Field of the invention

The invention relates to a mixture which offers a wide range of possible applications where opacity is desired, to a method for producing said mixture, to the use of said mixture as an opacifier or substitute material in opacifying compositions, as a surface coating material, and to laminates or coatings comprising said mixture as a component.

Background of the invention

In the state of the art, Ti0 ₂ is disclosed as a preferred opacifying agent due to its superior refraction index (Rutile Ti0 ₂ Rl 2.73, Anatase Ti0 ₂ Rl 2.55, calcium carbonate CaCC>3 Rl 1.63). According to the state of the art, the performance of Ti0 ₂ can be improved by reducing agglomeration of the Ti0 ₂ particles, for example by a physical spacing effect. Ti0 ₂ is used in paints, plastics, paper and laminates to provide high opacity white surfaces, as well as non-white surfaces when combined with other pigments or dyes to provide a desired colour. The availability and cost of Ti0 ₂ can be a significant factor in the manufacture of intermediate products such as paint and paper which has led to the development and industrial use of products that, while less efficient in providing opacity, are used as extenders for Ti0 ₂ to lower the cost and improve effectiveness of Ti0 ₂ . Examples are mineral extenders such as kaolin, synthetic extenders such as Evoque™ and Ropaque™(Dow Chemical Company), as well as Ti0 ₂ particles with a thicker protective coating Ti-Pure™ Select TS-6300 (Chemours).

Currently Ti0 ₂ (EC No. 236-675-5 CAS No. 13463-67-7) is suspected to be carcinogenic (Cat 2) by inhalation, the new ECHA classification being applied from 1.10.2021.

Patent WO2012/065230 describes the use of melamine cyanurate (MC) in an amount effective to provide or enhance opacity in the manufacture of decorative laminates. In the manufacture of decorative laminates, such as compact laminates, high pressure laminates (HPL), continuous pressure laminates (CPL) and low pressure laminates (LPL also referred to as DPL or LPM) the thermosetting resin component contains one or more of a formaldehyde based resin such as urea formaldehyde (UF), melamine formaldehyde (MF) or phenol formaldehyde (PF), or mixtures of these resin types, for example UF + M, or UF + MF. Laminates based on pre-impregnated d^cor paper where the impregnation is applied on the paper making machine predominately use non- formaldehyde containing resins.

Formaldehyde (EC No. 200-001-8) (CAS No. 50-00-0) is classified by the European Chemicals Agency ECHA as a category 1B carcinogen, and among other classifications, as category 1 skin sensitiser. A reduction in the amount of formaldehyde used in the manufacture of decorative laminates offers the potential to improve occupation health and safety, as well as addressing consumer and post consumer concerns about products that contain formaldehyde.

Summary of the invention

In a first aspect, the invention relates to a mixture comprising styrene maleic anhydride copolymer a ic acid, cyanuric acid, and melamine.

Styrene maleic anhydride copolymer is available as a solid material (example: Polyscope XIFtAN® grade SZ40005, 40% maleic anhydride and 5000 Mw). Styrene maleic anhydride copolymers are available with various maleic anhydride contents, various molecular weights and in solution at various solid contents. Through a known process styrene maleic anhydride copolymer can be solubilized in water by reaction with ammonia to form the styrene maleic anhydride copolymer amic acid, as shown in the following:

The styrene maleic anhydride copolymer used to produce the styrene maleic anhydride copolymer amic acid has preferably a maleic anhydride content in the range of 25 to 65 % by weight, more preferably in the range of 35 to 50 % by weight. The molecular weight of the styrene maleic anhydride copolymer used to produce the styrene maleic anhydride copolymer amic acid used in one version of the inventive mixture is preferably in the range of 3500 to 10000. According to the present invention the styrene maleic anhydride copolymer amic acid can be used with various solid contents and in with various viscosities. As an example, Polyscope XIRAN® grade SL40005 N30 amic acid is 40% maleic anhydride, 5000 Mw and 30% solids. According to the invention, the solid content refers to the amount of styrene maleic anhydride copolymer amic acid in the aqueous solution, meaning if the water were evaporated from 100g of a 30% solids styrene maleic anhydride copolymer amic acid solution there would be 30g of the styrene maleic anhydride copolymer amic acid remaining.

As used herein, the term "cyanuric acid'' refers to 1 ,3,5-Triazinane-2,4,6-trione, which is also known as isocyanuric acid, having the molecular formula C ₃ H ₃ N ₃ O ₃ or C ₃ N ₃ (OH) ₃ and CAS No.108-80-5.

Melamine is an organic compound with a preferred lUPAC name 1 ,3,5-Triazine-2,4,6- triamine and CAS No. 108-78-1. In one exemplary application melamine is used as starting material for the production of melamine formaldehyde resins. Melamine formldehyde resins cured under heat and pressure provide a clear, chemical resistant surface to a laminate surface. The mixture may comprise styrene maleic anhydride copolymer amic acid in an mount in the range between 0.5 to 25 % by weight. Preferably the mixture comprises styrene maleic anhydride copolymer amic acid in the range between 1 to 15 % by weight, most preferably in the range between 2 to 10% by weight.

Preferably, styrene maleic anhydride copolymer amic acid is the minor component in the mixture, and cyanuric acid and melamine are the major components. A preferred ratio of the mixture is:

• 100g of an aqueous solution of styrene maleic anhydride copolymer amic acid (30% by weight of styrene maleic anhydride copolymer amic acid)

• 166g cyanuric acid (powder)

• 165g melamine (powder)

• 653g water

The components ratio may be modified to achieve the desired outcome of a homoge nous suspension, however a decreasing amount of styrene maleic anhydride copolymer amic acid in the formulation leads to a solid mass that is difficult to maintain as a suspension. Nevertheless, if the amount of styrene maleic anhydride copolymer amic acid is reduced, a homogenous suspension can maintained by using additional water as a solvent. An example with a different ratio of the mixture is:

• 20g Styrene maleic anhydride copolymer amic acid (30% solids)

• 166g cyanuric acid (powder)

• 165g melamine (powder)

• 661g water

The mixture is preferably a suspension. The contained particles preferably have a particle size of less than 3 pm, more preferably in the range between 0.5 to <3 pm. Preferably the majority, i.e. more than 50 %, of the particles are smaller than 3pm. The particle size can be measured with a laser diffraction particle size analyzer, suitable for measuring particle sizes 0.1 pm - 3 mm (Malvern Mastersizer 3000). A small amount of sample (~0.25g) is required for analysis, and results can be recorded within 10 minutes/sample.

The mixture may further comprise a photocatalyst material. By the addition of at least one photocatalyst to the inventive mixture, an advantageous surface characteristic is gained. Said photocatalyst material preferably comprises Ti0 ₂ as the basic component of the photocatalyst material. The photocatalyst may be nano-scale Ti0 ₂ (as examples Kronoclean 7000/7050 or Aeroxide P25 or Ishihara ST/STS series or alternative suppliers) or modified Ti0 ₂ photocatalyst, for example but not limited to doping Ti0 ₂ with materials such as Wolfram, Molybdenum, Cerium, Copper, Silver or Nitrogen, or combinations of such materials incorporated to enhance antimicrobial, antibacterial and antiviral surface activity as well as an easier to clean surface.

The mixture may comprise one or more materials selected from the group consisting of pigments, dyes, antimicrobial material, antibacterial material, fire retardant material and hard anti-abrasion material.

Thus, the inventive mixture may be modified in colour by the addition of pigments or dyes, for example but not limited to colour pigments such as Bayferrox® and Color- therm® (Lanxess). Furthermore, the inventive mixture may be modified by the addition of functional chemicals such as but not limited to antimicrobial or antibacterial and/or antiviral materials.

If transport costs exert an intolerable negative economic impact to the cost of using the mixture, water may be removed from the mixture, preferably by evaporation. Later, the mixture can be reconstituted to a preferred solids content and viscosity.

According to a further aspect, the invention relates to a method for producing the mixture according to the invention. The method comprises the steps of a) mixing styrene maleic anhydride copolymer amic acid and cyanuric acid b) adding melamine.

In a first step, the styrene maleic anhydride copolymer amic acid and cyanuric acid are combined, and subsequently melamine is added. The mixture is preferably thoroughly stirred and blended including homogenization to a desired consistency.

The cyanuric acid in powder form may be added directly to an aqueous solution of styrene maleic anhydride copolymer amic acid, however this causes a rapid increase in viscosity and necessitates immediate strong mixing to achieve a homogenous suspension. Therefore, in a preferred step, the cyanuric acid is pre-dispersed in water before being mixed with the styrene maleic anhydride copolymer amic acid.

The melamine is is preferably pre-dispersed in water before being added to the mixture obtained from step a).

The cyanuric acid whether or not pre-dispersed in water, is combined with the aqueous styrene maleic anhydride copolymer amic acid solution. In one embodiment the cyanuric acid is dispersed in water followed by the addition of a liquid styrene maleic anhydride copolymer amic acid, for example Polyscope XIRAN® grade SL40005 N30 amic acid. During the mixing of the cyanuric acid and the styrene maleic anhydride copolymer amic acid there is a thickening of the dispersion. The viscosity can be reduced to a preferred level by the addition of water, subsequently the melamine powder is added and the combination of cyanuric acid, styrene maleic anhydride copolymer amic acid, melamine and water is thoroughly mixed to provide a homogenous suspension. In a preferred step the cyanuric acid and melamine are added to the styrene maleic anhydride copolymer amic acid while the styrene maleic anhydride copolymer amic acid is at an elevated temperature, for example immediately after the solid styrene maleic anhydride copolymer has been converted to the amic acid form, a process that usually takes place at around 90°C. The addition of water as a solvent at one or more stages in the manufacturing process enables easier blending, homogenization, viscosity control and to achieve a desired solids content. The particle size distribution of the melamine powder may be reduced in a separate process step prior to its addition to the combination of styrene maleic anhydride copolymer amic acid, cyanuric acid and water. According to the invention, the mixture obtained from step b) can be homogenized. The mixture obtained from step b) can be comminuted to achieve small particle sizes.

Optionally the method comprises the step of c) adding one or more materials selected from the group consisting of photocatalyst material, pigments, dyes, antimicrobial material, antibacterial material, fire retardant material and hard anti-abrasion material.

It is also foreseen that the pH of the suspension may be adjusted when the suspension is to be combined with other materials that are sensitive to pH change, for example impregnation or coating resins based on amino formaldehyde resins.

An exemplary use of the inventive mixture is in the manufacture of decorative or industrial laminates such as low pressure melamine laminates, high pressure laminates, continuous pressure laminates, compact laminates and pre-impregnated foils.

The mixture according to the invention may be used as an opacifier or extender of opacifying agents. Preferably, the inventive mixture may be used together with T1Ό2 to improve opacity effectiveness of the Ti02 in applications such as paints, plastics and paper. in the manufacture of a decor paper or pre-impregnated decor paper for decorative or industrial laminates the inventive suspension may be applied at one or more stages in the papermaking process. The mixture may be used as a component of a decor paper included in the mass before forming of the decor paper web on a paper making machine. The mixture may also be used as a component of a decor paper applied to the decor paper after formation of a paper web, preferably via a coating unit, for example a size press (leimpress). Use of the inventive mixture after formation of the paper as a surface coating to improve opacity and/or printability may be done with or without the addition of T1O2 or alternative mineral pigments which may have a nano-scale particle size distribution.

The inventive mixture may be applied to the printing surface of a decor paper before the printing step, preferably applied in-line before printing takes place. The printing method is not limited to the predominate method of rotogravure used for decor paper printing. The inventive mixture may be used in a digital inkjet printing process by application to the surface of raw decor paper, preimpregnated d6cor paper, impregnated decor paper followed by drying and then presented to the inkjet printing section of the printing machine. Depending on the colour of the raw base paper, the inventive mixture may be pigmented to complement the raw base paper colour.

The mixture may be used as a component of a formaldehyde free resin material used in the manufacture of a pre-impregnated decor paper. The mixture may also be used as a replacement material for a portion of an amino formaldehyde resin used in the saturation and/or coating of a decor paper. When used in the first stage of decor paper saturation by inclusion in a urea formaldehyde resin or melamine formaldehyde resin, an added benefit in addition to improved opacity is that there is a reduction in the physical amount of formaldehyde per square meter of decorative surfacing. For example, replacing 40% of the urea formaldehyde resin with the inventive suspension provides a reduction in physical formaldehyde content of about 25%, the reduction % dependent on the molar ratio of the urea formaldehyde resin and the amount of urea formaldehyde resin in the fully impregnated b-stage decor paper.

The reduction in the physical amount of formaldehyde in an impregnated decor paper, particularly the urea formaldehyde component, reduces the potential of unwanted formaldehyde emissions from impregnated decor paper during individual process steps, such as during drying and advancing the cure of the impregnated decor paper during the impregnation process, and during the hot pressing process where the impregnated decor paper has heat and pressure applied to achieve the final laminate surface.

According to a further aspect, the invention relates to a laminate comprising a mixture according to the invention. Preferably, a laminate component, e.g. a decor paper, comprises the mixture. In some laminate structures, it may be desirable to not include any formaldehyde in the laminate surface. An example is a substrate woodpanel manufactured with a binder that does not include formaldehyde, which in the industry are referred to as “no added formaldehyde” (NAF) or "zero added formaldehyde” (ZAF). As a non-limiting example, this could be oriented strand board (OSB) using pMDI as the binder, later overlaid with a glasvlies (nonwoven glass veil) which before or after attachment of the glasvlies to the OSB panel, is impregnated with the inventive mixture. The inventive mixture used to impregnate the glasvlies may be modified by the addition of functional chemicals such as but not limited to fire retardant additives, for example magnesium sulphate, preferably magnesium sulphate heptahydrate. Alternative fire retardant materials such as ammonium polyphosphate, or combinations of fire retardant materials may also be incorporated to modify the inventive mixture to achieve desired properties of the laminate surface material. Hard materials, such as corundum, may be incorporated into the inventive mixture, preferably as close as possible to the external surface uppermost in practical use of the laminate surface.

The present invention is further illustrated by the attached Figures and the Experimental part.

Fig.1 is a picture of a 53g/m2 decor paper 21% ash content to which a coating of the inventive mixture has been applied liberally to both surfaces of the decor paper, and the excess removed by squeezing between 2 steel rollers. The end weight of the coated decor paper is 67g/m2. Fig.2 is a picture of the front and reverse sides of the original 53g/m2 decor paper and the 67g/m2 coated decor paper showing that the ink from a Permanent Marker pen has less penetration through the decor paper.

Experimental part

Example 1

70g/m2 white decor paper with 32% ash content First bath saturation with urea formaldehyde resin, molar ratio 1 :1.6 50g/m2 urea formaldehyde resin with 1:1.6 m/r contains 22.2g formaldehyde Coating of the UF impregnated paper with melamine formaldehyde resin, molar ratio 1:1.8

40g/m2 melamine formaldehyde resin with 1:1.8 m/r contains 12g formaldehyde Combined formaldehyde content ca. 34.2g

Replacing 40% of the urea formaldehyde resin with the inventive mixture removes ca. 8.9g of formaldehyde, a reduction of ca. 26%. Furthermore when it is feasible to replace some of the melamine formaldehyde coating resin with the inventive mixture, for example in white laminates, the % reduction can be increased.

Example 2

In another example where heavier decor paper is used, for example 120g/m2 with 38% ash content , the possible % reduction is greater, as shown in the following calculation: 120g/m2 white decor paper 38% ash content First bath saturation with urea formaldehyde resin, molar ratio 1:1.6 75g/m2 urea formaldehyde resin contains 33.3g/m2 formaldehyde Coating of the UF impregnated paper with melamine formaldehyde resin, molar ratio 1:1.8

40g/m2 melamine formaldehyde resin with 1 :1.8 m/r contains 2g formaldehyde Combined formaldehyde content ca. 45.3g Replacing 40% of the urea formaldehyde resin with the inventive mixture removes ca. 13.3g of formaldehyde, a reduction of ca. 29%. Furthermore when it is feasible to replace some of the melamine formaldehyde coating resin with the inventive mixture, for example in white laminates, the % reduction can be increased.

Furthermore, if the 120g/m2 white decor paper 38% ash is used in a high pressure laminate application the resin in the decorative layer will usually predominately be melamine formaldehyde. Using the resin amount as 110% of the dry paper weight the amount of MF resin is 132g/m2 of which the formaldehyde content of MF with a molar ratio 1.8 would be 39.6g/m2. Replacing 40% of the total MF resin with the inventive mixture is a 40% reduction in formaldehyde content.