JP2003165862A - Biodegradable resin crosslinked foam and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biodegradable resin crosslinked foam having good surface characteristic and an appearance, wherein the crosslinking is accomplished with low energy. <P>SOLUTION: This biodegradable resin foam is obtained by crosslinking and expanding a biodegradable resin comprising a biodegradable resin such as a lactone resin, a thermally decomposable foaming agent and a crosslinking agent. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a biodegradable resin crosslinked foam and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, resin foams such as polyolefin resin foams and polyurethane resin foams are excellent in lightness, heat insulation, moldability, cushioning property, etc.
It has been widely used industrially. However, although these resin foams are lightweight, they are bulky when discarded,
It was difficult to reuse. Particularly, in the case of a crosslinked resin foam obtained by crosslinking a resin, there is a drawback that recycling is practically impossible. In addition, these resin foams remain in the ground semipermanently even if they are buried in the soil, polluting the global environment by securing a place for waste disposal by incineration or landfilling, and rarely impairing the natural landscape. There wasn't.

For this reason, biodegradable resins which are decomposed by microorganisms in the natural environment have been studied and developed, and have been commercialized as films and fibers. Further, a biodegradable resin extruded foam has also been developed, and for example, a foam using an aliphatic polyester resin as a biodegradable resin is known. However, the aliphatic polyester resin is difficult to have a high molecular weight due to a side reaction such as hydrolysis caused by water generated during polycondensation, and thus it is not possible to obtain a sufficient melt viscosity for retaining bubbles during extrusion foaming, and thus good bubbles are obtained. It was difficult to obtain a foam having a state and a surface state. As a method for solving this, for example, Japanese Patent Laid-Open No. 11-279
Japanese Patent No. 311 proposes a foamed resin using a lactone resin.

[0004]

However, since the lactone resin also undergoes disintegration at the same time when it is crosslinked, it is difficult to obtain a melt viscosity for sufficiently retaining bubbles during foaming, and a foam having a good surface morphology cannot be obtained. It was difficult. Further, there is a drawback that the radiation treatment must be performed with extremely high energy in order to obtain a foam having a high degree of crosslinking.

In view of such background of the prior art, the present invention is
An object of the present invention is to provide a biodegradable resin crosslinked foam which can be crosslinked with low energy and has a good surface morphology, and a method for producing the same.

[0006]

The present invention adopts the following means as a result of a sincere examination for solving the above problems. That is, the present invention provides (1) a biodegradable resin crosslinked foam obtained by crosslinking and foaming a resin composition containing a biodegradable resin containing a lactone resin, a thermal decomposition type foaming agent, and a crosslinking aid. (2) The biodegradable resin crosslinker according to (1), wherein the crosslinking aid is a polyfunctional monomer and is added in an amount of 0.5 to 10 parts by weight with respect to 100 parts by weight of the resin composition. Foam. (3) The biodegradable resin crosslinked foam according to (1) or (2), which has a gel fraction of 3% or more. (4) The biodegradable resin crosslinked foam according to any one of (1) to (3), which has an expansion ratio of 1.5 to 50 times. (5) A step of molding a resin composition containing a biodegradable resin containing a lactone resin, a thermal decomposition type foaming agent and a crosslinking aid to obtain a molded article, the resin composition being irradiated with ionizing radiation Biodegradable resin crosslinked foaming, which further comprises a step of crosslinking to obtain a crosslinked molded article, and a step of heat-treating the crosslinked molded article at a temperature not lower than the decomposition temperature of the pyrolytic foaming agent to form a crosslinked foamed product. Body manufacturing method. Is.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be specifically described below.

The lactone resin used in the present invention is
For example, ε-caprolactone, β-propiolactone,
γ-butyrolactone, δ-valerolactone, enanthlactone and 4-methylcaprolactone, 2,2,4-trimethylcaprolactone, homopolymers of various methylated lactones such as 3,3,5-trimethylcaprolactone, or copolymers, And mixtures thereof.

The biodegradable resin used in the present invention may be 100% lactone resin or may contain biodegradable resin other than lactone resin. Examples of biodegradable resins other than the lactone resin used in the present invention include synthetic polymers such as polylactic acid, polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, and polybutylene succinate carbonate. Examples thereof include biodegradable cellulose esters such as aliphatic polyester, cellulose acetate, cellulose butyrate, cellulose propionate, cellulose nitrate, cellulose sulfate, cellulose acetate butyrate and cellulose nitrate acetate. In addition, examples of synthetic polymers include polypeptides such as polyglutamic acid, polyaspartic acid, and polyleucine, and polyvinyl alcohol. Examples of the natural polymer include raw starch such as corn starch, wheat starch, and rice starch as starch, and modified starch such as acetic acid esterified starch, methyl etherified starch, and amylose. In addition, natural polymers such as cellulose, carrageenan, chitin / chitosan, and natural linear polyester resins such as polyhydroxybutyrate / valilate can be exemplified. Further, it may be a copolymer of components constituting these biodegradable resins. These biodegradable resins may be used alone or in combination of two kinds.

The biodegradable resin other than the lactone resin is preferably an aliphatic polyester, a biodegradable cellulose ester, a polypeptide, polyvinyl alcohol,
At least one selected from starch, cellulose, chitin / chitosan, and natural linear polyester resin is used.

The proportion of the lactone resin in the biodegradable resin used in the present invention is preferably 50% by weight or more, more preferably 60% by weight or more.

In the present invention, the ratio of the biodegradable resin to all the resin components in the resin composition is not particularly limited,
It is preferably 50% by weight or more. When the amount of biodegradable resin increases, the decomposition rate increases, and the deformability after decomposition improves. The resin component other than the biodegradable resin is not particularly limited, and examples thereof include ultra low density polyethylene, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, polypropylene, ethylene- Propylene rubber, polyvinyl acetate, polybutene and the like can be added.

The thermal decomposition type foaming agent used in the present invention is not particularly limited as long as it is a foaming agent having a thermal decomposition temperature. For example, azodicarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, toluenesulfonyl hydrazide, Examples thereof include azobisisobutyronitrile and barium azodicarboxylate. These may be used alone or in combination,
With respect to 100 parts by weight of the resin composition, preferably 1 to 50
It is used in a proportion of parts by weight, more preferably 4 to 25 parts by weight. If the amount of the thermal decomposition type foaming agent added is too small, the foamability of the resin composition will decrease, and if it is too large, the strength and heat resistance of the resulting foam will tend to decrease.

The crosslinking aid used in the present invention is not particularly limited, but conventionally known polyfunctional monomers such as 1,6
Acrylate-based compounds such as hexanediol dimethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, tetramethylolmethane triacrylate, 1,9-nonanediol dimethacrylate, and 1,10-decanediol dimethacrylate Methacrylate compound; trimellitic acid triallyl ester,
Allyl esters of carboxylic acids such as triallyl pyromellitic acid and diallyl oxalate; allyl esters of cyanuric acid or isocyanuric acid such as triallyl cyanurate and triallyl isocyanurate; N-phenylmaleimide, N, N'-m -A maleimide compound such as phenylene bismaleimide; a compound having two or more triple bonds such as dipropargyl phthalate and dipropargyl maleate; a polyfunctional monomer such as divinylbenzene can be used, and is easy to handle and biodegradable. From the viewpoint of the above, ester-based polyfunctional monomers such as 1,6-hexanediol dimethacrylate are preferably used.

These polyfunctional monomers may be used alone or in combination of two or more.

If the addition amount of these polyfunctional monomers is too small, it is difficult to obtain a good crosslinked foam, and if the addition amount is too large, the moldability of the obtained foam tends to decrease, so 100 parts by weight of the resin composition is used. On the other hand, it is preferably 0.5 to 10 parts by weight, more preferably 1 to 6 parts by weight.

In the resin composition used in the present invention, a thermal decomposition type foaming agent, in the range that does not impair the effects of the present invention,
Additive components other than the crosslinking aid may be added. For example,
Crosslinking agents, antioxidants, lubricants, heat stabilizers, pigments, flame retardants, antistatic agents, nucleating agents, plasticizers, antibacterial agents, biodegradation promoters, light stabilizers, UV absorbers, antiblocking agents as additives. , Filler, deodorant, thickener, foaming aid, foam stabilizer,
You may add a metal damage inhibitor etc. individually or in combination of 2 or more types.

In the present invention, the method of crosslinking the resin composition is not particularly limited, and examples thereof include a method of irradiating a predetermined dose of ionizing radiation, crosslinking with a peroxide, and silane crosslinking.

Examples of the ionizing radiation include α rays and β
Rays, γ rays, electron rays and the like can be mentioned. The irradiation dose of ionizing radiation varies depending on the type and amount of the crosslinking aid, the desired degree of crosslinking, and the like, but is usually 1 to 500 kGy, preferably 5 to 300 kGy. If the irradiation dose is too low, a sufficient melt viscosity for retaining bubbles during foam molding cannot be obtained, and if the irradiation dose is too high, the moldability of the resulting foam deteriorates.

In the present invention, foaming is usually carried out by heating the crosslinked resin composition to a temperature not lower than the thermal decomposition temperature of the thermal decomposition type foaming agent.

The expansion ratio of the foam of the present invention is 1.5 to 5.
It is preferably 0 times. When the expansion ratio is less than 1.5 times, the lightness and flexibility tend to decrease, and when the expansion ratio exceeds 50 times, the mechanical properties and molding processability tend to decrease.

The gel fraction of the foam of the present invention is preferably 3% or more. If the gel fraction is less than 3%, the resulting foam will tend to have poor secondary processability.

The gel fraction referred to in the present invention is a value calculated by the following method. That is, about 50 mg of the biodegradable resin cross-linked foam was precisely weighed, immersed in 25 ml of tetralin at 130 ° C. for 3 hours, filtered through a 200-mesh stainless steel wire net, and the wire net-like insoluble matter was vacuum dried. . Then, the weight of this insoluble matter is precisely weighed,
The gel fraction was calculated as a percentage according to the following formula. Gel fraction (%) = {weight of insoluble matter (mg) / weight of weighed biodegradable resin crosslinked foam (mg)} × 100 Next, preferred production of biodegradable resin crosslinked foam of the present invention The method will be described.

The production method of the present invention comprises a step of molding a resin composition containing a biodegradable resin containing a lactone resin, a thermal decomposition type foaming agent and a cross-linking aid to obtain a molded article, and the molded article having ionizing radiation. And a step of cross-linking the resin composition to obtain a cross-linked molded article, and a step of heat-treating the cross-linked molded article at a temperature equal to or higher than the decomposition temperature of the heat-decomposable foaming agent to form a cross-linked foam. Is a method for producing a biodegradable resin crosslinked foam. Specifically, for example, the following manufacturing method may be mentioned.

A single-screw extruder is used to obtain a resin composition containing a biodegradable resin containing a lactone resin, a thermal decomposition type foaming agent, and a crosslinking aid.
Twin screw extruder, Banbury mixer, kneader mixer,
Using a kneading device such as a mixing roll, the mixture is uniformly melt-kneaded at a temperature not higher than the decomposition temperature of the thermal decomposition type foaming agent and molded into a desired shape. In addition, these resin compositions may be mechanically mixed by a mixer or the like, if necessary, before melt-kneading. The melt-kneading temperature at this time is preferably 10 ° C. or more lower than the decomposition start temperature of the foaming agent. If the kneading temperature is too high, the thermal decomposition type foaming agent will decompose during kneading, and a good foam cannot be obtained.

Then, the obtained molded product is irradiated with a predetermined dose of ionizing radiation to crosslink the resin composition to obtain a crosslinked molded product.

Next, this crosslinked molded article is heat-treated at a temperature equal to or higher than the decomposition temperature of the thermal decomposition type foaming agent to foam. The heat treatment for foam molding may be carried out by a conventionally known method, for example, it can be carried out in a vertical or horizontal hot air foaming furnace, a chemical bath of molten salt or the like.

[0028]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited thereto.

Example 1 "TON" which is polycaprolactone as a biodegradable resin
E "(manufactured by UCC Co., Ltd.) 100 kg, azodicarbonamide 7.5 kg as a foaming agent, and 1,6-hexanediol dimethacrylate 5 kg as a cross-linking aid were prepared, and these were put into a Henschel mixer, and 200 to 400 rpm.
Mix at low speed for about 3 minutes, then 800-1000r
It was rotated at a high speed of pm and mixed for 3 minutes to obtain a resin composition for foaming. This foaming resin composition was introduced into an extruder with a vent heated to a temperature at which the foaming agent was not decomposed, specifically 120 ° C., extruded from a T-die, and molded into a cross-linking foaming sheet having a thickness of 1.5 mm. This sheet was irradiated with an electron beam of 80 kGy to be crosslinked, then continuously introduced into a vertical hot air foaming device, heated and foamed at 230 ° C. for 3 to 4 minutes, and wound as a continuous sheet-shaped crosslinked foam. The foam thus obtained had a thickness of 3.0 mm, a gel fraction of 40%, a foaming ratio of 12 times, and had a good surface morphology and a beautiful appearance. When this product was buried in soil, the strength decreased to an impractical level after one year, and changes in decomposition were observed.

Comparative Example 1 A foam was prepared in the same manner as in Example 1 except that the crosslinking aid was not used. The foam thus obtained had a thickness of 1.5 mm, a gel fraction of 2.5%, and a foaming ratio of 1.8.
The surface shape was uneven and the appearance was very poor. Further, since the gas generated during foaming cannot be sufficiently retained, the foamed state was not uniform.

[0031]

Industrial Applicability According to the present invention, a biodegradable resin crosslinked foam having a good surface morphology can be provided, and its practicality is great.

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Claims (5)

[Claims] 1. A biodegradable resin crosslinked foam obtained by crosslinking and foaming a resin composition containing a biodegradable resin containing a lactone resin, a thermal decomposition type foaming agent and a crosslinking aid. 2. The biodegradable composition according to claim 1, wherein the crosslinking aid is a polyfunctional monomer and is added in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the resin composition. Resin cross-linked foam. 3. The biodegradable resin crosslinked foam according to claim 1, wherein the gel fraction is 3% or more. 4. The biodegradable resin crosslinked foam according to claim 1, wherein the expansion ratio is 1.5 to 50 times. 5. A step of molding a resin composition containing a biodegradable resin containing a lactone resin, a thermal decomposition type foaming agent and a crosslinking aid to obtain a molded article, the molded article being irradiated with ionizing radiation. A biodegradable resin comprising a step of cross-linking the composition to obtain a cross-linked molded article, and a step of heat-treating the cross-linked molded article at a temperature not lower than the decomposition temperature of the heat-decomposable foaming agent to form a cross-linked foam. Method for producing crosslinked foam.