US3450562A - Cellulosic materials coated with an organic polycarbodiimide - Google Patents

Description

United States Patent 3,450,562 CELLULOSIC MATERIALS COATED WITH AN ORGANIC POLYCARBODIIMIDE Guenther Kurt Hoeschele, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed June 18, 1965, Ser. No. 465,145 lint. Cl. C08c 17/16; C0811 13/16; (309d 3/48 U.S. Ql. 117-155 8 Claims ABSTRACT OF THE DISCLOSURE Cellulosic materials coated on at least one surface with an organic polycarbodiimide having at least two carbodiimide groupings, said polycarbodiimide being dispersed or dissolved in a liquid carrier; the coating of at least one surface of said material is followed by drying and/or heating to improve the compressive strength of the coated material under high moisture conditions.

Products made from cellulosic materials are commonplace items in our present civilization. Paper and cardboard are particularly familiar examples. Cellulosic products are of great economic importance and are used in a wide variety of valuable applications, packaging being one of many. For some purposes it would be desirable to improve the properties of these materials. For instance, improved compression strength under high-moisture conditions is especially needed by corrugated paper containers. Although this type of packaging material has generally given satisfactory service under dry or low-moisture conditions, it has the disadvantage of losing a large portion of its strength when exposed to a very humid or high moisture environment. Boxes are often stacked in warehouses where the humidity becomes quite high. Frequently, the full capacity of the storage area is not utilized because boxes with insufficient top-to-bottom compressive strength topple. Fruit and vegetable growers need a more rigid package to minimize moisture problems that result when the containers they use are moved in and out of refrigerated areas to transport the products to the consumer. Military shipments are frequently sent to tropical areas where the humidity is high for prolonged periods of time.

It is a common practice today to resort to the use of heavier weight paper board components when the box fabricator is confronted with the problem of supplying a more rigid corrugated container for a high humidity application. While this heavier board gives some extra rigidity, it also adds to the weight of the container and increases the cost of shipment accordingly.

Coatings, such as waxes and films, have been applied to boxes for shipment and storage of produce which may be subjected to ice or water. Although such coatings are often elfective in excluding liquid water, they are frequently ineffective when boxes are exposed to high humidity for lengthy periods.

Accordingly, it is an object of the present invention to provide cellulosic materials which display improved properties such as compressive strength under high moisture conditions.

The above and other objects which will become apparent hereinafter are achieved by providing a cellulosic web having at least one surface coated with an organic polycarbodiimide.

Preferably the polycarbodiimide should be present in an amount of from about 1 to about 15% by weight of the cellulosic web, higher concentrations, up to about 30% are useful, although this is not critical.

The polycarbodiimide is applied to a preformed cellulosic web using a liquid carrier which can be water or an organic liquid or mixtures thereof. The polycarbodiimide is used as a solution, an emulsion, or a dispersion. In one embodiment, the polycarbodiimide is applied to the cellulosic web in the form of a solution in an organic liquid containing at least 10% by weight of a super solvent and in the absence of water. In another embodiment the polycarbodiimide is dissolved in a suitable solvent, the solution emulsified with water and the emulsion applied to the cellulosic web. The polycarbodiimide can also be applied in the form of a dispersion of solid particles in water or other liquid.

The concentration of the polycarbodiimide in the liquid carrier is not critical. The concentrations which can usefully be employed depends on the polycarbodiimide selected, upon its molecular weight and upon the particular method chosen for applying the polycarbodiimide to the cellulosic web. In general, however, concentrations of about 2 to about 50% by Weight of the polycarbodiimide in the liquid carrier are suitable for the practice of this invention. In some modern high speed coating techniques, even higher concentrations up to 90% can be used.

carbodiimide polymers which are useful in the present invention may be made by polymerizing organic polyisocyanates. Representative examples of the latter include: toluene 2,4 diisocyanate; an isomer mixture containing 2,4- and 20% 2,6-toluene diisocyanate; 4,4'-methylenebis-(phenyl isocyanate); 4,4-methylenebis(o-tolylisocyanate); 5-chloro-toluene-2,4-diisocyanate; m-phenylene diisocyanate, owl-toluene diisocyanate, 1,6-hexamethylene diisocyanate, methylene bis(4-cyclohexyl-isocyanate) and bis(2-isocyanato ethyl) carbonate. The invention is applicable to not only the pure distilled polyisocyanates but the undistilled reaction products resulting from the phosgenation of an organic polyamine. Procedures for making the polycarbodiimide polymers and representative examples are given in US. Patents 2,941,966; 2,941,983; 3,152,- 131; and 3,157,662.

The preferred materials are urethane-terminated aromatic polycarbodiimides which are described in US. Patent 2,941,983 and carbodiimide-terminated aromatic polycarbodiimides obtained from mixtures of monoand polyisocyanates.

The term aromatic in this connection is used to signify that the polycarbodiimide contains aromatic groupings which can be benzene or naphthalene rings, the carbodiimide groups being directly attached to an aromatic nucleus. The aromatic nucleus can be substituted with substituents which are inert to the carbodiimide linkages, including alkyl, cycloalkyl, aryl, aralkyl, alkoxy, aryloxy, unsaturated groups such as vinyl, allyl, butenyl groups, halogen particularly fluorine or chlorine, nitrile, nitro groups and the like.

While the aromatic polycarbodiimides are preferred, aliphatic cycloaliphatic and aliphatic-aromatic polycarbodiimides or mixtures thereof can be used in the process of this invention.

Urethane-terminated aromatic polycar-bodiimides are made by adding a catalyst for carbodiimide formation to an aromatic polyisocyanate or an isocyanate terminated polymer or their mixtures, initiating chain extension, and finally stopping the polymerization by adding a primary or secondary alcohol when the polymer has reached a certain desired number-average molecular weight. Preferably the alcohol is a long chain aliphatic alcohol having from 8 to 20 carbon atoms, including lower alkyl monoethers of polyethylene and polypropylene glycols such as the monoethyl ether of diethylene glycol or the monomethyl ether of tripropylene glycol. The use of a longchain alcohol to form a urethane-terminated polycarbodiimide tends to lower the melting point of the polycarbodiimide, in some cases forming a conveniently handled liquid product. In addition to alcohols other capping agents which do not readily undergo reaction with the carbodiimide function may also be employed. Aromatic primary amines such as aniline and toluidine, aromatic hydroxy compounds such as phenol and the cresols lactams such as epsilon caprolactam, ketoximes, or other compounds containing active hydrogen may be employed for this purpose. Chain termination by addition of monoisocyanates is of particular interest for preparing polycarbodiimide compositions having a high carbodiimide content. Because these polycarbodiimides can not form intramolecular hydrogen bonds, the lower molecular weight products are relatively low viscosity liquids. By varying the ratio of monoisocyanate to polyisocyanate the molecular weight of the resulting polycarbodiimide can be controlled over a wide range. Less reactive monoisocyanates can be mixed with the polyisocyanate at the beginning of the polycarbodiimide reaction or added to the isocyanateterminated polycarbodiimide during the reaction. More reactive monoisocyanates are preferably added slowly to polycarbodiimide reaction mixture to avoid extensive monocarbodiimide formation by self-condensation of the monoisocyanates. These considerations are discussed in J. Org. Chem. 28, 2072 (1963). Representative monoisocyanates are phenylisocyanate, o-tolylisocyanate, 4-chlorophenylisocyanate and cyclohexylisocyanate. The end capped products show satisfactory stability in solution and, hence, are particularly suited for the purposes of this invention.

As indicated hereinabove, polycarbodiimides which have not been end-capped i.e. which contain isocyanato end groups, can also be used. However inasmuch as these materials are not too stable in solution, it is generally necessary to prepare the solution of the polycarbodiimide immediately before the coating operation. The polymerization reaction can also be carried out concurrently with the coating operation i.e. an aromatic polyisocyanate is mixed with a catalyst for its polymerization applied to the cellulosic web, and then permitted to polymerize in contact therewith.

The polycarbodiimides must contain at least two carbodiimide groupings. Carbodiimides containing only one carbodiimide grouping are not effective in the practice of the present invention. Since the polycarbodiimides are formed in a polymerization reaction, mixed products are obtained containing 1, 2, 3 or more carbodiimide groupings. These materials are relatively difiicult to separate and are normally employed as a mixture. In this case the functionality or number of carbodiimide groups per molecule is specified as an average, thus the functionality of a compound having two carbodiimide groups is 2; an equimolar mixture of a polycarbodiimide having two carbodiimide groups with a polycarbodiimide having three carbodiimide groups would have a functionality of 2.5; polymers having an average functionality of at least two are suitable for the practice of this invention. The upper limit of molecular weight or average molecular weight is not critical. Generally, the polycarbodiimides should contain from 2 to 30 weight percent of N=C= groups. The higher molecular weight polycarbodiimides having melting points above about 150 C. tend to be insoluble in organic solvents and are therefore diflicult to apply by solution techniques. Accordingly, it is preferred to employ polycarbodiimides having melting points less than 150 C.

In preparing the treated cellulosic webs of the present invention, it is necessary to disperse or dissolve the polycarbodiimides in a liquid carrier and apply the resulting mixtures to at least one surface of the cellulosic substrate. When the polycarbodiimide is applied from solution, the liquid carrier can be any of the solvents which have been used for the preparation of the polycarbodiimide itself, for example, as described in US. Patents 2,941,983, and 2,941,966. Examples include ethyl acetate, toluene, methylene chloride, dimethyl sulfoxide, tetrahydrofuran and acetone. The best properties are obtained when the polycarbodiimide is applied from solution in a super solvent.

Super solvents are a special class of solvents which are known in the art and which have found use in dissolving linear polymers such as polyamides, polyesters, polyacrylonitrile and various linear polyurethanes, and linear polyureas. The super solvents are essentially neutral and many are completely miscible with water, but this is not a requirement. Super solvents may be solids at room temperature which form liquid solutions with the polycarbodiimide. The super solvents are inert toward carbodiimide groups in that they are free of reactive groups such as hydroxy or amino groups. In particular, the types of super solvents which are preferred for making the carbodiimide solutions include: N-alkylated ali hatic amides; N-alkylated ureas; N-alkylated sulfonamides; sulfoxides; and sulfones.

The N-alkylated aliphatic amides, may be represented by the general formula:

wherein R R and R may be alkyl, cycloalkyl, or arylalkyl, whereby the fully alkylated or N,N-dialkyl aliphatic amides are obtained. R may also be hydrogen. R R and R may be independently selected as long as the total number of carbon atoms contained in the three groups does not exceed 24. R R and R may bear substituents which are inert toward carbodiimide groups such as halogen and alkoxy. R or R; can be hydrogen whereby the corresponding N-alkyl aliphatic amides will be obtained. R and R can be alkylene groups and form a ring which may or may not contain a hetero-atom such as sulfur or oxygen. This general formula may also be used to represent an alkylated cyclic amide which would be formed by R with either R or R whereby the amide linkage is part of the cyclic structure. Diamides derived from dicarboxylic acids are contemplated for use since they contain the required alkylated amide structure. Suitable compounds represented by this general formula include N- methyl formamide, N-methyl acetamide, N-butylstearamide, N,N-dimethyl-formamide, N,N-dimethylacetamide, N,N-di-n-butylformamide, N,N-dimethylcaprylamide, N, N-dimethylstearamide, N-formylpiperidine, N-acetylpyrrolidine, N-formylmorpholine, N,N,N',N-tetramethyl oxalamide, N,N,N,N'-tetramethyladipamide, pyrrolidone, epsilon-caprolactam, N-methylpyrrolidone and N,N-di-nbutylacetamide. Especially preferred are N,N-dimethylformamide, N-N-dimethylacetamide and N-methylpyrro lidone. The fully alkylated ureas are closely related to amides and in a sense may be considered as diamides of carbonic acid. The alkylated ureas may be represented by the general formula:

wherein R R R and R may be alkyl, cycloalkyl or arylalkyl. The groups may be selected independently as long as the total number of carbon atoms in the four groups does not exceed 24. A preferred urea is N,N,N,N'- tetramethylurea, but many other ureas derived from other secondary amines may be obviously used. Compounds in which R; forms a ring with R and/ or in which R and R form a ring are also contemplated, such as the urea formed from piperidine. Compounds in which R or R forms a ring with either R or R may also be used. N,N'-dialkyl substituted ethylene-ureas are representative of ureas having this configuration.

'5 The alkylated sulfonamides can be represented by the general formula:

RgSOgN wherein R R and R may be independently selected as long as the total number of carbon atoms contained in the three groups does not exceed and wherein R R and R may be alkyl, cycloalkyl or arylalkyl. R may be also aromatic, R or R may be hydrogen, whereby the N-alkyl sulfonamide is obtained. A mixture of N-ethyl ortho and para toluene sulfonamides is a useful solvent of this class. Such a mixture is the commercially available Santicizer 8 (obtainable from the Monsanto Chemi cal Co.) which contains about equal parts of the ortho and para isomers and minor amounts of unsubstituted sulfonamides. Normally, the R R and R substituents should be selected so that the sulfonamide is a liquid or a low melting solid. Cyclic structures involving R and R are contemplated for the sulfonamides in the same manner disclosed for the carboxylic acid amides and the ureas. Representative sulfonamides include N,N-diethyl ethanesulfonamide, N-butyl neopentylsulfonamide, N,N-dimethyl benzenesulfonamide, N-ethyl-N-methyl benzenesulfonamide, N-N-diethyl toluene-a-sulfonamide, N-ethyl toluene-a-sulfonamide, and N-methyl-N-ethyl p-toluenesulfonamide.

The above-described cyclic amides, viz alkylated cyclic amides, cyclic ureas, and cyclic sulfonamides are included within the naming of their respective species of solvents.

Alkylated sulfoxides and the sulfones represent two other solvent types which are useful in the present invention. The sulfoxides may be represented by the formula:

u- IS -R12 and the sulfones by wherein R R R and R may be alkyl, cycloalkyl or aralkyl, selected so that the total number of carbon atoms contained in R plus R or in R plus R is no greater than 8. Cyclic structures formed by R and R or by R and R are also contemplated. Representative of these two solvent types are dimethyl sulfoxide, dimethyl sulfone, diethyl sulfoxide, diethyl sulfone, dibutyl sulfone, tetramethyl sulfoxide, and tetramethyl sulfone.

When super solvents are employed other solvents can also be present to act as diluents or thinners. Preferably, the diluents are more volatile than the super solvents such as fluorinated hydrocarbons or low molecular weight fluorochlorocarbons. The diluents can be gasses at atmospheric temperature and pressure and the mixture of super solvents and polycarbodiimide applied to the surface of the cellulosic web with a spray nozzle attached to a pressure vessel containing the polycarbodiimide, the super solvent and the diluent, e.g. from an aerosol bomb.

The polycarbodiimides can also be applied to the cellulosic web in the form of emulsicins or dispersions. The emulsions can be prepared by mixing a polycarbodiimide solution in an organic solvent with an aqueous phase containing minor amounts of surface active agents dispersing agents or other conventional aids in the manufacture of emulsions. Liquid polycarbodiimides can be used in place of polycarbodiimide solutions. The surface active agents include non-ionic, anionic and cationic types such as are described in the Encyclopedia or Surface Active Agents Sicily and Wood, Chemical Publishing Company, Inc., New York, N.Y., vol. 1, 1952 and vol. 2, 1964. In general, agents which do not cause excessive foaming, which are relatively insensitive to pH changes, and which do not react readily with carbodiimide groups are preferred. In addition to conventional surfactants of the type described hereinabove, other materials such as methyl cellulose may be used to thicken the emulsions, thus aiding emulsion formation and retarding phasing. Methyl cellulose may also be considered an emulsifying agent in its own right for preparing the emulsions. Finely divided insoluble solids such as bentonite clay or estersils can also be used to stabilize the emulsions.

The emulsions or dispersions can be prepared conventionally by batch or continuous processes. The organic phase can be liquid polycarbodiimide; a liquid mixture of a polycarbodiimide and a non-volatile plasticizer; a solution of polycarbodiimide in a volatile solvent (which can be stripped off before paper treatment if desired). In general the organic phase containing the polycarbodiimide is vigorously mixed with an aqueous phase which usually contains stabilizing agents; however, the stabilizers may be added as a part of the organic phase. Methyl cellulose is an example of this type. The stabilizing agents may also be added after the organic and aqueous phases have been given a preliminary mixing. The order in which the phases are mixed is not critical, but it is frequently more convenient to add the organic phase to the less viscous aqueous phase. In preparing the emulsions or dispersions it is preferred to make a concentrated composition by mixing approximately equal proportions of the organic and aqueous phases. The concentrated emulsions or dispersions produced can be diluted to any desired concentration by the addition of water. The compositions can, however, be prepared directly at low concentrations if so desired. The solutions, emulsions, or dispersions may contain minor amounts of additives of the type normally employed in coating the adhesive formulations, preferably of a type that do not react with the polycarbodiimide. Antioxidants, pigments, fillers, resins, plasticizers, for example, may be mixed or dispersed in the solutions, emulsions, or dispersions at any time prior to the paper treatment. These additional materials may be retained in the coated paper.

The coating operation, Whether using solutions, dispersions or emulsions, can be performed in a variety of conventional ways such as sizing, spraying, brushing, padding, wiping, roll coating, and dipping. The methods exemp lified hereinafter are merely illustrative; no restriction is intended. In a representative embodiment of sizing, a polycarbodiimide emulsion (or dispersion) is placed in the upper nip of a pair of horizontally co-acting rollers and paper is passed downwardly therebetween. In contrast to saturation i.e. immersion of the cellulosic web in a solution of the aromatic polycarbodiimide, sizing appears to produce an external coating and does not enter the interior portion of the cellulosic substrate. A Butter worth coater is an example of a commercially available device for performing the sizing operation. In one method of surface coating with solutions the cellulosic web is immersed for 10 seconds at room temperature in 210% by weight solution of an polycarbodiimide in dimethylformamide.

After the coating composition containing the polycarbodiimide and the liquid carrier has been deposited on the paper, heat is applied to remove the carrier. The amount of heat needed will depend on factor such as the proportion of carrier and its volatility under the prevailing pressure. The amount of heat supplied to a particular area will be determined by the temperature of the heating zone and the residence time of the coated paper in it. If intense heat is provided, quick passage of the coated area through the zone will suffice; conversely, more moderate heating will require a longer residence time. The proper combination can readily be determined by those skilled in the art to suit the equipment available and the coating composition at hand. When aqueous dispersion or emulsions are involved it is frequently convenient to heat 7 at 100 C. to 200. C. for about 1 to 30 minutes; 175 C. for 5 minutes is preferred.

The heating step provides an unexpected additional benefit. It has been found that the properties of the polycarbodiimide coated paper can be improved still more if heat is applied for a short while after the normal drying is finished. As is shown more particularly hereafter in an example, a sharp improvement can be obtained within 5 minutes. The improvement is more pronounced as the temperature is raised, but good results are noticed at temperatures as low as 100 C. and at least as high as 175 C.-200 C. In this heating step, there is generally a rapid gain in properties early in the cycle; continued heating may give further benefit but at a reduced rate. Those skilled in the art can select the appropriate time for heating based on the improvement needed and practical considerations of cost and the like.

The upper temperature limit will be governed, in any case, by the stability of the paper itself. Excessive heating will embrittle or char it.

After the paper has been coated with the polycarbodiimide, the resultant article will display the improvements mentioned before. It is possible, although not clearly established, that under some circumstances the polycarbodiimide undergoes one or more reactions which involve at least part of its N=C=N- groups. For example, they may form a few crosslinks of the type They may react with atmospheric water or residual water in the paper to form urea groups, although the Campbell et al. publication [J. Org. Chem. 28, 2070 (1963)] indicates that polycarbodiimides are rather stable even under drastic conditions. Alternatively, they may react with carboxyl groups in the paper to form acyl urea groups; less likely, they may be attacked by hydroxyl groups Speculatively, the extent of these reactions may depend on factors such as the temperature, the nature of the carbodiimide polymer, and the type of liquid carrier used to deposit the polymer.

The coated cellulosic webs of the present invention all show improvements in physical properties such as tensile strength and compressive strength, better abrasion and better scuff resistance, under dry, humid, and under moist conditions. When solution coating techniques are employed using super solvents in the absence of water, the wet strength properties of the cellulosic webs as so treated are very substantially improved over the properties of cellulosic webs treated with the polycarbodiimides in ordinary solvents. The reason for this distinction is not known but it is speculated that a super solvent produces a more favorable disposition of the polycarbodiimide in the web. When water forms at least a part of the carrier, as when the super solvents are used in formulating an emulsion, the super solvents display no particular advantage over the other solvents.

This invention is further illustrated by the following examples which are not however intended to fully delineate the scope of this invention. In these examples the following test methods and definitions are empolyed.

The rigidity was measured by the short column crush test. In this test a paper specimen 1 x 4 inches is placed lengthwise in a clamp allowing a linear 0.25 x 4 inch strip to extend outside the holder. The strip of paper is then compressed between the platens of a Hinde-Dauch Percent pickup X 100 crush tester and the maximum load applied at failure is measured. All compressive strength tests were conducted in the cross direction and are reported in pounds. All data represent average of 4 tests. The wet compressive strength was measured immediately after complete water immersion of the test specimens for 10 mins. or 24 hours as specified. The compressive strength at relative humidity was determined immediately after aging had been carried out at 90% relative humidity/ F. for 72 hours. The dry compressive strength was measured after the paper had been stored at 50% relative humidity/ 75 F. for 24 hours.

Tensile strength The tensile strength was determined on one-inch wide paper specimens in the machine direction with an Instron tester operated at a crosshead speed of 2 in./min. with a 2-inch span employed between the jaws. The results are reported in lbs/in. of width and are averages of 2 tests. The wet tensile strength of the paper was measured immediately after water immersion for ten minutes at 75 F.

Burst strength The burst strength of the paper was determined with a Mullen burst tester according to Tappi T403 immediately after the paper had been immersed in water for 24 hours at 75 F. The results are averages of 4 individual tests.

Abrasion resistance A continuous belt abrader (Custom Scientific Instrument) was used for these tests, the number or cycles (averages of 2 runs) being determined when the paperboard failed completely and was torn by the abrasive (grit size 320). The abrasion tests were conducted in the cross direction employing a load of 2.5 lbs.

EXAMPLE I A. Preparation of aromatic polycarbodiimide 112 parts of a mixture containing toluene 2,4-diisocyanate and 20% of toluene 2,6-diisocyanate were introduced under dry nitrogen into a clean dry reaction kettle which contained an atmosphere of dry nitrogen and was equipped with an agitator. After the charge had been cooled under dry nitrogen to a temperature below 20 C., 0.43 part of 1-phenyl-3-methyl 3-phospholine-1-oxide catalyst was introduced. Immediately thereafter the nitrogen stream was turned off and measurement of the carbon dioxide evolution was begun. The reaction mixture was slowly warmed to 45 C. over a period of about 5 hours. After 22.3 parts of carbon dioxide had been evolved, 11.90 parts of isopropyl alcohol were immediately added to stop the polycarbodiimide formation. The mixture was then heated to a temperature of 85:2" C. over a period of 2 hours. The melt obtained was discharged and allowed to crystallize at room temperature.

The polycarbodiimide had an average-molecular weight of about 800 (corresponding to an average of 4 N:C:N

groups) and melted in the range of 8085 C.

B. Coating of kraft linerboard of the aromatic polycarbodiimide Kraft linerboard (weighing 42 lbs/1000 sq. ft.) was immersed for 10 seconds at 25 C. in dimethylformamide solution containing 9.2, 4.6, and 2.3 weight percent respectively of the polycarbodiimide of part A. The treated board was then dried at C. for 30 minutes and kept at 50 relative humidity at 75 F. for 20 hours prior to testing.

For comparison an experiment outside the scope of the present invention was conducted. Procedure of part B above was essentially repeated substituting N,N-di-otolylcarbodiimide for the polycarbodiimide of part A.

The data summarized in Table I show that polycarbodiimides are highly efiective in improving the compressive strength of linerboard, while monocarbodiimides have practically no eifect at all.

The effect of heat treatment upon the compressive moved by fractional distillation at reduced pressure. The undistilled polyisocyanate contains about 85% of volatile toluene diisocyanates, the remainder being phosgenation by-products.

strength of linerboard treated with the polycarbodiimide 5 Preparatlon of polylsocyanate mlxture B of part A according to the procedure of part B described Crude 4,4-diaminodiphenylmethane, containing about above is shown in Table IA. It is evident from the data polyarnines, is prepared by adding 1 mole of aquethat heating of the coated paper at temperatures of 100 ous formaldehyde to an aqueous solution of 3 moles of C. to 175 C. results in greatly improved compressive aniline and 2.8 moles of hydrochloric acid at about strength under high humidity conditions. 10 30 C., followed by heating at 85 C. for 3 hours. The TABLE I Polyoarbodiimide Monoearbodiimide l Untreated 2.5? 5.57 9.07 4.27 6.1 lroperty Unit Control Pickup Pickup Pickup Picku Pickup Abrasion Resistance 145 225 280 395 Wet compressive Strength 4.05 7.9 13.0 20.7 4.5 5.8 Compressive Strength at 90% relative humidity 16 .2 20.9 26 .5 35 .7 17.8 18 .7 Dry Compressive Strength 25 .2 28.1 34.1 49 .1 25.2 26 .2

1 Outside the scope of the present invention; included for purpose of comparison. 2 After 24 hours water immersion at 75 F.

TABLE IA Heat Treatment 100 C. 150 C. 175 C. Untreated Air Property Control Dried 5 min. min. 5 min. 20 min. 5 min. 20 min. Pickup, Percent s .85 9 .3 9 .35 8.8 8.6 8.65 7.85 Compressive Strength at 90% relative humldlty (lbs 16 .6 24 .0 32 .0 30 .5 34 .8 35 .1 36 .2 39 .4 Wet Compressive Strength 1 (lbs) 4.0 7.2 10.5 11.5 17.1 18.6 20.0 23.5

1 10 min. water immersion.

EXAMPLE II A. Emulsification of polycarbodiimides Over a period of one minute a solution of parts of the polycarbodiimide of Example I in 35 parts of methylene chloride was added slowly with continuous agitation to an aqueous solution containing 10 parts of 10% Aquarex D wetting agent, parts of 10% aqueous ammonium caseinate, and 60 parts of water at 25 C. Aquarex D wetting agent (available from E. I. du Pont de Nemours & Co.) is a mixture of sodium salt of sulfate monoesters of a mixture of higher fatty alcohols consisting chiefly of the lauryl and myristyl derivatives of the type RSO Na. High speed agitation was continued for one more minute. The resulting emulsion was very white in color stable for at least one hour at 25 C. (no settling of solids or foaming took place) and resembled shaving lather.

B. Paper treatment with polycarbodiimide emulsions The aqueous emulsion of the polycarbodiimide made in part A above was applied to 42-lb. linearboard by sizing techniques using a Butterworth coater. The paper was then dried immediately by passing it through a paper drum dryer. For purposes of comparison, linerboard, which had not been coated, was tested at the same time as the sample made above. Table II gives the data obtained for all these samples.

condensation mass is then neutralized with sodium hydroxide. The organic layer subsequently separated from it is freed from unreacted aniline by distillation at reduced pressure. The mixture of diand higher polyamines left behind in the still pot is dissolved in o-dichlorobenzene and converted to the corresponding isocyanates by phosgenation following esentially the procedure disclosed in U.S. Patent 2,822,373. After the phosgenation, the odichlorobenzene is removed by fractional distillation at reduced pressure. The undistilled product left behind contains about 72% 4,4'-diisocyanatodiphenylmethane. The rest of the mixture consists of polyisocyanates and phosgenation by-products. The product contains about 31% by weight of isocyanato groups when assayed by the procedure of ASTM D163 8-60T.

A. Preparation of polycarbodiimides Polycarbodiimide 1.A mixture consisting of 10 parts of polyisocyanate mixture A, 50 parts of dimethylformamide and 0.2 part of phospholine oxide catalyst described in Example I (part A) was heated at 50? C. for 2 hours While stirred under dry nitrogen. The resulting polycarbodiimide formation caused the NCO-group content of the reaction mixture to drop from 7.0% to 1.1%. The NCO-terminated polycarbodiimide obtained was capped by adding an equivalent amount of aniline (1.5 parts). The resulting solution of the urea-terminated polycarbodi- TABLE II.--SIZING OF 42-LB. LINERBOARD WITH POLYCARBODIIMIDE- WATER EMULSIONS Dry Compressive Compressiv Strength at 90% p, Drying Strength Relative Wet Burst Percent Dry Weight Conditions (Lbs) Humidity (Lbs) (Points) s min/285 No drying min./302 F EXAMPLE III Preparation of polyisocyanate mixture A Tolylene diamine (80% 2,4-isomer; 20 2,6-isomer) is dissolved in o-dichlorobenzene and phosgenated essentially by the procedure disclosed in U.S. Patent 2,822,373. Following the phosgenation, o-dichlorobenzene is repholine oxide catalyst of Example 1. After a reaction time of about 45 minutes the NCO-group content of the reaction mixture was reduced from 4.24% to 1.74%. The resulting NCO-terminated polycarbodiimide was capped with 4 parts of aniline by the procedure described for polycarbodiimide 1.

Polycarbodiimide 3.-An NCO-terminated polycarbodiimide was prepared by heating 10 parts of polyisocyanate mixture B at 60 C. for 70 minutes in the presence of 100 parts of dimethylformamide and 0.1 part of the phospholine oxide catalyst of Example 1. Polycarbodiimide 3 was made by capping the isocyanate end groups with isopropyl alcohol (2.0 parts) at 60 C.

B. Application of dimetliylformamide solutions of polycarbodiimides The polycarbodiimides described in part A were applied on kraft linerboard by essentially the same procedure as described in Example 1, part B. The testing results shown in Table III demonstrate the greatly improved dry and wet properties of polycarbodiimide treated linerboard in comparison with the untreated linerboard.

A similar improvement to that described in paragraph 1 above was observed when corrugating medium (basis weight 33 lb./ 1000 sq. it.) was treated with the polycarbodiimide solutions of part A by the same saturation technique.

12. EXAMPLE v A. Preparation of Polycarbodiimide solution One hundred parts of polyisocyanate mixture A, described in Example III were agitated at C. in the presence of 0.2 part of the phospholine oxide catalyst of Example I. The temperature Was slowly raised to 60 within 3 hours and maintained at this value until the NCO-group content of the reaction mixture was reduced to about 20%. Then isopropyl alcohol parts) was added for end group capping While the temperature was kept at 60 C. for another hour. Dilution of the resulting urethane-terminated polycarbodiimide with 30 parts of a representative super solvent a mixture of N-ethyl-oand N-ethyl-p-t0luene sulfonamide 1 (30 parts) yielded a solution which was a very viscous liquid at 25 C.

Coniimereially available from Monsanto Chemical Co. as Santicizer 8 B. Application of dimethylformamide solution of the polycarbodiimide TABLE III Polycarbodilrnide No. 1 Polyearbodiimide N0. 2 Polycarbodiimide No. 3 Untreated 3. 0% 5. 5% 9. 0% 2.2 5.2% 10.6% 2. 1% 5. 2% 9.9% Unit Control Pickup Pickup Pickup Pickup Pickup P iekup Pickup Pieku p Pickup Wet Compressive Strength Pounds. 4.05 8. 5 13. 4 14. 4 5. 9 9. 3 16. 5 7. 3 12. 1 16. 7 Compressive Strength alter do 16. 2 21. 5 27. 5 29. 2 21. 2 26. 8 38.1 23. 6 30. 8 40. 5

aging at 90% relative humldlt 25. 2 25. 7 33. a 43. 1 9. 4 60. 5 90 102 Elongation at Break Percent. 1. 2 3.05 3. 4 3. 5

1 10 minutes water immersion. B For comparison, the untreated linerboard exhibited a dry tensile strength of 105 1bS./ll1.

EXAMPLE IV TABLE v A. Preparation of polycarbodiimides P t C t 1 P k m k P 1 ro er on ro 10 u 16' 174 parts of the toluene diisocyanate isomer mixture y P 0 up p t of Exam- Wet Compressive Strength L. 2. 1 6.0 9. 3 14. 8 and 0.35 part of the phospholine oxide cataly Compressive Strength at 90% ple 1 were heated at 60 C. while agitated in a y fi relative humidity 16.5 22. 9 27. 2 35.1 Dry Compressive Strength- 26. 0 31.8 32. 6 41. 2

By minutes, 30.5 parts of carbon dioxide had been evolved. The reaction product was then capped by adding 100 parts of n-octanol to stop further carbodiimide formation. The resulting urethane-terminated polycarbodiimide A-l had a number-average molecular weight of about 700 (corresponding to 2 N=C=N-- groups) and a melting range of -60 C.

The above-described polycarbodiimide preparation was essentially repeated except that 2(2-ethoxyethoxy) ethanol was substituted for n-octanol. The liquid polycarbodiimide A-2 obtained had a number-average molecular weight of about 700.

B. Application of dimethylformamide solutions of polycarbodiimides described in part A The polycarbodiimides described in part A were applied on kraft linerboard by saturation as outlined in Example I, part B. The paper properties before and after treatment are shown in Table IV.

1 10 minutes water immersion.

EXAMPLE VI The procedure of Example I was repeated except that the super solvent described therein was replaced by representative conventional solvents. The data obtained for the resulting coated cellulosic substrates are given in Table VI.

For comparison, the data obtained with a super solvent dimethyl sulfoxide, are included. It is evident from these results that when a super solvent is used during the paper treatment, the wet strength properties of the coated linerboard are substantially improved, as compared with the properties displayed by linerboard treated with the air aid of ordinary solvents. N0 solvent effect was found in respect to compressive strength under dry conditions or at relative humidity.

TABLE IV.-TREATMENT OF KRAFT LINERBOARD WITH AROMATIC POLYCARBODIIMIDES Polycarbodiimide A-l Polycarbodiimide A-2 Untreated 2. 1% 4. 57 8. 67 2. 6 7 4. 97 8. 07 Property Unit Control Pickup Pickup Pickug Picki ritkufi Picke Wet Compressive Strength 1 Pounds.--" 2.1 6.0 9.2 15.1 5.0 9.4 14.0 Compressive Strength at 90% relative humidity ..d0 16. 5 21. 3 24. 5 29. 1 20. 2 24. 5 30. 6 Dry Compressive Strength .d0 26. 0 26. 0 30. 5 36. 0 24.0 28.1 36.1

l 10 minutes Water immersion.

TABLE VI Untreated Methylene Dimethyl- Eth l Tet Solvent Control Chloride Toluene sulfoxide 1 Aceta te hydroil l ran Pickup, percent dry weight l0. 9 5. 7 2. 3 5. 9 2. 9 1. 0 7. 7 3 7 6. 1 2. 7 0. 7 7. 8 3. 9 1. 3 Wet Compressive strength (lbs.) 2 2. 2 8.9 7. 2 6. 6 5. 6 5. 3 4. 7 14. 30 6 7 6. 4 5. 9 4. 8. 3 6.9 5. 6 Compressive Strength at 90% relative humidity (lbs.) 20. 6 36 29 27. 3 31 27 23 29 23 33 28 24 34 27 22 Dry Compressive Strength (lhs.) 26 51 43 35 43 38 32 44. 3 26. 0 42 35 31 48 36 30 Dry Tensile Strength (lbs/1n.) 102 149 136 132 145 133 129 Wet Tensile Strength (lbs/in.) 16 66 53 35 84 65 Super solvent. 2 mlnutes water immersion.

EXAMPLE VII 30 parts of the polycarbodiimide described in Example dimethylformamide. Typical data obtained from the resulting coated linerboard are shown in Table VIII.

TABLE VIII Untreated Untreated Property Control 1 Polycarbodiimide 1 Control 2 Polycarbodiimide 2 Pickup, percent 4. 7 7. 9 4.0 8.1 Compresslve Strength at 90% relative humidity (lbs.) 24.1 29. 9 37. 1 17. 2 22. 25. 9 Dry Compressive Strength (lbs.) 33.1 37. 6 44. 3 23.0 33. 8 37. 8

1 For Polycarbodiimide 1.

I was dissolved in methylene chloride (70 parts). The resulting low viscosity solution was sprayed on linerboard (42-lb. basis weight) with an air brush sprayer. After the spraying operation the paper was dried in a drum drier for 8 minutes at 285 F. The data obtained from the treated liner are shown in Table VII.

EXAMPLE VIII A. Preparation of polycarbodiimides Polycarbodiimide 1.A mixture consisting of (a) 94.2 parts of o-tolylisocyanate, (b) 123.5 parts of a mixture containing 80% of toluene 2,4-diisocyanate and of toluene 2,6-diisocyanate, and (c) 0.75 part of phospholine oxide catalyst described in Example 1 (part A) is heated at 60-65" C. for several hours until the -NCO group content of the reaction mixture is reduced to 0.65%. The resulting polycarbodiimide composition is a viscous liquid at C. and contains about 23% of monocarbodiimide.

Polycarbodiimide 2.-3.6 parts of tetraisopropyl titanate are added to a stirred refluxing mixture consisting of 23.6 parts of methylene-bis(4-cyclohexylisocyanate) obtained by phosgenation of methylene-bis(4-cyclohexylamine) and having the following isomer content: 50% trans-trans, 40% cis-trans, 8% cis-cis and 2% 2,4-isomet) and 90 parts of monochlorobenzene. After 2.64 parts of carbon dioxide are evolved (4-5 hours reaction time) 7.5 parts of cyclohexylisocyanate are added. The reaction is completed by heating at reflux temperature for an additional 16 hours until another 2.64 parts of carbon dioxide are evolved. The resulting polycarbodiimide solution is free of isocyanato groups.

B. Application of solutions of polycarbodiimide The polycarbodiimides described in part A are applied on kraft linerboard by essentially the same procedure as described in Example I except that for polycarbodiimide 2 monochlorobenzene is used as solvent instead of N,N-

2 For Polycarbodiimide 2.

What I claim is:

1. An article of manufacture comprising a cellulosic web having at least one surface coated with an organic 25 polycarbodiimide, the coating being 1 to 15% by weight of the cellulosic web and the polycarbodiimide containing from 2 to weight percent of carbodiimide groups.

2. Article of claim 1 in which the organic polycarbodiimide is an aromatic polycarbodiimide.

3. Article of claim 1 in which the organic polycarbodiimide is a polymer of a mixture comprising toluene diisocyanates.

4. Article of claim 1 in which the organic polycarbodiimide is a polymer of 4,4-diisocyanato diphenylmethane.

5. Article of claim 1 in which the organic polycarbodiimide is a polymer of S-chloro-toluene diisocyanate.

6. Article of claim 1 in which the said organic polycarbodiiimide is a polymer of methylene bis(4-cyclohexylisocyanate).

7. Article of claim 2 in which the aromatic polycarbodiimide is urethane terminated by reaction with an aliphatic alcohol having from 8 to 20 carbon atoms.

8. Article of claim 2 in which the aromatic polycarbodiimide is terminated by reaction with an organic monoisocyanate.

References Cited UNITED STATES PATENTS 2,941,966 6/1960 Campbell.

2,941,983 6/1960 Smeltz 117-139.5 X 2,955,095 10/1960 Gollob 117-155 X 2,987,494 6/1961 Black 117-161 X 3,152,131 10/1964 Heberling 260-288 3,157,662 11/1964 Smeltz 260-288 3,178,310 4/1965 Berger et al 117-155 X 3,226,368 12/1965 Reischl et al 117-161 X 3,282,897 11/1966 Angelo 117-161 X 3,282,898 11/1966 Angelo 117-161 X 3,345,342 10/1967 Angelo 117-161 X WILLIAM D. MARTIN, Primary Examiner.

M. LUSIGNAN, Assistant Examiner.

US. Cl. X.R.