Poly(arylene Sulfide) Composition With Improved Insulation Resistance and Cracking Resistance

This invention relates to poly(arylene sulfide) compositions. In another aspect the invention relates to poly(arylene sulfide) compositions with improved electrical insulation resistance and cracking resistance. The invention also relates to a process for producing poly(arylene sulfide) compositions.

Poly(arylene sulfide) is a unique material that has been produced commercially for a number of years and has found application in a variety of areas. Poly(arylene sulfide) is resistant to most chemicals, it has a relatively high melting temperature compared to other thermoplastics and it has good dimensional stability and other properties which permit its wide variety of uses.

Poly(arylene sulfide) materials have found application in the electronics industry, but generally it is considered that the use of such materials in that industry is small in comparison to the potential that such materials have in that area. Electrical applications in which cracking resistance coupled with very high electrical insulation resistance are numerous and poly(arylene sulfide) compositions are highly desirable for such uses when one considers the inherent properties of poly(arylene sulfide) materials; however, thus far poly(arylene sulfide) compositions have not been formulated which have both good cracking resistance and electrical insulation resistance.

Therefore an object of the invention is a poly(arylene sulfide) composition having good cracking resistance and electrical insulation resistance.

Another object of the invention is a poly(arylene sulfide) composition which can be molded into articles having improved cracking resistance and electrical insulation resistance as compared to such compositions of the prior art.

According to the invention, the inventive composition comprises poly(arylene sulfide), a reinforcing material, low density polyethylene and at least one organosilane. Such a composition will generally contain from about 30 to 80 weight % of the poly(arylene sulfide) component, from about 20 to about 70 weight % of the reinforcing material, from about 0.5 to about 10 weight % of the low density polyethylene and from about 0.1 to about 5 weight % of at least one organosilane.

Prior to the present, poly(arylene sulfide) compositions were not available which provided good cracking resistance and at the same time an electrical insulation resistance of at least 1.0.times.10.sup.9 ohms. The present inventive compositions combine these two properties with the outstanding properties of poly(arylene sulfides) and provide a composition which is useful to mold a variety of articles including thick walled articles used in the electrical industry. Further, the compositions of the present invention can be improved in appearance by the addition of certain pigments such as certain carbon black materials and the mold life can be improved by the incorporation of the mold corrosion inhibitors such as hydrotalcite.

In its broadest aspect the present invention contains poly(arylene sulfide), reinforcing material, low density polyethylene and at least one organosilane. For convenience Table I is provided showing the broad, medium and narrow ranges of the above components with the value shown representing weight percent based on total weight of the composition, although inventive compositions outside Table I are possible.

Suitable poly(arylene sulfide) resins useful in the present invention for example are those described in U.S. Pat. Nos. 3,919,177 and 4,038,261 and these U.S. Patents are incorporated herein by reference. The preferred poly(arylene sulfide) is poly(phenylene sulfide). Generally, the poly(arylene sulfide) will have a melt flow of less than about 400 grams per 10 minutes, as measured by ASTM D-1238 using a 5 kilogram weight at 600.degree. F. through a 0.0825 inch diameter orifice. Suitable poly(arylene sulfide) resins useful in the present invention can be prepared according to the processes described in the patents referenced above, and particularly as described in U.S. Pat. No. 4,038,261 employing a minor amount of trichlorobenzene branching agent to achieve the desired melt flow. The most preferred poly(arylene sulfide) resins useful in the present invention are those manufactured by Phillips Petroleum Company and marketed as Ryton poly(phenylene sulfide) resins having a melt flow of from about 10 to about 400 grams per 10 minutes determined by the ASTM test referenced above. It is also within the scope of the invention to employ copolymers of poly(arylene sulfide). Generally, although not necessarily, such copolymers will contain at least 90 mole percent of unsubstituted phenylene units.

The preferred reinforcing material used in the present invention is glass fibers. While there are a variety of glass fiber reinforcing materials available, those specifically developed for electrical applications are preferred, which are often referred to as "E glass". If a finish or sizing is used on the glass fibers it should be one that is compatible with the other components of the composition, such as the organosilane. Glass fibers that have been used in the inventive composition with good results are those produced by Owens-Corning Corporation and marked as Fiberglas 497.

The compositions of the present invention also contain a minor amount of a low density polyethylene. Ethylene homopolymers and copolymers may be used, with ethylene polymers prepared by the incorporation of monomers comprising at least about 90 mole percent ethylene with 10 to 0 per mole percent of the remaining comonomer being preferably a 1-olefin. As used herein, low density polyethylenes are those generally having a density of from about 0.910 to about 0.940, preferably from about 0.910 to about 0.930, as determined by ASTM test method D-1505. Further although not essential it is desirable for the low density polyethylene component to have a melt index greater than about 100 grams per 10 minutes and more preferably greater than about 400 grams per 10 minutes as determined by ASTM test method D-1238 Condition E.

The last essential component of the present inventive composition is at least one organosilane. The organosilanes useful in the present invention are represented by the following generic formula: ##STR1## where R.sub.1 and R.sub.2 are individually selected from the group consisting of hydrogen, alkyl, alkaryl, aminoalkyl, carboxyalkylaminoalkyl, aryl, aralkyl, carbamoyl, hydroxyalkyl, and vinylaralkylaminoalkyl groups containing 1 to 10 carbon atoms, also may be where R.sub.1 and R.sub.2 are joined by a valence bond to form a cyclic structure of from 5 to 16 atoms including the nitrogen atom therein, R.sub.3 and R.sub.4 are individually selected from the group consisting of alkyl and cycloalkyl groups containing 1 to 6 carbon atoms, Q is a divalent hydrocarbon radical containing from 1 to 18 carbon atoms, and y is 0, 1 or 2.

Representative organosilanes are:

3-Aminopropyltrimethoxysilane,

3-Aminopropyltriethoxysilane,

3-Aminopropylmethyldiethoxysilane,

N-Phenyl-3-aminopropyltrimethoxysilane,

p-Aminophenyltrimethoxysilane,

3-(Diethylamino)propyltrimethoxysilane,

N-beta-(Aminoethyl)-gamma-aminopropyltrimethoxysilane,

N-(2-aminoethyl)-N'-[3-trimethoxysilyl)propyl]-1,2-ethanediamine,

N-(3-aminopropyl)-N'-[(trimethoxysilyl)methyl]-1,3-propanediamine,

Methyl 3-[2-(trimethoxysilylpropylamino)-ethylamino]-propionate,

N-{2-[3-(trimethoxysilyl)propylamino]ethyl}-p-vinylbenzylammonium chloride,

N-bis-(2-hydroxyethyl)-3-aminopropyltriethoxysilane,

gamma-Ureidopropyltriethyloxysilane, and

gamma-[1-(4,5-dihydroimidazoline]-propyltriethoxysilane.

In addition to the four essential components described above the inventive composition can also contain optional components such as mold corrosion inhibitors, pigments, processing aids and the like. Since one of the primary uses for the inventive composition will be as a molding compound and since poly(arylene sulfide) compositions are somewhat corrosive in nature, in order to increase mold life a mold corrosion inhibitor such as, for example, a hydrotalcite may be used without adverse effect to the cracking resistance and the electrical insulation resistance of the inventive composition. As shown in the Examples, the hydrotalcite DHT-4A sold by Kyowa Chemical Industry Company, Limited, Osaha, Japan was used with excellent results. Further it is frequently desirable to incorporate a pigment in the inventive composition so that the articles produced from the inventive composition have a uniform color. Often the parts produced from poly(arylene sulfide) compositions have a somewhat streaky or nonuniform appearance and the incorporation of a pigment, particularly those developed for electrical applications, may be used. For example, a pigment such as channel black has been used in the inventive composition and results in products having a uniform color without affecting the cracking resistance and the electrical insulation resistance. The pigment used in the inventive composition with excellent results was a channel black sold by the West German company Degussa, and marked as Special Black-4, regular color channel black.

For convenience Table II is provided to show the preferred broad, medium and narrow ranges for the amount of mold corrosion inhibitor and pigments. The amounts shown are in terms of weight percent based on total weight of the composition and are included as optional additional components to Table I above.

As indicated above other components may be incorporated into the inventive composition such as a processing aid and the like depending upon the particular needs and requirements of the user.

In accordance with the process of the present invention, it has been found essential to carry out the hot melt extrusion of the dry blended mix of the components of the present inventive composition at as low an average machine temperature as possible and still obtain good homogeneity of the resulting product. As used herein the term "average machine temperature" means the average temperature of at least four (4) and preferably eight (8) approximately equally spaced temperature sensing means located on the extruder. As the data shows in the following examples the higher the average machine temperature the lower the cracking resistance of the resulting composition. Good results regarding cracking resistance were obtained when the average machine temperature was less than about 675.degree. F., preferably less than about 650.degree. F. and more preferably less than about 630.degree. F.

As indicated earlier the inventive compositions are well adapted for use in applications where excellent electrical insulation resistance is important as well as those in which resistance to cracking is important. While the inventive compositions were developed for applications in the electrical apparatus field, they are useful in a variety of areas and their particular applicability in the electrical field should not be construed as a limitation upon the inventive compositions.

The following examples show the results obtained as a result of testing a number of compositions for cracking resistance and insulation resistance, some of which are outside the scope of the present inventive composition.

Twenty-four different compositions as shown in Table III were produced in 50 pound batches. Examples 1 through 11 and 18 and 19 illustrate compositions outside the scope of the present invention and examples 12 through 17 and 20 through 24 illustrate compositions in accordance with the present invention. The letters "NC" and "IC" shown in Table III mean non-inventive compositions and inventive compositions, respectively. Each composition was prepared by blending its components, except for glass, for about 3 minutes in a Henschel mixer at room temperature operating at about 1800 rpm. After this mixing period the glass reinforcement was added and mixing continued for about 3 additional seconds. Each mixture produced thereby was passed through a Crown Products 21/2 inch diameter single screw extruder with a length to diameter ratio of 40:1. The average machine temperature which the melt was exposed to is indicated in Table III. The extruded material was cut into pellets and injection molded according to the procedure described below in the section entitled "Internal Cracking Resistance Measurement". Also, the compositions were tested for their electrical insulation resistance according to the procedure described below.

The electrical insulation resistance was tested in accordance with the general method defined in ASTM test method D257 using a conditioning period of 48 hours in a 95.+-.1% relative humidity chamber at 90.degree. C. The ASTM recommended practice E104 for controlling relative humidity was followed. The resistance was measured employing a 500 volt potential and a GenRad Megohmeter (type 1862-C) having a capability of measuring resistance upto 2.times.10.sup.12 ohms.

The procedure to determine the resistance of poly(arylene sulfide) compounds to internal cracking is as follows: The resin composition is dried at 150.degree. C. for two hours in forced air oven in trays that are not more than 1.5 inches deep. A New Britain model 75 injection molding machine containing a water-cooled, centergated mold is used to produce flat disks that are 2.5 inches in diameter by 0.5 inches thick. The injection pressure and holding pressure may be varied to match resin compositions to effect disk production. The other operating conditions of injection molding must be set and maintained at values indicated below.

The shot size is sufficient to fill the mold with a 0.25 inch cushion and with no flash. The injection molder barrel is flushed three times with the resin composition to be tested. The next two or more shots are discarded before the next eighteen are collected and numbered in sequence. Immediately upon removal from the mold and while the disk is warm, the sprue is removed. Each disk is allowed to cool for at least two hours. Disks 5, 6, 7, 8, 10, 11, 12 and 13 are sawed parallel to the face to yield two disks each being approximately 0.25 inches thick. A Dayton metal cutting bandsaw (Model 3Z360G) equipped with a blade of ten teeth per inch is used to saw the disks. The sawn disks and the whole disks 1, 2, 3, 4, 14, 15, 16, 17 and 18 are annealed by being placed in a forced air oven at 204.degree. C. for two hours. The whole and half disks are then cooled for eighteen to twenty-four hours. Disks 1, 2, 3, 4, 14, 15, 16 and 17 are sawed parallel to the face to yield two disks approximately 0.25 inch thick. The disks are then allowed to set at room temperature for an additional eighteen to twenty-four hours before rating. Whole disks numbered 9 (unannealed) and 18 (annealed) are saved for reference. The non-sprue sides of each half-disk are rinsed under a stream of warm water to remove sawdust and visually examined for cracks. Each disk is classified as non-cracked or cracked. The number of cracked disks observed out of the total observed from each of the two groups, cut/annealed non-sprue and annealed/cut non-sprue are reported as a ratio of cracked disks to the total disks tested of that specific group, for example, a 4/8 annealed and cut non-sprue rating indicates that 4 disks were cracked out of 8 disks that were annealed, then cut and then examined for cracks. While the sprue sides can also be examined, the sprue side is subject to more variables which give somewhat less unreliable results compared to the non-sprue side. A resin composition yielding no more than a total of 9 cracked disks on the non-sprue side out of a total of 16 disks with 8 annealed and cut specimens and 8 cut and annealed specimens is required to be satisfactory for molding applications of thick articles.

It is also noted that the above-described Internal Cracking Resistance test was published in Plastics Engineering, April 1983, page 38, under the title "Screening Test for PPS Compounds" and is incorporated by reference herein.

The data in Table III illustrate the non-inventive compositions of Examples 1 through 8 fail because the insulation resistance is below 1.0.times.10.sup.9 ohms even though in some instances all four major components suitable for use in the present inventive composition are used, for example, as shown in Examples 5 and 7. It is believed that the high production rates for Examples 5 and 7 may have resulted in non-homogeneity of the compositions.

Examples 18 and 19 employed a silane within the scope of the present invention and had excellent insulation resistance, but the cracking resistance was unacceptable. These examples illustrate the importance of using a relatively low average machine temperature in order to not adversely affect the cracking resistance. It is also noted that there is a disparity between the results obtained in Examples 5 and 12 which are identical formulations except that in Example 12 the insulation resistance meets the minimum required where in Example 5 the insulation resistance was below the minimum. In both examples the cracking resistance was very good. It is believed that the high production rate in Example 5 caused some non-uniformity in the resulting polymer as compared to Example 12 which gave an insulation resistance value slightly below the minimum required. Examples 12 through 17 and 20 through 24 show the inventive compositions having both good cracking resistance and electrical insulation resistance.