JP2010111827A - Method for producing pre-expanded particle of styrene-modified polyethylene-based resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide pre-expanded particles of a styrene-modified polyethylene-based resin, which have excellent moldability and high anti-cracking properties even after a foaming agent is scattered. <P>SOLUTION: The pre-expanded particles of the styrene-modified polyethylene-based resin are produced by pre-expanding the styrene-modified polyethylene-based resin obtained by using 100 parts weight polyethylene-based resin and 150-300 parts weight styrenic monomer and contain 10-35 wt.% hot xylene-insoluble gel content. The method for producing the pre-expanded particles of the styrene-modified polyethylene-based resin comprises a step of continuously adding the styrenic monomer to the polyethylene-based resin of polymerization temperature so that the concentration of the styrenic monomer in the polyethylene-based resin when 35 wt.% of the amount of the whole styrene monomer to be added continuously is completed is made within 20-35 wt.% of the concentration of the styrenic monomer in the polyethylene-based resin when 75 wt.% of the amount of the whole styrenic monomer to be added continuously is completed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to styrene-modified polyethylene resin pre-expanded particles having excellent crack resistance and molding processability.

  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, Patent Document 1 describes a method for producing a graft reaction product of a polyolefin component and a styrene component to obtain a styrene-modified polyethylene resin having high impact resistance.

  Patent Document 2 describes a method for improving the impact resistance and chemical resistance of a styrene-modified polyethylene resin by making the resin surface rich in olefin by controlling the additional pattern of monomer and the power required for stirring. Among these, there is a description of making the surface olefin rich by setting the amount of styrene monomer during polymerization to 35% or less, but there is no mention about the influence on moldability as in this patent.

  Patent Document 3 describes a method of controlling the gel amount of the styrene-modified polyethylene-based expandable resin particles obtained by the polymerization temperature and the additional pattern of the styrene-based monomer. However, the influence of the concentration of the amount of styrene monomer during polymerization is not mentioned.

In addition, Patent Document 4 describes a gel amount and molecular weight range for achieving both crack resistance and molding processability by adding a part of a styrene monomer at once, and has excellent molding processability. It is disclosed that pre-expanded particles having can be obtained. However, there is no description on the molding processability of the pre-foamed particles after the foaming agent escapes, and styrene-modified polyethylene pre-foamed particles having excellent moldability after the foaming agent escapes of the pre-foamed particles are desired. It was.
JP 61-155413 A JP-A-2005-97555 W02004 / 085527 JP 2006-29895 A

  It is an object of the present invention to provide styrene-modified polyethylene resin pre-foamed particles having excellent moldability and high cracking resistance even after the foaming agent escapes.

  As a result of intensive studies, the inventors of the present invention, in the method for producing styrene-modified polyethylene resin pre-expanded particles, in the step of continuously adding the styrene monomer at the polymerization temperature, It has been found that by setting the concentration of the styrenic monomer within a predetermined range, it is possible to obtain a foam having excellent molding processability and excellent crack resistance.

  That is, the first of the present invention is obtained by pre-foaming a styrene-modified polyethylene resin in which a styrene monomer is used in an amount of 150 to 300 parts by weight with respect to 100 parts by weight of a polyethylene resin. A method for producing styrene-modified polyethylene resin pre-foamed particles in which the pre-foamed particles have a thermal xylene-insoluble gel content of 10 wt% or more and 35 wt% or less. And a step of continuously adding the styrenic monomer at the polymerization temperature, in the step of continuously adding 35% by weight of the styrenic monomer, and 75 Styrene-modified polyethylene resin pre-expanded particles, characterized in that the concentration of styrene monomer in the resin at the end of weight% is 20 wt% or more and 35 wt% or less It relates to a method for manufacturing.

As a preferred embodiment,
(1) In the step of continuously adding a styrene monomer to the polyethylene resin at the polymerization temperature, the concentration of the styrene monomer in the resin from the start of continuous addition of the styrene monomer to the end of continuous addition Is 15 wt% or more and 35 wt% or less,
(2) With respect to 100 parts by weight of polyethylene resin, 25 parts by weight or more and 100 parts by weight or less of styrene monomer are added and impregnated at a temperature at which polymerization does not proceed essentially, and the remaining styrene monomer is added. It is characterized by being added under heating.
(3) By adding a cross-linking agent having a 10-hour half-life temperature of 100 ° C. or higher and 125 ° C. or lower during or after polymerization, and 50% or more of the cross-linking agent is decomposed at 130 ° C. or higher and 150 ° C. or lower. can get,
(4) A cross-linking agent having a 10-hour half-life temperature of 100 ° C. or higher and 125 ° C. or lower is added during or after polymerization, and 50% or more of the cross-linking agent is present at 130 ° C. or higher and 150 ° C. or lower in the presence of a foaming agent. Obtained by being decomposed,
The present invention relates to a method for producing the styrene-modified polyethylene resin pre-expanded particles described above.

  2nd of this invention is related with the styrene modified polyethylene resin pre-expanded particle manufactured by the manufacturing method as described in any one.

  Since the styrene-modified polyethylene resin pre-expanded particles obtained by the production method of the present invention are excellent in moldability even after the blowing agent escapes from the styrene-modified polyethylene resin pre-expanded particles, Is industrially advantageous. In addition, a foam molded product obtained by in-mold foam molding of styrene-modified polyethylene resin pre-expanded particles obtained by the production method of the present invention has good surface properties and high crack resistance.

  The method for producing styrene-modified polyethylene resin pre-expanded particles according to the present invention comprises a styrene-modified polyethylene resin in which a styrene monomer is used in an amount of 150 parts by weight to 300 parts by weight with respect to 100 parts by weight of the polyethylene resin. A method for producing styrene-modified polyethylene resin pre-foamed particles obtained by pre-foaming, wherein the pre-foamed particles have a thermal xylene-insoluble gel content of 10 wt% or more and 35 wt% or less. And a step of continuously adding the styrenic monomer at the polymerization temperature. In the step of continuously adding the styrenic monomer at the polymerization temperature, the continuous addition of the styrenic monomer is 35% by weight. %, And the concentration of the styrene monomer in the resin at the end of 75% by weight is from 20% by weight to 35% by weight.

  In the present invention, a styrene monomer is used in an amount of 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 based on the polyethylene resin. Within this range, the resulting styrene-modified polyethylene-based pre-expanded particles can achieve 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, A polyethylene resin is impregnated with a styrene monomer and polymerized. In the polymerization, the weight average molecular weight of the styrene-modified polyethylene resin pre-expanded particles can be adjusted by arbitrarily selecting the addition rate of the styrene monomer to be added.

  In the present invention, the addition of a styrenic monomer to a polyethylene resin generally includes batch addition or divided addition. In the present invention, the polymerization temperature of a styrene monomer is added to a polyethylene resin. It is necessary to include the process of adding continuously. Here, the “step of continuously adding” refers to a step of adding a styrenic monomer without a time interval by a pump or the like.

  In the present invention, it is necessary to carry out such that the concentration of the styrene monomer in the resin is 20% or more and 35% or less when the continuous addition is completed 35% and when 75% is completed. Preferably, the continuous addition of the styrene monomer is performed so that the concentration of the styrene monomer in the resin is 15% or more and 35% or less from the start of the continuous addition to the end of the continuous addition. If the concentration of the styrene monomer in the resin is less than 20% when the continuous addition is completed 35% and 75%, a gap is generated in the particles of the foamed molded product when the volatile matter escapes, If it exceeds 35%, the crack resistance is lowered.

  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.

  The polyethylene resin used in the present invention is an ethylene homopolymer such as high-density polyethylene or low-density polyethylene, polyethylene, and α-olefin such as propylene, 1-butene, 1-pentene, 1-hexene, or 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. 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 molding may be deteriorated.

  Various additives can be used for the styrene-modified polyethylene resin. 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 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. 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, when performing pressure-reducing foaming to be described later, it is preferable to use an inorganic cell regulator, and the preferred amount used 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, and when the amount is more than 0.5 parts by weight, the fusion during molding tends to deteriorate. There is.

  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, 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 resin and water is preferably 1.0 / 0.6 to 1.0 / 4.0 in the resulting styrene-modified polystyrene resin / water.

  In the present invention, the pre-expanded particles of styrene-modified polyethylene resin need to have a gel content insoluble in hot xylene of 10% by weight or more and 35% by weight. Therefore, it is preferable to use a crosslinking agent. In the crosslinking reaction, it is preferable to use a radical species-generating crosslinking agent having a 10-hour half-life temperature of 100 ° C. or more and 125 ° C. or less. When a radical species-generating crosslinking agent having a 10-hour half-life temperature lower than 100 ° C. is used, the crosslinking reaction proceeds too much during polymerization, and crosslinking at 130 ° C. or more tends to be difficult. If the half-life temperature exceeds 125 ° C, it may take time to advance the crosslinking reaction 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 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.

  The crosslinking reaction using a crosslinking agent having a 10-hour half-life temperature of 100 ° C. or more and 125 ° C. or less is preferably performed at 130 ° C. or more and 150 ° C. or less, and 50% or more of the crosslinking agent is decomposed at 130 ° C. or more and 150 ° C. or less. It is preferred that If the crosslinking reaction is less than 130 ° C., it may be difficult to obtain a resin having both impact resistance and molding processability. When the crosslinking reaction temperature exceeds 150 ° C., the resin is too soft and the resin particles tend to aggregate. The amount of the cross-linking agent varies depending on the type of the cross-linking agent, but it is desirable to use 0.1 to 1.0 part by weight with respect to 100 parts by weight of the styrene-modified ethylene resin pre-expanded particles basically obtained. A gel amount in the range is easily obtained. Especially, it is preferable that 50% or more of the crosslinking agent is decomposed at 130 ° C. or more and 150 ° C. or less in the presence of a foaming agent.

  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 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 cannot be obtained, and it may be difficult to obtain styrene-modified polyethylene resin 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 to a temperature above the softening point of the styrene-modified polyethylene resin particles, and apply the resin particles under pressure above the vapor pressure of the foaming agent. After impregnating the foaming agent, the so-called “pressure-removal” is performed, in which the mixture of the styrene-modified polyethylene resin particles and the aqueous dispersion medium is released to a lower pressure region than in the pressure vessel while keeping the temperature and pressure in the pressure vessel constant. A method called “foaming”, (2) impregnating and polymerizing polyethylene-based resin particles with a styrene-based monomer, and then impregnating with a foaming agent to form expandable modified polyethylene-based resin particles. A method in which expandable modified polyethylene resin particles are placed in a container and heated by a heat source such as water vapor, and (3) a polyethylene resin particle is impregnated with a styrene monomer and polymerized to obtain modified polyethylene resin particles. For example, a method of impregnating a foaming agent in a container equipped with a stirrer and heating with a heat source such as water vapor can be used. In order to perform foaming in a series of operations, an excessive amount of foaming agent is not required, which is preferable.

  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 After charging the container and adding a foaming agent, the temperature is increased by overheating, 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 impregnated with the foaming agent is discharged from the pressure vessel, washed and dried, and then heated with water vapor or the like to obtain 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 vessel equipped with a stirrer for impregnating foaming agent, add a small amount of water, a dispersant and a foaming agent, impregnate the foaming agent, discharge it, heat with steam, etc. It can be set as expanded particles. 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 need to have a gel component amount insoluble in hot xylene of 10% by weight to 35% by weight, preferably 20% by weight to 30%. % By weight or less. 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 content insoluble in hot xylene in the present invention 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, when performing in-mold molding, a foamed molded article having good moldability tends to be obtained even when the foaming agent is dissipated.

  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 by filtering and obtaining a standard polystyrene sample as a reference by gel permeation chromatography.

  The styrene-modified polyethylene resin pre-expanded particles thus obtained can be molded by a general in-mold molding method to obtain a foam molded product. 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 tends to exhibit excellent crack resistance.

  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 molded body>
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 it is almost unknown 3: There are gaps in some places, but as a whole, the tolerance level 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 molded body molded 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 content>
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 defined as the amount of the gel component.

<Measurement of styrene monomer concentration in resin>
20 g of methylene chloride was added to 0.1 g of the sampled polymerization resin and stirred for 8 hours, and then the supernatant methylene chloride solution was collected and gas chromatographed (GC-14B, Shimadzu Corporation, column: 3 m, packing: PEG-20M 25%, column temperature: 110 ° C.).

<Decomposition amount of crosslinking agent>
From the 1 minute half-life temperature, 1-hour half-life temperature, 10-hour half-life temperature and activation energy of the radical species-generating crosslinking agent, the half-life at the polymerization and crosslinking temperature is calculated using the Arrhenius equation. It was determined by calculating the amount of decomposition in the polymerization / crosslinking time.

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 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 hours half-life temperature: 74 ° C.) as a polymerization initiator and 0.56 parts by weight of t-butyl peroxybenzoate (10 hours half-life temperature: 104 ° C.) as a crosslinking agent are dissolved. Solution was added. Thereafter, this aqueous suspension was heated to 70 ° C. over 1 hour and 10 minutes, 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. At this time, the temperature of the reaction system at the start of addition of the styrene monomer was 76.9 ° C., and reached 85 ° C. 42 minutes after the start of temperature increase. Then, after completion | finish of dripping, it hold | maintained at 85 degreeC for 1 hour. Then, it heated up to 120 degreeC over 1 hour and 20 minutes, and hold | maintained for 50 minutes, and superposition | polymerization of the styrene-type monomer was completed. The mixture was cooled to room temperature over 2 hours, washed, dehydrated and dried to obtain styrene-modified polyethylene resin particles. The decomposition amount of the crosslinking agent at this time was 44% by weight.

  Thereafter, 330 parts by weight of water, 2 parts by weight of tricalcium phosphate, 0.022 parts by weight of sodium n-paraffin sulfonate, 100 parts by weight of styrene-modified polyethylene resin particles, and 0.5 parts by weight of dibutyl sebacate were charged into a 10 L autoclave. It is. 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 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 concentration of the styrene monomer in the resin at the time of polymerization is as shown in Table 1, and the concentration of the styrene monomer in the resin at the time when the continuous addition of the styrene monomer was completed by 35% by weight was It was 24.7% by weight when 26.2% by weight and 75% were completed. From the start of continuous addition to the end of addition, the change was between 23.4 wt% and 26.2 wt%.

  The obtained styrene-modified polyethylene resin pre-expanded particles had a thermal xylene-insoluble gel content of 24.8% by weight.

  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 room at about 35 ° C. until the amount of remaining foaming agent is 1% by weight or less with respect to 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. It was 38 cm when the crack resistance of the molded body molded with the pre-expanded particles immediately after foaming was evaluated. The amount of the remaining 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, Measured by determining weight percent. The surface state of the foamed molded product that was molded when the volatile matter escaped was 4.

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

  Styrene-modified polyethylene resin particles were obtained in the same manner as in Example 1 except that the continuous addition of the styrene monomer was changed to 20 minutes from the start of raising the temperature to 85 ° C. The temperature of the reaction system at the start of continuous addition was 80.3 ° C., and reached 85 ° C. in 43 minutes from the start of temperature increase. The decomposition amount of the crosslinking agent at the end of the polymerization was 44% by weight.

  In a 10 L autoclave, styrene-modified polyethylene resin pre-expanded particles having an expansion bulk ratio of 31 times were prepared in the same manner as in Example 1.

  The concentration of the styrene monomer in the resin at the time of polymerization is as shown in Table 1, and the concentration of the styrene monomer in the resin at the time when the continuous addition of the styrene monomer was completed by 35% by weight was It was 21.0% by weight when 22.4% by weight and 75% by weight were completed. From the start of continuous addition to the end of addition, it varied between 17.3% and 22.4% by weight.

  The obtained styrene-modified polyethylene resin pre-foamed particles had a heat xylene-insoluble gel content of 24.7% by weight.

  The obtained pre-expanded particles were molded and evaluated in the same manner as in Example 1. The crack resistance was 40 cm. The surface state of the molded body molded at the time of volatile component dissipation was 3.

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

  Styrene-modified polyethylene resin particles were obtained in the same manner as in Example 1 except that the continuous addition of the styrene monomer was 39 minutes from the start of the temperature increase to 85 ° C. The temperature of the reaction system at the start of continuous addition was 84.5 ° C., and reached 85 ° C. in 42 minutes from the start of temperature increase. The decomposition amount of the crosslinking agent at the end of the polymerization was 44% by weight.

  In a 10 L autoclave, styrene-modified polyethylene resin pre-expanded particles having a foam volume ratio of 30 times were produced in the same manner as in Example 1.

  The concentration of the styrene monomer in the resin at the time of polymerization is as shown in Table 1, and the concentration of the styrene monomer in the resin at the time when the continuous addition of the styrene monomer was completed by 35% by weight was At the end of 14.4 wt% and 75 wt%, it was 11.1 wt%. From the start of continuous addition to the end of addition, it varied between 8.9 wt% and 17.7 wt%.

  The gel fraction insoluble in hot xylene of the obtained styrene-modified polyethylene resin pre-expanded particles was 24.2% by weight.

  The obtained pre-expanded particles were molded and evaluated in the same manner as in Example 1. The crack resistance was 39 cm. The surface state of the molded body molded at the time of volatile component dissipation was 2.

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

  Subsequently, 1 part by weight of tribasic calcium phosphate, 0.024 part by weight of sodium α-olefin sulfonate, and 35 parts by weight of polyethylene resin particles are suspended in 150 parts by weight of water in a 6 L autoclave, and the temperature is raised to 85 ° C. over 1 hour. Warm up. After reaching 85 ° C, 17.5 parts by weight of styrene, 0.24 parts by weight of benzoyl peroxide (10 hour half-life temperature: 74 ° C) as a polymerization initiator, and t-butyl peroxybenzoate (10 hour half-life) as a crosslinking agent (Temperature: 104 ° C.) A solution in which 0.56 parts by weight were dissolved was continuously added to the reaction system at a constant rate over 1 hour. Subsequently, 47.5 parts by weight of a styrene monomer was continuously dropped into the reaction system at a constant rate over 2 hours and 40 minutes. Then, after completion | finish of dripping, it hold | maintained at 85 degreeC for 1 hour. Then, it heated up to 120 degreeC over 1 hour, and hold | maintained for 1 hour, and superposition | polymerization of the styrene-type monomer was completed. After cooling to room temperature over 1 hour, styrene-modified polyethylene resin particles were obtained by washing, dehydrating and drying. The amount of crosslinking agent decomposed at the end of the polymerization was 47% by weight.

  The concentration of the styrene monomer in the resin at the time of polymerization is as shown in Table 1, and the concentration of the styrene monomer in the resin at the time when the continuous addition of the styrene monomer was completed by 35% by weight was 16.1% by weight and 75% by weight were 12.8% by weight. From the start of continuous addition to the end of addition, it varied between 0 wt% and 16.1 wt%.

  In a 10 L autoclave, styrene-modified polyethylene resin pre-expanded particles having a foam volume ratio of 30 times were produced in the same manner as in Example 1.

  The gel fraction insoluble in hot xylene of the obtained styrene-modified polyethylene resin pre-expanded particles was 24.2% by weight.

  The obtained pre-expanded particles were molded and evaluated in the same manner as in Example 1. The crack resistance was 45 cm. The surface state of the molded body molded at the time of volatile component dissipation was 2.

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

  Subsequently, 1 part by weight of tribasic calcium phosphate, 0.024 part by weight of α-olefin sodium sulfonate and 30 parts by weight of polyethylene resin particles are suspended in 150 parts by weight of water in a 6 L autoclave, and the temperature is raised to 85 ° C. over 1 hour. Warm up. After reaching 85 ° C., 15 parts by weight of styrene, 0.18 parts by weight of benzoyl peroxide as a polymerization initiator (10 hour half-life temperature: 74 ° C.), and dicumyl peroxide as a crosslinking agent (10 hour half-life temperature: 116 ° C.) ) A solution containing 0.29 parts by weight was continuously added to the reaction system at a constant rate over 2 hours. Subsequently, 55 parts by weight of a styrene monomer was continuously dropped into the reaction system at a constant rate over 3 hours and 40 minutes. Then, after completion | finish of dripping, it hold | maintained at 85 degreeC for 1 hour. Then, it heated up to 140 degreeC over 1 hour and 30 minutes, and hold | maintained for 3 hours, and superposition | polymerization of the styrene-type monomer was completed. After cooling to room temperature over 1 hour, styrene-modified polyethylene resin particles were obtained by washing, dehydrating and drying.

  The concentration of the styrene monomer in the resin at the time of polymerization is as shown in Table 1, and the concentration of the styrene monomer in the resin at the time when the continuous addition of the styrene monomer was completed by 35% by weight was At the end of 15.3% by weight and 75% by weight, it was 22.4% by weight. From the start of continuous addition to the end of addition, it varied between 0 wt% and 22.4 wt%.

  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 1 except that normal-rich butane was 20 parts by weight and the retention time at 140 ° C. was 30 minutes. did.

  The obtained xylene-insoluble gel content of the styrene-modified polyethylene resin pre-expanded particles was 20.1% by weight.

  The obtained pre-expanded particles were molded and evaluated in the same manner as in Example 1. The crack resistance was 28 cm. The surface state of the molded body molded at the time of volatile matter dissipation was 1.

(Comparative Example 4)
Polyethylene resin particles were prepared in the same manner as in Example 1.

  Polymerization was carried out 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.

  The concentration of the styrenic monomer in the resin at the time of polymerization is as shown in Table 1, and the concentration of the styrenic monomer in the resin at the time when the continuous addition of the styrenic monomer was completed by 35% by weight. Was 20.8% by weight and 40.1% by weight when 75% by weight was completed. From the start of continuous addition to the end of addition, it varied between 0 wt% and 43.9 wt%.

  In a 10 L autoclave, styrene-modified polyethylene resin pre-expanded particles having an expansion bulk ratio of 30 times were produced in the same manner as in Comparative Example 3.

  The resulting styrene-modified polyethylene resin pre-expanded particles had a thermal xylene-insoluble gel content of 7.7% by weight.

  The obtained 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 molded body that was molded when the volatile matter escaped was 4.

  In Examples 1 and 2, since the concentration of the styrene monomer in the resin during the continuous addition of the styrene monomer is a predetermined concentration, the surface condition of the foamed molded article when cracking resistance and volatile matter escape Is good. Comparative Example 1, Comparative Example 2, and Comparative Example 3 have low styrene monomer concentration in the resin during continuous addition of styrene monomer, and are inferior in moldability when volatile matter escapes. In Comparative Example 4, the concentration of styrene monomer in the resin is high and the gel content is out of the requirements for implementation, and the crack resistance is poor.

  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.

Claims (6)

  Pre-foamed particles insoluble in hot xylene obtained by pre-foaming a styrene-modified polyethylene resin in which a styrenic monomer is used in an amount of 150 to 300 parts by weight with respect to 100 parts by weight of the polyethylene resin. A method for producing styrene-modified polyethylene resin pre-expanded particles having a content of 10% by weight or more and 35% by weight or less, comprising a step of continuously adding a styrene monomer to a polyethylene resin at a polymerization temperature. In the step of continuously adding the styrenic monomer at the polymerization temperature, the styrene in the resin at the time when the continuous addition of the styrenic monomer is completed by 35% by weight and at the time when the 75% by weight is completed. A method for producing styrene-modified polyethylene resin pre-expanded particles, wherein the concentration of the monomer is 20% by weight or more and 35% by weight or less.   In the step of continuously adding the styrene monomer to the polyethylene resin at the polymerization temperature, the concentration of the styrene monomer in the resin is 15% by weight from the start of the continuous addition of the styrene monomer to the end of the continuous addition. The method for producing styrene-modified polyethylene-based pre-expanded particles according to claim 1, wherein the ratio is from 35% to 35% by weight.   25 parts by weight or more and 100 parts by weight or less of a styrene monomer are added and impregnated at a temperature at which polymerization does not proceed essentially with respect to 100 parts by weight of a polyethylene resin, and the remaining styrene monomer is heated. The method for producing pre-expanded particles of styrene-modified polyethylene resin according to claim 1 or 2, wherein the pre-expanded particles are added.   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 4. A method for producing styrene-modified polyethylene resin pre-expanded particles according to any one of Items 1 to 3.   During or after polymerization, a crosslinking agent having a 10-hour half-life temperature of 100 ° C. or more and 125 ° C. or less is added, and 50% or more of the crosslinking agent is decomposed at 130 ° C. or more and 150 ° C. or less in the presence of a foaming agent. The manufacturing method of the styrene modified polyethylene resin pre-expanded particle as described in any one of Claims 1-4 obtained by this.   A styrene-modified polyethylene resin pre-expanded particle produced by the production method according to claim 1.