BRIEF DESCRIPTION OF THE DRAWINGS
Various advantages are apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:
FIGS. 1A, 2A, and 3A are schematic top views of substrates for use in a cleaning wipe.
FIGS. 1B, 2B, and 3B are schematic top views of cleaning wipes incorporating polyisobutylene at the surface of the substrate of the cleaning wipes.
FIGS. 4A, 5, 6, and 7A are schematic side views of cleaning wipes incorporating polyisobutylene at the surface of the substrate of the cleaning wipes.
FIGS. 4B, 7B, and 7C are schematic side views of cleaning wipes incorporating polyisobutylene distributed through the bulk mass of the cleaning wipes.
FIG. 8 is a flow chart describing a method of manufacturing a cleaning wipe according to certain embodiments disclosed herein.
FIG. 9 is a photomicrograph of the surface of a typical stainless steel coupon used to test cleaning wipes.
FIGS. 10-13 are plots of test results of cleaning wipes.
DETAILED DESCRIPTION
Described herein are various embodiments of a cleaning wipe and methods of making cleaning wipes. FIG. 1A is a schematic representation of the top view of a substrate 10 for use in a cleaning wipe. The substrate 10 has a front surface 12. The substrate 10 is a fabric that includes random loop micro fibers 14. In some embodiments the micro fibers 14 are 20 μm-diameter cellulose fibers. FIG. 1B is a schematic top view representation of a cleaning wipe 20. The cleaning wipe 20 includes a substrate 10 and also includes polyisobutylene 22 disposed at the front surface 12 of the substrate 10.
As used herein, polyisobutylene (or “PIB”) refers to any polymer of isobutylene. It is also sometimes referred to as butylene or as polybutene. It is to be understood that the term “front surface” is used herein to refer to a surface of a substrate at which polyisobutylene is disposed, and the term is not intended to connote an orientation of the substrate. The term “disposed at” as used herein refers to a configuration where the polyisobutylene is either (a) disposed on the front surface or (b) is disposed within the substrate (e.g., among fibers comprising the substrate) at locations just below the front surface or (c) is disposed both on the front surface and within the substrate at locations just below the front surface. For example, referring to FIG. 1A, polyisobutylene 22 may be disposed at front surface 12 by either (a) being disposed on the front surface 12 of substrate 10 or (b) being disposed within the substrate 10 at locations just below the front surface 12 or (c) by being disposed both on the front surface 12 and within the substrate at locations just below the front surface 12. In some embodiments polyisobutylene is substantially uniformly distributed within the fibers of the substrate. For example, referring to FIG. 1A, polyisobutylene 22 may be substantially uniformly distributed within the random loop micro fibers 14 of the substrate 10.
In some particular embodiments the distribution of the polyisobutylene 22 is substantially uniform across the geometric plane established by the front surface 12. It is to be understood that the random loop micro fibers 14 in FIGS. 1A and 1B are stylistically depicted in a specific geometric pattern but in practice the orientation and layout of the random loop micro fibers 14 may vary from this depiction. Furthermore, it is to be understood that the polyisobutylene 22 in FIG. 1B is stylistically depicted as discrete deposits but in practice depositions may vary in morphology, ranging from discrete deposits to substantially uniform films.
FIG. 2A is a schematic representation of the top view of a substrate 30 for use in a cleaning wipe. The substrate 30 has a front surface 32. The substrate 30 is a cheesecloth fabric that includes woven cotton fibers 34. In some embodiments the woven cotton fibers 34 are 50 μm-diameter cellulose fibers that are spaced ˜50 μm apart. Cheesecloth with fibers spaced more than about five μm apart is referred to herein as open-weave cheesecloth. FIG. 2B is a schematic top view representation of a cleaning wipe 36. The cleaning wipe 36 includes substrate 30 and also includes polyisobutylene 22 disposed at the front surface 32 of the substrate 30. In some particular embodiments polyisobutylene (e.g., 22) is substantially uniformly distributed within the fibers (e.g., 34) of the substrate (e.g., 30). In some particular embodiments the distribution of the polyisobutylene 22 is substantially uniform across the geometric plane established by the front surface 32. It is to be understood that the woven cotton fibers 34 in FIGS. 2A and 2B are stylistically depicted in a specific geometric pattern but in practice the orientation and layout of the woven cotton fibers 34 may vary from this depiction. Furthermore, it is to be understood that in practice the polyisobutylene 22 in FIG. 2B is stylistically depicted as discrete deposits but in practice depositions may vary in morphology, ranging from discrete deposits to substantially uniform films.
FIG. 3A is a schematic representation of the top view of a substrate 40 for use in a cleaning wipe. The substrate 40 has a front surface 42. The substrate 40 is a hydro-entangled micro fiber cloth that includes densely packed cellulose and polyester fibers 44. In some embodiments the cellulose and polyester fibers 44 are approximately 20 μm in diameter. FIG. 3B is a schematic top view representation of a cleaning wipe 46. The cleaning wipe 46 includes substrate 40 and also includes polyisobutylene 22 disposed at the front surface 42 of the substrate 40. In some embodiments polyisobutylene (e.g., 22) is substantially uniformly distributed within the fibers (e.g., 44) of the substrate (e.g., 40). In particular embodiments the distribution of the polyisobutylene 22 is substantially uniform across the geometric plane established by the front surface 42. It is to be understood that the cellulose and polyester fibers 44 in FIGS. 3A and 3B are stylistically depicted in a specific geometric pattern but in practice the orientation and layout of the cellulose and polyester fibers 44 may vary from this depiction. Furthermore, it is to be understood that in practice the polyisobutylene 22 in FIG. 3B is stylistically depicted as discrete deposits but in practice depositions may vary in morphology, ranging from discrete deposits to substantially uniform films.
FIG. 4A depicts a schematic side view of cleaning wipe 50. The cleaning wipe 50 includes a substrate 52 made of fibers 54. The fibers 54 may be random loop micro fibers (e.g., 14 in FIGS. 1A and 1B), or woven cotton fibers (e.g., 34 in FIGS. 2A and 2B), or cellulose and polyester fibers (e.g., 44 in FIGS. 3A and 3B) or other fibers. Substrate 52 has a front surface 56 and an opposing back surface 58 and a bulk mass 60 between the front surface 56 and the back surface 58. The bulk mass 60 includes the fibers 54 and interstitial spaces 62 between fibers 54. The interstitial spaces 62 are an example of a plurality of voids in a bulk mass (e.g., 60). The cleaning wipe 50 includes polyisobutylene 22 disposed at the front surface 56 of the substrate 52. The polyisobutylene 22 may be deposited at the front surface 56 of the substrate 52 by spraying, rolling, brushing, or using other manufacturing techniques. The substrate 52 is an example of a porous substrate. The overall thickness 64 of substrate 52 is typically between 100 μm and a 10 mm. The maximum value for thickness 64 is generally limited, if at all, by design parameters such as the desired mechanical flexure of substrate 52 that are not related to the cleaning effectiveness of the front surface 56. FIG. 4A illustrates a configuration where the polyisobutylene 22 is disposed at the front surface 56 of the substrate 52. In this configuration the polyisobutylene 22 is disposed within the substrate 52 (i.e., among the fibers 54), at locations just below the front surface 56 to a depth 66 that is generally less than about 20 percent of the thickness 64 of the substrate 52.
FIG. 4B depicts a schematic side view of cleaning wipe 70. The cleaning wipe 70 includes the substrate 52 made of fibers 54 used in the cleaning wipe 50 of FIG. 4A. In the embodiment of FIG. 4B the cleaning wipe 70 includes polyisobutylene 72 that is disposed at the front surface 56 of the substrate 52 and the polyisobutylene 72 is further distributed substantially uniformly through the bulk mass 60 of the substrate 52.
FIG. 5 depicts a schematic side view of cleaning wipe 80. The cleaning wipe 80 includes a substrate 82 made of a micro porous sheet 84. Substrate 82 may have a thickness 86 ranging from less than a millimeter to several centimeters or so. In some particular embodiments the thickness 86 is about half a millimeter. The maximum value for thickness 86 is limited, if at all, by design parameters such as the desired mechanical flexure of substrate 82 that are not related to the cleaning effectiveness of the front surface 90 of cleaning wipe 80. The substrate 82 is an example of a porous substrate. In the embodiment of FIG. 5 the cleaning wipe 80 includes polyisobutylene 88 that is disposed at the front surface 90 of the substrate 82. Substrate 82 is micro porous (having voids much smaller than the interstitial spaces 62 of substrate 52 in FIG. 4A), and the depth 92 of penetration of polyisobutylene 88 from front surface 90 is in this embodiment about five percent of the thickness 86 of substrate 82. However, the five percent penetration of the polyisobutylene 88 is still regarded as a configuration where polyisobutylene is disposed at the front surface (e.g. 90) of the substrate (e.g., 82).
FIGS. 6, 7A, 7B, and 7C depict schematic side views of cleaning wipes made in various configurations from foam material. Such foam material includes foams made from polyethylene, polyurethane, polyvinyl chloride, and similar materials. Cleaning wipes depicted in FIGS. 6, 7A, 7B, and 7C have top views analogous to top views of cleaning wipes depicted in FIGS. 1B, 2B, and 3B.
FIG. 6 depicts a schematic side view of cleaning wipe 100. The cleaning wipe 100 includes a substrate 102 made of closed cell foam 104. Substrate 102 may have a thickness 106 ranging from about a millimeter to several centimeters or so. In some particular embodiments the thickness 86 is about half a millimeter. The maximum value for thickness 106 is limited, if at all, by design parameters such as the desired mechanical flexure of substrate 102 that are not related to the cleaning effectiveness of the front surface 108 of the cleaning wipe 100. Substrate 102 has a back surface 110 opposing the front surface 108 and a bulk mass 112 between the front surface 108 and the back surface 110. Closed cell foam 104 includes cells 114 that are substantially unopened to an exterior surface and includes cells 116 that are open to an exterior surface (e.g., open to the back surface 110 for the closed cells 116 specifically identified in FIG. 6). The cells 114 and 116 are an example of a plurality of voids in a bulk mass (e.g., 112). The substrate 102 is an example of a porous substrate.
In the embodiment of FIG. 6 the cleaning wipe 100 includes polyisobutylene 120 that is disposed on the front surface 108 of the substrate 102 and polyisobutylene 122 that is disposed on closed cell 124 that is open to front surface 108. In view of the pathway from closed cell 124 to the front surface 108, the polyisobutylene 122 is considered to be disposed on the front surface 108.
FIG. 7A depicts a schematic side view of cleaning wipe 130. The cleaning wipe 130 includes a substrate 132 made of open cell foam 134. Substrate 132 has a front surface 136 and an opposing back surface 138 and a bulk mass 140 between the front surface 136 and the back surface 138. The open cell foam 134 includes a plurality of cells 142, and substantially all of the cells 142 in open cell foam 134 have an open inter-cellular pathway to an exterior surface (e.g., to front surface 136 or to back surface 138). The cells 142 are an example of a plurality of voids in a bulk mass (e.g., 140). The substrate 132 is an example of a porous substrate. In embodiments where, as shown in FIG. 7A, polyisobutylene 144 is disposed at the front surface 136 of the substrate 52 in a configuration in which the polyisobutylene 144 is disposed both within the substrate (e.g., within cells 142) and on the surface (e.g. on surface 136), the polyisobutylene 22 is typically disposed below the front surface (e.g., 136) to a depth (e.g., 146) that is generally less than about 20 percent of the thickness (e.g., 148) of the substrate (e.g., 132).
FIG. 7B depicts a schematic side view of cleaning wipe 160. The cleaning wipe 160 includes the substrate 132 used in the cleaning wipe 130 of FIG. 7A. In the embodiment of FIG. 7B the cleaning wipe 160 includes polyisobutylene 162 that is disposed at the front surface 164 of the substrate 132 and disposed at the opposing back surface 138 and the polyisobutylene 162 is further distributed substantially uniformly through the bulk mass 140 of the substrate 132.
FIG. 7C depicts a schematic side view of cleaning wipe 170. The cleaning wipe 170 includes the substrate 132 used in the cleaning wipe 130 of FIG. 7A and cleaning wipe 160 of FIG. 7B. In the embodiment of FIG. 7C the cleaning wipe 170 includes polyisobutylene 172 that is disposed at the front surface 164 of the substrate 132 and the polyisobutylene 162 is further distributed substantially uniformly through a depth 146 of the bulk mass 140 of the substrate 132. Depth 146 represents about one half the thickness 174 of the substrate 132. In various embodiments polyisobutylene (e.g., 170) may be disposed through the depth (e.g., 164) of the substrate (e.g., 132) of a cleaning wipe (e.g., 170) that range from less than one percent of the thickness (e.g., 174) to one hundred percent of the thickness (e.g., 174) of the substrate (e.g., 132).
In the embodiments of FIGS. 1B, 2B, 3B, 4A, 4B, 5, 6, 7A, 7B, and 7C the polyisobutylene has a molecular weight of greater than approximately 30,000 and in some embodiments the molecular weight is between approximately 60,000 and 110,000. In some embodiments polyisobutylene may range in molecular weight between approximately 30,000 and 500,000 or between approximately 60,000 and 500,000 or between approximately 100,000 and 500,000. In some embodiments the polyisobutylene may range in molecular weight between approximately 30,000 and 1,000,000 or between approximately 60,000 and 1,000,000 or between approximately 100,000 and 1,000,000. Molecular weight 500,000 polyisobutylene is tacky, and molecular weight 1,000,000 polyisobutylene is slightly tacky. Polyisobutylene is all molecular weight ranges defined in this paragraph dissolve in hexane. A molecular weight of approximately 85,000 is an exemplary embodiment. Polyisobutylene is all molecular weights defined in this paragraph dissolve in hexane.
Various methods may be employed to manufacture a cleaning wipe. FIG. 8 presents a flow chart 190 describing steps of one process embodiment. In step 192 polyisobutylene having a molecular weight over 30,000 is dissolved in a solvent, such as hexane, to make a tackifier solution of approximately one half percent to approximately six percent polyisobutylene by weight. Various sub-ranges of the proportion of polyisobutylene may be employed, such as (a) approximately one half percent to approximately one and one half percent polyisobutylene by weight, or (b) approximately one and one half percent to approximately two and one half percent polyisobutylene by weight, or (c) approximately two percent to approximately three percent polyisobutylene by weight, or (d) approximately three percent to approximately six percent polyisobutylene by weight. In some embodiments, a more precise range of molecular weight of polyisobutylene may be used in step 192, such as polyisobutylene having a molecular weight between approximately 60,000 and 110,000. In some embodiments polyisobutylene may range in molecular weight between approximately 30,000 and 500,000 or between approximately 60,000 and 500,000 or between approximately 100,000 and 500,000. In some embodiments the polyisobutylene may range in molecular weight between approximately 30,000 and 1,000,000 or between approximately 60,000 and 1,000,000 or between approximately 100,000 and 1,000,000.
In step 194 the tackifier solution is applied to a substrate to produce a preform. For configurations in which the polyisobutylene is distributed substantially uniformly through the bulk mass of the substrate, such as the polyisobutylene 72 in FIG. 4B, the tackifier solution may be applied to a substrate by soaking the substrate in the tackifier solution and removing, such as by wringing, excess tackifier from the substrate. For configurations in which polyisobutylene is disposed at the surface of a substrate, such as the polyisobutylene 22 in FIG. 4A, the polyisobutylene may be deposited on the front surface 56 of the substrate 52 by spraying, rolling, brushing, or using other manufacturing techniques to apply the tackifier solution to the substrate (e.g., 52). For configurations in which polyisobutylene is disposed on the surface of a substrate, such as the polyisobutylene 118 in FIG. 6, the polyisobutylene may be deposited on the front surface 108 of the substrate 102 by spraying, rolling, brushing, or using other manufacturing techniques to apply the tackifier solution to the substrate (e.g., 102). The outcome of such manufacturing processes as to whether they in polyisobutylene that is disposed on the surface of a substrate or result in polyisobutylene that is disposed at the surface of a substrate is generally primarily influenced by the characteristics of the particular substrate.
Continuing with FIG. 8, in step 196 the preform is dried to form the cleaning wipe. Drying may be accomplished by leaving the preform in open air until the solvent evaporates, or drying may be accelerated by using a heat source, or a partial vacuum or forced air circulation over or through the preform. Solvent that is removed from the preform during drying may be recovered and recycled.
The total weight of a clean wipe, according to some embodiments described herein, is divided substantially between the weight of the substrate and the weight of the polyisobutylene retained after tackifier solution treatment and drying. Typically, in applications where polyisobutylene is disposed through a depth of a substrate, about ninety nine and one half percent to about ninety four percent of the weight of the portion of the wipe that is permeated by the polyisobutylene is the weight of the substrate that is permeated by the polyisobutylene, and the balance of the weight in the portion of the substrate permeated by the polyisobutylene is the permeated polyisobutylene.
In applications where polyisobutylene is disposed only on or only at the surface of the substrate, the weight percentage of the polyisobutylene is compared to a “reference portion” of the bulk mass of the substrate. That is, the substrate has a thickness and the bulk mass of the substrate has a reference portion. The reference portion of the bulk mass is a portion of the substrate to a depth of approximately the first one hundred to one thousand micrometers of the thickness of the substrate. If the thickness of the substrate is less than the indicated “first distance” of the thickness of the substrate, then the term the first distance (e.g. the term “the first one thousand micrometers” or “the first one hundred micrometers”) of the thickness of the substrate refers to the thickness of the substrate. The polyisobutylene has a weight and the reference portion of the bulk mass has a weight, and the weight of the polyisobutylene is generally approximately one half percent to six percent of the combined weight of the polyisobutylene and the weight of the reference portion of the bulk mass.
References to the comparative weights of components of a cleaning wipe typically excludes peripheral materials that may be added to the wipe for consumer appeal but that do not assist in the cleaning function of the wipe. Examples of such peripheral materials are moisture (water) or fragrances or other volatile compounds that are added to provide such features as a pleasant aroma and suppleness of the cleaning wipe in its consumer packaging. The “dry weight” of a cleaning wipe (and its weight distribution) refers to the weight of the cleaning wipe measured after such peripheral materials are evaporated from the wipe. Other ancillary materials that do not contribute to cleaning function may be incorporated into the cleaning wipes. Examples of such ancillary materials are dyes used to color the substrate and inks used to inscribe logos or other markings. Such ancillary materials obviously add some finite measurable weight to the dry weight of a cleaning wipe, but the weight of such materials is not considered to be part of the substantial weight of the wipe.
The total weight of a clean wipe, according to some embodiments described herein, is divided almost solely between the weight of the substrate and the weight of the polyisobutylene retained after tackifier solution treatment and drying. In such embodiments, the cleaning wipe has a total dry weight that includes a porous substrate. The porous substrate typically has a bulk mass with a plurality of voids and the porous substrate embodies a percentage of the total dry weight of the cleaning wipe. This leaves a remaining percentage of dry weight of polyisobutylene that is disposed within a least a portion of the plurality of voids. For example in these embodiments, if the substrate is substantially 90% percent of the dry weight of the cleaning wipe, the polyisobutylene is substantially 10% of the dry weight of the cleaning wipe, and except for ancillary components of the type previously described, the cleaning wipe includes no other component.
In some instances the substrate may be very thick, such as a wool pad. In such instances when the weight of the cleaning wipe is divided almost solely between the weight of the substrate and the weight of the polyisobutylene, the substrate may, for example, embody ninety four percent or more of the dry weight of cleaning wipe and the polyisobutylene will embody the remaining percent. In some instances the substrate may be very thin, such as a fine fabric, and in such embodiments the substrate may, for example, embody six or less percent of the dry weight of the cleaning wipe. Other embodiments between those limits are also feasible. In exemplary embodiments the polyisobutylene embodies less than approximately twenty percent of the dry weight of the cleaning wipe.
Typically, cleaning wipes prepared as disclosed herein are designed to be used dry, without any liquid cleaning agent. Heavily contaminated surfaces may be wiped first with a utility wipe and a surface cleaner such as Formula 409® and allowed to dry. The dry surface is then wiped with a surface of the cleaning wipe at which polyisobutylene is disposed. Vigorous wiping may be used in applications where contamination is difficult to remove.
EXAMPLE
Manufacturing operations that involve beryllium have very stringent limits on the amount of beryllium contamination that may remain on the surface of a part that is released to the public. Ideally, such parts would have no detectable amounts of beryllium, but typically a level of 0.2 μg/100 cm2 is considered acceptable as a “release-to-public” specification. Instrumentation is available to detect beryllium contamination at very low concentrations (typically (0.01 μg/100 cm2), and getting to “non-detect” levels is extremely difficult. Once a surface had been contaminated, it typically is very difficult to remove contamination below 0.040 μg/100 cm2, and achieving that level using prior art methods generally results in the generation of a considerable amount of beryllium-contaminated paper waste.
To address this problem several test cleaning wipes were prepared and tested. The first type of cleaning wipe (Cloth No. 1) that was prepared and tested used 250 μm (0.010″)-thick micro fiber cloths made of random loops of 20 μm-diameter cellulose fiber as the substrate. A second type of cleaning wipe (Cloth No. 2) that was prepared and tested used woven cheesecloth as the substrate. This particular cheesecloth was woven using 50 μm-diameter cotton thread, spaced ˜200 μm apart in a very open weave. The third type of cleaning wipe (Cloth No. 3) that was prepared and tested used as the substrate a non-woven, hydro-entangled micro fiber cloth made of densely packed cellulose and polyester fibers, the fibers of each type measuring approximately 20 μm in diameter. These wipes measured 0.33 mm (0.013 in.) thick.
For the purposes of testing, four concentrations of “dry” tackifier were prepared by dissolving 85,000 MW polyisobutylene (PIB) in hexane. Solutions of 1 wt %, 2 wt %, 2.5 wt %, and 5 wt % PIB in hexane were prepared. A number of the first type of cellulose wipes (Cloth No. 1) were soaked in three of the tackifier blends (1%, 2.5%, and 5%), wrung “dry”, and then allowed to dry in a laboratory hood. After drying the coated cloths felt dry and non-sticky to the touch. 85,000 MW PIB is a commonly available, solid, elastic form of polyisobutylene that is not excessively sticky to the touch. Lower molecular weights of PIB are available, but these are excessively sticky and flow too readily and therefore leave a sticky residue on the “cleaned surface.”
First Series of Tests
The effectiveness of these tack cloths was shown in tests conducted on a matte-finished stainless steel can. The roughness of this matte finish was measured to be 1.56+/−0.15 μm. FIG. 9 presents a Scanning Electron Micrograph 200 showing the roughness of the stainless steel surface 202, and FIG. 9 illustrates that the stainless steel surface 202 had a considerable amount of roughness where micron-sized particulate could become lodged. Industrial hygiene test smears were taken on this can that had been stored in a regulated beryllium area for four months. Contamination on three areas of the can averaged 0.0536+/−0.0197 μg/100 cm2 at the 95% confidence level. The can was then wiped with cleaning wipe prepared with 2.5 wt % solution of PIB in hexane. The results of these tests are shown in chart 220 presented in FIG. 10.
First test results 222 represent a reference test using a micro fiber cloth that did not have tackifier treatment. The cleaning was performed under ambient indoor lighting with no special technique employed to visually enhance visual perception of contamination. Results ranged from data point 224 to data point 226 with an average residual contamination after cleaning of 0.0723+/−0.1733 μg/100 cm2 at the 95% confidence level, as depicted by error bar 228. Second test results 230 represent results using utility wipes and Formula 409®. A fluorescent dye made up of fluorescent particles in the 5 μm range was used to simulate BeO particulate, since this contaminant is invisible to the naked eye. The fluorescent dye gave visual confirmation of removal of the particulate or of the effectiveness of the cleaning process. Subsequent testing of resultant cleanliness produced two test result data points 232 and 234 with average residual contamination of 0.0138+/−0.0090 μg/100 cm2 at the 95% confidence level, as depicted by error bar 236. The test can was then put in storage for four months and retested, producing test results 238. Results ranged from data point 240 to 242 with average residual contamination of 0.0536+/−0.0197 μg/100 cm2 at the 95% confidence level, as depicted by error bar 244.
In a further test, an area of the can was wiped with Cloth No. 1 made with a 2.5 wt % solution of PIB. The test results 246 were three “non-detect” data points 248 with a “0” error bar 250. Following this test, the can was deliberately contaminated with a heavy amount of fine beryllium oxide powder. Visible powder was removed in a superficial manner with a utility wipe and Formula 409®. Once dry, the contaminated surface was thoroughly wiped with the cellulose micro fiber tack cloth (Cloth No. 1) made with 5 wt % solution of PIB in hexane. Industrial hygiene test smears were once again made of the three contaminated-and-cleaned regions yielding test results 252. The three trials resulted in three “non-detects” as indicated by data points 254 and “0” error bar 256.
The contamination, cleaning, and the industrial hygiene test smear process was repeated two more times using the micro fiber tack cloth (Cloth No. 1) made first with a 2.5% solution of PIB and then a 1% solution of PIB. These test results 258 and 260 show three “non-detect” data points 262 with a “0” error bar 264 and three more “non-detect” data points 266 with a “0” error bar 268.
After determining the levels of beryllium oxide left on the matte finish of a stainless steel can, clean specimens of stainless steel were smeared with two of the lower levels of tackifier on two micro fiber cloths, those made with the 1 wt % and 2.5 wt % solutions of PIB in hexane. The purpose of this testing was to measure any residual PIB or other material that might be transferred from a cleaning wipe to a cleaned surface. For comparison purposes, a third steel specimen was vigorously wiped using a utility wipe and an industrial solvent, and a fourth stainless steel specimen was cleaned using an aggressive 20 kHz ultrasonic probe in 10% nitric acid with a small amount of hydrogen peroxide. This latter surface cleaning process represents an ultra level of cleaning, not ordinarily obtainable by wiping. The nitric acid and hydrogen peroxide chemically burns off any organic residue, while the ultrasonic probe provides a very aggressive mechanical cleaning. After smearing the steel coupons as just described the steel specimens were then analyzed using X-ray Photoelectron Spectroscopy or XPS to determine what kind of residue was left behind by the reference processes and the PIB cleaning wipes. XPS is a very sensitive test that is capable of detecting even partial mono-layers of residues left on surfaces. FIG. 11 shows the XPS results 300. Relative cleanliness is indicated by a residual carbon-to-iron XPS ratio.
FIG. 11 reveals that ultrasonic acid cleaning produced the cleanest surfaces as indicated by test results 302 where results ranged between data point 304 and data point 306, with a ratio of 0.114+−0.030 at a 95% confidence level, indicated by error bar 308. Wiping with the industrial solvent and a utility wipe left a rather broad range of carbonaceous (solvent) residue as indicated by test results 310. Results ranged from data points 312 to 314 with a ratio of 0.233+−0.391 at a 95% confidence level, as indicated by error bar 316. Wiping with the 1% and 2.5% polyisobutylene cleaning wipes left a very narrow range of residue. Test results 318 for the 1% cleaning wipe ranged from data point 320 to 322 with a ratio of 0.214+−0.042 at a 95% confidence level, as depicted by error bar 324. Test results 326 for the 2.5% polyisobutylene cleaning wipes ranged from data point 328 to 330 with a ratio of 0.202+−0.024 as indicated by error bar 332. Both error bars 324 and 332 were tighter than the error bar 316 for solvent wiping, and both fell within the range of the error bar 316 for solvent cleaning.
Second Series of Tests
Several sheets of commercial cotton cheese cloth (Cloth No. 2) measuring 0.25 mm in thickness and 85 cm×85 cm in area, and each weighing 29 g, were soaked in a 2 wt % solution of 85,000 MW polyisobutylene (PIB) in hexane. These cloths were wrung “dry” and then hung to dry in a lab hood. The dry weights of the coated cloths indicated that they had gained 3.3 wt % in PIB. After coating, the cloths felt dry to the touch and were not sticky.
The matte-finish stainless steel can was once again deliberately contaminated with a heavy amount of fine beryllium oxide powder. The excess contamination was wiped off in a superficial manner using Formula 409® surface cleaner and paper utility wipes. Final cleaning was done by wiping with the treated dry cheese cloths. Industrial hygiene test smears were made of the three contaminated-and-cleaned stainless steel surfaces. Test chart 400 in FIG. 12 shows the results of this cleaning, along with additional results of wiping with various other polyisobutylene cleaning wipes. Test results 402 represent initial contamination levels before cleaning. Results ranged from data point 404 to data point 406, with average contamination at 0.0536+/−0.0197 μg/100 cm2 at the 95% confidence level as depicted by error bar 408. Test results 410 were for the 2.0% cheese cloth (Cloth No. 2), and three “non-detect” data points 412 yielding “0” error bar 414.
Third Series of Tests
The third type of wipe that was treated and tested (Cloth No. 3) was a non-woven, hydro-entangled micro fiber cloth made of densely packed cellulose and polyester fibers, the fibers of each type measuring approximately 20 μm in diameter. These wipes measured approximately 0.33 mm (0.013 in.) thick and approximately 12″×12″ in area. Groups of ten wipes were rolled together and soaked in a 2 wt % solution of 85,000 molecular weight polyisobutylene in hexane. After soaking, the wipes were wrung “dry” of solvent, then allowed to dry in a chemical fume hood. The average gain in weight for three groups of ten wipes averaged 3.7+/−0.7 wt % (+/−1 standard deviation).
Returning to FIG. 12, test results 440 were for Cloth No. 3 with 2.5% tackifier solution, showing and 2 “non-detect” data points 442 and 1 detect data point 444 at 0.102, which is just above the detection limit. The two “non-detects” and the one detect data point resulted in error bar 446.
A final test was run to determine how effectively the tackified polyester/cellulose cloths (Cloth No. 3) could clean heavily contaminated surfaces. The surface of the stainless steel can was once again heavily contaminated with beryllium oxide powder. This time the surface was only lightly damp-wiped to protect the investigator from air-borne contamination. Once this surface was dry, it was thoroughly wiped with a tackified polyester/cellulose cloth (Cloth No. 3) treated with 2% tackifier solution. Test results 448 show three “non-detect” data points 450 yielding “0” error bar 452.
In summary, in 20 out of 21 tests involving tackified cloths made according to this disclosure, all but one (i.e., 95% of the tests) resulted in residual contamination below the limits of detection for beryllium. The only “detect” value was only 2% above the limit of detection for beryllium and may lie within the error band for experimental scatter.
Fourth Series of Tests
Monolithic specimens of BeO that are hot-pressed using lithium oxide as a sintering aid are notorious for shedding BeO particulate matter. Reducing the level of removable BeO particulate on the surfaces of hot-pressed BeO is very difficult. In order to test the effectiveness of the PIB tackified cleaning wipes, the cellulose cloth (Cloth No. 1) was impregnated with a 2.5 wt % of 85,000 MW PIB in hexane and allowed to dry. Three monolithic specimens of hot-pressed BeO were vigorously washed using Formula 409™ surface cleaner and a stiff polymer scrub brush under flowing water. All surfaces were thoroughly dried, and Industrial Hygiene test smears were taken of the dry surfaces. Chart 500 of FIG. 13 shows test results 502. Data points 504, 506, and 508 are widely scattered and average 9.16+/−12.83 μg/100 cm2 (+/−95% confidence) as indicated by error bar 510. The dry surfaces were then wiped with the tack cloth (Cloth No. 1) made with a solution of 2.5% PIB, and industrial hygiene test smears were once again taken and the test results 512 for three trials shown by data points 514, 516, and 518 show that wiping with the PIB tack cloth reduced the contamination by an order of magnitude to 0.91+/−0.92 μg/100 cm2, and also resulted in a significantly reduced error bar 520.
The foregoing descriptions of embodiments of this invention have been presented for purposes of illustration and exposition. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
Patent Application
20080057808
