Sunlight fabric and splicing method thereof

Abstract

The invention discloses a sunshine fabric and a splicing method thereof, and relates to the field of textile, the sunshine fabric comprises a base layer, the base layer comprises a main body part and two splicing parts, each splicing part comprises a first surface and a second surface, the first surfaces of the two splicing parts are coated with transparent coatings, and the second surfaces of the two splicing parts are coated with transparent coatings; the second surfaces of the two splicing parts are coated with functional coatings, shading particles with the concentration distributed in a gradient mode in the thickness direction are arranged in the functional coatings, and the closer the shading particles are to the second surfaces, the lower the shading particles are. The shading particles in gradient distribution are arranged in the thickness direction of the functional coating, so that when the fabric is independently used, the light transmittance of the splicing part is relatively consistent with that of the main body part, after the fabric is spliced, the light transmittance is relatively high when light enters from the first surface, and the light transmittance after stacking is relatively close to that of the main body part; therefore, no matter whether the splicing part is spliced or not, the light transmittance of the splicing part is similar to that of the main body part, and the use effect of the fabric is guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of textiles, more particularly, it relates to a sunlight fabric and a splicing method thereof. BACKGROUND

[0002] Sunlight fabric, usually refers to a kind of composite fabric which is woven by polyester fiber or glass fiber as the base and is treated by functional coating, because it has controllable light transmittance, excellent ultraviolet resistance, high strength and long-lasting weather resistance, it is widely used in our daily life.

[0003] In the production process of sunlight fabric products, due to the limited width of the roll material, it is usually necessary to splice multiple fabrics to meet the size requirements of actual application, therefore, the splicing technology directly determines the appearance, performance and service life of the final product, the more common splicing process in the industry is the lap joint method, the edges of the two fabrics to be spliced are overlapped, and the overlapping area is melted and bonded together by high-frequency heating. Although this method has high connection strength and good waterproofness, it has inherent defects, that is, the thickness of the spliced part is doubled due to the overlapping of the fabric, forming a significant opaque or low-transmittance dark band, which seriously damages the uniformity and beauty of the light transmittance of the product, and forms a grid that is difficult to ignore in vision, affecting the lighting quality.

[0004] Therefore, it is necessary to propose a new scheme to solve this problem. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a sunlight fabric and a splicing method thereof.

[0006] The above technical purpose of the present application is realized by the following technical scheme: a sunlight fabric, comprising a base layer, the base layer comprises a main body part and two splicing parts respectively located on both sides of the main body part, the base layer is woven by warp yarn and weft yarn, the warp yarn comprises main body yarn and transparent yarn, the main body yarn is arranged only in the main body part, and the transparent yarn is arranged only in the splicing part, the thickness of the splicing part is half of the thickness of the main body part. The two sides of the main body part are coated with a PVC coating, the splicing part comprises a first surface and a second surface, the first surfaces of the two splicing parts are coated with a transparent coating, the second surfaces of the two splicing parts are coated with a functional coating, the functional coating is provided with shading particles with a concentration gradient distribution in the thickness direction, and the closer to the second surface, the lower the concentration of the shading particles.

[0007] The present application is further provided as follows: the relative deviation between the light transmittance measured from the second surface of the splicing part and the light transmittance measured from the main body part is not greater than 20%.

[0008] The application is further configured that the light transmittance of the main body part is between 5% and 10%, and the light transmittance of the splicing part measured from the first surface is between 20% and 30%.

[0009] The application is further configured that the distance between adjacent transparent yarns is less than the distance between adjacent main body yarns, and the transparent yarns are twisted from polypropylene fibers.

[0010] A splicing method of a sunlight fabric, comprising: Step S1: overlapping the splicing parts of the first fabric and the second fabric to be spliced with each other to form an overlapping area, in which the first surface of the splicing part of the first fabric is attached to the second surface of the splicing part of the second fabric; Step S2: a hot melt adhesive sheet is arranged in the overlapping area and clamped between the first fabric and the second fabric; Step S3: a light source is arranged on one side of the overlapping area, and a light intensity sensor is arranged on the other side of the overlapping area, and visible light of the light source is emitted from the first surface of the second fabric; Step S4: at least one of the first fabric and the second fabric is relatively displaced in a direction parallel to the warp yarns, and the composite light transmittance of the overlapping area is monitored in real time through the light intensity sensor; Step S5: the real-time monitored composite light transmittance value is compared with a target light transmittance range, and when the monitored composite light transmittance value is in the target light transmittance range, the relative displacement is immediately stopped, and a hot pressing operation is performed on the overlapping area to complete the splicing.

[0011] The application is further configured that after the hot melt adhesive sheet is melted and solidified after step S5, the average light transmittance of the hot melt adhesive sheet in the visible light band is not less than 90%, and the haze is not greater than 5%.

[0012] The application is further configured that the softening points of the transparent coating and the functional coating are higher than the melting point of the hot melt adhesive sheet, and the hot pressing temperature of step S5 is higher than the melting point of the hot melt adhesive sheet and less than the softening points of the transparent coating and the functional coating.

[0013] The application is further configured that in step S5, the target light transmittance range is a corrected dynamic target light transmittance range, which is determined in advance by the following steps: Step A1: using a sample fabric of the same batch as the fabric to be spliced and a hot melt adhesive for pre-splicing test, recording the monitored composite light transmittance value Tm in the solid state of the hot melt adhesive before the hot pressing operation is performed, and measuring the final light transmittance value Tf of the corresponding splicing sample after the hot pressing operation is performed and the cooling is completed, and establishing a mapping relationship function Tf=f(Tm) between Tm and Tf; Step A2: According to the mapping relationship function Tf=f(Tm) and the preset finished product target light transmittance Tt, the dynamic target light transmittance range to be used in the step S5 is reversely calculated, and the center value Td of the range satisfies Tt=f(Td); Step A3: When the step S5 is executed, the calculated dynamic target light transmittance range is used as the judgment standard for stopping the relative displacement and triggering the heat pressing operation.

[0014] In summary, the present application has the following beneficial effects: By arranging the light-shielding particles in a gradient distribution in the thickness direction of the functional coating, the light transmittance of light incident from the first surface is greater than the light transmittance of light incident from the second surface, and the light transmittance of light incident from the second surface is close to the main body part, so that when the fabric is used alone, the light transmittance of the splicing part and the main body part is relatively consistent, and after the fabric is spliced, the light transmittance of light incident from the first surface is high, so that the light transmittance of the stacked part is also relatively close to the main body part, so that the splicing part has a similar light transmittance to the main body part whether it is spliced or not, ensuring the use effect of the fabric. The above method can dynamically find and lock the splicing point that best matches the light transmittance of the main body part of the fabric, and can produce a product with a light transmittance at the joint that is consistent with the main body, which is almost "invisible" in vision. By predicting the dynamic target light transmittance range, the melting of the hot melt adhesive sheet and the effect of the coating on the light transmittance are considered, and by establishing a quantitative relationship model, the optical performance of the final product is precisely controlled, and the precision of the final light transmittance is improved. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 It is a cross-sectional view of the fabric in the present application. Figure 2 It is a weaving structure schematic diagram of the fabric in the present application.

[0016] In the figure: 1, main body part; 2, splicing part; 3, main body yarn; 4, transparent yarn; 5, transparent coating; 6, functional coating; 7, weft yarn. DETAILED DESCRIPTION

[0017] The present application will be described in detail below in combination with the drawings and examples. EXAMPLE

[0018] A sunlight fabric, such as Figure 1 and Figure 2As shown, the base layer includes a main body part 1 and two splicing parts 2 located on both sides of the main body part 1, the base layer is woven by warp yarns and weft yarns 7, the warp yarns include main body yarns 3 and transparent yarns 4, the main body yarns 3 are only arranged in the main body part 1, the transparent yarns 4 are only arranged in the splicing parts 2, the thickness of the splicing part 2 is half of the thickness of the main body part 1, the diameter of the main body yarn 3 is larger than the diameter of the transparent yarn 4, the distance between adjacent transparent yarns 4 is smaller than the distance between adjacent main body yarns 3, the transparent yarn 4 is twisted by polypropylene fiber, the warp yarns and the main body yarn 3 are twisted by polyester fiber, in this embodiment, 150D polyester yarn is used as the main body yarn 3, this specification yarn has high strength and rigidity, which can provide the main body part 1 with main support structure and mechanical properties, 75D polypropylene yarn is used as the transparent yarn 4, polypropylene fiber has low density, strong hydrophobicity and is easy to process into fine denier fiber, this specification is selected to significantly reduce the thickness and visual presence of the splicing part 2 on the premise of ensuring necessary strength, the weft yarn 7 uniformly uses the same 150D polyester yarn as the main body yarn 3, the weft yarn 7 is a connecting line penetrating the main body part 1 and the splicing part 2, which ensures the firm combination between the two regions, the warp density of the main body part 1 is about 60 per centimeter, the warp density of the splicing part 2 is about 85 per centimeter, and the weft density of the base layer as a whole is 50 per centimeter, the thickness of the main body part 1 woven finally is about 0.6 millimeter, the thickness of the splicing part 2 is about 0.3 millimeter, the transparent yarn 4 is in a transparent state, which greatly reduces the influence of warp density on the transparency of the splicing part 2, thereby ensuring the light transmittance of the splicing area position, and the warp diameter of the splicing part 2 position is small and the density is high, so that the splicing part 2 is relatively dense, thereby ensuring the tensile strength of the splicing part 2, the thickness of the splicing part 2 is half of the main body part 1, which makes the thickness after subsequent splicing more consistent, and also facilitates the subsequent distinction between the splicing part 2 and the main body part 1.

[0019] As shown in Figure 1 and Figure 2 , the two sides of the main body part 1 are coated with a PVC coating, the splicing part 2 includes a first surface and a second surface, the first surfaces of the two splicing parts 2 are coated with a transparent coating 5, and the second surfaces of the two splicing parts 2 are coated with a functional coating 6, the functional coating 6 is provided with shading particles with a concentration gradient distribution in the thickness direction, the concentration of the shading particles is lower closer to the second surface, and the light transmittance of the main body part 1 is between 5% and 10%.

[0020] The light transmittance of the spliced substrate 2 is about 55%, the transparent coating 5 is a transparent PVC coating composed of pure PVC paste resin without any shading particles, and the dry-state light transmittance is ≥98%, which mainly plays the roles of protection, brightening and providing a flat bonding surface. The shading particles are selected from carbon black with a particle size of 0.1 μm to 1.0 μm. In the functional coating 6, the volume concentration of carbon black particles is linearly distributed along the thickness direction of the coating. The total thickness of the coating is 100 μm. The volume concentration of carbon black is the highest at the side of the functional coating 6 away from the second surface, which is defined as the A side in this embodiment, and the volume concentration of carbon black is the lowest at the side of the functional coating 6 close to the second surface, which is defined as the B side in this embodiment. The concentration distribution function is: c(x)=1.0%+2.8%*x, wherein x is the normalized thickness (x=0 is at the A side of the functional coating 6, and x=1 is at the B side of the functional coating 6).

[0021] The coating process of the functional coating 6 adopts a multi-stage gradient coating method, and the specific steps are as follows: Coating slurry preparation: mix the PVC paste resin with the diluent and the stabilizer uniformly to obtain the base slurry. Divide the base slurry into several parts, and add different mass fractions of carbon black shading particles (particle size: 0.1 μm-1.0 μm) to prepare gradient slurries with concentrations of 1.0%, 1.5%, 2.0%, 2.5%, 3.0% and 3.8%, respectively. Layer-by-layer coating: first, coat the slurry with a concentration of 1.0% on the second surface of the spliced part 2 to form a bottom layer; after the surface is dry, coat the slurries with increasing concentrations (1.5%→2.0%→2.5%→3.0%→3.8%) in turn, and the thickness of each layer is about 16.7 μm, and the total thickness is controlled to be 100 μm. Leveling and curing: after coating, perform leveling treatment at 80-90℃ to make the slurries of each layer moderately intermingle at the interface to form a continuous concentration gradient; then perform high-temperature curing at 160-180℃ to crosslink and shape the coating to form a linear gradient structure with the concentration of carbon black particles gradually increasing from the second surface to the inside; the total thickness of the coating is 100 μm. Quality control: by adjusting the viscosity of the slurry, the coating speed and the leveling time, the linearity of the gradient distribution can be controlled. Through cross-section microscopic observation and light transmittance test verification, the concentration distribution conforms to the function: c(x)=1.0%+2.8%*x, wherein x is the normalized thickness.

[0022] When the light is incident from the low-concentration side (A side), the light transmittance is relatively high, and the measured directional light transmittance T max is about 46.4%. When the light is incident from the high-concentration side (B side), the light transmittance is relatively low, and the measured directional light transmittance T min is about 17.1%.

[0023] The light transmittance of the splicing part 2 measured from the first surface: The measurement light path: the light ray is incident from the first surface, and successively passes through the transparent coating 5, the splicing part 2, and the functional coating 6, and is emitted from the second surface; The calculated value: T max *T 拼接部 *T 透明涂层 = 46.4% x 55% x 98% ≈ 25.0%; The light transmittance of the splicing part 2 measured from the second surface: The measurement light path: the light ray is incident from the second surface, and successively passes through the functional coating 6, the splicing part 2, and the transparent coating 5, and is emitted from the first surface; The calculated value: T min *T 拼接部 *T 透明涂层 = 98% x 55% x 17.1% ≈ 9.2%; In this way, the light transmittance of the splicing part 2 measured from the first surface is between 20% and 30%, and the relative deviation between the light transmittance of the splicing part 2 measured from the second surface and the light transmittance of the main part 1 is not greater than 20%. In this embodiment, the light transmittance of the main part 1 is about 8%. In this way, when the fabric is used alone, the second surface of the splicing part 2 is upward, so that the external light ray is incident from the second surface, and the light ray first encounters the high-concentration light-shielding particles, and most of the light ray is immediately reflected, scattered, and absorbed by these dense particles, and only a small part can pass through this layer of “high-concentration barrier” to continue to enter the coating inside, so that the light transmittance is relatively low, and at this time the light transmittance of the splicing part 2 is relatively consistent with the light transmittance of the main part 1, so that when the fabric is used alone, the overall light transmittance of the fabric is ensured. When the fabric needs to be spliced, the second surfaces of the splicing parts 2 of the two fabrics face the same direction, and after splicing, the light ray is incident from the second surface of one splicing part 2 and emitted from the first surface of the other splicing part 2, so that the light ray always enters the functional coating 6 from the low-concentration side. The light ray first encounters the low-concentration light-shielding particles, and most of the light ray can easily pass through this layer of “sparse barrier” to enter the deep part of the coating. When these light rays reach the high-concentration area, although a part is blocked, but due to the large initial number of light rays, finally still a considerable number of photons can be transmitted, so the light transmittance is relatively high. In this way, the light transmittance after superposition is also relatively close to the light transmittance of the main part 1, so that the light transmittance of the main part 1 and the light transmittance of the splicing part 2 after splicing are similar, and the thickness of the splicing part 2 is similar to the thickness of the main part 1, so that no obvious non-transmittance band is formed on the fabric, and the uniformity of the overall lighting of the fabric is ensured. Embodiment

[0024] A splicing method of sunlight fabric, comprising the following steps: Step S1: overlapping the splicing part 2 of the first fabric and the second fabric to be spliced with each other to form an overlapping area, in which the first surface of the splicing part 2 of the first fabric is attached to the second surface of the splicing part 2 of the second fabric; Step S2: providing a hot melt adhesive sheet in the overlapping area, the hot melt adhesive sheet being clamped between the first fabric and the second fabric; The hot melt adhesive sheet is an optical grade thermoplastic polyurethane, which has an average transmittance ≥92% and a haze ≤3% in the visible light band according to laboratory measurement. The high transmittance and low haze characteristics ensure that it does not significantly interfere with or attenuate the monitoring light path signal in step S4, and minimize the impact of the hot melt adhesive sheet on the overall transmittance; Step S3: providing a light source on one side of the overlapping area and a light intensity sensor on the other side of the overlapping area, and the visible light from the light source enters from the first surface of the second fabric; Step S4: causing at least one of the first fabric and the second fabric to produce a relative displacement in a direction parallel to the warp yarn, while monitoring the composite transmittance of the overlapping area in real time through the light intensity sensor; Through a precision linear slide driven by a servo motor, the second fabric is fixed, and the first fabric is driven to move in a direction parallel to the warp yarn, the displacement speed is set to 1mm / s, and the displacement accuracy is ±10μm. During the displacement process, the light intensity sensor collects light signals in real time, and the data acquisition system calculates and displays the real-time composite transmittance at a frequency of 100Hz; Step S5: comparing the real-time monitored composite transmittance value with a target transmittance range, and when the monitored composite transmittance value is within the target transmittance range, immediately stopping the relative displacement and performing a hot pressing operation on the overlapping area to complete the splicing; The transparent coating 5 is a transparent PVC coating, which is based on PVC with a softening point of 85 degrees Celsius. The main body of the functional coating 6 is also based on PVC with a softening point of about 82 degrees Celsius. The hot melt adhesive sheet is an optical grade thermoplastic polyurethane with a melting point of 65°C. The hot pressing temperature is set at 75 degrees Celsius, so as to ensure that the hot pressing temperature does not have a significant impact on the transparent coating 5 and the functional coating 6, and to reduce the impact of hot pressing on the coatings on both sides of the splicing part 2.

[0025] In step S5, the target transmittance range is a corrected dynamic target transmittance range, which is determined in advance by the following steps: Step A1.1: Cut 20 standard splicing parts 2 samples with size of 10cm x 10cm from the same batch of sunlight fabric as the product to be spliced, prepare 20 solid hot melt adhesive pieces which are exactly the same as the production model, according to the method of steps S1 and S2 in claim 5, overlap two samples, and place a hot melt adhesive piece in between, to form a test sample, repeat this operation, a total of 20 test samples are prepared; Step A1.2: Build a test platform to simulate steps S3 and S4 in claim 5, fix the test sample, make the light source vertically incident from the first surface of one of the samples, and the light intensity sensor receives on the other side, slightly adjust the relative position of the two samples in the warp direction, and record the composite light transmittance measured by the light intensity sensor in real time, in order to obtain uniformly distributed data, artificially adjust the sample to multiple different relative positions, and accurately record the corresponding stable solid-state light transmittance monitoring value Tm(i) (where i equals 1 to 20) of each position; Step A1.3: After recording Tm(i) of each test sample, immediately place it in a standard hot press, and use the same hot pressing process parameters as the production to perform hot pressing, after hot pressing is completed, take out the sample, and cool and stand for 1 hour in a standard environment to make its performance completely stable, use the calibrated light transmittance meter to measure the final product light transmittance Tf(i) of the splicing area of each sample; Step A1.4: Obtain 20 sets of effective data (Tm(1), Tf(1)), (Tm(2), Tf(2))…… (Tm(20), Tf(20)), perform one-dimensional linear regression analysis on this batch of data, The analysis result shows that there is a strong linear correlation between Tm and Tf, and the output optimal fitting function is: Tf=0.85*Tm+1.2%; This function is the mapping relationship function determined under this batch of materials and process parameters, its physical meaning is that the hot pressing and cooling process will make the light transmittance of the splicing area approximately 0.85 times the solid-state monitoring value, and shift upward by 1.2 percentage points in total.

[0026] Step A2: According to the product design requirements, the spliced finished product light transmittance Tt is expected to be 8.5%, which is substituted into the mapping relationship function to back-calculate the solid-state monitoring target value Td to be controlled in production; 8.5%=0.85*Td+1.2%; Td=8.59%, considering the slight fluctuations of online monitoring, set a tolerance, for example ±0.3%. Therefore, the dynamic target light transmittance range executed online is determined to be 8.29% to 8.89%.

[0027] Step A3: when performing step S5, the calculated dynamic target light transmittance range is used as the criterion for stopping relative displacement and triggering the hot pressing operation.

[0028] The above method can dynamically find and lock the splicing point that best matches the light transmittance of the main body part 1, and can produce a product with a seam light transmittance consistent with the main body height, which is almost "invisible" in vision. By predicting the dynamic target light transmittance range, the melting of the hot melt adhesive sheet and the effect of the coating on the light transmittance are considered. By establishing a quantitative relationship model, the optical performance of the final product is precisely controlled, the accuracy of the final light transmittance is improved, the light transmittance of the splicing part 2 is closer to the main body part 1, and the quality and aesthetic value of the final product are greatly improved. The consistency of the light transmittance of the product after splicing is ensured, and the use effect of the product is improved.

[0029] The above is only the preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical solutions falling within the scope of the present application should be considered within the protection scope of the present application. It should be noted that for ordinary skilled persons in the art, some improvements and refinements without departing from the principles of the present application should also be considered within the protection scope of the present application.

Claims

1. A type of sun-drying fabric, characterized in that: The base layer includes a main body (1) and two splicing parts (2) located on both sides of the main body (1). The base layer is woven from warp and weft yarns (7). The warp yarns include main yarn (3) and transparent yarn (4). The main yarn (3) is only provided in the main body (1), and the transparent yarn (4) is only provided in the splicing parts (2). The thickness of the splicing parts (2) is half the thickness of the main body (1). Both sides of the main body (1) are coated with PVC coating. The splicing part (2) includes a first surface and a second surface. The first surface of both splicing parts (2) is coated with a transparent coating (5). The second surface of both splicing parts (2) is coated with a functional coating (6). The functional coating (6) contains light-shielding particles with a gradient distribution in the thickness direction. The concentration of the light-shielding particles is lower as it approaches the second surface.

2. The sun-drying fabric according to claim 1, characterized in that: The relative deviation between the light transmittance of the splicing part (2) measured from the second surface and the light transmittance measured from the main body part (1) is no greater than 20%.

3. The sun-drying fabric according to claim 2, characterized in that: The light transmittance of the main body (1) is between 5% and 10%, and the light transmittance of the splicing part (2) measured from the first surface is between 20% and 30%.

4. The sun-drying fabric according to claim 1, characterized in that: The distance between adjacent transparent yarns (4) is less than the distance between adjacent main yarns (3), and the transparent yarns (4) are made of twisted polypropylene fibers.

5. A method for splicing a sun-protective fabric, applied to the sun-protective fabric according to any one of claims 1-4, characterized in that: include: Step S1: Overlap the splicing parts (2) of the first fabric and the second fabric that need to be spliced ​​to form an overlapping area. In the overlapping area, the first surface of the splicing part (2) of the first fabric is attached to the second surface of the splicing part (2) of the second fabric. Step S2: A hot melt adhesive sheet is provided in the overlapping area, the hot melt adhesive sheet being sandwiched between the first fabric and the second fabric; Step S3: A light source is set on one side of the overlapping area, and a light intensity sensor is set on the other side of the overlapping area. The visible light from the light source enters from the first surface of the second fabric. Step S4: Cause at least one of the first fabric and the second fabric to be relatively displaced in a direction parallel to the warp yarns, while the light intensity sensor monitors the composite light transmittance of the overlapping area in real time. Step S5: Compare the real-time monitored composite transmittance value with a target transmittance range. When the monitored composite transmittance value is within the target transmittance range, immediately stop the relative displacement and perform a hot pressing operation on the overlapping area to complete the splicing.

6. The splicing method of a sun-drying fabric according to claim 5, characterized in that: After the hot melt adhesive sheet is melted and solidified in step S5, its average transmittance in the visible light band is not less than 90%, and its haze is not greater than 5%.

7. The splicing method of a sun-drying fabric according to claim 5, characterized in that: The softening points of the transparent coating (5) and the functional coating (6) are both higher than the melting point of the hot melt adhesive sheet. The hot pressing temperature of step S5 is higher than the melting point of the hot melt adhesive sheet and lower than the softening points of the transparent coating (5) and the functional coating (6).

8. The splicing method of a sun-drying fabric according to claim 5, characterized in that: In step S5, the target transmittance range is a corrected dynamic target transmittance range, which is predetermined through the following steps: Step A1: Use sample fabric and hot melt adhesive from the same batch as the fabric to be spliced ​​to conduct a pre-splicing test. Record the composite transmittance value Tm monitored in the solid hot melt adhesive state before performing the hot pressing operation. Measure the final transmittance value Tf of the corresponding spliced ​​sample after performing the hot pressing operation and cooling and shaping. Establish the mapping relationship function Tf=f(Tm) between Tm and Tf. Step A2: Based on the mapping function Tf=f(Tm) and the preset target transmittance Tt, calculate the dynamic target transmittance range to be used in step S5. The center value Td of this range satisfies Tt=f(Td). Step A3: When performing step S5, the calculated range of dynamic target transmittance is used as the criterion for stopping relative displacement and triggering hot pressing operation.

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