US2390567A - Method of making cold shaped polymerized articles - Google Patents

Description

Dec. 11, 1945. w. E. WILLIAMS 7 2,390,567

METHOD OF MAKING COLD SHAPED POLYMERIZED ARTICLE Filed March 13, 1945 2 Sheets-Sheet 1 INVENTOR WILLIAM EWHRT WILYLIHMS BY v/m @TORNEY Dec. 11, 1945. w. E. WILLIAMS 9 I METHOD OF MAKING COLD SHAPED POLYMERIZED ARTICLE Filed March 13, 1943 2 Sheets-Sheet 2 INVENTOR WILLIAM EWHRT wlLunMs V Patented Dec. 11, 1945 V UNITE Sr 3 ENT or METIHUD OF G COLD SHAPED POLYMERIZED ARTICLES William Ewart Williams, Pasadena, Calif.

Application March 13, 1943, Serial No -179,052

6 Claims.

structure characterized by relatively weak cross- I linkages, which cross-linkages in the original material are still further weakened by chemical means, without appreciably destroying the said chain-like structure, so that this modified material may be bent, formed, molded or otherwise manipulated to any desired shapes at substantially ordinary room temperatures and then the original cross-linkage restored to its former condition and to such new treated material and to new and improved processes of accomplishing these results.

This application is a continuation in part of my copending application Serial Number 375,000, filed January 18, 1941.

v The principal object of this invention is to provide a method of forming articles without internal stress, strain or other irregularities thus substantially eliminating the tendency to return to their original shape or become deformed.

Another object of the'invention is to provide a method of forming a polymerized article which has been chemically treated so that it may be bent to any desired shape at substantially room temperature.

Another object of the invention is to provide a method of obtaining a treated polymerized material which is of such a nature that it may be reshaped without heat.

Another object Of the invention is to provide new and improved chemical processes for modifyingthe cross-linkage structure of a polymerized material.

Another object of the invention is to provide new and improved method of cold bending polymerized material without appreciably altering its surface texture or polish.

Other objects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanyin drawings. It is apparent that many changes may be made in the steps of the processes without departing from the invention as set forth in the accompanying claims. Therefore, it is not desired to limit the invention to the exact method shown and described as the preferred method has been set forth by way of illustration only.

Referring to the drawings:

Fig. I is a face view of a strip of polymerized material;

Fig. II is a perspective view of the strip after it has been chemically treated and illustrating one of the shapes to which it may be formed at ordinary room temperature;

Fig. III is a face view of a disk of material to be treated and reshaped;

Fig. IV is a diagrammatic sectional view illustrating a prior method of heat shaping polymerized material to the shape of a hemisphere;

Fig. V is a view similar to Fig. III of said ma.-'

terial treated according to the present invention and shaped to a hemisphere without heat;

Fig. VI is a sectional view of a tank diagrammatically illustrating the material under treatment immersed in the chemical bath;

Fig. VIII is a diagrammatic cross sectional view of a heating chamber in which the material, which has been treated and shaped, may be heated.

Prior to my invention polymerized material has been shaped through the action of heat which has the disadvantage of setting up intemal strains and stresses in the shaped article which materially reduces its permanence of form and usefulness. It is, therefore, a principal object of my invention to provide means by which this material may be reshaped without the application of heat and without materially changing or disturbing its surface texture and in which the reshaped article is substantially free of said internal strains and stresses.

By way of illustrating the process we will take a strip of polymerized methyl' methacrylate i. The polymerized methyl methacrylate material inherently has a chain-like molecular structure with relatively weak cross-linkages.

To form this material, according to the present invention, to the shape desired, the material I! is immersed in a bath 6 of concentrated (95% approximately) hydrogen peroxide as shown in Fig.

. VI. After immersing for a number of hours at approximately 25 C., the exact time being dependent upon the size and shape of the article to be formed and upon the degree of softness desired, longer soaking producing greater softening, the material I isremoved fromthe bath and is then shaped or molded as desired when cold, as diagrammatically illustrated in Figs. II and V. At this temperature the material is soft and plastic and in a stage something between that of ordinary para rubber and putty so that its molding or I forming can be carried out with a very small amount of force. If it be retained in this shape and warmed up to approximately 40 C. the material can be transformed in a few hours back to the original material but it will have the new desired shape without appreciable strain.

The material may be heated or warmed by placing it in a suitable heating device, such as illustrated in Fig. VII. The said device has a chamher I heated by suitable heating unit 8. In this instance the block 3 having the bent material 2 thereon is shown in the chamber.

One of the shapes shown by way of illustration is that of a spiral as illustrated in Fig. II of the drawings. It may be formed merely by twisting and then by being held in said twisted position with clamps and thereafter set to this shape by restoring the material to its original condition. As a further example, I can transform a disk 2, such as illustrated in Fig. 111, into the modified state which can then be pulled over, for example, a spherical form 3 to give a hemispherical shell as shown in Fig. V.

If disk of untreated material of the same size as disk 2 is heated in an oven to a temperature of about 100 to 150 C. and then formed over the hemispherical former 3 the resultant shell in this latter case, as is well known, will be much thinner at its top d than at its lower edges 5 while in my invention the corresponding reduction of thickness is very much less. In following the prior art of heat treating and forming the disc 2 to the shell, such as illustrated in Fig. IV, there is an inherent tendency to introduce internal strains and stresses since this is an elastic deformation Whereas by following the present method, as illustrated in Fig. V, a considerable amount of plastic flow is obtained which materially reduces these strains and stresses and thickness reduction is avoided.

While it is not certain, it is believed that a molecular change has been made in the material. What actually happens, it is believed, is that the hydrogen peroxide in effect, goes in solution in the polymerized material forming an sub chain. The material necessarily swells appreciably and the cross-linkage originally present is very considerably weakened if not entirely destroyed. When the hydrogen peroxide is removed the polymerized compound returns to its original state. If, after forming, the temperature of the plastic is reduced to approximately 4 C. the formed article becomes rigid and can be removed from the former. main at a low temperaturefor a considerable period during which the peroxide slowly comes out. As the material hardens the temperature can be raised somewhat and the hydrogen peroxide gradually difiuses out. At the last stage it can be completely dried at about 30 to 35 C. A curious modification of the methyl methacrylate can be obtained but the exact conditions of its creation have not been determined. In this modification, the otherwise transparent methacrylate becomes opalescent or milky and if this stage is arrived at it can only be made transparent again by heating up to approximately 45 or 50 C. If a piece of methyl methacrylate containing the peroxide is heated to approximately 60 to 80 C. either internal bubbles can be formed in the material or a real chemical change will take place at localized spots causing a variegated appearance of the substance which may make it useful in the production of articles for decorative purposes.

The modified material described, when reshaped under commercial processes, has but a It is allowed to re' i very slight tendency to return to the shape of the original material as compared with the pronounced tendency to do so where displacement has been made under the action of heat.

Where the polymerized material has been com-' mercially reshaped under the action of heat the change in the material is entirely .a. physical change but wher the shaping is done under my procedure it is believed that there has been a chemical change. The fact that the polymerization chains are not broken means that polished surfaces that were on the original material are not injured.

Containers for the hydrogen peroxide used in the immersion treatment should be made only of Pyrex or similar forms of glass which do not cause decomposition of the hydrogen peroxide. as most metals or ordinary glassware cause decomposition. The density of. the hydrogen peroxide is approximately 1.4 while the density of the methyl methacrylate is about 1.2. The result is that when a flat dish is used the methyl methacrylate cannot be fully immersed so it is better in practice to use narrow vertical containers and use weights or other methods of pulling the sheets down into the liquid to keepit totally immersed.

Contrary to accepted opinions inhibitors may be used successfully with high concentrations of hydrogen peroxide and retard the self decomposition very materially.

If the forming molds are made out of porous materials, such as partially sintered glass or quartz particles, then the removal of the hydrogen peroxide can be effected without removing the formers or mold so that the shape can be retained until the material is rigid enough to be self supporting or to maintain its shape without any deformation. Another method used is as follows: The article is molded between dies which may not be necessarily porous, then cooling the dies with the material in place to about below 10 C. and the molded article is then removed. The resulting chilled rigid material is then placed in temporary holding formers which are porous and the hydrogen peroxide is allowed to diffuse out of the material by means of fairly low heat treatment, about 35, 40 or 45 C.

Hydrogen peroxide of the type used is disclosed in The Merck Index, fifth edition, page 2G7 and other places.

Although methyl methacrylate is set' forth above by way of illustration, it is to be understood that the present invention is intended to include any polymerized material selected from a group comprising esters of acrylic, methacrylic or ethyl acrylic resins, materials known commercially as Plexiglass and Lucite, methyl methacrylate, plasticized methacrylate, internally plasticized methacrylate as by co-polymerization of methyl methacrylate with alkyl methacrylates, acrylates, etc., all of which are of the type having a. chain-like molecular structure with reladows and Windshields and the maintenance of the polished surfaces thereof.

Another important use is that of producing protection plastic lenses for goggles and eye protectors for fliers,- industrial workers, and motorcycle riders or troops, as thes lenses may be cold shaped to desired form without destruction of the polished and clear preformed optical surfaces thereon.

This is the first instance, as far as is known, where a chemical-change is effected in a polymerized substance without breaking up the polymerization thereof and without materially altering the finished surfaces thereon.

Having described my invention, I claim:

1. The process of forming an article of polymeric methyl methacrylate comprising treating said polymeric methyl methacrylate under controlled temperatures for controlled times with hydrogen peroxide having a concentration of approximately ninety-five percent in the absence of heating until said polymeric methyl methacrylate reaches a desired degree of softness, shaping said methyl methacrylate without heating, to a desired form, and thereafter removing the hydrogen peroxide from the methyl methacrylate by evaporation.

2. The process of forming an article of polymeric methyl methacrylate in the absence of heating, comprising treating said polymeric' methyl methacrylate under controlled temperature for a controlled time with concentrated hydrogen peroxide, treating said polymeric methyl methacrylate until it reaches a desired degree of softness, shaping said polymeric methyl methacrylate to a desired form, and thereafter removing the hydrogen peroxide from the polymeric methyl methacrylate.

3. The process of forming an article of polymeric methyl methacrylate in the 'absence of heating, comprising treating said polymeric methyl methacrylate under controlled temper-'- ature for a controlled time with concentrated hydrogen peroxide, treating said methyl methacrylate until it reaches a desired degree of softness, removing said polymeric methyl methacrylate from the presence of the concentrated hydrogen peroxide, shaping said methyl methacrylate to a desired form while still soft without heating,

and thereafter substantially freeing the methyl methacrylate from the hydrogen peroxide.

4. The-process of forming an article of polymeric methyl methacrylate-in the absence of heating, comprising treating said methyl methacrylate under controlled time with a liquid bath of hydrogen peroxide until said methyl methacrylate reaches a desired degree of softness, removing the methyl methacrylate from the hydrogen peroxide bath, shaping said methyl methacrylate to a desired form, and thereafter removing the hydrogen peroxide from the methyl methacrylate while the methyl methacrylate is held in the desired form.

5. The process of forming an article of a polymerized methacrylate material of the type having a chain-like molecular structure with weak cross-linkages comprising treating said polymerized methacrylate material with hydrogen peroxide tobring about a further weakening of said weak cross-linkages and for a time interval of treatment sufficient to soften said material by an amount which will enable the shaping of said material, shaping said material to a desired shape while in said softened state and without softening by heat and thereafter substan 'tia-lly restoring the cross-linkages to their original condition by substantially removing the' hydrogen peroxide from the polymerized methacrylate material.

6. The process of forming an article of a polymerized acrylate material, comprising treating the said material with highly concentrated hydrogen peroxide until the cross-linkages are substantially removed, forming the material without heat to the desired shape and restoring the cross-linkages by substantially removing the hydrogen peroxide from the polymerized material.

WILLIAM EWART WILLIAMS.

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