Patent Description:
The invention relates generally to the field of ink compositions. More specifically, the invention relates to radiation curable ink compositions comprising a dendritic or hyperbranched polyester acrylate component.

Radiation curable inks, e.g. for wide and super-wide inkjet printing have been known for some time. Ink compositions, however, have substantial problems meeting the increased demand for high performance inkjet ink, especially for the ink with fast curing speed, adhesion to a broad range of substrates, good resistance, and good flexibility.

Radiation curable inks are generally composed of monomeric and oligomeric materials, pigments, initiators, and additives, and optionally, a small amount of solvent. Radiation curable inks are printed on numerous substrates, both rigid and flexible, e.g. polyvinyl chloride (PVC), polystyrene, polycarbonate, acrylonitrile-butadiene-styrene (ABS), polyester, polyolefins, and textile materials. The ink performance, e.g. adhesion, scratch and rub resistance, flexibility, hardness, etc. are highly dependent on the ink compositions, especially if the properties of the monomeric and oligomeric materials used in the ink compositions. Some existing radiation curable ink compositions are found to have low adhesion, which results in premature peeling or flaking of ink film from substrates. In addition, some ink compositions show poor flexibility on flexible substrates when folded or wrinkled as evidence by cracking. The limited ability of ink compositions to adhere to a variety of substrates is increasingly problematic as the demand for using ink on a greater variety of substrates increases.

Existing radiation curable inks are generally based on (meth)acrylates and formulated by using mono-functional (meth)acrylate monomers as diluents and difunctional, trifunctional, or higher functional (meth)acrylate monomers as cross-linking agents to ensure that inks are cured with a certain amount of UV energy. Additional descriptions of (meth)acrylates can be found in <CIT>.

In existing ink compositions, low viscosity tri-functional or higher functional monomers are generally used to formulate fast curing inks where the ink dot is rapidly dried or cured after ejection from the nozzles of printing heads and deposited on the substrates using a small amount of radiation energy. These higher functional monomers sacrifice flexibility and adhesion for a fast drying capability, which significantly limits the application of the ink. Thus, there is a continuing need for radiation curable inks that have good adhesion to multiple substrates and improved flexibility that is capable of withstanding cracking during application.

<CIT> discloses a high amount of low viscosity tri-functional or higher functional monomers that are used in ink compositions to achieve a fast curing ink. Less than <NUM>% hyperbranched oligomers are used in the ink compositions due to their high viscosity.

<CIT> discloses radiation-curable mixtures comprising highly-branched polyesters having acrylate terminal groups that form high viscosity paint or ink mixtures where the viscosity is between <NUM>-<NUM> mPa·s.

<CIT> discloses a radiation curable ink containing a hyperbranched polymer as a photoinitiator to formulate radiation curable inks and coatings.

A UV-curable white composition, e.g. paint for solid wood plate, is disclosed in document <NPL>, & <CIT>).

<CIT> discloses ink compositions and methods for using them.

A discussion on photopolymerization of dendritic methacrylated polyesters is proposed by document <NPL>.

<CIT> relates to a hybrid radiation curable ink which can be utilized in impulse printheads. The composition includes a photoinitiator system which comprises both a photo cation polymerization initiator and a free-radical photoinitiator, an acrylate ester of a carboxylic acid ester, and a radiation curable material.

The invention generally relates to radiation curable ink compositions for ink-jet printing. The ink compositions comprise a dendritic and hyperbranched polyester acrylate component. The dendritic and hyperbranched polyester acrylate component comprises <NUM>-<NUM> by weight of the ink compositions and the dendritic and hyperbranched polyester acrylate in the component and preferably has a functionality of greater than <NUM>.

The ink compositions also comprise an oligomer component. The oligomer component comprises <NUM>-<NUM>% by weight of the ink compositions and preferably includes at least one of an acrylic oligomer and a urethane acrylate oligomer. An oligomer combined with a hyperbranched polyester acrylate component significantly improves ink adhesion to a wide range of substrates, including substrates that are difficult for radiation curable inkjet inks to adhere to, e.g. polyolefins.

The ink compositions also comprise a monomer component. The monomer component comprises <NUM>-<NUM>% by weight, which is selected based on good solvency to the dendritic and hyperbranched polyester acrylate component and the oligomer component used in the ink compositions. The ink compositions are free or substantially free of solvent or other non-reactive diluents. If any solvent or non-reactive diluents are present, they comprise less than <NUM>% by weight of the ink compositions, preferably less than <NUM>% by weight The ink compositions comprise a dendritic and hyperbranched polyester acrylate component, an oligomer component, a monomer component, a photoinitiator component, and an additive component. The compositions can have a viscosity of not greater than <NUM> mPa·s at <NUM>° Celsius. The compositions are radiation curable to form a cured film having an elongation of about <NUM>% to <NUM>%.

The ink compositions are directed to inkjet printing, which includes the delivery of the ink compositions to a substrate and subsequent exposure of the ink compositions to radiation to cure the ink compositions on the substrates.

The invention generally relates to radiation curable ink compositions, which comprise: (<NUM>) a dendritic and hyperbranched polyester acrylate component; (<NUM>) an oligomer component; (<NUM>) a monomer component; (<NUM>) a photoinitiator component; (<NUM>) a colorant component; and (<NUM>) an additive component.

The ink compositions include several chemical materials. These materials share a function or property in the ink compositions that is collectively referred to as a component. A functional group in the invention refers to compounds having unsaturated carbon-carbon groups that can be polymerized by radiation during the curing process to form an ink film.

A dendritic polymer is built up in stages from building blocks of lower molecular weight. The dendritic polymer forms a repeatedly branched species that is characterized by structural perfection. This is based on the evaluation of both symmetry and polydispersity. In contrast to the dendrimer, a hyperbranched polymer is easy to produce, preferably in a single stage or two stage reactions, but the structure lacks the highly branched symmetric structure.

In contrast to linear polymers, dendritic and hyperbranched polymers have spherical or three-dimensional globular structures that provide more interaction sites, have a low molecular volume for a given molecular weight, and have a high concentration of end groups. Suitable materials than can be employed to form the dendritic or hyperbranched component include, but are not limited to, hyperbranched polyester acrylates under the designations of CN2300, CN2301, CN2302, CN2303, CN2304 from Sartomer®. CN2300, CN2301, CN2302, CN2303, and CN2304 have a functionality of <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> respectively.

The ink compositions can be cured with a small amount of radiation energy, also known as low dosage or fast curing ink. The fast curing property of the ink compositions described in the invention is critical for high speed printers.

Fast curing inks can substantially reduce substrate heating during printing, which broadens the application of the radiation curable ink in inkjet printing to a wide variety of heat sensitive substrates.

An ultraviolet (UV) lamp is generally used to cure radiation curable inks. Infrared (IR) light is a by-product of the UV lamp. IR light substantially heats up and wrinkles the substrate during printing, which affects the quality of the printed images. More UV output from the UV lamp creates more IR output, and more substrate heating.

The dendritic and hyperbranched polyester acrylate component comprises <NUM>-<NUM>% by weight of the ink compositions. The dendritic and hyperbranched polyester acrylate component preferably comprises <NUM>-<NUM>% by weight of the ink compositions.

The dendritic and hyperbranched polyester acrylate in the component preferably has a functionality of greater than <NUM>. More preferably, the dendritic and hyperbranched polyester acrylate in the component has a functionality of in the range of <NUM>-<NUM>.

The ink compositions comprise an oligomer component. The amount of the oligomer component in the ink compositions is <NUM>-<NUM>% by weight. The oligomer component comprises at least one of an acrylic oligomer and a urethane acrylate oligomer.

It is preferable to use an oligomer component of low viscosity, low volatility, high reactivity, low glass transition temperature, and good adhesion to multiple substrates in the ink compositions. The functionality of the oligomer component is preferably not greater than <NUM>, and more preferably the functionality of the oligomer component is not greater than <NUM>. The low functionality contributes to more flexible ink compositions. An oligomer component combined with a hyperbranched polyester acrylate component can significantly improve ink adhesion to a wide range of substrates, including substrates that are difficult for radiation curable inkjet inks to adhere to, e.g. polyolefins.

Examples of suitable acrylic oligomers include, but are not limited to, those under the designations of CN820, CN152, and CN146, etc. from Sartomer®. Examples of suitable urethane acrylates include, but are not limited to, aliphatic and aromatic urethane acrylates under the designations of CN991, CN929, CN966, CN981, CN9006, CN9007, CN992, CN994, CN997, CN978, CN1963, etc. from Sartomer® and those from Cytek® Surface Specialty under the designations of Ebecryl <NUM>, Ebecryl <NUM>, etc..

The ink compositions comprise a monomer component. The amount of the monomer component in the ink compositions is <NUM>-<NUM>% by weight of the ink compositions. It is preferred that the monomer component offer good solvency to the dendritic and hyperbranched polyester acrylate component and the oligomer component in ink formulations, which dilutes the ink to a low viscosity. It is also preferred that the monomer component has low glass transition temperature, which contributes to the flexibility of ink after curing. The functionality of the monomer is preferably not greater than <NUM> to create more flexible ink compositions.

The monomer component comprises both monofunctional and difunctional monomers.

The mono-functional monomers include any of tetrahydrofurfuryl acrylate, vinyl caprolactam and isobornyl acrylate.

The di-functional monomer is propoxylated neopentyl glycol diacrylate.

The ink compositions comprise a photoinitiator component. In the radiation curing process, the photoinitiator component initiates the curing in response to incident radiation. The amount of a photoinitator component in the ink compositions is <NUM>-<NUM>% by weight. The selection of the type of the photoinitiator component in the ink compositions is generally dependent on the wavelength of curing radiation and the colorant employed in the ink compositions. It is preferred that the peak absorption wavelengths of selected photoinitiator vary with the range of wavelength of curing radiation to effectively utilize radiation energy, especially using ultraviolet light as radiation.

Examples of suitable photoinitiators include, but are not limited to, <NUM>-hydroxycyclohexylphenyl ketone, <NUM>-isopropylphenyl-<NUM>-hydroxy-<NUM>-methyl propan-<NUM>-one, <NUM>-[<NUM>-(<NUM>-hydroxyethoxy)-phenyl]-<NUM>-hydroxy-<NUM>-methyl-<NUM>-propan-<NUM>-one, <NUM>,<NUM>-dimethyl-<NUM>-hydroxy-acetophenone, <NUM>,<NUM>-dimethoxy-<NUM>-phenylacetophenone, <NUM>-hydroxy-<NUM>-methylpropionphenone, Diphenyl (<NUM>,<NUM>,<NUM>-trimethylbenzoyl) phosphine oxide, bis(<NUM>,<NUM>-dimethoxy-benzoyl)-<NUM>,<NUM>,<NUM> trimethyl phenyl phosphine oxide, <NUM>-methyl-<NUM>-<NUM>[<NUM>-(methylthio)phenyl]-<NUM>-morpholino-propan-<NUM>-one, <NUM>,<NUM>-bis(<NUM>-methyl-<NUM>-morpholino-propionyl)-<NUM>-n-octylcarbazole, <NUM>-benzyl-<NUM>-(dimethylamino)-<NUM> -(<NUM>-morpholinyl) phenyl)-<NUM>-butanone, benzophenone, <NUM>,<NUM>,<NUM>-trimethylbenzophenone, isopropyl thioxanthone. Suitable blends of photoinitiators commercially available include, but are not limited to, those under the designations of Darocur <NUM>, Irgacure <NUM>, Irgacure <NUM> from Ciba® Specialty Chemicals; and Esacure KT37, Esacure KT55, Esacure KTO046 from Lamberti®.

The photoinitiator component can further comprise a co-initiator. The amount of co-initiator component is <NUM>-<NUM>% by weight of the ink compositions, preferably <NUM>-<NUM>% by weight of the ink compositions, more preferably <NUM>-<NUM>% by weight of ink compositions. The co-initiator component is used to activate photoinitiators to initiate polymerization or is used to improve the surface curing of ink by mitigating oxygen inhibition to free radicals generated by photoinitiators. Examples of suitable co-initiators include, but are not limited to, those under the designations of CN386, CN384, and CN383 from Sartomer® and Ebecryl <NUM> from Cytec® Surface Specialty.

The ink compositions further comprise an additive component including a stabilizer, polyacrylate, and Polyether Modified Polydimethyl Siloxane, wherein the additive component is <NUM>% by weight of the radiation curable ink.

A stabilizer is used to improve shelf life and photolytic stability of ink compositions. Stabilizers in the ink compositions can include an ultraviolet light stabilizer, a free radical scavenger stabilizer, etc. Examples of ultraviolet light stabilizers include ultraviolet absorber stabilizer and hindered amine light stabilizer. These stabilizers are used to improve the outdoor durability and weatherability of cured ink. Commercially available ultraviolet light stabilizers include, but are not limited to, those under the designation of Tinuvin <NUM>, Tinuvin <NUM>, Tinuvin171, Tinuvin <NUM>, Tinuvin123, and Tinuvin <NUM> from Ciba® Specialty Chemicals, etc..

The ink compositions further comprise a colorant component in the form of a pigment. The amount of colorant component in the ink compositions is in the range of <NUM>-<NUM>% by weight.

Examples of suitable Pigments include, but are not limited to, those under the designation of Pigment Blue <NUM>, Pigment Blue <NUM>, Pigment Blue <NUM>:<NUM>, Pigment Blue <NUM>:<NUM>, Pigment Blue <NUM>:<NUM>, Pigment Blue <NUM>:<NUM>, Pigment Blue <NUM>:<NUM>, Pigment Blue <NUM>, Pigment Blue <NUM>, and Pigment Blue <NUM>; Pigment Brown <NUM>, Pigment Brown <NUM>, and Pigment Brown <NUM>; Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, and Pigment Yellow <NUM>; Pigment Green <NUM>, Pigment Green <NUM>, Pigment Green <NUM>, and Pigment Green <NUM>; Pigment Orange <NUM>, Pigment Orange <NUM>, Pigment Orange <NUM>, Pigment Orange <NUM>, Pigment Orange <NUM>, Pigment Orange <NUM>, Pigment Orange <NUM>, Pigment Orange <NUM>, Pigment Orange <NUM>, Pigment Orange <NUM>, and Pigment Orange <NUM>; Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>:<NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, and Pigment Red <NUM>; Pigment Violet <NUM>, Pigment Violet <NUM>, Pigment Violet <NUM>, Pigment Violet <NUM>, Pigment Violet <NUM>; and Pigment Black <NUM> or <NUM> (<NPL>and), Black PB <NUM> and <NUM>; carbon black; titanium dioxide (including rutile and anatase); zinc sulfide, and the like or a mixture thereof.

Preferably, the pigment is pre-dispersed prior to incorporation, generally into one or more of the monomer and/or oligomer components used in the ink compositions. Dispersion agents generally are used to improve the stability of dispersion by reducing or avoiding the possibility of pigment particle settling or agglomerating. Examples of suitable dispersion agents include, but are not limited to, those under the designations of Solsperse <NUM> from Lubrizol® Advanced Materials, and DisperBYK <NUM> and DisperBYK180 from Byk Chemie®. The pigment in the dispersion can be <NUM>-<NUM>% by weight. Other additives such as stabilizers, flowing additive, etc. can be incorporated during the dispersion process to improve the stability of dispersion.

The ink compositions have a viscosity suitable for ink-jet printing. They have a viscosity not greater than <NUM> mPa·s at <NUM>° Celsius. Preferably, the viscosity is not greater than <NUM> mPa·s at <NUM>° Celsius.

The ink compositions can be printed on an ink jet printer. Any conventional ink jet printer is acceptable.

In one embodiment, the ink jet printer includes a component for radiation curing of the ink. In another embodiment, the radiation curing component is a separate assembly. Non-limiting examples of suitable radiation sources for UV curing include high-pressure or low-pressure mercury vapor lamps, with or without doping, or electron beam sources. Their arrangement is known in principle and may be adapted to the circumstances of the substrate for printing and the process parameters.

Curing testing was conducted on a pressure-sensitive-adhesive (PSA) vinyl substrate, DPF2000 produced by Arlon®. The thickness of ink film was <NUM>-<NUM> micrometers prepared using #<NUM> drawdown rod. The ink film was then cured using a medium-pressure mercury vapor lamp.

The elongation was measured using a tensile tester from COM-TEN, Model: <NUM> Series. The ink sample was cut into strips with <NUM> (<NUM> inch) width, and placed in the two clamps, which was set <NUM> (<NUM> inches) apart. The speed crosshead is <NUM>,<NUM>/min (<NUM> inches/min), and the test was stopped when the sample broke. The elongation was measured at the point when the test stopped.

The adhesion measurement was based on ASTM D <NUM>. The test was conducted by cutting a cross-hatch pattern on the ink sample and applies a suitable tape, e.g. Permacel <NUM> adhesion test tape from Permacel® over the crosshatch area. The tape was rubbed firmly to remove any trapped air bubbles to ensure full contact, and the tape was then rapidly pulled off close to an angle of <NUM>. The Crosshatch area was evaluated based on ASTM D <NUM> method B.

The example depicts four cyan ink compositions comprising (<NUM>) a dendritic or hyperbranched polyester acrylate component; (<NUM>) an oligomer component; (<NUM>) a monomer component; (<NUM>) an additive component; (<NUM>) a photoinitiator component; and (<NUM>) a pigment component according to one embodiment of the invention. In this example, the ink composition exhibits a viscosity of below <NUM> mPa·s at <NUM>, a fast curing property, and good flexibility with elongation of <NUM>-<NUM>%. The ink composition is shown in table1 and the ink property is shown in table <NUM>.

As shown in table <NUM>, the dendritic or hyperbranched polyester acrylate component comprises CN2303 and CN2302 made by Sartomer®. The oligomer component comprises CN820, CN152, CN991, and CN3100 made by Sartomer®. The monomer component consists of a tetrahydrofurfuryl acrylate called SR285 made by Sartomer®, an isobornyl acylate (IBOA), and a vinyl-caprolactam (V-CAP). The photoinitiator component comprises a Diphenyl (<NUM>,<NUM>,<NUM>-trimethylbenzoyl) phosphine oxide called Genocure TPO made by Rhan®, a Irgacure <NUM> and a <NUM>,<NUM>-dimethyl-<NUM>-hydroxy-acetophenone called Darocur <NUM> made by Ciba® Specialty Chemicals. The additive component comprises a leveling additive called BYK361N made by BYK Chemie®, a surfactant called BYK377 made by BYK Chemie®, and a stabilizer call ST-<NUM> made by AlbemarleO.

In this example, a pre-dispersed pigment slurry was combined with the other ingredients to produce the ink composition. A person of ordinary skill in the art will recognize, though, that the ink composition can be created with dry pigment as well.

Example <NUM> describes four primary color inks generally used in the inkjet printing. The ink composition adheres to a broad range of substrates. In particular, the radiation curable ink strongly adheres to polyolefins, e.g. Coroplast, PVC, polycarbonates, polyesters, polystyrenes, ABS and textile materials, etc. The ink composition is shown in table <NUM> and the ink adhesion property is shown in table <NUM>.

Claim 1:
A radiation curable ink composition comprising:
(a) at least one of a dendritic and a hyperbranched polyester acrylate component, a total amount of the dendritic and hyperbranched polyester acrylate consisting of <NUM>-<NUM>% by weight of the ink composition;
(b) an oligomer component including any of Urethane Acrylate, and Acrylic Oligomers, wherein the oligomer component is <NUM>-<NUM>% by weight of the radiation curable ink;
(c) a monomer component, wherein the monomer component is <NUM>-<NUM>% by weight of the radiation curable ink composition and is comprised of a combination of mono-functional monomer and remainder di-functional monomer, wherein the mono-functional monomers include any of Tetrahydrofurfuryl Acrylate, Isobornyl Acrylate, and Vinylcaprolactam and comprise <NUM>-<NUM>% of the monomer component, and the di-functional monomer is Propoxylated Neopentyl glycol diacrylate;
(d) a photoinitiator component that is <NUM>-<NUM>% by weight of the radiation curable ink;
(e) an additive component including a stabilizer, polyacrylate, and Polyether Modified Polydimethyl Siloxane, wherein the additive component is <NUM>% by weight of the radiation curable ink; and
(f) a pigment component that is <NUM>-<NUM>% by weight of the radiation curable ink composition.