Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-02-25
2001-10-16
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S100000, C522S103000, C522S101000, C522S168000, C522S170000, C527S315000, C527S300000
Reexamination Certificate
active
06303670
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a novel ultraviolet-curable cellulosic coating composition having excellent adherence to metals, woods, polar plastics, etc. and being capable of forming a film excellent also in the solvent resistance, gloss and impact resistance.
Since cellulose esters are not only derived from cellulose that is one of the recyclable natural resources as a starting raw material, but also capable of forming films excellent in the solvent resistance, gloss, impact resistance, etc., they are applied to paint and ink additives, moldings such as film, and in other wide fields. Moreover, aiming at additional high functionalization of these cellulose esters, many crosslinking reactions that utilize the hydroxyl groups remaining in cellulose ester and being rich in reactivity are known.
In order to achieve good solvent solubility, the degree of ester substitution of cellulose is usually designed as low as around 1, and, as a result, the number of hydroxyl groups in one molecule of cellulose esters is very high. For this reason, in most crosslinking reactions utilizing cellulose esters, the control of crosslinking density is difficult, leading to many problems in actual application.
In order to solve the problems aforementioned, a technology for controlling the number of hydroxyl groups in cellulose acetate to about 1 or 2 at the end of molecule, and further a modifying technology for utilizing these esters are reported in U.S. Pat. No. 3386932, Japanese Unexamined Patent Publication Nos. Sho 60-135423 and Hei 2-48012, R. Amick et al; Polymer, 21, 648 (1980), etc.
With these conventional technologies, however, there arise problems of causing gelation at the stage of modifying these esters through urethane reaction etc., and the like, since it is difficult to accurately control the number and the position of hydroxyl groups in one molecule of cellulose acetate. In addition, these cellulose acetates being near 3-substitution form hardly dissolve into the solvents used commonly, thus making these technologies not to be used widely.
While, in the field of UV-curing resins, a cationic UV-curing resin comprising a combination of epoxy resin, hydroxyl group-containing crosslinking agent and photo initiator is developed widely in recent years from advantages such as less influence of oxygen etc. over conventional radical-polymerizable UV-curing resins. With respect to the application of cellulose esters in this field, there are little actual results in use, and they were at a level of insignificant use as additives. This is because of that, since the common cellulose esters have many hydroxyl groups as described above, if the use level becomes high, the crosslinking density would become too high, resulting in decreased physical properties of film.
As a result of diligent investigations, the inventors have found that cellulose acetate with adjusted number of hydroxyl groups in it has excellent compatibility with particular epoxy compound, hence it forms a homogeneous mixture even without solvent, and further that an excellent film can be formed under UV irradiation by adding photo initiator to this mixture, leading to the invention based on these knowledges.
SUMMARY OF THE INVENTION
As described above, the invention provides following (1) (2) and (3).
(1) Ultraviolet-curable coating composition comprising 5 to 30 parts by weight of cellulose acetate (A) with number average molecular weight of 1,500~5,000 and average number of free hydroxyl groups in one molecule of 1~3, 70 to 95 parts by weight of diepoxy compound (B) and not less than 0.1 part to not more than 5 parts by weight of photo cationic polymerization catalyst (C).
(2) The ultraviolet-curable coating composition, wherein the diepoxy compound (B) of (1) consists of at least one or more of aliphatic epoxy compound, alicyclic epoxy compound and glycidyl ether derived from aliphatic alcohol.
(3) The ultraviolet-curable coating composition described in (1) and (2), wherein the cellulose acetate (A) is compatible with the diepoxy compound (B) to give a homogeneous mixture without solvent.
DETAILED DESCRIPTION OF THE INVENTION
The cellulose acetate (A) with number average molecular weight of 1,500~5,000 and average number of free hydroxyl groups in one molecule of 1~3 suitable as the cellulose acetate to be used in the invention can be prepared by publicly known methods (e.g. method described in U.S. Pat. No. 3,386,932 etc.), for example, by methods of hydrolyzing cellulose triacetate with a mixture of acetic acid, acetic anhydride, sulfuric acid and water in particular proportion, and the like.
In the number average molecular weight is under 1,500, then it is difficult to recover after hydrolysis and the film after UV irradiation becomes brittle as well. If the number average molecular weight is over 5,000, then it is difficult to control the number of free hydroxyl groups to 1-3 and the viscosity of mixture with epoxy compound also increases, which is unpreferable.
If the average number of free hydroxyl groups in one molecule is under 1, then sufficient crosslinking does not occur, resulting in decreased physical properties of film. Also, if over 3, the crosslinking density becomes too high, leading to decreased physical properties of film.
The number average molecular weight of cellulose acetate can be measured by publicly known methods such as GPC (gel permeation chromatography) and the average number of free hydroxyl groups in a molecule can be determined using hydroxyl value measured by titration methods, NMR, etc. and number average molecular weight.
As the diepoxy compounds (B) to be used in the invention, aliphatic epoxy compounds such as 1,2,3,4-diepoxybutane, 1,2,7,8-diepoxyoctane and 1,2,9,10-diepoxydecane, glycidyl ether-based epoxy compounds derived from aliphatic alcohols such as 1,4-butanediol glycidyl ether, 1,6-hexanediol glycidyl ether, polyethylene glycol glycidyl ether and polypropylene glycol glycidyl ether, alicyclic epoxy compounds such as vinylcyclohexene diepoxide, 1,2,5,6-diepoxycyclooctane, 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohyxane carboxylate and its derivatives can be mentioned. Epoxy compounds other than above, for example, bisphenol A-based glycidyl ethers cannot be used, because of poor compatibility with the cellulose acetate of the invention.
The use level by weight of cellulose acetate (A) to diepoxy compound (B) is 5:95 to 30:70. If the amount of cellulose acetate is under this range, then decreased physical properties such as brittles film can result and, if the amount of cellulose acetate is over this range, then the viscosity increases or the insolubles generate, which is unpreferable.
The photo cationic polymerization catalyst (C) to be used in the invention is one to initiate the curing reaction through cationic polymerization mechanism by the use of ultraviolet rays, and publicly known catalysts, for example, aromatic iodonium salts such as hexafluoroarsenic acid-bis(dodecylphenyl)iodonium and hexafluoroantimonic acid-bis(dodecylphenyl)iodonium, aromatic sulfonium salts, aromatic diazonium salts, etc. can be used.
The use level of said photo cationic polymerization catalyst (C) is within a range from not less than 0.1% by weight to not more than 5% by weight based on total amounts of cellulose acetate (A) and diepoxy compound (B). If under 0.1% by weight, then the curing time becomes long and, if over 5% by weight, then decreased physical properties such as yellowing can result, which is unpreferable.
The coating composition of the invention has excellent adherence to metals, woods, polar plastics, etc. and forms a film excellent also in the solvent resistance, gloss and impact resistance. Moreover, additives such as leveling agent, viscosity modifier, photo stabilizer, moisture absorber, pigment, dye and reinforcing agent can be added to the composition of the invention for use. The use level of these additives can be determined appropriately depending on the purpose.
In following, the invention will be illustrated in more detail bas
Fujino Ken-ichi
Thames Shelby F.
McClendon Sanzei L.
Nippon Paper Industries Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seidleck James J.
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