Standard materials and methods for instrumental measurement for ASTM color of petroleum products using said standard materials

A set of standard materials, which comprises at least two kinds of standard materials, for calibration of a photoelectric colorimeter used for the instrumental measurement of petroleum products for their ASTM color, comprising at least two kinds of standard materials each of which is a mixed solution having a color corresponding to an ASTM color and comprises (a) at least five members selected from the group consisting of seven specific colorants such as 3-methyl-1-phenyl-4-(phenylazo)-pyrazol-5-ol, 1-(phenylazo)-2-naphthalenol and 1-[[4-[(dimethylphenyl)azo]dimethylphenyl]azo]-2-naphthalenol, (b) 1-phenyl-1-xylylethane as a solvent for said colorants, and (c) dodecane as a diluent; and a method for instrumental measurement of petroleum products for their ASTM color by a photoelectric colorimeter, which comprises calibrating the photoelectric colorimeter by the use of said at least two kinds of standard materials.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to standard (reference) materials for 
calibration of a photoelectric colorimeter (color and color-difference 
meter) which is used for instrumental measurement for ASTM color, said 
measurement being colorimetry of petroleum products such as various 
lubricating oils. petrolatum and microcrystalline wax. The present 
invention also relates to a method for Instrumental measurement for ASTM 
color of a petroleum product using said standard materials (standard 
samples). 
2. Prior Art 
There are two testing methods for colorimetry of petroleum products, one 
being a method for measuring ASTM color of petroleum products and the 
other a method for measuring Saybolt color thereof as prescribed in JIS K 
2580. 
Of these, the method for measuring ASTM color is applied to various 
lubricating oils and petrolatum, etc. and will indicate the color of a 
test material in terms of a symbol or a value ranging from 0.5 (light) to 
8.0 (dark) obtained by comparing the color of the test material with that 
of a standard (reference) colored grass (glass color standard) by 
generally using an ASTM chromometer. 
It is noted that the ASTM color of a material is expressed as a symbol or a 
value (any one of 0.5 to 8.0 in accordance with JIS K 2580) which is 
assigned to a standard colored glass whose color corresponds to the color 
of the material. 
The standard colored glass used in the above method is prescribed to have 
its color dispersion limited as indicated in the XYZ colorimetric system 
in accordance with JIS Z 8722, the luminous transmittances using the CIE 
standard Illuminant C and the chromaticity coordinates based on the RGB 
color system. 
However, in cases where the ASTM color of a material is measured by the use 
of the ASTM chromometer, the ASTM color so found is Judged by human vision 
and the results expressed by said measurement are not quantitative {when 
the thus found color of a test material used is between those (for 
example, 4.0 and 4.5 in ASTM color) of two different standard colored 
glasses, it is expressed as L 4.5 (this 4.5 is a symbol for the standard 
colored glass having a darker color), while when the color of the test 
material is darker than 8.0 in ASTM color then It is expressed as D 8.0} 
and, therefore, personal differences in judgment are apt to be made and 
time measurers practically worry about the judgement. This tendency is 
particularly remarkable when the color of the test material is dense or 
dark. 
Accordingly, even in such a colorimetry as above, automatization of 
judgment of color without resort to visual Judgment is eagerly desired at 
the present time. 
In view of the above, the present inventors attempted to investigate 
whether or not a commercially available photoelectric colorimeter 
(measuring instrument) can be used for measuring a test material for its 
ASTM color. 
A photoelectric colorimeter used must be one which will produce a favorable 
correlation with the testing method as prescribed in JIS K 2580 in the 
entire region of ASTM color ranging from 0.5 to 8.0. Furthermore, there is 
desired a universal method for testing a material, especially a liquid, 
for its color. 
For the perception of color with human eyes under natural light, the 
quantities of stimuli due to three primary colors of lights which are red, 
green and blue lights, are important. In measuring a color with an optical 
instrument, a light emitted from a light source is used instead of the 
natural light and what is important is not the quantities of stimuli but 
tristimulus values. 
Accordingly, it is desirable that a method testing a test material for ASTM 
color be a universal method, whose performance is close to the perception 
of color with human eyes, based on the tristimulus values by an optical 
instrument and that the expression of the results of measurement be a 
quantitative expression without the use of L OF D color expression. 
Therefore, it is desirable to adopt a testing method based on methods for 
measuring a material (methods for measurement of reflecting or 
transmitting objects for their color) which are recommended by Commission 
Internatlonale de l'Eclairage (hereinafter abbreviated as "CIE") and 
prescribed in JIS Z 8722 and also to adopt a method for quantitatively 
expressing measured results based on the color expression method using the 
XYZ colorimetric system prescribed in JIS Z 8701. 
In measuring a sample for its color by a photoelectric colorimeter, it is 
necessary to express the measured value of the sample obtained by a 
commercially available photoelectric colorimeter in terms of the ASTM 
color. Therefore, it is necessary to find the correlation between the 
tristimulus value and ASTM color. 
Comparing the sum (.SIGMA.D) of optical densities based on the XYZ 
colorimetric system of standard colored glasses with the ASTM color of the 
same, the present inventors have found a correlation therebetween as 
represented by the following correlation formula: 
EQU A=.alpha..SIGMA.D+.beta. 
wherein A is ASTM color, .SIGMA.D is the sum of optical densities 
(DX+DY+DZ), and .alpha. and .beta. are each a constant for calibration of 
instrumental errors. 
Therefore, the measured value of the ASTM color is obtained by processing 
the measured X, Y and Z values in the operation-display section of the 
measuring instrument on the basis of said correlation formula. 
As the above .SIGMA.D value varies with an instrumental error depending on 
an instrument used, it cannot always be constant even for the same 
material. It is necessary, therefore, to prepare at least two kinds of 
standard liquid materials for finding at least two ASTM colors to 
calibrate each instrument (photoelectric colorimeter) with the standard 
liquid materials. 
Such standard materials are required to be low volatile, highly resistant 
to oxidation, low degradable, for example low oxidizable, with the elapse 
of time and satisfactory in color stability. 
SUMMARY OF THE INVENTION 
The present invention has been made in view of the above facts, and an 
object thereof is to provide a set of standard materials to be used for 
measuring a test material for its ASTM color by the use of a photoelectric 
colorimeter (color and color-difference meter) and another object is to 
provide an instrumental measuring method using said standard materials. 
In attempts to achieve the above objects, the present inventors made 
intensive studies and found that mixed solutions of specific mixed 
colorants (dyestuffs) suited for such objects as above and specific 
solvents coincide in color with standard colored glasses to be used in 
ASTM colorimetry anti they are fully effective as standard materials. 
In one aspect of the present invention, it resides in a set of standard 
materials comprising at least two kinds of standard materials for 
calibration of a photoelectric colorimeter used for instrumentally 
measuring petroleum products for their ASTM color. A set of standard 
materials comprises at least two kinds of standard materials and said at 
least two kinds of standard materials are each a mixed solution whose 
color corresponds to a predetermined ASTM color. Said mixed solutions are 
respectively prepared by mixing together 
(a) at least five colorants selected from the group consisting of (i) 
3-methyl-1-phenyl-4-(phenylazo)-pyrazol-5-ol, (ii) 
1-(phenylazo)-2-naphthalenol, (iii) 
1-[[4-[(dimethylphenyl)azo]dimethylphenyl]azo]-2-naphthalenol, (iv) 1,5(or 
1,8)-bis[(4-methylphenyl)amino]-9,10-anthracenedione, (v) 
1-hydroxy4-[(4-methylphenyl)amino]-9,10-anthracenedione, (vi) 
1,4-bis(butylamino)-9,10-anthracenedione and (vii) 
1,4bis[(4-butylphenyl)amino]-5,8-dihydroxy-9,10-anthracenedione. 
(b) 1-phenyl-1-xylylethane as a solvent for said colorants, and 
(c) dodecane as a diluent for the resulting solution. 
In another aspect of the present invention, it resides in a method for 
instrumental measurement of petroleum products for their ASTM color by the 
use of a photoelectric colorimeter, which comprises calibrating the 
photoelectric colorimeter by using said at least two kinds of standard 
materials. 
The present Invention will be explained hereunder in more detail. 
Each of the colorants to be used in the present invention has the following 
chemical structure: 
(i) 3-methyl-1-phenyl-4-(phenylazo)-pyrazol-5-ol 
##STR1## 
(CAS No. 4314-14-1) 
Color index (CI): Solvent Yellow 16 
Example: Oil Yellow 5GS Extra (tradename) 
(ii) 1-(phenylazo)-2-naphthalenol 
##STR2## 
(CAS No. 842-07-9) 
Color index (CI): Solvent Yellow 14 
Example: Oil Orange Extra (tradename) 
(iii) 1-[[4-[(dimethylphenyl)azo]dimethylphenyl]azo]-2-naphthalenol 
##STR3## 
CAS No. 1320-06-5) 
Color index (CI): Solvent Viloet 14 
Example: Oil Red 5B Special (tradename) 
(iv) 1,5(or 1,8)-bis](4-methylphenyl)amino]-9,10-anthracenedione 
##STR4## 
(CAS No. 8005-40-1) 
Color index (CI): Solvent Viloet 14 
Example: Oil Violet 3R (tradename) 
(v) 1-hydroxy-4-[(4-methylphenyl)amino]-9,10-anthracenedione 
##STR5## 
(CAS No. 81-48-1) 
Color index (CI): Solvent Viloet 13 
Example: Oil Violet B-2R (tradename) 
(vi) 1,4-bis(butylamino)-9,10-anthracenedione 
##STR6## 
(CAS No. 17354-14-2) 
Color index (CI): Solvent Blue 35 
Example: Oil Blue SB (tradename) 
(vii) 1,4-bis[(4-butylphenyl)amino]-5,8-dihydroxy-9,10-anthracenedione 
##STR7## 
CAS No. 28198-05-2) 
Color index (CI): Solvent Green 28 
Example: Oil Green SG (tradename) 
In the present invention, at least two, preferably at least three, more 
preferably at least four kinds of standard materials are prepared from a 
mixed colorant consisting of five to seven kinds of colorants selected 
from the colorants (i)-(vii), together with a specific solvent and a 
specific diluent. The mixing ratio of the colorants (i)-(vii) is 
preferably selected from the following mixing ratios (by volume) (1)-(4): 
(1) (i)210:(ii)26:(iii)0:(iv)13:(v) 0:(vi)2:(vii)3, 
(2) (i)200:(ii)29:(iii)7:(iv)6:(v) 4:(vi)2:(vii)4, 
(3) (i)200:(ii)58:(iii)10:(iv)16:(v) 8:(vi)0:(vii)8, and 
(4) (i)183:(ii)53:(iii)13:(iv)11:(v)16:(vi)1:(vii)3. 
The use of not only a colorant mixture having a mixing ratio (1), (2), (3) 
or (4) but also the specific solvent and diluent, will produce a standard 
material whose color corresponds to an ASTM color 1, 3, 5 or 7. 
In the preparation of standard materials of the present invention, 
1-phenyl-1-xylylethane (hereinafter abbreviated to "PXE") and dodecane 
(hereinafter referred to as "n-C.sub.12) are used as a solvent for the 
colorants and as a diluent, respectively as mentioned above. 
A method for preparing a set of standard materials of the present invention 
will be concretely explained hereunder. 
First, a predetermined amount of each of five to seven kinds of colorants 
selected from the colorants (i)-(vii) mentioned above is dissolved in PXE 
solvent to obtain a 1000 ppm(wt/vol %) dilute solution of the colorant. 
Next, the five to seven kinds of dilute solutions thus obtained are mixed 
together in predetermined mixing ratios (for example, the aforesaid mixing 
ratios (1)-(4)) to obtain at least two, for example four, kinds of mixed 
solutions. Subsequently, a predetermined amount of each of these mixed 
solutions is diluted with n-C.sub.12 (for example, diluted to such an 
extent as specified in Table 1) to obtain a standard material whose color 
corresponds to a predetermined ASTM color. Thus there can be prepared a 
set of standard materials of the present invention comprising at least two 
kinds of standard materials whose colors correspond respectively to at 
least two different ASTM colors. 
The instrumental measuring method of the present invention will be 
described hereunder. 
First, one (having an ASTM color of 7.0 for example) of a set of standard 
materials of the present invention is measured for its ASTM color by a 
photoelectric colorimeter on the basis of the sum (.SIGMA.D) of optical 
densities of said standard material and a preliminarily obtained 
correlation formula. If the ASTM color found is 6.98. the photoelectric 
colorimeter will be calibrated so that it indicates an ASTM color of 7.0 
by the use of the correction key at the operation-display section of the 
photoelectric colorimeter. 
Subsequently, the photoelectric colorimeter is calibrated in turn by the 
use of another or other standard material(s) (having an ASTM color of 1.0 
for example) in the same manner as mentioned above. Such calibration 
(correction) of the photoelectric colorimeter makes it possible to 
correctly measure a petroleum product for its ASTM color by the use of a 
photoelectric colorimeter. The above calibration of the photoelectric 
colorimeter should be carried out on at least two, preferably at least 
three, more preferably at least four, ASTM colors in the range of 0.5 to 
8.0. 
As described hereinbefore, the instrumental measurement of a petroleum 
product for its ASTM color can be carried out quantitatively and 
accurately by the use of the standard materials of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be described in more detail by referring to the 
following Examples. 
EXAMPLE 1 
A predetermined amount of each of seven kinds of colorants, (i) 
3-methyl-1-phenyl-4-(phenylazo)-pyrazol-5-ol, (ii) 
1-(phenylazo)-2-naphthalenol, (iii) 
1-[[4-[(dimethylphenyl)azo]dimethylphenyl]azo]-2-naphthalenol, (iv) 1,5(or 
1,8)-bis[(4-methylphenyl)amino]-9,10-anthracenedione, (v) 
1-hydroxy-4-[(4methylphenyl)amino]-9,10-anthracenedione, (vi) 
1,4-bis(butylamino)-9,10-anthracenedione and (vii) 
1,4-bis[(4-butylphenyl)amino]-5,8-dihydroxy-9,10-anthracenedione, was 
dissolved in 1-phenyl-1-xylylethane to obtain a 1000 ppm(wt/vol %) dilute 
solution thereof. Next, seven kinds of the dilute solutions thus obtained 
were mixed together in the mixing ratios by volume of: 
(1) (i)210:(ii)26:(iii)0:(iv)13:(v) 0:(vi)2:(vii)3, 
(2) (i)200:(ii)29:(iii)7:(iv)6:(v) 4:(vi)2:(vii)4, 
(3) (i)200:(ii)58:(iii)10:(iv)16:(v) 8:(vi)0:(vii)8, and 
(4) (i)183:(ii)53:(iii)13:(iv)11:(v)16:(vi)1:(vii)3, 
to obtain four kinds of mixed solutions. Subsequently, a predetermined 
amount of each of the four kinds of mixed solutions was diluted with 
n-C.sub.12 to such an extent as specified in Table 1 to prepare four kinds 
of standard materials whose colors correspond respectively to ASTM colors 
1, 3, 5 and 7. 
The sum (.SIGMA.D) of optical densities of each of these standard materials 
was measured by the use of a photoelectric colorimeter(Chroma meter CT-210 
custom, produced by Minolta Camera Co., Ltd.) in which a sampling cell 
having a cell length of 33 mm and a CIE standard light source C were 
employed. Further, each of said standard materials was measured for its 
ASTM color by five measurers (A-E) by the use of a conventional ASTM 
chromometer. 
The results so obtained by the above measurement are shown in Table 1 and 
FIG. 1. 
TABLE 1 
__________________________________________________________________________ 
Mixing Sum of 
Standard ratio optical 
ASTM color measured 
material 
ASTM 
of densities 
Measurer 
Measurer 
Measurer 
Measurer 
Measurer 
No. color 
colorants 
Dilution 
.SIGMA.D 
A B C D E 
__________________________________________________________________________ 
1 1 (1) 100 0.87 1.0 L1.0 1.0 1.0 L1.0 
2 3 (2) 19 3.17 L3.0 3.0 3.0 L3.0 3.0 
3 5 (3) 10.3 5.20 5.0 5.0 5.0 5.0 L5.0 
4 7 (4) 5.9 6.82 L7.0 7.0 7.0 7.0 L7.0 
__________________________________________________________________________ 
As can be seen from Table 1 and FIG. 1, the sum (.SIGMA.D) of the optical 
densities of each of the standard materials corresponds appropriately to 
each ASTM color. Furthermore, the repetitive error of the .SIGMA.D value 
was favorably small. 
Therefore, by the use of the photoelectric colorimeter which was calibrated 
with the four kinds of standard materials mentioned above as to ASTM 
colors 1, 3, 5 and 7, time instrumental measurement of petroleum products 
for their ASTM color could be carried out quantitatively and accurately. 
EXAMPLE 2 
Dilute solutions of colorants (i)-(vii) obtained in the same manner as in 
Example 1 were mixed together in the mixing ratios by volume of: 
(1) (i)210:(ii)26:(iii)0:(iv)13:(v) 0:(vi)2:(vii)3, and 
(4) (i)183:(ii)53:(iii)13:(iv)11:(v)16:(vi)1:(vii)3, 
to obtain two kinds of mixed solutions. Subsequently, a predetermined 
amount of each of the two kinds of mixed solutions was diluted with 
n-C.sub.12 to obtain two kinds of standard materials whose colors 
correspond respectively to ASTM colors 1 and 7. 
The sum (.SIGMA.D) of optical densities of each of these standard materials 
was measured by the use of the same photoelectric colorimeter as used in 
Example 1. Further, each of said standard materials was measured for its 
ASTM color by 5 measurers (A-E) by the use of a conventional ASTM 
chromometer. 
The results thus obtained were the same as those obtained in Example 1. 
Therefore, even when there was used the photoelectric colorimeter which was 
calibrated with the two kinds of standard materials mentioned above as to 
ASTM colors 1 and 7, the instrumental measurement of petroleum products 
for their ASTM color could also be carried out quantitatively and 
accurately.