Coating formulators looking to achieve a high level of chemical and abrasion resistance have typically formulated their coatings with oligomers that have high Tg and crosslinking density. Unfortunately, this can lead to an unwanted increase in viscosity, which requires the use of more solvent and increases the volatile organic compound (VOC) content to as high as 60-70%. In this study, we evaluated a group of dendritic Bomar® oligomers to see if they could be used to produce top coats with high chemical and abrasion resistance that would overcome these common problems with viscosity and VOC content. We had positive results and were able to formulate several matte-finish top coats that displayed high chemical and abrasion resistance on plastic substrates while achieving high solids content (50%).

In the study, dendritic oligomers with high solids were employed to achieve the desired characteristics. These characteristics are attributed to high crosslinking density, which results from the dendritic oligomers’ high functionality. Oligomers with high functionality offer fast, tack-free curing, which speeds up production and ultimately reduces operational costs. Dendritic oligomers are also more spherical than rod-shaped; and because of this, have significantly lower viscosity than typical linear oligomers of comparable molecular weights. This makes them ideal for use in low VOC applications in a variety of industries where exceptional mechanical and physical properties are needed. The dendritic oligomers chosen for this study were tin and aromatic free. They provided exceptional chemical resistance, especially to yellow mustard, and had exceptional adhesion to PC/ABS and untreated PET.

In this study, a matte-finish, top coat with both scratch and chemical resistance was also formulated by combining a silicone urethane acrylate oligomer at additive levels (<10%) into the same top coat as the chemically resistant dendritic oligomers detailed above. This oligomer showed a further improvement of the matte-finish by reducing the gloss of the top coat that was maintained after abrading.

Thinner coatings historically are known to be less chemical and abrasion resistant, and it’s more difficult to reach low gloss, which is attributed to having less matting agent per surface area. The ideal gloss at 60 degrees for a matte-finish top coat is equal to or less than 5 at 25 microns. In this study, we’ve shown that a 13-micron top coat will achieve a gloss of 5, which is a cost saving benefit to the end-user.

Features & Benefits

Exceptional chemical and scratch resistance for more durable coatings

Superior retention of matte finish for products that look better, longer

Fast, tack-free curing

Low shrinkage for complete and uniform coverage

Low VOC applications with high solids contents at acceptable processing viscosities

Tin free

TESTING & RESULTS

Functionality, Viscosity, and Glass Transition Temperatures of the Oligomers

For this study, four Bomar® acrylate oligomers were chosen with varying acrylate functionalities and degrees of glass transition

temperatures (Tg) to help formulators balance properties as desired. Table 1 displays the acrylate functionalities, viscosities of the neat

oligomers, and cured Tgs of the four chosen oligomers.

Oligomers with higher functionality are relatively less prone to oxygen inhibition making them ideal for low-intensity, UV-curing methods

typically used by the coating market on plastic substrates. Due to their high functionality, Bomar® BDT-4330, XDT-1018, and BDT-1015 are

the preferred choices for low oxygen inhibition applications where fast, tack-free curing is desirable. It appears that BDT-1015 has the

lowest viscosity while BRS-14320S has the highest. To help formulators adjust formulation viscosity, dilution curves with various

monomers are included on our product data sheets. To measure the Tg of each cured oligomer, it was mixed with 2% photoinitiator and

cured with broad-spectrum UV light. BRS-14320S and BDT-4330 provided the lowest and highest Tg values, respectively.

Table 1. Acrylate Functionality, Viscosity, and Glass Transition Temperatures of Chosen Oligomers

Bomar® Oligomer Cured or Uncured Property BRS-14320S BDT-1015 BDT-4330 XDT-1018

Acrylate Functionality Uncured 2 15 30 18

Viscosity (cPs) Uncured 18,000 @50°C 31,275 @ 25°C 4,000 @ 50°C 50,000 @ 25°C

Tg (°C) Cured -112 47 >100 46

Viscosity, Pencil Hardness, and Adhesion

All four oligomers were tested for potential formulation of durable, matte-finish, UV-curing coatings on plastic substrates using a simple

model formula (Table 2). All formulations were cured using a Dymax 5000-EC flood lamp outfitted with metal-halide bulbs. Curing was

completed with an intensity of 200 mW/cm2 energy after 30 seconds of exposure. The curing intensity was recorded using an ACCU-CAL™

150 radiometer. The viscosity of each formulated topcoat was measured at 25°C using a Brookfield CAP 2000+ instrument using ASTM

D4287 test method. BDT-4330 and XDT-1018 have the lowest and highest formulated viscosity, respectively.

The pencil hardness of each formulation was also measured, using ASTM D3363 test method. During this test, all the oligomers provided at

least a pencil hardness of H. The formulation with BDT-4330 provided the highest pencil hardness at 2H. In order to reach the desired

hardness levels, oligomers given in Table 3 can be blended together in the formulations. Adhesion to black PC/ABS was excellent (5B) for

all coatings evaluated in this study.

Table 2. Model Formula

Ingredient Wt (%)

Oligomer 44.5

Matting Agent 3.0

Photoinitiator 2.5

Butyl Acetate 50.0

Figure 1. 5000-EC Lamps

Figure 2. ACCU-CAL™ 150 Radiometer

Table 3. Viscosity, Pencil Hardness, and Adhesion Results

Bomar® Oligomer 8:1 BDT-1015

with BRS-14320S BDT-1015 BDT-4330 XDT-1018

Viscosity (cP) 31 28 18 38

Pencil Hardness H H 2H H

Crosshatch Adhesion 5B 5B 5B 5B

Shrinkage/Warpage

Low shrinkage during cure is important for all coatings in plastic substrate applications where good mechanical properties and aesthetics

are expected. Coating shrinkage during cure can cause thin substrates to warp by bending or twisting. On 13 micron PET substrates, a 13

micron thick coating was cured and then tested for warpage. The warpage of the substrate was evaluated by measuring the height (mm)

of the substrate as it curled up from a flat plane during the cure.

Overall shrinkage of all of the oligomers varied (Table 4), yet two formulations in this study provided no noticeable warpage of the

substrate: the 8:1 blend of BDT-1015 with BRS-14320S and XDT-1018.

Table 4. Shrinkage Test Results

Bomar® Oligomer 8:1 BDT-1015

with BRS-14320S BDT-1015 BDT-4330 XDT-1018

Linear Shrinkage (mm) 0 4 11 0

Figure 3. Warpage Test Sample

BDT-4330 BDT-1015 with BRS-14320S Uncoated

Chemical and Abrasion Resistance

Chemical resistance was evaluated for each of the oligomers (ASTM1308) by exposing each of the cured topcoats to yellow mustard for 24

hours. All formulations in this study exhibited outstanding chemical resistance when used in matte finish topcoats on black PC/ABS.

Figure 4. Stain Resistance Test Sample – 8:1 BDT-1015 with BRS-14320S

Before After

Table 5. Chemical Resistance Test Results

Bomar® Oligomer 8:1 BDT-1015

with BRS-14320S BDT-1015 BDT-4330 XDT-1018

Chemical Resistance No stain No stain No stain No stain

Abrasion resistance was also evaluated. Each coating was cured on a black PC/ABS substrate using ASTM D523. A linear Taber Abrader was

employed with a 500 gram load and CS-10F Wearaser. The gloss at 60° was measured before and after abrading each topcoat and the

change in gloss value was calculated (Table 6).

The topcoat made from an 8:1 blend of BDT-1015 and BRS-14320S and the topcoat made with BDT-4330 provided the least change in gloss

indicating their greater abrasion resistance. To reach the desired matte finish (gloss equal to or less than 5), a higher loading of matting

agent would be required in most of the formulas, however, the chemical and abrasion resistance would likely be compromised. In order to

maintain the same level of chemical and abrasion resistance while achieving the desired level of gloss for a matte finish topcoat, then BRS-

14320S must be employed.

Table 6. Abrasion Resistance Test Results

Bomar® Oligomer 8:1 BDT-1015

with BRS-14320S BDT-1015 BDT-4330 XDT-1018

Starting Gloss 5.2 19.7 23.2 22.5

Ending Gloss 7.5 25.5 26.3 29.0

Change in Gloss 2.3 5.8 3.1 6.5

Figure 5. Abrasion Resistance Test Sample - 8:1 BDT-1015 with BRS-14320S

50 Cycles 100 Cycles

CONCLUSIONS

The Bomar® oligomers featured in this study offer many benefits to formulators looking to create durable, matte-finish, and UV-curing coatings for plastic substrates. Using these oligomers, formulators can design coatings with exceptional chemical and scratch resistance. They can also use these oligomers for applications that expect exceptional matte-finish retention with low shrinkage and low VOC.

CUSTOM OLIGOMERS

If you are interested in our Bomar® oligomers but one of our existing oligomers does not provide the desired properties for your

application, Dymax O&C can work with you to develop a custom oligomer that will fit your application needs. In addition to creating custom

oligomers, we also offer a range of scale up and manufacturing services. Our technical and senior production staff work directly with

companies to evaluate projects and provide cost-efficient manufacturing solutions. Each manufacturing partnership is unique and flexible,

allowing short- to long-term product manufacturing. Visit our website for more information.

RECOMMENDED EQUIPMENT FOR COATING

Dymax Dispensing Systems Suitable for Coating Applications

This material may be dispensed with a variety of manual, semi-automated and

fully automated fluid delivery systems. Dymax’s SG line of regular, high-flow

and super-flow spray guns can be utilized for spraying larger surface areas. The

fluid delivery systems are supported with various size cartridge containers and

ram pumps for larger volume applications. Small-area applications including

beads and small dots can be achieved using hand-held Dymax dispensing

systems like our SD-100 syringe dispenser and our Model 400 needle valve

systems. Dymax has several other dispensing systems that may be suitable for

use with UV coatings. Questions relating to and defining the best fluid delivery

system and curing equipment for specific applications should be discussed with

the Dymax Application Engineering Team.

UV Light-Curing Flood Systems

Dymax flood-lamp systems are designed for area curing or for curing

multiple assemblies at once. These flood lamp models use a powerful UV

light-curing lamp (up to 225 mW/cm2 for fast curing over a 5" x 5" (12.7

cm x 12.7 cm) area). Typical flood-lamp curing systems are composed of

three main components: a UV flood lamp, manual or automatic shutter,

and a light shield. CE-marked systems are available.

SG-200 Spray Gun System with Ram Pail Pump

Dymax ECE Flood Lamp System with ZIP™ Shutter & Light Shield

© 2016 Dymax Corporation. All rights reserved. All trademarks in this guide, except where noted, are the property of, or used under license by Dymax Corporation, U.S.A.

Technical data provided is of a general nature and is based on laboratory test conditions. Dymax does not warrant the data contained in this bulletin. Any warranty applicable to the product, its application and use is strictly limited to that contained in Dymax standard Conditions of Sale published on our website. Dymax does not assume responsibility for test or performance results obtained by users. It is the user’s responsibility to determine the suitability for the product application and purposes and the suitability for use in the user’s intended manufacturing apparatus and methods. The user should adopt such precautions and use guidelines as may be reasonably advisable or necessary for the protection of property and persons. Nothing in this communication shall act as a representation that the product use or application will not infringe on a patent owned by someone other than Dymax or act as a grant of license under any Dymax Corporation Patent. Dymax recommends that each user adequately test its proposed use and application before actual repetitive use, using the data in this communication as a general guideline. OCTB007 10/03/2016

Dymax Corporation +1.860.482.1010 | info@dymax.com | www.dymax.com

Dymax Engineering Adhesives Ireland Ltd. +353 21.237.3016 | info_ie@dymax.com | www.dymax.com

Dymax Asia (H.K.) Limited +852.2460.7038 | dymaxasia@dymax.com | www.dymax.com.cn

Dymax Oligomers & Coatings +1.860.626.7006 | info_oc@dymax.com | www.dymax-oc.com

Dymax UV Adhesives & Equipment (Shanghai) Co. Ltd. +86.21.37285759 | dymaxasia@dymax.com | www.dymax.com.cn

Dymax Asia Pacific Pte. Ltd. +65.6752.2887 | info_ap@dymax.com | www.dymax-ap.com

Dymax Europe GmbH +49 (0) 611.962.7900 | info_de@dymax.com | www.dymax.de

Dymax UV Adhesives & Equipment (Shenzhen) Co. Ltd. +86.755.83485759 | dymaxasia@dymax.com | www.dymax.com.cn

Dymax Korea LLC +82.2.784.3434 | info_kr@dymax.com | www.dymax.com/kr