JP2009126881A - Open cell foam and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an open cell foam having fine open cells and exhibiting appropriate flexibility in a simple process, and to provide an open cell foam. <P>SOLUTION: The method for manufacturing an open cell foam comprises incorporating (B) a nonionic surfactant into (A) a polymer composition containing (A1) polyolefin and (A2) ethylene-propylene rubber and/or a polystyrene thermoplastic elastomer, then impregnating the composition with a substance, which is gaseous at normal temperature and normal pressure, in a supercritical state, then releasing the pressure to obtain 10 or more times of an expansion ratio. The present invention discloses an open cell foam obtained by the above method. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing an open-cell foam, and more particularly to a method for producing an open-cell foam by a step of releasing a pressure after impregnating a substance that is gaseous at normal temperature and normal pressure in a supercritical state. . Moreover, this invention relates to the open-cell foam obtained by such a manufacturing method.

  Open-cell foams are used in various directions such as breathable clothing, fine filters, virus separation membranes, artificial lungs, liquid supply materials, and sound absorbing materials.

  As a method for producing an open-cell foam, after producing a closed-cell foam such as the method of Patent Document 1, as a second step, it is broken by mechanical stress by a method such as passing between a pair of rotating rolls. There is a method of foaming into an open cell foam.

Also, as a method for obtaining an open cell foam of an olefin resin, a method using a silicone compound (Patent Documents 2 and 3), a method of mixing a foaming agent having a strong nucleation ability and a foaming agent having a weak nucleation ability (Patent Documents) 4) and the like, and in the case of a styrene resin, there is a method of adding an anionic or cationic surfactant (Patent Document 5).
JP 2006-1096 A JP 60-49657 A JP 62-223243 A JP 2002-194128 A JP 2004-352927 A JP 2000-263621 A

However, there are various problems in the above-described conventional manufacturing method.
That is, in the method of breaking bubbles by mechanical stress as in Patent Document 1, equipment for a process of forming continuous bubbles by applying mechanical stress and a space for housing it are required. In addition, although this method can communicate large closed cells having a diameter of several hundreds of μm or more, it is difficult to communicate bubbles having fine cell diameters.
The methods of Patent Documents 2 and 3 not only have a large bubble diameter, but also use a chemical foaming agent and a foam stabilizer, and use a silicone compound.
With respect to the problem that the diameter of the bubbles is large, the method of Patent Document 4 is a general gas foaming method, but a fine open-cell body is obtained by mixing chlorofluorocarbon gas. However, it is difficult to implement the foaming method using Freon gas due to Freon regulations.
In a method for producing a polyolefin-based foam using a supercritical gas, although a foam having a clean and small bubble diameter is obtained, it is generally a closed cell. There is Patent Document 6 as an example in which slightly open cells can be obtained. However, the foam obtained by this method contains a large amount of a filler, and the foaming ratio is as hard as 10 times or less.
As described above, the gas foaming method by the supercritical method is a very excellent method for obtaining fine closed cells, but there has been no example of obtaining a sufficiently foamed open cell body.

  The subject of this invention is providing the method of manufacturing the fine open-cell foam which has moderate softness | flexibility by a simple process. Another object of the present invention is to provide an open cell foam obtained by such a method.

  The present inventors use a polyolefin-based polymer composition containing polyolefin and ethylene-propylene rubber and / or polystyrene-based thermoplastic elastomer as a polymer to be foamed, and a substance that is a gas at normal temperature and pressure is in a supercritical state. It was found that a fine open-celled foam can be produced by impregnating with, and then foaming by releasing pressure and in the presence of a nonionic surfactant. It came to complete.

That is, the present invention
(A) (A1) Polyolefin (excluding ethylene-propylene rubber) 50 to 95% by weight of (A); and (A2) 5 to 50 of ethylene-propylene rubber and / or polystyrene-based thermoplastic elastomer (A) weight%
(B) 0.2 to 10 parts by weight of a nonionic surfactant per 100 parts by weight of the polymer composition, and a substance that is a gas at normal temperature and pressure is in a supercritical state. The present invention relates to a method for producing an open-cell foam, characterized in that the pressure is released after impregnation with a foaming ratio of 10 times or more, and also relates to an open-cell foam obtained by such a production method. .

  According to the present invention, the foaming agent itself and its decomposition products remain in the system, do not use a foaming agent that affects the working environment, and do not require a process of breaking bubbles by mechanical stress. According to the process, an open-cell foam can be produced from the polyolefin polymer composition. This is because, during foaming, due to the action of the component (B) dispersed in the component (A), the wall surface of the closed cells to be formed becomes uneven and partially thinned. This is because the cells are solidified by being cooled in a state where the cell walls are torn, and an open-cell foam is formed.

  Moreover, the open-cell foam obtained by this invention is flexible also in the state which received high compression, and can improve the adhesiveness of members. Furthermore, since the foam is non-crosslinked, the foam can be recycled.

  (A) component used by this invention is (A1) polyolefin (however, except ethylene-propylene rubber) 50 to 95 weight%, Preferably it is 60 to 90 weight%, More preferably, it is 65 to 85 weight%, and ( A2) A polymer composition containing 5 to 50% by weight of ethylene-propylene rubber and / or polystyrene-based thermoplastic elastomer, preferably 10 to 40% by weight, and more preferably 15 to 35% by weight. When the proportion of (A1) exceeds 95% by weight and the proportion of (A2) is less than 5% by weight, there is a problem that the foam cannot obtain sufficient flexibility and it is difficult to obtain a high foam. On the other hand, when the proportion of (A1) is less than 50% by weight and the proportion of (A2) is more than 50% by weight, it is difficult to obtain a high foam, and the shrinkage of the resulting foam increases.

  Examples of (A1) polyolefin include polyethylene, polypropylene, polybutene-1, ethylene-propylene copolymer, ethylene-α-olefin copolymer, and polymer blends of these. The polyethylene may be any of high density polyethylene, medium density polyethylene, linear low density polyethylene, low density polyethylene, and the like, and polypropylene may be any of atactic, isotactic, syndiotactic, random, and the like. Also, polypropylene having a high extensional viscosity such as polypropylene having a long chain branch in the main chain skeleton (HMS-PP) suitable for foaming and polypropylene having a high molecular weight component and a wide molecular weight distribution may be used. The copolymer may be a random copolymer or a block copolymer, and may be a thermoplastic resin or a thermoplastic elastomer. Among these, random polypropylene is preferable because heat resistance can be imparted to the obtained foam and flexibility of the obtained foam can be maintained. Since there is no outgassing and foaming is easy, the melt flow rate of the component (A1) is preferably 0.1 to 5 g / 10 min, more preferably 0.3 to 2 g / 10 min at 230 ° C. and 2.1 kgf. The ethylene-propylene copolymer includes an ethylene-propylene copolymer (EPR) that is cured to become a rubber-like elastic body, but is excluded from (A1) because it is included in the component (A2). (A1) includes a resinous ethylene-propylene copolymer. In addition, other thermoplastic polymers may be present as long as the properties of the open-cell foam produced in the present invention are not impaired.

  The ethylene-propylene rubber (A2) is a copolymer of ethylene, propylene and a small amount of a non-conjugated diene; Certain EPDMs are included. Examples of non-conjugated dienes include ethylidene norbornene, dicyclopentadiene and 1,4-hexadiene, and any of them may be used in the present invention.

  The polystyrene-based thermoplastic elastomer (A2) may be a block copolymer in which polystyrene is bonded to one or both ends of a polymer comprising a hydrocarbon chain. For example, a block copolymer of styrene and butadiene, isoprene, isobutylene or the like. Or a styrene butadiene styrene block copolymer (SBS), a styrene ethylene butylene styrene block copolymer (SEBS) hydrogenated with SBS, or a styrene isoprene styrene block copolymer (SIS). ), And styrene ethylene propylene styrene block copolymer (SEPS) hydrogenated SIS, styrene isoprene butadiene isoprene styrene block copolymer And hydrogenated styrene ethylene ethylene propylene styrene block copolymer (SEEPS), styrene vinyl isoprene styrene block copolymer, and hydrogenated product thereof, styrene isobutylene styrene block copolymer, styrene butadiene block copolymer, and hydrogenated product thereof, styrene Examples thereof include isobutylene block copolymers and hydrogenated products thereof, and these may be used alone or in combination.

  About the said (A2) component, the one where the average molecular weight is higher is preferable. Further, the oil may be extended with process oil or the like. The component (A2) is used as it is without performing a crosslinking reaction.

(B) Nonionic surfactants include alkyl polyethers such as polyoxyethylene (polyoxypropylene) alkyl ether, fatty acid polyether esters such as polyoxyethylene (polyoxypropylene) fatty acid ester, and dipolyoxyethylene. Alkylpolyamine amines such as (dipolyoxypropylene) alkylamines such as di (dioxyethylene) stearylamine, polyoxyethylene (polyoxypropylene) dialkylamine, polyoxyethylene (polyoxypropylene) alkylalkylenediamine, Sorbitan esters such as polyoxyethylene (polyoxypropylene) sorbitan ester and sorbitan alkyl ester, polyoxyethylene (polyoxypropylene) alkyl glycerin Ethers, fatty acid (poly) glyceryls, alkyl glyceryl polyethers or esters such as monoglyceryl stearate, polyoxyethylene (polyoxypropylene) fatty acid glyceryl, alkanolamides such as fatty acid (di) ethanolamide, A mixture etc. are mentioned. The number of carbon atoms of the alkyl, fatty acid, and alkylene is preferably 10 or more from the viewpoint of compatibility with the polyolefin polymer composition. For example, C12 (such as lauryl or laurylate), C18 (such as stearyl or stearate). , C22 (such as behenyl or behenylate) and the like. Further, the number of repeating units of oxyalkyl such as polyoxyethylene and polyoxypropylene is preferably 1 to 20, and more preferably 10 or less. The number of repeating units of polyglyceryl is also preferably 1 to 20, and more preferably 10 or less.
Furthermore, one or a mixture selected from alkyl polyetheramine, fatty acid glyceryl and fatty acid (di) ethanolamide can be preferably used, and higher alcohols such as stearyl alcohol may be added.
On the other hand, anionic surfactants and cationic surfactants may not be open-celled, have poor degradability, have high toxicity such as protein denaturation and skin damage, and cause problems with human and environmental pollution. There is.

  The blending amount of the component (B) is required to be 0.2 to 10 parts by weight per 100 parts by weight of the polymer composition (A), preferably 0.3 to 5 parts by weight, more preferably 0.5 to 3 parts by weight. Part. When the component (B) is less than 0.2 parts by weight, necessary open cell formation cannot be obtained, and only a foam having low air permeability can be obtained. On the other hand, when the amount exceeds 10 parts by weight, the bubble breakage proceeds too much and the foam shrinks.

  In the present invention, the foamable composition is prepared by mixing the components (A1), (A2), (B), and optionally blended optionally by mixing means suitable for mixing the polymer materials. . At this time, as a component to be arbitrarily blended, in order to give suitable properties to the obtained foam or to facilitate the production and processing of the foam, the foamable composition may be liquid paraffin according to the purpose of use. Lubricants such as hydrocarbon process oils, higher fatty acid glycerin esters, higher fatty acid amides; phosphate esters, melamine phosphate or piperazine phosphate, aluminum hydroxide, magnesium hydroxide, antimony oxide, zinc carbonate, chlorinated paraffin, Flame retardants such as hexachlorocyclopentadiene; anti-aging agents such as aromatic amines, benzimidazoles, dithiocarbamates, phenolic compounds, phosphites; 2,6-di-t-butylphenol, 2,6 -Di-t-butyl-4-ethylphenol, 4,4'-butylidenebis (3-methyl Antioxidants such as (Ru-6-tert-butylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane; conductive carbon black, copper powder, nickel powder Conductive materials such as tin oxide; carbon black, organic pigments, dyes, colorants such as masterbatches containing them; and silica, alumina, titanium oxide, and the above-mentioned various additives as fillers Fillers such as those can be blended.

  As the substance that is impregnated in the supercritical state in the foamable composition and is a gas at normal temperature and pressure, any substance that penetrates the polymer in the foamable composition in this supercritical state may be used, such as nitrogen, helium, Carbon dioxide, propane, butane, and the like, and mixed gas thereof are exemplified, and carbon dioxide and nitrogen are preferred, and carbon dioxide is particularly preferred because of easy handling, high safety, and excellent working environment.

  The temperature at which the foaming composition is impregnated with a substance that is gaseous at normal temperature and normal pressure is a temperature at which the substance is brought into a supercritical state since a functional foam can be obtained efficiently. A differential scanning calorimeter It is particularly preferable that the temperature is 20 to 40 ° C. higher than the crystallization peak temperature of the polymer in the foamable composition obtained by the measurement according to 1.

  Further, the impregnation pressure is preferably 8 to 15 MPa so that the impregnation is completely performed and the impregnated material which is a gas at normal temperature and normal pressure is brought into a supercritical state. In order to make it difficult for gas to escape, 10 to 15 MPa is more preferable.

  The time for impregnating the foamable composition with a substance that is gaseous at normal temperature and normal pressure varies depending on the required impregnation amount and impregnation temperature and pressure, but is usually 3 to 30 minutes, preferably 5 to 20 minutes.

  In the present invention, after impregnating the polymer in the foamable composition with a substance that is gaseous at normal temperature and normal pressure under the above conditions, foaming is performed so that open cells are formed by releasing the pressure. By reducing the pressure at a decreasing rate of usually 0.3 to 3.0 MPa / s, preferably 0.5 to 2.0 MPa / s, foaming can be performed so as to form open cells.

  In the present invention, when the foamable composition is foamed so as to be open cells, the foaming ratio needs to be 10 times or more. If it is less than 10 times, there arises a problem that excellent flexibility cannot be imparted to the obtained foam. In order to make the foam of the present invention more flexible, a foaming ratio of 12 times or more, particularly 15 times or more is preferable. The upper limit of the expansion ratio is not particularly limited, but is 100 times or less, preferably 80 times or less, more preferably 50 times or less from the viewpoint of mechanical strength.

  Together with foaming that achieves a foaming ratio of 10 times or more, molding can be performed by a method such as extrusion molding to obtain an open-cell foamed molded product. As the extruder, a single-screw tandem extruder may be used, and in some cases, it may be used in combination with a twin-screw extruder.

  In the production method of the present invention, as a post-process, it can be processed into a predetermined size by cutting, removing the skin layer, and the like. Since the open cell foam is directly obtained in the foaming step, there is no need for a step of breaking the closed cells into bubbles by mechanical stress.

  According to the present invention, there is a microcell having a foaming ratio of 10 times or more and an average cell diameter of bubbles of 200 μm or less, and an open cell average pore diameter of 10 μm or less, which is highly foamed and subjected to a compressive load. An open-cell foam excellent in the above can be obtained. As the flexibility, the flexibility at 50% compression load is preferably 0.02 MPa or less, more preferably 0.015 MPa or less. If the flexibility exceeds 0.02 MPa, the followability to the concavo-convex portion tends to be poor, and it tends to be hard. In the present invention, an open-cell foam having a flexibility of 0.02 MPa or less is obtained, which is useful for a fine filter and a low-hardness sealing material.

  Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited by these examples.

In the examples and comparative examples, the following polymers were used. In addition, a part represents a weight part.
PP: random type polypropylene, PE: low density polyethylene, EPDM: EPDM (ethylene unit 29.5 mol%, propylene unit 66.0 mol%, ethylidene norbornene unit 4.5 mol%), SEBS: styrene butadiene triblock polymer Hydrogenated product (styrene ratio 20%, number average molecular weight about 100,000), nucleating agent: fumed silica, stabilizer: tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionic acid] Pentaerythritol, surfactant A: oleic acid diethanolamide, surfactant B: glyceryl monostearate, surfactant C: di (dioxyethylene) stearylamine, surfactant D: sodium dodecylbenzenesulfonate

The properties of the foams obtained in the examples and comparative examples were evaluated by the following methods.
(1) Apparent specific gravity: The apparent specific gravity of the foam was measured using an electronic hydrometer MD-200S (trade name of Mirage Trading Co., Ltd.) according to JIS K7112. The expansion ratio was calculated from the specific gravity of the unfoamed composition.
(2) Average cell diameter: Using a scanning electron microscope JXA-6100P (trade name of JEOL Ltd.), the short diameter and long diameter of all cells observed in the field of view were measured and averaged.
(3) Pore size distribution: Using a Perm-Polometer (Porous Material Inc. trade name) based on JIS K3832, the maximum pore size, the pore size distribution and the minimum pore size were measured, and the average pore size was calculated.
(4) Breathability: Breathability was measured according to JIS L1004 using a Frazier type breathability tester. That is, an appropriate orifice was installed on the table, the test piece was fixed and air was allowed to flow, the water level of the manometer at that time was read, and the flow rate was calculated from the flow rate conversion table.
(5) Flexibility: Using Autograph AGS-5KNB (trade name, Shimadzu Corporation), obtain the strain-stress curve when collapsed to 50% of the original thickness, and calculate the flexibility from it. did.

Example 1
A polymer composition was prepared by mixing with a mixer so as to be homogeneous so that the blending ratio shown in Table 1 was obtained. In a single-screw tandem type extruder, while heating at a resin temperature of 185 ° C., carbon dioxide was injected and dissolved at a pressure of 10 MPa, and after 10 minutes, the pressure was reduced at a rate of 1.5 MPa / s. The foam was obtained by extruding at a temperature of 168 ° C. while decreasing.
By slicing both sides of the foam with a splitting machine, a uniform open cell body having a thickness of 0.7 mm was obtained. Apparent specific gravity is 0.044 g / cm ³ , expansion ratio is 20.9 times (unexpanded specific gravity is 0.92 g / cm ³ ), average cell diameter is 180 μm, and continuous pore diameter is maximum 40 μm, minimum 5 μm, average 9 μm Yes, the air permeability was 7.0 cm ³ / cm ² / s, and the flexibility was 0.011 MPa.

Examples 2-6
In the same manner as in Example 1, mixing was performed so that the blending ratio shown in Table 1 was obtained, to obtain a foam. The results are shown in Table 1. In contrast to Example 1, in Example 2, the amount of nonionic surfactant was increased, in Examples 3, 4 and 5, the type and blending amount of nonionic surfactant were changed, and in Example 5, the type of resin was changed. Although they were changed, both were flexible and good air permeability was confirmed.

Comparative Examples 1-3
In the same manner as in Example 1, mixing was performed so that the blending ratio shown in Table 1 was obtained, to obtain a foam. The results are shown in Table 1. There was no air permeability in Comparative Example 1 having no nonionic surfactant, Comparative Example 2 having a nonionic surfactant, and Comparative Example 3 having a small amount of nonionic surfactant. Further, no open cells were observed, and the average pore diameter could not be measured.

  According to the present invention, an open-cell foam can be produced by a simple process. The open-cell foam obtained by the present invention is used in various directions such as breathable clothing (for example, anti-swelling clothing, underwear pads), fine filters, virus separation membranes, artificial lungs, liquid supply materials, sound absorbing materials, low hardness seals, etc. Useful for applications.

Claims (6)

(A) (A1) Polyolefin (excluding ethylene-propylene rubber) 50 to 95% by weight of (A); and (A2) 5 to 50 of ethylene-propylene rubber and / or polystyrene-based thermoplastic elastomer (A) weight%
(B) 0.2 to 10 parts by weight of a nonionic surfactant per 100 parts by weight of the polymer composition, and a substance that is a gas at normal temperature and pressure is in a supercritical state. A method for producing an open-cell foam, wherein the pressure is released after the impregnation with a foaming ratio of 10 times or more.   The method for producing an open-cell foam according to claim 1, wherein the substance that is a gas at normal temperature and pressure is carbon dioxide, and the foam is molded by an extruder.   The method for producing an open-cell foam according to claim 1 or 2, wherein the nonionic surfactant has 10 or more carbon atoms of alkyl, fatty acid, or alkylene.   The nonionic surfactant comprises one or more selected from alkyl polyetheramines, fatty acid glyceryls, and fatty acid (di) ethanolamides, according to any one of claims 1 to 3. A process for producing the open-cell foam described.   The open-cell foam manufactured by the manufacturing method of any one of Claims 1-4.   The foam according to claim 5, wherein the flexibility at 50% compressive load is 0.02 MPa or less.