CA1275521C

CA1275521C - Flame-retardant olefinic resin composition

Info

Publication number: CA1275521C
Application number: CA000541647A
Authority: CA
Inventors: Yasuo Nakagawa; Kazuo Hoshi
Original assignee: Sumitomo Bakelite Co Ltd
Current assignee: Sumitomo Bakelite Co Ltd
Priority date: 1987-03-02
Filing date: 1987-07-09
Publication date: 1990-10-23
Anticipated expiration: 2007-10-23
Also published as: NO872995D0; NO176967C; NO176967B; NO872995L; DE3784486T2; ATE86273T1; KR900006359B1; AU7539487A; EP0280761A3; FI873150A; KR880011264A; AU578184B2; EP0280761A2; FI92215C; FI873150A0; DE3784486D1; FI92215B; US4801639A; EP0280761B1

Abstract

ABSTRACT OF THE DISCLOSURE
A flame-retardant olefinic resin composition comprising (A) 100 parts by weight of a mixed resin consisting of an olefinic resin and a silane-grafted polymer obtained by grafting a silane to said olefinic resin, (B) 50 to 300 parts by weight of a hydrated metal compound, and (C) 0.1 to 30 paxts by weight of a dicarboxylic acid or dicarboxylic acid anhydride derivative.

Description

~75~i2~

1 The present invention relates to f]ame-retardant olefinic resin compositions which generate no hazardous and corrosive gas of halogen type during ~urning due to fire outbreak and which are intended to be applied particularly to electric wires and cables Imparting flame retardancy to polyolefin compo-sitions which have been extensively used as an insulating material for electric wires, cables and electric appliances, has conventionally been achieved by adding a halogen compound and antimony trioxide to a polyolefin. EIowever, the resulting compositions contain a halogen, and there-fore generate, during burning, a halide gas which is harmful to the human body and corodes metals. Moreover, these compositions produce, during burning, a large amount of fume making the visibility poor. This has imposed a remarkable restriction with respect to evacua-tion of people and fire fiyhting activity during fire.
Hence, it has recently become a strong desire for safety that these resin compositions produce no halogen-based gas upon burning. Under such situation, hydrated metal compounds have come to draw attention as an inorganic flame retardant, because their fuming property and harmfulness are very low.
Resin compositions containing a large amoun-~ of magnesium hydroxide, aluminum hydroxide or the like for ~;~, ~X75~ 1 25711-483 improving flame retardancy have been proposed in recent years.
However, these resin compositions have the following drawbacks.
(1) Magnesium hydroxide reacts with moisture and carbon dioxide present in the air and changes to magnesium carbonate.
Accordingly, on the surface of a resin composition containing magnesium hydroxide, there appear white crystals of magnesium carbonate.

(2) Magnesium hydroxide and aluminum hydroxide have very low resistances to acids and alkalis. Therefore, when a resin composition containing magnesium hydroxide or aluminum hydroxide i5 in contact with an acid or an alkali, magnesium hydroxide or aluminum hydroxide readily dissolves in the acid or alkali at the surface of the resin composition. It dissolves in a large amount even in a weak acid having a pH of abou-t 2 and, as a result, is liable to cause the deterioration of the resin composition surface.
These drawbacks have delayed the practical applications of the resin compositions containing magnesium hydroxide, aluminum hydroxide or the like to electric wires and cables.
A silane-grafted polymer causes crosslinking without requiring any catalyst. More specifically, hydroxyl groups (-OH) on the surface of a hydrated metal compound and silanol groups (~Si-OH) of a silane-grafted polymer cause a hydrolytic condensa-tion reaction to form strong silanol linkages ~-Si-O-MmOn (M is a metal)], under the influences of (a) a small amount of water present on the surface of the hydrated metal compound and (b) the hydrated metal compound which acts similarly to an organic metal .~ .

25711-~83 compound catalyst and in the presence of a frictional heat generated during kneading; in this reaction, no catalyst is required. Said strong silanol linkages are effective in providing a resin composition with excellent shape retention at high temperatures, improved drip prevention during burning and improved mechanical properties (e.g., improved whitening on bending, and improved wear resistance). The strong silanol linkages bring about improvements in mechanical properties, surface properties, thermal properties including heat deforma-tion, and burning properties including oxygen index.
As olefinic resins, there have conventionally been available polyethylene, polypropylene, ethylene-alpha-olein copolymers, ethylene~vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, and polyolefins modified with an unsaturated dicarboxylic acid which are obtained, for example, by reacting a liquid hydrocarbon (e.g., a liquid polybutadiene) as a polymer skeleton with maleic anhydride in the presence of a radical-generating agent such as a peroxide. A number of olefinic resins are being marketed in Japan also. The addition of such a modified olefinic resin to other resins or metal powders for imparting an adhesive property to the latter has been tried and reported in many papers. On this point r a number of patent applications have been filed. The examples are Japanese Patent Publication No. 5788/1987, Publication Date February 6, 1987 and Japanese Patent Publication No. 9135/1987, Publication Date February 26, 1987.
As another example of maleic anhydride utilization, maleic anhydride has been added to ethylene-alpha-olefin ,.~

~ 7 ~ Std~ 25711 483 copolymers in the presence of a peroxide or the like to improve the latter's heat resistance and mechanical strength, as described in Japanese Patent Application Kokai (Laid-Open) No. 10151/1987, Laid-Open Date January 19, 1987 and Japanese Patent Application Kokai ILaid-Open) No. 11745/1987, Laid-Open Date January 20, 1987.
In this approach, the polar group of maleic anhydride is added to a non-polar ol.efinic resin to merely improve the latter's affinity with a filler and to finally improve the mechanical strength and heat resistance of the latter. Therefore, the purpose of this approach is different from that of an approach intended by the present invention wherein siloxane linkages are formed between a silane-grafted polymer and water of a hydrated metal compound and further complex salt linkages are formed between the hydrated metal compound and a dicarboxylic acid or dicarboxylic acid anhydride derivative.
The present invention is intended to provide an olefinic resin composition capable of preventing the I r~

~5.5~ ~
7~16~-l deterioration and significant reduction in chemical resistance occurring at the surfaces of the above mentioned resins in various environmen-tal tests or in practical applications, when they con-tain a hydra-ted metal compound as a flame retardant.
According -to the present inven-tion, there is provided a flame-retardant olefinic resln composi-tion comprising (A) 100 parts by wéight of olefinic resin' at least 2% by weight of which is a silane-graf-ted polymer obtained by graf-ting an olefinic resin to an organic silane represented by a general formula given below, (~) 50 to 300 parts by weight of a hydrated metal compound, and (C) 0.1 to 30 parts by weight of a dicarboxylic acld or dicar-boxylic acid anhydride derivative.
The olefinic resin composition of the presen-t inven-tion is charac-terized in that it can prevent the surface deterioration and surface attack by chemicals in electric wires and cables when the present composition is used for these wires and cables, be-cause it comprises a silane-grafted polymer and a dicarboxylic acid or dicarboxylic acid anhydride deriva-tive.
In other words, the presen-t invention provides a resin composition capable of preven-ting the surface deterioration and severe surface attack by chemicals which occur with conven-tional resin compositions containing a hydra-ted metal compound as a flame retardant.

5r~'L 25711-483 The olefinic resin used in the present invention includes low density polyethylene, medium density polyethylene, high density polyethylene, ethylene-alpha-olefin copolymers, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-propylene rubber, ethylene-propylene-diene rubbers/ etc. As the alpha-olefin, there can be mentioned those having 3 to 12 carbon atoms, such as propylene, butene-l, pentene 1, hexene-l, heptene-1, octene-l, 4-methylpentene-1, 4-methylhexene-1, 4,4-dimethyl-pentene-l, nonene-l, decene-l, undecene-l, dodecene-l and the like. Of these alpha-olefins, most preferable are butene-l, pentene-l, hexene-l, heptene-l and 4-methylpentene-1.
The silane-grafted polymer is obtained by reacting the olefinic resin with an organic silane represented by the general formula RR'SiY2 ~wherein R is a monovalent olefinically unsaturated hydrocarbon group; Y is a hydrolyzable organic group;
and R' is a monovalent hydrocarbon group other than unsaturated aliphatic hydrocarbon groups or is same as Y) in the presence of a free-radical-generating compound. This reaction is conducted according to a known method described in Japanese Patent Publication No. 24373/1982, Publication Date May 24, 1982, Japanese Patent Publication No. 1711/1973, Publication Date January 19, 1973, Japanese Patent Application Kokai tLaid-open) No. 24342/1975, Laid-Open Date March 15l 1975, etc~ In a specific example, a polyolefin resin is reacted ~ith vinyltrimethoxysilane in the presence of an organic peroxide [e.g., DCP (dicumyl peroxide)~ having a strong polymerization-initiating action~
whereby a silane-grafted polymer is obtained.

~755~ 72164-l The amount of the silane-grafted polymer used is at least 2~ by weigh-t in the olefinic resin (A). When the amount is less than 2~ by weight, the resulting resin composition shows no improvement in shape retention at high temperatures and drip pre-vention during burning.
The crosslinking degree of the silane-grafted polymer is preferred to be 20 to 80% by weight in -terms of a gel fraction which is defined as a xylene insoluble. When the gel ~rac-tion is less than 20~ by weight, the resulting resin composition is low in shape retention at high temperatures and drip prevention during burning. When the gel fraction is more than 80% by weight, the resulting resin composition shows poor moldability.
The hydrated metal compound used in the present inven-tion is a compound having a decomposition:starting temperature of 150 to 450C and represented by the general formula MmOn-XH20 (wherein M is a metal; m and n are each an integer of 1 or more de-termined by the valency of the metal; and X is the number of molecules of bound water) or a double salt containing said compound. Suitably M is selec-ted from the metals of group IIA of the periodic table or M is selected from the metals of group IIIA of the periodic table.
Specific examples of the hydrated metal compound are aluminum hydroxide ~Al203.3H2O or ~l(OH)3], magnesium hydroxide [MgO.H20 or Mg(OH)2], calcium hydroxide ~ c~ t .r~

1 [CaO-H2O or Ca(OH)2], barium hydroxide [BaO-H2O or BaO-9H2O], zirconium oxide hydrate (ZrO nH2O), tin oxide hydrate (SnO-H2O), basic magnesium carbonate [3MgCO3-Mg(OH)2 3H2O], hydrotalcite (6MgO-A12O3-H2O), dawsonite (Na2CO3-A12O3-nH2O), borax (Na2O-B2O5~5H2O) and zinc borate (ZnB4O7 2H2O).
When the hydrated metal compound is added in an amount less than 50 parts by weight, the resulting resin composition is difficult to have desired flame retardancy. When the hydrated metal compound is added in an amount more than 300 parts by weight r the resulting resin composition shows poor mechanical properties (e.g. low tensile strength) and poor extrudability.
As the dicarboxylic acid derivative, there can be mentioned saturated aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and the like; unsaturated aliphatic dicarboxylic acids such as fumaric acid, maleic acid and the like; carbocylic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid and the like;
and salts and esters of these dicarboxylic acids, such as dibutyltin maleate, dioctyltin maleate ~these maleates are obtained by substituting the hydrogen ions of the carboxyl groups of maleic acid with another cation), diethyl malonate and the like.
The dicarboxylic acid or dicarboxylic acid anhydride derivative of the present invention further ~Ç ~755r~ ~L

1 includes all modified polymers obtained by modifying a polymer with one of the above mentioned dicarboxylic acid derivatives, such as (a) ternary copolymer of ethylene, maleic acid (or its anhydride~ and ethyl acrylate (or acrylic acid), (b) maleic anhydride-modified polyolefin resins obtained by grafting a polyolefin resin with maleic anhydride in the presence of a peroxide, (c) maleic acid (or maleic anhydride)-modified poly-butadiene obtained by adding maleic acid (or maleic anhydride) to a liquid polybitadiene hav.ing a molecular weight of 5000 or less, and (d) esterification products of maleic acid (or maleic anhydride)-modified poly-butadiene, and furthermore includes hydrogenation produts of said modified polymers obtained by subjecting such a modified polymer to hydrogenation to saturate the unsaturated bonds of the modified polymer.
The dicarboxylic acid anhydride derivative further includes mixed anhydrides between two different carboxylic acids such as acetic-benzoic anhydride in addition to structurally possible anhydrides of these dicarboxylic acids.
When the amount of the dicarboxylic acid or dicarboxylic acid anhydride derivative is less than 0.1 part by weight, the addition effect is too low. When ~5 the amount is more than 30 parts ~y weight, the reaction between the derivative and the hydrated metal compound takes place excessively and the composition shows poor extrudability and the extrudate shows deteriorated ~ r 1 appearance.
The flame-retardant olefinic resin composition of the present invention can further contain, if necessary, various additives conventionally used, such as antioxidant, neutralizing agent, UV absorber, antistatic agent, pigment, dispersing agent, lubricant, thickener, foaming agent, metal deterioration inhibitor, fungicide, flow control agent, flame retardant of phosphorus or phosphine derivative type, other inorganic fillers, crosslinking agent, crosslinking aid and the like and furthermore other resins. The present composi-tion can be subjected to crosslinking by electron rays.
In producing the olefinic resin composition of the present invention, the following reactions take place by kneading a system containing three components, namely, the silane-grafted polymer, the hydrated metal compound and the dicarboxylic acid or dicarboxylic acid anhydride derivative.
(1) The silane-grafted polymer causes cross-linking without requiring any catalyst. More specifically, hydroxyl groups (-OH? on the surface of the hydrated metal compound and silanol groups (~Si-oH) of the silane-grafted polymer cause a hydrolytic condensation reaction to form strong siloxane linkages [-Si-O-M O (M is a metal)], under the influences of (a) a small amount of water present on the surface of the hydrated metal compound and (b) the hydrated metal compound which acts S5~

l similarly to an organic metal compound catalyst and in the presence of a frictional heat generated during kneadin~; in this reaction, no catalyst is required.
(2) The dicarboxylic acid derivative reacts with the metal ion of the hydrated metal compound to form a complex salt.

(3) The dicarbo~ylic acid anhydride derivative is subjected to ring opening during kneading with heating, by the water of the hydrated metal compound and, simultaneously therewith, reacts with the hydrated metal compound to form a complex salt.
As mentioned above, there are formed (a) siloxane linkages between the silane-grafted polymer and the hydrated metal compound and (b) complex salt linkages between the dicarboxylic acid or dicarboxylic acid anhydride derivative and the hydrated metal compound.
The synergistic effect of these two types of linkages can remarkably reduce the surface deterioration and severe surface attack by chemicals which occur at conventional flame-retardant resin compositions using a hydrated metal compound. Severe requirements for flame-retardant resin compositions can be met only by the synergistic effect of the two types of linkages and can never be met by either one of the two linkages.
In producing the present composition, there occur independently the two reactions, that is, one between the silane-grafted polymer and the hydrated metal compound and the other between the hydrated metal 55P.,~L

1 compound and the dicarboxylic acid or dicarboxylic acid anhydride derivative. Therefore, in compounding the three components o~ the present composition, namely, (A) 100 parts by weight of a mixed resin consisting of an olefinic resin and a silane-grafted polymer obtained by grafting a silane to said olefinic resin, ~B) 50 to 300 parts by weight o~ a hydrated metal compound, and (C) 0.1 to 30 parts by weight of a dicarboxylic acid or dicarboxylic acid anhydride derivative, any of the following blending sequences can be adopted.
(1) The components (A), (B) and (C) are kneaded together.
(2) The components (A) and (B) are kneaded first; then, the component (C) is added; and all the components are kneaded.
(3) The components (B) and (C) are kneaded or the component (B) is subjected to a surface treatment by the component (C); then, the component (A) is added; and all the components are kneaded.
Depending upon the state (solid or liquid) of the component (C), one of the above blending sequences (1) to (3) may be selected appropriately. This is one of the advantages of the present invention.
The present invention has a combustion-controlling effect quite different from that of the prior art using carbon powders and accordingly can ~'7SS~

1 exhibit the combustion-controlling effect irrespective of various pigments which may be added to the present composition for easier identification in use. Hence, the present composition can be colored in any desired color depending on uses.
The present invention is explained specifically with reference to Examples and Comparative Examples.

Experiment I (Examples 1 to 7 and Comparative Examples 1 to 3) First, two silane-grafted olefinic resins (two silane-grafted polymers) were prepared according to the formulations shown in Table 1, using the following procedure. Dicumyl peroxide (DCP) was dissolved in vinyltrimethoxysilane. The solution was independently mixed with two low-crystalline polyethylenes, namely, (1) an ethylene-butene-l copolymer and (2) an ethylene-ethyl acrylate copolymer. Each mixture was kneaded and then extruded at 150 to 200C using a single-screw extruder o~ 50 mm~ to obtain silane-grafted polymers A and B in a pellet form. Each polymer was placed in an aluminum-laminated bag and the bag was sealed to prevent the incoming of external moisture.
The polymer was taken out by each necessary amount when-ever required.

~ 755~ 25711-483 Table l Formulations used in production of silane-grafted polymers (silane-grafted olefinic resins) Silane-grafted olefinic resins Materials A B
, (l) D 9052 100 (2) A 2150 - lO0 DCP 0.2 0.2 Vinyltrimethoxysilane 3 3 Gel raction, 57 60 g by weight*

(1) "~oftrex"**, a VLDPE manufactured by Nippon Petrochemicals Co., Ltd.
(2) "Rexlon"**, an EEA copolymer manufactured by Nippon Petrochemicals Co., Ltd.
* Insoluble (% by weight) after immersion in xylene at 120C for 20 hours.
Next, various components shown in Table 2 were mixed together in a container. Each of the resulting mixture was then kneaded in a Banbury roll and pelletized.
The pellets were roll-pressed to obtain a pressed sheet. From each sheet, various test pieces were prepared.
Some of these test pieces were immersed in water; carbon dioxide gas was blown thereinto; and the surface whitening due to forma-tion of magnesium carbonate was e~amined. Using other test pieces/ there were also examined their weight chan~e by 10%
sulfuric acid or 3% aqueous sodium hydroxide solution, their **Trade-mark -- 1~ --~;~755~

1 oxygen index as a measure of flame retardancy, and their extrudability as a measure of processability, using an extruder.
The results are shown in Table 2. As seen from Table 2, systems using a combination of a silane-grafted polymer and a dicarboxylic acid or dicarboxylic acid anhydride derivative show remarkable improvements in whitening and resistances to sulfuric acid and sodium hydroxide.

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1 Experiment II (Examples 8 to 14 and Comparative Examples 4 to 6) Using the formulations shown in Table 3, the same procedure as in Experiment I was conducted.
The results are shown in Table 3. As seen from Table 3, systems using a combination of the silane-grafted polymer A and a dicarboxylic acid or dicarboxylic acid anhydride derivative show remarkable improvements in whitening and resistances to sulfuric acid and sodium hydroxide.

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Claims

1. A flame-retardant olefinic resin composition comprising (A) 100 parts by weight of olefinic resin, at least 2% by weight of which is a silane-grafted polymer obtained by grafting an olefinic resin to an organic silane represented by the general formula RR'SiY2 (wherein R is a monovalent olefinic-ally unsaturated hydrocarbon group; Y is a hydrolyzable organic group: and R' is a monovalent hydrocarbon group other than unsaturated aliphatic hydrocarbon groups or is same as Y), (B) 50 to 300 parts by weight of a hydrated metal compound, and (C) 0.1 to 30 parts by weight of a dicarboxylic acid or dicar-boxylic acid anhydride derivative selected from the group consisting of saturated aliphatic dicarboxylic acids, unsaturated aliphatic dicarboxylic acids, carbocylic dicarboxylic acids, salts, esters and anhydrides of these dicarboxylic acids, mixed anhydrides between two different carboxylic acids, and polymers modified with these dicarboxylic acids or the esters or anhydrides thereof polyolefin resins modified with maleic anhydride, polybutadienes modified with maleic acid or the anhydride thereof, and the esterified products of the modified polybutadienes.

2. A flame-retardant olefinic resin composition according to Claim 1, wherein component (A) comprises an olefinic resin selected from the group consisting of low density polyethylene, medium density polyethylene, high density polyethylene, ethylene-alpha-olefin copolymers, ethylene-vinyl acetate copolymer, ethy-lene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-propylene rubber, and ethylene-propylene-diene rubbers.

3. A flame-retardant olefinic resin composition according to Claim 1 or 2, wherein component (A) comprises a silane-grafted polymer obtained by reacting an olefinic resin selected from the group consisting of low density polyethylene, medium density polyethylene, high density polyethylene, ethylene-alpha-olefin copolymers, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-propylene rubber, and ethylene-propylene-diene rubbers with the organic silane in the presence of a free-radical-generating compound.

4. A flame-retardant olefinic resin composition according to Claim 1, wherein the hydrated metal compound is a compound having a decomposition-starting temperature of 150° to 450°C and represented by the general formula MmOn.XH2O (wherein M is a metal; m and n are each an integer of 1 or more determined by the valency of the metal, and X is the number of molecules of bound water) or a double salt containing said compound.

5. A flame-retardant olefinic resin composition according to Claim 4, wherein the M is selected from the metals o-f groups IIA, and IIIA, of the periodic table.

6. A flame-retardant olefinic resin composition according to Claim 5, wherein the M is selected from the metals of group IIA
of the periodic table.

7. A flame-retardant olefinic resin composition according to Claim 5, wherein the M is selected from the metals of group IIIA of the periodic table.

8. A flame-retardant olefinic resin composition according to Claim 4, wherein the hydrated metal compound is magnesium oxide monohydrate.

9. A flame-retardant olefinic resin composition according to Claim 4, wherein the hydrated metal compound is aluminum oxide trihydrate.

10. A flame-retardant olefinic resin composition according to claim 1, wherein the dicarboxylic acid or dicarboxylic acid anhydride derivative is selected from the group consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, phthalic acid, isophthalic acid, terephthalic acid, dibutyltin maleate, dioctyltin maleate, diethyl malonate, acetic benzoic anhydride, and a ternary copolymer of ethylene, maleic acid or the anhydride thereof and ethyl acrylate or acrylic acid.