JP2000086802A - Electrically conductive resin composition for biodegradable foamed article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foamable resin compsn. having electrical conductivity, and biodegradability, while exhibiting excellent productivity. SOLUTION: A resin compsn. is made by compounding and reacting a polylactic acid consisting of the L-isomer and the D-isomer in a mole ratio of 95/5 to 60/40 or of 40/60 to 5/95, with 0.5-5 wt.%, based on the polylactic acid, of a polyisocyanate having isocyanate groups of 2.0 equivalents or more per mole and with an electrically conductive carbon; The compsn. has a melt index(MI) of 5 or less and a surface resistivity of 1010 Ω or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a resin composition for a foam used as a cushioning material for packing having biodegradability.

[0002]

2. Description of the Related Art Plastic foams utilizing light weight, cushioning properties, and moldability are widely used as packaging and packing materials, and are made of petroleum-based chemical products such as polystyrene (PS) and polyolefin. It is. Therefore, it is difficult to dispose after use, and even if it is incinerated, it burns high, and it does not decompose even if it is incinerated or buried, and it occupies the space of the disposal site because of its large volume. It is becoming a big social problem.

[0003] In addition, the adverse effects on natural resources, such as rivers and oceans, caused by foams that have been discarded without being disposed of have become insignificant. Therefore, resins that decompose in the ecosystem and have less impact on the global environment have been developed. For example, polyhydroxybutyrate resin synthesized in the body of a microorganism,
Polyesters composed of aliphatic glycols and aliphatic carboxylic acids, polyester resins containing caprolactone as the main component, etc. have been announced.The former is low in purity and extremely poor in productivity because it is produced by microorganisms. Limited.

[0004] The latter is certainly good in productivity because the raw material is inexpensive and available in large quantities, such as petroleum and natural gas. However, since it is a crystalline resin and has a low glass transition point, the biodegradable resin is used. Because it is not practical and the raw materials are petroleum and natural gas, when it is decomposed, carbon dioxide gas is newly added to the carbon dioxide present on the earth,
Does not contribute to suppression of increase in carbon dioxide gas. In the long term, since the raw material source is limited, it becomes difficult to obtain the material source soon, and it cannot contribute to global environmental protection in the true sense.

Further, as a biodegradable material, glycolic acid, lactic acid, and the like can be obtained as a polymer by ring-opening polymerization of glycolide or lactide, and are used as medical fibers. Because of its properties, it has not been used in a large amount as a foam as it is, as a packaging container or as a cushioning material.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a foamable resin composition having biodegradability and excellent productivity, that is,
An object of the present invention is to provide a foamable resin composition that can be decomposed by microorganisms, has little impact on the global environment even when disposed after use, has high productivity, and can withstand practical use. The present inventors have conducted detailed studies on base polymers, additives for increasing the molecular weight, additives for foaming, etc., which are indispensable conditions as a biodegradable resin having high foaming properties, and as a result, the A biodegradable resin having sufficient productivity has been found, and the invention has been proposed (open patent application number). However, although the foamed resin obtained by the present invention can be sufficiently applied to a general-purpose foamed molded product, its use is limited in specific applications, for example, applications in which static electricity is not preferable, such as electronic precision equipment and electronic components.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, by blending an appropriate amount of conductive carbon, the charged voltage of the foamed molded product can be reduced to a level which does not hinder practical use. This has led to the present invention.

That is, according to the present invention, the molar ratio of L-form to D-form is 95
/ 5 to 64/40, or 40/60 to 5/95, a polyisocyanate having an isocyanate group ≧ 2.0 equivalents / mol is added to the polylactic acid in an amount of 0.5 to 5% by weight based on the polylactic acid.
And conductive carbon or conductive metal oxide particles, and have a melt viscosity of 5 or less in melt index (MI) and a surface resistance of 10 ¹¹ Ω when formed into a foam.
A resin composition characterized by the following.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, it has biodegradability, which is one of the basic conditions, and minimizes the increase in carbon dioxide in nature.
In consideration of productivity and cost that can be put to practical use, a polylactic acid resin starting from lactic acid and starting from cereal starch, such as corn, is preferred. However, those usually used for fibers need to have crystallinity, so that the L-form of the optical isomer is used in almost 100%. On the other hand, in order to form a foam, at least the crystallinity must be as small as possible. The reason is that the crystallization of the crystalline resin proceeds in the step of impregnating the foaming agent, and the foaming property is impaired.

Therefore, the polylactic acid referred to in the present invention is a substantially amorphous polylactic acid, and the molar ratio of L-form to D-form is 9%.
Use 5/5 to 60/40 or 40/60 to 5/95 lactic acid. Those having a molar ratio of L-form / D-form exceeding 95/5 or less than 5/95 have high crystallinity and cannot be used because the expansion ratio does not increase or the foaming becomes uneven. Further, those having a ratio of 60/40 to 40/60 have poor heat resistance and cannot be used. Preferably 90/10 or less to 70 /
It is preferably 30 or more, or 30/70 or less to 10/90 or more.

On the other hand, the resin used for the foam is preferably a resin having good gas barrier properties in order to minimize volatilization of the impregnated foaming agent during storage. It is preferable to select a resin having a glass transition point (Tg). Among the biodegradable resins,
The polylactic acid resin has a higher lath transition point than other biodegradable resins, which is advantageous because it meets the object of the present invention. However, the glass transition point of polylactic acid decreases slightly but slightly according to the ratio of the L-form and the D-form, and reaches a minimum at 50/50. When the glass transition point is reduced, the foaming property is reduced with time for the above-mentioned reason, and the heat resistance of the foam is also undesirably reduced. That is, the glass transition point is preferably 50 ° C. or higher, and therefore, it is necessary that the ratio of the D-form is 40 mol or less or 60 mol% or more, preferably 30 mol or less or 70 mol or more.

The polylactic acid used in the present invention preferably has a melt viscosity of high molecular weight polylactic acid, and has a melt viscosity of 1 in terms of a melt index value (MI) in accordance with JIS K7210 (load 2.16 kgf). The range is from 10 to 10, more preferably from 1 to 5. A resin having a melt viscosity of polylactic acid of less than 1 is difficult to produce by a commonly used method described below, while a resin composition obtained from a polylactic acid having a melt viscosity of more than 10 has an expansion ratio of Only low foams are obtained, which is not a favorable result. The reason is that when the same ultra-high viscosity resin is obtained by reacting with the polyisocyanate described below using the melt viscosity of polylactic acid having a low melt viscosity and polylactic acid having a high melt viscosity, This is because the resin composition made of lactic acid has a higher branch density than that of a resin having a high melt viscosity, and is likely to have a crosslinked structure, which is considered to inhibit foaming.

As means for obtaining polylactic acid having a high melt viscosity,
It is not possible to obtain polylactic acid with a high melt viscosity by melt polymerization in a state of good stirring efficiency under high vacuum in a normal reaction vessel, melt polymerization by a twin-screw kneading reactor, and a combination of melt polymerization and solid phase polymerization. Although it is possible, due to the high viscosity, it is necessary to pay sufficient attention to a decrease in productivity due to a decrease in the reaction cycle and a decrease in quality due to thermal decomposition of the resin. By these methods,
Melt viscosity is JIS K7210 (load 2.16kgf)
Polylactic acid having a melt index value (MI) in the range of 1 to 10 can be obtained.

However, even if the polylactic acid obtained by the present invention is impregnated with a foaming agent and foamed, the foaming ratio is low and cannot be put to practical use. To obtain a high expansion ratio, a resin having a higher melt viscosity is required, and melt polymerization alone has a limit and is difficult.

The present inventors have conducted intensive studies and found that 0.5 to 5% by weight, preferably 1 to 3% by weight, of polyisocyanate having an isocyanate group ≧ 2.0 equivalents / mol relative to the polylactic acid was used. And melted in a molten state to make the melt viscosity JIS K 7210 (load 21.6 kg
A resin composition having a good foaming property having a melt index value (MI) based on f) of 5 or less could be obtained. When the polyisocyanate is less than 5% by weight, the melt viscosity of the resin composition does not increase so much. When the polyisocyanate exceeds 5% by weight, the melt viscosity of the resin composition increases but unreacted polyisocyanate remains or the branch density decreases. In addition, the cross-linking reaction proceeds, and a large amount of gelled matter is generated.

As a method of mixing and reacting polylactic acid and polyisocyanate in a molten state to make them ultra-high molecular weight, a commonly known method can be used. For example, a method in which a polyisocyanate is added to and mixed with a pelletized polylactic acid, and melt-mixed with a single-screw or twin-screw kneader or the like, or polyisocyanate is previously melted with a single-screw or twin-screw kneader or the like, and then the polyisocyanate is added. The desired resin composition can be obtained by a method, a method of producing polylactic acid by melt polymerization using a single-screw or twin-screw kneader, or adding a polyisocyanate during the production.

The polyisocyanates used include aromatic, alicyclic and aliphatic polyisocyanates.
For example, as the aromatic polyisocyanate, tolylene,
Diphenylmethane, naphthylene, tolidine, xylene,
A polyisocyanate having a triphenylmethane skeleton,
Examples of alicyclic polyisocyanates include isophorone and polyisocyanates having a skeleton of hydrogenated diphenylmethane, and examples of aliphatic polyisocyanates include polyisocyanates having a skeleton of hexamethylene and lysine. Tolylene, diphenylmethane, especially diphenylmethane is preferably used from the viewpoint of weather resistance and the like.

The polylactic acid resin composition thus obtained is
When a foaming agent and a foaming aid described below are impregnated and subjected to a foaming treatment, a foam having a high expansion ratio is obtained. However, since the molded article molded from the foam is easily charged by friction, applied charge and the like and is hardly discharged, when the molded article is used as a packaging material, the static electricity charged depending on the intended use becomes an obstacle to the contents. There are cases.

The present inventors have conducted various studies to overcome this problem. As a result, by blending and dispersing conductive carbon or conductive metal oxide particles in the polylactic acid resin composition, a level that does not hinder practical use is obtained. Was able to be reduced to the charged voltage.

In a general method of use, the charged voltage at a level that does not hinder practical use has a surface resistance of 10 ¹¹ Ω.
Or less, more preferably 10 ⁸ Ω or less.
Under the condition of high humidity, the surface resistance is 10
^{Since the} charging voltage is ¹¹ Ω or less and the charged voltage is low, troubles due to static electricity are unlikely to occur. For example, when the relative humidity is 40% RH or less, the troubles easily occur.

As the conductive carbon used as the conductive particles, any carbon can be used as long as it shows conductivity. Acetylene black or Ketjen black E
C (AkzoChemie) is preferably used for its performance. Even when acetylene black is blended with polylactic acid, thixotropic thickening phenomenon which occurs when blending inorganic particles is relatively small, but for example, 30% R
In order to reduce the surface resistance value to 10 ¹¹ Ω or less in an atmosphere of H, it is necessary to add a large amount of acetylene black carbon. On the other hand, Ketjen Black EC (Akz
oChemie) shows that although the thixotropic thickening phenomenon is greater than that of acetylene black carbon, it has an excellent conductive effect and has a surface resistance of 10 ¹¹ under the above conditions.
In order to reduce the resistance to Ω or less, the addition amount of several percent is sufficient.

On the other hand, conductive metal oxide particles are also preferably used. Metal particles such as silver, copper, and aluminum are the most conductive as the conductive particles, but the surface activity of the particles is large and it is dangerous if they come into contact with air or water, and the oxidized particles are conductive due to the oxide film. Is extremely low and cannot be used practically. On the other hand, tin oxide particles are oxides and exhibit good conductivity in the presence of a small amount of impurities, so-called doping agents, and are preferably used in the present invention. The addition amount varies depending on the purpose of use, but is usually 5 to 40%, and particularly preferably 510 to 30%. Tin oxide particles do not need to be a single substance, and the same effect can be obtained even if they are coated on the surface of other particles. In particular, titanium oxide particles are fine particles of 1 μm or less, which is advantageous because they can be obtained at low cost.

The particle diameter of these conductive particles is preferably 1 μm or less, more preferably 0.5 μm
It is as follows. When the thickness exceeds 1 μm, not only a large amount of addition is required to exhibit conductivity, but also the foam thickness is larger than the cell thickness of the foam, which hinders foamability.

Known methods can be used for blending the conductive particles with the polylactic acid. For example, a method in which polylactic acid, polyisocyanate and the conductive particles are preliminarily blended and then melt-mixed with a single-screw or twin-screw kneader, Various methods such as a method in which the polyisocyanate and the conductive particles are individually or mixed with the polylactic acid in the state can be used, but in consideration of the improvement in the dispersibility of the conductive particles in the resin, the powder is previously powdered and dried. A method in which a mixture of polylactic acid and polyisocyanate and conductive particles is melt-mixed with a twin-screw kneader is advantageous.

In order to form uniform and fine foam cells, it is preferable to add a foam nucleating agent. As the foaming nucleating agent to be used, solid particulate matter, for example, inorganic particles such as talc, silica, kaolin, zeolite, mica, and alumina are suitable. Among them, talc is preferably used for the resin composition of the present invention.

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, the flame retardant or the like is often a halide such as chlorine, and is preferably minimized from the viewpoint of biodegradability and generation of harmful substances during incineration.

The resin composition thus obtained is formed into pellets or bead-shaped particles and then impregnated with a foaming agent and a foaming aid. These particles are usually subjected to primary foaming (preliminary foaming) by heating, and the foaming ratio is temporarily increased from several times to 30 to 30 times.
These are expanded into 50-fold expanded particles, then placed in a mold, and further heated to secondary expansion to form a desired molded body.

The size and shape of the pellets and beads to be impregnated with a foaming agent or a foaming aid can be selected as appropriate, but usually those having a diameter of 0.5 to 2 mm are used. 0.5-1mm in diameter for precision molded products
Are generally used.

Examples of the foaming agent and foaming aid used herein include hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane and hexane, and halogens such as methylene chloride, methyl chloride and dichlorodifluoromethane. Hydrocarbons, dimethyl ether,
Ethers such as methyl ethyl ether as a foaming agent,
Also, alcohols having 1 to 4 carbon atoms, ketones, ethers,
Benzene, toluene and the like are used as foaming aids.

The combination of the foaming agent and the foaming auxiliary must be appropriately selected depending on the resin used. In the case of the L-form / D-form copolymerized polylactic acid polymer used in the present invention, butane or pentane is preferably used as a foaming agent.
Further, as a foaming aid to be combined with this, a carbon number of 1 to 4 is used.
Are preferred. There are various other combinations, and they can be selected in view of the purpose and economy.

The ratio of the foaming agent to the foaming assistant is as follows:
Foaming aid = 1/2 to 10/1 is possible, and this ratio varies depending on the combination of the foaming agent and the foaming aid.
2/1 is common. The content (ratio) of the foaming agent and the foaming aid varies depending on the desired expansion ratio and the storage period of the pellets or bead particles.
5% by weight apply. Generally, the content (ratio) of a low-foamed product may be low, and the content (ratio) of a highly foamed product may be high.

The pellets or bead particles containing the foaming agent and the foaming aid are pre-foamed, placed in a desired mold, and further heated to promote foaming, and the foamed beads are fused to form a solid. A molded body is formed. The method is basically the same as the method for molding a polystyrene (PS) foam, and steam having a large heat capacity is preferably used for both prefoaming and foaming. Foaming by hot air is also possible, but foaming efficiency is not good due to small heat capacity. Therefore, it is not suitable for high foam molding.

[0033]

The present invention will be described more specifically with reference to the following examples and comparative examples. In addition, evaluation was performed by the following method.

(Evaluation method) MI of polylactic acid: JIS K
Measured in accordance with 7210. (Measurement temperature 100
(° C., orifice diameter 2 mm, load 2.16 kg) MI of the resin composition: Measured by a method in accordance with JIS K 7210. (Measurement temperature 100 ° C, orifice diameter 2mm,
21.6 kg load condition) Expansion ratio: The volume of the foaming agent-impregnated pellet before foaming and the volume of the pre-expanded particles were measured using a measuring cylinder, and the expansion ratio was determined as follows. Expansion ratio (times) = volume of pre-expanded particles / volume of pellets impregnated with blowing agent (4) Surface resistance: A test piece of about 12 × 12 cm was subjected to 20 ° C.
After adjusting the humidity under the condition of 30% RH, the surface was set in a surface resistance measuring instrument, a DC voltage of 500 V was applied to the guard electrode, and the surface resistance was calculated from the current value flowing on the surface of the test piece by the following equation. R _S = V / I _S where R _S : surface resistance (Ω) V: applied voltage (V) I _S : measured current value (A) Measurement condition: 20 ° C. × 30% RH (5) Biodegradability :: The pre-expanded particles were put into compost for one month, and the appearance was evaluated as follows. ◎: Decomposed to a state where the original shape is not stopped. 300x300
A test piece of 100 × 300 × 30 mm was cut out from a molded product of × 30 mm and evaluated by dimensional change when treated at 100 ° C. for 2 hours in an oven. ：: No change at all ○: Change of less than 3% △: Change of less than 3 to 10% ×: Change of 10% or more-: Unable to compare foamed molded articles

Production Example Commercially available L-lactide and D-lactide were purified by recrystallization using ethyl acetate, respectively. Table 1 shows purified L-lactide, D-lactide and tin octylate as a catalyst.
Was charged into an autoclave equipped with a stirrer so as to have the following composition, and after degassing under reduced pressure, ring-opening polymerization was performed under N2 atmosphere under each polymerization condition. After completion of the reaction, the polymer was taken out of the autoclave, and the viscosity (ηr) was measured.
A polymer of 3.5 was obtained.

[0036]

[Table 1]

Examples 1-10, Comparative Examples 1-6 Isocyanate compound "Millionate MR-200" was added to polylactic acid powder (100 mesh pass) of P1 to P11.
(2.7 to 2.8 equivalents / mol of isocyanate groups, Nippon Polyurethane Industry Co., Ltd.), conductive carbon (Ketjen Black EC, (AkzoChemie)) and talc “LMP-100” (Fuji Talc Kogyo Co., Ltd.) ) 1.0
% Was preliminarily mixed so as to have the composition shown in Table 2, and kneaded with a twin-screw kneader (PCM-30, Ikegai Iron Works, Ltd.) at a cylinder temperature of 180 ° C. to obtain a pellet-shaped resin composition.

After measuring the MI of these resin compositions,
Into an autoclave were charged 2000 parts each, 1200 parts of isopentane as a foaming agent, and 240 parts of methanol as a foaming aid, sealed, and heated at a rate of 20 ° C./Hr.
C. for 1 hour. Then, after cooling to 25 ° C., the resin was taken out, air-dried, weighed, and the impregnation rate was determined. Next, the obtained pellet containing the blowing agent was steamed (92%).
At 1 ° C. for 1 minute) to evaluate bulk density and biodegradability.

Further, after aging for one day, the pre-expanded particles were filled in a closed mold, and the steam pressure was 0.5 kg with a steam molding machine.
/ Cm ² , heating for 30 seconds to form
A molded body of 00 × 30 mm was obtained. A test piece was cut out from this molded body and heat resistance was evaluated. As a control for each evaluation, a commercially available expanded polystyrene “Lyupearl 55KSY-3” was used.
171 "(manufactured by Dainippon Ink). Table 3 shows the evaluation results.
It was as follows.

[0040]

[Table 2]

[0041]

[Table 3]

Evaluation Results The crosslinking agent and conductive particles were mixed and kneaded with the resins P1 to P11 in which the L / D ratio of polylactic acid changed, respectively, and the MI, expansion ratio, decomposability, and When comparing the surface resistance and the heat resistance, P1 and P11 have low foaming ratios, which are not preferable. P6 has good foaming ratio, decomposability and surface resistance, but has poor heat resistance. In particular, heat resistance is an important factor for a foamed molded product for packaging used for export by ships. P2 to P5 and P7 to P10 are expansion ratios,
Decomposability, surface resistance and heat resistance all showed good results, and P3, P4, P8 and P9 were particularly good.

Examples 11 to 14, Comparative Examples 7 to 16 An isocyanate compound "Millionate MR-200" (2.7 to 2.8 equivalents / mole of isocyanate group, Nippon Polyurethane Industry Co., Ltd.) was added to the polylactic acid of P3. A predetermined amount of ketjen black, acetylene black, carbon black of oil furnace FEF and tin oxide particles coated on titanium oxide particles were blended as particles, and the same kneading machine and kneading conditions as in Examples 1 to 10 and Comparative Examples 1 to 6 were used. To obtain a pellet-shaped resin composition, and subsequently, the same treatment was performed and evaluated. Table 5 shows the results.

[0044]

[Table 4]

[0045]

[Table 5]

Examples 15 to 21 and Comparative Examples 17 to 19 The polylactic acid of P3 was added with a predetermined amount of an isocyanate having various functional groups and 5% by weight of Ketjen Black EC as conductive particles. The mixture was treated under the same kneader and kneading conditions as in Comparative Examples 1 to 6 to obtain a pellet-shaped resin composition, which was subsequently subjected to the same treatment and evaluated. The results are shown in Table 7.

[0047]

[Table 6]

[0048]

[Table 7]

[0049]

As described above, the resin composition of the present invention has foaming properties, heat resistance and mechanical properties comparable to those of the conventionally used expanded polystyrene (PS). It is a resin composition that has excellent biodegradability and contributes to global environmental protection.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08K 9/02 C08K 9/02 C08L 75/06 C08L 75/06 (72) Inventor Masahiro Yamaguchi Hofu City, Yamaguchi Prefecture 4-1 Kanebocho Kanebo Gosen Co., Ltd. (72) The inventor Hiroshi Naito 4-1 Kanebocho, Hofu City, Yamaguchi Prefecture Kanebo Gosen Co., Ltd. (72) Inventor Tsunahiro Nakae Osaki Osaki 276, Hofu City, Yamaguchi Prefecture −516 F-term (reference) 4F074 AA68 AA84 AB05 AC02 AC17 AC35 AE01 AG08 BA35 CA34 CA42 CA49 DA33 4J002 CF191 CK022 DA036 DE047 DE097 DE137 EA018 EA028 EA058 EB028 EB068 EC038 ED028 EE028 FB0117 FD01 GE018 FB077 FD01 AD02 JA023 JA093 JB023 JB043 JB063 JB123 JB143 JB153 JF323 JF373 KH01 4J034 BA03 DA01 DB03 DB07 DF11 DF24 HA01 HA07 HA08 HB12 HC03 HC09 HC12 HC13 HC 17 HC22 HC46 HC52 HC61 HC64 HC65 HC67 HC71 HC73 MA02 MA03 NA01 NA02 NA06 NA07 QA05 QB07 QB15 QC01 RA06

Claims (7)

[Claims] 1. The molar ratio of L-form to D-form is 95/5 to 64 /
40 or 40/60 to 5/95, polyisocyanate having an isocyanate group ≧ 2.0 equivalents / mol in 0.5 to 5% by weight based on the polylactic acid, and conductive carbon or conductive metal. A resin composition containing oxide particles, having a melt viscosity of 5 or less in melt index value (MI) and a surface resistance of 10 ¹¹ Ω or less when formed into a foamed molded article. 2. The molar ratio of L-form to D-form is 90/10 to 70.
The resin composition according to claim 1, wherein the ratio is 30/70 or 30/70 to 10/90. 3. The resin composition according to claim 1, wherein the amount of the polyisocyanate is 1 to 3% by weight. 4. The resin composition according to claim 1, wherein the polyisocyanate has an isocyanate group ≧ 2.3 equivalent / mol. 5. The resin composition according to claim 1, wherein a conductive carbon selected from acetylene black and Ketjen black is used as the conductive carbon. 6. The resin composition according to claim 1, wherein the conductive metal oxide particles are tin oxide or titanium oxide particles whose surfaces are coated with tin oxide. 7. The resin composition according to claim 1, wherein the surface resistance of the resin composition is 10 ⁸ Ω or less.