JP6971947B2 - Polylactic acid resin foam - Google Patents

Description

The present invention relates to a polylactic acid resin foam.

Conventionally, polyester resin foam has been used as a raw material for various molded products such as packaging materials because it is lightweight, has excellent cushioning properties, and can be easily molded into various shapes.
In recent years, there has been a demand for countermeasures against the problem that the landscape is spoiled by illegally dumped packaging materials in places such as mountains, rivers, or coasts.
Against this background, it is being studied to produce molded products using polylactic acid resin that can be biodegraded in the natural environment, and it is being studied to develop polylactic acid resin foams for various purposes. (See Patent Document 1 below).

Japanese Unexamined Patent Publication No. 2015-218327

Conventionally, the polylactic acid resin foam as described above has been required to improve its strength, but a technique for satisfying such a demand has not been sufficiently established.
Therefore, it is an object of the present invention to improve the strength of the polylactic acid resin foam.

The present inventor has conducted diligent studies to solve the above-mentioned problems, and found that the above-mentioned problems can be solved by forming a foam using a polylactic acid resin having a predetermined heat-melting property, and has found that the present invention can be solved. It has been completed.

The present invention for solving the above problems
It contains a polylactic acid resin, and the polylactic acid resin is
In the extensional viscosity measurement at 190 ° C., the extensional viscosity at the break point is 0.5 MPa · s or more, and
In the extensional viscosity measurement, a polylactic acid resin foam is provided, which is a polylactic acid resin in which the extensional viscosity increases as the extensional speed increases, and no peak appears in the graph with the horizontal axis as the extensional speed and the vertical axis as the extensional viscosity. do.

According to the present invention, the polylactic acid resin foam can exhibit excellent strength.

The schematic diagram which showed the molecular weight distribution of polylactic acid resin. The schematic diagram which showed the molecular weight distribution of polylactic acid resin. The schematic which shows the structure of the manufacturing apparatus of a foam sheet. Explanatory drawing which showed the method of measuring the average bubble film thickness of a foam sheet. The schematic perspective view which showed the folding box which is a foam molded product. SEM photograph of the cross section (MD, TD) of the extruded foam sheet of Test Example 3-1. SEM photograph of the cross section (MD, TD) of the extruded foam sheet of Comparative Test Example 4-1.

Hereinafter, embodiments of the present invention will be described.
Hereinafter, the present invention will be described with the case where the polylactic acid resin foam is an extruded foam sheet as a main example.

The polylactic acid resin foamed sheet of the present embodiment (hereinafter, also simply referred to as “foamed sheet” or the like) is an extruded foamed sheet as described above.
That is, the foamed sheet of the present embodiment is extruded into the atmosphere through a die attached to the tip of the extruder after the polylactic acid resin and the component for bringing the polylactic acid resin into a foamed state are melt-kneaded by the extruder. It was made by being made.

The polylactic acid resin of the present embodiment may be a homopolymer of lactic acid or a copolymer of lactic acid and another monomer.
Examples of the monomer in the copolymer include aliphatic hydroxycarboxylic acids other than lactic acid, aliphatic polyhydric alcohols, and aliphatic polyvalent carboxylic acids.
The monomer may be, for example, a polyfunctional polysaccharide or the like.

The lactic acid constituting the polylactic acid resin may be either one or both of the L-form and the D-form.
That is, the polylactic acid resin which is the homopolymer may be any of a poly (L-lactic acid) resin, a poly (D-lactic acid) resin, and a poly (DL-lactic acid) resin.

Examples of the aliphatic polyvalent carboxylic acid constituting the copolymer include oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, undecanedioic acid and dodecanedioic acid. Can be mentioned.
The aliphatic multivalent carboxylic acid may be anhydrous.

Examples of the aliphatic polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, and 3-methyl-1,5-pentane. Examples thereof include diol, 1,6-hexanediol, 1,9-nonanediol, neopentyl glycol, tetramethylene glycol, 1,4-cyclohexanedimethanol and the like.

Examples of the aliphatic hydroxycarboxylic acid other than lactic acid constituting the copolymer include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and 6-hydroxycaproic acid. And so on.

Examples of the polyfunctional polysaccharide include cellulose, cellulose nitrate, methyl cellulose, ethyl cellulose, celluloid, biscoast rayon, regenerated cellulose, cellophane, cupra, cuprammonium rayon, cuprophan, Bemberg, hemicellol, starch, acropectin, and dextrin. Examples include dextran, glycogen, pectin, chitin, chitosan, arabic gum, guar gum, locust bean gum, acacia gum and the like.

The polylactic acid resin in the present embodiment preferably contains a structural portion derived from lactic acid (L-form and D-form) in the molecule in a proportion of 50% by mass or more.
The content of the structural portion (L-form and D-form) is more preferably 60% by mass or more, further preferably 70% by mass or more, and particularly preferably 80% by mass or more.

The polylactic acid resin of the present embodiment exhibits specific characteristic values in the measurement of melt tension at 190 ° C. and the measurement of extensional viscosity at the same temperature.
Specifically, the polylactic acid resin exhibits a melt tension of 5 cN or more and 40 cN or less in the melt tension measurement at 190 ° C.
The melt tension of the polylactic acid resin is preferably 39 cN or less, more preferably 37 cN or less, and particularly preferably 35 cN or less.
The melt tension of the polylactic acid resin is preferably 8 cN or more, and more preferably 10 cN or more.

When the polylactic acid resin of the present embodiment has a melt tension of 5 cN or more, it is possible to suppress foam breakage during foaming.
Further, in the polylactic acid resin of the present embodiment, when the melt tension is 40 cN or less, the bubble film shows good elongation at the time of foaming and foam rupture can be suppressed.
Since the polylactic acid resin of the present embodiment suppresses foam breakage during foaming, the open cell ratio is unlikely to increase even when foamed at a high foaming ratio, and the appearance can be good.

The melting tension at 190 ° C. can be measured as follows using a twin-bore capillary rheometer Rheological 5000T (manufactured by CEAST).
(Measurement method of melt tension)
After vacuum drying at 80 ° C. for 5 hours, each sample is sealed and stored in a desiccator until just before measurement.
A barrel with a diameter of 15 mm heated to a test temperature of 190 ° C. is filled with the measurement sample resin, preheated for 5 minutes, and then the capillary die (diameter 2.095 mm, length 8 mm, inflow angle 90 degrees (conical)) of the above measuring device. While keeping the piston descent speed (0.07730 mm / s) constant and pushing it out in a string shape, the string-like object is passed through a tension detection pulley located 27 cm below the capillary die, and then the take-up roll. The winding speed is gradually increased at an initial speed of 4.0 mm / s and an acceleration of 12 mm / s ² , and the winding is carried out. The melt tension is used.
If there is only one maximum point on the tension chart, that maximum value is taken as the melt tension.

The polylactic acid resin of the present embodiment has an extensional viscosity of 0.5 MPa · s or more at the breaking point in the extensional viscosity measurement at 190 ° C.
The extensional viscosity of the polylactic acid resin is preferably 0.55 MPa · s or more, and more preferably 0.6 or more.
The extensional viscosity of the polylactic acid resin is preferably 1 MPa · s or less, and more preferably 0.9 MPa · s or less.

In the polylactic acid resin of the present embodiment, when the extensional viscosity is measured at 190 ° C., the elongational viscosity increases as the elongational speed increases, and no peak appears in the graph in which the horizontal axis is the extensional velocity and the vertical axis is the extensional viscosity. ..

The extensional viscosity measurement at 190 ° C. can be measured with a Leotens device, and can be measured as follows.
(Measurement of extensional viscosity by Leotens)
The term "measurement of extensional viscosity" as used herein refers to measurement of extensional viscosity using an apparatus capable of measuring extensional viscosity, and is not limited to the following, but is, for example, of Gottfert. Measurements can be made using Rheotens 71.97.
The extensional viscosity is measured by adjusting the optimum conditions for each sample. For example, the extensional viscosity can be measured under the following conditions.
(Example of measurement conditions)
The sample is vacuum dried at 80 ° C. for 5 hours in advance.
Leotens will be installed in Capillograph 1D (manufactured by Toyo Seiki Seisakusho Co., Ltd.).
The leotence is installed so that the distance from the die outlet of the capillograph 1D to the measuring portion is 80 mm.
If the interference cannot be brought close to 80 mm as it is, take measures to avoid the interference and set the rhetence in a predetermined place.
Dice diameter 2.095 mm, length 8 mm, inflow angle 90 degrees (conical)
Piston diameter 9.55mm
Piston speed 20 mm / min
Measurement temperature 190 ° C
Set the measurement conditions of Leotens as follows.
Between wheels 0.2mm above, 1.0mm below
Acceleration 10mm / s ²
Pick-up speed Initial speed 11.281 mm / s
"Graph with extensional speed on the horizontal axis and extensional viscosity on the vertical axis" is a graph of the extensional viscosity obtained from the above measurement results according to the extensional speed (adjusted by the take-up speed).
"No peak appears in the graph with the horizontal axis as the elongation rate and the vertical axis as the extensional viscosity" means that the peak does not appear in the above graph.
In the polylactic acid resin of the present embodiment, when the extensional viscosity is measured, no peak appears in the graph in which the horizontal axis is the elongation rate and the vertical axis is the extensional viscosity.
As a result, the polylactic acid resin of the present embodiment has high tensile strength.

If the measurement sample is in the form of pellets, the elongation viscosity can be measured by the above method without any special pretreatment, but the measurement sample is like a foam sheet and air is left as it is. If it gets in and it is difficult to make an accurate measurement, for example, press the sample with a hot press machine at 190 ° C to degas, make the sample into a film, and then cut the film-like sample. It may be used for measurement.

The polylactic acid resin preferably exhibits appropriate fluidity when melted by heat, and preferably has a melt mass flow rate (MFR) of 0.5 g / 10 min or more.
The MFR of the polylactic acid resin is more preferably 1.0 g / 10 min or more, further preferably 1.5 g / 10 min or more, and particularly preferably 2.0 g / 10 min or more.
The MFR is preferably 20 g / 10 min or less, more preferably 10 g / 10 min or less, and particularly preferably 6.0 g / 10 min or less.

The melt mass flow rate (MFR) of the polylactic acid resin can be measured using, for example, "Semi-automelt indexer 2A" manufactured by Toyo Seiki Seisakusho Co., Ltd.
In MFR, the piston described in JIS K7210-1: 2014 "Plastic-How to obtain melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastics-Part 1" B method moves a predetermined distance. It can be measured by a method of measuring time.
The measurement conditions are as follows in principle.
Sample: 3-8g
The sample for measurement is vacuum-dried at 80 ° C. for 5 hours, and after drying, it is sealed and stored in a desiccator until just before the measurement.
Preheating: 270 seconds Load hold: 30 seconds Test temperature: 190 ° C
Test load: 2.16 kg (21.18N).
Then, the number of test times of the sample is set to 3 times, and the average thereof is taken as the value of melt mass flow rate (g / 10 min).

The above-mentioned thermal melting characteristics can be exhibited by giving the polylactic acid resin a bulky molecular structure.
The polylactic acid resin preferably has a mass average molecular weight (Mw) of 100,000 or more and 1,000,000 or less.
The mass average molecular weight (Mw) of the polylactic acid resin is more preferably 150,000 or more, and further preferably 200,000 or more.
The mass average molecular weight (Mw) of the polylactic acid resin is more preferably 500,000 or less, further preferably 400,000 or less, and particularly preferably 350,000 or less.

As shown in FIGS. 1 and 2, the polylactic acid resin of the present embodiment preferably has a shoulder SL or another peak SP on the high molecular weight side of the maximum peak TP in the molecular weight distribution curve.
That is, the polylactic acid resin of the present embodiment has a component that exerts a shoulder SL or another peak SP on the high molecular weight side of the maximum peak TP (hereinafter, also referred to as “high molecular weight component”) and a component that exhibits the maximum peak TP. (Hereinafter also referred to as "main peak component").
The high molecular weight component is an effective component for demonstrating melt viscoelasticity suitable for foaming by melting with the main peak component when the polylactic acid resin is thermally melted.
In order to exert such an effect, it is preferable that the main peak component and the high molecular weight component have a relationship of having a shoulder SL rather than a separate peak SP.

The polylactic acid resin of the present embodiment preferably has a Z average molecular weight (Mz) of 500,000 or more, more preferably 600,000 or more, and particularly preferably 700,000 or more.
The Z average molecular weight (Mz) of the polylactic acid resin is preferably 1.2 million or less, more preferably 1 million or less, and particularly preferably 900,000 or less.

The polylactic acid resin of the present embodiment preferably has a ratio (Mz / Mw) of Z average molecular weight (Mz) to mass average molecular weight (Mw) of 2.5 or more, and more preferably 2.7 or more. It is particularly preferable that it is 2.9 or more.
The ratio (Mz / Mw) of the polylactic acid resin is preferably 4.0 or less, more preferably 3.5 or less, and particularly preferably 3.0 or less.

The mass average molecular weight (Mw) and Z average molecular weight (Mz) of the polylactic acid resin can be measured by using a gel permeation chromatograph (GPC), and can be obtained as values converted to polystyrene (PS).
Specifically, the average molecular weight of the polylactic acid resin can be obtained by the following procedure.

(How to find the average molecular weight)
Dissolve 20 mg of the sample in 6 mL of chloroform (immersion time: 6 ± 1.0 h), filter with a non-aqueous 0.45 μm syringe filter manufactured by Shimadzu GLC Co., Ltd., and then use a chromatograph under the following measurement conditions. Measure and obtain the mass average molecular weight of the sample from the standard polystyrene calibration curve prepared in advance.

Equipment used = "HLC-8320GPC EcoSEC" manufactured by Tosoh Corporation Gel permeation chromatograph (built-in RI detector / UV detector)
<GPC measurement conditions>
Sample side guard column = TSK guard temperature HXL-H (6.0 mm x 4.0 cm) x 1 made by Tosoh Corporation Measurement column = TSKgel GMHXL (7.8 mm ID x 30 cm) x 2 made by Tosoh Corporation Series reference side = resistance tube (inner diameter 0.1 mm x 2 m) x 2 series column temperature = 40 ° C
Mobile phase = Chloroform Mobile phase Flow reference side pump = 0.5 mL / min
Sample side pump = 1.0 mL / min
Detector = RI detector injection volume = 50 μL
Measurement time = 26min
Sampling pitch = 500msec

The standard polystyrene samples for the calibration curve are the product names "STANDARD SM-105" and "STANDARD SH-75" manufactured by Showa Denko KK, and have mass average molecular weights of 5,620,000, 3,120,000, and 1,250. Those of 000, 442,000, 151,000, 53,500, 17,000, 7,660, 2,900 and 1,320 are used.
The standard polystyrenes for the calibration curve are A (5,620,000, 1,250,000, 151,000, 17,000, 2,900) and B (3,120,000, 442,000, 53,500, After grouping into 7,660, 1,320), A is each dissolved in 30 mL of chloroform after weighing 2 to 10 mg, and B is also dissolved in 30 mL of chloroform after weighing 3 to 10 mg each.
A standard polystyrene calibration curve is obtained by injecting 50 μL of each of the prepared A and B solutions and creating a calibration curve (third-order equation) from the retention time obtained after the measurement, and using the calibration curve to determine the mass average molecular weight. calculate.

The polylactic acid resin having the above-mentioned melting characteristics and molecular weight distribution can be obtained by modifying a commercially available polylactic acid resin.
In the modification, the molecular structure of the polylactic acid resin can have a crosslinked structure or a long-chain branched structure, or the polylactic acid resin can be increased in molecular weight.
A chain extender such as carbodiimide can be used to increase the molecular weight of the polylactic acid resin.
Further, the modification with a chain extender is a functional group capable of having a condensation reaction with a hydroxyl group or a carboxyl group existing in the molecular structure of a polylactic acid resin, such as an acrylic organic compound, an epoxy organic compound, and an isocyanate organic compound. It can be carried out using a compound having one or more of.
That is, the modification can be carried out by a method of binding an acrylic organic compound, an epoxy organic compound, an isocyanate organic compound or the like to a polylactic acid resin by a reaction.
Modification of the polylactic acid resin by cross-linking or long-chain branching can be performed, for example, by a method of reacting the polylactic acid resins with each other using a radical initiator.

Among the above-mentioned modification methods, it is preferable to react the polylactic acid resins with a radical initiator in that the foamed sheet can be prevented from containing other components.
When polylactic acid resins are reacted with each other using a radical initiator having an appropriate reactivity, the decomposition starting point of the polylactic acid resin in the extruder is attacked by the free radicals generated by the radical initiator, and the location is concerned. Can be stabilized as a radical (branch point).
By making such a modification, the polylactic acid resin has increased thermal stability and is less likely to have a low molecular weight when passing through an extruder.

Examples of the radical initiator used for modifying the polylactic acid resin include organic peroxides, azo compounds, halogen molecules and the like.
Of these, organic peroxides are preferred.
Examples of the organic peroxide used in the present embodiment include peroxyesters, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, peroxyketals, and ketone peroxides. ..

Examples of the peroxyester include t-butylperoxy2-ethylhexyl carbonate, t-hexylperoxyisopropylmonocarbonate, t-hexylperoxybenzoate, t-butylperoxybenzoate, and t-butylperoxylaurate. t-Butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxyacetate, 2,5-dimethyl2,5-di (benzoylperoxy) hexane, and t-butylperoxyisopropylmono Examples include carbonate.

Examples of the hydroperoxide include permethane hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide and the like.

Examples of the dialkyl peroxide include dicumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di (t-butylperoxy) -hexyne-3. ..

Examples of the diacyl peroxide include dibenzoyl perxide, di (4-methylbenzoyl) peroxide, and di (3-methylbenzoyl) peroxide.

Examples of the peroxydicarbonate include di (2-ethylhexyl) peroxydicarbonate and diisopropyl peroxydicarbonate.

Examples of the peroxyketal include 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 1,1-di-t-butylperoxycyclohexane, and 2,2-di (t). -Butylperoxy) -butane, n-butyl 4,4-di- (t-butylperoxy) valerate, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, etc. Can be mentioned.

Examples of the ketone peroxide include methyl ethyl ketone peroxide and acetylacetone peroxide.

In the modification with the organic peroxide, a component having an excessive molecular weight such as a gel at the time of heat melting is mixed in the modified polylactic acid resin, and a problem of odor due to the decomposition residue of the organic peroxide occurs. There is a risk of causing it.
The organic peroxide is preferably a peroxy ester in that the possibility of causing such a problem can be suppressed and the polylactic acid resin can be easily modified into a state suitable for foaming.
Among the peroxy esters, the organic peroxide used for modifying the polylactic acid resin is preferably a peroxycarbonate-based organic peroxide such as peroxymonocarbonate or peroxydicarbonate.
The organic peroxide used for modifying the polylactic acid resin in the present embodiment is preferably a peroxymonocarbonate-based organic peroxide among the peroxycarbonate-based organic peroxides, and t-butylperoxyisopropyl. It is particularly preferable that it is a monocarbonate.

The above-mentioned organic peroxide is usually used in a ratio of 0.1 part by mass or more with respect to 100 parts by mass of the polylactic acid resin to be modified, although it depends on its molecular weight and the like.
The amount of the organic peroxide used is preferably 0.2 parts by mass or more, and particularly preferably 0.3 parts by mass or more.
The amount of the organic peroxide used is preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, and particularly preferably 1.0 part by mass or less.
By modifying the polylactic acid resin with an organic peroxide at such a ratio, the modified polylactic acid resin can be made suitable for foaming.

When the amount of the organic peroxide as described above is 0.1 parts by mass or more, the effect of the modification on the polylactic acid resin can be more reliably exhibited.
Further, when the amount of the organic peroxide used is 2.0 parts by mass or less, it is possible to suppress the mixing of the gel with the modified polylactic acid resin.

Examples of the component for foaming used when the polylactic acid resin as described above is used as a foaming sheet include a foaming agent and a bubble adjusting agent.

As the foaming agent, a general one can be adopted, a volatile foaming agent that becomes a gas at normal temperature (23 ° C.) and normal pressure (1 atm), and a decomposition type foaming agent that generates a gas by thermal decomposition. Can be adopted.
As the volatile foaming agent, for example, an inert gas, an aliphatic hydrocarbon, an alicyclic hydrocarbon, or the like can be adopted.

Examples of the inert gas include carbon dioxide and nitrogen.

Examples of the aliphatic hydrocarbon include propane, normal butane, isobutane, normal pentane, and isopentane, and examples of the alicyclic hydrocarbon include cyclopentane and cyclohexane.
Among the above, normal butane and isobutane may be particularly preferably used in the present embodiment.

Examples of the decomposition foaming agent include organic acids such as azodicarbonamide, dinitrosopentamethylenetetramine, sodium bicarbonate or citric acid, or a mixture thereof and a bicarbonate.

Examples of the bubble adjusting agent include polytetrafluoroethylene, talc, aluminum hydroxide, silica and the like.
The decomposing foaming agent can be used in combination with a volatile foaming agent to adjust the foaming state, and can also be used as a bubble adjusting agent.

The foamed sheet of the present embodiment is an extruded foamed sheet as described above.
Therefore, the foamed sheet of the present embodiment is usually obtained by extruding and foaming a resin composition containing the polylactic acid resin, the foaming agent, and the bubble adjusting agent (hereinafter, also referred to as “polylactic acid resin composition”). It is formed.

Various additives can be added to the polylactic acid resin composition, if necessary.
Examples of the additive include resins other than polylactic acid resin, inorganic fillers, and various chemicals.
Examples of the agent include lubricants, antioxidants, antistatic agents, flame retardants, ultraviolet absorbers, light stabilizers, colorants, antibacterial agents and the like.
The ratio of these additives is preferably 25 parts by mass or less, and more preferably 15 parts by mass or less with respect to 100 parts by mass of the polylactic acid resin.

The foamed sheet in the present embodiment has a step of modifying the polylactic acid resin using a twin-screw extruder (modification step) and a polylactic acid resin composition containing the modified polylactic acid resin at the tip of a circular die. It can be produced by carrying out a step of extruding and foaming through an extruder mounted on the above (extrusion foaming step).

In the reforming step, for example, the modified polylactic acid resin may be pelletized immediately after using a twin-screw extruder equipped with a granulation die (hot cut die).
Strand dies and T-dies are attached to the twin-screw extruder used in the reforming step, and in the reforming step, strands and sheets made of the modified polylactic acid resin are produced, and then the strands and sheets are cut. The step of granulating may be carried out separately.
If necessary, a tandem extruder may be used to carry out the extrusion foaming step in succession to the reforming step.
For example, the extrusion foaming step in this embodiment can be carried out using an apparatus as shown in FIG.

The apparatus illustrated in FIG. 3 includes a tandem extruder 10 and a circular die CD that discharges the polylactic acid resin composition melt-kneaded in the tandem extruder 10 into a cylindrical shape.
Further, this manufacturing apparatus includes a cooling device CL for air-cooling a foam sheet discharged in a tubular shape from a circular die CD, and a cylinder for expanding the diameter of the tubular foam sheet into a tubular shape having a predetermined size. A mandrel MD, a slit device that slits a foam sheet after passing through the mandrel MD and divides it into two sheets, and a winding roller for winding the slit foam sheet 1 after passing through a plurality of rollers 21. 22 is provided.
In the extruder on the upstream side of the tandem extruder 10 (hereinafter, also referred to as "first extruder 10a"), a hopper 11 for charging a polylactic acid resin which is a raw material of a foam sheet and a foaming agent such as a hydrocarbon are used. A gas introduction unit 12 is provided to supply the gas into the cylinder.
An extruder for melt-kneading the polylactic acid resin composition containing a foaming agent (hereinafter, also referred to as “second extruder 10b”) is provided on the downstream side of the first side extruder 10a.
When the extrusion foaming step is carried out by such an apparatus, the polylactic acid resin is modified by the first extruder 10a and foamed at the end portion of the first extruder 10a or the base end portion of the second extruder 10b. An agent or the like may be mixed to prepare a polylactic acid resin composition as a raw material for a foaming sheet, and extrusion foaming may be performed from the circular die CD.

Since the foamed sheet of the present embodiment exhibits the above-mentioned characteristics at the time of heat melting, it has excellent strength.
In the extrusion foaming step, microbubbles due to the foaming agent are generated in the melt-kneaded product immediately before being discharged from the circular die CD, and the microbubbles are generated at the moment when the melt-kneaded product is discharged from the circular die CD and the pressure is released. Will expand at once and new bubbles will be generated by the foaming agent dissolved in the melt-kneaded product.
Then, the extruded foam sheet is stretched in the circumferential direction by expanding the diameter in the mandrel MD, and is also stretched in the extrusion direction by winding in the winding roller 22.

In the extrusion foaming step as described above, the polylactic acid resin of the present embodiment does not stretch in an easy form, and the bubble film is unlikely to become excessively thin.
That is, in the foamed sheet of the present embodiment, when the bubble film containing the polylactic acid resin as described above is stretched by the foaming force of the foaming agent, it exhibits a certain level of resistance or more.
Further, in the foamed sheet of the present embodiment, the central portion of the bubble membrane is thin and the peripheral portion is likely to be thick.
Therefore, the foamed sheet of the present embodiment exhibits excellent mechanical properties when the thick bubble film is three-dimensionally connected over the entire sheet.
In the foamed sheet of the present embodiment, even when bubbles are broken during foaming and a hole is opened in the bubble film, the bubble film surrounding the hole does not remain as it is, but shrinks and has strength. Since the thickness is increased in a form effective for exertion, excellent strength can be exerted even if open cells are present at a certain ratio.

The foamed sheet of the present embodiment preferably has an open cell ratio of 10% or more in consideration of the above-mentioned biodegradability.
The open cell ratio of the foam sheet is more preferably 15% or more.
The open cell ratio of the foamed sheet is preferably 50% or less, more preferably 40% or less, and particularly preferably 30% or less in order to make the foamed sheet exhibit excellent strength.

The foaming ratio of the foamed sheet is preferably 3 times or more, more preferably 4 times or more, and particularly preferably 5 times or more in order to exhibit excellent lightness.
The foaming ratio of the foamed sheet is preferably 15 times or less, more preferably 12 times or less, and particularly preferably 10 times or less in order to exhibit excellent strength.

The open cell ratio of the foam sheet can be measured by the method shown below.
(Continuous bubble rate)
Multiple sheet-shaped samples with a length of 25 mm and a width of 25 mm are cut out from the foam sheet, and the cut samples are stacked so as not to leave a gap to form a measurement sample with a thickness of 25 mm. ) Measure to 1/100 mm using Mitutoyo's "Digimatic Caliper" to obtain the ^{apparent volume (cm 3).
Next, the volume (cm 3} ) of the measurement sample is determined by the 1-1 / 2-1 atm method using an air comparative hydrometer type 1000 (manufactured by Tokyo Science Co., Ltd.).
The open cell ratio (%) is calculated from these obtained values and the following formula, and the average value of 5 tests is obtained.
The measurement is performed under the environment of JIS K7100-1999 symbol 23/50, class 2 after adjusting the state of the measurement sample for 16 hours under the environment of JIS K7100-1999 symbol 23/50, class 2.
Further, the air comparative hydrometer corrects with a standard sphere (large 28.9 cc, small 8.5 cc).

Open cell ratio (%) = 100 x (apparent volume-measured volume with an air comparative hydrometer) / apparent volume

For the foaming ratio of the foamed sheet, the apparent density (ρ1) of the foamed sheet is obtained, the density (true density: ρ0) of the polylactic acid resin composition constituting the foamed sheet is obtained, and the true density (ρ0) is the apparent density. It can be obtained by dividing by the density (ρ1).
That is, the foaming ratio can be obtained by calculating the following formula.

Foaming magnification = true density (ρ0) / apparent density (ρ1)

The density of the foamed sheet can be determined by the method described in JIS K7222: 1999 "Measurement of foamed plastic and rubber-apparent density", and specifically, it can be measured by the following method.

(Density measurement method)
From the foam sheet, ^{a sample of 100 cm 3} or more is cut so as not to change the original cell structure, and this sample is adjusted to the state of JIS K7100: 1999 symbol 23/50 for 16 hours in a second grade environment, and then its dimensions, The mass is measured and the density is calculated by the following formula.

Apparent density (g / cm ³ ) = sample mass (g) / sample volume (cm ³ )

For sample size measurement, for example, "DIGIMATIC" CD-15 type manufactured by Mitutoyo Co., Ltd. can be used.

The density of the polylactic acid resin composition is determined by the Archimedes method (JIS K8807: 2012 "Measuring method of solid density and specific gravity" for a sample that has been made into a non-foamed material by hot-pressing a foamed sheet or the like. ) Can be performed and obtained.

The foamed sheet of the present embodiment preferably has a predetermined strength in a foamed state having a foaming ratio of, for example, about 3 to 8 times.
Specifically, the foamed sheet preferably has a tensile strength of 5.5 MPa or more, preferably 6 MPa or more, when a tensile test is performed on a sample collected so that the longitudinal direction is the extrusion direction. It is more preferable, and it is particularly preferable that it is 6.5 MPa or more.
The upper limit of the tensile strength of the foamed sheet does not need to be set in particular, but the tensile strength of the foamed sheet is usually 25 MPa or less.

The tensile strength of the foamed sheet can be measured based on JIS K6767: 1999 "Foam Plastic-Polyethylene-Test Method".
That is, using the "Tencilon UCT-10T" universal tester manufactured by Orientech Co., Ltd. and the "UTPS-458X" universal tester universal tester manufactured by Softbrain Co., Ltd., the tensile speed is 500 mm / min, and the grip interval is 100 mm. The test piece is a dumbbell type 1 (ISO1798 regulation), the thickness is 1.0 to 1.5 mm, and the tensile strength is measured.
However, the elongation is calculated from the distance between the grips before the test and at the time of cutting.
The number of test pieces is 5, and the test pieces are adjusted for 16 hours under the JIS K 7100: 1999 symbol "23/50" (temperature 23 ° C., relative humidity 50%) and a second-class standard atmosphere. , Make measurements under the same standard atmosphere.
The tensile strength is calculated by the following formula.

T = F / (W x t)

T: Tensile strength (MPa)
F: Maximum load up to cutting (N)
W: Width of test piece (mm)
t: Thickness of test piece (mm)

In the foamed sheet of the present embodiment, the polylactic acid resin exhibits the molecular weight distribution as described above, so that microprojections and bubbles called "butsu" or the like due to components having different behaviors at the time of thermal melting such as gel. It is possible to suppress the occurrence of tearing of the membrane.

The foamed sheet of the present embodiment preferably has an extensional viscosity of 0.05 MPa · s or more at the breaking point in the extensional viscosity measurement at 190 ° C.
The extensional viscosity of the foamed sheet is preferably 0.08 MPa · s or more, and more preferably 0.1 MPa · s or more.
The extensional viscosity of the foamed sheet is preferably 0.2 MPa · s or less, and more preferably 0.15 MPa · s or less.
The extensional viscosity of the foamed sheet can be measured by a leotence device in the same manner as the extensional viscosity of the polylactic acid resin.

In the foam sheet of the present embodiment, it is advantageous that the thickness of the resin film (bubble film) surrounding the individual bubbles is thick to some extent in order to exhibit excellent strength.
In general, foam sheets have finer bubbles if the mass per unit area is the same (same basis weight), and having many closed cells with a thin bubble film has better strength against compression in the thickness direction. Can be demonstrated.
On the other hand, it is advantageous to have a thick bubble film in order to make the foamed sheet exhibit excellent tensile strength.

Specifically, the foamed sheet of the present embodiment preferably has an average cell thickness of 5 μm or more and 50 μm or less, and more preferably 30 μm or more and 50 μm or less.
The average bubble film thickness can be measured based on an image taken with a scanning electron microscope (SEM) of a cross section that appears when the foamed sheet is cut in the thickness direction.
In this regard, to explain with reference to FIG. 4, which schematically shows the state of the cross section of the foam sheet, a straight line L1 passing through the central portion in the thickness direction of the foam sheet is drawn with respect to the image taken by the SEM. The thickness (t1, t2, ... Tn) of the bubble membrane MB is measured at the point where the straight line L1 passes, and the arithmetic mean value is calculated based on the measured thickness of each bubble membrane MB. The obtained arithmetic mean value can be used as the average bubble thickness.
In order to accurately calculate the arithmetic mean value, it is preferable to obtain the thickness of the bubble membrane MB at 10 or more points.

The foamed sheet of the present embodiment can be used as a raw material for various sheet molded products.
Foam sheets are given a three-dimensional shape by thermoforming such as vacuum forming, pneumatic forming, vacuum / pneumatic forming, press molding, match molding, etc., and foam molded products such as containers (for example, trays, bowls, cups, etc.) ).
Further, the foam sheet can be used as a material for forming a foam molded product such as a folded box while keeping the flat plate shape.
That is, as shown in FIG. 5, the foam sheet can be used as a forming material for the bottom plate 101, the side wall frame 102, the lid plate 103, and the like of the folding box 100.

In the present embodiment, a sheet outside the product (a foamed sheet in a portion that has not been extruded into a product by the time the foamed sheet is extruded to a set foamed state) generated when the foamed sheet is manufactured, or as described above. It is desirable to repellet the offcuts generated during the production of molded products and reuse them as recycled materials.
Therefore, in the polylactic acid resin used as the raw material of the foam sheet in the present embodiment, the MFR (190 ° C., 2.16 kg) measured in the initial state is set to "MFR ₀ (g / 10 min)" and melted once at 190 ° C. The MFR measured after kneading is referred to as "MFR ₁ (g / 10min)", and the MFR measured after being melt-kneaded again at 190 ° C. after this melt-kneading is referred to as "MFR ₂ (g / 10min)". , And when the MFR measured after melt-kneading at 190 ° C. at 3 degrees is "MFR ₃ (g / 10 min)", the value of "MFR primary change rate" represented by the following formula (A1). Is preferably 25% or less.
Further, the polylactic acid resin of the present embodiment preferably has a value of "MFR secondary change rate" represented by the following formula (A2) of 40% or less.
Further, the polylactic acid resin of the present embodiment preferably has a value of "MFR tertiary change rate" represented by the following formula (A3) of 55% or less.

MFR primary rate of change = (MFR _{1 − MFR 0} ) / MFR ₀ × 100 [%] ... (A1)
MFR secondary rate of change = (MFR _{2 -MFR 0} ) / MFR ₀ × 100 [%] ... (A2)
MFR tertiary rate of change = (MFR _{3 -MFR 0} ) / MFR ₀ × 100 [%] ... (A3)

The MFR primary change rate is more preferably 20% or less, and further preferably 15% or less.
The MFR secondary rate of change is more preferably 35% or less, and even more preferably 30% or less.
The MFR tertiary change rate is more preferably 52% or less, further preferably 50% or less.

The polylactic acid resin used as a raw material for the foam sheet in the present embodiment has a melt tension (at 190 ° C.) measured in the initial state as "MT ₀ (cN)" and is measured after being melt-kneaded once at 190 ° C. The melt tension is _{defined as "MT 1} (cN)", the melt tension measured after the melt-kneading and then melt-kneading again at 190 ° C. is "MT ₂ (cN)", and the melt is melted at 190 ° C. at 3 degrees. When the melt tension measured after kneading is "MT ₃ (cN)", the value of the "primary change rate of melt tension" represented by the following formula (B1) is preferably 60% or less. ..
Further, in the polylactic acid resin of the present embodiment, the value of the "secondary change rate of melt tension" represented by the following formula (B2) is preferably 70% or less.
Further, the polylactic acid resin of the present embodiment preferably has a value of "third-order change rate of melt tension" represented by the following formula (B3) of 80% or less.

Primary change rate of melt tension = (MT ₀ − _{MT 1} ) / MT ₀ × 100 [%] ・ ・ ・ (B1)
Melt tension secondary change rate = (MT ₀ − _{MT 2} ) / MT ₀ × 100 [%] ・ ・ ・ (B2)
Melt tension tertiary change rate = (MT ₀ − _{MT 3} ) / MT ₀ × 100 [%] ... (B3)

The primary change rate of the melt tension is more preferably 55% or less, further preferably 50% or less.
The rate of secondary change in melt tension is more preferably 65% or less, and even more preferably 55% or less.
The rate of tertiary change in melt tension is more preferably 75% or less, and even more preferably 70% or less.

The lower limit of each of the MFR primary change rate, the MFR secondary change rate, and the MFR tertiary change rate is usually 0%.
Further, the lower limit of each of the primary change rate of the melt tension, the secondary change rate of the melt tension, and the tertiary change rate of the melt tension is usually 0%.

The polylactic acid resin of the present embodiment has a primary change rate of melt tension of 60% or less, so that the use of recycled materials can be expanded.
Further, when the secondary change rate of the melt tension and the tertiary change rate of the melt tension are in the above ranges, the polylactic acid resin of the present embodiment can further expand the use of the recycled material.
That is, since the polylactic acid resin of the present embodiment has little change in characteristics due to heat history, there is little possibility that its characteristics will be significantly deteriorated even if it is added to a virgin material (commercially available pellets before modification).
Further, even if a recycled material is used as a part of the raw material for producing the foamed sheet, a high-quality foamed sheet can be produced without significantly changing the extrusion conditions and the like.
Therefore, the polylactic acid resin and the foamed sheet of the present embodiment can enable the production of more environmentally friendly products.

The above-mentioned "state after" melt-kneading "at 190 ° C." means, in principle, a state after extrusion by a twin-screw extruder.
More specifically, using a twin-screw extruder (L / D = 42) with a diameter of 30 mm, the temperature of the twin-screw extruder is set to 160 ° C. and 200 ° C. in order from the upstream side to the downstream side in the extrusion direction. Subsequent temperatures were set to 190 ° C., melt-kneaded in a twin-screw extruder under the condition of a rotation speed of 140 rpm, and 10 kg / h from a die with a diameter of 3 mm and two holes attached to the tip of the extruder. In terms of the discharge amount, the state after passing through this "two-screw extruder" is defined in the present specification as "the state after" melt-kneading "at 190 ° C.".
For the measurement of MFR and melt tension, polylactic acid resin was supplied to the "biaxial extruder" set as described above and extruded into a strand shape, and the strand-shaped sample was filled with water at 20 ° C. It can be obtained by passing it through a 1.5 m water tank, cooling it, and cutting the cooled sample to prepare pellets.
More specifically, by measuring the MFR and melt tension of the pellets, it is possible to measure the values of the MFR and melt tension of the polylactic acid resin after being melt-kneaded at 190 ° C.

In the foamed sheet of the present embodiment, since the polylactic acid resin used exhibits the above-mentioned thermal stability, a part of the polylactic acid resin used as a raw material may be used as a recycled material.
That is, the raw material of the foamed sheet may contain a polylactic acid resin composition that has passed through the extruder once or more.
The recycled material containing at least one of a polylactic acid resin foam sheet, a foam molded product obtained by thermally molding a polylactic acid resin foam sheet, and scraps produced during the production of the foam molded product is a foam sheet. In order to make the product environmentally friendly, it is preferable to include it in the foamed sheet so that the mass ratio of the total polylactic acid resin contained in the raw material of the foamed sheet is 1% or more, and it is preferably 5% or more. It is more preferable to include it in a foam sheet.
However, in order to improve the physical characteristics of the foamed sheet, the recycled material is preferably contained in the foamed sheet so that the mass ratio is 25% or less, and is contained in the foamed sheet so as to be 20% or less. It is more preferable to let it.
The recycled material may be used as a raw material for a foamed sheet as it is, or may be modified with t-butylperoxyisopropyl monocarbonate or the like and then used as a raw material for a foamed sheet.
When reforming the recycled material, it is preferable to mix the recycled material and the virgin material, supply the recycled material to a melt-kneading device such as a twin-screw extruder, and reform the recycled material together with the virgin material in the melt-kneading device.
If a part of the polylactic acid resin to be reformed is used as a recycled material in the reforming step, there is an advantage that it becomes easy to impart the above-mentioned heat melting characteristics to the modified polylactic acid resin.

In the present embodiment, the extruded foam sheet is exemplified as an example of the polylactic acid resin foam, but the specific embodiment of the polylactic acid resin foam of the present invention is limited to the extruded foam sheet. It's not something.
The polylactic acid resin foam of the present invention may be an injection molded product, a bead foam molded product, or the like.
That is, the present invention is not limited to the above examples.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

<First evaluation study>
(Test Example 1-1)
(1) Preparation of Modified Polylactic Acid Resin Polylactic Acid Resin (“Biopolymer Ingeo 8052D” manufactured by Nature Works, MFR = 7.4 g / 10 min, Density = 1.24 g / cm ³ ) 100 parts by mass and t- 0.5 parts by mass of butylperoxyisopropyl monocarbonate (“Kayacarboxylic BIC-75” manufactured by Kayaku Akzo Corporation, 1-minute half-life temperature T1: 158.8 ° C.) and 0.5 parts by mass are stirred and mixed with a ribbon blender to obtain a mixture. rice field.
The obtained mixture was supplied to a twin-screw extruder (L / D = 31.5) having a diameter of 57 mm.
The set temperature of the feed section is set to 170 ° C, the temperature thereafter is set to 230 ° C, the mixture is melt-kneaded in a twin-screw extruder under the condition of a rotation speed of 150 rpm, and the diameter is 3 mm attached to the tip of the extruder. The kneaded product was extruded into a strand shape from a die having 18 holes at a discharge rate of 50 kg / h.
Then, the extruded strand-shaped kneaded product was passed through a cooling water tank having a length of 2 m and containing water at 30 ° C. to be cooled.
The cooled strands were cut with a pelletizer to give pellets of modified polylactic acid resin.

(Test Examples 1-2-1-7)
Regarding Test Examples 1-2 to 1-7, the same as Test Example 1-1 except that the type of polylactic acid resin and the amount of organic peroxide added (the amount added to 100 parts by mass of polylactic acid resin (phr)) were changed. A modified polylactic acid resin was prepared by the same method.

(Test Examples 2-1 to 2-4)
Test Examples 2-1 to 2-4 are the same as those of Test Examples 1-1 to 1-7 except that they are modified with an organic peroxide different from that of t-butylperoxyisopropyl monocarbonate. A polylactic acid resin modified by the method was prepared.
In some cases, the modification is performed with a chain extender instead of an organic peroxide.

Types of polylactic acid resin and organic peroxide used in Test Examples 1-1 to 1-7 and Test Examples 2-1 to 2-4, and addition of organic peroxide to 100 parts by mass of polylactic acid resin. The amounts (phr) are shown in Tables 1 to 3.

(2) Preparation of foam 100 parts by mass of the polylactic acid resin obtained in Test Example 1-1 and 1.0 part by mass of a bubble adjusting agent (“Crown Talc” manufactured by Matsumura Sangyo Co., Ltd.) are dry-blended. , A mixture was prepared.
In a tandem extruder equipped with a first extruder (upstream side) having a diameter of φ50 mm and a second extruder (downstream side) having a diameter of φ65 mm, the obtained mixture is supplied to the first extruder having a diameter of φ50 mm through a hopper. , Heated and melted.
Then, butane (isobutane / normal butane = 70/30) was press-fitted into the first extruder as a foaming agent and melt-mixed together with the mixture.
Next, the melt mixture is transferred to a second extruder having a diameter of 65 mm, cooled uniformly to a temperature suitable for extrusion foaming, and then extruded and foamed from a circular die having a diameter of 70 mm at a discharge rate of 30 kg / h to form a cylindrical shape. A foam was obtained.
The obtained cylindrical foam is placed along a mandrel of φ206 mm whose inside is cooled with water at about 20 ° C., and its outer surface is cooled and molded by blowing air with an air ring larger than its diameter to form a circle. An incision was made with a cutter at one point on the circumference to obtain a strip-shaped foam sheet.

For Test Examples 1-2-1-7 and Test Examples 2-1 to 2-4, foam sheets were prepared in the same manner as described above.
However, in Test Examples 2-2 and 2-3, a foamed sheet could not be obtained because the melt tension of the resin was not sufficient and a stable sheet could not be taken.

For the polylactic acid resin modified in Test Examples 1-1 to 1-7 and Test Examples 2-1 to 2-4, the mass average molecular weight (Mw), the Z average molecular weight (Mz), and the ratio thereof. (Mz / Mw) was calculated.
Further, in the molecular weight distribution curve of these modified polylactic acid resins, it was confirmed whether the shoulder SL or another peak SP was present on the high molecular weight side of the maximum peak TP.
Further, the MFR (190 ° C., 2.16 kg) and the melt tension (at 190 ° C.) of the modified polylactic acid resin were measured.
Then, the apparent density and the open cell ratio of the produced foamed sheet were measured.
Further, the appearance of the foamed sheet was visually observed and judged according to the following criteria.

(Appearance of foam)
○: The foaming is uniform and the appearance is beautiful.
Δ: Foaming is uniform, but some bumps are seen on the sheet surface.
X: Bubbles are non-uniform and remarkable bubble rupture is observed. Or, a lot of bumps can be seen on the surface of the sheet.

The above evaluation results are shown in Table 4.

In Test Example 2-4 described above, it is considered that the cause is the decomposition residue of the organic peroxide (acetophenone, cumyl alcohol, etc.) when the polylactic acid resin is modified or the foamed sheet is extruded and foamed. I felt an odor.

From the above, it can be seen that by using t-butylperoxyisopropyl monocarbonate, it is possible to suppress the occurrence of odor problems when the polylactic acid resin is modified to a state suitable for foaming.

<Second evaluation study>
(Test Example 3-1)
Similar to Test Examples 1-4 in the first evaluation study, the ratio of polylactic acid resin (trade name “Biopolymer Ingeo 4032D”) manufactured by Nature Works and t-butylperoxyisopropyl monocarbonate to 100: 0.5. The modified polylactic acid resin used in the above was prepared.

The extensional viscosity (at 190 ° C.) of this modified polylactic acid resin was measured.
As a result, in the extensional viscosity measurement, it was found that the extensional viscosity increased as the elongational rate increased, and the graph with the extensional velocity on the horizontal axis and the extensional viscosity on the vertical axis did not show an upwardly convex peak. rice field.

Further, using the polylactic acid resin modified in Test Example 3-1 to prepare a foamed sheet in the same manner as in the "first evaluation study", the thickness, basis weight, foaming ratio, and open cells of the foamed sheet were prepared. I asked for the rate.
Further, a dumbbell-shaped test piece was collected from the foamed sheet so that the longitudinal direction was the extrusion direction, and the tensile strength was measured by the dumbbell-shaped test piece.

( Comparative Test Example 4-1)
A polylactic acid resin (trade name "Teramac HV-6250H", MFR: 1 to 3 g / 10 min, tensile strength: 69 MPa (manufacturer's published value)) commercially available from Unitika Ltd. for foaming was prepared (without modification). ).

Similar to Test Example 3-1 the polylactic acid resin of Comparative Test Example 4-1 was also investigated for its thermal melting characteristics using a rhetorence apparatus.
In the polylactic acid resin of Comparative Test Example 4-1, a peak was observed when the results of the extensional viscosity measurement were represented by a graph in which the horizontal axis was the elongation rate and the vertical axis was the extensional viscosity.
A foamed sheet was also prepared for the polylactic acid resin of Comparative Test Example 4-1 and evaluated in the same manner as in Test Example 3-1.
The results are shown in Table 5 below.

From the above results, it is a polylactic acid resin whose extensional viscosity at the break point is 0.5 MPa · s or more in the extensional viscosity measurement at 190 ° C. Moreover, in the extensional viscosity measurement, the extensional viscosity increases with the increase in the extensional viscosity. It can be seen that excellent strength is exhibited in the polylactic acid resin foam by using the polylactic acid resin in which the peak does not appear in the graph in which the horizontal axis is the elongation rate and the vertical axis is the extensional viscosity.

Images (SEM photographs) of the cross sections of the foam sheets of Test Example 3-1 and Comparative Test Example 4-1 taken with a scanning electron microscope (SEM) are shown in FIGS. 6 (Test Example 3-1) and FIG. 7, respectively. ( Comparative test example 4-1) is shown.
The photographs were taken of a cross section when cut along the extrusion direction (MD) and a cross section when cut along the direction orthogonal to the extrusion direction (TD).
From this photograph, it can be seen that in Test Example 3-1 a foamed sheet having a thick bubble film and advantageous for exhibiting high tensile strength was obtained.

<Third evaluation study>
(Test Example 5-1)
100 parts by mass of polylactic acid resin (“Biopolymer Ingeo 4032D” manufactured by Nature Works, MFR = 4.4 g / 10 min, density = 1.24 g / cm ³ ) and t-butylperoxyisopropyl monocarbonate (manufactured by Kayaku Akzo). "Kayacarboxylic BIC-75", 1 minute half-life temperature T1: 158.8 ° C.) 0.5 parts by mass was stirred and mixed with a ribbon blender to obtain a mixture.
The obtained mixture was supplied to a twin-screw extruder (L / D = 42) having a diameter of 30 mm.
The temperature of the twin-screw extruder is set to 160 ° C. for the feed section and 220 ° C. after that, and the mixture is melt-kneaded in the twin-screw extruder under the condition of a rotation speed of 180 rpm. The kneaded product was extruded into a strand shape at a discharge rate of 10 kg / h from a die having a diameter of 3 mm and two holes attached to the tip of the extruder.
Then, the extruded strand-shaped kneaded product was passed through a 1.5 m long cooling water tank containing water at 20 ° C. and cooled.
The cooled strands were cut with a pelletizer to give pellets of modified polylactic acid resin.

The MFR (190 ° C., 2.16 kg) and the melt tension (at 190 ° C.) of the modified polylactic acid resin obtained in Test Example 5-1 were measured.
Then, the modified polylactic acid resin obtained in Test Example 5-1 was subjected to melt kneading at 190 ° C. three times in total, and the MFR and the melt tension were measured each time to change the MFR primary change. The rate, the MFR secondary change rate, the MFR tertiary change rate, the melt tension primary change rate, the melt tension secondary change rate, and the melt tension tertiary change rate were measured.

(Test Examples 5-2, 5-3)
Test Example 5 except that the ratios of the polylactic acid resin and t-butylperoxyisopropyl monocarbonate were 100: 0.3 (Test Example 5-2) and 100: 0.7 (Test Example 5-3), respectively. The same evaluation as -1 was carried out.

(Test Example 6-1)
A polylactic acid resin manufactured by Nature Works (trade name “Biopolymer Ingeo 8052D”) was evaluated in the same manner as in Test Examples 5-1 to 5-3 without modification.

(Test Example 6-2)
The same evaluation as in Test Examples 5-1 to 5-3 was carried out on the polylactic acid resin (trade name "Teramac HV-6250H") commercially available from Unitika Ltd. without modification.
These results are shown in Table 6 below.

From the above results, it can be seen that a polylactic acid resin having excellent thermal stability can be obtained by subjecting a specific modification.

Claims (3)

A method for producing an extruded foamed sheet, wherein a polylactic acid resin composition containing a polylactic acid resin is supplied to an extruder, and the extruded foamed sheet is produced by the extruder .
The polylactic acid resin contained in the polylactic acid resin composition has an extensional viscosity of 0.5 MPa · s or more and 1 MPa · s or less at the break point in the extensional viscosity measurement at 190 ° C., and in the extensional viscosity measurement, the extensional viscosity is measured. It is a polylactic acid resin in which the extensional viscosity increases as the elongational rate increases, and no peak appears in the graph with the horizontal axis as the extensional velocity and the vertical axis as the extensional viscosity.
The extruded foam sheet to be manufactured is a method for manufacturing an extruded foam sheet, which is an extruded foam sheet having an extensional viscosity at a break point of 0.05 MPa · s or more and 0.2 MPa · s or less in an extensional viscosity measurement at 190 ° C. An extruded foamed sheet composed of a polylactic acid resin composition containing a polylactic acid resin.
The polylactic acid resin contained in the polylactic acid resin composition has an extensional viscosity of 0.5 MPa · s or more and 1 MPa · s or less at the break point in the extensional viscosity measurement at 190 ° C., and in the extensional viscosity measurement. , The extensional viscosity increases as the extensional velocity increases, and the horizontal axis is the extensional velocity and the vertical axis is the extensional viscosity.
The extruded foam sheet, in the measurement of extensional viscosity elongational viscosity below 0.05 MPa · s or more 0.2 MPa · s at break of 190 ° C., and a tensile strength in the extrusion direction is greater than or equal to 6 MPa, extrusion Foam sheet . The extruded foam sheet according to claim 2, wherein the open cell ratio is 10% or more .

Images