Curable Coatings Research Articles

Recent developments in photoinitiators

A new photoinitiator, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (1), has been developed for industrial applications. The absorption of this bisacylphosphine oxide (BAPO) compound in the near UV-Vis range is significantly higher than that of hitherto known photoinitiators for UV curing. Investigation of the photochemistry of 1 revealed the efficient formation of four radicals, which can all initiate polymerization. Since the photoreaction is accompanied by the destruction of the chromophore responsible for absorption in the near UV-Vis, photobleaching of the long wavelength absorption is observed and the photoinitiator does not impart yellowing in the cured lacquer. Studies using FTIR and RTIR techniques showed that these features result in a higher conversion of acrylic double bonds than obtained with other photoinitiators in formulations containing a high loading of rutile type titanium dioxide pigments. These findings were confirmed by application tests in different white pigmented coatings. Further, the new photoinitiator allows the fast curing of thick pigmented layers, which makes it suitable for use in pigmented furniture coating. This new class of high performance photoinitiators is expected to promote the development of UV curable white coatings of high opacity and other applications where light in the near UV-Vis range is essential for curing. A liquid containing 25 parts of the BAPO photoinitiator 1 and 75 parts of 2-hydroxy-2-methyl-l-phenyl-propan-l-one ( 2) is an excellent technical and economical solution for most applications. ▪

Polymeric systems bearing side‐chain 2,6‐dimethylbenzoyldiphenylphosphinoxide moieties for UV curable coatings: Synthesis and photoinitiation activity

AbstractPolymeric photoinitiators with pendant 2,6‐dimethylbenzoyldiphenylphosphinoxide moieties were prepared by reacting the hompolymer of 4‐acryloyloxy‐2,6‐dimethyl benzoic acid, and its copolymers with n‐butyl acrylate with thionyl chloride followed by methoxydiphenylphosphine. These polymeric systems were characterized and their photoinitiation activity checked in the UV curing of a standard acrylic mixture, by irradiation both at 330 and over 380 nm, the latter conditions being applied to simulate a TiO2‐pigmented coating formulation. The results were compared with those obtained by using the low molecular weight analog 2,4,6‐trimethylbenzoyldiphenylphosphinoxide and previously prepared polymeric systems based on the benzoyldiphenylphosphinoxide moiety. The stability to light and to hydrolytic conditions of the polymeric photoinitiators with respect to the model compound was also tested. The results obtained are discussed and related to the structural requirements of these systems. © 1995 John Wiley & Sons, Inc.

Application Equipment for Radiation Curable Coatings

Application Equipment for Radiation Curable Coatings

Polymeric photoinitiators bearing side‐chain benzoyldiphenylphosphinoxide moieties for UV curable coatings

AbstractPolymeric photoinitiators bearing side‐chain benzoyldiphenylphosphinoxide moieties have been prepared by reacting poly(4‐vinylbenzoic acid) or 4‐vinylbenzoic acid/methyl methacrylate copolymers with thionyl chloride followed by methoxydiphenylphosphine. The activity of the above polymeric systems has been checked in the UV curing of the acrylic clear‐coating formulation HDDA/BA and compared with that of the low molecular weight model 4‐isoprophylbenzoyldiphenylphosphinoxide. The stability to light and to hydrolytic conditions of the polymeric photoinitiators with respect ot the model has also been tested. The results obtained are discussed in terms of composition and structural features of these systems. © 1994 John Wiley & Sons, Inc.

Polymeric photoinitiators having benzoin methyl ether moieties connected to the main chain by the benzoyl group and their activity for ultra-violet curable coatings

Homopolymers of 4-acryloyloxybenzoin methyl ether (ABME) and 4-acryloyloxy- α -methylbenzoin methyl ether (AMBE) [poly(ABME) and poly(AMBE)] as well as copolymers of AMBE with (-)-menthyl acrylate (MtA) and with different N,N -dialkylaminoethyl acrylates have been employed in the photoinitiated polymerization and crosslinking of a standard acrylic formulation for u.v. clear curable coatings. The photoinitiation activity of the above systems, detected by microwave dielectrometry, has been compared with that found for the corresponding low molecular weight structural models. The results clearly indicate that high and low molecular weight photoinitiators promote u.v. curing at a similar rate; however, a significant decrease of the induction period and hence an improved overall activity is found for the polymeric systems. An interpretation of the experimental findings, related to the behaviour of previously reported polymeric photoinitiators based on the benzoin methyl ether moiety, is also reported.

UV curable coatings for electronic components

Military electronic components demand the highest reliability when applied to extreme environmental conditions. Demands placed upon component manufacturers are equally suitable to the consumer market. The most stringent military test to pass is the component's durability to withstand high temperatures concomitant with high humidities. Before designing a conformal coating for capacitors and resisters, a number of thin films were cast, cured and tested at 85/spl deg/C, 95% RH. The films were heat-cured silicones, epoxies, and ethoxy monomers, and UV-cured acrylated silicones, epoxies, and monomers. Acrylated polymers are free radical curing mechanisms. In this instance, free radicals were generated using UV light. The curing took place in seconds. Vapor transmission across a thin barrier film of these materials was measured to determine the film's integrity in withstanding simultaneously high temperatures and humidities. A number of correlations were discovered in regard to the chemistry needed to enhance a film's resistance to environmental conditions. There are a number of chemical reactions that take place within the film's structure when exposed to water. However, in the absence of chemical reactions, a film's integrity is related to its crosslink density and steric hinderance. The author investigated a number of heat-cured and UV-cured chemistries. In correlating vapor transmission data with a components electrical properties, solid tantalum capacitors were coated with ethoxylated epoxy and acrylated epoxy. Vapor transmission data strongly agreed with the electrical properties of a capacitor when subjected to 85/spl deg/C, 95% RH. Surprisingly the electrical properties were better for the high crosslinked, steric, acrylated epoxy. Rapid cure played a major role in the film's integrity to crosslink uniformly without gas egression or pinholes. The electrical values were consistent with the vapor transmission data.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Polymeric photoinitiators based on side‐chain benzoin methyl ether and tertiary amine moieties for fast UV curable coatings

AbstractThe synthesis is reported of a new series of polymeric photoinitiators obtained by copolymerization of a‐methylolbenzoin methyl ether acrylate (MBA) with different N,N‐dialkylamino alkyl acrylates.The copolymers have been fully characterized and employed in the photoinitiated polymerization and crosslinking reactions of a standard acrylic formulation for clear curable coatings.The photoinitiation activity of the above systems has been measured by using microwave dielectrometry and differential photocalorimetry, and compared with that found for the corresponding low‐molecular‐weight models.The results clearly indicate that the copolymeric systems display a remarkable decrease of the induction period and an improved overall activity in the UV curing of the acrylic coatings.An interpretation of the experimental findings is also reported.

Current Status of Urethane (Meth)Acrylate Oligomers and Polymers

Abstract Urethane (meth)acrylate (UA) oligomers have been extensively investigated in the past as (a) photo/radiation/laser curable coatings useful for protecting the surface of such materials as metals [1], wood [2], paper, plastics [3], optical fibers [4], concrete [5], and leather [6]; (b) photoresists for the fabrication of microelectronic devices and video discs [7]; (c) sealants [8] and adhesives [9]; (d) biomaterials useful in contact lenses [10] and surgical implants; (e) printing inks [11]; and (f) elastmeric and encapsulating coatings.

Investigation on the structure-property relationships for films obtained from UV curable coatings

A number of poly(ethyleneglycol)- and poly(propyleneglycol)- α, ω-diacrylates, with different MW in the range 200–2000, were subjected to UV curing as thin films and the properties of the obtained crosslinked polymers were investigated. The total double bond conversion was determined by Fourier transform infrared spectroscopy (FTIR). Direct scanning calorimetry (DSC), thermal mechanical analysis (TMA) and dynamic-mechanical thermal analysis (DMTA) were used to evaluate the thermal and dynamic-mechanical behaviour of the networks obtained. The double bond conversion was found to be always complete, with the exception of the lowest MW oligomers. T g values were found to decrease with increasing the MW of the oligomers used for both series. The equilibrium swelling in water was found to increase with increasing MW that is with decreasing the crosslinking density of the network. Mixtures of different oligomers with a typical epoxyacrylate resin were also examined. A sharp increase of the total double bond conversion in the presence of the oligomers was observed. The T g values of the obtained films were found to decrease with increasing oligomer MW in agreement with the data obtained by using the pure acrylate oligomers. The results obtained are discussed in terms of the crosslinking density of the networks formed in the curing process.

Adhesion of electron beam curable coatings on metal substrates

Electron beam (EB) curing is growing more and more important as a curing technique in industrial coatings, for example on substrates like wood, paper and plastics. However, commercial applications of EB curing on metal substrates are rather limited. The main technical cause for this originates from the insufficient adhesion and flexibility shown by EB cured coatings when applied on metal parts. However, adhesion and flexibility can be improved by various ways, in particular via a proper choice of the chemical pretreatment of the substrate. Adhesion of coatings, based on acrylated resins, on hot dipped galvanized steel can be improved dramatically by using a pretreatment, which is not usual in the current field of commercial coil coating. Pretreatments investigated show no relationship to surface tension, so it is highly probable that a chemical graft reaction, initiated by the electron beam, occurs at the interface of the coating and pretreatment layer. Experiments also show that cationic curing binder systems show promise with respect to adhesion and flexibility. Without optimizing the coating formulation (no wetting agents or other additives are used) relatively good adhesion and flexibility can be obtained on hot dipped galvanized steel, under both wet and dry conditions. The adhesion and flexibility are shown to be dependent on the radiation dose, and can be further improved by post-heating. In this case the polymer network gets the opportunity to relax internal stresses that are built up during the cure reaction.

Supercritical fluid chromatography and extraction in surface coatings analysis — review of representative applicationst

Supercritical fluid chromatography and extraction are investigated as techniques for analyzing surface coatings and many of the raw materials that go into their manufacture. Reactive oligomeric mixtures such as radiation curing coatings, polyisocyanate curing agents, and surface active agents are separated using capillary SFC with CO 2. Polar oligomeric mixtures such as epoxy, vinyl, and phenol-formaldehyde resins can be separated with modified mobile phases on packed columns. Optimization of chromatographic separation through pressure composition and flow programming is highlighted. On-line supercritical fluid extraction-capillary supercritical fluid chromatography is used to extract and separate ultraviolet light stabilizers incorporated into a cured automotive clear coating. Optimization of conditions for the extraction of polymers is discussed.

Silicone acrylates through the hydrosilation of polyacryloyloxy functional monomers with copolymers of dimethyl and hydrogen methylsiloxanes

AbstractSilicone acrylates, as possible electron beam (EB) curable release coatings for paper, were prepared by the platinum‐catalyzed hydrosilation of polyacryloyloxy functional monomers with copolymers of dimethylsiloxane and hydrogen methylsiloxane (PDMHMS). The hydrosilation of either 1,6‐hexanediol diacrylate (HDDA) or trimethylolpropane triacrylate (TMPTA) with PDMHMS occurs to only one of the 2 or 3 available olefinic groups, respectively, as long as excess monomer is present. The amount of excess monomer needed to prevent gelation during hydrosilation or subsequent storage in excess of 1 month appears to be dependent on the hydrogen methylsiloxane content of the PDMHMS. A release coating having excellent cohesive and adhesive strength on paper was obtained by the EB curing of the product of hydrosilation of TMPTA with a PDMHMS containing 4 mol % hydrogen methylsiloxane at a dose‐to‐cure of 2 Mrad, but the aged release force was excessively high. The poor aged‐release performance was likely due to dilution of the dimethylsiloxane content of the coating with excess monomer required to stabilize the silicone acrylate. © 1993 John Wiley &amp; Sons, Inc.

A novel approach to thermal Analysis of Thin films

A novel instrument is described called the Thin film Analyser (TFA) which quantitatively measures changes in mechanical and rheological properties of drying films in-situ on a test panel. It is based around a simple force-sensing device, capable of carrying various probes, which can be positioned in anX-Y plane over the panel. Temperature control is achieved by means of a heating block under the sample. By imposing a thermal gradient along the block, measurements can be obtained at a series of temperatures in a single experiment. Several applications of the TFA to the drying of curable and latex-based coatings are discussed, as well as some more specialized uses. The TFA concept represents a novel approach to the thermal analysis of thin films.

Radiation Curable Coatings and Pigment Binders for Textile Substrates

Radiation curing has found applications in many branches of industry. This technology can also be applied in textile finishing. Coating and pigment print ing, as well as other finishing processes, can be performed successfully with UV- curing and electron beam curing (EB). This paper discloses some results of a study for UV-curable coatings and the development of UV-curable binders for pigment printing.

Pollution prevention methods in the surface coating industry

The surface coating industry is rapidly changing to meet environmental and economic pressures. Some of the changes include new formulations which meet environmental regulations, higher performance finishes with improved properties, continued development of solventless technologies such as powder coatings and radiation curable coatings, and new application methods with improved transfer efficiencies. These changes will be accelerated by the 1990 amendments to the U.S. Clean Air Act. These new enviromnental laws will require industry through the Environmental Protection Agency (EPA) and state and local agencies to further reduce emissions of volatile organic compounds (VOCs) which are contributors to ozone formation in the lower atmosphere. The focus of this paper will be to examine the paints and coatings industry and those pollution prevention methods that are being applied to meet these environmental pressures. It will review the life cycle of paints and coatings; from its inception in the manufacturing facility to its ultimate application and disposal. It will also review developing low VOC technologies that are being considered worldwide to comply with increasing VOC regulations.

Synthesis, characterization and end-use evaluation of epoxy resins prepared from diallyl and dipropyl bisphenol A

We have synthesized 2,2'(6')-diallyl-4,4'-isopropylidenediphenol (diallyl bisphenol A), 2,2'(6')-dipropyl-4,4'-isopropylidenediphenol (dipropyl bisphenol A), and epoxy resins (glycidyl ether oligomers) of different average molecular weights. The acrylic and methacrylic esters were prepared by reacting the epoxy resin with acrylic and methacrylic acids, respectively. The amine-cured epoxy resins showed promise as general-purpose adhesives, while the epoxy acrylates were found to be useful as reactive oligomers in ultraviolet (UV) radiation curable coatings, and the epoxy methacrylates as anaerobic adhesives.

UV Curable Silicone Release Coatings and Controlled Release Additives

A background discussion of silicone release coatings is presented together with efforts to develop controlled release additives for photolytically cured systems A theory of release that correlates release, surface tension, and resin func tionality is presented Secondary ion mass spectrometry (SIMS) depth profiling has been used to determine the location of CRAs in cured coatings The CRAs were found to be uniformly distributed throughout the coating without preferential segregation at the air or adhesive interfaces Tight release is not obtained without CRAs suggesting that a minimum concentration at the surface which is necessary, is not greater than that found in the bulk.

The effects of cure temperature on the thermomechanical properties of UV curable coatings

AbstractA method is presented to study the mechanical behavior of soft, UV curable coating material as a function of temperature of the prepolymer at cure. For such materials, the crosslink density (hence, equilibrium modulus) is found to decrease with increasing cure temperature. The three primary coatings are: a polyurethane acrylate with a nominal equilibrium tensile modulus of 200 psi, a polyurethane acrylate with a nominal equilibrium modulus of 1200 psi, and a non‐urethane acrylate with a nominal equilibrium tensile modulus of 60 psi.

Microcolumn supercritical fluid chromatography with on‐line Fourier transform infrared detection

AbstractThe combination of capillary supercritical fluid chromatography (SFC) and Fourier transform infrared spectrometry (FTIR) is demonstrated using a low‐volume (0.8 μL) flow cell capable of withstanding high pressures. The design of the interface is presented, and its effect on peak shape and detector sensitivity is discussed. In order to optimize the system for use with 50‐μ i.d. capillary columns, makeup fluid is added to the column effluent before it passes through the flow cell to a flame ionization detector (FID). Loss in chromatographic resolution caused by the cell's dead volume is therefore minimized, which is clearly demonstrated by the analysis of two ultraviolet curing coatings using carbon dioxide as a mobile phase. This application highlights the analytical power of the system for separating and identifying reactive monomers, oligomers, and photoinitiators in low‐ to medium‐molecular‐weight polymer systems.

紫外線硬化被膜による鋼管の防錆処理法に関する研究 (第IV報)

鋼管の一時防錆処理被膜用並びにポリエチレン防食被覆のプライマー用に調製した2種の異なる紫外線硬化樹脂を用い, 照射する紫外線 (UV) 光源の種類並びに照射時の加熱が, 硬化樹脂被膜の物性に及ぼす影響について検討した。UV光源としては, 高圧水銀灯とメタルハライド灯とを比較検討した。前者は, 樹脂被膜表面の硬化効率が高く, 後者は, 樹脂被膜深部の硬化効率が高いことが認められた。これは, 前者は, 200～320nmの短波長UVエネルギー密度が高く, 後者は, 330nm以上の長波長UVエネルギー密度が高いためである。単色UVが得られるエキシマレーザー発振装置を用いて, UV 波長と硬化性の関係を検討した。その結果, 249nmの短波長UVは, 樹脂被膜表面の硬化に有効であり, 353nmの長波長UVは, 樹脂被膜深部の硬化に有効であることが明らかになった。また, 紫外線照射時に加熱を行うと, 加熱による被塗物温度の上昇と共に硬化度が向上することが認められた。これは, 温度の上昇と共に樹脂粘度が低下することの寄与が大きいと判明した。さらに, 粘度が3000cps 以下となる温度では, 硬化度がそれ以上向上しないことが認められた。従って, 常温において粘度が3000cpsを越えるUV樹脂の硬化では, 高温照射により被膜硬化度を高めることは可能である。