JPH0711037A - Continuous sheet-like fluororesin crosslinked foam - Google Patents

Abstract

PURPOSE:To obtain a continuous sheet-like fluororesin crosslinked foam excellent in surface smoothness and having a fine and uniform pore structure and a high foaming ratio. CONSTITUTION:This continuous sheet-like fluororesin crosslinked foam is produced by thermally foaming the ionizing radiation-crosslinked product of a polyvinylidene fluoride resin under the atmospheric pressure, and has a 25% compression hardness of 0.5-2kg/cm<2>, a moldability (L/D) of 0.3-0.8, a flame- resistant oxygen index of >=30, a crosslinking degree of 20-80% and a foaming ratio of 3-50times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous sheet type fluororesin crosslinked foam.

[0002]

Fluorine-based foams are generally excellent in flame resistance, heat resistance, chemical resistance, solvent resistance, abrasion resistance, and non-adhesiveness, and therefore seal materials, packing materials, gasket materials. Widely used as a heat insulating material and elastic roll coating material.

Conventionally, a fluorine resin foam has been disclosed in Japanese Patent Laid-Open No. 54-
41969, 59-11340, and 62-.
No. 112637 and No. 62-280236, an inorganic foaming nucleating agent and a decomposable foaming agent are added to the fluororesin, and the mixture is extruded and foamed. Alternatively, a decomposable foaming agent is replaced by a fluorine-containing volatile foaming agent. Or a fluororesin previously blended with a decomposing type foaming agent is molded into a sheet and then crosslinked by an electron beam or radical decomposition method to foam, or the fluororesin is There has been proposed a method in which the resin composition is molded into a dough-like shape, then crosslinked by an electron beam or radical decomposition method, then impregnated with a volatile foaming agent under pressure, and then heated, pressurized and released to foam.

However, in order to obtain a continuous sheet-like foam having a high expansion ratio, a specific method, that is, a method in which a foaming agent is blended and extrusion is carried out in a continuous sheet-like state and foaming is carried out simultaneously or a continuous sheet is formed. It is limited to one of the methods of foaming after being molded into a torch shape. A continuous sheet-like foam cannot be obtained by any other known method, that is, a method of impregnating with a volatile foaming agent and foaming.

These known techniques have the drawbacks that it is difficult to obtain a continuous sheet-like foam having a fine and uniform cell structure and a high expansion ratio, and it is difficult to obtain a stable product.

[0006]

DISCLOSURE OF THE INVENTION The present invention overcomes the drawbacks of the prior art, has excellent surface smoothness, has a fine and uniform cell structure, and has a high expansion ratio and is a continuous sheet type fluororesin crosslinked foam. To provide the body.

[0007]

As a result of intensive studies for overcoming the drawbacks of the present invention, the present invention has excellent sheet moldability by using a fluorine-based resin having specific characteristics and has a high radiation-induced crosslinking efficiency. Good, as a result, it was found that a continuous sheet-like fluororesin crosslinked foam with a high expansion ratio having a fine and uniform cell structure with excellent surface smoothness was obtained, and based on this finding, The invention was completed.

Namely, 25% compressive hardness of the ionizing radiation crosslinking of polyvinylidene fluoride resin was heated foamed normal pressure 0.5~2kg / cm ^2, the moldability (L / D) is 0.3
0.8, flame retardant oxygen index is 30 or more, crosslinking degree is 20-8
The object of the present invention is basically achieved by a continuous sheet-like fluororesin crosslinked foam characterized by 0% and an expansion ratio of 3 to 50 times.

The polyvinylidene fluoride resin used in the present invention is at least a polyvinylidene fluoride resin and MI.
Is preferably 2 g to 100 g / 10 minutes, more preferably 5
It is preferable that the resin contains 50 to 50% by weight of g to 30 g / 10 minutes. If the MI is less than 2 g / 10 minutes, the melt viscosity during melt extrusion during foaming continuous sheet molding is high, so that the compounded foaming agent is decomposed and a foam having uniform fine cells cannot be obtained. When it exceeds 100 g / 10 minutes, the molecular weight of the resin becomes small, so that the mechanical strength of the foam decreases and the foaming gas diffuses from the surface so much that the surface smoothness is impaired. On the other hand, if the content of the polyvinylidene fluoride resin is less than 50% by weight, the heat resistance will decrease, which is not preferable.

As the polyvinylidene fluoride resin, a copolymer of vinylidene fluoride and tetrafluoroethylene or vinylidene fluoride and propylene hexafluoride having a copolymerization ratio of 70 is used in order to improve resin flow characteristics. / 30 ~
95/5, more preferably 75/25 to 90/10 may be used. When the copolymerization ratio exceeds 30 and is copolymerized, the melting point of the resin is increased, and the resin fluidity is deteriorated to deteriorate the extruded sheet workability, which is not preferable and the chemical resistance is deteriorated. This deteriorates the quality, which is not preferable.

Resin flow characteristics are greatly improved and it is preferable for extruding sheet processability, but since the melting point is lowered, heat resistance,
It is not preferable because the chemical resistance deteriorates. On the other hand, when it is less than 5, the vinylidene fluoride homopolymer is not so different from the homopolymer product, and the effect of improving the flow characteristics by copolymerization becomes small, which is not preferable.

The polyvinylidene fluoride resin may have a mixture of vinylidene fluoride and tetrafluoroethylene or a copolymer of vinylidene fluoride and propylene hexafluoride. Alternatively, the mixing ratio of the copolymer of vinylidene fluoride and propylene hexafluoride is preferably suppressed to less than 50% by weight. 50% by weight of a copolymer of vinylidene fluoride and tetrafluoroethylene or vinylidene fluoride and propylene hexafluoride
If it exceeds, heat resistance is lowered, which is not preferable.

In the present invention, an acrylate or methacrylic resin is added to the polyvinylidene fluoride resin in an amount of 5 to 4
A mixture of 0% by weight can also be used. Since the composition in which acrylate or methacrylic acid is mixed can slow the melt flow characteristics and the crystallization rate during sheeting, a sheet having excellent flatness can be obtained without special cooling conditions. preferable. At this time, if the mixing ratio of the acrylate or methacrylic resin is less than 5% by weight, it is preferable from the viewpoint of heat resistance, but the melt flow characteristics are deteriorated and it is difficult to control the crystallization rate, and it becomes difficult to obtain a smooth sheet. It is not preferable. On the other hand, if it exceeds 40% by weight, it is preferable in terms of sheet moldability, but heat resistance, flame retardancy, and moldability (L / D) deteriorate, which is not preferable.

Further, in the present invention, the polyvinylidene fluoride resin is 50 to 80% by weight, and more preferably 55 to 7% by weight.
5% by weight, a copolymer of vinylidene fluoride and tetrafluoroethylene or a vinylidene fluoride and propylene hexafluoride is 5 to 45% by weight, more preferably 7 to 40% by weight, and an acrylate or methacrylic resin is used. A mixture of 5 to 15% by weight, preferably 7 to 12% by weight can also be used. The reason why the mixture of these three resins is not great, but the melt flow characteristics are remarkably better than those of the above-mentioned single resin or copolymer resin and mixed resin composition.
Since the crystallization rate at the time of sheet molding is suppressed, the range of cooling conditions is widened and it becomes easy to obtain a smooth sheet. At this time, if the polyvinylidene fluoride resin is less than 50% by weight,
Although it is preferable in terms of moldability, it is not preferable because it lowers heat resistance, and when it exceeds 80% by weight, it is preferable in terms of heat resistance, but melt flow characteristics are deteriorated and crystallization rate during sheet molding is controlled. It is difficult because it becomes difficult. If the copolymer of vinylidene fluoride and tetrafluoroethylene or the copolymer of vinylidene fluoride and propylene hexafluoride is less than 5% by weight, the flow characteristics, which are considered to be due to the synergistic effect of the three resins, are significantly deteriorated. If it exceeds 45% by weight, the heat resistance decreases, which is not preferable. On the other hand, if the amount of the acrylate or methacrylic resin is less than 5% by weight, it is difficult to suppress the melt fluidity and the crystallization rate during the sheet molding, which is not preferable, and if it exceeds 15% by weight, the heat resistance and the moldability (L / D) worsens, which is not preferable. Examples of the acrylate or methacrylic resin include polymethylmethacrylate, ethylene and acrylic acid or methacrylic acid, and acrylic acid alkyl ester resin. The foam according to the present invention has a 25% compression hardness of 0.2 to ² kg / cm ² , and a moldability (L / D) of 0.3 to 0.
8, flame retardant oxygen index is 30 or more, crosslinking degree is 20-80
%, And the expansion ratio is preferably 3 to 50 times. 25
When the% compression hardness is less than 0.2 kg / cm ² , the compression hardness is low and a soft value, but since the fluororesin foam is a rigid resin, recovery is poor and so-called “sagging” occurs. It is not preferable because the holding property is deteriorated. On the other hand, when it exceeds ² kg / cm ² , the rigidity becomes remarkable and the cushioning property of the foam is deteriorated, which is not preferable.

Further, the foamed product is used by being molded by various molding methods by taking advantage of the heat resistance and flame retardancy which are the characteristics of the fluororesin, and the moldability (L / D) is 0.3. If it is less than the above range, complicated shapes cannot be accommodated, which is not preferable. On the other hand, 0.8
If it exceeds the range, depending on the shape of the molded product, it becomes extremely thin and the shape cannot be maintained, and a reinforcing material is used, which is not preferable.

When the flame retardant oxygen index is less than 30 in the foam of the present invention, not only the smoke generation phenomenon but also the ignition phenomenon in the high temperature region is caused due to the combustibility in the field where electrical insulation and high flame retardancy are required at the same time. It is not preferable because it will burn.
When the degree of cross-linking of the foam of the present invention is less than 20%, it is preferable in terms of moldability, but it is not preferable because the degree of cross-linking is low, so that bubble breakage occurs due to escape of foaming gas from the surface of the foam. On the other hand, when it exceeds 80%, the heat resistance and the tensile strength are improved, which is preferable, but the tensile elongation is lowered and, consequently, the formability is lowered, which is not preferable.

If the expansion ratio is less than 3 times, the rigidity becomes remarkable, and even if a continuous sheet is obtained, it is difficult to wind it into a roll and it is not possible to supply it substantially in a continuous sheet, which is not preferable. On the other hand, if it exceeds 50 times, the foam film of the foam becomes extremely thin, which lowers the mechanical strength and the moldability, which is not preferable. The foam of the present invention has heat resistance, specifically 12
Unless the heat shrinkage rate at 0 ° C. is 3% or less, the fields to be used are limited, which is not preferable.

The initial melting torque is 1.3 to 3.0.
kg · cm, preferably 1.5 to 2.0 kg · cm. If the initial melting torque exceeds 3.0 kg · cm,
The foaming agent is decomposed by shearing heat generation during extrusion, and the foaming sheet contains air bubbles, which is not preferable.

In the foam of the present invention, an inorganic fine powder filler, a colorant, an antistatic agent comprising a fluorosurfactant, a known thio series, hindered phenol, etc. are used as long as the characteristics of the foam are not impaired. System heat stabilizer, hydroaromatic hydrocarbon compound,
Additives such as a reactive crosslinking aid containing two or more vinyl groups may be added.

In the present invention, it is necessary that the foam is cross-linked. As a cross-linking method, a radiation cross-linking method carried out by irradiating with ionizing radiation can be exemplified, but a peroxide such as peroxide is also used. However, the radiation dose is preferably in the range of 2 to 50 Mrad.

As a method for foaming the foam according to the present invention, a known method can be applied, and specific examples thereof include a hot air foaming method and a chemical solution foaming method. The foam according to the present invention is wound into a continuous sheet and then annealed at a temperature 20 ° C. lower than the melting point of the resin for 24 hours to obtain heat resistance, rigidity,
Properties such as strength can also be improved.

Next, a method for producing the continuous sheet type fluorine resin crosslinked foam according to the present invention will be described.

80 parts by weight of polyvinylidene fluoride resin as a fluorine-based resin and 20 parts by weight of copolymerized resin powder having a copolymerization ratio of vinylidene fluoride and tetrafluoroethylene of 70/30 were added to talc having a particle size of 0.3 to 3 μm. Prepare 3 parts by weight, 11 parts by weight of azodicarbonamide as a decomposing foaming agent, and 0.5 parts by weight of Irganox 1010 as a heat stabilizer so that the total amount becomes 200 kg, and use a Henschel mixer.
Then, the mixer is rotated, and mixing is carried out while paying attention so that the temperature does not rise to 80 ° C. or more, and uniformly dispersed. This mixed raw material was introduced into an extruder with a vent heated to a temperature at which the blowing agent was not decomposed, extruded from a set T die, and rapidly cooled with a cooling roll at 20 ° C to obtain a bubble-free thickness due to air entrainment. 1.0 mm in width and 430 in width
The sheet is wound into a continuous sheet of mm.

This sheet is irradiated with an electron beam to form a crosslink suitable for foaming, that is, a foam having a crosslinkage of 20 to 8 is obtained.
The electron beam is irradiated so that the concentration becomes 0% to give cross-linking. This sheet is continuously introduced into a vertical hot air foaming furnace of a hot air heating type heated to a temperature 30 to 100 ° C. higher than the decomposition temperature of the foaming agent, specifically 250 ° C. to foam.

The foam thus obtained has a thickness of 2.7 mm, a width of 1250 mm, a foaming ratio of 28 times, a length direction ratio of 3.5 times, and a width direction ratio of 2.9 times. It is a sheet-like foam.

This foam has a 25% compression hardness of 0.85 kg.
/ Cm ² , moldability (L / D) of 0.72, flame retardant oxygen index of 42, and degree of crosslinking of 47%.

The continuous sheet-like fluororesin foam according to the present invention makes use of elasticity, high flame retardancy, heat insulation, chemical resistance, and heat insulation properties, and is used as a cover for a sponsor or an alkaline plating bath and also for moldability. And electrical characteristics inherent in resin, especially low dielectric constant, electrical relations such as computer wiring cover (fire spread material) and electric wire coating, polishing cloth for precision polishing, air conditioning duct heat insulating material for freight trains and aircraft ( Fire spread prevention material), engine engine room partition plate for automobiles, light weight simple fire shutter compounded with metal plate, non-combustible board laminated with inorganic fiber mat for heat insulation of radiation exposure part related to nuclear power generation It can be applied to various fields with a composite material such as a lining material or a pipe cover, a metal plate, a metal foil, a film and an inorganic fiber.

The measuring methods and evaluation criteria in the present invention are as follows.

1.25% compression hardness A value measured according to JIS K6767.

2. Formability The diameter is 5 cm and the depth is 0.4, 0.5, 0.
A vacuum forming machine equipped with a cup-shaped mold set to a ratio of 6, 0.7, and 0.8 is heated to 150 to 230 ° C. and vacuum-formed, and the ratio of the formed product without breaking the foam is determined by the moldability. And

3. Flame retardant oxygen index A value measured by the ASTM D2863-70 method.

4. Degree of cross-linking The foam is chopped and weighed 0.2 g precisely. 150 this
Immerse in tetralin at ℃, heat for 3 hours with stirring to dissolve the dissolved part, take out the insoluble part and wash with acetone to remove tetralin, then wash with pure water to remove acetone and hot air at 120 ° C Water is removed with a dryer and naturally cooled to room temperature. The weight (W ₁ ) g of this product is measured, and the degree of crosslinking is determined by the following formula.

Crosslinking degree = (W ₁ /0.2)×100
(%) 5. Foaming ratio 10 × 10 cm is cut out from the foaming sheet, and the thickness t ₁
(Cm) and weight W1 (g) are measured, and the sheet density is calculated by the following formula.

Sheet density (Sρ ₁ ) = W ₁ / (10 × 10 × t ₁ ) (g / cm ³ ). Further, 10 × 10 cm was cut out from the foam to obtain a thickness t _2.
(Cm) and weight W ₂ (g) are measured, and the density of the foam of the present invention is calculated by the following formula.

Foam density (Fρ 1) = W ₂ / (10 × 10 × t ₂ ) (g / cm ³ ) The expansion ratio is calculated from the above-mentioned sheet density and foam density by the following formula.

Expansion ratio = Sρ1 / Fρ1 (times) 6. According to MI ASTM D-1238-70 (5kg load, 2
(Under 30 ° C) 7. Surface smoothness 10 black ink stock solution of magic ink on the surface of foam
After applying cm ² or more, wipe off with a gauze, and judge the state of ink remaining on the surface after wiping with the following criteria.

[0037] ◎ ink on the surface of the --10cm ² in the bubble torn portion of the surface of ○ --10cm ² that ink does not remain at all there is ink in the bubble torn part of one to five a △ --10cm ² of surface 8 to 5 or more is more ○ with the entire surface ink × --10cm ² pass. Heat resistance Exactly cut into 15 × 15 cm from the foam, measure the thickness, put in a hot air oven at 120 ° C. and heat for 1 hour.
After taking out and cooling at room temperature for 2 hours, measure each dimension,
Measure the rate of change.

The rate of change in length, width and thickness of 3% or more is rejected.

9. Initial melting torque 90g of the sample was put into the mixer of Plastomill (No655 manufactured by Toyo Seiki Co., Ltd.) heated to 190 ° C, held for 5 minutes, kneaded at a rotor speed of 40 rpm, and the torque at that time was recorded. The value immediately after the instruction is the melting torque.

[0040]

EXAMPLES Next, the embodiments of the present invention will be explained based on examples.

Example 1 Polyvinylidene fluoride resin (Foraflon HD-)
6000 MI 5) Showa Denko KK) Crushed product 180
12 parts by weight of azodicarbonamide (AC- ^# 3 Eiwa Chemical Industry Co., Ltd.) and 2 parts by weight of talc (LM-R classified product average particle size 1.0 μm Tsuchiya Kaolin Co., Ltd.) were mixed and dispersed in a Henschel mixer. Then, this was introduced into a 65 mm ^φ twin-screw extruder heated to 185 ° C. with a vent, extruded from a mounted T die, and rapidly cooled by a cooling drum at 15 ° C. to have a thickness of 1.9 mm and a width of 500 mm, An uncrosslinked sheet for foaming having a length of 450 m was prepared.

This sheet was irradiated with an electron beam of 8.5 Mrad from both sides to crosslink it. 220 ~ 2 for this sheet
It was continuously introduced into a silicone chemical solution foaming tank heated at 35 ° C. and foamed to obtain a continuous sheet-like foam having 7 rolls of 200 m in length as a continuous sheet-like foam. The characteristics of this product are shown in Table 2.

Examples 2 to 5 and Comparative Examples 1 to 5 Using the components shown in Table 1, a foam was obtained by the method shown in Table 1, and the properties of the obtained foams are shown in Table 2. It should be noted that, when kneading was performed at a rotor rotation speed of 20 rpm and the torque was 10 minutes after the kneading was started, Examples 1 to 5 and Comparative Example 1 were performed.
~ 5 are 2.2, 1.6, 1.8, 1.2, 0.
8, 1.7, 4.1, 1.6, 0.5, 1.0 (kg
cm).

[0044]

[Table 1]

[Table 2]

[0045]

As described above, the foam according to the present invention shown in the examples becomes a continuous sheet foam having a fine and uniform cell structure, and has excellent flame retardancy, elasticity, molding processability, and melting property. It is a fluororesin cross-linked foam having excellent flow characteristics.

On the other hand, with the fluorine-based crosslinked foams shown in Comparative Examples, it is difficult to obtain a continuous sheet foam according to the present invention by a known method, and the flame retardancy, elasticity, molding process and surface smoothness are obtained. The heat resistance and heat resistance were not satisfied.

Claims (5)

[Claims] 1. A 25% compression hardness of 0.5 to ² kg / cm ² and a moldability (L / D) of 0.3 to which are obtained by heating and foaming an ionizing radiation cross-linked product of a polyvinylidene fluoride resin under normal pressure. 0.
8, flame retardant oxygen index is 30 or more, crosslinking degree is 20-80
%, The expansion ratio is 3 to 50 times, a continuous sheet-like fluororesin crosslinked foam. 2. The polyvinylidene fluoride resin according to claim 1, wherein the polyvinylidene fluoride resin is a copolymer resin of vinylidene fluoride and tetrafluoroethylene or vinylidene fluoride and propylene hexafluoride, and the copolymerization ratio is 70/30 to 95/5. A continuous sheet-like fluororesin-crosslinked foam, which is characterized in that 3. The polyvinylidene fluoride resin according to claim 1, wherein the polyvinylidene fluoride resin is a mixture of a polyvinylidene fluoride resin, vinylidene fluoride and tetrafluoroethylene or a copolymer resin of vinylidene fluoride and propylene hexafluoride. The continuous sheet-like fluororesin crosslinked foamed product. 4. The polyvinylidene fluoride resin according to claim 1, wherein the polyvinylidene fluoride resin is 60 to 95% by weight,
Acrylate or methacrylic resin is 5-40
A continuous sheet-like fluororesin cross-linked foam comprising a mixture in a weight percentage. 5. The polyvinylidene fluoride resin according to claim 1, wherein the polyvinylidene fluoride resin is 50 to 80% by weight, the polyvinylidene fluoride resin, the vinylidene fluoride and 4
It is characterized in that the copolymer resin of ethylene fluoride or vinylidene fluoride and propylene hexafluoride has a mixed resin composition of 5 to 45% by weight, and the acrylate or methacrylate resin has a mixed resin composition of 5 to 15% by weight. Continuous sheet-like fluororesin crosslinked foam.