JP2009185108A - Solution of polylactic acid based resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a solution of a polylactic acid based resin, which hardly generates resin precipitates even when stored in low temperatures and is excellent in storage stability. <P>SOLUTION: The solution of the polylactic acid based resin consists of a polylactic acid based copolymer resin (A), whose D-lactic acid is derived from mesolactide, the molar ratio (L/D) of whose L-lactic acid to D-lactic acid is in the range of 1 to 9, whose lactic acid residue content is ≥50 wt% and whose reduced viscosity is 0.2-1.0 dl/g; and a solvent (B). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polylactic acid-based resin dissolved material in which a polylactic acid-based copolymer resin is dissolved in a solvent, and further aims to effectively use meso-lactide generated as a by-product in the process of synthesizing L-lactide. The present invention relates to a dissolved polylactic acid resin. This polylactic acid resin melt can be used in the fields of paints, inks, adhesives and the like.

  Due to the recent increase in awareness of environmental issues, the development of products using synthetic resins made of natural materials or biomass-derived materials has been actively conducted. Since the L-lactic acid obtained by fermenting biomass such as corn starch and the like is a synthetic raw material, various uses have been developed.

  When developing to paints, inks, and adhesives, it needs to be amorphous, and the inventors have already proposed a polylactic acid resin solution in which DL-lactide is copolymerized. (Patent Documents 1, 2, and 3)

In the polylactic acid-based resin, particularly when the lactide content is high, the stability of the resin melt is poor, and a small amount of resin precipitate is generated. The resin precipitate is likely to be generated when stored at a low temperature of about 15 ° C. or less, and is generated when stored for 3 to 6 months.
JP-A-8-92518 Japanese Patent No. 3680988 JP 2002-69352 A

  The subject of this invention is obtaining the polylactic acid-type resin melt | dissolution excellent in the storage stability which a resin deposit does not generate | occur | produce easily at the time of low temperature storage.

  As a result of intensive studies, the present inventors have found that when mesolactide is used as a raw material for copolymerizing D-lactic acid, compared with the case where DL-lactide is copolymerized, the polymer in the case of long-term storage at a low temperature is used. The present inventors completed the present invention by discovering that the stability of the lactic acid resin melt is good, that is, the resin precipitation is suppressed.

That is, this invention consists of the following structures.
(1) D-lactic acid is derived from meso lactide, the molar ratio of L-lactic acid to D-lactic acid (L / D) is in the range of 1 to 9, the lactic acid residue content is 50% by weight or more, and the reduced viscosity is A polylactic acid resin melt containing a polylactic acid copolymer resin (A) and a solvent (B) in the range of 0.2 to 1.0 dl / g.
(2) In the process of synthesizing L-lactide from biomass-derived fermentation L-lactic acid aqueous solution and synthesizing L-lactide through oligomerization of L-lactic acid, meso lactide is by-produced by racemization and separated from L-lactide by distillation purification. The dissolved polylactic acid resin according to (1), which is mesolactide.
(3) Solvent (B) contains at least one of an ester solvent, a ketone solvent, and an aromatic solvent, and dissolves the polylactic acid resin according to (1) or (2) object.
(4) Among the polymerization monomers constituting the polylactic acid copolymer resin (A), the polymerization monomer other than lactide is ε-caprolactone, and the amount of ε-caprolactone copolymerization is in the range of 10 to 50% by weight. The polylactic acid-based resin solution according to (1) or (2), which is characterized.
(5) Among the polymerization monomers constituting the polylactic acid copolymer resin (A), polyglycerin and / or sorbitol was copolymerized in the range of 0.5 to 10% by weight as a ring-opening polymerization initiator. The polylactic acid-based resin solution according to (1) or (2), which is characterized.

  According to the present invention, it is possible to obtain a polylactic acid-based resin solution in which resin precipitates are hardly generated even when stored for a long time at a low temperature and the stability of the resin solution is good. Further, in a preferred embodiment, there is an effect that the residual lactide can be easily removed and the durability (hydrolysis resistance) of the coating film is improved.

  The polylactic acid copolymer resin in the present invention is required to have a molar ratio (L / D) of L-lactic acid to D-lactic acid of 1 to 9. Preferably, it is 1-5.6, More preferably, it is 1. As lactide, it is most preferable to use only mesolactide. In the present invention, mesolactide is a cyclic dimer of L-lactic acid and D-lactic acid.

  When the molar ratio (L / D) of L-lactic acid to D-lactic acid exceeds 9, the solubility in a solvent is deteriorated, and it cannot be used as a raw material resin solution for a coating material.

  In the polylactic acid copolymer resin in the present invention, the lactide copolymerization amount needs to be 50% by weight or more. If it is less than 50% by weight, biodegradability in the composting process is delayed. Moreover, the adhesiveness to molded articles, such as a poly L-lactic acid film, falls, and the usefulness as a raw material for coating materials falls.

  In the polylactic acid resin in the present invention, as copolymerization components other than lactic acid and ε-caprolactone, glycolic acid, 2-hydroxyisobutyric acid, 3-hydroxybutyric acid, 16-hydroxyhexadecanoic acid, 2-hydroxy-2-methylbutyric acid Examples thereof include oxyacids such as 10-hydroxystearic acid, malic acid and citric acid, dicarboxylic acids such as succinic acid, and glycols such as ethylene glycol and propylene glycol.

  The reduced viscosity of the polylactic acid copolymer resin in the present invention needs to be in the range of 0.2 to 1.0 dl / g. When the reduced viscosity is less than 0.2 dl / g, the physical properties of the obtained coating film are too weak because the molecular weight is low. On the other hand, when the reduced viscosity exceeds 1.0 dl / g, the solution viscosity is too high and the coating suitability is deteriorated. The reduced viscosity is a value measured using an Ubbelohde viscosity tube at a sample concentration of 0.125 g / 25 ml, a measurement solvent chloroform and a measurement temperature of 25 ° C.

  In the case of a coating material that is spray-painted like a plastic paint, the reduced viscosity of the polylactic acid copolymer resin is preferably 0.2 to 0.6 dl / g.

  In the case of gravure ink use including a pigment, the reduced viscosity of the polylactic acid-based copolymer resin is preferably in the range of 0.3 to 0.7 dl / g.

  In the case of a dry laminate adhesive, the reduced viscosity of the polylactic acid copolymer resin is preferably in the range of 0.4 to 0.8 dl / g.

  The solvent (B) in the present invention must contain at least one of an ester solvent, a ketone solvent, and an aromatic solvent, and must not contain a halogen solvent such as chloroform. The solvent (B) in the present invention is more preferably at least one or two or more of an ester solvent, a ketone solvent, and an aromatic solvent.

  Examples of ester solvents in the present invention include methyl acetate, ethyl acetate, propyl acetate, and butyl acetate. Examples of ketone solvents include methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and cyclohexanone. Examples of the group solvent include toluene and xylene.

  The polylactic acid-based resin copolymerized with ε-caprolactone in the present invention is particularly useful in adhesive applications, and is preferably 10 to 20% by weight, particularly preferably about 10% by weight, thereby heat-sealing material. A useful polylactic acid-based resin solution can be obtained. Further, by copolymerizing preferably 30 to 40% by weight of ε-caprolactone, it can be used as an adhesive raw material having flexibility that is useful as an adhesive for dry lamination.

  In the present invention, polyglycerin and / or sorbitol can be copolymerized in the range of 0.5 to 10% by weight as an initiator for ring-opening polymerization. The polylactic acid resin using this initiator is effective when a curable resin coating such as a plastic paint, a dry laminate adhesive, or a pressure sensitive adhesive is useful. As the curing agent, a polyfunctional isocyanate compound is effective, and an aliphatic polyfunctional isocyanate is particularly effective.

  As a route for obtaining meso-lactide, an L-lactic acid oligomer is obtained by heat-dehydrating condensation of an aqueous L-lactic acid solution as a process for producing poly L-lactic acid, which is carried out in a large-scale plant, and is present in the reaction system. In the process of obtaining L-lactide, it is excellent from the viewpoint of economic rationality to use meso-lactide that is racemized and by-produced L-lactic acid.

  Furthermore, when meso lactide is used as a raw material, a secondary effect has been found that it is easier to remove the residual monomer under reduced pressure in a batch polymerization method than when DL-lactide is used. When the remaining lactide is removed from the polylactic acid-based copolymer resin, there is an effect that the durability (hydrolysis resistance) of the coating film is improved.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.

Example 1
Polymerization of polylactic acid resin A:
By adding 600 g of L-lactide, 400 g of meso lactide, 10 g of sorbitol and 250 mg of tin octylate to a flask, heating to 180 ° C. in a nitrogen atmosphere, carrying out ring-opening polymerization for 2 hours, and then distilling off unreacted monomers under reduced pressure. A polylactic acid resin A was obtained. The analysis results are shown in Table 1.

Preparation of polylactic acid resin A lysate:
500 g of the above-mentioned polylactic acid-based resin A, 250 g of ethyl acetate and 250 g of butyl acetate were added to the flask and heated and stirred at 60 ° C. for 5 hours to obtain a polylactic acid-based resin A solution.

Stability evaluation of polylactic acid resin A dissolved product:
The polylactic acid-based resin A solution was put in a glass bottle and sealed, and stored at 5 ° C. for 6 months, and the appearance was evaluated by visual judgment. The evaluation results are shown in Table 2.

Preparation and evaluation of white paint using polylactic acid resin A:
100 g of polylactic acid resin A dissolved material, 50 g of titanium oxide (white pigment), and 50 g of butyl acetate were added to a paint shaker and dispersed for 1 hour to obtain a white paint. The evaluation results are shown in Table 3. The pigment dispersibility was evaluated with a gloss meter. The adhesiveness to the test piece made of poly L-lactic acid was evaluated by cutting the grid and peeling the cello tape (registered trademark).

Example 2
Polymerization of polylactic acid resin B:
500 g of L-lactide, 400 g of meso lactide, 100 g of ε-caprolactone, 10 g of sorbitol and 250 mg of tin octylate are added to the flask, heated to 180 ° C. in a nitrogen atmosphere, and subjected to ring-opening polymerization for 2 hours, and then the unreacted monomer is reduced under reduced pressure. By distilling off, polylactic acid resin B was obtained. The analysis results are shown in Table 1.

Preparation of polylactic acid resin B lysate:
A polylactic acid resin B solution was obtained by adding 500 g of polylactic acid resin B and 500 g of ethyl acetate to the flask and stirring with heating at 60 ° C. for 5 hours.

Evaluation of heat sealability:
The polylactic acid resin B dissolved material is applied to a poly L-lactic acid film (thickness 28 μm) at a dry film thickness of 3 μm, dried at 60 ° C. for 15 minutes, and then attached to an untreated poly L-lactic acid film (thickness 28 μm). Matching was performed and evaluation as a heat seal material was performed. Heat sealing was performed at 100 ° C., 0.9 m / min, and 3 kgf / cm 2. The results are shown in Table 4. The adhesive strength was determined by a T-type peel test using a tensile tester. The T-type peel test was carried out under the following conditions: measurement temperature 20 ° C., sample width 10 mm, tensile speed 20 mm / min.

Example 3
Polymerization of polylactic acid resin C:
By adding 600 g of mesolactide, 400 g of ε-caprolactone, 8 g of sorbitol, and 250 mg of tin octylate to a flask under heating in a nitrogen atmosphere at 180 ° C. for 2 hours, and then distilling off unreacted monomers under reduced pressure. A polylactic acid resin C was obtained. The analysis results are shown in Table 1.

Preparation of polylactic acid resin C lysate:
A polylactic acid resin C melt was obtained by adding 500 g of polylactic acid resin C and 500 g of ethyl acetate to the flask and heating and stirring at 60 ° C. for 5 hours.

Evaluation of adhesion:
100 g of a polylactic acid resin C solution and 5 g of a curing agent (Coronate HX, manufactured by Nippon Polyurethane Co., Ltd., aliphatic isocyanate compound) are mixed, and the left is a poly L-lactic acid film (thickness 28 μm) so that the dry film thickness is 9 μm. ) And dried at 60 ° C. for 15 minutes. Next, dry lamination was performed with an untreated poly L-lactic acid film (thickness 28 μm) at 50 ° C., 0.9 m / min, 3 kgf / cm ² , and after aging at 40 ° C. for 3 days, the adhesive strength was evaluated. . The evaluation results are shown in Table 4. The adhesive strength was determined by a T-type peel test using a tensile tester. The T-type peel test was carried out under the following conditions: measurement temperature 20 ° C., sample width 10 mm, tensile speed 20 mm / min.

Comparative Example 1
Polymerization of polylactic acid resin D:
Add 600 g of L-lactide, 400 g of DL-lactide, 20 g of sorbitol, and 250 mg of tin octylate to a flask, heat to 180 ° C. in a nitrogen atmosphere, cause ring-opening polymerization for 2 hours, and then distill off unreacted monomers under reduced pressure. As a result, a polylactic acid resin D was obtained. The analysis results are shown in Table 1.

Preparation of polylactic acid resin D lysate:
A polylactic acid resin D solution was obtained by adding 500 g of polylactic acid resin D, 250 g of ethyl acetate, and 250 g of butyl acetate to the flask and stirring with heating at 60 ° C. for 5 hours.

Stability evaluation of polylactic acid resin D dissolved product:
The polylactic acid-based resin D solution was put in a glass bottle, sealed, stored at 5 ° C. for 6 months, and evaluated by visually judging the appearance. The evaluation results are shown in Table 2.

The lactic acid resin melt of the present invention can be used for applications such as coating agents, inks, and adhesives. In particular, it is useful for coating materials for spray painting such as plastic paints, gravure inks containing pigments, dry laminate adhesives, and the like.

Claims (5)

  D-lactic acid is derived from mesolactide, the molar ratio (L / D) of L-lactic acid to D-lactic acid is in the range of 1 to 9, the lactic acid residue content is 50% by weight or more, and the reduced viscosity is 0.2. A polylactic acid resin solution containing a polylactic acid copolymer resin (A) and a solvent (B) in the range of -1.0 dl / g.   In the process of synthesizing L-lactide from a fermentation-derived L-lactic acid aqueous solution derived from biomass and synthesizing L-lactide through oligomerization of L-lactic acid, mesolactide is a by-product generated by racemization and separated from L-lactide by distillation purification. The dissolved polylactic acid resin according to claim 1, wherein   The solvent (B) contains at least one of an ester solvent, a ketone solvent, and an aromatic solvent, and the polylactic acid resin solution according to claim 1 or 2.   Among the polymerization monomers constituting the polylactic acid copolymer resin (A), a polymerization monomer other than lactide is ε-caprolactone, and the amount of ε-caprolactone copolymerization is in the range of 10 to 50% by weight. The polylactic acid resin solution according to claim 1 or 2. Of the polymerization monomers constituting the polylactic acid copolymer resin (A), polyglycerin and / or sorbitol is copolymerized in the range of 0.5 to 10% by weight as a ring-opening polymerization initiator. The polylactic acid-based resin solution according to claim 1 or 2.