JP4582871B2 - Non-crosslinked resin foamable particles - Google Patents

Description

【００３０】
【表２】

（注）＊１；最適発泡温度条件が得られず。＊２；発泡体が得られず。
【００３１】
【発明の効果】
本発明によるポリ乳酸系樹脂発泡性粒子は、生分解性を有しプラスチック廃棄物問題を解決でき、且つ優れた型内成形性を有し、発泡成形後に実用上優れた緩衝性能と熱湯に対する耐熱性を有する型内発泡成形体を成形し得る、非常に有用な発泡性粒子である。
【図面の簡単な説明】
【図１】ＤＳＣで測定したＴ_５０＝１５２℃、Ｔ_７０＝１５８℃、（Ｔ_７０−Ｔ_５０）＝６℃の場合の結晶融解吸熱曲線を説明するグラフ（実施例）である。
【図２】ＤＳＣで測定したＴ_５０＝１５１℃、Ｔ_７０＝１５８℃、（Ｔ_７０−Ｔ_５０）＝７℃の場合の結晶融解吸熱曲線を説明するグラフ（実施例）である。
【図３】ＤＳＣで測定したＴ_５０＝１４８℃、Ｔ_７０＝１５７℃、（Ｔ_７０−Ｔ_５０）＝９℃の場合の結晶融解吸熱曲線を説明するグラフ（実施例）である。
【図４】ＤＳＣで測定したＴ_５０＝１５３℃、Ｔ_７０＝１５７℃、（Ｔ_７０−Ｔ_５０）＝４℃の場合の結晶融解吸熱曲線を説明するグラフ（比較例）である。[0001]
[Industrial application fields]
The present invention relates to foamable particles comprising a polylactic acid resin that can be a foamed molded article having biodegradability and practically sufficient buffering performance after foaming, and heat resistance obtained by heating and foaming the same in a mold. The present invention relates to a foam molded article having improved properties.
[0002]
[Prior art]
Lightweight plastic foam with excellent cushioning performance and moldability is very useful as a packaging material for precision machinery, fragile products such as glass products, optical devices that are vulnerable to impact, and computer-related equipment. Polystyrene, polyolefin, etc., and when it is discarded as unnecessary garbage after its use, the accumulated amount of waste disposed of in landfills or landfills increases due to the property that it is durable and does not rot. It is difficult to secure landfill site in the center.
Under such circumstances, a biodegradable plastic that can be decomposed by microorganisms and the like in nature has been desired as a material that enables volume reduction of plastic waste.
A number of biodegradable plastics have already been found centering on aliphatic polyester resins. Among them, polylactic acid resins are not derived from fossil fuels such as petroleum, and natural products such as corn are used as raw materials. It can be said that it is one of the most preferable resins as a resin that is biodegraded after use and circulated in nature from the point that it is produced and lactic acid, which is the raw material, is an extremely safe substance.
[0003]
However, since the polylactic acid resin is a crystalline resin and the temperature dependence of the melt viscosity is large, there is a problem that it is difficult to maintain the melt viscosity at a viscosity suitable for foaming.
Regarding expandable particles having biodegradability, JP-A-6-248106 discloses aliphatic polyester expandable particles mainly composed of two components of glycols and dicarboxylic acid. There is no disclosure of resin expandable particles.
Aliphatic polyesters consisting mainly of two components, glycols and dicarboxylic acids, have a different chemical structure from polylactic acid resins and different melt viscosity behavior during molding, and are more flexible than polylactic acid resins. The elastic modulus is low, and the mechanical properties of the foam are also different from those of the polylactic acid resin foam.
JP-A-10-324766 discloses aliphatic polyester resin foamed particles having a crosslinked structure, which requires a crosslinking reaction such as chemical crosslinking or radiation crosslinking. I can't get it. In addition, the Examples disclose only aliphatic polyester resin foamed particles composed of a diol and a dicarboxylic acid, and nothing is stated about improvement of foamability of non-crosslinked polylactic acid resin foamable particles.
Japanese Patent Application Laid-Open No. 2000-17037 requires the use of a specific amount of a specific polyisocyanate in polylactic acid, and does not disclose any method that does not use a polyisocyanate.
[0004]
[Problems to be solved by the invention]
The present invention is a polylactic acid-based resin foamable particle having a biodegradable, practically superior buffer performance and improved heat resistance, and having excellent foamability without crosslinking. It is an object of the present invention to provide expandable particles having the following.
[0005]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventor surprisingly uses the polylactic acid resin having a specific melt viscosity, a crystal melting heat amount ΔHm, and a crystal melting endothermic curve. The inventors have found that the object is achieved and have completed the present invention.
That is, the present invention:
(1) In a polylactic acid resin containing lactic acid monomer units of 50% by weight or more, temperature is 190 ° C., shear rate is 100 sec.^-1The melt viscosity at 1 × 10²~ 1x10^FivePa
S, and the crystal melting heat amount ΔHm existing between 100 ° C. and 200 ° C. when measured by raising the temperature from 0 ° C. to 200 ° C. with a differential scanning calorimeter (DSC) is 30 J / g or more, and The temperature that reaches the heat of crystal fusion corresponding to 50% of ΔHm (T₅₀) And the temperature that reaches 70% of the crystal melting heat (T₇₀) Difference (T)₇₀-T₅₀) Is 6 ° C. or higher, and non-crosslinked polylactic acid resin foamable particles comprising a polylactic acid resin and a foaming agent are provided. Also,
(2) When the polylactic acid resin is measured by raising the temperature from 0 ° C. to 200 ° C. with a differential scanning calorimeter (DSC), the heat of crystal fusion ΔHm existing between 100 ° C. and 200 ° C. is 30 J / g or more. The temperature at which the heat of crystal fusion corresponding to 50% of ΔHm is reached (T₅₀) And the temperature that reaches 70% of the crystal melting heat (T₇₀) Difference (T)₇₀-T₅₀) Is 8 ° C. or higher, and the expandable particles according to (1) are provided. Also,
(3) Polylactic acid resin containing 50% by weight or more of lactic acid monomer units, temperature 190 ° C., shear rate 100 sec.^-1The melt viscosity at 1 × 10²~ 1x10^FivePa
S, and the crystal melting heat amount ΔHm existing between 100 ° C. and 200 ° C. when measured by raising the temperature from 0 ° C. to 200 ° C. with a differential scanning calorimeter (DSC) is 30 J / g or more, and The temperature that reaches the heat of crystal fusion corresponding to 50% of ΔHm (T₅₀) And the temperature that reaches 70% of the crystal melting heat (T₇₀) Difference (T)₇₀-T₅₀) Is 6 ° C. or higher, and a foamed molded article obtained by heating and foaming non-crosslinked polylactic acid resin foamable particles comprising a polylactic acid resin and a foaming agent is provided. Also,
(4) When the polylactic acid resin is measured by raising the temperature from 0 ° C. to 200 ° C. with a differential scanning calorimeter (DSC), the heat of crystal fusion ΔHm existing between 100 ° C. and 200 ° C. is 30 J / g or more. The temperature at which the heat of crystal fusion corresponding to 50% of ΔHm is reached (T₅₀) And the temperature that reaches 70% of the crystal melting heat (T₇₀) Difference (T)₇₀-T₅₀) Is 8 ° C. or higher. (3) A foamed molded product according to (3) is provided.
[0006]
The present invention will be specifically described below.
The expandable particles of the present invention are made of a polylactic acid resin.
The polylactic acid-based resin is a polymer containing 50% by weight or more of lactic acid monomer units, and is a copolymer of polylactic acid and a compound selected from the group consisting of lactic acid and other hydroxycarboxylic acids and lactones. It is a composition containing mainly a polymer or a polymer containing 50% by weight or more of lactic acid monomer units.
When the content of the lactic acid monomer unit is less than 50% by weight, the heat resistance and mechanical strength of the foam tend to be lowered. A copolymer containing 80% by weight or more of lactic acid monomer units is preferred, and a copolymer containing 90% by weight or more of lactic acid monomer units is more preferred.
[0007]
The ratio of the L-lactic acid monomer unit to the D-lactic acid monomer unit in the polylactic acid resin of the present invention is measured by raising the temperature from 0 ° C. to 200 ° C. with a differential scanning calorimeter (DSC) described later. At which the heat of crystal fusion ΔHm existing between 100 ° C. and 200 ° C. is 30 J / g or more and reaches the crystal heat of fusion corresponding to 50% of ΔHm (T₅₀) And the temperature that reaches 70% of the crystal melting heat (T₇₀) Difference (T)₇₀-T₅₀) Is 6 ° C or higher, preferably 8 ° C or higher.
Examples of lactic acid include L-lactic acid and D-lactic acid.
Examples of other hydroxycarboxylic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid and the like.
Examples of lactones include glycolide, lactide, β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, and lactones substituted with various groups such as a methyl group.
Among the above compounds copolymerized with lactic acid, preferred are unsubstituted lactones such as glycolide, β-propiolactone, γ-butyrolactone, δ-valerolactone, and ε-caprolactone, particularly preferably ε- Caprolactone.
[0008]
As a polymerization method of the polylactic acid resin, known methods such as a condensation polymerization method and a ring-opening polymerization method can be employed.
Also, increase molecular weight by using binders such as polyepoxy compounds, polycarboxylic anhydrides, polycarboxylic acid chlorides, polyamines, polyvalent carboxylic acid alkyl esters, silicon tetrachloride and other polyfunctional silicon compounds It is also possible to use a method of
The weight average molecular weight of the polylactic acid resin is preferably in the range of 20,000 to 1,000,000, more preferably in the range of 40,000 to 800,000.
[0009]
In addition to the above resins, the polylactic acid-based resin expandable particles of the present invention include plasticizers, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, lubricants, mold release agents, nucleating agents, crystals. It is possible to mix | blend well-known additives, such as a chemical accelerator, in the range which does not impair the requirements and characteristics of this invention.
That is, as the antioxidant, hindered phenol antioxidants such as Pt butylhydroxytoluene and Pt butylhydroxyanisole;
Sulfur-based antioxidants such as distearyl thiodipropionate and dilauryl thiodipropionate;
Examples of heat stabilizers include triphenyl phosphite, trilauryl phosphite, and trisnonyl phenyl phosphite;
Examples of ultraviolet absorbers include 2-hydroxy-4-methoxy-2'-carboxybenzophenone, 2,4,5-trihydroxybutyrophenone, Pt butylphenyl salicylate;
[0010]
Lubricants include calcium stearate, zinc stearate, barium stearate, etc .;
Antistatic agents include N, N-bis (hydroxyethyl) alkylamine, alkylamine, alkylallyl sulfonate, alkyl sulfonate, etc .;
Examples of the flame retardant include hexabromocyclododecane, tris- (2,3-dichloropropyl) phosphate, pentabromophenyl allyl ether, etc .;
Examples of foam nucleating agents include calcium carbonate, silica, titanium dioxide, talc, and mica alumina;
Examples of the crystal accelerator include polyethylene terephthalate.
[0011]
In the polylactic acid resin used in the present invention, the temperature is 190 ° C. and the shear rate is 100 sec.^-1The melt viscosity under the conditions of 1 × 10²~ 1x10^FivePa · s
Preferably 5 × 10²~ 5x10^FourPa · s.
Melt viscosity is 1 × 10²If it is less than Pa · s, the viscosity becomes too low, and the closed cell ratio of the obtained foamed particles becomes low, and it becomes difficult to obtain a good foam. On the other hand, the melt viscosity is 1 × 10^FiveWhen Pa · s is exceeded, the viscosity is too high, so bubbles cannot grow and it becomes difficult to form a good foam.
In the present invention, the melt viscosity of the polylactic acid resin was measured using “Capillograph 1C-PDM-C” manufactured by Toyo Seiki Seisakusho.
[0012]
In addition, the polylactic acid resin used in the present invention has a crystal melting heat ΔHm of 30 J / ° C. existing between 100 ° C. and 200 ° C. when measured by raising the temperature from 0 ° C. to 200 ° C. with a differential scanning calorimeter (DSC). The temperature at which the heat of crystal fusion reaching 50% of ΔHm is reached (T₅₀) And the temperature that reaches 70% of the crystal melting heat (T₇₀) Difference (T)₇₀-T₅₀) Must be 6 ° C. or higher. ΔHm is preferably 40 J / g or more.
When ΔHm is less than 30 J / g, it is advantageous when foam molding is performed at 100 ° C. or less, but the resulting molded product is, for example, a molded product that tends to soften and melt when in contact with hot water near 100 ° C. and has poor heat resistance. It tends to be. Therefore, in order to obtain a heat resistance of 100 ° C. or higher, ΔHm needs to be 30 J / g or higher.
However, if ΔHm is 30 J / g or more, the temperature dependence of the melt viscosity of the polylactic acid resin in the vicinity of the melting point becomes large, and a sudden drop in viscosity occurs at a temperature above the melting point. When molding inside, it is difficult to adjust the temperature for maintaining the melt viscosity in a state suitable for foaming, and it becomes difficult to obtain a good molded product.
[0013]
Therefore, in order to prevent this sudden decrease in viscosity and to easily adjust the temperature to maintain the melt viscosity in a state suitable for foaming, the heat of crystal fusion corresponding to 50% of ΔHm when measured by raising the temperature is used. Reaching temperature (T₅₀) And the temperature that reaches 70% of the crystal melting heat (T₇₀) Difference (T)₇₀-T₅₀) Must be 6 ° C. or higher. Preferably (T₇₀-T₅₀) Is 8 ° C. or higher.
As can be seen from the above, ΔHm is 30 J / g or more and (T₇₀-T₅₀) Is less than 6 ° C., it becomes difficult to adjust the temperature to maintain the melt viscosity in a state suitable for foaming, and it becomes difficult to obtain a good molded product.
T₅₀~ T₇₀The reason why the temperature range is suitable for in-mold foam molding is that uniform foaming cannot occur in a molten state of less than 50% of the resin, and fusion between particles is extremely severe in a molten state of more than 70%. This is because the shape of particles that progress or flow violently and have a well-structured cell structure cannot be maintained.
[0014]
The crystal melting heat quantity ΔHm existing between 100 ° C. and 200 ° C. when measured by raising the temperature from 0 ° C. to 200 ° C. can be obtained by differential scanning calorimetry.
ΔHm is the amount of heat required to melt all the crystals when the temperature of the resin sample is raised at a rate of temperature increase of 10 ° C./min. From the area of the endothermic peak due to crystal melting that appears near the crystalline melting point of the polylactic acid resin. Desired.
Further, the temperature (T) that reaches the heat of crystal fusion corresponding to 50% of ΔHm.₅₀) And the temperature that reaches 70% of the crystal melting heat (T₇₀) And the difference (T₇₀-T₅₀) Is also obtained from the above differential scanning calorimetry.
As an example, in FIGS.₅₀, T₇₀And the difference (T₇₀-T₅₀1 to 3 are shown in FIGS.₇₀-T₅₀) Is an example (example) of 6 ° C. or higher, and FIG. 4 is an example (comparative example) of less than 6 ° C., and the shape of the curve is not limited to only these examples.
1 to 4 are graphs for explaining how to obtain the crystal melting endothermic curve measured by DSC, and the total area of the portion surrounded by the crystal endothermic curve obtained by DSC and the baseline corresponds to ΔHm. T₅₀The area on the left side (low temperature side) of the portion divided by 2 becomes 50% of ΔHm, and T₇₀So that the area on the left side of the portion divided by 2 becomes 70% of ΔHm.₅₀, T₇₀Is required.
[0015]
As a method for increasing ΔHm in the present invention, for example, (I) LH / D-lactic acid copolymer composition is brought close to 50/50 to 100/0 or 0/100 to increase the crystallinity of the resin, thereby increasing ΔHm. How to enlarge,
(2) A method of increasing ΔHm by decreasing the comonomer content in the polylactic acid resin to increase the crystallinity,
(3) There are a method of increasing ΔHm by annealing a polylactic acid resin at a temperature below the melting point to increase ΔHm, and a method of combining them.
[0016]
Also, (T₇₀-T₅₀) Is increased by (I) a method of blending a plurality of polylactic acid resins having different melting points so that the crystal melting endothermic curve of the resin at 100 ° C. or higher has a gentle peak,
(2) There is a method of making a curve having a plurality of peaks, but it is not limited to these.
Preferably, a resin obtained by blending a polylactic acid resin having a plurality of melting points in the polymerization machine as described above at the time of polymerization and having a plurality of resin components mixed more uniformly is used.
These DSC measurements were performed using a differential scanning calorimeter, “DSC-7”, manufactured by Perkin-Elmer, Inc., and about 10 mg of sample was raised from 0 ° C. to 200 ° C. at a rate of 10 ° C./min. Measured by warming.
[0017]
The polylactic acid-based resin expandable particles of the present invention do not use polyisocyanate by satisfying the above-mentioned requirements, have good expandability while being non-crosslinked particles, and have a practically sufficient buffer performance. Although it is an inner foamed molded article, the advantages of being non-crosslinked are (a) raw materials that a crosslinking operation and a crosslinking agent can be omitted, and (b) cost merit in terms of productivity.
[0018]
The method for molding expandable particles of the present invention is as follows. (I) A polylactic acid resin is heated and melted in an extruder, and after melting, a foaming agent is injected into the extruder, and the resin and the foaming agent are mixed well and then extruded. A method of extruding resin into cold water from a machine, quenching, pelletizing, and
(2) The resin is extruded and pelletized without injecting the foaming agent, and the particles are dispersed in a dispersion medium in the presence of the foaming agent in a sealed container, and the contents are heated to soften the particles to make the particles inside. (2) is more suitable as a method for obtaining expandable particles for in-mold foaming.
Here, the average particle diameter before foaming of the expandable particles of the present invention is preferably 0.1 mm to 20 mm, and more preferably 0.4 mm to 10 mm.
[0019]
The foamable particles of the present invention containing a foaming agent are usually pre-foamed by heating to a foaming ratio of 3 times or more by primary foaming, and then filled into a mold and further heated to form a foaming particle. Subsequent foaming can produce a foamed molded article with a high expansion ratio.
As a foaming agent used by this invention, it is necessary to have the boiling point below the melting | fusing point or softening point of polylactic acid-type resin.
For example, there are volatile blowing agents such as propane, butane, pentane, hexane, cyclobutane, cyclohexane, trichlorofluoromethane, 1,2,2,2-tetrafluoromethane, etc., but there is no destruction of the ozone layer and it is preferable from the viewpoint of handling. Those are butane, pentane and hexane.
[0020]
The volatile foaming agent is used in an amount of 0.5 to 40 parts by weight with respect to 100 parts by weight of the polylactic acid resin. Preferably, 2 to 20 parts by weight are used.
If the amount is less than 0.5 parts by weight, a foam having a sufficient expansion ratio cannot be obtained. If the amount exceeds 40 parts by weight, molding becomes difficult, and the resulting foam is unpractical.
As the inorganic foaming agent, water, nitrogen, carbon dioxide, argon, air and the like are used, but water, nitrogen, carbon dioxide and air which are inexpensive inorganic foaming agents are preferable.
When using a gaseous foaming agent at room temperature such as air, the amount used is 20-60 kgf / cm.²What is necessary is just to inject and pressurize a foaming agent to an airtight container so that it may become the pressure range of G.
In addition, for the purpose of adjusting the generation state of bubbles, for example, inorganic powders such as talc and silicon oxide; organic fine powders such as zinc stearate and calcium stearate; and further decomposition by heating such as citric acid and sodium bicarbonate. A bubble nucleating agent such as fine powder that generates gas may be added as necessary.
[0021]
In addition, the foamable particles of the present invention are once heated and foamed and then cooled, and then the foam is heated and foamed again in a state where the air is filled with air, thereby obtaining a foam having a higher magnification than that obtained by one foaming.
In general, one heating foaming expands to about 2 to 60 cc / g. However, by heating and foaming many times, foaming of 90 cc / g or more is possible.
The foamed particles of the present invention are subjected to primary foaming to a foaming ratio of 3 times or more, and the dried and aged product is filled in a mold and further heated with water vapor or the like, so that the foamed molded article having a high foaming ratio as usual. Can be obtained.
In this case, electrical equipment, computers, precision equipment such as watches, optical equipment such as glasses and microscopes, other fragile items such as ceramics and glass products, etc. are transported and stored, so that external shocks are reduced and the product is damaged. Effective as a cushioning material used to prevent failure, and as a foam container and foam molded body for keeping warm and cold for fish, vegetables, meat, foodstuffs, medical products, cup ramen containers, etc. It becomes.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be explained by examples and comparative examples.
First, evaluation methods used in Examples and Comparative Examples will be described below.
(1) Melt viscosity
Melt viscosity was measured using a Capillograph 1C-PMD-C manufactured by Toyo Seiki Seisakusho, using a nozzle with a nozzle diameter of 1.0 mm and L / D = 10 at 190 ° C., and a shear rate of 100 sec.^-1The melt viscosity at was measured.
(2) Weight average molecular weight
Water permeation gel permeation chromatography (GPC) was used, and chloroform was used as a solvent and the concentration of the sample chloroform solution was 1 mg / 1 cc. The solvent temperature was 40 ° C. and the solvent flow rate was 1 ml / min.
The weight average molecular weight was calculated in terms of polystyrene using standard polystyrene.
(3) Heat of crystal melting ΔHm, T₅₀, T₇₀
Using a differential scanning calorimeter (DSC) manufactured by Perkin-Elmer, “DSC-7”, a sample of about 10 mg was heated from 0 ° C. to 200 ° C. at a rate of 10 ° C./min. ΔHm, T₅₀, T₇₀Was measured.
[0023]
(4) Foaming ratio
The foaming ratio of the foam was evaluated by measuring the volume V (cc) of the foam having a known weight W (g) by a submersion method and dividing the volume by the weight to obtain V / W (cc / g).
(5) In-mold formability
The degree of fusion of the molded product obtained by in-mold foaming and the dimensional shrinkage against the mold were evaluated according to the following criteria.
That is, when a particularly good foamed molded product is obtained in both the degree of fusion and the dimensional shrinkage ratio to the mold, ◯ when both are equally good, △ when either is △, both are △ or × In the case of, it was evaluated as x.
(6) Heat resistance
A cup-shaped foamed molded article having a thickness of 2 mm and an internal volume of about 200 cc was molded, hot water at 100 ° C. was poured into this, and the degree of deformation of the container after 30 minutes was evaluated.
The case where the container was hardly deformed was evaluated as ◯, the case where there was deformation but no water spilled was evaluated as Δ, and the case where deformation was severe and water spilled was evaluated as x.
(7) Biodegradability test
The in-mold foam-molded product is cut into a plate with a thickness of about 1 mm, and about 0.1 g is sandwiched between stainless steel 0.3 mm mesh net-like sample holders and buried in a depth of about 10 cm in the ground. The weight of the sample remaining after a lapse of months was measured.
Those having a residual rate of 40% or less were evaluated as “◯”, those having a residual rate of 40 to 90% as “Δ”, and those having a residual rate of 90% or higher as “X”.
[0024]
The polylactic acid-based resins in the following examples and comparative examples are obtained by directly using L-lactic acid and D-lactic acid with tin powder as a catalyst according to the method described in JP-A-6-65360 for lactic acid homopolymers. Polylactic acid polymers were obtained by condensation (Polymers A to E and L in Table 1).
Moreover, about a copolymer, Journal of Polymer Science: PartB: Polymer Physics, Vol. 32, 2481-2489 (1994), a copolymer of L-lactide, D-lactide and ε-caprolactone was synthesized using a tin octoate catalyst, and adipic acid chloride was further used. Then, a coupling reaction was performed to obtain a polylactic acid polymer such as polymers F to K in Table 1.
In the following examples and comparative examples, all were carried out using the polylactic acid resin in Table 1.
[0025]
Example 1
Polymers A, C, and E in Table 1 were melt-kneaded using a twin screw extruder at the composition ratio shown in Table 2, extruded into strands, cooled with water, and particles having a diameter of 0.7 mm and a length of 1.3 mm Cut into shape.
Next, 100 parts by weight of the obtained resin particles and 300 parts by weight of water are charged into a 5 liter pressure vessel, the resin particles are heated to 80 ° C., and carbon dioxide gas is supplied at an internal pressure of 30 kg / cm.²It was press-fitted until G and impregnated. Thereafter, the foamable particles are taken out, transferred to a foaming apparatus, the temperature in the tank is increased from 80 ° C. to the foaming temperature over 20 seconds, and further heated with water vapor for 10 seconds while maintaining the temperature. Obtained.
The foaming temperature is T of the polymer in Table 2.₅₀, T₇₀, And the value of ΔHm was referred to in advance to find the optimum condition and adopted.
And the condition which becomes close to 4 cc / g which is the magnification which is the target magnification of the primary foamed particles and has a high closed cell ratio and a uniform cell diameter was defined as the optimum foaming temperature of the polymer.
Table 2 shows the expansion ratio of the primary expanded resin particles thus obtained.
[0026]
Next, the obtained primary expanded particles were dried and aged at 60 ° C. for 24 hours, filled in a mold having an internal space dimension of 200 mm in length, 100 mm in width and 20 mm in height, and heated at a temperature shown in Table 2 using steam. The foamed molded product thus obtained was cured at 60 ° C. under atmospheric pressure for 24 hours. Table 2 shows the expansion ratio of the obtained foamed molded product.
The heat resistance was evaluated by using a cup obtained by molding with a mold capable of obtaining a cup-shaped molded body having an internal volume of about 200 cc and a thickness of 2 mm in the same manner as above.
The evaluation results are shown in Table 2. The biodegradability test results are also shown in Table 2.
It is apparent that the primary expanded particles of this example achieve a high expansion ratio in the mold, have good moldability, heat resistance to hot water, and biodegradability.
[0027]
(Examples 2 to 7)
In Examples 2 to 7, primary foamed particles were prepared in the same manner as in Example 1 except that the polymers listed in Table 2 were used, and in-mold foam molded articles were obtained in the same manner.
The melt viscosity, crystal melting heat quantity ΔHm and T of the polymer used at that time₅₀, T₇₀Table 2 shows the expansion ratio of the primary expanded particles, the expansion ratio of the in-mold foam molding, the in-mold moldability, the heat resistance, and the biodegradability test results.
It is clear that the primary expanded particles of Examples 2 to 7 achieve a high expansion ratio, have good moldability, heat resistance against hot water, and also have biodegradability.
[0028]
(Comparative Examples 1-5)
In Comparative Examples 1 to 5, primary foam particles were molded in the same manner as in Example 1 except that the polymers listed in Table 2 were used, and in-mold foam molding was performed in the same manner as in Example 1. Carried out.
Further, the melt viscosity, heat of crystal melting ΔHm and T₅₀, T₇₀Table 2 shows the expansion ratio of the primary expanded particles, the expansion ratio of the in-mold foam molding, the in-mold moldability, the heat resistance, and the biodegradability test results.
In Comparative Example 1, the optimum foaming temperature condition was not obtained during primary foaming, and primary foamed particles were not stably obtained. In Comparative Example 2, temperature control in in-mold foam molding was difficult, the foaming ratio was low, and in-mold moldability was also poor.
In Comparative Examples 3 and 4, foaming is possible at 100 ° C. or lower, and when foaming is performed with water vapor at 100 ° C. in the mold, the fusion between the particles proceeds excessively, the moldability in the mold is Δ, and The heat resistance against hot water was also poor.
In Comparative Example 5, the melt viscosity was too low and the gas escaped during the primary foaming, and a foam was not obtained.
[0029]
[Table 1]

[0030]
[Table 2]

(Note) * 1; Optimal foaming temperature conditions cannot be obtained. * 2: No foam was obtained.
[0031]
【The invention's effect】
The polylactic acid-based resin foamable particles according to the present invention are biodegradable, can solve the plastic waste problem, have excellent in-mold moldability, and have practically excellent buffer performance and heat resistance to hot water after foam molding. It is a very useful foamable particle that can form an in-mold foam-molded article having the properties.
[Brief description of the drawings]
FIG. 1 T measured by DSC₅₀= 152 ℃, T₇₀= 158 ℃, (T₇₀-T₅₀) = Graph (Example) for explaining a crystal melting endothermic curve in the case of 6 ° C.
FIG. 2 T measured by DSC₅₀= 151 ℃, T₇₀= 158 ℃, (T₇₀-T₅₀) = Graph (Example) for explaining a crystal melting endothermic curve in the case of 7 ° C.
FIG. 3 T measured by DSC₅₀= 148 ℃, T₇₀= 157 ° C, (T₇₀-T₅₀) = Graph (Example) for explaining the crystal melting endothermic curve in the case of 9 ° C.
FIG. 4 T measured by DSC₅₀= 153 ℃, T₇₀= 157 ° C, (T₇₀-T₅₀) = Graph (comparative example) for explaining a crystal melting endothermic curve in the case of 4 ° C.

Claims (4)

A polylactic acid resin containing 50% by weight or more of a lactic acid monomer unit having a melt viscosity of 1 × 10 ² to 1 × 10 ⁵ Pa · s at a temperature of 190 ° C. and a shear rate of 100 sec ⁻¹ , and a differential scanning calorimeter (DSC) When the temperature is raised to 0 ° C. to 200 ° C. and measured, the heat of crystal fusion ΔHm existing between 100 ° C. and 200 ° C. is 30 J / g or more, and reaches the heat of crystal fusion corresponding to 50% of ΔHm. It consists of a polylactic acid resin and a foaming agent, characterized in that the difference (T ₇₀ -T ₅₀ ) between the temperature (T ₅₀ ) and the temperature (T ₇₀ ) that reaches the heat of crystal melting corresponding to 70% is 6 ° C. or more. Non-crosslinked polylactic acid resin foamable particles. When the polylactic acid-based resin is measured by raising the temperature from 0 ° C. to 200 ° C. with a differential scanning calorimeter (DSC), the crystal melting heat ΔHm existing between 100 ° C. and 200 ° C. is 30 J / g or more, and The difference (T ₇₀ -T ₅₀ ) between the temperature (T ₅₀ ) that reaches 50% of ΔHm and the temperature (T ₇₀ ) that reaches 70% of the crystal melting heat is equal to or higher than 8 ° C. The expandable particle according to claim 1. A polylactic acid resin containing 50% by weight or more of a lactic acid monomer unit having a melt viscosity of 1 × 10 ² to 1 × 10 ⁵ Pa · s at a temperature of 190 ° C. and a shear rate of 100 sec ⁻¹ , and a differential scanning calorimeter (DSC) When the temperature is raised to 0 ° C. to 200 ° C. and measured, the heat of crystal fusion ΔHm existing between 100 ° C. and 200 ° C. is 30 J / g or more, and reaches the heat of crystal fusion corresponding to 50% of ΔHm. It consists of a polylactic acid resin and a foaming agent, characterized in that the difference (T ₇₀ -T ₅₀ ) between the temperature (T ₅₀ ) and the temperature (T ₇₀ ) that reaches the heat of crystal melting corresponding to 70% is 6 ° C. or more. A foam molded article obtained by heating and foaming non-crosslinked polylactic acid resin foamable particles. When the polylactic acid-based resin is measured by raising the temperature from 0 ° C. to 200 ° C. with a differential scanning calorimeter (DSC), the crystal melting heat ΔHm existing between 100 ° C. and 200 ° C. is 30 J / g or more, and The difference (T ₇₀ -T ₅₀ ) between the temperature (T ₅₀ ) that reaches 50% of ΔHm and the temperature (T ₇₀ ) that reaches 70% of the crystal melting heat is equal to or higher than 8 ° C. . The foaming molding of Claim 3.

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