EP1814945A2

EP1814945A2 - Rubber modified thermoplastic resin

Info

Publication number: EP1814945A2
Application number: EP05807470A
Authority: EP
Inventors: Ata Yoosefinejad; Josef Michael Eder; Peter Toni Jung; Michael Downs
Original assignee: Nova Chemicals International SA
Current assignee: Nova Chemicals International SA
Priority date: 2004-11-23
Filing date: 2005-11-22
Publication date: 2007-08-08
Also published as: CA2588620A1; GB0425763D0; WO2006056758A3; WO2006056758A2; AR055534A1

Abstract

A rubber modified thermoplastic resin composition comprising styrene maleic anhydride copolymer and an acrylate rubber formed via compounding techniques, e.g. twin-screw extruder. The acrylate rubber may be an ethylene acrylate copolymer selected from the group consisting of methyl, ethyl, and butyl acrylates. The ethylene acrylate ranges from 10 to 30% by weight and the styene maleic anhydride copolymer ranges from 90% to 70% by weight based on the weight of the rubber modified thermoplastic resin composition. Fillers, e.g. glass fibers, may be added in an amount of about 30% by weight or less. The ethylene acrylate copolymer may be an ethylene methyl acrylate containing 75% by weight ethylene and 25% by weight methyl acrylate. An article of manufacture formed from the resin composition has at least improved toughness.

Description

"RUBBER MODIFIED THERMOPLASTIC RESIN"

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a rubber modified thermoplastic resin composition. More particularly, the present invention relates to a thermoplastic resin composition comprising a styrene maleic anhydride (SMA) copolymer, an acrylate rubber, and optionally, fillers, e.g. glass fibers; to an article of manufacture that is produced from the rubber modified thermoplastic resin composition and has improved toughness properties, e.g. notched impact; and to a method for producing the rubber modified thermoplastic resin composition.

Background Art

It is known to copolymerize styrene and maleic anhydride. Such processes have been described at length in the literature, especially in Baer U.S. Patent No.

2,971,939 and Hanson U.S. Patent No. 2,769,804, and beneficially as a solution as disclosed in U.S. Patent No. 3,336,267.

It is known to modify styrene maleic anhydride (SMA) copolymers with rubber. Generally, these copolymers are referred to as "rubber modified styrene/maleic anhydride copolymers". It is known that the rubber component provides increased impact resistance and that the maleic anhydride component provides a high heat distortion temperature.

There are various methods for forming rubber modified styrene/maleic anhydride copolymers, such as solution blending of the styrene/maleic anhydride copolymer with rubber and by mechanical milling of the rubber and suitable polymer at a sufficient temperature to heat plastify the styrene/maleic resin. Generally, in the various blending techniques it has been necessary to use a nitrile rubber rather than a diene or styrene/butadiene rubber in order to obtain a desirable rubber reinforced styrene-maleic anhydride copolymer. Further methods for forming rubber modified styrene/maleic anhydride copolymers involve polymerization techniques, such as solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization. A typical polymerization method is exemplified in Moore et al. U.S. Patent No. 3,919,354 (The Dow Chemical Company), which was issued on November 11 , 1975. The rubber modified styrene/maleic anhydride is prepared by providing a solution of rubber in styrene, initiating polymerization, and then adding maleic anhydride. The rubber modified SMA polymer contains from 5 to 35% by weight, and preferably from 10 to 25 percent by weight of a rubber component.

The above patent teaches that the type of rubber generally used when preparing rubber modified styrene/maleic anhydride copolymers via polymerization techniques include ethylene-propylene copolymers, ethylene propylene copolymers in which other polyunsaturated monomers have been copolymerized, polybutadiene, butadiene, styrene-butadiene rubber, butadiene-acrylonitrile rubber, polychloroprene, acrylate rubber, chlorinated polyethylene rubber, polyisoprene and cyclo-olefin rubbers. However, the rubber traditionally used in polymerization techniques is polybutadiene.

It is known to use glass fibers as a reinforcement additive in rubber modified styrene/maleic copolymers and in various types of thermoplastic resin compositions, as exemplified in U.S. Patent Nos. 6,605,665; 6,727,294; and 6,727,297. Generally, in rubber modified styrene-maleic copolymers, the glass fibers are added to the polymer during a separate extrusion-compounding step. With regard to the various thermoplastic resins taught in the aforesaid U.S. Patent Nos. 6,605,665; 6,727,294; and 6,727,297, the glass fibers may be mixed in with the other components of the resin in a manner using any known method or combination of mixing methods, such as extruding, kneading and/or milling the components together.

It is known to use a resin composition comprising a butadiene rubber modified styrene/maleic anhydride resin and glass fibers as a molding composition in producing various articles such as, for example, for the interior of automobiles. It is desirable to have a rubber modified thermoplastic resin composition with improved properties, such as impact resistance and flexibility, and which may be more suitable for some end-use applications than the presently available rubber modified resin compositions.

SUMMARY OF THE INVENTION

The invention has met this need in the industry. It has been found by the inventors that a styrene/maleic anhydride (SMA) copolymer that is modified with an acrylate rubber, e.g. a copolymer of ethylene and methyl acrylate, produces a rubber modified thermoplastic resin composition that may be particularly suitable as a molding composition for moldings used in applications that require a material with enhanced impact resistance, as well as flexibility and excellent mechanical and thermal properties. For example, the resin composition of the invention may be used in thermoplastic moldings, e.g. interior components of the automotive industry, e.g. door panels, consoles, etc.

The rubber modified thermoplastic resin composition preferably is prepared by compounding techniques, e.g. mixing a crystal, i.e. transparent, styrene/maleic anhydride (SMA) copolymer and the acrylate rubber, and optionally, fillers, e.g. glass fibers via an extruder, e.g. a twin-screw extruder.

The rubber modified thermoplastic resin composition comprises a styrene/maleic anhydride copolymer, and an acrylate rubber, and optionally, fillers, e.g. glass fibers. If fillers are not used, the weight percent of styrene/maleic anhydride will range from about 70% to about 90%; and more preferably from about 75% to about 85%, and most preferably about 80%, based on the weight of the composition. The weight percent of acrylate rubber will range from about 10% to about 30%; and more preferably from about 15% to about 25%, and most preferably about 20%, based on the weight of the composition.

If fillers are used, the weight percent of the fillers will be about 30% by weight or less, based on the weight of the composition. The weight percent of the styrene maleic anhydride copolymer will range from about 40% to about 90%, and the weight of the acrylate rubber will range from about 10% to about 30%, based on the weight of the resin composition.

The invention also provides for an article made from the rubber modified thermoplastic resin composition. This article may be formed via molding methods such as injection molding, compression molding, and blow molding, or via extrusion methods for film or sheet. Examples of articles include a variety of commercial products, such as parts of household electric appliances, automobile parts, building materials, hollow containers, medical supplies, and appliances.

These and other aspects of the present invention will be better appreciated and understood by those skilled in the art from the following description and appended claims.

DETAILED DESCRIPTION OF THE INVENTION

The rubber modified thermoplastic resin composition of the invention comprises a styrene maleic anhydride copolymer (SMA), an acrylate rubber, and optionally, fillers, e.g. glass fibers. More particularly, the rubber modified thermoplastic resin composition is comprised of at least a styrene/maleic anhydride copolymer and an acrylate rubber, which for example, may be an ethylene methyl acrylate copolymer.

If no fillers are used in the composition of the invention, the weight percent of styrene/maleic anhydride will range from about 70% to about 90%; and more preferably from about 75% to about 85% by weight, and most preferably about 80%, based on the weight of the composition. The weight percent of the acrylate rubber will range from about 10% to about 30%; and more preferably from about 15% to about 25%, and most preferably about 20%, based on the weight of the composition.

If fillers are used in the composition, the weight percent of the fillers will be about 30% or less, based on the weight of the resin composition. The weight percent of the acrylate rubber will range from about 10% to about 30%, and the weight of the styrene/maleic anhydride will range from about 40% to about 90%, based on the weight of the composition. The maleic anhydride content of the styrene/maleic anhydride copolymer generally will range from about 2% to about 25% by weight, and preferably from about 5% to about 18% by weight. The styrene content of the styrene/maleic anhydride copolymer ranges from about 75% to about 98% by weight, and preferably from about 82% to about 95% by weight, based on the weight of the styrene/maleic anhydride copolymer.

The acrylate rubber preferably is blended or mixed via compounding techniques to a crystal, i.e. translucent styrene maleic anhydride copolymer which may be in pellet form. The average particle size of the acrylate rubber prior to being compounded into the styrene maleic anhydride copolymer may range from about 0.1 micron to about 11 microns.

The reason for the improvements in the rubber modified thermoplastic resin composition of the invention is not clear, and the inventors do not wish to be bound to any theory. However, it is believed that the addition of the acrylate rubber to the styrene/maleic anhydride copolymer in a compounding technique results in an improved dispersion of the rubber particles in the polymer matrix. These particles may have a more uniform spherical shape and may be smaller compared to that generally achieved with polybutadiene rubber in a polymerization technique. This can be observed through examination of the polymer/acrylate rubber blend using a Scanning Electron Microscope (SEM).

Further, in the case of fiberglass-reinforced products, it is believed that the combined acrylate rubber and the SMA promotes better coupling between the matrix and the glass fibers. This may be due, in part, to the changes in the stress field around the fiberglass boundary. Freeze fractures, captured on SEM micrographs, show that with the copolymerized SMA/butadiene compositions, the glass fibers are only partially coupled with the polymer matrix. The addition of acrylate rubber seems to lead to better wetting of the glass fibers ultimately resulting in superior bonding of the reinforcing glass fibers to the polymer matrix. A more complete coverage of the glass fibers when using an acrylate rubber blended with SMA can be observed in SEM micrographs. This improved interaction between the reinforcing fibers and the polymer matrix enhances load transfer, resulting in significantly improved impact properties of the blend.

Compounding techniques are known to those skilled in the art. One such compounding technique entails the rubber added to the styrene maleic anhydride copolymer in an extruder, more about which will be discussed herein below.

Preferably, the acrylate rubber, and optionally, the fillers, e.g. glass fibers are added to the styrene/maleic copolymer in the compounding step. As discussed hereinabove, the amount of acrylate rubber added to the styrene/maleic anhydride copolymer generally will range from about 10% to about 30% by weight, and the styrene/maleic anhydride will generally range from about 70% by weight to about 90% by weight, if no fillers are used. These weight percentages will also be in the final resin composition. If fillers are used, the weight percentage of the fillers will be about 30% by weight or less. The weight percentage of the acrylate rubber will range from about 10% to about 30% by weight and the amount of styrene/maleic anhydride will range from about 40% to about 90% by weight. Again, these weight percentages will generally be in the final resin composition.

Suitable styrene/maleic anhydride crystal copolymers are commercially produced by and available from NOVA Chemicals Inc. under the trade names DYLARK® 332 and DYLARK® 232. Other grades of styrene/maleic anhydride copolymers may be used, however, these two specific transparent grades of SMA may be the most cost effective.

The fillers may be glass fibers, preferably made from E glass. The glass fibers may have an average length from about 4 to 12.7 mm, and preferably from 4 to 5 mm, and their diameter may range from 10 to 17 mu.m. A suitable grade of glass fibers is commercially available from Johns Manville under the trade name Star Stran 720 or ThermoFlow® 700 Series.

Other organic fibers, such as mineral fibers, carbon fibers, glass silk roving, and glass beads, may also be used. Other inorganic fillers, such as talc, clay, mica, and calcium carbonate may also be used in the resin composition of the invention. Suitable acrylate copolymers are ethylene acrylate copolymers. Suitable ethylene acrylate copolymers may be those commercially available from Dupont under the trademark ELV ALO Y®, which are available as methyl, ethyl, and butyl acrylates. These grades fall into three categories: ethylene methyl acrylate copolymers with an acrylate content of about 9 to about 25 weight percent; ethylene ethyl acrylate copolymers with an acrylate content of about 12 to about 16 weight percent; and ethylene butyl acrylate copolymers with an acrylate contents of about 7 to about 27 weight percent.

A suitable ethylene methyl acrylate copolymer is commercially available from Dupont under the trademark ELVALOY® 1125 AC and contains 25% methyl acrylate and 75% ethylene. Other grades of acrylate copolymers could also be used, but presently, this particular grade of acrylate copolymer seems to be the most effective. Other acrylate copolymers that may be suitable in the resins of the invention are ethylene/n-butyl acrylate/carbon monoxide copolymers. The average particle size of the acrylate rubber copolymer in the polymer matrix of the resin composition may range between about 1.0 and about 2.0 microns, or may be 1 micron or less, or may range between about 0.5 micron and 1 micron.

The rubber modified thermoplastic resin composition may also include the customary additives, such as stabilizers, antioxidants, lubricants, pigments, plasticizers, mold release agents, waxes, etc. These may be added to the polymerization mixture for forming the styrene/maleic anhydride copolymer or may be added to the polymer in the extruder when blending the styrene/maleic anhydride with the acrylate copolymer.

If desired, small amounts of antioxidants, such as alkylated phenols, e.g., 2,6-di-tert- butyl-p-cresol, phosphates such as trinonyl phenyl phosphite and mixtures containing tri (mono and dinonyl phenyl) phosphates, may be included in the feed stream. Such materials, in general, may be added at any stage during the polymerization process for producing the styrene/maleic anhydride copolymer or at any stage during the compounding operation for blending the styrene/maleic anhydride copolymer and the acrylate rubber. A method of the invention involves using a crystal styrene maleic anhydride, preferably, in pellet form and the acrylate rubber and mixing these components via a compounding technique. Generally, if fillers are used, these fillers preferably are added during the mechanical blending process.

The compounding step will generally include an extruder. The extruder may be a single or twin- screw extruder, and preferably, a twin-screw extruder. A suitable twin- screw extruder is one that carries out the compounding process under vacuum.

The resin composition may be formed using a Banbury mixer, a Brabender mixer and/or a twin-screw extruder, as discussed in the preceding paragraph. The thermoplastic resin composition may be blended and kneaded in a way known in the art at any suitable stage in the process until the point just before molding of the final product. Blending may be effected by various methods, such as using a suitable mixer such as tumbler, Henschel mixer, etc., or supplying the measured amounts of the component materials to the extruder hopper by a feeder and mixing them in the extruder. Kneading may also be accomplished by suitable known methods such as using a single-or double-screw extruder.

As stated herein above, the thermoplastic resin composition may include colorants, pigments, flame retardants, stabilizers, plasticizers, UV absorbers, antistatic agents, lubricants, compatilizing agents, foaming agents, antioxidants, etc. As is known to those skilled in the art, these additives may be included in any amount to obtain the desired characteristics in the melt polymer material or in the resultant molded bodies, and may be added to the styrene maleic/anhydride copolymer before, during, or after polymerization of the styrene maleic/anhydride copolymer, or may be added to the styrene maleic/anhydride copolymer and the acrylate copolymer in the compounding stage. Preferably, in the invention, these additives are added in the compounding stage.

The thermoplastic resin composition may be formed into desired products by using molding methods such as injection molding and blow molding. These formed products may be used to form a variety of commercial products, such as sheets, films, miscellaneous goods, parts of household electric appliances, automobile parts, e.g. instrument panels, building materials, hollow containers, medical supplies and appliances, etc.

The composition of the invention may also be used in other forming processes, i.e. injection molding, compression molding, co extrusion, and blowing molding or via extrusion methods for film or sheet, and thermoforming for producing parts such as those listed in the preceding paragraph.

The following example is intended to assist in understanding the present invention, however, in no way should the example be interpreted as limiting the scope thereof.

EXAMPLE

Resin compositions of the invention were injection molded into test specimens in a lab. These test specimens were then evaluated by the following methods. Tensile test was measured according to DIN EN ISO 527-1 ; Flexural test was measured according to DIN EN ISO 178; Charpy Impact Strength at 23°C unnotched and notched was measured according to DIN EN ISO 179; Heat Deflection Temperature (HDT) (Methods A and B) was measured according to DIN EN ISO 75; and ASH Content after heating up to 625°C.

The resins were melt compounded in temperature zones 1 to 9 in a twin screw extruder ZSK 40 with temperatures varying between 240°C and 260⁰C and an output rate of 30 kilograms/hour. The compounding process was carried out under vacuum. The twin-screw extruder that is generally used for lab purposes, is manufactured by Coperion Company, Germany.

Table 1 shows the temperature profiles for the melt compounding of these resins in zones 1 through 9 of the extruder. Table 1

Table 2 shows the processing details for Samples 1 through 4 of the inventive resins formed in the twin-screw extruder ZSK 40.

Table 2

DYLARK®332-SMA

GF = glass fibers grade 720 provided by Johns Manville.

EMA = Elvaloy®1125 AC (ethylene-methyl acrylate copolymer).

Table 3 compare Samples 1 through 4 with a Comparative Sample. The Comparative Sample is comprised of a styrene maleic/anhydride copolymer that was modified with 15 weight percent styrene butadiene rubber in a polymerization process. About 15 weight percent fiberglass was added to the polymer in a compounding technique in the lab. The particle size (SEM) of the styrene butadiene rubber in the resin composition of Comparative Example ranged between 1.0 to 2 microns; whereas the particle size of the EMA copolymer in Samples 1 through 4 ranged between 0.5 and 1.0 micron.

Charpy test

The results in Table 3 illustrate that the toughness, i.e. impact strength, of the compositions of the invention improves as the percentage content of acrylic rubber increases. These improvements are accompanied by a slight reduction in tensile modulus and to some extent thermal properties, e.g. heat deflection temperature

(HDT), are affected. It is believed that these reductions in stiffness (moduli) and heat distortion temperature will be less than the reductions seen for a polymerization product of equivalent compositions. While the present invention has been particularly set forth in terms of specific embodiments thereof, it will be understood in view of the instant disclosure that numerous variations upon the invention are now enabled yet reside within the scope of the invention. Accordingly, the invention is to be broadly construed and limited only by the scope and spirit of the claims now appended hereto.

Claims

1. A rubber modified thermoplastic resin composition having at least improved impact resistance properties comprising: from about 40% to about 90% by weight styrene maleic anhydride copolymer; from about 10% to about 30% by weight of acrylate rubber based on the weight of said resin composition, and from about 0% to about 30% by weight of fillers based on the weight of said resin composition, said resin composition prepared by a compounding technique.

2. A rubber modified thermoplastic resin composition of claim 1 wherein the amount of said acrylate rubber ranges from about 15% to about 25% by weight based on the weight of said rubber modified thermoplastic resin composition.

3. A rubber modified thermoplastic resin composition of either claim 1 or claim 2 wherein the amount of said styrene maleic anhydride copolymer ranges from about 75% to about 85% by weight.

4. A rubber modified thermoplastic resin composition of any one of claims 1 to 3 wherein said acrylate rubber is an ethylene acrylate copolymer.

5. A rubber modified thermoplastic resin composition of claim 4 wherein said ethylene acrylate copolymer is selected from the group consisting of ethylene methyl acrylate copolymer, ethylene ethyl acrylate copolymer, and ethylene butyl acrylate copolymer.

6. A rubber modified thermoplastic resin composition of claim 5 wherein said ethylene acrylate copolymer is an ethylene methyl acrylate copolymer having an acrylate content ranging from about 9 to about 25 weight percent, based on the weight of the ethylene methyl acrylate copolymer.

7. A rubber modified thermoplastic resin composition of claim 5 wherein said ethylene acrylate copolymer is ethylene ethyl acrylate copolymer having an acrylate content ranging from about 12 to about 16 weight percent based on the weight of the ethylene ethyl acrylate copolymer.

8. A rubber modified thermoplastic resin composition of claim 5 wherein said ethylene acrylate copolymer is ethylene butyl acrylate copolymer having an acrylate content ranging from about 7 to about 27 weight percent based on the weight of the ethylene butyl acrylate copolymer.

9. A rubber modified thermoplastic resin composition of any one of claims 1 to 8 wherein said fillers are glass fibers.

10. A rubber modified thermoplastic resin composition of any one of claims 1 to 9 wherein said rubber modified thermoplastic resin composition is prepared by adding said acrylate rubber to said styrene/maleic anhydride copolymer in a twin-screw extruder.

11. A rubber modified thermoplastic resin composition of any one of claims 1 to

10 wherein said styrene maleic anhydride copolymer is comprised of from about 2% to about 25% by weight of maleic anhydride and from about 98% to about 75% by weight of styrene based on the weight of said styrene maleic anhydride copolymer.

12. A rubber modified thermoplastic resin composition of claim 5 wherein said ethylene methyl acrylate copolymer is comprised of about 75% of ethylene and about 25% by weight of methyl acrylate based on the weight of said ethylene methyl acrylate copolymer.

13. A rubber modified thermoplastic resin composition of any one of claims 1 to 12 wherein the average particle size of said acrylate rubber in said resin composition ranges between about 0.5 and 1.0 micron.

14. A rubber modified thermoplastic resin composition of any one of claims 1 to 12 wherein the average particle size of said acrylate rubber in said resin composition is less than 1.0 micron.

15. A rubber modified thermoplastic resin composition of any one of claims 1 to 12 wherein the average particle size of said acrylate rubber in said resin composition ranges from about 1.0 micron to about 2.0 microns.

16. An article produced from the rubber modified thermoplastic resin composition of any one of claims 1 to 15.

17. A method for preparing the rubber modified thermoplastic resin composition of any one of claims 1 to 15 comprising: compounding said acrylate rubber, said styrene maleic anhydride copolymer, and said fillers in an extruder.

18. A method of claim 17 wherein said compounding involves a twin screw extruder.