JP2012188642A - Preliminary foamed particle of modified polypropylene-based resin and method of manufacturing expansion molding body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preliminary foamed particle of a modified polypropylene-based resin of an high expansion ratio excellent in mechanical characteristics, heat resistance, chemical resistance, and moldability or the like, and to provide a method of manufacturing an expansion molding body.SOLUTION: The method of manufacturing a preliminary foamed particle of modified polypropylene-based resin is characterized as follows. 100 pts.wt. of a polypropylene-based resin is modified by using a polymerization resin that originates in 40-100 pts.wt. of an aromatic vinyl monomer that contains 0.1-1 wt.% of a polyfunctional monomer to obtain a modified polypropylene-based resin particle, 20-50 pts.wt. of a foaming agent is used based on 100 pts.wt. of the modified polypropylene-based resin particle to be performed with an impregnation process to obtain a foaming modified polypropylene-based resin particle, the obtained foaming modified polypropylene-based resin particle is heated by a heated water vapor having 0.1-0.2 MPa of pressure for 5-60 seconds to be preliminarily formed to obtain a preliminary foamed particle of the modified polypropylene-based resin in which the bulk density is 0.01-0.07 g/cm.

Description

  The present invention relates to pre-expanded particles of a modified polypropylene resin and a method for producing a foamed molded product thereof. More specifically, the present invention relates to a method for producing pre-expanded particles of a modified polypropylene resin and a foamed molded product thereof by a general polystyrene resin foaming method, rather than a normal polypropylene resin foaming method.

As thermoplastic resin foams, those using mainly styrene resin particles, polyethylene resin particles and polypropylene resin particles are known.
Among these, foams using polypropylene resin particles are widely used for applications requiring heat resistance because of their high heat resistance.
However, in order to pre-expand the polypropylene resin, a volatile foaming agent is impregnated into the polypropylene resin particles using a pressure resistant container, and the temperature and pressure in the container are adjusted under a pressure higher than the vapor pressure of the volatile foaming agent. A special method is required in which a dispersion of polypropylene resin particles and water is released under a lower pressure atmosphere than the inside of the container (hereinafter referred to as “release foaming”) while being kept constant.
Polypropylene resins have high heat resistance, low gas retention and low foaming properties compared to polystyrene resins, and as a foaming method, release foam is widely used. The method itself is complicated, and there is a problem that a single facility is required.

In contrast, polystyrene resin foams are inferior in heat resistance to polypropylene resin foams, but in general, in order to pre-expand polystyrene resin particles, foam heat A method is used in which plastic particles are introduced and steam is circulated and heated while stirring (hereinafter referred to as “steam foaming”).
Therefore, a method has been desired in which a polypropylene resin can be foamed by vapor foaming in the same manner as a polystyrene resin.

  Japanese Patent Application Laid-Open No. 7-133398 (Patent Document 1) describes a modified polyolefin resin composition excellent in processability and the effect of improving the compatibility between a nonpolar polymer and a polar polymer, processability, impact resistance, and rigidity. And a polyolefin resin composition having excellent surface properties and a foamed molded article comprising the same, and vinyl monomer component (b) 1 to 500 parts by weight with respect to 100 parts by weight of crystalline polyolefin (a) and ( b) after heating an aqueous suspension containing 0.01 to 10 parts by weight of the radical polymerization initiator (c) with respect to 100 parts by weight under conditions where the component (b) is not polymerized by itself, A resin composition (d) obtained by impregnating component (b) into component (a), heating the aqueous suspension above the temperature at which the crystalline portion of component (a) starts melting, and polymerizing component (b) ) Stable to 100 parts by weight Agent (e) a modified polyolefin resin composition containing 0.01 to 20 parts by weight, the polyolefin resin composition comprising the same, foam molded body is disclosed consisting.

  Japanese Patent Laid-Open No. 9-194623 (Patent Document 2) discloses a polypropylene (a) 100 that provides pre-expanded particles made of a polypropylene-based resin having excellent processability and a foam-molded product obtained by molding the same in-mold. Aqueous suspension containing 1 to 500 parts by weight of vinyl monomer component (b) with respect to parts by weight and 0.01 to 10 parts by weight of radical polymerization initiator (c) with respect to 100 parts by weight of component (b) The liquid is optionally heated under conditions in which component (b) is not polymerized by itself, component (b) is impregnated in component (a), and the aqueous suspension is further crystallized in component (a). Pre-expanded particles comprising a modified polypropylene-based resin composition obtained by polymerizing component (b) by heating to a temperature higher than the temperature at which the part substantially starts to melt, and a foamed molded product obtained by molding the same in-mold Is disclosed

  In Patent Documents 1 and 2, an attempt is made to improve workability and impact resistance by adding a vinyl monomer component to a polypropylene resin, but sufficient workability is obtained when there are few vinyl monomer components. In order to obtain it, molding by the foam molding method has many technical problems and requires a special apparatus. On the other hand, when the vinyl component is increased, there is a problem that heat resistance is lowered.

Japanese Patent No. 4064811 (Patent Document 3) discloses a non-crosslinked polypropylene that can achieve fusion between foamed particles with low-temperature steam and can provide a foamed molded article having high rigidity (high compressive strength). Disclosed are methods for stably producing resin-based expanded resin particles and methods for industrially advantageously producing non-crosslinked polypropylene-based resin expanded particles.
In Patent Document 3, a high-melting polypropylene particle surface is modified with an organic peroxide to a substantially non-crosslinked surface, and pre-foaming that can be molded even with low-temperature steam without impairing the heat resistance of the foam-molded product. Although the particles are obtained, there is still a problem that the foaming needs to be foamed and the existing EPS foaming machine cannot be used.

  International Publication No. 2007/99833 (Patent Document 4) discloses modified polypropylene resin expanded particles modified with a large amount of polystyrene resin. These expanded particles are superior in chemical resistance, heat resistance, and perforation impact resistance compared to expanded polystyrene particles. However, if the proportion of polypropylene resin is increased, expanded foam particles with a high expansion ratio can be obtained by the conventional pre-expand method. There is a problem that cannot be obtained.

JP-A-7-133398 JP-A-9-194623 Japanese Patent No. 4064811 International Publication No. 2007/99833

  The present invention can improve the disadvantages of both the polystyrene resin foam molding and the polypropylene resin foam molding by the general polystyrene resin foaming method, rather than the usual polypropylene resin foaming method, It is an object of the present invention to provide a pre-expanded particle of a modified polypropylene resin having a high expansion ratio and excellent in mechanical properties, heat resistance, chemical resistance, moldability, and the like, and a method for producing the expanded molded body.

As a result of intensive research in order to achieve the above-mentioned problems, the present inventors have used polypropylene resin particles having a specific melting point as polypropylene resin particles, and obtained a crosslinkable aromatic vinyl monomer. In addition, by polymerizing in a specific temperature range, the aromatic vinyl resin is cross-linked, the amount of the polypropylene resin increases in the vicinity of the particle surface, the amount of the aromatic vinyl resin increases near the particle center, and the polypropylene. It was found that modified polypropylene resin particles in which a clear resin and an aromatic vinyl resin form a clear sea-island structure can be obtained.
Furthermore, the modified polypropylene resin particles having the sea-island structure manufactured in this way are pre-foamed with foamable resin particles obtained by impregnating a foaming agent, and then the foamed particles are filled into a mold and foamed in the mold. When molded, the advantages of each of polypropylene resin and polystyrene resin can be utilized to obtain a modified polypropylene foam molded article with excellent rigidity, foam moldability, heat resistance, chemical resistance and impact resistance. As a result, the present invention was completed.

Thus, according to the present invention, 100 parts by weight of a polypropylene resin is modified with a polymer resin derived from 40 to 100 parts by weight of an aromatic vinyl monomer containing 0.1 to 1% by weight of a polyfunctional monomer. And using the modified polypropylene resin particles having at least two peaks in the DSC curve of the first measurement and having the lowest peak in the range of 110 to 130 ° C. 100 parts by weight is impregnated with 20 to 50 parts by weight of a foaming agent to obtain foamable modified polypropylene resin particles, and the resulting foamable modified polypropylene resin particles are 0.1 to 0.2 MPa. and prefoamed by heating at a pressure of heating steam 5 to 60 seconds, this bulk density to obtain a pre-expanded particles of the modified polypropylene resin is 0.01~0.07g / cm ³ Method for producing pre-expanded particles, wherein is provided.

  Further, according to the present invention, the pre-expanded particles obtained by the above production method are filled in the mold, and then molded in the mold with steam under a cracking condition of 20 to 50% increase with respect to the volume in the mold. A method for producing a foamed molded product is provided.

According to the present invention, it is possible to improve the disadvantages of both the polystyrene resin foam molding and the polypropylene resin foam molding by the general polystyrene resin foaming method instead of the usual polypropylene resin foaming method. It is possible to provide a pre-expanded particle of a modified polypropylene resin having a high expansion ratio and excellent in mechanical properties, heat resistance, chemical resistance, moldability, and the like, and a method for producing the foamed molded product.
Specifically, pre-expanded particles of modified polypropylene resin and its foam by pressure foaming with steam, which is widely used for polystyrene resin foaming, etc., without using release foaming and requiring no special equipment A foamed molded product can be produced.

  The effect of the present invention is further exhibited by blending 0.1 to 2.0 parts by weight of an inorganic component and prefoaming with respect to 100 parts by weight of the expandable modified polypropylene resin particles.

The polypropylene resin has a melt flow rate at 230 ° C. of 5 to 10 g / 10 min, and the modified polypropylene resin particles have a melt flow rate at 230 ° C. which is 1 to 5 g / 10 min lower than the polypropylene resin. In addition, the first melting peak temperature according to the DSC curve at the time of the second temperature increase of the polypropylene resin is 125 to 145 ° C., so that the effect of the present invention is further exhibited.
Moreover, when the pre-foaming time is 10 to 30 seconds, pre-foamed resin particles with less coalescence can be obtained.

Further, according to the present invention, after filling the pre-expanded particles obtained by the above production method into the mold, when cracking is performed in the mold with water vapor, the cracking is 20 to 50% with respect to the volume in the mold. The low secondary foamability can be compensated for, and a foamed molded product having both excellent physical properties of polypropylene resin and polystyrene resin can be produced.
That is, in the pre-expanded particles of normal polystyrene resin, the secondary foaming power is high, so that the secondary foaming occurs before the vapor reaches the inside, but the pre-expanded particles of the modified polypropylene resin obtained in the present invention Has a low secondary foaming property, and steam flows into the inside to enable foam molding.
Furthermore, the effect of this invention is further exhibited because the water vapor pressure is 0.3 to 0.4 MPa.

It is a figure (calibration curve) which shows the relationship between the light absorbency ratio of an infrared absorption spectrum, and a polystyrene-type resin ratio for calculating | requiring a surface layer polystyrene component ratio. It is a DSC chart for demonstrating the low temperature side peak temperature of the DSC curve of the 1st measurement.

The method for producing pre-expanded particles of the present invention is a polymerization derived from 100 to 100 parts by weight of a polypropylene resin and 40 to 100 parts by weight of an aromatic vinyl monomer containing 0.1 to 1% by weight of a polyfunctional monomer. Modified polypropylene resin particles modified with resin and having at least two peaks in the first DSC curve and having the lowest peak in the range of 110 to 130 ° C. (hereinafter “modified resin particles”) )), And impregnating with 100 to 50 parts by weight of the modified resin particles using 20 to 50 parts by weight of a foaming agent to produce foamed modified polypropylene resin particles (hereinafter also referred to as “foamable resin particles”). The foamable resin particles obtained were prefoamed by heating with heated steam at a pressure of 0.1 to 0.2 MPa for 5 to 60 seconds, and the bulk density was 0.01 to 0.07 g / cm ^3. Is a modified polypro Characterized in that to obtain pre-expanded particles of polyphenylene resin (hereinafter referred to as "modified resin").

  The modified resin particles having the above physical properties include, for example, an aromatic vinyl monomer mixture containing 0.1 to 1% by weight of a polyfunctional monomer in polypropylene resin (hereinafter simply referred to as “aromatic vinyl”). It can also be produced by impregnating a monomer)) and polymerizing it.

(Polypropylene resin)
It does not specifically limit as a polypropylene resin used in this invention, The resin obtained by the well-known polymerization method is mentioned.
In a preferred embodiment of the present invention, examples of the polypropylene resin include a propylene homopolymer and a propylene-ethylene copolymer having a copolymer of propylene and ethylene as a main component. Another monomer that can be copolymerized may be contained in the molecule. Examples of such a monomer include one or more selected from α-olefins, cyclic olefins, and diene monomers.
The polypropylene resin may contain known additives such as a colorant, a flame retardant, an antioxidant, an ultraviolet absorber, and an anti-fusing agent as necessary.

It is preferable that the first melting peak temperature by the DSC curve at the time of the second temperature increase of the polypropylene resin is 125 to 145 ° C. In the case of having two peak temperatures, the first peak temperature (low temperature side) is defined as the melting peak temperature (also referred to as “melting point (mp)” in the present invention).
When the melting peak temperature of the polypropylene resin is less than 125 ° C., the heat resistance is poor, and the heat resistance of the foamed molded article produced using the modified resin particles may be low. On the other hand, when the melting peak temperature of the polypropylene resin exceeds 145 ° C., the polymerization temperature becomes high, and good polymerization may not be possible.

The polypropylene resin preferably has a melt flow rate at 230 ° C. of 5 to 10 g / 10 minutes. More preferably, it is 6-8 g / 10min.
If the melt flow rate of the polypropylene resin is less than 5 g / 10 minutes, sufficient foamability may not be obtained. On the other hand, if the melt flow rate exceeds 10 g / 10 min, sufficient impact resistance may not be obtained.
The method for measuring the melt flow rate (MFR) will be described in detail in Examples.

(Aromatic vinyl monomer)
The aromatic vinyl monomer used in the present invention contains 0.1 to 1% by weight of a polyfunctional monomer.
The aromatic vinyl monomer as the main component is not particularly limited, and examples thereof include styrene, α-methylstyrene, p-methylstyrene, and t-butylstyrene. The aromatic vinyl monomer may be used in combination with another copolymerizable monomer. Examples of other monomers include (meth) acrylic acid alkyl esters that do not contain a benzene ring in the structure such as butyl (meth) acrylate. You may use these other monomers in the range which does not exceed 5 weight% substantially with respect to an aromatic vinyl monomer.

  The polyfunctional monomer as the accessory component is not particularly limited, but an aromatic polyfunctional monomer is preferable, and divinylbenzene is particularly preferable.

When the polyfunctional monomer is less than 0.1% by weight, the degree of crosslinking of the polymer resin of the aromatic vinyl monomer is lowered, the gel fraction of the modified resin particles is not increased, and the strength of the foamed molded product is increased. In addition, heat resistance may not be improved. On the other hand, if the polyfunctional monomer is more than 1% by weight, the degree of cross-linking of the polymer resin of the aromatic vinyl monomer becomes too high, and the foamability of the modified resin particles is greatly reduced, resulting in a high foaming ratio. In some cases, pre-expanded particles that are excellent for molding may not be obtained. A more preferred polyfunctional monomer content is 0.2 to 0.5% by weight.
The weights of the monomer and polymer resin are considered to be approximately the same.

In the present invention, the aromatic vinyl monomer is used in an amount of 40 to 100 parts by weight, preferably 40 to 60 parts by weight, more preferably 40 to 50 parts by weight based on 100 parts by weight of the polypropylene resin.
If the amount of the aromatic vinyl monomer used is less than 40 parts by weight, the rigidity of the foamed molded article obtained by in-mold foam molding of the foamed particles may be lowered.
On the other hand, if the amount of the aromatic vinyl monomer used exceeds 100 parts by weight, the chemical resistance, heat resistance and impact resistance of the foam molded product obtained by in-mold foam molding of the foamed particles may decrease. is there.

(Modified resin particles and their expandable resin particles)
The modified resin particles of the present invention preferably have at least two peaks in the first measurement DSC curve, and the lowest peak is in the range of 110 to 130 ° C. A more preferable temperature range is 118 to 125 ° C.
The “DSC curve for the first measurement” means a DSC curve obtained by thermal analysis of resin particles that have not undergone a thermal history other than the manufacturing process of the modified resin particles.
When the lowest peak in the DSC curve is less than 110 ° C., the heat resistance may be lowered. On the other hand, if the peak exceeds 130 ° C., sufficient foamability may not be obtained.
The DSC curve measurement method will be described in detail in Examples.

The modified resin particles of the present invention preferably have a melt flow rate that is 1 to 7 g / 10 min lower than the melt flow rate at 230 ° C. of the polypropylene resin.
If the reduction in the melt flow rate of the modified resin particles is less than 1 g / 10 minutes, sufficient impact resistance may not be obtained in the foamed molded product. On the other hand, if the decrease in the melt flow rate exceeds 7 g / 10 minutes, the foaming property may decrease. A more preferable decrease width is 1 to 5 g / 10 minutes.

The modified resin particles of the present invention are not particularly limited. For example, the modified resin particles are produced by the following steps (A) to (C) and the expandable resin particles are further subjected to the next step (D). Can be manufactured efficiently and with good yield.
(A) Step (B) of dispersing a dispersion of 100 parts by weight of a polypropylene resin, 40 to 100 parts by weight of an aromatic vinyl monomer, and a polymerization initiator in an aqueous suspension containing a dispersant. Heating the liquid to a temperature at which the aromatic vinyl monomer does not substantially polymerize to impregnate the polypropylene resin particles with the aromatic vinyl monomer (C) melting point of the polypropylene resin in the polypropylene resin particles Is a process of obtaining modified resin particles containing an aromatic vinyl resin by polymerizing an aromatic vinyl monomer at a temperature of (T-20) ° C. to (T + 5) ° C. D) Next, a step of impregnating the obtained modified resin particles with a foaming agent to obtain expandable resin particles

  In the step (A), for example, the polypropylene resin is melted with an extruder and granulated into pellets by strand cutting, underwater cutting, hot cutting, or directly pulverized resin particles with a pulverizer. It is obtained by pelletizing. In addition, examples of the shape include a true spherical shape, an elliptical spherical shape (egg shape), a cylindrical shape, and a prismatic shape. The preferable resin particle diameter of this polypropylene resin is in the range of 0.5 to 1.5 mm, and more preferably in the range of 0.6 mm to 1 mm.

  Examples of the dispersant used in step (A) include organic dispersants such as partially saponified polyvinyl alcohol, polyacrylate, polyvinyl pyrrolidone, carboxymethyl cellulose, and methyl cellulose, magnesium pyrophosphate, calcium pyrophosphate, calcium phosphate, and calcium carbonate. And inorganic dispersants such as magnesium phosphate, magnesium carbonate, and magnesium oxide. Of these, inorganic dispersants are preferred. When using an inorganic dispersant, it is preferable to use a surfactant in combination. Examples of such a surfactant include sodium dodecylbenzene sulfonate and α-olefin sulfonic acid sodium.

  Moreover, as a polymerization initiator, the conventionally well-known polymerization initiator currently used widely for superposition | polymerization of an aromatic vinyl monomer can be used. For example, benzoyl peroxide, lauroyl peroxide, t-amyl peroxy octoate, t-butyl peroxybenzoate, t-amyl peroxybenzoate, t-butyl peroxybivalate, t-butyl peroxyisopropyl carbonate, t- Butyl peroxyacetate, t-butylperoxy-3,3,5-trimethylcyclohexanoate, di-t-butylperoxyhexahydroterephthalate, 2,2-di-t-butylperoxybutane, dicumyl peroxide And azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. In addition, a polymerization initiator may be used independently or may be used together.

  In addition, when adding a polymerization initiator, examples of the addition method include a method of directly adding a polymerization initiator to a polypropylene resin, a method in which a polymerization initiator is dissolved in a solvent, a plasticizer or an aromatic vinyl monomer. And a method of adding after dispersing the polymerization initiator in water. Among these, the method of adding after dissolving a polymerization initiator in an aromatic vinyl monomer is preferable.

  The aromatic vinyl monomer can be continuously or intermittently added to the aqueous medium in order to impregnate the polypropylene resin particles. The aromatic vinyl monomer is preferably gradually added to the aqueous medium. Examples of the aqueous medium include water and a mixed medium of water and a water-soluble medium (for example, alcohol).

In step (B), the dispersion obtained in step (A) is heated to a temperature at which the aromatic vinyl monomer does not substantially polymerize, and the polypropylene resin particles are impregnated with the aromatic vinyl monomer. The temperature at the time of making it, Preferably it is the range of 45-70 degreeC, More preferably, it is the range of 50-65 degreeC.
When the impregnation temperature is less than 45 ° C., the impregnation of the aromatic vinyl monomer is insufficient, and a polymer powder of the aromatic vinyl resin may be generated. On the other hand, when the impregnation temperature exceeds 70 ° C., polymerization may occur before the aromatic vinyl monomer is sufficiently impregnated into the polypropylene resin particles.

In the step (C), the polymerization temperature is an important factor, and when the melting point of the polypropylene raw material resin in the polypropylene resin particles is T ° C, in the step (C), (T-20) ° C to (T + 5) A temperature range of 0 ° C. is preferable.
By polymerizing in such a temperature range, the resin particle center part has a large amount of aromatic vinyl resin (that is, a large amount of polypropylene resin in the surface layer), and as a result, the polypropylene resin The modified resin particles having excellent rigidity, foam moldability, chemical resistance, and heat resistance can be provided by taking advantage of the advantages of each of the aromatic vinyl resin and the aromatic vinyl resin.

  If the polymerization temperature is lower than the above temperature range, the resin particles and the foamed molded article exhibiting good physical properties may not be obtained due to a small amount of the aromatic vinyl resin in the center of the obtained resin particles. In addition, when the polymerization temperature is higher than the above temperature range, polymerization starts before the aromatic vinyl monomer is sufficiently impregnated with the polypropylene resin particles, so modified resin particles exhibiting good physical properties and A foamed molded product may not be obtained. In addition, an expensive polymerization facility with excellent heat resistance that can withstand polymerization at high temperatures is required.

  In addition, the step of polymerizing the aromatic vinyl monomer impregnated with the polypropylene resin particles is divided into two steps, (C1) step (first polymerization) and (C2) step (second polymerization). It may be divided. The reason for dividing into two stages in this way is that when an aromatic vinyl monomer is impregnated in a polypropylene resin at once, the aromatic vinyl monomer is not sufficiently impregnated in the polypropylene resin, This is because it remains on the surface of the polypropylene resin. Therefore, by dividing into two stages, the aromatic vinyl monomer is surely impregnated in the center of the polypropylene resin in the step (C1), and the aromatic vinyl monomer is also polypropylene-based in the step (C2). Impregnation toward the center of the resin.

  When the melting point of the polypropylene resin in the polypropylene resin particles is T ° C, the polymerization temperature is set in the temperature range of (T-5) ° C to (T + 5) ° C in the (C1) step, and the polymerization is performed in the (C2) step. The temperature is preferably in the temperature range of (T−20) ° C. to (T + 5) ° C.

In the step (C), it is preferable to impregnate the resin particles after the completion of polymerization or the resin particles in the second polymerization in the case of two-stage polymerization with a flame retardant. The input temperature when adding the flame retardant is preferably in the range of 30 ° C to 90 ° C, more preferably in the range of 50 ° C to 70 ° C. After the addition, the impregnation temperature when impregnating the flame retardant is preferably in the range of t ° C. to (t + 20) ° C. when the melting point of the flame retardant is t ° C. If the temperature is lower than t ° C, the polypropylene resin particles may not be sufficiently impregnated with the flame retardant. If the temperature is higher than (t + 20) ° C, an expensive polymerization facility excellent in heat resistance is required.
(D) After superposition | polymerization of a process, a reaction tank is cooled and a modified resin particle is obtained by isolate | separating the formed modified resin particle from an aqueous medium.

Next, (D) process is performed and an expandable resin particle is obtained.
In the step (D), the foaming agent impregnated into the modified resin particles, preferably a readily volatile foaming agent, has a boiling point lower than the softening temperature of the polymer and has a readily volatile property, such as propane and n-butane. , I-butane, n-pentane, i-pentane, cyclopentane, carbon dioxide gas, and nitrogen, and these blowing agents can be used alone or in combination of two or more.

The amount of the foaming agent used is in the range of 20 to 50 parts by weight with respect to 100 parts by weight of the modified resin particles.
By setting the amount of the foaming agent used within the above range, sufficient foamability can be maintained even if the primary pressure state is released between the impregnation step and the foaming step.
If the amount of the foaming agent used is less than 20 parts by weight, the resin particles cannot be sufficiently plasticized and foamability may not be sufficiently obtained. On the other hand, when the amount of the foaming agent used exceeds 50 parts by weight, the amount becomes excessive with respect to the resin particles, which is disadvantageous in terms of cost, and combustible gas may be dangerous when foaming. The amount of the foaming agent used is preferably in the range of 20 to 40 parts by weight, more preferably in the range of 25 to 40 parts by weight with respect to 100 parts by weight of the modified resin particles.

  Furthermore, you may use a foaming adjuvant with a foaming agent. Examples of such foaming aids include solvents such as toluene, xylene, ethylbenzene, cyclohexane, and D-limonene, and plasticizers (high-boiling solvents) such as diisobutyl adipate, diacetylated monolaurate, and palm oil. . In addition, as an addition amount of a foaming adjuvant, 0.1-2.5 weight part is preferable with respect to 100 weight part of polypropylene resin particles.

  The method of impregnating the modified resin particles with the foaming agent can be appropriately changed according to the type of the foaming agent. For example, a foaming agent is pressed into an aqueous medium in which modified resin particles are dispersed, and the resin is impregnated with the foaming agent. The modified resin particles are supplied to a rotary mixer, Examples thereof include a method in which a foaming agent is injected and the resin particles are impregnated with the foaming agent. The temperature at which the modified resin particles are impregnated with the foaming agent is usually preferably 50 ° C to 140 ° C.

  Further, a surface treatment agent such as a binding inhibitor, an antistatic agent, or a spreading agent may be added to the expandable resin particles.

  The anti-bonding agent (anti-binding agent) plays a role of preventing the pre-expanded particles from being bonded to each other when the expandable resin particles are pre-expanded. Here, coalescence means that a plurality of pre-expanded particles are united and integrated. Specific examples include talc, calcium carbonate, aluminum hydroxide and the like.

  Examples of the antistatic agent include polyoxyethylene alkylphenol ether and stearic acid monoglyceride. Examples of the spreading agent include polybutene, polyethylene glycol, and silicone oil.

In the preliminary foaming of the modified resin particles, it is preferable that 0.1 to 2.0 parts by weight of an inorganic component is blended and prefoamed with respect to 100 parts by weight of the modified resin particles.
Examples of the inorganic component include inorganic compound particles such as calcium carbonate and aluminum hydroxide exemplified in the above binding inhibitor.

In the method of the present invention, since pre-foaming is performed under high-pressure steam, the organic anti-fusing agent melts during foaming, and it is difficult to obtain a sufficient effect. On the other hand, an inorganic anti-fusing agent such as calcium carbonate has a sufficient anti-fusing effect even under high-pressure steam heating.
Moreover, the preferable range of the particle diameter of an inorganic component is 2 micrometers or less. If the particle size of the inorganic component exceeds 2 μm, a large amount of addition is required, which may adversely affect (inhibit) the subsequent molding process.
The more preferable usage-amount of an inorganic component is 0.2-0.7 weight part with respect to 100 weight part of expandable resin particles.

(Pre-expanded particles of modified resin)
The pre-expanded particles of the modified resin of the present invention can be obtained by pre-expanding expandable resin particles obtained by impregnating the modified resin particles of the present invention with a foaming agent.

Since the modified resin particles of the present invention have low gas retention, the modified resin particles can be foamed by setting the gas impregnation amount (usage amount) to be equal to or higher than the melting point of the modified resin particles. . In addition, since foaming is performed in a temperature range equal to or higher than the melting point, pre-foaming can be performed without coalescence by shortening the foaming time.
Other pre-foaming conditions may be set as appropriate depending on the type of material to be handled and the desired foaming ratio.

The vapor pressure in the preliminary foaming tank is 0.1 to 0.2 MPa, more preferably 0.12 to 0.17 MPa.
By setting the vapor pressure in the pre-foaming tank to the above range, pre-foaming of the modified resin particles becomes possible.
If the vapor pressure in the preliminary foaming tank is less than 0.1 MPa, sufficient foamability may not be obtained. On the other hand, if the vapor pressure in the pre-foaming tank exceeds 0.2 MPa, the resin particles may coalesce in the pre-foaming step.

The pre-foaming temperature is preferably (melting point of modified resin particles−10) ° C. or higher and (melting point of modified resin particles + 5) ° C. or lower, and (melting point of modified resin particles−5) ° C. or higher and (modified) The melting point of the resin particles is more preferably at most 0 ° C. For example, if the melting point of the modified resin particles is 120 ° C, 110 to 125 ° C is preferable, and 115 to 120 ° C is more preferable.
The pre-foaming time is 5 to 60 seconds, preferably 10 to 40 seconds, and more preferably 10 to 30 seconds.

  The pre-expanded particles of the present invention preferably have an aromatic vinyl resin ratio of 40% by weight or less on the surface layer. The lower limit is about 5% by weight. That is, the pre-expanded particles of the present invention have a polypropylene resin exceeding 60% by weight on the surface layer. Thereby, the outstanding effect of this invention is exhibited.

The pre-expanded particles of the present invention have a bulk density (apparent density) of 0.01 to 0.07 g / cm ³ . More preferably, it is 0.04-0.07 g / cm < ³ >.

(Modified resin foam)
The foamed molded product of the modified resin of the present invention is obtained by filling the mold with the pre-expanded particles of the modified resin of the present invention, and then in the mold by cracking under a cracking condition of 20 to 50% increase relative to the volume in the mold. It can be obtained by molding.
If the cracking condition is less than 20%, voids may be generated inside the foam molded article or a foam molded article having excellent dimensional accuracy may not be obtained. On the other hand, if the cracking condition exceeds 50%, the fusion-bonding property of the foamed molded product may be lowered. A more preferable cracking condition is an increase of 20 to 30% with respect to the volume in the mold.

The water vapor pressure in the production of the foamed molded product is preferably 0.3 to 0.4 MPa.
In the production of polystyrene-based foamed molded articles, anti-fusing agents are generally used. However, in the production of polystyrene-based foamed molded products, the anti-fusing agent blended at the time of foaming is washed before the molding process, or stearic acid, which is a blending agent that promotes fusion at the time of molding, is added. The molding is carried out.
On the other hand, in the molding step of the polypropylene resin in the present invention, the anti-adhesion agent at the time of preliminary foaming is carried out by carrying out the heating steam pressure at the time of molding at a pressure higher than the molding pressure of the polystyrene foam molding. The inorganic blending agent added as can be molded without requiring an operation such as removal. A more preferable water vapor pressure is 0.35 to 0.37 MPa.

Hereinafter, specific examples of the present invention will be described by way of examples. However, the following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.
In addition, the gel fraction (vinyl-based component crosslinking degree) in the following examples, the low temperature side peak temperature of the DSC curve of the first measurement, the melting point, the amount of impregnation of the blowing agent, the ratio of the polystyrene component of the surface layer, the pre-foaming time, the bulk density The measurement method and evaluation method for bulk foaming ratio, presence / absence of coalescence, possibility of vapor foaming, moldability, fusion rate, MFR are described below.

(Gel fraction: wt%)
The gel fraction (vinyl component crosslinking degree) is measured by the following method.
0.8 mg of a sample obtained by cutting the modified resin particles or the foamed molded article into a 1 cm square is precisely weighed, and the sample is boiled and heated in 80 mL of xylene for 3 hours using a Soxhlet extraction apparatus. Filter through 80 mesh wire mesh. Thereafter, the insoluble resin on the wire mesh is naturally dried in a draft to evaporate xylene. Next, after confirming that the wire mesh had no xylene odor, the wire mesh was dried in a constant temperature dryer at 120 ° C. for 2 hours, allowed to cool in a desiccator, the weight of the wire mesh was measured, and the gel content (wt% ) Is calculated.
Insoluble resin weight (g) on wire mesh = wire mesh weight after filtration (g) −wire mesh weight before filtration (g)
Gel content (% by weight) = weight of insoluble resin on wire mesh (g) / sample weight (g) × 100

(Low-temperature side peak temperature of the first measurement DSC curve: ° C)
The low temperature side peak temperature (° C.) is measured from the DSC curve by the following method.
From a DSC curve obtained by heating 3 to 7 mg of resin particles from 30 ° C. to 220 ° C. at a heating rate of 10 ° C./min using a scanning differential calorimeter (manufactured by SEIKO, model: DSC200 type) The low temperature side peak temperature (° C) is obtained. The low temperature side means a temperature at a point that first protrudes downward in the DSC chart as shown in FIG.

(Melting point: first melting peak temperature according to DSC curve at second temperature increase: ° C.)
The melting point is measured by the method described in JIS K7122: 1987 “Method of measuring the transition heat of plastic”. That is, using a scanning differential calorimeter (Model: DSC200, manufactured by SEIKO), 7 mg of a sample was filled in a measurement container, and the temperature was 10 ° C. between room temperature and 220 ° C. under a nitrogen gas flow rate of 30 ml / min. The temperature is raised, lowered, and raised repeatedly at an ascending / falling speed of / min, and the melting peak temperature of the DSC curve at the second raising temperature is defined as the melting point. Further, when there are two or more melting peaks, the lower peak temperature is taken as the melting point.

(Foaming agent impregnation amount (foaming agent amount): parts by weight)
The impregnation amount of the foaming agent is calculated by the following formula based on the injection amount (cc) of the foaming agent.
Amount of foaming agent (parts by weight)
= Injection amount of blowing agent (cc) x specific gravity of blowing agent x 100 / amount of raw material (g)

(Surface component polystyrene component ratio: wt%)
The particle surface analysis is performed by ATR infrared spectroscopy by the following method, and the composition ratio of the polystyrene resin and the polypropylene resin is determined from the absorbance ratio of the infrared absorption spectrum. That is, based on a calibration curve prepared using a standard sample containing a known polystyrene component, the polystyrene component ratio is determined from the absorbance ratio of the infrared absorption spectrum of the resin foam particle sample.
Specifically, when the polypropylene resin is a product name “PC540R” manufactured by Sun Allomer Co., Ltd., and the polystyrene resin is a product name “SS142” manufactured by Sekisui Plastics Co., Ltd., the calibration curve shown in FIG. The composition ratio can be known. For example, when the absorbance ratio (D698 / D1376) is 10.0, the polypropylene resin is 20.2% by weight, the polystyrene resin is 79.8% by weight, and the absorbance ratio is 15.0. In this case, the polypropylene resin is 9.1% by weight and the polystyrene resin is 90.9% by weight.
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 are precisely weighed so that the composition ratio (polystyrene resin / polyethylene resin) becomes the following ratio, and mixed uniformly.
Composition ratio (PS / PE; weight ratio): 0/10, 1/9, 2/8, 3/7, 4/6, 5/5, 6/4, 7/3, 8/2, 10/0
This is heated and kneaded under the following conditions in 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

A calibration curve is obtained by the following method.
The absorbance ratio of the standard sample having the above ratio was measured with the above-mentioned measuring apparatus, and the vertical axis represents the polystyrene resin ratio (% by weight), and the horizontal axis represents the absorbance ratio (D698 / D1376). Obtain a calibration curve.
In FIG. 1, when the polystyrene resin ratio is less than 40 wt% and 40 wt% or more, the calibration curves are approximated by the following equations (1) and (2), respectively.
Y = −2.5119X ² + 22.966X (1)
Y = 27.591Ln (X) +16.225 (2)

(Pre-foaming time: seconds)
The pre-foaming time means the time (seconds) from when the foamable resin particles are put into the pre-foaming machine to when the resin particles are impregnated with a readily volatile foaming agent and subjected to pressure foaming. .
More specifically, the inlet of the preliminary foaming tank is opened, the foamable resin particles are introduced into the preliminary foaming tank, the inlet of the preliminary foaming tank is closed, and the time when the pressurized steam starts to flow is set to 0 second. Then, after the expandable resin particles reach the specified expansion ratio, it means the time from the end of steam heating to the extraction of the prefoamed particles from the prefoaming tank.

(Bulk density and bulk foaming ratio: g / cm ³ )
The bulk foaming ratio is measured by the following method.
Filling the pre-expanded particles to the scale of 500 cm ³ into the female cylinder of 500 cm ^3. The graduated cylinder is visually observed from the horizontal direction, and if any pre-expanded particles reach a scale of 500 cm ³ , the filling of the pre-expanded particles into the graduated cylinder is terminated at that point.
Next, the weight of the pre-expanded particles filled in the graduated cylinder is weighed with two significant figures after the decimal point, the weight is defined as W (g), and the bulk density (apparent density) of the pre-expanded particles is expressed by the following formula. The bulk foaming ratio is calculated by calculating and further dividing the resin density by the bulk density.
Bulk density (g / cm ³ ) = W / 500

(With or without fusing)
Pre-foamed particles remaining on top of the mesh after classification after pre-foamed particles are classified with a 1 cm mesh sieve when the resin particles are impregnated with a readily volatile foaming agent and subjected to pressure foaming The case where the weight exceeds 25% of the total amount of the pre-expanded particles is regarded as “attached”.

(Availability of steam foaming)
When the resin particles are impregnated with 40% by weight of a readily volatile foaming agent and foamed under pressure for 10 seconds using steam with a vapor pressure of 0.15 MPa, 15 times or more pre-expanded particles are obtained without coalescence. The case where it is obtained is “◯”, and the case where it is not obtained is “x”.

(Formability)
Pre-expanded particles are aged for about 24 hours, then pre-expanded particles are filled into the mold cavity and steam is introduced into the mold by introducing steam with a vapor pressure of 0.35 MPa into the mold. A foamed molded article having a desired shape is formed by molding and pre-expanded particles by fusing and integrating them. In this case, the case where the fusion rate of the foamed molded product is 5% or more is “◯”, and the case where it is less than 5% is “x”.

(Fusion rate:%)
A 300 mm long and 5 mm deep score line is placed on the surface of a rectangular parallelepiped foam molded body having a length of 400 mm × width of 300 mm × height of 50 mm with a cutter, and the foam molded body is divided into two along the score line. . Then, on the divided surface of the foamed molded product, the number of expanded particles (a) broken in the expanded particles and the number of expanded particles (b) broken at the interface between the expanded particles were measured. The arrival rate is calculated.
Fusing rate (%) = 100 × (a) / [(a) + (b)]

(MFR)
MFR is measured under the conditions of 230 ° C. and 2.16 kg load according to JIS K7210.

(Preparation of raw material A)
100 parts by weight of a polypropylene resin (manufactured by Prime Polymer Co., Ltd., trade name “F-744NP”, MFR: 7, melting point: 140 ° C.) is supplied to an extruder, melt-kneaded, granulated by an underwater cutting method, and elliptically spherical ( Egg-shaped) polypropylene resin particles were obtained. The average weight of the polypropylene resin particles at this time was adjusted to 74 mg per 100 grains.
Next, 1190 g of the obtained polypropylene resin particles are put into a 5 L autoclave with a stirrer, and 2.3 kg of pure water, 30 g of magnesium pyrophosphate, and 0.7 g of sodium dodecylbenzenesulfonate are added as an aqueous medium, and the mixture is stirred and mixed in an aqueous medium. The suspension was held for 10 minutes and then heated to 60 ° C. to obtain an aqueous suspension.
Next, 0.300 kg of a styrene monomer in which 0.6 g of dicumyl peroxide and 0.9 g of divinylbenzene (DVB) were dissolved in the obtained suspension was dropped in 30 minutes. After dropping, the mixture was held for 30 minutes to allow the polypropylene resin particles to absorb the styrene monomer.

Next, the temperature of the reaction system was raised to 140 ° C., the same as the melting point of the polypropylene resin, and held for 2 hours, and the styrene monomer was polymerized (first polymerization) in the polypropylene resin particles.
Next, the temperature of the first polymerization reaction solution is lowered to 120 ° C., which is 20 ° C. lower than the melting point of the polypropylene resin, 1.5 g of sodium dodecylbenzenesulfonate is added to the suspension, and then dicumyl peroxide 1 is added. 0.2 kg of styrene monomer in which 0.5 g and 0.65 g of divinylbenzene were dissolved was added dropwise over 1 hour and polymerized (second polymerization) while being absorbed by the polypropylene resin particles. After completion of dropping, the mixture was held at 120 ° C. for 1 hour, then heated to 140 ° C. and held for 3 hours to complete the polymerization, and modified resin particles were obtained.
Table 1 shows the gel fraction of the obtained modified resin particles (raw material A) and the low-temperature-side peak temperature of the first measurement DSC curve. The obtained modified resin particles had an MFR of 2.

(Preparation of raw material B)
Modified resin particles were obtained in the same manner as in the raw material A, except that a polypropylene resin (manufactured by Sumitomo Chemical Co., Ltd., trade name “Nobrene S-131”, MFR: 1.5, melting point: 133 ° C.) was used.
Table 1 shows the gel fraction of the obtained modified resin particles (raw material B) and the low temperature side peak temperature of the DSC curve of the first measurement. The obtained modified resin particles had an MFR of 1.

(Preparation of raw material C)
100 parts by weight of a polypropylene resin (manufactured by Prime Polymer Co., Ltd., trade name “F-744NP”, MFR: 7, melting point: 140 ° C.) is supplied to an extruder, melt-kneaded, granulated by an underwater cutting method, and elliptically spherical ( Egg-shaped) polypropylene resin particles were obtained. The average weight of the polypropylene resin particles at this time was adjusted to 74 mg per 100 grains.
Next, 850 g of the obtained polypropylene resin particles are put into a 5 L autoclave with a stirrer, and 2.3 kg of pure water, 30 g of magnesium pyrophosphate, and 0.7 g of sodium dodecylbenzenesulfonate are added as an aqueous medium, and the mixture is stirred and mixed in an aqueous medium. The suspension was held for 10 minutes and then heated to 60 ° C. to obtain an aqueous suspension.
Next, 0.210 kg of styrene monomer in which 0.4 g of dicumyl peroxide and 0.65 g of divinylbenzene (DVB) were dissolved in the obtained suspension was dropped in 30 minutes. After dropping, the mixture was held for 30 minutes to allow the polypropylene resin particles to absorb the styrene monomer.

Next, the temperature of the reaction system was raised to 140 ° C., the same as the melting point of the polypropylene resin, and held for 2 hours, and the styrene monomer was polymerized (first polymerization) in the polypropylene resin particles.
Next, the temperature of the first polymerization reaction solution is lowered to 120 ° C., which is 20 ° C. lower than the melting point of the polypropylene resin, and 1.5 g of sodium dodecylbenzenesulfonate is added to the suspension, and then dicumyl peroxide 2 is added. 0.64 kg of a styrene monomer in which 0.5 g and 2.0 g of divinylbenzene were dissolved was dropped over 3 hours and polymerized (second polymerization) while being absorbed by polypropylene resin particles. After completion of dropping, the mixture was held at 120 ° C. for 1 hour, then heated to 140 ° C. and held for 3 hours to complete the polymerization, and modified resin particles were obtained.
Table 1 shows the gel fraction of the obtained modified resin particles (raw material C) and the low-temperature-side peak temperature of the first measurement DSC curve. Moreover, MFR of the obtained modified resin particle was 1.5.

(Preparation of raw material D)
100 parts by weight of a polypropylene resin (manufactured by Prime Polymer Co., Ltd., trade name “F-744NP”, MFR: 7, melting point: 140 ° C.) is supplied to an extruder, melt-kneaded, granulated by an underwater cutting method, and elliptically spherical ( Egg-shaped) polypropylene resin particles were obtained. The average weight of the polypropylene resin particles at this time was adjusted to 74 mg per 100 grains.
Table 1 shows the gel fraction of the obtained polypropylene resin particles (raw material D) and the low-temperature-side peak temperature of the first measurement DSC curve. Further, the MFR of the obtained polypropylene resin particles was 7.
The raw materials A to D are summarized in Table 1. However, the raw material D is unmodified polypropylene resin particles.

Example 1
1 kg of raw material A and 3 L of water were put into a 5 L autoclave with a stirrer, and 350 ml (200 g) of butane as a blowing agent was poured into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 60 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
When the foamable resin particles obtained were heated and foamed for 15 seconds using 0.12 MPa steam in a pressure foaming machine, there was no coalescence, and a bulk foaming magnification of 22 times (bulk density 0.044 g / cm ³ ) Expanded particles were obtained.
Further, when the obtained pre-expanded particles were subjected to in-mold foaming by introducing water vapor with a vapor pressure of 0.35 MPa into the mold under cracking conditions with an increase of 20% with respect to the in-mold volume. The fusion molding rate of the obtained foamed molded product was 80%.

(Example 2)
1 kg of raw material A and 3 L of water were put into a 5 L autoclave with a stirrer, and 700 ml (400 g) of butane as a blowing agent was poured into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 60 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
When the obtained expandable resin particles are heated and foamed for 10 seconds using 0.17 MPa steam in a pressure foaming machine. Pre-expanded particles having a bulk expansion ratio of 26 times (bulk density of 0.037 g / cm ³ ) without coalescence were obtained.
Further, when the obtained pre-expanded particles were subjected to in-mold foaming by introducing water vapor with a vapor pressure of 0.35 MPa into the mold under cracking conditions with an increase of 20% with respect to the in-mold volume. The fusion molding rate of the obtained foamed molded product was 80%.

.
(Example 3)
1 kg of raw material B and 3 L of water were put into a 5 L autoclave with a stirrer, and 350 ml (200 g) of butane as a blowing agent was poured into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 60 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
When the foamable resin particles obtained were heated and foamed for 15 seconds using 0.12 MPa steam in a pressure foaming machine, there was no coalescence and a bulk foaming magnification of 18 times (bulk density 0.054 g / cm ³ ) Expanded particles were obtained.
Further, when the obtained pre-expanded particles were subjected to in-mold foaming by introducing water vapor with a vapor pressure of 0.35 MPa into the mold under cracking conditions with an increase of 20% with respect to the in-mold volume. The fusion molding rate of the obtained foamed molded product was 10%.

Example 4
C1 kg of raw material and 3 L of water were put into a 5 L autoclave with a stirrer, and 350 ml (200 g) of butane as a blowing agent was injected into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 60 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
When the obtained expandable resin particles were heated and foamed for 13 seconds using 0.10 MPa steam in a pressure foaming machine, there was no coalescence and a bulk expansion ratio of 32 times (bulk density 0.031 g / cm ³ ) Expanded particles were obtained.
Further, when the obtained pre-expanded particles were subjected to in-mold foaming by introducing water vapor with a vapor pressure of 0.35 MPa into the mold under cracking conditions with an increase of 20% with respect to the in-mold volume. The fusion molding rate of the obtained foamed molded product was 90%.

(Example 5)
1 kg of raw material A and 3 L of water were put into a 5 L autoclave with a stirrer, and 700 ml (400 g) of butane as a blowing agent was poured into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 60 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
When the foamable resin particles obtained were heated and foamed for 10 seconds using 0.10 MPa steam in a pressure foaming machine, a preliminarily 19-fold bulk density (bulk density 0.051 g / cm ³ ) without coalescence was obtained. Expanded particles were obtained.
Further, when the obtained pre-expanded particles were subjected to in-mold foaming by introducing water vapor with a vapor pressure of 0.35 MPa into the mold under cracking conditions with an increase of 20% with respect to the in-mold volume. The fusion molding rate of the obtained foamed molded product was 80%.

(Example 6)
1 kg of raw material A and 3 L of water were put into a 5 L autoclave with a stirrer, and 700 ml (400 g) of butane as a blowing agent was poured into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 60 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
When the foamable resin particles obtained were heated and foamed for 12 seconds using 0.15 MPa steam in a pressure foaming machine, pre-foaming with a foaming ratio of 32 times (bulk density 0.030 g / cm ³ ) without coalescence was achieved. Particles were obtained.
Further, when the obtained pre-expanded particles were subjected to in-mold foaming by introducing water vapor with a vapor pressure of 0.35 MPa into the mold under cracking conditions with an increase of 20% with respect to the in-mold volume. The fusion molding rate of the obtained foamed molded product was 80%.

(Example 7)
1 kg of raw material A, 10 g of calcium carbonate (particle diameter 0.05 μm) as additive A, and 3 L of water were put into a 5 L autoclave with a stirrer, and 700 ml (200 g) of butane as a blowing agent was injected into a 5 L autoclave with a stirrer. After the injection, the temperature was raised to 60 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
The obtained expandable resin particles were heated and foamed in a pressure foaming machine using steam of 0.20 MPa for 30 seconds, and had a bulk expansion ratio of 25 times (bulk density 0.039 g / cm ³ ) without coalescence. Expanded particles were obtained.
Further, when the obtained pre-expanded particles were subjected to in-mold foaming by introducing water vapor with a vapor pressure of 0.35 MPa into the mold under cracking conditions with an increase of 20% with respect to the in-mold volume. The fusion molding rate of the obtained foamed molded product was 80%.

(Example 8)
1 kg of raw material A, 20 g of calcium carbonate (particle diameter 2 μm) as additive B, and 3 L of water were put into a 5 L autoclave with a stirrer, and 700 ml (200 g) of butane as a blowing agent was injected into a 5 L autoclave with a stirrer. After the injection, the temperature was raised to 60 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
The obtained expandable resin particles were heated and foamed for 30 seconds using 0.20 MPa steam in a pressure foaming machine. As a result, a reserve with a bulk foaming ratio of 24 times (bulk density 0.040 g / cm ³ ) without coalescence was obtained. Expanded particles were obtained.
Further, when the obtained pre-expanded particles were subjected to in-mold foaming by introducing water vapor with a vapor pressure of 0.35 MPa into the mold under cracking conditions with an increase of 20% with respect to the in-mold volume. The fusion molding rate of the obtained foamed molded product was 80%.

(Comparative Example 1)
1 kg of raw material A and 3 L of water were put into a 5 L autoclave with a stirrer, and 175 ml (100 g) of butane as a blowing agent was poured into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 60 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
When the foamable resin particles obtained were heated and foamed for 10 seconds using 0.19 MPa steam in a pressure foaming machine, a preliminary foaming ratio of 12 times (bulk density 0.081 g / cm ³ ) without coalescence was obtained. Expanded particles were obtained.
Further, when the obtained pre-expanded particles were subjected to in-mold foaming by introducing water vapor with a vapor pressure of 0.35 MPa into the mold under cracking conditions with an increase of 20% with respect to the in-mold volume. The fusion molding rate of the obtained foamed molded product was 80%.
As a result, the expansion ratio did not reach 15 times.

(Comparative Example 2)
1 kg of raw material A and 3 L of water were put into a 5 L autoclave with a stirrer, and 350 ml (200 g) of butane as a blowing agent was poured into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 60 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
When the foamable resin particles obtained were heated and foamed for 10 seconds using 0.22 MPa steam in a pressure foaming machine, coalescence occurred frequently, and subsequent molding evaluation and the like were stopped.

(Comparative Example 3)
1 kg of raw material A and 3 L of water were put into a 5 L autoclave with a stirrer, and 700 ml (400 g) of butane as a blowing agent was poured into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 60 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
The obtained expandable resin particles were heated and foamed in a pressure foaming machine using 0.07 MPa steam for 120 seconds. As a result, there was no coalescence and a bulk expansion ratio of 9 times (bulk density of 0.107 g / cm ³ ) Expanded particles were obtained.
Further, when the obtained pre-expanded particles were subjected to in-mold foaming by introducing water vapor with a vapor pressure of 0.35 MPa into the mold under cracking conditions with an increase of 20% with respect to the in-mold volume. The fusion molding rate of the obtained foamed molded product was 80%.
As a result, the expansion ratio did not reach 15 times.

(Comparative Example 4)
D1 kg of raw material and 3 L of water were put into a 5 L autoclave with a stirrer, and 700 ml (400 g) of butane as a blowing agent was injected into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 60 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
When the foamable resin particles obtained were heated and foamed for 15 seconds using 0.20 MPa steam in a pressure foaming machine, there was no coalescence, and the bulk foaming magnification was 8 times (bulk density 0.091 g / cm ³ ). Expanded particles were obtained.
When the obtained pre-expanded particles were subjected to in-mold foaming by introducing water vapor with a vapor pressure of 0.35 MPa into the mold under cracking conditions with an increase of 20% with respect to the volume in the mold, It contracted and a foaming molding could not be obtained.
The foam molded articles of Examples 1 to 8 and Comparative Examples 1 to 4 are summarized in Table 2.

  From the results of Table 2, 100 parts by weight of the modified resin particles are put into a pre-foaming tank together with 20 to 50 parts by weight of the foaming agent, and the foaming agent is impregnated into the modified resin particles. It turns out that the pre-expanded particle | grains which have the outstanding physical property are obtained by heating with pressurized steam of -0.20MPa.

Claims (7)

First, 100 parts by weight of a polypropylene resin was modified with a polymer resin derived from 40 to 100 parts by weight of an aromatic vinyl monomer containing 0.1 to 1% by weight of a polyfunctional monomer. Using modified polypropylene resin particles having at least two peaks in the DSC curve and having the lowest peak in the range of 110 to 130 ° C., a foaming agent for 100 parts by weight of the modified polypropylene resin particles 20-50 parts by weight are impregnated to obtain expandable modified polypropylene resin particles, and the obtained expandable modified polypropylene resin particles are heated with steam at a pressure of 0.1 to 0.2 MPa in 5 to 5 parts. and prefoamed by heating 60 seconds, the pre-expanded particles bulk density and obtaining the pre-expanded particles of the modified polypropylene resin is 0.01~0.07g / cm ³ Manufacturing method.   The method for producing pre-expanded particles according to claim 1, wherein 0.1 to 2.0 parts by weight of an inorganic component is blended and pre-expanded to 100 parts by weight of the expandable modified polypropylene resin particles.   The polypropylene resin has a melt flow rate at 230 ° C. of 5 to 10 g / 10 minutes, and the melt flow rate at 230 ° C. of the modified polypropylene resin particles is 1 to 5 g / 10 minutes lower than the polypropylene resin. The method for producing pre-expanded particles according to claim 1 or 2, wherein:   The method for producing pre-expanded particles according to any one of claims 1 to 3, wherein an initial melting peak temperature according to a DSC curve at the second temperature rise of the polypropylene resin is 125 to 145 ° C.   The method for producing pre-foamed particles according to any one of claims 1 to 4, wherein the pre-foaming time is 10 to 30 seconds.   The pre-expanded particles obtained by the production method according to any one of claims 1 to 5 are filled in the mold, and then the interior of the mold with water vapor is cracked under an increase of 20 to 50% with respect to the volume in the mold. A method for producing a foamed molded article, comprising molding.   The method for producing a foamed molded product according to claim 6, wherein the water vapor pressure is 0.3 to 0.4 MPa.