EP0132110B1

EP0132110B1 - Process for producing composite monofilaments

Info

Publication number: EP0132110B1
Application number: EP84304721A
Authority: EP
Inventors: Masahiko Matsuno; Katsuhiro Shishikura; Kunio Gohda; Isao Fujimura; Taizoh Sugihara
Original assignee: Chisso Corp
Current assignee: JNC Corp
Priority date: 1983-07-14
Filing date: 1984-07-11
Publication date: 1988-01-07
Also published as: JPS633969B2; KR870000442B1; DE3468448D1; KR850001316A; EP0132110A2; JPS6021908A; EP0132110A3

Description

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to a process for producing composite monofilaments (hereinafter abbreviated to "composite MF") having heat-adhesive properties and excellent strengths. More particularly it relates to a process for producing composite MF of polyolefin resins having heat-adhesive properties and excellent strengths, obtained by using a low melting polylefin resin component on the sheath side and a high melting polypropylene (hereinafter abbreviated to "high melting PP") components on the core side, and melt-extruding these components through a sheath-and-core type spinneret, followed by cooling, solidifying and stretching.

Description of the Prior Art

In general, monofilaments as a single component (hereinafter abbreviated to "ordinary MF") obtained by melt-extruding a polyolefin resin, followed by cooling and then stretching are superior in mechanical strengths, chemical strengths, corrosion resistance, water resistance, mold-ability, etc.; hence they have been fabricated into ropes, materials of fishing such as fishermen's nets, nets for land such as insect screening, windbreak net, golf net, light-shielding net, filter, sheet for public works, etc, and the resulting products have been widely used.
Among them, nets for land have been in most cases knitted or woven and the resulting knitted or woven products have been used, and their specific feature for practical use consists in their high mechanical strengths. However, since the intersecting parts of warps and wefts of the nets (hereinafter referred to as "mesh") are not bonded together, but relatively free, the meshes shift at the time of knitting or weaving or at the time of applying net products or depending on the practical state of the nets; thus such drawbacks occur that the shielding or protecting effect of net products as their main object is lost or a good appearance thereof is damaged.
On the other hand, there have been known a technique of molding polymers directly into the form of net by melt-extrusion through a specific rotating spinneret to obtain a net having the meshes bonded together and a technique of further stretching the net product obtained above in both the longitudinal and lateral directions. However, as to the monofilaments (hereafter abbreviated to "MF") constituting these nets, as compared with conventional nets wherein the strength of each MF in the longitudinal direction and that in the lateral direction are both 0.26⁵ N/tex (3g/d) or more, the strength of each MF of the above particular nets in the longitudinal and that in the lateral direction are both 0.13² N/tex (1.5 g/d) or less, that is, extremely lower; thus a problem has been raised that the particular nets could have been applied only to extremely limited uses such as use for packaging simple, light-weight goods.
Further, in the field of non-woven fabrics, those obtained by processing composite fibers having a hot-melt adhesive function imparted thereto, into a bag form material, which is then subjected to heat- treatment to bring the mesh parts to hot-melt adhesion, have been in recent years applied to various uses. However, since hot-melt adhesive composite fibers used therefore have as very small a fineness as about 0.11 to 3.3 tex (1 to 30 d), if it is intended to use such composite fibers in the form of a thick material having 11.1 tex (100)d or more which has been used for ordinary MF, then it is necessary to process composite fibers into a fiber bundle; hence drawbacks occur that the process is complicated and accordingly very expensive.
In USA-A-4285748 there is disclosed a nonwoven fabric formed from self-bonded sheath/core composite polyolefin filaments. The sheath:core ratio is from 5:55 to 30:70 but we have found that for composite filament suitable for making nets the sheath:core ratio should be from 30:70 to 60:40 to give acceptable spinnability and stretchability and adequate backing force. Similarly we have found that the thickening and draw ratio of 'composite filaments suitable for making nets should be from 100 to 1000 denier (11.1 to 111.1 tex) and from 6 to 9 respectively, in contrast to a thicker of 10 to 20 denier (1.11 to 2.27 tex) and a draw ratio of 2 to 6 specified in US-A-4285748.
The object of the present invention is to provide a process for producing composite MF having heat-adhesive properties, superior strengths, no curl and no peeling between the layers thereof.

SUMMARY OF THE INVENTION

The present invention resides in a process for producing a composite MF having heat-adhesive properties and superior strengths which comprises subjecting a low melting polyolefin resin having a melting point of 135°C or lower, selected from high density polyethylene homopolymer (HDPE) or copolymer composed mainly of ethylene, linear chain low density polyethylene (LLDPE) homopolymer, low melting polypropylene (PP) homopolymer or copolymer composed mainly of propylene and mixtures of the foregoing, and a high melting polypropylene homopolymer or copolymer composed mainly of propylene having a melting point of 150°C or higher, to a sheath-and-core type composite spinning using the former low melting polyolefin resin as the sheath component and the latter high melting polypropylene homopolymer or copolymer composed mainly of propylene as the core component, into an unstretched monofilament, the melt flow index ratio of the former low melting polyolefin resin component to the latter high melting polypropylene component being in the range of 1.5 to 7, and the composite ratio being in the range of 30:70 to 60:40 and stretching the unstretched composite monofilament to 6 to 9 times the original length.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As for HDPE and polypropylene (herein after abbreviated to "PP") used in the present invention, homopolymer of ethylene or propylene is not only used, but also copolymers of ethylene with propylene, butene-1, etc. composed mainly of ethylene or copolymers of propylene with ethylene, butene-1, etc. composed mainly of propylene may be preferably used. Further, to these polymers or mixtures thereof may be, if necessary, added additives which are usually added to polyolefin resins, such as stabilizers, e.g. antioxidant, ultraviolet absorber, etc., coloring agent, lubricant, antistatic agent, delustering agent, etc.
In the present invention, in the case where HDPE, LLDPE or low melting PP is mixed with each other and the mixture is used as the sheath component, mixing may be carried out employing a conventional means such as extruder, Banbury^@ mixer, tumbler mixer, Henschel° mixer, etc. and in a conventional manner. Further, as for the composite extrusion method and apparatus, although known techniques may be employed such as composite extrusion by means of two extruders and composite spinnerets of side-by- side or sheath-and-core type, it is preferred in the present invention to employ composite spinnerets of sheath-and-core type which is advantageous in the aspects of spinning, stretching stability and peel resistance of the boundary surface layer between the sheath component and the core component of stretched composite MF.
As to the FR ratio in the present invention, the high melting PP and the low melting PP are based on MFR measured according to ASTMS D 1238 (L), and HDPE and LLDPE are based on MI measured according to ASTM D 1238 (E).
The melt flow index (MFR) of the high melting PP used on the core side of the composite MF may be in the range of 0.3 to 15 which has been used for ordinary MF, but its melting point is required to be 150°C or higher, and as for the FR ratio of the low melting polyolefin resin component on the sheath side to the high melting PP on the core side, when the ratio is in the range of 1.5 to 7, the effectiveness of the present invention is remarkable. If the melting point of the core component is lower than 150°C, its strength as a basic performance of the core component is reduced, and also its shrink properties increase so that when a net prepared by knitting or weaving the above composite MF is subjected to heat set, shrink-deformation is notable. If the FR ratio is lower than 1.5, spinning and stretching properties are unstable and the resulting net is inferior in heat-adhesive properties. If is is higher than 7, the fluidity of the sheath component in the nozzle is different from that of the core component therein, and also there occurs a large stress strain due to the difference in the crystallization behaviour between the two components or the difference in the volume shrinkage between the two components during the process from molten state to cooling and solidification, so that extruded unstretched MF bends or curls at the exit of the nozzle to make spinnability inferior. Further since the difference between the stretching stress applied to the sheath and core components increases; hence stretching troubles such as stretching breakage, curling of stretched MF, etc. are liable to occur.
The low melting polyolefin resin used as the sheath component constitutes a component by which adhesive properties due to heat-melt adhesion are imparted to composite MF, and the effectiveness is fully exhibited by single use of HDPE, LLDPE or a low melting PP, but even when two or more kinds thereof are used in admixture, the same effectiveness as in the single use is exhibited. In this case, as for the combination of the components, combinations of polymers having similar fluidities are preferred. When a low melting point PP is used as the sheath component, its melting point is necessary to be 135°C or lower. If it is higher than 135°C, when the resulting net is subjected to heat set, this is necessarily carried out at a high temperature and for a long time; hence even if heat adhesion is effected, the orientation of the core component of the composite MF is lost by the heat at the time of the heat set, to reduce its strength and thereby damage the strength-retaining characteristics of the core component.
The melting point of the low melting polyolefin resin is preferably 80°C or higher and more preferably 100°C or higher.
The composite ratio of the sheath component to the core component is preferably in the range of 30:70 to 60:40. If the sheath comoponent is less than 30%, spinnability and stretchability are liable to be inferior, and also since the amount of the heat-adhesive component of the composite MF is reduced, the bonding force at the adhesion part of the mesh of the net becomes weak. On the other hand, if the core component is less than 40%, the strength of the core component as a basic element of the role thereof is reduced.
As to the stretching in the present invention, general apparatus and process for stretching may be employed which have been employed for ordinary MF. The stretch ratio is suitably in the range of 6 to 9 times the original length. In the case of composite MF, since its strength is structurally somewhat lower than that of ordinary MF, if the ratio is lower than 6 times, its strength is low, while if it exceeds 9 times, its strength is sufficient, but due to the fact that composite MF is poor in the compotability of polymers at the boundary surface thereof, the difference in stretchability between the sheath component and the core component becomes remarkable so that troubles such as turnover or peel of the sheath component occur during the stretching step and also it is liable to curl after stretching, which causes troubles of bad take-up during the take-up step such as bad take-up shape or getting out of take-up shape. In order to improve the shrinkability of stretched filament after the stretching step, it may be also preferred to apply annealing for relaxation thereto employing a general apparatus and process.
The composite MF of the present invention may usually be preferably used in a thickness of 11.1 to 111.1 tex (100 to 1,000 d).
The composite MF obtained according to the present invention retains strength characteristics similar to those of ordinary MF and is at the same time provided with heat-adhesive properties. Further, the net-form product having its mesh part bonded together by heat-adhesion, obtained by subjecting a net-form material prepared by knitting or weaving the above composite MF, to heat treatment by way of a general means such as heating roll, heating calendar, hot air, steam treatment, etc., retains strengths similar to those of net-form products consisting of ordinary MF and hardly causes mesh deformation.
The present invention will be described below by way of Examples and Comparative examples. The standards based on which the evaluations of composite MF and nets obtained therefrom were made and the definitions of symbols in Tables listed later are as follows:

1) Ml― Melt flow index of polyethylene resin (a value according to ASTM D-1238 (E); i.e. a weight by gram of a sample obtained by extruding it for 10 minutes under conditions of an orifice hole diameter of 2.092 ± 0.002 mm, 190°C, and a load of 2.160 g).
2) MFR - Melt flow index of polypropylene resin (this is the same as above except that the temperature is 230°C; according to ASTMS D-1238(L).
3) FR ratio - Ratio of the melt flow index of the sheath component of that of the core component (i.e. ratio of MI (or MFR in case of low melting PP) to MFR, each measured in the items 1) (or 2)) and 2)).
4. Composite ratio - Ratio by weight of the sheath component to the core component, each obtained by singly extruding the corresponding component followed by measuring the weight of the resulting unstretched filament per unit time.
5. Spinnability ― State of extruded unstretched filament.
- 0: Normal.
- Δ: Unstretched filament bends at the exit of nozzle.
- x: Unstretched filament bends at the exit of nozzle to make spinning impossible.
6) Stretchability - Evaluated by the state of stretching.
- Symbol ^* represents impossibility of stretching.
- 0: Normal both for stretched filament and for stretching process.
- Δ: Stretched filament whitens.
- x: Stretching break occurs or filament curls and take-up troubles are liable to occur.
7) Peeling properties of composite MF― Separation properties of the sheaf component layer from the core component layer.
- 0: Sheath layer does not peel even when forcible peel is tried.
- Δ: Sheath layer peels when it is forcibly peeled, but usually no problem is raised.
- x: Sheath layer is liable to peel at the stretching and take-up steps.
8) Heat set (heat adhesion) process of net-form product.
- - Net form product obtained from composite MF in a conventional manner is allowed to strand in a hot air-heating vessel at 140 - 150°C for 1.5 minute.
9) Strength of composite MF after heat adhesion processing
- - Composite MF is collected from net-form product heat-adhered at the mesh part, followed by measuring and evaluating its tensile strength.
  - 0: Greater than 0.35³ N/tex (4.0 g/d)
  - Δ: 0.26³~ 0.35³ N/tex (3.0 - 4.0 g/d)
  - x: Less than 0.26⁵ N/tex (3.0 g/d)
  (Note) Measurement conditions for the tensile strength:
  - ① Tensile tester: Tensilon^® IV type manufactured by Toyo Baldwin Company.
  - ② Distance between chucks: 200 mm
  - ③ Tensile rate: 220 mm/min.
  - ④ Room temperature: 23°C
  - ⑤ Humidity: 50%
10) Adhesive properties of net-form product at the mesh parts - Bond strength at the mesh part is measured.
- O: Bond strength, greater than 2.94 N (300 g)
- Δ: Bond strength, 0.98 - 2.94 N (100 - 300 g)
- x: Bond strength, less than 0.98 N (100 ) (the mesh parts have have been adhered for the present, but a portion thereof is slight in adhesion).

Example 1 and Comparative example 1

Using as a core component, various kinds of PP having a melting point of 161°C and various MFR values and as a sheath component, HDPE or LLDPE having various MI values or PP having a melting point of 128°C, and employing two extruders each having a bore diameter of 40 mm and a composite spinneret of sheath-and-core type having a nozzle diameter of 1.5 mm, melt-extrusion was carried out at an extrusion temperature on the core side of 260°C, at an extrusion temperature on the sheath side of 240°C and at a composite spinneret temperature of 260°C, followed by spinning through cooling to obtain an unstretched composite filamant of sheath-and-core type having a composite ratio of 50:50, which was then stretched to 5 to 10 times by means of a wet type, heat stretching apparatus to obtain various kinds of composite MF of 50 tex (450 d). The results as to the spinnability and stretchability of the extruded, unstretched filament and the peeling properties of the sheath layer from the core layer are shown in Table 1. Further, various kinds of composite MF prepared according to the above process were each woven into a net-form product having a woven density of 5 warps/ 25 mm x 5 wefts/25 mm, which was then heat-set in a hot air-heating vessel at 140°C for 1.5 minutes, taken out and subjected to evaluations of the heat-adhesive properies at the mesh parts and the residual strength of the composite MF. The results are shown in Table 2.
From these Tables it is seen that when a high melting PPof m.p. 161°C is used as a core component and either one of HDPE or LLDPE or a low melting PP of m.p. 128°C is used as a sheath component, if the FR ratio is in the range of 1.5 to 7.0 and the stretch ratio is in the range of 6 to 9 times, it is possible to obtain a stretched MF having a stabilized composite structure without any peel, and also that among the above cases, when a low melting PP is used as a sheath component, a composite MF which is particularly difficult to peel is obtained. Further it is also seen that net-form products obtained by heat-setting net-form materials prepared from the above composite MF have the mesh parts bonded together by heat adhesion and have a sufficiently retained strength.

Example 2 and Comparative example 2

Using as a core component, PP having a m.p. of 161°C and a MFR of 3.1, and as a sheath component, either one of HDPE, LLDPE or PP of m.p. 128°, spinning was carried out under the same conditions as in Example 1 to obtain various unstretched composite filaments of sheath-and-core type, which were then stretched by means of a wet type, heat stretching apparatus to obtain composite MFs of 50 tex (450 d). The spinnability and stretchability of the resulting composite MFs and evaluations of the heat-adhesive properties and the residual strength of net-form products prepared from the above composite MFs in the same manner as in Example 1 are shown in Table 3.
From Table 3 it is seen that when the composite ratio of the sheath and core components is in the range of 30:70 to 60:40, the spinning and stretching stabilities of composite MF and the heat-adhesive properties and the residual strength of net-form products prepared from composite MF are superior.

Example 3 and Comparative example 3

Using as a core component, PP having a m.p. of 161°C and a MFR of 3.1 and as a sheath component, various low melting PPs having a MFR of 15.5 and various melting points, composite MFs were prepared under the same conditions as in Example 1. The heat-adhesive properties and the residual strength of net-form properties and the residual strength of met-form products prepared from the above composite MFs were evaluated. The results are shown in Table 4.
From Table 4 it is seen that in the case where a low melting PP is used as the sheath component, if its melting point exceeds 135°C, the contrary properties to each other of the heat-adhesive properties and the residual strength becomes greater depending on the heat melting setting conditions of net-form products, and as the melting points becomes higher, the heat adhesive properies become inferior, and if the heat setting temperature is raised in order to improve heat-adhesive properties, the strength of composite MF after heat-adhesive processing contrarily becomes too low.

Example 4

A PP having a m.p. of 161°C and a MFR of 3.1 was used as a core component, and three kinds of mixed resins obtained by mixing the respective two of HDPE, LLDPE or a PP of m.p. 128°C in a ratio of 1:1 by means of a Henschel mixer, followed by extruding and granulating the mixtures by means of an extruder having a bore diameter of 40 mm were used as a sheath component, respectively. Evaluation was made as in Example 1. The results are shown in Table 5.
From Table 5 it is seen that even when mixed resins of HDPE, LLDPE or a low melting PP are used as a sheath component, the same effectiveness as in the case of single use thereof is obtained.

Example 5 and Comparative example 4

PPs having similar MFRs and various melting points were used as core component, and HDPE, LLDPE or a PP of m.p. 128°C was singly used as a sheath component. Evaluation was made as in Example 1. The results are shown in Table 6.
From Table 6 it seems that when the melting point of core component is lower than 150°C, reduction in the residual strength is remarkable although no problem is raised as to heat-adhesive properties.

Claims

1. A process for producing a composite monofilament having a thickness if 11.1 to 111.1 tex which comprises subjecting a low melting polyolefin resin having a melting point of 135°C or lower, selected from high density polyethylene homopolymer or copolymer composed mainly of ethylene, linear chain low density polyethylene homopolymer, low melting propylene homopolymer or copolymer composed mainly of propylene and mixtures of the foregoing, and a high melting polypropylene homopolymer or copolymer composed mainly of propylene having a melting point of 150°C or higher, to a sheath-and-core type composite spinning using the former low melting polyolefin resin as the sheath component and the latter high melting polypropylene homopolymer or copolymer composed mainly of propylene as the core component, into an unstretched monofilament, the met flow index ratio of the former low melting polyolefin resin component to the latter high melting polypropylene component being in the range of 1.5 to 7, and the composite ratio being in the range of 30:70 to 60:40 and stretching the unstretched composite monofilament to 6 to 9 times the original length.

2. A process according to claim 1, wherein the low melting polyolefin resin and/or the high melting polypropylene is a homopolymer.

3. A process according to claim 1 or 2, wherein the melting point of the low melting polyolefin resin is 80°C or higher.

4. A net made from composite monofilaments produced according to any one of claims 1, 2 or 3.

5. A net according to claim 4, wherein the net is produced by weaving or knitting the composite monofilaments and then subjecting the net-form to a heat treatment.