JP2011068776A - Foam-molded article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin foam-molded article that is produced without the need of a special device or mold or a complicated operation and without accompanying an increase in the production cost, maintains sufficient hardness of a surface layer and has a little dimensional change rate after heating. <P>SOLUTION: The foam-molded article is derived from formed resin particles of the same kind, and has a ratio of an inner bulk foaming rate If to a bulk foaming rate Sf of the surface layer of the molded article satisfying 1.1&le;If/Sf&le;1.8. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a foam molded article. More specifically, the present invention relates to a foamed molded product in which the bulk foaming ratio of the surface layer of the foamed molded product is lower than the internal bulk foaming ratio.

In recent years, it has been desired to further increase the bulk foaming ratio of a resin foam molded body from the demand for weight reduction and cost reduction. However, generally, when the bulk foaming ratio of the resin foam molded article is further increased, the hardness of the surface of the resin foam molded article is lowered, and there is a problem that the required value of hardness cannot be satisfied depending on applications.
Therefore, in order to increase the hardness of the surface of the resin foam molded body, there is known a molded body having a uniform, high density and hard skin layer on substantially the entire surface portion of the molded body (Patent Document 1).
Further, there is known a foam-molded body in which a non-foamed layer (skin layer) having a constant thickness is formed on the surface of the foam-molded body to improve rigidity and decorate the surface (Patent Document 2).

Japanese Patent No. 3859330 JP 7-285141 A

  However, the resin foam molded articles described in Patent Documents 1 and 2 are obtained only by a special molding method for forming a high-density skin layer or a constant-thickness non-foamed layer on the surface of the molded article as described above. Therefore, there is a problem that a special apparatus / mold or complicated operation is required and the manufacturing cost increases.

  As a result of intensive studies to solve the above problems, the present inventors have found that the surface foam layer foam foam body has a lower bulk foaming ratio than the internal bulk foaming ratio. Thus, the present invention was completed.

  Thus, according to the present invention, it is a foam molded article derived from the same type of foamed resin particle, and the ratio of the bulk foaming magnification Sf of the surface layer of the foamed molded article to the internal bulk foaming magnification If is 1.1 ≦ If. There is provided a foamed molded article characterized by being a foam having /Sf≦1.8.

  ADVANTAGE OF THE INVENTION According to this invention, the resin foam molded object with favorable hardness can be provided, and also the resin foam molded object with a small dimensional change rate after a heating can be provided.

  The foamed molded product of the present invention is a foamed molded product derived from the same type of foamed resin particles, and the ratio of the bulk foaming magnification Sf of the surface layer of the foamed molded product to the internal bulk foaming magnification If is 1.1 ≦. A foam having If / Sf ≦ 1.8.

<Foamed resin particles>
The foamed resin particles of the present invention are particles obtained by impregnating resin particles with a foaming agent and foaming them to a predetermined bulk density.

(Resin particles)
The resin particles of the same type are used for the resin particles.
Examples of the resin particles include polyolefin resin particles, polystyrene resin particles, and composite resin particles of polystyrene resin and polyolefin resin.

  As the composite resin particles of polystyrene resin and polyolefin resin, resin particles obtained by mixing polystyrene resin and polyolefin resin, seed particles (micropellets) made of polyolefin resin are impregnated (absorbed) with styrene monomer. Thereafter, resin particles obtained by polymerization (hereinafter, also referred to as modified resin particles or modified polystyrene resin particles) can be used. The polyolefin resin constituting the composite resin particles is preferably a polypropylene resin.

  Among the resin particles, composite resin particles having properties of polystyrene resin and polyolefin resin at the particle level are preferable. In particular, modified resin particles are preferable. Hereinafter, the modified resin particles will be described.

The polyolefin resin, which is one of the resin materials of the modified resin particles, is not particularly limited, and a resin obtained by a known polymerization method can be used, and among them, a polypropylene resin is preferable. The polyolefin resin may be cross-linked.
The polypropylene resin is not particularly limited, and for example, a propylene-ethylene copolymer is used. The propylene-ethylene copolymer is mainly composed of a copolymer of ethylene and propylene, but may contain other monomers that can be copolymerized with ethylene or propylene in the molecule. Examples of such a monomer include one or more selected from an α-olefin, a cyclic olefin, and a diene monomer.

  As said polypropylene resin, what has melting | fusing point of the range of 120-145 degreeC is preferable. When the melting point of the polypropylene resin is lower than 120 ° C., the heat resistance is poor, and the heat resistance of the modified polystyrene resin foam molded article produced using the modified polystyrene resin particles may be lowered. On the other hand, if the melting point is higher than 145 ° C., the polymerization temperature becomes high and good polymerization may not be possible.

The polypropylene-based resin may contain additives such as a flame retardant, a flame retardant aid, an antioxidant, an ultraviolet absorber, a pigment, and a colorant as necessary.
In the modified polystyrene resin particles, the colorant may be an inorganic pigment or an organic pigment.
Examples of inorganic pigments include chromates such as chrome yellow, zinc yellow, and barium yellow, ferrocyan compounds such as bitumen, sulfides such as cadmium yellow and cadmium red, oxides such as iron black and red husk, and ultramarine blue. And silicates such as titanium oxide.
Examples of the tangible pigment include azo pigments such as monoazo pigments, disazo pigments, azo lakes, condensed azo pigments, chelate azo pigments, phthalocyanine-based, anthraquinone-based, perylene-based, perinone-based, thioindigo-based, quinacridone-based, dioxazine-based pigments. And polyindole pigments such as isoindolinone and quinophthalone.

  The polystyrene resin, which is one of the resin materials of the modified polystyrene resin particles, can be obtained by polymerizing styrene monomers such as styrene, α-methylstyrene, p-methylstyrene, t-butylstyrene, and the like. Resin. Furthermore, the polystyrene resin may be a copolymer of a styrene monomer and another monomer copolymerizable with the styrene monomer. Examples of the other monomers include polyfunctional monomers such as divinylbenzene, and (meth) acrylic acid alkyl esters that do not contain a benzene ring in the structure such as butyl (meth) acrylate. You may use these other monomers in the range which does not exceed 5 mass% substantially with respect to a polystyrene-type resin. In the present specification, styrene and monomers copolymerizable with styrene are also referred to as styrene monomers.

  The modified polystyrene resin particles can be obtained, for example, by adding and polymerizing a styrene monomer in an aqueous medium in which polyolefin resin particles are dispersed and held. A method for producing the modified polystyrene resin particles will be described below.

The polyolefin resin particles can be obtained by a known method. For example, first, polyolefin resin is melt-extruded using an extruder and then granulated by underwater cutting, strand cutting, etc., or resin particles are directly pulverized by a pulverizer to produce polyolefin resin particles. it can. Usually, the shape of the polyolefin resin particles to be used is, for example, a true sphere, an oval sphere (egg), a cylinder, a prism, a pellet, or a granular. Hereinafter, the polyolefin resin particles are also referred to as micropellets. The preferred resin particle size of the polyolefin resin particles is in the range of 0.5 mm to 1.5 mm, and more preferably in the range of 0.6 mm to 1.0 mm.
Moreover, as polyolefin-type resin, what is 100 to 150 degreeC melting | fusing point is preferable in the following (A) process, and what is 120 to 145 degreeC is further more preferable.

  Polyolefin resin particles include talc, calcium silicate, calcium stearate, synthetic or naturally produced silicon dioxide, ethylene bis-stearic acid amide, methacrylate ester copolymer and other cell regulators, triallyl isocyanurate hexabromide And a flame retardant such as carbon black, iron oxide, and a colorant such as graphite.

Next, the modified resin particles can be produced efficiently and with a high yield by using the polyolefin resin particles and the production method including the following steps (A) to (D).
(A) A step of dispersing polyolefin resin particles, a styrene monomer, and a polymerization initiator in an aqueous suspension containing a dispersant,
(B) heating the obtained dispersion to a temperature at which the styrenic monomer is not substantially polymerized to impregnate the polyolefin resin particles with the styrenic monomer;
(C) When the melting point of the polyolefin resin particles is T ° C., a step of performing the first polymerization of the styrene monomer at a temperature of (T−10) ° C. to (T + 20) ° C.,
(D) Subsequent to the first polymerization step, when a styrene monomer and a polymerization initiator are added and the melting point of the polyolefin resin particles is T ° C, (T-25) ° C to (T + 10) ) The step of impregnating the polyolefin resin particles with the styrenic monomer and performing the second polymerization by setting the temperature to ° C.

  Each of the steps (A) to (D) is performed by a well-known polymerization method such as a suspension polymerization method or a seed polymerization method of a polystyrene resin for producing beaded polystyrene resin particles using a styrene monomer as a raw material. Although it can carry out using the autoclave polymerization apparatus etc. which are used when performing, the manufacturing apparatus to be used is not limited to this.

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

  Moreover, as a polymerization initiator, the well-known polymerization initiator currently used widely for superposition | polymerization of a styrene-type monomer can be used. For example, benzoyl peroxide, lauroyl peroxide, t-amyl peroxy octoate, t-butyl peroxybenzoate, t-amyl peroxybenzoate, t-butyl peroxybivalley, t-butyl peroxyisopropyl carbonate, t -Butyl peroxyacetate, t-butylperoxy-3,3,5-trimethylcyclohexanoate, di-t-butylperoxyhexahydroterephthalate, 2,2-di-t-butylperoxybutane, dicumylper Examples thereof include organic peroxides such as oxide, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. In addition, a polymerization initiator may be used independently or may be used together.

  In addition, when adding a cross-linking agent, for example, as a method of adding, for example, a method of directly adding a cross-linking agent to a polyolefin-based resin, a method of adding after dissolving the cross-linking agent in a solvent, a plasticizer or a styrene monomer, Examples thereof include a method in which a crosslinking agent is dispersed in water and then added. Among these, the method of adding after dissolving a crosslinking agent in a styrene-type monomer is preferable.

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

In the step (B), the dispersion obtained in the step (A) is heated to a temperature at which the styrene monomer is not substantially polymerized, and the temperature when the polyolefin resin particles are impregnated with the styrene monomer is 45. The range is from 0 to 70 ° C., preferably from 50 to 65 ° C.
When the impregnation temperature is lower than 45 ° C., the impregnation of the styrenic monomer is insufficient and a polymerized polystyrene powder may be generated, which is not preferable. On the other hand, when the impregnation temperature is higher than 70 ° C., polymerization may occur before the styrene monomer is sufficiently impregnated into the polyolefin resin particles.

In the step (C) and the step (D), the polymerization temperature is an important factor. When the melting point of the polyolefin resin is T ° C., in the step (C) (first polymerization), (T-10 ) ° C. to (T + 20) ° C., and in the step (D) (second polymerization), the temperature range is (T−25) ° C. to (T + 10) ° C.
By performing polymerization in the above temperature range, the resin particles have a large amount of polystyrene resin at the center of the resin particles (that is, a large amount of polyolefin resin is present on the surface layer). As a result, polyolefin resin and polystyrene resin are present. By taking advantage of each advantage of the resin, modified polystyrene resin particles having excellent rigidity, foam moldability, chemical resistance and heat resistance can be obtained.

The shape and structure of the polymerization vessel are not particularly limited as long as they are conventionally used for suspension polymerization of styrene monomers.
Further, the shape of the stirring blade is not particularly limited, and specifically, a paddle blade such as a V-type paddle blade, a fiddler blade, an inclined paddle blade, a flat paddle blade, a pull margin blade, a turbine blade, a fan turbine blade, etc. Examples include a turbine blade and a propeller blade such as a marine propeller blade. Of these stirring blades, paddle blades are preferred. The stirring blade may be a single stage blade or a multistage blade. A baffle may be provided in the polymerization container.
The particle diameter of the resulting modified resin particles is preferably about 0.2 to 2 mm, more preferably 0.5 to 1.8 mm.

The polystyrene resin is preferably contained in the modified resin particles in an amount of 100 parts by mass or more and less than 400 parts by mass with respect to 100 parts by mass of the polyolefin resin (preferably a polypropylene resin), and 120 parts by mass or more and 300 parts by mass. More preferably, it is more preferably contained in an amount of 150 parts by mass or more and less than 250 parts by mass. Moreover, the compounding quantity of the styrene-type monomer of the raw material of the polystyrene-type resin with respect to 100 mass parts of polyolefin-type resin particles (preferably polypropylene-type resin particle) is also 100 mass parts or more and less than 400 mass parts same as a polystyrene resin.
When the content of the polystyrene-based resin is more than 400 parts by mass, the chemical resistance and heat resistance of the foamed molded product obtained by secondary foaming of the pre-expanded particles may be unfavorable. On the other hand, when the amount is less than 100 parts by mass, the rigidity of the foamed molded product obtained by secondary foaming of the pre-foamed particles may decrease, which is not preferable.

Additives such as flame retardants and flame retardant aids may be blended in the resulting modified resin particles.
Examples of the flame retardant include tri (2,3-diboromopropyl) isocyanate.
Examples of the flame retardant aid include 2,3-dimethyl-2,3-diphenylbutane.

(Foaming agent impregnation)
The impregnation with the foaming agent can be performed by a method known per se under pressure or normal pressure. The method of impregnating the modified polystyrene resin particles with the foaming agent can be appropriately changed according to the type of the foaming agent. For example, a method in which a foaming agent is pressed into an aqueous medium in which modified polystyrene resin particles are dispersed, and the foaming agent is impregnated in the resin, and the modified polystyrene resin particles are supplied to a rotary mixer. Examples thereof include a method in which a foaming agent is pressed into a rotary mixer and the resin particles are impregnated with the foaming agent. The temperature at which the modified polystyrene resin particles are impregnated with the foaming agent is usually preferably 50 ° C to 140 ° C.

  Examples of the foaming agent include those having a boiling point below the softening temperature of the polymer and easily volatile, such as propane, n-butane, i-butane, n-pentane, i-pentane, cyclopentane, carbon dioxide, and nitrogen. These foaming agents can be used alone or in combination of two or more. The amount of the readily volatile foaming agent used is preferably in the range of 5 to 25 parts by mass with respect to 100 parts by mass of the modified polystyrene resin particles.

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

In addition, a surface treatment agent such as a binding inhibitor, a fusion accelerator, an antistatic agent, or a spreading agent may be added to the expandable modified polystyrene resin particles.
The anti-bonding agent serves to prevent the pre-expanded particles from being bonded to each other when the expandable modified polystyrene resin particles are pre-expanded. Here, coalescence means that a plurality of pre-expanded particles are united and integrated. Specific examples include talc, calcium carbonate, zinc stearate, aluminum hydroxide, ethylene bis stearamide, tricalcium phosphate, dimethylpolysiloxane, and the like.

The fusion accelerator plays a role of promoting fusion between the pre-foamed particles when the pre-foamed particles are subjected to secondary foam molding. Specific examples include stearic acid, stearic acid triglyceride, hydroxystearic acid triglyceride, sorbitan stearate, and the like.
Examples of the antistatic agent include polyoxyethylene alkylphenol ether and stearic acid monoglyceride. Examples of the spreading agent include polybutene, polyethylene glycol, and silicone oil. In addition, as for the total addition amount of the said surface treating agent, 0.01-2.0 mass parts is preferable with respect to 100 mass parts of modified polystyrene resin particles.

(Manufacturing foamed resin particles)
The resin particles impregnated with the foaming agent (expandable resin particles) are heated using a heating medium such as water vapor as necessary to be pre-foamed to a predetermined bulk density, thereby obtaining foamed resin particles. it can.
As a method for producing foamed resin particles other than the above, the foamed resin particles can also be obtained by an extrusion foaming method. Here, the extrusion foaming method refers to supplying resin to an extruder, melting the resin in the extruder, including a foaming agent in the melted resin, and extruding a molten resin containing the foaming agent from the extruder to a low pressure region. In this method, the resin is foamed to form foamed resin particles at the same time as the extrusion. Two or more kinds of resins may be supplied to the extruder.

The foamed resin particles preferably have a bulk multiple of 5 to 60 times (bulk density 0.016 to 0.2 g / cm ³ ). If the bulk multiple is larger than 60 times, the closed cell ratio of the foamed particles is lowered, and the strength of the foamed molded product obtained by foaming the foamed resin particles may be lowered. On the other hand, if it is less than 5 times, the weight of the foamed molded product obtained by foaming the foamed resin particles may increase.

  The form of the foamed resin particles is not particularly limited as long as it does not affect the subsequent in-mold foam molding. For example, a true spherical shape, an elliptical spherical shape (egg shape), a cylindrical shape, a prismatic shape, and the like can be given. Of these, a true spherical shape and an elliptical spherical shape, which can be easily filled into the cavity of the mold, are preferable.

  The foamed resin particles may contain an additive. Additives include foaming nucleating agents such as talc, calcium silicate, ethylene bis-stearic acid amide, methacrylic ester copolymers, fillers such as synthetic or naturally produced silicon dioxide, hexabromocyclododecane, triallyl Flame retardants such as isocyanurate 6 bromine compounds, plasticizers such as diisobutyl adipate, liquid paraffin, glycerin diacetomonolaurate and coconut oil, colorants such as carbon black and graphite, UV absorbers, antioxidants, etc. .

<Foamed molded product>
Further, the foamed resin particles are usually stored and aged for about 24 hours. Thereafter, the resin mold is filled with foamed resin particles, heated again to foam the foamed resin particles in the mold, the particles are thermally fused, and cooled to obtain a foamed molded article. As the heating medium, water vapor having a gauge pressure of 0.05 to 0.45 MPa is preferably used, and the time for introducing water vapor is preferably 10 to 180 seconds.

The foamed molded article preferably has a bulk multiple of 5 to 60 times (bulk density 0.016 to 0.2 g / cm ³ ). If the bulk multiple is larger than 60 times, the strength of the foamed molded product may be lowered. On the other hand, if it is less than 5 times, the weight of the foamed molded product may increase.

  In the present invention, the surface layer and the inside of the foamed molded product are a length of 1/3 of the thickness from an arbitrary part having a horizontal surface of 30 mm × 30 mm or more including the skin, wherein the thickness of the foamed molded product is at least 20 mm or more. When a cube whose thickness is to be changed is divided into three equal parts in the thickness direction, the upper and lower divided pieces including the skin of the foam molded body of the three equally divided cubes are the surface layer and the surface layer not including the skin. The sandwiched piece is called the inside.

  The ratio of the bulk foaming magnification A of the surface layer of the foamed molded article to the internal bulk foaming magnification B is 1.1 ≦ B / A ≦ 1.8, preferably 1.15 ≦ B / A ≦ 1.7. It is.

Further, the obtained foamed molded article has an apparent bulk foaming ratio (bulk foaming ratio in the whole) in the range of 15 to 60 times, and the relationship between the surface hardness (CS hardness) Y and the bulk foaming ratio X is expressed by the following formula. (1):
−0.95X + 90 ≦ Y ≦ 100 (1)
Satisfying the following formula (2):
-0.90X + 90 ≦ Y ≦ 95 (2)
It is more preferable to satisfy the above.

  The obtained foamed molded products are used as cushioning materials (cushioning materials) for home appliances, electronic parts, various industrial materials, food containers, etc., automobile-related parts (for example, bumpers for automobiles, door cushioning materials, etc.) For example, an impact energy absorbing material. In particular, it can be suitably used for automobile interior materials (for example, lower limb impact absorbing materials, floor raising materials, tool boxes, etc.).

Hereinafter, although an example is given and explained further, the present invention is not limited by these examples. Various measurement methods and production conditions described in the examples will be described below.
<Pre-foaming conditions>
A PSX40 pre-foaming machine (manufactured by Kasahara Kogyo Co., Ltd.) preheated with steam is charged with 0.5 to 1.5 kg of resin particles impregnated with a foaming agent (foaming resin particles), and the gauge pressure is 0.005 to 0 while stirring. Steam is introduced at a setting of 0.09 MPa and foamed to a predetermined bulk density (bulk multiple) in 20 to 180 seconds to obtain foamed resin particles.

<Bulk density and bulk multiple of foamed resin particles>
The weight (a) of about 5 g of expanded resin particles is weighed to the second decimal place. Next, weighed foamed resin particles in a 500 cm ³ graduated cylinder with a minimum memory unit of 5 cm ³ , and this is a round resin plate slightly smaller than the caliber of the graduated cylinder, about 1.5 cm wide at the center, The volume (b) of the foamed resin particles is read by applying a pressing tool in which a rod-shaped resin plate having a length of about 30 cm is fixed upright, and the volume density (g) of the foamed resin particles is expressed by the formula (a) / (b). / Cm ³ ). The bulk multiple is the reciprocal of the bulk density, that is, the formula (b) / (a).

<Bulk density and bulk multiple of foam molded article>
The bulk density of the foam-molded product was determined by measuring the apparent volume (cm ³ ) (c) and weight (g) (d) of the foam-molded product obtained after foam molding, and using the formula (d) / (c) The bulk density (g / cm ³ ) of the expanded resin particles is determined. If the shrinkage after molding is not taken into account, the apparent volume of the foam molded body is equal to the volume in the mold cavity at the time when the foam molded body is obtained, and can be calculated from the dimensions of the mold drawing. The bulk multiple is the reciprocal of the bulk density, that is, the formula (c) / (d).

<Surface hardness of foam molding>
As a measuring device, an Asker rubber hardness meter CS type (manufactured by Kobunshi Keiki Co., Ltd.) (needle shape: height 2.54 mm, φ10 mm cylindrical shape) is used to measure the surface hardness of the foamed molded product.
A foam hardness is at least 20 mm or more, and a CS hardness meter is installed at a part arbitrarily selected from a horizontal surface of 30 mm × 30 mm or more including the skin, and a weight of 5 kg is used so that a load is applied vertically. The surface hardness of the foamed molded product was measured by pressing a CS hardness meter against the surface of the test body for 5 seconds. Similarly, measurement for a total of 20 points is performed, and the average value is defined as the surface hardness of the foamed molded product.
However, when the thickness of the foam molded body is less than 20 mm, or when the horizontal surface including the surface is less than 30 mm × 30 mm, these numerical values can be reduced to a level that does not hinder measurement.
Moreover, when it is difficult to measure a total of 20 points due to the shape of the foam molded article, the number of measurements can be reduced to a measurable number.

<Surface layer of foam molded article, bulk foaming ratio inside>
A cube having a thickness of at least 20 mm or more and having a horizontal surface of 30 mm × 30 mm or more including the outer skin is divided into three equal parts in the thickness direction with a length of 1/3 of the thickness as one side. And cut. Of the cube divided into three equal parts, the upper or lower test piece including the skin of the foam-molded product as viewed from the thickness direction is taken as test piece A, and the central test piece is taken as test piece B. For example, when the thickness of the part arbitrarily selected from the foam molded body is 30 mm, the test piece A is a cube of 10 mm on one side including the skin of the foam molded body, and the test piece B is one side not including the skin of the foam molded body. It becomes a 10 mm cube.
The bulk foaming ratio of this test piece A was measured, and the average value for a total of 10 points measured in the same manner was used as the bulk foaming ratio (Sf) of the surface layer of the foam molded article. Moreover, the bulk foaming magnification of the test piece B is measured, and the average value of 10 points measured in the same manner is defined as the bulk foaming magnification (If) inside the foamed molded product.
However, when the thickness of the foam molded body is less than 20 mm, or when the horizontal surface including the surface is less than 30 mm × 30 mm, these numerical values can be reduced to a level that does not hinder measurement.
Moreover, when it is difficult to measure a total of 10 points due to the shape of the foam molded article, the number of measurements can be reduced to a measurable number.
The ratio of internal / surface layer (If / Sf) is calculated from the surface layer of the foamed molded article and the internal bulk foaming ratio.

<Dimensional change rate after heating of foamed molded product>
Measured by the method B described in JIS K 6767: 1999K “Foamed Plastics-Polyethylene Test Method”. The test piece is 150 mm x 150 mm x 30 mm (thickness), and three straight lines are written in the center and parallel to each other in the vertical and horizontal directions at intervals of 50 mm. After 168 hours, the product is taken out, left in a standard state for 1 hour, and the vertical and horizontal line dimensions are measured by the following formula.
S = (L1-L0) / L0 × 100
In the formula, S represents a dimensional change rate (%) after heating, L1 represents an average dimension (mm) after heating, and L0 represents an initial average dimension (mm).

[Example 1]
By supplying 2000 g of polypropylene resin (manufactured by Prime Polymer Co., Ltd., trade name “F-744NP”, melting point: 140 ° C.) to an extruder, melt-kneading and granulating pellets by strand cutting, spherical (egg) Polypropylene resin particles were obtained.
The polypropylene resin particles at this time were adjusted to 60 mg per 100 particles and an average particle diameter of about 1 mm.
Next, 800 g of the polypropylene resin particles are put into a 5 L autoclave with a stirrer, and 2 kg of pure water, 20 g of magnesium pyrophosphate, and 0.5 g of sodium dodecylbenzenesulfonate are added as an aqueous medium, and the mixture is stirred and suspended in the aqueous medium. The mixture was made turbid and held for 10 minutes, and then heated to 60 ° C. to obtain an aqueous suspension.
Next, 340 g of styrene monomer in which 0.7 g of dicumyl peroxide was dissolved in this suspension was dropped in 30 minutes. After dropping, the mixture was held for 30 minutes, and the styrene monomer was absorbed by the polypropylene resin particles.
Next, the temperature of the reaction system was raised to 140 ° C., which is the same as the melting point of the polypropylene resin particles, and maintained for 2 hours to polymerize the styrene monomer in the polypropylene resin particles (first polymerization).
Next, the reaction liquid of the first polymerization is set to 120 ° C. that is 20 ° C. lower than the melting point of the polypropylene resin particles, and 1.5 g of sodium dodecylbenzenesulfonate is added to this suspension, and then the polymerization initiator is used. 860 g of a styrene monomer body in which 3.6 g of dicumyl peroxide was dissolved was dropped over 4 hours, and polymerization (second polymerization) was performed while absorbing the polypropylene resin particles.
After the completion of the dropping, the mixture was held at 120 ° C. for 1 hour, then heated to 140 ° C. and held for 3 hours to complete the polymerization, and modified resin particles were obtained.

Thereafter, the temperature of the reaction system is set to 60 ° C., and tri (2,3-
20 g of dibromopropyl) isocyanate (manufactured by Nippon Kasei Co., Ltd.) and 2,3-
10 g of dimethyl-2,3-diphenylbutane (manufactured by Kayaku Akzo) was added, and after the addition, the temperature of the reaction system was raised to 130 ° C., stirring was continued for 2 hours, and then cooled to room temperature. The modified resin particles were taken out from the 5 L autoclave. 2 kg of modified resin particles and 2 L of water after taking out were again put into a 5 L autoclave with a stirrer, and 300 g of butane as a blowing agent was injected into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 70 ° C. and stirring was continued for 4 hours.
Then, it cooled to normal temperature, took out from the 5L autoclave, and after dehydrating and drying, the resin particle (foamable resin particle) which the foaming agent was impregnated was obtained.

Next, the obtained expandable resin particles were pre-expanded to a bulk expansion ratio of 20 times to obtain expanded resin particles.
Further, the obtained foamed resin particles were allowed to stand at room temperature for one day, and then filled into the cavity of a mold having a cavity of 400 mm × 300 mm × 30 mm, and 0.25 MPa of water vapor was added to the mold for 50 seconds. It was introduced and heated, and then cooled until the maximum surface pressure of the foamed molded product was reduced to 0.001 MPa to obtain a foamed molded product.
Under these molding conditions, a foamed molded article having good appearance and fusion was obtained.
Then, using the obtained foamed molded article, the bulk foamed article, the apparent bulk foaming ratio, the CS hardness, and the dimensional change rate after heating were measured.
Various measurement results are shown in Table 1.

[Example 2]
A foamed molded article was produced in the same manner as in Example 1 except that the expandable resin particles formed in the same manner as in Example 1 were pre-expanded to a bulk expansion ratio of 40 times.
Various measurement results are shown in Table 1.

[Example 3]
Example except that foamable resin particles formed in the same manner as Example 1 were pre-expanded to a bulk expansion ratio of 50 times, and 0.20 MPa of water vapor was introduced into the mold for 50 seconds. In the same manner as in Example 1, a foam molded article was produced.
Various measurement results are shown in Table 1.

[Example 4]
By supplying 2000 g of polypropylene resin (manufactured by Prime Polymer Co., Ltd., trade name “F-744NP”, melting point: 140 ° C.) to an extruder, melt-kneading and granulating pellets by strand cutting, spherical (egg) Polypropylene resin particles were obtained.
The polypropylene resin particles at this time were adjusted to 60 mg per 100 particles and an average particle diameter of about 1 mm.
600 g of the polypropylene resin particles are placed in a 5 L autoclave with a stirrer, and 2 kg of pure water, 20 g of magnesium pyrophosphate, and 0.5 g of sodium dodecylbenzenesulfonate are added as an aqueous medium, and the mixture is stirred and suspended in an aqueous medium. The mixture was held for 1 minute, and then heated to 60 ° C. to obtain an aqueous suspension.
To this suspension, 250 g of styrene monomer in which 0.5 g of dicumyl peroxide was dissolved was dropped in 30 minutes. After dropping, the mixture was held for 30 minutes, and the styrene monomer was absorbed by the polypropylene resin particles.
Next, the temperature of the reaction system was raised to 140 ° C., which is the same as the melting point of the polypropylene resin particles, and maintained for 2 hours to polymerize the styrene monomer in the polypropylene resin particles (first polymerization).
The reaction solution in the first polymerization stage is set to 120 ° C., which is 20 ° C. lower than the melting point of the polypropylene resin particles, and 1.5 g of sodium dodecylbenzenesulfonate is added to this suspension, and then 4.2 g of dicumyl peroxide is added. Polymerization was carried out while 1150 g of a styrene monomer in which was dissolved was dropped over 5.5 hours and absorbed by polypropylene resin particles.
After completion of the dropping, the temperature was maintained at 120 ° C. for 1 hour, and then the temperature was increased to 140 ° C. and maintained for 3 hours to complete the polymerization (second polymerization stage) to obtain modified resin particles.

Thereafter, the temperature of the reaction system was set to 60 ° C., and 20 g of tri (2,3-dibromopropyl) isocyanate (manufactured by Nippon Kasei Co., Ltd.) and 2,3-dimethyl-2,3-diphenylbutane were added to this suspension. 10 g (made by Kayaku Akzo Co., Ltd.) is charged, and after the charging, the temperature of the reaction system is raised to 130 ° C., stirring is continued for 2 hours, then cooled to room temperature, and the modified resin particles are removed from the 5 L autoclave. It was. 2 kg of modified resin particles and 2 L of water after taking out were again put into a 5 L autoclave with a stirrer, and 300 g of butane as a blowing agent was injected into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 70 ° C. and stirring was continued for 4 hours.
Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
A foamed molded article was produced in the same manner as in Example 1 except that the foamable resin particles were prefoamed to a bulk foaming ratio of 40 times.
Various measurement results are shown in Table 1.

[Example 5]
By supplying 2000 g of polypropylene resin (manufactured by Prime Polymer Co., Ltd., trade name “F-744NP”, melting point: 140 ° C.) to an extruder, melt-kneading and granulating pellets by strand cutting, spherical (egg) Polypropylene resin particles were obtained.
The polypropylene resin particles at this time were adjusted to 60 mg per 100 particles and an average particle diameter of about 1 mm.
1000 g of the polypropylene resin particles are put in a 5 L autoclave with a stirrer, and 2 kg of pure water, 20 g of magnesium pyrophosphate and 0.5 g of sodium dodecylbenzenesulfonate are added as an aqueous medium, and the mixture is stirred and suspended in an aqueous medium. The mixture was held for 1 minute, and then heated to 60 ° C. to obtain an aqueous suspension.
To this suspension, 420 g of a styrene monomer in which 0.8 g of dicumyl peroxide was dissolved was dropped in 30 minutes. After dropping, the mixture was held for 30 minutes, and the styrene monomer was absorbed by the polypropylene resin particles.
Next, the temperature of the reaction system was raised to 140 ° C., which is the same as the melting point of the polypropylene resin particles, and maintained for 2 hours to polymerize the styrene monomer in the polypropylene resin particles (first polymerization).
The reaction solution in the first polymerization stage is set to 120 ° C., which is 20 ° C. lower than the melting point of the polypropylene resin particles, 1.5 g of sodium dodecylbenzenesulfonate is added to this suspension, and then 3 g of dicumyl peroxide is dissolved. The styrene monomer 580g was dripped over 2.75 hours, and it superposed | polymerized, making it absorb to a polypropylene resin particle.
After completion of the dropping, the temperature was maintained at 120 ° C. for 1 hour, and then the temperature was increased to 140 ° C. and maintained for 3 hours to complete the polymerization (second polymerization stage) to obtain modified resin particles.

Thereafter, the temperature of the reaction system was set to 60 ° C., and 20 g of tri (2,3-dibromopropyl) isocyanate (manufactured by Nippon Kasei Co., Ltd.) and 2,3-dimethyl-2,3-diphenylbutane were added to this suspension. 10 g (made by Kayaku Akzo Co., Ltd.) is charged, and after the charging, the temperature of the reaction system is raised to 130 ° C., stirring is continued for 2 hours, then cooled to room temperature, and the modified resin particles are removed from the 5 L autoclave. It was. 2 kg of modified resin particles and 2 L of water after taking out were again put into a 5 L autoclave with a stirrer, and 300 g of butane as a blowing agent was injected into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 70 ° C. and stirring was continued for 4 hours.
Then, it cooled to normal temperature, took out from the 5L autoclave, dehydrated and dried, and obtained expandable resin particles.
A foamed molded article was produced in the same manner as in Example 1 except that the foamable resin particles were prefoamed to a bulk foaming ratio of 30 times.
Various measurement results are shown in Table 1.

[Example 6]
The foamed resin particles having a bulk expansion ratio of 40 times obtained in the same manner as in Example 2 were allowed to stand at room temperature for 1 day, and then filled into the cavity of a mold having a cavity of 400 mm × 300 mm × 50 mm, 0.25 MPa of water vapor was introduced into the mold for 50 seconds and heated, and then cooled until the maximum surface pressure of the foamed article was reduced to 0.001 MPa to produce a foamed article.
Various measurement results are shown in Table 1.

[Example 7]
The foamed resin particles having a bulk expansion ratio of 40 times obtained in the same manner as in Example 6 were allowed to stand at room temperature for 1 day, and then filled into the cavity of a mold having a cavity of 400 mm × 300 mm × 100 mm, 0.25 MPa of water vapor was introduced into the mold for 50 seconds and heated, and then cooled until the maximum surface pressure of the foamed article was reduced to 0.001 MPa to produce a foamed article.
Various measurement results are shown in Table 1.

[Comparative Example 1]
Example except that foamable resin particles formed in the same manner as in Example 1 were pre-expanded to a bulk expansion ratio of 50 times, and 0.15 MPa of water vapor was introduced into the mold for 50 seconds. In the same manner as in Example 1, a foam molded article was produced.
Various measurement results are shown in Table 1.

[Comparative Example 2]
Except that foamable resin particles formed in the same manner as in Example 1 were pre-expanded to a bulk expansion ratio of 30 times, and 0.13 MPa of water vapor was introduced into the mold for 50 seconds to perform the example. In the same manner as in Example 1, a foam molded article was produced.
Various measurement results are shown in Table 1.

From the results shown in Table 1, Examples 1 to 7 in which the ratio of the apparent bulk foaming ratio between the inside of the foamed molded product and the surface layer (internal / surface layer) was large, the foaming rate was small and the good foaming rate was small. A molded product could be obtained, and good results were obtained for the CS hardness of the surface of the obtained foamed molded product.
On the other hand, Comparative Example 1 in which the ratio of the apparent bulk foaming ratio between the inside and the surface layer of the foamed molded body (internal / surface layer) became smaller was the same as Example 3 in which the apparent bulk foaming ratio of the entire foamed molded body was substantially the same. In comparison, the CS hardness of the surface of the foamed molded product was low.
Further, as in Comparative Example 1, Comparative Example 2 in which the ratio of the apparent bulk foaming ratio between the inside and the surface layer of the foamed molded product (internal / surface layer) is smaller is the apparent appearance of the entire foamed molded product compared to Example 2. Although the bulk foaming ratio was 10 or more, only the same CS hardness could be exhibited.

  From the above, the foamed molded article having a ratio of the bulk foaming ratio between the surface layer and the inside of 1.1 ≦ internal / surface layer ≦ 1.8, preferably 1.15 ≦ internal / surface layer ≦ 1.7, Since the hardness is good and the dimensional change rate after heating is small, it can be seen that it is excellent.

Claims (6)

  It is a foamed molded product derived from the same type of foamed resin particles, and the ratio of the bulk foaming magnification Sf of the surface layer of the foamed molded product to the internal bulk foaming magnification If is 1.1 ≦ If / Sf ≦ 1.8. A foamed molded product, characterized by being a foamed product.   The foamed molded product according to claim 1, wherein the ratio If / Sf is 1.15 to 1.7.   The foamed molded product according to claim 1 or 2, wherein the foamed resin particles are foamed resin particles containing 100 parts by mass or more and less than 400 parts by mass of a polystyrene resin with respect to 100 parts by mass of the polypropylene resin. The foamed molded article has a bulk foaming ratio of 15 to 60 times in its entirety, and the following formula (1)
−0.95X + 90 ≦ Y ≦ 100 (1)
(Where Y is the surface hardness (CS hardness) and X is the bulk foaming ratio)
The foaming molding as described in any one of Claims 1-3 which satisfy | fills. The surface hardness Y and the bulk foaming magnification X are expressed by the following formula (2).
-0.90X + 90 ≦ Y ≦ 95 (2)
The foaming molding of Claim 4 which satisfy | fills.   JIS K6767: The foamed molded product according to any one of claims 1 to 5, wherein a dimensional change rate after heating at 80 ° C and 168 hours measured by B method of 1999K satisfies 1.0% or less in absolute value.