Ultraviolet (UV) curing inkjet ink relies on an environmentally-friendly photochemical process to dry ink instantly after printing. This means that you can print on nearly any non-absorbing material, including metal, wood, glass, vinyl, and more. Unlike certain other types of printing, UV curable ink is cured on the surface of the substrate so the substrate can be nonporous, resulting in no smudging and no need for costly pre coatings. In this blog, we’ll discuss the process and key benefits of UV curing inkjet ink to help you determine if it’s the best option for your next printing project.
What Are UV Curing Inkjet Inks?
Rather than relying on absorption into substrates for drying, UV curing inkjet inks are formulated to remain in liquid form until they are cured via exposure to UV and LED lights as well as electron beam(EB) This initiates an instantaneous photochemical reaction in which the ink components are cross-linked, creating a durable polymer.
UV curing inks contain four primary components: monomers, oligomers, photointiators and additives such as pigments. These compounds are what allow the photochemical reaction to occur upon exposure to UV light. When the ink makes contact with UV light, the photoinitiators form radicals that begin the polymerization of the monomers. These inks contain no solvents and derive their color from pigment dispersion.
UV Curing Process
UV curable inkjet inks require efficient, consistent, and complete curing to ensure optimal functionality, durability, aesthetic appeal, and surface properties for printed products. As previously mentioned, UV curing is a photochemical process that relies on highly intense ultraviolet light to quickly cure or “dry” inks.
UV curing inks are formulated with oligomers and monomers combined with a small amount of photoinitiators and other additives. Once exposed to UV energy, the ink instantly hardens, allowing the printed product to quickly move on to the next processing step.
Benefits of UV Inkjet Inks
UV curing inks provide a range of benefits that make them ideal for various applications. The major advantages of using UV curing inks include:
High-quality properties such as excellent bond and adhesive strength, scratch resistance, and chemical resistance
Relies on less energy and solvent-free technology for a more environmentally friendly solution
Higher production capacity and speed
High image and color quality
Superior reliability and consistency
Product is immediately ready for the next process step
Compatible with 2D and 3D component geometries
No VOC emissions
Higher yield rates
UV Curable Solutions From Toagosei America Inc.
UV curing inkjet inks offer an eco-friendly, instant printing solution that creates a strong, durable print on a wide variety of substrates. As a global manufacturer of functional adhesive and chemical technologies, Toagosei America, Inc. delivers a range of UV curable solutions for industries such as 3D printing, UV adhesives, UV inks and inkjets, UV coating, electronics, and automotive. We offer various types of monomers designed to improve the performance of UV curing inkjet ink, including:
M-313. This monomer increases the durability of cured products and can enhance the elastic modulus of UV adhesives.
M-5700. This monomer increases the flexibility of a cured product and offers fast UV curability. When combined with M-313, it can enhance the overall adhesion of UV curing inkjet ink.
M-930. This monomer offers a low viscosity tri-functional acrylate with biobased content and increases the chemical resistance of the print.
In addition to M-313 and M-5700, we offer a wide range of other monomers that can increase scratch resistance, improve optical durability, provide hydrolysis resistance, and more. For more information about how our UV curable resins can meet your UV ink needs, contact us today.
Synthesis of Imide-Acrylates and Their Applications for UV Curable Resins
Eiichi Okazaki, Tetsuji Jitsumatsu TOAGOSEI CO., LTD
1-1 Funami-Cho, Minato-Ku, Nagoya 455 Japan
Tel: 052-611-9910 Fax: 052-613-1868
Several kinds of imide-acrylates were synthesized and were measured their physical properties. They were applied for UV curable resins. It was found that these irnide-acrylates have excellent UV curability and their cured films have good flexibility and adhesion for many kinds of substances.
Moreover, it was found that the acrylate with a maleimide-group can be cured without conventional photoinitiators. It is interesting that the maleimide-acrylate would be able to improve durability, odor, toxic problems that are caused by photocleavage of photoinitiators after UV irradiation.
UV curing technology has been utilized widely and esectively for numerous industrial applications, because UV cure system could bring us various advantages as follows, zero VOC, excellent productivity, superior physical properties, reduction of energy. Recently, this system has been accepted for not only coatings and inks of wood, metal and plastic but also technique of manufacturing LCD panel and photofabrication of 3D model Therefore, new materials which have an unique chemical or physical properties have been desired.
Today, most of the materials that have been applied to UV curable resins are monomers and oligomers including acrylic group for radical polymerization. Although some new cationic UV coating systems have introduced recently in order to improve the physical or chemical property, it isn’t sufficient for the newer various apphcations.
Acrylates including imide-group were focused because the group has strong chemical bond and high polarity for improving the properties. Then, several kinds of imide-acrylates were synthesized and were measured their physical properties as new unique UV curable monomers which would be able to be applied to newer various industrials.
In this report, acrylate with maleimide-group was attempted to apply photoinitiator- free system, because N-substituted maleimides are eificient photoinitiators of radical polymerization through the mechanism of hydrogen abstraction by excited N-substituted maleimide under UV irradiation.
III.EXPERIMENTAL I.SYNTHSIS OF IMIDE-ACRYLATES
Imide-acrylates were synthesized from cyclic anhydride, amino alcohol and acryhc acid on the same way which Azuma had reported . Synthesized compounds were shown in Tablet. PT-ETA-A which was synthesized from phthalic anhydride was crystal and difficult to dissolve in typical acrylates.
II.PROCEDURES Tensile strength. elongation and Tg
Formulations of imide-acrylate added 1wt% of benzildimethylketa1(BDK) were poured into EPDM rubber mold to gain their films of lmm and were cured in air under 60W/cm° medium pressure mercury vapor lamp with an irradiation of 5,000mJ/cm°. Tensile strength and elongation were measured in accordance with Japanese Industrial Standard (JIS) K6301. Tg was measured by DSC.
Curine speed. pencil hardness and adhesion
Imide-acrylate formulations added 2wt% of BDK were drawn down on several kinds of plates using a 10-micron wire bar. The coatings were cured in air under 80W/cm2 medium pressure mercury vapor lamp at 90mJ/cm2 by 1 pass. Curing speed was indicated the number of passes which the tackiness of coating surface was completely disappeared on metal plate. Pencil hardness and crosshatch tape adhesion test were conducted in the same way of JIS KS400 on metal and some plastic plates, respectively.
IV. RESULTS AND DISCUSSION I.PROPERTIES OF IMIDE-ACRYLATES
Table I gives the curing speed, pencil hardness and Tg of imide-acrylate itself. In spite of monofunctional acrylate, all imide-acrylates could be cured quickly and the essential dosage to cure were within 360mJ/cm°. The pencil hardness were relative hard and the level was from H to 2H.
The reason why imide-acrylate could be cured quickly was due to the reducible effect of inhibition of radical polymerization by oxygen in air, like a tertiary amine, because
Decker had reported that acrylate with a carbamate-group, similar heterocyclic compounds, could be cured excellently by the same reason.
The result of adhesion test was shown in Table II. 2-Hydroxy-3-phenoxypropy1 acrylate(HPPA) was used for this test as a typical good adhesion monomer. Adhesion of imide-acrylates was better than HPPA for several kinds of plastics. This can be attributed to the significantly higher polarity that imide group has.
The tensile strength, elongation and viscosity of formulations which consist of HH- ETA-A and some conventional urethane acrylates are shown in Fig.1-3, respectively. UA- 1(Aronix M-1100, Toagosei) and UA-2(Aronix M-1310, Toagosei) are typical aromatic polyester urethaneacrylates. And UA-3(Aronix M-1600, Toagosei) is typical aliphatic polyether urethaneacrylate. Though HH-ETA-A was a monofunctional acrylate, both tensile strength and elongation were not spoiled, but partially improved by adding to urethaneacrylates.
This can be aho attributed to the higher polarity of imide group. It was reasonable that the viscosity was decreasing and then treating was easier by adding imide-acrylate to the formulations.
Fig.4 shows the comparison between imide-acrylates and ethoxyethoxyethyl acrylate(EEEA), typical monoacrylate, as a diluent. It was found that curing speed was improved excellently by adding imide-acrylate in the case of TMPTA.
II.APPLICATION FOR PHOTOINITIATOR -FREE SYSTEM
Recently, N-substituted maleimides are efficient photoinitiators of radical polymerization through the mechanism of hydrogen abstraction by excited N-substituted maleimide. HT-ETA-A which consists of 2,3,4,5-tetrahydrophthalic anhydride, ethanolamine and acrylic acid has maleimide moiety, therefore it is expected that this imide- acrylate can polymerize itself and other acrylates without conventional photoinitiator.
Curing speed and pencil hardness of HT-ETA-A were shown in Table III. It was found that this acrylate can be cured fast enough, within 360mJ/cm°, without typical photoinitiator expectedly. Fig.5 shows the mechanism of polymerization through hydrogen abstraction by excited HT-ETA-A without photoinitiators under UV irradiation.
In this report, we have presented the results related to the properties of imide- acrylates as UV curable materials. We found that imide-acrylates have excellent UV curability, and their cured films have good 0exibiIity and adhesion for many kinds of substances.
Moreover, it was found that the acrylates which has a maleimide-group can be cured without conventional photoinitiators. It is interesting that these maleimide-acrylates would be able to improve durability, odor, toxic problems that are caused from photocleavage of conventional photoinitiators after UV irradiation.
Fushimi T., Kobunshi,45, 794, (1996) 2)
Ikuta K., ibid,45, 800, (1996)
Jonsson S.E., Hultgren , Sundell P., Shimose M., Owens J., Vaughn K., Hoyle C.E., Radtech Europe95 academic day, 34, (1995)
Clark S. C., Jonsson S. E., Hoyle C. E., Polymer Preprints,38(2), 363, (1997)
Azuma K., Kato , Tatemichi H., Kimura K., Japanese Laid-Open Patent Application (Kokai) No. 59481, (1975)
Selli E., Bellobono I.R., Radiation Curing in Polymer Science and Technology vol.3 Polymerisation Mechanisms, Fouassier J.P. and Rabek J.F., Elsevier, London, UK,1993, p.18
Abstract–A new method using an ester exchange reaction instead of the conventional dehydrative esterification reaction has been established to produce multifunctional acrylates. This method can provide lower viscosity and higher purity products compared to the conventional multifunctional acrylates.
Based on this method, new acrylates were synthesized from plant-derived raw materials, such as glycerol and sorbitol, and evaluated as light-curing resins. Glycerol triacrylate obtained via the direct acrylation of glycerol showed lower viscosity, higher hardness, and higher adhesion than the conventional acrylates with three or more functionalities. Ethylene oxide modified sorbitol
acrylate obtained from sorbitol as raw material is a multifunctional acrylate with high water solubility and has better properties than the conventional hydrophilic acrylates in terms of ultraviolet (UV) curability, coating film hardness, and water reducibility.
Multifunctional acrylates widely used as light-curing resins are mainly synthesized via the dehydrative esterification method using alcohol and acrylic acid as raw materials and a strong acid (e.g.: sulfuric acid, p-toluenesulfonic acid) as a catalyst. However, the disadvantage of this method is that the product is likely to change over time due to catalyst residue and side reactions such as Michael addition can lead to high molecular weight and viscosity [l].
These problems can be solved by switching the method to an esterification process that does not use strong acids as a catalyst but the conventional esterification process has not been applied to the synthesis of 3 or higher functional acrylates due to problems such as low catalyst activity and difficulty in removing the catalyst .
The authors successfully synthesized acrylates with three or more functionalities, which were previously difficult to produce, using an independently developed ester exchange method. The acrylates produced by this method will be described below.
Dipentaerythritol penta-/hexa-acrylate (DPHA), glycerol triacrylate (GTA), and ethoxylated sorbitol acrylate (ESA) were synthesized via the ester exchange reaction with reference to the patents  . This DPHA was designated as DPHA-1 to distinguish it from the conventional products.
For tetra (ethylene glycol) diacrylate (TEGDA), trimethylolpropane triacrylate (TMPT A), and pentarythritol triacrylate (PETA), “ARONIX M-240,” “ARONIX M-309,” and “ARONIX M-305,” respectively, manufactured via Toagosei were used without any modifications. For DPHA synthesized via the dehydrating esterification method, “ARONIX M-402” manufactured via Toagosei was used as it is, and it was designated as DPHA-2.
For poly(ethylene glycol) diacrylate (n approximately 14) (PEGDA), “Light Acrylate 14EG-A” manufactured by Kyoeisha Chemical was used as it was.
Figure 1 shows the structure of polyfunctional acrylates used in this study.
2.2 Evaluation of the Properties of Coated Films
A monomer/2-methyl-l-[4-(methylthio) phenyl]-2- morpholino-l-propanone (100 parts/5 parts) mixed solution was prepared and applied to an enhanced adherent PET film (Cosmoshine A-4300, made by
Toyobo, 50 μm) using a bar coater to obtain a film thickness of 10 μm. The film was then UV irradiated in air with a medium-pressure mercury vapor lamp (UV dose 800 mJ/cm2, maximum UV intensity 500 mW/cm2). Thereafter, the physical properties of the resulting coating films were evaluated by the following methods.
The pencil hardness was measured according to IlS K 5600-5-4.
Martens hardness was measured using a Fischer Scope H-lO0C ultra-micro hardness tester manufactured by Fischer Instruments, with a Vickers indenter, a maximum indentation load of 10 mN, and 10 s to reach the maximum load, and it was calculated from the maximum deformation of the coating film.
The scratch resistance was evaluated by rubbing the surface of the coating film with steel wool #0000 (under conditions of 1 kg load, reciprocating 100 times), and observing the appearance. If the appearance of the coating film after the test did not change at all, it was qualified as “excellent,” and if less than 10 scratches were observed, it was rated as “good.”
The adhesion was measured according to IlS K 5600- 5-6 (cross-cut test). Toyobo “Cosmoshine A-4300” (50 μm) (as enhanced adhesion treated polyethylene
terephthalate (PET)), Teijin “Panlite PC-2151” (125 μm) (as polycarbonate (PC)), and “FUilTAC-80UL” (80 μm) manufactured via FUilFILM Corporation (as triacetylcellulose (TAC)) were used as they were.
2.3 UV-LED Curability
An acrylate/diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (100 parts/10 parts) mixed solution was prepared and applied to an art paper sheet (manufactured via Mitsubishi Paper Mills) using a bar coater to set a film thickness of 5 μm. UV irradiation was then performed with a UV-LED (385 nm) (maximum UV intensity 200 mW/cm2). The UV dose was adjusted by varying the conveyor speed, the coating film surface was rubbed with a nonwoven cloth, and the UV-LED curability was defined as the lowest UV dose in which no scratches were observed on the film.
Ill. RESULTS AND DISCUSSION
Dipentaerythritol penta-/hexa-acrylate (DPHA) is extensively used in inks, coatings, and solder resists owing to its outstanding hardness and curability among multifunctional acrylates. However, conventional DPHA is produced via the dehydrative esterification method, which causes problems, including high molecular weight and viscosity, due to side reactions such as Michael addition as well as change in quality over time and metal corrosion because of the presence of a residual strong acid catalyst [ 1].
A comparison of the physical properties of DPHA-1 synthesized by the ester exchange method and DPHA-2 produced by the dehydrating esterification method is shown in Table I. DPHA-1 exhibits much lower viscosity due to a reduced amount of high molecular weight products formed via Michael addition, and deterioration with age and metal corrosion resistance are improved due to the absence of a residual strong acid catalyst. These characteristics make DPHA synthesized by the ester exchange method promising for automotive equipment and resist applications, which require high moisture/heat resistance and insulation properties.
Glycerol is a trivalent alcohol obtained from biomass animal fats or vegetable oils, and glycerol triacrylate (GTA), which is produced by acrylation of glycerol, is preferred from a carbon-neutral perspective. However, as glycerol has a hardly esterifiable secondary hydroxyl group, it has been difficult to synthesize high-purity GT A with conventional methods.
The authors succeeded in synthesizing high-purity GTA using the abovementioned ester exchange method. Table II compares the physical properties of the obtained GTA with those of trimethylolpropane triacrylate (TMPTA) and pentarythritol triacrylate (PETA) produced via conventional methods.
GT A showed substantially lower viscosity than TMPTA and PETA This can be explained by the smaller molecular weight of the ideal structure in GT A compared to that of TMPT A and PETA and by the suppression of increase in molecular weight caused by Michael addition. Upon comparing the physical properties of the cured products, GTA proved superior to TMPTA in both Martens hardness and scratch resistance, and its performance was similar to that of PETA, which contains tetra:functional acrylate with a higher crosslinking density.
Furthermore, the results of the cross-cut adhesion test showed that GTA has better adhesion than TMPTA and PET A. It has been reported that penetration into the base material is an important factor in the adhesion of light- curing resins to plastics , and it is assumed that GTA shows better penetration ability into plastics than TMPTA and PETA because of its low viscosity and molecular weight.
Summarizing the above results, GT A is a multifunctional acrylate characterized by lower viscosity, higher hardness, and higher adhesion compared to the conventional multifunctional acrylates and it can be considered superior in terms of carbon neutrality.
Sorbitol is a biomass-derived polyhydric sugar alcohol obtained by the reduction of glucose produced by starch hydrolysis. It has been reported that acrylate of 6 moles EO adduct of sorbitol, in which an average of 1 mole of ethylene oxide (EO) is added to the hydroxyl groups of sorbitol, has excellent UV curability . Recently, considering the reduction of environmental load, an increasing need emerged for UV-curable resins that use water as a diluent in paints to diminish VOCs. As sorbitol is a hexafunctional alcohol, by reducing the acrylation rate and leaving hydroxyl groups, it becomes possible to obtain multifunctional acrylates with high water solubility. However, because the dehydrative esterification method requires a water washing process to remove the residual acrylic acid and strong acid catalyst, it is difficult to retain the water-soluble components in the product.
The authors synthesized highly water-soluble ethoxylated sorbitol acrylate (ESA) by the ester exchange method that does not require the abovementioned water washing process, and evaluated its physical properties.
Because ESA synthesized this time has a comparatively small average number of 2 acryloyl groups per molecule and an extremely high hydroxyl value of 300 mg KOH/g, it can be dissolved in water at any ratio.
Table III shows the results of comparison of ESA with polyethylene glycol (n = 14) diacrylate (PEG14DA), a commercially available water-soluble multifunctional acrylate, and tetraethylene glycol diacrylate (TEGDA), a hydrophilic bifunctional acrylate with a relatively high Tg.
When comparing UV curability, ESA proved much better than PEG14DA and TEGDA. The plausible reason is that ESA is relatively less affected by oxygen inhibition due to its hydroxyl groups .
The Tg of the ESA cured product was much higher than that of PEG14DA and comparable to that of TEGDA, and the Martens hardness of ESA was also
higher than that of PEG14DA.
Comparing the water absorption of the cured films, the water absorption of ESA was about 30 wt%, which is equivalent to that of PEG14DA, and the hydrophilicity
was very high. When measuring the surface resistance of the cured coating film, it was much lower for ESA than for TEGDA and close to PEG14DA. The probable reason is that since ESA and PEG14DA give highly hydrophilic cured products, moisture is easily adsorbed on their coating film surfaces.
These results suggest that ESA has better properties than the conventional hydrophilic acrylates in terms of UV curability, coating film hardness, and water solubility, and it is useful as a raw material for water-soluble UV paints and antistatic UV coatings as well as antifog coatings that require hydrophilic properties.
This paper succeeds in synthesizing acrylates with three or more functionalities, which have been difficult to obtain in the past, using the author-developed ester exchange method. The multifunctional acrylates produced via this method exhibit outstanding properties including lower viscosity, higher purity, and lower deterioration with age than those of the conventional products.
New acrylates obtained from plant-derived raw materials, glycerol, and sorbitol were synthesized via this process and evaluated as light-curing resins. The glycerol triacrylate showed lower viscosity, higher hardness, and higher adhesiveness than the conventional trifunctional acrylates. Furthermore, the EO modified sorbitol acrylate obtained from sorbitol is a multifunctional acrylate with high water solubility, which offers better properties than the conventional hydrophilic acrylates in terms of UV curability, coating film hardness, and water reducibility.
You may be familiar with the videos of artists and crafters pouring colorful liquid resin over a wooden slab to create a beautiful table inlaid with color. UV curable resins are often used in the art world, but they are particularly useful in a wide range of industrial applications, including the medical field.
UV curable resins polymerize and cure quickly when exposed to ultraviolet light emissions. These specialized resins are sought after because they dry faster than normal resins and are versatile enough to reduce production costs. Because of their ability to conform to applications UV curable resins are used to create great works of art, to aid in the conduction of electricity, and even in the medical field to help improve the quality of life for patients.
What Are UV Curable Resins Used For?
UV curable resin consists of a mixture of powder and chemicals that may be colored and textured to produce a unique finish. In addition to art applications, UV curable resin is being increasingly adopted into a wide range of industries to provide durable coatings and adhesives. Some of the industries that often use UV curable resins include:
UV Curable Resin in The Medical Industry
For pressure-sensitive and bonding applications in the medical industry, UV curable resins are an excellent option due to their flexibility and resiliency. UV curable resins are often used to bond syringes, endoscopes, guidewire tips, and even accessories for heart surgery. Devices like hearing aids can be covered with UV curable resin to assist with durability and keep the electronic pieces clean.
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UV Curable Resin in the Electronics Industry
In the electronics field, electricians use the resin to bond and assemble components, create seals and gaskets, potting, masking, and conformational coating. Using UV curable resins in electronics creates stronger, more cost-effective electrical components that have adequate protection for sensitive parts.
UV Curable Resin for Graphic Arts
Resin in art is not a new concept. However, there are new ways UV curable resin is being used by artists. T-Shirt printers have begun to use the UV/EB curable inks to ensure a strong bond to the materials, resulting in longer-lasting designs. UV curable inks provide several advantages over water-based or solvent-based inks because they dry faster, have little or no VOC emissions, and have lower energy requirements.
UV Curable Resin for 3D Printing
Resin-based 3D printing uses UV curable resins to create designs from a digital file. The quick-drying abilities of UV curable resin are perfect for 3D printers, allowing the shapes to maintain their form during printing. Material jetting consists of ejecting resin droplets onto the printing platform while simultaneously applying UV light, resulting in an instant cure. This technique is quickly becoming one of the fastest and most precise 3D printing techniques.
Advantages and Disadvantages of UV Curable Resins
As with any material, there are advantages and disadvantages to its use. UV curable resins offer many advantages, including:
More environmentally friendly than solvents
Less shrinkage than other resin curing methods
It is important to understand the limitations that come with working with UV cure resins to ensure they are suitable for your application. Limitations include:
The resin must be applied in thin layers
Resin has to be cured with UV light quickly
Cost is greater than air-dry resin
How Long Does UV Resin Take to Cure?
One of the biggest advantages of UV curable resin is its ability to cure quickly. How long does it take to cure? Depending on the UV source, the thickness of the resin, and the design of the product, it can take anywhere from five minutes to a few hours. Other resins can take days to cure, making this a time-saving option. The best way to get a clear understanding of the UV resin’s cure time is by reviewing the original manufacturer’s specifications, or to get in touch with their team.
Learn More About UV Curable Resins
Founded in 1944, Toagosei America is a trusted chemical product company. We specialize in the production of polymers, oligomers, adhesives, and other commodity chemicals that are used to produce high-quality UV curable resins, as one of many examples. Browse our wide variety of UV curing resin solutions in our catalog to find the right fit for your requirements. For more information on how UV curable resins can be implemented in your application, contact Toagosei America today.