NO142083B - PROCEDURE FOR MANUFACTURING A DIFFERENTIALLY EXPANDED SHEET MATERIAL - Google Patents

Description

This invention relates to improvements in manufacturing

of sheet materials that have a relief effect. In particular, the present invention relates to the production of sheet materials by differentiated expansion of areas on a thermoplastic sheet.

The sheet material thus formed can be used as, for example, wall coverings, floor coverings, decorative laminates and transfer images.

Production of sheet materials that have a relief effect

by differentiated expansion of a thermoplastic sheet, the important advantage is that the use of relief printing rollers can be omitted during the manufacturing process. The effect of a relief printing roller is that it physically changes the surface character of the sheet material. A similar appearance can, however, be obtained by chemical means if selected areas of the sheet material are expanded to different degrees.

Expansion of a thermoplastic sheet can be effected by introducing a blowing agent into the sheet and heating the sheet to a temperature at which cleavage of the blowing agent takes place. The blowing agent is conveniently dispersed in the thermoplastic material before the sheet is formed in order to ensure good distribution of the blowing agent in the sheet. Differential expansion of the thermoplastic sheet can be achieved by means of a "kicker". "Kickers" are well known in the industry and their effect is that they lower the decomposition temperature of certain foaming agents. If a "kicker" is together with the blowing agent only in certain areas of the sheet, a reduction in the splitting temperature of the blowing agent is achieved only in these areas. Consequently, a greater degree of expansion will be obtained for the sheet areas that contain "kicker" than the sheet areas that do not contain "kicker",

when the sheet is heated to a given temperature for a suitable time.

Differential expansion of an expandable thermoplastic sheet material containing a blowing agent can be obtained by applying

lead a "kicker" only on certain areas of the surface of the sheet

before the sheet is heated to expand. Applying a "kicker" to the surface of the sheet provides attractive advantages since the sheet containing the blowing agent can be formed in one step and the need to incorporate a "kicker" into selected portions of the sheet-forming composition is eliminated. Furthermore, it prevents the use of complicated printing techniques that come with the application of selected printing colors on such areas of the sheet that contain "kickers",

due to the fact that the "kicker" can be applied together with the printing ink if desired. In reality, there is such difficulty in registering the "kicker" and ink when applied separately that in most cases they are applied together.

however, our experience is that when the "kicker" is applied together with the printing ink to the surface of an expandable thermoplastic sheet, the adhesion of the printing ink to the thermoplastic sheet will be insufficient during the subsequent processing of the sheet. Especially when multi-color printing is used, ink from one printing station has a tendency to peel off at a subsequent printing station or on a transfer roller. Also, the adhesion of the printing ink to the thermoplastic sheet must be sufficient to withstand the treatment between printing and expanding, which may or may not be aligned. If the adhesion of the printing ink is insufficient before the expansion of the thermoplastic sheet, it may occur that the printing ink is removed during the processing of the sheet material and that an inferior product is thus formed.

We have now found that the printing ink adhesion obtained in the manufacture of a differentiated expanded thermoplastic sheet can be significantly improved by applying a varnish containing a film-forming material and an organic solvent for the thermoplastic material to the surface of the sheet before the printing ink is applied. An advantage of applying a varnish is that with a coating the thermoplastic sheet can be treated with the organic solvent and with one or more additional agents present in the varnish, such as for example silicon dioxide or a silicate matting agent, a pigment or a metallic powder.

According to the present invention it is

therefore provided a method for producing a i

differentiated expanded sheet material, in which selected areas of a sheet of an expandable thermoplastic material containing a blowing agent are coated with a printing ink containing a "kicker" for the blowing agent, and the sheet is heated to a temperature at which the blowing agent in contact with the "kicker" is split so that they selected areas expand to a greater extent than the other areas of the sheet. The method is characterized by the fact that, in order to improve the adhesion of the printing ink to the sheet, the sheet is coated with a varnish containing a film-forming material and an organic solvent for the thermoplastic material, and the varnish is allowed to dry at least partially before applying the printing ink.

Satisfactory expansion through the full depth of the sheet is dependent on the "kicker" migrating through the depth of the sheet. Consequently, application of the varnish before the application of the "kicker" can be thought to provide a further physical . obstacle to the desired migration to the "kicker". But it is a further and unexpected advantage of the method according to the invention that the improvement of ink adhesion can be obtained without any significant reduction in the quality of the relief effect.

It is believed that the treatment of the sheet surface with the varnish causes some etching of the surface and therefore provides improved adhesion of the printing ink to the sheet and that the presence of the solvent facilitates the migration of the subsequently applied "kicker" into the depth of the thermoplastic sheet. The varnish can be applied over the entire surface of the sheet or only on such areas which will later be printed with printing colors containing the "kicker".

The method according to the invention is particularly valuable in the production of wall coverings since it thermo5? plastic sheet material can be formed as a sheet without backing or as a coating on paper, a non-woven synthetic fiber web, a spun bonded web or other suitable base material. Differential expansion of the thermoplastic material results in the formation of a sheet having a visually attractive appearance that is well suited for decorating a wall or a ceiling. However, the method according to the invention is not limited to the production of wall coverings and the sheet materials can also be used as yellow v-coverings, decorative laminates, decorated adhesive labels and transfer images. When producing floor coverings, the thermoplastic sheet will usually be formed on a relatively solid base material which can be a suitable plastic material, a folded sheet or a woven or knitted textile formed for example from natural or synthetic fibres.

The thermoplastic sheet can be made from any

preferably any suitable expandable synthetic resin material. Pre-

drawn materials include polymers of vinyl chloride or copolymers of vinyl chloride and another copolymerizable monomer such

such as vinyl acetate or an acrylic or methacrylic monomer such as an ester of acrylic or methacrylic acid or acrylic or methacrylic

acid itself. The expandable sheet can be formed from a plastisol, in which case the thermoplastic polymer or copolymer will be mixed with a blowing agent, a stabilizer which has regulated catalytic action on the blowing agent under the selected processing conditions, a plasticizer which can be any of the usual phthalate compounds, and pigments or extenders. The plastisol may be formed into a sheet in any suitable manner and may for example be applied to a base fabric of paper or a similar substance as discussed above, the weight of the plastisol being for example from 40 to 800 g/m<2>.

The exact choice of foaming agent will depend on the specific

or thermoplastic material used, and its decomposition temperature in the presence of the "kicker" should be appropriate for the thermoplastic material. Espressants are well known and have been

written in the literature. Suitable agents include azobis-

formamide and azobis-isobutyronitrile. The blowing agent can conveniently be present in the thermoplastic sheet in amounts of up to 15% by weight,

for example 1 to 15% by weight, preferably from 3 to 9% by weight, based on the weight of the expandable synthetic resin material.

An alternative technique for use in manufacturing

of the expandable thermoplastic sheet, is hot melt coating.

This technique can be used on a large number of materials such as polyethylene, polyvinyl chloride, polyester and acrylic polymers.

Since the function of the solvent in the varnish appears

to be, in part, to etch the sheet surface, the solvent should be chosen in accordance with the nature of the thermoplastic material. Thus, when it comes to expandable thermo-

'plastic sheets based on polymers of vinyl chloride or copolymers of vinyl chloride and other copolymerizable monomers, we prefer the organic solvent to be polar since such solvents usually have a greater affinity for the thermoplastic material than non-polar solvents.

Suitable solvents for application to the thermoplastic sheet include hydroxyl compounds, for example mono and polyhydric alcohols, aliphatic and alicyclic ethers such as tetrahydrofuran, esters such as ethyl acetate or isopropyl acetate, glycol ethers, glycol esters such as 2- ethoxyethyl acetate, aliphatic and alicyclic ketones such as methyl ethyl ketone, methyl isobutyl ketone or cyclohexanone, halogenated hydrocarbons and especially chlorinated aliphatic hydrocarbons, nitro compounds such as nitropropane or nitrobenzene, and Lewis bases such as substituted amides, for example dimethylformamide and dimethylacetamide, and di (lower alkyl)sulfoxides, for example dimethylsulfoxide.

In certain cases, there may be advantages associated with the use of strongly polar solvents and in such cases it may be desirable to use the selected solvent together with a less polar or non-polar solvent. The latter material serves as a diluent for the polar solvent and may suitably be a hydrocarbon such as toluene, xylene or methylated spirit.

In the particular case that the thermoplastic sheet is formed from vinyl chloride homopolymers or copolymers, we have found aliphatic ketones such as methyl ethyl ketone and aromatic hydrocarbons such as toluene or xylene to be advantageous solvents to use.

The amount of application of the selected solvent on the expandable thermoplastic sheet will depend on the application method used. An <p>application amount of from 10 to 700 g/m<2>, especially from 30 to 500 g/m<2>, which gives satisfactory results, is preferred. In the particular case where the varnish is applied by gravure printing, the amount of application can be from 25 to 300 g/m 2 , preferably from 50 to 150 g/m 2 .

As indicated above, the chosen solvent is applied as the solvent phase in a varnish. The use of a varnish is a convenient way to treat the surface of the thermoplastic material with an additional component such as a matting agent or pigment. The heat treatment in the expansion step can produce a shiny surface on the resulting sheet and it may be desirable to introduce a matting agent to reduce this effect. The varnish can contain as film-forming material any suitable resin such as a polymer or copolymer of ethylenically unsaturated monomers, for example vinyl and/or acrylic or methacrylic monomers. Other suitable film-forming materials for the lacquer include polyurethanes, polyesters and epoxy resins.

The varnish can be applied by any of the well-known methods

techniques such as engraving, roller coating, screen printing or flexographic printing and since these methods can also be used to apply the mixture containing a "kicker", the whole technique is easily suitable for an industrial operation on a line.

We particularly prefer to use gravure rollers when applying a varnish to the surface of the thermoplastic sheet. The gravure rollers are preferably engraved with 80 to 200 lines per

25.4 mm.

The "kicker" mix may include the selected "kicker"

as a solution or suspension in a printing ink. The mixture will thus typically include the "kicker" in mixture with a pigment, binder and dispersed phase. The "kicker" will usually be a compound of zinc, cadmium or lead, and it will suitably be a salt of zinc, cadmium or lead although other compounds of the selected metals, such as zinc oxide, may be used. Zinc, cadmium or lead salts can be prepared from inorganics

or organic acids. Inorganic acids that can be used in the salt formation include hydrochloric acid and nitric acid, while suitable organic acids include carbonic acid, oxalic acid, acetic acid, lactic acid, citric acid, formic acid, sebacic acid, octanoic acid, stearic acid, phthalic acid and benzoic acid. The ink mixture will conveniently contain up to 25% by weight of the "kicker", preferably from 5 to 20% by weight. A convenient "kicker" to use is zinc octoate.

The solvent for the printing ink can be any

preferably of the usual solvents for printing inks that are used in the production of printed wall coverings. Thus, for example, ketones, such as methyl ethyl ketone, esters, such as 2-ethoxy-ethyl acetate, nitro compounds> such as nitropropane, and hydrocarbons, such as toluene, can be advantageously used. The pigment content of the ink will vary according to the particular pigment selected, however, effective results will usually be obtained with ink mixtures containing up to 20% by weight, preferably 5-15% by weight.

with pigment.

The composition of the "kicker" mixture will depend

the specific way in which the ink is to be printed on the treated sheet material. However, the "kicker" mixture can be applied with equal advantage by printing using any of the conventional techniques, such as those listed above, for applying the varnish.

As mentioned above, the expandable thermoplastic sheet is preferably formed from a plastisol, and when it comes to such sheet materials, the degree of gelation of the expandable sheet material at the time the organic solvent and "kicker" is applied is of great importance. If the degree of gel formation is therefore too low, the surface character of the sheet will be destroyed during the application of the solvent, especially if such an application results in the sheet being passed through the clamp on pressure rollers. If, on the other hand, the degree of gel formation is too great, it will be difficult to achieve satisfactory expansion of the sheet. Satisfactory gel formation of the sheet can be obtained by heating to 110-140°C for a relatively short period of time. A few minutes of heating at low temperatures is usually sufficient, while heating for less than one minute may be appropriate at higher temperatures.

The expansion of the printed thermoplastic sheets can take place by on-line operation after the printing step. Alternatively, the printed sheets can be stacked as sheets or be wound up on a spool and then expanded. In the latter case, there may be a tendency for the "kicker" to migrate from one sheet into an adjacent stacked or wound sheet and cause unwanted expansion in areas of these adjacent sheets.

The thermoplastic sheet can be provided with a coating impermeable to the "kicker" after the printing step to avoid this problem, and the impermeable layer can be applied either to the back or to the front of the sheet before it is stacked or wound up. The layer is preferably applied as a transparent varnish to the top side of the printed sheet after the final printing step. It is preferred to apply the impervious layer on the top side since such a coating, in addition to providing a barrier to migration of the "kicker", can serve as a wear layer to protect the sheet in use. Also, applying a varnish in a final step after printing can provide a convenient way to introduce an additional agent

the surface of the sheet, such as a matting agent1.

If desired, the sheet material obtained in the process can

the method according to the invention, is provided with a coating of an adhesive on the side to be applied to the substrate. When it particularly concerns wall coatings, for example, the side of the sheet material to be applied to the wall or ceiling can be provided with a coating of a water-activatable adhesive. The adhesive coating can be provided at any point in the production of the sheet material.

When it comes to water-activatable adhesives, the coating can be applied as an aqueous solution, dispersion or emulsion to the surface of the sheet and then dried. The adhesive can be applied in an amount of 2 to 30 grams/square meter of the surface,

and the adhesive may be a natural or synthetic resin material, a vegetable gum, a soluble starch or starch ether or other suitable material.

It may be preferred to introduce other ingredients into the adhesive coating, such as, for example, surfactants to improve the water absorption properties of the adhesive coating and fungicides to prevent mold growth.

The method according to the invention can be used

in the production of sheet materials that have very diverse effects. Thus, for example, two or more applications of a "kicker" mixture can be carried out on different areas of the surface of the sheet after the treatment with a solvent. Different pigments can be used in the different "kicker" mixtures, which can also contain different concentrations of "kicker". After expanding such a sheet, a product is formed in which a multiplicity of varying expansions has been obtained and this gives a product which has a pleasing decorative effect.

In order for the invention to be well understood, the production of

a sheet material according to a preferred embodiment according to the invention be described for illustrative purposes with reference

ning to the accompanying drawings.

Figure 1 of the drawings illustrates a method to produce? line up a sheet material according to the invention. Figure 2 is an enlarged partial longitudinal section of an expandable thermoplastic sheet.

Figure 3 is a section of the sheet shown in Figure 2, as carrier

a varnish coating.

Figure 4 is a section of the sheet shown in Figure 3, after application of a printing color to the treated surface. Figure 5 is a section of the sheet shown in Figure 4, after expansion.

It should be understood that Figures 1-5 are purely schematic, and

no attempt has been made to show the relative thickness of the different layers of which the sheet material is composed.

An expandable thermoplastic layer 1 is, like a plastisol, applied to: a sheet of suitable paper 2 and is partially gelatinized in the oven 12 to produce a sheet material as shown in figure 2.

The thus formed sheet material is brought to the clamp between a

pair of rollers 6, as shown in figure 1, and receives a varnish coating 3

from a bath 7, after which it is partially dried in the oven 11 to produce a varnished sheet as shown in figure 3. The varnish contains a dispersion of a matting agent in a solution of a vinyl chloride homo- or copolymer in an organic solvent which has affinity for the thermoplastic sheet. Suitable varnishes are described more fully in Examples 1 and 2 below.

The varnished sheet then continues until the clamp between a pair of conventional printing rollers 8 and printing ink from bath 9 is applied only to certain areas of the varnished surface of the sheet. The ink contains a pigment and a "kicker" suitable for the blowing agent present in the thermoplastic layer 1, and compositions of such inks are described more fully in Examples 1 and 2 below. The sheet material then has an appearance as shown in Figure 4, and has a number of separate areas 4 coated with "kicker"-containing printing ink.

The printed sheet shown in Figure 4 is then taken to an oven 10 where the sheet reaches a temperature that lies between the cleavage temperature of the blowing agent and a mixture of the blowing agent and the "kicker". Differential expansion is thereby obtained to form a product, as shown in Figure 5, in which such parts of the sheet which have been applied with "kicker" ink are expanded to a greater extent than such parts of the sheet which have not been applied with any such coating. The resulting sheet material is visually attractive and can be used as a wall covering.

In order for the invention to be further understood, the following examples are given to illustrate it. Parts mentioned in the examples mean parts by weight.

Example 1

(a) Preparation of expandable thermoplastic sheet

was applied using a doctor knife with a thickness of

0.2 mm and a dried weight of 190 g/m 2 down on paper of 90 g/m 2 . The coating was gelatinized at a temperature of 120-130°C for 60 seconds to give an expandable thermoplastic sheet.

(b) Treatment of expandable sheet with varnish

A varnish was prepared by dispersing the following composition:

The viscosity of the varnish was adjusted to 30 seconds by the addition of methyl ethyl ketone (measured on Ford cup No. 4) and the varnish was then applied to the surface of the gelatinized polyvinyl chloride sheet prepared under (a) using gravure rollers engraved with 55 lines per . linear centimeter (140 lines per linear inch). After partial drying, the following ink mixture was applied to the treated sheet:

If necessary, the viscosity of the ink was adjusted to 30 seconds (measured on Ford cup No. 4) by the addition of methyl ethyl ketone. The printing ink was applied in a selected pattern using gravure rollers engraved with 47 lines per line. linear centimeter (120 lines per linear inch) and was blown out at 200°C for one minute after an interval of 20 hours.

The product obtained had an expansion in the ink-treated areas of more than 0.305 mm in relation to the non-printed areas and had a satisfactory degree of dullness, which together gave the material a visually attractive appearance. In addition, the product had good ink adhesion.

Example 2

A varnish was prepared by dispersing the following mixture:

By adding methyl ethyl ketone, the viscosity of the varnish was adjusted to 30 seconds (measured on Ford cup no. 4) and the varnish was then applied to the surface of a thermoplastic sheet prepared as described in example 1 (a). The application was carried out using gravure rollers with 39 lines per linear centimeter (100 lines per linear inch), and then the following ink mixture was applied to the treated sheet:

If necessary, the viscosity of the printing ink was adjusted

to 30 seconds (measured on Ford cup No. 4) by addition of methyl ethyl ketone. The printing ink was applied in a selected pattern using gravure rollers engraved with 59 lines per linear centimeter (150 lines per linear inch) and was blown out for 1 minute after an interval of 7 days.

The product obtained had an expansion in the ink-treated areas of more than 0.381 mm in relation to the non-printed areas, and had a satisfactory degree of dullness. The material was visually attractive and the ink adhesion to the product was good.

Examples 3-16

The sheet materials in these examples were produced in an analogous manner to that described in examples 1 and 2. Examples 3-16 illustrate the application of the invention when different expandable thermoplastic materials, solvents and "kickers" are used in the method according to the invention.

(a) Preparation of expandable thermoplastic sheets A and B

The following mixtures were applied by means of a doctor knife with a thickness of o 0.13 mm and a dried weight of 180 g/m 2 onto o paper of 90 g/m 2 . "

The coatings were gelatinized at 120°C for 60 seconds.

(b) Treatment of sheets A and B with varnish

The following varnishes were produced for

processing of sheets A and B.

The varnish was applied to the gelati-

ner te sheets A and B using engraving rollers engraved with 5 9 lines per linear centimeter (150 lines per linear inch). After partial drying, the following ink mixtures were applied to the treated sheets:

All printing inks were applied with a viscosity of 25 seconds (measured on Ford cup no. 4) and the viscosities were adjusted if necessary by adding methyl ethyl ketone. The printing colors were applied using gravure rollers engraved with 59 lines per linear centimeter (150 lines per linear inch) and be blown out at 200°C for one minute after an interval of 24 hours.

The examples and properties of the resulting expanded sheets are set forth in the following table. (1) Contrast is a measure of the difference in expansion in the ink-treated areas compared to the non-printed areas.

The products obtained in Examples 2, 4, 7, 8 and 11 were matte.

Claims (8)

1. Method for the production of a differentiated expanded sheet material, in which selected areas of a sheet of an expandable thermoplastic material containing a blowing agent are coated with a printing ink containing a "kicker" for the blowing agent, and the sheet is heated to a temperature at which the blowing agent in contact with the "kicker" splits so that the selected areas expand to a greater extent than the other areas of the sheet, characterized in that in order to improve the adhesion of the printing ink to the sheet, the sheet is coated with a varnish containing a film-forming material and an organic solvent for the thermoplastic material, and the varnish is allowed to dry at least partially before applying the printing ink. 2. Method according to claim 1, characterized in that the sheet is coated with a varnish containing as organic solvent an aliphatic or alicyclic ether, an ester, an aliphatic or alicyclic ketone or a nitro compound. 3. Method according to claim 2, characterized in that the sheet is coated with a varnish containing methyl ethyl ketone as an organic solvent. 4. Method according to claim 2, characterized in that the sheet is coated with a varnish containing as organic solvent a glycol ester, such as an etherified monoester of glycol. 5. Method according to any of the preceding claims, characterized in that the sheet is coated with a varnish containing as organic solvent a mixture of a polar solvent and a non-polar solvent. 6. Method according to claim 5, characterized in that the sheet is coated with a varnish containing toluene or xylene as a non-polar solvent. 7. Method according to any of the preceding claims, characterized in that the sheet is coated with the varnish in such an amount that the amount of the organic solvent is from 10 to 700 g/m 2 . 8. Method according to claim 7, characterized in that the sheet is coated with a varnish containing a matting agent.