WO1992004491A1

WO1992004491A1 - A process for preparing a unidirectional fiber web, the use thereof for preparing unidirectional composite materials

Info

Publication number: WO1992004491A1
Application number: PCT/EP1991/001748
Authority: WO
Inventors: Jean Pierre Thibaudeau; Hubert François Marie DE RANCOURT
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1990-09-10
Filing date: 1991-09-10
Publication date: 1992-03-19
Also published as: EP0548198A1; JPH06500831A; GB9019774D0

Abstract

A process for preparing a unidirectional fiber web is disclosed, which comprises disposing several rovings side by side, each having a plurality of individual fiber filaments, and needling transversally said rovings, thereby opening the rovings and forming a continuous fiber web therefrom. This continuous unidirectional fiber web can be used for preparing unidirectional composite materials through a wet method.

Description

A process for preparing a unidirectional fiber web, the use thereof for preparing unidirectional composite materials

The present invention essentially relates to a process for preparing a unidirectional fiber web, a unidirectional continuous fiber web obtained thereby, the use thereof for preparing unidirectional composite materials and unoirectional composite materials optained thereby.

In the p r i o r art, attempts have been made to manufacture unidirectional composites containing a layer of unidirectional fiber layer impregnated with a resin. An example of this prior art is JP-A-60-44344.

However, the processes of the prior art are complicated, thus costly, and cannot be easily adapted to the preparation of composite materials naving a wide range of properties.

Therefore, a main purpose of the present invention is to solve the technical problem of providing a unidirectional fiber web which can be adapted to a wide range of width, thickness, mechanical properties, in a reliable manner.

Another main purpose of the present invention, is to solve the technical problem of preparing unidirectional fiber webs, which can be used in the manufacture of unidirectional composite materials naving wide mecnanical properties while being adapted to the manufacture of said composite materials through a wet process, according to t he traditional paper technology.

A furtner main purpose of the present invention is to solve the technical prcolem of providing a unidirectional fiber web, which is well adapted to the manufacture of laminated unidirectional composite materials comprising a wide type of thermoplastic resin and of reinforcing materials, thereby increasing the versatility of the use of said composite materials.

All thes technical problems are solves simultaneously for the first time with the present invention according to a simple, reliaple and low costly solution, which is therefore usable at industrial level, and notably in traditional paper making plants.

Thus, in a first aspect, the present invention provides a process for preparing a unidirectional fiber web comprising disposing several rovings side by side, each having a plurality of individual fiber filaments, and needling transversally said rovings, thereby opening the rovings and forming a continuous fiber web therefrom. The continuous fiber web is obtained through overlapping of filaments of adjacent rovings.

According to a specific embodiment, said rovings comprise thousands of individual continuous fiber filaments bundling together.

According to another specific embodiment, said needling is performed with hundreds of needles, each needle having an enlarged basis and being provided on the lateral surface thereof with protuberances, such as spikes.

According to another specific embodiment, the rovings are continuous fiber glass rovings. Said rovings have preferably a width of some millimetres, for instance about 5 millimetres and the continuous fiber filaments have a diameter ranging between 10 and 50 micrometres, preferably between 15 and 25 micrometres.

According to another specific invention embodiment, the needling provides an opening of the rovings from 2 to 6 times the width of the initial roving width.

According to another specific invention embodiment, the needling is performed so as to reach a continuous unidirectional fiber web having a weight ranging between 50 and 1000 g/m², more preferably from 500 g/m ² to 700 g/m².

According to a second aspect, the invention also relates to a continuous unidirectional fiber web, which has been obtained from several rovings laid side by side and needled.

According to a third aspect, the present invention relates to a process for preparing unidirectional composite material, comprising preparing a unidirectional fiber web and sandwiching this unidirectional fiber web between at least one reinforced thermoplastic sheet through a web process.

Acccrcing to a specific process embodiment, said reinforced thermoplastic layer is laid en either side of the unidirectional fiber web on an inclined wire at the bottom part or at an intermediate part thereof.

Typically, the composite structure will be found by sandwiching the above-said unidirectional continuous fiber web between two outer layers of reinforced thermoplastic sheets.

Acccrαing to another emooαiment, two layers of unidirectional continuous web can be sandwiched between two outer layers of reinforced thermpplastic sheets. Of course, many comoinations of sheets can be performed at will.

According to a given embodiment, the thermoplastic material of the reinforced thermoplastic sheet can be selected from a polyolefine, in particular polyethylene, polypropylene and copolymers thereof, polyvynyl chloride, polystyrene and copolymers, polyamide, saturated polyesters, polyetnylene ether, a polycarbonate and any plastic alloy. A most preferred thermoplastic resin is polypropylene.

Preferably, the thermoplastic material is supplemented by a coupling agent which in the final product improves contact between the thermoplastic and the reinforcing material. Preferred coupling agents are acid or anhydride functionalized thermoplastics such as alpha, beta unsaturated carboxylic acid functionalized thermoplastics. One such example is maleic or itaconic anhydride grafted polypropylene.

The thermoplastic resin is advantageously under powder form having a mean particle size ranging between 200 micrometres and 1,000 micrometres, more preferaoly between 300 and 1,000 micrometres.

According to another specific embodiment, the reinforcing material of the thermoplastic composite is under fiber form and is selected from glass fibers, carbon fibers, ceramic fibers, boron fibers, glass wool, rock wood, metallic fibers, hot melt organic synthetic fibers, notably aromatic polyamide, polyesters and others. The length of the reinforcing fibers preferably ranges between 5 mm and 25 mm, and the diameter between 5 and 20 micrometers.

According to another specific invention embodiment, the reinforced thermoplastic composite sheets are prepared through a wet process according to the traditional paper making technology, from a dilute slurry, preferably having from 0.1 to 5 % by weight dry content, fed preferably onto an inclined wire.

According to a most preferred embodiment, the slurry composition, on a dry content basis, of the thermoplastic composite sheet, comprises :

- thermoplastic resin under powder form 40 - 78 %

(preferably 45 - 75%, most preferably 49 - 55%) - coupling agent 1 - 20 % - reinforcing fibers 15 - 40 % - dispersant 0.1 - 10 %

(with respect to reinforcing fibers) - optionally flocculent 0.25 - 1 % - anti-oxidant 0.1 - 2 %

Optionally, the slurry composition can contain a polyolefine pulp in a content from 2 to 20 %/

According to a specific embodiment, each thermoplastic composite sheet has a basis weight which ranges between 400 g/m² and 5 kg/m², and more preferably from 800 to 5000 g/m², and most preferably around 2800 g/m².

The general needling conditions of the continuous fiber rovings are as follows :

The unidirectional fiber web according to the invention can be prepared from a continuous mineral roving, for instance a continuous fiber glass roving commercially available from Owens Corning Fiberglas Europe under the reference R16 EX3, having a 5 mm width, 2400TEX (g/1000 m), each filament having a diameter of 24 microns. This roving is composed of thousands of individual continuous fiber glass filament bundling together. Additional sizing is added by the fiber glass suppliers so that to ensure these filaments can stay bundled together.

A needling machine commencially available, for instance from Asselin machine, usually used to produce non-woven can typically be provided with needles supplied by Singer reference 15*18*36/3.5BL 30A610 of triangular shape with protuberances such as spixes on each side of needle, said needle being held by a holder up to 4 metres wide. The principle of said needling machine is represented in the appended figures 1 and 2.

In figure 1, it is shown schematically the needling machine under reference number 10, which is fed with a plurality of continuous fiber rovings referenced 12 unrolled from rolls 14.

After the needling, at the outlet of the needling machine 10, it is obtained a continuous unidirectional fiber web 16.

In figure 2, it is shown a partial enlarged view of a needle 40 with protuberances 42 such as spikes, going through a roving 12 to provide an opened roving naving at least a double width referenced 16a since it is a part of the continuous web 16 of figure 1.

It is understandable that the needling machine consists of hundreds of needles, each needle having many spikes 42 as shown on figure 2.

It is also understandable that when the rovings are passed through the needling machine, the up and down motions of the needles served to destroy the sizing that binds the filaments together and to comb through the bundled filaments. As a result, the originally bundled filaments are now spread apart as clear from figures 1 and 2.

The main factors, which affect how wide the rovings can be opened, are the type and sizes of needles, the number of needles per cm², the speed of the machine and the penetration depth of the needles.

Generally, the needling conditions are :

for the speed of the machine : 1-40 m/minute, preferably 2 m/minute ; - for the nurnbe r of no t es punche red by the need l es de r cm² of web, debending on the num be r of need l es per cm² and t he speed o f the mac hine : 40 to 150 ho l es per cm², prefer ab l y 60 (at the nigh end, one obtained wider opening of rovings, but more breackage of the filaments) ;

- for the penetration depth of the needle : 10 to 20 mm, preferably 25 mm.

Under these above general conditions, typically 0.5 cm wide roving can be opened to a 1 to 3 cm wide continuous web, preferably 1.0 cm.

It can be easily understood that when a meter wide continuous web 16 is needed, preferably 200 rolls 14 of the 0.5 cm roving 12 are used to pass through the needing machine 10.

This is thereby obtained a continuous web 16 having a basis weight from 50 to 700 g/m², preferably 500 g/m².

Now, the general conditions of prepa ri ng the composite sheets are as follows, with reference to figure 3 for instance with regard to the preparation of a sheet having 3 layers, a core or a central layer 16 made with the unidirectional continuous fiber web as obtained at the outlet of the needling machine sandwiched two outlet layers of reinforced thermcpiastic material referenced 19 and 21, which are clearly seen on the enlarged cross-section, according to the lines IV-IV of figure 4. Each reinforced thermoplastic sheet 19 and 21 is obtained through the wet method of the traditional paper making technology from a first head box 18 and a second head box 20 feeding a slurry containing the composite sheet components in suspension therein onto an inclined wire 30, whicn filtrates water 32 with the aid of a small air depression, as it will be more c l ea r ly understood in reference to the following examples.

It is easily understandable that it is possible to produce more complicated sandwiched st ructures by adding further nead boxes and intermediate unidirectional fiber web 16 between the successive nead boxes. Also. it is easily possible to tailor the composite basis weight by adjusting the nature and percentage of the thermoplastic resin, of the fibers used and the basis weight of the unidirectional fiber weight 16, which can be itself adjusted as a result of varying the needling conditions.

It is for instance possible to produce a composite sheet having a 2400 g/m² basis weight with 20 % of unidirectional fiber web 16 having a one centimetre width from 2 x 2400 TEX rovings, and each outer sheets 19 and 21 having a basis weight of 960 g/m² with 25 % of chopped fiber glass and 75 % of polypropylene thermoplastic powder, preferably polypropylene powder.

Other purposes and advantages of the invention will appear from the following illustrative examples, which are not limited the scope of the invention.

In the examples, all parts are given by weight unless otherwise specified.

INVENTION EXAMPLE 1

In 7 liters of water containing 2.9 g of a cationic dispersant based on fatty acid (Cartarspers DS1 of Sandox), 29 g of glass fibers which are sized to have good dispersion in aqueous medium (reference R16 EX25 supplied by Owens Corning Fiberglas Europe) having an average length of 13 mm and 16 microns diameter were added with strong stirring. 6 g of synthetic pulp were then introduced with moderate stirring. After suitable dispersion, 59 g of polypropylene powder, of mean particle size of 700 microns and 6 g of coupling agent (maleic anhydride-grafted polypropylene supplied by EXXON CHEMICAL as EXXELOR 2011) were added. After dilution until the suspension contains about 5 g of solids per liter, the mixture was then splitted into two streams. Each stream was admitted onto a wire screen 30 through a head box 18 or 20, dewatered then dried according to the conventional paper making technique. A roll of continuous glass web 16 with a basis weight of 480 g/m² and a width of 28 cm was also laid onto the wire 30 between the first and second head box 18, 20. The arrangement of the head boxes 18, 20 and the continuous glass web 16 feeding is schematically illustrated in figure 3. The composite sheet thus obtained, illustrated in figure 4, had a basis weight of 2700 g/m² and comprised sufficient cohesion to be handled, stored, transported and in which the various components of the formulation have been perfectly retained.

To make the final industrial product from this sheet, three of such composite sheets may for example be superposed and, after having effected preheating up to a temperature of the order of 180ºC to 201ºC, the assembly may be moulded under pressures of 40 to 100 kg/cm² for a cycle less than 30 seconds.

INVENTION EXAMPLE 2

This example differs from the preceding one in that the composition of the slurry contained 2.65 g of dispersant, 26.5 g of fiberglass, 6 g of polypropylene pulpex, 1 g of flocculent, 61.5 g of polypropylene and 6 g of coupling agent. In addition to the compositional change, two rolls of continuous glass web 16 were introduced.

COMPARATIVE EXAMPLE 3

This example differs from Example 1 in that the composition of the slurry contained 4.2 g of dispersant, 42 g of fiberglass, 6 g of polypropylene pulpex, 1 g of flocculent, 46 g of polypropylene and 6 g of coupling agent. No continuous glass web 16 was introduced. INVENTION EXAMPLE 4

400 g of the moulded industrial product as described in Example 1 was placed into a infrared oven heated at a temperature of 300-320°C for 4.5 minutes. This well heated product was then transferred to a mould set at 60-80 °C and shaped like a box. The sample was moulded under pressures of 100 to 200 kg/cm² for a cycle time of less than 5 minutes. The moulded box was cut into 24 pieces as well known to those skilled in the composite art. Ash content analyzes showed that the minimum and maximum ash contents were 34.17% and 42.56 % respectively.

COMPARATIVE EXAMPLE 5

This example differs from Example 4 in that a competitive sample from Elastogran, Elastopreg^R B100M45, was preheated and moulded. On close examination of the moulded box, some wall sections are not filled.

Data from the examples 1 to 3 are detailed in the table below to illustrate the effect of unidirectional fibers on mechanical properties.

Example 1 and 2 contain two levels of unidirectional web, the properties are much higher than comparative Example 3 which contains only random chopped fibers. A competitive sample from Elastogran, Elastopreg B100 M45^R, was also analyzed and the properties are shown comparable to our Example 1, except the competitive sample contains 100 % unidirectional fibers versus only 18 % unidirectional fibers in the invention sample. When the sample was highly loaded with unidirectional fibers, poor fiberglass dispersion and incomplete filling of a mould are observed as shown by comparison of invention Example 4 versus comparative Example 5.

Claims

C LA I M S

1. A process for preparing a unidirectional fiber web comprising disposing several rovings sice by side, each having a plurality of inoivicual fiber filaments, and needling transversally said rovings, t he reby opening the rovings and forming a continuous fiber web therefrom.

2. The process of claim 1, wherein rovings comprise thousands of individual continuous fiber filaments bundling togetner.

3. The process of claim 1 or 2, wnerein said needling is performed with hundreds of needles, each needle having an enlarged oasis and being provided on the lateral surface thereof with prctuberances, such as spikes.

4. The crocess of any one of claims 1 to 3, wherein the rovings are continuous fiber glass rovings, having preferably a width of some millimetres, for instance about 5 millimetres and the continuous fiber filaments have a diameter ranging between 10 and 50 micrometres, preferably between 15 and 25 micrometres.

5. The process of any one of claims 1 to 4, wherein the needling provides an opening of the rovings from 2 to 6 times the width of the initial roving width.

6. The process of any one of claims 1 to 5, wherein the needling is performed so as to reach a continuous unidirectional fiber web having a weight ranging between 50 and 1000 g/m², more preferably from 500 g/m² to 700 g/m².

7. A continuous unidirectional fiber web, wnich has been obtained from several rovings laid side by side and needled, preferably according to the process of any one of claims 1 to 6.

8. A process for preparing a unidirectional composite material, comprising preparing a unidirectional fiber web as defined in claim 7 o r as obtained by the process of any one of claims 1 to 6, ana sandwiching this unoirectionaI fiber web between at least one reinforced thermoolastic sheet through a wet process.

9. The process of claim 8, wherein said reinforced thermoplastic layer is laid en either side of the unidirectional fiber web on an inclined wire at the bottom part or at an intermediate part thereof.

10. The process of claim 8 or 9, comprising sandwiching the above-said unidirectional continuous fiber web between two outer layers of reinforced thermoplastic sheets.

11. The process of claim 8 or 9, comprising sandwiching two layers of unidirectional continuous web between two outer layers of reinforced thermoplastic sneets.

12. The process of any one of claims 8 to 11, wherein the thermoplastic material of the reinforced thermoplastic sheet is selected from a polyolefine, in particular polyethylene, polypropylene and copolymers thereof, polyvynyl chloride, polystyrene and copolymers, polyamide, saturated polyesters, polyethylene ether, a polycarbonate and any plastic alloy.

13. The process of claim 12, wnerein the thermoplastic resin is under powder form having a mean particle size ranging between 200 micrometres and 1,000 micrometres, more preferably between 300 and 1,000 micrometres.

14. The process of any one of claims 8 to 13, wherein the reinforcing material of the thermoplastic composite is under fiber form and is selected from glass fibers, carbon fibers, ceramic fibers, boron fibers, glass wool, rock wool, metallic fibers, hot melt organic syntnetic fibers, notably aromatic polyami de, po lyeste rs and others ; the l engt h of the rei nforc i ng fibers preferably ranges between 5 mm and 25 mm, and the diameter between 5 and 20 micrαmetres.

15. The process of any one of claims 8 to 14, wherein the reinforced thermoplastic composite sneet0 are prepared through a wet process according to the traditional caper making technology, from a dilute slurry, preferably having from 0.1 to 5 % by weight dry content, fed preferably onto an inclined wire.

16. The process of claim 15, wherein the sturry composition, on a cry content tasis, of the thermoplastic composite sheet, comprises :

- thermoplastic resin under powder form 49 - 55 % - coupling agent 1 - 20 %

- reinforcing fibers 15 - 40 %

- dispersant 0.1 - 10 %

(with respect to reinforcing fibers)

- optionally flocculent 0.25 - 1 % - anti-oxidant 0.1 - 2 %

- optionally a colyciefine pulp 2 - 10 %

17. The process of claims 8 to 16, wherein each thermoplastic composite sheet has a basis weight which ranges between 400 g/m² and 5 Kg/m², and more preferably from 800 to 5,000 g/m², and most preferably around 2,800 g/m².

18. Undirectional thermoplastic composite materials a obtained by the process according to any one of claims 8 to 17.