JP2007254509A - Polylactic acid-based porous item - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biodegradable porous item that is mainly composed of a polylactic acid resin and exhibits excellent air permeability. <P>SOLUTION: The polylactic acid-based porous item has a water vapor transmission rate (WVTR) at 38&deg;C in 90% RH of at least 10,000 g &mu;m/(m<SP>2</SP>day), apparent density of at most 1.10 g/cm<SP>3</SP>and an absolute value of an orientation degree of at most 0.15, and is obtained by treating a polylactic acid molded item having a crystallinity of at most 30% with a mixed solvent of at least two solvents having a different penetration degree into an amorphous part of the polylactic acid. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a polylactic acid porous body having high air permeability.

As interest in environmental issues has increased in recent years, biodegradable plastics or plant-derived plastics that decompose in the natural environment after disposal have been required to reduce the burden on the environment and protect the natural environment. ing.
Polylactic acid resins, which are one of biodegradable plastics and plant-derived plastics, are in a class with relatively high oxygen permeability and moisture permeability, and generally has an oxygen permeability (OTR) at 23 ° C. and 65% RH. It is about 15000 cc · μm / (m ² · day · atm), or has a water vapor transmission rate (WVTR) at 38 ° C. and 90% RH of about 7500 g · μm / (m ² · day). However, for example, when polylactic acid resin is laminated on paper to make a wrapping paper such as a hamburger, the hamburger becomes messed up over time, and it is still transparent compared to paper alone or paper coated with an oil resistance agent. There has been a long-awaited demand for films with insufficient moisture and high moisture permeability.

As a polylactic acid-based porous film, a method by low temperature and high magnification stretching (Patent Document 1) is disclosed, but specific air permeability data is not shown. Since the production method is limited to stretching, it is not applied to a laminate film with paper produced by extrusion lamination. Moreover, although the method (patent documents 2-4) of extending | stretching by adding a lot of fine powder fillers is disclosed, in addition to the problem that a manufacturing method is limited to extending | stretching, a fine powder filler is contained in large quantities. Therefore, problems such as poor extrusion productivity, brittleness, contamination due to falling off of the filler, heavy film, and generation of a large amount of residue when incinerated may occur. Furthermore, as described in Patent Document 3 and Patent Document 4, it is difficult to stably obtain a porous body having a water vapor permeability exceeding 5000 g / (m ² · day).

On the other hand, Non-Patent Document 1 discloses a technique for crystallization when a 200 μm thick PLA sheet obtained by melt extrusion is immersed in acetone for 1 minute. There is no description about the breathability of the sheet, but the sheet density before and after immersion in acetone has decreased to 1.258 and 1.107 g / cm ³ , respectively. The increase of ² · day)) is estimated to be about 10%, which is still not enough.
JP-A-8-176331 JP-A-5-247245 JP 2003-82140 A JP 2004-149679 A Shigemitsu Murase, polylactic acid that contributes to the environment, molding process '05 Japan Society for Plastic Molding, May 31, 2005, p189-190

  An object of the present invention is to provide a biodegradable porous body excellent in air permeability mainly composed of a polylactic acid-based resin without requiring addition of a large amount of fine powder filler or stretching treatment.

The inventors of the present invention have reached the present invention as a result of intensive studies to achieve the above object. That is, the present invention is as follows.
(1) The water vapor transmission rate (WVTR) at 38 ° C. and 90% RH is 10,000 g · μm / (m ² · day) or more, the apparent density is 1.10 g / cm ³ or less, and the absolute value of the degree of orientation is 0 .Polylactic acid based porous material that is 15 or less.
(2) The polylactic acid based porous material according to (1), wherein the average pore diameter is 10 ⁻⁴ to 10 ³ μm.
(3) By treating a polylactic acid-based molded body having a crystallinity of 30% or less with a solvent, the water vapor transmission rate (WVTR) at 38 ° C. and 90% RH is 10000 g · μm / (m ² · day) or more. And a method for producing a polylactic acid based porous material having an apparent density of 1.10 g / cm ³ or less.
(4) The method for producing a polylactic acid based porous material according to (3), wherein the solvent is a mixed solvent of at least two kinds of solvents having different degrees of penetration into the amorphous part of polylactic acid.
(5) Use of the polylactic acid based porous material according to (1) or (2) as a gas permeable membrane.

  It is possible to stably provide a biodegradable porous body having a wide range of air permeability mainly composed of a polylactic acid-based resin without requiring addition of a large amount of fine powder filler or stretching treatment.

The porous body of the present invention needs to have a water vapor transmission rate (WVTR) at 38 ° C. and 90% RH of 10,000 g · μm / (m ² · day) or more. If it is below these transmittances, it cannot be said that the air permeability is significantly higher than that of a normal polylactic acid resin. Preferably, WVTR is 100000 g · μm / (m ² · day) or more, more preferably WVTR is 300000 g · μm / (m ² · day) or more, and most preferably WVTR is 1000000 g · μm / (m ² -Day) or more.

  The porous body of the present invention needs to be substantially non-oriented. When it is non-oriented, the dimensional change of the molded body is unlikely to occur, that is, an unacceptable change in transmittance due to the change in the hole shape is unlikely to occur. Furthermore, when it is non-oriented, a porous body can be efficiently obtained when obtaining a porous body by solvent treatment described later. Non-oriented means that the film is not actively stretched. For example, in the case of a film, the film is cooled and solidified by a tenter method, a double bubble method, etc., and then reheated and stretched at a temperature below the melting point. It means that the draw ratio is less than 4 times (preferably less than 3 times, more preferably less than 2 times, most preferably less than 1.5 times) as an area ratio obtained by multiplying the vertical and horizontal ratios. It can be said that the film and sheet obtained by the melt inflation method or the T-die cast method, the yarn obtained by the melt spinning method, and the hollow fiber are substantially non-oriented. A non-oriented porous body can be determined by, for example, the degree of orientation obtained from a diffraction peak of wide-angle X-ray diffraction. The degree of orientation takes a value of -0.5 to 1.0, and the complete orientation (alignment in the same direction) with respect to the orientation reference axis is 1 and the non-orientation is 0. The porous body in the present invention has an absolute value of the orientation degree within the porous body plane (through view) and within the porous body thickness plane (edge view / end view), preferably 0.15 or less, preferably 0.1 or less. More preferably, it is 0.05 or less, and most preferably 0.02 or less.

  The porous body of the present invention must contain a polylactic acid resin as a main component. The polylactic acid-based resin is a polylactic acid homopolymer and a copolymer containing lactic acid monomer units in an amount of 50% by weight or more, and is composed of a polylactic acid homopolymer and lactic acid, other hydroxycarboxylic acids and lactones It is a copolymer with a compound selected from the above. When the content of the lactic acid monomer unit is less than 50% by weight, the solvent resistance may change, and it may be difficult to obtain a porous structure by solvent treatment. Preferably, it is a polylactic acid homopolymer or a copolymer containing 80% by weight or more of a lactic acid monomer unit or a mixture of these copolymers, more preferably 90% by weight of a polylactic acid homopolymer or a lactic acid monomer unit. % Of a copolymer or a mixture of these copolymers.

  L-lactic acid and L-lactic acid are present as optical isomers in lactic acid, and polylactic acid obtained by polymerizing them contains about 10% by weight or less of D-lactic acid unit and about 90% by weight of L-lactic acid unit. Or a polylactic acid having an L-lactic acid unit of about 10% by weight or less and a D-lactic acid unit of about 90% by weight or more, an optical purity of about 80% or more, and a D-lactic acid unit of 10 It is known that there are polylactic acid having an L-lactic acid unit of 90% by weight to 90% by weight and 90% by weight to 10% by weight, and an amorphous polylactic acid having an optical purity of about 80% or less. The polylactic acid resin used in the present invention preferably contains at least 50% by weight of crystalline polylactic acid. In particular, when the porous body is made of a solvent, if the amorphous polylactic acid exceeds 50% by weight, the amorphous polylactic acid itself is inferior in solvent resistance, so that it is difficult to obtain a porous structure. In order to adjust the porous structure, it is preferable to add an amorphous polylactic acid resin to the crystalline polylactic acid in an amount of 50% by weight or less.

As a monomer used as a copolymerization component with lactic acid, as hydroxycarboxylic acid, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid Etc. Examples of the aliphatic cyclic ester include glycolide, lactide, β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, and lactones substituted with various groups such as a methyl group. Examples of the dicarboxylic acid include succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of the polyhydric alcohol include aromatic polyhydric alcohols such as bisphenol / ethylene oxide addition reaction products, Aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, glycerin, sorbitan, trimethylolpropane, neopentyl glycol, ether glycols such as diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, etc. Is mentioned. Examples of these copolymers include Puramate PD-150 (trade name) manufactured by Dainippon Ink and Chemicals, Inc. (lactic acid resin / sebacic acid-polypropylene glycol copolymer = 51/49 wt%, weight average molecular weight = 9. 81 × 10 ⁴ , molecular weight distribution = 1.91), Dai Nippon Ink Chemical Co., Ltd. Puramate PD-350 (trade name) (lactic acid resin / succinic acid-polypropylene glycol copolymer = 52/48 wt%, Weight average molecular weight = 60,000, molecular weight distribution = 1.82) can be used.

As a polymerization method of the polylactic acid resin, known methods such as a condensation polymerization method and a ring-opening polymerization method can be employed. Moreover, the method of increasing molecular weight using binders, such as a polyisocyanate, a polyepoxy compound, an acid anhydride, and polyfunctional acid chloride, can also be used.
The weight average molecular weight of the polylactic acid resin is preferably in the range of 10,000 to 1,000,000. When the molecular weight is 10,000 or more, the mechanical properties of the porous body tend to be excellent, and when it is 1000000 or less, the melt viscosity is in a range in which a porous body having stable physical properties can be easily obtained with a normal processing machine.
The porous body in the present invention has a so-called communication hole structure in which a large number of pores existing inside the molded body are connected to the surface of the molded body, and a desired excellent ventilation can be obtained by passing a substance such as a gas through the holes. It means something that has sex. In order to obtain a desired porous body, the apparent density (also referred to as bulk density) is preferably 1.10 g / cm ³ or less. The apparent density decreases as the porous structure develops. When comparing an example and a comparative example described later, when the apparent density is lower than about 1.10 g / cm ³ , the water vapor permeability increases rapidly. From this fact, it is presumed that a communication hole structure is taken when the apparent density is about 1.10 g / cm ³ or less. A more preferable apparent density is 1.00 g / cm ³ or less, a more preferable apparent density is 0.90 g / cm ³ or less, and a most preferable apparent density is 0.75 g / cm ³ or less.

As another index of the porous body, porosity can also be adopted. The porosity is calculated | required by the following formula | equation (1).
Porosity = 100-100 × (apparent density of porous body / density of material) (%) (1)
A preferable porosity is 15% or more, more preferably 20% or more, more preferably 30% or more, and most preferably 40% or more.
Since the water vapor particle diameter is about 10 ⁻⁴ μm and the water droplet particles are 10 ² to 10 ³ μm, a preferable average pore diameter is 10 ⁻⁴ to 10 in the case of a gas permeable membrane, particularly a waterproof / moisture permeable molded body described later. ² μm. The upper limit of the average pore diameter is more preferably 10 μm, and most preferably 1 μm. Further, the lower limit of the average pore diameter is more preferably 10 ⁻³ μm, and most preferably 10 ⁻² μm. Moreover, when using as a separation membrane, it is more preferable that the communicating hole has a network structure than the needle hole-like through hole. A preferred hole curvature is 1.1 or more, more preferably 1.5 or more, and most preferably 2.0 or more. The shape of the porous body is not particularly limited and may be a film, a sheet, a tube, a hollow fiber, or the like. When the porous body is obtained by immersing in a solvent, the thickness of the porous body is preferably smaller from the viewpoint of high air permeability when used as a highly permeable molded body, preferably 200 μm or less, More preferably, it is 100 micrometers or less, More preferably, it is 50 micrometers or less, Most preferably, it is 25 micrometers or less.

When the porous material of the present invention is added with an inorganic filler such as talc, calcium carbonate, silicon dioxide, titanium dioxide, mica, clay, carbon black, the weight thereof is 20% by weight or less based on the total amount of the porous material. Is preferred. Exceeding 20% by weight may cause problems such as poor extrusion productivity, brittleness, contamination due to falling off of filler, heavy film, and generation of a large amount of residue when incinerated.
A preferable method for obtaining a polylactic acid-based porous material having a water vapor transmission rate (WVTR) at 38 ° C. and 90% RH of 10,000 g · μm / (m ² · day) or more is a method of treating with a solvent. The water vapor transmission rate, apparent density, and porosity are within the desired range by selecting the solvent from the degree of crystallinity of the resin and the ease of erosion of the amorphous part of polylactic acid and adjusting the conditions for immersion in the solvent. can do.

  Examples of the solvent treatment method include a method of immersing the molded body in a solvent, a method of spraying a solvent on the molded body, and the like. For example, when the solvent is immersed in the molded body, the molded body is immersed for several seconds, and after the molded body is taken out, it is dried for several seconds to several minutes at room temperature or in a heated state. In addition, even if the immersion time is changed from several seconds to several tens of minutes, the porous forming ability does not change much, so a short time of several seconds to several tens of seconds is preferably selected from the viewpoint of productivity. At this time, the drying atmosphere can be reduced in pressure to increase the drying efficiency. The molded product before the solvent treatment is preferably obtained by heating and melting the resin once. The molded product obtained by extrusion molding such as a casting method or a melt inflation method, injection molding, hollow molding, powder Mention may be made of molded bodies obtained by molding or the like. In the case of a sheet / film, for example, in the casting method, the mixture is heated and melted and kneaded with an extruder, extruded into a sheet / film with a T-die or the like, and immediately cooled with a casting drum or the like to obtain a sheet / film. Also, in the inflation method, a sheet and a film are obtained by melting and kneading by heating and melting and kneading with an extruder, and melt-drawing the tubular resin extruded by the circular die from the molten state by the inflation method. The so-called solvent casting method for obtaining a film by removing the solvent from the polylactic acid solution is different from the solvent treatment according to the present invention, and the solvent treatment at the time of solvent casting is included in the solvent treatment for obtaining the porous body. I can't.

The mechanism for improving air permeability by solvent treatment is unknown, but voids are formed by crystallization of the solvent in the amorphous part, and the voids are connected by the generation of more than a certain amount of voids. It is thought that breathability increases by taking.
As the type of solvent, a solvent that erodes the amorphous part of polylactic acid, that is, a solvent having a high degree of penetration into the amorphous part, is preferred. Ketones such as acetone and methyl ethyl ketone, aromatic hydrocarbons such as toluene, ethers such as tetrahydrofuran, acetic acid A solvent that erodes the amorphous part of polylactic acid is selected from an ester such as ethyl. At this time, the polylactic acid molded body is preferably not highly oriented. The preferred degree of orientation of the polylactic acid molded body before the solvent treatment is such that the absolute values of the degree of orientation in the porous body plane (through view) and in the porous body thickness plane (edge view / end view) are both 0.15 or less. Is 0.1 or less, more preferably 0.05 or less, and most preferably 0.02 or less. Moreover, it is also preferable not to crystallize by heat treatment. The crystallinity of the polylactic acid molded product before the solvent treatment needs to be 30% or less, more preferably 20% or less, still more preferably 10% or less, and most preferably 1% or less. . If crystallization by oriented crystals or heat treatment is in progress, solvent resistance may be exhibited with respect to these solvents, and it may be difficult to obtain a desired porous structure.

  In addition, since solvent resistance (erosion to an amorphous part) changes with polylactic acid-type resin compositions, such as a D-lactic acid unit content and an L-lactic acid unit content, the solvent which is easy to erode the amorphous part of the polylactic acid mentioned above. That is, a solvent having a relatively high degree of penetration into the amorphous part and a solvent that does not easily erode into the amorphous part, that is, a solvent having a relatively low degree of penetration into the amorphous part, are mixed at an appropriate ratio. A method of adjusting the porous structure obtained by this is also preferably employed. Examples of the solvent that does not easily attack the amorphous part include water, alcohols such as ethanol, and aliphatic hydrocarbons such as hexane. For example, when immersing a thin film with a thickness of several tens of μm in a solvent treatment tank, if it is not sufficiently strong to resist feeding out the film due to excessive erosion of the solvent, for example, an acetone aqueous solution in which a small amount of water is added to acetone, Solvent treatment can be performed with a solvent obtained by mixing a small amount of alcohol with toluene. For example, in such a case, in the case of poly L-lactic acid, when the D-lactic acid unit content is about 4%, the acetone concentration of the acetone aqueous solution is preferably selected to be about 85 to 95%, and the D-lactic acid unit content is about 1 %, An acetone concentration of about 88 to 98% is preferably selected. Thus, the lower the D-lactic acid unit content, the higher the concentration of the solvent that easily erodes the amorphous part of polylactic acid such as acetone tends to be selected. Moreover, when the solvent concentration which is easy to erode an amorphous part is constant, there exists a tendency for a porosity to become low, so that D-lactic acid unit content is low.

  The porous structure can be adjusted by blending polylactic acid resin with other biodegradable resins that are resistant to solvents that easily attack the non-crystalline part of polylactic acid, or by copolymerizing with the above-mentioned polylactic acid resin. You can also This method can also improve the mechanical properties such as the elastic modulus and elongation at break of the porous body. The biodegradable resins used for this purpose include aliphatic polyesters obtained by polycondensation of aliphatic dicarboxylic acids and aliphatic diols as main components, aliphatic polyesters obtained by ring-opening polymerization of cyclic lactones, synthetic aliphatic polyesters, fungi Aliphatic fragrances having a structure in which aliphatic polyesters such as poly (hydroxyalkanoic acid) biosynthesized in the body, and a portion of these biodegradable polyesters are substituted with aromatic compounds within a range that does not lose biodegradability It is at least one biodegradable thermoplastic polyester resin selected from the group polyesters.

  Aliphatic polyesters obtained by polycondensation of aliphatic dicarboxylic acid and aliphatic diol as main components include aliphatic carboxylic acids such as succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid and dodecanedioic acid (raw It may contain aromatic carboxylic acids such as terephthalic acid and isophthalic acid as long as it does not interfere with degradability), ethylene glycol, 1,3-propion glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol Examples thereof include polycondensation selected from one or more aliphatic diols. Examples of aliphatic polyesters obtained by ring-opening polymerization of cyclic lactones include ring-opening polymers selected from one or more cyclic monomers such as ε-caprolactone, δ-valerolactone, and β-methyl-δ-valerolactone. Can be mentioned. Examples of synthetic aliphatic polyesters include copolymers of succinic anhydride, cyclic acid anhydrides such as ethylene oxide and propylene oxide, and oxiranes. In addition, as poly (hydroxyalkanoic acid) biosynthesized in the microbial cells, poly (3-hydroxybutyric acid), poly (3-hydroxypropionic acid), poly (3-hydroxyvaleric acid), poly (3-hydroxybutyric acid) -3-hydroxyvaleric acid) copolymer, poly (3-hydroxybutyric acid-3-hydroxyhexanoic acid) copolymer, poly (3-hydroxybutyric acid-3-hydroxypropionic acid) copolymer, poly (3-hydroxy Examples include butyric acid-4-hydroxybutyric acid) copolymer, poly (3-hydroxybutyric acid-3-hydroxyoctanoic acid) copolymer, poly (3-hydroxybutyric acid-3-hydroxydecanoic acid) copolymer, and the like. .

  Examples of the aliphatic aromatic polyester include polybutylene succinic acid terephthalic acid copolymer, polyethylene succinic acid terephthalic acid copolymer, polybutylene adipic acid terephthalic acid copolymer, polyethylene adipic acid terephthalic acid copolymer, polyethylene glutar Examples include acid terephthalic acid copolymer, polybutylene glutaric acid terephthalic acid copolymer, polybutylene succinic acid adipic acid terephthalic acid copolymer, and the like. As an example, Ecoflex (trade name) manufactured by BASF, Bionore (trade name) manufactured by Showa Polymer Co., Ltd., and Lunar (trade name) manufactured by Nippon Shokubai Co., Ltd. are marketed. Further, a thermoplastic starch-based polymer (for example, Matterby (trade name) manufactured by Novamont) and a resin whose chemical structure is partially modified (for example, corn pole (trade name) manufactured by Nippon Corn Starch Co., Ltd.) Can also be used. Of these, Bionore and Matterby, which are relatively excellent in moisture permeability, are preferably used when it is desired to obtain a highly moisture-permeable molded product. In addition, when importance is attached to the appearance of the porous body and the refinement and uniformity of the pore diameter, a resin excellent in compatibility with the polylactic acid resin (for example, Puramate PD-350 (trade name, manufactured by Dainippon Ink & Chemicals, Inc.) For example, when a thin film having a thickness of several tens of μm is immersed in a solvent treatment tank, a polylactic acid such as acetone or toluene is used by adding about 5 to 30% to the polylactic acid. Even if only the solvent that erodes the amorphous part of the film is used, the solvent can be processed without being excessively eroded to maintain the strength to resist the drawing of the film.

  As a polymerization method of the biodegradable thermoplastic polyester resin, a known method such as a direct method or an indirect method can be employed. In the direct method, for example, polycondensation is performed by selecting the dicarboxylic acid compound anhydride or derivative thereof as the aliphatic dicarboxylic acid component, and selecting the diol compound or derivative thereof as the aliphatic diol component and performing polycondensation. A high molecular weight product can be obtained while removing the water generated at the time. The indirect method can be obtained by adding a small amount of chain extender, for example, a diisocyanate compound such as hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate to the oligomer polycondensed by the direct method to obtain a high molecular weight. . The weight average molecular weight of the biodegradable thermoplastic polyester resin is preferably in the range of 20,000 to 5,000,000, and more preferably in the range of 50,000 to 500,000. When the molecular weight is 20,000 or more, the obtained porous material tends to have excellent practical properties such as mechanical strength and impact strength, and when the molecular weight is 5,000,000 or less, the moldability tends to be excellent.

Polymethyl methacrylate can be used as an impact modifier for polylactic acid resins. For example, TOYOTA Hybrid-PLA (trade name) manufactured by Toyota Motor Co., Ltd. can be used as the blended product of the polylactic acid resin and polymethyl methacrylate as long as the requirements and characteristics of the present invention are not impaired.
In any case, it is preferable that the proportion of lactic acid units in the resin in the porous body is 50% by weight or more. If it is less than 50% by weight, a porous structure with a solvent may not be obtained efficiently. More preferably, it is 70 weight% or more, More preferably, it is 80 weight% or more, Most preferably, it is 90 weight% or more.
In addition to the above resins, the porous body of the present invention contains known additives such as plasticizers, heat stabilizers, antioxidants, ultraviolet absorbers, antifogging agents, antistatic agents, rust inhibitors, It is possible to mix | blend in the range which does not impair the requirements and characteristics of this invention. Examples of the plasticizer used in the polylactic acid resin include an acetylated monoglyceride plasticizer (trade name: Riquemar PL-019 / manufactured by Riken Vitamin Co., Ltd.).

Next, the manufacturing method of the porous body of this invention is described.
As an example, a method for obtaining a porous body in which a porous polylactic acid resin film is laminated on paper will be described. After melt-kneading the polylactic acid resin with an extruder and extruding it into a sheet in a molten state with a T-die, it is cooled while laminating it on paper on a cast roll, and a laminate sheet of paper and polylactic acid resin film is formed. obtain. Then, after immersing in acetone or the like in a solvent treatment tank for a few seconds or spraying solvent fine particles on the polylactic acid side surface, the solvent is evaporated from the laminate sheet, and a highly breathable sheet of paper and porous polylactic acid resin film is formed. Obtainable. In addition, after obtaining a laminate sheet of paper and polylactic acid resin film by using a laminator with a polylactic acid film prepared separately with an adhesive or a thermal laminator without using an adhesive, a solvent is similarly used. After immersing in acetone or the like in a tank for several seconds and then evaporating the solvent, a highly breathable sheet of paper and porous polylactic acid resin film can also be obtained.

  In this case, an adhesive is selected that is highly breathable and that is resistant to the solvent used when the polylactic acid-based resin is made into a porous body and that maintains the adhesive strength within a practical range. Also, after immersing the polylactic acid resin film in acetone in a solvent tank for a few seconds, volatilize the solvent to obtain a porous polylactic acid resin film, and then dry laminate with paper using an adhesive. Alternatively, without using an adhesive, the temperature can be raised above the softening point of the porous polylactic acid-based resin film and thermally laminated with paper. Furthermore, after a paper is coated with a polylactic acid emulsion or the like, it can be treated with a solvent to form a porous body. In addition, when performing heat processing, it is preferable to carry out after solvent processing. It is not only energy efficient to perform heat treatment in combination with solvent drying, but if the heat treatment is carried out before solvent treatment and crystallization proceeds, the solvent resistance increases and the porous body becomes more efficient. It may be difficult to obtain.

The porous body thus obtained can be preferably used as a gas permeable membrane. The gas permeable membrane can selectively transmit only gas in an environment where liquid and gas coexist, for example. For example, in the case of a sheet or film, it is used for building materials such as dew condensation prevention, a bag for medical equipment for ethylene oxide gas sterilization treatment, a medical use as a base material for a patch, sanitary materials such as disposable diapers, and sports clothing.・ Agricultural uses such as rain clothing and soil covering films can be used as water vapor permeable sheets and films. Further, for example, the porous body of the present invention obtained after laminating or coating polylactic acid resin on paper is made of paper. The water resistance of the porous polylactic acid film can be added without hindering the excellent moisture permeability that it has. For example, when a wrapping paper such as a hamburger is used, the hamburger or the wrapping paper is messed up by excess moisture. The problems up to can be solved.
The porous body of the present invention can be made into a microfiltration membrane, an ultrafiltration membrane, a dialysis membrane, a reverse osmosis membrane, a gas separation membrane, and a liquid separation membrane depending on the pore diameter. As an oil-absorbing material or a drug release material in the form of fine particles, and as a hollow fiber, it is used in various applications such as various separation membranes such as leukocytes and bacteria. Other properties that can be expected as a porous material include weight reduction, heat insulation, soundproofing, and light diffusion function.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not specifically limited to an Example. In addition, the measuring method and evaluation method in an Example are as follows.
(1) Water vapor transmission rate Measured by the method of JIS K 7129B. The apparatus was PermaTran-W200 (product name) manufactured by Mocon, and the measurement conditions were 38 ° C. and 90 RH%.
When the measurement limit of the apparatus was exceeded, measurement was performed by appropriately reducing the measurement area with an aluminum mask. The unit is g · μm / (m ² · day).
(2) Apparent density (bulk density)
The measurement was performed according to the method of JIS K7222. A porous body having an area of 9 cm ³ is cut out, an average value of thickness is obtained with a micrometer, a volume is calculated, a weight of the porous body is measured, and an apparent density (g / cm ³ ) is calculated by dividing the weight by the volume. did. The measurement temperature was 23 ° C.

(3) Degree of orientation (fc)
The orientation degree of the porous body was measured using a wide-angle X-ray scattering measurement apparatus (RINT2500XG manufactured by Rigaku Corporation). The target is Cu and the wavelength of the generated X-ray is 1.54 angstroms. The tube voltage was 40 kV and the tube current was 100 mA. An imaging plate that is a two-dimensional detector was used as the detector. The diffraction intensity distribution in the azimuth direction of the diffraction peaks of the (200) and (110) planes of the polylactic acid resin having an X-ray scattering angle (2θ) of about 16.7 degrees is measured. It calculated from the degree of orientation (fc). When obtaining the degree of orientation in the porous body surface, X-rays are incident on the surface of the porous body from the vertical direction (through view), and when obtaining the degree of orientation in the thickness plane of the porous body, X-rays are applied to the surface of the porous body. Measurement is performed by entering from the parallel direction (edge view, end view). The porous body is thin in the form of a sheet film, and when measuring in edge view and end view, the sheet film is stacked so that the thickness is 2 to 3 times the incident X-ray beam diameter. X-rays are incident from (direction). The X-ray transmission thickness is set to an optimum value for each sample. In this measurement, it was about 1.5 mm. The orientation degree was calculated according to the following formula (2) and formula (3) as shown in “Plastic material in molding process (Sigma Publishing) p71-72”. I (φ) in the formula (3) was obtained from the formula (4). The calculation reference direction (azimuth angle 0 ° direction) for calculating the root mean square of the direction cosine of the azimuth is usually selected as a peak portion, but the situation differs depending on how the peak appears, and the present invention In, the calculation reference direction of the azimuth was selected so that the calculated degree of orientation was the largest, and the degree of orientation at that time was defined as the degree of orientation of the porous body.
fc = (3 <cos ² φ> −1) / 2 (2)

φ: azimuth angle from calculation reference direction I (φ): azimuth angle dependency of diffraction peak intensities of (200) and (110) planes

I (2θ, φ): Two-dimensional data 2θs obtained by performing necessary correction such as air scattering correction on the two-dimensional scattering pattern detected by the two-dimensional detector 2θs: The starting point 2θe of the diffraction peak on the (200) and (110) planes: End points of diffraction peaks of (200) and (110) planes

(4) Crystallinity The crystallinity of the molded body was measured using a wide-angle X-ray scattering measurement apparatus (RINT2500XG manufactured by Rigaku Corporation). The target is Cu and the wavelength of the generated X-ray is 1.54 angstroms. The tube voltage was 40 kV, the tube current was 100 mA, and Materials Data Inc. X-ray diffraction pattern analysis software Jade Ver. It calculated | required from the integrated intensity ratio by the multiple peak separation method using 6.0. A half width of 3 ° or more was handled as an amorphous peak.
(5) Ventilation resistance (sec / 100cc)
It measured with the Gurley type air permeability meter based on JIS P-8117. The pressure at this time is 0.01276 atm, the membrane area is 6.424 cm ² , and the amount of permeated air is 100 cc. The measurement temperature is 23 ° C.

(6) Average pore diameter and curvature The average pore diameter is the pore diameter measured by the “gas-liquid method” obtained by measuring the air permeability (venting resistance) and the water permeability described in Japanese Patent Application Laid-Open No. 11-130900. The average pore diameter was used. That is, the details will be described below.
First, for the measurement of water permeability, a porous body previously immersed in alcohol is set in a stainless steel liquid-permeable cell having a diameter of 42 mm, and after the alcohol in the porous body is washed with water, a differential pressure of about 0.5 atm is obtained. The water permeability per unit time, unit pressure, and unit area was calculated from the water permeability (cm ³ ) when 120 seconds passed, and this was calculated as the water permeability (cm ³ / (cm ² · sec · atm)). The measurement temperature is 23 ° C.

  The average pore diameter and curvature (= pore length / membrane thickness) are calculated as follows. It is known that the fluid inside the capillary follows the flow of Poiseuille when the mean free path of the fluid is smaller than the pore diameter of the capillary and the flow of Knudsen when it is larger. Here, assuming that the air flow in the air permeability measurement according to JISP-8117 follows the flow of Knudsen and the water flow in the air permeability measurement at room temperature follows the Poiseuille flow, the average pore diameter d (m) and the curvature ratio τ is air transmission rate constant Rgas, water transmission rate constant Rliq, water viscosity η (Pa · sec), standard pressure Ps (101325 Pa), porosity ε (dimensionless), film thickness L (m), gas From the molecular velocity ν (m / sec), the following equations (5) and (6) can be used.

d = 2 [nu] (Rliq / Rgas) (16 [eta] / 3) (1 / Ps) (5)
τ ² = dεν / (3L · Ps · Rgas) (6)
Here, Rgas is obtained from the air permeability (sec) using the following equation (7).
Rgas (m ³ / (m ² · sec · Pa)) = 0.0001 / air permeability / 0.0006424 / (0.01276 × 101325) (7)
Rliq is obtained from the water permeability (cm ³ / (cm ² · sec · atm)) using the following equation (8).
Rliq (m ³ / (m ² · sec · Pa)) = water permeability / 1000000 / 0.0001 / 101325 (8)
Furthermore, ν is obtained using the following equation (9) from the gas constant R (8.314), the absolute temperature T (K), the circumference ratio π, and the average molecular weight M (kg / mol) of the gas.
ν ² = 8RT / πM (9)

(7) Sheet / film thickness (μm)
The total thickness of the sheet / film was measured using a micrometer according to JIS K-7130.
Table 1 shows the resins or raw materials used.

[Example 1]
The crystalline polylactic acid D4 shown in Table 1 is extruded into a tube shape in a molten state using a melt inflation method, that is, a circular die (lip clearance 1.6 mm), and the air is blown into the tube while blowing air at about 25 ° C. from the cooling ring. The film obtained by injecting air into the film to form bubbles was led to a pinch roll, and the tube-shaped film was made into two flat films (thickness of each film 35 μm) and wound up by a winding roll. In the wide-angle X-ray scattering of the film, no clear crystal-based scattering peak was observed, confirming that the film was substantially amorphous. At this time, the degree of orientation was 0.028 (through view) and 0.069 (edge view). The film was immersed for 20 seconds in an acetone 90 wt% aqueous solution maintained at a temperature of 10 to 20 ° C. and taken out at room temperature. Further, after standing at room temperature for 3 days and sufficiently drying, the thickness, apparent density, and water vapor transmission rate of the porous film were measured and shown in Table 2. Moreover, the orientation degree of the obtained porous body was 0.005 (through view) and 0.017 (edge view).

[Examples 2 to 6]
A film having a thickness of 35 μm was obtained from the composition shown in Table 2 in the same manner as in Example 1. In wide-angle X-ray scattering of these films, no clear crystal-based scattering peak was observed, confirming that the film was substantially amorphous. Furthermore, the solvent process was performed by the method similar to Example 1 with the acetone aqueous solution of Table 2, and the porous film was obtained. The results of evaluating the porous film are shown in Table 2. It can be seen that the apparent density tends to increase even with the same acetone concentration by adding PES having solvent resistance to acetone. In any film, the orientation degree before the solvent treatment and the orientation degree of the porous body after the solvent treatment were the same as those in Example 1.

[Example 7]
After obtaining a film of the composition shown in Table 2 in the same manner as in Example 1, the film was sprayed with about 50 ml / m ² of the solvent shown in Table 2 (acetone 90% aqueous solution) and taken out at room temperature for 3 days. Allowed to dry thoroughly. Table 2 shows the results of obtaining a porous film and evaluating it in the same manner as in Example 1.

[Example 8]
After melting and kneading the crystalline polylactic acid D4 shown in Table 1 and extruding it into a sheet in a molten state with a T-die, it was cooled with a cast roll adjusted to 40 ° C. to obtain a sheet having a thickness of 150 μm. In the wide-angle X-ray scattering of the film, no clear crystal-based scattering peak was observed, confirming that the film was substantially amorphous. At this time, the degree of orientation was 0.0063 (through view) and 0.020 (edge view). The film was immersed for 20 seconds in an acetone 90 wt% aqueous solution maintained at a temperature of 10 to 20 ° C. and taken out at room temperature. Further, after standing at room temperature for 3 days and sufficiently drying, the thickness, apparent density, and water vapor transmission rate of the porous film were measured and shown in Table 2. Further, the degree of orientation of the obtained porous body was the same as that of the porous body of Example 1.

[Example 9]
After melt-kneading the highly crystalline polylactic acid D1 shown in Table 1 and extruding it into a sheet in a molten state with a T-die, the sheet was cooled with a cast roll adjusted to 40 ° C. to obtain a sheet having a thickness of 80 μm. In the wide-angle X-ray scattering of the film, no clear crystal-based scattering peak was observed, confirming that the film was substantially amorphous. Further, the degree of orientation at this time was equivalent to that in Example 8. The film was immersed for 60 seconds in an acetone 95 wt% aqueous solution maintained at a temperature of 10 to 20 ° C. and taken out at room temperature. Further, after standing at room temperature for 3 days and sufficiently drying, the thickness, apparent density, and water vapor transmission rate of the porous film were measured and shown in Table 2. Further, the degree of orientation of the obtained porous body was the same as that of the porous body of Example 1.

[Comparative Example 1]
The results of evaluating the film (thickness 35 μm) before solvent treatment in Example 1 in the same manner as in Example 1 are shown in Table 2.

[Comparative Example 2]
A film obtained by subjecting the composition described in Table 2 to a solvent treatment in the same manner as in Example 1 was obtained, and the evaluation results are shown in Table 2. This has an apparent density of 1.18 g / cm ³ and suggests the formation of voids. However, since the acetone concentration is low, the pore-forming ability is insufficient, and the apparent density is outside the scope of the present invention. Therefore, when compared with the porous body of the present invention, the water vapor permeability was very low.

[Comparative Example 3]
A film obtained by subjecting the composition described in Table 2 to a solvent treatment in the same manner as in Example 1 was obtained, and the evaluation results are shown in Table 2. However, after obtaining the film, it was allowed to stand at room temperature for one month until the solvent treatment. This is obtained by adding PL-019, which is a plasticizer used for polylactic acid-based resins. Normally, the addition of a plasticizer increases the gas permeability, but this has an apparent density of 1.15 g / cm ³ , suggesting the formation of voids, but has a crystallinity of 5% before solvent treatment. The apparent density is outside the scope of the present invention because the polylactic acid content is as low as 70% and the acetone concentration is low, and the water vapor transmission rate is very low when compared with the porous body of the present invention. .

[Comparative Example 4]
The film before the solvent treatment of Example 3 was further heat-treated at 110 ° C. for 10 minutes with a fixed temperature hot air dryer manufactured by Advantech, with the four sides fixed, and the crystallization was sufficiently advanced to a crystallinity of 40%. The solvent treatment was performed in the same manner as in Example 1 after setting the acetone concentration to 100%. As a result, the solvent hardly penetrated, and the apparent specific gravity and water vapor transmission rate were the same as those in Comparative Example 1.

  The porous body of the present invention is used as a gas permeable membrane, for example, in the case of a sheet or film, as a building material application such as dew condensation prevention, a medical instrument bag for ethylene oxide gas sterilization treatment, or a patch base material Hamburgers when used in medical applications, sanitary materials such as paper diapers, sports clothing and rain clothing, agricultural applications such as soil coating films, electronic materials such as battery separators, and paper laminates or coated paper It can be used as a food packaging material such as wrapping paper. In the case of fine particles, it can be used as an oil-absorbing material or a drug release material, and in the case of hollow fibers, it can be used for applications such as separation membranes for leukocytes and bacteria.

Claims (5)

The water vapor transmission rate (WVTR) at 38 ° C. and 90% RH is 10000 g · μm / (m ² · day) or more, the apparent density is 1.10 g / cm ³ or less, and the absolute value of the degree of orientation is 0.15 or less. A polylactic acid based porous material. Polylactic acid-based porous body according to claim 1, wherein the average pore size of ¹⁰ -4 ^{~10 2 μm.} By treating the polylactic acid-based molded body having a crystallinity of 30% or less with a solvent, the water vapor transmission rate (WVTR) at 38 ° C. and 90% RH is 10,000 g · μm / (m ² · day) or more, A method for producing a polylactic acid-based porous material having an apparent density of 1.10 g / cm ³ or less.   The method for producing a polylactic acid-based porous material according to claim 3, wherein the solvent is a mixed solvent of at least two kinds of solvents having different degrees of penetration into the amorphous part of polylactic acid.   Use of the polylactic acid based porous material according to claim 1 or 2 as a gas permeable membrane.