JP3311388B2 - Manufacturing method of polyurethane foam with integral skin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing polyurethane foam with integral skin used for automobile parts such as steering wheels and air spoilers, and furniture such as armrests and chair legs.

[0002]

2. Description of the Related Art A polyurethane foam with integral skin is characterized in that a skin layer and a foam layer can be formed simultaneously by injecting a reactive stock solution into a mold, foaming and curing, and removing the mold. Because of its superiority, it is widely used as a cushioning material in the fields of automobiles, furniture, and the like.
In order to form this skin layer, a low-boiling organic compound is required as a foaming agent, and particularly, trichlorofluoromethane (CFC-11) has been commonly used. However, in recent years, so-called C
FC compounds are found to destroy ozone in the atmosphere,
Regulations on the control of CFC compounds are being enacted worldwide.
As a foaming agent replacing the CFC compound, hydrochlorofluorocarbons (hereinafter abbreviated as HCFC) having a low ozone depletion potential (hereinafter abbreviated as ODP) have been proposed for the second generation, such as monochlorodifluoromethane (HCFC-). 2), dichlorodifluoromethane (HCF
C-123), dichloromonofluoroethane (HCFC
-1416), monochlorodifluoroethane (HCFC
-142b). Furthermore, O for 3rd generation
Hydrofluorocarbons having a DP of 0 (hereinafter abbreviated as HFC) have been proposed, such as tetrafluoroethane (HFC-134a).

[0003] However, there is concern that these HCFCs and HFCs are not foaming agents that can be used with sufficient security in protecting the global environment. That is, H
Although CFC has a small ODP, it is still a compound that destroys the ozone layer. HFC has an ODPT of 0 and there is no concern about depletion of the ozone layer.
WP) is high and is not a compound that can be safely used in the future. Thus, the so-called alternative CFC is only a measure for the short-term CFC regulation, and the development of a so-called water foaming technology that does not use permanent CFC at all has been desired. In the field of ordinary polyurethane foams, water foaming technology has been developed in each of the fields of flexible foams, semi-rigid foams and rigid foams, and at present, water foamed foams have already been produced at a considerable rate.

[0004] On the other hand, in the field of polyurethane foam with integral skin, it is advantageous to use a low boiling point foaming agent from the viewpoint of the skin layer formation mechanism. Has not been converted. That is, since the water foaming technique is a technique using carbon dioxide, which is a reaction product of water and isocyanate, as a foaming agent, carbon dioxide generated near the surface of the mold, that is, the surface of the polyurethane foam, is generally used. Under the reaction molding conditions in the case of the foaming agent CFC-11 (boiling point 27.5 ° C.) used for the polyurethane foam with integral skin, a foamed layer is formed. As a solution to this problem, Japanese Patent Application Laid-Open No. 3-32811 discloses a method in which the mold temperature is set to 15 to 40 ° C., the temperature of the reaction between water and isocyanate is large, and the temperature of the reaction between the isocyanate and the OH compound is temperature dependent. It has been proposed to use a "temperature-sensitive catalyst" having a low reactivity.
No. 0 discloses a specific example of the "temperature-sensitive catalyst". However, in the method using a "temperature-sensitive catalyst", even if a high-density skin layer is formed, the curing of the urethane surface is delayed due to the low surface temperature of the mold, resulting in poor appearance quality. And the foaming pressure has a small damping property, so that the urethane foam is liable to be blistered or cracked when taken out of the mold, and has a disadvantage that a longer demolding time is required.

[0005] Further, another problem of the water foaming technique is that a hard segment in which a urea bond formed by the reaction between water and an isocyanate forms a very strong urea bond, the resulting urethane foam has a high hardness and has a poor touch feeling. It is to become. On the other hand, a reaction type which reacts with isocyanate to generate carbon dioxide gas and does not generate urea bond is considered. For example, Japanese Unexamined Patent Application Publication No.
Japanese Patent No. 4108 discloses a method in which isocyanate groups react with each other to form a carbodiimide group, and carbon dioxide generated at that time is used as a foaming agent. Japanese Patent Application Laid-Open No. 3-152111 discloses a method in which a cyclic carbonate is reacted with an isocyanate. A method in which carbon dioxide generated when an oxazolidone group is generated is used as a blowing agent.
And JP-A-3-153721 have proposed a method of using carbon dioxide gas generated when an amide group is formed using an organic carboxylic acid as a foaming agent. However, these methods have problems such as difficulty in controlling the reaction rate, use of an expensive catalyst, and the necessity of using Freon in order to give a sufficient degree of foaming. It does not essentially solve the problem.

[0006]

As described above, a method for producing a polyurethane foam with integral skin using water as a foaming agent without using chlorofluorocarbon or alternative chlorofluorocarbon is an urgent need for the industry. Nevertheless, it has not been put to practical use because it has the following disadvantages as compared with the method using chlorofluorocarbon and alternative fluorocarbons. (1) The demolding time is prolonged, and productivity is deteriorated. (2) Thick molded products are liable to cause blisters, punctures, etc. at the time of demolding. (3) The urethane foam expands during demolding, and traces of the mold surface are likely to remain on the product surface. (4) The foam is hard and the feel is poor. (5) The skin layer is thin. Although a method for individually solving the disadvantages of (1) to (5) has been found, a water foaming technique which can solve all items at the same time and can be adopted in an actual production line has not yet been developed. .

The inventors of the present invention have intensively studied a method for obtaining a polyurethane foam with an integral skin using water as a blowing agent in order to solve these problems, and as a result, have found that a specific polymethylene polyphenylisocyanate is used. It has been found that the polyurethane foam with integral skin obtained by the above method can provide a molded product with good productivity and good tactile sensation which can solve all of the above-mentioned disadvantages, and has completed the present invention.

[0008]

Means for Solving the Problems That is, the present invention provides: (1) Polymethylene polyphenylisocyanate containing 60% by weight or more of a so-called polynuclear body of 3 or more nuclei as a polyisocyanate; (2) As a polyol, propylene oxide and ethylene oxide are added to an active hydrogen compound having an average number of functional groups of 2 to 4; OH value added with
55 mg KOH / g and ethylene oxide content of 10
-20% by weight, terminal primary OH conversion rate is 70-90 mol%
Or a polymer polyol obtained by graft-polymerizing an ethylenically unsaturated monomer with this, and (3) water as a foaming agent as essential components, and if necessary, a crosslinking agent, a catalyst, a foam stabilizer, and the like. A method for producing a polyurethane foam with integral skin having a molded article density of 0.4 to 0.8 g / cm ³ , characterized by reacting an auxiliary agent. 2. The polyurethane foam with integral skin according to claim 1, wherein a polymethylene polyphenylisocyanate having a trinuclear content of 25% by weight or more and a tetranuclear or more content of 35% by weight or more is used as the polyisocyanate. Manufacturing method. 3. The method for producing a polyurethane foam with integral skin according to claim 1, wherein a reaction injection molding method is used as a molding method. It is.

Hereinafter, the configuration of the present invention will be described in detail. As the polyisocyanate, polymethylene polyphenyl isocyanate having a trinuclear or higher polynuclear content of 60% by weight or more is used, but other known aromatic polyisocyanates are used in combination within a range not to impair the effects of the present invention. You can also. As the aromatic polyisocyanate that can be used in combination, for example, a urethane-modified prepolymer of diphenylmethane diisocyanate, a liquid diphenylmethane diisocyanate that has been converted into ureton imine, and the like are preferable.
Among polymethylene polyphenyl polyisocyanates having a trinuclear or higher polynuclear content of 60% by weight or more, particularly preferred are trinuclear content of 25% by weight or more and tetranuclear or higher polynuclear content. Is 35% by weight or more of polymethylene polyphenyl polyisocyanate. When the content of polynuclear bodies having three or more nuclei is 60% by weight or less, the resulting polyurethane foam with integral skin has a poor touch. Also, when used in combination with other aromatic polyisocyanate,
It is necessary to use a polymethylene polyphenyl polyisocyanate having a polynuclear body content of 60% by weight or more, at least 60% by weight or more of the total isocyanate component.

The polyol is prepared from water, propylene glycol, glycerin, trimethylolpropane, pentaerythritol, sorbitol, sucrose, triethanolamine, ethylenediamine, tolylenediamine, diaminodiphenylmethane, etc. so that the average number of functional groups is 2 to 4. A polyol obtained by addition polymerization of propylene oxide and ethylene oxide to an active hydrogen-containing compound alone or as a mixture, and having an OH value of 24 to
55 mg KOH / g, the content of ethylene oxide in the polyol is 10 to 20% by weight,
It is a polyol having a conversion of 70 to 90 mol%. Further, a polymer polyol (trade name) obtained by graft-polymerizing an ethylenically unsaturated monomer such as styrene, acrylonitrile, and methyl methacrylate to the above polyol is also preferably used. If the ethylene oxide content is lower than 10% by weight, the terminal primary OH conversion will also be lower than 70 mol%, the reactivity will be lowered and the productivity will be poor. In addition, the ethylene oxide content may exceed 20% by weight,
If the H conversion exceeds 90 mol%, the reactivity becomes too fast,
It is not preferable because blisters in the foam thickness portion and sink marks in the foam thickness variation portion occur.

Although water is used as the foaming agent, other foaming agents can be used in combination. Other foaming agents include, for the purpose of the present invention, low-boiling hydrocarbon compounds containing no chlorine or fluorine other than fluorocarbons, such as pentane.

As the crosslinking agent, a known crosslinking agent generally used for producing a polyurethane foam with an integral skin can be used. Examples include ethylene glycol, 1,3-propanediol, 1,4-
Polyalkylene glycols such as butanediol and 1,5-pentanediol; polyoxyalkylene glycols such as diethylene glycol, dipropylene glycol and triethylene glycol; alkanolamines such as diethanolamine and triethanolamine; polyvalents such as trimethylolpropane and glycerin. Alcohol and ethylenediamine, aniline, glycerin, 2,4- / 2,6
Low molecular polyols obtained by adding an alkylene oxide to the tolylenediamine isomer mixture in an amount of 1 to 2 mol per active hydrogen group. These can be used alone or in combination of two or more. A particularly preferred crosslinking agent is diethylene glycol.

As the catalyst, triethylenediamine,
N, N, N ', N'-tetramethylhexane-1,6-
Diamine, N, N, N ', N ", N" -pentamethyldiethylenetriamine, N, N'-bis (N ", N" -dimethyl-3-aminopropyl) N, N'-dimethylethylenediamine, N-methyl -N '-(2-dimethylamino) ethylpiperazine, N-ethylmorpholine, 1-
Methylimidazole, 1,2-dimethylimidazole,
A tertiary amine catalyst such as 3- (dimethylamino) propylimidazole and dimethylaminoethanol, and an organic metal catalyst such as dibutyltin dilaurate and dimethyltin dilaurate are used. These can be used alone or in combination of two or more. The amount used is 100 in total of the high molecular weight isocyanate-reactive compounds (A) and (B).
0.5 to 2.5 parts by weight per part by weight is preferred.

Examples of the foam stabilizer include L-5420 and L-3601 manufactured by Nippon Unicar, SRX-274C, SF-2961, and SF-2962 manufactured by Toray Silicone.
And other organic silicone-based foam stabilizers. Other auxiliary agents that can be used include a colorant, an antioxidant, an internal release agent, and the like, and known agents are used.

The equivalent ratio of isocyanato groups to hydroxyl groups during the production of the polyurethane foam with integral skin is 0.8
5 to 1.30, more preferably 0.95 to 1.10
Is appropriate. In addition, the polyurethane foam with integral skin of the present invention is formed by an open molding method,
A reaction injection molding method or the like is used, and particularly preferably a reaction injection molding method.

[0016]

The present invention will be specifically described below with reference to examples and comparative examples. Table 1 shows the results of Examples and Comparative Examples.

[0017]

[Table 1]

The polyols used in the examples and comparative examples,
The aromatic polyisocyanate, crosslinking agent, catalyst and blowing agent are as follows. Polyol: average number of functional groups 3, average molecular weight 6000,
A polyether polyol having a terminal ethylene oxide content of 15% by weight. Crosslinking agent: diethylene glycol. Catalyst (A): a 33% by weight dipropylene glycol solution of a mixture of 1 methylimidazole / triethylenediamine = 70/30 (weight ratio). Catalyst (B): dibutyltin dilaurate. Blowing agent (A): water Blowing agent (B): trichlorofluoromethane (CFC-1)
1) Polyisocyanate (A): a polymethylene polyphenylisocyanate, a polyisocyanate having an NCO content of 31.5% and containing 70% by weight of a polynuclear body having three or more nuclei Polyisocyanate (C): Polymethylene polyphenylisocyanate, a polyisocyanate having an NCO content of 31.5% and containing 50% by weight of polynuclears of three or more nuclei. Polyisocyanate (D): A polymethylene polyphenylisocyanate containing 31.5% or more polynuclears at 60% by weight and having an NCO content of 31.5%.

Example 1 100 parts of polyol, 13 parts of crosslinking agent, 1.5 parts of catalyst (A)
Part, (B) 0.01 part and 1 part of a foaming agent were mixed to obtain a polyol component. The polyol component was mixed with the aromatic isocyanate (A), and free foaming and mold foaming were performed. Free foaming time until foaming starts (cream time), time until foaming ends (rise time)
And the free density were measured. 40 ° C in advance for mold foaming
The urethane mixture is poured into a mold (400 × 100 × 10 mmt) adjusted to the above, the upper mold is closed, and the mold is left at room temperature for 4 minutes. Then, the molded product is taken out of the mold, and the surface hardness at the time of demolding (Asker Type C) ) Was measured. The final hardness was measured after standing for 24 hours after molding. The surface hardness was low at the time of demolding and both the final hardness was low, showing good results.

[0020]

Example 3 The same procedure as in Example 1 was carried out except that the polyisocyanate (D) was used instead of the polyisocyanate (A). Good results were shown.

COMPARATIVE EXAMPLE 1 In Example 1, polyisocyanate (C) having a low polynuclear content was used in place of polyisocyanate (A), and the other steps were carried out in the same manner. Both were too high compared to Examples 1 to 3 and showed poor results.

Comparative Example 2 The same procedure was followed as in Example 1 except that a freon-based foaming agent (B) was used instead of the foaming agent (A). The properties were poor.

[0024]

According to the present invention, even when water is used as a foaming agent for a polyurethane foam with an integral skin, the surface hardness is low, there is no blistering during demolding, the curing time is short, and good complete water foaming is achieved. A polyurethane foam with integral skin is obtained.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-295074 (JP, A) JP-A-3-32811 (JP, A) JP-A-3-292319 (JP, A) (58) Field (Int. Cl. ⁷ , DB name) C08G 18/00-18/87

Claims (3)

(57) [Claims] (1) Polymethylene polyphenylisocyanate containing 60% by weight or more of so-called polynuclear bodies of 3 or more nuclei as a polyisocyanate, and (2) Active hydrogen compound having an average number of functional groups of 2 to 4 as a polyol. OH with propylene oxide and ethylene oxide added
Having a value of 24 to 55 mg KOH / g, an ethylene oxide content of 10 to 20% by weight, and a terminal primary OH conversion of 70 to
90 mol% of a polyol, or a polymer polyol obtained by graft-polymerizing an ethylenically unsaturated monomer,
(3) A molded article having a density of 0.4 to 0.8 g, wherein water is used as an essential component as a foaming agent, and a crosslinking agent, a catalyst, a foam stabilizer and other auxiliaries are reacted as required. / Cm ³
Of polyurethane foam with integral skin. 2. The integral according to claim 1, wherein the polyisocyanate is a polymethylene polyphenylisocyanate having a trinuclear content of at least 25% by weight and a tetranuclear content of at least 35% by weight. Manufacturing method of polyurethane foam with skin. 3. The method for producing a polyurethane foam with integral skin according to claim 1, wherein a reaction injection molding method is used as a molding method.