CA1043925A - Metal titanate reinforced polyamides - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A polyamide containing a particulate mineral filler, a silane coupling agent and a fibrous alkali metal titanate. The presence of the titanate improves notch toughness, heat distortion temperature, stiffness and pro-duces molded articles with low warpage.

Description

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FIELD OF THE IN~ENTION
Thls inventlon relates to polyamide composltionscontainlng reinforclng materials. More partlcularly, the in-ventlon relates to compositlon~ Or polyamide resins contaln-ing a mineral flller and an alkali metal titanate~
BACKGROUND OF THE INVENTION
It is known in the art to rein~orce polyamide re-sins with varlous ~illers, for example, glass,asbestos, wollastonite, silica, and the like. The filler ls ususlly bonded to the polyamide through a silane coupling agent.
The flller is ordinarily chosen on the basis of the end use propertle~ deslred in the rinal article molded from the re~ln mixture. Fo~ some uses, such as automotlve body parts, a resln ls needed that ls strong and tough, ~ree o~ warpage, stl~, lmpact resi~tant and hlgh-temperature-dlstortlon reslstant 9 and has good surface appearance.
Polyamlde reslns contalnlng a mlneral riller such as wollas-tonlte, or sllica, have heat distortion temperatures that are generally too low to be of use ln auto body parts.
Furthermore, in molded parts that contain notches mineral rilled polyamide resins do not have as 800d strength as ls desirable in many applications. On the other hand, polyamide reslns contalning glass generally produce artlcles with a high heat distortion temperature and at high glass loadings (e.~., 30% by weight) acceptable notch toughness, but the hlgh loading tends to degrade other properties such as sur-face appearance and Gardner impact strength. Furthermore, they tend to warp on sub~ection to high temperatures. Poly-amides reinforced with wollastonite or slllca and glass ~ibers ofrer no advantage over glass relnforced polyamide.

. ' ' ,, ~(~4~Z5 In fact, notch toughness is inrerior to glass relnforced ; polyamide.
The mineral-rllled polyamide reslns contalning an alkall metal titanate that are provided by thls lnvention ; overcome the deficlencies mentioned above in glass fiber contalning products and produce molded articles having hlgh heat distortion temperatures and good strength properties : (both tensile and notch toughness) and generally good lm-pact strength. They also have better elongatlon propertles, have an esthetically pleaslng surface appearance, and pro-duce low warpage compared to polyamide reinforced wlth mix-tures of mineral and glass fiber.
SUMMARY OF THR INVENTION
. ___ __ Thls invention provldes a polyamide composition com-prlslng (1) 50-75% by wel~ht based on the wel~ht o~ the compo-sltlon of at least one hlgh molecular welght polyamide, (2) between about 20-48 . 5% by welght based on the welght of the composltion of a particulate mineral filler comprising sllica or a metalllc sillcate having a molsture content of less than 20 2% by weight of the flller and having at least 70% of its j partlcles less than 10 mlcrons ln size and having an average particle slze of between about 1-5 microns, (3) between a~out 0.25 and 2% by welght based on the weight Or the mlner-al flller of a silane coupling agent, and (4) between about 1 and 20~ by welght based on the welght of the composltion of a fibrous alkall metal tltanate contalning less than 5%
water by welght of the titanate.
DESCRIPTION OF THE INVENTION
The polyamides useful in this inventlon are the .
hlgh molecular weight polyamides normally employed in .

polyamlde reslns used to make molded artlcles. Thus the term "high molecular weight polyamlde" iEl u~ed in the moldlng art, and the polyamides employed ln the resln composition wlll have a relatlve viscoslty Or between about 40 and 80 as measured as de~crlbed ln ASTM D-789-72. Examples of 9uch hlgh molecular welght polyamldes lnclude polyhexamethylene adlpamlde, polycaprolactam, polydodecyl adlpamide, poly-`
tetramethylene adlpamlde, polyhexamethylene sebacamide, poly-hexamethylene dodecamide, and copolymers such as caprolactam and hexamethylene adlpamlde, as well as blends of the fore-going, particularly a blend of polyhexamethylene adlpamide and about 5-25% by weight Or polycaprolactam.
The particulate mineral flllers useful herein lnclude slllca tcrystalllne or amorphous) or a metalllc slllcate such as calclum slllcate or alumlnum sllicate.
The rlller should have a molsture (water)content of less than about 2% by weight ln order to obtain the lmpro~ed propertie~ of the articles molded from the reslns of thls invention, and thus, ln some lnstances the filler should be the calclned form. In addltlon, the properties of the molded artlcle depend in part on the size of mineral filler particles employed and it has been found that at least 75%
of the partlcles, by weight, should have a size less than 10 microns and that the average flller particle size should be between about 1 and 5 microns. Preferably, at least 98% of the particles by weight should have a slze less than 10 microns and the partlcles should have an average size less than 1-3 microns. Further, in a preferred composition the mineral filler will comprise between about 25% and about 35%
by weight.

The compositions require the presence of a silane coupling agent to bond the mineral filler and the alkali metal titanate to the polyamide. These are known coupling agents and include amino-, epoxy-, and vinyl-containing silanes such as 3-aminopropyltriethoxysilane, N-~ -(amino-ethyl)- y-aminopropyltrimethoxysilane, and the like.
The alkali metal titanate fibers are single crys-tals, and for use herein should contain less than 5~ water by weight, preferably less than 1~ water. The preferred titanate fiber is potassium titanate. The fibers should have a diameter of between about 0.05-0.3 micron, preferably 0.1-0.2 micron;
and a length to diameter ratio of at least 15:1, preferably at least 25:1, and most preferably between 30:1 and 50:1. The alkali metal titanate fibers should be present in an amount between about 1 and 20~ by welght based on the weight of the composltion, preferably between 5 and 10~. The alkali metal can be sodium, potassium, lithium, rubidium and the like.
The compositions of this invention may, of course, contain conventional additives. These include mold lubricants such as stearyl alcohol, metallic stearates, ethylene bis-stearamide~ and the like; heat stabilizers such as copper salts and alkali metal halides; and pigments.
Any of several methods ~or mixing the ingredients of the resin composites are used so long as good dispersi-bility is obtained. Ordinarily, the polyamide ingredient is in the form of a molding powder, i.e., as granules or cubes, although any form suitable as a feed to an extrusion appara-tus is satisfactory. Preferably, the ingredients are melt blended by feeding th~m into an extruder either individually, premixed, or partly premixed, in any combination. For con-venience, a twin-screw extruder is preferred.

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~0~ '25 The composltions of thls inventlon can be inJected under normal lnJectlon-molding pressure into molds for shap-lng i~nto molded artlcles.

In the examples whlch rOllOw:
Tenslle strength and Elong,ation were measured as described ln ASTM D-63~.
Flexural Modulus was measured as described ln ASTM D-790. It i8 a measure of stirfness.
Heat Dlstortion Temperature is a test comblning the effect of creep and flexural modulus versus temperature, mois-ture content and thermal history. It wasmeasured as described in ASTM D-648-72.
Izod Impact was measured as described in ASTM
D-256.
Gardner Impact was measured by usln~ a aardner Laboratory Impact tester (model Ia-1125) using a sample holder that had a 1.5 inch dlameter hole under the point of impact.
Thls openlng and the 0.25 lnch radlus tlp on the 4 pound dart correspond to the speclflcations of Procedure B ln ASTM
D-3029-72~ The test specimen, a 5 x 3 x 1/8 inch plaque, was placed over the hole, unclamped and the dart dropped from a helght determined by the staircase method as ln Sectlon 11, ASTM D-3029-72, varyln~ helght rather than welght. Data are reported as average lmpact at break in foot-pounds/lnch, correctlng for sample thickness.
Test specimens used to determine propertles were stored, prlor to testlng in glass ~ars sealed with tape untll tested dry-as-molded. All physlcal tests were on dry-as-molded 1/8 lnch thick specimens except Heat Dlstortlon 3C Temperature, whlch was measured on 5 x 1/2 x 1/8 inch bars annealed 0.5-hour ln 150C. silicone oll.

In the following exa~ples and comparison~, all parts and pel~centages are in parts by weight unless other-wise specified. The examples illustrate the compo~itions o~
the invention.

i A premix was made by surface coating 59.8~ poly-hexamethylene adipamide (Zyte ~ 101) having a relative vis-cosity of between about 43 and 52, with 0.2~ (0.5~ based ; on mineral filler) of 3-aminoprop~ltriethoxysilane. 35.0 of a mineral filler of wollastonite (calcium silicate, ob-tained from Interpace Corporation as P-4 sollastonite) con-taining less than 2~ water in which at least 70~ o~ the mineral filler particles were less than 10 microns in size and in which the particles had an average size between about 5 microns, and 5.0~ potassium titanate fibers (Fybe ~ D, obtained ~rom the Du Pont Compan~) containing less than 1~ ~, ` water, were then added.
The premix was starve fed at about 25 pph (11.36 kg/hr) to a screw extruder (a Werner & Pfleiderer ZSK-28).
The extruder had a screw configuration and barrel tempera-ture profile as follows:

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Temperature (C.) Screw Confi~ura ion -Rear 265-270 Type (No. o~ Elements) Front 270-280 031-024/024 Die 275-280 031-045/045/125/2 Feed 031-045/045 R Transition 031-045~045 Other Data 031-030/060 (3) Vacuum 30 in. (76.20 cm) 037-305/045 Kneading Block Screw 175-225 rpm 061-030/010 Reverse 031-045/045 (2) Vacuum Port 031-045/045 (2) 031-024/048 (2) Tlp ~ `
The pelletized product`was dried overnlght in a 70-80C. oven wlth about 20 lnch vacuUm, then molded into test bar~ (5 x 0~5 x 1/8 inch) (12.7 x 1.27 x 0.32 cm) on a 3-ounce Van Dorn reclprocatlng screw moldlng machine. Plaques (5 x 3 x 1/8 inch and 5 x 3 x 1/16 lnch) ~2.7 x 7.62 x 0.32 cm and ` 20 12.7 x 7.62 x 0.16 cm) were molded on a 6 ounce Van Dorn`re-ciprocatln~ screw moldin~ machlne. Generally, the molding conditlons were as follows:
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~ .- -. .. .. ~. - - .~ .

~rature (C.) 3-oz. Van Dorn 6~oz. Van Dorn Rear 270 280 Center 275 280 Front 280 280 Nozzle 280 280 Melt 295 295 Mold 90 90 Cycle (sec.) In~ectlon 15 or 20 15 or 20 Hold 25 or 20 25 or 20 Ram Fast Fast Screw ~rpm) 60 60 Physical propertles were measured on drg-as-molded test specimens and are tabulated in Table 1.
Comparison Te~ts Compo~ltlons for comparl~on were prepared as in Example 1. The compo~itions contalned ~he same polyamide, mlneral flller, and sllane as uqed ln Example 1. The compositlons are tested as rOllOws: :~
comParison B
Comparison A (Glass Containing~~
(Wollastonlte Composition) Composltlon) 59.8% polyamide 59.8% polyamide 0.2% 3-aminopropyl- 0.2% 3-amlnopropyl-trlethoxysilane trlethoxysllane 40% P-4 Wollastonite 35% P-4 Wollasto~ite 5% glass fiber (OCF
K 828, 1/8 in.
chopped strand 3 rlber) 3~'~S
Comparl~on C
A thlrd comparlson compos:ition was prepared by mlxing glass fibers (the same as used in Comparlson B) with the same polyamlde used ln Example 1 until the mixture con-talned 15~ glass by wei~ht and extrudlng the mixture through a 2 lnch Sterllng slngle screw extruder having a rear tèm-perature of 275-300C., a center temperature o~ 285C., a rront temperature Or 280C., a die temperature of 270-285C.
and a melt temperature Or 290-305C. The vacuum was 27-28 inches; the screw velocity 40-50 rpm and the screw a 31:1 L/Dgeneral purpose design with gradual transition and vacuum extension.
Plaques and bars were molded rrom these composi-tlon as ln Example 1 and physical properties measured on dry-as-molded test specimens. ~he propertles are tabulated - in Table 1.

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-- ,11 --1~ '3~i As shown by the Table, the compositlon Or Example l exhlblts better elongation and notched Izod values than either comparison composit~ons ~ or C' and al~o better than com~arl~on com~o~it1On U whlch is ~ resented herein to show there ~ ~ n~ ~yner~1~tlc erfect u~nn c:omhininF the mlneral riller and ~,la~s rlbers.
F,XAMPLE 2 The procedure of Example l was followed to prepare two compositions of the following ingredients:
Com~ositlon l Com~osltion 2 69.85% polyamlde (the 59.8% polyamlde (the polyamlde used polyamlde used ln Example l) ln Example l) 20% of a mlneral 30% Or the silica filler of sllica used ln compo-partlcles con- sition l tainlng less than 2% water ln ; which at least : 20 98% Or the par-tlcles are less than lO microns in slze and have ; an average size between about -- 1-5 mlcrons (Penna. Sand and Glass Company -Min-U-Sil~ lO) 0.15% 3-aminopropyl- 0.2~ 3-amlnopropyl-triethoxysilane trlethoxysilane - 10% of the fibrous 10% of the flbrous - potasslum titan- potassium tltan-ate used in ate used in - Example l Example l The mixture of each was extruded as in Example l, and molded as in Rxample l. :

.

Comparison Tests Comparlson ComPositlon A
A compositlon Or about 60% o~ the polyamlde used above, 0.2g of the sllane used above and 40% Or the slllca used above was prepared, extruded and molded as above.
Comparlson Composltlon B
A composltion Or about 60% Or the polyamlde used above, 0.2% Or the sllane used above, 30% Or the sllica used above and 10% Or the glass flber used ln Comparison Compo-sion C Or Example 1 was prepared, extruded and molded asabove.
Comparlson Compositlon C
Glass-contalnlng composltion C o~ ~xample 1 was used as Comparlson Composition C Or thl~ Example.
Properties are tabulated in Table 2.

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As shown in Table 2, the composltlons of thls ln-ventlon have better notched Izod values and better surface appearance than any other comparison composltlons ln Example

2. They also have better Heat Dlstortlon Temperatures than Comparison Composltion A and better elongation than Comparison Composltlons B and C.

The procedure of Example l was followed to prepare, extrude and mold the followlng composltions:
- lO A. 49.8% of the polyamlde used ln Example l 10% of polycaprolactam havlng a relatlve viscoslty between 41 and 52 (Pla~kon~ 8200 -Allied Chemlcal Company) 30~ of the sillca mlneral flller u8ed ln Example 2 0.2% 3-amlnopropyltrlethoxysllane 10% of the flbrous potasslum titanate used ln Example l B. 59.8~ polyamlde (same as ~sed ln Example l) 30% slllca (used in Example 2) 0.2% 3-aminopropyltriethoxysilane 10% fibrous potasslum titanate contalnlng less than 5% water (Fybex~ L) C. 49.8% of the polyamlde o~ Example 3A
10% of the polycaprolactam of Example 0.2~ 3-aminopropyltriethoxysilane 10~ of the fibrous potassium titanate used in Example 3B
30% of the silica mineral filler material of Example 3A
D. 49.8~ of the polyamide of Example 3A
10% of the polycaprolactam of Example ; 30% of the ~ollastonite mineral filler . 10 used in Example 1 0.2~ 3-aminopropyltriethoxysilane 10~ of the fibrous potassium titanate used in Example 3C.
PropertLe~ ere tebuleted in Teble 3.

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The preceding representative examples may be varled wlthln the scope of the disclosure hereln, as understood and ~racticed by one skilled ln the art, to achleve substantlally the same results.
The fore~oi.n~ det,a~léd descrl~tion has been F~lven for clearness Or understandin~ only and no unnecessary llml-tations are to be understood therefrom. The lnventlon ls not llmited to the exact details shown and descrlbed ror obvious modlfications will occur to those skllled ln the art~

.. . . .
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Claims (17)

The embodiments of the invention in which an exclusive prop-erty or privilege is claimed are defined as follows:

1. A polyamide composition comprising (1) 50-75%
by weight based on the weight of the composition of at least one high molecular weight polyamide, (2) between about 20-48.5% by weight based on the weight of the composition of a particulate mineral filler comprising silica or a metallic silicate having a moisture content of less than 2% by weight of the filler and having at least 70% of its particles less than 10 microns in size and having an average particle size of between about 1-5 microns, (3) between about 0.25 and 2%
by weight based on the weight of the mineral filler of a si-lane coupling agent, and (4) between about 1 and 20% by weight based on the weightof the composition of a fibrous alkali metal titanate containing less than 5% water by weight of the titanate.

2. An injection molded article of the composition of Claim 1.

3. The composition of Claim 1 wherein the alkali metal titanate is potassium titanate.

4. The composition of Claim 3 wherein the potassium titanate is present in an amount of between 5-10% by weight based on the weight of the composition.

5. The composition of Claim 1 wherein the mineral filler is silica.

6. The composition of Claim 5 wherein the silica comprises 25-35% by weight based on the weight of the compo-sition.

7. The composition of Claim 6 wherein the silica contains less than 2% water by weight and at least 98% of the silica particles are less than 10 microns and the average micron particle is 1-3 microns.

8. The composition of Claim 6 wherein the alkali metal titanate is potassium titanate.

9. The composition of Claim 8 wherein the potassium titanate is present in an amount between 5-10% by weight based on the weight of the composition.

10. The composition of Claim 1 wherein the mineral filler is calcium silicate.

11. The composition of Claim 10 wherein the alkali metal titanate is potassium titanate.

12. The composition of Claim 1 wherein the polyamide is polyhexamethylene adipamide, a blend of polyhexamethylene adipamide and polycaprolactam, or a copolymer of polyhexa-methylene adipamide and polycaprolactam.

13. The composition of Claim 12 wherein the silane coupling agent is 3-aminopropyltriethoxysilane or N-.beta. -(aminoethyl)-?-aminopropyltrimethoxysilane.

14. The composition of Claim 12 wherein the min-eral filler is silica.

15. The composition of Claim 14 wherein the alkali metal titanate is potassium titanate.

16. The composition of Claim 15 wherein the poly-amide is polyhexamethylene adipamide.

17. The composition of Claim 1 which contains additionally, mold lubricants, heat stabilizers, pigments, or mixtures thereof.