Patent Application
20060288494
The present invention relates to methods for the production of leather, and more particularly to a process for producing leather from wet blue pig skins.
A wide variety of methods are used commercially for producing leather from skins or hides. In general, leather production involves three broad phases. First, the skins or hides are prepared for tanning. This generally involves curing the skins so that they do not begin to decompose before tanning. At the tannery, the skins are typically soaked in water to remove all water-soluble materials, such as salt, blood, and dirt, and to replace moisture lost in the curing process. Typically, the next step is to remove hair from the skins. Often, this is done by soaking the skins in a lime solution and then mechanically removing the hair, along with extraneous flesh and tissue, by machine. The next general step is “deliming,” which removes the lime introduced during the dehairing step. The deliming process involves soaking the skins in a mild acid solution. Bating may also occur at this time. Bating is a process in which the skins are treated with enzymes that make the skins soft and flexible and provide them with a smoother grain.
The bated skins are then tanned using any of a variety of conventional tanning methods. For example, the skins may be tanned in a mineral tanning process. In mineral tanning, the skins are soaked in a mineral tanning agent, typically the salt compound of chromium. To prepare the bated skins for chrome tanning, the skins are pickled in a conventional salt and acid brine. Once pickled, the skins are tumbled in a chromium-sulfate solution containing liquors that enhance the skins' ability to absorb the tanning agent. Alternatively, the skins may be tanned in a vegetable tanning process. Vegetable tanning generally involves soaking the skins in a tannin solution containing liquors that improve and speed the absorption of tannin. Tannin is typically extracted from wood or bark, such as the chestnut wood or oak bark. The skins are soaked in successively stronger solutions until they have absorbed the appropriate amount of tannin for the particular application.
The tanned skins, which in the case of chrome tanned skins are sometimes referred to as “wet blue leather,” are then subjected to a variety of treatments that provide the skins with the desired characteristics. For example, the skins can be lubricated using a blend of oils and greases, and dyed to the desired color through drum dyeing, spraying, brush dyeing or staining processes. In some applications, the skins are retanned to introduce additives that provide the skins with desirable characteristics. For example, waterproofing agents are typically introduced during a retanning process. Waterproofing is a particularly important characteristic in many applications, including footwear applications. The waterproofness of leather is typically measured in Maeser flexes, which is essentially the number of flexes that leather can undergo before it loses the waterproof characteristic. The waterproofness standard set by the U.S. military is 15,000 Maeser flexes. Further, heat resistant and flame resistant agents are often introduced prior to and/or during the retanning process. Finally, the skins are staked and finished. Staking is a mechanical softening process in which the skins are repeatedly beat by fingers. Finishing typically involves the application of a finishing compound, such as oil blend, to the surface of the leather. The above described processes are typical steps involved in the production, but are not exhaustive. Alternative and additional processes are commonplace in the leather production industry.
Although there are a variety of well-known techniques for obtaining leather with one or more desired characteristics, such as softness, suppleness, waterproofness, flame resistance, and heat resistance, it is difficult to produce leather that has the appropriate combination of these characteristics. In fact, these characteristics are achieved only by carefully controlling a complex series of variables in the production process. For example, the precise additive formulation, the quantity of additives, the mixture ratio of additives to water in the various steps, the temperature of the solutions in which the skins are treated, the running time in a given liquor bath and the pH level of the solutions in which the skins are treated are all crucial to the production process. In many cases, the procedures for providing the leather with one desirable characteristic adversely affect other desirable characteristics. Accordingly, leather processing often involves a careful and delicate balance of processing techniques and additive choices.
In conventional processes, the skins are capped to remove or inactivate emulsifying agents. Capping typically involves the introduction of a metal salt that interacts with the emulsifying agent rendering it inactive. Although capping can improve the overall performance of the finished leather, it can have a number of disadvantages. For example, capping can cause the leather to shrink, thereby reducing the yield. Also, capping can have a negative impact on the ability of the leather to readily and uniformly accept coloring and dyes. In fact, capping can make it nearly impossible to obtain certain colors. As a result, capping can make it difficult or impossible to obtain uniform and even coloring of leather. This is particularly true with bright colors, which have a tendency to more clearly show any discontinuity in color. Accordingly, leather produced in a process involving a conventional capping step is typically not colored or dyed using bright colors. Rather, these leathers are typically colored using dark colors that inherently show less discrepancy in coloring.
As perhaps the result of these complexities, there remains an unmet need for leather that is soft and supple while at the same time being durable, highly oil resistant, water resistant and uniformly accepting of dyestuffs.
The aforementioned problems are overcome by the present invention wherein a leather production process is provided which produces leather that is soft and supple, yet durable, highly oil resistant, water resistant, while at the same time being suitable for use with bright colors. The production process generally includes the steps of: (a) providing wet blue, full grain skins, (b) applying a degreasing and emulsifying agent to the skins, (d) neutralizing the skins to provide the skins with a pH level of in the range of about 5.7-6.2, (e) applying a waterproofing agent to the skins, (f) introducing the skins to a dye bath, (g) fixing the dyestuff and waterproofing agents in the skins without chrome or other metal salts while reducing the pH level to about −3.2, (g) applying a water repellant and oil repellant agent to the skins in a fluorchemical process, (h) fixing the skins a second time without chrome or other metal salts while moving the pH level to the range of 3.0-3.5, (i) introducing the skins to a bath containing an antimicrobial treatment and an antistatic treatment, (j) washing and drying the skins, and (k) staking and otherwise finishing the skins. If desired, the skins can also be subjected to additional treatments, such as flame resistant/flame proof treatments.
In one embodiment, the skins are washed and drained after the neutralizing step, but not between the waterproofing and coloring steps. The first fixing step may occur immediately following the coloring step to fix both the waterproofing agents and the dyestuffs.
In another embodiment, the skins are washed and drained between the first fixing step and the fluorchemical step, but not between the fluorchemical process and the antimicrobial and antistatic treatments.
The present invention produces soft and supple leather that is durable, highly water resistant and oil resistant and that readily and uniformly receiving of dyestuffs. The process therefore provides leather capable of consistently and uniformly receiving color. Because the leather is highly oil resistant and water resistant, the leather is highly stain resistant. As a result of these characteristics, the process is particularly well-suited for use in producing high performance leather in bright colors.
These and other objects, advantages, and features of the invention will be readily understood and appreciated by reference to the detailed description of the preferred embodiment and the drawings.
An embodiment of the present invention is described in connection with the flowchart of
The following description sets forth an embodiment of the present invention that is optimized to provide finished leather with a particular set of desired characteristics. Those skilled in the field will readily appreciate that the specified times and quantities are approximate and that some variation in a specified time or in a specified quantity will typically yield acceptable results in the finished leather, and adjustments can be used to intentionally adjust the characteristics of the finished leather. The amount of acceptable variation in a particular time or quantity will vary depending primarily on the amount of acceptable variance in the finished leather. For example, variations in the range of approximately ±20% in the quantity of a particular additive are likely to be acceptable for each of the additives, except for the acidic and caustic materials used to adjust the pH level of the float (i.e. formic acid, sodium formate, sodium bicarbonate and aqua ammonia). However, even with the acidic and caustic materials, variation in the quantity of a particular additive may be compensated for by adjustment in the strength (e.g. percent of composition) of the additive or in time that the mill is run with the additive in the float provided that the specified pH levels are obtained. It should further be noted that, in the following paragraphs, the percentages of various additives are specified in parentheses following the specified weight or volume quantities. These percentages refer to the weight of the additive with respect to the total weight of the wet blue skins being processed.
In the illustrated embodiment, the process begins by loading the wet blue skins into a conventional mill. In this embodiment, approximately 1000 lbs. of skins are loaded into the mill. Typically, the wet blue skins have a pH of 3.5 or lower. As a first step, the skins may be washed. Initially, approximately 1,000 gallons of water are added to the mill. The water may be at a temperature of approximately 140° Fahrenheit (F.), but the temperature may vary, for example, between 105-150° F. The skins are washed and then the water is drained. After washing, the water is drained from the mill.
After the initial washing step, the skins undergo the degreasing and neutralizing phase 20, 30 (See
Following these steps, the skins are neutralized 30 (See
In the second stage of the neutralization process, approximately 12.5 lbs. of sodium bicarbonate (or 1.25%) are added 116 to the mill. The mill is then run 118 for approximately 2 hours, which will raise the pH level of the skins to a range of approximately 5.7-6.2. The mill running time may vary, for example, between 90-180 minutes.
The neutralized skins are next subjected to the waterproofing phase 35 (See
The skins next undergo the coloring and dyeing phase 40 (See
The skins next pass into the fixation phase 60. To aid in fixing 170 the waterproofing agents and dyestuff in the skins, formic acid is added to the mill in two sequential installments. First, approximately 6.0 lbs. (0.6%) of formic acid (90% concentration) is mixed 148 with approximately 11.111 gallons of water at approximately 100° F. The mixture is added 150 to the mill. The mill is run 152 for approximately 20 minutes. The runtime of the mill may vary, for example, between 15 to 45 minutes). Then, a second installment of approximately 6.0 lbs. (0.6%) of formic acid (90% concentration) and 11.111 gallons of water at approximately 100° F. are mixed 154 and added 156 to the mill. The mill is then run for approximately 20 minutes. The runtime of the mill may vary, for example, between 15 to 45 minutes). This should bring the skins to a pH level below approximately 3.5.
A water repellant and oil repellant agent is next added to the skins in a fluorchemical process 70. To prepare for this process, the skins are washed 160 in approximately 2000 gallons of water at approximately 135° F., and the mill is drained 172. The temperature of the water may vary, for example, between 115 to 150° F. The fluorchemical process begins by adding 162 approximately 111.11 gallons of water at approximately 135° F. to the mill to establish the float. Next, approximately 2.5 lbs. (0.25%) of formic acid (90% concentration) is mixed 164 with approximately 11.111 gallons of water at approximately 100° F. The mixture is added 166 to the mill. The mill is run 168 for approximately 15 minutes. The runtime of the mill may vary, for example, between 10 to 30 minutes). These steps should bring the skins to a pH level in the range of 3.2 to 3.6. After, approximately 30.0 lbs. (3%) of PM 4700 is mixed 170 with approximately 11.111 gallons of water at approximately 120° F. The mixture is added 172 to the mill, and the mill is run 174 for approximately 30 minutes. The runtime of the mill may vary, for example, between 20 to 60 minutes). The PM 4700 is a conventional leather protectant that renders the skins oil resistant and water resistant, and is available from 3M under the trade name “Scotch Guard®.” This protectant can be replaced or supplemented by other conventional protectants, if desired. The skins are next treated to fix the protectant in the skins. Approximately 10.0 lbs. (1%) of formic acid (90% concentration) is mixed 176 with approximately 11.111 gallons of water at approximately 100° F. The mixture is added 178 to the mill. The mill is run 180 for approximately 30 minutes. The runtime of the mill may vary, for example, between 20 to 60 minutes). These steps should bring the skins to a pH level in the range of 3.0 to 3.5.
If desired, the skins can be subjected to a variety of additional treatments. These various treatments are option. In one embodiment, the skins are treated with antimicrobial and antistatic treatments (See
If desired, additional treatments may be applied to the skins. For example, a flame resistant or flame proof treatment may be applied. The flame resistant or flame proof treatment may be applied to the skins in a dry or dissolved state, as desired. Further, additional antimicrobial treatments may be applied. Additional antimicrobial treatments may also be applied in a dry or dissolved state.
Next, the skins are subjected to a final washing. Approximately 1000 gallons of water at 100° F. are added to the mill while the mill is running. The washing door of the mill may be left open, permitting the water to slosh from the mill. The mill is run until nearly all of the water has sloshed from the mill. Then, the skins or leathers are dumped from the mill.
The leathers are preferably dried using conventional vacuum dryers or other similar machinery. The dried leathers can be staked and finished 80 as desired. Staking is a mechanical softening process that typically involves beating the leather repeatedly with small fingers. The leathers can also be sanded and milled, as appropriate. The leathers can undergo additional finishing, as desired. For example, oil can be applied to the leather to add to waterproofness and change the look and feel of the leather.
The above description is that of a preferred embodiment of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular.
