US2917425A - Electrical insulating paper containing polymethylol phenol - Google Patents

Description

United States Patent ELECTRICAL INSULATING PAPER CONTAINING POLYMETHYLOL PHENOL Donald K. Pattilloch, New York, N.Y., assignor to Michigan Research Laboratories, Inc., Long Island City, N.Y., a corporation of Michigan, and Electro-Chem Fiber Seal Corporation, New York, N.Y., a corporation of Delaware No Drawing. Application May 1, 1957 Serial No. 656,219

16 Claims. (Cl. 162-138) This invention relates to electrical insulating paper, and more particularly paper containing a polymethylol phenol.

Prior art electrical insulating paper has been prepared by impregnating paper with a resin or insulating varnish. It is among the objects of the present invention to prepare electrical insulating paper directly by paper-making techniques and avoid the added steps of impregnating or coating and subsequent drying or curing of the impregnated paper.

The method of the invention generally comprises reacting cellulose fibers while suspended in an aqueous medium with a water soluble polyaldehyde, reacting the resulting reaction product with a polymethylol phenol and forming the suspension into a sheet. by usual paper-making techniques and the polymethylol phenol is cured to an isoluble resinous form in the drying step. The paper of the present invention exhibits high insulating qualities, having an electrical breakdown strength in excess of 300 volts per mil of sheet thickness. The paper also exhibits excellent dimensional stability, high tensile strength and 50% higher bursting strength (Mullen strength) than conventional paper prepared from the same pulp stock. The paper may be used as electric motor slot insulation, wrappers for electrical cable and other applications.

The water soluble polyaldehyde reacts with the hydroxyl groups of the cellulose and leaves one or more reactive aldehyde groups free to react with the polymethylol phenol to link the same to the cellulose. The polyaldehyde must have two or more aldehyde groups in the molecule. Suitable Water-soluble polyaldehydes include:

Glyoxal a-Hydroxyadipaldehyde Glutaraldehyde Succinaldehyde Z-ethyl glutaraldehyde B-methyl glutaraldehyde Z-ethyl 3-methyl glutaraldehyde The polymethylol phenol useful in the present invention is a phenol having two or more methylol groups 2,4-dimethylol phenol and 2,6-dimethylol phenol. The compounds are water soluble monomers prepared by careful condensation of formaldehyde and phenol to avoid polymer formation. Their water solutions are alkaline and may contain a small percentage of free formaldehyde, which does not interfere in the reaction of the in- The paper is formed 2,917,425 Patented Dec. 15, 1959 vention. The polymethylol phenols are cured to an insoluble resin by suitable drying temperatures.

Example I Examples II-VIII Unbleached kraft pulp was beaten asin Example I with varying percentages of poly aldehydes in the following examples. Thereafter varying percentages of 2,4, 6-trimethylol phenol were added, beating continued, and hand sheets formed as in Example I. The electrical breakdown strength of the hand sheets formed from the stocks is set forth in the following table.

Percent Break- Ex. Polyaldehyde TMP down,

volts/mil 2% glyoxal 10 324 5% glutaraldeivde 5 314 5% m-hydroxyadipaldehyda- 5 308 3% glyoxal 10 336 do 3 306 10 329 5% glyoxal 10 342 TMP in the above table refers to 2,4,6-trimethylol phenol.

The insulating paper of the instant invention is conveniently made on conventional paper machines, including Fourdrinier and cylinder machines, using conventional techniques. Machine run paper of the invention, having a higher and more uniform density than hand sheets, shows electrical breakdown resistance in the range of 420-500 volts per mil.

It has been found that 2-5 of polyaldehyde and about 5-10% of polymethylol phenol produce electrical insulating paper of good quality. Higher percentages may be used but generally are uneconomical. The cellulose pulp may be of any type, bleached or unbleached, such as kraft, sulfite, soda or semichemical pulp. For most electrical insulating paper applications, unbleached kraft pulp is preferred.

Under certain operating conditions, it may be necessary to augment the normal drying cycle of the paper machine by the use of auxiliary drying equipment, such as infrared banks.

All percentages are by weight on the basis of added solids on fiber solids.

While the invention has been described in terms of certain examples, such examples are to be considered illustrative rather than limiting, and it is intended to cover all modifications and embodiments that fall within the spirit and scope of the appended claims.

What is claimed is:

1. The process for the preparation of electrical insulating paper which comprises reacting cellulose fibers while suspended in an aqueous medium with a water-soluble polyaldehyde, reacting the resulting reaction product with a polymethylol phenol, and forming the suspension into a sheet.

2. The process set forth in claim 1 wherein the polymethylol phenol is 2,4,6-trimethylol phenol.

3. The process set forth in claim 1 wherein the watersoluble polyaldehyde is glyoxal.

4. The process set forth in claim 1 wherein the water soluble polyaldehyde is glutaraldehyde.

5. The process set forth in claim 1 wherein the water soluble polyaldehyde is a-hvdroxyadipaldehyde.

, 6. The process for the preparation of insulating paper which comprises reacting cellulose fibers while suspended in an aqueous medium with glyoxal, reacting the resulting reaction product with 2,4,6-trimethylol phenol, and forming the suspension into a sheet.

: 7. Insulating paper comprising a cellulosic web, the individual fibers of which comprise cellulose fibers reacted with a water-soluble polyaldehyde and the reaction product thereof reacted with a polymethylol phenol.

8. Paper set forth in claim 1 wherein said water soluble polyaldehyde is glyoxal.

9. Paper set forth in claim 7 wherein said polymethylol phenol is 2,4,6-trimethylol phenol.

10. Paper settforth in claim 7 wherein said watersoluble polyaldehyde is glutaraldehyde.

11. Paper set forth in claim 7 wherein said watersoluble polyaldehyde is a-hydroxyadipaldehyde.

12. Insulating paper comprising a cellulosic web, the individual fibers of which comprise cellulose fibers reacted with glyoxal and the reaction product thereof reacted with 2,4,6-trimethylol phenol.

13. Insulating paper comprising a cellulosic web, the individual fibers of which comprise cellulose fibers reacted with glutaraldehyde and the reaction product thereof reacted with 2,4,6-trimethylol phenol.

14. Insulating paper comprising a cellulosic web, the individual fibers of which comprise cellulosic fibers reacted with a-hydroxyadipaldehyde and the reaction prod,- uct thereof reacted with 2,4,6-trimethylo1 phenol.

15. The process for the preparation of insulating paper which comprises reacting cellulose fibers while suspended in an aqueous medium with glutaraldehyde, reacting the resulting reaction product with 2,4,6-trimethylol phenol, and forming the suspension into a sheet.

16. The process for the preparation of insulating paper which comprises reacting cellulose fibers while suspended in an aqueous medium with a-hydroxyadipaldehyde, reacting the resulting reaction product with 2,4,6-trimethylol phenol, and forming the suspension into a sheet.

References Cited in the file of this patent UNITED STATES PATENTS 2,037,522 Lundback Apr. 14, 1936 2,285,490 Broderick June 9, 1942 2,495,232 Drisch et al. Jan. 24, 1950

Claims (1)

1. THE PROCESS FOR THE PREPARATION OF ELECTRICAL INSULATING PAPER WHICH COMPRISES REACTING CELLULOSE FIBERS WHILE SUSPENDED IN AN AQUEOUS MEDIUM WITH A WATER-SOLUBLE POLYALDEHYDE, REACTING THE RESULTING REACTION PRODUCT WITH A POLYMETHYLOL PHENOL, AND FORMING THE SUSPENSION INTO A SHEET.