JPH10193425A - Manufacture of extrusion foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an extrusion foam for a resinous fluidized bed germ solidifying carrier, which has an excellent affinity for water and a favorable fluidity, is low in price and excellent in a durability and further give a small bad influence upon a neighboring environment at waste disposal. SOLUTION: A resin composition, which is prepared by adding 0.15-0.40wt.% of lower temperature decomposition type foaming agent made of dinitrosopentamethylenetetramine, 0.15-1.50wt.% of high-temperature decomposition type foaming agent made of azodicarbonamide and 0.15-0.40wt.% of assistant made of urea to a composition of polyolefin-based resin and inorganic filler so as to be thermoformed by means of an extrusion foam molding in order to obtain an extrusion foam 1a having open cells.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a process for producing an extruded foam which can be suitably used as a carrier for immobilizing microorganisms on a fluidized bed in a fluidized bed bioreactor such as a sewage treatment apparatus for treating sewage using microorganisms. About the method.

[0002]

2. Description of the Related Art In a fluidized bed bioreactor such as a sewage treatment apparatus utilizing a biochemical reaction, microorganisms involved in sewage treatment (activated sludge) are obtained by fluidizing a carrier charged in a treatment tank by an aeration operation. Is immobilized on a carrier to purify sewage.

[0003] The microorganism-immobilized carrier for a fluidized bed of this sewage treatment apparatus is generally required to have, firstly, excellent fluidity so that it can be adapted to water early and uniformly flow in a treatment tank. Secondly, being porous so that microorganisms can easily adhere thereto, thirdly, strength capable of withstanding flow,
That is, it is excellent in durability such as abrasion resistance.

Under these circumstances, a porous inorganic substance such as diatomaceous earth has been used as a conventional microorganism-immobilized carrier, but this carrier has an apparent density of 2.0 g / cm.
^{Since it is} about ^{3 and} heavier than water, it requires a strong swirling force to fluidize it, and the increase in the fluidizing energy of the carrier increases the running cost. In addition, diatomaceous earth is liable to wear, rubs against each other when flowing, and cannot maintain its initial shape for a long time, and is inferior in durability.

Therefore, in recent years, a plastic carrier made of a synthetic resin, which can reduce the fluidization energy of the carrier to a value close to that of water and has excellent durability, that is, a plastic carrier made of synthetic resin has been developed, and its use has been rapidly increased. doing.

[0006] When a conventional resin-based carrier for immobilizing microorganisms for a fluidized bed is produced, a method using a porous technique such as a dropping foaming method or a sintering method is generally used. A method using extrusion foaming is also employed.

[0007]

However, the conventional carrier manufacturing method using the drop foaming method or the sintering method is inferior in mass productivity, and the resin material to be used is restricted, so that an inexpensive material cannot be selected and the cost is low. There is a problem that causes an increase in

Further, the conventional method for producing a carrier using extrusion foaming cannot achieve sufficient porosity, and the produced carrier has a problem that it has poor compatibility with water and poor fluidity. Was.

[0009] On the other hand, in recent years, the disposal of used plastic products has caused a concern about the adverse effects on the surrounding environment and has become a social problem. This problem is no exception in the technical field of fluidized bed bioreactors. At present, the use of resin-based carriers, which have very little adverse effect on the surrounding environment during disposal, has been strongly desired.

The present invention solves the above-mentioned problems of the prior art, has excellent compatibility with water, has good fluidity, is inexpensive, has excellent durability, and has little adverse effect on the surrounding environment during disposal. An object of the present invention is to provide a method for producing an extruded foam capable of obtaining a resin-based microorganism-immobilized carrier for a fluidized bed.

[0011]

Means for Solving the Problems The present inventor has conducted a thorough study to find a specific porous (bubble) structure for obtaining good fluidity in a resin-based fluidized bed microorganism-immobilized carrier. Clarified. Subsequently, based on the specific cell structure, the inventor repeatedly conducted detailed experiments and researches.As a result of intensive efforts, the present inventors have found out the optimal constituent elements that can achieve the above object, and have achieved the present invention. Reached.

That is, the method for producing an extruded foam according to the present invention is characterized in that a low-temperature decomposable foaming agent comprising dinitrosopentamethylenetetramine is added in an amount of 0.15% by weight or more to a blend of a polyolefin resin and an inorganic filler. .40% by weight
Less than 0.15% by weight and less than 1.50% by weight of a high-temperature decomposable blowing agent comprising azodicarbonamide, and 0.15% by weight and less than 0.40% by weight of an auxiliary agent comprising urea A composition is prepared, and the resin composition is thermoformed by extrusion foaming to obtain an extruded foam having open cells.

In the present invention, the above resin composition can be subjected to extrusion foam molding using a well-known extruder.
At the time of this extrusion molding, the resin composition is melted and kneaded by a screw in the cylinder of the extruder, and the temperature is gradually increased, so that the decomposition of the foaming agent gradually progresses, and immediately after being extruded from the mold. To form a molded body (extruded foam) having open cells therein. In this case, in the present invention, the foaming agent having a low foaming temperature (DPT) and the foaming agent having a high foaming temperature (ADCA) out of the two types of foaming agents have a difference in the timing of decomposition and foaming.
PT will foam first, followed by ADCA. That is, ADCA is gradually heated by external heat from a cylinder or a mold of an extruder to reach an activated state, and when foaming, heat (internal heat) generated at the time of foaming of DPT is applied. It foams with tremendous momentum, and a large amount of desired open cells described later in detail are formed,
A unique cell structure is formed in the molded body.

The extruded foam thus obtained has a large amount of open cells, and when used as a carrier for immobilizing microorganisms for a fluidized bed, water penetrates into the open cells and becomes compatible with water. Excellent fluidity and good fluidity can be obtained.

Further, since the production method of the present invention utilizes extrusion molding of a synthetic resin, it is excellent in mass productivity and cost can be reduced.

Moreover, since the foam obtained by the present invention contains a polyolefin resin as a main component, it has excellent abrasion resistance and sufficient durability. Disposal processing can be easily performed without any trouble as compared with a product or the like, and adverse effects on the surrounding environment during disposal processing can be reduced.

Hereinafter, the configuration of the present invention will be described in detail.

The resin composition in the production method of the present invention comprises:
A mixture of a polyolefin resin as a main component (base material) and an inorganic filler is mixed with a low-temperature decomposable foaming agent composed of DPT, a high-temperature decomposable foaming agent composed of ADCA, and an auxiliary composed of urea. It was added in proportions.

The polyolefin resin, which is the main component of the resin composition, is suitable for extrusion molding, is easy to dispose of, and is inexpensive, and is an essential requirement of the present invention. In order to obtain these effects more reliably, in the present invention, it is particularly preferable to use a polypropylene resin among polyolefin resins.

In the present invention, the inorganic filler compounded in the resin composition is not particularly limited, and any one can be used, but an inexpensive and chemically stable one is used. Is good. Specifically, those composed of calcium carbonate, barium sulfate, zeolite, titanium oxide, potassium titanate, aluminum hydroxide, and the like can be suitably used. Needless to say, these can be used in combination of two or more. good.

Further, the compounding amount of the inorganic filler is set at 5 to 50 parts by weight, preferably at a lower limit of 8 parts by weight or more and an upper limit of 20 parts by weight or less, based on 100 parts by weight of the polyolefin resin as a main component. Is good. That is, if the ratio is outside the specified range, it becomes difficult to obtain an apparent density close to water, and when used as a carrier, it may be difficult to obtain good fluidity.

Further, in the present invention, the density (material density) of the compound obtained by mixing the inorganic filler with the polyolefin resin as the main component is 0.90 to 1.20 g / cm ³ , preferably the lower limit. It is good to adjust it to 0.95 g / cm ³ or more and the upper limit to 1.00 g / cm ³ or less. That is, if the material density is too low, it may be difficult to obtain the required predetermined apparent density in order to obtain good fluidity, no matter how much the material density is adjusted. Conversely, if the material density is too high, foaming must be excessively promoted during extrusion molding to obtain a suitable apparent density, and there is a possibility that extrusion molding cannot be performed in a stable state.

The DPT as a low-temperature decomposition type foaming agent added to the resin composition contains 0.15% by weight in the resin composition.
It is necessary to contain (add) at least 0.40% by weight, preferably at least 0.20% by weight and 0.31% by weight.
It is better to contain less than. That is, if the content is too large, extrusion cannot be performed stably, and it is difficult to obtain a foam having a cell structure unique to the present invention. It is difficult to obtain an apparent density close to the above, and it is difficult to obtain good fluidity when used as a carrier, which is not preferable.

Further, the DPT has a particle diameter (average particle diameter, hereinafter the same) of less than 10 μm, preferably 9 μm.
It is better to use one having a diameter of less than μm. That is, if the particle size is too large, extrusion cannot be performed stably, and it is difficult to obtain an intended foam. If the particle size is too small, no particular disadvantage occurs.

ADCA as a high-temperature decomposition type foaming agent
Must be contained (added) in the resin composition at 0.15% by weight or more and less than 1.50% by weight.
The content is preferably 2% by weight or more and less than 0.31% by weight.
That is, if this content is too large, extrusion molding cannot be performed stably, and it is difficult to obtain the expected foam.On the contrary, if it is too small, the apparent density approximated to water is reduced. It is not preferable because it becomes difficult to obtain.

Further, ADCA having a particle diameter of 3 μm or more and less than 16 μm, preferably a lower limit of 3 μm or more and an upper limit of less than 11 μm is preferably used. That is, if the particle diameter is too large, the open-cell volume ratio increases, but the through-cell volume ratio decreases, making it difficult to obtain the expected foam.On the other hand, if the particle size is too small, It is difficult to form open cells, and it is difficult to obtain good fluidity when used as a carrier.

In the present invention, in order to control the foaming temperature of the two types of foaming agents, it is necessary to add an auxiliary agent composed of urea to the resin composition.

This urea is added to the resin composition in an amount of 0.1.
It is necessary to adjust the amount to 15% by weight or more and less than 0.40% by weight, and it is preferable to adjust the upper limit to less than 0.31% by weight. That is, if the amount of urea is out of the specified range, the volume ratio of open cells decreases, and when used as a carrier, it may be difficult to obtain good fluidity.

Further, in the resin composition of the present invention, if necessary, additives other than the above may be appropriately added.

In the present invention, the resin composition having the above structure is subjected to extrusion foam molding using a known extruder.

At the time of this extrusion molding, an extruded foam having a specific cell structure is formed by the synergistic effect of the two types of foaming agents as described above.

Here, the conditions at the time of the extrusion molding are not particularly limited, and may be appropriately set according to the situation during the molding process.
C. and the mold temperature are preferably set to 200 to 250.degree.

In the present invention, as shown in FIGS. 1 and 2, it is preferable to extrude the molded article into a tube and use it as a tube-shaped microorganism-immobilized carrier (1) for a fluidized bed.

As shown in FIG. 3, the foam (1a) such as the carrier for immobilizing microorganisms for a fluidized bed (1) obtained as described above comprises closed cells (2) completely surrounded by cell walls, as shown in FIG. At least a portion is divided into open cells communicating with the surface of the foam (1a), and the open cells (3) further include through cells (3a) communicating with both the inner surface and the outer surface of the foam (1a); The foam (1a) is divided into a semi-through cell (3b) which communicates with only one of the inner surface and the outer surface.

In the carrier (1), the ratio of the volume occupied by the open cells (3) in the total volume of the extruded foam (1a) (open cell volume ratio) is 20 to 70.
%, Preferably the lower limit is adjusted to 40% or more, and the upper limit is adjusted to 60% or less. In other words, if the open cell volume ratio (porosity) is too low, when introduced into the treatment tank of the sewage treatment apparatus, moisture does not sufficiently penetrate into the carrier (1), and good fluidity can be obtained. In addition, there is a possibility that the adhesion efficiency of microorganisms may be further reduced. Conversely, if the open cell volume ratio is too high, sufficient durability or the like may not be obtained due to a decrease in carrier strength.

In the carrier (1), the proportion of the through-cells (3a) in the volume of the open-cells (3) (percentage of the through-cell volume) is 20 to 80% or more, preferably 3 to 80%.
It is better to adjust it to 0% or more. In other words, the penetration bubble (3
a) has better water permeability than the semi-penetrating bubbles (3b), so that when the volume ratio of the penetrating bubbles is too low,
At the time of pouring into sewage, it has poor compatibility with water, and it is difficult to obtain good fluidity at an early stage. No matter how high the through-cell volume ratio is, no disadvantage is conceivable as a carrier, but a foam (1a) having a through-cell volume ratio of 80% or more can be formed by extrusion foaming with high quality. It is difficult.

Further, the carrier (1) has a density (apparent density) of the extruded foam (1a) excluding the volume of the open cells (3).
0.90 to 1.00 g / cm ³ , preferably with a lower limit of 0.94 g / cm ³ or more and an upper limit of 0.98 g / cm 3.
^It is better to adjust it to ³ or less. In other words, if the apparent density is too low, it will float in the upper layer when poured into sewage, and even if a strong swirling flow is applied, it may be difficult to make it flow uniformly. Conversely, if the apparent density is too high, it is necessary to give a strong swirling flow in order to make the fluid flow evenly, and when the swirling flow is stopped, it settles at the bottom of the processing tank, so that recovery may be difficult.

For reference, the density (bulk density) based on the volume including all cells in the carrier made of the foam obtained by the present invention is 0.30 to 0.70 g / cm ^3.
It is adjusted to.

When the foam of the present invention is used as a tubular carrier (1), as shown in FIG. 2, the outer diameter (D) is 2 to 20 mm, preferably 4 mm or more,
mm or less. That is, if the outer diameter (D) is too small, it is difficult to form the cell structure peculiar to the present invention by extrusion, and if it is too large, the resistance to water becomes large, and the flowability is lowered. May cause problems.

Further, the thickness (T) of the carrier (1) is set to a thickness of 4 to 40% with respect to the outer diameter (D), preferably 5% to 30%. That is, if the thickness (T) is too large, a large amount of through-cells (3a) cannot be formed, and it may be difficult to obtain good fluidity.

In the extrusion molding, the larger the outer diameter (D), the slower the extrusion speed. On the other hand, in forming the cell structure peculiar to the present invention, if the extrusion speed is too high, a thick skin layer is formed on the surface of the molded article, and it becomes difficult to form the cell structure peculiar to the extrusion speed. The thickness (T) can be made thinner when it is slower than in the case, that is, when it is larger than the outer diameter is smaller. Therefore, in the present invention, as described above, the thickness (T)
Is most appropriately specified in relation to the outer diameter (D), but when specified by specific numerical values, the wall thickness (T) is set to 0.1.
The lower limit is preferably set to 0.3 mm or more, and the upper limit is preferably set to 1.5 mm or less.

The length (L) of the carrier (1) is set to 50 to 200%, preferably 100% or more and 200% or less with respect to the outer diameter (D). That is, if the length is too long, the resistance to water becomes large, and there is a possibility that good fluidity may not be obtained. May not be obtained. In addition, carrier (1)
The length (L) is 1 to 40 when specified by specific numerical values.
mm, preferably 4 mm or more and 20 mm or less.

[0043]

EXAMPLES Examples related to the present invention and comparative examples for verifying the effects thereof will be described in detail below.

<Example 1>

[Table 1] As shown in Table 1 above, polypropylene (PP) resin 10
0 parts by weight, inorganic filler 1 composed of calcium carbonate
0 parts by weight, as well as 0.15% by weight of ADCA having a particle size of 3 μm as a high-temperature decomposition type foaming agent, 0.15% by weight of DPT having a particle size of 1 μm as a low-temperature decomposition type blowing agent, and 0.1% by weight of urea as an auxiliary agent. A resin composition for a carrier to which 15% by weight was added was prepared.

On the other hand, as a carrier manufacturing apparatus, as shown in FIG. 4, a full flight screw type single screw extruder (11) having a diameter of 40 mm and L / D = 32, and the extruder (1)
A cooling water tank (12) for cooling the extruded tubular foam (1a) foamed and molded by 1), and a pelletizer for cutting and pelletizing the foam (1a) cooled by the cooling water tank (12). (13) was prepared.

Using this carrier manufacturing apparatus, the above resin composition is molded and processed to have an outer diameter of 4 mm, a thickness of 0.5 mm, and a length of 4 mm.
mm extruded foam (1a) was obtained and used as a resin-based carrier.

The extrusion conditions at this time were appropriately changed depending on the state of the molded body, based on a screw rotation speed of 30 rpm, a cylinder temperature of 200 to 250 ° C., and a mold temperature of 250 ° C.

<Measurement of Physical Properties> With respect to the carrier thus obtained, the material density (g / cm ³ ) and apparent density (g / c
m ³ ), open cell volume ratio (%), and through cell volume ratio (%) were measured by the following methods.

(1) The material density was determined by kneading a composition obtained by mixing a PP resin and an inorganic filler by a Labo Plastomill, forming a 100 mm square plate by compression molding, and measuring its weight and thickness. The density was determined from.

(2) The apparent density was measured using a gas displacement type densitometer. Thus, this density corresponds to the density of the foam excluding the open cell volume.

(3) Volume ratio of open cells (porosity) Observed by an electron microscope, the size of open cells per unit area was measured to determine the volume, and the open cell volume ratio was determined from the volume.

(4) Permeable Bubble Volume Ratio Observed with an electron microscope, the size of the perforated cell per unit area was measured to determine the volume, and the perforated cell volume ratio was determined from the volume and the volume of the open cell. .

<Examples 2 to 4> Resin compositions having the compounding ratios shown in Table 1 above were molded in the same manner as described above.
Extruded foam carriers were obtained, and the physical properties of each carrier were measured in the same manner as described above.

Example 5 As shown in Table 1 above, a slightly larger amount of ADCA having a particle size of 3 μm was added, a carrier was obtained in the same manner as in Example 2, and the physical properties were measured in the same manner.

Example 6 As shown in Table 1 above, a carrier was obtained in the same manner as in Example 4 above using ADCA having a slightly larger particle diameter of 14 μm, and the physical properties were measured in the same manner.

<Example 7> As shown in Table 1 above, using the DPT having a relatively large particle diameter of 10 μm,
In the same manner as in the above, a carrier was obtained, and the physical properties were measured in the same manner.

Example 8 As shown in Table 1 above, a carrier was obtained and the physical properties were measured in the same manner as in Example 1 above, using ADCA having a large particle size of 15 μm.

<Example 9> As shown in Table 1 above, Example 3 was prepared using ADCA having a small particle size of 2 μm.
In the same manner as in the above, a carrier was obtained, and the physical properties were measured in the same manner.

Example 10 The thickness of the carrier to be produced was 1.
It was molded so as to be as thick as 5 mm (37.5% of the outer diameter), and the physical properties were measured in the same manner as described above.

<Example 11> The thickness of the carrier to be produced was 0.
It was molded so as to be as thin as 18 mm (4.5% with respect to the outer diameter), and the physical properties were measured in the same manner as described above.

<Comparative Example 1>

[Table 2] As shown in Table 2 above, a resin composition was prepared in which the amount of ADCA added was too small as compared with the examples, and molded in the same manner as above to obtain a carrier, and the physical properties were measured.

<Comparative Example 2> A resin composition containing too little DPT was prepared and molded in the same manner as above to obtain a carrier, and the physical properties were measured.

Comparative Example 3 A resin composition containing too little urea was prepared and molded in the same manner as described above to obtain a carrier, and the physical properties were measured.

Comparative Example 4 A resin composition containing an excessive amount of ADCA was prepared and molded in the same manner as described above to obtain a carrier, and the physical properties were measured.

Comparative Example 5 A resin composition containing an excessive amount of DPT was prepared and molded in the same manner as described above to obtain a carrier, and the physical properties were measured.

Comparative Example 6 A resin composition containing excessive amounts of ADCA and urea was prepared and molded in the same manner as described above to obtain a carrier, and the physical properties were measured.

Comparative Example 7 A composition was prepared without adding DPT, molded in the same manner as described above to obtain a carrier, and the physical properties were measured.

<Evaluation> Each carrier obtained by the above method was evaluated as follows.

(1) Moldability In the extruder (11), “○” indicates that a high-quality foam molded article was obtained, “△” indicates that a foam molded article of predetermined quality was obtained, When a molded article of a predetermined quality could not be obtained even when the extrusion conditions were changed, it was evaluated as "x".

(2) Fluidity 5 liters of water and 0.5 liter of a carrier were placed in a water tank having a diameter of 20 cm and a height of 40 cm, and air was aerated at a rate of 3 liters per minute from the bottom of the water tank. If the fluid flowed uniformly within a week, "○", although the fluidity was inferior to that, "△" if it flowed to such an extent that it could be practically used as sewage treatment, "X" if it did not flow or did not flow uniformly Was evaluated.

The results of each evaluation are shown in Tables 1 and 2 above.

As can be understood from the above evaluations, the carriers of the examples related to the present invention have excellent fluidity and moldability. In particular, those in which the mixing ratio and the size of each component were set in specific ranges (Examples 1 to 4) had more excellent fluidity and moldability. Further, as shown in Examples 7 to 9, when the size of the particle diameter of the foam is slightly small or large, although the moldability is slightly inferior,
It was possible to obtain a certain fluidity. Example 1
Thickness of the carrier, as shown in FIG. 0, is considered to be practically possible although the fluidity is slightly inferior. It is considered that the thickness of the carrier, as shown in Example 11, is slightly reduced. Although fluidity was poor, good fluidity could be obtained.

On the other hand, the carrier of the comparative example, which deviates from the gist of the present invention, cannot be flowed uniformly even after one week has passed since it was put into the water tank, was poor in water adaptability, and was good. In some cases, high fluidity could not be obtained or even extrusion could not be performed.

[0074]

As described above, according to the method for producing an extruded foam of the present invention, the extruded foam is excellent in compatibility with water, has good fluidity, is inexpensive, has excellent durability, and is excellent in waste disposal. There is an effect that a microorganism-immobilized carrier for a fluidized bed with less adverse effect on the surrounding environment can be produced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a microorganism-immobilized carrier for a fluidized bed relating to the method of the present invention.

2A is a sectional view taken along line AA of FIG. 1, and FIG. 2B is a sectional view taken along line BB of FIG.

FIG. 3 is an enlarged sectional view showing a portion surrounded by a dashed line in FIG.

FIG. 4 is a schematic side view showing a carrier manufacturing apparatus based on the method of the present invention.

[Explanation of symbols]

 1. Carrier 1a: Foam

Claims (5)

[Claims] 1. A blend of a polyolefin resin and an inorganic filler, a low-temperature decomposition type blowing agent comprising dinitrosopentamethylenetetramine being 0.15% by weight or more and less than 0.40% by weight, comprising azodicarbonamide. Preparing a resin composition to which a high-temperature decomposition type foaming agent is added in an amount of 0.15% by weight or more and less than 1.50% by weight, and an auxiliary agent composed of urea is added in an amount of 0.15% by weight or more and less than 0.40% by weight; A method for producing an extruded foam, wherein the resin composition is thermoformed by extrusion foaming to obtain an extruded foam having open cells. 2. The method for producing an extruded foam according to claim 1, wherein the extruded foam is used as a microorganism-immobilized carrier for a fluidized bed. 3. An average particle diameter of the DPT is 10 μm.
The method for producing an extruded foam according to claim 1 or 2, wherein the extruded foam is used. 4. The ADCA has an average particle diameter of 3 μm.
2. A material having a diameter of not less than m and less than 16 μm.
4. The method for producing an extruded foam according to any one of items 3 to 3. 5. A density (material density) in a molten state in a blend of the polyolefin resin and the inorganic filler.
But the production method of the extruded foam according to any one of 4 claims 1 becomes adjusted to 0.90~1.20g / cm ^3.