JP2003253029A - Biodegradable crosslinked resin foam and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a biodegradable crosslinked resin foam which is good in surface state regardless of the thickness of a material to be radiated, uniformly foamed inside the foam and excellent in mechanical properties. <P>SOLUTION: The biodegradable crosslinked resin foam is characterized in that a biodegradable resin is crosslinked at least through a structure derived from a crosslinking aid. <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. However, these resin foams
Although lightweight, it was bulky when discarded and 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. Moreover, even if these resin foams are buried in the soil, they remain semipermanently, polluting the global environment by securing a place for waste disposal by incineration or landfilling, and often impairing the natural landscape.

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, an extruded foam of a biodegradable resin has been developed, and for example, an uncrosslinked foam using an aliphatic polyester resin as the biodegradable resin is known. However, the aliphatic polyester resin is
Since it is difficult to increase the molecular weight due to side reactions such as hydrolysis caused by water generated during polycondensation, sufficient melt viscosity to hold bubbles during extrusion foaming cannot be obtained, and therefore foams having good bubble and surface conditions. It was difficult to get a body.

As a method for solving this, for example, Japanese Patent No. 2655796 discloses a structure in which a polyester prepolymer composed of an aliphatic glycol and an aliphatic dicarboxylic acid and having a number average molecular weight of 5,000 or more is chained via a urethane bond. Higher molecular weight is achieved by holding it,
Various methods for producing foams have been proposed, including extrusion foaming, chemical crosslinking, electron beam crosslinking, and the like. However, in the method by the above-mentioned ionizing radiation crosslinking method, when the thickness of the object to be irradiated exceeds 1 mm, the radiation does not reach the inside, so that there is a problem that the internal bubbles become coarse and non-uniform during foaming. It is also stated that even in an N2 atmosphere, the irradiation dose of 50 Mrad (500 kGy) or more is a high irradiation dose, so that the main chain collapse reaction proceeds at the same time as the crosslinking reaction, resulting in severe deterioration of the resin. It was very difficult to obtain a foam having various thicknesses and having sufficient mechanical properties by using.

Further, Japanese Patent Application Laid-Open No. 11-279311 also proposes a crosslinked resin foam using a lactone resin, but as described above, when the resin is crosslinked by the irradiation of ionizing radiation, the disintegration progresses at the same time. It is described that irradiation is required to be performed under special conditions that do not lead to crystallization after melting of the resin because the deterioration of the resin becomes severe, and a foam with a good surface and excellent mechanical properties including moldability is obtained. It was difficult.

Further, in recent years, various properties required of foams have become more diverse and sophisticated, and deep drawing property is required in fields requiring formability such as vacuum forming and press forming. It has been done, and there was no way to achieve it by the conventional method.

[0007]

In view of such background of the prior art, the present invention has a good surface condition regardless of the thickness of the object to be irradiated, and has uniform air bubbles inside the foam, which is excellent. It is intended to provide a biodegradable resin crosslinked foam having mechanical properties and a method for producing the same.

[0008]

The present invention adopts the following means as a result of intensive studies for solving the above problems. That is, the present invention is (A) a biodegradable resin crosslinked foam characterized in that the biodegradable resin is crosslinked via a structure derived from a crosslinking aid. (B) Preferably, the biodegradable resin is at least one selected from the group consisting of polylactic acid, a lactone polyester, and an aliphatic polyester mainly formed by polycondensing a diol and a dicarboxylic acid or the acid anhydride. The biodegradable resin crosslinked foam according to (A). (C) More preferably, the biodegradable resin crosslinked foam according to (A) or (B), wherein the crosslinking aid is a polyfunctional methacrylic acid compound. (D) Particularly preferably, the polyfunctional methacrylic acid compound is ethylene glycol dimethacrylate, 1,3-
At least one selected from butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, trimethylolpropane trimethacrylate and tetramethylolmethane tetraacrylate (A) to The biodegradable resin crosslinked foam according to any one of (C). (E) In the method for producing the foam, a foamable sheet is molded using a mixture of a biodegradable resin, a foaming agent, and a crosslinking aid, and then the foamable sheet is irradiated with ionizing radiation, It is characterized in that the biodegradable resin is cross-linked and then heated to a temperature above the decomposition temperature of the foaming agent for foaming.

[0009]

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

The biodegradable resin used in the present invention includes polylactic acid and the following lactone resins, for example,
Various methylated lactones such as ε-caprolactone, β-propiolactone, γ-butyrolactone, δ-valerolactone, enanthlactone, 4-methylcaprolactone, 2,2,4-trimethylcaprolactone and 3,3,5-trimethylcaprolactone A homopolymer or a copolymer thereof, and a mixture thereof, and an aliphatic polyester represented by the following, for example, ethylene succinate, polybutylene succinate, polybutylene succinate.
An aliphatic polyester obtained by polycondensing a diol such as adipate or polybutylene succinate / carbonate and a dicarboxylic acid or the acid anhydride, and a synthetic polymer such as polyvinyl alcohol, or polyhydroxybutyrate / vallate, etc. Examples thereof include natural polymers such as natural linear polyester resins.

The above biodegradable resin may be a cellulose ester such as cellulose acetate, cellulose butyrate, cellulose propionate, cellulose nitrate, cellulose sulfate, cellulose acetate butyrate or cellulose acetate acetate having a biodegradability. Synthetic polymers of polypeptides such as glutamic acid, polyaspartic acid and polyleucine, and / or natural polymers such as starch, raw starch such as corn starch, wheat starch, rice starch, acetic esterified starch, methyl Etherified starch,
Modified starch such as amylose may be mixed with the biodegradable resin of the present invention within a range that does not impair the melting property. The biodegradable resin may be used alone or in combination of two or more kinds.

The ratio of the biodegradable resin to all the resin components in the resin composition is not particularly limited, but is preferably 50 to 100% by weight, more preferably 70 to 100% by weight, and further preferably 100% by weight of the biodegradable resin. %. Is. When the proportion of the biodegradable resin in the resin composition is less than 50% by weight, the biodegradability is lowered, which is not preferable. 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, etc. may be added.

The foaming agent used in the present invention is a compound which is a liquid or solid at room temperature and decomposes or vaporizes when heated above the melting point of the biodegradable resin and does not substantially interfere with sheet formation or crosslinking reaction. As long as it is optional, it is a pyrolytic foaming agent with a decomposition temperature of 1
It is preferably in the range of 20 ° C to 270 ° C. Specific examples thereof include azo compounds such as azodicarbonamide and azodicarboxylic acid metal salts, hydrazodicarbonamide,
Hydrazine derivatives such as 4,4′-oxybis (benzenesulfonylhydrazide) and toluenesulfonylhydrazide, nitroso compounds such as N, N′-dinitrosopentamethylenetetramine, semicarbazide compounds such as toluenesulfonylsemicarbazide, and bicarbonates such as sodium hydrogencarbonate. Mention may be made of salt.

In order to control the decomposition temperature in the foaming agent, those containing a decomposition temperature controlling agent such as zinc oxide, zinc stearate and urea can be preferably used.

These foaming agents are used in the range of 0.1 to 40% by weight with respect to the biodegradable resin, and the mixing amount can be arbitrarily changed depending on each type and expansion ratio.

In the present invention, the above biodegradable resin is crosslinked with a structure derived from the crosslinking aid by irradiation with ionizing radiation using the crosslinking aid. In the case of a compound having two or more vinyl type double bonds in the molecule, for example, the structure derived from the agent means that the crosslinking assistant is radicalized by electron beam irradiation, and the double bond is opened to cause biodegradability. It has a structure that binds to a resin, but refers to a structure that has changed to such a state. Further, in the present invention, a structure including a partly changed structure is referred to as a derived structure.
Examples of such a cross-linking aid include divinylbenzene, diallylbenzene, divinylnaphthalene, divinylphenyl, divinylcarbazole, divinylpyridine and their nucleus-substituted compounds and their related analogs, ethylene glycol diacrylate, butylene glycol diacrylate, and triethylene glycol diethylene. Polyfunctional acrylic acid compounds such as acrylate, 1,6-hexanediol diacrylate, tetramethylolmethane tetraacrylate, ethylene glycol dimethacrylate, butylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate,
1,6-hexanediol dimethacrylate, 1,9-
Polyfunctional methacrylic acid compounds such as nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, trimethylolpropane trimethacrylate, tetramethylolmethane tetramethacrylate, divinyl phthalate, diallyl phthalate, diallyl malate,
Polyvinyl esters of aliphatic and aromatic polyvalent carboxylic acids such as bisacryloyloxyethyl terephthalate,
Polyallyl ester, polyacryloyloxyalkyl ester, polymethacryloyloxyalkyl ester, diethylene glycol divinyl ether, hydroquinone divinyl ether, polyvinyl ether and polyallyl ether of aliphatic and aromatic polyhydric alcohols such as bisphenol A diallyl ether, triallyl cyanurate , Allyl ester of cyanuric acid or isocyanuric acid such as triallyl isocyanurate, triallyl phosphate, trisacryloxyethyl phosphate,
It is possible to use a polyfunctional monomer such as a maleimide compound such as N-phenylmaleimide or N, N′-m-phenylene bismaleimide, or a compound having two or more triple bonds such as dipropargyl phthalate or dipropargyl maleate. it can.

Among them, polyfunctional methacrylic acid compounds are preferable from the viewpoints of easy handling and crosslinking reactivity, and ethylene glycol dimethacrylate and 1,6-hexanediol are particularly preferable from the viewpoints of crosslinking reactivity and production applicability. Dimethacrylate and trimethylolpropane trimethacrylate are more preferable, and 1,6-hexanediol dimethacrylate is particularly preferable.

The amount of these crosslinking aids added is 0.5 to 10% by weight, preferably 1 to 6% by weight, based on the biodegradable resin.
Used in the range of. Cross-linking aid content 0.5% by weight
If it is less than 10% by weight, the effect of addition is not sufficiently exhibited, which is not preferable, and if the amount of addition exceeds 10% by weight, the effect of addition is saturated, which simply leads to an increase in cost, which is not preferable. Some of these cross-linking aids also help plasticize during extrusion.

In the present invention, the above-mentioned crosslinking aid is used,
By irradiating with ionizing radiation, the structure derived from the cross-linking aid, which is to be cross-linked to the biodegradable resin described above, as the ionizing radiation, an electron beam from an electron beam accelerator, Α from CO60 and other radioisotopes
β- and γ-rays, especially electron beams are preferable, but X-rays and ultraviolet rays may be used. Although the irradiation dose of these radiations varies depending on the type of the crosslinking aid and the target crosslinking ratio,
The range is 00 kGy, preferably 5 to 100 kGy.

In the resin composition used in the present invention,
Additive components other than the foaming agent may be added as long as the effects of the present invention are not impaired. For example, as additives, antioxidants, lubricants, heat stabilizers, pigments, flame retardants, antistatic agents, nucleating agents, plasticizers, antibacterial agents, biodegradation accelerators, foaming agent decomposition accelerators, light stabilizers, UV absorption. Agent, anti-blocking agent, filler, deodorant, thickener, foaming aid, foam stabilizer,
You may add a metal damage inhibitor etc. individually or in combination of 2 or more types.

The form of the biodegradable resin crosslinked foam of the present invention is not particularly limited, but is preferably a sheet form. By making it into a sheet, not only the productivity is excellent, but also the biodegradation rate can be increased. The thickness of the biodegradable resin crosslinked foam sheet is preferably 0.1 mm to 100 m.
m. These sheets can be easily processed into a desired thickness by subjecting them to foam molding and then subjecting them to secondary processing such as slicing or fusion processing.

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 showing the degree of crosslinking of the foam of the present invention is preferably 10% or more. If the gel fraction is less than 10%, 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 (m
g) / weight of cross-linked biodegradable resin foam (m)
g)} × 100 The biodegradable resin crosslinked foam of the present invention is obtained by molding a foamable sheet using a mixture of a biodegradable resin, a foaming agent and a crosslinking aid, and then forming an ionizable layer on the foamable sheet. This can be achieved by irradiating with radiation to crosslink the biodegradable resin, and then heating at a temperature not lower than the decomposition temperature of the foaming agent to effect foaming. Preferred specific examples are shown below.

In the present invention, the biodegradable resin may be mixed with the foaming agent or the crosslinking aid by a conventionally known mixing method. For example, there are methods such as mixing with a Henschel mixer, mixing with a Banbury mixer, mixing with a mixing roll, mixing with a kneading extruder, foaming agent, and immersing a biodegradable resin in a solution in which a crosslinking accelerator is dissolved,
Used alone or in combination. In particular, when the resin is powdery, it is convenient to mix the powder with a Henschel mixer.
Since the degradable resin used in the present invention is easily hydrolyzed under heating, the moisture content in the vacuum dryer is set to 0.
It is preferable to reduce it to 1% by weight or less.

Next, the above mixture is formed into a sheet, preferably using a single screw extruder with a vacuum vent, or preferably a twin screw extruder. When a continuous sheet-like foam is produced, it is preferable to extrude into a sheet at a temperature not higher than the decomposition temperature of the foaming agent. The melt-kneading temperature during extrusion is preferably 10 ° C. or more lower than the decomposition start temperature of the foaming agent. At this time, the thickness of the sheet is preferably 0.1 mm to 50 mm.
If the thickness of the sheet is less than 0.1 mm, gas will often escape from the surface of the sheet during foam molding, and it will be difficult to form a uniform foam. If it exceeds 50 mm, the rigidity of the sheet will be too high, and windability during continuous production, etc. May cause problems with the.

Next, the above-mentioned foamable sheet-like material is crosslinked by irradiating with ionizing radiation. As the ionizing radiation, an electron beam from an electron beam accelerator is preferable, and the irradiation amount is The range is 1 to 300 kGy, preferably 5 to 100 kGy, although it varies depending on the kind of the crosslinking aid and the target crosslinking ratio.

Thereafter, the crosslinked sheet-like material is heat-treated at a temperature equal to or higher than the decomposition temperature of the foaming agent to foam. A conventionally known method may be used for the heat treatment for foam molding, and for example, it can be performed in a vertical and horizontal hot air foaming furnace, a chemical solution foaming furnace, or the like. When using a biodegradable resin such as aliphatic polyester that is susceptible to hydrolysis, foaming in a vertical or horizontal hot-air foaming furnace gives a better surface condition than foaming in a chemical bath. Foam is obtained. Further, if necessary, preheating is performed before foam molding to soften the resin, and a stable foam can be obtained with a small amount of heat.

[0030]

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

The molding draw ratio means that when a foam is heated on a vertical cylindrical female mold having a diameter D and a depth H under optimum heating conditions and straight molding is performed using a vacuum molding machine, It is the value of H / D at the limit where the foam can be expanded and expanded into a cylinder without breaking.

Example 1 As a biodegradable resin, "TONE" (U), which is polycaprolactone previously dried in a vacuum dryer at 50 ° C. for 5 hours.
CC stock), 100 parts by weight, 5.8 parts by weight of azodicarbonamide as a foaming agent, 6 parts by weight of 1,6-hexanediol dimethacrylate as a crosslinking aid, and 0.5 parts by weight of Irganox 1010 as a stabilizer. These were prepared, charged into a Henschel mixer under N2 atmosphere, and mixed for 6 minutes to prepare a foaming resin mixture. The temperature at which this foaming resin mixture does not decompose the foaming agent, specifically 150 ° C
The mixture was introduced into a twin-screw extruder having a vent and heated from above, and extruded from a T-die to obtain a foamable sheet material having a thickness of 1.5 mm.

Then, the sheet-like material was irradiated with an electron beam of 25 kGy to be cross-linked, and then continuously introduced into a vertical hot air foaming device, and heat-foamed at 230 ° C. for 3 to 4 minutes to continuously cross-link the sheet-like material. It was rolled up as a foam.

The foam thus obtained has a thickness of 3.0 m.
m, gel fraction 37%, foaming ratio 15 times, the surface morphology was good and the appearance was beautiful. When this foam was analyzed by infrared absorption spectrum (FT-IR) and nuclear magnetic resonance spectrum, it was confirmed that the foam was crosslinked through a structure derived from 1,6-hexanediol dimethacrylate used as a crosslinking aid. Was done.

When the obtained foam was evaluated for molding, it was found to have a molding draw ratio of 0.8, and it was excellent in moldability.

Comparative Example 1 An attempt was made to make a foam by using the same method as in Example 1 except that the crosslinking aid was not used, but the sheet melted in the foaming furnace and the foam could not be obtained. It was When the degree of cross-linking of the sheet-shaped product before foaming was measured, it was found that the gel fraction was 0.5%, and it was not cross-linked at all.

Comparative Example 2 Since the irradiation dose was low in Comparative Example 1, the dose was 200 k
Although it was changed to Gy, the sheet was still melted in the foaming furnace and the foam could not be obtained.

Example 2 A foam was obtained in the same manner as in Example 1 except that "Bionole"# 3001 (manufactured by Showa High Polymer Co., Ltd.), which was polybutylene succinate adipate, was used as the biodegradable resin. The obtained foam had a thickness of 3.1 mm and a gel fraction of 5
The foam had a foaming ratio of 2%, a surface morphology was good, the appearance was beautiful, and the bubbles inside the foam were uniform. It had a soft feel (texture) and excellent rubber elasticity. When the forming drawing ratio was measured, it was 1.0, which was excellent in deep drawing formability.

Comparative Examples 3 and 4 Foamable sheets were prepared in the same manner as in Example 2 except that the crosslinking aid was not used. After that, the irradiation dose is set to 25 kGy
(Comparative Example 3) and 150 kGy (Comparative Example 4) were changed to obtain a crosslinked sheet.

In Comparative Example 3, the sheet was melted in the foaming furnace and a foam could not be obtained. The gel fraction of the sheet before foaming was measured and found to be 7.5%.

In Comparative Example 4, after the crosslinking, the sheet itself became uneven due to irradiation energy due to irradiation energy, and the sheet could not be wound up. Therefore, since foaming in a vertical hot air foaming furnace is not possible, a small amount of sample was cut from the crosslinked sheet and heated in a laboratory oven to foam, but somehow a foam could be obtained, but it was obtained. The surface of the obtained foam was uneven, and the bubbles inside were various in size and non-uniform. The gel fraction of the foam was 63%.

[0042]

Industrial Applicability According to the present invention, it is possible to provide a resin crosslinked foam which is excellent in mechanical properties and appearance and has biodegradability.

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Claims (5)

[Claims] 1. A biodegradable resin crosslinked foam, wherein the biodegradable resin is crosslinked through a structure derived from a crosslinking aid. 2. The biodegradable resin is at least one selected from polyesters consisting of polylactic acid and lactone, and aliphatic polyesters mainly obtained by polycondensing diol and dicarboxylic acid or the acid anhydride. The biodegradable resin crosslinked foam according to claim 1, which is characterized in that. 3. The biodegradable resin crosslinked foam according to claim 1 or 2, wherein the crosslinking aid is a polyfunctional methacrylic acid compound. 4. The polyfunctional methacrylic acid compound is at least one selected from ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane trimethacrylate and 1,6-hexanediol dimethacrylate. The biodegradable resin crosslinked foam according to any one of claims 1 to 3, 5. A foamable sheet is molded using a mixture containing a biodegradable resin, a foaming agent, and a crosslinking aid, and then the foamable sheet is irradiated with ionizing radiation to obtain the biodegradable resin. A method for producing a biodegradable resin crosslinked foam, which comprises crosslinking, followed by heating at a temperature not lower than the decomposition temperature of a foaming agent to perform foaming.