WO2005100471A2

WO2005100471A2 - Thermoplastic elastomer resin composition

Info

Publication number: WO2005100471A2
Application number: PCT/GB2005/001481
Authority: WO
Inventors: Thomas Orr Craig
Original assignee: Nova Chemicals (International) S.A.
Priority date: 2004-04-19
Filing date: 2005-04-18
Publication date: 2005-10-27
Also published as: GB0408691D0; EP1745102A2; WO2005100471A3

Abstract

A thermoplastic elastomer resin composition comprising 70% to 99% by weight of a thermoplastic elastomer (TPE) and 1% to 30% by weight of a random styrene-butadiene copolymer (SBC) for use as a soft layer in a multi component molding system, e.g. two layers, i.e. a soft layer and a hard, rigid polymer substrate for improving the fusion and/or adhesive properties of the two layers. The random SBC is formed in a reactor under free radical suspension polymerization conditions, and is comprised of 80% to 95% by weight styrene and 5% to 20% by weight butadiene. The resin composition is formed via compounding techniques, and is co-injection molded as a layer onto the rigid polymer substrate. The random SBC has a low weight average molecular weight ranging from 100,000 to 140,000, preferably 120,000 and an MDW ranging from 2.0 to 8.0, preferably 3 to 4.

Description

THERMOPLASTIC ELASTOMER RESIN COMPOSITION AND RELATED ARTICLES AND USES

The present invention relates to a thermoplastic elastomer resin composition. More particularly, the present invention relates to a thermoplastic elastomer resin composition comprising a thermoplastic elastomer (TPE) and a random styrene- butadiene copolymer (SBC), and which resin composition when particularly used as a component in a multi component molding system has improved fusion and/or adhesive properties relative to an adjacent polymer substrate.

Multi component molding systems forming items, such as handles for tools and personal hygiene items, such as razors and toothbrushes, components for consumer and industrial appliances, and automotive parts are often designed such that a soft block copolymer layer is molded onto a hard, rigid plastic substrate. Some multi component molding systems may be used for sealing, insulation, damping, gripping and softness purposes. The relatively soft layer may be comprised of a thermoplastic elastomer, and the hard, rigid plastic substrate may be comprised of a rigid thermoplastic-engineered polymer that is strongly fusion bound to the soft layer.

For example, U.S. Patent No. 5,750,268 and EPO 771 846 B1 disclose a multi-layer polymer system comprising an engineering thermoplastic layer and a soft touch composition layer, which are in intimate contact with each other. The relatively soft layer composition comprises 5 to 50 wt % of a polar engineering thermoplastic; 0 to 80 wt% of an hydrogenated block copolymer having at least two poly(monovinyl aromatic) blocks and a poly(conjugated diene) block, wherein the residual ethylenic unsaturation after hydrogenation is at most 5%; from 5 to 85 wt% of a selectively hydrogenated block copolymer having at least two poly(monovinyl aromatic) blocks and at least one poly(conjugated diene) block wherein the residual ethylenic unsaturation after hydrogenation is at most 5%, said block copolymer being functionalized by means of introduced polar groups; and a plasticizer in an amount of from 0 to 40 wt%.

The relatively hard, rigid layer is comprised of a polar engineering thermoplastic selected from polyamides such as NYLON 6,6 or NYLON 6, polyesters derived from an aromatic acid such as polyethyleneterephthalate (PET), polypropylene terephthalate (PPT), and polybutylene terephthalate (PBT), optionally mixed with polyurethane resins, polycarbonates, and modified polycarbonates.

U.S. Patent No. 5,750,268 states that the multi-layer polymer composition meets the bonding requirements and can be manufactured in a one step operation, i.e. a co- molding step, in order to save production costs as compared to the use of two separate molding steps.

Other multi-layer polymer systems, which are said to require two separate molding steps, are disclosed in U.S. Patent Nos. 4,332,858; 5,002,625 and 5,149,589.

It is known to form a random copolymer of styrene and butadiene. One such process is disclosed and claimed in U.S. Patent No. 4,558,108, which issued on December 10, 1985 to Alexandru, et al. and which is assigned to the Xerox Corporation. This process involves the preparation of a suspension polymerized styrene butadiene resin that is useful as resin particles in toner composition. This process uses a free radical polymerization initiator, and the formed copolymer is a random styrene- butadiene copolymer (SBC) as opposed to a block copolymer of the above prior art.

Copolymers of styrene and butadiene may be made by various techniques other than the aqueous suspension of the aforesaid U.S. Patent No. 4,558,108. These include emulsion polymerization techniques that are said to be relatively expensive due to the complex processing steps required to form and separate the polymers.

Thermoplastic elastomers (TPE's) are known in the art. The term "thermoplastic elastomer" applies to a range of materials that have the characteristics of both rubber and plastic. They are available in different degrees of hardness. Some common TPE's include SBC (styrenic block copolymers), TPO (thermoplastic olefins), TPU (thermoplastic polyurethane), TPV (thermoplastic vulcanisates), COPE (copolyester elastomer), and COPA (copolyamide elastomer).

Two component molded articles, e.g. soft touch handles are known. The soft touch handles generally are constructed of a multi-layer polymer composition such as those in the aforesaid U.S. Patent Nos. 4,332,858; 5,002,625; 5,149,589 and 5,750,268, and in EP O 771 846 B1.

It is known that the combination of a thermoplastic elastomer and a polymer substrate in a multi component molding system needs an adhesion enhancing substance to achieve the required adhesion performance between the two materials.

For example, it may be desirable to use polystyrene polymers and copolymers as the polymer composition of a hard, rigid polymer substrate in multi-layer polymer systems, e.g. handles, in view of their low cost and ease of molding. However, it has been found that the soft touch layer of the prior art does not adequately adhere to the hard, rigid layer in that the layers easily separate after a short period of time and usage.

Summary

The invention improves the fusion and the adhesion properties of the components in a multi component molding system. The invention relates to a thermoplastic elastomer resin (TPE) composition comprising a thermoplastic elastomer and a random styrene-butadiene copolymer (SBC). The thermoplastic elastomer resin composition may be used in forming a first component that is molded to an adjacent second component in a multi component molding system.

The first component is a soft layer and the second component is a hard, rigid layer, and both layers are used to form various articles, such as handles for tools and personal hygiene items, such as toothbrushes and razors, components for consumer appliances, such as kitchen and bathroom appliances, industrial appliances, and automotive parts. Other articles may include elastomeric parts used for gas and liquid sealing, sound insulation, electrical insulation, vibration damping, dry and wet grip applications, etc.

In some embodiments of the invention, the random styrene-butadiene copolymer in the thermoplastic elastomer resin composition has a low weight average molecular weight ranging from about 100,000 to about 140,000; a molecular weight distribution (MWD) ranging from about 2.0 to about 8.0; and a ratio of styrene monomer to butadiene monomer ranging between about 80:20 and about 95:5 by weight.

In some embodiments, the random styrene-butadiene copolymer is comprised of about 86% by weight styrene and about 14% by weight butadiene, based on the ^• weight of the copolymer. In some embodiments, the weight average molecular weight of the random styrene-butadiene copolymer is about 120,000.

The amount of random styrene-butadiene copolymer in the thermoplastic elastomer resin composition ranges from about 1.0% by weight to about 20% or about 30% by weight, and the amount of thermoplastic elastomer (TPE) ranges from about 99% by weight to about 80% or about 70% by weight based on the weight of the thermoplastic elastomer composition. In some embodiments, the amount of random styrene-butadiene copolymer is about 10% to about 20% by weight and the amount of thermoplastic elastomer is about 80% to about 90% by weight. In some embodiments, the amount of random styrene-butadiene copolymer is about 10% to about 30% by weight and the amount of thermoplastic elastomer is about 70% to about 90% by weight, based on the weight of the resin composition. The resin composition may also comprise additional components such as processing aids, color additives, and additives to increase softness, such as oils and ethylene-octene copolymers.

In some embodiments, the random styrene-butadiene copolymer (SBC) and the thermoplastic elastomer (TPE) are compounded together to form the resin composition of the invention, and then molded to a hard, rigid substrate via co- injection molding techniques.

The invention also provides for articles comprising a multi-component molding system that comprises at least one component comprised of the thermoplastic elastomer resin composition of the invention and at least a second component comprised of a hard, rigid substrate.

The thermoplastic elastomer resin composition is comprised of a low molecular weight random styrene-butadiene copolymer, which is produced through a suspension polymerization process. This polymerization process involves the use of a free radical polymerization initiator. This is a relatively inexpensive technique due to the simple processing steps required to form and separate the polymers compared to emulsion polymerization techniques, and to other adhesion promoting styrene butadiene copolymers that are made by anionic polymerization and have a block copolymer structure. An end result is improved performance at lower costs associated in producing the thermoplastic elastomer resin composition of the invention.

Some embodiments of the invention involve a method for improving the adhesion and/or fusion properties of an article comprised of a multi component molding system comprising at least two components wherein at least one component is comprised of the thermoplastic elastomer resin composition.

It is therefore an object of the present invention to provide a unique thermoplastic elastomer resin composition for use as a component in a multi component molding system, whereby the number of parts per system, the costs for assembly of the individual parts in the system, and the logistics costs may be reduced.

It is a still further object of the present invention to provide a thermoplastic elastomer resin composition that readily fuses and adheres to an adjacent component in a multi component molding system.

And yet a still further object of the present invention to provide a thermoplastic elastomer resin composition with improved fusion and/or adhesion properties relative to an adjacent component comprised of a polymer or copolymer.

These and other objects 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

The thermoplastic elastomer resin composition of the invention comprises a thermoplastic elastomer resin (TPE) and a random styrene-butadiene copolymer (SBC).

The thermoplastic elastomer (TPE) resin is a material that exhibits rubber-like characteristics, yet may be melt processed with most thermoplastic processing equipment, such as by extrusion and co-injection molding. As used herein, TPE, i.e. thermoplastic elastomer, is any of a family of polymers that resemble elastomers in that they are highly resilient and can be repeatedly stretched to at least twice their initial lengths with full rapid recovery, but are true thermoplastics and thus do not require curing or vulcanization. Suitable TPE's include SBC (styrenic block copolymers), TPO (thermoplastic olefins), TPU (thermoplastic polyurethane), TPV (thermoplastic vulcanisates), TPS (thermoplastic styrene), COPE (copolyester elastomer), and COPA (copolyamide elastomer). Other TPE's include hydrogenated styrene-butadiene-styrene elastomers. A suitable hydrogenated styrene-butadiene- styrene elastomer is a product sold under the trade name Kraton 1651 , obtained from Kraton Polymers Research BN., Amsterdam, Netherlands.

The random styrene-butadiene copolymer has a low weight average molecular weight ranging from about 100,000 to about 140,000; a molecular weight distribution (MWD) ranging from about 2.0 to about 8.0; and a ratio of styrene monomer and butadiene monomer ranging between about 80:20 and about 95:5 by weight.

In some embodiments, for the random styrene-butadiene copolymer, the weight percent of styrene may be about 86%, the weight percent of butadiene may be about 14% based on the weight of the copolymer, and the molecular weight average molecular weight of the random styrene-butadiene copolymer is about 120,000. In some embodiments, the molecular weight distribution (MWD) for the random styrene- butadiene copolymer may be about 4. In some embodiments, the molecular weight distribution (MWD) for the random styrene-butadiene copolymer may be about 3. The molecular weight distribution (MWD) is obtained by dividing the weight average molecular weight by the number average molecular weight. Thus, if the weight average molecular weight is 120,000 and the MWD is 4, the number average molecular weight is 30,000.

In some embodiments, the random styrene-butadiene copolymer is one that is made through a suspension polymerization process via a free radical polymerization initiator. A suitable styrene-butadiene copolymer is that produced through the process taught in the aforesaid U.S. Patent No. 4,558,108, which is incorporated herein by reference in its entirety. A suitable random styrene-butadiene copolymer for use in the invention may be obtained from NOVA Chemicals (International) S.A., Fribourg, Switzerland under the trade name XP-808. This random styrene-butadiene copolymer has a weight average molecular weight of about 120,000 and a MDW of about 4.

The amount of the random styrene-butadiene copolymer (SBC) in the thermoplastic elastomer composition of the invention may range from about 1 % by weight to about 30% by weight, and the amount of thermoplastic elastomer (TPE) may range from about 99%> by weight to about 70% by weight based on the weight of the thermoplastic elastomer composition. In some embodiments, the amount of random styrene-butadiene-copolymer is about 10% to about 20% by weight and the amount of thermoplastic elastomer is about 80% to about 90% by weight.

In some embodiments, the random styrene-butadiene copolymer (SBC) and the thermoplastic elastomer (TPE) are compounded together to form the resin and then applied to the hard, rigid substrate via co-injection molding techniques to form an integral elastomer part. The substrate may be injection molded first and then the thermoplastic elastomer resin composition layer can be co-injection molded onto the substrate. Or both the substrate and the thermoplastic elastomer resin composition layer can be co-injection molded together at the same time. Thus, the thermoplastic elastomer resin composition of the invention comprises an integral elastomer part in a multi component molding system.

The second component in the multi component molding system may be a hard, rigid substrate that may be comprised of a polymer or a copolymer, which may be a styrene polymer or a styrene copolymer. A suitable styrene polymer is solid polystyrene (SPS), which can be defined as essentially a high molecular weight homopolymer of styrene in pellet form. A suitable styrene copolymer is a high impact polystyrene (HIPS) which is a solid polystyrene formulated during the reaction process with rubber. Such SPS and HIPS products are available from NOVA Chemicals Inc., U.S.A. under product names 172N and 731 N, respectively.

Additional suitable polymers for use as a second component or as a hard, rigid layer in the multi component molding system of the invention may be comprised of ABS, SMMA, styrene-maleic anhydride copolymers, SAN copolymers, styrenic based polymers, amide based polymers, polyester based polymers, polycarbonates and blends thereof, polyolefins, etc. The hard, rigid layer may be an engineered thermoplastic selected from polyamides such as NYLON 6,6 or NYLON 6, polyesters derived from an aromatic acid such as polyethyleneterephthalate (PET), polypropylene terephthalate (PPT), and polybutylene terephthalate (PBT), optionally mixed with polyurethane resins, polycarbonates, and modified polycarbonates.

It has been found by the inventors that the thermoplastic elastomer resin composition when used as an elastomer component in a multi component molding system has improved fusion and adhesion properties relative to an adjacent component. The reason for this improvement is not clear. The inventors do not wish to be bound by any theory, but it is believed that the addition of the random styrene-butadiene copolymer to the thermoplastic elastomer resin (TPE) reduces the interfacial tension of the molten TPE and enhances the ability of the thermoplastic elastomer resin to wet the surface of the adjacent component onto which it is injected, for example, in a co-injection molding step.

The thermoplastic elastomer (TPE) resin and the random styrene-butadiene copolymer (SBC) of the thermoplastic elastomer resin composition of the invention may be formed by blending via compounding techniques and then co-injection molded onto the adjacent component or substrate which may also be formed through co-injection molding techniques. These techniques are well known to those in the art. As mentioned herein above, the free radical polymerization technique for processing the random styrene-butadiene copolymer has several advantages, one of which is that the costs for producing the thermoplastic elastomer resin composition are reduced.

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

Examples 1-7

These Examples illustrate the use of a low molecular weight random styrene- butadiene copolymer (SBC) to improve the interfacial adhesion between a styrenic thermoplastic elastomer (TPE) to which the random SBC resin had been added and a polymer substrate onto which the TPE and random SBC resin composition had been molded as a layer.

The substrate polymer in Example 1 was a rubber-modified polystyrene; in Examples 2 and 3, it was ABS (acrylontrile-butadiene-styrene); in Example 4 it was PETG (polyester of triethyleneglycol and terephthalic acid); in Example 5 it was PMMA (polymethylmethacrylate); in Example 6 it was PC (polycarbonate); and in Example 7 it was ASA (acrylic rubber-modified styrene acrylonitrile copolymer). The TPE in each Example 1-7 was a hydrogenated styrene-butadiene-styrene elastomer (Kraton 1651). The low molecular weight random styrene-butadiene copolymer (SBC) was made by suspension copolymerization of a mixture of styrene (86 wt%) and butadiene (14 wt%). The random SBC has a melt flow index of 28 g/10 minutes (150°C, 2.16 kg. load). The random SBC is a product under the trade name of XP- 808 obtained from NOVA Chemicals (International), S.A., Fribourg, Switzerland, having an average molecular weight of about 120,000 and an MWD of about 4. In Example 2, the additive designated as ENGAGE is an ethylene-butene copolymer made by Dupont Dow.

In the Examples 1-7, the bond strength between the TPE resin composition of the invention and the polymer substrate was measured as follows: The substrate polymer was injection molded into a tensile test specimen (dog bone). The test specimen was cut transversely at its mid-point and placed into a compression mold in such a way that a 5mm gap existed between the cut faces of the tensile test specimen. The TPE and the indicated amount of random SBC were compounded in a twin-screw extruder to form a thermoplastic elastomer resin composition. This thermoplastic elastomer resin composition, in granulate form, was placed into the 5mm gap and the compression mold was closed. The mold was heated to a temperature of 140°C for two (2) minutes. The mold was then opened. The result was that the thermoplastic elastomer resin composition was fused to the cut faces of the tensile test specimen in such a way as to fill the 5mm gap. The tensile test specimen was then placed in a tensile test machine and the stress to failure was measured.

A control tensile test specimen was prepared in a manner similar to that above except that the 5mm gap was not filled with the resin composition of the invention. The results are shown in the Table.

Table

TPE: KRATON® 1561 styrene-ethylene-butene-styrene (SEBS) block copolymer ABS: POLIDUX® AAB781/1000 PETG: EASTAR® 6763 (Eastman Chemical) PMMA: DIAKON® ST 45G8 PC: Dow CALIBRE® 303 EP ASA: BASF LURAN® S 776

If adhesion at the hard-soft interface of the molded parts is so strong that tensile failure occurs within the soft material then these results are considered to be very good results. This is what was found for the invention of Example 1 relating to the HIPS/inventively modified TPE system. If tensile failure occurs at the hard-soft interface as in the invention of Examples 2-7, and the stress needed to cause the failure is higher compared to the unmodified TPE of the control of Examples 2-7 then these results are considered to be good results also.

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. For example, the multi component molding system may be comprised of more than two layers where one or more layers may be comprised of the thermoplastic elastomer resin composition of the invention. Or the molding system may be comprised of at least one layer that is comprised of the thermoplastic elastomer resin composition 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 thermoplastic elastomer resin composition comprising: from about 70% to about 99% by weight of a thermoplastic elastomer; and from about 1.0% to about 30% by weight of a random styrene-butadiene copolymer, based on the weight of said thermoplastic elastomer resin composition.

2. The thermoplastic elastomer resin composition of claim 1 wherein said random styrene-butadiene copolymer is blended with said thermoplastic elastomer via compounding techniques.

3. The thermoplastic elastomer resin composition of claim 1 wherein said random styrene-butadiene copolymer is prepared in a reactor under free radical suspension polymerization conditions.

4. The thermoplastic elastomer resin composition of any one of claims 1 to 3 wherein said random styrene-butadiene copolymer is comprised of about 80% to about 95% by weight styrene and of about 20% to about 5% by weight butadiene.

5. The thermoplastic elastomer resin composition of claim 4 wherein said random styrene-butadiene copolymer is comprised of about 86% by weight styrene and about 14% by weight butadiene.

6. The thermoplastic elastomer resin composition of any one of claims 1 to 5 wherein said thermoplastic elastomer ranges from about 70% to about 90% and said random styrene-butadiene copolymer ranges from about 30% to about 10% by weight based on the weight of the resin composition.

7. The thermoplastic elastomer resin composition of any one of claims 1 to 6 wherein said random styrene-butadiene copolymer has a low weight average molecular weight ranging from about 100,000 to about 140,000, and a molecular weight distribution (MWD) ranging from about 2.0 to about 8.0.

8. The thermoplastic elastomer resin composition of any one of claims 1 to 7 wherein said thermoplastic elastomer is selected from the group consisting of SBC (styrenic block copolymers), TPO (thermoplastic olefins), TPU (thermoplastic polyurethane), TPV (thermoplastic vulcanisates), COPE (copolyester elastomer), COPA (copolyamide elastomer), and hydrogenated styrene-butadiene-styrene elastomers.

9. The thermoplastic elastomer resin composition of claim 8 wherein said thermoplastic elastomer is hydrogenated styrene-butadiene-styrene elastomers.

10. An article comprising at least one component comprised of the composition of any one of claims 1 to 9.

11. The article of claim 10, wherein said article is a multi component molding system comprising said at least one component and further comprising a second component.

12. The article of claim 11 wherein said one component is co-injection molded onto said second component, and wherein said second component is a hard, rigid substrate.

13. The article of claim 12, wherein said one component has improved fusion and/or adhesive properties relative to said substrate.

14. The article of either claim 12 or claim 13 wherein said substrate is a polymer.

15. The article of claim 14 wherein said polymer is selected from the group consisting of polystyrene polymers, polystyrene copolymers, styrenic based polymers, amide based polymers, polyester based polymers, polycarbonates, polycarbonate blends, and polyolefins.

16. The article of any one of claims 11 to 15 wherein said article is selected from the group consisting of soft touch handles, automotive parts, components for appliances, and elastomeric parts.

17. A method for improving the adhesion and/or fusion properties of an article comprised of a multi component molding system comprising at least two components wherein at least one component is comprised of the thermoplastic elastomer resin composition of any one of claims 1 to 9.