Field of the Invention

This invention relates to a novel process of making molded articles,

with high temperature dimensional stability, from a suitable injection moldable thermoplastic resin. More specifically, it discloses a process of making parts from an injection moldable polyester which additionally

contains sized glass fiber and mica. Such a process surprisingly yields parts with significantly reduced warpage.

Background of the Invention

The art of making injection molded parts from thermoplastic resins is well known. Generally, parts molded from thermoplastic resins lack high temperature dimensional stability. Several attempts have been made to

improve such stability by adding fillers to the resin. See, for example, D.

Rosato, "Reinforced Plastics", Encyclopedia of Polymer Science and Engineering, Vol. 14, pages 327-391, John Wiley & Sons, New York

(1988). Many such reinforced thermoplastics are commercially available.

An example is the IMPET ^® brand reinforced moldable polyester resin

available from Hoechst Celanese Corporation, Somerville, New Jersey. This resin comprises polyethylene terephthalate reinforced with about

30% glass fiber. The IMPET ^® 830 resin comprises polyethylene terephthalate, glass and mica.

Several modifications have been attempted over the years in the

composition of such resins. For example, U.S. Pat. No. 5,026,760 discloses thermoplastic polyester compositions glass fibers and/or mineral fillers. The latter may be mica which may be treated with a silane coupling

agent. This treatment is often referred to in the industry as "sizing".

U.S. Pat. No. 4,861,515 discloses polyester compositions containing an inorganic filler such as, for example, mica, which has been surface-treated with an epoxysilane compound.

U.S. Pat. No. 4,386,027 discloses polyester compositions containing a flame retardant and finely divided mica or clay, and optionally glass fiber. The clay may be surface-treated with an aminosilane.

U.S. Pat. No. 5,147,920 discloses polyester compositions

containing glass fibers, talcum and a brominated polystyrene.

U.S. Pat. No. 4,442,243 discloses thermoplastic composites

reinforced with mica. The mica may be treated withγ-

aminopropyltriethoxysilane. This patent emphasizes polypropylene

compositions.

U.S. Pat. No. 4,560,715 discloses injection moldable thermoplastic resins, e.g. polyester resins, containing mica flakes, and optionally glass

fibers. The mica may be surface-treated withγ-aminopropyltriethoxysilane.

U.S. Pat. No. 4,414,352 discloses thermoplastic molding compositions containing a polyester, a copolymer of ethylene and vinyl

acetate in combination with an aromatic polycarbonate, polyethylene

terephthalate, a flame retardant, and a mineral filler and optionally a

reinforcing glass. The mineral filler may be mica which may treated with a

suitable aminosilane. While such modifications in the resin compositions have yielded parts with somewhat improved performance over parts from nonreinforced injection moldable thermoplastics, there are still certain disadvantages

with such materials, particularly in high temperature stability. There is still a great need for parts which possess dimensional stability at high temperatures. The need is particularly great for large parts which are

dimensionally stable and undergo significantly reduced warpage under

high temperature conditions.

It is therefore, an object of this invention to provide a process to make injection molded polymeric parts with significantly reduced warpage

at temperatures between the glass transition temperature (T _g ) of the

polymer and 250° C.

It is a further object of this invention to provide a process to make injection molded polymeric parts from thermoplastic resins with

significantly reduced warpage at temperatures between the glass transition temperature (T _a ) of the polymer and 250° C.

It is yet another object of this invention to provide a process to make injection molded from thermoplastic polyester resins, which parts

possess significantly reduced warpage at temperatures between the glass

transition temperature (T _g ) of the polymer and 250° C.

Other objects and advantages of the present invention will be apparent from the accompanying description and examples.

Summary of the Invention One or more of the foregoing objects are achieved by the provision of the present process of making a precision engineered injection molded article which process comprises: (a) providing an injection moldable

polymer composite which consists essentially of 30 to 85 weight percent of a suitable polymer, 10 to 50 weight percent of a suitable reinforcing agent, which has been surface-treated with a suitable sizing agent, and 5

to 35 weight percent of a suitable filler material which has also been

surface-treated with a suitable sizing agent which may or may not be the same as the sizing agent for the reinforcing agent; and (b) injection molding a part from said polymer composite. A part so processed surprisingly exhibits high temperature dimensional stability. High

temperature dimensional stability is defined herein as nominal deformation of equal to, less than but not more than 1 millimeter when the part is subjected to temperatures between the glass transition temperature

(T _g ) of the polymer and 250° C for about 30 minutes. The inventive process is suitable to prepare large parts which possess such stability.

Suitable polymers to prepare the composite include polyesters,

polyphenylene sulfide, polyarylates, nylon, and the like. Suitable reinforcing agents include glass fiber, ceramic fiber, carbon fiber, and the

like. Suitable filler materials include mica, talcum, clay, titanium dioxide, and the like, while suitable sizing agents include silanes such as, for

example, γ-aminopropyltriethoxysilane, vinyltrimethoxysilane, vinyl triacetoxysilane, and the like.

The invention further discloses parts made by the above-described

process.

Description of the Invention In one embodiment, the present invention teaches a process to

make precision engineered molded parts which have high dimensional

stability which, as defined above, is nominal deformation of not more than 1 millimeter when the part is subjected to temperatures between the glass transition temperature (T _g ) of the polymer and 250° C for about 30 minutes. The process comprises preparing a composite of a suitable

polymer with a suitable reinforcing agent that has been sized and a suitable filler material that has also been sized and molding the composite under suitable conditions to yield the desired part.

Suitable polymers are thermoplastics which are known to be amenable to molding to prepare parts. Such polymers should have the

requisite stability to the molding conditions as is well known to those with

skill in the art. Such polymers include, but are not limited to, polyesters,

polyphenylene sulfide, nylon, polyarylate, polycarbonate, polyamide and the like, and mixtures thereof. The process is particularly suitable to

polyesters. Suitable polyesters include, but are not limited to, polyethylene terephthalate ("PET"), polybutylene terephthalate ("PBT"), poly(ethylene-2,6-naphthalate, "PEN"), polyethylene naphthalate

bibenzoate (PENBB"), poly(1,4-cyclohexanedimethanol terephthalate)

("PCT"), the THERMX ^® brand polyester (available from Eastman

Chemicals, Kingsport, Tennessee), the VALOX ^® brand polyester

(available from General Electric Company, Pittsfield, Massachusetts), 1 ,4- cyclohexanedimethanol terephthalate, liquid crystal polymers ("LCPs")

such as, for example, the VECTRA ^® brand LCP (available from Hoechst

Celanese Corporation, Somerville, New Jersey), copolyesters such as, for example, poly(1 ,4-cyclohexylenedimethylene terephthalate-co-

isophthalate), poly (ethylene terephthalate-co-ethylene naphthalate,

"PETN"), and the like. PET and PBT are the most preferred due to their large availability as well as the fact that molding of such resins are well known in the industry.

The amount of the polymer in the composite ranges generally from 30 to 85 weight percent. Preferred ranges are from 45 to 70 weight percent, while the typical ranges are from 45 to 60 weight percent.

Suitable reinforcing agents include, for example, glass fiber, carbon

fiber, ceramic fiber, and the like. Glass is the most preferred. While fiber is

the most preferred form for the reinforcing agent, other suitable forms may

also be employed in the practice of the invention. If the reinforcing agent

is in the form of a fiber, the length of the fiber ranges generally from 1 -10

mm, preferably from 2-6 mm and typically from 3-5 mm. The diameter of

the fiber ranges generally from 6-30μm, preferably from 10-21 μm, and

typically from 11 -16 μm. The reinforcing agent is employed in the

composite generally in the range 10-50 weight percent, preferably 15-40

weight percent, and typically 25-35 weight percent.

Suitable fillers include, but are not limited to, mica, talcum, clay,

titanium dioxide and the like. There may be variants within the same filler

type such as, for example, the muscovite type mica (supplied by KMG

Minerals, Inc., Kings Mountain, North Carolina), the phlogopite type mica

(from Suzorite, Inc., Boucherville, Quebec, Canada) and the like. The size

of the filler particles is in the general range of 20-500 mm, preferably in

the range 30-100 mm and typically 40-60 mm. The filler is employed in the

composite generally in the range 5-35 weight percent, preferably 7-25

weight percent, and typically 10-20 weight percent.

As stated above, both the reinforcing agent and the filler are sized

prior to preparing the polymer composite. Sizing is well known in the

industry. In the inventive process, sizing of the reinforcing agent and filler

are performed with a suitable sizing agent. Preferred sizing agents are

silanes such as, for example, γ-aminopropyltriethoxysilane, vinyl-tris(b-

methoxyethoxyl) silane, octadecyl vinyl silane, g-

methacryloxypropyltrimethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriacetoxysilane, g- chloropropyltrimethoxysilane, b-(3,4-

epoxycyclohexyl)ethyltrimethoxysilane and the like, as well as mixtures thereof.

The composite may contain additional materials as will be obvious to those skilled in the art. Some of them include, for example,

antioxidants, stabilizers, lubricants, nucleating agents, impact modifiers and the like. Examples of suitable antioxidants include phosphites.

Examples of suitable stabilizers include bis-phenol A based epoxy compounds. Examples of suitable lubricants include olefinic waxes.

Examples of suitable nucleating agents include sodium salts of suitable acids. Examples of suitable impact modifiers include low melting

elastomers.

The invention is described below with reference to a composition

prepared from a polyester, for example, PET. The reinforcing agent used is glass fiber and the filler is mica. Both the glass fiber and mica are sized

with γ-aminipropyltriethoxysilane. The composition may be prepared by

first dry mixing the above three components. As stated before, other

ingredients may also be added into this composition. While glass fiber

may be mixed in at this stage, preferably it is fed downstream during the extrusion process, while all others are mixed prior to feeding into the main feeder.

The extrusion may be carried out in a suitable extruder such as for

example a twin screw extruder with down-stream feeding capability. Many such extruders are commercially available such as, for example, the 40 mm screw size (as well as the 30 mm screw size) Werner Pfleidererr twin

screw extruder (Model ZSK from Werner Pfleidererr Corporation, Ramsey, New Jersey). The extruder may be fed with the resin and additives stated above at the main feeder while the glass is fed downstream. The machine

temperature is kept at a suitable level. For PET, for example, the

temperature may range 250 - 300° C. The material is compounded and

then extruded into a suitable shape such as, for example, pellets. The pellets may then be injection molded into suitable parts.

Dimensional stability at a desired temperature, for example, 20CPC,

may be determined by methods known to those skilled in the art, or preferably by subjecting a molded test piece to a specified force while

being held isothermally at 200°C in a three point bending fixture. An

instrument such as, for example, the Perkin Elmer Model Number DMA7E (from Perkin-Elmer Corporation, Norwalk, Connecticut) may be used for this measurement. The flexural deflection may be measured at, for

example, 15 and 30 thirty minutes. This is referred to as the flexural strain. The test specimen is placed on knife edge supports at the two ends

producing a supported span of about 20 mm. A knife edged probe across the width of the specimen is lowered onto the topside of the piece producing the three point bending configuration. A force of about 7000 millinewtons is applied to the to the specimen by the top probe and the

temperature is rapidly raised to 200° C. The deformation of the test piece

is monitored by recording the probe position continuously during the 30

minute isothermal program. The probe position at 15 and 30 minutes is

used to calculate strain and to rank the performance of materials. A lower absolute strain indicates a material with higher dimensional stability at

200°C.

For comparison, a composite is prepared with the same polyester

resin, glass fiber but with unsized mica, and then extruded and molded into a part and its strain is evaluated similar to above. In a typical actual experiment, a part from a comparative resin exhibited higher strain and/or

unacceptable warpage at 200°C, while a similar part from an inventive

resin (with sized mica) exhibited much lower strain and substantially

reduced warpage at 200°C. In the laboratory comparative experiment, the

three point bending test, the inventive test piece maintained an absolute flexural strain of less than 2.0% than the comparative piece under the

same conditions (temperatures of 200° C for at least 30 minutes). More

details are described in the EXAMPLES section below.

The invention is further illustrated with EXAMPLES below. The Examples are for illustrative purposes only and not to be construed as

limiting the invention in any way.

EXAMPLES In the following Examples, PETN8 refers poly(ethylene terephthalate-co-ethylene naphthalate) containing 8 mole percent of the

naphthalate. The terms "kpsi" refers to kilopounds per square inch, HDT to heat deflection temperature and "psi" to pounds per square inch. Impact

resistance is expressed as Notched Izod. Sizing of the glass and mica

were performed withγ-aminopropyltriethoxysilane by methods known in

the literature. A Werner Pfleidererr twin screw extruder (Model Number ZSK) was used for compounding. All crystallinity evaluations were performed with a Perkin-Elmer DSC 7 instrument (available from Perkin-

Elmer Corporation, Norwalk, CT).

Examples 1-3. Comparative Examples using unsized mica: A dry mixture of the polyester, lubricants, stabilizers, antioxidants and nucleating

agents as shown in Table 1 was fed into the main feeder of the extruder while glass was added downstream. The compounding was performed in

the twin screw extruder at 270 °C. The extrudate was pelletized and dried.

The dried pellets were then injection molded at 280 °C for testing. The

formulations and properties of the molded parts are shown in TABLE 1.

TABLE 1

Compositions comprising polyesl ;er, glass, lubricants, stabilizers, antioxidants, nucleatinq agents.

Example Number

1 2 3

Composition (weight percentaqe)

PET 67

PEN 67

PETN8 67

Glass (14 mm in diameter, 1/8" long), 30 30 30 sized

Antioxidant 0.2 0.2 0.2

Stabilizer 0.4 0.4 0.4

Lubricant 2 2 2

Nucleating Agent 0.4 0.4 0.4

Properties of molded part

Tensile strength (kpsi) 23.81 23.30 23.20

Break Elongation (%) 2.15 2.27 2.15

Flexural Strength (kpsi) 36.69 34.23 31.70

Flexural modulus (kpsi) 156.0 134.0 148

Notched Izod Impact (ft-lb/in) 1.38 1.76 1.68

Unnotched Izod Impact (ft-lb/in) 12.79 10.87 13.03

HDT at 264 psi (°C) 221 113 165

Crystallinity (wt %) - - -

Strain at 15 min (absolute %) 4.78 147.6 4.30

Strain at 30 min (absolute %) 4.94 147.8 7.12 Although Example 1 which contains PET as the polymer matrix has low

strain at both 15 and 30 minutes and high HDT, the part from Example 1

warps at 200°C. The parts from Examples 2 and 3 have poor dimensional

stability at 200°C.

Examples 4-8. Inventive compositions containing sized filler and parts therefrom: Compositions similar to above Examples were prepared but

with added filler (mica) which had been sized withγ-

aminopropyltriethoxysilane. The extrusion and injection molding to parts

were performed similar to the prior Examples. The formulations and properties of the molded parts are shown in TABLE 2.

TABLE 2

Compositions comprising polyesti sr, glass, lubricants, stabilizers, antioxidants, nucleatinq agents.

Example Nu mber

4 5 6 7 8

Composition weiαht percentage)

PET 56.5 56.5 56.5 56.5

PETN8 56.5

Glass (14 mm in diameter, 1/8" long) 22.2522.25 22.25 22.25 22.25

Muscovite mica (135 mesh, no sizing) 13.25 13.25

Sized Muscovite mica (135 mesh) 13.25

Phologopite mica (135 mesh, unsized 13.25

Sized Phologopite mica (135 mesh) 13.25

Impact Modifier 5 5 5 5 5

Antioxidant 0.2 0.2 0.2 0.2 0.2

Stabilizer 0.4 0.4 0.4 0.4 0.4

Lubricant 2 2 2 2 2

Nucleating Agent 0.4 0.4 0.4 0.4 0.4

Properties

Tensile strength (kpsi) 16.84 14.79 17.12 17.16 17.49

Break Elongation (%) 1.9 1.70 2.1 1.97 1.96

Flexural strength (kpsi) 26.23 22.22 26.53 25.78 26.15

Flexural modulus (kpsi) 148 128 141 139 140

Notched Izod Impact (ft-lb/in) 1.26 1.25 1.34 1.12 1.18

Unnotched Izod Impact (ft-lb/in) 11.20 10.10 12.06 9.53 10.00

HDT at 264 psi (°C) 198 84 201 207 216

Crystallinity (wt %) ¹ 32.9 31.2

Strain at 15 min (absolute %) 1.72 6.55 0.84 3.38 4.65

Strain at 30 min (absolute %) 1.97 6.74 0.99 3.50 4.81

The results in TABLE 2 demonstrate that using sized mica leads to higher HDT and lower strains at 15 and 30 minutes, showing better dimensional stability.

¹ All the crystallinity studies were carried out on a Perkin-Elmer DSC 7. The bar samples were heated at 10°C/me to 290°C to measure the crystallinity of the polymer matrix. Crystallinity was then calculated based on the amount of polymer in the composition.

Examples 9-13. Effect of increasing the amounts of sized glass and sized

mica: In Examples 9-13, the levels of the sized glass and sized mica were

increased to more than in Examples 4-8. TABLE 3 summarizes the

formulations and the properties of molded parts.

TABLE 3

Compositions comprising polyester, glass, lubricants i, stabilizers, antioxidants. nucleating agents.

Example Nu mber

9 10 11 12 13

Composition (weight percentage)

PET 47 47 47 47 52

Glass (14 mm in diameter, 1/8" long) 30 30 30 30 30

Muscovite mica (135 mesh, no sizing) 15

Sized Muscovite mica (135 mesh) 15 15

Phologopite mica (135 mesh, unsized 15

Sized Phologopite mica (135 mesh) 15

Antioxidant 0.2 0.2 0.2 0.2 0.2

Stabilizer 0.4 0.4 0.4 0.4 0.4

Lubricant 2 2 2 2 2

Nucleating Agent 0.4 0.4 0.4 0.4 0.4

Properties

Tensile strength (kpsi) 17.83 17.65 18.85 18.61 19.79

Break Elongation (%) 1.59 1.78 1.90 2.39 2.36

Flexural strength (kpsi) 25.85 25.83 27.90 26.67 28.59

Flexural modulus (kpsi) 188 182 179 183 209

Notched Izod Impact (ft-lb/in) 1.10 1.18 1.21 1.21 1.17

Unnotched Izod Impact (ft-lb/in) 6.72 6.91 9.26 9.07 7.05

HDT at 264 psi (°C) 220 217 221 214 220

Crystallinity (wt %)* 32.1 31.3 33.6 29.8

Strain at 15 min (absolute %) 2.62 2.00 2.37 1.70 0.25

Strain at 30 min (absolute %) 2.75 2.12 2.50 1.80 0.37

The results demonstrate that higher levels of the glass and filler

improve the dimensional stability further.