TITLE OF THE INVENTION

AROMATIC VINYLIDENE COPOLYMER THERMOPLASTIC RESIN FORMULATIONS FEATURING SUPERIOR COLORABILITY, TRANSPARENCY, FLUIDITY AND CHEMICAL RESISTANCE

TECHNICAL FIELD

The present invention is directed to a binary copolymer thermoplastic formulation rendering with superior colorability and transparency in balance with fluidity, mechanical properties and chemical resistance as compared to conventional thermoplastic resin composition. BACKGROUND ART

Conventionally, transparent thermoplastic resins such as polymethylmethacrylate (PMMA) resin and polystyrene (PS) resin, are widely applied for food packaging, home appliances and so forth, because of their superior optical properties. Polymethylmethacrylate resin is commercially used as an ideal replacement for glass material in the standpoint of impact resistance and specific gravity, but it possesses inferior chemical resistance. Additionally, polystyrene resin with superior versatility and dimensional stability is widely applied for an extensive variety of consumer products, but it has inferior chemical resistance and thermal resistance.

Acrylonitrile-Styrene (herein after referred to as “SAN”) copolymer is a transparent copolymer thermoplastic with a well-balanced combination of clarity, fluidity, rigidity, thermal resistance and chemical resistance, and hence it is often used in place of PMMA and PS. It is well stated in the art with several different techniques of processing and formulations of SAN, where SAN is commonly prepared by copolymerizing the monomers of aromatic vinylidene and unsaturated nitrile with the typical composition of 60 - 80% by weight of aromatic vinylidene monomers and 20 - 40% by weight of unsaturated nitrile monomers. The increase in the composition of unsaturated nitriles enhances the mechanical properties and chemical resistance, in turn it contributes an inherent yellowing tint to the SAN copolymer. To further render an enhancement in toughness and stiffness, SAN resins may be toughening with a grafted elastomeric copolymer, for instance, preparation of acrylonitrile butadiene styrene thermoplastic resin, which is commonly known as ABS.

Noteworthy, SAN copolymer is also featured with high degree of impermeability to passage of carbon dioxide and/or oxygen, wherein it is favorably useful for application of cosmetic and lighter housings. To achieve high degree of gaseous impermeability and stiffness, SAN copolymer is ordinarily formulated with higher content of unsaturated nitriles and higher molecular weight system, but it practically leads to formation of extremely high viscous polymeric mass with wider molecular weight distribution, thereby worsening the mechanical properties and colorability of the materials.

In recent years, it has also been noted that there is an emerging demand, particularly in the field of household, electrical & electronic, cosmetics and packaging, for aesthetic optical products with the selection of a very extensive palette of chromatic colors. There is an inherent bottleneck in the preparation of highly colorable thermoplastic compositions containing unsaturated nitrile in which the presence of unsaturated nitrile attenuates the intensity of the color, resulting in a dull-colored finished article due to cyclization of adjacent pendant nitrile groups upon heating of the copolymer, for instance, during polymerization and even during subsequent lattering processing stages. The severity of discoloration is being proportionally intensified with the content of unsaturated nitrile and conditions of processing and application.

Therefore, the subject of the present invention is directed to a desire for an aromatic vinylidene copolymer thermoplastic resin formulation coupled with a synergistic color enhancing system rendering a well-balanced combination of colorability, transparency, chemical resistance and mechanical properties so as not to adversely affect the fluidity and processability of the composition.

DISCLOSURE OF THE INVENTION

The present invention is directed to a binary copolymer thermoplastic formulation rendering with superior colorability and transparency in balance with fluidity, mechanical properties and chemical resistance as compared to conventional thermoplastic resin composition. Therefore, the present invention is characteristically formulated with the unique composition comprising: A. An aromatic vinylidene copolymer

B. A color enhancing system

C. Other conventional additives

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with the present invention, there is described a binary copolymer thermoplastic resin formulation, comprising an aromatic vinylidene copolymer, a lubricant and a color enhancing system suitable for the preparation of molded or extruded articles rendering with enhanced resistance against degradation, discoloration and environmental stress cracking during its service lifetime.

In accomplishing the foregoing objects, there has been provided in accordance with one aspect of the present invention, the aromatic vinylidene copolymer is a glassy matrix component includes, a homo- or co-polymer (a random copolymer, a block copolymer or a graft copolymer) of an aromatic vinylidene monomer such as styrene, a-methylstyrene, o- methylstyrene, p-methylstyrene, t-butylstyrene, o-ethylstyrene, p-ethylstyrene, or a mixture thereto; a copolymer of the aromatic vinylidene monomer and an unsaturated nitrile monomer such as acrylonitrile, methacrylonitrile, ethacrylonitrile, phenylacrylonitrile, or a combination thereto. As for the monomeric composition of the monomer mixture of the copolymer, the aromatic vinylidene monomer is preferably substantially 60 to 80 parts by weight, more preferably substantially 63 to 80 parts by weight, and most preferably substantially 65 to 80 parts by weight, in view of processability and aesthetics; the unsaturated nitrile monomer is preferably substantially 20 to 40 parts by weight, more preferably substantially 20 to 37 parts by weight, and most preferably substantially 20 to 35 parts by weight, in view of stiffness and chemical resistance, based on 100 parts by weight, in relation to total weight of the copolymer composition.

It is well known in the art that copolymers of aromatic vinylidene and unsaturated nitrile monomers are often prepared in a substantial number of different techniques such as mass polymerization, suspension polymerization, solution polymerization or emulsion polymerization. In view of clarity and color retention, continuous mass polymerization is preferably employed for the preparation of the aromatic vinylidene copolymer with superior transparency and colorability, comprising the steps of continuously introducing a feed constituting a predetermined ratio of aromatic vinylidene and unsaturated nitrile monomers with the incorporation of an initiator and a chain-transfer agent into a reaction vessel to produce a reaction mixture by subjecting the reaction mixture to a controlled temperature and pressure under which said monomers copolymerize to produce an aromatic vinylidene copolymer.

To initiate mass polymerization of aromatic vinylidene copolymer in the present invention, any polymerization initiator may be utilized without limitation, particularly including hydrogen peroxide, di-tert-butyl peroxide, benzoyl peroxide, acetyl peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, t-butyl-peroxy-pivalate, and so forth. The constitution of initiator shall be optimized, whereby excessive initiator may impart a higher polymerization conversion rate with the resulting formation of highly viscous mass, causing difficulties in heat dissipation and distortion of rheological properties of finished articles. As described herein, the polymerization is particularly controlled to below 80%, by utilizing these initiators in conventional catalytic quantities, e.g., from about 0.01 to 5 parts by weight, based on total weight of the monomer or monomer mixture to be polymerized.

In achieving a well-balanced properties of the aromatic vinylidene copolymer in term of fluidity, stiffness and chemical resistance, the molecular weight of the copolymer of the present invention is controlled by incorporating the chain-transfer agents during the polymerization process, comprising without limitation alkyl mercaptans represented by the formula of R-SH, such as n-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, tert- dodecyl mercaptan, isopropyl mercaptan, n-amyl mercaptan, and so forth. In the present invention, the chain-transfer agents may constitute preferably from about 0.02 to 10 parts by weight, based on total weight of the monomer mixtures. As described herein, the aromatic vinylidene copolymer obtained therefrom may preferably possess an average molecular weight of 80,000 to 150,000, wherein if it is less than 80,000, stiffness and chemical resistance are inferior; and if more than 150,000, fluidity and processability are inferior.

Of equal importance to the polymerization of aromatic vinylidene copolymer, postpolymerization treatment such as devolatilization, plays a crucial role in filtering the unreacted monomers once the copolymer mixture leaves the reactor vessel. Due to uneven monomeric reactivity of two or more different monomer species, for instance, the monomer species of aromatic vinylidene and unsaturated nitrile, during polymerization propagation stages, a twin-screw extruder equipping with a multiple devolatilization system operated under reduced pressure to screen excessive residual monomers or/and oligomeric by-products so as a high-quality finished article is fabricated with uniform monomeric composition distribution, in which the content of residual monomers is preferably not greater than 10% by weight, based on total weight of the copolymer composition.

In exemplary embodiment of the invention, a synergistic color enhancing system is employed, selected from the stabilizing group essentially consisting of a phenol, an amine, or a combination thereof.

Phenolic stabilizers are radical scavengers that function by counteracting peroxyl radical intermediates formed in the oxidation process, whereby the resulting oxytoluene radicals are stabilized by the bulky substituents in a mean of steric hindrance and consequently attenuating the propagation of oxidative process. Apart from shielding the polymeric substrates from thermal, oxidative and light induced degradation during melt-processing stage, phenolic stabilizer also contributes to durable stabilization of the finished articles during its service lifetime. The phenols constituting the color enhancing system in the present invention is not particularly limited, and specific examples thereof include octadecyl-3-(3,5- di-tert-butyl-4-hydroxyphenyl) propionate, ethylene-bis(oxyethylene) bis[3-(5-tert-butyl-4- hydroxy-m-tolyl) propionate, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate), 4-[4,4-bis(5-tert-butyl-4-hydroxy-2-methylphenyl)butan-2-yl] -2-tert-butyl-5 methylphenol, 2-tert-butyl-4-[l-(5-tert-butyl-4-hydroxy-2-methylphenyl)-bu tyl]-5 methylphenol, 4-[[3,5-bis[(3,5-ditert-butyl-4-hydroxyphenyl)-methyl]-2,4,6 trimethylphenyl]-methyl]-2,6-di-tert-butylphenol, [2-[3-[l-[3-(3-tert-butyl-4-hydroxy-5- methylphenyl)-propanoyloxy]-2-methyl-propan-2-yl]-2,4,8,10-t etraoxaspiro[5.5]undecan-9- yl]-2-methylpropyl]-3-(3-tert-butyl-4-hydroxy-5-methylphenyl ) propionate, and the like. These phenols can be used alone or in combination of two or more types of functional stabilizers for effective performance endurance.

To further strengthen the durability of the aromatic vinylidene copolymer in term of colorability and stabilization during processing, storage and service, especially against thermal, oxidative and light induced degradation as well as against cyclization of adjacent pendant nitrile groups initiated either via free radical reaction mechanism or via ionic reaction mechanism, the phenols may be used in combination with an aminic stabilizer, which acts as a photon donor by deactivating free radicals formed during degradation of a polymeric material as well as to diminish the radical-inducement of discoloring cyclization reaction. As described herein, the amines may be derived from a substituted amine, a substituted piperidine, a hydroxylamine, a nitrone, an amide oxide, or a mixture thereof. Regardless of the compound from which it is derived, the amines are typically an oligomeric or polymeric derivative having a number average molecular weight of about 200 or more, more preferably from about 200 to about 1000, and most preferably from about 200 to about 500.

The components of the color enhancing system may be combined together and afterwards added to the polymeric resins, or the components may be blended directly into the polymeric resins. Its content in the composition is preferably 0.01 to 2 parts by weight, more preferably 0.1 to 2 parts by weight in some embodiment, and most preferably 0.1 to 1 parts by weight in some embodiment, based on total parts by weight of the copolymer composition. Noteworthy, the mixing ratio of the phenols to the amines is preferably substantially from 0.1 to 9, more preferably substantially from 0.25 to 9 in some embodiment, and most preferably substantially from 0.25 to 4 in some embodiment.

In another embodiment of the invention, the aromatic vinylidene copolymer thermoplastic resin composition may also incorporate a lubricant, serving primarily to facilitate the processing of the copolymer by lowering melt viscosity or/and by minimizing the friction between the polymer and the metallic parts of the processing equipment. Generally, lubricants are categorized into internal and external lubricants, depending on the functionality and consequently the application in which each type would be employed. By dissolving itself in the polymeric matrix, internal lubricants act to alter the cohesive forces between polymer chains so as to facilitate the fluidity of the polymer chains past over one another, thereby lowering melt viscosity. In contrast, due to immiscibility in the polymeric matrix, external lubricants tend to migrate to the surface of the polymer, contributing to the formation of a mono-layer on the surface of the polymer, serving as a lubricating aid between the molten and fused plastic composition and metallic parts of the processing equipment.

In the present invention, the types of lubricants are not particularly limited, and specific examples thereto include amide waxes, that are formed by reaction of a fatty acid with a monamine or diamine ethylenediamine) having 2 to 40, especially 2 to 30 carbon atoms; metallic salts of fatty acids such as sodium stearate, magnesium stearate, calcium stearate or zinc stearate, or a mixture thereto. As a specific example, ethylenebisamide wax, which is formed by the amidization reaction of ethylene diamine and a fatty acid, may be employed, which is having the carbon atoms in the range from C6 to C30, such as from stearic acid (Cl 8 fatty acid) to form ethylenebisstearamide wax, as a plasticizing aid or a releasing aid. As described herein, the constitution of lubricants to the polymeric composition is critical during processing, whereby excessive lubricant causes slippage by suppressing the friction for the mobility of polymer melt throughout the processing and consequently contributing to poor aesthetic features in the finished articles. Preferably, the lubricant may constitute from about 0.01 to 0.5 parts by weight, more preferably from about 0.01 to 0.3 parts by weight in some embodiments, and most preferably from about 0.05 to 0.3 parts by weight in some embodiments, where said lubricants may be incorporated into the polymeric composition during processing, or it may also be admixed directly in a mixing vessel into the polymeric resins.

The described thermoplastic resin composition of the present invention can be advantageously useful for the preparation of various articles by the mean of injection molding, sheet extrusion, profile extrusion, and so forth, with the implementation of typical melt processing temperature of 200°C to 250°C, in view of colorability and processability, wherein temperatures of above 250°C are undesirable due to discoloration and degradation of the polymer; and temperatures of below 200°C are also unpreferable due to higher melt viscosity leading to processability issue. Hence, the thermoplastic resin composition may widely be applied into home appliances, electrical and electronic products, cosmetic appliances, lighter products, and the like. These examples are merely illustrated without limitation.

The present invention may be better understood by reference to the following examples which are intended for the purpose of illustration and are not to be construed as in any way limiting the scope of the present invention, which is defined in the claims appended hereto.

EXAMPLES Example 1 - 9

A monomer mixture comprising 65 - 80 parts by weight of aromatic vinylidene, 20 - 35 parts by weight of unsaturated nitrile, 0.01 - 5 parts by weight of initiator and 0.02 - 10 parts by weight of chain-transfer agent are continuously supplied at a rate of 4500 - 5000 kg/hr into a polymerization reaction vessel equipping a stirring device of helical ribbon agitator with a volume of 50m ³ under continuous mass polymerization to form a homogeneous mass. The reaction is conducted at a temperature of 90 - 130°C at liquid level; a temperature of 90 - 110°C at gaseous phase, with a pressure controlled at 0.9 - 1.5 kg/cm G. The rate of polymerization is then operated at 69 - 72 %.

The polymerization reaction product is thereto continuously discharged from the vessel in a melted state into a twin-screw extruder equipped with multiple devolatilization system to filter off the residual monomers or/and oligomeric by-products under reduced pressure, whereby 0.05 - 0.3 parts by weight of lubricants and 0.1 - 1 parts of color enhancing system are fed into. The polymeric mass is subsequently extruded and injected into a test specimen. The physical, mechanical properties, color stability and chemical resistance of the test specimen are then examined with the result as summarized in Table 1 and 2. Illustratively, the comparative color stability result in term of Delta E of the present invention is further depicted in Graph 1.

The key elements in examining the properties performance of the test specimen are described as follows:

(1) Melt Flow Rate (MFR)

The melt flow rate is measured in accordance with ISO 1133 as the ability of the polymeric melt to flow under the load of 98N with temperature of 220°C.

(2) Charpy Impact Strength

The Charpy impact strength is measured as the amount of energy absorbed by the notched material under a sudden applied force prior to failure in accordance with ISO 179/leA.

(3) Deflection Temperature under Load (DTUL)

The deflection temperature under load is evaluated as the temperature at which the test specimen deforms under a load of 1.8MPa in an enclosed oil bath with a controlled heating rate of 120°C/hr in accordance with ISO 75.

(4) Tensile Strength and Tensile Modulus The tensile strength and tensile modulus are measured by subjecting the test specimen to a controlled tension at a controlled speed of 50 mm/min and 1 mm/min respectively until failure in accordance to ISO 527.

(5) Flexural Strength and Flexural Modulus The flexural strength and flexural modulus are measured by subjecting the test specimen to a controlled load at a controlled loading speed of 2 mm/min until failure in accordance to ISO 178.

(6) Density

The density is evaluated in accordance with ISO 1183 by means of a densimeter.

(7) Transparency

The transparency is examined as total light transmittance and haze by means of a spectrophotometer using a 3 mm ¹ test specimen in accordance with ASTM D1003.

Light Transmittance at all forward angles

Total Light Transmittance (%) x 100 Total Incident Light

Haze (

(8) Color Stability

The color stability of the thermoplastic resin is evaluated by subjecting it to 40 continuous cycles of injection molding process using a 3 mm' test specimen, whereby the degree of color changes is then quantified as total color difference (Delta E), calculated in all cases for illuminant “D-65”, 10° observation angle and specular included mode, expressed in CIE L*a*b* units, in accordance with ASTM D-2244. Delta E of the test specimens may be calculated from the equation:

Delta E = [(Li - L ₀ ) ² + (a, - ao) ² + (bi - b ₀ †] ^m wherein the measured values of the color of 1 ^st shot and subsequent shot of the test specimen are annotated as 0 and i respectively, and wherein L represents lightness and darkness of the test specimens, a represents redness and greenness of the test specimens, and b represents yellowness and blueness of the test specimens.

(9) Chemical Resistance

The chemical resistance is examined by coating or spreading a series of chemical agents on top of the test specimens (127 x 12.7 x 1.5t mm) where it is mounted on the jigs under a controlled strain of 3% based on the calculation as follows: 100

/ : Test Pieces Length = 127 mm : Test Pieces Length = 98 mm d : Strain = 3 % t : Test Pieces Thickness = 1.5 mm wherein the physical changes of the test specimens are judged as: A - No Defect; B Craze; C - Crack; and D - Break.

11

TABLE 1 GRAPH 1

Remark: A - No Defect; B - Craze; C - Crack; and D - Break EFFECT OF THE INVENTION

In accordance with the present invention, an aromatic vinylidene copolymer thermoplastic resin composition rendering superior colorability and transparency in balance with fluidity, mechanical properties and chemical resistance may advantageously be favorable for the preparation of molded or extruded articles with enhanced resistance against degradation, discoloration and environmental stress cracking during its service lifetime.

With these highly versatility and durability features, the thermoplastic resin composition can widely be applied as an aesthetic optical element into various applications such as home appliances, electrical and electronic products, cosmetic appliances, lighter products, and the like, in which high transparency, colorability and chemical resistance are desirable.