GB/T 11417.6-2012 PDF in English
GB/T 11417.6-2012 (GB/T11417.6-2012, GBT 11417.6-2012, GBT11417.6-2012)
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Ophthalmic optics -- Contact lenses -- Part 6: Mechanical properties test methods
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Standards related to (historical): GB/T 11417.6-2012
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GB/T 11417.6-2012: PDF in English (GBT 11417.6-2012) GB/T 11417.6-2012
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 11.040.70
C 40
Ophthalmic optics - Contact lenses -
Part 6: Mechanical properties test methods
ISSUED ON: DECEMBER 31, 2012
IMPLEMENTED ON: JUNE 01, 2013
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 5
4 Determination of radius of curvature ... 5
5 Diameter and width ... 20
6 Thickness ... 26
7 Inspection of edges, inclusions and surface defects ... 28
8 Bending deformation and fracture of hard lens ... 30
9 Hardness ... 34
Ophthalmic optics - Contact lenses -
Part 6: Mechanical properties test methods
1 Scope
GB/T 11417.6 gives test methods for the mechanical properties of contact
lenses including dimensions.
This Part is applicable to the testing of mechanical properties of contact lenses.
2 Normative references
The following referenced documents are indispensable for the application of
this document. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any
amendments) applies.
GB/T 2411-2008, Plastics and ebonite - Determination of indentation
hardness by means of a durometer (shore hardness)
GB/T 11417.1-2012, Ophthalmic optics - Contact lenses - Part 1: Vocabulary,
classification system and recommendations for labeling specifications
GB 11417.2-2012, Ophthalmic optics - Contact lenses - Part 2: Rigid contact
lenses specification
GB 11417.3-2012, Ophthalmic optics - Contact lenses - Part 3: Soft contact
lenses
GB/T 11417.4-2012, Ophthalmic optics - Contact lenses - Part 4: Saline
solution for contact lens testing
3 Terms and definitions
For the purposes of this document, the terms and definitions defined in GB/T
11417.1-2012 apply.
4 Determination of radius of curvature
4.1 General
Mechanical scales can be equipped with some devices to reduce empty back.
If the reading is in one direction, the error source can be ignored.
Illumination measurements usually contain 4 intersecting lines around the
center. Adjacent angle is 45°.
The spherometer shall be equipped with a lens holder that allows the lens to be
placed on a reference plane, usually on the optical axis of the instrument. The
holder shall be adjustable laterally so that the apex of the rear surface of the
lens falls on the optical axis. The holder shall be able to suppress the reflection
of the non-measuring surface of the contact lens.
NOTE: The term "scale" refers to both analog and digital instruments.
4.2.3 Calibration
4.2.3.1 It shall use the optical glass concave spherical surfaces with the
following 3 kinds of curvature radius for calibration:
Concave spherical surface 1: 6.30mm~6.70mm;
Concave spherical surface 2: 7.80mm~8.20mm;
Concave spherical surface 3: 9.30mm~9.70mm.
The precision of the radius of curvature of the concave spherical surface is
±0.0075mm.
4.2.3.2 Calibrate at room temperature of 20°C ± 5°C. The equipment shall be
preheated until equilibrium.
4.2.3.3 Place the concave spherical surface 1 on the measuring head so that
the optical axis of the microscope is perpendicular to the test surface. Adjust
the distance between the microscope and the head until the image is focused
on the concave spherical surface [Figure 1a]]. Observe a clear image of
measuring mark in the microscope. Set the scale to 0. Pull apart the distance
between the head and the microscope until a clear image of measuring mark is
observed for the second time in the microscope. The position of the microscope
and surface is shown in Figure 1b). 2 images shall be in the center of the field
of view. If not, move the test surface laterally, and/or tilt until a clear image is
produced. Record the reading shown on the scale at this time, which shall be
the radius of curvature of the concave spherical surface. Each piece is
measured 10 times independently. Calculate its arithmetic mean. Repeat the
above steps for the other 2 concave spherical surfaces. If the result is outside
the precision range of the instrument, the result is depicted as a calibration
curve and the results obtained in 4.2.4 are corrected.
NOTE: “Independent” is to remove the concave spherical surface from the test stand after each test
6 - eyepiece;
7 - object mirror plane = eyepiece plane;
8 - solution;
9 - prism;
10 - front surface of silver-plated lens;
11 - movable cover.
Figure 4 -- Schematic diagram of measurement in keratometer solution
4.3.4 Test method
4.3.4.1 General
Hard contact lenses are generally measured in air. But if required, it can also
be measured in solution.
4.3.4.2 Measurement in air
After balancing the lens and instrument under test at room temperature of 20°C
± 5°C, then measure.
Fix the rigid contact lens on the holder and perpendicular to the optical axis of
the keratometer.
Perform independent measurement 3 times. The measured value is rounded to
0.01mm. For the spherical surface, calculate the arithmetic mean of the three
test values (if necessary, correct with the calibration curve of 4.3.3). For the ring
surface, measure the two main meridians three times and calculate the average.
Record the test results. Correct them separately if needed.
4.3.4.3 Measurement in solution
This method is only applicable for measurements in the central area.
Soft lenses are equilibrated in a standard salt solution at 20°C ± 0.5°C. And
suspend and measure in the same standard salt solution at the same
temperature.
Position the soft contact lens on the holder and perpendicular to the optical axis
of the keratometer.
Perform independent measurement 3 times. The measured value is rounded to
0.01mm. For spherical lenses, calculate the arithmetic mean of 3
measurements. For the toroidal lens, measure the two main meridians three
times respectively. Calculate the average and record the test results. Correct
them separately if needed.
4.4 Vector height measurement
r - radius of curvature of the lens;
s - vector height;
y - external chord diameter of the lens holder.
Figure 5 -- Curvature radius measurement geometry
4.4.2 Equipment requirements
4.4.2.1 Optical projector
The magnification of the optical projector shall be greater than 10 times. There
shall be a measuring cell with a hollow cylindrical contact lens holder. As shown
in Figure 5, the contact lens is centered downwards, horizontally stationary. And
the chord length provided by the holder shall be 10 mm (as shown in Figure 5).
The minimum scale of the engraved line shall be 0.01mm. When measuring the
center of the contact lens (the contact lens is already centered), the repeatability
of the visual measurement of the vector height is ±0.02 mm or better. The
instrument shall be equipped with a temperature control device.
4.4.2.2 Mechanical spherometer
The spherometer shall project the contour of the contact lens, the lens holder
and the probe onto a screen (see Figure 6). The magnification of the projection
system is not less than 10 times. The projection system shall have the lens,
lens holder and probe on the same focal plane. And it shall enable the operator
to observe the center of the lens to ensure that the probe and the mirror axis
are close together. Finally, the probe just touches the back apex of the lens (see
Figure 7). The end point is the test value. The distance between the solid
mechanical probe from the plane of the contact lens holder to the apex of the
back surface is the vector height (s). The precision of the analog or digital meter
shall be no less than 0.01mm.
See 4.4.2.1 for requirements for measuring pool and holder.
4.4.3 Calibration
Calibration (precision measurement) shall use at least 3 concave hard spherical
calibration sheets made of plexiglass or glass. The curvature between the
calibration sheets is spaced to ensure the precision of the entire measurement
range. The calibration sheet shall include 7.50mm ± 0.10mm, 8.50mm ±
0.10mm, 9.50mm ± 0.10mm. The exact value of the curvature shall be within
0.01mm.
NOTE: It is convenient to make the calibration block into a flat concave type. Recommended center
thickness is 3mm. Recommended diameter is 12mm.
After the equipment is warmed up, the calibration block shall be balanced in a
standard salt solution. Calibrate optical projector and spherometer at room
temperature of 20°C ± 5.0°C. Calibrate ultrasound system at room temperature
of 20°C ± 0.5°C.
Each calibration piece shall be measured at least 20 times in the same direction.
And calculate the arithmetic mean. If applicable, the deviation between the
calculated and actual values shall establish a calibration curve.
4.4.4 Measurement method
The contact lens to be tested floats on the lens holder in a self-weight manner
and is centered. When measuring the aspherical height, it shall pay more
attention to the center of the lens. Prior to testing, the lens shall be equilibrated
for at least 30min at 20°C ± 0.5°C standard salt solution. Measure lenses at
20°C ± 0.5°C.
Optical projectors, mechanical methods and ultrasonic methods shall be
measured independently for 3 times. Record the minimum bit as 0.01mm.
Calculate the arithmetic mean of 3 times as the vector height of the contact lens
surface (s).
4.4.5 Conversion of vector height and radius of curvature
If required, the height (s) can be converted to the radius of curvature (spherical)
or the equivalent spherical radius of curvature (aspherical surface) by the
measured diameter (2y) by using equation (3).
Obtain radius of curvature from the calibration curve.
a calibration curve and used to correct the results measured in 5.1.2.4. For the
calibration of this method, the deviation of the diameter reading is considered
to be acceptable within ±0.02 mm.
5.1.2.4 Measurement
The temperature during the test is maintained at 20°C ± 5°C.
Place the dried test lens on the wide side of the V-groove tester. Raise the wide
side of the groove by approximately 45°, allowing the lens to slide by its own
weight without any external force slipping into the narrow part. The back surface
and edge of the lens are subject to some friction, making the speed slower. The
width of the groove is the diameter of the lens until the lens reaches a fixed
position. The scale corresponding to the upper edge of the lens is the diameter
of the lens.
Rotate lens. Measure the maximum and minimum diameters 3 times
independently. Be careful not to deform the lens during measurement. Assume
that the lens diameter is uniform. Calculate the arithmetic mean of 6 readings
and correct with the calibration curve. If not, calculate the average of the largest
and smallest diameters separately.
5.1.2.5 Repeatability expectations of results
Because the diameter measurement relies on visual readings, its precision
depends on the observer's visual ability. However, the change in position on the
scribe line is proportional to the reciprocal of the sine of the V-groove angle
(25:1 in the figure). Because the groove has a scribed width of 0.25mm and a
diameter change of 0.01mm, equivalent to a distance change of 0.25mm along
the diameter scale. Assuming a distance of 0.38mm is easy to distinguish, the
lens diameter repeatability is about 0.015mm. In addition, because interval
characterization diameter increment of scale is 0.1mm. 1/4 of this distance is
easily determined. For this reason, the precision of this algorithm is equal to
0.75 sin (0.5β), where β is the angle of the V-groove. The precision of the groove
shown in Figure 9 is 0.015mm.
5.1.3 Projection method
5.1.3.1 Projection method specification
The principle of the projection method is shown in Figure 12. The projection
system shall be able to measure to ±0.05mm. The range shall be 0mm~17mm.
As shown in Figure 12, the contact lens mount (6) is placed horizontally and
can be adjusted vertically. there shall be at least 15 times linear magnification
on the scale of the viewing screen (1). And the precision of measuring the
contact lens diameter is 0.05mm. The instrument has a telecentric optical path
to ensure that the aperture (3) is on the back focal plane of the objective lens
For hydrogel lenses, the standard salt solution at 20°C ± 0.5°C shall be
equilibrated for at least 30min unless otherwise specified by the manufacturer.
The ambient temperature is maintained at 20°C ± 5°C when tested in air.
Place the lens in the measuring pool. Maintain the temperature of the standard
salt solution in the measuring pool at 20°C ± 0.5°C.
Rotate lens. Measure the largest and smallest diameters 3 times independently.
Be careful not to deform the lens during measurement. Assuming the lens
diameter is uniform, calculate the arithmetic mean of 6 readings. If not, calculate
the average of the largest and smallest diameters separately. Correct with
correction curve if necessary.
When the diameters of any two directions of the four directions of the soft lens
differ by more than 0.4mm, the soft lens shall be identified as "non-circular".
5.2 Belt diameter and width
5.2.1 General
The diameter and width of the contact lens ring can be measured by projection
method (5.1.3) (e.g. optical zone diameter, secondary arc or outer arc diameter
or width). For hard lens, measurement can be performed in the air by using a
handheld amplifier (5.2.2). Because the boundaries of the edges of these areas
are often "mixed" and several areas blend together, it is difficult to measure.
5.2.2 Method of using handheld amplifier
5.2.2.1 Magnification requirement
The minimum magnification of the measuring amplifier is 7 times. The center of
the field of view of the magnifier shall have a suitable scale. The minimum scale
is 0.10mm.
5.2.2.2 Calibration
Calibration sheet of known diameter shall be used to determine the precision of
the magnification. Different sizes of calibration sheets shall be used to
determine the precision of different scales (see the calibration sheet
requirements in 5.1.2.3.1). Correction factor shall be given if necessary. Focus
precision shall be considered when calibrating. It shall be included in the
correction factor.
5.2.2.3 Measurement
The ambient temperature during the test is maintained at 20°C ± 5°C.
Table 2 -- Reproducibility value by using low force to measure lens
thickness
Thickness range
mm
Reproducibility a
mm
SR R
0.04 ~ 0.60 0.006 0.017
a These precision values are obtained from the geometric center thickness measurement of the lens.
These data cannot be used for lenses that are too thin or too thick.
7 Inspection of edges, inclusions and surface defects
7.1 Edge inspection
Visually evaluate the edge thickness and shape of the finished product at 7x to
10x magnification of direct illumination.
The inspector shall have the ability to check the edge of the contact lens.
7.2 Determination of inclusions and surface defects
7.2.1 General
The determination method of inclusion shall be capable of distinguishing any
inclusions greater than 6μm in the lens material, such as unevenness or
bubbles. The determination method for surface defects shall be able to resolve
any defects greater than 9μm, such as scratches or spots.
Purposeful surface markings are not surface defects.
7.2.2 Instrument specifications and test conditions
It shall use 2 magnifiers. Use 10 times when observing the contents. Use 7
times when observing the surface quality.
Check contact lens illumination is 350lx±35lx (including indoor lighting).
Figure 14 shows an example of a suitable instrument.
The ambient temperature during the test is maintained at 20°C ± 5°C.
7.2.3 Inspection method
Place the lens on the lens base (as shown in Figure 14). And ensure that the
lens is not deformed. Observe in the dark field by means of the magnifier and
record according to the contents shown in Table 3.
The observer must have the ability to discern the surface defects of the lens.
8 Bending deformation and fracture of hard lens
8.1 Principle
This test is destructive, that is, place the hard contact lens sample in an
experimental setup that continuously monitors the recorded load and bending
deformation. Gradually increase the load along the diameter of the edge of the
contact lens until the lens under test breaks. Test the load and bending
deformation value at the moment of lens breakage. The load value at 30%
deformation is obtained from the load and bending deformation curves. This
method can test conventional production and special structure hard contact
lenses.
It shall be noted that differences in lens manufacturing methods can result in
changes in the results, which do not reflect the properties of the material itself.
8.2 Sample
8.2.1 Conventional sample
In order to determine the degree of fracture resistance of a material made into
a lens, the sample to be tested is usually a conventional, commercially available
single-focus contact lens. It shall not be specially made or adjusted contact
lenses.
Do not use test lenses with ring surface areas or trimming.
The back-top power (F'v) of all samples shall be between -0.50D~+0.50D.
The radius of curvature or the radius of the apex surface of all samples shall be
between 7.75mm ~ 7.85mm.
8.2.2 Sample for material comparison
To compare special samples of different materials, the contact lens must meet
the following specifications:
- Front surface: single arc, radius of curvature is 8.00mm ± 0.025mm;
- Rear surface: single arc, radius of curvature is 7.80mm ± 0.025mm;
- Total diameter: 9.5mm ± 0.1mm;
- Center thickness: 0.20mm ± 0.01mm;
- Edge thickness: 0.24mm ± 0.01mm;
- Edge shape: round;
The total diameter of the contact lens is 9.6mm;
The relative movement rate of the holder is 20 cm/min (3.33 mm/s);
Deformation 30% = 2.9mm;
The time for the holder to move 2.9mm is 0.865s.
Then the bending deformation strength of 30% deformation is the load applied
from the start of deformation to 0.865s.
9 Hardness
9.1 General
There are two methods to determine the hardness of a material. Both methods
determine the hardness by pressing the thimble of the hardness tester on the
surface of the sample to a certain thickness. For contact lenses, these methods
have been derived from GB/T 2411-2008. The hardness is inversely
proportional to the depth of the indentation, independent of the elastic modulus
and the viscoelastic behavior of the material sample. The shape of the indenter
and the application conditions of the indenter affect the results. Therefore, there
is no simple equivalence between the hardness tester that uses some form of
indenter and the results obtained by other types of hardness testers with other
indenters. In addition, there is no simple connection between the hardness of
the indenter determined by these test methods and the basic properties of the
material being tested. The test method is an empirical conclusion and is mainly
used for control purposes.
9.2 Universal hardness tester
9.2.1 General
The hardness tester shall be equipped with a scale and an indenter, and a ruler
capable of ascending and descending in a direction perpendicular to the plane.
Add a known weight to the hardness tester so that the indenter can top the
surface of the sample to be tested.
9.2.2 Shore A hardness
The Shore A hardness tester shall be equipped with the indenter specified in
GB/T 2411-2008. The Shore A hardness test is very useful for testing the
properties of rubber polymers. Therefore, the Shore A hardness tester is mainly
used for hydrogel type, rubber non-hydrogel contact lens materials and some
soft "hard" contact lenses.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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