KR890000236B1 - Imprenation of leather with polyurethane dispersion - Google Patents

Abstract

A method for impregnating leather consists of (i) impregnating low d. (0.3-0.8 g/cc) leather sheets (split) with polyurethane (obtd. from reacting polyol with excess amts. of diisocyanates) dispersion aq. soln. contg. solid matter 5-50 wt.%, (ii) ionically coagulate polyurethane in dispersion soln. and (iii) drying the impregnated leather.

Description

Method of Impregnating Leather with Polyurethane Dispersion and Impregnated Leather

TECHNICAL FIELD The present invention relates to the treatment of leather, and more particularly, to a method of impregnating leather to improve the quality of less dense leather and to impregnated leather as a product thereof.

As used herein, “low density leather, ie, low density leather,” refers to leather splits of non-bovine animals or reptiles such as goats, pigs, sheep, rabbits, raccoons, foxes, snakes, and the like. It means. Usually these low density leathers have a bulk density of 0.3-0.8 g / cc, which distinguishes them from the top grain leather of dense bovine animals.

The upper side hides are veneers of the beast's raw hide that leave a large amount of leather known as "leather splits" after treatment. Therefore, the term "leather split" as used herein refers to the material remaining in the raw leather after removing the upper surface skin veneer. Upper silver skin is a useful material of good strength and has been used to produce the finest footwear when processed according to known processing methods. Those skilled in the art have been contemplated that it is possible to improve the quality of the upper silver skin, this quality improvement can be achieved by precisely improving the leather structure according to the present invention. For example, the upper bovine hide of bovines can be densified to a density comparable to that of horseskin, making it similar to "cordovan" leather.

The present invention is directed to all upper silver skins regardless of the method of tanning, such as leather splits made from the skin of mammals including reptiles, livestock and horses, from chrome-tanned, zirconium-tanned, vegetable-tanned or synthetic tanned. It can be applied to low density leather. The above tanning method is well known to those skilled in the art. Leather splits are of commercial use in hides, dyed leather, "reverse" leather or tanned leather products. However, as compared to the upper side shell, the split products have a lower strength and a relatively coarse structure, so they are not widely used in the upper of the shoe (above the sole). Due to the porosity of the split leather, it cannot be processed in the same way as the upper silver skin. This is because the conventional coating liquid used for the upper silver shell is penetrated into the split leather, resulting in an inflexible product which cannot be finished.

For example, in leather goods used in upper parts of shoes, it is important to absorb moisture from the feet into the leather, while preferably preventing moisture from seeping into the inside. However, although it is not yet desirable to flow the moisture, it has been recognized that the flow of moisture in the oral upper is such that the moisture is permeable or breathable. Since the coating liquid of the split leather prevents water from seeping into the liquid and also prevents the flow of moisture, it is used to make the coated product which does not penetrate moisture.

The effective use of leather splits to select cow's upper side shells to form a useful product in a wide range has long been a challenge for the leather industry. Experiments have been conducted on this subject with reference to US Pat. Nos. 3,827,930 and 4,218,505, which produce thin sections of leather splits and polyurethane membranes.

In another aspect of the present invention, the low density upper surface skin can be used to make things such as gloves, handbags, clothes, etc., but it is not useful for the upper of shoes because of its low preservation, memory and flex-layer properties. . Even if low-density leather is used for narrow applications, it does not have the characteristics of cow's upper hides that can be worn for a long time. The low density properties of these leathers are due in part to the high fat concentrations in animal hides, which are removed during the tanning process and remain a high porous network of loosely bound fibers. Therefore, the lower densities of the upper face masks have reduced physical properties compared to the upper face masks of cows. The appearance of the fiber is not suitable for processing into the upper silver skin used for oral uppers. On the other hand, when using the low density upper silver skin as a garment, the thickness of the leather was made as thin as possible, making the garment nice to hand and well-dressed when worn. However, it should be made of clothing with some preservation thickness as much as possible.

The method according to the present invention improves the physical and chemical properties of low density leathers, and according to the present invention, leather splits are made of a product having all the advantages of cow's upper side hides.

The present invention provides a method for producing the following impregnated leather. An ionic dispersion of the polyurethane polymer is impregnated into the low density leather sheet.

The polyurethane polymer impregnated in the leather sheet is ionically solidified from the dispersion. The impregnated was dried to produce impregnated leather. The low density leather sheet became a leather split and then the impregnated leather was dried and heat and pressure was applied to at least one surface of the composite into a masking layer.

Polyurethanes usefully used in practicing the process of the invention are known in the art as ionically water dispersible. Such dispersants differ significantly from emulsified isocyanate interpolymers prepared by dispersing in water with the aid of a detergent under the action of strong shearing forces, as described in US Pat. No. 2,968,575. Emulsified polyurethane has the disadvantage of using a detergent to form an emulsion, the detergent used in this case is usually left in the dried emulsion coating, which severely degrades the physical and chemical properties of the final product as a whole. Insufficient shear forces also create inadequate products and require such high shear forces that materials cannot usually be manufactured with conventional reaction vessels.

A preferred method of preparing an ionic polyurethane dispersion is to prepare a polymer having free acid groups, preferably a polymer having a carboxyl group covalently attached to the polymer chain. Neutralization of such carboxyl groups with amines, ie, aqueous mono-amines, provides hydrodilution. Since isocyanate, a necessary component of all polyurethanes, reacts spontaneously with carboxyl groups, compounds having carboxyl groups must be carefully selected. However, as described in US Pat. No. 3,412,054, which is incorporated herein by reference, 2,2-hydroxymethyl-substituted carboxylic acids are subject to intense reactions between acids and isocyanate groups due to steric hindrance of carboxyl by adjacent alkyl groups. It can react with organic pulley isocyanates without producing them. This method neutralizes a preferred carboxyl containing a polymer with a carboxyl group with a tertiary single-amine to make a quaternary ammonium salt to make it hydrolysable.

Suitable carboxylic acids and preferably sterically hindered carboxylic acids are well known and readily available. For example, they can be prepared from aldehydes containing at least two hydrogens in the α-position, in which two equivalents of formaldehyde react in the presence of a base to form 2,2-hydroxymethyl aldehyde. This aldehyde is oxidized to form an acid by methods known to those in the art. The acid thus prepared has a structure as follows.

(In this formula, R represents hydrogen or an alkyl group having up to 20 carbon atoms, preferably an alkyl group having up to 8 carbon atoms.)

Preferred acids include 2,2-di- (hydroxymethyl) propionic acid. Carboxylic polymers are characterized as anionic polyurethane polymers. In addition, another method of making the hydrodilution according to the present invention is to use a cationic polyurethane having an amino group. Such cationic polyurethanes are described in US Pat. No. 4,066,591, Patent Example 18, which is incorporated herein by reference. In this invention, it is preferable to use anionic polyurethane.

Particularly useful polyurethanes for practicing the present invention include those by reaction of complex reactive hydrogens with di or polyisocyanates or compounds suitable for producing polyurethanes. Such diisocyanate and reactive hydrogen compounds are described in detail in US Pat. Nos. 3,412,054 and 4,046,729, and examples of this patent specification describe polyurethane preparation methods. According to the invention, aromatic, aliphatic and cycloaliphatic diisocyanates or mixtures thereof can be used to form the polymer. Examples of such diisocyanates include tolylene-2,4-diisocyanate; Tolylene-2,6-diisocyanate; Meta-phenylenedi isocyanate; Biphenylene-4,4'- diisocyanate; Methylene bis (4-phenylisocyanate); 4-chloro-1,3-phenylene diisocyanate; Naphthylene-1,5-diisocyanate; Tetramethylene-1,4-diisocyanate; Hexamethylene-1,6-diisocyanate; Decamethylene-1,10-diisocyanate; Cyclohexylene-1,4-diisocyanate; Methylene bis (4-cyclohexyl isocyanate); Tetrahydronaphthylene diisocyanate; And isophorone diisocyanate. However, it is most preferred to use arylene and cycloaliphatic diisocyanate to carry out the process according to the invention. Arylene diisocyanate as a feature includes an isocyanate group attached to an aromatic ring. Most preferred isocyanates are mixtures of 2,4 and 2,6 isomers of tolylene diisocyanate by its reactivity and readily available availability. In addition, the cycloaliphatic diisocyanates most effectively required for carrying out the method of the present invention include 4,4'-methylene bis (cyclohexyl isocyanate) and isophorone diisocyanate.

Isocyanate reacts with complex reactive hydrogen compounds such as diols, diamines and triols. In the case of diols or triols, the complex reactive hydrogen compounds are polyalkylene ethers or polyester polyols. Polyalkylene ether polyols are preferred reactive hydrogens containing polymeric materials for forming polyurethanes. Most preferred polyglycols have a molecular weight of 50-10,000, especially in the case of the present invention most preferably having a molecular weight of about 400-7000. Polyester polyols also increase flexibility in proportion to the increase in molecular weight.

Examples of polyether polyols include, but are not limited to: That is, polyethylene ether glycol, polypropylene ether glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, polyoctamethylene ether glycol, polydecamethylene ether glycol, polydodecamethylene ether glycol, and mixtures thereof. It is also possible to use polyglycols containing several other radicals in the molecular chain, such as HO (CH2OC2H4O) nH compounds (n is an integer greater than 1).

The polyols may be hydroxy terminated or hydroxy dependent polyesters which may be used in combination with or instead of polyalkylene ether glycols. Such polyesters are formed by reacting acid esters or acid halides with glycols. Suitable glycols include polymethylene glycol such as ethylene, propylene, tetramethylene or decamethylene glycol, substituted glycols such as 2,2-dimethyl-1,3-propanediol, cyclic glycols such as cyclohexanediol and aromatic glycols, and the like. Can be mentioned. Aliphatic glycols are generally preferred to be flexible, such glycols react with aliphatic, cycloaliphatic or aromatic dicarboxylic acids or derivatives that form lower alkyl esters or esters with relatively low molecular weight polymers (melting points of about 70 ° C. or less). Preferably have a molecular weight as indicated by the polyalkylene ether glycol). Examples of acids for preparing such polyesters include phthalic acid, maleic acid, succinic acid, adipic acid, suberic acid, sebacic acid, terephthalic acid, texahydrophthalic acid, and derivatives of these acids substituted with alkyl groups and halogen groups. In addition, polycaprolactones terminated with hydroxyl groups can also be used.

Particularly useful polyurethane systems are the crosslinked polyurethane systems described in detail in US Pat. No. 947,544, filed October 2, 1978 by andrea russiello under the name "cross-linked polyurethane dispersion, Noncrosslinked polyurethane compositions are described in detail in US Pat. No. 4,171,391, incorporated herein by reference.

As used herein, the term "ionic dispersant" means an ionic acid or base capable of forming a salt with a solubilizer. Examples of such ionic dispersants include amines and acids. The amines are preferably water-soluble amines such as triethylamine, tripropylamine, N-ethylpyrefedine, and the like, and the acid is preferably water-soluble acid such as acetic acid, propionic acid, lactic acid, and the like. Acids and amines will of course be chosen from solubilizers which depend on the polymer chain.

Leather impregnated by the present invention preferably has a high flexibility similar to the flexibility of the cow's upper pulp when the leather is a low density leather starting material. When low density hides of the upper side hides are used as starting material for the leather, the final impregnated leather should be as flexible as the starting side skin. Therefore, polyurethane polymers must behave in the same way as elastomers. Preferred elastomeric behavior generally requires about 25-85% by weight of long chain polyols (ie 70-2,000 eq.wt.) in the polymer. The degree of stretch and elasticity vary widely depending on the desired properties of the final product.

Excess diisocyanate was reacted with the polyol to form a polyurethane useful for practicing the process of the present invention to form a polymer having an isocyanate at its end. In the case of using isocyanate and polyol, appropriate reaction conditions, reaction time, and temperature may vary, but those skilled in the art are well aware of such changes. Those skilled in the art know that the reactivity of the components contained requires a balance of reaction rates for unwanted secondary reactions that reduce color and molecular weight.

Usually the reaction takes place by stirring at a temperature of about 50-120 ° C. for about 1-4 hours. The polymer terminated with isocyanate is reacted with less than 1 mole dihydroxy acid for 1-4 hours at 50 ° C-120 ° C to form a prepolymer terminated with isocyanate to make a polymer with carboxyl groups. It was. Diacids are preferably added as N-methyl-1,2-pyrrolidone or -N-N-dimethylformamide as a solution. The solvent for the acid will usually not exceed about 5% of the total amount in order to minimize the organic solvent concentration in the polyurethane composition. After reacting the dihydroxy acid in the polymer chain, the dependent carboxyl group is neutralized with amine at about 58 ° C-75 ° C for about 20 minutes, and then stirred to add water while forming chain extender and dispersion. It was. Soluble diamine can then be added to the water as an additional chain extender. The remaining isocyanate and water react with the chain expansion to form urea groups, and further, by addition reaction, all isocyanate groups and the stoichiometric excess of water react with the resulting product and polymer. Polymerized. It should be noted that the polyurethanes of the present invention are natural thermoplastics, that is, they cannot be cured more extensively after they are formed except when an external hardener is added, and also forms impregnated leather without the addition of such hardeners. It is desirable to. Sufficient water was used to disperse the polyurethane at a weight ratio of solids at a concentration of about 10-40% and a dispersion viscosity of about 10-1,000 centipoise. The viscosity can be adjusted to be applied to the low density leather sheet in accordance with the particular impregnation properties required, by means of a special dispersion composition including all that is indicated by the final properties of the impregnated leather sheet. Those skilled in the art know how to modify the primary polyurethane dispersion according to the use of the end product. Examples of such methods include colorants or compatible vinyl polymer dispersions, ultraviolet filtering compounds, and stability to oxidation. These are methods of adding a topic.

The dispersion prepared according to the present invention can be characterized by measuring the non-volatile content, particle size and viscosity, and the stress characteristics of the cast film.

The concentration of polyurethane contained in dispersions useful in the practice of the present invention is controlled by the required percentage of polymer added into the low density leather sheet.

Dispersion viscosity is usually in the range of 10-1,000 centipoise. Comparing similar polymers containing the same concentration of solids in the polymer solution of the organic solvent, the dispersion at lower viscosity will penetrate faster and more completely into the low density leather. Useful polyurethane solutions usually have high viscosities ranging from thousands of centipoise to 50,000 centipoise at concentrations of 20-30%. As a useful measure of stability, particle size can be measured by light scattering. Dispersions with non-condensing properties have particles less than 1 micron in diameter.

In the method of the present invention, the low density leather sheet material may impregnate polyurethane by up to about 40% by weight to the total weight of the impregnated leather. The quality is improved when the polyurethane contained in the impregnated leather is about 5%, preferably about 10-20%. Properties such as tensile strength, tear strength and bias elongation characterize the impregnating composition related to leather products in shoemaking, furniture and garment manufacturing. Low density leather sheets can be impregnated into the polyurethane dispersion by standard impregnation methods. The most preferred impregnation method, however, is to "impregnate" enough that the polyurethane dispersion in the low density leather sheet is completely saturated to remove all voids in the leather sheet. This sufficiently impregnation method takes into account the addition of the final polyurethane with a controlled solids concentration in the polyurethane dispersion.

Coagulation occurs by contacting a low density leather sheet impregnated with an aqueous solution of an ionic medium designed to ionically dissolve soluble ions. Although this theory is not intended to limit the scope, in the case of polyurethanes solubilized in an anion, the amines that neutralize the carboxyl containing polyurethanes are replaced by hydrogen ions that return to the carboxy ions in which the anions are suspended. Under non-dilutable conditions the polyurethane polymer is converted into its original form. This reaction causes polymer coagulation in the leather structure.

In the case of anionic polymers, an aqueous solution of acetic acid concentrated to about 0.5-10% is a suitable ionic coagulant for the anionic dispersion, which is preferable to use in the presence of a stronger acid because of its relatively easy handling and low corrosion and partitioning power. Do. Other acids may be used which substantially dissolve in water at the same concentration. The coagulation takes place very quickly in nature so that the polymer remains completely in the leather structure without substantially losing the polymer due to migration to the ionic solution.

Although salting may be carried out by adding neutral salts to coagulate the dispersion, this requires about 10 times as much salt as the concentration of the acid and is undesirable because of the attendant problems that may contaminate the product.

The most preferred method of solidifying the anionic polyurethane dispersion is thermal coagulation. This method first impregnates with the addition of hydrogen fluorosilicate and then heats the impregnated, thereby generating an acid which causes coagulation of the dispersion. This method is described in detail in US Patent Application No. 234,464, filed February 17, 1981 by John McCartney, entitled “Thermal Coagulation of Polyurethane Dispersions”.

The aqueous phase remaining after the coagulation step was removed in a conventional manner. For example, the impregnated leather sheet was passed through a squeeze roll, rinsed with water, and dried by heating air or infrared radiation. In a typical process the low density leather sheet is fully saturated with the polyurethane dispersion in a suitable container. The surface of the impregnated leather sheet was wiped to remove excess dispersion and then the polyurethane was solidified with heat or counter ionic solution. The impregnated one was pressed to remove excess water and then dried in an oven.

If the low density leather sheet was a leather split, the dried impregnated leather was placed in a heated compressor and pressure was applied to at least one side of the impregnated leather. Heating and compression fused the polymer within the consolidation at the surface of the material, but insufficient to fully fuse the polymer inside the material. Therefore, the density gradient increases from the inside of the material to the outside of the material. Another physical technique for forming the masking layer is described in detail in US Patent Application No. 188,330 filed September 18, 1980 by John McCartney under the name "mock leather sheet material".

After forming the impregnated leather, it can be processed into the same method as the processing method or the standard leather process to make the split.

The following embodiments describe the present invention in detail.

Example I

Leather splits made of colored cowhide for sale have the following characteristics:

Instron tongue tear (Ibs.) 8.00 Density (g / cc) 0.63

Basic weight (g / ㎠) 1080.00 Thickness (cm) 0.17

2 parts (by weight) of cross-linked polyurethane dispersions prepared according to the method described in Example 3 of U.S. Patent Application 947,544, cited above, and the method described in U.S. Patent 4,171,391 used by reference herein. The split was impregnated with a polyurethane dispersion consisting of 1 part (by weight) of the crosslinked polyurethane dispersion prepared according to the above. The dispersion mixture was adjusted to 25% solids. The leather sheet was completely immersed in the polyurethane dispersion and then taken out of the bath and excess excess liquid was wiped off from the sheet. The impregnated was left in a 10% aqueous acetic acid bath for 10 days to solidify the polyurethane dispersion. The impregnated sheet was dried by washing with water and then dried for 2 minutes in a 135 ° F. hot press without using pressure except for transferring heat from the plate of the compressor to the impregnated leather.

Impregnated leather has the following characteristics:

Instron Tongue (Ibs.) 20.00 Density (g / cc) 0.85

Basic weight (g / ㎠) 1490.00 Thickness (cm) 0.17

As described in Example 1, the leather impregnated by the present invention has a tear strength at least three times greater than the tear strength of the leather split starting material. In addition, the impregnated leather is easy to handle and stylish.

Example II

Two sheets of thickness made of the impregnated leather of Example I were pressed back to back and pressed for 2 minutes at 150 ° C., 1900 psi on a heating press. While the surface of the impregnated leather in contact with the compression plate was improved with a dense layer of silver, the interior facing the surface of the impregnated leather remained a split. Two sheets were separated, each sheet having the following characteristics.

Instron Tongue (Ibs.) 23.00 Density (g / cc) 1450.00

Basic weight (g / ㎠) 0.80 Thickness (cm) 0.18

The impregnated leather sheet according to the present embodiment is easy to handle, well-groomed, and has characteristics similar to that of the cow's upper silver skin.

Example III

The method described in Example II was repeated except that the second cowhide leather sheet having properties similar to the splits of Examples I and II was compressed to 3,500 psi.

When the sheets were separated, the two sheets had the following characteristics.

Instron Tongue (Ibs.) 32.00 Density (g / cc) 1.30

Basic weight (g / ㎠) 180.00 Thickness (cm) 0.13

The impregnated leather according to this embodiment has properties similar to those of Kodoban upper silver skin.

Colored wet splits prepared according to standard leather manufacturing methods can also be used as starting materials according to the invention.

In addition, the silver layer of cowhide and wheat leather may be improved in quality by impregnation according to the present invention.

Although the present invention has been described with reference to specific materials and specific processes, it will be limited only as described in the appended claims.

Claims (24)

Impregnating an aqueous ionic dispersion of a polyurethane polymer with a low density leather sheet, ionically solidifying the polyurethane polymer in a dispersion impregnated with a low density leather, and then drying the impregnation. Acupuncture. The method of claim 1 wherein the polyurethane polymer contains an ionizable soluble group covalently bonded to the polymer chain that reacts with the ionic dispersant. The impregnation method of leather according to claim 1, wherein the polyurethane polymer has no N = C = O groups which are not substantially reacted. The method of claim 1 wherein the leather is a low density leather. 5. The method for impregnating leather according to claim 4, wherein the low density leather impregnated under heat and pressure is heated, wherein the heat and pressure form a silver layer on at least one surface of the impregnated leather. 5. The method of impregnating leather according to claim 4, wherein the leather of low density is completely impregnated with the polyurethane dispersion. The method of claim 1 wherein all dispersants are removed from the impregnated sheet prior to coloring the impregnated sheet. The method of claim 1 wherein the polyurethane dispersion is solidified by thermal coagulation. The method of claim 1 wherein the dispersion of ionic polyurethane polymer contains 5-50% solids by weight. The method of claim 1 wherein the viscosity of the ionic polyurethane polymer dispersion is 10-5,000 centipoise. 2. The method of impregnation of leather according to claim 1, wherein the impregnated and dried leather contains up to 40% by weight of polyurethane polymer. The impregnation method of leather according to claim 4, wherein the bulk density of the low density leather is 0.3-0.8 g / cc. The method of claim 1 wherein the dispersion is a crosslinked polyurethane dispersion. 5. The method of impregnation of leather according to claim 4, wherein the low density leather is a leather split. 5. The method of impregnating leather according to claim 4, wherein the low density leather is selected from the group consisting of pig skin and sheep skin. The method of claim 1 wherein the impregnated and dried leather has a bulk density of 0.5-1.3 g / cc. Impregnated leather, characterized in that it consists of leather impregnated with a polyurethane polymer by the impregnation method of claim 1, wherein the impregnated leather has a bulk density less than the actual density. 18. The impregnated leather according to claim 17, wherein the polyurethane polymer is a crosslinked polyurethane polymer. 18. The impregnated leather according to claim 17, wherein the impregnated leather has at least one layer of silver. 18. The impregnated leather according to claim 17, wherein the polyurethane polymer is impregnated up to 40% by weight. 18. The impregnated leather according to claim 17, wherein the leather is low density leather. The impregnated leather according to claim 21, wherein the low density leather is a leather split. The impregnated leather according to claim 21, wherein the bulk density of the low density leather is 0.3-0.8 g / cc. 23. The impregnated leather according to claim 21, wherein the low density leather is selected from the group consisting of pig skin and sheep skin.