Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1999-10-08
2001-05-15
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S028000, C522S042000, C522S064000, C522S071000, C522S075000, C522S081000, C522S182000, C523S160000, C106S031130, C106S031600
Reexamination Certificate
active
06232359
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to ink compositions that are curable by exposure to actinic radiation such as ultraviolet radiation and that contain an aliphatic acrylate functional macromonomer. The invention is also directed to protective coating compositions that contain these macromonomers.
BACKGROUND OF THE INVENTION
The use of actinic radiation, such as ultraviolet radiation, to cure ink compositions is generally known in the art. Ultraviolet radiation can be used to cure various types of inks, such as thiolene inks, inks made up of aryl diazonium salts and epoxy resins, and inks containing acrylates including acrylated epoxies and urethanes. Of these, acrylate containing inks are often preferred because they are available at a reasonable cost and have good storage stability in addition to their useful properties as inks.
Acrylate type UV curable inks are typically made up of a pigment dispersed in a reactive base that may contain photoinitiators, reactive monomers or oligomers, preservatives, flow agents, and so on. The properties of the ink such as viscosity, gloss, and crosslink density can be controlled by varying the types and/or proportions of reactive diluents used in the formulation.
Radlove et al., in U.S. Pat. No. 3,856,744 describe photopolymerizable ink compositions that comprise an ethylenically unsaturated beta-hydroxy ester, a polyitaconate, and optionally a polyacrylate which functions as a reactive diluent. The Radlove compositions must contain 2 to 10 wt-% of the polyitaconate.
In U.S. Pat. No. 4,826,890 Gupta teaches radiation curable coating compositions that comprise a copolymer of dialkyl muconate and p-acetoxystyrene, a polyethylenically unsaturated radiation polymerizable compound, and optionally a monoethylenically unsaturated monomer such as an acrylate or methacrylate. Additional examples of radiation curable coatings are found in Wojnarowicz, EP 457 499; Kistner, U.S. Pat. No. 4,668,601; Liu et al., U.S. Pat. No. 5,106,885; and Hesse et al., U.S. Pat. No. 4,265,723.
Macromonomers, also known as high molecular weight monomers, are large molecules made up of repeating monomeric units and terminated by a polymerizable end group. These large monomers have long been used in the preparation of graft copolymers to provide uniform side chains or branches. Milkovich, U.S. Pat. Nos. 3,786,116 and 3,842,059 are examples of the use of macromonomers in the synthesis of graft copolymers. Acrylate containing macromonomers are known, as seen for example in Mori, U.S. Pat. No. 5,147,952.
Attempts have been made to incorporate macromonomers into UV curable inks. In EP 187,045, Kerr teaches the use of macromonomers in the preparation of radiation curable printing inks. The macromonomers used by Kerr have a repeating unit that is a vinyl aromatic monomer. Properties such as storage stability, adhesiveness, durability and so on are attributed by Kerr to the large mass of vinyl aromatic in the macromonomer. However, compositions containing high proportions of an aromatic monomer can have certain undesirable properties. For example, these compositions may be vulnerable to degradation by ultraviolet light, resulting in poor durability and short product life for applications where significant outdoor exposure is required. Aromatic macromonomer containing ink compositions may not adhere well to non-aromatic polymer substrates such as polymethylmethacrylate, making them less well suited to use in constructions containing such materials.
A need exists for radiation curable ink compositions that are durable, resistant to ultraviolet light once cured, and that adhere well to acrylate substrates.
SUMMARY OF THE INVENTION
The invention provides a radiation curable ink made up of an aliphatic acrylate functional macromonomer; a reactive acrylate monomer; an effective amount of a colorant; and an effective amount of a photoinitiator. These inks offer good resistance to ultraviolet light once cured, have excellent adhesion to acrylate film substrates such as polymethylmethacrylate, and can be either transparent or opaque.
The invention further provides a radiation curable coating that comprises an aliphatic acrylate functional macromonomer; a reactive acrylate monomer; and an effective amount of a photoinitiator. Radiation curable coatings according to the invention provide a durable, protective layer to a wide variety of substrates.
As used herein, the term “aliphatic” is inclusive of all non-aromatic acyclic or cyclic functionalities. The aliphatic moieties may be saturated or unsaturated, and may be substituted.
The macromonomers used in the invention comprise one or more aliphatic repeating units and have a polymerizable end group. These macromonomers generally have a number average molecular weight of about 3,000 to 15,000.
The durability and ultraviolet light resistance of the inks makes them particularly useful in applications where outdoor use is contemplated, such as in the imaging of retroreflective sheetings for durable traffic signage applications. The inventive coating may be used alone or in combination with the ink to provide additional protection from ultraviolet light and resistance to weathering.
DETAILED DESCRIPTION OF THE INVENTION
The macromonomer component of the ink composition is an aliphatic molecule preferably having a number average molecular weight ({overscore (M)}n) of about 3,000 to 15,000, more preferably about 6,000 to 10,000, that is made up of one or more aliphatic repeating units and has a polymerizable end group. Inclusion of such a macromonomer improves the adhesion of the ink to acrylate type films such as polymethylmethacrylate (PMMA) and also provides good solvent resistance properties.
The repeating units that make up the macromonomer are aliphatic, i.e. they do not contain any aromatic functionality. These cyclic or acyclic aliphatic repeating units may be either saturated or unsaturated and may be substituted as desired with non-aromatic substituent groups. Examples of suitable repeating groups include aliphatic ethylenically unsaturated carboxylic acids, esters, and other groups that will not interfere with the curing of the ink. Of these, ethylenically unsaturated acids such as acrylic acid and methacrylic acid are among the preferred repeating groups in the macromonomer component of the inks. The repeating groups found in the macromonomer may be the same or different.
The polymerizable end group of the macromonomer is typically an aliphatic, ethylenically unsaturated group that is capable of reaction with one or more of the reactive acrylate monomers used to prepare the inks. This reactive functionality allows the macromonomer to be crosslinked directly into certain film substrates by free radical polymerization initiated by exposure to ultraviolet radiation. Examples of useful end groups for the macromonomer include the ethylenically unsaturated carboxylic acids, such as acrylic and methacrylic acid.
Preferred macromonomers include compounds of the formula (I) or (II):
R—(R1)
n
—(CH
2
)
1-5
—R2—X (I)
R—(R1)
n
—X (II)
wherein
R is H, C
1-20
alkyl which may be straight-chain or branched, or C
1-20
alkoxy which may be straight-chain or branched;
R2 is C
1-20
alkyl which may be straight or branched and which may be interrupted by one or more —CONR3—, —NR3CO—, —COO—, or —OCO— linkages;
R1 is
wherein R3 and R4 are each independently H or C
1-6
alkyl which may be straight-chain or branched;
X is
wherein R5 is H or C
1-6
alkyl; and
n is a number sufficient to provide the desired molecular weight, typically about 10 to 210.
Preferred macromonomers are those which have a methylmethacrylate, isobutyl methacrylate or isobutylmethacrylate/isooctylacrylate repeating unit. Especially preferred macromonomers have a methyl/methacrylate repeating unit and a methacrylic acid end group. Suitable methylmethacrylate macromonomers are available commercially as macromonomer resins AA-10 and AA-6 from Toagosei Co. LTD, Tokyo, Japan and macromonomer resin ELVACITE EP-M1010 from ICI Acrylics, Inc., Wilmington
3M Innovative Properties Company
Berman Susan W.
Fischer Carolyn A.
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