GB2105654A

GB2105654A - Nonwoven fabric from a combination of thermoplastic netting and oriented film

Info

Publication number: GB2105654A
Application number: GB08225554A
Authority: GB
Inventors: Alan Daniel Craig
Original assignee: Hercules LLC
Current assignee: Hercules LLC
Priority date: 1981-09-08
Filing date: 1982-09-08
Publication date: 1983-03-30
Also published as: FR2512393B1; GB2105654B; FR2512393A1; CA1181675A

Abstract

A family of reinforced net structures which include oriented polypropylene netting with oriented propylene/1-butene copolymer film as an adhesive, and a process for making these nonwoven fabrics.

Description

SPECIFICATION Nonwoven fabric from a combination of thermoplastic netting and oriented film This invention relates generally to reinforced composite structures that are formed by combining thermoplastic polymeric sheets and polypropylene netting by lamination or extrusion coating. The film of this invention has a unique combination of properties including strength and tear resistance.

It is known to laminate or extrusion coat woven or non-woven fabrics with thermoplastic films to increase their resistance to moisture and gas permeability and to obtain a reinforced film. However, in the case of polypropylene fabrics and netting, most thermoplastic materials that were previously known to adhere well to the polypropylene fabrics, such as low molecular weight polypropylene and copolymers or graft polymers of polypropylene, cause excessive shrinkage and distortion of the fabrics or netting at the temperature required for bonding. In polypropylene fabrics and netting, the polypropylene components are oriented and will shrink or become distorted on exposure to the high temperatures required to coat or laminate them with molten polypropylene or with the modified polypropylenes that are known to adhere well to such components.It has now been discovered that crystalline random copolymers of propylene and 1-butene, melting low enough so that such fabric distortion can be avoided in preparing such laminated structures, will adhere well to polypropylene.

Use of such copolymers, therefore, makes possible preparation of improved reinforced composite structures using polypropylene netting.

It is also known, for instance, from U.S. Patents 3,914,365 and 4,144,368, to form multilayer products by laminating two or more layers of polypropylene netting having the same or different configurations so that the main filaments cross in various directions. Another reference which discloses the lamination of extruded net fabrics under pressure and heat or by cementing is U.S. 2,919,467.

Disadvantages of such known laminates include low burst, tear and tensile strength, and a tendency to delaminate when bonded at temperatures at which the orientation strength and configuration of the polypropylene netting is retained.

According to the invention, a reinforced composite structure comprising a layer of oriented polypropylene netting to which is bonded a thermoplastic polymer sheet is characterized in that the sheet consists of a random copolymer having between 7% and 30% 1-butene and between 93% and 70% propylene, the copolymer having an intrinsic viscosity of between 1.1 and 4.0. According to a preferred modification of the invention, a second layer of oriented polypropylene netting is bonded to the thermoplastic copolymer sheet so that the said sheet is between the two layers of netting.When two layers of oriented netting are employed, preferably each netting layer has main filaments in one direction and smaller connecting filaments in the opposite direction, and the netting layers are arranged so that the main filaments of one of the netting layers are essentially perpendicular to the main filaments of the other netting layer.

Also according to the invention, a proces of making the composite structure according to the invention comprises disposing a layer of thermoplastic sheet material in contact with a layer of oriented polypropylene netting and applying heat and pressure, characterized in that the sheet material is the copolymer defined in Claim 1 and the temperature of heating is approximately 50 above the crystalline melting point of the copolymer and not more than 1 500 C. Preferably, the sheet material is a film having a thickness between .25 and 4 mils.

The invention may be adapted to provide either an imperforate laminate in which the integrity of the sheet material is maintained, or a netting structure in which the permeability of the netting is retained to a large degree, depending on whether unoriented or biaxially oriented polymeric sheet material is selected for bonding to the netting. Therefore, either a netting reinforced film structure or an open-weave reinforced netting can be produced according to the invention.

If an open-weave reinforced netting is desired, the oriented thermoplastic sheet material shrinks under the conditions of the lamination and opens up between the strands of the netting so as to provide an open net in which the shrunken copolymer sheet acts as a reinforcement to improve tearresistance. If two or more layers of netting are used, it also acts as a bonding agent betweeen the layers.

Referring to the drawings in detail, there is illustrated in Fig. 1 a netting reinforced film structure 10 comprising a layer of oriented polypropylene netting 1 2 bonded to a layer of unoriented propylene/l -butene copolymer film 14. The netting layer 12 preferably has main filaments 1 6 and tie filaments 18. Combining layers 12 and 14 in a continuous manner efficiently provides a product that is suitable for applications requiring strength and low moisture and gas permeability, such as bagging, other packaging applications, tarpaulins, and geotextiles.

The embodiment of Fig. 2 depicts an open weave reinforced netting 1 OA comprising a layer of nonwoven continuous linearly oriented polypropylene netting 1 2A bonded to propylene/l -butene copolymer 1 4A. The latter is formed from a thin biaxially oriented film of the copolymer under conditions of bonding such that the copolymer contracts until it essentially conforms to the open-weave of the netting. Netting layer 1 2A preferably has main filaments 1 6A and tie filaments 1 8A.

Combining layers 1 2A and 1 4A in a continuous manner can provide a product that is suitable for such applications as kraft paper reinforcement or reinforcing scrim for plastic film, and that can be used, for instance, as furniture skirt liners or duster covers.

Fig. 3 shows the use of apparatus for continuously preparing the netting-reinforced film shown in Fig. 1. A polypropylene netting layer 22 and a layer of unoriented thermoplastic copolymer film 24 being fed from supply rolls 26 and 28, respectively, to rolls 30, 32 and 34. Preferably, rolls 30 and 32 are made of steel covered with a Teflons polymer-glass cloth. They are heated to a temperature within the range of 1 000C. to 1 500 C. Roll 32 is a steel roll covered with silicone rubber.

Fig. 4 shows the apparatus of Fig. 3 being used for continuously preparing the open-weave reinforced netting shown in Fig. 2. The thermoplastic netting layer 22 and a layer of oriented thermoplastic film 36 are fed from supply rolls 26 and 28, respectively, to the rolls 30, 32 and 34, of the vertical calender stack shown in Fig. 3. Under the pressure and heat supplied by the rolls, the film adheres strongly to the netting and opens due to shrinkage so that the copolymer is essentially confined to the filaments and crossover points of the netting.

Fig. 5 shows another embodiment of the subject invention where a three-layer reinforced structure 38 is shown. The interlayer 40 represents an unoriented thermoplastic propylene/1 -butene copolymer film. Outer layer 42 is a layer of polypropylene nonwoven netting having main filaments 44 and tie filaments 46 which are orthogonal to main filaments 44. The other outer layer 48 also consists of a polypropylene nonwoven netting. Layer 48 has main filaments 50 and tie filaments 52 which are orthogonal to main filaments 50. Outer layers 42 and 48 are orthogonally oriented with respect to each other wherein, for example, the main filaments 44 of outer layer 42 are at a 900 angle to main filaments 50 of outer layer 48.Since the main filaments of the nonwoven netting layers may have higher strength properties as compared to the respective tie filaments, the orientation of layers 42 and 48 in the reinforced structure 38 can provide substantially enhanced strength characteristics.

Fig. 6 shows, schematically, a method which can be used for the manufacture of the reinforced film shown in Fig. 5. For that purpose, a netting layer 54 is supplied from supply roll 56 and another netting layer 58, having its main and tie filaments at a 900 angle to the main and tie filaments of layer 54, respectively, is fed from supply roll 60. Unoriented or oriented thermoplastic copolymer film 62 is fed from supply roll 64 to form the bonding member of the laminate. Optionally, unoriented film 62 can be supplied directly from an extruder. The three layers pass over heated roll 66, into the nip of heated pressure rolls 68 and 70 wherein the three layers are bonded together. The reinforced structure 72, which may be a netting-reinforced film as shown, or an open-weave reinforced netting, if oriented, copolymer film is used, then is fed to a take-up spool (not shown).

Typically, the process shown in Fig. 6, utilizes temperatures of the first two rolls between 1 000C.

and 1 500 C., at nip pressures between 50 and 500 pounds per inch. Such a lamination process, when unoriented film is used, can also be carried out in a compression press at temperatures in the same range and at moderate pressures, i.e., over 10 p.s.i. for short periods of time such as 10 seconds or more.

Optionally, a three-layer netting-reinforced film can be produced with a layer of netting between two layers of film. Such a reinforced structure might be useful for trash bags, for instance.

When oriented copolymer film is used in the method shown in Fig. 6, a blower can be used to blow air on the laminated fabric 72 after it exits the nip created by rolls 68 and 70. The air emerging from a blower and impinging on the laminated fabric 72 while it is still hot, aids in assuring that the oriented film will open subsequent to the application of heat and pressure to maintain the permeability of the netting. The thickness of the layer of the copolymer between or on the filaments of the polypropylene netting is preferably between about 0.25 mils and about 1.0 mil.

Fig. 7 shows a preferred method for preparing a three layer structure, involving two layers of oriented polypropylene netting bonded to a propylene/1-butene copolymer. This method includes extruding the copolymer as a sheet between two layers of netting and bonding the netting to the copolymer sheet in the nip of the two rolls. As shown in Fig. 5, netting layer 74 is supplied from supply roll 76. Netting layer 78 is fed from supply roll 80. Unoriented polypropylene film 82 is supplied from extruder (not shown) through die 86. The film 82 contacts netting layers 74 and 78 in the nip created by counter-rotating rolls 88 and 90. Roll 88 is preferably made of rubber and coated with Teflons polymer.The temperature or roll 88 and chill roll 90 should be below 1 500 C. to avoid shrinkage or distortion of the netting layers and to effect cooling of the film after it is bonded to the layers of netting.

The extrusion temperature should be above the crystalline melting point of the copolymer and may be as high as 2500C. A moderate nip pressure, e.g., in excess of 5 p.s.i., between rolls 88 and 90, is desirable to provide effective contact between the three layers of the composite structure. The product of the extrusion coating lamination 92 is fed to a take-up spool (not shown).

A similar extrusion coating lamination process can be used to form a two-layer structure consisting of a copolymer sheet extruded onto a single layer of netting.

The thermoplastic film used in this invention, is formed from a copolymer of propylene and 1butene containing approximate 7% to 30% 1 -butene. This copolymer provides excellent adhesion between two layers of oriented polypropylene netting at temperatures which do not cause a significant loss of orientation of the polypropylene. The preferred materals are random 1-butene/propylene copolymers which have crystalline melting points significantly below the crystalline melting points of polypropylene homopolymers, random ethylene-propylene copolymers containing up to 10% ethylene or block. copolymers containing up to 25% ethylene.The C3-C4 copolymers are compatible with and adhere well to polypropylene and C2-C3 copolymers and thus form an extremely good bond, without requiring melting or loss of orientation of the propylene homopolymers or C2-C3 copolymers.

Preferably the 1-butene content may range from 8 to 20%. The crystalline melting points of the copolymer containing 8% butene is about 1 400C, while the copolymer containing 18% butene has a crystalline melting point of about 1300 C. The thermoplastic copolymer film should have a thickness between about 0.25 and 4 mil, preferably between about 0.25 mils and 2 mil.

The oriented polypropylene netting or network structures used in this invention may be of the types disclosed in the prior art, for example, Mercer (U.S. Patents 4,020,208 and 4,059,713); Larsen (U.S. Patent4,152,479); Kim etal (U.S. Patents 3,914,365 and 4,144,368); and Liu (U.S. Patent 4,140,826).

This netting may be composed of either a polypropylene homopolymer, a propylene-ethylene random copolymer containing 2% to 10% ethylene or a propylene-ethylene block copolymer containing 2% to 25% ethylene and may be either natural or pigmented.

Preferably the netting should have uniform network structure and the hole size, spacing and design of the two nets in a laminate should be similar. Uniform network structure means that in each layer of netting, there are at least two sets of strands wherein each set of strands crosses another set of strands at a fixed angle and the openings in the netting are uniformly sized. Preferably, the average minimum dimension of the openings in each layer of netting is between 0.5 millimeters and 5 millimeters. Preferred types of thermoplastic netting useful in this invention are disclosed in U.S.

Patents 4,144,368 and 4,207,375 to Kim et al, incorporated herein by reference.

The network structure used in this invention may include one or more layers of netting. When two or more layers of netting are employed, the netting may have the same or different configurations such that the main filaments cross in various directions to provide a multilayer product having certain desired strength characteristics. For example, orthogonal constructions can be made wherein the main filaments of one layer cross at 900 to the main filaments of another layer to provide high strength and tear resistance in two directions. Structures may also be made from three or more layers of networks, each having the main filaments in different directions thus providing laminates having excellent dimensional stability, high strength and tear resistance in all directions and high burst strength.

In order to provide the shrinkage properties which assist in forming an open network structure during the lamination with polypropylene netting, the propylene-butene copolymer film must be biaxially oriented, i.e., drawn in perpendicular directions, at a temperature below its crystalline melting point. Such orientation increases its strength and provides a thin film which shrinks, on heating to temperatures approaching the orientation temperature and on subsequent melting. Such orientation can be carried out by sequential operations which normally involve a combination of machine direction stretching between differential speed rolls and lateral stretching using a tenter, or may be carried out simultaneously by lateral expansion of a tube of the plastic by air blowing while it is being drawn linearly. Such processes are well known and are not part of this invention.

The oriented films may be from about 0.25 mils to about 2 mils in thickness, and preferably from about 0.25 to about 1 mil in thickness.

Shrinkage properties of oriented films of copolymers of propylene and 1-butene are given in Table I, showing the effect of the composition and of the degree of orientation on films made from copolymers with various monomer ratios. It is apparent that the degree of orientation and the orientation temperature have a significant effect on the strength and shrinkage properties of the films. Table I %Butene Melting Degree temperature Tensile in Point of of Strength Modulus Elongation % Shrinkage Copolymer ~C Orientation Orientation ~C (P.S.I.) (P.S.I.) (%) 5 Min. at 110~C 8 140 4x4 115 20,000 180,000 120 10 8 140 6x6 120 36,000 460,000 50 16 14 135 4x4 110 17,200 232,000 87 20 14 135 6x6 110 33,000 430,000 50 25 18 130 2x2 105 7,800 98,000 320 15 18 130 4x4 105 16,200 162,000 100 30 18 130 6x6 105 30,000 390,000 40 35 Having set forth the general nature of the invention, the following examples illustrate some specific embodiments of the invention. It is to be understood, however, that this invention is not limited to these examples since the invention may be practiced by the use of various modifications.

Example 1 In this example, the netting components were of polypropylene and were in the form of linearly oriented continuous filament orthogonal networks. Two layers of the same type of netting were used in each test, one with strength primarily in the machine direction (MD) and one with strength primarily in the cross-machine direction (TD). The film used in this example was made from a propylene/1-butene copolymer containing 14% butene, and having an intrinsic viscosity of 1.1. The film had a thickness of 2 mil. The netting layers and the film were arranged to produce the laminate structure shown in Fig. 3.

The polypropylene netting employed had main filaments 150 microns in diameter and tie filaments 25 microns in diameter. There were 5 main filaments per centimeter and 10 tie filaments per centimeter so that the openings in the nets were about 1.3 by 1.2 millimeters across in the two perpendicular directions. these nets had a weight of 20 grams per square meter. The Frazier air permeability of the netting was 11 44 ft3/min/ft3 (CFM).

This three layer structure was heated in a platen press at 1 200C. under 38 p.s.i. pressure for 30 seconds. The product so prepared was a strong reinforced film, resistant to the passage of gas or liquids. A 1 800 T-peel test made according to ASTM D 1 876, giving a value of 3 pounds per inch, showed that effective adhesion of the two netting layers was obtained.

Example 2 This example illustrates preparation of a reinforced film by extrusion coating of a propylene/l butene copolymer containing 14% 1 -butene onto a single layer of oriented polypropylene netting. The netting employed was of the type used in Example 1, having main filaments oriented in the machine direction. The netting layer was 18 inches wide. Using a 2-1/2 inch diameter plastic extruder with a 24:1 length to diameter ratio and with a coathanger die 18 inches wide, a random copolymer containing 8% 1-butene and 92% propylene with an intrinsic viscosity of 1.9 was extruded at 2350C.

The 2 mil thick film so extruded contacted the netting layer at the nip between two 6 inch diameter .rolls which were two feet long. The roll corresponding to roll 88 in Fig. 5 was heated to 500 C. The other roll, corresponding to chill roll 90 in Fig. 5, was heated to 300 C. The pressure between the rolls was 10 pounds per inch. The coated netting was wound onto a take-up roll. The product was a reinforced film, resistant to the passage of gas and liquid, which was puncture and tear resistant.

Examples 34 In these examples, the netting components were of polypropylene and were in the form of linearly oriented continuous filament orthogonal networks. Two layers of the same type of netting were used in each test, one with strength primarily in the machine direction (MD) and one with strength primarily in the cross-machine direction (TD). Films used in each of the examples other than the control experiment were of propylene/1 -butene copolymer containing 14% butene with an intrinsic viscosity of 1.1 which had been oriented six times in each direction and having the thickness listed in Table II. The netting layers and the film were arranged to produce the composite structure prior to lamination shown in Fig. 3.

Two weights of polypropylene netting were employed. Type A nets had main filaments 1 50 microns in diameter and tie filaments 25 microns in diameter. There were 5 main filaments per centimeter and 10 tie filaments per centimeter so that the openings in the nets were about 1.3 by 1.2 millimeters across in the two perpendicular directions. These nets had a weight of 20 grams per square meter. The Frazier air permeability was 1144 ft3/min/ft2 (CFM). The Type B nettings had main filaments 100 microns in diameter and tie filaments 25 microns in diameter. There were 10 main filaments per centimeter and 1 5 tie filaments per centimeter so the openings that were in the nets were 0.9 by 0.7 millimeters across in the two perpendicular directions. These nets had a weight of 12 grams per square meter.The Frazier air permeability was 1 240 ft3/min/ft2.

The laminating step was carried out by a continuous process. The control sample and Examples 1 and 2 were processed using a three roll vertical calender stack, similar to the diagram of Fig. 4. The calender consisted of three 8-inch diameter rolls, each of which was 44 inches wide. The rolls corresponding to roll 68 and roll 70 in Fig. 4 were made of steel covered with a Teflon-glass cloth. The gap between these two rolls was adjusted to apply pressure of 80 pounds per linear inch. Roll 68 was oil heated to a temperature of 1 200C, and roll 70 was operated at 1 500 C. The roll corresponding to roll 72 was a steel rod covered with silicon rubber and oil heated to a temperature of 800 C. This roll was adjusted in spatial relationship to roll 70 to provide a linear pressure of 30 pounds per linear inch.

An air blower, which consisted of a pipe with a 25 mil slit, was used to blow air at 80 psi onto the laminate after it emerged from the nip between rolls 70 and 72 in Example 2. Dwell time on the heated roll surfaces was 10 seconds. The control sample was processed without film under the same conditions as were used with film present in the other examples.

Physical tests, the results of which are shown in Table II, were performed according to ASTM standards, with the exception of the seam strength test. For the seam strength test, 2 in. x4 in.

specimens were cut from sheets of the laminate. Then two of the specimens were placed face to face and the 2 inch-long edges were joined by sewing 6 stitches per inch, with cotton-wrapped polyester thread. The stitching was placed a half-inch from the edge of the specimen and the direction of stitching was the "test direction". The loose ends of the sewing thread were tied to prevent unraveling.

The force in pounds per inch to cause seam failure was determined by drawing the test specimen in a tensile tester at 12 inches per minute.

The results in Table II show that the laminated network structures of the invention have good adhesion, substantially improved seam strength and at least 20% of the permeability of the unlaminated network structure.ln the tests of interlaminar adhesion, the netting of the laminated structure actually tore before any separation of the netting layers occurred.

It is to be understood that the above description and drawings are illustrative of this invention and not in limitation thereof. As will be evident to those skilled in the art, various modifications can be made in light of the foregoing disclosure and discussion without departure from the spirit or scope of the disclosure or from the scope of the claims.

Table II Physical properties of laminated network structures Example No. Control Control 1 2 3 4 5 Netting Type A B A A B B B Film Thickness (mil) None None 0.3 0.3 0.3 0.4 0.5 Laminating Method Roll Roll Roll Roll Roll Roll Roll Weight, oz/yd2 1.5 1.1 1.7 1.7 1.3 1.4 1.5 Tensile Strength, Ivan. MD 25 11 25 27 25 28 35 Tensile Strength, Ib/in. TD 25 15 36 40 30 33 38 Elongation at break, MD, % 25 20 48 42 40 35 36 Elongation at break, TD, 25 24 26 26 25 25 28 Frazier Permeability, CFM 1000 800 250 300 200 350 200 Seam Strength, Ib/in. MD 4 2.7 10 8 7 9 11 Seam Strength, b/in. TD 5 2.2 9 9 6 5 7 Interlaminar Adhesion Poor Poor Good Good Good Good Good

Claims

1. A reinforced composite structure comprising a layer of oriented polypropylene netting to which is bonded a thermoplastic polymer film, characterized in that the film consists of a random copolymer having between 7% and 30% 1-butene and between 93% and 70% propylene, the copolymer having an intrinsic viscosity of between 1.1 and 4.0.

2. A reinforced composite structure as claimed in claim 1, further characterized in that a second layer of oriented polypropylene netting is bonded to the polymer film so that the said film is between the two layers of netting.

3. A reinforced composite structure as claimed in claim 1 or 2, further characterized in that each netting layer has main filaments extending in one direction and smaller connecting filaments extending in the opposite direction, and the netting layers are arranged so that the main filaments of one of the netting layers are essentially perpendicular to the main filaments of the other netting layer.

4. A composite structure as claimed in claim 1, 2 or 3, further characterized in that the polymer film has a thickness between .25 and 4 mils.

5. A composite structure as claimed in claim 1, 2, 3 or 4, further characterized in that the polymer film is unoriented.

6. A composite structure as claimed in claim 1, 2 or 3 or 4, further characterized in that the polymer film is biaxially oriented.

7. A process for making a composite structure comprising disposing a layer of thermoplastic polymer film in contact with a layer of oriented polypropylene netting and applying heat and pressure, characterized in that the film consists of the copolymer defined in claim 1 and the temperature of heating is approximately 50C. above the crystalline melting point of the copolymer and not more than 1 500C.

8. A process for making a composite structure as claimed in claim 7, further characterized in that the thermoplastic polymer film has a thickness between .25 and 4 mils.

9. A process for making a composite structure as claimed in claim 7 or 8, further characterized in that the thermoplastic polymer film is unoriented.

1 0. A process for making a composite structure as claimed in claim 7 or 8, further characterized in that the thermoplastic polymer film is biaxially oriented.

11. A composite structure as claimed in claim 1, 2 or 3, further characterized in that the first layer has a plurality of parallel continuous main filaments extending in a first direction, having a substantially uniform cross-section, and being substantially uniformly and continuously oriented, and a plurality of discontinuous parallel tie filaments extending in a second direction, the tie filaments interconnecting the main filaments and having no substantial portion thereof crossing over the main filaments, each of the tie filaments between each pair of adjacent main filaments having its longitudinal axis in the second direction in axial alignment with the longitudinal axis in the second direction of the adjacent tie filament.

1 2. The reinforced thermoplastic polymer sheet structure of any of the preceding claims further characterized in that the average minimum dimensions of each of the openings of the netting is between about 0.5 millimeters and 5 millimeters.

1 3. A process according to claim 7 substantially as hereinbefore described in any of the Examples.

14. A reinforced composite structure substantially as hereinbefore described in any of the Examples.