GB2169495A - Swab for cleanroom environment - Google Patents

Abstract

A swab 10 for a cleanroom environment comprises a stick 12 of a hard thermoplastic material such as polyethylene or polypropylene and a head 14 formed from non-woven, absorbent material 16 that is wound around one end of the stick. The material which may be cellulosic paper or a cellulosic polyester paper, has a low content of solvent-extractable matter, a low level of metallic ions, and a low tendency to generate particles when used. <IMAGE>

Description

SPECIFICATION Swab for cleanroom environment Tfa reserttinvention relates to a swab for a cleanroom envinonment. In particular, the present invention relatestoa swab having wiping material mounted to one end of an elongate stick for use in a cleanroom environmentwherein there are require ments for a low level of particle generation from the wiping material, and wherethewiping material must have low levels of metallic ions and must be low in matter removable with organic solvents.

There is alwaysthe need for a product that can be used for cleaning parts of equipment and for absorbing spills of liquid. However, the problem becomes compounded when that product must be used in a clean room. Cleanrooms are necessaryto manufacture properly and/or assemble certain devices, such as integrated circuits and high precision, miniaturized machines, orforthe proper operation of sensistive equipment, such as computer disk drives. Sometimes, the concerns in a cleanroom also involve the necessity for maintaining the sterility of both the air and the equipment located in thatcleanroom.

A problem, however, arises when it is necessary to use wiping materials in a cleanroom. Most conventional materials cannot be used because they tend to deposit contamination on theequipmentwhen they are used. What is needed is a wiper that has a low level of particle generation, can sorb a relatively large amount offluids and ata quick rate, has low levels of metallic ions, and is low in matter removable with organic solvents. Particle generation refers to the release of particles from the wiper as the wiper is used.

Generally, when the swab is wetted, the forces that hold the particles to the surface ofthe wiper are dissipated by the presence ofthe liquid, and a greater number of particles are available for release. Addi tionally, one ofthe primary functions of swabs isto soak up spills rapidly. Finally, since the wiper is often used with organic solvents for cleaning parts, the wiper must be low in matter that is removable by such solvents because that matter represents an impurity and is potentially harmful to the device being manufactu red.

While there are many swabs in the marketplace today, virtually all ofthem trace their lineage notto the cleaning of devices in a cleanroom, where particulate or other contamination is critical, but rather to medical or industrial uses where sensitivity to small amounts of debris are unimportant.Consequently, most conventional swabs are manufactured solely with view toward maximizing absorbency, convenience or ease of manufacture, and not toward minimizing the unwanted deposition of debris on the object being swabbed Clea itroora considerations mandate that attention mube paidto the choice of the wiping material usedto form the swab head and to the stick to which the swab head is attached because they can be a source of contamination. Also, the means for attaching the swab head (e.g. an adhesive) to the stick is important so that that means does not generate further contamination.

There is also the consideration of the costforthe materials. The total cost is a function of the cost of the particular material being used and a function of the absorbency of that material.

Many wiping materials have been investigated regarding theircompatibilityfor use in a cleanroom.

Cotton and most woven materials shed particles to an excessive degree and are therefore totally unacceptable. In addition, polyesterfiberswabs have the same problem of too much shedding. Swabs made from foam, while perhaps the best with respect to absorbency, suffer because of the large amount of organic matter which is extractable by the vast array of liquids that are present in manufacturing and fabrication area.

There are several patents disclosing swabs having some ofthe individual features ofthe present invention. For example, the U.S. Patent No. 3,542,025 to Gustafson discloses a swab formed from a non-woven material that is wound around an applicator stick. U.S.

Patents Nos. 3,368,549 to Barr et al, 2,842,790 to Castelli, and 3,443,562 to Gustafson disclose swab applicators in which the stick has barbs at the end to catch the material forming the swab. U.S. Patent No.

3,591,885 to Fritzen discloses a swab having a wad of fibrous material secured to the stick with a length of heat shrinkable synthetic polymeric material. Howev or for one reason or another discussed above, the swabs disclosed in these patents would be unacceptable in a cleanroom environment.

The present invention was designed from the position of selecting the material for the head ofthe swab from amongst the cleanest wiping materials available, yet materials that are still absorbent enough both in total quantity and in rate of absorption so as to be efficient.

Suitably, the present invention utilizes very clean sheets of specially made wiping materials that have the best combinations offeaturesfor making the swab head. These features include a low level of particulate debris, a low level of ionic constituents, and a low level of organic and inorganic extractables. Furthermore, the stick to which the swab head is attached was chosen only from materials that do not shed gross amounts of particulate debris (e.g., wood) or are soluble in fluids commonly used in a cleanroom environment (e.g. polystyrene and nylon). Accordingly, a stable, inert material was chosen that still had sufficient rigidity asto provide afunctional swab.

Furthermore, the present invention is economically competitive because of the selected materials, the shapes of the selected materials and the method in which the swab is constructed.

Accordingly, the invention according to one embodiment ofthe present invention comprises a swab that is usable in a cleanroom environment. The swab is comprised of a stick of rigid plastic material and a head made from a pice of wiping material that is wound around one end ofthe stick. The head material has a low level of particle generation, has a low level of metallic ions, and is low in matter removable with solvents.

Otherfeatures, advantages, and improvements of the present invention are set forth in orwill be apparent from the detailed description of the presently preferred embodiments set forth hereinbelow.

In the accompanying drawings showing preferred embodiments: Fig. 1 is an elevational viewof a swab according to the present invention.

Fig. 2 is a plan view of one shape of material that is wound around the swab stickto form the swab head.

Fig. 3 is a plan view of another embodiment of the unwound material used to form the head ofthe present invention.

Fig. 4 is an elevational view of a first embodiment of a swab stick.

Fig. 5 is an elevational view of a second embodi ment of a swab stick.

Fig 6 is an elevational view of a second embodi mentofaswabaccordingtothe present invention with some parts removed.

With reference now to thefigures wherein like elements are represented by the like numerals gthroughoutthe several views, and wherein similar elements ofdifferentembodiments are represented by numerals havingthe same lasttwo digits, a plurality of embodiments of swabs and swab compo nents according to the present invention are depicted.

With particularreferenceto Fig. a swab 10 according to a first embodiment is depicted. Swab f0 is comprised of a stick 12 and a head 14. Head 14is comprised of an elongate sheet of material 1 6 that is wound around stick 12. Material 16 has one end 18 (see Fig. 2) that is attached with means described below to one end of stick 12. The other end orthefree end 20 of material 16 is secured with a retaining means 22 to stick 12. Retaining means 22 is comprised of an annular collar 24 made of heatshrinkable material that encircles stick 12 and has one end thereof overlapping material free end 20. Collar 24 is locked in place by being shrunken by applied heat.

Material 16 having a shape according to a first embodiment is depicted in Fig. 2 in the unwound, flat state Material 16 in this state has a straight bottom edge 26 and a stra ig ht first end edge 18 that is generally orthogonal to bottom edge 26. Material 16 also has a top edge 28 with an overall arcuate shape thatterminates in a pointwhich forms free end 20.

Generally, the shape of top edge 28 is comprised of a first portion 30 that has a gradual, S-shaped upward slope terminating in a rounded peak 32and a second portion34that has a steep, rounded downward slope terminating in free end 20.

Material 16 is preferably madefrom a paperor non-woven material, such as "LABX" or"DURX" papers produced bythe Berkshire Paper Company.

"LABX" paper has a composition of natural fibers of abaca and wood togetherwith an inert binder. The "DURX" paper has a composition of 40% polyester and 60% wood fiber. Thus, both products are made from cellulosic materials, the "LABX" paper being 100% cellulosic material and the "DURX" paper being only partly cellulosic material.

Boththe"LABX"paperandthe"DURX" paper have the important characteristics of cleanliness, absorben cy, and purity. Cleanliness relates to low levels of particle generation. Onetestforcleanliness measures howmanyparticlesgreaterthan0.5m .003 10-6can be released bythewiper.Thetest is done on wipers in a wetted state because mostwipers get wet during use, and because the forces that hold particles to surfaces dissipate in the presence of a liquid. The characteristic of absorbency is important because of primary function of swab 10 isto soak upfluids.Atest for absorbency assesses the total amoujitoffluid the material can sorb.The results can be reported both per unitarea (in ce H20 persquare meter) or per unit weight (in cc H2O per gram). Another important feature of absorbency is the rate at which the liquid is absorbed. One measure of rate isthetime required for a wiperto sorb one-half of its total capacity and is called a half-sorption test. Finally, the material must be "pure." As used herein, purity means thatthe material has low levels of metallic ions such as sodium, potassium, calcium and magnesium. In addition,the material is low in matter extractable with solvents.This is important because such matter can be a potentially harmful contaminantwhich might not be removed by water, butwhich would be removed by certain fluids that are used in a cleanroom environment Atestfor metallic ions determines the total burden ofthe particular ion and is reported in parts per million. The testforextractables measuresthequanti- ty of matter soluble in the organicsolvent 1,1 ,1- trichloroethane. The extractable test is expressed both perunitarea and per unit mass.

The aforementioned "LABX" paper has a very low level of particlegeneration and is made of 100% natural cellulosicfibers. The paper has good sorptive captivity and a rapid rate of absorbency. The "DURX" paper is a cloth-like paperthat is durable, absorbent, low in particles and structurally strong. The results of the aforementioned tests on thesetwopapersare reported in Table I. The difference between the two reported "LABX" papers is the basis weight.

In order to provide a comparison between the "LABX" and "DURX"papers in the presentinvention and other commercial and priorart materials, the results of tests of other wiping materials have also been provided in Table I along generic classifications.

For example, while it can be seen that a reasonably low percentage of extractables is offered by a woven cotton fabric, that same fabric has an unacceptably high amountofparticle generation. On the other hand, the "LABX" and "DURX" papers have bettertest results for extractables and are far superior in terms of particle generation.

With reference now to Fig. 3, a material 116 is depicted having a different shape from material 16. In general, material 116 has the same, truncated first end 118that is orthogonal to a bottom edge 126, but bottom edge 126 is comprised of two portions. A first portion 136 of bottom edge 126, comprises a straight line and a second portion 138 comprises an arcuate linethatterminates in free end 120 and forms a concave portion 140 of material 116. Consequently, the free end 120 of mate rio 116 is located below the bottom edge 126. Material 116 has a top edge 128 that is similar in shape to top edge 28 of material 16 depicted in Fig. 2.

Thetotalarea orsize of metenals 16 and 116 is determined by the desirable absorbency ranges and thetotal length of stick 12. Commercial swabs generally fall into two absorbency ranges, a first range of 50to 1 microliters per swab, and second range of 700 to 900 microliters per swab. Thus, if it is desired to have a swab with a small head 14fitted on a relatively small stick 12 of, for exam ple, 50 mm, and it was further desired to have a swab with a capacity of approximately 100 microliters, then approximately 120. square centimers of"LABX" 124 material is required, or 98 square centimers of "LABX" 170 material is required, or about 35 square centimeters of "DURX" 670 material is required.Therefore it can be seen that by using a material having a greater absorbency the total amount of material needed to absorb a spill of a certain quantity of liquid is decreased. Conversely, by determining the amount of spill to be absorbed by one swab, the size of the swab material can be determined based on the absorbency characteristics forthat particular material.

With reference now to Fig. 4, a first embodiment of stick 12 is depicted. Stick 12 has a generally circular cross section taken along its length and is comprised of a tapered tip 150 integrally connected to a shaft 152.

Shaft 152 has a length that depends upon the desired overall length of swab 10. For example, stick 12 can have the aforesuggested length of 50 mm, which would be a short swab, or could have a length as long as 150 mm, which would be a long swab. A preferred length oftip 150 is 12.5 mm. Mounted nearthe end of tip 150 area plurality of radially extending barbs 154.

Barbs 154 comprise the means for attaching a first end of material 16to stick 12. Thus, it can be seen with respect to material 16 depicted in Fig. 2 and stick 12 depicted in Fig. 4, that when material 16 is wound about stick 12, first end 18 is grabbed by barbs 154 and attached to tip 150. Preferably, the width of first end 18 is determined by the length of tip 1 50 that is covered with barbs 154.

Material 16 having the shape depicted in Fig. 2 is applied or wound onto stick 12 as depicted in Fig. 4 as follows. Depending upon the desired spiral angle, which is determined by the total length of bottom edge 26 andthe height of peak 32, first end 18 is aligned at an appropriate angle to the axis of stick 12 such that end 18 is caught by barbs 154. In addition, material 16 is applied such that top edge 28 is closest to the end of tip 150. The hPight of peak and the slope offirst portion 30 is determined by the amount of material that is desired to overlap at the end of tip 150.For example, if it is desired that at least two turns or wraps of material 16 be made at tip 150, then the slope of first portion 30 with respect to bottom edge 26 is equal to the angle of wrap and the length of first portion 30 is at least twice the circumference of tip 150.

On the other hand, free end 20 terminates in a small tail portion which can be readily attached by collar 24 to stick 12 by after material 16 has been wound thereon.

Fig. 5 depicts a further embodiment of a swab stick denoted 212. Stick 12 has a means for attaching two first ends of two pieces of material 26 at each end of stick 212 for making two swab heads 14. In the embodiment of Fig. 5, the attaching means is comprised of a slot 213. Also, stick 212 does not have tapered tips as depicted in Fig. 4 because additional thickness ofthe stick 212 is required.

Stick 12 and 212 are preferably made from hard thermoplastic materials such as polypropylene or polyethylene. Preferably, the plastic is not colored.

Polyethylene and polypropylene plastics are nonabsorbent and do not readily deposit material when used. Furthermore,theyare resistant to chemical attacks by most liquids being sorbed.

With reference to Fig. 6, a swab 310 according to a further embodiment is depicted. Swab 310 is similar to swab 10 and is comprised of a stick 312 having a tapered tip 350 and a head 314. However, the difference between swab 310 and swab 10 of Fig. 1 is that head 314 is bulbous and narrows in thickness of the wrap up to free end 320. Free end 320 can be retained to stick 312 by a collar (not shown) similar to collar 22 depicted in Fig. 1. On the other hand, head 14 of swab 10, as can be seen in Fig. 1, is more cylindrical and thus can be used over a wider area.

The present invention has now been described with respectto several embodiments thereof having the aforedescribed advantages over the prior art. However, otherfeatures and other advantages ofthe present invention would be readily apparent to one of ordinary skill in the art.

T A B L E I Materials In Invention Conventional Materials A B C D 9 F -G K I J K L WEIGHT Basis Wt (g/m) 12.3 17.0 67.0 21.0 69.0 22.0 85.0 37.0 44.5 164 170 155 CLEANLINESS Particle Generation ( > 0.5 m) 0.44 0.48 2.8 12 30 0.79 3.5 0.44 0.66 22 4.1 17 (No. x 10-6) PURITY Sodium (ppm) 100 150 46 120 110 370 51 1800 97 64 410 12 Potassium (ppm) 27 18 9.4 5.9 14 8.7 1.6 19 11 12 20 0.53 Calcium (ppm) 1100 730 460 1200 280 350 7.9 1.0 19 170 45 6.6 Magnesium (ppm) 420 90 45 82 170 51 1.1 6.4 2.1 52 2.2 3.3 Extractables (1, 1, 1-trichloroethane) % 0.051 0.11 0.051 0.23 0.030 1.4 3.3 2.7 2.2 0.22 0.13 0.11 (g/m) 0.0063 0.019 0.034 0.048 0.021 0.29 2.7 1.0 0.96 0.37 0.22 0.17 ABSORBENCY Total (ccH20/m) 79.7 102 275 105 338 69.0 366 194 495 310 476 624 Specific (ccH2O/g) 6.5 6.0 4.1 5.0 4.9 3.3 4.3 5.3 11 1.9 2.9 4.0 Time to Half-Sorption (seconds) 20 20 4 400 1 300 13 80 600 5 5 3 MATERIALS A "LABX" 124 (Cellulosic) B "LABX" 170 (Cellulosic) C "DURX" 670 (Cellulose - Polyester) D Conventional (Cellulosic) E Conventional (Cellulosic) F Conventional (Cellulose - Polyester) G Non - woven Polypropylene H Non - woven Nylon I Polyurethane Foam J Woven Cotton K Knitted Nylon LKnitted Polyester

Claims (12)

1. A swabfor a cleanroom environmentcomprising: an elongate stick of a hard plastics material; and a wiping material wound around one end of said stick and comprising a piece of non-woven, absorbent material having a low level of metallic ions, a low tendencyto generate particles, and low in extractable matter.

2. A swab as claimed in claim 1 wherein said wiping material is made from cellulosicfiber.

3. A swab as claimed in claim 2 wherein said wiping material is madeentirelyfrom cellulosicfibers than can include abaca fibers and wood fibers.

4. Aswab as claimed in claim 2wherein said wiping material is made from a combination of cellulosicfibers and a polyester material.

5. Aswab as claimed in any one ofthe preceding claimswhereinsaidwiping material has a relatively high rate of absorbency of between about4seconds to about 20 seconds to half-sorption.

6 A swab as claimed in any one of the preceding claims wherein the total burden of metallic ions of said wiping material is between about 500 ppm to about 1700 ppm.

7. A swab as claimed in claim 6 wherein the combined burden of sodium and potassium ions is between about 50 ppm to about 175 ppm.

8. A swab as claimed in any one of the preceding claimswhereinthe number of particles having a size greaterthan 0.5 m x 10-6 generated per square meter of wiping material is between about 0.4 x 106to about3 x 106.

9. Aswab as claimed in any one ofthe preceding claims wherein the quantity of matterin said wiping material that is soluble in 1,1,1 -trichloroethaneis between about 0.05 percentofa unitareato about 0.15 percent of a unitarea or between about 0.0063g/m2to about0.04g/m2.

10. A swab as claimed in anyoneofthe preceding claims wherein said stick is a solid piece of material.

11. Aswab as claimed in claim 10 wherein said material is polypropylene ora polyethylene.

12. Aswabforacleanroom environmentsubstantially as described herein with reference to the accompanying drawings.