Abstract:
This invention relates to novel radiation-curable, rosin-based resins and the process for preparing them. In particular, the invention relates to unsaturated polyester resins containing fully fumarated rosin and/or fully maleated rosin which have softening points of at least 80° C. and are capable of being flaked into solid chips; a property that make the resins useful in formulating vehicles for lithographic printing inks and other coating applications.

Description:
FIELD OF INVENTION 
     This application is a continuation-in-part of my commonly assigned U.S. patent application Ser. No. 07/603,427 filed Oct. 26, 1990 entitled &#34;Radiation-Curable Rosin-Based Resins&#34;, now abandoned. This invention relates to novel radiation-curable, rosin-based resins and the process for preparing them. In particular, the invention relates to unsaturated polyester resins containing fumarated rosin and/or maleated rosin which exhibit properties that make them useful in formulating vehicles for lithographic printing inks and other coating applications. 
    
    
     BACKGROUND OF THE INVENTION 
     It is known in the art to react a polyol and a dibasic carboxylic acid to produce an unsaturated polyester resin. When a simple polyol is utilized to limit the chain extension to only a few units, the products are referred to as oligomers. Diluents are used with these resins to reduce the viscosity of formulation to levels suitable for the required method of coating. These diluents are usually distinct from resins in that they are discrete molecular units. Thus, the diluents are often termed monomers. 
     A wide range of reactive oligomers have been used as components in radiation (via electron beam or ultraviolet) curable inks and coatings. The majority of these employ acrylic functionality to induce a rapid cure. However, resins with maleic or fumaric functionality have found uses in certain applications such as wood coatings and, to a limited extent, lithographic inks. These resins, while not as reactive as acrylic-functional resins, are less expensive. In appropriate applications, coating formulators will trade a certain amount of cure speed for lower costs. 
     These lower cost resins are unsaturated polyesters typically produced from a glycol and a dibasic carboxylic acid, most often maleic anhydride. Usually phthalic anhydride or isophthalic acid is added to the polyester to control functionality and to increase hardness. Yet, even with the aromatic acid, these resins remain low-melting solids or semi-solids incapable of being flaked into solid chips. It is recognized in the art that a resin must have a softening point of at least 80° C. in order to be uniformly flaked. 
     This inability to be flaked requires that the resins be dissolved in monomers and sold as solutions. Monomers play the same rheological adjustment and pigment-wetting role in radiation-curable coatings as do solvents in conventional coatings. Thus, instead of the coatings formulator having one solid resin he can introduce into a number of systems, the formulator is currently required to specify the resin-containing monomer solution or solutions needed for each system. 
     Therefore, it is the object of this invention to produce a radiation-curable resin that is 100% solid at a temperature of 80° C., and thus is capable of being flaked. The invention would result in a lowering of shipping, handling, and inventory costs for coating and ink producers. 
     SUMMARY OF THE INVENTION 
     The object of this invention is met by the use of fully fumarated rosin and/or fully maleated rosin in the radiation-curable resin in lieu of the traditional phthalic anhydride or isophthalic acid. This rosin substitution produces a resin with a higher softening point than was previously attainable. This finding is significant since it allows a 100% solid resin to be produced which is capable of being flaked and utilized in that condition. 
    
    
     FIG. 1 depicts the formation of maleated or fumarated rosin via Diels-Alder adduction. 
     FIG. 2 depicts the incorporation of maleated rosin into an unsaturated polyester. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is well known in the art to react a polyol and a dibasic carboxylic acid to produce an unsaturated polyester resin. Examples of processes for producing these resins are described in U.S. Pat. No. 3,338,850 and in U.S. Pat. No. 4,316,835, both of which are incorporated herein by reference. 
     Polyols which are suitable for use in the reaction include, but are not limited to, the following: 
     1,3-butanediol, 
     1,4-butanediol, 
     1,4-cyclohexanedimethanol, 
     diethylene glycol, 
     ethylene glycol, 
     propylene glycol, 
     neopentyl glycol, 
     glycerol, 
     trimethylolethane, 
     trimethylolpropane, and 
     pentaerythritol. 
     Dibasic carboxylic acids which are suitable for use in the reaction include, but are not limited to, the following: 
     isophthalic acid, 
     phthalic anhydride, 
     ortho-phthalic acid, 
     terephthalic acid, 
     maleic anhydride, 
     fumaric acid, 
     azelaic acid, 
     adipic acid, and 
     dimer acid. 
     Diluents which are suitable for use with the resins include, but are not limited to, the following: 
     2-ethylhexyl acrylate, 
     hexanediol diacrylate, 
     n-vinylpyrrolidone, 
     trimethylolpropane triacrylate, 
     trimethylolpropane trimethacrytate, 
     styrene, and 
     tripropylene glycol diacrylate. 
     The invention resins are compatible with such common oligomers as urethane acrylates, epoxy acrylates, and the like. 
     These lists are intended to be representative and it will be obvious to those skilled in the art that a variety of other acids, polyols, diluents, and oligomers can be used. Therefore, other components suitable for use in the reaction can be considered part of this invention when used with the described composition of matter below. 
     The invention that is useful in raising the softening point of a radiation-curable unsaturated polyester resin to the point where the resin can successfully be flaked is produced by replacing 20% to 80% of the standard dibasic acid with fully maleated rosin, fully fumarated rosin, or a combination thereof. Specifically, the flakable resin is produced by reacting in a fusion reaction: (a) 12 to 68% by weight of a member selected from the group consisting of: fully maleated rosin, fully fumarated rosin, and combinations thereof; (b) 12 to 68% by weight of a member selected from the group consisting of: maleic anhydride, maleic acid, fumaric acid, and combinations thereof; (c) 15 to 40% by weight of a polyol; and (d) up to 20% by weight of a member selected from the group consisting of aromatic dibasic acid and saturated aliphatic dibasic acid. 
     The invention teaches the use of resins that contain maleic anhydride, maleic acid, and/or fumaric acid far in excess of the amounts that could be accommodated by the rosin via Diels-Alder adduction. This excess is incorporated into the resin via esterification. Maleic anhydride, maleic acid, or fumaric acid that is adducted via the Diels-Alder reaction loses its unsaturation in the process, whereas that which is incorporated by esterification retains its unsaturation. This unsaturation is what makes the application&#39;s resins curable. 
     For example, see FIG. 1. Note that a double bond (A) exists between the two carbonyl groups in the maleic anhydride or fumaric acid; and that these two carbonyl group are joined by single bonds (B) in their respective adducts (maleated or fumarated rosin). 
     FIG. 2 shows incorporation of maleic anhydride into a resin by esterification, thereby preserving the double bonds (C). A similar incorporation would occur if maleic acid or fumaric acid was substituted for the maleic anhydride.) It is these double bonds that are conjugated with carbonyl groups which are reactive towards styrene or acrylic esters during the radiation curing of the coating. ##STR1## 
     This aspect of the Diels-Alder reaction is well-known to those skilled in the art, as referenced by the article on rosin contained in the KIRK-OTHMER ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY at pages 475-508 (which is hereby incorporated by reference). Although several diterpene acids are found in rosin, levopimaric acid is the isomer that is subject to Diels-Alder adduction due to its cisoid conjugated double bonds. However, other acids (such as palustric, abietic, or neoabietic acids) will isomerize to levopimaric acid at high temperature (ca. 200° C.). These acids are known as PAN acids in the rosin industry. The amount of maleic anhydride, maleic acid, or fumaric acid that will react with the rosin via Diels-Alder adduction is thus determined by its PAN acid content, which can range from 50 mole-% for tall oil rosin to 90 mole-% for some gum rosins. 
     The tall oil rosin used in the examples below is a Westvaco sidestream rosin which has an equivalent weight per carboxyl group of 312 and a PAN acid content of 50%. Therefore, one equivalent of this rosin (312 parts by weight) should react with 0.5 mole of fumaric acid (58 p.b.w.). Thus, (58/312)×100=18.6 wgt.-% fumarated rosin as specified by the example. Since the reactive capacity of the PAN acids has now been satisfied, any additional fumaric acid that is added to the cook must either not react or react by some other mechanism. When there is a glycol present, that other mechanism will be esterification. Thus, each example cited in the application is fully maleinated or fully fumarated from a Diels-Alder perspective. 
     As appreciated in the art, the exact components and properties of components desired for any coating application can vary, and, therefore, routine experimentation may be required to determine the optional components and proportions of components for a given application and desired properties. 
     The following examples are provided to further illustrate the present invention and are not to be construed as limiting the invention in any manner. 
     EXAMPLE 1 
     Table I shows the physical properties of three unsaturated polyesters. The first resin was made as a control, and its composition is typical of unsaturated polyesters which are currently being used in the industry. The second and third resins were formulated replacing the phthalic anhydride with, respectively, fully fumarated rosin and fully maleated rosin. The maleic anhydride content was kept constant to maintain constant functionality (i.e. equal moles of reactive unsaturation per unit weight). The modified resins had much higher acid numbers than the control resin due in part to the tertiary carboxyl groups of the maleated or fumarated rosin not esterifying under the polymerization conditions used (200° C.). This high acid number does not interfere with radiation curing. 
     All resins were prepared by a conventional fusion procedure as illustrated by preparation of the fumarated rosin modified resin. To a 1 L flask fitted with a stirrer, nitrogen sparge tube, and Snyder column was charged 370.0 g of 18.6% fumarated tall oil rosin, 171.5 g of maleic anhydride, 171.0 g of propylene glycol, 0.71 g of phenothiazine, and 0.71 g of dibutyltin oxide. The charge was heated to 200° C. while the temperature at the head of the Snyder column was kept at 100° C. or less to prevent loss of glycol. Heating continued at 200° C. for about five hours to produce a polyester resin. All of the resins were soluble in styrene and various acrylic diluents such as 2-ethylhexyl acrylate, hexanediol diacrylate, and trimethylolpropane triacrylate. The cure speeds of the resins were evaluated by making respective solutions of 60 parts-by-weight of resin, 40 parts of styrene, and 1 part of benzoin isobutyl ether. These UV curable coating solutions were drawn down with a #10 wire-wound rod on Leneta drawdown cards. The cards were placed separately on the conveyer of a lab 6-inch Fusion Systems UV curer (which was set at a speed of 40 feet per minute). The number of passes required to cure to a tack-free state was measured, and recorded in Table I below. All of these polyester resin solutions cured to produce clear, glossy films. 
     
                       TABLE I______________________________________Resin No.   Composition              S.P. (°C.)                       Acid No.                              Visc.*                                    Cure**______________________________________1       23.8   MA      76      16    L-M   2   40.6   PG   35.6   PA2       24.1   MA      94     103    T     2   24.0   PG   51.9   FTOR3       24.4   MA      86     111    I     2   24.3   PG   51.3   MTOR______________________________________ *Viscosity 60% in Styrene **Passes to produce a tackfree cure (see text above) Key: FTOR 18.6% Fumarated tall oil rosin MA Maleic anhydride MTOR 15.7% Maleated tall oil rosin PA Phthalic anhydride PG Propylene glycol 
    
     Both the fumarated modified resin and the maleated modified resin achieved softening points which are sufficiently high to permit successful flaking. 
     Solutions of Resin No. 3 from Table I were made in a variety of reactive diluents. Drawdowns were performed with a wire-wound rod as described above and cured on the Fusion Systems curer at a rate of 120 feet per minute. The solutions contained 2% diethoxyacetophenone as a photoinitiator. 
     
                       TABLE II______________________________________Solution No.     Composition           Cure*______________________________________1         60.0 Rosin resin      3     30.0 Styrene     10.0 Hexanediol diacrylate2         60.0 Rosin resin      3     30.0 Styrene     10.0 Tripropylene glycol diacrylate3         60.0 Rosin resin      3     30.0 Styrene     10.0 Trimethylolpropane triacrylate4         60.0 Rosin resin      3     30.0 Styrene     10.0 Pentaerythritol triacrylate5         60.0 Rosin resin      2     30.0 Diethylene glycol diacrylate     10.0 Tripropylene glycol diacrylate6         60.0 Rosin resin      2     30.0 Diethylene glycol diacrylate     10.0 Trimethylolpropane triacrylate______________________________________ *Passes to produce a tackfree cure. 
    
     All of these resin solutions cured to produce clear, glossy films. 
     EXAMPLE 2 
     Following the procedure outlined in Example 1, a series of resins were produced to evaluate the effects of various glycols on the softening point of the resin. The results are listed in Table II below. 
     
                       TABLE II______________________________________Resin No.  Composition      Acid No.                              S.P. (°C.)______________________________________1          47.7   FTOR      103    86      26.2   FA      26.1   1,4-BD2          47.7   FTOR      102    90      26.2   FA      26.1   1,3-BD3          51.9   FTOR      105    96      28.5   FA      19.6   EG4          42.0   FTOR      103    98      23.1   FA      29.5   CHDM      5.4    DEG5          41.0   FTOR      108    102      22.5   FA      36.5   TMPD6          49.7   FTOR      102    103      27.3   FA      23.0   PG7          41.3   FTOR      100    118      22.6   FA      36.1   CHDM______________________________________ Key: 1,3BD 1,3butanediol 1,4BD 1,4butanediol CHDM 1,4cyclohexanedimethanol DEG Diethylene glycol EG Ethylene glycol FA Fumaric acid FTOR 18.6% Fumarated tall oil rosin PG Propylene glycol TMPD Trimethylpentanediol 
    
     As Table II shows, the more flexible the glycol moiety, the lower the softening point of the resin. The results range from 1,4-butanediol with a four methylene segment at 86° C. up to 1,4-cyclohexane dimethanol with a relatively rigid ring structure at 118° C. However, all the resins would be capable of successful flaking. 
     EXAMPLE 3 
     Following the procedure in Example 1, two resins were produced where maleic anhydride was substituted for fumaric acid to evaluate the effect on the softening points of the respective resins. The results are listed in Table III below. 
     
                       TABLE III______________________________________Resin No.    Composition Acid No.  S.P. (°C.)                                 Visc.*______________________________________1        49.7    FTOR    102     103    W    27.3    FA    23.0    PG2        51.3    MTOR    111      86    I    24.4    MA    24.3    PG______________________________________ *Viscosity 60% in styrene Key: FA Fumaric acid FTOR 18.6% Fumarated tall oil rosin MA Maleic anhydride MTOR 15.7% Maleated tall oil rosin PG Propylene glycol 
    
     Although both resins achieved softening points which are sufficiently high to allow flaking, the fumarated modified resin has a softening point and a viscosity which are substantially higher than its maleated counterpart. 
     EXAMPLE 4 
     Following the procedure outlined in Example 1, two resins were produced where the acid number was varied to evaluate its effect on the softening points of the resins. The results are listed in Table IV below. 
     
                       TABLE IV______________________________________Resin No.  Composition      Acid No.                              S.P. (°C.)______________________________________1          51.3   MTOR      111    86      24.4   MA      24.3   PG2          48.0   MTOR      126    93      29.3   MA      22.7   PG______________________________________ Key: MA Maleic anhydride MTOR 15.7% Maleated tall oil rosin PG Propylene glycol 
    
     While both resins achieved softening points sufficiently high to allow for successful flaking to occur, the resin with the higher acid number obtained the higher softening point. 
     EXAMPLE 5 
     Following the procedure of Example 1, three resins were produced to evaluate the effect of replacing ethylene glycol with diethylene glycol on the softening points of the resins. The results are listed in Table V below. 
     
                       TABLE V______________________________________Resin No.  Composition      Acid No.                              S.P. (°C.)______________________________________1          51.9   FTOR      105    96      28.5   FA      19.6   EG2          48.6   FTOR      107    70      26.6   FA      15.6   DEG      9.2    EG3          45.6   FTOR       99    65      25.0   FA      29.4   DEG______________________________________ 
    
     While the first resin formulated with ethylene glycol achieved a softening point which was capable of being flaked, the resins formulated with diethylene glycol had softening points which were too low to allow for consistent flaking. (For an example of a resin formulated with diethylene glycol that has a softening point over 80° C., see Table II, resin number 4.) 
     Many modifications and variations of the present invention will be apparent to one of ordinary skill in the art in light of the above teachings. It is therefore understood that the scope of the invention is not to be limited by the foregoing description, but rather is to be defined by the claims appended hereto.