| 5G communication technology has the virtues of extremely high transmission rate,extremely low delay and large transmission capacity,thus opening the era of"internet of everything".The high-frequency substrate material is the key component of 5G communication technology,and it mainly dominates the properties of 5G communication technology.In order to ensure the stability of signal transmission and avoid signal attenuation,the high-frequency substrate material is required to have lower dielectric constant and dielectric loss,and required stable dielectric properties in a wide frequency range.Polyolefin resin owns the advantages of low dielectric constant and low dielectric loss,which had the potential to replace PTFE resin,epoxy resin and other materials,and it could be applied in the field of high frequency substrate materials.At present,the RO4000?series from Rogers company is the main high-frequency substrate material of polyolefin resin on the market.The demand for these materials in China is completely dependent on imports,and the related research is still in its early stages.Therefore,the research on polyolefin-based composite dielectric materials have important scientific significance and potential application value.Polybutadiene(PB),styrene-butadiene copolymer(SBS)and ethylene-propylene-diene rubber(EPDM)were selected as the matrix resin,and silicon dioxide(SiO2)as the filler.The properties of polyolefin resin and its composites filled with SiO2 particles depended on the composition of resin,crosslinking reaction and interfacial interaction were detailedly studied in this dissertation.(1)The properties of PB/SBS/EPDM ternary composite resins were investigated.Firstly,the effect of the composition of resins on the properties of ternary composite resins were explored.The research results showed that the composite resin with PB content of100 parts,EPDM content of 15 parts and SBS content of 30 parts has the excellent mechanical properties,and its tensile strength is determined up to 8.72 MPa.Then,the effect of vinyl content in PB on the crosslinking reaction and the properties of the cured products were explored.It is found that the cross-linking reactivity is improved with the increase of vinyl content in PB.Besides,the degree of crosslinking,dielectric properties and volume resistivity of the ternary composites increased with the increase of vinyl content in PB.In the case of the same resin composition,the composite resin corresponding to PB90 exhibits a dielectric constant of 2.68 at 10 GHz,a dielectric loss of 0.0071 at 10 GHz and a volume resistivity of 11.68×1013?cm.In the subsequent research,the PB(90%1,2-vinyl)was selected as the resin matrix of the substrate material.(2)Effects of peroxide initiators on properties of ternary composite resin materials were also investigated.The peroxide initiator has a significant effect on the crosslinking reaction and the structure and properties of the cured product,so the effect of the type and content of peroxide initiators on the properties of the PB/SBS/EPDM composite resins were explored in the following work.Two structurally different organic peroxides,namely dicumyl peroxide(DCP)and bis(1-(tert-butylperoxy)-1-methylethyl)-benzene(BIPB),were used as peroxide initiators.Comparing to the peroxide-free system,DCP-cured system and BIPB-cured system yield better reactivity.Moreover,the effect of the BIPB-cured system is more obvious comparing with the DCP-cured system under the same content.After the thermal crosslinking reaction,PB/SBS/EPDM composites form a highly crosslinked network structure,which can significantly improve the thermal,mechanical and dielectric properties of the composites.The optimization results showed that the PB/SBS/EPDM composite has the remarkable comprehensive performance when the content of BIPB is 4 parts by weight(pbw),the dielectric constant is 2.37 and the dielectric loss is 0.0056 at 10 GHz.(3)The effects of surface modification of prepregs and PB content on the T-peel strength and dielectric properties of copper clad laminates(CCLs)were further investigated.The PB/SBS/EPDM(mass ratio of 6:2:1)prepreg was immersed in permanganate solution for 30 minutes and then prepared polyolefin CCLs by hot pressing process(P6-ox-30).Polar functional groups were successfully introduced onto the surface of polyolefin prepreg through oxidation treatment with permanganate solution,which was mainly attributed to the strong interfacial interaction between the polyolefin matrix and the copper foil.The T-peel strength of the P6-ox-30 sample was about 4 times that of the untreated sample.In addition,the effect of surface modification on the dielectric properties of CCL is not obvious.It is proved that the surface modification of prepregs can improve the T-peel strength of the CCL while ensuring the excellent dielectric properties.When the mass ratio of PB/SBS/EPDM is 8:2:1,the T-peel strength,dielectric constant and dielctrioc loss of the CCLs is decreased.The results showed that the P6-ox-30 sample has the optimal comprehensive performance,the dielectric constant and dielectric loss are 2.35 and 5.38×10-3 at 10 GHz,respectively,the T-peel strength is 20-25 N/25mm.(4)Influence of SiO2 surface modification and filling content of SiO2 particles on the dielectric properties of polyolefin/SiO2 CCLs is explored.SiO2 surface was treated with?-methacrylox-ypropyltrimethoxysilane(MPS,s-SiO2)and PB(v-SiO2),respectively.On this basis,the effect of modified SiO2 filling content on the dielectric properties of the CCLs was investigated.The study results indicated that the polyolefin/v-SiO2 CCLs have stronger interfacial interactions,which can reduce interface polarization,resulting in lower dielectric constant and dielectric loss,comparing to polyolefin/s-SiO2CCLs.Moreover,the dielectric constant and dielectric loss of the polyolefin/v-SiO2 CCLs with 50 wt%v-SiO2 are 3.42 and 3.55×10-3 at 10 GHz.Meanwhile,the CCL shows good dielectric stability in the range from 3 GHz to 18 GHz.(5)Influence of core-shell structured EPDM@SiO2 on the dielectric properties of polyolefin/SiO2 CCLs.First,EPDM@SiO2 particles with core-shell structured were designed and synthesized,and then the effect of shell thickness on the dielectric properties and thermal conductivity of polyolefin/SiO2 CCLs were explored.The results suggest demonstrated that the EPDM with excellent electrical insulating property can hinder the movement of charges,resulting in the reduction of the dielectric constant and dielectric loss.In addition,the EPDM shell layer can improve the dispersion and compatibility of SiO2 in the polyolefin matrix,thereby improving the thermal conductivity.Compared with the EPDM shell thicknesses of 0,6,and 9 nm laminates,the 13 nm-thick laminate has the optimal dielectric properties,dielectric stability and thermal conductivity. |
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