US3491178A

US3491178A - Method for spinning bicomponent polypropylene filaments

Info

Publication number: US3491178A
Application number: US774541A
Authority: US
Inventors: Morio Nishioka; Toshiyuki Nanbu; Hiroyuki Nakamura
Original assignee: Mitsubishi Rayon Co Ltd
Current assignee: Mitsubishi Rayon Co Ltd
Priority date: 1964-02-04
Filing date: 1968-11-08
Publication date: 1970-01-20
Anticipated expiration: 1987-01-20
Also published as: BE657850A; GB1085808A; FR1420793A; DE1494683A1

Description

Jan. 20, 1970 MORIO NISHIOKA' ETAL 3,

METHOD FOR SPINNING BICOMPONENT POLYPROPYLENE FILAMENTS Original Filed Dec. 24, 1964 United States Patent U.S. Cl. 264-168 18 Claims ABSTRACT OF THE DISCLOSURE A method for producing composite polypropylene fibers having good fibrous properties and crimpability on an industrial scale by composite-spinning polypropylene in such a way as at least one polymeric component possesses a beta-orientation of more than 0.2 and an intrinsic viscosity of more than 1.2, the difference in birefrigence between two polymeric components is more than 5 l0- and the difference in intrinsic viscosity between two polymeric components is less than 0.6 in the unstretched state.

This is a continuation of SN. 420,917 filed Dec. 24, 1964.

This invention relates to composite polypropylene fibers and methods for producing the same. More' particularly this invention relates to composite polypropylene fibers having superior crimp characteristics and methods for producing the same.

Polypropylene fibers have many advantages such as low specific gravity, high tenacity, high abrasion resistance, high elasticity, small creep and the like, but they are inferior to wool in the point of bulkiness. Excellent bulk of wool is based upon its characteristic crimps. Hence, many attempts have been made to produce polypropylene fibers having wool-like appearance and high bulkiness by crimping the fibers while retaining their well-known advantages.

Crimped polypropylene fibers have been heretofore produced by means of mechanical crimping process while utilizing their thermoplasticity as in the case of other thermoplastic fibers. Since the mechanical crimping process has various drawbacks, a process which is characterized in producing crimped fibers by providing fibers with potential crimp at the step of spinning and relaxing them at a step after stretching has been developed recently. According to this process, it is possible to omit the mechanical processing step necessary to produce crimped fibers.

An object of the present invention is to provide polypropylene composite fibers having superior properties and excellent crimp characteristics and to provide methods for producing the same.

Another object of the present invention is to produce polypropylene composite fibers having high percentage of crimp and high stability of crimp and to provide methods for producing the same.

Patented Jan. 20, 1970 A still further object of the present invention is to provide polypropylene composite fibers having good appearance and uniform crimps and to provide methods for producing the same.

Other and further objects and advantages of the present invention will become apparent to those skilled in the art upon consideration of the accompanying disclosures.

According to the present invention two kinds of propylene type polymers are spun into composite filaments in such a way as at least one kind of polymer possesses more than 0.2 of beta-orientation and more than 1.2 of intrinsic viscosity [1;] and the difference of birefringence of the two polymers is more than 5x10 in the state of unstretched filament, resulting unstretched filaments are stretched at a temperature lower than C. and then relaxed to develop crimps. The beta-orientation described here and elsewhere herein is a measure which indicates degree of orientation of microcrystal in fibers. It is expressed by ratio (IM/IE) of diffraction intensity at azimuthal angle of 80 from equator (IM) to diffraction intensity at equator (IE) based upon the minimum diffraction intensity in the azimuthal intensity distribution curve diffraction which appears at 20=14 in X- ray diffraction diagram.

The intrinsic viscosity [17L- is that of polymers in fiber state and measured in tetraline at a temperature of C. The birefringence is measured by means of a polarizing microscope and calculated by equation of R= a(n -n in which R is a retardation found from interference color and diagram of interference color, d is a thickness of fiber, n n is birefringence. The difference of bircfringence of the two polymers in a composite filament can be found by following procedure. In the case of sideby-side composite filament such as shown in figure, the retardation R and R in A and B parts can be measured individually in both dotted line zones of A and B parts by interference color and diagram of interference. Since both A and B parts are not circular cross-section, the thickness of each part can be calculated by assuming x and y coordinate having its origin at the center of fiber cross-section, measuring x coordinates of parts indicating interference colors at both A and B parts X and X and calculating Y and Y from the equation of circle. The thickness of two parts are 2Y and ZY Let ZY be d and 2Y be d then birefringence in both A and B parts can be calculated by equations of Thus the difference of birefringence can be calculated from the following equation,

In the present invention, propylene polymers having intrinsic viscosities of 0.8 to 3.5 measured at the state of polymer are used. A homopolymer of propylene can be used by itself but in general propylene polymer containing various stabilizers, fillers, plasticizers, substances capable to give fluidity and the like are used.

As regards light stabilizer, 2-hydroxy-4-octoxy-benzophenone, 2-hydroxy-4-dodecyloxy benzophenone, 2-[2'- hydroxy-5'-(l,1,3,3 tetramethyl butyl)phenyl]benzotriazole and the like are useful.

As oxidation stabilizer,

4,4'-thiobis-(6-tertiary butylmethacresol) 6-(4-hydroxy-3,5-di-tertiary butyl anilino)-4,4'-dioctyl- 1.3.5-triazine, 4,4'-7-thiobis(3-methyl-6-tertiary butyl phenol), 2,2'-thiobis(4-methyl-6-tertiary-butyl phenol) 4-hydroxy-3-methyl-5-tertiary-butyl benzil sulfide, 4,4-butylidene-bis(3-methyl-6-tertiary butyl phenol), 1.1.3-tris(2-methyl-4-hydroxy-5'-tertiary butyl phenol) butane, 2.6-di-tertiary butyl-4-octadecyl oxycarbonyl methyl phenol, 6-(4'-hydroxy-3'-.5-di-tertiary butyl anilino) -2.4-

dioctyl thio- 1 .3 .5 -triazine, 2.4-bis(4'-hydroxy-3'.5-di-tertiary butyl aniline)- 6-octyl thio-1.3.5-triazine, dioctadecyl-3-methyl-4-hydroxy-S-tertiary butyl benzyl phosphonate, 2.6-bis(2'-hydroxy-3'-tertiary butyl-'-methyl benzil)- 4-methyl phenol and the like are useful.

As agents conducting synergistic effect upon stabilizer i.e. as secondary oxidation stabilizer, trioctadecyl phosphite, didodecyl-3.3'-thiodipropionate, dioctadecyl 3.3- thio dipropionate, diethyl-l1.l1'-thio undecanate, tridodecyl phosphite, dodecyl sulfide, octadecyl sulfide and the like can be used.

1 As fillers, silicon oxide, titanium dioxide, and as plasticizers tricresyl phosphate, dioctyl phthalate and sebacate, decyl dilauryl stearate and the like are used.

As materials useful to afford fluidity for facilitating the crimp development, higher alcohols, esters of fatty acids, hydrocarbon Waxes, ketone and the like are used.

In the present invention well-known modified propylene polymers are preferably used instead of propylene homopolymer.

As well-known modified polymers, propylene polymers containing 1 to 30 percent of vinyl pyridine polymer or copolymers, those containing 1 to 20 percent of polyesters such as polyethylene terephthalate, those containing 1 to 20 percent of metal salt of alkylester of sulfoisophthalic acid, those graft-copolymerized with vinyl pyridine, those graft-copolymerized with vinyl pyridine and styrene, those graft-copolymerized with various vinyl compounds and those containing one or more than one kind of the compounds represented by a general formula of (in which R is an alkyl radical having 7 to 29 carbon atoms, R is an alkyl radical having 1 to 18 carbon atoms, M is Al, Zn, or Mg, m and n are either 1 or 2, m+n is always 2 or 3, R is an alkyl radical having 7 to 29 carbon atoms, M is Zn, Al, Sn or C0, m is 1, 2 or 3, n is 0, 1 or 2, m+n' is always 2 or 3, R is an alkyl radical having 4 to 18 carbon atoms, X is S, SO, S0 CH 0 or C0, Y is hydrogen atom or hydroxy radical, M is Ni, Zn, Cu, Co, Pb, or Al, B is H O, NH aliphatic or aromatic amine or nitrogen containing hetero aromatic compounds, n" is 0, 1 or 2) are used.

However propylene polymers admixed with emulsifiercontaining=vinyl pyridine, those admixed with vinyl pyridine copolymer and dyeing assistant, those admixed with sulfophthalic acid alkylester, those containing polyethylene and metal salt of higher fa y a id or normal hydrocarbon having molecular weight of 500 to 3000, those con taining fluid paraffine, kerosene or tetrachloroethane, those containing a compound represented by a formula of (in which R is hydrogen atom, alkyl radical, alkoxy radical or acyl radical, Y is hydrogen atom or hydroxy radi cal, Z is S, SO, S0 CH or CO, M is Co, Ni, Zn or Al) alone or together with metal alcoholate of higher aliphatic acid and/ or basic metal salt of higher fatty acid, are also preferably used.

The composition of two kinds of propylene polymers may be different or the same. In the present invention, two kinds of propylene polymers having different intrinsic viscosities at the state just before spinning are preferably used. The difference of intrinsic viscosities of polymers in the state of fiber is preferably less than 0.6. However at least one kind of polymer must possess an intrinsic viscosity [i of at least 1.2.

Two kinds of propylene polymers are heated to melt at a temperature of 170 C. to 320 C. and spun to form composite filaments. The heating temperature of two kinds of polymer can be different. Accordingly the object of the present invention can be attained by heating to melt two kinds of propylene polymers having the same intrinsic viscosity [:1] and the same composition at different temperature and spinning to produce composite filaments. And the object of the present invention can also be achieved by spinning two propylene polymers having the same intrinsic viscosity but different composition.

As regards spinning apparatus, there is no special limitation and well-known apparatus for producing composite filaments can be used.

In the present invention, it is necessary to spin filaments in such a way that two kinds of propylene polymers are disposed over the whole length of filament. Either way of side by side disposition or sheath core disposition may be used. However, side by side disposition is preferably used because of its ready crimp development. There is no need of limiting the proportion of two kinds of polymers into 50:50. It is possible to alter the proportion in the range of 20:80 to :20.

Extruded filaments are generally taken up at a velocity of 200 to 1000 m./min. to give unstretched filaments. In the present invention, at the state of unstretched filaments, at least one kind of polymer possesses more than 0.2 of B-orientation and more than 1.2 of intrinsic viscosity Besides these, it is necessary to select spinning temperature, cooling condition, take-up speed and the like such a way that the difference of birefringence of two polymers becomes more than 5 10 preferably more than 10 10- When these conditions are not satisfied, poly propylene composite fibers having superior properties and crimp characteristics cannot be produced. Unstretched filaments are stretched at a temperature lower than 80 C. and then relaxed to develop crimps. When the stretching temperature is higher than 80 C. fibers of superior crimp characteristics cannot be obtained. The stretch ratio is in general, 2 to 4 times. Even when stretched filaments are relaxed at room temperature, it is possible to develop crimps but when stretched filaments are heated by dry hot air, hot water, steam and the like in a relaxed state, it is possible to develop greater amount of crimp and to increase the stability of crimp. There is no special limitation as to the manner of heat treatment. Heat treatment may be carried out at the state of skein or between two sets of rollers. By the above-mentioned processes, polypropylene composite crimped fibers having a large stretchability can be produced, but in some fields polypropylene composite crimped fibers having high bulkiness and small stretchability are required. There are cases in which uniform crimped state of all spun composite filaments is rather harmful to the handling of yarns in the processing step or harmful in the point of properties of yarns required according to the end uses. In such cases, it is possible to improve spinning method in such a way as the proportions of two kinds of polymers in a spun composite filament are different among each filament. In the improved method also, one kind of polymer in spun composite filaments must possess more than 0.2 of fl-orienta tion and more than 1.2 of intrinsic viscosity [1;] difference of birefringence of the two polymers in spun composite filament is more than 5 X preferably more than 10 10- unstretched filaments must be stretched at a temperature lower than 80 C. and then relaxed to develop crimps. The method has following advantages. When the proportion of two polymers in composite filament is identical with all filaments, crimp forms to be developed are theoretically identical with all filaments. On this account, in some cases the periods of crimp are so overlapped that bulkiness of fibers may be lost. Whereas when the crimp forms are changed due to the different proportion of two polymers among each composite filament, there will be no overlapping of crimp period and then bulkiness of fiber is not lost. Owing to non-uniform crimps, the surface of knitted and woven fabrics loses a little of uniformity but since each filament is entangled, fabrics having firmness and high stretchability can be obtained.

As regards distribution of proportion of two polymers in a composite filament among each filament, it is possible to set a medium value of the distribution according to required crimp characteristics and to change the shape and width of the distribution according to the end uses. According to this method it is possible to spin some noncomposite filaments simultaneously with composite filaments having different proportions of two polymers each other. However it is most preferable to spin composite filaments in such way that the medium value of the distribution is 50:50 and the shape of distribution is normal in the range of 10:90 to 90:10.

There is no special limitation to spinning apparatus'lt is also possible to use well-known apparatus in which the arrangement of orifices at the surface of spinneret is improved.

In order to develop .more crimps, filaments can be subjected to heat treatment in a relaxed state, but it is also possible to apply heat treatment in a relaxed state to knitted or woven fabrics directly converted from filaments wound up on bobbins or pirns. Thus heat treatment can be carried out at various steps. Filaments are cut into suitable length and spun into yarns after being stretched and/or heat-treated. Blend spinning and mixed weaving with other fibers may be possible. Fibers thus obtained possess not only high crimp recovery but also high elasticity.

On this account these fibers show the function of elastic fibers after finishing the function of crimped fibers. By this characteristics property, the utilities of fibers are exceedingly enlarged. In other words, they are used as filaments like conventional processed yarns, and are used as staple fibers by controlling the development of crimps. From these staple fibers, fabric cloths having high stretchability can be produced.

When stretched filaments are directly relaxed as they are, resulting filaments possess so much shrinkage that handling at knitting step may be difficult and developed crimps are not beautiful. In order to develop beautiful, stable crimps according to the present invention, stretched filament are (d) maintained at the state under tension of less than 3 mg./d., and then heat treated under tension while giving 5 to 50 percent of shrinkage or (e) alternatively, are heat-treated at a temperature of 60 C. to 140 C. while over-feeding 5 to 30 percent. It is preferable to determine various conditions of overfeed amount, heat treatment temperature, and heat treatment time so as to give less than 10 percent of shrinkage of resulting filaments. This heat-treatment for relaxation can be carried out continuously with other step.

In order to develop uniform crimps, it is preferable that the stretched filaments are first provided with more than 0.1 g./d. of tension, then maintained under tension of less than 0.003 g./d., subsequently subjected to heat treatment under tension while giving 5 to 50 percent of shrinkage. By heat-treating stretched filaments for relaxation under slight tension, it is possible to prevent yarn from forming local clusters of the yarn-constructing filaments. When clustered filaments are present in yarn, the development of crimps after heat shrinkage treatment is not sufiicient and not uniform and appearance of crimped filaments is not preferable.

In order to carry out relaxation heat treatment in batch system, it is necessary to hang filament bundles in frames or to place them upon plate. The shrinkage of the filament contacting with the surface supporting filament bundles are controlled by the friction between the supporting surface and filament, and hence crimped form of fila- .ments being contacted with the surface becomes different from that of filament not being contacted thesurface, and which makes one origin of uneven crimp development after being made into fabrics. For the purpose of preventing such unevenness of crimp, it is preferable to subject the stretched filaments to the first heat-treatment at a temperature higher than 50 C. under tension of less than 3 mg./ d. and then to the second heat-treatment at a temperature of the same or higher than the first heattreatment in such a way as filament length becomes longer than that of the first heat-treated filament and shorter than that of non-heat-treated filament in a proportion of more than 5 percent.

The following examples are given to illustrate the present invention without limiting its scope.

EXAMPLE 1 Two kinds of polypropylene were made into composite filaments at conditions shown in Table 1 by use of spinning apparatus of screw-gear pump type and subjected to stretching. The spinning ratio of two kinds of polypropylenes was 50:50. Spun filaments were in crimped state when they were made into skein after being stretched but for the more sufiicient crimp development, they were heat-treated for 30 minutes by steam of C. in a relaxed state. Properties of resulting filaments are shown an intrinsic viscosity of more than 1.2, and wherein two in Table 1. In this table, Nos. 7 to 10 were control. polymers in said filaments have a difference in blrefrlng- TABLE 1 A component B component Spinning Spinning Spinning temp. at temp. at temp. at Experiment N o. nozzle C.) [1;]0 screw C.) [1 B-orientatlon AnX10 [1;]G screw C.)

275 2. 20 275 1. 50 0. 45 8. 1. 40 275 275 2. 20 275 l. 50 0. 24 16. 2 1. 40 275 275 2. 20 275 l. 50 0. 24 16. 0 2. 20 295 275 1 2. 20 275 1. 50 0. 30 13. 0 2. 80 275 265 2 2. 20 265 1. 55 0. 26 15. 0 3 1. 40 265 265 1. 80 265 1. 50 0. 24 16. 0 2 1. 40 265 275 2. 20 275 1. 50 0. 24 16. 2 1. 40 275 275 2. 20 275 1. 50 None 4. 0 2. 80 275 275 2. 20 275 1. 50 0. 20 23. 0 2. 80 275 295 1. 20 295 1. 00 None 6. 0 1. 40 295 B componentOontinued Take up Crimp speed Stretching Percentage stability Experiment No. [1 lit-orientation A1t 10 (m./m1n.) temp. 0.) Stretch ratio of crimp (percent) 1. 10 None 2. 5 300 20 3. 6 55 85 1. 10 None 5. 8 700 20 3. 0 78 92 1. None 4. 5 700 3. 0 8O 95 1. 65 0. 23 19. 2 700 20 2. 5 75 90 1. 12 None 3. 8 700 20 3. 0 78 92 1. 12 None 5. 0 700 20 3 0 80 95 1. 10 None 5. 8 700 100 3. 0 15 90 1. 65 None 7. 5 150 20 3. 8 0 1. 65 0. 17 26. 0 1200 20 2. 0 85 1. 15 O. 40 11. 0 1000 20 3. (i 55 55 1 This polymer contained 7 percent by weight of copolymer of methyl vinyl pyridine (50) :styrene (50).

2 This polymer contained 10 percent by weight of fluid parafline.

[ 11G means intrinsic viscosity of pelleted polymer.

In the measurement of crimp characteristic, yarn was used as a specimen. 20 cm. of this specimen under initial load of 1 mg./d. was made into (a) cm. and then made into (b) cm. at a time of 5 minutes elapse after applying a load of 0.05 g./d. If the length at a time 015 minutes elapse after removing load was (c), percentage of crimp and percentage of crimp recovery were defined as follows:

Percentage of crimp= X100,

. b-c Percentage of crimp recovery= 100 ex OrimptSstability is the percentage of recovery length at the 10th time to that at the first time after repetition of 10 times of the above-mentioned perimen EXAMPLE 2 ence of more than 5 10 and a difference in intrinsic viscosity of less than 0.6, said producing step including the steps of melting at least one propylene polymer having an intrinsic viscosity of 1.0 to 2.8 at a temperature of 170320 C., composite spinning the polymer to form composite filaments and taking up the filaments at a velocity of 200 to 1000 m./min., stretching the filaments to 2 to 4 times, and relaxing the stretched filaments.

2. A method according to claim 1 in which the spun unstretched filaments are heat-treated at a tem erature of EXAMPLE 70 C. to 160 C., stretched to 2 to 4 times ur ider condi- TW kinds of P yp py admlXed Wlth Percent tions not to make the elongation-at-break of the filaments by weight of nickel distearatc and 1.0 percent by weight lower h 70 Percent d h l i The non-stretched filaments of experiment No. 2 in Example 1 were stretched 4 times the original length at a temperature of 20 C., subjected to shrinkage by per- 40 cent at a temperature of 140 C. in an air bath installed between 2 sets of rollers and taken up on pirns. Percentage of crimp and crimp stability of resulting filaments were 75 percent and 90 percent respectively.

of zinc distearate were made into composite filaments, 3 A h d according to claim 1 in which the Stretch stretched and heat-treated at relaxed condition by the 5 m i carried out at a temperature lower than 0 Same condition as of eXpfirimeIlt 2 in Example 4. Amcthod according to claim lin which the stretched The Spinning ratio of P y A to B Was 7030- filaments are maintained under tension of less than 3 centage of Crimp and crimp Stability of resulting filaments mg./d., the filaments are heat-treated under tension while Were 30 Pemfint and 93 Pelicent respectively aiforded 5 to 50 percent shrinkage and then relaxed.

5. A method according to claim 1, in which the EXAMPLE 4 stretched filaments are heat-treated at a temperature of The same experiment as in No. 2 of Example 1 w C. to 140 C. while being overfed in a proportion of repeated except that the distribution of the proportion of 5 30Pefent and then aX two kinds of polymers in spun composite filaments is A method ccording to claim 1, in which the arranged at a normal distribution in the range of 10:90 60 stretched filaments are afforded more than 0.1 g./d. of to 90:10 with a medium value of 60 (higher shrinkage tension, maintained under tension of less than 0.03 g./d., component) :40 (lower shrinkage component). Mean perheat-treated under tension while afforded 5 to 50 percent centage of crimp and crimp stability of resulting filaments Shrinkage and then relaxed. were 60 percent and 90 percent respectively. Percentage 7- A meth d according to claim 1, in which the of crimp was h t lower th th t f experiment stretched filaments are subjected to a first heat-treatment No. 2 of Example 1 but bulkiness at the time of elongaunder tension of less than 3 mg./d. at a temperature tion was large and density of fibers, when made into higher than 50 C. and to a second heat-treatment at a fabrics, was small. On this account fabrics having soft temperature at least as high as that of the first heat hand and capable to give firm feeling at elongated state treatment and in such a manner that the filament length were obtained. is longer than that of the first heat-treated filament and What is claimed is: more than 5 percent shorter than that of non-treated 1. In a method for producing compositepolypropylene filaments, and thcnthe filaments are relaxed. fibers, the improvement comprising producing composite 8. A method according to claim 1, in which the spun unstretched filaments wherein at least one polymer in said unstretched filaments are strechcd at a low stretch ratio filaments possessesabeta-orientation of more than 0.2 and so as to make the elongation-at-break of filament not lower than 95 percent, heat-treated at a temperature of 70 C. to 160 C., further stretched at a low stretch ratio so as to make the elongation-at-break of filament not lower than 75 percent and then relaxed.

9. A method according to claim 1, in which the spun unstretched filaments are stretched at a low stretch ratio so as to make the elongation-at-break of filament not lower than 95 percent, heat-treated at a temperature of 70 C. to 160 C. and then relaxed.

10. A method according to claim 1, in which the proportion of two kinds of polymers in a single filament is varied among several filaments so produced.

11. A method according to claim 10, in which the stretching is carried out at a temperature lower than 80 C.

12. A method according to claim 10, in which the stretched filaments are maintained under tension of less than 3 mg./d., the filaments are heat-treated under tension while afforded 5 to 50 percent of shrinkage and then relaxed.

13. A method according to claim 10, in which the stretched filaments are heat-treated at a temperature of 60 C. to 140 C. while being overfed in a proportion of 5 to 30 percent and then relaxed.

14. A method according to claim 10, in which the stretched filaments are afiorded more than 0.1 g./d. of tension, maintained under tension of less than 0.03 g./d., heat-treated under tension while afforded 5 to 50 percent shrinkage and then relaxed.

15. A method according to claim 10, in which the stretched filaments are subjected to a first heat-treatment under tension of less than 3 mg./d. at a temperature higher than 50 C. and then to a second heat-treatment at a temperature at least as high as that of the first heattreatment and in such a manner that the filament length is longer than that of the first heat-treated filament and more than 5 percent shorter than that of non-treated filamerits, and then the filaments are relaxed.

16. A method according to claim 10, in which the spun unstretched filaments are heat-treated at a temperature of C. to 160 C., stretched at a low stretch ratio so as to make the elongation-at-break of filament not lower than 70 percent and then relaxed.

17. A method according to claim 10, in which the spun unstretched filaments are stretched at a low stretch ratio so as to make the elongation-at-break of filament not lower than 95 percent, heat-treated at a temperature of 70 C. to 160 C., further stretched at a low stretch ratio so as to make the elongation-at-break of filament not lower than percent and then relaxed.

18. A method according to claim 10, in which the spun unstretched filaments are stretched at a low stretch ratio so as to make the elongation-at-break of filament not lower than percent, heat-treated at a temperature of 70 C. to C. and then relaxed.

References Cited UNITED STATES PATENTS 2,952,033 9/1960 Goodwin 18-1 3,093,444 6/1963 Martin 264168 3,106,442 10/ 1963 Compostella et al.

3,215,486 11/1965 Hada et a1 874 3,233,023 2/1966 Benson 264-168 3,256,258 6/1966 Herrman 26093.7 3,323,190 6/1967 Boltniew 28-72 3,399,259 8/1968 Bradford 264-168 3,408,433 10/1968 Bradford 264168 FOREIGN PATENTS 979,083 1/ 1965 Great Britain. 1,342,403 9/1963 France.

JULIUS FROME, Primary Examiner US. Cl. X.R. 26417l