DE2122367A1 - Method for producing a porous material - Google Patents

Description

Method for producing a porous material

The invention relates to a method for producing an air-permeable, microporous material which is a contains crystalline thermoplastic resin and has increased strength. The invention particularly relates to a process for the production of a microporous material, which consists of a crystalline, thermoplastic Resin composed, and which the grinding of a mixture of a crystalline, thermoplastic resin, 4er

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is used as a carrier and one or more other thermoplastic Resins that do not fully interact with the crystalline thermoplastic resin at a temperature above the melting temperature are compatible with the mixture, the molding of a shaped body and the selective removal of the non-crystalline, thermoplastic resins therefrom by extraction with a suitable solvent.

The microporous material obtained according to the invention is used as a filter material, as a separating membrane for cells, as a material for plates, membranes and similar shaped bodies in which microporosity is required, usable.

For the production of a porous material from a high molecular weight A large number of processes are already known to the substance, which are listed below:

1. a process in which a variety of foaming agents can be used to foam a high molecular weight To effect substance;

2. a method in which foaming of a high molecular substance is effected by mechanical means;

3. a method in which a high molecular substance is mixed with organic ψ or inorganic fine particles having a high melting point, which can be easily leached with water or a solvent and, after molding, the fine particles having the high melting point are leached;

4. a method in which a solvent, plasticizer or the like is used to form a gel of a high molecular substance, and then the solvent, plasticizer or the like is removed therefrom by extraction or evaporation.

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5. a method in which fine particles or fibers of a high molecular weight substance can be sintered, and

6. a method in which fine particles or fibers of a high molecular weight substance can be bonded together using a binder.

However, the methods 1 and 2 have a disadvantage that a porous material having continuous cells and high strength can hardly be obtained by this method. The method 3 has disadvantages in that the fine particles are independently dispersed in the resin and a considerably large amount of the fine particles are required to form through pores if a thick molded material is to be produced and these fine particles are further added thereto tend to remain in the molded material. The method H has a disadvantage that a porous material having high strength can hardly be obtained by this method. The method 5 also has the disadvantage that a porous material obtained by this method is generally poor in strength or a thin-pored material can hardly be obtained.

It has now been found that a paper- or leather-like, microporous Material containing a crystalline thermoplastic resin by mixing the crystalline thermoplastic resin Resin as a carrier with a thermoplastic resin different therefrom by means of a grinding method and then selective removal of the thermoplastic resin other than the crystalline thermoplastic resin by extraction can be.

It is a characterizing feature of the present invention to provide a microporous material which is flexible and has excellent strength. A comparison of the tensile strength of a porous material made from polyvinylidene fluoride (hereinafter referred to as PVDF for the sake of simplicity), which had been obtained according to the method according to the invention, with

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a porous material made of PVDP, which according to the above method 4 for example by dissolving the PVDP in cyclohexanone with heating, pouring the solution onto a glass plate, air cooling of the solution causing gelation, replacement of the cyclohexanone obtained in the gel by methanol and drying the gel ' had been, and with a porous material of PVDP, which by the aforementioned method 5, for example by sintering PVDP powders obtained showed that the porous material was about three times larger by the method of the present invention Exhibited strength than the material by either of the other two methods.

Another characteristic feature of the present invention is an air-permeable, with through-going micropores to create provided material. The porosity of the material can be determined by the type of thermoplastic resin, the mixing ratio, the grinding conditions, etc. can be varied.

Another feature of the present invention is the use of a crystalline thermoplastic resin as the thermoplastic resin carrier _n. The higher crystallinity of the resin results in good porous materials.

If in particular a porous material made of PVDP according to the invention Process is produced, it has the inherent excellent properties of PVDP, i. H. the end-" Signed resistance to chemicals, heat resistance, weather resistance and mechanical strength. The application of the material is used in particular in the area where chemical resistance is required.

Thermoplastic resins _s in accordance with the present invention as carriers are useful "are, advantageously such resins as PVDP, polyvinyl fluoride, polytrifluorochloroethylene, isotactic polypropylene, a copolymer of vinyl chloride and vinylidene chloride, low pressure polyethylene, polyamides, polyesters and polycarbonates, since these resins easily very porous materials result in and through

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Extraction can hardly be deformed. In particular, PVDF is in view to the fact that it provides porous materials with excellent chemical resistant properties, the am most usable resin. A thermoplastic resin which is mixed with this carrier resin or, in other words, a resin, which can be removed by extraction after molding should be one which contains at least one solvent is easily extractable and which does not dissolve the crystalline carrier resin.

It is not preferred that the extractable resin be melted together State is completely compatible with the crystalline carrier resin. In doing so, under "is fully compatible in a fused state "understood that one apparently transparent, homogeneous phase is formed when the two types of resin are heated to a temperature at which both resins be completely molten in the mixture. When two kinds of resin without complete compatibility according to the present Invention are used, then the resins are melted at a temperature slightly above the Melting point of the crystalline resin is opaque. When mixing the crystalline thermoplastic resin carrier with one therewith incompatible resin, a small amount of a resin compatible with the thermoplastic resin can be added, to increase or decrease the melt viscosity of the thermoplastic resin. But even in this case the amount must be of the added resin must be limited to such a range in which the components of the mixture are not completely mixed with one another are compatible.

According to the present invention, an easily extractable or leachable substance selected from the organic substances such as plasticizer, starch, etc. and the inorganic substances such as calcium carbonate can be added to the mixture of the resin if necessary to improve the porosity and the To vary the pore size of the molded material obtained. not

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Extractable fillers and additives such as carbon black, titanium white, etc. can also be added to the mixture.

When using PVDP as a carrier can be used as extractable resins that are poorly compatible with the PVDP or those with a Solvents are extractable which does not dissolve the PVDP, e.g. B. the following resins can be used: Polyvinyl chloride, polyethylene, polypropylene, polystyrene, polyester and other homopolymers; Styrene / methyl methacrylate copolymer, Ethylene / vinyl acetate copolymer, copolymeric vinylidene fluoride (e.g. vinylidene fluoride / tetrafluoroethylene copolymer in a molar ratio from 80:20), vinylidene chloride / acrylonitrile copolymer and other copolymers; chlorinated polyvinyl chlorides, chlorinated polyvinylidene fluorides and other modified resins.

The ratio between the crystalline thermoplastic resin used as the carrier and the other thermoplastic resin, which is mixed therewith and removed by extraction after molding is important and desirably lies in a range of 20 to 75 percent by weight of the former and 80-25 percent by weight of the latter. The use of the former in an extremely small amount causes deformation of the molded material after extraction of the latter resin or allows the formation of pores with poor uniformity. On the other hand, the use of an excessively large amount of the resin serving as a carrier gives rise to difficulties the extraction of the latter resin and tends to form pores which have no uniformity even if one such extraction is achieved.

The following is an example of an explanation for the inventive Method given to produce porous PVDP materials.

If an extractable resin, for example poly (methyl methacrylate ) (which is hereinafter referred to as PMMA for the sake of simplicity), which has a good affinity for PVDP, for the production

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If a porous carrier made of PVDF is used, the two resins are completely homogeneous in the molten state around the melting point of the PVDF and form a completely transparent melt which, after solidification, results in a highly transparent, shaped material. In many cases, however, the extraction of the PMMA from the molded material does not result in an air-permeable, porous material. If the amount of the PMMA is excessively large, for example at least 70 % , a hardly air-permeable swan-like material may be produced. However, it is impossible to form a uniform pore structure. The use of a resin that is completely compatible with the PVDF, for example PMMA alone as the extractable resin, which is mixed with the PVDF, is therefore not to be preferred.

On the other hand, if polyvinyl chloride, hereinafter referred to as PVC for the sake of simplicity, is selected as the extractable resin, a mixture of PVDF and PVC remains opaque even if the mixture is melted by heating to a temperature above the melting point of PVDF will. The mixture is thoroughly ground to give a homogeneous dispersion and solidified into an opaque molded material, which by extraction of the PVC gives a porous PVDF material with a fibrous structure, which at first glance looks like paper or leather. If the compounding proportion of PVC is extremely small, the air permeability becomes poor. When the amount of PVC is less than 30 % , the air permeability is gradually lost. The milling treatment is carried out by known means commonly used for thermoplastic resins, such as a roller mill, a Banbury mixer, etc. The milling temperature should be above the temperature at which each thermoplastic resin is substantially completely melted. Further, the milling operation should be carried out so that the milling state is kept as uniform as possible. If necessary, an auxiliary substance such as a surface active agent or a lubricant may be added to facilitate dispersion or milling. Because the porosity

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the pore size and the distribution of the pore sizes of the obtained porous material vary with the kind of resins or fillers, mixing ratio, freeness, etc. ₃ , these conditions should be determined appropriately. In other words, the porosity and the like can be controlled by the aforementioned variables.

The milled mixture is then molded by thermoforming under pressure. When a mixture of thermoplastic resins, their each having low affinity and low melt viscosity is molded with heating, so the mixture that is homogeneously dispersed to some extent by grinding, can be separated into two individual phases. In such a In this case, the time required for stationary heating is expediently shortened as far as possible. However, this is true not for the case where the resin has a relatively good affinity or where the resin has a high viscosity and can hardly be separated into two phases.

The molded material thus obtained is then treated with a solvent extracted, which is suitable, a thermoplastic resin, which with the serving as a carrier crystalline, thermoplastic Resin mismatch, selectively dissolve. In this case, the extraction treatment can be carried out in several stages using several kinds of solvents according to the number and solubility of the formed from the Mixture of resin to be extracted are selected, If the solvents alone selectively dissolve the resin to be extracted, any of these can be used. When there is a risk that the molded material will contract in the extraction treatment or deformed, the extraction treatment is preferably carried out so that the molded material Is supported or held by means of a frame or the like.

The following is an example of the selection of extraction solvents given. For example, for the production of a porous PVDF material by selective extraction of PVC a molded material of the PVDF-PVC series, tetrahydrofuran

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(hereinafter referred to as THP for the sake of simplicity), nitrobenzene and chlorobenzene can be used. In addition to THP are made for the production of a porous polypropylene material by extraction of PMMA a molded material of the polypropylene / PMMA series acetone and cyclohexanone are useful. Similarly, the extraction of chlorinated PVDP with THP, etc. can be carried out to obtain a porous To produce PVDF material from PVDP-chlorinated PVDF.

Together with the extractable thermoplastic resin, a organic or inorganic extractable filler can be used. In this case, a known extraction method can be used using water or the like. Subsequent to the extraction of the resin are used to leach out such a substance. Even in the case of a thick material, the extraction solvent penetrates the material and causes complete Extraction. When expecting a material with excellent chemical resistant property such as a porous PVDF material it is desirable to use other resins and fillers or additives from the porous material that are relevant to chemical resistance are poor to fully extract because of the retention of these substances in the molded material adversely affects the quality of the product.

The porosity, the pore size and the distribution of the pore size of the microporous material thus produced is determined by (1) the kind and combination of the thermoplastic resins, (2) the mixing ratio when grinding and the degree of grinding, (3) the number of extractable ingredients and the degree of extraction and (4) influenced by the type and proportion of fillers.

In line with this, it is necessary to carefully weigh these factors in order to be microporous To produce materials with the desired porosity, pore size and distribution of the pore size.

The microporous materials produced as fiction, contemporary methods retain their original shape they had before the ex traction with the solvent at. It is also possible to use microporous materials with no apparent contraction or deformation.

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generation due to the extraction. For example, when PVC is extracted from a molded material with THP, which

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contains a PVDF mixture with a suitable mixing ratio, thus no visible change is found in the dimensions of the resulting porous PVDF material.

The materials produced according to the method of the invention are generally a white opaque solid. An air-permeable microporous material which is continuous Has micropores and allows gas or liquid to pass through, can also be produced according to the method according to the invention will.

Because of these advantageous properties, the porous materials obtained by the process according to the invention can be used as Filter materials, as separating membranes for cells, etc. are used. Because the porous PVDF material has excellent chemical resistance Has properties, it is particularly suitable as a filter material for corrosive substances.

example 1

PVDF powder and PVC powder, each made by suspension polymerization were ground in various mixing ratios by means of a roller. In this procedure PVDF was first ground and then PVC was added in small portions with grinding. After the completion of the milling treatment the mixture was shaped into a thin plate about 0.2 mm thick and then into plates measuring 5 cm × 5 cm cut. The PVC was made from these molded materials with tetrahydrofuran for about 10 hours at reflux temperature extracted.

After the extraction, drying turned white, uniform obtained porous sheet of PVDF with an excellent strength, the dimensions of which had hardly changed compared to the original material.

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About 2 % of a stabilizer was included in the PVC (they were also used in the examples below). The grinding treatment was carried out under the following conditions: grinding temperature 170-175 ° C; Meal 20-5 minutes. In this case the actual temperature of the resin mixture was 5-10 ° higher than the roller temperature and both PVDF and PVC were practically in a molten state (similar to the examples below). The tensile strength and gas permeability of the porous PVDF material thus obtained are shown in Table 1. The tensile strength was determined on a sample 10 mm wide and 50 mm long at a tensile speed of 100 mm / min.

Table 1 Conditions for hot compression set

Mahlver- Pressem- Heating pressing time ratio temperature ( ⁰ C) time (min.) (Min.)

PVDF / PVC = 70/30 200 2 1

PVDF / PVC = 60M0 220 2 1

PVDF / PVC = 50/50 200 2 1

Tensile strength He Op

(kg / mm ² ) permeability permeability

Permeability permeability

negligible low negligible-

bar low 9.78 χ ΙΟ "- ⁵ 5. Hl χ 10" «

1.5 9.78 χ 10 £ 5. * »1 x 10 '

1.3 I.80 χ 10 ~ ⁵ 8.33 x 10-6

(The permeability test was carried out with a pressure difference of 34 cmHg).

Example 2

10 g of PVDF powder, 8 g of PVC powder and 2 g of PMMA powder, each obtained by suspension polymerization

ground by means of a roller.

The roll temperature was 170 ⁰ C and the total rolling time was 25 minutes.

In this process the PVDF was first milled, then PMMA was added with milling and finally PVC was also added with milling. After completion of the grinding treatment, the mi-

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Schung formed by pressing at 200 ⁰ C, in a thin plate 0.36 mm thick. PVC and PMMA were extracted from part of this plate using THP at reflux temperature. The extraction time was about 12 hours. In this way, a white, porous PVDP material with excellent strength was obtained, the dimensions of which did not differ from the original plate. The weight loss due to the extraction was $ 48.

The air permeability of this porous PVDP was:

1.26 10-7 moles

mm

cm. min. cmHg. (The pressure difference was 3 ¹ J cmHg.)

Example 3

10 g of PVDF powder and 10 g of PVC powder, each obtained by suspension polymerization, were ^{ground together with 2.5 g of dioctyl phthalate (DOP) for 20 minutes at 175 °} C. with the aid of a roller. In this procedure, the PVDF was first milled and then a mixture of PVC and DOP was gradually added with milling. After completion of the milling treatment, the mixture was (1 minute long preheating to 200 ⁰ C and then 0.5 minutes press) by hot pressing in a thin plate of 0.1 mm thickness formed. The PVC and DOP were extracted from a portion of this molded material by extraction with THF for 16 hours at reflux temperature. Thus, a uniform, white, porous PVDP material excellent in flexibility and strength was obtained. The weight loss in the extraction was 55% _S 5>

/ s

The gas permeability of this porous PVDF material was:

ρ - α ηκ ν m " ¹ * mol. mm

He ~ ^3s ^ —2 ~

cm. min. cmHg.

ρ - «i 7Xvia""^ mol. mm
0 ~ ¹ S'- ^{5 x χυ} - ^

2 cm. min. cmHg

(The pressure difference was 5 cmHg.)

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Example 4

10 g PVDP powder and 10 g of PVC powder, which were respectively obtained by suspension polymerization, were ground together with 2.5 g of fine CaCO-j-powder by means of a roll at 170 ⁰ C for 20 minutes. In this process, PVDF was first milled, then CaCO3 was added with milling, and finally PVC was also added with milling.

After completion of the milling treatment of the mixture in a thin plate having a thickness of 0.26 mm by hot pressing (2 minutes long preheating to 200 ⁰ C and 1 minute long pressing) molded. The PVC was first extracted from part of this plate by treatment with THP for about 10 hours at reflux temperature. In this condition, the weight loss was about 45 %.

This white plate was then immersed in a 3% chlorine-hydrogen acid in order to leach out the CaCO (by standing for 2 days at room temperature). In this way, a uniform, white, porous PVDF material excellent in strength was obtained. The final weight loss was 51 %

The gas permeability of this porous PVDF material was:

P _H = 2.98 χ 10 " ⁵

cm. min. cmHg.

P ₀ = 1.73 x ICf ⁵

cm .min. cmHg.

(The pressure difference was 34 cmHg.)

Example 5

12 g of polypropylene pellets and 8 g of PMMA, which had been obtained by suspension polymerization, were ^{ground by means of a roller at 170 °} C. for 20 minutes. After completing

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supply of grinding treatment was formed the mixture into a thin plate having a thickness of 0.17 now by hot pressing (2 minutes long preheating to 200 ⁰ C and 1 minute long pressing). Part of this plate was cut open and, as described in the previous example, extracted by treating with THF for 10 hours. The weight loss was 40 %. The strength of the obtained uniform white porous polypropylene was 1.0 kg / mm and the gas permeability was:

ρ - 1 02 ~ 5 mol. mm cmHg. ¹ He cm min. . = 5, 10. ΙΟ " ⁶ mol. mm cmHe. 02 cm min.

fc (The pressure difference was 3 ^ cmHG.)

The tensile strength was measured on a sample 10 mm wide and 50 mm long at a tensile speed of 100 mm / min.

Example 6

10 g of polyethylene pellets, which were obtained by the low pressure method and 10 g of PVC powder, which had been obtained by suspension polymerization were 20 minutes milled at 17O ⁰ C for. The milled mixture was mm in a thin plate having a thickness of 0.27 by hot pressing (2 minutes long preheating to I70 ⁰ C and 1 minute long pressing) molded. The PVC was extracted from a portion of this plate as described in the previous example by treating with THF for 10 minutes.

The extracted amount was 50 % and a uniform porous polyethylene was obtained, which had the following gas permeability:

P - 1 ^ 7 m " ^{5 mo1} · ^mm He * * 2

cm. min. cmHg.

D -nc-, λγΓ & mol. mm

02 '· ° 3 · 10 -ρ-

cm. min, cmHg.

(The pressure difference was 3 ² J cmHg.)

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Claims (8)

Claims A method for producing a porous material, characterized in that a mixture of a crystalline, thermoplastic resin as carrier material and one or more other extractable thermoplastic resins, which in the melted together state are not completely compatible with the crystalline, thermoplastic resin, at a temperature are ground above the melting point of the mixture and form a molded material and then the extractable thermoplastic resin is extracted from the molded material by extraction with a solvent which does not dissolve the carrier resin. 2. The method according to claim 1, characterized in that the mixture is further inorganic or organic fillers, plasticizers or additives are mixed in with the solvent to dissolve the thermoplastic resin are extractable, the mixture is then at a temperature above the melting point of the mixture is ground and a molded material is formed. 3. A method for producing a porous material, characterized in that a mixture of a crystalline, thermoplastic resin as carrier material, one or more other extractable thermoplastics Resins that, when melted together, do not have full compatibility with the crystalline, thermoplastic Resin contain an inorganic or organic filler that does not use a solvent for dissolution of the extractable thermoplastic resin can be extracted, but extracted with a different solvent or is leached, and, if necessary, plasticizers or fillers that are not extractable with the solvents are milled at a temperature above the melting point of the resins contained in the mixture -16-209828 / 0828 and forms a molded material molded therefrom Material by extraction with a solvent that does not dissolve the resin carrier, but the extractable, thermoplastic one Resin dissolves alone, the extractable, thermoplastic resin is removed and then the in extractable or leachable filler left on the molded material from the molded material is removed by extraction with a solvent which does not dissolve the resin carrier. 4. The method according to claims 1-3 "characterized in that ,, serving as carrier material _s crystalline thermoplastic resin of the group of polyvinylidene fluoride ,, polyvinyl fluoride, poly (trifluorochloroethylene), isotactic polypropylene ,, the Copolyraeren of the vinyl chloride ^ and low pressure VinylidenchloridSs Polyethylene, polyamides, polyesters and polycarbonates are selected, 5. The method according to claims 1 ~ 5 ₃ characterized; that the extracted are the! »Plastic resin when the resin carrier consists of polyvinylidene fluoride, from the group consisting of polyvinyl chloride _s polyethylene, polypropylene ₃ polystyrene ,, polyesters _s styrene / Methy 1-methacrylate copolymers _s Ethylene / vinyl acetate copolymers, copolymer vinylidene fluoride, vinylidene chloride / acrylonitrile P copolymers !! ^ chlorinated polyvinyl chloride, chlorinated polyvinylidene fluoride and modified resins thereof. 6. The method according to claims 1-3, characterized in that that the solvent for dissolving the extractable thermoplastic resin when the resin carrier and the thermoplastic resin are polyvinylidene fluoride and polyvinyl chloride, from the group consisting of tetrahydrofuran, Nitrobenzene and chlorobenzene is selected- -17- 2098 2 9/0828 7. The method according to claims 1-3 » characterized in that the solvent for dissolving the extractable thermoplastic resin when the resin carrier and the thermoplastic resin are polypropylene .und poly" (methyl methacrylate), from the group consisting of tetrahydrofuran, acetone and cyclohexanone is selected. 8. The method according to claim 3, characterized in that the filler used with the Solvent is not extractable, is carbon black or titanium white. ORIGINAL INSPECTED 209829/0828