JP2006035666A - Multi-layer polylactic acid resin film and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer polylactic acid resin film that suppresses bleeding of a plasticizer on a film surface, prevents blocking between films, and does not cause blocking even in a crystallization treatment step, and a method for producing the same. thing.
SOLUTION: A polycrystal comprising 50 to 100% by weight of weakly crystalline or amorphous polylactic acid having a D-form concentration of 7 to 20% and 0 to 50% by weight of crystalline polylactic acid having a D-form concentration of 0 to 6%. A polylactic acid resin layer comprising a mixture of 15 to 50 parts by weight of a plasticizer per 100 parts by weight of a lactic acid resin, and an aliphatic polyester resin or aliphatic-aromatic polyester resin having a glass transition temperature of 0 ° C. or less A multilayer polylactic acid resin film characterized by being a multilayer film in which at least one polyester resin layer selected from the above is laminated, and a method for producing the same.

Description

  The present invention relates to a biodegradable multi-layer polylactic acid resin film, and more specifically, by laminating a polylactic acid resin layer and a specific polyester resin layer, the blocking property and plasticizer bleeding. The present invention relates to a multilayer polylactic acid-based resin film with suppressed properties and a method for producing the same.

In recent years, products that are rapidly decomposed after disposal and that do not accumulate in the natural environment have been desired, and various biodegradable resins are commercially available. As a biodegradable resin that can be formed into a film by a T-die extruder, an aliphatic polyester-based resin is known. For example, polylactic acid is excellent in transparency but lacks flexibility. For this reason, attempts have been made to impart flexibility to the film by blending a plasticizer.
However, when a plasticizer is blended with polylactic acid, a bleeding phenomenon occurs in which the plasticizer and additives exude over time on the surface of the molded film, and the films that have been formed and wound do not adhere to each other and peel off. There was a problem that a blocking phenomenon occurred.

Various proposals have been made for the purpose of solving such problems (see, for example, Patent Documents 1 to 5).
Patent Document 1 discloses a polylactic acid resin composition containing a crystallization accelerator, and Patent Document 2 discloses a highly crystalline polylactic acid resin containing a crystalline polylactic acid resin, a plasticizer, and a crystal nucleating agent as essential components. Patent Document 3 discloses an L-lactic acid polymer composition containing SiO _{2 in} a mixture of a specific L-lactic acid polymer and a specific plasticizer. Patent Document 4 discloses a specific lactic acid-based polyester. A lactic acid polyester molded product that is crystallized after molding a composition containing a plasticizer and is composed of a crystalline lactic acid resin and a plasticizer in Patent Document 5, and the lactic acid resin component in the film is specified A biodegradable soft film having a heat of crystallization and a heat of fusion is disclosed.
However, these proposals are not necessarily from the viewpoint of effectively suppressing bleed and plastic film blocking of the plasticizer film surface while maintaining transparency and flexibility in the plasticized soft polylactic acid film. It was not enough.
As a result of repeated researches to solve the above problems, the present applicant performs crystallization treatment on a film containing weak crystalline or amorphous polylactic acid having a D-form concentration of 7 to 20% and a plasticizer. Thus, it was found that the bleed of the plasticizer on the film surface can be suppressed and blocking between the films can be prevented while maintaining the transparency and flexibility of the film (see Patent Document 6). However, since the crystallization treatment usually requires curing at a relatively high temperature for a long time, there is a possibility that the films wound during the crystallization process may block each other. There were problems that had to be solved in production, such as the need to take measures to prevent the films from coming into direct contact with each other by winding paper.

JP 2003-301097 A Japanese Patent No. 3410075 Japanese Patent No. 3472644 Japanese Patent Laid-Open No. 10-36651 JP 2003-12934 A Japanese Patent Application No. 2004-005640 Specification and Drawing

  In the plasticized polylactic acid resin film, the present invention suppresses bleed of plasticizer on the film surface, prevents blocking between films, and does not cause blocking even in a crystallization treatment step. An object of the present invention is to provide a polylactic acid resin film and a method for producing the same.

As a result of intensive studies, the present inventors have found that the above problems can be solved by laminating a polylactic acid resin layer containing a plasticizer and a layer made of a specific polyester resin, and the present invention has been completed. did.
That is, the gist of the present invention is that 50 to 100% by weight of weakly crystalline or amorphous polylactic acid having a D-form concentration of 7 to 20% and 0 to 50% by weight of crystalline polylactic acid having a D-form concentration of 0 to 6%. A polylactic acid resin layer comprising a mixture of 15 to 50 parts by weight of a plasticizer per 100 parts by weight of the polylactic acid resin and an aliphatic polyester resin or aliphatic-aromatic having a glass transition temperature of 0 ° C. or less. The multilayer polylactic acid resin film is a multilayer film in which at least one polyester resin layer selected from group polyester resins is laminated.
The multilayer polylactic acid-based resin film is heat-treated, and the polylactic acid-based resin layer preferably has a heat of crystallization of 0 to 2 J / g and a heat of fusion of 3 to 20 J / g. The layer polylactic acid resin film is preferably a three-layer film obtained by laminating the polyester resin layer on both sides of the polylactic acid resin layer.
The gist of the present invention is that 50 to 100% by weight of weakly crystalline or amorphous polylactic acid having a D-form concentration of 7 to 20% and 0 to 50% by weight of crystalline polylactic acid having a D-form concentration of 0 to 6%. A polylactic acid resin layer comprising a mixture of a polylactic acid resin comprising a plasticizer and a polyester resin layer comprising an aliphatic polyester resin or an aliphatic-aromatic polyester resin having a glass transition temperature of 0 ° C. or lower; Is formed, and a crystallization treatment is performed on the multilayer film.
The crystallization treatment is preferably a heat treatment at a temperature of 20 to 100 ° C., and the mixture preferably contains a crystal nucleating agent.

  According to the present invention, by laminating a polylactic acid-based resin layer containing a plasticizer and a layer made of a specific polyester-based resin, the plasticizer bleed on the film surface and the blocking between the films are prevented, and the crystal A multilayer polylactic acid-based resin film having excellent transparency and flexibility that does not cause blocking even during the crystallization treatment is obtained.

In the present invention, the polylactic acid resin used in the polylactic acid-based resin layer is mainly composed of L-lactic acid or its cyclic dimer L-lactide and D-lactic acid or D-lactide, and condensation polymerization or ring-opening polymerization. Weakly crystalline or amorphous having a D-form concentration (composition ratio of D-lactic acid units in polylactic acid composed of L-lactic acid units and D-lactic acid units) of 7 to 20%. A ratio of 50% by weight or less of crystalline polylactic acid alone or crystalline polylactic acid mainly composed of the weak crystalline or amorphous polylactic acid and having a D-form concentration of 0 to 6%, preferably 0 to 5% It is blended with.
Since polylactic acid having a D-form concentration of 0 to 6% has high crystallinity, a film mainly composed of this tends to bleed the plasticizer on the surface.
The polylactic acid includes not only a polymer composed only of lactic acid but also a mixture of lactic acid with a small amount of hydroxycarboxylic acid as a copolymerization component. Examples of such hydroxycarboxylic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid and the like.
The molecular weight of the polylactic acid used in the present invention is not particularly limited, but a weight average molecular weight of about 10,000 to 1,000,000 is appropriate from the viewpoint of film strength and moldability, and particularly 30,000 to About 500,000 is preferable.
The polylactic acid resin layer may contain a small amount of other resin that does not cause a problem for the purpose of improving physical properties.

In the present invention, the plasticizer mixed with the polylactic acid resin is not particularly limited as long as it can be suitably used for the polylactic acid resin. For example, triethylene glycol is used. , Aliphatic alcohol plasticizers such as polyethylene glycol, acetylated monoglyceride plasticizers such as glycerol diacetomonolaurate and glycerol diacetomonooleate, aliphatic ester plasticizers such as lactic acid esters, and the degree of polymerization of polyglycerol 2 -4, and polyglycerin acetate ester plasticizers having an acetylation rate of 50 to 100%, adipate ester plasticizers, epoxidized soybean oil, epoxidized linseed oil, and the like, preferably, Acetylated monoglyceride plasticizer, polyglycerin acetate plasticizer, etc. And the like.
The blending amount of the plasticizer is 15 to 50 parts by weight, preferably 20 to 40 parts by weight per 100 parts by weight of the polylactic acid resin. If the blending amount of the plasticizer is less than 15 parts by weight, the plasticizing effect is not sufficient. If the amount exceeds 50 parts by weight, the tackiness of the film becomes excessive, so that the workability is deteriorated.

  In the present invention, it is preferable to contain a crystal nucleating agent in the resin composition in order to crystallize weakly crystalline or amorphous polylactic acid. Crystal nucleating agents include silicate compounds such as talc, kaolinite and montmorillonite, metal oxides such as zinc oxide and magnesium oxide, various inorganic crystal nucleating agents such as calcium carbonate and barium sulfate, and various organic crystal nucleating agents. About the compounding quantity, it is 0.05-10 weight part per 100 weight part of polylactic acid, Preferably it is 0.1-5 weight part.

In the present invention, the resin used for the polyester-based resin layer is an aliphatic polyester resin or an aliphatic-aromatic polyester resin having a glass transition temperature of 0 ° C. or less, and one or a mixture of two or more are used.
Specific examples of the aliphatic polyester resin include an aliphatic polyester obtained by condensation polymerization of a dicarboxylic acid component and a diol component, and polymerized with a polyfunctional isocyanate as necessary. Examples of the dicarboxylic acid component include aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and itaconic acid, and succinic acid is particularly preferable. Examples of the diol component include 1,4-butanediol, 2,3-butanediol, 1,3-butanediol, 1,4-pentanediol, 1,5-pentanediol, 2,4-pentanediol, Aliphatic diols such as 6-hexanediol, neopentyl glycol, ethylene glycol, and diethylene glycol are exemplified, and 1,4-butanediol is particularly preferable.
Another example of the aliphatic polyester resin is an aliphatic polyester obtained by condensation polymerization of the dicarboxylic acid component, preferably succinic acid, and the diol component, preferably 1,4-butanediol and lactic acid. It is done.
Furthermore, other examples of the aliphatic polyester resin include aliphatic polyesters obtained by ring-opening polymerization of cyclic lactones, preferably polycaprolactone. Polycaprolactone is not limited to a homopolymer of caprolactone, but may be a copolymer of caprolactone and another aliphatic hydroxycarboxylic acid.
Specific examples of the aliphatic-aromatic polyester resin include polyfunctional aliphatic aromatic polyesters obtained by condensing a dicarboxylic acid component composed of adipic acid and terephthalic acid and a diol component composed of 1,4-butanediol. The thing polymerized with isocyanate is mentioned. As the diol component, in addition to 1,4-butanediol, 2,3-butanediol, 1,3-butanediol, 1,4-pentanediol, 1,5-pentanediol, 2,4-pentanediol, Examples include 1,6-hexanediol, neopentyl glycol, diethylene glycol and the like.
When the glass transition temperature of the aliphatic polyester resin or aliphatic-aromatic polyester resin used in the polyester resin layer in the present invention exceeds 0 ° C., the flexibility and impact resistance of the multilayer polylactic acid resin film are lowered. This is not preferable.

  In the present invention, it is preferable to contain a lubricant in the polylactic acid resin layer or the polyester resin layer in order to make the roll separation of the film at the time of forming the laminated polylactic acid resin film good. Examples of the lubricant include polyethylene wax, fatty acid amide, stearic acid, and the blending amount thereof is 0.01 to 2 parts by weight, preferably 0.1 to 1 part per 100 parts by weight of the polylactic acid resin or polyester resin. .5 parts by weight.

  Moreover, in this invention, in order to prevent a film sticking to a metal roll at the time of shaping | molding, or preventing a film blocking, you may make the polylactic acid-type resin layer or the polyester-type resin layer contain the fine particle of an inorganic compound. . Examples of the inorganic compound include feldspar, silica, or talc or kaolin used as the crystal nucleating agent. The average particle diameter of the fine particles is 1 to 7 μm, and the blending amount is 0.01 to 2 parts by weight per 100 parts by weight of the resin. The amount is preferably 0.1 to 1.5 parts by weight. If the blending amount is less than 0.01 parts by weight, the effect of improving adhesion of the molten film to the processing roll and blocking between the films is poor, and if it exceeds 2 parts by weight, the transparency of the film is impaired.

  Other components can be added to the resin material used in the present invention without departing from the spirit of the present invention. Examples of such additive components include antioxidants, ultraviolet absorbers, hindered amine light stabilizers, antistatic agents, thermal stabilizers, tackifiers, pigments, and dyes. Moreover, it does not interfere with blending a small amount of other biodegradable resins that are also compatible.

  The multi-layer polylactic acid resin film according to the present invention is a laminated film of two or more layers comprising at least one polylactic acid resin layer and at least one polyester resin layer, on both surfaces of the polylactic acid resin layer. A three-layer film in which a polyester resin layer is laminated is preferable. The total thickness of the film is usually in the range of 10 to 300 μm, preferably 20 to 200 μm. In the case of the above three-layer film, the ratio of the thickness of each layer is suitably about 1: 8: 1 to 3: 4: 3.

  In the production of the multilayer polylactic acid resin film of the present invention, the resin composition constituting each layer is first kneaded, and the method is a commonly used kneading method. Specifically, pellets, powders, solid strips, etc. are dry-mixed with a Henschel mixer or ribbon mixer and supplied to a melt kneader such as a single or twin screw extruder, Banbury mixer, kneader or mixing roll. Can be melt-kneaded. For example, first, the resin composition is placed in a tumbler and stirred and mixed for 10 to 20 minutes. Subsequently, it can be melt-kneaded at a temperature of 140 to 210 ° C. by a single-screw or twin-screw extruder or the like to form pellets of the resin composition.

  Next, a multilayer film is formed by multilayer T-die extrusion molding or multilayer inflation molding using each resin composition. Formation and lamination of each resin layer can be performed by extrusion coating or the like, but a method in which pellets of each resin composition are supplied to different extruders and coextruded using a multilayer die is suitable.

In the present invention, the multilayer polylactic acid-based resin film molded as described above is subjected to crystallization treatment, and the non-crystalline portion of polylactic acid is sufficiently crystallized until the heat of crystallization described below becomes substantially zero. It is desirable to make it.
The crystallization treatment is usually performed by a method in which the film is heat-treated by placing it at a high temperature for a certain period of time. Examples of the film heating means include means for directly irradiating the film with microwaves in addition to the above means. The heat treatment temperature is usually not lower than the glass transition temperature of the pre-processed film and not higher than the melting start temperature, but about 20 to 100 ° C. is appropriate. Although the appropriate processing time varies depending on the processing temperature, for example, when the processing temperature is 60 ° C., the object of the present invention can be achieved by processing for about 6 hours, and crystallization gradually takes place even if more time is spent. It only goes.
By performing such a crystallization treatment, the elasticity is increased moderately, and the flexibility of the film particularly at low temperatures is improved. In addition, as a result of the crystallization treatment, a small amount of fine crystals are uniformly generated inside the film, and the blended plasticizer and the like are trapped between the fine crystals, and there is an effect of suppressing bleeding.

The progress of crystallization and the degree of crystallization by the crystallization treatment are determined by using a differential scanning calorimeter, and the amount of crystallization and melting per gram of sample measured from the area of the crystallization peak and melting peak appearing on the DSC curve chart. It can be determined by the amount of heat (J / g).
In the present invention, the crystallization treatment of the formed multilayer polylactic acid resin film is performed under conditions such that the amount of heat of crystallization is at least 0 to 2 J / g, preferably 0 J / g. About the crystallinity degree of a lactic acid-type resin film, it is desirable that heat of fusion is 3-20 J / g.

  Examples of the present invention will be described below, but the present invention is not limited to the examples. In the present invention, the anti-blocking property, anti-bleeding property, transparency and flexibility of the film were evaluated based on each criterion from the results of tests carried out by the methods described below.

(1) Anti-blocking property After being left for 1 week in a perfect oven maintained at a temperature of 60 ° C. in a state where two test pieces having a length of 160 mm, a width of 25 mm and a thickness of 0.05 mm are stacked and a load of 10 kg is applied. Two test pieces were peeled off and evaluated according to the following criteria.
○ It peels without resistance × There is resistance when peeling

(2) Bleed prevention property A test piece having a length of 160 mm, a width of 25 mm, and a thickness of 0.05 mm was left in a room maintained at a temperature of 40 ° C and a relative humidity of 90% for 3 days, and then visually evaluated according to the following criteria.
○ Almost no additive bleed △ Slight additive bleed × Many additive bleed observed

(3) Transparency Based on JIS K 7105, the total light transmittance and the diffuse transmittance were obtained and evaluated according to the following criteria based on the haze of the film sample calculated by the following formula.
Haze (%) = (diffuse transmittance / total light transmittance) × 100
○ Haze less than 20%
× Haze 20% or more

(4) Flexibility The Young's modulus of the film sample was measured and evaluated according to the following criteria.
○ Young's modulus less than 300 MPa × Young's modulus 300 MPa or more

Examples 1-6, Comparative Examples 1-3
As a film-forming resin and compounding agent,
Polylactic acid: two types of poly-DL lactic acid having D-form concentrations of 1% and 12%, respectively, and a weight average molecular weight of about 190,000,
Aliphatic-aromatic polyester resin: “Ecoflex” manufactured by BASF (polymerized polycondensation product of adipic acid, terephthalic acid and 1,4-butanediol with polyfunctional isocyanate, Tg: −30 ℃),
Aliphatic polyester resin A: “Bionole # 1001” manufactured by Showa Polymer Co., Ltd. (polycondensate of succinic acid and 1,4-butanediol polymerized with polyfunctional isocyanate, Tg: −32 ° C.)
Aliphatic polyester resin B: “Cell Green PH7” (polycaprolactone, Tg: −60 ° C.) manufactured by Daicel Chemical Industries, Ltd.
Aliphatic polyester resin C: “GS Pla AZ91T” manufactured by Mitsubishi Chemical Corporation (Tg: (polycondensate of succinic acid, 1,4-butanediol and lactic acid, Tg: −32 ° C.)
Plasticizer: “Rikemar PL-710” (polyglycerin acetate plasticizer) manufactured by Riken Vitamin Co., Ltd. and lubricant: erucic acid amide were prepared, and 3 according to the composition of each Example and each Comparative Example shown in Table 1. A resin composition for forming a kind of polylactic acid resin layer, a resin composition for forming five kinds of polyester resin layers, and a mixed resin composition of one kind of polylactic acid / polyester were prepared. Indicates the weight part of the component.)
Next, for each single-layer film (Comparative Examples 1 and 2) having only a polylactic acid-based resin layer and a polylactic acid / polyester mixed resin layer, each composition was supplied to an extruder, and a cylinder temperature was 140 ° C. and a die temperature was 135 ° C. The film was blown under the conditions described above to obtain a 50 μm thick film.
Moreover, about the multilayer film (Examples 1-6 and Comparative Example 3) which laminated | stacked the polylactic acid-type resin layer, the polyester-type resin layer, or the polylactic acid-type resin layer, each resin composition is set to another extruder, respectively. The film co-extruded from the multi-layer die is blown, the polylactic acid resin layer having a thickness ratio of 1: 3: 1 is used as the intermediate layer, and the polyester resin layer (or polylactic acid resin layer) is used as the inner and outer layers. A multilayer polylactic acid resin film having a thickness of 50 μm and comprising three layers was obtained.
Each of the nine types of films thus obtained was subjected to evaluation tests for anti-blocking, anti-bleeding, transparency and flexibility, and the evaluation results are shown in Table 1.

As shown in Table 1, in each comparative example, the single-layer film made of only the polylactic acid-based resin layer has poor anti-blocking properties and anti-bleeding properties, and the single-layer film made of only the polylactic acid / polyester mixed resin layer is In addition, the transparency and flexibility are poor, and the multilayer film having the polylactic acid resin layer as the inner and outer layers has poor antiblocking properties and flexibility.
On the other hand, in each Example, antiblocking property, bleed prevention property, transparency, and a softness | flexibility were all favorable.

  The multilayer polylactic acid resin film according to the present invention can be used for agricultural films, food packaging films, other packaging films, stretch films, protective films and the like.

Claims (7)

  100% by weight of polylactic acid resin comprising 50 to 100% by weight of weakly crystalline or amorphous polylactic acid having a D-form concentration of 7 to 20% and 0 to 50% by weight of crystalline polylactic acid having a D-form concentration of 0 to 6% At least selected from a polylactic acid-based resin layer composed of a mixture containing 15 to 50 parts by weight of a plasticizer per part, and an aliphatic polyester resin or an aliphatic-aromatic polyester resin having a glass transition temperature of 0 ° C. or lower. A multilayer polylactic acid resin film, which is a multilayer film in which one type of polyester resin layer is laminated.   2. The multi-layer polylactic acid resin film according to claim 1, wherein the multi-layer polylactic acid resin film is heat-treated, and the heat of crystallization of the polylactic acid resin layer is 0 to 2 J / g and the heat of fusion is 3 to 20 J / g. Multi-layer polylactic acid resin film.   2. The multilayer polylactic acid resin film according to claim 1, wherein the multilayer polylactic acid resin film is a three-layer film obtained by laminating the polyester resin layer on both sides of the polylactic acid resin layer.   Plasticizing polylactic acid-based resin comprising 50 to 100% by weight of weakly crystalline or amorphous polylactic acid having a D-form concentration of 7 to 20% and 0 to 50% by weight of crystalline polylactic acid having a D-form concentration of 0 to 6% A polylactic acid resin layer made of a mixture containing an agent and at least one polyester resin layer selected from an aliphatic polyester resin or an aliphatic-aromatic polyester resin having a glass transition temperature of 0 ° C. or lower are laminated. A method for producing a multilayer polylactic acid resin film, wherein the multilayer film is molded, and further, the multilayer film is subjected to a crystallization treatment.   The method for producing a multilayer polylactic acid resin film according to claim 4, wherein the crystallization treatment is a heat treatment at a temperature of 20 to 100C.   The method for producing a multilayer polylactic acid resin film according to claim 4, wherein the polylactic acid resin layer made of the mixture contains a crystal nucleating agent. The multilayer polylactic acid resin film according to claim 4, wherein the multilayer polylactic acid resin film is a three-layer film formed by laminating the polyester resin layer on both sides of the polylactic acid resin layer. A method for producing a resin film.