Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2001-12-05
2004-03-30
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C526S301000, C528S049000, C528S075000
Reexamination Certificate
active
06713525
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a urethane (meth)acrylate oligomer, a process for its production and a photo-curable composition. Particularly, it relates to a urethane (meth)acrylate oligomer which has a low viscosity and which gives a cured product excellent in flexibility and adhesive property and having a low surface stickiness (hereinafter referred to as a surface tackiness), a process for its production and a photo-curable composition containing such an oligomer.
2. Description of the Background
In recent years, in all technical fields, energy saving, resource saving and environmental measures have become important subjects, and various technical developments have been made. As one of them, a photo-curable resin composition has been developed and used in applications to e.g. coating materials, adhesives, coating agents, printing ink vehicles, resist inks, relief printing plate materials, optical fiber coating materials and optical shaping materials. Such a photo-curable resin composition comprises a photo-curable oligomer, a photo-polymerizable monomer, a photo-polymerization initiator, a sensitizer, a colorant and other additives and contains substantially no volatile solvent, and it undergoes a curing reaction by irradiation with light rays having a certain specific wavelength to give a cured product excellent in flexibility and adhesive properties.
The photo-curable oligomer to be used here, is usually one having from one to several (meth)acryloyl groups as photo-curable functional groups in its molecular structure. Among such oligomers, a urethane (meth)acrylate oligomer obtainable by reacting a polyol and a polyisocyanate compound, is used in a wide range of fields, as its cured product exhibits excellent performance in the toughness, hardness, chemical resistance, flexibility, adhesive property, light resistance, low temperature characteristics, etc.
With respect to such a urethane (meth)aczylate oligomer, molecular designing can easily be done by changing the starting material variously depending upon the particular purpose of its use. Especially, it is easy to change the performance by the polyol to be used. When a low molecular weight polyol having a molecular weight of about a few hundreds, is used, a hard and brittle cured product will be obtained, and when a high molecular weight polyol having a molecular weight of from a thousand to a few thousands, is employed, a flexible and tough cured product will be obtained. As such a high molecular weight polyol, a polyoxyalkylene polyol, a polyester polyol, a polycaprolactone polyol or a polycarbonate polyol is, for example, employed.
However, if a high molecular weight polyol is used, the viscosity of the resulting urethane (meth)acrylate oligomer will be high, and it has been difficult to let the urethane moiety have a high molecular weight so as to obtain sufficient flexibility. Further, because of the high viscosity, there has been a problem in working efficiency, and as shown in JP-A-9-48830, it used to be necessary to employ a low molecular weight (meth)acrylate compound as a viscosity-reducing agent.
As a low viscosity polyol, a polyoxyalkylene polyol is known. However, if a common polyoxyalkylene polyol as shown in JP-A-10-95640 is used, since such a polyol contains a substantial amount of a by-product monool, the curing tends to be slow, and there has been a problem that no adequate physical properties can be obtained, or the surface tackiness of the cured product remains.
SUMMARY OF THE INVENTION
Under these circumstances, the present inventors have conducted an extensive study, and as a result, have found it possible to obtain a photo-curable composition which has a low viscosity and excellent curability and which gives a cured product having little surface tackiness, by employing a certain specific urethane (meth)acrylate oligomer based on a polyoxyalkylene polyol having a low total degree of unsaturation (i.e. a small monool content). The present invention has been accomplished on the basis of this discovery.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention has been made to solve the above-mentioned problems. In the first aspect, the present invention provides a urethane (meth)acrylate oligomer obtainable by reacting a polyol component (A) comprising a polyoxyalkylene polyol which has from 2 to 4 hydroxyl groups, a hydroxyl value V
OH
(mgKOH/g) of from 5 to 115 and a total degree of unsaturation V
US
(meq/g) satisfying the formula 1, with a polyisocyanate compound (B) and a hydroxylated (meth)acrylate compound (C):
V
US
≦(0.45/
V
OH
)+0.02 Formula 1
In the second aspect, the present invention further provides a photo-curable composition comprising the above urethane (meth)acrylate oligomer and a photo-polymerization initiator.
In this specification, “(meth)acrylate” is used as a general term representing “acrylate” and “methacrylate”.
The polyoxyalkylene polyol which has from 2 to 4 hydroxyl groups, a hydroxyl value V
OH
(mgKOH/g) of from 5 to 115 and a total degree of unsaturation V
US
(meq/g) satisfying the formula 1, to be used in the present invention, can be obtained usually by employing diethyl zinc, iron chloride, metal porphyrin, a double metal cyanide complex, a cesium compound or the like, as a catalyst. Especially preferred is one obtained by using a double metal cyanide complex. In the case of a commonly employed alkali metal such as potassium hydroxide, the unsaturated degree tends to be high especially with a high molecular weight product, such being undesirable.
The double metal cyanide complex may preferably be a complex comprising zinc hexacyanocobaltate as the main component, particularly preferably its ether and/or alcohol complex. As its composition, one disclosed in JP-B-46-27250 can essentially be employed. As the ether, an ethylene glycol dimethyl ether (glyme) or a diethylene glycol dimethyl ether (diglyme) may, for example, be preferred, and particularly preferred is glyme from the handling efficiency for the production of the complex. As the alcohol, t-butanol or t-butylcellosolve may, for example, be preferred.
The polyoxyalkylene polyol in the present invention, is produced by reacting a polyfunctional initiator with a monoepoxide in the presence of the above-mentioned catalyst. The monoepoxide is a compound having one epoxy ring, such as an alkylene oxide, glycidyl ether or glycidyl ester. As a preferred monoepoxide, ethylene oxide, propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, or styrene oxide may be mentioned. Particularly preferred is ethylene oxide or propylene oxide. These monoepoxides may be used in combination as a mixture of two or more of them.
The number of hydroxyl groups of such a polyoxyalkylene polyol is from 2 to 4, preferably from 2 to 3. Namely, as the initiator, a compound having from 2 to 4 active hydrogen atoms, is used. As the initiator, a polyhydroxy compound having from 2 to 4 hydroxyl groups is preferred, and particularly preferred is a polyhydroxy compound having from 2 to 3 hydroxyl groups. Specifically, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol, 1,4-butandiol, 1,6-hexane diol, glycerol, trimethylol propane, pentaerythritol, and a polyol having a molecular weight lower than the desired product, obtained by reacting an alkylene oxide thereto, may be mentioned. These polyhydroxy compounds may be used alone or in combination as a mixture of two or more of them. The hydroxyl value V
OH
(mgKOH/g) of the polyoxyalkylene polyol is from 5 to 115, preferably from 7 to 80, more preferably from 9 to 30. With a hydroxyl value higher than this, no adequate flexibility can be obtained, and with a lower hydroxyl value, no adequate strength will be obtained. The total degree of unsaturation V
US
(meq/g) of the polyoxyalkylene polyol is required to satisfy the formula 1 relating to the hydroxyl value V
OH
(mgKOH/g), preferably satisfies the formula 2, more preferably satisfies the formula 3.
V
US
≦(0.4
Asahi Glass Company Limited
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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