JPH09221587A - Antistatic polylactic acid film and sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart antistatic properties to a polylactic acid film and sheet. SOLUTION: An antistatic polylactic acid film or sheet is prepd. by incorporating, into a polylactic acid polymer, at least one nonionic antistatic agent selected from among the following: a polyhydric alcohol (e.g. ethylene glycol, diethylene glycol, triethylene glycol, glycerin, trimethylolpropane, pentaerythritol, or sorbitol) and/or its fatty acid ester; polyethylene glycol and/or its fatty acid ester; and a polyethylene or polypropylene glycol adduct to a higher alcohol, a polyhydric alcohol, or an alkyl phenol.

Description

Detailed Description of the Invention

The present invention relates to biodegradable films and sheets having antistatic properties.

[0002]

2. Description of the Related Art Due to increasing environmental problems in recent years, when plastic products are discarded in the natural environment, they will decompose and
It is beginning to be demanded that it disappears and eventually does not adversely affect the natural environment.

Since conventional plastics are stable in a natural environment for a long period of time and have a low bulk specific gravity, problems such as accelerating the shortening of the life of landfills for waste and impairing the natural landscape and the living environment of wild animals and plants. The point was pointed out.

Therefore, biodegradable plastic materials have been attracting attention 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.

Biodegradable plastics that have been put into practical use include aliphatic polyesters, modified PVA, cellulose ester compounds, modified starches, and blends thereof. Each of these biodegradable plastics has its own unique characteristics, and it is possible to develop applications according to these characteristics. Among them, the polylactic acid-based polymer, which is one of the aliphatic polyesters, is another biodegradable plastic. Compared with other materials, it is superior in transparency, rigidity, heat resistance, workability, etc., and therefore, in the field of transparent films and sheets where hard polyvinyl chloride (PVC), polystyrene, polyethylene terephthalate (PET) has been used. It is about to be developed.

However, films and sheets made of polylactic acid type polymers have a large specific resistance, as seen in general-purpose plastics such as PVC, so that they are easily charged by friction or the like, and have the following defects. Had.

A person receives a shock when touched. Spark discharge may cause a fire. Repulsion or sticking between films or other objects reduces processing workability and handleability during use. Adhesion of dust impairs aesthetics and hygiene, and reduces product value.

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

[0009]

However, the polylactic acid-based polymer is remarkably inferior in thermal stability in an extruder to general-purpose plastics and is apt to cause a decrease in molecular weight. Usually, the addition of the antistatic agent further promotes the reduction of the molecular weight, so that the production stability is reduced, and the product quality including mechanical properties is reduced or varied. Therefore, it was substantially difficult to knead the antistatic agent in the extrusion process.

Antistatic agents are cation-based / anion-based
They are roughly divided into amphoteric ionic and non-ionic types, and are used properly according to the processing method and application. The most commonly used general-purpose plastic film and sheet applications are anionic compounds with a good balance of effect and economy, typically 1) fatty acid salts, 2) higher alcohol sulfate ester salts, and 3). Liquid fatty oil sulfate ester salts, 4) Sulfate salts of aliphatic amine and aliphatic amide, 5) Fatty alcohol phosphate ester salts, 6) Dibasic fatty acid ester salts, 7) Fatty acid amide sulfonates, 8) Alkyl Examples include aryl sulfonates, 9) formalin-condensed naphthalene sulfonates, and the like.

Further, as a cation system which is vulnerable to heat and is high in cost but has a high antistatic property, 1) aliphatic amine salts,
2) Quaternary ammonium salts, 3) alkylpyridinium salts and the like. Furthermore, as a zwitterionic system having slightly improved heat resistance, which is a weak point of the anionic system, 1) imidazoline derivatives, 2) ammonium carboxylates,
3) ammonium sulfates, 4) ammonium phosphates, 5) ammonium sulfonates and the like.

Although these ionic antistatic agents are used in a wide range and in large amounts in general-purpose plastic film and sheet applications, they cannot be suitably used in the polylactic acid-based polymer of the present invention. This is because, although the desired antistatic effect is obtained, the kneading of these causes the polylactic acid-based polymer to undergo significant thermal decomposition in the extruder, causing a decrease in the molecular weight.
A decrease in the molecular weight leads to a decrease in production stability, a decrease or variation in product quality such as mechanical properties and heat resistance, and a deterioration in appearance such as occurrence of flow unevenness, which is extremely undesirable in practice.

Further, the method of applying the antistatic agent to the surface of the film or sheet has the following problems. Since coating equipment is required and the number of processes is increased, the manufacturing cost is increased.
Since the liquid antistatic agent is scattered around, maintenance of the work environment is complicated. Quality problems such as stickiness, blooming, interference fringes, and blocking tend to occur.

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

[0015]

The present inventors have completed the present invention as a result of intensive studies in view of such a current situation.

The gist of the present invention is that the polylactic acid polymer contains 0.1 to 10 parts by weight of at least one nonionic antistatic agent selected from the following compound groups (1) to (3). It is a characteristic antistatic polylactic acid-based film and sheet.

(1) Polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, trimethylolpropane, pentaer slit, sorbit and / or fatty acid esters thereof (2) polyethylene glycol and / or fatty acid esters thereof ( 3) Polyethylene glycol adduct of higher alcohol / polyhydric alcohol / alkylphenol or polypropylene glycol adduct

[0018]

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, UV absorbers, light stabilizers, mildew-proofing agents, pigments, fluorescent agents, and modifiers are added for the purpose of adjusting molding processability and physical properties of films and sheets. It is also possible to add.

Examples of lactic acid include 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. Typical examples include 6-hydroxycaproic acid and the like.

As these polymerization methods, any known method such as condensation polymerization method and ring-opening polymerization method can be adopted, and further, a small amount of a chain extender for increasing the molecular weight, 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 polymer is melt extruded from a die using an extruder and formed into a film or a sheet. As a special case, pellet press molding or calender molding may be used as long as it is in a molten state.

When extruding the polylactic acid polymer, it is desirable to sufficiently dry the raw materials in advance in order to prevent thermal decomposition (hydrolysis) in the extruder.

When a film is to be obtained, a flat material or a cylindrical material melt-extruded from a T-die, an I-die, a round die or the like is rapidly cooled with a cooling cast roll, water, compressed air or the like, and if necessary, continuously rolled. Uniaxially or biaxially stretched by the method, tenter method, 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.

Further, by using the film stretching / heat-setting technology as disclosed in Japanese Patent Publication No. 5-508819 and Japanese Patent Laid-Open No. 6-23836, transparency, mechanical strength, rigidity, thermal dimensional stability, etc. can be obtained. It is possible to obtain an excellent polylactic acid-based film. 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 the sheet is a method of extruding the sheet in a plane form using a T-die and quenching it with a metal cast roll equipped with a temperature control device. If necessary, the sheet is made of a metal different from the cast roll. By nipping with a roll, a polylactic acid-based sheet having excellent transparency and smoothness can be obtained. The thickness of the sheet depends on the application
It is determined in the range of approximately 250 μm to 1 mm.

As the extruder to be used, all known forms such as a single-screw, same-direction twin-screw, and different-direction twin-screw extruder can be used. The most common method is to preliminarily pelletize a raw material containing the prescribed additive using a co-direction twin-screw extruder having a high kneading effect, and then feed it to a film / sheet extruder. The agent or the like may be directly mixed with the raw material when the film / sheet is extruded.

The set temperature of the extruder is appropriately determined depending on the chemical composition and molecular weight of the polylactic acid polymer, but 170 to 2
A range of 30 ° C. is preferred. Below 170 ° C, melting point is 1
The homopolymer at 75 ° C. does not melt, and at 230 ° C. or higher, thermal decomposition becomes remarkable.

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

In order to minimize the thermal decomposition of the polylactic acid type polymer and to make a practical film / sheet, the most important point in the present invention is the nonionic type shown in the following (1) to (3). It is to adopt an antistatic agent.

(1) Polyhydric alcohols such as ethylene glycol / diethylene glycol / triethylene glycol / glycerin / trimethylolpropane / pentael slit / sorbit and / or fatty acid esters thereof (2) polyethylene glycol and / or fatty acid esters thereof ( 3) Polyethylene glycol adducts of higher alcohols / polyhydric alcohols / alkylphenols, or polypropylene glycol adducts (1) The polyhydric alcohols can be used as they are, but in order to improve the compatibility with polylactic acid-based polymers. Furthermore, it is more desirable to form a fatty acid ester by an esterification reaction with a fatty acid. Fatty acids include, but are not limited to, lauric acid (C12) and palmitic acid (C1).
6), saturated fatty acids such as stearic acid (C18) and behenic acid (C22), unsaturated fatty acids such as palmitoleic acid, oleic acid, erucic acid, and linoleic acid are advantageously used in terms of cost. Also, a mixed fatty acid derived from a natural product such as coconut oil fatty acid, soybean oil fatty acid, beef tallow fatty acid, sardine oil fatty acid, etc. can 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 the hydroxyl groups are esterified, the antistatic effect is not sufficiently exhibited, especially in the case of ethylene glycol and glycerin.

When esterifying sorbit, it is dehydrated in the molecule at the same time to form sorbitan.
The resulting compound is a sorbitan ester.

The fatty acid ester of polyhydric alcohol is also produced by a transesterification reaction. The generally well-known monoglyceride 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 an ethylene oxide repeating unit of 4 to 1000. Polyethylene glycol can be used as it is as an antistatic agent, but it is not always necessary to leave the terminal hydroxyl group in the case of esterification with a fatty acid for the purpose of further increasing compatibility.

The higher alcohol (3) is not particularly limited as long as it has 6 or more carbon atoms, but typical industrially available ones are nonyl alcohol, decyl alcohol, lauryl alcohol, myristyl alcohol, Primary alcohols such as cetyl alcohol, stearyl alcohol and oleyl alcohol can be mentioned. It is also possible to use a mixture of sperm alcohol, jojoba alcohol, etc., or a reducing alcohol such as beef tallow alcohol, coconut alcohol, etc.

Further, examples of the polyhydric alcohol include glycerin, trimethylolpropane, pentael slit, sorbit, sucrose and the like. Examples of the alkylphenol include nonylphenol, dodecylphenol, octylphenol, octylcresol and the like.

In the compound (3), these higher alcohol / polyhydric alcohol / alkylphenol and polyethylene glycol or polypropylene glycol form an adduct, and the reaction includes two methods. That is, it is a dehydration etherification reaction of both, and an addition reaction of the latter monomer, that is, ethylene oxide and propylene oxide to the former. Industrially, the addition reaction of ethylene oxide and propylene oxide is
It is more preferably used. The number of moles of ethylene oxide or propylene oxide added is 1 to 10
It is determined in the range of 0, preferably 1 to 20.

Further, it is desirable that the antistatic agent is sufficiently dried in advance. Insufficient drying causes thermal decomposition of the polylactic acid polymer.

In the present invention, one or more kinds of the above antistatic agents are selected and the polylactic acid polymer 100 is selected.
0.1 to 10 parts by weight is blended with respect to parts by weight. If it is less than this 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. By setting the surface resistivity to 5 × 10 ¹³ or less, even if static electricity is generated on the film and the sheet in the process, the charge is quickly diffused.

On the contrary, if it exceeds the above range, thermal decomposition occurs, resulting in a decrease in viscosity and poor compatibility. As a result, extrusion becomes difficult, resulting in poor appearance of the film / sheet and poor sheeting. Specifically, 3 at 190 ℃ in a nitrogen atmosphere
The weight average molecular weight retention rate after heating for 0 minutes must be 50% or more. If it is less than 50%, a poor appearance and a poor sheeting are caused during melt extrusion.

[0041]

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.

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

(1) Weight average molecular weight Tolso Co., Ltd. gel permeation chromatography HLC-8120GPC, Shimadzu Corporation chromatographic column Shim-Pack series GPC-80.
0CP attached, solvent chloroform, solution concentration 0.2w
t / vol%, solution injection amount 200 μl, solvent flow rate 1.0
The measurement was carried out at a solvent temperature of 40 ° C. at 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, 110000, 35000, 10000, 400
It is 0,600.

(2) Thermal stability (weight average molecular weight retention rate) 2 g of the polylactic acid polymer of which the weight average molecular weight was measured and a predetermined amount of antistatic agent were dissolved in 500 ml of chloroform,
After sufficiently stirring, chloroform was volatilized with 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 put in a 50 cc test tube, purged with a large excess of nitrogen, capped and heated in a heat block at 190 ° C. for 30 minutes, and then the weight average molecular weight was measured again. The weight average molecular weight retention rate, which is an index of stability, was calculated. The unit is%.

Weight average molecular weight retention rate (%) = {(weight average molecular weight before heating) / (weight average molecular weight after heating)} × 10
0 (3) Surface resistivity After leaving a film-shaped test piece for 90 hours at 23 ° C. and 50% RH, using a surface resistivity measuring machine manufactured by ADVANTEST, under the same atmosphere, according to JIS K-6911. , Electrode treatment is vapor deposition method, diameter of main electrode is 5 cm, clearance between main electrode and counter electrode is 1 cm, applied voltage is 500 V, application time is 60
The measurement was performed 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 223000 (Lacty 1012 manufactured by Shimadzu Corporation) was used in a 40 mmφ single screw extruder.
A T-die was extruded at a set temperature of 210 ° C. and quenched with a cast roll to obtain a cast film having a thickness of 100 μm.

In the same manner, glycerin monostearate in the amount shown in Table 1 was added to the same raw material to obtain a cast film. The results of these evaluations are shown in Table 1.

[0048]

[Table 1] (Examples 4 to 9) Next, in the same manner, various nonionic antistatic agents in the amounts shown in Table 2 were added to obtain cast films. Table 2 shows the evaluation results.

[0049]

[Table 2] (Comparative Examples 4 to 9) Subsequently, in the same manner, the amounts of various anionic and cationic antistatic agents shown in Table 3 were added to obtain cast films. Table 2 shows these evaluation results.
Shown in

[0050]

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

On the other hand, Comparative Examples 4 to 9 using the anionic and cationic antistatic agents which are not included in the compound groups (1) to (3) have surface resistivity of more than 5 × 10 ¹³ , or The weight average molecular weight retention rate is less than 50%.

[0052]

As is clear from the above results, the biodegradable film and sheet of the present invention have good thermal stability during melt extrusion and practical antistatic properties.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area C09K 3/16 102 C09K 3/16 102 106 106

Claims (1)

[Claims] 1. The following compound group (1) is added to a polylactic acid polymer.
An antistatic polylactic acid-based film and sheet containing 0.1 to 10 parts by weight of at least one kind of nonionic antistatic agent selected from (3) to (3). (1) Polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, trimethylolpropane, pentaer slit, sorbit and / or fatty acid esters thereof (2) polyethylene glycol and / or fatty acid esters thereof (3) higher grade Polyethylene glycol adduct of alcohol / polyhydric alcohol / alkylphenol or polypropylene glycol adduct