US2117256A - Paper manufacture - Google Patents

Description

Patented May 10, 1938 UNITED STATES PATENT OFFICE PAPER MANUFACTURE of Massachusetts No Drawing. Application November 18, 1933, Serial No. 698,722

4 Claims.

This invention concerns the manufacture of paper.

The principal object of this invention is to provide an improved paper, which paper has re- 5 ceived a surface coating during its manufacture.

An important object is to provide an improved coated paper.

A further object is to provide a coated paper which shall have a substantially lessened amount of foam marks or pinholes, or shall be substantially free therefrom.

A further object is to provide a coated paper of improved finish.

A further object is to provide a coated paper 5 of improved printing or lithographing qualities.

A further object is to provide paper coating mixes possessing superior spreading qualities.

A further object is to provide pigmented coating mixes which spread well with paper coating instrurnentalities.

A further object is to provide a coating mix containing a substantially nonbreakable emul- A further object is to provide a coating mix .1 made with an emulsion containing substantially water soluble gum, particularly gum ghatti.

A further object is to provide a Coating mix made with an emulsion of substantially water insoluble organic material in the form of substantially nonbreakable emulsion, particularly such emulsion as contains a substantially water soluble gum, particularly gum ghatti.

A further object is to provide a paper coating mix containing a substantially nonbreakable parafiin emulsion, particularly an emulsion of paraffin containing gum ghatti.

A further object is the manufacture of paper using such mixes and the paper made therefrom.

Other objects and advantages of this invention will become apparent during the courseof the following description.

In the manufacture of the special type of paper known as coated paper, it is customary to provide a fibrous web with a surface coating derived from a coating mix, particularly one containing adhesive such as starch, glue, casein or the like, usually in aqueous suspension, emulsion, colloidal solution, solution, or thelike, in conjunction with a pigment or pigments usually inorganic such as clay, satin, white, blanc fixe, calcium carbonate, talc, calcium carbonate magnesium hydroxide and the like. Such pigmented mixes have inthe past been applied to a great extent on so-called coating machines", but in accordance with technologic advances which have been made relatively recently they have been applied successfully to the Web on the paper machine itself.

In applying pigmented coatings either to the web on the paper machine or On a special ma- 5 chine after the web has left the paper machine, it has been found that the application of such coatings at times presents considerable difficulty owing to the fact that they do not spread Well with the instrumentalities ordinarily employed for applying and/or spreading, for example, brushes, contact rolls, squeeze rolls, sprays, scrapers, smoothing rolls, or the like, and thus coatings result which are imperfect from the standpoint of smoothness, evenness and similar characteristics. Also at certain times, particularly with certain caseins, great difliculty has been experienced with froth marks or pinholes", which seem to be more pronounced with certain adhesives such as with certain grades of casein than with others, and under such conditions it becomes a problem to eliminate foam marks or pinholes in coated paper completely or substantially completely. Such marks or holes are a decided detriment to the resultant paper and 25 their elimination is greatly to be desired, so that coated paper substantially free from such marks may be produced. Certain palliating means have been used to get around or overcome to a certain extent some of these difficulties, e. g., poor 30 spreading, brush marks or roll marks, and foam marks, such as dilution, the addition of various adjuvants as soap solutions, emulsions, and the like, but none of these have been completely satisfactory. Moreover, the proper finish of coated 35 paper is always one of the problems confronting the coated paper manufacturer, and practically all of the present means or methods em ployed for obtaining this leave much to be desired 40 It is an object of this invention to provide means for overcoming the various difficulties set out above, and to provide suitable coating solutions, mixes or the like, which will have satisfactory working and/or spreading qualities, and to coat paper therewith, producing thereby coated paper of superior qualities, which may possess a substantially lessened degree of or be substantially free of brush or other spreading marks, foam marks and pinholes, have an improved appearance, and improved finish, and in some cases improved printing and /or lithographing qualities.

As mentioned above, it has been the custom in the past at times to add to coating mixes certain soap solutions, or emulsions of materials such as wax, particularly paraflin, but none of these have been wholly satisfactory.

I have found, however, that by the use of emulsions containing substantially water soluble gum, particularly gum ghatti, especially emulsions of substantially water insoluble organic material, such as paraflin, made with such gum, greatly and unexpectedly improved results can be obtained. I have found, for example, that a gum ghatti emulsion of paraffin when used even in relatively small quantity in a coating mix provides a smoother spreading and more readily flowing coating mix, greatly reduces or practically eliminates brush or other marking, greatly reduces or eliminates foam and pinholes, causes no or substantially no flocculation in the coating mix, and produces coated paper in general superior as to smoothness of coating, freedom from brush or other marks, pinholes and the like, as to improved finish, and printing or lithographing qualities, and in many cases as to improved collateral properties.

The emulsions used have in general the characteristic that when a gum is employed as the sole or substantially the sole emulsifying agent the resulting emulsions are what may be termed substantially nonbreakable; that is, no one chemical at the ordinary concentration at which it is used in papermaking will fiocculate or break the emulsion. However, by mixing in the presence of the emulsion two materials which are mutually precipitable, such for example as rosin size and alum, such precipitate will concentrate within itself the disperse phase of the emulsion.

As stated above, I may use as an emulsifying agent a substantially water soluble gum. The gum is thus present in the continuous phase of the emulsion. As the disperse phase of the emulsion I may use one or more of a number of substantially water insoluble .organic materials which may be either liquid, pasty, or solid; such as for instance oils, for example paraffin oil, linseed oil, pine oil, oleic acid, and the like; or pastes such for example as Vaseline, or soft fats; or solids such as resins, stearic acid, Waxes for example carnauba, japan or the like, or paraffin, or other hydrocarbon or insoluble soaps. These materials as will be evident are all substantially water resistant. Where I speak of the material as organic, I mean it may be entirely so, as in the case of pine oil or paraflin for example, or that it may have an organic radicle therein as in the case of an insoluble soap, such as aluminum stearate forexample, where the organic stearate radicle is combined with the inorganic aluminum radicle.

It is apparent as stated above that I may use either saponifiable or substantially unsaponifiable material for the disperse phase, but I have found unsaponifiable material very satisfactory. From the standpoint of effectiveness and economy, I have found that paraflin is a desirable material to employ. One suitable emulsion is made by melting paraffin, mixing it with a solution of gum ghatti in water above the melting point of the paraffin, preferably agitating the same, and then running the hot mix through some emulsifying device such as a colloid mill or homogenizer. As a homogenizer is very effective, I prefer to use that type of machine. The proportion of gum on the weight of the paraflin may be varied within wide limits but I have found particularly With gum ghatti, that although less than 1% may be used, this does not seem to be quite enough for wholly satisfactory emulsification, whereas from about 2% to 5% appears to be suflicient, but more may be used if desired. Thus, while not limiting myself in any way to the proportion of gum to emulsified material, nevertheless the range stated above gives very satisfactory commercial results. I may use paraiiin of any desired melting point but parafiin melting anywhere from 120 up to 150 F. or thereabouts has proven satisfactory. Any suitable concentration of paraffin in the emulsion may be employed. I have found 15-30% a convenient concentration. Instead of gum ghatti, I may use with a measure of success other water soluble gum such for example as gum arabic. In emulsifying liquid materials such for example as paraffin oil, the emulsification may conveniently take place in the cold.

I have spoken of using emulsions which are substantially nonbreakable. When a substantially water soluble gum is the sole or substantially the sole emulsifying agent, substantially nonbreakable emulsions are produced. I may however use other emulsifying agents in conjunction with a gum to make my emulsion, such as dextrin, soluble soaps, proteins, carbohydrates or the like, or derivatives thereof. Some of such emulsions are substantially nonbreakable, but in certain instances such admixtures produce an emulsion which may not be completely nonbreakable, but which in most cases will have a resistance to breaking, although in other cases this resistance to breaking will not be so manifest. Also I may use emulsions in which a, gum is present, but the gum may not be present as original agent acting to emulsify: for example I may first make a soluble soap emulsion of paraflin and then add a gum. I may use such emulsion in such condition or I may homogenize the emulsion, preferably heated, after the addition of the gum. Also if desired I may make up my emulsion originally with a gum as the emulsifying agent, and then may add a soap, protein, carbohydrate'or the like, or derivative thereof, and use such emulsion in such condition, or I may homogenize the emulsion, preferably heated. Or a breakable and a substantially nonbreakable emulsion may be mixed and the mixture employed. As will be apparent such admixtures and treatments as set forth above will serve in many cases to modify the character of the emulsion, making it in certain cases more suitable, as will be apparent to one skilled in the art, for obtaining specific results in particular cases.

In the preferred practice of my invention I prepare my emulsion and add it in the desired quantity to an aqueous coating solution, suspension, or mix, preferably admixing it thoroughly therewith before applying said mix to the paper web, i. e., to the paper body stock. Although any amount may be employed I find that advantageous results can be 'obtained from the use of a fractional percentage. (of a 30% concentration emulsion for-example) up to 5% or more on the weight of the solids in the coating mix. A convenient way is to make the coating mix first such as by mixing a casein solution with pigment or pigments, e. g., clay, satin white, calcium carbonate and the like, and other materials if desired, and when otherwise ready for application to the paper web add thereto with stirring a suitable amount of my emulsion which may vary from a fractional percent up to 5% or more (based on the weight of the solids in the mix) according to circumstances. The emulsion incorporates very readily with coating mixes and has a marked influence on the properties thereof and the paper coated therewith as indicated. If it is desired to improve a specific quality such as finish for example, the proportion of the emulsion used may be adjusted to obtain the desired efiect.

Whereas I may use my emulsion without the addition of mutually precipitable materials or agents, under certain conditions I may add such agents, or only one such if the other already be present in the mix or in the emulsion, such agents serving by their flocculation or precipitation to concentrate the disperse phase of the emulsion in the precipitate so formed. This procedure may be particularly useful in certain cases, e. g., where it is desired to especially enhance the lithographing qualities of the paper. As stated above, rosin size and alum may serve as agents, or barium chloride and sodium sulphate, or any other two mutually flocculating or precipitating agents. This flocculation may be effected in the emulsion prior to the addition thereof to the coating mix, or subsequent thereto; and unflocculated emulsion may also be present in the mix, for example by addition after the mutually precipitable materials have acted upon one another.

Where the emulsion has breakable characteristics, as by admixture of soluble soap or otherwise, such for example as described above, a single flocculating, precipitating or breaking agent may at times be employed instead of the mutually precipitating agents as above indicated.

Whereas I have described the admixture of these emulsions with coating solutions, suspensions, or mixes when such mixes are otherwise ready for use, it is to be understood that in certain cases the emulsion may equally well be incorporated with one or more of the ingredients from which said mixes are made prior to the time when the mixes are finally ready for use. I

After the coating mix which I desire to use has been suitably prepared with the emulsion present therein, the mix is applied as usual'to a paper web either on a coating machine, or on a paper machine if it be equipped with a coating device, and the paper web so treated is then dried and finished in the customary manner. In certain cases, however, where material which has a relatively high melting point is used as the disperse phase of the emulsion, it may be desirable in some instances to subject the coated web after drying to heat, as for example to hot air or other gas or heated roll or rolls, sumcient to cause the softening or fiuxing of said material, whereby to assist in its permeation of all parts of the already formed coating.

As will be apparent, the making of such pigmented coating solutions and mixes, the utilizing of such on paper machines and/or coating machines, and the paper made therefrom all represent distinct improvements in the manufacture of coated paper manufacture and the products made therefrom.

Where in the claims I speak of pigmen I mean any of the class of materials such as clay, talc, satin white, calcium carbonate, calcium carbonate magnesium hydroxide, calcium carbonate magnesium basic carbonate, calcium sulphate, barium sulphate, zinc oxide, zinc sulphide, titanium 'oxide, or their equivalents, which are suitable for use in coating paper: and by pigmented mix, I mean a mix suitable for coating paper in which such or equivalent pigment or pigments is or are used.

Where in the claims I speak of a so-called substantially nonbreakable emulsion I mean an emulsion characterized as follows: (1) that no one chemical at the ordinary concentration at which it is used in paper-making will fiocculate or break the emulsion; (2) that when two mutually precipitable materials, such for example, as rosin size and alum, are mixed in the presence of the emulsion, the precipitate so formed will concentrate within itself the disperse phase of the emulsion. And where in the claims I speak of the residue of an emulsion, I mean the remaining constituents of said emulsion after substantially all the water content of said emulsion has been removed.

Where in the claims I use the word paper herein, I use it in the broad sense to include products of manufacture of all types and of all weights and thicknesses, which contain as an essential constituent a considerable amount of prepared fibre and which are capable of being produced on a Fourdrinier, cylinder, or other forming, felting, shaping or molding machine; and when I use the words coated paper I mean such paper as above, to the surface of which has been applied a mixture comprising pigment and ad'- hesive. 7

While I have described in detail the preferred embodiment of my invention, it is to be understood that the details of procedure, the kind and proportions of ingredients, and the arrangement of steps may be widely varied without departing from the spirit of the invention or the scope of the subjoined claims.

I I claim:

1. The method of manufacturing paper which comprises applying to a fibrous web an aqueous mix made from ingredients comprising adhesive, pigment, and a so-called substantially nonbreakable emulsion of parafiin, said emulsion containing a substantially water soluble gum intimately incorporated as a component thereof, and drying said web.

2. Paper made in accordance with the method of claim 1..

3. The method of manufacturing paper which comprises applying to a fibrous web an aqueous mix made from ingredients comprising adhesive, pigment, and a so-called substantially nonbreakable emulsion of parafiin, said emulsion containing gum ghatti intimately incorporated as a constituent thereof, and drying said web.

4. Paper made in accordance with the method of claim 3. I

HAROLD ROBERT RAI I'ON.