JP3167411B2 - Porous film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrolyzable porous film, and more particularly, to a polylactic acid-based resin composition mainly composed of a lactic acid-based polymer having hydrolyzability in a natural environment, and a fine powder filler. The present invention relates to a hydrolyzable porous film containing: The porous film of the present invention is moisture-permeable, rich in air permeability, and excellent in flexibility, and is suitable for applications such as a leak-proof film of a sanitary material such as a disposable paper diaper, a packaging material, and a filtration material. In addition, since the polylactic acid-based resin composition is used, it has hydrolyzability. For this reason, it can be said that this material is also expected in the waste disposal problem, which has become a major problem in recent years.

[0002]

2. Description of the Related Art A porous film obtained by blending an organic or inorganic incompatible substance with a polyolefin resin or the like at a specific ratio, melt-forming the film, and then stretching is known. I have. (Japanese Patent Publication No. 53-12542
JP-A-56-99242, JP-A-57-5972
7, JP-A-60-129240, JP-A-62-13
No. 8541) The porous films disclosed therein are, among the above uses,
This is a so-called disposable application that is mainly used as a leak-proof film or packaging material for sanitary materials such as disposable paper diapers, and is generally discarded immediately after use. However, porous films formed from polyolefin-based resins do not hydrolyze in the natural environment or have extremely low hydrolysis rates, so if they are buried after use, they remain semi-permanently in the ground. Will be done. In addition, when speculation is carried out by the ocean, the landscape is damaged or the living environment of marine life is destroyed.

Hitherto, a porous film that is hydrolyzed in a natural environment has not been known. Polylactic acid and its copolymers are known as thermoplastic and hydrolyzable polymers. These lactic acid-based polymers are obtained by fermenting inexpensive raw materials such as corn starch and corn syrup, and also from petrochemical raw materials such as ethylene. U.S. Pat. No. 1,995,970 describes lactic acid,
A method for producing a lactic acid-based polymer for the polymerization of lactide or a mixture thereof is disclosed. This lactic acid-based polymer is used as a suture for surgery and a sustained-release material for medicine due to its biocompatibility and hydrolyzability. However, lactic acid-based polymers such as polylactic acid lack flexibility, and it has been difficult to process the polymer into a porous film. Therefore, a hydrolyzable porous film made of a polylactic acid resin has not been known.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a hydrolyzable porous film.

[0005]

Means for Solving the Problems The present inventors have studied diligently to achieve the above object, and have specified a specific amount of a lactic acid-based polymer.
By adding a specific amount of fine powder filler to a polylactic acid-based resin composition containing a specific amount of a plasticizer, forming a melt film, and stretching, a porous film having moderate softness and hydrolyzability can be obtained. This led to the completion of the present invention.

That is, the present invention relates to a polylactic acid or lactic acid-hydroxycarboxylic acid copolymer having an average particle diameter of 100 to 100 parts by weight of a polylactic acid-based resin composition containing 80 to 100% by weight and a plasticizer of 0 to 20% by weight. Is 0.3-4μ
m is a porous film obtained by melt-forming a mixture to which 40 to 250 parts by weight of a fine powder filler is added, and then stretching at least 1.1 times or more in at least one axial direction.

[0007] The hydrolyzable porous film of the present invention is characterized by having hydrolyzability. A polylactic acid-based resin composition having a specific composition is added with a fine powder filler having a specific particle size, and a Henschel mixer is used. After mixing, etc., pelletize or not, melt-knead using a single-screw or twin-screw screw extruder, extrude from an annular or linear die to form a film, and then expand it to make it porous. To form a porous film.

Hereinafter, the present invention will be described in detail. The lactic acid-based polymer used in the present invention is polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid. Examples of the hydroxycarboxylic acid used as a comonomer include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxypentanoic acid, hydroxycaproic acid, and hydroxyheptanoic acid. The molecular structure of a preferred polylactic acid is such that the units 85-1 of either L-lactic acid or D-lactic acid
It is composed of 00 mol% and 0 to 15 mol% of lactic acid units of each enantiomer. The copolymer of lactic acid and hydroxycarboxylic acid is composed of 85 to 100 mol% of either L-lactic acid or D-lactic acid units and 0 to 15 mol% of hydroxycarboxylic acid units. Preferred hydroxycarboxylic acids include glyceric acid and hydroxycaproic acid. These lactic acid-based polymers can be obtained by selecting a material having a required structure from L-lactic acid, D-lactic acid and hydroxycarboxylic acid as a raw material and subjecting it to dehydration polycondensation. Preferably, lactide, which is a cyclic dimer of lactic acid, glycolide, which is a cyclic dimer of glycolic acid, or caprolactone, is selected to have a required structure, followed by ring-opening polymerization. Lactide includes L-lactide which is a cyclic dimer of L-lactic acid, D-lactide which is a cyclic dimer of D-lactic acid, and D
-Meso-lactide in which lactic acid and L-lactic acid are cyclically dimerized, and DL-lactide which is a racemic mixture of D-lactide and L-lactide. In the present invention, any lactide can be used. However, the main raw material is preferably D-lactide or L-lactide.

The preferred lactic acid-based polymer used in the present invention is a unit of 85 to 1 units of either L-lactic acid or D-lactic acid.
A lactic acid-based polymer composed of 00 mol% and its enantiomer lactic acid unit or 0 to 15 mol% of a lactic acid unit and a glycolic acid unit of the enantiomer.
Can be obtained. About 85 mol% or more of L-lactide and about 15 mol% or less of D-lactide and / or glycolide are copolymerized. About 85 mol% or more of D-lactide and about 15 mol% of L-lactide and / or glycolide are used.
L-lactide is copolymerized with about 70 mol% or more and DL-lactide and / or glycolide is about 30 mol% or less.
Lactide is copolymerized with about 70 mol% or more and meso-lactide and / or glycolide about 30 mol% or less.
L-lactide and / or glycolide are copolymerized with about 30 mol% or less.
More than 0 mol% and less than about 30 mol% of meso-lactide and / or glycolide are copolymerized.

These lactic acid-based polymers preferably have a high molecular weight, and the inherent solution viscosity of a chloroform solution (25 ° C.) having a concentration of 0.5 g / dl is preferably 1 to 10, and more preferably 3 to 7 It is. If the inherent solution viscosity is less than 1, the melt viscosity is too low to flow down from the slit of the die of the extruder, and it is not only difficult to mold, but also too brittle and difficult to handle. Is too high, so that extrudability and the like are deteriorated.

In order to polymerize lactide or lactide and glycolide to obtain a high molecular weight polymer in a short time, it is preferable to use a catalyst. As such a polymerization catalyst, various catalysts having a catalytic effect on this polymerization reaction can be used. For example, as well-known substances, mainly polyvalent metals such as stannous octoate, tin tetrachloride, zinc chloride, titanium tetrachloride, iron chloride, boron trifluoride ether complex, aluminum chloride, antimony trifluoride, and lead oxide And a tin compound or a zinc compound is preferably used. Of the tin compounds, stannous octoate is particularly preferred. The amount used is preferably about 0.001 to 0.1% by weight based on the total amount of lactide or lactide and glycolide.

In the polymerization, a known chain-enhancing agent can be used. As the chain-enhancing agent, higher alcohols such as lauryl alcohol and hydroxy acids such as lactic acid and glycolic acid are preferably used. The coexistence of a chain-enhancing agent increases the polymerization rate, so that a polymer can be obtained in a short time. Also, the molecular weight of the polymer can be adjusted by adjusting the amount of the chain enhancer. However, if the amount of the chain-enhancing agent is too large, the molecular weight of the produced polymer tends to be small. Therefore, when the chain-enhancing agent is used, the amount is 0 to lactide or the total amount of lactide and glycolide. 0.1% by weight or less.

In the polymerization or copolymerization, a solvent may or may not be used. However, in order to obtain a high molecular weight polymer, it is preferable to carry out bulk polymerization in a molten state of lactide or glycolide. In the case of melt polymerization, the polymerization temperature may be, in principle, a temperature equal to or higher than the melting point of lactide as a monomer or lactide and glycolide (around 90 ° C.). For example, in the case of solution polymerization using a solvent such as chloroform, it is possible to perform polymerization at a temperature lower than the melting point of lactide or lactide and glycolide. In any case, if the temperature exceeds 250 ° C., decomposition of the produced polymer occurs, which is not preferable.

The polylactic acid-based resin composition used in the present invention is a resin composition containing 80 to 100% by weight of the lactic acid-based polymer and 0 to 20% by weight of a plasticizer.

Examples of the plasticizer used in the present invention include phthalic acid derivatives such as di-n-octyl phthalate, di-2-ethylhexyl phthalate and dibenzyl phthalate; isophthalic acid derivatives such as diisooctyl phthalate; -Adipic acid derivatives such as -butyl adipate and dioctyl adipate; maleic acid derivatives such as di-n-butyl malate; citric acid derivatives such as tri-n-butyl citrate; itaconic acid derivatives such as monobutyl itaconate; Examples include oleic acid derivatives, ricinoleic acid derivatives such as glycerin monoricinoleate, phosphate plasticizers such as tricresyl phosphate and trixylenyl phosphate, lactic acid, linear lactic acid oligomers, cyclic lactic acid oligomers, and lactide. it can. These plasticizers may be used alone or in combination of two or more. Among the above plasticizers, lactic acid, linear lactic acid oligomer, cyclic lactic acid oligomer or lactide is preferably used in terms of the plasticizing effect.

The lactic acid oligomer can be easily prepared by subjecting lactic acid to thermal dehydration condensation at 50 to 280 ° C. Usually, the degree of polymerization of the oligomer obtained by this method is about 1 to 30. In addition, glycolide or lactide is converted to 50 to 2 in the presence of water and glycolic acid or lactic acid.
It can also be prepared by heating to 80 ° C. The oligomer referred to in the present invention also includes lactide (a cyclic dimer of lactic acid) used as a monomer during the synthesis of the lactic acid-based polymer.

By adding the above-mentioned plasticizer to the lactic acid-based polymer, the lactic acid-based polymer is effectively plasticized, and the obtained resin composition becomes flexible. When the amount of the plasticizer in the resin composition is 5% by weight or more, flexibility becomes apparent, and when it exceeds 20% by weight, the moldability when the composition is melt-extruded and stretched becomes poor, and However, it is not preferable because the strength of the obtained molded article is weakened.

As a method of mixing a plasticizer with a lactic acid-based polymer, the lactic acid-based polymer is mixed with chloroform, methylene chloride,
Examples thereof include a method of dissolving in a solvent such as toluene and xylene, or a method of heating and melting a lactic acid-based polymer at 100 to 280 ° C. and adding and mixing a predetermined amount of a plasticizer. In the case of using lactic acid or a lactic acid oligomer (including lactide), which is a preferable plasticizer, the following two methods can be exemplified as a mixing method. (A) a method in which lactide or lactide and glycolide are polymerized to leave unreacted lactide without completing the reaction; (b) a predetermined amount of lactic acid or lactic acid oligomer after the polymerization of lactide or lactide and glycolide is completed (Including lactide). Further, the methods (a) and (b) may be used in combination. In the method (a), unreacted lactide is microscopically mixed well with the lactic acid-based polymer, and shows a good plasticizing effect. The monomer (lactide) is heated in the presence of a catalyst, possibly in the presence of a chain-enhancing agent, to start the reaction, and then, when the desired residual monomer concentration is reached, the heating is stopped to stop the reaction. The amount of residual monomer in the resulting lactic acid-based polymer can be determined by gas chromatography analysis and thermogravimetric analysis. In the method (b), after the polymerization reaction is completed, the obtained lactic acid-based polymer is dissolved in a solvent such as chloroform, methylene chloride, toluene, and xylene, or the lactic acid-based polymer is heated and melted at 100 to 280 ° C, A predetermined amount of lactic acid or lactic acid oligomer is added and mixed. This method has the advantage that the amount of lactic acid or lactic acid oligomer in the composition can be easily adjusted.

The polylactic acid-based resin composition obtained by the above method is formed at 180 to 280 ° C. by compression molding, melt extrusion molding or the like to form a film, sheet, rod or the like. After cooling to about −20 ° C. using a pulverizer, pulverizing using a hammer mill or the like,
Alternatively, it may be pelletized by melt extrusion or the like. A finely divided filler is mixed with the pulverized or pelletized polylactic acid-based resin composition. When the plasticizer is mixed with the polylactic acid-based resin, a fine powder filler may be mixed at the same time.

The fine powder filler used in the present invention is an inorganic fine powder or an organic fine powder. Examples of the inorganic fine powder include calcium carbonate, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, and the like. Zinc oxide, magnesium oxide, calcium oxide, titanium oxide, magnesium oxide, alumina, aluminum hydroxide, hydroxyapatite, silica, mica, talc, kaolin, clay, glass powder, asbestos powder, zeolite, silicate clay, and the like are particularly used. , Calcium carbonate, magnesium oxide, barium sulfate, silica,
Silicate clay is preferably used. Cellulose-based powders such as wood powder and pulp powder are used as the organic fine powder.

The average particle size of these fine powder fillers is preferably 0.3 to 4 μm. More preferably, it has the above particle size and a specific surface area of 15 m ² / g or less. Those having a specific surface area of 0.5 to 5 m ² / g are more preferred. If the average particle size is more than 4 μm, the stretchability of the film is poor, and the film may be broken before whitening uniformly. For this reason, the work stability is inferior and the film cannot be uniformly porous, which is not preferable. On the other hand, if it is less than 0.3 μm, the inorganic fine powder cannot be filled at a high level, and the film cannot be made porous. On the other hand, if the specific surface area exceeds 15 m ² / g, the shape of the inorganic fine powder becomes amorphous, plate-like, needle-like, etc., so that the particle size distribution becomes wide, the stretchability of the film decreases, and the film becomes porous. It is not preferable because the moldability for forming the film is reduced. The amount of the fine powder filler to be used is 40 to 250 parts by weight, preferably 60 to 150 parts by weight, per 100 parts by weight of the polylactic acid-based resin composition.
Parts by weight. If the amount is less than 40 parts by weight, sufficient porosity and insufficient communication holes cannot be obtained because of insufficient porosity, so that sufficient air permeability and moisture permeability cannot be obtained. And stretchability are reduced.

Next, a method for producing the porous film of the present invention will be described. Add a fine powder filler to the polylactic acid-based resin composition, and mixed at normal temperature for about 5 to 30 minutes using a Henschel mixer, a super mixer, a tumbler type mixer,
Thereafter, the mixture is kneaded by a usual single-screw or twin-screw extruder and pelletized. Next, the obtained pellets are formed into a film using an inflation molding machine or a T-die molding machine. It is also possible to form a film directly with an extruder without pelletizing. The extrusion temperature is preferably 100 to 270 ° C.
, More preferably in the range of 130 to 250 ° C. If the temperature is lower than 100 ° C., it is difficult to obtain extrusion stability, and it tends to be overloaded. If the temperature is higher than 270 ° C., the decomposition of the lactic acid-based polymer becomes unfavorable, which is not preferable.

The die of the extruder used in the present invention may have an annular or linear slit. The temperature of the die may be as high as the extrusion temperature range. Thereafter, stretching is performed at least in a uniaxial direction by a factor of 1.1 to 10, preferably 1.1 to 7 times. Stretching may be performed in multiple stages, or may be performed in a biaxial direction. If the stretching ratio is less than 1.1 times, the film becomes insufficiently porous. If it exceeds 10 times, the film often breaks, which is not preferable. The stretching temperature is preferably in the range of the glass transition point (hereinafter referred to as Tg) of the lactic acid-based polymer to Tg + 50 ° C. After stretching, heat setting may be performed to increase the morphological stability of the holes. The thickness of the porous film depends on the application, but is generally 10
About 300 μm.

In the present invention, it is possible to add a coloring agent, a reinforcing agent, other fillers and the like as long as the object of the present invention is not impaired.

[0025]

The present invention will be described in more detail with reference to the following examples. The evaluation method used in this example is as follows. After the completion of the polymerization reaction, the reaction mixture was dissolved in hexafluoroisopropanol or methylene chloride to obtain a solution having a known concentration, and the amount of the remaining monomer was quantified by gas chromatography. Solution viscosity Dissolve lactic acid-based polymer in chloroform (concentration 0.5g
/ Dl), 25 ± 0.05 using an Ubbelohde viscometer.
The solution viscosity was measured at ℃, and the intrinsic viscosity η was calculated by the following equation.

Η = log _e (T ₁ / T ₀ ) / C T ₀ : measurement time of solvent (sec) T ₁ : measurement time of sample solution (sec) C: concentration of sample solution (g / dl) Specific surface area It was measured by the BET adsorption method. Average particle diameter 3 g of a sample is filled into a sample cylinder having a cross-sectional area of 2 cm ² and a height of 1 cm using a powder specific surface area measuring device (permeation method) of model SS-100 manufactured by Shimadzu Corporation. It was calculated from the time of air permeation. The moisture permeability was measured according to ASTM-E-96-66. Bend-softness Measured according to JIS L-1096 6.19 Bend-softness A method (45-degree cantilever method). However, as a sample piece, an A4 plate having a long side in the winding direction was cut out from the obtained film, a steel scale having a width of 25 mm was placed in parallel with the long side, and after winding the sample side four times, a steel scale was used. Was used. Degree of polymerization of oligomer The oligomer was dissolved in tetrahydrofuran or chloroform, and the degree of polymerization distribution was measured and calculated by gel permeation chromatography.

Preparation Example To 1.8 kg of L-lactide placed in a reactor, 1.0 kg of an aqueous lactic acid solution (concentration: 87% by weight) was added, and heated at 100 ° C. for 2 hours. Upon cooling, a viscous transparent liquid was obtained at room temperature. As a result of measurement by GPC, this liquid contained lactic acid and lactic acid oligomer. The average degree of polymerization was 2.8. Hereinafter, it is referred to as LA oligomer.

Examples 1 to 15, Comparative Examples 1 to 4 Commercially available L-lactide (hereinafter referred to as L-LTD), D-lactide
Lactide (hereinafter referred to as D-LTD), DL-lactide (hereinafter referred to as DL-LTD) and glycolide (hereinafter referred to as GLD) were each recrystallized four times using ethyl acetate and purified. After drying ε-caprolactone (hereinafter referred to as CL) on calcium hydride,
Purified by distillation. The amounts of the above L-LTD and D-LT shown in Table 1 were placed in a glass reaction vessel whose surface was treated with silane.
D, DL-LTD, GLD, CL and stannous octoate as a catalyst were charged, and the inside of the vessel was degassed under reduced pressure and dried for one day. The reaction vessel was heated to a predetermined temperature shown in Table 1 and polymerized for a predetermined time. After the reaction is completed,
The reaction product was taken out. The obtained lactic acid-based polymer is
Called P1 to P6. The intrinsic viscosity and residual monomer amount of these lactic acid-based polymers were measured, and the results are shown in [Table 1].

[0029]

[Table 1] Next, after adding L-LTD or the LA oligomer obtained in the preparation example at a ratio shown in [Table 2] to these lactic acid-based polymers, they were mixed at a temperature shown in [Table 2] using a plastomill to obtain polylactic acid. The system resin compositions C1 to C8 were obtained.
Further, these resin compositions were heated at a temperature shown in [Table 2].
The sheet was pressed at 00 kg / cm ² to form a sheet having a thickness of 1 mm.

[0030]

[Table 2] After cooling the polylactic acid-based resin composition shown in [Table 3] using liquid nitrogen and pulverizing using a hammer mill pulverizer,
Fine powder filler having an average particle diameter shown in [Table 3] was added in an amount shown in [Table 3], and mixed at room temperature using a Henschel mixer. After pelletizing the mixture using a twin screw extruder, 230
Each was extruded from a T-die at a temperature of 0 ° C. and formed into a porous film having the thickness shown in Table 4 after stretching. Next, the film was roll-drawn uniaxially or biaxially at 60 ° C. at a draw ratio shown in [Table 4] to obtain a porous film. The physical properties shown above were evaluated for the obtained porous film, and the results are shown in [Table 4].

[0031]

[Table 3]

[0032]

[Table 4] Next, the porous film obtained in Examples 1, 2 and 5 and the porous film obtained from the polyolefin resin (Mitsui Toatsu Chemical Co., Ltd., trade name: ESPOIR N) were placed in distilled water at 37 ° C. After immersion, the weight loss rate after 120 days was measured. As a result, the weight reduction rates were 7%, 13%, 21% and 0%, respectively.

[0033]

Industrial Applicability The porous film of the present invention has air permeability, can have various rigidities, and has hydrolyzability. Therefore, it is useful as a leak-proof film for sanitary materials such as disposable diapers, and as a material for packaging materials. When discarded after use, it is hydrolyzed in nature and does not accumulate waste.

Claims (9)

(57) [Claims] 1. A polylactic acid or a lactic acid-hydroxycarboxylic acid copolymer of 80 to 100% by weight and a plasticizer 0
100 parts by weight of the polylactic acid-based resin composition containing 20 to 20% by weight, and a fine powdery filler 40 having an average particle size of 0.3 to 4 μm.
A porous film obtained by melt-forming a mixture to which -250 parts by weight has been added, and then stretching at least 1.1 times or more in a uniaxial direction. 2. The method according to claim 1, wherein the polylactic acid has an L-lactic acid unit of 85 to 100.
Mol% and 0 to 15 mol% of D-lactic acid unit, or D
-85 to 100 mol% of lactic acid units and 0 to L-lactic acid units
The porous film according to claim 1, which is a polylactic acid containing 15 mol%. 3. A lactic acid-hydroxycarboxylic acid copolymer comprising 85 to 100 mol% of L-lactic acid units and 0 to 15 mol% of glycolic acid units, or 85 to 1 mol of D-lactic acid units.
The porous film according to claim 1, which is a copolymer containing 00 mol% and 0 to 15 mol% of glycolic acid units. 4. The porous film according to claim 1, wherein the plasticizer is lactic acid, lactic acid oligomer or lactide. 5. The porous film according to claim 1, wherein the fine powder filler is an inorganic fine powder. 6. The polylactic acid (A) is composed of 85-1 L-lactic acid units.
The lactic acid-hydroxycarboxylic acid copolymer (B) contains L-lactic acid-hydroxycarboxylic acid copolymer (B) containing 00 mol% and 0 to 15 mol% of D-lactic acid units or 85 to 100 mol% of D-lactic acid units and 0 to 15 mol% of L-lactic acid units. 85-100 mol% of lactic acid units,
Or 85 to 100 mol% of D-lactic acid units and 0 to 15 mol% of glycolic acid units, wherein the plasticizer (C) is lactic acid, lactic acid oligomer or lactide, and
The porous film according to claim 1, wherein (D) the fine powder filler is an inorganic fine powder. 7. The porous film according to claim 1, wherein the finely divided filler is barium sulfate, calcium carbonate, or magnesium oxide. 8. The porous film according to claim 1, wherein the temperature of the melt film formation is in the range of 100 to 270 ° C. 9. The hydrolyzable porous film according to claim 1, wherein the stretching temperature is in the range from the glass transition point of the lactic acid-based polymer to the glass transition point + 50 ° C.