JPH0119332B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a foamed resin sheet, and more particularly to a method for easily producing a high-quality thermoplastic resin foamed sheet using an aqueous medium as a foaming agent.

When manufacturing thermoplastic resin powder foam sheets,
It is desirable for the cell wall of the resin to have a high film strength, and is generally produced in the lowest temperature range where the resin melts and flows. Various proposals have been made, such as using a foaming agent or adding certain additives.

In addition, resin foam sheets are often manufactured using an extruder, and regardless of whether a T-die (flat type) or circular die (circular type) extruder is used, the extruded sheet is (discharge port) expands in the production direction (longitudinal direction), lateral direction, and thickness direction. To prevent wrinkles from occurring due to the expansion, T-dies are expanded in width using a tenter, and circular dies are expanded in width using a tenter. At the same time, the diameter of the circular tube is being widened, which is called a method called curvature.

However, there are various restrictions on widening and taking off the discharged sheet in the low temperature range near the lowest temperature at which the resin melts and flows, and advanced manufacturing technology is required.
There are many operational and equipment issues that must be resolved.

The present inventors melt-kneaded a resin composition containing a foaming agent in an extruder, discharged the melt-kneaded resin composition from a die, and immediately after discharge, cooled both sides of the discharged sheet and stretched it in the production direction. By using a two-step foaming method in which a directional (unidirectional) foamed sheet is made by pulling the foam sheet, and then this foamed sheet is heated again to cause secondary foaming and widening, it is possible to replace the conventional one-step foaming method. It was discovered that a foamed resin sheet with a certain degree of homogeneity can be obtained compared to foaming, but with the commonly used thermal decomposition type or low boiling point liquid type foaming agents, the permeation of foaming gas from the discharge sheet, There was a problem that there was a lot of dissipation and secondary foaming could not be carried out sufficiently.

On the other hand, the present inventors have been conducting research on the manufacturing method of resin foams, and have recently found that by using a combination of an aqueous medium and a hydrophilic solid fine powder, thermoplastic resins can be made into aqueous foams. We discovered that foaming can be easily done depending on the medium, and first, we developed a method for producing (a) thermoplastic resin powder and the resin powder partially embedded in an exposed state on the surface of the resin powder. Aqueous resin compound consisting of partially fused porous aggregates of thermoplastic resin powder coated with hydrophilic solid fine powder that does not substantially melt at the melting temperature of the body. (b) melt-kneading the resin compound treated with the aqueous medium under pressurized conditions in which evaporation of the aqueous medium is substantially suppressed; (c) A method for producing a resin foam using an aqueous medium was proposed (Japanese Patent Application No. 58-47028), which is characterized in that the melt-kneaded resin composition is then released from the pressurized condition and foamed.

This time, by combining the above-mentioned method for producing a resin foaming agent using an aqueous medium with the aforementioned two-step foaming method previously discovered by the present inventors, it was possible to achieve excellent homogeneity without causing any industrial problems. It was discovered that a high quality resin foam sheet can be manufactured easily and easily, leading to the completion of the present invention.

Therefore, according to the present invention, (a) the melting temperature of the thermoplastic resin powder A and the resin powder A that is partially embedded in an exposed state on the surface of the resin powder A; In an aqueous medium, a resin compound C consisting of a partially fused porous aggregate of thermoplastic resin powder coated with a hydrophilic solid fine powder B that does not substantially melt is prepared. (b) applying the resin compound C treated with the aqueous medium in an extruder under pressurized conditions in which evaporation of the aqueous medium is substantially suppressed; (c) Melt and knead the melted and kneaded resin composition at a die temperature Td of the following formula: Tf+20≦Td≦Tf+50...(1) Td≦Tm−5...(2) Where, Tf=melting of the resin composition The sheet was discharged from a die maintained at the minimum flow temperature (℃), Tm = melt-kneading temperature of the resin composition (℃), Td = die temperature (℃), and the sheet was discharged immediately after discharge. By cooling both sides to a temperature lower than the lowest melt flow temperature of the resin composition and pulling it out while stretching in the production direction, a directional foam sheet D is obtained, and then (d) the directional foam sheet is obtained. A method for producing a foamed resin sheet is provided, which comprises heating D again to a temperature higher than the lowest melt flow temperature of the resin composition to expand the width while secondarily foaming the resin composition.

One major feature of the method of the present invention is that an aqueous medium is used as a foaming agent for the resin.

Since water is a liquid with a relatively low boiling point, it can theoretically be used as a blowing agent for thermoplastic resins.
In general, it is not compatible with hydrophobic resins, and the filler added to the resin is used after drying to remove moisture. Therefore, conventionally, it was completely unthinkable to use water as a foaming agent for resins.

Since water has a large latent heat of vaporization, the aqueous medium dispersed and trapped in the melt-kneaded resin composition evaporates and expands at the same time as it is extruded into the low pressure area, absorbing heat from the surroundings and increasing the bubble wall strength. It also reduces the bubble wall extension force. Therefore, according to the present invention, when a foamed sheet discharged from an extrusion die is rapidly cooled and taken out while being stretched in the production direction (longitudinal direction), the aqueous medium foaming agent rapidly increases its vapor pressure. Since the expansion power decreases without losing the foam, most of the water is retained in the form of low-pressure steam and/or fine water droplets in the foam sheet without permeating or escaping from the foam sheet, which greatly contributes to secondary foaming after reheating. This makes it possible to manufacture high-quality resin foam sheets with excellent homogeneity.

In addition, the aqueous medium used in the present invention does not produce decomposition residues that color the resin or generate bad odors, unlike conventional thermally decomposed blowing agents, and does not have the same low boiling point as conventional blowing agents. It is a clean and easy-to-handle blowing agent that is not flammable, explosive, or hygienic like other liquids or liquefied gases. Therefore, the method of the present invention is an industrially extremely advantageous method for producing a thermoplastic resin foam sheet.

The method of the present invention will be explained in more detail below.

The thermoplastic resin used in the present invention is not particularly limited, and any thermoplastic resin that has been conventionally used in various plastic moldings can be used.
For example, high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP),
Olefin resins such as polybutene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, petroleum resin; diene resins such as polybutadiene and polyisoprene; polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, polyvinyl alcohol, etc. Vinyl resins; Acrylic resins such as polymethyl methacrylate (PMMA); Styrenic resins such as general purpose polystyrene (GPPS), high impact polystyrene (HIPS), acrylic-styrene copolymers, and acrylic-butadiene-styrene copolymers Resins are included. Each of these can be used alone, or two or more kinds can be used in a blend.

On the other hand, the hydrophilic solid fine powder used in combination with the above resin is either hydrophilic itself or consists of an organic or inorganic substance imparted with hydrophilicity by a hydrophilic treatment.

Further, the hydrophilic solid fine powder used in the present invention does not substantially dissolve at the melting temperature of the resin powder used in combination with the hydrophilic solid fine powder, and preferably expands and becomes wetted by an aqueous medium. They are selected from those that do not dissolve easily even if they are present. In other words, the solubility in water is generally 10g/at 25°C.
Hereinafter, preferably 5 g/or less is advantageously used.

Examples of hydrophilic solid fine powders that can be preferably used in the present invention include shell powders such as starch and wheat flour; plant powders such as wood flour; hydrophilic solid powders such as urea resins, melamine resins, and phenolic resins Examples include resin powder; metal powder such as iron and aluminum; inorganic powder such as talc, clay, calcium carbonate, silica, alumina, and glass powder.

These solid fine powders have sufficient hydrophilicity by themselves, but they may also contain substances (hereinafter referred to as surfactants) that make the surface of these fine powders more susceptible to water, such as fatty acids. Nonionic surfactants such as alkanolamides, fatty acid monoglyceroids, and polyethylene glycol fatty acid esters; anionic surfactants such as fatty acid amides, fatty acid metal salts, alkyl sulfate types, and alkyl phosphate types; cationic surfactants such as ammonium salts Hydrophilic properties can be further increased by surface treatment with agents; fatty acids; polyhydric alcohols such as polyethylene glycol, polypropylene glycol, and glycerin; ethers such as polyethylene glycol diethyl ether; polyvinyl alcohol, etc., or a mixture thereof. The affinity bond between the resin and the fine powder can be improved.

Furthermore, even if a substance is hydrophobic, it can be made hydrophilic by surface treatment with a surfactant such as those mentioned above, or a hydrophilic substance such as polyvinyl alcohol, fatty acids, polyhydric alcohols, or ethers. It can be used in the same manner as the hydrophilic substances described above.

The hydrophilic solid fine powders described above can be used alone or in combination of two or more. In the present invention, talc, calcium carbonate, clay, silica, and alumina having an average particle size of 1 to 15 microns are particularly preferably used.

A portion of the above-mentioned hydrophilic solid fine powder, generally up to 20% by weight, preferably 10% by weight or less of the total amount of the solid fine powder used, may be added to, for example, pulp, cotton, silk, etc.
It can also be replaced by organic short fibers such as hemp, wool, synthetic fibers, and recycled fibers, or inorganic short fibers such as glass fibers, carbon fibers, and asbestos.
By using these short fibers in combination, the mechanical strength of the foam can be significantly improved.

The particle size of the hydrophilic solid fine powder used in the present invention is not strictly limited, and can be varied widely depending on the desired degree of foaming, type of resin, physical properties required of the foam, etc. However, it is generally appropriate that the average particle size is 100 microns or less, preferably in the range of 0.1 to 50 microns, and more preferably in the range of 0.5 to 30 microns. In addition, when using short fibers as described above, the fiber length is generally 10 mm or less, preferably 5 mm or less, and
The fiber diameter is generally less than 100 microns, preferably 1
A range of ˜50 microns is preferred.

From the thermoplastic resin and the hydrophilic solid fine powder described above, a thermoplastic resin powder coated with the hydrophilic solid fine powder (hereinafter sometimes referred to as "composite resin powder") is prepared. When doing so, it is important that the solid fine powder is adhered and buried in an exposed state on the surface of the resin powder (however, of course, the resin powder also has the solid fine powder inside it). (may contain dispersed powder). The amount of solid fine powder attached to and buried in the resin powder is determined by the fact that most of the surface of each resin powder is covered with the exposed solid fine powder, and the magnification is
It is desirable that the amount is such that when observed under a 300x electron microscope, the base of the resin powder is hardly visible.

Furthermore, it was found that a large number of the resin particles coated with the exposed hydrophilic solid fine powder aggregated, and the individual particles partially fused to each other to form a porous mass. is important. When such a porous aggregate is treated with an aqueous medium, it must be capable of stably adhering and retaining the aqueous medium, and therefore, the porous aggregate must have a water vapor adsorption rate of at least 0.05%, preferably 0.2%. It is highly desirable that the above is the case.
Here, "water vapor adsorption rate" means that a porous aggregate of ₁ g of W after being kept in a constant temperature and humidity chamber at a temperature of 25 °C, relative humidity of 30%, and pressure of 1 atm for 24 hours is After keeping it in a closed atmosphere of 1.2 atm for 1 hour, take it out and leave it on paper for 3 minutes, then
When placed in a drying oven at 105°C for 3 minutes and immediately weighed, the amount is defined as W ₂ g, and the value is calculated using the following formula.

Water vapor adsorption rate (%) = W ₂ − W ₁ /W ₁ ×100 The size of the above porous polymer mass is not important and can be any size, but it is easy to handle and melt-knead as described below. From the perspective of
A particle size range of 0.1 to 20 mm, preferably 0.3 to 5 mm is suitable. Therefore, if the particle size is larger than this, it is preferable to use a pulverizer, mixer, etc. to reduce the particle size to the above range.

One promising method for preparing such a porous aggregate is to mix the above-mentioned thermoplastic resin and hydrophilic solid fine powder with a high-speed (superflow) mixing mixer, such as a Hesshin Shell mixer (manufactured by Mitsui Miike Manufacturing Co., Ltd.). There is a method of high speed mixing while heating the thermoplastic resin to a temperature higher than the melting temperature of the thermoplastic resin in a mixing tank such as Super Mixer (manufactured by Kawada Seisakusho). Heating of the resin is carried out by circulating steam or oil through the jacket of the mixing tank, or by generating heat from mixing friction.

During heating and mixing at high speed rotation, when the resin reaches its melting temperature and begins to melt, the resistance to the mixing rotational force of the mixer rapidly increases, and the rotational resistance (or current) of the mixer motor fluctuates wildly. This high-speed mixing under turbulent fluctuations is generally carried out for about 50 to about 250 seconds, preferably about 70 to
Conveniently it lasts about 200 seconds.

The change in the shape of the resin at temperatures above the melting temperature of the resin in the mixing tank of the high-speed mixer is only caused by mutual fusion of the resins when only the resin is mixed by heating, but in the present invention. In this case, the situation is different from the above case because the solid fine powder adheres to the resin surface and the resin changes while preventing mutual fusion of the resins. That is, (1) Until the resin starts to melt and deform and the mixing rotary motor current starts to increase in a fluctuating manner, the resins are mutually fused regardless of whether the resin is supplied in the form of pellets or powder. It is simply a mixture and dispersion of resin and solid fine powder.

(2) However, the resin gradually melts and deforms into flat flakes, which are then sequentially torn off into fine flakes of powder. At the same time, the solid fine powder particles adhere to the surface of the powdery resin and are partially embedded, and the surface of the fine flaky resin powder is covered with the fine powder.

(3) Further, the adhesion of the solid fine powder particles to the resin surface progresses, and the solid fine powder particles are attached to the resin surface by the molten resin exuding from between the solid fine powder coating the resin surface, and/or through the free resin pieces, and/or by the solid particles. The resin powder particles coated with the solid fine powder are partially fused to each other on the minute exposed surfaces to which the fine powder is not attached, forming a porous aggregate.

(4) At this point, the porous agglomerate is discharged outside the mixing tank, sprinkled with water and/or blown with air, and optionally rotated at low speed to cool and solidify. Alternatively, by passing cooling water through the jacket of the mixing tank and blowing air thereon, the mixture can be cooled and solidified within the mixing tank, thereby obtaining the resin compound made of the porous agglomerates of the present invention.

The mixing device used in the present invention is not limited to a high-speed mixer, but any mixer having the same functions as those described above may be used. Among the equipment that is easily available today, high-speed mixers can be used as is and are often used, but other types of mixers, such as bomb blenders, can be modified to have a strong high rotational force. can be used.

The ratio of the hydrophilic solid fine powder to the thermoplastic resin when charged into the above-mentioned mixing mixer depends on the type of resin and solid fine powder, the water absorption rate and water vapor adsorption rate required for the resulting porous aggregate, etc. Although it can vary widely depending on the situation, in general, the solid fine powder is used in an amount of 30 to 250 parts by weight, preferably 60 to 150 parts by weight, and more preferably 80 to 120 parts by weight per 100 parts by weight of the thermoplastic resin. They can be used alone or in a mixture of two or more. As mentioned above, when a part of the solid fine powder is replaced with a fibrous substance, it is appropriate that the fibrous substance accounts for 20% by weight or less, preferably 10% by weight or less of the total solid fine powder. .

In addition, when preparing the above-mentioned porous polymer mass, in addition to the resin and solid fine powder, resin additives such as antioxidants, surfactants, colorants, ultraviolet absorbers, flame retardants, etc. may be added as necessary. . Examples of antioxidants that can be used include thiopropionic acid ester antioxidants such as dilauryl thiodipropionate; phenolic antioxidants such as alkylphenols and alkylbisphenols; or mixtures thereof. Examples of the surfactant include those mentioned above. The antioxidant is usually used in an amount of 0.01 to 5 parts by weight per 100 parts by weight of the fine solid powder, and the surfactant can be generally blended in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the fine solid powder. In addition, examples of colorants include dyes and pigments such as cadmium red, chrome orange, chrome yellow, chrome green, cobalt aluminate blue, titania, phthalocyanine blue, and azo dyes, and examples of ultraviolet absorbers include salicylic acid, Examples include benzophenone-based and benzotriazole-based ultraviolet absorbers, and examples of flame retardants include phosphoric acid esters, halogenated hydrocarbons, antimony oxide, etc., which have been conventionally used as resin additives, in normal amounts. Can be blended.

The porous mass thus prepared is used as is as a resin compound and treated with an aqueous medium as blowing agent according to the method of the invention.

Water is generally used as the aqueous medium, and the boiling point of the medium adjusts the vapor pressure, increases the affinity for the porous aggregate, improves the dispersion stability of the aqueous medium during melt-kneading of the resin compound, For the purpose of improving the uniformity of bubbles, a surfactant, a water-soluble polymer, a polyhydric alcohol, a water-miscible organic solvent, etc. can be appropriately added to the water. As surfactants, those mentioned above can be used, and they can be added generally in a concentration of 0.1 to 50 g/, preferably 1 to 10 g/water. Examples of water-soluble polymers and polyhydric alcohols include polyvinyl alcohol with a degree of polymerization of about 500 to about 2000 and a degree of saponification of 85% or more, mono- or polyethylene glycol with a number average molecular weight of up to 400, glycerin, etc. These are generally 1-
It can be added at a concentration of 100g/, preferably 10-50g/. Further, water-miscible organic solvents that can be used include, for example, alcohols such as methanol, ethanol, propanol, and cyclohexanol; esters such as ethyl acetate and butyl acetate; ethers such as diethyl ether, dioxane, and trioxane; acetone; Examples include Kents such as methyl ethyl ketone, which generally have a concentration of 1% in water.
It can be blended at a concentration of ~100g/, preferably 10-50g/.

The amount of the aqueous medium mentioned above can be varied over a wide range depending on the desired expansion ratio of the foam, but is generally 0.1 to 15 parts by weight, preferably 0.1 to 15 parts by weight per 100 parts by weight of the porous aggregate. can be 0.3 to 3 parts by weight. Treatment of the resin compound with an aqueous medium can be carried out by combining the two and mixing in a mixer.

The resin compound treated with the aqueous medium as described above is then melt-kneaded in an extruder under pressurized conditions in which evaporation of the aqueous medium is substantially suppressed. This melt-kneading can be carried out in the same manner as melt-kneading in the production of ordinary resin foams, and can be carried out, for example, using a non-vent extruder. Here, "pressurized conditions under which evaporation of the aqueous medium is substantially suppressed" refers to pressure conditions higher than the vapor pressure of the aqueous medium impregnated in the resin compound at the melt-kneading temperature. The operation of the extruder is not special and can be carried out by a method known per se.

The resin composition thus thoroughly melted and kneaded is discharged in a molten state from the die of an extruder in the form of a sheet (the term "sheet" in the present invention includes a relatively thin film). At that time, in the present invention, the die has the following formulas (1) and (2).
It is important to maintain the die temperature Td as shown below.

Tf+20≦Td≦Tf+50…(1) Td≦Tm−5…(2) In the formula, Tf=minimum melt flow temperature of the resin composition (°C) Tm=melt kneading temperature of the resin composition (°C) Td= Die temperature (℃) In this specification, the "lowest melt flow temperature" Tf of the resin composition refers to the melting temperature of the resin composition formed when the resin compound is supplied to the extruder and heated and kneaded. This refers to the lowest temperature at which the resin composition begins to flow, and this lowest melt flow temperature varies depending on the type of thermoplastic resin constituting the resin composition, but is generally determined by the heat deformation temperature (heat deformation temperature) of the thermoplastic resin.
distortion temperature point) [temperature measured at a load of 18.6 kg/cm ² according to ASTM D648] approximately 70 to
The temperature is approximately 100 (°C) plus about 100 (°C) [for olefin resins + about 100 (°C), for other thermoplastic resins it is generally about +70 (°C)], for example PP160 ± 5
℃; HDPE159±5℃; GPPS160±5℃;
HIPS155±5℃; PMMA165±5℃.

The "melt-kneading temperature" Tm of the resin composition refers to the temperature of the melt-kneaded resin composition itself at the final stage of the extruder to which the resin compound is supplied. During the transfer of the melted mixture in the extruder,
The temperature of the resin composition is maintained by heating or cooling the cylinder and screw, and when molding a foam, the maximum temperature of the cylinder is usually in the middle of the cylinder, and in the final stage it is 10°C below the maximum temperature.
Although the required temperature is often lower than that, the melt-kneading temperature Tm refers to the temperature of the resin composition measured past the extruder screw tip and before the breaker plate, or past the breaker plate and at the inlet of the die adapter. This temperature is approximately (Tf+40)
℃ to (Tf + 80) ℃, for example, in a resin composition with a weight ratio of talc and resin of 50/50, when the resin is PP, it is about 195 to about 245℃,
About 185 to about 235 °C for HDPE, about 195 to about 245 °C for GPPS, and about
The temperature is 190 to about 240°C.

"Die temperature" or "Die temperature" Td refers to the state in which the resin composition is melt-kneaded in an extruder and produced from the extruder die, and in the case of a circular die, the temperature is successively adjusted and the final heating and cooling is performed. The temperature measured as close as possible to the resin flow path at
In addition, in the case of a T-die (flat die), when the temperature in the width direction perpendicular to the discharge direction is within ±3°C, the center point in the width direction and the approximate center of the heating and cooling plate in the discharge direction (resin flow path This refers to the temperature measured as close as possible to the resin flow path at the intersection with the resin composition (preferably the temperature of the resin composition in the flow path).

The die temperature Td (°C) is within the range of Tf+20≦Td≦Tf+50, and is at a temperature (°C) below (Tm−5), that is, 5°C below the “melting and kneading temperature” Tm of the set resin composition. Lower temperature, preferably lower than Tm
It is important that the temperature is at least 10°C. Therefore, in the aforementioned resin composition with a weight ratio of talc and resin of 50/50, when the resin is PP, the Td is approximately 175.
~about 200℃, Td for HDPE is about 165 to about 190
℃, Td in the case of GPPS is within the range of about 175 to about 200℃, and Td in the case of HIPS is within the range of about 170 to about 195℃, and 10℃ below the "melt kneading temperature" Tm of the set resin composition. The temperature is lower than that.

The melt-kneading temperature Tm of the resin composition is generally (Tf+
40) If the temperature is below (Tf +
It is preferable that the temperature is 45)°C or higher, and if the temperature is too high, the die temperature will rise and temperature adjustment becomes difficult, so it is usually appropriate to set the temperature to be (Tf+80)°C or lower. In order to extrude the resin foam well and with high productivity, the melt-kneading temperature Tm is (Tf +
It is particularly advantageous to maintain the temperature in the temperature range from 45) to (Tf+60) (°C).

If the "die temperature" Td is higher than (Tf + 50) (℃), it will become impossible to adjust the temperature at the lip part, and the foamed shape will be disordered and foam breakage will occur (rough skin), resulting in poor foam sheet production. On the other hand, when the die temperature Td is lower than (Tf + 20) (℃),
Fluidized extrusion of a resin composition consumes a large amount of power, sometimes making fluidized extrusion of a resin composition difficult, and tends to impair uniformity of temperature and discharge, resulting in a decrease in productivity. However, the die temperature Td is (Tf+
25) (℃) or higher is desirable. However,
The preferred range of die temperature Td is (Tf+25) to (Tf+
40) (℃).

As stated above, the preferred range of die temperature Td is
The following formula Tf+25≦Td≦Tf+40...(1)'Td≦Tm−10...(2)' In the formula, Tf, Tm, and Td have the above-mentioned meanings, and are within the range shown by.

A method known per se can be used to maintain the die temperature Td at the temperature shown by the above equations (1), (2), (1)', (2)'. However, since the temperature of the resin composition entering the die is largely controlled, it is important to keep the temperature of the resin composition entering the die as close as possible to the required temperature of the die.

In order to feed the resin composition into the die at a temperature close to the required temperature of the die, it is necessary to use a screw with a design or mechanism that generates less extrusion heat, to rotate the screw at a low speed, or to increase the cooling of the cylinder screw. However, depending on the resin composition, it may be necessary to raise the melt-kneading temperature considerably, but in this case, use a long die adapter and set the die adapter in the long resin flow path. It is preferable to adjust the temperature (lower the temperature), and for example, a static mixer (Kenik Co., Ltd.) or the like may be placed in this resin flow path to help lower the temperature of the resin composition and make the temperature uniform. Therefore, the temperature of the resin composition flowing into the die can be set to the required temperature of the die.

It is desirable to precisely control the die temperature by not only using a heater but also cooling such as heating oil circulation, and it goes without saying that a uniform flow path and temperature in the width direction are required.

In addition, in foam extrusion, it is important to maintain a constant resin pressure when manufacturing general foam sheets, but
This is a particularly important requirement for producing the products of the present invention with high quality and high productivity, and the resin pressure is generally 160 to 300.
It is advantageous to keep it constant at Kg/cm ² , preferably in the range from 200 to 260 Kg/cm ² . In order to keep this resin pressure constant, a gear pump is installed between the extruder and the die, which is also a suitable means in the present invention. The resin pressure referred to here refers to the resin pressure at the same position as the "molten resin temperature" Tm, and when a gear pump is used, it refers to the resin pressure at a point past the gear pump.

Although either a T-die or a circular die can be used in the present invention, a T-die (flat die) is generally more suitable. In addition, the lip spacing of the die can be freely changed depending on the thickness of the resin foam sheet of the product, but it is generally 0.01 to 2.
mm, preferably within the range of 0.2 to 0.8 mm.

Since the sheet discharged from the die is released from the pressurized condition and immediately foams, both sides of the discharged sheet are cooled to a temperature lower than the minimum melt flow temperature Tf of the resin composition immediately after discharge (almost simultaneously with discharge). Then, it is pulled out while stretching in the production MD direction.

As a result of the above cooling, the vapor pressure of the aqueous medium expanded in the discharge sheet is reduced, and most of the aqueous medium is trapped and retained in the foam sheet in the form of steam and/or fine water droplets without permeating or escaping. At the same time, due to the expansion in the production direction, the bubbles solidify in a directional manner in the production direction.

The discharged sheet is cooled using direct cooling rolls (multiple pairs of small-diameter nip rolls whose surfaces are cooled by passing cooling water) installed near the mouth of the extruder, air knives, air rings, cooling fountains, cooling water tanks, etc. can be done. To explain this cooling more specifically, in the case of direct cooling rolls, the sheets are arranged so as to be in slightly compressed contact between the cooled double-sided rolls, or the cooled double-sided rolls are pressed against the produced sheet.
A suitable method is to make the sheet slightly meandering to increase the contact surface with the roll. For cooling with an air knife or cooling fountain, it is desirable to use a device that can blow air from both sides of the sheet, and in the case of a cooling water tank, it is desirable to provide a frame surrounding the produced sheet at the die outlet to stabilize the processing of the sheet.

The cooling temperature is not strictly limited as long as it is lower than the temperature of at least the surface of the discharge sheet or the minimum melt flow temperature Tf of the resin composition.
Generally speaking, cooling to a temperature 30° to 100°C, preferably 40° to 70°C lower than the minimum melt flow temperature Tf is a suitable temperature range from the viewpoint of production and quality.

The discharged sheet is taken up so that the sheet is stretched in the production direction. At that time, it is desirable that the sheet be taken up so that the stretching ratio of the sheet is generally 1.5 to 10 times, preferably 2 to 5 times. Here, the "stretching ratio" is expressed by the following formula: Stretching ratio = Actual drawing speed / Minimum drawing speed. Here, the "minimum drawing speed" means that the molten resin extruded in a sheet form almost retains its shape. This is the minimum speed at which the vehicle can be picked up while

As a result, the ejected sheet does not need to be widened substantially and can be taken out with approximately the same width as the mouthpiece lip, but depending on the case, the width may be slightly widened (width ratio of 2 times or less).

In this way, a resin foam sheet D having orientation in the production direction is obtained, which is then heated to a temperature higher than the lowest melt flow temperature Tf of the resin composition constituting the sheet, preferably from Tf + 5°C to Tf + 30°C. The sheet is expanded while being reheated to a temperature within a range to cause secondary foaming. As a result, the trapped steam and/or fine water droplets evaporate and expand again, and the bubbles oriented in the production direction in the sheet become substantially isotropic and uniform bubbles that do not lose their directionality. Become. The foamed sheet D is reheated by ordinary heating means,
For example, this can be done using a heater, hot air, infrared rays, etc., but if high-frequency heating is used, the water/steam contained in the sheet will be heated and expanded from the center of the sheet thickness, contributing to uniformity of foaming and making the skin non-foaming. It is also possible.

At that time, it has been found that if water or steam is applied to the foamed sheet D prior to or during heating of the foamed sheet D, secondary foaming can be further increased. Application of water or steam can be carried out, for example, by immersing the foam sheet in water (cold water or hot water), exposing it to a steam atmosphere, or spraying water or steam.

Further, the width can be generally widened using a tenter, but is not limited thereto, and any means that can widen the foamed sheet D substantially uniformly in a direction substantially perpendicular to the production direction can be used. There are various restrictions on processing when the stretching temperature is low (20°C or more lower than Tf), such as when stretching and widening crystalline resin films, but in the present invention, the widening temperature is high (10 to 30°C lower than Tf).
℃ high temperature), the expansion of the sheet is easy due to expansion of foaming, and a simple gripping device for the sheet is sufficient.

The degree of width expansion described above depends on the magnification of the secondary foaming, and can be set to at least a level that does not cause wrinkles in the sheet, but specifically, the width expansion rate is generally 1.5 to 10 times, preferably 2 to 10 times. It is convenient to widen the width to within a range of 5 times.

Here, "widening ratio" refers to the extruded resin foam sheet or It refers to the width ratio of a film product, and is expressed by the following formula.

Width ratio = Width of extruded resin foam sheet or film product / Width of extruder mouthpiece As described above, the foamed sheet that has been secondarily foamed by heating and expanded in width is cooled and taken off to form resin foam as a product. A sheet is obtained.

According to the method of the present invention described above, a high-quality foamed sheet with uniform and homogeneous foamed cells and little directionality in the sheet can be obtained, and the foaming ratio can be varied over a wide range, especially at high ratios. The foamed sheet can be easily manufactured, and the resin foamed sheet can be manufactured with simple equipment, easy operation, and high productivity. In addition, there is no risk of coloring, bad odor, flammability, explosiveness, etc., which occurs when conventional thermal decomposition type or low boiling point liquid or liquefied gas type blowing agents are used.

The foamed sheet provided by the present invention can have a wide range of thicknesses and expansion ratios. For example, thick foam sheets with a foaming ratio of several times or less can be used as structural materials, thin ones can be used as containers that require rigidity, and relatively thin foam sheets with a foaming ratio of several times to 10 times can be molded by vacuum forming. The scope of its use is extremely wide, including processing materials and, at a foaming ratio of 15 times or more, cushioning packaging materials.

The present invention will be explained in more detail with reference to Examples below.

Example 1 Blend amount (g) Resin: Polypropylene (Noblen manufactured by Mitsubishi Yuka Co., Ltd.
MA-8A; M1 = 0.7, density = 0.9) 10000 Fine powder; Talc (MS made by Nippon Talc Co., Ltd.; average particle size 9 μ) 10000 Dispersant: Fatty acid alkanolamide (Amizole LDE made by Kawaken Fine Chemical Co., Ltd.) 150 Low molecular weight polypropylene (Viscol 550-P manufactured by Sanyo Chemical Industries, Ltd.) 100 Colorant: Titanium oxide (anatase type, A100 manufactured by Ishihara Sangyo Co., Ltd.) 500 Antioxidant: Dilauryl thiodipropinate 30 1,1,3-tris (2-methyl- 4-Hydroxy-5-t-butylphenyl)butane 10 Using a high-speed mixing mixer (Kawada Seisakusho Super Mixer SMG100 mixing motor 22KW4P/8P),
The mixing tank (talc capacity: 100) was heated by circulating heated oil at 140° to 150°C through a jacket.
All of the above formulations were put into the mixing tank of the mixer and mixed at high speed.

After about 20 minutes, the mixing motor current started to fluctuate and increase (mixture temperature was 195℃), and after 80 seconds it suddenly increased.
Since the temperature reached 80A (mixture temperature 210°C) in 40 seconds (total 120 seconds), the outlet was opened and the mixture was discharged.

The discharged mixture is rapidly cooled and crushed by a low-speed rotating mixer with strong air cooling to obtain a resin compound consisting of a partially fused porous aggregate of resin powder coated with fine powder. Ta.

Next, a crusher (Morita Seisakusho TC-3 type 3)
Grind to a maximum particle size of 5 mm or less at 50 to 300 r.pm.
Transfer to a mixing rotary mixer and add 120 c.c. of tap water (approximately 0.6 parts by weight based on 100 parts by weight of the resin compound) as an aqueous medium containing 1% alkylbenzene sulfonate (Nitsun Yurex H manufactured by Nippon Oil & Fats Co., Ltd.). was added and mixed for 5 minutes or more to obtain a resin compound impregnated with an aqueous medium.

A long adapter/coat hanger type T-die was attached to the 90mm extruder, and 150℃ cooling oil was circulated through the T-die. Six direct rolls with hard chrome plating on the surface and cooling water running through them were placed opposite the sheet production direction and close to the die outlet so that the sheets could be slightly compressed. The operation was performed under the following conditions.

Cylinder maximum temperature: 240℃ Melting and kneading temperature of resin composition Tm: 225℃ Long adapter temperature gradient: 225→ ₂₀₀ ℃ Die temperature Td: 190± ⁵⁰ ℃ Thus, the aqueous medium has directionality in the production direction, and the aqueous medium is steam and A resin foam sheet in which fine water droplets were trapped was obtained.

The sheet was then immersed in a 90°C water bath containing 1% surfactant, and expanded 2.5 times in a 175°C oven to lose its orientation, resulting in substantially isotropic and uniform air bubbles. A resin foam sheet with a foaming ratio of about 5 times was obtained.

This foam sheet can be subjected to tertiary processing such as vacuum forming, and is suitable for use in packaging containers for foods and the like.

Example 2 Blend amount (g) Resin: Low density polyethylene (Mitsubishi Kasei Novatech LF101A; M1 = 0.45, density = 0.922)
9500 Ethylene-vinyl acetate copolymer (Mitsubishi Yuka Co., Ltd. Yucalon Eva EVA20F: MI = 2; density = 0.93) 500 Fine powder; heavy calcium carbonate (Shiraishi Calcium Co., Ltd. Whiten SSB: average particle size 1.5μ) 3000 Heavy Calcium carbonate (Whiten B manufactured by Shiraishi Calcium Co., Ltd.: average particle size 3.6μ) 7000 Surfactant: Fatty acid alkanolamide (Amizole CDE manufactured by Kawaken Fine Chemicals Co., Ltd.) 120 Polyethylene glycol (manufactured by Sanyo Chemical Co., Ltd.)
PEG6000) 60 Coloring agent: Titanium oxide (anatase type, A100 manufactured by Ishihara Sangyo Co., Ltd.) 300 Cobalt aluminate blue (manufactured by Dainichiseika Chemical Co., Ltd.) 0.1 Antioxidant: Dilauryl thiodipropionate 10 22′-Methylenebis(4-methyl -6-t-
Butylphenol) 20 Nonylphenyl phosphite 10 Using the same high-speed mixer as in Example 1, all the formulations were charged and mixed at high speed. After about 16 minutes, the mixing motor current began to fluctuate and increase slightly (mixture temperature: 185℃), and after 120 seconds, it rapidly increased and reached 50A (mixture temperature: 200℃) in 5 to 10 seconds (total of 125 to 130 seconds). So I opened the outlet and released the mixture.

The discharged mixture is rapidly cooled and coarsely crushed by a low-speed rotating mixer with strong air cooling to obtain a resin compound consisting of partially fused porous aggregates of resin powder coated with fine powder. Ta.

Next, a crusher (Morita Seisakusho Tc-3 type 3)
Grind it to a maximum particle size of 5 mm or less, transfer it to a mixer with a mixing rotation of 50 to 300 rpm, add an aqueous medium of 500 c.c. of tap water (2.5 parts by weight per 100 parts by weight of the resin compound), and mix for 10 minutes. The resin compound was impregnated with an aqueous medium.

A T-die was attached to the 50 mm extruder to circulate cooling oil at 150°C. An 85° C. cooling water tank with a frame surrounding the produced sheet was installed close to the die outlet, and the operation was carried out under the following conditions at a take-up speed of 4 times.

Cylinder maximum temperature: 200°C Melting and kneading temperature of resin composition Tm: 190°C Die temperature Td: 180±3°C Thus, there was directionality in the production direction, and the aqueous medium was trapped in the state of fine water droplets and/or steam. A resin foam sheet was obtained.

The sheet was then expanded twice in width in a 155° C. oven to lose its directional properties, to obtain a resin foam sheet with substantially isodirectional and uniform cells and a foaming ratio of about 10 times.

This foam sheet is useful as a packaging material with excellent cushioning properties.

Example 3 Blend amount (g) Resin: Acrylic-butadiene-styrene copolymer (JSRABS85 manufactured by Japan Synthetic Rubber Co., Ltd.; specific gravity = 1.05, MI = 1.7) 10000 Fine powder; heavy calcium carbonate (Whiten SB manufactured by Shiroishi Calcium Co., Ltd.; Average particle size: 1.8μ) 8000 Pulp powder (KC Flotz, manufactured by Sanyo Kokusaku Pulp; W200; particle size: 200M/S pass) 500 Dispersant: Fatty acid alkanolamide (Amizol LDE, manufactured by Kawaken Fine Chemical Co., Ltd.) 150 Fatty acid amide (NOF) Company-made Alflow P-
10) 50 Glycerin 100 Coloring agent: Ceramics Yellow 100 Titanium oxide (anatase type manufactured by Ishihara Sangyo Co., Ltd.)
A100) 300 Antioxidant: distearylthiopropionate 10 2,6-di-t-butyl p-cresol 10 Using the same high-speed mixer as in Example 1, all the formulations were added and mixed at high speed.

After about 18 minutes, the mixing motor current started to fluctuate and increase slightly (mixture temperature 200℃). After 160 seconds, it suddenly increased and reached 50A (mixture temperature 215℃) in 20-25 seconds (total 180-185 seconds). , the outlet was opened to release the mixture.

The discharged mixture is rapidly cooled and coarsely crushed by a low-speed rotating mixer with strong air cooling to obtain a resin compound consisting of partially fused porous aggregates of resin powder coated with fine powder. Ta.

Next, it was crushed to a maximum particle size of 5 mm or less using a crusher (Tc-3 type 3P manufactured by Morita Manufacturing Co., Ltd.), transferred to a mixer with a mixing rotation of 50 to 300 rpm, and polyoxyethylene fatty acid amine (Amit 308 manufactured by Kao Soap Co., Ltd.) 1 % of ion-exchange resin treated water (approximately 2 parts by weight based on 100 parts by weight of the resin compound) was added and mixed for more than 10 minutes to obtain a resin compound impregnated with an aqueous medium.

A 1000mm wide coat hanger die with oil circulation heated at 150℃ is attached to a 70mm extruder, and an air knife is installed near the die outlet to spray compressed air containing a large amount of mist water onto both sides of the produced sheet. The operation was carried out under the following conditions at a take-up magnification of 2.2 times.

Cylinder maximum temperature: 230°C Melting and kneading temperature of resin composition Tm: 220°C Die temperature Td: 200± ⁰ ₅ °C Thus, it has directionality in the production direction, and the aqueous medium is trapped in the form of fine water droplets and/or steam. A foamed resin sheet was obtained.

Next, the sheet was expanded to 1.8 times in a 170° C. oven to lose its directional properties, to obtain a resin foam sheet with substantially isotropic and uniform cells and an expansion ratio of about 7.5 times.

This foam sheet (plate) has high physical properties including rigidity, and is used as a structural material.

Claims (1)

[Claims] 1 (a) At the melting temperature of the thermoplastic resin powder A and the resin powder A that is partially embedded in an exposed state on the surface of the resin powder A, substantially A resin compound C consisting of a partially fused porous agglomerate of thermoplastic resin powder coated with a hydrophilic solid fine powder B that does not melt in the water is treated with an aqueous medium. (b) melting the resin compound C treated with the aqueous medium in an extruder under pressurized conditions that substantially suppresses evaporation of the aqueous medium; (c) Melt and knead the resin composition at a die temperature Td of the following formula: Tf+20≦Td≦Tf+50...(1) Td≦Tm−5...(2) Where, Tf=minimum melt flow of the resin composition Temperature (°C), Tm = melt-kneading temperature of the resin composition (°C), Td = temperature of the die (°C). By cooling the resin composition to a temperature lower than the lowest melt flow temperature and pulling it out while stretching in the production direction, a directional foam sheet D is obtained, and (d) the directional foam sheet D is A method for producing a foamed resin sheet, which comprises heating the resin composition again to a temperature equal to or higher than the lowest melt flow temperature to cause secondary foaming and widening.