JPH07330940A - Thermoplastic resin foam and its preparation - Google Patents

Abstract

PURPOSE:To obtain a thermoplastic resin foam having minute cells of a polyhedral structure which have substantially cell walls but are still interconnected by subjecting a thermoplastic resin blended with fine resin particles of a specific particle size to multi-stage blowing. CONSTITUTION:This thermoplastic resin foam has a cell size of 1-20mum, a rate of cell wall oxistence of 80-100%, a rate of interconnected cells of 90-100%, and a density of 20-100kg/m<3>. A thermo-plastic resin blended with 0.05-5wt.% of fine resin particles having a particle size of 0.01-0.3mum is expanded by multi- stage blowing at a primary expansion ratio of 1.5-7. The thermoplastic resin is preferably a polycarbonate resin with its crystallinity controlled in the range of 0.1-5% carbon dioxide impregnation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic resin foam which is fine cells and the cells are open cells, and relates to a foam which is used as a filler for various filters, adsorbents and the like. It is a thing. In particular, the present invention relates to a foam having a feature that when used as a filler for a vacuum heat insulating material, the weight can be remarkably reduced as compared with a conventional inorganic filler.

[0002]

2. Description of the Related Art Conventionally, as a method for obtaining a resin foam (or a resin porous body) having continuous fine pores,
After the resin and solvent are uniformly dissolved and mixed, the system is phase-separated by cooling or reaction, and in that state, if necessary, the solvent is extracted and the solvent is extracted to obtain a porous body. A method for obtaining a body (Japanese Patent Laid-Open No. 63-17904, Japanese Patent Publication No. 4-50339, etc.), a thermoplastic resin is extruded together with inorganic fine particles and a plasticizer to obtain a sheet-like or fibrous material, and then the plasticizer. And inorganic fine particles are extracted to obtain a porous sheet, hollow fiber or the like (Japanese Patent Publication No. 58-32171).
Japanese Patent Publication No. 60-23130, etc.), and a method for obtaining a sponge-like porous material such as a reaction-curable polyurethane resin (Japanese Patent Publication No. 44-30753, JP-A No. 61-
51021, JP-A-4-63845, etc.),
A method of obtaining an open-cell foam by applying a so-called extrusion foaming technique in which an olefin resin or the like is melted in an extruder, a foaming agent is further injected, and then decompressed to foam.
No. 3-309535, Japanese Patent Laid-Open No. 4-170443, Japanese Patent Publication No. 5-23297, etc.) are known.
However, although the method of (1) can obtain uniform and fine continuous pores having a resin skeleton portion corresponding to the cell diameter of the foam of several μm or less, the pore shape has few portions corresponding to the cell wall, and the resin is simply porous. It is nothing more than a pillar of a body skeleton. Further, the resin portion is formed by phase separation from the solution and then deposited, and there is no contribution to the improvement of strength by stretching orientation and the like, and the strength of the low density porous body of this kind as a whole is weak, and therefore its application is It was limited. With the method described above, fine continuous holes are formed and the strength is strong, but it is difficult to obtain a thick sheet-like material or a low-density material. The method is a continuous pore having a shape similar to that of (1) and a small proportion of the portion corresponding to the bubble wall, and its pore diameter is at most about 60 to 70 μm even if it is small, and it is variously studied to reduce the pore diameter. However, it was technically difficult. Although the method can be produced continuously, even if the bubble size is small, at most 20
It was about 0 μm, and it was technically difficult to reduce the bubble diameter.

As described above, various methods have been studied. However, in the foams having open cells, in the prior art, the cell diameter, the cell shape and the foam density are each limited by the manufacturing method. It was Among them, the bubble diameter is 2
A low-density resin foam which has a fine cell structure of 0 μm or less and which is an open cell with the cell wall left substantially unachievable.

On the other hand, for the purpose of reducing the amount of use of the thermoplastic resin, a fine cell resin foam which realizes weight reduction within a range in which the strength is not reduced has been studied, and various attempts have been made to reduce the cell diameter of the foam. Has been done. For example, US Pat. No. 4,473,665 and Polymer Eng.
Sc. , 27, P485-492, ANTEC. '9
1. P1406 to 1410 and the like describe a method for producing a resin foam having fine cells, but for the purpose, all of them are closed cells and have a foaming ratio of 2 to 3 times (about 10 times at most). It is a foamed material, and its intended point is obviously different from the resin foam of the present invention, which is an open cell and has a low density (highly expanded foam).

[0005]

DISCLOSURE OF THE INVENTION The present invention has fine cells having a polyhedral structure, which is a basic cell shape of a so-called resin foam, which cannot be achieved by the prior art, and the cells are substantially the same. It is an object of the present invention to provide a low-density resin foam which has open cells and has walls.

[0006]

[Means for Solving the Problems]
In addition, with fine bubbles that have not been studied at all in the past, and
Fine open-cell resin foam with substantially a cell membrane
As a result of earnest research on the above, the present invention has been completed.
It was That is, the thermoplastic resin foam of the present invention has a cell diameter of
1 to 20 μm, bubble wall existence rate is 80 to 100%, continuous air
Foam rate 90-100%, density 20-100kg / m ³so
It is a thermoplastic resin foam characterized by being present.

The production method of the present invention has a particle size of 0.0
A thermoplastic resin foam, characterized in that a thermoplastic resin blended with 1 to 0.3 μm resin fine particles in an amount of 0.05 to 5% by weight is foamed in multistage expansion at a primary expansion ratio of 1.5 to 7 times. It is a manufacturing method. The contents will be described below. The foam of the present invention is a foam consisting of bubbles having substantially bubble walls, and a substance such as a gas or a liquid passes through a part of the bubble walls while having a so-called bubble wall of a polyhedral-shaped bubble. The foamed body is characterized by having voids typified by possible holes and tears so that cells are communicated.

In the present invention, the bubble and the bubble wall refer to the book "For the use of cell structure / porous material", respectively.
(LJ Gibson, MF Ashby, translated by Masahisa Otsuka, Uchida Lao Tsuruga Publishing Co., Ltd.) and corresponds to the definition of cells and cell faces. Specifically, a cell is a polyhedral small space having an edge and a face (face), and a cell face is a portion defined by a face (face) surrounding the cell.

The bubble diameter of the foam of the present invention must be in the range of 1 to 20 μm. Here, the bubble diameter of the foam is
In an electron micrograph with a magnification of about 100 to 1000 times,
It is a value obtained by observing the cross section of the foam and averaging it according to ASTM D-3576. Features as fine bubbles,
For example, when used as a filler for vacuum insulation, 10
-20μ in order to exert the performance at a decompression degree of ^-1 mmHg or more
It must be m or less. In addition, a cell having a cell diameter of less than 1 μm is limited because it is difficult to obtain a cell having a low density (it is difficult to foam at a high ratio). The bubble diameter is preferably 2 to 15 μm, more preferably 3 to 10 μm, and further preferably 4 to 8 μm.

The foam wall of the present invention has a cell wall existence ratio of 80 to 1
Must be in the range of 00%. The bubble wall existence rate of the foam is specifically determined by the following measuring method. First, from an enlarged photograph of an arbitrary cross section of the foam obtained by observation with a scanning electron microscope (observed at a magnification at which at least 100 cells are observed), the presence or absence of a defect in the cell wall and its shape are sufficient. At least 20 observable bubbles
Select more than one. Next, using an image analysis device or the like, the cross-sectional area of each of the selected bubbles is calculated, and then the total sum (this value is A) is calculated. Furthermore, for bubbles with a defect, the area of each defect (the area when the defect is projected perpendicularly to the cross section, as can be measured on the photograph) is
Similarly, after being obtained by an image analysis device or the like, the total sum (this value is B) is obtained. Here, as the bubble wall existence rate, a value (%) obtained by {1- (B / A)} × 100 is adopted. Here, if the bubble wall existence rate is 100%,
It is considered that microcracks, which have an area and are difficult to observe with a scanning electron microscope, are present in the cell walls and the cells are in communication with each other. In particular, a foam characterized by a structure having 80% or more cell walls of the present invention has a partially missing portion in the cell wall, but since the cell wall stretched during foaming is substantially present, The greatest feature is high compressive strength. Those having a cell wall existence rate of less than 80% are limited because the compressive strength of the foam tends to decrease. The bubble wall presence rate is preferably 90 to 100.
%, More preferably 95 to 100%, and further preferably 98 to 100%. It should be emphasized again here that the foam shape of the foam of the present invention is the characteristic structure of the polyurethane foam having open cells and the porous body formed by the phase separation method described above. What is the structure in which the solid resin part is aggregated like slender linear struts on the ridges of the polyhedron (cell edge: means the edge part that borders the cell face as defined in the above-mentioned reference book)? The point is that the bubble shapes differ greatly.

The open cell ratio of the foam of the present invention is 90 to 10.
It must be in the range of 0%. Features as open cells,
For example, when used as a filler for vacuum heat insulation, it is necessary to be 90 to 100% in order to shorten the vacuum depressurization time and prevent the reduction of the degree of depressurization due to the diffusion of air from the closed cell portion. This open cell rate is a value calculated from the independent cell rate obtained according to ASTM D-2856. However,
In the case of an unfoamed layer on the surface of the foam, that is, a foam in which a so-called skin layer is formed, the value in the actual use state after removing or partially destroying the skin layer is adopted. As a method of removing or destroying the skin layer, a method of mechanically slicing and removing the skin layer portion, a method of forming holes or grooves in the skin layer, and an additive to plasticize the skin layer to make it easier to break A method or a method of causing heat to concentrate and generate heat during foaming heating can be appropriately selected by an additive. The open cell ratio is preferably 95 to 100%, more preferably 97 to 100%, and further preferably 99 to 100%.

The foam density of the foam of the present invention is 20 to 1
It should be 00 kg / m ³ . Density is 20 kg / m
Those having a density of less than ³ are limited because the strength of the foam tends to be weak, and those having a density of more than 100 kg / m ³ are limited because the tendency of the degree of weight reduction becomes small. The foam density of the present invention is preferably 30 to 80 kg / m ³ , more preferably 35 to 70 kg / m ³ , and further preferably 4
It is in the range of 0 to 60 kg / m ³ . This foam density is
It is a value determined according to JIS K-6767.

As the thermoplastic resin used in the foam of the present invention, generally known polycarbonate resin, polymethacrylate resin, polystyrene resin, polyphenylene ether resin, polyarylate resin, polysulfone resin, polyether are known. Amorphous thermoplastic resins such as sulfone-based resins and polyetherimide-based resins, polyethylene terephthalate-based resins, polyphenylene sulfide-based resins, polyamide-based resins, polypropylene-based resins,
A crystalline thermoplastic resin such as a polyethylene resin or a polyoxymethylene resin may be appropriately used in combination with the optimum foaming agent. Preferably, the glass transition point of the thermoplastic resin from room temperature compressive strength retention is room temperature or higher,
A so-called hard thermoplastic resin is used. Among them,
In particular, the amorphous hard thermoplastic resin has a characteristic that it is easy to form fine bubbles. More preferred are polycarbonate resins, polymethacrylate resins, polystyrene resins, and polyphenylene ether resins. Particularly preferred are polycarbonate resins containing so-called bisphenol A in the main chain and polymethacrylate resins containing methyl methacrylate in the main chain.

These resins may be used alone, but may be used in a blended form in order to improve the resin melt viscosity in the heated state during foaming and the retention of the foaming agent. 1. Further, if necessary, known additives such as lubricants, heat stabilizers, and ultraviolet absorbers may be added and used within a range that does not significantly change the foamability. Next, the manufacturing method of the present invention will be described.

In order to produce the foam of the present invention, at the initial stage of foaming, there are a prescription for uniformly forming extremely fine cells as compared with a normal foam and a prescription for making the produced fine cells into continuous cells. The combination is important. As a prescription for uniformly generating fine bubbles, a resin is impregnated with a physical foaming agent under high pressure and then foamed.In so-called impregnated foaming, a thermoplastic resin placed in a high-pressure container has a gas phase state and a liquid state. Impregnate high-temperature carbon dioxide, nitrogen gas, oxygen gas, air, etc. in the phase state and supercritical state in consideration of temperature and time,
A method of heating to generate fine bubbles can be used. In extrusion foaming, a method of injecting high-pressure carbon dioxide gas, nitrogen gas, oxygen gas, air, or the like into the resin melted in the extruder and adjusting the resin viscosity at the die outlet to a higher level to open and foam the resin can be used. In addition, as a prescription for making the generated fine cells into continuous cells, in the impregnation foaming, the relationship between the foaming temperature and the foaming ratio, which is the foaming condition after impregnation, is investigated, and the expansion ratio of the resin
It is possible to adopt a method of promoting bubble breakage (open cell formation in the formation of a defect due to partial destruction of the bubble wall) by heating at a temperature at which it shows a mark. However, a particularly suitable method for obtaining the foam of the present invention is the production method of the present invention shown below. The contents will be described below.

The production method of the present invention has a particle size of 0.01 to
A method for producing a thermoplastic resin foam, which comprises foaming a thermoplastic resin obtained by blending resin particles of 0.3 μm in an amount of 0.05 to 5% by weight with a primary expansion ratio of 1.5 to 7 in multistage expansion. Is. First, a description will be given of a formulation for generating fine bubbles. Conventionally, it has been studied to add inorganic fine particles such as talc, silica and magnesium oxide by extrusion foaming and use them as a foam nucleating agent at the time of foaming (for example, J.
Appl. Polym. Sci. , 28, 1983)
However, the bubble diameter was at most about 200 μm at the smallest. For the purpose of further reducing the bubble diameter, reference (ANT
EC. '92. P1078-1081, ANTEC. '
93. P1828-1831) describes a fine cell resin foam using HIPS (high impact polystyrene resin). Generally, a resin obtained by blending polystyrene resin with butadiene rubber fine particles is known for the purpose of improving the impact resistance of polystyrene. Various studies have been conducted on the size of rubber fine particles and the blending amount thereof, but in order to improve impact resistance, the diameter of rubber fine particles is 1-2.
It has been preferred that the blend amount is about 5 μm and the blend amount is 10 to 30% by weight. In this document, it is estimated that in HIPS, microvoids are generated in rubber particles having an average diameter of 2 μm due to thermal stress generated due to the difference in thermal expansion coefficient between the polybutadiene resin portion and the polystyrene resin, and they are considered to be foam nuclei. Density and cell density (The cell density is the number of cells per unit volume of foam, measured from a cross-sectional micrograph of the foam, expressed in units of cells / cm ³ , and the smaller the cell diameter, the greater the expansion ratio. Is higher, the bubble density is higher) is 10 ⁸ to 10 ¹⁰ cells / cm ³
Of the polybutadiene fine particles having a diameter of 2 μm are effective as foam nuclei.
Since it is not clear that the particle size of 025 μm is too small to exert its effect, it is also described that there exists a critical particle size of the particle size that contributes effectively. However, although there is no description regarding the expansion ratio, it is estimated that the expansion ratio is lower than that of the present invention. In the present invention, a level higher than the bubble density described in this document (10 ¹⁰ to 1 in terms of bubble density)
(The range is 0 ¹³ cells / cm ³ ), and in order to increase the expansion ratio in order to make the density low, it is necessary to improve the retention of the foaming agent in the cells, The contradictory task of breaking and forming open cells must be achieved. It is not possible with a system in which the fine particle diameter of 2 μm described in the literature is blended. That is, if the fine particles present in the cell walls are too large, the cell walls will break before reaching the required expansion ratio, and if the particles are too small, they will not be effective foam nuclei or will cause microcracks in the cell walls. Without it, the degree of communication bubbles becomes low. However, the behavior of the fine particles on the bubble wall is the rate of deformation following the bubble wall due to the degree of plasticization of the fine particles by the foaming agent,
Alternatively, some difference may occur depending on the change rate of viscoelasticity at the foaming temperature. Based on such results of the implementation, in advancing the present invention, the conditions for enabling fine foaming were found in a region different from what was considered in the conventional impact resistance improvement regarding the rubber fine particle diameter and the blending amount thereof. It was It is considered that this effect is due to the fact that the interface between the resin and the fine particles serves as the foaming nuclei in the initial stage of foaming, and further that this interface contributes to the generation of microcracks in the bubble wall for finally forming open cells. Conceivable. Specifically, by blending resin fine particles having a particle diameter of 0.01 to 0.3 μm with the thermoplastic resin in an amount of 0.05 to 5% by weight, fine foaming becomes possible. The resin fine particles referred to here are spherical fine particles polymerized by a generally known emulsion polymerization, seed polymerization, dispersion polymerization, suspension polymerization method or the like, and in consideration of the fine particle dispersibility and the foaming agent dispersibility after impregnation. Fine particles having a core-shell type or a multilayer structure may be used. Preferably, multi-layered acrylic (polymethylmethacrylate) rubber fine particles, styrene-butadiene rubber fine particles, acrylonitrile-styrene-butadiene fine particles, silicon fine particles, polystyrene fine particles, polymethylmethacrylate fine particles and the like are used. If the particle size is too small, it cannot form foaming nuclei, and if it is too large, open cell formation occurs at an early stage, and the expansion ratio tends to be low, so that it is limited. The particle size is preferably 0.05 to 0.2 μm, more preferably 0.07 to 0.15 μm. As the particle diameter here, a value obtained by averaging from observations such as an electron microscope is adopted. Further, if the blending amount of the fine particles is too small, the number of foaming nuclei is small (the bubble diameter becomes large), and if it is too large, continuous foaming occurs at an early stage, and the expansion ratio tends to be low, so that it is limited. The blending amount is preferably 0.05 to 1% by weight, more preferably 0.07 to
It is 0.5% by weight. A publicly known compatibilizer and the like may be used in combination, if necessary to improve dispersibility and adhesiveness at the interface.

In addition, in this formulation, a resin which is originally crystalline, such as a polycarbonate resin or a polyethylene terephthalate resin, but which can be in an amorphous state by quenching during processing, etc., will have fine crystals at the time of foaming. By forming it, very fine bubbles can be formed.
For example, heat treatment or solvent treatment before impregnation of the foaming agent and / or treatment capable of forming fine crystals at the time of impregnation of the foaming agent having a plasticizing ability such as carbon dioxide are appropriately selected. In particular,
The polycarbonate resin is immersed in an aliphatic hydrocarbon mixed solvent containing about 15% by volume of acetone for solvent treatment, then impregnated with carbon dioxide gas, and foamed to form a foam having very fine bubbles. This is in addition to solvent treatment
By impregnating with carbon dioxide gas, fine crystals (DSC: crystallinity of less than 5% at a temperature rise condition of 10 ° C./min is preferably less than 5%) are uniformly generated in the polycarbonate resin, which become foam nuclei and the number of bubble nuclei is increased. It is considered that the effect is due to the significant increase. In addition, the crystallinity is preferably adjusted to 0.1% or more from the viewpoint of exerting the effect of generating fine crystals that can serve as foam nuclei.

Next, a formulation for forming the generated fine bubbles into continuous cells will be described. In the production method of the present invention, as a method of foaming the resin prepared as described above, the resin is impregnated with a physical foaming agent under high pressure, so-called impregnation foaming and the foaming agent is uniformly pressed into the molten resin in the extruder. After mixing, the pressure can be released to cause foaming, so-called extrusion foaming, etc. can be appropriately selected, but in both cases, foaming and breakage (in the formation of a defect due to partial destruction of the bubble wall during normal one-step foaming) When the physical properties of the foam of the present invention cannot be satisfied at the same time by continuous foaming), it is very effective to carry out multi-stage foaming by impregnating the obtained foam again with a physical foaming agent and foaming again. In the first stage of foaming, the foaming ratio was suppressed to 1.5 to 7 times for the purpose of forming a large number of foam nuclei, and further, in the second and subsequent stages of foaming, a foam formed by primary foaming was formed. By increasing the bubble pressure inside the bubbles,
This is a formulation aimed at increasing the expansion ratio and breaking the foam. It goes without saying that a multi-stage foaming method of three or more stages in which impregnation and foaming are further carried out can be adopted if necessary. If the primary expansion ratio is less than 1.5 times, the bubbles tend to be non-uniformly generated, and if it exceeds 7 times, the bubble diameter increases due to coalescence of the bubbles at that stage, and the high expansion ratio due to the bubble breakage. Limited because it tends to be difficult to convert. The primary expansion ratio is preferably 2 to 6 times, more preferably 2.5 to 5 times. The impregnated amount of the physical foaming agent used in the primary impregnation can be appropriately selected within the range of 6 to 40 parts by weight in consideration of the foam density, that is, the expansion ratio. It is preferably 8 to 30 parts by weight, more preferably 10 to 24 parts by weight.

As the physical foaming agent used in the present invention, solvent-based foaming agents, organic and inorganic gas-foaming agents used for generally known foams can be appropriately selected. Specifically, normal butane, isobutane, normal pentane, cyclopentane, aliphatic hydrocarbons such as normal hexane, benzene,
Aromatic hydrocarbons such as toluene and xylene, ketone hydrocarbons such as acetone and methyl ethyl ketone, methanol,
Alcohol hydrocarbons such as ethanol, dihydrodifluoromethane, pentafluoroethane, 1,1,2,2-tetrafluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,1-trifluoroethane, 1 , 1-difluoroethane, 1,2-difluoroethane, and other fluorine-containing hydrocarbons, carbon dioxide, and inorganic gases such as nitrogen and oxygen. Carbon dioxide is particularly preferable in order to increase the number of cell nuclei per unit volume of the foam as much as possible, that is, to reduce the cell diameter at a constant expansion ratio. Also,
For the purpose of increasing the number of cell nuclei at the time of foaming, carbon dioxide may be used together with or additionally impregnated with another physical foaming agent. The impregnation amount of the foaming agent can be appropriately selected depending on the physical foaming agent used,
Usually 3 to 25 parts by weight are used. Preferably 5-20
Parts by weight, more preferably 7 to 15 parts by weight.

The physical foaming agent to be re-impregnated into the secondary and subsequent foams will be described later in consideration of the primary expansion ratio, the degree of plasticization due to the impregnation, the secondary and subsequent expansion temperatures, the expansion ratio, and the open cell formation rate. It can be appropriately selected from the physical foaming agents. During the secondary and subsequent foaming, it is necessary to foam while breaking the cell walls of the closed cells formed by foaming in the previous stage, so it is necessary to raise the gas pressure in the bubbles, and the foaming agent The impregnated amount can be appropriately selected within the range of 6 to 40 parts by weight in consideration of the foam density, that is, the expansion ratio.
Preferably 8 to 30 parts by weight, more preferably 10 to 24
Parts by weight.

The physical foaming agent which can be used in the present invention is introduced by a known method, for example, into a high-pressure container such as an autoclave containing beads, powders, pellets or sheet-like material of a thermoplastic resin, and under high pressure conditions. Impregnated. The impregnation condition and the impregnation amount can be appropriately selected in consideration of the required expansion ratio and expansion temperature. In the case of extrusion foaming, the impregnated state can be selected by a method of dispersing and mixing a physical foaming agent in a molten resin. When foaming a thermoplastic resin bead-like product that can be produced by suspension polymerization, a foaming bead can be obtained by adding a physical foaming agent in the latter half of the suspension polymerization.

As the heating means at the time of foaming, hot air heating, heating oil heating, far infrared heating, steam heating, etc., which are known methods including primary foaming and subsequent multi-stage foaming, are appropriately selected. In particular, a resin having a relatively high water vapor permeability such as a styrene resin or a polycarbonate resin can effectively utilize its characteristics to obtain a high-expanded foam when steam-heated.

The foam of the present invention is characterized in that a particle-shaped foam typified by a styrene-based bead foam or a sheet-shaped foam can be obtained by a simple process. Is.

[0024]

EXAMPLES The present invention will be described in detail below with reference to examples.

[0025]

Example 1 Pellets of polycarbonate resin (weight average molecular weight 56,000) produced from diphenyl carbonate and 2,2-bis (4-hydroxyphenyl) propane by the method described in JP-A-3-68627. Was melt-extruded at a cylinder temperature of 320 ° C. using an extruder to prepare a sheet having a thickness of 1 mm.

A sample of 20 × 30 mm was cut out from this sheet, placed in a small autoclave, and liquefied carbon dioxide gas was injected under pressure at 5 ° C. to 40 kg / cm ² and left for 24 hours. Then, the pressure was released and the weight of the sample was measured. As a result, 13.5 parts by weight of the sample was impregnated with carbon dioxide gas. This impregnated sample is heated to a temperature of 15
When it was immersed in an oil bath at 0 ° C. for 30 seconds and heated for primary foaming, a foam having a magnification of 4.8 was obtained.

The primary foamed product was again placed in the small autoclave, carbon dioxide gas was similarly injected up to 60 kg / cm ^2, and the mixture was left at 23 ° C. for 24 hours. Then, the pressure was released, and the sample was left at 23 ° C. until it was impregnated with 15 parts by weight of carbon dioxide gas based on the weight of the sample. When this impregnated sample was immersed in an oil bath at a temperature of 190 ° C. for 15 seconds and heated for secondary foaming, a foam having a density of 57 kg / m ³ and a cell diameter of 7 μm was obtained.

The cell wall existence rate was 98%, which was obtained by using an electron micrograph of a cross section of this foam with a magnification of 1000 times using an image processing analyzer (SPICCA-II manufactured by Nippon Avionics Co., Ltd.). The open cell ratio (measured by dividing the sample into four parts to remove the influence of the skin layer) was 99%. Therefore, it was found that, although most of the bubbles are continuous bubbles, they have substantially bubble walls.

[0029]

Examples 2 to 5 Examples 2 to 4 are the same resin as Example 1, and Example 5 is a polycarbonate resin having a weight average molecular weight of 30,000 (Panlite K-130 manufactured by Teijin Chemicals Ltd.).
0) was used in the same manner as in Example 1 to produce a foam under the conditions shown in Table 1. Table 1 shows the physical properties of the obtained foam.

[0030]

Example 6 Polymethylmethacrylate resin (Delpet 980N manufactured by Asahi Kasei Kogyo Co., Ltd.) and acrylic fine particles (Acrylic rubber SRS manufactured by Asahi Kasei Kogyo Co., Ltd .: particle size 0.
1 μm) was dry blended at a ratio of 0.1% by weight, then extruded at 250 ° C. with a meshing type co-directional twin-screw extruder, and then water-cooled and dried to obtain melt-blended pellets. This blended pellet was press-molded to obtain a sheet having a thickness of 1 mm. A sample of 20 × 30 mm is cut out from this sheet and placed in a small autoclave.
34a (1,1,1,2-tetrafluoroethane) 8
When impregnated at 0 ° C. for 60 hours, the impregnation amount was 25 parts by weight. This impregnated sample was immersed in a silicone oil bath at 150 ° C. for 30 seconds for foaming to obtain a primary foamed product with a foaming ratio of 6.5 times. When this sample was put into the autoclave again and impregnated with HFC134a in a gas phase state at 30 ° C. for 48 hours, the impregnation amount was 35 parts by weight. This impregnated sample was immersed in a silicone oil bath at 150 ° C. for 30 seconds to obtain a secondary foam. Cell diameter of this foam is 3μ
m, the cell wall existence rate was 95%, the open cell rate was 95%, and the density was 70 kg / m ³ .

[0031]

Example 7 30 × 20 mm from the same sheet as in Example 1
Sample was cut out, and acetone: n-pentane = 20:
Immerse in a mixed solution of 80 (volume ratio) for 24 hours at room temperature, and
A solvent-treated sheet containing 0 part by weight of a mixed solvent was obtained. Put this sheet into a small autoclave and add 40 kg of carbon dioxide.
/ Cm ² was press-fitted and left at 5 ° C for 24 hours. Then, the pressure was released and the weight of the sample was measured. As a result, 20 parts by weight of the sample was impregnated with carbon dioxide gas and a solvent. The crystallinity of a part of this impregnated sample was measured by DSC, and although it was 3% or less, some crystallization was observed, which was not observed in the sheet before impregnation.

This impregnated sample was immersed in an oil bath at a temperature of 150 ° C. for 30 seconds and heated for primary foaming, and a foam having a foaming ratio of 3.0 times was obtained. The primary foamed product was again placed in the small autoclave, carbon dioxide gas was similarly injected up to 40 kg / cm ^2, and the mixture was left at room temperature for 24 hours. Thereafter, the pressure was released and aging was carried out at room temperature, so that 13 parts by weight of carbon dioxide gas was impregnated with respect to the weight of the sample.

This impregnated sample was immersed in an oil bath at a temperature of 190 ° C. for 15 seconds to be heated for secondary foaming. The cell diameter was 5 μm, the cell wall existence rate was 99%, and the open cell rate was 90%. A foam having a density of 50 kg / m ³ was obtained. It is considered that, as compared with Example 1, the foamed nuclei increased in the foamed body due to the solvent treatment, and the cell diameter became smaller.

[0034]

COMPARATIVE EXAMPLE 1 A primary impregnated sample obtained using the same resin as in Example 1 under the same conditions as in Example 1 was immersed in an oil bath at a temperature of 190 ° C. for 30 seconds and heated to obtain a foam. The obtained foam had a cell diameter of 9 μm and a cell wall presence rate of 99.
%, The density was 45 kg / m ³ , but the open cell ratio was 5
The value was 7%, which was lower than that of the example.

[0035]

Comparative Example 2 The same polycarbonate resin as in Example 5 was used.
0 parts by weight of a mixed solvent of dioxane / cyclohexane (7
90 parts by weight (0: 30% by volume) was placed in a metal cylindrical container having a diameter of 50 cm to a depth of about 1 cm, and heated at 60 ° C. on an oil bath to uniformly dissolve the same. This container was rapidly immersed in a dry ice bath and rapidly cooled to below the solidification temperature to obtain a resin porous intermediate. The solvent was removed from the intermediate using a freeze dryer while maintaining the porous structure to obtain a resin porous body. The cell diameter of this resin porous body (the diameter of the portion corresponding to the cell diameter in the foam) was 5 μm, the cell wall existence rate was 0%, the open cell rate was 100%, and the density was 11%.
It was 5 kg / m ³ . As can be seen from the cell wall existence rate, this resin porous body had substantially no cell walls, and its compressive strength was significantly lower than that of the foam of the present invention.

[0036]

[Table 1]

[0037]

INDUSTRIAL APPLICABILITY The thermoplastic resin foam of the present invention is a low-density foam in which continuous fine cells are uniformly formed, and since the cells have substantially cell walls, they are excellent in strength. There is.

Claims (3)

[Claims] 1. A thermoplastic resin foaming having a cell diameter of 1 to 20 μm, a cell wall existence rate of 80 to 100%, an open cell rate of 90 to 100%, and a density of 20 to 100 kg / m ^3. body. 2. A thermoplastic resin obtained by blending 0.05 to 5% by weight of resin fine particles having a particle diameter of 0.01 to 0.3 μm by multistage foaming at a primary expansion ratio of 1.5 to 7 times. A method for producing a thermoplastic resin foam, comprising: 3. A thermoplastic resin foam according to claim 2, wherein the thermoplastic resin is a polycarbonate resin whose crystallinity is adjusted to 0.1 to 5% by impregnation with carbon dioxide. Manufacturing method.