JP2003321600A - Polylactic acid aqueous emulsion, method for producing the same and coating containing the polylactic acid aqueous emulsion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid aqueous emulsion which has excellent handling workability, safety, storage stability, and the like, to provide a method for producing the same, and to provide a coating containing the polylactic acid aqueous emulsion. <P>SOLUTION: This polylactic acid aqueous emulsion is characterized by containing a rosin-based resin. The method for producing the polylactic acid aqueous emulsion is characterized by emulsifying a mixture of the polylactic acid with the rosin-based resin in water. The coating is characterized by containing the polylactic acid aqueous emulsion. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polylactic acid aqueous emulsion, a method for producing the same, and a coating agent containing the polylactic acid aqueous emulsion. More specifically, the main component is polylactic acid synthesized from natural raw materials,
In addition, the present invention relates to a polylactic acid aqueous emulsion excellent in storage stability, workability and environmental suitability, a method for producing the same, and a coating agent containing the polylactic acid aqueous emulsion.

[0002]

2. Description of the Related Art Polylactic acid is known as a biodegradable plastic synthesized from natural raw materials such as corn. Polylactic acid has the same convenience as conventional plastics, and is characterized by having biodegradability that conventional plastics do not have. That is, polylactic acid is decomposed into water and carbon dioxide by enzymatic decomposition or hydrolysis and is reduced to the natural world, and the amount of heat consumed during incineration is small and no harmful dioxins are generated, so compared to conventional petroleum plastics. It is attracting attention as a resource-recycling material with high safety and low environmental load, and is already being used in various fields such as containers, packaging, textiles, agricultural materials, and cushioning materials.

Since polylactic acid has been conventionally supplied in a solid form such as pellets, its handleability when applied to the above-mentioned applications was insufficient. Therefore, there is an urgent need to supply in the form of easy handling, especially from the viewpoint of safety, to develop an aqueous emulsion, and the emulsion is used in the market for coating materials and additives for agricultural materials, building materials, and paper materials. Expected to be deployed.

Under these circumstances, studies on an aqueous emulsion of polylactic acid have been made, and JP-A-10-
101911 discloses a biodegradable emulsion composition having an average particle size of 0.05 to 10 µm obtained by emulsification using a specific emulsifier (having an anionic emulsifier content of 80% by weight or more in all emulsifiers). ing.

However, Japanese Patent Laid-Open No. 10-101911
The emulsion composition disclosed in Japanese Patent Laid-Open Publication No. 1994-242242 has insufficient storage stability as an emulsion and is unsatisfactory when applied to various applications as described above.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polylactic acid aqueous emulsion excellent in handling workability, safety, storage stability and the like, and a method for producing the same. Moreover, it aims at providing the coating agent containing the said polylactic acid aqueous emulsion.

[0007]

As a result of intensive studies to solve the above-mentioned problems of the prior art, the present inventors have found that a polylactic acid aqueous emulsion using a rosin resin in combination can achieve the above object. I found that. The present invention has been completed based on this new finding.

That is, the present invention relates to a polylactic acid aqueous emulsion characterized by containing a rosin resin; a polylactic acid aqueous emulsion characterized by emulsifying and dispersing a mixture of polylactic acid and a rosin resin in water. Manufacturing method;
And a coating agent comprising the polylactic acid aqueous emulsion.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The polylactic acid used in the present invention is
In general, lactic acid obtained by fermenting starch such as corn and potato is heat-treated to give lactide, and then obtained by lactide method of ring-opening polymerization of the lactide, and further direct polymerization method of direct dehydration polycondensation reaction of lactic acid Are obtained by. Since lactic acid which is a starting material has optical isomers of L-form and D-form,
Polylactic acid, which is the polymer, has been developed as a product having different properties such as changing the crystallinity by adjusting the abundance ratio of these isomers and changing the molecular weight depending on the difference in the polymerization conditions. Generally, the glass transition temperature of polylactic acid has a range of 40 to 60 ° C. depending on the difference in molecular weight,
The melting point also varies depending on the difference in crystallinity, but in the case of poly L-lactic acid, it is about 170 ° C. In the present invention, such known polylactic acid can be used without any particular limitation, but the polylactic acid has a weight average molecular weight of 10,000 to 10,000.
It is preferably about 200,000. Weight average molecular weight is 1
If it is less than 10,000, the mechanical strength of the resulting coating film tends to be poor, and if it is more than 200,000, handling workability tends to be poor and emulsification tends to be difficult. In addition, the weight average molecular weight in this specification is a polystyrene conversion value by a gel permeation chromatography (GPC) method.

In the present invention, it is necessary to blend a rosin resin as a modifier of polylactic acid for the purpose of improving the adhesion to a substrate, film-forming property, and emulsifying property. As rosin-based resins are also resins derived from natural products, they can be said to be environmentally friendly materials. As the rosin-based resin, gum rosin, raw rosin of wood rosin or tall oil rosin, or stabilized rosin or polymerized rosin obtained by disproportionating or hydrogenating the raw rosin, and further rosin esters that are derivatives of the rosins, Examples thereof include rosin phenols, and one of these can be used alone, or two or more can be used as a mixture. The rosin ester refers to an esterification reaction of the rosin and alcohols, and the rosin phenols refers to a rosin to which phenols are added and thermally polymerized, or an esterified product. The alcohols used for the esterification are not particularly limited, and may be 1 alcohol such as methanol.
Polyhydric alcohols; trimethylolethane, trimethylolpropane, ethylene glycol, ethylene glycol monoalkyl ether, diethylene glycol, diethylene glycol monoalkyl ether, triethylene glycol, triethylene glycol monoalkyl ether, polyethylene glycol, polyethylene glycol monoalkyl ether, propylene glycol , Propylene glycol monoalkyl ether, dipropylene glycol, dipropylene glycol monoalkyl ether, tripropylene glycol, tripropylene glycol monoalkyl ether, polypropylene glycol, polypropylene glycol monoalkyl ether, and other dihydric alcohols, or their monoalkyl ethers Glycerin Can be exemplified those various known polyhydric alcohols 3 or more valences such as pentaerythritol, these one can be used alone or in combination of two or more. Further, compounds obtained by addition reaction of alkylene oxides such as ethylene oxide and propylene oxide to the rosins can also be used in the same manner as the above rosin esters. Among these rosin-based resins, from the viewpoint of compatibility with polylactic acid, diethylene glycol ester of stabilized rosin and triethylene glycol monomethyl ester of stabilized rosin are preferable, and triethylene glycol monomethyl ether ester of stabilized rosin is particularly preferable. .

The method for producing the rosin resin is not particularly limited, and various known methods can be adopted. For example, the rosins and the alcohols may be heated at about 150 ° C. to 300 ° C. while removing generated water out of the system. In addition, it is preferable to perform the reaction in an atmosphere of an inert gas from the viewpoint of preventing coloration of the produced esterified product, and a known catalyst may be used for shortening the reaction time.

In the reaction between the rosins and the alkylene oxides, a generally known cyclic ether cleavage reaction method can be employed. For example, a catalyst such as an alkali metal hydroxide or alkoxide is added, and 7 to 9 × 10 ⁵ is added if necessary.
The reaction may be performed under a pressure of Pa at about 150 to 160 ° C. for about 1 to 5 hours.

The glass transition temperature (T
g) is not particularly limited, and solid ones of 150 ° C. or less to liquid ones of 0 ° C. or less can be appropriately selected and used according to various purposes, but in view of the plasticizing effect on polylactic acid, Tg is It is preferably less than 20 ° C, more preferably less than 0 ° C.

The proportion of polylactic acid and rosin resin used is usually 2 to 4 rosin resin per 100 parts by weight of polylactic acid.
The amount is about 0 parts by weight, preferably 5 to 30 parts by weight. When the amount of rosin resin is less than 2 parts by weight, the modification by adding rosin resin is hardly observed, and when it exceeds 40 parts by weight, the mechanical strength of the coating film tends to decrease. Yes Either case is not appropriate.

The emulsifier used for emulsifying and dispersing the polylactic acid and the rosin resin in water is not particularly limited, and various known anionic, cationic, amphoteric or nonionic low-molecular or high-molecular compounds are used. Emulsifiers can be used.

Examples of low molecular weight anionic emulsifiers include α-olefin sulfonates, alkyl sulphates, alkyl phenyl sulphates, polyoxyethylene alkyl ether sulphates, sulfosuccinic acid half ester salts of polyoxyethylene alkyl ethers and rosin soaps. Examples of the cationic emulsifier include alkyl trimethyl ammonium salt and alkyl pyridinium salt. Examples of the amphoteric emulsifier include various amino acid-type or betaine-type emulsifiers, and the nonionic emulsifiers include polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, sucrose fatty acid ester, sorbitan fatty acid ester, glycerin fatty acid ester. And so on.
Further, as a polymeric emulsifier, various anionic monomers,
Examples thereof include various anionic, cationic, amphoteric or nonionic copolymerization type emulsifiers obtained by copolymerizing a cationic monomer or a nonionic monomer. Among them, the polyoxyethylene alkyl ether sulfosuccinic acid half ester salt is preferable from the viewpoint of good emulsifying property and no concern about environmental hormones.

The type of the emulsifier used in the present invention may be appropriately selected depending on the use of the aqueous polylactic acid emulsion, and one of the emulsifiers may be used alone or two or more of them may be used in combination. The emulsifier is usually used in an amount of 1 to 20 parts by weight, preferably 3 to 10 parts by weight, based on 100 parts by weight of polylactic acid or a mixture of polylactic acid and a rosin resin.
10 parts by weight. When the amount of the emulsifier used is less than 1 part by weight, the storage stability of the aqueous emulsion becomes poor,
Further, if it is more than 20 parts by weight, the water resistance is deteriorated, which is not preferable.

In the present invention, polylactic acid or a mixture of polylactic acid and a rosin resin is emulsified and dispersed in water in the presence of an emulsifier to produce an aqueous emulsion of polylactic acid. The method of emulsification is not particularly limited, and various known methods such as an inversion emulsification method and a high-pressure emulsification method can be adopted, but a high-pressure emulsification machine using a high-pressure emulsifier is preferable because it is easy to obtain an emulsion having a fine and uniform particle size. Method is preferred. The pressure during high-pressure emulsification is preferably 10 to 50 MPa. High-pressure emulsification method, specifically, after dissolving the polylactic acid or a mixture of polylactic acid and a rosin-based resin in a solvent such as benzene and toluene, adding the emulsifier and soft water, and emulsifying using a high-pressure emulsifier. , The solvent is removed under reduced pressure.

The solid content concentration of the polylactic acid aqueous emulsion thus obtained is not particularly limited, but is usually 10 to 7.
It is used by appropriately adjusting it so as to be about 0% by weight. The average particle size of the obtained emulsion is usually 0.2.
˜2 μm, and most of them are uniformly dispersed as particles of 1 μm or less. The average particle diameter is a value measured by using a laser diffraction type particle size distribution measuring device "SALD-2000" (manufactured by Shimadzu Corporation). The emulsion has a white or milky white appearance and has a pH value of about 2-9.

The aqueous polylactic acid emulsion of the present invention comprises:
It can also be used by blending it with various known polymer emulsions, resin emulsions, water-based products such as rubber latex, etc. within the range not departing from the object of the present invention. In addition to these, if necessary, a filler, a plasticizer, a thickener,
Various known additives such as defoaming agents, antioxidants, ultraviolet absorbers, water resistance agents, film-forming aids, preservatives, rust preventives, pigments and dyes may be appropriately contained, and these additives may be added. By blending, the intended coating agent can be produced.

The coating agent containing the aqueous emulsion of polylactic acid of the present invention is used for printing paper, coated paper, paper pack, cardboard, paper bag for the purpose of substituting conventional plastic materials that are difficult to recycle or composting. It can be used as a surface material for paper materials such as, cloth, films and molded products of biodegradable plastics, wood, fertilizers, agricultural chemicals, seeds, and the like. Further, as a coating method on the surface of a substrate such as paper, a roll coater method,
Examples thereof include a method using a coating machine such as an air knife coater method and a blade coater method, and a method such as dipping and spraying.

[0022]

EFFECTS OF THE INVENTION According to the present invention, polylactic acid, which has been conventionally solid, can be provided in the form of an aqueous emulsion, and the handling property can be improved. For this reason, polylactic acid can be used by simple methods such as coating, dipping, and spraying, and it is easy to mix it with other water-based chemicals, which has been difficult until now, and it can be used for various coating agents and additives. Available. The obtained polylactic acid aqueous emulsion is highly safe and has good storage stability because it uses water as a medium. Furthermore, the coating agent containing the aqueous emulsion of polylactic acid of the present invention is characterized by excellent adhesion to various substrates, transparency, low-temperature film-forming property, water resistance, solvent resistance and biodegradability. have.

[0023]

EXAMPLES The present invention will be described in detail below with reference to production examples and examples, but the present invention is not limited to these examples. In each example, parts and% are based on weight.

Production Example 1 100 parts of polylactic acid having a weight average molecular weight of about 30,000 was dissolved in 400 parts of toluene at 100 ° C. for about 1 hour and then cooled to 80 ° C. Then, 10 parts of polyoxyethylene alkyl ether sulfosuccinic acid disodium salt and 300 parts of water were added as an emulsifier, and the mixture was added at 75 ° C. to 1
Preliminary emulsification was performed by vigorous stirring for a period of time. Further, the preliminarily obtained emulsion was mixed with a high-pressure emulsifying machine (manton gaurin company) to 3
High pressure emulsification was performed at a pressure of 0 MPa to obtain an emulsion. Then
Charge the above emulsion to a vacuum distillation apparatus, and heat at 50 ° C for 130 hours.
Vacuum distillation was performed for 6 hours under the condition of Pa to obtain a solid content of 35%,
An aqueous emulsion of polylactic acid having an average particle diameter of 0.5 μm (hereinafter referred to as emulsion (L-1)) was obtained.

Production Example 2 The same operation as in Example 1 was conducted except that polylactic acid having a weight average molecular weight of about 100,000 was used instead of polylactic acid having a weight average molecular weight of about 30,000. %, And an aqueous emulsion of polylactic acid having an average particle diameter of 1 μm (hereinafter referred to as emulsion (L-2)) was obtained.

Production Example 3 In Production Example 1, a diethylene glycol ester of stabilized rosin (“KE-364C”, manufactured by Arakawa Chemical Industry Co., Ltd., Tg: instead of polylactic acid having a weight average molecular weight of about 30,000) was used.
-13 ° C.) and the emulsifier amount was changed to 3 parts in terms of solid content, and the same procedure as in Production Example 1 was carried out to obtain an aqueous emulsion of a rosin resin having a solid content of 50% and an average particle size of 0.3 μm (hereinafter , Emulsion (R-1) was obtained.

Production Example 4 In Production Example 1, triethylene glycol monomethyl ether ester of stabilized rosin (“Pine Crystal GP-200” was used in place of polylactic acid having a weight average molecular weight of about 30,000.
1 ", manufactured by Arakawa Chemical Industry Co., Ltd., Tg: -51 ° C), and the amount of emulsifier was changed to 3 parts in terms of solid content.
50% solid content, average particle size 0.3μ
An aqueous emulsion of rosin resin of m (hereinafter referred to as emulsion (R-2)) was obtained.

Preparation Example 5 In Preparation Example 1, instead of 10 parts of polyoxyethylene alkyl ether sulfosuccinic acid disodium salt (solid content), 4.5 parts of sodium alkylbenzene sulfonate and polyoxyethylene (5 mol of ethylene oxide were added). The same operation as in Production Example 1 was carried out except that 0.5 part of nonylphenyl ether was used, and an aqueous emulsion of polylactic acid having a solid content of 30% and an average particle diameter of 1 μm (hereinafter referred to as emulsion (L-3)). Got

Example 1 80 parts of the emulsion (L-1) obtained in Preparation Example 1 and 20 parts of the emulsion (R-1) obtained in Preparation Example 3 were mixed,
An aqueous emulsion of the present invention (hereinafter referred to as emulsion (EX-1)) having a solid content of 38% and an average particle diameter of 0.4 μm was obtained.

Example 2 80 parts of the emulsion (L-1) obtained in Preparation Example 1 and 20 parts of the emulsion (R-2) obtained in Preparation Example 4 were mixed,
An aqueous emulsion of the present invention (hereinafter referred to as emulsion (EX-2)) having a solid content of 38% and an average particle diameter of 0.4 μm was obtained.

Example 3 80 parts of polylactic acid having a weight average molecular weight of about 50,000 and a diethylene glycol ester of a stabilized rosin ("KE-364").
C ", manufactured by Arakawa Chemical Industry Co., Ltd., Tg: -13 ° C) was dissolved in 200 parts of toluene at 100 ° C for about 1 hour, and then cooled to 80 ° C. Then, 5 parts of polyoxyethylene alkyl ether sulfosuccinic acid disodium salt as a solid content and 300 parts of water were added as an emulsifier, and 7
Preliminary emulsification was performed by vigorous stirring at 5 ° C for 1 hour. Further, the obtained preliminary emulsion was subjected to high pressure emulsification at a pressure of 30 MPa with a high pressure emulsifying machine (manton gaurin company) to obtain an emulsion. Then, the reduced pressure distillation apparatus is charged with the emulsion, and 50
Distillation under reduced pressure was performed for 6 hours at a temperature of 130 hPa to obtain an aqueous emulsion of the present invention (hereinafter referred to as emulsion (EX-3)) having a solid content of 50% and an average particle size of 0.5 μm.

Example 4 In Example 3, instead of the diethylene glycol ester of the stabilized rosin, triethylene glycol monomethyl ether ester of the stabilized rosin ("Pine Crystal GP-2001", manufactured by Arakawa Chemical Industry Co., Ltd., Tg:
-51 ° C) except that the same procedure as in Production Example 1 was performed,
An aqueous emulsion of the present invention (hereinafter referred to as emulsion (EX-4)) having a solid content of 50% and an average particle diameter of 0.4 μm was obtained.

(Evaluation of Storage Stability of Aqueous Emulsion)
Each aqueous emulsion obtained in Production Examples 1, 2, 5 and Examples 1 to 4 was placed in a glass container, sealed, and allowed to stand in a thermostatic chamber at 23 ° C. for 1 month, after which the occurrence of precipitates was visually observed. evaluated. The results are shown in Table 1. <Evaluation Criteria> ◯: Storage stability is good (precipitation is not generated) Δ: Storage stability is slightly poor (a small amount of precipitate can be confirmed) ×: Storage stability is poor (a large amount of precipitate can be confirmed)

(Measurement of minimum film forming temperature of coating film) Production Example 1,
2, 5 and each of the aqueous emulsions obtained in Examples 1 to 4 were subjected to a temperature range of 10 to 5 according to JISK 6828.
The minimum film forming temperature was measured under the condition of 0 ° C. The results are shown in Table 1. If the minimum film forming temperature is not higher than the ambient temperature, a uniform and transparent coating film can be formed without heating and drying.

[0035]

[Table 1]

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Claims (9)

[Claims] 1. A polylactic acid aqueous emulsion containing a rosin-based resin. 2. The polylactic acid aqueous emulsion according to claim 1, which is obtained by mixing an aqueous emulsion of a rosin resin and an aqueous emulsion of polylactic acid. 3. The polylactic acid aqueous emulsion according to claim 1, which is obtained by emulsifying and dispersing a mixture of polylactic acid and a rosin resin in water. 4. The polylactic acid aqueous emulsion according to claim 1, wherein the polylactic acid has a weight average molecular weight of 10,000 to 200,000. 5. The glass transition temperature of the rosin resin is 20 ° C.
The polylactic acid aqueous emulsion according to any one of claims 1 to 4, which is less than 1. 6. The polylactic acid aqueous emulsion according to claim 1, wherein the mixing ratio of the rosin-based resin (in terms of solid content) to 100 parts by weight of polylactic acid is 2 to 40 parts by weight. 7. The polylactic acid aqueous emulsion according to claim 1, which is emulsified and dispersed by a high-pressure emulsification method. 8. A method for producing an aqueous polylactic acid emulsion, which comprises emulsifying and dispersing a mixture of polylactic acid and a rosin resin in water. 9. A coating agent comprising the polylactic acid aqueous emulsion according to any one of claims 1 to 7.