JP4807765B2 - Method for producing thermoplastic polyurethane foam - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for producing a thermoplastic polyurethane foam, and in particular, a method for producing a thermoplastic polyurethane foam that has fine cells having recyclability and can be used for foam gaskets, foam seal materials, various cushion materials, synthetic leather, and the like. About.
[0002]
[Prior art]
Conventionally, polyurethane foam has been used for foam gaskets, foam seals, various cushioning materials, synthetic leather, etc., but conventional polyurethane foams are a mixture of raw materials such as polyols and isocyanates and foaming agents at the same time. And made to react. This reaction involves resinization at the same time as gasification, and requires extremely delicate management, so that the polyol and isocyanate are crosslinked so as to increase the viscosity of the reaction system so that bubbles do not collapse due to the pressure of the generated gas. It is molecularly designed and the resulting foam is thermosetting. Therefore, since these products do not melt even when heated, they cannot be recycled by remelting.
For this reason, the conventional polyurethane foam has been recycled by a so-called “chip foam” method in which the foam is pulverized into fine chips and then hardened with an adhesive. However, this chip foam is only applied to low-quality uses such as carpet underlays and cushioning materials, and is extremely limited to uses. On the other hand, a method of returning the polyurethane foam to the raw material by hydrolysis has also been studied, but it is hardly spread due to the insufficient quality of the recycled material and the high cost.
[0003]
In order to overcome such a situation, a thermoplastic polyurethane resin composition for foaming and a method for producing a thermoplastic polyurethane foam are described in JP-A-5-301988. According to the publication, there is provided a foaming thermoplastic polyurethane resin composition comprising a thermoplastic polyurethane resin in which a pyrolytic foaming agent is melted and a thermoplastic polyurethane resin in which a foaming accelerator is melted. A thermoplastic polyurethane resin in which a foaming agent is melted and a thermoplastic polyurethane resin in which a foaming accelerator is melted are melt-mixed, and the thermoplastic polyurethane is obtained by, for example, extrusion molding, calender molding, injection molding, press molding, or blow molding. A molded product is manufactured. However, in the method of foaming simultaneously with the decomposition described in this publication, the cells are usually large and non-uniform. Furthermore, compared to conventional polyurethane foams, the foaming magnification does not increase and the cost is high, resulting in poor cost / performance and not practical use.
In addition, a method for producing a thermoplastic resin that is advantageous for recycling by reflection injection molding using a special polyol and a special isocyanate is proposed in Japanese Patent Application Laid-Open No. 6-316617. Prepolymers are required and are limited to reflective injection molding. This publication does not disclose the production of foam.
[0004]
[Problems to be solved by the invention]
Under such circumstances, the inventor of the present invention has completed the present invention as a result of various investigations on a method for producing a thermoplastic polyurethane foam which is easy to recycle and has uniform and fine cells. The object is to provide a process for the production of thermoplastic polyurethane foam with recyclable uniform fine cells.
[0005]
[Means for Solving the Problems]
The gist of the present invention is that a decomposable foaming agent is continuously blended in a twin-screw extruder with a thermoplastic polyurethane resin produced from a monomer polyol, isocyanate, and chain extender using a twin-screw extruder. The obtained thermoplastic polyurethane foam compound containing a decomposable foaming agent is heated to a temperature higher than the decomposition temperature of the foaming agent under pressure that does not cause the foaming agent to foam, and the thermoplastic polyurethane resin is melted. This is a method for producing a thermoplastic polyurethane foam, characterized in that after cooling, the pressure is lowered to cause foaming. And it is preferable to perform the temperature which mix | blends a decomposition-type foaming agent with thermoplastic polyurethane at the temperature lower than the decomposition temperature of a decomposition-type foaming agent, and it is preferable to add a plasticizer to a thermoplastic polyurethane resin . In the present invention as this, since the thermoplastic polyurethane resin is heated to a temperature higher than the decomposition temperature of the pressure blowing agent to melt the thermoplastic polyurethane resin, a blowing agent is foamed for decomposing pressurization is suppressed Yes. After cooling in such a state, when the pressure is lowered, the melt thickens by cooling and foams by the pressure drop, so that a foam is formed without using a crosslinking agent. Therefore, since the obtained foam is thermoplastic, it has recyclability. And this foam can obtain any foam of a closed cell and an open cell, Furthermore, in order to foam in such a state with high melt viscosity, the foam which has a fine cell is obtained.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail.
The thermoplastic polyurethane resin used in the present invention is obtained by reacting a commonly used polyol, isocyanate, and chain extender. As the polyol, ester, ether, lactone, carbonate, and the like can be used. Specific examples of ester polyols that can be used include ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,4 butenediol, 1,3-butenediol, 1,6- It is a polyhydric alcohol such as hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,5-pentanediol, and examples of the ester polyol include adipic acid, sebacic acid, azelaic acid, terephthalic acid , Polyester diols obtained from fatty acids such as isophthalic acid and maleic acid, or aromatic carboxylic acids. Examples of the ether polyol include polyalkylene ether diols such as polyethylene glycol, polypropylene ether glycol, polytetramethylene ether glycol, and polyhexamethylene ether glycol. Examples of the lactone polyol include polycaprolactone glycol, polypropiolactone glycol, and polyvalerolactone glycol. Examples of carbonate-based polyols include ethylene glycol, propylene glycol, 1,4-butanediol, 1,3 butanediol, 1,5-pentanediol, methylpentanediol, methyloctanediol, and 1,9-nonanediol. Polycarbonate diol obtained by a dealcoholization reaction of a dihydric alcohol with, for example, diethylene carbonate, dipropylene carbonate and the like.
[0007]
Examples of the isocyanate used in the present invention include aromatic isocyanates such as diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, phenylene diisocyanate, and 1,5-naphthalene diisocyanate, hexamethylene diisocyanate, and isophorone. Examples thereof include alicyclic or aliphatic isocyanates such as diisocyanate and hydrogenated xylene diisocyanate.
In the present invention, a chain extender is used. Examples of the chain extender used include ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,4. -Bis (β-hydroxyethoxy) benzene, neopentyl glycol, methyloctanediol, 1,9-nonanediol and the like.
[0008]
The foaming agent used in the present invention is a pyrolytic foaming agent, which is azodicarbonamide (ADCA), azobisisobutyronitrile (AIBN), dinitropentamethylenetetramine (DPT), p-toluenesulfonyl hydrazide (TSH), p. , P′-oxy-bis (benzenesulfonylhydrazide) (OBSH), benzenesulfonylhydrazide (BSH), trihydrazinotriazine (THT) and the like. In addition, an inorganic hydrous compound having a decomposition temperature of 75 to 300 ° C. can be used. Examples thereof include boric acid, aluminum hydroxide, magnesium hydroxide, iron hydroxide, calcium sulfate dihydrate, calcium chloride hexahydrate, sodium sulfate decahydrate, magnesium sulfate decahydrate. A relatively high decomposition temperature of these thermally decomposable foaming agents facilitates the kneading operation, and is preferably about 160 to 250 ° C. At this temperature, the ease of foaming at the time of foaming is also favorable. The decomposition temperature of the blowing agent is most preferably 190 to 240 ° C., and ADCA and THT are preferable as such a blowing agent. The temperature (TU) at which the decomposable foaming agent is added to the thermoplastic polyurethane resin is lower than the decomposition temperature (TB) of the decomposable foaming agent.
[0009]
In the present invention, a foaming aid can be added to control the decomposition of the foaming agent. As the foaming assistant, there are an acceleration assistant that promotes the decomposition of the foaming agent and a suppression assistant that suppresses the decomposition. Accelerators include metal soaps such as zinc fatty acid soap and lead fatty acid soap, and acids such as boric acid, oxalic acid, succinic acid, and adipic acid. Inorganic salts such as zinc white, zinc nitrate, lead phthalate, zinc phthalate. Other examples include urea, ethanolamine, glycol, glycerin and the like. Inhibitors include organic acids such as maleic acid, fumaric acid, and phthalic acid. Organic acid anhydrides such as maleic anhydride and phthalic anhydride. In addition, hydroquinone, fatty acid amine, amide, mercaptam, dibutyltin malate and the like can be used.
[0010]
It is preferable to add a plasticizer to the thermoplastic polyurethane resin of the present invention. That is, various plasticizers and low molecular substances (plasticizers) can be blended to control the melt viscosity of the polyurethane resin. For example, as phthalic acid esters, obtained from phthalic acid esters such as dioctyl phthalate and dibutyl phthalate, plasticizers such as organic phosphates and epoxy compounds, glycols such as ethylene glycol, diethylene glycol, and low molecular weight polyethylene glycol, and benzoic acid. Various lubricants such as diesters, dimer acid esters, chlorinated paraffins, and fatty acid amides, fatty acid esters, and fatty acids may be used. By blending plasticizers, the resin viscosity is lowered and the temperature during kneading can be lowered. By blending these plasticizers with the polyurethane resin, the foaming agent blending temperature is preferably set to 230 ° C. or lower. In particular, the temperature at which the foaming agent is blended in a twin-screw extruder is preferably 200 ° C. or less, so that the decomposition of the foaming agent is difficult to proceed. In the present invention, using a twin-screw extruder, a decomposable foaming agent is continuously blended from the middle of the extruder while using a process for producing a thermoplastic polyurethane resin from the monomers polyol, isocyanate, and chain extender. It is preferred to produce a thermoplastic polyurethane foam using a process.
By using this step, there is an advantage that a decomposable foaming agent can be blended at a low temperature with a polyurethane resin having a relatively low viscosity during the reaction. Thereby, it becomes easy to mix | blend a foaming agent without decomposing | disassembling and the selection range of a foaming agent also spreads.
Since a thermoplastic polyurethane resin is used in the method of the present invention, other thermoplastic resins can be blended with the polyurethane resin. For example, blending a polyester resin can improve strength and rigidity, and blending a polyolefin resin improves thermoformability such as vacuum molding. In addition, polyamide resins, silicone resins, fluorine resins, and the like can also be blended. In order to blend these thermoplastic resins, various compatibilizers can be blended.
[0011]
In the present invention, the above-mentioned compounding agents may be blended into the thermoplastic polyurethane resin by any means, and for example, they can be kneaded using a mixing roll, a kneader, a Banbury mixer, a kneader ruder, or the like. Further, when the polyurethane resin using a twin-screw extruder is in a molten state, a foaming agent can be introduced from the middle of the cylinder and kneaded. Furthermore, it is preferable to use a masterbatch in which a foaming agent is kneaded in advance with a polyurethane resin because the thermal history of the foaming agent is small. As described above, it is preferable that the foaming agent is kneaded in a short heat treatment time because decomposition of the foaming agent can be suppressed.
[0012]
[Examples and Comparative Examples]
Reference example 1
Trihydrazino with respect to 100 parts of thermoplastic polyurethane resin A obtained from 500 parts of polyoxytetramethylene glycol (number average molecular weight 1000), 45 parts of 1,4-butanediol, and 200 parts of 4,4′-diphenylmethane diisocyanate 2 parts of triazine (THT) was blended at about 190 ° C. using a kneading roll. This compound was heated with a hot press at a pressure of 50 kg / cm ² at 235 ° C. for 15 minutes to decompose the foaming agent. Thereafter, it was cooled to 190 ° C. as it was and further released to normal pressure to obtain a polyurethane foam. This foam had a density of 0.5 g / cm ³ and a cell diameter of about 10 μm. The foam was finely crushed and then extruded with a short shaft extruder. As a result, a sheet was formed satisfactorily, and it was confirmed that recyclability was good.
[0013]
Comparative Example 1
When the compound obtained in Reference Example 1 was heated in a hot press at 235 ° C. for 15 minutes, the foaming agent was decomposed and then released to normal pressure without cooling, resulting in defoaming and no foam. .
Example 1
Using a twin screw extruder, the liquid composition of polyol, isocyanate, and crosslinking agent of Reference Example 1 was introduced from the hopper and reacted in a cylinder at about 200 ° C., and 10% of THT was previously applied to the resin A from the tip of the cylinder. A compound kneaded at a compounding ratio of / 2 was added, and a 0.3 mm sheet was formed from a die at about 200 ° C. Thereafter, the sheet was heated and cooled in a hot press in the same manner as in Reference Example 1 and then released to normal pressure to obtain a foam. This foam had a density of 0.5 g / cm ³ and a cell diameter of about 10 μm.
[0014]
Reference example 2
Low viscosity obtained from 500 parts of polyoxytetramethylene glycol (number average molecular weight 1700), 63.5 parts of 1,4-butanediol, 253.5 parts of 4,4′-MDI, 144 parts of aromatic ester plasticizer A compound was obtained by kneading 5 parts of azidocarbonamide (ADCA) with a kneading roll at about 170 ° C. with respect to 100 parts of thermoplastic polyurethane resin B. This compound was heated at 200 ° C. with a pressure of 50 kg / cm ² by a hot press. Then, it cooled to 180 degreeC with the pressure, was cancelled | released to normal pressure, and the polyurethane foam was obtained. The density of the obtained foam was 0.1 g / cm ³ and the cell diameter was about 30 μm. Moreover, this thing also had good recyclability.
Comparative Example 2
When the compound of Reference Example 2 was heated at 200 ° C. with a hot press and then released to normal pressure without cooling as it was, the foam was removed and no foam was obtained.
[0015]
【The invention's effect】
The effects of the present invention are listed as follows. By the method of the present invention, a thermoplastic polyurethane foam having fine cells can be obtained, and a product useful as a synthetic leather, a foamed gasket, or a foamed sealing material can be provided.
2. This cell is extremely fine and uniform, so it has a good appearance, and is optimal for applications such as synthetic leather that requires a good appearance.
3. Since the foam obtained by the method of the present invention is melted by applying heat, it can be applied to another product by melting the punching loss and the punching loss again in the production process. , Has excellent recyclability.
4). Furthermore, this foam can be produced continuously by using a process of producing polyurethane resin from polyol, isocyanate, etc., which are raw materials of polyurethane resin, using a twin-screw extruder. Is also a very reasonable method.
5. Furthermore, since a thermoplastic polyurethane resin is used in the present invention, a polyester resin, a polyamide resin, an olefin resin, or the like that cannot be blended with a normal polyurethane foam can be blended. As a result, functions such as imparting rigidity, improving strength, improving water resistance, and imparting water repellency can be improved, and since they are the same thermoplastic resin, recyclability is also good.

Claims (3)

Decomposable foaming obtained by continuously blending a decomposable foaming agent in a twin-screw extruder with a thermoplastic polyurethane resin produced from the monomers polyol, isocyanate, and chain extender using a twin-screw extruder. thermoplastic polyurethane foam formulation containing agent, under pressure of the blowing agent does not foam, the temperature was increased to higher than the decomposition temperature of the blowing agent to melt the thermoplastic polyurethane resin, after cooling a molten state followed, the pressure A process for producing a thermoplastic polyurethane foam, characterized in that the foam is lowered and foamed. The method for producing a thermoplastic polyurethane foam according to claim 1, wherein the temperature (TU) at which the decomposable foaming agent is added to the thermoplastic polyurethane resin is lower than the decomposition temperature (TB) of the decomposable foaming agent. The method for producing a thermoplastic polyurethane foam according to claim 1 or 2, wherein a plasticizer is blended with the thermoplastic polyurethane resin.