US3560332A - Paper moldproofed with di(phenyl-mercuric)-ammonium salts of aliphatic carboxylic acids - Google Patents

Abstract

MOLDPROOF PAPER PRODUCED BY ADDING WATER-SOLUBLE DI(PHENYLMERCURIC)-AMMONIUM SALTS OF ALPHATIC CARBOXYLIC ACIDS TO A PARTIALLY OR FULLY DRIED WEB OF PAPER.

Description

Feb. 2, 1971 c CRANDALL ETAL 3,560,332

PAPER MOLDPROOFED WITH DI(PHENYLMERCURIC) AMMONIUM SALTS 0F ALIPHATIC CARBOXYLIC ACIDS Filed Sept. 8, 1965 SOAP WRAPPER- TREATED WITH DI(PHENYLMERCURIC)-AMMONIUM SALT INNER. WRAPPER-TREATED WITH D!(PHENYLMERCURIC)-AMMONIUM SALT SOAP OUTER WRAPPER (TREATED OR UNTREATED) INVENTORS HENRY C. CRANDALL ALAN R.BOWERS ATTORNEY United States Patent US. Cl. 162161 3 Claims ABSTRACT OF THE DISCLOSURE Moldproof paper produced by adding water-soluble di(phenylmercuric)-ammonium salts of alpihatic carboxylic acids to a partially or fully dried web of paper.

In its general aspects, this invention relates to a moldproof paper having improved resistance to the growth of mold, and to a moldproof paper which is essentially free of odor and is more white in color, in comparison to typical prior art papers intended to inhibit mold growth. In a specific aspect, it relates to a soap package including at least one wrapper comprising moldproof paper hav ing the foregoing enchanced properties.

It is known that soap wrapped or packaged in paper, such as wrapped bars of toilet soap, is susceptible to attack by molds. Wrapped soap specimens stored in warehouses in various parts of the country have been found to have the following molds growing on the soap itself and also on the inner and/or outer wrapper: Aspergilli, Pencillia, and Verticillia, including Verticillium pum'ceum. Soap packages having mold growth of this nature are generally considered to be of reduced value, particularly because of the unattractive appearance which they present to a prospective purchaser or user.

A prior art solution to the problem of mold growth on soap wrappers, as well as other commodities, has been the incorporation in the wrapping paper of phenolic mold inhibiting materials, particularly sodium pentachlorophenate. However, so-called moldproof papers treated with this chemical have not proved entirely effective for inhibiting mold growth, possess a pink color that is often considered objectionable for most commercial purposes, and also have a sharp odor which is considered unsuitable by soap manufacturers as well as other packagers. Thus, an important objection to the use of sodium pentachlorophenate is that it is not particularly effective for inhibiting mold at concentration levels at which it does not give the paper an objectionable color and a disagreeable odor, thereby resulting in an unsatisfactory paper for wrapping soap and other articles.

In addition to the preceding disadvantages, paper treated with sodium pentachlorophenate in order to make it at least partially mo-ldproof, has a further disadvantage in that the chemical can be removed from the paper upon leaching with water. That is, the active ingredient is subject to removal from the paper upon exposure to water or high moisture conditions thereby further reducing the effectiveness of the treated paper in inhibiting mold if it should be used under certain adverse conditions.

An object of this invention is to provide a moldproof paper which has greatter resistance to mold growth than prior art materials such as paper treated with sodium pentachlorophenate. Another object is to provide moldproof paper of increased mold inhibition capability which can also exhibit a white color even when the active agent is present at mold inhibiting concentrations. Another object is to provide a moldproof paper which has no disagreeable odor. A further major object of this invention 'ice is to provide moldproof paper in which the active ingredient is not subject to being leached away upon exposure to moisture. A more specific object of this invention is to provide a soap package having at least one wrapper of sheet material surrounding a bar of soap in which the wrapper is treated to have enhanced mold resistance, has a white color, no disagreeable odor, and in which the mold inhibiting ingredient in the paper is not subject to removal upon exposure to moisture.

The foregoing objects, and others which will become apparent from the description which follows, are attained by the present invention through the treatment of either partly or completely dried paper with effective amounts of certain di(phenylmercuric)-ammonium salts. It has been discovered that wrapping paper treated with materials of the foregoing character has greater resistance to the growth of mold than the generally-known wrapping paper treated with sodium pentchlorophenate, and that it has a white color which is desirable in most packaging uses, that the paper does not have any disagreeable odor and that the active ingredient is not leached from the paper upon exposure to moisture.

In the drawings:

FIG. 1 is a perspective view of a soap package utilizing a wrapper treated according to this invention; and

FIG. 2 is a perspective view of another soap package using paper treated according to this invention.

In the ensuing description, the first eleven examples contrast a number of important properties of paper treated with a typical prior art compound, sodium pentachlorophenate in Examples l-S, with the enhanced properties of paper treated with a compound according to this invention, di(phenylmercuric)-ammonium propionate in Examples 6-11. F

PREPARATION OF TREATED PAPERS machine through an appropriate size press when the moisture content of the web was from approximately 10% to 20% by weight. Thereafter, the paper was dried in the dryer section of the machine by normal procedures, including the application of heat.

TESTING PROCEDURES Dried samples of the treated papers in the examples were tested for mold growth in the following manner. Petri dishes, millimeters in diameter and 1S millimeters in depth, were plated with a mineral salt agar inoculated with a spore suspension prepared from a pure culture of Aspergillus terreus. The agar was prepared from 1,000 parts by weight of boiled and cooled distilled water, 3 parts by weight of ammonium nitrate, 1 part by weight of dipotassium acid phosphate, 0.25 part by weight of potassium chloride, 0.25 part by weight of magnesium sulphate heptahydrate, 15 parts of agar, and 1 part of polyoxyethylene 20 sorbitan monolaurate. The nutrient agar was adjusted to a pH of 7 with a 1% solution of sodium hydroxide or a 1% solution of hydrochloric acid, as appropriate. After the agar had solidified in the Petri dishes, specimens of the paper to be tested, trimmed to 2" x 2" square, were placed on the surface of the agar. A sample of untreated paper of similar composition which was known to support mold growth was placed alongside each specimen. All of the foregoing manipulations were performed under aseptic conditions. Covers were placed on the Petri dishes containing the test specimens and blanks. The covered dishes were placed in an incubating oven maintained at a temperature of 28 C. i1 C. At the end of four days incubation, the specimens were removed from the incubator and the surface of each paper specimen and blank examined for the presence or absence of mold growth. This examination was conducted using a colony counter which provided 10 diameters of magnification. The percentage of the test specimens covered by mold growth was recorded. After the readings were completed, the Petri dishes were covered and replaced in the incubator and the examination was repeated at the end of seven days and again at the end of fourteen days. If desired, this test may be conducted using other test organisms such as Aspergillus niger, Chaetomium globosum, etc.

In addition to the above test for mold growth, each sample was visually examined for color and tested for odor characteristics.

EXAMPLES 1-5 In these examples, papers treated with sodium pentachlorophenate at four different levels of concentration were tested as described above for moldproofness, color and odor. The papers of Examples 1-4 showed too high a mold growth, especially after 14 days of incubation, to be good mildewproof papers. The paper in Example 5 possessed an acceptable degree of mildewproofness, but the sodium pentachlorophenate had to be applied at such a high concentration in order to achieve the desired effect that the paper was pink in color and had a disagreeable sharp odor; these latter two factors seriously impair its usefulness as a commercial moldproof wrapping paper. The papers of Examples 1-4 also had an undesirable pink color and an unsatisfactory odor. In Example 3, an attempt to remove the pink color problem was made by incorporating a paper whitening agent in the paper in the beater section and in the solution applied at the size press (the optical whitener is listed in the Color Index as Flu. Bri. 102); although the treated paper contained 0.07% of the whitener when dry, it still had a slightly pink color so that the incorporation of the optical whitener did not solve the discoloration problem. As to moldproofness, color and odor, the results of Examples 1-5 demonstrate deficiencies in a prior art so-called moldproof paper. The data for these examples are summarized in Table I.

EXAMPLES 611 In Examples 6-11, paper of the same type used in the preceding examples was treated with a compound according to this invention, di(phenylmercuric)-ammoni um propionate, hereinafter abbreviated as DPMAP. The results of the tests with these papers are set forth in Table I. It can be seen that the paper of Example 6 showed slight mold growth after 14 days and the papers of Examples 7-11 showed no mold growth at the end of 14 days; the treated papers in all instances showed no discoloration but remained white in color; and, additionally, the treated papers of Examples 6-11 possessed no sharp or otherwise disagreeable odor. Table I graphically demonstrates that papers treated according to this invention possess improved mildewproofness, enhanced color characteristics, and more acceptable odor properties when compared to the prior art papers of Examples 15.

EXAMPLE 12 Treated papers of Examples 3, 5, 6, and 7 were tested for their resistance to the removal of the active ingredient upon exposure to water. The specimens were leached with water by immersing one gram of each paper in 30 grams of water for 24 hours at 25 C. At the end of the immersion period, the paper was blotted, allowed to dry in air and then subjected to the mildew resistance test used in the preceding examples. The mold growth after 14 days incubation before and after leaching is set forth in Table II. It can be seen that the prior art papers of Examples 3 and 5 lost all of the mildew resistance they possessed and showed growth at the end of the test period; in sharp contrast, however, the papers of Examples 6 and 7 lost none of their mildewproofness and exhibited the same lack of mold growth after leaching that they possessed before leaching. This characteristic of the treated papers of this invention means that they can retain their moldproof efiectiveness even when subjected to high moisture conditions, thereby prolonging the protection of articles which may be wrapped in them even under adverse moisture conditions such as may arise during storage or use of the wrapped articles,

EXAMPLE 13 As stated previously, the treated papers of this invention are resistant to the growth of organisms other than that used in the above examples. Specimens of the treated paper of Example 9 were tested with Aspergillus niger and, separately, with Chaetomium globosum organisms according to the procedure described above. In each case, there was no evidence of mold growth after 14 days of incubation.

TABLE I [Results of tests of treated papers of Examples 111dwi(t1;h r]espeet to growth of Asperyillus tcrrcus, color of paper an 0 or.

Mold growth, percent;

coverage Quantity, After 4 After 7 After Example Chemical percent Color of paper Odor of paper days days 14 days 0.5 Slightly pink Slightly sharp None 25 75. 9 Pink Sharp.-. do 1 11 DPMAP .II'

Nora:

SPC =s0dium pentachlorophenate. D PMA P dl(phcnylmereuric) -t111lll1011lt1l11 pl'optona te.

TABLE II [Results of tests for growth of Aspergtllus terrcus after papers were leached with water] Mold growth, percent coverage after 14 days Before After leaching leaching Chemical 7.: .II. DPMAPN.

1 None.

Compounds useful in the practice of this invention consist of water-soluble di(phenylmercuric)-ammonium salts of aliphatic carboxylic acids. The term watersoluble as used in the description and claims is herein defined to mean that the compounds have a water solubility at 25 C. of at least about 2.5 grams/100 grams of solution. Specific compounds within this class which are effective are di(phenylmercuric)-ammonium acetate, di(phenylmercuric)-ammonium propionate, di(phenyl mercuric)-ammonium butyrate, and di(phenylmercuric)- ammonium methacrylate. The di(phenylmercuric)-ammonium propionate is particularly effective as to imparting mold-proofness and has a relatively high degree of water-solubility (6.1 g./100 g. solution at 25 C.); hence, it is presently considered the most useful compound within the above generic class for commercial practice of the present invention. Since compounds of this type are commercially available, their preparation will not be set forth herein. Their general formula is as follows, wherein R is an alkoxy radical as obtained from an allphatic carboxylic acid:

In order to produce the treated papers of this invention, water solutions of the class of active compounds described above are to be applied to either a partially dried or fully dried web of paper on a papermaking machine. The typical papermaking machine will include a sheet-forming section in which a web of paper is formed on a moving wire in the case of a 'Fourdrinier machine or on a cylinder mold with a cylinder machine, a press section which receives the web from the sheet-forming section and partially dries it by mechanical pressing or squeezing action, and a dryer section which removes additional water by the application of heat and which will include calenders by which the dried web is compacted and given a smooth finish. The mildewproofing agents for use with the invention are initially water-soluble and it is therefore impractical, in order to accomplish the pur poses of this invention, to incorporate them in the stock or slurry which is fed to the papermaking machine prior to the formation of the paper web. If, for example, the agents were added to the stock while in the heater or stuff box, all but a very small fraction of the added materials would be lost into the white water system of the paper machine and the finished paper would not have the properties required for this invention, particularly as to the desired amount of active agent. Hence, it is essential to this invention that the materials be applied to a partiallydried web of paper after it has advanced into the press section of a papermaking machine. This is best accomplished by passing the partially-dried web of paper through either a vertical or horizontal size press in order to apply the water solutions; for maximum pick-up of solution, the web should be dried so that its moisture content is from to percent. The usual size press apparatus consists of rubber-covered rolls positioned to be driven in contact with each other and adapted to be hydraulically loaded to increase or decrease the pressure at the nip along which the rolls are in contact. In applying the solutions to a paper web having a width of approximately inches, a pressure on the nip between the size press rolls of approximately 200 pounds per linear inch was found satisfactory, but this may be increased or decreased in order to change the characteristics of the sheet or the pick-up of treating solution; thus this pressure may be from about 50 pounds per linear inch up to 350 pounds per linear inch, or even higher. When applied to a partially-dried paper web, the solution pick-up, calculated as a percentage of the dry weight of the paper being treated, can be from 25 percent to 200 percent, depending on the type of paper being treated, and Within this range, from 60 percent to 80 percent is presently considered optimal.

Another possible point of application of the mildewproofing agents in order to form the treated papers of this invention is at the water box on the calender stack. In this instance, the sheet is dry at the point of application and the percent wet pick-up is relatively low, so that the solution concentration required is relatively high. For example, in the case of a calender stack application of di(phenylmercuric)-ammonium propionate, when the wet pick-up of the paper was 7 percent, a solution containing 0.11 percent of the compound was used for treating the paper which, after treatment included 0.008 percent of the active compound. In Examples 6ll, the solutions were applied at DPMAP concentrations of 0.005%, 0.008%, 0.015%, 0.0375%, 0.05% and 0.10% respectively.

After the specified compounds are applied to the paper, the web is dried by the application of heat to render the compounds at least substantially insoluble. As shown in Example 12, the dried papers are resistant to leaching of the active compound. While we are unable to explain definitely why the water-soluble compounds are to a considerable extent insolubilized by heating, this is probably due to either chemical or physical mechanisms. When the DPMAP-treated paper, for example, is dried, the heat may drive off ammonia and result in the formation of phenylmercuric propionate which would leave a phenylmercuric group available to react with a cellulosic hydroxyl or carboxyl group. Further, the phenylmercuric propionate might be further broken down into a phenylmercuric group which could react with a cellulosic carboxyl or hydroxyl, and the propionic acid formed could be volatilized in the dryer. On the other hand, any or all of these materials might be physically adsorbed by the cellulose. It is also possible that a combination of both physical and chemical mechanisms, of the foregoing or other types, causes the final effect. In any event, after application of the specified solutions, the paper web is dried and the compounds become at least partially insoluble and may undergo chemical change. The temperature range to obtain this elfect expressed in terms of the temperature of the dryer surfaces in the dryer section of papermaking machine, is from 390 F., with 285 F. being considered the optimum portion of this range. The operative temperature range based on the actual temperature of the paper web is from 35-250 F, with 100-225 F. considered optimum. Thus the finished papers of this invention contain the material formed from heating the paper web to which the specified water-soluble salts have been applied at the preceding temperature ranges, and such materials may be insoluble heat-conversion products of the salts or may be unconverted forms of the salts, or a mixture of both.

FIGS. 1 and 2 illustrate the use of the treated papers according to this invention for wrapping a bar of soap, which can be of any particular shape. In FIG. 1, a bar of soap is shown as completely enclosed in a wrapper comprising paper which has been treated with di(phenylmercuric)ammonium salt as described hereinabove. The

paper wrapper may be used after having the specified active ingredients applied as described, or may be further treated with paraffin, for example, paraffin having a melting point of 145 F. In the latter case, the paper preferably is treated with from to paraffin in such a manner that most of the parafiin is absorbed by the paper. The application may be to one or both sides, or may be of either of the types of waxing known to the trade as dry waxing or Wet waxing. The wrapper in FIG. 1 can be unprinted or may be printed to carry descriptive or decorative material.

A soap package of the type shown in FIG. 2 may also be utilized in which the bar of soap is wrapped in an inner wrapper comprising paper treated according to this inventions and this assembly is further wrapped in an outer wrapper which may be either treated or untreated; again, the outer wrapper may include printed descriptive or decorative material or remain unprinted, and can have coatings in addition to the mildewproofing treatment of the present invention. When bars of soap are wrapped in the manner described, it has been found that the moldproof papers of the present invention can protect the soap against mold growth to a greater degree than the previously known wrapping papers used for soap and at the same time they have the added advantages of a white color and lack of odor. Although soap packages are illustrated herein as a use of the treated papers, it is to be understood that other materials or articles which require protection against mold growth can also be wrapped in the paper of this invention.

Starch and protein based coatings of the type widely used in papermaking are known to be susceptible to attack by mold. Coatings of this type can be rendered moldproof by incorporation of di(phenylmercuric)-ammonium salts in accordance with this invention, and the following two examples are set forth to illustrate this aspect. In the examples, the term parts refers to parts by weight.

EXAMPLE 14 Three hundred parts of clay and parts of titanium dioxide were added with thorough agitation to 140 parts of water containing 1 part of sodium hexametaphosphate. To this mixture were added 7 parts of 10% sodium hydroxide solution and 85 parts of water. In a separate mixing vessel, parts of casein were slurried in 230 parts of water and, to this slurry, were added 0.012 part of DPMAP. The casein slurry which contained the DPMAP was added gradually with rapid agitation to the separately prepared pigment slurry.

EXAMPLE 15 In a jacketed bettle equipped with an agitator, a starch dispersion was prepared by adding 160 parts of oxidized starch to 480 parts of water. The mixture was stirred until the starch was well wet and suspended in the water after which the temperature was raised to 200 F. and the starch cooked for 20 minutes. The temperature was lowered 150 F. In a kneading machine, a clay slip was prepared by adding, with mixing, 950 parts clay, 50 parts titanium dioxide, 1 part soda ash and 4 parts sodium metaphosphate to 293 parts of water. Mixing was continued until the slip was substantially free of lumps of solid materials. The starch dispersion, prepared as de scribed, was added slowly with mixing to the clay slip along with 1 part sulphonated castor oil and 42 parts of a 10% soap solution. To the above color was added 0.048 part by weight of DPMAP. The coating was diluted with 1800 parts of water and screened for application to paper. For on-machine coating, color prepared in this manner can be used, after screening, with or without dilution and for off-machine coating, it is preferably diluted and screened prior to application.

Starch and protein coatings such as set forth in Examples 14 and 15 are well-known in the art and they can be applied to paper in any desired manner, such as by roll coater, brush coater or air knife coater, and then dried by conventional means. Inclusion of the active ingredients in accordance with this invention renders such coatings less susceptible to mold-growth and improves the mildew-proofness of papers coated with them. Coated papers according to these two examples can be used either as the sole wrapper or as an inner or outer wrapper for various articles.

There has thus been described moldproof papers capable of satisfying the objects of this invention, methods for manufacturing the papers and packages utilizing them as wrappers. The papers set forth herein have improved characteristics as to several important properties when compared to the prior art papers intended for a similar purpose. These new results are attained through the application to the paper of water solutions of a class of compounds herein defined as di(phenylmercuric-ammonium salts of aliphatic carboxylic acids, and the drying the paper by the application of heat. Several specific examples of this class of materials as set forth in the preceding description. In order to be effective, at least about 0.005% of the compound should be added to the paper, based on the dry weight of the paper; however, there may be some variation in the specific minimum amount required depending upon which particular compound is used and, in any event, the compound should be present in a fungistatic amount so as to substantially inhibit mold growth in the manner intended by this invention. In order to obtain this quantity of active ingredients in dry paper, this invention also provides for applying the active compounds to a partially-dried web of paper on a papermaking machine after the web has entered the press section of the machine; adding the compounds prior to this stage of the papermaking process will not produce a paper of the type contemplated by this invention. Claims using the phrase paper containing the defined materials are meant to refer to the fact that the materials can be distributed throughout a sheet of paper to partly cover the fibers or partly fill voids between fibers in the sheet as may occur when the materials are applied by a size press, and also to include the condition wherein the active ingredient is contained in a coating applied to the paper as set forth in Examples 14 and 15; thus the ac tive ingredients can be contained within a fibrous portion of the paper, as a coating over the fibers or in a coating applied on the exterior of the sheet.

While specific forms for practicing this invention have been described in detail to enable those skilled in the art to practice this invention, it is to be understood that other embodiments of the invention may be utilized and that changes in the embodiments herein may be made by those skilled in the art without departing from the true scope of the invention. Consequently, the above detailed description need not be taken in a limiting sense but should be interpreted broadly with reference to the purposes of this invention. It is further to be understood, that it is intended to cover all the changes and modifications of the exemplary embodiments, as well as other embodiments not described, which do not constitute a departure from the scope and spirit of this invention.

We claim:

1. A method of producing mildew-resistant paper on a papermaking machine including a sheet-forming section, a press section and a dryer section comprising the steps of applying a water-soluble di(phenylmercuric)- ammonium salt of an aliphatic carboxylic acid to a web of paper advancing through the papermaking machine after the web has advanced into the press section of the machine and has been partially dried, and thereafter drying the web of paper by the application of heat, the amount of said Water-soluble di(phenylmercuric)-ammonium salt applied to the paper being suflicient to pro 9 vide at least about 0.005% by weight, on a dry weight basis, of said salt in the paper.

2. A method according to claim 1 wherein said salt is selected from the group consisting of di(pheny1mercuric)-ammonium acetate, di(phenylmercuric)-ammonium propionate, di(pheny1mercuric)-amrnonium butyrate, and di(pheny1mercuric)-ammonium methacrylate.

3. A method according to claim 1 wherein said salt is diphenylmercuric) -amm0nium propionate.

References Cited UNITED STATES PATENTS 10 2,991,183 7/ 1961 Lederer et a1 16730F 2,423,262 7/ 1947 Sowa 260433 3,304,316 2/1967 Geraci et a1 117154X 3,393,196 7/1968 Lederer et a1. 260-433X OTHER REFERENCES Chemical Abstracts, vol. 35, p. 620, J an. 20, 1941.

Murdock: Merfenelopes, The Paper Industry and Paper World, September 1943, pp. 634, 637, 638.

Lederer et a1: Di(Phenylmercuric)-Ammonium Propionate A New Slime Control Agent, TAPPI, vol. 43, 1960, PP. 160-166.

HOWARD R. CAINE, Primary Examiner US. Cl. X.R. 117-154; 162184

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