CN111302757B

CN111302757B - High-whiteness MGO substrate, preparation method and decorative plate with substrate

Info

Publication number: CN111302757B
Application number: CN202010195099.0A
Authority: CN
Inventors: 黎国平
Original assignee: Jiangsu Langyue New Materials Technology Co Ltd
Current assignee: Jiangsu Langyue New Materials Technology Co Ltd
Priority date: 2020-03-19
Filing date: 2020-03-19
Publication date: 2022-05-17
Anticipated expiration: 2040-03-19
Also published as: CN111302757A

Abstract

The invention discloses a high-whiteness MGO substrate, a preparation method and a decorative plate with the substrate. The high-whiteness MGO substrate comprises a surface layer and a substrate, wherein the substrate is composed of a forming agent, a light filler, a modifier and water, and the high-whiteness MGO substrate comprises the following components in parts by mass: 40-49 parts of light-burned magnesia powder, 18-25 parts of magnesium sulfate heptahydrate, 16-25 parts of polyvinyl alcohol solution, 16-20 parts of plant powder and 0.5-2 parts of modifier; the modifier is citric acid: phosphoric acid: the sodium sulfate is mixed according to the mass ratio of 10:3: 6; the adhesive has the advantages of high internal bonding strength and difficult peeling and cracking; the preparation method of the substrate has the advantages of simple preparation process, effective improvement of the internal bonding strength of the substrate, and difficult peeling and cracking; the decorative plate has the advantages of wide application range and good practicability.

Description

High-whiteness MGO substrate, preparation method and decorative plate with substrate

Technical Field

The invention relates to the field of decorative materials, in particular to a high-whiteness MGO substrate, a preparation method and a decorative plate with the substrate.

Background

The glass magnesium fireproof board is also called as glass magnesium board, magnesium oxide board, magnesite board and magnesium board. The components for producing the glass magnesium fireproof plate material are active high-purity magnesium oxide (MgO) and high-quality magnesium chloride (MgCl)₂) The high-performance inorganic fiber board is mainly used for indoor non-bearing walls and suspended ceilings and base plates of various decorative boards.

At present, the Chinese patent with the publication number of CN101871246B discloses a glass magnesium board, which consists of a forming agent, a reinforcing material, a light filler, a modifier and water, wherein the forming agent is magnesium oxide, magnesium sulfate and magnesium chloride, the reinforcing material is glass fiber mesh cloth or other reinforcing materials, and the modifier comprises a whitening agent, a stabilizer and a toner.

In the prior art, the glass fiber mesh cloth is used as a reinforcing material and has excellent toughness, so that the internal bonding strength of the glass fiber mesh cloth is low when the glass fiber mesh cloth is combined with other materials; when the mortise is installed to the glass magnesium board in the external world, the mortise is easily stripped by shearing force, so that the phenomenon that the rabbet of the mortise is cracked is caused, and the practicability of the glass magnesium board is influenced.

Disclosure of Invention

In view of the disadvantages of the prior art, a first object of the present invention is to provide a high-whiteness MGO substrate having advantages of high internal bonding strength of a decorative sheet and being not easily peeled off and cracked.

In order to achieve the first object, the invention provides the following technical scheme:

a high-whiteness MGO substrate comprises a surface layer and a substrate, wherein the substrate comprises the following components in parts by mass: 40-49 parts of light-burned magnesia powder,

18-25 parts of magnesium sulfate heptahydrate,

16-25 parts of polyvinyl alcohol solution,

16-20 parts of plant powder,

0.5-2 parts of a modifier;

the modifier is prepared from citric acid: phosphoric acid: the sodium sulfate is mixed according to the mass ratio of 10:3: 6.

By adopting the technical scheme, the light-burned magnesium oxide and magnesium sulfate heptahydrate are used as basic raw materials for preparing the substrate; the polyvinyl alcohol solution is used as a binder, has good film forming property, wraps the light burned magnesium oxide and the plant powder, reduces bubbles on the surface and in the internal structure, effectively enhances the internal bonding strength of the substrate, and is not easy to peel and crack; the modifier with the mass ratio is easy to dissolve in water, good in stability and corrosion resistance, and prolongs the service life of the substrate.

Furthermore, the magnesium content of the light-burned magnesia is more than or equal to 85 percent, and the active magnesium content is more than 65 percent.

By adopting the technical scheme, the preparation speed is improved, the using amount of light-burned magnesium oxide is saved, and the use of production cost is reduced.

Furthermore, the fineness of the plant powder is 20-120 meshes, and the plant powder comprises one or two of poplar powder, white wood powder, bamboo powder, straw powder and rice hull powder.

By adopting the technical scheme, the plant powder with the fineness is selected, so that the plant powder has better dispersion performance when the base plate is prepared, is easier to be uniformly mixed with other components in the base plate, and effectively enhances the internal bonding strength between the base plates, thereby being difficult to peel and crack when the tenon hole is formed; the poplar powder, the white wood powder, the bamboo powder, the straw powder and the rice hull powder are used as light fillers, so that the weight of the whole substrate is reduced, and the use cost for preparing the substrate is reduced.

The second object of the present invention is to provide a method for preparing a high-whiteness MGO substrate, which has advantages of simple preparation process, effective improvement of internal bonding strength of the substrate, and less peeling and cracking.

In order to achieve the second object, the invention provides the following technical scheme:

a method for preparing a high-whiteness MGO substrate comprises the following steps:

s1, weighing light-burned magnesia powder, magnesium sulfate heptahydrate, a polyvinyl alcohol solution with the mass concentration of 20% -40%, plant powder and a modifier in proportion;

s2, mixing the plant powder with a bleaching agent in an amount enough to immerse the plant powder, soaking for 2-10min, stirring for 30-40min, and filtering; carrying out constant-temperature steam treatment on the filtered plant powder at the temperature of 120-130 ℃ for 5-8min to obtain bleached plant powder;

s3, blending and stirring the magnesium sulfate heptahydrate weighed in the S1 step and a polyvinyl alcohol solution with the mass concentration of 20% -40% uniformly, then adding light-burned magnesium oxide and a modifier in sequence, stirring, and stirring the bleached plant powder prepared in the step S2 uniformly to obtain a magnesium oxysulfate gel material;

s4, spreading the magnesium oxysulfate gel material prepared in the step S3 in a mold, then flatly pressing for 3-10min at the temperature of 100 ℃ and 220 ℃ and under the pressure of 5-20MPa, standing for 5-6h, and then demolding to obtain a molded semi-finished product;

s5, curing the molded semi-finished product obtained in the step S4 for 5-7 days at the temperature of 20-30 ℃ and the humidity of 40-60% to obtain a semi-finished product substrate; taking out the semi-finished substrate to perform trimming, cutting and polishing; and drying the polished semi-finished substrate at 50-95 ℃ for 20-30min to obtain the shaped substrate.

By adopting the technical scheme, the adding sequence of each raw material is strictly controlled, the uniform dispersion among the light-burned magnesium oxide, magnesium sulfate heptahydrate, the modifier, the wood fiber particles and the wood fibers can be ensured, and the internal binding force of the substrate is improved; the preparation method further reduces bubbles in the magnesium oxysulfate gel material, effectively improves the internal bonding strength of the substrate, and is not easy to peel and crack.

Further, the bleaching agent is prepared from hydrogen peroxide bleaching agent: the diamido stilbene disulfonic acid derivative is prepared from the following components in a mass ratio of 2: 3, and mixing the components in a ratio of 3.

By adopting the technical scheme: the proportion of the bleaching agent improves the whiteness of the substrate and effectively enhances the performance of lasting color and yellowing resistance of the substrate.

The third purpose of the invention is to provide a high-whiteness MGO decorative sheet which has the advantages of simple preparation process, effective improvement of the internal bonding strength of the decorative sheet and difficult peeling and cracking.

In order to achieve the third object, the invention provides the following technical solutions: a high-whiteness MGO decorative sheet, comprising a surface layer and a substrate, wherein the substrate is the high-whiteness MGO substrate obtained as described above for achieving the first and second objects of the present invention, and the surface layer is any one of marble, veneer, and PVC surface layers.

By adopting the technical scheme, when the surface layer is made of marble, the utilization rate of marble resources is increased; meanwhile, the composite board is prepared from marble, so that the problems that the marble is slow in construction, easy to crack and low in cost are solved. The surface layer is made of wood skin and can be prepared into the compound wood floor, and the influence of humidity on the warping of the wood floor is greatly reduced due to the action of the glass fiber surface felt of the substrate. The surface layer is a composite fireproof plate prepared by a PVC surface layer, the composite plate has super-strong dimensional stability and does not crack, and the composite fireproof plate can be quickly arranged in a wallboard, a floor and a ceiling after being grooved; can be applied to cold and dry areas and has the characteristic of high fire-proof rating.

Further, the PVC surface layer comprises a surface layer, a core layer and a bottom layer which are sequentially bonded through an adhesive; the surface layer and the bottom layer are both PVC films:

the preparation process of the PCV surface layer comprises the following steps:

1) immersing the core layer in the resin for 120-150min, and taking out to obtain a gum dipping core layer;

2) uniformly coating adhesives on two sides of the PVC film, and drying and curing to obtain a glue-coated PVC film;

3) adhering the gluing PCV film obtained in the step 2) on two surfaces of the gumming core layer obtained in the step 1), and then performing hot press molding at the temperature of 130-170 ℃ and under the pressure of 10-21MPa to obtain a PCV surface layer.

Through adopting above-mentioned technical scheme, preparation PVC surface course process is simple, obtains the PVC surface course that all directions intensity is impartial, effectively strengthens the difficult performance of peeling off the fracture of whole decorative board.

Further, the core layer is aluminum oxide wear-resistant paper or a glass fiber surface felt.

By adopting the technical scheme, the aluminum oxide wear-resistant paper and the glass fiber surface felt both have excellent wear-resistant and scratch-resistant performances, and the whole decorative plate is endowed with the performance of difficult peeling and cracking.

Further, the resin includes one or both of melamine resin and urea resin.

By adopting the technical scheme, the melamine resin and the urea-formaldehyde resin have high heat resistance and moisture resistance, and the moisture resistance of the integral decorative board is further improved.

In conclusion, the invention has the following beneficial effects:

firstly, the modifier with the mass ratio is preferably adopted in the invention, so that the generation of bubbles in the substrate is further reduced, the internal bonding strength of the decorative plate is effectively improved, and the decorative plate is not easy to peel and crack in the installation process.

Secondly, in the invention, aluminum oxide wear-resistant paper and a glass fiber surface felt are preferably adopted as materials for preparing the PVC surface layer, so that the whole decorative plate has excellent wear-resistant and scratch-resistant properties.

Detailed Description

The present invention will be described in further detail with reference to examples.

The raw material sources are as follows: see Table 1 below

TABLE 1 sources and specifications of raw materials for high whiteness MGO decorative sheet

Bleaching equipment adopts a bleaching powder stirrer and is purchased from Zhengzhou Youzhuo automation equipment limited company;

the press machine is a BY 214X 8/E series multi-layer plywood press machine, which is purchased from a mechanical manufacturing plant (Shundao machinery Co., Ltd.) in the Linyi city orchid mountain area;

series PG 02-numerical control slotter (self planer), available from shanghai constant force limited.

Examples

The components and ratios in the examples are shown in Table 2.

Table 2 components and proportions of the high-whiteness MGO substrate in each example:

the preparation methods of the high-whiteness MGO substrates of examples 1 to 11 above were as follows:

s1, selecting a 2440X 1220X 3(mm) die, and cleaning the die;

s2, weighing light-burned magnesium oxide powder, magnesium sulfate heptahydrate, 30% polyvinyl alcohol solution by mass concentration, plant powder and a modifier according to the weight powder in the table 2;

s2, putting the plant powder weighed according to the table 2 into a bleaching powder stirrer, adding a hydrogen peroxide bleaching agent and 4,4' -diaminodiphenylamine-2-sulfonic acid in a mass ratio of 2: 3, mixing the bleaching agent, immersing the plant powder for 6min, and operating bleaching equipment to carry out stirring bleaching for 35 min; taking out, placing into steam at 125 deg.C for 8min, taking out, and sun-drying to obtain bleached plant powder;

s3, adding magnesium sulfate heptahydrate into a polyvinyl alcohol solution with the mass solubility of 30%, uniformly stirring, sequentially adding light-burned magnesium oxide and a modifier, uniformly stirring to form mixed slurry, adding the bleached plant powder prepared in the step S2 into the mixed slurry, and uniformly stirring to obtain a magnesium oxysulfate gel material;

s4, flatly paving the magnesium oxysulfate gel material prepared in the step S3 in a mold, placing the mold containing the magnesium oxysulfate gel material in a hot press at the temperature of 160 ℃ for flattening, and demolding after 6 hours to obtain a molded semi-finished product;

s5, placing the molded semi-finished product obtained in the step S4 in a curing room according to the temperature, humidity and time in the table 2, taking out, trimming, cutting and polishing; and then, placing the polished molded decorative plate at the temperature of 85 ℃ for 10min to dry, thereby obtaining the molded substrate.

The performance of the high whiteness MGO substrates prepared in each of the above examples was tested by the following method.

Apparent performance: and (4) carrying out microscopic detection on the MGO substrate or the composite board standard test block by using a scanning electron microscope, and observing surface cracks of the MGO substrate or the composite board standard test block.

Measurement of whiteness: 1 piece of each 200mm plate is arbitrarily cut out from 3 plates of a group of samples, and then impurities, grease and the like which affect whiteness and color in the experimental sample are subjected to moisture conditioning (the sample with the extremely high moisture regain is pre-dried at 50 ℃ for 30min for pre-conditioning) to reach balance under the moisture absorption condition. The sample is then placed in the cartridge and the cartridge lid is tightened. And placing the sample in a colorimeter, sequentially testing three sample boxes, and recording colorimetric values.

The static bending strength is evaluated according to GB/T33544-2017 glass magnesium plate.

Breaking strength: the method is carried out according to the regulation of JC688-2006 magnesium oxide plate.

Impact strength: reference is made to GB/T1043.1 section 1 for the determination of impact properties of plastic simply supported beams: non-instrumented impact test.

Anti-dehalogenation: referring to JC688-2006 glass magnesium flat plate, 1 plate of 200mm to 200mm is cut off from each of 3 plates of a group of samples, and the cut plates are put into a constant temperature and humidity box with the relative humidity of more than or equal to 90% and the temperature of 30-35 ℃ and taken out for observation after 24h, and then water beads are absent or moisture regains are generated.

Measurement of screw holding force: referring to JC688-2006 glass magnesium flat plate, 1 plate of 50mm by 50mm is cut out from each of 3 plates of a group of samples, a hole with the diameter of 3.2mm is drilled at the intersection point of the diagonal lines of the sample in advance by a bench drill, then a wood screw is vertically screwed in, the depth is 10mm +/-1 mm from the opposite head, a hammer nail is not needed, loading is carried out at the speed of 50N/S, the wood screw is pulled out, and the limit load value is recorded.

After the mortise was drilled, 1 each of 300mm by 300mm plates was cut out from 3 plates of a set of samples by reference to JC688-2006 "glass magnesium flat plate", and the side edge of the diagonal corner point of the sample was grooved using a numerical control grooving machine and was grooved toward the inner depth of the sample at a speed of 50N/S until the sample was peeled and cracked, and the depth of the groove where the sample was peeled and cracked was recorded.

And (3) testing the wear resistance: the evaluation is carried out according to GB/T18301-2012 test method for the normal temperature wear resistance of refractory materials.

Testing of fire resistance: the evaluation is carried out according to JC688-2006 glass magnesium flat plate and GB/T8624-1997 building material combustion performance grading method.

TABLE 3 results of various tests on high whiteness MGO substrates

The high-whiteness MGO substrate prepared by the weight parts has the whiteness of 81-90 percent, no gap on the surface, the static bending strength of 30-35MPa, the breaking strength of 32-38MPa, the impact strength of 22-26kJ/m2 and the screw holding force of 30-36N/m, and the groove depth of the mortise in the above examples 1-11 with the phenomenon of stripping and cracking is 162-171 mm. From the comparison between the above examples, example 2 is the most preferred substrate.

The components and ratios of the high whiteness MGO substrates prepared in each ratio are shown in table 4.

TABLE 4 Components and proportions of high whiteness MGO substrates in respective proportions

In contrast to example 2, comparative example 1 had no modifier added; comparative example 2 addition of modifier parts by weight citric acid monohydrate: sodium sulfate: phosphoric acid ═ 8: 3: 7; comparative example 3 addition of modifier parts by weight citric acid monohydrate: sodium sulfate: phosphoric acid ═ 12: 2: 5.

comparative example 4

Comparing a glass magnesium board purchased from Zhang Jiagang Yide import and export Limited company with the substrate manufactured by the invention; the purchased glass magnesium board comprises the components of active magnesium oxide, high-quality magnesium chloride, alkali-resistant glass fiber cloth, plant fiber, non-combustible light perlite, chemically stable lithopone, high molecular polymer and a high-performance modifier.

Comparative example 5

Comparing a glass magnesium board purchased from Thai building materials Co., Ltd, Zhang hong Kong with the substrate manufactured by the invention; the purchased glass magnesium board comprises the components of active magnesium oxide, high-quality magnesium chloride, alkali-resistant glass fiber cloth, plant fibers with excellent flexibility, non-combustible light perlite, high-molecular polymer and a high-performance modifier.

The high-whiteness MGO substrates prepared in each of the above comparative examples 1 to 3 were prepared in the same manner as in the examples, comparative examples 4 and 5 were purchased from the market, and the test results of the high-whiteness MGO substrates prepared in each of the above comparative examples 1 to 5 are shown in table 5.

TABLE 5 Performance test results for high whiteness MGO substrates prepared in each comparative example

From the above data, it is clear that when the modifier is not added and the mass ratio of the modifier is more than or less than a certain value, fine bubbles are not stable when the magnesium oxysulfate gel material is prepared, and are easily fused with each other, and large pores are formed, and the phenomenon of peeling and cracking easily occurs after the mortise is opened. The strength of the substrate prepared in example 2 was much greater than that of the commercially available magnesium oxide board compared to comparative examples 4 and 5.

High whiteness MGO decorative sheet examples

Example 8, a high-whiteness MGO decorative sheet comprising a surface layer and a substrate, with marble as the surface layer, the MGO substrate prepared according to example 2 above was adhered to the cut marble plane by a polyurethane adhesive, cured for 15min, and then the marble was cut apart by connecting the MGO substrates, to obtain a marble surface compounded with the MGO substrate, the marble surface having a thickness of 0.5mm and the MGO substrate having a thickness of 4 mm; and taking out the marble surface compounded with the MGO decorative plate, and polishing and UV to obtain the high-whiteness MGO decorative plate.

Example 9, a high-whiteness MGO decorative sheet comprising a top sheet and a base sheet, wherein buxus wood veneer is used as the top sheet, the MGO base sheet prepared according to example 2 above is bonded to the plane of the veneer by a polyurethane adhesive, and a semi-finished product is obtained after 15min of curing time; and then sanding, UV or coloring the semi-finished product, cutting and grooving to obtain the high-whiteness MGO decorative plate.

Embodiment 10, a high whiteness MGO decorative sheet includes a surface layer and a substrate, the PVC surface layer is used as the surface layer, the PVC surface layer includes a surface layer, a core layer and a bottom layer sequentially bonded by a polyurethane adhesive; the surface layer and the bottom layer are both PVC films, and the preparation method of the PVC surface layer comprises the following steps:

immersing the aluminum oxide wear-resistant paper in a mixture of melamine resin and urea resin according to a mass ratio of 1: 1, soaking for 130min, and taking out to obtain the dipped aluminum oxide wear-resistant paper;

then coating polyurethane adhesive on both sides of the PVC film, drying and curing to obtain a coated PVC film;

adhering the glued PCV film obtained in the step 2) to both surfaces of the glue-dipped aluminum oxide wear-resistant paper obtained in the step 1), and then carrying out hot press molding at the temperature of 150 ℃ and the pressure of 20MPa to obtain a PCV surface layer. The surface texture of the PVC surface layer is formed by pressing a steel template or a plastic high-temperature-resistant template.

A preparation method of a high-whiteness MGO decorative plate comprises the following steps: the PVC face layer prepared in this example was bonded to the side of the base layer 2 prepared in example 2 with a polyurethane adhesive, and was hot-pressed and compounded by a hot press at a temperature of 150 ℃ and a pressure of 20MPa, thereby obtaining a high-whiteness MGO decorative sheet.

Embodiment 11, a high whiteness MGO decorative sheet includes a surface layer and a substrate, the PVC surface layer is used as the surface layer, the PVC surface layer includes a surface layer, a core layer and a bottom layer sequentially adhered by a polyurethane adhesive; the surface layer and the bottom layer are both PVC films, and the preparation method of the PVC surface layer comprises the following steps:

1) immersing the alkali-free glass fiber surface felt in a mixture of melamine resin and urea resin according to the mass ratio of 1: 1, soaking for 130min, and taking out to obtain the dipped aluminum oxide wear-resistant paper;

2) then coating polyurethane adhesive on both sides of the PVC film, drying and curing to obtain a coated PVC film;

3) adhering the glued PCV film obtained in the step 2) to two surfaces of the dipped alumina wear-resistant paper obtained in the step 1), and then performing hot press molding at the temperature of 150 ℃ and the pressure of 20MPa to obtain a PCV surface layer. The surface texture of the PVC surface layer is formed by pressing a steel template or a plastic high-temperature-resistant template.

High whiteness MGO trim panels examples 8-11 test structures are shown in table 6 below.

TABLE 6 test results for high whiteness MGO decorative panels

From the above data, the strength of the high-whiteness MGO decorative sheet prepared by the preparation method was significantly increased; meanwhile, the wear resistance of the decorative plate prepared by implementing 8-11 is more than AC3, and the incombustibility reaches A level.

The present embodiment is only for explaining the present invention, and it is not limited to the present invention, and those skilled in the art can make modifications of the present embodiment without inventive contribution as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present invention.

Claims

1. A high-whiteness MGO substrate is characterized by comprising the following components in parts by mass:

40-49 parts of light-burned magnesia powder,

18-25 parts of magnesium sulfate heptahydrate,

16-25 parts of polyvinyl alcohol solution,

16-20 parts of plant powder,

0.5-2 parts of a modifier;

the modifier is prepared from citric acid monohydrate: sodium sulfate: the phosphoric acid is mixed according to the mass ratio of 10:3: 6; the fineness of the plant powder is 20-120 meshes.

2. The MGO substrate with high whiteness according to claim 1, wherein the light-burned magnesia contains not less than 85% of magnesium and has an active magnesium content of more than 65%.

3. The high-whiteness MGO substrate according to claim 1, wherein the plant powder is a mixture of one or more of poplar powder, white wood powder, bamboo powder, straw powder and rice hull powder.

4. A method of manufacturing a high-whiteness MGO substrate according to any one of claims 1 to 3, comprising the steps of:

s3, blending and stirring the magnesium sulfate heptahydrate weighed in the step S1 and a polyvinyl alcohol solution with the mass concentration of 20% -40% uniformly, then adding the light burned magnesium oxide and the modifier in sequence, stirring, and stirring the bleached plant powder prepared in the step S2 uniformly to obtain a magnesium oxysulfate gel material;

s5, curing the molded semi-finished product obtained in the step S4 for 5-7 days at the temperature of 20-30 ℃ and the humidity of 40-60% to obtain a semi-finished product substrate; taking out the semi-finished substrate to perform trimming, cutting and polishing; and then drying the polished semi-finished substrate for 20-30min at the temperature of 50-95 ℃ to obtain the shaped substrate.

5. The method of claim 4, wherein the bleaching agent is selected from the group consisting of hydrogen peroxide bleaching agents: the diaminostilbene disulfonic acid derivative is prepared from the following components in a mass ratio of 2: 3, and mixing the components in a ratio of 3.

6. A high whiteness MGO decorative board which is characterized in that: the decorative sheet includes a surface layer and a substrate, the substrate adopts the high-whiteness MGO substrate of any one of claims 1-5, and the surface layer is any one of marble, veneer and PVC surface layer.

7. A high-whiteness MGO decorative sheet according to claim 6, wherein the PVC surface layer comprises a surface layer, a core layer and a bottom layer which are sequentially bonded through an adhesive; the surface layer and the bottom layer are both PVC films:

the preparation process of the PVC surface layer comprises the following steps:

3) and (3) after the glued PVC film obtained in the step 2) is attached to both sides of the glued core layer obtained in the step 1), carrying out hot press molding at the temperature of 130-170 ℃ and under the pressure of 10-21MPa to obtain the PVC surface layer.

8. A high-whiteness MGO decorative sheet according to claim 7, wherein the core layer is alumina wear-resistant paper or a glass fiber surfacing mat.

9. A high-whiteness MGO decorative sheet according to claim 8, wherein the resin is one or a mixture of melamine resin and urea resin.