US2303791A - Adhesives - Google Patents

Description

Patented Dec. 1, 1942 ADHESIVES Paul B. Davidson, Wilkinsburg, Pa., and Julius R.

Adams, Westiield, Mass, a'ssignors to old 001- l ony Envelope Company, Westfleld, Mass, a corporation of Massachusetts No Drawing; Application March 17, ran.

Serial No. 383,792

4 Claims. (c1. 106-210) This invention relates to improvements in adhesives and is more particularly related tosocalled gums for use in connection with envelopes or otherdevices where it is desired to adhesively secure .ftogether. adJacently-disposed surfaces, especiallv. paper surfaces 7 as in the case of envelopes v 1 ThIs'appIication is a continuation in part of an application Ser. No. 202,882 filed by us on April 19, 1938, issued as Patent No. 2,241,700.

It is a principal objector the invention to provide an.,adhesive for use with paper-which is so constructed chemically that it will not discolor or, otherwise deteriorate with age. That is to say. we have conceived an adhesive which will not have the tendency to discolor regardless of climate'or other conditions under which the envelopes or other articles are stored.

It has always heretofore been a serious difiiculty in the envelope industry that the envelopes, after storage on shelves or the like, will become discolored due to reaction between the gum or adhesive and elements in the paper. It appears that the cause of discoloration is the formation of colored or humus-like substances due toreac tion between degraded protein which is necessarily present in any ordinarily sized paper and the reducing sugars which are ordinary paper adhesive. 1 I

A further object of the invention is to provide an envelopeadhesive which has special properties andv characteristics particularly adapting them for use in the manufacture of envelopes. It is the usual practice in the envelope industry to apply the gumthereto by means of what is called an envelope machine and it will be appreciated that in order that application of the gumbe carried on efilciently and economically the adpresent in any heslve mustremaln suiljlciently fluid and nonpasty for an ample length of time. The gums of this inventionnot only have the non-discoloration properties above-mentioned but also they are properly fluid for use in the envelope machine. V v y After considerable research we have come to ,the conclusion that the problem of discoloration can be solved. Heretofore, to our knowledge, no one has ever even attempted todeal with the matter of discoloration, much less provide an adhesive adapted to eliminate it. Noris there any prior art which suggests any previous treatment or procedure to provide an envelope gum which is both suiiiciently fluid and not capable of causing discoloration.

Our invention consists f broadly in providing paper adhesives which have as a' base a certain amount of partially-'dextrinized starch and con-- tain one or more of'a group-of fluidify'ing sub stances which are capable of both sufliciently inhibiting objectionable gel formation and preventing'discoloration. That is to say, the composi tion is such that it is properljfluid to permit efilclent application to the'paper by the envelope machines andit is alsojsuch that it will not, after application to the paper, tend'to react with more or less degraded protein in the paper sizingsfso as to .form' coloredfc'ompounds' which are objectionable. I

7 After considerable.eirperiment wehave found that any gums or adhesives which contain appre ciably more than 2%" by weight oflreducing' sugars do react unfavorably with the protein in ordinary paper, sizings so astoproduce discoloration. In other 'words, we provide an adhesive composition which is so---constructed chemically as to have-a totalreducingsugarcontent which is preferably not more than 2% ,by weight of the gum and we accomplish this by a combination of partially-dextrinized starch and .a fiuidifying agent which is calculated toproduce the desired effect. 7 ,z

. Careful and scientifically conducted experiments' have clearly shown us that when the reducing-sugar content of1the gum doesrlse appreciably above: the percentage mentioned-there is, inevitably, discoloration. For example, a number of pieces of paper, all .the samekind, were stuck together'with various adhesives which have been heretofore known and with adhesives of this invention which'are aboutto be described.

as These pieces were aged by anaccelerated ageing test which had been standardized against natural conditions. This test consisted of placing the pieces in testtubes, sealing, them, and

placing the .tubes in anxoven regulatedto C. I for 48 hours.

dextrins by adding cc..-of 98% ethanol, ac-

cording to the method described asthe Starch Tentative? on page 385 of the third edition of .Oficial andTentativeMethods of Analysis of the Association of Ofiicial Agricultural Chemists.

The dextrins were allowed topsettle out of as dispersion for-'48 hours and then samples of the Association of Official Agricultural Chemists mentioned above. It was clear from the results that the particular adhesives embodying the -features of this invention did not show discoloration because the reducing sugar content was below 2%, all other thingshaving been kept equal.

We have further found thatthere are particular types of dextrin or starch which are most suitable for accomplishing our purpose. While, as a general rule, best results can be obtained if the .reducing sugar content. of the 'dextrin itself before cooking is below 2%, it is necessary that the final cooked gum contain less than 2% of reducing sugar to completely avoid discoloration. i

That is to say, the hydrolysis that takes place during the normal cooking of the gum may objectionably increase the reducing sugar content even though the'content oftlfie original dextrin was low. Accordingly, we preferably use a partially-dextrinized starch which is of such a composition that when it is cooked for about thirty minutes at a temperature of around 98 C. with an approximately 40% concentrated solution of acetic acid, it will have, upon cooling, a reducing sugar content of less than, or at least not appreciably more than, 2% by weight.

Another example of a preferred dextrin is one which, when cooked for-aboutthirty minutes at a temperature of about 85C. with the same acetic acid, will not have areducing sugar content of more than 2% by weight. That is to say, of all the variously dextrinized starches which are commercially available those which have the just-referred-to qualifications are most suitable for the practice of this invention.

When using the terms dextrin or partially dextrinized starch hereafter, we meanjust such substances as above defined. We .found that while such mixtures as just described might have the desired low reducing sugar content, they were not sufiiciently fluid for application by the machines so that it was incumbent upon us to fiuidify the mixtures in away which would not increase appreciably the sugar content. As stated, the common way to fiuidify'heretofore has been to add more sugar; this, of course, increases the sugar content so that the gum would have all of the above-mentioned objections.-

Such-substances as wehave found to produce the desired result include the amides of monocarboxylic acid containing from 2to 5 carbon atoms inclusive. We desire to here point out.

that we are concerned with amido compounds, such as acetamide, for example, which are to be distinguished from the so-called. amido acids heretofore disclosed in a United States Letters Patent #974,448 of 1910 to one Supf. According to Rule 5 adopted by the nomenclature committee of the joint congress of the British Chemical Society and the American Chemical Society held in 1923: The names of the groups NHz, NHR, NR2, NH or'NR should end in -ido only when they are substituents in an acid group, otherwise in -ino."

Other agents which we have found suitable are propianamide and butyramide.

That is, we are here concerned with amides or salts. of acids, as contrasted with what are now called amino acids and which in Supfs time were referred to as "amido acids. .To put it another way, while in 1910, for example, the usual definition for an amido group was one where an NH: group replaces a hydrogen of the hydrocarbon, today such terminology indicates the replacing the CH .of a carboxyiic acid to form an amido compound. We are concerned with present-day amido compounds rather than what was synonymous in 1910 with an amino group.

According to the preferred form of the method of this invention, water and the partially dextrinized starch are mixed intimately. If desired, a volatile acid, such as acetic, may be introduced to aid in the hydrolysis of the starch and the mixture is then agitated so that the ingredients thoroughly'blend.

I The composition is then heated'in any wellknown manner to within a range or preferably from 160 to 212 R, which temperature is preferably maintained for from 20 to 60 minutes. The length of time during which the gum is cooked depending, of course, upon the size of the batch, the temperature, the equipment used,-

and various other factors.

It is desirable that the mixture be cooked only -until hydrolysis to the desired degree of dextrinization is complete and not for such a length of time that the reducing sugar content be substan-' tially increased. The fiuidifying agent may be now added but we do not wish to be limited to any specific order in which the above ingredients may be added.

As final steps in-the process the gum is preferably chilled to about 100 F., or below, after which the mixture is ready to be drawn.

While the proportions of the above ingredients may be greatly varied, very favorable results have been obtained when staying within the following approximate ranges of proportions by weight:

' Per cent Water 10 to 18 Partially dextrinized starc to 62 Fluidifying agent 3 to 10 If' acetic acid or-some other volatile acid is added, about 10 to 20% thereof-may be used- If it' is desired to include glycerine, about 4 to 10% thereof may be used. While we have described the invention in great detail. and with respect to the. present preferred form thereof, it is not desired to be limited thereto since many changes and modifications may be made therein without departing from the spirit and scope of the invention. What it'is desired 'to claim and secure by Letters Patent of the United States is:

1. As 'a new article of manufacture, an envelope adhesive haying a reducing sugar content 3. As a new article of manufacture, a paperenvelope adhesive of the character described consisting of, a certain amount of partially-dextrinized starch, water, and an amide of monocarboxylic acid containing from two to five carbon atoms inclusive, said starch, water, and amide being in such relative proportions that the total reducing sugar content of the adhesive is limited to about 2% of the weight thereof.

4. As a new article of manufacture, a paperenvelope adhesive of the character described consisting of, a certain amount of partiallydextrinized starch, water, and an amide compound of the group consisting of acetamide, propianamide and butyramide, said starch, water and compound being in such relative proportions that the total reducing sugar content of the adhesive is limited to about 2% of the weight thereof.

PAUL B. DAVIDSON. 'JULIUS R. ADAMS.