JP2002114900A - Antistatic polylactic acid-based composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of difficulty in imparting antistaticity to a polylactic acid-based film and sheet which are a biodegradable material. SOLUTION: This antistatic polylactic acid-based composition is characterized in that the polylactic acid-based polymer contains 0.1-10 pts.wt. at least one kind of a nonionic antistatic agent selected from the compound group consisting of (1) a polyhydric alcohol such as ethylene glycol, diethylene glycol, triethylene glycol, glycerol, trimethylolpropane, pentaerythyritol and sorbitol, and/or a fatty acid ester thereof, (2) polyethylene glycol and/or a fatty acid ester thereof, and (3) a polyethylene glycol adduct or a polypropylene glycol adduct of a higher alcohol, a polyhydric alcohol and an alykylphenol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biodegradable polylactic acid composition having antistatic properties.

[0002]

2. Description of the Related Art In recent years, when plastic products are rejected in the natural environment due to the rise of environmental problems, the plastic products are decomposed over time.
There is a growing need to disappear and eventually have no adverse effect on the natural environment.

[0003] Conventional plastics are stable in the natural environment for a long period of time and have a low bulk specific gravity, so that the life of a waste landfill is promoted and the natural scenery and the living environment of wild animals and plants are impaired. The point was pointed out.

[0004] Attention has been paid to biodegradable plastic materials today. It is known that biodegradable plastics gradually decompose and decompose in soil or water due to hydrolysis or biodegradation, and eventually become harmless decomposition products due to the action of microorganisms.

[0005] Biodegradable plastics that have begun to be put into practical use include aliphatic polyesters, modified PVA, cellulose ester compounds, modified starches, and blends thereof. Each of these biodegradable plastics has unique characteristics, and applications can be considered in accordance with them. Among them, polylactic acid-based polymers, one of aliphatic polyesters, are other biodegradable plastics. Compared with, it is superior in transparency, rigidity, heat resistance, workability, etc., and is used for the field of transparent films and sheets in which rigid polyvinyl chloride (PVC), polystyrene, polyethylene terephthalate (PET) has been used. It is about to be developed.

However, films and sheets made of a polylactic acid-based polymer are easily charged due to friction or the like because of their high specific resistance, as seen in general-purpose plastics such as PVC, resulting in the following defects. Had.

A person receives a shock when touched. Spark discharge may cause a fire. The workability and handleability during use are reduced due to rebound and sticking between films or other objects. Adhesion of dust impairs aesthetics and hygiene and lowers product value.

In general-purpose plastic films and sheets, in order to solve such a problem, an improved technique of kneading an antistatic agent in an extrusion step or applying the antistatic agent to the surface is widely adopted.

[0009]

However, the polylactic acid-based polymer has significantly lower thermal stability in an extruder than a general-purpose plastic, and is likely to cause a decrease in molecular weight.
Usually, the addition of an antistatic agent further promotes a decrease in molecular weight, and thus causes a decrease in production stability and a decrease or variation in product quality such as mechanical properties. For this reason, kneading of the antistatic agent in the extrusion step was substantially difficult.

[0010] Antistatic agents include cationic, anionic and
They are broadly classified into zwitterionic and non-ionic types, and are properly used depending on the processing method and application. In general-purpose plastic film and sheet applications, the most commonly used are anionics having a good balance between effectiveness and economy, and are typically 1) fatty acid salts, 2) higher alcohol sulfates, 3). Liquid fatty acid sulfates, 4) aliphatic amine and aliphatic amide sulfates, 5) aliphatic alcohol phosphate esters, 6) dibasic fatty acid ester salts, 7) fatty acid amide sulfonates, 8) alkyl Arylsulfonic acid salts, 9) formalin-condensed naphthalenesulfonic acid salts, and the like.

[0011] In addition, cationic systems which are vulnerable to heat and high in cost but have high antistatic properties include 1) aliphatic amine salts,
2) quaternary ammonium salts, and 3) alkylpyridinium salts. Further, zwitterionic systems having slightly improved heat resistance, which is a weak point of anionic systems, include 1) imidazoline derivatives, 2) ammonium carboxylate,
3) Ammonium sulfates, 4) Ammonium phosphates, 5) Ammonium sulfonates.

These ionic antistatic agents are used in a very wide range and in a large amount in general-purpose plastic films and sheets, but cannot be suitably used in the polylactic acid-based polymer of the present invention. This is because, although the intended antistatic effect can be obtained, the polylactic acid-based polymer undergoes remarkable thermal decomposition in the extruder to reduce the molecular weight, because these are kneaded. A decrease in molecular weight leads to a decrease in product stability such as a decrease in production stability, mechanical properties and heat resistance, and a decrease in appearance such as generation of uneven flow, which is extremely undesirable in practical use.

The method of applying an antistatic agent to the surface of a film or sheet has the following problems. Coating equipment is required, and the number of processes is increased, resulting in an increase in manufacturing costs. Since the liquid antistatic agent scatters around, maintenance of the working environment is complicated. Stickiness / Blooming / Interference fringes /
Quality problems such as blocking are likely to occur.

As described above, it has been difficult to impart antistatic properties to polylactic acid-based films and sheets that are biodegradable materials.

[0015]

Means for Solving the Problems The present inventors have made intensive studies in view of such a situation, and as a result, have completed the present invention.

According to the present invention, there are provided polylactic acid-based polymers having the following compound groups (1) to (3): (1) ethylene glycol, diethylene glycol, triethylene glycol, glycerin, trimethylolpropane, pentael slit, sorbit and the like. Polyhydric alcohols and / or fatty acid esters thereof, (2) polyethylene glycol and / or fatty acid esters thereof, (3)
An antistatic composition comprising 0.1 to 10 parts by weight of at least one nonionic antistatic agent selected from higher alcohols, polyhydric alcohols, polyethylene glycol adducts of alkylphenols, and polypropylene glycol adducts. It is a polylactic acid-based composition.

According to the present invention, (1) the fatty acid ester of the polyhydric alcohol includes lauric acid (C12), palmitic acid (C16), stearic acid (C18) and behenic acid (C
22. The antistatic polylactic acid composition as described above, which is a saturated fatty acid ester selected from 22) or an unsaturated fatty acid ester selected from palmitoleic acid, oleic acid, erucic acid and linoleic acid.

The present invention provides (1) the antistatic polylactic acid composition as described above, wherein the fatty acid ester of the polyhydric alcohol has at least one hydroxyl group remaining per molecular structural unit of the polyhydric alcohol. .

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The polylactic acid-based polymer used in the present invention is polylactic acid, a copolymer of lactic acid and another hydroxycarboxylic acid, or a composition thereof, which inhibits the effects of the present invention. Other polymer materials may be mixed as long as they do not. In addition, additives such as plasticizers, lubricants, inorganic fillers, ultraviolet absorbers, light stabilizers, fungicides, pigments, and fluorescent agents, and modifiers are used for the purpose of adjusting the moldability and the physical properties of films and sheets. It is also possible to add.

Lactic acid includes L-lactic acid and D-lactic acid, and other hydroxycarboxylic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid and 4-hydroxyvaleric acid. And 6-hydroxycaproic acid.

As these polymerization methods, any known methods such as a condensation polymerization method and a ring-opening polymerization method can be adopted. Further, a small amount of a chain extender, for example, Diisocyanate compounds, diepoxy compounds, acid anhydrides, acid chlorides and the like may be used. The weight average molecular weight of the polymer is 50,000
Is preferably in the range of from 1,000,000 to 1,000,000, and if it is less than this range, problems such as practically no physical properties are exhibited. On the other hand, if it exceeds, the melt viscosity becomes too high, resulting in poor moldability. Further, in order to improve the thermal stability, it is preferable that the amount of the remaining monomer or the catalyst is small.

In the present invention, such a polylactic acid-based polymer is melt-extruded from a die using an extruder and formed into a film and a sheet. As a special case, pellet press molding or calender molding may be performed as long as the molten state is passed.

In extruding the polylactic acid-based polymer, it is desirable that the raw materials are sufficiently dried in advance in order to prevent thermal decomposition (hydrolysis) in the extruder.

When a film is obtained, a flat or cylindrical material melt-extruded from a T-die, an I-die, a round die or the like is quenched by a cooling cast roll, water, pressurized air or the like. The film is uniaxially or biaxially stretched by a method, a tenter method, a tubular method, or the like. Further, a so-called inflation method, in which melt extrusion is performed from a round die and air is blown into a cylindrical material that is still in a molten state to reduce the thickness, can also be preferably used.

Furthermore, if the film stretching and heat fixing techniques as disclosed in Japanese Patent Application Laid-Open No. 5-508819 and Japanese Patent Application Laid-Open No. 6-23836 are used, transparency, mechanical strength, rigidity, thermal dimensional stability, etc. Can be obtained. The thickness of the film is 10 to 10 depending on the application.
It is determined in the range of 250 μm.

The most preferable method for obtaining a sheet is a method in which the sheet is extruded into a flat shape using a T-die and quenched by a metal cast roll equipped with a temperature control device. By nipping with a roll, a polylactic acid-based sheet having extremely excellent transparency and smoothness can be obtained. The thickness of the sheet depends on the application.
It is generally determined in the range of 250 μm to 1 mm.

As the extruder to be used, any known form such as a single-screw, co-direction twin-screw, and different-direction twin-screw extruder can be used. The most common method is to preliminarily pelletize a raw material containing a predetermined additive by using a co-rotating twin-screw extruder having a high kneading effect, and then supply the pellet to a film / sheet extruder. An agent or the like may be directly mixed with the raw materials at the time of extruding a film or sheet.

The set temperature of the extruder is appropriately determined depending on the chemical composition and molecular weight of the polylactic acid polymer.
A range of 30 ° C. is preferred. Below 170 ° C, the melting point is 1
The homopolymer at 75 ° C. does not melt, and at 230 ° C. or higher, thermal decomposition becomes significant.

In the present invention, when a polylactic acid-based polymer is melt-extruded to form a film or sheet, a predetermined amount of a specific antistatic agent is added to the polylactic acid-based polymer, and these are added to the molded article. Knead it.

In order to minimize the thermal decomposition of the polylactic acid-based polymer and to produce a practical film / sheet, the most important points in the present invention are the following non-ionic polymers shown in (1) to (3). That is, an antistatic agent is used.

(1) Polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, trimethylolpropane, pentaerlit, sorbite and / or fatty acid esters thereof,
(2) polyethylene glycol and / or a fatty acid ester thereof, (3) a higher alcohol, a polyhydric alcohol, an alkylphenol adduct of polyethylene glycol or a polypropylene glycol adduct.

The polyhydric alcohol (1) can be used as it is, but it is more preferable to form a fatty acid ester by an esterification reaction with a fatty acid in order to increase the compatibility with the polylactic acid-based polymer. The fatty acid is not particularly limited, but may be a saturated fatty acid such as lauric acid (C12), palmitic acid (C16), stearic acid (C18), or behenic acid (C22), or a fatty acid such as palmitoleic acid, oleic acid, erucic acid, and linoleic acid. Unsaturated fatty acids and the like are advantageously used in terms of cost. Also, coconut oil fatty acids,
Mixed fatty acids derived from natural products such as soybean oil fatty acid, tallow fatty acid, and sardine oil fatty acid can also be used.

When the polyhydric alcohol is esterified with these fatty acids, it is preferable that at least one hydroxyl group remains per molecular structural unit of the polyhydric alcohol.
When all hydroxyl groups are esterified, the antistatic effect is not sufficiently exhibited, particularly in the case of ethylene glycol and glycerin.

When sorbitol is esterified, it is simultaneously dehydrated in the molecule to form sorbitan.
The resulting compound is a sorbitan ester.

The fatty acid esters of polyhydric alcohols can also be produced by a transesterification reaction. In the case of a generally well-known monoglyceride, it can be obtained by adding glycerin to animal and vegetable fats and oils and heating it together with a catalyst.

The polyethylene glycol (2) preferably has a repeating unit of ethylene oxide of 4 to 1,000. Polyethylene glycol can be used as it is as an antistatic agent, but it is not always necessary to leave a terminal hydroxyl group in the case of fatty acid esterification for the purpose of further increasing the compatibility.

The higher alcohol of (3) is not particularly limited as long as it has 6 or more carbon atoms. Typical examples of industrially easily available nonyl alcohol, decyl alcohol, lauryl alcohol, myristyl alcohol, Primary alcohols such as cetyl alcohol, stearyl alcohol and oleyl alcohol can be mentioned. Mixtures such as sperm alcohol and jojoba alcohol, and reduced alcohols such as tallow alcohol and coconut alcohol can also be used.

Examples of the polyhydric alcohol include glycerin, trimethylolpropane, pentaerlit, sorbitol, and sucrose. Examples of the alkylphenol include nonylphenol, dodecylphenol, octylphenol, octylcresol and the like.

In the compound (3), these higher alcohols / polyhydric alcohols / alkylphenols and polyethylene glycol or polypropylene glycol form an adduct. The reaction may be carried out in two ways. That is, the dehydration etherification reaction of both, and the addition reaction of the latter monomer, ie, ethylene oxide and propylene oxide, to the former. Industrially, an addition reaction of ethylene oxide and propylene oxide is more preferably used. Ethylene oxide added,
The number of moles of propylene oxide added is determined in the range of 1 to 100, preferably 1 to 20.

It is desirable that the antistatic agent be sufficiently dried in advance. Insufficient drying causes thermal decomposition of the polylactic acid-based polymer.

In the present invention, one or more antistatic agents are selected from the above-mentioned antistatic agents, and the polylactic acid-based polymer 100
0.1 to 10 parts by weight with respect to parts by weight. When the ratio is below the range, the antistatic effect is not sufficiently exhibited. Specifically, it is important that the surface resistivity of the polylactic acid-based film and sheet, which is 10 ¹⁴ units, be improved to 5 × 10 ¹³ or less. When the surface resistivity is 5 × 10 ¹³ or less, even if static electricity is generated in the film and sheet in the process, the charge is quickly diffused.

On the other hand, if it exceeds, thermal decomposition occurs, causing a decrease in viscosity and poor compatibility. For this reason, extrusion becomes difficult, resulting in poor appearance of the film / sheet and poor sheeting. Specifically, at 190 ° C. in a nitrogen atmosphere, 3
It is necessary that the weight average molecular weight retention when heated for 0 minutes is 50% or more. If it is less than 50%, poor appearance and poor sheeting are caused during melt extrusion.

[0043]

The present invention is not limited by the following examples. The measured values shown in the examples were calculated by measuring under the following conditions.

Further, the polylactic acid-based polymer to be extruded is placed in a dryer circulating dehumidified air having a dew point of -45 ° C.
It was dried at 0 ° C. for 4 hours and stored in a moisture-proof container until immediately before extrusion. The antistatic agent was vacuum dried at 48 ° C. for 6 hours and stored in a desiccator until immediately before extrusion.

(1) Weight-average molecular weight Gel permeation chromatography HLC-8120GPC manufactured by Tosoh Corporation and GPC-80 of Shimadzu Corporation's Shim-Pack series Shim-Pack series.
Equipped with 0CP, solvent chloroform, solution concentration 0.2w
t / vol%, solution injection volume 200 μl, solvent flow rate 1.0
The measurement was carried out at a solvent temperature of 40 ° C. at a ml / min, and the weight average molecular weight was calculated in terms of polystyrene. The weight average molecular weight of the standard polystyrene used was 2,000,000, 6700.
00, 110,000, 35,000, 10,000, 400
0,600.

(2) Thermal stability (weight-average molecular weight retention) 2 g of a polylactic acid-based polymer whose weight-average molecular weight was measured and a predetermined amount of an antistatic agent were dissolved in 500 ml of chloroform.
After sufficiently stirring, chloroform was volatilized by an evaporator, followed by vacuum drying at 60 ° C. for 6 hours, and the obtained coarse powder was ground in a mortar to obtain a white powder. This white powder was placed in a 50 cc test tube, purged with a large excess of nitrogen, plugged, heated in a 190 ° C. heat block for 30 minutes, and the weight-average molecular weight was measured again. The weight average molecular weight retention as an index of stability was calculated. The unit is%.

Weight average molecular weight retention (%) = {(weight average molecular weight before heating) / (weight average molecular weight after heating)} × 10
0

(3) Surface resistivity After the film-shaped test piece was allowed to stand at 23 ° C. and 50% RH for 90 hours, the surface resistivity was measured according to JIS K-6911 under the same atmosphere using a surface resistivity meter manufactured by ADVANTEST. In compliance with the above, the electrode processing was performed by a vapor deposition method, the main electrode diameter was 5 cm, the gap between the main electrode and the counter electrode was 1 cm, the applied voltage was 500 V, and the applied time was 60.
Measurements were taken in seconds. The unit is Ω.

(Examples 1 to 3 / Comparative Examples 1 to 3) Poly L-lactic acid having a weight average molecular weight of 223,000 (Lacty 1012 manufactured by Shimadzu Corp.) was extruded using a 40 mmφ single screw extruder.
A T-die was extruded at a set temperature of 210 ° C. and rapidly cooled with a cast roll to obtain a cast film having a thickness of 100 μm.

In the same manner, glycerin monostearate was added to the same raw materials in the amounts shown in Table 1 to obtain cast films. Table 1 shows the results of these evaluations.

[0051]

[Table 1]

Examples 4 to 9 Next, in the same manner, various amounts of nonionic antistatic agents shown in Table 2 were added to obtain cast films. Table 2 shows the evaluation results.

[0053]

[Table 2]

(Comparative Examples 4 to 9) Subsequently, in the same manner,
Various amounts of anionic and cationic antistatic agents shown in Table 3 were added to obtain cast films. Table 3 shows the evaluation results.

[0055]

[Table 3]

As shown in Table 1, when the nonionic antistatic agent contained in the present invention was contained in an amount of 0.1 to 10 parts by weight, the surface resistivity was 5 × 10 ¹³ or less and the weight average molecular weight was maintained. The rate is 50% or more. Also, as shown in Table 2,
Examples 4 to 6 using the compound group contained in (1),
Example 7 using the compound group included in (2), (3)
In Examples 8 and 9 using the compound group included in the above, the surface resistivity is 5 × 10 ¹³ or less, and the weight average molecular weight retention is 50% or more.

On the other hand, Comparative Examples 4 to 9 using an anionic or cationic antistatic agent not included in the compound group of (1) to (3) had a surface resistivity exceeding 5 × 10 ¹³ , or , The weight average molecular weight retention is less than 50%.

[0058]

As apparent from the above results, the biodegradable antistatic polylactic acid composition of the present invention has good thermal stability during melt extrusion and has practical antistatic properties.

Continued on the front page (72) Inventor Shigenori Terada 5-8, Mitsuya-cho, Nagahama-shi, Shiga F-term (reference) 4J002 CF18W CH022 CH052 EC046 EC056 EC066 ED036 EH036 EH046 EH056 EJ026 FD102 FD106

Claims (5)

[Claims] 1. A polylactic acid-based polymer having the following compound group (1):
To (3): (1) polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, trimethylolpropane, pentaerlit, and sorbite and / or fatty acid esters thereof, and (2) polyethylene glycol and / or fatty acids thereof. Esters, (3)
An antistatic composition comprising 0.1 to 10 parts by weight of at least one nonionic antistatic agent selected from higher alcohols, polyhydric alcohols, polyethylene glycol adducts of alkylphenols, and polypropylene glycol adducts. Polylactic acid-based composition. (1) The fatty acid ester of the polyhydric alcohol is lauric acid (C12), palmitic acid (C1
6), stearic acid (C18) and behenic acid (C22)
The antistatic polylactic acid-based composition according to claim 1, which is a saturated fatty acid ester selected from the group consisting of: an unsaturated fatty acid ester selected from palmitoleic acid, oleic acid, erucic acid, and linoleic acid. 3. The fatty acid ester of the polyhydric alcohol (1), wherein at least one hydroxyl group remains per molecular structural unit of the polyhydric alcohol.
2. The antistatic polylactic acid composition according to item 1. (2) The polyethylene glycol is:
The antistatic polylactic acid composition according to claim 1, wherein the repeating unit of ethylene oxide is 4-1000. (3) The higher alcohol is selected from nonyl alcohol, decyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol and oleyl alcohol. (3) The polyhydric alcohol is glycerin, trimethylol Selected from propane, pentaer slit, sorbitol and sucrose; (3) the alkylphenol is nonylphenol,
The antistatic polylactic acid-based composition according to claim 1, which is selected from dodecylphenol, octylphenol, and octylcresol.