JP3415103B2 - Polylactic acid-based biaxially stretched film excellent in antistatic property and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polylactic acid-based biaxially stretched film which is excellent in transparency, mechanical properties, slipperiness, and especially antistatic property.

[0002]

2. Description of the Related Art At present, a polyethylene terephthalate stretched film, a polypropylene stretched film or the like is known as a material having excellent mechanical strength, heat resistance and dimensional stability, and is widely used in industry.

However, when these plastic films are discarded in the natural environment, they are not decomposed due to their chemical stability, but they are accumulated as garbage. In the future, it is becoming more difficult to secure landfills and landfills, and there are concerns about problems such as adversely affecting the natural environment and wildlife. Instead of these plastic films,
Polylactic acid is one that can become a harmless decomposition product by hydrolysis in the soil and then by microbial decomposition.

An unstretched film or sheet of polylactic acid is a material having low strength and elongation and inferior impact resistance, and its practicality as a molded body is insufficient as it is. Therefore, in order to improve the brittleness of polylactic acid, uniaxially or biaxially stretching,
A method of aligning is known. The polylactic acid biaxially stretched film has been developed into information recording materials (magnetic cards), industrial packages, agricultural mulch films, and some of them have been put to practical use.

However, in these polylactic acid-based stretched films, since the polylactic acid-based resin itself has a high degree of electrical insulation, it is extremely easy to be charged, and due to the generation and accumulation of static electricity, printing, bag making, etc. Causes various problems in the secondary processing. Further, since dust and dirt are easily adsorbed, there is a problem that the appearance is impaired.

[0006] Generally, as a method of imparting antistatic properties to plastic films and sheets, a method of kneading an anionic alkyl sulfonate or a nonionic glycerin fatty acid ester or applying it on the surface is adopted. There is. However, when the conventional method is applied to the polylactic acid-based biaxially stretched film, not only the satisfactory antistatic property cannot be obtained by the kneading method, but also the transparency is deteriorated, and the mechanical properties are deteriorated due to hydrolysis inducing, It was poor in practicality. The method of applying to the surface, polylactic acid-based unstretched film, uniaxially stretched film, because both of the biaxially stretched film has a low critical surface tension, the use of an organic solvent, or the combined use of an organic solvent and water is unavoidable, Therefore, solvent evacuation / recovery equipment is required, resulting in higher costs. In addition, not only is it economically unfavorable because the number of steps increases in the so-called post-coating method in which the film is once wound and applied to the original film.
Since the heat resistance of the film was poor, it was likely to cause poor appearance due to thermal deformation.

[0007]

DISCLOSURE OF THE INVENTION The present invention is intended to solve such problems, and is a polylactic acid type excellent in slipperiness and antistatic property without impairing transparency and mechanical properties. It is intended to provide a biaxially stretched film and a manufacturing method thereof.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a specific anionic interface obtained by mixing a polylactic acid-based biaxially stretched film on at least one side in a specific ratio is used. The inventors have found that a film having a surfactant layer composed of an activator and a specific nonionic surfactant solves the above-mentioned problems, and has reached the present invention.

That is, the present invention is a polylactic acid-based biaxially stretched film having a surfactant layer on at least one surface, wherein the surfactant layer comprises the following compound groups (A-1) to (A-).
99% by mass of at least one anionic surfactant (A) selected from 3) and the following compound group (B-
1) to (B-4) and 1 to 90% by mass of at least one nonionic surfactant (B), and a surface specific resistance of 10 ¹¹ Ω or less. The main point is a polylactic acid-based biaxially stretched film having excellent properties. (A-1) Alkyl sulfonate and alkyl allyl sulfonate (A-2) Higher alcohol sulfate ester salt and ethylene oxide adduct thereof (A-3) Higher fatty acid salt (B-1) Aliphatic alkanolamide (B -2) Ethylene oxide adduct (B-3) sorbit, sorbitan fatty acid ester and / or its ethylene oxide adduct (B-4) poly, such as higher alcohol, alkylphenol, fatty acid, aliphatic amine, aliphatic amide, polypropylene glycol Glycerin fatty acid ester.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. In the present invention, the polylactic acid-based film means L-
A film made of a homopolymer having lactic acid as a main constituent unit or a polylactic acid-based polymer having L-lactic acid / D-lactic acid as a main constituent unit. The polylactic acid-based biaxially stretched film obtained in the present invention promotes oriented crystallization by biaxial stretching,
L-lactic acid / D-lactic acid = 10 to develop practical strength
It is preferable to satisfy a composition ratio of 0/0 to 90/10 (molar ratio). When the content of D-lactic acid is 10 mol% or more, the melting point becomes extremely low, and the heat resistance and dimensional stability of the resulting sheet are poor, which is not preferable. The number average molecular weight of the polylactic acid polymer is preferably in the range of 50,000 to 300,000,
It is more preferably 80,000 to 150,000. Number average molecular weight is 5
If it is less than 10,000, the mechanical strength of the obtained film will be insufficient, and cutting during the stretching and winding steps will frequently occur, leading to a decrease in operability. On the other hand, when the number average molecular weight is more than 300,000, the fluidity at the time of heating and melting becomes poor, and the film formability deteriorates.

As a polymerization method for obtaining polylactic acid, either a condensation polymerization method or a ring-opening polymerization method can be adopted, and a small amount of a chain extender such as a diisocyanate compound is used for the purpose of increasing the molecular weight. You may use a diepoxy compound, an acid anhydride, etc.

The polylactic acid-based biaxially stretched film of the present invention is
A surfactant layer is formed on the surface. The coating amount of the surfactant is preferably in the range of 0.001 to 0.1 g / m ² . Below this range, a sufficient antistatic effect cannot be obtained. On the other hand, if it exceeds the above range, the antistatic effect reaches saturation, so that not only the added amount is excessive with respect to the performance, but also the transparency is deteriorated and the blocking phenomenon between films under high temperature and high humidity is caused. Further, it is possible to form a surfactant layer on both sides, if necessary.

The surface specific resistance value of the polylactic acid biaxially stretched film of the present invention is required to be 10 ¹¹ Ω or less.
If the surface resistivity exceeds 10 ¹¹ Ω, electric shock may occur in the film winding and slitting processes, and 2
In the next processing, wrinkles are more noticeable than winding around a roll or meandering.

In the present invention, the surfactant applied to the film must be a combination of the anionic surfactant (A) and the nonionic surfactant (B). In the present invention, the anionic surfactant (A) refers to at least one kind of surfactant selected from the following compound groups (A-1) to (A-3). (A-1) Alkyl sulfonate and alkyl allyl sulfonate (A-2) Higher alcohol sulfate ester salt and its ethylene oxide adduct (A-3) Higher fatty acid salt Here, the alkyl group of (A-1) is C8 to C18 is desirable, and dodecylbenzene sulfonic acid can be preferably used. As the salt, an alkali metal salt, an alkaline earth metal salt or a triethanolamine salt can be preferably used. Further, a diester type sulfosuccinate (C8 to C16) can also be used. The alkyl group of the higher alcohol (A-2) is preferably C12 to C18, preferably lauryl (C12), cetyl (C16), stearyl (C1).
8) and oleyl (C18) are preferable. Although higher alcohols to which ethylene oxide is added can be used in the same manner, the ethylene oxide addition mole number is preferably 2 to 4. The higher fatty acid (A-3) is preferably C12 to C18, and a single saturated or unsaturated fatty acid such as lauric acid (C12) and oleic acid (C18) is preferably used. Also, mixed fatty acids such as coconut oil fatty acid and beef tallow fatty acid can be used. The above-mentioned anionic surfactants may be used alone or in combination as long as they are water-soluble or water-dispersible. The anionic surfactant which is particularly preferably used in the present invention is (A-1) an alkyl sulfonate and / or an alkylbenzene sulfonate.

In the present invention, the nonionic surfactant (B) means at least one surfactant selected from the following compound groups (B-1) to (B-4). (B-1) Aliphatic alkanolamide (B-2) Higher alcohol, alkylphenol, fatty acid, aliphatic amine, aliphatic amide, ethylene oxide adduct such as polypropylene glycol (B-3) sorbit, sorbitan fatty acid ester and / or The ethylene oxide adduct (B-4) polyglycerin fatty acid ester Here, the aliphatic alkanolamide (B-1) is synthesized by condensation of a higher fatty acid and an alkanolamide.
The higher fatty acid is not particularly limited, but C12 to C20 fatty acids can be preferably used. Specifically, lauric acid and coconut oil fatty acid are desirable. As the alkyl group of the higher alcohol (B-2), alkylphenol, fatty acid, aliphatic amine or aliphatic amide, C8 to C22 can be preferably used. The number of moles of ethylene oxide added depends on the bound hydrophobic group, but is usually 2 to 20 moles. Polypropylene glycol preferably has a molecular weight of 500 to 5,000. As the fatty acid (B-3), C12 to C18 can be preferably used. As the fatty acid (B-4), C12 to C18 can be preferably used. Glycerin is selected from di, tetra, and deca, with deca being preferred. The above-mentioned nonionic surfactants may be used alone or in combination as long as they are water-soluble or water-dispersible. The nonionic surfactant that is particularly preferably used in the present invention is (B-
It is the aliphatic alkanolamide of 1).

In the present invention, the surfactant layer must be composed of 99 to 10% by mass of anionic surfactant (A) and 1 to 90% by mass of nonionic surfactant (B). Yes, (A) 90 to 50 mass%, (B) 10
It is preferably composed of 50% by mass. As a method of mixing both surfactants, there are a case of mixing separately diluted with water (post-mixing) and a case of dissolving and diluting both with water at the same time (pre-mixing), but either method may be used. . When the anionic surfactant (A) is 99% by mass or more,
Although the antistatic effect is good, the wettability with respect to the polylactic acid-based film is deteriorated, resulting in poor appearance such as coat stripes and uneven density and deterioration of performance. 1 anionic surfactant (A)
When it is less than 0%, the wettability to the surface is improved, but a sufficient antistatic effect cannot be obtained.

As a method for applying the mixture to the surface of the polylactic acid-based film of the present invention, any known coating method can be applied. For example, a gravure roll method, a Meyer bar method, a reverse roll method, and a spray method are applied independently or in combination. The film to be applied is
The polymer is preferably an unstretched film after melt extrusion or casting, or a uniaxially stretched film after stretching in the machine direction, but a biaxially stretched film may be used. When it is dried after coating, it should be performed under a temperature condition that does not cause thermal deformation of the polylactic acid-based unstretched film or the uniaxially stretched film, and preferably does not exceed 100 ° C. Further, after coating, it may be supplied to a tenter without being dried, and may be dried by using a preheating and stretching process.

In the present invention, it is preferable to use a so-called in-line coating method when applying the surfactant. This method does not use an organic solvent and requires only one step, so there is no reduction in mechanical strength in terms of physical properties, and since there is one step in terms of the process, there is no loss of the raw material film, which leads to cost reduction. Although beneficial, a post-coating method of applying a surfactant to the biaxially oriented film may be used.

In the polylactic acid biaxially stretched film of the present invention, if necessary, a pigment, an antioxidant, a plasticizer, an ultraviolet absorber,
Lubricants, crystal nucleating agents and the like can be added at any ratio.

Examples of the method for producing the polylactic acid-based biaxially stretched film of the present invention include a T-die method, an inflation method, a calender method, and the like. The T-die method is preferable, in which the T-die is used for melt-kneading and extrusion. As a production example of the T-die method, a polylactic acid-based polymer, or a polylactic acid-based resin composition in which an appropriate amount of a plasticizer and a lubricant is blended is supplied to an extruder hopper, and the extruder is heated to, for example, a cylinder temperature of 180 to
It is heated to 260 ° C. and T-die temperature of 200 to 260 ° C., melt-kneaded, extruded and cooled by a cooling roll controlled at 20 to 40 ° C. to obtain an unstretched sheet having a thickness of 100 to 500 μm.

The method for biaxially stretching the unstretched sheet may be either coaxial biaxial stretching by a tenter system or sequential biaxial stretching by a roll and a tenter. As a specific stretching example, first, an unstretched sheet is longitudinally rolled at a roll surface temperature of 50 to 80 ° C. at a stretching ratio of 1.
The mixture is stretched at a stretch ratio of 5 to 5.0, and then the mixture is coated by the Meyer bar method so that the final coating amount after stretching becomes 0.01 g / m ^2, and then continuously in the transverse direction at a stretching temperature of 50 to 50. 9
0 ° C., draw ratio 1.5 to 8.0 times, heat setting temperature 100 to
A sequential biaxial stretching method of stretching at 150 ° C. may be mentioned.

The thickness of the polylactic acid-based biaxially stretched film according to the present invention is not particularly limited and may be appropriately set depending on the use, required performance, price and the like. Generally, 10-200 μm
The thickness can be exemplified. In addition, the printability of the film,
Surface treatment may be performed for the purpose of improving laminating property, coating suitability and the like. Examples of the surface treatment method include corona discharge treatment, plasma treatment, and acid treatment, and any method can be used. Among these, the corona discharge treatment can be exemplified as the most preferable one in terms of simplicity.

The polylactic acid-based biaxially stretched film of the present invention comprises
It is suitable as a film for packaging calendars, stationery, clothes, foods, etc., but is also suitable for shrink films such as video tapes, bags for packaging garbage, window sticking films for envelopes, wrapping for electric / electronic parts, and agricultural films. , Print laminating, etc. can be exemplified, and they can be used without particular limitation.

The present invention will be described below with reference to examples.
The present invention is not limited to the examples below. The measurement method and evaluation of each inspection item were performed by the following methods.

(1) After being left for 1 day in an environment having a surface resistivity of 23 ° C. and a relative humidity of 50%, it was measured under the same conditions according to JIS-K6911.
In the present invention, 10 ¹¹ Ω or less was regarded as a pass. (2) Half-life of electrification voltage After standing for 1 day under the conditions of temperature of 23 ° C and relative humidity of 50%, the half-life of electrification voltage was measured by static static nest meter. In the present invention, 60 seconds or less was passed. (3) Tensile Strength and Elongation According to the measuring method of ASTM-D882, a sample having a length of 10 cm and a width of 10 mm was measured. (4) Haze Measured according to JIS-K7105. In the present invention, 10 or less was passed. (5) Dynamic friction coefficient According to JIS-K7125, the slidability between the coated surface and the non-coated surface was measured. In the present invention, 0.70 or less was passed.

The surfactants used in the examples are as follows. A-1: Alkyl sulfonate (Chemist 3033N manufactured by Sanyo Kasei Co., Ltd.) A-2: Polyoxyethylene lauryl ether sulfate soda salt (Actinol SL manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.)
-3) A-3: Potassium coconut fatty acid soap (TY manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.
-1012) B-1: coconut fatty acid diethanolamide (Chemist 2500 manufactured by Sanyo Kasei Co., Ltd.) B-2: polyethylene glycol monolaurate (Bryan L manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.) B-3: polyoxyethylene sorbitan monolaurate (Matsumoto) Yushi-Seiyaku Co., Ltd. Sylvan T-20) B-4: Decaglycerin monolaurate (Matsumoto Yushi-Seiyaku Co., Ltd. Bryan PE-L100)

Example 1 L-form / D-form = 99/1 (molar ratio), number average molecular weight 9
Using a 50 mmφ extruder equipped with a coat hanger type T-die, a polylactic acid-based polymer having a MFR of 5,000 and an MFR of 5.0 g / 10 min (210 ° C.) was used, and the residence time was 5 min.
It was melt-extruded at a die temperature of 230 ° C. and closely adhered to a cast roll whose temperature was controlled at 25 ° C. to be rapidly cooled to obtain an unstretched sheet having a thickness of 210 μm. The obtained unstretched sheet is preheated by roll 6
The film was longitudinally stretched at 0 ° C. and a stretching roll 70 ° C. 3.0 times in the longitudinal direction. Next, as an antistatic agent, 1% by mass of a mixture of 80% by mass of Chemistat 3033N (manufactured by Sanyo Kasei Co., Ltd.), which is an alkyl sulfonate, and 20% by mass of Chemistat 2500 (manufactured by Sanyo Kasei Co., Ltd.), which is coconut fatty acid diethanolamide. After applying the diluted aqueous solution by means of a Meyer bar coat, subsequently, in a tenter,
After stretching 3.5 times in the transverse direction at a stretching temperature of 0 ° C., heat treatment was performed at 150 ° C. with a relaxation rate in the transverse direction of 5% to obtain a thickness of 2
A 0 μm sequentially biaxially stretched film was obtained.

Examples 2 to 8 Sequentially biaxially stretched films were obtained in the same manner as in Example 1 except that the kind, ratio and coating amount of the antistatic agent were changed.

Example 9 L-form / D-form = 99/1 (molar ratio), number average molecular weight 9
A polylactic acid-based polymer composition having a MFR of 5,000 and an MFR of 5.0 g / 10 minutes (210 ° C.) was coated with a coat hanger type T
Using a 50 mmφ extruder equipped with a die, a residence time of 5
Min, T-die temperature 230 ℃ melt extruded, and cooled rapidly to 25 ℃ with a temperature controlled cast roll, and rapidly cooled to a thickness of 200 μm
To obtain an unstretched sheet. Next, the antistatic agent shown in Table 1 was applied in the same manner as in Example 1, and subsequently in a tenter, at a preheating temperature of 60 ° C. and a stretching temperature of 70 ° C., 3.0 × 3.3.
The film was simultaneously biaxially stretched at a draw ratio of 2 times, and then heat-treated at 150 ° C. with a transverse relaxation rate of 5% to obtain a 20 μm-thick simultaneous biaxially stretched film.

Examples 10 to 11 Simultaneous biaxially stretched films were obtained in the same manner as in Example 9 except that the type of antistatic agent was changed.

Comparative Examples 1 to 3 except that the compounds shown in Table 1 were used as the antistatic agent.
A biaxially stretched film was sequentially obtained in the same manner as in Example 1.

[0032]

[Table 1]

As shown in Table 1, the biaxially stretched films of Examples 1 to 11 are excellent in antistatic property and at the same time, have transparency,
Excellent mechanical strength and slipperiness. In contrast, Comparative Example 1 using only coconut fatty acid diethanolamide has insufficient antistatic properties and does not reach a practical level. Comparative Example 2 using only the alkyl sulfonate has a good antistatic property, but since it causes coating unevenness and deteriorates the external appearance, it has a problem that the commercial value is impaired and the transparency is deteriorated, and its application is limited. It Comparative Example 3 in which no antistatic agent is applied
As with general-purpose plastics, the surface resistivity is high and static electricity tends to accumulate.

[0034]

INDUSTRIAL APPLICABILITY The polylactic acid-based biaxially stretched film of the present invention is excellent in transparency, mechanical strength and slipperiness, especially antistatic property, and is therefore useful as a packaging material for clothes, stationery, foods, pharmaceuticals and the like. It is highly likely. Also, when it is discarded as garbage, it is decomposed by microorganisms in the soil, and the environmental load on the natural environment and wild animals can be reduced.

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Claims (2)

(57) [Claims] 1. A polylactic acid biaxially stretched film having a surfactant layer on at least one surface, wherein the surfactant layer is at least one selected from the following compound groups (A-1) to (A-3). 99 kinds of anionic surfactants (A)
10 mass% and at least one nonionic surfactant (B) selected from the following compound groups (B-1) to (B-4) 1 to 90 mass% and having a surface resistivity of 10:
A polylactic acid-based biaxially stretched film having an excellent antistatic property, which is ¹¹ Ω or less. (A-1) Alkyl sulfonate and alkyl allyl sulfonate (A-2) Higher alcohol sulfate ester salt and its ethylene oxide adduct (A-3) Higher fatty acid salt (B-1) Aliphatic alkanolamide (B -2) Ethylene oxide adducts of higher alcohols, alkylphenols, fatty acids, aliphatic amines, aliphatic amides, polypropylene glycols (B-3) sorbit, sorbitan fatty acid ester and / or its ethylene oxide adduct (B-4) poly Glycerin fatty acid ester. 2. At least one kind of anionic surfactant selected from the following compound groups (A-1) to (A-3) on at least one surface of a polylactic acid-based film which is unstretched or stretched only in the uniaxial direction. A mixture of (A) 99 to 10% by mass and at least one nonionic surfactant (B) 1 to 90% by mass selected from the following compound groups (B-1) to (B-4). The method for producing a polylactic acid-based biaxially stretched film according to claim 1, wherein an aqueous solution is applied, and then the film is stretched biaxially or in a direction perpendicular to the initial stretching direction and heat-set. (A-1) Alkyl sulfonate and alkyl allyl sulfonate (A-2) Higher alcohol sulfate ester salt and its ethylene oxide adduct (A-3) Higher fatty acid salt (B-1) Aliphatic alkanolamide (B -2) Ethylene oxide adducts of higher alcohols, alkylphenols, fatty acids, aliphatic amines, aliphatic amides, polypropylene glycols (B-3) sorbit, sorbitan fatty acid ester and / or its ethylene oxide adduct (B-4) poly Glycerin fatty acid ester