Radiation Physics and Chemistry 63 (2002) 475–479

Development of hard materials by radiation curing technology

N.G. Salleha,*, H.J. Gl.aselb, R. Mehnertb

aMalaysian Institute for Nuclear Technology Research, MINT Technology Park, Bangi, 43000 Kajang, Malaysiab Institut f .ur Oberfl .achenmodifizierung e.V., Permoserstra�e 15, D�04318 Leipzig, Germany

Abstract

For studying nanoglobular modification effects in radiation cured polymeric composites, we prepared polymerization

active silico-organic nanoparticles. With their polymerization active ligands, these nanoparticles form crosslinks by

modifying the viscoelastic properties in radiation cured polymeric nanocomposites. In this process, there was a

polymerization activity imparted to the particle surfaces of nanopowders, thus applying the physico-chemical

modification scheme of a heterogeneous copolymerization to novel scratch and abrasion resistant coatings. By varying

the nanoparticle-monomer formulation and the curing method, additional property can be achieved. In this works, we

also investigated the influence of various factors such as addition of photoinitiators and other additives into the

formulations. The coating materials were applied to the substrate by using different type of coaters. These materials

were cured by ultraviolet light and electron beam irradiation. Properties of coatings were characterized using Universal

scratch tester and Taber abrasion tester. r 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Radiation curing technology; Nanocomposites

1. Introduction

There has been recently a strong and increasing

demand for scratch and abrasion resistance of the

coating materials that can be applied to various

substrates such as wood, plastic, metal and glass

products. For example, plastics have been widely used

as motor vehicle parts, optical lenses, optical disks,

signboards etc. due to their characteristic features such

as lightness, toughness, easy processing and low

production costs. However, they are vulnerable to

scratch and also have poor abrasion property. In order

to improve scratch and abrasion resistance of plastic

surfaces, radiation curing coatings have been utilized

widely.

The advantages of radiation curing technology

relative to conventional drying techniques are set out

below (Allen and Edge, 1990; Holman and Oldring,

1988; Stott, 1995):

1. Consist of 100% solids contentFno solvent emis-

sion.

2. Fast curing and processingFhigh production speeds.

3. Improved product characteristicsFexcellent film

properties.

4. Low temperature cureFgenerally heat sensitive

substrates can be coated.

5. Energy efficientFreduces energy consumption.

6. Low environmental pollution by eliminating volatile

organic compounds (VOC) to the atmosphere and

improve air quality.

In the fabrication of polymeric nanocomposites by

radiation curing, a considerable progress has been

achieved in the field of nanotechnology related to

studies of using organic and inorganic nanopowders.

So far, the modification effects like glass temperature

shifts of about 10 K and pronounced mechanical

reinforcement was observed only in the softening range*Corresponding author. Fax: +603-892-02968.

E-mail address: nik ghazali@mint.gov.my (N.G. Salleh).

0969-806X/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved.

PII: S 0 9 6 9 - 8 0 6 X ( 0 1 ) 0 0 5 4 2 - 4

(Landry and Coltrain, 1994; Lan and Pinnavaia, 1994;

Dufresne et al., 1996a,b).

2. Experimental

2.1. Materials

The acrylates such as tri(2-hydroxyethyl)isocyanurate

triacrylate (SR 368), aromatic urethane diacrylate (CN

976), ethoxylated pentaerythritol tetraacrylate (Sarto-

mer 494), ethoxylated trimethylolpropane triacrylate

(SR 454) and modified pentaerythritol triacrylate (SR

444) were obtained from Cray Valley, France. Other

acrylates such as 1,6-hexanediol diacrylate (HDDA),

pentaerythritol triacrylate and tetraacrylate (PETIA),

tetrafunctional polyester acrylate (IRR 443), aromatic

urethane triacrylate IRR 450(Radiation curable Protec-

tive Coatings: Technical Information on Wood Pro-

ducts), hexafunctional aliphatic urethane acrylate

(EB1290), aliphatic urethane triacrylate with 15%

HDDA (EB 264), dipropylene glycol diacrylate

(DPGDA), acrylated trifunctional oligomer (OTA 480)

and acrylated tetrafunctional oligomer (EB 40) were

obtained from UCB Chemicals, Belgium.

4-hydroxyanisole or 4-methoxyphenol was of gas

chromatography (GC) grade quality and used as a

stabilizer. Meanwhile, maleic anhydride was of analar

grade quality and used as a catalyst in the heterogeneous

condensation reaction. Both chemicals were obtained

from Sigma-Aldrich Chemical Company Limited, UK.

All the nanoparticles of silicium dioxide such as

AEROSIL OX50 used in this work were obtained from

Degussa-H .uls AG, Germany. They were normally used

as fillers for polymer reinforcement and scratch resistant

coatings. Meanwhile, the silanes such as VTMOS and

PTMOS were obtained from the same manufacturer and

used as coupling agent.

Finally, most of the photoinitiators such as Darocur

1173, Darocur 4265 and Irgacure 500 used in the

ultraviolet (UV) curing were obtained from Ciba

Specialty Chemicals Inc., Switzerland.

2.2. Preparation of silico-organic nanoparticles

Siloxane methacrylate (SIMA) nanoparticles from the

silica/acrylate systems were synthesized in a small batch

reactor. Maleic anhydride, dissolved in water, was

introduced in a mixture of several acrylates and 4-

methoxyphenol. The coupling agent such as VTMOS

was added within 30min. Finally, nano-sized silica

particles such as AEROSIL were dispersed under

intensive stirring during 1–2 h using a Dispermat

dissolver. The process for preparing these SIMA

nanoparticles is proton catalyzed and efficiently pro-

ceeds at 651C. Thereafter, the product was immediately

cooled to room temperature.

2.3. Preparation of polymeric nanocomposites by

radiation curing

The polymeric nanocomposite materials were pre-

pared basically from several acrylates and AEROSIL

OX50. These materials were coated on different types of

substrates such as paper, polyvinyl chloride (PVC),

polycarbonate (PC) and wood based panels using

automatic film applicator to give a thickness of 50 mm.

They were cured using a low energy electron beam

accelerator (EB) with dose of 50 kGy. Furthermore, in

spite of relatively high nanopowder content in the

nanodispersions, UV induced polymerization with the

aid of conventional mercury lamps proved to be an

efficient alternative to EB curing (Mehnert et al., 1998).

During irradiation, the chambers were degassed by inert

gas such as nitrogen. Films of radiation cured nano-

composite materials were characterized by several

methods such as scratch test and Taber abrasion test.

3. Results and discussion

Silico-organic nanoparticles have relatively large sur-

face areas than microparticles, therefore modification

effects from the polymerization activity should have a

great influence to the properties of the composites. In

these investigations, we use radiation such as ultraviolet

and electron beam to initiate polymerization and

interaction at the interface between the nanoparticles

and the monomeric materials. These polymerization

active nanoparticles were obtained by heterogeneous

hydrolytic condensation of the silane to the silanol

groups of the AEROSIL OX50 particles. The in situ

reaction is proton catalyzed and efficiently proceeds at

701C.

The above reaction could be verified by the applica-

tion of FT-Raman spectroscopy (intensity measure-

ments of the C¼C vibration band at 1640 cm�1) and gel

permeation chromatography to show that the polymer-

ization activity of the nanoparticles imparts to the silico/

acrylate dispersion (Gl.asel et al., 1999). In the curing

process, the nanoparticles form crosslinkages to produce

radiation-cured polymeric composites with improved

scratch and abrasion resistance.

In Table 1, the coating materials of Lack 1�5 exhibit

excellent property toward abrasion resistance compared

to Lack 6�8. There was no significant change in the

Taber abrasion data by changing acrylates such as from

CN 936 to CN 976 (aromatic) at the same amount of

compositions. Furthermore, these formulations consist

of a high degree crosslinking from a mixture of

pentaerythritol tri- and tetraacrylate (PETIA). In the

N.G. Salleh et al. / Radiation Physics and Chemistry 63 (2002) 475–479476

case of Lack 6, it exhibits better abrasion resistance by

curing with UV light rather than electron beam

irradiation. In the above formulation, one of the

materials used i.e. IRR 450 was reported by UCB

Radcure (http://www.chemicals.ucb-group.com, 2001)

to be a relatively soft and flexible product. The

mechanical properties of this material cured by EB with

100mm film thickness was 31% elongation and 11.8MPa

tensile strength.

In order to find the best mixture of oligomer and

monomer in the formulations, several combinations

were made using CN 936 and HDDA as shown in

Table 2. The coating materials were cured by UV light

using two sets of photoinitiators. Mixture of CN 936

and HDDA in the ratio 20:80 exhibits better combina-

tion in term of abrasion resistance compare to others.

Similar results were obtained by using the two sets of

photoinitiators as shown in Table 2.

Mixture of CN 936 and HDDA in the ratio 20:80 was

applied to synthesize Lack 9 using 35% AEROSIL

OX50 and 17.5% PTMOS. The abrasion resistance of

the polymeric nanocomposite was enhanced nearly

double as shown in Table 3. By reducing the amount

of nanoparticles and increasing the amount of acrylates

in the formulations, abrasion resistance of the compo-

sites using PTMOS was lower than the materials

prepared via VTMOS. This example was shown clearly

by Lack 11 and Lack 1, respectively.

Some modification has been made in the preparation

of polymer composites by using microparticles (HK 125)

instead of nanoparticles (AEROSIL OX50) as shown in

Table 4. The abrasion resistance of Lack 13 is slightly

lower than Lack 1 by using VTMOS in the silica/arylates

system. On the other hand, Lack 15 shows some

improvement in the abrasion resistance compared to

Lack 12 at similar composition using PTMOS.

Table 5 exhibits the abrasion property of polymeric

nanocomposites and pure acrylates. All the pure

acrylates have relatively low resistance to abrasion

property but good reactivity toward UV curing. With

addition of 30% AEROSIL OX50, 9% VTMOS and

61% acrylates, the nanocomposite materials improved

their abrasion property tremendously particularly by

curing with UV.

Furthermore, the addition of Lanco-wax into the first

formulation i.e. Lack 1 was aimed to increase the

abrasion resistance of the polymeric composites. From

Table 6, it was found that the coating material with

1.5% of Lanco-Wax TF 1780 show excellent resistance

to abrasion.

Finally, the performance of these composites is also

related other factors such as resistance to scratch. Two

Table 1

Abrasion resistance of the nanocomposites at 50 mm coating thickness using paper as a substrate and various type of acrylates

Lacquers Compositions Weight lost from Taber abrasion (mg)

UV irradiation EB irradiation

Lack 1 26.4% AEROSIL OX50/11.8% CN936/35.4% PETIA/26.4%

VTMOS

11.9 11.9

Lack 2 26.4% AEROSIL OX50/11.8% CN976/ 35.4% PETIA/ 26.4%

VTMOS

F 9.7

Lack 3 26.4% AEROSIL OX50/35.4% PETIA/1.2% SR368/4.7% EB1290/

5.9% CN936/26.4% VTMOS

8.5 7.4

Lack 4 26.4% AEROSIL OX50/35.4% PETIA/ 1.2% SR368/4.7% EB1290/

5.9% CN976/26.4% VTMOS

7.1 8.1

Lack 5 26.4% AEROSIL OX50/30% PETIA/6.6% SR368/4.7% EB1290/

5.9% CN976/26.4% VTMOS

11.8 11.9

Lack 6 26.4% AEROSIL OX50/34.7% IRR450/12.5% IRR443/26.4%

VTMOS

23.8 61.9

Lack 7 4.2% AEROSIL OX50/32.6% WKP-TiO2/30.6% SR454/32.6%

VTMOS

F 36.3

Lack 8 34% WKP-TiO2/13.3% HDDA/18.7% SR454/34% VTMOS F 40.6

Table 2

Data of abrasion resistance from the mixtures of CN 936 and

HDDA with films of 50mm thickness and cured by UV

irradiation

Mixtures of

CN 936:HDDA

Weight loss from Taber abrasion (mg)

I II

(2% DC 4265+

1% IC 500)

(1.5% DC 1173+

2% IC 500)

20:80 77.2 72.7

30:70 81.8 81.6

40:60 86.1 88.4

50:50 84.8 86.6

60:40 82.4 85.0

N.G. Salleh et al. / Radiation Physics and Chemistry 63 (2002) 475–479 477

types of needles were used for determining the resis-

tance of a single coat system of the composites to

penetration by scratching either with a diamond tip

or a steel ball (spherically tipped needle). The

method used was by applying increasing loads to the

needle to determine the minimum load at which

the coating was penetrated. In Table 7, most of the

composites exhibit excellent resistance to scratch

property except for Lack 19, which has slightly lower

value.

Table 3

Abrasion resistance of the polymeric nanocomposites with film thickness of 50mm

Lacquers Compositions Weight lost from Taber abrasion (mg)

UV irradiation EB irradiation

Lack 9 35% AEROSIL OX50/38% HDDA/9.5% CN936/17.5% PTMOS 39.4 FLack 10 30% AEROSIL OX50/27.5% HDDA/27.5% EB264/15% PTMOS F 45.2

Lack 11 25.6% AEROSIL OX50/11.5% CN936/34.4% PETIA/28.5% PTMOS 39.4 37.0

Lack 12 25.7% AEROSIL OX50/16% CN936/48% PETIA/10.3% PTMOS 17.8 F

Table 4

Abrasion resistance of the polymeric microcomposites with film thickness of 50mm

Lacquers Compositions Weight lost from Taber abrasion (mg)

UV irradiation EB irradiation

Lack 13 26.4% HK125/35.4% PETIA/11.8% CN936/26.4% VTMOS 15.3 15.1

Lack 14 22.2% HK125/55.6% SR494/22.2% VTMOS 17.8 22.3

Lack 15 25.7% HK125/16% CN936/48% PETIA/10.3% PTMOS 12.8 21.0

Lack 16 25% HK125/62.5% SR494/12.5% DYNASYLAN MEMO 20.9 21.2

Table 5

Abrasion resistance of the polymeric nanocomposites and pure acrylates with film thickness of 50 mm

Lacquers Compositions Weight lost from Taber abrasion (mg)

UV irradiation EB irradiation

DPGDA 100% DPGDA 46.3 FOTA 480 100% OTA 480 65.5 FEB 40 100% EB 40 55.7 FLack 17 30% AEROSIL OX50/61% EB 40/9% VTMOS 13.7 30.8

Lack 18 30% AEROSIL OX50/61% OTA 480/9% VTMOS 20.7 30.1

Lack 19 30% AEROSIL OX50/61% DPGDA/9% VTMOS 22.5 31.2

Table 6

Addition of several additives into Lack 1 (formulation)

Percentage of additives Weight loss from Taber abrasion (mg)

Lack 1 with 2.5% Lanco-Wax PE 1544F 17.0

Lack 1 with 1.5% Lanco-Wax PE 1500SF 14.7

Lack 1 with 1.5% Lanco-Wax TF 1780 9.4

Lack 1 with 2.0% Lanco-Wax D2S 13.5

Lack 1 with 1.5% Lanco-Wax TF 1778 15.5

N.G. Salleh et al. / Radiation Physics and Chemistry 63 (2002) 475–479478

4. Conclusions

Polymerization active silico-organic nanoparticles

could be prepared by heterogeneous condensation (in

situ reaction) and formed crosslinks in the polymeric

substrates. These polymeric nanocomposites were cured

by the low energy EB accelerator. However, with a

relatively high nanopowder content of the nanodisper-

sions, UV induced polymerization proved to be an

efficient alternative to electron beam curing. These

materials show excellent resistances toward scratch and

abrasion properties as compared to pure acrylates.

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Table 7

Scratch resistance of the polymeric composites with film thickness of 50 mm

Type of needles for scratch test Lack Pure acrylates

1 9 16 17 18 19 DPGDA OTA 480 EB 40

Diamond tip 901/N 3.0 3.0 3.0 3.0 3.0 2.0 3.0 3.0 3.0

Steel ball Diameter 1mm/N >10 10 >10 >10 >10 >10 >10 >10 >10

N.G. Salleh et al. / Radiation Physics and Chemistry 63 (2002) 475–479 479