US 3667481 A
A tobacco smoke filter employing two barriers in the smoke path, each having an opening to form a flow path past the barriers. The first barrier defines a small area flowpath in which smoke and entrained liquids and solids are accelerated and high kinetic energy is imparted to them. The second barrier diverts the smoke but, because of its closeness to the first barrier, the moisture and solids impinge on the latter. A third, downstream barrier marks off a smoke storage space from which smoke is drawn during initial phases of subsequent inhalation to overcome feeling that excessive suction is required to overcome filter impedence. The filter and storage unit is divided into two passageways and is made of plastic and surrounded by paper so that the latter is employed as a repository for moisture and solids and to retain the filter in situ.
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Description (OCR text may contain errors)
United States Patent Thomas  TOBACCO SMOKE FILTER Leonard L. Thomas, 14092 Ash Street, Westminster, Calif. 92683  Filed: Dec.5, 1969  App1.No.: 882,675
Primary Examiner-Aldrich F. Medbery Assistant Examiner-J. F. Pitrelli Attorney-Nienow & Frater  ABSTRACT A tobacco smoke filter employing two barriers in the smoke path, each having an opening to form a flow path past the barriers. The first barrier defines a small area flowpath in which smoke and entrained liquids and solids are accelerated and high kinetic energy is imparted to them. The second barrier diverts the smoke but, because of its closeness to the first barrier, the moisture and solids impinge on the latter. A third, downstream barrier marks of? a smoke storage space from which smoke is drawn during initial phases of subsequent inhalation to overcome feeling that excessive suction is required to overcome filter impedence. The filter and storage unit is divided into two passageways and is made of plastic and surrounded by paper so that the latter is employed as a repository for moisture and solids and to retain the filter in situ.
13 Claims, 7 Drawing Figures PATENTEDJUH 6 I97 NVENTOR. 1601mm) L. Ibo/ hwy/van;
TOBACCO SMOKE mm This invention relates to improvements in apparatus for filtering the liquid and solid components from tobacco smoke. The invention is applicable to any smoking device in which the tobacco is burned and its smoke is inhaled through a conduit leading to the users mouth. Thus, the invention is applicable for incorporation in cigarettes and in pipes and in filtering devices formed as series attachments for cigarettes and pipes. An object is to provide an improved tobacco filter generally and one which is readily produced at minimum cost but which accomplishes the filtering task effectively and efficiently.
Although the invention has broader application, it is particularly useful in connection with cigarettes and an object is to provide an effective filter which can be produced at a cost sufiiciently low to make it feasible to incorporate the filter within the cigarette during manufacture to be thrown away with the cigarette.
The liquid and solid components of tobacco smoke have much greater mass than do the molecules of smoke. This fact makes it possible to separate the gaseous constituents from the liquids and solids by applying forces to the smoke that will accelerate the gases to higher velocities than are achieved by the liquid and solid components. Alternatively, they may be separated by accelerating them all toward a barrier to a high velocity so that the kinetic energy in the liquids and solids is sufficiently great that they are not diverted with the gaseous components but impinge upon the barrier. The barrier is formed so that the deposits of liquid and solid materials are not subsequently carried away. It is known to employ this latter physical phenomenom for the filtering of tobacco smoke but it is difficult to do in practice because of the physical fact first mentioned above and because of space limitations coupled with the fact that the filter may not be permitted to impede the flow of smoke to the point where the user is forced to apply excessive inhalation suction to draw smoke through the filter. An object of the invention is to provide a filter which utilizes this kinetic energy phenomenom to accomplish its filtering action and which can be constructed in a form sufficiently inexpensive and small for incorporation within a cigarette. It is an object to realize that result without requiring an objectionable degree of inhalation suction. It is an object to accomplish this result by the use of a pair of smoke barriers arranged in series, the first so that the smoke is accelerated to high velocity and the second to provide a barrier requiring an abrupt change in direction in the highly accelerated smoke. It is another object to provide a filtering structure which incorporates a storage place for smoke in which smoke is stored at the end of an inhalation suction and from which it can be withdrawn with minimum inhalation suction pressure so that smoke enters the smokers mouth immediately at the beginning of his next inhalation. Suction pressures higher than the amount required to draw smoke through an unfiltered cigarette are easily tolerated by the smoker if the suction pressure at the beginning of the inhalation, and at the beginning of the users lung expansion, are relatively low. This factor is made use of in the invention.
.Accomplishing these tasks in an inexpensive structure small enough to fit within a cigarette has proven to be difficult. The form and dimensional tolerances in prior devices are very critical. A certain degree of criticality attends the form and dimension of filtering structures incorporating this invention. Nonetheless, an object is to provide a structure in which these requirements can be met at a minimum cost in the production of the filter and at a minimum cost of incorporating it within the cigarette to complete the filtering unit. Another object of the invention is to provide a filter which can be housed in an extension of the cigarette paper beyond the end of its tobacco charge and which has a form permitting its retention there without the need for adhesives or added fastening structures. Cigarette paper changes its dimension significantly whereby the inside diameter of the paper tube at the smokers end of the cigarette may change by several thousands of an inch over the temperature range to which it is subjected in use. This factor becomes significant in the attempt to produce a filter whose operational theory requires the provision of relatively large clear or open spaces and when the use of adhesives is to be avoided.
Certain objects of the invention are realized in part by utilizing the inner surface of the cigarette paper as a repository for some of the liquid and solid material that is removed from the smoke and the provision of that feature is another object of the invention.
In the drawings:
FIG. 1 is an isometric view of a cigarette with a portion 0 the cigarette paper at the smokers end cut away to expose the filtering and smoke storage element embodying the invention;
FIG. 2 is a view in side elevation of the filtering and smoke storage element of FIG. 1;
FIG. 3 is a view in end elevation of the right end of the element of FIG. 2;
FIG. 4 is a view in end elevation of the left end of the element of FIG. 2;
FIG. 5 is a view in cross-section taken on line 5-5 of FIG.
FIG. 6 is a cross-sectional view taken on line 6-6 of FIG. 2; and
FIG. 7 is a transverse cross-sectional view of a cigarette incorporating a filter of alternative form.
In FIG. 1 the cigarette is designated generally by the reference numeral 10. The cigarette paper, which is rolled to tubular form, is designated by the reference numeral 12. At its. right end in FIG. 1 the paper tube is filled with a charge 14 of cut tobacco. A conventional, rolled paper filter 16 in the form of a cylinder that just fits within the tube abuts the left end of the charge 14. The filter and storage element of the invention occupies a space within the tube from the left end of the filter 16 to the left end of the tube. The filter and storage element is generally designated by the reference numeral 18. It is formed of three barriers which advantageously are formed substantially as flat discs. The first of these discs is located upstream from the other two and is designated by the reference numeral 20. The second disc 22 is downstream from disc 20 and upstream from the third disc 24. The three discs are arranged in spaced, parallel relation on a common axis. Advantageously, and especially in the forms of the invention intended for incorporation in cigarettes, means are incorporated for holding the discs in that relative position independently of the structure within which they are mounted. In this embodiment that means comprises a pair of innerconnecting walls one of which innerconnects the discs 24 and 22 and is designated by the reference numeral 30 and the other of which is designated 32 and innerconnects discs 22 and 20. In this embodiment those two walls are flat and they are formed on a common plane.
' That is not essential. Both of them divide the space between discs they join into two chambers and that feature is preferred although a wall structure resulting in division into three or even four chambers is permissible within the invention.
A flow path must be formed through each of these barriers. In the preferred form of the invention the flow path is formed by notching the outer periphery of the three barrier discs. At least two notches must be formed in each barrier, in the form selected for illustration in the drawing, so that there will be a flow path past the filter on both sides of the dividing walls 30 and 32. The first barrier serves to accelerate the smoke. Its notches are the smallest in cross-sectional area. The second barrier 22 is arranged so that it diverts the smoke laterally after passing through the first barrier. It is placed sufficiently close to the first barrier so that highly accelerated liquid and solid particles cannot be efiectively diverted. The flow path through the second barrier 22 is larger so that the smoke flows easily from the space between the barriers 20 and 22 and maximum difi'erential pressure is developed across the first barrier 20. The third barrier 24 cooperates with barrier 22 to define a storage space for smoke between them. Its flow path area is not critical. The function of barrier 24 is to tend to confine the smoke within the end of the cigarette paper tube between inhalations and to offer minimum resistance to flow from that space in response to inhalation suction.
In forming a practical filtering system it is advantageous. to incorporate a means that will insure that the filter element is properly located and that smoke is free to collect in a space adjacent and upstream from the first barrier 20. In this embodiment that means comprises a locating pin 34 designed to cooperate with a Spacer or filler element. In this embodiment this spacer or filler comprises prefilter element 16. Prefiltering is not an essential function. More importantly it serves to insure that the tobacco of the charge 14 does not loosen and clog the passagewaythrough the barrier 20. It will be apparent that the element 16 may have a variety of forms and might be integrally formed with the barrier and storage element 18.
The two notches of the first barrier 20 are identified by the walls 40 and 42 which define them, respectively. The flow path or notches of the second barrier 22 are defined by the notch walls 44 and 46. Finally, the two notches of the third barrier 24 are identified by the walls 48 and 50 by which they are formed, respectively. The size and relative radial orientation of the flow passageways are selected, in practicing the invention, on the basis of the pressure differential that is desired across them and the character of the physical phenomenom employed in accomplishing the filtering action. The shape and the distance of the flow path from the axis of the unit is determined in part by the character of the materials employed in the filtering unit and partly by the cost of forming them. In the interest of cost reduction and simplicity in manufacture, and also to enhance the function of the unit, the discs 20, 22 and 24 are made relatively thin.
Before discussing these several variables, it is convenient to examine the factors that effect selection of the material to be employed in the filter unit. There is a requirement that any structure that is to be inserted within the cigarette paper tube during the course of automatic manufacture have its outside diameter held very closely to the optimum dimension. This requirement is easily met by molding element 18 of a plastic material. A number of plastic materials are sufficiently low in cost to be suitable for making elements destined to be incorporated in cigarettes. It is preferred that the material used be resilient and flexible in some degree to facilitate stripping from molding cavities and because these qualities are compatible with the requirements of the cigarette manufacturing machines. Both polyethylene and polypropalene are excellent materials. Polypropalene costs less and is preferred. However, these materials are sufficiently smooth so that they do not adhere naturally to the interior surface of the cigarette paper tube. It is important that the unit 18 be retained within the cigarette and that it not be free to slip out while the smoker is applying inhalation suction to the cigarette and drawing smoke into his lungs. This difficulty is overcome in the invention despite the tendency of cigarette paper to expand by arranging the element 18 so that it has an outside diameter very slightly larger than the inside diameter of the paper tube at the manufacturing temperature whereby the paper is stretched slightly at the places where it encompasses the discs and so that it is necked down slightly in the regions between the discs. The degree of this necking down" is very small, being in the order of one or two thousands of an inch and hardly discernible in the drawing of FIG. 1 although exaggerated there in some degree. In particular, the diameter of the paper tube in the regions 52, 54 and 56 around the discs is slightly greater than the diameter of the paper tube at region 58 between discs 22 and 24 and in region 60 between discs 20 and 22. The resiliency and flexiblity of element 18 permits it to contract during assemblage and subsequently to expand after assemblage is complete, causing the necking down" of the wrapper. Alternatively, the necking down" is accomplished by stretching the cigarette paper as it is rolled into a tube around the element. Within a short time the paper of the tube acquires a permanent set whereby its diameter in the regions between the barriers become fixed at less than the diameter of the barriers.
The solid constituents of smoke adhere easily to plastic materials. So do the liquids although the liquids can be evaporated away in some degree. Thus, the filter portion of the unit 18 will operate entirely satisfactorily despite the fact that it is fonned of a plastic material. Nonetheless, in the preferred form of the invention the cigarette paper that surrounds the unit is made to serve as part of the filter element. It is very effective as a repository for solids and liquids and it can be utilized simply by arranging the flow path past the barrier so that the flow of smoke is directed against the paper. This action is assured by forming the flowpath of the first element as a notch cut inwardly from the outer perimeter of the disc. This construction is least expensive to produce and therefore it is highly advantageous. Unlike the notches of the first disc, the notches or flow path openings of the second and third discs need not be located at their outer perimeters. However, because of the lower cost to form notches these discs are ordinarilynotched.
It is possible to design a notch which is so effective directing the moisture against the paper as to result in excessive wetting of the paper. This difficulty can be overcome by designing the notch so that less moisture reaches the paper, by using an alternative passageway form as illustrated in FIG. 7, or by reinforcing the paper tube at the smokers end of the cigarette in the manner which is common in cigarette manufacture. In FIG. 1 the reinforcing layer 62 is one of these conventional kinds. In this particular instance it comprises a layer of cork material. In FIG. 7 the disc 64 represents the first barrier of an alternative form of filtering device, Its passageways 66 and 68 are formed as circular openings at points removed from the outer perimeter of the disc. Flow through the openings 66 and 68 would not be directed against the cigarette paper 70 surrounding the disc.
Experimentation has demonstrated that an optimum flow path area through the first barrier is about 0.00066 square inches when the flowpath comprises a single, circular orifice. This corresponds to an opening 0.029 inches in diameter. However, the inhalation suction pressure exerted by a smoker can exceed his customary, non-smoking inhalation suction greatly without discomfort and he tends to increase suction pressure although flowrate is increased. These factors make it possible to design a filter in which flowrate is increased without reduction in filtering action, or to design a filter in which flowrate is not diminished while improving filtering action, by placing two or more filters in parallel. The latter effect is accomplished in the embodiment of FIG. 3 by forming the flowpaths as notches of the first barrier 0.025 inches wide and 0.016 inches deep so each has an area of 0.0004 square inches. Then each has an area less than the value 0.00066 which is optimum for a single hole unit. The smaller area results in better filtering as smoke velocity increases because of the smokers tendency to keep suction pressure at the same level. However, the flowpath area of the two openings is 0.0008 square inches which, being greater than optimum single hole area, results in smoke reaching the smokers lungs at a faster rate. Experimentation demonstrates that the flowpaths must be separate past the second barrier for the effect to be exhibited and that best operation results if they are separate entirely through the filter and storage space. The advantage in multiple paths is not increased greatly for more paths than two. It is observed that the volume of the storage space should be the same whether subdivided or not and the volume of the space between the first two barriers is not critical. These factors make the parallel arrangement easy to accomplish and advantageous in a unit no larger in diameter than a cigarette.
Whether employed singly or multiplied in the parallel filter arrangement, the area of each first barrier opening should not be less than 0.0003 square inches to avoid difficult suction and the total of all should not exceed 0.0014 square inches because filtering action then suffers even if multiple paths are employed.
The degree of moisture removal by the paper wall is increased by making the slot wider and less deep. Little moisture reaches the wall when the flowpath is removed from the periphery of the disc as it is in FIG. 7. The shape of the notches 42 and 40 is not critical except that if increased moisture removal by the paper is desired, notch width is increased. To avoid corresponding increase in flow area the depth is decreased. The rectangular notch is convenient in this respect, otherwise the pie-shaped notches 44 and 46 illustrated in FIG. 6 and the elongated or oval notches 48 and 50 illustrated in FIG. 4 or even circular openings or semi-circular openings, as illustrated and suggested in FIG. 7, are entirely satisfactory. If the cork layer 62 or other reinforcing layer is omitted, it may be desirable to protect against indenting the paper tube by using a notch form which minimizes the peripheral length of the discontinuity. This is accomplished by making the notch deeper and less wide.
Barrier width is not critical except that the width of the first barrier should not be so great that its resistance is increased or so that it becomes clogged by deposition of solids out of any turbulent portion of smoke flow. One sixteenth of an inch is entirely satisfactory in the cigarette application. The spacing between barriers is more critical and should be between 0.025 inches and 0.055 inches, and definitely less than three thirtyseconds of an inch. The optimum distance during any inhalation exercise depends upon inhalation suction pressure and is variable. Any value in the range 0.025 and 0.055 inches is acceptable. The mid-distance is best as the compromise most likely to be optimum. The size of the storage space is advantageously between 0.014 and 0.02 cubic inches. In a cigarette, a separation between the second and third barriers of about one-quarter of an inch is preferred unless the structure joining these two barriers has large volume.
The area of the flowpath through the second barrier is not critical and may be many times the flow area past the first barrier. However, if there is an appreciable pressure reduction across the second barrier there will be a cooling in the storage space which will operate to'minimize expansion of the paper tube in this region to the end that any tendency to release the filter unit 18 is negated. When this result is desired, the flowpath past the second barrier should be two to three times the area of the path past the first barrier.
Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.
1. A filter for inclusion in a tobacco smoke flowpath comprising in combination:
first, second and third discs arranged substantially in parallel on a common axis with the first upstream of the second and the second upstream of the third; each of said discs being notched inwardly from its circumference sufficiently to form a flowpath, the flowpath formed in the second and third discs each having an area greater than that of said first disc and the notched regions of the first and second discs being offset circumferentially relative to one another; the spacing between the first and second discs being less than three thirty-seconds of an inch and the second and third discs being spaced to provide a volume no less than 0.014 cubic inches between them.
2. The invention defined in claim 1 in which the area of the flowpath past said first disc is from 0.0003 to 0.0014 square inches, the separation of said first and second discs is between 0.025 and 0.055 inches.
3. The invention defined in claim 1 which further comprises a paper tube containing said discs and having an axis coincident with that of said discs, the tube being formed of paper.
4. The invention defined in claim 3 in which the inside diameter of said tube is slightly less, between discs, than the outside diameter of the discs such that the tube is necked slightylbetween discs.
. e invention defined in claim 4 which further comprises connecting means interconnecting said discs for maintaining them parallel with fixed spacing; said means being formed integrally with the discs.
6. The invention defined in claim 1 which further comprises means interconnecting said discs in the form of a dividing wall dividing the space between the first and second discs into separate spaces, each of said first and second discs being notched inwardly at at least two points along their perimeters to form a flowpath therepast to each of said separate spaces.
7. The invention defined in claim 6 in which the flow area of the flowpath past the first disc is between 0.0003 inches squared and 0.0014 inches squared and the separation of the first and second discs is between 0.025 and 0.055 inches.
8. The invention defined in claim 7 in which the second and third discs are separated by a distance nearly one quarter of an inch.
9. The invention defined in claim 8 in which the notches forming the flowpath past the first barrier are between 0.18 and 0.27 inches wide and the first barrier is approximately one-sixteenth of an inch thick.
10. The invention defined in claim 9 which further comprises a cylindrical tube surrounding said discs and means connecting said discs, the tube being formed of paper and the discs and connecting means between them being integrally formed of a plastic material.
11. A filter for inclusion in a tobacco smoke flowpath comprising, in combination:
a flowpath extending from an upstream to a downstream position and defined by flowpath walls;
first, second and third barriers extending across said flowpath to its walls with the first barrier upstream of the second and separated from the second a distance between 0.025 and 0.055 inches and the third separated from the second by approximately one-fourth of an inch;
said first barrier having a flowpath formed therethrough with an area between 0.0003 and 0.0009 inches squared, said second and third barriers having a flowpath area greater than the first and the flowpaths of the first and second barriers being arranged out of alignment.
12. The invention defined in claim 1 1 wherein said first barrier is notched inwardly from its margins to form the flowpath past it.
13. The invention defined in claim 11 which further comprises a first wall connecting the first and second barriers and a second wall connecting the second and third barriers, said walls dividing the passageway into two passageways in the region between the first and third barriers;
the flowpath past each barrier being formed by at least two openings, one communicating with each of said two passageways.