Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2002-04-25
2004-08-17
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S112000, C521S128000, C521S130000, C521S131000, C521S133000, C521S137000, C521S159000, C521S170000, C521S174000
Reexamination Certificate
active
06777455
ABSTRACT:
This application is the U.S. National Phase under 35 U.S.C. §371 of International Application PCT/JP01/04831, filed Jun. 7, 2001, which claims priority to Japanese Patent Application No. 2000-176732, filed Jun. 13, 2000. The International Application was not published under PCT Article 21(2) in English.
TECHNICAL FIELD
The present invention relates to a process for producing polyurethane foam having uniform fine cells. A polyurethane foam obtained by the process of the present invention may be suitably used as polishing materials for resins, glass, lens, rock crystals, and silicon for producing semiconductors, electronic substrates, optical substrates etc. Especially a polyurethane foam of the present invention, which is cut as necessary, is suitably used as polishing sheets for CMP.
BACKGROUND ART
As technology for producing a polyurethane foam, a method in which adding organic solvents having low boiling point, such as fluorocarbons and methylene chloride, into an ingredient composition for foaming and dispersing, and then foaming by polymerization heat vaporization; a method in which adding water into a ingredient composition for foaming and dispersing, and then foaming with carbon dioxide gas generated by a reaction of isocyanate groups and water, are well known. In a foam obtained by these methods, diameter of foamed cells (diameter of cells) has a minimum of 100 &mgr;m as an average, it is difficult to obtain a foam having more finely and uniform cells.
Following methods are known as a process for producing a polyurethane foam that has fine cells.
(1) A method that after fine-particles soluble in a solvent are dispersed into polyurethane polymer and are molded into a predetermined form, the molded body is immersed in a solvent that dissolves the fine-particles but does not dissolve the polyurethane polymer, the fine-particles are removed by dissolving to obtain a porous polyurethane resin, that is, polyurethane foam.
(2) A method that finely hollow foamed materials are dispersed in an ingredient composition forming polyurethane.
However, in a case where the above-mentioned method (1) is used, since much amount solvent is required, and treatment for the solvent containing material forming fine-particles is indispensable, high cost naturally occurs. Moreover only open-celled foam may be obtained, the foam obtained may not be used for usage where rigidity is needed, usage is limited. Besides, there is also a problem that a dissolving process and a solvent drying process are also needed, and a long time is needed in order to prepare a very thick molded body.
On the other hand, in the method of (2), since a finely hollow foam has a strong tendency to be floated up in a polyurethane forming solution based on a difference of density, a uniform foam is difficult to be produced. Besides, the finely hollow foam is comparatively expensive, and further since the raw material of the finely hollow foam is remained in the foam, there is a possible problem of inducing damage on a cutting edge in the case where the foam is cut. And the hollows fine-particles are scattered easily and then great costs are needed for facilities of working environmental maintenance.
By the way, a polyurethane foam is applied as a polishing sheet for producing silicon for semiconductors and the like, and producing an electronic substrates. In polishing sheet, highly precise polishing properties are required based on higher density of a formed circuit. Depend on types of particles and size of particles that are contained in polishing slurry used in polishing, a hardness of polishing sheet (polyurethane foam) and the like needs to be matched to those characteristics. For example, ceria derived slurry has a larger particle size than silica derived slurry, and when ceria derived slurry is used as polishing slurry, higher hardness is needed than silica derived slurry.
An object of the present invention is to provide a process for producing a polyurethane foam that have uniform fine cells and higher hardness than ones having the same density can be produced without using a chemically reactive blowing agent such as water, vaporizable expandable blowing agent such as fluorocarbon, or other substance such as a finely particulate hollow foam or solvent soluble substance.
Furthermore, another object of the present invention is to provide a polishing sheet adapted to polishing slurry by using polyurethane foam obtained by the above-mentioned process.
DISCLOSURE OF INVENTION
The present inventors found that a polyurethane foam having uniform finely cellular structure and a hardness higher than other foams with same density might be obtained by adding a predetermined amount of surfactant into either of material liquids for producing polyurethane, a first ingredient comprising an isocyanate compound (polyisocyanate compound), or a second ingredient comprising compound containing an active hydrogen groups (so-called polyol compounds, chain extenders), and agitating the liquid strongly in the presence of unreactive gas to prepare a bubble dispersion containing fine bubbles with unreactive gas, and subsequently polymerizing the liquid by mixed with another ingredient of reaction. Thus the present invention was completed.
The present invention relates to a process for producing a finely cellular polyurethane foam by mixing a first ingredient comprising an isocyanate compound and a second ingredient comprising a compound containing an active hydrogen group, characterized by comprising adding a nonionic silicone surfactant containing no hydroxyl group to at least one of the first ingredient and the second ingredient in an amount of 0.1 to 5 wt %, excluding 5 wt %, based on the total amount of the first ingredient and the second ingredient, subsequently agitating the surfactant containing ingredient together with an unreactive gas to disperse the unreactive gas as fine bubbles to prepare a bubble dispersion and then mixing the bubble dispersion with the remaining ingredient to cure the resultant mixture.
The above-mentioned surfactant is a nonionic silicone surfactant containing no hydroxyl groups. A polyurethane foam having finely and uniform cells may be stably obtained without failing to physical properties of polyurethane by using this type of surfactant.
An amount of the above-mentioned surfactant added is preferably 0.1 to 5 wt %, excluding 5 wt %, to total amount of material ingredients that is the first ingredient and the second ingredient. If the amount is less than 0.1 wt %, the foam having fine cells may not be obtained. In the point of such a reason, the amount of the surfactant is preferably no less than 1 wt %. On the other hand, in case that the amount is not less than 5 wt %, since a number of cells in a finely cellular polyurethane foam is excessively increased, a polyurethane foam having higher hardness is difficult to be obtained. In the point of such a reason, the amount of a surfactant added is preferably less than 4 wt %.
An “unreactive gas” is a gas composed only gaseous ingredient containing no reactivity to isocyanate group or active hydrogen group at ordinary temperature. Besides, gas may be positively sent into the liquid and only automatically involved into the liquid through agitation. Moreover, the fine cells preferably have an average diameter of not more than 50 micrometers, more preferably not more than 40 micrometers. According to a process of the present invention, fine cells having about an average diameter of 10 micrometers may be produced. The diameter of cells may be set up and controlled by selecting and adjusting suitably conditions, such as a type and an amount added of surfactant to be used, agitation conditions, and viscosity of the materials to be used. A density of the foam obtained is preferably approximately 0.6 to 0.95, and a hardness of the foam (ASKER D) is preferably 30 to 60. Especially as a foam for polishing, the hardness is preferably 50 to 56.
Although varied with performance of an agitator used and with viscosity of a reaction material solution that forms a polyurethane fo
Inoue Kaoru
Masui Takashi
Ogawa Kazuyuki
Ono Koichi
Seyanagi Hiroshi
Cooney Jr. John M.
Knobbe Martens Olson & Bear LLP
Toyo Tire & Rubber Co., Ltd.
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