US2241174A - Sizing composition - Google Patents

Description

tatented May 6, 1941 SIZING COMPOSITION Calvin L. Bachelder, Kalamazoo, Mich., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware No Drawing. Application Februa y 3, 1940, Serial No. 317,130

6 Claims.

This invention relates to paper sizing compositions, and more particularly to an improved surface sizing composition adapted to be applied to paper, paperboard and the like.

It has long been known that the surface characteristics of paper and board can be improved by applying to the surface of such paper products emulsions of parafiin or other waxes, either alone, or in conjunction with starch dispersions. There are certain benefits to be derived from a surface sizing operation as against an internal sizing operation. For example, there is no loss of sizing material in surface sizing corresponding to the loss in the white water which generally accompanies internal sizing. The sizing material is deposited near the surface of the sheet, where its effect is most desired, rather than being distributed throughout the interior of the sheet, where water resistance is usually of small importance. In the case of surface sizing it is not necessary to maintain the low pH required for efficient internal sizing thus giving the recognized advantages of low acidity of the sheet in addition to the economies resulting from the partial or complete elimination of alum from the furnish and improved machine operation. In addition, a smoother surface is obtained by surface sizing, resulting in better printability, higher gloss and greater scuff resistance.

The potential advantages of surface sizing procedures have not been fully achieved heretofore because of certain disadvantages of the sizing materials which have previously been available. In the first place, the application of appreciable quantities of wax to the surface of paper and board produces varying degrees of slipperiness which may cause operating difficulties due to excessive slippage during subsequent operations. In the second place, the degree of water resistance imparted to the sheet is limited, both by the low sizing efllciency of the emulsions used and by the limited amount of sizing material which may be applied without causing excessive slipperiness.

The present invention aims to eliminate these objections of excessive slipperiness and low sizing efiiciency and thus permit taking full advantage of the benefits to be derived by substantially or completely replacing the internal sizing operation with a surface sizing operation.

Generally, these improvements are accomplished by preparing a composition comprising water, starch, wax emulsion, rosin emulsion, and an aqueous protein dispersion, and thereafter applying this composition to the surface of paper or paperboard in any convenient manner. The treated sheet, when calendered and dried, will possess the desirable properties of smoothness and water resistance without objectionable slipperiness.

I have found that I may use any of the numerous grades of unconverted corn, tapioca, wheat, potato, or other starch; or, I may use starches which have been converted by enzyme treatment or other means to lower their viscosity in solution.

Likewise, I have found that a wide variety of wax emulsions may be employed to give suitable sizing compositions. The wax may be any one of the so called crystalline paraffin waxes whose melting points vary over a wide range or it may be an amorphous or microcrystalline wax of any I desired melting point. The type, melting point,

and color of the wax will be determined by the type of paper or board which is being treated and the specific properties which it is desired to impart to the surface of the paper or board. To emulsify the wax I may use any of a wide variety of well known emulsifying agents such as soaps, proteins, water soluble gums, sulfonated or sulfated organic products, and the like.

I may prepare the rosin emulsion by diluting with water a partially or completely saponified rosin soap, known to paper trade as rosin size, or I may employ a high free rosin size, consisting of substantially unsaponified rosin dispersed with the aid of a protective colloid. I may use any grade of gum or wood rosin which may be desired. Among the water or alkali dispersible proteins which I have found to be suitable are milk casein, soyabean protein, glue, and the like. I may, in some cases, add a water-softening agent, such as, for example, sodium carbonate or sodium phosphate, to the water or starch solution prior to the addition of the wax and rosin emulsions to soften the water and increase the stability of the resulting mixtures. I If it is desired to simplify the preparation of the sizing composition, I may melt together the desired quantities of wax and rosin and emulsify this mixture in an aqueous dispersion of the protein, for example, milk casein, either with or without a supplementary emulsifying agent. This emulsion may then be mixed with water and starch dispersion in the desired proportions and applied to the surface of paper or board at the calender stacks, size press, or some other convenient point on paper machine.

In'preparing these coating compositions it is convenient to add the alkaline water-softening heat the mixture to about 180 F. to render the starch water dispersible. Thereafter, the remainder of the cold water is added to th hot starch dispersion to dilute and lower the temperature of the dispersion. The desired quantities of wax emulsion, rosin emulsion, and aqueous protein dispersion are then added to the starch dispersion and mixed thoroughly therewith. The resulting mixture is then ready for application to paper. I do not limit myself to the above procedure for preparing the sizing compositions but have described it merely for illustrative purposes.

In these coating compositions the ratio of wax to rosin may be varied between about 3:1 and about 1:2. The ratio of protein to combined wax and rosin may be varied between about 1:5 and 1:33. The combined percentage of wax, rosin, and protein in the finished sizing composition may vary between about 0.5% and about 10% depending on the degree of water resistance desired in the finished paper. The percentage of watersoftener in the sizing composition may vary between and about .09% depending upon the hardness of the water and the stability of the emulsions used. The percentage of starch in the finished sizing composition may be varied between about 1% and about 6%.

The following examples represent application at the calender stack water boxes of various surface sizing compositions to the surface of board to which no internal sizing agents, 1. e., rosin size or alum, had been 'added. The percentage composition of the various sizing mixtures is given in tabular form with the corresponding sizing values as measured by the water drop absorption test. All sizing tests were made at 65% relative humidity and '70 F. after the test samples had come to equilibrium under the same conditions.

Surface sizing compositions and sizing values of treated paperboard Paperboard of the same composition as the pashow a marked improvement over heretofore,

known calender sizes and imparted less slipperiness to the sheet and gave a more uniform sizing eflect. These advantages can be attained in an economical manner. 7

It 'will be understood that the examples set forth above are illustrative only and that the invention as broadly described and claimed is in no way limited thereby.

What I claim and desire to protect by Letters Patent is:

1. An aqueous paper coating composition comprising, on a dry basis, between about 300 and about 500 parts by weight of starch, between about and about 200 parts by weight of wax emulsion, betweenabout 20 and about 40 parts by weight of rosin size. and between about 10 and about 30 parts by weight of casein.

\ 2. An aqueous paper coating composition com- Per cent Starch 4. Soda ash 04 Wax emulsion (dry basis) 1. 86 Rosin size (dry basis) 35 Casein solution (dry basis) 28 Water 92. 52

4. A paper coating composition comprising approximately:

Per cent Starch 3. 41 Soda ash 04 Wax emulsion (dry basis) 1. 28 Rosin size (dry basis) 35 Casein solution (dry basis) 19 Water 94. 73

5. A paper coating composition comprising approximately:

Per cent Starch 3. 46 Soda h 04 Wax emulsion (dry basis) .98 Rosin size (dry basis) l .25 Casein solution (dry basis) 15 Water 95. 12

6. An aqueous paper coating composition comprising emulsified wax and rosin size in a weight ratio between about 3:1 and about 1:2 on a dry basis; an amount of protein representing between about /5 and about 341, of the combined weight of wax and rosin size, an amount of water sufficient to provide a dispersion containing between about 0.5 and about 10 per cent by weight of the foregoing mixture of wax, rosin size, and protein, and starch in an amount representing between about 1 and about 6 per cent by weight 01 the entire composition.

CALVIN L. BQCHELDER.