THE INDIA RUBBER WORLD 



425 



Colors and Pigments in Rubber Compounds. 



Hv Calvi 



Stitt. 



THE USE of pigments and colors in the manufacture of rubber 

 goods is of extreme importance and it may be said that the 

 employment of these materials is of more consequence now 

 than ever before. To anyone who has had the opportunity to 

 note the various compounds that are being used at different rub- 

 ber factories and to see the unlike purposes for which in many 

 cases the same material is used, the results obtained are remark- 

 able. 



Sometimes a chemist will find that a special pigment will work 

 out nicely while another chemist will condemn its use. In the 

 main, it will be found that most rubbermakers use formulas that 

 are similar in many respects. I do not think they approach any 

 more nearness than this, surely they are far from being identical. 

 The cause lies mainly in the employment of the so-called human 

 element. It naturally follows that no two products of two dif- 

 ferent rubber factories are the same, as long as they are made 

 by differi.nt chemists who employ their own compounds. In 

 this case I mean the finished product naturally is not identical. 

 such as two tires. 



By means of certain pigments it is found that the rubber is 

 toughened. Some other fillers add elasticity, etc. In the case 

 of an automobile tire it is essential to have toughness and a cer- 

 tain elasticity as well. The reason why some tires wear out 

 quicker than others is not always due lo the fabrication or the 

 cure. It is often caused by the compound not being of the 

 proper proportion or containing pigments that harm rather than 

 benefit the rubber. This condition will prevail as long as the 

 rubbermaker neglects to standardize his ingredients and be sure 

 thai his raw materials are always as near alike as it is possible 

 for him to mke them. 



The selection of colors is of paramount importance. We will 

 disregard the aniline group and look into the pigments or dry 

 colors, because these are the most used, e.xcept in the manufac- 

 ture of balloons, toys and soine rubber sundries and mechanical 

 goods. 



The blacks are usually a carbon black, lamp black or mineral 

 black. In passing it may be well to note, that the advance in 

 price on carbon black aside from war conditions, has been due 

 largely to the enormous consumption by the rubber factories 

 during the past four years. 



It has not been found practical to use a cheap quality of car- 

 bon black, especially for tire treads and rubber sundries, but 

 rather the higher grades. The higher percentage of black is 

 more inert and is claimed to have no detrimental effects on the 

 stock where used. A very small amount of strong carbon black 

 will give a beautiful black color. Where an intense black is not 

 desired the carbon black can be cut down considerably. Some 

 chemists and experienced rubbermakers claim that this material 

 adds strength and better wearing qualities to the rubber, while 

 others claim it does not have this effect, and still others even go 

 so far as to say that it is detrimental in some cases. 



Perhaps the Veal truth may be that in one compound it works 

 out very well while in another which contains other component 

 parts and proportions, the result may be somewhat different. 

 Carbon black may therefore be blamed for conditions for which 

 its use is not responsible. 



Lamp black is not as strong as carbon black and gives a bluish 

 tone to the rubber. Some factories have a separate black room, 

 and collect the dust by blowers, etc. Many rubber boot manu- 

 facturers use lamp iilack and find it very satisfactory. The 

 mineral black pigments are not as strong as these other blacks. 

 Some grades of mineral rubber are used in black stock also. 



The reds are mostly the iron oxides, Indian red, antimony, 



vermilion red, Pari red and toloudine red. The toloudine red 

 and Para red are vivid shades, and are made from intermediates, 

 and really belong to the aniline group. 



English vermilion is a mercury product and is also very vivid. 

 It is employed extensively in dental rubber goods. It is not 

 necessarily made in England as some suppose. The name merely 

 implies the English process of manufacture. There are to-day in 

 this country several large makers of it an<l their product is very 

 satisfactory. 



Antimony, both crimson and golden, is used extensively in 

 tube stock, sometimes in connection with red oxide and some- 

 times alone. It is also used in the treads, boots, heels, etc. The 

 best antimony comes from England, but due to the difficulties 

 experienced in importing it, there has been a large consumption 

 of the dctfnestic grades. 



Red oxides are usually sold on their percentage of iron oxide 

 content. The greater percentage the higher the cost. Some are 

 natural or earth colors, while some are manufactured, especially 

 the higher grades. These higher grades are made from copperas 

 or the by-product of wire mills. This country produces some 

 excellent red oxide, but previous to the war most of the higher 

 grades were imported from England. 



Indian red is very closely allied to red oxide, and is used 

 principally on account of its large covering capacitv', and also 

 on account of its beautiful color, it being more of a maroon, or 

 purplish shade. The higher qualities of Indian reds are of ex- 

 tremely fine mesh, free from grit. It is interesting to note that 

 on account of its softness and freedom from coarse particles. 

 Indian red of the best quality will not scratch the surface of 

 highly polished gold. For this reason, it is used extensively in 

 jewelry factories, and there are many tons sold throughout the 

 country for this purpose. 



The yellow colors, such as zinc yellow, chrome yellow, etc., 

 as well as the blue shades, like Malori, Qiinese and Prussian 

 lilues, also the ultramarine blue, are used in a limited way. To 

 one who understands the various shades and combinations that 

 can be obtained by various mixtures of colors, the results are 

 very interesting to follow out. Each color has an effect upon 

 the fillers and pigments that are in the compound and is itself 

 affected by the pressure and heat applied in the vulcanization, 

 so that one has to know pretty certainly what he is doing in 

 order to be sure of getting what he started out for. Even the 

 most particular and experienced sometimes go wrong. There 

 are so many things that creep in before the product is finally 

 finished, that it makes it very hard sometimes to check out 

 results in advance. 



The white pigments and fillers arc by far the most important 

 and most largelj' used. Zinc oxide is the principal one. Some 

 time ago, the writer suggested that certain grades of leaded zinc 

 could be used in some compounds. Experiments were made 

 along this line, and to-day there are several rubber manufac- 

 turers who are using leaded zinc. They all turn out a highly 

 satisfactory article and, moreover, are saving money on their 

 zinc. It is not necessary to use a zinc that is free from lead 

 or even approximately lead free in all rubber goods. As previ- 

 ously stated, some rubber manufacturers use zincs that contain 

 lead, and find that the finished product is satisfactory. This is 

 especially true when the goods are not required to be white. 

 Zinc oxides that are free from lead are best for white rubber, 

 such as sheetings, some grades of automobile tires and druggists' 

 sundries. The writer has found that some brands of zinc oxide 

 cover better than others. The chemist has found that it is 

 profitable to experiment along this line, in order to determine 

 the most suitable zinc oxide to use in his compound. 



