CA1060622A - Methods for filling a depression in a surface and plastic solder compositions for use therein - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A method for filling depressions in a surface, e.g., of automobile bodies and the like, which comprises placing a partially cured shaped article of a thermosetting resin compo-sition in the depression whose surface defining the depression is heated to a temperature above the softening or melting temperature of the resin composition to fix the shaped article provisionally to the surface defining the depression, the resin composition being pre-fabricated so as to fit into the depression and to be substantially free of air bubbles, heating the shaped article under pressure from the surface of the shaped article e.g., using a heated applicator, and then surface-finishing the filled depression. The resin composition in general comprises a thermosetting resin. A curing agent, a metal powder and a metallic fiber.

Description

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-1. Field of the Invention This invention relates to a method for filling the spaces between joining parts of or depressions in a surface, ~ -e.g., an automobile body and the like, using a plastic solder, and to plastic solder compositions which can be used especially advantageously in the above method. More specifically, this invention relates to an improved method for filling the spaces between joining parts of a surface, e.g., of an automobile body and the like which occur at the time of fabricating steel body panels to form the surface, or the depressions in the surface, e.g., in the automobile body, resulting from spot welding, which comprises depressing the above joining parts or depressions to a certain extent, and filling the resulting depressed areas with a plastic solder so ~hat the finished surface, e.g., of the ~ -automobile body, is smooth. ~-

2 Descri tion of the Prior Art - -P ~. -Previously, metallic lead solders have been widely used as a filling material for automobile bodies or the like, but because of plumbism or the unsatisfactory operability of the solder, such lead solders have the following defects.
(a) Toxic lead gas that is generated when filling ~ -is performed using a spatula while exposing the metallic lead solder and the areas being filled to an acetylene burner, and lead dust that occurs at the time of sanding after filling are detrimental to the health of the working personnel, and also tend to cause pollution in areas where these solders are used. -~ b) Electrodeposition coating, intermediate coating and top coating are applied to automobile bodies, and higher bak-ing temperatures ~or the coatings give better quality coatings ,, ,,,:, ... .... . .

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1 with increased strength and luster. Since lead solder has amelting point of 183C, the baking temperatures for automobile bodies subjected to filling using lead solder is about 170C at the highest.
(c) Since lead solder softens during the baking operation, air entrapped at the time of filling expands during the baking, and tends to form projections or holes on the surface of the filled area.
(d) The amount of the solder now used is about 1 to 0.5 Kg for an average size automobile. Since the density of the solder is higher than that of steel, the solder adds to the weight of the car.
With a view to removing these defects, attempts have been made to use synthetic resins for filling.
One of these attempts is a method which involves the use of a thermosetting resin paste. Since, however, filling is performed using a spatula in this method, it is very difficult to avoid entrapping air bubbles in the filled areas. Moreover, because the filled areas are dried in the open, a sagging phenomenon occurs.
Another attempt involves bonding a solid thermosetting resin pre-fabricated to fit into the area to be filled and which does not to contain air bubbles, to area to be filled using an adhesive. This method has the defect that a complicated procedure is involved because the method includes the step of coating the adhesive.

SUMMARY OF THE INVENTION
An object of this invention is to provide a method for filling the spaces between joining parts of or depressions in a surface, e.g., of automobile bodies and the like, which is free from the above-described defects.

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1 This invention provides a method for filling depressions in a surface which comprises placing partially cured (B-state) article of a thermosetting resin composition, which has been fabricated so as to fit into the depression and which is as free of air bubbles as is possible, in the depression to be filled, and heating it to a temperature above the temperature at which the shaped articles softens or melts.
Another embodiment of this invention provides a method for filling the depressions in a surface, e.g., depressions in an automobile body or spaces between joining parts and the like, which comprises filling a depression with a partially cured article of a thermosetting resin composition or of a thermosetting resin composition paste, so as to fit into the depression to be filled, heating the article or paste under pressure from the surface, e.g., using an applicator capable of being heated and having a fluorine resin sheet adhered to the applicator surface, thereby to complete the filling without forming air bubbles on the surface of the depression to be filled. -Still another embodiment of this invention provides a method for filling a depression in a surface, e.g., spaced between joining parts or depressions in automobile bodies and the like, where air bubbles are eliminated, which comprises placing a shaped article of a thermosetting resin composition in the depression to be filled in a specific relation as described hereinafter, and curing the shaped article under heating, e.g.
using a heated applicator.
A further embodiment of this invention provides an epoxy resin solder composition that can be used especially advantageously in the above filling methods.
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Figure 1 is a sectional view showing the placing of the resin shaped article in a depression to be filled using a test panel.
Figure 2 is a sectional view showing the filling of the resin shaped artic]e in the depression to be filled after use of a heatable applicator.
Figure 3 (a) shows a test panel obtained by spot welding a cold-rolled steel plate used in an example.
Figure 3 (b) shows the placement of a partially cured article of a thermosetting resin on the test panel of Figure 3(a), and Figure 3 (c) shows the test panel of Figure 3(a) filled with the partially cured article of the thermosetting resin after subjection to heat and pressure.
Figure 4 and Figure 5 show additional embodiments of test panels used in the examples.
Figure 6 shows exothermic curing data obtained in an example for a thermosetting resin in an A-state degree of cure. ~-Figure 7 shows exothermic curing data obtained in an example for a thermosetting resin in a B-state degree of cure.
Figure 8 shows the particle size distribution of iron powders used in an example.
Figure 9 shows the particle size distribution of aluminum powders used in an example.
DETAILED DESCRIPTION OF THE INVENT ION
As is set forth above, the embodiments of the method of this invention are~ particularly useful in filling the spaces between body panels of an automobile body or depressions in the - 30 surface therein but the embodime~ts of the method of ~ '' . .
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" l.()f~O~'~' 1 this invention are not limited thereto, however~ For simplicity in the description to follow, the application of the embodiments of the method of this invention will be with reference to their utility in filling spaces and depressions in an automobile body surface but it will be recognized that the principles of this invention are appropriate to other applications as well.
According to a first embodiment of this invention, a method is provided for filling the spaces between joining parts of or depressions in a surface, e.g., of automobile bodies and the like, which comprises placing a partially cured shaped article ~ -of a thermosetting resin composition in the area to be filled and heating it to a temperature above the softening or melting temperature of the resin composition to fix the shaped article provisionally to the area, the resin composition being pre-fabricated so as to fit in the area to be filled and being as free from air bubbles as is possible, heating the shaped article under pressure using a heated applicator, and then surface-finishing the filled area.
According to this embodiment, a suitable curing agent, inorganic filler, and metal powder are added to a thermosetting resin, and mixed thoroughly to form a composition. Then, the thermosetting resin composition is converted to a partially cured (i.e., B-state) article by shaping the resin composition under heat and pressure e.g., using a temperature of about 50 to ~50C and a pressure above about 0 to about 50 Kg/cm2 so that the article fits into the area to be filled, or by mixing the thermosetting resin with additives under a reduced pressure, e.g., less than about 50 mmHg and injecting the resulting mixture into a receiving plate or mold. Then, the filling part is heated :

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1 to a temperature above the temperature at which the resin compo-sition softens or melts, e.g., at about 50C to about 250C
(in the case of an epoxy or polyester resin composition, the area to be filled is heated to about 100 to 200C). The above resin shaped article is placed in the heated area to be filled to soften or melt the surface of the resin shaped article in contact with the heated area to be filled, and then the back surface of the resin shaped article ~the surface not in contact with the area to be filled) is heated under pressure, for example, at about 200C and about 10 to 20 Kg of total pressure for less than about 3 minutes, using a heatable applicator to embed the softened resin shaped article in the area to be filled.
Then, the embedded resin shaped article is cured, e.g., by heating to about 100 to 250C at a pressure of about 0.3 to 10 Kg/cm2, to complete the filling, and the surface of the filled area is finished, for example, by sanding.
As used herein the term partial curing means that the thermosetting resin is cured to the extent that it has a vis-cosity at 140C of about 0.1 to 105 poise using a KOKA flowtester (a viscometer for plastics, manufactured by Shimazu Seisakusho Ltd. (Japan)~ and this term includes the B state degree of cure -as is generally employed in the art (see nsulation/Circuit Directory/Encyclopedia., June and ~uly, 19~3, page 3~.

When the resin shaped article used in this method is ~ ;
of the same shape as the area to be filled, no flow of resin between the steel panel on the body side and the heated applicator occurs until the shaped article is set, and air bubbles tend to be contained in the interface between the steel panel surface -and the resin layer. Therefore, the resin shaped article preerably has a certain shape and relationship with respect to the space or area to be filled as will be described in detail hereinafter.

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1 This method can be utilized primarily for the filling of welded parts of automobile bodies, but can also be used effectively in similar uses, for example, for building up depressed areas and raised parts of various steel materials to a desired shape, such as the filling of the joining parts of steel panels formed at the time of fabricating steel panels of vehicles or the depressions in steel panels resulting from spot welding of the panels or bad pressing of the panels.
Since a synthetic thermosetting resin composition is applied to a heated area to be filled, the softened resin adheres to the filled area, and upon setting, is firmly fixed thereto.
Thus, the use of an adhesive is not necessary in this method.
Furthermore, since a synthetic thermosetting resin is used instead of a metal solder, there is no danger of the generation of toxic gases or dust, and moreover, the filling of the spaces between joining areas or depressions of automobile bodies or the like can be performed using a simple procedure.
Examples of suitable thermosetting resins which can be used in this method are phenol resins, epoxy resins, silicone resins, urea resins, acrylic resins, urethane resins, melamine resins, and polyester resins, with epoxy resins being most preferred. Examples of suitable curing agents for these resins are those well known in the art for these thermosetting resins - and include aliphatic amines, aromatic amines, acid anhydrides, polyamides, and modified amines. A suitable particle size for Curlh~ :
these during agents is less than about 149 microns. The thermo-setting resin composition can of course contain inorganic fillers such as silica, talc, clay, mica, glass powder, carbon powder, calcium carbonate, or alumina, or metal powders such as aluminum powder, iron powder, copper powder, antimony powder or nickel _ 7 ,. . :

1 powder, e.g., in a volume % of about 5 to 50 of the total volume of the composition. A suitable particle size for the inorganic fillers and metallic powders is less than about 149 microns.
According to a second aspect of this invention, a method is provided for filling the spaces between joining parts or of depressions in automobile bodies and the like, which comprises placing a partially cured (B-state cure) shaped article of a thermosetting resin composition in an area to be filled -with the resin composition being pre-fabricated so as to fit into the area to be filled, or prefabricating a thermosetting resin composition paste in the area to be filled, and heating the thermosetting resin composition under pressure on the surface of the thermosetting resin composition using a heatable applicator having a surface capable of fitting into the area to be filled and including a fluorine resin sheet adhered to the surface of the applicator contacting the thermosetting resin composition, to fill the area.
According to the first embodiment described above, the surface of the resin layer after curing is not smooth. However, by using a special heatable applicator in the second embodiment, the adhesion of the applicator to the resin and the generation of air bubbles in the closed portion and the surface layer of the filled area can be prevented, and a smooth surface finish can be obtained.
The fluorine resin sheet used in this embodiment can be, for example, a sheet of polytetrafluoroethylene, polyvinylidene fluoride, or a tetrafluoroethylene/hexafluoropropylene copolymer.
The sheet may be a sheet of the fluorine resin alone produced by conventional means (for example, cutting or rolling), or a .

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1 sheet of a mixture of the fluorine resin and a filler such as molybdenum, glass fiber powders or copper powder, which may or may not be embossed in a raised and depressed pattern or per-forated. The sheet can also be an impregnated cloth obtained by impregnating a thermally stable fibrous cloth made, for example, of glass fibers, asbestos fibers, carbon fibers or metallic fibers, with a dispersion of the fluorine resin, and heating the cloth, or a laminate of a plurality o~ such impregnated cloths. Especially preferred sheets are the above-mentioned impregnated cloths or the laminates of these cloths,and those sheets having a depressed and raised pattern on their surfaces and containing gas passages adapted to permit the discharge of gases, such as air bubbles, air, reaction gases, or decomposition gases, generated between the applicator and the resin layer. In a more preferred embodiment, air-permeable holes or grooves are also provided on the surface of the applicator (heater) itself and the above-described preferred fluorine resin sheet is adhered to such a surface so that air bubbles generated at the time of filling can be discharged through the surface of the applicator.
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In this embodiment of the method of the invention, preferably, the area to be filled also is heated to a temperature above the softening or melting temperature of the resin because this permits the resin to be easily placed in the area to be filled and to adhere and fix the resin provisionally to the filling part.
; According to a third embodiment of the method of this invention which is especially advantageous and preferred, a method is provided for filling the spaces between ~oining parts of Qr depressions in, e.g., automobile bodies and the like, _ 9 -10~0~ f 1 which comprises placing a pre-~ormed partially cured (B-state cure) article of a thermosetting resin composition in an area to be filled so that the maximum length (~) of the normal that extends from the undersurface of said partially cured resin article to the surface at the area to be filled, e.g. r the steel panel surface of an automobile body, is not less than one-sixth of the maximum length (~') of the normal that extends from the top surface (outside surface) of the cured filled resin article to the surface at the area to be filled, e.g., -the steel panel surface of an automobile body (~>- V 6), and then heating the filled resin article under pressure using a heatable applicator to camplete the filling of the area.
This embodiment of the method of this invention will -be specifically described below by reference to the accompanying - drawings.
Figure l is a sectional view showing the setting of a resin shaped article in an area to be filled using a test panel, and Figure 2 is a sectional view showing the placing of the resin shaped article in the depression to be filled after use of a heatable applicator.
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Referring to Figure l, a pre-formed partially cured article 2 of a thermosetting resin composition is placed on the surface of a depressed area to be fllled l of a steel panel 3.
In this case, the maximum distance between the undersurface of the pre-formed partially cured article 2 and the point A which lntersects the normal that extends from the undersurface of the resin article towards the steel panel surface 3' of the area to be filled is designated as e. On the other hand, :: .
Figure 2 shows the shaped article 2 which has been heated under

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1 condition shown in Figure 1. B in Figure 2 shows a point of intersection of the normal extending from the top surface (outside surface) of the filled resin layer at the area filled towards the steel panel surface 3' at the area filled with the steel panel surface 3' at the area filled, and ~' shows the maximum distance between this point B and the steel panel surface 3'. According to this embodiment, the shape of the resin article is determined so as to satisfy the relation ~- 1/6 ~', and the pre-formed resin article is placed at the area to be filled. Then, the shaped article is cured using a heated applicator, thereby to complete the filling.
Various thermosetting resins can be used in this method, but epPxy resins are especially preferred because of their superior bond strength and mechanical strength. Since -~
rapid curing is required, dicyandiamide is especially preferred as a curing agent. As a curing promotor, an imidazole, e.g., -imidazole, 2-methyl-imidazole, 2-methyl-N-(cyanomethyl)imidazole, 2-ethyl-~-~ethyl-imidazole, 2-undecyl-N-(cyanomethyl)imidazole and 2-undecyl-imidazole, and alkyl guanidines, e.g., 1,1,3,3-tetramethyl guanidine, 1,1,3,3-tetraethylguanidine, etc., for example, can be used. A metallic powder and an inorganic filler can also be incorporated in the thermosetting resin composition , as a reinforcing agent. Preferred metallic powders are finely divided powders of iron or aluminum.
The thermosetting resin is mixed with such a curing agent, curing promotor and filler, and the resulting composition is pre-formed in a partially cured state in the part to be filled in a way that the above-described conditions are satisfied.
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According to this embodiment, the finished filled parts do not contain air bubbles therein.

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1 In the above embodiment, the thermosetting resin composition is pre-shaped so that the resin composition can flow on the steel body panel at the time of heatin~ under pressure, and then the pre-shaped article is placed in the area to be filled. At this time, preferably the area of contact between the steel bod~ panel and the pre-shaped article is minimized. By so doing, air bubbles are not generated between the steel panel surface and the resin layer after curin~ the pre-shaped article by heating under pressure.
An especially preferred thermosetting resin composition which can be used in the above embodiments of this invention is a plastic solder composition comprising a matrix of an epoxy resin and a curing agent therefor, and about 50 to 5% by volume of a metal powder containing about 5 to 30% by vol1lme, based on the composition, of a metallic fiber, e.g., iron, copper, nickel, -cobalt, aluminum, stainless steel, tungsten and the like whiskers. This plastic solder composition is a superior filling material which meets the following requirements of filling material for automobile bodies or the like.
(1) Electrodeposition coating of the composition should be possible. ~
(2) No blisters of the coating should occur at the ;
filled areas.
~3) The composition should have a heat resistant temperature of at least about 200C.

(4) The composition should have a coefficient of linear expansion of not more than about 4 x 10 5/Co. -

(5) The composition should have a high bond strength, -e.g., more than about 200 Kg/cm (JIS S-6040).
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1 (6) The compositlon should have the same abrasiveness as steel plate.
(7) The composition should not permit the inclusion of air bubbles in the filled area.
(8) The composition should not be toxic.
Specifically, the above plastic solder composition can be prepared by mixing an epoxy resin with a curing agent therefor, such as dicyandiamide, phthalic anhydride, diamino-diphenyl methane, diaminodiphenyl ether, or an alkyl imidazole, and if desired, a pigment, a filler or a reinforcing agent such as those generally used in the art, e.g., carbon titanium dioxide, iron dioxide, etc. as a pigment and carbon fibers, asbestos, glass fibers, etc., as a reinforcing agent to form a matrix, and mixing the resulting matrix with a metal powder, such as iron, copper or aluminum, in an amount of about 50 to 5~
by volume, the metal powder containing about 5 to 30% by vblume ~-of metallic fibers.
Any epoxy resin can be used in the plastic solder -composition described above, but preferably those which are semisolid or solid are satisfactory from the standpoint of operability. For example, an epoxy resin available under the trade nark EPI~OTE*1001 (trade mark for a glycidyl ether of bisphenol A, produced by Shell Chemical Company, U.S.A.) can be used.
Furthermore, any epoxy resin curing agent can be used, but dicyandiamide is especially preferred because of its ~ good storability and rate of curing.
`~ A preferred particle size of the metal powder is not more than about 149 microns.
~ he so-called metal whiskers are especially preferred ~as metallic fibers. For example, iron or copper whiskers ~ .

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1 can be used in this invention. The diameter of the metal whiskers is not more than about 100 microns, e.g., about 0.1 to 100 microns, and the length-to-diameter ratio of the whiskers is more than about 10, e.g., about 10 to 10,000, microns.
If the proportion of the metal powder in the plastic solder composition described above is less than about 5~ by volume, the resulting composition provides unsatisfactory results in a thermal shock test and a sedimentation test, and are inferior in electrode positability and abrasiveness. If the proportion of the metal powder is more than about 50% by volume, the resulting composition exhibits poor adhesion.
Where the amount of the metal powder is the same, the incorporation of the metallic fibers gives rise to an improved performance of the plastic solder composition both in a thermal shock test and in a sedimentation test, and the solder compo-sition provides especially preferred results for the filling purposes in accordance with this invention.
Since the metallic fibers have a high bulk density, the upper limit of their amount present in the composition must 2~ be adjusted to 30% by weight or less.
As a plastic solder composition capable of being cured at low temperatures and providing a cured product free from foaming or pinholes, the present invention also provides -a plastic solder composition comprising an epoxy resin, a filler, and a curing agent which is dicyandiamide having a particle diameter of less than about 74 microns, e.g., about 0.1 to less than about 74 microns.
With a view to providing a plastic solder composition having rapid low temperature curability and strong adhesion, experiments were performed in which an epoxy resin was cured 10~0~
1 with dicyandiamide using known curing promotors, i.e., (a) a tetra-alkyl guanidine, (b) a 3- or 4-substituted monoamino-pyridine, (c) a reaction product formed between phthalic anhydride and diethylene triamine, (d) an imidazolium halide, or (e) an inorganic acid salt of guanidine, biguanide or guanylurea, or an organic acid salt of guanidine, and it was found that in all cases, a temperature of at least 200C was required in order to completely cure the composition within 5 minutes, and foaming inevitably occurred. Further experimen-tation lead to the discovery that by adjusting the particlesize of the dicyandiamide in the above epoxy resin-dicyandiamide system to a particle size of less than about 74 microns, pre-ferably less than 63 microns, a plastic solder composition capable of being cured rapidly at low temperatures without foaming was obtained. This plastic solder composition can be -advantageously used in the filling method of this invention.
The present invention further provides a plastic solder composition capable of being coated electrostatically or by electrodeposition, which comprises a thermosetting resin and a curing agent therefor, and about 20 to 50~ by volume, based on the composition, of a metal powder, the metal powder compris-ing about 0 to 25% by volume of particles having a particle size of at least about 74 microns, and about 29 to 100% by volume of particles having a particle size of not more than about 44 microns.
The same metal powders and epoxy resins as described above can also be used in this plastic solder composition.
If the total amount of the metal powder in this composition is less than about 20 % by weight, the resulting plastic solder composition exhibits inferior characteristics . :

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1 in electrodeposition coating or electrostatic coating. If the amount of the metal powder is above about 50~ by volume, the solder composition has poor adhesion to the areas to be filled.
If the proportion of particles having a size of at least about 74 microns in the metal powder is more than 25% by volume~ pinholes occur on the surface coated by electrodeposition.
If the proportion of particles having a particle size of not more than 44 microns is less than ~9% by volume, an electro-deposited coating is difficult to form in the boundary between the steel panel part and the resin part. Especially preferably, the proportion of the particles having a particle size of not more than 44 microns is 100% by volume.
The curing agent that can be used in this composition can be any known curing agent for epoxy resins, but from the standpoint of storability, the rate of curing, abrasiveness, and good adhesion, dicyandiamide is especially preferred.
The following Examples are given to illustrate the present invention in greater detail. Unless otherwise indicated, all parts, per~ents, ratios, and the like are by weight.

This Example relates to the first embodiment of the method of the present invention.
An epoxy resin (EPIKOTE*1001), a nearly equivalent amount of dicyandiamide as a curing agent, and 20 to 50% by volume of iron powder were admixed with each other. The mixture was heated in vacuo at about 100 to 140C for about 3 hours.
The molten mixture was then injected in a mold conforming to the shape of an area to be filled, and aged and cooled to form a partially cured molded article of thermosetting resin. This resin molded article was placed in the area to be filled heated . ' .': "
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1 to about 100C, whereupon the surface of the resin molded article was softened, and adhered to the surfaces of the area to be filled. When the resin molded article was heated for 2 minutes at a pressure of about 10 to 20 Kg (total pressure) using an applicator heated at 200C, the resin softened and became completely buried in the area to be filled, and then cured. The surface of the filled resin was finished by sanding to complete the filling.

This Example relates to the second embodiment of the method of this invention.
EPIKOTE*1001, a nearly equivalent amount of dicyandiamide and 20 to 50% by volume of iron powder as a filler were admixed with each other. The mixture was pulverized, and then molded with a transfer molding technique. The molded article was placed on the surface of steel panel, and heated at 200C and at a pressure of 10 to 20 Kg(total pressure) for 3 minutes using a heated applicator having as a surface an impregnated cloth obtained by impregnating a glass fiber cloth (thickness 0.8 mm) with a dispersion of polytetrafluoroethylene.
The filled part so obtained was completely unitary, and no bubbles were formed on the surface of the filled part.
The following Examples 3 and 4 relate to the third embodiment of the method of this invention.

100 parts by weight of an epoxy resin (EPI~OTE*1001) were mixed with 300 parts by weight of iron powder which passed through a 350 mesh sieve (not more than 44 microns in size~ in a vacuum mixing kettle (5 liters) at 150C and 4 mmHg for 5 hours. Then 6 parts by weight of dicyandiamide was added :

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1 as a curing agent, and mixed with the above mixture at 100C
for 20 minutes. The mixture was injected in a mold with care being taken not to incorporate air bubbles into the mixture.
The mixture was then dried by heating at 100C for 3 hours to form a partially cured shaped article of the resin. The criterion for determining partial curing was that the resin has a'viscosity of about 5 x 102 poises at 140C as determined using a KOKA
flowtester ta viscometer for plastics, manufactured by Shimazu Seisakusho Ltd. (Japan)).
In order to examine the characteristics of the above resin composition, evaluations were performed using a test panel (P) obtained by spot welding a cold-rolled steel plate - ~- -(JIS-C 141) having a thickness of 0.8 mm and a width of 70 mm, and then pressing the steel plate into the form as shown in Figure 3(a). Each of the partially cured articles of thermo-setting resin as shown in Table 1 below was placed in or on the recessed area of this panel in the manner as shown in Figure 3tb) -and Figure 3(c), and then heated at 200C and at a pressure of -10 to 20 Kg (total pressure) for 2 minutes using a heated ~ applicator to fill the recessed area. Then, the surface of the filled area was finished by sanding, and the extent of foaming on the surface was observed. The results obtained are shown in Table 1. In Figure 3, Figure 3(b) is a sectional view showing the conditlon of shaped article 2 of Run Nb. 1 placed on the test panel P, and Figure 3(c) shows the same view except that the shaped article 2 is that of Run No. 3. -~

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1 Table 1 Run Number Conditions 1 2 3 4 Test Sample Thickness (mm) 5 5 5 7 Test Sample Length (mm) 30 25 23 20 (mm) 3 0 0 0 ~'(mm) 3 3 3 3 1~6~ ' 1/2 0 0 0 Air Bubbles at Point No Yes Yes Yes ~in Figure 2 Air Bubbles at PointsNo No No No other than Point ~

It can be seen from the results in Table 1 that no bubbles were formed in the test sample of Run No. 1 which is within the scope of this invention.

A test panel of the form shown in Figure 4 was prepared using a steel plate as described in Example 3, and each of the shaped articles of the thermosetting resin as shown in Table 2 : below was filled in the recessed area of the test panel in the same manner: as in Example 3. The occurrence of air bubbles was examined in the same manner as described in Example 3. The ~
results obtained are shown in Table 2. - :

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1 Table 2 Conditions _ Run Number

6 7 8 _ 9 10 Test Sample 5 5 5 5 5 7 Thickness (mm) Test Sample 35 28 27 26 25 20 Width (mm) (mm) 3 2 1.5 1 0.5 0 ~ (mm) 3 3 3 3 3 3 1/6 ~' 1/2 2/3 1/2 1/3 1/6 0 10 Air Bubbles at No No No No Yes Yes Point ~ (little~

Air Bubbles at No No No No No No Points other than Point ~

As can be seen from the results in Table 2, no bubbles were formed in Runs Nos. 5 to 9 which are within the scope of this invention, but a large amount o~ bubbles occurred in Run No. 10.
In a modified form of test panel as shown in Figure 5, air bubbles occurred at the point y when ~ was 0. In order to remedy this defect, the partially cured thermosetting resin article must be placed in such a way that it is separated from the area to be filled by the specified distance as in the case of Runs Nos. 1 and 5. This leads to a complete elimination of air bubbles.

This Example illustrates a plastic solder composition that can be used especially advantageously in this invention.
100 parts by weight of Epikote*1001 were mixed with 6 parts by weight of dicyandiamide having a particle size of less than 74 microns to form a matrix. The matrix was kneaded * Trade Mark .^..=. ,.

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1 with the metal powder shown in Table 3 below for 10 minutes using a roll kept at 100C to form various plastic solder compo-sitions which were used to prepare test samples used in the following tests. (in a sedimentation te.st a composition comprising 100 parts by weight of Epikote*828, trade name for a glycidyl ether of bisphenol A produced by Shell Chemical Company, and 80 parts of hexahydrophthalic anhydride was used as a composition.) Table 3 10 Sample Amount of Amount of Amount of Matrix Iron Powder Iron Whiskers (Vol. %) (Vol. %) (Vol. %) No. 1 95 0 5 No. 2 85 10 5 No. 3 80 15 5 No. 4 80 10 20 ;.
No. 5: 60 35 5 ~omparison.
- No. 1 100 0 0 ; No.r. 2~ 95 - 5 o :~ 20 No. 3 80 20 0 No. 4 50 50 0 ~ ..

~: Various test pieces were prepared, and the evalua-.tions shown in Table 4 below were conducted. The results obtained are shown in Table 4.
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1 Table 4 Samples Coeffi- Bond Electro- Resist- Thermal Resis-cient of Strength deposit- ance to Shock tance to Thermal (2) ion Pro- Blister Test Sedi-Expansion perties (4) (5) menta-(1) (3) tion (6 (xl 05) No. 1 5.2 380 Good Good 8 Good No. 2 4.0 320 Good Good 9 Good No. 3 3.7 300 Good Good > 10 Good No. 4 3.5 290 Good Good > 10 Good No. 5 2.5 250 Good Good > 10 Good Comparison No. 1 7.7 320 Poor Poor No. 2 5.8 355 Poor Poor 1 Poor No. 3 4.0 295 Poor Good 6 Poor No. 4 2.4 150 Good Good ~10 Good Note "/" designates that the property was not measurable.
Preparation of Test Pieces and Method of Testing (1) Coefficient of Thermal Expansion:

Test pieces were prepared, and tested, in accordance with JIS K-6911.
(2) Bond 5trength (tensile shear strength):
Test pieces were prepared, and tested, in accordance with JIS S-6040.
(3) Electrodeposition Properties:
A recess with a width of 30 mm, a length of 70 mm and a depth of 3 mm was formed in the central part of a rolled steel plate with a thickness of 0.8 mm, a width of 70 mm and a length of 150 mm. The recess was filled with each of the samples using an applicator at 2booc and a pressure of 10 to 20 (total pressure) for 2 minutes. The surface of the filled area was 1 smoothened to the same degree as the steel panel part.
Electrodeposition coating was performed on this test piece at a liquid temperature of 30 + 1C and a voltage of 200 V with the passage of a total of 42 coulombs. When the thickness of the coating on the filled area was more than 50~ of that of the coating on the steel panel portion, the electrodepositing pro-perties of the sample were evaluated as "good".
(4) Resistance to Blister:
The same test piece as used in the electrodeposition property test was used, and subjected to pretreatment (with iron phosphate), electrodeposition coating (under the same coating conditions as in the above test (3), washing with water, and then top coating. The coated test piece was immersed in warm water at 40c for 240 hours, and the occurrence Oc blister was observed visually.
(5) Thermal Shock Test:
The same test piece as used in the electrodeposition property test was used, and subjected to the following thermal shock cycling. The resistance to thermal shock was evaluated in terms of the number of such cycles required to peel off the filled resin portion of the test piece.
Each cycle comprised:
Immersion in distilled water 20C 10 minutes Water removal at room25C 10 minutes temperature Heating 150C 30 minutes Standing at room temperature 25C 30 minutes (6) Resistance to Sedimentation:
A sample having a length of 5 cm was placed in a test tube with an inside diameter of 1 cm. The test tube was held vertical, and the sample was cured at 170C for 2 hours.

,2~
1 A 1 cm-portion was cut off from the upper end and the lower end of each test piece. When the deviation from the average density of those cut pieces was within ~ 10%, the resistance to sedimentation was evaluated as "good".
As can be seen from the results in Table 4, the compositions shown in Example 5 had a superior coefficient of thermal expansion, bond strength, electrodeposition properties, resistance to blistering, resistance to thermal shock and resistance to sedimentation, and can be used as a solder.
The following Examples 6 to 11 illustrate~ plastic solder compositions of reduced foaming which can be used in this invention especially advantageously.

This Example demonstrates that the particle size of dicyandiamide used as a curing agent for epoxy resins is related to the occurrence of pinholes after foaming by heating with an application and water washing, and the properties of the cured product obtained.
100 parts by weight of an epoxy resin (Epikote 1001) -~ and 6 parts by weight of dicyandiamide were mixed at 100C
for 30 minutes using a 4-inch roll. The mixture (about l g) was cured on a hot plate at 200C-for lG minutss. In order to observe air bubbles in the cured product, the surface of this cured product was abraded, and washed with water, whereupon the number of holes in the surface were observed.
In order to evaluate this phenomenon, the exothermic properties at the time of curing were examined using a differen-tial thermal analyzer (a product of Rikaku Denki K.K.). The curing exothermic data shown in Figure 6 (A~state) were obtained, and it was found that this curing was a two-step reaction and :, 1 that the reaction at higher temperature~ was not comple-ted unless the-temperature was 250C or more.
The a~ove mixture was cured on a hot plate at 250C
for 10 minutes. A number of air bubbles were observed in the cured product, but even after washing, the number of the air bubbles did not increase. ~at a curing temperature of 230C
or more, foaming occurs.) From these two phenomena, it was thought that before curing, dicyandiamide is dispersed in an epoxy resin in the epoxy resin-dicyandiamide system, and performed the following experiments.
Dicyandiamide particles were sieved through a 600-mesh standard screen in accordance with Japanese Industrial Standards, and those particles which passed through a 600-mesh screen were used as a curing agent. In the same manner as above, differen-tial thermal analysis was performed to measure the amount of exothermic heat. As a result, the curing exothermic data as shown in Figure 7 (B~state~were obtained. A mixture of the epoxy resin and the finely divided~ dicyandiamide as a curing ~O agent was cured in the same way as described above on a hot plate at 200C for 10 minutes, and the surface abraded and washed with water. No pinholes were observed.
Accordingly, it was concluded that pinholes resulting from foaming by heating with a~ applicator and washing with water and the properties of the cured product have a great deal to do with the particle size of dicyandiamide as a curing agent.
Thus, dicyandiamide was sieved in the sizes shown below, and used in the following Examples 7 to 12. In these Examples, 100 parts by weight of an epoxy resin (Epikote 1001) were mixed with 6 parts of dicyandiamide of varying particle * Trade Mark o~
1 si~es using a 4-inch roll at 100C for 30 minutes. The nature of the samples prepared are shown in Table 5 below.
Table 5 Sample No. Sieve Dicyandiamide Particle Size (mesh) ~) 1 600 below 21 2 500 bel~w 25 3 400 below 37 4 350 below 44 280 below 53 6 250 below 63

7 200 below 74

8 170 below 88

9 120 below 125 100 below 149 11 80 below 177 12 70 below 210 Each of the samples as described in Table 5 was heat cured at 200~C for 10 minutes on a hot plate.
The state determined by differential thermal analysis and the occurrence of pinholes after washing with water are shown in Table 6.
Table 6 Samples No. State Determined by Occurrence of Pinholes Differential Thermal after Washing with Analysis Water 1 B No 2 B "

4 B "
B "

1 (Table 6 continued) 6 A Yes 7 A "
8 A "
9 A "
A "

12 A "

Each of the samples was cured on a hot plate at 200C
for 10 minutes using 0.1 part by weight of tetramethyl guanidir.e as a curing promotor. The results obtained are shown in -Table 7.
Table 7 Sample No. State Det:ermined by Occurrent of Pinholes Differential Thermal after Washing with Analysis _ Water 1 B No 2 B "
3 B "

B
6 B "
7 A Yes 8 A " :
9 A ..
A "
11 A "
12 A "

Each of the samples was cured on a hot ; :~
plate a~ 200C for 10 minutes using 0.2 part by weight of - . .... .. .: . . ::

1 guanidIne nitrate as a curing ~romotor. The results obtained are shown in Table 8.

Sample No. State Determined by Occurrence of Pinholes Differential Thermal after Washing with Analvsis Water .
1 to 6 B No 7 to 12 A Yes EXAMP~E 10 Each of the samples was cured on a hot plate at 200C
for 10 minutes using 0.2 part by weight of aminopyridine and 0.5 part by weight of 1-dodecyl-2-methyl-3-benzylimidazole fluoride as a curing promotor. SimiLar results to those obtained in Example 8 were obtained.
From the results of Examples 7 to 10, it was demonstrated that in order to pr w ent the occurrence of pinholes, the particle size of dicyandiamide must be adjusted to less than 74 microns, preferably less than 63 microns.

A recess (with a depth of about 2 to 3 mm) was provided on a cold-rolled steel plate (0.8 mm; JIS C-141) using a hammer. An epoxy resin composition of 50 parts by weight of Epikote*1001, 50 parts by weight of Epikote*828, 6 parts by weight of dicyandiamide of varying particle sizes as shown in Table 5, and 300 parts by weight of iron powder was placed in this recess, and heat cured at 200C for l0 minutes. The results obtained are shown in Table 9 below.
Table 9 Sample No. State Determined by Occurrence of Pinholes Differential Thermal after Washing with Anal sis Water Y

1 to 5 B No 6 to 12 A Yes * Trade ~ark - 2~ -~Si~
1 The following Ex~m~les 12 to 14 illustrate plastic solder com~ositions capable o, being coated electrostatically or by electrodeposition which can be used especially advantage~
ously in this invention.

Iron powder having the particle size destribution shown by curve D of Figure 8 was added in an amount of 10, 20, 25, 30, 40 and 50% by volume respectively to a mixture of 100 parts of an epoxy resin (Epikote*1001) and 6 parts by weight of dicyandiamide, and the resin and powder were mixed ~y using a 4-inch roll at 100C for 30 minutes.
A recess with a length of 50 mm, a width of 25 mm and a depth of 3 mm was provided in a steel plate with a width of 70 mm, a length of 150 mm and a thickness of 1 mm by press-forming.
This recess was filled with the above prepared composition, and the resin composition was cured at 200C for 3 minutes. The surface was then finished by disc sanding to form a test piece.
Using this test piece, electrostatic coating and electrodeposition coating were performed under the following conditions.
Electrostatic Coating Conditions Coater: Gema -720 Type Electrostatic Spray Coater Voltage: -70 V
Time: 3 seconds Electrodeposition_Coating Conditions Voltage: 150 V
Temperatur~: 30 + 2C
Time: 3 minutes * Trade Mark ,~`,f ¢: ' ' ' o~
1 Co~ting Composltions For electrostatic coating, an epoxy resin powder.
For electrodeposition, a melamine-alkyd type lacquer.

The quality of the coating was evaluated visually dye. When the coating was completely uniform, the evaluation was "good". Other coatings were evaluated as "poor".
The results obtained are shown in Table 10 below.
Table 10 Samples No. Iron Powder Electrostatic Electrodeposition Coating _ Coating (vol.%) 1 10 Poor Poor 2 20 Good Poor 3 25 Good Good 4 30 Good Good Good Good 6 50 Good Good A test piece was prepared in the same manner as described in Example 12 except that iron powders having the particle sizes shown by curves tA) to (E) in Figure 8 was used in an amount of 30% by volume. Using the test piece, the electrostatic coating and electrodeposition coating properties were examined. The results obtained are shown in Table 11 below.

iot;~;~
1 Table 11 _ Particle Size Iron Powder+ 200 mesh -350 mesh Electro- Electro-(+ 74 ~u) (- 44 ~u) static deposition Coatlnq Coatin~
.
A51 16 Poor Poor B34 28 Good Poor C22 46 Good Good D3 71 Good Good E0 91 Good Good Test pieces were prepared in the same manner as described in Example 13 except that 30% by volume of aluminum powders having the particle size distribution shown by curves (A') to (E') Figure 9 were used, and the electrostatic coating and electrodeposition coating properties were evaluated. The results obtained are shown in Table 12.
Table 12 Particle Size Results Aluminum + 200 mesh -350 mesh Electrostatic Electrode-Powder(+ 74 ~) (-44 ~) Coating position Coatinq ( % ) ( % ) A' 56 11 Poor Poor B' 26 20 Poor Poor C' 16 45 Good Good D' 8 45 Good Good E' 1 63 Good Good ~ -When copper powders were used, the same results as obtained in Examples 13 and 14 were obtained.

By using the plastic solder compositions shown in Examples 12 to 14, the surface of the filled area using the plastic solder can be coated electrostatically or by electro-iX~

1 deposition just the same as the surface of the steel panel.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departin~ from the spirit and scope thereof.

Claims (12)

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

1. A method for filling a depression in a surface which comprises:
(a) placing a prefabricated substantially air bubble free partially cured shaped article of a thermosetting resin composition in said depression in which the surface defining said depression has been heated to a temperature above the softening or melting temperature of said resin composition to fix the shaped article provisionally to the surface defining said depression;
(b) heating said shaped article under pressure using a heated applicator; and (c) surface-finishing the filled depression.

2. A method for filling a depression in a surface which comprises:
(a) placing a substantially air bubble free partially cured shaped article of a thermosetting resin composition in said depression, said resin composition being pre-fabricated so as to fit into said depression, the surface defining said depression having been heated to a temperature above the softening or melting temperature of said resin composition to fix the shaped article provisionally to the surface defining said depression;
(b) heating said resin composition under pressure on the surface of said resin composition with a heated applicator having a surface capable of fitting into the depression being filled and including a fluorine resin sheet adhered to the surface of the applicator;
and

Claim 2 continued ....
(c) surface-finishing the filled depression.

3. A method for filling a depression in a surface which comprises:
(a) placing a substantially air bubble free partially cured article of a thermosetting resin composition in said depression, in which the surface defining said depression has been heated to a temperature above the softening or melting temperature of said resin composition to fix the article provisionally to the surface defining said depression;
(b) fitting said resin composition in said depression;
(c) heating said resin composition under pressure on the surface of said resin composition with a heated applicator having a surface capable of fitting into the depression being filled and including a fluorine resin sheet adhered to the surface of the applicator;
and (d) surface-finishing the filled depression.

4. A method as claimed in claim 1 wherein said resin composition is a plastic solder composition comprising an epoxy resin and a curing agent therefor, and about 50 to 5% by volume of a metal powder containing about 5 to 30% by volume of a metallic fiber based on the composition.

5. A method as claimed in claim 2 wherein said thermosetting resin composition is a plastic solder composition comprising an epoxy resin and a curing agent therefor, and about 50 to 5% by volume of a metal powder containing about 5 to 30% by volume, based on the composition, of a metallic fiber.

6. A method as claimed in claim 3 wherein said thermo-setting resin composition is a plastic solder composition comprising an epoxy resin and a curing agent therefor, and about 50 to 5% by volume of a metal powder containing about 5 to 30% by volume, based on the composition, of a metallic fiber.

7. A method as claimed in claim 1 wherein said thermo-setting resin composition is a plastic solder composition comprising an epoxy resin, a filler and dicyandiamide having a particle diameter of less than about 74 microns as a curing agent.

8. A method as claimed in claim 2 wherein said thermo-setting resin composition is a plastic solder composition comprising an epoxy resin, a filler and dicyandiamide having a particle diameter of less than about 74 microns as a curing agent.

9. A method as claimed in claim 3 wherein said thermo-setting resin composition is a plastic solder composition comprising an epoxy resin, a filler and dicyandiamide having a particle diameter of less than about 74 microns as a curing agent.

10. A method as claimed in claim 1 wherein said thermo-setting resin composition is a plastic solder composition capable of being coated electrostatically or by electrodeposition, said composition comprising an epoxy resin and a curing agent therefor, and about 20 to 50% by volume, based on the composition, of a metal powder, said metal powder comprising about 0 to 25%
by volume of particles having a particle size of at least about 74 microns, and about 29 to 100% by volume of particles having a particle size of not more than about 44 microns.

11. A method as claimed in claim 2 wherein said thermo-setting resin composition is a plastic solder composition capable of being coated electrostatically or by electrodeposition, said composition comprising an epoxy resin and a curing agent therefor, and about 20 to 50% by volume, based on the composition, of a metal powder, said metal powder comprising about 0 to 25% by volume of particles having a particle size of at least about 74 microns, and about 29 to 100% by volume of particles having a particle size of not more than about 44 microns.

12. A method as claimed in claim 3 wherein said thermo-setting resin composition is a plastic solder composition capable of being coated electrostatically or by electrodeposition, said composition comprising an epoxy resin and a curing agent therefor, and about 20 to 50% by volume, based on the composition, of a metal powder, said metal powder comprising about 0 to 25% by volume of particles having a particle size of at least about 74 microns, and about 29 to 100% by volume of particles having a particle size of not more than about 44 microns.