CA1106995A

CA1106995A - Resin compositions for peel-off coatings comprising a polyvinyl acetal resin and an organopolysiloxane

Info

Publication number: CA1106995A
Application number: CA257,861A
Authority: CA
Inventors: Iwao Moriya; Toru Sema; Sigeyosi Hatasa
Original assignee: Lion Corp
Current assignee: Lion Corp
Priority date: 1975-07-31
Filing date: 1976-07-27
Publication date: 1981-08-11
Also published as: GB1521156A; DE2634437A1; NL7608484A; JPS5216537A; FR2319697A1; FR2319697B1

Abstract

ABSTRACT OF THE DISCLOSURE

A resin composition for peel-off coatings is disclosed comprising a polyvinyl acetal resin and an organopolysiloxane, the organopolysiloxane having polyoxyalkylene groups as its side groups, in a ratio of 100 parts by weight of polyvinyl acetal resin to 1 to 30 parts by weight of the organopolysiloxane. The resin composition is suitable for application to shaped articles and is quick drying. The coating films thus produced are tough and exhibit an excellent peelability even after lapse of a long term or after heating.

Description

This invention relates to resin compositions for peel-off coatings.
A variety of coating compositions have hitherto been used for forming peel-off coatings or strippable coatings that are serviceable for temporary protection of the surfaces of shaped articles such as parts of electrical appliances or machines, kit-chenwares, and the like. For example, aqueous coating composi-tions comprising a synthetic resin emulsion, such as polyvinyl acetate emulsion or an acrylic resin emulsion, are most exten-sively used. Such peel-off coating compositions based on an aqueous polymer emulsion, however, are not satisfactory in stor-age stability, thermal resistance and water resistance and other properties of the resultant coatings. As a further example are aqueous coating compositions prepared by admixing some floury materials, such as calcium carbonate, titanium dioxide and the like, silicone resins, and aqueous emulsion of paraffin wax and other supplemental ingredients. These compositions are also de-fective owing to instability in long storage, delay in drying after application, etc. (See, for example, Japanese Patent Pub-lication No. 14770/73.) In addition, solvent-type compositions for peel-off coat-ings are known. They are prepared by dissolving a polyvinyl bu-tyral resin and a plasticizer in an organic solvent. However, their formulation is disadvantaged by restrictions in the selec-tion and amount of plasticizers to be used. In addition, bleed-ing or migration of plasticizer often takes place, while the re-sultant coatings sometimes exhibit low peelability when applied to articles made of certain materials.
It is an object of this invention to provide a resin com-position for peel-off coatings useful for temporary protection of .. ~ .

s the surfaces of shaped articles, which avoids or reduces the above-described problems encountered in the prior art eomposi-tions, i.e. rigorism in formulation, instability in storage, de-lay in drying, possibility of bleeding of plasticizer or other components, imperfect peelability of the resultant coatings, etc.
According to one aspect of this invention there is pro-vided a resin composition for peel-off coatings consisting essen-tially of (A) 100 parts by weight of at least one polyvinyl acetal resin.
(B) 1 to 30 parts by weight of an organopolysiloxane represented by the average formula:
[(Rl )mSiO4-~3 (R2 ) nsiO3-n

2 x 1 2 ¦ -- (I) (CH2t--aO~C2H40) b~C3H60~HJ Y

wherein Rl and R2 are halogen-substituted or unsubstituted monovalent hydroearbon groups, m is an integer from 1 to 3, n is 0 or a positive integer, a is 0 or an integer from 1 to 5, b is an integer from 2 to 40, e is 0 or an integer from 1 to 40, and x and y are integers from 2 to 50.
According to another aspect of this invention there is provided a method of preparing a resin composition as reeited above eomprising blending eomponents (A) and (B) as defined above.
The term "peel-off eoatings" as used herein denotes eoat-ing films which are formed on the surfaces of a shaped article to temporarily proteet the surfaees from external damage of a meeh-anical or chemical nature during storage andjor transportation, and which ean be peeled off mainly by hand, without being torn into small pieees, immediately prior to use of the shaped article, so that the intrinsic surfaees of the shaped artiele are exposed.

~69~

Any shaped articles including parts of eleetric applian-ces and machines, kitchenwares, and the like ean be eoated with the resin eomposition when temporary protection is required.
Further, those articles eoated with the peel-off eoating eompo-sition may be used as sueh and, when the surface of the eoating film becomes stained with dirty matter, sueh as soot or grease, the coating film may readily be peeled off to expose a fresh sur-faee, which can then be re-coated with the same composition.
Generally it is required that peel-off coatings adhere firmly to the surface of the shaped article without lifting be-fore they are intentionally peeled off. The peelability of the eoatings should be maintained through the lapse of time and even in hot eonditions. The peel-off eoatings should have enough meehanieal strength, water resistance and ehemical resistanee.
On the other hand, the peel-off eoating compositions should be suitable for application by known methods, such as spraying or brushing. The layer of the coating composition applied to vari-ous surfaces should promptly dry and form films with a high de-gree of continuity. Resin compositions according to embodiments of the present invention satisfy all of these requirements.
The resin compositions are applicable to the various sur-faces, such as metals, plastics, ceramics and the like. The coating films formed are clear in appearance and have sufficient hardness, tensile strength and elongation.
Polyvinyl acetal resins whieh form component (A) in the resin composition include, for example, polyvinyl formal resins and polyvinyl butyral resins which are commereially available.
It is preferred that the polyvinyl formal resins have a degree of polymerization in the range from 400 to 1,000 and eontain at least 30 mole ~ of the formal component, and that the polyvinyl 6~

butyral resins have a degree of polymerization in the range from 400 to 1,100 and contain at least 30 mole ~ of the butyral compo-nent. The above-mentioned ranges of polymerization degrees for the polyvinyl formal resins and the polyvinyl butyral resins are not absolutely restrictive, but it may be acceptable that the average of polymerization degrees of any polyvinyl formal resins or polyvinyl butyral resins used falls in the range. Further, component (A) may be a mixture of at least one polyvinyl formal resin and at least one polyvinyl butyral resin.
Organopolysiloxane which form component (B) in accordance with the present invention are represented by the above-given average formula (I), in which symbols Rl and R2 are halogen-sub-stituted or unsubstituted monovalent hydrocarbon groups, such as alkyl groups (e.g., methyl, ethyl and propyl groups), alkenyl groups (e.g., vinyl, allyl and hexenyl groups), cycloalkyl groups (e.g., cyclohexyl and cycloheptyl groups), aryl groups (e.g., phenyl, tolyl and xylyl groups), aralkyl groups (e.g., benzyl and phenylethyl groups) and halogen-substituted monovalent hydrocar-bon groups (e.g., chlorophenyl, tetrachlorophenyl, chloromethyl and pentafluorobutyl groups).
It is natural that the molecule of component (B) is com-posed of siloxane units in which the group represented by symbol Rl and R2 is not limited to only one specific group. Different Rl groups and different R2 groups may be present in the molecule.
Similarly, the value denoted by m, n, a, b or c is not limited to one specific value in the molecule.
Among the oxyalkylene-containing organopolysiloxanes in conformity with the average formula (I) for component (B) are preferred the linear organopolysiloxanes represented by the fol-lowing general formula:

6~Q~S

R3 sio~ sio~ sl-o 1 siR3 . . . ( II ) lRI X-2 (CH2t~0~C2H40~C3El60~HJ v where Rl, R2, x, y, b and c have the same meanings as defined previously and a' is a positive integer from 1 to 5, from the standpoint of the compatibility of component (B) with component (~) and the stability of component (B) against hydrolysis.
Illustrative of component (B) in the resin composition in conformitv with the general formula (II) are the organopolysilox-anes expressed by the following formulas.

fH3 ~fH3l ~ fH3 1 fH3 C'13-SiO t SiO ~ 7iO I Si-CH3 (III) CH3 ~CH3)3al(cH2t~o-~c2H4ot~tc3H6ot~HJ2 CH3 fH3 ~ fM3l ~ fH3 ¦ fH3 CH3-SiO 7io. ~sio- _ fi-CH3 ... (IV) CH3 ~CH3 38 l(CH2 ~ ~-~C2H40 ~ C3H60 ~ H loCH3 o fH3 ~fH3l ~ fH3 1 fH3 .
t I ~ 7 _ fi-CH3 ... (V) CH3 ~cH3J3~3l~(cH2t~o-tc2H4ot~c3H6ot~H 36CH3 fH3 ~ fH3 1 fH3 CH3-SiO- - sio - ,Si-CH3 ... (VI) CH3 (CH2 ~ O-~C2H40 ~ H 5 CH3 fH3 ~ fH3 1 fH3 CH3-7iO t SiO - Si-CH3 ... (VII) CH3 l(CH2 ~ O-~C2H40~H, ~5 CH3 ., ~

~1~6g~5 fH3 ~ fH3 fH3 CH3-SiO t SiO Si-CH3 ... (VIII) CH3 (CH2~ 0-~C2H40~ H 38 CH3 CH3 ~CH3l ~ fH3 1 fH3 ~ fi-CH3 ... (IX) CH3 ~CH3)3a ~(CH2~ 0--tC2H40 ~ H, 38 CH3 fH3 ~fH3l ~fH3 1 fH
CH3-SiO- SiO ~ SiO - Si-CH3 ... (X) CH3 CH3 5 ~(cH2 ~ o-tc2H4o ~ c3H6o ~ H~ 38 CH3 fH3 ~fH3l ~ fH3 CH3 7 t I ~ I ~ Si-CH3 ... (XI)*
CH3 ~CH3)27 ~c2H4o ~ H~3 CH3 CU3-Si ~OSl~ O-tCZ~O ~ C3H~O ~ H~ ... (XII)~

fH3~ fH3~ fH3 fH3 CH3-SiO SiO- - Sio- Si- CH3 ... (XIII)*
l ! I
CH3 ~CH3 3 1 CH3 (C2H~,ot~H
in accordance with General Formula I.
The polyoxyalkylene groups in component (B) may be bonded to the silicon atoms through Si-C linkages or Si-O-C linkages, although the Si-O-C linkages are preferred owing to their rela-tively high stability against hydrolysis. Further these polyoxy-alkylene groups have hydroxy qroups at the terminals, by which component (B) is rendered sufficiently compatible with component 11~69~5 (A), and the coating films formed have excellent physical proper-ties as well as easiness in peeling-off. On the other hand, when the polyoxvalkylene groups bonded to the silicon atoms have a monovalent hvdrocarbon group, such as an alkyl group, an aryl group or the like at the terminals, the organopolysiloxanes con-cerned have lower compatibility with the polyvinyl acetal resins and are less suitable for formulating peel-off coating composi-tions.
In the resin composition 1 to 30 parts by weight, prefer-ably 5 to 20 parts by weight, of component (B) should be incor-porated uer 100 parts by weight of component (A). If the amount of component (B) used is smaller than 1 part by weight per 100 parts by weight of (A), the coatings obtained cannot be easily peeled off, while amounts of (B) used in excess of 30 parts by weight bring about inferior properties and economical disadvan-tages to the resultant coatings.
The resin compositions can be prepared simply by blending component (A) with component (B). In the blending, it is prefer-red to use an organic solvent or solvents. Included among such organic solvents are alcohols such as methanol, ethanol, propanol and butanol, aliphatic hydrocarbons such as hexane and pentane, aromatic hydrocarbons such as benzene, toluene and xylene, ke-tones such as acetone and methyl ethyl ketone, ethers such as di-ethyl ether, dioxane and tetrahydrofuran, esters such as ethyl acetate, propyl acetate and butyl acetate, and chlorinated hydro-carbons such as trichloroethylene and carbon tetrachloride.
I~hen, in particular, the resin composition is to be applied to a shaped article havinq portions of plastics, for example, from acrylic resin, polystyrene or the like, it is preferred to use alcohols, especially saturated alcohols having 1 to 4 carbon ~p~ 25 atoms, so that swelling or dissolution of the plastic portion may be prevented. The amount of the organic solvent used is not nar-rowly critical. In practice the amount of the organic solvent is not less than 5% by weight based on the total of components (A) and (B), so as to obtain a suitable viscosity of the coating composi-tion. The organic solvent is added to components (A) and (B) and mixed together with stirring, preferably in the presence of heat, to obtain a better peelability. The temperature in this case is between about 40 and about 150C depending on the kind, degree of polymerization, etc. of the polyvinyl acetal resin, with stirring continued for about 1 to about 6 hours.
In addition to the organic solvents, various other addi-tives, including plasticizers, such as phthalic esters, phospho-ric esters, fatty acid esters and g1YCO1 derivatives, fatty sub-stances such as vegetable oils, cellulose derivatives and pig-ments may be incorporated in the compositions to improve the pro-perties, for example, softness of the resultant coating films.
The resin compositions are useful as the protective coat-ing for various shaped articles of metals, plastics, ceramics as well as for painted surfaces. The articles include, for example, electric appliances such as ventilating fans, kitchen supplies, building materials, automobiles and the like.
The peel-off coatings are useful not only for the protec-tion of the surfaces of any article in storage or transportation prior to use but also for the protection of the articles durinq use. When the coating articles in use become stained on their surfaces, the coatings can be readily removed bv peeling off and then the exposed surfaces can be re-coated with the same composi~
tion. Even if the surface to be re-coated is oily or greasy to some extent, the re-coating work can be easily performed to ,. , i9~5 produce new coating films with satisfactory results.
The following examnles illustrate embodiments of the pre-sent invention. In the examples, parts are all parts by weight.
Further in the examples, the peeling-off tests were carried out by either of the following three methods, involving accelerated aging.
Method I: Clean aluminum plates were coated with the specified peel-off coating compositions, and the resulting coat-ings were subjected to heat treatment at 80C for 100 hours and thereupon their peelability was determined.
Method II: Aluminum plates covered by thin layers of soybean oil were coated with the specified peel-off coating com-positions and treated in the same manner as in Method I to deter-mine the peelability of coatings so formed.
Method III: Aluminum, polystyrene resin and glass plates were individually coated with the specified peel-off coating com-positions, and the thus resulting coatings were subjected to treatment first by heating at 70C for 5 hours and then by allow-ing to stand at room temperature for 1 hour, such treatment being repeated for 50 cycles. Thereupon the coatings were tested for peelability.
The results of the peel-off tests are expressed severally by symbols A, B, and C as follows.
A: The coating film was easily peeled off without trouble, such as tearing of the film into pieces.
B: Part of the coating film remained unpeeled and adher-ing to the substrate, due to resistance to the peeling-off oper-ation.
C: Peeling-off was impossible due to adhesion of the coating film to the substrate.

~6~5 Into a vessel equipped with a stirrer were charged lO0 parts of a mixed polyvinyl butyral resin composed of P(l), P(2) and P(3) given below in equal amounts, 20 parts of the organo-polysiloxane as expressed by the aforementioned formula (VIII), 510 parts of methanol and 60 parts of ethanol, followed by mixina with stirring for 2 hours at room temperature, to obtain a clear solution.
P(l): A polyvinyl butyral resin havinq 2 mole ~ of un-saponified acetyl groups, 35 mole % of hydroxy groups and 63 mole % of butyral substitution, with a degree of polymerization 1300.
P(2): A polyvinyl butyral resin having the chemicalassay identical to P(l) but with a degree of polymerization 600.
P(3): A polyvinyl butyral resin having the chemical assay identical to P(l) but with a degree of polymerization 400.
The solution of the resin composition thus obtained was applied to an aluminum plate by the brush coating method. The coating film formed was determined with respect to its physical properties and tested for peelability. The results are shown in Table I. In this table and certain tables to follow, "hardness"
expressed by mark "H" or "2H" was determined in accordance with the method for determination of hardness by use of pencils as described in JaPanese Industrial Standard (JIS) K 5400-1970, 6.14.

i9'~5 TABLE I
Physica~ Proper-tie 5 :
Appearance .............................. Clear Hardness .................................... H
Tensilé Strength ................... 200 kg/cm2 Maximum Elongation ......................... 10 Pee~abi~ity:
In accordance with Method I ................. B
In accordance with Method II ................ A

. . . _ The same procedure as in Example 1 was repeated except the stirring of the mixture was carried out at 60C, instead of room temperature, to obtain a clear solution. Similar tests on - the coating resulted as shown in Table II.

TABLE II
PhysicaZ Properties:
Appearance .............................. Clear Hardness ................................... 2H
Tensile strength .................. 230 kg/cm 2 Maximum Elongation ........................ 10%
Pee~abi~ity:
In accordance with Method I ................. A
In accordance with Method II ................ A

The same procedure as in Example 1 was repeated except that the organopolysiloxane as expressed by the aforementioned formula (V) was employed instead of the organopolysiloxane of 69~5 formula (VIII) to obtain a simi]arly clear solution. The results of similar tests on the thus obtained coating were as shown in Table III.
TABLE III
PhysicaZ Properties:
Appearance ......................... Clear Hardness ............................... H
PeeZabiZity:
In accordance with Method I ............ B
In accordance with Method II ........... A

The same procedure as in Example 3 was repeated except that the stirring of the mixture was carried out at 50C, instead of room temperature, to obtain a clear solution. Similar tests on the coating resulted as shown in Table IV.

TABLE IV
PhysicaZ Properties:
Appearance ......................... Clear Hardness .............................. 2H
PeeZabiZity:
In accordance with Method I ............ A
In accordance with Method II ........... A

Into a vessel equipped with a stirrer were charged 100 parts of polyvinylbutyral resin P(2) as used in Example 1, 20 parts of the organopolysiloxane expressed by the aforementioned formula (IX), 10 parts of butylphthalylbutyl glycolate, 10 parts 6~1~5 of glycerol tributyrate, 240 parts of methanol and 560 parts of ethanol, followed by mixing with stirring at 50C for 2 hours, to obtain a clear solution.
The thus obtained solution and the coating film formed therefrom were determined with respect to their various proper-ties, and further the coating film was tested for peelability.
The results are set out in Table V.

TABLE V
Of the SoZution:
Viscosity, at 25C ............. 200 cps Surface Tension ............ 15 dynes/cm Of the Coating Fi Zm:
Tack-free time, at 25C .......... 5 min Tensile Strength ............ 110 kg/cm2 Maximum Elongation ................ 100%
PeeZ~biZity: (in accordance with Method III) Aluminum plate ....................... A
Polystyrene Resin Plate .............. A
Glass Plate .......................... A

Apart from the above, the same solution of resinous com-position was applied on a methylmethacrylate-styrene copolymer resin plate by the aerosol-type spray method. The coating film thus formed was allowed to age at room temperature for 3 months, and then tested for peelability, to find that the peeling opera-tion was easy and the exPosed substrate surface was in good con-dition.

~?69~S

Into a vessel equipped with a stirrer were charged 100 parts of a mixture of polyvinyl butyral resins P(l), P(2), and P(3) in a weight ratio of 2:1:1, 20 parts of the orqanopolysilox-ane as used in Example 5, 10 parts of nitrocellulose, 10 parts of triethyleneglycol and 700 parts of ethanol, followed by mixing with stirring at 60C for 2 hours, to obtain a clear solution.
The various properties of the thus-obtained solution and the coating film formed therefrom as well as the peelability of the coating film were determined in the same fashion as in Exam-ple 5, with the results as shown in Table VI.

TABLE VI
Of the SoZution:
Viscosity, at 25C ............................ 200 cps Surface Tension ........................... 15 dynes/cm Of the Coating:
Tensile Strength ........................... 110 kg/cm2 Maximum Elongation ............................... 100~ !
PeeZabiZity: (in accordance with Method III) Aluminum Plate ...................................... A
Polystyrene Resin Plate ............................. A
Glass Plate ......................................... A

Into a vessel equipped with a stirrer were charged 100 parts of the same mixed polyvinyl butyral resins as used in Ex-ample 1, 20 parts of organopolysiloxane expressed by the afore-mentioned formula (X), 250 parts of methanol and 250 parts of ethanol, followed by mixing with stirring at 60C for 2 hours, to 6~5 obtain a clear solution.
The thus-obtained solution and the coating film formed therefrom were determined with respect to their various proper-ties and further the coating film was tested for peelability.
The results are set out in Table VII.

TABLE VII
Of the SoZution:
Viscosity, at 25C ............. 300 cps Surface Tension ............ 10 dynes/cm Of the Coating:
Tensile Strength ............ 130 kg/cm2 Maximum Elongation ................. 100 PeeZabiZity: (in accordance with Method III) Aluminum Plate ....................... A
Polystyrene Resin Plate .............. A
Glass Plate .......................... A

Into a vessel equipped with a stirrer were charged 100 parts of a mixture of polyvinyl butyral resins P(l), P(2) and P(3) in a weight ratio of 1:1:1, 20 parts of the organopolysilox-ane as expressed by the aforementioned formula (XII), 510 parts of methanol, 60 parts of ethanol, followed by mixing with stir-ring at 60C for 2 hours, to obtain a clear solution.
This solution was used to form a coating film in the same manner as in Example 1 and the resulting coating film was observed or tested for its various properties and peelability, with the results as shown in Table VIII.

6~1~S
TABLE VIII
PhysieaZ Properties:
Appearance ............................. Clear Hardness .................................. 2H
TensiLe Strength .................. 220 kg/cm2 Maximum Elongation ................ ,... 10 PeeZabiZity:
In accordance with Method I ........... .... A
In accordance with Method II .......... .... A

The same procedure as in Example 8 was repeated except only that the organopolysiloxane used was one expressed by the aforementioned formula (XIII) instead of formula (XII), to obtain a similarly clear solution. Similar observations or tests were carried out for the coating film formed from the solution, with the results identical to those shown in Table VIII of Example 8.

_ AMPLE 10 The same procedure as in Example 1 was repeated except that the organopolysiloxane was employed in an amount of 3 parts or 30 parts instead of 20 parts and that the temperature at which stirring was conducted was 60C instead of room temperature, re-sulting in producing a similarly clear solution. Similar obser-vations and tests were carried out with the coatinq films formed from these two solutions, with the results dS set out in Table IX.

6~S

TABLE IX
Amount of Organopolysiloxane3 parts 30 parts PhysicaZ Properties:
Appearance ..................... Clear Clear Hardness ....................... 2H 2H
Tensile Strength ............... 240 kg/cm2 200 kg/cm2 Maximum Elongation ............. 10% 10%
Pe e Zab i Z i ty :
In accordance with Method I A A
In accordance with Method II A A

For comparative purposes, the same procedure as in Exam-ple 1 was repeated except that the organopolysiloxane used was one of those expressed by the undermentioned formulas, instead of that expressed by formula (VIII) and that the temperature at which stirring was conducted was 60C, instead of room tempera-ture, resulting in producing a solution which was opaque in appearance.

fH3 (a) CH3-Si -Ofi-OC2Hs fH3 ~ fH3 ¦ CH3 (b) CH3-SiOt SiO ! Si-CH3 CH3 1(CH 2~0 - tC2 H 4 O~COCH3J3 8 CH3 f 3 ~ICH3l ~ fH3 1 CH3 (c) CH3-SiO~ SiO ~ SiO l Si-CH3 CH3 lCH3J 27 O CH3 (C H O) C H
- ~ 2 4 48 4 9 3 i9~

(d) CH3-Si -Of ~ O--~C~H40 ~ C3H60 ~ C4Hsl fH3 ~CH31 ¦ CH3 1 CH3 (e) CH3-fiO- fiO~ fiO ~ - fi-CH3 CH3 CH3 27 ~(CH2~o--~C2H4o) 24 (c3H6o ~ C4Hs 3 CH

Then, using this solution a coating film was prepared in the same fashion as in Example 1 and subjected to observations or tests with respect to its appearance, physical properties and peelability. The results are shown in Table X.

TABLE X
--------- OrganopoZysi?o~cane ---------(a) (b) (c) (d) (e) Appearance ................ Opaque lucanent Opaque Opaque Opaque Hardness .................. 2H 2H 2H 2H 2H
Tensile strength, kg/cm2 260 230 * * *
Maximum elongation, ~ ..... 10 10 * * *
Peelability: Method I C C C C C
Peelability: Method II B B B B B
*Film obtained was of dimensions insufficient for determining the property.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A resin composition for peel-off coatings consisting essentially of (A) 100 parts by weight of at least one polyvinyl acetal resin and (B) from 1 to 30 parts by weight of an organopolysiloxane repre-sented by the average formula, where R1 and R2 are halogen-substituted or unsubstituted monova-lent hydrocarbon groups, m is an integer from 1 to 3, n is 0 or a positive integer, a is 0 or an integer from 1 to 5, b is an inte-ger from 2 to 40, c is 0 or an integer from 1 to 40, and x and y are integers from 2 to 50.

2. A resin composition as claimed in claim 1 wherein the component B is represented by the formula where R1, R2, b, c, x, and y are as defined in claim 1 and a' is an integer from 1 to 5.

3. A resin composition as claimed in claim 1 wherein the component (B) is from 5 to 20 parts by weight per 100 parts by weight of the component (A).

4. A resin composition as claimed in claim 1, 2 or 3 wherein the component (A) comprises a polyvinyl butyral resin.

5. A resin composition as claimed in claim 1, 2 or 3 wherein the component (A) comprises a polyvinyl formal resin.

6. A resin composition as claimed in claim 1, 2 or 3 wherein the component (A) comprises a polyvinyl butyral resin having an average degree of polymerization between 400 and 1,100 and containing at least 30 mole % of butyral component.

7. A resin composition as claimed in claim 1, 2 or 3 wherein the component (A) comprises a polyvinyl formal resin having an average degree of polymerization between 400 and 1,000 and containing at least 30 mole % of formal component.

8. A resin composition as claimed in claim 1, 2 or 3 wherein the groups R1 and R2 are selected from the class consist-ing of alkyl groups, alkenyl groups, cycloalkyl groups, aryl groups, aralkyl groups and halogen-substituted monovalent hydro-carbon groups.

9. A resin composition as claimed in claim 1 which is obtained by heating a mixture of components (A) and (B) to a tem-perature in the range from 40 to 150°C for 1 to 6 hours.

10. A process for preparing a resin composition for peel-off coatings consisting essentially of (A) 100 parts by weight of at least one polyvinyl acetal resin and (B) from 1 to 30 parts by weight of an organopolysiloxane represented by the average formula, where R1 and R2 are halogen-substituted or unsubstituted monova-lent hydrocarbon groups, m is an integer from 1 to 3, n is 0 or a positive integer, a is 0 or an integer from 1 to 5, b is an inte-ger from 2 to 40, c is 0 or an integer from 1 to 40, and x and y are integers from 2 to 50, said process comprising blending said components (A) and (B) with at least one organic solvent and heating the resulting blend at a temperature of 40°C to 150°C for 1 to 6 hours with stirring.