JPH02110140A - Polyethylene composite - Google Patents

Abstract

PURPOSE:To obtain a polyethylene composite light in weight and excellent in tensile strength, tensile modulus, impact resistance, etc., by combining a high-strength fibrous polyethylene reinforcement with a crosslinked polyethylene matrix. CONSTITUTION:A reinforcement comprising a polyethylene fiber having a tensile strength >=20g/d and an initial tensile modulus >=500g/d is composited with a polyethylene matrix having an m.p. which is at least 5 deg.C lower than m.p. of the reinforcement and having a melt index >=20 (as measured at 145 deg.C) by means of impregnation or the like. The obtained polyethylene composite can be desirably used as a bumper of a helicopter, automobile, etc., or as a baseball helmet.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is lightweight, has high strength and high modulus of elasticity, and has excellent impact resistance. This invention relates to polyethylene composites useful as baseball helmets, leggings, security layers, helmets, etc.

[Conventional technology] In the past, metals were the main materials used for bulletproof plates and shields, but because these are heavy, recently non-metallic plastics reinforced with glass fiber or carbon fiber have been widely used. There is. However, glass fiber and carbon fiber also have a higher specific gravity than general plastics, so there is still room for improvement from the perspective of weight reduction. By the way, recently developed high-strength polyethylene fibers have low specific gravity and high strength, and are expected to be used as lightweight reinforced plastic materials. However, because polyethylene has poor affinity and adhesion with resins other than polyolefin resins, it is difficult to obtain reinforced plastics with sufficient strength even when combined with various general-purpose resins.Therefore, it is necessary to use general-purpose polyethylene resin as a matrix. A technology for compositing high-strength polyethylene fibers was proposed (Japanese Patent Application Laid-open No. 60-20
9228, 58-171951). However, high-density polyethylene, which has relatively excellent physical properties among general-purpose polyethylenes, has a small melting point difference with the high-strength polyethylene fibers that serve as the reinforcing material, making it difficult to allow the fibrous reinforcing material and the matrix to sufficiently penetrate each other. , voids tend to remain in the composite material, causing strength defects. Therefore, it has been considered to improve permeability and reduce voids by using low-density polyethylene, etc., which has a relatively low melting point, as a matrix, but in this case, the strength of low-density polyethylene itself is insufficient. The impact strength of the composite material could not be sufficiently increased, and the heat resistance could not be satisfied.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned drawbacks of the prior art, and its purpose is to prevent strength defects caused by remaining voids in a high-strength polyethylene fiber-reinforced composite material. The aim is to provide a lightweight polyethylene composite that is lightweight and has excellent impact resistance, by eliminating the drawbacks such as low impact resistance and heat resistance due to insufficient physical properties of the matrix resin itself.

[Means for Solving the Problems] The present inventors have completed studies to solve the above problems, and the structure has a tensile strength of 20 g/denier or more. , and a reinforcing material made of polyethylene fibers having an initial tensile modulus of 500 g/denier or more (hereinafter simply referred to as polyethylene fiber reinforcing material), and a polyethylene matrix in which crosslinks are formed. Here, as the polyethylene matrix to be composited with the polyethylene fiber reinforced material, a polyethylene polymer having a melting point 5°C or more lower than the melting point of the polyethylene fiber reinforced material and a melt index of 20 or more measured at 145°C is used. However, the material that is crosslinked after being composited with polyethylene fiber reinforcement exhibits the best physical properties. Furthermore, by forming a high-density polyethylene layer on the outer layer of the above composite, a composite with excellent surface strength can be obtained.

[Function] Examples of the polyethylene fiber used as a reinforcing material in the present invention include those disclosed in JP-A-60-45607 and JP-A-6
The tensile strength of the polyethylene fiber reinforcement must be 20 g/denier or more, and particularly preferably 30 g/denier. That's all. Further, the initial tensile modulus must be at least 500 g/denier, particularly preferably at least 800 g/denier. If the tensile strength is less than 20 g/denier, or if the initial tensile modulus is less than 500 g/denier, the mechanical strength in tensile, bending, impact, etc. of the resulting composite cannot be increased to the target level. .

On the other hand, the polyethylene used as the matrix layer constituent material has a
It must have a melting point as low as 15°C or more, and particularly preferred is one that has a melting point as low as 15°C or more. In addition, this polyethylene needs to have a large melt index in order to increase its affinity with the polyethylene fiber reinforcement and effectively exhibit the composite effect, and the melt index measured at 145°C is 20 or more, more preferably 40. The above are used. If the melt index is 20 or less, not only will the penetration of the matrix into the aggregate of polyethylene fibers serving as the fiber reinforcement become insufficient, but also the wettability of the fiber aggregate will be poor.
At the time of impact, the fiber reinforcement and the matrix tend to form an interface *uttt. From this point of view, low density polyethylene is preferred. The polyethylene that forms the matrix is not limited to pure polyethylene, and even partially modified polyethylene can be used as long as it has a predetermined melt index and a predetermined difference in melting point. However, when using modified polyethylene, it is necessary to use one in which the ethylene content in the polymer is 70 mol% or more; polyethylene with a lower content than this tends to have insufficient adhesion to the polyethylene fiber reinforcement material. This makes it difficult to obtain sufficient strength.

Various methods of combining fiber reinforcement material (hereinafter also referred to as reinforcing fibers) and matrix resin can be considered, but typical examples include reinforcing fibers arranged in one direction, or woven or knitted fabrics made of reinforcing fibers. Examples include methods such as impregnating a flat material such as a nonwoven fabric or paper with a molten matrix resin, or stacking sheet-like matrix resins and then heating and melting them to impregnate them. Alternatively, the matrix resin may be powdered and sprinkled on or mixed with the reinforcing fibers, and then heated and melted to impregnate the reinforcing fibers. Alternatively, the matrix may be melted and applied to the threads of the reinforcing fibers in advance to form a knitted fabric.

The polyethylene composite of the present invention is produced by combining the fiber reinforcing material and the matrix resin as described above, and then crosslinking the matrix resin. As means for crosslinking the matrix resin, dicumene oxide, tart-butyl hydroperoxide, t-
Examples include a method of blending organic peroxides such as ert-butyl perbenzoic acid and various benzoyl peroxides and heating, or a method of irradiation with radiation. The most common method is to mix an oxide, combine it with the ia fiber reinforcement, and then heat and crosslink it. In this case, it is of course possible to blend a third component such as an antioxidant or a coloring material into the matrix resin if necessary.

In this way, the present invention uses polyethylene, which has a lower melting point and a higher melt index than fiber reinforced materials, as a matrix and composites it with fiber reinforced materials, and then crosslinks the matrix. Since it has a relatively low melting point and a high melt index, it smoothly penetrates into the gaps between the fiber reinforcing materials and fills the gaps, eliminating the possibility of strength defects due to poor impregnation. Moreover, since the polyethylene matrix impregnated and composited in this way is then crosslinked to form a three-dimensional structure, there is no risk of defects due to insufficient strength of the matrix itself, and a polyethylene composite with excellent physical properties can be obtained. can.

Furthermore, if a high-density polyethylene layer with a high melting point is formed on the surface layer of the sheet-like composite obtained as described above, for example,
A composite material with even better surface hardness can be obtained.

[Example] Example 1 Polyethylene fibers having the following physical properties were used.

The average molecular weight obtained by substituting the intrinsic viscosity [η] obtained by measuring the viscosity of a decalin solution at 135°C according to ASTM D2857 into the following formula (1) is 2,000,000.

The tensile strength and initial tensile modulus determined according to JIS L 1013 are 30 g/denier and 10 g/denier, respectively.
00 g/denier, and the melting point is 145°C as measured using a differential scanning calorimeter at a heating rate of 10'e/min.

Using the above polyethylene fibers, a plain woven fabric with a total fineness of 300 deniers, a warp and a weft of 180 filaments, and a warp of 22 wood/inch was obtained. J on both sides of the fabric
Density determined according to IS K 6760 is 0.9
2 g/crn” and has a melting point of 105°C as measured using a differential scanning calorimeter at a heating rate of 10 t/min (particle size is 250 μm or less and melting point is 145°C).
melt index is 50 and 2.5
% of dicumene oxide) was placed as a matrix component, and the mixture was heated at 140°C x 10g/cm.
By heating and pressurizing for 10 minutes under the conditions of 2, a composite plate with a thickness of 0.3 mm was obtained. This composite plate was further laminated with 10 sheets to obtain a thickness of 3a+l11. The 1afa content in this laminated composite board was 43%.

The tensile strength of the laminated composite board thus obtained was 87Kg/mm.
, interlayer shear strength is 4.5 Kg/mm2. The flexural modulus was 6.5xlO'g/mm', and the impact strength determined by the falling weight test was 90 Joules (minimum energy to cause breakage in the falling weight test), both of which were very excellent.

Example 2 The molding conditions in Example 1 were changed to 135°C x 10Kg/cm.
The thickness was 0.3 in the same manner as in Example 1 except that the time was 2 x 5 minutes.
A composite plate of mm was obtained. After this composite plate was irradiated with an electron beam of 2 eV x 5 mA for 5 seconds, 10 sheets were laminated to obtain a composite plate with a thickness of 3 mm.

The tensile strength of the obtained composite laminate was 85 kg,/m2,
The interlaminar shear strength was 4.3 Kg/'mm', the flexural modulus was 6.5×10'g/mn+', and the impact strength determined by a falling weight test was 85 Joules.

Example 3 The same plain woven polyethylene fiber as used in Example 1 was composited with low density polyethylene (melting point 103°C) powder with a melt index of 45 (145°C),
Heat and pressurize at g/ca+2 for 5 minutes to a thickness of 0.3 m.
A composite board of m was obtained. After this composite plate was treated with an accelerated electron beam of 2 eV x 5 mA for 15 seconds, 10 of these composite plates were stacked to give a net thickness of 3+ nm. The tensile strength of the obtained laminated composite board was 85Kg/mm", and the bending modulus was 5.8X103
g/mm', and the interlaminar shear strength was 4.1 to 87 mm2.

Example 4 Short fibers (LA fiber length: 5 mm) made of the same polyethylene fibers used in Example 1 and low-density polyethylene powder used in Example 3 were mixed in a weight ratio of 4:6. and melt-mixed at 135°C. Using this molten mixture, it was molded into a sheet with a thickness of 10 mm using a mold (
Molding temperature: 140°C, pressure: 10 kg/cm'). The obtained sheet-like material was subjected to the same accelerated electron beam treatment as in Example 3 to crosslink the matrix layer.

The composite plate thus obtained had a tensile strength of 22 kg/n+m' and a bending modulus of 3.1 x lO' and 87 mm2.

Comparative Example 1 A plain weave fabric made of the same polyethylene fibers as used in Example 1 and a matrix made of the same polyethylene powder as in Example 1 except that dicumene oxide was not blended were used, and treated in the same manner as in Example 1. A laminated composite board with a thickness of 3 m+n was obtained.

The tensile strength of the obtained laminated composite plate was 73 to 87 mm2, and the flexural modulus was! , 5 x 102Kg/mm', the interlaminar shear strength was 2゜3g/mm2, and the impact strength determined by the falling weight test was 40 joules, all of which were inferior to the laminated composite board obtained in Example 1. It was something.

Comparative Example 2 A laminated composite board obtained in exactly the same manner as in Example 3 except that the accelerated electron beam treatment was omitted and the matrix layer was not crosslinked had a tensile strength of 75 to 870 m2 and a flexural modulus of 1.6.
X 10' Kg/mm2, interlaminar shear strength is 2.1
Kg/mm2, and both were inferior to the laminated composite board obtained in Example 3.

Comparative Example 3 The tensile strength of the composite plate obtained by omitting only the accelerated electron beam treatment in Example 4 was 13 g/mm'%, and the flexural modulus was 1.3 x 102 Kg/++m', both of which were in Example 4. It was significantly inferior to the composite board obtained in step 4.

Comparative Example 4 In place of the polyethylene powder in Example 1, polypropylene powder (melting point =
A laminated composite board was obtained in exactly the same manner except that the temperature at the time of heating and pressure molding was 170°C. The obtained laminated composite plate had a tensile strength of 25 Kg/mm2 and a flexural modulus of 2.3×102 g/mm2, both of which were considerably worse than the laminated composite plate obtained in Example 1.

Example 5 In place of the polyethylene powder in Example 1, polyethylene containing 3.5 mol% of unsaturated groups (melting point: 98°C, melt index: 50, cumene peroxide blending ratio: 2.0%) was used, Hereinafter, in the same manner as in Example 1, the thickness is 0.
．． A 3 mm composite plate was obtained, and 10 pieces were further laminated to form a laminated composite plate with a thickness of 3 m111.

The tensile strength of the obtained laminated composite board is 80 Kg/nun'
, the bending elastic modulus is 4.4 x 103Kg/mm2. The interlaminar shear strength was 4.2 Kg/mm''.

Comparative Example 5 The same polyethylene fiber plain woven fabric as used in Example 1,
Density calculated based on JIS-6760 is 0.97
g/cm3, and the heating rate was 1 using a differential scanning calorimeter.
Polyethylene powder (particle size 250 μm or less, melt index at 145°C 5, containing 2.5% dicumene oxide) with a melting point of 130°C measured at 0°C/min was used, and the following was the same as in Example 1. A laminated composite board having a thickness of 3n++n was obtained.

The tensile strength of this laminate was 78 g/mm', the flexural modulus was 5.6 x 102 Kg/ml', and the interlaminar shear strength was 2.4 g/mm2, all of which were better than the laminate obtained in Example 1. It was inferior to composite boards.

[Effects of the Invention] The present invention is constructed as described above, and is made of a polyethylene fiber reinforced material and a cross-linked polyethylene matrix that are integrated into a composite without void defects, and are lighter than conventional glass fiber reinforced plastics. And tensile strength, tensile elasticity,
It has excellent impact resistance and is suitable for automobiles and helicopters.
In addition to impact-resistant plates such as, it can be widely used as various protective members, such as security shields and helmets, baseball leggings and helmets, etc.

Claims (3)

[Claims] (1) A polyethylene composite comprising a reinforcing material made of polyethylene fibers having a tensile strength of 20 g/denier or more and an initial tensile modulus of 500 g/denier or more, and a crosslinked polyethylene matrix. (2) The polyethylene matrix is made of polyethylene fibers, using a polyethylene polymer that has a melting point at least 5°C lower than the melting point of the reinforcing material made of polyethylene fibers, and has a melt index of 20 or more when measured at 145°C. The polyethylene composite according to claim 1, wherein a crosslinking bond is formed after being composited with the reinforcing material. (3) A polyethylene composite obtained by forming a high-density polyethylene layer on the outer layer of the composite according to claim (1) or (2).