Paint masking tape

The paint masking tape comprises a substrate, an adhesive layer formed on one side of the substrate, and a backing resin layer formed on the back surface of the substrate. Here, the backing resin layer contains a urethane resin and an epoxy resin or a compound containing aziridine ring(s). The paint masking tape does not tear easily when peeled off from a paint object, inhibits the flaking-induced scattering of paint flakes, and provides clearly visible parting lines.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a paint masking tape, and more
 particularly to a paint masking tape that does not tear or scatter paint
 flakes easily when peeled off.
 2. Description of the Related Art
 The paint masking tapes widely used in the painting of vehicles or
 buildings are commonly configured in such a way that an adhesive layer for
 pasting the masking tape to the paint object is formed on one side of a
 tape substrate such as a plastic film (polyolefin film, polyester film, or
 the like) or paper.
 A paint masking tape must provide clearly visible "parting lines" (border
 lines between painted areas and unpainted areas, or border lines between
 areas painted in different colors). A paint masking tape must also be easy
 to handle and must not tear readily or cause flaking (a phenomenon in
 which the coat of paint on the tape separates in flakes from the tape
 substrate during tape removal) when peeled off, contaminating the painted
 surface.
 A technique in which a resin layer is formed in order to inhibit or
 otherwise affect flaking on the adhesive-free surface of the tape
 substrate of a paint masking tape (on the back surface of the substrate)
 has been widely used in the past in order to meet such requirements.
 For example, Japanese Patent Application Laid-Open No. 2-247272 describes a
 paint masking tape obtained by applying and forming a chlorinated
 polyolefin film on the back surface of a polyolefin film substrate, and
 has a statement that the chlorinated polyolefin film improves adhesion
 between the tape surface and the paint coat, preventing flaking in which
 the resulting paint flakes are peeled off and scattered, and making it
 possible to prevent the paint surface from being contaminated.
 In addition, Japanese Patent Application Laid-Open No. 7-82536 describes a
 paint masking tape obtained by applying and forming a specific vinyl
 copolymer film on the back surface of a paper substrate, and has a
 statement that the specific vinyl copolymer film imparts flexibility to
 the entire paint masking tape, preventing the tape from being fragmented
 when it is peeled off, and making parting lines on curved portions clearly
 visible.
 A disadvantage of this approach, however, is that when the paint masking
 tapes described in the aforementioned publications are actually used
 during the surface painting of vehicles, these tapes easily tear during
 their removal.
 The inventors have conducted a detailed study into the reasons for this
 phenomenon and found that the paints used for the surface painting of
 vehicles are usually so-called baking paints, which possess thermosetting
 properties and form extremely hard and brittle paint films when baked.
 Specifically, separating a paint masking tape from a painted surface
 (painted object) facilitates tape tearing because the masking tape and the
 paint film are firmly bonded and integrated, and the hardness and
 brittleness of the paint film in a laminate composed of a masking tape and
 a paint film remain dominant even when the tape substrate is rendered
 highly flexible. In the particular case of a paint object with a
 complicated or curved shape, it is very difficult even for an experienced
 person to peel off the tape without tearing it.
 To address such tape tearing problems of paint masking tapes, it has been
 proposed to reduce the adhesion between the paint masking tapes and paint
 films, but this approach is disadvantageous in that the paint films
 separate from the tape substrate and scatter in the form of flakes,
 contaminating the paint surface, during peeling operations. In addition,
 parting lines are often rendered indistinguishable when such paint flakes
 are formed.
 SUMMARY OF THE INVENTION
 An object of the present invention is to overcome the aforementioned
 drawbacks of prior art and to provide a paint masking tape that does not
 tear easily when peeled off, that inhibits the scattering of paint flakes
 formed by flaking, and that provides clearly visible parting lines.
 The inventors have accomplished the present invention upon discovering that
 the stated object can be attained by adopting an approach in which the
 resin layer designed to inhibit flaking is formed from a urethane resin
 and an epoxy resin or a compound containing aziridine ring(s) on the back
 surface of the substrate of a paint masking tape for painting
 applications.
 Specifically, the present invention provides a paint masking tape
 comprising a substrate, an adhesive layer formed on one side of the
 substrate, and a backing resin layer formed on the back surface of the
 substrate, wherein the backing resin layer contains a urethane resin and
 an epoxy resin or a compound containing aziridine ring(s).
 This and other objects, features and advantages of the present invention
 are described in or will become apparent from the following detailed
 description of the invention.
 This and other objects, features and advantages of the present invention
 are described in or will become apparent from the following detailed
 description of the invention.

DETAILED DESCRIPTION OF THE INVENTION
 The present invention will now be described in detail.
 The paint masking tape 1 of the present invention has an adhesive layer 3
 on the surface of a substrate 2, and a backing resin layer 4 for
 inhibiting flake formation on the back surface of the substrate 2, as
 shown in FIG. 1A, where this paint masking tape is characterized in that
 the backing resin layer 4 comprises a least a urethane resin and an epoxy
 resin or a compound containing aziridine ring(s). Forming the backing
 resin layer 4 at least from a urethane resin and an epoxy resin or a
 compound containing aziridine ring(s) in such a manner impairs tape
 tearing when the paint masking tape 1 is peeled off, inhibits the
 scattering of paint flakes formed by flaking, and provides clearly visible
 parting lines. Although the reasons for this are not yet understood, a
 tentative explanation will be given below by way of comparison with
 conventional paint masking tapes.
 In the case of a conventional paint masking tape 11, the initial result of
 separating the distal end 12 of the paint masking tape 11 from a paint
 object 13 after the formation of a paint film 10 (FIG. 3A) is the
 formation of a crack 14 in the paint film 10 (FIG. 3B). It is believed in
 this case that, provided there is adequate bonding between the masking
 tape 11 and the paint film 10, the crack 14 propagates in the direction of
 the arrow in the masking tape 11 having a substrate (FIG. 3C), ultimately
 leading to tape tearing (FIG. 3D).
 If bonding between the paint masking tape 11 and the paint film 10 is
 inadequate, the initial result of separating the distal end 12 of the
 paint masking tape 11 from the paint object 13 after the formation of a
 paint film 10 (FIG. 4A) will be the formation of a crack 14 in the paint
 film 10 (FIG. 4B), and continued peeling will cause the crack 14 to reach
 an adjacent crack 14' as a result of propagating in the direction of the
 arrow, that is, in the surface direction of the masking tape (FIG. 4C).
 This process results in the formation a paint flake 15 (FIG. 4D), which is
 then shed by the tape, released into the environment, and allowed to
 contaminate the paint surface.
 By contrast, the paint masking tape of the present invention is provided
 with a backing resin layer 4 composed of a urethane resin and an epoxy
 resin or a compound containing aziridine ring(s). As opposed to a paint
 masking tape devoid of such a backing resin layer 4, the tape substrate
 can be readily stretched by a very weak tensile force, and adhesion
 between the tape substrate and the paint film is kept sufficiently low.
 Consequently, the initial result of separating the distal end 12 of the
 paint masking tape 11 form the paint object 13 after the formation of a
 paint film 10 (FIG. 2A) is the formation of a crack 14 in the paint film
 10 (FIG. 2B), but the crack 14 thus formed in the paint film 10 does not
 propagate toward the paint masking tape 11 because the adhesion between
 the paint film 10 and the paint masking tape 11 is kept sufficiently low
 (FIG. 2C). Continued peeling then stretches the masking tape 11 even when
 a crack 14' has appeared adjacent to the crack 14, and this stretching
 prevents the crack 14 from propagating all the way to the crack 14',
 making it possible to prevent the formation and scattering of paint
 flakes.
 The present invention imposes no particular limitations on the substrate
 and allows any conventional plastic film to be used. Examples include
 films composed of polyesters, polyolefins, vinyl chloride, nylon, and the
 like.
 The thickness of the substrate 2 is commonly 25-200 .mu.m, but in the
 present invention a range of 50-150 .mu.m is preferred because the
 visibility of the parting lines tends to decrease with an increase in the
 thickness of the substrate 2.
 In the present invention, the backing resin layer 4 functions to adjust the
 adhesion between the paint masking tape 1 and the paint film formed
 thereon. The layer 4 also prevents the separation of paint flakes formed
 when the paint masking tape 1 is peeled off.
 In the present invention, such a backing resin layer 4 comprises at least a
 urethane resin and an epoxy resin or a compound containing aziridine
 ring(s).
 In this case, the urethane resin functions to endow the backing resin layer
 4 with film-forming properties. For example, ether-type urethane resins or
 ester-type urethane resins may be used. Commercially available products
 may be used as such urethane resins. Specific examples include Nipporan
 2301 (Polyurethane Kogyo) and Medium (Dainippon Ink & Chemicals).
 In addition, using a urethane resin together with an epoxy resin or a
 compound containing aziridine ring(s) ensures that the adhesion between
 the paint masking tape 1 and the paint film is reduced to an appropriate
 level and that the entire masking tape is rendered readily stretchable.
 A resin having two or more epoxy rings per molecule is preferred as such an
 epoxy resin from the standpoint of efficiency of reaction with the
 urethane resin. For example, a bisphenol-type epoxy resin is preferred for
 use. Specific examples include bisphenol A type epoxy resins, bisphenol F
 type epoxy resins, hydrogenation products of these resins, and epoxy
 resins modified with rubber on both sides of the bisphenol skeleton.
 The mixing ratio of the urethane resin and the epoxy resin in the backing
 resin layer 4 should preferably correspond to 4.0-10.0 weight parts epoxy
 resin per 100 weight parts urethane resin. When the proportion of the
 epoxy resin falls below this range, the adhesion between the
 flake-inhibiting layer and the paint film tends to increase excessively,
 and when the proportion exceeds the aforementioned range, the masking tape
 tends to resist stretching.
 In addition, a compound having two or more aziridine rings per molecule is
 preferred as a compound containing aziridine ring(s) from the standpoint
 of efficiency of reaction with the urethane resin. Preferred examples
 include trimethylol propane-tri-.beta.-aziridinyl propionate and
 trimethylol methyl-.beta.-aziridinyl propionate.
 Although no particular restrictions are imposed on the mixing ratio of the
 urethane resin and the compound containing aziridine ring(s) in the
 backing resin layer, it is preferable for the proportion of the compound
 containing aziridine ring(s) to be 0.2-10.0 weight parts per 100 weight
 parts of the urethane resin. A proportion of 0.75-7.5 weight parts is even
 more preferable from the standpoint of the visibility of parting lines.
 Acrylic resins, melamine resins, polyester resins, and other resins
 compatible with urethane resins and epoxy resins may also be added to the
 backing resin layer 4 as long as the object of the present invention is
 not compromised.
 Because an excessively thin backing resin layer 4 makes it impossible to
 achieve the effects of the present invention, the thickness should
 preferably be 1 .mu.m or greater, and particularly 3-10 .mu.m.
 In the present invention, the adhesive layer 3, which is designed for
 pasting the paint masking tape to a paint object, consists of base
 components and tackifying components.
 Examples of materials that can be used as base components include
 styrene-isoprene-styrene copolymers, styrene-butadiene-styrene copolymers,
 styrene-ethylene-butylene-styrene copolymers, and other styrene-based
 copolymers, as well as acrylic acid ester copolymers and other known
 materials.
 Aliphatic hydrocarbons, alicyclic hydrocarbons, hydrogenated starch, and
 other known adhesive resins may be used as tackifying components.
 The thickness of such an adhesive layer is commonly 20-50 .mu.m.
 It is also preferable for a colored layer 5 obtained by dispersing a
 colorant in a binder to be formed between the substrate 2 and the backing
 resin layer 4 of the paint masking tape pertaining to the present
 invention, as shown in FIG. 1B. Providing a colored layer 5 makes painted
 areas more visible and facilitates masking and peeling.
 Titanium oxide, clay, silica, mica, carbon, and the like may be used as the
 colorants for the colored layer 5, and urethane resins, polyester resins,
 acrylic resins, and the like may be used as binders. Here, the backing
 resin layer 4 contains a urethane resin, and using a urethane resin as a
 binder for the colored layer 5 is preferred from the standpoint of
 providing adequate adhesion between the backing resin layer 4 and the
 colored layer 5.
 When the proposed paint masking tape described above has an elasticity at
 break that is too low, it is possible that failure will occur unless the
 adhesion between the backing resin layer 4 and the paint film is set
 fairly low, and when elasticity at break is too high, it is possible that
 the masking tape w ill be readily deformed during peeling, adversely
 affecting the visibility of parting lines. It is therefore preferable for
 the elasticity at break of the paint masking tape to be set to 20-60% when
 an epoxy resin is used for the backing resin layer 4, and to 30-350% when
 a compound containing aziridine ring(s) is used. As used herein, the term
 "elasticity at break" refers to the value achieved when baking is
 completed following the formation of a paint film on the backing resin
 layer 4.
 In addition, the initial elastic modulus of the paint masking tape should
 be set to less than 10 kg/mm.sup.2, and preferably 6-9 kg/mm.sup.2,
 because a modulus that is too low results in excessive stretching and
 facilitates flaking, whereas a modulus that is too high makes failure more
 likely to occur.
 A release sheet should also be laminated on the surface of the adhesive
 layer 3 of the paint masking tape in order to prevent the adhesive layer
 from accidentally adhering to other surfaces.
 The paint masking tape of the present invention can be manufactured by a
 common method. For example, the desired paint masking tape can be
 manufactured by a method in which a gravure coater, knife coater, comma
 coater, or other coating apparatus is used to sequentially form first a
 flake-inhibiting layer or a colored layer and then a flake-preventing
 layer on a substrate. An adhesive layer is subsequently formed on the
 other side of the substrate, and a release sheet is optionally laminated
 on the adhesive layer.
 The proposed paint masking tape described above can be used in the same
 manner as a conventional paint masking tape. An example will now be
 described in which the masking tape of the present invention is used
 during the surface coating of a vehicle.
 The release sheet disposed on the adhesive layer side of the paint masking
 tape is first peeled off, and the surface of the adhesive layer is exposed
 and pasted to the desired location on the vehicle.
 A melamine-based, melamine/alkyl-based, acrylic/melamine-based, or other
 thermosetting paint is then sprayed over the vehicle surface and the
 masking tape, and the coating is baked to cure the paint. Because in this
 case the surface of the masking tape has been provided with a
 flake-inhibiting layer, the paint covers the paint object and the
 flake-inhibiting layer.
 Once baking has been completed, it is confirmed that the surface has
 returned to normal temperature, and the masking tape is peeled off,
 yielding the desired surface coat.
 EXAMPLES
 The present invention will now be described in further detail through
 examples.
 Examples 1-4 and Comparative Examples 1 and 2
 Fabrication of Paint Masking Tapes
 A urethane resin solution (Panacea CVL, manufactured by Dainippon Ink)
 containing titanium oxide was dried after being applied with the aid of a
 roll coater to a polypropylene film (P1146, manufactured by Toyobo) with a
 thickness of 80 .mu.m, yielding a colored layer with a thickness of 3
 .mu.m.
 The paints for backing resin layers shown in Table 1 were subsequently
 dried after being applied with the aid of a roll coater to the colored
 layer, yielding a backing resin layer with a thickness of 5 .mu.m.
 Comparative Example 2 pertains to a case in which no backing resin was
 used.
 TABLE 1
 (weight parts)
 Comparative
 Examples Examples
 Component 1 2 3 4 1 2
 Urethane resin 80 80 80 80 80 --
 solution*1
 Liquid epoxy 1.5 3.0 -- -- -- --
 resin*2
 Liquid epoxy -- -- 1.5 3.0 -- --
 resin*3
 MEK 100 100 100 100 100 100
 Notes to Table 1
 *1: Medium M (40% solids), manufactured by Dainippon Ink
 *2: EP4000, manufactured by Adeka
 *3: CY184, manufactured by Ciba Geigy
 An adhesive layer based on styrene rubber was subsequently formed by drying
 an adhesive composition based on styrene rubber after applying it in a dry
 thickness of 30 .mu.m to a surface obtained by the release treatment of a
 release sheet.
 The release sheet provided with the aforementioned adhesive layer was then
 laminated in such a way that the surface of the adhesive layer of the
 sheet faced the side of a polyolefin film substrate opposite from the
 backing resin layer of the substrate, yielding a paint masking tape.
 Fabrication of Coated Sample
 The release sheet of the resulting paint masking tape was subsequently
 peeled off, and the paint masking tape was pasted over a prescribed area
 of an aluminum plate, yielding a portion in which the masking tape was
 pasted over the aluminum plate, and a portion in which no masking tape was
 pasted.
 A melamine-based paint (manufactured by Nippon Paint) was subsequently
 sprayed as a paint for surface coating, yielding a 25 .mu.m coat. The
 product was then baked at 80.degree. C. for 10 minutes and at 150.degree.
 C. for an hour, yielding coated samples pertaining to the practical and
 comparative examples.
 Evaluation
 The samples thus obtained were evaluated in accordance with the criteria
 described below. The results are shown in Table 2.
 Peel Tests
 The masking tape sections of the aforementioned coated samples were
 manually pulled about 20 cm at a peel angle of about 180.degree., and tape
 tearing was evaluated.
 Here, "A" was assigned to cases in which no tape tearing occurred and the
 tape could be peeled off along a prescribed length; "B" was assigned to
 cases in which the tape, rather than tearing immediately after peeling,
 broke before a prescribed length had been peeled off; and "C" was assigned
 to cases in which the tape broke immediately after peeling and could not
 withstand usage.
 Flaking (Scattering of Paint Film)
 The flaking of the paint films on the samples subjected to the
 aforementioned peel tests was visually evaluated. Here, "A" was assigned
 to cases in which cracks in the paint films failed to produce paint
 flakes, or to cases in which the paint flakes were produced but were not
 shed by the masking tape, and "B" was assigned to cases in which the paint
 flakes were scattered to other areas.
 Parting Lines
 The visibility of parting lines between painted areas and unpainted areas
 was visually evaluated following the aforementioned peel tests. Here, "A"
 was assigned to cases in which the parting lines were clearly visible, "B"
 was assigned to cases in which the parting lines were not clearly visible
 but no problems were encountered in terms of actual usage; and "C" was
 assigned to cases in which the parting lines were not clearly visible and
 the tape was unsuitable for actual use.
 Breaking Strength and Elasticity at Break
 A coated sample was cut into widths of 20 mm, mounted on a Tensilon (a
 friction apparatus manufactured by Orientech), and measured for breaking
 strength and elasticity at break during peeling at a speed of 1000 mm/min.
 Initial Elastic Modulus (kg/mm.sup.2)
 During the aforementioned measurements of breaking strength, an elastic
 modulus corresponding to an elongation of up to 10% was measured.
 TABLE 2
 Initial
 Elasticity Breaking Elastic
 Peel Flak- Parting at Break Strength Modulus
 Test ing Line (%) (kgf) (kg/mm.sup.2)
 Example 1 A A A 30 2.80 8
 Example 2 A A A 55 2.80 7
 Example 3 A A A 24 2.50 8
 Example 4 A A A 27 2.70 7
 Comparative B A -- 15 2.00 10
 Example 1
 Comparative C A -- 10 1.50 35
 Example 2
 It can clearly be seen in Table 2 that the paint masking tapes of Examples
 1-4, which have a backing resin layer composed of a urethane resin and an
 epoxy resin, allow a prescribed length to be peeled off without being torn
 during tape separation. In addition, there is no flaking-induced
 scattering of paint flakes despite the formation of cracks, and the
 parting lines are clearly visible.
 On the other hand, the paint masking tape of Comparative Example 1, which
 has a backing resin layer but does not contain an epoxy resin, has lower
 elasticity at break (elongation) and is more apt to tear than any of the
 paint masking tapes belonging to Examples 1-4. In addition, the paint
 masking tape of Comparative Example 2, which does not have a backing resin
 layer, develops a strong bond between the substrate and the paint film and
 tends to tear immediately after the start of the peel test.
 Thus, the paint masking tapes of Practical Examples 1-4 do not tear easily
 when peeled off from a paint object, inhibit the flaking-induced
 scattering of paint flakes, and provide clearly visible parting lines.
 Examples 5-11 and Comparative Examples 3 and 4
 Fabrication of Paint Masking Tapes
 A urethane resin solution (Panacea CVL, manufactured by Dainippon Ink)
 containing titanium oxide was dried after being applied with the aid of a
 roll coater to a polypropylene film (P1146, manufactured by Toyobo) with a
 thickness of 80 .mu.m, yielding a colored layer with a thickness of 3
 .mu.m.
 The paints for backing resin layers shown in Table 3 were subsequently
 dried after being applied with the aid of a roll coater to the colored
 layer, yielding a backing resin layer with a thickness of 5 .mu.m.
 Comparative Example 3 pertains to a case in which no backing resin was
 used.
 TABLE 3
 (weight parts)
 Comparative
 Examples Examples
 Components 5 6 7 8 9 10 11 3 4
 Urethane resin 100 100 100 100 100 100 100 -- --
 solution*4
 Acrylic resin*5 -- -- -- -- -- -- -- -- 100
 Compound containing 0.75 1.25 2.50 5.00 7.50 10.00 0.2 -- 0.3
 aziridine ring(s)*6
 MEK 100 100 100 100 100 100 100 100
 Notes to Table 3
 *4: Nipporan 2301 (40% solids), manufactured by Polyurethane Kogyo
 *5: Methyl methacrylate/butyl acrylate copolymer
 *6: TAZM, manufactured by Sogo Yakko
 An adhesive layer based on styrene rubber was subsequently formed by drying
 an adhesive composition based on styrene rubber after applying it in a dry
 thickness of 30 .mu.m to a surface obtained by the release treatment of a
 release sheet.
 The release sheet provided with the aforementioned adhesive layer was then
 laminated in such a way that the surface of the adhesive layer of the
 sheet faced the side of a polyolefin film substrate opposite from the
 backing resin layer of the substrate, yielding a paint masking tape.
 Fabrication of Coated Sample
 The release sheet of the resulting paint masking tape was subsequently
 peeled off, and the paint masking tape was pasted over a prescribed area
 of an aluminum plate, yielding a portion in which the masking tape was
 pasted over the aluminum plate, and a portion in which no masking tape was
 pasted.
 A melamine-based paint (manufactured by Nippon Paint) was subsequently
 sprayed as a paint for surface coating, yielding a 50 .mu.m coat. The
 product was then baked at 150.degree. C. for an hour, yielding coated
 samples pertaining to the practical and comparative examples.
 Evaluation
 The same procedures as in Practical Example 1 were used to evaluate the
 samples for peeling, flaking (paint film scattering), parting line
 visibility, and breaking strength and elasticity at break. The results are
 shown in Table 4. The tests for breaking strength and elasticity at break
 were performed at a release sample peel velocity of 300 mm/min.
 TABLE 4
 Elasticity Breaking
 Peel Parting at Break Strength
 Test Flaking Line (%) (kgf)
 Example 5 A A A 30 2.00
 Example 6 A A A 45 2.50
 Example 7 A A A 100 2.50
 Example 8 A A A 200 3.00
 Example 9 A A A 350 2.95
 Example 10 A B B 350 2.95
 Example 11 B A A 30 2.00
 Comparative B A -- 10 2.50
 Example 3
 Comparative C A -- -- 3.00
 Example 4
 It can clearly be seen in Table 4 that the paint masking tapes of Examples
 5-9, which have a backing resin layer composed of a urethane resin and a
 compound containing aziridine ring(s), allow a prescribed length to be
 peeled off without being torn during tape separation. In addition, there
 is no flaking-induced scattering of paint flakes, and the parting lines
 are clearly visible.
 The results of Example 10 also demonstrate that when a comparatively large
 amount of a compound containing aziridine ring(s) is used, paint flakes
 tend to form despite the absence of tape tearing, and this trend is
 accompanied by a reduction in the visibility of parting lines. In
 addition, the results of Practical Example 11 demonstrate that the tape
 tends to tear more readily when the aziridine ring compound is used in a
 comparatively small amount.
 On the other hand, the paint masking tape of Comparative Example 3, which
 does not have a backing resin layer, develops a strong bond between the
 substrate and the paint film and tends to tear immediately after the start
 of the peel test. In addition, the paint masking tape of Comparative
 Example 4, which has a backing resin layer containing an aziridine ring
 compound but does not contain a urethane resin, has lower elasticity at
 break (elongation) and is more apt to tear than any of the paint a masking
 tapes belonging to Examples 5-11.
 In addition, it can be seen that, based on the elasticity at break achieved
 in Examples 5-11, the provision of a backing resin layer makes it possible
 to set the elasticity at break to at least 30-350%.
 Thus, the paint masking tapes of Examples 5-11 do not tear easily when
 peeled off from a paint object, inhibit the flaking-induced scattering of
 paint flakes, and provide clearly visible parting lines.
 The entire disclosures of the specifications, summaries, claims and
 drawings of Japanese Patent Applications Nos. 9-113070 filed on Apr. 30,
 1997 and 9-115486 filed on May 6, 1997 are herein incorporated by
 reference in their entirety.