WO2004063269A2

WO2004063269A2 - Flame retardant polypropylene resin composition with excellent weatherability

Info

Publication number: WO2004063269A2
Application number: PCT/KR2004/000063
Authority: WO
Inventors: In Sik Jung; Jae Whan Cho; Man Seang Her
Original assignee: Samsung Atofina Co. Ltd.
Priority date: 2003-01-15
Filing date: 2004-01-15
Publication date: 2004-07-29
Also published as: KR100901949B1; KR20040065078A; WO2004063269A3; CN1738859A; JP2006515036A; CN100336858C

Abstract

Disclosed herein is a flame retardant polypropylene resin composition with excellent weatherability. More specifically, the present invention relates to a flame retardant polypropylene composition comprising polypropylene resin having 4~40 g/min. melt flow index, halogen-based flame retardant having high-melting point, antimony oxide, inorganic filler, UV stabilizer, crosslinking agent and dripping-resistant agent. Using the composition of the present invention, there may be provided secondary product which has fire retardancy, maintainability of excellent early fire retardancy under the long term-UV exposure and hot water process, high-weatherability, and excellent mechanical property.

Description

FLAME RETARDANT POLYPROPYLENE RESIN COMPOSITION WITH EXCELLENT WEATHERABILITY

Technical Field

The present invention relates to a flame retardant polypropylene resin composition comprising a polypropylene resin as a main component. More particularly, the present invention relates to a flame retardant polypropylene resin composition with excellent weather resistance which comprises a polypropylene resin having a melt flow index of 4-40 g/10min., a high melting point halogen-based flame retardant, a flame retardant additive, a UN stabilizer, a crosslinking agent and an anti- dripping agent. The flame retardant polypropylene resin composition can maintain its early flame retardancy and exhibit a high retention of mechanical properties even after hot water immersion.

Background Art

Polypropylene resins are widely used in a variety of applications, e.g., household electric appliances, construction materials, interior decorative materials and automobile parts because of their excellent processability, chemical resistance, mechanical strength and the like. However, since polypropylene resins have poor flame retardancy, they have limited applications to automobile parts and electric/electronic components in a place where there is a large risk of fire. For this reason, a number of studies to impart satisfactory fire retardancy to various polyolefm resins by the addition of inorganic, organic and phosphorus-based flame retardants are being actively undertaken.

For instance, Japanese Patent Laid-open Νos. 53-92855, 54-29350, 54-77658, 56-26954, 57-87462 and 60-110738 disclose techniques for preparing a flame retardant polypropylene resin composition by adding magnesium hydroxide, aluminum hydroxide, hydrotalcite or the like as an inorganic flame retardant to impart flame retardancy to a polypropylene resin. These techniques, however, have problems that since 50% or higher of inorganic fillers must be added in order to achieve flammability class N-O, the processability is bad, gas may be evolved from the products and the impact strength is drastically deteriorated. Japanese Patent Publication No. 55-30739 reports a flame retardant polypropylene resin composition prepared by adding a halogen compound such as decabromodiphenyl ether and dodecachloro-dodecahydromethanodibenzocyclooctene as an organic flame retardant. Techniques are also known to prepare flame retardant polypropylene resin compositions by the addition of tetrabromobisphenol A bis- (dibromopropylether), bis-(tribromophenoxyethyl)tetrabromobisphenol A ether, hexabromo cyclododecane and tetrabromobisphenol A.

Japanese Patent Laid-open No. Hei 8-302102 discloses a flame retardant polypropylene resin composition having improved blooming resistance and weather resistance which comprises an organic halogen-based compound and a halogenated epoxy oligomeric flame retardant containing bromine. Although the above-mentioned compositions are superior in early flame retardant and processability, the weather resistance and hot water resistance are poor. Accordingly, after hot water immersion or under long-term UN exposure, the early flame retardancy is considerably deteriorated and the retention of mechanical properties is difficult. For these reasons, the conventional compositions cannot be applied to outdoor products, e.g., light bulb sockets for artificial Christmas trees which are constantly in contact with the external environment, e.g., light and rainwater, for a long period of time.

Disclosure of the Invention

Therefore, the present invention has been made in view of the above problems, and a feature of the present invention is to provide a flame retardant polypropylene resin composition which can be processed into secondary products having excellent early flame retardancy and a high retention of weather resistance and mechanical properties even under long-term light exposure and hot water immersion while exhibiting excellent flame retardancy even at a small thickness.

In accordance with the feature of the present invention, there is provided a flame retardant polypropylene resin composition, comprising (A) 37-67% by weight of a polypropylene resin having a melt flow index of 4-40 g/10min., (B) 17-29% by weight of a high melting point halogen-based flame retardant, (C) 4-14% by weight of an antimony oxide in the form of a white powder, (D) 2-22% by weight of an inorganic filler, (E) 0.35-4.0%) by weight of a UN stabilizer, (F) 0.15-2.5% by weight of a particulate tetrafluoroethylene polymer, and (G) 0.08-3.5% by weight of a crosslinking agent.

The present invention will now be described in more detail. As the polypropylene resin (A) contained in the flame retardant polypropylene resin composition of the present invention, a crystalline polypropylene homopolymer, or a crystalline copolymer of propylene and at least one compound selected from the group consisting of ethylene, 1-butene, 1-pentene, 1-hexene, 4-methylpentene, 1- heptene, 1-octene and 1-decene, may be used. The crystalline polypropylene homopolymer is preferred. The polypropylene resin (A) preferably has a melt flow index of 4-40 g/10min., and more preferably 5-30 g/lOmin. The content of the polypropylene resin (A) is in the range of 37-67% by weight and preferably 45-65 % by weight, based on the total weight of the resin composition.

Examples of the high melting point halogen-based flame retardant (B) include decabromodiphenyl ether, ethylene-bis(tetrabromo phthalimide), bispentabromo phenoxyethane, and mixtures thereof. Specifically, decabromodiphenyl ether (S-

102E, Albemarle Corp.), ethylene-bis(tetrabromo phthalimide) (BT-93, Albemarle Corp.) or bispentabromo phenoxy ethane (S-8010, Albemarle Corp.) are commercially available. The high melting point halogen-based flame retardant (B) is preferably present in an amount of 17~29%> by weight, based on the total weight of the resin composition. When the flame retardant is added in an amount of lower than 17%) by weight, flammability class V-0 cannot be achieved at a thickness of 1/32". On the other hand, when the flame retardant is added in an amount of higher than 29% by weight, the weather resistance is poor and the retention of mechanical properties is undesirably low. As the flame retardant additive (C) contained in the resin composition of the present invention, an antimony oxide is used. Specific examples of the antimony oxide include antimony trioxide, antimony pentaoxide and mixtures thereof. The amount of the antimony oxide added is preferably in the range of 4~14%> by weight and preferably 5-12%o by weight. The inorganic filler (D) contained in the resin composition of the present invention is talc, barium sulfate, calcium carbonate or a mixture thereof. The inorganic filler (D) is added in an amount of 2-22% by weight and more preferably 4-15% by weight.

As the UN stabilizer (E) contained in the resin composition of the present invention, a combination of a UN absorber and a HALS-based stabilizer is preferably used. The HALS-based stabilizer preferably has a molecular weight of 2,000 or higher. When the molecular weight of the HALS-based stabilizer is lower than 2,000, the UN stabilizer tends to bloom from the resulting secondary processed composition and long-term UN stabilization is thus impossible. The UN absorber and the HALS- based UN stabilizer are preferably added in an amount of 0.12-2.0%) by weight so that the total amount of the UN stabilizer (E) is in the range of 0.35-4.0%) by weight. If the UN absorber or the HALS-based UN stabilizer is added alone, flammability class N-0 can be achieved, but the retention of tensile impact strength after UN exposure is low, and thus an environment resistant composition having a high retention of physical properties belonging to the fl grade cannot be obtained. The particulate tetrafluoroethylene polymer (F) contained in the resin composition of the present invention preferably has a fluorine content of 65-76% by weight and more preferably 10-16% by weight. In addition to tetrafluoroethylene polymer, copolymers of fluorine-containing monomers and tetrafluoroethylene, or copolymers of copolymerizable ethylenic unsaturated monomers containing no fluorine and tetrafluoroethylene, can be used. Tetrafluoroethylene exists in a fibril form when molding of the resin composition, and prevents dripping of melted materials when burning molded articles. The tetrafluoroethylene is preferably used in the form of particles, and can be obtained by previously known processes (see, Houden-Weyl, Metrodender Organischem Chemie, Volume 14/1, p 842-849, Stuttgart, 1961). The amount of the particulate tetrafluoroethylene polymer added is preferably in the range of 0.15-2.5%) by weight. When the content of the particulate tetrafluoroethylene polymer is below 0.15% by weight, anti-dripping effects required for flammability class V-0 are not sufficiently obtained. At this time, flammability class N-O cannot be ensured due to dripping of the molten resin when burned at a thickness of 1/32". When the content of the particulate tetrafluoroethylene polymer is below 2.5%_> by weight, an excessive amount of the particulate tetrafluoroethylene polymer does not contribute to further improvement of anti-dripping effects, and the flowability of the resin is extremely deteriorated, making the molding process difficult.

As examples of the crosslinking agent (G) contained in the resin composition of the present invention, polyfunctional monomers, oxime-nitroso compounds, maleimide compounds and the like, may be mentioned. Specifically, triallyl isocyanurate, (di)ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate or pentaerythritol(meth)acrylate, trimethylolpropane triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, etc., can be used. Polyfunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate and pentaerythritol(meth)acrylate are preferred. The amount of the crosslinking agent added is in the range of 0.08-3.5%) by weight, and preferably 0.2-2%) by weight. When the amount of the crosslinking agent is below 0.1 %> by weight, the UN stability is poor upon UN exposure, and thus the retention of physical properties becomes inferior after UN exposure. When the amount of the crosslinking agent is above 3% by weight, imperfections in appearance such as flow marks are formed upon molding, causing rough surfaces of final molded articles.

The flame retardant polypropylene resin composition of the present invention exhibits excellent flame retardancy corresponding to flammability class N-0 at a thickness of 1/32", as measured by a vertical flammability test (hereinafter, referred to as a "UL 94 vertical flammability test") among "flammability tests of plastic materials for mechanical parts" described in UL Subject 94, and at the same time, maintains the same flammability class even under long-term light exposure and hot water immersion. Further, the flame retardant polypropylene resin composition of the present invention maintains its early flame retardancy even after long-term light exposure and hot water immersion for a long time, as measured by a test based on weather resistance and water immersion resistance (hereinafter, referred to as a "UL 746 environment resistance test") among "environment resistance tests of plastic materials for mechanical parts" described in UL Subject 746C, and at the same time, exhibits a high retention of mechanical properties. Accordingly, the resin composition of the present invention can be suitably used as a material for indoor/outdoor electric appliances, construction materials, interior/exterior decorative materials and automobile parts.

Best Mode for Carrying Out the Invention

The present invention will now be described in more detail with reference to the following examples. However, these examples are given for the purpose of illustration and are not to be construed as limiting the scope of the invention.

Example 1 5.9kg of a crystalline polypropylene homopolymer having a melt flow index

(melt flow rate under a load of 2.16kg at 230°C for 10 minutes) of 8 g/lOmin. as a polypropylene resin, 2.4kg of bispentabromo phenoxy ethane (S-8010, Albemarle Corp.) as a high melting point halogen-based flame retardant, 700g of antimony tri oxide (Sb2O3, Ilsung Antimony, Co. Ltd., Korea) as a flame retardant additive, 1.0kg of talc (KCM 6300, KOCH) as an inorganic filler, 50g of a UV absorber (Tinuvin 326,

CIBA GEIGY), 50g of a HALS-based UN stabilizer (Chimabsorber 944FD, CIBA GEIGY), 50g of a particulate tetrafluoroethylene polymer (Teflon 800J, Dupont) as an anti-dripping agent, 50g of a crosslinking agent (A-TMM-3L, Nippon Chemical, Japan), and lOg of calcium stearate, 20g of an antioxidant (IRGANOX 1010, CIBA GEIGY) and 20g of an antioxidant (IRGAFOS 168, CIBA GEIGY) as other additives were charged into a Henschel mixer, and then the mixture was stirred for 3 minutes. After the resulting mixture was fed into a twin-screw extruder (diameter: 30mm), it was melted and extruded at 190°C to produce pellets. The pellets thus produced were dried at 100°C for 3 hours, and were molded using an injection molding machine in which the maximum cylinder temperature was set at 200°C to manufacture test pieces. Using the test pieces, the flame retardancy and the tensile impact strength of the test pieces were measured. The results are shown in Table 1 below.

Treatments

Under the conditions for a weather resistance test among "environment resistance tests of plastic materials for electrical parts" described in UL Subject 746C

(Underwrites Laboratories Incorporation), the test pieces were exposed to Xenon Arc UN (UN exposure dose: 0.35 W/m² (340nm), black panel temperature: 63°C, Water spray type) in accordance with the ASTM 2565 Type A standard method. Hot water immersion treatment was done by standing the test pieces in a water bath at 70°C for 7 days. Thereafter, the flame retardancy and mechanical properties of the test pieces were measured.

Evaluation methods

The flame retardancy of the test pieces was evaluated by a vertical flammability test (NO) among "flammability tests of plastic materials for mechanical parts" described in UL Subject 94 (Underwriters Laboratories Incorporation). The test pieces used herein had a thickness of 1/32". The tensile impact strength and retention thereof of the test pieces were evaluated in accordance with the ASTM D- 1822 standard method using a tensile impact apparatus (TOYOSEIKI, Japan). The test pieces (S Type) used herein had a thickness of 1/32".

Evaluation grade

- fl represents flammability class N-0 and retention of tensile impact strength of 70%) or more in a UN exposure test and, 50% or more in a hot water immersion test; - £2 represents flammability class N-0 and retention of tensile impact strength of 70%) or more in a UN exposure test or, 50%> or more in a hot water immersion test; and

- When the flame retardancy and the retention of tensile impact strength did not fall under fl or f2, the grade was represented as "X".

Examples 2-4, and Comparative Examples 1 and 2 The procedure of Example 1 was repeated, except that bispentabromo phenoxy ethane (S-8010, Albemarle Corp.) as a flame retardant was added in the amounts shown in Table 1 below. The results are shown in Table 1.

Comparing the results of Examples 1-4 with those of Comparative Examples 1 and 2 shown in Table 1, in the case where appropriate amounts of bispentabromo phenoxy ethane (S-8010, Albemarle Corp.) as a flame retardant were added to a specified amount of the anti-dripping agent and the crosslinking agent, flammability class N-0 was maintained and retention of tensile impact strength was high. In addition, even under hot water immersion, flammability class N-0 was maintained and the retention of tensile impact strength was high. Accordingly, the resin compositions exhibited excellent environment resistance belonging to the fl grade specified in UL 746C.

Example 5 6.1kg of a crystalline polypropylene homopolymer having a melt flow index

(melt flow rate under a load of 2.16kg at 230°C for 10 minutes) of 8 g/lOmin. as a polypropylene resin, 2.4kg of bispentabromo phenoxy ethane (S-8010, Albemarle Corp.) as a high melting point halogen-based flame retardant, 500g of antimony trioxide (Sb2O3, Ilsung Antimony, Co. Ltd., Korea) as a flame retardant additive, 1.0kg of talc (KCM 6300, KOCH) as an inorganic filler, 50g of a UN absorber (Tinuvin 326,

CIBA_, GEIGY), 50g of a HALS-based UN stabilizer (Chimabsorber 944FD, CIBA GEIGY), 50g of a particulate tetrafluoroethylene polymer (Teflon 800J, Dupont) as an anti-dripping agent, 50g of a crosslinking agent (A-TMM-3L, Nippon Chemical, Japan), and lOg of calcium stearate, 20g of an antioxidant (IRGANOX 1010, CIBA GEIGY) and 20g of an antioxidant (IRGAFOS 168, CIBA GEIGY) as other additives were charged into a Henschel mixer, and then the mixture was stirred for 3 minutes. After the resulting mixture was fed into a twin-screw extruder (diameter: 30mm), it was melted and extruded at 190°C to produce pellets. The pellets thus produced were dried at 100°C for 3 hours, and were molded using an injection molding machine in which the maximum cylinder temperature was set at 200°C to manufacture test pieces.

Using the test pieces, the flame retardancy and the tensile impact strength of the test pieces were measured. The results are shown in Table 1.

Example 6, and Comparative Examples 3 and 4 The procedure of Example 5 was repeated, except that antimony trioxide as a flame retardant additive was added in the amounts shown in Table 1. The results are shown in Table 1.

Comparing the results of Examples 5 and 6 with those of Comparative Examples 3 and 4 shown in Table 1, only when the flame retardant additive was added above the predetermined amount, the flame retardancy was excellent and was maintained even under UN exposure and hot water immersion. When antimony trioxide as the flame retardant additive was added in an amount exceeding 14%> by weight, the flame retardancy was no longer improved. On the other hand, when antimony trioxide as the flame retardant additive was added in amounts of less than 4% by weight, the retention of physical properties was low, and thus environment resistance belonging to the fl grade could not be achieved.

Example 7 6.4kg of a crystalline polypropylene homopolymer having a melt flow index (melt flow rate under a load of 2.16kg at 230°C for 10 minutes) of 8 g/lOmin. as a polypropylene resin, 2.4kg of bispentabromo phenoxy ethane (S-8010, Albemarle

Corp.) as a high melting point halogen-based flame retardant, 700g of antimony trioxide (Sb2O3, Ilsung Antimony, Co. Ltd., Korea) as a flame retardant additive, 500g of talc (KCM 6300, KOCH) as an inorganic filler, 50g of a UN absorber (Tinuvin 326, CIBA GEIGY), 50g of a HALS-based UN stabilizer (Chimabsorber 944FD, CIBA GEIGY), 50g of a particulate tetrafluoroethylene polymer (Teflon 800J, Dupont) as an anti-dripping agent, 50g of a crosslinking agent (A-TMM-3L, Nippon Chemical, Japan), and lOg of calcium stearate, lOg of an antioxidant (IRGANOX 1010, CIBA GEIGY), 20g of an antioxidant (IRGAFOS 168, CIBA GEIGY) as other additives were charged into a Henschel mixer, and then the mixture was stirred for 3 minutes. After the resulting mixture was fed into a twin-screw extruder (diameter: 30mm), it was melted and extruded at 190°C to produce pellets. The pellets thus produced were dried at 100°C for 3 hours, and were molded using an injection molding machine in which the maximum cylinder temperature was set at 200°C to manufacture test pieces. Using the test pieces, the flame retardancy and the tensile impact strength of the test pieces were measured. The results are shown in Table 1 below.

Examples 8 and 9. and Comparative Examples 5 and 6 The procedure of Example 7 was repeated, except that the amounts of talc (KCM 6300, KOCH) as an inorganic filler and the polypropylene resin were changed to those shown in Table 1. The results are shown in Table 1.

As is apparent from Table 1, talc as an inorganic filler greatly affected the flame retardancy. When the content of talc was less than 2% by weight, the flame retardancy belonging to flammability class N-O class specified in UL Subject 94 could not be achieved. Whereas the content was more than 22% by weight, the retention of tensile impact strength was low. Accordingly, for better maintenance of physical properties and flame retardancy belonging to the fl grade, the content of the inorganic filler must be in the range of 3~20%> by weight.

Example 10 5.9kg of a crystalline polypropylene homopolymer having a melt flow index (melt flow rate under a load of 2.16kg at 230°C for 10 minutes) of 8 g/lOmin. as a polypropylene resin, 2.4kg of bispentabromo phenoxy ethane (S-8010, Albemarle Corp.) as a high melting point halogen-based flame retardant, 700g of antimony trioxide (Sb2O3, Ilsung Antimony, Co. Ltd., Korea) as a flame retardant additive, 1.0kg of talc (KCM 6300, KOCH) as an inorganic filler, 200g of a UN absorber (Tinuvin 326, CIBA GEIGY), 50g of a HALS-based UN stabilizer (Chimabsorber 944FD, CIBA

GEIGY), 50g of particulate a tetrafluoroethylene polymer (Teflon 800J, Dupont) as an anti-dripping agent, 50g of a crosslinking agent (A-TMM-3L, Nippon Chemical, Japan), and lOg of calcium stearate, 20g of an antioxidant (IRGANOX 1010, CIBA GEIGY) and 20g of an antioxidant (IRGAFOS 168, CIBA GEIGY) as other additives were charged into a Henschel mixer, and then the mixture was stirred for 3 minutes.

After the resulting mixture was fed into a twin-screw extruder (diameter: 30mm), it was melted and extruded at 190°C to produce pellets. The pellets thus produced were dried at 100°C for 3 hours, and were molded using an injection molding machine in which the maximum cylinder temperature was set at 200°C to manufacture test pieces. Using the test pieces, the flame retardancy and the tensile impact strength of the test pieces were measured. The results are shown in Table 2 below.

Example 11, and Comparative Examples 7 and 8 The procedure of Example 10 was repeated, except that the amounts of the UN absorber (Tinuvin 326, CIBA GEIGY) were changed to those shown in Table 2.

The pellets produced in Example 11 and Comparative Examples 7 and 8 were dried at 100°C for 3 hours, and were molded using an injection molding machine in which the maximum cylinder temperature was set at 200°C to manufacture test pieces.

Using the test pieces, the flame retardancy and the tensile impact strength of the test pieces were measured. The results are shown in Table 2 below.

As is evident from the data shown in Table 2, the addition of the UN absorber exhibited a high retention of tensile impact strength among mechanical properties even under UN exposure, and thus improved environment resistance belonging to the fl grade specified in UL736C. When the UN absorber was added in an amount of less than 0.15%), the UN absorbability was poor. Meanwhile, when the UN absorber was added in an amount exceeding 2% by weight, the UN absorbability was excellent but the appearance of molded product was bad due to blooming in the surface of the molded product. Accordingly, it was found that the amount of the UN absorber added is preferably in the range of 0.15-2% by weight.

Example 12

5.9kg of a crystalline polypropylene homopolymer having a melt flow index (melt flow rate under a load of 2.16kg at 230°C for 10 minutes) of 8 g/lOmin. as a polypropylene resin, 2.4kg of bispentabromo phenoxy ethane (S-8010, Albemarle Corp.) as a high melting point halogen-based flame retardant, 700g of antimony trioxide (Sb2O3, Ilsung Antimony, Co. Ltd., Korea) as a flame retardant additive, 1.0kg of talc (KCM 6300, KOCH) as an inorganic filler, 50g of a UN absorber (Tinuvin 326, CIBA GEIGY), 200g of a HALS-based UN stabilizer (Chimabsorber 944FD, CIBA GEIGY), 50g of a particulate tetrafluoroethylene polymer (Teflon 800J, Dupont) as an anti-dripping agent, 50g of a crosslinking agent (A-TMM-3L, Nippon Chemical, Japan), and lOg of calcium stearate, 20g of an antioxidant (IRGANOX 1010, CIBA

GEIGY) and 20g of an antioxidant (IRGAFOS 168, CIBA GEIGY) as other additives were charged into a Henschel mixer, and then the mixture was stirred for 3 minutes. After the resulting mixture was fed into a twin-screw extruder (diameter: 30mm), it was melted and extruded at 190°C to produce pellets. The pellets thus produced were dried at 100°C for 3 hours, and were molded using an injection molding machine in which the maximum cylinder temperature was set at 200°C to manufacture test pieces. Using the test pieces, the flame retardancy and the tensile impact strength of the test pieces were measured. The results are shown in Table 2 below.

Example 13, and Comparative Examples 9-13

The procedure of Example 12 was repeated, except that the type and the content of the HALS-based UV stabilizers were changed to those shown in Table 2, and PETA as a crosslinking agent was not added. The results are shown in Table 2.

As is apparent from Table 2, when various HALS-based UN stabilizers were used, but no crosslinking agent was added, desired flame retardancy (1/32") could be achieved. However, since the retention of mechanical tensile impact strength under long-term Xenon arc UN exposure was low, the environment resistance belonging to the fl grade could not be achieved.

Example 14 5.9kg of a crystalline polypropylene homopolymer having a melt flow index

(melt flow rate under a load of 2.16kg at 230°C for 10 minutes) of 8 g/lOmin. as a polypropylene resin, 2.4kg of bispentabromo phenoxy ethane (S-8010, Albemarle Corp.) as a high melting point halogen-based flame retardant, 700g of antimony trioxide (Sb2O3, Ilsung Antimony, Co. Ltd., Korea) as a flame retardant additive, 1.0kg of talc (KCM 6300, KOCH) as an inorganic filler, 50g of a UN absorber (Tinuvin 326,

CIBA GEIGY), 50g of a HALS-based UN stabilizer (Chimabsorber 944FD, CIBA GEIGY), 50g of a particulate tetrafluoroethylene polymer (Teflon 800J, Dupont), lOg of a crosslinking agent (A-TMM-3L, Nippon Chemical, Japan), and lOg of calcium stearate, 20g of an antioxidant (IRGANOX 1010, CIBA GEIGY) and 20g of an antioxidant (IRGAFOS 168, CIBA GEIGY) as other additives were charged into a

Henschel mixer, and then the mixture was stirred for 3 minutes. After the resulting mixture was fed into a twin-screw extruder (diameter: 30mm), it was melted and extruded at 190°C to produce pellets. The pellets thus produced were dried at 100°C for 3 hours, and were molded using an injection molding machine in which the maximum cylinder temperature was set at 200°C to manufacture test pieces. Using the test pieces, the flame retardancy and the tensile impact strength of the test pieces were measured. The results are shown in Table 2.

Examples 15 and 16, and Comparative Examples 14-16 The procedure of Example 14 was repeated, except that the contents of the crosslinking agent were changed to those shown in Table 2. The results are shown in Table 2.

Examples 17 and 18 The procedure of Example 14 was repeated, except that the kind of the crosslinking agent was changed to those shown in Table 3a. The results are shown in Table 3b.

As can be seen from Table 2, when the crosslinking agent was added in an appropriate amount, molded products having a high retention of mechanical properties could be manufactured. When the crosslinking agent was added in an amount of less than 0.08%) by weight, the retention of mechanical properties under long-term UN exposure was considerably low, and thus environment resistance belonging to the fl grade could not be achieved. Whereas, when the crosslinking agent was added in an amount exceeding 3.5% by weight, the flame retardancy was poor and thus flame retardancy belonging to flammability class N-0 specified in UL Subject 94 could not be achieved.

As can be seen from Table 3b, all pentaerythritol-based crosslinking agents contributed to a high retention of mechanical properties, and improved the flame retardancy and the environment resistance.

Example 20

5.9kg of a crystalline polypropylene homopolymer having a melt flow index (melt flow rate under a load of 2.16kg at 230°C for 10 minutes) of 8 g/lOmin. as a polypropylene resin, 2.4kg of bispentabromo phenoxy ethane (S-8010, Albemarle Corp.) as a high melting point halogen-based flame retardant, 700g of antimony trioxide (Sb2O3, Ilsung Antimony, Co. Ltd., Korea) as a flame retardant additive, 1.0kg of talc (KCM 6300, KOCH) as an inorganic filler, 50g of a UN absorber (Tinuvin 326, CIBA GEIGY), 50g of a HALS-based UN stabilizer (Chimabsorber 944FD, CIBA GEIGY), 50g of a particulate tetrafluoroethylene polymer (7AJ, Dupont), 50g of a crosslinking agent (A-TMM-3L, Nippon Chemical, Japan), and lOg of calcium stearate, lOg of an antioxidant (IRGANOX 1010, CIBA GEIGY) and 20g of an antioxidant (IRGAFOS 168, CIBA GEIGY) as other additives were charged into a Henschel mixer, and then the mixture was stirred for 3 minutes. After the resulting mixture was fed into a twin-screw extruder (diameter: 30mm), it was melted and extruded at 190°C to produce pellets. The pellets thus produced were dried at 100°C for 3 hours, and were molded using an injection molding machine in which the maximum cylinder temperature was set at 200°C to manufacture test pieces. Using the test pieces, the flame retardancy and the tensile impact strength of the test pieces were measured. The results are shown in Table 3b below.

Example 21, and Comparative Examples 17-19

The procedure of Example 14 was repeated, except that the contents of the particulate tetrafluoroethylene polymer were changed to those shown in Table 3a. The results are shown in Table 3b.

As is apparent from Table 3b, when the particulate tetrafluoroethylene polymer was added in an amount of less than 0.15% by weight, no anti-dripping effects were observed and thus dripping took place upon burning. Accordingly, flammability class N-0 specified in UL Subject 94 was not achievable. On the other hand, when the particulate tetrafluoroethylene polymer was added in an amount exceeding 2.5%o by weight, the flowability of the resin was considerably reduced and no improvement in anti-dripping effects could not be anticipated. Accordingly, particulate tetrafluoroethylene polymer in an appropriate amount can ensure flame retardancy and the retention of tensile impact strength belonging to the fl grade even under long-term UN exposure.

Example 22 5.9kg of a crystalline polypropylene homopolymer having a melt flow index

(melt flow rate under a load of 2.16kg at 230°C for 10 minutes) of 8 g/lOmin. as a polypropylene resin, 2.4kg of ethylene-bis(tetrabromo phthalimide) (BT-93, Albemarle Corp.) as a high melting point halogen-based flame retardant, 700g of antimony trioxide (Sb2O3, Ilsung Antimony, Co. Ltd., Korea) as a flame retardant additive, 1.0kg of talc (KCM 6300, KOCH) as an inorganic filler, 50g of a UN absorber (Tinuvin 326,

CIBA GEIGY), 50g of a HALS-based UN stabilizer (Chimabsorber 944FD, CIBA GEIGY), 50g of a particulate tetrafluoroethylene polymer (Teflon 800J, Dupont), 50g of a crosslinking agent (3-MM-T, Nippon Chemical, Japan), and 20g of calcium stearate, 20g of an antioxidant (IRGANOX 1010, CIBA GEIGY) and 20g of an antioxidant (IRGAFOS 168, CIBA GEIGY) as other additives were charged into a

Henschel mixer, and then the mixture was stirred for 3 minutes. After the resulting mixture was fed into a twin-screw extruder (diameter: 30mm), it was melted and extruded at 190°C to produce pellets. The pellets thus produced were dried at 100°C for 3 hours, and were molded using an injection molding machine in which the maximum cylinder temperature was set at 200°C to manufacture test pieces. Using the test pieces, the flame retardancy and the tensile impact strength of the test pieces were measured. The results are shown in Table 3b below.

Example 23, and Comparative Examples 20 and 21 The procedure of Example 22 was repeated, except that the kind of the high melting point flame retardant was changed to those shown in Table 3 a, or low melting point flame retardants were used instead of the high melting point flame retardant. The results are shown in Table 3b.

As can be seen from Table 3b, the compositions comprising a high melting point halogen-based flame retardant, a particulate tetrafluoroethylene polymer and a crosslinking agent exhibited excellent early flame retardancy, and a high retention of physical properties before and after UV exposure and hot water immersion without any deterioration in the flame retardancy. In contrast, the flame retardant resin compositions comprising a low melting point halogen-based flame retardant exhibited poor flame retardancy after UV exposure and hot water immersion. Specifically, the flame retardant compositions comprising a low melting point halogen-based flame retardant exhibited a retention of physical properties of 70% or lower before and after UV exposure and hot water immersion and could not maintain flame retardancy after hot water immersion. Accordingly, the compositions cannot satisfy the requirements defined in the QMTO2 category, which regulates polymer materials of light bulb sockets for artificial Christmas trees requiring a high retention of physical properties and flame retardancy.

Table 1

& t

H to or

IS

* Note

Component (A): Polypropylene resin [HJ400, Samsung General Chemicals Co.]

Component (B)-l: High melting point halogen flame retardant, bispentabromo phenoxy ethane [S-8010, Albemarle Corp., USA]

Component (B)-2: High melting point halogen flame retardant, decabromodiphenylether [S-102E, Albemarle Corp., USA]

Component (B)-3 : High melting point halogen flame retardant Component (B)-4: Low melting point halogen flame retardant, tetrabromo bisphenol A-bis(2,3-dibromopropylether) [PE68, Great Lakes, USA]

Component (B)-5: Low melting point halogen flame retardant, tetrabromo bisphenol S type [Nonnen52, Marubishi Chemical, Japan]

Component (C): Antimony trioxide [SW, Ilsung Antimony, Co. Ltd., Korea] Component (D): Inorganic filler, talc [KCM6300, KOCH] Component (E)- 1 : UV absorber [Tinuvin326, CIBA GEIGY]

Component (E)-2: HALS-based UN stabilizer [Chimabsorber 944FD, CIBA GEIGY]

Component (F): Particulate tetrafluoroethylene polymer [Teflon 800 J, Dupont] Component (G)-l : Crosslinking agent, pentaerythritol triacrylate [A-TMM-3L, Nippon Chemical, Japan]

Component (G)-2: Crosslinking agent, pentaerythritol tetraacrylate [A-TMM- L, Nippon Chemical, Japan]

Component (G)-3: Crosslinking agent, pentaerythritol tri(3- mercaptopropionate) [PET-3-MP, Bruno Bock Chemical, German] Component (G)-4: Crosslinking agent, trimethylolpropanetriacrylate [A-

TMPTMA, Nippon Chemical, Japan]

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A flame retardant polypropylene resin composition, comprising:

(A) 37-67% by weight of a polypropylene resin having a melt flow index of 4~40 g/10min.;

(B) 17-29% by weight of a high melting point halogen-based flame retardant;

(C) 4-14% by weight of an antimony oxide in the form of a white powder;

(D) 2-22% by weight of an inorganic filler;

(E) 0.35-4.0% by weight of a UN stabilizer; (F) 0.15-2.5% by weight of a particulate tetrafluoroethylene polymer; and

(G) 0.08-3.5% by weight of a crosslinking agent.

2. The composition according to claim 1, wherein the polypropylene resin is a polypropylene homopolymer or a crystalline copolymer.

3. The composition according to claim 1, wherein the high melting point halogen-based flame retardant is decabromodiphenyl ether, ethylene-bis(tetrabromo phthalimide), bispentabromo phenoxyethane or a mixture thereof.

4. The composition according to claim 1, wherein the antimony oxide is antimony trioxide, antimony pentaoxide or a mixture thereof.

5. The composition according to claim 1, wherein the inorganic filler is talc, barium sulfate, calcium carbonate or a mixture thereof.

6. The composition according to claim 1, wherein the UV stabilizer is a combination of a UN absorber having a molecular weight of 2,000 or higher, and a HALS-based stabilizer.

7. The composition according to claim 1, wherein the particulate tetrafluoroethylene polymer has a fluorine content of 65-76% by weight.

8. The composition according to claim 1, wherein the crosslinking agent is triallyl isocyanurate, (di)ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate or pentaerythritol(meth)acrylate, trimethylolpropane triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate or a mixture thereof.