JPH0721081B2 - Method for producing continuous porous sintered body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a porous body of a polyolefin resin having continuous pores of 10 to 150 μm, and various chemical resistance, strength or breathability of the porous body is utilized. It is used as a filter, a liquid absorbing material, or a gas or liquid conducting material.

(Prior Art) Generally, a thermoplastic resin powder is filled in a female mold having a desired shape, and the mold is heated to a temperature higher than the melting temperature of the resin, and the powder resin is melted at its interface and then cooled. , A method of forming a porous body having innumerable communicating pores is called sintering forming,
Further, the obtained sintered body is referred to as a continuous porous sintered body. The mechanical tensile strength of the thus obtained porous body is a continuous porous body, and therefore, it is usually possible to obtain a value which is considerably lower than that which the resin originally has. A technique often used to improve this strength is a method in which the powder is densely filled in a mold and sinter-molded to achieve the purpose. However, this method has major drawbacks. One of them is that when a mold filled with high density powder is heated, as the powder in the part in contact with the mold becomes molten, it cannot withstand the pressure and causes excessive melt flow, resulting in That is, the pores on the surface part are clogged. Another method used to solve this is to press the mold to fill the powder with high density, take out the block of the shaped powder, and heat-sinter under open pressure. However, with this method, the desired shape cannot be obtained, and therefore the shape needs to be corrected by post-processing (cutting).

As a thermoplastic resin powder for sinter molding, it has excellent chemical resistance, is industrially available at low cost, is available as a powder, and has good sinter moldability. Although the resin powder is widely used, its strength is as described above and is rather lower than that of other plastics, and its strength is desired to be improved.

(Problems to be Solved by the Invention) The tensile strength of the continuous porous sintered body is determined by the fusion strength between the resin particles in contact with each other. In order to increase the fusion strength, one is to increase the fusion area, and in the conventional technique, a method of filling powder with high density and sintering is used for that purpose. Another method is to increase the cohesive strength itself, but a raw material having a high cohesive strength usually causes clogging because it has a low viscosity at the time of melting and has not been put to practical use. In addition, when the powder is packed into the mold with an external force at a high density as in the conventional method, pressure distribution is generated depending on the mold shape.
The pore diameter and the porosity of the obtained porous body become uneven depending on the place, and the pressure loss becomes large in terms of air permeability. For these reasons, the raw material resin powder is preferably a material having a higher melt viscosity and less clogging. However, a material having a higher melt viscosity has a lower welding strength, and as a result, the resulting porous body has a lower tensile strength.

(Means for Solving the Problems) The present invention, under the circumstances as described above, can be easily sintered and molded using a commonly available material, has a high tensile strength, and has a pore diameter, It is intended to obtain a continuous porous sintered body having high uniformity in porosity and low airflow resistance.

That is, in the present invention, an ultra-high molecular weight polyethylene powder having an extremely high melt viscosity and a polyethylene resin or / and a polypropylene resin powder having a low melt viscosity and a low melt viscosity are mixed in a certain limited range to form a mixed powder. It is characterized in that it is used for consolidation. More specifically, the average particle size is 50 to 500 μm, the bulk density of the powder is 0.3 g / cc or more, and the powder has an ultrahigh molecular weight polyethylene powder (A) having an angle of repose of 45 degrees or less and MI. 0.02 to 30 g / 10 minutes, the average particle size is 50 to 500 μm, the range is 3/1 to 1/3 of the average particle size of (A), and the bulk density of the powder is 0.3 g / cc. The above is the polyethylene resin and / or polypropylene resin powder (B) having a repose angle of 45 degrees or less,
(A) / (B) = 85/15 to 40/60 (parts by weight), mixed and sintered to obtain an average pore diameter of 10 to 150 μm and an average porosity of 25 to 45 V% (volume%). It is characterized in that a porous sintered body having a continuous ventilation hole is obtained. As a result, the powder can be packed in the closest packed state without pressure packing, and a continuous porous sintered body having a uniform porosity distribution and high tensile strength can be obtained.

The ultra high molecular weight polyethylene powder (A) referred to in the present invention means
If the molecular weight measured by the viscosity method according to ASTM-D1601 is 600,000 or more, and the fluidity during melting is expressed using the melt index value of ASTM-D1238 (hereinafter referred to as MI value), MI ≒
A polyethylene resin powder showing a value of 0 g / 10 minutes (temperature: 190 ° C., load: 2.16 Kg). Further, such ultra-high molecular weight polyethylene resin powder can be obtained by crosslinking general polyethylene resin powder with electron beam irradiation, organic peroxide, etc., or by suspension polymerization using Ziegler-Natsuta catalyst or the like. Powder can be directly obtained by the polymerization method. In the present invention, what is referred to as powder means mechanically crushed resin, chemically crushed resin, or powder obtained directly by polymerization, and more preferably, the average particle diameter of the powder is 50 to 500 μm.
Within the range of m, the bulk density of the powder is 0.3 g / cc or more (JIS-
(Measured with K6721), the repose angle of the powder is 45 degrees or less (JIS-K6721
Is measured by the injection method). The polyethylene-based resin or / and polypropylene-based resin powder (B) referred to in the present invention means resin powder containing 70 mol% or more of ethylene or / and propylene units in its polymer structure, polyethylene resin, polypropylene resin. , Ethylene / propylene copolymer or a powder of a copolymer resin of ethylene or propylene and another monomer such as butene-1, 4 methylpentene-1, vinyl acetate, etc. The preferred properties are the same as those described above. In addition, these polyethylene-based resins and / or polypropylene-based resin powders have MI = 0.02 ~
It is in the range of 30g / 10 minutes (temperature; 190 ° C, load; 2.16kg). In the present invention, the above-mentioned ultra high molecular weight polyethylene powder (A) and the polyethylene resin or / and the polypropylene resin powder (B) are (A) / (B) = 85/15 to 40/60.
The mixture is used in the range of (parts by weight). Within the range of this mixing ratio, a continuous porous sintered body having a high homogeneity in the average pore diameter and the average porosity can be obtained by the sintering forming method which is usually carried out. (A) / (B) = 80 to 20 to 40/60, and most preferably 80/20 to 50/50 (parts by weight). 85/15
If the content of (B) is less than the mixing ratio of (A), the effect of improving the tensile strength of the obtained porous sintered body is poor, and if the content of (A) is large, the sintering formability is poor, which is not preferable. 40/6
When (A) is less than the mixing ratio of 0, that is, (A) is 40
If it is less, (B) exceeds 60, and since (B) is a raw material that easily causes clogging, the sintered body also causes clogging. That is, the ultra high molecular weight polyethylene powder becomes a porous sintered body without clogging in a wide range of sintering conditions, but has a drawback that the tensile strength is weak. In addition, the polyethylene-based resin and / or the polypropylene-based resin has the opposite tendency as the MI value increases, and has the same tendency as the powder particle diameter decreases. From this, in the present invention, the relative comparison value of the average particle diameters of the ultrahigh molecular weight polyethylene powder (A) and the polyethylene resin or / and the polypropylene resin powder (B) is preferable (hereinafter, the average particle diameter ratio). It is preferable to make such a combination that the value of 3) is within the range of 3/1 to 1/3. If the combination of the average particle diameter ratios is within this range, the layer separation phenomenon due to the difference in the particle diameters of both is unlikely to occur. The bulk density and angle of repose of the powder are characteristic values that correlate with the filling property of the powder into the sinter molding die, and the higher the bulk density and the smaller the angle of repose, the more the powder is packed. The sex is good. The polyolefin resin of the present invention is a resin which is difficult to mechanically pulverize into a powder having a large bulk density and a low angle of repose. For this reason, a proposal regarding the pulverization of olefin resin, for example, a method of obtaining a polymer powder having a good powder fluidity by the addition of a pulverizing auxiliary agent, a freeze pulverization method, or a polymerization method, and a bulk density of the powder of 0.3 g
/ cc or more, the angle of repose of the powder is 45 degrees or less, preferably the bulk density is 0.3
More than 5g / cc and less than 40 degrees of repose are more useful.
A powder having a low bulk density and a large repose angle tends to be unfavorable because of poor filling in a mold. In the present invention, a bulk density of 0.6 g / cc or more cannot be obtained. Also, the angle of repose cannot be practically less than 20 degrees.

If the raw material powders obtained by using these selected materials and performing an appropriate combination are filled in a sintering die having a desired shape and sintered by a usual method, the resulting porous sintered body has an average pore diameter. It is possible to obtain a continuous porous sintered body having a high homogeneity in pore diameter and porosity of 10 to 150 μm and an average porosity of 25 to 45 V%, good air permeability, and improved tensile strength. When the intended porous sintered body has a large thickness, a relatively high proportion of ultra-high molecular weight polyethylene powder within the scope of the present invention produces good results.

(Operation / Effect) The operation of the selected materials, characteristics and combination of the ultra high molecular weight polyethylene powders (A) and (B) according to the present invention is mainly effected mainly by the pore diameter, porosity, air permeability and The action and effect on the tensile strength will be described.

The ultrahigh molecular weight polyethylene used in the present invention retains its original shape even if it is heated above its melting point and unless a considerably large external pressure is applied, and is poor in mutual fusion and fusion. On the other hand, when the polyethylene resin and / or the polypropylene resin is heated above the melting point, the polyethylene resin exhibits fluidity even with a slight external pressure as shown by its MI value, and is excellent in mutual fusion and fusion. The porous sintered body obtained will be unfavorable in terms of performance regardless of which of these characteristics is biased. Although preferably having both advantages, in the application field of the polyolefin resin, the amount of resin demand occupied by sintering is too small, and therefore it is not industrially produced and sold. Therefore, in the present invention, the present invention has been studied in order to express this characteristic by the combination of existing materials.
It has been found that a combination of materials with the above properties makes it possible. That is, if the material in which both powders are homogeneously mixed is used as a raw material for sintering and molding, both defects are largely eliminated, and the advantages of both are expressed, and further, it is also effective for unpredictable improvement of air permeability. It turns out that there is. There are many unclear reasons why a specific combination of both resin powders produces such action / effect, but to explain within the range that can be inferred, both mixed powders are heated ~ melted ~ melted in the mold etc. The role of ultra-high molecular weight polyethylene powder in the so-called loose sintering process is that the self-fusing property is poor and the shape is retained, thereby maintaining the voids between particles (maintaining the pore diameter and porosity). ) Work. On the other hand, polyethylene-based resin and / or polypropylene-based resin powder rapidly fluidizes above the melting point and tries to self-bond and fuse with each other, but it is separated by ultra-high molecular weight polyethylene particles interposed between the particles and self-particles. Fusion of fellows is hindered,
The fusion and fusion stop between the adjoining particles. This phenomenon can be observed by observing the heating and melting state of the mixed powder under a microscopic view and observing the actual fusion-bonded surface of the porous sintered body. Further, the resin in the melt flow state seems to be fused at the contact interface with the ultra-high molecular weight polyethylene particles retaining the shape, and in that state, it is stabilized to a considerably high temperature. This stabilization is important, and when trying to obtain a thick-walled porous sintered body, the outside (particularly the part in contact with the mold) is further fluidized by the time the internal resin powder reaches such a temperature. Then, the fusion progresses, and it is usually in a clogging state. The heating in sinter molding is usually stopped in the state where the powder in the innermost portion is insufficient for sintering, and the process proceeds to cooling, but the inside is sintered due to residual heat. The timing of transition from this heating stop to cooling is more difficult to determine as the sintered thickness is thicker, and conventionally it is also a part that relies on years of experience and intuition, but in the present invention fusion between particles progresses Since it is highly stable after being processed, this timing is very easy to take, in other words, the range of sintering conditions is wide, and it is a raw material that does not easily clog. In this way, the raw material powder of the present invention sinter-molded works well with particles that maintain pores and particles that fuse and form a part with a strong interparticle bond, resulting in a uniform pore diameter and porosity. It becomes a sintered body with high tensile strength. In addition, even a thick-walled molded product can be a porous body having high to homogeneity with little or no difference in pore diameter and porosity between the outside and the inside. Further, according to the present invention, it is possible to obtain a porous material which is superior in air permeability to the continuous porous body made of each resin powder. This is also the case, for example, when both particles having the same particle size are combined, and in particular, the effect that the air permeability is better than that of the ultrahigh molecular weight polyethylene resin powder alone is recognized. Although there are some parts where the action and factors that cause this effect have not been clarified, it is speculated that the particle shape of one lump may be changed due to the flow of the polyethylene resin and / or polypropylene resin powder particles during the sintering process to completion. It is believed that it flows and becomes rod-shaped to flat, which reduces the ventilation resistance. By the way, when observing the pore shape of such a porous sintered body,
The lateral lengths are uneven, and are numerically expressed as an increase in average pore diameter and a decrease in ventilation resistance. In the present invention, the main purpose is to improve the tensile strength, for that purpose it is essential that the mutual particle fusion power is high, for that the fusion of mixed powder particles may occur. It is a premise. Therefore, the object cannot be achieved with a combination of powders which do not show mutual fusion. For this reason, in the present invention, the same kind of resin or a combination of similar kinds of resins is used.

FIG. 4 is a schematic view of a ventilation resistance measuring device used for evaluating the air permeability of the continuous porous sintered body of the present invention. In the figure, 1 is a flow control valve through which air 8 having a pressure of 3 kg / cm ³ · G is supplied. Reference numeral 2 is a flow meter, and 600 l / mm (atmospheric pressure conversion value) of air is sent into the conduit 3 by adjusting the flow rate to 200 l / mm with the valve of 1. 5 is a porous sintered pipe of the test subject, and the upper and lower parts of this pipe are sealed with the packings 4 and 7 and the flange. The sent air escapes from the communicating holes of the pipe, and the resistance (back pressure) at that time is detected by the differential pressure gauge 6.

In the present invention, the back pressure detected by the differential pressure gauge 6 is referred to as ventilation resistance.

(Example) Example 1 An ultra high molecular weight polyethylene powder (trade name: San Huain UH-900, manufactured by Asahi Kasei Co., Ltd.) having a number average molecular weight of about 3.3 million and a resin density of 0.942 g / cm ² and different powder characteristics. Three kinds were prepared. These are designated UH-1, UH-2, and UH-3, respectively, and their powder characteristics are shown in order, and the particle size distribution of the powder is 30 to 100 Mesh, 7
Within the range of 0-200Mesh, 120-325Mesh, the total weight is 99.5W% or more, and the average particle size of the powder is 250μm, 120
μm, 75 μm. Bulk density is 0.40g / cc, 0.49g / cc
It is cc, 0.48g / cc, and the angle of repose is 31, 35, and 39 degrees. In addition, a high-density polyethylene resin powder having a resin density of 0.958 g / cm ³ (trade name: Sunfine SH-800, manufactured by Asahi Kasei Kogyo Co., Ltd.) was prepared. This is designated as SH-1, and its powder characteristics are shown as MI = 0.05g / 10min, and the particle size distribution of powder is 80-
Having more than 99% of the total in 200 Mesh, average particle size 125 μm,
It has a bulk density of 0.43 g / cc and an angle of repose of 29 degrees. Mix these powders in the proportions given in Table 1 together, and mold with a mold thickness of 2.5 mm.
9.5φ x 32 cm long aluminum tube with a 2.5 mm outer diameter 2 in the center
Place an aluminum tube of 8.5φ x 32 cm in length and prepare a mold with lids on the top and bottom of the pipe.
Fill the part m) until it is full. At the time of this filling, the vibrator was used to fill the whole mold under vibration with the powder, and no other external pressure was applied during the powder filling. The filling powder volume ratio to the mold volume at that time was described as the filling rate. Then, it was covered and heated in a hot air oven kept at a constant temperature. Table 2 also shows the furnace temperature and the charging time. The heating conditions shown in Table 2 are the conditions selected as a result of searching the optimum molding conditions for the sample. After completion of heating, the mixture was left at room temperature for 10 minutes, and then blown with a fan to cool it. Both ends of the pipe-shaped sintered body taken out from the mold were cut off to have a length of 300 mm.
A differential pressure gauge was attached to one of the porous sintered pipes, and air of an amount of 600 l / mm was sent from the other side, and the differential pressure at that time was described as ventilation resistance. Next, the pipe was cut into a width of 25 mm (hereinafter, referred to as a sintered ring). In the sintering ring
Two 10 mmφ iron bars were passed through and the iron bars were pulled vertically using a tensile tester. The pulling speed at this time is 50 mm / min
As a result, the maximum load withstanding the fracture of the sintered ring was taken as the tensile breaking strength, and when the tensile breaking strength of sample UH-2 was set to 1, the ratio with that of other samples is shown in Table 1. Indicated. Based on the obtained data, the relationship between the raw material mixture ratio and the tensile breaking strength is shown in Fig. 1, the relationship with the ventilation resistance is shown in Fig. 2, and the relationship between the ventilation resistance and the tensile breaking strength is shown in Fig. 3. . From these data, in the range of the present invention, the tensile strength is improved, the ventilation resistance is small, and as shown in FIG. 3, the one having the same ventilation resistance has considerably high tensile strength.

Example 2 UH-2 used in Example 1 and resin density 0.955g / cm ³ , MI
20 g / 10 mm high density polyethylene resin powder (JP) was prepared. The particle size distribution of the JP powder is 99% or more of the whole between 45 to 200 mesh, the average particle diameter is 250 μm, the bulk density of the powder is 0.41 g / cc, and the angle of repose is 31 degrees. With this UH-2
Sufficiently mixed JP in the proportions shown in Table 2, and sintered and molded in the same manner as in Example 1. Table 2 shows the results of similarly evaluating the properties of the obtained pipe-shaped sintered body. From the obtained data, the polyethylene resin or / and the polypropylene resin to be combined with the ultra high molecular weight polyethylene powder having a high MI value shows a tendency that the pore diameter tends to become unstable when the amount exceeds a certain level,
Within the scope of the present invention, the effects of improving tensile strength and reducing ventilation resistance are recognized.

[Brief description of drawings]

FIG. 1 shows the relationship between the mixing ratio of (A) and (B) of the present invention and the tensile fracture strength of the product, FIG. 2 shows the relationship with the ventilation resistance, and FIG. 3 shows the ventilation resistance and the tensile fracture strength. Shows the relationship with. FIG. 4 is a schematic view of a ventilation resistance measuring device used for evaluating the air permeability of the continuous porous sintered body of the present invention. In the figure, 1 is a flow control valve, 8 is supply air, 2 is a flow meter, 3 is a conduit, 5 is a porous sintered pipe of a test object, 4 and 7 are seals by packing and flange, and 6 is resistance ( This is a differential pressure gauge for measuring back pressure.

Claims (1)

[Claims] 1. An ultra high molecular weight polyethylene powder (A) having an average particle diameter of 50 to 500 μm, a bulk density of powder of 0.3 g / cc or more, and a repose angle of 45 degrees or less, and MI. Is 0.02 ~
30 g / 10 minutes, the average particle size is 50 to 500 μm, the range is 3/1 to 1/3 of the average particle size of (A), and the bulk density of the powder is 0.3 g / cc or more. Yes, the polyethylene resin or / and the polypropylene resin powder (B) having an angle of repose of 45 degrees or less is (A) / (B) = 85/15 to 40/60
(Parts by weight) mixed and sintered to obtain a porous sintered body having continuous pores with an average pore diameter of 10 to 150 μm and an average porosity of 25 to 45 V% (volume%). A method for producing a continuous porous sintered body.