Thermoplastic hot melt adhesive composition comprising flame retardant

Abstract

The invention relates to a thermoplastic hot-melt adhesive composition comprising a flame retardant mixture, to a method for producing said composition and to the use thereof in low-temperature moulding.

Description

[0001] The present invention relates to a thermoplastic hot melt adhesive composition comprising a mixture of flame retardants, a method for preparing the composition, and its use in low temperature pressure molding.

[0002] Thermoplastic hot melt adhesives are widely used in various fields such as electric and electronic products and communication devices. Certain applications require thermoplastic hot melt adhesives to have flame retardancy to prevent the internal parts of devices and equipment from heating up and catching fire. To impart such flame retardancy, flame retardants are usually added. However, flame retardants are generally high-viscosity solids or compounds that have a negative impact on the viscosity of the hot melt adhesive, making the hot melt adhesive unsuitable for low temperature pressure molding techniques. In addition, thermoplastic hot melt adhesives are used for encapsulating electrical and electronic components such as printed circuit boards (PCBs), connectors, and sensors. In particular, the severe corrosion behavior of phosphorus-based flame retardants may affect sensitive encapsulation compounds.

[0003] EP 1 104 766 describes a crosslinked phenoxyphosphazene compound as a flame retardant and a flame retardant resin composition containing the flame retardant.

[0004] EP 1 975 217 mentions a flame retardant adhesive or sealing composition containing 0.1% to 99% by weight of an adhesive or a thermoplastic polymer and 0.1% to 99% by weight of a flame retardant comprising at least one metal or organic base salt of dialkyl or diaryl phosphinic acid and / or an alkylene or arylene - bisphosphinic acid metal or organic base salt.

[0005] CN 10340320 discloses a halogen-free flame retardant polyamide hot melt adhesive comprising 100 parts of a dimer acid type polyamide hot melt adhesive, 15 to 65 parts of a halogen-free flame retardant, and 0.3 to 3 parts of an antioxidant.

[0006] For use in the production of electrical or electronic compounds, a hot melt adhesive composition should achieve a V-0 flammability classification in the UL-94 flammability test (Testing for Flammability of Plastic Materials for Parts in Devices & Appliances), which is the standard test for evaluating flammability. To achieve a V-0 rating, the flame should not persist for more than a specified time, and no molten resin droplets should ignite the cotton beneath the test specimen. We have found that certain standard thermoplastic hot melt adhesive compositions can achieve a V-0 rating but cannot maintain that rating after aging and / or at different thicknesses. Accordingly, the object of the present invention is to provide a thermoplastic hot melt adhesive composition that can meet the requirements of a V-0 rating while having a low viscosity and good corrosion resistance for use in low-temperature molding techniques.

[0007] Surprisingly, this object is achieved by a thermoplastic hot melt adhesive composition based on polyamide and comprising a mixture of a phosphorus-based flame retardant and a halogen-free flame retardant.

[0008] Accordingly, a first object of the present invention is a thermoplastic hot melt adhesive composition which, based on the total weight of the composition, comprises:

[0009] a) at least one polyamide;

[0010] b) at least one phosphorus-based flame retardant in an amount of 0.1% to 5% by weight; and

[0011] c) at least one halogen-free flame retardant in an amount of 0.1% to 15% by weight,

[0012] wherein the at least one phosphorus-based flame retardant is different from the at least one halogen-free flame retardant.

[0013] We have found that the hot melt adhesive composition according to the present invention has improved thermal stability and can achieve a V-0 rating even after aging and at different thicknesses.

[0014] In a preferred embodiment, the at least one halogen-free flame retardant is selected from melamine cyanurate, melamine polyphosphate, ammonium phosphate, pentaerythritol, and zinc oxide. In particular, the at least one halogen-free flame retardant is melamine cyanurate.

[0015] Polyamide hot melt adhesives are typically characterized by their good adhesion properties and high chemical resistance. In particular, polyamides based on dimer fatty acids also exhibit good basic flame retardancy properties. Thus, in a preferred embodiment, the at least one polyamide is a polyamide based on dimer fatty acids.

[0016] Within the meaning of the present invention, dimer fatty acids or fatty acid polymers are those fatty acids that can be obtained in a known manner by dimerization of natural raw materials. They are produced from unsaturated long-chain fatty acids and then purified by distillation. As industrial-grade dimer fatty acids, depending on the degree of purity, they contain less than 5% of monobasic fatty acids, essentially C 18 fatty acids such as linolenic acid or oleic acid, and not more than 98% by weight of C 36 dibasic fatty acids (dimer fatty acids in the narrow sense) and a small proportion of higher polybasic fatty acids ("trimer acids"). The relative ratios of fatty acid monomers, dimer fatty acids, and trimer fatty acids in the fatty acid polymer mixture depend on the nature of the starting compounds used; the polymerization, dimerization, or oligomerization conditions; and the degree of distillation separation. Dimer fatty acids purified by distillation contain not more than 98% by weight of dimer fatty acids. In another processing step, these dimer fatty acids can also be hydrogenated. According to the present invention, these hydrogenated dimer fatty acids can also be used.

[0017] In a preferred embodiment, the at least one polyamide is obtained from a reaction mixture comprising at least one dimer fatty acid and at least one dicarboxylic acid (preferably selected from C6 to C 24 dicarboxylic acids). Examples of these dicarboxylic acids are succinic acid, adipic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, glutaric acid, suberic acid, or pimelic acid. A certain proportion of aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, or a mixture of the above dicarboxylic acids can also be used in the reaction mixture. However, it is preferred to select longer-chain aliphatic dicarboxylic acids, such as C 10 to C 18 aliphatic dicarboxylic acids; in this case, the water absorption of the resulting polyamide can be reduced.

[0018] The diamine component consists essentially of one or more aliphatic diamines having amino groups at the ends of the carbon chains. The aliphatic diamines can contain 2 to 20 carbon atoms, where the aliphatic chain can be linear or branched. Examples are ethylenediamine, diethylenetriamine, dipropylenetriamine, 1,4-diaminobutane, 1,3-pentanediamine, methylpentanediamine, hexamethylenediamine, trimethylhexamethylenediamine, 2-(2-aminomethoxy)ethanol, 2-methylpentamethylenediamine, C 11 neopentanediamine, diaminodipropylmethylamine, or 1,12-diaminododecane. Particularly preferred primary alkylene diamines are C2-C 12 diamines with an even number of carbon atoms.

[0019] The amino component may also contain a cyclic diamine or a heterocyclic diamine, such as 1,4 - cyclohexanediamine, 4,4′ - diaminodicyclohexylmethane, piperazine, cyclohexane dimethylamine, isophorone diamine, dimethylpiperazine, dipiperidyl propane, norbornanediamine or m - xylylenediamine. A particular embodiment uses a mixture of an alkylenediamine and a cyclic diamine.

[0020] The thermoplastic hot - melt adhesive composition of the present invention comprises at least one phosphorus - based flame retardant. The at least one phosphorus - based flame retardant is preferably selected from cyclic phosphonates and cross - linked phenoxyphosphazene compounds. In a particularly preferred embodiment, the at least one phosphorus - based flame retardant is a cross - linked phenoxyphosphazene compound, which comprises cyclic phosphazene groups and a linear or branched phosphazene chain cross - linked with at least one cross - linking group selected from phenylene and biphenylene. Suitable cross - linked phenoxyphosphazene compounds are described in EP 1 104 766. In a preferred embodiment, the solubility of the phosphorus - based flame retardant in water at 25°C is less than 0.05%, preferably less than 0.02%, particularly less than 0.01%. Surprisingly, the use of such a phosphorus - based flame retardant in the composition of the present invention improves the corrosion resistance and thermal stability properties.

[0021] In a preferred embodiment of the thermoplastic hot - melt adhesive composition of the present invention, the at least one polyamide is present in the composition in an amount of at least 80% by weight, preferably at least 85% by weight, based on the total weight of the composition.

[0022] The thermoplastic hot - melt adhesive composition is characterized by its low halogen - free flame retardant content. Furthermore, it has surprisingly been found that the amount of the phosphorus - based flame retardant can also be kept low without affecting the flame retardancy of the composition. Thus, in a preferred embodiment, the at least one phosphorus - based flame retardant is present in the composition in an amount of 0.2% to 2% by weight, based on the total weight of the composition.

[0023] In a further preferred embodiment, the halogen - free flame retardant is present in the composition in an amount of 1.0% to 12% by weight, more preferably 5% to 9.5% by weight, based on the total weight of the composition.

[0024] In a particularly preferred embodiment, the thermoplastic hot - melt adhesive composition comprises at least 80% by weight, preferably at least 85% by weight, of a polyamide based on dimer fatty acid, preferably 0.2% to 2% by weight of a cross - linked phenoxyphosphazene compound and 1.0% to 12% by weight, more preferably 5% to 9.5% by weight, of melamine cyanurate.

[0025] Low viscosity is a requirement for hot melt adhesives to be suitable for low-temperature compression molding technology. Thus, in a preferred embodiment, as measured according to ASTM D3236, the thermoplastic hot melt adhesive composition of the present invention has a viscosity of equal to or less than 10,000 mPas, preferably less than 5000 mPas, at 200 to 230 °C.

[0026] The innovative thermoplastic hot melt adhesive composition of the present invention is further characterized by high thermal stability, ensuring a V-0 rating even after aging. Thus, a preferred embodiment of the thermoplastic hot melt adhesive composition is provided, wherein the thermoplastic hot melt adhesive composition is thermally stable at a temperature not exceeding 210 °C. Thermal stability can be visually determined by comparing the color of the heated composition with a standard color card.

[0027] According to J-STD-004A, the corrosion resistance of the thermoplastic hot melt adhesive composition of the present invention at 40 °C and 90% relative humidity is preferably equal to or greater than 10 8 ohms. The high corrosion resistance makes the hot melt adhesive composition of the present invention particularly suitable for manufacturing electrical and electronic components.

[0028] Another object of the present invention is a method for preparing the thermoplastic hot melt adhesive composition of the present invention, wherein the at least one polyamide is melted, and the at least one phosphorus-based flame retardant and the at least one halogen-free flame retardant are added under stirring.

[0029] The hot melt adhesive composition of the present invention is specifically designed for low-temperature compression molding. Thus, in another aspect, the present invention relates to the use of the thermoplastic hot melt adhesive composition according to the present invention in low-temperature compression molding technology. Preferably, the composition is used for encapsulating electrical and / or electronic components.

[0030] Another object of the present invention is to obtain a molded article by low-temperature compression molding from the thermoplastic hot melt adhesive composition of the present invention.

[0031] The present invention will be explained in more detail with reference to the following examples, which should in no way be construed as limiting the scope or spirit of the present invention. Examples

[0032] Composition 1

[0033] 89.5% by weight of a dimer fatty acid-based polyamide with a softening point of 155 °C was melted, and a mixture of 1.5% by weight of a phosphorus-based flame retardant with a solubility greater than 0.05% in water at 25 °C and 9% by weight of melamine cyanurate was added under stirring.

[0034] It was found that the obtained hot melt adhesive composition meets the V-0 classification of UL 94V and has a viscosity of 2,500 mPas at 210 °C. However, the composition shows slight discoloration at a temperature of 190 °C.

[0035] Composition 2

[0036] 90% by weight of a dimer fatty acid-based polyamide with a softening point of 155 °C was melted, and 1.0% by weight of a phosphorus-based flame retardant with a solubility in water at 25 °C of less than 0.01% and 9% by weight of melamine cyanurate were added under stirring.

[0037] The obtained composition meets the requirements of UL 94V for V-0 classification both before and after aging at 70 °C for 168 hours, and has a viscosity of 4,500 mPas at 210 °C. In addition, after aging at 40 °C and 90% relative humidity for 168 hours according to J-STD-004A, the corrosion resistance of the composition is a satisfactory 10 8.6 ohms and there is no corrosion to the printed circuit board (PCB). No discoloration occurs when heated to 190 °C, and only slight discoloration is detected at a temperature of 210 °C.

[0038] Composition 3

[0039] 90% by weight of a dimer fatty acid-based polyamide with a softening point of 175 °C was melted, and 1.0% by weight of a phosphorus-based flame retardant with a solubility in water at 25 °C of less than 0.01% and 9% by weight of melamine cyanurate were added under stirring.

[0040] The obtained composition meets the requirements of the V-0 classification of UL 94V and has a viscosity of 4,500 mPas at 225 °C. In addition, the composition also has a satisfactory 10 8.2 ohms of corrosion resistance and does not show discoloration when heated to 210 °C. No corrosion to the PCB is detected after aging at 40 °C and 90% relative humidity for 168 hours. No change in flame retardancy is found after aging at 70 °C for 168 hours.

Claims

1. A thermoplastic hot-melt adhesive composition, based on the total weight of the composition, the composition comprising: a) at least one polyamide; b) at least one phosphorus-based flame retardant in an amount of 0.1% to 5% by weight; and c) at least one halogen-free flame retardant in an amount of 0.1% to 15% by weight, wherein the at least one phosphorus-based flame retardant is different from the at least one halogen-free flame retardant.

2. The thermoplastic hot melt adhesive composition according to claim 1, wherein The at least one halogen-free flame retardant is selected from melamine cyanurate, melamine polyphosphate, ammonium phosphate, pentaerythritol, and zinc oxide.

3. The thermoplastic hot melt adhesive composition according to any one of the preceding claims, characterized in that, The at least one halogen-free flame retardant is melamine cyanurate.

4. The thermoplastic hot melt adhesive composition according to any one of the preceding claims, characterized in that, The at least one polyamide is a polyamide based on dimer fatty acid.

5. The thermoplastic hot melt adhesive composition according to claim 4, characterized in that, The at least one polyamide is obtained from a reaction mixture comprising at least one dimer fatty acid and at least one dicarboxylic acid.

6. The thermoplastic hot melt adhesive composition according to any one of the preceding claims, characterized in that, The at least one phosphorus-based flame retardant is selected from cyclic phosphonates and crosslinked phenoxyphosphazene compounds.

7. The thermoplastic hot melt adhesive composition according to any one of the preceding claims, characterized in that, Based on the total weight of the composition, the at least one polyamide is contained in the composition in an amount of at least 80% by weight, preferably at least 85% by weight, respectively.

8. The thermoplastic hot melt adhesive composition according to any one of the preceding claims, characterized in that, Based on the total weight of the composition, the amount of the at least one phosphorus-based flame retardant in the composition is 0.2% to 2% by weight, respectively.

9. The thermoplastic hot melt adhesive composition according to any one of the preceding claims, characterized in that, Based on the total weight of the composition, the amount of the halogen-free flame retardant in the composition is 1.0% to 12% by weight, more preferably 5% to 9.5% by weight, respectively.

10. The thermoplastic hot melt adhesive composition according to any one of the preceding claims, characterized in that, As measured according to ASTM D3236, the viscosity of the composition at 200 °C to 230 °C is equal to or less than 10,000 mPas, preferably less than 5000 mPas.

11. The thermoplastic hot melt adhesive composition according to any one of the preceding claims, characterized in that, The composition is thermally stable at a temperature not exceeding 210 °C.

12. The thermoplastic hot melt adhesive composition according to any one of the preceding claims, characterized in that, According to J-STD-004A, the corrosion resistance of the composition at 40 °C and 90% relative humidity is equal to or greater than 10 8 ohms.

13. A method for preparing the thermoplastic hot-melt adhesive composition according to any one of claims 1 to 12, wherein the at least one polyamide is melted and the at least one phosphorus-based flame retardant and the at least one halogen-free flame retardant are added under stirring.

14. Use of the thermoplastic hot-melt adhesive composition according to any one of claims 1 to 12 in low-temperature molding technology.

15. A molded article obtained from the thermoplastic hot-melt adhesive according to any one of claims 1 to 12.