Method for manufacturing block-like molded article

Abstract

To provide a method for manufacturing a block-like molded article which has excellent fusion rate and surface appearance, and suppresses smoke generation and warpage.SOLUTION: A manufacturing method includes a pre-foaming step of foamable resin particles containing a base material resin containing 50 wt.% or more of a (meth)acrylate unit as a constitutional unit and a foaming agent, a curing step, and a molding step of filling a mold with the cured foamed particles, then introducing vapor into the mold and thereby heating and fusing the foamed particles, and obtaining a block-like molded article, wherein the molding step fills the mold with the cured foamed particles, then decompresses the mold so that a degree of vacuum becomes -0.05 MPa or less before initial vapor introduction, and then continuously performs initial vapor introduction simultaneously from at least two surfaces of the mold for 25 seconds or more, in which at least the two surfaces of the mold include at least a surface corresponding to a surface having a largest area out of the surfaces of the block-like molded article, and in the molding step, at least one of a vapor pressure in the mold reaches 0.040 MPa or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a block-shaped molded product, in particular a method for producing a block-shaped molded product for lost foam casting, and belongs to the field of molded product production, in particular lost foam casting. [Background technology]

[0002] In the field of metal casting, lost foam casting is known, in which a model made from a foam molded body is embedded in casting sand, molten metal is poured into the foam molded body, and a casting is produced by replacing the foam molded body with the metal. The foam molded body used in lost foam casting is usually a molded body obtained by cutting a large block-shaped molded body. Such block-shaped molded bodies have a problem of poor internal fusion due to their relatively large size.

[0003] As materials for forming block-shaped molded products, expandable polystyrene resin (abbreviation: EPS), expandable copolymer resin of methyl methacrylate and styrene (abbreviation: STMMA), and expandable polymethyl methacrylate resin (abbreviation: EPMMA) are usually used.

[0004] Among them, EPS is widely used because of its advantages such as low price and easy molding. Patent Document 1 discloses a method for producing an EPS block-shaped molding, including step a of closing the mold, locking the mold, and filling the raw material, step b of additionally filling or circulating the raw material under vacuum, step c of performing pre-vacuuming, step d of performing steam impregnation multiple times so that the total impregnation time is 18 to 29 seconds, step e of heating and maintaining pressure, step f of decompressing and cooling, and step g of unlocking, opening the mold, demolding, discharging, and resetting. In this method, the density of the EPS block-shaped molding produced is good due to the replenishing of raw material under vacuum, and the curing of the block-shaped molding is uniform due to the pre-vacuuming before heating, so that the mass of the surface part and the center part of the block-shaped molding are the same. On the other hand, since EPS is difficult to thermally decompose, when it is used for lost foam casting, residues are likely to be generated on the casting due to its smoke generation.

[0005] In order to reduce residues caused by EPS, Patent Document 2 discloses a method of producing a lost foam block-shaped molded product for actual mold casting by mixing STMMA beads and EPS beads in a weight ratio of 1:5 to 5:1, pre-expanding, and then sequentially drying and curing, molding, and drying. Patent Document 3 discloses a method of producing a large-sized STMMA block-shaped lost foam for actual mold casting by using STMMA with a relatively large particle size of 0.7 to 0.9 mm as the raw material beads for the foam. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] China Patent Publication No. 101456234A [Patent Document 2] China Patent Publication No. 113680965A [Patent Document 3] China Patent Publication No. 107552725A Summary of the Invention [Problem to be solved by the invention]

[0007] However, although the above-mentioned conventional techniques reduce smoke generation and residues by reducing the amount of EPS used or by not using EPS at all, the present inventors have found that the STMMA block-shaped molded products or EPMMA block-shaped molded products produced by the conventional methods have problems such as insufficient or non-uniform fusion. Such problems are particularly noticeable when producing large block-shaped molded products.

[0008] In view of the above circumstances, one aspect of the present invention aims to provide a manufacturing method capable of obtaining a block-shaped molded product that combines excellent fusion rate and surface properties with reduced smoke generation and warping, in particular a manufacturing method for a block-shaped molded product for a fading model. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have completed the following aspects of the invention. <1> A method for producing a block-shaped molded product, comprising the steps of: A method for producing a block-shaped molded product, comprising the steps of: a pre-expansion step of heating and expanding the expandable resin particles; a curing step of curing the expanded beads obtained in the pre-expanding step; and a molding step of filling a mold with the cured expanded beads and then introducing steam into the mold to heat and fuse the expanded beads to obtain a block-shaped molded product. The expandable resin particles include a base resin containing 50% by weight or more of (meth)acrylic acid ester units as constituent units, and a foaming agent, the molding step includes a step of reducing the pressure inside the mold to a vacuum degree of -0.05 MPa or less after filling the mold with the cured expanded beads and before the first steam introduction, and then continuously introducing the first steam from at least two sides of the mold simultaneously for 25 seconds or more; The at least two surfaces of the mold include at least a surface corresponding to the surface of the block-shaped molded object having the largest area, The manufacturing method includes a step of causing the steam pressure in the mold to reach 0.040 MPa or more at least once in the molding step. <2> In a preferred embodiment of the present invention, in the manufacturing method, steam is introduced into the mold three or less times in the molding step. <3> In a preferred embodiment of the present invention, in the manufacturing method, the molding step further includes a step of, after the initial steam introduction, introducing steam from at least one surface to which steam was not introduced in the initial steam introduction. <4> In a preferred embodiment of the present invention, in the above-mentioned production method, the base resin contains 50% by weight or more of methyl methacrylate units and acrylic ester units in total. <5> In a preferred embodiment of the present invention, in the production method, the acrylate unit is a butyl acrylate unit. <6> In a preferred embodiment of the present invention, in the above-mentioned manufacturing method, the density of the block-shaped molded product is 14 kg / m 3 More than 30kg / m 3 The following is the result. <7> In a preferred embodiment of the present invention, in the above-mentioned production method, the thickness of the thinnest part of the block-shaped molded product is 100 mm or more and 1200 mm or less. <8> In a preferred embodiment of the present invention, the production method further comprises a cooling step of cooling the block-shaped molded product obtained in the molding step. <9> In a preferred embodiment of the present invention, in the above-mentioned manufacturing method, the cooling step is a step of maintaining vacuum suction for 400 seconds or more without spraying water on the mold. <10> In a preferred embodiment of the present invention, in the above-mentioned manufacturing method, the block-shaped molded product is a block-shaped molded product for lost foam casting. Effect of the Invention

[0010] According to one aspect of the present invention, there is provided a manufacturing method capable of obtaining a block-shaped molded product having an excellent fusion rate and surface properties, and suppressing smoke generation and warping, in particular a manufacturing method for a block-shaped molded product for a fading model. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a three-dimensional view showing a rectangular parallelepiped mold. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Exemplary embodiments, features, and aspects of the present invention are described in detail below. As used herein, the term "exemplary" means "serving as an example, example" or "serving for illustration purposes." Any embodiment described herein as "exemplary" should not be construed as superior or better than other embodiments.

[0013] In addition, in order to more conveniently explain the present invention, numerous specific details are described in the following specific embodiments. However, it should be understood by those skilled in the art that the present invention can be similarly implemented without the description of specific details. In addition, in some other embodiments, in order to enhance the spirit of the present invention, methods, means, devices and procedures familiar to those skilled in the art are not described in detail.

[0014] Unless otherwise specified, the units used in this specification are based on the international standard. In addition, it should be understood that the numerical values ​​and numerical ranges according to the present invention include unavoidable system tolerances in industrial production.

[0015] In this specification, the expressions "may," "may," and "may" include both the meanings of performing some processing and not performing it, and the meanings of both the meanings of satisfying and not satisfying the requirements described using the expressions.

[0016] As used herein, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "embodiments," and the like, mean that the particular elements (e.g., features, structures, properties, and / or characteristics) described in connection with the embodiment are included in at least one embodiment described therein and may or may not be present in other embodiments. It should also be understood that such elements may be combined in any suitable manner in the various embodiments.

[0017] In this specification, a numerical range expressed as "numeric value A to numerical value B" means that both ends of the range, A and B, are included within the range.

[0018] In this specification, "normal temperature" and "room temperature" refer to a temperature of 10 to 40°C unless otherwise specified.

[0019] The method for producing a block-shaped molded product according to the present invention comprises the steps of: a pre-expansion step of heating and expanding the expandable resin particles; a curing step of curing the expanded beads obtained in the pre-expanding step; and a molding step of filling a mold with the cured expanded beads and then introducing steam into the mold to heat and fuse the expanded beads to obtain a block-shaped molded product. The expandable resin particles include a base resin containing 50% by weight or more of (meth)acrylic acid ester units as constituent units, and a foaming agent, the molding step includes a step of reducing the pressure inside the mold to a vacuum degree of -0.05 MPa or less after filling the mold with the cured expanded beads and before the first steam introduction, and then continuously introducing the first steam from at least two sides of the mold simultaneously for 25 seconds or more; The at least two surfaces of the mold include at least a surface corresponding to the surface of the block-shaped molded object having the largest area, The molding step includes a step of causing the steam pressure in the mold to reach 0.040 MPa or more at least once.

[0020] According to the above-described manufacturing method and the embodiment of the present invention, it is possible to obtain a block-shaped molded product for lost foam casting, which has both an excellent fusion rate and surface properties and is suppressed in smoke generation and warping, in particular a large block-shaped molded product having a high fusion rate in both the surface portion and the center portion. In this specification, the property of suppressing smoke generation is also referred to as "low smoke generation".

[0021] (Expandable resin particles) First, the expandable resin particles used in the pre-expansion step in the method according to the present invention will be described. Note that the "expandable resin particles" in the present invention refer to resin particles that have the property of being expandable (expandability) and have not undergone expansion (or pre-expansion).

[0022] (Base resin) The expandable resin particles used in the method according to the present invention include a base resin and a blowing agent. The base resin contains (meth)acrylic acid ester units as structural units in a weight percentage of 50% or more by weight relative to 100% by weight of the base resin. In this specification, "(meth)acrylic acid ester" is a general term for acrylic acid ester and methacrylic acid ester. If the content of (meth)acrylic acid ester units in 100% by weight of the base resin is less than 50% by weight, it is difficult to fully exhibit the effects of improving fusion and suppressing smoke generation. From the viewpoint of further exhibiting the technical effects of the present invention, the content of (meth)acrylic acid ester units in 100% by weight of the base resin is preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more. The upper limit of the content is not particularly limited, and may be 100% by weight, for example, 99% by weight, 98% by weight, or 95% by weight.

[0023] From the viewpoint of excellent foaming property and moldability, the base resin preferably contains methyl methacrylate units and acrylic ester units as structural units. From the same viewpoint, the base resin preferably contains methyl methacrylate units and acrylic ester units in total at a weight percentage of 50% or more by weight, more preferably 60% or more by weight, even more preferably 70% or more by weight, and even more preferably 80% or more by weight, based on 100% by weight of the base resin. The upper limit of the content is not particularly limited, and may be 100% by weight, for example, 99% by weight, 98% by weight, or 95% by weight. In this specification, the term "methyl methacrylate unit" refers to a structural unit derived from a methyl methacrylate monomer, and the term "acrylic ester unit" refers to a structural unit derived from an acrylic ester monomer.

[0024] From the viewpoints of excellent foamability and moldability and surface properties, the ratio of the contents of methyl methacrylate units and acrylic ester units in the above-mentioned base resin relative to the total content of methyl methacrylate units and acrylic ester units (100% by weight) is preferably (a) from 80% by weight to 99% by weight for methyl methacrylate and from 1% by weight to 20% by weight for acrylic ester, (b) more preferably from 90% by weight to 98% by weight for methyl methacrylate and from 2% by weight to 10% by weight for acrylic ester, (c) still more preferably from 94% by weight to 98% by weight for methyl methacrylate and from 2% by weight to 6% by weight for acrylic ester; and (d) particularly preferably from 94.5% by weight to 98.0% by weight for methyl methacrylate and from 2.0% by weight to 5.5% by weight for acrylic ester.

[0025] Examples of acrylic acid esters include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, etc., and butyl acrylate, which has a large effect of reducing the glass transition temperature of the base resin, is particularly preferred. In other words, the acrylic acid ester unit may include a butyl acrylate unit derived from butyl acrylate, and a butyl acrylate unit derived from butyl acrylate is preferred. According to this configuration, expandable resin particles with excellent expandability and moldability can be obtained.

[0026] Examples of methacrylic acid esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate. From the viewpoint of polymerization stability, methyl methacrylate is particularly preferred. In other words, the methacrylic acid ester unit may include a methyl methacrylate unit derived from methyl methacrylate, and a methyl methacrylate unit derived from methyl methacrylate is preferred. According to this configuration, it is possible to obtain expandable resin particles having excellent expandability and moldability.

[0027] In addition, from the viewpoint of increasing the strength of the foamed molded article, the base resin may contain a constituent unit derived from an aromatic vinyl compound as a constituent unit. Examples of aromatic vinyl compounds include styrene, α-methylstyrene, p-methylstyrene, tert-butylstyrene, and styrene chloride. From the viewpoint of suppressing ash generated during casting, the amount of aromatic vinyl compound used should be as small as possible, and the weight percentage relative to 100% by weight of the base resin is preferably less than 50% by weight, more preferably less than 20% by weight, and even more preferably less than 5% by weight. The lower limit of the content is not particularly limited, but may be, for example, more than 0% by weight, and from the viewpoint of obtaining excellent surface properties and suppressing ash, it is preferable that the base resin does not contain a constituent unit derived from an aromatic vinyl compound.

[0028] The base resin may also contain a structural unit derived from a crosslinking agent. Examples of crosslinking agents include compounds having two or more functional groups exhibiting free radical reactivity. Among compounds having two or more functional groups exhibiting free radical reactivity, bifunctional monomers having two functional groups can be preferably used as crosslinking agents. Examples of bifunctional monomers include (a) compounds obtained by esterifying hydroxyl groups at both ends of ethylene glycol or its oligomer with acrylic acid or methacrylic acid, such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate; (b) compounds obtained by esterifying hydroxyl groups of diol with acrylic acid or methacrylic acid, such as neopentyl glycol di(meth)acrylate, hexylene glycol di(meth)acrylate, and butylene glycol di(meth)acrylate; and (c) aryl compounds having two alkenyl groups, such as divinylbenzene. As the bifunctional monomer, from the viewpoint of facilitating adjustment of the molecular weight of the base resin, hexylene glycol di(meth)acrylate such as 1,6-hexanediol diacrylate is preferred.

[0029] The content of the structural unit derived from the crosslinking agent in the base resin may be 0.20% by weight or less, preferably 0.15% by weight or less, more preferably 0.10% by weight or less, based on 100% by weight of the base resin. The lower limit of the content is not particularly limited, but may be, for example, more than 0% by weight, and the base resin may not contain a structural unit derived from the crosslinking agent. The above-mentioned configuration has the advantages of (a) the expandable resin particles having excellent expandability, (b) the surface quality of the foamed molded article obtained by molding the expanded particles in a mold is excellent, and (c) the strength is excellent and the residue upon combustion is small.

[0030] (foaming agent) The foaming agent contained in the expandable resin particles used in the method according to the present invention is not particularly limited. Examples of the foaming agent include (a) aliphatic hydrocarbons, such as propane, isobutane, n-butane, isopentane, n-pentane, and neopentane, which belong to the hydrocarbon group having 3 to 5 carbon atoms; and (b) volatile foaming agents, such as hydrofluorohydrocarbons, which have an ozone depletion potential of 0, such as difluoroethane and tetrafluoroethane. These foaming agents may be used alone or in combination of two or more.

[0031] The content of the blowing agent in the expandable resin particles used in the method according to the present invention is preferably 5 to 12 parts by weight, more preferably 7 to 10 parts by weight, based on 100 parts by weight of the base resin. This configuration has the advantage that expandable resin particles having sufficient expandability can be provided and large-scale polymerization equipment is not required.

[0032] (foaming aid) The expandable resin particles used in the method according to the present invention may contain a foaming assistant. The foaming assistant is not particularly limited. As the foaming assistant, a solvent having a boiling point of 200°C or less under atmospheric pressure can be preferably used, and examples thereof include aromatic hydrocarbons such as styrene, toluene, ethylbenzene, and xylene; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and acetates such as ethyl acetate and butyl acetate.

[0033] The content of the foaming aid in the expandable resin particles used in the method according to the present invention is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 2 parts by weight, based on 100 parts by weight of the base resin. This has the advantage that it tends to easily produce a foamed molded article with excellent appearance.

[0034] (Other additives) The expandable resin particles used in the method according to the present invention may contain other additives other than the base resin and the blowing agent. The other additives include solvents, plasticizers, cell regulators, flame retardants, flame retardant assistants, heat radiation inhibitors, pigments, dyes, and antistatic agents. The types and amounts of these additives are not particularly limited, and may be selected based on ordinary knowledge within a range that does not impair the technical effects of the present invention.

[0035] (Weight average molecular weight) The molecular weight of the expandable resin particles used in the method according to the present invention is not particularly limited, and may be selected based on ordinary knowledge within a range that does not impair the technical effect of the present invention. The weight average molecular weight measured using gel permeation chromatography (GPC) in terms of polystyrene may be, for example, 50,000 to 800,000, preferably 100,000 to 400,000, and more preferably 250,000 to 350,000. According to this configuration, a foamed molded product with excellent surface quality and little residue at the time of combustion can be obtained. When measuring the weight average molecular weight of the expandable resin particles using gel permeation chromatography (GPC), the foaming agent contained in the expandable resin particles volatilizes during the GPC measurement, so that the weight average molecular weight of the base resin contained in the expandable resin particles is actually measured. Therefore, the "molecular weight of the expandable resin particles" referred to here may be understood as the molecular weight of the base resin contained in the expandable resin particles, and this molecular weight is not affected by the foaming agent. The same can be said even when a low molecular weight compound other than the foaming agent is contained. In other words, like the foaming agent, low molecular weight compounds other than the foaming agent do not affect the "molecular weight of the expandable resin particles."

[0036] (Volume average particle size) The volume average particle diameter (hereinafter sometimes abbreviated as average particle diameter) of the expandable resin particles used in the method according to the present invention is not particularly limited, and may be selected based on normal recognition within a range that does not impair the technical effects of the present invention. For example, it may be 0.30 mm to 1.50 mm. When the volume average particle diameter of the expandable resin particles is 0.30 mm or more, there is a tendency that the expandability of the expandable resin particles during expansion is not likely to decrease and / or the blocking amount during expansion is not likely to increase. When the volume average particle diameter of the expandable resin particles is 1.50 mm or less, there is a tendency that the filling property is not likely to deteriorate even in a narrow space when the expanded particles obtained by expanding the expandable resin particles are filled into a molding machine. The narrow space in the molding machine corresponds to a thin-walled portion in the obtained foamed molded product.

[0037] From the viewpoint of achieving both an excellent fusion rate and surface properties, the volume average particle size is preferably 0.40 mm to 1.20 mm, more preferably 0.50 mm to 1.20 mm, still more preferably 0.50 mm to 1.10 mm, still more preferably 0.60 mm to 1.00 mm, and particularly preferably 0.70 mm to 0.90 mm.

[0038] In this specification, the volume average particle diameter of the expandable resin particles refers to the particle diameter at which the cumulative volume becomes 50% when the particle diameter of the expandable resin particles is measured on a volume basis using a particle size analyzer (e.g., an image processing type Millitrac JPA particle size analyzer) and the cumulative distribution is used.

[0039] (particle size range) The particle size range of the expandable resin particles used in the method according to the present invention is not particularly limited, and may be selected based on general understanding within a range that does not impair the technical effect of the present invention. In the production of expandable resin particles, the particle size range is usually adjusted by sieving the expandable resin particles, and in this case, the range of the retained particle size (the particle size of the expandable resin particles obtained by sieving) (hereinafter sometimes abbreviated as the cutoff range) is set as the particle size range of the expandable resin particles.

[0040] From the viewpoint of obtaining both an excellent fusion rate and surface properties, the particle size range of the expandable resin particles is preferably a range consisting of a lower limit selected from 0.10 mm, 0.20 mm, 0.30 mm, 0.40 mm, and 0.50 mm, and an upper limit selected from 2.00 mm, 1.80 mm, 1.70 mm, 1.60 mm, 1.50 mm, and 1.40 mm. From the viewpoint of obtaining both an excellent fusion rate and surface properties, the difference between the upper limit and the lower limit is preferably 1.6 mm or less, more preferably 1.3 mm or less, and even more preferably 1.0 mm or less.

[0041] The expandable resin particles used in the method according to the present invention may be commercially available products or may be manufactured. Examples of commercially available expandable resin particles include Kanepearl series manufactured by Kaneka Corporation and STMMA manufactured by Zhejiang Kaiste New Materials Co., Ltd., China. The manufacturing method of the expandable resin particles is not particularly limited, and may be selected based on ordinary knowledge within a range that does not impair the technical effects of the present invention.

[0042] Generally, the preparation method includes a copolymerization process, a foaming agent impregnation process, a drying process and a screening process. The operation and conditions of each process are not particularly limited, and may be selected based on ordinary knowledge within the scope that does not impair the technical effects of the present invention.

[0043] The copolymerization step includes suspension polymerization in which polymerization is performed in an aqueous suspension. In the present invention, the term "aqueous suspension" refers to a liquid in which resin particles and / or monomer droplets are dispersed in water or an aqueous solution by a method such as stirring. The aqueous suspension may contain dissolved water-soluble surfactants and monomers, and may also contain dispersed water-insoluble dispersants, polymerization initiators, chain transfer agents, crosslinking agents, bubble regulators, flame retardants, solvents, plasticizers, and the like together with the monomers. Examples of the dispersants include poorly water-soluble inorganic salts such as calcium triphosphate, magnesium pyrophosphate, calcium pyrophosphate, hydroxyapatite, kaolin, calcium carbonate, magnesium carbonate, and magnesium phosphate.

[0044] In the foaming agent impregnation step, the resin particles obtained in the copolymerization step are impregnated with a foaming agent to obtain expandable resin particles. In the foaming agent impregnation step, the treatment temperature (also referred to as impregnation temperature) and treatment time (also referred to as impregnation time) when the foaming agent is impregnated into the copolymer are not particularly limited.

[0045] In the drying step, the expandable resin particles obtained in the foaming agent impregnation step are dried. The drying means is not particularly limited, but for example, a tank-type or cylindrical stirring dryer, a box-type or belt-type ventilation dryer, a fluidized bed dryer, etc. can be used. The drying step is preferably carried out at a temperature equal to or lower than the foaming temperature of the expandable resin particles, and more preferably at 30°C to 60°C from the viewpoint of productivity.

[0046] In the sieving step, the dried expandable resin particles are sieved to obtain expandable resin particles having a desired particle size range.

[0047] [Method for producing block-shaped molded product] (Pre-foaming process) In the pre-expansion step of the present invention, the expandable resin particles are heated to expand (i.e., pre-expand). The device, expansion conditions, and desired expansion ratio used for expanding the expandable resin particles are not particularly limited, and may be selected based on ordinary knowledge within a range that does not impair the technical effects of the present invention.

[0048] A specific example of the foaming method is a method in which the steps of (1) putting expandable resin particles into a container equipped with a stirrer, (2) heating the expandable resin particles using a heat source such as steam, and (3) foaming until a desired expansion ratio is reached in step (2) to obtain expanded particles are carried out in that order. When steam is used as the heat source, the pre-expansion temperature is generally 100°C or higher, preferably 101°C or higher. The upper limit of the pre-expansion temperature depends on the physical limit due to the temperature of the steam, but may generally be 110°C or lower.

[0049] From the viewpoint of saving raw materials and obtaining a block-shaped molded product that is excellent in strength and lightweight, the expansion ratio of the expandable resin particles in the pre-expansion step is preferably 20 times or more and less than 120 times, more preferably 30 times to 100 times, further preferably 35 times to 80 times, and particularly preferably 40 times to 75 times. The expansion ratio of the expandable resin particles (hereinafter also referred to as the volume ratio) refers to the increase ratio of the bulk volume after the expandable resin particles are expanded, that is, the ratio of the bulk volume of the expandable resin particles after expansion to the bulk volume before expansion.

[0050] From the viewpoint of achieving both an excellent fusion rate and surface properties, it is preferable to completely expand the expandable resin particles in the pre-expansion step, i.e., to the maximum possible expansion ratio until no further expansion is required in the subsequent step. In this case, the expansion ratio of the expandable resin particles is the expansion ratio of the block-shaped molding.

[0051] (Curing process) In the curing step of the present invention, the expanded beads obtained in the above pre-expansion step are cured. In the present specification, "curing the expanded beads" refers to leaving (storing) the expanded beads under predetermined curing conditions. The apparatus and curing conditions used in the present invention are not particularly limited, and may be selected based on ordinary knowledge within a range that does not impair the technical effects of the present invention. In general, for example, the obtained expanded beads are cured at room temperature for 8 to 200 hours. From the viewpoint of better realizing the effects of the present invention, the curing time is preferably 30 to 180 hours, and from the viewpoint of surface properties in particular, the curing time is more preferably 40 to 160 hours, and particularly preferably 48 to 150 hours.

[0052] (molding process) In the molding step of the present invention, the expanded beads are filled into a mold, and then steam is introduced into the mold from at least one surface of the mold to heat and fuse the expanded beads, thereby obtaining a block-shaped molded product. In order to obtain a block-shaped molded product for lost foam casting that has an excellent fusion rate and surface properties and is suppressed in smoke generation and warping, the manufacturing method according to one embodiment of the present invention must include the following steps in order to obtain a block-shaped molded product for lost foam casting that has an excellent fusion rate and surface properties and is suppressed in smoke generation and warping: (1) in the molding step, after filling the mold with the expanded beads after curing, the inside of the mold is depressurized to a vacuum degree of -0.05 MPa or less before the first steam introduction, and then the first steam introduction is simultaneously and continuously performed for 25 seconds or more from at least two surfaces of the mold; (2) the at least two surfaces of the mold include at least a surface that corresponds to the surface of the block-shaped molded product having the largest area; and (3) in the molding step, for example, a step in which the steam pressure in the mold reaches 0.040 MPa or more at least once in one or more steam introductions.

[0053] In the present invention, in order to sufficiently fuse the foamed particles in the block-shaped molded product, it is necessary to reduce the pressure in the mold to a vacuum level of -0.05 MPa or less, preferably -0.06 MPa or less, and more preferably -0.07 MPa or less, before the first steam introduction. The method for reducing the pressure in the mold is not particularly limited, but an example of the method is to evacuate the mold using a vacuum pump. The lower limit of the vacuum level is, for example, -0.1 MPa or more. In this specification, the value of the vacuum level is a gauge pressure.

[0054] In the present invention, as long as the inside of the mold is brought into a reduced pressure state with a predetermined vacuum degree before the first steam introduction, there is no particular restriction on whether or not to perform vacuum suction simultaneously with the introduction of steam. In the present invention, by bringing the inside of the mold into a reduced pressure state with a vacuum degree of -0.05 MPa or less before the first steam introduction, the foamed particles in the block-shaped molded product can be sufficiently fused without performing vacuum suction simultaneously with the introduction of steam. Therefore, from the viewpoint of energy saving, it is preferable not to perform vacuum suction simultaneously with the introduction of steam. When performing vacuum suction simultaneously with the introduction of steam, the vacuum suction may be performed continuously from the start to the end of the introduction of the steam, may be performed continuously during a part of the time during which the steam introduction is being performed, or may be performed intermittently while the steam introduction is being performed. In addition, when performing vacuum suction simultaneously with the introduction of steam, the surface to which the vacuum suction is performed is not particularly limited as long as it is a surface different from the surface to which the steam is introduced.

[0055] In the present invention, the process of reducing the pressure inside the mold before the first steam introduction is different from the process of performing vacuum suction simultaneously with the first steam introduction, and the two cannot be interpreted as interchangeable (replaceable). If vacuum suction is performed simultaneously with the first steam introduction without performing the process of reducing the pressure inside the mold in accordance with the conditions specified in the present invention, it is not possible to obtain a foamed molded product that has both excellent fusion properties and surface properties and is suppressed in terms of smoke generation and warping.

[0056] A manufacturing method according to one embodiment of the present invention includes a molding step in which the steam pressure in the mold reaches 0.040 MPa or more at least once. If the steam pressure in the mold reaches 0.040 MPa or more at least once throughout the entire molding process, a molded product with sufficient internal fusion and excellent appearance can be obtained. If the steam pressure in the mold is always less than 0.040 MPa in the molding step, the foamed molded product produced tends to have insufficient internal fusion and poor surface appearance. In this specification, the value of the steam pressure in the mold is a gauge pressure.

[0057] As long as the steam pressure in the mold in the molding process reaches 0.040 MPa or more at least once, the number of steam introductions and the steam blowing pressure used for each steam introduction are not particularly limited. The steam blowing pressure used for each steam introduction may be a general condition, for example, 0.01 to 0.80 MPa, preferably 0.05 to 0.50 MPa. Here, the "steam blowing pressure" refers to the pressure of steam supplied into the mold. In the molding process of the present invention, the steam pressure in the mold may usually be in the range of 0.01 MPa to 0.1 MPa, preferably 0.02 MPa to 0.08 MPa. The steam pressure in the mold can usually be measured by a sensor installed in the mold. From the viewpoint of further improving the fusion rate and surface properties of the molded body, it is preferable that the maximum achievable value of the steam pressure in the mold in the molding process is 0.08 MPa or less. In the present specification, the value of the steam blowing pressure is a gauge pressure.

[0058] The number of times steam is introduced is not particularly limited and may be one or more times. From the viewpoint of improving the fusion rate of the block-shaped molded product, it is preferable to introduce steam multiple times, for example, two or more times, three or more times, or four or more times. From the viewpoint of improving the surface properties of the block-shaped molded product, it is preferable to introduce steam into the mold five or less times, more preferably four or less times, and particularly preferably three or less times.

[0059] In the following, the first steam introduction will be described as an example. In the present invention, in the first steam introduction, the inside of the mold is first reduced in pressure as described above, and then the first steam introduction is performed continuously for 25 seconds or more simultaneously from at least two sides of the mold.

[0060] The time for the first steam introduction may be appropriately selected from a normal range, for example, 25 to 120 seconds, 28 to 90 seconds, or 30 to 60 seconds, so long as it includes a continuous 25 seconds. If the duration of the first steam introduction is less than 25 seconds, a foamed molded product with sufficient internal fusion cannot be obtained.

[0061] The steam introduction surface where the first steam introduction is performed is at least two surfaces of the mold. The at least two surfaces of the mold include at least a surface corresponding to the surface of the block-shaped molded product having the largest area. This means that one of the at least two surfaces of the mold where the first steam introduction is performed corresponds to the surface of the block-shaped molded product having the largest area. From the viewpoint of better realizing the effects of the present invention, the at least two surfaces of the mold are a surface corresponding to the surface of the block-shaped molded product having the largest area and a surface opposite to the surface. In general, the surface of the mold having the largest area corresponds to the surface of the block-shaped molded product having the largest area. In this specification, the "surface of the block-shaped molded product having the largest area" is also referred to as the "maximum surface of the block-shaped molded product".

[0062] If steam is introduced only once, the steam pressure in the mold must reach 0.040 MPa or more in the first steam introduction. If steam is introduced multiple times, the steam pressure in the mold may or may not reach 0.040 MPa or more in the first steam introduction.

[0063] In addition, when steam is introduced multiple times, the time for the second and subsequent steam introductions is not particularly limited, and normal conditions may be used, for example, the time may be the same as or different from the time for the first steam introduction. For example, the time for each steam introduction from the second time onwards may be 5 seconds or more and less than 25 seconds, preferably 8 seconds or more and 25 seconds or less.

[0064] In the molding process of the present invention, a reduced pressure state may be established only before the first steam introduction, and a reduced pressure state may be established before any steam introduction from the second onwards under the same or different conditions as those before the first steam introduction. From the viewpoint of improving productivity and simplifying the process, it is preferable not to carry out a process of establishing a reduced pressure state before the second or subsequent steam introductions.

[0065] In the molding process of the present invention, with regard to the second or subsequent steam introduction, from the viewpoint of better achieving the effects of the present invention, it is preferable to introduce steam after the first steam introduction from at least one surface to which steam was not introduced in the first steam introduction, and it is more preferable to introduce steam from all surfaces to which steam was not introduced in the first steam introduction.

[0066] The steam introduction from at least one surface to which the steam was not introduced during the initial steam introduction may be conducted simultaneously or in a number of separate times.

[0067] Also, steam may be introduced from at least one surface to which steam was not introduced in the initial steam introduction, and at the same time, steam may be introduced from at least one surface to which steam was introduced in the initial steam introduction. For example, specific examples of introducing steam from at least one surface to which steam was not introduced in the initial steam introduction include (1) introducing steam from at least one of the surfaces to which steam was not introduced in the initial steam introduction; and (2) introducing steam from at least one of the surfaces to which steam was not introduced in the initial steam introduction, and at least one surface to which steam was introduced in the initial steam introduction.

[0068] For convenience, the following description will be based on Fig. 1, which shows a three-dimensional view of a rectangular parallelepiped mold. The pair of faces of the mold with the largest area are defined as the front face 1 and the rear face (the front and rear sides of the paper on which the drawing is drawn), and the two faces located on the upper and lower sides of the drawing are defined as the upper face 3 and the lower face of the mold, respectively. The remaining two faces are defined as the left face and the right face 2 (the left and right sides of the drawing). The direction from the front face 1 to the rear face, or the direction from the rear face to the front face 1, is defined as the thickness direction 4.

[0069] From the viewpoint of better realizing the effects of the present invention, it is more preferable to (1) introduce steam for the first time from both front and back sides after a reduced pressure is created, and then introduce steam for the second time from all four sides, or from both top and bottom or both left and right sides, (2) introduce steam for the first time from both front and back sides after a reduced pressure is created, and then introduce steam for the second and third times from both top and bottom and both left and right sides, respectively, or (3) introduce steam for the first time from both front and back sides after a reduced pressure is created, and then introduce steam for the second time from all four sides, or from both top and bottom or both left and right sides, and then introduce steam for the third time from all sides. It is more preferable that steam is introduced to all sides of the mold in the molding process of the present invention.

[0070] With regard to the final steam introduction in the molding process of the present invention, from the viewpoint of better realizing the effects of the present invention, it is preferable to make the steam pressure in the mold reach 0.040 MPa or more in the final steam introduction, and it is more preferable to make the steam pressure in the mold reach 0.040 MPa or more in each steam introduction. Also, from the viewpoint of energy saving, it is preferable to make the steam pressure in the mold reach 0.040 MPa or more only in the final steam introduction, and it is more preferable to make the steam pressure in the mold reach 0.040 MPa or more upon completion of the final steam introduction. Note that when steam is introduced only once, the first steam introduction is also the final steam introduction.

[0071] (cooling process) The manufacturing method according to the present invention may further include a cooling step of cooling the block-shaped molded product obtained in the molding step. The operation and conditions for cooling are not particularly limited and may be set based on general understanding within a range that does not impair the technical effects of the present invention. From the viewpoint of better achieving the effects of the present invention, the block-shaped molded product may be cooled by maintaining vacuum suction for a certain period of time without spraying water on the mold (without pouring water on it).

[0072] In the cooling step, the time for which the vacuum suction is maintained is not particularly limited as long as it is sufficient to cool the block-shaped molded product. From the viewpoint of further suppressing warping of the foam molded product, the time for which the vacuum suction is maintained is preferably 400 seconds or more, more preferably 450 seconds or more, and even more preferably 500 seconds or more. From the viewpoint of economy, the time for which the vacuum suction is maintained is preferably less than 3000 seconds, more preferably less than 1500 seconds, and even more preferably less than 1000 seconds.

[0073] (Block-shaped molding) According to the method of the present invention, it is possible to produce a foamed molded product that has both excellent fusion rate and surface properties, and is suppressed from smoking and warping. In general, the foamed molded product may be a block-shaped molded product, and may be a block-shaped molded product for producing a lost foam mold in lost foam casting (also referred to as a "block-shaped molded product for lost foam casting"). The lost foam casting is a method in which a block-shaped molded product is cut as necessary to produce a mold of a desired shape, and the mold is buried in casting sand during metal casting, molten metal is poured into it, and a casting is cast by displacement. The lost foam obtained by using the block-shaped molded product produced by the method of the present invention has excellent surface quality and produces little residue during combustion, and is therefore preferably applied to various metal castings.

[0074] The technical effects of the present invention are particularly evident when a large block-shaped product is produced by the method of the present invention. Therefore, with regard to the size of the block-shaped product, it is preferable that the thickness of the thinnest part of the block-shaped product is 100 to 1200 mm.

[0075] The block-shaped molded product according to the present invention includes molded products called plates or sheets, and for example, plate material, sheet material, large plate, plate material molded product, plate-shaped molded product, sheet material molded product, and sheet-shaped molded product are all included in the category of the block-shaped molded product according to the present invention. The shape of the block-shaped molded product is not particularly limited, but from the viewpoint of productivity, a regular shape such as a rectangular parallelepiped is preferable. When the block-shaped molded product is a rectangular parallelepiped, the length of its shortest side corresponds to the thickness of the thinnest part, and is preferably 100 to 1200 mm. Furthermore, from the viewpoint of realizing a high fusion rate, the thickness of the thinnest part is preferably 650 mm or less, and more preferably 600 mm or less. The length of the side other than the shortest side of the rectangular parallelepiped is not particularly limited and may be appropriately set according to the size of the mold to be manufactured, and may be selected from the range of, for example, 200 to 7000 mm.

[0076] The density of the block-shaped molding is not particularly limited, but from the viewpoint of handling, it is preferably 14 to 30 kg / m 3 is preferable, and 15 to 28 kg / m 3 is more preferred.

[0077] In addition, the composition of the base resin does not change during the production of expandable resin particles. In addition, in the expanded beads produced from the expandable resin particles, the structure of the expandable resin particles changes, but the composition of the base resin contained in the expandable resin particles does not change. Furthermore, in the expanded molded article produced using the expanded beads produced from the expandable resin particles, the structure of the expanded beads changes, but the composition of the expanded beads does not change. Therefore, the type of structural unit, the content of each structural unit, and the weight average molecular weight obtained by analyzing the expandable resin particles, the expanded beads, or the expanded molded article may be regarded as the type of structural unit and the content of each structural unit contained in the base resin, which is the raw material, and the weight average molecular weight of the base resin, respectively. EXAMPLES

[0078] Hereinafter, the embodiments of the present invention will be described in detail with reference to examples. However, it will be understood by those skilled in the art that the examples described below are merely illustrative for the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, they will be carried out according to general conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are general products available on the market.

[0079] The expandable resin particles used in the examples and comparative examples will be described below.

[0080] Expandable resin particles A: Expandable MMA / BA polymer particles ("Kanepearl AX-B" manufactured by Kaneka Corporation, foaming agent butane, average particle size 0.8 mm, cut-off range 0.5-1.4 mm); used as expandable resin particles in Examples 1-8, Examples 13-18 and Comparative Examples 1-8; the base resin of expandable resin particles A contains only MMA units and BA units as constituent units, i.e., contains 100% by weight of (meth)acrylic acid ester units.

[0081] Expandable resin particles B: expandable MMA / BA polymer particles (produced in Production Example 1 described below, average particle size 0.8 mm, cutoff range 0.4 to 1.6 mm); used as expandable resin particles in Example 12.

[0082] Expandable resin particles C: Expandable MMA / St polymer particles (produced in Production Example 2 described below, average particle size 0.8 mm, cutoff range 0.5 to 1.4 mm); used as expandable resin particles in Example 9.

[0083] Expandable resin particles D: Expandable MMA / MA polymer particles (produced in Production Example 3 described below, average particle size 0.6 mm, cutoff range 0.5 to 1.4 mm); used as expandable resin particles in Example 10.

[0084] Expandable resin particles E: Expandable MMA / BA polymer particles (produced in Production Example 4 described below, average particle size 0.6 mm, cutoff range 0.5 to 1.4 mm); used as expandable resin particles in Example 11.

[0085] In addition, MMA refers to methyl methacrylate, BA refers to butyl acrylate, St refers to styrene, and MA refers to methyl acrylate.

[0086] (Production example) Production Example 1 (Production of Expandable Resin Particles B) In a 6L autoclave equipped with a stirrer, 150 parts by weight of water, 0.15 parts by weight of tribasic calcium phosphate, 0.0075 parts by weight of sodium α-olefin sulfonate, 0.08 parts by weight of lauroyl peroxide, 0.1 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane, 0.1 parts by weight of 1,6-hexanediol diacrylate, and 0.265 parts by weight of n-dodecyl mercaptan were charged. Then, 97.5 parts by weight of methyl methacrylate (MMA), 2.5 parts by weight of butyl acrylate (BA) (total amount of monomers is 100 parts by weight), and 1 part by weight of toluene were charged into the aqueous suspension in the autoclave, and the temperature of the aqueous suspension was raised to 80°C to carry out polymerization. When 1 hour and 45 minutes had elapsed since the temperature of the aqueous suspension reached 80°C (initiation of polymerization), 0.12 parts by weight of tribasic calcium phosphate was added to the aqueous suspension. At that time, the polymerization conversion rate was 43%.

[0087] Next, 4 hours and 20 minutes after the start of polymerization, 1.5 parts by weight of cyclohexane and 9 parts by weight of butane (normal / iso = 70 / 30) rich in normal butane as a blowing agent were charged into the aqueous suspension, and then the temperature of the aqueous suspension was raised to 101 ° C., and polymerization and blowing agent impregnation were carried out for 10 hours. Thereafter, the aqueous suspension was cooled, and the product obtained after cooling was washed, dehydrated and dried to obtain expandable resin particles.

[0088] The expandable resin particles obtained as described above were sieved to obtain expandable resin particles B.

[0089] Production Example 2 (Production of Expandable Resin Particles C) Expandable resin particles C were obtained in the same manner as in Production Example 1, except that the monomer mixture was changed to 70 parts by weight of methyl methacrylate and 30 parts by weight of styrene (St) and a sieve with different mesh sizes was used.

[0090] Production Example 3 (Production of Expandable Resin Particles D) Expandable resin particles D were obtained by carrying out the same procedures as in Production Example 1, except that the amount of calcium phosphate initially used (0.15 parts by weight) was changed to 0.13 parts by weight, the amount of n-dodecyl mercaptan was changed to 0.24 parts by weight, the monomer mixture was changed to 94.5 parts by weight of methyl methacrylate and 5.5 parts by weight of methyl acrylate (MA), the amount of additional calcium phosphate used was changed to 0.12 parts by weight, the timing of its addition was changed to 30 minutes after the start of polymerization, and a sieve with a different mesh size was used.

[0091] Production Example 4 (Production of Expandable Resin Particles E) Expandable resin particles E were obtained in the same manner as in Production Example 1, except that the amount of tricalcium phosphate initially used (0.15 parts by weight) was changed to 0.28 parts by weight.

[0092] In all the production examples, the final polymerization conversion rate was at least 99.0% or more (e.g., 99.8%) and can be regarded as approximately 100%. Therefore, the ratio of the amount of the monomer used in each production example can be regarded as the ratio of the structural unit in the base resin in the expandable resin particles obtained in each production example.

[0093] (Example) <Example 1> The expandable resin particles A were used as the expandable resin particles, and the following steps (1) to (10) were carried out in order to obtain a block-shaped molded product (that is, a foamed molded article).

[0094] (1) The expandable resin particles were placed into a pressurized foaming machine (BHP manufactured by Daikai Kogyo Co., Ltd.).

[0095] (2) Steam was blown into the foaming machine under the conditions of a steam blowing pressure of 0.10 to 0.16 MPa and a pressure inside the foaming machine of 0.005 to 0.030 MPa, and the expandable resin particles were heated. The maximum temperature inside the foaming machine was 105°C.

[0096] (3) Through the above step (2), the expandable resin particles were expanded to a volume expansion ratio of 65 times.

[0097] (4) The obtained expanded beads were left to stand at room temperature (25°C) for 72 hours to obtain expanded beads with a volume expansion ratio of 65 times.

[0098] (5) A molding machine (PEONY-205DS manufactured by DAISEN) equipped with a mold with inner dimensions of 2000 mm in length, 1000 mm in width, and 525 mm in thickness was filled with foamed particles at a volumetric expansion ratio of 65 times.

[0099] (6) After filling, the inside of the mold was evacuated with a vacuum pump to set the degree of vacuum inside the mold before heating to -0.07 MPa. Note that in the following steps, vacuum suction was not performed simultaneously with the introduction of steam, and furthermore, for the second and subsequent steam introductions, no prior process of reducing the pressure was performed.

[0100] (7) The inside of the mold was heated according to the procedure described in Table 1. Heating process <1> In this example, steam was introduced continuously for 40 seconds simultaneously to the sides (front and back) of the rectangular parallelepiped shown in FIG. 1 that had the largest area. <1> The steam pressure in the mold was set at 0.048 MPa.

[0101] (8)Heating process <2> Now, the heating process <1> Steam was introduced continuously for 20 seconds simultaneously on the four sides (top, bottom, left, right) to which steam had not been introduced in the heating process. <2> The steam pressure in the mold was set at 0.048 MPa. The above heating caused the foamed beads to fuse together.

[0102] Note that the "heating pressure" in Tables 1 and 2 refers to the set value of the steam pressure in the mold in each heating step, and indicates the maximum pressure reached in the molding step, and does not mean that the steam pressure in the mold necessarily reaches the set value throughout the entire heating step. Also, the item "Heating step in which the heating pressure was reached" in Tables 1 and 2 indicates in which heating step the steam pressure in the mold in each example reached the set value.

[0103] (9) Next, the inside of the mold was evacuated for 500 seconds using a vacuum pump to cool the inside of the mold. After that, the foamed molded body was removed from the mold.

[0104] (10) The foamed molded product was left at 60°C for 3 days to obtain a block-shaped foamed molded product. The block-shaped molded product obtained had a length of 2000 mm, a width of 1000 mm, and a thickness of 525 mm, and had a density of 18.5 kg / m 3 In the examples of the present application, the front and rear faces of the mold correspond to the faces of the block-shaped molded product to be obtained, the area of ​​which is calculated by the product of "length" and "width". The top and bottom faces of the mold correspond to the faces of the block-shaped molded product to be obtained, the area of ​​which is calculated by the product of "width" and "thickness". The right and left faces of the mold correspond to the faces of the block-shaped molded product to be obtained, the area of ​​which is calculated by the product of "length" and "thickness".

[0105] <Examples 2 to 18 and Comparative Examples 1 to 8> Except for changing the expandable resin particles and various production conditions as shown in Tables 1 and 2, the same procedure as in Example 1 was carried out to obtain foamed molded articles. In Examples 8 and 11, the volume expansion ratio of the foamed particles obtained by pre-expansion was set to 50 times, and the density of the molded article was set to 24 kg / m 3In Example 16, the block-shaped molded product had dimensions of 2000 mm in length, 1000 mm in width, and 500 mm in thickness. In Example 17, the block-shaped molded product had dimensions of 4750 mm in length, 1860 mm in width, and 660 mm in thickness. In Example 18, the molded product was heated. <2> The specified heating pressure (0.048 MPa) was reached at <1> and heating <3> In all of the Examples and Comparative Examples other than Example 18, the predetermined heating pressure was reached only in the final heating.

[0106] The block-shaped molded products obtained in the above-mentioned Examples and Comparative Examples were subjected to the following performance evaluations, and the results are shown in Tables 1 and 2.

[0107] (evaluation) <Evaluation of block-shaped molded products> (Method of measuring fusion rate (front, center, rear)) The obtained foam molded body was used to measure the ratio (D) of each fracture surface of the "front", "center", and "rear" of the foam molded body. (1) The foam molded body was cut perpendicular to the thickness direction of the foam molded body using a hot wire slicer so that the thickness direction (i.e., the length direction of the shortest side) of the foam molded body was divided into 5 equal parts. (2) Of the 5 parts divided into 5 equal parts, the two parts that corresponded to both ends of the foam molded body were designated as the "front" and "rear", respectively, and the part that corresponded to the center of the foam molded body was designated as the "center". For each of the "front", "center", and "rear" parts, the surface perpendicular to the thickness direction was folded from the center in the longitudinal direction along the width direction to break the parts. (3) The obtained fracture surface was visually observed, and the number of all particles constituting the fracture surface and the number of foam particles broken other than at the particle interface were counted, and the ratio (D) was calculated based on the following formula.

[0108] Percentage (D) (%) = {number of particles that broke at other than particle interfaces on the fracture surface / number of particles that make up the fracture surface} × 100 The ratio (D) calculated for each of the "front", "center", and "rear" parts was taken as the fusion rate. The results are shown in Tables 1 and 2. The fusion rate values ​​shown in Table 1 are rounded off to the nearest whole number.

[0109] (Surface property evaluation method (〇, △, ×)) The surface condition of the foamed molded article was visually observed. The surface properties of the foamed molded article were evaluated based on the observation results and the following criteria. If the foamed molded article was rated as ◯ or △ among the following criteria, it can be said that the foamed molded article has sufficient surface properties to solve the problems of the present invention. ◯ (Excellent): There were almost no gaps between particles on the surface, and the surface was very beautiful. △ (Good): There were gaps between particles on the surface, but they were few and the surface was beautiful. × (bad): There were many interparticle gaps on the surface, and the surface appearance was bad.

[0110] (Method of evaluating smoke generation) After drying the obtained block-shaped molded body, a 100 x 100 x 25 mm piece was cut out and ignited over an open flame in a ventilated room. The smoke generated during combustion was visually observed to confirm the generation of black smoke. If the product is rated as ◯ or △ among the following criteria, it can be said that the generation of black smoke is sufficiently suppressed and the product has sufficient low smoke generation properties, that is, the problem of the present invention is solved. In the following criteria, "low smoke generation" is expressed as "resistance to smoke generation". ◯ (Excellent smoke resistance): Almost no black smoke was generated. △ (good smoke resistance): The amount of black smoke generated was less than in the "×" case. × (poor smoke resistance): A large amount of black smoke was generated.

[0111] <Method for evaluating warpage of molded products> The obtained block-shaped molded product was visually observed in a direction parallel to the surface with the largest area, and evaluated based on the state of bending of the entire block-shaped molded product. If it was rated as ◯ or △ among the following criteria, it can be said that warping was sufficiently suppressed, that is, the problem of the present invention was solved.

[0112] ○ (No warping): There was no bending.

[0113] △(Small curvature): Slightly curved.

[0114] × (large warpage): Significantly warped.

[0115] [Table 1]

[0116] [Table 2]

[0117] As can be seen from the above examples, the manufacturing method of the present invention can obtain a block-shaped molded product that has both an excellent fusion rate and surface properties, and is suppressed in terms of smoke generation and warping, and is suitable for lost foam casting.

[0118] Although the technical configuration of the present invention has been described through specific examples, it will be understood by those skilled in the art that the present invention is not limited thereto.

[0119] Although each embodiment of the present invention has been described above, the above description is illustrative and not exhaustive, and is not limited to each disclosed embodiment. Various modifications and changes that do not depart from the scope and spirit of each described embodiment will be obvious to those skilled in the art. The selection of terms used in this specification is intended to optimally interpret the principles, practical applications, or technical improvements to the market in each embodiment, or to enable those skilled in the art to understand each embodiment disclosed in this specification.

[0120] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Industrial Applicability]

[0121] According to one embodiment of the present invention, there is provided a manufacturing method capable of obtaining a block-shaped molded product having an excellent fusion rate and surface properties, and suppressing smoke generation and warping, in particular a manufacturing method for a block-shaped molded product for a lost foam pattern. The one embodiment of the present invention can be suitably used in the fields of casting, automobiles, and architecture. [Explanation of symbols]

[0122] 1 Front 2 Right side 3 Top surface 4 Thickness direction

Claims

1. A method for producing a block-shaped molded product, comprising the steps of: a pre-expansion step of heating and expanding the expandable resin particles; a curing step of curing the expanded beads obtained in the pre-expanding step; and a molding step of filling a mold with the cured expanded beads and then introducing steam into the mold to heat and fuse the expanded beads to obtain a block-shaped molded product. The expandable resin particles include a base resin containing 50% by weight or more of (meth)acrylic acid ester units as constituent units, and a foaming agent, the molding step includes a step of reducing the pressure in the mold to a vacuum degree of -0.05 MPa or less after filling the mold with the cured expanded beads and before the first steam introduction, and then continuously introducing the first steam for 25 seconds or more simultaneously from at least two sides of the mold, The at least two surfaces of the mold include at least a surface corresponding to the surface of the block-shaped molded object having the largest area, The manufacturing method includes a step of causing the steam pressure in the mold to reach 0.040 MPa or more at least once in the molding step.

2. The method according to claim 1 , wherein in the molding step, steam is introduced into the mold three or less times.

3. The method according to claim 1 or 2, wherein the molding step further comprises a step of, after the initial steam introduction, introducing steam from at least one surface to which steam was not introduced in the initial steam introduction.

4. The method according to claim 1 or 2, wherein the base resin contains 50% by weight or more of methyl methacrylate units and acrylic ester units in total.

5. The method according to claim 4, wherein the acrylate ester units are butyl acrylate units.

6. The density of the block-shaped molding is 14 kg / m ３ Above, 30kg / m ３ The method according to claim 1 or 2, wherein:

7. The method according to claim 1 or 2, wherein the block-shaped molded product has a thickness of 100 mm or more and 1200 mm or less at its thinnest portion.

8. The method according to claim 1 or 2, further comprising a cooling step of cooling the block-shaped molded product obtained in the molding step.

9. The method according to claim 8, wherein the cooling step is a step of maintaining vacuum suction for 400 seconds or more without spraying water on the mold.

10. The method according to claim 1 or 2, wherein the block-shaped molded product is a block-shaped molded product for lost foam casting.

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