JP6280739B2 - Styrene-modified polyethylene pre-expanded particles and molded articles thereof - Google Patents

Description

  The present invention relates to styrene-modified polyethylene resin particles, pre-expanded particles, and molded articles thereof excellent in moldability in in-mold foam molding.

  Polyolefin resin foams are generally used as packaging materials and automotive parts because they are generally highly elastic and have excellent strain resistance against repeated stress, as well as excellent oil resistance and crack resistance. Has been. However, the polyolefin resin foam has the disadvantages that it has low rigidity, the foam molding after in-mold molding tends to shrink, and the compressive strength is low.

  As a method for improving such a defect, it is known to use, as a base resin, a styrene-modified polyethylene resin obtained by impregnating a polyethylene resin with a styrene monomer and performing polymerization.

  However, in order to foam-mold these styrene-modified polyethylene-based pre-expanded particles in advance, the pre-expanded particles are impregnated with a hydrocarbon-based foaming agent or air to give the pre-expanded particles foaming power. The foamed molded body is obtained with heated steam.

  For example, in Patent Documents 1 and 2, a linear low-density polyethylene is used as a polyethylene resin, and a styrene-modified polyethylene resin particle obtained by adjusting the amount of gel composed of a graft component is impregnated with a hydrocarbon foaming agent. The pre-expanded particles obtained by foaming the expanded resin particles thus formed are subjected to in-mold foam molding at a molding pressure of 0.08 to 0.12 MPa (G), thereby obtaining a foam molded article. However, the storage after paying attention to the escape and explosion of hydrocarbons in the pre-expanded particles is necessary with the passage of time after the production of the expanded molded article.

  In Patent Documents 3 and 4, styrene-modified polyethylene resin particles are decompressed and foamed using a hydrocarbon foaming agent to obtain pre-foamed particles, thereby obtaining a foamed molded article. Since a hydrocarbon-based foaming agent is used at the time of decompression foaming of the pre-foamed particles, an explosion-proof facility is required, and the production cost is high.

Patent Document 5 discloses a method for obtaining pre-expanded particles by decompressing and foaming styrene-modified polyethylene resin particles using an inorganic gas-based foaming agent such as carbon dioxide in the presence of dibutyl sebacate. .
However, in patent document 5, when obtaining a foaming molding, there exists a process which impregnates air beforehand in a pre-expanded particle and provides foaming power to a pre-expanded particle, and manufacturing cost is high.

Japanese Patent Laid-Open No. 10-147660 JP 2006-7020 A JP 2010-229325 A JP 2010-270284 A JP 2011-84593 A

In view of the above situation, the object of the present invention is to produce styrene-modified polyolefin resin pre-expanded particles with an inexpensive manufacturing facility using an inorganic gas blowing agent, Even without impregnation with a foaming agent or air, a styrene-modified ethylene-based preliminary can obtain a suitable foamed molded article by in-mold foam molding with a heating steam pressure of a molding pressure of 0.08 to 0.12 MPa (G). It is to provide expanded particles.
Furthermore, the objective of this invention is providing the foaming molding suitable for a motor vehicle member.

  As a result of intensive studies, the present inventors have found that 120 parts by weight or more and 500 parts by weight or less of a styrene monomer and 3 parts by weight of a specific (meth) acrylate monomer with respect to 100 parts by weight of polyethylene resin particles. The styrene-modified polyethylene resin pre-expanded particles obtained by depressurizing and foaming styrene-modified polyethylene resin particles impregnated with 30 parts by weight or less and polymerized together with sebacic acid ester with an inorganic gas are added with air. The inventors have found that in-mold foam molding under normal heating conditions is possible without going through the foaming ability imparting step by pressure, and completed the present invention.

That is, the present invention is as follows.
[1] Styrene-modified polyethylene resin pre-expanded particles obtained by foaming styrene-modified polyethylene resin particles using an inorganic gas,
The styrenic modified polyethylene resin particles are selected from 120 parts by weight to 500 parts by weight of a styrene monomer, 2-ethylhexyl acrylate, and butyl methacrylate with respect to 100 parts by weight of the branched low density polyethylene resin. At least one (meth) acrylic acid ester monomer is impregnated with 3 to 30 parts by weight and polymerized,
The styrene-modified polyethylene resin pre-expanded particles contain 0.1% by weight or more and less than 2% by weight of sebacic acid ester with respect to 100% by weight of styrene-modified polyethylene-based pre-expanded resin particles, and insoluble in xylene 5 to 20% by weight of styrene-modified polyethylene resin expanded particles,
[2] The styrene-modified polyethylene pre-expanded particles according to [1], wherein the styrene-modified polyethylene pre-expanded particles have a tetrahydrofuran-soluble part having a weight average molecular weight of 150,000 to 350,000.
[3] The styrene-modified polyethylene expanded particles according to [1] or [2], wherein the styrene-modified polyethylene resin pre-expanded particles contain 1% or less of a volatile component.
[4] Polymerization is performed by impregnating a polyethylene resin particle with a styrene monomer and at least one acrylate ester monomer selected from 2-ethylhexyl acrylate and butyl methacrylate in a pressure-resistant container. 100 parts by weight of the resulting styrene-modified polyethylene resin particles are dispersed in an aqueous dispersion medium together with 0.1 to 2 parts by weight of dibutyl sebacate, heated, and carbon dioxide gas is introduced as a blowing agent to withstand pressure. After pressurizing the inside of the container, one end of the pressure container 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 the pressure container. The manufacturing method of the styrene modified polyethylene resin pre-expanded particle in any one of [1]-[3].
[5] The styrene-modified ethylene resin foamed particles according to any one of [1] to [3] are filled into a molding space that can be closed but cannot be sealed, which is composed of two molds, and a heating medium. A method for producing a styrene-modified polyethylene-based resin foam molded article, which is obtained by heating by heating.

  The styrene-modified polyethylene resin pre-expanded particles of the present invention can be obtained by in-mold foam molding under normal heating conditions during the in-mold foam molding, without undergoing a step of previously applying an internal pressure in the pre-expanded particles. In addition, a foamed molded article having excellent surface wrinkles, fusion rate, and compressive strength can be obtained.

  The production process of the styrene-modified polyethylene pre-expanded particles and foamed molded article of the present invention is as follows: (1) Polyethylene resin particles obtained by adding a compounding agent to a polyethylene resin and pelletizing with an extruder or the like are produced. Step (2) A step of producing styrene-modified polyethylene resin particles obtained by adding a styrene monomer and an acrylate monomer to the polyethylene resin particles, impregnating them, and polymerizing them. (3) A step of producing styrene-modified polyethylene pre-expanded particles by decompressing and foaming the styrene-modified polyethylene resin particles using an inorganic foaming agent, and (4) the styrene-modified polyethylene system. The pre-expanded particles can be classified into a process of in-mold foam molding.

(1) Production of polyethylene resin particles Polyethylene resin particles are produced by melt-kneading polyethylene resin using an extruder, kneader, Banbury mixer, roll, etc., and formed into particles such as powder and pellets. It is obtained by doing.

  The average particle weight of the polyethylene resin particles used in the present invention is preferably in the range of 0.1 mg / particle to 3 mg / particle. If the average particle weight of the polyethylene resin particles is smaller than 0.1 mg / particle, the foaming agent may be dissipated rapidly, making it difficult to increase the magnification. If it is larger than 3 mg / particle, the filling property at the time of molding is deteriorated. There is a fear.

The melt flow rate (hereinafter abbreviated as “MFR”) of the polyethylene resin used in the present invention is preferably 0.1 g / 10 min or more and 1.0 g / 10 min or less, preferably 0.15 g / 10 min. More preferably, it is 0.5 g / 10 min or less.
If the MFR of the polyethylene resin exceeds 1.0 g / 10 min or less, the resins tend to be easily bonded together during polymerization, and if it is less than 0.1 g / 10 min, foaming tends to be difficult.
MFR is a value measured according to JIS K6924.

  The polyethylene-based resin used in the present invention is preferably a branched low-density polyethylene resin having a softening point close to the polymerization temperature of a general styrene monomer from the viewpoints of styrene impregnation polymerization and coalescence during polymerization.

  In the polyethylene resin particles used in the present invention, as various additives, a plasticizer, a bubble adjusting agent, and the like can be appropriately blended depending on the purpose.

  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, and sebacic acid Examples include fatty acid esters such as dibutyl, organic hydrocarbons such as liquid paraffin and cyclohexane, and organic aromatic hydrocarbons such as toluene and ethylbenzene. These are used in combination as long as they do not affect polymerization stability and flammability. There is no problem.

  Examples of the foam regulator include, for example, aliphatic bisamides such as methylene bis stearic acid amide, ethylene bis stearic acid amide, and organic foam regulating agents such as stearamide, talc, silica, calcium silicate, calcium carbonate, sodium borate, Inorganic bubble regulators such as zinc borate are listed.

(2) Production of styrene-modified polyethylene resin particles The styrene-modified polyethylene resin particles in the present invention are obtained by adding a styrene monomer and a (meth) acrylate monomer to polyethylene resin particles, It is obtained by impregnating and polymerizing.

The styrene monomer is preferably impregnated and polymerized by adding 120 parts by weight to 500 parts by weight, more preferably 150 parts by weight to 400 parts by weight with respect to 100 parts by weight of the polyethylene resin particles. Can be obtained.
If the total addition amount of the styrenic monomer is less than 120 parts by weight, it tends to be difficult to obtain a foaming force by carbon dioxide gas foaming, and if it exceeds 500 parts by weight, the moldability tends to be inferior.

  As the styrene monomer used in the present invention, for example, a styrene derivative such as styrene, α-methyl styrene, paramethyl styrene, t-butyl styrene, chlorostyrene or the like can be used as a main component.

The (meth) acrylic acid ester monomer is preferably impregnated by adding 3 to 22 parts by weight, more preferably 6 to 20 parts by weight, with respect to 100 parts by weight of the polyethylene resin particles. Obtained by polymerization.
If the total amount of (meth) acrylic acid ester monomer added is less than 3 parts by weight, the foaming power of the pre-expanded particles is weak, and the surface elongation of the resulting molded product is deteriorated. The physical properties are reduced.

  As the (meth) acrylic acid ester monomer used in the present invention, those having a glass transition temperature lower than room temperature are preferable. For example, as an acrylic acid ester monomer having an alkyl group with 1 to 12 carbon atoms, Examples thereof include ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. Examples of the methacrylic acid ester monomer having 4 to 16 carbon atoms in the alkyl group include butyl methacrylate and 2-ethylhexyl methacrylate. Can be mentioned. These may be used alone or in combination of two or more.

  Among these (meth) acrylic acid ester monomers, 2-ethylhexyl acrylate and butyl methacrylate are uniformly impregnated into the interior of the polyethylene resin particles, and the foaming power of the pre-expanded particles is increased, and the resulting molded product From the point that the surface elongation of is good.

  In the polymerization of the styrene-modified polyethylene resin particles of the present invention, a monomer that can be copolymerized with a styrene monomer and a (meth) acrylic acid ester monomer is used as the styrene-modified polyethylene resin of the present invention. They can be used in combination as long as the effects of the pre-expanded particles are not impaired.

  Examples of monomers that can be copolymerized include polyfunctional monomers such as acrylonitrile, dimethyl fumarate, ethyl fumarate, divinylbenzene, and alkylene glycol dimethacrylate.

  In the present invention, as a method for obtaining styrene-modified polyethylene resin particles, for example, an aqueous suspension containing polyethylene resin particles charged in a container equipped with a stirrer is mixed with a styrene monomer and (meth) acrylic. Examples include a method in which polyethylene resin particles are impregnated with a styrene monomer or a (meth) acrylic acid ester monomer and polymerized by adding an acid ester monomer continuously or intermittently. .

  In this method, 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.

In the polymerization of the styrene-modified polyethylene resin particles in the present invention, preferred embodiments include the total amount of (meth) acrylate monomer and a part of the styrene monomer to be added (that is, 100 parts by weight of polyethylene resin particles). In contrast, 30 parts by weight or more and 150 parts by weight or less of a styrene monomer is added and impregnated at a temperature at which polymerization does not proceed, and the remaining styrene monomer is subjected to polymerization at a temperature at which polymerization proceeds. It is to add continuously.
Here, “the temperature at which polymerization does not proceed essentially” means a temperature 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 weight average molecular weight of the modified polyethylene resin pre-expanded particles.

  The polymerization temperature when continuously adding the remaining styrenic monomer is preferably 80 ° C. or higher and 100 ° C. or lower. When the temperature to be continuously added is less than 80 ° C., the impregnation of styrene into the polyethylene resin is slow, and the polymerization in the polyethylene resin tends not to proceed. When the temperature to be continuously added is more than 100 ° C., the resin tends to be easily bonded.

  As the polymerization initiator used for the polymerization of the styrene-modified polyethylene resin particles in the present invention, a radical generating polymerization initiator generally used for the production of a thermoplastic polymer can be used. For example, benzoyl peroxide, lauroyl peroxide, t-butyl peroxy-2-ethylhexanoate, t-butyl perpivalate, t-butyl peroxyisopropyl carbonate, di-t-butyl peroxyhexahydroterephthalate, 1 , 1-di (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-di (t-butylperoxy) cyclohexane, azobisisobutyronitrile, azobis Examples include azo compounds such as dimethylvaleronitrile. These polymerization initiators may be used alone or in combination of two or more.

  Among these, the combined use of t-butylperoxy-2-ethylhexanoate (10-hour half-life temperature: 72 ° C.) and benzoyl peroxide (10-hour half-life temperature: 74 ° C.) is the weight of the tetrahydrofuran soluble part. The average molecular weight, the heat xylene insoluble component, and the amount of the heat xylene soluble methyl ethyl ketone insoluble component are preferable from the viewpoint that the predetermined amount is easily obtained.

The amount of the polymerization initiator used is preferably 0.05 parts by weight or more and 1.0 parts by weight or less, based on 100 parts by weight of the polystyrene-based monomer, and is 0.2 parts by weight or more and 0.7 parts by weight or less. It is more preferable that
When the amount of the polymerization initiator used is less than 0.05 part, the polymerization does not proceed sufficiently and the residual monomer tends to increase. When the amount exceeds 1.0 part by weight, the polymerization reaction occurs rapidly. It tends to be difficult to adjust the temperature.

  In particular, with respect to t-butylperoxy-2-ethylhexanoate, it is preferably used in an amount of 0.3 to 0.6 parts by weight, and used in an amount of 0.2 to 0.4 parts by weight. More preferably. With respect to benzoyl peroxide, it is preferably used in an amount of 0.05 to 0.3 parts by weight, and more preferably 0.2 to 0.4 parts by weight.

  In the polymerization of styrene-modified polyethylene resin particles in the present invention, it is generally used for polymerization of mercaptan chain transfer agents such as n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and acrylonitrile-styrene resin. Α-methylstyrene dimer used in the above may be used in combination.

  In the production of styrene-modified polyethylene resin particles in the present invention, polymerization is carried out in an aqueous suspension containing polyethylene resin particles. In this case, in order to prevent coalescence of the resin particles, a dispersant is used. It is preferable to use it.

Examples of the dispersant used in the present invention 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, Examples include poorly water-soluble inorganic salts such as kaolin.
Moreover, when using a poorly water-soluble inorganic salt, it is preferable to use an anionic surfactant such as α-olefin sodium sulfonate or dodecylbenzene sodium sulfonate in order to increase dispersion stability. These dispersants may be added during the polymerization.

  Although the usage-amount of the dispersing agent in this invention changes with kinds, 0.2 to 10 weight part is fundamentally preferable with respect to 100 weight part of water.

In addition, a water-soluble polymerization inhibitor can be used in combination for preventing adhesion between the resin particles. Examples of the water-soluble polymerization inhibitor include sodium nitrite and 3,5-dibutyl-4-hydroxytoluene (BHT).
When using these water-soluble polymerization inhibitors, it is preferable to use them so that the concentration in water is 150 ppm or less. If the concentration of the polymerization inhibitor in water exceeds 150 ppm, polymerization inhibition may occur.

  The “aqueous suspension” in the present invention refers to a state in which resin particles and monomer droplets are dispersed in water or an aqueous solution by using stirring or the like. The body may be dissolved, and a water-insoluble dispersant, initiator, crosslinking agent, bubble regulator, flame retardant, plasticizer, and the like may be dispersed together.

  The weight ratio of the resin and water in the present invention is preferably 1.0 / 0.6 to 1.0 / 3.0 as the ratio of the styrene-modified polystyrene resin / water obtained.

  In the production of the styrene-modified polyethylene resin particles in the present invention, it is preferable to use a radical species-generating crosslinking agent in order to generate hot xylene-insoluble matter in the styrene-modified polyethylene resin pre-expanded particles.

  As the radical species generating type crosslinking agent used for the crosslinking reaction, it is preferable to use a crosslinking agent having a 10-hour half-life temperature of 100 ° C. or more and 125 ° C. or less. When a radical species-generating crosslinking agent having a 10-hour half-life temperature lower than 100 ° C. is used, the crosslinking reaction proceeds too much during polymerization, and crosslinking at 120 ° C. or more tends to be difficult. If the half-life temperature exceeds 125 ° C, it takes time to advance the crosslinking reaction at a temperature of 120 ° C or higher.

  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 hours) 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-butylperoxybutane (10 hour half-life temperature: 103 ° C.) and the like.

  These crosslinking agents can be added to the polymerization system before the addition of the styrene monomer or the acrylate monomer or together with these monomers. In the case of performing foaming by decompression foaming, which will be described later, a crosslinking agent may be prepared at the time of preparation of decompression foaming and a crosslinking reaction may be performed at the time of impregnation of the foaming agent at the time of decompression foaming.

  In the present invention, 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 carried out at 120 ° C. or more. If the cross-linking reaction is less than 120 ° C., the cross-linking reaction takes time and the productivity is poor.

  The amount of the crosslinking agent used in the present invention varies depending on the type of the crosslinking agent, but basically it is desired to be 0.1 to 2.0 parts by weight with respect to 100 parts by weight of the polyethylene resin. Since the content of the hot xylene-insoluble component in the range can be obtained, it is preferable.

(3) Production of styrene-modified polyethylene-based pre-expanded particles In the present invention, as a method of impregnating a styrene-modified polyethylene-based resin particle with a foaming agent and pre-expanding, a styrene-modified polyethylene-based resin particle is used in a pressure-resistant container. Is dispersed in an aqueous dispersion medium, a foaming agent is placed in a pressure-resistant container, heated to a temperature equal to or higher than the softening point of the styrene-modified polyethylene resin particles, and the resin particles are subjected to a pressure higher than the vapor pressure of the foaming agent. After impregnating the foaming agent, the mixture of styrene-modified polyethylene resin particles and the aqueous dispersion medium is discharged to a lower pressure region than the pressure vessel while keeping the temperature and pressure in the pressure vessel constant. A method called “foaming” is preferred.

  Specifically, for example, styrene-modified polyethylene resin particles are charged into a pressure-resistant container for decompression foaming, and after adding a foaming agent, overheating is performed, and the temperature and pressure in the pressure-resistant container are kept constant. One end of the container is opened, and the contents are discharged into a low-pressure atmosphere, such as the atmosphere, for example, through an orifice having an opening diameter of 1 to 10 mm. Pre-expanded particles having a cellular structure can be produced.

  In the present invention, the styrene-modified polyethylene resin particles are impregnated with a plasticizer at the time of decompression foaming to plasticize the styrene-modified polyethylene resin particles, and can be doubled at the time of decompression foaming. The surface expansion of the inner foamed molded article is excellent, and the appearance can be improved.

In order to obtain good in-mold foam moldability, it has a boiling point equal to or higher than the heat treatment temperature during decompression foaming, remains in the pre-foamed particles even after elapse of time, and is styrene-modified polyethylene during decompression foaming. It is preferable to use a plasticizer that hardly generates agglomerates of the resin particles.
Examples of such plasticizers include phthalates such as diisodecyl phthalate (DIDP), bis (2-ethylhexyl) phthalate (DOP), and dibutyl phthalate (DBP); dioctyl adipate (DOA), adipine Aliphatic dibasic acid esters such as dibutyl acid (DBA) and dibutyl sebacate (DBS); acetylated products such as ricinoleic acid and glycerin; glycerin fatty acid esters such as epoxidized soybean oil and coconut oil. These plasticizers may be used alone or in combination of two or more.

  Among these plasticizers, sebacic acid ester is preferable because agglomeration of styrene-modified polyethylene resin particles is less likely to occur during decompression foaming. Examples of sebacic acid esters include dimethyl sebacate, diethyl sebacate, dibutyl sebacate, dioctyl sebacate, etc., but particularly dibutyl sebacate has good stability during decompression foaming, and in-mold foam molding It is preferable because the surface elongation of the body is excellent.

In the present invention, the sebacic acid ester is preferably added in an amount of 0.1 part by weight or more and less than 2 parts by weight to the aqueous dispersion medium with respect to 100 parts by weight of the styrene-modified polyethylene resin particles, and 0.5 parts by weight or more. It is more preferable to add less than 1 part by weight.
When the addition amount of sebacic acid ester is less than 0.1 parts by weight, the foamability of the pre-expanded particles tends to be deteriorated and the surface elongation of the molded product tends to be inferior. There is a tendency for agglomeration between polyethylene resins to occur.

The styrene-modified polyethylene pre-expanded particles of the present invention preferably contain 0.1 to 2% by weight of sebacic acid ester with respect to 100% by weight of the styrene-modified polyethylene pre-expanded particles. It is more preferable to contain 5% by weight or more and 1% by weight or less.
If the content of sebacic acid ester is less than 0.1% by weight, the foamability of the pre-expanded particles tends to deteriorate and the surface elongation of the molded product tends to be inferior. Tend to occur.

  The aqueous dispersion medium in “depressurization foaming” indicates a solution in which a dispersant is dissolved or dispersed in water. As the dispersant, the same type of dispersant as in the polymerization can be used.

As the foaming agent used in the present invention, known ones can be used, and from the viewpoint of safety and environmental load, inorganic gases such as air, nitrogen and carbon dioxide, water, and the like can be mentioned. These foaming agents may be used alone or in combination of two or more.
Among these foaming agents, carbon dioxide gas is particularly preferred because of its good foamability and cell stability.

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

  The amount of the foaming agent used in the present invention is 1 to 10 parts by weight, preferably 3 to 8 parts by weight, based on 100 parts by weight of the styrene-modified polyethylene resin particles. If the amount of the foaming agent used is less than 1 part by weight, it tends to be difficult to obtain a sufficient expansion ratio. If the amount of the foaming agent used exceeds 10 parts by weight, the dispersion state of the resin when impregnated with the foaming agent becomes unstable, and the resins tend to aggregate.

  The styrene-modified polyethylene resin pre-expanded particles in the present invention have a weight average molecular weight of 150,000 or more and 350,000 or less of a tetrahydrofuran-soluble component, and a content of insoluble matter of hot xylene of 5 to 20% by weight. It is necessary to be. As a more preferable range, the weight average molecular weight of the tetrahydrofuran-soluble part is 180,000 to 250,000, and the content of the heat xylene-insoluble content is 10% to 13% by weight.

  In the present invention, when the weight average molecular weight of the tetrahydrofuran-soluble component is less than 150,000, pre-foamed particles are broken, and the strength of the foam is decreased. When the weight average molecular weight exceeds 350,000, the foaming property is deteriorated. It becomes difficult to obtain a desired expansion ratio. Also, if the content of insoluble matter in the heat xylene is less than 5% by weight, the pre-foamed particles will be broken and the strength of the foam will be reduced. If it exceeds 20% by weight, the foamability will deteriorate and the desired expansion ratio will be obtained. It becomes difficult.

Here, the tetrahydrofuran-soluble component is a filtrate obtained by immersing 0.02 g of styrene-modified polyethylene resin pre-expanded particles in 20 ml of tetrahydrofuran at room temperature for 24 hours, and then filtering with a filter having a pore size of 0.2 μm. .
The weight average molecular weight of the tetrahydrofuran-soluble component is a value obtained by measuring the filtrate by a gel permeation chromatograph (GPC) method and using a standard polystyrene sample as a reference.
The weight average molecular weight of the tetrahydrofuran-soluble part can be controlled by adjusting the addition rate of the styrene monomer added during polymerization and the amount of the polymerization initiator.

Here, the hot xylene insoluble matter means that 1.0 g of styrene-modified polyethylene resin pre-foamed particles are added to 50 ml of xylene, boiled for 30 minutes, and then recovered using a decantation method and a 200-mesh wire mesh. It is an insoluble residue obtained.
The content of the hot xylene insoluble matter can be controlled by adjusting the amount of the crosslinking agent and the crosslinking time.

  Since the styrene-modified polyethylene-based pre-expanded particles of the present invention do not use a hydrocarbon-based foaming agent, the volatile component is 1% by weight or less. If the volatile component is 1% by weight or less, even if the content of the styrene component is large, the burning rate of the obtained molded product can be kept low.

(4) Production of styrene-modified polyethylene-based foam molded article The styrene-modified polyethylene resin pre-expanded particles of the present invention are molded by a general in-mold foam molding method. Specifically, styrene-modified polyethylene resin pre-expanded particles are filled in a mold that can be closed but cannot be sealed, and a heating water vapor pressure of a molding pressure of 0.08 to 0.12 MPa (G) is applied. Thereby, a suitable foaming molding can be obtained.

  In the case of in-mold foam molding of polyolefin, particularly polypropylene-based pre-expanded particles, a step of increasing the internal pressure of the pre-expanded particles with air or the like and previously imparting foaming force to the pre-expanded particles is necessary. The pre-foamed polyethylene resin particles do not require a step of imparting foaming force, and can be molded even if the internal pressure in the foamed particles remains at atmospheric pressure.

  The styrene-modified polyethylene resin pre-expanded particles of the present invention have good foamability even in carbon dioxide foaming and are highly safe in the production process. Since the styrene-modified polyethylene pre-expanded particles are excellent in moldability and have sufficient strength, they can be suitably used for, for example, automobile members.

(Example)
Examples and Comparative Examples will be given below, but the present invention is not limited thereto.

  In addition, about measurement evaluation, it implemented as follows.

<Amount of hot xylene insoluble matter>
To 1.0 g of the styrene-modified polyethylene resin pre-expanded particles obtained, 50 ml of xylene is added and heated. After boiling for 30 minutes, the soluble component is fractionated into a beaker by decantation. At this time, in order to prevent the insoluble matter from being mixed, a 200-mesh wire mesh is placed on the beaker of the soluble content.
The xylene addition, boiling, and decantation operations were performed twice on the obtained insoluble matter to recover the hot xylene insoluble matter. The collected material was vacuum-dried at 70 ° C. for 8 hours, and then the weight was measured.

<Measurement of dibutyl sebacate content>
The soluble matter fractionated with hot xylene was evaporated by boiling, and the dried product was vacuum dried at 70 ° C. for 8 hours, and then the weight of the dried product was measured.
Ortho-dichlorobenzene-d ₄ is added to the dried product obtained from the soluble matter, heated and dissolved at 130 ° C., and ¹ H-NMR measurement at a measurement temperature of 98 ° C. [Device used: INOVA AS600, manufactured by VARIAN, Inc.] Carried out.
From the ratio of the detected peak area derived from styrene and the peak area derived from dibutyl sebacate, the content of dibutyl sebacate in the dried product obtained from the soluble matter was calculated. Since dibutyl sebacate did not exist in the insoluble content of hot xylene, the content of dibutyl sebacate in the pre-expanded particles was obtained in terms of the content relative to the total amount of the hot xylene soluble content and insoluble content.

<Measurement of weight average molecular weight of tetrahydrofuran-soluble matter>
The obtained styrene-modified polyethylene resin pre-expanded particles (0.02 g) were immersed in 20 ml of tetrahydrofuran at room temperature for 24 hours, and then filtered through a filter having a pore size of 0.2 μm to obtain a filtrate (tetrahydrofuran soluble component). Obtained.
The obtained filtrate was calculated | required by the weight average molecular weight on the basis of the standard polystyrene sample by the gel permeation chromatography (GPC) method.
The measurement conditions of the GPC method are as follows.
Measuring device: manufactured by Tosoh Corporation, high-speed GPC device, HLC-8220
Column used: Tosoh Co., Ltd., SuperHZM-H x 2, SuperH-RC x 2
Column temperature: 40 ° C
Mobile phase: THF (tetrahydrofuran)
Flow rate: 0.35 ml / min, injection volume: 10 μl
Detector: RI.

<Molded body magnification>
The molded body weight W (g) after drying, length L ₁ (cm), width L ₂ (cm), and thickness t (cm) were measured and calculated by the following formula.
Molded article magnification = [W / (L ₁ × L ₂ × t)] / Density of styrene-modified polyethylene resin particles The density of the styrene-modified polyethylene resin particles is 1.0 g / cm ³ .

<Fusion rate of molded body>
After cutting about 3 mm with a cutter knife into the obtained foamed molded product, the foamed molded product was broken from the cut portion, and the fracture surface was observed.
The ratio of the number of styrene-modified polyethylene resin foam particles destroyed (breaking inside the particle, not the particle surface) to the number of styrene-modified polyethylene resin foam particles constituting the fracture surface is the fusion rate (%) As sought.

<Surface elongation of foam molded article>
The surface of the obtained foamed molded product was visually evaluated according to the following criteria and given a score.
Score 5: There is no intergranularity between the expanded particles. Point 4: There is a part where the intergranular spaces between the expanded particles are separated, but they are not noticeable.
Score 3: Although there are places where the particles of the expanded particles are separated, they are conspicuous.
Score 2: The foam particles are separated from each other on the entire surface of the molded body.
Score 1; The foam particles are greatly separated on the entire surface of the molded body.

<Wrinkles of foam molding>
The surface of the obtained foamed molded product was visually evaluated according to the following criteria.
○: Wrinkles are not present on the surface of the molded body, and it is beautiful.
Δ: Wrinkles on the surface of the molded body, but not noticeable.
X: There are wrinkles on the surface of the molded body.

<Compressive strength of molded body>
Five test pieces each having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm were cut out from the obtained foamed molded article, and the density of the test pieces was measured for each. About the test piece, in accordance with NDZ-Z0504, the compression stress of 25% compression when compressed at a speed of 10 mm / min is measured, and the relationship between the test piece density and 25% compression strength is graphed, and from the inclination, The 25% compressive strength at a density of 160 g / L (equivalent to a foam magnification of 6 times) was calculated.

<Measurement of volatile matter>
The weight W ₁ (g) of 100 ml of the pre-expanded particles is measured, left in a dryer at 150 ° C. for 30 minutes, and the weight W ₂ (g) is measured again. The difference in weight before and after drying (W ₁ −W ₂ ) is the amount of volatile matter in the pre-expanded particles.
The volatile content is calculated by the following formula.
Volatile content (wt%) = (W ₁ −W ₂ ) / W ₁

Example 1
[Production of polyethylene resin particles]
Using a branched low density polyethylene (LDPE) [NUC polyethylene DFDJ-6775, manufactured by Nippon Dow Chemical Co., Ltd.] as a polyethylene resin, 0.2 parts by weight of talc is mixed with 100 parts by weight of the polyethylene resin, and then 50 mm. In a single screw extruder, melt-mixed at a discharge rate of 25 kg / hour and a resin temperature of 240 ° C., extruded through a die installed at the tip of the extruder, and then cut to obtain a polyethylene resin having a grain weight of about 1 mg / grain. Particles were made.
[Production of styrene-modified polyethylene resin particles]
In a 6 L autoclave, 150 parts by weight of water, 2.0 parts by weight of tricalcium phosphate, 0.048 parts by weight of sodium α-olefin sulfonate, 0.009 parts by weight of sodium nitrite, and 25 parts by weight of the obtained polyethylene resin particles were added. Suspended.
18 parts by weight of styrene, 2 parts by weight of 2-ethylhexyl acrylate, 0.40 part by weight of t-butylperoxy-2-ethylhexanoate (10-hour half-life temperature: 72 ° C.) as a polymerization initiator, benzoyl peroxide ( 10 hours half-life temperature: 74 ° C.) 0.30 parts by weight and a solution in which 0.40 parts by weight of t-butyl peroxybenzoate (10 hours half-life temperature: 104 ° C.) as a crosslinking agent was dissolved in the above aqueous suspension Added to the liquid.
Thereafter, the temperature of the aqueous suspension was raised to 92 ° C., and 55 parts by weight of styrene was dropped into the reaction system over 3 hours and 10 minutes. After completion of the dropwise addition of the styrene monomer, the polymerization reaction was advanced by maintaining at 92 ° C. for 1 hour.
Thereafter, the temperature of the aqueous suspension was raised to 120 ° C. and held for 3 hours to carry out a crosslinking reaction, and after cooling, washing, dehydration and drying were performed to obtain styrene-modified polyethylene resin particles.

[Preparation of styrene-modified polyethylene resin pre-expanded particles]
In a 10 L pressure vessel, 300 parts by weight of water, 0.5 parts by weight of tricalcium phosphate, 0.028 parts by weight of sodium n-paraffin sulfonate, 100 parts by weight of the resulting styrene-modified polyethylene resin particles, 0 dibutyl sebacate .75 parts by weight and 5 parts by weight of carbon dioxide gas were charged.
After the aqueous dispersion was heated to 155 ° C., carbon dioxide gas was introduced, and the internal pressure of the container was increased to 2.0 MPa and held for 30 minutes. While maintaining the temperature and pressure in the pressure vessel, the valve at the bottom of the pressure vessel is opened and the aqueous dispersion is discharged through an orifice plate having a hole diameter of 3.6 mmφ into a cylinder filled with 94 ° C. saturated steam, Styrene-modified polyethylene resin pre-expanded particles were obtained. Then, the obtained styrene-modified polyethylene resin pre-expanded particles were left to dry for 12 hours with a 50 ° C. dryer.
The obtained pre-expanded styrene-modified polyethylene resin particles were measured for the amount of hot xylene insolubles, the content of dibutyl sebacate, the weight average molecular weight of the tetrahydrofuran soluble part, and the volatile content. The results are shown in Table 1.

[Production of styrene-modified polyethylene resin-in-mold foam]
The styrene-modified polyethylene resin pre-expanded particles are filled into a mold (length 400 mm × width 300 mm × thickness 50 mm) using an in-mold foam molding machine [manufactured by DAISEN, KR57], and molding heating pressure A foamed molded product was obtained at 0.11 MPa. Thereafter, the obtained foamed product was dried for 12 hours in a 35 ° C. drying room for 12 hours.
For the obtained in-mold foamed molded product, the molded product magnification, molded product surface elongation, surface wrinkle, fusion rate, and compressive strength were measured, and the results are shown in Table 1.

(Example 2)
In [Production of styrene-modified polyethylene resin particles], the same operation as in Example 1 except that the amount of styrene in the initially charged monomer was changed to 15 parts by weight and the amount of 2-ethylhexyl acrylate was changed to 5 parts by weight. Thus, resin particles, pre-foamed particles, and in-mold foam-molded bodies were prepared and evaluated in the same manner. The results are shown in Table 1.

(Example 3)
In [Production of styrene-modified polyethylene resin particles], resin particles, pre-foamed particles, and in-mold foam-molded bodies were produced in the same manner as in Example 1 except that the acrylic ester type was changed to butyl methacrylate. The same evaluation was performed. The results are shown in Table 1.

Example 4
In [Production of styrene-modified polyethylene resin particles], resin particles, pre-foamed particles, and in-mold foam-molded bodies were produced in the same manner as in Example 2 except that the acrylate ester type was changed to butyl methacrylate. The same evaluation was performed. The results are shown in Table 1.

(Example 5)
Resin particles, pre-expanded particles, in-mold foam molding were performed in the same manner as in Example 1 except that the amount of dibutyl sebacate was changed to 0.3 parts by weight in [Production of styrene-modified polyethylene-based pre-expanded particles]. A body was prepared and evaluated in the same manner. The results are shown in Table 1.

(Example 6)
Resin particles, pre-expanded particles, in-mold foam molding were performed in the same manner as in Example 1 except that the amount of dibutyl sebacate was changed to 1.5 parts by weight in [Production of styrene-modified polyethylene-based pre-expanded particles]. A body was prepared and evaluated in the same manner. The results are shown in Table 1.

(Example 7)
In [Production of styrene-modified polyethylene-based pre-expanded particles], resin particles, pre-expanded particles, and the like, except that the foaming pressure was changed to 3.0 MPa and the initial carbon dioxide gas was changed to 7 parts by weight. An in-mold foam molded product was produced and evaluated in the same manner. The results are shown in Table 1.

(Example 8)
In [Production of styrene-modified polyethylene resin particles], resin particles, pre-expanded particles, and the like, by the same operation as in Example 1, except that the polymerization initiator was changed to 0.35 parts by weight of t-butyl peroxybenzoate. An in-mold foam molded product was produced and evaluated in the same manner. The results are shown in Table 1.

Example 9
In [Production of styrene-modified polyethylene resin particles], resin particles, pre-expanded particles, and the like, by the same operation as in Example 1, except that the polymerization initiator was changed to 0.45 parts by weight of t-butyl peroxybenzoate. An in-mold foam molded product was produced and evaluated in the same manner. The results are shown in Table 1.

（比較例１）
［スチレン改質ポリエチレン系樹脂粒子の作製］において、初期仕込みスチレン量を２０重量部に、２−エチルヘキシルアクリレート量を０重量部に変更した以外は、実施例１と同様の操作により、樹脂粒子、予備発泡粒子、型内発泡成形体を作製し、同様の評価を行った。結果は、表２に示した。

(Comparative Example 1)
In [Production of styrene-modified polyethylene-based resin particles], resin particles, by the same operation as in Example 1, except that the initial charge amount of styrene was changed to 20 parts by weight and the amount of 2-ethylhexyl acrylate was changed to 0 parts by weight. Pre-expanded particles and in-mold foam molded bodies were prepared and evaluated in the same manner. The results are shown in Table 2.

(Comparative Example 2)
In [Production of Styrene-modified Polyethylene Resin Particles], resin particles and spares were prepared in the same manner as in Example 1 except that the initial charge amount of styrene was changed to 12 parts by weight and the amount of 2-ethylhexyl acrylate was changed to 8 parts by weight. Foamed particles and in-mold foam-molded bodies were produced and evaluated in the same manner. The results are shown in Table 2.

(Comparative Example 3)
In [Production of styrene-modified polyethylene-based resin particles], resin particles, pre-expanded particles, and in-mold foam-molded articles were obtained in the same manner as in Example 1 except for 12 parts by weight of initially charged styrene and 8 parts by weight of butyl methacrylate. The same evaluation was performed. The results are shown in Table 2.

(Comparative Example 4)
In [Production of styrene-modified polyethylene resin particles], resin particles, pre-foamed particles, and in-mold foam-molded bodies were produced in the same manner as in Example 1 except that the acrylic ester type was changed to butyl acrylate. The same evaluation was performed. The results are shown in Table 2.

(Comparative Example 5)
In [Production of styrene-modified polyethylene resin particles], resin particles, pre-foamed particles, and in-mold foam-molded bodies were produced in the same manner as in Example 2 except that the acrylic ester type was changed to butyl acrylate. The same evaluation was performed. The results are shown in Table 2.

(Comparative Example 6)
In [Production of styrene-modified polyethylene-based pre-expanded particles], resin particles, pre-expanded particles, and in-mold foam-molded articles were prepared in the same manner as in Example 1 except that butyl was not used during sebacic acid. The same evaluation was performed. The results are shown in Table 2.

(Comparative Example 7)
Resin particles, pre-expanded particles, and in-mold foam molding were performed in the same manner as in Example 1 except that the amount of dibutyl sebacate was changed to 2.2 parts by weight in [Preparation of styrene-modified polyethylene-based pre-expanded particles]. A body was prepared and evaluated in the same manner. The results are shown in Table 2.

(Comparative Example 8)
In [Production of Styrene-modified Polyethylene Resin Particles], the polymerization initiator species and amount were 0.2 parts by weight of t-butylperoxy 2-ethylhexanoate, 0.4 parts by weight of benzoyl peroxide, t-butylperoxy. Resin particles, pre-expanded particles, and in-mold foam molded articles were prepared in the same manner as in Example 1 except that the amount was changed to 0.5 parts by weight of benzoate, and the same evaluation was performed. The results are shown in Table 2.

Claims (5)

Styrenic modified polyethylene resin pre-expanded particles obtained by foaming styrene modified polyethylene resin particles using an inorganic gas,
The styrenic modified polyethylene resin particles are selected from 120 parts by weight to 500 parts by weight of a styrene monomer, 2-ethylhexyl acrylate, and butyl methacrylate with respect to 100 parts by weight of the branched low density polyethylene resin. At least one (meth) acrylic acid ester monomer is impregnated with 3 to 22 parts by weight and polymerized,
The styrene-modified polyethylene resin pre-expanded particles contain 0.1% by weight or more and less than 2% by weight of sebacic acid ester with respect to 100% by weight of the styrene-modified polyethylene resin pre-expanded particles, and are insoluble in hot xylene 5 to 20% by weight of styrene-modified polyethylene resin pre- expanded particles, characterized in that The styrene-modified polyethylene resin pre-expanded particles according to claim 1, wherein the styrene-modified polyethylene resin pre-expanded particles have a weight average molecular weight of 150,000 to 350,000 in the tetrahydrofuran-soluble part. The styrene-modified polyethylene resin pre-expanded particles according to claim 1 or 2, wherein the styrene-modified polyethylene resin pre- expanded particles contain 1% or less of a volatile component.   Polymerization is carried out by impregnating polyethylene resin particles with a styrene monomer and at least one (meth) acrylic acid ester monomer selected from 2-ethylhexyl acrylate and butyl methacrylate in a pressure vessel. 100 parts by weight of the resulting styrene-modified polyethylene resin particles are dispersed in an aqueous dispersion medium together with 0.1 to 2 parts by weight of sebacic acid ester, heated, and carbon dioxide gas is introduced as a blowing agent to withstand pressure. After pressurizing the inside of the container, one end of the pressure container 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 the pressure container. The manufacturing method of the styrene modification polyethylene-type resin pre-expanded particle in any one of Claims 1-3. Styrene-modified poly ethylene resin pre-expanded particles of any one of claims 1 to 3, but may be closed consists of two mold was filled into the molding space which can not be sealed, and heated by a heating medium A method for producing a styrene-modified polyethylene resin foam molded article, which is obtained by: