JPH0415251B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to polyurethane prepolymers from which sponges can be made that have the general appearance and wiping properties of cellulose sponges with minimal swelling when wet and non-curling properties during drying. It has been a goal of the sponge industry to replace cellulose foam with polyurethane foam in sponge-based composites such as wiping sponges or cleaning pads or bath mats. In general, prior art polyurethane foams that are sufficiently water-based to be useful tend to swell significantly if they are wetted by more than 75-100% by volume. They dry slowly and unevenly and curl or wrinkle as they dry. This characteristic is not desirable for household sponge applications. The use of polyurethane foam as an alternative to flocked wall coverings has been proposed. However, in view of the curling and wrinkling nature of these foams and the resulting buchling, these foams are not suitable for use as replacements for flocked wall coverings. In US Pat. No. 3,806,474 a hydrophilic polyester urethane foam is disclosed. However, this foam does not wet out quickly and does not wipe to obtain a clean surface. In US Pat. No. 4,160,076 a pseudo-natural sponge based on hydrophilic polyurethane is disclosed. However, even though this simulates a natural sponge, polyurethane sponges still have the problem of swelling extensively when they get wet. A commonly used polyurethane foam is made from MDI, which is methylene-bis(phenylisocyanate). These forms are rigid or semi-rigid due to the crystallinity imparted by MDI. They are generally hydrophobic since MDI itself is hydrophobic. In British Patent No. 874430, the flexible polyurethane foam is a polyisocyanate mixture consisting of a polyether polyol having at least two hydroxyl groups, a diarylmethane diisocyanate and 5 to 10% by weight of a polyisocyanate with a functionality greater than 2. It is produced by reaction with a small amount of water. Catalysts can be used in any embodiment. These foams are not hydrophilic and are not manufactured using sufficient amounts of water to transport large amounts of fibers, fillers, preservatives, or other water-soluble or water-dispersible ingredients into the foam; The disadvantage with any catalyst is that undesirable catalyst residues may remain. In U.S. Pat. No. 4,237,240, a flexible
MDI-based foams are formed by reacting diphenylenemethane diisocyanate with a polyester polyol or a mixture of polyester polyols and polyether polyols in which the polyester polyol content is at least 60% by weight of the polyol mixture and a small amount of water. It will be done. Catalysts are used as claimed, these foams have the same drawbacks as that of GB 874,430, including undesirable catalyst residues in the foam, and in addition they are more expensive than the more expensive polyesters. Requires the use of polyols. In British Patent No. 1209058, a flexible hydrophilic polyurethane foam is comprised of at least 10% by weight of a block copolymer of ethylene oxide capped with propylene oxide to provide hydrolytic stability.
It can be produced by reacting a polyether polyol containing polyisocyanate. This process requires the use of at least one divalent tin salt of a fatty acid and/or at least one tertiary amine as a catalyst. The foam products produced by this method are hydrophilic, but have the disadvantage that they can only be made using small amounts of water. Furthermore, there is no teaching of using MDI, which is hydrophobic, to produce hydrophilic foam products, and the resulting foam would contain undesirable catalyst residues. The ultimate objective of the present invention is to have good water retention and wiping stability, shrinkage less than 15% by volume, no curling and quick drying ^. An object of the present invention is to provide an improved polyurethane foam having a density of 1/ft ³ ). Another ultimate object of this invention is to provide an improved polyurethane foam having good dimensional stability that can be used as a substrate for flocked wall coverings or various other foam applications as well as for sponge applications. The basic object of the present invention is to provide a prepolymer which, when mixed with water, is capable of forming polyurethane foams having the above-mentioned properties similar to cellulose-based foams. These and other objects will become apparent as the description of the invention proceeds. According to the invention, there is provided a process for producing a prepolymer for producing polyurethane sponges using water as blowing agent, comprising: a at least 50% by weight of oxyethylene groups and a nominal number average molecular weight of at most 1100; a poly( _oxyC2-4 alkylene) diol having a nominal 2-hydroxyl equivalents per mole; b a predominant amount of pure diphenylmethane diisocyanate and a minor amount of a carbodiimide and trifunctional cyclic adduct _of diphenylmethane diisocyanate; and a monomeric polyol crosslinking agent having 3 or 4 hydroxyl equivalents per c mole; substance b) is greater than 50% by weight based on the total weight of components a), b) and c), and the molar ratio of diol a) to polyol crosslinker c) is in the range 4:1 to 8:1. A method is provided, characterized in that components a), b) and c) are used in such a ratio that the ratio of isocyanate equivalents to total hydroxyl equivalents ranges from 3:1 to 4:1. A novel polyurethane prepolymer consists of a poly( _oxyC2-4 alkylene) diol having at least 50% by weight of oxyethylene groups, a diphenyl with a functionality greater than 2.0 and a mixture of isocyanates containing MDI and derivatives of MDI. isocyanate containing methane diisocyanate, and 3
or derived from a monomeric polyol crosslinker with a hydroxy functionality of 4. This prepolymer can be reacted with water in the absence of a catalyst to produce a durable polyurethane sponge that has many of the properties of cellulose sponge. These foams are white in color and are therefore aesthetically pleasing and suitable for medical and health supervision applications.
desirable for health care applications). Preferred ingredient is Carbo Wax 1000
Diols with more than 80% by weight of oxyethylene groups such as (carbowax 1000), trimethylolpropane (TMOP) as a crosslinking agent and Upjohn Polymer chemical with a functionality of about 2.1 as an isocyanate.
Isonate 143L, methylene-bis(phenyl isocyanate), hereinafter referred to as MDI, based on the isocyanate products of
(isocyanate Isonate 143L). In a preferred formulation, Union Carbide's poly(oxyethylene) diol product, Carbowax, is used to impart water absorption properties to the final product. The preferred TMOP is added to impart strength to the foam product through its action as a crosslinking agent. It is important that the molar ratio of diol (such as Carbowax) to monomeric polyol crosslinker (such as TMOP) is in the range of approximately 4:1 to 8:1, preferably about 6:1. At the same time, the ratio of isocyanate equivalents to hydroxyl equivalents in the prepolymer should be in the range 3-4:1, preferably 3.3-3.7:1. The isocyanate product is the total prepolymer
It should be more than 50% by weight and it should have a functionality greater than 2.0. This would exclude pure MDI with a functionality of only 2.0 as only a single isocyanate. Isocyanates as preferred isocyanate sources
Use of 143L is preferred. This is because it contains dimers, trimers, and carbodiimide components that increase functionality to levels greater than 2.0 and are believed to contribute to the storage stability of the prepolymer and the strength and dimensional stability of the foam. The actual content of free MDI can be adjusted up or down in this isocyanate-containing product as long as the functionality is greater than 2.0. For example, you can add additional pure MDI. To further improve the durability of the sponge, approx.
% or less relatively short approximately 1.27 cm (1/
2 inches) or less of fiber is added to the aqueous suspension. The preferred fiber is polyester fiber. Thickening or suspending agents can be added to the aqueous phase to allow the mixture to be pumped through a foaming machine. For example, Carbopol 941, a high molecular weight acrylic acid polymer, can be added, which can be neutralized to a pH level of 7 with a base such as ammonium hydroxide. Sponge foam is made by reacting water and a prepolymer, preferably while heating both. Surfactants can be added to the water to control form cells. Isocyanate products with functionality greater than 2.0 include, for example, isocyanate 143L obtained by reacting MDI to form a carbodiimide and then reacting to form a trifunctional cyclic adduct, i.e. MDI, carbodiimide and Mixtures in which the cyclic adducts are in equilibrium are preferred. The mixture includes a predominant amount of pure diphenylmethane diisocyanate and a minor amount of the carbodiimide and trifunctional cyclic adduct of diphenylmethane diisocyanate. The mixture of components A and B below constitutes the 143L system. In the formula R=

The diol used to prepare the prepolymer is a poly( _oxyC2-4 alkylene) diol having at least 50% by weight oxyethylene groups, preferably at least 80% by weight oxyethylene groups. Thus, if the diol contains oxypropylene or oxybutylene or mixtures thereof, this minimum amount of oxyethylene must also be present. Preferred diols are at least 80
% by weight of oxyethylene groups, and is a hydrophilic poly(oxyethylene) diol made by Union Carbide under the product name Carbowax. When using Isocyanate 143L as the sole isocyanate source, the molecular weight is approximately 1000.
It is preferable to use a carbo wax of
The most preferred form has a molecular weight of 950-1050, although other carbo wax formulations having a molecular weight of 600-1100 can be used. It is this range of products that is produced when manufacturing the commercial grade Carbo Wax 1000. If a molecular weight type lower than about 600 is used, the resulting sponge formulation made from the prepolymer will also require large amounts of relatively hydrophobic isocyanate. Similarly, if a molecular weight form higher than 1100 is used, the resulting sponge will significantly lose its crosslink density and its dimensional stability and stiffness. Relatively short, low molecular weight monomeric polyols having 3 or 4 hydroxyl equivalents per mole are added to provide crosslinking strength to the final foam product to be produced from the prepolymer. Examples are trimethylolethane, trimethylolpropane, glycerol, triethanolamine, pentaerythritol or mixtures thereof. Preferred polyols have the formula is trimethylolpropane, TMOP. It is also desirable to control the ratio of diols such as carbowaxes to short crosslinked polyols in making the prepolymers. Generally, the molar ratio is about 4:1
The ratio should be in the range from 8:1 to 8:1, with a preferred ratio of about 6:1. If the proportion is too low such that too much polyol is present, the resulting sponge made from the prepolymer will lose its hydrophilicity and the foam will also have poor foam structure. On the other hand, if the proportion is increased such that less polyol such as TMOP is present, then a weak, brittle foam is obtained, which is characterized by fine and partially closed cells. There is. The molar ratio expressed for these two materials defines the relative number of hydroxy equivalents present from each material. Thus, at a ratio of 1 mole of preferred diol carbowax to 1 mole of preferred polyol TMOP, the carbowax contributes 12 equivalents of hydroxyl to 3 equivalents from TMOP. Carbo Wax 1000 is based on hydroxyl groups.
has an equivalent weight of 500 but has a molecular weight of 134
TMOP has an equivalent weight of 45 per hydroxyl group.
Since isonate 143L is used in combination with the hydroxyl group, the amount of isonate required is very sensitive to the amount of TMOP, so the amount of TMOP is relatively carefully controlled. The ratio of isocyanate to hydroxyl groups in the reactants should be in the range of 3 to 4, more preferably about 3.3 to 3.7. When the prepolymer is prepared, one isocyanate group of the polyisocyanate component reacts with the hydroxyl groups leaving unreacted residual isocyanate groups. These free isocyanate groups of the prepolymer react with water to form polyurea bonds, with a concomitant increase in molecular weight and the release of _CO2 , which facilitates the formation of a foamed sponge. To give the sponge the necessary stiffness, more than 50% by weight of the isocyanate product should be used. When reacting the components to form a prepolymer, it is useful to measure the isocyanate level by titration after the reaction has been conducted for about one hour. From this reading and subsequent titration, the additional reaction time required to reduce the isocyanate level below or near the theoretical point at which all of the hydroxyl groups would react with the isocyanate can be determined. If the reaction continues for too long, the isocyanate level is further reduced, in which case the prepolymer viscosity increases, making subsequent mixing of the prepolymer with water more difficult. Overreacting the prepolymer components increases the foam density and reduces the water absorption of the resulting foam. The fibers are preferably added to the aqueous phase for insertion into the foam composition to provide sufficient structural rigidity. Polyester fibers are particularly advantageous, and they can be cut to lengths of about 1/2 inch or less. For aqueous suspensions, the fibers can be added in varying amounts, although preferably they constitute no more than about 10% by weight. This is because above that level the suspension is too difficult to pump. High molecular weight suspending or thickening agents are added to serve two functions. First, it keeps the ingredients in suspension so water does not drain out of the fibers and the fibers do not float. Second, the thickener acts as a lubricant to the fibers so they do not tangle, dehydrate and jam up as they pass through the mixing pump. Examples of thickeners are Polyox WSR, Natrosol, Xanthan gums, and Dow's Separan AP30 with a high molecular weight such as approx.
AP30). Preferred suspending agents or thickening agents are Carbopol 934, Carbopol 940
(Carbopol940) and especially Carbopol 941
BFGoodrich Chemical such as (Carbopol941)
Carbopol resins manufactured by Co. Since Carbopol resins are acrylic acid polymers with acid moieties, neutralizing agents such as sodium or ammonium hydroxide can be added. There is an advantageous increase in the viscosity of the aqueous phase when adding ammonium hydroxide as a neutralizing agent for carbopol.
Since ammonium hydroxide is more stable than carbopol, a more economical formulation with the same amount of thickening can be created, which uses less carbopol. Some of the suspending agents or thickeners may have surface-active properties, so they may also be part of a surfactant system that controls the cell size of the resulting sponge. The surfactant has the correct cell size, shape,
It is chosen to give a form with good appearance without collapse or splits. Surfactants known to be useful with polyurethane foams can be used in this case. An example of a preferred surfactant is Wyandotte, Michigan.
BASF Wyandotte
oxyethylene and oxypropylene block copolymers, such as the Pluronic Polyol surfactants manufactured by Co., Ltd. A preferred surfactant is Pluronic L-62. In producing polyurethane foams, the preferred process is to add approximately equal amounts of the aqueous suspension with the prepolymer mixture and then mix the two together. The composition of the aqueous suspension is a prepolymer resin
It can also be expressed based on 100 copies. Thus, 100 parts water per 100 parts resin is written as 100 phr water.
The ratio of amounts of prepolymer mixture to aqueous suspension can vary over a wide range. However, if the amount of aqueous suspension is too large, the strength of the resulting foam will be reduced. On the other hand, if the amount of aqueous suspension is reduced too much, it will be impossible to add enough fiber and filler to be delivered via the aqueous suspension. A preferred method of foaming the prepolymer is to heat an aqueous suspension, such as a 2% solution of Pluronic L-62 surfactant, and the prepolymer to a temperature of about 35°C. These are poured or pumped together in a ratio of about 100 parts by weight of aqueous suspension to about 80 parts by weight of prepolymer and are mixed with a mechanical agitator, such as a blade attached to a drill motor, for 15 to 10 minutes.
Stir immediately for up to 30 seconds. This length of time allows complete mixing but does not allow any appreciable chemical reaction to occur. This mixture is immediately poured into a mold, where rising and curing of the foam product occurs. Depending on the fibers, pigments, and thickeners added, the best surfactant is L-520 (Union
from highly hydrophobic silicone type or other silicone surfactants such as Brij-58 (ICI-
America) or even very hydrophilic types such as ICI's other Brij, Span or Tween products. Pluronics for general use, especially L
-62, L-72, L-92, P-75 or P-85
Nonionic surfactants such as (BASF-Wyandotte) are preferred. The use of these surfactants will be familiar to those skilled in the art of formulating polyurethane foam products. Depending on the conditions of foaming, these foams ^may be
can have a similar advantageous structure. The sponge has the appearance and wiping properties of a cellulosic sponge. It has large cells (pores) that are several millimeters in diameter, but the walls of these cells are perforated with numerous pinholes. This gives the sponge a high degree of strength and stiffness due to the thick cell walls but excellent ability to wick and absorb water through the capillary action of the openings. It differs from other flexible urethane foams that are graded as fine-celled (smooth) or reticulated. The reticulated foams have most of the cell membrane removed so that they have a fibrous appearance. They are used as filters in furnaces and air conditioners. SEA
The SPONGE foam and the foam of the present invention are
In contrast, it has an intact but perforated cell membrane. This is different from the familiar polyurethane sponges on the market. This is because they absorb water into the polymer itself and wipe dry. Having described the basic aspects of the invention, the following examples illustrate specific aspects thereof. Tests Used to Evaluate Sponges The following test methods are used. All foam samples to be tested are dry and uniform 2.54 cm x 7.62 cm.
Cut to x12.7cm (1″ x 3″ x 5″) dimensions, and
Dry at 105±5°C to a constant weight without moisture.
The weight of the sample is approximately 0.1 grams. A group of 10 representative samples were used for testing. A Complete wet time from dry state (Wet-
Outtime) In a pan filled with water, float the sufficiently dry foam to the surface. The time required for the entire sample to become wet, ie, for water to appear and wet the entire top surface of the sample, is recorded in seconds. B. Complete wetting time from wet condition The foam is fully wetted and passed through a washing machine wringer to obtain uniform wetness. The wet foam rises to the surface of the water-filled pan. The time required for complete wetting of all samples is recorded as 0.1 seconds. C Determination of washing machine durability A 2.54cm x 7.62cm x 12.7cm (1″ x 3″ x 5″) sample
After drying at 105℃±5℃ for 1 hour, the weight was
Weigh to the nearest 0.02 grams. Maytag type (Maytag
(type), 48 samples are placed in a vertical washer filled with water and stirred for 72 hours. Dry the sample and reweigh it. Weight % loss = (Initial dry weight - Final dry weight) x 100 / Initial dry weight Even though the foam does not last in one piece for a period of 72 hours, this test is very demanding and the sponge or other foam applications may be satisfactory. If the sponge does not persist for a period of 72 hours, the results record the observation period in hours during which visible deterioration is observed. D Determination of tear strength A 2.54cm x 7.62cm x 12.7cm (1″ x 3″ x 5″) sample
6.35cm (2-1/2″ distance) 2.54cm x 7.62cm (1″ x
3"). Tear the tube of a Scott Tester, Model J-1 (or equivalent) between the upper and lower tubes.
Set to inch opening. Clamp one of the tear areas to each of the jaws of the Scott tester. Activate the tester and record the tear resistance in pounds. E. Determination of breaking stress An Instron tester equipped with an instrument for testing sponges or similar materials.
Determine tenacity using a tester. Set the Instron tester's jaws to a 2.54 cm (1 inch) opening between the upper and lower jaws. Clamp the 7.62 cm (3 inch) dimension in each tube and activate the tester. Record the toughness at the pump. Convert this value to kg/cm ² (pounds per square inch) by dividing the toughness by the width of the tube in contact with the sample. F. Determination of air permeability The test apparatus used consists of a fan connected to the tube by a part of the sample located on the end of the tube. Measure the air pressure upstream of the sponge. The air gauge pressure is configured to read 0.60 if the material is impermeable. If the reading is zero, it indicates very high porosity and a very open cell structure with very little pressure drop across the sponge. G Modulus of Elasticity This is measured from the stress-strain curve at 1% elongation. Example 1 This example illustrates the preparation of a prepolymer according to the invention. A mixture of Carbo Wax 1000 (412 g, 0.4 mol) and trimethylolpropane (9.05 g, 0.0675 mol) was dried by heating at 70° C. for 2 hours under a vacuum of 0.003 atm (2 Torr). dry,
Isocyanate to degassed polyol mixture
507.5 g of 143 L (3.55 equivalents of isocyanate) were added. The temperature was held at 70°C for 2-1/2 hours and after this time the isocyanate content of the product per gram
It was found to be 2.67 meq. That's 25
It had an initial viscosity of 19000 cp at °C. 80
After a two week storage test at 0.degree. C. the viscosity increased only to 30,000 cp. Example 2 (Reference Example) This example describes the preparation of a foam using the prepolymer of Example 1. 700g of prepolymer heated to 35℃ in a beaker
and heated to 35°C, and Pluronic L-
62, Wyandot's nonionic surfactant 14
686 g of an aqueous solution containing g. They were stirred together with a drill motor for 15 seconds and then poured into molds. The dried foam product had a density of 34.05 Kg per cubic meter (2.1 pounds per cubic foot). Approximately 2.54cm x 7.62cm x 13.97cm (1″ x 3″ x 5-1/
A sponge with dimensions of 2") was cut from the foam block. When saturated with water, the
Holds 9 times more water without dripping, capacity ranges from 275.35 ^cm3 to 308.13 ^cm3 (16.8 cubic inches
18.8 cubic inches) (12% increase). When squeezed by hand, all but about 90% of its dry weight was released. It had a similar appearance and wiping properties to a cellulose sponge of the same dimensions. Example 3 This prepolymer was made using the same reactants and conditions as Example 1, except that the reaction was stopped after the product had an isocyanate content of 2.61 milliequivalents per gram. Example 4 This prepolymer has a product yield of 2.70 g/g.
It was prepared using the same reactants and conditions as Example 1, except that the reaction was stopped after having milliequivalent isocyanate content. Examples 5 and 6 (Reference Examples) These examples illustrate the effect of using the prepolymers of Examples 3 and 4 and adding reinforcing fibers. In Example 5, the prepolymer of Example 3
700g of water and 686g of surfactant Pluronic L-
An aqueous solution containing 14 g of 62 was mixed. In Example 6, the prepolymer of Example 4
700g, water 683.2g, surfactant Pluronic L-
62 14g, Weber, Virginia
Mini Fiber Co., Ltd. (City Virginia)
35 g of Polyester Fiber 2, a 1.27 cm (1/2 inch) fiber manufactured by Fiber, Inc., 2.8 g of the thickener Carbopol 941 neutralized with 7.0 g of a 33% solution of ammonium hydroxide. mixed with the containing aqueous solution. The results are listed in Table 1.

Table: The product of Example 5 contained only water and surfactant from the aqueous phase. These sponges had unusual properties. They had a bright white color and a well-developed uniform SEA SPONGE type structure. The density is 34.54Kg/ ^m3 (2.13lb/
ft ³ ), which was a very low value. When this sponge is dry, it may be rigid depending on the surrounding conditions, but when wet it is soft. Although the initial drying time is relatively long, it is highly absorbent when wet. Sponges hold large amounts of water, clean well, wipe well, and have reasonable machine durability values. Air permeability is moderate, but volume swelling is very low. This sponge has a good appearance and surface feel. The sample from Example 6 is a fiber reinforcement of the foam of Example 5 containing Carbopol 941 and 5 phr fibers in the aqueous suspension used to make the sponge. This sponge was able to pass a very aggressive 72 hour washer test with 0% weight loss. Tear strength for wet and dry conditions was high. Very good air permeability,
Shows open cell structure. Although the cellular structure may not be considered aesthetically pleasing as the foam in Example 5, this foam can be thoroughly cleaned and
Then wipe it off to your satisfaction. This is very durable and has a large sponge. Example 7 (Reference Example) This example describes the production of sponge foam without adding any surfactant to the water. The foam was prepared according to the method in Example 2, except that no surfactant was present in the water. The hydrophilic foam obtained is 48.64Kg/m ³ (3
lbs/cubic foot) and was similar to the foam in Example 2 except that it had a finer texture due to the small, partially closed cell structure.

Claims (1)

[Scope of Claims] 1. A process for producing a prepolymer for producing polyurethane sponges using water as a blowing agent, comprising: a) at least 50% by weight of oxyethylene groups and a nominal number average molecular weight of at most 1100; a poly( _oxyC2-4 alkylene) diol having a nominal 2- _hydroxyl equivalent per mole; b a carbodiimide and trifunctional cyclic of a predominant amount of pure diphenylmethane diisocyanate and a minor amount of diphenylmethane diisocyanate; a monomeric polyol crosslinking agent having 3 or 4 hydroxyl equivalents per c mole; The product b) is greater than 50% by weight based on the total weight of components a), b) and c), and the molar ratio of the diol a) to the polyol crosslinker c) is in the range from 4:1 to 8:1. A process characterized in that components a), b) and c) are used in such a ratio that the ratio of isocyanate equivalents to total hydroxyl equivalents ranges from 3:1 to 4:1. 2. The method of claim 1, wherein the poly( _oxyC2-4 alkylene) diol has a molecular weight of 600 to 1100, and the diol has at least 80% by weight of oxyethylene groups. 3. The method of claim 1, wherein the polyol crosslinker is selected from the group consisting of trimethylolpropane, trimethylolethane, glycerol, triethanolamine, pentaerythritol, and mixtures thereof.