WARP KNIT ELASTOMERIC FABRICS

Industry Practices
(Published 1983)

Following are test methods, tolerances, and practices in relation to them, used by manufacturers of warp knit elastomeric fabrics. Warp knit elastomeric fabrics include Raschel or tricot warp knitted fabrics where at least one warp is wholly or substantially of elastomeric fibers (spandex or rubber).

These methods and practices are not to be construed as industry standards or association policies and are reported here only to promote uniform understanding of prevailing industry practices. Individual companies will prepare, test, market and distribute using methods suitable for their own products and consistent with company practices.

Warp Knit Division

Elastic Fabric Manufacturers Council

Northern Textile Association

PURPOSE

To establish a uniform method for determining, quantifying and measuring the quality of warp knit elastomeric fabrics; and a method for measuring length, width, and other physical properties. This document seeks to promote a uniform under-standing of certain technical terms by establishing definitions.

APPLICABILITY

This standard applies to:

· Plain, flat-finished WARP KNIT ELASTOMERIC fabrics without raised fiber surfaces.

· WARP KNIT ELASTOMERIC fabrics having a raised fiber surface produced either in knitting or by finishing procedures.

METHOD

· Four-Point System - Penalty points are attributed to a piece of fabric according to the length of its defects measured in inches. The following schedule of penalty points is based on fabrics 60/62 inches in width for defects visible when inspected on face side of fabric only:

Length of Defects

3 inches or less

Over 3, but not over 6 inches

Over 6, but not over 9 inches

Over 9 inches

Number of Penalty Points

1

2

3

4

· Four penalty points per linear yard are the maximum assessable for fabrics up to 60/62 inches in width.

· For fabrics over 60/62 inches in width, maximum allowable penalty points are to be increased in proportion as the width exceeds 60 inches.

· Regardless of the length of fabric, the quality shall be expressed in the number of penalty points per 100 yard length. (Example: A 40-yard piece width six penalty points is to be rated as 15 points per 100 yards.)

· Identification and Rating Defects:

Examples of defects in evaluating quality are these:

Knitting defects, including holes other than pinholes

Grease/oil spots

Dye spots

Stains

Slubs-except where they are an inherent part of the yarn

Picks

· Bowing and Skewing (bias): bowing and skewing may not exceed 5% of overall width. Examples:

60" width - 3" tolerance

72" width - 3.5" tolerance

Any yard containing bowing or skewing in excess of these limits shall be penalized four points.

· Fabrics are to be examined for these defects only on the agreed upon selling face (which may be the technical face, or technical back).

EXCLUSIONS

In evaluating quality, the following conditions are to be excluded in determining points:

· General aesthetic fabric characteristics.

· Pin holes (whether caused by knitting or by tenter frame pins); they shall be judged by the extent and degree to which they occur and their probable effect on the type of garment or other end use.

· Defects appearing outside the selling width (the selling width being centered in the total width of the fabric).

· Defects resulting from napping, shearing and other surface treatments (which shall be otherwise evaluated).

· Course and wale count shall not be considered.

· Irregularities normal to the existing state of the art or beyond reasonable control of the manufacturer, or inherent in WARP KNIT ELASTOMERIC knitted fabrics (for instance, streaks).

QUALITY DETERMINATION

Determining first quality WARP KNIT ELASTOMERIC fabrics shall be done as follows:

· Plain Flat WARP KNIT ELASTOMERIC fabrics shall be classified as first quality if the number of penalty points does not exceed 50 points per 100 yards.

· Fabrics with any raised fiber surface shall be classified as first quality if the number of penalty points does not exceed 60 points per 100 linear yards.

NOTE: Laps: No more than 3 lapped pieces per 100 yards are allowable. The shortest unlapped portion of a piece shall not be less than 10 yards.

LENGTH, WIDTH, WEIGHT, MEASUREMENT AND TOLERANCES

· Length - Length shall be measured with any surface contact device (Tru-meter or equivalent) that is calibrated regularly. The device shall contact the back or a smooth surface of WARP KNIT ELASTOMERIC fabrics. (Preferred calibration method: Measure a known length of canvas or other stable, low elongation fabric--less than 2% in either direction--through the measuring device. Reference: ASTM D3773-84 Hand Method.) Actual yardage of each piece shall be accurate to within plus or minus 3% when measured by the above method.

· Shortages shall be evaluated based on the sum total of each piece contained within the shipped lot in question, as opposed to on a piece basis. This method allows for possible overages on some pieces which might reconcile shortages on other pieces.

· Width - Width shall be measured with an accurate tape after laying WARP KNIT ELASTOMERIC fabric flat on a table without tension or elongation.

· Overall Width - From fabric edge to fabric edge (including pin marks and/or gummed edges, if present).

· Minimum Width - Measurement of fabric inside pin marks of gummed edges, if any. If no pin marks or gummed edges, Minimum Width is the same as Overall width as defined above.

· Tolerances:

· Weight: Weight of WARP KNIT ELASTOMERIC fabrics per square yard may not vary more than 5% (plus or minus) from the weight stated in the contract. However, on fabrics weighing less than 4oz/yd², the minimum weight variation will be + 0.2oz/yd². Testing will be done in accordance to ASTM-3776.

· Wales: Variation in wales per inch may not exceed the values as stated below:

· Plain, flat fabrics--5 wales across the actual width of the fabric.

· Fabric with a raised fiber surface--7 wales across the actual width of the fabric.

· Courses: Variation in courses per inch may not exceed the values as stated below:

· Plain, flat fabrics + 3 courses.

· Fabrics with a raised fiber surface
+ 5 courses.

ELONGATION AND MODULUS

Test Method

In the absence of any agreement to the contrary, it is recommended that mills use the methods of testing stretch and tension of WARP KNIT ELASTOMERIC fabrics set forth in ASTM Standard Test Method 1775, "Tension and Elongation of Wide Elastic Fabrics."

Zwick-CRE (Constant Rate of Elongation) is the recommended test machine. Sample size, load, and test procedure to be agreed upon by customer and seller.

Elongation

The tolerance on WARP KNIT ELASTOMERIC fabric stretch is plus or minus 10% of the specified stretch with a minimum of plus or minus 10 points. Certain fabric constructions may require additional tolerances.

Modulus

Tolerances for Modulus have to be based on the actual fabric style specification sheet.

BOW AND SKEW (BIAS)--DEFINITION AND MEASUREMENTS

Definitions:

· Bow - A fabric condition resulting when knitted courses are displaced from a line perpendicular to the selvages and form one or more arcs across the width of the fabric (see Fig. 1).

· Skew (Bias) - A fabric condition resulting when knitted courses are angularly displaced from a line perpendicular to the edge of the fabric (see Fig. 2).

Measurement Method

· Bow - A straightedge is placed across the fabric between the points at which a marked filling yarn or knitting course meets the two selvages or edges. The greatest distance between the straightedge and the marked filling yarn or course is measured parallel to the selvages (Fig. 1 Distance "D").

· Skew or Bias - Measure the skew in three places spaced as widely as possible along the length of the fabric or along a minimum of 1 linear yard. If possible, make no measurement closer to the ends of the roll or piece of fabric than 1 yard. Draw a line perpendicular to the selvage across the fabric from a point C where the marked yarn or course meets one selvage, meeting the other selvage at point B. Measure the distance between points A and B or D and B, and B and C, as shown in Fig. 2. Record the three or more skew or bias measurements. Calculate the maximum skew or bias as a percentage of the fabric width using the equation:

"% Skew = Distance AB or DB x 100 / width BC"

FIBER CONTENT

Test Method

Mechanical separation tests (where possible; otherwise, chemical analysis) are made on finished goods at a point halfway between the selvage and the center of the tested piece.

Tolerance

The allowance between the amount of fiber stated and that actually appearing in a test should be in accordance with the Textile Fiber Products Identification Act regulations. The Act provides:

". . .that in the case of a textile fiber product which contains more than one kind of fiber, deviation in the fiber content of any fiber in such product from the amount stated on the stamp, tag, label, or other identification shall not be a mis-branding under this section unless such deviation is in excess of reasonable tolerances which shall be established by the Commission: and provided further, that any such deviation which exceeds said tolerances shall not be a misbranding if the person charged proves that the deviation resulted from unavoidable variations in manufacture and despite due care to make accurate the statements on the tag, stamp, label or other identification."

Rule 43 of the FTC under the Act interprets fiber tolerances as follows:

"A textile fiber product which contains more than one fiber shall not be deemed to be mis-branded as to fiber content percentages if the percentages by weight of any fibers present in the total fiber content of the product, exclusive of permissive ornamentation, do not deviate or vary from the percentages stated on the label in excess of 3% of the total fiber weight of the product.

For example, where the label indicates that a particular fiber is present in the amount of 40%, the amount of such fiber present may vary from a minimum of 37% of the total fiber weight of such product to a maximum of 43% of the total fiber weight of such product."

COLOR PERFORMANCE STANDARD

Pre-agreed standard lighting source, viewing conditions and target sample presentation should be set for the viewing of color. All matches are commercial unless otherwise stated.

SHADE MATCHING

Shade Standards

Customers will provide a consistent (unshaded) physical shade standard. Because standards can change due to handling, dirt and fiber degradation, standards should be read and stored in the spectro-photometer computer. The CIE L*a*b values and the date will then be recorded on the back of the standard card. Standards should be replaced by the manufacturer every six months. In the absence of new shade standards, the active standard will remain in effect.

Standards will be stored in non-BHT plastic bags and will be mounted on a non-optical card. Lab dips will be done to establish the shade on the supplier's substrate. The approved lab dip will become the primary target for shade matching with consideration given to the customer standard. Customers will select a production dye lot as standard upon receipt of a suitable dye lot. Customers must notify suppliers of any changes in their standards and supply new standards to the supplier. Suppliers will determine if a new lab dip is required based on the degree of change.

Visual Shade Matching

Visual shade checks will be made either in a MacBeth shade box with CWF lighting OR in a shade room with CWF lights in the ceiling. The shade room will be smoke free and will be free of any lighting interference (windows, incandescent lamps, etc.). The walls should be painted a neutral color, e.g., MacBeth grey. The viewing surface should be clean, a neutral color and free of optical. The illumination should be 110 - 150-foot candles at the center of the viewing area. A log of bi-monthly foot-candle readings should be maintained. Bulbs will be inspected for burn out, flickering or any sign of wear and will be cleaned/dusted on a monthly basis. Because bulbs experience a shift in radiant light due to chemical degradation, All bulbs will be changed using the following schedule:

If bulbs are used 8 hours per day, change every 18 months.

If bulbs are used 16 hours per day, change every 9 months,

If bulbs are used 24 hours per day, change every 6 months.

All bulb replacements should be recorded in the shade booth log book using only MacBeth approved bulbs. The same brand of bulbs should be used to maintain consistency.

Customers will provide specific instructions for viewing shades such as number of plies, direction, face, secondary lighting requirements, matching method (butted versus overlapped), etc.

When evaluating shades, the sample and standard will be placed flat and viewed from a 45 degree angle. Materials with high luster will be viewed by tilting and rotating, providing multiple viewing angles. Metamerism will be assessed by switching from the primary to the secondary light source as defined by the customer during color development. Both supplier’s and customer’s shade matchers must be screened for their ability to see color. No associate wearing tinted glasses or contacts is qualified to match shades.

Spectrophotometric Shade Matching

Although spectrophotometers assure accuracy and dependability, several variables such as measurement technique, instrument drift and maintenance can cause poor results. In order to minimize these effects, the following guidelines should be followed:

Use the CIE L*a*b measurement system.

Always use the largest aperture possible making sure the sample fully covers the opening. The fabric is read at two ply with the warp direction going from side to side. The sample will be relaxed and not stretched or pillowed in the chamber.

The spectrophotometer should be calibrated on a schedule that meets the manufacturer's specifications. These readings are used to determine weekly and monthly variances. Color sort tolerances will be set at + 1.0 for L*a*b.