US2689980A - Process for the production of seamless hollow structures - Google Patents

Description

'Sept 28 1954 w. B. oPAvsKY 2,689,980

PROCESS FOR THE PRODUCTION OF SEAMLESS HOLLOW STRUCTURES Filed March 7, 1951 I #EAN/v6 Z oms I INVEN TOR.

WA L rse @PA V510 Patented Slept. 28, 1954 UNITED STATES PATENT OFFICE i PROCESS FOR THE PRODUCTION OF SEAMLESS HOLLOW STRUCTURESv Walter Bernhard Opavsky, Coburg, Germany Application March 7, 1951, Serial No. 214,235

Claims priority, application Germany May 30, 1950 17 claims. (o1. 18-48) which is completely surrounded by the swollen.

mass of the blank and holds the structure together. This structure is then subjected to a preferably abrupt heat .treatment in a temperature range which causes a rapid complete or partial evaporation of the swelling agent lpresent in the surface layer and consequently a solidification of said surface layer. Simultaneously herewith the thin core layer is swollen or even dissolved by the combined action of the swelling agent which has penetrated into said layer, and the heat treatment, whereby the vapor generated inside the structure, which vapor cannot escape through the solidified surface layer, causes splitting up of the structure in the core layer and ination with .formation of a seamless hollow structure.

As vswelling agents I prefer to use low boiling liquids which are capable of diffusing quickly at room or slightly .elevated temperature into the material of the blank and of .causing thereby `a uniform, preferably strong ,swelling with the vexclusion of objectionable side effects, e. g. without strong dissolving action. In general I have found it advisable to use .solvents yor solvent mixtures which are capable of exerting in addition to the swelling action a slight dissolving action at room temperature and of swelling `and dissolving the previously not affected core layer of the blank when the temperature is raised.

Infcarrying out the invention uniform liquids may be vused which possess the desired properties with respect to the material of the blank. Such liquids are for instance methylene chloride kor methanol for cellulose triacetate. In general, however, I prefer to use mixtures of solvents which consist of two, three or .more 4components and `form a combination most suitable to attain the desired effect. `Such mixtures may be composed, :for instance, of solvents for the respective material of the blank, and non-solvents; they may Ifconsist either .entirely of low b'oilingor 'relatively low boiling components, for instance `.so .as

to have a boiling point between about 35 to 100 C., -or of low and higher yboiling components, for instance so as to have a boiling point between about to 200 C. A critical feature of the invention is that the swelling agents contain a proportion of low boiling components suflicient `to ensure that in the heat treatment of the swollen blanks, in which thin stable core layers are still present, a lquick evapora-tion from the surface layers takes place so as to bring about a quick strengthening and compacting of said surface layer, thereby preventing an undesired escape of vapors from the interior of the swollen blanks.

When mixtures of solvents and non-solvents areused it has been 'found lof advantage to provide for the presence of low boiling solvents.

The swelling agents may conta-in additional components capable of obtaining specific effects, such as softeners.

Accordingto the invention lms, foils or sheets are cut to blanks of a shape corresponding to the desired hollow article, vfor instance, strips or bands will be used for the production of cylindrical hollow structures. The swelling is obtained by suitable operations such as hanging the blanks in a bath containing the swelling agent or, in the case of strips, of passing said strips or bands through the bath. T-he contact time is so controlled 'that the desired swelling takes place but that a stable core layer of the vblank remains unaffected; for a blank of about .1 mm. thickness,

the thickness of said unaffected core Alayer may amount to .01 to .02 mm., which core layer -serves to support the structure. 'I'he necessary time of contact for blanks of rparticular materials land particular swelling agents is readily ascertained by tests. y

The swollen structure obtained as set forth hereinbefore is then subjected, preferably abruptly, to a temperature which is substantially above the boiling point of the swelling agent oi at least of the more volatile components of the swelling agent. In this manner, the swelling agent or the volatile components thereof in the surface layer of the blank are vaporized so quickly as to cause solidica-tion Yof said surface layer, which is thereby stabilized, retains vits form and prevents the escapeI of vapors vfrom the 'inside of the' swollen structure. The heating of the structures, which progresses from the outside towards the inside, will .cause a further effective swelling and convert the lcore layer, not swollen during the pretreatment, by swelling andor solution into -a state which Aallows :a ready splitting of the ,structure Vby the vapor genera-ted by the heat treatment. During the heat treatment, therefore, an inversion of the conditions takes place insofar as at the beginning the blanks have an inner stabilizing core, which disappears during heating, whereas the outer surfaces of the structures are strengthened. The strengthening of the outer faces is, of course, not limited to the upper and lower face of the structures but extends also to the small lateral faces (cut edges), which is of utmost importance for the aim of the invention, i. e. the production of seamless hollow articles. When the pretreated swollen blanks are passed into the heating zone and the swelling agent is rapidly driven out of the surface layer, a superficial and transitory dissolution of the edges joining the main surfaces and the cuts takes place, which results in rounding off said edges.

The heating of the pretreated blanks may be carried out by introducing, e. g. by hanging the same in a heating zone (oven) maintained at a suitable temperature, or by passing e. g. stripshaped blanks through the heating zone. The heat treatment may, however, also be carried out by passing the blank in or through a heating liquid such as paraiiln oil. In this way specic effects may be obtained, for instance by incorporating in the heating bath softeners, such as phthalic esters, vulcanization accelerators, or the like.

The heat may preferably be produced by means of heat generating radiation, e. g. infrared or high frequency radiation. In this way, the heating of the core layer is accelerated while the outer layers enclosing the core layer are not adversely affected.

By the action of the vapor of the swelling liquid generated during the heat treatment of the blanks splitting up in the coreV layer of the blanks is obtained with separation of the walls by distention. The seamless structures thus obtained may be subjected to an after-treatment, for instance for driving out swelling agents still embedded in the walls. This after-treatment may be carried out, for instance in the case of cylindrical structures, by passing gases, gas mixtures or liquids at suitable temperatures in or through said structures. This treatment may be combined with the application of agents modifying or improving the propertiesk of the structures, e. g. by introducing softeners, vulcanizing agents, vulcanization accelerators, and the like. K

Generally, the structures are, split up in the center so as to produce seamless hollow structures of uniform wall strength. It is, however, also possible to-split the blanks in another plane or place so as to produce hollow structures of which one wall has e. g. sa@ and the other wall e. g. only 2 of the thickness of the original blank.

This effect may be obtained in a simple manner by screening the one main surface against the action of the swelling agent in such a way that less swelling agent penetrates into said surface than in the other main surface. Sucha differential action of the swelling agent in the two main surfaces of the blanks may be brought about for instance by passing a strip-shaped blank on a support into or through the swelling agent so as to protect the surface lying on the support against the penetration of the swelling agent at the beginning of thetreatment and to expose said surface to the action of the swelling agent only later by disengaging it from the support.

In the accompanying drawings,

Fig. 1 is a perspective view of a rectangular` blank of a swellable vthermoplastic material;

Fig. 2 is a view of the same blank in cross section along line A-A of Fig. 1 after it has been subjected to the action of a swelling agent in accordance with the process of the invention, and shows the outer swollen layer surrounding an unswollen core, and

Fig. 3 is a perspective view of the finished hollow structure;

Fig. 4 is a plan view of a blank suitable for the production of an air cushion; and

Fig. 5 is a diagrammatic cross-section along line B-B of Fig. 4, showing the air cushion prepared from said blank;

Fig. 6 is a diagrammatic side view of an apparatus suitable to carry out the novel process in continuous operation.

In the drawings, the numeral I designates the swollen outer layers, and 2 the substantially unswollen core of the blanks which are obtained and treated as more fully explained in the following examples which are given to illustrate the process of the invention and are not to be considered as limiting the invention. Unless indicated otherwise, parts are given by volume.

Example 1 A strip of .2 mm. thickness of acetyl cellulose or cellulose triacetate is submerged for 30 seconds in a swelling bath which consists of 50 parts of methylene chloride and 50 parts of methanol or ethanol. The strip is then brought into a drying oven which has a temperature of to 130 C. At 120 C. splitting of the blank in the core layer and distending to a seamless structure takes place in 40 seconds.

Eample 2 A nitrocellulose film which has a thickness of .5 mm. is submerged for 3 minutes in a bath which consists of 1 part of methanol, 2 parts of ethanol, 2 parts of acetone and 1 part of toluene, and which contains as much water as is compatible with said mixture (about 12%) After soaking, the lm is placed in a heating chamber having a temperature of C. After 45 seconds the seamless structure has been formed.

Example 3 A strip of a nitrocellulose-chambei` mixture known under the trade-name Celluloid, which has a thickness of .5 mm., is dipped for 2 minutes in a bath consisting of 4 parts of acetone and 3 parts of methylene chloride. By subsequent heat treatment at C.v the seamless hollow article r is formed in 60 seconds.

Example 4 An uncured rubber sheet of a thickness of .5 mm. is placed for 2 minutes in a bath composed of 3 parts of benzine, 1 part of benzene and 1 part of methanol. The strongly swollen sheet is then passed into a drying oven and maintained for 90 seconds at a temperature of 150 C. At the end of that period of time a seamless hollow body of uncured rubber has been formed which may be used as such or which may be subsequently vulcanized.

Example 5 A polyvinyl chloride (Igelit) foil of .5 mm. thickness is treated for l minute in a bath consisting of 5 parts of methylene chloride and l part of methanol. Subsequently, the structure is heated in a drying chamber at 130 C. for 120 seconds whereby the foil is converted to a seamless hollow body.y

. Example .6

A gelatin nlm of vav thickness pf .5 mm. is treated minutes in a bath vconsisting of 13 parts of water,2 parts of methanol and 1 part of glycerol. The proportion of kglycerol may be increased by one more part in order'to :soften the final product. The swollen foil is -subjected toa heat treatment of 2 minutes at 120"C. which results in the formation of a seamless hollow body.

An apparatus suitable for the continuous'production of tubes or easings is shown in Fig. 6. A strip of the swellable `plastic material is placed on the roll 3, passes through the swelling baths 4 and 5 and subsequently through the `lfieatinjg zone 6 where the splitting up is obtained, and lis wound up on roll 1. The obtained hollow structure vmay then be cut into tubes or casings of the desired length.

It was proposed already, some time ago, to make hollow articles fromcellulose .derivatives by splitting up suitably shaped solid blanks. According to that known process, `-the strength of the solid cellulosic blanks wasreduced in a progressively greater degree from the outside towards the inside by partial saponification, e. g. with caustic soda, and by the simultaneous action of swelling agents; subsequently, the blanks were split up, whereby the connection between the edge layers was maintained. This method has, among others, the drawback that the partial saponication causes a chemical modification, for instance a depolymerization or deacetylation of the cellulose derivative. Thus, the saponiflcation converts a cellulose acetate fllm more or less to a form of regenerated cellulose which has other properties than the starting material. A cellulose acetate tube or casing made by the process referred to is, in its whole structure, sensitive to water, and swells therein, whereas, due to the absence of saponifying agents, a tube prepared from the same starting material according to the process of the present invention does not present these objectionable properties. The known process for the preparation of seamless hollow articles from cellulose derivatives did not find commercial application.

Although I have described my invention setting forth specific embodiments thereof, my invention is not limited to the details described, for instance, instead of blanks having a rectangular cross section, I may use blanks of other, for instance circular cross section, and of various shapes. The blanks may be subjected to a step- Wise swelling treatment in subsequent baths of the same or of different composition. It will be understood by those skilled in the art that my novel process is susceptible of considerable variations and that my invention is not to be limited except by the scope of the claims appended hereto.

What I claim is:

l. A process for the production of seamless hollow structures comprising the steps of subjecting a solid blank of a swellable plastic composition to a swelling treatment with a swelling liquid, said swelling liquid containing a portion of low boiling liquid sufficient to produce an impervious surface layer on the outside of the blank when it is heated, completely swelling said blank from the outside toward the inside except the innermost core thereof, and heating the blank to a temperature above the boiling point of said low boiling portion of the swelling liquid to solidify the surfaces of said blank by the evaporation of said low boiling liquid, to cause the previously unswollen innermost core to become swollen, to

force .apart said solidified surfaces by the development of vaporized liquid under pressure infthe swollen innermost core, and thus to convert said blank to a seamless hollow structure.

2. A process as defined in claim 1 wherein the swelling treatment is carried .out at temperatures between about 60 C. .to 200 1C.

3. A process as defined in claim 1 wherein the swelling liquid contains softening agents.

Y 4. A process as ydefined in claim 1 wherein the swollen blanks are heated in a liquid bath.

5. A process as defined in claim 4 wherein the swollen blanks are heated in a liquid bath containing a softening agent. v

6. A process -as defined -in claim 1 wherein the swollen `blanks are heated by means of heat 'ygenerating radiation. y

'7. Aprocessy as defined in claim 6 whereininfrared radiation is used for heating the swollen blanks. y

l8. A process as Vdefined in claim 6 wherein high frequency radiation is used for heating -t-he swollen blanks.

-9. A -process as defined in claim l wherein the split and extended hollow structures vare subjected to an aftertreatment by the introduction surfaces of the blank are uniformly subjected tov the action of the swelling agent so as to obtain a symmetrical diffusion of said swelling agent towards the inside and retaining a substantially unswollen core layer in the center of the blank.

13. A process as defined in claim 1 wherein one main surface of the blank is treated with a larger amount of the swelling liquid than the other main surface, so as to obtain a substantially unswollen core layer located nearer to said second surface than to said first surface.

14. A process for the production of seamless hollow structures comprising the steps of subjecting a solid blank of a swellable plastic composition to a swelling treatment with a swelling liquid, said swelling liquid being capable of dissolving said plastic composition at higher temperatures and containing a portion of low boiling liquid suflioient to produce an impervious surface layer on the outside of the blank when it is heated, completely swelling said blank from the outside toward the inside except the innermost core thereof, and heating the blank to a temperature above the boiling point of said low boiling portion of the swelling liquid to solidify the surfaces of said blank by the evaporation of said low boiling liquid to 'dissolve at least partially the previously unswollen innermost core, to force apart said solidified surfaces by the development of vaporized liquid under pressure in the at least partially dissolved innermost core, and thus/to convert said blank to a seamless hollow structure.

15. A process as defined in claim 14 wherein the swelling liquid is a mixture of at least two components, one component being a solvent for the material of the blank and the other component decreasing the solvent action of the first component.

16. A process for the production of seamless hollow structures comprising the steps of subjecting a solid blank of a swellable plastic composition to a swelling treatment with a swelling liquid, said swelling liquid containing a portion of low boiling liquid suiiicient to produce an impervious surface layer on the outside of the blank when it is heated, completely swelling said blank from the outside toward the inside except the innermost core thereof, and heating the blank quickly to a temperature above the boiling point of said low boiling portion of the swelling liquid to solidify the surfaces of said blank by the evaporation of said low boiling liquid, to cause the previously unswollen innermost core to become swollen, to force apart said solidied surfaces by the development of vaporized liquid under pressure in the swollen innermost core, and thus to convert said blank to a seamless hollow structure.

17. A process for the production of seamless hollow structures comprising the steps of subjecting a solid blank of a swellable plastic composition to a swelling treatment with a swelling liquid, said swelling liquid being capable of dis- 25 solving said plastic composition at higher tem- 8. peratures and containing a portion of low boiling liquid suflicient to produce an impervious surface layer on the outside of the blank when it is heated, completely swelling said blank from the outside toward the inside except the innermost core thereof, and heating the blank quickly to a temperature above the boiling point of said low boiling portion of the swelling liquid to solidify the surfaces of said blank by the evaporation of said low boiling liquid, to dissolve at least partially the previously unswollen innermost core, to force apart said solidied surfaces by the development of vaporized liquid under pressure in the at least partially dissolved innermost core, and thus to convert said blank to a seamless hollow structure.

References Cited in the iile of this patent UNITED STATES PATENTS

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