JP5046079B2 - Flame retardant polylactic acid resin composition - Google Patents

Description

  The present invention relates to a flame retardant polylactic acid resin composition obtained by imparting flame retardancy to polylactic acid.

  Conventional general-purpose plastics such as polyethylene and polypropylene use petroleum as a fossil fuel as a raw material, and increase carbon dioxide in the air when incinerated. For this reason, the problem of exhaustion of petroleum resources and global warming has arisen.

  For this reason, polylactic acid that can be produced from biomass such as sugarcane has attracted attention. Polylactic acid uses starch as a raw material as a result of photosynthesis of carbon dioxide in plants such as sugarcane, and is decomposed by microorganisms in the soil to return to the atmosphere as carbon dioxide or water. For this reason, it does not lead to an increase in carbon dioxide in the atmosphere, and it is a very convenient material for building a sustainable recycling society. Moreover, since polylactic acid is relatively inexpensive, has high mechanical strength, can be injection molded, and has excellent transparency, it is widely used as a biodegradable plastic for producing molded products.

  In addition, in order to overcome the brittleness that is a drawback of polylactic acid, a biodegradable plastic such as soft polybutylene succinate is blended as a plasticizer to improve impact resistance. Furthermore, a technique for improving flexibility, impact resistance and moldability by crosslinking a polyfunctional isocyanate compound or a polyhydric phenol compound to such a polylactic acid resin composition has been developed (Patent Document 1).

  However, there are still many problems that have yet to be solved with regard to the technology for flame retarding polylactic acid. In conventional general-purpose plastics, bromine compounds such as antimony chloride and decane bromide are used as flame retardants. By adding a small amount of these flame retardants to general-purpose plastics, excellent flame retardant effects can be obtained. can get. However, polylactic acid is a biodegradable plastic selected in consideration of the environment. If such a harmful substance is mixed, its properties as an environmentally compatible material are impaired. In addition, the use of these flame retardants has been subject to usage regulations in recent years (RoHS directive based on Article EC95, etc.), and flame retardants with excellent safety in place of these flame retardants are required. .

  As a flame retardant considering such safety, a flame retardant made of aluminum hydroxide or magnesium hydroxide is used in general-purpose plastics. Furthermore, a technique for adding aluminum hydroxide or magnesium hydroxide as a flame retardant to a biodegradable plastic has also been proposed (see, for example, Patent Document 2). These flame retardants are highly safe in terms of toxicity.

  A flame retardant for polylactic acid has also been proposed. For example, Patent Document 3 discloses a combination of various resins containing polylactic acid and a silicone flame retardant. Furthermore, Patent Document 4 shows that urea, ammonium phosphate, ammonium polyphosphate and guanidine are effective as flame retardants for polylactic acid resins.

JP 2004-346241 A JP-A-8-252823 JP 2000-319532 A Japanese Patent Laid-Open No. 2004-27079

  However, the flame retardant composed of aluminum hydroxide or magnesium hydroxide described in Patent Documents 1 and 2 cannot obtain a sufficient flame retardant effect unless it is added in a considerably large amount to the plastic. For this reason, when aluminum hydroxide or magnesium hydroxide is added as a flame retardant to polylactic acid which is brittle and inferior in impact resistance as compared with general-purpose plastics, there arises a problem that brittleness is further increased and impact resistance is inferior. In addition, there is a problem that kneading is difficult due to lack of fluidity at the time of molding, and cracking is likely to occur and molding becomes difficult. This is an obstacle to the general use of polylactic acid as an engineering plastic, and development of a flame retardant suitable for polylactic acid is desired. Furthermore, during the molding, these hydroxides generate water, which may cause polylactic acid to be hydrolyzed and deteriorate.

  In addition, the flame retardant for polylactic acid described in Patent Document 3 is a method in which a silicone-based flame retardant is made by a sol-gel method in a solution of a polylactic acid resin composition. Compared with a simple kneading method, such as a flame retardant, it takes much time and the production cost increases.

  Furthermore, the flame retardant for polylactic acid described in Patent Document 4 is effective in terms of flame retardancy, but is not considered in terms of impact resistance and flexibility, and is simply a polylactic acid composition. Just kneading into an object increases the brittleness, resulting in problems such as poor impact resistance and flexibility.

  The present invention has been made in view of the above-described conventional situation, and solves the problem of providing a flame-retardant polylactic acid resin composition that is easy to manufacture and mold, and excellent in impact resistance and flexibility. It should be a challenge.

  The inventors have developed a polylactic acid resin composition in which polylactic acid and a soft biodegradable plastic are cross-linked with a polyfunctional isocyanate compound as a polylactic acid resin composition excellent in flexibility, impact resistance and moldability. Selected and considered adding a flame retardant to it. However, when aluminum hydroxide or magnesium hydroxide is added as a flame retardant, a considerable amount (50% by weight or more based on the resin) is added to develop flame retardancy, and the flame retardant itself aggregates. As a result, it became clogged in the extruder and became impossible to mold. If the amount of aluminum hydroxide or magnesium hydroxide is reduced, molding becomes possible, but the flame retardant effect is insufficient. On the other hand, when ammonium polyphosphate was used as a flame retardant, the surprising fact that contrary to expectation, rather than lowering impact resistance and flexibility, was improved, and the present invention was made. It was.

That is, the flame retardant polylactic acid resin composition of the present invention has polylactic acid, a polyfunctional isocyanate compound having a plurality of isocyanate groups in one molecule, and a functional group capable of chemically bonding to the isocyanate group. Soft biodegradable plastic and ammonium polyphosphate are mixed,
The mixing ratio of the polylactic acid and the soft biodegradable plastic is 95: 5 to 20:80 by mass ratio, and the mixing ratio of the total of the polylactic acid and the soft biodegradable plastic and ammonium polyphosphate is mass. The ratio is 96: 4 to 80:20.

In the flame-retardant polylactic acid resin composition of the present invention, since polylactic acid, a polyfunctional isocyanate compound, and a soft biodegradable plastic are mixed, the polylactic acid and the soft biodegradable plastic are heated during molding. Cross-linking is performed by the polyfunctional isocyanate compound, and phase separation from each other is suppressed. As a result, the peeling phenomenon at the interface between different phases is suppressed, and the impact resistance is improved.
Moreover, since ammonium polyphosphate is mixed as a flame retardant, flame retardancy is exhibited. In addition, by mixing ammonium polyphosphate, impact resistance is dramatically improved and flexibility is also improved. Although the cause of the improvement in impact resistance and flexibility contrary to conventional technical common sense is not necessarily clear, in addition to the increase in mechanical strength such as impact due to the crosslinking effect by the polyfunctional isocyanate compound, polyphosphorus It is presumed that because the ammonium acid powder is uniformly dispersed, stress is evenly applied to the ammonium polyphosphate fine powder, and the stress is dispersed.

  The mixing ratio of the total of polylactic acid and soft biodegradable plastic and ammonium polyphosphate is required to be 96: 4 to 80:20 by mass ratio. If the content of ammonium polyphosphate is less than this, the flame retardant effect may be insufficient. Moreover, when there is more content of ammonium polyphosphate than this, ammonium polyphosphate will aggregate and form a large secondary particle, and impact resistance and flexibility will fall.

  Moreover, the mixing ratio of polylactic acid and soft biodegradable plastic is required to be in the range of 95: 5 to 20:80 by mass ratio. If the polylactic acid is more than 95% by weight, it is difficult to improve the impact resistance. Conversely, if the polylactic acid is less than 20% by weight, the high rigidity characteristic of polylactic acid is impaired. Particularly preferred is the range of 85:15 to 70:30.

  In the present invention, the soft biodegradable plastic having a functional group capable of chemically bonding with an isocyanate group is an isocyanate such as a hydroxyl group or a carboxylic acid group among all elastomers biodegradable by microorganisms in soil. It means anything having a functional group capable of chemically bonding to a group. Specifically, soft biodegradable plastics derived from natural polymers such as starch, cellulose acetate, (chitosan / cellulose / starch) polymerization systems, polycaprolactone, polybutylene succinate, polyethylene succinate, poly (butylene succinate) / Adipate), poly (butylene succinate / carbonate), polyethylene succinate, poly (butylene succinate / terephthalate), soft polymer biodegradable plastics such as polyvinyl alcohol, and poly (hydroxybutyrate / hydroxyvalylate). Microbial production type soft biodegradable plastics such as Moreover, these can also be mixed and used.

  In addition, the polylactic acid may be synthesized by the user himself, but it is also possible to use a commercially available product because it is easily available. Specifically, Natur re Works (registered trademark) manufactured by Cargill-DOW, U'z (registered trademark) manufactured by Toyota Motor Corporation, TONE (registered trademark) manufactured by UCC, Shimadzu Corporation Lacti (registered trademark) manufactured by Unitika Ltd., Terramac (registered trademark) manufactured by Unitika Co., Ltd., Lacia manufactured by Mitsui Chemicals, Inc., Lactron (registered trademark) manufactured by Kanebo Gosei Co., Ltd. Examples thereof include Plastarch (registered trademark) manufactured by Kuraray Co., Ltd., Palgreen (registered trademark) manufactured by Tosero Co., Ltd., and the like.

  Specific examples of the polyfunctional isocyanate compound in the present invention include hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate. Narate, dicyclohexylmethane-4,4′-diisocyanate, 2,6-diisocyanatohexanoic acid methyl ester, 2-isocyanatoethyl-2,6-diisocyanatocaproate, 3-isocyanatopropyl-2 Aliphatic isocyanates such as 1,6-diisocyanatocaproate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate and 2,6-tolylene diene Mixed isocyanate with isocyanate, 4,4'-diphenyl meta Aromatics such as isocyanates, hydrogenated diphenylmethane diisocyanate, diphenylmethylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate Examples thereof include triisocyanates such as isocyanates, adducts of trimethylolpropane and toluylene diisocyanate, adducts of trimethylolpropane and 1,6-hexamethylene diisocyanate, and the like. One or more of these can be used.

From the above-mentioned polyfunctional isocyanate, it can be appropriately selected according to the characteristics of the intended flame-retardant polylactic acid resin composition. For example, when a flame retardant polylactic acid resin composition having excellent impact resistance is intended, a polyfunctional isocyanate having a structure in which an aromatic ring as an electron-withdrawing group is adjacent to the isocyanate is selected. This is because the rigidity of the cross-linked portion is enhanced. When a flame retardant polylactic acid resin composition having excellent biodegradability is intended, an aliphatic polyfunctional isocyanate compound that does not contain an aromatic ring and is easily decomposed by microorganisms is selected.
Also preferred is 2-isocyanatoethyl-2,6-diisocyanatocaproate having three isocyanate groups in one molecule. Since this polyfunctional isocyanate has three functional groups in the molecule, there is a high possibility of co-chain extension between polylactic acid and a soft biodegradable plastic, and the effect of improving mechanical strength by cross-linking is enhanced. Because.

  The polyfunctional isocyanate compound is preferably contained in an amount of 0.1 to 2.0% by weight based on the total of polylactic acid and soft biodegradable plastic. When the addition amount of the polyfunctional isocyanate compound is less than 0.1% by weight, the crosslinking effect by the polyfunctional isocyanate becomes insufficient, and the effect of improving impact resistance and flexibility cannot be sufficiently obtained. Moreover, when the addition amount of the polyfunctional isocyanate compound exceeds 2.0% by weight, excess isocyanate groups cause cross-linking between molecules, leading to an increase in gelation fraction, impact resistance and flexibility. Decreases.

  Either polylactic acid or soft biodegradable plastic has either a hydroxyl group at both ends, a carboxylic acid group at both ends, or a telechelic structure having one hydroxyl group and the other end having a carboxylic acid group It is preferable that If this is the case, the isocyanate group in the polyfunctional isocyanate compound reacts with the terminal hydroxyl group or terminal carboxylic acid group of polylactic acid or soft biodegradable plastic, and the cross-linking reaction between polylactic acid or soft biodegradable plastics. Crosslinking reaction between the polylactic acid and the soft biodegradable plastic occurs, and the impact resistance and flexibility of the flame retardant polylactic acid resin composition can be improved.

  Also, the soft biodegradable plastic can be a polyester elastomer. The polyester elastomer has a hydroxyl group or a carboxylic acid group at the terminal and can be easily bonded to a polyfunctional isocyanate compound. The inventors have confirmed that, when polybutylene succinate is used as the polyester elastomer, excellent impact resistance and excellent flexibility can be obtained with certainty.

  As the molecular weight of the polylactic acid used in the present invention, those having a weight average molecular weight in the range of 50,000 to 1,000,000 are preferable. If the thickness is below this range, the mechanical strength is weakened, and if the molecular weight is higher than that, the processability is inferior.

  The flame-retardant polylactic acid-based resin composition of the present invention can be produced by heating and melting and mixing polylactic acid, a soft biodegradable plastic, a polyfunctional isocyanate compound, and ammonium polyphosphate. The method of heat-melt mixing is not particularly limited, but industrially preferred is a method capable of continuous treatment. Specifically, for example, a mixture obtained by mixing the above components at a predetermined ratio can be melted with a single screw extruder or a twin screw kneading extruder, and immediately molded into a molded product. Further, a mixture of the above components in a predetermined ratio may be once pelletized and then melt-molded as necessary. The method of forming after pelletizing is preferable because the composition becomes more uniform. In addition, the above components may be weighed out at a predetermined ratio and uniformly dissolved with a solvent, and then the solvent may be distilled off. However, the polyfunctional isocyanate compound has an isocyanate group that is highly reactive with moisture and the like. Since it contains, it is necessary to use the solvent which does not contain moisture.

  The melt extrusion temperature in the case of extrusion molding by an extruder may be appropriately selected in consideration of the melting point of the polylactic acid or soft biodegradable plastic used and the mixing ratio thereof, but generally 150 to 220 ° C. Is preferable, and a range of 180 to 200 ° C. is more preferable. In order to prevent deterioration or alteration during heat-melt molding, it is preferable to mix within as short a time as possible. Specifically, the extrusion is preferably performed within 20 minutes, preferably within 10 minutes.

  The polyfunctional isocyanate compound may be added after heat-melt mixing of polylactic acid and a soft biodegradable plastic, and may be heat-melt-mixed again, or all components may be heat-melt-mixed simultaneously as described above. May be.

  The flame retardant polylactic acid-based resin composition of the present invention can be subjected to various modifications by adding secondary additives as necessary within a range that does not impede achievement of the problems of the invention. Examples of secondary additives include antioxidants, ultraviolet absorbers, colorants, pigments, antibacterial agents, stabilizers, electrostatic agents, nucleating materials, various other fillers, and the like.

  Examples in which the present invention is further embodied will be described below in comparison with comparative examples.

(Examples 1-3)
Polylactic acid dried by 100 ° C for 4 hours (Unitika Ltd., Terramac TE4000) and polybutylene succinate dried by 50 ° C for 24 hours (Showa High Polymer Co., Ltd., Bionore (registered trademark)) # 1020) (hereinafter abbreviated as “PBS”), 2-isocyanatoethyl-2,6-diisocyanate caproate (manufactured by Kyowa Hakko Co., Ltd., LTI (registered trademark)) (hereinafter abbreviated as “LTI”) and polyline Ammonium acid (manufactured by Clariant Japan Co., Ltd., PEKOFLAM (registered trademark)) is weighed in the proportions shown in Table 1.

  After mixing these chemicals, the mixture was put into a medium-sized twin screw extruder (manufactured by Technobel Co., Ltd., KZW15-30TGN), heated, melted, kneaded and pelletized, and then an injection molding machine (Sumitomo Heavy Industries, Ltd. 18S) was used for injection molding to obtain a test piece having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm. The set temperatures for heat melting were 170 ° C, 190 ° C, 190 ° C, and 190 ° C at four locations from the hopper side to the tip side.

Further, Comparative Examples 1 to 6 having the compositions shown in Table 2 below were produced by the following method.

(Comparative Example 1)
Only polylactic acid was injection-molded by the same method as described above to prepare a test piece of Comparative Example 1.

(Comparative Example 2)
Polylactic acid and aluminum hydroxide were weighed out in a mass ratio of 63:37, and this was injection-molded in the same manner as in Example 1 to produce a test piece of Comparative Example 2.

(Comparative Example 3)
PBS and aluminum hydroxide were weighed out in a mass ratio of 63:37, and this was injection molded in the same manner as in Example 1 to produce a test piece of Comparative Example 3.

(Comparative Example 4)
Polylactic acid and PBS were heat-kneaded at a mass ratio of 90:10, and the polylactic acid resin composition thus obtained and magnesium hydroxide were weighed out at a mass ratio of 63:37, and this was the same as in Example 1. The test piece of Comparative Example 4 was produced by injection molding according to the above method.

(Comparative Example 5)
Polylactic acid and PBS were heat-kneaded at a mass ratio of 90:10, and the polylactic acid resin composition thus obtained and ammonium polyphosphate were weighed out at a mass ratio of 95: 5, and this was the same as in Example 1. The test piece of Comparative Example 5 was produced by injection molding according to the above method.

(Comparative Example 6)
Polylactic acid and ammonium polyphosphate were weighed out at a mass ratio of 95: 5, and this was injection molded in the same manner as in Example 1 to produce a test piece of Comparative Example 6.

<Evaluation>
About the test piece of Examples 1-3 produced as mentioned above and the test piece of Comparative Examples 1-6, the combustion test according to UL specification, the Charpy impact test based on JISK7111, and the flexibility test were done.

(Combustion test)
About the test piece of Examples 1-3 and Comparative Examples 1-4, the flame retardance test was done. The test method was performed according to UL94 standard. That is, as shown in FIG. 1, the flame of a gas burner is brought into contact with the lower end of the sample held vertically for 10 seconds. If the combustion stops within 30 seconds, indirect flame for another 10 seconds. The evaluation is performed with the following three types of V-0, V-1 and V-2.
V-0
No sample continues to burn for more than 10 seconds after any flame contact.
The total combustion time for 10 flames on 5 samples does not exceed 50 seconds.
There is no sample that burns to the position of the clamping clamp.
There is no sample that will drop the burning particles that ignite absorbent cotton placed under the sample.
V-1
No sample continues to burn for more than 30 seconds after any flame contact.
The total burning time for 10 flames on 5 samples does not exceed 250 seconds.
There is no sample that burns to the position of the clamping clamp.
There is no sample that will drop the burning particles that ignite absorbent cotton placed under the sample.
After the second flame contact, there is no sample that continues to heat red for more than 60 seconds.
V-2
No sample continues to burn for more than 30 seconds after any flame contact.
Total burning time for 10 flames on 5 samples
Does not exceed 250 seconds.
There is no sample that burns to the position of the clamping clamp.
The absorbent cotton placed under the sample is ignited. The burning particles are allowed to fall.
After the second flame contact, there is no sample that continues to heat red for more than 60 seconds.

Results Table 2 shows the results of the combustion test.

  As shown in Table 2, V-0 was achieved in Examples 2 and 3, and V-2 was achieved even in Example 1 where the amount of ammonium polyphosphate added was as small as 5%. Compared to this, in Comparative Example 1 containing no flame retardant, Comparative Examples 2 and 3 containing 37% aluminum hydroxide as a flame retardant, and Comparative Example 4 containing 37% magnesium hydroxide as a flame retardant Even V-2 was not achieved. From these results, it was found that the flame retardant polylactic acid resin composition of the present invention can provide an excellent flame retardant effect with a small amount of flame retardant added.

(Charpy impact test and flexibility test)
Example 1, Comparative Example 5 and Comparative Example 6 were evaluated by a Charpy impact test in accordance with JIS K7111 (the tester was manufactured by JT Toshi Co., Ltd., load W = 1.38 kgf by hammer mass, hammer rotation shaft) The distance from the center to the center of gravity is R = 0.327m.The test piece is No. 1 test piece (80 × 10 × 4 mm) shown in JISK7111, the notching direction is the edgewise direction, 23 ° C, 50% before the test Conditioned for more than 88 hours in a RH thermostatic chamber). The results are shown in Table 4.

  As shown in Table 4, Example 1 in which LTI and PBS were added to polylactic acid was more resistant to impact than Comparative Example 5 in which LTI was not added and Comparative Example 6 in which LTI and PBS were not added. Was found to be much better.

In addition, the test pieces of Example 1 and Comparative Examples 5 and 6 were subjected to a flexibility test in which bending from the center to 180 ° and bending to the opposite side by 180 ° were repeated. As a result, as shown in Table 5, in Comparative Example 5, it broke before being bent by 180 °, and in Comparative Example 6, it broke after 2-3 bending, whereas in Example 1, it was 3-4 times. As a result, it was found that it was excellent in flexibility.

(Observation with laser microscope)
Example 1 and Example 1 and resin compositions having different amounts of ammonium polyphosphate added were prepared, and the fracture surface was observed with a laser microscope. As a result, as shown in FIG. 2, it was found that when the amount of ammonium polyphosphate added was increased to 15%, the ammonium polyphosphate aggregated into large secondary particles. Since this secondary agglomeration phenomenon brings about a reduction in impact resistance and flexibility, the mixing ratio of the total of polylactic acid and soft biodegradable plastic to ammonium polyphosphate is 96: 4 to 80:20 in mass ratio. The degree is preferred.

  The present invention is not limited to the description of the embodiments of the invention. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

It is a photograph of a place where a combustion test is being performed. It is a laser micrograph of the fracture surface of the resin composition from which Example 1 and Example 1 and the addition amount of ammonium polyphosphate differ.

Claims (6)

Polylactic acid, a polyfunctional isocyanate compound having a plurality of isocyanate groups in one molecule, a soft biodegradable plastic having a functional group that can be chemically bonded to the isocyanate group, and ammonium polyphosphate are mixed. And
The mixing ratio of the polylactic acid and the soft biodegradable plastic is 95: 5 to 20:80 by mass ratio, and the mixing ratio of the total of the polylactic acid and the soft biodegradable plastic and ammonium polyphosphate is mass. A flame retardant polylactic acid resin composition characterized in that the ratio is 96: 4 to 80:20. 2. The flame retardant polylactic acid resin composition according to claim 1, wherein the polyfunctional isocyanate compound is 2-isocyanate ethyl-2,6-diisocyanate caproate.   The flame retardant polylactic acid according to claim 1 or 2, wherein the polyfunctional isocyanate compound is contained in an amount of 0.1 to 2.0% by mass based on the total of polylactic acid and soft biodegradable plastic. Resin composition.   Either polylactic acid or soft biodegradable plastic has either a hydroxyl group at both ends, a carboxylic acid group at both ends, or a telechelic structure having one hydroxyl group and the other end having a carboxylic acid group The flame-retardant polylactic acid resin composition according to claim 2 or 3, wherein   The flame retardant polylactic acid resin composition according to claim 4, wherein the soft biodegradable plastic is a polyester elastomer.   6. The flame retardant polylactic acid resin composition according to claim 5, wherein the polyester elastomer is polybutylene succinate.