JP2008296482A - Multilayer film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer film which has an improved molding property, has biodegradability and can be used suitably for a compost bag, an agricultural film, a packaging film or the like. <P>SOLUTION: The multilayer film comprises: a middle layer with a composition including oxidized starch having such a structure that a part of glucose unit in the starch is cut between C-2 and C-3 and carboxyl groups are formed at C-2 and C-3, and a biodegradable polymer; and an outer layer and inner layer which contain biodegradable resins respectively. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a multilayer film. More specifically, the present invention relates to a multilayer film having improved biodegradability suitable for compost bags, agricultural films, packaging materials and the like, with improved moldability and 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 shaped product, and it is even more difficult to form a thin film. Even if it could be molded, the film properties were 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, there may be no problem with injection 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. .
In order to solve this problem, a gelatinized product of oxidized starch and a biodegradable resin into which a specific chemical structure has been introduced are used as a composition, and compared with a composition of an unmodified starch gelatinized product and a biodegradable resin. In particular, it has been found that a film having significantly improved film formability and mechanical properties of the film, particularly tear strength in the machine direction, can be obtained. However, this composition was an opaque film having a thickness of 20 μm and was opaque with a haze of 80 to 90%. In the case of agricultural multi-films and packaging bags, there are fields that can be used even when opaque, but there is a great demand for transparency. Especially in agricultural multi-films, transparency is one of the important characteristics because it affects the growth. Furthermore, the moisture permeability is remarkably high because it contains starch. Compared with so-called polyolefins such as polyethylene and polypropylene, the biodegradable resin that is an aliphatic polyester is also not low in moisture permeability. There is a high feature. This is because the agricultural multi-film has a problem that the farmland dries, and in the compost bag, odor components in the garbage are diffused to the outside together with water vapor, which causes a bad odor.

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 transparency and water vapor permeability of the film, to improve the tearing strength in the machine (stretching) direction, and to introduce components derived from natural products, Another object of the present invention is to provide a multilayer film having biodegradability that is suitable for compost bags, agricultural films, packaging materials, and the like and has excellent economic efficiency.

As a result of intensive studies in order to solve the above problems, the present inventors have found that the above problems can be solved by using a multilayer film having a specific layer configuration and composition, and the present invention has been completed. It came to do.
That is, the present invention includes the following:
(1) A composition comprising oxidized starch and a biodegradable resin having a structure in which a part of glucose units is cleaved between C-2 and C-3 and a carboxyl group is formed in C-2 and C-3 A multilayer film comprising an intermediate layer, and an outer layer and an inner layer each containing a biodegradable resin,
(2) The multilayer film according to (1) above, wherein the thickness ratio of the outer layer, the intermediate layer, and the inner layer is 1: 1: 1 to 1: 16: 1.
(3) The composition containing the oxidized starch and the biodegradable resin is based on the total amount of the gelatinized product of the oxidized starch and the biodegradable resin, and 20 to 50% by mass of the gelatinized product of the oxidized starch and the biodegradable resin A multilayer film according to the above (1) or (2), comprising 80 to 50% by mass of
(4) The multilayer film according to any one of (1) to (3), wherein the biodegradable resin is a condensation polymer of ethylene glycol and / or 1,4-butanediol and succinic acid and / or adipic acid. ,
(5) The biodegradable resin is an aliphatic aromatic polyester, a condensation polymer of an aromatic polycarboxylic acid and an aliphatic polyol and / or an aliphatic polycarboxylic acid and an aromatic polycarboxylic acid and an aliphatic polyol, The multilayer film according to any one of (1) to (3), which is a condensation polymer of
(6) The multilayer film according to (5), wherein the aliphatic polycarboxylic acid is adipic acid, the aromatic polycarboxylic acid is terephthalic acid, and the aliphatic polyol is butanediol,
(7) The multilayer film according to any one of (1) to (6), wherein the gelatinized product of oxidized starch is produced using sodium hypochlorite,
(8) The multilayer film according to any one of (1) to (7), wherein gelatinization of the oxidized starch is performed using a vented extruder simultaneously with mixing of the biodegradable resin,
(9) The multilayer film according to any one of (1) to (8), wherein the composition containing the oxidized starch and the biodegradable resin further contains a solvent having a high boiling point,
(10) The multilayer film according to any one of (1) to (9) above, wherein the intermediate layer, outer layer or inner layer further contains a plasticizer, and
(11) The multilayer film according to (10), wherein the plasticizer is at least one selected from polyglycerin acetate, derivatives thereof, and adipic acid diester.

  According to the present invention, a multi-layer film having biodegradability with improved transparency, water vapor barrier properties, and mechanical properties is provided.

The present invention will be specifically described below.
The layer structure in the multilayer film of the present invention is 3 layers or more. The inner layer and the outer layer are layers on the surface of the film, and in the case of a three-layer blown film, they correspond to the inside and the outside of the bubble, respectively. In the case of a T-die film, the side that contacts the cooling roll is the inside, and the side that contacts the nip roll is the outside.
In order to obtain a gelatinized product of oxidized starch which is one component in the composition of starch and biodegradable resin used for the intermediate layer in the multilayer film of the present invention, first, the following structure, that is, in the starch, It is necessary to produce oxidized starch having a structure in which C-2 and C-3 in some glucose units are 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.
Oxidation of starch with sodium hypochlorite is about 40 to 50% by mass of starch concentration, preferably about 45% by mass of aqueous suspension is adjusted to pH 8 to 11 and chlorine concentration of about 8 to 12% by mass, Preferably, about 10 mass% sodium hypochlorite aqueous solution is added and it reacts 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.
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 as the raw material of an oxidized starch, 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 resin which is the other resin component in the composition containing oxidized starch and biodegradable resin used for the intermediate layer in the multilayer film 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.), aliphatic aromatic polyester (polybutylene, etc.) Terephthalate-adipate copolymer, etc.), polyvinyl alcohol, acetyl cellulose and the like. 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, and it is preferable to use ethylene glycol or 1,4-butanediol. 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.
As the aliphatic aromatic polyester, there are commercially available products, for example, “Ecoflex” manufactured by BASF 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.
As the aliphatic polyester, it is preferable to use “Bionore” series.

  The gelatinized product of oxidized starch in the composition used for forming the intermediate layer in the multilayer film of the present invention (for gelatinization reaction, the gelatinized product of oxidized starch and the biodegradable resin are mixed to obtain a biodegradable resin composition As the content ratio of the biodegradable resin), in particular, from the viewpoint of moldability when producing the intermediate layer by molding the same composition and physical properties of the obtained intermediate layer, Based on the total amount of gelatinized product of oxidized starch and biodegradable resin, it is preferable to contain 20-50% by mass of gelatinized product of oxidized starch (80-50% by mass of biodegradable resin), more preferably 30 -50 mass% (biodegradable resin is 70-50 mass%). By making the gelatinized product of oxidized starch 20% by mass or more, economic efficiency is exhibited, and an improvement effect of moldability when producing the intermediate layer and an improvement in tear strength of the obtained intermediate layer are obtained. Moreover, it is prevented that the physical property of an intermediate | middle layer falls by making gelatinized material of an oxidized starch into 50 mass% or less.

As a method for producing a composition containing oxidized starch and a biodegradable resin used for forming an intermediate layer in the multilayer film of the present invention, an extruder that is usually used when melt-mixing a thermoplastic resin is used. It is preferable.
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 the pressure increase in the extruder is prevented with an open vent at the completion of gelatinization of the oxidized starch by heating and mixing, and further in the second step, oxidized starch is used. 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 160 ° 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.

In order to gelatinize the 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, elasticity, etc., but it is necessary to complete the 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 composition containing the oxidized starch used for the intermediate layer of the present invention and the biodegradable resin is obtained by the procedure as described above.

Next, the biodegradable multilayer film of the present invention will be described.
As a method for producing a biodegradable multilayer film of the present invention, for example, as described above, a gelatinized product of oxidized starch and a biodegradable resin are melt-mixed using an extruder to form an intermediate layer. As a composition, the extruder outlet is connected to a known water-cooled or air-cooled multilayer inflation molding, a T-die multilayer film molding machine, and continuously manufactured by coextrusion with a biodegradable resin as an outer layer and an inner layer. Alternatively, the composition for forming the intermediate layer is once pelletized or flaked, and separately, using a known water-cooled or air-cooled multilayer inflation molding or T-die multilayer film extrusion machine, the outer layer and the inner layer are similarly formed. You may shape | mold by a coextrusion method with the biodegradable resin used as.
Furthermore, after a film to be an intermediate layer is produced, a solution of a biodegradable resin may be applied to both surfaces thereof to form a film to be an outer layer and an inner layer.
As the biodegradable resin for forming the outer layer and the inner layer, a biodegradable resin such as the above-mentioned aliphatic polyester, which is the other resin component in the composition used for forming the intermediate layer, is used in appropriate combination. Can do.
When forming into the biodegradable multilayer film of the present invention, each of the intermediate layer, outer layer and inner layer 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, for each layer of the intermediate layer, outer layer or inner layer of the biodegradable multilayer film of the present invention, additives usually used in the technical field as desired, for example, antioxidants, heat stabilizers, UV protection An agent, an antistatic agent, a flame retardant, a crystallization accelerator and the like may be added as long as the characteristics of the present invention are not impaired.
Specifically, 1,1,3-tris (2-methyl-4hydroxy-5-t-butylphenyl) butane and n-octadecyl-3- (3,5-di-t-butyl) are used as antioxidants. -4-hydroxyphenyl) propionate, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, triethylene glycol bis [3- (3-t-butyl-4- Hindered phenolic antioxidants such as hydroxy-5-methylphenyl) propionate] and tris (3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate; triphenyl phosphite as the thermal stabilizer; Trisnonylphenyl phosphite, etc .; UV absorbers include pt-butylphenyl salicylate, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2 ^, -carboxybe Nzophenone, 2,4,5-trihydroxybutyrophenone, etc .; N, N-bis (hydroxyethyl) alkylamine, alkylamine, alkylarylsulfonate, alkylsulfonate, etc. as antistatic agent; Hexabromocyclododecane as flame retardant, Tris- (2,3-dichloropropyl) phosphate, pentabromophenyl allyl ether and the like; Examples of the crystallization accelerator include talc, holon nitride, polyethylene terephthalate, poly-transcyclohexanedimethanol terephthalate and the like.

As described above, the starch and biodegradable resin once pelletized or flaked instead of continuously producing a film following the preparation of the composition of oxidized starch and biodegradable resin used for the intermediate layer When a multilayer film is produced using a composition containing, the preset temperature of the multilayer inflation molding, T-die type multilayer film extruder is the same as that of the second step, that is, about 130 to 180 ° C., preferably 145 to 170 ° C.
The biodegradable multilayer film of the present invention may be further uniaxially or biaxially stretched.
The ratio of the outer layer: intermediate layer: inner layer thickness in the layer structure of the biodegradable multilayer film of the present invention is preferably 1: 1: 1 to 1: 16: 1, more preferably 1: 2: 1. 1: 8: 1. However, the thickness of the outer layer and inner layer does not necessarily have to be the same. Considering the stability, flexibility, biodegradability, cost, etc. when forming different films depending on the application of the multilayer film and the type of biodegradable resin used And can be appropriately changed.
If the thickness of the intermediate layer is significantly smaller than the thickness of the outer layer or the inner layer, the mechanical properties and low cost characteristic of the composition containing oxidized starch and biodegradable resin used for the intermediate layer cannot be utilized. When the thickness of the intermediate layer is 16 times or more of the thickness of the outer layer or the inner layer, the outer layer and the inner layer become too thin and molding stability cannot be obtained. Even if molding can be performed, the surface haze does not improve, and the total haze is reduced. It cannot be improved.
The total thickness of the multilayer film is preferably 10 to 100 μm, more preferably 15 to 50 μm, from the viewpoints of ease of handling, flexibility, film strength, cost, and the like.
The composition containing oxidized starch and biodegradable resin used for forming the intermediate layer in the multilayer film of the present invention has improved moldability when it is formed into a film, so that productivity is improved, And since the multilayer film obtained by using it has improved mechanical properties, especially the impact strength of the multilayer film, it is suitably used for compost bags, agricultural films and packaging materials having biodegradability.

  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 1-6 and Comparative Examples 1-3]
The resin materials used in each example are shown in Table 1, and the measured values of each characteristic are shown in Table 2. In Table 1, numerical values other than the example number, the comparative example number, and the thickness ratio in the layer structure all represent mass%.
The column of the intermediate layer in Table 1 shows the types of starch and biodegradable resin used in the intermediate layer, and the respective blend amounts (mass%). The raw materials and additives in each example were mixed with a super mixer, melt-kneaded using a 65 mm screw twin screw extruder (L / D is 35) equipped with a vent for dehydration, and biodegradable resin A pellet of the composition was obtained. The set temperature is 80 to 140 ° C. for the first step, 120 to 160 ° 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 80 ° C. for 20 hours, and then a three-layer three-layer inflation molding machine (extruder 40 mmφ, die diameter 100 mm, lip interval 1.5 mm) manufactured by Tommy Machine Industries, Ltd. A multilayer film having a thickness of 20 μm (outer layer and inner layer thickness of 5 μm, intermediate layer thickness of 10 μm) and a folding width of 350 mm (equivalent to a blow-up ratio of 2.2) was coextruded. When two types of biodegradable resins were used for the outer layer and the inner layer, the pellets were mixed in advance with a tumbler, and then charged into the hopper of each extruder to perform molding.
The measuring method of each characteristic is shown below.

<Young's modulus>
Measured according to ASTM D-822.
<Tensile breaking strength>
It measured according to JIS Z-1702.
<Tensile rupture elongation>
It measured according to JIS Z-1702.
<Tear strength>
It measured according to JIS P-8116.
<Transparency (Haze)>
It measured according to JIS K-7136.
<Biodegradability>
Using the soil from the field of SDS Biotech “Minori Agricultural Experiment Station”, the water content was adjusted to 50% of the maximum water volume. The soil was adjusted by acclimatization by pre-exposure for 1 month with a 20 μm film made from “Bionole 3001G”.
The multilayer film obtained in each example cut to 5 cm square was sandwiched between nylon meshes and embedded for one month, and then the mass loss was measured, and the degree of biodegradation was evaluated in% from the reduction ratio. The soil in which the test sample of the multilayer film is embedded is managed under constant temperature and humidity at a temperature of 23 ° C. and a relative humidity of 50%, and the moisture in the soil is determined from the decrease in the total mass (sample plus soil) every week. Calculated, added and controlled to retain 50% of maximum water usage.
<Water vapor permeability>
For water vapor permeability, using a molded 20 μm thick film according to JIS K 7129 (Method A) (40 ° C., 90% RH), using a water vapor permeability tester L80-4000 manufactured by LYSSY, g / m ² · 24 hour).
<Film formability>
In the two-stage evaluation, a case where a film having a predetermined dimension was obtained was indicated as ◯, and a case where the film could not be formed was indicated as ×.
Among the above properties, mechanical properties were measured for each film only when the film formability was evaluated as ◯ and a film was obtained. The mechanical properties 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. [Bionole 3001G (melting point: 95 ° C., MFR; 1.2 g / 10 min)]
(2) Biodegradable resin B: dehydrated condensation type aliphatic / aromatic polyester [Ecoflex (melting point: 120 ° C., MFR; 4.0 g / 10 min)] manufactured by BASF Corporation
(3) Biodegradable resin C: dehydration condensation type aliphatic polyester manufactured by Showa Polymer Co., Ltd. [Bionole 1001G (melting point: 114 ° C., MFR; 1.2 g / 10 min)]
(4) Starch A: Oxidized starch manufactured by Oji Corn Starch Co., Ltd. [Ace A: Carboxyl group substitution degree 0.01, viscosity 300 plus or minus 50 BU (Brabender viscosity, concentration 20% by mass, measured after 1 hour at 50 ° C.), moisture 12% by mass (atmospheric 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 1100 plus or minus 50 BU (Brabender viscosity, concentration 8 mass%, measured after 50 ° C. after 1 hour), water content 12 mass% (Normal pressure heating method 105 ° C, 4 hours)
(6) Water: Deionized water
(7) High-boiling polar solvent: Sakamoto Pharmaceutical Co., Ltd., purified glycerin
(8) Plasticizer A: RIKEN Vitamin Co., Ltd. polyglycerin acetate [Riquemar PL-710]
(9) Plasticizer B: Adipic acid diester [Adekasizer RS-107] manufactured by Asahi Denka Co., Ltd.

  From the measurement results of the respective characteristics shown in Table 2, it can be seen that the multilayer film of the present invention is superior in balance of mechanical strength, transparency and film formability as compared with the comparative example.

Claims (11)

  An intermediate composition comprising oxidized starch and a biodegradable resin having a structure in which C-2 and C-3 in some glucose units are cleaved and carboxyl groups are formed in C-2 and C-3 A multilayer film comprising a layer and a layer in which the outer layer and the inner layer each contain a biodegradable resin.   The multilayer film according to claim 1, wherein the thickness ratio of the outer layer, the intermediate layer, and the inner layer is 1: 1: 1 to 1: 16: 1.   The composition containing the oxidized starch and the biodegradable resin is based on the total amount of the gelatinized product of the oxidized starch and the biodegradable resin, 20 to 50% by mass of the gelatinized product of the oxidized starch and 80 to 80% of the biodegradable resin. The multilayer film according to claim 1 or 2 comprising 50% by mass.   The multilayer film according to any one of claims 1 to 3, 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 is an aliphatic aromatic polyester, and a condensation polymer of an aromatic polycarboxylic acid and an aliphatic polyol and / or a condensation polymer of an aliphatic polycarboxylic acid or an aromatic polycarboxylic acid and an aliphatic polyol. The multilayer film according to any one of claims 1 to 3, which is a coalescence.   The multilayer film according to claim 5, wherein the aliphatic polycarboxylic acid is adipic acid, the aromatic polycarboxylic acid is terephthalic acid, and the aliphatic polyol is butanediol.   The multilayer film according to any one of claims 1 to 6, wherein the gelatinized product of the oxidized starch is produced using sodium hypochlorite.   The multilayer film according to any one of claims 1 to 7, wherein gelatinization of the oxidized starch is performed using a vented extruder simultaneously with mixing of the biodegradable resin.   The multilayer film according to any one of claims 1 to 8, wherein the composition containing the oxidized starch and the biodegradable resin further contains a solvent having a high boiling point.   The multilayer film according to any one of claims 1 to 9, wherein the intermediate layer, the outer layer, or the inner layer further contains a plasticizer.   The multilayer film according to claim 10, wherein the plasticizer is at least one selected from polyglycerin acetate, derivatives thereof, and adipic acid diester.