Biodegradable laminate

Abstract

A biodegradable laminate, wherein a polyvinyl alcohol resin layer is laminated on at least one surface of an aliphatic polyester resin layer through an adhesive layer, which is excellent in biodegradability and gas barrier properties, and also excellent in interlayer adhesiveness, is obtained. The adhesive layer comprises, as a main component, a polyester resin (A) which has a polar group and is obtained by graft polymerization of an ,-unsaturated carboxylic acid or an anhydride thereof on a biodegradable polyester resin (A) comprising at least one structural unit selected from structural units represented by the following general formulae (1), (2), and (3): ##STR00001##

Claims

1. A biodegradable laminate comprising a polyvinyl alcohol resin layer laminated on at least one surface of an outer layer through an adhesive layer, the outer layer comprising at least one of polylactic acid and a succinic acid/1,4-butanediol/lactic acid polycondensate, wherein the adhesive layer comprises, in an amount of 90% by weight or more, a polyester resin (A) which has a polar group and is obtained by graft polymerization of an anhydride of maleic acid or itaconic acid on a biodegradable polyester resin (A) comprising an adipic acid/terephthalic acid/1,4-butanediol polycondensate; wherein the amount of the anhydride of maleic acid or itaconic acid used in the graft polymerization is 0.025 to 0.5 parts by weight with respect to 100 parts by weight of the polyester resin (A).

2. The laminate according to claim 1, wherein the polyester resin (A) comprises the polar group in an amount of 0.0001 to 6% by mole with respect to the structural units.

3. The laminate according to claim 1, wherein the polyvinyl alcohol resin has a structural unit represented by the following formula (4): ##STR00009## wherein each of R.sup.1, R.sup.2, and R.sup.3 independently represents a hydrogen atom or an organic group; X represents a single bond or linking chain; and each of R.sup.4, R.sup.5, and R.sup.6 independently represents a hydrogen atom or an organic group.

4. The laminate according to claim 1, wherein the outer layer comprises a succinic acid/1,4-butanediol/lactic acid polycondensate.

5. The laminate according to claim 1, wherein the polyvinyl alcohol resin layer is laminated on at least one surface of a layer comprising polylactic acid.

6. An agricultural film, comprising the biodegradable laminate according to claim 1.

7. The laminate according to claim 1, wherein the polyvinyl alcohol resin has a saponification degree of from 98% to 99.9% by mole.

8. The laminate according to claim 1, wherein the outer layer comprises polylactic acid and a succinic acid/1,4-butanediol/lactic acid polycondensate.

Description

EXAMPLES

(1) Hereinafter, the present invention is explained with reference to Examples, however, the invention is not limited to the description of the Examples as long as it does not depart from the gist of the invention.

(2) The terms part(s) and % in the description are in terms of weight unless otherwise indicated.

Example 1

(3) [Preparation of Polyester Resin (A)]

(4) As a polyester resin (A), 100 parts of an adipic acid/1,4-butanediol polycondensate (Ecoflex C1200 manufactured by BASF Corporation), 0.1 parts of maleic anhydride, and as a radical initiator, 0.01 parts of 2,5-dimethyl-2,5-bis(t-butyloxy)hexane (Perhexa 25B manufactured by NOF Corporation) were dry-blended, and then, the resulting mixture was melt-kneaded under the following conditions by a twin-screw extruder and extruded in the form of a strand, followed by cooling with water. Then, the strand was cut by a pelletizer, whereby a polyester resin (A) having a polar group in a cylindrical pellet form was obtained.

(5) Twin-Screw Extruder

(6) Diameter (D): 15 mm

(7) L/D: 60

(8) Revolutions of screw: 200 rpm

(9) Mesh: 90/90 mesh

(10) Processing temperature: 210 C.

(11) [Preparation of PVA Resin]

(12) In a reactor vessel equipped with a reflux condenser, a dropping funnel, and a stirrer, 68.0 parts of vinyl acetate, 23.8 parts of methanol, and 8.2 parts of 3,4-diacetoxy-1-butene were charged, and then, azobisisobutyronitrile was added thereto at 0.3% by mole (with respect to the amount of the charged vinyl acetate). Then, the temperature was increased in a nitrogen gas stream while stirring to initiate polymerization. When the polymerization degree of vinyl acetate reached 90%, m-dinitrobenzene was added thereto to terminate the polymerization. Subsequently, by a method of blowing methanol vapor, the unreacted vinyl acetate monomer was removed from the system, whereby a methanol solution of a copolymer was formed.

(13) Then, the thus prepared methanol solution was further diluted with methanol to adjust the concentration to 45%, and charged in a kneader. While maintaining the temperature of the solution at 35 C., a methanol solution containing 2% sodium hydroxide was added thereto in an amount of 10.5 mmole with respect to 1 mole of the total amount of the vinyl acetate structural unit and the 3,4-diacetoxy-1-butene structural unit in the copolymer to carry out saponification. As the saponification proceeded, a saponified product was deposited, and when the form of the deposited saponified product was turned into a particle, the saponified product was separated by filtration, washed well with methanol, and dried in a hot-air dryer, whereby a desired PVA resin having a 1,2-diol structure in its side chain was prepared.

(14) The saponification degree of the obtained PVA resin was analyzed based on an alkali consumption required for hydrolysis of remaining vinyl acetate and 3,4-diacetoxy-1-butene, and found to be 99.2% by mole. Further, the average polymerization degree was analyzed according to JIS K 6726, and found to be 450. Further, the content of the 1,2-diol structural unit represented by the general formula (4) was calculated based on an integrated value determined by .sup.1H-NMR (300 MHz proton NMR, a d6-DMSO solution, internal standard substance: tetramethylsilane, 50 C.), and found to be 6% by mole.

(15) [Preparation of Laminate]

(16) By using polylactic acid (Ingeo 4032D manufactured by NatureWorks LLC) as an aliphatic polyester resin, a PVA resin, and a polyester resin (A) having a polar group as an adhesive, a laminate having a three-type five-layer structure of a polylactic acid layer/an adhesive layer/a PVA resin layer/an adhesive layer/a polylactic acid layer was prepared by a three-type five-layer multilayer film forming apparatus provided with three extruders. The thickness of the obtained laminate was 120 m, and the thicknesses of the respective layers were as follows: 50 m/5 m/10 m/5 m/50 m.

(17) The set temperatures of the respective extruders and the roll are as follows.

(18) Set temperatures

(19) Polylactic acid: C1/C2/C3/C4/H/J=180/190/200/200/200/200 C.

(20) PVA resin: C1/C2/C3/C4/H/J=180/200/210/210/210/210 C.

(21) Adhesive resin: C1/C2/H/J=180/200/210/210 C.

(22) Die: FD1/FD2/D1/D2/D3=200/200/200/200/200 C.

(23) Roll: 60 C.

(24) <Evaluation of Interlayer Adhesiveness>

(25) The adhesion states between the polylactic acid layer and the adhesive layer and between the PVA resin layer and the adhesive layer in the obtained laminate were evaluated by hand peeling and determined according to the following criteria. The results are shown in Table 2.

(26) A: The layers are strongly adhered to each other in either case, and when the layers are tried to be peeled from each other, the polylactic acid layer is torn off.

(27) B: The layers are adhered to each other, however, when the layers are tried to be peeled from each other, they are separated from each other at the interface.

(28) C: The layers are easily separated from each other (the layers are not adhered to each other).

Examples 2 to 5

(29) Polyester resins (A) were prepared in the same manner as in Example 1 except that the blended amounts of the maleic anhydride and the radical initiator with respect to 100 parts of the polyester resin (A) in the preparation of the polyester resin (A) in Example 1 were changed as shown in Table 1, and also laminates were prepared in the same manner as in Example 1. Further, thus prepared laminates were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Example 6

(30) A laminate was prepared in the same manner as in Example 1 except that as the polyester resin (A) which is the starting material of the polyester resin (A) in Example 1, a succinic acid/1,4-butanediol polycondensate (GsPla manufactured by Mitsubishi Chemical Corporation) was used, and the thus prepared laminate was evaluated in the same manner as in Example 1. The result is shown in Table 2.

Comparative Example 1

(31) A laminate was prepared in the same manner as in Example 1 except that as the polyester resin which is the starting material of the polyester resin (A) in Example 1, polylactic acid which is an aliphatic polyester resin having no structural units represented by the general formulae (1) to (3) was used, and the thus prepared laminate was evaluated in the same manner as in Example 1. The result is shown in Table 2.

(32) TABLE-US-00001 TABLE 1 Biodegradable polyester resin Maleic anhydride Radical initiator Example 1 Ecoflex 100 parts 0.1 parts 0.01 parts Example 2 Ecoflex 100 parts 0.5 parts 0.05 parts Example 3 Ecoflex 100 parts 0.05 parts 0.005 parts Example 4 Ecoflex 100 parts 0.025 parts 0.0025 parts Example 5 Ecoflex 100 parts 0.5 parts 0.25 parts Example 6 GsPla 100 parts 0.1 parts 0.01 parts Comparative PLA 100 parts 0.1 parts 0.01 parts Example 1

Comparative Example 2

(33) A laminate was prepared in the same manner as in Example 1 except that as the adhesive resin in Example 1, a polyester resin (A) which was not subjected to graft polymerization of maleic anhydride was used, and the thus obtained laminate was evaluated in the same manner as in Example 1. The result is shown in Table 2.

(34) TABLE-US-00002 TABLE 2 Adhesiveness Example 1 A Example 2 B Example 3 A Example 4 A Example 5 A Example 6 B Comparative Example 1 C Comparative Example 2 C

(35) As apparent from these results, the laminates of the Examples obtained by laminating a polylactic acid resin layer and a PVA resin layer using a polyester resin (A) obtained by graft polymerization of maleic anhydride which is an ,-unsaturated carboxylic acid derivative on a polyester resin (A) having a structural unit with an alkylene chain having 2 to 6 carbon atoms as an adhesive resin layer had excellent interlayer adhesiveness. On the other hand, in the laminate of Comparative Example 1 in which a resin obtained using polylactic acid which does not have such an alkylene chain by a graft polymerization operation thereon in the same manner as Example 1 was used as an adhesive layer, and in the laminate of Comparative Example 2 in which the polyester resin (A) which was not subjected to graft polymerization was used, sufficient interlayer adhesiveness could not be obtained.

(36) This application is based on Japanese Patent Application filed on Nov. 11, 2011 (Patent Application No. 2011-247332) and Japanese Patent Application filed on Mar. 7, 2012 (Patent Application No. 2012-050716), and the contents thereof are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

(37) The laminate according to the present invention has gas barrier properties and biodegradability, and further has excellent interlayer adhesiveness, and therefore is useful as a variety of packaging materials for foods and drugs or as agricultural films.