Replasticization of an already manufactured flexible vinyl product to prevent cracking or tearing of said product

A process is described that can be employed in the field for preventing the formation of cracks and tears in already manufactured and fabricated flexible vinyl products from plasticizer loss induced embrittlement involving replasticization by spreading on the vinyl product a uniform coating of a liquid, vinyl plasticizer at temperatures between 4.degree. C. and 60.degree. C. followed by allowing the product to remain undisturbed for up to ten days at temperatures between 4.degree. C. and 60.degree. C. when the plasticizer will have been absorbed into the interior of the vinyl product as evidenced by the surface of the product exhibiting reduced resiliency, and feeling dry and non tacky to the touch.

BACKGROUND OF THE INVENTION 
Flexible vinyl sheet, film, and flexible vinyl coated fabric are very 
versatile materials and find a wide variety of uses. Curtains for windows 
and showers, coverings for home and office furniture, automotive seat 
covers, single ply flexible vinyl membranes for covering industrial roofs, 
wall coverings, shoe uppers, purses and agricultural sheet illustrate the 
diversity of uses for this material. 
Despite its wide utility there are some problems associated with the use of 
flexible vinyl in many applications. One of the more serious problems 
involves cracks or tears that develop in a flexible vinyl product after a 
period of use as the vinyl becomes stiff and brittle with age. These 
cracks or tears generally mark the end of the useful life of the vinyl. 
It is known that loss of plasticizer from flexible vinyl is responsible for 
this stiffening and embrittlement of the vinyl (P. Dunn, et. at. J. Appl. 
Poly. Sci., 14, 2107-2116, 1970). The vinyl gradually loses flex fatigue 
resistance, becomes progressively shiffer, harder, and more brittle with 
further losses of plasticizer until cracks already develop. 
Flexible vinyl film, sheet, coated fabric etc. can lose plasticizer by a 
variety of mechanisms: 
(1) the most common cause of plasticizer loss and subsequent embrittlement 
of flexible vinyl materials is plasticizer volatilization. 
(2) plasticizer loss by rub off represents the second most frequent cause 
of plasticizer loss. 
(3) a less often encountered cause of plasticizer loss is extraction by 
cooking fats and oils which condense on flexible vinyl coated products 
located in the food preparation area of the home during cooking. 
The number of methods of preventing plasticizer loss that have been 
proposed reflect the substantial economic implications of the problem. For 
example, it has been proposed to plasticize polyvinyl chloride with 
materials having molecular weights that are sufficiently high that 
plasticizer loss due to volatilization would be negligible. Such high 
molecular weight non volatile materials are generally not as efficient 
plasticizers for polyvinyl chloride resin as the low molecular weight more 
volatile plasticizers. Impermeable coatings for the surface of flexible 
vinyl film, sheet, and coated fabric have been proposed that would prevent 
loss by inhibiting plasticizer migration to the surface and subsequent 
evaporation from the surface of the flexible vinyl product. 
Although all of the foregoing techniques for preventing plasticizer loss 
are effective to some degree they are not universally employed by 
manufacturers in the highly cost competitive flexible vinyl industry owing 
to their expense. All of the foregoing methods for preventing crack or 
tear development in flexible vinyls owing to plasticizer loss are designed 
to be implemented at the time the flexible vinyl product is being 
manufactured. For example, it is well known that plasticizers can be 
incorporated in vinyl plastic at the time when the vinyl plastic compound 
is being manufactured. Conditions which must be met in order to 
incorporate vinyl plasticizers in vinyl products at the time of 
manufacture according to the Plastics Engineering Handbook include 
temperatures of 300.degree. to 350.degree. F. in order to fuse the vinyl 
dispersion, high shear, low speed mixing in order to disperse the resin in 
the plasticizer, and the use of special very fine particle size, high 
porosity resins known as dispersion grade resins in order to insure that 
the plasticizer permeates the resin thoroughly. 
A need, however, exists for a method of preventing plasticizer loss induced 
cracking after vinyl products have been manufactured, fabricated, and 
purchased by the consumer. U.S. Pat. No. 2,622,038 attempts to respond to 
this need by disclosing a method for preventing deterioration of vinyl 
plastics by applying plasticizer to the surface of the flexible vinyl 
plastic and allowing it to be absorbed. Although this method has proven 
useful it is not without its disadvantages. 
When certain U.S. Pat. No. 2,622,038 plasticizers are applied neat to a 
flexible vinyl surface they do not wet that surface. Failure to wet the 
surface of vinyl products by these plasticizers leads to blisters, 
blotchiness, pigment extraction, and surface disfigurements on the surface 
of the vinyl product once the isolated pools of plasticizer on the product 
surface have been absorbed. Other U.S. Pat. No. 2,622,038 plasticizers 
when applied neat require excessively long times for absorption into the 
surface of a flexible vinyl product. In addition all plasticizers of U.S. 
Pat. No. 2,622,038 when tested are readily extracted from flexible vinyl 
products by kerosene, a test which assesses the sensitivity of flexible 
vinyl plastics to accidental spillage of automotive fluids. The number of 
plasticizers which are truly satisfactory for replasticization of flexible 
vinyl plastic products is remarkably small given the large number of 
plasticizers that are available commercially at this time. 
When any plasticizer including U.S. Pat. No. 2,622,038 plasticizers are 
applied as a solution or dispersion in a diluent which will not attack 
flexible vinyl plastics such as mineral oil the surface of the vinyl 
plastic is wetted, but the rate of absorption of the solution or 
dispersion into the surface of the vinyl plastic is greatly retarded. 
SUMMARY OF THE INVENTION 
It has been found that the disadvantages of the prior art replasticization 
methods can be substantially overcome by application of 0.002 to 0.2 lbs. 
per sq.ft. of flexible vinyl surface of neat plasticizers having room 
temperature surface tensions below 34 dynes/cm., plasticizer absorption 
times less than 10 days at 4.degree. C. for plasticizer applications of 
0.0088 lbs./sq. ft., and kerosene extraction resistance values less than 
10% at 23.degree. C. from 40 mil milled and molded flexible PVC sheet. 
OBJECT OF THE INVENTION 
It is the object of the present invention to provide an improved method for 
replasticization of an already manufactured flexible vinyl product. 
Another object of the present invention is to provide a method for the 
replasticization of an already manufactured vinyl product that can easily 
be employed in the field. 
Another object of the present invention is to provide a method having a 
short treatment time for the replasticization of an already manufactured 
vinyl product. 
Another object of the present invention is to provide a method for the 
replasticization of an already manufactured, flexible vinyl product which 
results in a non tacky, non resilient surface.

DESCRIPTION OF THE INVENTION 
The method of the present invention contemplates preparation of the vinyl 
product to be replasticized by first cleaning it with either a solvent or 
an aqueous detergent solution to remove grease and other soils which might 
interfere with the wetting of the vinyl product surface by the plasticizer 
solution. Suitable cleaning solvents are those which will not attack vinyl 
products and include mineral spirits, hexane, heptane, VM&P naphtha, and 
the like. Suitable aqueous detergents include any household spray cleaner 
designated by the manufacturer on the label as suitable for flexible 
vinyl. Detergent cleaning of vinyl should be followed by a rinse with 
clear water, followed by a period sufficient to allow thorough drying of 
the product before application of the replasticization liquid. 
The suitable neat liquid vinyl plasticizer is typically applied at levels 
of 0.002 to 0.2 lbs. per sq. ft. of vinyl surface per application. 
Multiple applications of the liquid may be required to achieve higher 
treatment levels. It is critically important that the plasticizer does not 
come in contact with a shear cut or knife cut edge of the vinyl product. 
Initially the freshly applied plasticizer remains on the surface but 
eventually it is absorbed into the interior of the vinyl product so that 
the initial "wet" and greasy feel from the fresh plasticizer application 
disappears as the plasticizer is absorbed by the vinyl leaving the vinyl 
surface feeling non tacky, and dry to the touch. For liquid plasticizers 
of this invention complete absorption occurs within ten days at 
temperatures between 4.degree. and 60.degree. C. for plasticizer 
applications of 0.0088 lbs. per sq. ft. or less. 
Suitable liquid plasticizers are limited to those, having 25.degree. C. 
surface tensions below 34 dynes/cm. so as to insure that the plasticizers 
will uniformly wet a clean flexible vinyl surface, rates of absorption 
into flexible vinyl sufficiently high that a plasticizer application of 
0.0088 lbs. per sq. ft. is completely taken up within ten days at use 
temperatures as low as 4.degree. C., and kerosene extraction levels less 
than 10% at 23.degree. C. for 40 mil milled and molded flexible PVC. 
Examples of suitable liquid plasiticizers include 2,2,4-trimethyl 
1,3-pentanediol diisobutyrate, dibutyl isophthalate, diisobutyl phthalate, 
the diester of phthalic acid with a commercial mixture Oxo process hexyl 
alcohol isomers(Jayflex DHP, EXXON chemical), and mixtures of C4 thru C10 
dialkyl phthalates and other plasticizers that meet the foregoing surface 
tension, absorption rate, kerosene extraction resistance, low surface 
tack, and low resiliency requirements. Solutions or dispersions of 
plasticizer in non vinyl attacking diluents such as VM&P naphtha, or 
mineral oil and the like are not suitable for this invention because the 
presence of such diluents in plasticizer greatly extends absorption time. 
Plasticizers may be applied to the vinyl surface to be replasticized with a 
plasticizer saturated cloth, towel, paint brush, paint roller, sponge, and 
porous flexible urethane foam applicator for paint. In general any of the 
application means found useful for low viscosity liquids such as oil based 
paints, furniture polish, or liquid car wax may be used. Plasticizer 
should never be placed directly on the vinyl surface but rather should 
always be applied to the vinyl with an applicator. Pouring the plasticizer 
directly on the vinyl surface may lead to a surface plasticizer pool which 
could either raise a blister or extract pigment or coloring from the vinyl 
surface before the pool can be spread over the entire vinyl surface 
uniformly. Application of plasticizers by dipping will not provide 
acceptable results owing to the potential for blistering, or pigment 
extraction problems mentioned earlier as well as the difficulty in 
predicting the quantity of plasticizer that will be absorbed for any given 
immersion period. Dipping vinyl fabric into plasticizer will cause the 
vinyl coating to separate from the fabric backing if the immersion period 
is long enough. 
EXAMPLES 
The following examples serve to further illustrate the invention. 
EXAMPLE 1 
2,2,4-Trimethyl 1,3-pentanediol diisobutyrate plasticizer, 1 g., was 
applied with a paint brush to a clean 6 in..times.6 in. rectangle centered 
within an 8 in..times.8 in. piece of 1.55 lbs./sq. yd. commercial, white, 
flexible vinyl fabric at room temperature. A uniform application of 
plasticizer over the vinyl surface was observed indicating that the 
plasticizer readily wets the vinyl fabric surface. Tack free time or the 
time for the plasticizer to be completely absorbed by the vinyl fabric at 
room temperature was 41 hours. 
COMITIVE EXAMPLE 
Prior art plasticizer, tricresyl phosphate, 1 g., was applied to a clean 6 
in..times.6 in. rectangle centered within an 8 in..times.8 in. piece of 
1.55 lbs./ sq. yd. commercial, white, flexible vinyl fabric at room 
temperature. The tricresyl phosphate did not wet the surface of the vinyl 
fabric at all as evidenced by the discrete pools of plasticizer present on 
the surface of the vinyl fabric at all times after application. The 1 g. 
of tricresyl phosphate was not absorbed after 30 days at 4.degree. C. 
COMITIVE EXAMPLE 
Prior art plasticizer, dibutyl phthalate, 1 g., was applied to a clean 6 
in..times.6 in. rectangle centered within an 8 in..times.8 in. piece of 
1.55 lbs./sq. yd. commercial, white, flexible vinyl fabric at room 
temperature. The dibutyl phthalate did not wet the surface of the vinyl 
fabric at all as evidenced by the discrete pools of plasticizer present on 
the surface of the vinyl fabric within a minute or two after application. 
The 1 g. of dibutyl phthalate was absorbed within twenty-four hours at 
room temperature. 
EXAMPLE 2 
Diisobutyl phthalate, 1 g., was applied to a 6 in..times.6 in. rectangle 
centered within an 8 in..times.8 in. piece of 1.55 lb/sq. yd. commercial, 
white, flexible vinyl fabric at room temperature. A uniform coating of 
plasticizer over the vinyl surface was observed indicating the plasticizer 
readily wet the vinyl fabric. Complete absorption of the plasticizer 
occurred within 48 hours at room temperature. 
COMATIVE EXAMPLE 
Prior art plasticization compound consisting of tricresyl phosphate in 
white mineral oil, 50:50 w:w, 1 g., was applied to a 6 in..times.6 in. 
rectangle centered within an 8 in..times.8 in. piece of 1.55 lbs./sq. yd. 
commercial, white, flexible vinyl fabric at room temperature. All 
plasticization compounds and plasticizers in these examples are always 
applied within a 6 in..times.6 in. rectangle centered within an 8 
in..times.8 in. piece of fabric so as to provide a 1 in. border all around 
the area of applied plasticizer which insures that all the plasticizer 
must be absorbed through the top surface of the fabric and is not absorbed 
at all through the side edges of the fabric. Although the dispersion of 
tricresyl phosphate in mineral oil did wet the vinyl fabric surface, 
absorption of the dispersion into the fabric required 168 hours at room 
temperature. 
While the present invention has been described with respect to application 
of selected plasticizers having room temperature surface tensions below 34 
dynes/cm., absorption times less than ten days at 4.degree. C. for 
plasticizer applications of 0.0088 lbs./sq. ft., and kerosene extraction 
resistance levels of less than 10% at 23.degree. C., etc., it will be 
evident to one skilled in the art that many other plasticizers may be 
employed in the practice of this invention that also meet the above 
requirements and therefore the scope of this invention should not be 
construed to be limited only to just those plasticizers listed above.