EP0388072A2

EP0388072A2 - Improved needling process

Info

Publication number: EP0388072A2
Application number: EP19900302428
Authority: EP
Inventors: Anthony Thomas Greatorex; Albert Harding
Original assignee: Emhart Materials UK Ltd; TEXON FOOTWEAR INVESTMENTS Inc
Current assignee: TEXON FOOTWEAR INVESTMENTS INC.; Emhart Materials UK Ltd
Priority date: 1989-03-14
Filing date: 1990-03-07
Publication date: 1990-09-19
Also published as: EP0388072A3; GB8905789D0

Abstract

A method of strengthening and/or densifying a non-woven batt which comprises at least 5% by weight of melt or bicomponent fibres by a combination of thermal and mechanical bonding is described. Thermal and mechanical bonding are carried out in a single operation, by needling the non-woven batt in a needleloom provided with barbed or forked needles, at an elevated temperature of at least the softening temperature of the melt or bicomponent fibres. The properties of the non-woven batt which has been strengthened and/or densified by the method according to the invention can be adapted as required by varying the processing conditions.

Description

The present invention relates to a method of strengthening and/or densifying a non-woven batt by a combination of thermal and mechanical bonding.
It is known to carry out both thermal, or fusion, bonding and mechanical bonding, or needling, on a non-woven batt during felt making. These are separate operations which are carried out on separate pieces of equipment. It is not practicable to needle a felt after fusion bonding, because the bonded fibres cannot move in the felt without breaking themselves or the bond. In the known method, fusion bonding is carried out after needling. It is a disadvantage of the known method that the operations have to be carried out as two separate operations, which leads to inefficiency and increased capital costs, and limits the effects which are available.
It is an object of the present invention to provide a method of strengthening and/or densifying a non-woven batt, by a combination of thermal and mechanical bonding, in which the disadvantages of the known methods are reduced or substantially obviated.
The present invention provides a method of strengthening and/or densifying a non-woven batt comprising at least 5% by weight of melt or bicomponent fibres by a combination of thermal and mechanical bonding, characterised in that thermal and mechanical bonding are carried out in a single operation, by needling the non-woven batt in a needleloom provided with barbed or forked needles, at a temperature of at least the softening temperature of the melt or bicomponent fibres.
The fibre stock from which the non-woven batt is produced may contain a single fibre or blend of fibres, comprising bicomponent or melt fibres at a percentage of from 5% to 100% of the total. Bicomponent fibres are synthetic fibres comprising two components, one with a relatively low melting or softening point, and the second with a relatively high melting or softening point. Such bicomponent fibres may be in the form of a sheath with a relatively low melting or softening point surrounding a core with a relatively high melting or softening point, or in a side by side design in which the sheath does not completely surround the core.
By using the method according to the invention, there is an improvement in efficiency and a reduction in capital expenditure. It is also possible to achieve effects which cannot otherwise be obtained.
In particular, it is an advantage of the method according to the invention, that the particular effects of the operation can be controlled by adjusting the needle punch density, temperature, needle type, needle penetration, fibre type and the proportion of fusible fibres added.
Thermal bonding can be concentrated on one or both surfaces of the felt, or throughout the material, depending on the method of heating used.
It is a further advantage of the method according to the invention is that the effect of changing settings can immediately be assessed, without awaiting the results of a further operation to check if the changes have produced the desired effect.
It is also an advantage of the method according to the invention, that the movement of fibres while needling with barbed needles at or above the softening temperature of the melt polymer, or the relatively low melting or softening polymer in the case of bicomponent fibres will create more fibre crossover points and provide greater felt reinforcement.
It is additionally found that the felt width loss associated with some fibres at elevated temperature, is minimised due to the holding effect of the needling operation.
Non-woven batts are used for a number of applications, both with and without further treatment. Without further treatment, non-woven batts produced according to the invention are particularly suitable for use as absorbents, for example as industrial wipes. The non-woven batts produced according to the invention are also particularly suitable for further processing, for example impregnation and/or coating, to produce non-woven materials for use, for example, in shoe-making. The increased mechanical strength of the non-woven batts produced according to the invention, compared to conventionally produced non-woven batts, means that they can be subjected to such further processing without any deleterious effects.
The method according to the invention may be carried out in a conventional needleloom, which has been modified to apply heat.
The loom may needle either from above or from below, or may provide a conbination of these two. It may have one or more heads and any or all of these may be used at elevated temperatures.
Heat is applied during the needling process by one or more of the following, depending on the effect to be created. The bedplate may be heated by means of one or more flat heaters bolted across the width, the stripper plate may be similarly heated or hot air may be applied under the bedplate or above the stripper plate or by enclosing the needling operation in a hot air chamber.
The needleloom may be adjusted using the conventional adjustments of needle punch density, penetration, stripper gap, head speed and throughput.
The method according to the invention is carried out using barbed or forked needles. Barbed needles comprise a blade portion at the end of the needle remote from the needle board. In the conventional barbed needle, the blade portion is triangular in cross-section, and provided with barbs arranged spirally around the blade, at the angles of the triangular cross-section. The barbs are cut or pressed from the blade portion. Needles with alternative arrangements of barbs and different cross-sections are produced, and these can also be used in the method according to the invention, to achieve special effects.
The processing temperature can be adjusted to suit the type of bonding fibre to be used and the effect to be produced on the felt. Surface smoothing and reinforcement is effected by heating the bed and/or stripper plates while a more penetrating effect is achieved by using hot air above and/or below the felt.
The fibre batt is introduced into the loom in the normal way. The fibre blend will contain a percentage of bicomponent or melt fibres which may be between 100% and 5% of the total.
Suitable melt fibres for use in the method according to the invention include polypropylene and low melt polyesters.
Suitable bicomponent fibres include those which have a polypropylene sheath surrounding a polyester core; those with a relatively low melt polyester sheath and a relatively high melt polyester core and those with a relatively low melt nylon sheath and a relatively high melt nylon core.
The temperature to which the fibre is heated in the method according to the invention depends upon the softening temperature of the particular fibre used. Details of softening or melt temperatures for particular fibres are available from the technical specifications of the manufacturers of the fibre.
The heating may be arranged so that some needling is carried out at ambient or below the desired fusing temperature, and the final needling is carried out at or above the fusing temperature. The non-woven batt may alternatively be partially fused by heating, before needling is carried out.
The method according to the invention will now be further described with reference to the accompanying drawing, which shows an embodiment of a needleloom adapted to carry out the method according to the invention.
The drawing shows a standard laboratory scale needleloom which has been adapted so that it can be used to carry out the method according to the invention.
The loom 10 comprises a bedplate 12 and a stripper plate 14, which together define a gap 16 through which material to be needled is conveyed. The loom 10 further comprises a reciprocating loom head 18 on which is mounted a needleboard 20, comprising a plurality of barbed or forked needles 22, arranged in an array. Corresponding arrays of holes 24, 26 are arranged in the bedplate 12 and the stripper plate 14 respectively, to allow the needles to pass through the plates as the needleboard is raised and lowered in the direction shown by the arrow 28.
The loom 10 is further fitted with a hot air chamber 30, located underneath the bedplate 12. The hot air chamber 30 can be supplied with air at elevated temperature via ducting 32 and means (not shown) are provided to supply air, the temperature and flow of which are variable depending on the heating effect required. The loom 10 is provided with a hood 33 to help maintain an elevated temperature during needling.
The loom 10 is provided with endless belts 34, 36, driven, by rollers 38, 40 which convey material to be needled in the needleloom. Guide rollers 42, 44 are located adjacent to the entrance and exit of the loom respectively, to guide the material as it enters and leaves the loom.
In operation, material to be needled is conveyed by the endless belts 34, 36 and the guide rollers 42 into the loom via the gap 16. Hot air is passed through the ducting 32 into the hot air chamber 30 to heat the bedplate 12, stripper plate 14 and needleboard 20 with needles 22, and surrounding atmosphere. As the material passes through the heated loom for needling, there is an increase in the temperature of the material.
The following examples were carried out in a needleloom as shown in the accompanying drawing.

Example 1

A non-woven fibre batt having a batt weight of 136g/sq metre was prepared from a fibre blend of 80% by weight high melt polyester and 20% by weight low melt polypropylene. The high melt polyester used was Trevira Type 290, manufactured by Hoechst, having a gauge of 1.7 dtex and a staple length of 60 mm. The polyester has a softening temperature above 220°C. The low melt polypropylene used was Montefibre Polypropylene manufactured by Montiedison, having a gauge of 2.5 dtex and a staple length of 40 mm, and a softening point of 150°C. The batt was needled on a laboratory scale DILO needleloom, 600 mm wide, with 2000 needles per linear metre width.
The needles used were conventional 40 gauge regular barbed needles. The batt was first subjected to a tacking pass, without heat, at a needle punch density of 30 punches per square centimetre, with a penetration of 9 mm. The batt was then needled with a needle punch density of 150 punches per square centimetre, to a penetration of 10 mm. The needleloom was heated with hot air at a temperature of 180°C.
As can be seen from the test results in the Table, the resultant felt had increased density and mechanical strength, compared to a conventionally needled felt. The dimensional stability was improved.

Example 2

A non-woven fibre batt having a batt weight of 156g/sq metre was prepared from a fibre blend of 80% by weight of the high melt polyester used in Example 1 and 20% by weight of a low melt polyester, Wellbond 4080, manufactured by Wellman, having a gauge of 4.4 dtex and a staple length of 51 mm. The polyester had a softening temperature of 110°C. The batt was needled on a laboratory scale DILO needleloom 600 mm wide, with 2000 needles per linear metre width.
The needles used were conventional 40 gauge regular barbed needles. The batt was first subjected to a tacking pass, without heat, at a needle punch density of 30 punches per square centimetre, with a penetration of 9 mm. The batt was then needled with a needle punch density of 150 punches per square centimetre, to a penetration of 10 mm. The needleloom was heated with hot air at a temperature of 130°C.
As can be seen from the test results in the Table, the resultant felt had increased density and mechanical strength, compared to a conventionally needled felt. The dimensional stability was improved and the felt was particularly well bonded, and was suitable for use either as a finished product or for further processing.

Example 3

The non-woven batt used in Example 2 was needled on a laboratory scale DILO needleloom, 600 mm wide, with 2000 needles per linear metre width.
The needles used were conventional 40 gauge regular barbed needles. The batt was first subjected to a tacking pass, without heat, at a needle punch density of 30 punches per square centimetre, with a penetration of 9 mm. The batt was then needled with a needle punch density of 150 punches per square centimetre, to a penetration of 5 mm. The needleloom was heated with hot air at a temperature of 180°C.
In comparison to the felt produced in Example 2, the felt produced had increased loft. It was particularly suitable for use as an insulating or wadding felt. TABLE

Gauge (mm) Weight (gsm) Density (g/cc) Load at 20% ext N/cm)

Example 1

Control (Un-needled) 2.6 148 0.056 0.22

Test 2.2 132 0.060 0.37

Example 2

Control (Un-needled) 2.2 144 0.065 0.24

Test 1.8 151 0.084 2.45

Example 3

Test 3.4 173 0.051 n/a

Claims

1. A method of strengthening and/or densifying a non-woven batt comprising at least 5% by weight of melt or bicomponent fibres by a combination of thermal and mechanical bonding, characterised in that thermal and mechanical bonding are carried out in a single operation, by needling the non-woven batt in a needleloom provided with barbed or forked needles, at an elevated temperature of at least the softening temperature of the melt or bicomponent fibres.

2. A method as claimed in claim 1, characterised in that the fibre stock from which the non-woven batt is produced comprises bicomponent or melt fibres at a percentage of from 5% to 100% of the total.

3. A method as claimed in claim 2, characterised in that the melt fibres are polypropylene or low melt polyester fibres.

4. A method as claimed in claim 2, characterised in that the bicomponent fibres have a polypropylene sheath surrounding a polyester core, a relatively low melt polyester sheath surrounding a relatively high melt polyester core or a relatively low melt nylon sheath surrounding a relatively high melt nylon core.

5. A method for the strengthening and/or densifying of a non-woven batt substantially as herein described with reference to the Examples.

6. A method for the strengthening and/or densifying of a non-woven batt substantially as herein described with reference to the accompanying drawing.

7. A non-woven batt which has been strengthened and/or densified by a method as claimed in any of claims 1 to 6.