JP4135732B2 - Biodegradable resin crosslinked foam and method for producing the same - Google Patents

Description

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

  Conventionally, resin foams such as polyolefin resin foams and polyurethane resin foams have been widely used industrially because they are excellent in lightness, heat insulation, moldability, buffering properties, and the like. However, although these resin foams are lightweight, they are bulky when discarded and difficult to reuse. In particular, in the case of a crosslinked resin foam obtained by crosslinking a resin, there is a drawback that recycling is virtually impossible. In addition, these resin foams remain in the ground semi-permanently even if they are buried in the soil, contaminating the global environment by securing garbage disposal sites by incineration or landfill, etc., and rarely damage the natural landscape. There wasn't.

For this reason, biodegradable resins that are decomposed by microorganisms and the like in the natural environment have been researched and developed and commercialized as films and fibers. In addition, an extruded foam of a biodegradable resin has been developed. For example, a foam using an aliphatic polyester resin as a biodegradable resin is known. However, aliphatic polyester resins are difficult to increase in molecular weight due to side reactions such as hydrolysis with water generated during polycondensation, so that sufficient melt viscosity to retain bubbles during extrusion foaming cannot be obtained, and good bubbles It was difficult to obtain a foam having a state and a surface state. As a method for solving this problem, for example, a foamed resin using a lactone resin has been proposed. (See Patent Document 1)
JP-A-11-279711

  However, since the lactone resin also collapses at the time of crosslinking, it is difficult to obtain a melt viscosity for sufficiently retaining bubbles during foaming, and it is difficult to obtain a foam having a good surface form. Furthermore, in order to obtain a foam having a high degree of cross-linking, there is a drawback in that radiation treatment must be performed with very high energy.

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

The present invention adopts the following means as a result of sincerity studies to solve such problems. That is, the present invention
(1) A biodegradable resin cross-linked foam obtained by cross-linking and foaming a resin composition containing a biodegradable resin containing a lactone resin, a thermal decomposable foaming agent, and a polyfunctional monomer as a cross-linking aid.
(2) The biodegradable resin crosslinking according to (1), wherein the crosslinking assistant 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), wherein the gel fraction is 3% or more.
(4) The biodegradable resin crosslinked foam according to any one of (1) to (3), wherein the expansion ratio is 1.5 to 50 times.

  ADVANTAGE OF THE INVENTION According to this invention, the biodegradable resin crosslinked foam with a favorable surface form can be provided, and the utility is large.

  Hereinafter, preferred embodiments of the present invention will be specifically described.

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

  As the biodegradable resin used in the present invention, 100% of a lactone resin may be used, or a biodegradable resin other than the lactone resin may be included. Examples of biodegradable resins other than the lactone resin used in the present invention include, for example, polylactic acid, polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, and polybutylene succinate carbonate as synthetic polymers. Examples include aliphatic polyesters, cellulose acetate, cellulose butyrate, cellulose propionate, cellulose nitrate, cellulose sulfate, cellulose acetate butyrate, and biodegradable cellulose esters such as cellulose nitrate acetate. 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, processed starch such as acetate esterified starch, methyl etherified starch, and amylose. Further, natural polymers such as natural linear polyester resins such as cellulose, carrageenan, chitin / chitosan, and polyhydroxybutyrate / valerate can be exemplified. Moreover, the copolymer of the component which comprises these biodegradable resin may be sufficient. These biodegradable resins may be used alone or in combination of two kinds.

  The biodegradable resin other than the lactone resin is preferably at least selected from aliphatic polyester, biodegradable cellulose ester, polypeptide, polyvinyl alcohol, starch, cellulose, chitin / chitosan and natural linear polyester-based resin. One kind is used.

  The ratio 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 the total resin components in the resin composition is not particularly limited, but is preferably 50% by weight or more. If the amount of biodegradable resin is increased, the decomposition rate is increased and the deformability after decomposition is improved. Resin components other than biodegradable resins are not particularly limited. For example, 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 has a thermal decomposition temperature. For example, azodicarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, toluenesulfonylhydrazide, azobisiso Examples include butyronitrile and barium azodicarboxylate. These may be used alone or in combination, and are preferably used in a proportion of 1 to 50 parts by weight, more preferably 4 to 25 parts by weight, relative to 100 parts by weight of the resin composition. If the amount of the pyrolytic 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-hexanediol dimethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, tetra Acrylate or methacrylate compounds such as methylol methane triacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate; trimellitic acid triallyl ester, pyromellitic acid triallyl ester, oxalic acid diallyl, etc. Allyl esters of carboxylic acids; cyanuric acids such as triallyl cyanurate and triallyl isocyanurate or allyl esters of isocyanuric acid; N-phenylmaleimide, N, N′-m-fe Maleimide compounds such as lenbismaleimide; compounds having two or more triple bonds such as dipropargyl phthalate and dipropargyl maleate; polyfunctional monomers such as divinylbenzene can be used, and handling ease and biodegradability, etc. In view of the above, ester-based polyfunctional monomers such as 1,6-hexanediol dimethacrylate are preferably used.

  These polyfunctional monomers can 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 it is too much, the moldability of the obtained foam tends to be lowered. The amount is preferably 0.5 to 10 parts by weight, more preferably 1 to 6 parts by weight.

  In the resin composition used for this invention, you may add additive components other than a thermal decomposition type foaming agent and a crosslinking adjuvant in the range which does not inhibit the effect of this invention. For example, as additives, crosslinking agents, antioxidants, lubricants, heat stabilizers, pigments, flame retardants, antistatic agents, nucleating agents, plasticizers, antibacterial agents, biodegradation accelerators, light stabilizers, UV absorbers, blocking Inhibitors, fillers, deodorizers, thickeners, foaming aids, cell stabilizers, metal damage inhibitors and the like may be added alone or in combination of two or more.

  In the present invention, the method for 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, β rays, γ rays, and electron beams. The irradiation dose of ionizing radiation varies depending on the type and amount of the crosslinking aid, the target degree of crosslinking, and the like, but is usually 1 to 500 kGy, preferably 5 to 300 kGy. If the irradiation dose is too small, a sufficient melt viscosity cannot be obtained to hold the bubbles during foam molding, and if it is too large, the moldability of the resulting foam is lowered.

  In the present invention, foaming is usually performed by heating the crosslinked resin composition to a temperature equal to or higher than the thermal decomposition temperature of the pyrolytic foaming agent.

  The expansion ratio of the foam of the present invention is preferably 1.5 to 50 times. If the expansion ratio is less than 1.5 times, the lightness and flexibility tend to decrease, and if the expansion ratio exceeds 50 times, the mechanical properties and moldability tend to decrease.

  The gel fraction of the foam of the present invention is preferably 3% or more. When the gel fraction is less than 3%, the secondary processability of the obtained foam tends to decrease.

The gel fraction as used in the field of this invention is the value computed with the following method. That is, about 50 mg of the biodegradable resin-crosslinked foam is precisely weighed, immersed in 25 ml of tetralin at 130 ° C. for 3 hours, filtered through a 200 mesh stainless steel wire mesh, and the wire mesh insoluble matter is vacuum dried. . Next, the weight of this insoluble matter was precisely weighed, and 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, the preferable manufacturing method of the biodegradable resin crosslinked foam of this invention is demonstrated.

  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 decomposable foaming agent, and a crosslinking aid to obtain a molded product, and irradiating the molded product with ionizing radiation. A biodegradation comprising a step of obtaining a crosslinked molded product by crosslinking the resin composition, and further comprising a step of heat-treating the crosslinked molded product at a temperature equal to or higher than a decomposition temperature of the thermally decomposable foaming agent to form a crosslinked foamed product. This is a method for producing a crosslinked resin foam. Specifically, the following manufacturing method etc. are mentioned, for example.

  Using a kneading apparatus such as a single screw extruder, a twin screw extruder, a Banbury mixer, a kneader mixer, a mixing roll, etc., for a resin composition containing a biodegradable resin containing a lactone resin, a thermally decomposable foaming agent, and a crosslinking aid. Then, it is melt-kneaded uniformly below the decomposition temperature of the heat decomposable foaming agent and formed into a desired shape. These resin compositions may be mechanically mixed with a mixer or the like as necessary before melt-kneading. The melt kneading temperature at this time is preferably a temperature lower by 10 ° C. or more than the decomposition start temperature of the foaming agent. If the kneading temperature is too high, the pyrolytic foaming agent is decomposed during kneading, and a good foam cannot be obtained.

  Next, 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 pyrolytic foaming agent and foamed. The heat treatment for foam molding may be performed by a conventionally known method, for example, in a vertical or horizontal hot-air foaming furnace or a chemical bath such as a molten salt.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this.

Example 1
Prepare 100 kg of polycaprolactone "TONE" (UCC Co.) as biodegradable resin, 7.5 kg of azodicarbonamide as foaming agent, and 5 kg of 1,6-hexanediol dimethacrylate as crosslinking aid. The mixture was mixed at a low speed of 200 to 400 rpm for about 3 minutes, then at a high speed of 800 to 1000 rpm and mixed for 3 minutes to obtain a foaming resin composition. This foaming resin composition was introduced into an extruder equipped 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 crosslinked foamed sheet having a thickness of 1.5 mm. The sheet was irradiated with an 80 kGy electron beam and crosslinked, and then continuously introduced into a vertical hot-air foaming apparatus, heated and foamed at 230 ° C. for 3 to 4 minutes, and wound up as a continuous sheet-like crosslinked foam.
The foam thus obtained had a thickness of 3.0 mm, a gel fraction of 40%, a foaming magnification of 12 times, a good surface form and a beautiful appearance. When this material was buried in soil, after 1 year, the strength dropped to a non-practical strength and a degradation change was observed.

Comparative Example 1
A foam was prepared using the same method as in Example 1 except that no crosslinking aid was used. The foam thus obtained had a thickness of 1.5 mm, a gel fraction of 2.5%, a foaming ratio of 1.8 times, and an irregular surface shape, and had a very poor appearance. Moreover, since the gas generated at the time of foaming cannot be sufficiently retained, the foamed state did not become a uniform foam.

Claims (4)

A continuous sheet obtained by crosslinking and foaming a resin composition containing a biodegradable resin containing 50% by weight or more of a lactone resin , a thermal decomposable foaming agent, and a polyfunctional monomer as a crosslinking aid. Biodegradable resin cross-linked foam.   The continuous sheet-like biodegradable resin crosslinking 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. Foam.   3. The continuous sheet-like biodegradable resin crosslinked foam according to claim 1 or 2, wherein the gel fraction is 3% or more.   The continuous sheet-like biodegradable resin crosslinked foam according to any one of claims 1 to 3, wherein the expansion ratio is 1.5 to 50 times.