JP2003201615A - Shock absorbing material for helmet and helmet provided with the shock absorbing material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shock absorbing material for a helmet made of a styrene- based resin expansion molded product having extremely stable dimensions over a long period even under a high-temperature atmosphere and an ultralow content of volatile organic compounds and the helmet using the shock absorbing material. <P>SOLUTION: This shock absorbing material having a hollow nearly hemispherical shape is obtained by carrying out in-mold expansion molding of preexpanded styrene-based resin particles prepared by impregnating styrene-based resin particles with gaseous carbon dioxide. The rate of dimensional change before and after heating is ≤±0.5% when the expansion molded product is heated at 80°C for 600 h. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shock absorbing material for a helmet and a helmet provided with the shock absorbing material, and more specifically, ensuring safety when riding a two-wheeled vehicle, ensuring safety when working at a high place or on site. Alternatively, the present invention relates to a shock absorber for a helmet used as an inner body of a helmet for the purpose of preventing bullets from a firearm and the like, and a helmet including the shock absorber.

[0002]

2. Description of the Related Art Generally, foamed polyethylene, urethane type sponge, rubber type sponge, gel type, etc. are used as impact absorbing materials for helmets used in the above-mentioned applications. It is usual that the shock absorber having the required shape is fixed to the inside of a cap body made of fiber reinforced plastic or metal with adhesive or double-sided tape. As a material, shock absorbers made of styrene-based resin foam moldings such as expanded polystyrene that can satisfy both high rigidity and high shock-absorbing properties may cause serious effects on the human body such as skull fractures. It has been highly evaluated as a shock absorber for helmets used in.

[0003]

Generally, a foamed molded article of a styrene resin is obtained by heating pre-expanded particles obtained by heating expandable styrene resin particles containing butane, pentane or the like as a foaming agent with steam or the like. It is produced by filling the cavity of a foam molding mold and heating with steam to subject the styrene resin pre-expanded particles to foam molding in the mold. However, it is common to use butane or pentane as a foaming agent, and when left in a high temperature environment of about 80 ° C for a certain period of time, the dimensional change rate is as large as ± 1.5%, and it is fixed inside the cap body. There was a problem that the shock absorbing material made of the foamed styrene resin foamed product was peeled off.
A helmet may be placed in a high temperature environment of 80 ° C. or higher for a long time, and a shock absorber having a small dimensional change rate even under a high temperature and long time atmosphere is strongly desired.

On the other hand, in recent years, there has been a strong demand for reducing the content of residual volatile organic compounds related to sick houses (indoor air pollution), and organic compounds such as butane and pentane have been strongly demanded. Instead, styrene-based resin pre-expanded particles using carbon dioxide as a blowing agent have been proposed (see Japanese Patent Laid-Open No. 4-351646). A molded product obtained by foaming pre-expanded particles of this kind in a mold has a small amount of residual gas because carbon dioxide is used as a foaming agent, and the dimensional change rate when left at a high temperature of about 80 ° C. for a long time is small. It can be suppressed to about ± 0.8%, which is superior to that using butane or pentane as the foaming agent.
However, in the experiments conducted by the present inventors, as a shock absorbing material for a helmet, it is still insufficient even if the dimensional change rate in a high temperature environment can be improved to about ± 0.8%. Considering the safety of the wearer in various usage environments while preventing peeling, the dimensional change rate is required to be 0.5% or less.

[0005]

The present invention has been made in order to meet the above demands, and the shock absorbing material for helmets according to the present invention is obtained by impregnating styrene resin particles with carbon dioxide gas. Styrene-based resin pre-expanded particles obtained by in-mold foam molding, when heated at 80 ° C. for 600 hours,
The shock absorbing material for a helmet is characterized in that it is a shock absorbing material for a helmet, which is made of a styrene resin foam molded product having a hollow approximately hemispherical shape with a dimensional change rate within ± 0.5% before and after heating.

In the present invention, “heating at 80 ° C. for 600 hours” means that the maximum value of the temperature environment in which the helmet is used is 80 ° C. and the safety factor is 600 hours. This is because it is required to solve the above problems even under the condition of heating in this high temperature region. In this environment, the one in which the dimensional change rate satisfies ± 0.5% or less can solve such a problem.

The impact absorbing material for a helmet having a dimensional change rate within the above range can be obtained by in-mold foaming of styrene resin pre-expanded particles produced as follows. That is, first, carbon dioxide gas is impregnated into styrene-based resin particles to form expandable styrene-based resin particles, and in the next step, the expandable styrene-based resin particles are charged into a pre-expanding machine equipped with a steam charging line and an exhaust line. , While supplying steam from the steam charging line at a charging pressure of 0.5 to 5.0 kg / cm ² G, exhausting the atmospheric gas containing steam from the exhaust line, and during that time, the foaming machine internal pressure from the steam charging pressure Styrenic resin pre-expanded particles obtained by pre-expanding while maintaining a low level of 0.05 to 1.0 kg / cm ² G are used.

By using the styrene resin pre-expanded particles described above, it is possible to obtain a styrene resin foam molded article having a dimensional change rate of ± 0.5% or less by in-mold foaming. Therefore, the shock absorbing material for the helmet manufactured in this manner is a shock absorbing material for a helmet that satisfies the above-mentioned required performances for the helmet. Further, it is possible to make the content of the residual volatile organic compound in the impact absorbing material for helmet extremely small. The details will be described below.

As the styrene resin particles, generally known styrene resin particles can be used. Specifically, such resin particles include styrene, α-methylstyrene, paramethylstyrene, t
-Homopolymer particles of styrene-based monomers such as butylstyrene, chlorostyrene, divinylbenzene (bifunctional monomer) or copolymer particles in which two or more kinds of these monomers are combined, methyl acrylate, butyl acrylate, Ester of acrylic acid and methacrylic acid such as methyl methacrylate, ethyl methacrylate, cetyl methacrylate,
Alternatively, copolymer particles with a monomer other than a styrene-based monomer such as acrylonitrile, dimethyl fumarate, ethyl fumarate, and alkylene glycol dimethacrylate (bifunctional monomer) can be used. Further, it may be resin particles obtained by extrusion-blending with a resin other than the styrene resin within a range in which the styrene component in these styrene resin particles exceeds 50% by weight. Examples of the resin other than the styrene resin include a polyphenyl ether resin, a polyolefin resin, and a rubber component. In particular, polystyrene resin particles are preferable as the styrene resin particles. The particle size of the resin particles can be appropriately selected according to the application of the helmet, and for example, particles having a particle size of 0.2 to 5 mm can be used. It is preferable that the amount of residual styrene monomer in the styrene resin particles is as small as possible, and it is particularly preferable that the amount of the residual styrene monomer is 0 to 500 ppm.

In order to reduce the amount of residual styrenic monomer in the styrenic resin particles, for example, in suspension polymerization, 0.05% by weight or more of a high temperature initiation type polymerization catalyst is used with respect to the styrenic monomer. It is preferable to use the final polymerization temperature of 115 ° C. or higher. As the high temperature initiation type polymerization catalyst, t-
Butyl peroxybenzoate, t-butyl peroxypivalate, t-butyl peroxy isopropyl carbonate, t-butyl peroxy acetate, 2,2-t
It is particularly preferable that the temperature for obtaining a half-life of 10 hours such as -butylperoxybutane is 100 to 115 ° C. However, if they are used more than necessary, they will contain decomposition by-products such as t-butanol, and therefore, depending on the type of polymerization catalyst, the upper limit of the amount used is preferably 0.5% by weight.

The molecular weight of the styrene resin particles is preferably 200,000 to 400,000 as a weight average molecular weight measured by the GPC method. When it is less than 200,000, the strength of the foamed molded product may be lowered, and when it exceeds 400,000, it is difficult to obtain sufficient foaming property, which is not preferable.

The above-mentioned styrene resin particles are impregnated with carbon dioxide gas as a foaming agent to obtain expandable styrene resin particles. The carbon dioxide gas as the foaming agent may be 100% carbon dioxide gas, but other foaming agents may be added as long as the effect of the present invention is not impaired. Other blowing agents include air, inorganic blowing agents such as nitrogen, aliphatic hydrocarbons such as propane, butane, pentane and hexane, alicyclic hydrocarbons such as cyclobutane, cyclopentane and cyclohexane, and fluorohydrocarbons. It is also possible to mix an organic blowing agent. As the fluorohydrocarbon, it is preferable to use difluoroethane, tetrafluoroethane or the like, which has an ozone depletion potential of zero. Here, the organic foaming agent is preferably used in a range not exceeding 20% by weight of the total amount of the foaming agent. The content ratio of carbon dioxide gas in the styrene resin particles is 1 to 15% by weight.
Is preferred.

To impregnate the styrene resin particles with carbon dioxide gas, for example, after putting the styrene resin particles in a pressure-resistant airtight container, the carbon dioxide gas is injected under pressure and the resin particles are contacted with the pressurized carbon dioxide gas. Can be done. The impregnation temperature may be increased to a temperature at which the styrenic resin particles do not agglomerate with each other, but usually 0
-40 ° C.

The pressure for impregnating the styrene resin particles with carbon dioxide is preferably 10 kg / cm ² G or more, more preferably 15 to 40 kg / cm ² G. The impregnation time can be appropriately adjusted so that the styrene-based resin particles have the above-mentioned carbon dioxide gas content.
0 hours is preferable, and 2 to 8 hours is more preferable.

When impregnating the styrene resin particles with carbon dioxide gas, various surface treatment agents can be applied to the surfaces of the resin particles. Examples of such a surface treatment agent include an anti-bonding agent that prevents the pre-expanded particles from bonding during heat-foaming, a fusion promoter during molding, an antistatic agent, and a spreading agent.

Examples of the binding inhibitor include talc, calcium carbonate, silica, zinc stearate, aluminum hydroxide, ethylenebisstearic acid amide, tribasic calcium phosphate, dimethyl silicon and the like. Examples of the fusion promoter include stearic acid, stearic acid triglyceride, hydroxystearic acid triglyceride,
Examples thereof include sorbitan stearate and polyethylene wax. Examples of the antistatic agent include polyoxyethylene alkylphenol ether and stearic acid monoglyceride. Examples of the spreading agent include polybutene, polyethylene glycol, silicone oil and the like.

As other additives, flame retardants such as hexabromocyclododecane and tetrabromocyclooctane, methacrylic acid ester-based copolymers, ethylenebisstearic acid amide, and polyethylene wax may be optionally added to the styrene resin particles. A bubble regulator such as ethylene-vinyl acetate copolymer may be contained in advance. The above-mentioned binding inhibitor, fusion promoter during molding, antistatic agent, spreading agent and other additives may be used alone or in admixture of two or more.

The styrenic resin pre-expanded particles may contain a flame retardant. As a method for obtaining pre-expanded styrenic resin particles containing a flame retardant, for example, in a suspension of styrene resin particles and water, resin under a temperature atmosphere of the melting point or higher of the flame retardant dissolved or suspended in water. Styrene resin particles containing a flame retardant are obtained by a method of incorporating a flame retardant in the particles, or a method of incorporating a flame retardant in a styrene resin particle by extrusion blending, etc. There is a method of doing. Examples of flame retardants that can be used at this time include hexabromocyclododecane and tetrabromocyclooctane. The flame retardant content is preferably 0.1 to 4% by weight, more preferably 0.5 to 3.0% by weight, based on the entire resin particles. When the flame retardant content is less than 0.1% by weight, it becomes difficult to obtain a sufficient flame retardant effect, which is not preferable. If the flame retardant content exceeds 4% by weight, the pre-expanded styrenic resin particles tend to adhere to each other, which is not preferable. The particle size of the pre-expanded particles is 0.3 to
About 10 mm is preferable.

The styrenic resin pre-expanded particles are produced as follows. That is, as described above, the expandable styrene resin particles are obtained by impregnating the styrene resin particles with carbon dioxide gas, and in the next step, the expandable styrene resin particles are placed in a pre-expanding machine equipped with a steam injection line and an exhaust line. Particles are charged, and steam is injected from the steam injection line for 0.5 to 5.
While supplying with an input pressure of 0 kg / cm ² G, atmospheric gas containing steam is exhausted from the exhaust line, and during that time,
The pressure inside the foaming machine is 0.05 to 1.0k from the steam input pressure.
Pre-expanding is performed while maintaining low g / cm ² G to obtain pre-expanded styrenic resin particles. In this method, it is preferable to perform prefoaming immediately after the step of impregnating carbon dioxide gas.

Further, in this method, it is necessary to control so that the pressure in the pre-foaming machine is always lower than the supply pressure by an exhaust control valve or the like so that the steam is always supplied into the foaming machine. For example, when the steam input pressure is set to 1.2 kg / cm ² G and the pressure in the pre-foaming machine is set to 0.8 kg / cm ² G, the pressure is released while removing 0.4 kg / cm ² G pressure from the exhaust line. Will be controlled. In particular,
The pressure can be adjusted by linking and controlling the pressure inside the foaming machine and the exhaust control valve.

The difference between the input pressure and the pressure inside the foaming machine is 0.0
If it is less than 5 kg / cm ² G, it is difficult to obtain styrene-based resin pre-expanded particles having a low bulk density, and the appearance and internal fusion of the foamed molded product are poor, resulting in low commercial value. Further, if it exceeds 1.0 kg / cm ² G, bonding during pre-foaming increases, which is not preferable. A more preferable pressure difference is
It is 0.1 to 0.7 kg / cm ² G.

The expandable styrenic resin particles in the pre-expansion machine are usually preferably heated to about 110 to 160 ° C, and more preferably heating temperature is 110 to 130 ° C. When the heating temperature is lower than 110 ° C, the bulk density is 0.5 g /
Pre-expanded styrenic resin particles having a size of ³ cm ³ or less are difficult to obtain, which is not preferable. If the heating temperature exceeds 160 ° C, the pre-expanded styrenic resin particles tend to adhere to each other, which is not preferable.

FIG. 1 shows an example of a pre-foaming machine which can be used for producing the styrene resin pre-expanded particles as described above. In the figure, 2 is a stirring motor, 3 is a stirring blade, 4 is a baffle bar, 5 is a foam tank upper surface detector, 6 is a foamable particle transporter, and 7
Is an expandable particle metering tank, 8 is an expandable particle feeder, 9 is a steam injection control valve, 10 is a steam chamber, 11 is a condensed water discharge valve, 12 is an exhaust control valve, 13 is a pre-expanded particle discharge port, 1
4 is a temporary receiver for pre-expanded particles, 15 is pneumatic transportation equipment, 16
Is an internal pressure detection / control device, 17 is a steam injection hole, 18 is a steam injection pressure gauge, 19 is a pressure reducing valve, and 20 is a steam source pressure gauge.

The foamed molded product obtained by foaming the above-mentioned styrene resin pre-expanded particles is excellent in dimensional stability for a long period of time. In particular, the dimensional change rate when heated at 80 ° C. for 600 hours can be kept within ± 0.5%. In addition, the content of volatile organic compounds is 1000p
It can be extremely reduced to pm or less.

The foam molding method is not particularly limited, and any known method can be used. For example, by filling the pre-expanded styrene resin particles into the cavity of the foam molding die and blowing the steam to heat the pre-expanded particles, the particles are brought into close contact with each other and fused together to form the desired foamed molding. You can get the body. The density of the foamed molded product is preferably about 0.015 to 0.5 g / cm ³ .

[0026]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In the examples, the dimensional change rate and the content of the volatile organic compound were evaluated as follows.

<Dimensional change rate> A foam molded article taken out from the foam molding die (actually, a shock absorbing material for a helmet having a hollow, substantially hemispherical shape shown in FIG. 2, and a thickness h: 20).
mm, outer diameter length a in the longitudinal direction: 260 mm, outer diameter length in the lateral direction b: 220 mm), temperature 23 ° C., relative humidity 5
After leaving it in a 0% constant temperature and humidity room (standard temperature and humidity state of JIS-K7100) for 24 hours, it was used as a test sample according to JIS-K6767.

This test sample was placed horizontally in a hot air circulation dryer maintained at 80 ° C., heated for 600 hours, taken out, and then left in the constant temperature and constant humidity chamber again for 1 hour. JIS-K6 measures the dimensions of test samples before and after heating.
It carried out according to 767. For the measurement, as shown in FIG. 3a, an aluminum inspection tool 50 having a recess 51 having the same shape as the outer shape of the test sample S before heating was used, and as shown in FIG. 3b, before and after heating. The degree of shrinkage t of the test sample S in the lengthwise direction was determined by inserting a gap gauge. The dimensional change rate was obtained according to the following formula.

Dimensional change rate P (%) = (a2-a1) × 100 / a1 (where a1 is 23 ° C. and relative humidity 50 after in-mold molding)
%, The outer diameter length in the longitudinal direction of the test sample left for 24 hours, a2 is the outer diameter length in the longitudinal direction of the test sample after heating the test sample at 80 ° C. for 600 hours).

<Content of Volatile Organic Compound> The foamed molded product taken out from the foam molding mold was dried in a thermostatic chamber at 50 ° C. for 7 days, and then the values obtained by the following three kinds of measuring methods were measured. Totally calculated. a. (Measurement of Hydrocarbons Having 5 or Less Carbons) The foamed molded article was placed in a thermal decomposition furnace at 150 ° C., and the vaporized hydrocarbons were measured by gas chromatography. Gas chromatography (GC): Shimadzu G
C-14B Pyrolysis furnace: PYR-1A manufactured by Shimadzu Corporation Column: Porapack Q 80/100 (3 mmφ × 1.
5m) Column temperature: 100 ° C Detector (FID) temperature: 120 ° C

B. (A hydrocarbon having 6 or more carbon atoms,
Measurement of hydrocarbon up to styrene peak appearing in gas chromatogram) The foamed molded product was dissolved in dimethylformamide, an internal standard solution (cyclopentanol) was added, and measurement was performed by GC. However, peaks that could not be identified were quantified by converting to the amount of toluene detected.

GC: Shimadzu Corporation GC-14A column: PEG-20M PT25% 60/80
(2.5m) Column temperature: 105 ° C Detector (FID) temperature: 220 ° C

C. (From the next peak of styrene that appears in the gas chromatogram, the carbon number is 16 (n-hexadecane).
Measurement of hydrocarbons up to) The foamed molded product was dissolved in chloroform and measured with a gas chromatograph mass spectrometer (GCMS). However, a blank test was performed only with a solvent that did not dissolve the test sample, and the amount of the detected substance in the blank test was subtracted. Furthermore, peaks that could not be identified were quantified by converting to the amount of toluene detected.

GCMS: Shimadzu QP5000 column: J & W Scientific DB-1
(1 μm × 60 m 0.25 mmφ) Measurement conditions: Column temperature (after holding at 60 ° C. for 1 minute, 10
Temperature rises to 300 ° C at ℃ / min) Split ratio: 10 Carrier gas: He (1 ml / min) Interface temperature: 260 ° C

[Example 1] 40 kg of pure water and 2.5 parts of sodium dodecylbenzenesulfonate were placed in a 100-liter reactor.
g and 58 g of magnesium pyrophosphate were added to obtain an aqueous medium. Next, benzoyl peroxide (purity 75%) 16
44 g of styrene in which 7 g, 30 g of t-butyl peroxybenzoate and 22 g of polyethylene wax (molecular weight 1000) were dissolved was added with stirring to suspend it.
The temperature was raised to 0 ° C. to initiate polymerization. When the polymerization conversion measured by the specific gravity method reached 95% by weight, the reactor was cooled to 12%.
After heating to 3 ° C. and holding for 2.5 hours, the temperature was cooled to room temperature, and styrene resin particles were taken out. The residual styrene in the styrene resin particles obtained here was measured by gas chromatography and found to be 452 ppm.
The weight average molecular weight measured by the method was 278,000.

Of the styrene resin particles, the particle size is from 0.7 to
After placing 15 kg of 1.0 mm in a rotary pressure-resistant container having an internal capacity of 30 liters, 7.5 g of polyethylene glycol 300 as a spreading agent, 7.5 g of glycerin monostearate and carbonic acid as a binding inhibitor. 30 g of calcium was added, the container was rotated, and it was made to adhere to the surface of the resin particle. Then, after the rotation was stopped, carbon dioxide gas was pressed into the container and kept at 25 ° C. and 30 kg / cm ² G for 6 hours to impregnate the carbon dioxide gas into the resin particles to obtain expandable styrene resin particles.

The expandable styrene resin particles thus obtained were taken out of the pressure vessel and charged into a foaming machine equipped with a stirrer in the next step, and then steam having a charging pressure of 1.2 kg / cm ² G was introduced into the foaming machine can. . The pressure inside the foaming machine at this time was controlled to 0.8 kg / cm ² G, and while controlling the opening of the exhaust control valve with an electric signal, excess pressure was released to the outside using the exhaust line (input pressure). And the pressure inside the foaming machine is 0.4 kg / cm ² G). In this way, the steam was continuously introduced into the foaming machine and pre-expanded to obtain styrene resin pre-expanded particles. The particle size of the pre-expanded particles was 2.3 to 4.0 mm.

Six hours after the pre-foaming, the styrene resin pre-foamed particles were placed in the cavity of the foam molding die whose cavity shape after mold clamping was designed to have the shape of the impact absorbing material for helmet shown in FIG. Fig. 2
A foamed molded body having a density of 0.020 g / cm ^{3 having} the shape shown in FIG. With respect to the obtained foamed molded product, the dimensional change rate and the content of the volatile organic compound were evaluated by the above-described evaluation methods. The results obtained are shown in Table 1.

Example 2 Immediately after taking out the expandable styrene resin particles from the pressure resistant container, the charging pressure was 1.5 kg / c.
The vapor of m ² G was introduced into the foaming machine, and the pressure inside the foaming machine was adjusted to 0.8 kg / cm ² G (the difference between the input pressure and the pressure inside the foaming machine was 0.7 kg / cm ² G). Except for this, the pre-expanded particles and the foamed molded product were obtained in the same manner as in Example 1. Table 1 shows the evaluation results of the dimensional change rate and the content of the volatile organic compound of the obtained foamed molded product. The particle size of the pre-expanded particles was 2.3 to 4.0 mm, and the density of the foamed molded product was 0.025 g / cm ³ .

[Comparative Example 1] Immediately after taking out the expandable styrene resin particles from the pressure resistant container, the charging pressure was 2.0 kg / c.
The vapor of m ² G was introduced into the foaming machine, and the pressure inside the foaming machine was adjusted to 0.8 kg / cm ² G (the difference between the input pressure and the pressure inside the foaming machine was 1.2 kg / cm ² G). Except for this, the pre-expanded particles and the foamed molded product were obtained in the same manner as in Example 1. The evaluation results of the obtained foamed molded product are shown in Table 1. The particle size of the pre-expanded particles is 2.2 to 3.6 mm.
The density of the foamed molded product was 0.025 g / cm ³ .

Comparative Example 2 Immediately after taking out the expandable styrene resin particles from the pressure resistant container, the charging pressure was 0.8 kg / c.
Except that m ² G of steam was introduced into the foaming machine and the pressure inside the foaming machine was adjusted to 0.8 kg / cm ² G (the difference between the input pressure and the foaming machine internal pressure was 0 kg / cm ² G). A pre-expanded particle and a foamed molded product were obtained in the same manner as in Example 1. The evaluation results of the obtained foamed molded product are shown in Table 1.
The particle size of the obtained pre-expanded particles was 1.8 to 2.8 m.
In m, the density of the foamed molded product was 0.050 g / cm ³ .

[Comparative Example 3] 2.0 kg of styrene resin particles having a particle size of 0.7 to 1.0 mm among the styrene resin particles obtained in Example 1 and ion-exchanged water were placed in a pressure vessel equipped with a stirrer and having an internal volume of 5 liters. 2.2 liters, tricalcium phosphate 6.0
g, and sodium dodecylbenzene sulfonate 0.2
g was added and stirring was started. Next, after raising the temperature to 90 ° C.,
140 g of butane was pressed in and held for 5 hours. Then 3
It cooled to 0 degreeC and obtained the expandable styrene resin particle. The particles taken out were dried and then aged in a thermostatic chamber at 15 ° C. for 5 days. Zinc stearate as a binding inhibitor at the time of pre-foaming and hydroxystearic acid triglyceride as a fusion promoter are coated on the surface of the particles, and then charged into a foaming machine with a stirrer, and then the charging pressure is 0.5 kg / cm.
² G of steam was introduced into the foaming machine. While controlling the opening of the exhaust control valve with an electric signal so that the pressure in the foaming machine at this time would be 0.1 kg / cm ² G, excess pressure was released to the outside using the exhaust line. And the pressure inside the foaming machine is 0.4 kg / cm ² G). In this way, the steam was continuously introduced into the foaming machine and pre-expanded to obtain styrene resin pre-expanded particles. The particle size of the pre-expanded particles was 2.3 to 4.0 mm.

Six hours after the pre-foaming, the pre-foamed particles were filled in the cavity of the same foam-molding mold used in Example 1 and heated with steam to foam-mold and have a density of 0.020.
A styrene resin foam molded article having the same shape as in Example 1 having g / cm ³ was obtained. The evaluation results of the obtained foamed molded product are shown in Table 1.
Shown in.

[0044]

[Table 1]

From the above results, in-mold expansion-molded articles of styrene resin pre-expanded particles obtained by impregnating styrene resin particles with carbon dioxide gas, expandable styrene having carbon dioxide gas as styrene resin pre-expanded particles. Styrene-based resin molded product with excellent dimensional stability for a long period of time even in a high temperature atmosphere by foam molding using pre-expanded particles by adjusting the difference between the input pressure of the resin-based resin particles and the pressure inside the foaming machine. It can be seen that Further, the content of the volatile organic compound can be extremely reduced.

[0046]

INDUSTRIAL APPLICABILITY The impact absorbing material for a helmet according to the present invention is made of expanded polystyrene which can satisfy both high rigidity and high cushioning property, but its dimensions are very stable for a long time even in a high temperature atmosphere. It was done. Therefore, the helmet with the shock absorbing material fixed to the inside of the cap body can avoid a situation in which the shock absorbing material and the cap body are separated from each other during use. Become. Further, the content of the volatile organic compound in the shock absorbing material can be extremely reduced.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a pre-foaming machine used for producing pre-expanded particles of a ethylene resin that can be used in the present invention.

FIG. 2 is a diagram showing an outline of a foam molded article as a shock absorbing material for a helmet used in Examples and Comparative Examples.

FIG. 3 is a diagram illustrating an actual example in which the degree of shrinkage of the test sample in the lengthwise direction is measured in order to obtain the dimensional change rate.

[Explanation of symbols]

2 stirring motor 3 stirring blades 4 baffles 5 Foam tank top detector 6 Effervescent particle transporter 7 Effervescent particle measuring tank 8 Expandable particle feeder 9 Steam injection control valve 10 Steam chamber 11 Condensed water discharge valve 12 Exhaust control valve 13 Pre-expanded particles outlet 14 Pre-expanded particle temporary receiver 15 Air transportation equipment 16 Internal pressure detection / control device 17 Steam injection hole 18 Steam input pressure gauge 19 Pressure reducing valve 20 Steam source pressure gauge 50 Aluminum inspection tool S test sample

Claims (2)

[Claims] 1. A styrene-based resin pre-expanded particle obtained by impregnating styrene-based resin particles with carbon dioxide gas, obtained by in-mold foam molding, and when heated at 80 ° C. for 600 hours, before and after heating. A shock absorber for a helmet, which is made of a styrene resin foam molded product having a hollow substantially hemispherical shape with a dimensional change rate of ± 0.5% or less. 2. A helmet comprising the helmet shock absorbing material according to claim 1 inside a cap body.