obtain styrene-modified polyethylene resin pre-expanded particles having an expansion bulk ratio of 30 times. During the discharge under atmospheric pressure, the pressure in the autoclave was adjusted to be kept constant by introducing high-pressure nitrogen.

  The obtained styrene-modified polyethylene resin pre-expanded particles were molded and evaluated in the same manner as in Example 1. The crack resistance was 42 cm. The surface state of the foamed molded article that was molded when the residual foaming agent of the styrene-modified polyethylene resin pre-expanded particles was 0.9% was 3.

  Since the cross-linking reaction was performed during pre-foaming by decompression foaming, the same operation was performed for TEM photographs until just before decompression foaming, and the pressure-resistant container was cooled to normal pressure and foamed immediately before decompression foaming. The resin particles were taken out and measured. When TEM observation of the obtained styrene modified polyethylene resin particles was performed, the central part of the styrene modified polyethylene resin particles formed a co-continuous structure of polyethylene resin and polystyrene resin, and the average thickness of the layer was It was 0.40 μm. The ratio of the polyethylene resin component at the center of the styrene-modified polyethylene resin particles was 44%. The diameter of the polystyrene resin in the surface layer portion of the styrene-modified polyethylene resin particles was 1 μm or less.

(Comparative Example 1)
In the polymerization in a 6 L autoclave, the example is except that the crosslinking agent is t-butyl peroxybenzoate (10 hour half-life temperature: 104 ° C.) 0.45 part, and the temperature rise at 140 ° C. during the crosslinking reaction is 125 ° C. In the same manner as in Example 1, styrene-modified polyethylene resin particles were obtained.

  When TEM observation of the obtained styrene modified polyethylene resin particles was performed, the central part of the styrene modified polyethylene resin particles formed a co-continuous structure of polyethylene resin and polystyrene resin, and the average thickness of the layer was It was 0.29 μm. The ratio of the polyethylene resin at the center of the styrene-modified polyethylene resin particles was 47%. The diameter of the polystyrene resin in the surface layer portion of the styrene-modified polyethylene resin particles was 1 μm or less.

  Further, pre-expansion was carried out in the same manner as in Example 1 except that 24 parts of normal rich butane was used as a foaming agent to obtain styrene-modified polyethylene resin pre-expanded particles having an expansion bulk ratio of 30 times. The obtained styrene-modified polyethylene pre-expanded particles were molded and evaluated in the same manner as in Example 1. The crack resistance was 37 cm. The surface state of the foamed molded article that was molded when the residual foaming agent amount of the styrene-modified polyethylene resin pre-expanded particles was 0.9% by weight was 2.

(Comparative Example 2)
Styrene-modified polyethylene resin particles were obtained in the same manner as in Example 2 except that the temperature was raised to 125 ° C. by polymerization in a 6 L autoclave and the crosslinking reaction was completed by setting the holding time at 125 ° C. to 3 hours.

  When TEM observation of the obtained styrene modified polyethylene resin particles was performed, the central part of the styrene modified polyethylene resin particles formed a co-continuous structure of polyethylene resin and polystyrene resin, and the average thickness of the layer was It was 0.25 μm. The ratio of the polyethylene resin at the center of the styrene-modified polyethylene resin particles was 46%. The diameter of the polystyrene resin in the surface layer portion of the styrene-modified polyethylene resin particles was 1 μm or less.

  Furthermore, by the same operation as in Example 2, styrene-modified polyethylene resin pre-expanded particles having an expansion bulk ratio of 30 times were obtained.

  The obtained styrene-modified polyethylene resin pre-expanded particles were molded and evaluated in the same manner as in Example 1. The crack resistance was 43 cm. The surface state of the foamed molded article that was molded when the residual foaming agent amount of the styrene-modified polyethylene resin pre-expanded particles was 0.9% by weight was 1.

(Comparative Example 3)
Polyethylene resin particles were prepared in the same manner as in Example 1.

  Subsequently, 1 part by weight of tricalcium phosphate, 0.024 part by weight of sodium α-olefin sulfonate, and 30 parts by weight of polyethylene resin particles were suspended in 150 parts by weight of water in a 6 L autoclave. Thereafter, the aqueous suspension was heated to 85 ° C., 15 parts by weight of styrene, 0.18 parts by weight of benzoyl peroxide (10 hour half-life temperature: 74 ° C.) as a polymerization initiator, and a radical species generating type crosslinking agent. As a solution, 0.29 parts by weight of dicumyl peroxide (10-hour half-life temperature: 116 ° C.) was continuously added over 1 hour. Further, 55 parts by weight of a styrene monomer was dropped into the reaction system over 3 hours and 40 minutes, and maintained at 85 ° C. for 1 hour after the completion of the dropping. Thereafter, the temperature was raised to 140 ° C. and held for 3 hours to carry out a crosslinking reaction, and after cooling, washing, dehydration and drying were performed to obtain styrene-modified polyethylene resin particles.

  When TEM observation of the obtained styrene modified polyethylene resin particles was performed, the central part of the styrene modified polyethylene resin particles formed a co-continuous structure of polyethylene resin and polystyrene resin, and the average thickness of the layer was It was 0.71 μm. The ratio of the polyethylene resin at the center of the styrene-modified polyethylene resin particles was 23%. The diameter of the polystyrene resin on the surface layer of the styrene-modified polyethylene resin particles was 1 μm or less.

  Further, pre-expansion was carried out in the same manner as in Example 1 except that 20.5 parts of normal rich butane was used as a foaming agent to obtain styrene-modified polyethylene resin pre-expanded particles having an expansion bulk ratio of 30 times.

  The obtained styrene-modified polyethylene pre-expanded particles were molded and evaluated in the same manner as in Example 1. The crack resistance was 29 cm. The surface state of the foamed molded article that was molded when the residual foaming agent amount of the styrene-modified polyethylene resin pre-expanded particles was 0.9% by weight was 2.

(Comparative Example 4)
Styrene-modified polyethylene resin particles were obtained in the same manner as in Comparative Example 3, except that 0.11 part by weight of benzoyl peroxide and 0.18 part by weight of dicumyl peroxide were used.

  When TEM observation of the obtained styrene modified polyethylene resin particles was performed, the central part of the styrene modified polyethylene resin particles did not form a co-continuous structure of the polyethylene resin and the polystyrene resin. The diameter of the polystyrene resin in the surface layer portion of the styrene-modified polyethylene resin particles was 1 μm or less.

  Further, pre-foaming was performed in the same manner as in Example 1 except that 19.5 parts of normal rich butane was used as a foaming agent to obtain styrene-modified polyethylene resin pre-foamed particles having a foam volume ratio of 30 times.

  The obtained styrene-modified polyethylene resin pre-expanded particles were molded and evaluated in the same manner as in Example 1. The crack resistance was 15 cm. The surface state of the foamed molded product that was molded when the amount of the remaining foaming agent of the styrene-modified polyethylene resin pre-expanded particles was 0.9% was 4.

  In Examples 1 and 2, in the molding with a residual foaming agent of 0.9% by weight or less, an evaluation of 3 or more was obtained in the surface state of the obtained foamed molded product, and the pre-expanded particles when the foaming agent escaped It can be seen that the moldability is excellent. On the other hand, Comparative Examples 1 to 4 were inferior to either the crack resistance or the surface condition in the molding when the foaming agent escaped.

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

2 is a TEM photograph of the center part of the styrene-modified polyethylene resin particles of Example 1. FIG. 2 is a TEM photograph of a surface layer portion of a styrene-modified polyethylene resin particle in Example 1. FIG. 4 is a TEM photograph of a central part of a styrene-modified polyethylene resin particle of Example 2. 2 is a TEM photograph of a surface layer portion of a styrene-modified polyethylene resin particle in Example 2. 4 is a TEM photograph of a central part of a styrene-modified polyethylene resin particle of Comparative Example 1. 4 is a TEM photograph of a surface layer portion of a styrene-modified polyethylene resin particle in Comparative Example 1. 4 is a TEM photograph of a central part of a styrene-modified polyethylene resin particle of Comparative Example 2. 4 is a TEM photograph of a surface layer portion of a styrene-modified polyethylene resin particle in Comparative Example 2. 4 is a TEM photograph of a central part of a styrene-modified polyethylene resin particle of Comparative Example 3. 4 is a TEM photograph of a surface layer portion of a styrene-modified polyethylene resin particle in Comparative Example 3. 4 is a TEM photograph of a central part of a styrene-modified polyethylene resin particle of Comparative Example 4. 4 is a TEM photograph of a surface layer portion of a styrene-modified polyethylene resin particle in Comparative Example 4.

Claims (5)

  In the styrene-modified polyethylene resin particles obtained by polymerizing 100 parts by weight of a polyethylene resin by impregnating 150 parts by weight or more and 300 parts by weight or less of a styrene monomer, the center of the styrene-modified polyethylene resin particles Part forms a co-continuous structure of polyethylene resin and polystyrene resin having an average layer thickness of 0.3 μm or more and 1.0 μm or less, and the ratio of the polyethylene resin of the central part co-continuous structure is 30% Further, the styrene-modified polyethylene resin particles in which the xylene-insoluble gel component of the styrene-modified polyethylene resin pre-expanded particles obtained from the styrene-modified polyethylene resin particles is 10% by weight or more and 35% by weight or less. .   2. The styrene-modified polyethylene resin according to claim 1, wherein a spherical polystyrene resin having a diameter of 1.0 μm or less is dispersed in the polyethylene resin in a surface layer portion within a depth of 5 μm from the surface of the styrene-modified polyethylene resin particles. particle.   Claims obtained by adding a crosslinking agent having a 10-hour half-life temperature of 100 ° C. or more and 125 ° C. or less during or after polymerization, and decomposing 50% or more of the crosslinking agent at 130 ° C. or more and 150 ° C. or less. Item 3. The styrene-modified polyethylene resin particles according to Item 1 or 2.   A styrene-modified polyethylene resin pre-expanded particle obtained by pre-expanding the styrene-modified polyethylene resin particle according to any one of claims 1 to 3.   A foam-molded article obtained by molding the styrene-modified polyethylene resin pre-expanded particles according to claim 4.