JP2012026551A - Shock absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shock absorber having substantially constant impact energy absorbing capacity regardless of the temperature.SOLUTION: The problem is solved by this shock absorber being a foaming body of a composite resin including 100 pts.wt. of a high density polyethylene-based resin having density of 931-950 kg/mand 100-500 pts.wt. of a polystyrene-based resin and characterized in that the ratio Q1/Q2 of a breaking point displacement quantity Q1 at +23°C to a breaking point displacement quantity Q2 at -50°C is 1.5 or less.

Description

  The present invention relates to a shock absorber used as a median strip block of a motorway, a fender for ships, and the like. More particularly, the present invention relates to a shock absorber whose ability to absorb impact energy does not change greatly even when the environmental temperature changes.

The shock absorber is used as a flanking material provided in ships and harbor facilities as a median strip block of an automobile road. Such a shock absorber is generally formed of a single rubber or a single foam rubber because it is excellent in strength and durability. However, in the shock absorber made of rubber or foam rubber,
(1) Because of the large repulsive force when a car or ship collides, there is a risk of applying a large impact or vibration to the car or ship.
(2) Because it is heavy, handling such as installation is not easy.
(3) normal rubber is black and difficult to color;
There was a problem.

  As a buffer that can solve these problems, a buffer that includes a core made of a polyolefin resin foam and a synthetic resin skin that encapsulates the core is known (patents). Reference 1).

JP-A-7-172387

  However, the core material of the shock absorber described in Patent Document 1 has a high temperature dependency of the ability to absorb impact energy, and a shock absorber such as a median strip block or a fender that is installed outdoors is placed. It was found that the numerical value of the bending break point displacement indicating the impact energy absorption capability greatly fluctuates within a temperature range of about 50 to + 23 ° C. An object of the present invention is to provide a shock absorber having a substantially constant impact energy absorbing ability regardless of temperature.

Thus, according to the present invention, a foam of a composite resin containing 100 parts by weight of a high-density polyethylene resin having a density of 931 to 950 kg / m ³ and 100 to 500 parts by weight of a polystyrene resin, and the displacement at break at + 23 ° C. A buffer body is provided in which the ratio Q1 / Q2 between the amount Q1 and the breaking point displacement amount Q2 at −50 ° C. is 1.5 or less.

  In the buffer according to the present invention, since the numerical value of the bending break point displacement indicating the impact energy absorption capacity does not vary greatly within the temperature range of about −50 to + 23 ° C., the shock energy absorption capacity is almost constant regardless of the temperature. Have.

Moreover, when the surface layer of a foam shows the amount of polystyrene-type resin of 50 weight% or less, the buffer body which has the impact energy absorption ability stabilized irrespective of temperature can be provided.
Moreover, when a foam shows the fusion rate of 50% or more, the buffer which has the impact energy absorption ability stabilized irrespective of temperature can be provided.

  Moreover, when a foam has a foaming ratio of 5 to 40 times, the buffer body which has the further outstanding impact energy absorption capability can be provided.

  Moreover, when a foam contains 20-100 weight part of high density polyethylene-type resin, the buffer which has the further outstanding impact energy absorption capability can be provided.

  Since the shock absorber according to the present invention has a stable impact energy absorption capability regardless of changes in temperature and temperature depending on the season and time zone, when used as a median strip block of an automobile road, the vehicle or facility in the event of a collision accident. Expected to help reduce damage to In addition, when the shock absorber according to the present invention is used as a fender for ships and harbor facilities, the ship is in contact with the quay when the ship leaves or shores, regardless of the change in temperature or temperature depending on the season or time zone. Can be prevented from being damaged.

It is a graph of a calibration curve showing the relationship between the polystyrene resin ratio (% by weight) and the absorbance ratio (A698 / A2850) used in Examples and Comparative Examples of the present invention.

The buffer according to the present invention is a foam of a composite resin containing 100 parts by weight of a high-density polyethylene resin having a density of 931 to 950 kg / m ³ and 100 to 500 parts by weight of a polystyrene resin. In addition, the buffer of the present invention has a property that the ratio Q1 / Q2 between the breaking point displacement amount Q1 at + 23 ° C. and the breaking point displacement amount Q2 at −50 ° C. is 1.5 or less. A more preferable ratio Q1 / Q2 is in the range of 1 to 1.3.
The amount of displacement at break showing the impact energy absorption capacity is measured by a bending test in accordance with JIS K7221-2: 2006 “Rigid foamed plastic—Bending test—Part 2: Determination of bending characteristics”. This measurement method will be described in Examples.

(Foam)
The foam was obtained by impregnating composite resin particles (hereinafter also referred to as resin particles) with a foaming agent to obtain expandable resin particles, and pre-expanding the obtained expandable resin particles to obtain pre-expanded particles. It is obtained by in-mold foam molding of pre-expanded particles.
The composite resin particles are obtained, for example, by a method of mixing a high density polyethylene resin and a polystyrene resin and then granulating, a method of impregnating and polymerizing a high density polyethylene resin particle with a styrene monomer. Of these, the latter method is preferable, and the method will be described in detail.

(A) High-density polyethylene resin The resin particles having the following properties (1) to (4) are used as the high-density polyethylene resin in the composite resin particles. It is preferable from the viewpoint of suppressing.
(1) An ethylene homopolymer or a copolymer of ethylene and an olefin having 3 or more carbon atoms.
(2) The density [d (kg / m ³ )] is 931 or more and 950 or less.
(3) The melt flow rate [MFR (g / 10 minutes)] measured at 190 ° C. and a load of 2.16 kg is 0.1 or more and 20 or less.
(4) The relationship between the melt tension [MS160 (mN)] measured at 160 ° C. and MFR satisfies the following formula (1).
MS160> 90-130 × log (MFR) (1)

(1) The high-density polyethylene resin is composed of an ethylene homopolymer or a copolymer of ethylene and an olefin having 3 or more carbon atoms.
Examples of the olefin having 3 or more carbon atoms include propylene, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-butene, vinylcycloalkane (for example, vinylcyclopentane, Vinylcyclohexane), cyclic olefins (eg, norbornene, norbornadiene), dienes (eg, butadiene, 1,4-hexadiene) and the like. The proportion of the olefin-derived component having 3 or more carbon atoms in the high-density polyethylene resin is not particularly limited, but is preferably 50% by weight or less, and more preferably 20% by weight or less.
Styrene may be copolymerized with ethylene as long as the invention is not impaired.

(2) Density ^{[d (kg / m 3)} ] for not more than 931kg / m ³ or more 950 kg / m ^3, more preferably from 931~945kg / m ^3, a 935~940kg / m ³ Is more preferable. When the density is less than 931 kg / m ³ , since the melting temperature is low, the heat resistance of the obtained foam may be insufficient. On the other hand, if it exceeds 950 kg / m ³ , the foamed product is inferior in impact resistance in addition to the high foaming temperature due to the high melting temperature and a decrease in productivity. In addition, the density of ethylene-type resin means what was measured using A method (underwater substitution method) prescribed | regulated by JIS K7112: 1999 "The measuring method of the density of plastic-non-foamed plastic and specific gravity".

Regarding (3) The melt flow rate [MFR (g / 10 min)] (hereinafter referred to as MFR) measured at 190 ° C. and a load of 2.16 kg is 0.1 g / 10 min or more and 20 g / 10 min or less. When the MFR is less than 0.1 g / 10 minutes, the expansion ratio may decrease. On the other hand, if it exceeds 20 g / 10 minutes, the melt tension becomes small and the foaming ratio decreases, and the strength of the foam may also decrease. More preferable MFR is 2 to 10 g / 10 min. The measuring method of MFR is described in the column of an Example.

Regarding (4) The relationship between the melt tension [MS ₁₆₀ (mN)] (hereinafter referred to as MS ₁₆₀ ) measured at 160 ° C. and the MFR measured at 190 ° C. with a 2.16 kg load is represented by the following formula (1) ) Is satisfied.
MS ₁₆₀ > 90-130 × log (MFR) (1)
In particular, the MS ₁₆₀ preferably satisfies MS ₁₆₀ > 110-130 × log (MFR).
Here, an olefin resin having MS _{160 in} the range of [90-130 × log (MFR)] or less may have insufficient gas retention and poor foamability. As a result, the expansion ratio may not be sufficiently increased, and a foam having uniform bubbles may not be obtained.
The upper limit of MS is preferably 240, and more preferably 180. If it exceeds 240, the expansion ratio may decrease. The measurement method of MS is described in the column of Examples.

  Furthermore, the high density polyethylene resin used in the present invention preferably has a weight average molecular weight (Mw) of 40,000 to 120,000 in terms of linear polyethylene. When Mw is less than 40000, the strength of the foam may be low. On the other hand, when it is larger than 120,000, the viscosity of the high-density polyethylene resin becomes high, and foam molding may be difficult.

  The high density polyethylene resin preferably has a ratio (Mw / Mn) of Mw to the number average molecular weight (Mn) of 3.5 to 10. Within this range, the molecular weight distribution of the high-density polyethylene resin can be narrowed, so that a foam with little variation in properties can be obtained. In addition, Mn means the value of linear polyethylene conversion.

  The high density polyethylene resin may or may not be crosslinked. When not crosslinked, there is an advantage that recycling is easy. The presence or absence of crosslinking can be determined by measuring the gel fraction. When the value is large, the crosslinking is large, and when the value is small, the crosslinking is small.

  The high-density polyethylene resin is preferably a resin obtained by polymerizing an olefin in the presence of a macromonomer, for example, by the following method.

  Here, the macromonomer is a homopolymer of ethylene having a vinyl group at the terminal or a copolymer of ethylene having a vinyl group at the terminal and an olefin having 3 or more carbon atoms, Mn of 2000 or more, and 2 to 5 It is preferable to have Mw / Mn. Examples of the olefin having 3 or more carbon atoms include propylene, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-butene, vinylcycloalkane (for example, vinylcyclopentane, vinyl Cyclohexane) and the like. These olefins may be used alone or in combination of two or more.

The Mn of the macromonomer is more preferably 5000 or more, and further preferably 10,000 or more. The upper limit is preferably 100,000. Further, Mw / Mn is more preferably 2 to 4, and further preferably 2 to 3.5.
An example of a method for measuring Mn and Mw is given below.
The GPC apparatus used for the measurement is HLC-8121 GPC / HT manufactured by Tosoh Corporation, TSKgel GMHhr-H (20) HT manufactured by Tosoh Corporation is used as the column, the column temperature is set to 140 ° C., and 1,2 as the eluent. , 4-trichlorobenzene is used. The measurement sample is adjusted to a concentration of 1.0 mg / ml, and the amount injected into the GPC device is 0.3 ml. The calibration curve for each molecular weight is calibrated using a polyethylene sample with a known molecular weight. Mn and Mw are determined as linear polyethylene equivalent values.

Furthermore, when the number of vinyl ends per 1000 methylene carbons as the main chain of the macromonomer is X and the number of saturated ends per 1000 methylene carbons as the main chain of the macromonomer is Y, the formula Z = X / [(( X represented by (X + Y) × 2] is preferably 0.5 to 1. Z is more preferably 0.25 to 1. It is well known to those skilled in the art that the number of vinyl ends and saturated ends can be measured by ¹ H-NMR, ¹³ C-NMR or FT-IR. For example, in the case of ¹³ C-NMR, vinyl ends have peaks at 114 ppm and 139 ppm, and saturated ends have peaks at 32.3 ppm, 22.9 ppm, and 14.1 ppm, and the number can be measured from these peaks.
An example of a method for calculating the number of vinyl ends and the number of saturated ends of the macromonomer is given below.
The terminal structure of the macromonomer is confirmed by ¹³ C-NMR using a JNM-ECA400 nuclear magnetic resonance apparatus manufactured by JEOL. The solvent used tetrachloroethane -d _2. The number of vinyl ends (X) is determined from the average value of the peaks at 114 ppm and 139 ppm as the number per 1000 main chain methylene carbons (chemical shift: 30 ppm). On the other hand, the number of saturated terminals (Y) is determined from the average values of 32.3 ppm, 22.9 ppm, and 14.1 ppm peaks, similarly to the number of vinyl terminal groups. From the obtained vinyl terminal number X and saturated terminal number Y, Z is determined by the formula Z = X / [(X + Y) × 2].

  By copolymerizing the macromonomer and the olefin, a high-density polyethylene resin suitable for use in the present invention can be obtained. Here, the ratio of the new resin other than the macromonomer to the total resin is preferably 1 to 99% by weight, more preferably 5 to 90% by weight, and still more preferably 30 to 80% by weight. The ratio of the new resin can be measured by comparing the GPC chart of the resin with the GPC chart of the macromonomer. Specifically, a peak derived from a new resin is determined by comparing both charts, and the ratio of the area of the peak to the area of all peaks corresponds to the ratio of the new resin.

The outline of the method for producing a high-density polyethylene resin is described below.
First, ethylene is polymerized in the presence of a catalyst comprising a crosslinked biscyclopentadienyl zirconium complex in which two cyclopentadienyl groups are crosslinked by a crosslinking group and a clay mineral treated with an organic compound, or ethylene And a olefin having 3 or more carbon atoms are copolymerized to produce a macromonomer. Examples of the complex include dimethylsilanediylbis (cyclopentadienyl) zirconium dichloride, diethylsilanediylbis (cyclopentadienyl) zirconium dichloride, diphenylsilanediylbis (cyclopentadienyl) zirconium dichloride, and the like.

Moreover, hectorite can be normally used as a clay mineral. Furthermore, examples of the organic compound include amine compounds such as N, N-dimethyl-octadecylamine and N, N-dioleylmethylamine.
Next, a high-density polyethylene-based resin can be obtained by copolymerizing a macromonomer and an olefin in the presence of a crosslinked (cyclopentadienyl) (fluorenyl) zirconium complex. Examples of the complex include diphenylmethylene (1-cyclopentadienyl) (2,7-di-tert-butyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (1-cyclopentadienyl) (9-fluorenyl) zirconium dichloride. Etc.

  As the olefin copolymerized with the macromonomer, an olefin having 2 or more carbon atoms can be used. Specifically, ethylene, propylene, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-butene, vinylcycloalkane (for example, vinylcyclopentane, vinylcyclohexane) Etc. These olefins may be used alone or in combination of two or more.

The high-density polyethylene-based resin may contain other resins without departing from the object of the present invention. Examples of other resins include α-olefin homopolymers and copolymers having 2 to 20 carbon atoms. Specifically, low density polyethylene, linear low density polyethylene, polypropylene, poly 1-butene, poly (4-methyl-1-pentene), poly 1-pentene, ethylene / propylene copolymer, ethylene / 1- Butene copolymer, propylene / 1-butene copolymer, ethylene / propylene / 1-butene copolymer, 4-methyl-1-pentene / ethylene copolymer, ethylene / propylene / polyene copolymer, various propylene Examples thereof include a system block copolymer and a propylene random copolymer.
The blending ratio of these other resins is preferably 50% by weight or less, more preferably 5 to 30% by weight based on the total amount of the high density polyethylene resin.

  For high-density polyethylene resins, if necessary, colorants, stabilizers, fillers (reinforcing materials), higher fatty acid metal salts, flame retardants, antistatic agents, lubricants, natural or synthetic oils, waxes, UV absorbers In addition, additives such as a weathering stabilizer, an antifogging agent, an anti-blocking agent, a slip agent, a coating agent, and a neutron shielding agent may be contained. Among these, as the colorant, both inorganic and organic colorants (pigments or dyes) can be used. In particular, inorganic colorants such as iron oxide and carbon black are preferred.

Examples of the iron oxide include α-FeOOH (hydrous crystal) as a yellow type, α-Fe ₂ O ₃ as a red type, and (FeO) x (Fe ₂ O ₃ ) y as a black type. . In these iron oxides, part of Fe may be replaced with other metals such as Zn and Mg. Further, these iron oxides may be mixed and used in order to obtain a desired color. Among them, the black line _{(FeO) x (Fe 2 O} 3) is preferably Fe ₃ O ₄ contained to y.

  The iron oxide preferably has an average particle size of 0.1 to 1 μm, and more preferably 0.2 to 0.8 μm. The average particle size can be measured with a laser diffraction particle size distribution meter (manufactured by JEOL Ltd .: Rhodos).

  The iron oxide is preferably contained in the high-density polyethylene resin in the range of 1.5 to 70% by weight, more preferably in the range of 5 to 40% by weight, and still more preferably in the range of 10 to 30% by weight. . If it is less than 1.5% by weight, the high-density polyethylene resin may not be sufficiently colored. On the other hand, when it exceeds 70 weight%, it may become difficult to mix in a high density polyethylene-type resin. In addition, since the specific gravity of iron oxide is larger than that of the high-density polyethylene resin, the high-density polyethylene resin particles may be heavy and it may be difficult to uniformly impregnate the styrene monomer.

Examples of carbon include carbon black such as furnace black, channel black, thermal black, acetylene black, graphite, and carbon fiber.
Carbon is preferably contained in the range of 1 to 50% by weight in the high-density polyethylene resin, and more preferably in the range of 2 to 30% by weight. If it is less than 1% by weight, the high-density polyethylene resin may not be sufficiently colored. On the other hand, when it is more than 50% by weight, it may be difficult to mix in the high-density polyethylene resin.

A stabilizer plays the role which prevents oxidation deterioration, thermal deterioration, etc., and can use all well-known things. For example, a phenol type stabilizer, an organic phosphite type stabilizer, a thioether type stabilizer, a binderd amine type stabilizer, etc. are mentioned.
Examples of the filler include talc and glass, and the shape is not particularly limited, such as a spherical shape, a plate shape, or a fiber shape.

  Examples of higher aliphatic metal salts include salts of higher fatty acids such as stearic acid, oleic acid, and lauric acid with alkaline earth metals (magnesium, calcium, barium, etc.) and alkali metals (sodium, potassium, lithium, etc.). It is done.

(B) Composite resin particles The composite resin particles are preferably obtained by impregnating and polymerizing a high-density polyethylene resin particle with a styrene monomer. Specifically, as described below, high-density polyethylene resin particles are dispersed in an aqueous medium containing a dispersant, and then a styrene monomer and a polymerization initiator are added to form a dispersion. By producing and heating this dispersion, high-density polyethylene resin particles are impregnated with a styrene monomer and polymerized to obtain composite resin particles.

  The high density polyethylene resin particles are produced in a known manner. For example, the high-density polyethylene resin obtained by the above production method is melt-kneaded and extruded in an extruder together with an inorganic nucleating agent and additives as necessary, and a strand is obtained. The method of granulating by cutting in the air, cutting in water, and cutting while heating is mentioned.

  The high-density polyethylene-based resin particles are cylindrical, substantially spherical or spherical with L / D of 0.6 to 1.6 when the particle length is L and the average diameter is D, and the average particle diameter is It is preferable that it is 0.2-1.5 mm. When L / D is less than 0.6 and when the flatness is larger than 1.6, the foamed resin particles are pre-foamed and filled into a mold to obtain a foamed molded product. Fillability may deteriorate. In addition, the shape of the high density polyethylene resin particles is more preferably approximately spherical or spherical to improve the filling property. When the average particle diameter is less than 0.2 mm, the retention of the foaming agent is lowered, and it may be difficult to reduce the density. When it exceeds 1.5 mm, not only the filling property is deteriorated, but also it is difficult to reduce the thickness of the foamed molded product.

Examples of the inorganic nucleating agent include talc, silicon dioxide, mica, clay, zeolite, calcium carbonate and the like.
The amount of the inorganic nucleating agent used is preferably 2 parts by weight or less, more preferably 0.2 to 1.5 parts by weight with respect to 100 parts by weight of the high-density polyethylene resin.
Examples of the aqueous medium constituting the aqueous suspension include water and a mixed medium of water and a water-soluble solvent (for example, lower alcohol).

  As the polymerization initiator, those generally used as an initiator for suspension polymerization of a styrene monomer can be used. For example, benzoyl peroxide, di-t-butyl peroxide, t-butylperoxybenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, t-butylperoxy Organic peroxides such as −3,5,5-trimethylhexanoate and t-butyl-peroxy-2-ethylhexyl carbonate. These polymerization initiators may be used alone or in combination of two or more.

  0.1-0.9 weight part is preferable with respect to 100 weight part of styrene-type monomers, and, as for the usage-amount of a polymerization initiator, 0.2-0.5 weight part is more preferable. If it is less than 0.1 part by weight, polymerization of the styrene monomer may take too much time, which is not preferable. Use of a polymerization initiator exceeding 0.9 parts by weight is not preferable because the molecular weight of the styrene resin may be lowered.

  A dispersant may be added to the aqueous suspension as necessary. The dispersant is not particularly limited, and any known dispersant can be used. Specific examples include hardly soluble inorganic substances such as calcium phosphate, magnesium pyrophosphate, sodium pyrophosphate, magnesium oxide. Further, a surfactant such as sodium dodecylbenzenesulfonate may be used.

Next, the obtained dispersion is heated to a temperature at which the styrene monomer is not substantially polymerized to impregnate the styrene monomer with high density polyethylene resin particles.
The time for impregnating the styrene monomer inside the high density polyethylene resin particles is suitably from 30 minutes to 2 hours. This is because if the polymerization proceeds before sufficient impregnation, a polymer powder of styrene resin is produced. The higher the temperature at which the monomer is not substantially polymerized, the more advantageous is to increase the impregnation rate, but it is necessary to determine it in consideration of the decomposition temperature of the polymerization initiator.

  The styrene monomer impregnated in the high density polyethylene resin particles is not particularly limited. For example, styrene, α-methyl styrene, vinyl toluene, chlorostyrene, ethyl styrene, isopropyl styrene, t-butyl styrene, dimethyl styrene. Etc.

  The total amount of the styrenic monomer added to the dispersion is adjusted to be 100 to 500 parts by weight of the polystyrene resin component with respect to 100 parts by weight of the high density polyethylene resin component in the resulting composite resin. Is done. It is further preferable that the polystyrene resin component is adjusted to 150 to 400 parts by weight with respect to 100 parts by weight of the high density polyethylene resin component.

  As described above, the weight ratio of the polystyrene resin component and the high-density polyethylene resin component in the composite resin is limited to the above-mentioned ratio. When the content of the polystyrene resin component in the composite resin is small, the weight ratio is high. The amount of the polyethylene resin component is increased, the heat resistance is increased too much, and when the composite resin particles are pre-foamed, it cannot be foamed to a desired bulk density, and the lightness of the resulting foam is impaired while being large. This is because the mechanical strength and chemical resistance of the resulting foam are impaired. Moreover, the problem that the temperature dependency of the ability to absorb the impact energy of the obtained foam will increase also occurs.

Next, the styrene monomer is polymerized. Although superposition | polymerization is not specifically limited, It is preferable to carry out at 115-140 degreeC for 1.5 to 5 hours. The polymerization is usually carried out in an airtight container that can be pressurized.
The impregnation and polymerization of the styrene monomer may be performed in a plurality of times. By dividing into multiple times, the generation of polystyrene polymer powder can be minimized.
Composite resin particles can be obtained by the above process.

The composite resin particles are cylindrical, substantially spherical or spherical with L / D being 0.6 to 1.6 when the particle length is L and the average diameter is D, and the average particle diameter is 0.3. It is preferable that it is -3.0mm.
When L / D is smaller than 0.6 or larger than 1.6 and the flatness is large, pre-foamed particles obtained from the composite resin particles are filled into the mold to obtain the foam. In some cases, the filling property of the resin becomes worse.
The shape is more preferably approximately spherical or spherical in order to improve the filling property.
When the average particle diameter of the composite resin particles is less than 0.3 mm, when used as expandable resin particles, the retention of the foaming agent may be lowered, and it may be difficult to reduce the density. On the other hand, when it exceeds 3.0 mm, the filling property is likely to deteriorate, and it may be difficult to reduce the thickness of the foam.

  The composite resin particles obtained by the above method may be treated to reduce volatile organic compounds (VOC) and odors. An example of a method for reducing VOC and odor will be described below. Here, the VOC is derived from the raw material and production method of the composite resin particles, and examples thereof include unreacted monomers such as styrene, ethylbenzene, xylene, and reaction solvents. Odor is derived from the raw material and production method of composite resin particles, but is different from VOC, and currently derived from a polymerization initiator when producing a polystyrene resin constituting the composite resin. For example, its decomposition products.

The reduction method introduced here is that the composite resin particles are contained in a container, and the softening temperature of the composite resin particles is T ° C., a gas of (T-40) ° C. to (T-10) ° C. is converted into the composite resin particles. The VOC and odor contained in the entire composite resin particle are blown from the lower part of the container until the amount becomes a predetermined amount or less.
Here, the gas is air, an inert gas (for example, nitrogen) or the like, and usually air is used.
The predetermined amount refers to 50 ppm in VOC. The predetermined amount of odor indicates that the average value of the odor intensity is 3 or less in an odor test in which the odor of isovaleric acid diluted 100000 times is used as a standard odor of 3 in odor intensity 0 to 5.

In order to reduce VOC and odor, the container in which the composite resin particles are put is a container that can flow the particles in the container while blowing the gas from the lower part of the container. If there is a mouth, it will not be specifically limited. The container usually has a discharge port in the upper part for discharging the blown gas. It is preferable to provide a countersunk plate for preventing the composite resin particles from entering the blowing port at the lower part of the container. A number of holes through which gas can normally pass are provided in the eye plate. This hole may have a shape that blows gas vertically or may have a shape that blows obliquely.
From the viewpoint of increasing the VOC and odor reduction efficiency, it is preferable to use a countersink plate having holes of both shapes. Furthermore, in order to raise the effect of reducing VOC and odor, a stirring device may be provided in the container. As such a container, for example, a fluidized bed drying apparatus generally used for drying granular materials can be used. Specifically, a swirl type fluidized bed drying device with a built-in bug (for example, Slit Flow (registered trademark) (FBS type) manufactured by Okawara Seisakusho Co., Ltd.) may be used.

  The composite resin particles may be put into the container before the gas is blown from the lower part of the container, or may be put into the container with the gas blown from the lower part of the container. Among these, it is preferable from the viewpoint of improving the VOC and odor reduction efficiency that gas is blown into the container from the lower part of the container.

  The gas used has a temperature of (T-40) ° C. to (T-10) ° C. when the softening temperature of the composite resin particles is T ° C. When it is lower than (T-40) ° C., the reduction of VOC and odor may be insufficient. When the temperature is higher than (T-10) ° C., the composite resin particles may be bonded together. A more preferable gas temperature is (T-20) ° C to (T-10) ° C. In addition, the softening temperature here means the penetration temperature referred to in JIS K7196.

  The flow rate of the gas can be changed according to the air volume of the blown gas, and the fluidity can be adjusted by adjusting the air volume. When the air volume is small, the composite resin particles may not be able to flow sufficiently. Further, when the air volume is large, the composite resin particles may be scattered. There is an appropriate air flow range for efficiently flowing the composite resin particles. A preferred range is 0.5 to 2.0 m / sec, more preferably 0.7 to 1.6 m / sec. The appropriate air volume can be determined by the pressure loss experienced when the blown gas passes through the composite resin particles. The pressure loss is preferably in the range of 1 to 10 kPa, more preferably in the range of 2 to 6 kPa. If the pressure loss due to the gaseous resin is within this range, the composite resin particles can be reliably flowed.

  The gas blowing time varies depending on the gas temperature and the flow velocity. When the gas temperature is constant, the time decreases as the flow velocity increases, and conversely, the time increases as the flow velocity decreases. On the other hand, when the gas flow rate is constant, the time is shortened if the temperature is high, whereas the time is long if the temperature is low. In any case, the time for blowing the gas is until the amount of VOC contained in the entire composite resin particles is 50 ppm (= μg / g) or less, and the odor contained in the foamed molded product obtained from the composite resin particles is In an odor test in which the odor of isovaleric acid diluted 100000 times is used as a standard odor of 3 with an odor intensity of 0 to 5, the average value of the odor intensity is 3 or less.

(C) Expandable resin particles Expandable resin particles are obtained by impregnating the composite resin particles during or after polymerization with a foaming agent. Impregnation can be performed by a known method. For example, the impregnation during the polymerization can be performed by performing the polymerization reaction in a sealed container and press-fitting a foaming agent into the container. The impregnation after the completion of the polymerization is performed by press-fitting a foaming agent in a sealed container.
Examples of the foaming agent include volatile foaming agents such as propane, n-butane, isobutane, pentane, isopentane, cyclopentane, hexane, and dimethyl ether. These foaming agents can be used alone or in admixture of two or more.

  The content of the foaming agent is preferably 5 to 25 parts by weight with respect to 100 parts by weight of the composite resin particles. The L / D and average particle diameter of the expandable resin particles can be set to the same level as the composite resin particles. Further, the shape is more preferably approximately spherical or spherical to improve the filling property.

(D) Pre-expanded particles Pre-expanded particles are obtained by pre-expanding the expandable resin particles.
The pre-expanded particles preferably have a bulk expansion ratio of 5 to 40 times. More preferably, it is 20 to 40 times. If the bulk foaming ratio is less than 5 times, the weight of the resulting foam may increase. On the other hand, if it exceeds 40 times, the closed cell ratio may be lowered when foamed, and the strength of the foam obtained from the pre-foamed particles may be lowered. A method of calculating the bulk foaming ratio will be described in the column of the examples.

(E) Manufacturing method of foam A foam (foaming molding) is obtained by carrying out in-mold foam molding of the pre-expanded particles. Specifically, it can be obtained by filling pre-expanded particles in a mold of a foam molding machine and heat-sealing the expanded particles while heating again to expand the pre-expanded particles. Water vapor can be suitably used as the heating medium.
The foaming ratio of the foam is preferably 5 to 40 times. More preferably,
20 to 40 times. If the expansion ratio is less than 5 times, the weight of the resulting foam may increase. On the other hand, when it exceeds 40 times, the closed cell ratio may be lowered when foamed, and the strength of the obtained foam may be lowered.
The surface of the foam preferably exhibits a polystyrene resin amount of 50% by weight or less. Considering that the amount of polystyrene resin in the entire foam is in the range of 100 to 500 parts by weight with respect to 100 parts by weight of the high density polyethylene resin, the polystyrene resin is less on the surface of the foam, This means that there are many polyethylene resins on the surface. By having a large amount of polyethylene resin on the foam surface, it is possible to provide a component packaging material that can maintain sufficient strength and shock-absorbing properties even at low to normal temperatures. A more preferable upper limit of the amount of polystyrene resin is 35% by weight. The lower limit is 0% by weight.

  The fusion rate of the foam is preferably 50% or more in order to obtain the strength required as a buffer. Here, the fusion refers to a state in which the pre-foamed particles are heated and melted and welded during foam molding, and the fusion rate is the number of foam particles broken in the foam particles at the fracture surface of the foam. The ratio of visual inspection. The method for measuring the fusion rate will be described in the Examples section.

  The resulting foam cushion is excellent in chemical resistance, heat resistance, impact strength and rigidity, and has a bending break point displacement that exhibits absorption capability within a temperature range of about -50 to + 23 ° C. Since the numerical value of does not fluctuate greatly, it has a substantially constant impact energy absorption capability regardless of temperature. The shock absorber according to the present invention is expected to help reduce damage to an object in the event of a collision when used as a median strip block on an automobile road or a fender for a ship or port facility.

  Hereinafter, although an example is given and explained further, the present invention is not limited by these examples. Various measurement methods and production conditions described in the examples will be described below.

(Melting tension)
What added the heat-resistant stabilizer (The Ciba Specialty Chemicals company make, Irganox 1010TM; 1500 ppm, Irgaphos 168TM; 1500 ppm) to the polyolefin resin using an internal mixer (the Toyo Seiki Seisakusho make, brand name Labo Plast Mill) A sample for measurement was kneaded for 30 minutes at 190 ° C. and 30 rpm in a nitrogen stream.
For melt tension, a capillary viscometer (Toyo Seiki Seisakusho, trade name Capillograph) with a barrel diameter of 9.55 mm is mounted with a dice sample with a length of 8 mm and a diameter of 2.095 mm so that the inflow angle is 90 °. Then, the melt tension is measured.
MS160 is a load (mN) necessary for take-up by setting the temperature to 160 ° C., the piston lowering speed to 10 mm / min, and the stretch ratio to 47. When the maximum draw ratio is less than 47, the load (mN) required for taking-up at the highest draw ratio that does not break is MS160.
(Density of high-density polyethylene resin)
The density of the high density polyethylene resin is measured by a density gradient tube method in accordance with JIS K6922-1: 1998.

(MS)
MS is equipped with a capillary viscometer (capillograph manufactured by Toyo Seiki Seisakusho Co., Ltd.) with a barrel diameter of 9.55 mm and a die with a length (L) of 8 mm, a diameter (D) of 2.095 mm, and an inflow angle of 90 °. Measure with The sample temperature is set to 160 ° C., the piston lowering speed is set to 10 mm / min, the stretch ratio is set to 47, and the load (mN) required for taking-up under this setting is MS.

(MFR)
MFR is measured at 190 ° C. and a 2.16 kg load in accordance with JIS K6922-1: 1998.

(Bulk expansion ratio of pre-expanded particles)
The bulk expansion ratio of the pre-expanded particles has a reciprocal relationship with the bulk density of the pre-expanded particles.
The bulk density of the pre-expanded particles is measured as follows.
First, pre-expanded particles are filled in a measuring cylinder to a scale of 500 cm ³ . However, the graduated cylinder is visually observed from the horizontal direction, and if at least one pre-expanded particle reaches the scale of 500 cm ³ , the filling is finished. Next, the weight of the pre-expanded particles filled in the graduated cylinder is weighed with two significant figures after the decimal point, and the weight is defined as W (g). The bulk density of the pre-expanded particles is calculated by the following formula.
Bulk density (g / cm ³ ) = W / 500
Therefore, the bulk expansion ratio of the pre-expanded particles can be derived by calculating the reciprocal of the above bulk density.
Bulk foaming magnification (times) of pre-foamed particles = 500 / W

(Foaming ratio of foam)
The expansion ratio of the foam is inversely related to the density of the foam.
The density of the foam is measured as follows by the method described in JIS K7222: 2005 “Foamed plastics and rubber—Measurement of apparent density”.
A test piece of 50 cm ³ or more (100 cm ³ or more in the case of semi-hard and soft materials) is cut so as not to change the original cell structure of the material, its weight is measured, and it is calculated by the following formula.
Density (g / cm ³ ) = Test specimen weight (g) / Test specimen volume (cm ³ )
Test specimen condition adjustment and measurement specimens were cut out from samples that had passed 72 hours or more after molding, and were subjected to atmospheric conditions of 23 ° C ± 2 ° C x 50% ± 5% or 27 ° C ± 2 ° C x 65% ± 5%. It has been left for more than an hour.
Therefore, the expansion ratio of the foam is derived by calculating the reciprocal of the above density.
Foaming ratio (times) of the foam = test piece volume (cm ³ ) / test piece weight (g)

(Fusion rate)
On the surface of the foam having a rectangular parallelepiped shape of length 400 mm × width 300 mm × height 50 mm, a cutting line having a length of 300 mm and a depth of 5 mm is put in a horizontal direction with a cutter, and the foam is divided into two along the cutting line. . Then, on the divided surface of the foam, the number of foam particles broken in the foam particles (a) and the number of foam particles broken at the interface between the foam particles (b) are measured and based on the following formula: Calculate the fusion rate.
Fusing rate (%) = 100 × (a) / [(a) + (b)]

(Displacement of bending break point)
The bending strength is measured according to the method described in JIS K7221-2: 2006 “Hard foamed plastic—bending test—Part 2: Determination of bending characteristics”.
That is, using a Tensilon universal testing machine UCT-10T (manufactured by Orientec Co., Ltd.), for a test piece of size 75 mm × 300 mm × 25 mm, the compression speed is 10 mm / min, the tip jig is a pressure wedge 10R, and a support base 10R. The distance between fulcrums is measured as 200 mm.
The breaking point displacement amount of bending is defined as the breaking point displacement point where the following phenomenon occurs in the bending test.
The disconnection detection sensitivity is set to 0.5%, and when the decrease exceeds the set value of 0.5% compared with the immediately preceding load sampling point, the immediately preceding sampling point is measured.

(Measurement of compressive strength)
The compressive strength is measured by the method described in JIS K7220: 2006 “Rigid foamed plastic-Determination of compression characteristics”. That is, using a Tensilon universal testing machine UCT-10T (manufactured by Orientec Co., Ltd.), the compression strength at the time of 25% compression (at the time of 10 mm displacement) is set at a compression speed of 10 mm / min. taking measurement.

(Drilling impact energy (total absorbed energy))
The perforation impact energy is measured according to ASTM D-3763, which is a Dynatap impact test. As a test apparatus, a Dynatap impact test apparatus GRC 8250 manufactured by General Research was used, and the test piece was cut into five pieces of 100 mm in length, 100 mm in width, and 20 mm in height with the single-sided skin remaining. Measurement conditions are as follows: test temperature is −20 ° C., test speed is 1.55 m / sec, span is round hole inner diameter 76 mm, drop height 59 cm, test load 3.17 kg, drop weight distance 13 cm, n = 5, Let the average value be the value of perforation impact energy.

(Measurement method of total volatile content (VOC))
In a 20 mL vial, put 0.2 g of the foam or thermoplastic resin particles obtained in Examples or Comparative Examples, add 1 mL of diethylbenzene (DEB) -containing dimethylformamide (DMF) as a solvent, dissolve the sample in the solvent, and sample Adjust the solution.
Next, after the vial containing this sample solution was heated at 90 ° C. for 1 hour, the vapor of this sample solution was collected, and this vapor was converted into a gas chromatograph (trade name “GC-18A” manufactured by Shimadzu Corporation). And quantified by internal standard method.
The measurement conditions are as follows.
As the column, a column having a diameter of 0.25 mm × a length of 30 m and a film thickness of 0.25 μm (manufactured by J & W, trade name “DB-WAX”) is used. As a detector, a flame ionization detector (FID) is used.
Column temperature condition: held at 50 ° C. for 2 minutes, then raised to 100 ° C. at 10 ° C./min, held at 100 ° C. for 5 minutes, then raised to 220 ° C. at 40 ° C./min, and at 220 ° C. for 2 minutes Hold.
The column inlet temperature is 150 ° C. and the detector temperature is 250 ° C.
The measurement sample solution injection volume is 2 mL.
The split ratio is 70: 1, the column flow rate is 1.6 mL / min (He), and the gas pressure is 122 kPa.

(Thermal conductivity)
A test piece having a rectangular parallelepiped shape having a length of 200 mm, a width of 200 mm, and a height of 10 to 25 mm is cut out from the foamed molded body.
Using a measuring device commercially available from EKO SEIKI under the trade name “HC-074 / 200”, the low temperature plate of the measuring device is 15 ° C. lower than the average temperature of the test piece, and the high temperature plate is lower than the average temperature of the test piece. Is set 15 ° C. higher, and the thermal conductivity of the test piece is JIS A 1412-2: 1999 “Method of measuring thermal resistance and thermal conductivity of thermal insulation material—Part 2: Heat flow meter method (HFM method)” Measure according to the method described. In addition, the average temperature of a test piece shall be 3 points | pieces, 0, 20, and 30 degreeC. Based on the obtained thermal conductivity, a regression line is drawn with the horizontal axis representing temperature and the vertical axis representing thermal conductivity, and the thermal conductivity of the test piece at 23 ° C. is calculated.

(Polystyrene resin ratio (surface layer PS amount) on the surface layer of the foamed molded product)
The absorbance ratio (A698 / A2850) is measured in the following manner, and the amount of the polystyrene-based resin (surface layer PS amount) in the surface layer of the foamed molded product is measured.
Ten surface layers of the foam-molded product are arbitrarily collected, and the surface layer is subjected to ATR infrared spectroscopy to obtain an infrared absorption spectrum.
The absorbance ratio (A698 / A2850) is calculated from each infrared absorption spectrum, and the minimum absorbance ratio and the maximum absorbance ratio are excluded. The arithmetic average of the remaining eight absorbance ratios is defined as the absorbance ratio (A698 / A2850)). The absorbance is measured using a measuring device sold by Nicolet under the trade name “Fourier transform infrared spectrophotometer MAGNA 560”.

A standard sample is obtained by the following method. First, a total of 2 g of a polystyrene resin and a polyethylene resin having the same composition as those contained in the composite resin to be measured so that the composition ratio (polystyrene resin / polyethylene resin) is the following ratio is precisely weighed.
Composition ratio (PS / PE; weight ratio): 0/10 = PE resin only, 1/9, 2/8, 3/7, 4/6, 5/5, 6/4, 7/3, 8 / 2, 10/0 = PS resin only This is heated and kneaded under the following conditions with a small injection molding machine and molded into a cylindrical shape having a diameter of 25 mm and a height of 2 mm to obtain a standard sample.
In addition, as a small-sized injection molding machine, it can shape | mold on the following conditions, for example using the thing sold by CSI with the brand name "CS-183".
Injection molding conditions: heating temperature 200 to 250 ° C., kneading time 10 minutes The absorbance ratio of the standard sample of the above ratio was measured with the measuring device, and the relationship between the polystyrene resin ratio (% by weight) and the absorbance ratio (A698 / A2850) was determined. The calibration curve of FIG. 1 is obtained by graphing.
In FIG. 1, when the polystyrene resin ratio is 30% by weight or less, the calibration curve is approximated by the following equation (1).
Y = 21.112X (1)

In FIG. 1, when the polystyrene resin ratio is 30 wt% or more and less than 80 wt%, the calibration curve is approximated by the following equation.
Y = 28.415Ln (X) +20.072 (2)
Furthermore, in FIG. 1, when the polystyrene resin ratio is 80% by weight or more, the calibration curve is approximated by the following equation.
Y = 12.577Ln (X) +53.32 (3)
In the above formula, X represents the absorbance ratio (A698 / A2850), and Y represents the amount of polystyrene resin.
The amount (% by weight) of the polystyrene-based resin on the surface layer of the foamed molded product is calculated based on the calibration curve in FIG.

(Heating dimensional change rate)
The heating dimensional change rate is measured by the B method described in JIS K 6767: 1999 “Foamed plastics-polyethylene test method”.
The test piece is 150 x 150 x original thickness (mm), and three straight lines are written in the center part in parallel with each other in the vertical and horizontal directions at intervals of 50 mm. 168 hours and then left for 1 hour in a standard location, and the vertical and horizontal line dimensions are measured by the following formula.
S = (L1-L0) / L0 × 100
In the formula, S represents a heating dimensional change rate (%), L1 represents an average dimension (mm) after heating, and L0 represents an initial average dimension (mm).
The heating dimensional change rate S is evaluated according to the following criteria.
A: 0 ≦ S <1.5; the rate of dimensional change was low, and the dimensional stability was good.
(Triangle | delta): 1.5 <= S <5; Although the change of a dimension was seen, it was usable practically.
X: S ≧ 5; dimensional change was remarkably observed, and practical use was impossible.

(Burning rate)
The burning rate is measured by a method in accordance with the US automobile safety standard FMVSS 302. The test piece is 350 mm × 100 mm × 12 mm, and at least two surfaces of 350 mm × 100 mm have epidermis. In the evaluation method of the combustion rate, “◯” indicates that the combustion rate is 80 mm / min or less, and “x” indicates that the rate exceeds 80 mm / min.

Example 1
High-density polyethylene (manufactured by Tosoh Corporation, grade name: 09S53B) [(1) an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms, (2) a density of 936 kg / cm ³ , (3 ) 100 parts by weight of pellets with an MFR of 2.6 g / 10 min when loaded with 2.16 kg and (4) MS (melt tension (mN) at 160 ° C.)> 90-130 × log (MFR)] in the extruder It was supplied, melted and kneaded, and granulated by an underwater cutting method to obtain elliptical (egg-like) high-density polyethylene resin particles. The average weight of the resin particles was 0.6 mg.

  Next, 50 g of magnesium pyrophosphate and 3.5 g of sodium dodecylbenzenesulfonate were dispersed in 2 kg of pure water in a 5 liter autoclave equipped with a stirrer to obtain a dispersion medium.

  The above high-density polyethylene resin particles (600 g) were dispersed in a dispersion medium at 30 ° C. and held for 10 minutes, and then heated to 60 ° C. to obtain a suspension.

  To the obtained suspension, 300 g of a styrene monomer in which 0.6 g of dicumyl peroxide was dissolved as a polymerization initiator was dropped over 30 minutes. After the dropping, the styrene monomer was impregnated in the high density polyethylene resin particles by holding for 30 minutes. After impregnation, the temperature was raised to 130 ° C., and polymerization was carried out at this temperature for 2 hours (first polymerization).

  Next, 1100 g of a styrene monomer in which 4.2 g of dicumyl peroxide was dissolved was dropped into the suspension lowered to 120 ° C. over 4 hours and 30 minutes. After dropping, the high-density polyethylene resin particles were impregnated with a styrene monomer by holding at 120 ° C. for 1 hour. After impregnation, the temperature was raised to 140 ° C., and this temperature was maintained for 3 hours for polymerization (second polymerization). As a result of this polymerization, composite resin particles could be obtained.

Subsequently, it cooled to normal temperature (about 23 degreeC), and took out the composite resin particle from the autoclave. 2 kg of composite resin particles and 2 liters of water were placed in a 5 liter autoclave with a stirrer. Furthermore, 300 g (520 ml) of 15 parts by weight of butane (n-butane: i-butane = 7: 3) as a blowing agent was placed in an autoclave. Thereafter, the temperature was raised to 70 ° C. and stirring was continued for 4 hours, whereby expandable resin particles could be obtained.
Thereafter, the mixture was cooled to room temperature, and the expandable resin particles were taken out from the autoclave and dehydrated and dried.

Pre-expanded particles were obtained by pre-expanding the obtained expandable resin particles to a bulk expansion ratio of 40 times (bulk density: 0.025 g / cm ³ ). The obtained pre-expanded particles were allowed to stand at room temperature (23 ° C.) for 1 day, and then placed in a molding die having a size of 400 mm × 300 mm × 30 mm. Thereafter, water vapor of 0.10 MPa is introduced for 50 seconds and heated, and then cooled until the maximum surface pressure of the foam is reduced to 0.01 MPa, whereby the expansion ratio is 40 times (density 0.025 g / cm ³ ). Foam was obtained. In addition, ACE-3SP (made by Sekisui Koki Co., Ltd.) was used for foam molding.

  Both the appearance and fusion of the obtained foam were good. The obtained foam was measured for the bending break point displacement and the compressive strength at an environmental temperature of 23 ° C. and 50 ° C., respectively. The results measured at 23 ° C. were taken as Q1, and the results measured at −50 ° C. were taken as Q2, and from Q1 / Q2, the influence on physical properties accompanying temperature change was calculated. Measurements were also made on the burning rate, fusion rate, surface PS (polystyrene) amount, thermal conductivity, total absorbed energy, heating dimensional change rate, and VOC. The results are shown in Table 1.

(Example 2)
(1) The high-density polyethylene 600 g at the time of the first polymerization is 400 g,
(2) 0.6 g of dicumyl peroxide at the time of the first polymerization is 0.4 g,
(3) 0.3 kg of styrene monomer at the time of the first polymerization is 0.2 kg,
(4) 4.2 g of dicumyl peroxide at the time of the second polymerization is set to 4.8 g,
(5) 1.1 kg of styrene monomer during the second polymerization is changed to 1.4 kg,
(6) Styrene dropping time in the second polymerization 4 hours 30 minutes for 5 hours,
Except that, foaming resin particles were obtained in the same manner as in Example 1. The foamable resin particles obtained were pre-foamed to a bulk foaming ratio of 40 times (bulk density 0.025 g / cm ³ ) in the same manner as in Example 1, and various physical properties of the resulting foam were obtained in the same manner as in Example 1. It was measured. The results are shown in Table 1.

(Example 3)
(1) 800 g of high-density polyethylene at the time of the first polymerization is changed to 800 g,
(2) 0.6 g of dicumyl peroxide at the time of the first polymerization is 0.8 g,
(3) 0.3 kg of styrene monomer at the time of the first polymerization is set to 0.4 kg,
(4) 4.2 g of dicumyl peroxide at the time of the second polymerization is 3.6 g,
(5) 1.1 kg of styrene monomer in the second polymerization is 0.80 kg,
(6) Styrene dropping time in the second polymerization 4 hours 30 minutes 4 hours 15 minutes,
Except that, foaming resin particles were obtained in the same manner as in Example 1. The foamable resin particles obtained were pre-foamed to a bulk foaming ratio of 40 times (bulk density 0.025 g / cm ³ ) in the same manner as in Example 1, and various physical properties of the resulting foam were obtained in the same manner as in Example 1. It was measured. The results are shown in Table 1.

Example 4
(1) 600 g of high-density polyethylene during the first polymerization is set to 1000 g,
(2) 0.6 g of dicumyl peroxide in the first polymerization is 1.0 g,
(3) 0.3 kg of styrene monomer at the time of the first polymerization is 0.5 kg,
(4) 4.2 g of dicumyl peroxide during the second polymerization is set to 3.0 g,
(5) 0.5 kg of 1.1 kg of styrene monomer during the second polymerization,
(6) Styrene dropping time in the second polymerization 4 hours 30 minutes 4 hours,
Except that, foaming resin particles were obtained in the same manner as in Example 1. The foamable resin particles obtained were pre-foamed to a bulk foaming ratio of 40 times (bulk density 0.025 g / cm ³ ) in the same manner as in Example 1, and various physical properties of the resulting foam were obtained in the same manner as in Example 1. It was measured. The results are shown in Table 1.

(Example 5)
The same procedure as in Example 1 was carried out to obtain expandable resin particles. The obtained foamable resin particles were prefoamed at a bulk foaming ratio of 20 times (bulk density 0.05 g / cm ³ ), and various physical properties of the obtained foam were measured in the same manner as in Example 1. The results are shown in Table 1.

(Example 6)
The same procedure as in Example 1 was carried out to obtain expandable resin particles. The obtained foamable resin particles were prefoamed at a bulk foaming ratio of 60 times (bulk density 0.017 g / cm ³ ), and various physical properties of the obtained foam were measured in the same manner as in Example 1. The results are shown in Table 1.

(Example 7)
It carried out like Example 2 and obtained expandable resin particles. The obtained foamable resin particles were prefoamed at a bulk foaming ratio of 20 times (bulk density 0.05 g / cm ³ ), and various physical properties of the obtained foam were measured in the same manner as in Example 1. The results are shown in Table 1.

(Example 8)
It carried out like Example 2 and obtained expandable resin particles. The obtained expandable resin particles were pre-expanded to a bulk expansion ratio of 80 times (bulk density 0.013 g / cm ³ ), and various physical properties of the obtained foam were measured in the same manner as in Example 1. The results are shown in Table 1.

Example 9
Implemented in the same manner as in Example 3 to obtain expandable resin particles. The obtained foamable resin particles were prefoamed at a bulk foaming ratio of 30 times (bulk density 0.033 g / cm ³ ), and various physical properties of the obtained foam were measured in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
Ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVA) (manufactured by Nippon Unicar Co., Ltd .: NUC-3450, vinyl acetate content: 5 wt%, melting point: 107 ° C., melt flow rate: 0.5 g / 10 min) [ (1) Copolymer of ethylene and vinyl acetate, (2) Density 93 kg / m ³ , (3) MFR at 2.16 kg load 0.5 g / 10 min, (4) MS (melt tension at 160 ° C. (MN))> 110-100 × log (MFR)] is supplied to an extruder, melted and mixed, granulated by an underwater cutting method, and oval (egg) EVA resin particles (polyethylene resin particles) Got. The average weight of the EVA resin particles was 0.6 mg. The melt flow rate and density of EVA are values measured according to JIS K6992-2.

  Next, 50 g of magnesium pyrophosphate and 3.5 g of sodium dodecylbenzenesulfonate were dispersed in 2 kg of pure water in a 5 liter autoclave equipped with a stirrer to obtain a dispersion medium.

  The dispersion medium was set to 30 ° C., and 600 g of the EVA resin particles were dispersed therein and held for 10 minutes, and then heated to 60 ° C. to obtain a suspension.

  To the obtained suspension, 300 g of a styrene monomer in which 0.6 g of dicumyl peroxide was dissolved as a polymerization initiator was dropped over 30 minutes. After the dropping, the styrene monomer was impregnated in the high density polyethylene resin particles by holding for 30 minutes. After impregnation, the temperature was raised to 130 ° C., and polymerization was carried out at this temperature for 2 hours (first polymerization).

  Next, 1100 g of a styrene monomer in which 4.2 g of benzoyl peroxide was dissolved was dropped into the suspension lowered to 90 ° C. over 4 hours and 30 minutes. After dropping, the EVA resin particles were impregnated with a styrene monomer by holding at 90 ° C. for 1 hour. After impregnation, the temperature was raised to 140 ° C., and this temperature was maintained for 3 hours for polymerization (second polymerization). As a result of this polymerization, styrene EVA composite resin particles could be obtained.

Subsequently, it cooled to normal temperature (about 23 degreeC), and took out the composite resin particle from the autoclave. 2 kg of composite resin particles and 2 liters of water were placed in a 5 liter autoclave with a stirrer. Furthermore, 300 g (520 ml) of 15 parts by weight of butane (n-butane: i-butane = 7: 3) as a blowing agent was placed in an autoclave. Thereafter, the temperature was raised to 70 ° C. and stirring was continued for 4 hours, whereby expandable resin particles could be obtained.
Thereafter, the mixture was cooled to room temperature, and the expandable resin particles were taken out from the autoclave and dehydrated and dried.

Pre-expanded particles were obtained by pre-expanding the obtained expandable resin particles to a bulk expansion ratio of 40 times (bulk density: 0.025 g / cm ³ ). The obtained pre-expanded particles were allowed to stand at room temperature (23 ° C.) for 1 day, and then placed in a molding die having a size of 400 mm × 300 mm × 30 mm. Thereafter, water vapor of 0.10 MPa is introduced for 50 seconds and heated, and then cooled until the maximum surface pressure of the foam is reduced to 0.01 MPa, whereby the expansion ratio is 40 times (density 0.025 g / cm ³ ). Foam was obtained. In addition, ACE-3SP (made by Sekisui Koki Co., Ltd.) was used for foam molding.

  Both the appearance and fusion of the obtained foam were good. In the same manner as in Example 1, various physical properties of the obtained foam were measured. The results are shown in Table 1.

(Comparative Example 2)
Expanded polypropylene resin with an expansion ratio of 30 times (density 0.033 g / cm ³ ) [(1) random copolymer of propylene and ethylene, (2) density 900 kg / m ³ , (3) MS (melt tension at 160 ° C. (MN))> 110-100 × log (MFR)] was used to obtain a propylene-based resin foam having the same shape and the same dimensions as in Example 1 and an expansion ratio of 30 times (density 0.033 g / cm ³ ). . In the same manner as in Example 1, various physical properties of the obtained foam were measured. The results are shown in Table 1.

(Comparative Example 3)
(1) 200 g of 600 g of high-density polyethylene during the first polymerization,
(2) 0.6 g of dicumyl peroxide in the first polymerization is 0.2 g,
(3) 0.3 kg of styrene monomer at the time of the first polymerization is 0.1 kg,
(4) 4.2 g of dicumyl peroxide in the second polymerization was changed to 5.4 g,
(5) 1.1 kg of styrene monomer at the time of the second polymerization is 1.7 kg,
(6) Styrene dropping time in the second polymerization 4 hours 30 minutes to 5 hours 30 minutes,
Except that, foaming resin particles were obtained in the same manner as in Example 1. The foamable resin particles obtained were pre-foamed to a bulk foaming ratio of 40 times (bulk density 0.025 g / cm ³ ) in the same manner as in Example 1, and various physical properties of the resulting foam were obtained in the same manner as in Example 1. It was measured. The results are shown in Table 1.

(Comparative Example 4)
(1) 600 g of high-density polyethylene during the first polymerization is changed to 1400 g,
(2) 0.6 g of dicumyl peroxide at the time of the first polymerization is changed to 0.84 g,
(3) 0.3 kg of styrene monomer at the time of the first polymerization is 0.42 kg,
(4) 4.2 g of dicumyl peroxide during the second polymerization is 1.8 g,
(5) The styrene monomer 1.1 kg in the second polymerization is 0.18 kg,
(6) Styrene dropping time in the second polymerization 4 hours 30 minutes 3 hours 30 minutes,
Except that, foaming resin particles were obtained in the same manner as in Example 1. The foamable resin particles obtained were prefoamed in the same manner as in Example 1, but foamed only to a bulk foaming ratio of 7 times (bulk density 0.143 g / cm ³ ). Therefore, subsequent foam evaluation was not performed.

HDPE: High density polyethylene (09S53B)
EVA: ethylene-vinyl acetate copolymer PP: polypropylene PS: polystyrene

  From the results of Examples 1 to 9 and Comparative Examples 1 to 4, high density polyethylene resin particles were impregnated with polystyrene so as to be in the range of 100 to 500 parts by weight of styrene with respect to 100 parts by weight of high density polyethylene. It can be seen that the foam obtained using the obtained composite resin particles has little difference in bending break point displacement between 23 ° C. and −50 ° C.

Claims (6)

It is a foam of a composite resin containing 100 parts by weight of a high-density polyethylene resin having a density of 931 to 950 kg / m ³ and 100 to 500 parts by weight of a polystyrene resin, and has a displacement at break Q1 at + 23 ° C. and −50 ° C. A shock absorber characterized in that the ratio Q1 / Q2 to the breaking point displacement amount Q2 is 1.5 or less.   The buffer according to claim 1, wherein a surface layer of the foam shows an amount of polystyrene resin of 50% by weight or less.   The shock absorber according to claim 1 or 2, wherein the foam exhibits a fusion rate of 50% or more.   The shock absorber according to any one of claims 1 to 3, wherein the foam has an expansion ratio of 5 to 40 times.   The shock absorber according to any one of claims 1 to 4, wherein the foam includes 20 to 100 parts by weight of the high-density polyethylene resin.   The shock absorber according to any one of claims 1 to 5, wherein the shock absorber is a shock absorber for a median strip block or a fender.