Acrylic TPE Approaching Automotive 7KHUPRSODVWLF (ODVW PDJD]LQH LQWHUQDWLRQDO

J. Oertel, S. Kishii, D. Kilian,

K. Hamada, Y. Morishita, T. Kurihara, T. Ito V RPHU

Acrylic TPE approaching automotive 7KHUPRSODVWLF (ODVW PDJD]LQH LQWHUQDWLRQDO

Volume 2, March 2010

P. O. Box 10 41 25 40852 Ratingen/Germany 1| 2010 acrylic tpe

PMMA modifications and for combinations Acrylic TPE approaching automotive of LA-Polymer with engineering plastic PBT for targeting automotive applications. J. Oertel, S. Kishii, D. Kilian, K. Hamada, Y. Morishita, T. Kurihara, T. Ito* Figure 1 shows the molecular structure of LA-Polymer, which is fully (meth)acrylic tri- Recently, Kuraray has developed a novel all (meth)acrylic block polymer named block copolymer. It is sequentially prepared LA-Polymer by using its own polymerisation technologies. The structures of LA- by using our living anionic polymerisation Polymer­ are triblock copolymers. i. e. poly(methyl methacrylate)-block-poly(n-butyl system. The LA-Polymer is built of two ter- acrylate)-block-poly(methyl methacrylate) [1]. LA-Polymer is processed in Kuraray’s minal hard PMMA blocks (Tg = 100 ~ 120 °C) pilot plant at commercial level in Japan. In this paper, characteristics and some pos- and one inner soft rubbery PnBA block sible application examples of LA-Polymer and its modifications with engineering plas- (Tg = -40 ~ -50 °C). In general LA-Polymer tics for potential automotive use are shown. can be used as a thermoplastic elastomer.

The result of SEC (Size Exclusion Chroma- 1. Introduction proofed also for LA-Polymer as well as a high tography) and molecular weight distribution level of transparency (fig. 3). curves of LA-Polymer and conventionally made After Kuraray developed key technology PMMA are depicted in figure 2a. The molecular for mass production of specialised PMMA- In looking at the polar nature of LA-Poly- weight distribution of LA-Polymer is more nar- PnBA-PMMA triblock copolymers, (fig. 1) mer we found good compatibility and adhe- row than the one of a conventional acrylic pol- the use of flexibilised PMMA with no change sion to other polar plastics like PC, ABS, SAN ymer. Moreover, LA-Polymer has a well-defined in transparency was the first exiting char- and even PVC. In fact the polarity seems also structure and a very low content of mono­mers acteristic feature. Furthermore, we found causal for good paintablity. With inorganic and oligomers. In figure 2b the grade map monomers and oligomers are absent which fillers we found a good dispersion effect be- is shown with three grades, LA2140e, LA2250 provides basically odourlessness in applica- side good compatibility. Depending on the and LA4285, being produced as pellets in dif- tion. This is also supported by a very narrow molecular weight and structure, LA-Polymer ferent Shore hardnesses (A32-soft, A65-mid- molecular weight distribution (fig. 2a) [2]. show a low to very low melt viscosity. This dle, A95-hard). Hardness generally depends on Because of the intrinsic elastic part PnBA fact is used for adjusting well-set elastified the content of PMMA blocks. rubber, no additional plasticisers are need- ed to get flexibilisation of PMMA in broad hardness and elasticity ranges. The well- All acrylic ABA type triblock copolymer CH HCH known weatherability aspects of PMMA were 3 3

(– CH2 – C –) n – b – (– CH2 – C –) m – b – (– CH2 – C –) n – C = OC = OC = O * Joerg Oertel, Shiro Kishii, Dr. Dirk Kilian OCH3 OC4H9 OCH3 Kuraray Europe GmbH, Frankfurt, Germany PMMA PnBa [email protected] Fig. 1: PMMA Structure of LA-Polymer - by using our living ani- Kenichi Hamada, Yoshihiro Morishita, onic polymerisation Soft block Toyoaki Kurihara, Toshiyuki Ito Hard block system, the acrylic block T − 40 ~ − 50 °C T 100 ~ 120 °C g Kuraray Co. Ltd, Tokyo, Japan copolymers were se- g quentially polymerised.

Fig. 2b: Grade map of different LA-Polymer types

LA-Polymer 50 Hard LA4285 (Living polymerisation) Hardness A 95, D57 Mw/Mn = 1.28 40 Acrylic polymer wt % (Radical polymerisation) LA2250 Mw/Mn = 11 30 Hardness A 65 Soft LA2140e Fig. 2a: 20 Hardness A 32

SEC (Size Exclusion Chro- PMMA block cont. matography) and mole­ 10 cular weight distribution 102 103 104 105 106 107 curves of LA-Polymer MW and conventionally made 50K 75K 100K 125K Total Mw PMMA

30 TPE Magazine · 1|2010 2. Characteristics The TEM photo also shows that LA-Poly- For structure analysis, TEM micrographs of mer has a well-defined structure. The mi- LA-Polymer are compiled in figure 3. Here 2.1 Morphologies cro-phase separation is very clear and the the black parts represent the PMMA and sample shows cylindrically arranged dark white parts are the PnBA. The LA-Polymer By using Kuraray’s specified staining PMMA micro-domains with an approxi- have different micro-phase separated mor- method, an observation of LA-Polymer with mate diameter size of 10 – 20 nm in a light phologies, which depend on the content ra- TEM has become possible (fig. 3). PnBA matrix. tio of PMMA block and PnBA block:

• LA2140e short cylindrical morphology • LA2250 long cylindrical morphology TEM of LA-Polymer • LA4285 lamellar morphology.

Black: PMMA domain White: PnBA matrix (hard domain) (rubbery matrix) 2.2 Transparency and durability LA2140e LA2250 LA4285 The dependence of several resins’ trans- mittance on wavelength has been measured (fig. 4). In the range of visible light wave- Fig. 3: length (380 – 780 nm), LA-Polymer has ex- Morphology investiga- cellent transparency (ca. 92 %). It is on the tion of LA-Polymer by same level as polymethyl methacrylate, and 100 nm TEM (Transmission Elec- tron Microscopy) it is suggested to be better than polycar- bonate and polystyrene (ca. 90 %). Fig. 4: Transparency of LA-Polymer compared to polycarbonate (PC) and polystyrene (PS) Figure 5 shows the weather resistance of Sample: 140 µm film LA-Polymer by Sunshine Weather-O-Meter 100 (SWOM) with retention of tensile strength and colour stability. After the specimen (2 mm thickness injection moulded sheets) had been

90 exposed, the values of factors (δa*,δb*,δYI) re- mained low with only little change. Suggest- ing that, the weather resistance of LA-Poly­ mer is relatively stable with steady tensile ansmittancy (%)

Tr 80 strength and very low yellowing. LA (PMMA = 30 %) PMMA PC TGA curves are shown in figure 6. The PS thermal stability is accounted by a tem- 70 400 500 600 700 800 perature of 5 % loss which is 316 °C in N2 Wave length (nm) atmosphere and 282 °C in air. As indicated above, LA-Polymer has good flow ability and it can be processed below the degrade tem- Fig. 5: Weather resistance test on tensile properties and colour change perature in injection moulding, extrusion moulding, compression moulding, hot-melt Test Method: JASO M346 (Xenon Arc Weather-O-Meter, Samples Before irradiation After irradiation coating, etc. Blending with other polymers 2 BPT 89 ºC, 50 % RH, 100 W/m ) (200 MJ/m2) can be conducted in a mixer or kneader such 200 MJ/m2 means about 10 years exposure = about 10 years for automobile interior parts. as kneader-ruder, extruder, mixing-roll, Ban- 140 LA4285 bury mixer, etc. 120 100 TPU 2.3 Flow properties polyester 80 type

60 TPU Compared to an HSBC with equivalent polyether 40 type molecular weight and hard block content, 20 LA2250 the LA-Polymer shows an extremely high LA4285 TPO Retention of tensile strength (%) 0 melt fluidity (means low melt viscosities) 0255075 100 125 MJ/m2 and softness properties, caused by the PnBA block (tab. 1).

TPE Magazine · 1|2010 31 acrylic tpe

In a study on the dynamic mechanical by mixing. A mix of LA2250 and LA4285 was 6. Comparison to TPO and TPU properties it was also indicated that LA- done without loss of transparency. Table 2 Polymer is softer than SEBS, and has a good shows properties of the injection-moulding When looking at the key properties of LA- high temperature performance, caused by a grades LA2250 and LA4285 and a 1:1 mix Polymer, it is useful to check the standard higher glass transition temperature (Tg) of of both. materials in these applications, thermoplas- the syndiotactic PMMA block. Molecular Hardness MFR [g/10 min] Because of their high flow and easy to characteristics paint properties, LA-Polymer can be effec- Mw Hard block [Shore A] 190 °C, 230 °C, content 2.16kg 2.16kg tively used in moulding materials, especially Tab. 1: Flow properties of LA-Polymer 77,000 30 wt.% 60 7.0 110 injection moulding. The melt viscosity as a LA-Polymer and HSBC function of shear rate at various tempera- (SEBS) SEBS 80,000 30 wt.% 80 0.04 0.46 tures is given in figure 7. This demonstrates the good processability of LA-Polymer with- out using plasticisers. TG Start Temp.: 30 °C End Temp.: 500 °C Rate: 10 °C/min 100 90 3. Adhesion to polar plastics 80 N2 70 Air Adhesion to plastics is generally request- 60 50 Standard moulding ed for all 2K applications. Conventional TPE eight (%) temperature

Fig. 6: W based on HSBC has good adhesion to non- 40 Thermal stability ana- 30 polar plastics (PP, PS, PPE, etc.) but it is dif- lysed by TGA in air and 20 nitrogen. Measurement ficult to bond to polar plastics such as PC, 10 condition: The sample ABS, and PMMA. Recently, a TPV “bondable 0 was heated from 30 °C 0 100 200 300400 500 grade” was developed that shows improved to 500 °C at a rate of Temperature (°C) adhesion to polar plastics. It is used here as 10 °C/min. reference material. Fig. 7: Melt viscosity of LA-Polymer (MnBM) as a function of shear rate at various temperatures To investigate adhesion to polar plastics, an insert moulding system was prepared LA-Polymer SEBS 1.E+05 1.E+05 (fig. 8). The LA-Polymer shows high ad- 190 °C 230 °C hesion to polar plastics and PS, compared 210 °C 240 °C a-s ) to the TPV bondable grade. In addition it 1.E+04 a-s ) 1.E+04 maintains good transparency whereas the TPV gets turbid. 1.E+03 1.E+03

190 °C 230 °C Complex viscosity (P 4. Paintability Complex viscosity (P 210 °C 240 °C 1.E+02 1.E+02 110 100 110 100 Because of the adhesion properties the idea Angular velocity (rad/s) Angular velocity (rad/s) of over painting seemed reasonable. There- fore the interesting process of coloration was studied and other useful plastics have been checked in the same manner. The result is de- 10.0 picted in figure 9, where solvent-based and 8.0 water-based acrylic paints have been used 6.0 versus LA-Polymer, PVC, EMMA, and TPO. The adhesion was checked by pulling a tape. 4.0 Adhesion (N/mm) 2.0

5. Physical properties Fig. 8: 0.0 Adhesion to polar PC PMMA ABS PS plastics in peel test; LA-Polymer: Transparency TPV (Special Grade): Opacity The hardness and mechanical properties photograph shows dou- of the LA-Polymer can be easily controlled ble moulded samples.

32 TPE Magazine · 1|2010 tic poly olefins (TPO) and thermoplastic poly- mer as an impact modifier for polar plastics formulations (tab. 5) was established and urethanes (TPU). The superior features of LA- (PC/PBT blend) was studied and compared to the blending of LA-Polymer with engineering Polymer are highlighted in table 3. SEBS (tab. 4). Impact strength is improved plastics like PBT under a new product name without losing flow ability and HDT. The effect “LC-Series” was defined. at low temperatures is especially good. 7. Modifier for polar plastics Certainly important in fact is the change (LC-Series) of transparency into translucent or turbid 8. Abrasion resistance while mixing polar plastics LA-Polymer with As commonly known HSBC are used as im- PBT, PVC, etc. which is dependent on the Abrasion tests were carried out under con- pact modifiers of non-polar polymers and matching of the refractive indices. Never- ditions described in JASO M312 with cot- blends (PP, PS, PPE, etc.). As mentioned above, theless, the combination of good scratch and ton cloth and steel wool rubbing (fig. 10). LA-Polymer is more flexible than HSBC and it oil resistance was found as a main require- LC150B is between TPUs (ester and ether is a polar material. The behaviour of LA-Poly­ ment of the automotive industry. A set of type) and TPOs which are generally worse.

Tab. 2: General properties of LA-Polymer injection-moulding grades LA2250/LA4285 9. Oil resistance Test method LA2250 LA4285 = 50/50 Hardness [type A] (-) ISO 7619-1 65 78 95 Various fats, oils and lubricants are either Specific gravity (-) ISO 1183 1.08 1.10 1.11 used in cars or are part of dirt that cars are Modulus at 100 % (MPa) ISO 37 3.7 9.1 19 exposed to. Therefore information on oil re- Tensile strength (MPa) ISO 37 9.0 12 19 sistance is important, mainly for automo- Tensile elongation (%) ISO 37 380 190 120 tive interior applications. The assessment was MFR [190 ºC 2.16 kg] (g/10 min) ISO 1133 25 3.8 1.5 done according to ISO 1817; volume change MFR [230 ºC 2.16 kg] (g/10 min) ISO 1133 330 68 31 and weight change (uptake) were investi- Transmittance [3 mm] (%) ISO 13468-1 91 91 91 gated. The results show a better perform- Haze [3 mm] (%) ISO 14782 2 2 2 ance of the LC-Series which is a 50:50 LA/ Table shows typical values which are not specific values. PBT blend (tab. 6).

Tab. 3: Performance map of LA-Polymer versus TPO and TPU Tab. 4: Properties of PC/PBT/LA-Polymer blend LA-Polymer TPO (non-DV) TPU

Polar/non-polar Polar Non-polar Polar 1 Ref. 1 Ref. 2 Melt viscosity Excellent Good Not good [Formulation] Transparency Excellent Bad Not good PC 60 60 60 Weatherability Excellent Not good Bad (yellowish) PBT 40 40 40 Softness Excellent Not good Bad LA-Polymer triblock, PMMA=23 %, MW=80,000 10 – – Colouring/paintability Excellent/excellent Good/not good Good/excellent SEBS triblock – 10 – Elasticity Not good Not good Excellent [Charpy notched impact strength] Tensile strength Not good Good Excellent 23 °C [KJ/m2] 85 68 11 Heat resistance Good Good Good -40 °C [KJ/m2] 21 9 10 Oil resistance Good Not good Excellent [MFR] 250 °C, 2.16 kg [g/10 min] 12 11 10 Alcohol resistance Bad Good Good [HDT] 1.82 MPa 84 89 80 Abrasion resistance Not good Good Excellent [Flexible modulus] 23 °C [MPa] 1610 1530 1760

Tab. 5: Examples of LA/PBT formulations 10. Comparison of LA-Polymer 1 2 3 4 5 and LC-Series LA2250 25 33 50 67 75 PBT Novaduran 5010L (MEP) 75 67 50 33 25 As a result of our development we were Hardness (Type A) ISO 7619-1 91 88 80 78 76 able to show key properties for potential Tensile strength (MPa) ISO 37 30 23 16 10 9.0 automotive applications. The main benefits Tensile elongation (%) ISO 37 40 40 90 170 250 of these materials are their durability and MFR (230 ºC, 2.16 kg) (g/10 min) ISO 1133 17 32 70 140 180 weatherability. Properties and features of the Flammability – (UL94) HB HB HB HB HB materials can further be adjusted to specific Table shows typical values which are not specific values. OEM design standards.

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The following collection is to be seen as Fig. 9: an initial study on applications: For LA- Paintability test of Cross cut test LA-Polymer compared to Polymer we focus on their superior com- PVC, EMMA, and TPO LA-Polymer PVC EMMA TPO bination of transparency and elasticity Acrylic paint: leading to light guiding applications in il- Solvent base lumination of switches, safety guards or optical communication parts. Application requirements in touch and feel can be sup- ported because of the wide hardness range of LA-Polymer. Soft LA-Polymer are more Water base tacky than harder ones. Because of their fully miscibility with each other and with PMMA all soft-touch nuances can be ad- justed by simple mix. Water base for PC In the harder and more rigid ranges, com- binations of LA-Polymer with engineering plastics deliver improved oil and abrasion resistance. LA-Polymer/PBT combination Fig. 10: Abrasion assessment according to JASO M312 test with cotton cloth and steel wool. Delta of colour was found to show good adhesion to ABS. change (left) and gloss (right) is measured. Specimen are 200 x 50 x 2 mm. (JASO M312 = Test method In general the adhesion to polar plastics of plastics parts for automobiles, Japanese Automobile Standard Organisation). in 2K applications is promoted at higher content of LA-Polymer in the blend. In ad- Abrasion resistance by cotton cloth (mirror surface) Abrasion resistance by cotton cloth (grain) 25 100 25 100 dition, parts made of neat LA-Polymer or 20 20 in combination with other plastics obtain ( ∆ L* ) 50 ( ∆ L* ) 50 15 15 improved paintability on top. This results 0 0 10 10 in improved cost efficiency, i. e. in grip or -50 -50 5 5 protecting applications, where colour va- 0 -100 0 -100 rieties of the plastic parts are required. An Retention of gloss (%) Retention of gloss (%) CIE colour standard CIE colour standard low low low low low low -5 low -150 -5 low -150 overview is shown in table 7. high high high high high high high high

Abrasion resistance by steel wool (mirror surface) Abrasion resistance by steel wool (grain) 25 100 25 100 11. Possible applications 20 20 ( ∆ L* ) 50 ( ∆ L* ) 50 15 15 0 0 Potential applications in automotive in- 10 10 -50 -50 terior are i. e. in instrument panels, dash 5 5 board skins, inner door grips, parking le- 0 -100 0 -100 Retention of gloss (%) Retention of gloss (%) vers, shift grips, steering wheel covers, as- CIE colour standard CIE colour standard low low low low low low -5 low -150 -5 low -150 high high high high high high high high sist grips, switches and many others more in system parts. An exemplary map and dem- LC 150B TPU 1: polyether type ∆L*: Gs·R: onstration examples are depicted in figures TPU 2: polyester type TPO: standard grade 11 and 12.

Tab. 6: Oil resistance assessment according to ISO 1817. Tab. 7: Overview of key properties of LA-Polymer and LC-Series with regard to Data show delta V (volume change) and delta W (weight change). automotive applications Specimen are 200 x 50 x 2 mm. Properties LA ( / LA) LC-Series

Δ V (%) / Δ W (%) Transparency ++ -- LA/PBT Printability ++ ++ TPEE = 50/50 Oil resistance + ++ Machine lubricant 65 ºC, 24 h 1.3 / 5.8 4.2 / 8.6 Heat resistance + ++ Castor oil Room temperature, 168 h 0.5 / 1.8 2.3 / 3.0 Stickiness Yes Dry touch 50 vol.% aqueous ethanol Room temperature, 168 h 7.1 / 5.3 10 / 7.7 Adhesion to polar plastics (2K moulding) ++ + Hand cream Room temperature, 168 h 1.1 / 1.4 1.4 / 1.5 Hardness (Shore) > 65A > 80A Table shows typical values which are not specific values. High flow (thin parts moulding ) ++ ++

34 TPE Magazine · 1|2010 12. Conclusion with fillers, combined with transparency or benefit in this material. But also more tough oil/abrasion resistance they show the strong requirements in surface skins for automotive The new materials LA-Polymer and LC-Se- ability for high class applications. are possible and already tested. ries have been presented and an overview on key properties for potential automotive In addition some outline for applications application has been given. We showed the was given. For a combination of LA-Poly- 13. References characteristics of materials ascribed as nov- mer with PBT we showed resistivity against el (meth)acrylic thermoplastic elastomers, mechanical forces and oils. If this is used in [1] LA-Polymer Brochure, Kuraray 2006 containing no monomers and oligomers, nor combination with downstream colouration it [2] Details are shown in patents plasticisers. Because of the low melt viscosity, may dedicate these compounds to grip and (United States Patent 6,329,480, good weatherability, transparency, paintabil- protection applications. In general transpar- United States Patent 6,555,637). ity, adhesion to polar plastics, compatibility ent flexible applications are able to take a

Fig. 11: Exemplary field map for potential automo- Fig. 12: Demonstration samples: Light guide in LED demonstration socket of 6 mm diameter (LA-Polymer) and tive interior application gear grip application in three colours (LC-Series)

TPE Magazine · 1|2010 35