JP2007277353A - Biodegradable resin composition and biodegradable film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biodegradable resin composition with an improved moldability, and a biodegradable film suitable for a biodegradable compost bag, an agricultural film, a packaging material, etc. <P>SOLUTION: The biodegradable resin composition contains a gelatinized product of oxidized starch and a biodegradable resin, provided that the oxidized starch has a structure wherein a bond between C-2 and C-3 is cut and carboxyl groups are formed at C-2 and C-3 in some glucose units in the starch. The biodegradable film is obtained by molding the biodegradable resin composition. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a biodegradable resin composition and a biodegradable film. More specifically, the present invention relates to a biodegradable resin composition with improved moldability and a biodegradable film suitable for compost bags, agricultural films, packaging materials, and the like having biodegradability with improved mechanical properties. .

Biodegradable resins are known to decompose relatively easily without producing harmful substances in water or soil. For this reason, it is attracting worldwide attention from the viewpoint of environmental conservation such as the problem of waste disposal. Among these, the aliphatic polyester resin may have physical properties close to that of polyethylene, and the film obtained by molding the resin may be used for films such as agricultural materials, civil engineering materials, vegetation materials, and packaging materials. It is expected (see, for example, Patent Documents 1 and 2).
However, all of the conventional biodegradable films have a problem in practical use because the tear strength, particularly the tear strength in the machine (stretching) direction of the film is not sufficient.
On the other hand, building a recycling-oriented society by switching from depleted resources to renewable resources has attracted attention, not only biodegradability but also materials derived from natural products, not materials synthesized from petroleum. There is growing interest. At present, starch is a material that is put into practical use as a natural product.
Starch to which moldability and physical properties as a film are imparted are esterified vinyl ester graft polymerized starch (Patent Document 3) and starch ester (Patent Document 4), and polyester graft polymerized starch and polyester alloy (Patent Document 5). Has been proposed. Further, it is considered that if the starch is highly modified, the moldability and physical properties as a film can be further improved, but this is not practical in terms of cost.
It has also been proposed to combine starch gelatinized material with a thermoplastic resin (see, for example, Patent Documents 6 and 7). Furthermore, various proposals have been made for systems to which modified starch is added (for example, see Patent Documents 8, 9, 10 and 11).
However, all of these compositions have insufficient fluidity when heated and melted. For this reason, it was possible to obtain a molded product having a simple shape, such as a sheet, by extrusion molding to some extent. It is difficult to obtain a molded product having a shape, and it is difficult to form a thin film, and even if it can be formed, the film properties are not practical. Moreover, the gelatinization process and the blending process of starch are needed separately, and there was a problem that the manufacturing cost becomes high.
As a method for solving these problems, a composition of oxidized gelatinized starch and biodegradable resin has been proposed (Patent Document 12). This is a method in which gelatinization and oxidation are performed simultaneously, but in practice, it is necessary to control starch degradation by an oxidizing agent in the presence of water and a plasticizer for gelatinization and to sufficiently blend with a resin. However, there is a problem that the manufacturing cost becomes high. In other words, if gelatinization, oxidation, and compounding are performed simultaneously, the molecular weight of the biodegradable resin also decreases, and it is difficult to achieve film moldability and physical properties. As illustrated, it is oxidized during molding. When gelatinized starch pellets and biodegradable resin pellets are molded by dry blending, it may not be a problem in injection molding, but in thin film molding, it is usually mixed in a melt extruder in inflation film molding. Insufficient kneading causes a problem in moldability and physical properties. In addition, the oxidizing agent used is a peroxide, and since the compatibility of gelatinized starch and biodegradable resin is insufficient, the moldability when processing the resin composition into a film is not sufficiently improved. .

Japanese Patent Laid-Open No. 5-271377 Japanese Patent Laid-Open No. 6-170941 JP-A-8-239402 Japanese Patent No. 2939586 JP-A-9-31308 JP-A-1-217002 Japanese Patent Laid-Open No. 2-14228 Japanese Patent Laid-Open No. 3-56543 JP-A-3-70752 Japanese Patent Laid-Open No. 3-74445 Japanese Patent Laid-Open No. 3-74446 Japanese Patent No. 3078478

  In view of the above problems of the prior art, the object of the present invention is to improve the tear strength, particularly the tear strength in the machine (stretching) direction, introduce components derived from natural products, and compost bags, agricultural films and packaging materials. It is desirable to provide a biodegradable resin composition and a biodegradable film that are suitable for the above-mentioned and excellent in economy.

As a result of intensive studies to solve the above problems, the present inventors have used an oxidized starch in which a carboxyl group is formed on the carbon atom by cutting the bond of a carbon atom at a specific position. It has been found that the above problems can be solved, and the present invention has been completed.
That is, the present invention includes the following:
(1) It contains a gelatinized product of oxidized starch and a biodegradable resin, and the oxidized starch is cleaved between C-2 and C-3 in some glucose units in the starch, and C-2 and C-3 A biodegradable resin composition characterized by having a structure in which a carboxyl group is formed in
(2) The above-mentioned (1) containing 20-50% by mass of gelatinized starch of oxidized starch and 80-50% by mass of biodegradable resin based on the total amount of gelatinized product of oxidized starch and biodegradable resin A biodegradable resin composition according to claim 1,
(3) The biodegradable resin composition according to the above (1) or (2), wherein the biodegradable resin is a condensation polymer of ethylene glycol and / or 1,4-butanediol and succinic acid and / or adipic acid ,
(4) The biodegradable resin composition according to (3), wherein the biodegradable resin further contains polylactic acid,
(5) The biodegradable resin composition according to any one of (1) to (4) above, wherein the gelatinized product of oxidized starch is produced using sodium hypochlorite,
(6) The biodegradable resin composition according to any one of the above (1) to (5), wherein gelatinization of oxidized starch is performed using a vented extruder simultaneously with mixing of the biodegradable resin,
(7) The biodegradable resin composition according to any one of (1) to (6), further comprising a solvent having a high boiling point,
(8) The biodegradable resin composition according to any one of (1) to (7), further comprising a plasticizer,
(9) The biodegradable resin composition according to (8), wherein the plasticizer is at least one selected from polyglycerin acetate, derivatives thereof, and adipic acid diesters,
(10) Provided is a biodegradable film obtained by molding the biodegradable resin composition according to any one of (1) to (9).

  According to the present invention, by improving moldability (compatibility), a biodegradable resin composition having a reduced load during production and biodegradability with improved physical properties molded using the resin composition A film is provided.

The present invention will be specifically described below.
In order to obtain a gelatinized product of oxidized starch which is one resin component in the biodegradable resin composition of the present invention, first, the following structure, that is, C-2 in some glucose units in starch It is necessary to produce an oxidized starch having a structure in which C-3 is cleaved and carboxyl groups are formed in C-2 and C-3.

In order to convert the glucose unit in the starch into the structure as described above, for example, it is usually performed by oxidizing the starch with sodium hypochlorite. When starch is oxidized with an oxidizing agent such as a peroxide, open polymerization occurs due to the cleavage of C—C bonds and glycosidic bonds, and the cleavage between C-2 and C-3 is not sufficiently performed. The amount formed is insufficient.
The oxidation of starch with sodium hypochlorite adjusts the aqueous suspension with a starch concentration of 40 to 50% by mass, preferably about 45% by mass, to a pH of 8 to 11, and a chlorine concentration of 8 to 12% by mass, preferably, About 10 mass% sodium hypochlorite aqueous solution is added, and it is made to react at about 40-50 degreeC for about 1 to 2 hours. The reaction is preferably carried out with stirring in a corrosion-resistant reaction vessel under normal pressure. After completion of the reaction, the desired product can be obtained by separating using a centrifugal dehydrator or the like, thoroughly washing with water and drying.
The amount of the carboxyl group is represented by the degree of carboxyl group substitution, and the ordinary one has a degree of carboxyl group substitution (neutralization titration) of 0.001 to 0.100, preferably 0.01 to 0.00. 035.
Commercially available starch can be used as the oxidized starch.
In addition, the method of oxidizing starch with sodium hypochlorite is, for example, Eiji Fuwa, “Dictionary of Starch Science”, Asakura Shoten Co., Ltd., March 20, 2003, p408 and Jiro Jikuni, “Starch Science Handbook” "Asakura Shoten Co., Ltd., July 20, 1977, p501".

  There is no restriction | limiting in particular about the starch used by this invention, Any starch can be used. For example, potato starch, corn starch, sweet potato starch, tapioca starch, sago palm starch, rice starch, wheat starch, and other unmodified starches, and various esterified starches, etherified starches, and the like can be exemplified.

The biodegradable tree that is the other resin component in the biodegradable resin composition of the present invention is not particularly limited. The resin itself may be a biodegradable resin, and is preferably thermoplastic considering moldability. Resins belonging to any of chemically synthesized resins, microbial resins, natural product utilizing resins, and the like may be used. For example, aliphatic polyester (for example, polybutylene succinate, polybutylene succinate-adipate, polyethylene succinate, polycaprolactone, polylactic acid, polyhydroxybutyrate / valerate copolymer, etc.), polyvinyl alcohol, acetylcellulose, etc. be able to. These may be used alone or in combination of two or more.
Among these, aliphatic polyester is preferable in view of film moldability and physical properties. Further, the aliphatic polyester preferably has a melting point of 50 to 180 ° C. and a weight average molecular weight of 50000 or more in order to obtain a good molded product, and these are usually glycols and aliphatic dibasic acids. Is obtained by dehydration cocondensation.
Examples of the glycol include ethylene glycol, 1,4-butanediol, 1,6-hexanediol, decamethylene glycol, neopentyl glycol and the like. Examples of the aliphatic dibasic acid include succinic acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and anhydrides thereof.
Moreover, what added a small amount of trihydric or tetrafunctional polyhydric alcohol, oxycarboxylic acid, or polyhydric carboxylic acid as another component may be used.
As the aliphatic polyester, there are commercially available products, for example, “Bionore” series manufactured by Showa Polymer Co., Ltd. is well known.
Polylactic acid can also be used in combination to adjust the softening temperature of the biodegradable film finally obtained and the flexibility of the film.

  Oxidized starch gelatinized product in the biodegradable resin composition of the present invention (The gelatinization reaction is described together with preparing the biodegradable resin composition by mixing the gelatinized gelatinized starch and the biodegradable resin. ) And the biodegradable resin content, in particular, from the viewpoint of moldability when the resin composition is molded to produce a biodegradable film and the physical properties of the resulting biodegradable film, the starch starch paste Based on the total amount of the chemical compound and the biodegradable resin, it is preferable to contain 20-50% by mass of the gelatinized starch starch (80-50% by mass of the biodegradable resin), more preferably 30-50% by mass. (The biodegradable resin is 70 to 50% by mass). By making the gelatinized product of oxidized starch 20% by mass or more, economic efficiency is exhibited, and an improvement in formability when producing a biodegradable film and an improvement in the tear strength of the resulting film are obtained. Moreover, it is prevented that the physical property of a film falls by making gelatinized material of an oxidized starch into 50 mass% or less.

As a method for producing the biodegradable resin composition of the present invention, it is usually preferable to use an extruder used when melt-mixing a thermoplastic resin.
Specifically, it is equipped with a vent for dehydration with a twin screw system in order to simultaneously gelatinize, dehydrate, and melt-mix the gelatinized oxidized starch and biodegradable resin. is important. Furthermore, in order to ensure a sufficient production amount, sufficient L / D is an important factor, and usually L / D is 32 or more. As a more efficient method of dehydration and mixing, in the first step, the backflow due to pressure rise in the extruder is prevented with an open vent at the completion of gelatinization of the oxidized starch by heating and mixing, and in the second step, oxidized starch is further processed. The dehydration is performed with a vacuum vent while further mixing the gelatinized product and the biodegradable resin.

In order to complete these two steps with a single extruder, it is important that the L / D is 32 at the minimum, and it is possible to increase the discharge amount with an apparatus having a larger L / D. The manufacturing cost can be reduced. In the first step, the set temperature is set to about 60 to 130 ° C., preferably 80 to 140 ° C. according to the softening temperature (or melting point) of the biodegradable resin. Since many biodegradable resins soften (melt) in this temperature range, gelatinized oxidized starch and biodegradable resin are mixed in a molten state simultaneously with gelatinization of the oxidized starch. The residence time in the first step is usually 30 to 180 seconds, preferably 60 to 120 seconds. By setting the residence time to 30 seconds or longer, gelatinization of the oxidized starch proceeds sufficiently, and by setting it to 180 seconds or shorter, decomposition can be suppressed and productivity can be ensured.
In the second step, the set temperature is about 130 to 180 ° C, preferably 150 to 170 ° C. Thereby, the gelatinized product of oxidized starch and the biodegradable resin composition are completely melt-mixed. The residence time in the second step is usually 30 to 120 seconds, preferably 60 to 90 seconds. By setting the residence time to 30 seconds or more, the gelatinized oxidized starch and the sexolytic resin can be sufficiently mixed, and by setting it to 120 seconds or less, decomposition can be suppressed and productivity can be secured. it can.

For the gelatinization of oxidized starch in the first step, it may be possible only with the moisture retained by the oxidized starch itself, depending on the temperature, residence time, resilience, etc., but necessary to complete gelatinization Water and / or polar high-boiling solvents can be added. Examples of the high boiling polar solvent include ethylene glycol, propylene glycol, glycerin, sorbitol, polyethylene glycol, and polypropylene glycol.
Among these, glycerin is preferably used from the viewpoints of compatibility with starch and biodegradable resin, a balance between pasting ability and cost.
The biodegradable resin composition of the present invention is obtained by the procedure as described above.

Next, a biodegradable film formed by molding the biodegradable resin composition of the present invention will be described.
As a method for producing the biodegradable film of the present invention, for example, as described above, the gelatinized product of oxidized starch and the biodegradable resin are melt-mixed using an extruder to obtain a biodegradable resin composition, and the exit of the extruder May be continuously produced by connecting to a known water-cooled or air-cooled inflation molding, T-die type film molding machine, or once pelletized or flaked, then known water-cooling or air-cooled inflation molding, T-die type You may shape | mold using a film extrusion molding machine.
When the biodegradable resin composition of the present invention is formed into a film, it may further contain a plasticizer. The effect of adding a plasticizer is exhibited when the biodegradable resin further contains polylactic acid. As the plasticizer to be used, a glycerin derivative is preferable, and polyglycerin acetate or a derivative thereof or adipic acid diester is particularly preferable. The addition amount is usually about 1 to 10% by mass, preferably 2 to 8% by mass. By setting the content to 1% by mass or more, film properties, particularly tensile elongation and film impact strength are improved, and by setting the content to less than 10% by mass, the plasticizer bleeds to prevent appearance defects.

In addition, the biodegradable film of the present invention may contain additives that are usually used in the technical field as desired, for example, antioxidants, heat stabilizers, UV inhibitors, antistatic agents, flame retardants, and crystallization accelerators. Etc. may be added within a range not impairing the characteristics of the present invention.
Specifically, hindered phenolic antioxidants such as pt-butylhydroxytoluene and pt-butylhydroxyanisole as antioxidants; triphenyl phosphite, trisnonylphenyl phosphite as thermal stabilizers Etc .; Examples of ultraviolet absorbers include pt-butylphenyl salicylate, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2 ^, -carboxybenzophenone, 2,4,5-trihydroxybutyrophenone, etc. N, N-bis (hydroxyethyl) alkylamines, alkylamines, alkylarylsulfonates, alkylsulfonates etc. as inhibitors; hexabromocyclododecane, tris- (2,3-dichloropropyl) phosphate, pentabromo as flame retardants Feni Allyl ether; the crystallization promoter talc, Holon nitrite, polyethylene terephthalate, poly - trans cyclohexanedimethanol terephthalate and the like.

As described above, when the film is produced using the biodegradable resin composition once pelletized or flaked, instead of continuously producing the film following the preparation of the biodegradable resin composition The preset temperature of the inflation molding and T-die type film extrusion molding machine is the same preset temperature as in the second step, that is, about 130 to 180 ° C, preferably 145 to 170 ° C.
The biodegradable film of the present invention may be obtained by further uniaxially or biaxially stretching the film.
Since the biodegradable resin composition of the present invention has improved moldability when it is formed into a biodegradable film, the productivity is improved, and the obtained biodegradable film has mechanical properties. In particular, since the impact strength of the film is improved, it is suitably used for compost bags having biodegradability, agricultural films, packaging materials, and the like.

  The present invention will be described in more detail with reference to examples and comparative examples below, but the present invention is not limited to the following examples.

[Examples 1 to 5 and Comparative Examples 1 to 4]
Table 1 shows the types of starch and biodegradable resin, and the respective amounts (% by mass). The raw materials and additives in each example are mixed using a super mixer, melt-kneaded using a 80 mm screw twin screw extruder (L / D is 32) equipped with a vent for dehydration, and biodegraded. Pellets of the conductive resin composition were obtained. The set temperature is 80 to 140 ° C for the first step, 150 to 180 ° C for the second step, the residence time is 60 to 90 seconds for the first step, and 60 to 90 seconds for the second step.
Each pellet obtained was dried with a dehumidifying air circulation dryer at a temperature of 70 ° C. for 3 hours, and then a film having a thickness of 30 μm and a folding width of 300 mm (equivalent to a blow-up ratio = 3) was formed using an inflation molding machine manufactured by Yoshii Tekko. Molded.
The measuring method of each characteristic is shown below.

<MFR>
Based on JIS K7210, the measurement was performed under conditions of a temperature of 190 ° C. and a load of 21.18 MPa.
<Biodegradability>
A 10cm square film was cut into a 10cm square from the ground in Showa Polymer Co., Ltd.'s Tatsuno Plant, and embedded in a nylon mesh for 1 month. The four grades were evaluated.
A: 80% or more B: 50 to less than 80% B: 10 to less than 50% <Film formability>
In a two-stage evaluation, the case where a film having a predetermined size was obtained was evaluated as ◯, and the case where the film could not be formed was evaluated as x.
<Tensile breaking strength>
It measured according to JIS Z-1702.
<Tensile rupture elongation>
It measured according to JIS Z-1702.
<Young's modulus>
Measured according to ASTM D-822.
<Tear strength>
It measured according to JIS P-8116.
<Impact strength>
It measured according to JIS P-8134.
The above-mentioned mechanical properties were measured for each film only when the film formability was evaluated as ◯ and a film was obtained. Mechanical properties other than impact strength were measured in both the vertical direction (film take-up direction, MD) and the horizontal direction (TD).

<Materials used>
(1) Biodegradable resin A: dehydration condensation type aliphatic polyester manufactured by Showa Polymer Co., Ltd. [Bionore 3001G (melting point: 95 ° C., MFR; 1.2 g / 10 min)]
(2) Biodegradable resin B: dehydrated condensed aliphatic / aromatic polyester [Ecoflex (melting point: 120 ° C., MFR: 4.0 g / 10 min)] manufactured by BASF Corporation
(3) Biodegradable resin C: polycaprolactone manufactured by Daicel Chemical Industries, Ltd. [Placcel H-7 (melting point: 60 ° C., MFR; 3.5 g / 10 min)]
(4) Starch A: Oxidized starch manufactured by Oji Cornstarch Co., Ltd. [Ace A; carboxyl group substitution degree 0.01, viscosity 300 ± 50 BU (Brabender viscosity, concentration 20%, measured after 1 hour at 50 ° C.), moisture 12 % (Normal pressure heating method 105 ° C, 4 hours)
(5) Starch B: Corn starch manufactured by Oji Corn Starch Co., Ltd. [Raw starch; Carboxyl group substitution degree 0, Viscosity 1 100 ± 50 BU (Brabender viscosity, concentration 8%, measured after 1 hour at 50 ° C.), moisture 12% (normally Pressure heating method 105 ° C, 4 hours)
(6) Starch C: Oxidized starch manufactured by Oji Cornstarch Co., Ltd. [Ace C; degree of carboxyl group substitution 0.03, viscosity 200 ± 50 BU (Brabender viscosity, concentration 30%, measured after 50 ° C. after 1 hour), moisture 12% (Normal pressure heating method 105 ° C, 4 hours)
(7) Water: Deionized water
(8) High boiling polar solvent: Glycerin
(9) Plasticizer A: Polyglycerin acetate [Riquemar PL-710] manufactured by Riken Vitamin Co., Ltd.
(10) Plasticizer B: Adipic acid diester [Adekasizer RS-107] manufactured by Asahi Denka Co., Ltd.

  All numerical values other than the example number and the comparative example number in Table 1 represent mass%. The measurement results are shown in Table 2.

From the results shown in Table 2, it can be seen that the biodegradable resin composition of the present invention is superior in mechanical strength and film moldability as compared with the comparative example.

Claims (10)

  A gelatinized product of oxidized starch and a biodegradable resin, and the oxidized starch is cleaved between C-2 and C-3 in some glucose units in the starch, and carboxyl groups are present in C-2 and C-3. A biodegradable resin composition having a structure in which is formed.   The raw material according to claim 1, comprising a gelatinized product of oxidized starch in a proportion of 20 to 50% by mass and a biodegradable resin in a proportion of 80 to 50% by mass based on the total amount of the gelatinized product of oxidized starch and the biodegradable resin. Degradable resin composition.   The biodegradable resin composition according to claim 1 or 2, wherein the biodegradable resin is a condensation polymer of ethylene glycol and / or 1,4-butanediol and succinic acid and / or adipic acid.   The biodegradable resin composition according to claim 3, wherein the biodegradable resin further contains polylactic acid.   The biodegradable resin composition according to any one of claims 1 to 4, wherein the gelatinized product of oxidized starch is produced using sodium hypochlorite.   The biodegradable resin composition according to any one of claims 1 to 5, wherein gelatinization of oxidized starch is performed using an extruder with a vent simultaneously with mixing of the biodegradable resin.   Furthermore, the biodegradable resin composition in any one of Claims 1-6 containing a high boiling point solvent.   Furthermore, the biodegradable resin composition in any one of Claims 1-7 containing a plasticizer.   The biodegradable resin composition according to claim 8, wherein the plasticizer is at least one selected from polyglycerin acetate, derivatives thereof, and adipic acid diester. The biodegradable film formed by shape | molding the biodegradable resin composition in any one of Claims 1-9.