JP2019183140A - Method for producing modified polylactic resin - Google Patents

Abstract

To prevent the problem of an odor from occurring in modifying a polylactic resin to improve molten tension.SOLUTION: In this invention, t-butyl peroxy isopropyl monocarbonate is used to modify a polylactic resin.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a modified polylactic acid resin.

Conventionally, polyester resin foams are lightweight and excellent in cushioning properties, and because they are easy to be molded into various shapes, they are used as raw materials for various molded products including packaging materials.
In recent years, countermeasures against the problem that the landscape is damaged by illegally dumped packaging materials in places such as mountains, rivers, or coasts have been required.
With such a background, it has been studied to produce a molded product using a polylactic acid resin that can be biodegraded in a natural environment, and the development of a polylactic acid resin foam for various uses is being studied. (See Patent Document 1 below).

Japanese Patent Laying-Open No. 2015-218327

For the formation of the polylactic acid resin foam as described above, a resin having a somewhat high melt tension is more advantageous.
Therefore, it has been conventionally studied to modify polylactic acid resin using a chain extender or the like.
However, a polylactic acid resin modified so as to sufficiently satisfy the demand for melting characteristics has not been obtained.
The present inventor has intensively studied to satisfy the above-mentioned demand and found that a polylactic acid resin excellent in melt tension can be obtained by carrying out modification using a radical initiator such as an organic peroxide. .
On the other hand, the present inventor has found that when reforming is performed using an organic peroxide, a new problem arises that an odor problem occurs depending on the type of the organic peroxide.
Then, this invention makes it a subject to provide the polylactic acid resin modified | denatured so that the said request can be satisfied, suppressing generating such a problem.

  As a result of extensive studies by the present inventors, it has been found that the above-mentioned problems can be solved by modifying a polylactic acid resin with a specific organic peroxide, and the present invention has been completed.

The present invention for solving the above problems is as follows.
A method for producing a modified polylactic acid resin comprising a modification step of modifying a polylactic acid resin by reacting the polylactic acid resins with a radical initiator,
Provided is a method for producing a modified polylactic acid resin, wherein the radical initiator is t-butyl peroxyisopropyl monocarbonate.

  According to the present invention, a polylactic acid resin excellent in melt tension can be obtained while suppressing the occurrence of odor problems.

Schematic which showed molecular weight distribution of the polylactic acid resin. Schematic which showed molecular weight distribution of the polylactic acid resin. Schematic which shows the structure of the manufacturing apparatus of a foam sheet. The schematic perspective view which showed the folding box which is a foaming molded product. The SEM photograph of MD cross section of the foam sheet of Test Example 1-1. The SEM photograph of the TD cross section of the foam sheet of Test Example 1-1. The SEM photograph of MD section of the foam sheet of Test Example 1-4. The SEM photograph of the TD cross section of the foam sheet of Test Example 1-4. The SEM photograph of MD cross section of the foam sheet of Test Example 1-5. The SEM photograph of TD cross section of the foam sheet of Test Example 1-5. The SEM photograph of MD cross section of the foam sheet of Test Example 2-1. The SEM photograph of the TD cross section of the foam sheet of Test Example 2-2.

Embodiments of the present invention will be described below.
Below, this invention is demonstrated as a main example when the polylactic acid resin foam is an extrusion foam sheet.

The polylactic acid resin foam sheet of the present embodiment (hereinafter also simply referred to as “foam sheet” or the like) is an extruded foam sheet as described above.
That is, the foamed sheet of this 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 making the polylactic acid resin foamed are melt-kneaded by the extruder. It is produced by doing.

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

The lactic acid constituting the polylactic acid resin may be either the L-form or the D-form, or both.
That is, the polylactic acid resin that 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 polyvalent carboxylic acid may be an anhydride.

  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 include diol, 1,6-hexanediol, 1,9-nonanediol, neopentyl glycol, tetramethylene glycol, 1,4-cyclohexanedimethanol and the like.

  Examples of the hydroxycarboxylic acid other than lactic acid constituting the copolymer include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid and the like. Can be mentioned.

  Examples of the polyfunctional polysaccharide include cellulose, cellulose nitrate, methyl cellulose, ethyl cellulose, celluloid, viscose rayon, regenerated cellulose, cellophane, cupra, copper ammonia rayon, cuprophan, bemberg, hemicellulose, starch, acropectin, dextrin, Examples include dextran, glycogen, pectin, chitin, chitosan, gum arabic, guar gum, locust bean gum, and acacia gum.

In the polylactic acid resin in the present embodiment, it is preferable that a structural portion derived from lactic acid (L-form and D-form) is contained in the molecule at a ratio of 50 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 melt tension measurement at 190 ° C. and elongational viscosity measurement at the same temperature.
Specifically, the polylactic acid resin exhibits a melt tension of 5 cN or more and 40 cN or less in 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.

Since the polylactic acid resin of this embodiment has a melt tension of 5 cN or more, it can suppress foam breakage during foaming.
Moreover, since the polylactic acid resin of this embodiment has a melt tension of 40 cN or less, the cell membrane exhibits good elongation during foaming and can suppress bubble breakage.
The polylactic acid resin of the present embodiment is suppressed in foaming at the time of foaming, so that even when foamed at a high foaming ratio, the open cell ratio is hardly increased and the appearance can be improved.

The melt tension at 190 ° C. can be measured as follows using a twin bore capillary rheometer Rheological 5000T (manufactured by CEAST).
(Measuring method of melt tension)
Each sample is vacuum-dried at 80 ° C. for 5 hours and then sealed until immediately before measurement and stored in a desiccator.
After filling the measurement sample resin into a 15 mm diameter barrel heated to a test temperature of 190 ° C. and preheating for 5 minutes, the capillary die of the above measuring device (caliber 2.095 mm, length 8 mm, inflow angle 90 degrees (conical)) While the piston descending speed (0.07730 mm / s) is kept constant and extruded into a string shape, the string-like material is passed through a tension detection pulley located 27 cm below the capillary die, and then a winding 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 average of the maximum value and the minimum value immediately before the string-like material is cut is measured. Let melt tension.
When there is only one maximum point on the tension chart, the maximum value is taken as the melt tension.

The polylactic acid resin of the present embodiment has an extensional viscosity at the breaking point of 0.5 MPa · s or more in the extensional viscosity measurement at 190 ° C.
The elongational viscosity of the polylactic acid resin is preferably 0.55 MPa · s or more, and more preferably 0.6 or more.
The elongational 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 this embodiment, in the extensional viscosity measurement at 190 ° C., the extensional viscosity increases as the extension rate increases, and no peak appears in the graph with the horizontal axis indicating the extension rate and the vertical axis indicating the extensional viscosity. .

The extensional viscosity measurement at 190 ° C. can be measured with a rhetence apparatus, and can be measured as follows.
(Measurement of elongational viscosity by rheotensity)
In the present specification, “measurement of elongational viscosity” refers to measurement of elongational viscosity using an apparatus capable of measuring elongational viscosity, and is not limited to the following, but, for example, Gottfeld's It can be measured using rheotens (Rheotens 71.97).
The measurement of the extensional viscosity is carried out by adjusting the optimum conditions according to each sample, and can be carried out, for example, under the following conditions.
(Example of measurement conditions)
The sample is vacuum dried in advance at 80 ° C. for 5 hours.
The rheotens is installed in Capillograph 1D (manufactured by Toyo Seiki Seisakusho).
The rheotens is installed so that the distance from the die exit of the capillograph 1D to the measuring section is 80 mm.
In the case where the interference occurs as it is, and the rheotens cannot be brought close to 80 mm, a measure for avoiding the interference is taken and the rheotens is set at a predetermined place.
Set the Capillograph measurement conditions as follows.
Dice diameter 2.095mm, length 8mm, inflow angle 90 degrees (conical)
Piston diameter 9.55mm
Piston speed 20mm / min
Measurement temperature 190 ℃
The rheotens measurement conditions are set as follows.
Between wheels 0.2mm above, 1.0mm below
Acceleration 10mm / s ²
Pickup speed Initial speed 11.281mm / s
“A graph in which the horizontal axis indicates the extension speed and the vertical axis indicates the extension viscosity” is a graph of the extension viscosity obtained from the above measurement result by the extension speed (adjusted by the take-up speed).
“A peak does not appear in a graph in which the horizontal axis indicates the extension rate and the vertical axis indicates the extension viscosity” means that no peak appears in the graph.
In the polylactic acid resin of this embodiment, when the extensional viscosity is measured, no peak appears in the graph with the horizontal axis indicating the extension rate and the vertical axis indicating the extensional viscosity.
Thereby, the polylactic acid resin of this embodiment has high tensile strength.

The polylactic acid resin preferably exhibits an appropriate fluidity at the time of heat melting, 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-auto melt indexer 2A” manufactured by Toyo Seiki Seisakusho.
MFR is JIS K7210-1: 2014 "Plastics-Determination of melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastics-Part 1" The piston described in Method B moves a predetermined distance It can be measured by a method of measuring time.
In principle, the measurement conditions are as follows.
Sample: 3-8g
The sample for measurement is vacuum-dried at 80 ° C. for 5 hours, and after drying, it is sealed until immediately before measurement and stored in a desiccator.
Preheating: 270 seconds Load hold: 30 seconds Test temperature: 190 ° C
Test load: 2.16 kg (21.18 N).
The number of test of the sample is 3 times, and the average is the value of melt mass flow rate (g / 10 min).

The heat melting characteristics as described above 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 to 1,000,000.
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 more, 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 is a component that exhibits a shoulder SL or another peak SP on the higher molecular weight side than 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 dissolving the main peak component when the polylactic acid resin is melted by heat and exhibiting melt viscoelasticity suitable for foaming.
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 becoming a shoulder SL rather than being a different 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.

In the polylactic acid resin of the present embodiment, the ratio (Mz / Mw) of the Z average molecular weight (Mz) to the mass average molecular weight (Mw) is preferably 2.5 or more, and more preferably 2.7 or more. It is especially 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 the Z average molecular weight (Mz) of the polylactic acid resin can be measured using a gel permeation chromatograph (GPC), and can be obtained as a value converted to polystyrene (PS).
Specifically, the average molecular weight of the polylactic acid resin can be determined by the following procedure.

(How to find the average molecular weight)
20 mg of a sample was dissolved in 6 mL of chloroform (immersion time: 6 ± 1.0 h), filtered through a non-aqueous 0.45 μm syringe filter manufactured by Shimadzu LLC, and then chromatographed under the following measurement conditions. Measure and obtain the weight average molecular weight of the sample from a standard polystyrene calibration curve prepared in advance.

Equipment used = “HLC-8320GPC EcoSEC” manufactured by Tosoh Corporation Gel permeation chromatograph (with built-in RI detector and UV detector)
<GPC measurement conditions>
Sample side guard column = Tosoh Co., Ltd. TSK guardcolumn HXL-H (6.0 mm x 4.0 cm) x 1 Measurement column = Tosoh Co., Ltd. TSKgel GMHXL (7.8 mm ID x 30 cm) x 2 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 rate Reference side pump = 0.5 mL / min
Sample side pump = 1.0 mL / min
Detector = RI detector injection volume = 50 μL
Measurement time = 26 min
Sampling pitch = 500 msec

The standard polystyrene samples for the calibration curve are 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, 1,250. , 442,000, 151,000, 53,500, 17,000, 7,660, 2,900, 1,320 are used.
The standard polystyrenes for the calibration curve were A (5,620,000, 1,250,000, 151,000, 17,000, 2,900) and B (31,220,000, 442,000, 53,500, 7, 660, 1,320), A is weighed 2 to 10 mg each and then dissolved in 30 mL chloroform, and B is also weighed 3 to 10 mg each and dissolved in 30 mL chloroform.
A standard polystyrene calibration curve is obtained by injecting 50 μL of each of the prepared A and B lysates and preparing a calibration curve (tertiary equation) from the retention time obtained after the measurement, and using the calibration curve, the mass average molecular weight is obtained. calculate.

The polylactic acid resin having the 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 cross-linked structure or a long chain branched structure, or the polylactic acid resin can have a high molecular weight.
A chain extender such as carbodiimide can be used to increase the molecular weight of the polylactic acid resin.
In addition, modification with a chain extender is a functional group capable of undergoing a condensation reaction with a hydroxyl group or a carboxyl group present in the molecular structure of a polylactic acid resin, such as an acrylic organic compound, an epoxy organic compound, or an isocyanate organic compound. It can carry out using the compound which has one or more.
That is, the modification can be performed by a method in which an acrylic organic compound, an epoxy organic compound, an isocyanate organic compound, or the like is bonded to the polylactic acid resin by a reaction.
The modification of the polylactic acid resin by crosslinking or long-chain branching can be performed by, for example, a method of reacting the polylactic acid resins with a radical initiator.

Among the above-described modification methods, it is preferable to react the polylactic acid resins with a radical initiator in terms of suppressing the inclusion of other components in the foamed sheet.
In addition, when the 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 free radicals generated by the radical initiator, Becomes a crosslinking point (branch point) and can be stabilized.
With such modification, the polylactic acid resin is increased in 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, and halogen molecules.
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-butyl peroxy 2-ethylhexyl carbonate, t-hexyl peroxyisopropyl monocarbonate, t-hexyl peroxybenzoate, t-butyl peroxybenzoate, t-butyl peroxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxyacetate, 2,5-dimethyl2,5-di (benzoylperoxy) hexane, and t-butylperoxyisopropylmono And carbonate.

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

  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 peroxide, di (4-methylbenzoyl) peroxide, and di (3-methylbenzoyl) peroxide.

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

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

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

In the modification with the organic peroxide, the polylactic acid resin after modification is mixed with a component having an excessive molecular weight that becomes a gel when melted by heat, or the problem of odor due to the decomposition residue of the organic peroxide is generated. There is a risk of letting
It is preferable that the organic peroxide is 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 peroxyesters, the organic peroxide used for modifying the polylactic acid resin is preferably a peroxycarbonate organic peroxide such as peroxymonocarbonate or peroxydicarbonate.
In the present embodiment, the organic peroxide used for modifying the polylactic acid resin is preferably a peroxymonocarbonate organic peroxide among the peroxycarbonate organic peroxides, and t-butylperoxyisopropyl. Particularly preferred is monocarbonate.

The organic peroxide as described above is usually used at a ratio of 0.1 parts by mass or more with respect to 100 parts by mass of the polylactic acid resin to be modified, although it depends on the molecular weight thereof.
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 the organic peroxide at such a ratio, the modified polylactic acid resin can be made suitable for foaming.

By using the organic peroxide as described above in an amount of 0.1 parts by mass or more, the polylactic acid resin can exhibit the effect of modification more reliably.
Moreover, an organic peroxide can suppress that a gel is mixed in the polylactic acid resin after modification because the usage-amount is 2.0 mass parts or less.

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

A general thing can be employ | adopted as said foaming agent, The volatile foaming agent used as gas at normal temperature (23 degreeC) and a normal pressure (1 atmosphere), and the decomposition | disassembly type foaming agent which generate | occur | produces gas by thermal decomposition Can be adopted.
As said volatile foaming agent, an inert gas, an aliphatic hydrocarbon, an alicyclic hydrocarbon etc. are employable, for example.

  Examples of the inert gas include carbon dioxide 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.

Examples of the bubble adjusting agent 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 also be used as a bubble regulator.

The foam sheet of this embodiment is an extruded foam sheet as described above.
Therefore, the foam sheet of this embodiment is usually obtained by extrusion foaming a resin composition (hereinafter also referred to as “polylactic acid resin composition”) containing the polylactic acid resin, the foaming agent, and the cell regulator. It is formed.

Various additives can be added to the polylactic acid resin composition as necessary.
Examples of the additive include resins other than polylactic acid resins, inorganic fillers, and various drugs.
Examples of the drug include a lubricant, an antioxidant, an antistatic agent, a flame retardant, an ultraviolet absorber, a light stabilizer, a colorant, and an antibacterial agent.
In addition, it is preferable that it is 25 mass parts or less with respect to 100 mass parts of polylactic acid resins, and, as for the ratio of these additives, it is more preferable that it is 15 mass parts or less.

  The foam sheet in the present embodiment has a step of modifying a polylactic acid resin using a twin screw extruder or the like (modification step), a polylactic acid resin composition containing the modified polylactic acid resin, and a circular die at the tip. And an extrusion foaming process (extrusion foaming process) through an extruder attached to the substrate.

In the modification step, for example, the modified polylactic acid resin may be immediately pelletized using a twin screw extruder equipped with a granulation die (hot cut die).
The twin-screw extruder used in the reforming process is equipped with a strand die or T-die, and in the reforming process, a strand or a sheet made of a modified polylactic acid resin is produced, and then the strand or sheet is cut. The granulating step may be performed separately.
If necessary, the extrusion foaming step may be carried out continuously with the reforming step using a tandem extruder.
For example, the extrusion foaming process in the present embodiment can be performed 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, the manufacturing apparatus includes a cooling device CL for air-cooling the foam sheet discharged in a cylindrical shape from the circular die CD, and a diameter for expanding the cylindrical foam sheet into a cylindrical shape having a predetermined size. A mandrel MD, a slitting device that slits the foam sheet after passing through the mandrel MD and splits it into two sheets, and a take-up roller for winding the slit foam sheet 1 after passing the plurality of rollers 21 22 is provided.
In the upstream side of the tandem extruder 10 (hereinafter also referred to as “first extruder 10a”), a hopper 11 for introducing a polylactic acid resin as a raw material of the foam sheet, and a foaming agent such as a hydrocarbon Is provided in the cylinder.
On the downstream side of the first side extruder 10a, an extruder (hereinafter also referred to as "second extruder 10b") for melt kneading a polylactic acid resin composition containing a foaming agent is provided.
When the extrusion foaming process is performed with such an apparatus, the polylactic acid resin is modified by the first extruder 10a, and foaming is performed at the end portion of the first extruder 10a or the base end portion of the second extruder 10b. A polylactic acid resin composition to be a raw material of the foam sheet may be prepared by mixing an agent and the like, and extrusion foaming may be performed from the circular die CD.

The foamed sheet of this embodiment has excellent strength because it exhibits the above-mentioned characteristics when melted.
In the extrusion foaming step, microbubbles 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 material is discharged from the circular die CD and the pressure is released. Expands all at once, and new bubbles are generated by the foaming agent dissolved in the melt-kneaded product.
The extruded foam sheet is stretched in the circumferential direction by the diameter expansion by the mandrel MD and is also stretched in the extrusion direction by winding by the winding roller 22.

In the extrusion foaming process 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 this embodiment, when the cell membrane containing the polylactic acid resin as described above is stretched by the foaming force of the foaming agent, a certain level of resistance is exhibited.
Moreover, in the foam sheet of this embodiment, it is easy to be in the state where the center part of a bubble film is thin and a peripheral part is thick.
Therefore, the foamed sheet of the present embodiment exhibits excellent mechanical properties when the thick bubble film is three-dimensionally connected to the entire sheet.
Note that the foam sheet of the present embodiment has a bubble breakage at the time of foaming, and even when a hole is opened in the bubble film, the bubble film surrounding the hole is not left as it is, but is shrunk and has a high strength. Since the thickness is increased in a form effective for exhibiting, excellent strength can be exhibited even with open cells at a certain rate.

The foam sheet of this embodiment preferably has an open cell ratio of 10% or more in consideration of the biodegradability as described above.
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 exhibit excellent strength in the foamed sheet.

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 foamed sheet can be measured by the method shown below.
(Open cell ratio)
A plurality of sheet-like samples having a length of 25 mm and a width of 25 mm are cut out from the foamed sheet, and the cut-out samples are overlapped so that there is no gap between them to obtain a measurement sample having a thickness of 25 mm. ) Measure to 1/100 mm using “Digimatic Caliper” manufactured by Mitutoyo, and obtain the apparent volume (cm ³ ).
Next, the volume (cm ³ ) of the sample for measurement is obtained by the 1-1 / 2-1 atmospheric pressure method using an air comparison type hydrometer 1000 type (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 in a JIS K7100-1999 symbol 23/50, second grade environment after conditioning for 16 hours in a JIS K7100-1999 symbol 23/50, second grade environment.
The air-comparing hydrometer corrects with a standard sphere (large 28.9 cc, small 8.5 cc).

Open cell ratio (%) = 100 × (apparent volume−volume measured with an air-based hydrometer) / apparent volume

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

Foaming ratio = 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 can be specifically measured by the following method.

(Density measurement method)
A sample of 100 cm ³ or more is cut from the foamed sheet so as not to change the original cell structure, and the sample is conditioned in JIS K7100: 1999 symbol 23/50, second grade environment for 16 hours, The mass is measured, and the density is calculated by the following formula.

Apparent density (kg / m ³ ) = Sample mass (kg) / Sample volume (m ³ )

For example, “DIGIMATIC” CD-15 type manufactured by Mitutoyo Corporation can be used for measuring the dimensions of the sample.

  The density of the polylactic acid resin composition is determined by the Archimedes method (JIS K8807: 2012 “Method for measuring density and specific gravity of solids”) in a liquid weighing method for a sample which is not foamed by hot pressing a foamed sheet. ) Based on measurement.

For example, the foamed sheet of this embodiment preferably has a predetermined strength in a foamed state in which the foaming ratio is about 3 to 8 times.
Specifically, the foamed sheet preferably has a tensile strength of 5.5 MPa or more and 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 that the pressure is 6.5 MPa or more.
The upper limit of the tensile strength of the foamed sheet is not particularly required, but the tensile strength of the foamed sheet is usually a value of 25 MPa or less.

The tensile strength of the foamed sheet can be measured based on JIS K6767: 1999 “Foamed plastic-polyethylene test method”.
In other words, using Tenteclon UCT-10T universal testing machine manufactured by Orientec Co., Ltd., and “UTPS-458X” universal testing machine data processing manufactured by Softbrain Co., Ltd. The test piece is dumbbell type 1 (ISO 1798 standard), and the tensile strength is measured at a thickness of 1.0 to 1.5 mm.
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 was five, and the test pieces were conditioned in accordance with JIS K 7100: 1999 symbol “23/50” (temperature 23 ° C., relative humidity 50%) over the course of 16 hours in a second grade standard atmosphere. Measure in the same standard atmosphere.
The tensile strength is calculated by the following formula.
T = F / (W t)

T: Tensile strength (MPa)
F: Maximum load until cutting (N)
W: Specimen width (mm)
t: thickness of test piece (mm)

  The foam sheet according to the present embodiment has a molecular weight distribution as described above, so that microprotrusions and bubbles referred to as “butsu” or the like due to a component different in behavior at the time of heat melting such as a gel. It is possible to suppress the tearing of the film.

The foam sheet of this embodiment can be used as a raw material for various sheet molded products.
Foamed sheets are given a three-dimensional shape by thermoforming such as vacuum forming, pressure forming, vacuum / pressure forming, press forming, match mold forming, etc., and foam formed products such as containers (for example, trays, baskets, cups, etc.) ).
Moreover, a foam sheet can also be made into the forming material of foam molded articles, such as a folded box, with flat form.
That is, 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 folded box 100 as shown in FIG.

In the present embodiment, a sheet outside the product generated when the foamed sheet is produced (the foamed sheet of the portion that has been extruded and foamed until the foamed sheet becomes a foamed state as set) and has not become a product, or the above It is desirable to recycle pellets and the like produced when producing a molded product and reuse them as recycled materials.
Therefore, the polylactic acid resin used as the raw material of the foam sheet in this embodiment is MFR (190 ° C., 2.16 kg) measured in the initial state as “MFR ₀ (g / 10 min)” and melted once at 190 ° C. The MFR measured after kneading is referred to as “MFR ₁ (g / 10 min)”, and the MFR measured after melt-kneading and then melt-kneading again at 190 ° C. is referred to as “MFR ₂ (g / 10 min)”. The value of “MFR primary change rate” represented by the following formula (A1) when the MFR measured after being melt-kneaded at 190 ° C. at 3 ° C. is “MFR ₃ (g / 10 min)”. Is preferably 25% or less.
In addition, the polylactic acid resin of the present embodiment preferably has a “MFR secondary change rate” value represented by the following formula (A2) of 40% or less.
Furthermore, the polylactic acid resin of this embodiment preferably has a “MFR tertiary change rate” value of 55% or less represented by the following formula (A3).

MFR primary change rate = (MFR ₁ −MFR ₀ ) / MFR ₀ × 100 [%] (A1)
MFR secondary change rate = (MFR ₂ −MFR ₀ ) / MFR ₀ × 100 [%] (A2)
MFR tertiary change rate = (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 change rate is more preferably 35% or less, and further preferably 30% or less.
The MFR tertiary change rate is more preferably 52% or less, and further preferably 50% or less.

The polylactic acid resin used as the raw material of the foam sheet in the present embodiment is measured after being melt-kneaded once at 190 ° C. with the melt tension (at 190 ° C.) measured in the initial state being “MT ₀ (cN)”. The melt tension is “MT ₁ (cN)” and the melt tension measured after melt-kneading and then melt-kneading again at 190 ° C. is “MT ₂ (cN)”. When the melt tension measured after kneading is defined as “MT ₃ (cN)”, it is preferable that the value of “melting tension primary change rate” represented by the following formula (B1) is 60% or less. .
Further, the polylactic acid resin of the present embodiment preferably has a “melting tension secondary change rate” represented by the following formula (B2) of 70% or less.
Furthermore, the polylactic acid resin of the present embodiment preferably has a “melting tension tertiary change rate” represented by the following formula (B3) of 80% or less.

Melt tension primary change rate = (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 melt tension primary change rate is more preferably 55% or less, and further preferably 50% or less.
The melt tension secondary change rate is more preferably 65% or less, and further preferably 55% or less.
The melt tension tertiary change rate is more preferably 75% or less, and further preferably 70% or less.

In addition, the lower limit value of each value of the MFR primary change rate, the MFR secondary change rate, and the MFR tertiary change rate is usually 0%.
Moreover, the lower limit value of each value of the melt tension primary change rate, the melt tension secondary change rate, and the melt tension tertiary change rate 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.
Moreover, when the melt tension secondary change rate and the melt tension tertiary change rate are in the above ranges, the polylactic acid resin of the present embodiment can further expand the use of recycled materials.
That is, since the polylactic acid resin of this embodiment has little change in properties due to thermal history, there is little risk of greatly reducing the properties even when added to a virgin material (commercially available pellets before modification).
Moreover, even if a recycled material is used as a part of the raw material for producing the foam sheet, a high-quality foam sheet can be produced without greatly changing the extrusion conditions.
For these reasons, the polylactic acid resin and foamed sheet of the present embodiment can make a more environmentally friendly product.

The “state after being“ melt-kneaded ”at 190 ° C.” in the above means the state after being extruded by a twin-screw extruder in principle.

More specifically, using a twin screw extruder (L / D = 42) with a diameter of 30 mm, the temperature setting of the twin screw extruder is 160 ° C., 200 ° C. in order from the upstream side to the downstream side in the extrusion direction. The subsequent temperature was set to 190 ° C., melt-kneaded in a twin-screw extruder under the condition of a rotational speed of 140 rpm, and from a die having a diameter of 3 mm and a hole number of 2 attached to the tip of the extruder, 10 kg / h In this specification, the state after passing through the “double-screw extruder” in terms of the discharge amount is defined as “the state after being“ melt-kneaded ”at 190 ° C.”.
The measurement of MFR and melt tension was performed by supplying a polylactic acid resin to the “biaxial extruder” set as described above and extruding it into a strand shape. It can be obtained by passing through a 1.5 m water tank and cooling, cutting the cooled sample, and producing pellets.
More specifically, by measuring the MFR and melt tension of the pellet, the MFR and melt tension values after the polylactic acid resin is melt-kneaded at 190 ° C. can be measured.

The foamed sheet of this embodiment may use a part of the polylactic acid resin used as a raw material as a recycled material because the polylactic acid resin used exhibits the above-described thermal stability.
That is, the raw material of the foam sheet may contain a polylactic acid resin composition that has passed through the extruder one or more times.
A recycled material including at least one of a polylactic acid resin foam sheet, a foam molded article obtained by thermoforming a polylactic acid resin foam sheet, and an end material produced when the foam molded article is manufactured is a foam sheet. In order to make an environmentally friendly product, it is preferable that the foamed sheet contains 5% or more of the polylactic acid resin contained in the raw material of the foamed sheet so that the mass ratio is 1% or more. It is more preferable to make it contain in a foam sheet.
However, in order to improve the physical properties of the foam sheet, the recycled material is preferably contained in the foam sheet so that the mass ratio is 25% or less, and contained in the foam sheet so as to be 20% or less. More preferably.
The recycled material may be used as a raw material for the foamed sheet as it is, or as a raw material for the foamed sheet after modification with t-butylperoxyisopropyl monocarbonate or the like.
When reforming the recycled material, it is preferable to mix the recycled material and the virgin material, supply the mixed material to a melt kneading apparatus such as a twin-screw extruder, and modify the recycled material together with the virgin material.
If a part of the polylactic acid resin to be modified is used as a recycled material in the modification step, there is an advantage that it becomes easy to give the modified polylactic acid resin the above-mentioned heat melting characteristics.

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

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

<First evaluation study>
(Test Example 1-1)
(1) Production of modified polylactic acid resin 100 parts by mass of polylactic acid resin (“Biopolymer Inge 8052D” manufactured by Nature Works, MFR = 7.4 g / 10 min, density = 1240 kg / m ³ ), and t-butyl par 0.5 parts by mass of oxyisopropyl monocarbonate (“Kaya-Carbon BIC-75” manufactured by Kayaku Akzo Co., Ltd., 1 minute half-life temperature T1: 158.8 ° C.) was stirred and mixed with a ribbon blender to obtain a mixture.
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 part is set to 170 ° C., the temperature after that 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 in a strand form from a die having 18 holes with a discharge rate of 50 kg / h.
Next, the extruded strand-like kneaded product was cooled by passing through a cooling water tank having a length of 2 m containing 30 ° C. water.
The cooled strand was cut with a pelletizer to obtain modified polylactic acid resin pellets.

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

(Test Examples 2-1 to 2-4)
Test Examples 2-1 to 2-4 were the same as Test Examples 1-1 to 1-7, except that modification was performed using an organic peroxide different from 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 amount (phr) is shown in Tables 1 to 3.

(2) Production of Foam Dry-blend 100 parts by mass of the polylactic acid resin obtained in Test Example 1-1 and 1.0 part by mass of a bubble regulator (“Crown Talc” manufactured by Matsumura Sangyo Co., Ltd.) A mixture was made.
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. And melted by heating.
Thereafter, butane (isobutane / normal butane = 70/30) as a blowing agent was press-fitted into the first extruder and melt-mixed with the mixture.
Next, this molten mixture is transferred to a second extruder having a diameter of 65 mm and uniformly cooled 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 was cooled and molded by blowing air on its outer surface with an air ring having a diameter larger than that of a mandrel having a diameter of 206 mm, the inside of which was cooled with about 20 ° C. water. An incision was made at one point on the circumference with a cutter to obtain a band-shaped foam sheet.

For Test Examples 1-2 to 1-7 and Test Examples 2-1 to 2-4, foamed sheets were produced in the same manner as described above.
However, in Test Examples 2-2 and 2-3, a foamed sheet was not obtained because there was no melt tension of the resin and a stable sheet could not be taken up.

About the polylactic acid resin after modification 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 determined.
Further, in the molecular weight distribution curve of the modified polylactic acid resin, it was confirmed whether a shoulder SL or another peak SP was present on the higher molecular weight side than the maximum peak TP.
Further, the MFR (190 ° C., 2.16 kg) and melt tension (at 190 ° C.) of the modified polylactic acid resin were measured.
And the apparent density and the open cell ratio were measured about the produced foam sheet.
Furthermore, about the foam sheet, the external appearance was observed visually and it determined with the following references | standards.

(Appearance of foam)
○: Uniform foaming and beautiful appearance.
(Triangle | delta): Although foaming is uniform, a part is seen in the sheet | seat surface.
X: Air bubbles are non-uniform and significant bubble breakage is observed. Or a large number of irregularities are seen on the sheet surface.

The above evaluation results are shown in Table 4.

(Internal observation of foam)
A cross section (hereinafter also referred to as “MD cross section”) of the foam sheet cut along a plane parallel to the extrusion direction (MD) of the foam sheet and perpendicular to the plane direction of the foam sheet, and the extrusion direction (MD) of the foam sheet A scanning electron microscope (SEM) with respect to a cross section (hereinafter also referred to as “TD cross section”) obtained by cutting the foam sheet in a plane parallel to the sheet width direction (TD) perpendicular to the plane and perpendicular to the plane direction of the foam sheet The photograph was taken at a magnification of about 50 times.
Photography was performed in Test Example 1-1 (MD: FIG. 5a, TD: FIG. 5b), Test Example 1-4 (MD: FIG. 6a, TD: FIG. 6b), Test Example 1-5 (MD: FIG. 7a, TD). : FIG. 7b), it implemented with respect to four foam sheets of Test Example 2-1 (MD: FIG. 8a, TD: FIG. 8b), and calculated the average bubble diameter based on the photographed photograph.
The average bubble diameter was calculated as follows.

<Measurement of average cell diameter of foam sheet>
From the center in the width direction of the foamed sheet, cut out perpendicularly to the surface of the foamed sheet along the MD direction (extrusion direction) and the TD direction (width direction), and each cross section is “SU1510 manufactured by Hitachi High-Technologies Corporation. "Photographed using a scanning electron microscope.
At this time, the microscopic picture was taken so as to have a predetermined magnification when printed in a state where two images (total of four images in total) were arranged on one A4 paper in landscape orientation.
Specifically, on the image printed as described above, an arbitrary straight line of 60 mm parallel to each direction of MD and TD, and 60 mm in a direction orthogonal to each direction (also referred to as a thickness direction or a VD direction). When the straight line was drawn, the photographing magnification with an electron microscope was adjusted so that the number of bubbles existing on the straight line was about 3 to 10.
For each of the cross-section cut along the MD direction (MD cross-section) and the cross-section cut along the TD direction (TD cross-section), a microscopic image of a total of 4 visual fields was taken, and A4 as described above. Printed on paper.
Three arbitrary straight lines (length 60 mm) parallel to the MD direction are drawn on each of the two images of the MD cross section, and three arbitrary straight lines parallel to the TD direction of each of the two images of the TD cross section ( A length of 60 mm) was drawn.
Moreover, three straight lines (60 mm) parallel to the VD direction are drawn on one image of the MD cross section and one image of the TD cross section, and an arbitrary straight line of 60 mm parallel to the MD direction, the TD direction, and the VD direction. Are drawn in six in each direction.
It should be noted that in any given line, bubbles were prevented from contacting only at the contact points as much as possible, and when they contacted, these bubbles were added to the number.
The number of bubbles D counted for six arbitrary straight lines in each of the MD, TD, and VD directions was arithmetically averaged to obtain the number of bubbles in each direction.
From the image magnification obtained by counting the number of bubbles and the number of bubbles, the average chord length t of the bubbles was calculated from the following equation.

Average chord length t (mm) = 60 / (number of bubbles x image magnification)

The image magnification was determined by the following equation by measuring the scale bar on the image to 1/100 mm with “Digimatic Caliper” manufactured by Mitutoyo Corporation.

Image magnification = Scale bar measured value (mm) / Scale bar display value (mm)

And the bubble diameter in each direction was computed by following Formula.

Bubble diameter D (mm) = t / 0.616

Furthermore, the cube root of the product was taken as the average bubble diameter.

Average bubble diameter (mm) = (D _MD × D _TD × D _VD ) ^1/3
D _MD : Bubble diameter in the MD direction (mm)
D _TD : Bubble diameter in TD direction (mm)
D _VD : Bubble diameter in the VD direction (mm)

The results are shown in the table below.

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

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

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

With respect to this modified polylactic acid resin, the extensional viscosity (at 190 ° C.) was measured.
As a result, in the extension viscosity measurement, the extension viscosity increases as the extension rate increases, and it is clear that no upward convex peak appears in the graph with the abscissa indicating the extension rate and the ordinate indicating the extension viscosity. It was.

Further, using the polylactic acid resin modified in Test Example 3-1, a foamed sheet was prepared in the same manner as in “First Evaluation Study”, and the thickness, basis weight, foaming ratio, and open cell of the foamed sheet were produced. The rate was determined.
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 using the dumbbell-shaped test piece.

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

Similar to Test Example 3-1, the heat melting characteristics of the polylactic acid resin of Test Example 4-1 were investigated using a rhetence apparatus.
In addition, in the polylactic acid resin of Test Example 4-1, the peak was observed when the result of the measurement of the extension viscosity was represented by a graph in which the horizontal axis represents the extension rate and the vertical axis represents the extension viscosity.
For the polylactic acid resin of Test Example 4-1, a foamed sheet was prepared and evaluated in the same manner as Test Example 3-1.
The results are shown in Table 6 below.

  From the above results, the polylactic acid resin having an elongational viscosity at the breaking point of 0.5 MPa · s or higher in the elongational viscosity measurement at 190 ° C., and in the elongational viscosity measurement, the elongational viscosity increases as the elongation rate increases. It can be seen that by using a polylactic acid resin in which a peak does not appear in a graph in which the horizontal axis indicates the elongation rate and the vertical axis indicates the extension viscosity, an excellent strength is exhibited in the polylactic acid resin foam.

<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 = 1240 kg / m ³ ), t-butylperoxyisopropyl monocarbonate (manufactured by Kayaku Akzo Co., Ltd.) 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 setting of the twin screw extruder is set to 160 ° C. and the temperature after that to 220 ° C., and the mixture is melt-kneaded in the twin screw extruder at 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 a hole number of 2 attached to the tip of the extruder.
Subsequently, the extruded strand-like kneaded material was cooled by passing through a cooling water tank having a length of 1.5 m containing 20 ° C. water.
The cooled strand was cut with a pelletizer to obtain modified polylactic acid resin pellets.

With respect to the modified polylactic acid resin obtained in Test Example 5-1, MFR (190 ° C., 2.16 kg) and melt tension (at 190 ° C.) 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 each time MFR and melt tension were measured, thereby MFR primary change. Rate, MFR secondary change rate, MFR tertiary change rate, melt tension primary change rate, melt tension secondary change rate, and melt tension tertiary change rate were measured.

(Test Examples 5-2 and 5-3)
Test Example 5 except that the ratio of the polylactic acid resin to t-butylperoxyisopropyl monocarbonate was 100: 0.3 (Test Example 5-2) and 100: 0.7 (Test Example 5-3), respectively. Evaluation similar to -1 was performed.

(Test Example 6-1)
Evaluation similar to Test Examples 5-1 to 5-3 was performed on the polylactic acid resin (trade name “Biopolymer Inge 8052D”) manufactured by Nature Works without modification.

(Test Example 6-2)
Evaluation similar to Test Examples 5-1 to 5-3 was performed on the polylactic acid resin (trade name “TERRAMAC HV-6250H”) commercially available from Unitika Corporation without modification.
These results are shown in Table 7 below.

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

Claims (4)

A method for producing a modified polylactic acid resin comprising a modification step of modifying a polylactic acid resin by reacting the polylactic acid resins with a radical initiator,
A method for producing a modified polylactic acid resin, wherein the radical initiator is t-butylperoxyisopropyl monocarbonate.   The modified polylactic acid resin has a mass average molecular weight (Mw) of 200,000 to 350,000, a Z average molecular weight of 600,000 to 1,000,000, and a ratio of the Z average molecular weight to the mass average molecular weight (Mz / The method for producing a modified polylactic acid resin according to claim 1, wherein Mw) is 2.5 or more, and a shoulder or another peak is present on the higher molecular weight side than the maximum peak in the molecular weight distribution curve. The modified polylactic acid resin has a melt tension at 190 ° C of 10 cN or more and 40 cN or less, a melt mass flow rate at a temperature of 190 ° C and a nominal load of 2.16 kg of 1 g / 10 min or more and 10 g / 10 min or less. 3. A process for producing a modified polylactic acid resin according to 1 or 2.   The said modification | reformation process WHEREIN: The said t-butyl peroxy isopropyl monocarbonate is used in the ratio of 0.1 to 1.5 mass parts with respect to 100 mass parts of said polylactic acid resin. A method for producing the modified polylactic acid resin according to claim 1.