JP3737396B2 - Expanded particles and molded bodies - Google Patents

Description

【００４５】
【表２】

【００４６】
評価結果
実施例１〜７は発泡倍率４５倍以上であり、生分解性、軽量性、成形性、２次加工性に優れ、発泡ポリエチレン並みの物性（柔軟性、緩衝性）を有するため、発泡ポリエチレンを使用している緩衝材に適用できる。一方、４５倍未満のポリ乳酸系樹脂からなる発泡粒子の成形体は（比較例１、２）、柔軟性、緩衝性が不十分であり、発泡ポリエチレンを使用している緩衝材の代替用途には適用できない。また、比較例４の発泡ポリエステルは成形性、２次加工性が不良であり、発泡ポリエチレンを使用している緩衝材の代替用途には適用できない。
【００４７】
【発明の効果】
本発明のポリ乳酸系樹脂を主成分とする発泡倍率４５倍以上の発泡粒子の成形体は、生分解性、軽量性、成形性、２次加工性に優れ、発泡ポリエチレン並みの物性（柔軟性、緩衝性）を有するため、広く梱包材として適用でき、地球環境保全に資する発泡体である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to expanded particles and molded bodies used as cushioning materials for packaging having biodegradability.
[0002]
[Prior art]
Plastic foams that take advantage of lightness, shock-absorbing properties, and moldability are used in large quantities as packaging and packaging materials, but the materials are chemical products made from petroleum such as polystyrene (PS) and polyolefin. For this reason, disposal after use is difficult, and even if incinerated, the calorie burned is high, and it will not decompose even if it is incinerated or landfilled, and it will occupy the space of the disposal site because it has a large volume It has become a big social problem.
[0003]
In addition, the influence of natural foams, such as rivers and oceans, caused by foams that have been discarded without being disposed of has become impossible to ignore. Therefore, a resin was developed that decomposes in the ecosystem and has little adverse effect on the global environment.
[0004]
As a biodegradable material, glycolic acid and lactic acid are also obtained by ring-opening polymerization of glycolide and lactide, and using such a polymer, a biodegradable foamed resin composition having practically sufficient productivity has been found. An invention proposal (Japanese Patent Application No. 9-314479) was made. The foamed particles or molded product obtained from the foamed resin composition obtained in the present invention had good moldability and secondary processability, and could be used satisfactorily as a normal packing cushioning material.
However, the foamed molded article in the above invention has insufficient physical properties in a cushioning material (for example, an alternative use of foamed polyethylene) that particularly requires flexibility, buffering properties, etc., because the expansion ratio of the foamed particles is low. Was restricted.
[0005]
[Problems to be solved by the invention]
The object of the present invention is to provide a foamed molded article having light weight and physical properties (flexibility, cushioning properties, etc.) similar to foamed polyethylene, secondary processability, biodegradability and low environmental impact. It is in.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to solve such problems, the present inventors have succeeded for the first time in producing polylactic acid-based expanded particles having an expansion ratio of 45 times or more, and the above object is achieved by making this into a molded body. The present invention has been found and the present invention has been completed.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The polylactic acid-based expanded particles having an expansion ratio of 45 times or more according to the present invention can be achieved not only by the foaming method but also by a combination with the properties of the resin composition used. For example, based on the resin composition described below, (1) a method of pre-foaming by impregnating a foaming agent, a foaming aid and the like, followed by dry heat treatment, (2) a gas having a low boiling point such as propane as a foaming agent And (3) a method of impregnating a foaming agent and a foaming aid, foaming under reduced pressure, cooling to Tg of the resin or lower, and gradually returning to normal pressure.
[0008]
The resin composition that is the basis of the 45-fold expanded particles will be described in detail below.
The polylactic acid that is the basis of the resin composition preferably used in the present invention is a substantially amorphous polylactic acid, that is, a polylactic acid having a heat of fusion (2nd scan ΔH) of 0.1 J / g or less as measured by DSC. Lactic acid having a molar ratio of L-form to D-form of 95/5 to 5/95, more preferably 92/8 to 8/92. This is because when the molar ratio of L-form / D-form is within this range, the foaming ratio is easily increased and foaming becomes uniform because of low crystallinity.
[0009]
Moreover, it is preferable that polylactic acid is high molecular weight, It is the range of 1-10 by the melt index value (MI) based on JISK7210 (load 21.18N), More preferably, it is the range of 1-5. .
The reason for this is that when the MI is in the above range, when an ultrahigh viscosity resin is obtained by reacting with the polyisocyanate described below, an appropriate crosslinking density is obtained and a crosslinked structure suitable for foaming is obtained.
[0010]
As a means to obtain such a high melt viscosity polylactic acid, melt polymerization with good stirring efficiency under high vacuum in a normal reaction vessel, melt polymerization with a biaxial kneading reactor, melt polymerization and solid phase polymerization However, due to its high viscosity, it is necessary to pay sufficient attention to the reduction in productivity due to a reduction in reaction cycle and the reduction in quality due to thermal decomposition of the resin.
[0011]
However, even if the above-mentioned polylactic acid is impregnated with foaming agent and foamed, it is difficult to increase the expansion ratio, and it cannot be practically used. In order to obtain a high expansion ratio, a resin having a higher melt viscosity is required, and there is a limit to mere polymerization.
[0012]
To further increase the viscosity, 0.1 to 5% by weight, preferably 1 to 3% by weight of a polyisocyanate having an isocyanate group ≧ 2.0 equivalents / mol is mixed with the polylactic acid in a molten state and reacted. Further, it is achieved by gradually reacting with moisture in the solid state after melt-kneading and proceeding with crosslinking by allophanate bond or urea bond, and melt viscosity value according to JIS K 7210 (load 211.8N) ( It is possible to obtain a resin composition having good foamability in the range of MI) of 5 or less. When a polyisocyanate having an isocyanate group <2.0 equivalent / mol is used, the rise in melt viscosity is insufficient. When the polyisocyanate content is 0.1% by weight or more, the melt viscosity of the resin composition is likely to increase. When the polyisocyanate content is 5% by weight or less, there is little residual unreacted polyisocyanate, and there is little generation of gelled products that have undergone a crosslinking reaction. , Foaming becomes higher.
[0013]
As a method of mixing polylactic acid and polyisocyanate in a molten state, an ordinary known method can be used. For example, polyisocyanate is added to and mixed with pelletized polylactic acid, and melt-mixed with a single-screw or twin-screw kneader or the like. After polylactic acid is previously melted with a single-screw or twin-screw kneader or the like, polyisocyanate is added. Examples thereof include a method, a method of adding polyisocyanate when polylactic acid is produced by melt polymerization using a uniaxial or biaxial kneader or the like.
[0014]
Examples of the polyisocyanate used include aromatic, alicyclic and aliphatic polyisocyanates. Examples of the aromatic polyisocyanate include polyisocyanates having a skeleton of tolylene, diphenylmethane, naphthalene, tolidine, xylene and triphenylmethane. The cycloaliphatic polyisocyanate includes isophorone, polyisocyanate having a hydrogenated diphenylmethane skeleton, and the aliphatic polyisocyanate has a polyisocyanate having a skeleton of hexamethylene and lysine. From the viewpoint of properties and weather resistance, tolylene, diphenylmethane, particularly isocyanate having diphenylmethane as a skeleton is preferably used.
[0015]
In order to form uniform and fine foam cells, it is preferable to add a foam nucleating agent. As the foam nucleating agent to be used, solid particles such as talc, silica, kaolin, zeolite, mica and alumina are suitable. Among these, talc is preferably used for the resin composition of the present invention.
[0016]
Further, other additives can be appropriately added according to the purpose, and examples thereof include a heat stabilizer, an antioxidant, a flame retardant, an ultraviolet absorber, and a plasticizer. However, flame retardants are often halides such as chlorine and should be kept to a minimum from the viewpoint of biodegradability and generation of harmful substances during incineration.
[0017]
The resin composition thus obtained is made into pellets or beads, and then impregnated with a foaming agent and a foaming aid.
[0018]
Examples of the blowing agent used here include hydrocarbons such as n-butane, isobutane, n-pentane, isopentane, cyclopentane, and hexane, halogenated hydrocarbons such as methylene chloride, methyl chloride, and dichlorodifluoromethane, dimethyl ether, and methyl. Examples include ethers such as ethyl ether, and examples of foaming aids include alcohols having 1 to 4 carbon atoms, ketones, ethers, benzene, and toluene.
[0019]
The combination of the foaming agent and the foaming aid may be appropriately selected depending on the resin used. In the case of a polymer such as L-form / D-form copolymer polylactic acid used in the present invention, a low molecular weight alkane is preferably used as a foaming agent. 4 monohydric alcohols are preferred. There are various other combinations and can be selected in view of the purpose and economy.
[0020]
The use ratio of the foaming agent and the foaming aid can be foaming agent / foaming aid = 1/2 to 20/1, but this ratio varies depending on the combination of the foaming agent and the foaming aid. / 1 is common.
[0021]
The size and shape of the pellets and beads impregnated with the foaming agent or foaming aid can be appropriately selected as necessary, but those having a diameter of 0.5 to 2 mm are usually used. In the case of a precise molded body, particles having a diameter of 0.5 to 1 mm are preferable.
[0022]
Usually, particles impregnated with a foaming agent are foamed by heating. In this case, the foaming ratio is several to 40 times, and even if this is molded, a molded product having the same performance as a polystyrene foam can be obtained. A molded article having high flexibility and high buffering performance comparable to polyethylene could not be obtained.
[0023]
As a result of intensive studies, the inventors of the present application have succeeded in producing pre-foamed particles having a foaming ratio exceeding 45 times by further subjecting the above-mentioned foamed particles to dry heat treatment, and by molding this, foamed polyethylene is obtained. A polylactic acid-based foamed molding having comparable flexibility and buffering performance has been obtained.
[0024]
Any known method and apparatus for heat treatment of the expanded particles used in the present invention can be used, but an apparatus that can be heat-treated with temperature-controlled hot air is preferred. Examples thereof include an oven and a hopper dryer. The temperature of the heat treatment is preferably 40 to 70 ° C., more preferably 50 to 60 ° C., and the heat treatment time is usually several minutes to several days, although it varies depending on the apparatus and the expansion ratio.
[0025]
In addition, as a result of further investigation on a method for obtaining a foaming ratio of 45 times or more, as a foaming agent, propane, which is rarely used because of its volatility and difficulty in handling, is used as a foaming agent, and preliminary foaming is reduced in pressure. It was found that 45-fold or more expanded particles can be obtained by a method of performing under an environment, cooling to Tg of the resin or lower, and gradually returning to normal pressure, and molding these to obtain similar molded bodies.
[0026]
Any known decompression method and apparatus for prefoaming can be used in the present invention. For example, the pressure in the pre-foaming machine is reduced to 0 to 0.1 MPa before foaming, and after foaming at a foaming ratio of 45 times or more with water vapor, Tg or less of the foamed particles (in the case of polylactic acid resin, usually 60 ° C. or less) This can be achieved by cooling to room temperature and gradually returning to normal pressure.
[0027]
The bulk density of the molded product obtained by molding the expanded particles of the present invention is preferably 0.030 g / cm ³ or less, more preferably 0.025 g / cm ³ . It is because it is excellent in a softness | flexibility in it being 0.030 g / cm < ³ > or less.
[0028]
Further, the flexural modulus of the molded article (JIS K-7221) is, for the purpose of foamed polyethylene alternative, less preferred 9.80MPa in terms of flexibility, more preferably 7.85MPa or less, most preferably 5. 88 MPa or less.
[0029]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The evaluation was performed by the following method.
[0030]
(Evaluation methods)
(1) MI: Measured by a method based on JIS K7210.
(Measurement temperature: 190 ° C., orifice diameter: 2 mm, load: polylactic acid: 21.18 N, kneaded resin: 211.8 N)
[0031]
(2) Foaming ratio of the foamed particles: The bulk density (g / L) of the foamed particles was measured using a 1 L graduated cylinder and calculated as follows.
Expansion ratio (times) = 1000 / bulk density (g / L)
[0032]
(3) Bulk density of compact: 300 × 300 × 30 mm The weight and volume of the board were measured and calculated as follows.
Bulk density (g / cm ³ ) = weight (g) / volume (cm ³ )
[0033]
(4) Physical properties: Measured according to JIS.
Bending stress, initial elastic modulus: JIS K-7221
Dynamic buffer coefficient: JIS Z-0235
[0034]
(5) Biodegradability: A molded body of 30 × 30 × 30 mm was put in compost for 2 months, and the appearance was evaluated as follows.
○: Decompose until the original shape does not remain ×: No change at all [0035]
(6) Secondary workability: Using a 300 × 300 × 30 mm board, evaluation was made by punching workability and heat weldability by a dryer.
[0036]
Comparative Example 1
MI1.4, L / D = 88.5 / 11.5 polylactic acid (manufactured by Cargill Japan Co., Ltd.) and isocyanate compound “Millionate MR-200” (2.7 to 2.8 equivalents / mol of isocyanate groups, Japan) Polyurethane Industry Co., Ltd. 2.0% by weight and talc “LMP-100” (Fuji Talc Industrial Co., Ltd.) 3.0% by weight in a twin-screw kneader (TEM35B, Toshiba Machine Co., Ltd.) with a cylinder temperature of 185 The mixture was kneaded at 0 ° C. to obtain a pellet-shaped resin composition.
[0037]
After measuring MI of this resin composition, an autoclave was charged with 5000 parts of the resin composition, 2000 parts of isobutane as a foaming agent, and 240 parts of methanol as a foaming aid, sealed, heated, and held at 85 ° C. for 3 hours. . Then, after cooling at 25 ° C., the resin was taken out, air-dried, weighed, and the impregnation rate was determined. Next, the obtained foaming agent-impregnated pellets were prefoamed with water vapor (94 ° C., 1 minute) to obtain expanded particles, and the expansion ratio was evaluated.
[0038]
After aging for one day, the foamed particles were filled into a closed mold and molded by heating with a steam molding machine at a water vapor pressure of 0.07 MPa for 20 seconds to obtain a molded body of 300 × 300 × 30 mm. A test piece was cut out from the molded body and evaluated for biodegradability and physical properties. Moreover, secondary workability was evaluated using this molded object. The evaluation results are as shown in Tables 1 and 2.
[0039]
Examples 1-5
Except that the expanded particles of Comparative Example 1 were heat-treated in an oven at 50 ° C. for 1 hour (Examples 1 and 2), 2 hours (Example 3), 12 hours (Example 4), and 24 hours (Example 5), respectively. It implemented by the completely same method as the comparative example 1, and obtained the result of Tables 1 and 2.
[0040]
Comparative Example 2
The results of Tables 1 and 2 were obtained in the same manner as in Comparative Example 1 except that the addition amount of the isocyanate compound “Millionate MR-200” was changed to 1.0% by weight.
[0041]
Example 6
Except that the blowing agent was changed to propane, the same procedure as in Comparative Example 1 was performed, and the results shown in Tables 1 and 2 were obtained.
[0042]
Example 7
In the same manner as in Comparative Example 1, isobutane-impregnated expandable particles were obtained. 100 g of the expanded particles were put into a 20 L test foam container, and the inside of the container was evacuated to 0.07 MPa. Next, water vapor is introduced into the container and foamed at a stretch while maintaining at 85 ° C. for 1 minute, and then cooled to 25 ° C. with the inside of the container sealed, and the pressure inside the container is gradually brought to normal pressure over 24 hours. This was returned to obtain expanded particles.
The foamed particles were filled in a hermetically sealed mold and molded by heating with a steam molding machine at a water vapor pressure of 0.07 MPa for 20 seconds to obtain a molded body of 300 × 300 × 30 mm. A test piece was cut out from the molded body and evaluated for biodegradability and physical properties. Moreover, secondary workability was evaluated using this molded object. The evaluation results are as shown in Tables 1 and 2.
[0043]
Comparative Examples 3 and 4
A commercially available foamed polyethylene (Comparative Example 3) and a polyester foam (Comparative Example 4) composed of succinic acid and 1,4-butanediol were evaluated, and the results shown in Tables 1 and 2 were obtained.
[0044]
[Table 1]

[0045]
[Table 2]

[0046]
Evaluation results Examples 1 to 7 have an expansion ratio of 45 times or more, are excellent in biodegradability, lightness, moldability, secondary processability, and have physical properties (flexibility, buffering properties) similar to foamed polyethylene. Applicable to cushioning material using polyethylene. On the other hand, the molded article of expanded particles made of a polylactic acid resin less than 45 times (Comparative Examples 1 and 2) has insufficient flexibility and buffering properties, and can be used as an alternative to cushioning materials using expanded polyethylene. Is not applicable. Further, the foamed polyester of Comparative Example 4 has poor moldability and secondary processability, and cannot be applied to an alternative use for a cushioning material using foamed polyethylene.
[0047]
【The invention's effect】
The molded product of expanded particles having a foaming ratio of 45 times or more mainly composed of the polylactic acid-based resin of the present invention is excellent in biodegradability, lightness, moldability, and secondary processability, and has the same physical properties (flexibility as expanded polyethylene). Therefore, it is a foam that can be widely applied as a packaging material and contributes to global environmental conservation.

Claims (4)

A method for producing foamed particles by making a resin composition comprising polylactic acid into pellets or bead-like particles and then foaming the particles impregnated with a foaming agent and a foaming aid by heating to produce the foamed particles. A method for producing expanded particles having an expansion ratio of 45 times or more, wherein the particles are further subjected to a dry heat treatment. A method for producing foamed particles by making a resin composition comprising polylactic acid into pellets or bead-like particles and then foaming the particles impregnated with a foaming agent and a foaming aid by heating, wherein the foamed particles are prefoamed. In a reduced pressure environment, cooled to below Tg of the resin, and then gradually returned to normal pressure. A method for producing expanded particles having an expansion ratio of 45 times or more .   The manufacturing method of the molded object formed by shape | molding the expanded particle manufactured by the manufacturing method of Claim 1 or 2. The method for producing a molded body according to claim 3, wherein the bulk density of the molded body is 0.030 g / cm ³ or less.