JP5912925B2 - Production method of foamed sheet of polyglycolic acid resin - Google Patents

Description

The present invention relates to a polyglycolic acid resin foam sheet manufacturing how, and more particularly, polyglycolic acid resin foam sheet of the resin composition containing the polyglycolic acid resin by extrusion foaming to prepare a polyglycolic acid resin foam sheet about the manufacturing how.

2. Description of the Related Art Conventionally, resin foams made of polyester resin, polystyrene resin, and the like are widely used for packaging materials and the like because they are lightweight and excellent in cushioning properties and can be easily molded into various shapes.
In particular, a sheet-like resin foam called a foamed sheet is widely used as a slip sheet or a packaging bag.
In recent years, countermeasures against the problem that the scenery is damaged by illegally dumped packaging materials in places such as mountains, rivers, or coasts have been required, and biodegradable resins that can be decomposed in the natural environment. It has been studied to form a foam.
As a specific measure for obtaining such a biodegradable resin foam, it is considered to form a foam by extrusion foaming a resin composition containing a polyglycolic acid resin excellent in heat resistance and biodegradability. (See Patent Document 1 below).

However, since polyglycolic acid resin is easily hydrolyzed in the extruder to reduce the molecular weight, it has a problem of easily lowering its melt tension.
For this reason, foaming in a good foamed state becomes noticeable when the resin composition containing a polyglycolic acid resin is simply subjected to extrusion foaming without taking any measures against hydrolysis, and the foam breakage due to the decrease in melt tension becomes significant. It is difficult to get a body.
As a method for forming a polyglycolic acid resin foam by extrusion foaming while preventing such hydrolysis, the polyglycolic acid resin is supplied to the extruder under a nitrogen gas stream in paragraph [0038] of Patent Document 1 below. And producing a strand-like foam.

By the way, the foam obtained by extrusion foaming is usually influenced by the foaming speed at the time of extrusion foaming, the shearing force applied to the molten resin, the melt tension of the molten resin at that temperature, etc. The foaming state may be greatly affected by the extrusion conditions.
In particular, the surface layer of the foam is a region where bubbles grow quickly and is a region that receives a strong shearing force with the edge of the die outlet, so it is likely to be affected by the foaming state due to extrusion conditions, and the surface area relative to the volume. The sheet-like resin foam having a larger ratio than the strand-like foam or the like is more likely to affect the foamed state depending on the extrusion conditions than the strand-like foam or the like.
Therefore, when producing a polyglycolic acid resin foamed sheet by extruding and foaming a resin composition containing a polyglycolic acid resin, good quality can be obtained even if measures are taken by nitrogen supply as described in Patent Document 1. You can't always get things.
In addition, since there is a limit to maintaining the foamed state of the polyglycolic acid resin foamed sheet in a good state by devising the extrusion conditions, measures from other directions such as materials used have come to be required. Yes.

  However, no specific measures have been found so far, and it has been difficult to produce a foamed polyglycolic acid resin sheet in a good foamed state.

Japanese Patent No. 3944281

  The present invention aims to solve the above problems, and provides a method for producing a polyglycolic acid resin foamed sheet capable of producing a polyglycolic acid resin foamed sheet in a good foamed state. An object of the present invention is to provide a polyglycolic acid resin foam sheet.

  The present inventor has intensively studied to solve the above problems, and adds a chain extender having an epoxy group to the polyglycolic acid resin at a predetermined ratio so that the epoxy equivalent becomes a predetermined value. The present invention found that a suitable melt tension can be imparted to the resin composition by carrying out extrusion foaming using the resin composition, and that a polyglycolic acid resin foamed sheet can be produced in a good foamed state. The invention has been completed.

  That is, in the method for producing a polyglycolic acid resin foam sheet according to the present invention for solving the above-described problems, the polyglycolic acid resin has an epoxy group and an epoxy equivalent of 100 g / eq or more and 500 g / eq or less together with a chain extender. Polyglycolic acid resin foamed by extrusion-foaming the resin composition containing the chain extender so that the content thereof is 0.05 to 1 part by mass with respect to 100 parts by mass of the polyglycolic acid resin. It is characterized by producing a sheet.

According to the method for producing a polyglycolic acid resin foamed sheet of the present invention, a polyglycolic acid resin foamed sheet exhibiting excellent characteristics in heat resistance and biodegradability can be produced in a good foamed state.
That is, according to this invention, the polyglycolic acid resin foam sheet which has a favorable foaming state can be provided.

Embodiments of the present invention will be described below.
First, raw materials for forming a polyglycolic acid resin foam sheet will be described.
In the method for producing a polyglycolic acid resin foamed sheet (hereinafter also simply referred to as “foamed sheet”) of the present embodiment, a resin composition containing a polyglycolic acid resin and a chain extender is used.

  As the polyglycolic acid resin, a glycolide homopolymer or a polymer containing a repeating unit derived from glycolide represented by the following formula (1) can be employed as a main component of the foam sheet. .

In addition, as a polyglycolic acid resin used in this embodiment, the ratio of the repeating unit represented by the above formula (1) can be usually 70% by mass or more, and the above formula (1) can be used. The ratio of the repeating unit represented is preferably 80% by mass or more, more preferably 90% by mass or more.
The repeating unit other than the repeating unit represented by the formula (1) is, for example, one or more selected from the group consisting of ethylene oxalate, lactide, lactones, trimethylene carbonate, and 1,3-dioxane. What originates in a monomer can be employ | adopted, For example, the repeating unit represented by following formula (2)-(6) can be mentioned.

（式中、ｎ＝１〜１０、ｍ＝０〜１０）

(Where n = 1 to 10, m = 0 to 10)

（式中、ｊ＝１〜１０）

(Where j = 1 to 10)

（式中、Ｒ₁及びＲ₂は、それぞれ独立に、水素原子または炭素数１〜１０のアルキル基である。ｋ＝２〜１０）

(Wherein R ₁ and R ₂ are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, k = 2 to 10).

In addition, by introducing these repeating units (2) to (6), the melting point and crystallinity of the polyglycolic acid resin are reduced as compared with those using only the repeating unit (1) (homopolymer). Therefore, the foamed sheet of this embodiment can adjust the molten state of the resin composition and the like by adjusting the repeating units constituting the polyglycolic acid resin used for the production thereof.
That is, in terms that the melting point and crystallinity can be adjusted, it is preferable to use a polyglycolic acid resin containing a repeating unit other than the above (1) to some extent, as shown in the above (2) to (6) It is preferable to use a polyglycolic acid resin containing 1% by mass or more of a repeating unit other than the above (1).

In addition, the polyglycolic acid resin used for producing the foamed sheet of the present embodiment exhibits a melt viscosity of 500 Pa · s or more and 50000 Pa · s or less under a measurement condition of a melting point + 20 ° C. and a shear rate of 100 sec ^−1. Those are preferred.
Moreover, as said polyglycolic acid resin, it is preferable that melting | fusing point is 180 degreeC or more, It is more preferable that it is 190 degreeC or more, It is further more preferable that it is 200 degreeC or more.
Moreover, as polyglycolic acid resin used for manufacture of the foam sheet of this embodiment, it is preferable that melting enthalpy is 10 J / g or more, More preferably, it is 20 J / g or more, More preferably, it is 30 J / g or more. It is particularly preferred.
Further, as the polyglycolic acid resin used for producing the foamed sheet of the present embodiment, the density of the non-oriented crystallized product is preferably 1.50 g / cm ³ or more, and preferably 1.51 g / cm ³ or more. More preferably, it is particularly preferably 1.52 g / cm ³ or more.

The melting point of the polyglycolic acid resin can be determined by performing differential scanning calorimetry (DSC) analysis using an amorphous sample. For example, a differential scanning calorimeter device (manufactured by SII Nano Technology) This can be confirmed by using DSC 6220 type) and raising the temperature to about 270 ° C. at a rate of temperature increase of 10 ° C./min under a nitrogen gas stream and determining the peak temperature of the endothermic peak.
In addition, the melting enthalpy value can be confirmed by obtaining the integrated value (peak area) of this endothermic peak.
Further, the melt viscosity can be measured based on the method described in JIS K 7199: 1999 “Plastic-capillary rheometer and slit die rheometer plastic flow characteristic test method”.
That is, the melt viscosity can be measured using a twin-bore capillary rheometer (Rheological 5000T (manufactured by Chiast, Italy)), and the sample is contained in a barrel having an inner diameter of 15 mm arranged in the vertical direction. After preheating and melting for 5 minutes at a temperature 20 ° C. higher than the melting point of the polyglycolic acid resin thus required, a piston is inserted from the top of the barrel, and the descending speed of the piston is set to 0.0556 mm / s ( A constant speed of shear rate: 100.1 s ^-1 ), and molten resin is stringed from a capillary (die diameter: 1.0 mm, die length: 10 mm, inflow angle: 90 degrees (conical)) provided at the lower end of the barrel. The apparent viscosity observed at this time can be measured to obtain the melt viscosity.
The density of the non-oriented crystallized product can be measured according to JIS R 7222 (pycnometer method using n-butanol).

The chain extender used for forming the foamed sheet together with the polyglycolic acid resin has an epoxy group, and it is important that the epoxy equivalent is 100 g / eq or more and 500 g / eq or less.
In addition, in this specification, this epoxy equivalent means the value calculated | required based on JISK7236.

The chain extender is 0.05 parts by mass or more and 1 part by mass or less when the content of the polyglycolic acid resin in the resin composition for forming the foamed sheet is 100 parts by mass. It is important to make it contain in the said resin composition, and it is more preferable to set it as 0.1 to 0.5 mass part.

This chain extender can bond the epoxy group in the molecule to the polyglycolic acid resin to form a crosslinked product of the polyglycolic acid resin in the system, so that only the polyglycolic acid resin is heated. The resin composition can exhibit a higher melt viscosity than when melted, and the melt viscosity of the resin composition can be adjusted to a value suitable for extrusion foaming.
The epoxy group also acts effectively to capture and stabilize the hydrolysis product when hydrolysis occurs in the polyglycolic acid resin.
The chain extender usually has a plurality of reactive functional groups effective for binding the chain extender to the polyglycolic acid resin. In this embodiment, the chain extender epoxy is used as described above. It is preferable to employ one having a plurality of epoxy groups in the molecule because the group is effectively used.

However, if the number (mole number) of epoxy groups brought to the resin composition by the addition of this chain extender is excessively large, the melt viscosity of the resin composition exceeds the range suitable for extrusion foaming. There is a risk that the workability in extrusion foaming may be reduced by making the load of the resin excessive or setting the resin temperature to a high temperature in order to lower the melt viscosity to some extent.
On the other hand, if the number of epoxy groups brought to the resin composition by addition of the chain extender is excessively small, it is naturally difficult to expect the above effects.
That is, it is important for the resin composition that the epoxy equivalent of the chain extender is within the above range and that the addition amount of the chain extender to the polyglycolic acid resin is within the above range. This is because the melt tension suitable for extrusion foaming is more reliably exhibited and the workability in the extrusion foaming is improved.

The chain extender will be described in more detail. Examples of the chain extender include olefins such as polyethylene, polypropylene, polystyrene, polybutene, polybutadiene, polybutadiene hydrogenated polymer, polyethylene butylene, polyisobutylene, and cycloolefin. Alternatively, a resin structure such as vinyl, acrylic, ester, or amide can be used, and the skeleton portion may be a copolymer structure.
The epoxy group may be directly added to the above resin structure, or may be a structure obtained by grafting an epoxy group added polymer onto the above resin structure.

The chain extender is preferably an epoxy group-containing acrylic-modified styrene resin, that is, one containing at least one (meth) acrylic monomer having an epoxy group and a styrene monomer as a repeating unit.
Specific examples of the (meth) acrylic monomer having an epoxy group include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, glycidyl ethacrylate, and glycidyl itaconate.
Furthermore, examples of the styrenic monomer constituting the chain extender include styrene, α-methylstyrene, vinyltoluene, p-methylstyrene, t-butylstyrene, o-chlorostyrene, and vinylpyridine.

  The chain extender may contain a (meth) acrylic acid ester as another repeating unit. Examples of the (meth) acrylic acid ester include methyl (meth) acrylate and (meth) acrylic acid. Ethyl, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, s-butyl (meth) acrylate, i-butyl (meth) acrylate, (meth) T-butyl acrylate, n-amyl (meth) acrylate, i-amyl (meth) acrylate, isobornyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylbutyl (meth) acrylate, ( 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, n-decyl (meth) acrylate, methylcycloacrylate (meth) acrylate Sil, (meth) cyclopentyl acrylate, and cyclohexyl (meth) acrylate.

The resin composition containing the chain extender and the polyglycolic acid resin can be used for forming a foamed sheet by extrusion foaming using a general foaming agent.
In that case, a foam regulator may be included in the resin composition to adjust the foamed state of the foamed sheet.

As the foaming agent, a volatile foaming agent that becomes a gas at normal room temperature and normal pressure, or a decomposable foaming agent that generates a gas by thermal decomposition can be used. An active gas, an aliphatic hydrocarbon, an alicyclic hydrocarbon, or the like can be used.
Examples of the inert gas include carbon dioxide gas and nitrogen.
Examples of the aliphatic hydrocarbon include propane, normal butane, isobutane, normal pentane, and isopentane. Examples of the alicyclic hydrocarbon include cyclopentane and cyclohexane.
In the present embodiment, normal butane and isobutane can be preferably used among the above.

Examples of the decomposable foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, organic acid such as sodium bicarbonate or citric acid or a mixture of a salt thereof and bicarbonate.
If the amount of the foaming agent used is too small, a low-density foam sheet cannot be obtained, and if it is too large, bubble breakage occurs and a good foam sheet cannot be obtained.
Therefore, in order to form an excellent foamed foam sheet, the ratio of the foaming agent to 100 parts by mass of the polyglycolic acid resin in the resin composition is preferably 0.1 parts by mass or more and 5 parts by mass or less. More preferably, the content is 0.2 parts by mass or more and 3 parts by mass or less.

Examples of the air conditioner include polytetrafluoroethylene, talc, aluminum hydroxide, and silica.
In addition, the said decomposable foaming agent can adjust a foaming state by using together with a volatile foaming agent, and can be used as a bubble regulator.
As a usage-amount of a bubble regulator, it is preferable to set it as 0.05 to 5 mass parts with respect to 100 mass parts of said polyglycolic acid resin in the resin composition for forming a foam sheet.

  In the present embodiment, various additives such as a lubricant, an antioxidant, an antistatic agent, a flame retardant, an ultraviolet absorber, a light stabilizer, a colorant, and an inorganic filler are added to the resin composition used for forming the foam sheet. Can further be included.

Subsequently, the manufacturing method which manufactures a polyglycolic acid resin foam sheet is demonstrated.
In the method for producing a polyglycolic acid resin foam sheet according to the present embodiment, a resin composition containing a polyglycolic acid resin or a chain extender as described above, using an extruder and a die attached to the tip of the extruder. It is possible to employ a method in which a product is melt-kneaded in the extruder and the melt-kneaded product obtained by melt-kneading is extruded and foamed from the discharge port of the die into a sheet.
In the production of the foam sheet, the resin may be formed into a cylindrical sheet or a flat sheet by using a circular die having an annular discharge port or a flat die having a linear discharge port as the die. The composition can be extruded and foamed.

Of these, it is preferable to use a circular die.
In addition, when using a circular die, after carrying out the extrusion foaming to form a cylindrical polyglycolic acid resin foamed sheet (extrusion foaming step), the outer diameter is continuously larger than the discharge port. The diameter of the polyglycolic acid resin foamed sheet is expanded and cooled so that the inner surface of the cylindrical polyglycolic acid resin foamed sheet is brought into contact with the outer peripheral surface of a cylindrical cooling mandrel having a large diameter. (Expansion process) is carried out. Further, following this diameter expansion process, a step (development process) in which the tubular polyglycolic acid resin foam sheet is cut and expanded along the extrusion direction is carried out to form a long band. The polyglycolic acid resin foam sheet can be produced.

  Specifically, the cooling mandrel is disposed in front of the circular die in the extrusion direction so that the approximate center of the discharge port of the circular die is positioned on the extension line of the virtual central axis of the cooling mandrel, and the cooling mandrel A cutting blade is installed on the downstream side of the cylinder, and the polyglycolic acid resin foam sheet is taken up downstream from the installation position of the cutting blade, so that the cylindrical polycrystal extruded from the discharge port of the circular die is used. The glycolic acid resin foamed sheet is expanded along the outer peripheral surface of the cooling mandrel, and the cooling mandrel is cooled by sliding the polyglycolic acid resin foamed sheet on the cooling mandrel. A long band by a method in which it is continuously cut along the extrusion direction with a cutting blade, and this is flattened and wound into a roll. The polyglycolic acid resin foam sheet can be fabricated of.

In the extrusion foaming step, it is preferable to adjust the shear rate at the die within a predetermined range in order to obtain a foamed sheet having a good foamed state.
That is, in the present embodiment, the polyglycolic acid resin is easily decomposed as described above, and the melt tension is easily lowered during extrusion foaming. Therefore, if extrusion foaming is performed at an excessively low shear rate, extrusion from the discharge port is performed. In the previous stage (the inside of the die), foaming starts and there is a possibility that a foam sheet having a good foamed state cannot be obtained. On the other hand, if extrusion foaming is performed at an excessively high shear rate, bubble breakage or the like may occur. It is preferable to adjust the shear rate at the die within a predetermined range because it may occur.
Specifically, it is preferable to be extruded foam such that the shear rate in order to obtain a foam sheet having an excellent state of foaming is 800 sec ^-1 or more 4000Sec ^-1 or less, and of 1,000 sec ^-1 or more 3500Sec ^-1 or less It is particularly preferable to perform extrusion foaming.

The shear rate can be calculated from the volume of the resin composition discharged from the die per unit time including the foaming agent and the bubble adjusting agent, the opening area of the die, and the like. It can be obtained as follows.

(How to determine the shear rate in a circular die)
The shear rate at the discharge port of the circular die is calculated by the following formula.

Shear rate γ (sec ⁻¹ ) = (6 × Q) / [π × (D / 10) × (t / 10) ² ]

However, “Q (cm ³ / s)” is the volume of the resin composition extruded per unit time, and “D (mm)” is the diameter of the inner opening edge of the discharge port, “t (mm)”. Is the opening width of the discharge port.

(How to determine the shear rate in a flat die)
The shear rate at the discharge port of the flat die is calculated by the following calculation formula.

Shear rate γ (sec ⁻¹ ) = (6 × Q) / [(W / 10) × (t / 10) ² ]

However, “Q (cm ³ / s)” is the volume of the resin composition extruded per unit time, “W (mm)” is the length of the discharge port, and “t (mm)” is the discharge volume. The opening width of the outlet.

Further, in the diameter expansion step, according to a ratio (hereinafter also referred to as “blow-up ratio”) between the diameter of the discharge port (average diameter obtained by averaging the inner diameter and the outer diameter of the discharge port) and the outer diameter of the cooling mandrel. The cylindrical foamed sheet is stretched in the radial direction (the width direction in the strip-shaped foamed sheet after the unfolding step).
In this embodiment, by using a specific chain extender, the molten resin extruded from the die discharge port can be made to have a melt viscosity suitable for foaming, particularly at a temperature of melting point + 20 ° C. and a shear rate of 100 sec ⁻¹ . The polyglycolic acid resin having a melt viscosity of 500 Pa · s or more and 50000 Pa · s or less under measurement conditions is used to reduce bubble breakage in the extrusion foaming process, but excessive stretching is performed in the subsequent diameter expansion process. If added, the stretching may cause the bubble film to break.

Therefore, even when a polyglycolic acid resin having a melt viscosity of 500 Pa · s or more and 50000 Pa · s or less under measurement conditions of a melting point + 20 ° C. and a shear rate of 100 sec ⁻¹ is used, the blow-up ratio (of the cooling mandrel The outer diameter / the diameter of the discharge port is preferably 3.5 or less.
On the other hand, if it is too small, wavy stripes (corrugated) may appear on the foamed sheet, and the directionality of physical properties may increase, so it is preferably 1.5 or more.

In addition, in the manufacturing method of the polyglycolic acid resin foam sheet of this embodiment, a polyglycolic acid resin foamed sheet having a thickness of 0.1 mm or more and 3.0 mm or less can usually be produced. In the conventional manufacturing method, A foamed sheet having an apparent density of 0.1 g / cm ³ or more and 1.0 g / cm ³ or less obtained in accordance with JIS K 7222 is obtained while containing 90% by mass or more of the polyglycolic acid resin that is difficult to obtain. be able to.
That is, in the method for producing a polyglycolic acid resin foamed sheet of the present embodiment, a polyglycolic acid resin foamed sheet having excellent heat resistance and biodegradability and having a good foamed state can be produced.

In addition, in this invention, a polyglycolic acid resin foam sheet and its manufacturing method are not limited to the said illustration.
In addition, regarding items not exemplified above, conventionally known items regarding the forming material and manufacturing method of the polyglycolic acid resin foamed sheet can be appropriately adopted in the present invention.

  EXAMPLES Hereinafter, examples will be shown to specifically describe a method for producing a polyglycolic acid resin foam sheet, but the present invention is not limited to these specific examples.

Example 1
The melt viscosity measured at a temperature (melting point + 20 ° C.) and a shear rate of 100 sec ⁻¹ / sec is 1250 Pa · s, the melting point is 220 ° C., the melting enthalpy of the single crystal is 200 J / g, and the density of the non-oriented crystallization product is 1.56 g / cm ³ polyglycolic acid resin (trade name “Kredux100R60” manufactured by Kureha Co., Ltd.) dried for 4 hours at a temperature of 100 ° C., bubble regulator (powder talc manufactured by Nippon Talc Co., Ltd., trade name “micro” ACE L-1 ") and a chain extender (epoxy group-containing acrylic modified styrene resin (epoxy equivalent: 285 g / eq) manufactured by BASF, trade name" JONCRYL ADR-4368-F ") and the dried The foam regulator is contained in an amount of 0.1 parts by mass and the chain extender is contained in a proportion of 0.1 parts by mass with respect to 100 parts by mass of the polyglycolic acid resin. The resin composition is supplied to an extruder (first extruder) on the upstream side of the tandem extruder to melt and knead the resin composition, and a blowing agent (butane) is added to the polyglycolic acid resin in the first extruder. The melt kneading was further performed by pressing 0.6 parts by mass with respect to 100 parts by mass.
The kneaded material melt-kneaded by this first extruder is sent to a downstream-side extruder (second extruder) connected to the tip of the first extruder in the extrusion direction, and the melt-kneading is continued in this second extruder. While performing, the temperature of the melt-kneaded product was lowered to finally reach a temperature of 224 ° C.
Then, melted at a discharge rate of 28 kg / h from a circular die having an annular discharge port (discharge port opening width: 0.4 mm) having a diameter of 70 mm and adjusted to a temperature of 226 ° C. attached to the tip of the second extruder. The kneaded product was extruded and subjected to extrusion foaming.
The shear rate at the tip of the mold at this time was 1020 sec ⁻¹ as determined by calculation with the density of the melt-kneaded product being 1.3 g / cm ³ .
Thereafter, a cylindrical foam sheet extruded from a circular die using a cooling mandrel having an outer diameter of 200 mm is expanded in diameter (blow-up ratio: 2.9) and expanded after cooling to an apparent density of 0.62 g / A flat strip-shaped foam sheet of cm ³ was produced.
In Example 1, the state of extrusion foaming was also stable, and a foamed sheet having a good foamed state could be obtained.

(Example 2)
The ratio of the chain extender (JONCRYL ADR-4368-F) to 100 parts by mass of the polyglycolic acid resin (Kredux 100R60) was changed to 0.2 parts by mass, and the temperature of the melt-kneaded material supplied from the second extruder to the circular die Was adjusted to 224 ° C., and the foamed sheet of Example 2 was produced in the same manner as Example 1 except that the temperature of the circular die was 220 ° C.
The apparent density of the foamed sheet of Example 2 was 0.35 g / cm ³ .
Also in Example 2, the state of extrusion foaming was stable, and a foamed sheet having a good foamed state could be obtained.

(Example 3)
The ratio of the chain extender (JONCRYL ADR-4368-F) to 100 parts by mass of the polyglycolic acid resin (Kredux 100R60) was changed to 0.3 parts by mass, and the temperature of the melt-kneaded material supplied from the second extruder to the circular die Was adjusted to 230 ° C., the temperature of the circular die was set to 220 ° C., and the discharge rate was set to 28 kg / h. A foamed sheet of Example 3 was produced in the same manner as Example 1. The shear rate at the die tip at this time was 1020 sec ⁻¹ .
The apparent density of the foamed sheet of Example 3 was 0.32 g / cm ³ .
Also in Example 3, the state of extrusion foaming was stable, and a foamed sheet having a good foamed state could be obtained.

Example 4
The ratio of the chain extender (JONCRYL ADR-4368-F) to 100 parts by mass of the polyglycolic acid resin (Kredux100R60) was changed to 0.4 parts by mass, and the bubble regulator was polytetrafluoroethylene resin fine particles (product) manufactured by Asahi Glass Co., Ltd. Name “Full-on brilicant L169J”) was changed to 0.4 parts by mass, the temperature of the melt-kneaded material supplied from the second extruder to the circular die was adjusted to 230 ° C. and the temperature of the circular die was adjusted to 220 ° C. The foamed sheet of Example 4 was produced in the same manner as in Example 1 except that the discharge rate was 29 kg / h. At this time, the shear rate of the die tip was 1057 sec ⁻¹ .
The apparent density of the foamed sheet of Example 4 was 0.22 g / cm ³ .
Also in Example 4, the state of extrusion foaming was stable, and a foamed sheet having a good foamed state could be obtained.

(Comparative Example 1)
The resin composition supplied to the first extruder did not contain a chain extender (JONCRYL ADR-4368-F), and the temperature of the melt-kneaded material supplied from the second extruder to the circular die was adjusted to 220 ° C. At the same time, extrusion foaming was carried out in the same manner as in Example 1 except that the temperature of the circular die was 225 ° C. and the discharge rate was 28 kg / h. The shear rate at the die tip at this time was 1020 sec ⁻¹ .
In Comparative Example 1, the obtained sheet was hardly foamed, and could not be called a “foamed sheet”.
The reason for this in Comparative Example 1 seems to be that the melt viscosity of the melt-kneaded product was low and foam breakage occurred in the initial stage of bubble formation by the foaming agent.

(Comparative Example 2)
The chain extender is changed to a maleic acid-modified styrene resin (trade name “SMA1000P”) manufactured by Cray Valley which does not contain an epoxy group, and the ratio of the resin composition contained in 100 parts by mass of the polyglycolic acid resin. The temperature of the melt-kneaded material supplied from the second extruder to the circular die was adjusted to 225 ° C, the temperature of the circular die was 225 ° C, and the discharge rate was 28 kg / h. Except that, extrusion foaming was carried out in the same manner as in Example 1. The shear rate at the die tip at this time was 1020 sec ⁻¹ .
In Comparative Example 2, gelation occurred in the extruder and a foam sheet could not be obtained.

(Comparative Example 3)
The ratio of the chain extender (JONCRYL ADR-4368-F) to 100 parts by mass of the polyglycolic acid resin (Kredux 100R60) was changed to 2.0 parts by mass, and the temperature of the melt-kneaded material supplied from the second extruder to the circular die Was adjusted to 230 ° C., the temperature of the circular die was 230 ° C., and the extrusion foaming was performed in the same manner as in Example 1 except that the discharge rate was 28 kg / h. The shear rate at the die tip at this time was 1020 sec ⁻¹ .
In Comparative Example 3, as in Comparative Example 2, gelation occurred in the extruder and a foam sheet could not be obtained.

The above results are summarized as shown in Table 1 below.

In addition, when the density of the melt-kneaded product extruded from the discharge port of the circular die was 1.3 g / cm ^{3 and} the shear rate in the circular die was calculated, the results were as shown in Table 2 below.

  Also from the results shown in this table, it can be seen that according to the present invention, a polyglycolic acid resin foamed sheet having a good foamed state can be provided.

Claims (2)

A polyglycolic acid resin is contained together with a chain extender having an epoxy group and an epoxy equivalent of 100 g / eq or more and 500 g / eq or less, and a ratio with respect to 100 parts by mass of the polyglycolic acid resin is 0.05 parts by mass or more and 1 part by mass or less. A resin composition containing the chain extender is extruded and foamed to produce a polyglycolic acid resin foam sheet ,
The resin composition contains the polyglycolic acid resin having a melt viscosity of 500 Pa · s or more and 50000 Pa · s or less under the measurement conditions of a melting point + 20 ° C. and a shear rate of 100 sec ^−1. Yes,
An extrusion foaming step in which the resin composition is extruded and foamed using a circular die having an annular discharge port to form a tubular polyglycolic acid resin foam sheet;
A cylindrical polyglycolic acid resin obtained by the extrusion foaming step along the outer peripheral surface of a cooling mandrel having a diameter larger than that of the discharge port and not more than 3.5 times the discharge port. Diameter expansion process for expanding and cooling the foam sheet, and
The expansion step of cutting and expanding the tubular polyglycolic acid resin foam sheet cooled in the diameter expansion step along the extrusion direction,
A method for producing a polyglycolic acid resin foamed sheet, wherein a continuous polyglycolic acid resin foamed sheet is produced by continuously performing the extrusion foaming process to the unfolding process . Polyglycolic acid resin foam sheet prepared for the polyglycolic acid resin are contained more than 90 wt%, polyglycol according to claim 1, wherein the apparent density is less than 0.1 g / cm ³ or more 1.0 g / cm ³ The manufacturing method of an acid resin foam sheet.