Antistatic drafting films

A matte drafting sheet composite at least one side of which comprises a single polymeric matrix layer containing particulates to provide a matte or drafting surface and a quaternary ammonium salt of high charge density at a concentration sufficient to provide a resistivity of said matrix layer of at most about 1.times.10.sup.13 ohms/square.

FIELD OF THE INVENTION 
This invention relates to antistatic matte thermoplastic drafting layers 
suitable for both manual drafting and plotting purposes. 
BACKGROUND OF THE INVENTION 
Matte drafting films have long been used as media for engineering drawings, 
and their compositions are well known in the art. Conventional drafting 
film construction consists of an underlayer and an overlying surface layer 
on at least one side of a base support such as polyethylene terphthalate. 
Pencil tooth for drafting purposes is obtained primarily through the 
underlayer which is comprised of a finely divided pigment dispersed within 
a cross-linked binder. The surface layer is comprised of a polymeric 
matrix which provides ink receptivity and adhesion, and also pencil and 
ink erasability. At times, the surface layer employs an antistatic agent 
to reduce static charge to correct the problem of static cling and 
attraction of foreign matter. 
More recently, use of matte drafting surfaces have also been provided on 
the opposing side of electronically imaging media which has placed 
additional requirements on the drafting surface. These requirements 
include the following: (1) Effective inhibition of dust and dirt 
attraction due to static electricity. Static is particularly serious in 
electronic imaging processes, because dust or foreign matter will 
frequently cause voids and consequent loss of information. (2) Inhibition 
of spurious electrostatic charges which cause toner background problems, 
especially in electrostatic printing. (3) Reliable transport and stacking 
in automated imaging devices. (4) Good toner adhesion in 
electrophotographic imaging processes where the matte drafting surface is 
the imaged side. (5) Reduction in the number of layers in the matte or 
drafting matrix to help reduce cost and improve quality control. 
Antistatic agents have long been used as a means of reducing static charge 
in a variety of applications. In the past, however, the use of antistatic 
agents in drafting media have often been accompanied by undesirable 
properties which has discouraged their use in such media. This has been 
particularly true with respect to newer electronic copying and printing 
applications. 
The literature abounds in the listing of antistats and their applications. 
These antistats may be broadly classified as cationic, anionic and 
non-ionic. The cationic classification includes protonated amines and 
quaternary ammonium, sulfonium and phosphonium cations. The quaternary 
ammonium cations may be divided into six different sub-classes of varying 
structure and molecular weight. While there is an enormous diversity of 
both molecular structure and applications for antistats, there is little 
teaching to be found as to which are most appropriate for drafting 
surfaces. Most work for the drafting application has been empirical and 
has addressed a rather narrow set of product performance requirements. 
SUMMARY OF THE INVENTION 
The present invention provides a single-layer matte drafting surface on a 
film which inhibits the development of static electricity thereon. It 
provides a matte drafting surface with antistatic properties without 
causing deleterious drafting defects such as ink feathering, ink line 
discontinuities and pencil ghosting on erasure. It also provides a film 
having a single layer matte drafting surface thereon and an imaging 
surface on the opposing side thereof, wherein there is minimized the 
attraction of dust or dirt due to static and thereby also minimized voids 
and other visual defects in the imaging layer of the imaging and drafting 
film. The invention further provides an imagable matte drafting surface 
having good toner adhesion for electrophotographic applications and having 
few, if any spurious charges thereon. Thus, the present invention provides 
a single layer general purpose drafting surface that is advantageously 
suited for a variety of manual and electronic copying and printing 
applications.

DETAILED DESCRIPTION OF THE INVENTION 
We have discovered that quaternary ammonium salts of certain molecular 
structure having a high charge density can provide highly advantageous and 
unexpectedly beneficial antistatic properties to single layer matte 
drafting surfaces without also producing detrimental effects on drafting 
and imaging properties. Importantly, these quaternary compounds are 
soluble in aqueous and organic solvents and are capable of significant 
reduction of surface resistivity with the use of relatively small 
quantities of the antistatic agent. 
Previous use of quaternary ammonium compounds in a single layer drafting 
surface produced undesirable properties such as ink line feathering and 
discontinuities, poor erasure properties and loss of toner adhesion. The 
results of our discovery are unexpected as the reasons for the good 
performance of our high charge density quaternary compounds are not 
apparent. The unusually good performance of our quaternary compounds of 
this invention may be explained in several ways. For one, their 
effectiveness at low concentrations may be due to their high charge 
density. However, possibly the absence of fatty acids or alcohols of 
comparable chain length as constituents in our quaternary ammonium salt 
structure may also be a factor. Another possibility may be that our 
antistatic agents are adsorbed on the surface of the particulates. One or 
more of the above factors may be responsible for the unusual properties 
provided by the antistats of this invention, however, the present 
invention is not limited thereby. 
Exemplary of the quaternary ammonium salts which provide unexpectedly good 
results when employed in the matte drafting films herein disclosed are the 
following formula I compounds. 
##STR1## 
In Formula I, R.sub.1 -R.sub.4 and X may possess any of the following 
values. 
R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are the same or different and are 
selected from the group consisting of: 
substituted or unsubstituted C.sub.1 -C.sub.3 alkyl groups wherein the 
alkyl groups may be substituted by hydroxy, C.sub.1-3 alkoxy (e.g., 
methoxy, ethoxy, propoxy and 2-propoxy), amido (e.g., --NHC(O)H), or acyl, 
substituted or unsubstituted C.sub.2 -C.sub.3 alkenyl groups wherein the 
alkenyl groups may be substituted by hydroxy, C.sub.1-3 alkoxy (e.g., 
methoxy, ethoxy, propoxy and 2-propoxy) or amido (e.g., --NHC(O)H), and 
substituted or unsubstituted C.sub.2 -C.sub.3 alkynyl groups wherein the 
alkynyl groups may be substituted by hydroxy, C.sub.1-3 alkoxy (e.g., 
methoxy, ethoxy, propoxy and 2-propoxy), or amido (e.g., --NHC(O)H), X is 
the anion of a strong acid (e.g., Cl.sup.-, CH.sub.3 SO.sub.4.sup.- or 
H.sub.2 PO.sub.4.sup.-); 
with the proviso that the formula weight of the Formula I compound cation 
is from 74 to about 300 amu (preferably from 74 to about 150), and that 
the charge density, defined below, of the quaternary ammonium cation is 
from 3.33.times.10.sup.-3 to 13.5.times.10.sup.-3 and preferably from 
6.67.times.10.sup.-3 to 13.5.times.10.sup.-3. 
The primary application of drafting films is to record information. This 
may be done by hand or by electronic copying or printing means on the 
drafting surface. Recently, drafting surfaces have been provided on the 
opposing side of imaging films so as to provide a means of adding or 
modifying information to the imaged print. Typical imaging films which are 
encompassed hereby would employ a drafting surface on the opposing side of 
the imaging layer wherein said imaging layer employs any one of a number 
of technologies including electrophotography (e.g. reprocopier materials), 
electrostatic or dielectric plotters, ink jet printing, clear or matte pen 
plotting, thermal transfer printing and direct thermal printing. In the 
case of reprocopier films, which usually have a matte layer on both sides 
of a film support, it is important to control the range of surface 
resistivity between about 1.times.10.sup.10 to 1.times.10.sup.13 ohms/sq. 
at 50% RH. If the surface resistance is much lower there will result a 
loss in image density. Electrostatic imaging films, however, will benefit 
from lower resistivity, preferably in the range of about 1.times.10.sup.8 
to 1.times.10.sup.11 ohms/sq at 50% RH. This is necessary to avoid the 
development of static charge on the film during the various manufacturing 
operations. Such spurious electrostatic charges will attract toner during 
the developing stage of electrostatic imaging causing deleterious black or 
colored marks upon toning. Thus, each imaging system will have an optimum 
range of resistivity within a broader range of about 1.times.10.sup.8 to 1 
.times.10.sup.-- ohms/square and the antistatic agents used must not only 
achieve this optimum range, but do so without also producing deleterious 
effects. 
As a major application of the present invention, there is envisioned the 
use of unsupported clear, translucent or opaque films as the base sheet 
for the layers of the composite. Nonetheless, the invention also 
encompasses the use of any base film which would benefit from an 
antistatic matte or drafting surface. For example, it would be beneficial 
to have an antistat matte surface film in mechanical printing, such as 
offset printing. 
There are generally two main constructions of the present invention. The 
first is solely for drafting purposes, either manual or electronic, such 
as a pen plotter. This construction may have a drafting surface on one or 
both sides of the film. The drafting layers of this construction may be of 
the same or differing composition. The second construction employs a 
drafting surface on one side of a film and an imaging layer on the 
opposite side of the film. The imaging layer may utilize any of the 
imaging technologies described in the foregoing section. Such imaging 
technologies are well known to those skilled in the art. 
Polymers which may be employed in the drafting surface matrixes of the 
present invention include those comprised of a hard polymer with a Tukon 
hardness greater than about 15 and a softer polymer which is hydrophilic. 
In this regard, the hard polymer helps provide clean pencil erasure and 
dig resistance, while the softer hydrophilic polymer provides good ink 
receptivity without feathering, ink erasure and promotes bonding to 
toners. The ratio of the harder and softer polymers are generally from 
about 1:3 to about 6:1 and preferably they are about 3:1. 
A preferred embodiment of the present invention is a single layer 
thermoplastic matrix comprising a 3:1 mixture of polymethyl methacrylate 
(PMMA) and the copolymer of polyvinyl pyrolidone and vinyl acetate 
(PVP-VA), silica and at least one high charge density quaternary ammonium 
cation and a strong acid anion. 
A wide variety of pigments may be employed to achieve suitable pencil tooth 
or abrasivity for drafting purposes. Additionally, when a drafting surface 
is employed herein on the side opposite the imaging side of an imaging 
film, said surface must have appropriate surface roughness to feed through 
a copying or printing device. Drafting properties of films are 
characterized by pencil tooth (abrasivity), pencil line continuity and 
erasure and the feed properties by the static and dynamic friction. Pencil 
tooth and erasure are determined by standard test procedures described in 
Federal Specification L-P-519C. The coefficients of static and dynamic 
friction are respectively usually in the range of about 0.235 to 0.75 and 
about 0.20 to 0.70. Particulates useful herein which provide the required 
combination of abrasivity and friction are selected from the group 
consisting of crystalline silica, alumina trihydrate, calcium carbonate, 
amorphous silica, diatomateous earth, calcined clay, organic pigments, and 
the like. 
The antistatic agents which are useful in the present invention are 
quaternary ammonium salts of high charge density which are soluble in 
organic solvents or water as utilized in drafting formulations. The 
Formula I compounds outlined above are useful as such antistat agents. In 
general, the antistatic agents encompassed hereby should not polymerize in 
drafting film formulations. In this respect, polymerization is not 
believed to be desirable as it is likely to reduce the effectiveness of 
the antistats. 
For the purpose of this invention, charge density is defined herein as the 
number of ionizable groups divided by the formula weight of the quaternary 
ammonium cation. The number of ionizable groups for the antistatic agents 
described herein is one. Thus, the lower the formula weight of the cation 
the higher the charge density. 
For example, the (CH.sub.3).sub.4 N.sup.+ cation has a mass of 74 amu and a 
charge of 1, so that the cationic charge density of 1 divided by 74 is 
13.5.times.10.sup.-3. The desired antistatic properties are achieved by a 
charge density, in the range of 3.33.times.10.sup.-3 to 
13.5.times.10.sup.-3 and preferably in the range of 6.67.times.10.sup.-3 
to 13.5.times.10.sup.-3. The anionic constituent of the quaternary 
ammonium salt usually is derived from any of a number of strong acids. 
Typically Cl.sup.-, CH.sub.3 SO.sub.4.sup.- and H.sub.2 PO.sub.4.sup.-. 
The choice of anion helps determine the water and organic solvent 
solubility of the quaternary salt. 
Those of Formula I provided herein, typical compounds exemplifying said 
class of antistats include Calgon's dimethyl diallyl ammonium chloride, 
Allied Colloid's DP6-4143 and DuPont Chemical's AVITEX E. The effective 
concentration of the antistat agent in drafting layer formulations should 
provide a surface resistivity of at most 1.times.10.sup.-- ohms/sq at 50% 
RH. In this respect, a concentration in the range of about 0.3 to about 
0.5% by weight will achieve a resistivity of about 1.times.10.sup.12 
ohms/sq and a concentration of about 0.8-1.2% by weight will provide a 
resistivity of about 1.times.10.sup.10 ohms/sq, both at 50% RH. In both 
instances the resistivity will be higher or lower depending on the 
formulation employed and the thickness of the film. The lower 
concentrations of antistats utilized in this invention help avoid the 
deleterious effects of previously employed antistatic agents. 
The antistats which are useful herein are either commercially available or 
can easily be manufactured by those of ordinary skill in the art, through 
known methodology and reaction sequences. 
The supporting layer of the present invention is a polymeric material which 
has suitable dimensional stability, transparency or opacity, tensile 
strength, adhesion characteristics, thermal stability and hardness. 
Suitable polymeric materials for use as a supporting layer are transparent 
or opaque thermoplastic polymers, including polyesters, polysulfones, 
cellulose acetate, polycarbonates, polystyrene, polyimides, polyolefins, 
poly(methyl methacrylate), cellulose esters such as cellulose acetate and 
others. A polyethylene terephthalate polyester film is particularly 
preferred The thickness of the layer is not particularly restricted, but 
typically is in the range of about 2 to 10 mils, preferably about 3.0 to 
about 5.0 mils. The supporting layer may be pretreated to enhance adhesion 
of the polymeric coating thereto. 
Although this invention pertains to matte drafting surfaces, the present 
discovery may also be applied to the manufacture of imaging surfaces such 
as clear plotting, electrophotographic and ink jet films. 
The following Examples are provided to further aid those desiring to 
practice the present invention. However, the present invention is not 
limited thereby. 
EXAMPLE I 
Onto a 4 mil ICI MELINEX 505 polyester film, a mixture of the following 
composition is coated, using an 18 Mayer rod to give a dried coating 
thickness approximately 0.30-0.35 mil. The coating is dried at 120.degree. 
C. for 60 seconds. 
______________________________________ 
Composition % By Weight 
______________________________________ 
1. MIN-U-SIL Grind Composition* 
28.84 
2. Polyvinyl Pyrollidone-Vinyl acetate 
8.83 
Copolymer (E-735), manufacturing by 
GAF at 50% w/w 
3. ACRYLOID A101, manufacturing by Rohm & 
29.43 
Haas at 40% solid W/W 
4. Propylene Glycol Monomethyl Ether 
30.78 
5. TINT AYD AC-66-04, manufacturing by 
1.12 
Daniel at 82% solid w/w 
6. AVITEX E, manufacturing by DuPont at 
1.00 
40% solid w/w 
______________________________________ 
Ingredients are mixed under stirring in order listed. 
______________________________________ 
* MIN-U-SIL Grind Composition 
% By Weight 
______________________________________ 
10 micron MIN-U-SIL (Pennsylvania 
57.95 
Glass Sand Corporation) 
Propylene Glycol Monomethyl Ether 
29.07 
ACRYLOID A101, (Rohm & Haas) 
11.15 
40% w/w 
MPA - 2000X (NL Industries, Inc.) 
1.83 
______________________________________ 
Ingredients are charged into a ball mill and milled for 12 hours. 
The coated sheet is tested for surface resistivity at 50% RH and found to 
be 1.times.10.sup.10 Ohm/sq. The ink and pencil drafting and erasure 
properties of the drafting surface were evaluated according to standard 
manual test procedures with excellent results being achieved therewith. 
EXAMPLE II 
The coated film as described in Example I is coated on the opposing side 
with an electrostatic imaging formulation as described in Example I of 
U.S. patent application Ser. No. 07/514,217, filed on Apr. 25, 1990, which 
is incorporated herein by reference. The imaging side of the sheet is 
printed on a VERSATEC electrostatic plotter and provided excellent results 
without any electrostatic background from the toner being noticed. 
EXAMPLE III 
Example I is repeated using DP.sub.6 -4143, 1.1% weight. The coated sheet 
is tested for surface resistivity at 50% and there was found a resistivity 
of 5.times.10.sup.10 Ohms/sq. 
EXAMPLE IV 
Onto a 4 mil ICI MELINEX 505 polyester film, a mixture of the following 
composition is coated using an 18 Mayer rod to give a desired coating 
thickness 0.3-0.35 mil. The coating is dried at 120.degree. C. for 60 
seconds. 
______________________________________ 
Composition % By Weight 
______________________________________ 
1. MIN-U-SIL Grind 29.44 
2. Polyvinyl Pyrollidone - Vinyl Acetate 
8.66 
copolymer (E-735), manufacturing by 
GAF at 50% w/w 
3. ACRYLOID A101, manufacturing by Rohm 
29.44 
& Haas at 40 solid w/w 
4. Propylene Glycol Monomethyl Ether 
31.41 
5. TINT AYD AC-66-04, manufacturing by 
0.71 
Daniel at 80% solid w/w 
6. DP.sub.6 -4143, manufacturing by Allied 
0.34 
Colloids at 50% solid w/w 
______________________________________ 
Ingredients are mixed under stirring in the order mentioned. The coated 
sheet is tested for surface resistivity at 50% RH and found to possess a 
resistivity of 7.times.10.sup.11 ohms/sq. The ink and pencil drafting and 
erasure properties of the drafting surface were evaluated according to 
standard test procedures with excellent results being obtained. 
EXAMPLE V 
The same formulation as in Example IV was coated on both sides of the 
polyester substrate and was evaluated in a XEROX 2510 reprocopier. Results 
indicated that excellent toner adhesion and transport were obtained. 
EXAMPLE VI 
Example IV is repeated using 0.22% weight of diallyl dimethyl ammonium 
chloride (Calgon Corporation, 65% solid w/w) instead of DP6-4143. The 
coated sheet is tested for surface resistivity at 50% RH and found 
5.times.10.sup.11 ohms/sq. This sheet was evaluated for both manual 
drafting properties and in XEROX 2510 reprocopier, both provided excellent 
results. 
EXAMPLE VII 
Example IV is repeated using each of the following quaternary ammonium salt 
of Formula I in separate trials wherein R.sub.1 -R.sub.4 and X are as 
defined in Formula I. 
__________________________________________________________________________ 
R.sub.1 R.sub.2 R.sub.3 
R.sub.4 
X 
__________________________________________________________________________ 
(a) 
--CH.sub.3 
--CH.sub.3 
--CH.sub.3 
--CH.sub.3 
Cl.sup.- 
(b) 
--CH.sub.3 
--CH.dbd.CHOH 
--CH.sub.3 
--CH.sub.2 --CH.sub.3 
CH.sub.3 SO.sub.4.sup.- 
(c) 
--CH.dbd.CH.sub.2 
--CH(CH.sub.3).sub.2 
--CH.sub.3 
--CH.sub.3 
H.sub.2 PO.sub.4.sup.- 
(d) 
--CH.sub.2 NHC(O)H 
--CH.sub.3 
--CH.sub.3 
--CH.dbd.CH.sub.2 
Cl.sup.- 
(e) 
--C.tbd.CH 
--CH.dbd.CH.sub.2 
--CH.sub.3 
--CH.sub.2 OCH.sub.3 
Cl.sup.- 
(f) 
--CH.sub.3 
--CH.sub.2 C(O)CH.sub.3 
--CH.sub.3 
--CH.sub.2 CH.sub.3 
H.sub.2 PO.sub.4.sup.- 
__________________________________________________________________________ 
Each of the sheets which is produced and is tested for surface resistivity 
and good results are achieved. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded as a departure 
from the spirit and scope of the invention, and all such modifications as 
would be obvious to one skilled in the art are intended to be included 
within the scope of the following claims.