US2315128A - Shrinkproof paper and method of manufacture, and laminated product - Google Patents

Description

March 30, 1943. N w m 2,315,128

SHRINKE'ROOF PAPER AND METHOD OF MANUFACTURE, AND LAMINATED PRODUCT Filed Nov. 27, 1939 INVENTOR V va-1K5 Newkvk' ATTORNEY [CO(NCH2)2], that is,

atented 30, 1943 SHRINKPROOF PAPER 3:

UFACTURE, LAATED PROD- UCT METHQD F Francis F. Newkirk, Attleboro, Mass assighor to erican Reenio'rced Paper Company, Atticboro, Mass, a corporation of Massachusetts Application November 27, 1939, Serial No. 306,304

18 Claims.

.in situations where it is subject to frequent wetting and drying. For example, when kraft paper is used for building purposes it will shrink upon exposure to changing weather conditions so as to cause it to tear away from its securin nails or to split. Kraft paper may shrink as much as 4% or over crosswise of the sheet and somwhat less in the machine direction whenit is alternately wetted and dried 7 times, which may be taken as representative of exposure to normal changes in weather conditions during a period of 3 summer months.

It is the object of. my invention to treat paper, as for example kraft paper, in such a way that without materially detracting from its qualities of tearing and folding strength and flexibility it will be rendered shrinkprooi to such a degree that its residual capacity to shrink crosswise in such a 7 cycle test is about 1% or preferably as little as So far as I am aware, paper such as kraft paper has never been produced with such a low residual shrinkage capacity prior to my invention.

In my treatment I preferably employ urea ECOINHg) a] or thiourea and formaldehyde [HCI-IO] in an aqueous solution which is weakly acidified by a material such as ammonium thiccyanate [NEiCNS]. -As will be described, I treat formaldehyde, that is, equal parts of urea and formaldehyde by weight when heated will be converted into a urea-formaldehyde resin 1100mm) i+znnciio=icomcmmn+znmo and ithas heretofore been suggested to treat In my process, on the contrary, I employ a bath which contains a substantial deficiency of urea as compared with that which would be required according to the foregoing reaction to form the resin. I use less than one-half, although greater than one-fourth, as much urea as formaldehyde and preferably as little as about one-third as much or slightly over,i. e. between limits of 1:3 and 3:7. With the urea. and formaldehyde 1 make an aqueous solution that is very dilute,.

employing preferably around thirty times as much water as urea. The percentage by weight of urea to water should be below 5% and above 2%, preferably between 3% and 4% and in the example given below is approximately 3.4%. This bath is acidified within a pH range of approximately 2 to 4.5 using a weak acidifler preferably chosen from the following group:

Ammonium thiocyanate Ammonium chloride Mon-ammonium phosphate Iii-ammonium phosphate Tri-ammonium phosphate Ammonium bromide Formic acid My preferred formula for the bath is as follows, in parts by weight:

Where sized papers are to be treated, I would add to the above bath a small amount of wettin agent, such as .25 parts by weight of a 10% solution of aerosol" (comprising an ester of sulfonated bicarboxylic acid) in water.

Kraft paper to be treated is wetted with the above bath as by immersion therein for a brief interval of two or three seconds, and I then remove, as by doctoring, a large quantity of the bath that has been taken up. The damp paper should be less than 75% and is preferably from 30% to 50% heavier than the dry paper.

I then heat the paper to a temperature of from apprcxirriately 250 F. to 300 F. (or higher but I without slngeing the paper) for a brief interval such as one-half minute or less, by passing the paper through a hot air dryer. The paper is then ready for use and it has increased in weight less than 10% and usually about 5% to 7%, al-

though I have been able to reduce the shrinkage in paper with an extremely limited increase in weight such, for example as only 0.5%.

In the drawing I have illustrated diagrammatically apparatus which I have used effectively for my purpose. At 2 is indicated a tank in wetting agent, such asaerosol, is' employed. I,

may store it with the formaldehyde. At 6 and 8 are pumps for delivering the solutions in tanks 2 and 4 respectively through pipes .IO and I! respectively past the flow meters [4 and into mixing tank IS. The mixed solution is drawn by pump i8 from tank l6 and is forced through line 20 to trough 24 containing application roller 26 and through line 28 to spray pipe 30. The paper to be treated, supplied in a roll 32, is guided over rolls 34 and 36,.over application roll 26, around guide roll 40 to conveyer belt 42 and into a dryer 48. The dryer illustrated has three sections designated 50,- 52v and 54, suitably partitioned and into which hot air from a supply pipe 56 is blown through the ducts 58, 60 and 62- respectively. An exhaust in the-central compartment 52 suffices as I have indicated at. The dryer illustrated is approximately 150 feet long over all and the paper is conveyed through the dryer by a conveyer-belt l advancing the paper at 400 feet a minute or thereabouts. The temperature in the three. compartments may be uniform and within the approximate temperature limits above noted, but in the specific apparatus illustrated the temperature in practice has been approximately 250 F. in compartment 50, 280 F. in compartment 52 and 260 F. in compartment 54.

After the paper has been thoroughly wetted on both sides by passage between the application roll 26 and spray pipe 30, the excess solution, particularly on the surfaces, is removed by a rubber doctor blade and an air doctor 12. The paper passes thence through the dryer and as it emerges it is wound up at 80 by engagement with a surface winding r'oller 82. The rolls 84 are idle rolls and serve to tension the paper for a tightly wound roll at 80.

The paper thus produced is substantially unimpaired in its original qualities of flexibility, han- I composite reenforced sheets made by uniting two layers of kraft with interposed asphalt adhesive in which are embedded reenforcing filaments such as unspun sisal fibers, strings or the like, which composite sheets heretofore have had exception-v ally high shrinkages, such as 8% in the crosswise direction.

Although I have made extensive and careful experiments, I have as yet been unable to determine precisely the reactions which take place between the chemicals of the bath or between them and the cellulose of the paper, or the relative effects of those materials. My product, however, clearly lacks the characteristics of a paper or pulp that has been treated with urea and formaldehyde in the conventional resin forming proportions. The products of such methods vary in their characteristics with the quantity of resin present from a hard resin loaded slabthat is water impervious to a lightly impregnated sheet that is brittle and weak in tearing and folding strength and has a residual capacity to shink which is as great, if not greater than that of untreated paper.

The treatments embodying my invention may be performed at low cost due to the brief time interval required in the heating operation and thereby my invention doe not add materially to the cost of paper whose cheapness commends it for mostcommercial uses.

The word urea" when used in the specification and claims is intended to include thiourea in molecularly equivalent proportions.

This application is a continuation in part of my prior application Ser. No. 135,261, filed April 6, 1967.

I claim:

1. A sheet of paper rendered substantially shrinkproof by impregnation with the product of the reaction within its structure of formaldehyde and an amount of urea which is substantially less than equal parts by weight with the formaldehyde, the said paper being at least 0.5% and no more th.n 10% heavier than the same paper without said'impregnation.

2. A sheet of paper rendered substantially shrinkproof by impregnation with the product of the reaction within its structure of an acidifiedbath of formaldehyde and an amount of urea which is by weight less than approximately one-half and more than approximately onefourth that of the formaldehyde, the said paper being at least 0.5% and no more than 10% heavier than the same paper without said impregnation.

3. A sheet of paper rendered substantially shrinkproof by impregnation with the product of the reaction within its structure of a weakly acidifled bath of formaldehyde and an amount of urea which by weight is in proportion to the formaldehyde of from 3:7 to 1:3, the said paper being from approximately 5% to 7% heavier than the same paper without said impregnation.

' 4. A sheet of kraft paper impregnated with the product of the reaction within its structure of formaldehyde and an amount of urea which is by weight less than approximately one-half and more than approximately one-fourth that of the formaldehyde, the said paper being at least 0.5% and no more than 10% heavier than the same paper without said impregnation and being capable of a shrinkage of not more than 1% in its cross direction when alternately wetted and dried seven times.

5. A composite reenforced sheet of paper composed of two superposed sheets of the paper defined in claim 4 united by interposed asphalt 1.1 which reenforcing strands are embedded, said composite sheet having a very inhibited capacity to shrink when repeatedly wetted and dried.

6. A composite reenforced sheet of paper formed of a plurality of superposed plies of the paper defined in claim 4 and united by interposed adhesive, said composite sheet having a very inhibited capacity to shrink when repeatedly wetted and dried.

'7."The'method of reducing the shrinkage in paper when repeatedly wetted and dried which consists in wetting the paper to substantially below its saturation point with a dilute aqueous bath of urea and formaldehyde containing by low' its saturation point with a. bath of formaldehyde and urea containing by weight less than approximately one-half and more than approximately-one-i'ourth as much urea as formaldehyde and about 30 times as much water as urea, and

heating the damp paper so that its dry weight is increased at least 0.5% and no more than 10%.

'9. The method of reducing the shrinkage of paper when repeatedly wetted and dried which consists in wetting the paper to substantially below its saturation point with a dilute aqueous bath of urea and formaldehyde containing by weight less than approximately one-half and more than approximately one-fourth as much urea as formaldehyde and acidified by a weakly less than approximately one-half and more than approximatehrone-fourth as much urea. as formaldehydesaid bath being acidified to a pH of between 2 and 4.5 by an acidifier chosen from the group consisting of ammonium thiocyanate, ammonium chloride, mon-ammonium phosphate, diammonium phosphate, trieammonium phosphate, ammoniumbromide and formic acid, and heat- I ing the damp paper to above 200 F. for a brief interval to reduce its shrinkage while increasing its weight at least 0.5% and no more than 10%. p

11. The method of reducing the shrinkage of T paper when repeatedly wetted and dried which consists in applying to the paper a dilute, aqueous bath, in an amount between and 50% of the dry weight of the paper, containing urea and formaldehyde in the proportions of from 3:7 to 1:3 by weight, and between approximately 3% and 4% urea by weight to water. said bath being acidified to a pH of between 2 and 4.5 with a weakly acidic material, and heating the damp paper.

12. The method of reducing the shrinkage in paper when repeatedly wetted and dried which consists in wetting the paper with an amount of bath approximating 30% to 50% of the dry weight of the paper containing by weight approximately 22 parts of 40% formaldehyde, 3 parts urea, 2 parts ammonium thiocyanate and '75 parts water, and heating the damp paper to a temperature of from 250 F. to 300 F. for approximately one half minute. v 13. The method of reducing the shrinkage in paper when repeatedly wetted and dried which consists in applying to the paper an aqueous bath of formaldehyde and urea containing approximately one-third as much urea by weight as formaldehyde and sufficient water so that the percentage by weight of urea to water is below 5% and above 2%, treating the paper to remove a large portion of the bath which it has absorbed and then heating the damp paper to an elevated temperature suiiicient to cause the materials absorbedby it from the bath to react.

14. The method of reducing the shrinkage of.

paper when repeatedly wetted and dried which consists in wetting the paper to substantially below its saturation point with a dilute aqueous bath of urea and formaldehyde containing by weight less than approximately one-half and more than approximately one-fourth asmuch urea as formaldehyde, and heating the paper to from 250 F. to 300 F. for no more than a few minutes so that the dry weight of the paper is increased-at least 0.5% and .no more than 10% and so that its shrinkage is reduced without sub stantially impairing its normal flexibility, handle,

hygroscopicity and folding and tearing strength. 15. A sheet of paper rendered substantially shrinkproof by impregnation with the product oi the reaction within its structure of iorineldehyde and an amount of urea which is by weight less than approximately one-half and more than ap proximately one-fourth that of the formaldehyde, the said paper being at least 0.5% and no more than 10% heavier than the same paper without said impregnation.

. 16. The method of reducing the shrinkage in paper when repeatedly wetted and dried which includes applying to the paper a dilute bath of urea and formaldehyde containing by weight less than approximately one-halr and more than ap-- proximately one-fourth as much urea as formaldehyde and subsequently heating the paper to an elevated temperature sufficient to cause the materials taken by it from the bath to react so that the dry weight of the paper is increased at least 0.5% and no more than 10%.

17. The method of reducing the shrinkage in paper when repeatedly wetted and dried which includes applying to the paper a dilute'aqueous bath of urea and formaldehyde containing by weight less than approximately one-half and more than approximately one-fourth as much urea as formaldehyde, the said bath containing a material adapted to impart acidity of a pH of between 2 and 4.5 and heating the paper to cause the materials taken by it from the bath to react so that the dry weight of the paper is increased at least 0.5% and no more than 10% and so that its shrinkage is reduced without substantially im pairing its normal flexibility, handle, hygroscopicity and folding and tearing strength.

18. A multiply paper having a substantially reduced ability to shrink when alternately wetted and dried which comprises two sheets of paper united by asphalt in which reeniorcing strands are embedded, each of said sheets having its ability to shrink reduced by impregnation with the product of the reaction within its structure of a weakly acidified bath of formaldehyde and an amount of urea which is by weight less than a proximately V, and more than approximately that of the formaldehyde, each of said sheets being at least 0.5% and no more than 10% heavier than the same paper without said impregnation.

. FRANCIS F. NEWKJRK.

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