DK161711B - Flame-retardant material - Google Patents

Description

DK 161711B

The present invention relates to a flame retardant material containing ethylene copolymer and with improved fire retardant properties.

Flame retardant ethylene copolymer materials have for a long time been the subject of research in the field of fire retardants and a number of materials have been developed using flame retardant methods.

One type of such material achieves flame retardancy and flame barrier protection by decomposing when exposed to excessive heat and high temperature to form a rigid foam of ceramic ash composed of numerous cells. The cells form a barrier to heat transfer. Furthermore, such materials are composed so that they also release water vapor during decomposition and cell formation, which also helps to delay the spread of fire.

Such materials disclosed in U.S. Patent No. 4,543,281 include an ethylene copolymer base or matrix containing alumina trihydrate and calcium carbonate or calcium magnesium carbonate. Under ambient conditions, these materials are conventional, melt-processable thermoplastic materials. Under high heat or fire conditions, the compositions act as a fire barrier and have a low fuel value and low smoke emission. As the material decomposes or burns, the Al and Ca constituents form a ceramic ash having cellular structure. Due to the cell formation as the ceramic ash builds up, the ash becomes a heat insulator. Potential applications include fire stopping, insulating wiring for wiring and cable designs, 30 where high temperature wiring integrity is required, and many other applications, such as protection of steel I-beams.

It has now been found that by the addition of certain phosphate esters, these materials swell less with fire, and their ceramic ash has a smaller and more uniform cell formation than compositions without such esters.

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It has also been found that the addition of certain meltable glasses will make the stiff foam of ceramic ash harder.

The presence of the phosphate ester causes the formation of ceramic ash with a small cell structure and lower volume swelling. As a rule, the cell size of ash found according to the materials of the invention is in the range of 1-2 micrometers. A small cell structure is advantageous because there is less risk of structural failure.

Thus, the flame retardant material of the invention is of the type comprising (a) a matrix constituting 10-40 wt% of the material comprising at least one ethylene copolymer, 15 (b) 35-89 wt% of the material of a mixture of ( (i) alumina trihydrate and (ii) calcium carbonate or calcium magnesium carbonate or both, the mixture containing a weight percent between (i) 20 and (ii) of 30:70 to 70:30, and this material is peculiar in that it additionally contains (c) at least one compound which constitutes 1-25% by weight of the material which is a tri (hydrocarbyl) phosphate ester.

The ethylene copolymer matrices used in the materials of the invention comprise ca. 40-95% by weight of ethylene, preferably 45-90 and most preferably 60-85%. A comonomer or a mixture of comonomers constitutes the remainder of the copolymer. Examples of comonomers include vinyl esters of carboxylic acids having 2 to 18 carbon atoms such as vinyl acetate; esters of unsaturated carboxylic acids or diacids of 4 to 18 carbon atoms, such as methacrylates or acrylates; as well as α-olefins of 3-12 carbon atoms. In addition, smaller amounts of other polymeric units such as carbon monoxide (CO) may occur. Examples of copolymers include ethylene / vinyl acetate, ethylene / ethyl acrylate, 3

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ethylene / propylene, ethylene / octene and ethylene / methyl acrylate.

When appropriate, such as. with the acrylate comonomers, up to 15% by weight CO may occur.

The melt index of the copolymers is generally between 5 0.1 and 150 g / 10 min, preferably 0.3-50 g / 10 min. and in particular 0.7-10 g / 10 min. In addition, mixtures of copolymers can be used. The amount of ethylene copolymer present is from 10 to 40% by weight of the material, preferably 15-35 and especially 18-30%.

The alumina trihydrate has the formula AI2O3.3H2O and preferably has an average particle size of 1-2 µτα. Larger particles tend to give a larger volume expansion under fire, resulting in a weaker ceramic ash. Smaller particles, especially those less than 0.5 µm, tend to increase the viscosity of the composition melt, providing less convenient processing.

The calcium carbonate or calcium magnesium carbonate preferably has a particle size of 1-3 μτα in diameter.

Larger particles tend to give a weaker ash-20 structure due to the smaller surface area available for ceramic sintering. Smaller particles, especially those with a diameter of less than 0.07 µm, produce a hard ceramic ash, but the foaming under fire is low and the composition viscosity tends to be high.

The ratio of alumina trihydrate to the calcium compound is, as mentioned, between a weight ratio of 30:70 to 70:30, preferably between 40:60 and 60:40 and especially between 45:55 and 55:45. The total amount of both compounds in the material will generally be between 35 and 89% by weight of the material, preferably 50-83% by weight, especially 60-78% by weight.

The phosphate ester increases the flexibility of the material and reduces the processing viscosity. It works by fire surprisingly by producing a uniform structure with small cells in the ceramic ash. As indicated above, the phosphate esters are tri (hydrocarbyl) phosphates. The hydrocarbyl groups may be alkyl groups having 2-20 carbon atoms or

DK 161711B

4 aryl groups with 6-20 carbon atoms. They may be substituted or interrupted by oxygen. The amount of ester that can be used will be between 1 and 25 wt%, based on the material, preferably between 2 and 15 wt%, especially between 4 and 10 wt%.

The materials can be prepared by simply mixing the ingredients in a polymer melt. An industrial scale Banbury plant operating in batches or a similarly intensive mixer is suitable for making the materials of the invention. Dry ingredients are added on a routine 10 basis. In most cases, it is convenient to inject the phosphate component directly into the mixing chamber of any unit, as is widely used with this type of equipment.

The material may optionally also contain a borosilicate glass. This helps to harden the ceramic ash that forms at lower temperatures than those that normally activate the Ca-Al complex. The glass is a glass that melts at low temperature (i.e., meltable at 600-1000 ° C) and is usually sodium, potassium, calcium, magnesium or zirconium borosilicate. When used, it can occur in amounts of up to 30% by weight of the material, but too much borosilicate can reduce structural stability at curing temperatures. A balance must therefore be maintained between the structural integrity of the ashes and the tendency to harden the ashes.

Furthermore, the material may contain shredded fiberglass threads to increase the stiffness of the material. In the event of fire, a material containing fiberglass expands to a lesser extent than one without fiberglass. The fiberglass is preferably cut into sections of 6.35 mm and may be present in amounts up to 20% by weight based on the material.

As a surfactant, an aliphatic carboxylic acid such as stearic acid may be added to facilitate dispersion of the Ca-Al mixture. The surfactant also appears to increase fracture elongation and increase the melt index.

DK 161711B

Examples

All mixtures in the following examples are prepared in a mixer such as a Banbury or Brabender "Prep Center" mixer. All constituents are added to the mixing chamber at a level of 70-80% of the internal volume of the mixer, based on melt or mold. The ingredients are mixed for 5-10 minutes at a rotor speed adjusted to maintain a temperature between 160 and 190 ° C. The materials are then removed after cooling and then molded at 150 ° C in the forms required for testing.

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Example 1 In this example, seven mixture samples are prepared.

The constituents / occurring in each are listed in Table I along with the measured properties.

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Comparative Samples 1, 2 and 3 are examples of ethylene / vinyl acetate copolymer (EVA) filled with minerals as described in US Patent No. 4,543,281 and also contain "common" plasticizers.

Samples 4, 5 and 6 are examples of materials 20 of the invention. They (1) exhibit good thermoplastic properties, e.g. extension, melt index and flexibility.

(2) has low flammability as evidenced by the Limiting Oxygen Index (LOI).

25 (3) produces heat insulating ash when burned at high temperatures (1000 ° C / 3 hours).

(4) and surprisingly exhibit a controlled lower volume swelling on fire.

This gives a self-supporting ash with far finer cell structure than samples 1-3.

Examples 4-6 are highly flexible materials with fracture extensions greater than 500%. In addition, the controlled lower volume swelling under fire gives better ash 35 in terms of structural integrity.

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DK 161711 B

Notes to Table I

Components: (1) EVA copolymer (25 wt% VA, 2.01 melt index).

(2) "Hydral" 710: Alcoa alumina trihydrate; 5 nominal particle size 1 micron diameter.

(3) "Atomite": CaCO 2 from Thompson-Weineman Co.; particle size 1-3 µm diameter.

(4) "Sundex" 790: aromatic processing oil from Sun Oil Co.

10 (5) "Circosol" 4240: naphthenic processing oil from Sun Oil Co.

(6) DOP: dioctyl phthalate softener.

(7) TCP: tricreasylphosphate plasticizer.

(8) "Kronitex" means a triaryl plasticizer from FMClnc. a mixture of isopropylphenyl-phenylphosphates of the formula [CH3] \ (CH4- (yy-o-j-_ P = o \ ch3 ^ J oTs J 3 20 (9) TBEP: tributoxyethylphosphate plasticizer.

Testing: (10) Working load: ASTM-D-1708, 5,080 cm / min; 32 mm nominal pressure cast plate.

(11) Melt Index: ASTM-1238, Condition E.

(12) Bending module: ASTM-D-790: 3.2 mm nominal die-cast plate.

i13) Volume increase (in case of fire): a 2.54 x 7.62 x 0.63 mm die cast plate is placed in a cold muffle furnace. It turns on and the oven reaches the temperature of 1000 ° C for 45 minutes. The sample stays in the oven for a total of 3 hours. Dimensions (length, width and height) are measured with fits before and after burning. Volume increase is calculated as 35%% increase over original volume.

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(14) Crush strength: the ceramic ash sample from the aforementioned firing (cf. 14) is tested for compressive strength as follows: Attach to the upper crosshead of an "Instron Tensile Tester" a 5-diameter 2.54 cm tapered rod . At a cross head speed of 5.08 cm / min, the resistance of the rod pushed through the ash is measured.

Crush resistance is measured while the rod bumps through the upper 2/3 height of the sample. The guide reading is divided by the rod end surface area (5.065 cm).

(15) Heat conduction test: A die cast plate (11.4 x 11.4 x 0.51 cm) is supported on a ring stand and wire grid over a "Fisher" laboratory burner with a 15 flame temperature of 1000 ° C near the bottom of the plate. The temperature of the top surface of the plate is monitored with an "Omega" infrared pyrometer supported 30 cm above the plate. Relative insulation capacity is indicated at the temperature after 30 minutes of burning.

20 (16) Limiting Oxygen Index: ASTM-D-2863.

Microphotographs show that samples according to Ex.

4-6 have a uniformly small cell size, but do not sample according to. Examples 1-3. Microphotography with 2x magnification is made from cut samples and the largest voids or cells are measured. The cells in the samples according to Examples 1-3 have an average size between 3.5 and 4.5 mm in diameter, while the samples according to. Examples 4-6 have cells having a diameter between 1 and 2 mm.

Example 2

Samples are prepared as shown in Table II.

Sample 1 is a preferred material of the invention showing the use of a particular phosphate ester plasticizer. Examples 2 and 3 are further embodiments of the invention in which glass frit and fiberglass cut into strands increase the strength of the ash at the lower 10s.

DK 161711 B

o burning temperatures. The data presented shows that these materials are good heat insulators and that samples 2 and 3 have higher crush resistance than 1 at lower firing temperatures. This means that in many conditions of fire in buildings, the temperature rises more slowly and peaks at a lower temperature than fires fueled by hydrocarbon fuel. It is therefore important that the ash is strengthened at these lower temperatures. In Comparative Examples 2 and 3, the fiberglass may appear synergistic, as the fryer helps to maximize the crush resistance of the ash. Therefore, in this regard, sample # 3 may be the preferred one for certain applications.

One limitation of the use of glass frites is that at higher fryer loads or higher temperatures, the ash begins to function more like "glass" because it begins to flow. Thus, the ash at a frying load of 20% and fire at 1000 ° C after three hours has large glassy bubbles and has mediated volume expansion relative to the original level. On the other hand, sample 3 at 1100 ° C forms a reasonably normal ash immediately after fire, but the ash has shrunk considerably after one hour. Decreased volume expansion or large bubbles in the ash reduce the insulation capacity of the material.

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Table II

Mixture with glassless and fiberglass wires

Sample # 1_2_3

Composition, weight% 5 Ethylene copolymer 21 21 21

Aluminum trihydrate 36.5 31 30.5

Calcium Carbonate 36.5 31 30.5 "Ferro Frit 3185" · ^ 10 10

Fiberglass, PPG 3540 ^ 2 10 Triaryl Phosphate Ester 4.5 4.5 4.5

Stearic acid 1.5 1.5 1.5 3)

Physical properties

Workload (D1708)

Fracture elongation,% 491 453 495 15 Flow (MPa) 2.73 2.23 2.38

Tensile Strength (MPa) 2.77 2.18 2.7

Melt Index (Condition E) 1.37 1.38 1.11 Bending Module (MPa) 131 117 138

Burning properties 20 25.4 x 76.0 x 6.35 mm samples burn in an oven for different periods of time and at different temperatures.

Crushing strength (MPa) (Burning temp. / Burning time) 1000 ° C / 3 hours 0.2 1.76 1.76 25 900 ° C / 3 hours 0.069 0.3 0.41 800 ° C / 3 hours 0.003 0.014 0.062

Volume swelling (%) 1000 ° C / 3 hours 135 155 900 ° C / 3 hours 155 203 155 30 800 ° C / 3 hours 177 222 117

Heat conduction test Upper surface temperature 285 281 266 (° C for 30 minutes) 35

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Comments (1) "Ferro Frit 3185", a low fusion temperature sodium borosilicate glass of 750 ° C, 200 mesh powder, from Ferro Corp.

5 (2) PPG 3540, cut fiberglass wire, type E glass, from PPG Industries.

(3) Cf. Table I for comments on other components and test details.

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Claims (4)

A flame retardant material comprising (a) a matrix constituting 10-40% by weight of the material comprising at least one ethylene copolymer, 5 (b) 35-89% by weight of the material of a mixture of (i) alumina trihydrate and (ii) calcium carbonate or calcium-magnesium carbonate or both, the mixture containing a weight ratio of 10% between (i) and (ii) of 30:70 to 70:30, characterized in that the material further contains (c) at least one compound constituting 1-25% by weight of the material which is a tri (hydrocarbyl) phosphate ester. Material according to claim 1, characterized in that component (c) is a mixture of isopropylpropyl-phenylphosphates. Material according to claim 1 or 2, characterized in that it further contains a glass with a low 2-foot ion temperature. Material according to claim 1, 2 or 3, characterized in that it further contains shredded fiberglass.