HK1117859A - Method of producing a polyurethane foam molded article - Google Patents

Description

Process for producing polyurethane foam molded article

Technical Field

The present invention relates to a method for producing a polyurethane molded article having a high-density portion and a low-density foamed central portion in an arbitrary ratio.

Background

Unlike substances covering skin layers made of other materials, polyurethane foam molded articles having a high-density surface layer (hereinafter, referred to as "skin layer") have very good surface properties in various uses such as mattresses and cushions. Accordingly, flexible polyurethane foams and semi-rigid polyurethane foams are commonly used for furniture, automotive interior components such as armrests, steering wheels and gear lever handles, shoe soles, and sporting goods. Rigid polyurethane foams have many uses, such as artificial wood and building materials.

Articles such as automobile steering wheels and shoe soles require high abrasion resistance and are typically made, for example, from a molded part covered with a skin on its surface (or bottom for shoes) where a lower density in the interior (center) is desired for better feel.

Bicycle seats are also often covered with a skin layer because the surface that comes into contact with the body of the rider and the portion of the seat mounted on the bicycle require high strength, and a lower density and flexibility in the center is desirable for more comfortable riding. In order to make the paint surface look better, the surface layer density needs to be high.

In the case of building materials made of rigid polyurethane foam, it is also common to provide a skin layer to give the molded article a better painted surface appearance, and it is necessary to prepare the core portion from a low-density foamed material to reduce the weight of the molded article.

According to the desired properties, if the skin is formed only at a portion required during use and the center portion is made of a foamed material of lower density and lower hardness, the polyurethane foam molded article has a higher industrial value and has a wider application.

As a method for foaming polyurethane, a technique is known which uses a foaming machine into which carbon dioxide or a so-called low boiling point liquid (e.g., fluorinated hydrocarbon) serving as a foaming agent and a colorant component as a third component are metered. Foaming machines specifically designed for metering and mixing at least three components to prepare foamed polyurethane products are also commercially available.

However, the apparatus and these molding techniques envision that molded articles having uniform density, uniform hardness, and uniform composition in any portion of the molded article can be obtained. Therefore, the aim of the foaming machine is to add the raw material (including the foaming agent) having a uniform composition throughout the course of adding the raw material.

Plastics, vol.24, No. 8, page 118 discloses a molded article having a skin layer, and a so-called polyurethane integral skin foam can be once molded based on a difference in foaming reaction caused by a temperature difference between an inner core portion and a skin layer contacting a mold at the time of molding, using a liquid foaming agent (e.g., fluorinated hydrocarbon) having a low boiling point near room temperature, which is a known technique.

One method of preparing Polyurethane foam molded articles using a Polyurethane resin foaming machine is described in Polyurethane World Congress, 1997, page 185, in which the components required for foaming (e.g., isocyanate, polyol, catalyst, crosslinking agent, and low boiling blowing agent such as fluorocarbon) are added separately from their respective tanks to the mixing head by metering pumps.

Urethane Technology (Urethane Technology), 10/11.1994, discloses a process using the most common water as a polyurethane resin blowing agent. However, it is very difficult to form a sufficient skin layer on a polyurethane molded article using this method.

JP-A-5-59146 discloses ｃA method for imparting ｃA skin layer to ｃA polyurethane resin molded article, in which the reactivity of the raw materials is increased by using ｃA large amount of ｃA urethane reaction catalyst or ｃA crosslinking agent, while the viscosity of the raw materials for preparing polyurethane is increased.

JP-A-5-305629 discloses ｃA method using ｃA pyrolysis type blowing agent. JP-A-6-1820 discloses ｃA method in which water in the form of ｃA hydrated salt is added to control the reaction between water as ｃA blowing agent and isocyanate.

In the technique disclosed in Plastics, volume 24, stage 8, page 118, the ratio of the skin layer to the foamed core is almost constant, the skin layer cannot be formed only on the portion of the molded article where the skin layer is to be formed, the density cannot be changed, and the hardness of each portion cannot be changed.

In the production process disclosed in Polyurethane World Congress, 1997, page 185, molding techniques, equipment, etc. for metering and mixing at least three of these components to produce Polyurethane foamed molded articles are designed such that a constant ratio of raw materials (including low boiling liquid blowing agents) is continuously metered, mixed and added. Therefore, the ratio of the skin layer to the foamed core is approximately constant. Therefore, the skin cannot be formed only at the portion of the molded article where the skin is to be formed, the density cannot be changed, and the hardness of each portion cannot be changed.

Urethane Technology (Urethane Technology), 10/11 months 1994, JP-A-5-59146, JP-A-5-305629 and JP-A-6-1820 disclose ｃA method of forming ｃA skin layer on ｃA polyurethane foam molded article. However, a molded article having a satisfactory skin layer is not obtained. Further, although a stable polyurethane foam molded article having a constant ratio of the skin layer to the foamed core can be produced, such a polyurethane foam molded article cannot be produced: the ratio of skin to foamed core can vary, providing a skin or high density only in the portions of the molded article where a skin or high density is actually desired.

Therefore, although the conventional methods can mold a polyurethane molded article having uniform properties, these conventional methods cannot produce a desired molded article because it is difficult to selectively form a skin layer on the surface of the molded article where the skin layer is actually required and to change the density or hardness of each portion by arbitrarily changing the ratio of the skin layer to the foamed core layer. There is no satisfactory method.

Summary of The Invention

The present invention provides a method for preparing a polyurethane foam molded article having a skin layer selectively formed on a portion of the molded article where the skin layer is actually required, in which the ratio of the skin layer to a low-density foamed core can be arbitrarily changed and the density or hardness of each portion can be changed, in a single step.

Detailed Description

The present invention will now be described for purposes of illustration and not limitation. Except in the operating examples, or where otherwise indicated, all numbers expressing quantities, percentages, OH numbers, functionalities and so forth, are to be understood as being modified in all instances by the term "about". Unless otherwise specified, equivalent weights and molecular weights given herein in daltons (Da) are number average equivalent weights and number average molecular weights, respectively.

The present invention provides a process for producing a polyurethane molded article from (a) one or two polyisocyanate components and (b) two polyol components, the process comprising providing a molding machine which can feed said one or more polyisocyanate components and said two polyol components in a unique manner, feeding a first polyurethane mixture liquid containing a polyisocyanate and a first polyol component without a blowing agent into a mold of the molding machine, finishing feeding the first polyurethane mixture liquid for at least 0.1 second, and feeding a second polyurethane mixture liquid containing a polyisocyanate and a second polyol component with a blowing agent into the mold.

The invention can prepare the product with average density of 0.2-0.8g/cm³The polyurethane foam molded article of (1), wherein the molded article has a skin and/or a high-density portion and a low-density foamed core selectively on a portion of the molded article actually required, and the ratio of the skin and/or the high-density portion to the low-density foamed core can be arbitrarily changed. Further, since the skin or the high-density portion is selectively provided at a portion where the molded article is actually required, the density of the molded article can be reduced while maintaining the properties similar to those of the articles in the art.

In the present invention, a polyurethane resin foaming machine equipped with tanks containing components necessary for molding a polyurethane resin, such as a polyisocyanate component and a polyol component and a blowing agent (if necessary), metering pumps for metering and pumping the components, and a mixing head for mixing the components can be used.

According to the present invention, various kinds of foaming machines can be used as polyurethane foam molding machines, such as a low-pressure foaming machine, in which a polyisocyanate component and a polyol component are metered and added to a mixing head (a reaction and mixing device for mixing the components and feeding the mixture into a mold) at a pressure of 0.1 to 5MPa, preferably about 2MPa, followed by mixing by a mixer provided in the mixing head; and a high-pressure polyurethane foaming machine for mixing the components by collision in a mixing head at a high pressure of 10MPa or more, preferably 12 to 25 MPa. High pressure polyurethane foaming machines are particularly preferred.

It is required that the polyurethane molding machine used in the present invention can add two distinctly different polyurethane mixture liquids to a mold. When one molding machine is used for one polyisocyanate component and two polyol components, it is necessary that the polyurethane molding machine independently have pumps for metering and adding at least three components respectively into one mixing head, or when one molding machine is used for two polyisocyanate components and two polyol components, it is necessary that the molding machine independently have pumps for metering and adding four components respectively into one mixing head.

A combination of two polyurethane molding machines can be used for molding, but when two molding machines are used in combination, two mixing heads are required. In the Reaction Injection Molding (RIM) method, it is preferable that only one inlet of the mold for the polyurethane mixture liquid is provided so that the second polyurethane mixture liquid for the center of the low-density partially foamed layer pushes and extends the first polyurethane mixture liquid uniformly from the center around which the first polyurethane mixture liquid for the skin layer and the high-density portion flows.

A timer is preferably provided which controls the switching from the first polyurethane mixture liquid to the second polyurethane mixture liquid, i.e. for starting and ending the feed into the mixing head in increments of 0.1 second, preferably 0.01 second.

In the RIM method, a polyurethane mixture liquid is injected into a closed mold through an injection port, a first polyurethane mixture liquid added in advance is stayed near the injection port, and it is filled in the entire space of the mold by the pressure of injecting a mixture of a second polyurethane mixture liquid added later or by the pressure generated by a foaming reaction. Since the first polyurethane mixture liquid has a resistance to movement on its surface which is in contact with the mold surface, the second polyurethane mixture liquid flows through the central portion of the interior space of the mold under the tunnel effect according to the dynamics of the liquid flow, and the first polyurethane mixture liquid which is not in contact with the mold surface moves to fill the interior space while being in contact with the mold surface. The first polyurethane mixture liquid in contact with the mold surface forms a skin on the surface of the molded article. Since the second polyurethane mixture liquid added later contains most of the foaming agent, it is foamed in the mold to form a foamed core having a lower density than the skin layer prepared from the first polyurethane mixture liquid.

The proportion and thickness of the skin layer formed in the molded article can be controlled according to the amount of the first polyurethane mixture liquid injected earlier. The amount of the first polyurethane mixture liquid is determined based on the desired ratio and thickness of the skin layer. When the molded article is a complicated shape variable in thickness and width, since the first polyurethane mixture liquid can occupy not only the surface but also the entire thickness direction, the second polyurethane mixture liquid can flow only in the central portion where the second polyurethane mixture liquid easily flows. The first polyurethane mixture liquid does not always have to cover the entire surface of the molded article. The first polyurethane mixture liquid may cover only a desired portion (e.g., at least 30%, particularly at least 50% of the entire surface).

When the time for adding the first polyurethane mixture liquid is longer, the formed skin layer can be thickened, and a large amount of the first mixture liquid can be provided on a desired portion. The amount of the first reaction mixture liquid injected before the injection of the second polyurethane mixture liquid is preferably at least 10% by weight, for example, 10 to 50% by weight, of the total amount of the first polyurethane mixture liquid and the second polyurethane mixture liquid injected into the mold.

However, the second polyurethane mixture liquid needs to be injected before the reaction is completed and before the earlier injected first polyurethane mixture liquid loses its fluidity. When the first polyurethane mixture liquid has fluidity, it is easily spread in the mold.

The injection time of the first polyurethane mixture liquid is preferably at least 0.1 second, more preferably 0.15 second to 3.0 seconds. It is preferable that the time interval from the completion of the injection of the first polyurethane mixture liquid to the start of the injection of the second polyurethane mixture liquid is short, and the completion and the start may be continuous. For example, when both the first and second polyurethane mixture liquids are used as the polyisocyanate component, such components may be continuously added, and the polyol component may be changed.

The first polyurethane mixture liquid may also be injected into the mold after the second polyurethane mixture liquid is injected into the mold so that only the first polyurethane mixture liquid may remain near and at the injection gate. Therefore, a high-density portion can be formed at this portion. When an unnecessary injection port in the product is cut, a foaming center having a larger pore diameter does not appear on the cut surface, thus solving problems inherent in the art, such as painting failure and low heat resistance.

The proportion of the high-density portion near and at the sprue and the proportion of the high-density portion formed near the molded article in contact with the sprue are determined according to the amount of the first polyurethane mixture liquid injected into the mold after the second polyurethane mixture liquid is completely injected into the mold.

The amount of the first polyurethane mixture liquid injected into the mold after the second polyurethane mixture liquid is completely injected into the mold is preferably at least 1.0% by weight, more preferably 1.0 to 5.0% by weight, of the total amount of the first polyurethane mixture liquid and the second polyurethane mixture liquid injected into the mold.

Also, when the injection of the first polyurethane mixture liquid is started after the injection of the second polyurethane mixture liquid is completed, it is preferable that the time interval from the completion of the injection of the second polyurethane mixture liquid to the start of the injection of the first polyurethane mixture liquid is short, and the completion and the start may be continuous. For example, when both the first and second polyurethane mixture liquids are used as the polyisocyanate component, such components may be continuously added, and the polyol component may be changed.

It is also necessary to control the discharge rate of the second polyurethane mixture liquid. When the discharge rate is too high, the first polyurethane mixture liquid injected in advance may be flushed away by the pressure of the second polyurethane mixture liquid injected later. The discharge rate is preferably 800g/s or less, more preferably 50 to 800g/s, depending on the size of the molded article.

With respect to the viscosities of the polyisocyanate component and the polyol component at 25 ℃ in the first polyurethane mixture liquid for forming the high-density portion, it is preferable that the viscosity of the polyisocyanate component is not more than 2,000MPa · s, more preferably 30MPa · s to 1,000MPa · s, and the viscosity of the polyol mixture is not more than 10,000MPa · s, more preferably 500MPa · s to 5,000MPa · s. When the viscosity is within this range, the first polyurethane mixture liquid is liable to spread in the mold since the first polyurethane mixture liquid is liable to be pushed and flowed by the second polyurethane mixture liquid for forming the lower density portion. It is preferable that the viscosity of the polyisocyanate component and the polyol component at 25 ℃ in the second polyurethane mixture liquid is in the same range as the viscosity of the polyisocyanate component and the polyol component in the first polyurethane mixture liquid.

The total duration of injection into the mold is preferably controlled to be 1.0 second or more, for example, 1.2 to 10 seconds. By controlling the total duration of injection into the mold to be at least 1.5 seconds, it is advantageous to easily change from the first polyurethane mixture liquid to the second polyurethane mixture liquid, that is, to easily arrange the skin layer and the low-density portion in proportion on the portions of the molded article. A selector timer can be controlled to start and stop the injection to change the ratio of skin to foam core. A molded article having a clear skin layer and a foamed core can be obtained.

In the RIM molding method, in order to obtain a skin layer having a high density on both the top surface and the bottom surface of the molded article under the above-mentioned conditions, the thickness of the molded article is preferably 20mm or less, more preferably 10mm or less, and most preferably 2 to 8 mm. When the thickness is not more than 10mm, it is easier to form a skin on the actual surface of the molded article, so that the high-density sprue residue is integrated. However, when the thickness is 2mm or less, there may be a portion not including the foamed core layer, and in the case where the thickness of each portion of the molded article to be formed is different, the present invention is not limited to the above thickness range.

Preferably, the sprue is located at the bottom of the mold (lower side of the molded article). When it is preferable that the injection port is located at the bottom of the mold, the injected first polyurethane mixture liquid and second polyurethane mixture liquid advantageously move from the injection port to the end of the mold while filling the inner space of the mold in the thickness direction.

When an open type injection mold without an injection port is used, the first polyurethane mixture liquid added in advance is pressurized by a pressure generated by a foaming reaction of the second polyurethane mixture liquid added subsequently so as to spread mainly on the bottom surface of the entire space of the mold, and thus, a portion which becomes the lower bottom of the molded article and which is in contact with the mold surface forms a skin. The second polyurethane mixture liquid forms a foamed core. The thickness and location of the formed skin can be controlled by varying the amount and injection pattern of the earlier injected first polyurethane mixture liquid, for example shoe soles and saddles (saddles) that require a thicker skin on one surface (corresponding to at least 50% of the total surface of the molded article).

After stopping the injection of the second polyurethane mixture liquid, the first polyurethane mixture liquid may be injected. For example, by changing the injection mode of the first polyurethane mixture liquid and the second polyurethane mixture liquid to the lateral injection, a skin layer can be formed on a desired molded article portion to achieve a desired arrangement of the foaming centers.

Also, in the open injection method, it is preferable that the time interval of the change and the amount of injecting the first polyurethane mixture liquid and the second polyurethane mixture liquid are the same as in the RIM molding method.

Although the thickness of the molded article produced by the open injection method depends on the density of the second polyurethane mixture liquid used for foaming to form the core, it can be set relatively freely. Moulded articles having a thickness of at least 10mm, in particular from 10 to 200mm (for example 100mm), can be prepared.

In the open injection method, in order to form a skin on the surface of a desired molded article or selectively form a high-density portion at a specific position, it is desirable to maintain a fixed injection pattern by using a robot (robot) or the like so as to secure the reproducibility of a foamed portion and the skin-to-center ratio. When the molded article has a large surface area, it is preferable to connect a nozzle having a fan (or triangular) or shark fin shape to the mixing head so that the first polyurethane mixture liquid spreads out from the mixing head while being injected.

Also with respect to the free-rise foam which foams in the container having the top opening, by adjusting conditions such as the time interval and the amount of the injected first polyurethane mixture liquid and second polyurethane mixture liquid, it is possible to prepare a foam which forms a skin layer on the surface of the foam (at the bottom of the expanded foam) and a low-density foaming core inside.

The process of the present invention may use a RIM process (in which a closed mold with an injection port is used) or an open injection process without an injection port, preferably a RIM process. In the tunnel effect, the RIM method makes it easier to control the proportion of the surface of the molded article covered with the skin layer, particularly to form a high-density portion near the injection port.

As described above, according to the present invention, a polyurethane foam molding machine equipped with a timer for controlling the change of the injection of the first polyurethane mixture liquid and the second polyurethane mixture liquid into the mixing head (i.e., a timer for injecting the mixture liquid into the mold in increments of 0.01 second) can be used. In the RIM method, molded articles having a skin layer, a high-density portion and a foamed core in different proportions can be prepared, that is, the skin layer is formed only in a desired portion of the molded article and the high-density portion is formed in the sprue gate. It has also been found that a molded article having a skin formed in a desired portion and a low-density foamed core can also be produced by the open injection method.

All polyurethanes, such as rigid polyurethane, flexible polyurethane and semi-rigid polyurethane, can be used for the polyurethane used to form the low density core, high density portion and skin. Depending on the application of the product, various polyurethane systems may be used, such as a combination of a skin layer of a flexible polyurethane elastomer and a core of a rigid polyurethane. Furniture or automotive interior trim having a flexible surface and a rigid core can be made, for example, by using a combination of a skin layer of a flexible polyurethane elastomer and a core of a rigid polyurethane. In addition, by using a system in which a structural material supports a combination of a skin layer of a flexible/semi-rigid elastomer and a center layer of a flexible polyurethane foam or a semi-rigid polyurethane foam, an automobile instrument panel, a door trim, a rear side panel, a cushion and furniture having satisfactory tactile sensation can be produced. Further, by using a colored weather-resistant aging system (e.g., an aliphatic isocyanate polyurethane system) as the surface portion and using a rigid polyurethane having high rigidity and containing a reinforcing material as the central portion, a molded article can be produced without using a painting method. Further, when the molded article is molded, a molded article having a skin covered with an in-mold paint can be prepared by in-mold coating on a mold in advance.

Polyurea resins in which a few or most of the resins prepared by using a polyol having an amino group at the terminal thereof as a reactive group have a urea bond can be used for the combination.

The density of a free-rise foam produced in an open state in a lidless container by using a first polyurethane mixture liquid containing a polyol component substantially free of other blowing agents except water (contained during or previously contained in the raw materials during mixing of the raw materials) is preferably at least 0.8g/cm³More preferably at least 0.85g/cm³. When the density is at least 0.80g/cm³In this case, the properties of the high-density skin layer formed from the first polyurethane mixture liquid can also be satisfied.

The NCO index of the polyisocyanate component and the polyol component in the first polyurethane mixture liquid and the second polyurethane mixture liquid is preferably 80 to 120. The NCO index is the index of isocyanate to polyol when molding polyurethane. When the polyisocyanate component and the polyol component were mixed and molded at an equal ratio (NCO of the polyisocyanate component to average isocyanate-reactive active hydrogen of the polyol component), the NCO index was 100.

Preferably, the polyurethane foam molded article has an average density of 0.2 to 0.8g/cm³。

The polyurethane foam molded article is composed of a high-density portion and a low-density portion (i.e., a foamed portion). Preferably wherein the high density portion has a density of at least 0.8g/cm³(e.g., 0.8 to 1.2g/cm³) And at least 50% of the entire surface of the molded article is covered with the high-density portion. The density of the low-density portion is preferably 0.7g/cm³Below, for example, 0.05 to 0.5g/cm³。

When the density of the high-density part is at least 0.8g/cm³When used, sufficient performance as a skin layer can be achieved. When at least 50% of the entire surface of the molded article is covered with the high-density portion, the resulting polyurethane foam article has various uses such as shoe soles and saddle plates, in which at least 50% (corresponding to one side) of the molded article may be covered with the skin layer.

The raw materials for producing the polyurethane molded article of the present invention will now be described.

That is, the polyisocyanate component and the polyol of the polyol component used in the first polyurethane mixture liquid and the second polyurethane mixture liquid, the catalyst, the crosslinking agent and the foam stabilizer (if necessary), the reinforcing material and other auxiliaries, and the blowing agent used in the second polyurethane mixture liquid will be described in detail below.

Suitable polyisocyanate components include diphenylmethane diisocyanate, polymethylene polyphenylene polyisocyanate, toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, modified polyisocyanates prepared by modifying these polyisocyanates with urethane, allophanate, carbodiimide or isocyanurate, and mixtures thereof.

As the polyol used as the polyol component, there can be used polyether polyols having 2 to 6 hydroxyl groups in the molecule and an average hydroxyl equivalent weight of 100-3,000, which are obtained by adding an alkylene oxide (e.g., ethylene oxide or propylene oxide) to hydroxyl group-containing compounds (e.g., propylene glycol, diethylene glycol, glycerin, trimethylolpropane, pentaerythritol, sorbitol and sucrose), amino group-and hydroxyl group-containing compounds (e.g., triethanolamine and diethanolamine) or amino group-containing compounds (e.g., ethylenediamine and diaminotoluene), or polymer polyols obtained by addition polymerization of a vinyl compound to these polyether polyols.

It is also possible to use polyester polyols made from polycarboxylic acids and low molecular weight hydroxyl-containing compounds, lactone-based polyesters made by ring-opening polymerization of caprolactone, polycarbonate polyols, poly-1, 4-butanediol made by ring-opening polymerization of tetrahydrofuran, and polyether polyamines made by aminating the hydroxyl groups of polyether polyols or hydrolyzing isocyanate prepolymers of polyether polyols, with an average active hydrogen equivalent of 100-3,000.

The amounts of the isocyanate component and the polyol component are preferably adjusted so that the isocyanate index is 80 to 120.

As the catalyst, tertiary amines such as triethylenediamine, pentamethyldiethylenetriamine, 1, 8-diazabicyclo-5, 4, 0-undecene-7, dimethylaminoethanol, tetramethylethylenediamine, dimethylbenzylamine, tetramethylhexamethylenediamine and bis (2-dimethylaminoethyl) ether; and organic metal compounds such as dibutyltin dilaurate, tin octoate, and dibutyltin diacetate.

As the crosslinking agent, there can be optionally used dihydric alcohols having a molecular weight of 62 to 300, such as ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, neopentyl glycol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol and polypropylene glycol; and divalent amines such as diethyltoluenediamine, t-butyltoluenediamine, diethyldiaminobenzene, triethyldiaminobenzene, and tetraethyldiaminodiphenylmethane. Polyether polyols obtained by adding alkylene oxides thereto may also be used. These crosslinking agents are described in JP-B-54-17359, JP-A-57-74325, JP-B-63-47726 and JP-B-01-34527.

As the auxiliary, a foam regulator or foam stabilizer, such as a silicone-based foam stabilizer; a reinforcing material; surfactants (compatibilizers); anti-aging agents such as antioxidants; an ultraviolet absorber; stabilizers such as 2, 6-di-tert-butyl-4-methylphenol and pentaerythritol tetrakis [3- (3 ', 5' -di-tert-butyl-4-hydroxyphenyl) propionate ]; and a colorant.

As reinforcing materials, fibers made of glass, minerals and minerals, such as ground glass fibers, wollastonite fibers and processed mineral fibers; and flakes, such as mica and glass flakes.

The blowing agent may be mixed with the polyol component beforehand, or may be mixed with the isocyanate component later. Alternatively, the blowing agent may be mixed with the polyol component while being mixed with the polyisocyanate component.

As the blowing agent, water (which reacts with the polyisocyanate compound to release carbon dioxide gas), carbon dioxide, fluorocarbons such as chlorofluorocarbons, hydrocarbons such as pentane and cyclopentane and fluorinated hydrocarbons such as HCFC141b, HFC245fa and HFC365mfc can be used according to the design of the polyurethane foaming machine. Combinations of blowing agents may also be used. As the blowing agent, a carbonate of an amine compound (which is dissociated at the time of urethanization and emits carbon dioxide gas) or an organic acid such as formic acid (which is reacted with a polyisocyanate compound and emits carbon dioxide gas) may be used. Further, air or nitrogen may be dispersed in the polyol component in advance, for example, by using an air-loading device.

Preferably the blowing agent is at least one of carbon dioxide, a hydrocarbon, a fluorinated hydrocarbon and water. A particularly preferred blowing agent is carbon dioxide. The second polyurethane mixture liquid for forming the low-density portion containing carbon dioxide as a blowing agent causes foaming when injected into the mold, resulting in the low-density portion. Therefore, the second polyurethane mixture liquid does not penetrate into the earlier injected first polyurethane mixture liquid for forming the high-density portion, and thus a clear interface boundary is formed between the skin layer and the core layer. More specifically, in the open injection method, the second polyurethane mixture liquid remains on the upper portion of the first polyurethane mixture liquid injected earlier, and does not permeate into the first polyurethane mixture liquid, thus forming a clear interfacial boundary between the skin layer and the core layer.

The following examples and comparative examples further illustrate the present invention in detail. The parts in these examples are parts by weight.

Examples

Example 1

The following polyisocyanate component and polyol component were used for the first polyurethane mixture liquid.

Polyisocyanate A: carbodiimide-modified diphenylmethane diisocyanate (NCO content: 29.0%, viscosity: 35 MPa. multidot.s/25 ℃ C.).

Polyol component a: 45 parts of polyether polyol with the hydroxyl value of 35mg KOH/g, which is prepared by the addition polymerization of glycerol, propylene oxide and ethylene oxide; 45 parts of polyether polyol with a hydroxyl value of 45mg KOH/g, which is prepared by the addition polymerization of propylene glycol, propylene oxide and ethylene oxide; 7 parts of monoethylene glycol; 0.9 part dimethylaminopropylamine; and 0.5 part of black paste (mixture of carbon and polyether polyol) for changing the color to black, and the above were mixed to obtain 20kg of a polyol component mixture (hydroxyl value: 160mg KOH/g, viscosity: 1,000MPa · s/25 ℃ C.).

Polyol component A and polyisocyanate A were mixed in a weight ratio of 100: 43 and the NCO index of the mixture was 105. The resulting free rise foam was black in color and had a density of 0.90g/cm³The gel time (the time when the liquid almost lost its fluidity) was 34 seconds.

The following polyisocyanate and polyol components were used for the second polyurethane mixture liquid.

Polyisocyanate B: polymethylene polyphenyl polyisocyanate (NCO content: 31.0%, viscosity: 130MPa · s/25 ℃ C.).

Polyol component B: 41 parts of polyether polyol with the hydroxyl value of 870mg KOH/g, which is prepared by the addition polymerization of trimethylolpropane and propylene oxide; 31 parts of polyether polyol with the hydroxyl value of 28mg KOH/g, and is prepared by the addition polymerization of propylene glycol, propylene oxide and ethylene oxide; 11.25 parts monoethylene glycol; 4.26 parts monoethanolamine; 0.5 part of water; 1.384 parts of carbon dioxide; 1.4 parts of a silicone surfactant (cell stabilizer)) (ii) a 0.88 parts of pentamethyldiethylenetriamine; 0.88 parts of a triethylenediamine salt catalyst and 8 parts of a compatibility improver were mixed to give 20kg of a polyol component mixture (polyol for rigid polyurethane foam formulation having a free-rise foam density of 0.15 g/cm)³The hydroxyl value: 620mg KOH/g, viscosity: 1,700MPa · s/25 ℃ C.

Polyol component B and polyisocyanate B were mixed in a weight ratio of 100: 157 and the NCO index of the mixture was 105. The resulting free rise foam was yellow in color and had a density of 0.15g/cm³The gel time was 27 seconds.

Each of the polyurethane raw material components was supplied in each tank of a polyurethane molding machine of type HK270 (manufactured by Maschinenfabrik Hennecke GmbH) to which four components were added. The pour rate of each component was set at 550 g/s.

Each of the polyurethane raw material components was poured into a mold 6mm thick, 30cm wide and 50cm long, having a pouring gate 30cm wide and 2mm thick at the end of the mold, the temperature was set to 60 ℃, and RIM molding was used.

The first polyurethane mixture liquid was poured for 0.35 seconds (195 g was poured out). After the first polyurethane mixture liquid was poured for 1 second, pouring of the second polyurethane mixture liquid was started, and the second mixture liquid was poured for 0.43 second (237 g was poured out), followed by molding. And (5) filling the mold. The upper and lower surfaces of the molded article were black within about 36cm of the pour spout. The remaining part, 14cm from the flow end, was mainly yellow and black lines in the flow direction. The surface of the black part is not foamed and is in an unexpanded solid state. It was confirmed by observing the cross section that 195g of the black first polyurethane mixture liquid (22% of the mold volume) was spread to 72% of the surface of the molded article. The black portions near the upper and lower portions of the pouring spout are about 0.2mm and 0.27mm thick, and the black portions at the upper and lower portions of the central portion are about 0.4mm and 0.5mm thick.

Example 2

A polyurethane raw material component was molded in the same manner as in example 1 except that the pouring time of the first polyurethane mixture liquid was changed to 0.53 seconds (poured 290g) and the pouring time of the second polyurethane mixture liquid was changed to 0.41 seconds (poured 223 g). And (5) filling the mold. Within about 45cm of the length from the pour spout, the upper and lower surfaces of the molded article were both black, with the remainder 5cm from the flow end being predominantly yellow polyurethane with black lines in the direction of flow. It was confirmed that 290g of the black first polyurethane mixture liquid (32% by volume of the mold) was spread to 95% of the surface of the molded article. By observing the cross section, the black portions near the upper and lower portions of the pouring spout were about 0.2mm and 0.3mm thick. Distinct skin layers with thicknesses of about 0.8mm and 1.0mm were observed in the upper and lower parts of the central portion.

Example 3

The polyurethane raw material components were molded in the same manner as in example 1 except that the pouring time of the first polyurethane mixture liquid was changed to 0.59 seconds (poured out 320g) and the pouring time of the second polyurethane mixture liquid was changed to 0.60 seconds (poured out 330 g). And (5) filling the mold. It was confirmed that 320g of the black first polyurethane mixture liquid (35% by volume of the mold) almost completely covered the upper and lower surfaces of the molded article. By observing the cross section, the black portions near the upper and lower portions of the pouring spout were about 0.2mm and 0.3mm thick. A distinct skin layer with a thickness of about 1.0mm was observed in the upper and lower parts of the central portion. A portion 2cm from the flow end was almost filled with the first polyurethane mixture liquid, and the center thickness of the second polyurethane mixture liquid was 1 mm.

Example 4

Polyol component C: 94 parts of polyether polyol with the hydroxyl value of 28mg KOH/g, which is prepared by the addition polymerization of glycerol, propylene oxide and ethylene oxide; 4.2 parts monoethylene glycol; 1.5 parts of diethanolamine; 0.7 part of water; 0.2 part of a surfactant; 1.2 parts of a solution of triethylenediamine in ethylene glycol; and 1.0 part of a UV absorber were mixed to obtain a polyol mixture (20kg) (hydroxyl value: 158mg KOH/g, viscosity: 1,100 MPa. multidot.s/25 ℃ C.), which was used as a polyol component of the second polyurethane mixture liquid (II).

Polyol component C and polyisocyanate B were mixed in a weight ratio of 100: 40 and had an NCO index of 105. The first polyurethane mixture liquid was the same as that of example 1.

The pouring rates of the first polyurethane mixture liquid and the second polyurethane mixture liquid were each set to 170 g/s. The components were poured into open molds 10cm wide, 20cm long and 1cm thick. The first polyurethane mixture liquid was poured for 0.35 seconds (60 g was poured out), and then the second polyurethane mixture liquid was poured for 0.25 seconds (43 g was poured out). The mold was closed, and a molded article was prepared after 6 minutes. The surface of the molded article was covered with a 3mm thick unexpanded black layer, and the remaining 7mm thick portion was an expanded central portion having a density of 0.30g/cm³. A molded article having a surface black layer and a foamed core was obtained.

Comparative example 1

The polyurethane raw material components were molded in the same manner as in example 1 except that the first polyurethane mixture liquid was poured for 0.06 second (poured out 33g), and the second polyurethane mixture liquid was poured for 0.60 second (poured out 330 g). After 6 minutes of complete filling of the mold, the molded article was released from the mold. The black portions of the upper and lower surfaces of the molded article did not reach a portion 25cm from the pouring gate, and the remaining portion from the flow end was mainly yellow, with black lines along the flow direction. It was confirmed that the surface of the black portion was not foamed, but 33g (3.7% of the volume of the mold) of the black portion was not spread to 50% of the surface of the molded article with respect to the 900cc mold. The observation of the cross-section revealed that the black portions near the upper and lower portions of the pouring spout were approximately 0.16mm and 0.27mm thick.

The present inventors contemplate that the polyurethane molded articles of the present invention (e.g., flexible polyurethane foam and semi-rigid polyurethane foam) may be used for furniture, automotive interior parts such as arm rests, steering wheel and gear shift lever handles, shoe soles, and sporting goods. Rigid polyurethane foams have many uses, such as artificial wood and building materials.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (7)

1. A process for preparing a polyurethane molded article from:

(a) one or two polyisocyanate components, and

(b) two polyol components are used as the polyol component,

the method comprises the following steps:

providing a molding machine that can add the one or more polyisocyanate components and the two polyol components in a unique manner;

adding a first polyurethane mixture liquid containing a polyisocyanate component and a polyol component, which is free of a blowing agent, to a mold of a molding machine; it takes at least 0.1 second for the first polyurethane mixture liquid to be added,

a second polyurethane mixture liquid containing a polyisocyanate component and a polyol component containing a blowing agent is added to the mold.

2. The method for producing a polyurethane molded article according to claim 1, wherein the amount of the first polyurethane mixture liquid added before the addition of the second polyurethane mixture liquid is at least 10% by weight of the total amount of the first polyurethane mixture liquid and the second polyurethane mixture liquid.

3. The method for producing a polyurethane molded article according to claim 1, wherein the first polyurethane mixture liquid is added after the second polyurethane mixture liquid is added.

4. The method for producing a polyurethane molded article according to claim 3, wherein the amount of the first polyurethane mixture liquid added after the addition of the second polyurethane mixture liquid is completed is at least 1.0% by weight of the total amount of the first polyurethane mixture liquid and the second polyurethane mixture liquid.

5. The process for producing a polyurethane molded article according to claim 1, wherein the blowing agent is at least one member selected from the group consisting of carbon dioxide, hydrocarbons, fluorinated hydrocarbons and water.

6. A polyurethane molded article prepared by the process of claim 1, the article having a high density portion and a low density portion, wherein the high density portion has a density of at least 0.8g/cm³Covering at least 50% of the entire surface of the molded article.

7. A method of making a polyurethane molded article from at least one polyisocyanate component and two polyol components, the method comprising:

adding a first polyurethane mixture liquid containing a polyisocyanate component and a first polyol component, which is free of a blowing agent, to a mold of a molding machine; it takes at least 0.1 second for the first polyurethane mixture liquid to be added,

adding a second polyurethane mixture liquid containing a blowing agent and comprising a polyisocyanate component and a second polyol component to a mold of a molding machine; and

curing the polyurethane molded article.