JP7148795B2 - Expandable acrylic resin particles, expanded acrylic resin particles, expanded acrylic resin particles - Google Patents

Description

The present invention provides expandable acrylic resin particles impregnated with a physical blowing agent, expanded acrylic resin particles obtained by expanding the expandable particles, and expanded acrylic resin particles formed by molding the expanded particles in a mold. Regarding.

Conventionally, foamed resin moldings have been used as disappearance patterns for casting. Specifically, the foamed resin molded article is used in the following casting method. First, a foamed resin molded article having a desired shape is embedded in sand that serves as a mold. Molten metal is then poured into the foamed resin molding in the sand. At this time, the foamed resin molding is thermally decomposed and replaced with molten metal. After that, by cooling and solidifying the molten metal, a metal casting having the same shape as the foamed resin molding can be obtained.

As a foamed resin molded body for a disappearing model, a foamed particle molded body made of a polystyrene-based resin has been used. However, in the case of using an expanded particle molded article made of a polystyrene resin, there is a problem that a large amount of soot is generated when the molded article is thermally decomposed. This soot stains the casting surface and causes pinholes inside the casting. It is considered that the soot is generated because the polystyrene resin has an aromatic ring.

In order to reduce the amount of soot generated, Patent Document 1 discloses a technique of using, as a disappearance pattern, a foam molded article made of a (meth)acrylic acid ester polymer having no aromatic ring. However, the polymer described in Patent Document 1 has a relatively high thermal decomposition rate. Therefore, when casting using the foam molded article of Patent Document 1, when the molten metal is poured into the mold, the generation rate of the pyrolysis gas generated from the foam molded article is less than the diffusion of the pyrolysis gas from the inside of the mold to the outside. velocity and can lead to pressure build-up in the mold. If the pressure inside the mold rises excessively, there is a risk that the molten metal will not be able to sufficiently spread inside the mold, or that the molten metal will blow out of the mold.

Therefore, in order to reduce the amount of soot generated and to avoid the deterioration of castability due to the pressure increase in the mold, a (meth)acrylic acid ester having a polycyclic saturated hydrocarbon group was used as the base resin for the foam molded product. Techniques using acrylic resins containing components have been proposed.

For example, Patent Document 2 describes expanded acrylic resin particles containing a methacrylic ester component and an acrylic ester component, at least one of which contains a component having a polycyclic saturated hydrocarbon group, and the expanded acrylic resin particles. An acrylic resin foamed particle molded product obtained by molding particles in a mold is disclosed. Since the foamed bead molded article of Patent Document 2 generates thermal decomposition gas at a lower rate than the foamed molded article of Patent Document 1, it is possible to avoid deterioration of castability due to pressure increase in the mold.

JP-A-1-126348 JP 2015-183111 A

In order to obtain a casting having a smooth casting surface in casting using a disappearance pattern, it is preferable to use an expanded particle molded product with a highly smooth surface as the disappearance pattern. However, in the case of using a mold having a complicated cavity shape when the acrylic resin foamed particles of Patent Document 2 are molded in a mold with a heating medium such as steam, the heating of the foamed particles depends on the part of the cavity. may differ. Therefore, if the molding steam pressure (hereinafter also simply referred to as molding pressure) is lowered, there is a risk that there will be areas where the expanded particles are not sufficiently fused together, or that gaps will be formed between the expanded particles, resulting in poor foaming. There was a risk that the smoothness of the body would decrease.

As described above, the acrylic resin foamed particles of Patent Document 2 require relatively high molding steam pressure during in-mold molding in order to sufficiently fuse the foamed particles together and to improve the smoothness of the molded product. However, there is still room for improvement from the viewpoint of moldability in in-mold molding and a wide range of molding conditions.

The present invention has been made in view of the above background, and the range of molding pressure that can reduce the generation rate of pyrolysis gas, can reduce the generation rate of pyrolysis gas, and can form a good molded article. An object of the present invention is to provide expandable acrylic resin particles capable of obtaining expanded acrylic resin particles having excellent moldability under a wide range of molding conditions, and to provide an acrylic resin expanded particle molded product obtained by molding the expanded particles in a mold. It is something to do.

One aspect of the present invention is expandable acrylic resin particles containing an acrylic resin and a physical blowing agent,
The acrylic resin is
It is a copolymer of methacrylic acid ester and acrylic acid ester,
The molar ratio of the methacrylic acid ester component (A) to the total 100 mol% of the methacrylic acid ester component (A) and the acrylic acid ester component (B) in the acrylic resin is 85 to 99 mol%,
At least one of the methacrylic acid ester component (A) and the acrylic acid ester component (B) contains a component having a polycyclic saturated hydrocarbon group,
The acrylic resin has a glass transition temperature of 112 to 125° C.,
The acrylic resin has a weight average molecular weight of 50,000 to 110,000,
The physical foaming agent is
Containing a chain saturated hydrocarbon having 3 to 6 carbon atoms and an alicyclic saturated hydrocarbon having 5 to 7 carbon atoms,
The content of the physical foaming agent in the expandable acrylic resin particles is 6 to 10% by mass,
In the expandable acrylic resin particles, the content of the alicyclic saturated hydrocarbon in the expandable acrylic resin particles is 0.5 to 1.6 % by mass.

Another aspect of the present invention resides in expanded acrylic resin particles obtained by expanding the expandable acrylic resin particles of the above aspect.

According to still another aspect of the present invention, there is provided an acrylic resin foamed particle molded product obtained by in-mold molding the acrylic resin foamed particles of the above aspect.

The expandable acrylic resin particles (hereinafter referred to as "expandable particles" as appropriate) contain the acrylic resin having the specific composition and a physical blowing agent. As a result, it is possible to obtain expanded acrylic resin beads (hereinafter referred to as “expanded beads” as appropriate) that generate less soot during thermal decomposition and can reduce the generation rate of thermal decomposition gas.

Moreover, the weight average molecular weight of the acrylic resin is within the specific range, and the content of the alicyclic saturated hydrocarbon in the expandable particles is within the specific range. The expanded particles obtained by expanding such expandable particles have excellent fusion bondability even when the molding steam pressure during in-mold molding is reduced. Therefore, the expanded beads have excellent moldability under a wide range of molding conditions.

The acrylic resin foamed bead molded article obtained by in-mold molding of the foamed particles (hereinafter referred to as "expanded bead molded article" as appropriate) reduces the amount of soot generated during combustion and casting, and reduces the amount of soot generated during combustion and casting. Gas generation speed can be slowed down. As a result, castability can be improved. Further, according to the expanded beads, it is possible to easily produce an expanded bead molded article having a complicated shape. Further, the expanded beads can provide an expanded bead molded article having excellent dimensional stability, less voids and less melting on the surface of the expanded bead molded article, and excellent smoothness. Therefore, the foamed particle molded article is particularly suitable for a disappearing model for casting.

FIG. 2 is an explanatory diagram showing the relationship between the weight-average molecular weight of acrylic resins and the content of alicyclic saturated hydrocarbons in Examples.

Next, preferred embodiments of the expandable particles, the expanded particles, and the expanded particle molded product will be described. In this specification, when a numerical value or a physical property value is sandwiched before and after the "~", it is used to include the values before and after it.

The expandable particles contain at least an acrylic resin and a physical blowing agent. Acrylic resin is a copolymer of methacrylic acid ester and acrylic acid ester. The acrylic resin contains a methacrylate component (A) and an acrylate component (B).

As component (A), methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate and 2-ethylhexyl methacrylate can be used. As the component (A), one type of methacrylic acid ester may be used alone, or two or more types may be used in combination. Among these methacrylates, methyl methacrylate is preferably used as component (A).

As component (B), alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate and 2-ethylhexyl acrylate can be used. As the component (B), one type of acrylic acid ester may be used alone, or two or more types may be used in combination. Among these acrylates, it is preferable to use methyl acrylate as the component (B).

In the acrylic resin, the molar ratio of component (A) to the total 100 mol % of component (A) and component (B) is 85 to 99 mol % as described above. By setting the molar ratio of the component (A) within the above specific range, it is possible to reduce the generation rate of pyrolysis gas and improve the expandability of the expandable particles and the moldability during in-mold molding.

The molar ratio of component (A) is preferably 98 mol % or less, more preferably 97 mol % or less. In this case, the effect of improving the expandability of the expandable particles and the moldability at the time of in-mold molding can be obtained, and the generation rate of the pyrolysis gas can be further reduced, and the castability can be further improved. Also, the molar ratio of component (A) is preferably 90 mol % or more, more preferably 92 mol % or more. In this case, it is possible to improve the expandability of the expandable particles and the moldability during in-mold molding while obtaining the effect of further reducing the generation rate of pyrolysis gas.

If the molar ratio of component (A) is too high, a large amount of tertiary radicals are likely to be generated due to thermal decomposition of component (A) during decomposition of the acrylic resin. Since tertiary radicals are relatively stable, when the amount of tertiary radicals increases, depolymerization called a zipper reaction tends to proceed. Therefore, in this case, the decomposition reaction rate of the acrylic resin increases, which may lead to an increase in the generation rate of thermal decomposition gas.

On the other hand, if the molar ratio of component (A) is too low, the zipper reaction can be suppressed and the generation rate of pyrolysis gas can be reduced, but the expandability of the expandable particles and the moldability during in-mold molding can be reduced. may decrease.

At least one of the component (A) and the component (B) contains a component having a polycyclic saturated hydrocarbon group. That is, the component containing a polycyclic saturated hydrocarbon group may be the methacrylic acid ester component (A) or the acrylic acid ester component (B). Moreover, both the methacrylate component (A) and the acrylate component (B) may contain a component having a polycyclic saturated hydrocarbon group.

Further, when component (A) contains a component having a polycyclic saturated hydrocarbon group, even if a part of component (A) is a component having a polycyclic saturated hydrocarbon group, Alternatively, all of them may be components having a polycyclic saturated hydrocarbon group. Similarly, when component (B) contains a component having a polycyclic saturated hydrocarbon group, a part of component (B) is a component having a polycyclic saturated hydrocarbon group Alternatively, all of them may be components having a polycyclic saturated hydrocarbon group.

In component (A) and/or component (B), polycyclic saturated hydrocarbon groups are ester-bonded to (meth)acrylic acid. (Meth)acrylic acid is a concept including acrylic acid and/or methacrylic acid. More preferably, the polycyclic saturated hydrocarbon group is contained in component (A).

A component having a polycyclic saturated hydrocarbon group can enhance impregnation of the blowing agent into the acrylic resin. Therefore, the acrylic resin containing a component having a polycyclic saturated hydrocarbon group can improve the expandability of the expandable particles. Furthermore, since the polycyclic saturated hydrocarbon group is a bulky substituent, it becomes easy to adjust the glass transition temperature of the acrylic resin within the above range. Therefore, since the moldability during in-mold molding is improved, even when molding is performed using a mold having a cavity with a complicated shape, an expanded bead molded article with excellent smoothness and good appearance can be easily obtained. becomes possible to obtain.

The acrylic resin may contain one polycyclic saturated hydrocarbon group, or two or more polycyclic saturated hydrocarbon groups. The polycyclic saturated hydrocarbon group is preferably a dicyclopentanyl group, an adamantyl group, a norbornyl group, or an isobornyl group, more preferably a dicyclopentanyl group or an isobornyl group, and an isobornyl group. is more preferred. In this case, the effects described above can be further enhanced. From the same point of view, in the acrylic resin, it is particularly preferable that the component (A) is methyl methacrylate and isobornyl methacrylate, and the component (B) is methyl acrylate.

The molar ratio of the component having a polycyclic saturated hydrocarbon group to 100 mol % of the total of components (A) and (B) is preferably 7 mol % or less. Within this range, it becomes easier to adjust the glass transition temperature to the range described above, and the moldability during in-mold molding can be further improved. From the same point of view, the molar ratio of the component containing a polycyclic saturated hydrocarbon group is more preferably 6 mol % or less with respect to the total 100 mol % of component (A) and component (B). In addition, from the viewpoint of obtaining the above-mentioned effects more reliably, the molar ratio of the component containing the polycyclic saturated hydrocarbon group is 1 mol per 100 mol% of the total of the component (A) and the component (B). % or more, more preferably 2 mol % or more.

The acrylic resin has a weight average molecular weight of 50,000 to 110,000. If the weight-average molecular weight is too small, problems such as melting of the resin on the surface of the molded article, reduction in smoothness of the molded article, and deterioration in appearance may occur. Moreover, in this case, the mechanical properties of the resulting molded article may deteriorate. On the other hand, if the weight-average molecular weight is too large, the foamed particles may become difficult to fuse together when the molding steam pressure is lowered, or gaps may easily occur between the foamed particles on the surface of the resulting molded product. be. From the viewpoint of avoiding these problems more reliably, the weight average molecular weight of the acrylic resin is more preferably 60,000 to 100,000.

The weight average molecular weight of the acrylic resin is a polystyrene equivalent molecular weight measured by gel permeation chromatography using polystyrene as a standard substance. A method for measuring the weight-average molecular weight of the acrylic resin will be described more specifically in Examples.

The glass transition temperature of acrylic resin is 112 to 125° C. as described above. The glass transition temperature of the acrylic resin can be adjusted by, for example, the blending ratio of the component (A) and the component (B) and the type and amount of the polycyclic saturated hydrocarbon group. If the glass transition temperature of the acrylic resin is too low, when the expanded beads are molded in the mold, the surface of the expanded bead molded product cannot withstand the heat of the steam during the in-mold molding, and part of the surface melts. Otherwise, the foamed particles may be excessively expanded to reduce the smoothness of the surface of the molded product. On the other hand, when the glass transition temperature of the acrylic resin is too high, it becomes difficult to expand the expandable particles using a general expansion machine used for expanding expandable polystyrene particles, etc., resulting in foaming with a low apparent density. It becomes difficult to obtain particles. Further, in this case, the in-mold moldability of the expanded beads may be deteriorated under the condition that the molding steam pressure is low.

The glass transition temperature of the acrylic resin is preferably 114.degree. Also, the glass transition temperature is preferably 123° C. or lower, more preferably 122° C. or lower, and even more preferably 121° C. or lower. In this case, the range of molding conditions for the foamed beads in the in-mold molding becomes wider, and it is possible to more easily produce foamed beads having a complicated shape.

The acrylic resin may contain other monomer components in addition to the component (A) and the component (B) as long as the object of the present invention is not impaired. That is, the acrylic resin may be a copolymer of the component (A), the component (B), and other monomer components. However, if the content of the monomer component having an aromatic ring is excessively high, the amount of soot generated during casting may increase. From the viewpoint of avoiding an increase in the amount of soot, the content of the component having an aromatic ring in the acrylic resin is preferably 5% by mass or less, more preferably 3% by mass or less, Most preferred is 0% by weight, ie no components with aromatic rings.

Moreover, other resins, additives, and the like can be added to the expandable particles within a range that does not hinder the object of the present invention. The content of other components is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less with respect to 100 parts by mass of the acrylic resin.

The expandable particles contain a chain saturated hydrocarbon having 3 to 6 carbon atoms and an alicyclic saturated hydrocarbon having 5 to 7 carbon atoms as a physical foaming agent. Examples of chain saturated hydrocarbons having 3 to 6 carbon atoms include propane, n-butane, isobutane, n-pentane, isopentane, neopentane and n-hexane. These chain saturated hydrocarbons may be used alone or in combination of two or more. Among these, pentane is preferably used as the chain saturated hydrocarbon.

As the C5-C7 alicyclic saturated hydrocarbon, for example, cyclopentane, cyclohexane, cycloheptane and the like can be used. These alicyclic saturated hydrocarbons may be used alone or in combination of two or more. Alicyclic saturated hydrocarbons such as cyclopentane and cyclohexane have the function of a plasticizer in addition to the function of a foaming agent.

The content of the physical foaming agent in the expandable particles is 6-10% by mass. Thereby, expandable particles having excellent expandability can be obtained.

Also, the content of the alicyclic saturated hydrocarbon in the expandable particles is 0.5 to 1.6 % by mass. If the content of the alicyclic saturated hydrocarbon is too low, the fusion between the expanded particles may deteriorate, or gaps may occur between the expanded particles on the surface of the resulting molded product. On the other hand, if the content of the alicyclic saturated hydrocarbon is too high, the resin melts on the surface of the molded article, which may reduce the smoothness and appearance of the molded article. The content of alicyclic saturated hydrocarbons in the expandable particles was adjusted to 0.5 . These problems can be easily avoided by making it 5 to 1.6% by mass.

From the viewpoint of enhancing moldability during in-mold molding of expanded beads, the content of the alicyclic saturated hydrocarbon in the physical blowing agent is preferably 20% by mass or less, more preferably 18% by mass or less. More preferably, it is 16% by mass or less.

In the present invention, the weight-average molecular weight of the acrylic resin and the content of the alicyclic saturated hydrocarbon in the expandable particles are each set within the above specific ranges, so that when the expanded beads are molded in the mold, The foamed particles can be fused to each other even at a low molding steam pressure, and a molded article with high smoothness can be obtained with few gaps between the expanded particles. Therefore, it is possible to obtain expanded beads that can form good molded articles under a wide range of molding conditions.

It is preferable that the content C _CH [mass %] of the alicyclic saturated hydrocarbon in the expandable particles and the weight average molecular weight Mw of the acrylic resin satisfy the relationship of the following formula (1).
Mw≦(−10×C _CH +25)×10 ⁴ (1)

The expandable particles that satisfy the above formula (1) can further improve the fusion between the expanded particles in the obtained expanded bead molded product, and can further increase the mechanical strength.

From the same point of view, it is preferable that the content C _CH [mass %] of the alicyclic saturated hydrocarbon and the weight average molecular weight Mw of the acrylic resin satisfy the relationship of the following formula (2).
(−10×C _CH +12)×10 ⁴ ≦Mw (2)

Further, it is more preferable that the content C _CH [mass %] of the alicyclic saturated hydrocarbon in the expandable particles and the weight average molecular weight Mw of the acrylic resin satisfy the relationship of the following formula (3). .
Mw<(−10×C _CH +23)×10 ⁴ (3)

The expandable particles satisfying the above formula (3), in addition to the effect of satisfying the above formula (1), improve the fusion bondability of the obtained expanded beads, and fuse the expanded beads together even at a low molding steam pressure. can be made Furthermore, in this case, it is possible to reduce the gaps between the expanded particles in the resulting molded article and further improve the smoothness of the surface.

From the same point of view, it is preferable that the content C _CH [mass %] of the alicyclic saturated hydrocarbon and the weight average molecular weight Mw of the acrylic resin satisfy the relationship of the following formula (4).
(−10×C _CH +14)×10 ⁴ ≦Mw (4)

The content of volatile components in the expandable particles is preferably 10% by mass or less, more preferably 9% by mass or less. If the content of the volatile component is within this range, moldability during in-mold molding is further improved, and the foamed bead has a better cell structure. As a result, the strength of the expanded bead molded article can be further improved. In addition, the content ratio of the volatile component in the expandable particles is generally 5% by mass or more.

The average particle size of the expandable particles is preferably 0.3 to 1.5 mm. If the average particle diameter is within this range, the fillability of the expanded particles obtained by expanding the expandable particles into a mold is further improved, so that a molded article having a complicated shape such as a disappearance model can be produced more easily. It becomes possible to obtain easily, and the appearance of the expanded bead molded article is further improved. From the same point of view, the average particle size of the expandable particles is more preferably 0.4 to 1.0 mm.

The method for producing the expandable particles is not particularly limited, and they can be produced by a conventionally known method such as suspension polymerization. When producing expandable particles by suspension polymerization, first, the methacrylic acid ester described above is added to an aqueous medium in which a suitable suspending agent or suspension aid is dispersed in a closed vessel equipped with a stirrer. or an acrylic acid ester is added together with a plasticizer, a polymerization initiator, a chain transfer agent and the like, and the methacrylic acid ester and the like are dispersed in the aqueous medium. Next, the polymerization reaction between the methacrylic acid ester and the acrylic acid ester is started. A physical foaming agent is added into the sealed container during or after the polymerization, and the acrylic resin produced by the polymerization reaction is impregnated with the physical foaming agent. In this way, expandable particles can be obtained.

The weight average molecular weight of the acrylic resin can be adjusted by adjusting the amount of chain transfer agent added during polymerization. The amount of the chain transfer agent to be added is preferably approximately 0.20 to 0.60 parts by mass, more preferably 0.25 to 0.50 parts by mass, with respect to 100 parts by mass of the (meth)acrylic acid ester. is more preferred. By setting the addition amount of the chain transfer agent within the specific range, it is possible to easily adjust the weight average molecular weight of the acrylic resin to the specific range.

As the chain transfer agent, conventionally known chain transfer agents such as n-octylmercaptan and α-methylstyrene dimer can be used, but n-octylmercaptan is more preferably used.

Expanded beads are obtained by expanding expandable particles by, for example, a conventionally known method. Foaming can be performed, for example, by supplying a heating medium such as steam to the expandable particles to heat the expandable particles. Specifically, for example, a cylindrical foaming machine equipped with a stirrer is used to heat the expandable particles with steam or the like to foam them.

The apparent density of the expanded particles is preferably 10-100 kg/m ³ . In this case, it is possible to obtain an expanded bead molding having both physical properties such as strength and lightness. The apparent density of the expanded beads is more preferably 12 to 80 kg/m ³ , and more preferably 15 to 60 kg/m ³ from the viewpoint of obtaining an expanded bead molded article having an excellent balance between physical properties and lightness. More preferred.

The secondary expansion ratio of the expanded beads, which is calculated by the method described later, is preferably 1.0 to 1.5. When the secondary foaming rate is within this range, steam efficiently reaches the interior of the molded article during in-mold molding, making it easier to obtain a molded article with good internal fusion. From this point of view, the secondary foaming ratio is more preferably 1.0 to 1.3, more preferably 1.0 to 1.2.

The expanded bead molded article is produced, for example, as follows. First, a mold having a cavity corresponding to the shape of a desired molded article is filled with expanded particles, and a large number of expanded particles are heated in the mold with a heating medium such as steam. The expanded particles in the cavity are further expanded by heating and fused together. As a result, a large number of expanded beads are integrated to obtain an expanded bead molded article that conforms to the shape of the cavity.

The apparent density of the expanded bead molded product is preferably 10 to 100 kg/m ³ . In this case, both mechanical properties such as strength and light weight can be achieved. The apparent density of the expanded particles is more preferably 12-80 kg/m ³ , still more preferably 15-60 kg/m ³ . In this case, it is possible to obtain an expanded bead molded article having an excellent balance between mechanical properties and lightness.

The foamed particle molded product has properties suitable as a disappearance model for casting, such as less soot generation during combustion, a low generation rate of pyrolysis gas, and excellent surface smoothness. Therefore, the expanded bead molded article is suitable as a disappearance pattern for casting.

The content of water in the expanded bead molded article is preferably 1.0% by mass or less. If the water content is within this range, defects during casting are less likely to occur. The lower limit of the content of water in the expandable particles is approximately 0.3% by mass.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples, and various modifications are possible as long as they do not exceed the gist of the present invention. The temperature in the autoclave means the temperature of the aqueous medium.

(Example 1)
First, 700 g of deionized water, 6.0 g of suspending agent, 4.2 g of surfactant, 1.1 g of sodium acetate as an electrolyte, 2.0 g of sodium acetate as an electrolyte, and 2.0 g of a suspending aid were placed in an autoclave having an internal volume of 3 L and equipped with a stirrer. 5 g was added. The suspending agent is specifically a slurry containing 20.5% by mass of tribasic calcium phosphate (manufactured by Taihei Kagaku Sangyo Co., Ltd.). Further, the surfactant is specifically a disodium dodecyldiphenyl ether sulfonate aqueous solution with a concentration of 1% by mass (specifically, "Pelex (registered trademark) SSH" manufactured by Kao Corporation). Further, the suspension aid is specifically an aqueous potassium persulfate solution having a concentration of 0.01% by mass.

A mixture of 425 g of methyl methacrylate, 50 g of isobornyl methacrylate, and 25 g of methyl acrylate was prepared as a monomer component. In this example, the compounding amount of methyl methacrylate corresponds to 89 mol%, the compounding amount of isobornyl methacrylate corresponds to 5 mol%, and acrylic The compounding amount of methyl acid corresponds to 6 mol %.

To this mixture, 0.66 g of t-butylperoxy-2-ethylhexanoate (specifically, "Perbutyl (registered trademark) O" manufactured by NOF Corporation) as a polymerization initiator and t-butylperoxy -2-Ethylhexyl monocarbonate (specifically, "Perbutyl E" manufactured by NOF Corporation) 0.66 g, cyclohexane 10 g as a physical blowing agent, and n-octyl mercaptan as a chain transfer agent (Tokyo Chemical Industry Co., Ltd. Company) 1.40 g was dissolved. As described above, cyclohexane has a function as a plasticizer in addition to a function as a physical blowing agent.

The melt was introduced into deionized water while stirring the inside of the autoclave at a stirring speed of 400 rpm. After the air inside the autoclave was replaced with nitrogen, the inside of the autoclave was sealed.

The temperature in the autoclave was raised to 70° C. over 1 hour and 15 minutes while the inside of the autoclave was continuously stirred, and the temperature in the autoclave was maintained at 70° C. for 6 hours to carry out the first stage polymerization step. In the first-stage polymerization step, pentane as a physical blowing agent (specifically, a mixture of 80% by mass of n-pentane and 20% by mass of i-pentane) was added 5 hours after reaching 70°C. 80 g was added over 1 hour. The stirring speed was then reduced to 350 rpm after addition of the blowing agent.

After the pre-stage polymerization process was completed, the temperature inside the autoclave was raised to 115° C. over 4 hours, and the post-stage polymerization process was performed while maintaining the temperature at 115° C. for 5 hours. After completing the post-polymerization step, the temperature inside the autoclave was cooled to 35° C. over 4 hours, and further cooled to room temperature.

After cooling, the expandable particles were removed from the contents of the autoclave. The expandable particles were washed with nitric acid to dissolve tribasic calcium phosphate adhering to the surface. After that, the expandable particles were dehydrated and washed using a centrifuge, and water adhering to the surfaces of the expandable particles was removed using a flash dryer.

The expandable particles were then sieved to remove particles with a diameter of 0.30-0.54 mm. Next, 0.03 parts by weight of dimethyl silicone as a liquid additive and 0.04 parts by weight of N,N-bis(2-hydroxyethyl)alkylamine as an antistatic agent are added to 100 parts by weight of the expandable particles. added. Furthermore, a mixture of 0.20 parts by mass of zinc stearate, 0.30 parts by mass of calcium stearate, and 0.07 parts by mass of glycerin monostearate was added and mixed with 100 parts by mass of expandable particles. In this manner, the expandable particles were coated with various additives.

Table 1, which will be described later, shows the charging composition and the like of this example. In the table, MMA is methyl methacrylate, IBOMA is isobornyl methacrylate, MADMA is adamantyl methacrylate, and MA is methyl acrylate. These are monomers. In addition, the value shown in the "molar ratio of component having a polycyclic saturated hydrocarbon group" column in the table is the polycyclic saturated hydrocarbon group with respect to the total 100 mol% of the component (A) and the component (B) and the values shown in the columns of "n-pentane", "i-pentane" and "cyclohexane" are the contents of each physical blowing agent incorporated in the expandable particles.

Using the expandable particles obtained above, the molecular weight, glass transition temperature, content of volatile components, and water content of the acrylic resin were measured and foamability was evaluated by the methods described later.

Next, 200 g of the expandable particles were put into a normal pressure pre-expanding machine with a volume of 30 L. Then, while stirring the expandable particles, steam was supplied into the pre-expanding machine to expand the expandable particles, thereby obtaining expanded particles having an apparent density of 23 kg/m ³ . The obtained expanded particles were allowed to stand at room temperature for 1 day to ripen.

After that, the foamed particles were filled into the mold cavity of a molding machine (DSM-0705VS manufactured by DABO). Next, steam having a pressure of 0.04 MPa, 0.06 MPa, 0.08 MPa or 0.10 MPa (both gauge pressures) is supplied into the cavity to heat the expanded particles for 20 seconds, and then cooled for a predetermined time. did. After that, the expanded bead molding was taken out from the mold. The apparent density of the obtained expanded bead molded product was 23 kg/m ³ . The mold cavity has a rectangular parallelepiped shape of 300 mm long×75 mm wide×25 mm thick. After drying the obtained expanded bead molded article at a temperature of 40° C. for one day, the moldability was evaluated by the method described later.

(Example 2)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of cyclohexane added was changed to 7 g and the amount of chain transfer agent added was changed to 2.00 g. Table 1, which will be described later, shows the charging composition and the like of this example.

(Example 3)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of cyclohexane added was changed to 4.50 g. Table 1, which will be described later, shows the charging composition and the like of this example.

(Example 4)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of the chain transfer agent added was changed to 1.60 g. Table 1, which will be described later, shows the charging composition and the like of this example.

(Example 5)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that 50 g of isobornyl methacrylate as the methacrylate ester component (A) was changed to 50 g of methyladamantyl methacrylate. Table 1, which will be described later, shows the charging composition and the like of this example.

( Reference example 1 )
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of cyclohexane and the chain transfer agent were changed to 2.5 g and 2.5 g, respectively. Table 1, which will be described later, shows the charging composition and the like of this example.

( Reference example 2 )
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of cyclohexane added was changed to 18.5 g. Table 2, which will be described later, shows the charging composition and the like of this example.

(Example 6 )
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of cyclohexane added was changed to 14.0 g. Table 2, which will be described later, shows the charging composition and the like of this example.

( Reference example 3 )
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of cyclohexane added was changed to 14 g, and the amount of chain transfer agent added was changed to 1.6 g. Table 2, which will be described later, shows the charging composition and the like of this example.

( Reference example 4 )
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of cyclohexane added was changed to 12 g, and the amount of chain transfer agent added was changed to 1.9 g. Table 2, which will be described later, shows the charging composition and the like of this example.

(Example 7 )
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of methyl methacrylate added was changed to 465 g and the amount of isobornyl methacrylate added was changed to 10 g. Table 2, which will be described later, shows the charging composition and the like of this example.

(Example 8 )
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of methyl methacrylate added was changed to 415 g and the amount of isobornyl methacrylate added was changed to 60 g. Table 2, which will be described later, shows the charging composition and the like of this example.

(Comparative example 1)
The amount of cyclohexane added was 30 g, the amount of chain transfer agent added was 0.85 g, the holding time at 70 ° C. was 8 hours, the temperature rising time from 70 ° C. to 115 ° C. was 2 hours, and the timing of pentane addition was changed. Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the time required for adding pentane was changed to 30 minutes after 6 hours from reaching 70°C. Table 3, which will be described later, shows the charging composition and the like of this example.

(Comparative example 2)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Comparative Example 1, except that 50 g of isobornyl methacrylate was changed to 50 g of methyladamantyl methacrylate. Table 3, which will be described later, shows the charging composition and the like of this example.

(Comparative Example 3)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of cyclohexane added was changed to 3.5 g, and the amount of chain transfer agent added was changed to 0.85 g. Table 3, which will be described later, shows the charging composition and the like of this example.

(Comparative Example 4)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of the chain transfer agent added was changed to 3.50 g. Table 3, which will be described later, shows the charging composition and the like of this example.

(Comparative Example 5)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of the chain transfer agent added was changed to 0.85 g. Table 3, which will be described later, shows the charging composition and the like of this example.

(Comparative Example 6)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of cyclohexane added was changed to 30 g. Table 3, which will be described later, shows the charging composition and the like of this example.

(Comparative Example 7)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of cyclohexane added was changed to 1 g. Table 3, which will be described later, shows the charging composition and the like of this example.

(Comparative Example 8)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of the chain transfer agent added was changed to 1 g. Table 4, which will be described later, shows the charging composition and the like of this example.

(Comparative Example 9)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that cyclohexane was not added and the added amount of the chain transfer agent was changed to 1.2 g. Table 4, which will be described later, shows the charging composition and the like of this example.

(Comparative Example 10)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of cyclohexane added was changed to 20.0 g and the amount of chain transfer agent added was changed to 2.5 g. Table 4, which will be described later, shows the charging composition and the like of this example.

(Comparative Example 11)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of the chain transfer agent added was changed to 3.5 g. Table 4, which will be described later, shows the charging composition and the like of this example.

(Comparative Example 12)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of cyclohexane added was changed to 4 g and the amount of chain transfer agent added was changed to 1.1 g. Table 4, which will be described later, shows the charging composition and the like of this example.

(Comparative Example 13)
Expandable beads, expanded beads, and expanded bead moldings were produced in the same manner as in Example 1, except that the amount of the chain transfer agent added was changed to 1.1 g. Table 4, which will be described later, shows the charging composition and the like of this example.

A method for measuring the molecular weight, glass transition temperature, content of volatile components, and water content of the acrylic resin using expandable particles, and a method for evaluating expandability will be described below.

"Molecular weight measurement"
A chromatogram of the acrylic resin was obtained by a gel permeation chromatography (GPC) method using polystyrene as a standard substance. Then, based on the obtained chromatogram, the number average molecular weight Mn, weight average molecular weight Mw and z average molecular weight Mz of the acrylic resin were calculated.

HLC-8320GPC EcoSEC manufactured by Tosoh Corporation was used to obtain the chromatogram. After dissolving expandable particles as a measurement sample in tetrahydrofuran (THF) to prepare a sample solution with a concentration of 0.1 wt%, TSKguardcolumn SuperH-H x 1 and TSK-GEL SuperHM-H x 2 are connected in series. Using a column with eluent, tetrahydrofuran (THF), flow rate of THF: 0.6 ml/min, gel permeation chromatography (GPC) was performed to separate the measurement samples according to the difference in molecular weight to obtain a chromatogram. As a measurement sample, expanded particles may be used instead of expandable particles, or an expanded particle molding may be used.

Then, the retention time in the chromatogram obtained by the calibration curve created using standard polystyrene was converted into molecular weight to obtain a differential molecular weight distribution curve. From this differential molecular weight distribution curve, the number average molecular weight Mn, weight average molecular weight Mw and z average molecular weight Mz of the acrylic resin were calculated. These values were as shown in Tables 1-4.

"Measurement of glass transition temperature"
The acrylic resin was extracted from the expandable particles by reprecipitation purification using methanol. Specifically, 1 g of expandable particles was dissolved in 10 mL of methyl ethyl ketone. Next, a container containing 500 mL of methanol was prepared, and the methyl ethyl ketone solution was added dropwise to the methanol while stirring the methanol in the container. This dropwise addition precipitated the resin. The precipitate was collected by filtration and vacuum dried at room temperature to constant weight. The precipitate thus obtained is the acrylic resin. The acrylic resin can also be extracted by performing reprecipitation purification using expanded particles or an expanded particle molded product instead of the expandable particles.

2 mg of the acrylic resin extracted from the expandable particles was weighed, filled into a simple closed pan, and used for measuring the glass transition temperature. The glass transition temperature was measured using a differential scanning calorimeter (“Q1000” manufactured by T.A. Instruments) in accordance with JIS K 7121 (1987). The midpoint temperature of the DSC curve was taken as the glass transition temperature. The glass transition temperatures of the acrylic resins were as shown in Tables 1 to 4.

"Measurement of moisture content"
First, approximately 0.28 g of expandable particles were weighed. By heating the expandable particles to a temperature of 160° C. using a heating moisture vaporizer, the moisture inside the expandable particles was vaporized. This water content was introduced to a Karl Fischer moisture measuring device (“AQ-6” manufactured by Hiranuma Sangyo Co., Ltd.) connected to a heating and moisture vaporizer, and the water content was measured. The water content in the expandable particles was as shown in Tables 1 to 4.

"Measurement of content of volatile components"
About 1 g of expandable particles accurately weighed to four decimal places were dried for 4 hours in a hot air dryer set at a temperature of 120°C. After cooling the dried expandable particles to room temperature, the expandable particles were weighed. The total volatile content was determined from the change in mass before and after heating, and the content of volatile components was determined by subtracting the water content from the total volatile content. The calculation formulas are as follows. Contents of volatile components in the expandable particles were as shown in Tables 1 to 4.
Total volatile content (mass%) = {mass before heating (g) - mass after heating (g)} ÷ mass before heating (g) × 100
Volatile component content (mass%) = total volatile content (mass%) - moisture (mass%)

"Measurement of content of physical blowing agents (cyclohexane, pentane) in expandable particles"
1 g of precisely weighed expandable particles was dissolved in 25 ml of N,N-dimethylformamide (DMF), and measurement was performed by gas chromatography (GC) to determine the content of the physical blowing agent (cyclohexane, pentane) in the expandable particles. quantified. The measurement conditions for gas chromatography are as follows.
Measuring device: Gas chromatograph GC-9A manufactured by Shimadzu Corporation
Column material: glass column with an inner diameter of 3 mm and a length of 3000 mm Column packing:
[Liquid phase name] PEG-20M
[Liquid phase impregnation rate] 25% by mass
[Carrier particle size] 60/80 mesh [Carrier treatment method] AW-DMCS (water washing, baking, acid treatment, silane treatment)
Carrier gas: _N2
Detector: FID (flame ionization detector)
Quantification method: internal standard method

"Measurement of average particle size"
The expandable particles were sieved using a test sieve meeting the specifications of JIS Z8801, and the expandable particles were classified based on the particle size range. By measuring the mass of the expandable particles remaining on the sieve, the mass fraction of the expandable particles in each particle size range was calculated. After determining the particle size distribution from these mass fractions using the Rosin-Rammler distribution formula, based on the obtained particle size distribution, the cumulative under-sieve percentage, that is, the cumulative mass fraction integrated from the small particle side The particle size with a value of 63% by mass was calculated. This value was taken as the average particle size of the expandable particles. The average particle size of the expandable particles was as shown in Tables 1-4.

"Evaluation of foamability"
The evaluation of expandability was carried out by expanding the expandable beads using a tray type foaming machine and measuring the apparent density of the obtained expanded beads. Specifically, first, the expandable beads were expanded by supplying steam of 3 kPa (gauge pressure) to the expandable beads in the shelf foaming machine for 270 seconds to obtain expanded beads. The resulting expanded beads were allowed to air dry at room temperature for 1 day. After that, the expanded beads were filled in a 1 L measuring cylinder, and the mass (g) of the expanded beads per 1 L volume was measured. Then, the apparent density (kg/m ³ ) was calculated by converting the mass per liter of volume into units. In addition, it has shown that foaming property is so high that this apparent density is low. The foamability evaluation results were as shown in Tables 1 to 4.

Next, a method for evaluating secondary foamability using expanded particles will be described below.

"Evaluation of secondary foamability"
The secondary foamability was evaluated based on the secondary foaming ratio, which is the foaming ratio when the foamed beads having an apparent density of 20 kg/m ³ are further foamed (secondary foaming). Specifically, first, expandable particles were expanded using a tray type expansion machine to prepare expanded particles having an apparent density of 20 kg/m ³ . The expanded beads were placed in a tray type expansion machine, and steam was supplied to the tray type expansion machine at 3 kPa (gauge pressure) for 60 seconds to secondary expand the expanded beads to obtain secondary expanded beads. The obtained secondary expanded particles were air-dried at room temperature for 1 day. After that, the secondary expanded particles were filled in a 1 L graduated cylinder, and the mass (g) of the secondary expanded particles per 1 L volume was measured. Then, the apparent density (kg/m ³ ) after the secondary expansion was calculated by converting the mass of the secondary expanded particles per liter of volume.

The secondary expansion rate is a value calculated by dividing the apparent density after secondary expansion (that is, the apparent density of secondary expanded particles) by the apparent density before secondary expansion (20 kg/m ³ ). The secondary foaming rate of each example , reference example and comparative example was as shown in Tables 1 to 4.

Next, evaluation methods for moldability, castability, combustibility and strength using the expanded bead molded article will be described below.

"formability"
The moldability during in-mold molding is evaluated based on the fusion rate and surface properties (gap and surface fusion) of the expanded particles in each of the expanded bead molded articles produced by changing the steam pressure during in-mold molding. be able to.

-Fusion rate The foamed bead molded body was bent in the longitudinal direction so as to be divided into approximately equal parts, and the molded body was broken. After that, the fracture surface of the test piece was observed, and the number of expanded particles broken (material failure) inside the molded article and the number of expanded particles peeled off at the interface of the expanded particles were visually counted. Next, the ratio of the number of foamed particles broken inside the molded body to the sum of the number of foamed particles broken inside the molded body and the number of foamed particles peeled off at the interface was calculated, and expressed as a percentage, fusion rate (%) and Tables 1 to 4 show the fusion rate between the expanded particles in the expanded particle molded article. In the evaluation of the fusion rate, the case where the fusion rate was 60% or more was determined as acceptable, and the case where the fusion rate was less than 60% was determined as unacceptable.

・Surface properties (gap, surface melting)
The surface of the expanded bead molded article was visually observed to evaluate whether or not there were gaps between the expanded particles exposed on the surface and whether or not there were melt marks on the surface of the expanded bead molded article. did.

In the "Gap" column of Tables 1 to 4, almost no gaps between the expanded particles were observed on the surface of the expanded bead molded article, and the symbol "A" was given when the entire surface was smooth. The symbol "B" is given when interstices between the expanded particles are found here and there. In the evaluation of the gap, the cases of symbol "A" and symbol "B" were judged to be acceptable because the surface properties were good, and the case of symbol "C" was judged to be unacceptable because the surface properties were poor.

In addition, in the "surface melting" column of Tables 1 to 4, the symbol "A" is given when almost no melting traces are observed on the surface of the expanded bead molding, and when there are scattered traces of melting on the surface of the expanded bead molding. , and the symbol "C" is indicated when melt traces are observed everywhere on the surface of the expanded bead molded article. In the evaluation of surface melting, the cases of symbol "A" and symbol "B" were judged to be acceptable because the surface properties were good, and the case of symbol "C" was judged to be unacceptable because the surface properties were poor. .

The moldability was evaluated by evaluating the fusion rate, gaps, and surface melting of the foamed particle molded bodies produced at molding steam pressures of 0.04 MPa, 0.06 MPa, and 0.08 MPa as described above, and the results of bending, which will be described later. Based on strength and. In the "Moldability" column of Tables 1 to 4, the gap and surface fusion are "A" and the fusion rate is A symbol "A" is given when the ratio is 60% or more. In addition, in any of the molded bodies produced at a molding steam pressure of 0.04 to 0.08 MPa, the gap and surface fusion are "B" or more (including at least one "B"), and the fusion rate is When it is 60% or more and the bending strength is 270 kPa or more, the symbol "B" is written in the same column.

In addition, in any of the molded bodies produced at a molding steam pressure of 0.04 to 0.08 MPa, the gap and surface fusion are "B" or more (including at least one "B"), and the fusion rate is When it is 60% or more and the bending strength is less than 270 kPa, the symbol "C" is entered in the same column. Then, if the gap or surface melting in at least one of the expanded bead molded articles produced at a molding steam pressure of 0.04 to 0.08 MPa is "C", or the fusion rate is less than 60% In some cases, the symbol "D" was entered in the same column.

In the evaluation of moldability, the above-mentioned symbols "A", "B", and "C" were judged to be acceptable because the moldability was good, and the symbol "D" was rejected because the moldability was poor. I judged.

"Measurement of Moisture Content of Expanded Beads"
First, about 0.3 g of expanded bead molding was weighed. This foamed bead molded article was placed in a heating and moisture vaporizer and heated to a temperature of 160° C. to vaporize the moisture inside the molded article. The vaporized moisture was led to a Karl Fischer moisture measuring device (“AQ-6” manufactured by Hiranuma Sangyo Co., Ltd.) connected to a heating moisture vaporizer, and the moisture content in the compact was measured. The water content in the molded body was as shown in Tables 1 to 4.

Furthermore, castability, combustibility and strength were evaluated by the following methods.

"Castability"
Castability was evaluated by the casting surface of the casting and the appearance during casting. First, expandable particles were expanded to produce expanded particles having an apparent density of about 30 kg/m ³ . Next, the expanded beads were molded in a mold to produce an expanded bead molded body having an apparent density of 30 kg/m ³ and exhibiting a rectangular parallelepiped shape of 75 mm wide×150 mm long×40 mm thick.

A metal was cast by a full mold casting method using this foamed particle molded product as a disappearance model. Specifically, first, an expanded bead molded article coated with a zircon-based mold wash was placed in a flask together with runners and weirs. Then, the flask was filled with sand as a mold. As the sand, an alkali phenol gas curing binder resin (Kaostep (registered trademark) C-800 manufactured by Kao Corporation) was used.

Next, carbon dioxide gas was filled throughout the flask to harden the sand. After attaching the sprue and the escape port, the molten metal was poured from the sprue and casting was performed. As the molten metal, spheroidal graphite cast iron (that is, FCD) was used. The temperature of the molten metal during casting was about 1400°C. After casting was completed, the metal solidified in the flask to form a casting with a shape corresponding to the expanded bead compact. After sufficiently lowering the temperature of the casting in the flask, the casting was removed from the flask and subjected to shot blasting.

・Evaluation of casting surface Castings were visually observed to evaluate the presence or absence of soot defects. Soot defects are cavities and dents that occur on the casting surface and inside the casting caused by the thermal decomposition products of the foamed particle compact (that is, the disappearance model) not being discharged well during casting and remaining in the sand mold. It's about. If there are no or few soot defects, it means that little or no soot is generated during combustion.

In the "casting surface" column of Tables 1 to 4, the symbol "A" indicates that the casting has no soot defects, the symbol "B" indicates that the casting has slight soot defects, and the symbol "B" indicates that the casting has soot defects. The symbol "C" is indicated when many are found.

・When pouring the molten metal into the sprue as described above, it is possible to visually check for the phenomenon that the molten metal blows back from the sprue, that is, the phenomenon that the molten metal blows out from the sprue due to the pyrolysis gas generated from the expanded bead compact. It was judged. In Tables 1 to 4, the column "state of molten metal pouring" shows the symbol "A" when there is no blowback, the symbol "B" when there is a slight blowback, and the symbol "C" when there is severe blowback. ” was described.

"Amount of generated soot"
A test piece having dimensions of 75 mm long×25 mm wide×25 mm thick was cut out from an expanded bead molded product having an apparent density of 20 kg/m ³ . The specimen was mounted horizontally in a clamp and the flame was brought into contact with the specimen. At this time, the amount of generated soot was visually observed and evaluated according to the following criteria. In the "soot amount" column of Tables 1 to 4, the symbol "A" indicates little soot generation, the symbol "B" indicates little soot generation, and the symbol "C" indicates large soot generation. Described.

"Bending strength"
By performing in-mold molding of the expanded particles at a molding steam pressure of 0.08 MPa, an expanded particle molded article having an apparent density of 22 kg/m ³ and exhibiting a plate shape of 300 mm long × 75 mm wide × 25 mm thick was produced. did. Using this molded body as a test piece, a three-point bending test was performed in accordance with the bending test method using a large test piece described in Annex 1 of JIS K7221-2 (1999) to obtain a stress-strain curve. . The bending stress at the maximum load calculated based on this stress-strain curve was defined as the bending strength of the expanded bead molded article. For the three-point bending test, a universal testing machine ("Autograph (registered trademark)" manufactured by Shimadzu Corporation) was used, and the test was performed under the conditions of a distance between lower fulcrums of 200 mm and a test speed of 10 mm/min. The flexural strengths of the expanded bead moldings were as shown in Tables 1 to 4.

"compressive strength"
A rectangular parallelepiped specimen having a length of 50 mm, a width of 50 mm and a thickness of 25 mm was cut from the central portion of an expanded bead molded product having an apparent density of 22 kg/m ³ produced by in-mold molding of the expanded beads at a molding steam pressure of 0.08 MPa. Taken. Using this test piece, a three-point bending test was performed according to JIS K6767 (1999), and the compressive load at a strain of 10% was measured. The compressive stress (10% compressive stress) was obtained by dividing the compressive load at a strain of 10% by the pressure-receiving area of the test piece. For the three-point bending test, a universal testing machine ("Autograph (registered trademark)" manufactured by Shimadzu Corporation) was used, and the test was performed under the conditions of a distance between lower fulcrums of 200 mm and a test speed of 10 mm/min. The 10% compressive stress of the expanded bead molding was as shown in Tables 1-4.

In Comparative Examples 3 to 13 shown in Tables 3 and 4, good expanded bead moldings could not be obtained at molding steam pressures in the range of 0.04 to 0.10 MPa. was not evaluated.

In FIG. 1, the weight average molecular weight Mw (C) of the expandable particles of Examples 1 to 8, Reference Examples 1 to 4, and Comparative Examples 1 to 13 is plotted on the vertical axis, and the weight average molecular weight Mw (C) of the saturated alicyclic hydrocarbon is plotted. A plot with content (D) values on the horizontal axis is shown. 1 indicate Examples 1-8 and Reference Examples 1-4 , and diamond-shaped markers indicate Comparative Examples 1-13. In addition, in FIG. 1, a straight line L1 with a weight average molecular weight Mw (C) of 50000, a straight line L2 with a weight average molecular weight Mw (C) of 110000, and an alicyclic saturated hydrocarbon content (D) of 0 A straight line L3 with a content of .2% by mass and a straight line L4 with a saturated alicyclic hydrocarbon content (D) of 2.5% by mass are shown.

As shown in Tables 1 and 2, the expandable particles of Examples 1 to 8 contain the acrylic resin having the specific composition and the physical blowing agent. Therefore, the expanded particle molded article obtained from these expandable particles reduces the amount of soot generated during thermal decomposition, reduces the generation rate of thermal decomposition gas, and suppresses the occurrence of blowback during casting. can be done.

Furthermore, the weight average molecular weight Mw (C) of the acrylic resin in the expandable particles of Examples 1 to 8 was within the above-mentioned specific range, and the content of alicyclic saturated hydrocarbons in the expandable particles (D ) is within the specified range. As a result, even when the molding steam pressure during molding in the mold is low, for example, when the molding steam pressure is 0.04 MPa or 0.06 MPa, it has excellent fusion bondability and excellent smoothness with few gaps. An expanded bead molded article can be obtained. Therefore, the expanded beads obtained from the expandable beads of Examples 1 to 8 have excellent in-mold moldability under a wide range of molding conditions.

On the other hand, in the expandable particles of Comparative Examples 1 to 13 shown in Tables 3 and 4, at least one of the weight average molecular weight Mw (C) of the acrylic resin and the content (D) of the alicyclic saturated hydrocarbon is does not meet a certain range. Therefore, the expanded beads obtained by expanding the expandable beads of Comparative Examples 1 to 13 have moldability at a low molding steam pressure, such as when the molding steam pressure is 0.04 MPa or 0.06 MPa, compared to Examples 1 to 8 . was inferior to the expanded beads obtained from the expandable beads of No. 1, and the range of molding conditions was narrow.

Claims (9)

Expandable acrylic resin particles containing an acrylic resin and a physical blowing agent,
The acrylic resin is
It is a copolymer of methacrylic acid ester and acrylic acid ester,
The molar ratio of the methacrylic acid ester component (A) to the total 100 mol% of the methacrylic acid ester component (A) and the acrylic acid ester component (B) in the acrylic resin is 85 to 99 mol%,
At least one of the methacrylic acid ester component (A) and the acrylic acid ester component (B) contains a component having a polycyclic saturated hydrocarbon group,
The acrylic resin has a glass transition temperature of 112 to 125° C.,
The acrylic resin has a weight average molecular weight of 50,000 to 110,000,
The physical foaming agent is
Containing a chain saturated hydrocarbon having 3 to 6 carbon atoms and an alicyclic saturated hydrocarbon having 5 to 7 carbon atoms,
The content of the physical foaming agent in the expandable acrylic resin particles is 6 to 10% by mass,
The expandable acrylic resin particles, wherein the content of the alicyclic saturated hydrocarbon in the expandable acrylic resin particles is 0.5 to 1.6 % by mass. 2. The expandable acrylic resin particles according to claim 1, wherein the alicyclic saturated hydrocarbon content C _CH [mass %] and the weight average molecular weight Mw satisfy the following formula (1).
Mw≦(−10×C _CH +25)×10 ⁴ (1) 3. The expandable acrylic resin particles according to claim 1, wherein the alicyclic saturated hydrocarbon content C _CH [mass %] and the weight average molecular weight Mw satisfy the following formula (2).
(−10×C _CH +12)×10 ⁴ ≦Mw (2) 2. The molar ratio of the polycyclic saturated hydrocarbon group-containing component to the total 100 mol % of the methacrylic acid ester component (A) and the acrylic ester component (B) is 7 mol % or less. 4. The expandable acrylic resin particles according to any one of 1 to 3. The expandable acrylic resin particles according to any one of claims 1 to 4, wherein the saturated polycyclic hydrocarbon group is a dicyclopentanyl group, adamantyl group, norbornyl group, or isobornyl group. The expandable acrylic resin particles according to any one of claims 1 to 5, wherein the content of said alicyclic saturated hydrocarbon in said physical blowing agent is 20% by mass or less. Expanded acrylic resin particles obtained by expanding the expandable acrylic resin particles according to any one of claims 1 to 6. A molded article of expanded acrylic resin particles obtained by molding the expanded acrylic resin particles according to claim 7 in a mold. 9. The acrylic resin expanded bead molded article according to claim 8, wherein the moisture content is 1.0% by mass or less.

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