NO301286B1 - Procedure for gluing paper - Google Patents

Description

The present invention relates to a method for gluing paper to provide paper and cardboard with resistance to being wet by liquids by using fluorochemical phosphate salts.

Various fluorochemical wet-pick-up and internal adhesives for paper processing are described, e.g. in Rengel and Young, "Internal Sizing of Paper and Paperboard," Tappi monograph series no. 33, pp. 170-189 (1971), Colbert "Fluorochemicals-Fluid Repellency for Non-Woven Substrates," Tappi, The Journal of the Technical Association of the Pulp and Paper Industry, 59.9 (Sept. 1976); Banks, Ed., Organofluorine Chemicals and their Industrial Application, pp. 231-234 (1979) and Schwartz, "Oil Resistance Utilizing Fluorochemicals," Tappi conference preprint, 1980 Sizing Short Course, Atlanta, GA.

US-PS 3,094,547 (Heine) and US-PS 3,083,224 (Brace) describe fluorochemical phosphate salts which are useful for gluing fabric to impart both water repellency and resistance to absorption and insolation of oily and greasy materials and for coating and impregnation of matrices such as paper and leather. Fluorochemical phosphate salts are prepared in the presence of a solvent such as benzene, toluene, xylene, benzotrifluoride, etc. by reacting a fluorochemical alcohol with phosphorus oxychloride.

Several such fluorochemical phosphate salts are controlled by U.S. Pat. Food and Drug Administration to provide safe use of cartons in direct contact with food for human consumption. These fluorochemical phosphate salts can be used as wet pick-up, i.e. applied to the surface of the paper, such as by dipping or spraying an aqueous solution or dispersion of the fluorochemical phosphate salt, or in internal treatments, i.e. fluorochemical phosphate salts are added to the aqueous pulp slurry before the sheet watered or in a size press, i.e. dry paper passes through a flooded nip and a solution or dispersion of the fluorochemical phosphate salt is in contact with both sides of the paper. These salts primarily provide resistance to oil and are used e.g. on paper plates, bags for baked goods and snack foods, cartons and trays for fast food and in bags and cartons for pet food.

The fluorochemical phosphate salts, provided as an aqueous/organic solvent solution, which provide good oil repellency as judged by measurement with the "Kit Test" precipitate from the solution or slurry when the water used to prepare the solution or slurry is hard. This can be overcome by adding a chelating agent to the solution or slurry prior to the addition of the fluorochemical phosphate salt. If the chelating agent is inadvertently omitted or added in insufficient quantity before the addition of the fluorochemical phosphate salt, the precipitate is formed and an inferior product is produced or production must be stopped until the precipitate is removed.

EP-PS 0 280 115 (Daikin) describes that the addition of an anionic surface-active agent to the fluorochemical phosphate salt can also provide a paper mixture, which is resistant to oil, which does not precipitate in hard water and can give the paper good resistance to oil. Addition of surface-active agent to the fluorochemical phosphate salt can, however, have an adverse effect on wrinkle properties, i.e. oil penetration into a wrinkle, and foaming problems, such as the build-up of foam in the treatment bath can occur.

It is therefore an aim of the invention to provide a method without the above-mentioned disadvantages.

This has been achieved by the present invention, characterized by what appears in the claims.

The present invention relates to a method of sizing paper to improve its resistance to liquid wetting under hard water conditions, and comprises (a) contacting either a paper sheet material or a pulp slurry in hard water with a hydrocarbon surfactant-free, substantially organic solvent-free, aqueous dissolving an N-alkyl-fluoroaliphatic sulfonamide alkyl phosphate salt in hard water, said phosphate salt forming substantially no precipitate and (b) drying the sheet material, or forming said slurry into paper and then drying the paper.

As used herein, the term "paper" is used with reference to both paper and cardboard.

As used herein, the term "hard water" is used with reference to containing at least approximately 85 ppm divalent salt, e.g. calcium and magnesium salts.

The method according to the invention is particularly useful for providing paper and cardboard with resistance to wetting by liquids. The method according to the invention can be used in conditions with hard water without the addition of chelating agents or hydrocarbon surfactants. Generally, fluorochemical phosphate salts are provided as aqueous solutions containing significant amounts of organic solvent, e.g. 2 0% or more, and leads to precipitation when placed directly in hard water and causes production problems. Precipitation can be prevented by adding chelating agents to the water before adding the fluorochemical phosphate salt, but occasionally the chelating agent is unexpectedly omitted or added after the addition of the fluorochemical phosphate salt and precipitation occurs.

In the method according to the present invention, the fluorochemical phosphate salt can surprisingly be added directly to hard water without the use of a chelating agent and does not precipitate to any particular extent.

N-alkyl-fluoroaliphatic sulfonamide alkyl-phosphate salts, usable in the present invention, can be represented by

the formula

wherein R is hydrogen or an alkyl group having from 1 to approximately 12, preferably 1 to 6, carbon atoms; r' is an alkylene bridging group containing 2 to approximately 12 carbon atoms, preferably from 2 to 4 carbon atoms and may be straight or branched; Rf is a perfluoroaliphatic radical; m is an integer from 1 to 3; and X is a monovalent salt forming ion. The fluoroaliphatic group is denoted here as Rf. Rf is a stable, inert, non-polar, preferably saturated monovalent moiety that is both oleophobic and hydrophobic. Rf preferably contains at least approximately 3 carbon atoms, more preferably 3 to approximately 20 carbon atoms and most preferably approximately 6 to approximately 12 carbon atoms. Rf may contain a straight chain, branched chain or cyclic fluorinated alkyl groups or a combination thereof, or combinations with straight chains, branched chains or cyclic alkyl groups. Rf is preferably free of polymerizable olefinic unsaturation and can optionally contain catenane heteroatoms, such as oxygen, divalent or hexavalent sulphur, or nitrogen. It is preferred that each Rf contains approximately 40 to approximately 78 weight percent fluorine, more preferably approximately 50 to approximately 78 weight percent fluorine. The terminal part of the Rf group contains a fully fluorinated terminal group. This terminal group preferably contains at least 7 fluorine atoms, e.g. CF3CF2CF2-, (CF3)2CF- - CF2SF5, or the like. Perfluorinated alphatic groups, i.e. those with the formula CnF2n+i/, are the most preferred embodiments of Rf.

In general, the fluorochemical phosphate salts are a mixture of monoesters, diesters and triesters. The amount of triesters present should not exceed approximately 5% by weight of the product since they are not easily dispersible and contribute little to repellency. Typically, the ester distribution is approximately 5 to 10 weight percent monoester, approximately 75 to 90 weight percent diester and approximately 2 to 5 weight percent triester.

These phosphate salts include, for example; ammonium- bis-(N-ethyl-perfluorooctanesulfonamideethyl)- phosphate, sodium- bis-(N-ethyl-perfluorooctanesulfonamideethyl)- phosphate, lithium- bis-(N-ethyl-perfluorooctanesulfonamideethyl)- phosphate, diethanol-ammonium-bis-(N -ethyl perfluorooctanesulfonamideethyl)-phosphate, sodium mono-(N-hexyperfluorodecanesulfonamideethyl)-phosphate, ammonium bis-(N-propylperfluorocyclohexanesulfonamideethyl)-phosphate, lithium mono-(perfluorohexanesulfonamidebutyl)-phosphate, ammonium bis-(N-ethyl perfluoroethylcyclohexanesulfonamideethyl) )-phosphate, ammonium-di-phenyl-(N-hexylperfluorocyclohexanesulfonamideethyl)-phosphate, etc. Such compounds are described e.g. in VS - PS 3 094 547 (Heine).

These N-alkyl fluoroaliphatic sulfonamide alkyl phosphate salts can be prepared according to the following reaction schemes: After the formation of the fluorochemical phosphoric acid,

the solvent can be stripped off

the reaction product~and an aqueous solution of the base, e.g. NH4OH, is added to the liquid (molten) reaction product to form the salt. Alternatively, a water-miscible solvent, e.g. isopropyl alcohol is added after the reaction solvent, e.g. toluene, is stripped to control viscosity. The aqueous solution of base is then added and the isopropyl alcohol is stripped. Suitable bases for neutralizing the fluorochemical phosphoric acid include, e.g. ammonium hydroxide, sodium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate and diethanolamine. Although the mixture useful in the present invention is essentially solvent-free, small amounts of organic solvents may be present in the final product, but such amounts must be sufficiently low so that precipitation of the product does not occur in hard water. In general, isopropanol is preferably present in an amount of less than approximately 8 percent by weight; butyl alcohol is preferably present in an amount of less than approximately 5 percent by weight; ethylcarbitol is preferably present in an amount of less than approximately 10 percent by weight; 2-butoxyethanol is preferably present in an amount of less than approximately 5 percent by weight; propylpropasol is preferably present in an amount of less than 10 percent by weight, and propylsolv is preferably present in an amount of less than approximately 5 percent by weight.

The fluorochemical phosphate salt can be applied to paper, either by internal addition in which the mixture is dispersed in a pulp suspension or slurry for papermaking or by external addition by dipping or spraying an aqueous solution of the mixture on the paper or by using a size press, all methods are well known to the person skilled in the art. Preferably, the fluorochemical phosphate salt is applied to the paper in an amount of approximately 0.05 to 1, more preferably 0.1 to 0.5 percent by weight, based on the weight of the paper.

The following non-limiting examples are provided to further illustrate the invention. In the examples, all parts and percentages are calculated by weight unless otherwise noted. In the performance evaluation in the examples, all tests were performed on 16.4 kg/270 m<2> (36.5 lb/3000 sq ft) solid bleached sulfate water sheet paper by glue press application. In the event precipitation is observed, "light" indicates approximately 5 to 10% precipitation, "moderate" indicates approximately 20 to 40% precipitation, and "heavy" indicates approximately 50 to 100% precipitation. The following test (Kit Test) was used to evaluate the extent to which the paper was resistant to grease, oil and wax:

The reagents are prepared as follows:

A paper test sample is placed on a clean flat surface and a drop of the test solution is released from a height of 25 mm (1 in). After 15 seconds, excess liquid is removed with a clean napkin or piece of cotton fabric and the moistened area is examined. A failure is noticed by a significant darkening of the test sample. The kit rating is the highest numbered solution that stays on the test surface for 15 seconds without causing a failure.

The Ralston Crease Test is used to determine the amount of oil penetration through a paper sample. The sample has been treated for at least 24 hours at 22.8 ± 0.8°C and 50 ± 2% relative humidity. A 10 cm x 10 cm treated sample is placed on a smooth glass plate and folded through the center parallel to an edge to provide a preliminary light wrinkle. A wrinkle roller weighing 2040 ± 46 g and 9.5 cm in diameter and 4.5 cm wide with a rubber coating approximately 0.6 cm thick and having a "Shore A Durometer" hardness of 75 ± 5 is rolled a once over the wrinkle without extra pressure. The paper is unfolded and the crease line is again rolled over. The paper is folded 90° to the first crease with the side on the outside of the first fold now on the inside, rolled folded up and rolled again.

The sample is placed on a grid sheet that has squares of limb x limb placed on an unprinted sheet which is again placed on a background plate. A metal ring 7.5 cm in diameter, 1.25 cm high, wall thickness of 15.9 mm is placed on the sample. A 2.5 cm high tube having an internal diameter of 2.5 cm is placed in the center of the ring and 5 g of sand is poured into the tube and the tube is then removed. 100 g of synthetic oil is colored by mixing it with 0.lg of red dye. 1.3 cm<3> of the red colored synthetic oil is transferred to the sand pile. The oiled sand samples are placed in an oven at 60 ± 1.1°C for 24 ± 0.25 h, removed from the oven and examined for stains. Each square of the grid represents 1%. The Crease Rating is the number of squares that have been colored. All equipment and materials for this Crease Test are available from the Ralston Purina Company.

Intermediate A

A clean dry 250 mL three-necked flask fitted with a condenser, a "Dean Stark" trap filled with toluene, a stirrer, a thermometer, and devices for controlling the temperature was charged with 23 g of phosphorus oxychloride (P0C13) (0.15 mol) and cooled to 15°C. After reaching 15°C, 2.65 g of water (0.147 mol) was added, resulting in an instant exotherm to 59°C. Then 30 g of toluene, of 167.9 g of N-ethyl-perfluoro-octanesulfonamide ethyl alcohol with 5 g of further toluene were added. The temperature of the solution was raised to reflux. Reflux began at approximately 105°C and was continued for 4 h at approximately 115°C. The resulting solution was transferred to a 250 ml vessel and allowed to cool to room temperature.

Intermediate B.

A clean, dry 250 ml wooden necked flask fitted with a condenser,

a nitrogen inlet, a stirring device, a thermometer and a device for controlling the temperature were charged with 23 g of phosphorus oxychloride (POCl 3 ) (0.15 mol) and 8 g of toluene and cooled to 15°C. After reaching 15°C, 2.65 g of water (0.147 mol) was quickly added using a 3 ml syringe. This resulted in an immediate exotherm to 59°C. The portion was kept at 60°C for 1 h. Then 37 g of toluene, 167.9 g of N-ethyl-perfluorooctaxulfonamidethyl alcohol were added to the flask. The mixture temperature was raised to reflux (approximately 115°C). Reflux was continued for approximately 6 h under nitrogen purging. The portion was then cooled to approximately 90°C and 1 g of deionized water was added to hydrolyze any residual POCl 3 . The toluene and residual water were removed by applying a vacuum at 90°C for approximately 30 min. The portion was then cooled to approximately 75°C and 44g of isopropyl alcohol (IPA) was added to give a solution of 80% solids.

Intermediate C

A clean dry 1000 mL three-necked flask fitted with a condenser, a stirrer, and an additional stopcock was charged with 38.38 g (0.25 mol) of POCl 3 and 50 g of toluene. 4.41 g (0.245 mol) of deionized water was added by means of a syringe for 30 sec. The exothermic reaction raised the temperature to 40°C. The hydrochloric acid (HCl) formed was passed through a sodium hydroxide (NaOH) cleaning solution at the outlet of the chiller. A heating mantle was placed under the flask and the reaction was continued for 1 h at approximately 60°C. The solution was allowed to stand overnight (approximately 15 h) with a large DRIRITE trap placed on the outlet from the cooler. The next day, 232.26 g (0.49 mol) of premelted Z ON YL «i- BA, Cn<F>2n+iCH2CH2OH, n=6-12 , available from DuPont, was added through an additional funnel followed by a toluene purge of the tract. The mixture was allowed to react for 5 h at reflux. An additional 1 mL of deionized water was added to hydrolyze any residual POCl 3 . The toluene and water were stripped at 90°C using vacuum. The vacuum was maintained for approx. 30 min. during which period approximately 50 g of toluene with a small amount of water was collected. 50 g of IPA was added to provide a solids content of approximately 80-82%

Example 1

Fluorochemical phosphate salt I (FCPS I) was prepared as follows: a clean dry 500 ml three-necked flask was fitted with a "Dean-Stark" trap, a stirring device, a thermometer and a device for controlling the temperature. The vessel containing Intermediate A prepared as above was placed in an oven at approximately 100°C to melt the material to facilitate the transfer and 79.3 g of Intermediate A was added to the flask. This was heated to approx. 100°C where vacuum stripping of toluene was started. The temperature was increased during the stripping to about 120°C. The stripping was completed in approximately 35 minutes. 14.9 g of condensate was collected in the "Dean Stark" trap. The temperature of the solution was lowered to approx. 78°C. A two-phase system resulted when 150 g of deionized water was slowly added to the remaining 64.4 g of stripped intermediate A. Another 160 g of deionized water was added. The two-phase mixture was maintained at approx. 80°C while 3.0 g of ammonium hydroxide was added. The two phases began to disperse into each other. An additional 3.1 g of ammonium hydroxide was added. An additional 23.7 g of deionized water was added, heating was terminated and the solution was allowed to cool to room temperature with shaking. The resulting solution had a pH value of 10 and a solids content of 16.4%.

A treatment bath was prepared by diluting FCPS I in 50 g of hard water (about 250 ppm divalent salt). The amount of FCPS I added to the hard water was calculated to precipitate 0.2% of the fluorochemical solids on the 15.4 kg/270 m<2> (36.51b /3000sq ft) solid bleached sulfate water sheet paper by size press application. Wet pickup in the glue press was determined to be 93.6%

The resulting diluted mixture was then immediately observed for precipitation of solids. The treated solution was placed in a sizing press treatment bath and a sample of the paper was saturated by being drawn through the bath. The saturated substrate was then padded with a set of rubber rollers set at 137.8 kN/m<2> at a speed of 0.45 m/min. The treated paper was dried in a 3M model 9014 "Imaging System Dryer", set at 140°C for 10 sec. The dried, treated paper was processed overnight (approx. 15h) at 22°C and 50% relative humidity. The conditioned samples were then tested for resistance to oil using the Kit Test. The kit rating was 7.

Example 2

Fluorochemical phosphate salt II (FCPS II) was prepared as follows: a clean dry 500 ml three-necked flask was fitted with a condenser and a "Dean-Stark" trap, a stirrer, a thermometer and devices for controlling temperature. The vessel containing intermediate B, prepared as above, was placed in an oven at approx. 70°C to melt the contents. Then 100 parts of intermediate B was added to the flask and diluted to 15% by the addition of a first portion of 250 parts of deionized water, added slowly to minimize foaming with the temperature of the mixture maintained at 65°C to 70°C. The resulting product was a gummy semi-solid material. Another portion of 203 parts of deionized water and 8.1 parts of ammonium hydroxide was added and the neutralization reaction was allowed to proceed for approx. 2 h. The alcohol was then stripped from the product at a temperature of approx. 60°C to 75°C using nitrogen purging. The resulting product contained 15% solid fluorochemical phosphate salt and 0.9% rest isopropyl alcohol.

A treated solution was prepared as in Example 1. No precipitation occurred. Paper was treated, dried and processed as in Example 1 and tested for Kit assessment. The kit rating was 7+.

Examples 3-7.

Fluorochemical phosphate salts III-VII (FCPS III-VIII) were prepared. For FCPS III, a clean dry 500 mL three-necked flask was fitted with a condenser and "Dean Stark" trap, a tubing assembly, a thermometer, and a temperature control device. The vessel containing intermediate B, prepared as above, was placed in an oven at approximately 70°C to melt the contents. Then 100 g of intermediate B was added to the flask. The isopropyl alcohol was stripped at a temperature of 60°C to 75°C, using vacuum. The vacuum was adjusted to control foaming. From this stripping, 18.5 g of isopropyl alcohol was collected. The resulting 81.5 g of solids was diluted to 15% by the addition of a first portion of 250 g of deionized water, added slowly to minimize foaming while maintaining the temperature of the mixture at approximately 65°C to 70°C. The resulting product was a gummy semi-solid material. A second portion of 203 g of deionized water and 8.1 g of ammonium hydroxide was added. While the addition was taking place, the gummy solids changed to a viscous opaque solution which could be easily stirred within approx. 30 min. When completely added, the viscosity increased and the pH increased to approximately 9-10.

FCPS IV-VII were prepared in a similar manner. For FCPS IV, the second charge of deionized water contained 243 g of water, 6.7 g of diethanolamine, and no ammonium hydroxide. This neutralization was allowed to proceed for approximately 2 hours at approximately 65°C and resulted in a somewhat opaque solution having a pH of approximately 9. For FCPS V, the second charge contained 229 g of deionized water, 2.6 g of sodium hydroxide and no ammonium hydroxide. The pH value was adjusted to 9-10 with sodium hydroxide pellets. For FCPS VI, the second charge contained 229 g of deionized water, 2.7 g of lithium hydroxide monohydrate, and no ammonium hydroxide. The pH was adjusted with 0.27 g of lithium hydroxide monohydrate.

A treatment solution was prepared using each of FCPS III-VII and paper was treated, dried and processed as described in Example 1. Each sample was observed for precipitation and tested with Kit Rating and Crease Rating ). The results are presented in table 1.

As can be seen from the data in Table 1, each of the treatment solutions gives good Kit and wrinkle assessments without any precipitation of FCPS.

Comparative examples C1-C6.

To prepare fluorochemical phosphate salt VIII (FCPS VIII), 50 g of premelted intermediate C was added to a 500 mL three-necked flask, fitted with a stirrer, thermometer, temperature control device, and a Dean Stark trap with a condenser. To this was added a mixture of 221.6 g of deionized water and 5.1 of ammonium hydroxide dropwise for 30 min while heating to 65°C. The reaction was continued for 1 h at approximately 65°C. The isopropyl alcohol was stripped over a temperature range of 60°C to 75°C using vacuum. Sufficient deionized water was added to result in 15% solids. Fluorochemical phosphate salts IX and X (FCPS IX and X) were prepared in the same way as FCPS VIII with the exception that for FCPS IX 1.67g of lithium hydroxide monohydrate and for FCPS X 4.2g of diethanolamine were added instead of ammonium hydroxide.

Treatment solutions were prepared as in Example 1 and samples of the paper were treated, dried and processed as in Example 1. Treatment solutions were also prepared using deionised (DI) water instead of hard water and samples of the paper were treated, dried and processed in the same way like the hard water samples. Each solution was observed for precipitation and the paper was tested for Kit assessment. The results are shown in table 2.

As can be seen from the data in Table 2, fluoroalkanal alkyl phosphate salts (RfCH2CH2)mP(0) (0X)3_m, m = 1,2 or 3, provide good Kit estimates without any precipitate when used in deionized water, but provide no oil repellency and precipitates a lot in hard water.

Examples 7 and 8 and Comparative Examples C7-C12.

For Examples C7-C12, anionic surfactants were added to the fluorochemical phosphate salts as set forth in Table 3 to provide 5 percent by weight surfactant solids in each example.

These mixtures were used to prepare treatment baths as in example 1. For examples 7 and 8, the treatment baths were prepared as in example 1 by using respectively FCPS III and FCPS IV without the addition of a surfactant. Samples of the paper were treated, dried and processed as in Example 1, the treatment baths were observed for precipitation. The treated samples of paper were tested for Kit assessment and wrinkle assessment. The results are shown in table 4.

As can be seen from the data in Table 4, the addition of anionic surfactant to the fluorochemical phosphate salt can reduce precipitation somewhat, but the Kit assessment is somewhat reduced and the oil resistance, measured by the wrinkle test, is significantly reduced.

Claims (7)

1. A method of sizing paper to improve resistance to wetting by liquids under hard water conditions comprising (a) contacting either a paper sheet material or a pulp slurry in hard water with an aqueous solution of N-alkyl fluoroaliphatic sulfonamide alkyl phosphate salt which is free of anionic surfactants and substantially free of organic solvents, and wherein said phosphate salt forms substantially no precipitate and (b) drying said sheet material, or forming said slurry into paper and then drying the paper. 2. Method as stated in claim 1, characterized in that said phosphate salt is present in an amount of 0.05 to 1.0 percent by weight. 3. Method as stated in claim 1, characterized in that said phosphate salt is present in an amount of 0.1 to 0.5 percent by weight. 4. Method as stated in claim 1, characterized in that said phosphate salt is represented by the formula where R is an alkyl group having from 1 to 12, preferably from 1 to 6 carbon atoms; R' is an alkylene bridging group containing 2 to 12 carbon atoms, preferably from 2 to 4 carbon atoms, and may be straight chain or branched; Rf is a perfluoroaliphatic radical; m is an integer from 1 to 2; and X is a monovalent salt forming ion. 5. Method as stated in claim 4, characterized in that said phosphate salt comprises 5 to 10 weight percent m=1, 75 to 90 weight percent m=2 and 2 to 5 weight percent m=3. 6. Method as stated in claim 1, characterized in that said phosphate salt is ammonium, sodium, lithium or diethylammonium salt of N-ethyl-perfluorooctane sulfonamide ethyl phosphate. 7. Method as stated in claim 1, characterized in that said phosphate salt is an ammonium, sodium, lithium or diethylammonium salt of N-methyl perfluorooctane sulfonamide ethyl phosphate.