PROCESS FOR PROTECTING SURFACES FROM WELD SPATTER AND METAL SPARKS

Background ofthe Invention This invention relates to protecting surfaces from weld spatter and metal sparks.

Repairs in automotive body shops frequently involve processes such as abrasive grinding and welding. The metal sparks generated in such processes (e.g., by the friction of an abrasive grinding operation or by micro-explosions caused by rapid heating of metal in the vicinity ofthe tip of a welding torch or arc) can have initial temperatures ranging from about 2500-3500°C. Welding processes such as Metal Inert Gas (MIG) or wire welding produce weld spatter (e.g., wire fragments and globules of molten metal). Both metal sparks and weld spatter can cause substantial damage to surfaces they contact such as the upholstery, glass, or paint of an automobile, necessitating protective measures. It is particularly difficult to obtain effective, easy-to-apply protection, however, where the surfaces involved are substantially vertical surfaces such as automobile glass and doors.

Summary ofthe Invention In a first aspect, the invention features a method for protecting a surface from the spatter of molten metal or metal sparks during welding or grinding operations that includes the steps of: removably attaching to the surface a thin protective sheet having a pair of opposed faces, one of which is integrally provided with a pressure sensitive adhesive for removably attaching the sheet to the surface; conducting welding or grinding operations in the vicinity ofthe surface; and removing the protective sheet from the surface at the conclusion ofthe welding or grinding operations.

In preferred embodiments, the protective sheet is removably attached to a substantially vertical surface (e.g., a surface in which the magnitude ofthe component of the surface vector in the direction of gravitational force is greater than about 10% ofthe magnitude ofthe surface vector, where "surface vector" refers to the vector lying in the plane defined by the major face ofthe surface). The thickness ofthe protective sheet preferably is no greater than about 500 micrometers.

Preferred materials for the protective sheet include paper Particularly preferred paper sheets include sheets having a density of at least about 0 20 g/cm ³ Preferred pressure sensitive adhesives include microsphere adhesives (e g , ofthe type described in Silver, U.S. 3,691,140 and Baker et al , U S 4,166,152, both of which are hereby incoφorated by reference) The entire face ofthe sheet may be integrally provided with the pressure sensitive adhesive Alternatively, only a portion ofthe face ofthe sheet may be provided with the adhesive

In a second aspect, the invention features a method for protecting a surface from the spatter of molten metal or metal sparks during welding or grinding operations that includes the steps of: inteφosing between the surface and a source of molten metal or metal sparks a thin, protective, paper sheet; and conducting welding or grinding operations in the vicinity of said surface Preferably, the thickness ofthe paper sheet is no greater than about 500 micrometers The invention provides a simple, effective method for protecting surfaces such as automobile windshields, doors, and upholstery from weld spatter and metal sparks encountered during welding and grinding Although the protective sheets are thin, they provide suφrisingly good protection against weld spatter and metal sparks In addition, it is not necessary to treat the sheets with flame retardants in order to obtain effective protection

Other features and advantages ofthe invention will be apparent from the following description ofthe preferred embodiments thereof, and from the claims Description ofthe Preferred Embodiments The invention features the use of thin protective sheets for protecting surfaces from weld spatter and grinding sparks The invention is particularly usefiil for protecting substantially vertical surfaces such as automobile windows and upholstery Suitable sheets for this puφose preferably have a thickness of not greater than about 500 micrometers, even more preferred are sheets having thickness values ranging from about 70 to about 400 micrometers They may be provided, for example, in the form of rolls, stacked sheets, or folded sheets, with the particular configuration being selected based upon ease of dispensability

A wide variety of materials may be used for the protective sheet. Examples include paper, paperboard, plastic film (e.g., polyvinyl chloride, polyethylene terephthalate, polyurethane, polyethylene, polyvinyl fluoride, or cellulose acetate), and woven and non-woven fabric sheets (e.g., cotton duck). Paper is particularly preferred because ofits relatively low cost and ease of disposability. Particularly preferred are paper sheets having a density greater than about 0.20 g cm ³ . The inventors have found that when the density ofthe paper sheet exceeds about 0.20 g/cm ³ , the paper, upon contact with weld spatter, tends to char, rather than burn, when in intimate contact with a substrate because there is insufficient oxygen available to support combustion. Suitable paper sheets are commercially available and include Kraft papers commercially available from a variety of sources, including Mosinee of Appleton, WI, James River Coφ. of Parchment, MI, and Research Products Coφ. of Madison, WI. If desired, one or more flame retardant ingredients may be incoφorated in the sheets. Examples of suitable flame retardant/resistant papers are commerically available from the sources listed above.

The protective sheet is positioned between the surface to be protected and the source ofthe weld spatter and grinding sparks (e.g., a welding torch or grinder). For example, if the surface to be protected is an automobile window or door, the sheet can be hung in front ofthe surface just as one would hang a curtain. The sheet can also be attached directly to the surface itself, in which case the sheet is preferably coated on one side with a pressure sensitive adhesive for adhering the sheet to the surface. The adhesive may be provided as a continuous coating covering the entire side ofthe sheet. Alternatively, it may be provided in the form of a continuous strip running along one or more edges ofthe sheet, or in the form of a discontinuous coating (e.g., as a series of dots or diamonds).

To prevent blocking ofthe adhesive, the uncoated side ofthe protective sheet may be provided with a low adhesion backsize (LAB) coating. Examples of suitable LAB coatings include acrylates (e.g., as disclosed in U.S. Patents 2,607,711 and 3,011,988, hereby incoφorated by reference), silicones (e.g., as disclosed in U.S. Patents 4,313,988 and 4,728,571, hereby incoφorated by reference), silicone-urea block copolymers (e.g., as disclosed in U.S. Patent 5,290,615, hereby incoφorated by

reference), and fluorocarbons (e.g., as disclosed in U.S. Patent 3,318,852, hereby incoφorated by reference).

The pressure sensitive adhesive, as well as the coating weight and extent of coverage on the protective sheet, is selected such that the protective sheet can be readily removed from the surface to which it is adhered at the conclusion of welding and/or grinding operations. The adhesive may be applied to the sheet in the form of an aqueous-based composition, a solvent-based composition, or a 100% solids composition.

Although a wide variety of conventional pressure sensitive adhesives (e.g., acrylate adhesives) can be used, particularly preferred adhesives include microsphere adhesives, e.g., ofthe type generally described in Silver, U.S. 3,691,140 and Baker et al., U.S. 4,166,152. Such adhesives are infusible, solvent-dispersible, solvent-insoluble, inherently tacky, elastomeric, polymeric or copolymeric spheres having diameters on the order of about 1 to about 250 microns. They are prepared in an aqueous suspension polymerization process utilizing an emulsifier in an amount greater than the critical micelle concentration. Such microspheres permit bonding of materials such as paper to various substrates, but also permit easy removal ofthe bonded material without tearing, as well as re-bonding ofthe material without application of additional adhesive. The invention will now be described by way ofthe following examples. EXAMPLES

Test Procedures

The following procedures were used to measure sheet density and to evaluate the performance of various protective sheets when exposed to welding sparks and grinding sparks. Sheet Density

Three sheets, each having the same surface area, were weighed to determine an average sheet weight value. The individual sheet thicknesses were measured using a Model #49-62-01 TMI Digital Micrometer from Testing Machines, Inc. of Amityville, NY fitted with 5 cm diameter anvils to provide a dead weight load sufficient to apply a force of 1.44 KPa to the sheet. An average value was then obtained from the three measurements. The average sheet density was determined by dividing the average sheet

weight value by the average sheet volume (determined by multiplying the average sheet thickness by the average surface area ofthe sheet). Welding Sparks

A glass test coupon measuring 4 in. x 8 in. (10 cm x 20 cm) was partially covered with a 4 in. x. 4 in. (10 cm x 10 cm) sample ofthe sheet being tested; the exposed glass surface was used as a control. In the case of pressure sensitive adhesive- containing sheets, the sheet was adhered to the test coupon by means ofthe pressure sensitive adhesive. In the case of non-pressure sensitive adhesive-containing sheets, one edge ofthe sheet was taped to the center ofthe glass coupon using a 2.5 cm wide piece of No. 233 Scotch™ Brand Automotive Refinishing Masking Tape from 3M Co. of St. Paul, MN.

The partially covered test coupon was placed horizontally on a welding blanket ofthe type described in U.S. Patent 4,849,272, hereby incoφorated by reference, and positioned 15 cm beneath a 0.5 m length of a 90° angle iron. A Metal Inert Gas (MIG) wire-fed welding torch (DAN-MIG 140 ( 195-1 lb) welder) was adjusted to maximize the creation of welding sparks by melting a wire onto the angle iron. The wire was a Type SI-4405 Autobody MIG carbon steel welding wire AWS-A5.18, ASME-SFA 5.18 having a diameter of 760 micrometers. The welding torch settings were as follows: wire speed of 4, welding power of 5, and a manual fill setting. The coupon was showered with sparks for 15 seconds; the spark velocity was on the order of 5 m sec. The exposed glass surface was then compared to both the surface ofthe protective sheet and the glass surface underlying the protective sheet after cleaning the underlying glass surface with glass cleaner (3M Glass Cleaner #051135-08968 available from 3M Co. of St. Paul, MN). The results from individual protective sheets are shown in Table I, where the following legends apply:

"1" means that char spots and char trails were observed on the sheet surface from the skittering of molten metal sparks, but no pinholes or penetration ofthe sheet was evident, nor was there any evidence of damage to the underlying glass surface.

"2" means that intense charring/pyrolization ofthe sheet material and/or partial penetration ofthe sheet was observed, resulting in smudges on the underlying glass. The smudges, however, could be removed using a commercially available glass cleaner

(3M Glass Cleaner #051135-08968 available from 3M Co. of St. Paul, MN). There was no evidence of damage to the glass surface following cleaning.

"3" means that penetration ofthe sheet occurred, resulting in the formation of pits in the underlying glass surface. Grinding Sparks

Samples were prepared as described above in the case ofthe test procedure for welding sparks. The glass coupon was positioned vertically 15 cm from a 0.5 m length of a 90° angle iron. A Sioux portable electric high speed H.D. sander (catalogue #1267) commercially available from Sioux Tools Inc. of Sioux City, IA was fitted with an 18 cm diameter disc pad (3M brand Paint Buster Disc Pad Assembly #051144-05634 commercially available from 3M Co. of St. Paul, MN) and an 18 cm grinding disc (3M Coated Abrasive Grinding Disc, Grade 24 Green Coφs Fibre Disc, #051144-01923 commercially available from 3M Co. of St. Paul, MN). This heavy duty (5000 φm) abrasive grinding tool was used to grind the end ofthe angle iron, thereby generating an intense stream of high velocity grinding sparks that were horizontally directed at the vertically positioned test coupon.

The test coupon was exposed to the grinding sparks for 15 seconds; spark velocity was on the order of about 50 m/s. The exposed glass surface was then compared to both the surface ofthe protective sheet and the glass surface underlying the protective sheet. The results from individual protective sheets are shown in Table I, where the following legends apply:

"1" means no visible penetration ofthe sheet by metal sparks and no build-up of metal debris on the sheet surface. In some samples, a slight graying ofthe surface was observed due to slight charring. There was no damage to the underlying glass. "2" means the sheet surface exhibited distinct speckled charring. There was no visible penetration ofthe sheet by metal sparks and no build-up of metal debris on the sheet surface. In addition, there was no damage to the underlying glass.

"3" means the sheet material was penetrated by extreme charring or pinholes from grinding sparks. There was no build-up of iron filings and no damage to the underlying glass.

"4" means charring, pinholing, and/or disintegration ofthe sheet occurred. Pits formed in the underlying glass surface. Example 1

The sample was a sheet of Mosinee 107# Natural Tube Winding Kraft paper, Spec. 0635-D (107#/3000 ft ² ) available from Mosinee of Appleton, WI. The thickness ofthe sheet measured 260 microns. The average sheet density was 0.67 g/cm ³ and the Gurley porosity (supplied by the manufacturer) was 11. The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above. The results are shown in Table I. Example 2

The sample was a sheet of Mosinee 98# Natural Machine Finish Converting Kraft paper, Spec. M-2713 (98#/3000 ft ² ) available from Mosinee of Appleton, WI. The thickness ofthe sheet measured 230 microns. The average sheet density was 0.67 g/cm ³ and the Gurley porosity (supplied by the manufacturer) was 15-25. The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above. The results are shown in Table I. Example 3

The sample was a sheet of Mosinee 81.5# Natural Tube Winding Kraft paper, Spec. 0789-B (81.5#/3000 ft ² ) available from Mosinee of Appleton, WI. The thickness ofthe sheet measured 190 microns. The average sheet density was 0.71 g/cm ³ and the Gurley porosity (supplied by the manufacturer) was 90-150. The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above. The results are shown in Table I. Example 4 The sample was a sheet of Mosinee 40# Machine Finish Converting Kraft paper,

Spec. 2519-A (40#/3000 ft ² ) available from Mosinee of Appleton, WI. The thickness of the sheet measured 90 microns. The average sheet density was 0.71 g/cm ³ and the Gurley porosity (supplied by the manufacturer) was 28. The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above. The results are shown in Table I.

Example 5

The sample was a sheet of Mosinee 109# Natural Partial Flame Resistant Kraft paper, Spec. 2377 (109#/3000 ft ² ) available from Mosinee of Appleton, WI. The thickness ofthe sheet measured 300 microns The average sheet density was 0.59 g/cm ³ and the Gurley porosity (supplied by the manufacturer) was 12. The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above The results are shown in Table I.

Example 6

The sample was a sheet of Mosinee 100# CW White Bleached Flame Resistant Kraft paper, Spec. 2459 (100#/3000 ft ² ) available from Mosinee of Appleton, WI The thickness ofthe sheet measured 270 microns The average sheet density was 061 g/cm ³ and the Gurley porosity (supplied by the manufacturer) was 22 The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above The results are shown in Table I. Example 7

The sample was a sheet of Mosinee 80# Natural Utility Flame Resistant Kraft paper, Spec. 2027-A (80#/3000 ft ² ) available from Mosinee of Appleton, WI The thickness ofthe sheet measured 205 microns The average sheet density was 0 65 g/cm ³ and the Gurley porosity (supplied by the manufacturer) was 15-25 The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above. The results are shown in Table I

Example 8

The sample was a sheet of Mosinee 40# Natural Utility Flame Resistant Kraft paper, Spec. 1564-F (40#/3000 ft ² ) available from Mosinee of Appleton, WI The thickness ofthe sheet measured 110 microns The average sheet density was 0 59 g/cm ³ and the Gurley porosity (supplied by the manufacturer) was 10-25 The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above The results are shown in Table I

Example 9 The sample was a sheet of Mosinee 41 # Natural Utility Flame Resistant Kraft paper, Spec. 1970-A (41#/3000 ft ² ) available from Mosinee of Appleton, WI The

thickness ofthe sheet measured 100 microns. The average sheet density was 0.70 g cm ³ and the Gurley porosity (supplied by the manufacturer) was 16-30. The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above. The results are shown in Table I. Example 10

The sample was a sheet of Pepperell Spark Guard Boothliner Flame Resistant Kraft paper (54#/3000 ft ² ) available from Pepperell of Pepperell, MA. The thickness of the sheet measured 175 microns. The average sheet density was 0.64 g/cm ³ . The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above. The results are shown in Table I. Example 11

The sample was a sheet of Booth Floor Kraft paper, stock #3041 available from Research Products Coφ. of Madison, WI. The thickness ofthe sheet measured 210 microns. The average sheet density was not determined due to limited availability of samples. The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above. The results are shown in Table I. Example 12

The sample was a sheet of 55# Flame Resistant Kraft Kraft paper (03965) (55#/3000 ft ² ) available from James River Coφ. of Parchment, MI. The thickness of the sheet measured 120 microns. The average sheet density was 0.77 g/cm ³ . The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above. The results are shown in Table I. Example 13

The sample was a sheet of 30# Kraft paper treated with Pyrofas 7202 available from Fire & Thermal Protection, Inc. of Carmel, C A The thickness ofthe sheet measured 130 microns. The average sheet density was not determined due to limited availability of samples. The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above The results are shown in Table I. Example 14 The sample was a piece of Post-It™ Brand Cover Up Tape commercially available from 3M Co. of St. Paul, MN. The thickness ofthe sheet measured 95

microns (including the adhesive). The average sheet density was 0.85 g/cm ³ . The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above. The results are shown in Table I. Example 15 The sample was a piece of Safe Release™ Masking Tape #2075 commercially available from 3M Co. of St. Paul, MN. The thickness ofthe sheet measured 115 microns (including adhesives). The average sheet density was 0.75 g/cm ³ . The sheet was exposed to welding sparks and grinding sparks, as described in the Test Procedures, above. The results are shown in Table I.

TABLE I

Example

Weld Grind

1 1

2 2

3 3

4 2

5 2

6 1

7 2

8 2

9 4

10

11

12

13 4

14

15

Other embodiments are within the following claims.