JPH06155604A - Resin foam and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide resin foam, which has an infinite number of fine bubbles and mechanical strength comparable to the mechanical strength of unformed material, and its manufacturing method. CONSTITUTION:After blowing agent is infiltrated in a resin formed body having resin region, in which the permeability of the gas blowing agent is low, and resin region, in which the permeability of the gas blowing agent is high, and, after that, the body is expanded by heating so as to produce resin foam having non-foamed region and foamed region, the ration Vuf/Vf of 0.1 or more, in which Vuf is the volume of the non-foamed region and Vf is the volume of the whole foam, and the average bubble diameter of 50mum or less.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a resin foam having high strength and excellent moldability, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, foamed materials such as polyethylene, polystyrene and polypropylene have been widely used for building materials, packaging materials and the like by taking advantage of their characteristics such as flexibility, light weight and heat insulation. However, these foams are insufficient in terms of mechanical strength, elastic recovery, heat resistance and the like.

Therefore, as foams having these properties improved, for example, foams obtained by adding a foaming agent to resin are molded at the same time or once and then foamed by heating. However, such a foam is composed of inhomogeneous cells, has a large cell diameter, and has a small cell density, so that the performance is still unsatisfactory for the intended use.

As a technique for solving these problems, as disclosed in US Pat. No. 4,473,665, plastics having very small uniformly distributed cells, that is, Microcellular.
A method for manufacturing Plastic Foam is known.
In this method, an inert gas is first pressurized and dissolved in a resin molded body that has been molded or is being molded in order to form nuclei of bubbles. At this time, a preformed molded body is introduced into a pressure vessel and pressurized with an inert gas, or a sheet obtained by extruding a resin into a molded body such as a sheet is introduced into a pressure vessel and is inert. Pressurize the gas to dissolve it. After that, the pressure is released, and the product is immersed in a high-temperature heat medium to heat and foam, and then cooled to obtain a desired foam.

With respect to the foam produced by such a method, the thickness of the non-foamed layer on the surface is several tens of μm, and the ratio of the thickness of the non-foamed layer to the total thickness of the foam is from several% to several tens. %. The mechanical strength per unit area is improved as compared with a conventional foam having an average cell diameter of several hundred to several thousand μm, but is 1/3 that of a resin sheet before foaming. It will be about 1/2.
In recent years, materials having contradictory properties such as strength and weight reduction have been demanded in response to lighter, thinner, shorter, and smaller products, and the foam produced by the above method can meet such demands. I can't.

Further, when a fine foam is produced by the above method, the gas diffusion coefficient and the gas solubility greatly contribute to the characteristics of the resin foam. For example, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polyethylene (PE), polypropylene (PP), etc. do not give a sufficient amount of permeation even if gas is permeated in a high-pressure container, and thus it is It was difficult to make.

Further, since the conventional fine foam is three-dimensionally foamed, it is inconvenient when dimensional stability in the plane direction is required in the secondary molding.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is a resin foam having an infinite number of fine bubbles and a mechanical strength comparable to that of an unfoamed body. It is an object to provide a body and a method for producing the body.

[0009]

The resin foam of the present invention has a non-foaming region and a foaming region, and has a volume (V _uf ) of the non-foaming region relative to the volume (V _f ) of the entire foam. Ratio V _uf
/ V _f is 0.1 or more and the average bubble diameter is 50 μm or less.

The method for producing a resin foam of the present invention comprises the steps of injecting a gas foaming agent into a resin molding having a resin region having a low gas-penetrating agent permeability and a resin region having a high gas-penetrating agent permeability. It is characterized by heating and foaming.

The unfoamed resin molding before foaming used in the method of the present invention is a resin region having a low gas-foaming agent permeability (hereinafter referred to as a low-permeability resin region) and a resin having a high gas-foaming agent permeability. And a region (hereinafter referred to as a high-penetration resin region). The resin constituting the low-penetration resin region and the high-penetration resin region, if the object of the present invention can be achieved,
The same resin or different resins may be used.

When the low-permeability resin region and the high-permeability resin region are made of the same type of resin, it is preferable to use a crystalline resin in order to have a different gas permeability. Examples of such a crystalline resin include polyethylene terephthalate (PET) and polybutylene terephthalate (PB).
T), saturated polyester resins such as polyethylene naphthalate (PEN); polyphenylene sulfide (PP)
S), special engineering plastics such as polyether ether ketone (PEEK); polyethylene (P
E), general-purpose resins such as polypropylene (PP); fluororesins, etc. are preferably used. Among these, polyethylene terephthalate (PET) and polyphenylene sulfide (PPS) are preferable because they have good heat resistance and impact resistance.

The resin used in the present invention may be added with a pigment or a reinforcing agent such as glass fiber or carbon fiber.

When the low-permeability resin region and the high-permeability resin region are made of different resins, PE, PP and PPS are used as the resin constituting the low-permeability resin region in order to have a different gas permeability. , PFA or the like is a crystalline resin such as PET, PB
Crystalline resins such as T and CTFE are preferable. Since an amorphous resin generally has good gas permeability, as the resin constituting the highly permeable resin region, in addition to the above, polycarbonate (PC) and polyphenylene ether (PP
E), polyether sulfone (PES), polysulfone (PSF), polyetherimide (PEI), polyamideimide (PAI) and the like can also be used.

The difference in crystallinity between the low permeability resin region and the high permeability resin region measured by DSC is preferably 10% or more, and more preferably 30% or more. When an amorphous resin is used as the high permeability resin region, the crystallinity of the low permeability resin region is preferably 10% or more, and more preferably 30% or more. This is because when the difference in crystallinity between the low-penetration resin region and the high-penetration resin region is less than 10%, the low-penetration resin region also foams and the non-foaming layer is reduced, and When inconvenience such as large bubble diameter occurs,
Foaming may be incomplete or may not stop,
In either case, the desired foam cannot be obtained.

The structure of the unfoamed resin molded product before foaming is not particularly limited, and may be, for example, any of the structures shown in FIGS.
FIG. 1 shows a three-layer structure in which two layers of low-permeability resin regions 1 are provided on both sides of a high-permeability resin region 2. Figure 2
Two layers of high permeability resin region 2 on both sides of low permeability resin region 1
To form a three-layer structure. FIG. 3 shows a sea-island structure in which high permeability resin regions 2 are dispersed in an island shape inside a low permeability resin region 1 in a sea shape. FIG. 4 shows an island-shaped low-penetration resin region 1 inside a sea-like high-penetration resin region 2.
It has a sea-island structure with dispersed. Such an unfoamed resin molding can be molded by various methods as described below.

For example, the following method is used to mold an unfoamed resin molding having the layered structure shown in FIG. (A) A resin having a high degree of crystallinity, which is a low-permeability resin region, is formed into a sheet by slowing the cooling rate at the die outlet to promote crystallization. On the other hand, the crystalline resin is rapidly cooled to form a resin having a low crystallinity, which becomes a highly permeable resin region, into a sheet shape, or an amorphous resin is formed into a sheet shape. The latter sheet is used as a central layer, the former sheet is laminated on both sides, and these three layers are integrated by adhesion or heat fusion to form the molded product. (B) After forming a sheet in which the crystallization nucleating agent is dispersed only on the surface by adding the crystallization nucleating agent near the exit of the die at the time of forming the sheet,
Only the surface is crystallized by crystallization treatment such as heat treatment to form a low-penetration resin region.

The following method is used to mold the unfoamed resin molding having the sea-island structure shown in FIG. That is, after sparsely dispersing a crystallization nucleating agent having a high crystallization rate inside the crystalline resin, and then subjecting it to a crystallization treatment such as heat treatment, an island portion having a high crystallinity is formed in a sea portion having a low crystallinity. Can be formed. Further, an unfoamed resin molded product having a sea-island structure can also be obtained by forming a polymer alloy using two or more polymers that are incompatible and have different gas permeability.

The following method is used for foaming the unfoamed resin molding having the above-mentioned structure.
First, a pre-formed unfoamed sheet is enclosed in a high-pressure container, gas that serves as bubble nuclei is injected into the container, and the gas is permeated into the unfoamed sheet. Regarding the osmotic pressure and time, for example, if the osmotic pressure is about 60 kg / cm ^2, it is 4
About 24 hours are preferable. Examples of the gas include nitrogen, oxygen, carbon dioxide gas, argon, hydrogen, methane, and fluorocarbon gas. Among these, carbon dioxide gas is preferable in consideration of the permeability to the unfoamed sheet before foaming and the crystallization promoting property. This unfoamed sheet is heated to foam, and cooled to obtain a foam.

With respect to the resin foam of the present invention produced as described above, the ratio V _uf / V _f of the volume (V _uf ) of the non-foamed region to the volume (V _f ) of the whole foam is 0.1. That is all. In particular, for a thin foam having a thickness of 1.0 mm or less, V _uf / V _f is preferably 0.3 or more. When V _uf / V _f is less than 0.1, the obtained foam has no great difference from the fine foam produced by the conventional method, and the effect of improving the mechanical strength does not appear due to the non-foamed layer.

In the method of the present invention, the effect of suppressing gas desorption during foaming may be obtained in some cases. Therefore, even when a resin, which has been conventionally difficult to produce a fine foam, is used, the fine foam can be easily obtained by the method of the present invention.

Further, when a layered molded article having a low-penetration resin region on the surface is used, a non-foamed layer is formed on the surface, so that the growth of bubbles is suppressed in the plane direction and the thickness direction is formed. A foam may be obtained in which only bubbles have grown.
Such a foam has an additional effect that secondary processing is facilitated and rigidity is increased.

As described above, when the method of the present invention of foaming the unfoamed resin molding having the low-penetration resin region and the high-penetration resin region is used, for example, the cell density is 1 × 1.
0 ¹¹ / cm ³ or more, an average cell diameter 50μm or less uniform, dense, and has fine bubbles, resin foam ratio foam total volume of the volume of the non-foam layer is 0.1 or more You can get the body. Such resin foam of the present invention, compared with the fine foam produced by the conventional method,
Very high mechanical strength.

[0024]

EXAMPLES Examples of the present invention will be described below.

In the following examples, the crystallinity of the resin was measured by using DSC200 manufactured by Seiko Denshi Kogyo Co., Ltd.

Example A sheet having a three-layer structure was formed by using a sheet of polyphenylene sulfide having a crystallinity of 15.3% as a central layer and a sheet of polyphenylene sulfide having a crystallinity of 41.3% as both surface layers. Place this sheet in a high-pressure container and press at pressure 62
The mixture was allowed to stand in a carbon dioxide gas of kg / cm ² for 8 hours to permeate the gas. After releasing the pressure, the sheet was allowed to stand in a hot air oven at 270 ° C. for 30 seconds to heat-foam to obtain a polyphenylene sulfide foam.

The cross section of each foam obtained was observed by SEM (scanning electron microscope) to determine the average cell diameter and the thickness of the non-foamed layer on the surface. From the thickness of the non-foamed layer and the thickness of the whole foam, the volume of the whole foam (V _uf ) of the volume of the non-foamed region (V _uf )
_The ratio V _uf / V _f to _f ) was determined. Moreover, the expansion ratio was determined. Further, a drop impact test was conducted to measure impact fracture energy (fall impact energy).

As a result, the average cell diameter was 14 μm and the thickness of the non-foamed layer was 220 μm. Further, V _uf / V _f was 0.12 and the expansion ratio was 3.4 times. Furthermore, the impact fracture energy was 7.5 J.

[0029]

Industrial Applicability As described in detail above, according to the present invention, it is possible to provide a resin foam which contains a very large number of extremely fine bubbles and which is particularly excellent in impact resistance. Extremely large.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of an unfoamed resin molded body used in the method of the present invention.

FIG. 2 is a cross-sectional view showing an example of an unfoamed resin molded body used in the method of the present invention.

FIG. 3 is a sectional view showing an example of an unfoamed resin molding used in the method of the present invention.

FIG. 4 is a cross-sectional view showing an example of an unfoamed resin molded body used in the method of the present invention.

[Explanation of symbols]

 1 ... Low permeability resin region, 2 ... High permeability resin region.

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[Procedure amendment]

[Submission date] February 2, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

The crystallinity of the resin is determined by the following formula based on the thermal analysis result measured using a differential scanning calorimeter. χ _c = {(ΔH _m −ΔH _c ) / ΔH ₀ } × 100 where χ _c : crystallinity [%] ΔH _m : heat quantity of crystal melting peak [J / g] ΔH _c : heat generation during crystal growth Peak [J / g] ΔH ₀ : Calorific _value of melting endothermic peak of 100% crystal [J /
g] (for example, 117.8 [J / g] for PET, P
In the case of PS, 146.2 [J / g]. The structure of the unfoamed resin molded product before foaming is not particularly limited and may be, for example, any of the structures shown in FIGS. 1 to 4. FIG. 1 shows a three-layer structure in which two layers of low-permeability resin regions 1 are provided on both sides of a high-permeability resin region 2. FIG. 2 shows a three-layer structure in which two layers of the high permeability resin region 2 are provided on both sides of the low permeability resin region 1. FIG. 3 shows a sea-island structure in which high permeability resin regions 2 are dispersed in an island shape inside a low permeability resin region 1 in a sea shape. FIG. 4 shows a sea-island structure in which the low-permeability resin regions 1 are dispersed like islands inside the sea-like high-permeability resin region 2. Such an unfoamed resin molding can be molded by various methods as described below.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Ono 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Naoki Yoshida 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (3)

[Claims] 1. A non-foamed region and a foamed region, wherein the ratio V _uf / V _f of the volume (V _uf ) of the non-foamed region to the volume (V _f ) of the entire foam is 0.1 or more, Average bubble diameter is 50
A resin foam characterized by having a size of not more than μm. 2. A resin molding having a resin region having a low gas-foaming agent permeability and a resin region having a high gas-foaming agent permeability is infiltrated and then heated to foam. And a method for producing a resin foam. 3. The difference in crystallinity measured by DSC is 10% or more between the resin region having low permeability of the gas blowing agent and the resin region having high permeability of the gas blowing agent. Item 3. A method for producing a resin foam according to item 2.