JP3907047B2 - Method for producing foamed molding - Google Patents

Description

【００３６】
（実施例１〜７、比較例１〜４）
該ビーズを２日熟成後、内容積２００Ｌのオートクレーブに仕込み、空気で０．３ＭＰａに加圧し、１０時間保持した。その後降圧し、縦３００ｍｍ、横３００ｍｍ、厚み３０ｍｍの金型を装着したＰＳ成形機に充填して水蒸気圧０．１ＭＰａ、３０秒加熱し成形物を得た。評価の対照として市販の発泡ポリスチレン「リューパール５５ＫＳＹ−３１７１」（大日本インキ製）を同条件で行いそれぞれ成形物を得た。但し、発泡ポリスチレンは空気による加圧処理は行わなかった。
【００３７】
次いで該成形物を２５℃、湿度６５％の条件下に２日間放置した後、６０℃、湿度８０％の条件下に２４時間処理し、それぞれの寸法を測定し体積を算出した。処理前の成形物体積（Ｓ１）及び処理後の成形物体積（Ｓ２）から変形率を算出した。評価結果は表２の通りであった。
【００３８】
【表２】

【００３９】
（評価結果）
比較例１（Ｐ１）及び比較例３（Ｐ１０）は結晶性樹脂であるため、殆ど発泡しなかった。本発明である実施例１〜６（Ｐ２〜Ｐ７）及び実施例７（Ｐ９）は発泡性、寸法安定性（変形率）及び生分解性いずれも良好であった。比較例２（Ｐ８）は発泡性及び生分解性は良好であったが寸法安定性（変形率）不良であり、本発明の趣旨に沿う結果とはならなかった。一方、ＰＳ成形物は生分解性が全く認められなかった。
【００４０】
（実施例８〜１３ 比較例５）
実施例３（ポリマーＰ４）の発泡ビーズを使用し、加圧する気体の種類を変更した以外は表２の実施例１〜７と同様な操作を行い成形物を得た。得られた成形物の寸法安定性（変形率）を評価した。結果を表３に示した。
【００４１】
【表３】

【００４２】
（評価結果）
気体として、空気、炭酸ガス、窒素、ヘリュウム、アルゴン、空気／窒素混合ガス及び空気／炭酸ガス混合ガスについて評価した結果、いずれも寸法安定性（変形率）は良好であった。一方、気体で処理しないビーズから得た成形物は変形率３５．５％と不良であった。
【００４３】
（実施例１４〜２０、比較例５〜７）
実施例３（ポリマーＰ４）の発泡ビーズを使用し、加圧する空気の圧力及び加圧時間を変更した以外は表２の実施例１〜７と同様な操作を行い成形物を得た。得られた成形物の寸法安定性（変形率）を評価した。結果を表４に示した。
【００４４】
【表４】

【００４５】
（評価結果）
表４から明らかなように空気加圧処理しない比較例５及び空気圧の低い比較例６は寸法安定性（変形率）が不良であった。寸法安定性（変形率）が良好であったのは空気圧が０．１０５ＭＰａ〜１．０ＭＰａであり、特に空気圧が０．１５ＭＰａ〜０．５ＭＰａの範囲が良好であった。
【００４６】
【発明の効果】
以上、本発明の製造方法により得られる発泡成形物は、従来から課題であった寸法安定性（変形率）が改善され、生分解性、軽量性、機械物性は従来の性能を維持していた。現在使用されているＰＳ又はＰＯ発泡成形体を代替することにより地球環境保全に資することが出来る。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a foamed molded article having excellent biodegradability, lightness, mechanical properties, and dimensional stability using a natural material as a starting material.
[0002]
[Prior art]
Plastic foams that make use of characteristics such as lightness, shock-absorbing properties, and moldability are used in large quantities as packaging and packaging materials. These materials are chemicals that use petroleum such as polystyrene (PS) and polyolefin (PO) as raw materials. Because it is a product, it is difficult to dispose of it after use, and its combustion heat is high even if it is incinerated. It will not decompose even if it is incinerated or landfilled. It has become a big social problem.
[0003]
Recently, polylactic acid having biodegradability starting from natural materials has attracted attention, and various products are being developed and marketed. As a result of the inventors focusing on the polylactic acid and focusing on the development of the foam from the past, the foamable beads having excellent functions such as biodegradability, light weight, and mechanical properties, and foam molding obtained from the beads Get things and make proposals to the market. However, since the foamed molded article has a problem that the dimensional stability at high temperatures is inferior, the usage of export packaging materials and the like that are expected to be high is limited.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-17037
[Problems to be solved by the invention]
The present invention has excellent functions such as biodegradability, light weight, and mechanical properties made of polylactic acid or a composition thereof, and dimensions at high temperature and high humidity (60 ° C. × 80% RH) that are practically problematic. An object of the present invention is to provide a method for producing a foam molded article having excellent stability.
[0006]
[Means for Solving the Problems]
The present invention intensively studied to solve the above problems, polylactic acid or the composition molar ratio of the L-form and D-form is 95 / 5-6 0/40, or 40/60 to 5/95 The present invention has found a method for producing a foam-molded product characterized in that a biodegradable foam bead made of a product is held in a gas atmosphere of 0.105 MPa or more, and then the bead is introduced into a mold and molded in-mold. Has reached
[0007]
DETAILED DESCRIPTION OF THE INVENTION
As polylactic acid, a resin usually used for fibers or films needs to have crystallinity, and therefore polylactic acid having an L isomer of nearly 100% is used. On the other hand, in order to form a foam, at least the crystallinity needs to be as small as possible. The reason is that the crystalline resin progresses in crystallization in the step of impregnating the foaming agent, thereby inhibiting the foamability.
[0008]
Therefore, the polylactic acid referred to in the present invention is a polylactic acid that is substantially non-crystalline obtained by dehydration condensation of lactic acid or ring-opening polymerization of lactide, and the molar ratio of L-form to D-form is 95/5. ~ 60/40 or 40 / 60-5 / 95 lactic acid is used.
Those in which the molar ratio of L-form / D-form exceeds 95/5 or less than 5/95 has high crystallinity and cannot be used because the foaming ratio does not increase or foaming becomes uneven. Also, those having a D-form ratio exceeding 40% and less than 60% are inferior in heat resistance and cannot be used. Preferably, 93 / 7-70 / 30 or 30 / 70-7 / 93 is good .
[0009]
The polylactic acid composition referred to in the present invention is preferably a composition containing other additives such as a thickener, a filler, a heat-resistant agent, an ultraviolet absorber, an antistatic agent, etc. in polylactic acid or other compounds, preferably 10 mol% or less. Means a blend of polylactic acid, polybutylene succinate, polycaprolactone, polybutylene terephthalate copolymer, cellulose derivative and the like copolymerized at 5 mol% or less.
[0010]
However, the polylactic acid or its composition is impregnated with a foaming agent, and foamed beads obtained by foaming are introduced into a mold, and a molded product obtained by performing a molding process using water vapor that is normally produced is biodegradable, It is excellent in light weight and mechanical properties, but cannot be used for packaging materials such as export packaging because it is inferior in dimensional stability, such as large changes in dimensions in a short time when left under high temperature and high humidity (60 ° C x 80% RH). Its use is greatly limited.
[0011]
As a result of intensive studies to solve this problem, the present inventors processed foamed beads under predetermined conditions, and then introduced them into a mold and performed molding processing using steam that is normally produced, thereby greatly improving dimensional stability. I found it to be improved. That is, after processing the foamed beads obtained from the polylactic acid according to the present invention or a composition thereof in a gas atmosphere of 0.105 Mpa or more, the above molding is performed, thereby the dimensions at high temperature and high humidity (60 ° C. × 80% RH). We found that the change was very small.
[0012]
As the gas to be used, any of air, nitrogen, carbon dioxide, helium, argon or a mixed gas thereof can be used. However, it is economical to use air, nitrogen, carbon dioxide or a mixed gas thereof. To preferred. Although organic gases such as hydrocarbons and halogenated hydrocarbons can be used, it is not preferable because of an increase in global environmental load.
[0013]
Next, the working pressure of the gas is 0.105 MPa or more, preferably 0.11 MPa or more and less than 1 MPa, more preferably 0.15 MPa or more and less than 0.5 MPa. If the working pressure is less than 0.105 MPa, it takes a very long time to obtain the foamed beads necessary to obtain a molded article having good dimensional stability, and if the pressure is too high, the wall membrane of the foamed beads is affected by the pressure. Since it is destroyed, a good molded product cannot be obtained. The pressurizing method can be either instantaneous or time-consuming, but it is preferable to take time in consideration of damage to the bead wall membrane.
[0014]
The time for processing the expanded beads under a predetermined pressure is influenced by the temperature to be processed or the humidity held by the gas and cannot be uniquely determined, but is generally 1 hour or more, preferably 3 hours or more. . This optimum shortest processing time tends to be shortened as the processing temperature is higher and the humidity of the gas used is higher.
The equipment for processing the expanded beads under a predetermined pressure can be used regardless of the shape and size as long as the pressure resistance is guaranteed. Although it is more preferable if the container can be heated in the range of 30 ° C. to 50 ° C., it is not always necessary, and the same gas is used.
[0015]
As the polylactic acid having foamability or a composition thereof, a highly viscous and branched polymer is advantageous, but as a method for producing these polylactic acid or a composition thereof, for example, under a high vacuum in a normal reaction kettle, It can be obtained by melt polymerization with good stirring efficiency, melt polymerization by a biaxial kneading reactor, or a combination of melt polymerization and solid phase polymerization. Furthermore, it is possible to obtain a highly viscous and branched polymer by adding a thickener such as an epoxy compound, an acid anhydride compound, or an isocyanate compound.
[0016]
Various compounds can be blended in the polylactic acid used in the expanded beads of the present invention. For example, various polymers such as polybutylene succinate, aliphatic polyester typified by polycaprolactone, polybutylene terephthalate copolymer, and cellulose acetate can be blended. The blending amount varies depending on the properties of the resin, but it is preferably suppressed to 50% by weight or less in order to maintain the properties of polylactic acid or a composition thereof.
[0017]
The epoxy compound used in the present invention is a glycidyl ether compound, pyromellitic acid is trimellitic acid as an acid anhydride compound, tolylene is an isocyanate compound, aromatic polyisocyanate having diphenylmethane as a skeleton, and fat having hydrogenated diphenylmethane as a skeleton. There are cyclic polyisocyanates and aliphatic polyisocyanates typified by hexamethylene groups.
Although the addition amount of these thickeners can be selected arbitrarily, 5 wt% or less is preferably used.
[0018]
Furthermore, various fillers can be mix | blended with this invention. As the inorganic filler, there are talc, silica, kaolin, zeolite, mica, alumina, montmorillonite, etc., and any amount thereof can be blended alone or a mixture thereof, but the blending amount is from 0.1% by weight to 20% by weight. % Range, preferably 1% to 5% by weight is used. On the other hand, polyolefins, aromatic polyesters, polyamides, polycarbonates, celluloses, and polyalkylene glycols can be used as organic fillers, but within a range that does not substantially impair the biodegradability of polylactic acid or its composition. Generally, it is preferably 10% by weight or less.
[0019]
Further, other additives can be appropriately added according to the purpose, and examples thereof include antistatic agents, heat stabilizers, antioxidants, flame retardants, ultraviolet absorbers, and plasticizers. 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.
[0020]
In order to obtain foam beads, polylactic acid or a composition thereof is kneaded with various additives to form pellets or bead-like particles, and then impregnated with a foaming agent and a foaming aid. Subsequently, these impregnated particles are usually foamed by heating with steam to obtain expanded beads of several to 100 times.
Pellet and bead size, the shape or the like may be suitably selected, usually, those having a diameter of 0.5~2mm used. In the case of a precise molded body, particles having a diameter of 0.5 to 1 mm are common.
[0021]
The foaming agent and foaming aid used here are hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane and hexane, and halogenated hydrocarbons such as methylene chloride, methyl chloride and dichlorodifluoromethane. Ethers such as dimethyl ether and methyl ethyl ether are used as blowing agents, and alcohols having 1 to 4 carbon atoms, ketones, ethers, benzene, toluene and the like are used as foaming aids.
[0022]
The foamed bead molding processing equipment used in the present invention may be any equipment as long as the object is achieved, but a PS or PO molding equipment is preferably used.
[0023]
As an example of the present invention, the foam after filling beads in the tank, the air under pressure of 0.3 MPa, the molded product obtained by molding in the usual way with the step-down and PS molding machine was maintained for 6 hours of the invention Even when exposed to high temperature and high humidity (60 ° C. × 80% RH), there is almost no dimensional change.
[0024]
The molded product obtained by the present invention can be used for various applications. For example, cushioning materials for precision instruments, electrical appliances, electronic devices, electronic parts, packaging materials for foods, liquors, chemicals, cosmetics such as display panels, mannequins, decorations, foods, machine parts, electronic parts, etc. There are heat insulation materials such as box boxes, heat insulating materials, building materials, ice cream, frozen foods, and the like.
[0025]
【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.
[0026]
(Evaluation methods)
(1) Solution viscosity: 0.5 g of a sample is dissolved in a phenol / tetrachloroethane (60/40) mixed solution to 50 ml, and an automatic capillary viscometer model SS-600-L1 (Shibayama Kagaku) is used at 25 ° C. The relative viscosity of was measured.
[0027]
(2) Melting point (° C.): A resin amount of 10 mg was collected and determined from an endothermic peak of DSC (manufactured by Differential Scanning Calipermeter PerkinElmer). Measurement conditions were measured by raising the temperature from 25 ° C. to 200 ° C. at a rate of 10 ° C./min in a nitrogen flow.
[0028]
(3) Impregnation rate (%): It was calculated from the weight of beads before impregnation (W ₀ ) and the weight of beads after impregnation (W ₁ ) by the following formula.
Impregnation rate (%) = (W ₁ / W ₀ −1) × 100
[0029]
(4) Foaming ratio: Using a graduated cylinder, the weight (g) of the foaming agent-impregnated pellet and the volume of the beads after foaming (mL) were measured, and the foaming ratio was determined as follows.
Expansion ratio (times) = volume of expanded beads / weight of impregnated pellets
(5) Dimensional stability: A mold having a length of 300 × width of 300 × height of 30 mm was placed in a foam molding machine, filled with foam beads, and processed at a steam pressure of 0.1 MPa for molding. The obtained molded body was allowed to stand for 4 days under conditions of 25 ° C. and 60% RH, and each dimension was measured.
Subsequently, after processing for 24 hours under conditions of 60 ° C. and 80% RH, each dimension was measured in the same manner. The dimensional stability was calculated by the following formula.
Dimensional stability (deformation rate%) = ((the compact volume of the preform volume (S2) / treatment after treatment (S1)) - 1) × 100
Evaluation: Deformation rate ≧ 10% or Deformation rate ≦ −10% : poor dimensional stability
5% ≦ deformation rate <10% : good dimensional stability
−5% <deformation rate <5% : dimensional stability is particularly good
−10% <deformation rate ≦ −5% : good dimensional stability
(6) Biodegradability: Each sample was embedded in a compost during fermentation mainly composed of cow dung, and the decomposition state after 48 hours was visually observed.
Evaluation ○: Almost decomposed ×: The original shape is not decomposed. [0032]
(Production example)
Purified L-lactide, D-lactide and tin octylate as a catalyst were charged into an autoclave equipped with a stirrer so as to have the composition shown in Table 1, degassed under reduced pressure, and then subjected to ring-opening polymerization under each polymerization condition in a nitrogen atmosphere. After completion of the reaction, the polymer was taken out from the autoclave and the viscosity (ηr) was measured to obtain a polymer having ηr of 3.3 to 3.5.
[0033]
Next, an isocyanate compound “Millionate MR-200” (2.7 to 2.8 equivalents / mol of isocyanate groups, Nippon Polyurethane Industry Co., Ltd.) and talc “LMP-100” (Fuji Talc Industry Co., Ltd.) were added to these polylactic acids. 2 wt% and 3 wt% were kneaded at a cylinder temperature of 180 ° C. with a twin-screw kneader (PCM-30, Ikegai Iron Works Co., Ltd.) to obtain a pellet-shaped resin composition.
[0034]
Each of these resin compositions was charged in an autoclave with 2000 parts each, 800 parts isobutane as a foaming agent, and 100 parts methanol as a foaming aid, sealed, heated at a rate of 20 ° C./hour, and held at 85 ° C. for 2 hours. . Then, after cooling to 25 ° C., the resin was taken out, air-dried, weighed, and the impregnation rate was determined. Next, the obtained foaming agent-impregnated pellet was treated with water vapor (92 ° C., 1 minute) to obtain expanded beads. The impregnation rate and expansion ratio of each composition are described together with the examples or comparative examples.
[0035]
[Table 1]

[0036]
(Examples 1-7, Comparative Examples 1-4)
The beads were aged for 2 days, charged into an autoclave with an internal volume of 200 L, pressurized to 0.3 MPa with air, and held for 10 hours. Thereafter, the pressure was reduced, and a PS molding machine equipped with a mold having a length of 300 mm , a width of 300 mm, and a thickness of 30 mm was filled and heated to a water vapor pressure of 0.1 MPa for 30 seconds to obtain a molded product. As a control for evaluation, commercially available expanded polystyrene “Ryupearl 55KSY-3171” (manufactured by Dainippon Ink) was used under the same conditions to obtain molded products. However, the polystyrene foam was not pressurized with air.
[0037]
Next, the molded product was allowed to stand for 2 days under conditions of 25 ° C. and humidity 65%, and then treated for 24 hours under conditions of 60 ° C. and humidity 80%. The respective dimensions were measured, and the volume was calculated. The deformation rate was calculated from the molded product volume (S1) before treatment and the molded product volume (S2) after treatment. The evaluation results are shown in Table 2.
[0038]
[Table 2]

[0039]
(Evaluation results)
Since Comparative Example 1 (P1) and Comparative Example 3 (P10) are crystalline resins, they hardly foamed. Examples 1 to 6 (P2 to P7) and Example 7 (P9) according to the present invention were good in foamability, dimensional stability (deformation rate) and biodegradability. Comparative Example 2 (P8) had good foamability and biodegradability, but had poor dimensional stability (deformation rate), and did not result in the spirit of the present invention. On the other hand, no PS biodegradability was observed in the PS molded product.
[0040]
(Examples 8-13 Comparative Example 5)
Using the foam beads of Example 3 (Polymer P4) and changing the type of gas to be pressurized, the same operation as in Examples 1 to 7 in Table 2 was performed to obtain a molded product. The dimensional stability (deformation rate) of the obtained molded product was evaluated. The results are shown in Table 3.
[0041]
[Table 3]

[0042]
(Evaluation results)
As a result of evaluating air, carbon dioxide, nitrogen, helium, argon, air / nitrogen mixed gas and air / carbon dioxide mixed gas as gases, all had good dimensional stability (deformation rate). On the other hand, a molded product obtained from beads not treated with gas was poor at a deformation rate of 35.5%.
[0043]
(Examples 14-20, Comparative Examples 5-7)
Using the expanded beads of Example 3 (Polymer P4) and changing the pressure of the pressurized air and the pressurizing time, the same operations as in Examples 1 to 7 in Table 2 were performed to obtain a molded product. The dimensional stability (deformation rate) of the obtained molded product was evaluated. The results are shown in Table 4.
[0044]
[Table 4]

[0045]
(Evaluation results)
As is apparent from Table 4, Comparative Example 5 without air pressure treatment and Comparative Example 6 with low air pressure had poor dimensional stability (deformation rate). The dimensional stability (deformation rate) was good when the air pressure was 0.105 MPa to 1.0 MPa, and particularly when the air pressure was within the range of 0.15 MPa to 0.5 MPa.
[0046]
【The invention's effect】
As described above, the foam molded product obtained by the production method of the present invention has improved dimensional stability (deformation rate), which has been a problem in the past, and has maintained the conventional performance of biodegradability, light weight, and mechanical properties. . Substituting PS or PO foam moldings currently used can contribute to global environmental conservation.

Claims (4)

The molar ratio of L-form and D-form is 95 / 5-6 0/40, or 40/60 to 5/95 in a polylactic acid or 0.105MPa or more biodegradable foam beads made of the composition, 1.0 MPa A method for producing a foamed molded product, comprising: holding in the following gas atmosphere, then introducing the beads into a mold and molding the mold in the mold. The method for producing a foamed molded product according to claim 1, wherein the gas used is air, nitrogen, carbon dioxide, helium, argon, or a mixed gas thereof. The method for producing a foamed molded product according to claim 1, wherein the pressure of the gas used is 0.11 MPa or more and less than 1.0 MPa. The method for producing a foamed molded product according to claim 1, wherein the pressure of the gas used is 0.15 MPa or more and less than 0.5 MPa.