JP5493606B2 - Styrene-modified polyethylene resin foamed molded article and method for producing styrene-modified polyethylene resin pre-expanded particles - Google Patents

Description

The present invention relates to a method for producing a styrene-modified polyethylene resin foamed molded article and styrene-modified polyethylene resin pre-expanded particles.

  Styrene-modified polyolefin resin foam moldings have the characteristics of high elasticity and crack resistance of polyolefin resin foams, and easy molding of styrene resin foams and high compression strength. Foam molded body, widely used as packaging material.

  When used as a packaging material, not only the buffer performance but also the appearance of the foamed molded product is often required. In order to obtain a foam molded article with a beautiful surface, the condition of the cell of the pre-expanded particles is also an important factor while leaving the in-mold foam molding conditions, and the control of the cell structure of the pre-expanded particles is an important technique. .

  As methods for controlling the cell structure, methods such as selection of a foaming agent and use of a cell regulator have been proposed so far.

  For example, in Patent Document 1, in order to suppress cell refinement of styrene-modified polyethylene resin pre-expanded particles, styrene-modified polyethylene resin particles containing a predetermined amount of hydrous silicon dioxide are impregnated with a volatile foaming agent. And prefoaming by vapor foaming. In general, foaming of styrene-modified polyethylene resin pre-foamed particles by vapor foaming tends to have a larger cell diameter than styrene resin foamed particles (EPS).

  Moreover, although it is a technique regarding a polyolefin-type resin foam, in patent document 2, the cell structure is devised by the method of equalizing the cell structure of polyolefin resin by controlling the resin structure, and patent document 3 by devising the foaming agent composition. A method for homogenizing is described. However, since the styrene-modified polyethylene resin pre-expanded particles have different resin compositions, it is difficult to control the cell structure by the same method.

  Patent Documents 4 and 5 describe a method for achieving both impact resistance and moldability of styrene-modified polyethylene resin pre-expanded particles, and foaming is performed by decompression foaming. However, the surface state of the foam molded article is only described for the gaps between the particles.

Japanese Patent Laid-Open No. 4-130143 JP 2003-327740 A JP 2007-308577 A JP 2006-29895 A JP 2008-260928 A

  However, in the styrene-modified polyethylene resin foamed molded article in which the gap between the particles is reduced as described in Patent Documents 4 and 5, when the surface is observed, pinholes (hypertrophic cells) in the pre-foamed particles are observed. It has been found that a part that is swollen due to ()) appears on the surface of the foamed molded product, which may contribute to a reduction in surface beauty.

  The present invention provides a styrene-modified polyethylene resin foam molded article in which the bulges caused by pinholes (hypertrophic cells) on the surface of the styrene modified polyethylene resin foam molded article are reduced and a styrene modified polyethylene resin foam molded article having a beautiful appearance is obtained. Another object of the present invention is to provide pre-expanded particles of high quality polyethylene resin.

  As a result of intensive studies, the present inventors have found styrene-modified polyethylene resin pre-expanded particles having a relatively small average cell diameter and few pinholes (hypertrophic cells).

That is, this invention consists of the following structures.
[1] A styrene-modified polyethylene resin foam obtained by in-mold foam molding of styrene-modified polyethylene resin pre-expanded particles containing 0.01% to 0.5% by weight of talc, the styrene Modified polyethylene resin pre-expanded particles are in a pressure vessel, styrene-modified polyethylene resin particles are made of a poorly water-soluble inorganic salt and an anionic surfactant, and a poorly water-soluble inorganic salt / anionic surfactant (weight ratio). In a water-based dispersion medium used in the range of 80 to 150, and a foaming agent is placed in the pressure vessel and heated to a temperature higher than the softening point of the styrene-modified polyethylene resin particles to form styrene-modified polyethylene resin particles. After impregnating 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 placed in a lower pressure region than in the pressure vessel. Are those obtained by pre-expansion by releasing dividing pressure foam method, the average cell diameter is not less 50μm or 300μm or less, the number of pinholes of the styrene-modified polyethylene-based resin foamed molded cross-styrene A styrene-modified polyethylene resin foamed molded article having 10 or less per 200 modified polyethylene resin pre-expanded particles.
[2] The styrene-modified polyethylene resin foam according to [1], wherein 100 parts by weight or more and 400 parts by weight or less of water is used as an aqueous dispersion medium with respect to 100 parts by weight of the styrene-modified polyethylene resin. Molded body .
[3] The styrene-modified polyethylene resin foam molded article according to [1] or [2], wherein the poorly water-soluble inorganic salt is calcium phosphate and the anionic surfactant is sodium n-paraffin sulfonate .
[4] The styrene-modified polyethylene resin foam molding according to any one of [1] to [3], wherein the L * value of the surface of the styrene-modified polyethylene resin foam molding body measured by a color difference meter is 85 or more. body.
[5] In a pressure-resistant container, styrene-modified polyethylene resin particles containing 0.01% by weight or more and 0.5% by weight or less of talc are converted into a hardly water-soluble inorganic salt and an anionic surfactant. Disperse in an aqueous dispersion medium with an anionic surfactant (weight ratio) of 80 or more and 150 or less , put a foaming agent in the pressure vessel and heat to a temperature above the softening point of the styrene-modified polyethylene resin particles. Then, after impregnating the styrene-modified polyethylene 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 lower than the pressure vessel. A method for producing styrene-modified polyethylene resin pre-expanded particles, wherein
[6] with respect to 100 parts by weight of styrene-modified polyethylene-based resins, styrene-modified polyethylene-based resin according to, characterized by using 100 parts by weight to 400 parts by weight of water as the aqueous dispersion medium [5] A method for producing expanded particles.
[7] The method for producing styrene-modified polyethylene resin expanded particles according to [5] or [6] , wherein the sparingly water-soluble inorganic salt is calcium phosphate and the anionic surfactant is sodium n-paraffin sulfonate.

  When the styrene-modified polyethylene resin pre-expanded particles of the present invention are subjected to in-mold foam molding to obtain a styrene-modified polyethylene resin foam molded body, the surface of the foam molded body is swollen due to pinholes (hypertrophic cells). The number of places has been reduced.

  Surprisingly, it has been found that the styrene-modified polyethylene resin foam molded article of the present invention having an average cell diameter in a predetermined range and having reduced pinholes has a whiteness equivalent to that of polystyrene foam. Styrene-modified polyethylene resin foamed moldings are often accepted in the market as an alternative to or improved products of the old foamed polystyrene. For this reason, the color, especially whiteness, may be required to be equivalent to the foamed polystyrene. It has surface beauty that can be used as an alternative or improved product of polystyrene foam.

  In addition, according to the method for producing pre-expanded styrene-modified polyethylene resin particles of the present invention, the styrene-modified polyethylene resin pre-expanded particles have a relatively small average cell diameter and fewer pinholes (hypertrophic cells) than conventional products. Expanded particles can be provided.

  The styrene-modified polyethylene resin pre-expanded particles of the present invention have an average cell diameter of 50 μm to 300 μm, preferably 70 μm to 200 μm. When the average cell diameter is within the above range, the surface of the styrene-modified polyethylene resin foam molded product obtained by in-mold foam molding of the styrene-modified polyethylene resin pre-expanded particles becomes white at the same level as the polystyrene foam. Specifically, the value of L * on the surface of the styrene-modified polyethylene resin foam molded article measured with a color difference meter is preferably 85 or more, and more preferably 90 or more.

  In addition, the average cell diameter of the styrene-modified polyethylene resin pre-expanded particles is calculated from the scanning electron micrograph of the cut surface of the pre-expanded particles, and the average chord length is calculated from the number of bubbles on a straight line (2 mm) of the cut surface. The average cell diameter was measured.

  The number of pinholes per 200 styrene-modified polyethylene resin pre-expanded particles of the present invention is 10 or less. Preferably it is 5 or less, more preferably 2 or less. When the number of pinholes is within the above range, the surface of the styrene-modified polyethylene resin foamed molded article becomes beautiful. The pinhole referred to in the present invention means a cell having a diameter of 1 mm or more.

The number of pinholes of styrene-modified polyethylene-based resin pre-expanded particles, Ru determined by counting the number by observing the cross-section through the approximate center of the 200 modified polyethylene-based resin pre-expanded particles.

  In order to make the number of pinholes within the above range, for example, the type and amount of the air conditioner are adjusted, the foaming method (foaming by the decompression foaming method, etc.), the foaming conditions (temperature, dispersion conditions, etc.), or There is a tendency that it can be achieved by a combination of these.

  In the styrene-modified polyethylene resin of the present invention, the styrene monomer is preferably used in an amount of 150 to 300 parts by weight, preferably 180 to 250 parts by weight, based on 100 parts by weight of the polyethylene resin. More preferably. Within this range, the resulting styrene-modified polyethylene resin pre-expanded particles tend to have both moldability and crack resistance. Specifically, a polyethylene resin is impregnated with a styrene monomer.

  As a method of polymerizing styrene-modified polyethylene resin particles, for example, by adding a styrene monomer to an aqueous suspension containing a polyethylene resin in a particle shape charged in a container equipped with a stirrer, Examples include a method in which a polyethylene resin is impregnated with a styrene monomer and polymerized. In the impregnation 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.

  In a preferred embodiment of the present invention, 100 parts by weight of polyethylene resin particles are impregnated by adding 25 parts by weight or more and 100 parts by weight or less of a styrene monomer at a temperature at which polymerization does not proceed substantially. The addition of a styrenic monomer under heating. “At a temperature at which polymerization does not proceed essentially” means that the temperature is not higher than the 10-hour half-life temperature of the main 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.

  Examples of the polyethylene resin used in the present invention include ethylene homopolymers such as high-density polyethylene and low-density polyethylene, polyethylene, and α- such as propylene, 1-butene, 1-pentene, and 1-hexene. Examples thereof include copolymers with olefins, vinyl acetate, acrylic acid esters, 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. When 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 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 powder, pellets or the like. The average particle weight of these 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 in-mold foam molding may be deteriorated.

  The styrene-modified polyethylene resin pre-expanded particles of the present invention preferably contain talc in an amount of 0.01% to 0.5% by weight, more preferably 0.1% to 0.4% by weight. When talc is less than 0.01% by weight, it tends to be difficult to stably generate bubbles, and when used more than 0.5% by weight, fusion during in-mold foam molding tends to deteriorate. There is. It is preferable to mix talc into the polyethylene resin particles in advance. Although talc is generally known to function as a bubble regulator, in the present invention, as will be described later, by using pre-expanded particles by a decompression foaming method, the average cell diameter is 50 μm or more and 300 μm. It tends to be easier to:

  Various additives can be used in the styrene-modified polyethylene resin of the present invention. Examples of various additives include plasticizers and flame retardants. 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, and organic hydrocarbons such as liquid paraffin and cyclohexane, and organic aromatic hydrocarbons such as toluene and ethylbenzene. These may be used in combination.

  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.

  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 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 -Organic peroxides such as 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 polymerization initiator, reaction temperature, and monomer addition rate.

  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, polymerization is carried out in an aqueous suspension containing polyethylene resin particles. At this time, it is preferable to use a dispersant in order to prevent fusion of 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 hardly water-soluble inorganic salts.

  In addition, when a poorly water-soluble inorganic salt is used, an anionic surfactant such as sodium α-olefin sulfonate, sodium alkylbenzene sulfonate, sodium n-paraffin sulfonate, etc. is effective because the dispersion stability increases. This is preferable. 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” in 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 the water or aqueous solution. 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 resin and water is preferably 1.0 / 0.6 to 1.0 / 4.0 in the styrene-modified polystyrene resin / water obtained.

  The styrene-modified polyethylene resin pre-expanded particles of the present invention preferably have a thermal xylene-insoluble gel content of not less than 10% by weight and not more than 35% by weight. Therefore, it is preferable to use a crosslinking agent. As the crosslinking agent, a radical species-generating crosslinking agent can be used, such as di-t-butyl peroxide, dicumyl peroxide, t-butyl peroxybenzoate, t-butyl peroxyacetate, 2,2-bis- Examples thereof include t-butyl peroxybutane. These can be added to the polymerization system before addition of the styrene monomer or together with the styrene monomer. When foaming by decompression foaming, which will be described later, is performed, a crosslinking agent may be charged at the time of decompression foaming and the crosslinking reaction may be performed in the presence of the foaming agent at the time of decompression foaming.

  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, 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 by the radical species-generating crosslinking agent, but may be added before the crosslinking reaction is completed.

  Further, 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 styrene-modified polyethylene resin pre-expanded particles having good moldability. When the amount exceeds 30 parts by weight, the dispersion state of the resin when impregnated with the foaming agent becomes unstable, and the resin particles 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 The particles were dispersed in an aqueous dispersion medium, and a foaming agent was placed in a pressure vessel and heated to a temperature equal to or higher than the softening point of the styrene-modified polyethylene resin particles to impregnate the styrene-modified polyethylene resin particles with the foaming agent. Thereafter, one end in the pressure vessel is opened and a mixture containing styrene-modified polyethylene resin particles and an aqueous dispersion medium is released to a lower pressure region than in the pressure vessel, so-called “pressure-removal foaming” ( 2) Polyethylene resin particles are impregnated with a styrene monomer and polymerized, then impregnated with a foaming agent to form expandable styrene-modified polyethylene resin particles, and equipped with a stirrer. A method of placing foamable styrene-modified polyethylene resin particles in a heated container and heating with a heat source such as water vapor, (3) styrene-modified polyethylene resin particles impregnated with styrene monomer and polymerized in polyethylene resin particles And a method of impregnating a foaming agent in a container equipped with a stirrer and heating with a heat source such as water vapor, and the like. There is a tendency that the average cell diameter of the polyethylene resin pre-expanded particles tends to be an average cell diameter of 50 μm or more and 300 μm or less, and an excessive amount of the foaming agent is not required to perform impregnation of the foaming agent and pre-foaming in a series of operations. ,preferable.

  In the method (1), specifically, the styrene-modified polyethylene resin particles obtained by carrying out the polymerization reaction are once taken out from the pressure vessel, washed and dried, and then depressurized together with the aqueous dispersion medium. Prepared and dispersed in a pressure-resistant container for foaming, put a foaming agent in the pressure-resistant container, and then heated and heated, and impregnating the resin particles with the foaming agent under pressure higher than the vapor pressure of the foaming agent, One end of the container is opened while keeping the temperature and pressure inside the pressure vessel constant, and for example, styrene is introduced into an atmosphere at a lower pressure than the inside of the pressure vessel through an orifice having a hole diameter of 1 mm to 10 mm. By releasing and foaming a mixture comprising modified polyethylene resin particles and an aqueous dispersion medium, styrene-modified polyethylene resin pre-expanded particles having a uniform fine cell structure are produced. It is possible to elephants.

  It is preferable that the aqueous dispersion medium referred to in this decompression foaming is water. The aqueous dispersion medium preferably contains a dispersant, and the dispersant can be the same type of dispersant as used in the polymerization, but is used in combination with a poorly water-soluble inorganic salt and an anionic surfactant. It is preferable.

  The hardly water-soluble inorganic salt and the anionic surfactant are hardly water-soluble inorganic salt / anionic surfactant (weight ratio) and are preferably used in the range of 80 to 150. If the ratio of sparingly water-soluble inorganic salt / anionic surfactant is outside the above range, an oversized pinhole is easily generated in the pre-expanded particles of styrene-modified polyethylene resin when decompression foaming is performed. Tend to be difficult to obtain.

  Furthermore, it is more preferable that the poorly water-soluble inorganic salt is calcium phosphate and the anionic surfactant is n-paraffin sulfonic acid soda because the effect of reducing pinholes is remarkable.

  Furthermore, in decompression foaming, it is preferable to use 100 parts by weight or more and 400 parts by weight or less of water as an aqueous dispersion medium with respect to 100 parts by weight of the styrene-modified polyethylene resin. If the amount of water is less than 100 parts by weight, dispersion of the resin particles may become unstable. If the amount of water exceeds 400 parts by weight, there may be a problem in productivity.

  Various additives may be impregnated in the decompression foaming stage. 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.

  The styrene-modified polyethylene resin pre-expanded particles of the present invention can be foam-molded in a mold by a general in-mold foam molding method to obtain a styrene-modified polyethylene resin foam molded body. Specifically, styrene-modified polyethylene resin pre-expanded particles are filled in a mold that can be closed but cannot be sealed, and heat-sealed to obtain a styrene-modified polyethylene resin foam molded article. The obtained styrene-modified polyethylene resin foam molded article has an average cell diameter of 50 μm or more and 300 μm or less, and the number of pinholes in the cross section of the styrene-modified polyethylene resin foam molded article is It is 10 or less per 200 expanded particles. Preferably it is 5 or less, more preferably 2 or less.

  The method of measuring the average cell diameter of the foam molded article is to measure the average chord length from the number of bubbles applied on a straight line (60 mm) of the cut surface of the styrene-modified polyethylene resin foam molded article to obtain the average cell diameter.

  The number of pinholes in the styrene-modified polyethylene resin foam molded article should be counted by observing a cross section passing through the approximate center of 200 styrene-modified polyethylene resin pre-expanded particles on the cut surface of the foam molded article. Ask for.

  The styrene-modified polyethylene resin foam molded article of the present invention obtained as described above can be used suitably as a packaging material because of its beautiful appearance and excellent buffer performance.

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

<Average cell diameter of pre-expanded particles>
For the average cell diameter of the pre-expanded particles, a cut surface passing through the approximate center of the pre-expanded particles was observed with a microscope, and the average chord length was measured from the number of bubbles on a straight line (2 mm) of the cut surface. The average chord length was measured for 10 pre-expanded particles, and the average value was taken as the average cell diameter of the pre-expanded particles.

<Average cell diameter of foamed molded product>
The average cell diameter of the foam molded article was determined by observing the cut surface of the foam molded article with a microscope, measuring the average chord length from the number of bubbles on a straight line (60 mm) of the cut surface, and setting the average cell diameter.

<Measurement of the number of pinholes of pre-expanded particles>
200 pre-expanded particles were cut with a slicer so as to pass through substantially the center, and the number of cells having a diameter of 1 mm or more in the cross section was counted as a pinhole.

<Measurement of the number of pinholes in the foam molding>
The foamed molded body was cut with a slicer, and the number of cells having a diameter of 1 mm or more in 200 pre-expanded particles in cross section was counted as a pinhole.

<Measurement of L *>
The measurement was performed by reflection measurement using a Spectro Color Meter SE 2000 manufactured by Nippon Denshoku. The measurement was carried out using a 10 mm slit and a 10 mm slit lens, and a foamed molded product was placed on the measurement part, and the upper surface of the measurement site was suppressed with a sample press attached to the apparatus. Three points were measured at different measurement positions, and the average value was calculated.
Standard alignment was performed using Nippon Denshoku standard white plate SE-11015 (X93.06, Y94.91, Z112.52).

Example 1
As the polyethylene-based resin, “Evatate F1103-1” manufactured by Sumitomo Chemical Co., Ltd. is used, 0.2 parts by weight of talc is mixed with 100 parts by weight of the polyethylene-based 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 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 30 parts by weight of styrene. 0.77 parts by weight of t-butylperoxy-2-ethylhexanoate (10 hour half-life temperature: 74 ° C.) as an agent, and t-butyl peroxybenzoate (10 hour half-life temperature: 104 ° C.) as a crosslinking agent A solution in which 45 parts by weight were 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 80 ° C. and held for 1.5 hours. Thereafter, a solution obtained by cooling to 70 ° C. and dissolving 0.06 part by weight of benzoyl peroxide in 40 parts by weight of the styrene monomer was dropped into the reaction system over 1.5 hours, and after completion of dropping, the solution was kept at 70 ° C. for 3 hours. The polymerization reaction was allowed to proceed by maintaining the temperature and further raising the temperature to 85 ° C. and maintaining for 0.5 hours. Thereafter, the temperature was raised to 125 ° C. and held for 3 hours to carry out a crosslinking reaction. After cooling, washing, dehydration and drying were performed to obtain styrene-modified polyethylene resin particles.

  Thereafter, 330 parts by weight of water, 2 parts by weight of tribasic calcium phosphate, 0.022 parts by weight of sodium n-paraffin sulfonate, and 100 parts by weight of styrene-modified polyethylene resin particles were charged into a 10 L autoclave. After adding 24 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 50 minutes to impregnate the foaming agent. Thereafter, the styrene-modified polyethylene resin particles together with the aqueous dispersion medium were discharged from the autoclave through an orifice having an opening diameter of 5 mm under atmospheric pressure 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 cell diameter of the obtained styrene-modified polyethylene resin pre-expanded particles was 91 μm. The number of pinholes per 200 styrene-modified polyethylene resin pre-expanded particles was two.

  The pre-expanded styrene-modified polyethylene resin pre-expanded particles obtained were washed, dehydrated and dried, then cured at room temperature for 2 days, and a 300 × 450 × 25 (t) mm size mold using a Daisen KR-57 molding machine In-mold foam molding was carried out to obtain a styrene-modified polyethylene resin foam molding. The average cell diameter of the foam molded article was 118 μm, and L * was 90.09. When a pinhole was observed in 200 styrene-modified polyethylene resin pre-expanded particles in the cross section of the styrene-modified polyethylene resin foam molded article, the number of pinholes was one.

(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. A solution in which 0.24 parts by weight of benzoyl peroxide as a polymerization initiator and 0.56 parts by weight of t-butyl peroxybenzoate as a crosslinking agent were 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. Further, the temperature was raised to 85 ° C. over 50 minutes, and 47.5 parts by weight of the styrene monomer was continuously dropped into the reaction system at a constant rate over 2 hours and 40 minutes after 10 minutes from the start of the temperature rise. Then, after completion | finish of dripping, it hold | maintained at 85 degreeC for 1 hour. Then, it heated up at 120 degreeC and hold | maintained for 50 minutes, and superposition | polymerization of the styrene-type monomer was completed. By cooling to room temperature and washing, dehydrating and drying, styrene-modified polyethylene resin particles were obtained.

  In a 10 L autoclave, 0.5 parts by weight of dibutyl sebacate as a plasticizer was added together with a resin, and the amount of butane used was changed to 22 parts by weight. -Based resin pre-expanded particles were prepared. The cell diameter of the obtained styrene-modified polyethylene resin pre-expanded particles was 98 μm. When 200 pinholes of styrene-modified polyethylene resin pre-expanded particles were observed, the number of pinholes was two.

  The obtained pre-expanded particles were evaluated by in-mold foam molding in the same manner as in Example 1. The cell diameter of the foamed molded product was 120 μm, and L * was 92.29. The number of pinholes in the cross section of the foamed molded product was 2 per 200 prefoamed particles.

(Example 3)
Similarly to Example 2, polyethylene resin particles and styrene-modified polyethylene resin particles were produced. In a 10 L autoclave, styrene-modified polyethylene-based pre-expanded particles having an expansion volume ratio of 33 times were prepared in the same manner as in Example 2 except that the amount of sodium n-paraffin sulfonate used was 0.020 parts by weight. The cell diameter of the obtained styrene-modified polyethylene resin pre-expanded particles was 110 μm. When 200 pinholes of styrene-modified polyethylene resin pre-expanded particles were observed, the number of pinholes was zero.

  The obtained pre-expanded particles were evaluated by in-mold foam molding in the same manner as in Example 1. The cell diameter of the foam molded article was 147 μm, and L * was 93.00. The number of pinholes in the cross section of the expanded molded body was 0 per 200 pre-expanded particles.

(Example 4)
Similarly to Example 2, polyethylene resin particles and styrene-modified polyethylene resin particles were produced. In a 10 L autoclave, styrene-modified polyethylene resin pre-expanded particles having an expansion bulk ratio of 30 times were prepared in the same manner as in Example 2 except that the amount of sodium n-paraffin sulfonate used was 0.018 part by weight. The cell diameter of the obtained styrene-modified polyethylene resin pre-expanded particles was 96 μm. When 200 pinholes of styrene-modified polyethylene resin pre-expanded particles were observed, the number of pinholes was one.

  The obtained pre-expanded particles were evaluated by in-mold foam molding in the same manner as in Example 1. The cell diameter of the foam molded article was 134 μm, and L * was 91.84. The number of pinholes in the cross section of the foamed molded product was 1 per 200 prefoamed particles.

(Example 5)
In the same manner as in Example 2, except that the amount of talc used for preparing the polyethylene resin particles was 0.1 parts by weight with respect to the polyethylene resin particles, the polyethylene resin particles and the styrene modified polyethylene resin particles Produced. Styrene-modified polyethylene resin pre-expanded particles having an expansion bulk ratio of 30 times were prepared in the same manner as in Example 2 except that the amount of butane used was 23.5 parts by weight. The cell diameter of the obtained styrene-modified polyethylene resin pre-expanded particles was 90 μm. When 200 pinholes of styrene-modified polyethylene resin pre-expanded particles were observed, the number of pinholes was one.

  The obtained pre-expanded particles were evaluated by in-mold foam molding in the same manner as in Example 1. The cell diameter of the foamed molded product was 128 μm, and L * was 93.10. The number of pinholes in the cross section of the expanded molded body was 1 per 200 pre-expanded particles.

(Comparative Example 1)
Similarly to Example 1, polyethylene resin particles and styrene-modified polyethylene resin particles were produced. Furthermore, 100 parts by weight of water, 100 parts by weight of styrene-modified polyethylene resin particles, 1 part by weight of tricalcium phosphate, and 0.024 parts by weight of α-olefin sulfonate sodium were charged in a 6 L autoclave, and the temperature was raised to 70 ° C. After adding 30 parts by weight of normal rich butane (normal butane / isobutane = 75/25) as a blowing agent to the autoclave over 30 minutes, the mixture was kept at 70 ° C. for 3 hours. After cooling to room temperature, the expandable styrene-modified polyethylene resin particles were taken out and immediately dried with a blower.

Pre-foaming was performed by heating with water vapor at a pressure of 1.0 kg / cm ² for 50 seconds to obtain styrene-modified polyethylene resin pre-foamed particles. The cell diameter of the obtained styrene-modified polyethylene resin pre-expanded particles was 450 μm. When 200 pinhole particles of styrene-modified polyethylene resin pre-expanded particles were observed, the number of pinholes was 5.

  The obtained pre-expanded particles were molded and evaluated in the same manner as in Example 1. The cell diameter of the foam molded article was 498 μm, and L * was 81.82. The number of pinholes in the cross section of the foamed molded product was 5 per 200 prefoamed particles.

(Comparative Example 2)
Similarly to Example 2, polyethylene resin particles and styrene-modified polyethylene resin particles were produced. In the same manner as in Comparative Example 1, expandable styrene-modified polyethylene resin particles were prepared, pre-expanded by heating with water vapor at a pressure of 0.8 kg / cm ² for 60 seconds, and styrene-modified polyethylene resin pre-expanded particles were Obtained. The cells of the obtained styrene-modified polyethylene resin pre-expanded particles had many coarse cells of 1 mm or more and were in a so-called rough cell state, and the average cell diameter could not be measured.

(Comparative Example 3)
Similarly to Example 2, polyethylene resin particles and styrene-modified polyethylene resin particles were produced. In a 10 L autoclave, styrene-modified polyethylene resin pre-expanded particles were prepared in the same manner as in Example 2 except that 2 parts by weight of tertiary calcium phosphate and 0.01 parts by weight of sodium n-paraffin sulfonate were used. Dispersion during pressure foaming was unstable, and a large amount of resin remained in the autoclave.

(Comparative Example 4)
Similarly to Example 2, polyethylene resin particles and styrene-modified polyethylene resin particles were produced. In a 10 L autoclave, styrene-modified polyethylene resin pre-expanded particles having an expansion bulk ratio of 32 times were prepared in the same manner as in Example 2 except that 1 part by weight of tricalcium phosphate and 0.0175 part by weight of sodium n-paraffin sulfonate were used. did. The cell diameter of the obtained styrene-modified polyethylene resin pre-expanded particles was 94 μm. When 200 pinholes of styrene-modified polyethylene resin pre-expanded particles were observed, the number of pinholes was 21.

  The obtained pre-expanded particles were molded and evaluated in the same manner as in Example 1. The cell diameter of the foamed molded product was 120 μm, and L * was 90.34. The number of pinholes in the cross section of the foamed molded product was 21 per 200 prefoamed particles.

(Reference example)
In accordance with the method of Example 1 of JP2003-64212A, polystyrene-based pre-expanded particles and polystyrene-based resin foam molded articles were produced. The cell diameter of the polystyrene-based resin foam molding was 98 μm, and L * was 94.03.

Claims (7)

A styrene-modified polyethylene resin foam formed by in-mold foam molding of styrene-modified polyethylene resin pre-expanded particles containing 0.01% to 0.5% by weight of talc, the styrene-modified polyethylene Resin-based pre-expanded particles in a pressure vessel, styrene-modified polyethylene resin particles with a hardly water-soluble inorganic salt and an anionic surfactant in a slightly water-soluble inorganic salt / anionic surfactant (weight ratio) of 80 or more Disperse in an aqueous dispersion medium of 150 or less, put a foaming agent in the pressure vessel and heat to a temperature above the softening point of the styrene-modified polyethylene resin particles, and add the foaming agent to the styrene-modified polyethylene resin particles. After impregnation, one end of the pressure vessel is opened and a mixture containing styrene-modified polyethylene resin particles and an aqueous dispersion medium is discharged to a lower pressure region than in the pressure vessel. That are those obtained by prefoaming in divided pressure foaming method, the average cell diameter is at 50μm or 300μm or less, the number of pinholes of the styrene-modified polyethylene-based resin foamed molded cross section, styrene modified A styrene-modified polyethylene resin foamed molded product, wherein the number is 10 or less per 200 pre-expanded polyethylene resin particles. The styrene-modified polyethylene resin foam molded article according to claim 1, wherein 100 parts by weight or more and 400 parts by weight or less of water is used as an aqueous dispersion medium with respect to 100 parts by weight of the styrene-modified polyethylene resin. . The styrene-modified polyethylene resin foam molded article according to claim 1 or 2, wherein the hardly water-soluble inorganic salt is calcium phosphate, and the anionic surfactant is n-paraffin sulfonic acid soda . The styrene-modified polyethylene resin foam molded article according to any one of claims 1 to 3, wherein the L * value of the surface of the styrene modified polyethylene resin foam molded article measured by a color difference meter is 85 or more. In a pressure-resistant container, styrene-modified polyethylene resin particles containing talc in an amount of 0.01% by weight to 0.5% by weight are used as a water-insoluble inorganic salt and an anionic surfactant as a water-insoluble inorganic salt / anionic interface. Disperse in an aqueous dispersion medium used in an active agent (weight ratio) of 80 or more and 150 or less , put a foaming agent in the pressure vessel and heat it to a temperature above the softening point of the styrene-modified polyethylene resin particles, and modify the styrene. After impregnating the foamed polyethylene 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. A process for producing styrene-modified polyethylene resin pre-expanded particles. Relative to 100 parts by weight of styrene-modified polyethylene-based resins, styrene-modified polyethylene-based resin foamed particles according to claim 5, characterized in that the use of 100 parts by weight to 400 parts by weight of water as the aqueous dispersion medium Production method. The method for producing styrene-modified polyethylene resin expanded particles according to claim 5 or 6 , wherein the hardly water-soluble inorganic salt is calcium phosphate and the anionic surfactant is sodium n-paraffin sulfonate.