Photosensitive medium comprising a cyclic acetal of furfural, a lower haloalkane, and silica

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to improved, negative-working, copying materials and to coating compositions useful in the preparation thereof. More particularly, the invention relates to a copying material comprising a paper or film substrate having coated thereon an amine-free layer comprising a cyclic acetal of furfural, a photosensitive lower haloalkane, a resinous binder and silica. The copying materials are negative-working and images are formed thereon by exposure to ultraviolet light and fixed by subsequent heating.

SUMMARY OF THE INVENTION 5

In accordance with the present invention, improved, negative-working, copying materials are prepared comprising a paper or film substrate having coated thereon an amine-free layer comprising a cyclic acetal of furfu¹⁰ ral, a photosensitive lower haloalkane, a resinous binder and silica. Images are formed on said copying materials by exposure to ultraviolet light and fixed by subsequent heating.

DESCRIPTION OF THE PREFERRED

EMBODIMENTS

2. Description of the Prior Art

Copying materials, as that term is commonly used, refers to any one of any products useful in the repro- ²⁰duction of graphic originals. On the basis of the type of copy obtained, these materials are either positiveworking or negative-working. With the positive working materials, a print which is the exact duplicate of the original being reproduced is obtained. With the nega- ²⁵tive-working materials, however, the print obtained is the opposite of the original, i.e., the non-image, or clear, areas of the original will appear as the imaged portions of the copy and the imaged, or printed, areas ₃θ of the original will not appear on the copy.

The most widely used negative-working copying materials are those employing silver halides. These materials, in addition to being expensive, generally require complex equipment and lengthy processing operations 35 for development of the images. Many attempts have been made to produce negative-working, non-silver halide, copying materials, but none of those which have been developed and are reported in the literature have achieved significant commercial success due to a num- 40 ber of limitations which are inherent in these materials also.

Several negative-working imaging systems have been proposed in which a photosensitive haloalkane, such as iodoform, which is known to release hydrogen iodide 45 (HI) when exposed to light, is combined with a compound containing a furan ring. See, for example U.S. Pat. Nos. 1,587,269; 1,587,272; 1,587,273 and 1,587,274 issued to Beebe and U.S. Pat. No. 3,394,391 issued to Wiswell, No. 3,394,392 issued to Mattor and ⁵⁰No. 3,394,394 and No. 3,394,395 both of which were issued to Mattor et al. Limitations of these systems which have restricted their use include, for example, (a) the presence of impurities in the coatings resulting in discoloration of the non-image areas of the copies ⁵⁵produced, (b) the high temperatures required to fix the images resulting in a softening and distortion of the imaged material, (c) the use of amines which have a tendency to migrate away from the photosensitive layer during storage of the materials and (d) residual haloalkane in the imaged and fixed materials resulting in discoloration of the imaged materials.

It is also known that silica can be employed in copying materials as a toothing agent to make the materials receptive to pencil and ink lines. See, for example, U.S. Pat. No. 2,999,016 issued to Beeber et al., U.S. Pat.

No. 3,447,947 issued to Abbott et al., U.S. Pat. No.

According to the present invention, improved negative-working copying materials are prepared by coating a paper or film substrate with an amine-free formulation comprising a cyclic acetal of furfural, a photosensitive lower haloalkane, a resinous binder and silica. It has been found that the inclusion of silica in the copying materials of the present invention results in an improved material which does not soften upon exposure to heat, does not become distorted upon exposure to high temperatures, and allows the photosensitive lower haloalkane present to be removed from the non-image areas faster and at lower temperatures. These improvements are achieved without adversely affecting the other properties of the copying materials.

Substrates useful in preparing copying materials in accordance with the present invention may be either paper or film. Preferred bases include paper, cellulose acetate films and polyester films which have been treated with a suitable subbing layer including, for example, cellulose acetate butyrate.

The coating formulation is prepared by dissolving the soluble components in an organic solvent such as, for example, acetone, toluene, methyl ethyl ketone and tetrahydrofuran.

As described in the patent application entitled “Copying Material and Method for Preparation and Use Thereof” filed concurrently herewith by Edward Zarebski preferred resinous binders for use in the copying materials of the present invention are polyvinyl chloride homopolymers. As pointed out in that application, these polymers are soluble in conventional, nontoxic solvents and result in copying materials which have a reduced tendency to soften when heated, remain clear and colorless in the non-image areas during the light exposure and heat fixing steps, and allow iodoform, or other haloalkane, to pass from the copying material during the fixing step. A cyclic acetal of furfural is also required. While some of the prior art systems have employed other types of compounds containing a furan ring, it has been found that only the cyclic acetals of furfural can be employed in the copy materials of this invention. Other compounds, such as those containing basic nitrogen groups result in problems such as poor image density, discolored background or nonimage areas and poor aging characteristics of the coated, unimaged materials. Cyclic acetals useful in carrying out the present invention include, but are not limited to, the following:

3,753,718

<img file="US3753718A_D0001.tif" />

difurfurylidene pentaerythritol

<img file="US3753718A_D0002.tif" />

2-(2-furyl)-l,3 dioxane

<img file="US3753718A_D0003.tif" />

2-(2-furyl)-5-methyl-5-nitro-l ,3-dioxane

<img file="US3753718A_D0004.tif" />

2-( 2-furyl )-5,5-dimethyl-l ,3-dioxane

<img file="US3753718A_D0005.tif" />

2-(2-fury 1)-5,5-diethyl-1,3-dioxane

<img file="US3753718A_D0006.tif" />

2-( 2-furyl )-4-methyl-1,3-dioxane

<img file="US3753718A_D0007.tif" />

2-( 2-furyl )-4,6-dimethyl-1,3-dioxane

Cyclic acetals of the type useful in the present invention can be prepared by the following general procedure:

0.50 moles of the corresponding diol and 1.0 grams of paratoluenesulfonic acid are dissolved in 150 cc of tetrahydrofuran and the resulting solution is placed in a 1,000 cc 4-necked flask equipped with stirring apparatus, an addition funnel, a dean-stark trap and a thermometer. 150 cc of pentane are added and the reaction mixture is heated to reflux and 0.50 moles of furfural (1.0 moles when the diol is pentaerythritol) are added dropwise through the additional funnel. After the addition of the furfural is complete, the reaction mixture is allowed to reflux until no more water is evolved. The reaction mixture is then neutralized with an aqueous solution of sodium carbonate resulting in the formation of two phases. The upper, organic phase, containing the product, is separated, extracted with warm water to remove any unreacted diol or furfural, and the solvent is removed on a flash evaporator. The product may be either a solid or a liquid. If a solid, the product can be recrystallized from a suitable solvent such as methanol. Liquid products are purified prior to use by fractional distillation at reduced pressure.

Melting Point or Compound Physical State Boiling Point (°C) white crystals 161°-162°

II colorless liquid 6I°-63° at 0.5 mm

III white crystals 95°-97°

IV colorless crystals 24°-26° (boiling point

81° at 0.45 mm) V white crystals 24°-26°

Any photosensitive lower haloalkane may be employed in carrying out the present invention. Useful compounds include, for example, pentabromomethane and iodoform. In preparing copying materials in accordance with the present invention it is especially preferred to employ iodoform as the photosensitive lower haloalkane.

The silica which can be employed in carrying out the present invention includes any of those currently available. These include, for example, OK-412 available from DeGussa, Inc., Kearny, New Jersey and ST-2, HS-5, HS-7 and Siianox No. 1, all of which are available from Cabot Corporation, Boston, Mass. The amount of silica employed is preferably equal to up to about 5% by weight based on the weight of the coating formulation.

After the photosensitive lower haloalkane, resinous binder, and cyclic acetal of furfural are dissolved in the organic solvent, the silica is added to the formulation. It is especially preferred to add the silica in a form such that it will be completely dispersed. For this reason it is preferred to subject the silica to a mechanical treatment, such as in a ball mill, to reduce its particle size prior to addition to the coating formulation.

The coating formulation is applied to the substrate by conventional coating methods. These are well-known in the art and include, for example, bead-coating, reverse roll, between-the-roll coating and spray coating.

Negative-working copying materials prepared in accordance with the present invention can be imaged by exposing, beneath a partially opaque master, to ultraviolet light in the range of from about 3,000 Angstroms to about 5,000 Angstroms. It is especially preferred to employ a light source having an output in the range of from about 3,300 Angstroms to about 4,500 Angstroms. The light exposure results in the formation of an image in the light-struck areas of the copy material — i.e., those areas corresponding to the non-image areas of the master. After exposure the print is fixed by heating. It is especially preferred to heat the copy material to a temperature of from about 140° C to about 160° C for approximately two minutes. The effect of the heating is to remove the photosensitive lower haloalkane from the background, or non-image areas of the print and to develop, or fix, the image formed upon exposure to light.

Copying materials prepared in accordance with the present invention are useful in the reproduction of graphic originals such as microfilm, microfiche and engineering drawings. In order to describe the present in3,753,718 vention so that it may be more clearly understood, the following examples are set forth. These examples are set forth primarily for the purpose of illustration, and any specific enumeration of detail contained therein should not be interpreted as a limitation on the concept of this invention.

EXAMPLE I

A coating formulation was prepared comprising 76.48 grams methyl ethyl ketone

14.32 grams of GAP-852 — a polyvinyl chloride homopolymer available from Great American Plastics, Inc., Fitchburg, Mass.

1.91 grams of difurfurylidene pentaerythritol

1.91 grams of iodoform and

4.30 grams of OK-412, silica, available from DeGussa, Inc. Kearny, N. J.

This formulation was coated onto a polyester base which had been treated with a suitable bonding layer. After drying, a sample was exposed beneath a partially opaque master to ultraviolet light resulting in the formation of an image in the light-struck areas — i.e., those areas corresponding to the clear or non-image areas of the original. The image was fixed by heating to a temperature of about 150°C for about 2 minutes.

The resulting print had a maximum density of about 3.0 when measured on a photoelectric densitometer calibrated for visual density according to the ASA specification for diffuse transmission density, PH2.19-1959.

EXAMPLE II

A coating formulation was prepared comprising 76.49% methyl ethyl ketone

14.32% GAP 852 — a polyvinyl chloride homopolymer available from Great American Plastics, Inc., Fitchburg, Mass.

4.87% OK412 — a silica available from DeGussa

2.16% difurfurylidene pentaerythritol and

2.16% iodoform.

The formulation was reverse roll coated on a Crane 100 percent rag 14 pound paper base and dried. The material was exposed, beneath a partially opaque master, to ultraviolet light in a Super Ozamatic operating at 10 feet per minute. The result was an image in the light-struck areas — i.e., those areas corresponding to the clear or non-image areas of the original. The image was fixed by heating the exposed material to a temperature of about 150°C for about 2 minutes.

The print had a density of about 3.0 when measured on a photoelectric densitometer calibrated for visual density according to the ASA specification for reflectance density, PH2.17-1958.

EXAMPLE III

A coating formulation was prepared, as in Example II, and coated onto a polyester base which had been treated with a suitable bonding layer. The coated material was then dried, exposed and fixed as in Example II. The resulting black image had a density of about 2.2 when measured as in Example I.

EXAMPLE IV

A coating formulation was prepared comprising 76.49% methyl ethyl ketone 14.32% GAP 852

4.87% OK412

3.26% 2-(2-furyl)-5-methyl-5-nitro-l,3-dioxane, and 2.16% iodoform.

The formulation was reverse roll coated on Crane 100% rag, 14 pound, paper base and dried. The material was exposed and fixed, as in Example II, resulting in a black image on a clear background. The image areas had a maximum density of 3.10 when measured as in Example II.

EXAMPLE V

A coating formulation was prepared comprising 76.49% methyl ethyl ketone 14.32% GAP 852 4.87% OK412

2.34% 2-(2-furyl)-4-methyl-l,3 dioxane

2.16% iodoform.

The formulation was reverse roll coated on Crane 100 percent rag, 14 pound, paper base and dried. The material was exposed and fixed, as in Example II, resulting in a black image on a clear background. The print had a maximum density of 3.10 when measured as in Example II.