DD284643A5 - POLYMOUS COMPOSITE MATERIALS BASED ON SPREADING FOILS AND METHOD FOR THEIR PRODUCTION - Google Patents

Abstract

The invention relates to polymeric composite materials based on splice foils and to a process for their preparation. The composites have a higher toughness, a greater resistance to propagation of cracks and a higher cohesion in the transverse direction than oriented one-component films. The polymer composite according to the invention has as reinforcing element at least one fibrillated splice film and at least one unfibrillated matrix film, which films may contain particulate or fibrous fillers. The composites are prepared by laminating the films at a temperature above the melting point of the unfibrillated matrix film and below the temperature at which the starting structure of the fibrillated reinforcing films is broken, and laminating at a pressure between 1 to 100 kPa ; Composite material; Spleiszfolie; Verstaerkungselement; Lamination; Matrix; polyethylene; cold stretching; Reiszfestigkeit}

Description

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Field of application of the invention

The invention relates to polymeric composite materials based on splicing films and to a process for their preparation. The composites according to the invention generally have a higher toughness, a greater resistance to crack propagation and higher cohesion in the transverse direction than oriented one-component films. Due to their strength they are suitable for. B. as packaging material. During the cold stretching of semicrystalline polymers, their strength and stiffness increase with simultaneous decrease of cohesion in the transverse direction.

Characteristic of the known state of the art

By mechanical treatment, films of some semicrystalline polymers can be relatively easily spliced into a system of parallel fibrils, sometimes even microscopically. This phenomenon is called fibrillation. Isotactic polypropylene (PP) fibrillates most easily, while the tendency for fibrillation in other polymers decreases in the following order: higher density polyethylene (PE), polyamide (PA) and polyethylene (PETP) (Polymer Testing 6 [1986],

5. 447). Fibrillated fibers have been used for woven and non-woven textiles, insulating panels and as reinforcement material for building materials (replacement of asbestos).

The tendency of the isotactic PP to fibrillate is also exploited for the production of composite materials. According to SU-US No. 103 504, first a mixture of PE and PP is heated. The result is a material consisting of fine and strong PP fibers in a PE matrix. Another method (Vysokomol Soed 29 [1987], p 778) uses the stretching of high density PE in liquid monomers (styrene, butyl methacrylate, etc.), which is polymerized after completion of the fibrillation of the PE and thus the matrix of the resulting composite forms. It has also been described to produce composite films formed by laminating ultrafine PE fibers in high and low density PE films (CS patent PV 7237-85). Since the reinforcing fibers of such composites have about 100 times higher strengths than the matrix, even a small volume concentration of such high performance fibers has a significant effect. A disadvantage of such films in some applications is the relatively low adhesion between the components, the high price of high performance fibers, and problems of even introduction of the reinforcing fibers in random or oriented configuration.

Object of the invention

The aim of the invention is a polymeric composite material based on splicing foils, which has a high strength, toughness and tear resistance, as well as an economically favorable process for its preparation.

Explanation of the essence of the invention

The object of the invention is to develop a polymer composite based on splicing films and a technically advantageous process for its production. In this case, a targeted orientation of the reinforcing fibrils is secured in the composite and thus a greater resistance to crack propagation and a higher cohesion in the transverse direction over oriented one-component films can be achieved.

According to the invention, the polymeric composite material consists of at least one fibrillated splicing film as reinforcing element and at least one unfibrillated matrix film, wherein both the fibrillated reinforcing film and the unfibrillated matrix film may contain particulate or fibrous fillers. As splice films, semi-crystalline polymers are used in a state before splitting into fibers. Thus, the targeted orientation of the reinforcing fibrils is secured in the composite from the outset.

According to the invention, the process for producing the polymer composite is based on the films being at a temperature which is above the melting point of the unfibrillated matrix film and below the temperature at which the starting structure of the fibrillated reinforcing splice films is destroyed, and at a pressure between 1 and 10OkPa be laminated. The fibrillated splicing films are alternately laminated with unfibrillated matrix films having a different degree of orientation, and then form the matrix. The lamination temperature is chosen between the melting temperature of the matrix layers and below the temperature at which the starting fibril structure of the reinforcing films is destroyed. It is favorable if the fibrillated films are in a preloaded state during lamination, since they may then solidify in a state of recrystallization instead of the unfavorable shrinkage. For example, in the lamination of the fibrillated films of isotactic PP between sheets of low density PE, the lamination temperature can be selected at about 160 ° C in the interval between 130 ⁰ C and 170 ° C, optimal. At the same time, one can laminate several layers having the same or different arrangement of the fibrillated splice films. Likewise, one can selectively reinforce areas with the expected higher mechanical stress of the unfibrillated matrix films, z. At the edges and bands of supporting elements and holes, etc. The starting films are exposed by lamination to a vertical pressure of from 1 to 10 kPa up to a maximum of 2 hours. The applied films may also contain particulate or fibrous fillers. After lamination, the material is either slowly cooled in air or quenched in a liquid. The composites produced according to the present invention exhibit anisotropy in mechanical properties and the yield strength is approximately determined by the mixing rule of the volumes in place of the components. Due to the high strength and rigidity of the fibrillated splice films, the stretching limit of the matrix can already be increased by a relatively small proportion of the reinforcing elements. The toughness and crack resistance are even more markedly increased. The fibrillated film alone fails to readily interfere with interfiber brittle fracture, while the fibrillated splice layer composite sandwiched between 2 matrix layers can even be used for cold stretching transverse to the fibril direction. In this case, one uses both the significant influence of the surface on the plasticity of the polymer material and the property that the matrix material fills in interfibrillar gaps and longitudinal cracks. At the same time, the fibrillated layer retains the property of blocking cracks that grow across the fibrils. The following examples characterize the subject matter of the invention without limiting it. The composite films given in the examples were produced from 4 starting films: 2 fibrillated reinforcing films V ₁ , V ₂ and 2 unfibrillated matrix films M ₁ , M ₂ . The fibrillated films showed pronounced anisotropy in mechanical properties and had significantly higher strength and stiffness in the direction of orientation (along the fibrils) than in the transverse direction. In contrast, the unfibrillated films had a less pronounced orientation (predominantly planar), which arises during the blowing technology. These films were made in the form of a closed tube, which was not cut for Examples 1 and 2, but only folded longitudinally. Therefore, in these cases, the layer thickness of the matrix was about twice as large as that of the original starting film. An overview of the starting films is given in Table I.

Table I - Characteristics of the starting film

output specification thickness foil in μσι V ₁ High density PE LitenPEVB33 fibrillated CSFR product 25 V ₂ isotactic PP Mosten 58412 with a salary of 30% by volume micro-milled Limestone, fibrillated CSFR product 30 M ₁ Low-density PE, Ring Trial 83, Slide D, DDR, unfibrillated 100 M ₂ High density PE, DDR product, unfibrillated 100

By mutual combination of the starting films, the composites K ₁ to K ₅ were prepared. Table II gives a scheme of composition and preparation.

Table II

Production conditions and composition of the composite film

foil layer sequence Conditions of lamination print Time Cooling proportion of kPa min to Ver Temp. 10.9 60 A strengthening. "С 9.9 5 A factor K ₁ 2 x Μ, / ν, / 2 x M, 136 10.9 30 B 6 K ₂ 2 χ M / V _2/2 χ M ₁ 157 10.9 30 B 7 K ₃ ІѴУѴг / ІѴуѴгІбОЧІѴІ, 139 10.9 10 A 14 K ₄ M ₂ / V ₂ / M ₂ / V ₂ (60 °) M ₂ 139 14 K ₅ M ₂ / V ₂ / M ₂ 175 13

Cooling conditions: A-cooling in air 3K / min

B - Cooling in H ₂ O at 2O ⁰ C Table III gives the results achieved in Examples 1 to 4.

Table III

Properties of the starting and laminated films

material MPa % e Jy ₂ 20O ⁺ 6O ⁺ Pa kJ / m ² V, 23O ⁺ 2O ⁺ 2.5 1800 V ₂ 9 9.5 2.9 800 M ₁ 9 9.5 0.30 13 M ₁ . 18 10 0.30 13 M ₂ 20 60 0.60 25 K ₁ 15 13.5 0.30 170 K ₁ . 23 21 0.30 80 K ₂ 13 14 0.33 65 K ₃ 24 12 0.40 30 K ₄ 0.75 35

- stretching limit ⁺ ) breaking stress

- deformation of the stretching limit ⁺ ) breaking elongation E - tensile modulus

Jy - specific deformation energy until failure of the material

Test conditions: temperature 25 ± 1 ° C,

Test speed 1 cm / min

Clamping length 20 mm

Width 10 mm

*) Test specimen with side notch 0.5 mm deep

The test direction was in the fibril direction of the reinforcing layer (foil K ₁ , K ₂ ) or along the axis of the smaller angle between the fibrils (K ₃ , K ₄ ).

embodiments

example 1

The high density PE fibrillated sheet LITEN PE VB 33 (reinforcing sheet V ₁ ) was laminated between low density PE sheets made as sheet D of ring trial 83 (matrix M ₁ ). This film was produced as a closed tube (Figure 1), which was used as a double layer during lamination and melted through. The lamination of composite material (composite K ₁ ) prepared from fixed-end splice sheets was carried out at a temperature of 136 ° C and a pressure of 10.9 kPa with a treatment time of 60 minutes, cooling at 3 K / min Air was made. The resulting composite K ₁ was made from 3 layers with two 200 μm thick outer layers and a 25 m thick reinforcing layer. The volume fraction of the reinforcing layer was only 6%. The mechanical properties of the composite K ₁ were measured along the orientation of the reinforcing layer Vi. The results are summarized in Table III.

It can clearly be seen that the relatively low proportion of the reinforcing layer increases the toughness J _{y of} the starting film M ₁ by more than 13 times and the energy of the crack propagation by at least 6 times. Figure 2 shows the stress-strain curves of the starting materials V ₁ , M ₁ and the resulting composite K ₁ . The crack direction can be seen in Figure 1.

Example 2

A fibrillated sheet of isotactic PP MOSTEN 58412 with 30% by volume micro-milled limestone (reinforcing material V ₂ ) was laminated between layers of low density PE (matrix M ₁ ) as in Example 1. The lamination was carried out at a temperature of 157 ° C, a pressure of 9.9 kPa and a treatment time of 5 minutes. The cooling was carried out in air at a rate of 3 K / min. The resulting composite K ₂ was composed of 3 layers with 200 μΐη thick side layers and 30 μπη central layer. The volume fraction of the solidification material was 7% by volume. The results of the mechanical tensile measurements in the direction of orientation of the fibrillated splice layer V ₂ are shown in Table III and in FIG.

The composite K ₂ shows about 5 times toughness J _y until failure compared to the matrix material. In this case, the toughness of the composite is determined by the failure of the fibrillated layer.

Example 3

Two layers of isotactic PP MOSTEN 58412 containing 30% by volume micro-milled limestone (reinforcing sheet V ₂ ) were laminated on both sides with 3 layers of low density PE (matrix M ₁ ). In this case, the directions of the reinforcing layers V _{2 were arranged} at an angle of 60 ° to each other. The lamination was carried out at a temperature of 139 ⁰ C, a pressure of 10,9kPa and a treatment time of 30 min. Thereafter, the composite was quenched in H ₂ O at a temperature of 20 ° C.

The resulting composite material K ₃ was composed of 5 layers: 3 layers of matrix material PE low density (M ₁ ) with a thickness of 100 μιτι and 2 layers of fibrillated PP (V ₂ ) with a thickness of 25 μιη. The volume fraction of the reinforcing material was 14% by volume. The mechanical properties of the tensile test were measured in a direction of 30 ° to the direction of orientation of the fibrillated reinforcing layers. The data are summarized in Table III and Figure 3. There is a significant reinforcing effect. Significant is the increase in the yield strength (almost 2.5 times). These values were also achieved outside the fibrillation direction of the reinforcing sheet.

Example 4

A five-layered composite film K ₄ was produced in the same manner as in Example 3, but the matrix film employed was a PE film of high density (matrix M ₂ ). The tensile mechanical measurements were carried out as in Example 1. The results are summarized in Table III and Figure 3. In this case, the influence of the fibrillated film on the strength properties of the composite was less pronounced than in Example 3, since a matrix with higher stretch limit and stiffness was used.

Example 5

A fibrillated sheet of isotactic PP MOSTEN 58412 having a vol. Content of 30% micro-milled limestone (reinforcing sheet V ₂ ) was laminated between layers of PE sheet with higher density PE (matrix M ₂ ). The lamination was carried out at a temperature of 175 ° C, a pressure of 10.9 kPa and a treatment time of 10 minutes. The cooling rate was 3K / min.

During lamination, uneven, low shrinkage of individual layers occurred. The material became irregularly wavy and contained bubbles. In this case, the lamination temperature was too high to produce a useful film.

Claims (4)

1. Polymeric composite materials based on splice foils, characterized in that they consist of at least one splicing film as a reinforcing element and at least one unfibrillated matrix film. 2. Polymeric composite materials according to claim 1, characterized in that the reinforcing film and / or the matrix film contains particulate or fibrous fillers. 3. A process for the preparation of polymeric composite materials based on splice foils, characterized in that the films at a temperature which is above the melting temperature of the unfibrillated matrix film and below the temperature at which the starting structure of the fibrillated reinforcing film is destroyed, and a pressure be laminated between 1 and 100 kPa. 4. The method according to claim 3, characterized in that at the same time several film layers are laminated, which have an identical or different arrangement of the fibrillated splice films.