Process To Manufacture High Opacity Knitted Fabric, The Fabric Produced Thereby And Use Of The Fabric In Vehicles

Abstract

A process is disclosed for decreasing the light transmission of a knitted fabric without reduction of its abrasion resistance. The process comprises the steps of forming a flat circular knitted fabric on a knitting machine and then needling the fabric using a needle punch with an elliptical needle action.

Description

The invention will now be further described, by way of example only, and with reference to the drawings, which are briefly described as:

FIG. 1 is a magnified side elevation of a barbed portion of a needle;

FIG. 2 is a stereo microscope photograph of an unneedled circular knit fabric;

FIG. 2A is a stereo microscope photograph of the fabric of FIG. 2 after 30 000 Martindale cycles;

FIG. 3 is a stereo microscope photograph of the fabric of FIG. 2 after conventional needling;

FIG. 3A is a stereo microscope photograph the fabric of FIG. 3 after 30 000 Martindale cycles;

FIG. 4 is a stereo microscope photograph of the fabric of FIG. 2 after “Hyperpunch” needling; and

FIG. 4A is a stereo microscope photograph of the fabric of FIG. 4 after 30 000 Martindale cycles.

FIG. 1 shows the fabric penetrating part of one of the needles 100 used to needle the circular knit fabric. The needle 100 is a 38-gauge needle and has a pointed end 110 and barbed notches 120 along the length of the needle 100. This “tear drop” needle has six barbed notches 120 along a rib 130 on one side of the needle. The barbed notches are spaced apart 1.35 mm. The pointed end 110 of the needle 100 facilitates the passage of the needle 100 through the yarn or fabric. The barbed notches 120 of the needle 100 pick up or “hook” fibres of the yarns as the needle 100 passes through the yarn or fabric. As the needle 100 continues to pass through the yarn and/or fabric, the fibres previously hooked by the barbed notches 120 of the needle 100 are moved. The directionality of the barbed notches 120 means that they mainly engage yarn fibres during the penetration stroke of the needle 100.

The fabric used in the examples was a circular-knit fabric formed from two yarns of different shades. The darker yarn formed the commercial back of the fabric and the lighter yarn formed the commercial face of the fabric. The dark yarn was a single ply 167 decitex 34 filament RCS Semi Matt Yarn and the light yarn was a double ply 167 decitex 34 filament RCS Semi Matt Yarn.

The circular knit fabric was slit into a flat sheet as shown in FIG. 2. Some of this fabric was retained for testing an unneedled fabric; the remainder was subjected to one of two needling processes, one being conventional needling, and the other being the needling according to the inventive process.

In the case of each process the knitted fabric was fed into a needling machine that needled the fabric by the insertion of a bed of needles into the fabric. The needling machine inserted the needles into the fabric, and withdrew the needles in a direction generally perpendicular to the surface of the fabric. Backing plates provided support to the fabric on the opposite side of the needle bed, and had openings to allow the needles to pass completely through the fabric. The needles could be inserted and withdrawn from either side of the fabric, or from both sides of the fabric. If it was required to make more needle insertions per unit area than could be provided by a single insertion of the bed of needles, then the bed of needles could be inserted more than once per unit area of fabric, or multiple beds of needles could be used. We used a Dilo-Hyperpunch Double Needle Loom (from Dilo GmbH) to needle the fabric. The needle bed contained the type of is needle shown in FIG. 1. The needle bed was constructed so that half of the ribs 130 pointed in one cross-machine direction and the other half pointed in the other cross-machine direction. About 800 needle insertions were made per square centimetre of the fabric when high density needling was used and about 400 needle insertions were made per square centimetre of the fabric when low density needling was used. The fabric was needled from both sides at the same density and with the same type of needles and the same degree of needle penetration. High and low penetration refers to the extent to which the needle penetrates the fabric during needling. For low needle penetrations approximately two of the barbed notches enter the fabric, for high penetration approximately all six of the barbed notches enter.

For the control examples we set the Dilo-Hyperpunch to use a non-elliptical needling motion that had little to no relative motion in the machine direction between the fabric and the needle bed. This was considered to mimic the conventional needling as may have been used in U.S. Pat. No. 2,991,536.

We produced two control samples, one using low needle density and high needle penetration (Control 1A) and another using high needle density and low needle penetration (Control 2A).

The fabric treatment was then repeated, on a new piece of untreated fabric, now using the “Hyperpunch” action. With this action turned on the Dilo-Hyperpunch machine needles with an elliptical needle beam movement. We made two “Hyperpunch” samples using a low needle density: Example 1 using a low penetration depth and Example 1A using a high penetration depth. We also made two “Hyperpunch” samples using a high needle density: Example 2 with low penetration depth and Example 2A using high penetration depth.

Testing Method for Light Transmission

To measure the light transmission of a fabric sample a Hancock's light box was provided with a template over the box to ensure the same measuring position was used for each sample. The template did not transmit light and had a rectangular aperture measuring 70 mm by 70 mm near to its centre. The fabric sample was placed commercial face up over the aperture in the template. A Lux-Meter Testerterm 0500 was positioned with its sensor in contact with the fabric on the opposite side of the fabric from the light source. The light reading was recorded and the sample moved around and re-measured so as to generate a total of 10 light readings per sample. The ten readings were averaged to give the Transmission value for the sample.

Calculation of Opacity Increase

The Opacity increase for an sample was calculated to be the percentage change in light transmission of the fabric sample before and after needling. Thus the higher the opacity the more the light was blocked by the fabric and consequently the less the underlying substrate could be seen through the fabric.

Abrasion Testing

Fabric was tested for its resistance to abrasion damage by using the Martindale method. A 38 mm diameter circular sample of the fabric, as required in DIN EN ISO12947-3 (December 1998), was subjected to controlled abrasion wear by moving the sample under a 795 g load against a flat woollen fabric having a diameter greater than 140 mm and corresponding to the requirements of DIN EN ISO 12947-1 tab 1. The pattern of movement was approximately in the form of a Lissajous figure. After completion of a specified number of cycles, we used 30 000 and 50 000, the samples corresponding to Example 2, Control 2 and the unneedled fabric were compared visually with one another and ranked for their appearance by expert visual assessment.

Table 1 summarises, for the unneedled fabric, the two controls and the four examples according to the invention, the needling process used, including the needle settings, the measured light transmission, the calculated opacity increase and cross refers to the photographs of the samples which were ranked for visual appearance before and after abrasion testing. The visual rankings are recorded in Table 1.

	TABLE 1
	Example
	Unneedled			Example			Example
	fabric	Control 1A	Example 1	1A	Control 2	Example 2	2A
Ref. No.	72-02	72-07	72-10	72-04	72-08	72-03	72-09
Needle Density	—	Low	Low	Low	High	High	High
Needle penetration	—	High	Low	High	Low	Low	High
depth
Transmission value	3256	2724	2984	2261	2386	2606	2260
(lumens)
Opacity Increase %	0	16	8	31	27	20	31
Photo before	FIG. 2				FIG. 3	FIG. 4
abrasion
Photo after	FIG. 2A				FIG. 3A	FIG. 4A
abrasion cycles
Ranking of fabric	1				3	2
before abrasion
Ranking of fabric	2				3	1
after abrasion

The visual ranking of the appearances of Control 2 (FIG. 3), Example 2 (FIG. 4) and the unneedled fabric (FIG. 2) shows that Example 2 had a structure which bore a much closer resemblance to the unneedled fabric than did the conventionally needled Control 2 (FIG. 3). Examination of the stereomicroscope photographs (FIG. 2, FIG. 3, and FIG. 4) enables confirmation of this ranking. The damage caused by the conventional needling (Control 2) is apparent from FIG. 3, broken filaments and dislocated filaments which can easily be damaged by abrasion can be seen.

The visual assessment and ranking was repeated after the Martindale abrasion testing of the samples. We found that the sample needled with the “Hyperpunch” action, Example 2, had the best visual appearance after 30 000 cycles as shown in FIG. 4A. The next best appearance was the untreated fabric (FIG. 2A). The worst performing sample was that which had been conventionally needled (FIG. 3A). Without wishing to be bound by theory it is believed that the damage caused by the needles which is apparent from FIG. 3 results in the very poor abrasion performance seen in FIG. 3A versus FIG. 2A and FIG. 4A. The ranking order remained the same after 50 000 cycles.

From Table 1 it can be seen that in all cases the needled samples exhibited increased opacity compared with the unneedled fabric. Increasing the needle penetration depth caused more restructuring of the fabric and disturbance to fibres than increasing the needle density. This can be seen from the larger increase in opacity between Examples 1 and 1A than the increase in opacity between Examples2 and 2A. It is believed that if the amount of “needling”, as created by a combination of the density and the number of barbs passing through the fabric (the depth) goes beyond an optimum, holes are created in the fabric. The holes allow more light to pass, which reduces the increase in opacity. Example 2A exhibited this problem and the opacity increase compared to Example 2 was lower than might have been expected.

Comparison of the conventionally needled controls with the “Hyperpunch” needled samples indicates that in some instances conventional needling gives a greater increase in opacity or cover than use of the “Hyperpunch” needle action according to the inventive process (Control 2 vs. Example 2), whereas in other instances the “Hyperpunch” process gave a greater increase in opacity than the control (Control 1A vs. Example 1A).

Without wishing to be bound by theory it is thought that the “Hyperpunch” process gives the required restructuring of the fabric to increase opacity, without at the same time breaking too many filaments to destroy the appearance of the fabric surface and reduce its resistance to abrasion damage. This advantage clearly relates to fabrics made from filament yarns to a much greater extent than those made from spun yarns which already have many fibre terminations before needling commences.

Each fabric sample, including the controls, is used to cover vehicle components of varying colours. The fabrics according to the invention exhibit an excellent ability to mask the underlying colour and to therefore overcome the problem of that colour showing through and “discolouring” the fabric as is found with the unneedled sample.

Claims

1. A process for decreasing the light transmission of a knitted fabric without reduction of its abrasion resistance the process comprising the steps of: forming a flat circular knitted fabric on a knitting machine, thenneedling the fabric using a needle punch with an elliptical needle action.

2. A process according to claim 1 in which the fabric comprises filament yarn.

3. A process according to claim 1 or claim 2 in which the fabric has a weight of less than 200 g/m2.

4. A process according to any preceding claim in which the fabric has been needled only once and has a light transmission value of less than 3000 lumens.

5. A process according to any preceding claim in which the needle density is between 400 and 800 per cm2.

6. A process according to any preceding claim in which the needle penetration is such that the number of barbs passing into the fabric per cm2 is between 800 and 4800.

7. A process according to any preceding claim in which the needles are barbed needles with substantially all of the barbs in alignment.

8. A process according to claim 7 in which the needle orientation has the barbs aligned in the cross machine direction.

9. A process according to claim 8 in which approximately half of the needles are aligned with barbs in one cross machine direction and substantially the remainder are aligned with barbs in the opposite cross machine direction.

10. A process according to any preceding claim in which the fabric is heat set after it has been needled.

11. A circular knitted fabric formed from continuous filament yarns which has an average light transmission value, as hereinbefore defined, of less than 3000 lumens and which passes the Martindale 30 000 cycle abrasion test.

12. A fabric as claimed in claim 11 which passes the Martindale 50 000 cycle abrasion test.

13. A fabric as claimed in claim 11 or claim 12 which has a weight of less than or equal to 320 g/m2.

14. A fabric as claimed in claim 13 with a weigh of less than 200 g/m2.

15. A fabric as claimed in claim 14 with a weight of less than 150 g/m2.

16. A fabric according to any one of claims 11 to 15 which comprises twisted continuous filament yarn.

17. A fabric according to claim 16 in which the yarn comprises polyester.

18. Use of a fabric according to any one of claims 11 to 17 as a cover for at least one vehicle component.

19. Use according to claim 18 in which the at least one vehicle component comprises at least one component selected from a seat, a door panel, a bolster and a sun visor.

20. Use according to claim 18 in which the at least one vehicle component comprises at least two different components selected from a seat, a door panel, a bolster and a sun visor.

21. Use according to claim 18 in which the at least one vehicle component comprises at least three different components selected from a seat, a door panel, a bolster and a sun visor.