Matrix material for production of plastic printing plates

[57] ABSTRACT

A matrix material comprises a sheet of fibrous cellulosic material impregnated with a thermosetting resin, a coating of a thermosetting resin on one surface of said sheet, and a precast sheet of polypropylene film affixed to the coated side of the impregnated cellulosic sheet with an adhesive.

Claims, 1 Drawing Figure

PATENTEDJUH 6197?

3,668,058

<img file="US3668058A_D0001.tif" />

COATING CELLULOSE BASE

3,668,058

MATRIX MATERIAL FOR PRODUCTION OF PLASTIC PRINTING PLATES

This invention relates to matrix materials used in the printing industry. More particularly, it relates to matrix materials used in the preparation of duplicate plates for high-speed rotary presses.

The manufacture of duplicate printing plates is important to that segment of the printing industry that concerns itself with the printing of newspapers, magazines, brochures and the like, which are advantageously printed on a rotary press and which often require the use of several presses to fulfill the requirements of a specific job. Duplicate plates have many well known advantages over original printing material in that their printing characteristics can be made equal to or better than those of the original by quality control; they are easily replaced; they relieve the original from press-wear; and they can be curved without difficulty to meet the needs of the rotary press. One method of preparing duplicate plates is by stereo-typing which generally involves the following processing steps: The original type is locked into a steel frame which is called a chase. A sheet of stereo-type flong material made of a cellulosic, wax-coated composition, which may be treated with a releasing agent, is placed on the chase and pressed against the type. The sheet takes an impression from the type, thereby forming a mold or matrix. Molten lead is poured into the matrix, cooled and hardened, and removed from the matrix as the duplicate plate. Variations of this process are accomplished by using, in place of the lead, sheet rubber, sheet plastic, or other plastic compositions. In these processes sheets or rubber or plastic are pressed against the matrix, or the plastic compositions are cast in the matrix to form duplicate plates.

The advent of new plate materials, which will respond adequately to the new high speed rotary presses in terms of fidelity, longevity, fine screen half-tone dots and printability, has created a need for a matrix material that will accept, mold, and release these new plate materials in the form of printing plates that meet the highest standards for the aforementioned characteristics.

Among the polymeric materials that are of interest as plate materials in the printing field at the present time are polyester resins. The known flong materials, such as cellulosic materials impregnated with phenolic resins, are not capable of producing high quality curved printing plates when they are used as the matrix for polyester resins. Problems of fidelity in reproduction from engravings, type forms, combination forms, and wood-or metal-mounted originals and patterns have arisen. In addition excessive shrinkage, warping, nonuniformity of floor and relief and type damage have occurred which cause difficulties with the matrices themselves and lead to poor fidelity in the duplicate plates.

To be useful in the production of polyester printing plates, the matrix material must not only be such that it can be readily contoured under the heat and pressure used in preparing the matrix from the original plate, but it must also have a high enough heat distortion point so that it will not distort during this process. It must also have the property of releasability, so that duplicate plates made of polyester resin will be readily released after molding without adhering or sticking and preferable without the necessity for using mold release agents.

It is an object of this invention to provide a matrix material which will accept, mold, and release polyester resin and other printing plate materials in such a manner as to provide duplicate printing plates of high fidelity that are substantially free of distortion.

A further object is to provide a matrix material which can be molded with a minimum of shrinkage and warping, which will have a uniform floor and relief, and which will be of a soft enough composition to avoid type damage.

Other objects and advantages will become apparent hereinafter.

In accordance with this invention, a matrix material has been provided which comprises a sheet of fibrous material impregnated with a thermosetting resin, a coating of a ther2 mosetting resin on one surface of said sheet, and a preformed sheet of polyolefin film attached to the coated surface of said fibrous sheet.

The invention may be more clearly understood when it is 5 considered in conjunction with the attached drawing, which illustrates a preferred embodiment of the invention.

This drawing is a side view of the matrix material which shows its laminated structure. The various layers are not drawn in proportion with respect to thickness. The matrix ¹⁰ material shown in the drawing is a board-like laminated material consisting of a base, which is a sheet of cellulosic material impregnated with a phenolic resin, which has been coated with a phenolic resin and a sheet of polypropylene film which has been affixed to the coated surface of the base with an adhesive.

The base that is used in the preparation of the novel matrix materials is a sheet of fibrous material which may be made up of cellulose fibers as shown in the drawing or of other material 2q or synthetic fibers, such as cotton, hemp, wool, rayon, polyamide, or polyester fibers. It is generally preferred that the base be prepared from a cellulose material that contains both short and long pulp stock fibers. The base is impregnated with a thermosetting resin, such as a phenol-formaldehyde resin, a 25 urea-formaldehyde resin, a melamine-formaldehyde resin, an aniline-formaldehyde resin, and alkyd resin, or the like. In most cases resins of the phenol-formaldehyde type are preferred. Natural resins, such as rosin and copal, and novolaks may, if desired, be substituted for a portion of the 30 thermosetting resin. The thermosetting resin content of the impregnated base is generally from about 35 percent to 65 percent in terms of saturation of the base and is preferably 45 percent to 55 percent. The thickness of the impregnated base layer may be between 0.05 inch and 0.30 inch and is 35 preferably between 0.07 inch and 0.10 inch.

The impregnated base is coated with a thermosetting resin that may be the same resin as that used to impregnate the base or a different thermosetting resin. The preferred resin for coating the impregnated base is a general purpose, two-stage, 40 mineral and woodflourfilled, low pressure molding phenol-formaldehyde resin possessing a fast cure and a long flow. The thickness of the coating may range from 0.002 inch to 0.040 inch and is preferably 0.005 inch to 0.020 inch.

To the coated side of the impregnated base is affixed a preformed film of a polyolefin resin. It is necessary that the polyolefin resin be applied as a preformed film or sheet rather than by spraying the surface of the coated base with a solution of the polyolefin because the spray-on route does not provide 50 ^{a satisfactor}y distortion-free matrix material. As has been indicated, in order to obtain the superior matrix materials of this invention a thermoplastic polyolefin film must be affixed to a thermosetting resin coated base that has been impregnated with a thermosetting resin. The polyolefin film that is affixed ₅₅ to the coated impregnated fibrous base may be a film of an polymer consisting of α-olefin units having from 2 to 8 carbon atoms, such as polyethylene, polypropylene, or polybutylene. The useful polyolefins have flow rates as determined by ASTM Method D - 1238 -65 T in the range of 12 to 24. The 60 preferred polyolefin is polypropylene which has a flow rate of about 16. To insure satisfactory bonding, one side of the polyolefin film is usually primed or subjected to flame treatment, treatment with an electrical discharge, or treatment with ozone or other oxidizing agent before it is brought into 65 contact with the adhesive.

The adhesive that is used to bond the polyolefin film to the coated impregnated fibrous base is usually a solution of an organic polymer and fillers in an organic solvent. Among the preferred adhesives are those prepared from thermoplastic 70 polymers, such as polyvinyl acetate, polyvinyl formal, polyvinyl butral, polyvinyl alcohol, polyvinyl alkyl ethers, polystyrene, styrene - butadiene copolymers, homopolymers and copolymers derived from acrylic acid, methacrylic acid, lower alkyl acrylates, lower alkyl methacrylates, alkyl 2 75 cyanocryjates, acrylonitrile, methacrylamide,

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The resulting matrix material was about 0.085 inch thick and provided a 0.035 inch floor. It did not shrink on molding and its floor was more uniform than that of previously-known matrices.

methacrylonitrile, acrylamide, and the like. The thickness of the layer of the adhesive solution that is applied to the polyolefin film is generally in the range of 0.5 mil. to 1.0 mil. The invention is further illustrated by the examples that follow.

Example 1

The following procedure was used to prepare the matrix material of this invention:

A. To a primed surface of a polypropylene film was applied . , ₃ θ a thin layer of an adhesive. The polypropylene film was mils thick and had the following properties:

<td> Tensile Strength</td><td> MD* TD**</td><td> 6600psi 5900psi</td>

<td> Elongation (%)</td><td> MD</td><td> 850</td>

<td></td><td> TD</td><td> 900</td>

<td> Tensile Modulus</td><td> MD</td><td> 120,000psi</td>

<td></td><td> TD</td><td> 120,000psi</td>

<td> Tear Strength</td><td> MD</td><td> 40 g./mil</td>

<td></td><td> TD</td><td> 90 g./mil</td>

<td> Machine Direction</td><td></td><td></td>

•MO.

.· *TD — Transverse Direction

The adhesive that was applied to the polypropylene film was a dispersion of an acrylonitrile-butadiene copolymer in methyl isobutyl ketone. This adhesive had the following properties:

Viscosity (Brookfield Model LVF at 30 rpm, 180-250 cps.

No. 2 Spindle at 72° F.)

SolidsContent 20-24%

Specific Gravity 0.89-0.91

A coating machine equipped with gravure rollers was used to apply the adhesive and mayer rods were used to smooth the adhesive layer. The adhesive-coated polypropylene was passed through a two-zone drying chamber to remove the solvent from the adhesive and then cooled on a chiller roll.

B. A sheet of cellulosic material made up of short and long pulp stock fibers was impregnated with a general purpose, two-stage, mineral and woodflour filled phenol-formaldehyde resin. The amount of resin added to the cellulose sheet was about 50 percent of the amount that would completely saturate it. The phenolic resin impregnated cellulose base was then coated with a 20 percent solution of the same phenol-formaldehyde resin in ethanol. Automatic spray equipment was used to apply a uniform 10 to 12 mil coating of the phenolic resin to the impregnated cellulose base. The coated base was placed on a rack which was inserted into a circulating air oven at 190°F for 45 minutes to remove the ethanol. It was then placed on a platen heated at 295°F for 2 minutes to effect a partial cure of the phenolic resin, that is, to bring the phenolic resin to the “B” stage.

C. The adhesive-coated polypropylene film was brought into contact with the coated surface of the impregnated cellulose base and heated to form the novel matrix material. The polypropylene and base layers of the matrix material were formed into a lay-up or sandwich prior to heating. This lay-i was made up of the following consecutive layers:

1. Foundation blanket

2. Sponge rubber blanket

3. Foundation blanket

4. Nylon creeper molding blanket

5. Polypropylene film

6. Adhesive affixed to said polypropylene film

7. Phenolic resin coating on impregnated cellulosic base

8. Impregnated cellulosic base

9. Release paper

10. Steel pan

The lay-up was preheated for 2 minutes at 295°F. under 20 pounds per square inch pressure. Then in a cold molding press sufficient pressure was applied to it for 2 minutes to effect lamination. After cooling, the laminate was removed from the lay-up.

up

Example!

The following procedure was used to demonstrate the use of the matrix material of this invention in the preparation of polyester printing plates:

An original printing plate with no release coating was contacted with a matrix material prepared by the procedure of Example 1. The plate and matrix material were inserted into a hydraulic press and preheated at 290°F. for one minute under no pressure but with the platens closed. A pressure of 200-500 psi was applied for nine minutes. The plate and matrix were removed from the press. After cooling, the matrix was separated from the original plate.

The matrix was placed on the bottom platen of a hydraulic two platen press with both platens maintained at 180°F. A dam of putty was constructed around the perimeter of the matrix. A shim of sufficient thickness to form a polyester plate of the desired thickness was also placed around the perimeter of the matrix. A polyester resin containing a curing catalyst was poured into the dammed area. The tap platen was brought into contact with the shim and maintained at 180°F. for less than 15 minutes. The plate was cooled while it was in contact with the matrix, and it was then separated from the matrix. The resulting polyester printing plate had excellent printing characteristics in terms of fidelity, fine screen half tone dots, and printability.

The terms and expressions which have been employed are used as terms of description and not of limitation. There is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.