JP3398851B2 - Moisture resistant biodegradable resin foam - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a biodegradable resin foam having moisture resistance. BACKGROUND ART Conventionally, resin foams such as expanded polystyrene have been used as buffers for trays of fresh foods, containers for cup noodles, home electric appliances and the like. However, synthetic resin products such as polystyrene have been converted to biodegradable resin foams because of problems in processing such as incineration and burying after use. However, none of the conventional biodegradable resin foams has moisture resistance, and cannot be used in places with high humidity. The present invention relates to a biodegradable resin foam that has solved such a problem relating to moisture resistance. Conventionally, natural materials such as straw and rice hulls have been used as they are as cushioning materials for packing and transporting fruits such as apples and ceramics, and some natural materials such as cotton and old newspaper have been used. I've used processed ones. Later, with the development of the synthetic resin industry, polystyrene foam was developed.Polystyrene foam was used not only in cushioning materials for mechanical parts, electrical parts and home appliances, but also in trays for fresh food and containers for cup noodles. Until it was used. However, synthetic resin products used in the packaging of other foodstuffs, daily necessities, furniture, etc., including these polystyrene foams, are disposed of as garbage after use. However, unlike natural products such as straw and cotton, if they are dumped in landfills, they will not be decomposed by microorganisms,
It will remain bulky for a long time, hindering the growth of the local plants, impairing the stability of the ground,
Occasionally, birds, wild animals, fish, and the like have inadvertently eaten the food, causing problems such as impairing the health of these animals. Therefore, development of biodegradable plastics has been promoted. [0003] Among the biodegradable plastics, the first to be developed is a plastic mixed with starch such as low-density polyethylene mixed with corn starch. Thereafter, polypropylene was used as a resin for the base material from the viewpoint of strength and the like, and polyvinyl alcohol and the like were also used from the viewpoint of hydrophilicity and the like. When such a starch-containing plastic is disposed of in soil, first, the portion of the starch mixed therein is decomposed by microorganisms, whereby the plastic is made porous and the surface area is increased. It is likely to be susceptible to weathering and the action of other microorganisms and eventually assimilated into the soil. It is said that even if it is made porous, polyethylene and polypropylene are not completely decomposed by microorganisms and remain in the soil as it is, but polyvinyl alcohol is decomposed by Pseudomonas putida in the soil. Is revealed. Biodegradable plastics mixed with starch having such properties generally do not have water resistance. In addition, taking advantage of this lack of water resistance, some of them are characterized by being able to shrink to 1/20 in about 30 minutes when water is applied and to reduce the weight. On the other hand, polyesters obtained by ester-polymerizing hydroxy fatty acids such as glycolic acid and lactic acid which are present in living organisms have also been developed and used as medical materials such as bioabsorbable sutures used in surgery. Further, in these polyesters, if the length of the methylene chain is increased, the water resistance is improved, but the hydrophilicity is reduced, and the polyester is not degraded in vivo, and the rate of biodegradation by microorganisms is considered to be slow. With ethylene glycol,
Polyesters obtained by condensing low-molecular-weight monomers having 10 or less methylene chains, such as condensates of succinic acid and 1,4-butanediol and condensates of adipic acid and 1,4-cyclohexanedimethanol. It is known to collapse rapidly in soil. [0005] As described above, at present,
As biodegradable plastics, those used in large amounts are plastics mixed with starch, but all have poor water resistance and moisture resistance, and when used as cushioning foam for packing, etc. It was necessary to use it in a moisture-proof bag made of a polyethylene film or the like, which involved cumbersome operations such as insertion into the bag, caution and inspection for tearing of the bag, and disposal of the bag after use. Even when there is no danger of the package being wet at all, if the foam for cushioning is used as it is for packaging home appliances and machine parts, it absorbs the humidity in the air, and the foam may fall off or be removed from the stored goods. There is a gap between them, impairing the function as a cushioning material, or, if used for packing fruits and vegetables, absorbs the moisture of fruits and vegetables and muddy the foam, thus functioning as a cushioning material However, problems such as disappearance at all occurred. The problem to be solved by the present invention is to provide a biodegradable plastic foam used for such a cushioning material for packing and the like, which has moisture resistance. Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors initially mixed natural solid fats and oils such as natural wax and the like with a plastic master patch mixed with starch. And tried to produce a foam. However, during the treatment with an extruder, problems such as separation of water and oils and fats occurred, and a uniform foam could not be produced. Then, as a result of further research, they have reached the present invention. The present invention relates to 40-80% by weight of starch, 10-20% by weight of polyvinyl alcohol, and
It is a moisture-resistant biodegradable resin foam comprising 10 to 40% by weight of an aliphatic polyester. [0007] The starch used in the present invention is not necessarily limited to corn starch, and may be any starch degraded by microorganisms. Grain starch that swells due to the water content is more preferred. Further, any polyvinyl alcohol may be used as long as it has an affinity for starch and has a certain degree of saponification and is used as a resin. In addition, as for aliphatic polyester, from the viewpoint of biodegradability alone, it is better that the length of the fatty chain between ester bonds is short, such as lactic acid and glycolic acid.
In order to increase the moisture resistance, the length of the fatty chain between the ester bonds is preferably long as long as the biodegradability is not lost. The other components include surfactants, pigments, and other additives for resins. [0008] The amount of starch used in the present invention is 4
It must be in the range of 0-80% by weight, 40% by weight
If it is less than 1, the biodegradation rate becomes slow and the foaming property becomes weak.
On the other hand, if it exceeds 80% by weight, the moisture resistance is lost and the strength is lowered. The amount of polyvinyl alcohol must be in the range of 10 to 20% by weight, and if it is less than 10% by weight, the strength is reduced, and if it exceeds 20% by weight, the biodegradation rate is slowed and the foamability is weakened. . The amount of aliphatic polyester is
It is necessary to be in the range of 10 to 40% by weight, and if it is less than 10% by weight, moisture resistance is lost, and if it exceeds 40% by weight, foamability becomes poor. The moisture-resistant biodegradable resin foam according to the present invention comprises 40 to 80% by weight of starch, polyvinyl alcohol 1
0 to 20% by weight and an aliphatic polyester 10 to 40
% By weight and adjusted to have a water content of 10 to 15% by weight, and then supplied to an extruder at 200 ° C to 2%.
It is manufactured by heating and pressurizing to 70 ° C. and 60 to 100 atm, extruding from a nozzle under atmospheric pressure, and foaming by rapid vaporization of contained water. In this case,
Starch 40-80% by weight and polyvinyl alcohol 10-
Pellets kneaded with 20% by weight may be used. Further, kneaded pellets of a commercially available starch and polyvinyl alcohol, such as "Matter-Bi" (PE01U) manufactured by Novamont, may be used. The moisture-resistant biodegradable resin foam according to the present invention is composed of starch, polyvinyl alcohol and aliphatic polyester which are decomposed by microorganisms, and therefore has biodegradability as a whole. Also, when released from a high temperature and high pressure state to a normal temperature and normal pressure state, water contained in the starch particles is rapidly vaporized to be porous, and polyvinyl alcohol having a large number of hydrophilic groups is formed in the pores. The toughness is given to the wall, and the aliphatic polyester is
It is estimated that the wall surfaces of the pores are provided with moisture resistance.
In addition, it is also possible to produce a moisture-resistant biodegradable resin foam using polypropylene instead of aliphatic polyester.However, since polypropylene does not have biodegradability, complete biodegradability can be obtained. I can't say it has. DETAILED DESCRIPTION OF THE INVENTION Production of Foam According to the Present Invention [Example 1] 57 parts by weight of corn starch (manufactured by Kagoshima Starch Co., Ltd.), 30 parts by weight of polyvinyl alcohol ("Gohsenol" NM-11 manufactured by Nippon Synthetic Chemical Co., Ltd.), Butylene succinate (“Bionore” manufactured by Showa High Polymer Co., Ltd.)
3) To a mixture of 10 parts by weight and 3 parts by weight of calcium carbonate, water is replenished so that the water content becomes 10% by weight, and the mixture is supplied to a twin-screw extruder at a maximum set temperature of 250 ° C. and a maximum pressure of 60 atm. Then, the mixture was extruded into the atmosphere from a nozzle having an inner diameter of 2 mm to produce a substantially cylindrical foam (hereinafter referred to as "foam 1"). Example 2 82 parts by weight of corn starch and 18 parts by weight of polyvinyl alcohol for resin were kneaded well and pelletized, and the mixture was adjusted to a water content of 13% by weight. 10 parts by weight of the salt, and the same as in Example 1,
The foam was produced using a twin screw extruder. Its appearance and the like were exactly the same as those in Example 1. 2. Production of Foam Using Polypropylene [Reference Example] 82 parts by weight of corn starch and 18 parts by weight of polyvinyl alcohol for resin were kneaded well and pelletized, and the mixture was adjusted to have a water content of 13% by weight. , 3 parts by weight of polypropylene for resin, mixed with a twin-screw extruder,
Maximum set temperature 270 ° C, maximum pressure 70 atm, inner diameter 2m
m, and extruded into the atmosphere to produce a foam (hereinafter referred to as “foam 2”). Its appearance and the like were exactly the same as those in Example 1. 3. For comparison of the preparation of comparative examples, “Eco-Home” (hereinafter referred to as “Foam 3”) manufactured by Oji Bag Co., Ltd. and “Renaissance” (hereinafter referred to as “Foam 4”) manufactured by Strapack, having almost the same shape. Was selected. 4. Moisture resistance test 50 × 50 cm in height and width, water is placed in the bottom of a 70 cm high container, an inner lid having pores is provided thereon, and the space above it is divided into a 25 × 25 cm vertical and horizontal room with a height of 60 cm,
Foams 1 to 4 were packed in each room at a height of 50 cm, and a 3.5 kg weight was placed in each room, and changes over time in height and moisture absorption were examined. The result was as shown in FIG. From FIG. 1, after 72 hours, the foams 3 and 4 of the comparative example
Is about half of the original height and about 1/4 of the original height, respectively, whereas the foam 1 according to the present invention and polypropylene are used. The foam 2 thus obtained maintains the height of about 80% of the original height, and the moisture absorption of the foams 3 and 4 of the comparative example after 72 hours is about 7%. On the other hand, since the moisture absorption of the foam 1 according to the present invention and the foam 2 using polypropylene is about half of that, the foam according to the present invention is equivalent to the foam using polypropylene. It is clear that it has a moisture resistance. 5. Use test Furthermore, as a result of experimentally using the foam according to the present invention as a cushioning material for packing several kinds of articles, in a normal climate or under normal weighting conditions, the foamed body was completely sagged or had a gap. It was able to function as a cushioning material without any possibility. The moisture-resistant biodegradable resin foam according to the present invention has the above-described structure and characteristics, and is not only degraded by microorganisms in the soil but also used in ordinary packaging. Since it has the moisture resistance required as a cushioning material, it not only contributes to the development of industry through the transportation of goods, but also contributes to the prevention of environmental pollution.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the weight of a foam 1 of Example 1 of the present invention, a foam 2 using polypropylene of a reference example, a foam 3 of a comparative example, and a foam 4 of a comparative example. FIG. 4 is a diagram showing a change in shrinkage and a change in moisture absorption depending on the degree of change.

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Claims (1)

(57) [Claim 1] A moisture-resistant biodegradable resin foam comprising 40 to 80% by weight of starch, 10 to 20% by weight of polyvinyl alcohol, and 10 to 40% by weight of aliphatic polyester.