Polyamide resin foamed particle, and polyamide resin foamed molding

Abstract

To provide a polyamide resin foamed particle having a foaming temperature lower than before, and excellent in foamability and uniformity.SOLUTION: A polyamide resin foamed particle includes a polyamide resin where there is one endothermic peak derived from melting of a polyamide crystal in a dry DSC curve obtained by rising temperature to 280°C from 30°C by a temperature rising rate of 10°C / min using a differential scanning calorimeter, and there are two or more endothermic peaks derived from melting of a polyamide crystal in a wet DSC curve obtained by rising temperature to 280°C from 30°C by a temperature rising rate of 10°C / min using a differential scanning calorimeter after immersing a sample in water for 24 hr. at 25°C.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to expanded polyamide resin particles and expanded molded polyamide resin articles. [Background technology]

[0002] Polyamide resins such as polyamide 6 and polyamide 66 (hereinafter sometimes abbreviated as "PA6" and "PA66", respectively) have excellent moldability, mechanical properties, and chemical resistance. For this reason, polyamides are widely used as various parts and materials for automobiles, electrical and electronics, industrial machinery, industrial materials, daily necessities, household goods, etc.

[0003] Furthermore, polyamide resins can be used as polyamide resin foam molded articles that require chemical resistance and heat resistance. For example, Patent Document 1 discloses polyamide foam beads suitable for forming foam molded articles with a high expansion ratio by secondary expansion in a bead expansion method, and a foam molded article made of the polyamide foam beads.

[0004] However, since common polyamide resins such as PA6 have a high melting point and are highly crystalline, there was an issue that in order to obtain a foamable molded product, heating at high temperatures was required, which required a lot of time and thermal energy. In addition, since the viscoelasticity of typical polyamide resins drops sharply near the melting point, it has been difficult to achieve a high expansion ratio while maintaining closed cells. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-105879 A Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, an object of the present invention is to provide polyamide-based resin foamed beads which have a lower foaming temperature than conventional ones and are excellent in foaming property and uniformity, and a polyamide-based resin foamed molded article which is formed from the polyamide-based resin foamed beads and has excellent lightweight properties. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors conducted extensive research and found that, by using a specific polyamide resin, in a DSC curve obtained by heating from 30°C to 280°C at a heating rate of 10°C / min using a differential scanning calorimeter during water absorption, multiple endothermic peaks resulting from polyamide crystalline melting become visible and the peak temperatures become broader, and accordingly the melting point and foaming temperature of the polyamide resin can be lowered, and further, since the temperature range of the endothermic peaks is broadened, the foaming ratio can also be improved, which led to the completion of the present invention.

[0008] That is, the present invention is as follows. (1) A polyamide-based resin foamed particle containing a polyamide resin, In the DSC curve when the material is dried and heated from 30°C to 280°C at a heating rate of 10°C / min using a differential scanning calorimeter, there is one endothermic peak due to the crystalline melting of the polyamide. The DSC curve of the product, which is immersed in water at 25°C for 24 hours and then heated from 30°C to 280°C at a heating rate of 10°C / min using a differential scanning calorimeter, shows two or more endothermic peaks due to the crystalline melting of the polyamide. 1. A polyamide resin foam particle comprising: (2) The expanded polyamide resin particles according to (1), characterized in that they contain 5 to 40 mass % of amorphous polyamide. (3) The expanded polyamide resin particles according to claim (2), wherein the amorphous polyamide is polyamide 6I. (4) The expanded polyamide resin particles according to any one of (1) to (3), wherein the polyamide is an alloy of two or more kinds of polyamides. (5) The expanded polyamide resin particles according to (4), wherein the polyamide is an alloy of three or more kinds of polyamides. (6) The width of the endothermic peak due to the crystalline melting of polyamide in the DSC curve of the polyamide-based resin foamed particles when absorbing water is heated from 30° C. to 280° C. at a heating rate of 10° C. / min using a differential scanning calorimeter is 30 The expanded polyamide resin particles according to any one of (1) to (3), characterized in that the temperature is 0.2 ° C. or higher. (7) The expanded polyamide resin beads according to any one of (1) to (3), characterized in that the expanded polyamide resin beads have a melting initiation temperature of 125° C. or lower when absorbing water. (8) The expanded polyamide resin particles according to any one of (1) to (3), characterized in that the closed cell ratio is 80% or more. (9) The expanded polyamide resin particles according to any one of (1) to (3), characterized in that the coefficient of variation of cell diameter is 15% or less. (10) The expanded polyamide resin particles according to any one of (1) to (3), characterized in that the sphericity is 1.2 or less. (11) A polyamide resin foamed molded article, which is formed from the polyamide resin foamed particles according to any one of (1) to (3). (12) The polyamide resin foam molded article according to (11), characterized in that the bead density is 500 g / L or less. Effect of the Invention

[0009] According to the present invention, it is possible to provide polyamide-based resin expanded beads having a lower expansion temperature than conventional ones and excellent expandability and uniformity, and a polyamide-based resin expanded molded article formed from the polyamide-based resin expanded beads and having excellent lightweight properties. [Brief description of the drawings]

[0010] [Figure 1]FIG. 1 is a schematic diagram showing endothermic peaks resulting from polyamide crystalline melting in a DSC curve, in which (a) shows the endothermic peak of conventional expanded polyamide-based resin beads, and (b) shows the endothermic peak of the expanded polyamide-based resin beads of the present embodiment upon water absorption. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The following embodiments are merely illustrative for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be modified appropriately within the scope of the gist thereof.

[0012] In this specification, the term "polyamide" refers to a polymer having an amide group (-NHCO-) ​​in the main chain.

[0013] [Polyamide resin foam particles] The expanded polyamide resin beads of the present embodiment are expanded polyamide resin beads containing a polyamide resin.

[0014] (Constituents of polyamide resin foam particles) Hereinafter, each component constituting the expanded polyamide resin beads of the present embodiment will be described in detail.

[0015] The expanded polyamide resin particles of the present embodiment contain a polyamide resin. Examples of the polyamide resin include polyamide, polyamide copolymer, and mixtures thereof. Examples of the polyamide include polyamide 66, polyamide 610, polyamide 612, polyamide 46, polyamide 1212, polyamide 6I, polyamide 6T, etc., which are obtained by condensation polymerization of diamine and dicarboxylic acid, and polyamide 6 and polyamide 12, etc., which are obtained by ring-opening polymerization of lactam. Examples of the polyamide copolymer include polyamide 6 / 66, polyamide 66 / 6, polyamide 66 / 610, polyamide 66 / 612, polyamide 66 / 6T (T represents a terephthalic acid component), polyamide 66 / 6I (I represents an isophthalic acid component), polyamide 6T / 6I, etc. These may be used alone or in combination of two or more.

[0016] Among these, the polyamide preferably contains at least an amorphous polyamide, and more preferably contains polyamide 6I as the amorphous polyamide. By including an amorphous polyamide as the polyamide, it is possible to obtain two or more endothermic peaks resulting from the crystalline melting of the polyamide upon water absorption, as described below.

[0017] In addition, from the viewpoint of being able to have two or more endothermic peaks resulting from the crystalline melting of the polyamide upon water absorption, as described below, the polyamide is preferably an alloy of two or more types of polyamide. Examples of the alloy of two or more kinds of polyamides include a mixture of polyamide 66 and polyamide 6, a mixture of polyamide 66 / 6 and polyamide 6, a mixture of polyamide 66 and polyamide 612, a mixture of polyamide 66 and polyamide 610, a mixture of polyamide 6 and polyamide 610, a mixture of polyamide 6 and polyamide 6I, a mixture of polyamide 6 and polyamide 6I / 6T, etc. These may be a mixture of two kinds, or a combination of three or more kinds may be used. Among these, from the viewpoints of recyclability, raw material procurement, and the balance between heat resistance and foaming properties, it is preferable to use a mixture of polyamide 6 and polyamide 6I, or a mixture of polyamide 6, polyamide polyamide 6I, and polyamide 6 / 66.

[0018] In addition, when two or more kinds of the polyamides are contained, a compatibilizer can be further contained appropriately from the viewpoint of improving the compatibility. The compatibilizer to be used can be a generally known non-reactive or reactive compound. As the non-reactive type, AB random copolymer, AB block copolymer, A polymer grafted with B polymer, etc. are preferable, and specifically, polyamide 6 / 66, polyamide 66 / 6I, polyamide 66 / 610, etc. can be mentioned. Therefore, the combination of polyamides contained in the expanded polyamide resin particles of the present embodiment described above is particularly preferably a mixture of polyamide 6, polyamide polyamide 6I, and polyamide 6 / 66. The content of the compatibilizer is preferably 1% by mass or more from the viewpoint of improving the compatibility of the polyamide, and the amount of the compatibilizer added is preferably 30% by mass or less from the viewpoint of maintaining the mechanical properties and heat resistance of the base polyamide resin.

[0019] Furthermore, when the expanded polyamide resin particles of this embodiment contain the amorphous polyamide, the content of the amorphous polyamide is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less. When the content of the amorphous polyamide is 5% by mass or more, crystal growth of the polyamide can be suppressed, and thus the number of endothermic peaks resulting from crystalline melting of the polyamide upon water absorption, as described below, can be made two or more. When the content of the amorphous polyamide is 40% by mass or less, a decrease in crystallinity can be suppressed, and better foamability can be obtained.

[0020] Furthermore, in the case of the polyamide resin expanded beads of the present embodiment, from the viewpoint of increasing the crystallinity of the polyamide resin expanded beads and the foamed molded article and thereby ensuring sufficient heat resistance and fusion rate, the polyamide resin in the case of the mixture preferably contains more than 50 mass % of aliphatic polyamide, more preferably 60 mass % or more, while from the viewpoint of reducing the weight of the expanded beads, it is preferably 80 mass % or less.

[0021] In addition, for the polyamide, the highly reactive functional groups (amino groups and carboxyl groups) at the terminals can be converted into less reactive functional groups (terminals of the polyamide resin can be blocked) by adding a terminal blocking agent during the synthesis of the polyamide. In this case, the timing for adding the end-capping agent may be when the raw materials are charged, at the start of polymerization, during or at the end of polymerization. The end-capping agent is not particularly limited as long as it is a monofunctional compound capable of reacting with the amino group or carboxyl group of the polyamide, and examples thereof include monocarboxylic acids, monoamines, acid anhydrides, monoisocyanates, monoacid halides, monoesters, monoalcohols, etc. These may be used alone or in combination of two or more.

[0022] The expanded polyamide resin particles of the present embodiment may contain components (other components) other than the polyamide resin described above, such as stabilizers, impact modifiers, flame retardants, lubricants, pigments, dyes, weather resistance improvers, antistatic agents, impact resistance modifiers, crystal nucleating agents, glass beads, inorganic fillers, crosslinking agents, nucleating agents such as talc, and other thermoplastic resins. The content of other components in the polyamide resin expanded particles of the present embodiment may be 15 parts by mass or less, preferably 6 parts by mass or less, and more preferably 3 parts by mass or less, based on 100 parts by mass of the polyamide resin.

[0023] The stabilizer is not particularly limited, and examples thereof include organic antioxidants and heat stabilizers such as hindered phenol antioxidants, sulfur antioxidants, phosphorus antioxidants, phosphite compounds, and thioether compounds; light stabilizers and ultraviolet absorbers such as hindered amines, benzophenones, and imidazoles; metal deactivators, etc. These may be used alone or in combination of two or more.

[0024] As the heat stabilizer, from the viewpoint of effectively preventing long-term heat aging in a high-temperature environment of 120°C or more, a copper compound is preferable, and a combination of this copper compound and an alkali metal halide compound is also preferable. Here, examples of the alkali metal halide compound include lithium chloride, lithium bromide, lithium iodide, sodium fluoride, sodium chloride, sodium bromide, sodium iodide, potassium fluoride, potassium chloride, potassium bromide, and potassium iodide. These may be used alone or in combination of two or more.

[0025] The flame retardant is not particularly limited, but a combination of a halogen-based flame retardant and an antimony compound is preferred. Here, preferred halogen-based flame retardants include brominated polystyrene, brominated polyphenylene ether, brominated bisphenol type epoxy resin, brominated styrene-maleic anhydride copolymer, brominated epoxy resin, brominated phenoxy resin, decabromodiphenyl ether, decabromo biphenyl, brominated polycarbonate, perchlorocyclopentadecane, and brominated crosslinked aromatic polymers, and preferred antimony compounds include antimony trioxide, antimony pentoxide, and sodium antimonate. As the flame retardant, a combination of dibromopolystyrene and antimony trioxide is preferred from the viewpoint of thermal stability. In addition, non-halogen flame retardants may also be used as the flame retardant. Specific examples of the flame retardant include melamine cyanurate, red phosphorus, metal phosphinates, and nitrogen-containing phosphate compounds. In particular, a combination of a metal phosphinate with a nitrogen-containing phosphate compound (including, for example, a reaction product or mixture of melamine or a melamine condensate (melam, melon, etc.) with polyphosphoric acid) is preferred.

[0026] In addition, when it is necessary to adjust the average bubble diameter of the expanded polyamide resin particles of the present embodiment, a bubble regulator may be added. As the bubble regulator, inorganic nucleating agents include talc, silica, calcium silicate, calcium carbonate, aluminum oxide, titanium oxide, diatomaceous earth, clay, sodium bicarbonate, alumina, barium sulfate, aluminum oxide, bentonite, etc., and the amount of the bubble regulator added is usually 0.005 to 5 parts by mass based on the total amount of the raw materials of the expanded polyamide resin particles.

[0027] (Endothermic peak of polyamide resin foam particles) The expanded polyamide resin particles of the present embodiment have one endothermic peak due to polyamide crystal melting in a DSC curve when the particles are dried and heated from 30° C. to 280° C. at a heating rate of 10° C. / min using a differential scanning calorimeter; The polyamide is immersed in water at 25°C for 24 hours, and when the polyamide absorbs water, the DSC curve obtained by heating the polyamide from 30°C to 280°C at a heating rate of 10°C / min using a differential scanning calorimeter shows two or more endothermic peaks due to crystalline melting of the polyamide. Conventionally, there is only one endothermic peak resulting from the crystalline melting of a polyamide. However, by using a specific polyamide, it is possible to obtain two or more endothermic peaks resulting from the crystalline melting of the polyamide when absorbing water. This broadens the endothermic peak width and shifts the endothermic peak to the lower temperature side. As a result, it is possible to obtain a lower foaming temperature than conventionally and to improve the foamability.

[0028] Here, Fig. 1 is a schematic diagram showing a DSC curve having an endothermic peak derived from polyamide crystalline melting. Conventional expanded polyamide resin beads have one endothermic peak derived from polyamide crystalline melting as shown in Fig. 1(a), but the expanded polyamide resin beads of the present embodiment have two or more endothermic peaks derived from polyamide crystalline melting (two in Fig. 1(b)) when absorbing water as shown in Fig. 1(b). This is thought to be because new crystals are generated simultaneously with the melting of a certain polyamide (e.g. polyamide 6), and as a result, the crystalline melting peak and the crystallization exothermic peak overlap, resulting in the acquisition of multiple peaks. In addition, the polyamide resin expanded particles of the present embodiment have two or more endothermic peaks resulting from polyamide crystalline melting when absorbing water, as shown in Fig. 1(b), but have only one endothermic peak resulting from polyamide crystalline melting when dried, as shown in Fig. 1(b), because new crystals are not formed under dry conditions.

[0029] The term "dry polyamide-based resin expanded beads" refers to a state in which there is no moisture in the polyamide-based resin expanded beads, specifically, the state after the polyamide-based resin expanded beads have been vacuum-dried at 80°C for 6 hours. In addition, the term "polyamide-based resin expanded particles when absorbing water" refers to a state in which moisture is contained in the polyamide-based resin expanded particles, specifically, the state after the polyamide-based resin expanded particles are immersed in water at 25°C for 24 hours and the water adhering to the surface is removed.

[0030] In this embodiment, the endothermic peak resulting from the crystalline melting of the polyamide is obtained from a DSC curve obtained by heating from 30° C. to 280° C. at a heating rate of 10° C. / min using a differential scanning calorimeter.

[0031] In the polyamide resin expanded beads of this embodiment, the peak temperature of the endothermic peak derived from the crystalline melting of polyamide in the DSC curve when the temperature is raised from 30°C to 280°C at a heating rate of 10°C / min using a differential scanning calorimeter during drying is preferably 150°C to 275°C, more preferably 155°C to 250°C, and even more preferably 160°C to 220°C. When the peak temperature of the endothermic peak is within the above range, foam molding using saturated steam becomes easy, which tends to be preferable in practical use. The endothermic peak temperature is the point at which the value of the DSC curve of the endothermic peak derived from the crystalline melting of polyamide becomes 0 when differentiated with respect to temperature.

[0032] In addition, in the polyamide resin expanded particles of the present embodiment, the peak temperature of the endothermic peak resulting from polyamide crystal melting in a DSC curve obtained by heating from 30° C. to 280° C. at a heating rate of 10° C. / min using a differential scanning calorimeter during water absorption is preferably 130° C. or higher and 275° C. or lower, more preferably 140° C. or higher and 200° C. or lower. When the peak temperature of the endothermic peak is within the above range, expansion molding using saturated steam becomes easy, which tends to be preferable in practical use.

[0033] Furthermore, in the polyamide resin expanded particles of this embodiment, the DSC curve when absorbing water is set to a straight line approximating the DSC curve after the end of melting at a high temperature side from the endothermic peak as a baseline, and the width of the endothermic peak corresponding to the difference between the extrapolated melting start temperature, which is the temperature of the intersection between the tangent at the inflection point on the low temperature side of the endothermic peak at the lowest temperature side and the baseline, and the extrapolated melting end temperature, which is the temperature of the intersection between the tangent at the inflection point on the high temperature side of the endothermic peak at the highest temperature side and the baseline, is preferably 30°C or more, more preferably 40°C or more. The width of the endothermic peak is preferably 80°C or less, more preferably 70°C or less. If the width of the maximum endothermic peak is 30°C or more, the foamable temperature range becomes wider, and better foamability can be obtained.

[0034] Moreover, in the DSC curve when absorbing water, the expanded polyamide resin particles of the present embodiment preferably have a melting start temperature of 130° C. or lower, more preferably 120° C. or lower. This makes it possible to obtain a lower expansion temperature than before, and also to enhance the expandability. The melting initiation temperature of the expanded polyamide resin beads is the temperature at which polyamide crystal melting begins in the DSC curve obtained when the beads are immersed in water at 25°C for 24 hours and then heated from 30°C to 280°C at a heating rate of 10°C / min using a differential scanning calorimeter after absorbing water.

[0035] (Shape of polyamide resin foam particles) The shape of the expanded polyamide resin particles of the present embodiment can be given any three-dimensional shape. This three-dimensional shape can generate interconnected voids in the foamed molded product, thereby imparting sound absorbing performance. The orthogonal projection image of the expanded polyamide resin particles can have any shape, but a general solid bead shape means an approximately spherical shape having a circular or elliptical orthogonal projection image. In one embodiment of the present invention, having a hollow portion means that the orthogonal projection image of a polyamide-based resin foamed particle has a hollow region inside and an outer peripheral region surrounding the outer hollow circular region, and that there exists a direction in which an orthogonal projection image having such a hollow region and outer peripheral region can be obtained. In addition, the term "having a concave outer shape" refers to selecting the shape of the resin foam particles so that the concave outer shape satisfies the conditions of the concave portion and / or the conditions of the through holes, thereby allowing the formation of good interconnected voids (continuous voids, interconnected voids) in the polyamide resin foam molded article after fusion molding.

[0036] In addition, from the viewpoint of improving the secondary expansion property of the expanded polyamide resin beads of the present embodiment, it is preferable that the cell diameter of the expanded polyamide resin beads is uniform. Here, the bubble diameter of the expanded polyamide resin beads is calculated by taking an image of the central surface of the expanded polyamide resin beads using an electron microscope or the like, taking the longest line segment passing through the center of the bead cross section as the maximum diameter μ, cutting out an area of ​​μ / 2 square from the center of the bead, calculating the area of ​​the closed bubbles for all the bubbles, and approximating the diameter to a circle, d = 2(S / 3.14) 1 / 2 is calculated for each bubble. If the number of independent bubbles is less than 30, images of multiple expanded polyamide resin beads are used so that the total number of independent bubbles is 30 or more. The average value, standard deviation, and coefficient of variation (= standard deviation / average value) are calculated from the values ​​of all the bubbles.

[0037] In this embodiment, the expanded bead is cut through its center and divided into two, and an image is taken with a scanning electron microscope at a magnification of 50 times. The image is binarized into bubble films and closed bubbles using image analysis software "Image J", and the total bubble area in an area 500 μm square from the center is calculated, and the diameter of the bubble that approximates a circle is calculated. However, there are no limitations on the manufacturer of the electron microscope or the image analysis software, as long as the method can calculate the bubble diameter in a similar manner.

[0038] The polyamide-based expanded beads of the present embodiment preferably have a closed cell ratio of 80% or more, and more preferably 85% or more. Here, the closed cell ratio was determined by measuring the mass W (kg) of the obtained polyamide resin foamed beads, and then measuring the apparent volume Va (m 3 The mass W was then divided by the apparent volume Va to obtain W / Va (kg / m 3 ) was taken as the density of the expanded polyamide resin beads. The true volume (Vx) of the expanded polyamide resin beads whose apparent volume Va and mass W were measured above was measured using an air comparison type specific gravity meter (manufactured by Beckman Co., Ltd.). The closed cell ratio S (%) was calculated according to the formula described below. S(%)={(Vx-W / ρ) / (Va-W / ρ)}×100 In the formula, ρ is the density of the polyamide resin foam particles (g / cm 3 ). It can be calculated as follows.

[0039] Furthermore, from the viewpoint of improving the mold filling property during expansion molding, the cross-sectional sphericity of the expanded polyamide resin beads of this embodiment is preferably 1.2 or less, and more preferably 1.1 or less. In measuring the cross-sectional sphericity, the expanded polyamide resin bead is first divided into two parts passing through its center. In an image of the cross-section taken with an electron microscope or a microscope, the longest line passing through the center is taken as the maximum diameter, and the line perpendicular to this is taken as the minimum diameter. The cross-sectional sphericity of the expanded polyamide resin bead is calculated as follows: cross-sectional sphericity = maximum diameter / minimum diameter.

[0040] Furthermore, the number average cell diameter of the closed cells of the expanded polyamide resin particles of the present embodiment is preferably 20 μm or more and 1000 μm or less, which allows processing into an expanded molded product with a high expansion ratio and excellent mechanical properties without breaking the intercellular membrane during the expansion process.

[0041] The particle size of the polyamide resin foam particles of the present embodiment is not particularly limited, but may be, for example, 0.2 mm to 4 mm, in which case a polyamide resin foam molded article having better mechanical properties can be obtained.

[0042] (Method of manufacturing polyamide resin foam particles) The method for producing the expanded polyamide resin particles of the present embodiment is not particularly limited. For example, a method utilizing the thermoplasticity of a thermoplastic resin, a method of post-processing such as cutting of solid particles, etc. are possible, and any method that can give a desired outer shape to the particles can be applied. Among these, the melt extrusion method using a die with an extrusion cross section can be suitably used as a method that is excellent in productivity and can produce particles with a stable shape.As the melt extrusion method, a method of melt extruding a thermoplastic resin by an extruder, pelletizing the pellets obtained by a method commonly used in industry such as strand cutting or underwater cutting, and expanding the pellets to obtain expanded particles; a method of injecting a foaming agent into an extruder from the middle of the barrel, foaming at the same time as discharging, and then underwater cutting or strand cutting to obtain expanded particles directly after cooling; a method of melting in an extruder, extruding from a die with a desired cross section, cutting to a predetermined length by a pelletizer after cooling to produce a base resin pellet, impregnating the base resin pellet with a foaming agent, and expanding at a predetermined expansion ratio by heating; and the like; can be produced by arbitrarily applying a conventionally known method.

[0043] In the melt extrusion step, from the viewpoint of improving the compatibility between the raw polyamide resins, the resin temperature is preferably 260° C. or higher, more preferably 280° C. or higher, and even more preferably 300° C. or higher. In addition, from the viewpoint of suppressing decomposition of the raw polyamide resins, the resin temperature in the melt extrusion step is preferably 350° C. or lower, and even more preferably 330° C. or lower. The resin temperature during the melt extrusion can be adjusted, for example, by setting the cylinder temperature of the extruder, the screw rotation speed, etc. By obtaining expanded beads through production conditions in which the resin temperature is controlled within the above range, expanded polyamide resin beads having excellent uniformity in internal cell size can be obtained.

[0044] [Polyamide resin foam molding]

[0045] The polyamide resin foamed molded article of the present embodiment is formed from the above-mentioned polyamide resin foamed beads. As a result, the polyamide resin foam molded article of this embodiment has excellent lightweight properties.

[0046] The polyamide-based resin foamed molded article of the embodiment can be molded into any three-dimensional shape by fusing the above-mentioned polyamide-based resin foamed particles to each other. The polyamide resin foam molded article of the present embodiment is produced by filling a closed mold with polyamide resin foam particles and foaming the particles, but a method of filling an unsealable mold and heating the mold particles to fuse the resin foam particles together may also be used. Depending on the type of resin and molding conditions, a general-purpose automatic in-mold foam molding machine may be used.

[0047] Moreover, the polyamide resin foam molded article of this embodiment preferably has a bead density of 500 g / L or less, because this allows the foam molded article to have excellent lightweight properties.

[0048] The heating temperature of the polyamide resin expanded particles is preferably 100°C or more and 270°C or less, since the fusion between the particles proceeds, and more preferably 105°C or more and 260°C or less. The molding method is not particularly limited, but for example, the polyamide resin expanded particles are filled into the cavity of a molding die and heated to cause foaming and simultaneously heat-fuse the polyamide resin expanded particles to each other, and then the product is solidified by cooling and molded. Here, the method of filling the polyamide resin expanded particles is not particularly limited, but examples thereof include a cracking method in which the polyamide resin expanded particles are filled with the die slightly open, a compression method in which the polyamide resin expanded particles compressed under pressure are filled with the die closed, and a compression cracking method in which the above-mentioned cracking method is carried out after the compressed polyamide resin expanded particles are filled into the die.

[0049] In this embodiment, from the viewpoint of applying a certain gas pressure to the bubbles of the polyamide-based resin expanded beads to make the size of the bubbles (cell size) inside the beads uniform, it is preferable to perform a gas pressure treatment on the polyamide-based resin expanded beads before filling the polyamide-based resin expanded beads into the cavity of the molding die. The method of the pressure treatment is not particularly limited, and for example, from the viewpoint of efficiently carrying out the gas pressure treatment on the polyamide-based resin expanded beads, the atmospheric pressure is preferably 0.3 MPa or more and 6.0 MPa or less, and the atmospheric temperature is preferably 5°C or more and 50°C or less.

[0050] The gas used in the pressurization treatment is not particularly limited, but may be inorganic compounds such as carbon dioxide, nitrogen, oxygen, hydrogen, argon, helium, and neon; fluorocarbons such as trichlorofluoromethane (R11), dichlorodifluoromethane (R12), chlorodifluoromethane (R22), tetrachlorodifluoroethane (R112), dichlorofluoroethane (R141b), chlorodifluoroethane (R142b), difluoroethane (R152a), HFC-245fa, HFC-236ea, HFC-245ca, and HFC-225ca; HF Examples of such hydrocarbons include hydrofluoroolefins such as O-1234y and HFO-1234ze(E); saturated hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, and neopentane; ethers such as dimethyl ether, diethyl ether, methyl ethyl ether, isopropyl ether, n-butyl ether, diisopropyl ether, furan, furfural, 2-methylfuran, tetrahydrofuran, and tetrahydropyran; chlorinated hydrocarbons such as methyl chloride and ethyl chloride; and alcohols such as methanol and ethanol. Among these, it is preferable to use inorganic gases from the viewpoints of flame retardancy, heat resistance, and dimensional stability. These compounds which can be converted into air or gas may be used alone or in combination of two or more.

[0051] The heat transfer medium used when molding the polyamide-based resin foamed beads may be a general-purpose heat transfer medium, and from the viewpoint of suppressing oxidative deterioration of the foamed molded body, saturated steam or superheated steam is preferable, and from the viewpoint of enabling uniform heating of the foamed molded body, saturated steam is more preferable.

[0052] When saturated steam is used as the heat transfer medium, it is preferable to set the molding temperature to 100°C or higher, heat (preheat) the material with saturated steam at a temperature of the molding temperature -5°C or lower for 1 to 10 seconds, and then heat-seal the material with saturated steam at the molding temperature. The temperature of the saturated steam used for the preheating is not higher than the molding temperature −5° C., preferably not higher than the molding temperature −6° C., and more preferably not higher than the molding temperature −7° C. The temperature of the saturated steam is preferably not lower than the molding temperature −15° C., more preferably not lower than the molding temperature −14° C., and even more preferably not lower than the molding temperature −13° C. When the temperature is within the above range, there is a tendency that moisture can be diffused into the expanded polyamide resin particles while suppressing the expansion and fusion of the expanded polyamide resin particles. The heating time with saturated steam used for the preheating is from 1 to 10 seconds, preferably from 1 to 5 seconds, and more preferably from 1 to 3 seconds. Conventionally, the step of preheating the expanded polyamide resin beads to a temperature close to the molding temperature has been problematic in that the total time required for molding is extended and productivity is reduced, but when the heating time is within the above range, moisture can be diffused into the expanded polyamide resin beads within a range that is practically acceptable for solving the problem, and fusion property at the molding temperature tends to be improved.

[0053] In another aspect of the method for producing a polyamide-based resin foamed molded article of the present embodiment, expanded polyamide-based resin particles having a water content of 0% by mass or more and 12% by mass or less are filled into a mold, the particles are heated at a molding temperature of 100°C or more for 15 seconds or more using saturated steam at a temperature of the molding temperature -5°C or less, and then the particles are heat-fused using saturated steam at the molding temperature. By using the above-mentioned production method, the fusion property between the expanded polyamide resin particles during molding is improved, and a polyamide resin foamed molded article having excellent mechanical strength can be produced.

[0054] In another aspect of the method for producing a polyamide-based resin foamed molded article of the present embodiment, the method for filling the cavity of the molding die with the polyamide-based resin foamed particles is not particularly limited, and examples of the method include the cracking method, compression method, and compression cracking method described above. The expanded polyamide resin particles may be subjected to a solvent treatment before being filled into the cavity of the molding die. The solvent and the solvent treatment method used for the solvent treatment may be the same as those described above. Furthermore, the expanded polyamide resin particles are preferably subjected to a pressure treatment with a gas before being filled into the cavity of the molding die. The pressure treatment method and the gas used for the pressure treatment can be the same as those described above.

[0055] In another aspect of the method for producing a polyamide resin foamed molded article of the present embodiment, the molding temperature of the polyamide pre-expanded particles is 100°C or higher, and from the viewpoint of promoting fusion between the particles, the molding temperature is preferably 100°C or higher and 270°C or lower, and more preferably 105°C or higher and 260°C or lower.

[0056] In another aspect of the method for producing a polyamide-based resin foamed molded article of the present embodiment, the polyamide-based resin foamed particles are heated (preheated) for 15 seconds or more with saturated steam at a temperature of the molding temperature -5°C or lower before being heated with saturated steam at the molding temperature. The temperature of the saturated steam used for the preheating is not higher than the molding temperature −5° C., preferably not higher than the molding temperature −6° C., and more preferably not higher than the molding temperature −7° C. The temperature of the saturated steam is preferably not lower than the molding temperature −15° C., more preferably not lower than the molding temperature −14° C., and even more preferably not lower than the molding temperature −13° C. When the temperature of the saturated steam is within the above range, there is a tendency that moisture can be diffused into the expanded polyamide resin particles while suppressing the expansion and fusion of the expanded polyamide resin particles. The heating time with saturated steam used for the preheating is 15 seconds or more, preferably 15 to 120 seconds, and more preferably 30 to 90 seconds. Conventionally, the step of preheating the expanded polyamide resin beads to a temperature close to the molding temperature has been problematic in that the total time required for molding is extended and productivity is reduced, but when the heating time is within the above range, moisture can be diffused into the expanded polyamide resin beads within a range that is practically acceptable for the problem, and the fusion property at the molding temperature tends to be improved.

[0057] In another aspect of the method for producing a polyamide-based resin foamed molded article of the present embodiment, the water content of the polyamide-based resin foamed particles is from 0% by mass to 12% by mass, and from the viewpoint of fusibility, it is preferably from 1.5% by mass to 12% by mass, and more preferably from 3% by mass to 12% by mass. In this other embodiment, the polyamide and other components other than polyamide contained in the expanded polyamide-based resin particles, and the shape of the expanded polyamide-based resin particles may be the same as those described above. EXAMPLES

[0058] The present invention will be described in detail below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

[0059] Example 1 80 parts by mass of polyamide 6 (product name: UBE Nylon 1030B, manufactured by Ube Industries, Ltd.) as a polyamide-based resin, 20 parts by mass of polyamide 6I (product name: Leona 7000, manufactured by Asahi Kasei Corporation), and 1 part by mass of talc as a nucleating agent were melt-kneaded in an extruder at an extrusion temperature of 310°C, and then extruded into a strand shape, water-cooled in a cold water tank, and cut to prepare resin pellets. The prepared resin pellets were immersed in water at 30° C. for 1 hour, and then the solvent was removed using a commercially available washing machine to obtain resin pellets containing 10% by mass of water. The water-containing resin pellets were placed in a pressure cooker at 10°C, and carbon dioxide gas was blown in at 5 MPa for 3 hours to absorb the gas, resulting in 1.9% impregnation by mass. The carbon dioxide-impregnated resin pellets were then transferred to a foaming device, and air at 200°C and 210°C was blown in to obtain expanded polyamide resin particles. Thereafter, air at 210°C was blown in to obtain polyamide resin expanded particles, which were then placed in a water-permeable nonwoven bag and immersed in a thermostatic water bath heated to 50°C for 30 minutes, after which the particles were dehydrated at 1000 rpm / min in a dehydrator to obtain hydrated polyamide resin expanded particles. The water content of the polyamide resin expanded particles was 12%. The obtained hydrous polyamide resin foamed particles were placed in an autoclave, and compressed air was introduced into the autoclave over a period of 1 hour until the pressure inside the autoclave reached 0.4 MPa. Thereafter, the pressure was maintained at 0.4 MPa for 24 hours, thereby subjecting the polyamide resin foamed particles to a pressure treatment. The pressurized polyamide resin foam particles were filled into the cavity of an in-mold molding die (cavity dimensions: length: 300 mm, width: 300 mm, height: 25 mm), and then the die was clamped. Then, this die was attached to an in-mold foam molding machine. Thereafter, saturated steam at 135°C was supplied into the cavity for 10 seconds, and then saturated steam at 145°C was supplied into the cavity for 30 seconds to expand and heat-seal the polyamide resin foam particles, thereby forming the polyamide resin foam particles into a foam. The foam obtained was cooled by supplying cooling water into the cavity of the mold, and then the mold was opened to remove the polyamide foam molded article.

[0060] Example 2 Polyamide-based resin expanded particles and expanded molded bodies were produced under the same conditions as in Example 1, except that 60 parts by mass of polyamide 6 (product name: UBE Nylon 1030B, manufactured by Ube Industries, Ltd.) as the polyamide-based resin, 20 parts by mass of polyamide 6 / 66 (product name: Leona 9200, manufactured by Asahi Kasei Corporation), and 20 parts by mass of polyamide 6I (product name: Leona 7000, manufactured by Asahi Kasei Corporation) as the polyamide-based resin, and 1 part by mass of talc as the nucleating agent, as shown in Table 1, were used.

[0061] Example 3 Polyamide-based resin expanded particles and expanded molded bodies were produced under the same conditions as in Example 1, except that 60 parts by mass of polyamide 6 (product name: UBE Nylon 1030B, manufactured by Ube Industries, Ltd.) as the polyamide-based resin, 10 parts by mass of polyamide 6 / 66 (product name: Leona 9200, manufactured by Asahi Kasei Corporation), and 30 parts by mass of polyamide 6I (product name: Leona 7000, manufactured by Asahi Kasei Corporation) as the polyamide-based resin, and 1 part by mass of talc as the nucleating agent, as shown in Table 1, were used.

[0062] Example 4 Polyamide-based resin expanded particles and expanded molded bodies were produced under the same conditions as in Example 1, except that 50 parts by mass of polyamide 6 (product name: UBE Nylon 1030B, manufactured by Ube Industries, Ltd.) as the polyamide-based resin, 10 parts by mass of polyamide 6 / 66 (product name: Leona 9200, manufactured by Asahi Kasei Corporation), and 40 parts by mass of polyamide 6I (product name: Leona 7000, manufactured by Asahi Kasei Corporation) as the polyamide-based resin, and 1 part by mass of talc as the nucleating agent, as shown in Table 1, were used.

[0063] Example 5 Polyamide-based resin expanded particles and foamed molded articles were produced under the same conditions as in Example 1, except that 60 parts by mass of polyamide 6 (product name: UBE Nylon 1030B, manufactured by Ube Industries, Ltd.) as the polyamide-based resin, 40 parts by mass of polyamide 6I (product name: Leona 7000, manufactured by Asahi Kasei Corporation) as the polyamide-based resin, and 1 part by mass of talc as the nucleating agent, as shown in Table 1, were used.

[0064] Example 6 Polyamide-based resin foamed particles and foamed molded articles were produced under the same conditions as in Example 1, except that the following polyamide-based resins shown in Table 1 were used: 60 parts by mass of polyamide 6 (product name: UBE Nylon 1030B, manufactured by Ube Industries, Ltd.), 20 parts by mass of polyamide 6 / 66 (product name: Leona 9200, manufactured by Asahi Kasei Corporation), and 20 parts by mass of polyamide 6I (product name: Leona 7000, manufactured by Asahi Kasei Corporation); and 1 part by mass of talc as a nucleating agent. The polyamide-based resin foamed particles and foamed molded articles were produced under the same conditions as in Example 1, except that the polyamide-based resins were melt-kneaded at an extrusion temperature of 280°C in an extruder.

[0065] Comparative Example 1 As shown in Table 1, 100 parts by mass of polyamide 6 (product name: UBE Nylon 1030B, manufactured by Ube Industries, Ltd.) as a polyamide-based resin and 1 part by mass of talc as a nucleating agent were used, and the mixture was melt-kneaded in an extruder at an extrusion temperature of 280°C, and then extruded into a strand shape, cooled in a cold water tank, and cut to prepare resin pellets. Thereafter, in the expansion molding process, saturated steam at 140°C was supplied into the cavity for 10 seconds, and then saturated steam at 150°C was supplied into the cavity for 30 seconds to expand the polyamide resin foamed beads. Except for this, polyamide resin foamed beads and foamed molded bodies were produced under the same conditions as in Example 1.

[0066] Comparative Example 2 As shown in Table 1, 60 parts by mass of polyamide 6 (product name: UBE Nylon 1030B, manufactured by Ube Industries, Ltd.) as a polyamide-based resin, 40 parts by mass of polyamide 6 / 66 (product name: Leona 9200, manufactured by Asahi Kasei Corporation), and 1 part by mass of talc as a nucleating agent were used, and these were melt-kneaded in an extruder at an extrusion temperature of 310°C, and then extruded into strands, water-cooled in a cold water tank, and cut to produce resin pellets. Thereafter, in the expansion molding process, saturated steam at 140°C was supplied into the cavity for 10 seconds, and then saturated steam at 150°C was supplied into the cavity for 30 seconds to expand the polyamide resin foamed beads. Except for this, polyamide resin foamed beads and foamed molded bodies were produced under the same conditions as in Example 1.

[0067] <Physical properties and evaluation> For the samples of the expanded polyamide resin beads obtained in the above-mentioned Examples and Comparative Examples, various physical property measurements and evaluations were carried out.

[0068] (1)DSC curve (1-1) A differential scanning calorimeter (DSC) (Hitachi High-Tech Science Corporation, "EXSTAR DSC7020") was used to obtain a DSC curve of the polyamide when the polyamide-based resin foamed particles were dried. The polyamide-based resin foamed particles were vacuum dried at 80°C for 6 hours, and then filled into an aluminum sealed container and measured in a nitrogen gas flow of 50 mL / min. Specifically, the polyamide-based resin foamed particles were heated from 30°C to 280°C at 10°C / min, and the change in heat was measured to obtain a DSC curve. From the obtained DSC curve, the number, temperature and width of endothermic peaks resulting from the crystalline melting of the polyamide in the expanded polyamide resin beads were measured, and further the melting initiation temperature was calculated. (1-2) In addition, a differential scanning calorimeter (DSC) (Hitachi High-Tech Science Corporation, "EXSTAR DSC7020") was used to obtain a DSC curve of polyamide when the polyamide-based resin foamed particles absorbed water. The polyamide-based resin foamed particles were immersed in water at 25°C for 24 hours to remove the water adhering to the surface, and then the polyamide-based resin foamed particles were filled into an aluminum sealed container and measured in a nitrogen gas flow of 50 mL / min. Specifically, the polyamide-based resin foamed particles were heated from 30°C to 280°C at 10°C / min, and the DSC curve was obtained by measuring the change in heat quantity. From the obtained DSC curve, the number, temperature and width of endothermic peaks resulting from the crystalline melting of the polyamide in the expanded polyamide resin beads were measured, and further the melting initiation temperature was calculated.

[0069] (2) Density of foam particles The mass W (kg) of the obtained polyamide resin foam particles was measured, and then the apparent volume Va (m 3 The mass W was then divided by the apparent volume Va to obtain W / Va (kg / m 3 ) was taken as the density of the expanded polyamide resin beads. Here, the 210°C foaming density refers to the density of foamed beads obtained when hot air at 210°C is blown into them, and the 200°C foaming density refers to the density of foamed beads obtained when hot air at 200°C is blown into them.

[0070] (4) Closed cell ratio Regarding the closed cell ratio, the mass W (kg) of the obtained polyamide resin foam particles was measured, and then the apparent volume Va (m 3 The mass W was then divided by the apparent volume Va to obtain W / Va (kg / m 3 ) was taken as the density of the expanded polyamide resin beads. The true volume (Vx) of the expanded polyamide resin beads whose apparent volume Va and mass W were measured above was measured using an air comparison type specific gravity meter (manufactured by Beckman Co., Ltd.). The closed cell ratio S (%) was calculated according to the formula described below. S(%)={(Vx-W / ρ) / (Va-W / ρ)}×100 In the formula, ρ is the density of the polyamide resin foam particles (g / cm 3 ).

[0071] (5) Uniformity of bubble size The bubble diameter of the polyamide resin expanded beads is calculated by cutting out a 500 μm square area from the center of the expanded beads from an image taken with an electron microscope or the like of the central surface of the polyamide resin expanded beads, calculating the area of ​​the closed bubbles for all the bubbles, and approximating the diameter to a circle, d = 2(S / 3.14). 1 / 2 The average value, standard deviation, and coefficient of variation (= standard deviation / average value) are calculated from the values ​​of all the bubbles. In this embodiment, the expanded bead is cut through its center and divided into two, and an image is taken with a scanning electron microscope at a magnification of 50 times. The image is binarized into bubble films and closed bubbles using image analysis software "Image J", and the total bubble area in an area 500 μm square from the center is calculated, and the diameter of the bubble that approximates a circle is calculated. However, there are no limitations on the manufacturer of the electron microscope or the image analysis software, as long as the method can calculate the bubble diameter in a similar manner.

[0072] (6) Sphericity of bead cross section To measure cross-sectional sphericity, first divide a polyamide resin expanded bead into two parts that pass through its center. From an image of the cross-section taken with an electron microscope or a microscope, the longest line segment passing through the center is taken as the maximum diameter, and the line segment perpendicular to this is taken as the minimum diameter. The cross-sectional sphericity of the polyamide resin expanded bead is calculated as cross-sectional sphericity = maximum diameter / minimum diameter.

[0073] (7) Density of foamed product The density of the foam molded article was measured by cutting the polyamide resin foam molded article into a rectangular parallelepiped shape, measuring the mass W (g), calculating the volume V (cc), and calculating V / W (cc / g) as the density of the foam molded article. [Table 1]

[0074] The results in Table 1 show that the expanded polyamide resin beads of each Example are excellent in expandability and light weight, and also have good foaming rate and foam uniformity. [Industrial Applicability]

[0075] According to the present invention, it is possible to provide polyamide-based resin expanded beads having a lower expansion temperature than conventional ones and excellent expandability and uniformity, and a polyamide-based resin expanded molded article formed from the polyamide-based resin expanded beads and having excellent lightweight properties.

Claims

1. A polyamide-based resin expanded particle containing a polyamide resin, In the DSC curve when the temperature is increased from 30° C. to 280° C. at a heating rate of 10° C. / min using a differential scanning calorimeter during drying, there is one endothermic peak due to crystalline melting of the polyamide, The product is immersed in water at 25°C for 24 hours, and when the product absorbs water, the DSC curve obtained by heating the product from 30°C to 280°C at a heating rate of 10°C / min using a differential scanning calorimeter shows two or more endothermic peaks due to the crystalline melting of the polyamide.

1. A polyamide resin foam particle comprising:

2. 2. The expanded polyamide resin particles according to claim 1, comprising 5 to 40% by mass of amorphous polyamide.

3. 3. The expanded polyamide resin particles according to claim 2, wherein the amorphous polyamide is polyamide 6I.

4. 4. The expanded polyamide resin particles according to claim 1, wherein the polyamide is an alloy of two or more kinds of polyamides.

5. 5. The expanded polyamide resin particles according to claim 4, wherein the polyamide is an alloy of three or more kinds of polyamides.

6. The expanded polyamide resin beads according to any one of claims 1 to 3, characterized in that in a DSC curve of the expanded polyamide resin beads when absorbing water, the width of an endothermic peak resulting from polyamide crystalline melting is 30°C or more when the expanded polyamide resin beads are heated from 30°C to 280°C at a heating rate of 10°C / min using a differential scanning calorimeter.

7. 4. The expanded polyamide resin beads according to claim 1, wherein the expanded polyamide resin beads have a melting initiation temperature of 125° C. or lower when absorbing water.

8. 4. The expanded polyamide resin particles according to claim 1, wherein the closed cell ratio is 80% or more.

9. 4. The expanded polyamide resin particles according to claim 1, wherein the coefficient of variation of cell diameter is 15% or less.

10. The expanded polyamide resin particles according to any one of claims 1 to 3, characterized in that the sphericity is 1.2 or less.

11. A polyamide resin foamed molded article, which is formed from the polyamide resin foamed beads according to any one of claims 1 to 3.

12. The polyamide resin foam molded article according to claim 11, wherein the bead density is 500 g / L or less.

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