US2434106A

US2434106A - Impregnation of cellulosic material

Info

Publication number: US2434106A
Application number: US572752A
Authority: US
Inventors: William E Flood; Kosinszki Edward
Original assignee: Catalin Corp of America
Current assignee: Catalin Corp of America
Priority date: 1945-01-13
Filing date: 1945-01-13
Publication date: 1948-01-06
Anticipated expiration: 1965-01-06

Description

* Patented Jan. 6 1948 2,434.1 mnremrron or CELLULOSIC MATERIAL William E. Flood,

sinszki, Fords, N.

notation of America,

lgetnchen, and Edward Koassiznorl to Catalin Cora corporation of Delaware No Drawing. Application January 13,1945, Serial N0. 572,752 7 This invention relates to cellulosic material impregnated with a polyvinyl resin and the method of making the impregnated product.

Claims. (Cl. 154-138) The invention is particularly useful in connection with the formationof paper containing polystyrene as the impregnating material and will be illustrated in detail by description in connection with this product.

When it is attempted to impregnate paper directly with polystyrene in fluid condition or emulsified in the best manner possible, adequate penetration is not obtained. The polystyrene becomes concentrated on the surface of the paper and does not impregnate satisfactorily the interior parts of the paper. As a result the paper so impregnated absorbs moisture and tacted with water.

In an attempt to overcome this diflicult it ha been proposed to use agents to modify the electrical nature of the paper, as, for instance, to increase the difference of electrical potential between the paper and the polystyrene resin. Thus there have been used certain mordants or mordant-like materials to modify the electrical charge on the cellulose fibers when suspended in water.

In general, the polystyrene treated paper heretofore available has retainedthe disadvantages of excessive concentration ("riding) of the resin on the surface portions of the paper and general unevenness of distribution, resulting frequently in surface freckling, warping of the product on contact with water, or checking on standing.

The present invention provides a convenient and effective impregnation of paper to produce a product free from these disadvantages. The invention also makes possible commercial impregnation of paper in roll form with a large of paper to each other, and

vent, and then removing the said solvent subsequent to the polymerization. In the preferred embodiment, the invention comprises impregnating paper in roll form with a solution of styrene, polymerizing the,styrene in the paper in a closed vessel, unrolling the paper, and then evaporating the solvent therefrom. In one embodiment, the invention comprises the additional steps of laminating individual sheets of paper or the like so impregnated by plying the sheets together after removal of the solvent, warming the composite to a temperature at least as high as the fiow point of the resin present in the sheets, consolidating th plied sheets under pressure at the elevated temperature, cooling the thus consolidated article to a temperature below the solidification point of the resin present, and then releasing the pressure.

The polymerization of the monomer, before the evaporation of the solvent used to introduce the monomer into the paper, not only serves the purpose Of forming a thermoplastic polymer but also converts the monomer used to such form that it does not migrate to an objectionable extent to the surface of the cellulosic material during the subsequent evaporation of the solvent. It will be'appreciated that a material dissolved in a solvent ordinarily migrates with the solvent to the surface of the article from which the solvent is being evaporated. If the dissolved material is non-volatile, it is then deposited at that surface, to form a crust or concentrated surface film. In the present instance, the polymerization to the large molecules prevents this migration to any objectionable extent. As a result,

the impregnated and then polymerized material .sidered that the decreased migration i due in large measure to the conversion of the monomer to a polymer of such very high molecular-weight, of the order of 10,000 at least, that the large molecules do not move, by either eapillarity or diffusion, through the paper orother cellulosic material to an objectionable extent as the. solvent evaporates from the surface thereof. This non-migration is favored also by the quick evaporation of the solvent, as will be described.

The paper used may be that made from rag, kraft, sulflte, or like stock. Preferably it is of pregnating solution into oxide, and dilauryl peroxide.

a relatively porous nature as compared to the averagerun of paper.

As the solvent used to dissolve the monomer before impregnation, there may be used xylene,

toluene, ethyl acetate, dioxane or like known volatile solvents for the monomer or a,mixture of two or more of them. These solvents are known to be inert, that is, non-polymerizing under the conditions of treatment described herein.

The monomer is dissolved in the selected solvent in proportion to give about as concentrated a solution as is free flowing and permit drainage of the excess solution from the impregnated cellulosic material after the polymerization is completed.

Thus there is used in the volatile solvent that is about as high as possible without producing a viscous solution. There may be used, for example, a solution containing 35 to 50 parts of styrene in 100 parts of solution. The higher the concentration of the monomer, the higher ordinarily will be the concentration of polymer in the impregnated product, if the impregnation is satisfactorily effected before the polymerization. It is desired for many purposes to obtain and we do obtain by our method polymer concentrations in the finished product of 25 to 50%, proportions here and elsewhere herein being expressed as parts by weight.

The restriction of the evaporation of solvent during the polymerization is effected conventionally by use of a thick mass of the cellulosic material in a closed vessel. Thus, paper in roll form is impregnated and subjected to the polymerization, the impregnated roll being enclosed in a substantially vapor-tight vessel during the polymerization. The roll is preferably submerged at the time in an excess of the impregnating solution.

To improve the impregnation the roll of paper is preferably predried, subjected to a vacuum, and maintained in the treated evacuated condition until the vacuum is broken by flowing the imthe evacuated vessel and around and over the roll of paper. Impregnation is increased to advantage by the application to the impregnating liquid of pressures that are substantial and preferably up to approximately 25 to 100 pounds or more to the square inch. In an alternative procedure, undried paper is immersed in benzene, toluene, xylene or like liquid, the liquid distilled off so as to remove water from the paper, remaining liquid is drawn oir, adhering liquid is evaporated in vacuo, and the paper then impregnated as described with styrene or like monomer.

The solution used to effect the initial impregnation includes not only the solvent and the monomer but preferably also a catalyst of the polymerization. Thus, there may be used catalytic proportions of benzoyl peroxide, butyl hydroper- The catalyst accelerates the polymerization and results, when the polymerization is cor ipleted, in a polymer of lower average molecular weight than would be the case if the polymerization were completed in the absence of the catalyst.

The temperature of polymerization in every case must be below the point or objectionable decomposition of the selected cellulosic material. At the same time it should be sufllciently elevated to make the rate of polymerization satisfactory for commercial purposes. I Room temperature, for instance, is somewhat too slow practically. Ordinarily the range of temperature is a concentration of styrene days, the exact about 50 to 125 C. and for most purposes within the range 65 to 100 G. Since the polymerization is strongly exothermic, the reaction is difficult to control at temperatures much above 110 C. In small operations; however, and with effective means of moderating the reaction by cooling, the temperature may range from those stated up to about 140 C.

The course of the polymerization is readily followed by withdrawing samples of the excess of liquid from time to time or samples of the impregnated paper and determining the molecular weight and degree of polymerization of the resin therein.

The time of the polymerization used in the present invention is ordinarily that required to give substantially complete polymerization or at least the conversion of the monomer to a nonvolatile polymer. This time requirement is ordinarily measured in days as, for instance, 5 to 30 time required depending upon the temperature, proportion and kind of catalyst, and other conditions affecting in known manner the rate of polymerization of the monomer.

After completion of the polymerization, the molecular weight of the resulting polystyrene is about 10,000 to 120,000 and in commercial operations usually 65,000 to 120,000.

As an aid in preventing the molecular weight of the polymer from either increasin too little or too slowly or becoming objectionably large when the polymerization is completed, it is preferred ,to use not only the catalyst or accelerator but also a relatively low temperature at the start of the polymerization and follow this later by a somewhat higher temperature. Thus, there may be used 65 to C., then 80 to 100 C., and finally 100 to 125 0., preferably 80 C. for 2 days, followed by a temperature of C. for 5 additional days, and then to C. for 3 days. The low temperature is used to keep the average molecular weight high or in the commercial range and compensate in this regard for the presence of the catalyst.

After the impregnation of the paper and the polymerization, the roll is removed from the polymerization vessel after cooling, as for instance, to well below the boiling point of the solvent at normal pressure and usually to room temperature.

While the paper is still wet with solvent, it is unrolled and the unabsorbed solvent and polymerized styrene are drained off.

The solvent is then removed from the unrolled paper. This removal is effected conveniently by passage of the unrolled paper through a conven tional drying chamber in which the paper is floated in a rising current of steam heated air. While other methods of drying may be used, this floating of the paper through the chamber of warm air is particularly satisfactory in avoiding excessive contact with parts of the mechanism and giving a rapid rate of evaporation of the solvent. This leaves the sheet and even the fibers themselves impregnated with styrene polymerized in situ but the surface of the sheet does not carry .an excessive layer of the polymerized styrene.

The sheeted product can readily be stored without danger of undesired adherence between adjacent layers.

The dried paper venient storage. structural sheet.

In this plyingtogether, the polystyrene impregnated paper is cut into strips ofthe desired dimensions', then assembled together face to back, to give the proper number for the ultimate thickness desired for the consolidated product, the

may then be rerolled for con- It is used in making a plied assembly is placed in a press provided with means for heating the assembly, the temperature is raised to a point at least equal to'and suitably moderately above the flowing point of the thermoplastic polymer present in the paper, and

, pressure is applied to force the sheets together and consolidate them while the elevated temperature is maintained. 'After the consolidation is effected, the composite is cooled to below the softening point of'the resin and the pressure of consolidation then released.

In-this manner there has been made a structural material that is strong, uniform, substantially water impenetrable, non-checking on aging,

free from warping on exposure to moisture even though out or machined to expose fresh surfaces, and, in moderate thicknesses, is resiliently 'fiexible.

- give and, therefore, non-brittleness.

If desired, coloring material, plasticizers or other modifiers conventionally used in the polyvinyl plastics industry, and parting compounds and lubricants may be incorporated into the impregnating solution originally introduced into the paper. Thus, there may be used dyes and pigments, and stearic acid or calcium stearate in the proportion of 0.1% to 1%.

In place of the paper used as the base material in the above illustration of the invention, there may be used cotton fabric, wood fiber insulating boards, or other cellulosic material that has substantial porosity so that it may be entered by the impregnating solution of the monomer in a volatile solvent. The cellulosic material selected in place of the paper is suitably treated in the manner described for paper, including the preliminary drying, evacuation and impregnation under pressure. In any case the polymerizationis effected while restricting evaporation of the solvent.

In place of the styrene used as a monomer and converted by the polymerization to polystyrene, there may be used other monomer that is heat polymerizable to a thermoplastic resin. ,Examples of such monomers that may be substituted pound for pound for the styrene are methyl methacrylate, vinyl chloride, vinyl acetate, vinylchloracetate, and mixtures with each other or with styrene. The temperature of polymerization of the impregnated cellulosic product must be below the temperature of decomposition of cellulose and may be the temperature conventionally used in curing the selected monomer, the time period of polymerization being also conventional for the temperature chosen.,

The invention will be further illustrated by description in connection with the following specific examples.

. Example 1 A inch roll of rag paper '(Hurlburt paper #499) containing 16% of zinc sulfide was impregnated with a solution containing styrene monomer N99 in the proportion of 35 parts, xylene as S01? vent 65 parts, and t-butyl hydroperoxide aspolymerization catalyst 0.07 part. The roll as'used had a 2.5 inch core, that is, a cylindrical free space of that diameter extending through the center of the roll. Before impregnation, the roll was dried'ior 16 hours in a steam jacketed autoclave carrying 15 pounds of steam in the jacket, evacuation being applied for 6 hours.

The roll so dried was then immersed in approximately 50 pounds of the styrene solution described. The autoclave was closed and polymerization then eflected at 75 to 78 C. for 18 days.

The roll was then cooled to room temperature, removed from the autoclave, unwound, and passed, as unwound, through a floating paper drier at such speed that the paper at any given point was in the drier for about 5 minutes, a temperature of 275 F. being maintained in the warm air chamber through which the paper was floated.

Example 2 The procedure described in the immediately preceding example was followed except that the vacuum in the autoclave was broken by admitting the solution of styrenein xylene and pressure was'then applied above the surface of the solution in the autoclave, this pressure improving the rate of penetration of the impregnated solution. Proceeding as described, there has been obtained impregnated paper containing satisfactorily uniform proportions of the polymer in sheets from all parts of the roll of paper originally immersed and sufiicient polymer to flow together during the use of the impregnated paper in laminating the sheets together. Thus there have been obtained impregnated rolls which differ by less than 3.5% in the resin content of the paper from the exposed outer or inner. surface of the hollow roll and the part of the paper which' was midway between the exposed inner and outer surfaces during the impregnation.

Example 3 .are consolidated into a structural sheet in the following manner.

Ten sheets of the paper made as described in Examples 1 or 2 are laid face to back upon each other and the assembly warmed to 320 F. and compresed at 1,000 pounds to the square inch for a period of 30 minutes. The product so made and then cooled had a water absorption of 9% on immersion in liquid water and was substantially free from warping and checking.

4 surface treated with a solution of prepolymerized styrene, that is, polystyrene dissolved in five times its weight of xylene. The thus coated paper was dried. It was then plied together in 10 sheet thickness and consolidated at 320 F. and pressure of 1,000 pounds to the square inch for 30 minutes. was 6.85%.

It will be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of illustration which do. not constitute depiartures from the spirit and scope of the invent on.

What. is claimed is: Y

1. The method of impregnating cellulosic material which comprises applyingthereto styrene monomer and an inert volatile liquid that is a solvent for the said monomer and readily volatile,

In this instance the water absorption 7 preventing loss of volatile solvent, and then evaporating the volatile solvent from the product.

2. The method of impregnating paperwhich comprises drying the paper introducing into the paper in roll form a solution of styrene and a polymerization catalyst in solution in an inert volatile solvent, warming the thus treated roll of paper to cause polymerization of the styrene to a thermoplastic resin, continuing the warming until the resin comes tohave a molecular weight of at least 10,000, restricting evaporation so as to prevent substantial loss of volatile solvent during this polymerization, unwinding the roll of paper, and then evaporating volatile solvent from the impregnated paper.

3. The method described in claim 2, the proportion of volatile solvent being in excess of the proportion of styrene and the roll of paper being cooled before being unwound.

4. The method described in claim 2, the catalyst of polymerization being an organic peroxide.

5. In making a resin impregnated and bonded product, the method which comprises forming an impregnated sheet as described in claim 1, plying together a plurality of such sheets in face to REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 2,147,824 Webb Feb. 21, 1939 2,013,865 Sloan Sept. 10, 1935 1,953,083 Lawson Apr. 3, 1934 2,365,646 New Dec. 19, 1944 OTHER REFERENCES Styrene," article published in Plastics, July 1942, page 233.