JPH0813918B2 - Molded polyvinylidene fluoride - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyvinylidene fluoride molded article having a reduced linear expansion coefficient and excellent mechanical properties.

(Prior Art) Polyvinylidene fluoride (PVdF) has excellent mechanical properties, chemical resistance, abrasion resistance, stain resistance, etc.
Since it has particularly excellent weather resistance, it is mainly used for weather resistant paints, electric wire coating materials and molded articles for chemical processes. Further, in recent years, it has come to be applied as an electrically functional material used for a piezoelectric element, a pyroelectric element, etc. by utilizing its high dielectric property. However, although polyvinylidene fluoride has the above-mentioned excellent characteristics, it has a large coefficient of linear expansion, and therefore may be thermally deformed under conditions where the temperature changes drastically or when used in a high temperature range. Therefore, it is difficult to apply the polyvinylidene fluoride molded body to parts requiring high precision, particularly in the electronics field, and pipes and lining materials used in chemical industrial equipment.

In order to reduce the linear expansion coefficient of the polyvinylidene fluoride molded body, it has been proposed to use a composite molded body with asbestos or the like, or a laminated body with a metal material or fiber reinforced plastic (FRP) ( For example, Japanese Patent Publication Sho 53-
43149, etc.). However, such a composite molded article does not sufficiently reduce the linear expansion coefficient of polyvinylidene fluoride even if a large amount of filler is used, and conversely, it has excellent mechanical properties (for example, friction coefficient) that polyvinylidene fluoride has. Properties and wear characteristics) are impaired. On the other hand, in the case of the laminate, although the problem is solved in terms of physical properties, new problems such as an increase in weight due to lamination, peeling between layers due to a difference in linear expansion coefficient, and a decrease in degree of freedom in molding processability occur. .

(Problems to be Solved by the Invention) The present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to significantly reduce the linear expansion coefficient without impairing the excellent properties of polyvinylidene fluoride. Is
Another object of the present invention is to provide a polyvinylidene fluoride molding having excellent mechanical properties.

(Means for Solving the Problems) The polyvinylidene fluoride molded article of the present invention comprises 49 to 95% by weight of polyvinylidene fluoride, 4 to 50% by weight of a polymer exhibiting an anisotropic melting form, and 1 to 20% by weight of polyvinyl methyl ketone. %
Consists of

Polyvinylidene fluoride, which is the main component of the composition constituting the polyvinylidene fluoride molded article of the present invention, may be any one capable of ordinary melt molding, and the degree of polymerization thereof is 500 to 300.
It is preferably about 0.

Examples of the polymer (hereinafter, abbreviated as liquid crystal polymer) showing an anisotropic melting form which is an integral part of the above-mentioned molded product include aromatic-aliphatic polyester, wholly aromatic polyester, aromatic polyazomethine, and polyimide ester. Then, of these, a compound exhibiting an anisotropic melting form is selected.
As the aromatic-aliphatic polyester, for example, there is a copolymer of polyethylene terephthalate and parahydroxybenzoic acid. Examples of the safe aromatic polyester include a copolymer of para-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid: or a copolymer of para-hydroxybenzoic acid, terephthalic acid and 6-hydroxy-2-naphthol. Examples of aromatic polyazomethines include poly (nitrilo-2-methyl-1,4-phenylenenitroethylideine-1,4-phenyleneethylideine). Examples of the polyimide ester include a copolymer of 2,6-naphthalenedicarboxylic acid, terephthalic acid and 4- (4'-hydroxyphthalimide) phenol, or diphenol and 4- (4'-hydroxyphthalimide).
There is a copolymer with benzoic acid.

In order to determine that these copolymers are liquid crystal polymers, it is preferable to use that the liquid crystal polymers exhibit optical anisotropy in a molten state. The optical anisotropy can be confirmed by using an ordinary polarization microscope. For example, a test piece adjusted to a thickness of 1 mm or less is placed on a heating stage of a polarization microscope, and heated in a nitrogen atmosphere at a heating rate of 2 ° C./min. This can be easily confirmed by making the polarizer of the polarizing microscope orthogonal in this state and observing at a magnification of 40 times or 100 times. In such a method, the temperature at which these copolymers transition to the liquid crystal phase can be measured at the same time.
This transition temperature can also be measured by differential scanning calorimetry (DSC).

As the liquid crystal polymer, a polymer that exhibits an anisotropic melting form in a temperature range from the crystal melting point of polyvinylidene fluoride (about 180 ° C.) to the thermal decomposition temperature of the polyvinylidene fluoride (about 350 ° C.) is preferably used. It This is because, as a procedure for producing the molded article of the present invention, a method including a step of dispersing the above composition in a molten state is generally used. In such a method, when any one of the polyvinylidene fluoride and the liquid crystal polymer constituting the molded product is not suitable for the molten state, or when one of them causes thermal decomposition, the obtained molded product is obtained. It is not preferable because it reduces the physical properties of the body. Generally, the preferable molding temperature of polyvinylidene fluoride is 200 to 300 ° C., and therefore it is preferable to select a liquid crystal polymer that can be molded within such a temperature range. Therefore, among the above liquid crystal polymers, aromatic-aliphatic polyesters and wholly aromatic polyesters are particularly preferable.

Moldings consisting only of the above-mentioned liquid crystal polymers usually have excellent mechanical properties (eg strength, elastic modulus and impact strength). Further, in the molded body obtained by injection molding or extrusion molding, the mechanical properties are improved because the polymer molecules are oriented parallel to the resin flow direction during melting. This is a self-reinforcing effect due to the liquid crystal polymer exhibiting an anisotropic melting morphology, and its degree of improvement is governed by the degree of orientation of polymer molecules. Therefore, the mechanical properties of the melt-molded body of the liquid crystal polymer often differ depending on the molding method and the shape of the molded body. For the same reason, the molded product of the liquid crystal polymer exhibits remarkable anisotropy with respect to mechanical properties. Further, since the molecular structure of the liquid crystal polymer is linear, it usually has a small coefficient of thermal expansion (coefficient of linear expansion). Moreover, in the flow state, the linear expansion coefficient in the direction parallel to the flow becomes smaller. Since the polyvinylidene fluoride molded article of the present invention is composed of a composition containing a liquid crystal polymer having such characteristics and polyvinylidene fluoride, the linear expansion coefficient is reduced as compared with a molded article composed only of polyvinylidene fluoride. . In addition, this molded product also has excellent mechanical properties and molding processability.

Polyvinyl methyl ketone, which is one component of the above-mentioned molded article, improves the compatibility between polyvinylidene fluoride and a liquid crystal polymer, and may be a homopolymer of vinyl methyl ketone, or mainly composed of vinyl methyl ketone. It may be a copolymer with the copolymerizable monomer of.

The ratio of each component constituting the polyvinylidene fluoride molded body of the present invention is 49 to 95 wt% polyvinylidene fluoride,
The liquid crystal polymer is 4 to 50% by weight, preferably 5 to 30% by weight
Is. If the content of the liquid crystal polymer is less than 4% by weight, the effect of reducing the linear expansion coefficient cannot be expected. When it approaches 50% by weight, the effect converges to a substantially constant value. And if it exceeds 50% by weight, the fibrils of the liquid crystal polymer are difficult to be finely divided,
The physical compactness of the molded body cannot be obtained.

The content of polyvinyl methyl ketone is 1 to 20% by weight, preferably 8 to 15% by weight. When the amount of polyvinyl methyl ketone added is reduced, the effect of improving the compatibility between polyvinylidene fluoride and liquid crystal polymer disappears. Is damaged.

The polyvinylidene fluoride molded article of the present invention is generally produced by melt molding. Examples of such a manufacturing method include any molding method of melt-molding a composition comprising polyvinylidene fluoride, a liquid crystal polymer and polyvinyl methyl ketone. For example, polyvinylidene fluoride,
Melting liquid crystal polymer and polyvinyl methyl ketone
Kneading, followed by extrusion molding, blow molding, injection molding,
It is molded by calender molding. Alternatively, the kneaded product is pelletized or powdered, and then the molding process is performed using these.

In such molding, the liquid crystal polymer is easily formed into a fibril form by being subjected to extensional flow or shear flow in a molten state, and the major axes thereof are often arranged substantially parallel to each other. Such orientation of fibrils is effective in reducing the linear expansion coefficient of the molded body. Therefore, promoting the fibrillation of the liquid crystal polymer,
It is useful to use a means to increase the degree of fibril orientation. For example, in extrusion molding, it is effective to place a static mill in series with a molding machine and use a molding die having a relatively large length / diameter ratio. This is because, when the composition sufficiently dispersed in the extruder passes through the static mill, the extensional flow and the shear fluid are efficiently added to the liquid crystal polymer in the liquid crystal state. Further, if the molded body is stretched uniaxially or biaxially before it solidifies in the cold legs, the fibrillation of the liquid crystal polymer becomes remarkable, which is extremely effective. In injection molding, increasing the shear rate of the resin in the mold (for example, increasing the injection speed and reducing the thickness of the clearance in the mold) is effective.

In the molded product thus obtained, the long fibers of the liquid crystal polymer are uniformly dispersed in the polyvinylidene fluoride, and therefore, the linear expansion coefficient is smaller than that of the molded product made of polyvinylidene fluoride alone. Moreover, the molded product has improved mechanical properties and excellent stain resistance. Because, when a liquid crystal polymer takes a fibril form, the molecules of the polymer are in the highest orientation state, so that the liquid crystal polymer has both a larger elastic modulus and a smaller (sometimes negative) linear expansion coefficient, This is because it is considered to be particularly effective in reducing the linear expansion coefficient of the molded product containing the polymer. The liquid crystal polymer fibrils preferably have a diameter of 10 μm or less. And, the average length / diameter ratio (L / D) of this fibril is preferably 10 ² or more, more preferably 10 ³ or more. Since the fibrils of the liquid crystal polymer having such a shape are dispersed, the linear expansion coefficient of the polyvinylidene fluoride molded product is sufficiently lower than that of the molded product made of polyvinylidene fluoride alone. Further, it is preferable that the fibrils are substantially uniaxially oriented in the molded body, because the linear expansion coefficient in that direction is selectively reduced.

Glass fibers, inorganic fillers, modifiers, lubricants, heat stabilizers, plasticizers and the like may be further added to the molded product of the present invention in order to improve mechanical properties, moldability and the like.

The polyvinylidene fluoride molded article of the present invention has a sheet shape,
It is formed into a desired shape such as a rod shape, a film shape, a pipe shape, a fiber shape, or a lump shape. Molded article of the present invention, pipes, tubes, joints, valves, used under various strengths and solvents,
It is used in a wide range of applications as plant parts such as tanks and filters: mechanical parts such as piston rings and bearings; wire coating materials that require high dimensional accuracy and electronic parts.

(Examples) The present invention will be described below with reference to Examples.

Examples 1 to 4 and Comparative Examples 1 and 2 Predetermined amounts of polyvinylidene fluoride (K polymer # 1000 manufactured by Kureha Chemical Co., Ltd.), wholly aromatic polyester liquid crystal polymer (LCP100E manufactured by Idemitsu Petrochemical Co., Ltd.) Further, polyvinyl methyl ketone was supplied to a twin-screw kneading extruder, and was sufficiently melt-kneaded at a resin temperature of 210 ° C. This was extruded as a strand-shaped molded product having a diameter of about 2 mm, and this was cut into pellets having a length of about 4 mm using a pelletizer. The obtained pellets were extruded as a sheet-shaped molded product having a thickness of 1 mm by a 35 mm single-screw extruder, and at the same time, roll-drawing was performed to obtain a sheet-shaped polyvinylidene fluoride molded product. The molding conditions at this time were that the maximum heating temperature of the extruder heating cylinder was 210 ° C., the molding die temperature was 200 ° C., and the screw rotation speed was 60 rpm. The dimensions of the molding die were 1 mm in thickness and 100 mm in width. Further, the draw ratio by drawing (calculated from the cross-sectional area of the molded product) was 0%, 20% or 50% (described in Table 1).

The linear expansion coefficient of the extrusion direction of the obtained molded body is measured,
A tensile test was conducted and the results are shown in Table 1. The linear expansion coefficient was measured according to ASTM D696, and the tensile test was measured according to ASTMD638.

In addition, an electron micrograph of the fracture surface of the obtained film (10
00 times) to average diameter of fibrils of liquid crystal polymer (D)
Is measured, the film is dissolved with dimethylacetamide,
The average length (L) of the fibrils of the liquid crystal polymer was measured from the polarization micrograph (100 times) of the remaining fibrils, and L / D
Was calculated and shown in Table 1.

As is apparent from the table, the polyvinylidene fluoride molded article of the present invention has a reduced linear expansion coefficient and excellent mechanical properties and moldability. A molded product made of only polyvinylidene fluoride without containing a liquid crystal polymer has a large tensile elongation as a property peculiar to polyvinylidene fluoride.
However, the linear expansion coefficient is large and the tensile elastic modulus is small, so the mechanical properties are poor.

(Effects of the Invention) Since the polyvinylidene fluoride molded article of the present invention contains the polymer (liquid crystal polymer) exhibiting an anisotropic melting morphology and polyvinyl methyl ketone in this manner, it has excellent properties possessed by polyvinylidene fluoride. (I.e., weather resistance, chemical resistance, abrasion resistance, stain resistance, etc.), the linear expansion coefficient is significantly reduced, and excellent mechanical properties and moldability are obtained. Such molded products require plant components such as pipes, tubes, joints, valves, tanks and filters used under various strong acids and solvents; mechanical parts such as piston rings and bearings; and high dimensional accuracy. Widely used as a wire coating material and electronic parts.

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Claims (1)

[Claims] 1. A polyvinylidene fluoride molding comprising 49 to 95% by weight of polyvinylidene fluoride, 4 to 50% by weight of a polymer exhibiting an anisotropic melting form, and 1 to 20% by weight of polyvinyl methyl ketone.