JP2021031586A - Molded foam and production method therefor - Google Patents

Abstract

To provide a molded foam that can easily achieve weight reduction by foaming and its control.SOLUTION: The molded foam has a matrix composed of a fluororesin composition comprising a thermoplastic fluororesin as a main component, and a plurality of cells present in the matrix. The thermoplastic fluororesin has a melting point of 165-200°C, and the cells are closed cells, which have a size of 50-200 μm in terms of volume-based median diameter.SELECTED DRAWING: Figure 1

Description

The present invention relates to a foam molded product and a method for producing the same.

Resin molded products are used in various technical fields. As the resin molded body, for example, a foam molded body having a plurality of bubbles in the molded body is known for weight reduction. Examples of the technique for producing such a foam molded product include (1) a method of producing a fluororubber foam by foaming using a thermoplastic microcapsule and then sulfurizing (see, for example, Patent Document 1). , (2) A method of producing a fluororesin foam molded product by foaming a chemical foaming agent at the time of molding (see, for example, Patent Document 2), (3) Impregnating an inorganic physical foaming agent such as carbon dioxide in a high pressure region. A method for producing foamed particles of polyvinylidene fluoride (see, for example, Patent Document 3), and (4) heat-expandable microcapsules and a thermoplastic resin are melt-kneaded before the molding step. A method for producing a foam molded product of a thermoplastic resin (see, for example, Patent Document 4) is known.

Japanese Unexamined Patent Publication No. 2005-146030 Japanese Unexamined Patent Publication No. 2014-058625 Japanese Unexamined Patent Publication No. 2014-118548 JP-A-2017-101190

However, when a chemical foaming agent or a physical foaming agent is used in the production of a foamed molded product, open cells are likely to be generated depending on the type of resin constituting the foamed molded product matrix, and the mechanical strength of the foamed molded product is determined. The physical characteristics of the period may not be fully expressed. Further, when a physical foaming agent is used, a special device is generally required, and it tends to be difficult to control the specific gravity of the foamed molded product. Further, when the heat-expandable microcapsules are used, it may be difficult to achieve the desired weight reduction depending on the resin constituting the matrix and the type of the heat-expandable microcapsules. As described above, the conventional technique has room for study from the viewpoint of easily realizing the weight reduction of the foam molded product and easily controlling it.

One aspect of the present invention is to realize a foamed molded product capable of easily realizing weight reduction by foaming and its control.

In order to solve the above problems, the foam molded product according to one aspect of the present invention includes a matrix composed of a fluorine-based resin composition containing a fluorine-based thermoplastic resin as a main component, and a plurality of foam molded products existing in the matrix. The fluoroplastic resin has a melting point of 165 to 200 ° C., the cells are closed cells, and the size of the closed cells is 50 in terms of volume-based median diameter. It is ~ 200 μm.

Further, in order to solve the above-mentioned problems, the method for producing a foamed molded article according to one aspect of the present invention includes a matrix composed of a fluororesin composition containing a fluoroplastic resin as a main component and the matrix. A method for producing a foamed molded product having a plurality of bubbles existing therein, the step of mixing the fluororesin composition and the heat-expandable microspheres, and the fluorine mixed with the heat-expandable microspheres. The step of molding the fluororesin composition while expanding the heat-expandable microspheres by heating the based resin composition to the molding temperature of the fluororesin composition, and comprising the step of molding the fluororesin composition of the fluoroplastic resin. The melting point is 165 to 200 ° C., the content of the heat-expandable microspheres in the fluororesin composition is 0.05 to 2% by mass, and the expansion start temperature of the heat-expandable microspheres is 180 to 220. The maximum displacement of the thermally expandable microspheres as measured by thermomechanical analysis is 1000 μm / mg or more, and the molding temperature is a temperature equal to or higher than the expansion start temperature.

According to one aspect of the present invention, it is possible to realize a foamed molded product that can easily realize weight reduction by foaming and its control.

It is an image which magnified a part of the cross section of the foam molded article in one Example of this invention with an optical microscope. It is an image of the cross section of the foam molded product in one embodiment of the present invention that has been processed for observation, taken with an optical microscope at a magnification of 100 times.

Hereinafter, embodiments of the present invention will be described. In the present specification, "~" represents the above range unless otherwise specified.

[Effervescent molded product]
<Structure of foam molded product>
The foam molded article of the embodiment of the present invention has a matrix and a plurality of bubbles existing in the matrix. The matrix is composed of a fluorinated resin composition containing a fluorinated thermoplastic resin as a main component. The bubbles present in the matrix are closed cells.

(matrix)
In the present embodiment, the matrix is a continuous phase constituting the foamed molded product, and is composed of a fluororesin composition. The fluorine-based resin composition may contain a fluorine-based thermoplastic resin as a main component. For example, the fluorine-based resin composition may contain at least 50% by mass or more of a fluorine-based thermoplastic resin, preferably 70% by mass or more, more preferably 90% by mass or more, and 95% by mass or more. It is more preferably contained in an amount of 99% by mass or more, and even more preferably 99% by mass or more.

(Fluorine-based thermoplastic resin)
The melting point of the fluorine-based thermoplastic resin is 165 to 200 ° C. The fluorine-based thermoplastic resin can be appropriately selected within the range having the above melting point. The melting point may be an actually measured value or a catalog value. Further, the fluoroplastic resin may be one kind or more, and may be a homopolymer or a copolymer.

The fluorinated thermoplastic resin is preferably polyvinylidene fluoride or a copolymer thereof. The content of vinylidene fluoride constituent units in polyvinylidene fluoride or a copolymer thereof is not limited, but is preferably 96.0% by mass or more from the viewpoint of having the above melting point and sufficiently exhibiting the characteristics as a copolymer. , 97.0% by mass or more, more preferably 99.5% by mass or less, and more preferably 99.0% by mass or less.

The structural units other than the vinylidene fluoride structural unit in the copolymer are not limited, and may be one or more. The other building blocks may be evenly arranged or unevenly arranged in the copolymer. Examples of other building blocks include chlorotrifluoroethylene building blocks, trifluoroethylene building blocks, fluoroalkyl vinyl ether building blocks, ethylene tetrafluoroethylene building blocks and propylene hexafluoride building blocks. The content of other structural units in the copolymer is preferably 0.5% by mass or more, preferably 1.0% by mass or more, from the viewpoint of having the above melting point and sufficiently expressing the characteristics of the copolymer. Is more preferable, and 4.0% by mass or less is preferable, and 3.0% by mass or less is more preferable.

(Components other than the fluorine-based thermoplastic resin in the matrix)
The fluorinated resin composition constituting the matrix may further contain components other than the fluorinated thermoplastic resin as long as the effects of the present embodiment can be obtained. The content of the above-mentioned other components in the fluororesin composition can be appropriately determined from the viewpoint that the desired effect of the addition of the other components is sufficiently exhibited. Examples of such other components include other thermoplastics, additives and colorants.

The other thermoplastic resin is a thermoplastic resin other than the fluorine-based thermoplastic resin. Examples of the other thermoplastic resin include olefin resins such as polyethylene and fluororesins such as polyphenylene sulfide and polytetrafluoroethylene. Examples of additives include flame retardants, dyes, colorants, lubricants, antioxidants, antioxidants, light stabilizers, antistatic agents, fillers, crosslinkers and compatibilizers. Examples of colorants include titanium oxide and carbon black, other inorganic pigments, organic pigments and organic dyes.

For example, in the present embodiment, the inner surface of the closed cells in the matrix may further have a portion containing another thermoplastic resin. Another thermoplastic resin existing on the inner surface of the closed cell is also referred to as a "first thermoplastic resin". The portion containing the first thermoplastic resin may be a part of the inner surface of the closed cell or the entire inner surface of the closed cell. The portion containing the first thermoplastic resin is, for example, a portion derived from shell particles in the heat-expandable microspheres described later. The first thermoplastic resin in this case will be described in more detail later.

Further, in the present embodiment, the fluororesin composition may contain 0.1 to 0.6% by mass of a further thermoplastic resin. This further thermoplastic resin is also referred to as a "second thermoplastic resin". The second thermoplastic resin may be the same as the above-mentioned fluorine-based thermoplastic resin, may be the same as the first thermoplastic resin, or may be a resin different from these. For example, it may be the resin that is the main component of the masterbatch described later. The masterbatch will be described in more detail later. From the viewpoint of enhancing the characteristics of the fluoroplastic resin in the foam molded product, the content of the second thermoplastic resin is preferably small, for example, 3.0% by mass or less, and 1.0. It is preferably 0% by mass or less, and more preferably 0.6% by mass or less.

The content of the second thermoplastic resin in the fluororesin composition can be appropriately determined according to the use of the second thermoplastic resin. Such applications include the main components of the masterbatch described below. In the case of this application, the content of the second thermoplastic resin in the fluororesin composition is 0.05% by mass or more from the viewpoint of sufficiently enhancing the dispersion uniformity of closed cells in the foamed molded product. It is more preferably 0.1% by mass or more, and even more preferably 0.15% by mass or more.

(Closed cell)
In the present embodiment, substantially all the bubbles contained in the matrix are closed cells. A closed cell is a fine closed space formed in a matrix. In this embodiment, the closed cell may be a space having both a defined shape and a defined size, especially in the matrix. The number of closed cells in the matrix is not limited as long as it is plural. Further, in the matrix, the plurality of closed cells may be uniformly dispersed or may be unevenly present. It is preferable that the plurality of closed cells are uniformly dispersed in the matrix from the viewpoint of exhibiting the desired characteristics of the foamed molded product by having the closed cells.

(Closed cell ratio)
In the present embodiment, the closed cell ratio of the foamed molded product may be 98% or more. The closed cell ratio is the ratio of the number of closed cells to the bubbles contained in the foamed molded product. When the closed cell ratio is 98% or more, substantially all the bubbles in the foamed molded product may be closed cells.

In the present specification, the closed cell is the smallest unit cell that exists independently in the foam molded product. For example, in the present embodiment, when substantially spherical cells are adjacent to each other in the foamed molded product, any of the adjacent cells is specified as a closed cell. On the other hand, in the foam molded product, a bubble in which two or more cells are united and has one common cavity is not specified as a closed cell. Whether or not it is a closed cell can be determined, for example, by observing the cross section of the foamed molded product. Even when a plurality of closed cells overlap to form one bubble in the cross section, it can be determined as a set of a plurality of closed cells if the contours of the individual cells can be visually recognized.

For the closed cell ratio, for example, an image having a predetermined range size (for example, D50 described later) and a shape (for example, average circularity described later) is extracted from an image of a cross section of the foamed molded product, and all of the images in the image. It is obtained by calculating the ratio of the number of extracted images to the number of bubbles in. The closed cell ratio can be determined by using a known image processing technique.

The closed cell ratio can be appropriately determined from various viewpoints such as the desired characteristics to be expressed in the foamed molded product or the use of the foamed molded product. From such a viewpoint, the closed cell ratio may be 90% or more, 95% or more, or 98% or more. Further, from the above viewpoint, the closed cell ratio may be 100% or less, 99% or less, or 98% or less.

(Size of closed cells)
In the present embodiment, the size of the closed cell is 50 to 200 μm in terms of volume-based median diameter (D50). The size of the closed cells is preferably 50 μm or more from the viewpoint of weight reduction of the molded product, and 200 μm or less is preferable from the viewpoint of sufficiently ensuring the mechanical strength of the foamed molded product. The size of the closed cell can be measured by a known measuring device, for example, using an enlarged image of a cross section obtained by appropriately slicing the foamed molded product.

The size of the closed cell can be appropriately determined according to the application of the foamed molded product or the physical properties required for the foamed molded product, and the lower limit thereof may be, for example, a median diameter of 75 μm or more, and 80 μm or more. It may be 85 μm or more. Similarly, the upper limit of the size of the closed cell may be 150 μm or less, 120 μm or less, and 95 μm or less in terms of median diameter.

(Average circularity)
The shape of each closed cell is not limited, but it is preferable to have a predetermined shape from the viewpoint of sufficiently expressing the desired characteristics expressed by the closed cell in the foam molded product. For example, the closed cells may be substantially spherical, in which case the average circularity of the closed cells in plan view may be 0.980 or higher. From the above viewpoint, the average circularity is more preferably 0.985 or more, and further preferably 0.990 or more. For the average circularity, for example, an image of a sufficient number of closed cells is extracted from the enlarged image of the cross section of the foamed molded product described above, the circularity is measured by a known measuring device, and the average value of the obtained measured values is measured. Can be obtained by calculating.

(Distribution of closed cell size)
The size of the closed cells may include some variations, but it is preferable that the sizes of the closed cells are substantially uniform from the viewpoint of sufficiently expressing the desired characteristics expressed by the closed cells in the foamed molded product. For example, it is preferable that the half width W1 of the peak representing the volume-based distribution in the size of closed cells is 45 μm or less, and the peak width W2 is 3.2 × W1 or less. From the above viewpoint, W1 is more preferably 40 μm or less, and further preferably 38 μm or less. Further, from the above viewpoint, W2 is more preferably 3.0 × W1 or less, and further preferably 2.7 × W1 or less.

The full width at half maximum W1 is the peak width at a position half the height at the peak. The peak height is the height from the baseline to the peak top. The baseline is a straight line connecting the peak start and peak end, which is determined according to a predetermined amount of change in the measured value. The peak width W2 is the distance between the intersections of the respective peak tangents and the baseline at the inflection points of the peaks above and below the peak top.

Alternatively, the 10% size (D10) of the cumulative distribution based on the volume of the closed cell size is 0.8 × D50 μm or more, and the 90% size (D90) of the cumulative distribution is 1.2 × D50 μm. It may be as follows. It is preferable that the foamed molded product has such a sharp particle size distribution with respect to the closed cells from the viewpoint of sufficiently exhibiting the desired characteristics expressed by the closed cells in the foamed molded product, as described above. From this point of view, D10 is more preferably 0.85 × D50 μm or more, and further preferably 0.9 × D50 μm or more. Further, from the above viewpoint, D90 is more preferably 1.15 × D50 μm or less, and further preferably 1.1 × D50 μm or less.

<Physical characteristics of foam molded product>
Since the foam molded product of the present embodiment has a plurality of the above-mentioned closed cells, it is lighter than the case without the closed cells, and therefore can have various characteristics.

(specific gravity)
For example, the specific gravity of the foam molded product may be 1.0 to 1.7. In the present embodiment, the specific gravity of the foamed molded product can be appropriately controlled at least within the range. The specific gravity can be appropriately determined from various viewpoints such as the desired characteristics to be expressed in the foamed molded product or the use of the foamed molded product. From such a viewpoint, the specific gravity may be 1.1 or more, 1.2 or more, or 1.4 or more. Further, from the above viewpoint, the specific gravity may be 1.6 or less, and may be 1.5 or less. The specific gravity can be measured using a known measuring device.

(Lightening rate)
The weight reduction rate of the foam molded product may be 5 to 50%. The weight reduction rate can be calculated from the following formula. In the following formula, the "non-foamed molded product" is a molded product substantially consisting of only a matrix. The specific gravity of the non-foamed molded product may be an actually measured value or a calculated value.
Weight reduction rate (%) = 100-{(specific gravity of foamed molded product) / (specific gravity of non-foamed molded product)} x 100

Similar to the specific gravity, the weight reduction rate can be appropriately determined from various viewpoints such as the desired characteristics to be expressed in the foamed molded product or the use of the foamed molded product. From such a viewpoint, the weight reduction rate may be 10% or more, 15% or more, or 20% or more. Further, from the above viewpoint, the weight reduction rate may be 45% or less, 40% or less, or 37% or less.

(Porosity)
The porosity of the foam molded product may be 5 to 50%. Porosity is represented by the proportion of closed cells in the volume of the foamed molded product. The porosity can be obtained from, for example, the above-mentioned specific gravity and the volume of closed cells.

Similar to the specific gravity and the weight reduction rate, the porosity can be appropriately determined from various viewpoints such as the desired characteristics to be expressed in the foamed molded product or the use of the foamed molded product. From such a viewpoint, the porosity may be 10% or more, 15% or more, or 20% or more. Further, from the above viewpoint, the porosity may be 45% or less, 40% or less, or 37% or less.

(Hardness)
The hardness of the foam molded product may be 80 or more. If the hardness of the foamed molded product is too low, the closed cells generated during molding shrink with cooling and become smaller, which may result in an insufficient weight reduction rate. The hardness can be determined by using the hardness tester described in JIS S6050. Further, the hardness can be appropriately adjusted depending on the type of the fluorine-based thermoplastic resin or the composition of the fluorine-based resin composition. From the viewpoint of sufficiently increasing the weight reduction rate, the hardness is more preferably 90 or more, and further preferably 92 or more. The upper limit of the hardness of the foamed molded product is not limited, but can be appropriately determined within a range feasible with the fluororesin composition, and may be, for example, 95 or less.

[Manufacturing method of foam molded product]
The foam molded product of the present embodiment can be produced by a method including the following mixing step and molding step.

<Mixing process>
The mixing step is a step of mixing the above-mentioned fluorine-based resin composition and the heat-expandable microspheres. The fluorine-based resin composition is as described above.

(Thermal expansion microsphere)
Thermally expandable microspheres are particles that expand when heated. For example, the heat-expandable microspheres expand at the molding temperature of the fluororesin composition to form closed cells in the foamed part. The molding temperature of the fluorine-based resin composition is a temperature at which the fluorine-based resin composition softens in a moldable manner, and may be, for example, the melting point or the softening point of the fluorine-based thermoplastic resin.

(Expansion start temperature)
The expansion start temperature of the heat-expandable microspheres is 180 to 220 ° C. In the present embodiment, the heat-expandable microspheres thermally expand during molding of the fluororesin composition to form closed cells. If the expansion start temperature is too low, the thermally expandable microspheres may thermally expand before the melt-kneading state in the molding of the fluororesin composition, and good closed cells may not be formed in the matrix. If the expansion start temperature is too high, the thermally expandable microspheres may not thermally expand even if the fluororesin composition is in a melt-kneaded state in molding, and sufficient closed cells may not be formed in the matrix.

From the viewpoint of forming good and sufficient closed cells in the matrix of the foam molded product, the expansion start temperature may be 180 ° C. or higher, or 190 ° C. or higher. From the above viewpoint, the expansion start temperature may be 230 ° C. or lower, or 220 ° C. or lower. The expansion start temperature can be determined by thermomechanical analysis, which will be described later, and can be adjusted according to the structure, material, or both of the thermally expandable microspheres.

(Maximum displacement due to thermal expansion)
In the present embodiment, the maximum displacement measured by thermomechanical analysis of the thermally expandable microspheres is 1000 μm / mg or more. If the maximum displacement amount is too small, the weight reduction of the molded product may be insufficient. The maximum displacement amount may be 1500 μm / mg or more, or 2000 μm / mg or more, from the viewpoint of sufficiently increasing the weight reduction rate in the foamed molded product and adjusting it to a desired range. The above-mentioned maximum displacement amount can be appropriately adjusted within a range in which the desired weight reduction rate can be obtained and, if necessary, other arbitrary characteristics such as mechanical strength are exhibited. From such a viewpoint, the maximum displacement amount may be 3000 μm / mg or less, and may be 2500 μm / mg or less.

The maximum displacement is determined by heating the heat-expandable microspheres housed in a predetermined container at a predetermined temperature rise rate using a known thermomechanical analyzer, and determining the bulkiness of the heat-expandable microspheres per hour or temperature. Obtained by measuring the change. The maximum displacement can also be adjusted according to the structure, material or both of the thermally expandable microspheres.

(Average particle size)
The thermally expandable microspheres may have other physical characteristics other than the above-mentioned expansion start temperature and maximum displacement amount. For example, the average particle size of the heat-expandable microspheres is preferably 15 to 30 μm in terms of volume-based average particle size (d50) from the viewpoint of forming closed cells in a sufficient number or density in the foamed molded product. If the average particle size is too small, closed cells of sufficient size may not be formed, and if the average particle size is too large, the distribution of closed cells in the foamed molded product becomes overcrowded, which is the desired cause of the closed cells. Insufficient expression of properties may occur.

The average particle size may be 18 μm or more, 20 μm or more, and 28 μm or less from the viewpoint of realizing the desired size and desired distribution of closed cells in the foamed molded product. It may be 25 μm or less. The average particle size can be determined by using a known technique for measuring the particle size of the particles, and can be adjusted by classifying the thermal expansion microspheres and mixing the classified products.

(Constitution)
The composition of the heat-expandable microspheres can be appropriately determined within the range having the above-mentioned characteristics. For example, it is preferable that the heat-expandable microspheres have shell particles composed of a shell resin composition and a heat-expanding agent contained in the shell particles from the viewpoint of having the above-mentioned properties. The heat-expandable microspheres are core-shell particles composed of the heat-expanding agent and the shell particles, with the heat-expanding agent contained in the shell particles as the core.

(Shell particles)
The shell particles are composed of a shell resin composition. The shell resin composition contains the above-mentioned first thermoplastic resin as a main component. The content of the first thermoplastic resin in the shell resin composition can be appropriately determined within a range in which it sufficiently expands at the molding temperature of the fluororesin composition, and may be at least 50% by mass or more. The content may be, for example, 96.0% by mass or more, 97.0% by mass or more, and 99.0% by mass or more.

The first thermoplastic resin is preferably a resin that softens at a temperature higher than the melting point of the fluorine-based thermoplastic resin. Examples of the first thermoplastic resin include (meth) acrylic resins.

The (meth) acrylic resin is, for example, a radical polymer having a carboxylic acid having an unsaturated bond between carbons or a derivative thereof as a monomer. Examples of such monomers include unsaturated carboxylic acids, esters thereof, and derivatives thereof.

Examples of unsaturated carboxylic acids include (meth) acrylic acid. Methacrylic acid is preferable from the viewpoint of further increasing the temperature at which the first thermoplastic resin softens (melting point, glass transition point, etc.).

Examples of unsaturated carboxylic acid esters include methyl (meth) acrylates.

Examples of unsaturated carboxylic acid derivatives include (meth) acrylonitrile. The first thermoplastic resin composed of acrylonitrile as a monomer and the matrix containing the same may turn yellow over time. Methacrylonitrile is preferable from the viewpoint of raising the temperature at which the first thermoplastic resin softens and suppressing coloring over time.

In the present specification, "(meth) acrylic" is a general term for acrylic and methacrylic, and means one or both of them.

The first thermoplastic resin is preferably a radical polymer of methacrylnitrile and an unsaturated carboxylic acid from the viewpoint of softening at the above-mentioned high temperature.

(Other components in the shell resin composition)
Alternatively, the shell resin composition may further contain a cross-linking agent for cross-linking the first thermoplastic resins from the viewpoint of strengthening the wall portion of the closed cells formed after thermal expansion.

Alternatively, the material of the shell particles may be substantially free of the particular material. For example, in the present embodiment, since the bubbles formed in the foamed molded product are closed cells, it is possible to control the formation of the bubbles so that the wall portion of the bubbles exhibits a desired strength. Therefore, since it is not necessary to contain a component that enhances the strength of the bubbles, the shell resin composition does not have to substantially contain the above-mentioned cross-linking agent.

(Thermal expansion agent)
The thermal expansion agent is a component that expands at the molding temperature of the fluororesin composition. The thermal expansion agent can be appropriately selected from known foaming agents. For example, the thermal expansion agent may be an organic physical foaming agent, an inorganic physical foaming agent, an organic chemical foaming agent, or an inorganic chemical foaming agent. You may. The physical foaming agent is a component that expands in response to a physical phenomenon such as heat, and the chemical foaming agent expands by generating gas, for example, in response to a chemical phenomenon such as a chemical reaction. It is an ingredient.

In this embodiment, it is preferable to expand the thermal expansion agent at the molding temperature. The type of thermal expansion agent can be appropriately selected according to the desired expansion start temperature or molding temperature when producing the foam molded product. In the present embodiment, since the heat-expandable microspheres are expanded by "heat", the heat-expandable agent is preferably a physical foaming agent.

Examples of physical foaming agents include hydrocarbons, more specifically methane, ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutane, n-pentane, isopentan, neopentane, n-. Hydrocarbons such as hexane, isohexane, n-heptane, isoheptane, n-octane, isooctane, n-nonane, isononan, n-decane, isodecan, n-dodecane, isododecane, petroleum ether, isoparaffin mixture; its isomers; CCl ₃ Includes chlorofluorocarbons such as F, CCl ₂ F ₂ , _{CClF 3} , _{CClF 2- CClF 2} ; tetraalkylsilanes such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, trimethyl-n-propylsilane;

The thermal expansion agent can be used alone or in combination of two or more. Among these, isooctane, an isomer thereof, or a mixture thereof is preferable because sufficient foaming performance is exhibited. Further, the thermal expansion agent may contain a compound which is thermally decomposed by heating to become a gas, if necessary.

In the present embodiment, the content of the heat-expandable microspheres with respect to the fluoroplastic resin is 0.05 to 2% by mass. If the content is too small, the amount of closed cells in the foamed molded product may be insufficient. If the content is too large, the amount of air bubbles in the foamed molded product may be too large and open cells may be generated, or mechanical properties such as the strength of the foamed molded product may be insufficient.

In the present embodiment, the above-mentioned content of the heat-expandable microspheres and the amount of closed cells generated in the foamed molded product are the types of the fluoroplastic resin and the first thermoplastic resin in the heat-expandable microspheres. It is possible to appropriately adjust according to one or more of the type and the type and amount of the thermal expansion agent. In particular, in the present embodiment, by appropriately adjusting one or more of these, it is possible to form more bubbles in the foamed molded product with a small amount of the heat-expandable microspheres used.

For example, the fluoroplastic resin is PVDF, the first thermoplastic resin is a hydrocarbon containing a radical polymer of methacrylnitrile and an unsaturated carboxylic acid as a main component, and the thermal expansion agent is a hydrocarbon containing isooctane as a main component. In some cases, the weight reduction rate of the foamed molded product can be adjusted in the range of 5 to 50%. Further, in the combination of the above materials, the ratio (A / B) of the weight reduction rate (A) in the foamed molded product to the content (B) of the heat-expandable microspheres in the fluororesin composition is set to 15 to 85. It is possible.

Further, when the fluoroplastic resin is PVDF, the first thermoplastic resin is a radical polymer containing methacrylonitrile, methacrylic acid and methyl acrylate as monomers, which is independent during molding of the foam molded product. It is preferable from the viewpoint of generating bubbles well. From the above viewpoint, the thermal expansion agent in this case is preferably one or both of isooctane and its isomers.

If the amount of methacrylonitrile in the above-mentioned monomer is too large or too small, the heat-expandable microspheres may not be sufficiently thermally expanded in the foamed molded product. From the viewpoint of forming good closed cells in the foamed molded product, the amount of methacrylonitrile in the above monomer is preferably 25% by mass or more, more preferably 35% by mass or more, and 50% by mass. The above is more preferable. From the above viewpoint, the amount of methacrylonitrile in the above-mentioned monomer is preferably 70% by mass or less, more preferably 65% by mass or less, and further preferably 60% by mass or less.

If the amount of methacrylic acid in the above-mentioned monomer is too small, the heat-expandable microspheres may not expand sufficiently in the foamed molded product. From the viewpoint of forming good closed cells in the foamed molded product, the amount of methacrylic acid in the above-mentioned monomer is preferably 25% by mass or more, more preferably 35% by mass or more, and 40% by mass or more. Is more preferable.

The amount of methyl acrylate in the above-mentioned monomer can be appropriately determined from the range of 0.1 to 5% by mass from the viewpoint of forming good closed cells in the foamed molded product.

(Use of masterbatch)
The above mixing step can be carried out using a masterbatch. The use of a masterbatch is preferable from the viewpoint of rapidly and uniformly dispersing the heat-expandable microspheres in the fluororesin composition.

The mixing step using the masterbatch includes, for example, a step of preparing a first pellet containing a melt-kneaded product of the masterbatch resin composition and a heat-expandable microsphere, and a second step containing a fluoroplastic resin. A step of preparing the pellets of the above and a step of mixing the first pellet and the second pellet are included.

(Preparation of the first pellet)
The first pellet is a melt-kneaded product of a masterbatch resin composition and a heat-expandable microsphere. The masterbatch resin composition is a composition containing the above-mentioned second thermoplastic resin as a main component. The content of the second thermoplastic resin in the masterbatch resin composition may be at least 50% by mass or more. The content may be, for example, 96.0% by mass or more, 97.0% by mass or more, and 99.0% by mass or more. The second thermoplastic resin may be one kind or more. In addition, the masterbatch resin composition may further contain the above-mentioned various additives as appropriate within the range in which the effects of the present embodiment can be obtained.

The second thermoplastic resin preferably has sufficiently good compatibility with the above-mentioned fluorine-based thermoplastic resin. Further, it is preferable that the second thermoplastic resin can be melt-kneaded at a temperature sufficiently lower than the expansion start temperature of the thermally expandable microspheres. For example, the second thermoplastic resin preferably has sufficient softness at a temperature well below the expansion start temperature, or has a melting point well below the expansion start temperature, for example 50-120 ° C. It is preferable to have.

Examples of the second thermoplastic resin include low density polyethylene, polyolefins such as polypropylene, ethylene-vinyl acetate copolymer (EVA), and regenerated olefin resin (EMMA).

The first pellet may be obtained by production or may be a commercially available product. The first pellet is prepared, for example, by kneading a heat-expandable microsphere and a second thermoplastic resin in a range equal to or lower than the expansion start temperature of the heat-expandable microsphere using a known kneading device. It is possible.

If the content of the second thermoplastic resin in the first pellet is too small, the dispersibility of the heat-expandable microspheres in the fluororesin composition may be insufficient. If the content is high, the influence of the second thermoplastic resin on the physical properties of the fluororesin composition may be large. In the step of preparing the first pellet, the amount of the second thermoplastic resin used with respect to the heat-expandable microspheres is 20 from the viewpoint of exhibiting good dispersibility of the heat-expandable microspheres in the fluororesin composition. It is preferably 3% by mass or more, more preferably 30% by mass or more, and further preferably 40% by mass or more. The amount used is preferably 80% by mass or less, preferably 75% by mass or less, from the viewpoint of sufficiently suppressing the influence of the second thermoplastic resin on the physical properties of the fluororesin composition. More preferably, it is 70% by mass or less.

(Preparation of second pellet)
The second pellet is a resin composition containing a fluorine-based thermoplastic resin as a main component. The resin composition may contain at least 50% by mass or more of the fluorinated thermoplastic resin, and may be substantially composed of only the fluorinated thermoplastic resin. For example, the content of the fluorinated thermoplastic resin in the resin composition may be, for example, 96.0% by mass or more, 97.0% by mass or more, and 99.0% by mass or more. Good.

The second pellet may be obtained as a commercially available product, or can be prepared by molding a fluorine-based thermoplastic resin or a fluorine-based resin composition into pellets by a known technique.

(Mixing of first pellet and second pellet)
The first pellet and the second pellet need only be mixed substantially uniformly as the resin molding material, and can be appropriately mixed using a known stirring device for pellets.

<Molding process>
In the molding step, the fluororesin composition produced as described above is heated to the molding temperature, and the fluororesin composition is molded while expanding the heat-expandable microspheres. The molding step can be carried out by a known resin molding method. Examples of molding steps include extrusion molding and injection molding. The molding process can be appropriately determined according to the shape of the foam molded product to be manufactured. For example, the molding step is carried out by extrusion molding if the shape of the foam molded body is a simple shape such as a tubular shape or a plate shape, and by injection molding using an appropriate mold if the shape of the foam molded body is other complicated. It is possible.

The molding temperature (Tm) in the molding step in the present embodiment is a temperature equal to or higher than the expansion start temperature (Ts) of the heat-expandable microspheres. If the Tm is too high with respect to Ts in the molding step, the dispersion of the heat-expandable microspheres during molding becomes insufficient, and the distribution of closed cells in the foamed molded product may be biased. From the viewpoint of sufficiently evenly distributing closed cells in the foam molded product, the difference (Tm-Ts) between Tm and Ts is preferably 90 ° C. or lower, more preferably 80 ° C. or lower. It is more preferably 60 ° C. or lower.

The molding temperature Tm is a temperature immediately before the fluororesin composition is molded. The molding temperature Tm may be, for example, the temperature of the die in the case of extrusion molding, or the outlet temperature of the cylinder in the case of injection molding.

[Action effect]
As described above, according to the present embodiment, when molding a resin composition containing a fluorine-based thermoplastic resin as a main component, foaming having closed cells is performed by foaming the above-mentioned heat-expandable microspheres as a foaming agent. Obtain a molded product. According to this embodiment, it is possible to form a plurality of closed cells having a substantially uniform shape and size in the matrix. Therefore, according to the present embodiment, the weight of the fluoroplastic resin molded product can be reduced by the closed cells with a small amount of foaming as compared with the foamed molded product manufactured by using the conventional physical foaming agent or chemical foaming agent. It can be done efficiently and easily with an agent.

As is clear from the above description, the foam molded product of the present embodiment contains a matrix composed of a fluorine-based resin composition containing a fluorine-based thermoplastic resin as a main component and a plurality of bubbles existing in the matrix. Have. The melting point of the fluorinated thermoplastic resin is 165 to 200 ° C., the cells are closed cells, and the size of the closed cells is 50 to 200 μm in terms of volume-based median diameter. According to this configuration, a foam molded product capable of easily realizing weight reduction by foaming and its control is provided.

The foam molded product of the present embodiment may further have a portion containing a first thermoplastic resin other than the fluoroplastic resin on the inner surface of the closed cells in the matrix. According to this configuration, it is possible to construct a heat-expandable microsphere using an appropriate thermoplastic resin, from the viewpoint of making the size and shape of the closed cells uniform and uniformly distributing the closed cells in the foam molded body. It is more effective.

In the foam molded product of the present embodiment, the above-mentioned first thermoplastic resin may contain a radical polymer of methacrylnitrile and an unsaturated carboxylic acid as a main component. According to this configuration, it is possible to generate closed cells in the matrix at a relatively high temperature close to the molding temperature of the resin composition containing a fluorine-based thermoplastic resin as a main component. Therefore, it is more effective from the viewpoint of making the size and shape of the closed cells uniform and uniformly distributing the closed cells in the foam molded body.

In the foam molded product of the present embodiment, the fluorine-based thermoplastic resin may be polyvinylidene fluoride. According to this configuration, it is suitable for obtaining a foamed molded product of a fluoroplastic resin having crystallinity.

In the foam molded product of the present embodiment, the fluororesin composition may contain a second thermoplastic resin, and the content of the second thermoplastic resin in the fluororesin composition is 0.1 to 0. It may be 6% by mass. According to this configuration, in the foamed molded product, it is possible to sufficiently express the physical characteristics required for the matrix containing the fluorine-based thermoplastic resin as the main component.

The specific gravity of the foam molded product of the present embodiment may be 1.0 to 1.7. According to this configuration, for example, a foam molded product that is appropriately lightened according to the application can be obtained.

In the foam molded product of the present embodiment, the half width W1 of the peak representing the volume-based distribution in the size of closed cells may be 45 μm or less, and the peak width may be 3.2 × W1 or less. According to this configuration, the uniformity of the size of the closed cells is enhanced, and it is more effective from the viewpoint of precisely controlling the physical properties of the foamed molded product due to the presence of the closed cells.

In the foam molded product of the present embodiment, when the median diameter of the closed cell is D50, the size of 10% of the cumulative distribution based on the volume of the closed cell size may be 0.8 × D50 μm or more. , 90% of the cumulative distribution may be 1.2 × D50 μm or less.
This configuration also enhances the uniformity of the size of the closed cells, and is even more effective from the viewpoint of precisely controlling the physical properties of the foamed molded product due to the presence of the closed cells.

Further, the method for producing a foamed molded article in the present embodiment is a foamed molded article having a matrix composed of a fluororesin composition containing a fluoroplastic resin as a main component and a plurality of bubbles existing in the matrix. The step of mixing the fluororesin composition and the heat-expandable microspheres and the fluororesin composition mixed with the heat-expandable microspheres are heated to the molding temperature of the fluororesin composition. This includes a step of molding the fluororesin composition while expanding the heat-expandable microspheres. The melting point of the fluoroplastic resin is 165 to 200 ° C., the content of the thermally expandable microspheres in the fluororesin composition is 0.05 to 2% by mass, and the expansion of the thermally expandable microspheres starts. The temperature is 180 to 220 ° C., the maximum displacement of the thermally expandable microspheres as measured by thermomechanical analysis is 1000 μm / mg or more, and the above-mentioned molding temperature is a temperature equal to or higher than the expansion start temperature. According to this configuration, it is possible to manufacture a foam molded product in which weight reduction by foaming and its control can be easily realized.

In the production method of the present embodiment, the heat-expandable microspheres are contained in shell particles composed of a shell resin composition containing a first thermoplastic resin other than the fluorothermoplastic resin, and shell particles. It may have a thermal expansion agent. According to this configuration, it is possible to appropriately adjust the expansion start temperature of the thermally expandable microspheres. Therefore, it is more effective from the viewpoint of producing a foamed molded product in which the size and shape of the closed cells are substantially uniform and the closed cells are substantially uniformly distributed.

In the production method of the present embodiment, the first thermoplastic resin may contain a radical polymer of methacrylnitrile and an unsaturated carboxylic acid as a main component, and the thermal expansion agent may be one of isooctane and an isomer thereof or one of the isomers thereof. Both may be included. According to this configuration, it is suitable to set the expansion start temperature of the thermally expandable microspheres to a relatively high temperature close to the molding temperature of the resin composition containing a fluorine-based thermoplastic resin as a main component. Therefore, it is more effective from the viewpoint of producing a foamed molded product in which the size and shape of the closed cells are substantially uniform and the closed cells are substantially uniformly distributed.

In the production method of the present embodiment, the above-mentioned mixing step is performed by forming a first pellet containing a melt-kneaded product of a masterbatch resin composition containing a second thermoplastic resin as a main component and a heat-expandable microsphere. It may include a step of preparing, a step of preparing a second pellet containing a fluorine-based thermoplastic resin as a main component, and a step of mixing the first pellet and the second pellet. According to this configuration, it is possible to sufficiently enhance the dispersibility of the heat-expandable microspheres in the fluororesin composition. Therefore, it is even more effective from the viewpoint of uniformly dispersing closed cells in the foamed molded product.

In the production method of the present embodiment, in the step of preparing the first pellet, the second thermoplastic resin may be used in an amount of 40 to 70% by mass with respect to the heat-expandable microspheres. According to this configuration, since the heat-expandable microspheres are uniformly dispersed in the fluororesin composition even in a small amount, it is more effective from the viewpoint of efficiently realizing weight reduction in the foam molded product. ..

In the production method of the present embodiment, polyvinylidene fluoride may be used as the fluorine-based thermoplastic resin. According to this configuration, a foam molded product of a fluoroplastic resin having crystallinity can be suitably produced.

The foam molded product of the present embodiment is mainly composed of a fluorinated thermoplastic resin. Further, the foam molded product of the present embodiment can be made relatively hard. Therefore, the foam molded product of the present embodiment is useful as a building material, an automobile material, or the like.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention.

An embodiment of the present invention will be described below.

[Manufacture of thermally expandable microspheres]
(1) Preparation of Aqueous Dispersion Medium The following components were mixed in the following amounts to prepare an aqueous mixture. The "50% by mass diethanolamine-azipic acid condensation product" is an equal amount mixture of diethanolamine and adipic acid condensation product, and its acid value is 78 mgKOH / g.
20% by mass Colloidal silica 6.5% by mass 50% by mass Diethanolamine-adipic acid condensation product 0.65% by mass Sodium nitrite 0.48% by mass 25% sodium chloride aqueous solution 89 parts by mass

Water was further added to the obtained aqueous mixture to adjust the total amount of the aqueous mixture to 310 parts by mass. Next, a 5 mass% hydrochloric acid aqueous solution was added to the aqueous mixed solution to adjust the pH of the aqueous mixed solution to 3.5. In this way, an aqueous dispersion medium was prepared.

(2) Preparation of Polymerizable Monomer Composition The following components were mixed in the following amounts to prepare a polymerizable monomer composition 1.
Methacrylonitrile (MAN) 55 parts by mass Methacrylic acid (MAA) 43 parts by mass Methyl acrylate (MA) 2 parts by mass Isooctane (IO) 30 parts by mass 2,2'-azobisisobutyronitrile 1 part by mass

(3) Suspension Polymerization The polymerizable monomer composition 1 is added to the prepared aqueous dispersion medium, and the aqueous dispersion medium is stirred with a homogenizer to allow the aqueous dispersion medium to contain minute amounts of the polymerizable monomer composition 1. A droplet was formed. Next, an aqueous dispersion medium in which the polymerizable monomer composition 1 was dispersed as fine droplets was charged into a polymerization can (1.5 L) equipped with a stirrer. Then, while stirring the aqueous dispersion medium with a stirrer, the polymerizable monomer was reacted in the droplets by heating at 60 ° C. for 15 hours and further at 70 ° C. for 10 hours using a warm water bath.

After the polymerization, the slurry containing the produced particles was filtered, washed with water, and dried. In this way, a heat-expandable microsphere (MS) 1 in which isoparaffin was contained in the shell particles of the acrylic resin was obtained.

(4) Measurement of particle size of heat-expandable microspheres The slurry of heat-expandable microspheres 1 was sieved by a sieve mesh # 100 (opening 150 μm). 0.5 g of the heat-expandable microspheres 1 separated by sieving was dispersed in 20 mL of pure ion-exchanged water, and ultrasonic waves were dispersed over 15 minutes. The obtained dispersion was measured using a flow-type particle size analyzer (product name "FPIA-3000", manufactured by Sysmex Co., Ltd.), and the cumulative number of thermally expandable microspheres 1 in the dispersion was 50 based on the volume. The particle size (median diameter, d50) of% was measured. The total count in the measurement was 10000 (the number of photographed particles was 10000).

(5) Measurement and evaluation of foamability 0.5 mg of heat-expandable microsphere 1 was placed in a container as a sample. Using a thermomechanical analyzer (TMA, model number "TMA / SDTA840", manufactured by METTLER Trade Co., Ltd.), the heat-expandable microsphere 1 in the container is heated at a heating rate of 5 ° C./min per second. The displacement of the height of the portion occupied by the heat-expandable microsphere 1 was continuously measured. Further, the temperature at the time when the height displacement started was measured and used as the expansion start temperature (Ts).

Among the above-mentioned measured displacements, the displacement at the largest height was defined as the maximum displacement (Vmax), and the displacement at the smallest height was defined as the minimum displacement (Vmin). Then, the foam displacement (V) was calculated from the following formula.
V (μm / mg) = (Vmax-Vmin) / amount of sample contained in the container (mg)

Further, based on the foaming displacement V, the foamability of the heat-expandable microsphere 1 was evaluated according to the following criteria. If it is "G", it can be determined that the foaming performance is practically sufficient, and if it is "NG", it can be determined that the foaming performance is not practically sufficient.
G: Foaming displacement is 1000 μm / mg or more.
NG: Foaming displacement is less than 1000 μm / mg.

For the heat-expandable microsphere 1, d50 was 21.9 μm, Ts was 197 ° C, and V was 2414 μm / mg.

[Example 1]
(1) Preparation of masterbatch (MB) Using a pressurized kneader, linear low-density polyethylene (LLDPE, MFR 30 g / 10 minutes (190 ° C., 21.2 N), melting temperature 66 ° C.) and heat-expandable microspheres 1 and 1 were heat-kneaded at 70 to 80 ° C. so as to have a weight ratio of 4: 6 (LLDPE: MS). The resulting composition was transferred to an extruder, extruded at 70-80 ° C. and pelletized. In this way, MS pellet 1 containing the heat-expandable microsphere 1 was obtained.

(2) Preparation of Fluorine-based Thermoplastic Resin As a fluorine-based thermoplastic resin, KF Polymer H1100 (MFR 2-4 g / 10 minutes (230 ° C., 5 kg), melting temperature 173 ° C.) manufactured by Kureha Corporation was prepared. The polymer is polyvinylidene fluoride (PVDF) and its dosage form is pellets.

(3) Manufacture of foamed molded article Using a single-screw extruder (manufactured by Pura Giken Co., Ltd .: PEX-40-24H), the above-mentioned fluoroplastic resin pellets and MS pellet 1 were mixed by weight ratio of 99. The mixture was mixed in an amount of 66: 0.34 (PVDF: MS pellet), and extruded at a screw rotation speed of 30 R / min, a cylinder temperature (T1) of 200 ° C., and a die temperature (T2) of 190 ° C. The size of the opening of the die is 3 mm × 30 mm. In this way, a plate-shaped foam molded product 1 having a thickness of about 3 mm and a width of about 30 mm was produced.

[Examples 2 to 7]
Examples 2 and 2 were the same as in the foam molded product 1 except that the mixing ratio of the fluorinated thermoplastic resin pellets and the MS pellets, the cylinder temperature (T1) and the die temperature (T2) were changed as shown in Table 1. The foam molded products 2 to 7 of No. 7 were produced, respectively.

[Comparative Example 1]
The molded product C1 was manufactured in the same manner as the foam molded product 1 except that MS was not used.

[Evaluation]
(1) Specific gravity (d)
The specific gravity of each of the foam molded products 1 to 7 and the molded product C1 was measured. The specific gravity was measured according to ASTM D792. More specifically, the foam molded product was cut in a direction orthogonal to the extrusion direction (Traverise Direction, TD) to prepare a test piece having a width of 1 to 2 mm. Next, the specific gravity of the test piece was measured in water at 23 ° C. using an automatic hydrometer (Densimeter DSG-1) manufactured by Toyo Seiki Seisakusho. The measurement was performed three times per test piece, and the average value was taken as the specific gravity d of the foamed molded product. The results are shown in Table 1.

(2) Weight reduction rate (Rl)
For each of the foam molded products 1 to 7 and the molded product C1, the weight reduction rate Rl was determined using the following formula. The results are shown in Table 1.
Weight reduction rate Rl (%) = 100-{(specific gravity of each foam molded product / specific gravity of molded product C1) x 100}

(3) Size of closed cell (D50)
For each of the foam molded products 1 to 7 and the molded product C1, the foamed molded product was cut in a direction orthogonal to the extrusion direction, and the size of closed cells was measured from the cut surface. More specifically, using an optical microscope VHX-5000 (magnification: 100 times) manufactured by KEYENCE CORPORATION, repeated measurement is performed in the measurement condition "automatic area measurement" mode so that the number of effective particles is 1000 or more. went. In this way, the size of the cumulative 50% of the volume standard was defined as the size D50 of the closed cells of the foamed molded product.

(3) Distribution of size of closed cells From the observation results of the cut surface of each of the foamed molded bodies 1 to 7 and the molded body C1, the peaks in the volume-based size distribution of the closed cells are thermally expandable micros. The half-value width W1 and the peak width W2 were obtained in the same manner as in the sphere 1. Moreover, these ratios W2 / W1 were determined. The results are shown in Table 1.

(4) Measurement of hardness of foam For each of the foam molded bodies 1 to 7 and the molded body C1, two molded bodies were used using a hardness tester (durometer type A (TECLOCK Co., Ltd. TECLOCK GS-619R-G)). Was used as a sample, and the A hardness was measured. The results are shown in Table 1. In the table, "A1" is an instantaneous value, which is a measured value immediately after the hardness tester is brought into close contact with the sample (within one second after being brought into close contact with the sample). “A15” is a value for 15 seconds, which is a measured value 15 seconds after the hardness tester is brought into close contact with the sample. Each measured value is the average value of the measured values at five arbitrarily selected points in the sample.

[Discussion]
FIG. 1 shows an image of a cross section of the foam molded product 1 taken with an optical microscope at a magnification of 100 times. FIG. 2 shows an image of the cross section of the foam molded product 1 that has been processed for observation taken with an optical microscope at a magnification of 100 times. The treatment is to immerse the cross section of the independent foam molded product 1 in a red paint and then wipe off the paint for the purpose of more clearly showing the closed cells in the cross section.

As shown in FIGS. 1 and 2, the bubbles in the foamed molded product 1 are all closed cells having a substantially spherical shape and a substantially constant size. For example, in FIG. 1, a portion in which a plurality of bubbles appear to overlap can be seen, but none of the bubbles appearing to overlap in this way is coalesced even if they are adjacent to other bubbles. It is considered that this is because when each particle of the heat-expandable microsphere is thermally expanded, even if the shell particles expand and come into contact with each other, the shell does not come into direct contact because PVDF is interposed between them. Further, it is considered that the shell resin composition containing a methacrylic resin as a main component repels PVDF at the abutting portion and suppresses the bursting of the shell at the abutting portion.

When the cross sections of the foam molded products 2 to 7 were observed with an optical microscope, it was confirmed that these foam molded products had closed cells as in the foam molded product 1.

Further, as is clear from Examples 1 to 3 and Examples 4 to 6, it can be seen that the larger the amount of the masterbatch, the lower the specific gravity d of the foamed molded product and the larger the weight reduction rate Rl. This is thought to be because the larger the amount of masterbatch used, the larger the number of closed cells generated.

Further, as is clear from Examples 1, 4 and 7, when the cylinder temperature T1 at the time of molding is increased, the specific gravity d of the foamed molded product becomes smaller and the weight reduction rate Rl becomes larger. It is considered that this is because the higher the temperature at the time of kneading, the easier it is for the heat-expandable microspheres to expand.

Further, as is clear from Examples 1, 4 and 7, when the cylinder temperature T1 at the time of molding is increased, the median diameter D50 of the closed cell tends to decrease. It is considered that this is because the thermal expansion agent is more likely to expand as the cylinder temperature T1 is increased, and the expansion speed of the shell particles is also increased, but not as fast as the expansion speed of the thermal expansion agent.

Further, as is clear from Examples 1, 4 and 7, when the cylinder temperature T1 at the time of molding is increased, the peak width W2 of the closed cell and the ratio W2 / W1 of the peak width W2 and the half width W1 eventually become. Also tends to be smaller. It is considered that this is because the higher the cylinder temperature T1, the more uniform the degree of thermal expansion of the thermally expandable microspheres.

Further, as is clear from Examples 1 to 7 and Comparative Examples, the hardness of Type A in the durometer of the foamed molded article of Example was substantially the same as that of the molded article of Comparative Example.

The present invention can be used for a foam molded product made of a fluorine-based thermoplastic resin.

Claims (13)

A foam molded product having a matrix composed of a fluorine-based resin composition containing a fluorine-based thermoplastic resin as a main component and a plurality of bubbles existing in the matrix.
The fluorinated thermoplastic resin has a melting point of 165 to 200 ° C.
The bubbles are closed cells and
The size of the closed cell is 50 to 200 μm in terms of volume-based median diameter.
Foam molded product. The foamed molded product according to claim 1, further comprising a portion containing a first thermoplastic resin other than the fluoroplastic resin on the inner surface of the closed cells in the matrix. The foamed molded product according to claim 2, wherein the first thermoplastic resin contains a radical polymer of methacrylnitrile and an unsaturated carboxylic acid as a main component. The foamed molded product according to any one of claims 1 to 3, wherein the fluorine-based thermoplastic resin is polyvinylidene fluoride. The fluororesin composition contains a second thermoplastic resin and has a second thermoplastic resin.
The foamed molded product according to any one of claims 1 to 4, wherein the content of the second thermoplastic resin in the fluororesin composition is 0.1 to 0.6% by mass. The foamed molded product according to any one of claims 1 to 5, which has a specific gravity of 1.0 to 1.7. The foaming according to any one of claims 1 to 6, wherein the half width W1 of the peak representing the volume-based distribution in the size of the closed cell is 45 μm or less, and the peak width is 3.2 × W1 or less. Molded body. A method for producing a foam molded product having a matrix composed of a fluorine-based resin composition containing a fluorine-based thermoplastic resin as a main component and a plurality of bubbles existing in the matrix.
The step of mixing the fluororesin composition and the heat-expandable microspheres,
A step of molding the fluorine-based resin composition while expanding the heat-expandable microspheres by heating the fluorine-based resin composition mixed with the heat-expandable microspheres to the molding temperature of the fluorine-based resin composition. , Including
The fluorinated thermoplastic resin has a melting point of 165 to 200 ° C.
The content of the heat-expandable microspheres in the fluororesin composition is 0.05 to 2% by mass.
The expansion start temperature of the thermally expandable microspheres is 180 to 220 ° C.
The maximum displacement of the thermally expandable microspheres as measured by thermomechanical analysis is 1000 μm / mg or more.
The molding temperature is a temperature equal to or higher than the expansion start temperature.
A method for manufacturing a foam molded product. The heat-expandable microspheres include shell particles composed of a shell resin composition containing a first thermoplastic resin other than the fluorine-based thermoplastic resin, and a heat-expanding agent contained in the shell particles. The method for producing a foamed molded product according to claim 8. The first thermoplastic resin contains a radical polymer of methacrylnitrile and an unsaturated carboxylic acid as a main component, and the thermal expansion agent contains one or both of isooctane and an isomer thereof, according to claim 9. The method for producing a foamed molded product according to the description. The mixing step is
A step of preparing a first pellet containing a melt-kneaded product of a resin composition containing a second thermoplastic resin as a main component and the heat-expandable microspheres, and a step of preparing the first pellet.
A step of preparing a second pellet containing the fluorine-based thermoplastic resin as a main component, and
The step of mixing the first pellet and the second pellet,
The method for producing an effervescent molded product according to any one of claims 8 to 10. In the step of preparing the first pellet, the second thermoplastic resin is used in an amount of 40 to 70% by mass with respect to the heat-expandable microspheres.
The method for producing an foam molded product according to claim 11. The method for producing an effervescent molded product according to any one of claims 8 to 12, wherein polyvinylidene fluoride is used as the fluorine-based thermoplastic resin.

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