US 3617326 A
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United States Patent Inventors John R. Zuber Piscataway; Herbert Foxman, Raritan, both of NJ. Appl. No. 802,675 Filed Feb. 26, 1969 Patented Nov. 2, 1971 Assignee RCA Corporation METHOD OF BRANDING SILICON PLASTIC SURFACE R, 8, 38,138.8 B; 260/564 A Primary ExaminerAlfred L. Leavitt Assistant Examiner-M. F. Esposito Attorney-Glenn H. Bruestle ABSTRACT: A method of branding the surface of a silicone plastic body so as to improve the adherence of printed trademark and type number indicia on said surface is described. The method comprises treating the surface of the silicone plastic body with a solution consisting of l,l,3,3, tetramethylguanidine and a surfactant dissolved in an organic solvent. Conveniently, a bibulous material is saturated with the solution, and a silicone plastic body is positioned thereon so that the surface of the body to be branded is in contact therewith. After a few minutes, the silicone plastic body is removed, any excess solution remaining on the body surface is wiped off, and the desired indicia are then printed on the treated surface.
1 METHOD or BRANDING SILICON PLASTIC SURFACE BACKGROUND OF THE INVENTION This invention relates to improved methods of branding the surface of silicone plastic bodies.
Silicone plastics are widely used in the form of sheets, rods and tubes. They are also used to package many types of semiconductor devices, including both discrete units such as diodes or transistors or thyristors, and alsointegrated circuits.
The identification of sheets; rods and tubes of silicone plastic by the brand or trademark of the manufacturer is useful, but is not critical. However, when a wide variety of the difierent types of semiconductor devices are supplied in a similar package consisting of a silicone plastic, it is imperative that the different type numbers which identify the devices should be clearly and permanently marked on the surface of the plastic package. it has been found that when the surface of a conventional silicone plastic body, such as the silicone plastic package of a semiconductor device, is marked with brand SUMMARYOF THE INVENTION The surface of a silicone plastic body is treatedwith-a solu-' tion consisting of1,1,3,3, tetramethylguanidine and a surfactant dissolved in an organic solvent, and'the'excess solutionis removed from the body surface. Desired indicia which are subsequently printed on the treated surface of the plastic body adhere firmlythereto, land are not removed by rubbing, or by dipping in conventional solvents.
THE PREFERRED EMBODIMENTS Silicone plastics or resins are high molecular weight polymers characterized by having a long chain composed of alternating atoms of silicon and oxygen, with various organic constituents bonded to the silicon atoms. The typical formula for a silicone resin is [R,R,Si],,. The two organic groups or constituents R and R, attached to the silicon atom may be different from each other, or may be the same alkyl radical. Silicone resins have properties which make them useful for the packaging of semiconductor devices. These resins are inert, resistant to water and oxidation, stable at temperatures as high as 300 C., and have good dielectric properties. 7
A surfactant is a substance which even in small amount is capable of producing marked changes in the surface energy of liquid or solid surfaces. Surfactants which are added to a liquid are also known as wetting agents, and tend to lower the surface tension of any system which includes an interface between a liquid phase and another phase. Surfactants have been broadly divided into three types. The first type is the anionic type, which includes compounds having carboxylate groups, and derivatives of sulfuric acid or sulfonic acid. The second type is the cationic type, which generally consists of nitrogen compounds, such as the salts of primary or secondary or ternary amines. The third type is the nonionic type, and includes polyethylene glycol, polyvinyl alcohol, polyethers, polyesters, and polyhalides. A large variety of surfactants are commercially available, many of them being identified by trade names rather than by composition.
The' term "organic solvent generally refers to an organic compound which is a liquid at room temperature, and is capable of dissolving some organic substances. Organic solvents commercially available include hundreds of simple or complex alcohols, amines, esters, ethers, hydrocarbons, and ketones. Both straight chain and branched chain compounds bean integrated circuit that has been encapsulated in a rectangular mass of the resin, is positioned on'the saturated are utilized as organic solvents.Also utilized are cyclic compounds such as benzene, toluene, xylene, and cyclohexanol; petroleum fractions such as petrolic ether and kerosene and naphtha; and aliphatic hydrocarbonssuch as pentane, hexane and heptane. Certain organic solvents such as CJ-MOC, H030", and are generally identified by trade names.
The compound l,1,3,3, trimethylguanidine is a water-white liquid which boils at about 165 C., and has a molecular weight of 115.18, corresponding to the molecular formula C H N. The structural formula of this compound may be written as (CH NC(NH)N(CH,),;
EXAMPLEI I A solution is prepared consistingof about 30 milliliters 1,1,2,2, trimethylguanldine in about 70 milliliters of an or- "ganic solvent, which in this example is xylenefAbout l or 2 milliliters of a surfactant, which in this example consists of polyethylene glycol, is added to the solution. The precise composition of the solution is not critical, and mayrange from about 5 to 50 volumepercent of 1,l,3,;l, trimethylguanidine.
A bibulous material suchas a paper towel or blotting paper or cotton'cloth or the like is saturated with the solution. This silicone plastic article to' be branded, which may for example bibulous 'material so that the surface of d the article to be branded is in contact with the saturated bibulous material. After a few minutes, the silicone plastic article is removed. Any excess solution remaining on the surface of the article is wiped off, or is removed by any convenient method, such as by spinning the article, or by directing a stream of dry air against the treated surface. 7 I I The desired indicia, such as trademark and type numbers, are then printed on the treated surface of the silicone plastic article in the conventional manner. When a silicone plastic article is branded in this manner, it is found that the printed in- .dicia do not rub off easily, and are resistant to theaction of common solvents. I r U I An unexpected advantage of this'method is that the silicone plastic articles which have been treated as described do not require prompt branding with the desired indiciaJAfter the silicone plastic articles havebeen treated by the method of this invention, they may be stored for an indefiniteperiod of time before they are branded. It appears that the treatment described changes the nature of the surface of the silicone plastic article in a manner which is either irreversible, or of very long duration.
EXAMPLE 11 In the previous example, a nonionic surfactant was utilized. in the example, the solution consists of about 5 to 50 volume percent l,1,3,3, trimethylguanidine, the balance being one of the organic solvents previously mentioned. About 1 or2 milliliters of one of the anionic surfactants is added for each milliliters of the solution. A surface of a silicone plastic article isthen treated as described in example I prior to branding this surface by printing the desired indicia thereon.
EXAMPLE lll ln this example, the solution consists of about 5 to 50 volume percent l,1,3,3, trimethylguanidine, the balance being one of the organic solvents previously mentioned. About 1 to 2 milliliters of one of the cationic surfactants is added for each 100 milliliters of the solution. A surface of a silicone plastic article is then treated as described in example 1 prior to branding this surface by printing the desired indicia thereon. 7
We claim: y
1. The method of brandingthesurface of a silicone plastic body, comprising the steps ofti'eating said surface with a solution consisting of 5 to 50 volume percent of 22.214.171.124, tetramethylguanidine and a surfactant dissolved in an organic solvent;
positioning a silicone plastic article on said bibulous material so that the surface of the article to be branded is in contact with the bibulous material for a few minutes;
removing said article from said bibulous material;
removing from said surface of said article any of said solution remaining thereon;
and printing indicia on said treated surface of said silicone plastic article.
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