IE42528B1 - Improvements in or relating to transfer materials - Google Patents

Abstract

1477799 Transfer sheets CARIBONUM Ltd 5 March 1976 [26 March 1975] 12609/75 Heading D2B A transfer sheet comprises a base sheet provided with a layer of porous material containing an ink within its pores, said porous material comprising a mixture of at least one cellulose ester and one or more acrylic resins in a ratio of 6:1 to 1:6 by weight. The base sheet may be paper or a plastics film, e.g. a polyester or polypropylene film. The cellulose ester may be cellulose acetate butyrate, or cellulose acetate propionate. The acrylic resin may be a poly(methyl methacrylate), poly- (ethyl methacrylate), poly(n-butyl methacrylate) or a copolymer of methyl and n-butyl methacrylates. The base sheet may be coated with a layer comprising polyurethane before application of the transfer layer. The ink may contain a colourless colour former or pigment(s).

Description

This invention relates to transfer materials of the kind usually referred to as carbon paper and more particularly to the kind referred to as solvent coated carbon papers. Such solvent coated carbon papers consist of a base sheet to which is firmly bonded a layer of porous material and the pores of such material contain ink, which ink is squeezed out of the porous layer when pressure is exerted on it by a writing implement or a typewriter print face. Such solvent coated carbon papers are described for example in British Patent Specifications Nos. 392220, 780492 and 840673. In British Specification No, 392220 there is described a porous coating having as a major constituent one or more cellulose esters and in British Patent Specifications Nos. 780492 and 840673 there are described porous coatings having as a constituent a Vinyl polymer. Other constituents for the porous coatings have also been proposed including acrylic resins (particularly polymethyl. methacrylate resins).

It is well-known that transfer layers of solvent coated carbon papers, based on polymethyl methacrylate resins, are capable of producing copies of good intensity and yet are resistant to producing marks when subjected to non-imaging pressures, e.g., by passage through the rollers on a typewriter, even after the surface of the transfer layer has been broken through use.

Ktich transfer layers have two major defects however:i) the ink release characteristics are such that only a limited number of copies can be obtained before the copy intensity becomes unacceptably low or even uneven, ii) the ink containing resin layers have poor adhesion properties, particularly to bases of film material such as polyester or polypropylene.

It is also well known that solvent carbon systems based on cellulose acetate butyrate resins can yield layers which are particularly clean to handle, yet which give copies of good intensity whilst still retaining good use-life characteristics.

These layers also have drawbacks namelyχί) although resistance to roller-marking can be high when used only a limited number of times, this resistance is lost after extended use, ii) odour is a difficult problem to over-come, this being largely (although not entirely) a function of the free buytric acid contained in the C-Λ-Β resin, iii) the solvent carbon inks or dopes have unstable viscosity characteristics, showing a marked tendency to increase with age, necessitating high percentage additions of expensive solvents such as methyl ethyl ketone to reduce to a coatable viscosity.

It is an object of the present invention to provide an improved transfer material of the solvent coated carbon kind.

It is another object of the present invention to provide a solvent coated carbon paper capable of use in different applications.

According to the present invention a transfer material comprises a base sheet, a precoat layer, a layer of porous material and ink contained within the pores of 43538 the porous material wherein the porous material comprises a mixture of cellulose acetate butyrate and medium molecular weight polymethyl methacrylate resins in a ratio of 6:1 to 1:1 by weight. In particular it has now been found that the use of a mixture of cellulose acetate butyrate resin with medium molecular weight polymethyl methacrylate resin can reduce the problem of the single resin component systems to a very considerable degree. The particular ratio chosen is governed by the end-use application. For handwriting or roller imprint applications, a higher proportion of C-A-B resin is preferred, than for typewriter or other impact strockes.

It is found that having a ratio of 1 part C-A-B resin to 1 part methyl methacrylate resin by weight gives a coating useful for both handwriting and typing applications .

Transfer material in accordance with the present invention may be made according to the following example.

EXAMPLE.

A porous coating layer with colouring matter is formed from the following constituents: parts by weight Part 1 (colouring material).

Substantially non-drying vegetable oils or mixture of same (for example rapeseed, groundnut, castor oil 10.5 Vegetable lecithin 1.0 Raven 1255 carbon black 6.4 Reflx blue toning pigment 1.0 Di iso butyl phthalate 1.0 Tolene 6.4 2 5 2 8 Part 2 (porous coating).

Cellulose acetate buytrate resin (¾ sec) Elvacite (RTM 2009) (medium molecular weight poly methyl methacrylate resin (ex Du Pont) Methyl ethyl ketone Ethyl acetate 6.5 6.5 51.1 9.6 Part 1 above referred to is prepared by grinding the constituent parts in a pebble mill for 16 hours. The mill is unloaded.

Part 2 above referred to is prepared by adding the Elvaci te resin to the solvent whilst st irring and I lie mixture is stirred until the rosin is dissolved. The cellulose acetate butyrate is likewise dissolved in the solvent and this solution is then added to the Elvacite resin solution with stirring.

Part 1 is then added to Part 2 and stirred until mixed.

The mixture is then applied by any suitable web coating technique (for example the reverse roller and scraper techniques to paper or film such as polypropylene or polyester film), bearing a key coating based on polyurethane resin as is hereinafter described. The coating so produced was found to be suitable for both typewriter and pencil applications.

Furthermore other pigments or other colours may be included replacing part or all of the pigments referred to in the above examples. Similarly suitable colour formers may be used instead of the pigments to be used in conjunction with colour developing components (for example acidic or electron accepting compounds).

It is considered necessary to apply a precoat layer - 6 to the base sheet film. In such a case a precoat of the following formula may be applied:Precoat Formulae.

Daltosec RTM 1350 (ICI) moisture curing isocyanate resin (polyurethane) 24.0 Gasil RTM 937 (filler), (Joseph crosfield) 1.3 Dispercel chips 33/2019 (Columbia) (pigmented nitrocellulose chips) 6.0 Ethyl acetate (P grade) (solvent) 68.7 The precoat layer is then applied to the base material (paper or film) by gravure printing techniques.

If desired the dispercel chips may be replaced by PGHX 30-50 20% DBP (ICI) nitrocellulose chips in equal amounts.

Within this specification the term medium molecular weight refers to a molecular weight of 80,000 to 100,000.

Claims (3)

1. CLAIMS:1. Transfer material comprising a base sheet, a precoat layer, a layer of porous material and an ink contained within the pores of the porous material wherein 5 the porous material comprises a mixture of cellulose acetate buyI rate and medium molecular weight polymethyl methacrvlate in a ratio of 6:1 to 1:1 by weight.

2. Transfer material according to claim 1 wherein the ink comprises a colour former. 10

3. Transfer material according to Claim 1, substantially as herein described.