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Evaluating contrast gloss of textured polymeric surfaces.

INTRODUCTION

The concept of perceived quality of products is of increasing importance in for instance the automotive industry. In the specific case of the interior of an automobile, the surface appearance of the components plays a major role for the overall quality impression of the vehicle. The appearance attribute gloss is perceived by an observer as the shiny and lustrous appearance of a surface. From the perspective of an automobile customer, low gloss of the components in the interior is generally associated with high quality and considered more premium. Furthermore, an even gloss level throughout the part and a harmonious gloss level between adjacent components is of great importance for the quality impression.

Polymeric materials are frequently used in automotive interiors, often in the form of injection-molded components. A range of different polymers are used in different applications in order to fulfill requirements for instance related to crash safety, ageing and heat resistance. Among the most commonly used polymers are acrylonitrile-butadiene-styrene copolymer (ABS), polypropylene (PP), a blend of polycarbonate and acrylonitrile-butadiene-styrene copolymer (PC/ABS) and polyamide (PA).

The appearance of gloss is sometimes referred to as glossiness and can as such not be measured, however the reflectance properties of the surface that can be linked to gloss can be characterized. In general, gloss is measured only in the specular angle by the means of a glossmeter. Such measurements have in many cases shown to correlate well with the visually perceived gloss, especially on surfaces having fairly high or high gloss. However, at Volvo Car Corporation, the engineers involved in the assessment, measuring and analysis of the surface appearance of automotive components frequently experience poor correspondence between the gloss measurements and the visual impression of gloss. This is especially the case for surfaces having a relatively low gloss and when comparing the gloss on components manufactured in different polymers or having different color.

For the visual perception of gloss, especially in the case of low-gloss surfaces, the angular distribution of reflected light from the surface may be of greater significance than merely the specular reflectance. The aim of the present work was to examine the concept contrast gloss or luster and its relation to the visually perceived gloss of textured injection-molded specimens. Contrast gloss relates to the difference in intensity between the light reflected in the specular angle and that diffusely distributed in other directions. The ability of a conventional multiangle spectrophotometer in order to characterize contrast gloss has here been evaluated. This instrument is normally used for evaluating color of a specimen in different reflection angles.

BACKGROUND

Measuring Gloss

From a physical perspective, gloss is generally associated with the surface light reflection of an object in the specular angle which is the opposite to the incident angle as measured from the normal (1). When a surface is not perfectly smooth, some of the reflected light from the surface is scattered in a diffuse manner, the amount of which is determined by the characteristics of the surface topography. Consequently the gloss will be reduced.

Glossiness refers to the appearance of gloss and is the result of the reflectance properties of the surface but it is also influenced by the illumination conditions and by the viewing direction (2). Already in the 1930s, a number of different types of gloss was identified or suggested; specular gloss, sheen, contrast gloss, haze, distinctness of image and surface nonuniformities such as orange peel (1), (2).

Characterizing and measuring specular gloss involves quantification of the specular reflectance of an object at specified incident and viewing angles and the gloss level is conventionally determined by the means of a glossmeter. Some of the most frequent incident and viewing angles employed in glossmeters are 20[degrees], 60[degrees], 75[degrees], and 85[degrees] (1). Traditionally, the 60[degrees] angle has been preferred within the automotive industry and it is the recommended angle for specular gloss measurements on textured and polymeric surfaces (3), (4). These kinds of glossmeters measures the gloss g as the ratio between the specular reflectance of the surface of the test specimen ([R.sub.[S specimen]]) and that of a smooth standard surface ([R.sub.[S standard]]) at a specified angle;

g = 100 x ([[R.sub.[S specimen]]/[R.sub.[S standard]]])

The standard surface is often a highly polished, black glass tile with a refractive index of 1.567 and is assigned a specular gloss value of 100 gloss units (GU). The illuminant used is spectrally corrected to yield CIE luminous efficiency with CIE standard illuminant C (4). The use of this kind of glossmeter, measuring specular gloss, is the customary method for gloss characterization both in the plastics and in the automotive industry. The gloss level in the case of textured polymeric components in the interior of an automobile is typically of the order of 1-5 GU when measured with the 60[degrees] geometry. In most cases, an experienced observer can distinguish differences in gloss as small as 0.1 GU for such surfaces.

The concept of gloss can, as already noted, not only be considered as a physical property but it also involves a significant part of visual perception. A glossmeter relies on a scale defined according to a physical principle and is detecting the quantity of light reflected at the specular angle, cf. Hunter (1). Furthermore, the glossmeter measures only on a limited area of the surface with a fixed illumination and fixed viewing geometry, whereas in visual perception the whole object is viewed and evaluated. The relation between the measured and the perceived gloss can thus be quite complex.

For the visual perception of gloss, especially in the case of low-gloss surfaces, the contrast between the amount of light reflected in the specular angle and that reflected in other directions can be of greater significance than the specular gloss itself (2), (5), (6). Contrast gloss, sometimes referred to as luster or subjective gloss, is associated with the contrast between bright and less bright adjacent areas of a surface and can, as indicated, be quantified in terms of the difference in intensity of the light reflected in the specular angle and that scattered in any direction away from the specular angle (3). As expected, its magnitude increases with increasing difference in the intensities of the reflected lights (or an increasing equivalent ratio between the reflectances) (1), (3).

Clearly, the most detailed information regarding the angular distribution of the reflected light from a given surface is obtained through goniophotometry (1). In a sense, this was recognized by Fleischer (7) who found correlations between the characteristics of the distribution of the reflected light (obtained from goniophotometric measurements) and the scaling of the perceived gloss. More time-efficient but also less informative methods would rely on reflectance measurements in the specular angle and in another angle away from that. In fact, several decades ago, recognizing the importance of contrast gloss, several instruments, mainly for laboratory studies, were developed for this purpose, cf. (8-14). Most of them relied on measuring the difference between the reflectance in the specular direction and that in another direction. For example, Jones (11) and Shook (9) used already in the 1920s instruments for evaluating the reflected light in the directions 45[degrees] (specular angle) and 0[degrees] (normal to the surface). Goerz used a similar glossmeter as Jones and Shook, but the corresponding angles were 60[degrees] and--30[degrees] (relative to the normal), respectively (8). Attempts to correlate such contrast gloss measurements to visual ratings of the gloss were also made, cf. (13). Interestingly, despite the early recognition of the importance of contrast gloss, most glossmeters and gloss evaluations today only involve measurements in the specular angle, cf. (15).

As mentioned in the "Introduction" section, for some textured and low-gloss surfaces, the correspondence between the measured specular gloss and the visually perceived gloss is less satisfactory. An aim of the present work was to in a sense "re-establish" the contrast gloss concept and to clarify if this measure displayed a better correspondence to the visual rating in the case of textured polymeric surfaces used today in low-gloss applications.

Perceived Gloss Through Psychometric Evaluation

The concept of appearance is clearly linked to subjective perception, which is of great importance for e.g., the automobile manufacturer. Sensory testing is a psychometric approach seeking to numerically characterize for example the visual perception. The intention is to quantify sensory attributes in order to be able to assess the relationship between a given physical stimulus and the perceptual response of the subject (16).

In an earlier work (17), the relation between glossmeter measurements and the visual perception of gloss of textured polymeric specimens was studied by the means of a psychometric evaluation. In that study, however, a conventional glossmeter measuring only the specular gloss at 60[degrees] was used, i.e., not the reflectance properties in different angles as done in the present study.

EXPERIMENTAL

Materials

The same type of injection-molded specimens manufactured from three different polymers as used in a previous work (17) were employed also in the present case (specimens A-H). Additionally four specimens denoted I-L were included in order to study the impact of color on measured and visually perceived gloss and furthermore two injection-molded automotive components (X and Y). The acrylonitrile-butadiene-styrene copolymer (ABS) used was a commercial grade from BASF AG (Ludwigshafen, Germany), denoted Terluran GP 22, with a density of 1.04 g/[cm.sup.3] (ISO 1183) and a melt volume-flow rate at 220[degrees]C and 10 kg of 20.0 [cm.sup.3]/10 min (ISO 1133). The polypropylene was an injection-molding grade for automotive interior applications from Basell (Bayreuth, Germany), denoted Hostacom PPU X9067 HS, with a density of 0.91 g/[cm.sup.3] (ISO 1183) and a melt mass-flow rate at 230[degrees]C and 2.16 kg of 15.0 g/10 min (ISO 1133). The third material was a blend of polycarbonate and acrylonitrile-butadiene-styrene copolymer (PC/ABS) which is an injection-molding grade from GE Plastics (Cartagena, Spain), denoted Cycoloy Resin C1100HF. This blend had a density of 1.12 g/[cm.sup.3] (ISO 1183) and a melt mass-flow rate at 260[degrees]C and 2.16 kg of 6.0 g/10 min (ISO 1133).

Specimen Preparation

The specimens were injection-molded plaques with a fairly isotropic surface texture typical for automotive interior panels. Figure 1 is a photomicrograph of the imposed surface pattern.

[FIGURE 1 OMITTED]

Two different molds, denoted Cavity I and Cavity II, were used to mold the plaques. Both molds were essentially rectangular cavities with the width 138 mm, the length 78 mm and the thickness 2.7 mm. The molds were equipped with a film-edge gate with the width 123 mm, the length 2 mm and a thickness of 1 mm. The mold cavities were photo-etched with identical surface textures but Cavity II was subjected to an additional light etching giving a slightly more detailed pattern, cf (17).

The injection molding procedure is described in detail in ref. (17). Only an overview of the process parameters and the specimens produced are given in Table 1. The colors of the three polymers used for the specimens A-H were adjusted in order to minimize the color differences among the final specimens. The total color difference between the polymers was less than [DELTA]E = 1.3 measured on a smooth, glossy injection-molded plaque with a spectrophotometer in the specular-component-included (SCI) mode.
TABLE 1. An overview of the specimens and process parameters.

Specimen  Material  Cavity  Color       Mold temperature      Melt
                                          ([degrees]C)    temperature
                                                          ([degrees]C)

A         ABS         I     Dark gray          65             250
B         ABS         II    Dark gray          65             250
C         PP          I     Dark gray          45             245
D         PP          II    Dark gray          45             245
E         PP          I     Dark gray         110             250
F         PC/ABS      I     Dark gray         110             270
G         PC/ABS      II    Dark gray         110             270
H         PC/ABS      II    Dark gray          65             250
I         ABS         II    Brown              65             250
J         ABS         II    Gray               65             250
K         ABS         II    Dark beige         65             250
L         ABS         II    Light gray         65             250

Specimen  Material  Cavity  Back pressure (MPa)  Holding pressure (MPa)

A         ABS         I              5                     53
B         ABS         II             5                     53
C         PP          I              8                     49
D         PP          II             8                     49
E         PP          I              8                     49
F         PC/ABS      I             10                     65
G         PC/ABS      II            10                     65
H         PC/ABS      II             5                     53
I         ABS         II             5                     53
J         ABS         II             5                     53
K         ABS         II             5                     53
L         ABS         II             5                     53


Two injection-molded interior automotive components, denoted X and Y, having the same surface texture as the specimens produced in Cavity I were also included in the study. The components were trim panels to be positioned next to each other in the compartment and selected parts of the components can be seen in Fig. 2. The objective was to have a matching appearance of the two components despite that they were manufactured in ABS and PP, respectively. Nevertheless the appearance of these components did not match exactly, especially not their glossiness. There was an apparent visual difference in gloss between the two components, but the glossmeter was not been able to discern this difference giving identical gloss values of both components, see Table 2.

[FIGURE 2 OMITTED]
TABLE 2. Measured gloss at 60[degrees] and visual assessment of the
gloss of the two interior automotive components.

Component  Material  Gloss (GU)  Visual gloss assessment

X            ABS         1.7           Higher gloss
Y            PP          1.7           Lower gloss


Specular Gloss Measurements

In the present work, a portable glossmeter, BYK Gardner micro-gloss 60-S was used, which measures specular gloss at an incident angle of 60[degrees]. The instrument is in accordance with ISO 2813-1994 and ASTM D2457-03. The repeatability of the instrument is [+ or -]0.1 GU in the range 0-10 GU (18). The standard deviation of the measurements performed here was significantly smaller than 0.1 GU.

Ignell et al. (17) measured the gloss of the plaques A-H at an angle of 60[degrees] at 23[degrees]C using this glossmeter. The gloss of the additional specimen I-L was measured in the same manner. Their results are shown in Table 3 below.
TABLE 3. Measured gloss at 60[degrees] and contrast gloss factor for
the specimens.

Specimen  Gloss (GU)  Contrast gloss factor (CGF)

A             1.6                   5.6
B             1.2                   3.9
C             1.6                   4.4
D             1.2                   3.4
E             1.2                   3.0
F             1.6                   5.6
G             1.2                   4.0
H             1.7                   5.5
I             1.2                   2.4
J             1.2                   2.1
K             1.3                   1.6
L             1.6                   1.3


Multiangle Spectrophotometer Measurements

The reflectance measurements were performed with a MA68II multiangle spectrophotometer from X-rite which conforms to ISO 7724. The instrument is equipped with a gas-filled tungsten lamp giving an incident light angle of 45[degrees]. The spectral range is 400-700 nm and the spectral interval is 10 nm. The instrument simultaneously measures the reflectance properties at five different angles relative to (and in the same plane as) the specular angle, 15[degrees], 25[degrees], 45[degrees], 75[degrees], and 110[degrees]. The instrument has a repeatability with a CIELAB total color difference of [DELTA]E* = 0.02.

For the evaluation of contrast gloss the reflectance data in two different angles were chosen. The reflectance data at 15[degrees] angle ([R.sub.15[degrees]]), being the closest to the specular angle, was used as a measure of specular reflectance and the reflectance data at 110[degrees] angle ([R.sub.110[degrees]]) being the furthest away from the specular angle as a measure of diffuse reflectance. The reflectance data refers to the integrated value of the measured reflectance between 400 nm to 700 nm. A contrast gloss factor was calculated as;

Contrast gloss factor (CGF) = R[([lambda]).sub.15[degrees]]/R[([lambda]).sub.110[degrees]]

where [lambda] is the wavelength of the light.

The result of the contrast gloss factor evaluation is shown in Table 3. The standard deviation was typically about 0.2. In case of the specimens used here, the contrast gloss factor was more or less independent of wavelength, [lambda].

The Psychometric Evaluation

To assess how the attribute of gloss is visually perceived, a psychometric evaluation was performed. A pair-comparison test was applied, in which the observers were asked to react to two new specimens at a time and state the difference between them. Compared to other sensory evaluation methods, the advantages of the pair-comparison test are its simplicity and the fact that the observer does not have to relate assessments to previous responses or to keep track of a scoring system (19).

Two specimens were placed beside each other on a specimen holder and were masked by a covering plate that had an opening displaying the textured field of the specimens. The specimen holder, the covering plate and the inside of the cabinet were painted neutral gray. The specimen positioned to the right was always regarded as the reference, and the difference relative to the specimen positioned to the left was visually assessed. The specimen to the left was classified to he higher, lower, or equal in gloss. The observers were asked to disregard any difference in color between the specimens. A new protocol was presented to the observer before each comparison and the pairs were presented randomly in order to avoid possible sequential effects such as probability matching or the possibility of inducing a tendency for the observer to make an expected number of assessments in each category (20). Combining the results from the pair-comparison evaluations a ranking of all the specimens could be obtained.

To evaluate the influence of color on the perceived gloss, a sensory evaluation ranking technique was used. The observers were asked to separately rank a group of specimens containing five specimens in the order of perceived gloss. The color of the specimens varied significantly, particularly in lightness, but also slightly in hue and chroma. For this kind of evaluation, with a limited number of specimens involved, ranking is a suitable and straightforward sensory method for analyzing magnitudes of a stimulus (20).

Ten observers participated in the test panel. Their ages ranged from 28 to 63 years and five of them were male and five female. All observers had extensive experience in assessing the appearance of polymeric components and were professionals in the fields of both engineering and design. Each evaluation was performed by one observer at a time to avoid interactions among the observers (20). The assessments were performed in a light cabinet in accordance with ASTM D 1729 with a CIE daylight illuminant D65 in order to simulate normal daylight viewing conditions.

The consistency of the evaluation was also assessed and reported in the previous work (17).

RESULTS AND DISCUSSION

Multiangle Reflectance Measurements for Characterization of Gloss

The relation between the contrast gloss factor and the perceived gloss ranking of specimens A-H is shown in Fig. 3. The perceived gloss ranking was obtained from the psychometric pair-comparison test. Specimens having equal ranking were assessed to be equal in gloss by the observers. The ranking was in fair correspondence with the measured contrast gloss factor. The correspondence between the measured (specular) gloss and the perceived gloss was significantly poorer as will be shown and discussed in the following.

[FIGURE 3 OMITTED]

The ability of the contrast gloss factor to distinguish between specimens having visually perceived gloss differences is shown in Table 4. In those cases, the specular glossmeter measurements did not reveal any difference between the specimens.
TABLE 4. Gloss measured at 60[degrees], contrast gloss factor and
perceived gloss for specimens and the two interior components in pairs
having the same measured gloss.

Specimen  Material  Gloss (GU)  Contrast gloss  Visual gloss assessment
                                 factor (CGF)

A           ABS        1.6            5.6             Higher gloss
C            PP        1.6            4.4             Lower gloss
B           ABS        1.2            3.9             Higher gloss
D            PP        1.2            3.4             Lower gloss
X           ABS        1.7            6.0             Higher gloss
Y            PP        1.7            4.2             Lower gloss


Unlike the glossmeter measurements, the contrast gloss factor thus revealed the difference in the perceived gloss of the specimens. In a similar manner and in contrast to the specular gloss measurements, the contrast gloss factor was also able to discern the gloss difference between the two interior components exhibiting a visually apparent gloss difference as shown also in Table 4.

Table 4 shows three examples when the specular gloss measurements were not able to discern visually apparent gloss differences of surfaces manufactured in different polymers. To further evaluate the influence of the polymer on measured and perceived gloss, the contrast gloss factor for a large number of specimens in the three polymers ABS, PC/ABS, and PP were evaluated. All specimens were virtually equal in color (dark gray) and the aim when producing the specimens was to obtain a texture identical to that shown in Fig. 1. However, due to slight differences in the processing conditions, the specimens differed in specular gloss as illustrated in Fig. 4. The relation between the specular glossmeter values and the values of contrast gloss factor depended on the type of polymer as shown in Fig. 4.

[FIGURE 4 OMITTED]

The PP specimens exhibited lower values of contrast gloss factor for given specular gloss values than both ABS and PC/ABS which may also be associated with a lower perceived gloss for those specimens. The reason for the lower contrast gloss factor of PP is not entirely clear at present. Compared to the other two materials, the reflectance in the 110[degrees]-direction was significantly higher for the PP specimens. Neither any difference in surface topography, reported in (21), nor color between the plaques can seemingly account for this enhanced reflectance. Possibly, an evaluation of the entire angular distribution of the reflected light can provide relevant information regarding the lower CGF of the PP specimens. This will be dealt with in a forthcoming work. A difference between the ABS and the PC/ABS specimens, however less evident, could also be discerned where the PC/ABS specimens had slightly higher contrast gloss factors relative to the ABS specimens for a given gloss value below 2.5 GU. These relations corresponded fairly well with the practical experience regarding the influence of different types of polymer on the perceived gloss and its relation to the gloss values obtained with a conventional glossmeter.

Characterizing the Influence of the Color on the Gloss

The potential influence of color on the visual perception of gloss was studied by means of the sensory evaluation ranking technique described earlier. Five of the specimens (B, I-L) produced in ABS in cavity 11 were used. The color of those specimens varied from dark gray to light gray, of Table 1. The observers in the test panel were asked to rank the specimens in each group with regard to the perceived gloss. Generally, when employing ranking techniques, ties are avoided in order to facilitate statistical analysis of the data obtained. However, in the present case the observers were allowed to evaluate the specimens as equal. The reason for this was that the specimens were produced at constant processing conditions and thus expected to replicate the mold surface in an identical manner. The surface texture can consequently be assumed to be independent of the color and equal for all five specimens in each group. In a strict manner, gloss is a surface-related feature, determined by the reflectance properties and the topography of the surface. From a strict physical perspective, it is then expected that the specimens should exhibit an identical gloss. However, in a previous study by the authors (22), it was indicated that there was a significant contribution from bulk scattering to the measured specular gloss for these specimens resulting in a higher measured gloss in case of the lighter specimens. Figure 5 shows the measured gloss, obtained with a conventional glossmeter, of the five ABS specimens as a function of the CIELAB lightness coordinate L* and clearly a higher lightness corresponded to a higher measured gloss.

[FIGURE 5 OMITTED]

In the qualitative assessment of the gloss, the observers ranked the perceived gloss of the specimens essentially in the opposite order compared to the glossmeter measurements, Fig. 6. The reported ranking is the mean value of the individual rankings of the 10 observers. Some of the observers stated, that the task was fairly difficult and that the perceived differences between the specimens were very small. Two of the observers were not able to distinguish differences between the specimens and rated them as equal. Furthermore, it cannot be presumed that the observers were entirely capable of disregarding the color of the specimen and only assessing the perceived gloss. To evaluate the significance of the differences between the means of the data, a statistical Friedman two-way analysis of variance by ranks was applied. The analysis implied that there was a significant difference in the ranking of all specimens except for specimen I and J. Specimens I and J can therefore be considered to be identical in terms of perceived gloss.

[FIGURE 6 OMITTED]

The perception of the gloss was mainly influenced by the lightness, L* of the specimens. The specimens differed slightly also in chroma and hue, however no significant influence of these on the perceived gloss could be determined.

In conclusion, combining Figs. 5 and 6 yields a negative correlation between the measured specular gloss and the perceived gloss ranking.

Gloss is, as mentioned previously, from a physical perspective generally expressed in terms of the amount of light reflected in the specular direction. However, when visually evaluating gloss, the eye can not assess the magnitude of gloss in an absolute sense and for the visual perception the contrast gloss is of greater significance (3), (6). The contrast gloss is the result of an intraspecimen assessment and the magnitude of the contrast gloss can be obtained by comparing the intensity of the light reflected in the specular angle to that of the light scattered in any direction away from the specular angle, such as the normal of the surface (3). As the difference between the amount of light reflected in the specular angle and that reflected in other directions is larger in case of a darker object, a darker specimen is expected to exhibit a higher contrast gloss (5), (6). The visually perceived gloss will consequently depend on the lightness of the specimen. Furthermore, it can be assumed that the impact of lightness on the perceived gloss may possibly be more pronounced in case of textured specimens having a lower gloss since for such specimens, the relative contribution from bulk scattering to the specularly reflected light will be larger than for high gloss (smooth) specimens.

When evaluating the contrast gloss factor of the five specimens, the values were in fair correspondence with the visually perceived gloss ranking as shown in Fig. 7. This implies that the contrast gloss factor is a better measure of perceived gloss of textured polymeric surfaces.

[FIGURE 7 OMITTED]

CONCLUSIONS

Characterizing contrast gloss and evaluating its relation to perceived gloss using a multiangle spectrophotometer on textured polymeric surfaces has shown to be rewarding despite that its measurement angles are not optimized for this purpose. The measurement angle at 15[degrees] relative to the specular angle seemed to be sufficiently close to the specular angle in order to provide a reasonable estimate of the specular reflectance, i.e., for the aim of the study. In the present case only textured specimens having relatively low gloss were included and such surfaces may be expected to have a fairly broad angular distribution of reflected light in the specular region. It was therefore assumed that reflected light at 15[degrees] from the specular angle contained a sufficient part of reflected light associated with specular gloss. It is however clear that this restriction could be eliminated with another type of measuring device, e.g., a goniophotometer.

The contrast gloss factor showed a better correlation with the visual assessments of gloss compared to the gloss values obtained with a conventional glossmeter and the CGF was in many cases able to discern visually apparent differences between specimens not discriminated by their glossmeter values. This was especially the case when comparing specimens manufactured in different polymers. Also when evaluating specimens having different color, the contrast gloss factor corresponded well with the visual ranking. This was in contrast to the specular glossmeter measurements which ranked the specimens essentially in the opposite order.

In conclusion, characterizing contrast gloss relates better to the visual perception of gloss of textured and low-gloss polymeric surfaces compared to conventional specular gloss evaluations.

ACKNOWLEDGMENTS

The authors thank BASF AG (Ludwigshafen, Germany), SABIC (Laholm, Sweden) and Basell (Bayreuth, Germany) for supplying the materials. International Automotive Components, IAC (Fargelanda, Sweden), and Standex (Rolvsoey, Norway) are gratefully acknowledged for their technical support.
NOMENCLATURE

ABS          acrylonitrile-butadiene-styrene copolymer

C CIE        standard illuminant, average daylight with a color
             temperature of 6770 K

CGF          contrast gloss factor

CIE          Commission Internationale de l'Eclairage

CIELAB       CIE color coordinates

D65          CIE standard illuminant, average daylight with a color
             temperature of 6500 K

GU           gloss units

PA           polyamide

PC/ABS       polycarbonate/Acrylonitrile-butadiene-styrene
             copolymer

PP           polypropylene

8            gloss (GU)

L *          CIELAB lightness

R([lambda])  spectral reflectance of an object

[R.sub.s]    specular reflectance captured by the detector of a
             glossmeler

[DELTA]E *   CIELAB total color difference

[lambda]     wavelength of light (nm)


REFERENCES

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(19.) E.T. Klemmer, Basic Principles of Sensory Evaluation, ASTM STP 433, American Society for Testing Materials, Philadelphia, USA, 58 (1968).

(20.) Manual on Sensory Testing Methods, ASTM Special Technical Publication No. 434, Philadelphia, USA (1968).

(21.) S. Ignell, R. Arino, G. Iannuzzi, U. Kleist, and M. Rigdahl, Three-dimensional Scanning Electron Microscopy Characterization of the Topography of Textured Polymeric Surfaces [accepted for publication 2010].

(22.) S. Ignell, U. Kleist, and M. Rigdahl, Color Res. Appl, 34, 291 (2009).

Correspondence to: Sofie Ignell; e-mail: signell@volvocars.com

Contract grant sponsors: Swedish Agency for Innovation Systems (Vinnova), Volvo Car Corporation, Chalmers University of Technology.

Published online in Wiley Online Library (wileyonlinelibrary.com). [C] 2010 Society of Plastics Engineers

Sofie Ignell, (1), (2) Ulf Kleist, (1) Mikael Rigdahl (2)

(1) Department of Perceived Quality, Volvo Car Corporation, Goteborg SE-405 31, Sweden

(2) Department of Materials and Manufacturing Technology, Chalmers University of Technology, Goteborg SE-412 96, Sweden

DOI 10.1002/pen.21742
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Publication:Polymer Engineering and Science
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Date:Nov 1, 2010
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