JPH0249612B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a fiber-reinforced heat insulating foam used in storage containers for low-temperature liquefied gases, particularly ultra-low-temperature liquefied gases such as LNG. BACKGROUND OF THE INVENTION The production of continuous polyurethane foam rigid panels with reticular reinforcement consisting of elongated glass filaments is known (Japanese Patent Publication No. 30233/1983). This method involves vertically pulling a condensed cocoon made of glass filament tape, in which glass filaments longer than the panel thickness are arranged transversely to the length of the tape. cross-distributed in various directions, and the thickness is approximately 20% smaller than the initial thickness of the tape.
This method involves expanding the glass filament to double its original size, laminating a glass film or glass mesh above and below it, pressing it to the desired panel thickness, then spraying a polyurethane stock solution and foaming and curing it, but it is difficult to uniformly disperse the glass filament within the foam. On the other hand, the air initially contained in the glass filament tends to remain in the foam, creating a large space, which is not a big problem if used as a heat insulating panel for building materials, etc.
Insulating materials for LNG at temperatures of 162°C not only deteriorated insulating properties, but also caused cracks, resulting in a fatal defect of not being able to withstand long-term use. Also, it is composed of multiple layers of filament or strand glass fibers, the multiple layers of glass fibers are substantially parallel to each other, and the longitudinal direction of the glass fibers of each layer intersects the longitudinal direction of the glass fibers of each adjacent layer,
Structural laminates are also known (Japanese Patent Publication No. 57-58294) characterized in that a rigid foam completely fills the gaps between the glass fibers of the mat. however,
The glass fiber reinforced foam obtained by this method is
Since there is no entanglement between the glass filaments, it exhibits extremely favorable performance in terms of heat insulation, but -
The disadvantage is that the foam tends to crack under extremely low temperature conditions of 162°C. So far, the most suitable insulation method has been the ML system, which consists of lining a glass fiber mesh as a low-temperature side layer, as introduced in Plastic Materials Vol. 16, No. 10 (1975), but this method is Because it is a construction method, there is a large amount of urethane spray loss.
The problem was that factory production was difficult. (Purpose of the Invention) The present application aims at producing a fiber-reinforced foam that can be stably mass-produced and has excellent heat insulation properties and a reinforcing effect that can withstand long-term use when used as a heat insulating material for ultra-low temperature liquefied gas containers such as LNG. The purpose is to provide a method. That is, it is a belt-shaped strand mat consisting of long fibers, each fiber is interlaced in a random direction and coarsely partially bonded with as little as possible of a powdered binder, and is made up of at least two layers, preferably three to six. After laminating the layers and spraying the foamable synthetic resin stock solution, the foaming stock solution is compressed until it oozes out on the top surface of the strand mat before it starts to foam, and the air trapped between each fiber is compressed. be completely discharged. Then, by foaming the foaming stock solution, the foaming pressure dissociates the bonds formed by the unpowdered binder, and fills the spaces between each fiber with foam, eliminating air pockets (voids) that cause cracks. By passing through a pressurized zone that inherently limits free foaming while preventing formation.
This is a method of manufacturing a reinforced foam in which the upper surface flatness and thickness of the foam molded body are controlled, and the fibers are uniformly dispersed in the foam while maintaining the intertwining of each fiber. (Structure of the Invention) Glass fiber is most suitable for the strand mat used in the present application, and other synthetic fibers such as polyamide and polyester, inorganic fibers such as carbon fiber and ceramic fiber, etc. can also be used. There are no particular restrictions on the fiber filament, but it is preferably a strand mat made from long filaments of 25 microns or less, with each mat having a thickness of about 3 to 5 mm, and usually a long strip of 50 m or more. of pine are used for production. In this strand mat, for example, in the case of glass fiber, each filament is treated with a fiber binding agent such as polyurethane resin, and partially bonded with a powdered resin binder to maintain the intertwining of the filaments with each other. use something The amount of unpowdered resin binder should be as small as possible within the range that maintains the mat shape, and is usually 5% or less of the weight of the fibers, most preferably 1.5 to 3.5% by weight. When the amount of the unpowdered resin binder used exceeds 5% by weight, it becomes difficult to dissociate it under the foaming pressure of the foamable synthetic resin stock solution, and it becomes difficult to obtain a foam with uniform fiber dispersion. while 1.5
If the amount used is less than % by weight, the filaments will not be bonded together sufficiently and it will be difficult to maintain the shape of the strand mat. The fiber-reinforced foam of this application can be used as a membrane method.
When used as insulation for LNG, the preferred content of glass fibers in the foam ranges from 6 to 30% by weight, optimally from 8 to 15% by weight. This is because if it is less than 6% by weight, the effect of preventing cracks at low temperatures is poor, while if it is more than 30% by weight, it may cause cracks in the foam or abnormal foaming when the synthetic resin foaming stock solution is foamed. Generally, fiber strand mats with a thickness of 3 to 5 mm and a weight per unit area of 200 to 600 g/m ² are used, and 2 to 6 layers are laminated to reduce the weight per 1 m ² to 1200 g/m 2.
The final molding thickness of the foam is 100 to 150 g.
It is best to perform foam molding so that the diameter is mm. It should be noted that when connecting the strand mats in the longitudinal direction, it is advantageous to slightly shift the connecting portions of each layer in the longitudinal direction, so that the joints feel less strange and it is convenient to obtain a uniform dispersion state. The stock solution of the foamable synthetic resin used in this application is preferably one with a relatively slow initial reaction, with a cream time of about 1 to 3 minutes until it starts to become cloudy due to foaming after being mixed at room temperature. Generally, rigid polyurethane foam or phenolic foam is used. This system with a slow cream time is used because while the foaming stock solution discharged onto the strand mat is still at a low viscosity, the strand mat is compressed to expel the air trapped between the filaments, and the foaming stock solution is This is because it is extremely important to achieve the object of the present application by replacing the oscillator with a sufficient amount of vibration. At this time, the degree of compression of the strand mat is also an important factor; if the compression rate is too high, the foam is likely to crack during foaming, and if the compression rate is too low,
The foam cannot be uniformly impregnated with the foaming stock solution and air remains, forming cavities in the foam and causing cracks in the foam at low temperatures. A preferred degree of compression is such that the raw solution oozes over the entire upper surface of the strand mat. This compression may be carried out by any means, but in the case of continuous production, it is desirable to arrange a large number of rolls so that the gap between the rolls and the conveyor gradually becomes smaller. When the strand mat is compressed with a roll, the foaming stock solution tends to gather at the edges in the width direction, so the pressure roll should have a cross-sectional shape of a concave lens, with a small diameter at the center and a large diameter at both ends. It is recommended to use a roll that has been When using rolls of uniform diameter, weirs may be provided at both ends of the conveyor to push back the stock solution. Furthermore, in order to prevent the stock solution from being pushed back and mixing with the newly discharged stock solution when pressurized, the conveyor in this containing zone may be provided with an inclination. Alternatively, in order to avoid applying too much pressure, it is desirable to add a device to the pressure roll that lifts up when the pressure exceeds a certain level to obtain a more preferable impregnation state. The foaming stock solution may be sprayed onto the strand mats by a traverse method in which the discharge nozzle is moved in a direction substantially perpendicular to the direction of travel of the strand mats,
Alternatively, a method of spraying by arranging a plurality of spray guns horizontally may be used. Alternatively, depending on the number of stacked strand mats, a method may be used in which the undiluted solution is spread on the conveyor in advance and then the strand mats are placed on the conveyor, or these methods may be used in combination. At the stage where the strand mat is uniformly impregnated with the foaming stock solution and then foaming begins, the thickness of the foam is controlled by suppressing the free foaming of the solution with a pressure slightly higher than the foaming pressure of the foaming stock solution. It is necessary to control the thickness of the foam and to ensure that the top surface of the foam is flat. This pressurizing means consists of a variable pressure device, in which a large number of rolls are lined up on the upper and lower surfaces of the material, the lower roll is fixed, and the upper roll is pressurized with a pressure slightly higher than the foaming pressure of the liquid. It is desirable to use a roll with The foaming pressure of the foaming stock solution varies depending on the formulation and is usually about 1 to 3 kg/cm ² in the case of rigid polyurethane foam, so in this case it is preferable to adjust the pressure to 1.1 to 5 kg/cm ² . In this case as well, in the initial stage of foaming, the upper roll is made to float with a slight pressure, and in the later stage of foaming, consideration is given to applying pressure that is considerably higher than the foaming pressure of the liquid.
It is desirable to adjust the thickness of the foam molded product to a desired value. The molded product that has almost completed its foaming will gradually harden. At this stage, steel belt conveyors are placed above and below to apply large pressure to maintain the dimensions and shape of the molded product. It can also be used as an auxiliary means for driving to feed the cutting process to the next cutting process. The steel belt may be heated to accelerate the hardening of the foam, or a heating device may be disposed between the steel belt and the cutting device to accelerate the hardening. The facing material to be laminated on the top and bottom surfaces of the foam molded product is preferably a flexible material such as paper, synthetic resin film, thin metal plate, or cloth-like material, but if necessary, a rigid gypsum board or plastic board may be used. It is also possible to use various known plate-like bodies used for building materials, such as wood plates, metal plates, etc., on the top and bottom or on one side.
Alternatively, paper may be subjected to mold release treatment, or synthetic resin films such as fluororesin or polyolefin with low adhesive properties may be used as upper and lower surface materials, and the molded product may be peeled off after curing to produce a foamed molded product without surface materials. You can also do it. (Examples) Example 1 A glass fiber-reinforced polyurethane foam was manufactured using the manufacturing apparatus shown in FIG. 1 using a two-component stock solution for rigid polyurethane foam consisting of a P liquid and an R liquid. The stock solution for cured polyurethane foam has a viscosity of 450 centipoise (measured at 20°C with a B-type viscometer) for the P solution (polyisocyanate component) and 2200 centipoise for the R solution (component prepared by premixing various compounding agents with polyol). 20℃, using a B-type viscometer), adjust the temperature of the P liquid to 20℃ and the liquid temperature of the R liquid to 25℃, and mix both in equal amounts at a ratio of 1:1.The cream time is 1 minute 35 After reaching the maximum thickness by foaming, it took 10 minutes to become tack-free. The device shown in Fig. 1 has a width of 1.2 m, and a distance of 1.5 m from the delivery position 1 of the glass fiber strand mat to the discharge port 2 of the hard polyurethane foam stock solution.
The distance from the discharge port to the pressure start point 3 of the glass strand mat is 1 m, the distance of the pressure impregnation zone 31 to 33 is 2 m, the distance from the foaming start point 4 to the steel belt conveyor 5 is 3 m, and the length of the steel belt conveyor is 6m, and the speed of conveyor 6 is
The traverse speaker in the width direction of the mixing head was adjusted to 1.5 m/min and 30 m/min, and the mixed stock solution for rigid polyurethane foam was discharged at 29 kg/min. The glass fiber used has a filament diameter of 15μ, a weight per unit area of 300g/ ^m2 , and a thickness of approximately 5mm.
The unpowdered binder resin was used in a strand mat of 2.5% by weight based on the weight of the glass fibers, which were lightly intertwined, and 4 layers of 1 m wide and 50 m long were stacked. In addition, for both the upper and lower surface materials 10 and 11, kraft paper having a weight per unit area of 75 g/m ² was used. In addition, after the glass strand mat is sent out, the pre-compression jig 12 is used.
The hard polyurethane foam stock solution is discharged from the discharge port 2 of the mixing head, and the hard polyurethane foam stock solution is gradually compressed using impregnated rolls 31, 32, and 33 until the hard polyurethane foam stock solution oozes out onto the top surface of the glass strand mat. It was compressed by increasing the ratio. At the beginning of this compression, the foaming reaction of the rigid polyurethane foam stock solution had not yet begun, but it began to become cloudy midway through, and expansion due to rapid foaming began near the foaming start point 4. At this time, height-adjustable pressure rolls 41, 42, 43, and 44 capable of applying light pressure to flatten the upper surface of the foamed material that had started foaming were sequentially arranged at a desired height to apply pressure. The height of the pressure roll was set at a position 5% lower than the relationship between the foam height and the time required for free foaming. By the time 44 pressure rolls were reached, the height of the foam was approximately 150 mm.
After that, the form is passed through a pair of upper and lower steel conveyors 5, 5' that are synchronized with the speed of the conveyor 6, and the height of the form is adjusted to 150 mm.
Once fully cured, the desired length will be 3000mm, for example.
Cut to height using a cutter (not shown).
A glass fiber reinforced polyurethane foam of 150 mm and width of 1000 mm was obtained. Foam density is 0.087g/ ^m3
It was hot. The resulting glass fiber-reinforced polyurethane foam has a height of 75 mm, a width of 500 mm, a height of 75 mm, a width of 500 mm, a height of 75 mm, a width of 750 mm, a width of 2250 mm, a height of 110 mm, and a width of 110 mm. Three specimens of 30 x 30 x 30 mm were cut from each position at 500 mm and 2250 mm from the front in the longitudinal direction, and the tensile Young's modulus was measured according to the method described in ASTM D-1632-1972. The average value μ was determined, and the coefficient of variation C of the tensile Young's modulus was determined using the following formula from the standard deviation σ of the dispersion of individual measured values. can be seen to be evenly distributed. Comparative Example A glass fiber-reinforced polyurethane foam was produced in the same manner as in Example 1, except that glass fiber strand pine was used in which the amount of unpowdered resin binder was 5.5% relative to the weight of the glass fibers, which was bonded relatively tightly. I got it. The density of the obtained foam is 0.089
(g/m ³ ), but the coefficient of variation C of the tensile Young's modulus was as large as 0.25, and therefore the dispersion of glass fibers was considerably inferior to that of the present invention. Examples 2 to 7 Table 1 shows the weight per unit area of glass fiber strand mats using a polyurethane foaming stock solution with a free foaming density of 0.085 (g/m ³ ), the number of laminated layers, and the discharge amount of the stock solution. Glass fiber-reinforced polyurethane foams were obtained in the same manner as in Example 1, in which the content of glass fibers in the foam was varied by changing the content within a range. The foam density and glass fiber content of each were as listed in Table 1.

[Table] The glass fiber reinforced rigid polyurethane foam thus obtained has a thickness of 150 mm, a width of 600 mm, and a length of
A specimen with a size of 600 mm was cut out and tested according to the small membrane type test described in "ML System" Inner Heat Insulation with Urethane Foam, published in Plastic Materials Vol. 16, No. 10 (1975).
Crack resistance in a static test in which a wooden frame was glued around the four circumferences of the specimen and cooled for 8 hours from one side with liquid nitrogen, and a test in which no cracks occurred in the static test. A notch with a length of 50 mm and a depth of 10 mm was made in the center of each piece, and cooling was continued with liquid nitrogen for an additional 6 hours to examine the propagation of cracks from the notch. Next, the cooled specimen was subjected to a wedge drop impact test to investigate the occurrence of cracks. The results are shown in Table 2.

【table】

[Table] (Effects of the invention) Forms that are not reinforced with glass fiber strand mats develop cracks simply by cooling them with liquid nitrogen, whereas glass strand mat reinforced forms do not cause cracks even when simply cooled. I couldn't help it. However, the results of the notch test and the wedge drop impact test showed that the glass fiber content was 8 to 8% based on the weight of the glass fiber reinforced foam.
By coarsely bonding the glass strand mat in a range of 15% and within a range where the proportion of the powder-free resin binder of the glass strand mat can be dissociated by the foaming pressure of the urethane foam, a uniform glass fiber dispersion state can be created. This makes it possible to obtain a fiber-reinforced foam that is an excellent insulator and has long-term durability as an insulator for containers for storing ultra-low-temperature gases such as liquefied natural gas, making it an extremely industrially useful technology from an energy-saving perspective. It can be said that.

[Brief explanation of the drawing]

FIG. 1 is a side view of an apparatus showing an embodiment of the present invention for producing a fiber-reinforced foam. 1...Strand mat, 2...Discharge nozzle,
31, 32, 33...containing roll, 41, 42,
43, 44... Pressure roll, 5, 5... Steel belt, 6... Conveyor, 10, 11... Face material, 12... Pre-compression jig.

Claims (1)

[Claims] 1. A method for manufacturing a fiber-reinforced foam by integrally foaming and curing a continuous band-shaped strand mat and a synthetic resin foamable stock solution, in which the fibers are intertwined in random directions and coarsely mixed with a small amount of powdered binder. At least two layers of bonded strand mats are used, and at the stage where the sprayed synthetic resin foaming stock solution does not start a foaming reaction, the strand mats are compressed until the synthetic resin foaming stock solution oozes out on the top surface of the strand mat. The unpowdered binder of the strand mat is then bonded by foaming while passing through a pressurized zone that substantially limits the thickness that the synthetic resin foamable stock solution can reach by free foaming. A method for producing fiber-reinforced foam, characterized by dissociating fibers and uniformly dispersing fibers in a synthetic resin foam.