CA1049389A - Masking films - Google Patents

Abstract

MASKING FILMS

Abstract of the Disclosure A substantially transparent and colored masking film for photoengraving has a substantially transparent supporting plastic film on which an adhesive undercoating, a color resin lay and a pressure-sensitive adhesive are successively laminated. A strippable plastic film is set over the adhesive layer of said laminate.

Description

The present invention relates to a novel masking fiIm and a method for preparing the same.
The present invention provides a masking film which has opacity to light that is active to expose photo-sensitive materials and which has trans-parency to other visible light, which comprises: a) a substantially trans-parent supporting plastic film, at least one surface having been treated by roughening or oxidation; b) a coloured resin layer adhered on said treated surface through an adhesive undercoating; and c) a strippable film having at least one strippable surface adhered to said coloured resin layer through a pressure-sensitive adhesive.
Purthermore, the present invention provides a laminate which is an intermediate for the above described masking film which has opacity to light that is active to expose photo-sensitive materials and which has transparency to other visible light, which comprises a substantially transparent supporting plastic film in which at least one surface is roughened or oxidized, and a coloured resin layer adhered on said surface through an adhesive undercoating.
The objects and advantages of the invention will become apparent in light of the following explanation.
The masking film which is provided by the present invention is useful in photoengraving. Photoengraving is generally conducted by a plate-making process wherein artwork is transferred to a photo original plate having masking properties.
One of the masking films of the prior art provided a laminate which was prepared by applying a rubber pressure-sensitive adhesive agent upon a strippable sheet of glassine paper, wax paper or vinyl chloride resin. The masking film carried a nitrocellulose lacquer as a masking layer (e.g. United States Patent No, 2,576,491). Another prior art development comprised a poly-ethyleneterephthalate film applied to a vinyl chloride resin containing a dye.
Formerly such masking films had the disadvantage that they were subject to variance of their dimensions under the influence of temperature and humidity in the ambient atmosphere. Furthermore, they exhibited an un-desired expansion and contraction due to the heat of the light source which 1~ ~ -1- ~

~0d~9389 is generally used in the preparation of a photo original plate. The masking films of the prior art suffered from a lack of thermal and hygroscopic dimensional stability. Exact duplication of a picture, using the masking - la -~ql film of the prior ar~ results in a poor resolution of the image due to the comparatively thick nitrocellulose layer. Also, the pattern which is separ-ated from the strippable layer is easily broken and lengthened.
The masking film of the prior art comprising a polyethylenetere-phthalate film carrying a vinyl chloride resin containing a dye, suffers from the fact that it is difficult to adhere the vinyl chloride resin layer on artwork, a silk screen, or a photographic plate Furthermore, there was a problem in the lack of durability of the stripped layer.
The present invention seeks to provide a novel masking film which has opacity to the light of a wave length which is active to expose photo-sensitive materials and which has transparency to other visible light and overco~es the trawbacks of the prior art.
The masking film of the invention is prepared by laminating to the treated surface of a substantially transparent supporting plastic film, in which at least one surface is roughened or oxidized, a colored resin layer through an adhesive undercoating, and adhering to the resin layer a stripp-able surface of a film having at least one strippable surface through a pressure-sensitive adhesive layer.
The main characteristic of the masking film of the invention is its excellent dimensional stability, such as thermal dimensional stability, hygroscopic dimensional stability, dimensional stability on standing, and the like~ Hhile it is sasy to remove the release film ti.e. the strippable surface) from the masking film, the remainir.g film will retain its shape and adherence properties. The masking film of the present invention is suitable for re-use for purposes of amendment, such as arrangement of ca~era ready art, or other objects. Furthermore, the masking film of the invention is useful in the exact reproduction of artwork. In addition, the film hss the industrial advantage that it ~ay be easily manufactured using commercially available machi~es.
The supporting plastic film to be used in accordance with the present inventi~n may be oriented or non-oriented polyester or polyether films such as polyethyleneterephthalate, polybutyleneterephthalate, poly-.

terephthalate, poloxybenzoate or polyisobutyleneoxide film and the like; homo-polymeric or copoly~eric films such as polycarbonate, polystyrene, nylon-6, nylon-66, nylon-10, nylon-ll or nylon-12 film and the like; polyethylene, poly-propylene, polybuten-l or poly(4-~ethylpentene-1) film or copolymeric film in which the main components are these polyolefines.
It is desirable to use as the supporting plastic fil~ a biaxially oriented polypropylene, polyethyleneterephthalate or a nylon~-12 film which is sbout 6-200 microns in thickness, most preferably 9-50 microns, which is sub-stantially transparent.
These plastic films are used according to the invention after a con_ ventional roughening or oxidizing treatment on at least one surface of the film.The film surface ~ay be oxidized by a corona discharge treatment or a roughen_ ed using a sand-blasting or a solvent etching treatment.
The colored resin layer is adhered on the treated surface of the ;.
above mentioned pl~stic film with an adhesive undercoating.
The undercoatings which may be used in carrying out the invention are those which strongly adhere to both the plastic supporting film and the i colored resin layer, are transparent and not coloret, ant have good thermal ant hygroscopic stability.
The following have been found to be suitable adhesive undercoatings;
a mixturo of an isophthalic polyester, butyl-etherified melamine and a small amount of sulfuric acid; a mixture of an isophthalic polyester and a prelimin-ary condensate of a polyol and a diisocyanate having remaining active isocyan-ate groups; and a mixture of a copolymer of vinyl chloride and vinyl acetate with a preliminary condensate of a polyol with a diisocyanate having remaining active isocyanate groups.
When a polyolefine, polystyrene, polyester or polyether plastic film is used as the supporting plastic film it is desirable to use a mixture of an isophthalic polyester, butyl-etherified melamine and a small amount of sulfuric acid as the adhesive undercoating.
The isophthalic polyester in the above mixture is a condensate of isophthalic acid with a diol, in which the diol may be a saturated alcohol, such as ethylene glycol, propylene glycol or the like or an unsaturated *Trademark 3 alcohol such as butenediol, hexenediol or the liko The butyl-etherified melamine is obtained by reacting ~elamine with formaldehyde to giVR a melamine-formaldehyte condensate ant subsequently butyl-etherifying this product with a large amount of butanol. The resulting product is soluble in benzene. The product is used as a solution in a ~ol-vent mixed with toluene and ethyl acetate by replacing the ~edium of butyl-etherification with said solvent.
The preferred weight ratio of isophthalic polyester to butyl-etherified melamine is from about 2:8 to 9:1, most desirably from about 6:q to 8:2. Sulfuric acid is added to said mixture as a hardening catalyst in an amount from about 0.5 to 1 part per 100 parts by weight of the butyl-etherified melamine. This results in a well hardened coat at the temperature of 80-150 C.
It is possible to add to the undercoating other ingredients such as an antistatic agent, antioxidant, ultraviolet ray absorbent, heat stabilizer, dye or pigment, waxes or inorganic fine powders as an antiblocking agent or lubricant, as long as they will not have any unfavorable influence on the binding ability of the undercoating. Such undercoating shoult be applied as tbin as possible, preferably in the thickness of about 0.5-3 microns.
The reSinQ used for the formation of the coloret resin layer may .
be nitrocellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butylate, ethoxy cellulose, viny~ chloride resin, styrene resin, acrylic acid or acrylic ester resin, polyester resin, polyurethane resin, polyamide resin, amino resin, aminoalkyd resin and the like. Colorants, in the form of colored lacquer or ink, are added to the resins.
The opacity of the masking film to the light that is active to photo-sensitive materials and has transparency to other visible light may be adjusted by the colored resin layer. For exa~ple, to mask for blue sensitive material, the colored resin layer should be deep blue, deep green, deep yellow-orange or deep red. Por an ortho sensitive material, the resin layer shoultbe deep orange or deep red. For a semi-panchro~atic material, the resin layer should be deep green.

~q ~049389 The most preferred resin used 85 the colored resin layer is nitro-cellulose, such as a conventional nitrocellulose lacquer (SS type cotton or RS type cotton) having a viscosity from 1/8 to 120 seconds. When a nitro-cellulose having a ~iscosity less than 1/8 second is used, the layer coated from the nitrocellulose lacquer is brittle. When the viscosity is over 120 seconds, application of the lacquer becomes difficult.
As colorants for nitrocellulose dyes or a mixture of dyes and pig-ments may be used. Dyes are not limited in their color tone or structure, so long as they are oil soluble and compatible wi~h nitrocellulose ~or other resin used) and have minimized variance of color tone as a result of exposure to heat ultraviolet rays. However the pigment must have sufficient masking properties for the masking film to be preparod.
An organic or inorganic pigment may also be used if it does not have any unfavorable influence on the transparency of the nitrocellulose coating for light of a desired wave length range The extinction of light as it passes through the colored resin layes ~ay be controllet by both the amount of dye in this resin layer and the thickness of the resin layer.
It i5 possible to add other ingredients to the colored lacquer used to fo D the coloret resin layer, such as an antioxidants, heat stabilizers, ultraviolot ray absorbers, antistatic agents, plasticizers, antiblocking agents and lubricants when thoy are neeted. The method for applying said lacquer may be any method, such as using a rotogravure printing machine, roll coater, bar coater, spray gun or dipping coater. A coloret lacquer of nitrocellulose is adhered to the roughenet or oxidized surface of the plastic film through the undercoating, When other resins are used, colored lacquers may be prepared in a maMer analogous to nitrocellulose, It is desirable to apply the colored resin layer as thinly as possible, e.g. the thickness of the layer after evaporation of solvent should be 3-10 microns. Accordingly, the concentration of the colorant in the lacquer should be high. For example, the colorant may be preferably from about 80-120 parts by weight per 100 parts by weight of resin.
The undercoating to be uset in the invention improves the adhesion ~.~

between the plastic film and the colored resin layer. In addition, when the masking film is used for photoengraving, there is no problem resulting from a shift of the masked wave length range by reason of color change in the colored layer or other layers. The plastic film set on said ~ndercoating is excellent in thermal resistance, resistance to weathering, hot water resistance and the like.
A pressure-sensitive adhesive layer may be applied to said colored resin layer. Suitable pressure-sensitive adhesives which may be used, are rubber or other transparent pressure-sensitive adhesives, which may contain the same dyes or pigments as are used in coloring the nitrocellulose lacquer, unless they give an unfavorable influence on pressure-sensiti~o adhesiveness.
A laminate having masking properties may be prepared by pressing and adhering the adhesive surface of the pressure-sensitive adhesive surface of the masking film of the invention to the strippable surface of a stripp-able plastic film.
Altornatively, the laminate may be prepared by apply~ng and trying a pressure-sensitive adhesive layer on a transparent strippable film and then laminating this to the coloret resin layer of the masking film of the invention, The transparent strippable film has as its base a film which is similar to the plastic film used as the support in the invention as explained above has on at least one side a strippable proporty. The strippable property is obtainet by using a release agent, which ~ay be a silicone resin, a cop-olymer of methacrylic acit or acrylic acid having a long side chain such as polystearyl acrylate or waxes ~e.g. wax release agent referred to in Japanese Patent Publication No. 3382/1959), or any other agent that gives a transparent strippable coat. Ho~ever, it is especially preferred to use a vinylsilane silicone resin along with an organic peracid fro~ the viewpoints of the strippable property and transparency. It is recom~ended to apply, dry and cure this combinat~on on the strippable plastic fil~ by which silicone resin crosslinking is carried out.
In the masking film of the invention it is preferable that the ~/

., -- - , ~

thickness of all layers, excluding the transparont strippable film, is about 15-70 ~icrons, desirably about 15-35 microns. The thickness of the layers, excluding the strippable fil~ and the support fil~, is most preferably in ~he range of about 5 5-20 microns.
The invention will be illustrated by the following Examples, without being limited to them.

Example 1 An isotactic polypropylene film, having a melt index of 2.0 and being oriented in machine tirection and transverse direction seven times to give a biaxially oriented polypropylene film having thickness of 18 microns, was subject to a corona-discharged to obtain a film having a contact angle of the discharged treatment surface to water of 70C.
The resulting film was coated with the following composition:
Isophthalic polyester 50 parts Butyl-etherified melamine 50 parts Sulfuric acid 0.5 parts Ethyl acetate 420 parts Toluene 210 parts Methyl ethyl ketone 210 parts Methyl alcohol 58.4 parts Stearic acid amide 1.0 parts Fine silica powder 0.1 parts taverage dia~eter: 0.3y) The coating was applied using a gravure coater and the coated film was dried for about 1.5 min. in an oven at 120C to give a film in which the thickness of the coated layer was ly. The thickness of both layers was l9y.
Said film showed transmission of 90%. There was no noticeable change in its adhesiveness and appearance after being dipped in boiling water for 30 min.
The film was not discolored after irradiation for 150 hrs. with ultraviolet rays.
The following composition was prepared as the colored nitrocellulose lacquer:

-10493~9 Nitrocellu~ose (SS, 1/2 second)150 parts Red dye (Neozaphon red) 75 parts Yellow dye tNeozaphon yellow) 75 parts Methyl ethyl ketone 460 parts Isopropyl alcohol 40 parts Toluene 200 parts The nitrocellulose lacquer was applied to the undercoating of thepolypropylene film by a gravure coater and driet to remove the solvent re-sulting in a deep red film in which the thickness of the coated nitrocellulose layer was S~ and the total thickness was 24~. The transmission of said film, using a Beckmann spectrophotometer, was 0~ at a wave length from 200 to 590 millimicrons. The passage of light was recorte~ at a wave length greater than 590~.
On the surface of said red nitrocellulose layer an acrylic adhesive was applied so as to provide a dried athesive layer 7~ thick The resulting prossure-sensitive masking film hat a total thickness of 31~.
Urethane wax was applied on a biaxially oriented polypropylene base fil~ to provide a coated layer 0.2~ thick. The resulting strippable fil~
having a total thickness o 110~. The masking film and the strippable film were laminatod together by pressing the strippable film against the pressure-sensitivo athesive surface of the masking film, with the urethane wax layor therebetween. It was found that said laminate possossod excellent hygroscopic dimensional stability, since variance in its di~ension was ~ 0.001~ turing a change in relative humidity from 0~ to 90~ (or 90~ to 0~ reversely) at ~0C
as measured by a cathetometer.
The laminate was then heated in an oven at different temperatures for 10 min. and its thermal dimensional stability was measured relati~e to variances of dimension before and after heat treatment, as reported belo~;
~ Variance rate of dimension .
50C ~ 0.00 60C ~ 0.01~
70C ~ 0.02%

The pressur~-sensitive adhesive ~asking film of the laminate was peeled from the strippable film to prepare a strip 15 ~D x lS0 mm which showed a tensile serength of 4,5 Kg/~ and an elongation of 12~ a~ measured with a tensile tester.
The la~inste was put on an artwork and the ~asking layer was cut in the shape of the artwork. Those parts of the masking layer not corresponding to the artwork were re~oved from the laminate to give a masking film having a pattern idontical to the artwork on a transparent strippable film.
The laminate carrying the pattern was closely attached to "Fuji lith-ortho film type F" of Fu~i Photo F~lm Co., Ltd. and development was con-ducted after exposing it for l min, to the light of a xenon lamp, It was found that the film possessed an excellent shading property, with no photo-sensitive development on the part corresponding to the pattern in the masking fil~, Example 2 A solution containing vinylsilane silicone resin and a small amount of benzoyl peroxide as a hardening agent was applied to a biaxially osientet polypropylene film of 120~ and dried and curet for 3 min, at 130C to obtain a transparent strippable film in which the thicknoss of the driet coatet 29 layer was 0,1~ ant the total thickness was 120~, This transparent strippable film was laminated to the masking film of Example 1 in the same way as in Examplo 1.
The masking layer of sait laminate was cut in the outline of an art-work and the resulting masking pattern was, utilizing its adhesiveness, adhered to PS plate under the trademark of "PLANOSUPPER POSITIVE GRENC~AT" of Fuji Photo F~lm Co., Ltd. which was exposed for 6 min. to a xenon lamp and etched, It was found that no photo image was formed on the part corresponding to the pattern in the ~asking film, Peeling tests were conducted by adhering the masking layer from this Exa~ple and the masking film cut from the laminate of Example 1 to the photo-sensitive emulsion face of a photo-sensitive film and allowing them to stand for 24 hrs, at room te~porature and then stripping off the ~asking layers. It ,~1 iO49389 was found that the ~asking film of this Example was more easily stripped than that of Exa~ple 1, The peeling strength at 90C of the masking film of this Example was 1~0 g/ 25 ~m, while that of the ~asking film of Exa~ple 1 was 320 g~ 25 ~, Examples 3-9 The fol~owing undercoating compositions were applied to the treated surface of a biaxially orientet polyethyleneterephthalate film which hat been subj0ct to corona-tischarging or sand-blasting treat~ent, using a gravure printing ~achine set on gravurecylinder of line numbers being 150 lines ant teepness of cell being 35~. The thickness of the undercoating was 2~ in each product, -TABLE I

TEST THICKNESS OP PRE-TReATMENT UNDERCOATING
NO. POLYETHYLENE COMPOSITION
TEREPHTHALATE
PILM

1 6~ corona-discharge A 100 parts S 400 parts B 10 parts

2 6~ corona-discharge C 100 parts S 400 parts B 15 parts

3 9p corona-dischasge A 100 parts S 400 parts B 10 parts

4 9~ corona-discharge C 100 parts S 400 parts B 15 parts 12~ corona-discharge A 100 parts S 400,'parts B 10 parts 6 12~ sant-blast on C 100 parts S 400 parts one surface B 10 parts 7 20~ sand-blast on A 100 parts S 400 parts both surfaces B 10 parts Notes:
"S" means a ~ixture of methyl ethyl ketone and toluen~
"A" ~eans VINYLITE VAGH a trade mark for a copoly~er of vinyl ~, chloride/ ~inyl acetate/ vinyl alcohol in weight ~atio of 91:4:5 of Union Carbide Co " Ltd, - "C" means TOYOBO STER RESIN a trade Mark for a polyester resin of Toyobo Co., Ltd.

.. .. . . :

"B" means a condensate of toluenediisocyanate and hexantriol of Japan Polrurethane Co,, Ltd. haYing a trade mark of CORONATE L.
The following co~position was prepared a~ a vinyl chlorite color lacquer:
VINYLITE VMCH 150 (parts by weight) Ret dye (Neozaphon ret) 75 (parts by weight) Yellow tye tNeozaphon yellow)75 (parts by weight) Methyl ethyl ketone 460 tparts by weight) Toluene 240 tparts by weight~
~VINYLITE VMCH is a trade mark for a copolymer of vinyl chloride/vinyl acetateAmaleic acit in weight ratio or 86:13:1 of Union Carbide Co., Ltt.
Deep ret films having a thickness of 5~ were prepared by applying the above color lacquer on each of the undercoatet films of Test Nos, 1-7 and trying them for 30 seconds in an oven at 70C to evaporate the solvent.
The characteristics of the resultant red films were as follo~s:
TABLE II
Example Base Film Adhesive- Appearance Variance Rate in No. ness of Dimension t60C) Color Lacquer Control No pre-treat- Non- Red ~ 0.01 t~) ment ~ under- athesion transparent coating 12 of PET
3 Test No. 1 film Excellent Red _ 0.05 (%) transparent 4 Test No. 2 film Excellent Red - 0.05 t%) transparent Test No. 3 film Excellent Red ~ 0,02 t~) transparent 6 Test No. 4 film Excellent Red ~ 0,02 t%) transparent 7 Test No. 5 film Excellent Red 1 0.01 t%) transparent 8 Test No. 6 fil~ Excellent Red ~ 0.01 t%) transparent 9 Test No. 7 film Excellent Red se~ 0.005 (~) transparent ~q Note:
~PET~ is a biaxially orientet polyethyleneterephthalate fil~.
Transparency of the red films was measured using a Beckmann spec-trophoto~eter. Their transparency was 0~ in the wave len~th range from 200 to 590 m~ while light passed through the film at wave lengths greater than 590 m~.
Then lamina~es ~ere prepared by applying an acrylic adhesive on the surface coated with the vinyl chloride lacquer so as to provide a 7~
thick dried coated layer, and pressing each of the resulting masking films having pressure-sensi~ive adhesiveness with a strippable film of 125~ thick-ness which was obtained by applying a urethane wax on a biaxially oriented polyethyleneterephthalate film as a base film to provide a coated wax layer of about 0.2~ of thickness.
Among these lsminates, the colored layers in the films of Examples 3-6 could be cut easily with a razor in the outline of an artwork to give a pattern. Also, the colored layers in the films of Exa~ples 7-9 could be smoo~hly cut with a ruby or diamond cutter.
It was possible to write or draw ~pon the film of Example 9 with a pencil before cutting because the outer surface of the support film was roughened.
The colored layers, except for Examples 3 and 4, were easy to handle and could adhere to an object to be masked and then peeled away.
Example 10 A colored film was prepared by applying the colorant as used in Example 3, using the undercoating of Test No. 2 in Table I, on a cast nylon-12 which film has been subject to corona-discharge, having a thickness of 18~.
The film was made from a polymer having an average molecular weight of 100,000 obtained by polymerization of laurolactam. A transparent strippable film having a total thickness of 120~ was prepared by applying a solution contain-ing vinylsilane silicone resin as the main component and a small amount ofbenzoyl peroxide as hardening agent on a biaxially oriented polypropylene film of 120~ and drying and curing for 3 min. at 130C.

. ~ , 10493~S9 A laminate ~as prepared by applying the following pressure-sensitive adhesive co~position to said transparent ~trippable film so as to provide a coated layer of 7~ thickness after drying, and pressing the thus-coated poly-propylene film over the above coloret nylon-12 film:

ALLON S-1602 (acrylic adhesi~e, 100 parts by weight Toa Chem, Ind. Co., Ltd.) CORONATE HL 2 parts by weight Methyl ethyl ketone 100 parts by weight No "CORONATE HL" is a preliminary condensate of urethane prepared from hexamethylene-diisocyanate, The laminate was easily separated into a transparent strippable film layer and a pressure-sensitive adhesi~e masking film layer, the latter of which possessed the following characteristics:
TABLE III
Control Exa~ple 10 Pre-treat~ent no corona-discharge Undercoating no Test No. 2 composition in Examples 3-9 Athesi~eness of poor excellent Colored Lacquer Variance Rate in 60C ~ 0.02 ~ 0.02 Dimension of Masking film layer 70C ~ 0.07 ~ 0.07 80C - 0.10 -0.10 The masking layer of said laminate was cut in the form of an art-~ork and the resulting masking pattern was adhered to a PS plate as describet in Example 2, which was exposed for 6 min. to a xenon lamp and etched. No photo-image was formed on the part corresponding to the pattern of the ~asking film.

Trademark _13-,rl

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A masking film which has opacity to light that is active to expose photo-sensitive materials and which has transparency to other visible light, which comprises: a) a substantially transparent supporting plastic film, at least one surface having been treated by roughening or oxidation; b) a coloured resin layer adhered on said treated surface through an adhesive undercoating; and c) a strippable film having at least one strippable surface adhered to said coloured resin layer through a pressure-sensitive adhesive.

2. A masking film in accordance with claim 1, in which the sub-stantially transparent supporting plastic film is an oriented or non-oriented film of polyethyleneterephthalate, polybutyleneterephthalate, polyterephthal-ate, polyoxybenzoate, polyisobutyleneoxide, polycarbonate, polystyrene, nylon-6, nylon-66, nylon-10, nylon-11, nylon-12, polyethylene, polypropylene, polybuten-1 or poly(4-methylpentene-1).

3. A masking film in accordance with claim 1, in which the substan-tially transparent supporting plastic film is a biaxially oriented poly-propylene or polyethyleneterephthalate film, or a non-oriented nylon-12 film.

4. A masking film in accordance with claim 1 in which the adhesive undercoating comprises a mixture containing isophthalic polyester, butyl-etherified melamine and a small amount of sulfuric acid, a mixture containing isophthalic polyester and a preliminary condensate of a polyol with a diisocyanate having remaining active isocyanate groups or a mixture containing a vinyl chloride/vinyl acetate copolymer and a preliminary con-densate of a polyol with a diisocyanate having remaining active isocyanate groups.

5. A masking film in accordance with claim 1 in which the adhesive undercoating comprises a mixture containing isophthalic polyester, butyl-etherified melamine and sulfuric acid in which the weight ratio of isophthalic polyester and butyl-etherified melamine is about 2:8 to 9:1 and the weight ratio of sulfuric acid and butyl-etherified melamine is about 1:100 to 0.5:100.

6. A masking film in accordance with claim 1 in which the coloured resin layer comprises a resin selected from the group consisting of nitro-cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butylate, ethoxy cellulose, vinyl chloride resin, styrene resin, acrylic acid resin, acrylic ester resin, polyester resin, polyurethane resin, polyamide resin, amino resin and aminoalkyd resin, and 80 to 120 parts by weight of a colorant per 100 parts by weight of the resin.

7. A masking film in accordance with claim 1 in which the thickness of layers A) and B) and the pressure-sensitive adhesive is about 15 to 70 microns and the thickness of all layers except the strippable film and the substantially transparent supporting plastic film is about 5.5 to 20 microns.

8. A masking film in accordance with claim 1 which comprises a laminate of a substantially transparent biaxially oriented polypropylene film having a corona discharged surface, a reddish nitrocellulose layer adhered to said surface through an adhesive undercoating containing isophthalic poly-ester, butyletherified melamine and sulfuric acid, and a biaxially oriented polypropylene film over said nitrocellulose layer, a urethane wax layer on said polypropylene film being against said nitrocellulose layer.

9. A masking film in accordance with claim 1, which comprises a laminate of a substantially transparent biaxially oriented polypropylene film having a corona discharged surface, a reddish nitrocellulose layer adhered to said surface through an adhesive undercoating containing isophthalic polyester, butyletherified melamine and sulfuric acid, and a biaxially oriented polypropylene film over said nitrocellulose layer, a vinylsilane silicone resin surface coated on said biaxially oriented poly-propylene film being against said nitrocellulose layer.

10. A masking film in accordance with claim 1, in which the substan-tially transparent supporting plastic film is a biaxially oriented poly-propylene film and the strippable film is a biaxially oriented polyethylene-terephthalate film.

11. A masking film in accordance with claim 1, in which the substan-tially transparent supporting plastic film is a biaxially oriented poly-ethyleneterephthalate film and the strippable film is a biaxially oriented polypropylene film.

12. A masking film in accordance with claim 1, in which both of the substantially transparent supporting plastic film and the strippable film are each a biaxially oriented polyethyleneterephthalate film.

13. A laminate which is an intermediate for the masking film according to claim 1 which has opacity to light that is active to expose photo-sensitive materials and which has transparency to other visible light, which comprises a substantially transparent supporting plastic film in which at least one sur-face is roughened or oxidized, and a coloured resin layer adhered on said surface through an adhesive undercoating.

14. A laminate in accordance with claim 13, in which the substantially transparent supporting plastic film is a biaxially oriented polypropylene or polyethyleneterephthalate film, the coloured resin layer comprises a mixture containing nitrocellulose and at least one colorant, and the adhesive undercoating comprises a mixture containing isophthalic polyester, butyl-etherified melamine and a small amount of sulfuric acid.