BS 7344:1990 pdf free download.Specification for Reeled low density polyethylene film for general purpose application.
1 Scope
BS 7344 specifies unprinted low density ( 927 kg/rn3) polyethylene film in the form of sheet or layflat tubing, excluding coextrusions, in the thickness range 25 pm to 300 pm, available in widths up to 2 m (i.e. up to 4 m centre folded). It includes tolerances on the length. width, weight and thickness of the film, and a classification system covering certain basic physical characteristics. BS 7344 excludes special films.
NOTE The titles of the publications referred to in this standard are listed on the inside back cover.
2 Definitions
For the purposes of BS 7344 the following definitions apply.
2.1
yield
area of film per unit mass
NOTE Average thickness is inversely proportional to yield.
2.2
haze
percentage of transmitted light which, in passing through the specimen, deviates from the incident beam by forward scattering. For the purposes of this standard, only light flux deviating by more than 2.5° is considered to be haze
2.3
gloss
ten times the percentage of an incident light beam collected at 135° to the plane of the film, when the incident beam strikes the film at an angle of 45°. The gloss value is expressed in “gloss units”
2.4
clarity
a function of gloss and haze properties
NOTE See Table 3.
2.5
opacity
a function of light transmission; the lower the opacity, the higher the light transmission
NOTE See Table 4.
3 Composition
The polyethylene film shall be manufactured from a base material consisting of polyethylene, or a copolymer in which ethylene is the major constituent.
Polyethylene film intended for the exclusion of light and for maximum resistance to weathering shall be manufactured from a base material containing sufficient finely dispersed carbon black to give the film a light transmittance of less than 1 % (see Appendix A). When determined by BS 2782:Method 823A the numerical rating of the carbon black dispersion shall be 5 or less.
NOTE The material may contain stabilizers, pigments or other additives. For compositions and raw material requirements see BS 3412.
4 Appearance and finish
The film shall be in the form of sheet or layflat tubing.
NOTE I The film may be supplied folded in any form if agreed between the purchaser and the supplier.
NOTE 2 The film should have an appearance conforming with that produced by good commercial practice. It should be as free from gels, streaks, pinholes, foreign matter or undispersed raw material as is commercially possible.
There should be no visible defects such as holes, tears and blisters.
NOTE 3 The film may be treated to promote adhesion if required by the purchaser. e.g. corona surface treatment.
5 Conditioning of test specimens
All samples shall be conditioned at 23 ± 2 °C for not less than 1 h before testing or the measurement of dimensions, and all testing and measurement shall be carried out at 23 ± 2 °C. Polyethylene films are insensitive to changes in the relative humidity of the atmosphere and there is no necessity for the preconditioning of samples to a standard relative humidity.
6 Dimensional tolerances
6.1 Length
The length of film on a reel shall be at least the stated length.
NOTE 1 Where a number of short length reels are supplied the number in any consignment should be subject to agreement between supplier and customer.
In cases of dispute the length shall be determined in accordance with BS 2782:Method 632A.
NOTE 2 For routine testing any method shown to give accurate results may be used to determine the length.
Reels shall contain no more than one break or join per 1 000 m of film. Any such breaks or joins shall be identified by suitable marks on tags visible on the outside of the reel.
The average width of the film shall be within the following deviations from the
stated width. Tubular film and edge-slit film:
up to and including 250 mm width ± 5 mm
above 250 mm width ± 2 %
Trimmed film:
up to and including 350 mm width * 5 mm
above 350 mm width ± 1.5 %.
In cases of dispute the width shall be determined in accordance with BS
2782:Method 632A.
NOTE For routine testing any method shown to give equivalent
results may be used.
6.3 Thickness
6.3.1 Spot thickness
When tested in accordance with
BS 2782:Method 630A, individual spot thickness measurements shall comply with
the spot thickness tolerances given in Table 1.
Sufficient test strips shall be taken from a reel to allow a minimum of 20
measurements to be made and at least two test strips shall be tested.
6.3.2 Average thickness
When tested in accordance with section 1 of BS 2782:Method 631A:1982, the
average thickness measurements on specimens from a reel shall comply with the
average thickness tolerances given in Table 1.
In cases of dispute and for pigmented material the density shall he determined
in accordance with BS 2782:Method 620D.
NOTE For routine testing of unpigmented film the density may be taken as 920
kg/rn1.
6.4 Weight
The net weight of film on a reel shall be at least the stated weight.
6.5 Yield of a consignment of reels
When tested in accordance with section 2 of BS 2782:Method 631A:1982, the yield
of reels in a consignment shall comply with the relev
7 Classification
7.1 The classification system given in 7.2, in which the polyethylene film is classified according to its form, its density and various attributes, shall be used.
7.2 The classification system shall consist of the following elements given in the order presented, with each element separated by a comma:
a) the number and date of BS 7344;
b) the form and description of the material;
S Sheet
T Tubing
N Naturallnot coloured
C Coloured (including white and black not intended for classification B below)
B Black for exclusion of light and maximum resistance to weathering
P P Surface treated for special properties;
C) classifying properties as coded in Table 3.
7.3 An example of a complete classification is as follows. Layflat tubing (T), not coloured (N) surface treated for special properties (P) with an unspecified impact strength (0), a coefficient of kinetic friction of 0.35 (2) and high clarity (3) would have the following classification:
BS 7344:1990, TNP, 023.
8 Marking
Each reel or pallet shall be marked with the following information:
a) the name and/or trade mark of the manufacturer;
b) the full classification of the material’ as described in clause 7;
c) the nominal thickness;
d) the width, length and net weight of the film; e) the batch number and/or order number, or other suitable means of identification.