A urea-formaldehyde resin gasket plate, its preparation process and application

Abstract

The application discloses a urea-formaldehyde resin cushion plate and a preparation process and application thereof. The preparation process of the urea-formaldehyde resin cushion plate comprises the following steps: using urea-formaldehyde resin to impregnate surface paper, baking the impregnated surface paper to prepare a prepreg, then respectively stacking the prepreg on the upper and lower sides of a wood fiber plate, and finally pressing and forming by using a press to obtain the cushion plate. The urea-formaldehyde resin is obtained by reacting a compound of polyoxymethylene and a formaldehyde solution with a solubility of 35-40% with urea. The urea-formaldehyde resin cushion plate prepared by the preparation process has the characteristics of high hardness, low warping and excellent punching performance. The preparation process reduces the manufacturing cost of the drilling cushion plate, is environmentally friendly, can meet the market demand and is widely applied.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board drilling technology, and particularly to a urea-formaldehyde resin pad, its preparation process, and its application. Background Technology

[0002] As printed circuit boards (PCBs) evolve towards higher integration, higher density, and higher reliability, micro-hole drilling (hole diameter of 0.2mm and below) has become widespread. Micro-hole drilling typically uses phenolic resin backing boards, requiring a center thickness of 1.50mm, good surface flatness (tolerance ±0.10mm), good Shore hardness (80 and above) and pencil hardness (5H and above), and minimal warpage (<0.5%). Currently, these backing boards are made by laminating multiple sheets of phenolic resin-impregnated paper and then pressing them together under high temperature and pressure. The phenolic resin impregnation process requires the addition of a large amount of solvent to improve the paper's wettability, leading to increased costs and air pollution, which is detrimental to environmental protection. Furthermore, phenolic resin is expensive, and the use of multiple sheets of paper results in high processing costs for the phenolic resin backing boards, all of which contribute to the consistently high cost of using phenolic resin backing boards. Currently, there are also pads made with cheaper and more environmentally friendly urea-formaldehyde resin impregnated paper. The impregnated paper is stacked on top of the wood fiberboard and pressed into shape under high temperature and pressure to make an environmentally friendly pad for drilling small holes. However, it is prone to large warping, especially at high humidity (above 60%), where the warping exceeds the standard.

[0003] Therefore, there is an urgent need for a low-cost, environmentally friendly manufacturing process that can produce pads with low warpage and high hardness to meet market demands. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a urea-formaldehyde resin pad, its preparation process, and its applications.

[0005] This invention provides a process for preparing urea-formaldehyde resin pads, comprising the following steps:

[0006] Urea-formaldehyde resin is used to impregnate the face paper, which is then baked to make a semi-cured sheet. The semi-cured sheet is then stacked on the top and bottom sides of the wood fiberboard, and finally pressed into shape by a press to obtain the pad.

[0007] The urea-formaldehyde resin is obtained by reacting a complex of paraformaldehyde and a formaldehyde solution with a solubility of 35-40% with urea.

[0008] Urea-formaldehyde resin is synthesized from a urea and formaldehyde compound, using water as a diluent, making it more environmentally friendly. Furthermore, its price is only 50% of phenolic resin, significantly reducing the cost of the mat. The high concentration of formaldehyde after lamination exhibits better stability and no leaching issues. Additionally, using wood fiberboard as a support layer, replacing the multiple layers of impregnated paper in the phenolic resin mat, significantly reduces drill bit wear, extends drill bit lifespan, further reduces the overall cost of the mat, and makes the manufactured mat more environmentally friendly.

[0009] The inventors discovered that urea-formaldehyde resin, made by reacting a compound of paraformaldehyde and formaldehyde aqueous solution with urea, has excellent waterproof performance after the glue is cured. This improves the problem of PP easily absorbing moisture and sticking after impregnation, increases production efficiency, and can better prevent the pad from warping in high humidity environments.

[0010] The urea-formaldehyde resin pad prepared by this invention has a simpler structure than the phenolic resin pad.

[0011] Furthermore, the basis weight of the face paper is 80-200 g / m². 2 (Unimpregnated plain face paper weight), such as 80, 100, 120, 140, 160, 180, 200 g / m² 2 By using high-grammage face paper impregnated with resin, the resulting prepreg has better strength and shape retention after being pressed at medium temperature and high pressure, further solving the problem of wood fiberboard warping easily after high-temperature pressing.

[0012] Furthermore, the thickness of the wood fiberboard is 1.0-1.5mm, such as 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5mm.

[0013] Furthermore, the solid content of the urea-formaldehyde resin is 50-70%. The solid content of the urea-formaldehyde resin adhesive produced by this invention can be increased from about 45% to 50%-70%, which can effectively improve the production efficiency of adhesive making, and the storage period of the adhesive can also be maintained at 4 days. The increase in the solid content of the adhesive means that the heat energy and water required for adhesive making are reduced. When used in impregnation production, the heat required for baking during impregnation is reduced due to the increased solid content of the urea-formaldehyde resin of this invention. Compared with urea-formaldehyde resin impregnated paper prepared by simply using formaldehyde solution (baking speed is 16-18m / min), the baking speed will be increased by more than 50% under the same conditions (the baking speed of the impregnated paper of this invention is 25-30m / min). Moreover, the PP (impregnated paper) is less prone to moisture absorption and adhesion after impregnation, which is more conducive to production and use.

[0014] Furthermore, the pressing operation temperature is 90-120℃, such as 90, 95, 100, 105, 110, 115, 120℃, the pressure is 15-30MPa, such as 15, 18, 20, 22, 25, 28, 30MPa, and the pressing time is 30-120min, such as 30, 50, 60, 80, 100, 120min. The pressing temperature of the present invention is lower than that of phenolic resin pads (pressing temperature is above 140℃), thus resulting in lower energy consumption during production. Moreover, since the pads of the present invention can be pressed at medium temperature, warping can be further reduced.

[0015] Furthermore, the pressing process also includes cooling the pressed pad in a cold press for 20-40 minutes before unloading the pad.

[0016] Furthermore, the mass ratio of paraformaldehyde to formaldehyde solution with a concentration of 35-40% in the urea-formaldehyde resin is 1:(0.33-3). If too much paraformaldehyde is added, paraformaldehyde precipitates will occur during glue preparation, causing glue precipitation and unstable glue synthesis. After paper impregnation, the precipitates will be introduced, and problems such as off-center holes and low CPK will easily occur when drilling holes in the pad.

[0017] Furthermore, the molar ratio of the complex to urea is (1.5-2.5):1.

[0018] Furthermore, the preparation method of the urea-formaldehyde resin includes the following steps:

[0019] S1. A high-concentration formaldehyde complex (50-80% solubility) is prepared by compounding paraformaldehyde and formaldehyde solution with a solubility of 35-40%. The inventors found that if the formaldehyde complex exceeds this compounding solubility, paraformaldehyde will not be able to dissolve, resulting in precipitates and causing the adhesive to be unstable. If the compounding solubility is lower than this compounding solubility, the desired effect of the present invention will not be achieved.

[0020] S2. The complex is mixed with urea in a molar ratio to carry out an addition (hydroxymethylation) reaction to generate monohydroxy, dihydroxy and trihydroxymethylurea.

[0021] The inventors discovered that by adjusting the formaldehyde compound to increase the formaldehyde concentration by a large proportion, it is more conducive to the formation of dihydroxymethylurea and trihydroxymethylurea. The increased formation ratio of polyhydroxymethylurea is beneficial to improving the connection stability of the two-dimensional and three-dimensional structures of the resin, and the water absorption rate is reduced by more than 50% after curing.

[0022] The present invention also provides a urea-formaldehyde resin pad prepared by the aforementioned preparation process.

[0023] Furthermore, the pad has a Shore hardness ≥80, a pencil hardness ≥5H, and a warpage <0.5%.

[0024] The present invention also provides the application of the urea-formaldehyde resin pad as a PCB drilling pad, especially as an environmentally friendly pad for PCB micro-hole drilling.

[0025] In summary, compared with the prior art, the present invention achieves the following technical effects:

[0026] (1) The urea-formaldehyde resin pad provided by the present invention has high hardness and low warpage, which can better protect the PCB board when used as a drilling pad.

[0027] (2) The urea-formaldehyde resin pad provided by the present invention has high accuracy of drilling position when applied to drilling, and can reduce the wear of drill bit and improve the life of drill bit.

[0028] (3) The drilling performance of the urea-formaldehyde resin pad provided by the present invention is comparable to that of phenolic resin, and the cost is significantly reduced compared to the phenolic resin pad, which has a high cost performance.

[0029] (4) The urea-formaldehyde resin pad preparation process provided by the present invention can significantly reduce the manufacturing cost of drilling pads, and the preparation process is environmentally friendly. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the structure of the urea-formaldehyde resin pad of the present invention;

[0032] Figure 2 This is a schematic diagram of the structure of a phenolic resin pad. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0034] Example

[0035] The present invention will be further illustrated below with reference to specific embodiments and comparative embodiments. The following specific embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the following embodiments, and are not in particular limited to the types of raw materials used in the following specific embodiments.

[0036] I. The sources of raw materials for the examples and comparative examples are as follows:

[0037] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this invention are all commercially available.

[0038] Urea-formaldehyde resin #1: It is obtained by compounding paraformaldehyde and formaldehyde solution with a concentration of 37% in a 1:1 ratio to form a high-concentration formaldehyde complex (concentration of 66.5%), and then adding it to urea in a molar ratio of 1:2.

[0039] Urea-formaldehyde resin #2: The difference between it and urea-formaldehyde resin #1 is that the compounding ratio is 3:1, and it is a formaldehyde complex (solubility of 80%).

[0040] Urea-formaldehyde resin #3: The difference between it and urea-formaldehyde resin #1 is that the compounding ratio is 1:3, and it is a formaldehyde complex (solubility of 50%).

[0041] Urea-formaldehyde resin #4: The difference between it and urea-formaldehyde resin #1 is that the compounding ratio is 4:1, and it is a formaldehyde complex (solubility of 85%).

[0042] Urea-formaldehyde resin #5: The difference from urea-formaldehyde resin #1 is that it uses only a formaldehyde solution with a concentration of 37%.

[0043] The phenolic resin pad used in Comparative Example 3 was sourced from commercially available products.

[0044] II. Performance Testing Methods

[0045] (1) Pressure plate warping / pad warping under high humidity conditions (warping degree (bowing and twisting) test): The test shall be conducted in accordance with CPCA4403-2010.

[0046] (2) PP storage period (adhesion) test: adhesion means that PP is bonded together and cannot be separated or breaks after separation, and there are defects in appearance. The time from PP impregnation to the appearance of adhesion is recorded as the PP storage period.

[0047] (3) CPK index test of pad: Tested using AOI precision scanner.

[0048] (4) Hardness test of pad: The test shall be conducted in accordance with GB / T 2411—2008.

[0049] Example 1

[0050] The preparation process of the urea-formaldehyde resin pad in Example 1 includes the following steps:

[0051] The face paper is impregnated with urea-formaldehyde resin #1 (face paper weight is 100g / m²). 2 The impregnated paper is baked to make a semi-cured sheet, which is then stacked on the top and bottom sides of the wood fiberboard (1.0 mm thick). Finally, it is pressed into shape by a press (pressing temperature 100℃, pressure 20 MPa, time 60 min) to obtain the pad.

[0052] Example 2

[0053] The difference from Example 1 is that the paper is impregnated with urea-formaldehyde resin #2.

[0054] Example 3

[0055] The difference from Example 1 is that the paper is impregnated with urea-formaldehyde resin #3.

[0056] Example 4

[0057] The preparation process of the urea-formaldehyde resin pad in Example 4 includes the following steps:

[0058] The face paper is impregnated with urea-formaldehyde resin #1 (face paper weight is 180g / m²). 2 The impregnated paper is baked to make a semi-cured sheet, which is then stacked on the top and bottom sides of the wood fiberboard (1.5mm thick). Finally, it is pressed into shape by a press (pressing temperature 120℃, pressure 28MPa, time 110min) to obtain the pad.

[0059] Example 5

[0060] The preparation process of the urea-formaldehyde resin pad in Example 5 includes the following steps:

[0061] The face paper is impregnated with urea-formaldehyde resin #1 (face paper weight is 140g / m²). 2 The impregnated paper is baked to make a semi-cured sheet, which is then stacked on the top and bottom sides of the wood fiberboard (1.2mm thick). Finally, it is pressed into shape by a press (pressing temperature 95℃, pressure 16MPa, time 40min) to obtain the pad.

[0062] Comparative Example 1

[0063] The difference from Example 1 is that the paper is impregnated with urea-formaldehyde resin #4.

[0064] Comparative Example 2

[0065] The difference from Example 1 is that the paper is impregnated with urea-formaldehyde resin #5.

[0066] Comparative Example 3

[0067] Commercially available phenolic resin pads.

[0068] Table 1. Results of Examples and Comparative Examples

[0069]

[0070] In Examples 1-5, the urea-formaldehyde resin pads were prepared by reacting a composite of paraformaldehyde and a formaldehyde solution with a concentration of 35-40% with urea. The pads were formed by impregnating paper with a specific resin, baking to form a semi-cured sheet, and then pressing it onto a wood fiberboard. The resulting pads have high hardness, low warpage, and excellent punching performance. The preparation process is simple and environmentally friendly, greatly reducing the production cost of drilled pads. Compared with commercially available phenolic resin pads, the pads in this application can achieve comparable performance and can be widely used.

[0071] Comparative Examples 1-3 were all compared with Example 1. In Comparative Example 1, the urea-formaldehyde resin used to make the pad contained excessive amounts of paraformaldehyde, resulting in poor flatness and a significantly reduced CPK value. In Comparative Example 2, only 37% formaldehyde solution and urea were used to synthesize urea-formaldehyde resin, resulting in a pad with a high warpage rate, making it unsuitable for stable use in high-humidity environments. Comparative Example 3 used phenolic resin pads, which had high production costs, making them unsuitable for large-scale market production. Furthermore, the production process of phenolic resin involved a large amount of organic solvents, causing environmental pollution. None of the above comparative examples could produce a drilling pad that simultaneously possessed excellent drilling performance, reduced production costs, and made the manufacturing process environmentally friendly.

[0072] Based on the test data of warpage, CPK, and hardness of the prepared pads in Table 1, the urea-formaldehyde resin pads prepared by Examples 1-5 have significant advantages over the comparative examples and can effectively meet the high standards of customers and the market.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A preparation process for a urea-formaldehyde resin pad, characterized in that, Includes the following steps: Urea-formaldehyde resin is used to impregnate the face paper, which is then baked to make a semi-cured sheet. The semi-cured sheet is then stacked on the top and bottom sides of the wood fiberboard, and finally pressed into shape by a press to obtain the pad. The urea-formaldehyde resin is obtained by reacting a complex of paraformaldehyde and a formaldehyde solution with a solubility of 35-40% with urea. The mass ratio of paraformaldehyde and formaldehyde solution with a concentration of 35-40% in the urea-formaldehyde resin is 1:(0.33-3).

2. The preparation process according to claim 1, characterized in that, The basis weight of the face paper is 80-200 g / m². 2 .

3. The preparation process according to claim 1, characterized in that, The thickness of the wood fiberboard is 1.0-1.5 mm.

4. The preparation process according to claim 1, characterized in that, The solid content of the urea-formaldehyde resin is 50-70%.

5. The preparation process according to claim 1, characterized in that, The pressing operation is performed at a temperature of 90-120℃, a pressure of 15-30 MPa, and a pressing time of 30-120 min.

6. The preparation process according to claim 1, characterized in that, The molar ratio of the complex to urea is (1.5-2.5):

1.

7. The urea-formaldehyde resin pad prepared by the preparation process according to any one of claims 1-6.

8. The urea-formaldehyde resin pad according to claim 7, characterized in that, The pad has a Shore hardness ≥80, a pencil hardness ≥5H, and a warpage <0.5%.

9. The application of the urea-formaldehyde resin pad as a PCB drilling pad according to claim 8.

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