Electron beam irradiating method and object to be irradiated with electron beam

A process of accelerating electrons with a voltage applied thereto in a vacuum, guiding the accelerated electrons into a normal-pressure atmosphere, and irradiating the electron beam (EB) onto an object. The electron beam irradiation process uses a vacuum tube-type electron beam irradiation apparatus, and with the acceleration voltage for generating an electron beam set at a value smaller than 100 kV, the electron beam is irradiated onto the object.

TECHNICAL FIELD
 The present invention relates to an electron beam irradiation process for
 irradiating an object with an electron beam (EB) which is obtained by
 accelerating electrons with a voltage applied thereto in a vacuum and
 guiding the accelerated electrons into a normal-pressure atmosphere, and
 to an object irradiated with such an electron beam.
 BACKGROUND ART
 There has been proposed a process utilizing electron beam irradiation to
 crosslink, cure or modify a coating material applied to a substrate or
 base, such as paint, printing ink, adhesive, pressure sensitive, etc., or
 other resin products, and extensive studies have been made up to the
 present. In this process, electrons are accelerated with a voltage applied
 thereto in a vacuum and the accelerated electrons are guided into a
 normal-pressure atmosphere, such as in the air, so that an object may be
 irradiated with an electron beam (EB).
 Crosslinking, curing or modification by means of electron beam irradiation
 have the following advantages:
 (1) Organic solvent need not be contained as a diluent, and thus the
 adverse effect on the environment is small.
 (2) The rate of crosslinking, curing or modification is high (productivity
 is high).
 (3) The area required for crosslinking, curing or modification is small,
 compared with heat drying treatment.
 (4) The substrate or base is not applied with heat (electron beam
 irradiation is applicable to those materials which are easily affected by
 heat).
 (5) Post-treatment can be immediately carried out (cooling, aging, etc. are
 unnecessary).
 (6) It is necessary that the conditions for electrical operation be
 controlled, but the required control is easier than the temperature
 control for heat drying treatment.
 (7) Neither initiator nor sensitizing agent is required, and thus the final
 product contains less impurities (quality is improved).
 According to conventional electron beam irradiation techniques, however, a
 high-energy electron beam is used to crosslink, cure or modify objects at
 a high rate, and no consideration is given to energy efficiency.
 Conventional techniques are also associated with problems such as the
 problem that much initial investment is required because of large-sized
 apparatus, the problem that inerting by means of an inert gas such as
 nitrogen, which is high in running cost, is needed in order to eliminate
 inhibition to the reaction at surface caused due to generation of oxygen
 radical, and the problem that shielding from secondary X-ray is required.
 Specifically, conventional electron beam curing or crosslinking uses an
 acceleration voltage which is usually as high as 200 kV to 1 MV and thus
 x-rays are generated, making it necessary to provide a large-scale shield
 for the apparatus. Also, where such a high-energy electron beam is used,
 care must be given to possible adverse influence on the working
 environment due to generation of ozone. Since the reaction at the surface
 of an object is inhibited due to generation of oxygen radical, moreover,
 inerting by means of an inert gas such as nitrogen is required.
 Further, an electron beam generated with a high acceleration voltage
 applied thereto penetrates to a great depth and thus can sometimes
 deteriorate the substrate or base such as a resin film or paper. In the
 case of paper, for example, disintegration of cellulose due to the
 breakage of glycoside bond takes place at a relatively small dose, and it
 is known that deterioration in the folding strength is noticeable even at
 an irradiation dose of 1 Mrad or less. Especially in the case where the
 substrate or base has a coating material (printing ink, paint, adhesive,
 etc.) of 0.01 to 30 .mu.m thick printed thereon or applied thereto, the
 thickness of the coating material is small and the substrate or base may
 have an exposed surface having no coating material thereon, often giving
 rise to a problem that the substrate or base is deteriorated.
 Accordingly, there is a demand for low-energy electron beam irradiation
 apparatus and process which use low acceleration voltage and which permit
 reduction in size of the apparatus.
 To meet the demand, various apparatus and process using low acceleration
 voltage for electron beam irradiation have been proposed, and Japanese
 Patent Disclosure (KOKAI) No.5-77862, for example, discloses a process for
 30-Mrad irradiation at 200 kV, as an example of electron beam irradiation
 at a low acceleration voltage. However, even with this process, the
 acceleration voltage is not low enough to prevent deterioration of the
 substrate or base and also inerting is required.
 Japanese Patent Disclosure No. 6-317700 discloses an apparatus and process
 for irradiating an electron beam with the acceleration voltage adjusted to
 90 to 150 kV. According to this technique, a titanium or aluminum foil of
 10 to 30 .mu.m in thickness is used as a window material which intervenes
 between an electron beam generating section of the electron beam
 irradiation apparatus, in which electrons released from the cathode are
 guided and accelerated to obtain an electron beam, and an irradiation room
 in which an object is irradiated with the electron beam.
 However, even with this technique, when the acceleration voltage is set to
 100 kV or less in actuality, the penetrating power of the electron beam is
 very low, and since most of the electron beam is absorbed by the window
 material, the electron beam cannot be efficiently guided into the
 irradiation room. Also, the temperature of the window material may
 possibly rise up to its heat resistance temperature or higher.
 Consequently, the apparatus is in practice used with the acceleration
 voltage set at a level higher than 100 kV, and even with such acceleration
 voltage, deterioration of the substrate or base can be caused.
 Thus, the electron beam curing technique has been attracting attention as a
 process which serves to save energy, does not require the use of solvent
 and is less harmful to the environment, but it cannot be said that the
 technique has been put to fully practical use because of the
 aforementioned problems.
 DISCLOSURE OF THE INVENTION
 The present invention was created in view of the above circumstances, and
 an object thereof is to provide an electron beam irradiation process
 capable of irradiating an electron beam with high energy efficiency and an
 object irradiated with such an electron beam, without entailing problems
 with apparatus etc.
 According to a first aspect of the present invention, there is provided an
 electron beam irradiation process for performing electron beam irradiation
 by using a vacuum tube-type electron beam irradiation apparatus, wherein
 an object is irradiated with an electron beam with an acceleration voltage
 for generating the electron beam set at a value smaller than 100 kV. Also,
 according to this aspect of the invention, an electron beam irradiation
 process is provided wherein the acceleration voltage is 10 to 60 kV and
 the object comprises a coating of 0.01 to 30 .mu.m thick formed on a
 substrate or base.
 According to a second aspect of the present invention, an electron beam
 irradiation process for irradiating an object with an electron beam is
 provided, wherein an electron beam is irradiated in such a manner that a
 rate of absorption y (%) of the irradiated electron beam by an object,
 which rate of absorption is expressed as "absorbed dose for a certain
 depth/all absorbed dose", fulfills a relationship indicated by expression
 (1) below, where x is a product of penetration depth (.mu.m) and specific
 gravity of the object. Also provided according to this aspect of the
 invention is an electron beam irradiation process wherein an acceleration
 voltage for generating the electron beam is 100 kV or less and the object
 has a thickness of 50 .mu.m or less. Further, an electron beam irradiation
 process is provided wherein irradiation of the electron beam is performed
 using a vacuum tube-type electron beam irradiation apparatus.
EQU y.gtoreq.-0.01x.sup.2 +2x(0&lt;x.gtoreq.100) (1)
 The penetration depth indicates a distance in the thickness direction of
 the object for which the irradiated electron beam penetrates.
 According to a third aspect of the present invention, there is provided an
 electron beam irradiation process for irradiating an object with an
 electron beam, wherein when an acceleration voltage of an electron beam to
 be irradiated is lower than or equal to 40 kV, the electron beam is
 irradiated in such a manner that an oxygen concentration of a region
 irradiated with the electron beam is substantially equal to or lower than
 air, and when the acceleration voltage of an electron beam to be
 irradiated is higher than 40 kV, the electron beam is irradiated in such a
 manner that the oxygen concentration of the region irradiated with the
 electron beam fulfills a relationship indicated by expression (a)
EQU Y.ltoreq.1.19.times.10.sup.2.times.exp(-4.45.times.10.sup.-2.times.X) (a)
 where X is the acceleration voltage (kV) and Y is the oxygen concentration
 (%) of the region irradiated with the electron beam.
 Preferably, in this case, when an acceleration voltage of an electron beam
 to be irradiated is lower than or equal to 40 kV, the electron beam is
 irradiated in such a manner that an oxygen concentration of a region
 irradiated with the electron beam is substantially equal to or lower than
 air, and when the acceleration voltage of an electron beam to be
 irradiated is higher than 40 kV, the electron beam is irradiated in such a
 manner that the oxygen concentration of the region irradiated with the
 electron beam fulfills a relationship indicated by expression (b)
EQU 1.19.times.10.sup.2.times.exp(-4.45.times.10.sup.
 -2.times.X).gtoreq.Y.gtoreq.0.05 (b)
 where X is the acceleration voltage (kV) and Y is the oxygen concentration
 (%) of the region irradiated with the electron beam.
 According to a fourth aspect of the present invention, there is provided an
 electron beam irradiation process, wherein an object having a curved or
 uneven surface is irradiated with an electron beam while an electron beam
 generating section of an electron beam irradiation apparatus is moved for
 scanning. Also, according to this aspect of the invention, an electron
 beam irradiation process is provided wherein the electron beam generating
 section is moved for scanning while a distance between the electron beam
 generating section and the object is kept at a constant value by means of
 a sensor.
 According to a fifth aspect of the present invention, there is provided an
 electron beam irradiation process, wherein a distribution of degree of
 crosslinking, curing or modification is created in a thickness direction
 of an object by irradiating the object with an electron beam.

BEST MODE OF CARRYING OUT THE INVENTION
 Embodiments according to the present invention will be hereinafter
 described in detail.
 FIG. 1 is a schematic view of an irradiation tube which is used as an
 electron beam generating section in an electron beam irradiation apparatus
 for carrying out the present invention. The apparatus includes a
 cylindrical vacuum container 1 made of glass or ceramic, an electron beam
 generating section 2 arranged within the container 1 for guiding and
 accelerating electrons released from a cathode to obtain an electron beam,
 an electron beam emitting section 3 arranged at one end of the vacuum
 container 1 for emitting the electron beam, and a pin section 4 for
 feeding power to the apparatus from a power supply, not shown. The
 electron beam emitting section 3 is provided with a thin-film irradiation
 window 5. The irradiation window 5 of the electron beam emitting section 3
 has a function of transmitting electron beam, and not gas, therethrough
 and is flat in shape, as shown in FIG. 2. An object placed in an
 irradiation room is irradiated with the electron beam emitted through the
 irradiation window 5.
 Namely, this apparatus is a vacuum tube-type electron beam irradiation
 apparatus, which differs basically from a conventional drum-type electron
 beam irradiation apparatus. In the conventional drum-type electron beam
 irradiation apparatus, electron beam is radiated while a vacuum is drawn
 all the time within the drum.
 An apparatus provided with an irradiation tube having such configuration is
 disclosed in U.S. Pat. No. 5,414,267 and has been proposed by American
 International Technologies (AIT) INC. as Min-EB apparatus. With this
 apparatus, reduction in the penetrating power of electron beam is small
 even at a low acceleration voltage of as small as 100 kV or less, and an
 electron beam can be obtained effectively. It is therefore possible to
 allow an electron beam to act upon a coating material on a substrate or
 base for a small depth, and also to decrease damage on the substrate or
 base as well as the quantity of secondary X-rays generated, making it
 almost unnecessary to provide a large-scale shield.
 Further, since the energy of electron beam is low, inhibition to the
 reaction at the surface of the coating material due to oxygen radical can
 be decreased, thus diminishing the need for inerting.
 The inventors hereof diligently investigated the acceleration voltage to be
 applied to an electron beam and the allowable oxygen concentration in a
 low acceleration voltage region. As a result of investigation, they found
 that, where the acceleration voltage applied to the electron beam was
 higher than 40 kV, predetermined crosslinking, curing or modifying power
 could be achieved by irradiating an object with the electron beam in such
 a manner that the oxygen concentration of a region irradiated with the
 electron beam fulfilled the relationship indicated by expression (a)
 below, without entailing inhibition to the reaction at the surface of the
 coating material etc. due to oxygen radical.
EQU Y.ltoreq.1.19.times.10.sup.2.times.exp(-4.45.times.10.sup.-2.times.X) (a)
 where X is the acceleration voltage (kV) and Y is the oxygen concentration
 (%) of the region irradiated with the electron beam.
 It was also found that, for irradiation at 40 kV or lower, electron beam
 irradiation could be satisfactorily performed at an oxygen concentration
 of 20% or thereabouts, that is, almost without the need for inerting.
 According to the present invention, therefore, where the acceleration
 voltage applied to the electron beam is 40 kV or lower, electron beam
 irradiation is performed at an oxygen concentration lower than or
 substantially equal to that of the air, and where the acceleration voltage
 is higher than 40 kV, the electron beam is irradiated onto an object with
 the oxygen concentration controlled so as to fulfill the relationship
 indicated by the above equation (a), wherein X represents the acceleration
 voltage (kV) and Y represents the oxygen concentration (%) of the region
 irradiated with the electron beam.
 Taking account of the oxygen radical-induced inhibition to the reaction at
 the surface of the object such as the coating material etc., the oxygen
 concentration should preferably fall within the range indicated by
 expression (b) below, though there is no lower limit on the oxygen
 concentration, from the point of view of the running cost incurred by the
 replacement with nitrogen.
EQU 1.19.times.10.sup.2.times.exp(-4.45.times.10.sup.
 -2.times.X).gtoreq.Y.gtoreq.0.05 (b)
 It is also known that, with such a low acceleration voltage, the quantity
 of ozone produced could be greatly cut down at the same time.
 Irradiating an electron beam in the air without the need for inerting
 provides various advantages including reduction of the running cost. In
 view of this, according to the present invention, in order to eliminate
 inhibition to polymerization due to oxygen radical, which is a problem
 associated with electron beam irradiation in the air, an object is first
 irradiated with ultraviolet rays to such an extent that only a surface
 region thereof is crosslinked, cured or modified, and then is irradiated
 with the electron beam. This permits the object to be more satisfactorily
 crosslinked, cured or modified without the oxygen inhibition to
 polymerization.
 Also, by first irradiating an object in the air with an electron beam at an
 acceleration voltage of 40 kV or lower and then with ultraviolet rays, it
 is possible to obtain an equally satisfactorily cured object without the
 oxygen inhibition to polymerization.
 A similar effect can be achieved by first irradiating an object in the air
 with an electron beam at an acceleration voltage of 40 kV or lower and
 then with an electron beam at a higher acceleration voltage. Preferably,
 in this case, the electron beam is irradiated first at an acceleration
 voltage of 30 kV or lower and then at a higher acceleration voltage.
 According to a typical process embodying the present invention, an array 11
 is constituted by combining a plurality of electron beam irradiation
 apparatus 10 having the configuration described above, as shown in FIG. 3,
 and electron beams are irradiated from the individual electron beam
 irradiation apparatus 10 constituting the array 11 onto an object 13
 transported at a predetermined speed in an irradiation room 12 which is
 located beneath the array 11. In the figure, reference numeral 14 denotes
 an X-ray shield and 15 denotes a conveyor shield.
 Thus, the shields can be reduced in size, the degree of inerting can be
 lowered, and also the electron beam generating section can be reduced in
 size because the acceleration voltage is low; therefore, the electron beam
 irradiation apparatus can be drastically reduced in size and its
 application to a variety of fields is expected.
 The apparatus uses a low acceleration voltage, thus providing a small depth
 of penetration of the electron beam, and since the acceleration voltage
 can be controlled with ease, it is possible to control the electron beam
 penetration depth. This will be explained with reference to FIG. 4. FIG. 4
 shows the relationship between electron beam penetration depth and
 irradiation dose observed when electron beam is irradiated at different
 acceleration voltages with the use of the aforementioned apparatus. The
 figure reveals that, where the acceleration voltage is low, the electron
 beam can exert a marked effect within a certain range of thickness, and
 where the acceleration voltage is high, the electron beam penetrates
 through the coating to the substrate or base.
 This implies that, in the case of electron beam irradiation at low
 acceleration voltage, low energy generation suffices to obtain an
 irradiation dose required to crosslink, cure or modify the coating with
 the electron beam.
 With conventional electron beam irradiation apparatus, an electron beam
 cannot be obtained but at high acceleration voltage, and therefore, an
 electron beam of excessively high energy must be irradiated onto ink,
 paint, adhesive or the like to crosslink, cure or modify the same, thus
 leaving no room for consideration of the rate of absorption of the
 electron beam.
 By contrast, according to the present invention which is based on the
 assumption that the aforementioned vacuum tube-type electron beam
 irradiation apparatus excellent in controllability is used, the electron
 beam is irradiated in such a manner that a rate of absorption y (%) of the
 irradiated electron beam by an object, which rate of absorption is
 expressed as "absorbed dose for a certain depth/all absorbed dose",
 fulfills the relationship indicated by expression (1) below.
EQU y.gtoreq.-0.01x.sup.2 +2x(0&lt;x.ltoreq.100) (1)
 where x is the product of the depth of penetration (.mu.m) and the specific
 gravity of the object.
 Namely, the electron beam is irradiated in an upper region in FIG. 5
 defined by the curve.
 The rate of the electron beam absorption as defined above increases with
 reduction in the acceleration voltage applied to the electron beam, and
 therefore, in the case where an electron beam is irradiated using the
 vacuum tube-type electron beam irradiation apparatus capable of
 effectively emitting an electron beam even at a low acceleration voltage,
 high rate of absorption can be achieved. The curve in FIG. 5 illustrates
 the case where the acceleration voltage is 100 kV, and the present
 invention is intended to irradiate an electron beam with a rate of
 absorption higher than or equal to that on the curve, that is, at an
 acceleration voltage lower than or equal to 100 kV. For an identical
 acceleration voltage, the rate of absorption increases with increase in
 the product of the penetration depth and the specific gravity of an
 object, and shows a maximum value when the product takes a certain value.
 In this case, the object to be irradiated with the electron beam preferably
 has a thickness of approximately 100 .mu.m or less.
 To measure the irradiation dose of an electron beam, a method using a film
 dosimeter is very often employed. The film dosimeter uses a dose
 measurement film whose spectral properties change on absorbing energy when
 irradiated with an electron beam and utilizes the fact that there is a
 correlation between the amount of such change in the spectral properties
 and the absorbed dose.
 Since high rate of absorption can be achieved as described above, it is
 possible to irradiate an electron beam with high energy efficiency that is
 not achievable with conventional apparatus. Consequently, where an object
 is irradiated with an electron beam for the purpose of crosslinking,
 curing or modification, for example, the purpose is fulfilled with the use
 of low energy which is about 1/4 to 1/2 of that needed in conventional
 apparatus.
 The present invention uses an electron beam irradiation apparatus provided
 with the aforementioned irradiation tube as the electron beam generating
 section, and when an object having a curved or uneven surface is to be
 irradiated with an electron beam, the irradiation tube itself is moved for
 scanning. Specifically, a sensor is mounted to the irradiation tube so
 that the distance to the surface of the coating material etc. on the
 substrate or base may be controlled to a constant value, and the
 irradiation tube is moved for scanning by a three-dimensional robot etc.
 having an articulated arm. This prevents uneven curing and permits the
 electron beam to be irradiated more efficiently. In this case, the width
 of irradiation may be suitably selected in accordance with the size or the
 shape of the surface, curved or irregular, of an object to be irradiated
 or of the substrate or base having a coating material thereon. The
 electron beam emitted through the window of the irradiation tube reaches
 the coating material and cures, crosslinks or modifies the coating
 material.
 Since, in this case, the electron beam is irradiated to the entire surface,
 time is required for the scanning with the use of the irradiation tube,
 but no problem arises because the rate of reaction by means of electron
 beam is by far higher than that of thermal curing or UV curing, as is
 already known in the art.
 FIG. 6 shows a specific arrangement of an electron beam irradiation
 apparatus for carrying out the present invention. In the figure, reference
 numeral 20 denotes a main body including an electron beam irradiation
 tube, and an optical sensor 21 is mounted to the main body 20. As shown in
 FIG. 7, the main body 20 comprises an irradiation tube 27 having an
 irradiation window 28, and a shielding member 29 surrounding the
 irradiation tube.
 The optical sensor 21 is attached to the shielding member 29 and emits
 light from a distal end thereof to detect the distance between the surface
 of a coating material 26 on a curved substrate or base 30 and the
 irradiation window 28.
 The main body 20 is mounted to a distal end of an articulated expansion arm
 22, which is actuated by an arm driving robot 23. The arm robot 23 is
 controlled by a control unit 24. Reference numeral 25 denotes a power
 supply unit.
 In the apparatus having such arrangement, the control unit 24 supplies a
 command to the arm robot 23 in accordance with information from the
 optical sensor 21 and set information, to move the main body 20 including
 the irradiation tube for scanning via the articulated arm 22 in such a
 manner that the distance between the irradiation window 28 and the coating
 material 26 is kept constant.
 The apparatus uses the articulated expansion arm 22 and thus can freely
 follow up the object or the substrate or base even if it has a curved
 surface. Also, the use of the optical sensor 21 permits the distance
 between the irradiation window 28 and the coating material 26 to be kept
 constant. Consequently, uneven curing is prevented and the electron beam
 can be irradiated with higher efficiency.
 Taking advantage of the fact that the electron beam penetration depth is
 controllable, the present invention creates a distribution of the degree
 of crosslinking, curing or modification in the thickness direction of an
 object by irradiating the object with an electron beam.
 Specifically, an object is irradiated with an electron beam at an
 acceleration voltage having a predetermined intermediate penetration depth
 along the thickness of the object, so that while the surface region of the
 object up to the penetration depth is crosslinked, cured or modified, the
 deeper region than the penetration depth is lower in the degree of
 crosslinking, curing or modification than the surface region or is not
 crosslinked, cured or modified at all. As a result, a distribution of the
 degree of crosslinking, curing or modification in the thickness direction
 is produced. To put it in another way, the object can be partially
 crosslinked, cured or modified with respect to the thickness direction
 thereof. As a typical example, only the surface region of the object may
 be crosslinked, cured or modified.
 Thus, the degree of crosslinking, curing or modification can be
 distributed, so that the present invention has a wide variety of
 applications.
 Specifically, the present invention can provide a structure of which the
 surface alone has high hardness while the interior of which is soft, a
 structure of which the surface alone has low hardness, a gradation
 structure or layered structure of which the degree of crosslinking,
 hardness or modification varies gradually.
 Crosslinking and curing achieved by the present invention also include
 graft polymerization, and modification signifies breakage of chemical
 bond, orientation, etc., exclusive of crosslinking and polymerization.
 To form a gradation structure or layered structure without fail, preferably
 the object is first crosslinked, cured or modified partially with respect
 to the thickness direction and then heat-treated to crosslink, cure or
 modify the non-crosslinked, non-cured or non-modified portion to a certain
 extent, thereby creating a distribution of the degree of crosslinking,
 curing or modification.
 The apparatus to which the electron beam irradiation process according to
 the present invention is applied is not particularly limited, but the
 aforementioned vacuum tube type is preferred in view of controllability.
 Namely, a vacuum tube-type electron beam irradiation apparatus, a typical
 example of which is Min-EB, can effectively radiate an electron beam even
 at low acceleration voltage as described above; therefore, the electron
 beam can be made to act upon a small depth with good controllability and
 also controllability of the penetration depth is high.
 From the point of view of controllability of the penetration depth, the
 acceleration voltage applied to the electron beam is preferably 150 kV or
 less, more preferably 100 kV or less. The still more preferred range of
 the acceleration voltage is from 10 to 70 kV. To carry out the electron
 beam irradiation process of the present invention at such a low
 acceleration voltage, an object to be irradiated with the electron beam
 preferably has a thickness of 10 .mu.m or more, more preferably 10 to 300
 .mu.m. The still more preferred range of thickness is approximately 10 to
 100 .mu.m. The thickness of the object may of course be less than 10
 .mu.m, that is, in the range of 1 to 9 .mu.m, or may be greater than 300
 .mu.m.
 Objects to which the present invention is applicable include not only a
 relatively thin material formed on a substrate or base, such as printing
 ink, paint, adhesive, pressure sensitive, etc., but a plastic film, a
 plastic sheet, a printing plate, a semiconductor material, a controlled
 release material of which the active ingredient is gradually released,
 such as a poultice, and a golf ball.
 Among these, for printing ink and paint formed on a substrate or base, only
 the surface region is crosslinked or cured, whereby shrinkage of the
 portion adjoining the substrate or base is suppressed and thus the
 adherence to the substrate or base can be enhanced. For adhesive or
 pressure sensitive,only the surface region is crosslinked or cured while
 the soft, adhesive interior is left as it is, whereby such adhesives can
 be applied to a variety of fields.
 Objects to be irradiated with electron beam, to which the present invention
 can be applied, also include, for example, a coating material applied to a
 substrate or base, such as printing ink, paint, adhesive, etc.
 Among these, printing ink maybe ink which crosslinks or cures when exposed
 to activation energy such as ultraviolet rays, electron beam or the like,
 for example, letterpress printing ink, offset printing ink, gravure
 printing ink, flexographic ink, screen printing ink, etc.
 Examples of paint include resins such as acrylic resin, epoxy resin,
 urethane resin, polyester resin, etc., various photosensitive monomers,
 and paints which use oligomers and/or prepolymers and which crosslink or
 cure upon exposure to activation energy such as ultraviolet rays, electron
 beam or the like.
 For adhesive, adhesives of reactive curing type (monomer type, oligomer
 type, prepolymer type) such as vinyl polymer type (cyanoacrylate,
 diacrylate, unsaturated polyester resin), condensation type (phenolic
 resin, urea resin, melamine resin), and polyaddition type (epoxy resin,
 urethane resin) may be used. Such adhesive may be used to bond
 those,materials which are easily affected by heat, such as lens, glass
 sheet, etc., besides conventional applications.
 Substrates or bases to be coated with the coating material may be metals
 such as treated or untreated stainless steel (SUS) or aluminum, plastic
 materials such as polyethylene, polypropylene, polyethylene terephthalate
 or polyethylene naphthalate, paper, fibers, etc.
 The coating materials mentioned above may contain various additives
 conventionally used. Such additives include, for example, pigment, dye,
 stabilizer, solvent, antiseptic, anti-fungus agent, lubricant, activator,
 etc.
 EXAMPLES
 Examples according to the present invention will be now described. In the
 following description, the terms "parts" and "%" represent "parts by
 weight" and "% by weight", respectively.
 (Example 1)
 As an example of curable coating composition, offset printing ink was used.
 The offset printing ink was prepared following the procedure described
 below.
 [Preparation of Varnish]
 A vessel was charged with 69.9% dipentaerythritol hexaacrylate and 0.1%
 hydroquinone, and after the mixture was heated to 100.degree. C., 30 parts
 of DT (diallyl phthalate resin from Tohto Kasei) were charged by degrees.
 After the constituents were dissolved, the mixture was bailed out. The
 mixture at this time had a viscosity of 2100 poises (25.degree. C.).
 [Preparation of Printing Ink]
 A mixture specified below was dispersed using a three-roll mill, thereby
 obtaining offset printing ink.

Blue pigment (LIONOL BLUE FG7330) 15 parts
 Varnish prepared as stated above 50 parts
 Dipentaerythritol hexaacrylate 25 parts
 Pentaerythritol tetraacrylate 10 parts
 Using an RI tester (handy printing machine generally used in the printing
 ink industry), the ink prepared as stated above was used to obtain a print
 on which about 2-.mu.m thick ink was printed.
 After the printing, EB irradiation was performed using a Min-EB apparatus
 from AIT Corporation. The conditions for irradiation were as follows:
 acceleration voltage: 40 kV; electric power used: 50 W; and conveyor
 speed: 20 m/min. For the inerting, nitrogen was used.
 Following the irradiation, the drying property was evaluated by touching
 the surface with fingers to thereby evaluate. the degree of curing. As the
 criteria for evaluation, a five-grade system was employed wherein "5"
 indicates "completely cured" and "1" indicates "not cured."
 The result obtained is shown in Table 1.
 (Example 2)
 Except that the formulation of Example 1 was changed as stated below,
 printing was performed in the same manner, EB irradiation was performed
 under the same conditions, and the degree of curing was evaluated based on
 the aforementioned criteria. The evaluation result is also shown in Table
 1.

Blue pigment (LIONOL BLUE FG7330) 12 parts
 Varnish prepared as stated above 50 parts
 Dipentaerythritol hexaacrylate 28 parts
 Pentaerythritol tetraacrylate 10 parts
 (Example 3)
 After printing was performed in the same manner as in Example 1 by using
 ink identical with that used in Example 1, EB irradiation was performed
 under the same conditions as in Example 1 except that the acceleration
 voltage was changed to 60 kV, followed by evaluation of the degree of
 curing based on the aforementioned criteria. The result of evaluation is
 shown in Table 1.
 (Example 4)
 After printing was carried out in the same manner as in Example 1 by using
 ink identical with that used in Example 1, EB irradiation was performed
 under the same conditions as in Example 1 except that the acceleration
 voltage was raised to 90 kV, and the degree of curing was evaluated based
 on the aforementioned criteria. The evaluation result is shown in Table 1.
 (Example 5)
 In this example, paint for can coating was used as the curable coating
 composition. The paint was prepared according to the following
 formulation:

Bisphenol A epoxy acrylate 55 parts
 (EBECRYL EB600 from Daicel UCP Corp.)
 Triethylene glycol diacrylate 35 parts
 Ketone formaldehyde resin 20 parts
 (Tg: 83.degree. C.; Mn: 800; synthetic resin
 SK from Hules Corp.)
 Titanium oxide (rutile type) 100 parts
 (TIPAQUE CR-58 from
 Ishihara Sangyo Kaisha, Ltd.)
 These were mixed and then dispersed for one hour in a sand mill to obtain
 the paint.
 The paint was applied to a PET film which had a tin-free steel plate of 300
 .mu.m thick laminated with a PET film of 100 .mu.m, to form a 10-.mu.m
 thick coating of the paint thereon, and EB irradiation was performed under
 the same conditions as in Example 1. To evaluate the degree of curing, the
 drying property was evaluated by touching the surface with fingers, as in
 the case of the printing ink of Example 1. Also, as the criteria for
 evaluation, the five-grade system was employed wherein "5" indicates
 "completely cured" and "1" indicates "not cured." In addition, to evaluate
 the hardness of the coating, pencil hardness was measured according to JIS
 K-5400. The obtained results are shown in Table 1.
 (Example 6)
 After the paint identical with that used in Example 5 was applied in the
 same manner as in Example 5, EB irradiation was performed under the same
 conditions as in Example 5 except that the acceleration voltage was
 changed to 60 kV, and the degree of curing was evaluated based on the
 aforementioned criteria. The evaluation results are shown in Table 1.
 (Example 7)
 After the paint identical with that used in Example 5 was applied in the
 same manner as in Example 5, EB irradiation was carried out under the same
 irradiation conditions as in Example 5 except that the acceleration
 voltage was raised to 90 kV, and the degree of curing was evaluated based
 on the aforementioned criteria. The results of evaluation are also shown
 in Table 1.
 (Comparative Examples 1 to 4)
 For Comparative Examples 1 to 3, prints and coatings were prepared under
 the same conditions as in Examples 1, 2 and 5, respectively, and using a
 CURETRON EBC-200-20-30 from Nisshin High Voltage Corporation as the EB
 irradiation apparatus, EB irradiation was performed under the following
 conditions: acceleration voltage: 100 kV; electric power used: 100 W; and
 conveyor speed: 20 m/min. In Comparative Example 4, the paint identical
 with that used in Example 5 was applied in such a manner that the coating
 of the paint had a thickness of 35 .mu.m, and EB irradiation was performed
 in the same manner as in Example 5. These prints and coatings were then
 evaluated as to degree of curing based on the aforementioned criteria, and
 for the coatings, pencil hardness was also measured in the same manner as
 described above. The results are shown in Table 1.
 TABLE 1
 Coating
 Acceleration Degree of Coating thickness
 voltage (kV) curing hardness (.mu.m)
 Example 1 40 5 2
 Example 2 40 5 2
 Example 3 60 5 2
 Example 4 90 5 2
 Example 5 40 5 3H 10
 Example 6 60 5 4H 10
 Example 7 90 5 4H 10
 Comparative 100 3 2
 Example 1
 Comparative 100 3 2
 Example 2
 Comparative 100 3 B 10
 Example 3
 Comparative 40 4 H 35
 Example 4
 As shown in Table 1, it was confirmed that sufficient degree of curing
 could be achieved by performing EB irradiation at low acceleration voltage
 with the use of the above-stated apparatus.
 (Example 8)
 In this example, dose rate of absorption measurement was made and an
 electron beam irradiation process meeting the requirements of the present
 invention was confirmed.
 Dosemetric films (FAR WEST films) of 50 .mu.m thick from Far West
 Technology Corporation, U.S.A., whose absorbance varies when irradiated
 with electron beam, were prepared. First, two FAR WEST films overlapped
 one upon the other were irradiated with an electron beam from one side,
 and using a spectrophotometer, it was confirmed that all radiation was
 absorbed by the film located on the side of the electron beam generation
 source while no radiation was absorbed by the other film. Subsequently, a
 PET film of 10 .mu.m thick was laid over one FAR WEST film and was
 irradiated with an electron beam. Change in the absorbance was measured
 using a spectrophotometer and the absorbed dose was calculated based on
 the calibration curve from Far West Technology Corporation. Then, based on
 the absorbed doses of n films laid one upon another, the value (x) of the
 product of specific gravity and thickness and a rate of dose absorption
 (y) of coating corresponding to the value x were obtained.
 In this case, y was calculated by the method indicated below.
EQU y=(1-F/T).times.100 (%)
 where F is the absorbed dose of the FAR WEST film, and T is the absorbed
 dose of the FAR WEST film as measured in the case where no PET film is
 laid thereon. In the calculation, the specific gravity of the PET film was
 assumed to be 1.4.
 Using the electron beam irradiation apparatus from AIT Corporation, U.S.A.,
 as the irradiation apparatus, EB irradiation was performed at an
 acceleration voltage of 70 kV, a current value of 400 .mu.A, and a
 conveyor speed of 7 m/min. The results are shown below.

n (No. of films) Rate of absorption y (%)
 1 42
 2 72
 3 88.3
 4 99.2
 5 100
 6 100
 The relationship between the product x of specific gravity and thickness
 (.mu.m) and the rate of dose absorption y (%) observed in this case is
 shown in FIG. 8.
 As shown in the figure, the curve is given by
EQU y=-0.0224x.sup.2 +3.0066x(0&lt;x.ltoreq.70),
 proving that the irradiation process fulfills the range according to the
 present invention.
 (Example 9)
 In this example, paint for can coating was used as the curable coating
 composition. The paint was prepared as specified below.

Bisphenol A epoxy acrylate 55 parts
 (EBECRYL EB600 from Daicel UCP Corp.)
 Triethylene glycol diacrylate 35 parts
 Ketone formaldehyde resin 20 parts
 (Tg: 83.degree. C.; Mn: 800; synthetic resin
 SK from Hules Corp.)
 Titanium oxide (rutile type) 100 parts
 (TIPAQUE CR-58 from
 Ishihara Sangyo Kaisha, Ltd.)
 These were mixed and then dispersed for one hour in a sand-mill to obtain
 the paint.
 The paint was applied to a PET film which had a tin-free steel plate of 300
 .mu.m thick laminated with a 100-.mu.m PET film, followed by electron beam
 irradiation.
 The electron beam irradiation was in this case performed at acceleration
 voltages of 70 kV and 150 kV separately. The irradiation at 70 kV was
 performed using the Min-EB apparatus from IT Corporation, U.S.A., under
 the conditions of the current value 400 .mu.A and the conveyor speed 7
 m/min. On the other hand, the irradiation at 150 kV was carried out with
 the use of the electron beam irradiation apparatus CURETRON EBC200-20-30
 from Nisshin High Voltage Corporation, under the conditions of the
 currrent value 6 mA and the conveyor speed 11 m/min. Nitrogen gas was used
 for the inerting.
 After the paint was cured by electron beam irradiation, the hardness of the
 coatings was evaluated in terms of pencil hardness. Measurement of the
 pencil hardness was carried out according to JIS K5400, paragraph 6.14. As
 a result, the pencil hardness was HB in both cases. The coatings had a
 thickness of 6 .mu.m and a specific gravity of 1.7.
 Based on the above data, the rate of absorption of the electron beam of the
 paint was calculated and found to be about 28% for the paint irradiated
 with the electron beam at the acceleration voltage 70 kV and about 11% for
 the paint irradiated with the electron beam at the acceleration voltage
 150 kV. From FIG. 8, where the thickness is 6 .mu.m and the specific
 gravity is 1.7, x=10.2, and substituting this value in expression (1),
 that is, y.gtoreq.-0.01x.sup.2 +2x, provides y.gtoreq.19.36 (%), revealing
 that the irradiation with the use of the vacuum tube-type electron beam
 irradiation apparatus Min-EB from AIT INC., U.S.A., fulfills the range
 according to the present invention and that the irradiation with the use
 of the electron beam irradiation apparatus CURETRON EBC200-20-30 from
 Nisshin High Voltage Corporation fails to fulfill the range of the present
 invention.
 (Example 10)
 Using the printing ink identical with that used in Example 1, printing was
 performed in the same manner as in Example 1. After the printing, EB
 irradiation was carried out using the Min-EB apparatus from AIT
 Corporation. The irradiation conditions were as follows: acceleration
 voltage: 40 to 150 kV; current value: 600 .mu.A; and conveyor speed: 10
 m/min. For the inerting, nitrogen was used. The oxygen concentration was
 varied through adjustment of the flow rate of nitrogen. Also, in this
 case, the oxygen concentration was measured using an oxygen content meter
 (zirconia type LC-750H from Toray Engineering).
 After the irradiation, degree of curing was evaluated as to the drying
 property by touching the surface with fingers and the adhesion by applying
 and then peeling off a cellophane adhesive tape. The criteria for
 evaluation were as follows:
 Drying property:
 (completely cured) 5 to 1 (not cured)
 Adhesion:
 (excellent) 5 to 1 (poor)
 The results obtained are shown in Table 2.
 Based on the results, a range of oxygen concentration in which excellent
 degree of curing could be achieved was determined for each of the
 acceleration voltages. The results are shown in FIG. 9. As shown in the
 figure, it was confirmed that, for an acceleration voltage of 40 kV or
 higher, it was effective to irradiate the object (coating on the substrate
 or base) with an electron beam in a region of oxygen concentration Y below
 the straight line indicated by equation (1) in the figure, where X is the
 acceleration voltage (kV) and Y is the oxygen concentration (%) of a
 region irradiated with the electron beam, that is, in the region indicated
 by expression (a) below.
EQU Y.ltoreq.1.19.times.10.sup.2.times.exp(-4.45.times.10.sup.-2.times.X) (a)
 It was also found that a region defined between equations (1) and (2) in
 FIG. 9, that is, the region indicated by expression (b) below, was more
 preferable from the point of view of economy etc.
EQU 1.19.times.10.sup.2.times.exp(-4.45.times.10.sup.
 -2.times.X).gtoreq.Y.gtoreq.0.05 (b)
 TABLE 2
 Acceleration 40 Oxygen 20 13 8 1.0 0.5
 voltage (kV) concentration
 (%)
 Degree of 5 5 5 5 5
 curing
 Adhesion 4 4 4 4 4
 60 Oxygen 20 8.2 3.0 0.6 0.2
 concentration
 (%)
 Degree of 3 5 5 5 5
 curing
 Adhesion 2 5 5 5 5
 80 Oxygen 8.2 3.5 1.0 0.4 0.2
 concentration
 (%)
 Degree of 2 5 5 5 5
 curing
 Adhesion 2 5 5 5 5
 100 Oxygen 3.5 1.5 0.7 0.2 0.09
 concentration
 (%)
 Degree of 3 5 5 5 5
 curing
 Adhesion 3 5 5 5 5
 120 Oxygen 0.2 0.16 0.17 0.05 0.03
 concentration
 (%)
 Degree of 2 5 5 5 5
 curing
 Adhesion 4 5 5 5 5
 (Example 11)
 In this example, metallic paint was used as the curable coating
 composition. This paint was prepared as specified below.

Bisphenol A epoxy acrylate 20 parts
 (EBECRYL EB600 from Daicel UCP Corp.)
 Polyurethane acrylate 15 parts
 (CN963B80 from Sartomer Corp.)
 Ketone formaldehyde resin 10 parts
 (Synthetic resin SK from Hules Corp.)
 Isoboronyl acrylate 30 parts
 Hydroxyethyl acrylate 25 parts
 Titanium oxide (rutile type) 100 parts
 (TIPAQUE CR-58 from Ishihara Sangyo
 Kaisha, Ltd.)
 Additive (BYK-358 from BYK Corp.) 0.5 part
 These were mixed and then dispersed for one hour in a sand-mill to obtain
 the paint. The paint was applied to a metal plate having a basecoat on a
 curved surface thereof (a steel plate previously applied with primer paint
 and then subjected to wet rubbing by means of sandpaper #300), followed by
 electron beam irradiation.
 The apparatus shown in FIG. 6 was used as the irradiation apparatus. As the
 irradiation tube serving as the electron beam generating section, the
 Min-EB apparatus from AIT INC. was used. The conditions for irradiation
 were as follows: acceleration voltage: 60 kv; current value: 800 .mu.A;
 irradiation width: 5 cm; and irradiation tube scanning speed: 20 m/min.
 Nitrogen gas was used for the inerting.
 As a result of the electron beam irradiation, the coating obtained was
 uniform and had a sufficient hardness of 2H in terms of pencil hardness.
 (Example 12)
 In this example, metallic paint was used as the curable coating
 composition. This paint was prepared as specified below.

Polyurethane acrylate 35 parts.
 (ARONIX M 6400 from Toagosei Chemical
 Industry Co., Ltd.)
 Bisphenol A epoxy acrylate 10 parts
 (EBECRYL EB600 from Daicel UCP Corp.)
 Isoboronyl acrylate 25 parts
 Hydroxyethyl acrylate 30 parts
 Titanium oxide (rutile type) 100 parts
 (TIPAQUE CR-95 from Ishihara Sangyo
 Kaisha, Ltd.)
 Additive (BYK-358 from BYK Corp.) 0.5 part
 These were mixed and then dispersed for one hour in a sand-mill to obtain
 the paint. The paint was applied to a metal plate having a basecoat
 thereon (a steel plate previously applied with epoxy primer paint) such
 that the paint applied had a thickness of 30 .mu.m, followed by electron
 beam irradiation.
 As the irradiation apparatus, the Min-EB apparatus from AIT Corporation was
 used. The irradiation conditions were as follows: acceleration voltage: 50
 kV; current value: 500 .mu.A; and conveyor speed: 10 m/min. Nitrogen gas
 was used for the inerting.
 The hardness of the coating was evaluated in terms of pencil hardness, and
 the adhesion of the coating was evaluated by a cross-hach adhesion test.
 Also, using a vibration-type rubbing fastness tester (from Daiei Kagaku
 Kiki), scratch resistance of the coating was evaluated by visually
 inspecting scratches on the coating produced by nonwoven fabric after the
 coating was shaken 500 times with a load of 500 g applied thereto. The
 criteria for evaluation were as follows:
 Scratch resistance: (excellent) 5 to 1 (poor)
 The evaluation results are shown in Table 3.
 (Example 13)
 The paint identical with that used in Example 12 was applied such that the
 paint applied had a thickness of 20 .mu.m, and electron beam irradiation
 was performed under the same conditions as in Example 12 except that the
 acceleration voltage was changed to 40 kV. The coating was evaluated as to
 the same items as in Example 12 based on the same criteria for evaluation.
 The obtained results are shown in Table 3.
 (Example 14)
 In this example, a pressure sensitive sheet was used.

N-butyl acrylate 41 parts
 2-ethylhexyl acrylate 41 parts
 Vinyl acetate 10 parts
 Acrylic acid 8 parts
 These were copolymerized in toluene, distilled off solvent o obtain acrylic
 copolymer.

Obtained copolymer 100 parts
 N-butylcarbamoyl oxyethyl acrylate 60 parts
 Polyethylene glycol diacrylate 3 parts
 These were mixed together to obtain an electron beam-curing pressure
 sensitive composition.
 The electron beam-curing pressure sensitive composition thus obtained was
 applied to a separator such that the composition applied had a thickness
 of 25 .mu.m, then electron beam irradiation was performed under the same
 conditions as in Example 12, and wood free paper was overlapped to obtain
 a pressure sensitive sheet. The obtained sheet was measured in respect of
 adhesion strength, tack, and retentive force. The results obtained are
 shown in Table 4. The adhesion strength, tack and repeelability of the
 pressure sensitive sheet and the quantity of unreacted monomer were
 measured by methods described below.
 (1) Measurement of Adhesion Strength
 A test piece of 25 mm wide was applied to a stainless steel plate, and
 after a lapse of 30 minutes of adhesion, the test piece was peeled off at
 a peel angle of 180 degrees at a rate of pulling of 300 mm/min to measure
 the adhesion strength. The result of measurement is expressed in the unit
 g/25 mm. A practical range was set using 1000 g/25 mm as a criterion,
 though it depends on uses.
 (2) Measurement of Tack
 Using a test piece with a width of 25 mm, tack was measured by a ball tack
 test and is expressed by the number of the largest possible steel ball
 that could be stuck at an inclination angle of 30 degrees. For steel ball
 numbers of 7 or above, tack was judged to fall within a practical range,
 though it depends on uses.
 (3) Repeelability Test
 The test piece mentioned above was applied to a stainless steel plate and
 then left to stand at 23.degree. C. for 7 days, and repeelability and
 paste left on the exposed surface of the adherend (stainless steel plate)
 was evaluated by visual inspection. The criteria for evaluation were as
 follows:
 Repeelability:
 .smallcircle.: excellent; .DELTA.: partly peelable; .times.: could not
 peeled off.
 Paste left on adherend:
 .smallcircle.: no paste left; .DELTA.: partly left; .times.: paste left on
 entire surface.
 (4) Measurement of the Quantity of Unreacted Monomer After curing, a given
 quantity of the pressure sensitive composition was picked from the
 pressure sensitive sheet, admixed with 50 ml of tetrahydrofuran and then
 left to stand for 24 hours. Subsequently, the mixture was filtered, and
 the filtrate as a sample was measured by gel permeation chromatography to
 determine the weight (%) of the unreacted monomer n-butylcarbamoyl
 oxyethyl acrylate in the cured pressure sensitive composition. An
 unreacted monomer quantity of less than 1.0% in the cured pressure
 sensitive composition was judged to fall within a practical range.
 These evaluation results are shown in Table 4.
 (Example 15)
 A pressure sensitive composition was prepared under the same conditions as
 in Example 14, and electron beam irradiation was performed under the same
 conditions as in Example 14 except that the acceleration voltage was
 changed to 60 kV. Evaluation was also carried out by the same methods as
 employed in Example 14.
 (Comparative Example 5)
 A coating was prepared under the same conditions as in Example 12, and
 using the CURETRON EBC-200-20-30 from Nisshin High Voltage Corporation as
 the electron beam irradiation apparatus, electron beam irradiation was
 performed under the following conditions: acceleration voltage: 200 kV;
 current value: 5 mA; and conveyor speed: 20 m/min. For the inerting,
 nitrogen gas was used. The obtained coating was evaluated as to the
 hardness, adhesion and scratch resistance, based on the same criteria as
 used in Example 12. The obtained results are shown in Table 3.
 (Comparative Example 6)
 The electron beam-curing pressure sensitive composition was applied in the
 same manner as in Example 14, and was irradiated with an electron beam by
 using CURETRON EBC-200-20-30 from Nisshin High Voltage Corporation as the
 electron beam irradiation apparatus under the following conditions:
 acceleration voltage: 200 kV; current value: 6 mA; and conveyor speed: 7.5
 m/min. Nitrogen gas was used for the inerting. The adhesion strength, tack
 and retentive force of the obtained pressure sensitive sheet were
 evaluated based on the same criteria as used in Example 14. The obtained
 results are shown in Table 4.
 (Comparative Example 7)
 The electron beam-curing pressure sensitive composition was applied in the
 same manner as in Comparative Example 6, and using the same electron beam
 irradiation apparatus, electron beam irradiation was performed under the
 following conditions: acceleration voltage: 200 kV; current value: 6 mA;
 and conveyor speed: 22.5 m/min. In this case, since the conveyor speed was
 trebled, the irradiation dose was reduced to about 1/3. The obtained
 pressure sensitive sheet was evaluated as to the same items based on the
 same criteria as employed in Example 14. The obtained results are shown in
 Table 4.
 TABLE 3
 Accelera- Coating
 tion thick- Coating Scratch
 voltage ness hard- resis-
 (kV) (.mu.m) ness tance Adhesion
 Example 12 50 30 2H 5 100/100
 Example 13 40 20 2H 5 100/100
 Comp. 200 30 2H 5 30/100
 Example 5
 TABLE 4
 Accelera-
 tion Adhesion Repeelability Unreacted
 voltage strength Peel- Paste monomer
 (kV) (g/25 mm) Tack ability left (%)
 Ex. 14 50 1260 10 O O &lt;0.5
 Ex. 15 60 1150 9 O O-.DELTA. &lt;0.5
 Comp. 200 880 6 O O &lt;0.5
 Ex. 6
 Comp. 200 950 13 X .DELTA. 2.9
 Ex. 7*
 *The conveyor speed was trebled.
 As seen from Table 3, Examples 12 and 13 were excellent in adhesion of
 their coating while Comparative Example 5 showed poor adhesion. Namely,
 Examples .12 and 13 had a crosslink density distribution in the thickness
 direction and had a lower crosslink density at a portion of the coating
 adjoining the metal plate, and thus no shrinkage occurred at this portion,
 with the result that the adhesion of the coating improved. In Comparative
 Example 5, on the other hand, since the coating was crosslinked up to a
 portion thereof adjoining the metal plate (crosslink density was high
 throughout the entire thickness), shrinkage occurred at the portion
 adjoining the metal plate, with the result that the adhesion lowered.
 Also, as seen from Table4, in Examples 14 and 15, the adhesion strength
 with respect to the stainless steel plate as the adherend, the tack
 measured using steel balls, and the repeelability were all excellent, and
 the quantity of the unreacted monomer was small. This proves that the
 pressure sensitives of Examples 14 and 15 had a crosslink density
 distribution. By contrast, Comparative Example 6 showed low adhesion
 strength with respect to the stainless steel plate as the adherend and had
 low tack as measured with the use of steel balls. This proves that the
 pressure sensitive of Comparative Example 6 had no crosslink density
 distribution and had a high crosslink density throughout the entire
 thickness thereof. In Comparative Example 7, the conveyor speed was
 trebled to reduce the irradiation dose to approximately 1/3, and as a
 result, the crosslink density lowered while the adhesion strength and tack
 improved. However, as seen from a large quantity of the unreacted monomer,
 the crosslink density was low throughout the entire thickness, and as a
 consequence the repeelability was poor.
 As described above, according to the present invention, an object is
 irradiated with an electron beam at low acceleration voltage so as to be
 crosslinked, cured or modified, and therefore, remarkable advantages are
 obtained, for example, adverse influence on the working environment is
 small, the need for inerting using an inert gas is lessened, and
 deterioration of the substrate or base is reduced.
 According to the present invention, an electron beam irradiation process
 capable of electron beam irradiation with high energy efficiency and an
 electron beam-irradiated object can be provided without entailing problems
 with apparatus etc.
 Also, in the present invention, the electron beam is irradiated while the
 electron beam irradiation apparatus is moved for scanning, and therefore,
 even an object having a curved or uneven surface can be satisfactorily
 irradiated with the electron beam, without causing problems with apparatus
 or deterioration in quality such as uneven curing.
 Further, according to the present invention, instead of uniformly
 crosslinking or modifying an entire object, a distribution of crosslink
 density or hardness is created in the thickness direction of the object or
 the object is partially crosslinked or cured with respect to its thickness
 direction, whereby objects can be given a variety of crosslinking or
 curing patterns. Also, the use of the vacuum tube-type electron beam
 irradiation apparatus eliminates the problems associated with conventional
 apparatus.