WO2004096569A2

WO2004096569A2 - Manufacture of gravure printing rollers

Info

Publication number: WO2004096569A2
Application number: PCT/GB2004/001880
Authority: WO
Inventors: Charles Jeremy Franklin; Lister Charles Cumming; Peter John Williams
Original assignee: Hyperlast Limited
Priority date: 2003-05-02
Filing date: 2004-04-30
Publication date: 2004-11-11
Also published as: WO2004096569A3; GB2417711A; GB0523844D0; GB2417711B

Abstract

A gravure printing roller is manufactured by mounting a core (10), of steel, cardboard or plastics material for rotation, and moving a dispensing head (11) relatively to the core (10) to build up a body (14) of a polyurethane material on the core, and then machining the body (14) to accord with a required diameter. The mixing head combines at least two components of a syntactic or non-syntactic polyurethane immediately before application to the core, and fast reacting amines may be used to produce a gel-like intermediate to aid retention on the core, before complete curing of the polyurethane takes place in the body (14).

Description

MANUFACTURE OF GRAVURE PRINTING ROLLERS

This invention relates to the manufacture of gravure printing rollers. In WO 00/59727 we describe improved gravure printing rollers

comprising a body or shell moulded from syntactic compositions comprising

microbeads of a plastic glass or ceramic material in an e.g. polyurethane

matrix. The shell is moulded to an approximate size and then machined to the exact size required and a copper coating is deposited on the machined

surface and chrome treated. An electrically conductive coating of a

conductive agent such as finely divided metal is however first deposited on

the machined surface. The body or shell is provided on a tubular core which

can be adapted for mounting in a printing machine.

This method of preparation enables gravure printing rollers to be

produced by moulding in a number of stock sizes which are then adapted to

the customers needs by machining the moulded shell. In practice this means "fine tuning" by shaving off a few millimetres of thickness to ensure a

perfectly smooth cylindrical surface without moulding flaws, and then

preparing the printing surface. Thus it is necessary, as with the general practise of the gravure printing industry using steel rollers, to hold large

stocks of rollers to satisfy the many variations in length and diameter which

are required. This requires considerable space, and ties up a considerable

amount of capital.

Using steel rollers, or the moulded rollers described above, a new set

of rollers is required whenever a different diameter is specified and it is not economic to satisfy one off or bespoke orders for non-standard lengths and /

or diameters. Any requirement for rollers according to a new specification

takes several days to satisfy as the manufacture of a steel roller is a slow

process, and to produce moulded rollers, the mould must first be constructed and machined.

It is an object of the invention therefore, to provide a method for the

manufacture of gravure printing rollers which will enable such rollers to be

manufactured economically to any required dimensions of length and

diameter, including non-standard sizes, and thus enable differing

requirements to be met quickly.

According to the invention there is provided a method for the

manufacture of gravure printing rollers comprising rotating a core, applying a polyurethane material to the core from a dispensing head, moving the core

< and the dispensing head relative to one another in the direction of the

longitudinal axis of the core to apply said material to the core along a selected part of the length of the core, in one or more passes to build up a

body of said material on said core to a selected thickness, and machining the

body thus produced to a selected diameter.

A variety of materials may be used in producing the core, which is preferably of steel, but could for example be of any other suitable metal, or

of any of a range of synthetic plastics and other synthetic materials such as

high density polyethylene, polypropylene or other synthetic materials such as

high density .polyethylene, polypropylene or other polyalkene, polycarbonate, rigid expanded or unexpended polyurethane, PVC, glass, reinforced plastics,

timber, cardboard, or indeed any other material which has a rigidity or other

properties necessary to support a roll in a printing machine.

The core may be tubular or solid without any central bore or passage and in the latter case the end trunnions used for mounting the roll in a machine may be formed integrally with the core.

One embodiment of roll may for example comprise a core formed from

a cardboard tube with a low density syntactic polyurethane sheath formed

therein by the method of the invention to form a light-weight roller.

The surface of the body is then preferably treated to apply a chrome

treated copper printing layer, and this may include the steps of rendering the

surface of the polyurethane body conductive by either an electrochemical

process or application of a conductive coating to the surface, followed by

electro-deposition of copper on the conductive surface or coating, engraving

and chrome treating. The steel core may or may not have been used

previously as a printing roller.

The polyurethane material may be a syntactic polyurethane as defined below, or may be non-syntactic - e.g. a homogenous solid, non-expanded

material. It is however possible that dense cellular (partly expanded)

materials could be used.

For the purpose of this description, a syntactic polyurethane is defined

as being a matrix of polyurethane polymer including pre-formed hollow beads or microbeads providing discrete bubbles. Such a composition is capable of providing a uniform cellular construction of homogenous and consistent

density which can be machined without leaving a porous or void containing surface.

The syntactic polyurethane composition may preferably comprise

preformed plastic beadlets each comprising an individual shell surrounding an

interior void and bonded in a matrix of a polyurethane composition. The beadlets may be of sizes in the range of 10 - 1 50 microns weight average

diameter. Alternatively the hollow beadlets may be of polymers such as

polyurethane, PVDC or glass or a ceramic material.

Non-syntactic polyurethanes may be high or low density as desired.

The material of the polyurethane matrix may as is usual be formed by

mixing an isocyanate component, containing one or more diisocyanates, and

a polyo! component including one or more polyesters and / or polyols.

The mixture is preferably formed by mixing immediately before

application in the dispensing head of the isocyanate and polyol components,

and the polyol component preferably contains fast-reacting compounds.

These may comprise one or more primary, secondary or hindered amines which react rapidly with the diisocyanate(s) in the other component to

produce a partially gelled material with sufficient viscosity to stay on the rotating roller. Further reactions of the remaining compounds in the polyol

component (typical hydroxyl group bearing molecules) with the remaining

isocyanates then produces the fully cured matrix encapsulating the beadlets to forrri the syntactic polyurethane material. In a variant, the fast reacting amine or amine mixture may be added as

a third component. This may be necessary when the microspheres, which

are preferably contained in the polyol component are made from a plastic

which is unstable in the presence of amines. This may be carried out using a three-component mixing and dispensing machine. A further advantage of

this variant is that the amount of amine component can be varied which

could be of advantage if the flow characteristics need to be slightly altered

for instance to accommodate variations between large diameter and small

diameter substrates.

The polyurethane used in the composition can be manufactured from a range of ingredients. For example, polyether or polyester polyols

may be used, with any of the common isocyanates, including methylene

dipheny! diisocyanate (MD!), toluene diisocyanate (TDI), naphthalene

diisocyanate, tetramethyl xylidene diisocyanate, isophorone diisocyanate,

phenylene diisocyanate, cyclohexyl diisocyanate, xylidene diisocyanate, hexamethylene diisocyanate, as well as biuret, allophanate and

prepolymeric adducts of these. Diol, triol, polyol or polyamine crosslinkers

may be used, together with amine or metal catalysts. Additionally reactive

amines may be used, together with amine or metal catalysts. Additionally

reactive amines may be incorporated to provide the initial viscosity to

provide "non-slumping" characteristics which are important for the rotational casting process. These amines may be aliphatic, aromatic or

hindered polyamines. The preparation of the gravure printing roller may be

completed by coating the machined surface of the body with a conductive coating, for example by depositing a layer of chrome treated copper on

the machined surface to provide a printing face.

The invention also provides a gravure printing roller made by the

method according to the invention, and apparatus for carrying out the

method according to the invention including a dispensing head capable of

mixing two or more components to produce a single output, means for

holding a core and for rotating the core, and means for moving the

dispensing head and the core relatively to each other in the axial direction of

the core.

The apparatus may include adjustable means for limiting the relative

movement of the dispenser head and the core, to thereby define the length

of the roller to be produced, and preferably also further adjustable means for

radial movement of the head to enable rolls of pre-set diameters to be

produced.

A preferred method and apparatus, and gravure printing roller

produced thereby according to the invention will now be further described by

way of example, with reference to the accompanying drawings, wherein:-

Fig. 1 is a diagram illustrating apparatus for carrying out the method of

the invention;

Fig. 2. shows a cross-section showing application of polyurethane

syntactic material, to a core; Fig. 3 is a view similar to Fig. 2 showing a machining step,

Fig. 4 is a diagram, much magnified, of a syntactic polyurethane

material used on the method of the invention;

Fig. 5 is an axial sectional view of a variant embodiment of roll

produced according to the invention, and

Fig. 6 is a similar view of a second variant of roll.

In a method according to the invention a gravure printing roller is

formed by building up a body of syntactic polymeric material on a tubular

steel core 10. The material is dispensed from a mixing and dispensing head

1 1 which is mounted on a carriage 12 to be moved along a rail 1 3 between limit switches MS-1 and MS-2 which are adjustable in position along the rail

1 3 to alter the length of the core 10 which is covered with material to build

up a roll body 14. the head 1 1 is movable radially to and from the core 1 0

on guides 1 5 which may include an adjustable limit switch (not shown) to

limit outward travel to thereby set a (variable) diameter for the body 14 built

up in the core 1 0.

An isocyanate component may be fed to the head 1 1 by a line A, and

a polyol component may be fed to the head 1 1 by a line B each controlled

by a flow control valve to finely control the relative proportions of the

components. A third component comprising a fast-reacting amine component may if required be fed by a third line C shown in broken lines. If

no separate amine component is supplied, the rapid reacting amines may be

added to the polyol component fed through line B. This component will normally contain microspheres for inclusion in the syntactic polyurethane

material.

As suggested by Fig. 2, the body 14 of the polyurethane material may

be built up on the core 10 over two or more rotations to build up the body to

the required diameter, at the same time the dispensing head being moved

back and forth along the core 10.

The core 10 is mounted on trunnions 1 5, mounted on bearings in a

frame 16, and one incorporating a clutch connected to a drive motor 1 .

After building up the body 1 , the surface is machined e.g. using a

blade such as 1 8, to exactly the required diameter.

Fig. 4 shows diagrammatically the structure of a syntactic polymer

such as used in the body 14. The polymer comprises a matrix 20 of a

polyurethane material formulated according to the properties desired, and

encapsulates a multitude of hollow microspheres or beadlets 21 , each

comprising a shell and an interior void. These microspheres can be of

polyurethane or PVDC, but can be of glass, ceramic or another polymeric

material.

After machining, the surface of the roll produced is treated to render it

conductive by an electrochemical process or application of a conductive coating, then copper is electro-deposited thereon engraved and chrome

treated.

The roller is then ready for processing for use as a gravure printing

roller in the known manner. Two variant embodiments of roll produced by the inventions are

shown in Figs. 5 and 6.

In Fig. 5, a solid high density polyurethane core 30 is provided with a

syntactic polyurethane sheath 31 by the method disclosed above. The core

30 has integral trunnions 32 for mounting the roll in a printing machine.

Fig. 6 however shows a tubular core 40 of cardboard, with low-

density polyethylene end plugs 41 with trunnions, 42. The core .40 is

provided with a low-density syntactic polyurethane sheath 43 which

incorporates hollow glass microspheres.

Where a metal core is used this may be of metal other than steel, or

example aluminium alloy tube where a light-weight roll is required, and the

interior of the core may be packed with material of higher specific gravity,

such as iead, where a high pressure roll is required.

The materials used may be as set out above, and variations to the

apparatus may be made within the scope of the invention, particularly with regard to the way in which the core is mounted and rotated, the dispenser

mounted and traversed and fed with the components of the material, and

provision made for varying the dimensions of rollers which can be made.

This latter capability means that the apparatus may ^"be quickly set up

to produce rollers of different length and / or diameter between batches, and

short runs and one off production contemplated together with production of

non-standard, bespoke unique examples.

Claims

1 . A method for the manufacture of gravure printing rollers

comprising rotating a core ( 0) applying a polyurethane

material to the core ( 10) from a dispensing head ( 1 1 ),

moving the core ( 10) and dispensing head ( 1 1 ) relative to one another in the direction of the longitudinal axis of the

core (10) to apply said material to the core ( 10) along a

selected part of the length of the core, in one or more

passes, to build up a body ( 14) of said material on said

core (10) to a selected thickness and machining the body

( 14) thus produced to a selected diameter.

2. A method according to claim 1 , wherein the polyurethane

material comprises a syntactic polyurethane as defined hereinbefore.

3. A method according to claim 2 wherein the syntactic

polyurethane composition comprises preformed plastic

beadlets each comprising an individual shell surrounding

an interior void and bonded in a matrix of a polyurethane composition.

4. A method according to claim 1 wherein the polyurethane material comprises a non-syntactic polyurethane material.

5. A method according to claim 4 wherein the non-syntactic polyurethane material comprises a homogenous solid non- expanded material.

6. A method according to any preceding claim wherein the

polyurethane is formed by mixing an isocyanate

component and a polyol component immediately before

application in the dispensing head, the polyol component containing fast reacting compounds.

7. A method according to claim 6 wherein the fast reacting

compounds comprise one or more primary, secondary or

hindered amines which react rapidly with the isocyanate

component to produce a partially gelled material with

sufficient viscosity to stay on the rotating roller.

8. A method according to claim 7 comprising further reacting

hydroxy! group bearing molecules in the polyol component

with remaining isocyanates to fully cure the polyurethane

material.

9. A method according to claim 6, 7 or 8 wherein the fast

reacting compounds are added as a third component.

1 0. A method according to any preceding claim wherein the machined surface of the body is coated with a conductive

coating.

1 1 . A method according to claim 9 wherein the conductive

coating is applied by depositing a layer of chrome treated

copper on the machined surface to provide a printing face.

2. A gravure printing roller made by a method according to

any of claims 1 to 1 1 , comprising a core ( 10) having a

body (14) therein built up by moving the core (10) relative

to a dispensing head (14), of a polyurethane material.

3. Apparatus for carrying out a method according to any of

claims 1 to 1 1 including a dispensing head capable of mixing two or more components to produce a single

output, means for holding a core and for rotating the core, and means for moving the dispensing head and core

relatively to each other in the axial direction of the core.