JP2005125674A - Biodegradable heat-shrinkable material and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biodegradable heat-shrinkable material which improves heat resistance and increases a shrinkage ratio. <P>SOLUTION: This heat-shrinkable material is formed through the following processes: a monomer with an allyl group is added and mixed into a biodegradable aliphatic polyester in a low concentrations; a mixture is molded in a required shape; after that, ionizing radiation is applied in a range of ≥ 1 kGy and ≤150 kGy, so as to cause crosslinking reaction and set a gel content ratio in a range of ≥10% and ≤90%; and after the application of the ionizing radiation, the mixture is stretched while being heated in a range of 60-200°C. The heat-shrinkable material is manufactured in such a manner as to be shrunk in the range of a shrinkage ratio of ≥40% and ≤80%, when heated at a temperature as high as/higher than a temperature in orientation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a biodegradable heat-shrinkable material and a method for producing the biodegradable heat-shrinkable material. Specifically, the biodegradable heat-shrinkable material is made of a synthetic biodegradable polymer material and has heat resistance and a large heat shrinkage rate. , Film, packaging material, protective material, sealing material, etc., can be suitably used as an alternative to products that have been molded with conventional plastics. Is.

Various products such as films, containers, and heat-shrink materials are formed from petroleum synthetic polymer materials, but there is a problem in the disposal of combustion after use. In other words, global warming due to heat and exhaust gas generated during combustion, problems such as effects on food and health due to toxic substances in combustion gas and post-combustion residues, and securing of disposal treatment disposal buried land Has become a serious problem.
In response to these problems, biodegradable polymers such as starch and polylactic acid have been attracting attention as materials for solving the problems of disposal of petroleum synthetic polymers. Biodegradable polymers do not adversely affect the global environment, including ecosystems, as compared to petroleum synthetic polymers, the amount of heat associated with combustion is small and the cycle of decomposition and resynthesis in the natural environment is maintained. Among them, aliphatic polyester resins having properties comparable to petroleum synthetic polymers in terms of strength and processability are materials that have attracted attention in recent years.

In particular, polylactic acid is made from starch supplied from plants, and is currently becoming much cheaper than other biodegradable polymers due to cost reduction due to mass production in recent years. Consideration has been made.
Polylactic acid is the closest biodegradable resin to its substitute material because it has processability and strength comparable to general-purpose petroleum synthetic polymers in terms of its characteristics. In addition, it is expected to be applied to various uses such as substitution from transparency comparable to acrylic resin and substitution of ABS resin such as a casing of electrical equipment from the viewpoint of high Young's modulus and shape retention.

However, polylactic acid has a glass transition point at a relatively low temperature of around 60 ° C., and the so-called glass plate suddenly becomes a vinyl table cloth before and after that temperature. It has a fatal defect that it is difficult to maintain the shape of time.
In addition, the polylactic acid crystal part that does not melt until it reaches a relatively high melting point of 160 ° C. is a microcrystal that does not show a large lump shape, and in a normal crystallinity, the crystal part alone supports the overall strength. Although it is also a cause of drastic Young's modulus change, since the change occurs before and after the glass transition temperature, which is the temperature at which the amorphous part can move freely, the amorphous part is 60 ° C. or higher. So, it can be said that there is a big cause in losing the interaction between molecules.

In order to improve heat resistance, it is conventionally known to form a crosslinked structure by irradiation with radiation. For example, heat-resistant polyethylene is obtained by irradiating polyethylene of about 100 kGy with respect to polyethylene that melts near 100 ° C., which is a general-purpose resin. In addition, it is also known that when a polymer alone is easily decomposed or a material having low crosslinking efficiency, the addition of a highly reactive polyfunctional monomer can promote crosslinking by radiation.
Regarding the improvement of heat resistance of biodegradable polymers, it is known that polylactic acid only decomposes when irradiated with radiation, and an effective crosslinking cannot be obtained.

On the other hand, as biodegradable materials used in medical applications, JP 2002-114921 A (Patent Document 1) and JP 2003-695 A (Patent Document 2) are not for improving heat resistance but for sterilization. Is disclosed.
That is, in Patent Document 1, by adding a polyfunctional monomer such as triallyl isocyanurate to a biodegradable polymer, a decrease in weight average molecular weight after thermoforming and radiation sterilization is suppressed to 30% or less of the initial stage. A composition is provided.
In Patent Document 2, a polymer such as collagen, gelatin, polylactic acid, polycaprolactone and the like used in vivo contains a polyfunctional triazine compound such as triallyl isocyanurate and can be sterilized by irradiation with radiation. Medical materials are provided.
In the compositions of Patent Documents 1 and 2, a polyfunctional monomer is added to suppress the thermal history during thermoforming of the biodegradable polymer and the molecular weight of the biodegradable polymer during the sterilization process due to radiation irradiation. .

In this case, the polyfunctional monomer is usually added at a high concentration of 5% by weight or more of the whole. However, even if the biodegradable material to which the polyfunctional monomer is added at a high concentration is irradiated with radiation, it is allowed to react 100%. This is difficult, and there is a problem that unreacted monomer remains in the crosslinking monomer, resulting in poor crosslinking efficiency, easily deformed by heating, and poor heat resistance.
Generally, 99% or more of biodegradable materials are classified as those that are degraded by the action of microorganisms. Therefore, when applying a crosslinking technique using a polyfunctional monomer to a biodegradable material, it is multifunctional. Depending on the monomer concentration, it will fall outside the category of biodegradable materials.

  Conventionally, heat-shrinkable materials using polyethylene are commercially available. This kind of heat-shrinkable goods is used for covering the connecting portion of the electric wire, but the electric wire may exceed 100 ° C. due to heat generation during use. If it deforms at 70-80 ° C. and shrinks at 50-60 ° C., it cannot be used for such applications. Further, even in normal applications, for example, there may be an environment where the temperature is 60 ° C. or higher, such as in the interior of a car in summer, so the applications are very limited.

For heat-shrinkable materials having biodegradability, a heat-shrinkable material that can be shrunk at a temperature of 100 to 120 ° C. or more and a shrinkage rate of 40% or more like a general heat-shrinkable material, It has not been provided in the past.
As a heat-shrink material made of this type of biodegradable material, in Japanese Patent Application Laid-Open No. 2003-221499 (Patent Document 3), a mixture of a polylactic acid polymer and an aliphatic polyester other than the polylactic acid polymer is added to There has been provided a polylactic acid heat-shrinkable material containing carbodiimide to improve transparency.
However, in the polylactic acid heat-shrinkable material containing polylactic acid, as described above, since polylactic acid has a glass transition temperature of 50 to 60 ° C., there is a problem that it is easily deformed by heating and inferior in heat resistance. Further, in the polylactic acid heat-shrink material of Patent Document 3, at the time of stretching, it is stretched by heating at 70 to 80 ° C., which is slightly higher than the glass transition temperature of polylactic acid (a little less than 60 ° C.), and stretched above the melting point of polylactic acid. Therefore, the heat shrinkage during heating is a shrinkage of a crystal portion having a weak restoring force against deformation, and thus the heat shrinkage rate is about 30 to 40%.
JP 2002-114921 A JP 2003-695 A JP 2003-221499 A

In view of the above problems, an object of the present invention is to provide a heat-shrinkable material that has high heat-shrinkability by increasing the heat resistance of the biodegradable material so that it can be suitably used in a high-temperature environment.
Specifically, it is an object of the present invention to provide a heat shrinkable material made of polylactic acid and a method for producing the same that improve shape retention properties that are drastically lowered at the glass transition point or higher and are also excellent in industrial productivity.

  As a result of intensive research on this problem, the present inventor solved this problem by mixing allylic monomers with biodegradable aliphatic polyester and cross-linking molecules over a certain condition by irradiation or the like. I found out that I can do it. In particular, for polylactic acid, which was previously considered to be a radiation-disintegrating type and not to be crosslinked with common monomers, the shape retention at high temperatures is greatly improved by sufficiently crosslinking the amorphous part with an allylic monomer. I found what I could do.

The present invention made on the basis of the above knowledge is firstly composed of a mixture of a biodegradable aliphatic polyester and a monomer having a low-concentration allyl group, and has a crosslinked structure by irradiation with ionizing radiation or mixing of a chemical initiator. Stretched under heating in a state where
A biodegradable heat-shrinkable material is provided, which is configured such that when it is heated at a temperature equal to or higher than the stretching temperature, the shrinkage rate is contracted in a range of 40% to 80%.

Specifically, polylactic acid is used as the biodegradable aliphatic polyester, the gel fraction by crosslinking (gel dry weight / initial dry weight) is 10 to 90%, and the shrinkage is less than 10% at 140 ° C. or less. It is preferable to use a biodegradable heat shrinkable material having a shrinkage ratio of 40 to 80% at 160 ° C. or higher. The shrinkage rate is defined as follows.
For sheets,
(Length) Shrinkage rate (%) = (Length before shrinkage-Length after shrinkage) / (Length before shrinkage) x 100
For tubes,
(Inner diameter) Shrinkage rate (%) = (Inner diameter before shrinkage-Inner diameter after shrinkage) / (Inner diameter before shrinkage) x 100
Therefore, the shrinkage rate 50% is 1/2 (50%) of the original length (inner diameter),
The shrinkage rate of 80% is 20% of the original length (inner diameter).

The biodegradable heat-shrinkable material has the same characteristics as the heat-shrinkable material made of general-purpose petroleum synthetic polymer in various characteristics, and becomes a biodegradable heat-shrinkable material that can replace it.
Examples of the aliphatic polyester used as the biodegradable raw material include polylactic acid, L-form, D-form, or a mixture thereof, polybutylene succinate, polycaprolactone, and polyhydroxybutyrate. These can be used alone or in combination of two or more, but polylactic acids are particularly suitable from the viewpoint of cost and characteristics.

  Furthermore, as an additive to the biodegradable aliphatic polyester, for the purpose of improving flexibility, glycerin, ethylene glycol, triacetylglycerin and other liquid plasticizers at room temperature, or solid plasticizers at room temperature, It is possible to add other biodegradable fatty acid polyesters, such as adding biodegradable resins such as polyglycolic acid and polyvinyl alcohol, or adding a small amount of polycaprolactone to polylactic acid as a plasticizer. It is not essential in the invention.

Examples of the crosslinkable polyfunctional monomer mixed with the aliphatic polyester include acrylic and methacrylic polyfunctional monomers having two or more double bonds in one molecule, such as 1,6-hexanediol diacrylate, trimethylol. Propane trimethacrylate (hereinafter referred to as TMPT) is effective, but in order to obtain a high degree of crosslinking at a relatively low concentration, the following monomer having an allyl group is used.
Triallyl isocyanurate, trimethallyl isocyanurate, triallyl cyanurate, trimethallyl cyanurate, diallylamine, triallylamine, diacrylic chlorate, allyl acetate, allyl benzoate, allyl dipropyl isocyanurate, allyl octyl oxalate Allylpropyl phthalate, bityl allyl malate, diallyl adipate, diallyl carbonate, diallyl dimethyl ammonium chloride, diallyl fumarate, diallyl isophthalate, diallyl malonate, diallyl oxalate, diallyl phthalate, diallyl propyl isocyanurate, diallyl sebacate, Diallyl succinate, diallyl terephthalate, diallyl tartrate, dimethylallyl phthalate, ethyl allyl Over DOO, methyl allyl fumarate, methyl meta-allyl maleate.

  Among the monomers having an allyl group, triallyl isocyanurate (hereinafter referred to as TAIC) and trimethallyl isocyanurate (hereinafter TMAIC) are desirable, and TAIC is particularly effective for polylactic acid. Further, TAIC, TMAIC and triallyl cyanurate and trimethallyl cyanurate, which can be mutually converted by heating, have substantially the same effect.

When the concentration ratio of the monomer having an allyl group is 0.5% by weight relative to 100% by weight of the polylactic acid, the crosslinking reaction hardly occurs. Therefore, in order to obtain a gel fraction of 10 to 90% in order to obtain heat resistance and high shrinkage which are the objects of the present invention, a monomer concentration of 0.5% by weight is not sufficient, and 0.7% by weight to 3% by weight is preferred.
Further, when the concentration is 3% by weight or more, there is no remarkable difference in the effect, and when the concentration is as high as 5% by weight, the gel fraction immediately increases to 80% or more and is difficult to control.
In order to increase the heat shrinkage rate, the gel fraction is preferably 50 to 70%. For this purpose, the monomer may be in the range of 0.7 to 2% by weight, and 0.8 to 0.9% by weight. Is most preferred.

The degree of crosslinking can be evaluated by the gel fraction.
As for the gel fraction, a predetermined amount of the film subjected to irradiation crosslinking or chemical crosslinking is wrapped in a 200 mesh wire net and boiled in a chloroform solvent for 48 hours. Next, the gel content remaining in the gold-copper except for the dissolved sol content is dried at 50 ° C. for 24 hours, and the weight is determined. The gel fraction is calculated by the following formula.
Gel fraction (%) = (gel content dry weight) / (initial dry weight) × 100

In order to make the said mixture into a crosslinked structure, although ionizing radiation is irradiated, you may mix a chemical initiator and generate | occur | produce a crosslinking reaction.
When irradiating with ionizing radiation, the ionizing radiation used for bridging can be γ-ray, X-ray, β-ray or α-ray, but for industrial production, it is irradiated with γ-ray irradiation by cobalt-60 or electron accelerator. An electron beam is preferred. The amount of irradiation depends somewhat on the monomer concentration, and even at 1 to 150 kGy, crosslinking is observed, but the bridging effect and the strength improvement effect at high temperatures appear at 5 kGy or more, and more desirably 10 kGy where the effect is more reliable. That's it.
On the other hand, since polylactic acid preferable as an aliphatic polyester has a property of being disintegrated by radiation when the resin is used alone, excessive irradiation causes decomposition to proceed contrary to crosslinking. Therefore, the upper limit is 80 kGy, preferably 50 kGy.

As described above, in the present invention, the amount of the cross-linked polyfunctional monomer added is within a range in which gelation is performed to some extent, and by reducing the concentration as low as possible, the ionization radiation can be irradiated in the subsequent step. The gel fraction is set to 10 to 90%, preferably 50 to 70%, to improve the heat resistance and at the same time increase the shrinkage rate. If the gel separation is too low, as a matter of course, a network to be memorized is not formed and the gel separation does not shrink.
In contrast to conventional petroleum synthetic resin heat shrinkable materials, the gel fraction required for shrinkage is 10 to 30%. In the present invention, the gel fraction of aliphatic polyester, particularly polylactic acid, is increased to 90%. However, heat shrinkability can be imparted.
If the gel fraction is too high, the bridged network is too strong and the shrinking force is high, but the amount of deformation, that is, the amount that can be stretched is small, and as a result, the shrinkage rate is small. As described above, the fraction is preferably 50 to 70%.

Originally, polylactic acid is a radiation-disintegrating resin, but even if crosslinked polylactic acid is partially decomposed, if it is connected to a partially crosslinked network, the gel fraction does not seem to decrease. However, in view of the purpose of shape memory, the cross-linked polylactic acid molecules are connected in many respects and are stronger than the net structure rather than the structure having many gel parts that are not useful for shape memory. It can be said that the more the non-crosslinked portion that forms a skeleton and moves freely during heating, the higher the shrinkage force and the amount of deformation and the higher the shrinkage rate. Therefore, in the case of the present invention, the state is ideally immediately after the completion of the monomer crosslinking reaction.
In more detail, in the graph shown in FIG. 1 in which the horizontal axis represents the irradiation amount and the vertical axis represents the gel fraction, the gel fraction increases as the irradiation amount increases, It can be said that it is near the inflection point of the graph immediately before the rise stops and the gel fraction becomes flat.
The ideal state naturally depends on the monomer concentration. Saturates at a high gel fraction at high concentrations and saturates at a low gel fraction at low concentrations.
According to the study by the present inventors, the ideal gel fraction is 50 to 70% as described above, and the monomer concentration reaching the inflection point in this ideal state and graph is 0.7 as described above. -1.3 wt%.
In addition, if irradiation of ionizing radiation is continued after completion of the crosslinking reaction, the polylactic acid molecules themselves are dissolved, and the gel fraction is crosslinked, so that even if the gel fraction increases, As a result, the cross-linked molecule does not contribute to shape memory. Therefore, even if it is the same gel fraction, for example, 50 to 70%, after the gel fraction has passed the peak with the increase of the irradiation dose, it has become too low to become 50 to 70%.

As described above, by setting the gel fraction to 10 to 90%, preferably 50 to 70%, an innumerable three-dimensional network structure is generated in the polymer, and heat resistance that does not deform even at the glass transition temperature or higher is imparted. be able to.
On the other hand, as will be described later, at the time of stretching, since the film is heated and stretched at a temperature equal to or higher than the melting point of polylactic acid, the polylactic acid is stretched along with the non-crystalline portion as well as the crystalline portion. When cooled in its shape, the amorphous portion and the crystalline portion are solidified and the stretching is maintained, but a strong three-dimensional network structure of the monomer stores the strain due to stretching. After that, when heated again, even if the amorphous part melts at the glass transition temperature, stretching is maintained by the crystalline part, and the strain stored in the three-dimensional network structure is released and contracts only after the melting point is reached and the crystalline part melts. To restore the original shape.
For example, in the case of a polylactic acid biodegradable heat-shrinkable material, if the temperature during stretching is 160 to 180 ° C., the material shrinks by heating at 160 ° C. or higher, and the shrinkage rate is 40 to 40% more than a strong three-dimensional network structure. It can be dramatically increased to 80%.

When a cross-linking reaction is generated using a chemical initiator instead of irradiation, a monomer having an allyl group and a chemical initiator are added to the biodegradable material at a temperature equal to or higher than its melting point, and the mixture is thoroughly kneaded and mixed uniformly. Thereafter, the molded article made of this mixture is raised to a temperature at which the chemical initiator is thermally decomposed.
Chemical initiators that can be used in the present invention are dicumyl peroxide, propionitrile peroxide, pensoyl peroxide, di-t-butyl peroxide, diacyl peroxide, and verargonyl peroxide that generate peroxide radicals by thermal decomposition. , Peroxide catalyst such as myristoyl peroxide, t-butyl perbenzoate, 2,2′-azobisisobutylnitrile, or any catalyst that initiates polymerization of monomers. As in the case of irradiation, the crosslinking is preferably performed under an inert atmosphere or a vacuum excluding air.

The method for producing a biodegradable heat shrinkable material of the present invention basically includes adding a low-concentration cross-linked polyfunctional monomer to a biodegradable raw material, kneading, and pressing the mixture by heating and pressing. After rapid cooling and shaping into a required shape, ionizing radiation is irradiated to cause a crosslinking reaction, the gel fraction is set to 10% or more and 90% or less, and after irradiation with the ionizing radiation, the biodegradable raw material It is formed by stretching while heating in the range of the melting point of the biodegradable raw material + 20 ° C.
According to this manufacturing method, it can be set as the heat-shrinkable material which shrink | contracts in 40% or more of the range of 80% or more when it heats above the temperature at the time of the said extending | stretching.

As a method for producing a biodegradable heat shrinkable material having a heat shrinkage rate of 40 to 80%, specifically,
A monomer having an allyl group is added to the biodegradable aliphatic polyester at a low concentration and kneaded, and the mixture is molded into a required shape.
Irradiating with ionizing radiation at 1 kGy or more and 150 kGy or less to cause a crosslinking reaction, the gel fraction is 10% or more and 90% or less,
Stretching while heating in the range of 60 ° C to 200 ° C after irradiation with the electron beam,
When heated at a temperature equal to or higher than the temperature at the time of stretching, the heat shrinkable material shrinks in a range of 40% to 80%.

When polylactic acid is used as the biodegradable aliphatic polyester, the monomer having the allyl group to be blended is added in an amount of 0.7% by weight to 3.0% by weight with respect to 100% by weight of the polylactic acid, and kneaded. And
After forming the mixture into a thin film, a thick sheet, or a tube, ionizing radiation is irradiated at 5 kGy or more and 50 kGy or less to generate a crosslinking reaction, and the gel fraction is set to 50 to 70%.
After making it the said crosslinked structure, it heats at 150 degreeC or more and 180 degrees C or less, and is extended | stretched by 2-5 times of draw ratio.

  More preferably, triallyl isocyanurate is used as the monomer having an allyl group, and the amount of the triallyl isocyanurate is 0.7 wt% or more and 2.0 wt% or less with respect to 100 wt% of polylactic acid, After forming the mixture, an electron beam is irradiated at 10 kGy or more and 30 kGy or less, and is heated at 160 ° C. or more and 180 ° C. or less during the stretching.

  The monomer having an allyl group is 0.7% by weight to 3.0% by weight with respect to 100% by weight of polylactic acid, as described above, in order to obtain heat resistance and high shrinkage, 0.7% by weight is necessary, and even if it exceeds 3% by weight, there is no difference in effect, and if the concentration exceeds 5% by weight, crosslinking that hardly gels is not promoted.

The amount of electron beam irradiation is 5 kGy or more and 50 kGy or less, as described above, the irradiation amount depends somewhat on the monomer concentration, and crosslinking is observed even at 1 to 150 kGy, but the bridging effect and strength at high temperature The improvement effect comes out at 5 kGy or more, and when polyklactic acid exceeds 50 kGy, the decomposition progresses contrary to crosslinking.
Preferably they are 10 kGy or more and 50 kGy or less, Most preferably, they are 15 kGy or more and 30 kGy or less.

  As described above, the gel fraction at the end of the crosslinking reaction is 10 to 90%, preferably 50 to 70%. As described above, within this range, the heat resistance can be improved by improving the crosslinking, and at the same time, the heat shrinkage rate. It is because it can enlarge. In addition, 40 to 80% contractility can be obtained by heating at 160 ° C. or higher by setting the gel fraction to around 60%.

In the stretchability evaluation, the gel fraction was ◎ for 50 to 70%, ○ for 10 to 50 and 70 to 90%, Δ for 10 to 6%, and × for 5 to 0% and 90 to 96.
This is because the shape is memorized by the network by cross-linking, and when the cross-link density is lower than 50%, especially when it is reduced to less than 10%, shrinkage and heat resistance are lost. Since it progresses too much and it becomes difficult to deform | transform and a shape becomes difficult, stretchability and shrinkability will fall. Therefore, the range which can provide both heat resistance and heat-shrinkability is 10 to 90%, and it was recognized that the range of 50 to 70% would be excellent in stretchability and heat-shrinkability.

The relationship between the network structure corresponding to the gel fraction before stretching, stretching, and heat shrinkage is shown in FIG.
In FIG. 1, the black circle is the crystal part A, the other part is the non-crystal part B, and the oblique line is the mesh C. When the sheet 10 shown in FIG. 1 (A) having a crosslinked structure with a gel fraction of 50 to 70% is stretched under heating at 160 to 180 ° C., the inclination angle of the mesh C is as shown in FIG. 1 (B). It will change and become stretched. When this stretched sheet is heated at a glass transition temperature of 60 ° C. or higher of polylactic acid, the non-crystalline portion B is melted as shown in FIG. Furthermore, when the polylactic acid is heated at a melting temperature of 160 ° C. or higher, the crystal part A is also melted, but the network C is not completely melted because the molecules are completely bonded, and the network has a high shape memory property. As a result, the mesh C that has been stretched by the process returns to the original shape shown in FIG. 1D and contracts.

  2 shows the case of a sheet made of polylactic acid as a raw material and not having a cross-linked structure, and the sheet 1 shown in FIG. 2 (A) is shown in FIG. 2 (B) under heating conditions of 70 to 80 ° C. After stretching the film, the amorphous portion B melts and deforms in the vicinity of the glass transition temperature of polylactic acid as shown in FIG. 2 (C), and when heated above the melting point as shown in FIG. 2 (D). The crystal part A will also melt.

The heating conditions during stretching after crosslinking are 60 ° C. to 200 ° C., preferably 150 ° C. or more and 180 ° C. or less, and most preferably 160 ° C. or more and 180 ° C. or less. The temperature at which the amorphous polylactic acid starts to move ( This is because the glass transition temperature is slightly less than 60 ° C. and the melting point at which crystals can be dissolved is 150 to 160 ° C.
When stretched in the range from the glass transition temperature to the melting point (60 to 150 ° C.), the amorphous material dissolves and deforms at the glass transition temperature, and heat shrinkage occurs at 60 ° C., but the crystal portion does not shrink. Shrinkage does not increase. Therefore, in order to increase the thermal contraction rate, the thermal contraction rate can be increased to 40 to 80% by stretching at 150 ° C. or higher where the crystal part can be dissolved and contracting at 150 ° C. to 160 ° C. .
Therefore, the heating temperature during stretching is preferably 150 ° C. or higher. In addition, since it is necessary to extend | stretch in a short time when it is 200 degreeC, 180 degrees C or less is preferable. Most preferably, the melting point is 160 ° C. or higher and 160 ° C. or higher.

When extending | stretching at the said heating temperature, the draw ratio shall be 2-5 times. This corresponds to the fact that the polylactic acid biodegradable heat-shrinkable material has a heat shrinkage rate of 40 to 80%.
The thermal shrinkage rate is 5% or less at temperatures up to 140 ° C. regardless of the stretch rate, and the shrinkage rate is around 40% at 150 ° C. However, since it will be 65 to 70% when heated to 160 ° C. or higher, the draw ratio is 2 to 3 times, more preferably 2.5 times or less.
The stretching may be uniaxial, biaxial, or multiaxial, and is performed by a method such as a roll method, a denter method, or a tube method.

  As described above, according to the present invention, crosslinking of biodegradable aliphatic polyester such as polylactic acid is promoted upon irradiation with ionizing radiation by adding a monomer having an allyl group, and the gel fraction is set to 10 to 90%. Therefore, it can be stretched up to about 5 times by stretching, and when the stretched heat-shrinkable material is heated to the melting point or more, it is thermally shrunk to a shrinkage rate of about 40 to 80% by the mesh memorized. Can do. Moreover, the shape is not deformed by crystal parts and networks that do not melt at the glass transition temperature of polylactic acid, and it has heat resistance.

Embodiments of the present invention will be described below.
In the biodegradable heat-shrink material of the embodiment, TAIC (triallyl isocyanurate) is blended into polylactic acid at a low concentration, and TAIC is blended at 0.7 to 0.9% by weight with 100% by weight of polylactic acid. ing.
TAIC is added and kneaded with the polylactic acid dissolved, and the mixture is press-heated and molded at 180 ° C. (hot pressing), and then rapidly cooled at about 100 ° C./min. Molding.
The sheet is irradiated with an electron beam at an applied voltage of 2 MeV and a current value of 1 mA at 10 to 30 kGy in an inert atmosphere excluding air, and crosslinking of polylactic acid molecules and dissolution of the polylactic acid molecules themselves are performed by TAIC. The gel fraction is set to 50 to 70% at the same time when the crosslinking is completed.
The sheet after electron beam irradiation is heated to 160 ° C. to 180 ° C. and uniaxially stretched up to 5 times. After stretching, the film is cooled to room temperature while the stretched state is fixed to produce a biodegradable heat shrinkable material.

  Since it has a crosslinked structure with a gel fraction of 10 to 90% as described above, it can be stretched up to about 5 times in the stretching step, while it is 40 to 80% in shape memory due to crosslinking network when heated above the melting point. It can be contracted to some extent. And unless it heats more than melting | fusing point or more, it can suppress that a shape deformation | transformation generate | occur | produces with the network by a bridge | crosslinking structure, and can improve heat resistance.

  The biodegradable heat-shrinkable material of the present invention is not limited to the above-described embodiment, and by changing the type of raw material of the biodegradable material, the type of monomer having an allyl group, and the blending amount, The gel fraction due to crosslinking by electron beam irradiation, the heating temperature during stretching, the stretching ratio, and the like can be changed within the scope of the present invention. In that case, the heating temperature at the time of extending | stretching is heated more than the melting | fusing point of the raw material of a biodegradable material, and it is near melting | fusing point), and is extended | stretched on this heating condition, and heat-shrinkable material is manufactured. Thereby, when it heats more than this heating temperature, a thermal contraction rate can be raised to about 80%.

(Examples and Comparative Examples)
42 types of samples shown in Table 1 below were prepared.
As the aliphatic polyester, finely powdered polylactic acid (Lacia H-100J manufactured by Mitsui Chemicals) was used. Polylactic acid was melted at 180 ° C in a substantially closed kneader, Labo Plast Mill, and melted and kneaded until it became transparent. TAIC (Nippon Kasei Co., Ltd.), a kind of allyl monomer, was converted into polylactic acid. On the other hand, as shown in Table 1 below, 0 wt%, 0.5 wt%, 1.0 wt%, 2.0 wt%, and 3.0 wt% were blended, and 10 minutes at a rotation speed of 20 rpm. Kneaded and mixed.
Thereafter, the kneaded product was heated at 180 ° C. to produce a 1 mm thick sheet. This sheet was irradiated with an electron beam by an electron accelerator (acceleration voltage 2 MeV current amount 1 mA) under an inert atmosphere excluding air. As shown in Table 1 below, the dose was set to 0 kGy, 10 kGy, 20 kGy, 30 kGy, 50 kGy, 80 kGy, and 120 kGy.
Then, the sheet after electron beam irradiation was heated at 180 ° C. and stretched up to 2.5 times.
After stretching, the sample was fixed in that state and cooled to room temperature to produce a heat-shrinkable sample.

The stretchability of 42 types of samples was evaluated, the gel fraction was measured, and the results are shown in Table 1. The gel fraction is measured by the method described above. The gel fraction is shown in the lower part of each sample.
The relationship between the gel fraction and the electron beam dose is shown in the graph of FIG.

"Evaluation method of stretchability"
About the sample which was not able to extend | stretch a draw ratio to 2.5 time of the original length, the magnification which can be extended without cutting was evaluated in steps, and it described in the upper stage of each sample.
X = Sample that can hardly be stretched △ = Sample that has been stretched by 1.2 to 2.0 times ○ = 2.0 to 2.5 times ◎ = 2.5 times or more

In Table 1, a sample of a portion surrounded by a double line where the stretchability evaluation is ◎ and ◯ is an example, and a sample of a portion of the outer peripheral region where Δ and × are other than that is a comparative example.
The samples of the comparative examples having the above Δ and × had an electron beam irradiation amount of 0 kGy or a TAIC compounding amount of 0.5% by weight or less. Or the electron beam irradiation amount was 80 kGy and 120 kGy irrespective of the compounding quantity of TAIC.

  From the measurement results shown in Table 1, the comparative example having a TAIC concentration of less than 1.0% by weight (0.5% by weight) did not increase the gel fraction to 9% or less even when irradiated with an electron beam. Moreover, it turned out that a gel fraction is the maximum at 30-50 kGy in any TAIC density | concentration, and it is the effect of about 80-90% in 20 kGy. It was also confirmed that the gel fraction gradually decreased as the irradiation amount increased.

In the stretchability evaluation, the gel fraction was 50 to 70% ◎, 10 to 50% and 70 to 90% ○, 10 to 6% Δ, 5 to 0% and 90 to 96% x.
This is because the shape is memorized by the network by cross-linking, and when the cross-link density is lower than 50%, especially when it is reduced to less than 10%, shrinkage and heat resistance are lost. Since it progresses too much and it becomes difficult to deform | transform and a shape becomes difficult, stretchability and shrinkability will fall. Therefore, it was recognized that the range of 50 to 70% would be excellent in stretchability and heat shrinkability.

Moreover, the preferable range of the irradiation amount of the electron beam was 10 kGy to 50 kGy as described above.
This is because when the cross-linking reaction by TAIC is completed at 30 to 50 kGy, only the decomposition reaction of the polylactic acid molecule itself proceeds. That is, it was recognized that after completion of the crosslinking reaction, the cross-links were broken in various ways due to the decomposition of the polylactic acid molecules, and the cross-linked molecules did not contribute to shape memory, resulting in a decrease in heat shrinkability.

The sheet-like heat-shrinkable materials of the above samples ◎ and ○ are stretched under a heating condition of 150 to 160 ° C. or more and a melting temperature of polylactic acid with a gel fraction of 50 to 70%. . At this time, the film can be stretched by 2.5 times or more. Therefore, when heated to 160 ° C. or higher for heat shrinkage, the cross-linking is partially broken by TAIC and the cross-linked molecule returns to the memorized shape. If it is at least%, it will shrink to nearly 70%.
Moreover, since the thermal shrinkage is 10% or less at the glass transition temperature of polylactic acid (less than 60 ° C.) and the gel fraction is 50 to 70% to promote crosslinking, it is not easily deformed at room temperature. Since the heat resistance is improved, it is suitably used as a heat shrink material used for vehicles and outdoors.

When Table 1 is summarized, the samples having an extensibility evaluation of “◎” or “○” satisfy the following three conditions.
(1) The amount of TAIC is 1.0 wt% to 3.0 wt%
In particular, 1.0 was large at 1.0 to 2.0% by weight.
(2) The electron beam dose is 10 kGy to 50 kGy
(3) Gel fraction is 50% to 70%

"Measurement of heat shrinkage"
The sample after stretching was heated to measure the degree of recovery before stretching.
The measuring method put the extending | stretching sample in the thermostat, and warmed to predetermined temperature, Then, the length of the extending | stretching direction was measured. The temperature was raised from 40 ° C. by 10 ° C., and each temperature was applied.
(Length) Shrinkage rate (%) = (Length before shrinkage−Length after shrinkage) / (Length before shrinkage) × 100

The graph of FIG. 5 shows the measurement result of the thermal shrinkage rate of a sample having a TAIC compounding amount of 1.0% by weight and an electron beam irradiation amount of 20 kGy.
As shown in the graph of FIG. 4, the shrinkage rate is 5% or less up to 140 ° C., regardless of the stretch rate, starts shrinking when it exceeds 140 ° C., around 40% at 150 ° C., 65 to 65% at 160 ° C. or more. 70%.

  Using the same polylactic acid and TAIC as in Example 1, a heat shrinkable tube was formed from this kneaded product. The tube was irradiated with an electron beam at a different dose in the same manner as in Example 1. After irradiation, the sample was stretched in the same manner as in Example 1 and stretched up to 2.5 times to prepare a sample of a heat-shrinkable tube.

  Even in the case of a shrinkable tube, it was confirmed that TAIC is required to be 1.0% by weight or more, and the gel fraction can be 10 to 90% at an electron beam irradiation amount of 10 to 50 kGy.

  As described above, the biodegradable heat-shrinkable material of the present invention is irradiated with an electron beam to have a gel fraction of 10 to 90%, preferably 50 to 70%, and thus has heat resistance and stretched. Later, when the film is thermally shrunk at the temperature at the time of stretching, the cross-linked network is shrunk by shape memory, and the shrinkage rate can be made 40-80% larger than the conventional product.

(A)-(D) are the schematic which shows the bridge | crosslinking structure of the sheet | seat of this invention, an extending | stretching structure, the structure at the time of a glass transition temperature, and a heat contraction structure, respectively. (A)-(D) are the schematic when not having a crosslinked structure. It is a graph which shows the relationship between an electron beam irradiation amount and a gel fraction. It is a graph which shows the relationship between shrinkage temperature and shrinkage rate.

Explanation of symbols

A Crystal part B Non-crystal part C Network

Claims (6)

It consists of a mixture of a biodegradable aliphatic polyester and a monomer having a low concentration of allyl groups, and is stretched under heating in a state of a crosslinked structure by irradiation with ionizing radiation or mixing of a chemical initiator,
A biodegradable heat-shrinkable material, characterized in that when it is heated at a temperature equal to or higher than the temperature at the time of stretching, the shrinkage rate is shrunk in a range of 40% to 80%.   Polylactic acid is used as the biodegradable aliphatic polyester, and the gel fraction (gel fraction dry weight / initial dry weight) is 10% or more and 90% or less, and the shrinkage is less than 10% at 140 ° C. or less, and 160 ° C. or more. The biodegradable heat-shrinkable material according to claim 1, wherein the shrinkage ratio is 40% or more and 80% or less. After adding a crosslinkable polyfunctional monomer in a biodegradable raw material at a low concentration and kneading, and molding the mixture into a required shape,
Irradiating with ionizing radiation to cause a cross-linking reaction with a gel fraction of 10% or more and 90% or less, and after irradiation with the ionizing radiation, a range from the melting temperature of the biodegradable raw material to the melting temperature + 20 ° C. It is formed by stretching while heating with
A method for producing a biodegradable heat-shrinkable material, wherein the heat-shrinkable material shrinks when heated at a temperature equal to or higher than the temperature at the time of stretching within a range of 40% to 80%. A monomer having an allyl group is added to the biodegradable aliphatic polyester at a low concentration and kneaded, and the mixture is molded into a required shape.
Irradiating with ionizing radiation at 1 kGy or more and 150 kGy or less to cause a crosslinking reaction to form a crosslinked structure, and a gel fraction (gel content dry weight / initial dry weight) of 10% to 90%,
Heat that is stretched while being heated in the range of 60 ° C. to 200 ° C. after irradiation with the ionizing radiation, and contracts in a range of 40% to 80% when contracted at a temperature equal to or higher than the temperature during the stretching. A method for producing a biodegradable heat-shrinkable material, characterized by comprising a shrinkable material. Polylactic acid is used as the biodegradable aliphatic polyester, and the monomer having an allyl group to be blended is added in an amount of 0.7% by weight to 3.0% by weight with respect to 100% by weight of the polylactic acid, and is kneaded.
After the mixture is formed into a thin film, a thick sheet, or a tube, ionizing radiation is irradiated at 5 kGy or more and 50 kGy or less to generate a crosslinking reaction to form a crosslinked structure, and the gel fraction is 50%. More than 70%,
The method for producing a biodegradable heat-shrinkable material according to claim 4, wherein after the cross-linked structure is formed, the film is heated at 150 ° C or higher and 180 ° C or lower and drawn at a draw ratio of 2 to 5 times.   Triallyl isocyanurate is used as the above-mentioned monomer having an allyl group, the blending amount of the triallyl isocyanurate is 0.7% by weight or more and 2.0% by weight or less with respect to 100% by weight of polylactic acid, and the mixture is molded. The method for producing a biodegradable heat-shrinkable material according to claim 5, wherein the electron beam is irradiated at 10 kGy or more and 30 kGy or less and heated at 160 ° C or more and 180 ° C or less during the stretching.