US 3737398 A
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United States Patent Oflice 3,737,398 Patented June 5, 1973 US. Cl. 2602.5 F 13 Claims A TRACT OF THE DISCLOSURE A sponge buff suitable for use in polishing or finishing surfaces of stainless steels, aluminum and other metals is made by reacting polyvinyl alcohol with a lower aldehyde selected from the group consisting of formaldehyde, acetaldehyde and butyraldehyde, and dialdehyde starch at a pH of at least 1 in the presence of an acidic catalyst, suitable foaming agent and 20-70% by weight based on the reaction mixture of heat resistant fibers, and forming the reaction produced in any desired form.
BRIEF SUMMARY OF INVENTION The invention relates generally to a method of making a sponge buif suitable for use in polishing or finishing surfaces of stainless steels, aluminum and other metals and excellent in abrasion resistance and heat resistance.
It has been well known to prepare a grinding stone for surface polishing by mixing grinding grains of alumina or silicon carbide type with polyvinyl formal, which is a soft grinding stone generally called PVA grinding stone and having the effect of mirror surface polishing.
It has also been known to reinforce the binder of PVA grinding stone by the joint use of natural, arificial or synthetic fibers.
In these methods of making such PVA grinding stones, polyvinyl formal, prepared from polyvinyl alcohol and formaldehyde is generally used as a binder because the object is to achieve a grinding effect only. The grinding stone obtained by any of these methods has no buff finishing effect. This buff finishing effect is attained by the surface polishing due to surface friction in contrast to polishing or grinding by grinding grains.
As a surface buff finishing material there have hitherto been employed natural fibers such as cotton and hemp, woven cloths thereof and, of late, unwoven cloths of synthetic fibers However, the following disadvantages are unavoidable in the case of effecting polishing by the use of these materials, since cloths made of these materials with a suitable binder are cut in the form of a disk, combined and fitted to a shaft, followed by rotary polishing.
(1) Many operational steps are necessary for polishing an irregular surface of workpiece because of the use of the cross-section of fiber.
(2) Much trouble is encountered in sewing conventional buifing cloths together and a polished surface is non-uniform sometimes due to fraying of the sewn cloths. Furthermore, there occurs much dust which creates a health hazard.
(3) Emanation of heat on a polished surface is not good, resulting in baking and breaking of the buff.
(4) Synthetic fibers are readily molten by heat of friction, resulting in breaking of the buff, deterioration of a surface lustre and occurrence of adhered matter.
Under the present state of the art, polyvinyl formal sponges have been studied as a bufi' material by reinforcement with various kinds of fibers instead of grinding grains, but have not been put to practical use as a buff because of the following reasons:
(1) The so obtained buffs have a tendency of breaking due to the small binding force.
(2) The abrasion resistance is inferior.
(3) The buffs tend to expand and to be deformed so that the polishing effect is lowered in uniformity.
The present invention is developed as a result of our various studies to overcome the foregoing disadvantages.
DETAILED DESCRIPTION OF INVENTION I, the inventor, have already proposed a method of making a sponge excellent in water-carrying softness and soap resistance, which comprises reacting polyvinyl alcohol with a lower aldehyde such as formaldehyde, acetaldehyde or butyraldehyde, as a reactive aldehyde, and dialdehyde starch at a pH of at least 1 in the presence of an acidic catalyst and suitable foaming agent, disclosed in Japan Patent 574,000 (publication No. 28,997/ 69). The sponge resin obtained by this method is excellent in softness and brittleness resistance. This is probably due to the fact that dialdehyde starch used herein has a long molecular structure and, consequently, yields a molecular bridge which distance between the main chains is greater than with the ordinary reaction of formalin alone.
The feature of this invention consists in the addition of 20-70% by weight of heat resistant fibers. That is to say, the present invention provides a method of making a sponge buff, which comprises reacting polyvinyl alcohol with a lower aldehyde selected from the group consisting of formaldehyde, acetaldehyde and butyraldehyde, and dialdehyde starch at a pH of at least 1 in the presence of an acidic catalyst, suitable foaming agent and 20-70% by weight based on the reaction mixture of heat resistant fibers, and forming the reaction product in any desired form.
The heat resistant fibers used in the method of the invention are fibers which are not molten or carbonized by friction heat (about 250 C.) generated during polishing by the buff material. Natural fibers are preferred, but synthetic fibers such as polyesters, nylons, vinylons and the like may be used. The sisal hemp occurring in Africa, excellent in polishing ability, rigidity and abrasion resistance, is most preferred.
The most important feature of the invention is to incorporate uniformly the heat resistant fibers in the particular polyvinyl acetal sponge produced according to the method of the foregoing Japanese patent, whereby the sponge is effectively reinforced. The amount of such reinforcing fibers ranges from 20% to 70% by weight, preferably 40% to 50% by weight based on the reaction mixture. The incorporation of the fibers is carried out by one or more of the following procedures:
(1) Fibers of 10-50 mm. in length are added to a polyvinyl alcohol solution not yet reacted, and formed.
(2) Fibers are cut so as to accommodate themselves to the radius of a circular sponge and are placed radially thereon in a forming frame and the particular polyvinyl acetal reaction liquid is then poured followed by forming.
(3) Unwoven cloths made of such fibers using a heat resistant resin as a binder are placed on a forming frame and the particular polyvinyl acetal reaction liquid is then poured therein followed by impregnation and formation.
The dialdehyde starch used in the invention may be prepared by oxidation of starch with periodic acid and a lower aldehyde such as formaldehyde, acetaldehyde or butyraldehyde.
The acidic catalyst used in the invention may be chosen from inorganic and organic acids. Hydrochloric acid is preferably used. The acid maintains the pH of the reaction system above 1.
polyvinyl acetal sponge. Consequently, the buff material of the invention depends mainly on the finishing property of the fibers due to friction.
The general characteristics of the present invention and prior art are tabulated below:
Grinding property. Large Medium- Medium- Small- Small. Rotary strength do Small do Large Large. Finishing property Not good Good- Good Better Best. Abrasion resistance. Large Small"-.- Medium. Small Medium.
NrE.-(1)=Ordinary grinding stone; (2)=PVA grinding stone; (3)=Fiber-containing PVA grinding stone; (4) =Woven cloth buff; =Buif of the invention.
The advantages of the sponge buff of the invention are as follows:
(1) Since forming is readily practised and any cut surface is available for polishing, longitudinal and lateral inner surfaces of an L-type work-piece, for example, can simultaneously be polished. In particular, it is suitable for polishing the inner wall of a cylindrical form.
(2) Since the foam of the sponge is of an open cell structure, that is an air-cooling effect by the air in the cells, thereby preventing the fibers from fraying. There is no baking of the polishing surface and no formation of dust even after continuous polishing for a long time.
(3) Since it is highly elastic, the effective Width of the polishing surface is large and a polished surface is thus finished well.
(4) The variety of fibers, size of the diameter and softness of the sponge may be varied with the forming conditions and a desirable buff material of any type of rough polishing, medium polishing, finish polishing and mirror polishing can be performed depending on the ob ject of use.
(5) The absorption property of the polyvinyl acetal type sponge is so excellent that a liquid polishing agent is well adhered and the polishing surface is held constant for a long time.
(6) Since forming is easy, any type of polishing machine can be used with the ease of fitting.
The following example is given in order to illustrate the invention without limiting the same.
EXAMPLE 3 parts of 35% hydrochloric acid and 1 part of a 1% aqueous solution of a surfactant (oleylhydroxyethylimidazoline) were added with vigorous agitation to a mixed solution of 100 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 1700, degree of saponification 95%), 20 parts of a 25% aqueous solution of dialdehyde starch (aldehydized 90%) and 15 parts of 35% formalin. When the viscosity of the mixture rose rapidly up to 20 centipoises, parts of sisal hemp dust in a length of 50 mm. was added thereto while stirring to insure a uniform mixture which was poured in a mold and reacted at 40 C. for 24 hours. After the reaction, the reaction product was washed with water and dried.
The so obtained sponge was subjected to a test at 2300 r.p.m. with the commercially sold polyvinyl formal sponge and cloth buff for comparison using a same polishing machine, thus obtaining the following results:
Dimension before test:
255 mm. diameter 25 mm. thickness Test piece:
stainless western-style tableware aluminum flat plate.
TABLE 1 Stainless tableware Aluminum flat plate Finished Buff Finished Buff Abrasion Steps surface surface suraice surface resistance Dimension after use Cloth bufi 6 Good. Much fraying Baking Good Not good. Average diameter 216 mm. Solid polyvinyl formal sponge 4 Baking Plneked do Plucked .do Roughened average diameter 193 mm. Sponge of the invention 3 2 Best Good Good Good. Good 1 The cloth buff requires much trouble for sewing up. Adhesion of polishing agents is not good. Much dust occurs.
2 Many surface breakages occur in the soild polyvinyl formal sponge.
* The rising state of the fibers according to the invention is very good.
(7) A wide range of polishing speeds, i.e., from high speed polishing to low speed polishing is possible through.
reinforcement by fibers.
The buff material of the invention differs clearly from the known fiber-containing PVA grinding stone. The largest difference between a grinding stone and buff material consists in the polishing or grinding ability. The grinding ratio, for example, in the case of a steel workpiece is ordinarily as follows:
Grinding stone-above 1 Buff materialless 0.01
What is claimed is:
1. In a method of making a sponge buff, by reacting polyvinyl alcohol with a lower aldehyde selected from the group consisting of formaldehyde, acetaldehyde and butyraldehyde, and dialdehyde starch at a pH of at least 1 in the presence of an acidic catalyst and a foaming agent the improvement which comprises adding to the reaction mixture 20-70% by weight, based on the reaction mixture, of heat resistant fibers.
2. The method of claim 1, wherein, the dialdehyde starch is prepared by oxidation of starch with periodic acid and a lower aldehyde.
3. The method of claim 1, wherein the acidic catalyst is a mineral acid.
4. The method of claim 3 wherein the mineral acid is hydrochloric acid.
5. The method of claim 1, wherein the foaming agent is a sunfactant.
6. The method of claim 1, wherein the heat resistant fibers are used in the form of an unwoven cloth.
7. The method of claim 1, wherein the heat resistant fiber is sisal hemp.
8. The sponge buff produced by the process of claim 1.
9. The method of claim 1 wherein the reaction mixture, including said fibers, is first prepared and then poured into a mold wherein the reaction is completed.
10. The method of claim 1 wherein the, reaction mixture, including said fibers, is prepared in forming frame and the reaction is completed within said frame.
11. The sponge buff produced by the process of claim 6. .v
12. The sponge buff produced by the process of claim 7.
13. A method of making a sponge buff according to claim 1 wherein 100 parts of an aqueous polyvinyl alcohol solution with 20 parts of a 25% aqueous solution of dialdehyde starch and 15 parts of 35% formaldehyde 6 References Cited UNITED STATES PATENTS 2,846,407 8/ 1958 Wilson 260-2.5 F
3,324,057 6/1967 Suzumura et al. 26017.4 ST
2,653,917 9/1953 Hammon 2602.5 F FOREIGN PATENTS 573,966 12/1945 Great Britain 2602.5 F
10 JOHN C. BLEUTGE, Primary Examiner W. J. BRIGGS, 8a., Assistant Examiner US. Cl. X.R.
are employed in conjunction with sisal hemp fibers of 15 51--296; 260-2.5 L, 17.4 ST, 17.4 UC, 41 C, 73 L 91.3