NONWOVEN SUBSTRATE AND METHOD FOR ITS MANUFACTURE

Description

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to a nonwoven substrate, containing lyocell fibers with a titer of between 1.5 and 1.9 dtex, viscose fibers with a titer of between 1.5 and 1.9 dtex and cellulosic man-made fibers with a stiffening cross-section, in particular either round at more than 2 dtex or multilobal cross-section. It further relates to a method of manufacturing such nonwovens as well as to their use and to wipes containing them.

SUMMARY OF THE INVENTION

The problem to be solved consisted in providing a substrate suitable for wipes, which is completely biodegradable and gives to the wipes the same convenient use characteristics as conventional wipe substrates containing synthetic fiber materials.

DETAILED DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a nonwoven substrate, containing lyocell fibers with a titer of between 1.5 and 1.9 dtex, viscose fibers with a titer of between 1.5 and 1.9 dtex and cellulosic man-made fibers with a stiffening cross-section and with a cut length of between 30 and 70 mm. “Cellulosic man-made fibers with a stiffening cross-section” shall mean—for the purposes of the present invention—fibers with a titer of 2.0 dtex or more and—optionally—a round or multilobal cross-section, in particular with either a round cross-section at more than 2 dtex or a multilobal cross-section

In a preferred embodiment of the present invention, the cellulosic man-made fibers with a stiffening cross-section in the nonwoven substrate show a round cross-section and a titer of between 5.5 and 7.5 dtex. Cellulosic man-made fibers with a round cross-section are available e.g., by the modal and the lyocell process, while the viscose process produces non-round fibers with a kidney-shaped cross-section. Such kidney-shaped cross-section should not be understood as multilobal in the sense of the present invention. “Round” further means that the maximum ovality, i.e., the difference between biggest and smallest outer diameter of the fibers is 20% or less, preferably 10% or less.

In particular, the nonwoven substrate contains 35% to 45% lyocell fibers with a cut length of between 28 mm and 48 mm, 35% to 45% viscose fibers with a cut length of between 30 mm and 50 mm and 15% to 25% cellulosic man-made fibers with a stiffening cross-section with a round cross-section and a cut length of between 50 mm and 70 mm.

Preferably, the cellulosic man-made fibers with a stiffening cross-section according to this embodiment of the invention are lyocell fibers.

In another preferred embodiment of the present invention, the cellulosic man-made fibers with a stiffening cross-section in the nonwoven substrate show a multilobal cross-section and a titer of between 2.5 and 4.5 dtex.

In particular, the nonwoven substrate of this embodiment contains 10% to 20% lyocell fibers with a cut length of between 28 mm and 48 mm, 65% to 75% viscose fibers with a cut length of between 30 mm and 50 mm and 10% to 20% cellulosic man-made fibers with a stiffening cross-section with a cut length of between 30 mm and 50 mm.

Preferably, the cellulosic man-made fibers with a stiffening cross-section according to this embodiment of the invention are viscose fibers. Mulitlobal viscose fibers with a stiffening cross-section may be manufactured according to EP 1606439 A1. Such fibers are commercially available from Lenzing Aktiengesellschaft, Lenzing, Austria.

Preferably the nonwoven substrate according to the invention shows a cross direction tensile strength of at least 17 N/5 cm, preferably at least 20 N/5 cm, in dry stage before converting. Preferably the nonwoven substrate according to the invention shows a lotion consumption of less than 5 ml/wipe.

Preferably the nonwoven substrate according to the invention shows an elongation of less than 25%/5 cm in MD (machine direction) For example it may show 13.6%/5 cm, which is about 60% less than standard viscose/polyester or viscose/polypropylene blends, and less than 130%/5 cm in CD (Cross direction). For example, it may show 103.1%/5 cm which is about 40% less than standard viscose/polyester or viscose/polypropylene blends. These properties were determined according to the test method NWSP 110.4.R0 (15) [EN]. This property profile provides more dimensional stability in the nonwoven substrate and therefore less process variations needed during further converting steps, as well as an easier dispensing and consumer usage. Furthermore, it gives to the material more of a “textile feel” instead of the typical “synthetic” feeling of touching a nonwoven material.

Another object of the present invention is a method for the manufacture of a nonwoven substrate—in particular a nonwoven substrate according to the present invention—, comprising the following sequence of steps in an inline process:

a. Providing lyocell fibers with a titer of between 1.5 and 1.9 dtex, viscose fibers with a titer of between 1.5 and 1.9 dtex and cellulosic man-made fibers with a stiffening cross-section with a cut length of between 30 and 70 mm,

b. opening and mixing all 3 fiber types of step a. until getting a homogeneous fiber fleece,

c. carding the fiber fleece through a conventional commercial carding equipment,

d. condensing the carded fiber fleece into a 30 to 70 g/m² XYZ orientated fiber fleece (dry nonwoven web, 2 to 6 layers),

e. conveying this dry nonwoven web into a spunlacing unit for applying a high pressure hydro-entanglement,

f. conveying the nonwoven web through a dewatering unit and

g. through a drying unit to removing moisture until natural moisture level of the fibers (10%+/−1%),

h. winding the nonwoven web into a “mother roll” form, wherein in the spunlacing unit (step e.) Z consolidation and nonwoven surface embossing are performed by 4 or more high pressure jet beams.

Condensing is the last action on card exits in order to randomize fibers in XYZ directions and deliver a fiber layer at a given basis weight onto the next conveyor belt. Spunlace lines usually have 1 to 3 cards, each card having 1 to 2 exits, each exit delivering 1 layer. The invention works with minimum 1 card/2 layers, and in practice could work also with up to 3 cards/6 layers. Cards without condensors exist but would not be able to give similar thickness nor CD tensile strength. Preferably the carded fiber fleece is condensed into a 45 to 55 g/m² XYZ orientated fiber fleece and even more preferably into a 47 to 53 g/m² XYZ orientated fiber fleece.

Yet another object of the present invention is the use of the nonwoven substrate as described above for the manufacture of wipes, in particular wet wipes packed in cross-folded wipe packs, showing a wipe dispensing of less than 2 missed dispensings per 22 wipes.

A further object of the present invention are wipes, showing a wipe dispensing of less than 2 missed dispensings per 22 wipes, which are containing a nonwoven substrate—in particular a nonwoven substrate according to the present invention—, containing lyocell fibers with a titer of between 1.5 and 1.9 dtex, viscose fibers with a titer of between 1.5 and 1.9 dtex and cellulosic man-made fibers with a stiffening cross-section and with a cut length of between 30 and 70 mm. In a preferred embodiment of the present invention these wipes are wet wipes.

The invention will now be illustrated by examples. These examples are not limiting the scope of the invention in any way. The invention includes also any other embodiments which are based on the same inventive concept

Examples

Methods:

The Cross Direction Tensile strength was measured before converting at a dry stage with test method EN ISO 9073-3/NWSP 110.4.R0, using a Zwick/Zwicki 1120 (Q427F144) device.

Elongation in MD (machine direction) and CD (Cross direction) were measured according to test method NWSP 110.4.R0 (15) [EN], using a Zwick/Zwicki 1120 (Q427F144) device.

Bulkiness/thickness was measured according to test method NWSP 120.6.R0 (15) [EN], using a Rainbow-Schroder, Q161 F835 device.

Lotion migration was evaluated as follows: Wipe packs are stored 8 weeks after production in a dark place under defined conditions (NWSP 003.0.R0 (15)/23° C. (+/−2° C.)/50% (+/−5%) relative moisture). Then the pack is opened and the top wipe and the bottom wipe are weighed. The moisture difference is calculated in grams and %.

Missed Dispensing was evaluated as follows: Wipe by wipe is pulled out of the pack, like a consumer does. One mistake is counted when pulling more than one wipe at a time.

Dispensing feel was evaluated as follows: this is a panel test method where consumers pull the wipes out of the pack with low finger force (easy), or it feels “sticky” and you need several attempts to grab one wipe and then need higher finger force to pull it out of the pack.

The wicking rate was measured according to PAL 255 ISO 9073-6 [DE] resp. NWSP 010.1.R0 (15) [EN] in machine direction (MD) and cross direction (CD).

Opacity was determined with a Konica Minolta spectrophotometer under the following conditions: Calibration according to the manufacturer's manual, samples dried, observation angle 10°, wavelength 570 nm, light mode C, measuring head without glass.

Test material was produced according to the process of the invention. All cellulosic fiber types are commercially available fiber types and were obtained from Lenzing Aktiengesellschaft, Lenzing, Austria. CLY means lyocell fibers, CV means viscose fibers of conventional cross section, CY means viscose fibers with trilobal cross section. Polyester fibers (PET) and trilobal polypropylene (PPT) fibers were commercially available products, as well.

General Manufacturing Process:

Nonwoven substrates were produced as follows:

Step #1) opening and mixing all 2 or 3 fiber types until getting a homogeneous fiber fleece, then

Step #2) carding the fiber fleece through a conventional commercial carding equipment,

Step #3) condensing the carded fiber fleece into a 47 to 53 g/m² XYZ orientated fiber fleece (dry nonwoven web), then

Step #4) conveying this dry nonwoven web into a spunlacing unit with high pressure hydro-entanglement with 4 high pressure jet beams for Z consolidation and—for the respective samples for nonwoven surface embossing, then

Step #5) conveying the nonwoven web through a dewatering unit and then

Step #6) through a drying unit to removing moisture until natural moisture level of the fibers (10%+/−1%), then

Step #7) winding the nonwoven web into a “mother roll” form.

Step #8) unwinding and converting the nonwoven roll “mother roll” into packs of wet wipes, through cross-folding or inter-folding or any other wet wipe converting equipment.

All production steps 1 to 7 were made in one run (inline process).

The basic composition and properties of the samples are show in Table 1. Samples 1, 2, 15 and 16 are comparative samples according to the state of the art. The dimensions of fibers, like e.g., “1.7/38” means “1.7 dtex/38 mm cut length”.

TABLE 1
Composition of the samples

	weight
Sample	[g/m2]	Blend	Structure

1	50	20% CLY 1.7/40-40% PET 3.3/40-40% PPT 1.0/40	Embossed
2	40	20% CV 1.7/40-80% PPT 1.0/40	Embossed
3	50	40% CLY 1.7/38-40% CV 1.7/40-20% CLY 6.7/60	Embossed
4	50	40% CLY 1.7/38-40% CV 1.7/40-20% CLY 6.7/60	Flat
5	50	40% CLY 1.7/38-40% CV 1.3/38-20% CLY 6.7/60	Flat
6	50	40% CLY 1.7/38-40% CV 1.3/38-20% CLY 6.7/60	Embossed
7	50	15% CLY 1.7/38-70% CV 1.7/40-15% CY 3.3/30	Embossed
8	50	15% CLY 1.7/38-70% CV 1.7/40-15% CY 3.3/30	Flat
9	40	40% CLY 1.7/38-40% CV 1.7/40-20% CLY 6.7/60	Flat
10	40	40% CLY 1.7/38-40% CV 1.7/40-20% CLY 6.7/60	Embossed
11	40	40% CLY 1.7/38-40% CV 1.3/38-20% CLY 6.7/60	Embossed
12	40	40% CLY 1.7/38-40% CV 1.3/38-20% CLY 6.7/60	Flat
13	40	15% CLY 1.7/38-70% CV 1.7/40-15% CY 3.3/30	Flat
14	40	15% CLY 1.7/38-70% CV 1.7/40-15% CY 3.3/30	Embossed
15	50	100% CV 1.7/40	Flat
16	50	20% CV 1.7/40-80% PET 1.7/38	Flat

Bulkiness/Thickness:

40-50 g/m² embossed substrates, with fiber blends according to the invention with 10-20% CY or with 15-25% CLY 6.7/60 combined with carded spunlacing production process according to the general manufacturing process described (samples 3, 6 and 7) above achieve similar or better thickness (>0.65 mm) compared to the same nonwoven substrate made of 100% cellulosic blends of other fibers—flat and embossed—(samples 4, 5 and 8), and a result of 0.15 mm additional thickness compared with the same nonwoven substrate made of 100% standard viscose (sample 15) at a thickness of 0.5 mm (see FIG. 1).

40-50 g/m² flat substrates, with Fiber blends according to the invention with 10-20% CY combined with carded spunlacing production process according to the general manufacturing process described (sample 8) above achieve similar thickness (0.6 mm) compared with commonly used flat substrate 50 g/m² 20% CV 1.7/40-80% PET 1.7/38 (sample 16).

Lotion Holding and Lotion Distribution:

Void volume was calculated according to the formula:

(average thickness [mm]×1 m²)−(basis weight [g/m²]×fiber density)

Lotion pickup was measured as follows: There is no industry standard to define lotion pickup. For the evaluation a 180×200 mm substrate format was used. We started with the standard 5.7 ml/wipe (for CV/PET substrate) and reduced to 4.8 ml/wipe (i.e., 15.8% less lotion consumption). Ideal lotion consumption was evaluated by 1.) looking at converting efficiency (machine jams if wipe too saturated or too dry; this is more or less a go/no go-effect) and 2.) by “touch” (the wipe should not feel dry nor spongeous, but somewhere in between; this is a subjective evaluation, however widely used in the industry, nearly like a standard).

With similar void volume (see FIG. 2) than benchmark substrate (sample 16), and much higher capillarity force, lotion pickup during converting has been reduced from standard 5.7 ml/wipe to 4.8 ml/wipe, i.e., 15.8% less lotion consumption occurs with the substrates according to the invention.

Lotion Migration:

Lotion migration is a well-known effect appearing inside a flow pack or a canister of wipes, where the lotion migrates over time to the bottom of the packaging through gravity. As a frustrating consequence for the consumer, wipes on top feel “dry” and wipes at bottom feel “spongeous”.

Fiber blends according to the invention with 10-20% CY show high wicking rate combined with high void volume (Table 2 and FIG. 2) compared with comparative samples containing synthetic fibers. The same was found for fiber blends according to the invention with 15-25% CLY 6.7/60 if the substrate was embossed. The comparative samples 1 and 2 during the test methods did not pick up the liquid but stayed at the surface of the liquid. This provides following advantages of the fiber blends according to the invention:

• • A homogeneous moisture management, i.e., a homogeneous spread of lotion, together with the inherent capillarity properties of the CY fiber, helps for lotion retain in the packaging over time, and therefore limits drastically lotion migration: after 8 weeks storage, there is only 4-8% moisture difference (in weight) between the top wip Nonwoven substrate, containing lyocell fibers with a titer of between 1.5 and 1.9 e and the bottom wipe with the fiber blends according to the invention, versus 21% for the comparative samples at 70% to 80% synthetic fibers. Measurements were made on packs containing between 20 and 23 cross-folded wipes—see Table 3.
  • Less variation in wiping efficiency from the top wipe to the bottom wipe.
  • Less variation in dispensing (see also the evaluation of wipe dispensing below)

TABLE 2
Wicking length

x

cv

x

cv

x

cv

x

cv

x

cv

x

cv

x

cv

x

cv

Sample

10 s

[%]

30 s

[%]

60 s

[%]

300 s

[%]

10 s

[%]

30 s

[%]

60 s

[%]

300 s

[%]

1
2
3	55	5	78	3	94	4	143	2	42	2	61	3	76	5	116	2
4	57	2	84	2	105	3	164	1	43	4	61	5	76	3	120	2
5	59	3	87	3	112	2	174	3	45	3	67	3	88	2	135	1
6	55	3	83	2	102	2	162	1	40	4	57	4	73	2	114	2
7	56	2	84	2	105	1	171	1	42	2	61	1	76	2	121	1
8	55	2	84	2	107	2	173	3	41	0	62	2	79	3	131	1
9	54	2	79	1	98	3	150	1	37	3	53	3	65	3	101	2
10	48	3	70	2	86	2	130	0	35	2	47	1	57	2	84	4
11	50	2	73	3	91	1	145	2	36	2	50	1	65	3	98	1
12	51	5	77	4	98	4	152	3	39	3	54	5	67	1	103	2
13	57	1	85	3	106	1	169	0	43	2	62	3	77	2	122	2
14	56	2	78	1	95	2	152	2	36	4	53	3	65	2	100	1

Wipe Dispensing:

“Dispensing” is a word commonly used in the nonwoven industry for describing the action of a consumer pulling a dry or wet wipe out of a flow pack or a canister. Depending on the nonwoven substrate characteristics, wipe dispensing can be perceived as “easy”, versus “painful” or “upsetting” by the consumer, which is a key driver for consumers to choose the right product.

Lotion holding and lotion distribution, lotion migration and elongation, together with the fact that CY fibers provide uneven surface, are key factors to improve air permeability of the wipes. The same was found for fiber blends according to the invention with 15-25% CLY 6.7/60 if the substrate was embossed. This improved wipe-to-wipe airflow management decreases the wipe-to-wipe surface tension, and therefore ease the dispensing action (see Table 3). “Missed Dispensing” means that by a single pulling trial 2 or more wipes were pulled at a time, or the pulled wipe breaks. “Dispensing feel” describes the consumer feeling by pulling out, evaluated by a panel of several average consumers.

TABLE 3
Lotion migration and dispensing

	Top	Bottom	Lotion migration after	Missed	Wipe	Missed	Dispensing
Sample	wipe [g]	wipe [g]	8 weeks ([g], [%])	Dispensing	count	Ratio	feel

1	7.60	9.17	1.57	21%	1	22	4.5%	easy
2	6.02	7.53	1.51	25%	1	21	4.8%	easy
3	6.83	7.58	0.75	11%	0	21	0.0%	easy
4	7.24	7.94	0.70	10%	1	22	4.5%	sticky
5	7.46	7.32	−0.14	−2%	0	23	0.0%	sticky
6	7.25	7.32	0.07	1%	0	23	0.0%	easy
7	7.28	7.70	0.42	6%	1	21	4.8%	easy
8	6.76	6.23	−0.53	−8%	2	23	8.7%	easy
9	6.64	7.14	0.50	8%	1	22	4.5%	difficult
10	6.10	6.88	0.78	13%	0	22	0.0%	easy
11	6.12	6.82	0.70	11%	0	22	0.0%	easy
12	6.74	6.90	0.16	2%	0	22	0.0%	difficult
13	6.49	6.75	0.26	4%	2	20	10.0%	difficult
14	6.50	6.77	0.27	4%	0	22	0.0%	easy

Elongation:

Fiber blends according to the invention with 10-20% CY combined with a carded spunlacing production process according to the general manufacturing process described above achieve an average elongation of 17.4%/5 cm in MD (machine direction), which is about 60% less than standard viscose/polyester or viscose/polypropylene blends, and 102.3%/5 cm in CD (Cross direction), which is about 40% less than standard viscose/polyester or viscose/polypropylene blends. The same was found for fiber blends according to the invention with 15-25% CLY 6.7/60.

This provides more dimensional stability in the nonwoven substrate and therefore less process variations during further converting steps, as well as an easier dispensing and consumer usage (textile feel).

Opacity:

Opacity is one of the strongest attributes of a wipe substrate for consumers. Many consumer panel tests show high opacity wipe substrates perceived as “strong” and/or “high quality”.

Fiber blends according to the invention with 10-20% CY (Sample 4) provide higher opacity to the substrate (see FIG. 2) compared to other cellulosic blends and close to the opacity of the benchmark substrate with synthetic fibers (Sample 1).