JP2015183137A - Polyvinylidene fluoride-based resin expanded particle, production method and molded product thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinylidene fluoride-based resin expanded particle that can yield an in-mold molded product excellent in light-weight and conductivity; and a production method thereof.SOLUTION: Provided is a polyvinylidene fluoride-based resin expanded particle in which polyvinylidene fluoride-based resin is the base resin of the expanded particle, and in which the polyvinylidene fluoride-based resin has a flexural elasticity of 450 MPa or more, has a melt flow rate at 230°C and loading of 2.16 kg, of 1 g/10 minutes or more, carbon black is incorporated in the base resin, and the apparent density of the polyvinylidene fluoride-based resin expanded particle is 25 to 700 g/L.

Description

The present invention relates to a foamed polyvinylidene fluoride resin particle, a method for producing a polyvinylidene fluoride resin foam particle, and a molded article of a polyvinylidene fluoride resin foam particle.

Polyvinylidene fluoride resin is used as a non-contaminating material for components used in clean rooms, parts for high-performance analytical instruments, and the like. Furthermore, it has excellent weather resistance and is also used in paints for outdoor use. Polyvinylidene fluoride resins are also excellent in flame retardancy, and are used in the field of flame retardant materials that make use of advanced flame retardancy.

  Conventionally, a polyvinylidene fluoride resin foam is obtained by crosslinking a polyvinylidene fluoride resin, kneading a decomposable foaming agent that decomposes at the melting temperature of the raw resin, and thermally decomposing the foaming agent to foam. However, there are restrictions on the shapes that can be obtained, such as a sheet shape, a plate shape, and a rod shape. The present applicant has previously proposed polyvinylidene fluoride resin expanded particles that can be heat-molded in a mold, and by using the expanded particles, various shapes of polyvinylidene fluoride-based resins can be formed in accordance with the shape of the mold. It became possible to obtain a resin foam (Patent Document 1).

JP 2010-209224 A

  However, the foamed particles shown in Patent Document 1 tend to shrink when the foamed particles having a high foaming ratio are obtained in order to obtain a molded article having a relatively high foaming ratio. Therefore, it is necessary to strictly control the density of the expanded particles, and there remains a problem to be improved in terms of productivity. Further, when the foamed particle molded body obtained by in-mold molding of the foamed particles is a molded body having a high expansion ratio, the molded body obtained is likely to shrink like the foamed particles. Problems still remained from the point of reproducibility and dimensional stability.

Also, in recent years, in order to use foam for applications such as packaging of electronic parts and radio wave absorbers, the foam has a conductivity with a volume resistivity of 1 × 10 ² to 1 × 10 ⁸ Ω · cm. There is a need for expanded polyvinylidene fluoride resin foam particles that are electrically conductive and have excellent lightness, and molded polyvinylidene fluoride resin particles formed by molding the expanded particles in a mold. It was.

  The present invention has been made to solve the above-mentioned problems of the prior art, and provides a polyvinylidene fluoride resin expanded particle capable of obtaining an in-mold molded article excellent in lightness and conductivity and a method for producing the same. With the goal. Another object of the present invention is to provide a molded article of polyvinylidene fluoride-based resin expanded particles obtained by molding in a mold the expanded polyvinylidene fluoride-based resin particles having excellent lightness and conductivity.

That is, the present invention
(1) Expanded particles having a polyvinylidene fluoride resin as a base resin,
The flexural modulus of the polyvinylidene fluoride resin is 450 MPa or more,
The melt flow rate at 230 ° C. and a load of 2.16 kg of the polyvinylidene fluoride resin is 1 g / 10 min or more,
Carbon black is blended in the base resin,
The polyvinylidene fluoride resin expanded particles have an apparent density of 25 to 700 g / L,
Polyvinylidene fluoride resin expanded particles, characterized in that
(2) The polyvinylidene fluoride resin expanded particles according to (1), wherein the carbon black has a dibutyl phthalate oil absorption of 200 to 500 ml / 100 g,
(3) The polyvinylidene fluoride resin expanded particles according to (1) or (2) above, wherein the amount of the carbon black is 3 to 15 parts by weight with respect to 100 parts by weight of the base resin.
(4) The DSC curve of the first heating obtained when the expanded particles are heated from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min by a heat flux differential scanning calorimetry is a polyvinylidene fluoride type It has an intrinsic endothermic peak unique to the resin and one or more high temperature side endothermic peaks on the higher temperature side than the intrinsic endothermic peak, and satisfies the condition of the following formula (1) in the DSC curve of the first heating. The expanded polyvinylidene fluoride resin particles according to any one of (1) to (3) above,
(Equation 1)
0.05 ≦ Eh / Et ≦ 0.25 (1)
(In the above formula, Et represents the total heat of fusion (J / g) of the endothermic peak of the DSC curve of the first heating, and Eh represents the heat of fusion (J / g) of the high temperature side endothermic peak.)
(5) The polyvinylidene fluoride resin expanded particles according to any one of (1) to (4), wherein the apparent density of the expanded particles is 40 to 250 g / L,
(6) The polyvinylidene fluoride resin expanded particles according to any one of the above (1) to (5), wherein the closed cell ratio of the expanded particles is 80% or more,
(7) Resin particles having a polyvinylidene fluoride resin as a base resin are dispersed in a dispersion medium in a sealed container and impregnated with a foaming agent under heating to form expandable resin particles. A method for producing foamed particles by discharging particles together with a dispersion medium from a sealed container to a pressure lower than the pressure in the sealed container,
The polyvinylidene fluoride resin has a flexural modulus of 450 MPa or more, a melt flow rate at 230 ° C. and a load of 2.16 kg of 1 g / 10 min or more, and carbon black is blended in the base resin. A method for producing expanded polyvinylidene fluoride resin particles,
(8) A molded article of polyvinylidene fluoride resin foamed particles obtained by molding the foamed particles according to any one of (1) to (6) above,
Is a summary.

The expanded polyvinylidene fluoride resin particles of the present invention using a polyvinylidene fluoride resin having specific physical properties as a base resin have low apparent density and conductivity.
Further, the foamed particle molded body obtained by in-mold molding of the foamed particles has a low apparent density, and even a foamed particle molded body in which carbon black is blended with a base resin has a small shrinkage of the molded body, In addition to excellent dimensional stability, it also excels in mold shape reproducibility.
Furthermore, when the dibutyl phthalate oil absorption of the carbon black contained in the expanded particles is in a specific range, particularly good in-mold moldability is obtained.
For this reason, the polyvinylidene fluoride resin expanded particles of the present invention are molded into various shapes and used in various fields such as structures in the aviation industry and electrical and electronics industry, packaging materials for electronic components, heat insulating materials, radio wave absorbers, etc. Can be used.

The typical example of the DSC curve of the 1st heating obtained when the expanded particle which concerns on this invention is heated from 30 degreeC to 200 degreeC by the heat flux differential scanning calorimetry method at the temperature increase rate of 10 degreeC / min is shown. FIG.

  In the present specification, the polyvinylidene fluoride resin expanded particles are sometimes simply referred to as “expanded particles”. In addition, a polyvinylidene fluoride resin expanded particle molded body obtained by molding the expanded particles in a mold may be simply referred to as “foamed particle molded body” or “foamed molded body”. Further, the DSC curve obtained by the heat flux differential scanning calorimetry may be simply referred to as “DSC curve”.

  The base resin for the expanded particles in the present invention is mainly composed of a polyvinylidene fluoride resin. In the present specification, the base resin mainly composed of polyvinylidene fluoride resin means that the content of the polyvinylidene fluoride resin is 50% by weight or more of the total weight of the base resin constituting the expanded particles. It is preferably 70% by weight or more, more preferably 80% by weight or more, and still more preferably 90% by weight or more.

  The polyvinylidene fluoride resin has a flexural modulus of 450 MPa or more and a melt flow rate (MFR) at 230 ° C. and a load of 2.16 kg of 1 g / 10 min or more. The polyvinylidene fluoride-based resin needs to satisfy both the requirements for the flexural modulus and the melt flow rate. The value of the melt flow rate is an index related to the ease of elongation of the polyvinylidene fluoride resin at the time of foaming, that is, an index related to the quality of bubble growth at the time of foaming when obtaining expanded particles having a low apparent density. On the other hand, the value of the flexural modulus is an index related to the strength of the bubble film of the expanded particles. That is, when either the melt flow rate or the flexural modulus does not satisfy the above range, it is an intended purpose to obtain expanded particles having an apparent density of 25 to 700 g / L and having conductivity. It may not be possible. Moreover, there exists a possibility that the foaming molding excellent in dimensional stability, mold reproducibility, etc. may not be obtained.

  When the flexural modulus of the polyvinylidene fluoride-based resin is less than 450 MPa, especially when trying to obtain expanded particles with a high expansion ratio (low apparent density), the bubbles may coalesce in the process in which the bubbles grow during expansion. There is a possibility that bubbles may break and foamed particles having a high expansion ratio cannot be obtained. Alternatively, even if expanded particles with a high expansion ratio are obtained, the foam film is less likely to be stretched and oriented during foaming, or the foaming agent dissipates in the foamed foam and changes in pressure due to temperature changes occur. Then, the expanded particles tend to shrink, and the variation in the apparent density of the expanded particles increases, and as a result, the expanded particles having a desired apparent density may not be obtained. Further, if the foamed particles are easily contracted, the foamed particle molded body is easily contracted, so that there is a possibility that a foamed particle molded body having excellent mold reproducibility and dimensional stability cannot be obtained. The upper limit of the flexural modulus of the polyvinylidene fluoride resin is approximately 1300 MPa. From the above viewpoint, the flexural modulus of the polyvinylidene fluoride-based resin is preferably 500 to 1200 MPa, and more preferably 600 to 1100 MPa. The flexural modulus can be measured according to JIS K7171 (2002).

  The melt flow rate (MFR) of the polyvinylidene fluoride resin is 1 g / 10 min or more (230 ° C., load 2.16 kg). When the melt flow rate is less than 1 g / 10 min, local stress concentration occurs during foaming, and there is a problem that open cells are easily formed, and it is difficult to obtain good foamed particles having a low apparent density and difficult to shrink. There is a fear. On the other hand, the upper limit of the melt flow rate is not particularly limited, but is approximately 20 g / 10 minutes from the viewpoint of preventing coalescence of bubbles during foaming and bubble breakage. The melt flow rate is more preferably 1.5 to 15 g / 10 minutes. In addition, the value of melt flow rate (MFR) is measured under test conditions: temperature 230 ° C. and 2.16 kg load based on ASTM D1238.

  As the polyvinylidene fluoride resin expanded particles of the present invention, a homopolymer of vinylidene fluoride or a copolymer of vinylidene fluoride and other monomers, and a copolymer containing vinylidene fluoride as a main component Coalescence is included. Here, the copolymer having vinylidene fluoride as a main component means a copolymer containing at least 50% by weight, preferably 70% by weight or more of the vinylidene fluoride component in the copolymer. Examples of other monomers copolymerizable with vinylidene fluoride include ethylene tetrafluoride and propylene hexafluoride, but vinylidene fluoride copolymer containing propylene hexafluoride as a copolymerization monomer component. Polymers are preferred.

  Furthermore, the vinylidene fluoride copolymer is preferably a copolymer containing 3 wt% to 14 wt% of a propylene hexafluoride component as a copolymerization monomer component. Furthermore, from the above viewpoint, the upper limit of the content of the propylene hexafluoride component of the copolymer is preferably 12% by weight, and more preferably 11% by weight.

  Examples of the polyvinylidene fluoride resin whose bending elastic modulus and MFR satisfy the above-described conditions include Solef 20808, Solef 11008, and Solef 11010, which are commercially available from Solvay Specialty Polymers.

The polyvinylidene fluoride resin may be a non-crosslinked polyvinylidene fluoride resin, for example, a crosslinked polyvinylidene fluoride resin crosslinked by a conventionally known method. In view of the properties, non-crosslinked polyvinylidene fluoride resin is preferable. In addition, as the polyvinylidene fluoride resin, two or more kinds of polyvinylidene fluoride resins can be mixed and used. The density of the polyvinylidene fluoride resin is approximately 1.7 to 1.9 g / cm ³ .

  Other polymer components and additives can be added to the base resin of the expanded particles of the present invention within a range not impairing the effects of the present invention.

  Examples of other polymer components that can be added include, for example, high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear ultra-low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, and ethylene. -Acrylic acid copolymer, ethylene-methacrylic acid copolymer, polyolefin resin such as polypropylene resin, polystyrene, styrene-maleic anhydride copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer Polystyrene resins such as polymers, ethylene-propylene rubber, ethylene-1-butene rubber, propylene-1-butene rubber, ethylene-propylene-diene rubber, isoprene rubber, neoprene rubber, nitrile rubber and other rubber, styrene-diene block Copolymer, styrene Styrenic thermoplastic elastomer such as hydrogenated enblock copolymer, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxyethylene copolymer, tetrafluoroethylene-6-fluoropropylene copolymer, 4 Examples thereof include a fluorinated ethylene-ethylene copolymer, a polytrifluorinated ethylene, a trifluorinated ethylene-ethylene copolymer, and a mixture thereof. When adding another polymer component, it is preferable to add so that the ratio of the other polymer in base resin may be 10 weight% or less.

  In the foamed particles of the present invention, carbon black is blended in the base resin. When carbon black having a dibutyl phthalate oil absorption (DBP oil absorption) of 200 to 500 ml / 100 g is used, it is preferable because in-mold moldability such as foamability and fusion property of the expanded particles is further improved. The amount of dibutyl phthalate oil absorption of carbon black is the amount of dibutyl phthalate (cc) included per 100 g of carbon black, and is a value measured by an absorption meter according to the oil absorption amount A method (mechanical method) described in JIS K6221. It is.

  Moreover, the average particle diameter of carbon black is preferably 1 to 100 nm, and more preferably 5 to 80 nm. The average particle diameter of the carbon black is measured using an electron microscope. Specifically, take an electron micrograph containing hundreds of particles in the field of view, measure 1,000 random samples with the directional diameter (Green diameter) as the representative diameter, and count distribution based on the number obtained. A curve is prepared and the 50% diameter of the cumulative distribution based on the number is adopted as the average particle diameter.

The specific surface area of carbon black is preferably 50 to 1400 m ² / g, particularly preferably 60 to 1200 m ² / g. The specific surface area is a value measured by the BET method (nitrogen adsorption method).

The proportion of carbon black in the expanded particles is preferably 3 to 15 parts by weight, more preferably 5 to 13 parts by weight per 100 parts by weight of the polyvinylidene fluoride resin. If it is in the said range, it will become an expanded particle which is excellent in especially electroconductivity and in-mold moldability. When carbon black is added, the apparent density of the expanded particles tends to increase, and the expandability and in-mold moldability of the expanded particles tend to decrease. Therefore, the use of a specific polyvinylidene fluoride resin in the present invention is particularly preferable because foamed particles having a high expansion ratio can be obtained without deteriorating foamability and in-mold moldability.
Furthermore, when carbon black is added, the flame retardancy of the expanded particles tends to decrease. However, when the polyvinylidene fluoride resin of the present invention is used, sufficient flame retardancy can be achieved without adding a flame retardant. It becomes the expanded particle which has.

  The expanded particles of the present invention are obtained by the first heating when 1 to 5 mg of expanded particles are heated from 30 ° C. to 200 ° C. at a rate of temperature increase of 10 ° C./min by heat flux differential scanning calorimetry. The curve (hereinafter referred to as the DSC curve of the first heating) has an intrinsic endothermic peak (intrinsic peak) unique to the polyvinylidene fluoride resin and one or more high temperature side endothermic peaks (high temperature peak) on the high temperature side of the intrinsic endothermic peak. ), And the heat of fusion of the high-temperature endothermic peak observed in the DSC curve of the first heating is preferably 2 J / g or more. If it has the said high temperature side endothermic peak and the heat of fusion is in the said range, an expanded particle with a low apparent density can be obtained more easily. The upper limit of the heat of fusion at the high temperature side endothermic peak is preferably about 30 J / g in order to obtain good secondary foamability of the foamed particles during in-mold molding. Furthermore, since the secondary foamability of the foamed particles is good and the meltability between the foamed particles is excellent, the heat of fusion at the high temperature side endothermic peak is preferably 2.5 to 15 J / g, more preferably Is 3 to 10 J / g.

  In addition, when two or more high temperature side endothermic peaks appear, the heat of fusion of the high temperature side endothermic peak means the total amount of heat of fusion of all the high temperature side endothermic peaks. The high-temperature side endothermic peak can adjust the heat of fusion of the high-temperature side endothermic peak by a temperature holding operation at the time of producing expanded particles, which will be described later.

  A method for measuring the heat of fusion of the high-temperature endothermic peak of the expanded particles in the present invention will be described with reference to FIG. In the DSC curve of the first heating obtained when the foamed particles 1 to 5 mg are heated from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min by a heat flux differential scanning calorimetry method, An intrinsic endothermic peak Pc having an apex temperature PTmc intrinsic to the resin appears. In addition, one or more high temperature side endothermic peaks Pd having apex temperature PTmd appear in the temperature region on the high temperature side of the intrinsic endothermic peak.

  This high-temperature endothermic peak Pd appears in the DSC curve of the first heating measured as described above, but after obtaining the DSC curve of the first heating, once from 200 ° C. to 10 ° C./min, once around 30 ° C. The DSC curve of the second heating obtained when the temperature is lowered to 200 ° C. at 10 ° C./min again does not appear in the DSC curve of the second heating, and the intrinsic endothermic peak inherent in the polyvinylidene fluoride resin Therefore, the intrinsic endothermic peak and the high temperature side endothermic peak can be easily distinguished.

  The heat of fusion of the high temperature side endothermic peak is calculated by a heat flux differential scanning calorimetry method by determining the area (D) of the high temperature side endothermic peak Pd. The area of the high temperature side endothermic peak Pd can be determined as follows, for example.

  As shown in FIG. 1, a straight line α-β connecting a point α corresponding to 80 ° C. of the DCS curve and a point β corresponding to the melting end temperature Te of the expanded particles is drawn. Next, a straight line parallel to the vertical axis of the graph is drawn from the point γ on the DSC curve corresponding to the valley between the intrinsic endothermic peak Pc and the high temperature side endothermic peak Pd, and the intersection with the straight line α-β is defined as δ. . The area (D) of the high temperature side endothermic peak Pd is a portion surrounded by a DSC curve showing the high temperature side endothermic peak Pd of the DSC curve, a line segment δ-β, and a line segment γ-δ (shown by diagonal lines in FIG. 1). Defined as the area of the part (D)). In the measurement method, in order to draw the baseline α-β, the point α on the DSC curve is a point corresponding to a temperature of 80 ° C. This is because the base line with the end temperature as the end point is suitable for stably obtaining the heat quantity of the high-temperature endothermic peak with good reproducibility.

  The expanded polyvinylidene fluoride resin particles of the present invention are higher in temperature than the intrinsic endothermic peak inherent in the polyvinylidene fluoride resin in the DSC curve of the first heating in the DSC curve obtained in the above-mentioned heat flux differential scanning calorimetry. It is preferable that the heat of fusion Eh (J / g) and the total heat of fusion Et (J / g) of the high-temperature endothermic peak appearing satisfy the following formula (1).

(Equation 2)
0.05 ≦ Eh / Et ≦ 0.25 (1)
(In the formula, Et is the total heat of fusion (J / g) of the endothermic peak of the DSC curve of the first heating, and Eh is the heat of fusion (J / g) of the high temperature side endothermic peak.)

When the above formula (1) is satisfied, the amount of crystal components present in the resin particles at the time of producing the foamed particles is such that the foamability when foaming the resin particles and the obtained foamed particles are molded in the mold. It is suitable for moldability. That is, bubbles are not coalesced immediately after the generation of bubbles when foamed particles are obtained, or the bubble growth rate does not increase so much that bubbles are broken, and when the obtained foamed particles are molded in the mold In addition, the expandability (foamability) of the expanded particles is excellent.
From the above viewpoint, Eh / Et preferably satisfies the above formula from both the foamability of the resin particles when obtaining the foamed particles and the in-mold moldability of the obtained foamed particles. ) Is more preferable, and it is more preferable that the following formula (3) is satisfied.

(Equation 3)
0.08 ≦ Eh / Et ≦ 0.20 (2)
(Equation 4)
0.10 ≦ Eh / Et ≦ 0.16 (3)

The apparent density of the expanded particles of the present invention is 25 to 700 g / L. If the apparent density of the expanded particles is too low, the expanded particles may become too shrinkable to stably obtain the expanded particles. On the other hand, if the apparent density of the expanded particles is too high, the intended lightness may not be satisfied. From the above viewpoint, the apparent density of the expanded particles is preferably 30 to 500 g / L, more preferably 40 to 250 g / L, and still more preferably 50 to 200 g / L. The apparent density of the expanded particles of the present invention is an apparent density after the expanded particles are pressurized with air and then cured under atmospheric pressure and stabilized, and corresponds to the maximum expansion ratio at the time of expansion. . Specifically, it is a value obtained by measuring the apparent density after pressurizing with compressed air of 0.10 MPa at 30 ° C. for 48 hours and then leaving at 30 ° C. for 240 hours. In addition, the apparent density obtained by the above measuring method may hereinafter be referred to as an apparent density (A) or an apparent density after recovery.

  In the case of producing expanded particles having a low apparent density, first, expanded particles having an apparent density of about 150 to 300 g / L are obtained (one-stage expansion), and then an internal pressure is applied to the expanded particles obtained by the first-stage expansion with a pressurized gas. It is also possible to employ a two-stage foaming method in which it is further foamed (two-stage foaming) by heating with steam or the like to obtain foam particles with lower density.

  If the strength of the foam film of foamed particles is weak, the foamed particles will shrink excessively after reaching the maximum foaming ratio during foaming, but the foamed particles of the present invention have a high foaming ratio as described above. However, it has a feature that shrinkage is small. The shrinkage ratio of the expanded particles represented by the following formula (4) is preferably 50% or less, and more preferably 45% or less.

(Equation 5)
Shrinkage rate of expanded particles = [1- (A / B)] × 100 (4)
(However, A is the apparent density of the expanded particles after the recovery, and B is the apparent density of the expanded particles after foaming and drying at 60 ° C. for 1 hour.)

  The foamed particles of the present invention preferably have an average cell diameter of 20 to 800 μm. When the cell diameter is in the above range, a foamed particle molded article having good appearance and mechanical properties can be obtained. The average cell diameter of the expanded particles is preferably 30 to 500 μm, more preferably 40 to 350 μm.

  The average cell diameter of the expanded particles is determined as follows. First, the foamed particles can be cut into approximately two equal parts, and the cross section can be obtained by the following operation based on an enlarged photograph taken with a microscope. In the enlarged photograph of the bubble cross section, four straight lines passing through the center of the foam particle cross section from one point on the surface of the foam particle (periphery in the cross section) to another point on the periphery are drawn. Next, the total number of bubbles intersecting the four straight lines: N (number) is obtained. The total length of the four straight lines: L (μm) divided by the total number of bubbles: N (L / N) is taken as the average bubble diameter of the expanded particles.

  Moreover, it is preferable that the closed cell rate of the expanded particle of this invention is 80% or more. When the closed cell ratio is too low, the secondary foamability of the foamed particles is inferior, and the mechanical properties of the obtained foamed particle molded body are likely to be inferior. In obtaining a foamed particle molded body having excellent secondary foamability and mechanical properties of the foamed particles, the closed cell ratio is more preferably 85% or more, and still more preferably 90% or more. In the present invention, the use of a specific polyvinylidene fluoride resin prevents coalescence and bubble breakage during foaming, so that foamed particles having a high closed cell ratio can be obtained. The measurement of the closed cell ratio can be obtained according to the procedure C described in ASTM-D-2856-70.

  The foamed particles of the present invention can be filled into a mold cavity for molding, and heated with a heating medium to perform in-mold molding to obtain a foamed particle molded body. The shape of the foamed particle molded body that can be obtained by in-mold molding of the foamed particles of the present invention is not particularly limited, and is not limited to a plate shape, a column shape, a container shape, a block shape, or a three-dimensional complicated shape, The thing with thick thickness etc. are mentioned.

  The apparent density of the foamed particle molded body obtained by in-mold molding of the foamed particles of the present invention is generally 15 to 500 g / L, preferably 20 to 400 g / L, more preferably 30 to 200 g / L. Note that the lower the apparent density of the foamed particle molded body, the more it is possible to reduce the amount of hydrogen fluoride gas (HF) generated when it is burned. It can be used in a wide range of fields.

  The closed cell ratio of the foamed particle molded body is preferably 60% or more, more preferably 70% or more, and further preferably 80% or more, like the foamed particles. If the closed cell ratio is too low, mechanical properties such as compression strength of the foamed particle molded body may be lowered. In addition, the measurement of the closed cell rate of a molded object can also be calculated | required based on the procedure C described in ASTM-D-2856-70 similarly to the said foaming particle.

  The measurement of the closed cell ratio of the foamed particle molded body is the same as the measurement of the closed cell ratio of the foamed particles, except that the sample cut from the center of the cross section of the foamed particle molded body and cut off all the molding skin is used as the measurement sample. Can be obtained.

  Moreover, since the expanded particle of this invention is excellent in the meltability of expanded particles, the expanded particle molded object with a high fusion rate between expanded particles can be obtained. The fusion rate between the foamed particles of the foamed particle molded body is at least 50% or more, more preferably 60% or more, and particularly preferably 80% or more. A foamed particle molded body having a high fusion rate is excellent in mechanical properties, particularly bending strength. In addition, this fusion rate means the ratio (material destruction rate of foamed particles) at which the foamed particles themselves are destroyed in the total foamed particles of the fractured surface in the fractured surface when the foamed particle molded body is broken. In order to obtain a foamed particle molded body having an increased fusion rate, it is particularly preferable to produce foamed particles using the above-mentioned polyvinylidene fluoride resin.

  The foamed particles of the present invention have a small shrinkage rate, but the foamed particle molded body obtained by molding the foamed particles of the present invention in the mold also has a small shrinkage rate, excellent dimensional stability and mold reproducibility, and good appearance. It becomes. From the viewpoint of dimensional stability and mold reproducibility, the shrinkage ratio of the foamed particle molded body is preferably 5% or less, more preferably 4% or less, and further preferably 3.5% or less. preferable. In order to obtain a foamed particle molded body having a lower shrinkage rate, it is preferable to produce foamed particles using a specific polyvinylidene fluoride resin and perform in-mold molding using the foamed particles.

  In the production of the foamed particles of the present invention, for example, resin particles obtained by granulating a polyvinylidene fluoride resin blended with carbon black and a foaming agent are dispersed in a dispersion medium such as water in a pressure-resistant sealed container. The resin particles are softened by heating with stirring, and after the resin particles are impregnated with the foaming agent, the foaming agent is introduced into the low-pressure region (usually under atmospheric pressure) from the inside of the sealed container at a temperature equal to or higher than the softening temperature of the resin particles. It is possible to apply a method in which the impregnated expandable resin particles are discharged together with a dispersion medium and foamed. In addition, after impregnating the resin particles with a foaming agent, the resin particles are cooled without being discharged to a low pressure region to obtain expandable resin particles, and the expandable resin particles are expanded by heating to form expanded particles. it can. Hereinafter, a method for discharging foaming resin particles together with a dispersion medium from a container to a low pressure region and foaming will be described in more detail.

  The resin particles are heated to a temperature at which the polyvinylidene fluoride resin is melted and kneaded by an extruder, and then the kneaded product is extruded into a string shape from a small hole in a die attached to the tip of the extruder, and this is made to an appropriate length. It can be obtained by cutting and granulating into a cylindrical shape having a size suitable for producing expanded particles. The average weight per resin particle is usually 0.01 to 20 mg, and preferably 0.1 to 10 mg. The particle diameter (diameter) of the resin particles is preferably 0.1 to 3.0 mm, and more preferably 0.3 to 1.5 mm. Furthermore, usually, the resin particles are preferably adjusted to have a length / diameter ratio of 0.5 to 3.0, more preferably 0.8 to 2.5. preferable. When resin particles are obtained using an extruder, the particle diameter, length / diameter ratio and average mass of the resin particles are adjusted from, for example, a die having a large number of fine holes attached to the tip of the extruder. In the case of strand cutting methods such as extrusion speed and cutter speed by extruding a polyvinylidene fluoride resin melt, it can be carried out by changing the take-up speed as appropriate and cutting it into a predetermined size.

  The resin particles include various commonly used cell conditioners, antistatic agents, lubricants, antioxidants, ultraviolet absorbers, flame retardants, metal deactivators, pigments, dyes, crystal nucleating agents, or fillers. These additives can be appropriately contained as desired.

  As the above-mentioned bubble regulator, talc, sodium chloride, calcium carbonate, silica, titanium oxide, gypsum, zeolite, borax, aluminum hydroxide, carbon and other inorganic substances, other phosphate nucleating agents, phenolic nucleating agents, amines And organic nucleating agents such as polynuclear nucleating agents and polytetrafluoroethylene (PTFE). The addition amount of various additives such as a bubble regulator varies depending on the purpose of addition, but is preferably 25 parts by weight or less, more preferably 15 parts by weight or less, based on 100 parts by weight of the polyvinylidene fluoride resin. Part by weight or less is particularly preferred.

  The dispersion medium for dispersing the resin particles in the production of the expanded particles is not limited to the above-described water, and any solvent that does not dissolve the resin particles can be used. Examples of the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol and the like, but usually water is used.

  In the above method, in the dispersion medium, aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, mica, talc, etc., as necessary, so that the resin particles are uniformly dispersed in the dispersion medium. It is preferable to add a dispersing agent such as a poorly water-soluble inorganic substance or a dispersing aid such as an anionic surfactant such as sodium dodecylbenzenesulfonate or sodium alkanesulfonate. The amount of the dispersant and the dispersion aid added to the dispersion medium when producing the expanded particles is the ratio of the weight of the resin particles to the total weight of the dispersant and the dispersion aid (resin particle weight / dispersant). And the total weight of the dispersion aid) is preferably 20 to 2000, more preferably 30 to 1000. Further, it is preferable to add so that the ratio of the weight of the dispersing agent to the weight of the dispersing aid (the weight of the dispersing agent / the weight of the dispersing aid) is 1 to 500, and further 5 to 100.

  As the foaming agent used in the production of the foamed particles, an organic physical foaming agent, an inorganic physical foaming agent, or a mixture thereof can be used. Examples of organic physical blowing agents include aliphatic hydrocarbons such as propane, butane, hexane, and heptane, alicyclic hydrocarbons such as cyclobutane and cyclohexane, chlorofluoromethane, trifluoromethane, 1,1-difluoromethane, 1 , 1,1,2-tetrafluoroethane, halogenated hydrocarbons such as methyl chloride, ethyl chloride, and methylene chloride, and dialkyl ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether. These can be used in combination of two or more. Moreover, as an inorganic type physical foaming agent, nitrogen, carbon dioxide, argon, air, water, etc. are mentioned, These can be used in mixture of 2 or more types. When mixing and using an organic physical foaming agent and an inorganic physical foaming agent, the compound arbitrarily selected from the organic physical foaming agent and the inorganic physical foaming agent can be used in combination.

  Among the foaming agents, it is preferable to use an inorganic physical foaming agent that does not cause environmental pollution, among which nitrogen, air, carbon dioxide, and water are preferable. When water is used as a dispersion medium together with resin particles in a pressure-resistant airtight container when obtaining expanded particles, water that is a dispersion medium is efficiently used by mixing the resin particles with a water-absorbing substance. It can be used as a blowing agent.

  The amount of the foaming agent used is determined in consideration of the apparent density of the desired foamed particles or the type of the foaming agent, but is usually 5 to 50 weights per 100 parts by weight of the resin particles for the organic physical foaming agent. In an inorganic physical foaming agent, it is preferable to use 0.5 to 30 parts by weight.

  The expanded particles having the high-temperature side endothermic peak are obtained in the step of obtaining expanded particles, the heating temperature when the resin particles are dispersed in a dispersion medium in a closed container and heated with stirring, the melting of the resin particles is completed. Temperature: Melting point of resin particles: temperature not lower than Te: 15 ° C. lower than Tm (Tm−15 ° C.) or higher, melting end temperature: Arbitrary temperature within range of Te: Ta, temperature : Ta is held for a sufficient time, preferably about 10 to 60 minutes, and then the melting point of the resin particles: a temperature 15 ° C. lower than Tm (Tm-15 ° C.) to a melting end temperature: a temperature 5 ° C. higher than Te (Te + 5) It can be obtained by adjusting the temperature to an arbitrary temperature in the range of ° C.): Tb, and releasing the resin particles together with the dispersion medium from the inside of the sealed container into the low pressure region and foaming at that temperature: Tb. Further, the temperature within the range of (Tm−15 ° C.) or more and less than Te for forming the high temperature side endothermic peak may be maintained in multiple stages at different temperatures within the temperature range. In this temperature range, a sufficient time may be required and the temperature may be raised slowly, and by holding at a temperature between (Tm−15 ° C.) and Te for a sufficient time, the high temperature side endothermic peak is increased. It is possible to obtain expanded particles having the same.

  The formation of the high temperature side endothermic peak in the expanded particles and the magnitude of the heat quantity of the high temperature side endothermic peak are mainly due to the temperature: Ta, the retention time at the temperature: Ta, and the temperature of the resin particles when the expanded particles are produced. : Tb as well as the rate of temperature rise in the range of (Tm−15 ° C.) to (Te + 5 ° C.). The amount of heat of the high-temperature endothermic peak of the expanded particles is such that the lower the temperature: Ta or the temperature: Tb within each of the above temperature ranges, the longer the holding time in the temperature range of (Tm−15 ° C.) or more and less than Te. As the rate of temperature rise in the temperature range of (Tm−15 ° C.) or higher and lower than Te is lower, the tendency is larger. In addition, 0.5-5 degreeC / min is normally employ | adopted for the said temperature increase rate. On the other hand, the higher the temperature: Ta or the temperature: Tb in each of the temperature ranges, the higher the (Tm-15 ° C) or higher, the shorter the holding time in the temperature range lower than Te, and the higher (Tm-15 ° C) or higher. The higher the rate of temperature rise within the temperature range below Te, the lower the rate of temperature rise within the temperature range of Te to (Te + 5 ° C.). By conducting a preliminary test in consideration of these points, it is possible to know the production conditions of the expanded particles exhibiting a desired high-temperature side endothermic peak calorific value. In addition, the temperature range which concerns on formation of the said high temperature side endothermic peak is a suitable temperature range at the time of using an inorganic type physical foaming agent (for example, carbon dioxide) as a foaming agent. Therefore, when the foaming agent is changed to, for example, an organic physical foaming agent, the appropriate temperature is about 0 to 30 ° C. on the low temperature side in each step from the above temperature range depending on the type and amount of use. shift.

  In addition, when the contents in the pressure-resistant airtight container are discharged from the airtight container to the low pressure region in order to produce the foamed particles, the back pressure is put into the airtight container with the used foaming agent or an inorganic gas such as nitrogen or air. It is preferable to release the contents while maintaining the pressure so that the pressure in the container does not drop rapidly, in order to make the apparent density of the obtained expanded particles uniform.

  As described above, the foamed particles can be obtained by releasing the resin particles impregnated with the foaming agent from the inside of the sealed container under a low pressure and foaming (single-stage foaming). Furthermore, when the purpose is to obtain expanded particles with a high expansion ratio, after applying internal pressure to the expanded particles obtained by one-stage expansion, the expanded particles are further expanded (two-stage expanded) by heating with steam or the like. You can also.

  Specifically, the foamed particles obtained by being discharged into the low-pressure region from the inside of the closed container by the above-described method are subjected to curing usually performed after the release, and then the foamed particles (single-stage foamed particles) are used for pressurization. After filling the airtight container and pressurizing with a pressurized gas such as air to adjust the pressure inside the foamed particles to 0.01 to 0.9 MPa (G), the foamed particles are taken out of the container and steamed. By using a heating medium such as hot air or the like, foam particles having a lower apparent density (two-stage foam particles) can be obtained.

  The foamed particle molded body of the present invention is filled with the above-mentioned foamed particles in a mold of a conventionally known thermoplastic resin foam particle molding mold that can be heated and cooled, and that can be opened and closed and sealed, and has a saturated vapor pressure. Is supplied with a saturated water vapor of 0.05 to 0.48 MPa (G), preferably 0.08 to 0.42 MPa (G) to heat and expand the expanded particles in the mold cavity to melt the expanded particles. To form a foamed particle molded body, and then the obtained foamed particle molded body is cooled and taken out from the cavity by a batch type in-mold molding method (for example, Japanese Patent Publication No. 4-46217, Japanese Patent Publication No. 6-49795). It can be manufactured by adopting a molding method described in a publication or the like.

  In addition, when performing in-mold molding, when obtaining the above-mentioned two-stage expanded particles, the same operation as that for pressurizing the first-stage expanded particles is performed to increase the pressure in the expanded particles, and the pressure in the expanded particles is reduced. The foamed particles adjusted to 0.01 to 0.3 MPa (G) can be filled in a mold and molded. Further, it is possible to adopt a compression filling method in which the expanded particles are compressed and filled into a mold.

  As a method of heating with saturated steam in the in-mold molding method, a conventionally known method in which heating methods such as one heating, reverse one heating, and main heating are appropriately combined can be adopted. A method of heating the foamed particles in the order of reverse one-side heating and main heating is preferable. Here, the preheating means that the air existing in the chamber or the like is discharged and the entire mold is heated. On the other hand, heating refers to heating the cavity by supplying a heating medium from one side of the male mold or female mold to the inside of the mold (chamber), and then supplying the heating medium supplied into the chamber to the male mold or female mold. It means discharging from (the other mold with respect to the mold on the side to which the heating medium is supplied). In addition, the case where the heating medium is heated and discharged after the heating medium is supplied and discharged on the opposite side is called reverse one-side heating. The saturated vapor pressure of 0.05 to 0.48 MPa (G) at the time of foamed particle molding is the maximum value of the saturated vapor pressure of water vapor supplied into the mold in the in-mold molding step.

  The foamed particle molded body can also be produced by a continuous molding method described in, for example, JP-A-9-104026, JP-A-9-104027, and JP-A-10-180888.

  The present invention will be specifically described with reference to examples.

(I) The evaluation method of expanded particles is shown below.

(A) Apparent density In the present invention, the apparent density (A) of the expanded particles is obtained by placing the obtained expanded particles in a sealed container and pressurizing with compressed air of 0.1 MPa at 30 ° C. for 48 hours. The foamed particles after the operation of releasing the pressure and allowing to stand for 240 hours at an atmospheric pressure of 30 ° C. were used to submerge the foamed particle group whose weight had been measured in advance into the water in the graduated cylinder using a wire mesh. It calculated | required by remove | dividing the weight of a foaming particle group by the volume of the foaming particle group calculated | required, and converting it into g / L.

(B) The closed cell ratio of the expanded particles was measured as follows.
The obtained foamed particles were put in a sealed container, pressurized at 30 ° C. with compressed air of 0.1 MPa for 48 hours, released, and left at 30 ° C. under atmospheric pressure for 10 days. Next, the foamed particles were allowed to stand for 10 days in a temperature-controlled room at atmospheric pressure and a relative humidity of 50% and 23 ° C. for curing. Next, using the foamed particles having a bulk volume of about 20 cm ³ left for 10 days in the same constant temperature room as a measurement sample, the apparent volume value: Va was accurately measured by the submersion method as described below. Apparent volume value: After sufficiently drying the measurement sample for which Va was measured, according to the procedure C described in ASTM-D2856-70, "Air comparison type hydrometer 930" manufactured by Toshiba Beckman Co., Ltd. The true volume value of the measurement sample to be measured: Vx was measured. Then, based on the measured apparent volume value: Va and true volume value: Vx, the closed cell ratio is calculated by the following formula, and the average value of 5 samples (N = 5) is calculated as the closed cell ratio of the expanded particles. It was.

(Equation 6)
Closed cell ratio (%) = (Vx−W / ρ) × 100 / (Va−W / ρ) (5)
However,
Vx: the sum of the true volume of the expanded particles measured by the above method, that is, the volume of the resin constituting the expanded particles and the total volume of bubbles in the closed cell portion in the expanded particles (cm ³ )
Va: The apparent volume of the expanded particles (cm ³ ) measured from the rise in the water level after the expanded particles are submerged in a graduated cylinder containing water.
W: Weight of the foam particle measurement sample (g)
ρ: Density of resin constituting expanded particles (g / cm ³ )

(Ii) The physical property measurement method and evaluation method of the foamed particle molded body will be specifically described below.

(C) Apparent density of foamed particle molded body A test piece of 50 mm × 50 mm × 25 mm was cut out from a portion having no molding skin of the foamed particle molded body, and the volume of the test piece: V2 (L) and weight: W2 (g) I asked for it.

(D) Fusion rate between foam particles of the foamed particle molded body The length of the molded body molded with a mold cavity of 200 mm long, 250 mm wide, and 50 mm thick is placed on one surface of a surface of 200 mm long and 250 mm wide with a cutter knife. In order to divide the length of the molded body into two equal parts, an incision of about 10 mm is made in the other direction, and then the number of foamed particles (n The ratio (m / n × 100) of the number (m) of foamed particles whose material was destroyed was calculated. In addition, it becomes a foaming molding with favorable mechanical properties, such as bending strength and tensile strength, so that the value of the fusion | melting rate between expanded particles is large. The number (n) of foamed particles is the sum of the number of foamed particles peeled between the foamed particles and the number of foamed particles (m) whose material has been destroyed in the foamed particles.

(E) Shrinkage ratio of foamed particle molded body Based on the dimension of the mold having a horizontal length of 250 mm and the length (X) of the foamed particle molded body corresponding to the mold dimension cured at 80 ° C. for 24 hours after molding. The shrinkage ratio of the foamed molded product was calculated from the following formula and evaluated.

(Equation 7)
Shrinkage rate (%) of foamed molded product = [(250−X) / 250] × 100 (6)

(F) Heat resistance of molded foamed body (heated dimensional stability)
The heated dimensional stability of the foamed particle molded body was evaluated as follows.
It was measured in accordance with the thermal stability (dimensional stability at high temperature, method B) described in JIS K6767 (1999). A test piece having a length of 150 mm, a width of 150 mm, and a thickness of the molded body (thickness of 50 mm) was cut out from the center portion of the obtained foamed particle molded body. Measure the length of each of the three lines in the vertical and horizontal directions of the skin, determine the average value, and set the dimensions before heating. Then, place the test piece in a gear oven maintained at 100 ° C. Put it in for 22 hours and then take it out, leave it in a constant temperature and humidity chamber at 23 ° C and 50% relative humidity for 1 hour, measure the dimensions after heating using the following formula from the dimensions before and after heating, Asked.

(Equation 8)
Heating dimensional change rate (%)
= (Dimension after heating -dimension before heating) / dimension before heating × 100 (7)

(G) Volume specific resistance of foamed particle molded body The volume specific resistance value is based on the measurement method of JIS K7194 (1994), and cut out a test piece 80 mm × 50 mm × thickness 20 mm from which the skin layer was removed from the foamed molded body. The measurement was performed on a sample that was left in an atmosphere of 23 ° C. and 50% humidity for 60 hours. Using this sample, the resistivity after 1 minute was measured, and the volume specific resistance value was obtained from the obtained measured value. In addition, the measurement location measured 5 places of the said test piece according to JISK7194.

(H) Appearance of foamed particle molded body The appearance of the molded body was evaluated according to the following criteria.
○: Almost no wrinkles due to unevenness and shrinkage on the surface.
X: Wrinkles due to unevenness and shrinkage are observed on the entire surface.

Example 1
(Preparation of conductive resin composition)
93% by weight of polyvinylidene fluoride resin (vinylidene fluoride-6-propylene copolymer; resin 1: Solvay Specialty Polymers, Inc., product name: Solef 20808) shown in Table 1 and conductive carbon black shown in Table 2 (CB: manufactured by Lion Co., Ltd. Product name: Ketjen Black EC300J, DBP oil absorption: 360 ml / 100 g, BET specific surface area: 800 m ² / g) 7% by weight is charged into a twin screw extruder, melt kneaded and conductive. A resin composition (Composition 1) was produced.

(Production of resin particles)
0.15 parts by weight of polytetrafluoroethylene (PTFE) as a cell regulator is added to the composition 1 with respect to 100 parts by weight of the conductive resin composition, and the mixture is melt-kneaded with a single-screw extruder having an inner diameter of 40 mm. The product was extruded into a strand shape from a small hole in the die attached to the tip of the extruder, and the strand was cooled and cut to obtain resin particles having a weight of about 4 mg.

(Production of expanded particles)
1 kg of the resin particles were charged into a 5 liter pressure-resistant airtight container equipped with a stirrer together with 3 liters of water as a dispersion medium. Furthermore, 0.3 part by weight of kaolin as a dispersant, 0.004 part by weight of sodium alkylbenzene sulfonate and 0.01 part by weight of aluminum sulfate as surfactants were added to 100 parts by weight of the resin particles. Under stirring, the temperature was raised to a temperature 5 ° C. lower than the foaming temperature described in the foamed particle production conditions in Table 3, and carbon dioxide was added as a foaming agent in the sealed container to 0.2 MPa (from the pressure in the sealed container shown in Table 3). G) Press-fit until low pressure, and hold at that temperature for 15 minutes. Next, after the temperature was raised to the foaming temperature shown in Table 3, carbon dioxide was injected so that the pressure in the sealed container shown in Table 3 was reached, and the foaming temperature shown in Table 3 was 15 so that the high-temperature side endothermic peak endotherm was obtained. Hold for a minute.
Then, while adjusting the pressure inside the container to be constant by applying a back pressure with nitrogen, the foamable resin particles impregnated with the foaming agent are discharged together with the dispersion medium from the container to atmospheric pressure, and Table 3 Expanded particles shown in the following were obtained.
Table 3 shows the results obtained by measuring and evaluating the physical properties of the obtained expanded particles, such as the apparent density, the shrinkage rate, the endothermic amount of the high-temperature endothermic peak, the total heat of fusion, the closed cell ratio, and the average cell diameter.

(Forming foamed particle compacts)
Using a general-purpose expanded particle molding machine equipped with a flat plate mold having a length of 200 mm, a width of 250 mm, and a thickness of 50 mm, and applying the internal pressure shown in the molding conditions of Table 4 to the expanded particles obtained above, Filled into the cavity of the flat plate forming mold, heated with steam having a molding vapor pressure shown in Table 4, and performed in-mold to obtain a plate-like foamed particle molded body. The foamed particle molded body was cured in an oven at 80 ° C. for 12 hours to obtain a polyvinylidene fluoride resin expanded particle molded body. Various physical properties of the obtained foamed particle molded body were measured. The results are shown in Table 4.

  Also in Examples 2 to 4, expanded particles were obtained in the same manner as in Example 1 except that they were described in Table 3. The results are shown in Table 3. In addition, a foamed particle molded body was obtained in the same manner as in Example 1 for the foamed particle molded body. The results are shown in Table 4.

Comparative Example 1
Resin particles shown in Table 1 were used in the same manner as in Example 1 except that conductive carbon black was not used in the resin 1 and foamed particles were obtained in the same manner as in Example 1 using the obtained resin particles. Got. Table 3 shows the physical properties of the obtained expanded particles. The foamed particles were molded in the same manner as in the flat plate mold as in Example 1 to obtain a foamed particle molded body. Various physical properties of the obtained foamed particle molded body are shown together in Table 4.

Comparative Example 2
Resin particles shown in Table 1 were used in the same manner as in Example 1 except that conductive carbon black was not blended, and the obtained resin particles were used in the same manner as in Example 1 to obtain expanded particles. Got. Table 3 shows the physical properties of the obtained expanded particles. The foamed particles were molded in the same manner as in the flat plate mold as in Example 1 to obtain a foamed particle molded body. Various physical properties of the obtained foamed particle molded body are shown together in Table 4.

The point corresponding to the melting start temperature of the resin in the α DSC curve The point corresponding to the melting end temperature of the resin in the β DSC curve On the DSC curve corresponding to the valley between the intrinsic endothermic peak and the high temperature side endothermic peak in the DSC curve Point δ Intersection of a straight line parallel to the vertical axis of the graph and a straight line connecting points α and β PTmc Peak temperature of the intrinsic endothermic peak of the resin in the DSC curve of the first heating PTmd High temperature of the resin in the DSC curve of the first heating Peak temperature of side endothermic peak Pc Intrinsic endothermic peak in DSC curve of first heating Pd High temperature side endothermic peak in DSC curve of first heating

Claims (8)

Expanded particles using a polyvinylidene fluoride resin as a base resin,
The flexural modulus of the polyvinylidene fluoride resin is 450 MPa or more,
The melt flow rate at 230 ° C. and a load of 2.16 kg of the polyvinylidene fluoride resin is 1 g / 10 min or more,
Carbon black is blended in the base resin,
The apparent density of the polyvinylidene fluoride resin expanded particles is 25 to 700 g / L.
Polyvinylidene fluoride resin expanded particles, characterized in that   The expanded polyvinylidene fluoride resin particles according to claim 1, wherein the carbon black has a dibutyl phthalate oil absorption of 200 to 500 ml / 100 g.   The polyvinylidene fluoride resin expanded particles according to claim 1 or 2, wherein the amount of the carbon black is 3 to 15 parts by weight with respect to 100 parts by weight of the base resin. The DSC curve of the first heating obtained when the foamed particles are heated from 30 ° C. to 200 ° C. at a rate of temperature increase of 10 ° C./min by the heat flux differential scanning calorimetry is unique to the polyvinylidene fluoride resin. And one or more high temperature side endothermic peaks on the higher temperature side than the intrinsic endothermic peak, and the DSC curve of the first heating satisfies the condition of the following formula (1): The expanded polyvinylidene fluoride resin particles according to any one of claims 1 to 3.
(Equation 1)
0.05 ≦ Eh / Et ≦ 0.25 (1)
(In the above formula, Et represents the total heat of fusion (J / g) of the endothermic peak of the DSC curve of the first heating, and Eh represents the heat of fusion (J / g) of the high temperature side endothermic peak.)   The polyvinylidene fluoride resin expanded particles according to any one of claims 1 to 4, wherein the expanded density of the expanded particles is 40 to 250 g / L.   The foamed polyvinylidene fluoride resin particles according to any one of claims 1 to 5, wherein the foamed particles have a closed cell ratio of 80% or more. Resin particles containing polyvinylidene fluoride resin as a base resin are dispersed in a dispersion medium in a closed container, and after impregnation with a foaming agent under heating to form expandable resin particles, the expandable resin particles are dispersed. A method for producing foamed particles by discharging the inside of a closed container together with a medium to a pressure lower than the pressure in the closed container,
The polyvinylidene fluoride resin has a flexural modulus of 450 MPa or more, a melt flow rate at 230 ° C. and a load of 2.16 kg of 1 g / 10 min or more, and carbon black is blended in the base resin. A method for producing expanded polyvinylidene fluoride resin particles characterized by the following.   A molded article of polyvinylidene fluoride resin foamed particles obtained by molding the foamed particles according to any one of claims 1 to 6 in a mold.

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