JP2013067740A - Thermoplastic resin bead foam, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for foaming beads which have a light weight and a high compression strength even in a large average foam diameter, and to provide a method for manufacturing a foam thereof.SOLUTION: The thermoplastic resin bead foam is obtained by making an inert gas infiltrate in an unfoamed thermoplastic resin particle in a pressure vessel, thereafter releasing the pressure in the pressure vessel and taking out the unfoamed resin particle containing the gas having infiltrated therein, and heating and foaming the particle at temperature equal to or higher than the glass transition temperature of the resin constituting the particle, and has a numerical value σ/ρ of ≥5 obtained by dividing a 10% compression stress σ(kPa) by a density ρ (kg/m).

Description

  The present invention relates to a thermoplastic resin bead foam, in particular, a lightweight and high compressive strength thermoplastic resin bead foam, and a method for producing a thermoplastic resin bead foam.

  In recent years, shock-absorbing pads and the like for protecting the head of an occupant in the event of a vehicle collision have been made of a material that is lightweight and has high compressive strength from the perspective of increasing interest in low fuel consumption and increasing awareness of safety performance. It has been demanded. For example, a bead foam is often used as a material for the impact absorbing pad, and this is a foam obtained by thermally fusing pre-expandable particles in a mold.

Conventionally, polypropylene has been often used as a raw material for such bead foam (Patent Documents 1 and 2). A bead foam made of polypropylene is easy to mold, but the compressive strength of the foam itself is not sufficient, and in order to improve the compressive strength, it was necessary to reduce the expansion ratio of the bead foam.
However, if the expansion ratio is reduced, there is a problem that the mass of the foam increases and the weight of the automobile increases.

  Therefore, with the conventional thermoplastic resin bead foam, it has been difficult to achieve both weight reduction and compressive strength of the bead foam.

JP 2007-320275 A JP 2009-256460 A

  An object of the present invention is to provide a bead foaming method that is lightweight, has a large average cell diameter, and has a high compressive strength, and a method for producing the same.

The object of the present invention has been achieved by the following means.
The inventors of the present invention have made extensive studies in order to obtain a bead foam having a high average cell diameter and a high compressive strength. As a result, the 10% compressive stress σ ₁₀ (kPa) and the density ρ (kg / m ³ ) It was found that the ratio is related, and based on this finding, the present inventors made the present invention.
That is, the present invention
<1> Thermoplastic resin bead foam, wherein a numerical value σ ₁₀ / ρ obtained by dividing 10% compression stress σ ₁₀ (kPa) by density ρ (kg / m ³ ) is 5 or more,
<2> The thermoplastic resin bead foam according to <1>, wherein the thermoplastic resin is a polyester resin;
<3> The thermoplastic resin bead foam according to <1> or <2>, wherein the thermoplastic resin is polyethylene terephthalate or polycarbonate;
<4> The thermoplastic resin bead foam according to any one of <1> to <3>, wherein the foam has a number average cell diameter of more than 0 μm and 50 μm or less,
<5> In producing the thermoplastic resin bead foam according to any one of <1> to <4>, after impregnating an inert gas into unfoamed thermoplastic resin particles in the pressure vessel, the pressure vessel A thermoplastic resin foam characterized by releasing unfoamed resin particles into which gas has permeated by releasing the pressure inside, and heating the particles to a temperature equal to or higher than the glass transition point of the resin constituting the particles. Body manufacturing method,
Is to provide.

In the present invention, the numerical value obtained by dividing the compressive strength (kPa unit) by the density (kg / m ³ unit) is set to 5 or more, so that the compressive strength per unit density satisfies the requirement of absorbing the impact at the time of vehicle collision. Even if the expansion ratio increases, the desired compressive strength can be maintained, and a foam that is lightweight, has high compressive strength, and is resistant to impact can be obtained.

It is a flowchart which shows an example of the manufacturing method of a thermoplastic resin bead foam.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
The thermoplastic resin bead foam of the present invention is characterized in that a numerical value obtained by dividing 10% compression stress (kPa) by density (kg / m ³ ) is 5 or more.

  If the above numerical value is less than 5, the foam itself becomes too heavy to increase the compressive strength, and if the weight is reduced, the compressive strength may decrease. On the other hand, if it exceeds 10, the compressive strength becomes too high and the impact may not be absorbed. The numerical value is preferably 7 or more, more preferably 7 to 10.

In order to satisfy this requirement, for example, the 10% compressive stress is preferably 400 to 5000 (kPa), more preferably 500 to 3000 (kPa). The density is preferably 50 to 500 (kg / m ³ ), more preferably 100 to 400 (kg / m ³ ).
Here, the 10% compressive stress is a value obtained by measuring the stress when contracted by 10% in the direction of applying compression at a certain position of the foam in accordance with JIS K 7220 (2006).
The density is a value measured according to JIS K7222.

Preferably, the bead foam has an average cell diameter of 50 μm or less. With this configuration, the weight can be reduced without reducing the compressive strength. In order to form a foam, the average cell diameter is preferably more than 0 μm.
Here, let an average bubble diameter be the value measured based on JIS-K7112.
When the average cell diameter exceeds 50 μm, the average cell diameter becomes too large and the compressive strength tends to decrease.
Further, from the viewpoint of further increasing the compressive strength, the average bubble diameter is more than 0 μm and 30 μm or less, more preferably more than 5 μm and 30 μm or less, particularly preferably 10 to 30 μm.

<Raw material for bead foam>
The thermoplastic resin used as the base material for the thermoplastic resin bead foam is not limited, but polyester-based thermoplastic resins are preferable in terms of availability, resin strength, cost, recyclability, and the like. A group polyester-based thermoplastic resin is preferred.

  Examples of the aromatic polyester-based thermoplastic resin include, but are not limited to, polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polycarbonate. One kind of these may be used alone, or two or more kinds may be mixed and used. Among these, polyethylene terephthalate and polycarbonate are particularly preferable because they are excellent in terms of resin strength, cost, availability, recyclability, ease of bubble miniaturization, and the like.

The aromatic polyester-based thermoplastic resin can reduce the degree of crystallinity by modifying some of the monomer unit molecules constituting the resin in order to increase the adhesion between the beads during the molding of the beads. As a modification method, in addition to phthalic acid or isophthalic acid, terephthalic acid is further modified to a dicarboxylic acid component such as adipic acid, diphenylcarboxylic acid, diphenyl ether dicarboxylic acid, diphenylsulfone dicarboxylic acid, sebacic acid, naphthalenedicarboxylic acid, Ethylene glycol, ethylene glycol, propylene glycol, 1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentane Diol, 1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, thiodiethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 2,2,4,4 -Tetramethyl-1,3-cyclobut Njioru, diethylene glycol, can be suitably selected such as those modified diol component such as triethylene glycol or tetraethylene glycol is not limited thereto. You may use resin which used these 1 type, or resin which combined 2 or more types. When polyethylene terephthalate is used as the aromatic polyester-based thermoplastic resin, considering the balance of physical properties, it is particularly desirable to use terephthalic acid modified to isophthalic acid or ethylene glycol modified to neopentyl glycol. .
Here, modifying means replacing a part of the main chain of the polyester-based thermoplastic resin with another monomer. For example, in the case of polyethylene terephthalate, this corresponds to replacing terephthalic acid with isophthalic acid or replacing ethylene glycol with diethylene glycol.

  With respect to the amount of modification when the aromatic polyester-based thermoplastic resin is modified, it is preferably more than 0 and less than 30% in terms of molar fraction with respect to the composition 100. This is because if the modification amount is too small, the density increases, and conversely if the modification amount increases, it may be difficult to make the bubbles fine. Considering the average cell diameter and density, the amount of modification is preferably 0.1 to 10%, more preferably 0.25 to 5%, particularly preferably 1 with respect to the composition 100 as a molar fraction. To 3.75%.

A method for confirming the amount of modification when the aromatic polyester-based thermoplastic resin is modified can be performed using ¹ H-NMR, but is not limited thereto. For example, using ¹ H-NMR, the measurement of the component ratio of isophthalic acid or neopentyl glycol is performed by comparing the integrated intensity ratio of the peak observed in a specific region with the integrated intensity ratio of terephthalic acid or ethylene glycol. Can be sought.

  You may add the cell nucleating agent for refine | miniaturizing a bubble to the bead foam of this invention as needed. As the cell nucleating agent, inorganic fine particles such as talc, calcium carbonate, titanium oxide, and barium sulfate, heat-decomposable organic cell nucleating agent, thermoplastic elastomer, and melt-type crystallization nucleating agent can be used. It is not limited to.

  In the bead foam, in addition to the bubble nucleating agent, as long as the purpose of the present invention is not impaired, a foaming agent, a crystallization accelerator, an antioxidant, an antistatic agent, an ultraviolet ray preventing agent, Light stabilizers, fluorescent brighteners, pigments, dyes, compatibilizers, lubricants, reinforcing agents, flame retardants, crosslinking aids, plasticizers, thickeners, thickeners, thermal stabilizers, processing aids, impact modifiers Various additives such as a quality agent and a filler can be blended.

  The foaming agent is classified into a solid compound that decomposes to generate a gas, a liquid that vaporizes when heated, an inert gas that can be dissolved in a resin under pressure, and any of these can be used. Among these, as solid compounds, for example, azodicarbonamide, dinitrosopentamethylenetetramine, hydrazole dicarbonamide, sodium bicarbonate, p, p'-oxybisbenzenesulfonylhydrazide (OBSH), N, N'-dinitrosopentamethylene Examples thereof include tetramine (DPT), p-toluenesulfonyl hydrazide, benzenesulfonyl hydrazide, diazoaminobenzene, N, N′-dimethyl-N, N′-dinitroterephthalamide, and azobisisobutyronitrile. Examples of the liquid to be vaporized include saturated aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane and hexane, aromatic hydrocarbons such as benzene, xylene and toluene, methyl chloride and chlorofluorocarbon. And halogenated hydrocarbons such as dimethyl ether and ether compounds such as methyl tert-butyl ether. Further, examples of the inert gas include inert gases such as carbon dioxide, nitrogen, helium, and argon, and alternative chlorofluorocarbons. Carbon dioxide (carbon dioxide gas) is more preferable in consideration of the solubility in the resin and the ease of miniaturization of the bubbles.

<Bead Foam Molding Method>
In producing such a thermoplastic resin bead foam, first, pre-foam particles are formed using the thermoplastic resin or the like.
Here, the pre-expandable particles mean particles having an ability to become a foam by heating, and may be already slightly foamed or not foamed.

  The pre-expandable particles can be produced by either an extrusion method or a batch method. In the case of the extrusion method, the foamed particles can be obtained by later cutting the rod-like foam extruded from the extruder by extrusion foaming into an appropriate length. The timing of cutting the rod-like foam into particles may be immediately after the rod-like foam is extruded, or may be after the foam is cooled and the shape is stabilized after extrusion. In the case of the batch method, first, thermoplastic resin particles mixed with a blowing agent in a pressure vessel are prepared. The particles may be pre-expanded particles that are foamed by heating and foaming, or may be non-foamed pre-expandable particles in which a foam is mixed in a resin. The size of the pre-expandable particles is preferably about 0.5 to 2 mm.

  For example, as shown in FIG. 1 (a), a non-foamed thermoplastic resin 3 is sealed in a pressure vessel 1 having a pressure gauge 2, and an inert gas such as carbon dioxide, nitrogen, or helium is injected. Thereafter, the unexpanded pre-expandable particles 4 which are held in an atmosphere of a gas press-fitted at a desired pressure until immediately before being used for in-mold foam molding in a mold, are released immediately before molding and the gas has penetrated. Can be manufactured. In particular, when carbon dioxide gas is used as the gas, the solubility of the gas in the resin is high, so that the resin can be easily foamed and the bubbles can be made finer.

The amount of impregnation of the inert gas into the unfoamed thermoplastic resin 3 is preferably 6% by mass or more, whereby the bubbles can be made finer in the bead foam.
The pressure in the pressure vessel 1 is preferably maintained at 4 to 8 MPa, more preferably 5 to 7 MPa. In this range, the thermoplastic resin can be sufficiently replenished with the inert gas, It can be miniaturized.

Next, the pressure in the pressure vessel is released and the pre-expandable particles 4 into which the gas has permeated are collected, and the bead molding die 5 that can be closed but cannot be sealed as shown in FIG. The pre-expandable particles 4 are supplied in a short time.
Supplying to a metal mold | die for a short time can be supplied to the following process, without impairing the shape of a pre-expandable particle, etc., Preferably it is less than 10 minutes, More preferably, it is performed in 5 minutes.

The volume filling rate of the unfoamed resin of the pre-foamed material with respect to the inner volume of the bead molding die 5 is preferably 1 / φ or more, where φ is the target expansion ratio.
By setting it within the above range, a foam filled in the mold can be obtained without lowering the expansion ratio.

Next, heating to a temperature equal to or higher than the glass transition point of the supplied thermoplastic resin, or steam as a heating medium is introduced into the bead molding die 5 and the inside of the die is heated to perform in-mold foam molding, pre-foaming property The bead foam 6 can be manufactured by molding the particles 4 simultaneously with foaming.
If it is above the glass transition point, the thermoplastic resin can be sufficiently foamed.

  As the heating medium, hot air, oil, or the like can be used in addition to steam, but steam is most effective for efficient molding. When performing in-mold foam molding with steam, as described above, a general-purpose foam molding machine can be used to perform foam molding under normal molding conditions.

  And as shown in FIG.1 (c), the shape | molded foaming molding 6 can be manufactured by taking out from a metal mold | die after cooling.

  According to such a manufacturing method, it is possible to manufacture a thermoplastic resin bead foam that is light and has high compression rigidity, as defined in the present invention, using a conventional mold.

  Since the above-mentioned bead foam is a material that is lightweight and has high compressive strength, it can be used as a core material in various shock absorbing pads of automobiles and blades of wind power generation by utilizing this characteristic. As a member of an automobile, for example, it can be used as a shock absorbing pad installed in a door trim or a pillar on the side of a windshield, but is not limited thereto. As the bead foam of the present invention, one molded into a three-dimensional shape may be used alone, or it may be used with a skin material coated around it. When a soft texture sheet is used for the skin material, there is an advantage that the tactile sensation can be improved while maintaining the impact absorbing performance.

  Further, in order to maintain the overall shape of the automobile member, a shape holding material formed in a plate shape or a frame shape may be incorporated. In addition, various design changes can be made without departing from the scope of the present invention.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these.

Example 1
300 g of resin particle pellets (diameter 3 to 4 mm, glass transition point 69 ° C.) of IP252B (PET resin manufactured by Bell Polyester Products Co., Ltd.) are allowed to stand in a pressure vessel, and carbon dioxide is filled in the pressure vessel. Was set to 5.3 MPa. Then, this container was left for one week under an atmospheric temperature of 17 ° C., and carbon dioxide gas was infiltrated into the pellets. Thereafter, the pressure in the pressure vessel was released to normal pressure, and unfoamed pre-expandable particles into which the gas had permeated were taken out from the vessel. Within 10 minutes after taking out 248 g of these particles, a bead-molding die (the dimensions of the inner surface of the die is 10 cm wide × 10 cm long × 5 cm high) is filled with steam (150 ° C.) with steam. The inside was filled and bead foam molding was performed.
The density of the obtained bead foam was 496 kg / m ³ , and the average cell diameter calculated by observing the cross section with an electron microscope was 15 μm. When a 50 mm square test piece was cut out from the obtained bead foam and subjected to a compression test according to JIS K 7220 (2006), the 10% compression stress was 4,757 kPa and the value of σ ₁₀ / ρ was 9.6. It became.

(Examples 2 to 5)
Examples 2 to 5 were made of the same material as in Example 1 and infiltrated with gas under the same conditions using the unfoamed resin particle filling amount as shown in Table 1. Thereafter, the pressure in the pressure vessel is released, and the unfoamed resin particles into which the gas has permeated are taken out from the vessel, and a predetermined amount of unfoamed resin particles are put into the same bead molding die as in Example 1 within 10 minutes after taking out. Filled and bead foamed with water vapor. The density, average cell diameter, compressive stress, and σ ₁₀ / ρ values of the obtained bead foam were as shown in Table 1.

(Comparative Example 1)
196 g of foamed beads of Eperan PP (polypropylene resin foam beads manufactured by Kaneka Corp.) (glass transition point -10 ° C) in a bead molding die (the dimensions of the inner surface of the mold are 10 cm wide x 10 cm long x 5 cm high) Filled and bead foamed with water vapor.
The density of the obtained bead foam was 391 kg / m ³ , and the average cell diameter calculated by observing the cross section with an electron microscope was 188 μm. When the compression test was performed on the obtained bead foam, the 10% compression stress was 1,392 kPa, and the value of σ ₁₀ / ρ was 3.6.

(Comparative Examples 2 to 4)
Comparative Examples 2 to 4 are the same materials as Comparative Example 1, and using a filling amount of unfoamed resin particles as shown in Table 1, a bead molding die (the dimensions of the mold inner surface are 10 cm wide × 10 cm long × height 5 cm rectangular parallelepiped), and bead foam molding was performed with water vapor. Table 2 shows the density, average cell diameter, compression stress, and σ ₁₀ / ρ values of the obtained bead foam.

(Comparative Example 5)
43 g of resin particles (3 to 4 mm in diameter) of IP252B (PET resin manufactured by Bell Polyester Products Co., Ltd.) were allowed to stand in a pressure vessel, and 3.5 MPa carbon dioxide gas was filled in the pressure vessel. Then, this container was left for one week under an atmospheric temperature of 17 ° C., and gas was infiltrated into the pellet. Thereafter, the pressure in the pressure vessel is released, and the unfoamed resin particles in which the gas has permeated are taken out from the vessel. X a rectangular parallelepiped having a height of 5 cm), and bead foam molding was performed with water vapor.
The density of the obtained bead foam was 138 kg / m ³ , and the average cell diameter calculated by observing the cross section with an electron microscope was 91 μm. When the compression test was performed on the obtained bead foam, the 10% compression stress was 662 kPa. Therefore, the value of σ ₁₀ / ρ was 4.8.

From the results shown in Tables 1 and 2, Examples 1 to 5 can be molded to satisfy σ ₁₀ / ρ with respect to Comparative Examples 1 to 5, and the compression rigidity can be improved by reducing the weight. It was.

DESCRIPTION OF SYMBOLS 1 Pressure vessel 2 Pressure gauge 3 Thermoplastic resin 4 Pre-expandable particle 5 Bead molding die 6 Bead foam

Claims (5)

A thermoplastic resin bead foam, wherein a numerical value σ ₁₀ / ρ obtained by dividing 10% compression stress σ ₁₀ (kPa) by density ρ (kg / m ³ ) is 5 or more.   The thermoplastic resin bead foam according to claim 1, wherein the thermoplastic resin is a polyester resin.   The thermoplastic resin bead foam according to claim 1 or 2, wherein the thermoplastic resin is polyethylene terephthalate or polycarbonate.   The thermoplastic resin bead foam according to any one of claims 1 to 3, wherein the foam has an average cell diameter of more than 0 µm and 50 µm or less.   In producing the thermoplastic resin bead foam according to any one of claims 1 to 4, after infiltrating an inert gas into unfoamed thermoplastic resin particles in the pressure vessel, the pressure in the pressure vessel And removing the unfoamed resin particles permeated with gas and heating the particles to a temperature equal to or higher than the glass transition point of the resin constituting the particles to produce a thermoplastic resin foam Method.

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