JP2004107430A - Foam molded article and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cushioning material which comprises a polylactic acid-based resin foam, scarcely varies the dimension, even when exposed to the conditions of high temperature and high humidity, when transported, can easily be taken out from an outer package such as a cardboard box, and to provide a method for producing the same. <P>SOLUTION: This polylactic acid-based resin composition foam molded article is characterized by having the D- and L-isomers of the polylactic acid component constituting the polylactic acid-based resin composition in a D-isomer / L-isomer ratio of 8/92 to 92/8, an apparent specific gravity of ≤0.05 g/cm<SP>3</SP>, and a coefficient of cubic expansion of ≤15% at 60°C and at a relative humidity of 80% after a week. <P>COPYRIGHT: (C)2004,JPO

Description

【００４０】
実施例１〜４、比較例１〜２から明らかなように、Ｄ体比率が８％以下では、発泡は条件を工夫することによって可能となるものの、成形が困難である。また、実施例１〜３と比較例３および比較例４〜７より、有機過酸化物単独では、添加量を単に増加させても発泡せず、イソシアネート単独では発泡はしても高温高湿下での体積膨張率が著しく大きく、見かけ比重０．０５ｇ／ｃｍ^３以下の高倍率発泡と高温高湿下における寸法安定性の両立には有機過酸化物と末端反応型架橋剤の併用が必須であることが明かである。また、実施例４，６および実施例７〜９から、有機過酸化物と末端反応型の架橋剤は添加順によらずほぼ同等の性能が得られるが、これらを同時添加した場合の架橋構造を制御することは、２軸混練機によるドライプロセスでは困難であることがわかる。
【００４１】
次に、実施例２および比較例３の発泡粒子を用いて、ＶＨＳビデオデッキの緩衝材を成形し、発泡スチロールの緩衝材の代りに用いて元の包材に格納した。これを６０℃、８０％ＲＨで１週間処理した後、ビデオデッキを取出そうとしたところ、実施例２の成形品を用いた方は容易に取出すことができたが、比較例４の成形品を用いた方は段ボール箱が樽型に変形するほど膨脹しており、段ボール箱を破壊しないと取出せなかった。
【００４２】
【発明の効果】
このように、本発明の製造方法に基づき適正な処方を選択することによって、４０倍近い発泡倍率（見かけ比重０．０２５ｇ／ｃｍ^３）でありながら、高い寸法安定性を確保する事が可能となり、該発泡成形体を緩衝材として用いることにより、高温高湿下に曝される輸送条件に曝される用途にも対応できるポリ乳酸系樹脂発泡緩衝材が得られる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a foamed molded article which is biodegradable and has excellent durability under high-temperature conditions, particularly excellent dimensional stability, and a method for producing the same.
[0002]
[Prior art]
Conventionally, foamed polystyrene has been mainly used as a cushioning material for home electric appliances and the like. However, polystyrene has a very high heat of combustion of 40.2 kJ / g, and when burned in a general incinerator, the furnace is damaged. In addition, they tend to be shunned because they use limited petroleum resources as raw materials. In recent years, based on these circumstances, a trade association has been established for the purpose of recycling, and attempts have been made for material recycling.However, the use of material recycling is slow and the collected items are stagnant. It is the current situation.
[0003]
As a recently proposed buffer foam that can be disposed of by incineration in old incinerators with low heat of combustion or buried in the soil or composted, the condensation of aliphatic dicarboxylic acids and diols A foam using the obtained biodegradable aliphatic polyester as a raw material has been proposed, and although this foam has biodegradability,
(1) Even under normal use conditions, the degradation progresses due to resident bacteria, so the service life varies significantly depending on the use environment.
{Circle around (2)} Although it has flexibility, it has a low load-bearing capacity and is not suitable as a substitute for a cushioning material requiring a load-bearing capacity comparable to that of styrene foam.
There is a disadvantage that. In addition, since it uses fossil resources as raw materials, it is no different from polyethylene or polystyrene from the viewpoint of protecting global resources and protecting the environment.
[0004]
On the other hand, in WO99 / 21915, foamed particle molded products using polylactic acid as a main raw material have been proposed, and these foamed molded products are obtained by lactic acid fermentation of starch, a non-petroleum resource, by lactic acid fermentation. Since it is used as a raw material, it does not biodegrade under normal use conditions, but it can be composted, has a load resistance and cushioning property comparable to styrene foam, and has excellent heat resistance at high temperatures (60 ° C.). However, it has poor heat resistance in the cargo space at the time of export, which is hot and humid, and in the enclosed space under the hot sun in the summer, and its dimensional change is particularly remarkable at high foaming ratio. Absent. For this reason, the use of the foamed molded article has been limited to those that are not exposed to high temperature and high humidity.
[0005]
[Patent Document 1]
WO 99/21915 pamphlet [Patent Document 2]
Japanese Unexamined Patent Publication No. Hei 9-501456
[Problems to be solved by the invention]
The present invention has been made in view of the current situation as described above, and has a small dimensional change even when exposed to high-temperature and high-humidity conditions during transportation, and is a polylactic acid-based resin that can be easily taken out of an exterior such as a cardboard box. It was intended to provide a cushioning material made of a foam.
[0007]
[Means for Solving the Problems]
The present inventors have applied an organic peroxide to a polylactic acid-based resin having a D-form / L-form ratio of 8/92 to 92/8 of the polylactic acid component constituting the polylactic acid-based resin composition, By impregnating a foaming gas into a polylactic acid-based resin composition that has been treated with one or more of a polyfunctional isocyanate, a polyfunctional epoxy compound, and a polybasic anhydride, and foaming and molding, a high foaming ratio is obtained. Despite this, the inventors succeeded in suppressing the volume change under high temperature and high humidity conditions, and completed the present invention.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The polylactic acid resin used in the present invention contains at least 60 mol% of lactic acid as a monomer unit. If the ratio of the D-form or L-form of lactic acid is less than 8%, crystallization proceeds during pre-foaming and molding with steam (vapor pressure =＝ 150 kPa) becomes difficult, so that the D / L ratio of the polylactic acid-based resin is It is necessary to be 8/92 to 92/8.
[0009]
The polylactic acid-based resin composition constituting the polylactic acid-based resin foam molded article used in the present invention is not particularly limited as long as the composition contains the polylactic acid-based resin in an amount of 51% or more. The preferred content of the polylactic acid-based resin is 70% or more.
[0010]
The polylactic acid-based resin composition of the present invention, as long as it can be compounded with the polylactic acid-based resin as a main component, a desired foaming ratio and moldability, as long as it does not impair the other compostable synthetic polymer, Natural polymers and their derivatives may be mixed.
[0011]
Compoundable synthetic polymers include, for example, polyvinyl acetate, vinyl resins such as polyvinyl alcohol, polyethylene glycol, polyethylene succinate, polyethylene succinate adipate, polybutylene succinate, polybutylene succinate adipate, polymalic acid, and polymalic acid. Examples thereof include aliphatic polyesters such as glycolic acid, and aliphatic aromatic polyesters such as polyethylene terephthalate adipate, polybutylene terephthalate adipate, polybutylene terephthalate succinate, and polybutylene terephthalate succinate. Further, a resin obtained by blending or copolymerizing two or more of these resins, or a resin having a crosslinked thickened material may be used.
[0012]
Examples of natural polymers and derivatives thereof that can be mixed include cellulose, acetyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, ethyl cellulose, methyl cellulose, chitin, cellulose derivatives such as chitosan, poly-L-leucine, poly-L-lysine, and the like. Examples thereof include polyamides such as polyaspartic acid, and proteins of gelatin, collagen, gluten, and zein.
[0013]
To the polylactic acid-based resin composition used in the present invention, a bubble regulator (foam nucleating agent) such as an inorganic powder may be added for the purpose of making the foam cells uniform and forming pores. Specifically, talc, mica, clay mineral, calcium carbonate, sodium bicarbonate / citric acid, and the like can be used, but are not particularly limited thereto.
[0014]
The polylactic acid-based resin composition used in the present invention may be added with a coloring component or a component imparting functionality at the time of compounding or impregnation with a foaming gas. For example, it is possible to compound or impregnate an antistatic agent, a fragrance, a deodorant, a preservative, an antibacterial agent, a dye, a pigment and the like.
[0015]
Examples of the organic peroxide used in the present invention include 2,5-dimethyl-2,5-di (t-butylperoxy) 3-hexyne and 2,5-dimethyl-2,5-di (t-butylperoxy) hexane. 2,5-dimethyl-2,5-di (t-amylperoxy) hexane, 4- (t-butylperoxy) -4-methyl-2-pentanol, bis (t-butylperoxyisopropyl) benzene, peroxide Dicumyl, ethyl 3,3-bis (t-butylperoxy) butyrate, ethyl 3,3-bis (t-amylperoxy) butyrate, dibenzoyl peroxide, and the like.
[0016]
From the viewpoint of crosslinking efficiency, an organic peroxide having two or more peroxide residues in one molecule, specifically, 2,5-dimethyl-2,5-di (t-butylperoxy) 3-hexyne 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-amylperoxy) hexane, 3,3-di (t-butylperoxy) Ethyl butyrate and ethyl 3,3-bis (t-amylperoxy) butyrate are preferred, and those supported on CaCO ₃ or the like are particularly preferred from the viewpoint of ease of handling and low risk. Commercially available products include Perhexa 25B-40 manufactured by NOF Corporation (2,5-dimethyl-2,5-di (t-butylperoxy) hexane having a peroxide content of 40% in the carrier) and the like. Is mentioned.
[0017]
Japanese Patent Application Laid-Open No. 9-501456 discloses a method for improving rheology (elongational viscosity properties) so as to achieve sufficient interaction between polymer chains for sheets and films and to suppress necking and the like. Is usually sufficient when using a molar ratio of organic peroxide to polymer of about 0.01: 1 to 10: 1 (more preferably 0.05 / 1 to 3/1). It is described that an interaction occurs to achieve an improvement in rheology. However, in the case of polylactic acid-based foamed particles, the organic peroxide alone does not provide elongational viscosity properties for obtaining sufficient foamability. For this reason, in the present invention, the addition amount is generally 0.02 to 1% by mass (based on the resin composition), and preferably 0.05% to 0.4%, although it depends on the required expansion ratio and dimensional stability level. %, And a desired elongational viscosity property is obtained by using a polyfunctional crosslinking agent of a terminal group (hydroxyl group, carboxyl group) reaction type in combination.
[0018]
The type of the terminal group reactive cross-linking agent used in combination with the organic peroxide is not particularly limited as long as it is a cross-linking agent that reacts with a terminal group of a resin having a different cross-linking mechanism from the organic peroxide. For example, polyfunctional epoxy compounds, polybasic anhydrides, polyfunctional isocyanates and the like can be mentioned. In particular, in a dry process using a twin-screw kneader or the like, the load on the machine at the time of kneading is small, and polyisocyanates capable of post-crosslinking by allophanate bonds or urea bonds by gradually reacting with moisture after kneading. It is preferably used.
[0019]
Examples of the polyisocyanate compound used include aromatic, alicyclic, and aliphatic polyisocyanates. For example, aromatic polyisocyanates include polyisocyanate compounds having a skeleton of tolylene, diphenylmethane, naphthylene, tolidine, xylene, and triphenylmethane; isophorone and polyisocyanate compounds having a skeleton of hydrogenated diphenylmethane as an alicyclic polyisocyanate; Hexamethylene and polyisocyanate compounds having a lysine skeleton as the group III polyisocyanate can be used, and any of them can be used, but from the viewpoint of versatility, handleability, weather resistance, etc., polyisocyanates of tolylene, diphenylmethane, especially diphenylmethane are preferably used. You.
[0020]
Although the compound of the polylactic acid-based resin composition of the present invention may be produced by any method, it is most commonly carried out by using a twin-screw kneader having high kneading efficiency. Either of the organic peroxide and the terminal group reactive crosslinking agent may be added first, but if added simultaneously, the direct reaction between the organic peroxide and the terminal group reactive crosslinking agent is dominant. This makes it difficult to control the reaction, so it is preferable to add one of them first, knead it to some extent, and then knead the other.
[0021]
The method for producing the expanded particles of the polylactic acid-based resin composition of the present invention is not particularly limited. For example, as in WO99 / 21915, a polylactic acid-based resin composition is impregnated with a foaming gas, and then heated with steam or the like to form pre-expanded particles, which can be molded.
[0022]
As the foaming gas for impregnating the foamed particles of the polylactic acid-based resin composition of the present invention, nitrogen, an inorganic gas such as carbon dioxide, propane, butane, isobutane, pentane, hydrocarbons such as isopentane, and mixtures thereof are used. . Fluorocarbons are also suitable as foaming gases, but should be avoided when environmental considerations are required.
[0023]
Preliminary foaming of the foaming gas-impregnated beads can be performed by a method of foaming with steam, hot air, high frequency, or the like, but a method using a pre-foaming machine for styrofoam is most simple and general.
[0024]
The molding of the foamed particles is most easily and generally performed using a molding machine that uses the pre-foamed particles for molding styrofoam, foamed polyethylene, foamed polypropylene, etc. Foaming and molding can be performed simultaneously.
[0025]
【Example】
Hereinafter, the embodiment will be described in detail.
<Apparent specific gravity of expanded particles>
Apparent specific gravity of expanded particles = mass of expanded particles / apparent volume (2 L)
The foamed particles were placed in a 2 L container, the mass thereof was measured, and the number was rounded to the fourth decimal place and found to the third decimal place.
[0026]
<Moldability>
Under the same conditions of water vapor pressure of 98.1 kPa (1 kg / cm ² ), a block of 30 cm × 30 cm × 3 cm was molded and cut in half, and the cross section was observed. = Number of foam particles broken in the particles / number of foam particles in cross section x 100%
The three-point average was calculated, and 100% to 90% was evaluated as ○, 90% to 80% as Δ, and 80% or less as ×, and particularly those that could not be molded were regarded as unacceptable.
[0027]
<Apparent specific gravity of molded product>
A small piece of about 15 cm × 15 cm × 3 cm was cut out, calculated from the volume and mass, and the number was rounded to the fourth decimal place and calculated to the third decimal place.
[0028]
<Dimensional stability of molded product>
After cutting out a small piece of about 15 cm x 15 cm x 3 cm, accurately measuring the front, back, side and side, and the thickness, and leaving it for one week under the condition of 60 ° C x 80% RH, the front, back, back, side, and thickness were measured in the same manner. The volume expansion rate was calculated by multiplying the dimensional change rate of the width and thickness, and was used as an index.
[0029]
(Examples 1-4 and Comparative Examples 1-2)
Predetermined amount of perhexa 25B-40 (containing 40% of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane: manufactured by NOF Corporation) in four kinds of polylactic acids having different isomer ratios Then, the mixture was kneaded with a twin-screw kneader (TEM35B, Toshiba Machine Co., Ltd.) at a cylinder temperature of 175 ° C., and particles having an average particle diameter of 1.3 mmφ were obtained using an underwater cutter.
[0030]
A biaxial kneader (TEM35B) is added to these perhexa-crosslinked polylactic acid resin particles while adding a predetermined amount of an isocyanate compound “Millionate MR-200” (2.7 to 2.8 equivalents / mol of isocyanate groups, Nippon Polyurethane Industry Co., Ltd.). The mixture was kneaded at a cylinder temperature of 175 ° C. by means of a Toshiba Machine Co., Ltd., into particles having an average particle diameter of 1.3 mmφ using an underwater cutter, and then aged in hot water at 45 ° C.
[0031]
(Example 5)
BT-30-S2-42-L (Plastics Engineering Laboratory, L / D = 42) was used as a twin-screw kneader, and isomer ratio (L / D) = 90/10, 1% by mass chloroform solution. A mixture of polylactic acid having a solution viscosity (RV) of 3.7 and perhexa 25B-40 was charged from a hopper, and millionate MR-200 was added at a predetermined ratio from the middle of the cylinder to continuously knead and underwater cutter. And then ripened in warm water at 45 ° C.
[0032]
(Example 6)
A polylactic acid having an isomer ratio (L / D) = 90/10 and a solution viscosity (RV) of a 1% by mass chloroform solution = 3.7 was added from a hopper, and a millionate MR-200 was added from a side of the hopper at a predetermined rate. Except that Perhexa 25B-40 was added at a predetermined ratio from the middle of the cylinder and kneaded, and a crosslinking reaction was carried out, particles having an average particle diameter of 2 mmφ were obtained in the same manner as in Example 5, and heated at 45 ° C. in warm water. Matured.
[0033]
(Examples 7 to 9)
Using BT-30-S2-42-L (Plastic Engineering Laboratory Co., Ltd.) as a twin-screw kneader, polylactic acid was charged from a hopper, and Perhexa 25B-40 and Millionate MR-200 were added to the resin in a predetermined manner. The mixture was added at the same time from the center of the cylinder and kneaded so as to obtain the ratio, and the particles were formed into particles having an average particle size of 2 mmφ using an underwater cutter, and then aged in hot water at 45 ° C.
[0034]
(Comparative Example 3)
Biaxial kneading while adding millionate MR-200 to polylactic acid having isomer ratio (L / D) = 90/10, solution viscosity (RV) of 1 mass% chloroform solution = 3.7 so as to have a predetermined ratio. The mixture was kneaded with a mill (TEM35B, Toshiba Machine Co., Ltd.), formed into particles having an average particle diameter of 1.3 mmφ using an underwater cutter, and then aged in hot water at 45 ° C.
[0035]
(Comparative Examples 4 to 7)
Polyhexalactic acid having an isomer ratio (L / D) = 90/10 and a solution viscosity (RV) of a 1% by mass chloroform solution = 3.7 was added to perhexa 25B-40 (2,5-dimethyl-2,5-di ( After a predetermined amount of t-butylperoxy) hexane containing: 40% by Nippon Oil & Fat Co., Ltd. was sprinkled on the resin, the mixture was kneaded with a biaxial kneader (TEM35B, Toshiba Machine Co., Ltd.) at a cylinder temperature of 175 ° C. Particles having an average particle diameter of 1.3 mmφ were obtained using a cutter.
[0036]
In an autoclave, 5000 parts of the polylactic acid-based resin composition particles obtained in these Examples and Comparative Examples, 2,000 parts of isobutane as a foaming agent, and 250 to 500 parts of methanol as an impregnation aid were charged into a pressure-resistant vessel, and the temperature was raised while stirring. And maintained at 85 ° C. for 3 hours. Then, after cooling to 25 ° C., the resin was taken out and air-dried to obtain foamed gas impregnated particles.
[0037]
Next, the foaming agent-impregnated pellets were prefoamed with steam (94 ° C., 1 minute) to form foamed particles, and the apparent specific gravity was determined.
[0038]
The foamed particles obtained in the Examples and Comparative Examples were molded using a mold of 30 cm × 30 cm × 3 cm with a general-purpose styrofoam molding machine, and the moldability was evaluated. The volume expansion coefficient at 60 ° C. and 80% RH was determined. Table 1 shows the results.
[0039]
[Table 1]

[0040]
As is clear from Examples 1 to 4 and Comparative Examples 1 and 2, when the D-form ratio is 8% or less, foaming is possible by devising conditions, but molding is difficult. Further, from Examples 1 to 3 and Comparative Examples 3 and 4 to 7, the organic peroxide alone does not foam even if the added amount is simply increased, and the isocyanate alone foams even under high temperature and high humidity. The combination of organic peroxide and terminal-reaction type cross-linking agent is indispensable in order to achieve both high expansion ratio with an apparent specific gravity of 0.05 g / cm ³ or less and dimensional stability under high temperature and high humidity. It is clear that there is. From Examples 4 and 6 and Examples 7 to 9, the organic peroxide and the terminal-reaction type cross-linking agent can obtain almost the same performance regardless of the order of addition. It can be seen that control is difficult in a dry process using a twin-screw kneader.
[0041]
Next, a cushioning material for a VHS video deck was molded using the foamed particles of Example 2 and Comparative Example 3, and stored in the original packaging material instead of the cushioning material of Styrofoam. After this was treated at 60 ° C. and 80% RH for one week, when the video deck was taken out, the one using the molded product of Example 2 could be easily taken out, but the molded product of Comparative Example 4 The person who used was expanded so that the cardboard box was deformed into a barrel shape, and could not be removed without destroying the cardboard box.
[0042]
【The invention's effect】
As described above, by selecting an appropriate formulation based on the production method of the present invention, it is possible to secure high dimensional stability while maintaining a foaming ratio close to 40 times (apparent specific gravity 0.025 g / cm ³ ). By using the foamed molded article as a cushioning material, a polylactic acid-based resin foamed cushioning material that can be used in applications exposed to transportation conditions exposed to high temperature and high humidity can be obtained.

Claims (2)

The D-form / L-form ratio of the polylactic acid component constituting the polylactic acid-based resin composition is 8/92 to 92/8, the apparent specific gravity is 0.05 g / cm ³ or less, and 60 ° C., relative humidity A foamed molded article of a polylactic acid-based resin composition having a volume expansion coefficient of 80% or one week later is 15% or less. The polylactic acid-based resin composition having a D-form / L-form ratio of 8/92 to 92/8 contains (a) an organic peroxide and (b) any of a polyfunctional isocyanate, a polyfunctional epoxy compound, and a polybasic anhydride. A method for producing a foamed molded article of a polylactic acid-based resin composition, comprising impregnating a foaming gas, foaming and molding after acting one or two or more.