JP2011084593A - Method for producing styrene-modified polyethylene-based resin preliminary foamed particles - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing styrene-modified polyethylene-based resin preliminary foamed particles, which have physical properties equivalent to those produced with an organic foaming agent, using an inorganic gas that is safe and has a small environmental load, without using any organic foaming agent. <P>SOLUTION: There is provided the method for producing styrene-modified polyethylene-based resin preliminary foamed particles which are obtained by using an inorganic gas as a foaming agent to foam styrene-modified polyethylene-based resin particles prepared by impregnating and polymerizing polyethylene-based resin particles with a styrene-based monomer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  Polyolefin resin foams are generally highly elastic and have a high strain recovery ability against repeated stresses, as well as excellent oil resistance and crack resistance, so they are widely used as packaging materials and automotive parts. It's being used. However, it has the disadvantages of low rigidity, easy shrinkage of the foam molded product after in-mold foam molding, and low compressive strength. Among polyolefin resins, polypropylene and the like have a relatively high compressive strength, but have a high melting point and require a high temperature at the time of in-mold foam molding, resulting in expensive equipment and energy costs and poor economic efficiency. In addition, when the strength is high, the expansion ratio can be increased, which is advantageous for weight reduction.

  As a method for improving such a defect, a styrene-modified polyethylene resin obtained by polymerizing a polyethylene resin by impregnating a styrene monomer is known. The resin particles produced by such a method can easily change the structure and composition in the particles as in Patent Documents 1 and 2, and have excellent chemical resistance, impact resistance, and in-mold foam moldability. Resin particles having can be produced. As a method for producing styrene-modified polyethylene resin pre-expanded particles, an organic foaming agent having a boiling point lower than the melting point of the resin such as propane, butane, pentane, or chlorofluorocarbon gas is injected into the molten resin and released under a low-pressure atmosphere. And a method of foaming by heating the resin particles impregnated with an organic foaming agent with steam or the like.

  However, although Patent Document 2 exemplifies inorganic gas as a foaming agent that can be used in decompression foaming, only an embodiment using an organic foaming agent is specifically disclosed in the examples.

  In the case of a low-boiling organic solvent such as propane or butane, an explosive gas is generated during the production of the foam, which may cause an explosion. In addition, since the foaming agent remains in the pre-expanded particles and the in-mold foam molded article and gradually leaks, there is a risk of explosion during storage, and a VOC problem occurs.

  When using chlorofluorocarbon as a blowing agent, there is no risk of explosion, but chlorofluorocarbon has a problem from the viewpoint of the environment.

  In order to solve the problems in the case of using an organic foaming agent, Patent Document 3 discloses a modified polyolefin obtained by melt-mixing a polyolefin resin, a polystyrene resin, an aromatic vinyl monomer, and a radical polymerization initiator. A manufacturing method in which a carbon-based resin is foamed with carbon dioxide gas is disclosed. The styrene-modified polyethylene resin pre-expanded particles produced by such a method are made into a modified polyolefin resin by melting and mixing a polyolefin resin, a polystyrene resin, an aromatic vinyl monomer and a radical polymerization initiator. Therefore, it seems that the structure control inside the particle is difficult.

JP-A-2005-97555 JP 2009-114432 A Japanese Patent Laid-Open No. 9-1224827

  In view of the circumstances as described above, the present invention does not use an organic foaming agent, and uses a safe and environmentally friendly inorganic gas, and a styrene-modified polyethylene resin preliminary produced using a conventional organic foaming agent. An object of the present invention is to provide a method for producing styrene-modified polyethylene resin pre-expanded particles having the same physical properties as the expanded particles.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that polyethylene resin particles are impregnated with a styrene monomer and polymerized, and styrene-modified polyethylene resin particles are used as a blowing agent with an inorganic gas. Styre-modified polyethylene resin pre-expanded particles obtained by foaming using styrene-modified polyethylene resin in-mold foam obtained when in-mold foam molding is performed, as in the case of using an organic foaming agent It has been found that the appearance of the molded product is good. Furthermore, surprisingly, a styrene-modified polyethylene resin in-mold foam molded product obtained by in-mold foam molding of styrene-modified polyethylene resin pre-expanded particles obtained using inorganic gas as a foaming agent is an organic foaming agent. The present inventors have found that the compressive strength is higher than that produced by using, and have completed the present invention.

That is, this invention consists of the following structures.
[1] A styrene-modified polyethylene resin particle obtained by impregnating and polymerizing a polyethylene resin particle with a styrene monomer is foamed using an inorganic gas as a foaming agent, and the expansion ratio is 3 times or more and 60 times A method for producing pre-expanded particles of styrene-modified polyethylene resin less than double.
[2] Polyethylene resin particles impregnated with a styrene monomer and polymerized styrene-modified polyethylene resin particles are dispersed in an aqueous dispersion medium in a pressure vessel and heated, and an inorganic gas is used as a foaming agent in the pressure vessel. And then pressurizing the inside of the pressure vessel, and then opening one end of the pressure vessel to release the mixture containing the styrene-modified polyethylene resin particles and the aqueous dispersion medium in a lower pressure atmosphere than in the pressure vessel. [1] The method for producing pre-expanded styrene-modified polyethylene resin particles according to [1].
[3] The process for producing styrene-modified polyethylene resin pre-expanded particles according to [2], wherein the low-pressure atmosphere is filled with saturated steam.
[4] The method for producing styrene-modified polyethylene resin pre-expanded particles according to any one of [1] to [3], wherein the inorganic gas is carbon dioxide.
[5] The styrene-modified polyethylene resin by pressurizing the styrene-modified polyethylene resin pre-expanded particles obtained by the production method according to any one of [1] to [4] with an inorganic gas. A method for producing styrene-modified polyethylene resin pre-foamed particles, wherein the pre-foamed particles are further foamed by heating after the pressure in the pre-foamed particles is higher than atmospheric pressure.
[6] Styrene-modified polyethylene resin pre-expanded particles obtained by the production method according to any one of [1] to [5].
[7] The styrene-modified polyethylene resin pre-expanded particles according to [6], wherein the average cell diameter is 50 μm or more and 800 μm or less.
[8] A styrene-modified polyethylene resin in-mold foam-molded product obtained by in-mold foam molding of the styrene-modified polyethylene resin pre-expanded particles according to [6] or [7].

  The production method of the present invention is capable of obtaining a styrene-modified polyethylene resin-in-mold foam-molded article having no risk of explosion or the like, less environmental load, and having the same surface properties as conventional organic foaming agents. Styrene-modified polyethylene resin pre-expanded particles can be produced. The styrene-modified polyethylene resin pre-expanded particles obtained by the production method of the present invention have higher compressive strength than those using an organic foaming agent when subjected to in-mold foam molding.

  The method for producing styrene-modified polyethylene resin pre-expanded particles according to the present invention uses styrene-modified polyethylene resin particles obtained by impregnating and polymerizing polyethylene resin particles with a styrene monomer, using an inorganic gas as a blowing agent. It is made to foam.

  As a method of foaming and pre-foaming styrene-modified polyethylene resin particles obtained by impregnating and polymerizing polyethylene resin particles with a styrene monomer using an inorganic gas as a foaming agent, (1) Polyethylene resin particles The styrene-modified polyethylene resin particles impregnated and polymerized with the styrene monomer are dispersed in a water-based dispersion medium in a pressure vessel and heated, and an inorganic gas is introduced into the pressure vessel as a foaming agent. After pressurization, one end of the pressure vessel is opened to release a mixture containing styrene-modified polyethylene resin particles and an aqueous dispersion medium in a lower pressure atmosphere than in the pressure vessel. (2) Polyethylene resin particles are impregnated with a styrene monomer and polymerized, and then impregnated with an inorganic gas as a foaming agent to produce a foamable styrene-modified polyethylene resin. 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 monomer and polymerized. And a method of impregnating an inorganic gas as a foaming agent in a container provided 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 for impregnation and foaming in a series of operations.

  In the method (1), specifically, after the styrene-modified polyethylene resin particles obtained by carrying out the polymerization reaction are once taken out from the pressure vessel, washed and dried, the pressure resistance for decompression foaming Charge the container, disperse it in an aqueous dispersion medium, heat it, introduce inorganic gas as a foaming agent into the pressure vessel and pressurize the inside of the pressure vessel, then keep the temperature and pressure inside the pressure vessel constant. One end is opened, and the styrene modification is performed by releasing and foaming the mixture in a low-pressure atmosphere, for example, an atmosphere filled with saturated steam, through an orifice having an opening diameter of 1 to 10 mm, for example. Polyethylene resin pre-expanded particles can be produced.

  The polyethylene resin constituting the polyethylene resin particles in the present invention is an ethylene homopolymer such as high-density polyethylene or low-density polyethylene, ethylene and, for example, propylene, 1-butene, 1-pentene, 1-hexene, etc. Examples thereof include copolymers with α-olefin, vinyl acetate, acrylic acid ester, vinyl chloride and the like. Moreover, you may mix | blend an acrylonitrile styrene copolymer with these polyethylene-type resin. Among these, an ethylene / vinyl acetate copolymer is preferable because of its high stability during polymerization.

  The polyethylene resin is melted in advance using, for example, an extruder, a kneader, a Banbury mixer, a roll or the like, extruded into water or air, and cut into strands or underwater to form polyethylene resin particles. The shape is preferably a particle state such as powder or pellet. 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 molding may be deteriorated. Among them, a pellet made by extruding a polyethylene resin and using an underwater cutting method is preferable because it can be easily spheroidized.

  In the present invention, various additives such as a plasticizer and a cell regulator can be used depending on the purpose, such as improvement of moldability and improvement of expansion ratio.

  Examples of the plasticizer include fatty acid glycerides such as stearic acid triglyceride, palmitic acid triglyceride, lauric acid triglyceride, stearic acid diglyceride, and stearic acid monoglyceride, vegetable oils such as coconut oil, palm oil, and palm kernel oil, 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 air conditioner include organic air conditioners such as aliphatic bisamides and stearamide such as methylene bis stearic acid amide and ethylene bis stearic acid amide, inorganic air bubbles such as talc, silica, calcium silicate, and calcium carbonate. Examples thereof include regulators.

  Among the bubble regulators, it is preferable to use an inorganic bubble regulator, and the preferred 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. When the amount of the inorganic cell regulator is less than 0.01 parts by weight, it may be difficult to stably generate bubbles. When the amount is more than 0.5 parts by weight, fusion during in-mold foam molding may occur. There is a tendency to get worse.

  These various additives can be added and impregnated at the time of polymerization or impregnation with a foaming agent, or can be used by mixing in the polyethylene resin in advance.

  As the styrene monomer used in the present invention, for example, styrene and styrene derivatives such as α-methyl styrene, paramethyl styrene, t-butyl styrene, chlorostyrene and the like can be used as a main component. Further, for example, monomers capable of copolymerization with acrylic acid and methacrylic acid esters such as methyl acrylate, butyl acrylate, methyl methacrylate, and ethyl methacrylate, or styrene derivatives such as acrylonitrile, dimethyl fumarate, and ethyl fumarate. You may use together 1 type, or 2 or more types. Furthermore, polyfunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate can also be used.

  The styrenic monomer is preferably polymerized in an amount of 150 to 400 parts by weight, more preferably 180 to 300 parts by weight, based on 100 parts by weight of the polyethylene resin particles. If it is in the said range, there exists a tendency to become a styrene modified polyethylene resin pre-expanded particle with favorable in-mold foam moldability and physical properties.

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

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

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

  In the present invention, in order to improve the crack resistance of the styrene-modified polyethylene resin-in-mold foam-molded product, the inside of the styrene-modified polyethylene resin particles is preferably cross-linked. In order to perform crosslinking, a radical species generating type crosslinking agent can be used. Examples of such radical species-generating crosslinking agents include di-t-butyl peroxide (10-hour half-life temperature: 123 ° C.), dicumyl peroxide (10-hour half-life temperature: 116 ° C.), and t-butyl peroxy. Benzoate (10-hour half-life temperature: 104 ° C.), t-butyl peroxyacetate (10-hour half-life temperature: 102 ° C.), 2,2-bis-t-butyl peroxybutane (10-hour half-life temperature: 103 ° C.) Etc. These crosslinking agents can be added to the polymerization system before addition of the styrene monomer or together with the styrene monomer. The cross-linking reaction is usually performed at the time of polymerization, but when performing decompression foaming, it may be performed at the time of decompression foaming.

  The method for producing styrene-modified polyethylene resin pre-expanded particles of the present invention is preferably a water-based dispersion of styrene-modified polyethylene resin particles obtained by impregnating and polymerizing polyethylene resin particles with a styrene monomer in a pressure vessel. Disperse in a medium and heat, introduce an inorganic gas as a foaming agent into the pressure vessel and pressurize the inside of the pressure vessel, then open one end of the pressure vessel and styrene modified polyethylene resin particles and an aqueous dispersion medium. It is characterized in that the mixture comprising it is discharged in a lower pressure atmosphere than in the pressure vessel.

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

  In the present invention, an inorganic gas is used as the foaming agent. Examples of the inorganic gas include nitrogen, oxygen, carbon dioxide gas, air, helium, argon, and water. Of these, carbon dioxide is preferred. These inorganic gases may be used in combination.

  When dispersing the styrene-modified polyethylene resin particles in the aqueous dispersion medium, it is preferable to use a dispersant in order to prevent adhesion between the resins. Examples of the dispersant include inorganic dispersants such as tricalcium phosphate, magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay.

  As necessary, for example, sodium dodecylbenzenesulfonate, sodium n-paraffin sulfonate, sodium α-olefin sulfonate, magnesium sulfate, magnesium nitrate, magnesium chloride, aluminum sulfate, aluminum nitrate, aluminum chloride, iron sulfate, iron nitrate It is preferable to use a dispersion aid such as iron chloride in combination.

  Among these, combined use of tricalcium phosphate and sodium n-paraffin sulfonate is more preferable. The amount of the dispersant and the dispersion aid varies depending on the type and the type and amount of the polypropylene resin used, but usually 0.2 parts by weight or more and 3 parts by weight or less of the dispersant with respect to 100 parts by weight of the dispersion medium. It is preferable to add 0.001 part by weight or more and 0.1 part by weight or less of a dispersion aid. The styrene-modified polyethylene resin particles are usually used in an amount of 20 to 100 parts by weight with respect to 100 parts by weight of the aqueous dispersion medium in order to improve the dispersibility in the aqueous dispersion medium. It is preferable.

  The mixture prepared in the pressure vessel as described above is heated to the foaming temperature under stirring and pressurized to the foaming pressure with an inorganic gas, and is preferably 5 minutes to 180 minutes, more preferably 10 minutes. The temperature and pressure are maintained for not less than 60 minutes and not more than 60 minutes. Thus, the styrene-modified polyethylene resin particles held at the foaming temperature and the foaming pressure are opened in a lower pressure atmosphere than the inside of the pressure vessel by opening a valve provided at one end of the pressure vessel, generally at the lower part of the pressure vessel ( Usually, styrene-modified polyethylene resin pre-expanded particles can be obtained by releasing them under atmospheric pressure.

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

  The foaming temperature is preferably 120 ° C. or higher and 180 ° C. or lower, and more preferably 130 ° C. or higher and 165 ° C. or lower. When the foaming temperature is high, the load on the equipment is large and the resin may be decomposed. When the foaming temperature is low, the expansion ratio tends to be low, and styrene-modified polyethylene resin pre-expanded particles having a target expansion ratio may not be obtained. The foaming pressure is preferably 2 MPa or more and 10 MPa or less, and more preferably 2.5 MPa or more and 7 MPa or less. More preferably, it is 3 MPa or more and 5 MPa or less. When the foaming pressure is high, the load on the equipment is large and the equipment tends to be expensive. When the foaming pressure is low, the expansion ratio tends to be low, and styrene-modified polyethylene resin pre-expanded particles having a target expansion ratio may not be obtained.

  It is desirable that the styrene-modified polyethylene resin pre-expanded particles obtained as described above contain a gel insoluble in xylene. The amount of gel insoluble in xylene is preferably 10% by weight or more and 50% by weight or less, and more preferably 15% by weight or more and 40% by weight or less in the pre-expanded particles of styrene-modified polyethylene resin. Within the range, when performing in-mold foam molding, the pre-foamed particles tend to be doubled, and a styrene-modified polyethylene resin in-mold foam molded article having good moldability and physical properties tends to be obtained.

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

  The styrene-modified polyethylene resin pre-expanded particles obtained by the production method of the present invention preferably have a weight-average molecular weight of a component soluble in tetrahydrofuran of 100,000 to 250,000. Within the range, in-mold foam moldability tends to be good when performing in-mold foam molding.

  The weight average molecular weight of the component soluble in tetrahydrofuran is determined by immersing 0.02 g of styrene-modified polyethylene resin pre-expanded particles in 20 ml of normal temperature tetrahydrofuran for 24 hours, and filtering the extracted component with a 0.2 μm filter. The value obtained on the basis of a standard polystyrene sample by gel permeation chromatography.

  The closed cell ratio of the styrene-modified polyethylene resin pre-expanded particles of the present invention is preferably 88% or more and 100% or less, more preferably 92% or more and 100% or less, and still more preferably 95% or more and 100% or less. . When it is not within the range, foamability by steam heating is inferior at the time of in-mold foam molding, and the resulting styrene-modified polyethylene resin in-mold foam-molded product may shrink or physical properties may be lowered.

  The expansion ratio of the styrene-modified polyethylene resin pre-expanded particles of the present invention is 3 to 60 times, preferably 4 to 50 times, more preferably 5 to 40 times. If it is outside the range, the moldability of in-mold foam molding and the physical properties of the styrene-modified polyethylene-based resin in-mold foam molding may be lowered, for example, the open cell ratio is increased.

  In order to obtain beads with a high expansion ratio, styrene-modified polyethylene resin pre-expanded particles that have been produced by the above-described foaming method, preferably with a expansion ratio of 3 to 25 times, are added using an inorganic gas. The styrene-modified polyethylene having a higher expansion ratio by a so-called two-stage foaming method in which the pressure in the styrene-modified polyethylene-based resin pre-expanded particles is increased by higher pressure than atmospheric pressure and then further heated by heating. -Based resin pre-expanded particles.

  When the expansion ratio is increased by the two-stage expansion method, it is desirable that the expansion ratio is within 7 times the expansion ratio of the original pre-expanded particles. Even the styrene-modified polyethylene resin pre-expanded particles having a low expansion ratio can be made into styrene-modified polyethylene resin pre-expanded particles having a high magnification by using the two-stage expansion method.

  The average cell diameter of the styrene-modified polyethylene resin pre-expanded particles obtained by the present invention is preferably 50 μm or more and 800 μm or less, more preferably 70 μm or more and 600 μm or less, and further preferably 100 μm or more and 500 μm or less. Within this range, a styrene-modified polyethylene resin in-mold foam molded article having good moldability and good physical properties when performing in-mold foam molding tends to be obtained. The average cell diameter is measured in accordance with JIS K6402 by arbitrarily removing 30 pre-expanded particles from styrene-modified polyethylene resin pre-expanded particles.

  In the case where the styrene-modified polyethylene resin pre-foamed particles of the present invention are subjected to in-mold foam molding, a) a method of using the styrene-modified polyethylene resin pre-foamed particles, and b) an inorganic gas such as air is press-fitted into the styrene-modified polyethylene resin pre-foamed particles in advance. And (c) a method of imparting foaming ability, and (c) a method of filling pre-expanded styrene-modified polyethylene resin particles in a mold in a compressed state and foam-molding in the mold, and the like.

  As a specific method for in-mold foam-molding of a styrene-modified polyethylene resin in-mold foam molded body from the styrene-modified polyethylene resin pre-foamed particles of the present invention, for example, the styrene-modified polyethylene resin pre-foamed particles are preliminarily formed into a pressure vessel. The inside of the styrene-modified polyethylene resin pre-expanded particles is given a foaming ability by pressurizing the air into the molding space that can be closed but cannot be sealed. Then, using water vapor as a heating medium and molding at a water vapor pressure of about 0.03 to 0.2 MPa for a heating time of about 3 to 70 seconds, the pre-expanded particles of styrene-modified polyethylene resin are fused together, and then a mold And a method of obtaining a styrene-modified polyethylene resin-in-mold foam-molded product after cooling the mold by water cooling or the like.

The density of the styrene-modified polyethylene resin-in-mold foam-molded article obtained using the styrene-modified polyethylene resin pre-expanded particles of the present invention is preferably 10 kg / m ³ or more and 300 kg / m ³ or less, more preferably. Is 15 kg / m ³ or more and 250 kg / m ³ or less, more preferably 15 kg / m ³ or more and 150 kg / m ³ or less.

  In addition, the static compression strength of the styrene-modified polyethylene resin in-mold foam molding obtained by using the styrene-modified polyethylene resin pre-expanded particles means that the in-mold foam molding is gradually compressed. It is the stress at each strain that occurs. The static compressive stress was measured by compressing a 50 mm × 50 mm × 25 mm sample at a test speed of 10 mm / min in accordance with NDS Z 0504-69.

  Examples and Comparative Examples are given below, but the present invention is not limited thereby. Measurement and evaluation were performed as follows.

<Foaming ratio>
The weight w (g) of the styrene-modified polyethylene resin pre-expanded particles and the ethanol submerged volume v (cm ³ ) are obtained, and the density d (g / cm ³ ) of the styrene-modified polyethylene resin particles before foaming is obtained by the following equation. It is what I have sought.
Foaming ratio = d × v / w

<Closed cell ratio>
Using an air comparison type hydrometer (type 930 manufactured by BECKMAN), the closed cell volume of the obtained styrene-modified polyethylene resin pre-expanded particles was obtained, and the closed cell volume was determined by an ethanol immersion method. The closed cell ratio was calculated by dividing.

<Average bubble diameter>
Thirty pre-expanded particles were arbitrarily taken out from the styrene-modified polyethylene resin pre-expanded particles, the bubble diameter was measured according to JIS K6402, and the average bubble diameter was calculated.

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

<Surface properties of styrene-modified polyethylene resin in-mold foam molding>
The appearance of the styrene-modified polyethylene resin-in-mold foam-molded product was judged according to the following criteria.
○: There are no gaps between the pre-expanded particles. Δ: There are gaps in some places, but the tolerance level as a whole ×: There are many gaps.

<Compression stress at 50% compression>
In accordance with NDS Z 0504-69, 50 mm × 50 mm × 25 mm is cut out from the in-mold foam-molded product with a vertical slicer, and a test piece is prepared so that all surfaces become cut surfaces. A compression test was performed at a test speed of 10 mm / min so that the surface of 50 mm × 50 mm was up and down, and the compression stress at 50% compression was measured.

The density of the test piece is obtained from the following equation by determining the volume v (cm ³ ) from the weight w (g), length, width, and thickness length.
Test piece density = w / v (g / cm ³ )

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

  Subsequently, 150 parts by weight of water, 2 parts by weight of tricalcium phosphate, 0.048 parts by weight of sodium α-olefin sulfonate, and 35 parts by weight of polyethylene resin particles are suspended in a 6 L autoclave and polymerized to 17.5 parts by weight of styrene. 0.26 parts by weight of benzoyl peroxide as an initiator (10-hour half-life temperature: 74 ° C.), and t-butyl peroxybenzoate (10-hour half-life temperature: 104 ° C.) as a radical species-generating crosslinking agent 0.65 weight 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. Further, the temperature was raised to 85 ° C., 47.5 parts by weight of a styrene monomer was dropped into the reaction system over 2 hours and 40 minutes to perform polymerization, and after 1 hour from the completion of the addition, the temperature was raised to 120 ° C. and held for 50 minutes. After cooling, washing, dehydration, and drying were performed to obtain styrene-modified polyethylene resin particles.

(Examples 1-6)
In a 10 L autoclave, 300 parts by weight of water, 2.0 parts by weight of tricalcium phosphate, 0.02 parts by weight of sodium n-paraffin sulfonate, 100 parts by weight of styrene-modified polyethylene resin particles, and dibutyl sebacate in the amount shown in Table 1 were added. The mixture was charged and pressurized to 1.0 MPa with carbon dioxide gas. These mixtures were heated to the foaming temperature shown in Table 1, adjusted to the foaming pressure shown in Table 1 with carbon dioxide, and held for 50 minutes. While maintaining the temperature and pressure, the valve at the bottom of the pressure vessel is opened, and the aqueous dispersion is discharged through a orifice plate having an aperture diameter of 4.0 mm into a cylinder filled with saturated water vapor, thereby pre-expanding particles of styrene-modified polyethylene resin Got. About the obtained pre-expanded particle, the expansion ratio and the closed cell ratio were measured. The results are shown in Table 1.

  The obtained styrene-modified polyethylene resin pre-expanded particles are impregnated with air to give an internal pressure of 0.15 to 0.5 MPa, heated with steam of 0.04 to 0.08 MPa (gauge pressure), and an expansion ratio of about 20-fold styrene-modified polyethylene resin pre-expanded particles were obtained. The obtained pre-expanded particles were measured for closed cell ratio, average cell diameter, and gel amount. The results are shown in Table 2.

  Next, pre-expanded styrene-modified polyethylene resin pre-expanded particles, which are pressurized with air in a pressure-resistant container and applied with an internal pressure of 0.14 to 0.17 MPa, are filled in a 400 mm × 300 mm × 60 mm mold, and the pre-expanded particles are pressurized together. Heating and fusing with water vapor of 0.10 MPa (gauge pressure) gave a styrene-modified polyethylene resin in-mold foam molded product. About the obtained in-mold foam molded article, surface properties, compression stress at 50% compression, and test piece density were measured. The results are shown in Table 2.

(Example 7)
Depressurization foaming was performed in the same manner as in Example 3 to obtain styrene-modified polyethylene resin pre-foamed particles having a foaming ratio of 9.2 times. The obtained pre-expanded particles were measured for closed cell ratio, average cell diameter, and gel amount. The results are shown in Table 2.

  Next, in-mold foam molding was performed in the same manner as in Examples 1 to 6 to obtain a styrene-modified polyethylene resin in-mold foam molded body. About the obtained in-mold foam molded article, surface properties, compression stress at 50% compression, and test piece density were measured. The results are shown in Table 2.

(Comparative Example 1)
A 10 L autoclave is charged with 300 parts by weight of water, 0.5 parts by weight of dibutyl sebacate, 2.0 parts by weight of tricalcium phosphate, 0.02 parts by weight of sodium n-paraffin sulfonate, and 100 parts by weight of styrene-modified polyethylene resin particles. Then, 22 parts by weight of normal rich butane (normal butane / isobutane = 70/30) was added to the autoclave as a blowing agent. After these mixtures were heated to 140 ° C., the pressure was adjusted to 2.30 MPa with normal rich butane and held for 50 minutes. While maintaining the temperature and pressure, the valve at the bottom of the pressure vessel is opened, and the aqueous dispersion is discharged into the atmosphere through an orifice plate having a hole diameter of 4.0 mmφ, thereby pre-foaming a styrene-modified polyethylene resin having a foaming ratio of about 20 times. Particles were obtained. The obtained pre-expanded particles were measured for closed cell ratio, average cell diameter, and gel amount. The results are shown in Table 2.

  Next, in-mold foam molding was performed in the same manner as in the above example to obtain a styrene-modified polyethylene resin in-mold foam molded body. About the obtained in-mold foam molded article, surface properties, compression stress at 50% compression, and test piece density were measured. The results are shown in Table 2.

(Comparative Example 2)
A 10 L autoclave is charged with 300 parts by weight of water, 0.5 parts by weight of dibutyl sebacate, 2.0 parts by weight of tricalcium phosphate, 0.02 parts by weight of sodium n-paraffin sulfonate, and 100 parts by weight of styrene-modified polyethylene resin particles. As a blowing agent, 16 parts by weight of normal rich butane (normal butane / isobutane = 70/30) was added to the autoclave. After these mixtures were heated to 140 ° C., the pressure was adjusted to 1.80 MPa with normal rich butane and held for 50 minutes. While maintaining the temperature and pressure, the valve at the bottom of the pressure vessel is opened, and the aqueous dispersion is discharged into the atmosphere through an orifice plate having a hole diameter of 4.0 mmφ, so that a styrene-modified polyethylene resin having an expansion ratio of about 9.5 times is obtained. Pre-expanded particles were obtained. The obtained pre-expanded particles were measured for closed cell ratio, average cell diameter, and gel amount. The results are shown in Table 2.

  Next, in-mold foam molding was performed in the same manner as in the above example to obtain a styrene-modified polyethylene resin in-mold foam molded body. About the obtained in-mold foam molded article, surface properties, compression stress at 50% compression, and test piece density were measured. The results are shown in Table 2.

  Even when an inorganic gas that is safe and has little impact on the environment was used, pre-expanded particles and in-mold foam molded articles equivalent to those obtained using an organic foaming agent were obtained. Further, regarding the compressive stress at the time of 50% compression, the result when the inorganic gas was used was 5 to 10% higher.

Claims (8)

  A styrene-modified polyethylene resin particle obtained by impregnating and polymerizing a polyethylene resin particle with a styrene monomer is foamed using an inorganic gas as a foaming agent. A method for producing pre-expanded particles of styrene-modified polyethylene resin.   Styrene-modified polyethylene resin particles impregnated and polymerized with polyethylene resin particles are dispersed in an aqueous dispersion medium in a pressure vessel and heated, and an inorganic gas is introduced into the pressure vessel as a blowing agent. After pressurizing the inside of the pressure vessel, one end of the pressure vessel is opened, and the mixture containing the styrene-modified polyethylene resin particles and the aqueous dispersion medium is discharged in a lower pressure atmosphere than in the pressure vessel. The method for producing styrene-modified polyethylene resin pre-expanded particles according to claim 1.   The method for producing pre-expanded particles of styrene-modified polyethylene resin according to claim 2, wherein the low-pressure atmosphere is filled with saturated steam.   The said inorganic gas is a carbon dioxide gas, The manufacturing method of the styrene modified polyethylene resin pre-expanded particle as described in any one of Claims 1-3.   The styrene-modified polyethylene resin pre-expanded particles obtained by the production method according to any one of claims 1 to 4 are pressurized with an inorganic gas, thereby forming the styrene-modified polyethylene resin pre-expanded particles in the styrene-modified polyethylene resin pre-expanded particles. A method for producing pre-expanded styrene-modified polyethylene resin particles, wherein the foaming is further performed by heating after raising the pressure to higher than atmospheric pressure.   A styrene-modified polyethylene resin pre-expanded particle obtained by the production method according to claim 1.   The styrene-modified polyethylene resin pre-expanded particles according to claim 6, having an average cell diameter of 50 µm or more and 800 µm or less.   A styrene-modified polyethylene resin in-mold foam molded product obtained by in-mold foam molding of the styrene-modified polyethylene resin pre-expanded particles according to claim 6 or 7.