US3677802A

US3677802A - Process for strong,durable press fabrics

Info

Publication number: US3677802A
Application number: US22029A
Authority: US
Inventors: Richard N Knowles
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1970-03-23
Filing date: 1970-03-23
Publication date: 1972-07-18
Anticipated expiration: 1989-07-18

Abstract

DURABLE PRESS CELLULOSIC FABRICS WITH GOOD TENSILE STRENGTH AND ABRASION RESISTANCE ARE PREPARED BY TREATING THE FABRIC WITH A SOLUTION OF A POLYISOCYANATE SUCH AS BIS-(4-ISOCYANATOCYCLOHEXYL) METHANE IN AN ORGANIC SWELLING SOLVENT SUCH AS DIMETHYL SULFOXIDE AND CURING THE FABRIC PRIOR TO THE PAD-DRY-CURE DURABLE PRESS TREATMENT.

Description

United States Patent O 3,677,802 PROCESS FOR STRONG, DURABLE PRESS FABRICS Richard N. Knowles, Hockessin, Del., assignor to E. I. du

Pont de Nemours and Company, Wilmington, Del. No Drawing. Filed Mar. 23, 1970, Ser. No. 22,029 Int. Cl. B44d 1/092 US. Cl. 117--56 12 Claims ABSTRACT OF THE DISCLOSURE Durable press cellulosic fabrics with good tensile strength and abrasion resistance are prepared by treating the fabric with a solution of a polyisocyanate such as his (4 isocyanatocyclohexyl)methane in an organic swelling solvent such as dimethyl sulfoxide and curing the fabric prior to the pad-dry-cure durable press treatment.

BACKGROUND OF THE INVENTION This invention relates to the use of polyisocyanates as agents for increasing the tensile strength and abrasion resistance of heat cured, durable press fabrics, and to the strong, abrasion resistant fabrics thus produced.

In recent years the durable press characteristics of cellulose fabrics have been greatly improved. Smooth drying and wrinkle resistant fabrics can now be obtained by the application of various thermosetting resins. However, the thermosetting resins currently in use reduce the tensile strength and abrasion resistance of all-cotton fabrics by about 40-60% under normal treating conditions. Allcotton durable press garments, such as slacks and shirts, have such poor durability that their use is limited. At the present time, the most widely used method for improving tensile strength of cellulosic, durable press fabrics is to use a blend of, say cotton and a polyester. Thus, the durable press qualities are obtained with the resin treated cotton and improved strength is obtained from the polyester.

Although blended, durable press fabrics have satisfactory tensile properties, their abrasion resistance is unsatisfactory. In a durable press blend, frosting and pilling are commonly encountered, and detract from the appearance of the garment. The frosting and pilling are caused by the cotton wearing out of the fabric at a much higher rate than the synthetic, which results in shade changes at points of high wear (frosting) or the accumulation of detritus on the surface of the fabric (pilling).

I have discovered that durable press, cellulosic fabrics can be made which have both improved tensile strength and abrasion resistance. These improvements are achieved by treating the cellulose-containing fabric with a polyisocyanate in a suitable swelling solvent before giving the fabric the standard durable press treatment. The term cellulosic fabric as used herein, and the fabrics suitable for the treatment of this invention, include cotton, rayon and linen, and blends of these fibers with other natural or synthetic fibers. Particularly useful are cotton-polyester blends.

While it is disclosed in US. Pat. No. 2,339,913 that treatment of cellulosic fabrics with polyisocyanates improves the fabric strength it is urged there that the fabric first be treated with water to swell the cellulose, followed by washing out the water prior to treatment with the polyisocyanate. The disclosure of US. Pat. No. 2,339,913 also favors the use of inert hydrocarbon solvents for the polyisocyanate, and somewhat severe heat-curing conditions. More particularly, the preferred curing conditions exceed 2000 degree-minutes and ordinarily run from 5000 to 'ice 10,000 degree-minutes. In addition, there is no disclosure in U.S. Pat. 2,339,913 that the polyisocyanate treatment will work to increase the tensile strength or abrasion resistance of durable press fabrics, and in fact the strength improvement disclosed in US. Pat. 2,339,913 does not survive the curing conditions required for durable press cross-linking. That is, the tear strength of resin treated, durable press fabric having the pretreatment of US. Pat. 2,339,913 is substantially lower than that for untreated fabric, while the tear strength for resin treated, durable press fabric having the polyisocyanate treatment of this invention is comparable in strength to untreated fabric. In addition, the mild curing conditions of this invention result in substantial savings in processing times and processing costs and reduced adverse effects on the treated fabrics.

SUMMARY In summary, this invention is directed to an improved process for preparing durable press, cellulosic fabrics by the pad-dry-cure durable press treatment, the improvement comprising first treating the cellulosic fabric with a polyisocyanate selected from among the alkyl, cycloalkyl, and aryl, di-, triand tetraisocyanates in an organic swelling solvent, and curing the fabric at a temperature between 25 and 250 C. in from 1 to minutes, such that the time-temperature product is between about and about 2000 degree-minutes, the polyisocyanate being present in the solvent at a concentration of from 1 to 50 percent by weight based on the weight of solution, and the polyisocyanate add-on ranging from 0.5 to 20 percent based on the weight of cured fabric. This invention is further directed to the durable press, cellulosic fabrics produced by the improved process of this invention.

The fabrics of this invention are characterized by wrinkle recovery comparable to fabrics which have had conventional durable press treatment alone, while the fabrics of this invention also possess tensile strength and abrasion resistance far superior to conventional durable press fabrics and in fact almost equivalent to untreated cellulosic fabrics.

DESCRIPTION OF THE INVENTION As stated above, this invention is directed to an improved process for preparing durable press, cellulosic fabrics, the improvement comprising treating the fabric with a polyisocyanate in an organic swelling solvent and curing the fabric prior to the standard pad-dry-cure durable press treatment. This invention is further directed to the improved durable press fabrics which are produced by the process of this invention.

Polyisocyanates The polyisocyanates suitable for use in this invention include alkyl, cycloalkyl and aryl, di-, trior tetraisocyanates. The preferred polyisocyanates are diisocyanates having from 2 to 16 atoms between the isocyanate groups and most preferably from 7 to 12 atoms between the isocyanate groups. The following are illustrative of suitable polyisocyanates:

bis- (2-isocyanatoethyl carbonate; bis-(3-isocyanatopropyl)carbonate; bis-(4-isocyanatocyclohexyl)methane; 1,6-hexamethylene diis-ocyanate; 1,2-didecamethylene diisocyanate; 1 ,8-octamethylene diisocyanate; 1,4-diisocyanatomethyl cyclohexane; tolylene-2,4-diisocyanate; 1,4-diisocyanatocyclohexane; 1,4-phenyldiisocyanate; 1,9-nonamethylenediisocyanate;

3 1 -methy1-2,4-diisocyanato cyclohexane 1, 3 -trirnethylenediisocyanate; 1 ,Z-dimethylenediisocyanate; 1,16-hexadecarnethylenediisocyanate; bis- [2- (2-isocy anatoethoxy ethyl] carbonate; a,ot'-diisocyanato-o-xylene; bis- (2-isocyaoethoxy) ethane; bis- Lisoeyanatophenyl methane; 2,4,6-triisocyanato toluene;

and polyisocyanate mixtures such as Kaiser Aluminum and Chemicals NCO120, NCO-10 and NCO-20 having an average of 3.2, 2.3 and 2.6 isocyanate groups per molecule respectively.

The polyisocyanates suitable for use in this invention can be prepared by methods well-known to those. skilled in the art or can be obtained commercially.

Solvents The polyisocyanates of this invention are applied from an organic cellulose-swelling solvent such as dimethyl sulfoxide, dimethyl acetamide, N-methyl pyrrolidone or pyridine. Suitable swelling solvents are those having a swelling index rated as medium or higher as defined by B. L. Porter and R. S. Orr, Textile Research Journal, 159 (1965). The preferred swelling solvent is dimethyl sulfoxide. In addition to the use of these solvents alone, mixtures of these solvents with non-swelling solvents can also be used. For example, the polyisocyanate can be applied to the fabric from a dirnethylsulfoxide solution, or it can be applied from a mixture of dimethyl sulfoxide or N-methyl pyrrolidone and 1,1,1-trichloroethane, perchloroethylene or trichloroethylene. The use of perchloroethylene o rtrichloroethylene or other chlorinated and/ or fluorinated hydrocarbon solvents is desirable because of cost and ease of solvent recovery. One particularly effective mixture is a solution of 5% dimethylsulfoxide in trichloroethylene.

Durable press agents Suitable durable press agents are well known in the art and described in detail in P. K. Shenoy and J. W. Pearce, American Dyestufl' Reporter, 17, May 6, 1968; C. D. Egginton and C. P. Vale, Textile Research Journal, 140, February 1969; B. M. Kopacz and R. M. Perkins, Textile Chemist and Colorist, 1, 80 (1969); and T. A. Calamari et al., Textile Industries, 115, November 1968. Examples of the crosslinking agents which can be used to impart durable press qualities are formaldehyde and methylol derivatives of nitrogen containing compounds such as urea, N,N'-ethylene urea, 4,5-dihydroxy-N,N'- ethylene urea, methyl carbamate, propylene urea, ethyl carbamate, melamines, substituted melamines, triazones, and urons.

Process conditions The polyisocyanates are applied from solutions having a concentration of 1 to 50 percent by Weight of polyisocyanate in solution. The polyisocyanate concentration will usually range from 2 to percent. More concentrated solutions of polyisocyanates can be used depending on the pressure between the nip rollers which governs the fabric pick-up of solution. The polyisocyanate add-on should range from 0.5 to percent based on the fabric Weight. The preferred add-on is 1 to 7 percent. When solvent mixtures are used, the swelling solvent should make up 1 to percent by weight of the solvent mixture. The preferred amount should range from 1 to 20 percent and most preferably from 3 to 10 percent of the mixture. The following is exemplary of suitable polyisocyanate formulations.

Three component polyisocyanate formulation Percent by weight Polyi'socyanate l5 0 Swelling solvent 2-30 Non-swelling solvent 2097 4 Two component polyisocyanate formulation Percent by weight Polyisocyanate 1-50 Swelling solvent 50-99 After the polyisocyanate solution is applied, the fabric is dried to remove the solvent at 25 to 250 C.; temperatures of 50 to 160 C. are preferred. When low-boiling swelling solvents are used, the drying is carried out under pressure in order to raise the fabric temperature to the point where the polyisocyanate and cellulose will react while the cellulose is still swollen by the solvent. The drying time can range from 1 to minutes depending on the temperature. Generally longer, cooler drying periods will be used for batch operations, and shorter, hotter drying periods will be used for continuous operations such as are commonly used in the finishing industry. The following is exemplary of preferred drying times and temperatures.

Drying time, minutes Temperature, C.

Thus it can be seen that the curing conditions for this application are milder than those of the prior art. More specifically the product of the drying times and temperatures of the process of this invention are limited to from about to about 2000 degree-minutes, which results in savings in process costs and reduced adverse effects on the treated fabrics.

After the polyisocyanate curing, the fabric is subjected to a conventional pad-dry-cure durable press treatment as disclosed in the four literature references given hereinbefore. Two typical durable press formulations are as follows:

FORMULATION I Percent Permafresh 183, a 45% aqueous solution of din-rethyloldihydroxyethylene urea sold by Sun Chemical Co. 20 Catalyst X-4, a modified zinc nitrate solution sold by Sun Chemical Co. 4 Velvamine 732, a non-ionic polyethylene emulsion fabric softener sold by Millmaster Onyx Corp. 4

Triton X-100, isooctyl phenyl poleythoxyethanol Fabric treated with a polyisocyanate solution and then with Formula I or H exhibits a high wrinkle recovery angle, a high tear strength and good abrasion resistance.

The following examples illustrate the methods of this invention. The fabric used in these examples, unless otherwise specified, is 80 x 80 cotton print cloth from Testfabn'cs, Inc., Catalog Number 8/400 WM. Parts and percentages in the examples are by weight unless otherwise indicated.

The wrinkle recovery angle is determined using the recovery angle method (AATCC Test Method 661968). A total of 8 warp and 8 fill specimens are measured for each treatment. The reported wrinkle recovery angle (WRA) is the sum of the means for the 8 warp and 8 fill specimens.

The tear strength is determined by the falling pendulum method (Elmendorf) (ASTM Test Method D1424-63).

A total of six warp and six fill specimens are measured for each treatment. The reported tear strength is the sum of the means for warp and fill specimens.

The abrasion resistance as measured by weight loss is determined using the accelerator method (AATCC 93- 1966T). Four specimens are abraded for 3 minutes each at 3600 revolutions per minute with a No. 250 liner for each treatment, and the reported percent weight loss is the mean for the four samples.

EXAMPLE 1 Two 23 x 91 cm. samples of print cloth are padded to 100% pick-up with a by weight solution of bis-(4-isocyanotocyclohexyl)methane in dimethyl snlfoxide. The fabric samples are put on a pin frame and heated at 50 C. for 30 minutes in a forced draft textile curing oven. The add-on of the isocyanate is about 5%. The strips of fabric are removed from the pin frame, and padded to 100% pick-up with Formulation I. The strips are again placed on the pin frame, and dried for 30 minutes at 25 C. The pin frames of dry fabric are then cured for 6 minutes at 160 C. in a forced draft textile curing oven. The cured fabric is run through two wash cycles consisting of one minute in Dnponol RA (alcohol ether sodium sulfate, 0.05%) and sodium carbonate (0.1%) at 43- 49" C. then rinsed 5 minutes at ambient temperature, placed on a pin frame and conditioned for 24 hours at 35-45% relative humidity.

In order to have a comparison with untreated fabric, two strips of the same fabric are washed and conditioned as above. In addition, two further strips of the same fabric are treated with Formulation I as described above to give a standard durable press treatment for comparison. The wrinkle recovery angle (WRA), tear strength and abrasion weight loss data for the above three treat- Two strips of fabric are treated with a 5% solution of bis-(4-isocyanatocyclohexyl)methane in dimethyl sulfoxide according to the procedure of Example 1. The addon of the diisocyanate is about 5%. The fabric is then padded to 100% pick-up with Formulation II. The treated fabric is placed on a pin frame, dried 30 minutes at 25 C. and cured for 6 minutes at 160 C. in a forced draft textile curing oven. The treated fabric is Washed and conditioned as in Example 1. Fabric samples treated only With Formulation II are prepared for comparison. In Table II are summarized wrinkle recovery angle, tear strength and abrasion weight loss data for these treatments. The untreated data are the same as those in Table I.

As can be seen from these examples, the isocyanate treatment produces a significant improvement in tear strength and abrasion resistance over fabric treated with Formulation I or Formulation II alone.

6 EXAMPLE 3 Fabric samples are treated according to Example 1 with a 10% solution of bis-(4 isocyanatocyclohexyl) methane rather than the 5% solution of Example 1. The add-on of the diisocyanate is about 10%. All other treatments and operations are as described in Example 1. Wrinkle recovery angle, tear strength and abrasion weight loss data are summarized in Table III.

TABLE III Treatment: 10% bis-(4-isocyanatocyclohexyl) methane followed by Formulation I:

WRA 281 Tear (g.) 1033 Weight loss (percent) 34 These data in comparison with the Formulation I data in Table I show a significant improvement in tear strength and abrasion resistance.

EXAMPLE 4 Fabric samples are treated according to the methods of Example I with a 1% solution of bis-(4-isocyantocyclohexyl)methane rather than the 5% solution of Example 1. The add-on of the diisocyanate is about 1%. All other treatments and operations are as described in Example 1. Wrinkle recovery angle, tear strength and abrasion weight loss data are summarized in Table IV.

TABLE IV Treatment: 1% bis (4 isocyanatocyclohexyl)methane followed by Formulation I:

WRA 301 Tear (g.) 922 Weight loss (percent) 29 These data in comparison with the Formulation I data in Table I show a significant improvement in tear strength and abrasion resistance.

EXAMPLE 5 Fabric samples are treated according to the methods of Example 1 with a 5% solution of toluene-2,4-diisocyanate in dimethyl sulfoxide in place of the diisocyanate of Example 1. The add-on of the diisocyanate is about 5%. All other treatments and operations are as described in Example 1. Wrinkle recovery angle, tear strength and abrasion weight loss data are summarized in Table V.

TABLE V Treatment: 5% toluene-2,4-diisocyanate followed by Formulation I:

WRA 304 Tear (g.) 920 Weight loss (percent) 42 These data in comparison with the Formulation -I data in Table I show a significant improvement in tear strength and improved abrasion resistance.

EXAMPLE 6 Treatment: 5% hexamethylene diisocyanate followed by Formulation I:

WRA 310 Tear (g.) l n 9 64 Weight loss (percent) 41 These data in comparison with the Formulation I data in Table I show a significant improvement in tear strength and improved abrasion resistance.

The following diisocyanates when substituted for the diisocyanate of Example 6 give similar results.

Percent Octamethylene diisocyanate in dimethyl sulfoxide 1,4-(isocyanatomethyl) cyclohexane in dimethyl sulfoxide 5 Bis-(4-isocyanatophenyl) methane in N-methyl pyrrolidone 5 EXAMPLE 7 TABLE V11 Treatment: 5% dodecamethylene diisocyanate followed by Formulation:

282 Tear (g.) 1042 'Weight loss (percent) 23 These data in comparison with the Formulation I data in Table I show a significant improvement in tear strength and abrasion resistance.

By substituting 5% 1,16-hexadecamethylene diisocyanate in dimethyl sulfoxide for the diisocyanate solution in Example 7 results are obtained comparable to those in Table VII.

EXAMPLE 8 Fabric samples are treated according to the methods of Example 1 with a 5% solution of bis-(2-isocyanatoethyl)carbonate in dimethyl sulfoxide in place of the diisocyanate of Example 1. The add-on of the diisoeyanate is about 5%. All other treatments and operations are as described in Example 1. Wrinkle recovery angle, tear strength and abrasion weight loss data are summarized in Table VIII.

TABLE VIII Treatment: 5% bis-(Z-isocyanatoethyl)carbonate followed by Formulation I:

WRA 290 Tear (g.) 1038 Weight loss (percent) 21 These data in comparison with the Formulation I data in Table I show a signicant improvement in tear strength and abrasion resistance. 7

EXAMPLE 9 Treatment: 5% bis (2 isocyanatoethyl)carbonate followed by Formulation I:

WRA 282 Tear g.) Weight loss (percent) These data in comparison with the Formulation I data in Table I show a significant improvement in tear strength and abrasion resistance.

8 EXAMPLE 10 Fabric samples are treated according to the methods of Example 9 with a 5% solution of bis-(2-isocyanatoethyl)carbonate in N-methyl pyrrolidone in place of the dimethyl acetamide of Example 9. The add-on of the diisocyanate is about 5%. All other treatments and operations are as described in Example 1. Wrinkle recovery angle, tear strength and abrasion weight less data are summarized in Table X.

TABLE X Treatment: 5% bis (2 isocyanatoethyl)carbonate followed by Formulation I:

WRA 279 Tear (g.) 963 Weight loss (percent) 33 These data in comparison with the Formulation I data in Table I show a significant improvement in tear strength and abrasion resistance.

EXAMPLE 11 Fabric samples are padded to about pick-up with a 5% solution of bis(4-isocyanatocyclohexyl)methane in dimethyl sulfoxide. The fabric samples are placed on a pin frame and heated at 121 C. for 3 minutes in a forced draft textile curing oven. The fabric is then treated with Formulation I and Washed as described in Example 1. The wrinkle recovery angle, tear strength and abrasion weight loss data are summarized in Table XI.

TABLE XI Treatment: 5% bis-(4-isocyanatocyclohexyl)meth ane followed by Formulation I:

WRA 294 Tear (g.) 1080 Weight loss (percent) 37 These data in comparison with the Formulation I data in Table I show a significant improvement in tear strength and improved abrasion resistance.

EXAMPLE 12 Fabric samples are treated according to the methods of Example 1 with a 5% solution of bis(4-isocyanatocyclohexyl)rnethane is dimethyl acetamide in place of the dimethyl sulfoxide. The add-on of the diisocyanate is about 5%. All other treatments and operations are as described in Example 1. Wrinkle recovery, tear strength and abrasion weight loss data are summarized in Table XII.

TABLE XII Treatment: 5% bis-(4-isocyanatocyclohexyl)methane followed by Formulation I:

WRA 284 Tear (g) 1074 Weight loss (percent) 29 These data in comparison with the Formulation I data m Table I show a significant improvement in tear strength and abrasion resistance.

EXAMPLE 13 Fabric is padded to about 100% pick-up with a solution consisting of 3.5% bis(4-isocyanatocyclohexyl)methane, 5% dimethyl sulfoxide and 91.5% perchloroethylene. The fabric is dried on a pin frame at 50 C. for 30 minutes in a forced draft textile curing oven. Formulation I is then applied and the fabric treated further as described in Example 1. Wrinkle recovery angle, tear strength and abrasion resistance data are summarized in Table XIII.

TABLE XIII Treatment: 3.5% bis-(4-isocyanatocyclohexyl)methane+5% dimethyl sulfoxide+9l.5% perchloroethylene followed by Formulation I:

WRA 291 Tear (g.) 804 Weight loss (percent) 44 These data in comparison with the Formulation I data in Table I show improvement in tear strength and abrasion resistance.

EXAMPLE 14 TABLE XIV Treatment: 3.5% bis-(2-isocyanatoethyl)carbonate +5% dimethyl sulfoxide+91.5% trichloroethylene followed by Formulation I:

WRA 279 Tear (g.) 1010 Weight loss (percent) 24 These data in comparison with the Formulation I data in Table I show a significant improvement in tear strength and abrasion resistance.

EXAMPLE 15 A sample of 65/35 Dacron polyester/cotton shirtiug (Testfabrics, Inc., Cat. No. 8/7406) is padded to 100% pick-up with a solution consisting of 3.5% bis-(2- isocyanatoethyl)carbonate, 5% dimethyl sulfoxide and 91.5% trichloroethylene. The fabric is dried on a pin frame at 50 C. for 30 minutes in a forced draft textile curing oven. Formulation I is then applied and the fabric is treated further as described in Example 1. Another piece of fabric is given the standard durable press treatment of Example 1 with Formulation I to serve as a comparison with the bis-(Z-isocyanatoethyl)carbonate treated fabric. An additional piece of fabric is given the washing treatment of Example I alone to also serve as comparison with the two above treatments.

The wrinkle recovery angle and abrasion weight loss data (5 minutes at 3600 revolutions per minute with No. 250 grit) are given in Table XV.

1. An improved process for preparing a durable press cellulosic fabric by the pad-dry-cure durable press treatment, the improvement comprising first treating the cellulosic fabric with an alkyl or cycloalkyl diisocyanate in 10 an organic swelling solvent, and curing the fabric at a temperature between 25 and 250 C. in from 1 to 80 minutes, so as to maintain the time-temperature product between about 150 and about 2000 degree-minutes, said diisocyanate being present in the solvent at a concentration ranging from 1 to 50 percent by weight, and the diisocyanate add-on ranging from 0.5 to 20 percent based on the weight of the dried treated fabric; then treating the fabric with a durable press formulation comprising dimethyloldihydroxyethyleneurea as the durable press agent.

2. The process of claim 1 wherein the diisocyanate contains from 2 to 16 atoms between the isocyanate groups.

3. The process of claim 1 wherein the diisocyanate contains from 7 to 12 atoms between the isocyanate groups.

4. The process of claim 1 wherein the organic swelling solvent is selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, N-methyl pyrrolidone, pyridine and solvent mixtures containing from 1 to 30 percent by weight of one of these organic swelling solvents.

5. The process of claim 1 wherein curing is carried out at a temperature between 50 and 121 C. for from 2.0 to minutes.

6. The process of claim 1 wherein the concentration of the diisocyanate in the solvent is between 2 and 10 percent.

7. The process of claim 1 wherein the polyisocyanate add-on is between 1 and 7 percent.

8. The process of claim 4 wherein the organic swelling solvent is dimethyl sulfoxide.

9. The process of claim 4 wherein the solvent mixtures contain from 3 to 10 percent by weight of one of the organic swelling solvents.

10. The process of claim 4 wherein the diisocyanate is present in the solvent at a concentration ranging from 1 to 10 percent by weight, and the solvent is a mixture of 1 to 20% organic swelling solvent and to 99% chlorinated hydrocarbon.

11. The process of claim 1 wherein the diisocyanate is bis(4 isocyanatocyclohexyl)methane, and the organic swelling solvent is dimethyl sulfoxide.

12. A durable press cellulosic fabric prepared by the process of claim 1.

References Cited UNITED STATES PATENTS 3,097,050 7/1963 HurWitz et a1. 117139.4 X 3,190,716 6/1965 Gordon 8116.3 X 3,007,763 11/1961 Adams 8116.2 2,731,364 1/1956 Reibnitz et al. 117139.4 X 3,528,849 9/1970 Vullo et al 117139.5

WILLIAM D. MARTIN, Primary Examiner T. G. DAVIS, Assistant Examiner US. Cl. X.R.