Method of Preparing Zinc-Modified Phenol-Aldehyde Novolak Resins and Use as a Color-Developing Agent

The present invention relates to zinc-modified phenolaldehyde novolak resins, and more particularly, to an improved method for making zinc-modified phenol-aldehyde novolak resins which are particularly useful in carbonless copy paper manifold systems as color-developing agents (coreactants) for colorless chromogenic materials.

The carbonless manifold systems generally comprise a substantially colorless developing agent, a substantially colorless chromogenic material and a common solvent or solvent mixture for each. The color-developing agents in the chromogenic material are isolated from each other on the surface of a substrate such as paper. The solvent may be isolated from each of the other ingredients or may contain either ingredient, usually the chromogenic material, in solution. Preferably, the colorless chromogenic material and the solvent are encapsulated in microcapsules as disclosed in U.S. Pat. Nos. 2,800,457; 3,041,289; 3,533,958 and 4,001,140. The configuration and relationship of either reactive component in the solvent can be of any of those disclosed in U.S. Pat. No. 3,672,935. The microcapsules containing a solution of the colorless chromogenic material may be applied with an adhesive or binder to one surface of a substrate such as paper. The color-developing agent may be applied as a coating to a second substrate, either alone or mixed with other ingredients such as adhesives or binders and mineral particles. When the two substrates are superimposed one on the other with the coated surfaces in contact with each other and then subjected to pressure, the microcapsules are ruptured in the configuration of the applied pressure, and the solution of colorless chromogenic material is transferred in the same configuration to the surface of the substrate containing the coating of the colordeveloping agent to form a colored mark on the surface, again in the configuration of the applied pressure. The microcapsules and color-developing agent may also be applied to the same surface of a substrate such as paper either as a mixture or as separate coatings. Pressure applied to several of these sheets superimposed one on the other produces a mark in the pattern of the indicia of the applied pressure. Other configurations include microcapsules containing a solution of the color-developing agent in which case the colorless chromogenic material is applied as a second coating to the same or a different substrate.

Zinc-modified-phenol-aldehyde novolak resins and methods of producing such resins for use as a color-developing agent for basic colorless chromogenic materials are known. U.S. Pat. No. 3,732,120 discloses a method of making such zinc-modified phenol-aldehyde novolak resins wherein a zinc compound such as zinc dibenzoate is added to a para-substituted phenolaldehyde novolak resin. The resulting zinc-modified novolak resin is cooled, ground and then coated onto a paper substrate in one or more of the configurations previously described. Improved resistance to print fade and increased color intensity were obtained by the use of the zinc-modified resin product when compared to the novolak resin material alone as a color-developing agent for oil-soluble basic colorless chromogenic materials in carbonless copy paper manifold systems.

U.S. Pat. No. 3,737,410 discloses a method of making zinc-modified para-substituted phenol-formaldehyde novolak resins which comprises mixing together and heating a zinc compound such as zinc dibenzoate, a weak base such as ammonium bicarbonate and an unmodified phenol-aldehyde resin material. Again, the resulting zinc-modified novolak resin provides improved color intensity and fade resistance as well as increased print speed and improved resistance to coreactant-surface sensitivity.

U.S. Pat. No. 4,025,490 discloses a similar method of producing zinc-modified para-substituted phenol-formaldehyde novolak resins comprising melting together with mixing, a composition of a material such as zinc formate, ammonia or an ammonium compound such as ammonium carbonate, and a para-substituted phenol-aldehyde novolak resin. It is stated that the resulting zinc-modified resin material provides an improved rate of color image development, fade resistance, and storage stability in a carbonless copy paper manifolding system prior to imaging the coreactant surface. It is also disclosed that the inclusion of the weak ammonium compound (ammonium carbonate) or ammonia gas suppresses the formation of metal oxide during the melting process. The metal oxide formed during the melting in effect prevents that portion of the metal from entering into modification of the novolak resin.

Accordingly, an object of the present invention is to provide an improved method of making zinc-modified phenol-aldehyde novolak resins for use as a color developing agent in pressure-sensitive record sheet material.

Another object of the invention is to provide zinc-modified para-substituted phenol-formaldehyde resins which are resistant to heat desensitization while in a wet coating mixture.

A further object of the present invention is to provide an improved method of making zinc-modified phenol-aldehyde novolak resins which, when used in a coating applied to a substrate, produces a reactive surface capable of developing images which exhibit excellent light stability (fade resistance).

These and other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following specification and claims.

The present invention comprises a method of producing a zinc-modified phenol-formaldehyde novolak resin by reacting an unmodified phenol-formaldehyde resin with a specific, dry particulate zinc compound and an ammonium carboxylate salt in dry particulate form. Specifically, the unmodified phenol-formaldehyde resin is reacted with solid particulate zinc oxide or zinc carbonate and solid particulate ammonium formate.

This reaction can be accomplished by adding the zinc compound selected from zinc oxide and zinc carbonate and the ammonium formate either to a novolak resin still in the liquid state from its preparation or to a novolak resin which has been melted. The mixture is reacted at a temperature of about 155.degree.-170.degree. C. and for a sufficient time to achieve the modification of the phenol-formaldehyde resin with the zinc compound. The resulting zinc-modified novolak resin is then cooled and ground with a small amount of dispersant and water. Advantageously, the mixture is reacted for about 45 to 90 minutes.

The use of the specific zinc-containing compounds provides a zinc-modified novolak resin which reacts with a colorless chromogenic material to develop an image which exhibits improved light stability (fade resistance). Moreover, the use of the zinc-modified novolak resins of the present invention in aqueous coating slurries results in improved resistance to heat desensitization. This property can be an improved factor in an actual production situation.

As aforementioned, the specific zinc-containing compounds useful in the present method are zinc oxide and zinc carbonate. Zinc oxide is the preferred zinc compound.

The phenol-formaldehyde novolak resins employed in the present invention preferably are substituted in the para-position of the phenol moiety. Particularly desirable novolak resins are para-octylphenol-formaldehyde resins, para-nonylphenol-formaldehyde resins, para-tertiary-butylphenol-formaldehyde resins and para-phenylphenol-formaldehyde resins. Of these, the most preferred of the para-substituted novolak resins is para-octylphenolformaldehyde resin. Other phenol-aldehyde novolak resins useful in this invention are disclosed in the aforementioned U.S. Pat. No. 3,732,120.

The ammonium compound utilized in the present invention is ammonium formate.

The phenol-aldehyde novolak resin is preferably used in the liquid state to which is added the dry particulate zinc material and the dry particulate ammonium material, the latter two compounds being added as a dry substantially homogeneous mixture. Particularly desirable results are achieved when the ammonium compound is present in an amount of about 2.85 to 11.28% by dry weight based upon the dry weight of the phenol-aldehyde novolak resin, preferably about 4.00 to 6.75% by dry weight. Likewise, particularly desirable results are achieved when the zinc material is present in an amount of about 1.85 to 7.24% by dry weight based upon the dry weight of the phenol-aldehyde novolak resin, preferably about 2.00 to 6.75% by dry weight. More preferably, the zinc material and the ammonium material are added simultaneously.

During the entire preparation process of this invention, it is preferable to carry out the process in an inert atmosphere, for example, under a blanket of inert nitrogen or helium gas. In general, a stream of such inert gas is made to flow over the surface of the reaction mixture in a closed reaction vessel.

The following examples are given merely as illustrative of the present invention and are not to be considered as limiting. Unless otherwise noted, the percentages therein and throughout the application are by weight.

The test results shown therein were determined in the following manner.

The typewriter intensity (TI) and calender intensity (CI) tests are measures of responses of carbonless paper to deliberate marking pressures. In the Typewriter Intensity (TI) test, a standard pattern is typed on a CF-DB (coated front-coated back) pair. The reflectance of the printed area is a measure of color development on the CF sheet and is reported as the ratio of the reflectance of the printed area to that of the untyped area (I/I.sub.o) and is expressed as a percentage. A high value indicates little color development and a low value indicates a good color development. The faded print intensity is measured in the same manner.

A CI test is essentially a rolling pressure test as opposed to the impact pressure of the TI test and is conducted to determine the amount of color developed from the transfer of marking liquid obtained by such rolling pressure. Again, the results are reported as the ratio of the reflectance of the marks produced on the CF sheet as compared to the background reflectance of the paper (I/I.sub.o) expressed as a percentage. In both the TI and CI test results the lower the value, the more intense the mark and the better the system as to visibility.

Typewriter and Calender Intensity tests were also conducted before and after exposure of the print as well as after exposure of the CF sheet itself at the noted times to fluorescent light and within an oven. The fluorescent light test device comprises a light box containing a bank of 18 daylight fluorescent lamps (21 inches long, 13 nominal lamp watts) vertically mounted on 1-inch centers placed 11/2 inches from the sample being exposed.

The following procedure is used to prepare the various zinc modification formulations shown in Table I.

Para-octylphenol-formaldehyde resin (POP resin) is melted in a heated reaction kettle and brought to 155.degree. C. The dry zinc compounds and the ammonium formate are completely mixed together before use, and slowly added over an 8 minute period to the melted resin. This mixture is reacted for an additional 52 minutes at a temperature range of 158.degree. C. to 165.degree. C. During the entire reaction period, the vapor above the melt is alkaline as evidenced by moistened litmus paper. After the allotted reaction time, the zinc-modified resin is poured from the kettle into an aluminum tray and cooled. No residual zinc-modifying materials can be seen on the kettle bottom. The cooled resin itself is clear, indicating that complete reaction has occurred.

The prepared zinc-modified POP resins are individually dispersed in an attritor by grinding a 54% aqueous mixture comprised of a small amount of dispersant and the zinc-modified resin. Each resin dispersion is then evaluated in the following coating mixture:

67.9 parts kaolin clay

6.0 parts calcium carbonate

6.5 parts hydroxyethyl starch

13.6 parts zinc-modified resin dispersion

6.0 parts styrene-butadiene latex

and enough water to make a 30% solids coating. The coatings are applied to a suitable paper substrate in an amount of 4.5 to 5.0 pounds per ream (3300 square feet) with a No. 10 wire-wound coating rod and dried.

The coated sheets are tested with a standard CB paper (described in U.S. Pat. No. 3,732,120, namely, paper sheets coated with gelatin capsules containing oily solution droplets of a substantially colorless chromogeneous dye precursor mixture comprising 1.7% of Crystal Violet Lactone (CVL), 0.55% of 3,3-bis(1-ethyl-2-methylindol-3-yl) phthalide (Indolyl Red), 0.55% of 2'-anilino-6'-diethylamino-3'-methylfluoran (N-102) and 0.50% of benzoyl leuco methylene blue (BLMB). The zinc-modified POP resins produce a reactive CF receiver surface capable of developing an image which exhibits excellent light stability or fade resistance as shown by the data presented in Table II.

The CI data in Table II show that the CF sheets made in accordance with the present invention exhibit an improved fade resistance or light stability as compared with the unmodified POP and zinc dibenzoate POP control CF sheets. This conclusion is apparent from the CI Initial values read at 10 minutes as compared with the values obtained after 24 hours of exposure in the light box. That is, the controls show changes in print intensity of 16 and 14 units, respectively, whereas Examples 1-14 show an average intensity change of about 9.4 units, with Examples 12 and 14 demonstrating a particular effectiveness against print fade in showing a print intensity change of only 5 units after exposure in the light box.

The TI light fade data show similar results. The controls show print intensity changes of 16 and 9 units, respectively, after exposure for 24 hours in the light box, as compared to the TI Initial values read after 20 minutes, whereas Examples 1-14 show an average intensity change of only 6.6 units.

Table II shows the results of other comparative tests made with respect to CI Light Decline, CI Heat Decline and TI Light Decline. The data indicate substantially comparable results for the controls as well as Examples 1-14 for these tests.

Thus, it is clear that the zinc-modified phenol-aldehyde novolak resins made in accordance with the present invention provide a reactive CF receiver surface having excellent print fade resistance when used in a carbonless copy paper system.

Another significant advantage obtained with the zinc oxide-modified novolak resin of the invention is its resistance to heat desensitization in the wet coating mixture. Excellent light stability is obtained with the zinc oxide-modified resin even after heating the wet coating mixture for 30 minutes at 140.degree. F. in a hot water bath. This fade resistance property is not obtained with either the zinc dibenzoate-modified resin or the zinc formate-modified resin as shown by the data presented in Table III.

Table III shows that an aqueous coating slurry comprising a zinc oxide-modified POP resin made in accordance with the invention is highly resistant to heat desensitization. Part A of Table III shows the various CI and TI values obtained in connection with the noted tests for CF coatings prepared from zinc dibenzoate-, zinc formate- and zinc oxide-modified POP resins. These results are to be compared with the corresponding values shown in Part B of Table III, wherein the aqueous coating slurry is first aged for about 30 minutes at 140.degree. C. in a hot water bath before coating on the substrate sheet. The values obtained indicate that the zinc oxide-modified POP resin of the invention is superior to the zinc dibenzoate- and zinc formate-modified POP resins in substantially all of the test categories. For example, the TI Initial value shows an increase of only 1 unit (from 36 to 37) with the zinc oxide-modified resin, whereas the zinc dibenzoate-modified resin shows an increase of 5 units (from 39 to 44), and the TI Light Fade increases such 4 units (from 44 to 48) with the resin of the invention as compared to an increase of 16 units (from 42 to 58) for the zinc formate-modified resin.

Such a result is significant since, as a practical matter, the coating slurry may have to be held at an elevated temperature for an indefinite amount of time before being applied to the substrate sheet in an actual manufacturing situation. Thus, when utilizing the zinc-modified resins prepared in accordance with the invention, there is substantially no loss in quality in the resulting CF sheets even when the coating is effected after the slurry has been maintained at an elevated temperature for an extended period of time.

By a similar procedure to that used for Examples 1-14, zinc modification of several different novolak resins is performed with zinc oxide and ammonium formate. These resins are paraoctylphenol-formaldehyde resin (POP) resin), para-tertiary-butylphenol-formaldehyde resin (PTB resin), para-phenylphenol-formaldehyde resin (PPP resin) and para-nonylphenol-formaldehyde resin (PNP resin).

The prepared zinc-modified resins and corresponding non-zinc-modified resins are individually dispersed, coated and dried in a procedure similar to that used in Examples 1-14. The coated sheets are tested with a standard CB paper in TI, CI and light exposure tests, similar as described in connection with Table II. The zinc-modified resins produce a reactive CF receiver surface capable of developing an image which exhibits excellent light stability or fade resistance as shown by the data presented in Table IV.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications are intended to be included within the scope of the following claims.