JP2005171064A - Open-cell foam and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain open-cell foam that hardly causes clogging in foam parts and exhibits functions such as support function, etc., for a long period of time and to provide a method for producing the same. <P>SOLUTION: The open-cell foam is obtained by kneading a raw material composition comprising a polyolefin-based resin, a blowing agent, a crosslinking agent and powder nonmeltable in kneading as essential components and expanding the composition. Powder having a melting point ≥10 °C higher than that of the polyolefin-based resin is preferable as the powder. The average particle diameter of the powder is 50-200 μm. The content of the powder is 20-50 vol.% based on the polyolefin-based resin. The average foam diameter of foam formed after expansion is 0.7-2.0 mm. The open-cell foam is suitably useful as a carrier for water treatment for supporting a microorganism. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an open-cell foam used as a water treatment carrier for supporting microorganisms, for example, and a method for producing the same.

Conventionally, the following techniques are known as this type of open-cell foam. The first conventional technique is to obtain a final foam that is foamed 10 times or more by primary foaming using a mixture comprising a polyolefin, a crosslinking agent and a foaming agent, followed by secondary foaming (Patent Document 1). reference). The second prior art is a crosslinked polyethylene resin foam containing 1 to 30 parts by weight of polypropylene particles and having an open cell structure with respect to 100 parts by weight of a polyethylene resin (see Patent Document 2).
Japanese Patent Application Laid-Open No. 5-212811 (pages 2 to 4) JP 2003-213029 A (2nd to 4th pages)

  However, in the first prior art, since the average bubble diameter of the bubbles of the final foam obtained is as small as 250 to 450 μm, the surface area increases, but when fine particles in water such as microorganisms adhere, the bubble portion It will cause clogging. Therefore, when used as a carrier for microorganisms, there is a problem that microorganisms are not supported on the bubble portion and cannot function stably over a long period of time. On the other hand, in the second prior art, since the average bubble diameter of the foam of the obtained foam is as large as 2 to 3 mm, there is a problem that the surface area becomes small and the supporting function cannot be sufficiently exhibited. there were.

  The present invention has been made paying attention to such problems existing in the prior art. An object of the present invention is to provide an open-cell foam and a method for producing the same, in which the bubble portion is less likely to be clogged and functions such as a supporting function can be exhibited over a long period of time.

  In order to achieve the above object, the open-cell foam of the invention according to claim 1 is a raw material composition comprising a polyolefin resin, a foaming agent, a cross-linking agent, and a non-melting powder during kneading as essential components. Foamed after kneading, the powder has an average particle diameter of 50 to 200 μm, the content of the powder is 20 to 50% by volume with respect to the polyolefin resin, and the average cell diameter of the bubbles formed after foaming is It is 0.7 to 2.0 mm.

The open-cell foam according to a second aspect of the present invention is the polyolefin according to the first aspect, wherein the powder is a polyolefin resin having a melting point higher by 10 ° C. or more than the polyolefin resin.
The open-cell foam of the invention described in claim 3 is used as a carrier for water treatment for supporting microorganisms in the invention of claim 1 or claim 2.

  The method for producing an open-cell foam according to claim 4 is a raw material composition comprising a polyolefin resin, a foaming agent, a crosslinking agent and a non-melting powder at the time of kneading as essential components, After kneading a raw material composition having an average particle size of 50 to 200 μm and a powder content of 20 to 50% by volume with respect to the polyolefin resin, it is foamed in two stages, and the average cell of the resulting open cell foam The diameter is 0.7 to 2.0 mm.

  According to a fifth aspect of the present invention, there is provided a method for producing an open-cell foam according to the fourth aspect of the present invention, wherein after the foaming is performed in the two steps, mechanical pressure is applied.

According to the present invention, the following effects can be exhibited.
According to the open-cell foam of the invention described in claim 1, the bubble portion is not easily clogged, and functions such as a supporting function for supporting microorganisms and the like can be exhibited over a long period of time.

  According to the open-cell foam of the invention described in claim 2, in addition to the effect of the invention according to claim 1, since the non-melting powder does not melt during kneading, the boundary part between the melting part and the non-melting part A larger bubble can be formed.

According to the open-cell foam of the invention described in claim 3, in addition to the effects of the invention according to claim 1 or 2, microorganisms are supported in the bubble part and are suitably used as a carrier for water treatment.
According to the method for producing an open-cell foam of the invention according to claim 4, an open-cell foam having an average cell diameter of 0.7 to 2.0 mm can be easily produced.

  According to the open-cell foam of the invention described in claim 5, in addition to the effect of the invention according to claim 4, open-cells can be easily formed.

Hereinafter, embodiments of the present invention will be described in detail.
The open-cell foam of the present embodiment is a foam formed by foaming after kneading a raw material composition containing a polyolefin resin, a foaming agent, a crosslinking agent and a non-melting powder as an essential component during kneading. The average bubble diameter is 0.7 to 2.0 mm. The average particle size of the powder is 50 to 200 μm, and the content of the powder is 20 to 50% by volume with respect to the polyolefin resin. Here, the open cell foam refers to those having an open cell rate of 80% or more measured according to ASTM D 1940-62T, preferably close to 100%.

  Since polyolefin-based resins are stable to water and excellent in durability, they are preferably used as carriers for water treatment. Examples of such polyolefin resins include polyethylene resins, copolymer resins of ethylene and other monomers, such as ethylene-vinyl acetate copolymer resins (EVA), polypropylene resins, and the like. The melting point of the polyethylene resin is 107 to 124 ° C. for the low density polyethylene, 120 to 140 ° C. for the high density polyethylene, and the melting point of the polypropylene resin is 130 to 160 ° C.

  The foaming agent is for foaming a polyolefin resin to form a polyolefin resin foam, and has a decomposition temperature equal to or higher than the melting temperature of the polyolefin resin. Examples of the foam include azo compounds such as azodicarbonamide (ADCA) and barium azodicarboxylate, and hydrazine compounds such as p, p′-oxybisbenzenesulfonyl hydrazide.

  The cross-linking agent is a free radical generator that has a decomposition temperature equal to or higher than the softening temperature of the polyolefin-based resin and generates free radicals by decomposition to form cross-links between or within the molecules of the polyolefin-based resin. Examples of the crosslinking agent include dicumyl peroxide, tertiary butyl peroxybenzoate, tertiary butyl peroxyketone, 2,5-dimethyl-2,5-ditertiary butyl peroxyhexine, and 2,5-dimethyl-2. Organic peroxides such as 1,5-ditertiary butyl peroxyhexane and 1,1-ditertiary butyl peroxy-3,3,5-trimethylcyclohexane are used.

  Next, the non-melting powder during kneading will be described. When the raw material composition (compound) is kneaded and the polyolefin-based resin or the like is melted, the non-melting powder does not melt at the time of kneading. Therefore, the powder portion does not contain a crosslinking agent or a foaming agent. On the other hand, the polyolefin resin melts and contains a crosslinking agent and a foaming agent. For this reason, when the foaming agent is heated to its decomposition temperature and foamed, the resin portion containing the foaming agent is expanded by the foaming gas, but the resin portion not containing the foaming agent is not expanded. Accordingly, an elongation shift occurs between the expanding portion and the non-expanding portion, and voids are formed in the boundary portion to form larger bubbles.

  As such a non-melting powder at the time of kneading, a powder of resin, metal, metal salt or the like having a melting point higher than that of polyolefin resin by 10 ° C. or more is used. Examples of the resin having a melting point higher by 10 ° C. or more than the polyolefin resin include high-density polyethylene (melting point 120 to 140 ° C.), polypropylene resin (melting point 130 to 160 ° C.), and the like. Examples of the metal include iron and aluminum. Examples of the metal salt include calcium carbonate. Among these, it is preferable to select a polyolefin resin having the same melting point as that of the polyolefin resin to be used as a foam, in consideration of reuse at the time of disposal. For example, low-density polyethylene (melting point 107 to 124 ° C.) can be used as the polyolefin-based resin, and high-density polyethylene (melting point 120 to 140 ° C.) can be used as the non-melting powder during kneading. The upper limit of the melting point of the non-melting powder at the time of kneading is not limited, but it is usually about 50 ° C. higher than the melting point of the polyolefin resin.

  The size of the larger bubbles described above changes based on the size of the powder, and the average bubble size tends to increase as the average particle size of the powder increases. Therefore, the average particle size of the non-melting powder during kneading is set to 50 to 200 μm. When the average particle size of the powder is less than 50 μm, bubbles having a sufficiently large average cell size cannot be obtained. On the other hand, when the average particle diameter exceeds 200 μm, the number of powder particles is reduced, the number of large bubbles is reduced, and coarse bubbles are scattered in the fine bubbles. Cannot be used.

  In order to set the average cell diameter of the open-cell foam obtained after foaming to 0.7 to 2.0 mm, not only the average particle diameter but also the content of non-melting powder during kneading is set. There is a need to. The content of the non-melting powder at the time of kneading is 20 to 50% by volume with respect to the polyolefin resin. When the content is less than 20% by volume, the average cell diameter of the open cell foam becomes too small. On the other hand, when it exceeds 50 volume%, the ratio of the part which does not foam becomes large and it becomes impossible to exhibit a function as an open-cell foam.

  By the way, the polyolefin resin is hydrophobic and does not settle in water immediately, and since the workability and initial performance are low, a hydrophilizing agent such as a surfactant is used to impart hydrophilicity to the polyolefin resin. It is desirable to blend. As such a hydrophilizing agent, acetylene glycol or the like is used as a nonionic surfactant.

  In addition to the above components, the raw material composition contains a foaming aid, a foam stabilizer, a filler, rubber, a stabilizer, a colorant, a flame retardant, a plasticizer, and the like. As the foaming aid, for example, zinc oxide, stearic acid, salicylic acid, urea compound, etc. are used. As the filler, carbon black, wood powder, pulp or the like is used. As the rubber, ethylene-propylene copolymer rubber (EPM), ethylene-propylene-diene copolymer rubber (EPDM), styrene-butadiene copolymer rubber (SBR) or the like is used.

Next, the manufacturing method of the open cell foam comprised as mentioned above is demonstrated.
First, a raw material composition containing a polyolefin resin, a foaming agent, a crosslinking agent, and a non-melting powder during kneading as essential components is prepared. In this case, the average particle diameter of the powder is 50 to 200 μm, and the content of the powder is 20 to 50% by volume with respect to the polyolefin resin. Next, the raw material composition is melted using a kneader (melt kneader) such as a kneader. As a kneading apparatus, a kneader, a mixing roll, an extruder, or the like can be used. The kneaded raw material composition is foamed in two stages, primary foaming and secondary foaming.

  Primary foaming is performed by heating and injecting the raw material composition into a molding recess of a pressure press apparatus. The heating temperature is set to about 110 to 180 ° C. The expansion ratio by primary foaming is about 1.0 to 1.2 times. Subsequently, secondary foaming is performed by heating at normal pressure. The heating temperature is set to about 140 to 200 ° C. In order to make the foam obtained by secondary foaming into an open cell structure, mechanical pressure is applied. That is, the foam after completion of the secondary foaming is pressed with a constant speed roll, and for example, continuous foaming is performed by applying a mechanical pressure so as to be 1/5 of the original thickness.

  The average cell diameter of the obtained open-cell foam is 0.7 to 2.0 mm. When the average bubble diameter is less than 0.7 mm, the bubble portion is clogged, and when used as a microorganism carrier, the microorganism is not carried on the bubble portion. On the other hand, when it exceeds 2.0 mm, the surface area of the bubble portion becomes small, and the supporting function cannot be exhibited. The cell diameter of the open-cell foam does not need to be within the range of 0.7 to 2.0 mm as the minimum value or the maximum value, and the average cell diameter may be within the range of 0.7 to 2.0 mm. . In addition, a larger difference between the maximum value and the minimum value of the bubble diameter, that is, a wider distribution of the bubble diameter, shows a preferable tendency in order to exhibit the function of supporting the open-cell foam for a long time.

  The open-cell foam obtained in this way can be used as a water treatment carrier for supporting microorganisms such as bacteria in the bubble part, a body sponge used during bathing, and the like.

  Now, an open-cell foam is obtained by kneading a polyolefin resin, a foaming agent, a crosslinking agent and a raw material composition containing a non-melting powder as an essential component during kneading and foaming in two stages. At this time, non-melting powder is blended as a foreign substance at the time of kneading, the average particle diameter of the powder is 50 to 200 μm, and the content of the powder is 20 to 50 volume with respect to the polyolefin resin. % Is set. Therefore, when the foaming agent is foamed, the polyolefin resin part is expanded by the foaming gas, and the part of the powder not containing the foaming agent is not expanded. A hole having a size of 2.0 mm is formed.

The effects exhibited by the above embodiment will be described below.
-According to the open cell foam of the embodiment, since the average bubble diameter of the bubbles is in an appropriate range of 0.7 to 2.0 mm, the bubble portion is less likely to be clogged, a supporting function for supporting microorganisms, etc. The function can be demonstrated over a long period of time.

  ・ Also, the non-melting powder during kneading is a polyolefin resin whose melting point is 10 ° C. or higher than that of the polyolefin resin. Larger bubbles can be formed at the boundary with the portion.

-The open-cell foam can support microorganisms in the cell portion and can be suitably used as a carrier for water treatment.
-An open cell foam having cells with an average cell diameter of 0.7 to 2.0 mm is easily manufactured by a manufacturing method in which the raw material composition containing the powder is kneaded and then foamed in two stages. be able to. And it can be set as a high foaming body whose expansion ratio is 30 to 40 times.

  -After foaming in two stages, open cells can be easily formed by applying mechanical pressure with a roll or the like.

Hereinafter, the embodiment will be described more specifically with reference to examples and comparative examples. In each example, “part” means “part by mass” and “%” means “% by mass”.
(Examples 1-5 and Comparative Examples 1 and 2)
An open-cell foam was prepared with the following raw material composition and foaming conditions.

Raw material composition:
80 parts ethylene-vinyl acetate copolymer resin (EVA) (manufactured by Sumitomo Chemical Co., Ltd., EVAFLEX P1403, melting point 85 ° C., vinyl acetate content 15%) as polyolefin resin, azodicarbonamide (ADCA) as foaming agent: low Density polyethylene (LDPE) = 60 parts: 30 parts of a foaming agent master batch of 40 parts, 0.07 part of active zinc white and 0.2 part of stearic acid as foaming aids, 1.05 part of dicumyl peroxide as a crosslinking agent, Formulated with 5.0 parts of acetylene glycol (produced by Kawaken Fine Chemicals Co., Ltd., acetylenol E40) as a nonionic surfactant and high-density polyethylene (HDPE, melting point 130 ° C.) as the non-melting powder in the amounts shown in Table 1. Thus, a raw material composition was obtained. In Table 1, the addition amount of the powder indicates the addition amount (volume part) with respect to 100 parts by volume of the polyolefin resin. The raw material composition was put into a kneader heated to 80 ° C. and kneaded for 5 minutes. Subsequently, primary foaming and secondary foaming were performed under the foaming conditions shown below.

Foaming conditions:
Primary foaming: Heating was performed at a foaming temperature of 135 ° C., and foaming was performed for 35 minutes using a pressure press apparatus. The size of the molding part of the heating and pressure press apparatus was 165 mm in length and width and 35 mm in depth. The foaming ratio of the foam obtained by the primary foaming was 1.0 to 1.2 times.

  Secondary foaming: foaming was carried out at a foaming temperature of 160 ° C. for 120 minutes at normal pressure. The size of the secondary mold was 500 mm in length and width, and 100 mm in depth. The expansion ratio of the foam obtained by secondary foaming was 30 to 40 times. The foam after the completion of the secondary foaming was reciprocated 5 times with a constant speed roll and pressed to form a continuous foam so that the thickness was 1/5 of the original thickness.

  Table 1 shows the average cell diameter of the obtained open cell foam. In Table 1, the maximum value (mm) represents the maximum cell diameter for the cells of the open cell foam, the minimum value (mm) represents the minimum cell diameter for the cells of the open cell foam, and the difference (mm) represents the maximum value. Represents the difference between the minimum values.

表１に示したように、実施例１から実施例５においては、得られた連続気泡発泡体の平均気泡径は０．８〜１．８ｍｍであり、水処理用担体として適切なものであった。一般に、粗大気泡を有する連続気泡発泡体を得ようとする場合、一次発泡において発泡剤の分解を抑制するために加熱温度を低く、加熱時間を短く設定する必要から架橋剤の反応も抑制され、二次発泡で強度が不足する可能性がある。これに対し、実施例１から実施例５では混練時に非溶融性の粉体を用いたことから、一次発泡の加熱温度を高く、加熱時間を長くすることができた。

As shown in Table 1, in Examples 1 to 5, the obtained open cell foam had an average cell diameter of 0.8 to 1.8 mm, which was suitable as a carrier for water treatment. It was. In general, when trying to obtain an open-cell foam having coarse cells, the reaction of the crosslinking agent is also suppressed from the need to set the heating temperature low and the heating time short in order to suppress the decomposition of the foaming agent in the primary foaming, Secondary foaming may cause insufficient strength. On the other hand, in Examples 1 to 5, since non-melting powder was used during kneading, the heating temperature for primary foaming could be increased and the heating time could be extended.

  On the other hand, in Comparative Example 1 in which the amount of non-melting powder added is too small during kneading and in Comparative Example 2 in which the average particle diameter of non-melting powder is too large during kneading, the average cell size of the obtained open cell foam The diameter was 0.5 mm and coarse bubbles were scattered, which was inappropriate as a carrier for water treatment.

In addition, this embodiment can also be changed and embodied as follows.
-A hydrophilic resin such as vinyl acetate resin or polyvinyl alcohol can be used in combination with a polyolefin resin as a hydrophilizing agent to impart hydrophilicity.

-The average particle size of the powder used is not limited to one type. It is also possible to prepare two or more types of powders having different average particle diameters, and after blending these powders, molding can be performed to prepare an open-cell foam.
-As the foaming method, methods such as extrusion foaming, injection foaming and bead foaming can also be adopted.

-It can also be configured to obtain an open-cell foam by breaking the cell membrane at the time of foaming by forming a polyfunctional monomer or the like, forming open cells and foaming in one stage.
Further, the technical idea that can be grasped from the embodiment will be described below.

  (1) The open-cell foam according to any one of claims 1 to 3, further comprising a hydrophilizing agent for hydrophilizing the polyolefin resin in the raw material composition. When comprised in this way, when using an open-cell foam as a support | carrier for water treatment, it can be quickly settled in water, and input workability | operativity and initial stage performance can be improved.

  (2) The open-cell foam according to the technical idea (1), wherein the hydrophilizing agent is a surfactant. When comprised in this way, the hydrophilic property of an open-cell foam can be improved effectively.

Claims (5)

A raw material composition containing a polyolefin resin, a foaming agent, a crosslinking agent and a non-melting powder as an essential component during kneading is foamed after kneading, and the powder has an average particle size of 50 to 200 μm and contains powder. An open-cell foam having an amount of 20 to 50% by volume based on the polyolefin resin, and an average cell diameter of bubbles formed after foaming of 0.7 to 2.0 mm. The open-cell foam according to claim 1, wherein the powder is a polyolefin resin having a melting point higher than that of the polyolefin resin by 10 ° C or more. The open-cell foam according to claim 1 or 2, which is used as a water treatment carrier for supporting microorganisms. A raw material composition comprising a polyolefin resin, a foaming agent, a crosslinking agent and a non-melting powder at the time of kneading as an essential component, wherein the average particle diameter of the powder is 50 to 200 μm, and the content of the powder is a polyolefin resin. After kneading the raw material composition that is 20 to 50% by volume with respect to the continuity, foaming is performed in two stages, and the average cell diameter of the obtained open cell foam is 0.7 to 2.0 mm. A method for producing a cellular foam. The method for producing an open-cell foam according to claim 4, wherein mechanical pressure is applied after foaming in the two steps.