- Email: [email protected]
UV treatment of protective coatings for porous materials
Radiation Physics and Chemistry 57 (2000) 393±397
www.elsevier.com/locate/radphyschem
EB/UV treatment of protective coatings for porous materials E. Bemporad a,*, F. Carassiti a, A. Tata b, G. Gallinaro c, M. Paris d a
University of Rome TRE, Via Vasca Navale 79, 00146, Rome, Italy ENEA, Innovation Departmento, C.R. Casaccia, P.O. Box 2400, Rome, Italy c IVECO SpA, Lungo Stura Lazio 49, 10156, Turin, Italy d UNICEM SpA, Centro Ricerche, Via S. Angelo Romano 14, 00012, Guidonia, Rome, Italy b
Abstract A method for improving surface properties of porous inorganic materials is presented. The method is particularly tailored to cement-based materials in order to obtain properties suitable for mechanical applications such as dies manufacturing, where hardness, abrasion resistance and low friction are requested. The coating system is based upon using two coatings of dierent characteristics. The underlying base coating layer is in®ltrated in air on three dierent formulations of hardened cement composite. Two dierent bi-component resins, one relatively soft and the other relatively hard, were tested as underlying surface coating. The outer surface coating, based upon a bicomponent resin characterized by high hardness, is added after hardening and curing of the ®rst layer. Both coatings were chemically hardened and then cured with EB. UV curing is also suitable for the outer surface coating. An experimental campaign was carried out in order to evaluate the in¯uence of radiation processing as curing treatment with reference to particular investigated materials. Hardness and resistance to peeling of coating systems have been measured and are presented. 7 2000 Published by Elsevier Science Ltd. All rights reserved. Keywords: Curing; Coatings; Cement composite; Dies; EB treatment
1. Introduction Moulding technologies of thermoplastic or thermosetting resins usually require very expensive equipment. Manufacturing of dies is concerned with the availability of very skilled manpower; manufacturing also requires a long time to market. Rapid prototyping and rapid tooling are also dicult to use in die manufacturing because of the high tolerance limit requested. The introduction of cement-matrix-based dies is cur-
* Corresponding author.
rently in development in order to allow advanced forming technologies to take place. Cement-based dies are cheap, show adequate mechanical resistance and hardness, but the surface is highly abrasive. A surface modi®cation characterized by lower friction coecient, equivalent hardness and low wear is a sound option to allow cement-based dies to be adopted. However, a cement surface modi®cation process of industrial interest for dies application in the ®eld of thermoplastics or thermosetting is not yet mature. A new surface treatment has been set up, taking into consideration previous experiences (Hodnett, 1992; Holl, 1995; Morohashi et al., 1981; Shiryaeva et al.,
0969-806X/00/$ - see front matter 7 2000 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 9 9 ) 0 0 4 4 7 - 8
394
E. Bemporad et al. / Radiation Physics and Chemistry 57 (2000) 393±397
Table 1 Cement composite formulationsa Cement composite type Components
KN
KD5
KDF
Mixture of hydraulic binders (%) Siliceous aggregates (%) Metallic aggregates (%) Proprietary additives (%) Water (%) Water/binders ratio
22.2 66.7 ± ± 11.1 0.50
25.5 63.6 ± 1.8 9.1 0.36
17.9 4.2 70.8 1.4 5.7 0.32
a
UNICEM/IVECO, proprietary.
1995), tailored to proprietary cement composites developed for dies by UNICEM and IVECO. Commercial bi-component resins, developed for other purposes, become suitable for hardened cement composite surface modi®cation when EB secondary curing is taken into consideration in order to obtain improved properties. EB curing, after chemical hardening, is likely to enhance cross-linking in the resins and improve adhesion of the ®rst coating with the substrate, as well as between the coatings. UV curing in air at room temperature, together with chemical hardening (Cantor, 1994), resulted in a suitable repair to the scars on outermost surface coatings which could take place in operation.
2. Experimental Cement composite prisms measuring 40 40 Table 2 Dosesa and resinsb 1st coating (inner)
2nd coating (outer)
Sample
Dosea
Resin system 1b
Dosea
Resin system 2b
1 2 3 4 5 6 7 8 9
High High Low Low High High Low Low ±
Polyurethane Polyurethane Polyurethane Polyurethane Acrylic1 Acrylic1 Acrylic1 Acrylic1 ±
High Low High Low High Low High Low ±
Acrylic2 Acrylic2 Acrylic2 Acrylic2 Acrylic2 Acrylic2 Acrylic2 Acrylic2 ±
a
Dose: High=7.5+7.5 kGy; low=7.5 kGy. Resins: acrylic1=hydroxylated acrylic, isocyanate (Matsunaga et al., 1999); acrylic2=melamine acrylic, isocyanate (Noritake et al., 1999 Ð Decker et al., 1996); polyurethane=polyurethane, isocyanate (Schwartz et al., 1997). b
160 mm3 were prepared by UNICEM, based upon proprietary (UNICEM/IVECO) formulation, shown in Table 1. The utilized irradiation facility has been the Hitesys Co. (Aprilia, Rome) plant; the main EB machine (LINAC type, s-band) features are: energy in the 4 to 10 MeV range, mean beam current of 0.1 mA, pulse frequency of 0±300 Hz and beam power (max) of 1 kW (Tata et al., 1998). The experimental campaign was planned considering a matrix (see Table 2) of three cement composite formulations, two types of resins for inner coating and one resin for the outer coating. Radiation processing was performed considering two dierent absorbed doses (7.5 kGy in one irradiation or 15 kGy in two irradiations). The experiments were carried out as follows. The cement composite prisms were soaked with resin system 1 in air at room temperature. The impregnated resin was chemically hardened (by reaction of the isocyanate for 24 h), irradiated at doses as reported in Table 2 (column 1). The prisms were then aged, soaked with resin system 2, brushed; the resin ®lm was chemically hardened, irradiated again at doses reported in Table 2 (column 4). The irradiation process was performed in steps: all the prisms were treated with a ®rst step of 7.5 kGy for each coating (`low' dose). The second step of additional 7.5 kGy was performed for each coating only on the samples marked `high'. The resulting eects were characterized by the Rockwell hardness test (P-scale 14 0, 150 Kg) and tape peeling for testing adhesion of the outer surface coating layer. The friction coecient was nearly the same for all the coating systems, with lower dose of about 30% with respect to the bare cement composite surface.
3. Results and conclusions The main results can be summarized as follows: . hardness of coated samples is no lower than the hardness of bare cement composite only in the case of KN and KDF formulation, treated with high doses to both inner and outer coatings and when the inner coating (resin system 1) is based upon polyurethane; . resistance to peeling is better in the case of KDF formulation, treated with high doses to both inner and outer coatings and when the inner coating (resin system 1) is based upon polyurethane; . the EB treatment in¯uences both hardness and adhesion, but not friction; . the formulation of cement composite in¯uences the eectiveness of treatments;
E. Bemporad et al. / Radiation Physics and Chemistry 57 (2000) 393±397
. when the inner surface coating (resin system 1) is based upon hydroxylated acrylic±isocyanate, the radiation treatment is less eective for KN and KD5, but not nearly eective for KDF; . the outer coating could be repaired by UV treatment by adding a proper photo-initiator (liquid mixture of an oligomeric hydroxy ketone and hydroxy methyl phenyl propane); . sliding causes the outer coating to form non-abrasive debris; . Rockwell indentation marks, analysed by scanning electron microscopy (SEM), show coating thicknesses of about 10 mm for the inner coating and 20 mm for the outer coating; . when the inner coating is based upon acrylic resin, the indentation marks show brittle cracks. In Fig. 1 (left column) are reported the results of hard-
395
ness testing of the resins identi®ed in Table 2. The ordinate shows the measured value in the Rockwell scale `P' (steel ball b 14 0, load 150 kg). The right column of Fig. 1 shows the results of peel testing of the resins identi®ed in Table 2. The ordinate shows the fraction of surface which suered coating removal by tape. For all graphs the abscissa shows the number of the sample as identi®ed in Table 2. The header of each ®gure is referred to cement composite type, as shown in Table 1. Figs. 2 and 3 show the SEM image of samples KDF1 and KDF5, respectively. It is possible to notice the thickness of both coatings and the dierent damage caused by the hardness test. Sample KDF1 (which demonstrates the best properties) shows that the coatings did not suer debonding from cement substrate and between each other. Sample KDF5 shows that the coatings suered sliding and then jus-
Fig. 1. Rockwell hardness and peel testing (see text for details).
396
E. Bemporad et al. / Radiation Physics and Chemistry 57 (2000) 393±397
Fig. 2. KDF1 SEM image (1050) of the cracked surface after the Rockwell hardness test.
Fig. 3. KDF5 SEM image (450) of the cracked surface after the Rockwell hardness test.
E. Bemporad et al. / Radiation Physics and Chemistry 57 (2000) 393±397
tify minor resistance to peeling and minor protection of the substrate.
References Cantor, S.E., 1994. One part, room temperature, shadow-curing UV conformed coatings. Radiation Curing 21 (2), 10± 16. Decker, C., et al., 1996. Performance analysis of thermosetting polymers and radiation cured coatings. Polym. Mater. Sci. Eng. 75, 124±125. Hodnett, W.P. 1992. Protective coatings system for imparting resistance to abrasion, impact and solvents. US Patent 5,114,783. 12 May, 1992 (with 27 references). Holl, P., 1995. Two ideal applications for the low energy EB accelerator: vulcanization of pressure sensitive adhesives and controlled through-curing of coatings on parquet. Rad. Phys. Chem. 46 (46), 979±982.
397
Matsunaga, S. et al. 1999. Coating composition curable by irradiation. JP Patent 49047254 (quest accession number 83:81499 G Ð 1999). Morohashi, Y. et al. 1981. Method for improving surface properties of porous inorganic material by coating. US Patent 4,269,869. 26 May, 1981 (with 9 references). Noritake, Y. et al. 1999. Method for modi®cation of coating surface. JP Patent 96-339574 (quest accession number 127:235748 G Ð 1999). Schwartz, M. et al. 1997. Use of radiation curable composition and method for coating molded mineral binder containing products. DE Patent 97-19732621. 29 July, 1997. Shiryaeva, G.V., et al., 1995. Application of UV/EB cured coatings to dierent substrates. Rad. Phys. Chem. 46 (46), 995±998. Tata, A., et al., 1998. A new irradiation plant in Italy: technical features and activities performed. Rad. Phys. Chem. 52 (16), 465±468.
www.elsevier.com/locate/radphyschem
EB/UV treatment of protective coatings for porous materials E. Bemporad a,*, F. Carassiti a, A. Tata b, G. Gallinaro c, M. Paris d a
University of Rome TRE, Via Vasca Navale 79, 00146, Rome, Italy ENEA, Innovation Departmento, C.R. Casaccia, P.O. Box 2400, Rome, Italy c IVECO SpA, Lungo Stura Lazio 49, 10156, Turin, Italy d UNICEM SpA, Centro Ricerche, Via S. Angelo Romano 14, 00012, Guidonia, Rome, Italy b
Abstract A method for improving surface properties of porous inorganic materials is presented. The method is particularly tailored to cement-based materials in order to obtain properties suitable for mechanical applications such as dies manufacturing, where hardness, abrasion resistance and low friction are requested. The coating system is based upon using two coatings of dierent characteristics. The underlying base coating layer is in®ltrated in air on three dierent formulations of hardened cement composite. Two dierent bi-component resins, one relatively soft and the other relatively hard, were tested as underlying surface coating. The outer surface coating, based upon a bicomponent resin characterized by high hardness, is added after hardening and curing of the ®rst layer. Both coatings were chemically hardened and then cured with EB. UV curing is also suitable for the outer surface coating. An experimental campaign was carried out in order to evaluate the in¯uence of radiation processing as curing treatment with reference to particular investigated materials. Hardness and resistance to peeling of coating systems have been measured and are presented. 7 2000 Published by Elsevier Science Ltd. All rights reserved. Keywords: Curing; Coatings; Cement composite; Dies; EB treatment
1. Introduction Moulding technologies of thermoplastic or thermosetting resins usually require very expensive equipment. Manufacturing of dies is concerned with the availability of very skilled manpower; manufacturing also requires a long time to market. Rapid prototyping and rapid tooling are also dicult to use in die manufacturing because of the high tolerance limit requested. The introduction of cement-matrix-based dies is cur-
* Corresponding author.
rently in development in order to allow advanced forming technologies to take place. Cement-based dies are cheap, show adequate mechanical resistance and hardness, but the surface is highly abrasive. A surface modi®cation characterized by lower friction coecient, equivalent hardness and low wear is a sound option to allow cement-based dies to be adopted. However, a cement surface modi®cation process of industrial interest for dies application in the ®eld of thermoplastics or thermosetting is not yet mature. A new surface treatment has been set up, taking into consideration previous experiences (Hodnett, 1992; Holl, 1995; Morohashi et al., 1981; Shiryaeva et al.,
0969-806X/00/$ - see front matter 7 2000 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 9 9 ) 0 0 4 4 7 - 8
394
E. Bemporad et al. / Radiation Physics and Chemistry 57 (2000) 393±397
Table 1 Cement composite formulationsa Cement composite type Components
KN
KD5
KDF
Mixture of hydraulic binders (%) Siliceous aggregates (%) Metallic aggregates (%) Proprietary additives (%) Water (%) Water/binders ratio
22.2 66.7 ± ± 11.1 0.50
25.5 63.6 ± 1.8 9.1 0.36
17.9 4.2 70.8 1.4 5.7 0.32
a
UNICEM/IVECO, proprietary.
1995), tailored to proprietary cement composites developed for dies by UNICEM and IVECO. Commercial bi-component resins, developed for other purposes, become suitable for hardened cement composite surface modi®cation when EB secondary curing is taken into consideration in order to obtain improved properties. EB curing, after chemical hardening, is likely to enhance cross-linking in the resins and improve adhesion of the ®rst coating with the substrate, as well as between the coatings. UV curing in air at room temperature, together with chemical hardening (Cantor, 1994), resulted in a suitable repair to the scars on outermost surface coatings which could take place in operation.
2. Experimental Cement composite prisms measuring 40 40 Table 2 Dosesa and resinsb 1st coating (inner)
2nd coating (outer)
Sample
Dosea
Resin system 1b
Dosea
Resin system 2b
1 2 3 4 5 6 7 8 9
High High Low Low High High Low Low ±
Polyurethane Polyurethane Polyurethane Polyurethane Acrylic1 Acrylic1 Acrylic1 Acrylic1 ±
High Low High Low High Low High Low ±
Acrylic2 Acrylic2 Acrylic2 Acrylic2 Acrylic2 Acrylic2 Acrylic2 Acrylic2 ±
a
Dose: High=7.5+7.5 kGy; low=7.5 kGy. Resins: acrylic1=hydroxylated acrylic, isocyanate (Matsunaga et al., 1999); acrylic2=melamine acrylic, isocyanate (Noritake et al., 1999 Ð Decker et al., 1996); polyurethane=polyurethane, isocyanate (Schwartz et al., 1997). b
160 mm3 were prepared by UNICEM, based upon proprietary (UNICEM/IVECO) formulation, shown in Table 1. The utilized irradiation facility has been the Hitesys Co. (Aprilia, Rome) plant; the main EB machine (LINAC type, s-band) features are: energy in the 4 to 10 MeV range, mean beam current of 0.1 mA, pulse frequency of 0±300 Hz and beam power (max) of 1 kW (Tata et al., 1998). The experimental campaign was planned considering a matrix (see Table 2) of three cement composite formulations, two types of resins for inner coating and one resin for the outer coating. Radiation processing was performed considering two dierent absorbed doses (7.5 kGy in one irradiation or 15 kGy in two irradiations). The experiments were carried out as follows. The cement composite prisms were soaked with resin system 1 in air at room temperature. The impregnated resin was chemically hardened (by reaction of the isocyanate for 24 h), irradiated at doses as reported in Table 2 (column 1). The prisms were then aged, soaked with resin system 2, brushed; the resin ®lm was chemically hardened, irradiated again at doses reported in Table 2 (column 4). The irradiation process was performed in steps: all the prisms were treated with a ®rst step of 7.5 kGy for each coating (`low' dose). The second step of additional 7.5 kGy was performed for each coating only on the samples marked `high'. The resulting eects were characterized by the Rockwell hardness test (P-scale 14 0, 150 Kg) and tape peeling for testing adhesion of the outer surface coating layer. The friction coecient was nearly the same for all the coating systems, with lower dose of about 30% with respect to the bare cement composite surface.
3. Results and conclusions The main results can be summarized as follows: . hardness of coated samples is no lower than the hardness of bare cement composite only in the case of KN and KDF formulation, treated with high doses to both inner and outer coatings and when the inner coating (resin system 1) is based upon polyurethane; . resistance to peeling is better in the case of KDF formulation, treated with high doses to both inner and outer coatings and when the inner coating (resin system 1) is based upon polyurethane; . the EB treatment in¯uences both hardness and adhesion, but not friction; . the formulation of cement composite in¯uences the eectiveness of treatments;
E. Bemporad et al. / Radiation Physics and Chemistry 57 (2000) 393±397
. when the inner surface coating (resin system 1) is based upon hydroxylated acrylic±isocyanate, the radiation treatment is less eective for KN and KD5, but not nearly eective for KDF; . the outer coating could be repaired by UV treatment by adding a proper photo-initiator (liquid mixture of an oligomeric hydroxy ketone and hydroxy methyl phenyl propane); . sliding causes the outer coating to form non-abrasive debris; . Rockwell indentation marks, analysed by scanning electron microscopy (SEM), show coating thicknesses of about 10 mm for the inner coating and 20 mm for the outer coating; . when the inner coating is based upon acrylic resin, the indentation marks show brittle cracks. In Fig. 1 (left column) are reported the results of hard-
395
ness testing of the resins identi®ed in Table 2. The ordinate shows the measured value in the Rockwell scale `P' (steel ball b 14 0, load 150 kg). The right column of Fig. 1 shows the results of peel testing of the resins identi®ed in Table 2. The ordinate shows the fraction of surface which suered coating removal by tape. For all graphs the abscissa shows the number of the sample as identi®ed in Table 2. The header of each ®gure is referred to cement composite type, as shown in Table 1. Figs. 2 and 3 show the SEM image of samples KDF1 and KDF5, respectively. It is possible to notice the thickness of both coatings and the dierent damage caused by the hardness test. Sample KDF1 (which demonstrates the best properties) shows that the coatings did not suer debonding from cement substrate and between each other. Sample KDF5 shows that the coatings suered sliding and then jus-
Fig. 1. Rockwell hardness and peel testing (see text for details).
396
E. Bemporad et al. / Radiation Physics and Chemistry 57 (2000) 393±397
Fig. 2. KDF1 SEM image (1050) of the cracked surface after the Rockwell hardness test.
Fig. 3. KDF5 SEM image (450) of the cracked surface after the Rockwell hardness test.
E. Bemporad et al. / Radiation Physics and Chemistry 57 (2000) 393±397
tify minor resistance to peeling and minor protection of the substrate.
References Cantor, S.E., 1994. One part, room temperature, shadow-curing UV conformed coatings. Radiation Curing 21 (2), 10± 16. Decker, C., et al., 1996. Performance analysis of thermosetting polymers and radiation cured coatings. Polym. Mater. Sci. Eng. 75, 124±125. Hodnett, W.P. 1992. Protective coatings system for imparting resistance to abrasion, impact and solvents. US Patent 5,114,783. 12 May, 1992 (with 27 references). Holl, P., 1995. Two ideal applications for the low energy EB accelerator: vulcanization of pressure sensitive adhesives and controlled through-curing of coatings on parquet. Rad. Phys. Chem. 46 (46), 979±982.
397
Matsunaga, S. et al. 1999. Coating composition curable by irradiation. JP Patent 49047254 (quest accession number 83:81499 G Ð 1999). Morohashi, Y. et al. 1981. Method for improving surface properties of porous inorganic material by coating. US Patent 4,269,869. 26 May, 1981 (with 9 references). Noritake, Y. et al. 1999. Method for modi®cation of coating surface. JP Patent 96-339574 (quest accession number 127:235748 G Ð 1999). Schwartz, M. et al. 1997. Use of radiation curable composition and method for coating molded mineral binder containing products. DE Patent 97-19732621. 29 July, 1997. Shiryaeva, G.V., et al., 1995. Application of UV/EB cured coatings to dierent substrates. Rad. Phys. Chem. 46 (46), 995±998. Tata, A., et al., 1998. A new irradiation plant in Italy: technical features and activities performed. Rad. Phys. Chem. 52 (16), 465±468.